ENCYCLOPEDIA OF DAIRY SCIENCES SECOND EDITION
ENCYCLOPEDIA OF DAIRY SCIENCES SECOND EDITION Editor-in-Chief John W. Fuquay Mississippi State University, Mississippi State, MS, USA
Editors Patrick F. Fox University College, Cork, Ireland
Paul L. H. McSweeney University College, Cork, Ireland
AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Academic Press is an imprint of Elsevier
Academic Press is an imprint of Elsevier 32 Jamestown Road, London NW1 7BY, UK The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 525 B Street, Suite 1900, San Diego, CA 92101-4495, USA Copyright Ó 2011 Elsevier Ltd. All rights reserved The following articles are US Government works in the public domain and are not subject to copyright: ANALYTICAL METHODS: DNA-Based Assays DISEASES OF DAIRY ANIMALS: Infectious Diseases: Johne’s Disease FEED INGREDIENTS: Feed Concentrates: Co-Product Feeds GENETICS: Selection: Evaluation and Methods; International Flow of Genes LACTATION: Galactopoiesis, Effects of Hormones and Growth Factors; Galactopoiesis, Effect of Treatment with Bovine Somatotropin No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email:
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EDITORS’ BIOGRAPHIES
John W. Fuquay, Professor Emeritus of Dairy Science at Mississippi State University, served on the faculty there from 1969 to 1999. His areas of emphasis in teaching and research were environmental physiology and reproductive physiology. He received his BS and MS degrees from North Carolina State University and his PhD degree from Pennsylvania State University, all in the area of dairy science. After completing the PhD degree in 1969, he accepted a teaching and research position at Mississippi State University, where he progressed through the ranks from assistant professor to professor before retiring in 1999. Professor Fuquay served as Coordinator for the Graduate Program in Animal Physiology from 1986 to 1999. He was a Visiting Professor in the Animal Sciences Department, University of California-Davis in 1979 and in 1985–86. Professor Fuquay was active in his professional society, The American Dairy Science Association. He was a member of the editorial board of Journal of Dairy Science for seven years, an editor for four years, and served as the first Editor-in-Chief for six years (1997–2002). For his professional contributions and service to the Association, Professor Fuquay was recognized as a Fellow in the American Dairy Science Association in 2001 and received the Association’s Award of Honor in 2002. Other recognitions include the World Association of Animal Production Jean Boyazoglu Award in 2003, the Distinguished Dairy Science Alumnus Award from Pennsylvania State University in 2003, and several teaching and research awards from his university. Professor Fuquay has participated in a variety of international activities. He has presented short courses and lectures as well as provided consultations in a number of countries, primarily in Asia and Latin America. In addition to his research publications, he is the coauthor of a textbook, Applied Animal Reproduction (Prentice Hall), that has been widely used by universities in the United States and internationally. The first edition was published in 1980 and the last (sixth) edition in 2004. In 2010, he published a memoir, Musings of a Depression-Era Southern Farm Boy (Vantage Press), which reflects on how the experience of growing up on a farm in the southern United States during the great depression instills one with an understanding of the importance of strong family bonds and a sound work ethic in meeting the challenges of the adult world.
Patrick F. Fox was Professor and Head of the Department of Food Chemistry at University College, Cork (UCC), Ireland, from 1969 to 1997; he retired in December 1997 and is now Emeritus Professor of Food Chemistry at UCC. Prof. Fox received his BSc degree in Dairy Science from UCC in 1959 and PhD degree in Food Chemistry from Cornell University in 1964. After postdoctoral periods in Biochemistry at Michigan State University and in Food Biochemistry at the University of California, Davis, he returned to Ireland in 1967 to take up a research position at the Dairy Products Research Centre at Moorepark before moving to UCC in 1969. Prof. Fox’s research has focused on the biochemistry of cheese, the heat stability of milk, physicochemical properties of milk proteins, and food enzymology. He has authored or coauthored about 520 research and review papers, and authored or edited 25 text books on Dairy Chemistry. He was one of the founding editors of the International Dairy Journal. In recognition of his work, Prof. Fox has received the Research & Innovation Award of the (Irish) National Board for Science and Technology (1983), the Miles-Marschall Award of the American Dairy Science Association (1987), Medal of Honour, University of Helsinki (1991), the DSc degree of the National University of Ireland (1993), the Senior Medal for Agricultural & Food Chemistry of the Royal Society for Chemistry (2000), the ISI Highly Cited Award in Agricultural Science (2002), the International Dairy Federation Award (2002), Gold Medal of the UK Society of Dairy Technology (2007), and an autobiography published in Annual Review of Food Science & Technology (2011). Prof. Fox has been invited to lecture in various countries around the world. He has served in various capacities with the International Dairy Federation, including President of Commission F (Science, Nutrition and Education) from 1980 to 1983.
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Editors’ Biographies
Paul McSweeney is Professor of Food Chemistry in the School of Food and Nutritional Sciences, University College, Cork, Ireland (UCC). He graduated with a BSc degree in Food Science and Technology in 1990 and a PhD degree in Food Chemistry from UCC in 1993 and also has an MA in Ancient Classics. He worked for a year in the University of Wisconsin (1991–92) as part of his PhD and as a postdoctoral research scientist in UCC (1993–94). He was appointed to the academic staff of UCC in 1995. The overall theme of his research is dairy biochemistry with particular reference to factors affecting cheese flavor and proteolysis during cheese maturation including the role of non-starter lactic acid bacteria and smear microorganisms, the ripening of hybrid and non-Cheddar varieties, the specificity of proteinases on the caseins, proteolysis and lipolysis in cheese during ripening, and characterization of enzymes important to cheese ripening (proteinases, peptidases, amino acid catabolic enzymes). He is the coauthor or coeditor of eight books, including the third edition of Cheese: Chemistry, Physics and Microbiology (Amsterdam, 2004) and the Advanced Dairy Chemistry Series (New York, 2003, 2006, 2009), and has published numerous research papers and reviews. Prof. McSweeney is an experienced lecturer and researcher and has successfully managed research projects funded through the Food Industry Research Measure and its predecessors administered by the Irish Department of Agriculture and Food, the EU Framework Programmes, the US–Ireland Co-operative Programme in Agriculture/Food Science and Technology, and Bioresearch Ireland and Industry. He was awarded the Marschall Danisco International Dairy Science Award of the American Dairy Science Association in 2004 and in 2009 a higher doctorate (DSc) on published work by the National University of Ireland.
EDITORIAL ADVISORY BOARD
Ryozo Akuzawa Nippon Veterinary and Life Sciences University, Tokyo, Japan Arie Brand Utrecht University, Utrecht, The Netherlands Hilton Deeth University of Queensland, Brisbane, QLD, Australia Cathy Donnelly University of Vermont, Burlington, VT, USA Nana Farkye California Polytechnic State University, San Luis Obispo, CA, USA Harsharn Gill Department of Primary Industries, Melbourne, VIC, Australia Marco Gobbetti University of Bari, Bari, Italy Mansel Griffiths University of Guelph, Guelph, ON, Canada T P Guinee Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
Michael Keane University College, Cork, Ireland Hannu Korhonen MTT Agrifood Research Finland, Jokioinen, Finland Sylvie Lortal INRA Rennes, Rennes, France John P McNamara Washington State University, Pullman, WA, USA Vikram Mistry South Dakota State University, Brookings, SD, USA Stephen C Nickerson University of Georgia, Athens, GA, USA Donatus Nohr University of Hohenheim, Stuttgart, Germany Jorge C Oliveira University College, Cork, Ireland Robert R Peters University of Maryland, College Park, MD, USA Morten D Rasmussen Aarhus University, Tjele, Denmark Geoffrey E. Robards Glenbrook, NSW, Australia
George F W Haenlein University of Delaware, Newark, DE, USA
John Roche DairyNZ Ltd, Hamilton, New Zealand
Peter Hansen University of Florida, Gainesville, FL, USA
Hubert Roginski University of Melbourne, Melbourne, VIC, Australia
Claus Heggum Danish Agriculture & Food Council, Aarhus, Denmark
Harald Rohm Technical University of Dresden, Dresden, Germany
Thom Huppertz NIZO Food Research, Ede, The Netherlands
Harjinder Singh Massey University, Palmerston North, New Zealand
Erica Hynes Universidad Nacional del Litoral, Santa Fe, Argentina
George R Wiggans United States Department of Agriculture, Beltsville, MD, USA
Paul Jelen University of Alberta, Edmonton, AB, Canada
Andrew Wilbey University of Reading, Reading, UK
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CONTRIBUTORS A Abbas University College, Cork, Ireland M H Abd El-Salam National Research Center, Cairo, Egypt C F Afonso University of Porto, Porto, Portugal S A Aherne University College, Cork, Ireland A Ahmadzadeh University of Idaho, Moscow, ID, USA S L Aitken Michigan State University, East Lansing, MI, USA R M Akers Virginia Polytechnic Institute and State University, Blacksburg, VA, USA R Akuzawa Nippon Veterinary and Life Science University, Tokyo, Japan G A Alhadrami UAE University, Al-Ain, United Arab Emirates R A Almeida The University of Tennessee, Knoxville, TN, USA V B Alvarez The Ohio State University, Columbus, OH, USA L Amigo ´ en Ciencias de Alimentacion ´ Instituto de Investigacion (CIAL, CSIC-UAM), Madrid, Spain S K Anand South Dakota State University, Brookings, SD, USA ´ A Andren Swedish University of Agricultural Sciences, Uppsala, Sweden
J Andrews Department of Primary Industries, Mutdapilly, QLD, Australia and Dairy Research and Development Corporation, Melbourne, VIC, Australia K Antelli Technical University of Crete, Chania, Greece Y Ardo¨ University of Copenhagen, Frederiksberg C, Denmark S Arora National Dairy Research Institute, Karnal, Haryana, India A M Arve Danish Dairy Board, Aarhus, Denmark S Asakuma National Agricultural Research Center for Hokkaido Region, Sapporo, Hokkaido, Japan H Asperger Veterinary University, Vienna, Austria Z Atamer University of Hohenheim, Stuttgart, Germany M Auldist Department of Primary Industries, Ellinbank, VIC, Australia P Aureli Istituto Superiore di Sanita`, Rome, Italy M Auty Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland ˜ L Avendano-Reyes ´ Universidad Autonoma de Baja California, Mexico G Averdunk Landesanstalt fu¨r Landwirtschaft, Mu¨nchen, Germany S Awad Alexandria University, Alexandria, Egypt ix
x Contributors V Azaı¨s-Braesco VAB-Nutrition, Clermont–Ferrand, France H-P Bachmann Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland E I Back Novartis Pharma GmbH, Nu¨rnberg, Germany R L Baldwin University of California, Davis, CA, USA J M Banks NIZO Food Research, Ede, The Netherlands
Z Bercovich Institute for Animal Science and Health, Lelystad, The Netherlands T P Beresford Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland J K Bernard University of Georgia, Tifton, GA, USA D P Berry Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
N Bansal The University of Queensland, Brisbane, QLD, Australia
E Beuvier Institut National de la Recherche Agronomique, Poligny, France
J Bao Heilongjiang Bayi Agricultural University, Heilongjiang, PR China
V Bhandari Massey University, Palmerston North, New Zealand
E Barrio Cavanilles of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
W G Bickert Michigan State University, East Lansing, MI, USA
M D Barton University of South Australia, Adelaide, SA, Australia D E Bauman Cornell University, Ithaca, NY, USA
H K Biesalski Universita¨t Hohenheim, Stuttgart, Germany P Billon Institut de l’Elevage, Le Rheu, France
L H Baumgard University of Arizona, Tucson, AZ, USA
A G Binetti Instituto de Lactelogı´a Industrial (Universidad Nacional del Litoral–CONICET), Santa Fe, Argentina
C R Baumrucker The Pennsylvania State University, University Park, PA, USA
M Bionaz University of Illinois, Urbana, IL, USA
H J Bearden Mississippi State University, Mississippi State, MS, USA
W Bisig Agroscope Liebefeld-Posieux Research Station ALP, Bern, Switzerland
S T Beckett Formerly Nestle´ Product Technology Centre York, York, UK
J Bjo¨rkroth University of Helsinki, Helsinki, Finland
C J M Beeren Leatherhead Food Research, Leatherhead, UK
A Blais AgroParisTech, Paris, France
C Belloch Institute of Agrochemistry and Food Technology (IATA), CSIC, Valencia, Spain
W Bockelmann Federal Research Institute of Nutrition and Food (Max Rubner Institute), Kiel, Germany
R J Bennett Massey University, Palmerston North, New Zealand
M J Boland Riddet Institute, Palmerston North, New Zealand
G A Benson North Carolina State University, Raleigh, NC, USA
M P Boland University College, Dublin, Ireland
Contributors
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U Bolmstedt Tetra Pak Processing Components AB, Lund, Sweden
M F Budinich University of Wisconsin, Madison, WI, USA
J Bonke GEA Process Engineering – Niro, Søborg, Denmark
J Burger BurgerMetrics SIA, Jelgava, Latvia
A Borghese Animal Production Research Institute, Monterotondo, Italy
S Burgess Fonterra Research Centre, Palmerston North, New Zealand
F H M Borgsteede Central Veterinary Institute of Wageningen UR, Lelystad, The Netherlands
A M Burgher Pfizer Nutrition, Collegeville, PA, USA
R Boston University of Pennsylvania, Kennett Square, PA, USA J S Bowen Bowen Mobile Veterinary Practice, Wellington, CO, USA J Boyazoglu Aristotle University of Thessaloniki, Greece
H Burling Arla Foods amba, Lund, Sweden E M Buys University of Pretoria, Pretoria, South Africa E Byrne University College, Cork, Ireland
R L Bradley, Jr. University of Wisconsin–Madison, Madison, WI, USA
R J Byrne Jacobs Engineering, Mahon Industrial Estate, Blackrock, Cork, Ireland
P Bremer University of Otago, Dunedin, New Zealand
C Caddick Fonterra Research Centre, Palmerston North, New Zealand
K Brew Florida Atlantic University, Boca Raton, FL, USA
R Di Cagno University of Bari, Bari, Italy
J R Broadbent Utah State University, Logan, UT, USA
M Calasso DIBCA, University of Bari, Bari, Italy
C Brockman Leatherhead Food Research, Leatherhead, UK
C Cantoni University of Milan, Milan, Italy
J Brooks AUT University, Auckland, New Zealand
A V Capuco US Department of Agriculture, ARS, Beltsville, MD, USA
M C Broome Dairy Innovation Australia, Werribee, VIC, Australia
B Carnat World Organisation for Animal Health (OIE), Paris, France
N Brunton Ashtown Food Research Centre, Dublin, Ireland
K D Cashman University College, Cork, Ireland
N R Bu¨chl Technische Universita¨t, Mu¨nchen, Germany
B G Cassell Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
U Bu¨tikofer Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland D S Buchanan Oklahoma State University, Stillwater, OK, USA S Buchin Institut National de la Recherche Agronomique, Poligny, France
S Cattaneo Universita` degli Studi di Milano, Milan, Italy C Cebo Institut National de la Recherche Agronomique, Jouy-en-Josas, France W Chalupa University of Pennsylvania, Kennett Square, PA, USA
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Contributors
D Champion ENSBANA–Universite´ de Bourgogne, Dijon, France
´ A Correa-Calderon ´ Universidad Autonoma de Baja California, Mexico
J Charlier Ghent University, Merelbeke, Belgium
M Corredig University of Guelph, Guelph, ON, Canada
L E Chase Cornell University, Ithaca, NY, USA
A Corsetti Universita` degli Studi di Teramo, Mosciano S. Angelo (TE), Italy
D E W Chatterton University of Copenhagen, Frederiksberg C, Denmark F Chevalier ´ Institut de Radiobiologie Cellulaire et Moleculaire, Fontenay aux Roses, France A Christiansson Swedish Dairy Association, Lund, Sweden C J Cifelli The Council, Rosemont, IL, USA E Claerebout Ghent University, Merelbeke, Belgium S Claps Consiglio per la Ricerca e la sperimentazione in Agricoltura, Muro Lucano, Italy R Cocker Ayndo Tree Farm, County Cork, Ireland B Cocks Biosciences Research Division, Melbourne, VIC, Australia A Coffey Cork Institute of Technology, Bishopstown, Cork, Ireland T M Cogan Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland R J Collier University of Arizona, Tucson, AZ, USA M T Collins University of Wisconsin–Madison, Madison, WI, USA G Comi University of Udine, Udine, Italy
P D Cotter Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland L K Creamer Riddet Institute, Massey University, Palmerston North, New Zealand K Cronin University College, Cork, Ireland V Crow Formerly at Fonterra Research Centre, Palmerston North, New Zealand M A Crowe University College, Dublin, Ireland B Curry Formerly at Fonterra Research Centre, Palmerston North, New Zealand S E Curtis University of Illinois–Urbana, Urbana, IL, USA C B G Daamen DSM Food-Specialties, Delft, The Netherlands J Dalton University College, Cork, Ireland A Darragh Massey University, Palmerston North, New Zealand N Datta Victoria University, Melbourne, VIC, Australia G Davey Fonterra Research Centre, Palmerston North, New Zealand
T Coolbear Fonterra Research Centre, Palmerston North, New Zealand
T Davison Department of Primary Industries, Mutdapilly, QLD, Australia and Dairy Research and Development Corporation, Melbourne, VIC, Australia
S Cooney University College, Dublin, Ireland
M De Angelis University of Bari, Bari, Italy
S Coppola Universit`a degli Studi di Napoli Federico II, Portici NA, Italy
L C P M G de Groot Wageningen University, Wageningen, The Netherlands
Contributors C J A M de Koning Wageningen UR Livestock Research, AB Lelystad, The Netherlands
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M A Drake North Carolina State University, Raleigh, NC, USA
I De Noni Universita` degli Studi di Milano, Milan, Italy
D Dupont INRA Agrocampus Ouest, UMR Science et Technologie du Lait et de l’Œuf, Rennes, France
H C Deeth University of Queensland, Brisbane, QLD, Australia
E M Du¨sterho¨ft NIZO Food Research, Ede, The Netherlands
P J T Dekker DSM Food-Specialties, Delft, The Netherlands
M L Eastridge The Ohio State University, Columbus, OH, USA
C M Delahunty CSIRO, North Ryde, Sydney, NSW, Australia
E I El-Agamy Qassim University, Qassim, Saudi Arabia
C Delaney University of Vermont, Burlington, VT, USA
F Eliskases-Lechner Federal Institute of Alpine Dairying, Jenbach, Austria
P Desmarchelier Consultant, Pullenvale, QLD, Australia
H Engelhardt University of Waterloo, Waterloo, ON, Canada
S M Deutsch INRA, Agrocampus, Ouest, Rennes, France
W Engels NIZO Food Research, Ede, The Netherlands
C Devendra Jalan Awan Jwa, Kuala Lumpur, Malaysia
T E Engle Colorado State University, Fort Collins, CO, USA
R Di Cagno University of Bari, Bari, Italy
I Eppert Chr. Hansen A/S, Hørsholm, Denmark
J Dijkstra Wageningen University, Wageningen, The Netherlands
D Ercolini Universita` degli Studi di Napoli Federico II, Portici NA, Italy
M G Diskin Teagasc, Animal & Grassland Research and Innovation Centre, Mellows Campus, County Galway, Ireland
B L Erven Ohio State University, Columbus, OH, USA
A D W Dobson University College, Cork, Ireland W Dominguez University of Minnesota, St Paul, MN, USA
C T Estill Oregon State University, Corvallis, OR, USA K G Evans Cornell University, Ithaca, NY, USA
S S Donkin Purdue University, West Lafayette, IN, USA
M H Fahmy International Genetics Consulting Service, Ottawa, Canada
I A Doolan University of Limerick, Limerick, Ireland
H Falentin INRA, Agrocampus, Ouest, Rennes, France
M Doreau Institut National de la Recherche Agronomique, Saint` Champanelle, France Genes
S Fanning University College, Dublin, Ireland
Z Dou University of Pennsylvania, Kennett Square, PA, USA P T Doyle Future Farming Systems Research, Tatura, VIC, Australia
Z Farah Swiss Federal Institute of Technology, Zu¨rich, Switzerland N Y Farkye California Polytechnic State University, San Luis Obispo, CA, USA
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Contributors
H M Farrell Jr., USDA, Eastern Regional Research Center, Wyndmoor, PA, USA N Fegan Food Science Australia, Brisbane, QLD, Australia C Ferris Agri-Food and Biosciences Institute, Hillsborough, County Down, UK S Feyo de Azevedo University of Porto, Portugal J L Firkins The Ohio State University, Columbus, OH, USA
J France University of Guelph, Guelph, ON, Canada G Franciosa Istituto Superiore di Sanita`, Rome, Italy J F Frank South Dakota State University, Brookings, SD, USA and University of Georgia, Athens, GA, USA S T Franklin University of Kentucky, Lexington, KY, USA E Frede Federal Dairy Research Centre, Kiel, Germany
W J Fischer Syngenta International AG, Basel, Switzerland
M-T Fro¨hlich-Wyder Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland
R J FitzGerald University of Limerick, Limerick, Ireland
H Fujimoto Teikyo Heisei University, Chiba, Japan
D Fitzpatrick University College, Cork Ireland
W J Fulkerson Formerly at the University of Sydney, Sydney, NSW, Australia
J J Fitzpatrick University College, Cork, Ireland S Flint Massey, University Palmerston North, New Zealand A Flynn University College, Cork, Ireland E A Foegeding North Carolina State University, Raleigh, NC, USA
D A Funk ABS Global, Inc., DeForest, WI, USA J W Fuquay Mississippi State University, Mississippi State, MS, USA ¨ M G Ganzle University of Alberta, Edmonton, AB, Canada G Garcı´a de Fernando Universidad Complutense, Madrid, Spain
J Fontecha ´ en Ciencias de Alimentacion ´ Instituto de Investigacion (CIAL, CSIC-UAM), Madrid, Spain
B Garin-Bastuji French Agency for Food, Environmental & Occupational Health Safety (ANSES), Maisons-Alfort, France
R H Foote Cornell University, Ithaca, NY, USA
D L Garner GametoBiology Consulting, Graeagle, CA, USA
I A Forsyth The Babraham Institute, Cambridge, UK
H A Garverick University of Missouri, Columbia, MO, USA
S Fosset Institut National Agronomique de Paris–Grignon, Paris, France
F Gaucheron INRA Science et Technologie du Lait et de l’Œuf, Rennes, France
T J Foster Trinity College, Dublin, Ireland
J M Gay Washington State University, Pullman, WA, USA
P D Fox Ballincollig, 90 Old Quarter, Cork, Ireland
V Gekas Cyprus University of Technology, Limassol, Cyprus
P F Fox University College, Cork, Ireland
N Gengler Gembloux Agricultural University, Gembloux, Belgium
Contributors P Georgieva University of Aveiro, Aveiro, Portugal
M Guo University of Vermont, Burlington, VT, USA
J B German The University of California, Davis, CA, USA
M Gue´guen University of Caen Basse–Normandie, Caen, France
G Gernigon UMR 1253 INRA-Agrocampus Ouest, Rennes, France
G F W Haenlein University of Delaware, Newark, DE, USA
J Gibbs Lincoln University, Canterbury, New Zealand
D Haisman Massey University, Palmerston North, New Zealand
M B Gilsenan Leatherhead Food Research, Leatherhead, UK
M B Hall US Dairy Forage Research Center, Madison, WI, USA
H Gjøstein ˚ Norway Norwegian University of Life Sciences, As,
H O Hansen University of Copenhagen, Copenhagen, Denmark
J D Glennon University College, Cork, Ireland
P J Hansen University of Florida, Gainesville, FL, USA
M Gobbetti University of Bari, Bari, Italy
J Harnett Fonterra Research Centre, Palmerston North, New Zealand
M E Goddard University of Melbourne, Parkville, VIC, Australia H D Goff University of Guelph, Guelph, ON, Canada E Gootwine The Volcani Center, Bet Dagan, Israel P K Gopal Fonterra Research Centre, Palmerston North, New Zealand A A Gowen University College, Dublin, Ireland
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W J Harper The Ohio State University, Columbus, OH, USA R Harrison University of Bath, Bath, UK S P Hart Langston University, Langston, OK, USA R W Hartel University of Wisconsin-Madison, Madison, WI, USA K J Harvatine Pennsylvania State University, University Park, PA, USA
R Grappin Formerly at Institut National de la Recherche Agronomique, Poligny, France
J F Hasler Bonner Creek Ranch, Laporte, CO, USA
B Graulet INRA, Unite´ de Recherche sur les Herbivores, Saint Gene`s Champanelle, France
A N Hassan South Dakota State University, Brookings, SD, USA and University of Georgia, Athens, GA, USA
M W Griffiths University of Guelph, Guelph, ON, Canada
J Hatziminaoglou Aristotle University of Thessaloniki, Greece
P Grolier INRA, Laboratoire PsyNuGen, Universite´ Bordeaux 2, Bordeaux, France
P Haughton University College, Dublin, Ireland
T P Guinee Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
E J Havilah Formerly New South Wales Primary Industries and New South Wales Agriculture, Berry, NSW, Australia
H D Guither University of Illinois–Urbana, Urbana, IL, USA
A A Hayaloglu Inonu University, Malatya, Turkey
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Contributors
B J Hayes Biosciences Research Division, Melbourne, VIC, Australia
A Hosono Japan Dairy Technical Association, Tokyo, Japan
B Healy University College, Dublin, Ireland
J T Huber University of Arizona, Tucson, AZ, USA
C Heggum Danish Agricultural & Food Council, Aarhus, Denmark
D E Hume Grasslands Research Centre, Palmerston North, New Zealand
K E Herold University of Maryland, College Park, MD, USA B Herr Leatherhead Food Research, Leatherhead, UK C Heydel Justus Liebig University, Giessen, Germany B Heymann GEA Westfalia Separator Process GmbH, Oelde, Germany M Hickey Michael Hickey Associates, Charleville, County Cork, Ireland C Hill University College, Cork, Ireland J P Hill Fonterra Research Centre, Palmerston North, New Zealand T R Hill University College, Cork, Ireland J Hinrichs University of Hohenheim, Stuttgart, Germany W Hoffmann Max Rubner-Institut, Kiel, Germany H Hogeveen Wageningen University, Wageningen, The Netherlands
T Huppertz NIZO Food Research, Ede, The Netherlands W L Hurley University of Illinois, Urbana, IL, USA M F Hutjens University of Illinois, Urbana, IL, USA N Hyatt Dyadem International Ltd, Toronto, ON, Canada H E Indyk Fonterra Co–operative Group Ltd., Waitoa, New Zealand B Ismail University of Minnesota, St. Paul, MN, USA D Isolini Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland C Iversen University College, Dublin, Ireland J A Jackson University of Kentucky, Lexington, KY, USA E Jakob Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland
Ø Holand ˚ Norway Norwegian University of Life Sciences, As,
R E James Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
R Holland Fonterra Research Centre, Palmerston North, New Zealand
G Jan INRA, Agrocampus, Ouest, Rennes, France
C Holt University of Glasgow, Scotland, UK
D Jaros ¨ Dresden, Dresden, Germany Technische Universitat
R M Hopper Mississippi State University, MS, USA
R Jeantet UMR 1253 INRA-Agrocampus Ouest, Rennes, France
D S Horne Formerly at Hannah Research Institute, Ayr, UK
P Jelen University of Alberta, Edmonton, AB, Canada
Contributors xvii T C Jenkins Clemson University, Clemson, SC, USA
A Kilara Nutri + Food Business Consulting, Chapel Hill, NC, USA
E Jesse University of Wisconsin–Madison, Madison, WI, USA
K N Kilcawley Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
T Ji The Ohio State University, Columbus, OH, USA M E Johnson Wisconsin Center for Dairy Research, Madison, WI, USA K A Johnston Fonterra Research Centre, Palmerston North, New Zealand C M Jones Virginia Polytechnic Institute and State University, Blacksburg, VA, USA M Jones Centre for Food Technology, Toowoomba, QLD, Australia
G J King University of Guelph, Guelph, ON, Canada M Kitaoka National Food Research Institute, Tsukuba, Ibaraki, Japan P J Kononoff University of Nebraska-Lincoln, Lincoln, NE, USA J Koort University of Helsinki, Helsinki, Finland H Korhonen MTT, Agrifood Research Finland, Biotechnology and Food Research, Jokioinen, Finland
M Juarez Instituto de Investigatio´n en Ciencias de la Alimentac´ion (CSIC-UAM), Madrid, Spain
N Krog Danisco, Brabrand, Denmark
M T Kaproth Genex Cooperative, Ithaca, NY, USA
D Krogmeier Landesanstalt fu¨r Landwirtschaft, Mu¨nchen, Germany
Y Kato Kinki University, Nakamachi, Nara, Japan
T P Labuza University of Minnesota, St. Paul, MN, USA
M Keane University College, Cork, Ireland
R H Laby Ellinbank Centre, Ellinbank, VIC, Australia
K M Keener Purdue University, West Lafayette, IN, USA
G Laible Ruakura Research Centre, Hamilton, New Zealand
E B Kegley University of Arkansas, Fayetteville, AR, USA
K A Lampel Food and Drug Administration, College Park, MD, USA
D W Kellogg University of Arkansas, Fayetteville, AR, USA
S Landau The Volcani Center, Bet Dagan, Israel
A L Kelly University College, Cork, Ireland
V A Landells Fonterra, Melbourne, VIC, Australia
P M Kelly Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
I J Lean SBScibus and University of Sydney, Camden, NSW, Australia
W Kenifel ¨ Bodenkultur, Vienna, Austria Universitat
M-N Leclercq-Perlat INRA – GMPA, Thiverval-Grignon, France
R S Kensinger Oklahoma State University, Stillwater, OK, USA
J-H Lee University of Minnesota, St Paul, MN, USA
M S Khan University of Agriculture, Faisalabad, Pakistan
C Lefevre Deakin University, Geelong, VIC, Australia
xviii
Contributors
D Lefier Institut National de la Recherche Agronomique, Poligny, France G Leitner Kimron Veterinary Institute, Bet Dagan, Israel ´ e´ J-L Le Quer UMR Flavour, Vision and Consumer Behaviour, INRA, Dijon, France Z Libudzisz ´ z, Poland Technical University of Łod´ G K Y Limsowtin Formerly at Australian Starter Culture Research Centre, Werribee, VIC, Australia D Lindsay Fonterra Research Centre, Palmerston North, New Zealand S-Q Liu National University of Singapore, Kent Ridge, Singapore A L Lock Michigan State University, East Lansing, MI, USA P Lonergan University College, Dublin, Ireland B Lo¨nnerdal University of California, Davis, CA, USA J J Loor University of Illinois, Urbana, IL, USA A Lopez-Hernandez University of Wisconsin–Madison, Madison, WI, USA L Lopez-Kleine Institut National de la Recherche Agronomique (INRA), Jouy-en-Josas, France S M Loveday Riddet Institute, Massey University, Palmerston North, New Zealand K F Lowe Formerly Queensland Primary Industries and Fisheries, Peak Crossing, QLD, Australia
J Lyne Chr Hansen Inc, Milwaukee, WI, USA C Macaldowie Moredun Research Institute, Penicuik, Midlothian, UK A K H MacGibbon Fonterra Research Centre, Palmerston North, New Zealand F E Madalena Federal University of Minas Gerais, Brazil A L Magliaro-Macrina Pennsylvania State University, University Park, PA, USA A Malet AgroParisTech, Paris, France J Malmo Maffra Veterinary Centre, Maffra, VIC, Australia A G Marangoni University of Guelph, Guelph, ON, Canada F Mariette Cemagref, UR TERE, Rennes, France, Universite´ ´ Europeenne de Bretagne, Rennes, France P Marnila MTT, Agrifood Research Finland, Biotechnology and Food Research, Jokioinen, Finland R Marsili Rockford College, Rockford, IL, USA H Martens ¨ Berlin, Berlin, Germany Freie Universitat B Martin INRA, Unite´ de Recherche sur les Herbivores, Saint Gene`s Champanelle, France D Martin Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kiel, Germany P Martin Institut National de la Recherche Agronomique, Jouy-en-Josas, France
J A Lucey University of Wisconsin–Madison, Madison, WI, USA
W Martin-Rosset Institut National de la Recherche Agronomique, Saint-Gen`es Champanelle, France
P Luck North Carolina State University, Raleigh, NC, USA
I H Mather University of Maryland, College Park, MD, USA
M C Lucy University of Missouri, Columbia, MO, USA
J-L Maubois INRA Dairy Research Laboratory, Rennes, France
Contributors S Mayne Agri-Food and Biosciences Institute, Hillsborough, County Down, UK O J McCarthy Massey University, Palmerston North, New Zealand J McCaughey Agri-Food and Biosciences Institute, Hillsborough, County Down, UK M E McCormick Louisiana State University Agricultural Center, Franklinton, LA, USA B T McDaniel North Carolina State University, Raleigh, NC, USA
M Messer University of Sydney, Sydney, NSW, Australia L Meunier-Goddik Oregon State University, Corvallis, OR, USA O Mills British Sheep Dairying Association, Alresford, Hants, UK S Mills Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland F Minervini Universita` degli Studi di Bari, Bari, Italy
R K McGuffey Formerly at Elanco Animal Health, Indianapolis, IN, USA
G Miranda Institut National de la Recherche Agronomique, Jouy-en-Josas, France
M A McGuire University of Idaho, Moscow, ID, USA
V V Mistry South Dakota State University, Brookings, SD, USA
R McLaughlin Seattle University, Seattle, WA, USA
T Miura Nippon Veterinary and Life Science University, Tokyo, Japan
P McLoughlin Ashtown Food Research Centre, Dublin, Ireland D J McMahon Utah State University, Logan, UT, USA J P McNamara Washington State University, Pullman, WA, USA J D McPhee Guelph University, Guelph, ON, Canada P L H McSweeney University College, Cork, Ireland M Medina National Institute for Agricultural and Food Research and Technology (INIA), Madrid, Spain P Melendez University of Florida, Gainesville, FL, USA M Mellado University Autonoma Agraria Antonio Narro, Saltillo, Mexico K Menzies Deakin University, Geelong, VIC, Australia U Merin The Volcani Centre, Bet Dagan, Israel P Mermillod INRA, Physiologie de la Reproduction et des Comportements, Nouzilly, France
xix
P J Moate Ellinbank Centre, Ellinbank, VIC, Australia B Moioli Animal Production Research Institute, Monterotondo, Italy G Molle Istituto Zootecnico e Caseario per la Sardegna, Olmedo, Italy E M Molloy University College, Cork, Ireland D R Monke Select Sires, Inc., Plain City, OH, USA V Monnet Institut National de la Recherche Agronomique (INRA), Jouy-en-Josas, France A J Morgan Centenary Institute of Cancer Medicine and Cell Biology, Camperdown, NSW, Australia P A Morrissey University College Cork, Ireland B K Mortensen Tikøb, Denmark O S Mota University of Porto, Porto, Portugal
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Contributors
L D Muller The Pennsylvania State University, University Park, PA, USA
C J Oberg Weber State University, Ogden, UT, USA
D M Mulvihill University College, Cork, Ireland
B O’Brien Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, County Cork, Ireland
M Murphy Cork County Council, County Cork, Ireland
N M O’Brien University College, Cork, Ireland
M R Murphy University of Illinois at Urbana-Champaign, Champaign, IL, USA
S O’Brien University College, Dublin, Ireland
M Naum Food and Drug Administration, College Park, MD, USA
D J O’Callaghan Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
R L Nebel Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
D M O’Callaghan Wyeth Nutritionals Ireland, Askeaton, County Limerick, Ireland
F Neijenhuis Livestock Research, Lelystad, The Netherlands K F Ng-Kwai-Hang McGill University, Montreal, QC, Canada K R Nicholas Deakin University, Geelong, VIC, Australia S C Nickerson LSU Agricultural Center, Homer, LA, USA and University of Georgia, Athens, GA, USA S S Nielsen Purdue University, West Lafayette, IN, USA
J E O’Connell University College, Cork, Ireland M J O’Connell Chr. Hansen (UK) Ltd., Hungerford, Berkshire, UK D O’Connor Institute of Technology, Cork, Ireland T P O’Connor University College, Cork, Ireland A M O’Donnell Cornell University, Ithaca, NY, USA C P O’Donnell University College, Dublin, Ireland
M Nieminen Finnish Game and Fisheries Research Institute, Kaamanen, Finland
J A O’Donnell California Dairy Research Foundation, Davis, CA, USA
J A Nieuwenhuijse Friesland Campina Research, Deventer, The Netherlands
G R Oetzel University of Wisconsin–Madison, Madison, WI, USA
D Nohr Universita¨t Hohenheim, Stuttgart, Germany
O T Oftedal Smithsonian Environmental Research Center, Edgewater, MD, USA
A B Nongonierma University of Limerick, Limerick, Ireland J P Noordhuizen University of Utrecht, The Netherlands
A C Oliveira University of Porto, Porto, Portugal J C Oliveira University College, Cork, Ireland
˜ M Nunez National Institute for Agricultural and Food Research and Technology (INIA), Madrid, Spain
R Oliveira New University of Lisbon, Portugal
H Nursten University of Reading, Reading, UK
S P Oliver The University of Tennessee, Knoxville, TN, USA
Contributors E O’Mahony Cork County Council, Cork, Ireland
A Patrick Fonterra Research Centre, Palmerston North, New Zealand
J A O’Mahony Wyeth Nutritionals Ireland, Askeaton, County Limerick, Ireland
S Patton La Jolla, CA, USA
J O’Regan University College, Cork, Ireland
L Pearce Fonterra Research Centre, Palmerston North, New Zealand
N O’Shea University College, Cork, Ireland G Osthoff University of the Orange Free State, Bloemfontein, South Africa D J O’Sullivan University of Minnesota, St Paul, MN, USA M O’Sullivan University College, Dublin, Ireland A C Ouwehand Danisco, Enteromix, Kantvik, Finland W E Owens LSU Agricultural Center, Homer, LA, USA J Palmer Massey University, Palmerston North, New Zealand J M Panoff University of Caen Basse–Normandie, Caen, France E Parente Universita` degli Studi della Basilicata, Potenza, Italy S M Parish Washington State University, Pullman, WA, USA Y W Park Fort Valley State University, Fort Valley, GA, USA J E Parks Cornell University, Ithaca, NY, USA P W Parodi Dairy Australia, Melbourne, VIC, Australia M A Pascall The Ohio State University, Columbus, OH, USA A H J Paterson Massey University, Palmerston North, New Zealand
xxi
L Pellegrino Universita` degli Studi di Milano, Milan, Italy M C Perotti Universidad Nacional del Litoral (UNL) – Consejo Nacional de Investigaciones Cientı´ficas y Tecnolo¨gicas (CONICET), Santa Fe, Argentina G M Pighetti The University of Tennessee, Knoxville, TN, USA A Pihlanto MTT Agrifood Research Finland, Jokioinen, Finland M Pizzillo Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Muro Lucano, Italy H W Ploeger Utrecht University, Utrecht, The Netherlands S Pochet Institut National de la Recherche Agronomique, Poligny, France C Poppe Public Health Agency of Canada, Guelph, ON, Canada I B Powell Dairy Innovation Australia, Werribee, VIC, Australia R L Powell USDA Beltsville Agricultural Research Center, Beltsville, MD, USA V Prabhakar The Ohio State University, Columbus, OH, USA M Pravda University College, Cork, Ireland A Querol Institute of Agrochemistry and Food Technology (IATA), CSIC, Valencia, Spain A Quiberoni Instituto de Lactelogı´a Industrial (Universidad Nacional del Litoral–CONICET), Santa Fe, Argentina
xxii
Contributors
E M M Quigley University College, Cork, Ireland
J R Roche DairyNZ, Hamilton, New Zealand
K S Ramanujam Pfizer Nutrition, Collegeville, PA, USA
L Rodriguez-Saona The Ohio State University, Columbus, OH, USA
M Ramos Instituto de Investigatio´n en Ciencias de la Alimentac´ion (CSIC-UAM), Madrid, Spain
H Roginski The University of Melbourne, VIC, Australia
A R Rankin University of Wisconsin–Madison, Madison, WI, USA
H Rohm ¨ Dresden, Dresden, Technische Universitat Germany
S A Rankin University of Wisconsin–Madison, Madison, WI, USA
D Romagnolo University of Arizona, Tucson, AZ, USA
M D Rasmussen University of Aarhus, Horsens, Denmark
Y H Roos University College, Cork, Ireland
A Rasooly National Institutes of Health, Rockville, MD, USA
M Rosenberg University of California–Davis, Davis, CA, USA
F P Rattray Chr. Hansen A/S, Hørsholm, Denmark E Refstrup GEA Process Engineering – Niro, Søborg, Denmark D J Reinemann University of Wisconsin-Madison, Madison, WI, USA J A Reinheimer Universidad Nacional del Litoral–CONICET, Santa Fe, Argentina C K Reynolds The University of Reading, Reading, UK M A Reynolds Fonterra Research Centre, Palmerston North, New Zealand F Riedewald CEL-International, Cork, Ireland C A Risco University of Florida, Gainesville, FL, USA C G Rizzello University of Bari, Bari, Italy G L Robertson University of Queensland, Brisbane, QLD, Australia A-L Robin Leatherhead Food Research, Leatherhead, UK R K Robinson Formerly at University of Reading, Reading, UK
Y Rosnina Universiti Putra Malaysia, Selangor, Malaysia R P Ross Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland E Roth Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland Z Roth The Hebrew University of Jerusalem, Rehovot, Israel G Roudaut ENSBANA–Universite´ de Bourgogne, Dijon, France J-P Roy ´ St-Hyacinthe, QC, Canada Universite´ de Montreal, R Rubino Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Muro Lucano, Italy E O Rukke ˚ Norway Norwegian University of Life Sciences, As, P L Ryan Mississippi State University, MS, USA E T Ryser Michigan State University, East Lansing, MI, USA T Sako Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan
Contributors xxiii E Salimei Universita` degli Studi del Molise, Campobasso, Italy
B Seale University of Otago, Dunedin, New Zealand
S Salminen University of Turku, Turku, Finland
K M Seamans University College, Cork, Ireland
S Sandra University of Massachusetts, Amherst, MA, USA
H Seiler Technische Universita¨t, Mu¨nchen, Germany
O Santos Mota University of Porto, Porto, Portugal
N P Shah Victoria University, Melbourne, VIC, Australia
J E P Santos University of Florida, Gainesville, FL, USA
Shakeel-Ur-Rehman California Polytechnic State University, San Luis Obispo, CA, USA
L D Satter University of Wisconsin, Madison, WI, USA A B Saunders Fonterra Research Centre, Palmerston North, New Zealand P Sauvant ENITA de Bordeaux, Unite´ de Formation QENS, Gradignan, France L Sawyer The University of Edinburgh, Edinburgh, Scotland C Scalfaro Istituto Superiore di Sanita`, Rome, Italy K K Schillo University of Kentucky, Lexington, KY, USA B Schilter Nestle´ Research Center, Lausanne, Switzerland E Schlimme Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kiel, Germany B Schobinger Rehberger Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland D T Scholl ´ St-Hyacinthe, QC, Canada Universite´ de Montreal,
M Shamsuddin Bangladesh Agricultural University, Mymensingh, Bangladesh J A Sharp Deakin University, Geelong, VIC, Australia K Shea Horizon Organic, Longmont, CO, USA J J Sheehan Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland P A Sheehy University of Sydney, Sydney, NSW, Australia M Shelton Texas A & M University, San Angelo, TX, USA J E Shirley Kansas State University, Tompkinsville, KY, USA J N B Shrestha Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada R Sieber Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland D Simatos ENSBANA–Universite´ de Bourgogne, Dijon, France
R S Schrijver Veteffect Veterinary and Public Health, Bilthoven, The Netherlands
J S Sindhu National Dairy Research Institute, Karnal, Haryana, India
P Schuck INRA Agrocampus Ouest, Rennes, France
R P Singh University of California-Davis, Davis, CA, USA
C G Schwab University of New Hampshire, Durham, NH, USA
H Singh Massey University, Palmerston North, New Zealand
xxiv Contributors M Skanderby GEA Niro A/S, Soeborg, Denmark
´ V B Suarez Instituto de Lactelogı´a Industrial (Universidad Nacional del Litoral–CONICET), Santa Fe, Argentina
B Slaghuis Research Institute for Animal Husbandry, Lelystad, The Netherlands
A Subramanian The Ohio State University, Columbus, OH, USA
T R Smith Mississippi State University, MS, USA
I S Surono University of Indonesia, Jakarta, Indonesia
M El Soda Alexandria University, Alexandria, Egypt N Sommerer INRA UMR, Montpellier, France L M Sordillo Michigan State University, East Lansing, MI, USA T Sørhaug ˚ Norway Norwegian University of Life Sciences, As, J W Spears North Carolina State University, Raleigh, NC, USA S B Spencer Pennsylvania State University, University Park, PA, USA
B J Sutherland Sutherland Dairy Consulting, Melbourne, VIC, Australia N Suttle Moredun Foundation, Penicuik, UK J D Sutton The University of Reading, Earley Gate, Reading, UK K Svendsen Danish Agriculture and Food Council, Arhus, Denmark D M Swallow University College London, London, UK S Tabata Tokyo Metropolitan Institute of Public Health, Tokyo, Japan
D E Spiers University of Missouri, Columbia, MO, USA
D Tait Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kiel, Germany
J R Stabel National Animal Disease Center, Ames, IA, USA
T Takano Calpis Co. Ltd, Kanagawa, Japan
R H Stadler Nestle´ Product Technology Center, Orbe, Switzerland
R Tanaka Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan
C R Staples University of Florida, Gainesville, FL, USA J L Steele University of Wisconsin, Madison, WI, USA K Stelwagen Hamilton, New Zealand
M W Taylor Massey University, Palmerston North, New Zealand W W Thatcher University of Florida, Gainesville, FL, USA A Thierry INRA, Agrocampus, Ouest, Rennes, France
L Stepaniak ˚ Norway Agricultural University, As,
´ Thiry E ` ` University of Liege, Liege, Belgium
J S Stevenson Kansas State University, Manhattan, KS, USA
D L Thomas University of Wisconsin–Madison, Madison, WI, USA
R J E Stewart University of Zimbabwe, Harare, Zimbabwe
D Tome´ AgroParisTech, Paris, France
C R Stockdale Future Farming Systems Research, Tatura, VIC, Australia
P S Tong California Polytechnic State University, San Luis Obispo, CA, USA
Contributors xxv A M Tritscher World Health Organization, Geneva, Switzerland
M Walton Society of Dairy Technology, Appleby in Westmorland, UK
Y Tsunoda Kinki University, Nakamachi, Nara, Japan
G M Wani Sher-e-Kashmir University of Agricultural Sciences and Technology, Srinagar, Kashmir, India
C Tyburczy Cornell University, Ithaca, NY, USA T Uniacke-Lowe University College, Cork, Ireland T Urashima Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan L Vaccaro Universidad Central de Venezuela, Maracay, Venezuela B Vallat World Organisation for Animal Health (OIE), Paris, France S Valmorri Universita` degli Studi di Teramo, Mosciano S. Angelo (TE), Italy G van den Berg NIZO Food Research, Ede, The Netherlands H H Van Horn University of Florida, Gainesville, FL, USA W A van Staveren Wageningen University, Wageningen, The Netherlands
D Wechsler Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland B C Weimer University of California, Davis, CA, USA W P Weiss The Ohio State University, Wooster, OH, USA H Whelton University College Cork, Ireland C H White Mississippi State University, Starkville, MS, USA, Randolph Associates, Inc., Birmingham, AL, USA P Whyte University College, Dublin, Ireland M Wiedmann Cornell University, Ithaca, NY, USA G Wiener Roslin Institute, Edinburgh, UK
B Vardhanabhuti University of Missouri, Columbia, MO, USA
G R Wiggans United States Department of Agriculture, Beltsville, MD, USA
C Varming University of Copenhagen, Frederiksberg C, Denmark
L Wiking Aarhus University, Tjele, Denmark
P Vavra OECD, Paris, France
R A Wilbey The University of Reading, Reading, UK
J Vercruysse Ghent University, Merelbeke, Belgium E Villalobo Universidad de Sevilla, Seville, Spain W Vosloo Australian Animal Health Laboratory, Geelong, VIC, Australia H Wahid Universiti Putra Malaysia, Selangor, Malaysia B Walther Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland
G Wildbrett Technical University of Munich, Weihenstephan, Germany M G Wilkinson University of Limerick, Limerick, Ireland S T Willard Mississippi State University, Mississippi State, MS, USA H Willems Justus Liebig University, Giessen, Germany M Wilson University of Georgia, Athens, GA, USA
xxvi Contributors C M Wittho¨ft Swedish University of Agricultural Sciences, Uppsala, Sweden G Wolters Research Institute for Animal Husbandry, Lelystad, The Netherlands
R Yacamini Formerly at University College, Cork, Ireland N Yamamoto Calpis Co. Ltd, Kanagawa, Japan
D C Woollard NZ Laboratory Services, Auckland, New Zealand
C A Zalazar Universidad Nacional del Litoral (UNL) – Consejo Nacional de Investigaciones Cientı´ficas y Tecnolo¨gicas (CONICET), Santa Fe, Argentina
J Worley University of Georgia, Athens, GA, USA
R Zanabria Eyzaguirre University of Guelph, Guelph, ON, Canada
A J Wright University of Guelph, Guelph, ON, Canada
P Zangerl Federal Institute of Alpine Dairying BAM, Rotholz, Austria
W M D Wright University College, Cork, Ireland P C Wynn E H Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Wagga Wagga, NSW, Australia Z Z Xu Livestock Improvement Corporation Ltd., Hamilton, New Zealand
P Zhou Jiangnan University, Wuxi, Jiangsu Province, People’s Republic of China A Zittermann University of Bochum, Bad Oeynhausen, Germany S E Zorrilla Instituto de Desarrollo Tecnolo´gico para la Industria Quı´mica (INTEC), Santa Fe, Argentina
GUIDE TO USE OF THE ENCYCLOPEDIA STRUCTURE OF THE ENCYCLOPEDIA The material in the Encyclopedia is arranged as a series of entries in alphabetical order. Some entries comprise a single article, whilst entries on more diverse subjects consist of several articles that deal with various aspects of the topic. In the latter case the articles are arranged in a logical sequence within an entry. To help you realize the full potential of the material in the Encyclopedia we have provided three features to help you find the topic of your choice.
1. CONTENTS LISTS Your first point of reference will probably be the contents list. The complete contents list appearing in each volume will provide you with both the volume number and the page number of the entry. On the opening page of an entry a contents list is provided so that the full details of the articles within the entry are immediately available. Alternatively you may choose to browse through a volume using the alphabetical order of the entries as your guide. To assist you in identifying your location within the Encyclopedia a running headline indicates the current entry and the current article within that entry.
2. CROSS REFERENCES All of the articles in the Encyclopedia have been extensively cross referenced. The cross references, which appear at the end of an article, have been provided at three levels: i. To indicate if a topic is discussed in greater detail elsewhere. ii. To draw the reader’s attention to parallel discussions in other articles. iii. To indicate material that broadens the discussion. Example The following list of cross references appear at the end of the entry entitled Bacteria, Beneficial|Lactic Acid Bacteria: An Overview See also: Bacteria, Beneficial: Bifidobacterium spp.: Applications in Fermented Milks; Bifidobacterium spp.: Morphology and Physiology. Lactic Acid Bacteria: Citrate Fermentation by Lactic Acid Bacteria; Lactic Acid Bacteria in Flavor Development; Lactobacillus spp.: General Characteristics; Lactobacillus spp.: Lactobacillus acidophilus; Lactobacillus spp.: Lactobacillus casei Group; Lactobacillus spp.: Lactobacillus delbrueckii Group; Lactobacillus spp.: Lactobacillus helveticus; Lactobacillus spp.: Lactobacillus plantarum; Lactobacillus spp.: Other Species; Lactococcus lactis; Leuconostoc spp.; Pediococcus spp.; Physiology and Stress Resistance; Proteolytic Systems; Streptococcus thermophilus; Taxonomy and Biodiversity. Pathogens in Milk: Enterobacteriaceae.
3. INDEX The index will provide you with the volume number and page number of where the material is to be located, and the index entries differentiate between material that is a whole article, is part of an article, or is data presented in a table or figure. Detailed notes are provided on the opening page of the index.
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Guide to Use of the Encyclopedia
4. COLOR PLATES The color figures for each volume have been grouped together in a plate section. The location of this section is cited in the contents list. Color versions of black and white figures are cited in figure captions within individual articles.
5. CONTRIBUTORS A full list of contributors appears at the beginning of each volume.
6. GLOSSARY A glossary of terms used within the work is provided in Volume Four before the Index.
PREFACE
W
e are pleased to present the second edition of the Encyclopedia of Dairy Sciences. The first edition was published in 2003 by the Major Reference Works Division of Academic Press, now part of Elsevier Sciences, and it comprised 427 articles. The objective was to satisfy the need for an authoritative source of information for people involved in the integrated system of production, manufacture, and distribution of dairy foods. It was realized from the beginning that a program of revision would be needed to keep the Encyclopedia up to date. This goal has been met in the second edition through 503 articles, of which 121 are new articles and 382 are revised articles. We express appreciation to the Editorial Advisory Board for its role in evaluating articles for needed revision, reviewing new and revised articles, and for help in identifying new topics to be included along with appropriate authors. Likewise, we are grateful for the contributions of the many authors who have either revised their articles or prepared new articles. The main topics related to milk production and dairy technology are addressed in addition to providing information on nutrition, public health, and dairy industry economics including aspects of trade in milk and dairy products. All species that produce milk for human consumption have been included in this work. Some of these species are of regional significance only, but they have been included because of the essential role that their milk plays in the nutrition of people inhabiting various regions of the world. A significant addition to the second edition is four introductory articles addressing the history of Dairy Science and Technology. A synopsis has been prepared for each article in the second edition and will appear with the online listing of the articles in this publication. The primary aim of the Encyclopedia is to provide a complete resource for researchers, students, and practitioners involved in all aspects of the dairy sciences as well as those involved with economic and nutritional policy and members of the media. We have tried to do this with a writing style that is easily comprehended by persons who are not highly trained in the technical aspects of the Dairy Sciences. Users should be able to access information on topics that are peripheral to their areas of expertise. We express appreciation to the staff of the Major Reference Works Division, responsible for this Encyclopedia, for their timely responsiveness to the needs of the editors and their essential administrative role in keeping this major reference work on-track toward a satisfactory completion within the desired time schedule. We remember Nancy Maragioglio, Senior Life Sciences Editor, who initiated the work and was ever responsive to queries by the editors, as well as Sera Relton, Esmond Collins, Milo Perkins, and Claire Byrne, Development Editors, and Charlotte (Charlie) Kent, Publishing Administrator, who kept things moving through their communication with editors, authors, and reviewers and who exhibited almost flawless administrative skills. Sera Relton was particularly helpful as she assisted us in moving through the final submission and review stages. Laura Jackson is recognized for her contributions as Production Manager of the Encyclopedia. Special recognition is due to Ms Anne Cahalane, Senior Executive Assistant, School of Food & Nutritional Sciences, University College, Cork, whose stylized representation of a cow, a milk can, and a wedge of cheese adorns the cover of the first and second editions of the Encyclopedia of Dairy Sciences. John W. Fuquay Patrick F. Fox and Paul L. H. McSweeney
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FOREWORD
The cow is the foster mother of the human race. From the days of the ancient Hindoo to this time have the thoughts of men turned to this kindly and beneficent creature as one of the chief sustaining forces of human life. William Dempster Hoard (1836-1918) Former governor, state of Wisconsin, USA (1889-1891) Founder of Hoard’s Dairyman (1885)
W
e must never forget that milk and milk products are and will always be important sources of basic food nutrients for humans both young and old. The more scientific facts we can discover, understand, and apply related to producing, processing, and marketing milk and milk products, the better we will serve the nutritional needs of humanity throughout the world. More than 2000 years ago Aristotle noted, Everyone honors the wise and excellent. We are indebted to those wise enough to conceptualize and envision the favorable global impact that is certain to follow by bringing together this exhaustive, rich collection of 503 pertinent articles written and reviewed by more than 700 world-renowned disciplinary experts representing 50 countries – persons each of whom bears the mark of excellence. Happily these timely topics are now recorded in four informative, important, engaging volumes. We thank, commend, and salute the prodigious efforts of the wise and excellent authors who generated, compiled, and put the spotlight on the useful information and data, and who now share them through their well-written articles. One noteworthy value and enduring virtue of these articles is bringing into clear perspective the context of both the state-of-the-art and the future of dairy sciences. When the history and contributions of scholarly publications related to the all-important global dairy industry are recorded, the second edition of the Encyclopedia of Dairy Sciences will be cited often and with great respect and appreciation. Fundamental to continued progress and success in the dairy industry have been the signal service, cooperation, and collective contributions of dedicated scientists, teachers, agricultural advisors/extension workers, and representatives of governments and industries. Additional exciting breakthroughs in applying new findings and developments in research and technology to the production and processing of milk are sure to follow as we move surefootedly through the twentyfirst century. This continued growth and success will be aided immensely by the vast and extraordinarily useful knowledge base made available by the idea-rich, insightful authors, editorial advisory board members, editors, and publisher of the second edition of the Encyclopedia of Dairy Sciences. Indeed, by perusing the comprehensive and authoritative articles of this greatly needed and monumental encyclopedia, readers will be made even more aware of the tremendous progress that has occurred in the basic and applied sciences underpinning the global dairy industry. Ours is an internationally competitive and incredibly technological world. And unless talented, creative scientists continue to work together in researching and applying the most effective and economical ways and means of providing
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Foreword
an abundant, safe supply of milk and milk products for an ever-increasing world population, we will never reach our noble goal of adequately feeding all the earth’s people. May we utilize the comprehensive scientific knowledge base made available through this second edition of the Encyclopedia of Dairy Sciences as we pledge to realize advances in the health and well-being of the undernourished millions – including many who need and deserve to be rescued from the ugly grip of hunger – by increasing the availability of nature’s most nearly perfect food – milk! Pure milk from healthy animals is a luxury of the rich, whereas it ought to be the common food of the poor. Mohandas Gandhi (1869-1948) Indian nationalist leader
John R. Campbell, Ph.D., D.Sc. (Hon.) President Emeritus and Professor of Animal Science Oklahoma State University Dean Emeritus and Professor Emeritus of Animal Sciences College of Agriculture, University of Illinois Professor Emeritus of Animal Sciences University of Missouri Past President, ADSA (1980-81) April 2010
CONTENTS VOLUME 1 INTRODUCTION History of Dairy Science and Technology History of Dairy Farming
P F Fox, R K McGuffey, J E Shirley and T M Cogan
R K McGuffey and J E Shirley
History of Dairy Products and Processes History of Dairy Chemistry
P F Fox
2 12
P F Fox
History of Dairy Bacteriology
1
18
T M Cogan
26
A ADDITIVES IN DAIRY FOODS Types and Functions of Additives in Dairy Products
B Herr
Consumer Perceptions of Additives in Dairy Products Legislation Safety
C Brockman and C J M Beeren
A-L Robin
41 49
M B Gilsenan
Emulsifiers
34
55
N Krog
61
ANALYTICAL METHODS Sampling
R L Bradley, Jr.
72
Proximate and Other Chemical Analyses
M O’Sullivan
Statistical Methods for Assessing Analytical Data Multivariate Statistical Tools for Chemometrics Spectroscopy, Overview
E Parente E Parente
R McLaughlin and J D Glennon
Infrared Spectroscopy in Dairy Analysis
A Subramanian, V Prabhakar and L Rodriguez-Saona
Hyperspectral Imaging for Dairy Products Light Scattering Techniques
A A Gowen, C P O’Donnell, J Burger and D O’Callaghan
D S Horne
Atomic Spectrometric Techniques
Nuclear Magnetic Resonance: Principles
83 93 109 115 125 133
D Fitzpatrick and J D Glennon
Nuclear Magnetic Resonance: An Introduction
76
P McLoughlin and N Brunton F Mariette
141 146 153
Chromatographic Methods
Y Ardo¨, D E W Chatterton and C Varming
169
Immunochemical Methods
D Dupont
177
Electrophoresis
F Chevalier
Electrochemical Analysis
M Pravda
185 193
xxxiii
xxxiv
Contents
Mass Spectrometric Methods Ultrasonic Techniques Microbiological
F Chevalier and N Sommerer
198
W M D Wright
206
S K Anand
DNA-Based Assays
215
M Naum and K A Lampel
221
Microscopy (Microstructure of Milk Constituents and Products) Biosensors
M Auty
A Rasooly and K E Herold
Physical Methods
235
V Bhandari and H Singh
Differential Scanning Calorimetry
226
248
P Zhou and T P Labuza
256
Principles and Significance in Assessing Rheological and Textural Properties H Rohm and D Jaros
264
Rheological Methods: Instrumentation
272
Sensory Evaluation
H Rohm and D Jaros
M A Drake and C M Delahunty
279
ANIMALS THAT PRODUCE DAIRY FOODS Major Bos taurus Breeds
D S Buchanan
284
Minor and Dual-Purpose Bos taurus Breeds
G Averdunk and D Krogmeier
Bos indicus Breeds and Bos indicus Bos taurus Crosses Goat Breeds
F E Madalena
293 300
C Devendra and G F W Haenlein
310
Sheep Breeds
M H Fahmy and J N B Shrestha
325
Water Buffalo
M S Khan
340
Yak
G Wiener
343
Camel
G A Alhadrami
351
Horse
M Doreau and W Martin-Rosset
358
Donkey Reindeer
E Salimei
365
Ø Holand, H Gjøstein and M Nieminen
374
B BACTERIA, BENEFICIAL Bifidobacterium spp.: Morphology and Physiology
N P Shah
Bifidobacterium spp.: Applications in Fermented Milks
N P Shah
381 388
Brevibacterium linens, Brevibacterium aurantiacum and Other Smear Microorganisms T M Cogan
395
Lactic Acid Bacteria: An Overview
401
Propionibacterium spp.
P F Fox
A Thierry, H Falentin, S M Deutsch and G Jan
Probiotics, Applications in Dairy Products BACTERIOCINS
S Salminen, W Kenifel and A C Ouwehand
E M Molloy, C Hill, P D Cotter and R P Ross
403 412 420
BACTERIOPHAGE Biological Aspects
A Quiberoni, V B Sua´rez, A G Binetti and J A Reinheimer
Technological Importance in the Diary Industry
J Lyne
430 439
BIOFILM FORMATION S Flint, J Palmer, P Bremer, B Seale, J Brooks, D Lindsay and S Burgess
445
M Nun˜ez and M Medina
451
BIOGENIC AMINES
Contents
xxxv
BODY CONDITION Measurement Techniques and Data Processing
J P McNamara
Effects on Health, Milk Production, and Reproduction
J P McNamara
457 463
BULL MANAGEMENT Artificial Insemination Centers Dairy Farms
D R Monke
468
J Malmo
475
BUSINESS MANAGEMENT Roles and Responsibilities of the Manager Management Records and Analysis
G A Benson G A Benson
481 486
BUTTER AND OTHER MILKFAT PRODUCTS The Product and Its Manufacture Modified Butters
B K Mortensen
B K Mortensen
Properties and Analysis
500
E Frede
506
Anhydrous Milk Fat/Butter Oil and Ghee Milk Fat-Based Spreads Fat Replacers
492
B K Mortensen
B K Mortensen
515 522
T P O’Connor and N M O’Brien
528
C CHEESE Overview
P F Fox
534
Preparation of Cheese Milk
M E Johnson
Starter Cultures: General Aspects
I B Powell, M C Broome and G K Y Limsowtin
Starter Cultures: Specific Properties Secondary Cultures
M C Broome, I B Powell and G K Y Limsowtin
F P Rattray and I Eppert
Rennet-Induced Coagulation of Milk
D J O’Callaghan
T P Guinee and B J Sutherland R J Bennett and K A Johnston
Membrane Processing in Cheese Manufacture Microbiology of Cheese
Non-Starter Lactic Acid Bacteria
J R Broadbent, M F Budinich and J L Steele
Cheese Rheology
607 618
632 639 645
H-P Bachmann, M-T Fro¨hlich-Wyder, E Jakob, E Roth, D Wechsler, E Beuvier and S Buchin J J Sheehan
Biochemistry of Cheese Ripening
595
625 D Ercolini and S Coppola
T M Cogan
Avoidance of Gas Blowing
Cheese Flavor
V V Mistry
T M Cogan
Use of Microbial DNA Fingerprinting
Public Health Aspects
585 591
Mechanization of Cheesemaking
Raw Milk Cheeses
579
J A Lucey
Salting of Cheese
559
574 J A Lucey
Gel Firmness and Its Measurement
552
567
A Andre´n
Rennets and Coagulants
Curd Syneresis
544
661
P L H McSweeney
J-L Le Que´re´
667 675
T P Guinee
Acid- and Acid/Heat Coagulated Cheese
652
685 J A Lucey
698
xxxvi
Contents
Cheddar-Type Cheeses
J M Banks
706
Swiss-Type Cheeses
H-P Bachmann, U Bu¨tikofer, M-T Fro¨hlich-Wyder, D Isolini and E Jakob
712
Dutch-Type Cheeses
E M Du¨sterho¨ft, W Engels and G van den Berg
721
Hard Italian Cheeses
R Di Cagno and M Gobbetti
728
Pasta-Filata Cheeses: Low-Moisture Part-Skim Mozzarella (Pizza Cheese) Pasta-Filata Cheeses: Traditional Pasta-Filata Cheese Smear-Ripened Cheeses
D J McMahon and C J Oberg
M De Angelis and M Gobbetti
W Bockelmann
767
Camembert, Brie, and Related Varieties
M-N Leclercq-Perlat
Cheese with Added Herbs, Spices and Condiments Cheeses Matured in Brine
M El Soda and S Awad
T P Guinee
790
799
814
T P Guinee
Low-Fat and Reduced-Fat Cheese
822
M E Johnson
Current Legislation for Cheeses
783
805
T P Guinee
Cheese as a Food Ingredient
773
795
M G Wilkinson, I A Doolan and K N Kilcawley
Pasteurized Processed Cheese Products Cheese Analogues
A A Hayaloglu and N Y Farkye
M El Soda, S Awad and M H Abd El-Salam
Accelerated Cheese Ripening Enzyme-Modified Cheese
745 753
Y Ardo¨
Blue Mold Cheese
737
833
M Hickey
843
CHOCOLATE Milk Chocolate
S T Beckett
856
CONCENTRATED DAIRY PRODUCTS Evaporated Milk
J A Nieuwenhuijse
Sweetened Condensed Milk Dulce de Leche Khoa
862
J A Nieuwenhuijse
869
C A Zalazar and M C Perotti
874
N Bansal
881
CONTAMINANTS OF MILK AND DAIRY PRODUCTS Contamination Resulting from Farm and Dairy Practices A M Tritscher and R H Stadler Environmental Contaminants
W J Fischer, B Schilter,
W J Fischer, B Schilter, A M Tritscher and R H Stadler
Nitrates and Nitrites as Contaminants
H E Indyk and D C Woollard
887 898 906
CREAM Manufacture Products
W Hoffmann
912
W Hoffmann
920
VOLUME 2
D DAIRY EDUCATION Dairy Production
L D Muller
1
Dairy Technology
P Jelen
6
Contents
xxxvii
DAIRY FARM LAYOUT AND DESIGN Building and Yard Design, Warm Climates
J Andrews and T Davison
13
DAIRY FARM MANAGEMENT SYSTEMS Seasonal, Pasture-Based, Dairy Cow Breeds
P T Doyle and C R Stockdale
Non-Seasonal, Pasture Optimized, Dairy Cow Breeds in the United States
M E McCormick
Non-Seasonal, Pasture-Based Milk Production Systems in Western Europe Dry Lot Dairy Cow Breeds
29
S Mayne, J McCaughey and C Ferris
M F Hutjens
38 44 52
Goats
R Rubino, M Pizzillo, S Claps and J Boyazoglu
59
Sheep
J N B Shrestha
67
DAIRY PRODUCTION IN DIVERSE REGIONS Africa
R J E Stewart
77
China
J Bao
83
Latin America
L Vaccaro
88
Southern Asia
M Shamsuddin
94
DAIRY SCIENCE SOCIETIES, AND ASSOCIATIONS
P F Fox
101
DEHYDRATED DAIRY PRODUCTS Milk Powder: Types and Manufacture
P Schuck
108
Milk Powder: Physical and Functional Properties of Milk Powders Dairy Ingredients in Non-Dairy Foods Infant Formulae
P Schuck
W J Harper
117 125
D M O’Callaghan, J A O’Mahony, K S Ramanujam and A M Burgher
135
DISEASES OF DAIRY ANIMALS Infectious Diseases: Bluetongue
J-P Roy, D T Scholl and E´ Thiry
146
Infectious Diseases: Brucellosis
J Gibbs and Z Bercovich
153
Infectious Diseases: Foot-and-Mouth Disease
R S Schrijver and W Vosloo
160
Infectious Diseases: Hairy Heel Warts
C T Estill
168
Infectious Diseases: Johne’s Disease
M T Collins and J R Stabel
174
Infectious Diseases: Leptospirosis Infectious Diseases: Listeriosis
H J Bearden
181
M Wiedmann and K G Evans
184
Infectious Diseases: Salmonellosis
C Poppe
190
Infectious Diseases: Tuberculosis
M T Collins
195
Non-Infectious Diseases: Acidosis/Laminitis Non-Infectious Diseases: Bloat
J P McNamara and J M Gay
P J Moate and R H Laby
Non-Infectious Diseases: Displaced Abomasum Non-Infectious Diseases: Fatty Liver
S S Donkin
Non-Infectious Diseases: Grass Tetany Non-Infectious Diseases: Ketosis Non-Infectious Diseases: Milk Fever
S M Parish
230
G R Oetzel
239
I J Lean
246 R M Hopper
L Avendan˜o-Reyes and A Correa-Caldero´n
Parasites, Internal: Gastrointestinal Nematodes
212
224
I J Lean
Parasites, External: Mange, Dermatitis and Dermatosis Parasites, External: Tick Infestations
206
217
H Martens
Non-Infectious Diseases: Pregnancy Toxemia
199
J Charlier, E Claerebout and J Vercruysse
250 253 258
xxxviii
Contents
Parasites, Internal: Liver Flukes
F H M Borgsteede
264
Parasites, Internal: Lungworms
H W Ploeger
270
E ENZYMES EXOGENOUS TO MILK IN DAIRY TECHNOLOGY -D-Galactosidase Lipases
P J T Dekker and C B G Daamen
276
A Kilara
Proteinases
284
A B Nongonierma and R J FitzGerald
Transglutaminase
289
D Jaros and H Rohm
297
Catalase, Glucose Oxidase, Glucose Isomerase and Hexose Oxidase
P L H McSweeney
301
ENZYMES INDIGENOUS TO MILK Lipases and Esterases
H C Deeth
304
Plasmin System in Milk
B Ismail and S S Nielsen
308
Phosphatases Lactoperoxidase
Shakeel-Ur-Rehman and N Y Farkye E M Buys
Xanthine Oxidoreductase Other Enzymes
314 319
R Harrison
324
N Y Farkye and N Bansal
327
F FEED INGREDIENTS Feed Concentrates: Cereal Grains
M L Eastridge and J L Firkins
Feed Concentrates: Co-Product Feeds
M B Hall and P J Kononoff
Feed Concentrates: Oilseed and Oilseed Meals Feed Supplements: Anionic Salts
J K Bernard
342 349
G R Oetzel
Feed Supplements: Fats and Protected Fats
335
356 T C Jenkins
363
Feed Supplements: Macrominerals
L D Satter and J R Roche
371
Feed Supplements: Microminerals
J W Spears and T E Engle
378
Feed Supplements: Organic-Chelated Minerals
D W Kellogg and E B Kegley
Feed Supplements: Ruminally Protected Amino Acids Feed Supplements: Vitamins
C G Schwab
W P Weiss
384 389 396
FEEDS, PREDICTION OF ENERGY AND PROTEINS Feed Energy Feed Proteins
W P Weiss
403
J E P Santos and J T Huber
409
FEEDS, RATION FORMULATION Systems Describing Nutritional Requirements of Dairy Cows Models in Nutritional Research Models in Nutritional Management Dry Period Rations in Cattle
I J Lean
418
J France, J Dijkstra and R L Baldwin
429
R Boston, Z Dou and W Chalupa
436
T R Smith
Lactation Rations in Cows on Grazing Systems Lactation Rations for Dairy Cattle on Dry Lot Systems
448 J R Roche
453
L E Chase
Transition Cow Feeding and Management on Pasture Systems
J R Roche
458 464
Contents
xxxix
FERMENTED MILKS Types and Standards of Identity Starter Cultures
I S Surono and A Hosono
I S Surono and A Hosono
Health Effects of Fermented Milks Buttermilk
T Takano and N Yamamoto
483 489
H Roginski
Middle Eastern Fermented Milks Asian Fermented Milks
Kefir
477
Z Libudzisz and L Stepaniak
Nordic Fermented Milks
Koumiss
470
496
M H Abd El-Salam
503
R Akuzawa, T Miura and I S Surono
507
T Uniacke-Lowe
512
F P Rattray and M J O’Connell
Yogurt: Types and Manufacture
518
R K Robinson
Yogurt: Role of Starter Culture
525
R K Robinson
FLAVORS AND OFF-FLAVORS IN DAIRY FOODS
529 R Marsili
533
FORAGES AND PASTURES Annual Forage and Pasture Crops – Species and Varieties
E J Havilah
Annual Forage and Pasture Crops – Establishment and Management Perennial Forage and Pasture Crops – Species and Varieties
E J Havilah
K F Lowe, D E Hume and W J Fulkerson
Perennial Forage and Pasture Crops – Establishment and Maintenance K F Lowe and D E Hume Grazing Management
552 563 576
W J Fulkerson,
W J Fulkerson and K F Lowe
586 594
G GAMETE AND EMBRYO TECHNOLOGY Artificial Insemination Cloning
R H Foote and J E Parks
602
Y Kato and Y Tsunoda
In Vitro Fertilization
610
P Mermillod
616
Multiple Ovulation and Embryo Transfer Sexed Offspring Transgenic Animals
P Lonergan and M P Boland
J F Hasler and D L Garner
623 631
G Laible
637
B T McDaniel
646
GENETICS Selection: Concepts
Selection: Evaluation and Methods
G R Wiggans and N Gengler
Selection: Economic Indices for Genetic Evaluation Cattle Genomics
B G Cassell
B J Hayes, B Cocks and M E Goddard
International Flow of Genes GENETIC DEFECTS IN CATTLE
649 656 663
R L Powell
669
D A Funk
675
H HAZARD ANALYSIS AND CRITICAL CONTROL POINTS HACCP Total Quality Management and Dairy Herd Health Processing Plants
M Jones
J P Noordhuizen
679 687
xl
Contents
HEAT TREATMENT OF MILK Thermization of Milk
E O Rukke, T Sørhaug and L Stepaniak
Ultra-High Temperature Treatment (UHT): Heating Systems
693 H C Deeth and N Datta
Ultra-High Temperature Treatment (UHT): Aseptic Packaging
G L Robertson
699 708
Sterilization of Milk and Other Products
J Hinrichs and Z Atamer
714
Non-Thermal Technologies: Introduction
H C Deeth and N Datta
725
Non-Thermal Technologies: High Pressure Processing
N Datta and H C Deeth
732
Non-Thermal Technologies: Pulsed Electric Field Technology and Ultrasonication H C Deeth and N Datta
738
Heat Stability of Milk
744
J E O’Connell and P F Fox
HOMOGENIZATION OF MILK Principles and Mechanism of Homogenization, Effects and Assessment of Efficiency: Valve Homogenizers R A Wilbey
750
High-Pressure Homogenizers
755
T Huppertz
Other Types of Homogenizer (High-Speed Mixing, Ultrasonics, Microfluidizers, Membrane Emulsification) T Huppertz HORMONES IN MILK
C R Baumrucker and A L Magliaro-Macrina
761 765
HUSBANDRY OF DAIRY ANIMALS Buffalo: Asia
H Wahid and Y Rosnina
Buffalo: Mediterranean Region
772
A Borghese and B Moioli
Goat: Feeding Management
780
S P Hart
785
Goat: Health Management
J S Bowen
797
Goat: Milking Management
P Billon
804
Goat: Multipurpose Management
G M Wani
814
Goat: Replacement Management
S P Hart and C Delaney
825
Goat: Reproductive Management
M Mellado
834
Predator Control in Goats and Sheep Sheep: Feeding Management
M Shelton
841
G Molle and S Landau
848
Sheep: Health Management
C Macaldowie
857
Sheep: Milking Management
O Mills
865
Sheep: Multipurpose Management
J Hatziminaoglou and J Boyazoglu
875
Sheep: Replacement Management
D L Thomas
882
Sheep: Reproductive Management
E Gootwine
887
I ICE CREAM AND DESSERTS Ice Cream and Frozen Desserts: Product Types Ice Cream and Frozen Desserts: Manufacture Dairy Desserts
A B Saunders
IMITATION DAIRY PRODUCTS
H D Goff H D Goff
893 899 905
D Haisman
913
Contents xli
VOLUME 3 L LABELING OF DAIRY PRODUCTS
C Heggum
LABOR MANAGEMENT ON DAIRY FARMS
1
B L Erven
9
LACTATION Lactogenesis
R M Akers and A V Capuco
Induced Lactation
15
R S Kensinger and A L Magliaro-Macrina
Galactopoiesis, Effects of Hormones and Growth Factors
A V Capuco and R M Akers
Galactopoiesis, Effect of Treatment with Bovine Somatotropin Galactopoiesis, Seasonal Effects
20
A V Capuco and R M Akers
R J Collier, D Romagnolo and L H Baumgard
26 32 38
LACTIC ACID BACTERIA J Bjo¨rkroth and J Koort
Taxonomy and Biodiversity Proteolytic Systems
45
L Lopez-Kleine and V Monnet
Physiology and Stress Resistance
49
B C Weimer
Genomics, Genetic Engineering
56
D J O’Sullivan, J-H Lee and W Dominguez
Lactobacillus spp.: General Characteristics
M De Angelis and M Gobbetti
Lactobacillus spp.: Lactobacillus acidophilus
P K Gopal
Lactobacillus spp.: Lactobacillus casei Group
F Minervini
67 78 91 96
Lactobacillus spp.: Lactobacillus helveticus
R Di Cagno and M Gobbetti
105
Lactobacillus spp.: Lactobacillus plantarum
A Corsetti and S Valmorri
111
Lactobacillus spp.: Lactobacillus delbrueckii Group Lactobacillus spp.: Other Species
C G Rizzello and M De Angelis
M Calasso and M Gobbetti
119 125
Lactococcus lactis
S Mills, R P Ross and A Coffey
132
Leuconostoc spp.
R Holland and S-Q Liu
138
Streptococcus thermophilus Pediococcus spp.
J Harnett, G Davey, A Patrick, C Caddick and L Pearce
R Holland, V Crow and B Curry
Enterococcus in Milk and Dairy Products
G Garcı´a de Fernando
Lactic Acid Bacteria in Flavor Development
T Coolbear, B Weimer and M G Wilkinson
Citrate Fermentation by Lactic Acid Bacteria
T P Beresford
143 149 153 160 166
LACTOSE AND OLIGOSACCHARIDES Lactose: Chemistry, Properties Lactose: Crystallization
P F Fox
P Schuck
Lactose: Production, Applications Lactose: Derivatives
Maillard Reaction Lactose Intolerance
182 A H J Paterson
M G Ga¨nzle
Lactose: Galacto-Oligosaccharides
196 202
M G Ga¨nzle
H Nursten
209 217
D M Swallow
Indigenous Oligosaccharides in Milk
173
236 T Urashima, S Asakuma, M Kitaoka and M Messer
241
LIQUID MILK PRODUCTS Liquid Milk Products: Pasteurized Milk
L Meunier-Goddik and S Sandra
274
xlii
Contents
Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk) A Lopez-Hernandez and A R Rankin Liquid Milk Products: UHT Sterilized Milks
S A Rankin, 281
M Rosenberg
288
Liquid Milk Products: Modified Milks
M Guo
297
Liquid Milk Products: Flavored Milks
W Bisig
301
Liquid Milk Products: Membrane-Processed Liquid Milk
J-L Maubois
Pasteurization of Liquid Milk Products: Principles, Public Health Aspects Recombined and Reconstituted Products
307 E T Ryser
P S Tong
310 316
M MAMMALS
I A Forsyth
320
MAMMARY GLAND Anatomy
S C Nickerson and R M Akers
Growth, Development and Involution
328
W L Hurley and J J Loor
Gene Networks Controlling Development and Involution
J J Loor, M Bionaz and W L Hurley
338 346
MAMMARY GLAND, MILK BIOSYNTHESIS AND SECRETION Milk Fat
D E Bauman, M A McGuire and K J Harvatine
Milk Protein Lactose
K Stelwagen
352 359
K Stelwagen
367
Secretion of Milk Constituents
I H Mather
373
MAMMARY RESISTANCE MECHANISMS Anatomical
S C Nickerson
Endogenous
381
L M Sordillo and S L Aitken
386
MANURE / EFFLUENT MANAGEMENT Systems Design and Government Regulations Nutrient Recycling
J Worley and M Wilson
H H Van Horn
392 399
MASTITIS PATHOGENS Contagious Pathogens
S C Nickerson
Environmental Pathogens
408
S P Oliver, G M Pighetti and R A Almeida
415
MASTITIS THERAPY AND CONTROL Automated Online Detection of Abnormal Milk Management Control Options Medical Therapy Options
H Hogeveen
S C Nickerson
429
W E Owens and S C Nickerson
Role of Milking Machines in Control of Mastitis MICROORGANISMS ASSOCIATED WITH MILK
422
F Neijenhuis A N Hassan and J F Frank
435 440 447
MILK Introduction
P F Fox
Physical and Physico-Chemical Properties of Milk Bovine Milk Goat Milk Sheep Milk
P F Fox L Amigo and J Fontecha M Ramos and M Juarez
458 O J McCarthy
467 478 484 494
Contents xliii Buffalo Milk
J S Sindhu and S Arora
503
Camel Milk
Z Farah
512
Equid Milk
T Uniacke-Lowe and P F Fox
518
Milks of Other Domesticated Mammals (Pigs, Yaks, Reindeer, etc.) Milks of Non-Dairy Mammals
G Osthoff
Milk of Monotremes and Marsupials Milk of Marine Mammals Human Milk Colostrum
Y W Park
538
J A Sharp, K Menzies, C Lefevre and K R Nicholas
O T Oftedal
581
P Marnila and H Korhonen
591
Seasonal Effects on Processing Properties of Cows’ Milk
Milk of Primates
553 563
A Darragh and B Lo¨nnerdal
Milk in Human Health and Nutrition
530
B O’Brien and T P Guinee
S Patton
598 607
T Uniacke-Lowe and P F Fox
613
MILKING AND HANDLING OF RAW MILK Milking Hygiene
B Slaghuis, G Wolters and D J Reinemann
Influence on Free Fatty Acids
632
L Wiking
638
Effect of Storage and Transport on Milk Quality
C H White
642
MILK LIPIDS General Characteristics Fatty Acids
M W Taylor and A K H MacGibbon
649
M W Taylor and A K H MacGibbon
Conjugated Linoleic Acid Triacylglycerols
655
D E Bauman, C Tyburczy, A M O’Donnell and A L Lock
M W Taylor and A K H MacGibbon
Phospholipids
665
A K H MacGibbon and M W Taylor
Fat Globules in Milk
675 I H Mather
680
Buttermilk and Milk Fat Globule Membrane Fractions Analytical Methods
R Zanabria Eyzaguirre and M Corredig
A K M MacGibbon and M A Reynolds
Rheological Properties and Their Modification Nutritional Significance Lipid Oxidation
670
P F Fox
Milk Fat Globule Membrane
A J Wright, A G Marangoni and R W Hartel
716
H C Deeth
721 S A Aherne
Removal of Cholesterol from Dairy Products
704 711
N M O’Brien and T P O’Connor
Cholesterol: Factors Determining Levels in Blood
691 698
N M O’Brien and T P O’Connor
Lipolysis and Hydrolytic Rancidity
660
727
R Sieber, B Schobinger Rehberger and B Walther
734
MILK PROTEINS Analytical Methods
D Dupont, R Grappin, S Pochet and D Lefier
Heterogeneity, Fractionation, and Isolation
K F Ng-Kwai-Hang
Casein Nomenclature, Structure, and Association Casein, Micellar Structure -Lactalbumin -Lactoglobulin
751
H M Farrell, Jr.
765
D S Horne
772
K Brew
780
L K Creamer, S M Loveday and L Sawyer
Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins Lactoferrin
741
H Korhonen and P Marnila
787 P C Wynn, A J Morgan and P A Sheehy
795 801
xliv
Contents
Immunoglobulins
P Marnila and H Korhonen
807
A Malet, A Blais and D Tome´
Nutritional Quality of Milk Proteins
816
Inter-Species Comparison of Milk Proteins: Quantitative Variability and Molecular Diversity P Martin, C Cebo and G Miranda
821
Proteomics
843
F Chevalier
MILK PROTEIN PRODUCTS Milk Protein Concentrate
P M Kelly
848
Caseins and Caseinates, Industrial Production, Compositional Standards, Specifications, and Regulatory Aspects J O’Regan and D M Mulvihill
855
Membrane-Based Fractionation
864
Whey Protein Products
P M Kelly
E A Foegeding, P Luck and B Vardhanabhuti
Bioactive Peptides
873
A Pihlanto
879
Functional Properties of Milk Proteins
H Singh
887
MILK QUALITY AND UDDER HEALTH Test Methods and Standards
A L Kelly, G Leitner and U Merin
Effect on Processing Characteristics
894
M Auldist
902
MILK SALTS Distribution and Analysis
F Gaucheron
908
Interaction with Caseins
C Holt
917
Macroelements, Nutritional Significance
K D Cashman
925
Trace Elements, Nutritional Significance
K D Cashman
933
MILKING MACHINES Principles and Design Robotic Milking
S B Spencer
941
C J A M de Koning
952
MILKING PARLORS
D J Reinemann and M D Rasmussen
MOLECULAR GENETICS AND DAIRY FOODS
959
S Mills, R P Ross and D P Berry
965
D Martin, E Schlimme and D Tait
971
N NUCLEOSIDES AND NUCLEOTIDES IN MILK NUTRIENTS, DIGESTION AND ABSORPTION Fermentation in the Rumen
M R Murphy
Fiber Digestion in Pasture-Based Cows Small Intestine of Lactating Ruminants Absorption of Minerals and Vitamins
980
J Gibbs and J R Roche
985
J D Sutton and C K Reynolds
989
N Suttle
996
NUTRITION AND HEALTH Nutritional and Health-Promoting Properties of Dairy Products: Contribution of Dairy Foods to Nutrient Intake C J Cifelli, J B German and J A O’Donnell Nutritional and Health-Promoting Properties of Dairy Products: Bone Health
1003 A Zittermann
Nutritional and Health-Promoting Properties of Dairy Products: Colon Cancer Prevention
E M M Quigley
1009 1016
Nutritional and Health-Promoting Properties of Dairy Products: Fatty Acids of Milk and Cardiovascular Disease P W Parodi
1023
Nutritional and Oral Health-Promoting Properties of Dairy Products: Caries Prevention and Oral Health H Whelton
1034
Contents Milk Allergy
E I El-Agamy
1041
Diabetes Mellitus and Consumption of Milk and Dairy Products Galactosemia
xlv
J P Hill, M J Boland and V A Landells
A Flynn
1046 1051
Nutrigenomics and Nutrigenetics
K M Seamans and K D Cashman
1056
S Fosset and D Tome´
Nutraceuticals from Milk
1062
Effects of Processing on Protein Quality of Milk and Milk Products S Cattaneo and I De Noni
L Pellegrino, 1067
VOLUME 4 O OFFICE OF INTERNATIONAL EPIZOOTIES Mission, Organization and Animal Health Code ORGANIC DAIRY PRODUCTION
B Vallat and B Carnat
K Shea
1 9
P PACKAGING
V B Alvarez and M A Pascall
16
PATHOGENS IN MILK Bacillus cereus Brucella spp.
A Christiansson
24
B Garin-Bastuji
Campylobacter spp.
31
P Whyte, P Haughton, S O’Brien, S Fanning, E O’Mahony and M Murphy
40
Clostridium spp.
P Aureli, G Franciosa and C Scalfaro
47
Coxiella burnetii
C Heydel and H Willems
54
Escherichia coli
P Desmarchelier and N Fegan
60
Enterobacteriaceae
S K Anand and M W Griffiths
Enterobacter spp.
S Cooney, C Iversen, B Healy, S O’Brien and S Fanning
Listeria monocytogenes Mycobacterium spp. Salmonella spp. Shigella spp.
67
E T Ryser
81
J Dalton and C Hill
87
C Poppe
93
E Villalobo
99
Staphylococcus aureus – Molecular Staphylococcus aureus – Dairy Yersinia enterocolitica
72
T J Foster
104
H Asperger and P Zangerl
111
M D Barton
117
PLANT AND EQUIPMENT Process and Plant Design
R P Singh and S E Zorrilla
Materials and Finishes for Plant and Equipment
124
K Cronin and R Cocker
Flow Equipment: Principles of Pump and Piping Calculations
J C Oliveira
134 139
Flow Equipment: Pumps
J C Oliveira
145
Flow Equipment: Valves
K Cronin and E Byrne
152
Agitators in Milk Processing Plants
K Cronin and J J Fitzpatrick
160
xlvi
Contents
Centrifuges and Separators: Types and Design
B Heymann
Centrifuges and Separators: Applications in the Dairy Industry Heat Exchangers
O J McCarthy
175
U Bolmstedt
Pasteurizers, Design and Operation Evaporators
166
184 A L Kelly and N O’Shea
193
V Gekas and K Antelli
Milk Dryers: Drying Principles Milk Dryers: Dryer Design
200
E Refstrup and J Bonke
208
M Skanderby
216
Instrumentation and Process Control: Instrumentation
R Oliveira, P Georgieva and S Feyo de Azevedo
234
Instrumentation and Process Control: Process Control
P Georgieva
242
Robots
J C Oliveira
Corrosion
252
P D Fox
257
Continuous Process Improvement and Optimization Quality Engineering
J C Oliveira
263
J C Oliveira
Safety Analysis and Risk Assessment In-Place Cleaning
273 N Hyatt
277
M Walton
283
POLICY SCHEMES AND TRADE IN DAIRY PRODUCTS Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy
H O Hansen
286
Agricultural Policy Schemes: European Union’s Common Agricultural Policy M Keane and D O’Connor
295
Agricultural Policy Schemes: United States’ Agricultural System
300
Agricultural Policy Schemes: Other Systems Codex Alimentarius
E Jesse
P Vavra
306
C Heggum
Standards of Identity of Milk and Milk Products
312 C Heggum
Trade in Milk and Dairy Products, International Standards: Harmonized Systems
322 K Svendsen
331
Trade in Milk and Dairy Products, International Standards: World Trade Organization
A M Arve
338
World Trade Organization and Other Factors Shaping the Dairy Industry in the Future
P Vavra
345
PREBIOTICS Types
T Sako and R Tanaka
Functions
354
T Sako and R Tanaka
365
PSYCHROTROPHIC BACTERIA Arthrobacter spp.
G Comi and C Cantoni
Pseudomonas spp.
372
J D McPhee and M W Griffiths
Other Psychrotrophs
L Stepaniak
379 384
R REPLACEMENT MANAGEMENT IN CATTLE Growth Standards and Nutrient Requirements Pre-Ruminant Diets and Weaning Practices Growth Diets
R E James R E James
R E James
Breeding Standards and Pregnancy Management Health Management
S T Franklin and J A Jackson
390 396 403
J S Stevenson and A Ahmadzadeh
410 417
Contents
xlvii
REPRODUCTION, EVENTS AND MANAGEMENT Estrous Cycles: Puberty
K K Schillo
Estrous Cycles: Characteristics
421
M A Crowe
Estrous Cycles: Postpartum Cyclicity
428
H A Garverick and M C Lucy
Estrous Cycles: Seasonal Breeders
434
S T Willard
Control of Estrous Cycles: Synchronization of Estrus
440 Z Z Xu
448
Control of Estrous Cycles: Synchronization of Ovulation and Insemination Mating Management: Detection of Estrus
R L Nebel, C M Jones and Z Roth
Mating Management: Artificial Insemination, Utilization Mating Management: Fertility
W W Thatcher and J E P Santos
M T Kaproth and R H Foote
M G Diskin
Pregnancy: Characteristics
454 461 467 475
H Engelhardt and G J King
485
Pregnancy: Physiology
P J Hansen
493
Pregnancy: Parturition
P L Ryan
503
Pregnancy: Periparturient Disorders
C A Risco and P Melendez
RHEOLOGY OF LIQUID AND SEMI-SOLID MILK PRODUCTS RISK ANALYSIS
514
O J McCarthy
520
C Heggum
RODENTS, BIRDS, AND INSECTS
532 K M Keener
540
S STANDARDIZATION OF FAT AND PROTEIN CONTENT
P Jelen
545
STRESS IN DAIRY ANIMALS Cold Stress: Effects on Nutritional Requirements, Health and Performance Cold Stress: Management Considerations
W G Bickert
Heat Stress: Effects on Milk Production and Composition Heat Stress: Effects on Reproduction
L E Chase
550 555
C R Staples and W W Thatcher
P J Hansen and J W Fuquay
Management Induced Stress in Dairy Cattle: Effects on Reproduction and D E Spiers
561 567
M C Lucy, H A Garverick 575
U UTILITIES AND EFFLUENT TREATMENT Water Supply Heat Generation Refrigeration
582
O S Mota
589
A C Oliveira and C F Afonso
Compressed Air Electricity
F Riedewald
596
O Santos Mota
602
R Yacamini
Dairy Plant Effluents
610
G Wildbrett
Design and Operation of Dairy Effluent Treatment Plants
613 R J Byrne
Reducing the Negative Impact of the Dairy Industry on the Environment V B Alvarez, M Eastridge and T Ji
619 631
xlviii
Contents
V VITAMINS General Introduction
D Nohr
636
Vitamin A
P Sauvant, B Graulet, B Martin, P Grolier and V Azaı¨s-Braesco
639
Vitamin D
W A van Staveren and L C P M G de Groot
646
Vitamin E
P A Morrissey and T R Hill
652
Vitamin K
T R Hill and P A Morrissey
661
Vitamin C
P A Morrissey and T R Hill
667
D Nohr, H K Biesalski and E I Back
Vitamin B12 Folates
C M Wittho¨ft
Biotin (Vitamin B7) Niacin
D Nohr, H K Biesalski and E I Back
687 690
D Nohr, H K Biesalski and E I Back
694
D Nohr, H K Biesalski and E I Back
Vitamin B6
Riboflavin
678
D Nohr, H K Biesalski and E I Back
Pantothenic Acid
Thiamine
675
697
D Nohr, H K Biesalski and E I Back
701
D Nohr, H K Biesalski and E I Back
704
W WATER IN DAIRY PRODUCTS Water in Dairy Products: Significance
Y H Roos
Analysis and Measurement of Water Activity
707
D Simatos, G Roudaut and D Champion
WELFARE OF ANIMALS, POLITICAL AND MANAGEMENT ISSUES
H D Guither and S E Curtis
715 727
WHEY PROCESSING Utilization and Products Demineralization
P Jelen
731
G Gernigon, P Schuck, R Jeantet and H Burling
738
Y YEASTS AND MOLDS Yeasts in Milk and Dairy Products Kluyveromyces spp.
744
C Belloch, A Querol and E Barrio
754
F Eliskases-Lechner, M Gue´guen and J M Panoff
Geotrichum candidum Penicillium roqueforti
A Abbas and A D W Dobson
Penicillium camemberti
776
T Sørhaug
780
A D W Dobson
785
Mycotoxins: Classification, Occurrence and Determination Mycotoxins: Aflatoxins and Related Compounds
765 772
A Abbas and A D W Dobson
Spoilage Molds in Dairy Products Aspergillus flavus
N R Bu¨chl and H Seiler
S Tabata
H Fujimoto
792 801
Glossary
813
Index
833
COLOR PLATE SECTIONS At end of each volume
O OFFICE OF INTERNATIONAL EPIZOOTIES
Mission, Organization and Animal Health Code B Vallat and B Carnat, World Organisation for Animal Health (OIE), Paris, France ª 2011 Elsevier Ltd. All rights reserved.
Introduction The need for a global approach in the fight against animal diseases is now very clear. The World Organisation for Animal Health (which is also known by its historical acronym OIE (Office International des Epizooties)) is leading this fight worldwide. The OIE is the international standard-setting organization for animal disease control, the safety of international trade of animals and animal products, animal disease prevention, surveillance, control, and information, animal welfare, animal production, and food safety. The purpose of this article is to describe the OIE and its efforts and importance in improving animal health in the world, thereby improving human health. In order to better understand the organization, its history, structure, mandate and activities, and its major publications such as the Animal Health Codes for Terrestrial and Aquatic Animals will be examined.
A Brief History of the OIE In 1920, rinderpest, a devastating plague of cattle, was introduced to Belgium, through the port of Antwerp by zebu cattle that were en route by boat to Brazil from India. This was the impetus for an international conference to examine the animal health situation in the world, to discuss the exchange of animal health information, and to consider export health measures and disease control methods. This so-called ‘Paris Conference’ expressed the wish that an ‘international office of epizootics for the control of infectious animal diseases’ be
set up in Paris. Thus, in 1924, more than 20 years before the creation of the United Nations, an agreement was signed by the veterinary authorities of 28 countries from Europe, North and South America, Africa, and Asia to establish the OIE in Paris – where it remains to this day. In 1995, the World Trade Organisation (WTO) recognized the OIE as the international standard-setting organization for trade in animals and animal products under the agreement on the application of sanitary and phytosanitary (SPS) measures. The WTO’s SPS agreement states that ‘‘to harmonize sanitary and phytosanitary measures on as wide a basis as possible, Members shall base their sanitary or phytosanitary measures on international standards, guidelines or recommendations’’. The agreement names the OIE as the relevant international standard-setting organization for animal health, including diseases transmissible to humans. In May 2003, the representatives of all OIE members agreed to change the name of the organization from ‘Office International des Epizooties’ to ‘World Organisation for Animal Health’ but decided to keep its historical acronym ‘OIE’. As of 2009, the organization has 175 member countries and territories and more than 200 reference laboratories and collaborating centers. It has formal agreements with 35 international and regional organizations such as FAO, WHO, the World Bank, Codex Alimentarius, and non-governmental organizations representing producers and animal welfare groups. The OIE’s financial resources are derived principally from regular annual contributions, backed up by voluntary contributions from members. The amount of the annual budget of the organization makes the OIE one of the most cost-efficient international organizations.
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2 Office of International Epizooties | Mission, Organization and Animal Health Code
In 2004, the OIE established the World Animal Health and Welfare Fund, for the purpose of projects of international public utility relating to the control of animal diseases, including those transmissible to humans, and the promotion of animal welfare and animal production food safety. This effort was funded initially by international donors, including the World Bank, the United States Department of Agriculture, Switzerland, Japan, France, Canada, and Australia.
Structure of the OIE The World Assembly of Delegates The General Assembly of Delegates is the highest authority and the governing body of the OIE. It is comprised of one delegate per country, who is usually the chief veterinary officer (CVO), and is officially nominated by the Government of the member country. It meets every year at the annual general session in May in Paris. The main functions of the General Assembly of Delegates are to adopt international standards in the field of animal health and the control of animal diseases; to elect the members of the governing bodies (President and Vice President of the general assembly, members of the council, members of the regional and specialist commissions); to appoint the Director General (by secret ballot); and to examine and approve the annual report of activities, the financial report of the Director General, the annual budget, and the strategic plans of the OIE. Voting by delegates within the World Assembly of Delegates respects the democratic principle of ‘one country, one vote’. All resolutions voted by the World Assembly must be implemented by the Director General. Council The Council represents the World Assembly of Delegates during the interval between the assemblies. It meets at least twice a year to examine technical and administrative matters and, in particular, the working program and the proposed budget to be presented to the members. There are six elected members in addition to the President, Vice President, and past president of the World Assembly. The members are elected to reflect the regional balance. Headquarters The OIE headquarters is based in Paris, France. Under the authority of the Director General, the headquarters implements and coordinates disease information, and the scientific and administrative activities that the members have decided upon, as well as the World Fund for Animal Health and Welfare.
Furthermore, it provides the secretariat for the annual World Assembly of Delegates and for the meetings of the specialized commissions and other technical meetings. Assistance is also given by the headquarters to the secretariat of the OIE regional and technical conferences. Regional Commissions There are five regional commissions, for Africa; the Americas; Asia, the Far East, and Oceania; Europe; and the Middle East, whose objective is to promote cooperation and organize regional activities in the field of prevention and control of animal diseases and animal welfare promotion. The President and three other members of each regional commission are elected by countries of each region for a 3-year term. A regional commission conference is organized once every 2 years in one of the countries of the region. These conferences are devoted mainly to technical items and to regional cooperation in the control of animal diseases. Regional Representations The OIE maintains representations in Africa, the Americas, Asia and the Pacific, eastern Europe, and the Middle East, and maintains close links with the relevant regional commissions. The goal of these representations is mainly to provide regionally adapted capacity building programs to relevant policy makers of OIE members. There are also currently sub-regional representations for the Southern African Development Community (SADC) in Botswana, in Tunis for northern Africa, in Brussels for western Europe, in Panama for Central America, and in Thailand for southeast Asia. Specialized Commissions and Companion Groups and Supports There are four specialized commissions. Their role is to use current scientific information to study the problems of epidemiology and the prevention and control of animal diseases, to develop and revise OIE’s international standards, and to address scientific and technical issues raised by member countries. The members of these commissions are elected at the World Assembly for a 3-year term. Terrestrial Animal Health Standards Commission and Aquatic Animal Health Standards Commission (Code Commission)
Founded in 1960, these commissions are responsible for the preparation of standards adopted by members contained in the Terrestrial Animal Health Code and the Aquatic Animal Health Code (Terrestrial and Aquatic
Office of International Epizooties | Mission, Organization and Animal Health Code
Code) to ensure that they reflect current scientific information on the protection of international trade and surveillance methods for terrestrial and aquatic animal diseases. They work with internationally renowned specialists in ad hoc and permanent working groups to prepare proposed standards in light of advances in veterinary science. The Aquatic Animal Health Standards Commission is also responsible for the Manual of Diagnostic Tests and Vaccines for Aquatic Animals. The Scientific Commission for Animal Diseases
The Scientific Commission for Animal Diseases, founded in 1946, assists in identifying strategies and measures for animal disease control. It also examines member country submissions for requests to be certified free of the four diseases for which the OIE can officially certify country freedom: foot-and-mouth disease, bovine spongiform encephalopathy, rinderpest, and contagious bovine pleuropneumonia. The Biological Standards Commission
The Biological Standards Commission, founded in 1949, also referred to as the Laboratories Commission, is responsible for the preparation of the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. It establishes standards for methods of diagnosing diseases of animals and for testing biological products, such as vaccines. Permanent and ad hoc working groups
Comprising leading specialists from all OIE members, these expert groups are brought together to support specialist commissions for the preparation of draft standards and guidelines. There are currently three permanent working groups: on wildlife disease, on animal production food safety, and on animal welfare. Ad hoc groups are not permanent. Recently, they have been convened on a wide range of topics including biotechnology, brucellosis, communication, diseases of camels, epidemiology, and the evaluation of veterinary services (VSs). OIE reference laboratories and collaborating centers
OIE reference laboratories are centers of expertise designated to pursue all the scientific and technical problems relating to a disease on the OIE list. The reference (leading) expert, responsible to the OIE and its member countries with regard to these issues, is an active researcher helping the reference laboratory to provide scientific and technical assistance and expert advice to the OIE and its member countries on diagnostics and topics linked to surveillance and control of the disease for which the reference laboratory is responsible. The laboratories also provide and
3
coordinate scientific and technical studies in collaboration with other laboratories or relevant stakeholders. By the end of 2009, the OIE had a global network of 187 reference laboratories with 161 experts covering 100 diseases/topics in 36 countries. The network brings together experts from many fields. This is an incalculable resource for the OIE headquarters and developed and developing countries, promoting research and encouraging development of laboratory standards. The laboratories provide members with confirmation of diagnostics, current methods for diagnosis, vaccine production, disease surveillance for animal diseases and zoonoses, and safe trade in animals and animal products. OIE collaborating centers are centers of expertise in a specific designated sphere of competence relating to the management of general questions on animal health issues such as epidemiology, risk analysis, veterinary training, or validation of diagnostic tests. Twenty-nine collaborating centers are currently involved in the network covering 27 topics in 18 countries. In its designated field of competence, an OIE collaborating center provides its expertise internationally, and operates as a center of research, standardization, capacity building, and dissemination of techniques. Laboratory twinning
Since a large majority of OIE member countries are developing countries and have variable scientific capacity or access to scientific expertise within their national veterinary laboratories, a project of laboratory twinning was developed, the main objective of which is to assist laboratories in developing or in-transition countries to build their capacity and scientific expertise with the eventual aim that some of them could become OIE reference laboratories in their own right. To apply this concept, a direct link between an existing OIE reference laboratory or collaborating center and another laboratory or institution in a developing or in-transition country is established on a strictly voluntary basis for exchange of scientific expertise and capacity building.
OIE Mandate The core mandate of the OIE is to improve animal health in the world. Under this overarching mandate, the OIE is dedicated – to guarantee the transparency of animal disease status worldwide, – to collect, analyze, and disseminate veterinary scientific information, – to provide expertise and promote international solidarity for the control of animal diseases,
4 Office of International Epizooties | Mission, Organization and Animal Health Code
– to guarantee the sanitary safety of world trade by developing sanitary rules for international trade in animals and animal products, – to improve food safety from the farm to the abattoir, – to develop standards for animal welfare, and – to improve the legal framework and resources of national VSs.
Disease Information Obligations of member countries
Information on the presence of disease is essential for controlling it. With the goal of minimizing the spread of disease comes the obligation to share information about disease outbreaks. Member countries of the OIE are therefore obligated to report disease outbreaks of the OIE-listed diseases, as well as any new relevant epidemiological event. The OIE list of diseases: There are almost 100 OIE-listed diseases included in the first chapter of the Terrestrial Animal Health Code. The criteria used to determine whether a disease appears on the list are as follows: – Is there international spread of disease, that is, has it spread internationally in the past, or is it currently affecting three or more countries? – Does it have zoonotic potential, that is, can this animal disease affect people? – If not, is it spreading in the native population with important morbidity (infecting a high percentage of animals) or mortality (killing an important percentage of the animals that are infected)? – Is it an emerging disease with rapid spread or zoonotic potential? A positive answer to any of these – international spread, zoonosis or high morbidity or mortality or an emerging disease – means that the disease is included on the OIE list. Member countries are committed to report as follows. Immediate notification is required for the first occurrence of a listed disease or infection, the reoccurrence following a report, the first occurrence of a new strain of a pathogen, a sudden and unexpected increase in the morbidity, mortality, or distribution of a disease, or a change in the epidemiology of a disease. The immediate notification is to be by e-mail, fax, telephone, or telegraph. These are to be followed by weekly updates. Members are further committed to semi-annual reports describing the situation regarding OIE-listed diseases in each country and annual reports, which also include information on diseases that are not on the OIE list and diseases of wildlife, the impact of zoonoses on the human population, animal population statistics, the structure of the VSs, national reference laboratories and the diagnostic
tests they can perform, and, where appropriate, vaccine manufacturers and the vaccines they produce. Tools for transparency
WAHIS is the World Animal Health Information System. It is the web interface that is available to member countries for disease notification, allowing countries to notify electronically in a rapid and simple manner. However, when the capacity for electronic reporting is not available, submission of paper reports is acceptable. Many countries have nominated a focal point for specific diseases, or species, whose responsibility is to report disease information to the OIE. This focal point receives specific training from the OIE. WAHID – World Animal Health Information Database – is openly available on the OIE website. With the capacity to search by country or by disease, it provides a rapid, clear, and evident overview of the disease status of a country, the presence or absence of a disease, disease outbreaks or timelines, and the populations of animals in a country, even allowing a comparison of the animal health status of two countries. The OIE publishes ‘World Animal Health’ every year, which is a compilation of all the information listed above. This publication is unique worldwide. Disease tracking
OIE is also engaged in active search and verification of disease outbreaks. Seeking unofficial information from the reference laboratories, the regional representations, collaborating centers, internet resources, or the press, the OIE gathers information, analyzes it, and asks the member for verification where relevant. This is an extremely effective tool. The OIE does not work alone. The Global Early Warning System for Animal Disease including Zoonoses (GLEWS) is a joint OIE/FAO/WHO initiative that synergistically builds on combining and coordinating the disease tracking and alert and response mechanisms of the three organizations. Through sharing of information on animal disease outbreaks and epidemiological analysis, the GLEWS initiative aims at improving global early warning as well as transparency among countries for controlling animal disease as well as zoonoses including food-borne diseases. Veterinary Scientific Information Reference laboratories, collaborating centers, and the four specialist commissions develop and gather scientific information on animal disease prevention and control methods, including zoonoses and food-borne diseases, and on animal welfare. The OIE provides this information through various channels including
Office of International Epizooties | Mission, Organization and Animal Health Code
5
– – – –
global and regional scientific conferences, web site, The Bulletin, the yearly publication of the World Animal Health Situation, – The Scientific and Technical Review, and – other publications (handbooks).
while contributing to help free countries safeguard their free status. OIE offers to developing countries independent evaluation of their animal health policies and infrastructures, gap analysis, and donor opportunities if needed (see ‘Strengthening Veterinary Services’).
The Bulletin is published 4 times yearly. Each issue is focused on a specific topic (e.g., animal welfare, wildlife diseases, or food safety). It also provides member countries with an update on current issues, on activities of headquarters and regional offices, and upcoming events and notifications of self-declarations of the disease status of member countries on a voluntary basis. The World Animal Health is a yearly publication on the occurrences of animal disease throughout the world. It also contains information on the most important control, prevention, and prophylaxis measures adopted and the number of animals slaughtered, destroyed, or vaccinated. Figures on animal population are also provided. Other sections provide detailed information on human cases of the OIE-listed zoonotic diseases, veterinary personnel, national reference laboratories, and vaccine production. This publication is unique in the world. The Scientific and Technical Review is a peer-reviewed journal that contains in-depth studies devoted to current scientific and technical developments in animal health and veterinary public health worldwide. The particular distinction of this publication lies in relating specialized research to practical problems encountered in safeguarding animal health and veterinary public health, an essential aspect for the improvement of animal production and the protection of public health. It appears 3 times per year. Other technical publications include technical series on a variety of topics such as assessment and management of pain in animals, or epidemiology, and global or regional scientific conference proceedings.
International Trade in Animal and Animal Products
International Solidarity More than 120 members are developing countries or countries in transition. These countries often find it difficult to free themselves from epizootics, including zoonoses. This leaves a reservoir of pathogens that threatens the status of countries that have attained disease freedom, often at great expense. The OIE influences the wealthier countries to help developing countries and offers its expertise and that of the networks as well as its own resources to help them meet the OIE standards. This results in a ‘win-win’ situation because the control of diseases in developing countries also results in reduction of poverty and increases food security, market access, and public health
As described above, the OIE is the international organization given the responsibility by the WTO for establishing standards in animal diseases and zoonoses. The standards contained in the Terrestrial and Aquatic Code are intended to prevent and control the spread of animal disease while avoiding unjustified sanitary barriers to the international trade of animals and animal products. The OIE certifies countries free of four diseases (rinderpest, foot-and-mouth disease, contagious bovine pleuropneumonia, and bovine spongiform encephalopathy) according to specific guidelines by which a country can demonstrate that the disease is not present in its animal population. This allows importing countries to take decisions without having to control the situation in the exporting country directly in the field. For other diseases, such as avian influenza, there are specified criteria by which a country can certify itself as free from a disease. The OIE can also play a role in mediating trade disputes between countries by offering a voluntary dispute settlement mechanism. This is a science-based approach to finding alternative solutions and resolving differences, as distinct from the legalistic approach used in the formal WTO system. The mechanism is voluntary and the agreement of both parties is needed before the OIE can initiate the process. Animal Production Food safety Preventing or eliminating hazards at their source, at the farm level, is clearly more effective than trying to detect and eliminate them downstream. A permanent working group on food safety was established in 2002, sharing membership with Codex Alimentarius, FAO, and WHO, to establish standards for food safety from the farm to the abattoir in order to eliminate hazards existing during production at the farm and prior to the slaughter of animals or the primary processing of animal products (meat, milk, eggs, etc.) that could pose a risk to consumers. This group is also working to prevent gaps and duplications between Codex Alimentarius and the OIE standards. Veterinarians have an established role at the farm level. Under OIE guidelines, veterinarians working at the abattoir screen for diseases particularly during anteand post-mortem inspection. They verify that animal
6 Office of International Epizooties | Mission, Organization and Animal Health Code
welfare standards are met, and assure the humane slaughter. VSs are well placed as part of a multidisciplinary team of professionals, to work for the safe production of food, including dairy products from the farm to the fork. As part of the effort to ensure the safety of food of animal origin, and indeed for the purpose of controlling animal disease outbreaks, there must be a reliable and effective way to trace the animal back to the farm of origin. This should be based on the identification of farms, individual animal identification, or identification of groups of homogeneous animals, the ability to track movement of animals, and a record-keeping system. Traceability has important implications for trade as well as for animal health, disease control, and food safety. Therefore, the OIE developed standards for animal traceability. In addition, the OIE organized a world conference in 2009 bringing together governments, international organizations, industry, and primary producers with the purpose of supporting the implementation of the relevant international standards for identification and traceability of live animals and facilitating the bridge of traceability between animals and animal food products globally. Animal Welfare Animal welfare was identified as a priority when OIE member countries mandated the organization to take the lead internationally on animal welfare and to elaborate recommendations and guidelines covering animal welfare practices. This is all the more relevant to the OIE since animal health is a key component of animal welfare. The Permanent Animal Welfare Working Group was inaugurated at the 70th World Assembly of Delegates in May 2002. To date, the OIE has developed guidelines for the transport of animals by land, sea, and air, for the slaughter of animals, and for killing animals for disease control purposes. The next standards to be developed are on the control of stray dog populations, livestock production systems, and laboratory animal welfare. To further progress on animal welfare standards, the OIE has held two global conferences, in 2004 and 2008, in order to promote the worldwide implementation of OIE animal welfare standards, to raise the profile of animal welfare, and to encourage veterinarians and VSs to take greater responsibility for animal welfare. Strengthening Veterinary Services In order to adequately implement OIE standards, a country requires a VS with adequate human, physical, and financial resources, technical authority and capacity, interaction with stakeholders, and access to markets. However, more than 120 of the 175 OIE
members are developing countries where VSs may not always comply with international OIE standards on the quality and performance of VS. The OIE sees VSs as a global public good and their compliance with international standards as a priority for public investment. The OIE is therefore actively engaged in the evaluation and improvements of the capacities of national VS. The process chosen by the OIE consists of the democratic adoption of quality standards contained in the Terrestrial Animal Health Code, and the creation of a tool to analyze the conformity of the countries to the standards. The OIE’s tool for the evaluation of the performance of VSs, the PVS tool, is designed to assist VSs to establish their current level of performance, to identify gaps and weaknesses regarding their ability to comply with standards described above, and to establish priorities and carry out strategic initiatives. This tool is the principal lever of the OIE to bring compliance with quality standards in the governance of VSs of all countries. The PVS establishes a diagnostic. The OIE also offers a gap analysis in collaboration with FAO and various key funding agencies, permitting members to define detailed priorities for investment in order to be able to comply using their national budget and priorities and, if needed, soliciting aid from the international community. For member countries requesting assistance with capacity building, the OIE also provides expertise and training for national senior officials, both to improve sanitary governance and to help prepare and implement animal disease control and eradication programs.
Standard Setting Procedures and Publication of International Animal Health Codes The Terrestrial Animal Health Code, now in its 17th edition (2008), and the Aquatic Animal Health Code, in its 10th edition, are intended to assure the sanitary safety of international trade in terrestrial and aquatic animals and their products and to provide surveillance methods for important animal diseases. This is achieved through the detailing of health measures to be used by veterinary authorities to avoid the transfer of agents pathogenic to animals or humans, while avoiding unjustified sanitary barriers and while implementing surveillance of major diseases. They are written in two sections: the first contains recommendations that apply to a wide range of topics, production sectors, and/or diseases (so-called ‘horizontal standards’) and the second contains recommendations on specific diseases (so-called ‘vertical standards’) including
Office of International Epizooties | Mission, Organization and Animal Health Code
recommendations on agent inactivation and on surveillance and risk assessment. The horizontal standards include most notably the general and ethical obligations for importing and exporting countries, methodologies for risk analysis, and the criteria by which diseases are included on the list and by which countries are to report disease outbreaks to the OIE. Other horizontal standards are animal welfare standards, veterinary public health measures such as the role of VSs in food safety, and the responsible use of antimicrobials in veterinary medicine. The second section of the Codes consists of recommendations applicable to specific diseases on the OIE list. The diseases selected for inclusion in this list affect fish, shellfish, mammals, birds, or bees. These include diseases that are considered the most serious due to their potential for rapid spread beyond national borders, or for transmission to humans, as well as diseases that are less highly contagious but whose economic or health importance justifies their being taken into consideration in international trade. Each disease is dealt with in a separate chapter. Diseases are grouped as those that affect multiple species and those that affect a single species. There are more than 100 terrestrial and aquatic animal diseases for which standards have been developed. These standards are related to the risks of transmission of the diseases or disease-causing agents linked to animal and animal products. But certainly it should be noted that certain products or commodities subjected to specific treatments may in fact pose no risk, no matter the sanitary status of the country. The recommendations contained in the OIE Animal Health Codes are developed with the active participation of member countries, knowing that these will apply equally to themselves and to others. They are the fruit of a consensus of very senior veterinary authorities of member countries, thus accounting for their value and their very wide practical application. Procedures for Updating the Codes All standards are prepared and submitted by the elected specialized commissions to the World Assembly of National Delegates. They are adopted following the rule of ‘one country – one vote’.
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laboratories. Their purpose is to contribute to the international harmonization of methods for the surveillance and control of the most important animal diseases. Standards are described for laboratory diagnostic tests and the production and control of biological products (principally vaccines) for veterinary use across the globe, providing internationally agreed diagnostic laboratory methods. The Manuals set laboratory standards for all OIE-listed diseases as well as several other diseases of global importance. In particular, they specify those ‘prescribed tests’ that are recommended for use in health screening for international trade or movement of animals.
Other OIE Activities Communication In recognition of the centrality of communication for the VSs, which underpins everything they do, including disease surveillance, prevention, control and response, animal welfare, public health, and food safety, guidelines on communication useful for national VSs are being developed for inclusion in the Code. Veterinary Education In line with OIE’s efforts to strengthen VSs is the recognition that veterinary education is basic to an effective VS. Society has placed increasing demands on veterinarians in the fields of food security, food safety, public health, and animal welfare. The OIE recognizes these, seeing them as integral to veterinary education. The harmonization and quality of veterinary curricula are a crucial component of sound national animal health systems. A principal mandate of the regional representations and the subregional representations is to develop programs for capacity building in the members for the benefit of the delegates, and their national focal points, the people officially identified as national contacts with the OIE in specific areas. As part of its multifaceted approach to improve VSs, the OIE has organized a meeting of all the world’s veterinary schools with the aim of helping them incorporate into their curricula the concepts with the international public good principles expected from veterinary missions and activities.
Other OIE Standards and Guidelines While the Codes are highly important documents, it should be noted that they must be used with the companion documents, the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (Terrestrial Manual) and the Manual of Diagnostic Tests and Vaccines for Aquatic Animals, the reference standards for veterinary
Conclusion A Global Public Good Among the many challenges facing the world, the dramatic increase of human and domestic animal populations, globalization and the unprecedented movement
8 Office of International Epizooties | Mission, Organization and Animal Health Code
of people and commodities worldwide, and the increasing encroachment on natural ecosystems are leading to increasing disease threats. As the interrelationships between animal and human health and the health of the ecosystem are better understood, it becomes clear that the consequence of an effective VS is a healthier animal and human population, less afflicted by zoonotic diseases, better nourished, and participating in an improved world economy. This entails prevention and control of emerging diseases at the human–animal interface. The concept of ‘One World, One Health’ has been developed jointly by the WHO, FAO, UNICEF, World Bank, and OIE, and accepted by most other international health organizations. It is based on more preventative actions, increased cooperation between VSs and public health authorities, and on strengthening emergency response capabilities while helping the poorest nations and strengthening animal and public health systems. The result should be a better capacity to respond to emerging disease situations. All countries must be prepared in face of these new disease threats and it is widely accepted that the work of the VSs is a global public good.
Since its inception in 1924, the OIE has been the global leader in animal disease prevention and control, has served as a focal point for international cooperation on animal health issues, has promoted global safe trade in animal products, has promoted transparency on the global situation of animal diseases including zoonoses, and has shared veterinary expertise among member countries. With increasing trade, growing demand for foods of animal origin, growing disease threats, unprecedented movements of people and animals, and a changing climate, the role of the OIE has increasing importance. The larger vision of the OIE of contributing to improving public health, food safety and security, and the livelihoods of poor farming communities can only be achieved if governments agree to foster closer cooperation between all the sectors in the health system, to support VSs, and to share information.
Relevant Websites http://www.oie.int – World Organisation for Animal Health.
ORGANIC DAIRY PRODUCTION K Shea, Horizon Organic, Longmont, CO, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2193–2199, ª 2002, Elsevier Ltd.
History In the early days of organic agriculture, products were sold at farmers’ markets, cooperatives and directly from the farm. The definition of ‘organic’ and the actual methods for raising the products as organic varied from place to place and farm to farm. Gradually private and public institutions began emerging to set organic farming standards and provide third-party verification of label claims. Many producers turn to organic farming systems in order to take advantage of the high-value niche market and improve farm income, thereby enabling themselves to compete in today’s vertically integrated agriculture system. Organic producers have an intense belief that their farming system is superior in its ability to care properly for the land and its finite resources. Today, organic production is well defined and has matured into a significant market segment.
Market Trends According to the US Department of Agriculture, the amount of farmland managed under certified organic practices has expanded dramatically, as has consumer demand for organically grown food. In the United States, organic farming became one of the fas test-growing trends in agriculture during the 1990s. Certified organic cropland more than doubled from 1992 to 1997, and two organic livestock sectors – eggs and dairy – grew even faster. Organic foods are one of the top consumer trends today, accounting for more than US$7.8 billion in annual sales, and doubling every 4 years since 1990. The Western Agricultural Economics Association published information on sales of organic milk in mainstream supermarkets showing a growth over the last 8 years, reaching US$75.7 million in 1999. Organic dairy products can be found in conventional supermarkets and natural-food stores across the United States and in the
United Kingdom, where the demand for organic milk and dairy produce is now growing strongly. One leading retailer is predicting a 10-fold increase in its sales over the next 5 years. The Soil Association shows the United Kingdom organic food market currently growing at around 40% year 1 and by 2002 it is expected to top £1 billion. The organic sector in Canada is small but growing rapidly. According to industry sources, farm cash receipts from this industry reached about Can$500 million in 1999, with an estimated retail value of Can$1 billion, including processed and nonprocessed products. Canadian organic retail sales growth is expected to rise from Can$0.7 billion in 1997 to Can$3.1 billion in 2005, which equates to an average growth of 20% annually. The industry anticipates that its market share will increase to 10% of the Canadian retail market by 2010. Worldwide, growth in organic retail sales is between 20% and 30% per annum. At this rate, 30% of the land in Europe is predicted to be in organic production or in conversion to organic by 2010. In Europe, organic retail sales are estimated at approximately US$7.5 billion, in the United States at US$6.5 billion and in Japan at US$1.5 billion. It is predicted that, by 2005, the industry in Japan will hit the US$10 billion mark. Although still fledgling in Australia, the organic industry turns over US$250 million per year in retail sales of organic food and it exports approximately US$25–30 million worth of organic produce. The Organic Products Exporters of NZ Inc. (OPENZ) was formed to encourage and support companies and organizations, which have an interest in the New Zealand organic export industry. OPENZ reported a significant increase in the value of organic exports to June 2000. Survey results showed that New Zealand certified organic exports reached over NZ$60 million for the year 1999–2000. This was an increase of 77% on the previous year’s figure of NZ$34.08 million. The survey was administered by Trade New Zealand and received responses from 34 out of the 40 exporter members of OPENZ.
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Organic Dairy Production
A report suggesting organic dairy products will become a profitable, long-term niche market worth up to NZ$200 million a year within a decade has convinced the Dairy Board to foster organic farming in New Zealand. New Zealand currently exports about NZ$60 million-worth of organic products, mostly fruit and vegetables. It has been estimated that the organic market will be unlikely to exceed 5% of the board’s NZ$7.6 billion business, but it is a niche that the board wishes to exploit.
International Organic Standards Comparisons There have been organic standards in the European Union (EU), and EU regulation 2092/91 has been in force since 1991. In many European countries, organic agriculture is known as ecological agriculture, reflecting the reliance on ecosystem management rather than external inputs. According to the Codex Alimentarius Commission: Organic agriculture’s increased momentum is due to consumer demand and to positive environmental impact. Many aspects of organic farming are important elements of a systems approach to sustainable food production, including in developing countries, both for domestic consumption and export. The Committee on Food Labeling of the Codex Alimentarius Commission has developed Guidelines for the Production, Processing, Labelling, and Marketing of Organically Produced Foods (Table 1). The International Federation of Organic Agriculture Movements (IFOAM) represents, internationally, the organic movement in parliamentary, administrative and policy-making forums. IFOAM has consultative status with the UNO and FAO. It sets and regularly revises the international IFOAM Basic Standards of Organic Agriculture and Food Processing, which are translated into 19 languages. IFOAM also operates the International Organic Accreditation Services, Inc. (IOAS), in order to administrate the IFOAM Accreditation Program to ensure equivalency of certification programs worldwide. In the United Kingdom, the integrity of organic food is safeguarded by international legislation. Organic livestock production is regulated by EU Regulation 804/ 1999. The United Kingdom Register of Organic Food Standards (UKROFS) is the British control body for the organic sector. Food sold as organic anywhere in the EU must be certified as produced under an approved system authorized by an official inspection and certification service. The Soil Association is the best known of the UKROFS validating bodies.
Canadian organic dairy products have been widely distributed since 1995 and, in Canada, there is more information available on organic dairy farming, than on other types of livestock farming. The Canadian Organic Advisory Board Inc. (COAB) was established in 1992 as a national, nonprofit advisory body to represent the interests of organic production and certification groups across Canada. The Board is a vehicle for collaboration of stakeholders within the organic industry and, notably, agencies within the federal and provincial government that have been involved in the development of organic standards. The Certified Organic Associations of British Columbia (COABC) works on a voluntary basis to maintain a credible set of organic production and processing standards. COABC ensures compliance with the standards by administrating the accreditation and auditing process in partnership with the British Columbia Ministry of Agriculture, Fisheries and Food (BCMAFF). The United States signed into law the Organic Foods Production Act (OFPA) in 1990. The final rule implementing OFPA was published in the Federal Register in December of 2000. This final rule establishes the National Organic Program (NOP) under the direction of the Agricultural Marketing Service (AMS), an arm of the US Department of Agriculture. The goal of this national program is to facilitate domestic and international marketing of fresh and processed food that is organically produced and to assure consumers that such products meet consistent, uniform standards. To ensure that access of New Zealand organic products into the EU is maintained, the Organic Products Exporters Group Inc. (OPEG) has requested that the Ministry of Agriculture and Forestry (MAF) Food establish an Official Organic Assurance Program for organic products exported to the EU. The objective of this program is to provide an official assurance to the EU that organic products exported from New Zealand comply with the requirements of Council Regulation 2092/91. Japan’s Ministry of Agriculture, Forestry and Fisheries (MAFF) have completed the development of their own national standard for organic production using the Codex Guidelines for the Production, Processing, Labelling, and Marketing of Organically Produced Foods as a base. The Japan standard covers plant products only and Japan’s MAFF have advised that imported products labeled as organic will need to comply with the standard by April 2001. A comparison of standards around the world shows that they are mostly consistent but do vary in a few areas. These areas are pasture requirements, percent of total feed which must be organic and the use of antibiotics.
Table 1 Standards for organic dairying International Federation of Organic Agricultural Movements
Codex (1999 Draft only, not agreed upon)
Living conditions as related to access to pasture or free range
Access to open air and/ or grazing appropriate to type of animals and season
Herbivores must have access to pasture. May allow exceptions in certain circumstances
Conversion: dairy herds
Not less than 30 days
Still under discussion
Feed
Health care
12 months organic feed, 90 days health and living conditions 100% organically grown feed, with 50% coming from farm or produced within the region. If impossible, allowance for 15% of feed from nonorganic sources Natural medicines and methods emphasized. Use of conventional veterinary medicines allowed when no alternatives are available
Should be 100% organically grown. If operator can demonstrate such feed is not available, livestock will maintain status with 85% organic feed Use of veterinary drugs prohibited in absence of an illness. If no alternative permitted treatment or management, vaccinations and therapeutic uses permitted. Should not withhold necessary treatment to maintain organic status
Canada June 1999 Environment suited to their needs that provides regular access to pasture, free-range open-air runways or other areas subject to weather and ground conditions In accordance with the standards for at least 12 months
Certified Organic Associations of British Columbia 1997 Free access to pastures, paddocks or runways. Access to grazing land 120 days of the year
12 months incorporating all required practices. Replacements 90-day transition if certified livestock not available but must be heifers or 120-day dry-treated cows
US Department of Agriculture NOP 2000
Soil Association UK 1998
Access to outdoors and direct sunlight. Access to pasture for ruminants. Allows temporary exemptions in case of certain circumstances or to protect soil 12 months incorporating all required practices. New herd conversion, 80% organic feed for first 10 months
All stock must have access to pasture during grazing season unless specifically exempted
12 weeks
100% from organic sources. May be 85% for ruminants in the short term only
Certified organic required, certified transitional feed is regulated
Certified organically produced feed and pasture required
Livestock systems should be planned to provide 100% in accordance with standards. Allowed 90% on a daily basis, or 85% dairy stock
Vaccination and use of veterinary drugs allowed only when disease cannot be combated by other means. Withholding of necessary treatments to maintain organic status is not permitted
Vaccinations allowed as appropriate to each bioregion. Withholding of necessary medical treatment that would disqualify organic status is prohibited
Vaccinations allowed. Administrations of medications in absence of illness prohibited. Withholding treatment to maintain organic status causing suffering or death shall be grounds for decertification
Use of veterinary medical products where no known problem exists prohibited. Medications must never be withheld where it will result in unnecessary suffering. Vaccines restricted to known disease risk that cannot be controlled by other means (Continued )
Table 1 (Continued) International Federation of Organic Agricultural Movements
Codex (1999 Draft only, not agreed upon)
Use of antibiotics
When conventional veterinary medicines are used the withholding period shall be at least double
Withdrawal periods double that required by legislation. After 2005 antibiotics not allowed
If veterinary drugs used, withdrawal period at least double
Use of parasiticides
When conventional veterinary medicines are used the withholding period shall be at least double
Withdrawal periods double that required by legislation
If veterinary drugs used withdrawal at least double
Canada June 1999
Certified Organic Associations of British Columbia 1997 Not permitted for slaughter animals. Allowed for breeding animals but not in a subtherapeutic manner. Use on animals in 3rd trimester or during lactating will disqualify offspring for slaughter. Milk to be withheld for 30 days or twice withdrawal period if longer Not permitted for slaughter animals. Allowed for breeding herd use but use in 3rd trimester or during lactation disqualifies offspring as organic for slaughter purposes
US Department of Agriculture NOP 2000
Soil Association UK 1998
Not permitted
Permitted in clinical cases where no other remedy is effective. Withdrawal at least three times that permitted on product license and not less than 14 days
Not permitted for slaughter stock. Allowed in breeder stock if sickness or infection present; routine use not allowed. Progeny can be sold as organic but not if used during 3rd trimester of gestation or during lactation. 90day withdrawal or dairy animals
Permitted when used therapeutically when clinical symptoms appear. Restricted use on routine basis over a specific time period as part of the disease reduction program. Ivermectin-based products prohibited
Organic Dairy Production
Before the NOP rule was published, certification agency standards in the United States varied in regards to antibiotics. Some allowed none; other allowed their use with a 30–90-day withdrawal period. During this withdrawal period, the milk or milk products could not be sold as organic, and the meat could never be used as organic. Today under the NOP, antibiotics are never allowed on organic cattle. Under COABC regulations, cows can be brought back into the milking string after 30 days. Though the particulars of organic livestock production may vary between nations, around the world the standards emphasize proactive health care, the principle of prevention versus treatment. Healthy cow care and early sick-cow recognition are crucial. By doing the utmost to control the animals’ environment, and thereby prevent illness and lower stress, the animals remain healthier than similar cows where these preventative practices are not performed. Standards usually require access to the outdoors, fresh air, sunlight and shelter, and they recognize species-appropriate behavior and make allowances for it. Using the NOP as a model, here is a glimpse into organic certification requirements: The farmland itself must have no prohibited materials applied to it for at least 36 months before the harvest of organic crops. It must have distinct, defined boundaries and buffer zones such as runoff diversions to prevent the unintended application of a prohibited substance to the crop or contact with a prohibited substance applied to adjoining land that is not under organic management. The producer must select and implement tillage and cultivation practices that maintain or improve the physical, chemical and biological condition of soil and minimize soil erosion. The producer must manage crop nutrients and soil fertility through rotations, cover crops, and the application of plant and animal materials. Milk or milk products must be from animals that have been under continuous organic management beginning no later than 1 year prior to the production of such products, except for the conversion of an entire, distinct herd to organic production. For the first 9 months of the year of conversion, the producer may provide the herd with a minimum of 80% feed that is either organic or produced from land included in the organic system plan and managed in compliance with organic crop requirements. During the final 3 months of the year of conversion, the producer must provide the herd with 100% organic feed. The producer of an organic livestock operation must maintain records sufficient to preserve the identity of all organically managed livestock and all edible and nonedible organic livestock products produced on his or her operation. The producer must not use animal drugs, including hormones, to promote growth in an animal or provide feed supplements or additives in amounts above those
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needed for adequate growth and health maintenance for the species at its specific stage of life. The producer of an organic livestock operation must establish and maintain preventive animal health care practices. The producer must establish appropriate housing, pasture conditions and sanitation practices to minimize the occurrence and spread of diseases and parasites. Animals in an organic livestock operation must be maintained under conditions that provide for exercise, freedom of movement and reduction of stress appropriate to the species. Additionally, all physical alterations performed on animals in an organic livestock operation must be conducted to promote the animals’ welfare and in a manner that minimizes stress and pain. The producer of an organic livestock operation must administer vaccines and other veterinary biologics as needed to protect the well-being of animals in his or her care. When preventive practices and veterinary biologics are inadequate to prevent sickness, the producer may administer medications included on the National List of synthetic substances allowed for use in livestock operations. The producer may not administer synthetic parasiticides to breeder stock during the last third of gestation or during lactation if the progeny is to be sold, labeled, or represented as organically produced. After administering synthetic parasiticides to dairy stock, the producer must observe a 90-day withdrawal period before selling the milk or milk products produced from the treated animal as organically produced. Every use of a synthetic medication or parasiticides must be incorporated into the livestock operation’s organic system plan subject to approval by the certifying agent. The producer of an organic livestock operation must not treat an animal in that operation with antibiotics, any synthetic substance not included on the National List of synthetic substances allowed for use in livestock production, or any substance that contains a nonsynthetic substance included on the National List of nonsynthetic substances prohibited for use in organic livestock production. The producer must not administer any animal drug, other than vaccinations, in the absence of illness. The use of hormones for growth promotion is prohibited in organic livestock production, as is the use of synthetic parasiticides on a routine basis. The producer must not administer synthetic parasiticides to slaughter stock or administer any animal drug in violation of the Federal Food, Drug, and Cosmetic Act. The producer must not withhold medical treatment from a sick animal to maintain its organic status. All appropriate medications and treatments must be used to restore an animal to health when methods acceptable to organic production standards fail. Livestock that are treated with prohibited materials must be clearly identified and shall not be sold, labeled or represented as organic.
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Organic Dairy Production
A livestock producer must document in his or her organic system plan the preventative measures he or she has in place to deter illness, the allowed practices he or she will employ if illness occurs, and his or her protocol for determining when a sick animal must receive a prohibited animal drug. These standards will not allow an organic system plan that envisions an acceptable level of chronic illness or proposes to deal with disease by sending infected animals to slaughter. The organic system plan must reflect a proactive approach to health management, drawing upon allowable practices and materials. Animals with conditions that do not respond to this approach must be treated appropriately and diverted to nonorganic markets. The producer of an organic livestock operation must establish and maintain livestock living conditions for the animals under his or her care which accommodate the health and natural behavior of the livestock. The producer must provide access to the outdoors, shade, shelter, exercise areas, fresh air and direct sunlight suitable to the species, its stage of production, the climate, and the environment. This requirement includes access to pasture for ruminant animals. The producer must also provide appropriate clean, dry bedding, and, if the bedding is typically consumed by the species, it must comply with applicable organic feed requirements. The producer must provide shelter designed to allow for the natural maintenance, comfort level, and opportunity to exercise appropriate to the species. The shelter must also provide the temperature level, ventilation and air circulation suitable to the species and reduce the potential for livestock injury. The producer may provide temporary confinement of an animal because of inclement weather; the animal’s stage of production; conditions under which the health, safety, or well-being of the animal could be jeopardized; or risk to soil or water quality. The producer of an organic livestock operation is required to manage manure in a manner that does not contribute to contamination of crops, soil or water by plant nutrients, heavy metals or pathogenic organisms and optimizes nutrient recycling.
Future of Organic Dairying Nitrogen self-sufficiency through the use of legumes and biological nitrogen fixation, as well as effective recycling of organic materials, including crop residues and livestock manure, will positively affect the impact of the farming system on the wider environment. These practices, coupled with conservation of wildlife and natural habitats, are some of the many benefits of organic production practices. Livestock manures are one of the most valued resources on an organic farm or ranch. Conservation of manure and its proper application are a key means of
recycling nutrients, building soil and improving the sustainability of an organic operation. Ideally, manures for organic crop production are composted. However, uncomposted manures are allowed with restrictions. Raw, uncomposted livestock manures may not be applied to crops destined for human consumption unless incorporated into the soil a minimum of 120 days prior to harvest. At the same time, water resources must be protected. Fertilizers and manures must be applied to prevent runoff and leaching, fields must be managed to prevent erosion, and ‘catch crops’ must be used where necessary to soak up excess nitrogen. Riparian zones must be stabilized and protected, natural wetlands must be maintained and protected, and waterways must be protected from livestock and livestock waste through the use of fencing and water tanks to prevent fouling natural streams. Fliebach, Mader, Pfiffner, Dubois and Gunst recently released results of a 21-year field trial in Switzerland, comparing organic and nonorganic farming systems. The study shows dramatic differences in soil health. It was reported that there were more microorganisms (which play a role in soil fertility and delivering nutrients to roots) in the organically managed field than in the conventionally managed field. Consumers have become increasingly aware of these environmental issues. The alleged liberal use of pesticides by farmers and the purported suffering of livestock have been highlighted in the press over recent years, and caused rising numbers of consumers to turn to organic products. The organic sector is growing with sales projected to increase from $US1.31 billion in 1995 to $US4.37 billion in 2005. At present highest demand in the market is for single ingredients in the form of organic milk, cheese or yogurt. An increase in unit shipments of organic dairy desserts and organic ready-made meals is expected and should increase revenues over the rest of the forecast period. See also: Manure/Effluent Management: Nutrient Recycling; Systems Design and Government Regulations. Office of International Epizooties: Mission, Organization and Animal Health Code. Policy Schemes and Trade in Dairy Products: Codex Alimentarius; Trade in Milk and Dairy Products, International Standards: Harmonized Systems.
Further Reading Canford P (2001) The Origins of the Organic Movement. Edinburgh: Floris Books. Fliebach A and Mader P (2000) Microbial mass and size-density actions differ between soils of organic and conventional agricultural systems. Soil Biology and Biochemistry 32, pp. 757–768. Lampkin N, Foster C, and Padel S (1999) Organic Farming in Europe: Economics and Policy. Germany: Hohenheim, Stuttgart.
Organic Dairy Production Macey A (ed.) (2000) Organic Livestock Handbook. Ottawa, Canada: Canadian Organic Growers Inc. Willer H and Yussefi M (2001). Organic Agriculture Worldwide: Statistics and Future Prospects. http://www/soel.de/inhalte.publikationen/ s74ges.pdf /.
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Information on organic farming is available for the following countries at the website addresses below: Canada: http://www.cog.ca Europe: http://www.organic-europe.net New Zealand: http:// www.organicsnewzealnd.org.nz/index.htm United States: http:// www/ams.usda.gov/nop.
P PACKAGING
V B Alvarez and M A Pascall, The Ohio State University, Columbus, OH, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The packaging of food can be traced to ancient times although its early beginning was with crude materials. Early reports document wine being stored in animal skin and various liquids including water being packaged and stored in earthen vessels. Increases in the complexity of human civilization also saw the development and use of diverse types of packages made from varying types of materials. The Industrial Revolution, which started during the 1700s, also had an effect on food packaging because the new industrial workers demanded a more convenient manner for transporting and storing meals. Beginning in the 1950s and within modern times, the growth of the fast-food industry has significantly influenced the food-packaging industry. Examples of foods in this category include gravy preparations, dry cake mixes, boil-in-bag foods, and TV dinners. These developments created a demand for new types of packages. The packaging of fluid milk started prior to the 1950s when Gail Borden discovered and patented the process for condensed milk. This occurred in 1856 and was followed by the development of the glass milk bottle in 1884, the invention of the automatic bottle filler and capper in 1886, and the introduction of the first plastic-coated paper milk carton in 1932. Due to the properties of milk and dairy products, packaging is considered to be a critical step in the processing operations. The reason is that packaging is the last link in the processing chain. If the choice of packaging is inappropriate or its failure occurs during handling, transportation, and storage of milk products, the processing steps would be useless, even if they were properly executed. In an attempt to minimize food
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safety hazards associated with inadequately processed and/or packaged milk products, the Pasteurized Milk Ordinance (PMO) enacted by the US government mandates regulatory guidelines for the dairy industry. Figure 1 shows a typical fluid milk filling room that complies with the PMO’s requirements. The filling room is separated from other processing operations, and the equipment and facilities have the infrastructure to prevent any contamination of milk.
Purpose of Packaging of Dairy Products The systems and requirements for packaging of dairy products are similar to those of other foods. Milk and dairy products are packed in various types of packaging materials depending on the specific product properties, processing conditions, storage, handling, and end use. The primary purposes of packaging are to preserve and protect dairy products against spoilage and harmful factors in the outside environment, to contain specific amounts of the product in units that are easy to handle during production, storage, transportation, and consumption, and to provide information about the product to the consumer and regulators. Important considerations about materials used to package dairy products are toxicity and compatibility with the product, resistance to impact, maintenance of sanitation, odor and light protection, tamper resistance, size specifications, shape and weight requirements, marketing appeal, printability, and cost. Examples of packaging types used for dairy products include glass and plastic bottles, gable-top and bricktype cartons, bags, pouches, two- and three-piece cans, aerosol containers, plastic tubs, and other containers.
Packaging 17
Figure 1 Traditional milk filler room that meets the Pasteurized Milk Ordinance requirements to prevent milk contamination. Courtesy of Seiberling Inc.
Table 1 lists the common packaging materials, their properties, advantages, and disadvantages, and dairy products that are packaged in containers fabricated from them.
Packaging of Dairy Products Fluid Milk This is currently marketed as standardized low-fat milk with 0.5, 1.0, 1.5, or 2.0% fat content. It is also marketed as skim milk with <0.5% fat and as homogenized whole milk with a fat content of 3.25%. Milk flavor results mainly from proteins, lipids, and carbohydrates, and small amounts of other components. Depending on the way milk is handled, processed, and stored, its quality and flavor can deteriorate. This decline may be due to bacterial growth, enzymatic activity, and environmental factors such as oxygen and temperature. Additionally, milk is susceptible to the development of light-activated or light-induced off-flavors and vitamin A degradation. Therefore, the properties of the selected packaging materials are important if the quality and nutritional value of milk are to be maintained during storage. Glass bottles were introduced in 1884 and were the first modern packaging material for fluid milk. An important property of glass that makes it suitable for milk and other foods in general is its fairly inert nature. As a result, it is not associated with the leaching of chemicals that might alter the taste of the product. Its impermeability makes it desirable for long-term storage of foods that are susceptible to volatile loss or the ingression of spoilage gases. Flint glass is transparent and allows product visibility. Due to its rigidity, glass maintains its shape and volume under vacuum or pressure. Glass is stable at high temperatures and has good consumer appeal. In
spite of these advantages, glass is breakable and relatively heavy, and has a high manufacturing energy requirement and high cost of production. Several types of laminated materials are used to package fluid milk. Single-use containers made of plastic/paper laminates (polyethylene (PE)-coated to paperboard) have been used widely because of their low cost, easy printability, and forming versatility. However, they have poor barrier properties against moisture and gases. Since this type of milk package is single use, only the carrying crates used to transport the unit containers require washing and reuse. Another type of laminated material that is used for milk packaging generally consists of seven separate layers that may include PE/adhesive/paperboard/adhesive/aluminum foil/adhesive/PE (or an ionomer). The heat-sealing material in this structure is the PE or ionomer that is bonded to the aluminum foil. The paperboard layer provides rigidity and strength while the aluminum is the oxygen barrier film. Packages made from this type of material are capable of extending the shelf life of the product at ambient temperatures if it is aseptically processed. In these materials, individual films are combined into a single structure to provide physical strength, resistance to puncture, machinability, sealability, environmental resistance, and barrier against moisture, oxygen, carbon dioxide, odor, and light. High-density polyethylene (HDPE) blow-molded bottles are the single biggest types of milk package used in the United States. HDPE is easy to shape and mold into dispensers; it can be extruded into films to make pouches, or laminated with other materials such as aluminum foil, paper, and other packaging films. HDPE is a good barrier to moisture and is resistant to most solvents; however, it is a poor barrier to carbon dioxide and oxygen and offers little protection against light. To make HDPE opaque, colored resin or shrink-wrapping
Table 1 Properties of common materials used to fabricate packaging for dairy products Gas permeability constant b
Material
Water vapor transmissiona
O2
N2
CO2
Advantages
Disadvantages
Products
Glass
Low
Low
Low
Low
Impermeable, easily recycled, inert
Metal
Low
Low
Low
Low
Excellent gas barrier, rigid, easily recycled
Heavy weight, breakable, high energy costs of manufacturing Requires coatings to prevent corrosion
Fresh milk, yogurt, cream Milk powder, condensed and evaporated milk
Films PVDC (Saron)
3.1
0.91
0.91
0.78
0.07
0.07
0.07
Produces toxic compounds when incinerated Not strong for heavy products
Chesses, MAPc
4.7
Excellent barrier to water vapor, gases, fatty and oily products Excellent clarity and sparkle, can be used in coatings and laminations
7.8
0.03
0.03
0.03
20.2
28.60
28.60
11.38
Very flexible, highly resistant to most solvents, good moisture barrier
Useless for rigid containers, poor barrier for gases
High-density polyethylene
4.7
7.15
7.15
3.25
Moderately flexible, stiffer, tasteless, odorless
Polyvinyl chloride Polyethylene terephthalate
62.0
9.75
9.75
-
Low
Low
Low
Low
Versatile material, compounded with a wide range of additives (plasticized) High tensile strength, low gas and moisture permeability, high use-temperature range, high scuff resistance, excellent oil barrier
Poor barrier for oxygen and other gases, softness, low softening point, poor clarity Difficult to recycle, poor moisture barrier properties Lack of heat sealability
Milk
Low
Low
Low
Low
Poor barrier for gases
Butter
Low
Low
Low
Low
Laminated to aluminum foil and extrusion coated with PE offers barrier to moisture, flavor, and UV light Barrier against moisture, gas, odor, light, and UV light
Cost
Milk, milk powder, yogurt
High
Low
Low
Low
Moisture barrier, low cost, good resistance, good heat-sealing characteristics
Difficult to keep folded
Tubs for ice cream or cream, butter
Cellophane, nitrocellulose coated Polymer coated Plastics Low-density polyethylene
Paper Laminated papers Coextruded laminated (aseptic) Waxed papers a
Cheeses
Liquid milk (pillow packs), condensed milk (squeeze bottles) Milk, yogurt, sour cream, ice cream Cheese, yogurt, MAP
g per m2 ? day at 38 C and 90% RH. cc?mil per m2 ? day ? atm at 25 C and 50% RH (cm3 per m2 ? day). c MAP, modified atmosphere packaging; PE, polyethylene; PVDC, polyvinylidene dichloride. From Hanlon FJ, Kelsey JR, and Forcinio EH (1998) Handbook of Package Engineering. Pennsylvania, PA: Technomic Publishing Company Inc.; Soroka W (2002) Packaging Technology, 3rd edn. Naperville, IL: Institute of Packaging Professionals. b
Packaging 19
with a suitable label is used to protect against UV or fluorescent light in display cases.
Evaporated Milk Evaporated milk is manufactured by a process of evaporation, concentration, homogenization, and sterilization of whole milk. The approximate composition of evaporated low-fat milk is 7.5–9.0% fat and 18–22% non-fat milk solids. In this process, the whole milk is exposed to an ultra-high temperature (UHT) process and then packaged aseptically. To prevent contact and reaction with the metal in tin cans, a protective coating is used. The base material in these cans is steel, but most cans are tin-plated, or coated with enamel, epoxy, or lacquers to prevent rusting or attack from the packaged product. Cans used to package milk are sealed by locking the curl on the lids to the flange on the body of the opened can. Once the seal is accomplished, it is called a double seam. Hermetically sealed cans are capable of safely storing evaporated milk for several months without refrigeration.
Sweetened Condensed Milk Sweetened condensed milk is a product that has been concentrated by evaporation, to which sucrose is added to form an almost saturated sugar solution, after which it is canned. Concentration is usually done by evaporation, but reverse osmosis can also be used. The approximate composition of sweetened condensed milk is 8–9% fat, 20–22% non-fat milk solids, 10–11% lactose, 43–45% sucrose, and 25–27% moisture. This high sugar content helps to maintain the quality of the product during its shelf life. Normally, sweetened condensed milk is packaged in metal cans. In addition, sweetened condensed milk can be kept in the refrigerator for a brief period of time in order to prevent mold growth after it has been opened. Properties of Coated Cans Cylindrical cans are the most commonly used containers for condensed and evaporated milk. They are made from rigid steel or aluminum, and are capable of withstanding pasteurization and sterilization processes and still act as good gas and light barriers. Important characteristics of these containers are their design for easy opening, inexpensive costs, ease of processing on high-speed lines, and recyclability. There are several disadvantages associated with the use of metal cans for milk packaging. These include interactions between the metal and packaged products, and susceptibility of the empty container to damage, which could subsequently compromise the safety of the product.
Powder Milk Non-fat milk powders and whole milk powders (WMPs) are made by evaporating fluid milk to dryness. Dried whole milk contains 26–40% fat and up to 5.0% moisture (by weight). This high fat concentration is a major cause of deterioration due to lipid oxidation during processing and storage. Thus, materials selected to package dried whole milk must limit photodeterioration in order to maintain the product’s quality for extended shelf life (ESL).
Metal Cans The use of three-piece tinplate cans was the traditional method for dried milk packaging for retail marketing. After filling but before sealing these containers, air is withdrawn from the powder and replaced by an inert gas such as nitrogen. This serves to reduce rancidity and extends the product shelf life. Metal cans are popular in many parts of the world due to their mechanical strength, ease of transport and handling, and the possibilities of reuse. Resealable cans usually have a pressure plug lid that provides a gas-tight seal. These types of cans usually have an aluminum foil diaphragm that is affixed to the underside of the sealing rim. This diaphragm provides an extra layer of protection to the unopened can.
Laminates Within recent time, composite cans made from aluminum foil/polymer/paperboard laminates and pouches made from aluminum foil/polymer have been replacing metal cans for powdered milk packaging. Some of these laminated packages could be fabricated on form–fill–seal (FFS) machines. Gas flushing of the product is not uncommon prior to sealing the package. This is done by saturating the powder with inert gas (nitrogen) prior to filling the container. These materials have a light weight but have the disadvantage of not having the mechanical strength or durability of rigid metal containers. Also, they are difficult to recycle and sealing could be problematic for pouches if the dry powder contaminates the sealing area. The strength of a laminate is dependent upon the composition of the material. For instance, a laminate made from aluminum foil, paperboard, and low-density polyethylene (LDPE) has a lower burst strength than a similar laminate in which the paperboard is replaced by a PET film. These laminates could be mounted as roll-stock on FFS machines where they could be used to make gusseted or nongusseted pouches. Typically, a pouch used for dried milk packaging, and made on an FFS machine, would have a laminate made with a PET (17 mm)/LDPE (9 mm)/aluminum foil (9 mm)/ LDPE (70 mm) structure.
20
Packaging
Composite Cans Composite cans are made by the spiral winding of paperboard strips. They can be produced with a wide variety of liners. Cans made from these materials have mechanical strength comparable with aluminum foil/LDPE/paper bags and metal cans. Composite packages have the added advantages of being lighter than metal cans and do not corrode under high-humidity conditions. Composite cans are filled in the same manner as metal cans but they cannot be cleaned with hot water. The material specifications for cans used to package whole or skim milk powders are 0.9 mm thick paperboard and 0.5 mm thick aluminum foil coating with a nitrocellulose lacquer to protect it from abrasion by the powder. An outer decorative label incorporating a fiber sealing material gives increased protection against moisture penetration. When compared with the filling of metal cans, the occluded air trapped in vacuoles within the milk powder is not removed during the gas flushing phase of fiber cans or laminate package filling. This means that the headspace oxygen in these composite packages is higher than in milk stored in metal cans. This has the potential to cause milk in composite packages to spoil faster. For ESL of milk power, residual oxygen concentrations should not exceed 0.02 – 0.03 ml g 1. A reduced oxygen environment could be created by conditioning the milk powder under vacuum for 24–48 h before gas flushing to remove the occluded air.
Ice Cream The packaging of ice cream is often a complicated operation, especially if mixed flavors or exceptional shapes are required. Frozen dessert packages are designed to contain bulk product for the sale of dipped products such as ice cream cones or to package ice cream product into small containers for direct retail sale. The packaging steps may start in the hardening area to retain the shape of the portioned dessert. Practically all frozen desserts for bulk use are packaged in singleservice containers made of paperboard or plastic. Some are packaged in reusable plastic containers, but the use of steel cans is limited. Packages for retail sale vary in size (US sizes vary from 100 ml to 1 l). The most common retail size package is the 250 ml carton. Typical metric package sizes are 100 ml, 250 ml, 500 ml, 1 l, 2 l, and 4 l with shapes that are rectangular, cylindrical (round), or conical (tapered cylinder). A relatively new shape called square/round (squround) is a modification of the conical container. The shape is rectangular, tapered, and rounded at the corners. Ice cream packaged in these containers is easier to scoop out when compared
with ice cream in either the round or rectangular containers. Also, these squround containers have tighter seals and tend to fit better in the freezer compared with the round ones. The traditional rectangular 250 ml carton is made of plastic-coated paperboard. During the fabrication process, the label is printed on the carton, which is folded into a collapsed shape and then sealed on one side. Ice cream mixes are regularly packaged in polymeric cups or tubs, flexible plastic bags, or wax-coated paper. All types are distributed in either cartons or plastic shipping cases.
Cheese Cheesemaking is a complex system with different reactions taking place during the manufacturing, maturation, and storage stages. In unpackaged cheese, quality and water loss depend on the chemical properties of the cheese and on the storage conditions. In packaged cheeses, quality and water loss depend not only on the storage conditions, but also on the permeability and protection provided by the packaging material. Factors that may be considered when selecting a package are the type of cheese and the resulting resistance to mechanical damage (hard or soft cheese); the presence of a specific microorganism; wholesale or retail packaging; permeability to water vapor, oxygen, CO2, NH3; and light; and labeling facilities. Waxing can be applied to low-moisture cheese shortly after manufacturing. In the past, semi-hard cheese was often covered with paraffin wax. However, a latex emulsion is currently used to coat this type of cheese. Soft cheese is commonly wrapped in a three-layer film consisting of a wax/paper/varnish structure; in this material, the wax is in contact with the cheese. This combination results in a packaging material with low O2 and water vapor transmission rates. Fresh and cream cheeses are susceptible to photooxidation. Therefore, they require a packaging material that protects against transmitted light. Genuine vegetable parchment or grease-proof paper was frequently used to package fresh cheese but is currently being used for Petit Suisse. Paper coated with paraffin or polyvinyl chloride/ polyvinylidene chloride (PVC/PVDC) copolymer is sometimes used in the form of a banderole. While a number of plastics have been introduced over the years, the standard material is polystyrene (PS), which is thermoformed on FFS machines. PS is also co-extruded or extrusion coated with PVC or PVC/PVDC co-polymer to improve its barrier properties. The coated PS is sometimes pigmented with TiO2 to provide a better barrier against light.
Packaging 21
Yogurt Yogurt is a highly perishable product and packaging protects it during handling and helps to maintain its physicochemical, nutritional, and sensory characteristics. The package should also prevent loss of volatile flavors and/or the absorption of undesirable odors. Packaging for yogurt is classified into three main categories depending on the physical strength of the container. Semi-rigid Containers These types of containers are normally manufactured from plastic. The properties of different types of plastic materials that are important for yogurt packaging are water vapor, oxygen, and nitrogen transmission rates. Furthermore, yogurt containers must be acid resistant and prevent the loss of volatile flavors. Materials that are used to package yogurt are PE, polypropylene (PP), PS, PVC, and PVDC laminates. Flexible Containers These types of yogurt containers are mainly in the form of paperboard cartons and plastic pouches. Paper-based cartons are made from laminates (PE/aluminum foil/PE or PE/paper/aluminum foil/PE) and are used only to package dehydrated yogurt. An important property of flexible containers for yogurt packaging is permeability to gases and water vapor. Paperboard cartons had been used for yogurt packaging in the past. This type of container was susceptible to leakage. Consequently, its use as a yogurt container is limited despite improvements in its manufacture. Rigid Containers Glass bottles are still used in some countries (France and eastern Europe) to package yogurt. Although glass is an excellent packaging material, its high cost of manufacture and current market trends that favor single-use containers limit the use of glass for yogurt packaging. Other rigid containers that are used to package some yogurt-based products (e.g., dried yogurt) are metal cans.
fluorescent light and sunlight are the cause of oxidation of milk fats found in butter. Thus, the selection of an appropriate packaging material can significantly reduce the incidence of oxidation caused by light and the development of oxidized flavors. Butter is normally wrapped in wet waxed, dry waxed, grease-proof, or vegetable parchment paper, or aluminum foil laminated with vegetable parchment or grease-proof paper. Dairy spreads are usually packaged in thermoformed PP or LDPE containers with lids of, for example, aluminum foil, PVC, or PE. Bulk butter is packed in 25 kg LDPE-lined paperboard cartons. For long-term storage, it is sometimes packaged in cans. Several components of butter are known to influence its spoilage. These include free fatty acids, fat-soluble amino acids, and carotene, which promote autoxidation under the influence of light. Spoilage by microorganisms may cause several off-flavors (putrid, volatile acid, etc.). Therefore, the packaging material must not have a high permeability to water vapor because this could increase the risk of surface mold growth in areas where pockets of moisture could accumulate. Lipolysis also produces a soapy-rancid flavor and the degree of its formation depends on the light source, wavelength of the light, exposure time, distance from the light source, and carotene content of the butter. These conditions should be taken into account when selecting an appropriate packaging material.
Probiotic Dairy Foods The selection of packaging materials to protect and assure the therapeutic activity of these foods is important for the commercialization of these products. It is also important that the level of oxygen within the package should be minimized in order to avoid toxicity and death of the microorganism and a resultant loss of product functionality. Glass bottles provide the best protection for probiotic products, with plastic being the second best alternative. Active and intelligent packaging is becoming increasingly important as a choice for these products. These packages function by (1) absorption of compounds that induce spoilage, (2) release of compounds that extend the shelf life of the product, and (3) monitoring of the shelf life.
Butter
Trends and New Concepts
Butter has a minimum milk fat content of 80–82%, total fat-free dry milk solids of 2%, and a maximum moisture content of 16%. Butter may also have some approved additives such as beta-carotene, sodium chloride, and cultures of harmless lactic acid-forming bacteria. Butter is very susceptible to light-induced flavors, as a result of its susceptibility to lipid oxidation. It is well known that
Both the dairy and the wider food industries face similar challenges with respect to product packaging. Some of these challenges are related to the need to maintain efficiency and sustainability of the manufacturing process and to respond to current market trends. Food safety, governmental regulations, and the demand to use sustainable packaging are the issues that seem to be influencing
22
Packaging
the direction in which the industry is heading. The following are examples of current trends in packaging that are impacting the dairy industry. The increased use of bio-based materials such as polylactic acid (PLA) to fabricate pouches has influenced packaging manufacturers to use ultrasonic sealing as the method of choice for these materials. The traditional method of heat-sealing used for PLA packages causes it to distort at the sealing areas. This is so because PLA shows poor heat stability. The use of ultrasonic sealing solves this problem because it is considered a cold-sealing technique. Containers made from PLA are compostable and/or biodegradable. Using PLA, a British company developed a milk bottle with a smart two-part system to aid its recyclability. The outer layer consists of recycled cardboard, which is lined with an inner sleeve of PLA made from corn starch. The outer layer protects the paperboard from becoming wet and soggy, but upon emptying, it decomposes in landfills. The protection of milk, yogurt, and dairy beverages from the oxidative effects of light is still a concern because of its potential to reduce quality and lower the shelf life of the products. Lactra is an opaque white liquid technology that has been developed primarily for dairy packaging applications, and it is suitable for both singleand multilayered containers. This technique blocks the transmission of light at wavelengths of up to 550 nm while maintaining the aesthetics of the container. LactraTM protects and extends the shelf life of dairy products packaged in PET and complies with the European Union (EU) and Food and Drug Administration (FDA) food contact regulations (Figure 2). In another example, an aseptic flexible pouch developed in Europe was made with a polymeric film having calcium carbonate as two-fifths of its volume. This film is stronger and significantly lighter than currently used
Figure 2 New plastic milk bottles. ColorMatrix’s Lactra barrier protection for PET dairy packaging. Courtesy of color Matrix Europe Ltd.
materials. This new aseptic pouch is sterilized with an electron beam emitter before shipment and this eliminates the need for chemicals and water sterilization before use. Another recent development is a new aseptic PET bottle for shelf-stable UHT milk. The package is sterilized by a system that uses a dry decontamination technique in which vaporized hydrogen peroxide is applied to sterilize preforms just before they are blown into bottles. These bottles can be made of 20% less plastic because the blown bottle never has to withstand the rigors of conventional hydrogen peroxide sterilization and the thermal abuse associated with it. This dry decontamination provides additional energy-saving benefits because it virtually eliminates the use of a water rinse or hot air drying. Active packaging is a relatively new technology for powdered milk. Active packaging (also called smart packaging) is the response of a package to a change in the internal or external environment. This response is designed to change the environment within the package and extend the shelf life of the product. As an example, an active package was created by the use of a plastic sachet made with PVC and PS materials. This system was designed to release -tocopherol in the powdered milk at a controlled rate if the storage temperature exceeded a given threshold. Since -tocopherol is an antioxidant, its controlled release reduces the potential for rancidity of the milk. In a second example of active packaging, a saturated salt solution was incorporated into the package of a cheese product. When this system absorbs oxygen, it adjusts the humidity within the package. This humidity control was accomplished by a two-way system that continually responded and adjusted to match the outside relative humidity (RH) by either adding or removing water to maintain a predetermined level of RH inside the package. The FDA’s approval of a linear aseptic filler for HDPE bottles for low-acid food and beverages is a significant recent event that has influenced food packaging. Consequently, the traditional paperboard and laminated box packages are being replaced by blowmolded plastic bottles. Products such as flavored milk shakes and coffee drinks that are packed in this linear aseptic filler can now be shipped at ambient temperatures with a 180-day shelf life. This feature is found in an ESL system that has a new sanitary valve without O-rings that does not come in contact with the bottle during filling. This eliminates the possibility of bacterial contamination. High speed is another feature found in two new fillers. One has 64 valves with 32-pocket starwheels. This filler is designed to fill plastic and glass bottles with a maximum diameter of 3.09 (76 mm) at speeds of up to 800 bottles per minute. The other ESL high-speed filler is designed for half gallon and 2 l sizes at speeds of up to 120–140 cartons per minute,
Packaging 23
Figure 3 Tetra Lactenso production solutions are engineered to meet the product interacting areas of food safety, quality, efficiency, and sustainability. Courtesy of Tetra Pak.
depending on the carton size. An example of the new fillers is the aseptic system shown in Figure 3. The important features of the filler are the automated instrumentation, longer running time capabilities, shorter presterilization times, easy cleaning, and low maintenance.
Further Reading Coles R, McDowell D, and Kirwan M (eds.) (2003) Food Packaging Technology. London, UK: Blackwell Publishing. Gordon LR (2005) Food Packaging: Principles and Practice, 2nd edn. Boca Raton, FL: CRC Press. Granda-Restrepo D, Peralta E, Troncoso-Rojas R, and Soto-Valdez H (2009) Release of antioxidants from co-extruded active packaging developed for whole milk powder. International Dairy Journal 19: 481–488.
Granda-Restrepo D, Soto-Valdez H, Peralta E, et al. (2009) Migration of -tocopherol from an active multilayer film into whole milk powder. Food Research International 42: 1396–1402. Hanlon FJ, Kelsey JR, and Forcinio EH (1998) Handbook of Package Engineering. Pennsylvania, PA: Technomic Publishing Company Inc. Marshall TR, Goff DH, and Martel WR (2003) Ice cream, 6th edn. New York: Kluwer Academic; Plenum Publishers. PMO (2009) Grade ‘A’ Pasteurized Milk Ordinance, 2009 revision. Washington, DC: US Department of Health and Human Services; FDA. Smet K, De Block J, De Campeneere S, et al. (2009) Oxidative stability of UHT milk as influenced by fatty acid composition and packaging. International Dairy Journal 19: 372–379. Soroka W (2002) Packaging Technology, 3rd edn. Naperville, IL: Institute of Packaging Professionals. Spreer E (1998) Milk and Dairy Product Technology. New York: Marcel Dekker. Tamime YA and Robinson KR (1999) Yoghurt: Science and Technology, 2nd edn. Boca Raton, FL: CRC Press LLC.
PATHOGENS IN MILK Contents Bacillus cereus Brucella spp. Campylobacter spp. Clostridium spp. Coxiella burnetii Escherichia coli Enterobacteriaceae Enterobacter spp. Listeria monocytogenes Mycobacterium spp. Salmonella spp. Shigella spp. Staphylococcus aureus – Molecular Staphylococcus aureus – Dairy Yersinia enterocolitica
Bacillus cereus A Christiansson, Swedish Dairy Association, Lund, Sweden ª 2011 Elsevier Ltd. All rights reserved.
Introduction Bacillus cereus is an aerobic spore-forming bacterium, whose spores are commonly present at low levels in raw milk. In the 1960s and earlier, B. cereus was clearly a quality problem, due to coagulation (sweet curdling) of pasteurized milk and formation of flakes in cream when added to coffee (bitty cream). This was due to poorly cleansed equipment (e.g., milk cans) at the farm and in dairy factories and a lack of adequate refrigeration. Nowadays, these problems are rarely seen in countries where milk is kept at temperatures below 6 C. However, when pasteurized milk is stored at higher temperatures, B. cereus may still be a limiting factor for the keeping quality. Bacillus cereus can produce several enterotoxins causing diarrhea and vomiting. There are few dairy-related cases, but milk and cream have been incriminated in both types of illnesses.
Characteristics Morphology and Cultivation Bacillus cereus is a Gram-positive, rod-shaped, motile bacterium with peritrichous flagella. The cells tend to grow in chains but may occur singly as well. The length
24
of the bacterium varies between 3 and 5 mm and the diameter is more than 1 mm. Spores are oval or cylindrical, located centrally or paracentrally/subterminally, and do not distend the cell. A typical trait of the B. cereus group is the presence of storage granules of poly- hydroxybutyrate in the cytoplasm. These are easily seen by phase contrast microscopy. Bacillus thuringiensis, B. mycoides, B. weihenstephanensis, B. pseudomycoides, and B. anthracis have similar characteristics, except that B. mycoides, B. pseudomycoides, and B. anthracis are nonmotile. The species concept within the B. cereus group (which includes the genetically very closely related entities mentioned above) is still under debate. Bacillus weihenstephanensis and B. mycoides are better adapted to growth at low temperature than the other members within the B. cereus group. If not mentioned specifically in the text, ‘B. cereus’ refers to the entire group (B. cereus sensu lato) except B. anthracis. Bacillus cereus forms colonies with typical appearance on agar media, generally with dull or frosted, grayish/whitish surface. Bacillus mycoides and B. pseudomycoides form rhizoid colonies. Widely used selective agar media for cultivation from food are mannitol egg yolk polymyxin agar (MYP) and polymyxin pyruvate egg yolk mannitol bromothymol blue agar (PEMBA). The detection of B. cereus is based on the absence of
Pathogens in Milk | Bacillus cereus
mannitol fermentation and positive egg yolk reaction (lecithinase). Bacillus cereus can also be enumerated on blood agar with polymyxin added. Colonies with clear zones of hemolysis and a very sharp margin are a useful diagnostic feature. Strains producing emetic toxin have a narrow zone of hemolysis or none at all. The zone does not enlarge upon further incubation, which is the case with nonemetic isolates. A chromogenic selective plating agar (BCM, B. cereus group plating medium) that stains colonies expressing phosphatidylinositol-specific phospholipase C turquoise blue has proven to be a good alternative to standard media. It is not possible to differentiate between the species of the B. cereus group based on colony morphology only. Physiology Bacillus cereus is a versatile microorganism with respect to growth substrates. Most strains produce proteases that can degrade casein and gelatin and enzymes for starch hydrolysis. Enzymes such as lecithinase and sphingomyelinase for degradation of phospholipids and lipase, with activity against triglycerides, can also be produced. Sweet curdling of milk is due to a protease and bitty cream due to phospholipase activity. Several carbohydrates are utilized, for example, glucose, fructose, trehalose, N-acetylglucosamine, and maltose. Others are utilized by only certain strains, for example, salicin, cellobiose, inositol, and mannose. A majority of strains do not grow on lactose. Mannitol is generally not used. Bacillus cereus is in general Voges–Proskauer (VP) positive and utilizes citrate, but not urea. Most strains can reduce nitrate. The minimum growth temperature differs among strains and is generally not lower than 5–6 C, although a few strains have been shown to grow at 4 C. Increased temperature from 6 to 9 C markedly affects the growth rate among psychrotrophic (psychrotolerant) isolates (Table 1). Some strains have temperature minima as high as 10–15 C. The optimum growth temperature is 30–37 C and the maximum growth temperature is 37–50 C. Strains producing emetic toxin do not grow below 10 C and are able to grow at 48 C. The psychrotolerant B. weihenstephanensis and B. mycoides are able to grow at 7 C or below and do not grow at 43 C. These species possess a cold-shock protein (CspA) that is detectable by PCR. Some strains that grow with a minimum temperature of 7 C and above do not have cspA and are classified as B. cereus (sensu stricto). The minimum pH for growth is 4.3–4.9 and the upper limit is 9.3. However, in the presence of organic acids, the minimum pH is higher, for example, pH 5.6 in 0.1 mol l 1 lactate. Although B. cereus grows best under aerobic conditions, anaerobic growth by fermentation of glucose or other carbohydrates or by anaerobic respiration with
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Table 1 Growth of Bacillus cereus (log cfu ml 1) in pasteurized milk at various storage temperatures Days of storage
6 C
7 C
8 C
9 C
1 2 3 4 5 6 7 8 9 10
-a 0.2 0.6 1.0 1.4
0.5 1.3 2.0 2.8 3.5
0.0 1.0 2.0 3.0 4.0 5.0 ND
1.0 2.4 3.7 5.0 ND ND ND
a Less than log 0. ND, not done. The values represent average data for pasteurized milk from 10 Swedish dairy plants in August. One milk package was collected from each plant and the milk from each package was divided aseptically into four aliquots, which were incubated in glass bottles in water baths with accurate temperature regulation (0.1 C). Original data from Christiansson A.
nitrate is possible. Bacillus cereus is able to grow in media with up to 7% NaCl if other conditions are optimum. Minimum water activity for growth is 0.92–0.95.
Spores Spores are formed on a variety of growth media under aerobic conditions, upon starvation. The presence of manganese and magnesium ions stimulates sporulation. Sporulation is a fairly lengthy and complicated process, occurring in the late logarithmic and early stationary phase of growth. Even under favorable conditions, sporulation may take up to 16–24 h to complete. Spores are never formed as a result of chilling if nutrients are available, that is, refrigeration of milk does not induce sporulation. For example, high levels of spores are not found in refrigerated pasteurized milk although the B. cereus counts may grow to 107 ml 1. On the other hand, milk diluted 1:50 with water is still a good growth medium, but nutrients will be depleted after growth and spores are formed abundantly, particularly if the milk is present in thin layers. This is relevant to the cleaning situation in a dairy plant. The spores may germinate and grow out to vegetative cells again under favorable conditions. Germination is much faster than sporulation. The germination rate is highly temperature dependent and may occur within much less than an hour at favorable temperature. In milk, it is stimulated by high-temperature, short-time (HTST) pasteurization, that is, heat treatment. The spores become activated and substances that stimulate germination may be formed as a result of heat treatment. Increased pasteurization temperature in the range of 72–85 C will lead to activation and germination of more spores. However,
26
Pathogens in Milk | Bacillus cereus
initiation of growth in refrigerated milk will occur only after a lag phase of several days. The heat resistance of B. cereus spores is comparatively low. However, there is considerable variation in heat resistance among strains. Although not inactivated by HTST pasteurization, B. cereus spores are easily killed upon ultra-high temperature (UHT) treatment. Typical D-values at 100 C are in the range of 0.3–10 min. For comparison, D100 C for Bacillus stearothermophilus has been estimated to be approximately 3000 min. Strains producing emetic toxin produce spores that are among the most heat resistant within the B. cereus group. Generally, psychrotrophic strains tend to be less heat resistant than mesophilic strains, for example, with D-values of 2–9 min at 90 C. Vegetative cells are easily killed by pasteurization.
Milk-Borne Illness Bacillus cereus is a common contaminant in many food types, including milk, and a significant cause of foodborne illness worldwide. Bacillus cereus can cause diarrhea and/or vomiting when food (most often) containing large numbers of B. cereus is consumed. The symptoms are generally mild and transient, lasting no more than 24 h, generally without sequelae. Two types of outbreaks are known: diarrhealtype outbreak and emetic-type outbreak. Diarrheal-Type Outbreak The illness is characterized by a fairly long incubation period of 8–22 h. Watery diarrhea is very common, together with abdominal cramps, rectal spasms, and moderate nausea. Vomiting is rare. The duration of illness is generally 12–24 h. The delayed onset of symptoms indicates that illness is most likely due to growth of B. cereus in the small intestine, since the toxin(s) are very susceptible to inactivation by low pH and degradation by proteases. Preformed toxin in food will thus be inactivated in the stomach and ileum. Foods associated with diarrheal outbreaks generally contain high numbers of B. cereus, that is, 105–108 per gram food. Foods incriminated in diarrheal outbreaks include meat products, soups, vegetables, puddings, and milk products. Emetic-Type Outbreak The incubation period is short, that is, 0.5–5 h. The rapid onset of nausea and vomiting is due to a preformed toxin in the food. Abdominal cramps and diarrhea occur occasionally. Recovery is rapid, within 6–24 h. The level of B. cereus in incriminated food can vary between a few thousand and up to more than 5 1010 g 1, although it
is generally high. Fried and cooked rice are typical foods frequently involved, but milk-borne cases are also known. Toxins The nature of the enterotoxins produced by B. cereus has remained elusive for decades. However, during the last 15 years, the knowledge about these toxins has increased considerably. At least three types of enterotoxins capable of causing diarrhea have been identified. Two of these, hemolysin BL (HBL) and the nonhemolytic enterotoxin (NHE), are protein toxins consisting of three subunits each. All subunits are needed for full activity. Both toxins have been isolated from B. cereus strains involved in food poisoning. The third toxin, cytotoxin K (cytK), is a single protein toxin. CytK was involved in a rare foodborne outbreak, which caused the death of three persons, where the symptoms included bloody diarrhea. Additional toxins have been described but their involvement in foodborne illness is uncertain. The enterotoxin genes can be found in all species of the B. cereus group as judged by various PCR methods. Most strains are able to produce more than one toxin. Nhe genes are present in almost all strains, whereas Hbl and cytK genes can be found in approximately 50% of all strains, including strains in raw milk. However, cytK genes were not found in strains growing in pasteurized milk at refrigeration temperature. The toxin production potential (expression of the genes) varies considerably between strains and toxins. Strains involved in foodborne illness are generally more toxigenic than the average food or environmental isolate. They are often mesophilic, that is, they have a minimum growth temperature above 10 C, but food poisoning strains growing at or above 7 C are also known. However, strains belonging to B. weihenstephanensis and B. mycoides are generally less toxic than the other members of the B. cereus group. Bacillus thuringiensis and B. cereus (sensu stricto) have similar toxigenicity. From the point of food safety, there is therefore no need to differentiate between these two species as far as milk products are concerned. The toxins are heat labile and are considered to be inactivated by heating above 60 C for 5 min. PCR primers have been published for detection of all enterotoxin subunits. However, the mere presence of the genes is not sufficient to judge the pathogenicity of B. cereus. Monoclonal antibodies have been developed for all subunits of NHE and HBL and can be used for evaluation of the toxin production potential. Cytotoxicity tests using, for example, Vero cells or Caco cells can be employed to assess the overall cytotoxicity of strains. NHE seems to be the most cytotoxic toxin followed by HBL and cytK. The emetic toxin is a cyclic peptide, cereulide, which contains 12 modified amino acids and resembles the ionophore valinomycin. The molecular weight is
Pathogens in Milk | Bacillus cereus
1.2 kDa. The toxin is quite heat resistant and cannot be destroyed even by heating at 121 C for 1 h. Unlike the diarrheal toxins, the emetic toxin is encoded by a plasmid. The expression of the toxin varies strongly among strains and also depends on the composition of the food. The emetic toxin is a more serious health hazard than the diarrheal toxins and has been the cause of death in rare cases. Strains producing emetic toxin are rare in the dairy production chain (less than 1% of all isolates). Emetic strains do not grow in pasteurized milk that is kept refrigerated. A large number of cells (more than 5 log cfu g 1) are needed for toxin production. Recently, a real-time PCR method with PCR primers for detection of genes has been developed. Furthermore, a detection method for the toxin, based on the motility of boar sperm, has become available and can be used for foodstuffs. In addition to enterotoxins, several proteases, phospholipases, and hemolysins may have a role in the pathogenesis of B. cereus.
27
may be at higher risk than the general population. Several factors may explain why milk-borne cases are few: Milk is generally kept at refrigeration temperature and growth of B. cereus is slow, thus the risk of exposure to high levels of bacteria is limited, although significant. In addition, sweet curdling often occurs when the product contains 106–107 B. cereus per ml of milk, with decreased risk of consumption. Psychrotrophic strains, in particular B. weihenstephanensis, will be enriched in pasteurized milk upon cold storage and these strains seem to be less toxigenic than B. cereus (sensu stricto). Psychrotrophic strains have a slower growth rate at the temperature of the human intestine (37 C; close to their maximum temperature of growth) than mesophilic strains, which grow faster. They are therefore less likely to cause food poisoning. However, temperature abuse will increase the risk of illness. Highly toxigenic (mesophilic) strains have been found in raw milk and they may be important in other products such as milk powder.
Outbreaks Related to Dairy Products Outbreaks related to dairy products are rare. Some cases are presented in Table 2. Both diarrheal and emetic symptoms have been recorded. Consumption of (refrigerated) raw milk is never associated with illness, due to the low numbers of B. cereus present. Growth to high numbers is always necessary in order to cause food poisoning. From the table, it seems that young people and elderly
Incidence in Dairy Products Vegetative B. cereus cells are found in raw milk at <10 ml 1 to a few hundred per ml. These cells are killed by pasteurization. Spores are found from <10 l 1 to a few thousand per liter milk, that is, at much lower levels. There is a marked seasonal variation in psychrotrophic
Table 2 Outbreaks of milk-borne illness caused by Bacillus cereus Product
Year
Country
People ill
Symptoms
Analytical data
Unpasteurized milk (heated and then kept at room temperature overnight) Cream, pasteurized
1972
Romania
221 school children
Diarrhea and abdominal cramps after 8–11 h
20 106 B. cereus per ml in milk. Bacillus cereus found in children’s feces
1975
England
Two 15-year-old girls
5 106 B. cereus per gram in cream
Milk, pasteurized
1981
Denmark
1-year-old boy
Vomiting after 8–10 h. One girl had diarrhea Vomiting after 1.5 h, no diarrhea
Milk powder, infant formula Human breast milk
1981
Chile
1981
India
35 neonate children Child, 6 months
Milk, pasteurized
1988
The Netherlands
42 elderly people
Ultra-high temperature milk (process failure)
1991
Japan
201 people
Diarrhea Diarrhea, occasional vomiting Nausea and vomiting after 2–14 h Vomiting 95%, average after 5 h Diarrhea 55%
2.6 106 B. cereus per ml in milk. Remaining milk was sweet curdled 1 h after consumption Bacillus cereus found in stool cultures Bacillus cereus found in breast milk 0.4 106 B. cereus per ml in milk Milk distributed at room temperature
Compiled from Christiansson A (1992) The toxicology of Bacillus cereus. International Dairy Federation Bulletin 275: 30–35; Van Netten P, van de Moosdijk A, van Hoensel P, Mossel DAA, and Perales I (1990) Psychrotrophic strains of Bacillus cereus producing enterotoxin. Journal of Applied Bacteriology 69: 73–79; Shinagawa K (1993) Serology and characterization of toxigenic Bacillus cereus. Netherlands Milk and Dairy Journal 47: 89–103; Cohen JV, Marmabio E, Lynch B, and Moreno A (1984) Bacillus cereus in food poisoning amid newborns. Revista Chilena de Pediatrica 55: 20–25.
28
Pathogens in Milk | Bacillus cereus
spores, with the highest levels in summer and early autumn.
microbiological standards for powdered infant formula products, the limits for B. cereus are n = 5, c = 0, and m = 100 cfu g 1.
Milk and Cream The number of B. cereus in pasteurized milk and cream depends on the quality of the raw milk, the process hygiene at the dairy plant, the storage temperature of the product, and age of the product at the sampling time. Bacillus cereus grows slowly at temperatures below 6 C and will not be a quality problem, unless the sell-by date is set at several weeks. After 7 C storage for 7 days, the incidence of B. cereus can typically vary between 5 and 90% (winter and summer) at <10 to 105 ml 1 (including differences in dairy hygiene). When stored below 5 C, B. cereus is rarely detected unless there is a cleaning problem in the dairy plant. Fermented Milks and Cheese Bacillus cereus is rapidly inactivated in traditional yogurt manufacture as well as in the manufacture of fermented milk with lactococci. Some growth is possible within the first hours of fermentation. Multiplication in semihard cheese is likewise restricted to the first hours in the cheesemaking process. Inhibition occurs due to lactic acid at pH 5.6 but other inhibitors are also active. As the pH is lowered, vegetative B. cereus cells will die whereas spores that have not germinated may still be present. When present in these products, B. cereus seldom exceeds 100 g 1. Milk Powder Bacillus cereus is frequently found in low numbers in milk powder and infant formula. The frequency of isolation varies between 30 and 100% of samples with origin worldwide. Under certain circumstances, there may be some opportunity for growth of B. cereus in the evaporation process. Most samples contain <10 cfu g 1 but samples with more than 103 cfu g 1 have been found. These are due to hygienic problems in the factory or due to raw milk with a high degree of contamination. High levels of B. cereus in infant formula may constitute a health risk. Regulation (EC) 1771/2007 on microbiological criteria for foodstuffs in the European Union defines process hygiene criteria for presumptive B. cereus in dried infant formulae and dried dietary foods for special medical purposes intended for infants below 6 months of age. These are n (sample size) = 5, c (number of sample units giving values between m and M) = 1, acceptable limits (m) = 50 cfu g 1, and unsatisfactory limits (M) = 500 cfu g 1. In standard 1.6.1 of the Australia New Zealand Food Standards Code, which specifies
Source At the Farm Bacillus cereus is a ubiquitous microorganism. The spores are present in soil from 102 cfu g 1 and up to more than 105 cfu g 1. Consequently, food products of plant origin frequently contain B. cereus spores. Soil is an important source of contamination for milk. There is a marked seasonal variation in the spore content of raw milk, with higher levels during the pasture period, when the teats of the cow may be contaminated with soil. Dirty teats that are not cleansed before milking are an important contamination source, particularly during wet weather. Bacillus cereus is able to grow and sporulate on insufficiently cleaned milking equipment, so equipment may be a secondary source of contamination. Used bedding material and feed may also contain spores of B. cereus. In the Dairy Plant There has been considerable disagreement whether the occurrence of B. cereus in dairy products is caused by recontamination of milk at the dairy plant or by contamination at the farm. To some extent, this was due to the inability to detect the low levels of spores in raw milk, whereas B. cereus was easily detected in pasteurized milk after storage. It is now generally agreed that the original contamination occurs at the farm from soil. The seasonal variation in the occurrence of B. cereus in dairy products, kept at temperatures above 6 C, can to a large extent be explained by the increased contamination rate of the milk during the grazing period. However, additional contamination may occur from the dairy plant equipment. Since spores survive pasteurization, they will be present in the milk throughout the dairy process. Spores of B. cereus are very hydrophobic and will attach to surfaces of equipment, where they may germinate and form biofilms at sites that are difficult to clean. Several strain-typing methods (e.g., Random Amplified Polymorphic DNA-Polymerase Chain Rection analysis (RAPDPCR), Amplified Fragment Length Polymorphism analysis (AFLP), riboprinting, Repetitive element sequence polymorphism-PCR analysis (rep-PCR), and pulsed field gel electrophoresis (PFGE)) have recently been applied to strains of B. cereus. These methods demonstrate a high discriminatory power and could be helpful in finding contamination sites in dairy plants. There is a very strong diversity among strains of B. cereus in raw milk. Recontamination of milk by B. cereus has been demonstrated in silo tanks, pasteurizers, milk pipelines
Pathogens in Milk | Bacillus cereus
29
The Dairy Plant
(a) (b) 96
100
(c)
At the dairy factory, cleaning and maintenance is essential. Attention must be given to proper concentrations of cleaning agents, sufficiently high cleaning temperature (at least 75 C for alkaline cleaning agents with 1–1.5% NaOH and at least 60–65 C for acid cleaning agents with 0.6–0.9% nitric acid), and proper flow rates during cleaning, since spores are difficult to remove and to kill. Bacillus cereus is considerably more resistant in a biofilm with spores than in a planktonic state. The spores are not killed by hot water disinfection, but sodium hypochlorite at pH 6–7 is effective. Regular replacement of gaskets and other rubber parts is important.
In Dairy Products
Figure 1 Examples of strain typing of Bacillus cereus isolates. (a) A milk stainless-steel pipeline with a very rough welded seam (arrow) was replaced at a dairy plant (to the left). Spores were recovered from the seam by rinsing with water and ultrasonication, collected by filtration, and then grown on blood agar plates (to the right). (b) All isolates showed the same RAPD fingerprint, which indicates that the welded seam was a source of recontamination. Similar fingerprints were found in pasteurized milk. (c) Examples of various RAPD fingerprints of strains from pasteurized milk. Lanes 1, 8, and 15 are molecular weight markers. A Christiansson, unpublished data.
with bad welding, and in packaging machines using RAPD-PCR (Figure 1). Automated ribotyping and repPCR have been used to identify surfaces of dairy equipment involved in recontamination of milk.
Control The Farm At the farm, measures to control B. cereus include careful teat cleansing before milking and proper cleaning and disinfection of the milking equipment. Since the teats become dirty with soil when the cows are outdoors during the grazing period, it is essential that they are clean before attaching the teat cups. During the indoor season, high levels of B. cereus spores may be found in used bedding material, if not replaced daily, and may contaminate the teats. The best cleansing routine includes the use of one moistened cloth per cow, followed by a dry paper towel. In addition, the milking equipment must be kept clean by careful cleaning after milking. Teat liners and other rubber material must be replaced regularly since aged rubber with cracks can harbor milk residues where B. cereus can propagate and sporulate.
The best control measure for B. cereus in pasteurized milk and cream is to keep a low storage temperature in the whole chain from the dairy plant to the customer. Below 5–6 C, growth of most strains of B. cereus is insignificant. If the temperature is higher, the sell-by date must be shortened. Suitable time/temperature combinations may be found by storage tests. Seasonal variation, occurrence of recontamination at the dairy plant as well as possible moderate temperature abuse by the customer must be taken into consideration when choosing the recommended last consumption date of the products. Milk powder is microbiologically stable and no growth of B. cereus can occur in the powder, although occurrence of contamination with B. cereus is frequent. However, milk powder is frequently used in infant formulae and in infant foods. When such powders are reconstituted, it is important that the product is consumed shortly after preparation unless it is not cooled to below 8 C. Spores of B. cereus are able to germinate rapidly at the reconstitution temperature and will grow rapidly if the product is kept at room temperature. Young children may be more susceptible to toxins that may be produced than adults.
See also: Analytical Methods: DNA-Based Assays. Biofilm Formation. Dehydrated Dairy Products: Infant Formulae; Milk Powder: Types and Manufacture. Heat Treatment of Milk: Thermization of Milk. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk; Liquid Milk Products: UHT Sterilized Milks; Pasteurization of Liquid Milk Products: Principles, Public Health Aspects. Microorganisms Associated with Milk. Milking and Handling of Raw Milk: Effect of Storage and Transport on Milk Quality; Milking Hygiene. Plant and Equipment: In-place Cleaning. Psychrotrophic Bacteria: Other Psychrotrophs.
30
Pathogens in Milk | Bacillus cereus
Further Reading Anonymous (2005) Opinion of the scientific panel on biological hazards on Bacillus cereus and other Bacillus spp in foodstuffs. EFSA Journal 175: 1–48. Becker H, Schaller G, von Wiese W, and Terplan G (1994) Bacillus cereus in infant foods and dried milk products. International Journal of Food Microbiology 23: 1–15. Christiansson A (1992) The toxicology of Bacillus cereus. International Dairy Federation Bulletin 275: 30–35. Cohen JV, Marmabio E, Lynch B, and Moreno A (1984) Bacillus cereus in food poisoning amid newborns. Revista Chilena de Pediatrica 55: 20–25. Fricker M, Reissbrodt R, and Ehling-Schultz M (2008) Evaluation of standard and new chromogenic selective plating media for isolation and identification of Bacillus cereus. International Journal of Food Microbiology 121: 27–34. Granum PE (2007) Bacillus cereus. In: Doyle MP and Beuchat LR (eds.) Food Microbiology: Fundamentals and Frontiers, 3rd edn., pp. 445–455. Washington, DC: ASM Press. Guinebretie`re M-H, Thompson FL, Sorokin A, et al. (2008) Ecological diversification in the Bacillus cereus group. Environmental Microbiology 10: 851–865. IDF (1992) Bacillus cereus in milk and milk products. Bulletin of the International Dairy Federation No. 275. Brussels:IDF.
Langeveld LPM and Cuperus F (1980) The relation between temperature and growth rate in pasteurized milk of different types of bacteria which are important to the deterioration of that milk. Netherlands Milk and Dairy Journal 34: 106–125. Notermans S, Dufrenne J, Teunis P, Beaumer R, te Giffel M, and Peeters Weem P (1997) A risk assessment study of Bacillus cereus present in pasteurized milk. Food Microbiology 14: 143–151. Shinagawa K (1993) Serology and characterization of toxigenic Bacillus cereus. Netherlands Milk and Dairy Journal 47: 89–103. Stenfors Arnesen LP, Fagerlund A, and Granum PE (2008) From soil to gut: Bacillus cereus and its food poisoning toxin. FEMS Microbiology Reviews 32: 579–606. Svensson B, Montha´n A, Guinebretie`re M-H, Nguyen-The´ C, and Christiansson A (2007) Toxin production potential and the detection of toxin genes among strains of the Bacillus cereus group isolated along the dairy production line. International Dairy Journal 17: 1201–1208. Van Netten P, van de Moosdijk A, van Hoensel P, Mossel DAA, and Perales I (1990) Psychrotrophic strains of Bacillus cereus producing enterotoxin. Journal of Applied Bacteriology 69: 73–79. Wijnands LM, Dufrenne JB, Zwietering MH, and van Leusden FM (2006) Spores from mesophilic Bacillus cereus strains germinate better and grow faster in simulated gastro-intestinal conditions than spores from psychrotrophic strains. International Journal of Food Microbiology 112: 120–128.
Brucella spp. B Garin-Bastuji, French Agency for Food, Environmental & Occupational Health Safety (ANSES), Maisons-Alfort, France ª 2011 Elsevier Ltd. All rights reserved.
Introduction Brucella spp. are the causative agent of brucellosis, a zoonosis of worldwide importance. Human brucellosis is usually characterized by an intermittent influenza-like clinical pattern, which may be severe and may be followed by chronic, intermittent relapses. The main manifestations of animal brucellosis are reproductive failure, for example, abortion and birth of unthrifty offspring in the female, and orchitis and epididymitis in the male, and rarely arthritis. Persistent infection with shedding of Brucella in reproductive and mammary secretions is common. Genetic and immunological evidence indicates that all members of the genus Brucella are closely related. However, due to relevant differences in host preference and epidemiology displayed by the major variants, as well as molecular evidence of genomic variation, the classification of the genus includes nine species (Table 1). Brucella abortus primarily infects cattle but may be transmitted to buffaloes, camels, deer, dogs, goats, horses, pigs, sheep, and humans. Brucella melitensis causes a highly contagious disease in sheep and goats although cattle and other species can be infected. It is the most important species in human infection. Brucella suis covers a wider host range than most other Brucella species. Brucella canis causes epididymo-orchitis in the male dog and abortion and metritis in the bitch. It has not been reported in other animals except humans. Brucella ovis is responsible for epididymitis in rams and occasionally infects ewes, but does not infect other animals or humans. Brucella neotomae is only known to infect the desert wood rat under natural conditions, and no other cases have been reported. In the last decade, isolations of previously unidentified species of Brucella have been reported from sea mammals (B. ceti and B. pinnipedialis). Finally, a new species, Brucella microti, was recently isolated in central Europe from the common vole (Microtus arvalis).
Characteristics
morphology of Brucella spp. is fairly constant except in old cultures, where pleomorphic forms may occur. Brucellae are nonmotile and do not form spores, and flagella, pili, or true capsules are not produced. They usually do not show bipolar staining and resist decolorization by weak acids. Culture and Growth Characteristics Brucella spp. are aerobic, but many strains require an atmosphere containing 5–10% added CO2 for growth (Table 2). The optimum pH for growth varies from 6.6 to 7.4, and culture media should be adequately buffered near pH 6.8 for optimal growth. The optimal growth temperature is 36–38 C, but most strains can grow between 20 and 40 C. Growth in liquid media favors dissociation of smooth-phase cultures to nonsmooth forms and is usually poor unless the culture is vigorously agitated. On suitable solid media, colonies are visible after 2 days of incubation. After 4 days of incubation, the colonies are round, 1–2 mm in diameter, with smooth margins, translucent, and a pale honey color when plates are viewed in the daylight through a transparent medium. When viewed from above, the colonies appear convex and pearly white. Later, the colonies become larger and slightly darker. Smooth Brucella spp. cultures have a tendency to undergo variation during growth, especially with subcultures, and dissociate to rough (R) forms, and sometimes mucoid (M) forms. Biochemical Characteristics The metabolism of Brucella spp. is oxidative, and cultures show no ability to acidify carbohydrate media in conventional tests. The Brucella species are catalase-positive and usually oxidase-positive (except otherwise stated in Table 1), and reduce nitrates to nitrites (except B. ovis and some B. canis strains). Brucella suis biovar 1, B. neotomae and biovars 1–4 and 9 of B. abortus produce H2S from sulfur-containing amino acids (Table 2). Urease activity varies from fast to very slow. Indole is not produced from tryptophan, and acetylmethylcarbinol is not produced from glucose.
Morphology Bacteria included in the genus Brucella are Gram-negative coccobacilli or short rods (0.6–1.5 mm 0.5–0.7 mm) arranged singly and rarely in pairs or small groups. The
Antigenic Characteristics All smooth Brucella spp. strains show complete crossreaction with each other, but not with nonsmooth variants,
31
Table 1 Differential characteristics of species of the genus Brucella Lysis by phagesb Tb
Wb
Iz1
R/C
Species
Colony morphologya
Serum requirement
RTDc
104RTD
RTD
RTD
RTD
Oxidase
Urease activity
Preferred host
B. abortus
S
d
þ
þ
þ
þ
þe
þf
B. suis
S
þ
þg
þg
þ
þh
B. melitensis B. neotomae B. ovis B. canis B. ceti B. pinnipedialis B. microti
S S R R S S S
þ
k þm þm
þ
i þ þn þn þ
þ þ þo þo þ
þ þ
þ þ þ þ þ
þj þh þh þ þ þ
Cattle and other Bovidae Biovar 1: swine Biovar 2: swine, hare Biovar 3: swine Biovar 4: reindeer Biovar 5: wild rodents Sheep and goats Desert wood ratl Rams Dogs Cetaceans Pinnipeds Common vole
a
Normally occurring phase: S, smooth; R, rough. Phages: Tbilisi (Tb), Weybridge (Wb), Izatnagar1(Iz1), and R/C. c RTD: routine test dilution. d B. abortus biovar 2 generally requires serum for growth on primary isolation. e Some African isolates of B. abortus biovar 3 are negative. f Intermediate rate, except strain 544 and some field strains that are negative. g Some isolates of B. suis biovar 2 are not or partially lysed by phage Wb or Iz1. h Rapid rate. i Some isolates are lysed by phage Wb. j Slow rate, except some strains that are rapid. k Minute plaques. l Neotoma lepida. m Some isolates are lysed by Tb. n Most isolates are lysed by Wb. o Most isolates are lysed by Iz. b
þ
Pathogens in Milk | Brucella spp. 33 Table 2 Differential characteristics of the biovars of Brucella species
Species
B. melitensis
B. abortus
B. suis
B. neotomae B. ovis B. canis B. ceti B. pinnipedialis B. microti
Growth on dyesa
Agglutination with monospecific sera
Biovar
CO2 requirement
H2S production
Thionin
Basic fuchsin
A
M
R
1 2 3 1 2 3 4 5 6 9 1 2 3 4 5 – – – – – –
þb þb þb þb þ or þ þ
þ þ þ þ þ þ þ
þ þ þ þ þ þ þ þ þ þ þ f þ þ þ þ þ
þ þ þ þ þ þc þ þ þ d þ e e f þ þ þ
þ þ þ þ þ þ þ þ þ þ þ þ þ
þ þ þ þ þ þ þ e e þ
þ þ
Dye concentration in serum dextrose medium: 20 mg ml1. Usually positive on primary isolation. c Some basic fuchsin-sensitive strains have been isolated. d Some basic fuchsin-resistant strains have been isolated. e Negative for most strains. f Growth at a concentration of 10 mg ml1 thionin. a
b
in agglutination tests with unabsorbed polyclonal antisera. Cross-reactions between nonsmooth strains can be demonstrated as well with unabsorbed anti-R sera. Lipopolysaccharide (LPS) comprises the major surface antigens of the corresponding colonial phase involved in agglutination. The S-LPS molecules carry the A and M antigens, which show different quantitative distribution among the smooth Brucella spp. strains (Table 2). Serological cross-reactions have been reported between smooth brucellae and various other Gram-negative bacteria, and especially Yersinia enterocolitica O:9, which can induce significant levels of antibody cross-reacting with S-LPS Brucella spp. antigens in diagnostic tests.
Susceptibility to Dyes and Antibiotics
Susceptibility to Phages
Resistance and Survival
Over 40 phages have been reported to be specifically lytic for Brucella spp. Thus, lysis by specific phages is a useful test to confirm the identity of Brucella spp. and for speciation within the genus. The phages mainly used for Brucella spp. typing are Tbilisi (Tb), Weybridge (Wb), Izatnagar1 (Iz1), and R/C (Table 1).
The ability of Brucella spp. to persist outside its mammalian host is relatively high as compared with most other non-spore-forming pathogenic bacteria, under suitable conditions. Thus, when conditions of pH, temperature, and light are favorable, that is, pH > 4, cool temperature, high humidity, and absence of direct sunlight, brucellae
Susceptibility to the dyes thionin and basic fuchsin, which varies between biovars, is one of the routine typing tests of Brucella spp. (Table 2). On primary isolation, all brucellae are usually susceptible in vitro to gentamicin, rifampin, and tetracyclines. Most strains are also susceptible to ampicillin, chloramphenicol, cotrimoxazole, erythromycin, kanamycin, novobiocin, spectinomycin, and streptomycin, but variation in susceptibility may occur. In vivo, most strains are resistant at therapeutic concentrations to amphotericin B, bacitracin, -lactamins, cephalosporins, clindamycin, cycloheximide, lincomycin, nalidixic acid, nystatin, polymyxin, and vancomycin.
34
Pathogens in Milk | Brucella spp.
may retain infectivity for several months in aborted fetuses and fetal membranes, feces and liquid manure, water, wool, and hay, and on equipment and clothes. Brucellae are able to withstand drying particularly in the presence of extraneous organic material and will remain viable in dust and soil. Survival is prolonged at low temperatures, especially when freezing. The persistence of brucellae in milk and dairy products is related to a variety of factors including the type and age of product, humidity level, temperature, changes in pH, moisture content, biological action of other bacteria present, and conditions of storage. The results of several studies are presented in Table 3. At low numbers in liquid media, brucellae are fairly heat-sensitive. Thus, dilute suspensions in milk are readily inactivated by pasteurization (high-temperature short-time or flash methods) or prolonged boiling (10 min). Brucellae do not remain viable for prolonged periods in ripened fermented cheese. The optimal fermentation time to ensure safety is not known but is estimated at 3 months. However, in normally acidified soft cheese, the strictly lactic and short-time fermentation and drying increase the survival of Brucella. Pasteurization of milk or cream is the only means to ensure safety of these products. Brucellae are fairly sensitive to ionizing radiation and are readily killed by normal sterilizing doses of gamma rays, under conditions that ensure complete exposure, especially in colostrum. In contrast to dairy products,
the survival time of brucellae in meat is extremely short, due to acidic fermentation of the meat except in frozen carcasses where the organism can survive for many years. Therefore, meat consumption is less likely to be a source of infection. Direct contamination of abattoir workers and carcasses by milk and uterovaginal secretions is prevented by a proper and hygienic removal of mammary glands, reproductive organs, and lymph nodes, which are the most heavily contaminated organs. Most commonly available disinfectants readily kill brucellae at normally recommended concentrations (phenol 10 g l1, formaldehyde, xylene 1 ml l1), except in the presence of organic matter or at low temperature, which drastically reduce their efficacy. Where possible, decontamination should be carried out by heat treatment, especially for surfaces. Diluted hypochlorite solutions, ethanol, iodophors, or isopropanol, and optimally substituted phenols, but not the alkyl quaternary ammonium, are effective for decontamination of exposed skin.
Animal Brucellosis Brucellosis in Cattle Brucella-infected cattle generally develop granulomatous inflammatory responses often located within lymphoid tissues and organs with a prominent reticuloendothelial component. There is a predilection for selected body sites
Table 3 Studies on Brucella survival time in dairy products Product
Species of Brucella
Survival time
Temperature ( C)
pH
Milk
B. abortus B. abortus B. abortus B. abortus Brucella spp. B. abortus B. melitensis B. abortus B. abortus
5–15 s <9 h 24 h 18 months >10 days 6 weeks 4 weeks 30 days 142 days
71.7 38 25–37 0 4 4 4 0 8
– 4.00 – – <4 – – – –
B. abortus B. melitensis B. melitensis B. melitensis B. abortus and B. melitensis B. abortus B. melitensis B. abortus B. melitensis B. abortus B. abortus
6–57 days 15–100 days 4–16 days <90 days 20–60 days <21 days 44 days 6 months 1–8 weeks <4 days >6 days
– – – – – – – – – 17–24 5
– – – – – – – – – 4.3–5.9 5.4–5.9
Fermented milk Cream Ice cream Butter Cheese Various Various Feta Pecorino Roquefort Camembert Erythrean Cheddar White Whey
From Davies G and Casey A (1973) The survival of Brucella abortus in milk and milk products. British Veterinary Journal 129: 345–353; Zu´n˜iga Estrada A, MotadelaGarza L, Sa´nchez Mendoza M, Santos Lo´pez EM, Filardo Kerstupp S, and Lo´pez Merino A (2005) Survival of Brucella abortus in milk fermented with a yoghurt starter culture. Revista Latinoamericana de Microbiologi´a 47: 88–91; Garin-Bastuji B and Verger JM (1994) Brucella abortus and melitensis. In: Hahn G (ed.) The Significance of Pathogenic Microorganisms in Raw Milk, pp. 167–185. Brussels: IDF.
Pathogens in Milk | Brucella spp. 35
such as reproductive organs, udder, and supramammary lymph nodes, and sometimes joints and synovial membranes. The localization and persistence of brucellae in these organs and tissues follow in the wake of a widespread distribution of Brucella during a generalized stage of infection. During this first stage of infection, the major clinical symptom is abortion but other signs due to a localization of brucellae may be observed (e.g., orchitis, epididymitis, hygroma, arthritis, metritis, subclinical mastitis). However, numerous animals develop self-limiting infections or they become asymptomatic latent carriers and potential excretors. The second stage is characterized by the elimination of brucellae or, more frequently, by a persistent infection of the mammary glands and supramammary and genital lymph nodes, with a constant or intermittent shedding of the organisms in the milk and genital secretions. Animals generally abort once, from 5 to 8 months of gestation, but reinvasion of the uterus occurs in subsequent pregnancies through shedding of the microorganism in fluids and membranes. The pregnancy can also be full-term. Vaginal discharges after abortion or normal calving are the main source of contamination of congeners, other animal species, and man. The interherd spread of infection generally follows the movement or gathering of infected animals. Persistent infection of mammary glands is associated with constant or intermittent shedding of the organisms in the milk in succeeding lactation periods and a drop in milk production estimated at 10%. The number of brucellae excreted in milk is relatively low and does not allow transmission through direct contact, except through the milker’s hands. In the male, localization in the reproductive organs generally results in brucellae being shed in the semen. Congenital infection is of major epidemiological significance, since 2–20% of heifer calves born to infected cows may be persistently infected. Other calves fed with infected milk usually become infected, but most recover from these infections. Brucellosis in Small Ruminants (Specific Features) Brucella melitensis is the main causative agent of brucellosis in sheep and goats, but sporadic cases due to B. abortus have been observed. Pathologically and epidemiologically, B. melitensis infection in sheep and goats is very similar to B. abortus infection in cattle. The excretion from the vagina is more copious and prolonged than in the case of cows and last in goats for at least 2–3 months. In goats, about two-thirds of acute infections acquired naturally during pregnancy lead to infection of the udder and excretion of the organisms in the milk during the next lactation. Excretion may cease during a lactation
period. Infection reduces milk production more drastically than in cattle. Brucellosis in Other Species In other milk-producing domestic ruminants (buffaloes, camels, reindeer, yaks), the risks associated with the shedding of brucellae in milk are comparable with those in cattle, sheep, and goats.
Human Brucellosis Humans are accidental and almost always dead-end hosts of Brucella infections. The disease is primarily an occupational hazard in professionals who work with animals and their products, namely, veterinarians, farmers, laboratory technicians, abattoir workers, and others. The primary route of infection is through either direct or indirect contact on skin or mucous membranes. Another source is the ingestion of contaminated fresh dairy products. Humans are susceptible mainly to B. abortus, B. melitensis, and B. suis. Brucella melitensis and B. suis often give rise to the most severe form of infection. After an average 8- to 20-day (up to several months) incubation period, illness occurs in different forms. The asymptomatic form is frequent and mainly due to B. abortus, and is characterized by serologic evidence in persons with no symptoms consistent with brucellosis. The acute form is also common and symptoms include lassitude, headache, and muscular or joint pain, and drenching sweats, especially at night, are characteristic. The manifestations of brucellosis are sometimes most pronounced in or limited to a specific system or organ. Complication occurs in the course of acute infection, and localized brucellosis occurs in the absence of other signs of systemic illness (spondylitis and peripheral arthritis, especially of the hip, knee, and shoulder, epididymo-orchitis and thrombophlebitis). Nervous, genitourinary, hepatosplenic, and cardiovascular complications may be observed as well. Chronic brucellosis includes one or more of the signs described above and persists or recurs over a period of 6 months or more. Finally, Brucella dermatitis has traditionally been ascribed to allergy to brucellae. Brucellosis may be diagnosed on medical history but definitive diagnosis needs bacteriological and serological tests. Bacteriological studies consist essentially in blood cultures. However, cultural examinations are time-consuming, hazardous, and not sensitive, and cultural analysis must be performed in well-equipped laboratories with highly skilled personnel and are generally limited to hospital laboratories. Thus, diagnosis is frequently based on the detection of high or rising titers in serological tests such as serum agglutination test and the Rose Bengal test (RBT) as screening tests, and
36
Pathogens in Milk | Brucella spp.
Coombs’ or complement fixation tests, or ELISA for confirmation. Treatment of choice in acute brucellosis consists of antibiotic therapy. The best results are now achieved with rifampin (600–900 mg day1) combined with doxycycline (200 mg day1) given orally for at least 6–7 weeks. Treatment generally needs to be prolonged or repeated in persistent forms before a cure is achieved.
Diagnosis of Animal Brucellosis In the absence of pathognomonic signs, the specific diagnosis of brucellosis can only be made on the basis of laboratory testing, especially in domestic animals. Bacteriological Methods There is no single test by which a bacterium can be identified as Brucella spp. A combination of growth characteristics, and serological and bacteriological methods is usually required.
of Brucella spp. from blood and other body fluids or milk, where enrichment culture is usually advised. Selective media
All the basal media mentioned above can be used for the preparation of selective media. Appropriate antibiotics are added in order to suppress growth of organisms other than Brucella spp. The selective medium most widely used is Farrell’s medium, which is prepared by the addition of six antibiotics to a basal medium. A freezedried antibiotic supplement is available commercially. A selective biphasic medium made of the basal Castan˜eda medium with the addition of antibiotics to the liquid phase is sometimes recommended for isolation of Brucella spp. in milk. These media allow the isolation of most strains of Brucella spp.; however, some strains of B. melitensis may be partially inhibited by bacitracin, included in the supplement. Sensitivity increases significantly by the simultaneous use of both Farrell’s and the modified Thayer–Martin’s medium. Collection and culture of specimens
Staining methods
Stamp’s modification of the Ziehl–Neelsen method is the usual procedure for the examination of smears of organs or biological fluids. However, this method shows a low sensitivity on milk and dairy products where brucellae are often present at low numbers and interpretation is frequently impeded by the presence of fat globules. Furthermore, staining methods are not specific, and other organisms causing abortion, for example, Chlamydophila abortus (formerly Chlamydia psittaci) or Coxiella burnetii, are very difficult to differentiate from Brucella spp. organisms. The results, whether positive or negative, should be confirmed by culture. Culture Basal media
Direct isolation and culture of Brucella spp. are usually performed on solid media that enable the developing colonies to be isolated and recognized clearly, and limit the establishment of nonsmooth mutants and overgrowth of contaminants. However, the use of liquid media may be recommended for specimens where brucellae may be in small numbers. A wide range of commercial dehydrated basal media is available, for example, Brucella medium base, Tripcase or Trypticase soy agar, and Bacto tryptose. Addition of 2–5% bovine or equine serum is necessary for the growth of strains like B. abortus biovar 2, and many laboratories systematically add serum to the basal media, with excellent results. Other media such as serum dextrose agar or glycerol dextrose agar can be used satisfactorily. A nonselective, biphasic medium, known as the Castan˜eda medium, is recommended for the isolation
Brucellosis is one of the most easily acquired laboratory infections; hence, safety precautions for sampling, and shipping, handling, and processing of the samples are extremely important, and work should only be carried out under level 3 containment (biosafety) conditions and by personnel adequately trained and made aware of the risks. Milk
Samples of milk have to be collected aseptically after washing and drying of the whole udder and disinfection of the teats. It is essential that the samples contain milk from all quarters, and 10–20 ml of milk should be taken from each teat, avoiding contact of milk with the milker’s hands. The first few streams are discarded and the sample is directly milked into a sterile vessel. Milk specimens should be cooled immediately after they are taken and sent to the laboratory by the most rapid route. If they are to spend more than 12 h in transit, they should be treated with boric acid (0.1%), or preferably frozen. On arrival at the laboratory, samples are frozen if they are not to be cultured immediately. Then, milk is centrifuged at 5–700 g for 15 min, and cream and deposits are spread on solid selective medium, separately or mixed. Brucellae are usually present in low numbers in bulk tank samples, and isolation from such specimens is very unlikely. Dairy products
These materials are likely to contain small numbers of organisms, and enrichment culture is advised. Sampling methods are those classically recommended
Pathogens in Milk | Brucella spp. 37
for bacteriological examination of dairy products and adapted to each sort of product. Specimens need to be carefully homogenized before culture, after they have been ground in a tissue grinder or macerated and pounded in a stomacher or an electric blender, with an appropriate volume of sterile phosphate-buffered saline. The superficial strata (rind and the underlying parts) and core of the product should be cultured. Brucellae grow, survive, or disappear more or less rapidly according to the local physicochemical conditions linked to specific process technologies, and their distribution among the different parts of the product varies. A previous inoculation into guinea pigs or mice may sometimes provide the only means of detecting the presence of Brucella spp., especially when the specimens are heavily contaminated or likely to contain a low number of brucellae. Spleen is then cultured and, if possible, a serum sample is subjected to specific tests. Other specimens
The most valuable other specimens include aborted fetuses (stomach contents, spleen, and lung), fetal membranes, vaginal secretions, semen, and arthritis or hygroma fluids. On animal carcasses, the tissues preferred for culture are those of the reticuloendothelial system (i.e., head, mammary and genital lymph nodes, and spleen), the pregnant or early postparturient uterus, and the udder. Identification and typing
Species identification is routinely based on lysis by phages and on simple biochemical tests (oxidase, urease, etc.). For B. melitensis, B. abortus, and B. suis, the identification at the biovar level is currently performed by four main tests: carbon dioxide requirement, production of hydrogen sulfide, dye (thionin and basic fuchsin) sensitivity, and agglutination with monospecific A and M antisera. The polymerase chain reaction (PCR), including the real-time format, based on selected sequences of the Brucella spp. genome, provides an additional means of Brucella detection and identification, which is unaffected by the colonial phase. A number of other methods including a multilocus sequencing scheme and several typing schemes based on the use of multiple locus VNTR analysis (MLVA) have recently been described, which can add useful epidemiological information allowing isolates to be differentiated to the species level or to be further subdivided at the subspecies level. Serological Diagnosis Diagnosis of Brucella spp. infection often has to be based on serological methods, in situations where bacteriological examination is not practicable. In routine veterinary tests, anti-Brucella antibodies are detected in serum and
milk. The most widely used and recommended serumtesting procedures are (1) buffered Brucella antigen tests (BBAT), that is, card test and the RBT, or buffered plate agglutination test (BPAT), (2) complement fixation test (CFT), and (3) indirect ELISA tests. The milk ring test (MRT) or indirect ELISA performed on bulk tank samples have great usefulness for locating infected herds or flocks (the MRT is not usable in small ruminants). These tests are also of great interest to identify infected animals. The World Health Organization, the World Organization for Animal Health (OIE), the US Department of Agriculture, and the European Union have adopted specific recommendations for standardization of performance of the tests and interpretation of the results for all the different methods mentioned above. In small ruminants RBT and CFT are the most effective and the most widely used methods. Allergic Tests Delayed-type hypersensitivity reactions associated with cell-mediated immunity may be induced by either infection or immunization with living or adjuvant killed vaccines. Thus, a number of skin tests have been developed. Antigens free of S-LPS, such as Brucellin-INRA, should be preferred to crude preparations that interfere with serological diagnosis. Reactions are thus specific to the genus Brucella. Allergic skin test is now more and more widely used for nonvaccinated cattle, sheep, and goat herd surveillance, notably as a complementary test.
Control Control, eradication, and prevention of brucellosis require the implementation of regional programs based on vaccination and/or test and slaughter of infected animals, and general nonspecific management practices and hygienic measures that reduce exposure potential. These measures would not be effective without health education, training, and mobilization of livestock owners and others engaged in animal production, and if animal identity is not well recorded and stock movements are not well controlled. General Measures General nonspecific control measures help to reduce the spread of infection. Field personnel should be aware of simple safety measures to prevent human contamination and passive intra- and interherd transmission. Isolation of females at parturition, and incineration or deep burying of nonliving products and fetal membranes are essential to limit the spread of infection. Contaminated materials and premises should be disinfected by heat
38
Pathogens in Milk | Brucella spp.
treatment or by the use of the chemicals previously mentioned. All personnel handling contaminated material should wear disinfected or single-use protective clothing. Body surfaces that have been accidentally exposed to infection should be systematically washed and then decontaminated. Abattoir workers should take similar precautions, especially when handling udder and uterus, which should be systematically destroyed when infection is suspected. In the laboratory, Brucella spp. present a very serious risk to workers handling heavily infected materials and cultures. Even when processing milk or dairy products risk exists but is lower. However, special safety precautions are not required for personnel engaged in routine serological diagnosis. All personnel regularly exposed to infection should be kept under close clinical and serological surveillance. Currently no vaccine is efficient or safe enough to be recommended. In infected areas, trade in fresh milk and dairy products should be strictly controlled and limited to officially declared brucellosis-free farms. The milk produced on infected farms should be heat treated whatever its commercial purpose. Eradication by Test and Slaughter Considering the low efficacy and the cost of antimicrobial chemotherapy in farm animals, test and slaughter of sero-positive animals is one of the two major forms of control and prevention of brucellosis. Such a strategy of eradication is justified on economic grounds when the prevalence rate of infected herds is 1% or below. The epidemiological surveillance of brucellosis-free herds is generally based on regular control by the use of bulk MRT (in cattle only) and/or individual serological testing. All susceptible animals should be permanently identified and movements of animals closely controlled. Eradication programs usually require an abortion notification and investigation scheme as well to detect infection. When positive results or abortions occur, safety measures should be undertaken and reactors or aborted females slaughtered. In some circumstances, for example, in free areas or in heavily infected herds, slaughter of the whole herd is advisable. Herd replacement should not subsequently occur and contaminated premises or pastures should not be used for animal housing or grazing, for 2–3 months. Immunization In high-prevalence areas or where the herds are large, or in extensive pastoral areas, it may be impossible to conduct the test-and-slaughter regime outlined above. Therefore, mass immunization is the only way to reduce
the rate of infection. At present, the most widely used vaccines are the live attenuated vaccines S19 in cattle and Rev.1 in small ruminants. These vaccines have proved to be effective in reducing the number of abortions and also limiting the spread of infection. The RB51 vaccine, usable only in cattle, has become the official vaccine for the prevention of brucellosis in cattle in some countries. However, its efficacy as compared to the reference S19 vaccine remains controversial. Vaccination cannot be expected to eradicate the disease from a herd. Furthermore, when used in adult animals, these vaccines induce long-term serological reactions and sometimes abortions. To reduce these reactions, immunization is generally restricted to young animals between the ages of 3 and 6 months and the conjunctival route is preferred to subcutaneous delivery. When the epidemiological situation improves, a combined scheme including immunization of young animals and test and slaughter of infected adults may be applied. Then, when the prevalence rate of infected herds becomes sufficiently low, test and slaughter as outlined above may be applied.
See also: Diseases of Dairy Animals: Infectious Diseases: Brucellosis. Husbandry of Dairy Animals: Sheep: Health Management. Office of International Epizooties: Mission, Organization and Animal Health Code.
Further Reading Alton GG, Jones LM, Angus RD, and Verger JM (1988) Techniques for the Brucellosis Laboratory. Paris: INRA. Beerens H and Luquet FM (1987) Recherche des Brucella. In: Guide pratique d’analyse microbiologique des laits et produits laitiers. Paris: Lavoisier-APRIA. Blasco JM (1997) A review of the use of B. melitensis Rev1 vaccine in adult sheep and goats. Preventive Veterinary Medicine 31: 275–281. Corbel MJ and Brinley-Morgan WJ (1984) Genus Brucella Meyer and Shaw 1920, 173AL. In: Krieg NR and Holt JG (eds.) Bergey’s Manual of Systematic Bacteriology, Vol. 1, pp. 377–388. Baltimore, MD: Williams & Wilkins. Davies G and Casey A (1973) The survival of Brucella abortus in milk and milk products. British Veterinary Journal 129: 345–353. Foster G, Osterman BS, Godfroid J, Jacques I, and Cloeckaert A (2007) Brucella ceti sp. nov. and Brucella pinnipedialis sp. nov. for Brucella strains with cetaceans and seals as their preferred hosts. International Journal of Systematic and Evolutionary Microbiology 57: 2688–2693. Franco MP, Mulder M, Gilman RH, and Smits HL (2007) Human brucellosis. Lancet Infectious Diseases 7: 775–786. Garin-Bastuji B, Blasco JM, Grayon M, and Verger JM (1998) B. melitensis infection in sheep: Present and future. Veterinary Research 29: 255–274. Garin-Bastuji B and Verger JM (1994) Brucella abortus and melitensis. In: Hahn G (ed.) The Significance of Pathogenic Microorganisms in Raw Milk, pp. 167–185. Brussels: IDF. Joint FAO/WHO Expert Committee on Brucellosis (1986) 6th Report, Technical Report Series 740. Geneva: WHO.
Pathogens in Milk | Brucella spp. 39 Nielsen K and Duncan JR (1990) Animal Brucellosis. Boca Raton, FL: CRC Press. Osterman B and Moriyo´n I (2006) International Committee on Systematics of Prokaryotes, Subcommittee on the taxonomy of Brucella, Minutes of the meeting, 17 September 2003, Pamplona, Spain. International Journal of Systematic and Evolutionary Microbiology 56: 1173–1175. Pappas G, Papadimitriou P, Akritidis N, Christou L, and Tsianos EV (2006) The new global map of human brucellosis. Lancet Infectious Diseases 6: 91–99. Scholz HC, Hubalek Z, Sedlacek I, et al. (2008) Brucella microti sp. nov., isolated from the common vole Microtus arvalis. International Journal of Systematic and Evolutionary Microbiology 58: 375–382.
World Organisation for Animal Health (OIE) (2008a) Bovine brucellosis. In: The OIE Manual of Standards for Diagnostic Tests and Vaccines for Terrestrial Animals, 6th edn., pp. 624–659. Paris: OIE. World Organisation for Animal Health (OIE) (2008b) Caprine and ovine brucellosis (excluding B. ovis infection). In: The OIE Manual of Standards for Diagnostic Tests and Vaccines for Terrestrial Animals, 6th edn., pp. 974–982. Paris: OIE. Young EJ and Corbel MJ (1989) Brucellosis: Clinical and Laboratory Aspects. Boca Raton, FL: CRC Press. Zu´n˜iga Estrada A, MotadelaGarza L, Sa´nchez Mendoza M, Santos Lo´pez EM, Filardo Kerstupp S, and Lo´pez Merino A (2005) Survival of Brucella abortus in milk fermented with a yoghurt starter culture. Revista Latinoamericana de Microbiologi´a 47: 88–91.
Campylobacter spp. P Whyte, P Haughton, S O’Brien, and S Fanning, University College Dublin, Dublin, Ireland E O’Mahony and M Murphy, Cork County Council, County Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction to Campylobacter and Relevance to Milk Introduction and History Campylobacter spp. have been associated with disease in animals for many years. More recently, their role in human disease was established when they were isolated from stool samples of individuals with diarrhea using a direct technique developed by Skirrow in 1977. Thermotolerant species, in particular Campylobacter jejuni and to a lesser extent Campylobacter coli, have since emerged as major zoonotic human enteropathogens in most developed countries, being more frequently recovered from patients than salmonellae. These are predominantly transmitted to humans via the handling or consumption of contaminated foods of animal origin (particularly poultry meat and raw milk) or untreated surface water. Reported incidences of human campylobacteriosis tend to be single cases or small clusters, with larger outbreaks of disease seldom observed. The infective dose for Campylobacter is thought to be low, and clinical disease following infection varies from a mild self-limiting enterocolitis lasting 24 h to severe illness lasting in excess of 10 days. Sequelae to Campylobacter infection can manifest as meningitis, pneumonia, miscarriage, and a severe form of Guillain–Barre´ syndrome (GBS). The epidemiology of Campylobacter spp. in livestock and wildlife, and contamination of foods of animal origin at harvest and postharvest phases of the food chain is highly complex with many data gaps remaining despite considerable research efforts made internationally over the last 30 years. Also due to the fastidious nature of these organisms, it is likely that much progress remains to be made in relation to optimal isolation and identification. Furthermore, with advances in molecular subtyping of zoonotic pathogens, it has become evident that considerable genotypic diversity in C. jejuni populations circulating in animals and foods of animal origin exists, making progress in understanding their epidemiology difficult. It is likely that these organisms were first observed in 1886 by Theodor Escherich as nonculturable spiralshaped bacteria. In 1913 McFadyean and Stockman isolated Vibrio-like organisms from aborted ovine fetuses, while in 1918 Smith observed spiral bacteria in aborted bovine fetuses and suggested that they belonged to the same Vibrio species as those recovered by McFadyean and
40
Stockman 5 years earlier and proposed the name Vibrio fetus. In 1931, Jones and coworkers discovered a new Vibrio species in calves with dysentery and subsequently named the organism Vibrio jejuni. Another Vibrio species was isolated from pigs with diarrhea in 1944 by Doyle and was named as Vibrio coli. In 1963, Sebald and Ve´ron created a new genus, Campylobacter, and transferred V. fetus and V. bubulus to this new genus based on their DNA base composition, microaerophilic growth requirements, and nonfermenting metabolism. Subsequently in 1973, Ve´ron and Chatelain published a taxonomic study of microaerophilic Vibrio-like organisms and suggested four species within the genus Campylobacter: C. fetus, C. coli, C. jejuni, and C. sputorum. As the intestinal tracts of livestock are frequently colonized by C. jejuni and C. coli, including bovines, milk may be exposed to fecal contamination and hence to these enteropathogens during harvest. As a consequence, there are significant risks to public health associated with the consumption of contaminated milk, and the implementation of management interventions is required at both harvest and postharvest phases of the food chain.
Detection of Campylobacter in Milk Growth Conditions Campylobacter species are Gram-negative, curved, rodshaped bacteria. They are motile by a single flagellum attached to either or both poles. They can become coccoid following prolonged culture or exposure to oxygen. Campylobacter species have an optimal growth temperature range of 37–42 C. They require microaerophilic conditions (5% oxygen, 10% carbon dioxide, and 85% nitrogen). The optimum pH for growth is 6.5–7.5, and these organisms do not grow below pH 4.9. Survival at acid pH values is temperature dependent, but inactivation is rapid at pH values less than 4.0, especially above refrigeration temperatures. Thermal Resistance Campylobacter species are heat sensitive and the cells are destroyed at temperatures above 48 C. Z-values for C. jejuni are in the range of 5.07–8.02 C. A Z-value of 6.10 C has been reported for C. coli. Continuous change in
Pathogens in Milk | Campylobacter spp. 41
morphology from the spiral to coccoid form has been observed during heating. Campylobacter species are destroyed by commercial pasteurization treatments.
rDNA gene, and the 23S rDNA gene. Campylobacter spp. do not utilize carbohydrates. Serology
Susceptibility to Antibiotics Campylobacter jejuni are generally susceptible to erythromycin and gentamicin. Resistance of C. jejuni and C. coli to other antibiotics varies between strains and has been reported at low rates for clindamycin, azithromycin, and meropenem. Resistance to ciprofloxacin, nalidixic acid, and particularly tetracycline is on the increase. Campylobacter upsaliensis and C. fetus have been reported as being resistant to nalidixic acid along with many strains of C. jejuni and C. coli. The use of antibiotic susceptibility for differentiating between strains is less reliable due to the increasing frequency and variability of resistance among Campylobacter species.
Biochemical Properties Biochemical tests can further confirm and differentiate between different Campylobacter species; however, some biochemical properties are dependent on the age of culture and test conditions applied. Rapid catalase and cytochrome oxidase tests suggest presence of C. jejuni, C. coli, and C. lari. Only the two subspecies of C. jejuni possess the enzyme hippuricase (hippurate hydrolase) and can hydrolyze sodium hippurate to benzoic acid and glycine. Campylobacter coli and C. jejuni can also be differentiated based on polymorphism in a number of gene sequences including ceuE, the GTPase gene, the 16S
Penner (1980) and Lior (1982) described two methods of serotyping for Campylobacter. The Penner serotyping scheme involves detection of the heat-stable O-polysaccharide antigen by an indirect hemagglutination assay. The Lior serotyping scheme involves detection of the heatlabile flagellar and capsular antigens by a slide agglutination assay. Campylobacter serology is poorly standardized and various crude bacterial antigen preparations have been used in the detection of C. jejuni-specific antibodies in patients suffering with GBS. The Campylobacter flagellar protein is the dominant immunogen recognized during C. jejuni infection in humans. Complement fixation assays (CFAs), immunoblotting, and enzyme-linked immunosorbent assays (ELISAs) have all been used for detecting these antibodies. Antigenic cross-reactivities, however, can result in low specificity of assays. Isolation and Identification The United States Food and Drug Administration (US-FDA)-recommended procedure for isolating Campylobacter from milk is extensively used and is outlined in Figure 1. This particular method proposes the Bolton formulation as the enrichment broth, but others including Preston broth, Brucella broth, and Campy pack broth can also be used. Some procedures recommend that the initial
Preparation of milk samples Adjust sample pH to 7.5 ± 0.2 with sterile 1−2 mol l−1 NaOH Centrifuge 50 g sample at 20 000 g for 40 min Discard supernatant and resuspend pellet in 10 ml of enrichment broth Transfer resuspended pellet to 90 ml of enrichment broth Incubate 4 h at 37 °C under microaerophilic conditions followed by 48 h at 42 °C Isolation and identification Streak enriched culture onto modified Charcoal Cefperazone Deoxycholate Agar (mCCDA) plates and incubate for 48 h 42 °C in a microaerophilic atmosphere Examine colonies for morphology, Gram stain, and biochemical profiles
Figure 1 Procedure for isolation and identification of Campylobacter from milk. From US-FDA (2010) Bacteriological Analytical Manual. http://www.fda.gov (accessed 22 April).
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Pathogens in Milk | Campylobacter spp.
enrichment be carried out at 37 C for 4–6 h in the absence of selective supplements, in order to allow damaged cells to recover. Following incubation of selective plates, Campylobacter species appear as round- to irregular-shaped colonies with smooth edges. They can show thick translucent white growth to spreading, filmlike transparent growth. Colonies are confirmed by Gram stain, catalase, oxidase, and other biochemical tests. This procedure can be lengthy, requiring 4–5 days to complete. Nucleic acid methods can be used and these are giving a more reliable and conclusive result. Such methods have been applied for the identification and quantification of Campylobacter in a wide range of food samples, including milk. They can be used to identify Campylobacter at the species level, which is often difficult and unreliable by traditional methods. In addition, samples with very low numbers of viable, but nonculturable cells may go undetected on agar media but may be detected by molecular methods. Real-time PCR assays can be performed on enriched samples in as little as an hour with a detection limit of 1 cfu per PCR. An immunocapture PCR method that uses an avidin capture assay to detect PCR products also exists. This quantitative method does not require an enrichment step, requires 8 h to complete, and has a detection limit of 1 cfu ml 1. A rapid hybridization assay using a fluorescently labeled specific DNA probe can be applied for detecting C. jejuni at very low levels (3–105 cfu per PCR) in milk and poultry rinse samples. This method involves filtering samples through 0.22-mm hydrophobic grid membrane filters (HGMFs) and labeling with a 1475-bp chromagen-labeled DNA probe (pDT1720). Hybridized cells are subsequently detected in a colorimetric immunoassay. Campylobacter jejuni in food and clinical samples can also be detected by an immunomagnetic-hybridization technique. This method involves directing a monoclonal antibody against a specific outer membrane protein of C. jejuni. Captured C. jejuni cells are subjected to lysis by ultrasonication and the genomic DNA is reacted with a microtiter plate-immobilized RNA probe. Detection of the RNA–DNA hybrids formed in wells is then carried out using a monoclonal anti-RNA–DNA hybrid antibody. Overall, molecular-based methods are more specific, reliable, and faster at identifying Campylobacter at the species level compared with conventional identification methods.
Molecular Characterization of Campylobacter Detection Although food laboratories generally use conventional culture methods for the detection and identification of
Campylobacter, more rapid alternative methods are available, including molecular methods. Alternative methods can be used as a screening tool to quickly assay a large number of samples and eliminate negatives at an early stage. Molecular methods can also be used to confirm the identity of a particular Campylobacter strain. In addition to commercially available kits/assays, a number of publications report on the use of traditional PCR or, more recently, real-time PCR to screen for Campylobacter. A useful feature of nucleotide-based assays is the ability to speciate the strain. Subtyping Approaches Epidemiological investigations often benefit from rapid, reliable subtyping techniques. Several methods have been used to subtype Campylobacter. Subtyping methods based on analysis of the flagellin A gene include flaA restriction fragment length polymorphism (flaA-RFLP) and sequencing of a 321 bp short variable region (SVR). RFLP has sufficient discriminatory power to be considered a valuable epidemiological tool. However, DNA sequence based methods have advantages over RFLP. The flaASVR typing protocol is useful for discriminating between even closely related Campylobacter strains and is widely employed because of its speed and simplicity. Multilocus sequence typing (MLST) is a nucleotide sequencing technique that characterizes Campylobacter spp. based on the sequence heterogeneity present in seven housekeeping genes. These genes evolve slowly due to their critical role in central metabolism and are therefore particularly useful for the long-term analysis of diverse bacterial populations with weak clonal population structures. Sequence data determine the allelic profiles or sequence types (STs), which are then grouped into clonal complexes (CCs). MLST has confirmed the genetic diversity of C. jejuni and shown its population structure to be weakly clonal. MLST is a highly discriminatory typing system and is the current ‘gold standard’ for molecular typing of Campylobacter. Whole-genome microarray analysis is a robust and sensitive method to determine genetic relatedness of bacterial populations. A whole-genome DNA microarray containing all 1654 genes from C. jejuni NCTC 11168 was constructed in 2001. Comparisons with 11 different strains identified 1300 core genes common to all, and 354 genes (21%) that were absent or highly divergent in at least 1 of the 11 samples. Core genes appear to encode proteins with a housekeeping function, while many of the remaining 21% encode surface-located structures including flagella, lipooligosaccharide, and the capsule. Wholegenome analysis offers the potential to identify genes encoding pathogenic factors and could prove useful as an epidemiological and/or diagnostic tool.
Pathogens in Milk | Campylobacter spp. 43
Antibiotic Resistance
Methods to Determine Resistance
Epidemiology of Resistance
A lack of any agreed standardized approach for the testing of antimicrobial resistance in Campylobacter led to the issue being addressed by the Clinical and Laboratory Standards Institute (CLSI). Subsequently, an agar dilution reference method for Campylobacter, establishing quality control (QC) ranges for five agents, was introduced. In 2006, a new approved broth microdilution method, with QC ranges for 13 agents, was developed. The aim of broth and agar dilution methods is to determine the lowest concentration of the antimicrobial compound (minimal inhibitory concentration (MIC)) that, under defined test conditions, inhibits the visible growth of Campylobacter. Agar dilution involves the incorporation of different concentrations of the antimicrobial substance into an agar medium followed by the application of a standardized number of cells to the surface of the agar plate. Plates are read by observing the lowest drug concentration that inhibits visible bacterial growth. The broth microdilution test is the standard method for determining levels of resistance to an antibiotic. Bacteria are inoculated into a liquid growth medium in the presence of different concentrations of an antimicrobial agent. Growth is assessed after incubation for a defined period of time and the MIC value is determined. The lowest concentration (highest dilution) of antibiotic preventing appearance of turbidity is recorded as the MIC. The epsilometer test (E-test) has been found to compare favorably with agar dilution and broth microdilution methods, although economic reasons can prevent its use in routine laboratory screening. The E-test consists of a plastic strip containing a predefined gradient of antimicrobial compound concentrations. In this method, the strip is applied directly onto the surface of an inoculated agar plate. The drug on the strip then diffuses into the agar. Following incubation, an elliptical zone of inhibition is visible around the test strip. The point at which the zone edge intersects the plastic strip at a specific drug concentration is taken as the MIC.
Treatment of campylobacteriosis with antibiotics may be required in cases of immunocompromised patients or those showing no signs of improvement once the diagnosis has been made. Macrolides and fluoroquinolones are the antimicrobial agents currently chosen when therapeutic intervention is required. Resistance to erythromycin is low in most countries, and in general it remains the drug of choice. Fluoroquinolones such as ciprofloxacin may also be used, but resistance can be a problem in some regions. The frequency of fluoroquinolone resistance has been reported to be as high as 90% in Spain, Thailand, and Taiwan. Although lower rates of up to 45% have been reported elsewhere, current trends show that resistance is increasing. Antibiotic use in both animal production and human medicine can influence the development of antibiotic-resistant Campylobacter. Therefore, the emergence of antimicrobial resistance in enteric Campylobacter spp. due to the use of antimicrobial agents in husbandry is a matter of concern.
Resistance to Fluoroquinolones and Macrolides Fluoroquinolones are a subgroup of quinolones, derived from nalidixic acid, and have a fluorine at the C-6 position of the quinolone structure. The targets of these agents are the type II topoisomerase DNA gyrase and topoisomerase IV. These enzymes are essential for DNA replication, recombination, and transcription. Inhibition appears to occur by interaction of the drug with complexes composed of DNA and either of these two target enzymes. Resistance to fluoroquinolones is mainly due to chromosomal mutations in the gyrA and gyrB genes encoding the subunits of DNA gyrase, in genes that affect the expression of porin channels in the outer membrane, and in the genes encoding multidrug resistance efflux systems. Efflux was first postulated as a mechanism of multidrug resistance in Campylobacter in 1995. In 2002, a chromosomally encoded multidrug resistance–nodulation–cell division (RND) efflux system CmeABC was identified and characterized in C. jejuni, and later in C. coli. Erythromycin is a protein synthesis inhibitor that binds to the ribosome causing dissociation of the peptidyl-tRNA, rather than blocking the peptidyltransferase activity as in the case of larger macrolides. In C. jejuni and C. coli, erythromycin resistance is chromosomally mediated and can be due to an alteration of the 23S rRNA gene, modification of the antibiotic, or efflux. Sequencing of the 23S rRNA genes from erythromycinresistant Campylobacter spp. identified mutations that are associated with high-level resistance.
Campylobacter and Disease Clinical Disease Experimental C. jejuni infections in humans have revealed that a low infectious dose of approximately 500 cells is sufficient to induce illness. Approximately 30% of patients experience an influenza-like prodrome of fever, headache, and myalgias lasting up to 24 h. The actual incubation period after ingestion is typically 2–5 days, but can range from 1 to 10 days. Symptoms include
44
Pathogens in Milk | Campylobacter spp.
profuse diarrhea (often bloody), fever, and acute abdominal pain that may mimic appendicitis. Vomiting is uncommon, but nausea, headache, backache, and aching of the limbs may be experienced. The peak of the illness usually lasts for 24–48 h, with the symptoms resolving themselves within a week. The vast majority of patients suffering from Campylobacter enteritis do not require chemotherapy. Fluid and electrolyte replacement should enable a full recovery. Stools remain positive for several weeks, and minor relapses can occur. Approximately 1 in 1000 cases of C. jejuni infection develops GBS, an acute, autoimmune, polyradiculoneuropathy affecting the peripheral nervous system. Pathogenesis Bacterial gastroenteritis results from a complex set of interactions between the host and the invading organism. Consequently, the mechanisms by which Campylobacter spp. cause disease are not well understood. Pathogenesis will depend on the susceptibility of the patient as well as the virulence of the infecting strain. The role of several virulence factors has been studied and the mechanisms of pathogenicity are becoming clearer. Factors such as motility, chemotaxis, colonization, adherence, invasion, translocation, and toxin production, including the holotoxin cytolethal distending toxin (Cdt), have been implicated in the pathogenesis of Campylobacter enteritis.
Epidemiology of Outbreaks Associated with Milk The main reservoir of Campylobacter is the gastrointestinal tract of warm-blooded animals, with studies describing the isolation of Campylobacter spp. from a broad range of animals. While Campylobacter spp. are commonly recovered from food animals, they have also been isolated from other vectors such as insects, wild birds, marine mammals, and both wild and domestic animals. Furthermore, these pathogens are also routinely isolated from environmental sources in close proximity to livestock and poultry farms. These sources include rivers, streams, lakes, sewage, drinking water, livestock and poultry farms, as well as slaughter line environments. Transmission of Campylobacter to humans can occur through direct contact with infected animals or fecal matter and indirectly by the consumption of contaminated food or water. The primary source of foodborne campylobacteriosis seems to be from raw poultry meat through cross-contamination of ready-to-eat foods during food preparation, with the consumption of undercooked poultry being an alternate but less common source of infection.
Unpasteurized milk is commonly implicated in Campylobacter outbreaks. Cow’s milk typically contains bacterial loads in the range of 103–104 cfu ml 1. These numbers may represent bacteria on the lower end of the teat, organisms that have colonized the teat canal, and those from fecal contamination on the outside of the teat. The use of good hygiene practices when milking can significantly reduce the prevalence and levels of bacterial contamination in milk; these practices may involve thoroughly washing and drying udders before milking. However, the principal risk factor associated with milkborne gastrointestinal illnesses such as campylobacteriosis is insufficient or no heat treatment, with the consumption of unpasteurized milk and milk products a well-documented source of Campylobacter infection. Cases of campylobacteriosis associated with pasteurized milk have generally been linked with postpasteurization contamination or a failure in the pasteurization processing step. Prevalence data on Campylobacter from 21 different countries showed that 30% (mean positives) of dairy cows sampled were positive for Campylobacter spp., with prevalence ranging from 6 to 64%. The same study also reported 3.2% (mean positives) of raw milk samples positive for Campylobacter spp., with prevalence ranging from 0 to 9.2%. There is little evidence to suggest that Campylobacter poses a significant threat in fermented dairy products such as cheese and yogurt. The low prevalence of these pathogens in such products is due to their poor survival in acidic conditions. Other cases of campylobacteriosis outbreaks from milk have come from milk contaminated by bird pecking through the packaging.
Control of Milk Quality at Pre- and Postharvest Phases Milk is an important nutritional component for humans in many societies throughout the world. It is a natural secretion of the mammary gland and is not a sterile commodity in this state. Milk derived from animals can contain pathogens and historically has been identified as a vehicle responsible for transmitting a significant burden of disease to humans in both developing and developed countries. Recent analysis of human outbreak data and other estimates suggest that milk is responsible for a small but substantial proportion of foodborne infectious disease (2–9%) in Ireland and the United Kingdom. Interestingly, Salmonella, Campylobacter, and enterohemorrhagic Escherichia coli were the most frequently implicated agents in milkborne disease. Differences in the burden of human disease attributed to milk consumption are likely to vary widely due to regional or cultural differences, jurisdictional/legislative restrictions on the marketing of raw milk, and differences in consumer preferences for
Pathogens in Milk | Campylobacter spp. 45
drinking raw milk or dairy products. In countries where the marketing of liquid raw milk is prohibited, consumption by families on dairy farms is still prevalent even in developed regions. The subclinical carriage and intermittent shedding of C. jejuni and C. coli in bovines and other animal species from which milk is derived is a public health concern. Raw milk is frequently found to contain these significant Campylobacter species and is primarily indicative of fecal contamination during milking. In addition, less frequent reports of subclinical infection of mammary glands have also been observed, which can result in preharvest contamination of milk. The milking of animals is not a sterile process and contamination of milk with organisms of fecal origin is common and to an extent unavoidable even with the implementation of high standards of hygiene. Milk may also be contaminated with fecal organisms, including Campylobacter spp., at any stage postharvest, for example during bulk storage on-farm, transportation, processing, or postprocessing. Integrated control and intervention is required along the milk production chain to manage risks and adequately protect public health. At farm level, good farming and husbandry practices are essential so that feed quality is controlled, waste is effectively managed, mastitis is prevented and managed in herds, and adequate standards of housing and stocking are maintained. In addition, drinking water should be of a potable standard and drinking troughs should be designed to minimize fecal contamination. Fecal soiling of hides, tails, and udders should be minimized as much as possible by, for example, adequate provision of clean bedding and prevention of enteritis within the herd. During harvesting of milk from cows, visibly contaminated teats should be cleaned and dried prior to attaching clusters. Milking equipment should be well maintained and adequate cleaning and sanitizing should be carried out between milking sessions using recommended cleaning agents, procedures, and a potable water supply. All milk should be pumped through a milk filter or ‘sock’ to remove any visible traces of fecal material or other suspended particulates, and milk should be cooled and stored appropriately before transportation to the processing plant. The main public health intervention for liquid milk in developed countries is pasteurization, which involves the rapid heating of milk using plate heat exchangers to a minimum of 71.7 C and holding at that temperature for 15 s. Once satisfactorily heated, the milk is then rapidly cooled again using plate heat exchangers, thus largely preserving the desired organoleptic properties of raw milk. Individual processing operations can vary this time–temperature treatment to achieve an equivalent reduction in bacterial populations. Pasteurization is sufficient to eliminate bacterial pathogens, including C. jejuni and C. coli, in milk. In terms of food safety assurance in a
commercial processing facility, it is imperative that the pasteurization conditions are met consistently by monitoring time–temperature recording equipment, for example, thermographs, and the completion of routine microbiological testing to detect fecal indicator organisms (Enterobacteriaceae, E. coli). In addition, levels of the phosphatase enzyme, which is naturally found in raw milk, can be readily measured in pasteurized samples. This enzyme is relatively heat labile and is denatured at pasteurization temperatures; therefore, detection of active phosphatase indicates incomplete pasteurization or postpasteurization contamination with raw milk. Several studies have highlighted the risks of inadequate pasteurization or postprocess contamination of liquid milk associated with the transmission of Campylobacter spp. to humans. For example, an outbreak in the United Kingdom in which 110 people became ill (41 were confirmed to be infected with C. jejuni) was associated with the consumption of inadequately pasteurized milk from a local dairy. Other studies have highlighted the risk of equipment failure in the dairy plant resulting in the mixing of raw with pasteurized milk. The phenomenon of wild birds pecking the foil caps on milk bottles delivered to consumer’s doorsteps resulting in contamination of milk with Campylobacter spp. and infection in humans have also been well reported, again highlighting the risks associated with postprocess contamination and human health. Although documented, the transmission of Campylobacter spp. to humans via the consumption of dairy products is rare and is considered to be a minor route of exposure to humans. The survival of C. jejuni in cheeses (including soft varieties) and fermented products such as yogurt is poor, most likely a result of the organisms intolerance to high salt concentrations and low pH, respectively. In soft cheeses artificially inoculated with 7 log10 cfu ml 1, a 1 log10 reduction can be achieved within 4 h, the reduction increases to 3 log10 following 24 h storage and the organism is not detected after 336 h storage. For fermented dairy products with a pH of 4.2, the inoculated cells (7 log10 cfu ml 1) did not survive beyond 3 days storage. These data suggest that such products manufactured from raw milk would not pose any substantial risk to consumers once products were sufficiently processed (e.g., to ensure adequate salt concentrations or pH levels were achieved) and matured/aged before being marketed for consumption. Finally, in order to adequately and consistently protect public health, it is imperative that an integrated approach is taken based on the principles of hazard analysis critical control point (HACCP) systems at all stages of milk production (preharvest, harvest, and postharvest). This approach should be adapted by all stakeholders, including producers, processors, retailers, and legislators, so that increased levels of food safety assurance are achieved for liquid milk and dairy products.
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Pathogens in Milk | Campylobacter spp.
Future Issues The complex epidemiology of campylobacteriosis is widely acknowledged and the extensive dissemination of Campylobacter spp. within livestock and the environment has made its control difficult. In addition, molecular subtyping studies, using techniques such as pulsed-field gel electrophoresis, MLST, and others, have revealed the highly diverse nature of strains of this zoonotic agent in circulation in these animal and environmental reservoirs. Ongoing research is required in a number of areas to ascertain how this pathogen is introduced to livestock and to identify effective interventions to reduce its prevalence and potential transfer to raw milk and dairy products. Further work is also required in relation to food attribution studies so that more accurate and detailed estimates of numbers of human cases of campylobacteriosis caused by the consumption of contaminated milk can be completed. Such data on the associated public health burden would provide valuable information for health professionals, the dairy industry, regulatory agencies, and other risk managers. It would also facilitate an impetus to communicate such risks to consumers of raw milk and other dairy products made from unpasteurized milk. The standardization and dissemination of laboratory techniques used to detect, quantify, and characterize Campylobacter spp. in animals, foods of animal origin, and humans would also be beneficial, enabling the generation of more accurate and reproducible prevalence data and risk assessments. In recent years, the prevalence of antimicrobial resistance among Campylobacter spp. of animal and food origin has increased. The corresponding antibiotic resistance profile of Campylobacter spp. implicated in human disease is similar. Antimicrobial therapy may be required in a minority of human campylobacteriosis cases where the drugs of choice are often macrolides and fluoroquinolones. Therefore, increased and multidrug resistance
now represents a significant health risk where drug therapy is necessary. Strict licensing and prudent use of antibiotics in animal production and treatment are recommended. This strategy must be supported by the development and application of standardized methods to monitor antimicrobial resistance in Campylobacter populations, allowing reliable surveillance data to be generated on an ongoing basis, review of resistance trends and making interventions as required. This is an important component of public health protection, given the more recent hypotheses, for example, that infection in humans by quinolone-resistant strains of C. jejuni tends to cause more prolonged and severe symptoms. In addition, the development and promotion of herd health management programs on dairy farms should be encouraged so that a preventive approach to disease is taken, thus reducing the dependence on antimicrobials.
Further Reading Humphrey T, O‘Brien S, and Madsen M (2007) Campylobacters as zoonotic pathogens: A food production perspective. International Journal of Food Microbiology 117: 237–257. Ketley JM and Konkel ME (eds.) (2005) Campylobacter: Molecular and Cellular Biology. Norfolk, UK: Horizon Bioscience. Moore JE and Matsuda M (2002) The history of Campylobacter: Taxonomy and nomenclature. Irish Veterinary Journal 55: 495–501. Nachamkin I and Balser MJ (eds.) (2000) Campylobacter, 2nd edn. Washington, DC: American Society for Microbiology. O’Mahony M, Fanning S, and Whyte P (2009) The safety of raw liquid milk. In: Tamime AY (ed.) Milk Processing and Quality Management, 1st edn., pp. 139–167. Oxford, UK: Blackwell Publishing. Rosenquist H, Bengtsson A, and Hansen TB (2007) A collaborative study on a Nordic standard protocol for detection and enumeration of thermotolerant Campylobacter in food (NMKL 119, 3. Ed., 2007). International Journal of Food Microbiology 118: 201–213. US-FDA (2010) Bacteriological Analytical Manual. http://www.fda.gov/ Food/ScienceResearch/LaboratoryMethods/ BacteriologicalAnalyticalManualBAM/UCM072616 (accessed 22 April) Yang C, Jiang Y, Huang K, Zhu C, and Yin Y (2003) Application of realtime PCR for quantitative detection of Campylobacter jejuni in poultry, milk and environmental water. FEMS Immunology and Medical Microbiology 38: 265–271.
Clostridium spp. P Aureli, G Franciosa, and C Scalfaro, Istituto Superiore di Sanita`, Rome, Italy ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. Aureli and G. Franciosa, Volume 1, pp 456–463, ª 2002, Elsevier Ltd.
Introduction The interest in Clostridium spp. in milk products mainly pertains to two aspects, sanitary and technological. Of utmost importance is the presence of pathogenic clostridia in milk products because of their potentially harmful effects on human health: although cases of food-borne diseases attributed to clostridia in dairy products are rare (<70 cases in the last 10 years), some have even recently been reported, including a few related to commercial foods, which makes the risk more threatening due to the wide distribution such products can reach on the market. However, most of the Clostridium species relevant to dairy products are nonpathogenic to humans, yet their multiplication can cause deterioration and/or serious defects in the final products with consequent economic losses. Clostridia are widely distributed in soil, dust, water, sediments, sewage, animal carcasses, and vegetation; healthy animals and humans normally carry low numbers of spores in their intestines (100 g1 feces). Contamination of feeds and especially silage, where clostridia can grow under certain conditions of water activity (aw), pH, and temperature, contributes to the spread of spores. Raw milk can become contaminated with spores during the milking process, as a result of environmental cross-contamination. Clostridium sporogenes, Cl. perfringens, Cl. butyricum, Cl. tyrobutyricum, and Cl. beijerinckii are the most frequently encountered species, along with other rare species such as Cl. botulinum. Usually, processing of raw milk either kills the spores of clostridia or inhibits their multiplication in the dairies; however, depending upon the conditions applied and the characteristics of the strains, some can occasionally survive and grow. This article will focus on Clostridium spp. commonly found in milk-based products and the control measures to be taken to ensure the wholesomeness and integrity of such widely consumed foods.
Morphology and Physiology Clostridium spp. The genus Clostridium comprises a heterogeneous group of microorganisms. They are Gram-positive, anaerobic,
rod-shaped, and endospore-forming bacteria: the shape and length of the rods, and the position of the spores may vary considerably. Spores are very resistant to extreme chemical/physical conditions and therefore are widely distributed in terrestrial environments where they can germinate when conditions become favorable, that is, in low oxygen tension areas and in the presence of sufficient nutrients. The growth temperatures vary from 3.3 to 80 C, with an optimum between 25 and 40 C for most clostridia. Historically, the taxonomic definition of species within the genus has relied on the phenotypic characteristics displayed by the bacteria, such as metabolic activities, cultural conditions, chemical composition of the bacterial cell wall, and toxicity and pathogenicity. Some distinctive phenotypic features of the Clostridium spp. relevant to dairy products are given in Table 1. Subsequent studies of the microbial genetic material allowed a more precise classification of species. Although the overall DNA base composition is of limited value for determining the relatedness of groups – the G þ C content of members of the genus ranging from 22 to 50% – more recent phylogenetic studies based on similarities of 16S rRNA/DNA sequences have confirmed many of the preexisting species, while excluding others. Moreover, Clostridium spp. are distributed into 19 different clusters (I–XIX), the first of which essentially includes the clostridia most frequently found in milk and dairy products, often referred to as Clostridium sensu stricto.
Pathogenesis of Clostridium spp. Contaminating Dairy Foods The pathogenic Clostridium spp. that can potentially spoil milk products are those associated with botulism (Cl. botulinum and neurotoxigenic Cl. butyricum), enterocolitis (Cl. perfringens), and possibly sudden infant death syndrome (SIDS) (Cl. perfringens, Cl. botulinum) and neonatal necrotizing enterocolitis (NE) (Cl. butyricum). Additionally, Clostridium spp. must be regarded as potential producers of harmful biogenic amines in cheese products. The highly potent neurotoxin (lethal dose for humans: 1 ng kg1 body weight) produced by Cl. botulinum is responsible for the serious neuroparalytic disease of botulism.
47
Table 1 Some metabolic and physiological features of clostridia associated with milk products
Fermentation of Glucose Lactose Sucrose Mannose Digestion of Milk Meat Range of growth temperature ( C) D100 (min)d Minimum aW Minimum pH a
Clostridium sporogenes
Clostridium perfringens
Clostridium butyricum
Clostridium tyrobutyricum
Clostridium beijerinckii
Clostridium botulinum (proteolytic)
Clostridium botulinum (nonproteolytic)
va – – –
þ þ þ þ
þ – þ þ
þ – þ þ
þ þ þ þ
V – – –
þ – þ þ
db d
cc d
c –
– –
c –
d d
c –
25–45 C
20–37 C 0.2 0.98 6
10–37 C 2.3–2.5
10–37 C
25–45 C
4.6
4.6
4.6
10–40 C 25 0.93 4.6
3.3–37 C <0.1 0.97 5.0
5.7
v, variable. d, digested (proteins are totally metabolized, with consequent clarification of the medium). c c, clotted (proteins are partially metabolized and tend to aggregate, causing formation of ‘clots’ in the medium). d D100 (min) ¼ time in minutes required to inactivate 90% of the specific clostridial population at 100 C. b
Pathogens in Milk | Clostridium spp. 49
Although seven serologically distinct botulinum toxins (A–G) exist, all have common protein structures and mode of action, consisting of zinc endopeptidase activity against specific protein targets of the presynaptic vesicles that contain the neurotransmitter acetylcholine. Cleavage of these proteins blocks the neurotransmitter release at the nerve terminal ends and ultimately produces the flaccid paralysis of botulism. Generally, one strain of Cl. botulinum produces a single type of neurotoxin: type A, B, and E botulinum neurotoxins account for nearly all of human botulism. Two forms of botulism may result from ingestion of food contaminated with either preformed toxin (food-borne botulism) or neurotoxigenic clostridial spores, which subsequently may colonize the intestine of the host – generally infants under 1 year of age and adults suffering from gastrointestinal distress – and synthesize the toxin in vivo (intestinal toxemia botulism). Enterotoxin-producing Cl. perfringens type A is responsible for a form of mild enteritis. Classical symptoms include diarrhea, abdominal cramps, and, less frequently, nausea, vomiting, and fever, which follow shortly after ingestion of food contaminated with at least 108 Cl. perfringens cells per gram. The ingested microorganisms that succeed in surviving the high acidity of the stomach sporulate within the small bowel and release the enterotoxin by cell lysis into the intestinal lumen. Here, it rapidly binds the intestinal epithelial cells, causing cytotoxic effects by alterations to membrane permeability. In addition, a role for Cl. perfringens type A in SIDS has been proposed, because many SIDS infants have symptoms of gastrointestinal infections prior to death, and Cl. perfringens and its enterotoxin are found in a significantly high number of feces from such infants. Clostridium butyricum has been hypothesized as a causative agent of neonatal NE, a disease mostly affecting premature infants even though neonates with no predisposing factors may also be affected. Mucosal necrosis of the ileum and colon is the main symptom: although the exact etiology of the disease is still unknown, different bacteria are thought to cause the intestinal lesions, including Cl. butyricum. This microorganism is normally considered a harmless saprophyte: typically, it does not produce any toxin but an in vitro cytotoxic effect due to the production of butyrate has been demonstrated on various cells. Besides, unique strains of Cl. butyricum producing botulinum toxin type E have been implicated in intestinal toxemia botulism and food-borne botulism in Italy and China. These peculiar strains seem to have acquired the genetic information coding for botulinum toxin type E through DNA mobile vectors from an ancestral strain at some point during evolution. Although the actual roles of Cl. perfringens type A and Cl. botulinum in SIDS, and Cl. butyricum in neonatal NE, are still questionable, it has been recommended to maintain the number of spores of Clostridium low in products intended for use by infants.
Finally, different Clostridium spp. commonly found in cheese products are decarboxylase-positive microorganisms and may thus contribute to the decarboxylation of free amino acids to biogenic amines, such as histamine from histidine. High levels of these substances may exert toxic effects, including dilatation of peripheral blood vessels resulting in hypotension, flushing, and headache, and induction of contraction of intestinal smooth muscle, which may be the cause of vomiting and diarrhea.
Significance of Clostridium spp. in Dairy Foods Incidence of Clostridia in Milk and Dairy Products Raw milk usually contains large numbers of bacteria. Of these bacteria, clostridia represent a minority, the contamination levels being around 10–102 spores ml1. These levels can increase to >103 spores ml1 when lactating animals are fed on heavily contaminated silage. Percentages of the different Clostridium spp. are variable, but Cl. sporogenes, Cl. perfringens, Cl. butyricum, and Cl. tyrobutyricum generally predominate, accounting for about 75% of the whole anaerobic spore-forming flora; other species of importance, such as Cl. botulinum, may be present at levels of less than 1 spore l1. The redox potential of raw milk does not allow for growth of clostridia in this medium. Clostridia in dairy products mainly originate from the raw milk. They have been recovered from a variety of cheeses, cheese sauces and creams, pasteurized milk, powdered milk, sweetened condensed milk, yogurt, and ice cream: numbers generally do not exceed 10–102 spores g1, reflecting those in the original milk even for species composition. The intrinsic properties of some dairy products, that is, pH, aw, redox potential (Eh), nutrient availability, and microflora, can be compatible with the germination and multiplication of certain clostridial strains, especially when the extrinsic factors such as storage temperature and time are also suitable for growth (see section ‘Control’). The consequences of growth of clostridia in dairy foods are described below. Technological Problems Both texture and flavor quality of dairy products may be affected by growth and metabolism of clostridia. One of the major concerns in cheese manufacturing is the so-called ‘late blowing’ defect, consisting of formation of holes, which can crack the cheese, accompanied with undesirable off-flavors. It appears during the course of cheese ripening in a large variety of hard and semihard cheeses, including Parmesan, Grana Padano, Emmental, Gruye`re, Gouda, and Provolone. Processed canned cheese and cheese spreads can also be affected.
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Pathogens in Milk | Clostridium spp.
Considerable amounts of CO2 and H2 are responsible for the appearance of holes and blowing of cheese, while butyric acid and minor organic volatile acids negatively affect the flavor and taste of cheese. Gas and acids in the cheese result from fermentation of lactate mainly by Cl. tyrobutyricum and, to a lesser extent, by other Clostridium spp. (Cl. sporogenes, Cl. butyricum, and Cl. beijerinckii). The occurrence of ‘late blowing’ in cheese depends on different factors, including the number and species of clostridia originally contaminating the milk, the manufacturing process, and the characteristics of the final product. Silage is identified as the main source of milk contamination. When silage fermentation conditions are not prone to rapid decrease in pH and maintenance of uniformly anaerobic conditions, germination of clostridial spores and subsequent multiplication of vegetative cells can occur. In grass silage, clostridial numbers range from below the detection limit to a maximum of 6.89 log10 CFU g–1, whereas for maize silage, clostridial counts range from below the detection limit to a maximum of 4.69 log10 CFU g–1. Defective cheeses generally result from milk originally contaminated with at least 200–103 Cl. tyrobutyricum spores per liter. The growth of clostridia is critically influenced by ripening time and temperature, lactic acid concentration, salt concentration, pH values, fat content, and presence of other microorganisms. The shape, size, and structure of the cheese, including normal eye formation, can also play a significant role. The numbers of spores detected in defective cheeses vary from 104 to 107 g1 for Cl. tyrobutyricum, and from 103 to 106 g1 for Cl. sporogenes. Although the latter microorganism causes more frequent spoilage of milk, its growth requirements and predominantly proteolytic metabolism are the possible reasons why it is more rarely involved in the ‘late blowing’ of cheese. Diseases Associated with Clostridia in Dairy Foods Botulism
Dairy products have rarely been involved in outbreaks of food-borne botulism, probably because their intrinsic and extrinsic properties are generally unsuitable for
growth of Cl. botulinum. However, some outbreaks have been reported, the more recent being listed in Table 2. Raw milk was the likely source of spores in all outbreakrelated dairy foods, except for the Brie cheese, the commercial cheese sauce implicated in the 1993 US outbreak, the hazelnut yogurt, contaminated with botulinum spores and/or toxin from different sources (specifically, the straw used for cheese ripening; potato skins; and the hazelnut conserve added to the yogurt), formula milk powder, and su¨zme (condensed) yogurt buried under soil. Numbers of Cl. botulinum spores naturally contaminating raw milk are very low (1 spore l1); however, the preliminary steps used in dairy production, such as centrifugation and filtration, contribute to the concentrating of microbial spores to 10 or more per gram of cheese product, depending on the manufacturing procedures. Even low numbers of Cl. botulinum spores per gram of product can be harmful, if conditions are met for their growth and toxin production. Some common features can be traced for all the outbreaks of food-borne botulism linked to consumption of dairy products. First, proteolytic strains of Cl. botulinum were always the causative agents: spores of these microorganisms are more heat- and acid-resistant than the nonproteolytic ones (Table 1). Second, both commercial and homemade milk products were made from pasteurized milk: the temperatures and times generally used for thermal treatment of these products are not sufficient to kill the proteolytic spores of Cl. botulinum, but they do eliminate viable cells of nonsporing organisms, which are potential competitors of Cl. botulinum, such as lactic acid bacteria, thus facilitating the growth of Cl. botulinum in the product. Finally, the intrinsic factors (pH, aw, Eh) of the cheese products, as well as abused storage temperature/time, and packaging conditions in the case of commercial products, were suitable for the outgrowth of spores and consequent toxin production. Although the source of Cl. botulinum spores is rarely detected in intestinal toxemia botulism, an infant formula milk powder contaminated with Cl. botulinum type B
Table 2 Most recent outbreaks of botulism caused by consumption of spoiled dairy products Year
Location
Food source
Botulinum toxin type
1974 1974 1978 1989 1993 1996 1997 2001 2005
Argentina France and Switzerland France UK USA Italy Iran UK Turkey
Commercial cheese spread with onions Soft ripened cheese (Brie) Soft cheese Hazelnut yogurt Commercial cheese sauce Commercial soft-spread cheese Locally made cheese Formula milk powder Condensed yogurt
A B B B A A A B A
Pathogens in Milk | Clostridium spp. 51
spores has very recently been associated with a case of infant botulism. Finally, it must be noted that type E neurotoxigenic Cl. butyricum has not yet been involved in any case of botulism from consumption of contaminated dairy products. However, since Cl. butyricum is a frequent spoiler of milk, the risk posed by the neurotoxigenic variant of the species does exist, particularly since it has already been implicated in both food-borne botulism and intestinal toxemia botulism. Clostridium perfringens enteritis
Although the food most frequently involved in Cl. perfringensassociated diarrhea is undercooked meat, other foods including dairy products have also been implicated in outbreaks. Precise epidemiological data are lacking because hospitalization is not necessary in most cases and sporadic cases remain unknown, as does the source of illness. Histamine poisoning
Cheese is the second leading source of histamine poisoning, after fish. However, the problem is largely underestimated because of the mild symptoms; hence, the incidence is difficult to determine. Moreover, many species of bacteria can contribute to the production of amines such as histamine in cheese, and the main role played by each one can be hardly determined. Safety of Milk and Dairy Products from Cattle Affected by Botulism Since the recent marked increase in the reported incidence of suspected cattle botulism, the potential human health risk associated with consumption of meat or milk derived from animals from herds affected by botulism has been raised. Using current scientific evidence, the Food Standards Agency (FSA) recently considered the restrictions (movement of the cattle and meat and milk from affected herd into the food chain) previously adopted on unaffected animals within the flock to be overprecautionary. In addition, FSA recommends that in the absence of other signs, there should be no restrictions on milk or meat from healthy cattle, sheep, and goats from affected farms.
Detection and Enumeration of Clostridium spp. Analyses for clostridial contamination are performed not only on defective cheeses and milk products or those implicated in disease outbreaks, but also on the milk intended for dairy production, as a significant preventive measure. Hence, methods of choice should be able to
detect very high as well as very low numbers of spores; in addition, they should be rapid, specific, reproducible, and easy to perform. Although such methods are needed for routine assessment of clostridial contamination in milk and its derivative products, no standardized technique is yet available for this purpose. In theory, isolation and enumeration should be equally suitable for both vegetative cells and spores of clostridia; in practice, killing of viable cells cannot be completely avoided, because all samples are generally subjected to a heating step before incubation, in order to eliminate vegetative cells of other microorganisms and stimulate spore germination. For this reason, only the total number of clostridial spores can be determined. Different heating temperature/time conditions can be applied, taking into account that spores of some species are less heat-resistant than others (Table 1), and they might be inactivated as well. For adequately sensitive detection and enumeration of clostridia in fluid milk, concentration of microorganisms by membrane filtration or centrifugation may be required. Alternatively, direct incubation of the milk under anaerobic conditions after thermal treatment has been proposed. However, milk is not an ideal substrate for supporting growth of clostridia, due to the absence of any reducing agent, or because of the growth and metabolism of other thermal-resistant bacteria, resulting in a decrease in pH values to inhibitory levels. Certain Clostridium spp. that are not able to ferment lactose, specifically Cl. butyricum and Cl. tyrobutyricum, do not grow in milk unless their appropriate carbon sources – lactate and acetate – are added. Because clostridia include organisms with very different cultural and metabolic characteristics, selective agents that equally favor all relevant species while inhibiting other microorganisms are hard to find. However, since sulfite reductase activity is a common property among clostridia, broth and agar media used for their detection and enumeration often depend on sulfite reduction as a key differential criterion. These media generally include sodium sulfite (<0.05%, because some Clostridium strains are sensitive to this substance) and an iron salt in their formulations. Reducing conditions are maintained by inclusion of cysteine or thioglycolate in the medium. Precipitation of dark iron sulfide in these media, or gas formation in lactate-containing media, is presumptive for clostridial growth, even if confirmation is desirable since a few other bacteria also reduce sulfite or ferment lactate. Enumeration of clostridia may be achieved by both direct counting and most probable number (MPN) methods. Direct counting is carried out by streaking dilutions from the original product onto selective solid media, such as sulfite–polymixin–sulfadiazine (SPS) agar. Polymyxin is the only antibiotic that appears to
52
Pathogens in Milk | Clostridium spp.
be partially, but not entirely, selective for clostridia. Black colonies are enumerated after anaerobic incubation of plates at 30 or 37 C for up to 3 days. The MPN method consists of inoculating serial dilutions of the test food in three or five replicates of broth medium, such as differential reinforced clostridial medium (DRCM) or lactate RCM. After thermal treatment of the inoculated tubes and subsequent incubation under anaerobic conditions for 5–7 days, blackening or production of gas (depending on the medium used) is suggestive of clostridial growth. Numbers of clostridia are then extrapolated from appropriate tables. Although the MPN test is more sensitive in detecting low numbers of spores than the direct counting, because of the larger inoculum, it is less accurate because it assumes that blackening and production of gas are due to clostridia only, and it is also more time consuming. Recently, several PCR assays (i.e., PCR-DGGE nested PCR, real-time PCR) for detection and quantification of cluster I clostridia, identified as the major causal agent of late blowing in cheese, have been reported. Identification of Clostridium spp. may be necessary in some investigations: this relies on recognition of differential characteristics of strains, such as the metabolic or genetic properties. Biochemical tests including sugar fermentation patterns and enzymatic activities have proven useful for identification at the species level. Amplification through PCR of species-specific DNA sequences, such as those coding for toxins in toxigenic clostridia or those for nonconserved ribosomal RNA in other Clostridium spp., is also widely applied for early detection and identification of these microorganisms. For toxin-producing species, such as Cl. botulinum and Cl. perfringens, demonstration of toxicity is required in any case. Conventional methods for botulinum toxin detection involve the use of animals and specific antitoxins: many alternative in vitro tests, including enzyme-linked immunosorption assay (ELISA) tests and assays for the detection of the enzymatic activity of botulinum toxins, have been devised, some of the most recent ones approaching the sensitivity and specificity of the standard in vivo assay. Clostridium perfringens type A toxin is also commonly demonstrated by in vivo tests or by cytotoxicity in cultured cells: slide latex agglutination and ELISA tests are also applicable.
Control Several control measures are effective in preventing or minimizing contamination of milk with clostridia and inhibiting their growth in dairy products.
Good Manufacturing Practices Selection of high-quality raw milk with low levels of clostridial spores helps ensure that the final products are safe and wholesome. Special attention should be paid to the quality of the silage fed to animals, since preservation of crops by lactic acid fermentation and maintenance of anaerobic conditions may facilitate the growth of contaminating clostridia, particularly Cl. tyrobutyricum because of its ability to ferment lactic acid. Spores ingested by animals concentrate in the feces, which is one of the main sources of milk contamination. In many countries, regulations specify requirements relating to the health and care of milk-producing animals and to the hygiene of milking, handling, and transportation. Raw milk intended for Parmesan and traditional Swiss-type cheese production is collected from cows not fed on silage. Reduction of Spores in Raw Milk High-speed centrifugation (bactofugation) removes most spore-forming organisms from milk and does not affect the composition, flavor, and nutritional value of milk: efficacy in reduction of spores is a function of initial contamination in the milk and the operating conditions. Heat treatment is effective only at the temperature/ time conditions of sterilization (>135 C for 2–3 s), but sterilized milk is unsuitable for the manufacture of most dairy products. Pasteurization includes a variety of temperature/time combinations, but generally temperatures do not exceed 90 C, which is destructive to vegetative cells but not to bacterial spores; besides, this thermal treatment might activate spore germination and outgrowth, especially in the absence of microbial competition, if intrinsic and extrinsic properties of the pasteurized processed milk product are permissive. Prevention of Spore Outgrowth in Dairy Products Depending on the type of milk product, milk product technology, and duration of storage or ripening, inhibition of clostridia may be achieved by use of chemical additives, biopreservation, refrigerated storage, aw and pH reduction, and combination of preservative factors, according to the ‘hurdle’ concept. Nitrates, hexamethylenetetramine (HMT), and polyphosphates are the chemicals more commonly used against clostridia in cheese technology. Nitrates are converted into the functional nitrites through the metabolic activity of other contaminating microorganisms in the product; small amounts of nitrites (10–50 ppm) exert inhibitory effects against clostridial spores, possibly by enhancing their heat sensitivity. However, there are
Pathogens in Milk | Clostridium spp. 53
concerns on the use of these substances, due to the production of carcinogenic and mutagenic nitrosamines by chemical and/or microbial transformation, and for this reason their use in cheesemaking is not allowed in some countries; in other countries, 10–30 g of nitrates per 100 l of milk is permitted for the manufacture of some hard cheeses, such as Gouda. HMT is used in the production of the Italian hard cheese Provolone. HMT is a precursor of formaldehyde, since under acidic conditions it is decomposed to ammonia and formaldehyde. The latter compound inhibits spore development in cheese because it reduces the availability of certain macromolecules by combining with them. However, because of its high reactivity with nucleic acids also, its use is allowed only within certain limits, that is, 15–25 ppm in the milk at the beginning of the production; at the end of ripening, formaldehyde in the product must be <0.5 ppm, set as the upper limit for safe human consumption. Polyphosphates have been demonstrated to control clostridial growth in pasteurized processed cheese spreads stored at refrigeration temperatures, but their mechanism of action is still unknown. In the European Union, the maximum level of total phosphate permitted in processed cheese and cheese spreads is 2%, even if lower quantities may be sufficient to completely inhibit clostridia. Biopreservatives such as lysozyme and bacteriocins, especially nisin, also show some effectiveness against clostridia, thus representing valuable alternatives to the use of chemical additives in cheese. Egg white lysozyme, added ‘quantum satis’, disrupts microbial vegetative forms and delays the germination of spores by cleavage of the bacterial cell wall. Some clostridial strains, however, are resistant to lysozyme. Its anticlostridial activity has been well demonstrated in hard cheeses, such as Grana Padano and Emmental. On the other hand, nisin – a bacteriocin produced by Lactococcus lactis – has been widely used to prevent clostridial germination in pasteurized processed and spread cheeses, with high moisture and reduced salt contents. Nisin is directly added during cheesemaking to levels up to 250 ppm, depending on aw and pH of the product. Lactic acid bacteria starter cultures used to ferment milk products such as yogurt consistently inhibit clostridia by lowering the pH of the food, and thus represent another means of biopreservation. Low-temperature storage, pH and aw reduction, and other factors, including many of the preservative substances listed above, often function in synergy to control
clostridia in dairy products. A combination of techniques leads to establishment of multiple barriers (‘hurdles’) more restrictive than that achieved with individual factors. Refrigerated storage of dairy products, for instance, cannot prevent by itself the growth of psychrotrophic clostridia; also, any storage temperature abuse might be risky in the absence of other inhibitory agents. aw and pH reduction has classically been applied for inhibiting growth of any microorganisms in foods: however, addition of salts and various acidulants to reach values that are inhibitory for most clostridia (Table 1) is possible only to a certain extent in some dairies, in order to obtain organoleptically acceptable products. In conclusion, given the wide distribution of clostridia in nature, keeping the contamination level as low as possible or inactivating contaminating spores as early in processing as possible should be ensured through appropriate quality control procedures, specifically by proper application of HACCP (hazard analysis critical control point) programs. See also: Cheese: Avoidance of Gas Blowing.
Further Reading Berge`re JL and Hermier J (1970) Spore properties of clostridia occurring in cheese. Journal of Applied Bacteriology 33: 167–179. Bottazzi V, Battistotti B, Cappa F, Rebecchi A, Bertuzzi S, and Brambilla E (1993) [Clostridium spore germination and lysozyme action in grana cheese]. Scienza e Tecnica Lattiero-Casearia 44: 79–96. Byrne RD and Bishop JR (1998) Control of micro-organisms in dairy processing: Dairy product safety systems. In: Marth EH and Steele JL (eds.) Applied Dairy Microbiology, pp. 405–430. New York: Marcel Dekker. Choisy C, Gueguen M, Lenoir J, Schmidt JL, and Tourneur C (1987) Microbiological aspects. In: Eck A (ed.) Cheesemaking, pp. 259–292. New York: Lavoisier Publishing. Collins-Thompson DL (1993) Control in dairy products. In: Hauschild HW and Dodds KL (eds.) Clostridium botulinum, pp. 261–277. New York: Marcel Dekker. Hatheway CL (1990) Toxigenic clostridia. Clinical Microbiology Reviews 3: 66–98. Johnson S and Gerding DN (1997) Enterotoxemic infections. In: Rood JI, McClane BA, Songer JG, and Titball RW (eds.) The Clostridia. Molecular Biology and Pathogenesis, pp. 117–140. London: Academic Press. Julien MC, Dion P, Lafrenie`re C, Antoun H, and Drouin P (2008) Sources of clostridia in raw milk on-farm. Applied and Environmental Microbiology 74: 6348–6357. Mead GC (1992) Principles involved in the detection and enumeration of clostridia in foods. International Journal of Food Microbiology 17: 135–143.
Coxiella burnetii C Heydel and H Willems, Justus Liebig University, Giessen, Germany ª 2011 Elsevier Ltd. All rights reserved.
Characteristics Coxiella burnetii is the etiological agent of the zoonosis Q fever, which was first described in Australia. It is a pleomorphic, Gram-negative bacterium with a size of 0.2–0.7 mm with obligate intracellular propagation and worldwide distribution. Studies based on comparison of 16S rRNA encoding gene sequences demonstrate that this pathogen is most closely related to Legionella spp. and resides within the
-subdivision of the Proteobacteria while members of the family Rickettsiaceae, the former family of C. burnetii, are grouped in the -subdivision. Genotyping of C. burnetii isolates revealed the heterogeneity of this organism. Pulsed-field gel electrophoresis (PFGE) of NotI-restricted DNA was the first method applied for differentiation of North American C. burnetii isolates, which could be classified into four groups. With the same technique, 80 C. burnetii isolates derived from animals and humans within Europe, the United States, Africa, and Asia could be distinguished in 16 additional restriction patterns. Genome sizes, calculated by summing up the NotI restriction fragment sizes, ranged from 1.6 to 2.4 Mbp. With the availability of whole genome sequences of C. burnetii, typing methods were developed based on markers consisting of variable numbers of tandem repeats (VNTRs). This method, termed multiple loci variable number of tandem repeat analysis (MLVA), was found to be highly discriminatory. Thus, out of 42 isolates investigated with MLVA, 36 different genotypes were identified. In mammals, C. burnetii propagates in alveolar macrophages before disseminating and infecting other cells of the mononuclear phagocyte system, and infrequently fibroblasts or endothelial cells. In vitro, C. burnetii may be cultivated in a broad range of epithelial, fibroblast, and macrophage-like cell lines. Coxiella burnetii is internalized into host cells by microfilament-dependent, parasitedirected endocytosis after engaging the leukocyte response integrin avb3 (phase 1) or the CR3 receptor (phases 1 and 2). The pathogen then resides and multiplies within the harsh and acidic environment (pH 4.8) of parasitophorous vacuoles resembling secondary lysosomes. During multiplication, C. burnetii undergoes a unique developmental cycle with two cellular types termed small cell variants (SCVs) and large cell variants (LCVs). It has
54
been suggested that metabolically dormant SCVs are phagocytosed by eukaryotic host cells. Conditions in the vacuole trigger vegetative differentiation of SCVs into metabolically active LCVs. Apart from size, SCVs and LCVs differ markedly in ultrastructure, antigenicity, and metabolic capability. Furthermore, specific small, spore-like particles (SLPs) are described, which are supposed to be responsible for the high resistance of C. burnetii against environmental conditions. SCVs and SLPs are considered as extracellular survival stages. Viable organisms can be recovered after heating at 63 C for 30 min, exposure to 10% salt solution for 180 days at room temperature, exposure to 0.5% formalin for 24 h, or sonication in distilled water for >30 min. After serial cell culture passages, C. burnetii undergoes a phase variation. Virulent phase I coxiellae, synthesizing amphiphilic full-length lipopolysaccharides (LPSs), are replaced by low-virulent phase II variants producing truncated LPSs. The isolation of virulent phase I C. burnetii from specimen homogenates is accomplished by inoculation into immunocompetent hosts (e.g., guinea pigs). Subsequently, homogenates of infected spleens are passed serially in cell culture or yolk sacs of embryonated hen’s eggs to generate less virulent phase II C. burnetii. The size of the C. burnetii genome is less than 40% that of Escherichia coli, that is, about 1.2 109 Da or 2.0 106 bp. The G þ C content is 43 mol%. Until now, genomes of five C. burnetii isolates have been sequenced completely. Progress in understanding the genetics of C. burnetii has been hampered because of the inability to genetically manipulate the organism. Intracellular dependence, slow growth rates, and the tendency to infect persistently rather than lyse host cells made application of known genetic techniques fairly difficult. Recently, C. burnetii was transformed after electroporation and the cloning and characterization of a mutant generated by transposon mutagenesis were reported. This may facilitate the study of the unique and exemplary biology and pathogenicity of C. burnetii. Five different plasmid types (36–56 kb) and one plasmid-homologous sequence integrated into the chromosome may be distinguished, which comprise about 2% of the genome. Although their function is still cryptic, they are supposed to be of essential importance, since every isolate contains exactly one type of plasmid or plasmid-homologous sequence. In contrast to initial
Pathogens in Milk | Coxiella burnetii 55
studies, C. burnetii plasmids are no longer considered to be responsible for either acute or chronic Q fever. Epidemiological studies confirm that host factors play a key role in the clinical outcome of the disease.
Symptoms Acute Q fever in humans is most often described as influenza-like, self-limited, febrile illness, although the majority of C. burnetii infections are asymptomatic (60%). After an incubation period of 2–6 weeks, high fever, rigor, profuse sweats, fatigue, severe headache with retroorbital pain, photophobia, nausea, general malaise, myalgia, and arthralgia are characteristic. In more severe cases, pneumonia or hepatitis can occur. Rare manifestations include encephalitis, pericarditis, and myocarditis. Illness normally lasts 1–6 weeks, but can show a prolonged course. In more than 10% of cases, especially after repeated exposure to the infective agent, acute disease fades to the mostly afebrile Q fever fatigue syndrome. It is characterized by fatigue, muscle aches and pains, night sweats, headaches, photophobia, sleep disorder, loss of libido, and weakness of short-term memory, and can last for more than 1 year. Some patients, probably about 2%, develop chronic disease 1–20 years after the initial illness or exposure. The most frequent manifestation of chronic Q fever, particularly in patients with underlying valvulopathy, is endocarditis. Most cases involve the aortic valve and about 30% the mitral valve. Further occasional symptoms of chronic Q fever can be vasculitis, osteomyelitis, and granulomatous hepatitis, especially under immunocompromising conditions. In women, premature delivery or spontaneous abortion has also been reported. Similar to humans, in animals the most common route of infection seems to be inhalation of aerosols. They, however, usually do not develop illness from C. burnetii infection. Coxiella burnetii infection does not induce respiratory pathology in any animal species. Furthermore, chronic infection with cardiac or hepatic localization does not occur in animals. After infection, C. burnetii can be isolated from the organs of clinically healthy animals. The colonization of the female reproductive system and proliferation of C. burnetii in both uterus and mammary gland often lead to spontaneous abortion, stillbirth, or premature delivery, and shedding of C. burnetii by birth fluids and milk. Miscarriages due to C. burnetii are most frequently seen in small ruminants. In sheep, late abortions occur sporadically and rarely epidemically in as many as 60% of gravid ewes. In goats, abortion is predominantly seen 15 days before term. Flocks with an abortion history also show an increase of weak newborns. Although ovine and caprine C. burnetii infection is often described as transient
and tends to spontaneous cure as in dogs, cats, and humans, some studies suggest that it has rather an enzootic character as in cattle where C. burnetii circulates from generation to generation. In cattle, abortion and generally reduced fertility due to C. burnetii are described. The infection may cause subclinical mastitis with elevated somatic cell counts and might have an effect on coinfection with common mastitis pathogens. Manifest mastitis has rarely been seen but there are some descriptions in sheep and goats. In a mass outbreak in Bulgaria, sheep developed a progressive severe inflammation of the milk gland, with disappearance of the milk secretion, and general intoxication leading to death of some animals.
Coxiella burnetii in Milk After initial infection and bacteremia, C. burnetii may be detected in the udder during successive lactations. As confirmed by real-time PCR, 101–104 cells ml1 can be excreted with the milk. A common shedding pattern could not be identified. Shedding can be continuous, intermittent, sporadic, or even absent in infected animals. In a follow-up study comprising 7 concomitant milk samplings of 139 dairy cows of which 60% showed positive PCR results in feces, vaginal mucus, or milk samples, approximately 40% were detected as milk shedders. Two predominant milk shedding patterns, persistent (34.5%) and sporadic (51.7%), were found. Shedding was not restricted to the time following parturition and could not be linked to shedding by feces or vaginal mucus. Another PCR analysis of samples from 110 shedder cows revealed that 53.6% shed the C. burnetii via milk. Parallel detection in feces and/or vaginal mucus was possible in 11.9 and 25.4% of these, respectively; 62.7% shed only via milk. The study claims that excretion via milk might be more important in cows and goats than in sheep where fecal and vaginal excretion prevailed. The serological status of an animal does not allow prediction of milk shedding. It seems, however, that animals with high titers in enzyme-linked immunosorbent assay (ELISA), immunofluorescent assays (IFAs), or complement fixation tests (CFTs) have a higher probability of being shedders or even heavy shedders spreading large amounts of particles. In an infected herd, between 15 and 76% of the lactating animals were shown to excrete Coxiellae with milk. This wide margin is probably not only due to a regional clustering of C. burnetii infection but also due to the method of preparation of the milk samples and the sensitivity of the applied detection method. In a major PCR study testing the bulk tank milk of dairy herds from all over the United States over 3 years, more than 94% of the samples were tested positive.
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Pathogens in Milk | Coxiella burnetii
Due to the high prevalence of C. burnetii in the milk of domestic ruminants, the zoonotic risk of oral infection is of special interest. Most reported Q fever cases can be assigned to airborne infections. When milk is suspected as the source, different probable modes of transmission occur at the same time. Therefore, distinguishing true oral infections and evaluating the risk potential of contaminated milk are difficult. The efficiency of oral infection, that is, occurrence and proportion of associated illness, is doubted. In guinea pigs, experimental oral infection led to seroconversion in 8 of 25 animals and in 5 of these C. burnetii was found in internal organs. The manifestation of infection probably depends on the infective dose and virulence of the strain. Administration of high doses of corticoids favored the infection, whereas alternating the intestinal permeability by chemical or mechanical means had no influence upon antibody formation or distribution of the infective agent in the host. Coxiella burnetii was estimated to be less efficiently transmitted by the oral route than by aerosols. Effective infection in mice requires 10 000 times more Coxiellae by oral versus intraperitoneal administration. In humans particularly, the ingestion of contaminated raw milk is suspected of causing Q fever. This is still a matter of controversy as no conclusive evidence proves the alimentary infection of humans. This issue gains relevance as there are efforts under way in the United Kingdom, Canada, and the United States to promote increased human consumption of fluid raw milk. Pasteurization is generally accepted as sufficient for inactivating C. burnetii in milk. Mandatory pasteurization parameters were adjusted to the heat stability of C. burnetii when it was recognized as the most heat-resistant organism of public health significance. It is largely accepted that ingestion of C. burnetii-contaminated food can result in serological conversion, but cases of Q fever have been documented rarely. In addition, it is likely that seroconversion follows the ingestion of inactivated cells as well as of live cells. A study undertaken among hundreds of individuals, living several miles away from dairy farms, revealed that persons consuming raw milk had a higher rate of seropositive reactions. In a group of prisoners, some showed seroconversion after ingestion of contaminated raw milk for more than half a year, but the majority of the inmates remained seronegative. In another study, a small number of volunteers did not develop symptoms or an immunologic response after drinking contaminated, unpasteurized milk. Q fever was observed in creamery workers with practically no contact with the livestock but exposed to large amounts of contaminated milk. Unpasteurized goats’ milk has been described as a potential source of infection during a Q fever outbreak among patients and staff of a psychiatric institution in southern France.
To summarize, the possibility of oral infection by C. burnetii via milk cannot be denied. Possibly a relatively high oral infective dose impedes outbreaks of Q fever. Single cases in not yet identified risk groups could easily be overlooked because of the flu-like character of the disease. Furthermore, it is unclear whether milk infection might evoke the chronic form of Q fever after years of incubation.
Reservoirs and Routes of Infection Coxiella burnetii exhibits extreme geographical distribution and is endemic in every part of the world except for New Zealand and Antarctica. Its broad host range includes mammals, birds, and arthropods. However, the most common animal reservoirs are cattle, sheep, and goats, in which C. burnetii infections are far more frequent than generally expected. Studies in the 1960s and 1970s demonstrated that 10% of US dairy cows are constantly infected with an increasing seroprevalence among cattle. In herds with reported infertility problems, the proportion of infected animals may be up to 80%. Today, C. burnetii must be regarded enzootic in US dairy herds with more than 90% of bulk tank milk samples testing positive via PCR. Infection cycles may occur among arthropods and mammals in nature, and numerous species of ticks are considered as reservoirs for C. burnetii. Ticks acquire the organism by bloodsucking and transmit it with their feces. However, various investigations suggest that only some species, like Dermacentor reticulatus, might be of importance as reservoirs. Although infection cycles may occur among arthropods and mammals in nature, C. burnetii maintains an independent and more important airborne infection cycle among domestic livestock. Domestic ruminants shed the desiccation-resistant organism in urine, feces, and especially birth products, contaminating the environment. Parturient placentas of infected ruminants were shown to contain as many as 1012 cells g1. Dissemination of contaminated straw and manure or birth products rotting on pastures may cause the spread of the organism via dust especially in periods of dry and windy weather. The highly infectious particles (minimal infectious dose by aerosol transmission is one Coxiella cell per individual) can be spread by the wind over distances of several kilometers. In this way, subsequent Q fever occurs even in distant urban areas. In Europe, the majority of Q fever outbreaks can be assigned to airborne infections originating from birth products of sheep and goat flocks during lambing season.
Pathogens in Milk | Coxiella burnetii 57
Diagnostics
Treatment
Prior to implementation of specific control measures, precise and reliable diagnosis of C. burnetii infection in animals and humans is required. For the detection of C. burnetii, the most relevant techniques include isolation, immunodetection in tissue samples, and DNA amplification. Initially, C. burnetii was isolated by inoculation of specimen into laboratory animals (i.e., guinea pigs, mice) or embryonated hen’s eggs. Nowadays, isolation and propagation are mainly carried out by means of conventional, permanent cell cultures. The recent development of a new medium, suitable for cultivation of Coxiella in the absence of host cells, will probably further simplify cultivation. Since isolation of C. burnetii requires much time and experience, immunodetection of C. burnetii antigen in tissue samples, smears, or secretions is applied increasingly in routine diagnostics. To increase sensitivity and specificity of C. burnetii detection, DNA amplification methods were established. Several procedures have been described for PCR detection of C. burnetii in milk. Meanwhile, several real-time PCR assays were developed not only to detect but also to quantify C. burnetii cells in clinical specimens. Despite improved methods for the detection of the pathogen, the diagnosis of Q fever and C. burnetii infections still relies mainly upon serology. Particularly, surveys with large numbers of specimens are most commonly performed serologically. Usually, IFA or CFT and ELISA techniques are applied. To summarize, CFT is very specific but lacks sensitivity; moreover, a prozone phenomenon is present with specimens of chronic cases that could lead to false negative results. ELISA tests in general are satisfactory for diagnosis. Nevertheless, for Q fever, diagnostic IFA is still the reference method, since it is both sensitive and highly specific. No crossreactions with other organisms have been documented. Antibodies against C. burnetii can also be detected in milk by capillary tube agglutination tests. For the diagnosis of Q fever, sera should be tested at different time points to demonstrate seroconversion. A fourfold increase in anti-Coxiella titers is considered to be characteristic of acute Q fever. Alternatively, antibody subclasses against C. burnetii should be differentiated and additionally phase I and phase II antigens may be applied in the test system. The results of serology are positive between 2 and 4 weeks after the onset of disease. In acute Q fever, IgM antibodies against phase II antigen rise prior to antiphase I IgM or IgG antibodies. IgM persists for 6–8 months and diagnosis can be made even when a single sample is IgM positive. In chronic Q fever, antiphase I antibodies predominate at very high levels. Coxiella burnetii serology in animals is predominantly carried out by CFT or ELISA.
If Q fever is diagnosed early during illness, a regimen of tetracycline compounds especially doxycycline (200 mg day1) for 15–21 days is still recommended. Quinolones, like ofloxacin (600 mg day1) and pefloxacin (800 mg day1), were reported to be effective in Q fever pneumonia and Q fever meningoencephalitis. In prolonged Q fever, a combination of pefloxacin (800 mg day1) and rifampicin (1200 mg day1) applied for 15 days has been successful. In chronic Q fever (i.e., mainly endocarditis), tetracycline is usually combined with either rifampicin or quinolones and even chloroquine. However, since antimicrobial treatment ranges from 1 year to unlimited administration, valve replacement is often proposed for hemodynamic reasons. So far, no satisfactory treatment scheme for coxiellosis exists in animals. Cattle and sheep, treated with tetracycline, continued to shed the organism. Nevertheless, a potential protective effect on pregnancies was not excluded.
Prevention To prevent Q fever and coxiellosis, vaccination and hygiene management strategies must be applied. Despite great efforts to develop Q fever vaccines, only one vaccine, Q-Vax, is commercially available and is restricted to Australia. The formalin-inactivated whole cell vaccine provides reliable protection. Unfortunately, it can induce mild to severe adverse reactions, especially when administered to individuals with prior exposure to the agent. Thus, strict prevaccination screening, for example, exclusion of persons with positive skin reactions, is necessary. Booster inoculations are problematic for the same reason. In the area of veterinary medicine, two vaccines against coxiellosis of ruminants, Chlamyvax FQ and Coxevac, are commercially available. Chlamyvax FQ, a whole cell vaccine containing inactivated C. burnetii phase II particles and a Chlamydia component, is solely approved in France. For Coxevac, which contains inactivated phase I particles, European registration is in progress. Generally, vaccines prepared with phase II particles are considered to be less protective. This was confirmed by a recent comparative study in which goats were challenged after vaccination. Only vaccination with Coxevac led to a reduction of abortion incidence and shedding. The complete effectiveness of the vaccine against bacterial shedding in milk led the authors to suggest that vaccination might represent the microbiological quality assurance awaited by the producers of raw milk.
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Pathogens in Milk | Coxiella burnetii
Possibly, the effectiveness of Coxevac in small ruminants can be finally evaluated when results of obligatory vaccination programs for goat and sheep holdings in southern regions of the Netherlands, ordered to control a large Q fever outbreak, become available. Coxevac reduced the probability of susceptible (i.e., noninfected) dairy cattle becoming a shedder to one-fifth. This result was not seen if vaccinees were pregnant. Furthermore, Coxevac failed to prevent or reduce C.burnetii shedding in cows that were infected prior to vaccination. Thus, vaccination with the phase I vaccine might protect noninfected herds. Nevertheless, infected herds need further hygienic and medical measures to reduce effectively the bacterial burden. During Q fever outbreaks, predominantly originating from small ruminants, official recommendations regulate hygiene management measures in most countries. Following for example the recommendations of the German Robert Koch institute, sheep and goat herds must be kept at a distance of >500 m from inhabited areas. For disinfection of contaminated stables, solutions of 10–20% bleaching powder, 1% Lysol, or 5% hydrogen peroxide are recommended. Contaminated manure should be ploughed under after decontamination for 5 weeks with quicklime packages. Special care has to be taken with the highly infectious birth products, which must be eliminated from stables or pastures immediately for proper disposal. After lambing, dams and offspring must be kept in closed stables for 2 weeks. Shearing and storage of wool are restricted to closed rooms outside residential areas. Shearing personnel are obliged to wear dusk masks. If ticks are suspected as vectors, acaricides should be administered. As discussed above, it is difficult to evaluate the risk originating from contaminated raw milk. Following the precautionary principle, pasteurization should be advised. Meat, unlike udder and placental tissue, is not regarded as a source of infection. Eradication of C. burnetii-infected livestock is discussed periodically when Q fever outbreaks occur but cannot be recommended due to the high prevalence of coxiellosis in general, the environmental stability of the infective agent, and the unavoidable contact with wildlife reservoirs. Nevertheless, identification and culling of persistently heavy shedding individuals could reduce the bacterial burden. Altogether, identification and proper disposal of material potentially contaminated with C. burnetii are the main objectives in Q fever prevention. Besides, physicians should be encouraged to include Q fever in their differential diagnosis to promote early and efficient therapy or control measures if infection occurs.
See also: Analytical Methods: DNA-based Assays. Cheese: Public Health Aspects. Hazard Analysis and Critical Control Points: HACCP Total Quality Management and Dairy Herd Health. Heat Treatment of Milk: Thermization of Milk; Non-thermal Technologies: Introduction; Liquid Milk Products: Pasteurization of Liquid Milk Products: Principles, Public Health Aspects. Microorganisms Associated with Milk.
Further Reading Arricau-Bouvery N, Souriau A, Bodier C, Dufour P, Rousset E, and Rodolakis A (2005) Effect of vaccination with phase I and phase II Coxiella burnetii vaccines in pregnant goats. Vaccine 23(35): 4392–4402. Barlow J, Rauch B, Welcome F, Kim SG, Dubovi E, and Schukken Y (2008) Association between Coxiella burnetii shedding in milk and subclinical mastitis in dairy cattle. Veterinary Research 39(3): 23. Berri M, Souriau A, Crosby M, and Rodolakis A (2002) Shedding of Coxiella burnetii in ewes in two pregnancies following an episode of Coxiella abortion in a sheep flock. Veterinary Microbiology 85(1): 55–60. Berri M, Rousset E, Hechard C, et al. (2005) Progression of Q fever and Coxiella burnetii shedding in milk after an outbreak of enzootic abortion in a goat herd. The Veterinary Record 156(17): 548–549. Berri M, Rousset E, Champion JL, Russo P, and Rodolakis A (2007) Goats may experience reproductive failures and shed Coxiella burnetii at two successive parturitions after a Q fever infection. Research in Veterinary Science 83(1): 47–52. Berri M, Laroucau K, and Rodolakis A (2000) The detection of Coxiella burnetii from ovine genital swabs, milk and fecal samples by the use of a single touchdown polymerase chain reaction. Veterinary Microbiology 72(3–4): 285–293. Cerf O and Condron R (2006) Coxiella burnetii and milk pasteurization: An early application of the precautionary principle? Epidemiology and Infection 134(5): 946–951. Chiu CK and Durrheim DN (2007) A review of the efficacy of human Q fever vaccine registered in Australia. New South Wales Public Health Bulletin 18(7–8): 133–136. Fishbein DB and Raoult D (1992) A cluster of Coxiella burnetii infections associated with exposure to vaccinated goats and their unpasteurized dairy products. The American Journal of Tropical Medicine and Hygiene 47(1): 35–40. Fournier PE, Marrie TJ, and Raoult D (1998) Diagnosis of Q fever. Journal of Clinical Microbiology 36(7): 1823–1834. Guatteo R, Beaudeau F, Berri M, Rodolakis A, Joly A, and Seegers H (2006) Shedding routes of Coxiella burnetii in dairy cows: implications for detection and control. Veterinary Research 37(6): 827–833. Guatteo R, Beaudeau F, Joly A, and Seegers H (2007a) Assessing the within-herd prevalence of Coxiella burnetii milk-shedder cows using a real-time PCR applied to bulk tank milk. Zoonoses and Public Health 54(5): 191–194. Guatteo R, Beaudeau F, Joly A, and Seegers H (2007b) Coxiella burnetii shedding by dairy cows. Veterinary Research 38(6): 849–860. Guatteo R, Seegers H, Joly A, and Beaudeau F (2008) Prevention of Coxiella burnetii shedding in infected dairy herds using a phase I C. burnetii inactivated vaccine. Vaccine 26(34): 4320–4328. Heinzen RA, Hackstadt T, and Samuel JE (1999) Developmental biology of Coxiella burnetii. Trends in Microbiology 7(4): 149–154. Martinov S (2007) Studies on mastites in sheep, caused by Coxiella burnetii. Biotechnology, Biotechnological Equipment 21(4): 484–490.
Pathogens in Milk | Coxiella burnetii 59 McQuiston JH, Gibbons RV, Velic R, et al. (2003) Investigation of a focus of Q fever in a nonfarming population in the Federation of Bosnia and Herzegovina. Annals of the New York Academy of Sciences 990: 229–232. Omsland A, Cockrell DC, Howe D, et al. (2009) Host cell-free growth of the Q fever bacterium Coxiella burnetii. Proceedings of the National Academy of Sciences of the United States of America 106(11): 4430–4434. Raoult D (1993) Treatment of Q fever. Antimicrobial Agents and Chemotherapy 37(9): 1733–1736.
Rodolakis A, Berri M, He´chard C, et al. (2007) Comparison of Coxiella burnetii shedding in milk of dairy bovine, caprine, and ovine herds. Journal of Dairy Science 90(12): 5352–5360. Souriau A, Arricau-Bouvery N, Bodier C, and Rodolakis A (2003) Comparison of the efficacy of Q fever vaccines against Coxiella burnetii experimental challenge in pregnant goats. Annals of the New York Academy of Sciences 990: 521–523. Thompson HA and Suhan ML (1996) Genetics of Coxiella burnetii. FEMS Microbiology Letters 145(2): 139–146.
Escherichia coli P Desmarchelier, Consultant, Pullenvale, QLD, Australia N Fegan, Food Science Australia, Brisbane, QLD, Australia ª 2011 Elsevier Ltd. All rights reserved.
Introduction The genus Escherichia derives its name from Theodor Escherich, who first isolated this organism from feces in 1885. The type strain of the genus is E. coli, a common bacterium found in the gastrointestinal tract of humans and other vertebrates where most strains are nonpathogenic commensals. However, there are several groups of E. coli that can be pathogenic, causing a variety of diseases, some of which are fatal. The three clinical syndromes resulting from E. coli infection are urinary tract infections caused by uropathogenic E. coli, meningitis and septicemia resulting from necrotoxigenic E. coli infection, and diarrheal diseases. In food safety, the most important E. coli are those that cause diarrheal diseases. E. coli can also cause spoilage in dairy products, for example, blowing of cheese and ropiness in milk and cheese brines can be caused by E. coli growth.
General Characteristics E. coli is a member of the family Enterobacteriaceae, which includes Gram-negative facultatively anaerobic rod-shaped bacteria (possessing both a fermentative and respiratory metabolism) and which do not produce the enzyme oxidase. E. coli cells are typically 1.1–1.5 mm wide, 2–6 mm long and occur as single straight rods. They can be either motile or nonmotile, and when motile produce lateral, rather than polar, flagella. In addition to flagella, many strains produce other appendages such as fimbriae or pili, which are proteinaceous structures (or appendages or fibers) that extend outward from the bacterial surface and play a role in attachment to surfaces including other cells or host tissues. E. coli have strain-specific O lipopolysaccharide antigens on their cell wall (at least 181 O antigens are currently recognized) and flagella or H antigens if present (53 H types are recognized). There are also 80 different capsular polysaccharide (K) antigens. E. coli are serotyped based on the combination of O, H, and K antigens, although generally only the O and H types are listed, for example, E. coli O157:H7. Serotyping of E. coli, together with genome, virulence, and phage typing, is a useful epidemiological tool.
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E. coli is closely related to Shigella spp., although Shigella tends to be less biochemically active than most strains of E. coli. Shigella and E. coli can be considered to be within a single genus based on genetic relatedness, but historically the two have remained separate to prevent confusion in medical diagnosis.
Pathogenic Types of E. coli E. coli causing human diarrhea are assigned to groups based on their virulence properties and clinical manifestations. Enterohemorrhagic E. coli and Shiga Toxigenic E. coli The enterohemorrhagic E. coli (EHEC) group have a common ability to produce cytotoxins that are active on monkey kidney (Vero) tissue culture cells. These cytotoxins are mediated by genes carried by lysogenic bacteriophages and act in a similar manner by interfering with protein synthesis in eukaryotic cells. The toxins belong to two major antigenically distinct groups, Stx1 and Stx2, with various subgroups. Stx1 is similar to the Shiga toxin produced by Shigella dysenteriae; consequently, Shiga toxin-producing E. coli are referred to as both STEC (Shiga toxin-producing E. coli) and VTEC (verotoxigenic E. coli). EHEC is a term commonly used to refer to those STEC that cause enterohemorrhagic disease. Since their recognition in the 1980s, EHEC have become the most notable of the enteropathogenic E. coli (EPEC) that are transmitted by food, including dairy products. They can cause illness in humans and diarrheal illness in young animals. Human EHEC infection can be asymptomatic or result in symptoms ranging from mild diarrhea to hemorrhagic colitis and life-threatening hemolytic–uremic syndrome (HUS). Strains causing hemorrhagic syndromes frequently, but not exclusively, carry accessory virulence factors to the Shiga toxins located on a chromosomal pathogenicity island, the locus for enterocyte effacement (LEE). The LEE encodes genes that lead to the formation of attaching and effacing lesions typically seen in the intestinal epithelium in both EHEC and EPEC (see below) infections. EHEC strains also frequently carry a unique 92-kb plasmid, pEHEC,
Pathogens in Milk | Escherichia coli
that encodes several potential virulence factors, although none is considered essential in EHEC pathogenesis at this time. The pEHEC carries genes encoding an EHEC hemolysin that is used as a differential characteristic for putative EHEC in some agar isolation media. There are many serotypes of STEC, although a limited number are commonly associated with HUS. The most common is the O157:H7 serotype and others include O26, O111, O45, and O103. Clinical isolates of these types often carry the same virulence determinants, for example, Stx1 and/or Stx2, the LEE, and pEHEC.
Enterotoxigenic E. coli Enterotoxigenic E. coli (ETEC) produce the E. coli heat-labile (LT) and/or heat-stable (ST) toxins. ETEC are important causes of diarrhea among children in developing countries and of traveler’s diarrhea. Symptoms include acute watery diarrhea that may be mild and of short duration and which in some cases is similar to cholera. ETEC strains are host specific, that is, some strains can cause diarrhea in young animals (e.g., calves, lambs, and piglets), while other strains will specifically infect only piglets, and others only humans. The major virulence factors of ETEC are intestinal colonization factors, for example, fimbriae, and the enterotoxins. The host specificity of individual strains is determined by the type of colonization factors and fimbriae produced. The LTs are high-molecular-weight proteins similar to cholera toxin and consist of five enterocyte-binding B subunits and a biologically active A subunit. The internalized A subunit causes electrolyte imbalance and a net fluid loss to the gut lumen by activation of adenylate cyclase and accumulation of cyclic adenosine monophosphate. The STs are small polypeptides that act similarly through activation of guanylate cyclase and accumulation of cyclic guanosine monophosphate.
Enteropathogenic E. coli EPEC are a major cause of acute or chronic enteritis in children in developing countries. EPEC typically produce attaching and effacing lesions on the intestinal epithelium. The genes encoding this activity are carried on a 60 MDa EPEC adherence factor plasmid and the LEE pathogenicity island, which is also present in many EHEC. The clinical symptoms are a consequence of the ensuing electrolyte loss and epithelial damage. There have been a limited number of outbreaks of EPEC disease linked to food- and waterborne transmission.
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Enteroinvasive E. coli Enteroinvasive E. coli (EIEC) invade the host intestinal epithelial cells where they multiply, causing cell destruction and an acute inflammatory response similar to shigellae. Patients may first develop watery diarrhea prior to onset of dysentery with a low volume of stools containing blood and mucus. Other symptoms are headache, fever, and cramping. Humans appear to be the main reservoir of EIEC, with little evidence to support EIEC carriage in animals or foods of animal origin. EIEC outbreaks are usually associated with water or food contaminated with human feces or person-to-person transmission. The incidence of the disease caused by EIEC is generally low in developed countries.
Enteroaggregative E. coli and Diffusely Adherent E. coli Two other groups of diarrheagenic E. coli characteristically adhere to Hep-2 tissue cells. Those that adhere in an aggregative pattern resembling microcolonies are termed enteroaggregative E. coli (EAEC) and those producing a more diffuse adherence on the Hep-2 cell surface are known as diffusely adherent E. coli (DAEC). The mechanisms of pathogenesis of these groups are poorly understood, as is their epidemiology. Both groups are isolated from diarrheal cases in children in developing countries and there is limited evidence of foodborne outbreaks. E. coli Outbreaks from Milk and Dairy Products Milk and Cream
Raw milk has been implicated as the vehicle of sporadic cases and several outbreaks of EHEC-associated illness in North America, Europe, and the United Kingdom. While cows’ milk is the most common source, goats’ and sheep milk has been implicated in E. coli O157 infection. Outbreaks of EHEC infection have been associated sheep with raw milk and pasteurized milk contaminated postprocessing. In an outbreak of EHEC infection where nine children developed HUS in the United Kingdom, E. coli O157 was found in pipes and on a discarded rubber gasket from a milkbottling machine, suggesting postpasteurization contamination. Postpasteurization contamination was also believed to have caused an outbreak of E. coli O104:H21 linked to pasteurized milk in the United States. Cheese
Outbreaks of illness caused by EAEC, EIEC, ETEC, and EHEC have been attributed to the consumption of cheese. Cases of EAEC O92:H33 were associated with Pecorino cheese made from raw milk thought to be inadequately
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processed. An outbreak of EIEC O124 involved 387 people following consumption of Camembert cheese. Contamination was traced to river water used for cleaning processing equipment that had been filtered through a malfunctioning treatment system. ETEC serotype O27:H20 was isolated in an outbreak caused by the consumption of French Brie and Camembert that had been mishandled during shipping and distribution. Cheese has been the attributed vehicle in several EHEC outbreaks. Outbreaks of E. coli O157:H7 have been attributed to a variety of cheeses such as farmproduced cheese, fresh cheese curds, a semihard Lancashire cheese, and a Gouda made from unpasteurized milk. Other serotypes have included EHEC O103:H2 contaminating soft cheese made from a mixture of unpasteurized cows’ and goats’ milks; O119 EHEC in fromage frais; and O26 EHEC from a raw milk Camembert cheese in France. The use of contaminated raw milk or postprocessing contact with raw milk and subsequent survival of the EHEC during the cheesemaking process have been the major contributing factors. Other Milk Products
An outbreak of E. coli O157:H7, which affected 16 people and caused 5 HUS cases among children, was linked to a live yogurt made on a farm from pasteurized milk. Postpasteurization contamination of milk was likely due to either inadequate cleaning or contamination from farmyard material. Ice cream contaminated with STEC O145:H28 and O26:H11 has been attributed to cases of HUS. Cases were guests at two birthday parties on the same farm where the ice cream was also made. STEC of the same serotypes were isolated from calves and the farm environment. There have been no documented cases of E. coli infection caused by dried or condensed dairy products, or by butter.
Incidence in Milk and Dairy Products The primary source of E. coli on a farm is the animals and wildlife. Although EHEC and STEC are the most studied pathogenic E. coli in farm environments, other types (EAEC and EPEC) have been detected. Humans may be a significant source of other pathogenic types. Animal isolates of E. coli are dispersed via feces and can be found on hides and hair and in saliva. Fecal contamination is widely disseminated on dairy farms in soil, dust, nonpotable water, and on pastures and dissemination is assisted by wildlife, for example, rodents, birds, and flies, and personal and farm equipment. Animal excretion of specific E. coli types may be intermittently varying with season and animal age, for example, EHEC O157:H7 may be carried by up to one-third of dairy herds and 4–10% of cattle within the herd may be excreting at any time.
Milk can be contaminated during collection indirectly via udders soiled with contaminated feces, soil, water, feed, and bedding, or directly if the animal has E. coli mastitis. Workers, either asymptomatic or ill, may excrete E. coli in their feces and poor personal hygiene practices can lead to contamination of dairy products and equipment. Equipment at farms and factories can become contaminated by raw milk, water, and soil, and contamination can be transferred from farm to factory via soil on bulk milk tankers and other transport vehicles. Table 1 lists various studies on the incidence of E. coli in dairy products. Generally, dairy products produced from pasteurized milk and with good hygiene and sanitation protocols, as expected, are less often contaminated with E. coli.
Growth and Survival Information on the growth and survival of E. coli in foods is generally not specific to the individual pathogenic types. Where this is available, this information is specified. The optimal temperature for growth of E. coli is 35–40 C, the minimum being 7–8 C and the maximum about 46 C. O157 EHEC have a more limited growth range and will not grow below 8 C and grow poorly or not at all at 44–45.5 C, the temperature often used in routine methods for detecting E. coli. The growth medium used can limit the ability of a particular strain to grow or produce gas at temperatures above the optimum. E. coli is sensitive to heat and this depends on the composition, pH, and water activity (aw) of the suspending medium or food matrix. The D-value or time required to reduce E. coli numbers by one log cycle in cows’ milk at 58 C (D58) is 0.78 min, while in nonfat dry milk powder, the D58 value increases with the increasing percentage of milk solids. As the aw decreases, the heat resistance can increase depending on the solute; for example, at an aw of 0.98, sodium chloride has a greater effect than glucose. E. coli is somewhat more sensitive to heat than other enteric pathogens, for example, Salmonella, and will not survive adequate pasteurization. E. coli survives well in chilled and frozen foods. In pasteurized, unpasteurized, and skim milk, E. coli O157:H7 does not grow at 5 C, although at 8 C, 1–2 and 2–3 log increases may occur after 4 and 7 days, respectively. After initial freezing, there is normally a decrease in viable E. coli, and then the population can remain stable for periods greater than 12 months. E. coli can grow at a pH between 4.4 and 10, the optimal being 6–7. The minimal pH allowing growth is influenced by the type of acidulant, the presence of inhibitory substances, for example, nitrite, temperature, and aw. For example, strains of E. coli O157 will grow at 37 C in a medium of pH 4.5 acidified with hydrochloric acid but
Table 1 A summary of some surveys of milk and milk products for E. coli
Product
E. coli group
Number tested
Percent positive for E. coli
Country
References
Raw milk Milk products Raw milk Raw milk (bulk tank) Raw milk (bulk tank) Raw milk Raw milk Raw milk Raw milk (milk filters) Naturally soured milk Cultured pasteurized milk Pasteurized milk Pasteurized milk and cream Raw milk cheese (soft) Raw milk cheese (soft and semisoft) Raw milk cheese (soft, hard, unripened, and blue) Raw milk cheese (Castellano) Raw milk cheeses (soft, semihard, and hard) Camembert Pasteurized milk soft cheese Butter (pasteurized and unpasteurized) Ice cream Frozen yogurt Cream confectionery
EPECa Generic E. coli Generic E. coli Generic E. coli E. coli O157:H7 Toxigenic E. colib E. coli O157:H7 E. coli O157:H7 E. coli O157:H7 Toxigenic E. colib Toxigenic E. colib EPEC and ETEC Generic E. coli Toxigenic E. colib E. coli O157:H7 STEC STEC STEC Generic E. coli Toxigenic E. colib Generic E. coli Generic E. coli Generic E. coli Generic E. coli
Unknown 5760 1154 175 268 12 930 250 536 21 27 32 430 221 153 1039 83 796 102 75 60 73 170 92
19 29 46 47 0.8 17 34 0.4 3 33 26 0 6 1.4 0 3 2 2 3 0 22 30 0 10
India Europe Europe Trinidad United States of America Zimbabwe Malaysia Hungary Ireland Zimbabwe Zimbabwe Brazil Sweden Spain Belgium France Spain Switzerland Japan Spain Italy Turkey Spain Italy
Singh et al. (1970) Otenhajmer et al. (1989) Otenhajmer et al. (1989) Adesiyun et al. (1997) Murinda et al. (2002) Gran et al. (2003) Chye et al. (2004) Hucker et al. (2006) Murphy et al. (2005) Gran et al. (2003) Gran et al. (2003) Jakabi and Franco (1991) Lindberg et al. (1998) Quinto and Cepeda (1997) Vivegnis et al. (1999) Vernozy-Rozand et al. (2005) Caro and Garcia-Armesto (2007) Stephan et al. (2008) Takeba et al. (1996) Quinto and Cepeda (1997) Bianchi and Geminiani (1994) Arslan et al. (1996) Lopez et al. (1997) Simoni et al. (1983)
a
Uncertain definition of enteropathogenic E. coli (EPEC). Enterotoxigenic E. coli (ETEC), Shiga toxigenic E. coli (STEC), and necrotoxigenic E. coli were isolated. From Adesiyun AA, Webb LA, Romain H, and Kaminjolo JS (1997) Journal of Food Protection 60: 1174–1181; Arslan A, Gonulalan Z, Ates G, and Guven A (1996) Turkish Journal of Veterinary and Animal Sciences 20: 109–112; Bianchi E and Geminiani G (1994) Industrie Alimentari 33: 833–837; Caro I and Garcia-Armesto MR (2007) International Journal of Food Microbiology 116: 410–413; Chye FY, Abdullah A, and Ayob MK (2004) Food Microbiology 21: 535–541; Gran HM, Wetlesen A, Mutukumira AN, Rukure G, and Narvhus JA (2003) Food Control 14: 539–544; Hucker A, Mike-Schummel I, Unger A, and Varga L (2006) Milchwissenschaft – Milk Science International 61: 11–14; Jakabi M and de Franco BDGM (1991) Ciencia e Tecnologia de Alimentos 11: 170–181; Lindberg AM, Ljungh A, Ahrne S, Lofdahl S, and Molin G (1998) International Journal of Food Microbiology 39: 11–17; Lopez MC, Medina LM, Cordoba MG, and Jordano R (1997) Alimentaria 288: 39–45; Murinda SE, Nguyen LT, Ivey SJ, et al. (2002) Journal of Food Protection 65: 752–759; Murphy BP, Murphy M, Buckley JF, et al. (2005) International Journal of Hygiene and Environmental Health 208: 407–413; Otenhajmer I, Mijacevic Z, and Asanin R (1989) Acta Veterinaria 39: 127–136; Quinto EJ and Cepeda A (1997) Letters in Applied Microbiology 24: 291–295; Simoni F, Baldaccini G, and Bianucci P (1983) Industrie Alimentari 22: 337–341; Singh RS, Ranganathan B, and Laxminarayana H (1970) International Dairy Congress, Sydney 1E: 148; Stephan R, Schumacher S, Corti S, Krause G, Danuser J, and Beutin L (2008) Journal of Dairy Science 91: 2561–2565; Takeba K, Umeki F, Nakama A, Fujinuma K, and Kokubo Y (1996) Annual Report of Tokyo Metropolitan Research Laboratory of Public Health 47: 82–89; Vernozy-Rozand C, Montet MP, Berardin M, Bavai C, and Beutin L (2005) Letters in Applied Microbiology 41: 235–241; Vivegnis J, El-Lioui M, Leclercq A, Lambert B, and Decallonne J (1999) Biotechnologie Agronomie Socie´te´ et Environnement 3: 159–164.
b
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not with lactic acid. E. coli have several different regulatory systems that enable cells to adapt to and survive acid stress. Both acid-resistant and acid-sensitive strains have been found among nonpathogenic E. coli, and EIEC, EPEC, EHEC, and ETEC groups. The minimum aw allowing growth of E. coli is 0.95 (8% sodium chloride) and the optimal aw is 0.995, with variations between strains. Combinations of parameters are often present as hurdles for controlling growth of E. coli in dairy products. For example, during cheese manufacture, low pH produced by starter cultures metabolizing lactose into lactic acid, low aw developed with the addition of salt and during ripening, and temperature control inhibit E. coli growth. Curd cooking temperatures of 30–38 C (for soft and semisoft cheeses) and 38–55 C (for hard cheeses) can provide conditions suitable for the growth of E. coli; therefore, careful control of pH and aw is essential to limit the growth of any pathogens present. In the initial stages of fermentation of soft and semisoft cheeses, any E. coli present (including pathogenic types) can grow until the pH drops, salt is added, and the temperature is reduced. However, it is possible for E. coli to survive beyond the ripening stages of some semihard, soft, and fresh cheeses. Zones of these intrinsic parameters are established during processing, for example, in soft and mold-ripened cheeses, and the behavior of any E. coli strain varies accordingly.
Control Common factors causing outbreaks of E. coli disease due to dairy products include the use of contaminated raw milk, faulty pasteurization or failure of processing equipment, starter culture failure, and postpasteurization contamination. The application of a hazard analysis critical control point (HACCP)-based approach together with the prerequisites of good manufacturing practices (GMPs) and good hygiene practices (GHPs) is now required through the dairy food chain in many countries. Effective sanitation and cleaning of equipment at all processing steps and meticulous personal hygiene of food handlers are essential, whether on farm, during transport, or in factories. Equipment sanitation is important, as any residues of product on equipment or machinery may allow growth of E. coli contaminants at ambient temperatures, leading to subsequent product contamination. Use of potable water for cleaning and during manufacture is important and failures to adhere to this have resulted in outbreaks of E. coli. Effective monitoring at control points and corrective action in the event of a deviation are fundamental in this process. Processing plants should be designed to ensure that contamination is not transferred from raw to final products. Movement of personnel and equipment between
milk receival bays and processing areas should be prevented with similar separation of raw and pasteurized product areas. Specific control measures for particular products are discussed below.
Milk and Cream As E. coli is part of the bacterial flora in feces of healthy dairy animals, contamination of raw milk can easily occur during collection. On-farm controls include the supply of safe feed and water, maintenance of animal health, and removal and rapid treatment of any animals with mastitis. GHPs on farm, including cleaning and disinfecting of udders before milking and effective cleaning of surfaces and equipment in the dairy parlor and on milk transport tankers, are essential to minimize contamination of the raw milk during collection and storage. Preventing environmental contamination of raw milk via dust and other particulate matter and ensuring personal cleanliness and hygiene are also important. Raw milk contains various antimicrobial factors that may restrict microbial growth (lysozyme, lactoferrin, lactoperoxidase, immunoglobulin); however, this alone is insufficient and chilling is also required. Chilling raw milk to below 4 C within 2 h of collection restricts growth of E. coli, and regulations for milk storage are established in most countries. Raw milk is potentially contaminated with E. coli and consumption of raw milk poses a threat to human health, particularly for young children, the elderly, and those who are immunocompromised. Heat treatment is the most common method for enhancing the safety of liquid milk. Any E. coli present in pasteurized milk is a consequence of ineffective pasteurization or postprocessing contamination. Pasteurization at 63 C for 30 min and high-temperature, short-time (HTST) pasteurization at 72 C for 15 s or equivalents are effective in reducing E. coli contamination to levels considered safe for human consumption. The effect of thermization varies depending on the temperature and time used. Low treatments (57 C for 15 s) sometimes used in cheesemaking will have little or no effect in destroying E. coli compared with higher temperatures (62–65 C for 15–20 s). Similar measures apply to cream, although the higher fat content can protect bacteria from the effects of heat, and higher temperature limits of these treatments are required. After pasteurization, considerable care is required to prevent recontamination, and pasteurized milk and cream are held chilled (preferably at less than 5 C) to prevent growth if contamination occurs. Critical controls include storage and pasteurization conditions (temperature and holding time), with prerequisites being effective cleaning and sanitation of all product contact surfaces, controlled airborne contamination, personal and environmental hygiene.
Pathogens in Milk | Escherichia coli
Cheese The likelihood of E. coli contamination of cheese depends largely on the quality of the milk used and the performance criteria for the process. If milk is adequately pasteurized, the risk is minimal. When raw milk or low temperature thermised milk is used, there may be some loss of viability of E. coli; however, whether they survive or grow and their presence in the final product will depend on the combined effect of subsequent processing hurdles. Therefore, raw milk cheeses may pose similar threats to health as raw milk, depending on the method of cheese processing. The health risk has to be weighed up against cheese quality benefits when making raw milk cheese. There is a diversity of cheese types and processes, each of which has control points with critical limits that have to be monitored. Use of starter cultures for rapid acidification contributes significantly to controlling pathogens; therefore, ensuring the activity of the starter culture is essential. Ensuring adequate temperature control during fermentation, cooking, and storage, and control of moisture and salt are required. In some countries, holding cheese made from raw milk for more than 60 days is required to ensure safety. This can no longer be relied on for control of some pathogenic E. coli, as O157:H7 strains have been found to survive, for example, in Cheddar cheese, beyond this time.
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of the milk or dairy mix. Growth of E. coli in ice cream and frozen dairy desserts is limited by low aw and storage temperature; however, growth of E. coli can occur if products are in the liquid state. Freezing may have little effect on the number of bacteria present; it is therefore important to maintain good hygiene and sanitation throughout manufacture. Control measures for ice cream and frozen dairy desserts include provision of raw ingredients of good microbiological quality (especially those that cannot be pasteurized), appropriate pasteurization or heat treatment, prevention of postpasteurization contamination, and storage at low temperatures. Attention to hygiene in serving frozen dairy products is important, as E. coli have been found contaminating ice cream and ice cream scoop water.
Dried and Concentrated Products The heat treatment used in the manufacture of dried and concentrated dairy products is equivalent to, if not greater than, pasteurization and is sufficient to destroy viable E. coli. Such products, due to their low aw, do not support the growth of E. coli. Prevention of postprocessing contamination is an important control measure in the manufacture of these dairy products.
Other Products Fermented Milk Products Production of fermented milk products, like cheese, relies principally on the production of organic acids from the activity of starter cultures. The resultant level of acid varies among products. Control of starter culture activity and the resultant pH is essential. This may need to be combined with other hurdles such as refrigeration in ensuring the safety of fermented products. Some strains of E. coli are capable of surviving at low pH and prevention of contamination of the product after pasteurization is essential. Fruits, nuts, and other flavorings added after pasteurization must be of high microbiological standard. Aseptic packaging of products is also important in reducing postprocessing contamination.
Ice Cream and Other Frozen Dairy Desserts In addition to milk and other dairy products, ingredients such as sugar, eggs, fruits, nuts, flavors, and colors are used in the manufacture of ice cream and other frozen dairy products. These additional ingredients may introduce E. coli contamination, especially if added after pasteurization
Butter has not been directly implicated as a source of human E. coli infections. Pasteurization of cream in the manufacture of commercial butter and the inhibitory qualities of the product ensure that it is unlikely to be a vehicle of E. coli infection. The addition of ingredients, for example, fresh herbs, may introduce contamination as described for frozen products (above). See also: Cheese: Microbiology of Cheese; Raw Milk Cheeses. Contaminants of Milk and Dairy Products: Contamination Resulting from Farm and Dairy Practices; Environmental Contaminants. Microorganisms Associated with Milk. Liquid Milk Products: Pasteurization of Liquid Milk Products: Principles, Public Health Aspects. Risk Analysis.
Further Reading Adesiyun AA, Webb LA, Romain H, and Kaminjolo JS (1997) Prevalence and characteristics of strains of Escherichia coli isolated from milk and feces of cows on dairy farms in Trinidad. Journal of Food Protection 60: 1174–1181. Arslan A, Gonulalan Z, Ates G, and Guven A (1996) Determination of Listeria, Salmonella, E. coli type 1, and K. pneumoniae in ice cream samples marketed in Elazig˘ Turkish Journal of Veterinary and Animal Sciences 20: 109–112.
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Bianchi E and Geminiani G (1994) Review on the hygienic conditions of Italian butters on the market. Industrie Alimentari 33: 833–837. Caro I and Garcia-Armesto MR (2007) Occurrence of Shiga toxinproducing Escherichia coliin a Spanish raw ewe’s milk cheese. International Journal of Food Microbiology 116: 410–413. Chye FY, Abdullah A, and Ayob MK (2004) Bacteriological quality and safety of raw milk in Malaysia. Food Microbiology 21: 535–541. Desmarchelier P and Grau FH (1997) Escherichia coli. In: Hocking AD, Arnold G, Jenson I, Newton K, and Sutherland P (eds.) Foodborne Microorganisms of Public Health Significance, 5th edn., pp. 231–263. Sydney, NSW: Australian Institute of Food Science and Technology. Gran HM, Wetlesen A, Mutukumira AN, Rukure G, and Narvhus JA (2003) Occurrence of pathogenic bacteria in raw milk cultured pasteurised milk and naturally soured milk produced at small-scale dairies in Zimbabwe. Food Control 14: 539–544. Hucker A, Mike-Schummel I, Unger A, and Varga L (2006) Evaluation of methods for detection of Escherichia coli O157 : H7 in milk, and occurrence of E. coli O157 : H7 in ex-farm raw milks in Hungary. Milchwissenschaft. Milk Science International 61: 11–14. ICMSF (1996) Microorganisms in Foods, Vol. 5: Characteristics of Microbial Pathogens. London: Blackie Academic and Professional. ICMSF (1998) Microorganisms in Foods, Vol. 6: Microbial Ecology of Food Commodities. London: Blackie Academic and Professional. Jakabi M and Franco BDGM (1991) Incidence of pathogenic Escherichia coli in foods of animal origin. Ciencia e Tecnologia de Alimentos 11: 170–181. LeJeune JT and Rajala-Schultz PJ (2009) Unpasteurized milk: A continued public health threat. Clinical Infectious Diseases 48: 93–100. Lindberg AM, Ljungh A, Ahrne S, Lofdahl S, and Molin G (1998) Enterobacteriaceae found in high numbers in fish, minced meat and pasteurised milk or cream and the presence of toxin encoding genes. International Journal of Food Microbiology 39: 11–17. Lopez MC, Medina LM, Cordoba MG, and Jordano R (1997) Evaluation of the microbiological quality of frozen yoghurt. Alimentaria 288: 39–45. Marth EH and Steele JL (2001) Applied Dairy Microbiology, 2nd edn. New York: Marcel Dekker. Murinda SE, Nguyen LT, Ivey SJ, et al. (2002) Prevalence and molecular characterization of Escherichia coli O157 : H7 in bulk tank milk and
fecal samples from cull cows: A 12-month survey of dairy farms in east Tennessee. Journal of Food Protection 65: 752–759. Murphy BP, Murphy M, Buckley JF, et al. (2005) In-line milk filter analysis: Escherichia coli O157 surveillance of milk production holdings. International Journal of Hygiene and Environmental Health 208: 407–413. Nataro JP and Kaper JB (1998) Diarrheagenic Escherichia coli. Clinical Microbiology Reviews 11: 142–201. Otenhajmer I, Mijacevic Z, and Asanin R (1989) Incidence of pathogenic Escherichia coli strains in milk and milk-products. Acta Veterinaria 39: 127–136. Pandey A, Joshi VK, Nigam P, and Soccol CR (2000) Enterobacteriaceae, coliforms and E. coli. In: Robinson RK, Batt CA, and Patel PD (eds.) Encyclopedia of Food Microbiology, Vol. 1, pp. 604–617. London: Academic Press. Quinto EJ and Cepeda A (1997) Incidence of toxigenic Escherichia coli in soft cheese made with raw or pasteurized milk. Letters in Applied Microbiology 24: 291–295. Simoni F, Baldaccini G, and Bianucci P (1983) Quality inspection for cream confectionery. Industrie Alimentari 22: 337–341. Singh RS, Ranganathan B, and Laxminarayana H (1970) International: Incidence of pathogenic Escherichia coli in milk and milk products. International Dairy Congress 1E: 148. Stephan R, Schumacher S, Corti S, Krause G, Danuser J, and Beutin L (2008) Prevalence and characteristics of Shiga toxin-producing Escherichia coli in swiss raw milk cheeses collected at producer level. Journal of Dairy Science 91: 2561–2565. Takeba K, Umeki F, Nakama A, Fujinuma K, and Kokubo Y (1996) Estimation of chemical and microbiological quality of domestic cheese (II). Annual Report of Tokyo Metropolitan Research Laboratory of Public Health 47: 82–89. Vernozy-Rozand C, Montet MP, Berardin M, Bavai C, and Beutin L (2005) Isolation and characterization of Shiga toxin-producing Escherichia coli strains from raw milk cheeses in France. Letters in Applied Microbiology 41: 235–241. Vivegnis J, El-Lioui M, Leclercq A, Lambert B, and Decallonne J (1999) Detection of Shiga-like toxin producing Escherichia coli from raw milk cheeses produced in Wallonia [Belgium]. Biotechnologie Agronomie Socie´te´ et Environnement 3: 159–164.
Enterobacteriaceae S K Anand, South Dakota State University, Brookings, SD, USA M W Griffiths, University of Guelph, Guelph, ON, Canada ª 2011 Elsevier Ltd. All rights reserved.
Introduction The family Enterobacteriaceae comprises a very large group of morphologically and physiologically similar bacteria. They are of great importance, as some of these organisms are involved in food spoilage, some are foodborne pathogens, and some are indicators of fecal contamination of food products. The genera belonging to the Enterobacteriaceae family are often associated with intestinal infections, but can be found in almost all natural habitats. They are the causative agents of such diseases as meningitis, bacillary dysentery, and typhoid. The most commonly encountered members of the Enterobacteriaceae in dairy products belong to 27 genera and include Escherichia, Salmonella, Shigella, Yersinia, Klebsiella, Enterobacter, Serratia, Citrobacter, Proteus, Edwardsiella, Erwinia, Morganella, and Providencia. Several of the genera contain species that are psychrotrophic. Typically, Enterobacteriaceae can be isolated from 6% of pasteurized milk samples, and among the predominant species are Hafnia alvei, Rahnella aquatilis, and Serratia liquefaciens.
Morphology and Physiology The Enterobacteriaceae are Gram-negative, non-sporeforming, non-acid-fast, straight rods (0.3–1.0 1.0–6.0 mm). They lack cytochrome oxidase and are referred to as oxidase negative. They are nonhalophilic facultative anaerobes, with optimal growth between 22 and 37 C. Being chemoautotrophs (i.e., able to grow on simple organic carbon and nitrogen compounds), they have both respiratory and fermentative metabolism. The base composition of the DNA is 38–60 mol% GC. An important distinguishing feature splitting the Enterobacteriaceae into two groups is the type of fermentation, either the mixed acid fermentation carried out by the Escherichia–Salmonella–Shigella group that is characterized by the production of acetate from pyruvate through acetylCoA, or the butanediol fermentation characteristic of the Erwinia–Enterobacter–Serratia group resulting in the formation of butanediol as the end product of fermentation. All members of Enterobacteriaceae ferment glucose with acid production and reduce nitrates (NO3 to NO2 or all the way to N2). Certain physiological groups of
organisms may be recognized within the family Enterobacteriaceae. The most important of these are ‘coliforms’, which ferment lactose vigorously to acid and gas at 35–37 C within 1 or 2 days. Most strains found in the genera Escherichia, Enterobacter, and Klebsiella fit the description of coliforms and are used as indicators of hygiene in food analysis. In addition, many strains of Citrobacter are also considered coliforms. Certain other enterics may ferment lactose, but minimal gas production and/or a lower temperature optimum for most of these organisms preclude them from being termed ‘coliforms’. In contrast, Salmonella and Shigella, which stand out as the major pathogens of the family, do not ferment lactose or sucrose. Therefore, inclusion of these sugars in plating media assists in their isolation, as nonfermenting colonies can be selected for further testing. Another physiological group comprises the genus Proteus and its relatives, Morganella and Providencia. These organisms often appear on plating media used for the isolation of Salmonella and Shigella and may appear nonfermenting. A distinguishing characteristic of these organisms is their possession of the enzyme phenylalanine deaminase, for which a test can be easily carried out. Many organisms in this group also hydrolyze urea rapidly. The members of Enterobacteriaceae are motile via peritrichous flagellae, with the exception of Shigella and Klebsiella, which are nonmotile. The Enterobacteriaceae also possess fimbriae (pili) and may have a capsule or slime layer. The cell wall is complex and the antigenic structure plays an important role for some species in epidemiology and classification.
Significance in Milk and Dairy Foods Although milk may be contaminated by a number of routes like bovine feces, udder infection, milking personnel, and environmental sources, the most important with respect to Enterobacteriaceae is the contamination of milk by feces, which usually occurs at milking. Even with modern milking practices, it is impossible to entirely eliminate the possibility of contamination of milk. Escherichia coli and other Enterobacteriaceae have often been used as indicators of microbial quality and hygienic processing methods.
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Milk Consumption of raw milk is considered a risk factor for enteric infections including salmonellosis. The commercial distribution of raw milk in California has led to continuing outbreaks caused by Salmonella Dublin, while, in Scotland, the introduction of mandatory pasteurization eliminated the problem of milk-borne salmonellosis. However, there have been some outbreaks of salmonellosis caused by pasteurized milk, primarily due to poor plant design and incorrect operation of the pasteurizer. The largest salmonellosis outbreak where pasteurized milk was identified as the vehicle occurred in Chicago, USA in 1985, and involved 16 284 known cases, while the actual number of people affected might have been as high as 250 000. In another study of bulk tank milk in US dairies in 2004, coliforms were detected in 95% (818 of 860) of the samples. Twenty-two samples (2.6%) were found to be culture-positive for Salmonella, and eight serotypes identified were Montevideo, Newport, Muenster, Meleagridis, Cerro, Dublin, Anatum, and 9,12: nonmotile. A study conducted in downgraded Danish bulk tank milk during 2004 also reported the presence of coliforms in 20% of the samples. Enterobacteriaceae were also found to be present in 212 (61.6%) goat’s milk samples and 45 (71.4%) ewe’s milk samples in ewe’s bulk tank milk in Switzerland. Campylobacter spp. and Salmonella spp. were not isolated from any of the samples. However, 16.3% of goat’s milk samples and 12.7% of ewe’s milk samples were polymerase chain reaction-positive for shiga toxin-producing E. coli. On the other hand, foodborne shigellosis almost invariably involves contamination by a food handler or from sewage-contaminated environmental sources such as water or soil. Thus, any dairy product that has been handled by a Shigella-infected person, and that is not to be heated directly before consumption, is a potential vehicle of foodborne shigellosis. Although Yersinia enterocolitica is well established as an enteric pathogen, the number of cases that are associated with dairy foods remain small. Milk has been responsible for at least three large outbreaks of yersiniosis in the United States. In one such outbreak, chocolate milk was involved. The organism was introduced with the chocolate syrup, which was added after the milk was pasteurized. Pasteurized milk was linked to at least two other outbreaks among hospitalized children. The general consensus is, however, that the Y. enterocolitica strains isolated from milk belong to nonpathogenic serotypes. As far as spoilage is concerned, coliforms cannot compete well at refrigeration temperatures and at a pH below 5.5, but Klebsiella, Enterobacter, Citrobacter, and Serratia do grow well in refrigerated milk and are responsible for several milk defects that include significant proteolysis
and lipolysis. These genera produce heat-stable proteases and lipases that have similar properties to those synthesized by Pseudomonas spp. Dried Milk Infant dried milk was the cause of a significant outbreak involving Salmonella Ealing in the United Kingdom during 1985. Insulation surrounding the drying chamber was found to be the source of contamination. A similar outbreak, involving infant formula, was reported in Australia, where the causative agent was Salmonella Bredeney. A survey conducted following these events suggested that Salmonella contamination in the environment of spray-drying plants was common. Enterobacter sakazakii has been implicated in a rare but severe form of neonatal meningitis, with dried infant formula being implicated as the mode of transmission. The high mortality rate (40–80%) and the lack of information about this organism led to a study of the heat resistance of E. sakazakii in reconstituted dried infant formula. Enterobacter sakazakii strains (five clinical and five food isolates) were used to determine the heat resistance of this organism at 52, 54, 56, 58, and 60 C in reconstituted dried infant formula and D-values of 54.8, 23.7, 10.3, 4.2, and 2.5 min were obtained for each temperature, respectively. The overall calculated z-value was 5.82 C. In a comparison of the D-values of several members of the Enterobacteriaceae in dairy products, E. sakazakii was among the most thermotolerant organisms. Cheese Salmonella is normally destroyed or inactivated during fermentation of high-acid products (lactic acid c. 1%, pH value less than 4.55) such as yogurt and soft cheese. The degree of inactivation, however, was found to be less in cheese due to protection provided by casein and possibly fat. Also, Salmonella may grow in the curd of low-acid cheese (pH value greater than 4.95). As a small number of salmonellae may persist for significant periods, the practice of aging of raw milk cheese for 60 days at not less than 4.4 C would not be an effective control measure. Although cheese-borne salmonellosis is often associated with raw milk cheese, a large outbreak that occurred in Canada in 1984 was attributed to improper pasteurization. An estimated 10 000 people were affected, and the causative serovar was identified as Salmonella Typhimurium PT10. Similarly, Citrobacter freundii in Camembert cheese was suspected in a diarrhea outbreak in Washington. In addition to being potential pathogens, Enterobacteriaceae can cause spoilage of low-acid cheeses. Enterobacter spp. have been shown to be involved in slimy curd spoilage of Cottage cheese and Enterobacter aerogenes is able to oxidize
Pathogens in Milk | Enterobacteriaceae
diacetyl to acetoin, a flavorless compound. This results in a cheese with a flat, bland taste. A number of amines, such as tyramine and histamine, formed by members of the Enterobacteriaceae are toxic to humans. Cheeses, especially Swiss cheeses, can contain these biogenic amines. Amines were determined in the Emmental cheese milk, in cheese before brining, in cheese ripened for up to 49 days, and in cheese blocks or grated cheese stored for up to 5 months at 5 or 15 C. Amine concentrations increased throughout cheesemaking, ripening, and storage. Histamine and tyramine dominated up to the end of ripening, and the concentration of putrescine and cadaverine increased during storage. Amine formation increased at higher storage temperatures, and was higher in grated than in intact cheese. Formation of biogenic amines in Emmental cheese was strongly influenced by the microflora, with high counts of Enterobacteriaceae being associated with high concentrations of putrescine and cadaverine.
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fermenter of lactose, while Shigella, Salmonella, and Yersinia are nonfermenters. Several commercial media, including ready-to-use petrifilms manufactured by 3M, are available for the detection of Enterobacteriaceae, and the International Dairy Federation has approved standard methods for their enumeration. Several tests relying on the detection of -glucuronidase are also approved for the detection of E. coli, although not the enterohemorrhagic serovars. A hydrophobic grid membrane filtration (HGMF) method for the enumeration of coliforms has also gained the status of an official method. All Enterobacteriaceae isolates are identified biochemically using systems like API 20E manufactured by bioMe´rieux. Important serotypes can also be differentiated by their O (lipopolysaccharide), H (flagellar), and K (capsular) antigens.
Sources Other Milk Products Enterobacteriaceae infections have been occasionally associated with other dairy products like ice cream. In addition, cream-filled pastries are also known to constitute a foodborne disease problem. In a survey of 439 outbreaks in the United States associated with milk products, about 12.5% were attributed to Salmonella. Similarly, caprine raw colostrums were also found to be positive for Enterobacteriaceae. A study conducted during the milk fermentation and preparation of buffalo’s milk yogurt revealed that S. enterica Typhimurium PT8 had longer generation times in mixed cultures. Lactobacillus bulgaricus or its combination with Streptococcus thermophilus was found to be more inhibitory to the growth and survival of Salmonella than Str. thermophilus alone. In a recent study, E. coli 0157:H7 was found to survive in different yogurt products like yogurt drink, plain yogurt, and salted yogurt (yogurt native to Hatay, Turkey) at both 4 and 22 C. At least 2.13 log cfu g 1 of Enterobacteriaceae was reported in ‘Kurut’, a dairy product obtained by drying yogurt under the sun in rural areas of Turkey. Similarly, Klebsiella, Escherichia, and Enterobacter were found to be predominant among Enterobacteriaceae in Ethiopian traditional dairy products that included milk, butter, buttermilk, naturally fermented milks, and Cottage cheese.
Enumeration Enterobacteriaceae are often isolated from fecal matter on agar containing lactose and a pH indicator. Colonies that ferment lactose would produce sufficient acid to cause a color shift in the indicator. For example, E. coli is a
Due to problems caused by recontamination of pasteurized milk with Gram-negative psychrotrophs, critical contamination sites for psychrotrophic Enterobacteriaceae were investigated. Milk samples were collected in three dairy plants at the silo tank; just before and just after the pasteurizer; from the buffer tank of pasteurized milk; just before the filling machine; and as filled and sealed consumer packages. There was a relatively high frequency of recontamination of refrigerated milk with psychrotrophic bacteria. Gram-negative bacteria were isolated from 40% of 87 packages, with pseudomonads being isolated from all contaminated packs, and Enterobacteriaceae from 9%. Recontamination occurred mainly during filling procedures, and it is considered that efforts to improve hygiene should be concentrated in this area.
Control The vast majority of milk consumed in developed nations is cow’s milk, although goat’s milk is increasing in popularity in the United Kingdom and significant quantities of sheep’s milk are consumed in Australia. In developing countries, sheep and goat may be of greater importance than cattle as sources of milk, while other sources of milk are buffalo, camels, and mares. The chemical composition of milk of different species varies considerably, but although this affects the organoleptic properties and, possibly, the development of the spoilage microflora, there is no evidence that the survival or growth of pathogenic microorganisms is significantly affected, except in camel milk. Hazards from Enterobacteriaceae can be prevented by heating milk sufficiently to kill the bacteria, holding
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chilled milk and dairy products below 4.4 C (40 F), preventing postpasteurization cross-contamination, and prohibiting people who are ill from working in dairy food operations. The infective dose of virulent members of Enterobacteriaceae is dependent upon the particular strain, and it varies from only a few organisms to millions. For this reason, time/temperature abuse of food products may or may not result in illness. Pasteurization is an essential process in providing milk that is free of hazardous microorganisms. Alternatively, ultra-high temperature (UHT) treatment wherein a temperature of 132 C for not less than 1 s is employed is another popular process that has a good safety record. The microbiological problems in UHT milk are usually restricted to spoilage due to the heat-stable proteolytic enzymes alone. The same is true for milk products like cream and butter as well. Thermal stress (curd cooking at 55 C) during the production of Grana cheese was found to be only partially effective in the control of selected pathogens including E. coli 0157:H7 and Salmonella Typhimurium. Similarly, differences in pH values due to temperature-dependent whey retention accounted for the effect of cooking temperature on coliforms and fecal coliform counts during the manufacture and ripening of Manchego cheese prepared from ewe’s milk. Although brine-salting had no effect on Enterobacteriaceae counts, a significant effect of salting time on Enterobacteriaceae and fecal coliform counts was detected. In addition to this, ripening temperature was the most important manufacturing variable with greatest influence on Enterobacteriaceae and fecal coliform counts during the whole curing period. In concentrated milk preparation, the milk is heated to a high temperature prior to entry into the evaporator and this, together with operating temperatures in the first stages of the evaporator, would kill any vegetative pathogens present. Furthermore, the higher sugar levels in condensed milk lead to lowering of water activity, thereby preventing the growth of pathogenic organisms. Dried milk may be made by either the roller process or the spray process. Due to the extensive heat treatment, the products generally do not pose any threat from the presence of Enterobacteriaceae in such products. In Caprine colostrums, heat (56 C for 60 min and 63 C for 30 min) and high pressure (400 and 500 MPa for 10 min at 20 C) were found to significantly reduce Enterobacteriaceae. In addition to this, in the case of fermented milk products like hard and soft cheeses, yogurt, and several intermediate products, the heat treatment of milk and the controlled fermentation are important to prevent the growth of Enterobacteriaceae. Even in traditionally made yogurt and some unripened soft cheeses, the high acidity of the final product is sufficient to inactivate many pathogens including members of the Enterobacteriaceae.
Moreover, these pathogenic contaminants are unable to grow in hard cheeses during ripening, and conditions of storage are intended to maximize the inactivation of any pathogen present. In the case of Ragusano cheese, presalting of curd (with 2% added salt) before stretching reduced the coliform counts in cheese by 1.41 log and also resulted in major reduction in early gas formation. Another approach is the addition of bacteriocin-producing adjunct cultures during cheesemaking that can help in inhibiting Enterobacteriaceae. Prevention of recontamination is, however, the key factor in the safety of such products.
See also: Cheese: Mechanization of Cheesemaking. Enzymes Indigenous to Milk: Plasmin System in Milk. Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity. Stress in Dairy Animals: Heat Stress: Effects on Milk Production and Composition.
Further Reading AOAC (1985) Official first action hydrophobic grid membrane filter method for detecting total coliforms, faecal coliforms and E. coli in foods. Journal of Association of Official Analytical Chemists 68: 481. Akdermrevrendlek G (2007) Survival of Escherichia coli 0157:H7 in yogurt drink, plain yogurt and salted (tuzlu) yogurt: Effects of storage time, temperature, background flora and product characteristics. International Journal of Dairy Technology 60: 118–122. Barrett NJ (1986) Communicable diseases associated with milk and dairy products in England and Wales: 1983–1984. Journal of Infection 12: 265–272. Black RG, Jackson RJ, and Tsai M (1978) Epidemic Yersinia enterocolitica infection due to contaminated chocolate milk. The New England Journal of Medicine 298: 76–79. Bryan FL (1976) Public health aspects of cream filled pasteries. A review. Journal of Milk and Food Technology 39: 289–296. Chapman H and Sharpe ME (1981) Microbiology of cheese. In: Robinson RK (ed.) Dairy Microbiology, Vol. 2: The Microbiology of Milk and Milk Products. Essex, England: Applied Science Publishers. D’Aoust JY, Emmary DB, McKellar R, et al. (1987) Thermal inactivation of Salmonella species in fluid milk. Journal of Food Protection 50: 494–501. Ercolini D, Fusco V, Blaiotta G, Sarghini F, and Coppola S (2005) Response of Escherichia coli 0157:H7, Listeria monocytogenes, Salmonella Typhimurium, and Staphylococcus aureus to the thermal stress occurring in model manufactures of Grana Padano cheese. Journal of Dairy Science 88: 3818–3825. Holm C, Jepsen L, Larsen M, and Jespersen L (2004) Predominant microflora of downgraded Danish bulk tank milk. Journal of Dairy Science 87: 1151–1157. Hutchison ML, Thomas DJ, Moore A, Jackson DR, and Ohnstad I (2005) An evaluation of raw milk microorganisms as markers of on-farm hygiene practices related to milk. Journal of Food Protection 68: 764–772. ICMSF (1989) Microorganisms in Foods. Oxford: Blackwell Scientific Publications. Jay JM (2000) Modern Food Microbiology, 6th edn. Gaithersburg, MD: Aspen Publishers. Juven BJ, Gordin S, Rosenthal I, and Laufer A (1981) Changes in refrigerated milk caused by Enterobacteriaceae. Journal of Dairy Science 64: 1781–1784. Kessel V, Karns JS, Gorski L, McCluskey BJ, and Perdue ML (2004) Prevalence of salmonellae, Listeria monocytogenes, and fecal
Pathogens in Milk | Enterobacteriaceae coliforms in bulk tank milk on US dairies. Journal of Dairy Science 87: 2822–2830. Marshall RT (ed.) (1992) Standard Methods for the Examination of Dairy Products, 16th edn. Washington, DC: American Public Health Association. Marth EH and Steele JL (2001) Applied Dairy Microbiology, 2nd edn. New York: Marcel Dekker. Melilli C, Barbano DM, Caccamo M, Calvo MA, Schembari G, and Licitra G (2004) Influence of brine concentration, brine temperature, and presalting on early gas defects in raw milk pasta filata cheese. Journal of Dairy Science 87: 3648–3657. Mossel DA and Struijk CB (1995) Escherichia coli, other Enterobacteriaceae and additional indicators as markers of microbiologic quality of food: Advantages and limitations. Microbiologia 11: 75–90. Muehlherr JE, Zweifel C, Corti S, Blanco JE, and Stephan R (2003) Microbiological quality of raw goat’s and ewe’s bulk tank milk in Switzerland. Journal of Dairy Science 86: 3849–3856. Munez M, Gaya P, and Medina M (1985) Influence of manufacturing and ripening conditions on the survival of Enterobacteriaceae in Manchego cheese. Journal of Dairy Science 68: 794–800. Nassib TA, El-Din MZ, and El-Sharoud WM (2006) Effect of thermophilic lactic acid bacteria on the viability of Salmonella serovar Typhimurium PT8 during milk fermentation and preparation of buffalo’s yogurt. International Journal of Dairy Technology 59: 29–34. Pintado AIE, Pinho O, Ferriera IMPLVO, Pintado MME, Gomes AMP, and Malcata FX (2008) Microbiological, biochemical and biogenic
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amine profiles of Terrincho cheese manufactured in several dairy farms. International Dairy Journal 18: 631–640. Ratnam S and Marsh SB (1986) Laboratory studies on Salmonellacontaminated cheese involved in a major outbreak of gastroenteritis. Journal of Applied Bacteriology 61: 51–56. Ray B (1996) Fundamental Food Microbiology. Boca Raton, FL: CRC Press, Inc. Robinson RK and Tamime AY (1981) Microbiology of fermented milks. In: Robinson RK (ed.) Dairy Microbiology, Vol. 2: The Microbiology of Milk and Milk Products. Englewood, NJ: Applied Science Publishers. Rodriguez E, Calzada J, Arques JL, Rodriguez JM, Nunez M, and Medina M (2005) Antimicrobial activity of pediocin-producing Lactococcus lactis on Listeria monocytogenes, Staphylococcus aureus, and Escherichia coli O157:H7 in cheese. International Dairy Journal 15: 51–57. Rubin HE (1985) Protective effect of casein towards Salmonella typhimurium in acid milk. Journal of Applied Bacteriology 58: 251–255. Smith JL (1987) Shigella as a foodborne pathogen. Journal of Food Protection 48: 887–894. Ufuk K (2008) The manufacture and some quality characteristics of Kurut, a dried dairy product. International Journal of Dairy Technology 61: 146–150. Zelalem Y, Bernard F, and Gerard L (2007) Occurrence and distribution of species of Enterobacteriaceae in selected Ethiopian traditional dairy products: A contribution to epidemiology. Food Control 18: 1397–1404.
Enterobacter spp. S Cooney, C Iversen, B Healy, S O’Brien, and S Fanning, University College Dublin, Dublin, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Enterobacter species are widely dispersed in nature and exist in a diverse range of environments such as soil, water, households, food processing establishments, vegetation, and vertebrate and invertebrate hosts. Enterobacter are also increasingly recognized as potential human pathogens, especially as agents of nosocomial infections in the clinical environment. Currently, only Enterobacter sakazakii (Cronobacter) are considered foodborne pathogens and have been associated with cases of bacteremia, meningitis, and necrotizing enterocolitis (NEC) in infants. Powdered infant formula (PIF) has been identified as a major route of infection, and therefore these organisms are of particular concern to manufacturers of formula milk powders and milk derivatives that supply this industry.
Enterobacter sakazakii, which was previously referred to as ‘yellow-pigmented E. cloacae’, has now been recognized as a group of multiple genomospecies and a novel genus, Cronobacter, has been proposed. Cronobacter consists of C. sakazakii, C. dublinensis, C. malonaticus, C. muytjensii, C. turicensis, and the as yet unnamed Cronobacter genomospecies 1. The genus Cronobacter is contaxic (synonymous) with E. sakazakii, and these organisms are known to cause serious invasive disease and are recognized as a particular problem for infection in neonates and, to a lesser extent, in older infants and immunocompromised adults. Neonatal infections have been epidemiologically linked to consumption of contaminated reconstituted PIF in neonatal intensive care units (NICUS).
Physiology Growth
Classification The genus Enterobacter comprises a heterogeneous group of organisms in the Enterobacteriaceae family. They are Gram-negative, generally motile, oxidase-negative, nonsporing, flagellated, rod-shaped, facultative anaerobes. The genus Enterobacter was derived from members of the genus Aerobacter in 1960 when the motile and ornithine decarboxylase (ODC)-positive strains were separated as Enterobacter from the nonmotile and ODC-negative Klebsiella strains. Originally genera and species were defined based on phenotypic characteristics. The development of techniques such as DNA–DNA hybridization and nucleic acid sequence analysis has enabled the measurement of evolutionary distances and made it possible to determine more accurately the relationships between organisms. This has led to the proposed reclassification of several Enterobacter species and the transfer of E. intermedius to the genus Kluyvera as K. intermedia, E. agglomerans to the genus Pantoea, and E. sakazakii to the genus Cronobacter (Table 1). Species closely related to E. cloacae, such as E. dissolvens, E. asburiae, E. hormaechei, E. kobei, E. ludwigii, and E. nimipressuralis, are often referred to as belonging to the ‘Enterobacter cloacae complex’. All species within this complex are of clinical significance and are increasingly being implicated in cases of hospitalacquired infections. However no link has been established between ingestion of contaminated food and infection due to these species.
72
Enterobacter spp. generally grow well, aerobically and anaerobically, between 20 and 37 C on nonselective laboratory media at neutral pH. The growth ranges of different species vary; Cronobacter can grow between 6 and 47 C with a pH range of 4.5–10 at 37 C. Most Enterobacter strains will grow and produce typical colonies on selective media for Enterobacteriaceae, such as Violet Red Bile Agar (containing glucose or lactose) and Hektoen or MacConkey agar. Some strains of Enterobacter/Cronobacter are reported to be unusually sensitive to antimicrobial agents commonly used in Enterobacteriaceae selective media, including antibiotics, brilliant green, crystal violet, bile salts, and sodium lauryl sulfate. Cronobacter are the only species for which specific isolation media have been developed.
Resistance Water Activity In general Enterobacter are not considered particularly resistant to low-water activity (aw) environments. However, Cronobacter are noted for their ability to survive during desiccation and their persistence in dried formula for 1–2 years. High concentrations of osmolytes and humectants have been proposed as selective strategies. Cronobacter strains can grow in media containing up to 7% sodium chloride or 20% sucrose.
Pathogens in Milk | Enterobacter spp. 73 Table 1 Nomenclature of Enterobacter spp. and relevance to foodborne disease Enterobacter species
Taxonomic note
Clinical source
Food/environment sources
E. aerogenes E. agglomerans
Klebsiella mobilis Pantoea agglomeransa Biogroup 1 Biogroup 2 (Enteric group 17) E. taylorae Subsp. cloacae Subsp. dissolvens
All sites All sites
Ubiquitous (dairy) Ubiquitous (dried food, PIF)
B, F, R, W AT, B, BF, F, L, R, U, W AT, B, CSF, F, O, R, U, W All sites
Milk, cream, Spanish pork sausage, plants (sugar beets) Farm machinery, water, cucumber Trees, water, food Ubiquitous (meat, dairy, infant food)
B, P, SM, R, U, W A, AS, B, S
Food Ubiquitous (plants)
AT, B, R, U, W B, CSF, R, SM, W BE, B, G, F, W A, B, R, F, U B, R, S, F, U B, CSF B, CSF
Water, cosmetics Infant food, fruit powder Unknown (frog) Water, soil Food Trees, plants Wild rice Trees, plants Trees, plants Plants Fruit powder, infant food Ubiquitous (dried food, PIF, grains, cut meat) Fruit powder
E. amnigenus E. asburiaeb E. cancerogenous E. cloacaeb E. cowanii E. dissolvens b E. gergoviae E. helveticus E. hormaechei b E. intermedius E. kobei b E. ludwigii b E. oryzae E. nimipressuralis E. pyrinus E. radicincitans E. pulveris E. sakazakii c
E. cloacae subsp. dissolvens
Enteric group 75 Kluyvera intermediaa
Cronobacter – 6 speciesa
E. turicensis
A, AS, AT, B, CSF, F, O, R, S, SM, U, W -
a
Current taxonomy. Enterobacter cloacae complex. c Known to cause illness through ingestion of contaminated food. - , no known clinical isolates; A, abdomen; AS, abscess; AT, anatomic tissue; B, blood; BE, bile; BF, body fluids; CSF, cerebrospinal fluid; F, feces; G, gallbladder; L, lochia; N, nose; O, bone; P, pus; R, respiratory tract; S, skin; SM, sputum; U, urine; W, wound. b
pH Cronobacter is classified as a moderately resistant member of the Enterobacteriaceae that can withstand transitory exposure to a pH of 3.0. It can survive for extended periods of time (>5 h) at a pH of 3.5.
agents within the hospital setting has led to the development of resistance to many -lactam antibiotics via extendedspectrum -lactamases (ESBLs), with 25% of Enterobacter spp. being resistant to extended-spectrum cephalosporins. Cronobacter is notably more sensitive to antibiotics than other Enterobacter species.
Thermal Inactivation Enterobacter do not survive pasteurization; however, there is a great diversity of thermotolerance among strains. Use of water at 70 C has been recommended for reconstitution of powdered formula to inactivate possible Cronobacter/Enterobacter contaminants. Antibiotic Susceptibility Enterobacter species are naturally susceptible to a range of antibiotics. Enterobacter hormaechei is the species most susceptible to fosfomycin. Natural antibiotic resistance in Enterobacter spp. is similar to that of other Enterobacteriaceae. High-level cefoxitin resistance is also seen in species of the E. cloacae complex. Increasing prevalence of antibiotic resistance among Enterobacter spp. is an emerging problem worldwide. An increase in the use of antimicrobial
Prevalence and Distribution Environment and Host Reservoirs Enterobacter are ubiquitous in the environment, and E. cancerogenous, E. cloacae, E. asburiae, and Cronobacter have been isolated from environmental and domestic water sources. Plants (including crops and trees), soil, and the microbial rhizosphere can harbor Enterobacter spp. They can be recovered from vertebrate and invertebrate hosts, and species of the E. cloacae complex can routinely be found in the feces of humans and animals. Although there are a few reports of Cronobacter isolates from fecal samples of asymptomatic colonized individuals, these organisms are not recognized as normal inhabitants of the human gut. In a farm environment, Cronobacter have been found in dried pellets of animal feed but not in cattle
74
Pathogens in Milk | Enterobacter spp.
feces. Cronobacter strains were previously tested in a model of a bovine gut to establish whether they can survive a bovine digestive system. No survival of strains was recorded, which indicates that cattle may not be an important vector in the transmission of Cronobacter.
contaminants in dry raw ingredients, via inefficient air filtration, water leaks, and human carriage. The majority of factory environment samples contaminated with Cronobacter appear to be found around spray dryer towers; this may be related to the relatively high desiccation resistance of Cronobacter as compared to other Enterobacteriaceae.
Food Contamination Enterobacter species can be found on a wide range of foods. These include fresh, frozen, or powdered fruits and vegetables, legume products, tea, herbs, spices, animal feed (dried pellets), grains, nuts, seeds, flour, pasta, chocolate, beverages, and water. Other food sources include meat, fish, eggs, dairy products, and PIF. Enterobacter cloacae is a recognized contaminant of raw milk and dairy produce such as yogurt and cheese. Although they do not survive pasteurization, Enterobacter have been found in pasteurized milk and cream and in dried dairy products, possibly due to postprocess contamination. PIF is used as an alternative to breast milk to provide nutritional requirements in addition to breast-feeding or where breast-feeding is not feasible. While ready-to-use liquid formula is marketed as sterile, the powdered form (including dried bovine milk and milk products) often contains bacterial spores and may contain low levels of pathogenic microorganisms. The most frequently isolated Enterobacteriaceae species from powdered milk products are E. cloacae, Cronobacter, E. agglomerans (Pantoea), E. pulveris, E. helveticus, and Klebsiella pneumoniae. Currently the recovery of Cronobacter from PIF is reported to be at approximately 2% of commercially available packages, and illness is reported to be at approximately six incidents per year. Therefore, the vast majority of contaminated formula consumed does not result in infection and the organisms have relatively low pathogenicity. Investigation of potential contamination routes in infant formula factories has indicated that raw milk and liquid ingredients are probably not the primary hazard. A diverse range of Enterobacteriaceae enter as
Foodborne Outbreaks The earliest report of Cronobacter contamination in powdered milk was in 1950. The first case of neonatal illness attributed to Cronobacter occurred in London in 1958. The link between neonatal illness and PIF was first proposed in 1983. A number of outbreaks in NICUs have been epidemiologically linked to consumption of contaminated food, particularly reconstituted infant formula (Table 2). In Iceland (1986), three neonatal cases shared identical biotypes, plasmid DNA profiles, and antibiograms with strains isolated from infant formula. In Belgium (1998), arbitrarily primed PCR typing partially confirmed strain similarity between isolates from milk and those from patients in an outbreak of necrotizing entercolitis. In the United States (2001), pulsed-field gel electrophoresis (PFGE) showed that Cronobacter isolates from opened and unopened containers of a nutritional supplement were indistinguishable from the isolate obtained from a neonate with meningitis. Finally, in France (2004), cases occurring in five hospitals were linked to the use of a hypoallergenic formula, which was subsequently recalled by the manufacturer. Investigation revealed failures in hospital practices with regard to the preparation, handling, and storage of feeding bottles. In some instances no direct link has been made to batches of PIF. In these cases extrinsic contamination of prepared formula and horizontal transmission from other infected/colonized hosts are the possible causes of infection. Multiple strains of Cronobacter have simultaneously been isolated from the
Table 2 Clinical cases caused by Enterobacter linked to milk
Region
Countries
Africa Asia
Ethiopia China, India, Israel, Korea, Singapore, Thailand Belgium, Czechoslovakia, Denmark, England, France, Germany, Greece, Iceland, Italy, Netherlands, Portugal, Scotland, Spain, Switzerland Canada, Mexico, USA New Zealand Worldwide
Europe
North America Oceania Total NS, not stated.
Cases (deaths)
Milk product suspected
Children (deaths)
Adult (deaths)
NS 13 (2)
NS 5
NS 9 (1)
0 4 (1)
85 (24)
54
76 (24)
9
39 (6) 5 (1) 142 (33)
16 55 (1) 80
33 (3) 0 123 (29)
6 (3) 19 (4)
Pathogens in Milk | Enterobacter spp. 75
same food containers, or single infected children, further complicating the epidemiology.
Clinical Relevance Enterobacter spp. are increasingly recognized as opportunistic pathogens in a wide variety of settings and rarely cause disease in healthy individuals. They are common contaminants of hospital surfaces, medical supplements, catheters, and other medical and feeding equipment, as well as medical staff. In general, Enterobacter organisms are responsible for around 50% of nosocomial infections, mostly in immunocompromised patients, and can affect people of all ages. Community-acquired infections can occur through open wounds or severe crush injuries. Enterobacter aerogenes and the E. cloacae complex are the most frequently encountered Enterobacter species in clinical samples. Immunocompromised individuals are at particular risk of acquiring infection. Enterobacter cloacae, along with E. aerogenes, E. hormaechei, E. gergoviae, and Cronobacter, has been associated with infections in neonates. Risk factors in neonates include premature birth and low birth weight. Infants of normal gestational age and birth weight infected during the first month postpartum are more likely to develop meningitis, with high case fatality rates as compared to premature, low-birth-weight infants, who usually develop later onset of infections resulting in bacteremia. This may be due to sterile, parenteral initial feeding and administration of prophylactic antibiotics prior to exposure to contaminated nutritional products. Cronobacter infections are uncommon in adults and mainly comprise cases of wound infection, bacteremia, and aspiration pneumonia in elderly patients. Necrotizing Enterocolitis NEC is an inflammatory process of the small and large intestine. This condition is one of the most common causes of death in NICUs and the most relevant acquired intestinal complication during the neonatal period. NEC has an incidence of 2–5% in all preterm infants and up to 13% in those with low birth weight. The reported case fatality rates range between 0 and 20% in infants weighing >2500 g and between 10 and 55% in low-birthweight infants (<1500 g). Initial symptoms include feeding intolerance, delayed gastric emptying, abdominal distension and/or tenderness, decreased bowel sounds, and bloody stools. NEC has no definitive known cause, and research suggests involvement of a combination of factors leading to intestinal damage, including intestinal mucosal immaturity/dysfunction, ischemia and/or reperfusion injury, the release of inflammatory mediators and bile acids, and downregulation of cellular growth factors. Empirical antibiotic use and intestinal
bacteria are thought to be associated factors, though no common infectious agent has been identified. Decreased levels of bactericidal/permeability-increasing protein (BPI), particularly in premature low-birth-weight neonates, may be significant in cases where bacterial invasion is a contributing factor. BPI binds to lipopolysaccharides produced by Gram-negative organisms neutralizing the endotoxin and reducing intestinal wall disruption. NEC is rarely seen in infants prior to initiation of oral feeding. The use of infant formula as opposed to breast milk greatly increases the risk of NEC. Infant formula contaminated with Cronobacter has been associated with outbreaks of NEC. Bloodstream Infections Bacteremia is the presence of viable bacteria in the bloodstream, whether associated with active disease or not. When associated with the release of bacterial toxins into the circulation, bacteremia can elicit a vigorous immune response resulting in systemic inflammatory response syndrome. This is characterized by rapid breathing, low blood pressure, and fever, which may lead to multiple organ failure (septic shock). Enterobacter cause 3–9% of all bloodstream infections and up to 15% of bacteremia in the elderly. Case fatality rates for Enterobacter sepsis range from 20 to 50%. Enterobacter cloacae, followed by E. aerogenes, is the species most frequently isolated in Enterobacter bacteremia and is responsible for over 90% of all cases. Enterobacter asburiae, E. cancerogenous, E. amnigenus, and Cronobacter have also been reported to cause bacteremia in adults. Enterobacter are estimated to account for up to 8.7% of all bacteremia and approximately 20% of Gram-negative sepsis cases in children, with case fatality rates of 6–20%. Most infections are nosocomially acquired, with molecular fingerprint epidemiology suggesting that horizontal transmission plays a significant role. Risk factors associated with Enterobacter sepsis in children include parenteral nutrition and use of antibiotics and catheters. As with adults, E. cloacae and E. aerogenes are responsible for over 90% of cases. However, Cronobacter are notable for their association with cases in neonates and links to ingestion of contaminated infant food. Enterobacter hormaechei and E. gergoviae have also been responsible for outbreaks in NICUS. Central Nervous System Infections Enterobacter are rare aetiological agents of central nervous system (CNS) disease. Bacterial meningitis is a serious and frequently fatal infection of the protective membranes covering the brain and spinal cord. Infections can increase inner cranial pressure, requiring aspiration of fluid and drainage of cerebral infarction to prevent cerebral damage. Meningitis can lead to long-term
76
Pathogens in Milk | Enterobacter spp.
complications in survivors, including mental and motor disabilities, convulsive disorders, hydrocephalus, and deafness. Common symptoms include headache, neck stiffness, fever, confusion/delirium, vomiting, and photophobia. These symptoms may not be obvious in young children, who may present with irritability and lethargy. Enterobacter spp. are estimated to cause 2.4–4.5% of meningitis cases in adults and up to 10.4% of cases in children. In adults the main species implicated are E. cloacae and E. aerogenes with a case fatality rate of 16–20%. However, in children Cronobacter are the most frequently reported species with case fatality rates of up to 80%. Ingestion of contaminated infant formula has been implicated in several outbreaks. Low birth weight, prematurity, length of hospital stay, invasive procedures, and overuse of antibiotics put infants at an increased risk. Patients with Cronobacter neonatal meningitis may suffer more severe outcomes than those with meningitis attributed to E. cloacae and other Gram-negative bacteria. Cronobacter causes cystic changes, abscesses, fluid collection, dilated ventricles, and infarctions. Cases of Cronobacter meningitis have been reported in children between the ages of 3 days and 4 years, with half of the cases occurring in the first week after birth and almost three-quarter during the first month. A retrospective study of 46 infants with Cronobacter infections indicated that meningitis was more prevalent in infants of normal gestational age and birth weight, with the onset of disease usually occurring within the first week following birth. In contrast, low-birth-weight, premature infants were more likely to develop bacteremia with no progression to CNS disease, and the age of onset was usually over 1 month. It is probable that Cronobacter has a developmental dependence on access to the CNS. Other Infections Enterobacter species cause up to 5% of nosocomial pneumonias, being a significant cause of ventilatorassociated and early post-lung transplant pneumonia. They are also associated with other lower respiratory tract infections. Case fatality rates are particularly high in elderly patients. Enterobacter skin and soft-tissue infections include cellulitis, fasciitis, myositis, abscesses, and wound infections (including burns and crush injuries). Enterobacter species can infect wounds in any body site. Most are nosocomially acquired, with surgical complications and cephalosporin prophylaxis being associated with increased risk of infection. Enterobacter species that colonize the digestive tract may be isolated from intraabdominal sites following intestinal perforation or surgery and are responsible for approximately 10% of postsurgical peritonitis cases. A few examples of endocarditis due to Enterobacter have been reported. In most cases there was underlying cardiac disease,
particularly mitral valve infection. Enterobacter cause up to 4% of nosocomial urinary tract infections (UTIs), usually associated with urinary catheters and/ or prior antibiotic therapy. They are also occasionally associated with osteomyelitis and septic arthritis in adults and children. Enterobacter bone and joint infections can be difficult to cure, with relapses requiring additional treatment.
Isolation, Identification, and Subtyping Detection Methods There are no microbiological media specifically designed for the genus Enterobacter. These organisms grow well on nonselective laboratory media and can be easily cultured from clinical samples. All Enterobacter species ferment glucose, and the majority ferment sucrose (except E. cancerogenous) and lactose (except E. cancerogenous and E. hormaechei). Therefore most Enterobacter isolates will appear as typical Enterobacteriaceae colonies on selective media for this family, such as Violet Red Bile, MacConkey, or Hektoen Enteric agars. Enterobacter are not generally considered foodborne pathogens but contribute to the overall microbial presence in foods and, as members of the Enterobacteriaceae, are relevant as hygiene indicators in food production processes. The process hygiene criteria for pasteurized milk, milk/whey powder, and dried infant formula allow only very low levels of Enterobacteriaceae (less than 5 cfu ml1, and 10 and 0.01 cfu g1, respectively). The EC regulation for the detection of Enterobacteriaceae refers to ISO 21528-1:2004, which entails preenrichment in buffered peptone water (BPW), followed by selective enrichment in Enterobacteriaceae enrichment (EE) broth, streaking on Violet Red Bile Glucose (VRBG) agar, and confirmation of typical colonies based on negative oxidase activity and positive glucose fermentation. Owing to their status as neonatal pathogens associated with infant formula, specific isolation methods have been developed for Cronobacter. Initially these were based on ISO 21528-1:2004 mentioned above, followed by culturing of Enterobacteriaceae isolates on nonselective media at a low temperature (25 C) and biochemical confirmation of yellow-pigmented colonies. In recent years various fluorogenic and chromogenic media have been developed for the detection of Cronobacter. These are mainly based on detection of the enzyme -glucosidase, which is constitutively expressed in Cronobacter spp. However, E. helveticus, E. pulveris, and E. turicensis, which can be found in the same ecological niches as Cronobacter (including dried food products and factory environments), can also produce presumptive colonies on these agars.
Pathogens in Milk | Enterobacter spp. 77
There is currently an ISO technical specification for the detection of Cronobacter in milk-based infant formula (ISO/TS 22964:2006). This entails preenrichment in BPW and selective enrichment in a modified lauryl sulfate tryptose (mLST) broth (incorporating 0.5 mol l1 NaCl and 10 mg ml1 vancomycin hydrochloride), followed by streaking on a chromogenic agar. It has been reported that some Cronobacter strains do not grow well in selective media commonly used for Gram-negative organisms, and a differential method, incorporating Cronobacter screening broth (10 g l1 peptone, 3 g l–1 meat extract, 5 g l1 NaCl, 0.04 g l1 bromocresol purple, 10 g l1 sucrose, and 10 mg l1 vancomycin hydrochloride) in place of mLST, has been proposed for the EN ISO horizontal standard currently in development. Carbohydrate fermentation results in a color change from purple to yellow, and only positive (yellow) broths are streaked onto chromogenic media. The US Food and Drug Administration (USFDA) proposes a method involving preenrichment, centrifugation, plating on two chromogenic agars (one containing a chromogenic -D-cellobioside in addition to -D-glucopyranoside), and a real-time PCR assay based on the dnaG gene, which is a component of the macromolecular synthesis (MMS) operon. Alternative methods for the detection of Cronobacter include the MATRIX PSAK50 cationic paramagnetic particle capture technique and enzyme-linked immunoassays (Assurance and TECRA HELIX). Genetic-based assays include the BAX and foodproof Enterobacteriaceae plus E. sakazakii detection systems. The latter simultaneously qualitatively detect Enterobacteriaceae DNA and the presence of Cronobacter. Both DNA-FISH (Vermicon) and PNA-FISH techniques have been developed for the detection of viable Cronobacter cells in infant formula.
some biochemical confirmation galleries such as API 20 E has been questioned as species of the E. cloacae complex can be misidentified as E. sakazakii (Cronobacter). The ID 32 E kit has been proposed as a more accurate alternative, successfully confirming 90% of isolates with no false positive or false negative results. The use of yellow pigmentation as an identification for Cronobacter is unreliable and has been discontinued.
Phenotypic Identification
Subtyping Methods
The Enterobacter genus is heterogeneous and difficult to define using biochemical criteria. Owing to their close relationships, phenotypic identification of individual Enterobacter species can also be unreliable. To ensure the safety of infant formula and at the same time to reduce unnecessary disposal of product, it is important to identify between Cronobacter and Enterobacter species. Cronobacter can generally be distinguished from Enterobacter species based on hydrolysis of 5-bromo-4chloro-3-indolyl--D-phosphate, ornithine decarboxylation, and use of the 2,3 butanediol fermentation pathway (determined by Methyl Red and Voges– Proskauer reactions). Individual Cronobacter species can be separated by their different phenotype profiles using fermentation of 1-0-methyl-alpha-D-glucopyranoside and dulcitol combined with production of indole and utilization of malonate (Table 3). The reliability of
A number of approaches have been developed that can be used to characterize strains of Enterobacter, including antibiograms, biotyping, serogrouping, plasmid profiling, ribotyping, random amplification of polymorphic DNA (RAPD), arbitrarily primed PCR (AP-PCR), repetitive sequence-based PCR (rep-PCR), enterobacterial repetitive intergenic consensus (ERIC) PCR, amplified fragment length polymorphism (AFLP), and PFGE. Typing techniques are more discriminatory and reliable than classic techniques such as biotyping or antibiograms. Although there is frequent plasmid carriage within Enterobacter species, problems can arise due to plasmid instability and lack of extrachromosomal elements in some strains. PFGE has been used to investigate outbreaks in NICUs involving E. cloacae, E.aerogenes, E. gergoviae, and Cronobacter and is currently seen as the ‘gold standard’ for molecular subtyping of
Molecular Identification Oligonucleotide probes have been designed to detect the 16S and 23S rRNA gene sequences of the family Enterobacteriaceae; however, there are no molecular probes designed specifically to identify the genus Enterobacter. Multilocus sequence analysis (MLSA) using the recN, rpoA, and thdF genes can be used to extrapolate genetic similarities between the species of Enterobacteriaceae. The rpoA and rpoB gene sequences provide useful diagnostic tools to identify and differentiate species of this family and can be more discriminatory than 16S rRNA sequencing. A number of molecular approaches have been developed to identify Cronobacter. Targets for conventional PCR assays include the 16S rRNA gene, the ompA gene, the gene coding for the 1,6 -glucosidase, and a gene encoding a zinc-containing metalloprotease. Real-time PCR assays target the 16S rRNA gene, the region located between the 16S and 23S rRNA genes, the region between the tRNA-glu and 23S rRNA genes, and the dnaG gene in the MMS operon. The -glucosidase and dnaG gene-based methods have proved to be 100% sensitive and specific for Cronobacter using a broad panel of target as well as nontarget strains.
Table 3 Differentiation of Enterobacter species Enterobacter sakazakii (Cronobacter)
Other Enterobacter
E. E. E. E. E. E. E. E. E. C. C. C. C. E. E. E. malonaticus muytjensii sakazakii turicensis aerogenes cancerogenous cloacaea cowanii gergoviaeb helveticus hormaechei ludwigiic oryzae pulveris radicincitans turicensis
Test
C. dublinensis
Oxidase Hydrolysis of 5-bromo-4chloro-3-indolyl--Dphosphate Lysine decarboxylase Ornithine decarboxylase Methyl Red Voges–Proskauer Indole production (Kovacs) Malonate utilization Yellow pigmentation Acid from: D-Arabitol Dulcitol -Methyl-D-glucoside D-Sorbitol D-Sucrose
þ
ND
þ
ND
ND
þ
ND
þ
þ þ þ þ () þ þ 7090% of strains; can be transient
þ
þ
(þ) () þ
þ þ þ
þ (þ) þ
þ þ þ ND ND
þ v
þ v þ þ
()
þ þ
þ þ þ þ
þ þ
þ þ v
þ þ þ
þ þ þ þ
() () (þ) þ þ
þ þ þ
þ þ
þ þ
(þ) (þ) þ
þ þ þ
þ þ þ þ
(þ) v – þ
ND ND – þ þ
þ þ –
a
() þ þ
þ
þ
þ
þ
þ þ
Similar percentages are obtained for E. asburiae, E. amnigenus, E. dissolvens, and E. nimipressuralis (with the exceptions that E. asburiae does not utilize malonate and E. nimipressuralis does not produce acid from D-sucrose). Similar percentages are obtained for E. pyrinus. c Similar percentages are obtained for E. kobei except that some strains produce acid from dulcitol. ND, no data; , 0–10; (), 11–20; v, 21–79; (þ), 80–89; þ, 90100% of strains positive. b
þ
þ
þ
Pathogens in Milk | Enterobacter spp. 79
foodborne pathogens. The most common restriction enzymes used for Enterobacter are XbaI, SpeI, NotI, and SmaI. PFGE has been successfully used to analyze the dissemination of Cronobacter strains within infant formula and milk protein factories. A standard protocol for Cronobacter PFGE typing is currently being developed by the PulseNet International Program.
Prevention and Control Manufacture Owing to the high costs associated with product recalls, the risk associated with an unsafe product, and the impact of negative media attention, it is critical that Enterobacter and Cronobacter spp. are kept under control along the infant formula production chain. Hygienic standards within facilities are key to keeping contamination events to a minimum. Accumulation of food residues on structural surfaces can harbor potential pathogenic bacteria and act as continuous culture systems. Air is a potential source of contamination, and Cronobacter and Enterobacter spp. have been isolated from air filters. Contamination in infant formula production facilities has been previously found in the form of dust, water droplets, and airborne microorganisms. General handling of materials, spray drying, and milling and cleaning operations can create aerosols that disseminate through the plant. Molecular profiling of isolates from production facilities can identify the persistence of clonal strains and key contamination points within the manufacturing environment. This provides a basis to develop and implement continuous quality control and prevention strategies. Contamination of milk powders by Enterobacter spp. may occasionally be due to failures in the pasteurization process or more likely due to postdrying contamination during mixing with other ingredients, packing, and filling. Over three-quarters of raw milk concentrate and 85% of the nonproduct processing line may be positive for Enterobacteriaceae. It is not possible with current technology to eliminate Enterobacteriaceae from a manufacturing plant but effective cleaning-in-place (CIP) strategies and limited passage of personnel into high-risk areas can act as control measures. Sampling protocols should be implemented to monitor plant hygiene and presence of potential pathogens. Reduction in Enterobacteriaceae levels in many factories has been achieved by implementing a policy of systematic dry cleaning when possible. It is critical to maintain a lowmoisture environment postpasteurization, and the absence of water prevents proliferation and dissemination of microorganisms. PIF has a low water activity (0.2); therefore, this desiccated state limits the survival of many Gram-negative organisms. Cronobacter have been
previously seen to be very resistant to osmotic stress and drying in comparison to other Enterobacter spp. Ineffective cleaning of the processing equipment promotes the buildup of residues where the bacteria can grow and proliferate and subsequently contaminate the powder. Adhesion of microorganisms and the formation of biofilms are a concern in the food industry. Bacterial biofilms that are difficult to remove via CIP procedures can form within the equipment and be a constant source of contamination. They may compromise food quality and represent a significant public health risk. It is known that several groups of bacteria can attach to surfaces commonly found in the manufacturing environment, such as stainless steel and rubber. Bacterial within a biofilm may be more resistant to disinfectants and sanitizers when compared to bacteria in a planktonic state. Consumers Education of end users is an important factor in preventing foodborne illness due to contaminated infant foods. There is an ongoing debate as to the inclusion of warnings on packaging that powdered breast milk substitutes are not sterile products. The FAO/WHO recommends that powdered breast milk substitutes be reconstituted with water at 70 C to reduce the risk posed by any contaminating Enterobacter. In several outbreaks in hospital settings the feed preparation equipment has been found to be the likely source of contamination. Guidelines on preparation, storage, and feeding times have been issued to professionals to reduce the risk of further outbreaks in NICUs. These include the recommendation that sterile ready-to-use products be used whenever possible and appropriate hygiene and sterilization protocols be in place.
Conclusions and Future Perspectives The WHO recommends exclusive breast-feeding for up to 6 months and then complementary feeding with continued breast-feeding for 2 years and above. Natural breast milk has been shown to enhance the neonatal gut barrier and protect against infection, diarrheal disease, and also NEC. PIF is used as an alternative to breast milk to provide nutritional requirements in addition to breast-feeding or where breast-feeding is not feasible. PIF constitutes over 80% of the infant formula used worldwide. The focus to date has been on Cronobacter (E. sakazakii) in infant formula, with contamination by other Enterobacter being given less consideration. Enterobacter spp. have the ability to cause infections and have been previously seen to contaminate infant formula. The FAO/WHO categorizes Cronobacter and Salmonella enterica as Category A organisms with a clear evidence of causality, whereas Category B
80
Pathogens in Milk | Enterobacter spp.
organisms (causality plausible, but not yet demonstrated) include E. cloacae and E. (Pantoea) agglomerans. For organisms that are regularly acquired by vertical transmission during birth or are endemic in the hospital environment, it is less likely that sufficient epidemiological evidence may be found to link cases of infection to powdered breast milk substitutes. However, measures implemented to control Cronobacter contamination also reduce the likelihood of the presence of other Enterobacteriaceae. Understanding of the physiology and survival strategies of Cronobacter is an important step in the efforts to eliminate this bacterium from the critical food production environments.
Further Reading Farmer JJ, III, Boatwright KD, and Michael Janda J (2007) Enterobacteriaceae: Introduction and identification. In: Murray PR (ed.-in-chief) Baron EJ, Jorgensen J, Pfaller MA, and Landry ML (vols. eds.) Manual of Clinical Microbiology, 9th edn., Vol. 1, chapter 2, 649p. Washington, DC: ASM Press Inc. Food and Agriculture Organization-World Health Organization (2006) Enterobacter sakazakii and Salmonella in powdered infant formula. Meeting Report, MRA Series 10, Microbiological Risk Assessment Series 10. Geneva, Switzerland: World Health Organization. Healy B, Cooney S, O’Brien S, et al. (2010) Gonobacter (Enterobacter sakazakii ): An opportunistic foodborne pathogen. Foodborne Pathogens and Disease 7: 339–350. Janda JM and Abbott SL (2005) The Enterobacteria, 2nd edn. Washington, DC: ASM Press Inc.
Listeria monocytogenes E T Ryser, Michigan State University, East Lansing, MI, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction Listeria monocytogenes, the causative agent of listeriosis in humans and animals, was first isolated by British researchers at Cambridge University in 1924 from the blood of infected rabbits. These animals exhibited a typical monocytosis, after which the bacterium was named. Although widely recognized as a cause of miscarriage in pregnant women and meningitis, encephalitis, and septicemia in newborn infants and immunocompromised adults, this organism did not emerge as a serious foodborne pathogen until 1985. Unlike most other foodborne illnesses, the outcome of listeric infections can be particularly devastating with a mortality rate of about 20%. During the 1980s, three major dairy-related outbreaks of listeriosis – two in the United States and one in Switzerland – were linked to consumption of pasteurized milk, Mexican-style cheese, and Vacherin Mont d’Or softripened cheese, which together resulted in over 100 fatalities. These outbreaks, combined with a then presumed low oral infectious dose for susceptible individuals, prompted the United States to institute a policy of ‘zero tolerance’ for L. monocytogenes in all cooked/ready-to-eat foods, including dairy products. Since 1985, over 112 Class I recalls have been issued in the United States for Listeria-contaminated domestic and imported cheeses with an additional 58 Class I recalls involving unfermented dairy products, principally ice cream, at a financial cost exceeding $120 million. Although L. monocytogenes accounted for 13 of 18 (72%) dairy-related Class I recalls issued during 1994 and 1995, only 1 of 36 Listeria-related Class I recalls in 2000 involved a dairy product (domestically produced Cheddar cheese). Furthermore, the fact that only 29 Listeria-related recalls involving 27 cheeses and 2 other dairy products were issued since 2001 indicates that dairies in the United States and elsewhere have generally taken sufficient measures to minimize Listeria contamination within their processing facilities. However, in the United States the availability of Queso Fresco and other soft Mexican-style cheeses that have been illegally prepared from raw milk or have been illegally imported has become an increasing public health concern among the growing Hispanic population.
Characteristics of Listeria spp. The genus Listeria, which is included among the coryneform bacteria, contains six species: L. monocytogenes, L. ivanovii, L. seeligeri, L. innocua, L. welshimeri, and L. grayi; the first
three species are -hemolytic on laboratory media containing blood. Listeria monocytogenes is the only Listeria species that is of public health significance as a foodborne pathogen. Listeria ivanovii, widely recognized as pathogenic to domestic livestock, only rarely infects humans as is also true for L. seeligeri. Listeria innocua, the most commonly isolated species, is nonpathogenic as is also generally true for L. welshimeri and L. grayi. Listeria monocytogenes is a Gram-positive, non-sporeforming, facultatively anaerobic, short, rod-shaped bacterium that occurs singly or in short chains. The organism is psychrotrophic, generally growing in nonselective laboratory media at temperatures between 1 and 45 C with optimal growth occurring at 30–37 C. However, L. monocytogenes strains reportedly can grow at temperatures as low as 0.1 C in pasteurized milk during extended storage. At 4 C, growth of Listeria is somewhat faster with generation times of 30–40 h. However, the growth rate triples (generation times of 10–13 h) when milk is held at mildly abusive temperatures (8 C). When incubated at room temperature, broth cultures of Listeria exhibit a characteristic tumbling motility, which can be seen microscopically. Colonies on clear laboratory media are small, smooth, and bluish-gray when examined under obliquely transmitted light. Biochemically, all listeriae produce catalase and ferment glucose to acid without producing gas, whereas typical L. monocytogenes isolates ferment rhamnose but not xylose. All Listeria species hydrolyze aesculin, which leads to a characteristic blackening of commonly used Listeria-selective enrichment (e.g., Fraser broth) and plating media (e.g., modified Oxford agar) that contain aesculin and ferric ammonium citrate. In addition to a wide range of commercial biochemical-, antibody-, and DNA-based test kits for identifying L. monocytogenes, several chromogenic plating media have become available that can differentiate L. monocytogenes from other Listeria species. Of particular concern to the dairy industry is the ability of L. monocytogenes to tolerate environmental extremes found in dairy processing facilities, grow at pH 4.3–10.0, grow in the presence of up to 10% NaCl (aw 0.92), survive for several months in refrigerated 25.5% NaCl brine tanks, and develop limited tolerance to heat and acid. Based on somatic (O) and flagellar (H) antigens, 13 different L. monocytogenes serotypes have been identified. Serotype 4b has been most commonly associated with outbreaks of human illness followed by serotypes 1/2b and 1/2a, with most of the major
81
82
Pathogens in Milk | Listeria monocytogenes
dairy-related outbreaks traced to just a few strains of serotype 4b that have now been well characterized by various genetic typing methods including pulsed-field gel electrophoresis (PFGE) and ribotyping.
Symptoms of Listeriosis Listeriosis, the disease caused by L. monocytogenes, is a relatively rare infection that most often occurs in three well-defined risk groups, namely pregnant women, newborn infants, and immunocompromised adults, with the last group including the elderly and individuals with predisposing conditions such as cancer, organ transplants, cirrhosis of the liver, and HIV/AIDS infections. Approximately 2500 cases occur annually in the United States, with 1–4 cases per 106 population reported in most developed countries. Unlike other more common foodborne illnesses caused by Campylobacter and Salmonella, listeriosis has a mortality rate of approximately 20%, making it among the deadliest of the foodborne diseases with an estimated annual cost of $2.33 billion in the United States. In addition to host susceptibility, development of listeriosis in humans is also affected by gastric acidity, inoculum size, and variations in virulence between different strains of L. monocytogenes. Despite repeated exposure of the general population to Listeria through the food supply, individuals not included in the three well-defined risk groups seldom develop invasive listeriosis, with healthy individuals rarely infected. However, a far less severe form of noninvasive listeriosis characterized by symptoms of gastroenteritis has also been described, including one well-documented outbreak traced to highly contaminated chocolate milk. Based on several recent risk assessments, ingestion of foods containing >106 organisms g1 is now presumed to be responsible for the majority of invasive listeriosis cases among susceptible individuals. Invasive listeriosis in immunocompromised adults frequently leads to meningitis, encephalitis, or septicemia.
Symptoms that develop suddenly after an initial incubation period of 2–70 days include severe headache, dizziness, stiff neck or back, incoordination, and other disturbances of the central nervous system. Without proper antibiotic therapy, approximately 20% of those infected will die, with some survivors developing permanent neurological complications. In pregnant women, L. monocytogenes produces a mild flu-like illness characterized by sudden chills, fever, sore throat, headache, dizziness, lower back pain, discolored urine, and occasionally diarrhea. While expectant mothers almost invariably recover without complications, infection of the fetus can result in miscarriage, stillbirth, or premature delivery of an infant with perinatal septicemia – a severe infection of the respiratory, circulatory, and central nervous systems that can either terminate fatally or lead to permanent mental retardation. Two factors, namely the growth of L. monocytogenes as an intracellular pathogen within macrophage cells of the spleen and liver and the inability of many antibiotics to effectively penetrate the blood–brain barrier, complicate treatment of listeric infections. Hence, a favorable prognosis depends on rapid diagnosis and appropriate antibiotic therapy, with oral administration of large doses of amoxicillin together with an aminoglycoside (e.g., gentamicin) for 2–4 weeks now the recommended treatment.
Outbreaks The oral route for listeriosis was established from animal feeding studies conducted during the 1920s. However, evidence for L. monocytogenes as a human foodborne pathogen did not emerge until the 1950s when a sharp increase in stillbirths was observed among pregnant women in post–World War II Germany who consumed raw milk, sour milk, cream, and Cottage cheese (Table 1). The eventual isolation of identical L. monocytogenes serotypes from a mastitic cow and stillborn twins whose
Table 1 Dairy-related listeriosis outbreaks involving 10 or more cases Location
Year
Number of cases
Product
Halle, Germany Massachusetts, USA California, USA Vaud, Switzerland Illinois, Michigan, Wisconsin, USA France France Finland North Carolina, USA Quebec, Canada Quebec, Canada
1949–57 1983 1985 1983–87 1994 1995 1997 1998–99 2000 2002 2008
100 49 300 122 66 33 14 25 13 17 22
Raw milk, sour cream, cream, Cottage cheese Pasteurized milk Mexican-style cheese Vacherin Mont d’Or cheese Chocolate milk Brie de Meaux cheese Pont l’E´veˆque cheese Butter Mexican-style cheese Raw milk cheese Raw milk soft cheese
Pathogens in Milk | Listeria monocytogenes
mother consumed the same raw milk before delivery confirmed raw milk as the source of infection. Despite the presence of L. monocytogenes in about 2.5–5% of the raw milk supply from the United States and most other developed countries, current pasteurization practices are sufficient to destroy Listeria in raw milk. Few additional cases have been traced to raw milk since most milk is now pasteurized before consumption to eliminate Listeria and other pathogens. In 1981, the status of L. monocytogenes as a foodborne pathogen began to change following a major outbreak in the Maritime Provinces of Canada that was traced to consumption of contaminated coleslaw. Two years later, one particular brand of pasteurized milk in the United States was epidemiologically linked to 42 adult and 7 infant cases of listeriosis in Massachusetts. Fourteen patients died, giving a mortality rate of 29%. Inspection of the milk-processing facility failed to uncover any evidence of improper pasteurization or postpasteurization contamination. Although the dairy factory received milk from farms on which veterinarians diagnosed several cases of bovine listeriosis during the outbreak, L. monocytogenes was never recovered from the incriminated milk, which in turn raises questions concerning the role of pasteurized milk in this outbreak. In 1994, an unusual outbreak was reported in the United States in which consumption of pasteurized chocolate milk was directly traced to 66 cases of illness in Illinois, Wisconsin, and Michigan. Unlike previous outbreaks, symptoms of gastroenteritis predominated, with only four individuals requiring short-term hospitalization. Postpasteurization contamination of the chocolate milk followed by repeated episodes of temperature abuse allowed this atypical strain of L. monocytogenes serotype 1/2b to attain populations of 108–109 cfu ml1 in the milk at the time of consumption. Except for one additional outbreak recently traced to consumption of butter in Finland, repeated attempts have generally failed to confirm culturally other unfermented dairy products, including fluid milk and ice cream, as vehicles of listeric infection. Ingestion of Listeria-contaminated cheese has been more commonly linked to listeriosis, with seven major outbreaks and numerous sporadic cases having been reported. The first and largest of these outbreaks occurred in the United States in the Los Angeles area during the first half of 1985 and involved an estimated 300 cases. Consumption of California-made Jalisco brand Mexicanstyle cheese contaminated with L. monocytogenes serotype 4b was linked to 142 listeriosis cases in Los Angeles County alone, including 48 deaths (mortality rate of 34%). The contaminated cheese was subsequently recalled nationwide. Factory records indicated that raw milk may have been intentionally added to pasteurized milk used in cheesemaking. Although not isolated from the incoming raw milk supply, the epidemic strain
83
was widespread in the factory environment, which also suggests ample opportunity for postpasteurization contamination. In the second of these outbreaks, consumption of Vacherin Mont d’Or – a soft surface-ripened cheese – contaminated with L. monocytogenes serotype 4b was traced to 122 listeriosis cases in Switzerland from 1983 to 1987. Thirty-four patients died, giving a mortality rate of 28%. Two different epidemic-associated strains of L. monocytogenes serotype 4b were isolated from patients and the incriminated cheese as well as from the wooden shelves and brushes used in 40 different cheese ripening cellars. Surface samples from the cheese contained the epidemic strain at levels of 104–106 cfu g1, thus suggesting both contamination and growth of L. monocytogenes on the cheese surface during ripening. The outbreak ceased after installation of metal ripening shelves and thorough cleaning/sanitizing of the ripening rooms. During the mid-1990s, two major dairy-related listeriosis outbreaks in France were traced to different varieties of soft surface-ripened cheese. In 1995, 20 individuals including 11 pregnant women developed listeric infections after consuming Brie de Meaux cheese that was prepared from raw milk. Unlike previous outbreaks, no geographic clustering was observed, with cases reported in 8 of 22 French regions. Isolates from patients were identical to those from the incriminated cheese, with this organism likely present in the raw milk used for cheesemaking. Two years later, 14 cases of listeriosis were linked to consumption of Pont l’E´veˆque cheese manufactured in Normandy. The implicated raw milk cheese contained L. monocytogenes serotype 4b at a level of >1000 cfu g1. Improper manufacture of soft and semihard cheese is now responsible for the majority of both outbreak and sporadic cases that have been traced to dairy products, with consumption of such cheeses best avoided by high-risk individuals. One 2002 outbreak in Quebec, Canada, involving 17 cases of listeriosis (5 pregnant and 12 nonpregnant adults) was linked to consumption of commercially produced raw milk soft and semihard cheese that had undergone less than the legally required 60 days of aging. In late August and September of 2008, 22 cases of listeriosis (7 pregnant and 15 nonpregnant adults), including 1 adult fatality, 1 stillbirth, and 6 premature deliveries, were again traced to consumption of several soft French-style cheeses that were commercially produced from raw milk in Quebec, Canada. In the United States, concerns surrounding consumption of soft cheese have generally focused on soft, unripened Mexican-style varieties that are frequently homemade and either illegally produced from raw milk in the United States or illegally imported from Mexico. In 2000, 13 cases of listeriosis including 11 perinatal infections and 5 stillbirths were traced to soft Mexican-style
84
Pathogens in Milk | Listeria monocytogenes
cheese that was locally prepared from raw milk and then sold either door-to-door or through small markets or street vendors to Mexican immigrants in North Carolina. Unlike the previous outbreaks, this epidemic strain of L. monocytogenes serotype 4b exhibited a rarely seen PFGE profile. Another similar but smaller outbreak in 2003 was also traced to raw milk Queso fresco cheese that was illegally produced in Texas. These outbreaks along with a growing number of sporadic cases among Hispanics have prompted renewed efforts to curtail the illegal importation, production, and sale of such raw milk cheeses in the United States.
Sources Primary reservoirs for Listeria include soil, feces, water, and decaying vegetation. Consumption of aerobically spoiled and improperly fermented silage having a pH >4.5 has been routinely linked to listeriosis outbreaks in ruminant farm animals. Numerous wild and domestic animals, including cows, sheep, and goats, are susceptible to listeric infections, with large numbers of healthy asymptomatic carriers excreting high numbers of L. monocytogenes in their feces. Long-term survival of Listeria under adverse environmental conditions typically leads to further spread of this pathogen through the food chain. The hardy nature of this ubiquitous psychrotrophic food-borne pathogen, along with its ability to colonize, multiply, and persist in food production facilities for months or years, makes L. monocytogenes a major threat to manufacturers of dairy products as well as ready-to-eat meat and poultry products, smoked fish, prepared sandwiches, and delicatessen products, all of which have been frequently found to harbor Listeria. Being unable to survive pasteurization, this pathogen most often enters dairy products and other ready-to-eat foods as a postpasteurization contaminant. While most frequently isolated from floor drains, conveyor belts, and areas with condensate, L. monocytogenes has also been recovered from cheese vats and filling machines, which lends further support to this pathogen being a postpasteurization contaminant.
Incidence and Behavior in Milk and Dairy Products Dairy cattle, sheep, and goats can intermittently shed L. monocytogenes in their milk at levels of up to 104 cfu ml1 as a result of Listeria-related mastitis, encephalitis, or abortion. Milk from severely infected cows is unlikely to reach consumers due to a variety of overt symptoms, including excessive salivation, inability to eat or drink, impaired locomotion, and ‘circling disease’, all of which are related to disturbances of the central nervous system.
However, mildly infected and apparently healthy animals can shed L. monocytogenes in their milk for many months and are thus of far greater public health concern. Composite results from numerous bulk tank surveys conducted since 1983 indicate that 2.5–5% of the North American and European raw milk supply can be expected to contain low levels (i.e., <10 cfu ml1) of L. monocytogenes at any given time. Hence, proper refrigeration is important, given several reports indicating that L. monocytogenes populations in naturally contaminated raw milk can increase 1000-fold after 4 and 10 days of storage at 10 and 4 C, respectively. Listeria monocytogenes is more thermally tolerant than most other non-spore-forming foodborne pathogens. However, current vat (63 C for 30 min) and hightemperature–short-time pasteurization (72 C for 15 s) practices will ensure total destruction of L. monocytogenes. Despite the ability of L. monocytogenes to attain populations of 106 cfu ml1 in commercial skim milk, whole milk, chocolate milk, and whipping cream after 8 days of storage at 8 C (a not uncommon temperature of home refrigerators), this organism has been rarely detected in pasteurized fluid milk products. While L. monocytogenes has been occasionally recovered from commercially produced butter with survival up to 70 days being reported in butter prepared from inoculated cream, this pathogen is a far more frequent postpasteurization contaminant of ice cream. Since May 1986, 47 of 58 Listeria-related Class I recalls issued in the United States for unfermented dairy products involved ice cream, ice cream novelties, and related frozen desserts containing very low levels of L. monocytogenes. Increased prevalence of this pathogen in frozen rather than fluid dairy products coincides with the relatively complex handling of such products, particularly ice cream novelties, during manufacture and packaging. However, given the presumed low levels of contamination, the inability of Listeria to grow in frozen dairy products, and the recall of over 3.1 million gallons of ice cream without incident, consumption of such products does not appear to pose a major public health threat. As one might surmise from the aforementioned outbreaks, L. monocytogenes is a more frequent contaminant of cheese, most notably soft surface-ripened varieties such as Brie, Camembert, and certain Mexican-style varieties, which support growth of the organism during cheese ripening. Since 1986, 81 Class I recalls were issued in the United States for domestically produced cheese, principally Mexican-style cheese, contaminated with L. monocytogenes. During this same period, 31 imported cheeses, including French Brie, Danish Esrom, and Anari (goat’s milk cheese from Cyprus), were also recalled. Results from extensive surveys suggest that about 1–5% of cheeses produced in Europe, primarily soft and semisoft varieties surface-ripened by mold or
Pathogens in Milk | Listeria monocytogenes
bacteria, may contain L. monocytogenes, with this pathogen seldom found in aged hard cheeses (e.g., Cheddar) or cheeses that undergo severe heat treatments during manufacture (e.g., Cottage, Mozzarella, Parmesan, Swiss, processed cheese). Following the 1985 outbreak in California involving Mexican-style cheese, work was initiated to assess the behavior of L. monocytogenes during the manufacture and storage of yogurt, buttermilk, and a wide range of cheeses, with most of these studies describing the outcome of preparing these products from artificially contaminated pasteurized milk. Listeria populations generally increase <10-fold when milk is fermented with a traditional starter culture containing mesophilic or thermophilic lactic acid bacteria at an inoculum level of 1%, with growth ceasing at pH <5.2. In one of several studies that examined postpasteurization contamination, L. monocytogenes persisted an average of 3 weeks in refrigerated cultured buttermilk and yogurt inoculated to contain 103–104 cfu g1 of L. monocytogenes. Regardless of the cheese variety manufactured, physical entrapment of Listeria in the curd during milk coagulation results in a 10-fold increase in numbers. Thereafter, the behavior of Listeria is dictated by the manufacturing steps for the particular cheese. The extent of acid development and curd cooking during cheesemaking along with pH, salt content, moisture content (water activity), and type/ extent of ripening will determine the ultimate fate of L. monocytogenes in the final product. Growth of Listeria in cheese is primarily confined to soft/semisoft varieties ripened by mold (e.g., Brie, Camembert, Roquefort) or bacteria (e.g., French cheeses, Brick) and certain Mexican-style cheeses (Queso Fresco) with populations increasing to >106 cfu g1 as the cheese attains a pH >6.0 during ripening (Table 2).
Although L. monocytogenes is generally unable to grow in cheeses having a pH <5.2, it can survive in many such cheeses for weeks or months and has even been recovered from experimentally produced 434-day-old Cheddar cheese. These findings raise legitimate concerns regarding the adequacy of the mandatory 60-day holding period at >1.7 C to completely inactivate L. monocytogenes (and other pathogens) in Cheddar and other hard cheeses that can be legally prepared from raw milk or milk subjected to subpasteurized heat treatments. However, barring contamination during packaging, cheeses such as Cottage and Mozzarella that undergo severe heat treatments during manufacture should be free of Listeria.
Control Given the widespread distribution of Listeria in the environment, control of Listeria must begin at the farm level with attention given to good animal husbandry practices, use of only high-quality feed/silage, hygienic milking practices, and proper refrigeration to minimize growth of the pathogen during bulk tank storage of milk. Current vat and high-temperature–short-time pasteurization practices are the only commercially practical means for destroying L. monocytogenes in raw milk. Thus, barring postpasteurization contamination, properly pasteurized fluid milk products will be free of Listeria. Well-designed sanitation programs that include weekly sampling for Listeria in problem areas within the factory are essential if the incidence of this pathogen is to be minimized in the production facility and in the finished product. Postpasteurization contamination most frequently occurs during extruding, filling, and packaging operations when the product is exposed to airborne contamination and
Table 2 Fate of Listeria monocytogenes in fermented dairy products as affected by composition pH Product Fermented milks Buttermilk Yogurt Cheeses Blue Brie/Camembert Cheddar Cottage Feta Mexican-style Mozzarella Parmesan Ricotta Swiss
85
% moisture
% NaCl in water phase
Initial
Final
Growth
4.2 4.1
4.4 4.1
39 55 37 79 55 51 47 32 72 33
11.5 4.7 4.6 1.2 4.6 4.0 4.4 5.0 0.5 2.7
4.6 4.6 5.1 5.0 4.6 6.2 5.4 5.1 6.0 5.5
6.3 7.5 5.1 5.0 5.1 6.2 5.4 5.1 6.0 5.5
þ þ þ
86
Pathogens in Milk | Listeria monocytogenes
difficult-to-clean food contact surfaces. Programs for reclaiming and reworking returned or expired product are also discouraged to minimize the chance of reintroducing temperature-abused products that may harbor higher numbers of Listeria into the processing facility. See also: Cheese: Public Health Aspects. Diseases of Dairy Animals: Infectious Diseases: Listeriosis. Mastitis Pathogens: Environmental Pathogens.
Further Reading Lianou A and Sofos JN (2007) A review of the incidence and transmission of Listeria monocytogenes in ready-to-eat products in retail and food service environments. Journal of Food Protection 70: 2172–2198. Liu D (2008) Handbook of Listeria monocytogenes. Boca Raton, FL: Taylor and Francis.
Norton DM and Braden CR (2007) Foodborne listeriosis. In: Ryser ET and Marth EH (eds.) Listeria, Listeriosis, and Food Safety, 3rd edn., pp. 308–356. Boca Raton, FL: Taylor and Francis. Painter J and Slutsker L (1999) Listeriosis in humans. In: Ryser ET and Marth EH (eds.) Listeria, Listeriosis, and Food Safety, pp. 85–109. Boca Raton, FL: Taylor and Francis. Rocourt J (2007) The genus Listeria and Listeria monocytogenes: Phylogenetic position, taxonomy, and identification. In: Ryser ET and Marth EH (eds.) Listeria, Listeriosis, and Food Safety, pp. 1–20. Boca Raton, FL: Taylor and Francis. Ryser ET (2001) Public health concerns. In: Marth EH and Steele JL (eds.) Applied Dairy Microbiology, pp. 397–545. New York: Marcel Dekker. Ryser ET (2007a) Incidence and behaviour of Listeria monocytogenes in cheese and other fermented dairy products. In: Ryser ET and Marth EH (eds.) Listeria, Listeriosis, and Food Safety, 3rd edn., pp. 405–501. Boca Raton, FL: Taylor and Francis. Ryser ET (2007b) Incidence and behaviour of Listeria monocytogenes in unfermented dairy products. In: Ryser ET and Marth EH (eds.) Listeria, Listeriosis, and Food Safety, 3rd edn., pp. 357–403. Boca Raton, FL: Taylor and Francis. Seeliger HP (1961) Listeriosis. New York: Hafner.
Mycobacterium spp. J Dalton and C Hill, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction The genus Mycobacterium is a member of the Actinobacteria. Mycobacteria are aerobic, acid-fast, nonmotile (with the exception of Mycobacterium marinum), nonspore forming bacilli (although recent findings indicate that some strains such as M. marinum may have the ability to form spores), which are widely distributed in the environment. There are over 100 different species of mycobacteria, most of which are nonpathogenic to humans and are found mainly in soil and water. However, tuberculosis and leprosy, two of the most notorious diseases known to man, are caused by members of this genus. While they are generally considered to be Gram positive, this is not strictly true. The unique cell envelope of mycobacteria contains a very high proportion of lipids that give the members of this genus unique characteristics such as resistance to acid, alcohol, and chlorination. It is the thick, waxy, lipid-rich cell wall that gives mycobacteria their characteristic pink/red color following acid-fast staining procedures (e.g., Ziehl-Neelson, see Figure 1). Although most mycobacteria live in soil, water (including chlorinated tap water supplies), and foodstuffs, some members of the genus are not free-living bacteria but are instead found living in animal hosts. These include M. tuberculosis and M. bovis, both of which are pathogens in both humans and cattle. Mycobacteria consist of both fast- and slow-growing members, with the quicker-growing species usually being nonpathogenic saprophytes (feeding on dead or decaying organic matter) and the majority of the pathogenic strains belonging to the slower-growing species. Mycobacteria that form colonies visible to the naked eye on suitable substrates within a period of seven days are generally classified as fast-growing species (e.g., M. smegmatis), while species that take longer than this are considered to be slow growers (e.g., M. tuberculosis). From a clinical perspective, mycobacteria are classified into two groups: the M. tuberculosis complex (e.g., M. tuberculosis, M. bovis, M. africanum) and the nontuberculous mycobacteria (e.g., M. avium, M. intracellulare, M. avium paratuberculosis).
Mycobacterium tuberculosis Complex The members of the Mycobacterium tuberculosis complex (MTC) (with the exception of strain BCG) are all pathogenic and capable of causing a deadly disease of the
pulmonary system, tuberculosis, in a variety of hosts. Its members include M. tuberculosis, M. bovis, M. africanum, M. microti, M. canetti, M. caprae, and M. bovis Bacille Calmette-Gue´rin (BCG). Strains of the MTC are approximately 99.9% similar at a genetic level but there are distinct differences phenotypically with regard to the level of their pathogenicity. Approximately one-third of the world’s population is infected with mycobacteria capable of causing tuberculosis, but most of these are asymptomatic and will never develop the disease. Nonetheless, tuberculosis is a leading global cause of death due to infectious disease. Although primarily a disease of the lungs, infections of the gastrointestinal tract are not uncommon. All members of this group are reportable to public health authorities, although many laboratories are not equipped to distinguish between the different species. As a result the exact number of tuberculosis cases caused by each species is not available. Tuberculosis has been prevalent in human society since ancient times. Large-scale outbreaks such as the White Death have been recorded throughout history. With the development of antimycobacterial antibiotics, tuberculosis disease was thought to be under control. However, a resurgence in tuberculosis has been seen in recent times, especially among immunocompromised individuals, such as those affected by HIV (AIDS).
Mycobacterium bovis The most commonly reported mycobacterial infection in cattle is caused by M. bovis. It causes bovine tuberculosis characterized by the development of granulomatous lesions in the lung tissue, lymph nodes, intestine, and other tissues. The primary hosts of M. bovis are cattle species, but it has the ability to infect a very wide range of mammalian hosts such as humans, deer, goats, pigs, dogs, cats, and badgers. M. bovis can cause tuberculosis in humans, with AIDS patients being the most at-risk group. Infection usually occurs through ingestion of contaminated milk, especially raw milk. Upon oral infection the bacterium can cause localized infections in the gut, and through infection of macrophages can establish infections of the lymph nodes and disseminate throughout the body, which can also lead to pulmonary disease. Symptoms of M. bovis infection include weight loss, fever, and general weakness. It is thought to have
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Mycobacterium tuberculosis
Figure 1 Acid-fast stain of Mycobacterium avium paratuberculosis (MAP). MAP cells appear stained red.
originally derived from an ancestral soil-dwelling saprophyte that lived in cow dung. It has been estimated that M. bovis accounts for approximately 3.1% of all human tuberculosis disease with the vast majority being nonpulmonary infections. Infection is greatest in developing countries; M. bovis tuberculosis is quite rare in developed countries, accounting for less than 1% of infection. Members of the MTC have a pattern of pathogenesis distinct from most other bacteria. Unless a host has an underdeveloped or compromised immune system the mycobacteria will not initially cause disease. Upon entering the body, bacteria encounter macrophages, cells of the immune system that engulf and kill bacteria. Mycobacteria can survive this process and replicate inside the macrophage. They can subsequently exist in a quiescent state for many years. This is referred to as latent infection. In 90% of the cases of infection with M. tuberculosis, the infection will not lead to disease in the host. However, in the remaining 10% of infected individuals the mycobacteria can reactivate and cause disease. This leads to active disease, and it is at this point that individuals in turn become infective. The reasons for reactivation of the mycobacterium are unknown, but it is more likely to occur in an individual who is malnourished or whose immune system has become impaired. This can be due to infection with the human immuno deficiency virus (HIV), which can cause a breakdown in the capability of the immune system to fight disease; old age; or the use of corticosteroids which inhibit the immune system. In the developed world mortality from tuberculosis is approximately 10% of those with active disease; in the developing world this percentage is much higher.
This bacterium is the etiological agent of most tuberculosis in humans. Although pulmonary infection is more common with M. tuberculosis, intestinal infection can also occur and is more common in immunocompromised hosts. Any part of the gastrointestinal tract can become infected. M. tuberculosis shows a strong tropism for lung tissue, and when injected intravenously it can translocate to the lungs and cause pulmonary infection. It is primarily associated with human disease, although it can also colonize cattle and a wide variety of other mammals. M. tuberculosis is thought to have evolved from M. bovis, gradually developing into a different species. Symptoms of intestinal infection include ulcers, thickening of the bowel wall, weight loss, diarrhea, and fatigue. Infection from dairy products usually occurs due to the consumption of contaminated, unpasteurized milk or cheese.
Mycobacterium africanum, M. microti, M. canetti, and M. caprae M. africanum is commonly found in West African countries and, although it is rarely identified outside of this region, it has been detected in a small number of tuberculosis patients worldwide. Both humans and cattle are susceptible to colonization and infection. Its contribution to tuberculosis disease in the above regions is thought to be up to 50%. While its infectivity in humans is comparable to that of M. tuberculosis, the extent of its virulence is unknown. Again, it causes disease in a large number of HIV-positive patients. M. microti primarily infects small rodents, in which it causes tuberculosis. It has also been reported to be present in cattle. It very rarely causes disease in humans but has been reported both in immunocompetent and in immunosuppressed patients. M. canetti was first described in 1969. It grows more quickly than M. tuberculosis and forms smooth, shiny colonies. Infection in humans has only rarely been reported. Locations include the Horn of Africa, France, Madagascar, and French Polynesia. It is unknown if this species can infect cattle and cause infection through contaminated milk. M. caprae is the most recent addition to the MTC, and was only identified in 1999. It has been isolated from symptomatic cattle and very infrequently from humans.
Nontuberculous Mycobacteria Nontuberculous mycobacteria (NTM) consist of species not part of the M. tuberculosis complex or M. leprae. They are also known as ‘mycobacteria other than tuberculosis’
Pathogens in Milk | Mycobacterium spp. 89
(MOTT). These bacteria are usually saprophytic but they can be opportunistic pathogens and can cause deadly infections in a susceptible host. Unlike in M. tuberculosis complex bacteria, person-to-person contact is not the primary source of infection. Infection normally occurs through contact with the bacteria from environmental sources via ingestion, inhalation, or through exposed wounds. Detection of infections of humans by these bacteria has increased in recent years for several reasons. Better diagnostic and culturing techniques have allowed for better isolation of these bacteria from infected individuals; there has also been a rise in the numbers of susceptible hosts (such as individuals suffering from AIDS) which has led to this increased infection. In contrast to M. tuberculosis complex infections, NTM infections are not reportable to public health bodies, possibly resulting in an underestimation of the extent to which they cause disease. NTM can cause both local infections and body-wide disease depending on the strain, host physiology, and point of entry. NTM infections were initially thought to cause disease only in the immunocompromised, but they are now also recognized as being capable of causing disease in immunocompetent hosts. They can cause a wide range of diseases, which can be pulmonary, intestinal, and disseminated throughout the host. NTM have been found in both raw milk and pasteurized samples. These include the following: M. avium complex M. avium paratuberculosis M. ulcerans M. fortuitum M. gordonae M. marinum M. kansassii M. scrofulaceum
Mycobacterium avium Complex The Mycobacterium avium complex (MAC) consists of a group of closely related mycobacteria that are difficult to identify and differentiate. The members are very similar at a genetic level but they vary greatly in their host tropisms, disease phenotypes, and pathogenicity. The MAC consists of both saprophytes and opportunistic pathogens. Members of the MAC include M. avium, M. avium avium, M. intracellulare, M. avium paratuberculosis, M. haemophilum, and M. avium hominis. Symptoms of a MAC infection can include the following:
• Fever pain • Abdominal Weight loss •
• Fatigue • Diarrhea • Night sweats These mycobacteria are capable of survival and replication under a wide variety of environmental stresses which include large variations in temperature, low pH, and chlorination. Members of the MAC are slow-growing and usually nonpigmented. MAC bacteria are common in the environment and can cause infection in a susceptible host when inhaled or swallowed. Diarrhea and abdominal pain are associated with gastrointestinal involvement. Members of the MAC are pathogens of low virulence, but infections are common in immunocompromised individuals. In AIDS the risk of infection by these bacteria is inversely related to the CD4 count of a patient. Unlike other opportunistic infections in AIDS, infection by members of the MAC is not thought to be a result of the reactivation of a latent infection but rather a new infection. Infections by members of the MAC are difficult to eradicate with antibiotics and many are resistant to antituberculosis antibiotics.
Mycobacterium avium paratuberculosis Mycobacterium avium paratuberculosis (MAP) was first described in 1895 and originally named Johne’s bacillus. It is a member of the MAC and is very similar to the other members of this group. Unlike other members of MAC and NTM, it is a specific agent of intestinal inflammation in a wide variety of animals. It is the causative agent of Johne’s disease, which is primarily a disease of ruminants but which can also be seen in some nonruminants such as birds, foxes, dogs, and some primates. It causes an intestinal infection that results in a chronic wasting disease that ultimately ends in the death of the animal. Infection usually occurs years before the animal displays symptoms of the disease. Chronic inflammation may emerge after a long latent period. This emergence of disease has been linked to stress on the animals and hormonal changes. Hundreds of millions of dollars are lost annually due to infection by MAP on account of decreased milk yields and culling of infected animals. Like many mycobacteria, it is capable of surviving and replicating inside macrophages. The principal route of infection is through ingestion, with calves being at greatest risk. MAP can be passed from mother to calf in both the colostrum and milk, and in utero transmission of MAP has also been observed. MAP bacteria are also shed intermittently in high numbers in the feces of the infected cattle, contaminating bedding, pasture, and water sources. However MAP displays a strong tropism to the intestine and will cause intestinal inflammation
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if experimentally administered intravenously or subcutaneously. The primary symptoms of Johne’s disease include diarrhea, weight loss, and decreased milk yield. Unlike all other mycobacteria, MAP requires the presence of mycobactin, an iron chelating agent, for growth in laboratory media. Detection of the incidence of MAP in cattle herds has risen in the mid-twentieth century, which is possibly due to better laboratory cultivation techniques. Cattle displaying Johne’s symptoms are usually culled to prevent further infection in the herd. Subclinically infected cattle are seen to secrete MAP in their milk, exposing the young with an underdeveloped immune system to the pathogen at an early age. The presence of MAP has been demonstrated in pasteurized retail milk, perhaps as a result of postpasteurization contamination. Some studies have shown a high degree of tolerance in MAP toward the pasteurization process, unlike in M. tuberculosis or M. bovis, which are effectively killed during standard high temperature short time (HTST) pasteurization. An increase in the hold time in HTST pasteurization has been shown to have a greater killing effect on MAP compared to an increase in temperature. MAP has also been shown to be capable of surviving in some cheeses for long periods in the environment. Amoebae have been shown to be a host in pastureland and allow for replication outside of a bovine host. MAP has been linked to Crohn’s disease, a gastrointestinal disorder in humans that is currently thought to be autoimmune in nature. Symptoms of Crohn’s disease include weight loss, abdominal pain, diarrhea, and ileac obstruction. This link has proven to be controversial and no firm consensus has been reached on the matter. The link was first postulated in the early twentieth century, when the first comparisons were made between the pathology and symptoms of Crohn’s and Johne’s diseases (see Table 1). MAP strains have been detected and isolated from the blood, feces, and tissue biopsies of patients with Crohn’s disease. MAP bacteria isolated in this way have been shown to cause Johne’s disease in goats after experimental infection.
Table 1 Comparison of the major symptoms of bovine Johne’s disease and Crohn’s disease
Cause MAP DNA present MAP cultivated from biopsy Diarrhea Dormant periods Weight loss Lethargy Extra GI complications Intestinal blockage Fever Loss of appetite Decreased milk production Cramping and abdominal pain Nausea and vomiting
Johne’s disease
Crohn’s disease
MAP Yes Yes
Unknown Frequently Intermittently
Yes Yes Yes Yes Yes No No No Yes
Yes Yes Yes Yes Yes Yes Yes Yes N/A
N/A
Yes
N/A
Yes
GI, Gastro intestine; MAP, Mycobacterium avium paratuberculosis.
chronic enteritis in calves, possibly being spread from cow to calf via contaminated milk. Other species of NTM have been isolated from raw milk products from cattle not suffering from any clinical infection. M. flavescens, M. gordonae, M. abscessus, M. mucogenicum, M. marinum, M. terrae, M. kansassii, M. haemophilum, and M. agri as well as several unidentified species have all been observed. Not much is known about how infectious these mycobacteria are when orally ingested by humans, but several have been shown to cause infections in immunocompromised individuals, especially transplant patients on immunosuppressing agents and those with AIDS. The NTM group has doubled in number since 1990, probably due to the increasing use of modern genetic techniques and improvements in mycobacterial culture techniques. Though the virulence of these organisms is generally considered very low, they can still play a role in infections of immunocompromised individuals through contaminated milk supplies.
Other Nontuberculous Mycobacterium of Relevance to Dairy Production
Mycobacterial Contamination of Milk
A number of other NTMs are capable of causing skin infections and opportunistic wound infections. Several mycobacterial species have been reported to cause mastitis in cattle, including M. chelonei, M. fortuitum, M. phlei, and M. smegmatis. Infections of this nature in cattle can result in the pathogen contaminating the milk, leading to possible infection of young calves. The recently identified strain M. avium silvaticum has been suspected of causing
Milk supplies can become contaminated at many stages of milk collection and processing. Cattle infected with pathogenic strains can secrete bacterium in milk itself. The bacterium can also be shed in huge numbers in the feces of the animal, leading to contamination of the external surface of the udder due to contact with the feces itself or with contaminated bedding. Washing of the udders before milking has been shown to decrease bacterial
Pathogens in Milk | Mycobacterium spp. 91
contamination; however, some contamination still does occur. Contamination can also take place postpasteurization. Some mycobacterial pathogens such as M. tuberculosis and M. bovis have been shown to be capable of establishing infections at very low doses. Most data pertains to pulmonary infection, however, and the numbers required to establish intestinal infection are unknown.
Infection within the Herd Cattle can become naturally infected with mycobacteria through the respiratory or oral route. Infection via the respiratory system is the most common route in cattle, especially in the context of intense farming. Oral infection is more common in suckling calves. Cows can shed the bacterium in their colostrum and milk, or teats can become contaminated with feces, thus passing it on to calves. Apart from infection from inside the herd, a number of other avenues exist for the transmission of this disease. Drinking water can easily become contaminated and lead to infection. Mycobacteria survive quite well in treated water supplies. Apart from oral infection, aerosols could also lead to respiratory infection. Many mycobacterial species have been detected in the milk of the infected cattle, including M. bovis and MAP. Other sources of mycobacteria include the urine and feces of infected cattle. As a result bedding, pastures, and water can easily become contaminated. Shedding can be intermittent and occurs in sublinically infected cattle. The minimum dose of mycobacteria required to establish a lasing infection in cattle varies from species to species, and also depends on the route of infection and the health of the animal. Infected cattle are most likely to have been repeatedly exposed to a variety of doses.
Prevalence of Mycobacteria in Dairy Herds Cattle are susceptible to colonization and infection by a wide variety of mycobacteria, M. bovis being the most commonly reported species. Prevalence varies depending on a number of factors, including the following: programs • eradication policy • farming reservoirs of mycobacterium • wildlife • geographical location Eradication programs in industrialized countries have greatly reduced the prevalence of M. bovis infection in both animals and humans. This is a result of the monitoring programs that identify and eliminate the infected cattle, vaccination, and widespread pasteurization of
milk. Farming policy can greatly impact Mycobacterium levels. Regulation of animal movement, animal identification systems, and coordination between agricultural and health authorities all play a part in the control of disease spread. Conversely a lack of these systems or breakdown in established systems can lead to an increased prevalence in the national herd of a country. As already mentioned, mycobacterial species have wide host ranges, and apart from infecting domesticated animals they can also infect wildlife. Other species can act as reservoirs of infection, reintroducing the bacterium to pasturelands and water supplies. Reported reservoirs of mycobacteria include badgers, possums, ferrets, wild deer, and assorted domesticated animals. Control measures have at times focused on this area as a means to control spread of mycobacterial disease. Culling of infected wildlife has been attempted in several species with varying degrees of success. Culling of badger populations has been shown to decrease levels of M. bovis in cattle inside the culling regions. However, in some instances this was seen to lead to an increased infection of cattle in adjacent regions. Mycobacterial infection in humans due to contamination of dairy supplies has become less relevant in developed countries. With improvements in milk hygiene and mass pasteurization of dairy supplies, these countries have a vastly decreased mycobacterial load as compared to the prepasteurization era. These improvements in conjunction with vaccination, monitoring, and eradication programs for the tuberculosis complex bacterium have led to retail milk supplies that are safe from pathogens such as M. bovis and M. tuberculosis. A small percentage of the dairy in developed countries still involves making use of raw milk in the cheese-making process. Although the process itself can kill mycobacteria, this alone would not be sufficient to protect the consumer. If the process is coupled with effective monitoring and control programs the risk is greatly reduced. Even though the monetary cost of such surveillance is high, it is essential to safeguard human health and consumer confidence. This holds true for the majority of the NTM group of mycobacteria. However, the potential zoonotic capability of MAP continues to be a possible threat to the dairy industry. Its possible resistance to pasteurization process is a cause for concern should a link between MAP and Crohn’s disease be proven. Even without the link to Crohn’s disease, MAP still represents a substantial danger to economically important farmed animals through its presence in milk. The main danger to human health as a result of mycobacterial contamination of milk supplies lies in the developing world where pasteurization is not practiced to as great an extent as is common in the developed world. Infections by mycobacteria of importance to human health are higher in cattle in these regions due to a lack of regulation in the industry coupled with a lack
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of effective monitoring and control programs. In the developed world the incidence of AIDS infection has remained low in the general population. However, this is not the case in the developing world, where the numbers of infected individuals have been seen to rise steadily. This, coupled with malnutrition, exacerbates the problem of mycobacterial disease in these countries. See also: Diseases of Dairy Animals: Infectious Diseases: Johne’s Disease; Infectious Diseases: Tuberculosis.
Further Reading Ayele WY, Neill SD, Zinsstag J, Weiss MG, and Pavlik I (2004) Bovine tuberculosis: An old disease but a new threat to Africa. The International Journal of Tuberculosis and Lung Disease 8(8): 924–937.
Behr MA and Vivek K (2008) The evidence for Mycobacterium paratuberculosis in Crohn’s disease. Current Opinion in Gastroenterology 24(1): 17–21. Biet F, Boschiroli ML, Thorel MF, and Guilloteau LA (2005) Zoonotic aspects of Mycobacterium bovis and Mycobacterium aviumintracellulare complex (MAC). Veterinary Research 36: 411–436. Cosma CL, Sherman DR, and Ramakirshnan L (2003) The secret lives of the pathogenic mycobacteria. Annual Review of Microbiology 57: 641–676. Greenstein RJ (2003) Is Crohn’s disease caused by a mycobacterium? Comparisons with leprosy, tuberculosis and Johne’s disease. The Lancet Infectious Diseases 3: 507–514. Hermon-Taylor J and Bull T (2002) Crohn’s disease caused by mycobacterium avium subspecies paratuberculosis: A public health tragedy whose resolution is long overdue. Journal of Medical Microbiology 51: 3–6. Thoen C, LoBue P, and de Kantor I (2006) The importance of Mycobacterium bovis as a zoonosis. Veterinary Microbiology 112: 339–345. Tortoli E (2006) The new mycobacteria: An update. FEMS Immunology and Medical Microbiology 48: 159–178. White PCL, Bohm M, Marion G, and Hutchings MR (2008) Control of bovine tuberculosis in British livestock: There is no ‘silver bullet’. Trends in Microbiology 16(9): 420–427.
Salmonella spp. C Poppe, Public Health Agency of Canada, Guelph, ON, Canada ª 2011 Elsevier Ltd. All rights reserved.
Culture and Identification of Salmonella in Milk and Dairy Products Different methods have been used for the isolation and identification of Salmonella bacteria in milk and dairy products. A standard cultural procedure is the ISO 6785:2001 method of the International Organization for Standardization whereby 25 ml of milk or milk product is preenriched in 225 ml of buffered peptone water (BPW), incubated for 16–20 h at 37 C, after which 0.1 ml of the preenriched BPW is added to 9.9 ml of prewarmed Rappaport Vassiliadis (RV) selective enrichment broth and incubated at 42 C for 20 2 h and then plated onto selective agars for determination of the presence or absence of Salmonella. Presumptive Salmonella isolates are further confirmed by biochemical testing and serologically by typing with poly- and monospecific Salmonella somatic and flagellar antisera. Polymerase chain reaction (PCR)based methods are increasingly used to detect the presence of DNA sequences, such as a part of the invA or spaQ gene (both required for invasion) located within the Salmonella Pathogenicity Island (SPI) 1 or the ttrRSBCA gene complex (required for tetrathionate respiration) located adjacent to the SPI 2. These genes are specific for nearly all Salmonella serovars. The cultural and identification methods employed have a significant impact on the percentage of samples that test positive for the presence of Salmonella or a DNA sequence thereof. An advantage of cultural methods is that an isolate is obtained that can be further examined for characteristics including the phage type (PT), antimicrobial susceptibility, the presence of plasmids, and the plasmid profile; the presence of virulence and other genes; and the pulsed field gel electrophoresis (PFGE) pattern. Determination of the PFGE pattern is commonly done in the case of outbreaks to determine if the isolates can be traced to the same source or sources and to direct the institution of control and preventative measures. An advantage of PCR-based methods is that they have attained a high level of sensitivity and specificity and often result in a higher percentage of samples that are identified as contaminated with Salmonella than the cultural methods.
Incidence of Salmonella in Milk and Dairy Products Raw or Nonpasteurized Milk Raw milk may contain a variety of food-borne pathogens including Salmonella spp., verotoxigenic Escherichia coli (VTEC), Campylobacter spp., Listeria monocytogenes, and Yersinia spp. Before pasteurization and the institution of eradication and control programs for brucellosis and tuberculosis, Brucella spp. and Mycobacterium spp. could also occasionally be isolated from raw milk. Studies have been conducted to determine the incidence, prevalence, and occurrences of Salmonella bacteria in milk and dairy products. During a 2002 survey of 854 farms in 21 US states, Salmonella were isolated from 2.6% of the raw milk samples, whereas a real-time PCR indicated that Salmonella were present in 11.8% of the samples. In another study conducted in 2007 in 17 US states, 541 raw bulk tank milk samples and 523 in-line milk filters were collected and examined for the presence of Salmonella by a cultural method and by real-time PCR. Salmonella isolates were cultured from 6.7% of the milk samples and 19.9% of the milk filters, while PCR analysis indicated that Salmonella were present in 13.9% of the milk samples and 33.3% of the milk filters. Twenty-five Salmonella enterica subsp. enterica (hereafter denoted as Salmonella) serovars were identified; the most common serovars were S. Cerro (34 isolates), S. Kentucky (20), S. Muenster (14), S. Newport (10), S. Anatum (10), S. Montevideo (8), and S. Mbandaka (8). In a recent study in California, samples of bulk tank milk were taken at intervals of 2–3 months during a 29-month period and cultured for Salmonella. At each sampling period, 10–21% of the dairy farms were positive for Salmonella. The most commonly isolated Salmonella serovars in that study were S. Montevideo (33%), S. Typhimurium (14%), S. Dublin (13%), and S. Give (11%). Pasteurization of milk is a process whereby the milk is heated at 72 C for at least 15 s or at other temperature and time combinations. It is very effective in killing Salmonella and other pathogens in milk. Occasionally, pasteurized milk becomes contaminated as a result of faulty processing procedures. Investigation of a large outbreak of salmonellosis in the United States in 1984 showed that
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2% low-fat pasteurized milk processed at the dairy plant in northern Illinois had become contaminated with S. Typhimurium. The likely cause of contamination was a cross-connection of a skim milk transfer line between tanks containing raw milk and a tank with pasteurized skim milk. Examination of the possible sources of contamination of the raw milk showed that 28 (5.5%) of pooled raw milk samples from 2786 milk producers in Wisconsin and Illinois contained Salmonella. Certified Milk Certified milk is raw nonpasteurized milk produced under conditions that comply with standards of sanitation. In California, outbreaks of salmonellosis due to S. Dublin occurred when people consumed certified milk. Cheese Soft cheeses or cheeses made from unpasteurized or insufficiently pasteurized milk may be contaminated with Salmonella. The largest food-borne outbreak of salmonellosis in Canada occurred during the spring and summer of 1984, affecting about 2700 people in the four Atlantic provinces (Newfoundland, New Brunswick, Prince Edward Island, and Nova Scotia) and in the more central province of Ontario, and the affected were note to have consumed Cheddar cheese contaminated with S. Typhimurium PT10. Production of the cheese was traced to a single plant on Prince Edward Island. Cheese was manufactured from either pasteurized (16 s at 73.8 C) or heat-treated (16 s at 66.7 C; not pasteurized) milk. The contamination level of the cheese was low. The level ranged from 0.36 to 9.3 Salmonella bacteria per 100 g of cheese made from the heat-treated milk, and it ranged from 0.36 to 4.3 Salmonella bacteria per 100 g of cheese manufactured from the pasteurized milk. Up to 60 samples per lot of cheese had to be examined to find a positive lot. Examination of raw milk samples from 327 farms on Prince Edward Island, Canada, supplying milk to the cheese processing plant showed that the bulk tank milk of one farm contained S. Typhimurium PT10. One of 24 cows in the herd, although clinically healthy, shed the same S. Typhimurium PT10 intermittently in the milk from one quarter of the udder during a 36-day observation period. Not all the milk used to produce the cheese was properly pasteurized since manual turning of an electronic flow diversion valve in the plant allowed some raw milk to flow into vats used for cheesemaking. The presence of alkaline phosphatase (a temperature-sensitive enzyme that is inactivated during pasteurization) in samples of cheese associated with human illness indicated that the milk had not been fully pasteurized. Examination of the isolates of S. Typhimurium by plasmid profiling and digestion of plasmid DNA with restriction endonucleases showed that two subgroups
(I and II) of S. Typhimurium PT10 contaminated the cheese. Salmonella Typhimurium PT10 subgroup I was isolated from raw milk and cattle associated with the incriminated dairy, whereas subgroups I and II were recovered from employees at the dairy plant, from cheese obtained at the plant and in stores, and from consumers who became ill after consumption of the cheese. Investigation of the outbreak suggested that only a few Salmonella bacteria might cause infection in consumers. Studies on the fate of S. Typhimurium in the manufacturing and ripening of lowacid Cheddar cheese showed that after a rapid initial decline, the number of Salmonella remains the same and can survive refrigerated storage for more than 40 weeks. Similarly, during an outbreak of S. Newport in 2007 in northeastern Illinois, samples of 85 patients, a Mexicanstyle aged cheese (cotija) obtained at a local Hispanic grocery store, and raw milk from a bulk tank at a local dairy farm consumed by the patients tested positive for S. Newport. The isolates had indistinguishable PFGE patterns. Raw goats’ milk may also contain Salmonella, and the drinking of raw goats’ milk and consumption of cheese made from raw goats’ milk have resulted in several outbreaks of salmonellosis in humans. In a large outbreak in France in 1993, consumption of goats’ milk cheese made from unpasteurized milk caused a large number of consumers to be infected with S. Paratyphi B. The organism was isolated from milk at the processing plant on 2 of 5 occasions and was found in the milk from only 1 of 40 farms that supplied the plant. Dried Milk Products Dried milk products are occasionally contaminated with Salmonella. In an outbreak of salmonellosis in infants in the United Kingdom, all infected infants had been fed a reconstituted dried milk product from one manufacturer. Salmonella Ealing was isolated from 4 of 267 sealed packets that were examined. Other outbreaks of salmonellosis due to S. Tennessee or S. Anatum have occurred in infants after consumption of powdered milk products and infant formula in England, Wales, Belgium, France, Canada, and the United States. The prevalence of Salmonella serovars in dairy products is undoubtedly influenced by, but does not appear to entirely coincide with, the prevalence of Salmonella serovars causing infection or shedding in dairy cattle. The reason the two parameters are not in complete congruence with one another may lie in the fact that dairy products are commonly produced on a very large scale and contamination with a less common serovar may result in widespread outbreaks of salmonellosis. Also, the Salmonella serovar isolated from the milk or processed dairy product is whatever serovar happens to be present or has survived in the
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product when samples are taken for analysis, whereas differences among serovars in geographic distribution, host specificity, virulence, and infectious dose influence whether infection and shedding in cattle occur.
Sources Excretion of Salmonella in the Milk Excretion of Salmonella by cows in the milk occurs when the animal is febrile and experiencing an acute episode of salmonellosis. This happens most frequently during the postpartum period. Cows infected with the host-adapted S. Dublin may shed Salmonella bacteria with the milk, but shedding of Salmonella via this route has also occurred with a number of other Salmonella serovars including S. Typhimurium, S. Muenster, S. Give, S. Heidelberg, and S. Enteritidis. Occasionally, mastitis occurs in infected cows. Nonsymptomatic carrier animals may excrete Salmonella intermittently with the milk. Salmonella bacteria may be shed for prolonged periods of time from one quarter of the udder. In one study, S. Enteritidis PT8 was repeatedly isolated over a period of 7 months from the right hindquarter of the udder of a 5-year-old Holstein cow. The milk appeared normal at all times. In a study in the United Kingdom, 26 of 70 milk filters examined during a 4-year period (1983–86) tested positive for S. Typhimurium PT49a. At the end of the study period when milk samples were collected from 131 lactating cows, Salmonella bacteria were found in one milk sample. Milk samples taken 3 months later from 152 cows in milk at the same farm showed the same results; one milk sample cultured positive for S. Typhimurium. The affected cow shed Salmonella from one quarter of the udder. The number of Salmonella bacteria shed in the milk may vary considerably. During an outbreak of S. Muenster infections in dairy cattle, one cow in midlactation in a herd of 35 cows shed S. Muenster at a rate of approximately 200 cfu ml 1. The cow continued to shed the organism during the rest of the lactation period and at the next calving S. Muenster was again isolated. One of the quarters of the udder showed signs of clinical mastitis at calving. During the same outbreak affecting more than 200 herds, 3 other cows in 3 herds continued to shed S. Muenster in the milk, although the fecal samples were negative. Chronically infected carriers may shed 10–30 bacteria per ml of milk, but shedding of as many as 105 bacteria per ml of milk has been reported. Contamination of Milk from Other Sources Milk is most often contaminated after it leaves the cow by various means including fecal matter, contaminated equipment, dust, and other environmental sources. Adult cattle that recover from clinical disease may become
active carriers and such apparently healthy animals may excrete Salmonella in large numbers in the feces for prolonged periods. Carrier animals are a major source of environmental contamination and infection of animals and humans. Cows excreting Salmonella may infect neighboring cows in a barn, which then in turn may excrete Salmonella in the milk and the feces. During an outbreak of salmonellosis in dairy cattle in Quebec, Canada, S. Give was isolated from the feces of cows with clinical salmonellosis and from the bulk tank milk of two herds. In one herd, the infection was so widespread that S. Give was isolated from the feces of 41% of the cows. Milk production was considerably reduced. Ten of 24 positive cows shed Salmonella in their feces for more than 6 weeks, and 5 of 23 cows for 11 weeks or longer. The only clinically affected cow had profuse diarrhea in its postpartum period. Salmonella Give was isolated from 2 of 5 cats that frequented the feeding alley in the barn. In a neighboring dairy herd, a febrile and diarrheic cow excreted S. Give in the feces, and a week later the two adjacent cows shed the same Salmonella serovar in the feces. The distribution of the infection appeared to be limited to the immediate environment of the clinically ill animal since feces from none of the other cows in the herd tested positive for Salmonella. One cow in this herd shed S. Give in the feces for at least 26 weeks. Milking equipment may be contaminated with Salmonella before and during milking the cows. Dust, bedding, manure, other debris, and aerosols may be aspirated by the vacuum pump of the milking systems and contaminate the milk with Salmonella and other pathogens. Plant fibers and other particulate debris have been found on milk filters, suggesting that fecal matter, bedding, and other debris may have contaminated the milk. Farmers and farm workers may be infected and transfer Salmonella from themselves or from sources in the immediate environment to the milking equipment and the milk. Salmonella-infected cats and dogs on the farm may play a role in contaminating the milk. Direct or indirect contamination of the milk may occur when cows drink Salmonella-contaminated water or when the water contaminates the udder or the milking equipment. Farmers and their helpers may also contract the disease by direct transfer of Salmonella from infected cattle or calves via feces or saliva. Cattle that drink from contaminated streams and creeks may ingest Salmonella and the water may contaminate the udder and teats. In the United Kingdom, cattle and calves grazing on pasture contaminated with human sewage became infected and S. Dublin, S. Typhimurium, and other Salmonella serovars were repeatedly isolated from milk filters. Dried milk products may be contaminated with Salmonella. In one outbreak, the source of contamination was traced to a spray-dryer that had a hole in its inner lining, allowing contamination of the milk powder to occur.
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Utensils used for cheesemaking may be contaminated with Salmonella. In an outbreak of salmonellosis caused by the consumption of cheese contaminated with S. Berta, the unpasteurized soft cheese was made by ripening the skim milk curds at room temperature in large buckets. One of the buckets had previously been used for the soaking of chicken carcasses before they were frozen for later consumption. Salmonella Berta was also isolated from the chicken carcasses.
Control Measures There are many measures that can be taken to prevent salmonellosis. The most important public health control measure is undoubtedly pasteurization of the milk; if properly done, pasteurization is extremely effective in eliminating the risk of infection. Regulations under the US Public Health Service and a variety of state and local regulatory agencies requiring pasteurization of milk and a comprehensive set of sanitary procedures resulted in a decrease in the outbreaks of milk-borne illness from approximately 25% of all reported food-borne illness outbreaks in 1938 to less than 1% in 2008. Measures other than pasteurization include prevention of contamination, inhibition of bacterial growth, prevention of gastrointestinal infection in infants and adults by the consumption of fermented milk products, and control of the feeding of Salmonella-contaminated feeds to animals. The growth of Salmonella can be inhibited by lowering the pH of foods, by treating foods with organic acids or sodium chloride, and by refrigeration. Such preventative measures have been described in the literature (see ‘Further Reading’). Vaccination of cattle is also used to prevent and control salmonellosis (see Diseases of Dairy Animals: Infectious Diseases: Salmonellosis). Measures to curtail the drinking of unpasteurized milk have been highly successful in preventing infections. The implementation of legislation in 1983 in Scotland prohibiting the retail sale of untreated cows’ milk effectively controlled the large general community outbreaks of milk-borne salmonellosis and Campylobacter enteritis. However, the drinking of raw milk by dairy farmers and their families and friends continues to be a common practice in many countries. It has caused numerous cases of salmonellosis among these groups. Dairy farmers and their families should be informed about the dangers of drinking of raw milk and the ensuing cases of illness and number of deaths due to infections with Salmonella, Campylobacter, Listeria, and VTEC. Such information can be provided by placing articles about milk-borne illnesses and measures to control such illnesses in dairy producers’ magazines and other publications for farmers and their families. The public at large, and especially chronically ill elderly patients and the parents of young children, should
be cautioned against the drinking of raw milk, an increasingly popular ‘health food’. Some consumers claim that drinking raw milk has health benefits including decreased risks for artherosclerosis, arthritis, and lactose intolerance. However, such claims are not supported by scientific evidence. Large outbreaks in the United States and Canada of milk- and cheese-borne salmonellosis in humans occurred as a result of misdirecting the flow of raw milk into containers and vats intended to receive pasteurized milk. It is therefore imperative to maintain proper control of the flow of pasteurized milk and to maintain a strict separation of unpasteurized and pasteurized products in dairy processing plants. Outbreaks of salmonellosis after consumption of reconstituted dried milk products prompted recommendations to manufacturers such as increased monitoring of the drying process so that defects in the process may be readily recognized and remedied, not to blend products with high counts of bacteria with batches with a low viable count, and not to keep raw milk and whey on-site at milk-drying plants. The average number of milking cows per dairy worker has increased significantly during the last few decades in many countries and less time is available for attention to the hygiene of individual animals. In the process, the potential exposure of milk to contamination during production has also increased. Thus, strict hygienic measures before, during, and after milking the cows should be maintained. Such measures include a clean milking parlor, proper disinfecting and cleaning of the udder and teats, good maintenance, cleaning and disinfecting of milking equipment before and after use, and the institution of other measures to promote hygiene and prevent contamination of milk during production. Good manufacturing practices must be maintained in order to produce cheese free from Salmonella contamination. Investigation of an outbreak of salmonellosis due to S. Heidelberg in Denver and Pueblo, CO, showed that the raw milk used at the dairy processing plant to make the cheese contained more than 3 million bacteria per ml. The raw milk was stored for 1–3 days in insulated but unrefrigerated holding tanks and the milk was filtered only after pasteurization, a violation of guidelines for pasteurization. Also, bacterial culturing and determination of the presence of phosphatase in the milk used to make the cheese were not carried out. The manufacturer was urged to take appropriate corrective measures.
Salmonellosis in Humans Throughout the world, much of the milk consumed is still not pasteurized. In many countries, unpasteurized milk or certified milk is available for sale or can be obtained
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directly from the farm. In Canada, the sale of raw milk directly to consumers is prohibited. The distribution of raw milk is illegal also in Scotland. However, in England, registered producers are allowed to sell raw milk directly to the consumer. Although Food and Drug Administration (FDA) regulations in the United States require mandatory pasteurization of packaged milk and milk products for human consumption in interstate commerce, in 27 US states raw milk can still be bought directly from the farmer. Raw milk is sometimes available to the consumer through a ‘cow share’ purchasing program. The drinking of unpasteurized milk and the consumption of soft cheeses made from raw or improperly pasteurized milk or milk contaminated after the pasteurization process have resulted in numerous single case and small and large outbreaks of salmonellosis. Cases of food-borne outbreaks due to consumption of Salmonellacontaminated raw milk have been reported in many countries. The majority of milk-borne epidemics of salmonellosis in humans in the United Kingdom have been caused by S. Dublin and S. Typhimurium. These two Salmonella serovars have also been the most commonly isolated serovars from cattle in the western European countries, whereas in the United States and Canada S. Typhimurium has been the most frequently isolated serovar from bovine sources. Such outbreaks continue to occur. For example, the consumption of Mexican-style soft cheese made from raw milk caused several outbreaks of S. Typhimurium DT (definitive phage type) 104 infection in people in California and Washington State. In another recent outbreak of salmonellosis in Pennsylvania, 29 cases of diarrheal illness, 16 of them in children less than 7 years of age, occurred as a result of drinking raw milk or consuming a soft cheese (queso fresco) made from raw milk; all isolates had the same PFGE pattern (the DNA was digested using the XbaI restriction enzyme) and could be traced to the same dairy farm that held a state-issued permit to sell raw milk to customers. Symptoms The symptoms observed in cases of human salmonellosis are diarrhea, abdominal cramps, nausea, vomiting, fever, headache, and blood in the feces. The frequency and severity of the symptoms may vary. In the soft cheeserelated outbreaks of infection with S. Typhimurium DT 104 mentioned above, diarrhea was observed in 100%, abdominal cramps in 93%, fever in 93%, bloody stools in 72%, and vomiting in 53% of cases, while 9% of patients were hospitalized. In California, during the period 1971–74, there were 79 cases of human salmonellosis due to S. Dublin; 74 of these 79 cases drank certified raw milk produced at a single large dairy farm. In 52 of the 79 cases, the organism was isolated from blood, urine, or
deep tissue sites, demonstrating the invasiveness of the pathogen. Sixteen of the 79 patients died, of whom 13 had preexisting chronic debilitating diseases. In 1993, in France, consumption of a raw goats’ milk cheese was associated with a S. Paratyphi B infection in 273 patients; in 240 patients the organism was isolated from the feces, in 15 from blood, in 14 from tissues, and in another 4 the site was unknown. Thirty-seven percent of the patients were hospitalized and one died. The largest single foodborne epidemic in the United States affected an estimated number of more than 160 000 persons who became ill as a result of S. Typhimurium infection from contaminated 2% low-fat milk produced by a dairy plant in Illinois in 1985. There were more than 16 000 culture-confirmed cases, 2777 patients were hospitalized, and 14 associated deaths occurred. Patients infected and shedding Salmonella with the stool may experience sequelae to the primary infection such as extraintestinal salmonellosis and isolation of the Salmonella from the blood, from cases with septicemia, cystitis, and pyelonehritis, and from cases with abscesses and tissues. Sterile or reactive arthritis of the knees and occasionally of the ankles and other joints is not uncommon in patients who experienced a bout of diarrhea and from whom previously or concomitantly S. Typhimurium, S. Enteritidis, or other Salmonella serovars were isolated from the stool. Human leukocyte antigen (HLA) typing of such patients shows that they are usually B27 positive. Susceptibility to Salmonella Infection and Severity of Illness Susceptibility to, and severity of, Salmonella infection in humans depends on various factors including the dose and virulence of the pathogen for the human host, the type of food contaminated with Salmonella that was consumed, the age of the host, and factors known to affect the immune status of the host, such as infection with the human immunodeficiency virus (HIV), leukemia, and/or the use of immunosuppressive drugs. Other host-associated risk factors include diabetes, partial gastrectomy, and the low gastric acidity associated with these conditions. The very young and the elderly are most susceptible to the infection. The fat content of contaminated foods such as cheese may influence the dose required to cause an infection. Salmonella present in foods with a high fat content such as cheese may be trapped in hydrophobic lipid moieties and survive the acidic conditions of the stomach to subsequently attach to and invade the enterocytes lining the intestines. Cases in which humans became infected after ingestion of an estimated dose of 100–500 S. Heidelberg or, in another outbreak, less than 10 S. Typhimurium in Cheddar cheese, support this hypothesis.
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See also: Diseases of Dairy Animals: Infectious Diseases: Salmonellosis.
Further Reading Berge ACB, Champagne SC, Finger RM, and Sischo WM (2007) The use of bulk tank milk samples to monitor trends in antimicrobial resistance on dairy farms. Foodborne Pathogens and Disease 4: 397–407. Bezanson GS, Khakhria R, Duck D, and Lior H (1985) Molecular analysis confirms food source and simultaneous involvement of two distinct but related subgroups of Salmonella typhimurium bacteriophage type 10 in major interprovincial Salmonella outbreak. Applied and Environmental Microbiology 50: 1279–1284. Brian FL (1983) Epidemiology of milk-borne diseases. Journal of Food Protection 46: 637–649. CDC (2007) Salmonella Typhimurium infection associated with raw milk and cheese consumption – Pennsylvania, 2007. Morbidity and Mortality Weekly Report 56: 1161–1164. CDC (2008) Outbreak of multidrug-resistant Salmonella enterica serotype Newport infections associated with consumption of unpasteurized Mexican-style aged cheese – Illinois, March 2006–April 2007. Morbidity and Mortality Weekly Report 57: 432–435. D’Aoust J-Y, Warburton DW, and Sewell AM (1985) Salmonella Typhimurium phage-type 10 from Cheddar cheese implicated in a major Canadian foodborne outbreak. Journal of Food Protection 48: 1062–1066. Descenclos J-C, Bouvet P, Benz-Lemoine E, et al. (1996) Large outbreak of Salmonella enteric serotype Paratyphi B infection caused
by a goats’ milk cheese, France, 1993: A case finding and epidemiological study. British Medical Journal 312: 91–94. El-Gazzar F and Marth EH (1992) Salmonella, salmonellosis and dairy foods: A review. Journal of Dairy Science 75: 2327–2343. Fierer J (1983) Invasive Salmonella Dublin infections associated with drinking raw milk. Western Journal of Medicine 138: 665–669. Galbraith NS, Forbes P, and Clifford C (1982) Communicable disease associated with milk and dairy products in England and Wales 1951– 80. British Medical Journal 284: 1761–1765. Karns JS, Van Kessel JS, McCluskey BJ, and Perdue ML (2005) Prevalence of Salmonella enteric in bulk tank milk from US dairies as determined by polymerase chain reaction. Journal of Dairy Science 88: 3475–3479. Malorny B, Ma¨de D, Teufel P, et al. (2008) Multicenter validation study of two blockcycler- and one capillary-based real-time PCR methods of the detection of Salmonella in milk powder. International Journal of Food Microbiology 117: 211–218. Potter ME, Kaufmann AF, Blake PA, and Feldman RA (1984) Unpasteurized milk: The hazards of a health fetish. Journal of the American Medical Association 252: 2050–2054. Ryan CA, Nickels MK, Hargrett-Bean NT, et al. (1987) Massive outbreak of antimicrobial-resistant salmonellosis traced to pasteurized milk. Journal of the American Medical Association 285: 3269–3274. Schmidt RH and Davidson PM (2008) Milk pasteurization and the consumption of raw milk in the United States. Food Protection Trends 28: 45–47. Sharp JCM (1989) Milk-borne infection. Journal of Medical Microbiology 29: 239–242. Villar RG, Macek MD, Simons S, et al. (1999) Investigation of multidrugresistant Salmonella serotype Typhimurium DT104 infections linked to raw-milk cheese in Washington State. Journal of the American Medical Association 281: 1811–1816.
Shigella spp. E Villalobo, Universidad de Sevilla, Seville, Spain ª 2011 Elsevier Ltd. All rights reserved.
Introduction Dysentery is an intestinal disorder caused by microorganisms: bacteria, amoebas, or viruses. Bacillary dysentery or shigellosis refers to the disease caused by bacteria of the genus Shigella. This name was adopted in 1950 in honor of Kiyoshi Shiga, the scientist who first differentiated amoebic from bacterial dysentery, and who isolated Bacillus dysenteriae in 1898. Shigella spp. are enteric bacteria essentially found in humans and primates, but they spread into the environment, especially into water and food, due to human activities. Milk and dairy products are susceptible to being contaminated by shigellae, causing thousands of outbreaks a year. Indeed, outbreaks are more and more common, due to adoption of new life styles. Consequently, dysentery is an emerging disease of worldwide public dimension that attracts the attention of food and health administrations in an attempt to minimize its societal impact. The following sections are devoted to the bacteriology of Shigella spp. and their occurrence in milk. Special attention is paid to pathogenesis, outbreaks, safety, and detection/identification methods.
Bacteriology Shigellae (genus Shigella, family Enterobacteriaceae, according to Bergey’s Manual, Section 5: ‘‘Facultatively Anaerobic Gram-Negative Rods’’) are straight rodshaped, facultatively anaerobic, oxidase-negative bacteria that stain Gram-negative. Shigellae, unlike their closest relative Escherichia coli, are nonmotile, and do not ferment lactose or produce gas from glucose, nor reduce sulfate to hydrogen sulfide. However, enteroinvasive E. coli (EIEC), which also causes dysentery, is practically indistinguishable from shigellae. Infective dose, 1000-fold higher for EIEC than for shigellae, is perhaps one difference between these two pathovars. The four species of the genus Shigella are Sh. dysenteriae, Sh. flexneri, Sh. boydii, and Sh. sonnei. A few serovars have been differentiated in each species, even though all serovars within each species share a specific O side chain in their lipopolysaccharide (LPS). This is the reason why Sh. dysenteriae, Sh. flexneri, Sh. boydii, and Sh. sonnei are usually referred by epidemiologists as subgroups A, B, C, and D, respectively.
The natural hosts of shigellae are humans and monkeys, with the intestinal tract being their common habitat. However, these pathogens remain viable in the skin. Person-to-person transmission by the fecal/oral route is common, though sexual transmission is also possible. They are also viable in food, water, and beverages; consequently, these are additional modes of transmission. Special attention must be paid to asymptomatic carriers and flies, as both serve as silent transmission vehicles.
Pathogenesis The main pathogenicity or virulence property of Shigella is cell invasion, which is responsible for most of the symptoms of dysentery. The invasion occurs mainly in the colon, though it can also be observed in the last part of the ileum. The process starts with the adhesion of pathogens to the surface of M cells of the follicle-associated epithelium. The host–pathogen contact causes internalization of the bacteria into vacuoles, in a process resembling macropinocytosis. After lyzing the vacuolar membrane, the pathogens escape to the cytoplasm, move to the edge of the nucleus, where they grow and form a microcolony. Cell-to-cell spreading occurs via bacteriacontaining protrusions phagocyted by the adjacent cells. Spreading is not limited to the epithelial lining but proceeds to the lamina propria, where the bacteria are released and ingested by macrophages. The pathogens, rather than being killed by macrophages, escape the phagosome, induce release of interleukin-1 , and cause apoptotic death of the macrophages. The overall result is an inflammatory response that attracts polymorphonuclear leucocytes, which loosen the cellular junctions. Now, the pathogens at the colonic lumen are free to pass through the epithelial lining and to gain access to the basolateral surface. Then, more epithelial cells are invaded and the inflammatory response is amplified. This recurrent event results in the formation of colonic ulcers, a macroscopic hallmark of dysentery. The dysenteric stool is bloody and mucoid due to the infiltration of red blood cells and serum proteins. Genetic Determinants of Virulence Virulence is a multifactorial property in which both a nucleoid and a plasmid are involved. All pathogenic
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shigellae and EIEC bear a large plasmid ranging from 180 to 220 kb, called the virulence plasmid. This plasmid contains a pathogenicity island, needed for invasion and essentially composed of three operons: ipa (invasion plasmid antigens), mxi (membrane expression of invasion plasmid antigens), and spa (surface presentation of invasion plasmid antigens). While mxi and spa genes code for subunits of the type III secretion system, the ipa genes code for the effectors secreted by this system. Some other genes located in the virulence plasmid, such as virG (icsA), which codifies for an outer membrane protein, are also needed for invasion. The nucleoid-encoded genes, mainly responsible for the survival of the pathogen in the host, are also organized in a few pathogenicity islands. Enumerating all the nucleoid-encoded genes would require extensive discussion; but, due to its significance, the locus stx stands out, as it codifies for the shiga toxin in Sh. dysenteriae 1. This toxin is a potential inhibitor of mammalian protein synthesis and is responsible for the most severe pathogenic phenotypes. Recently, two new enterotoxins responsible for the clinical manifestation of dysentery have been characterized. Shigella enterotoxin 2 is codified in the virulence plasmid and is present in most shigellae isolates. Disease Symptoms and Complications Clinical manifestation of dysentery varies greatly from asymptomatic infections to fulminating dysentery, though mild diarrhea is also common. The severity of the disease depends not only on the person but also on the shigellae strain. For obvious reasons, immune-compromised or malnourished individuals and children are prone to suffer more severe infections. By species, Sh. dysenteriae and Sh. flexnery produce severe infections, while Sh. sonnei is more benign. The typical symptoms of dysentery are fever, permanent emission of bloody and mucopurulent stools that leads to dehydration, and intestinal discomfort characterized by cramps and tenesmus. Complications can cause death, due to septicemia and hypoglycemia, especially in children. Reiter’s syndrome is a common sequela of dysentery in individuals expressing the HLAB127 histocompatibility antigen. Hemolytic uremic syndrome, with renal failure, is not infrequent when infected with Sh. dysenteriae 1. Though very infrequent, ulcerative keratitis due to shigellae infection has also been reported.
Occurrence in Milk Milk is a rich substance that supports bacterial growth; therefore, after contamination, bacterial counts increase within a wide range of time and temperatures. Consequently, the shelf life, quality, and safety of raw
milk are determined by the types and load of bacteria. High loads of spoilage flora imply high enzymic activity of lipases and proteases, sometimes thermostable, that reduce the fat and protein content, consequently lowering the quality of raw milk. These enzymic activities have other undesirable organoleptic effects: bitterness, rancidity, and off-flavors. Pathogenic bacteria, such as Shigella spp., primarily affect food safety; hence, pathogen contamination must simply be avoided in milk. Shigella spp. remain viable for at least 72 h at 4 C or proliferate at 15–37 C in raw milk. As the infective dose is very low – 10 to 100 bacteria are enough to trigger an infection – special care must be taken to avoid contamination of raw milk and dairy products by these pathogens. Occurrence of Shigella spp. is sometimes reported in milk, as in Sudan, where analysis of bulk tank cow milk indicates that 20% of the samples contain Shigella spp. in the range of 1 106 cfu ml 1. Occurrence of Shigella spp. in dairy products is lower than in raw milk, due to the special properties of these foods, as discussed below.
Outbreaks There are no accurate data available regarding the total number of dysentery outbreaks each year, but most likely millions of humans are affected worldwide. Estimates indicate 145 million cases per year, with mortality reaching between 0.5 and 1.5 million; children below 5 years of age are the main victims. Outbreaks take place worldwide, with the majority occurring in countries suffering from poor sanitation, hunger, wars, or catastrophes. There is also a general seasonal trend: in tropical areas the incidence is higher in the rainy season, due to flooding, while in subtropical areas the incidence is higher in summer, due to high temperature and drought. Shigella flexneri and Sh. dysenteriae account for most cases of dysentery in developing countries. The former relates to the endemic disease, and the latter to epidemics. Shigella sonnei essentially affects well-developed countries. Finally, Sh. boydii rarely causes outbreaks except in the Indian subcontinent. An epidemiological transition from flexneri to sonnei is considered an indicator of economic development; such a transition should be seen in the near future in emerging economies such as India. Milk and dairy products are suspected of being responsible for several dysentery outbreaks. Between 1998 and 2007, 83 foodborne pathogen-related outbreaks were publicly reported, of which 14.5% had been associated with dairy products. One of the recent outbreaks occurred in 2004 in Vilnius, Lithuania. Of the 41 cases detected, 36 were diagnosed as dysentery; 50% of the patients were children under 14 years of age, and 16% of the affected individuals were above 65 years.
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As expected, all patients were positive for Sh. sonnei. Unpasteurized milk curd was the vehicle for transmission, and contamination of this product was due to handlers either in the dairy facility or in the market. Indeed, the same Sh. sonnei serotype was confirmed in patients, workers, and inhabitants of the dairy facility, and workers of the market. This case clearly shows the importance of microbiological safety measures needed in dairy production.
Microbiological Safety There are several ways to reduce shigellae in raw milk, the most effective one being thermal treatment. Pasteurization and ultra-high temperature (UHT) treatment are very effective. For Sh. dysenteriae, the decimal reduction time (D value) in milk at 82.2 C is 0.8 s, while in nutrient broth at 63 C it is 5 min. Thus, the common thermal treatments applied to milk significantly reduce the total counts of Shigella.
Detection, Enumeration, and Identification Methods Coliform bacteria are indicative of fecal contamination; therefore, a milk sample with a high coliform count is suspicious of harboring enteric pathogens also, such as Shigella or Salmonella. The prevalence of shigellae in milk is not negligible, and from time to time they appear in the dairy industry. When this occurs, it is important to monitor the possible sources of contamination in order to adopt control measures. Thus, it is worthy to review the traditional and molecular methods for detection and identification of shigellae. There are no specific media for growing Shigella spp. Normally, the media used to cultivate these pathogens are of a broad bacterial spectrum, or designed either for enterobacteria or Salmonella. Typical enrichment media are Hajna (Gram-negative) broth, buffered-water peptone, selenite cystine broth, tetrathionate broth, and brilliant green bile glucose broth. As the counts of shigellae in milk are high, enrichment is not only unnecessary but contradictory, given that these pathogens outgrow in the presence of other enteric bacteria. If enrichment is needed, addition of novobiocin to the media greatly improves the recovery of Shigella spp. A successful strategy is to use this antibiotic along with a low carbohydrate concentration in the medium. Typical isolation (selective) media are Salmonella–Shigella agar, xylose lysine deoxycholate agar, deoxycholate citrate agar, its modified version deoxycholate lactose sucrose agar, eosin methylene blue agar, and tergitol-7 agar. Typical differential media are Hektoen enteric agar, MacConkey agar, and
triple sugar iron agar slant. Chromogenic media have been developed, such as chromogenic Shigella plating medium (CSPM), which contains a proprietary mix of carbohydrates, selected pH indicators, and chromogens. Identification of Shigella spp. in CSPM is easy, since they produce white to clear colonies, while bacterial competitors produce colored colonies. Recovery of Shigella spp. from food in this medium is similar to that reported for MacConkey and Salmonella–Shigella agars; however, CSPM needs further evaluation with different shigellae serotypes. A single-tube screening test has also been developed for Salmonella and Shigella. This method, based on a four-layered semisolid medium, has 100% sensitivity (56 Shigella isolates tested) and 95% specificity (56 nonShigella isolates tested). After detection/isolation in culture media, the presumptive isolates must be further characterized by molecular tests, even if a differential medium had been used. The reason for the deeper characterization is that Shigella spp. are difficult to identify based solely on the abovementioned media. In addition, from a medical point of view, it is very important to determine which shigellae serotype is isolated. Primary biochemical characterization of Shigella spp. involves four distinctive properties of these bacteria: (swarming) motility, production of H2S, production of gas from glucose, and fermentation of lactose. These tests, which are carried out on agar media, are negative for most Shigella serovars. At this point, it must be mentioned that Sh. sonnei ferments lactose very slowly, and that Sh. flexneri 6, Sh. boydii 13 and 14, and Sh. dysenteriae 3 produce gas from glucose. Further biochemical characterization is also desirable though, once again, no specific tests for Shigella spp. are available. Test strips for bacterial identification, such as API20E or similar tests, are very popular in diagnostic laboratories. These systems have two major drawbacks: they need expert interpretation and are time consuming. These concerns are overcome, at least in part, with automated systems such as Vitek. The EPS (enteric pathogens) card of this system has been evaluated for enteric pathogens. The card gave a sensitivity of 99.5% for enteric pathogens, including several shiegellae serovars, and a specificity of 90.1% for nonpathogens. An automated system for the enumeration (based on the most-probable-number technique) and confirmation of enterobacteria, Tempo EB (enterobacteria), has also been released; use of this system must be considered when fast results are required. Similar methods are becoming available in the market. More recently, a simple, fast, and inexpensive method specifically developed for Shigella spp. has been reported. It is a colorimetric method based on the detection of apyrase, a periplasmic enzyme necessary for intracellular spread of pathogen. The assay shows 96% sensitivity (over 23 isolates of Shigella and EIEC) and 80% specificity (over 34 isolates
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tested). Though the assay has been successfully applied on stools, it requires further validation and domains of application. Immunological identification of Shigella spp. is based on surface antigens, such as LPS. This molecule is composed of three different regions: the lipid A, which anchors the LPS to the outer bacterial membrane, the core oligosaccharide, and the O-antigen. The latter, a polymer of repeating saccharide units, is strain specific, with all strains having the same O-antigen belonging to the same serotype. Serotype acknowledgment depends on various authors of different studies, but less than 46 seem to be acceptable. Shigella boydii can be subdivided in 20 serotypes, Sh. dysenteriae in 15, Sh. flexneri in 6, and Sh. sonnei in only 1 serotype. Interestingly, most of the Sh. flexneri serotypes share the same O-antigen basic structure. Different commercial kits for serotyping are available. Most of them use polyclonal sera raised in rabbit against reference strains, and slide/latex/tube agglutination, enzyme immunoassay, or immunomagnetic platforms for detection. The main drawback of serotyping is that sera can fail in detecting particular serotypes. In Bangladesh, for instance, 3% of isolates from patients with diarrhea have the typical biochemical properties of shigellae but they fail to be detected with the currently available sera. These are known as Shigella-like organisms, one of which has had a high prevalence over several years, and has been classified by molecular methods as a novel serovar of Sh. dysenteriae. Likewise, 180 isolates classified as Shigella-like organisms in France between 2000 and 2004 were recently identified by molecular methods as Sh. boydii. Several commercial kits for serotyping have been evaluated, and only one gave a performance lower than the conservative standard of 90% of accuracy. Genetic identification is based on genotyping, that is, determining the identity of a strain based on its genetic material using a biological assay. The most popular and widely used method is the polymerase chain reaction (PCR), which consists of specific amplification of a small portion of the genetic material of an organism, such as bacteria, in a complex sample, such as food. Dozens of publications a year deal with PCR identification of Shigella spp. in food, as many as the genetic targets to be amplified, among them the loci ial, virA, or ipaH. A plethora of PCRbased assays are also popular, though their use in food is limited. Noteworthy is fingerprinting, based on the generation by PCR of a specific DNA pattern that serves to identify microorganisms. Restriction fragment length polymorphism (RFLP-PCR), amplified fragment length polymorphism (AFLP-PCR), enterobacterial repetitive intergenic consensus (ERIC-PCR), and repetitive extragenic palindromic sequence-based PCR (rep-PCR) are also notable. Recently, an automated system based on repPCR, called DIVERSILAB, has been commercialized.
This system allows rapid and specific detection of Shigella spp., though it has been applied in epidemiology only. Before ending this section, identification methods based on a cell’s ome, the units that define a cellular constituent or function, should be mentioned. Collectively these methods are called ‘omics’. The most popular are transcriptomic, such as DNA (microarrays) chips; proteomic, such as mass spectrometry; and genomic, such as DNA sequencing. DNA sequencing is becoming very popular, since a few devices for fast, reliable, and cheap whole-genome sequencing have been developed in the last 5 years. Based on this highthroughput technology, new methods for identification are becoming available. An example is multiple loci sequence typing (MLST), an identification method halfway between genomics and genotyping. Conceived as a universal, portable, and definitive method, it consists in raising indexes of variation in multiple housekeeping genes of a particular organism, such as Neisseria meningitidis, for which the method was originally developed. A similar method, called variable-number tandem-repeat (VNTR) analysis (MLVA) has been applied to Shigella spp. A panel of 15 VNTRs has been released to detect Shigella spp., though the main drawback is that E. coli is also detected. More work in this area is needed to release a panel specific enough to detect only shigellae. See also: Analytical Methods: DNA-based Assays; Microbiological. Milking and Handling of Raw Milk: Milking Hygiene. Pathogens in Milk: Escherichia coli; Salmonella spp. Risk Analysis.
Further Reading Barbano DM, Ma Y, and Santos MV (2006) Influence of raw milk quality on fluid milk shelf life. Journal of Dairy Science 89: E15–E19. Day WA and Maurelli AT (2002) Shigella and enteroinvasive Escherichia coli: Paradigms for pathogen evolution and host-parasite interactions. In: Donnenberg MS (ed.) Escherichia coli: Virulence Mechanisms of a Versatile Pathogen, ch. 7, pp. 209–237. Elsevier Science. Greig JD and Ravel A (2009) Analysis of foodborne outbreak data reported internationally for source attribution. International Journal of Food Microbiology 130: 77–87. Gupta A, Polyak CS, Bishop RD, Sobel J, and Mintz ED (2004) Laboratory-confirmed shigellosis in the United States, 1989–2002: Epidemiologic trends and patterns. Clinical Infectious Diseases 38: 1372–1377. Hayes MC, Ralyea RD, Murphy SC, Carey NR, Scarlett JM, and Boor KJ (2001) Identification and characterization of elevated microbial counts in bulk tank raw milk. Journal of Dairy Science 84: 292–298. Holt JG, Krieg NR, Sneath PH, Staley JT, and Williams ST (1994) Genus Shigella. In: Holt JG (ed.) Bergey’s Manual of Determinative Bacteriology, pp. 187–188. Baltimore, MD: Williams & Wilkins. Keusch GT (2001) Shigella. In: Sussman M (ed.) Molecular Medical Microbiology, ch. 61, pp. 1279–1290. San Diego, CA: Academic Press. Kleter GA and Marvin HJP (2008) Indicators of emerging hazards and risks to food safety. Food and Chemical Toxicology 47: 1022–1039. Lefebvre J, Gosselin F, Ismaı¨l J, Lorange M, Lior H, and Woodward D (1995) Evaluation of commercial antisera for Shigella serogrouping. Journal of Clinical Microbiology 33: 1997–2001.
Pathogens in Milk | Shigella spp. 103 McMeekin T, Bowman J, McQuestin O, Mellefont L, Ross T, and Tamplin M (2008) The future of predictive microbiology: Strategic research, innovative applications and great expectations. International Journal of Food Microbiology 128: 2–9. Niyogi SK (2005) Shigellosis. The Journal of Microbiology 43: 133–143. O’Hara CM (2005) Manual and automated instrumentation for identification of Enterobacteriaceae and other gram-negative bacilli. Clinical Microbiology Reviews 18: 147–162. Parsot C (2005) Shigella spp. and enteroinvasive Escherichia coli pathogenicity factors. FEMS Microbiology Letters 252: 11–18. Percival S, Chalmers R, Embrey M, Hunter P, Sellwood J, and Wyn-Jones P (eds.) (2004) Shigella. Microbiology of Waterborne Diseases, ch. 13, pp. 185–195. San Diego, CA: Academic Press. Ruegg PL (2003) Practical food safety interventions for dairy production. Journal of Dairy Science 86: E1–E9. Sansonetti PJ, Egile C, and Wenneras C (2001) Shigellosis: From disease symptoms to molecular and cellular pathogenesis. In: Groisman EA (ed.) Principles of Bacterial Pathogenesis, ch. 8, pp. 335–385. San Diego, CA: Academic Press. Sharma M and Anand SK (2002) Characterization of constitutive microflora of biofilms in dairy processing lines. Food Microbiology 19: 627–636. Uyttendaele M, Bagamboula CF, De Smet E, Van Wilder S, and Debevere J (2001) Evaluation of culture media for enrichment and
isolation of Shigella sonnei and S. flexneri. International Journal of Food Microbiology 70: 255–265. Warren BR, Parish ME, and Schneider KR (2006) Shigella as a foodborne pathogen and current methods for detection in food. Critical Reviews in Food Science and Nutrition 46: 551–567. Woteki CE and Kineman BD (2003) Challenges and approaches to reducing foodborne illness. Annual Review of Nutrition 23: 315–344.
Relevant Websites http://www.cfsan.fda.gov/ebam/bam-toc.html#intro – Bacteriological Analytical Manual On-line. http://www.eurosurveillance.org – Eurosurveillance. http://www.cdc.gov/FoodNet – Foodborne Diseases Active Surveillance Network. http://www.icmsf.iit.edu/main/home.html – International Commission on Microbiological Specifications for Foods. http://www.cdc.gov/mmwr – Morbidity and Mortality Weekly Report.
Staphylococcus aureus – Molecular T J Foster, Trinity College, Dublin, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction
Population Structure
The genus Staphylococcus comprises more than 20 species, of which S. aureus is the most pathogenic. Staphylococcus aureus is a commensal of humans and being colonized with S. aureus is a risk factor for infection. Staphylococcus aureus can cause minor skin infections (abscesses, boils) but occasionally it can gain access to the bloodstream where it can cause serious invasive infections such as endocarditis, septic arthritis, and osteomyelitis. Staphylococcus aureus can also secrete potent enterotoxins that cause food poisoning if ingested. Staphylococcus aureus can colonize the udder of cattle from where it can infect the mammary gland epithelia causing mastitis. A lactating dairy cow with mastitis will excrete bacteria into milk. Bacterial cells will be killed by pasteurization but enterotoxins are heat resistant and if they are secreted into milk prior to heat treatment they will survive.
The population of S. aureus is described as being clonal. This means that discrete clones of the organism have emerged as a result of genetic divergence due to spontaneous mutations, with relatively minor contributions from gene transfer by recombination. Phylogenetic analysis by several methods agrees that the population is divided into two major groups. It is also evident that the carriage of S. aureus by domesticated animals (ruminants, rabbits) and chickens is the result of transmission from humans followed by a period of adaptation to the new host. The most widespread bovine clone diverged from ancestral human-associated clones by acquiring mutations, some of which have resulted in gene decay. Several genes important for human infection are no longer functional due to acquisition of mutations that result in truncation of the protein. Allelic variation occurs in genes encoding proteins involved in colonization, toxins, iron metabolism, and regulation, suggesting adaptation to the nonhuman host. Superimposed upon the basic clonal population is the occasional emergence and rapid dissemination of new clones. This is exemplified by the recent emergence and spread of the virulent community-associated MRSA (CA-MRSA) strain of the USA300 PFGE type and the ST398 MRSA strain associated with intensively reared pigs.
Molecular Typing Methods A variety of molecular typing methods have been applied for studying collections of S. aureus. Most effort has gone into analysis of human clinical isolates, notably MRSA (methicillin-resistant S. aureus) strains. Some methods (pulsed field gel electrophoresis, random amplified polymorphic DNA) are highly discriminatory and are best applied to analysis of local outbreaks. Other methods are less discriminatory and are suited for studying the population as a whole. Multilocus sequence typing (MLST) has the advantage that it does not suffer from lack of reproducibility inherent in other methods. Segments of seven housekeeping genes are sequenced. Each unique gene sequence is given a numeric code (a bar code) and the unique combination given a sequence type (ST) number. A strain with a single nucleotide polymorphism in any of the seven genes is denoted a single locus variant. A collection of single locus variants are analyzed to form a clone with an ancestral ST in the center. The clone can be expanded to include double locus variants. A detailed analysis of human strains has been performed. Much less data are available for animal strains.
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Colonization: Bacterial and Host Factors Staphylococcus aureus colonizes the moist squamous epithelium of the anterior nares of humans. This is regarded as the primary site of colonization. The presence of the bacterium on the skin is usually a consequence of nasal carriage. Nevertheless, temporary residence on the skin is a prerequisite for transmission from host to host. It is conceivable that the ability to adhere to keratinized epithelium is also important in colonization of the ruminant. Recently, advances have been made in our understanding of bacterial and host factors that contribute to bacterial survival on the moist squamous epithelium of the nares and on skin of humans. Staphylococcus aureus permanently colonizes about 20% of the population and intermittently colonizes another 60%, whereas 20% of
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individuals are never colonized. This strongly suggests that host factors determine whether an individual is colonized or not. Individuals admitted to hospital who were permanently colonized developed bacteremia at a slightly higher rate (1.2%) than those who were not colonized (0.4%). Conversely, infected carriers had a lower mortality rate (8%) than infected noncarriers (32%). Carriers had higher levels of antibodies to certain virulence factors, which might have offered some protection when they acquired a bloodstream infection. The ability to adhere to squamous cells in vitro is regarded as a correlate of proficiency in colonization of cornified epithelial tissue. Adherence is a multifactorial process involving teichoic acids and up to five different surface proteins, the best characterized of which are clumping factor B (ClfB) and iron-regulated surface determinant A (IsdA). Mutants defective in these proteins adhered poorly to isolated human squamous cells and colonized less effectively the nares of rodents, and in the case of ClfB, humans. The ligands recognized by these proteins are cytokeratin 10 and loricrin, which are major protein components of the corneocyte envelope. Polymorphisms in the glucocorticoid receptor gene contribute to the effectiveness of host immune responses and seem to determine in part the carriage status of the host. This indicates that colonization of the nares is controlled by host factors expressed in the nasal mucosal secretions. The ability to survive on skin is promoted by the ability of the bacteria to resist the bactericidal effects of skin lipids in sebum, the acidic pH, and cationic antimicrobial peptides.
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Staphylococcus aureus expresses a diverse array of secreted and surface-associated proteins that promote virulence in experimental rodent models of infection and most likely do so in humans as well. Due to the unique environment of the mammary gland, it is likely that some of these factors are not relevant to the ruminant infection. Indeed several important factors in human strains are not expressed by a widespread bovine mastitis-causing strain of multilocus ST 151. The function of virulence factors can be categorized as (1) adherence to host cells or extracellular matrix proteins, (2) evasion of innate and induced immune responses, and (3) toxins that cause localized or systemic damage. Some factors are multifunctional and contribute to more than one category.
(fibrinogen, fibronectin, collagen, elastin) and thereby support bacterial adhesion to host tissue. At least four proteins (ClfA, ClfB, and fibronectin binding proteins A and B) bind to soluble fibrinogen and promote adhesion to immobilized fibrinogen and fibrin. However, each is multifunctional and can interact with other host proteins. ClfA, the dominant fibrinogen binding protein expressed by bacteria in stationary phase, also binds to and activates complement factor I. ClfB is expressed in exponential phase and binds to fibrinogen and to cytokeratin 10, the latter interaction being important in nasal colonization. Apart from binding to fibronectin, the eponymous fibronectin binding proteins A and B also bind to fibrinogen and elastin. Protein A (Spa) is best known for its ability to bind to immunoglobulin (Ig)G at the Fc region, thereby inhibiting opsonophagocytosis. However, Spa is a multifunctional protein: it can also bind to (1) IgM and activate a subset of B cells, thereby exhibiting superantigen activity; (2) von Willebrand factor, contributing to thrombus formation and endocarditis; and (3) tumor necrosis factor receptor-1 on airway epithelial cells, thereby triggering inflammatory reactions that contribute to the pathogenesis of staphylococcal pneumonia. When the genomes of S. aureus strains were sequenced, a number of novel putative surface proteins were identified. The serine aspartate repeat protein (SdrC, SdrD, and SasG) proteins have been shown to promote adhesion to desquamated epithelial cells and may contribute to nasal colonization. However, the ligand(s) involved are not known. Expression of SasG also promotes biofilm formation. The Isd proteins are expressed only in iron-limited conditions. They allow the acquisition of iron from hemoglobin. The IsdA protein also has important roles in promoting resistance to bactericidal lipids on skin, resistance to the bactericidal host protein lactoferrin (this could be important for bovine strains), and adhesion to desquamated epithelial cells. The IsdH protein also contributes to resistance to phagocytosis by promoting accelerated degradation of C3b by an as yet unidentified mechanism. The fibronectin binding proteins are required for bacteria to become internalized by host cells that are not professional phagocytes. This is triggered by fibronectin acting as a bridge between bacteria and the 5 1 integrin located on the surface of epithelial and endothelial cells. The ability of bacteria to invade mammary gland epithelial cells promoted by this mechanism could be important in the pathogenesis of mastitis.
Adhesins
Evasins
Staphylococcus aureus can elaborate on its cell surface up to 20 different proteins (Figure 1), some of which have been shown to bind to components of the extracellular matrix
Evasion of innate immune responses of the host is crucial to the success of S. aureus as a commensal and pathogen. In humans, this centers around compromising the function
Virulence Factors
106 Pathogens in Milk | Staphylococcus aureus – Molecular CH3
S R N Cytolytic toxins and enzymes
β-Lactam antibiotic (e.g., penicillin)
CH3 H
N
O
COOH mecA
Surface protein adhesins
PBP2a
att X
Chromosome SCCmec
att Attachment site att
WTA
mecA
att
Cell wall Membrane
PVL CHIP
Phage
Figure 1 Schematic diagram illustrating how Staphylococcus aureus acquires resistance to methicillin and its ability to express different virulence factors. The bacterium expresses surface protein adhesins and wall teichoic acid (WTA), and also secretes many toxins and enzymes by activation of chromosomal genes. Adhesins and WTA have been implicated in nasal and skin colonization. Resistance to methicillin is acquired by insertion of a horizontally transferred DNA element called SCCmec. Five different SCCmec elements can integrate at the same site in the chromosome by a Campbell-type mechanism involving site-specific recombination. The mecA gene encodes a novel -lactam-insensitive penicillin binding protein, PBP2a, which continues to synthesize new cell wall peptidoglycan even when the normal penicillin binding proteins are inhibited. Some virulence factors such as Panton and Valentine leucocidin (PVL) and the chemotaxis inhibitory protein, CHIP, are encoded by genes located on lysogenic bacteriophages. Reproduced from Foster TJ (2004) The Staphylococcus aureus ‘superbug’. Journal of Clinical Investigation 114: 1693–1696.
of neutrophils, the first line of defense against invasion by Staphylococcus. Several small secreted proteins interfere with the migration of neutrophils from the blood vessels to the site of infection (Figure 2). The staphylococcal superantigen-like proteins SSL5 and SSL12 inhibit binding of neutrophils to inflamed endothelial cells in small blood vessels by blocking P-selectin glycoprotein ligand-1 (PSGL-1) on neutrophils from binding to P-selectin on endothelial cells. The extracellular adherence protein (Eap) (also called Map (MHC class II analog protein)) inhibits extravasation of neutrophils (diapedesis) by blocking leukocyte function-associated antigen LAF-1 from binding to intercellular adhesion molecule-1 (ICAM-1) on endothelial cells. The chemotaxis inhibitory protein, CHIPS, inhibits neutrophil migration toward the focus of infection by blocking receptors for chemoattractants N-formyl peptide and complement C5a peptide. Opsonophagocytosis of bacterial cells is important for efficient uptake and killing by neutrophils. Several secreted proteins prevent the efficient deposition of the
complement opsonin C3b. The Staphylococcus complement inhibitor (SCIN) and the extracellular fibrinogen binding protein Efb (and the related protein relative Ecb) block complement C3b and C5a convertases. Surface proteins contribute to reducing the efficiency of phagocytosis by enhancing the degradation of C3b. ClfA binds to and activates the complement regulator factor I, which results in enhanced degradation of the C3b opsonin. IsdH also promotes accelerated degradation of C3b. The capture of host plasminogen on the cell surface and its activation by staphylokinase destroys cell-bound IgG and C3b opsonins. Protein A binds to IgG by the Fc region, which then cannot engage in complement fixation or promote phagocytosis. Coating of the bacterial cells by plasma proteins (e.g., fibrinogen binding to clumping factor) and the presence of a polysaccharide capsule also contribute to reduced opsonophagocytosis. If S. aureus is successfully engulfed by functional neutrophils or macrophages, bacteria can evade killing mechanisms in the phagosome. Expression of enzymes
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Endothelial cells lining blood vessels
Polymorphonuclear leukocytes
Flow
SSL5 & SSL11 bind PSGL-1 & block P-selectin mediated neutrophil rolling
Map blocks LAF-1 binding to ICAM-1 & inhibits diapedesis
Chemotactic gradient – C3a, C5a, N-formyl peptides
CHIPS blocks neutrophil chemoattractant receptors FPR-1 and C5aR FLIPr blocks FPRL1
Interference with fixation of complement
Inhibition of phagocytosis
Infection
Survival within neutrophils
Figure 2 Migration of neutrophils from bloodstream to the site of infection summarizing the mechanisms of interference by Staphylococcus aureus secreted proteins. SSL5 and SSL11, staphylococcal superantigen-like proteins 5 and 11; PSGL-1, P-selectin glycoprotein ligand-1; Map, MHC class II analog protein; ICAM-1, intercellular adhesion molecule-1; LAF-1, leukocyte functionassociated antigen-1; CHIPS, chemotaxis inhibitory protein of S. aureus; FPR-1, formyl peptide receptor 1; C5aR, receptor for complement C5a; FPRL1, FPR-like 1; FLIPr, FPR-like 1 inhibitory protein.
that modify cell surface teichoic acids and cytoplasmic membrane phosphatidyl glycerol by the addition of D-alanine and L-lysine, respectively, reduces the negative charge of the cell surface and reduces susceptibility to cationic peptides. Staphylokinase binds to and neutralizes antibacterial peptides. Cell wall peptidoglycan is modified to render it impervious to the bacteriolytic enzyme lysozyme. Staphylococcus aureus expresses catalase and superoxide dismutase, which counteract the reactive oxygen intermediates of the phagosome oxidative burst.
Toxins Staphylococcus aureus expresses several membrane-damaging cytolytic toxins (-, -, -, and -toxins and several leucocidins) that cause damage to the membranes of host cells leading ultimately to lysis (Figure 1). At subinhibitory concentrations, damage to the integrity of the cells is manifested by expression of proinflammatory cytokines. The -toxin is the archetypal -barrel pore-forming toxin. It is composed of a heptamer, which assembles from monomers bound to the host cell membrane. The process of assembly results in a conformational change that creates the transmembrane -barrel pore.
The two-component -toxin and leucocidins (including the Panton and Valentine leucocidin (PVL)) form similar -barrels composed of two subunits forming hexamers or heptamers. The PVL is particularly associated with the recently emerged CA-MRSA clones. The -toxin is a small cationic peptide with detergent-like properties. The -toxin is a sphingomyelinase, which lyses cells with membranes that are rich in the lipid sphingomyelin. Staphylococcus aureus also expresses a number of small peptides with detergent-like properties called phenol-soluble modulins, which have potent cytolytic activity. Some toxins target a variety of host cells including erythrocytes, where the release of hemoglobin can provide a source of iron in the iron-restricted environment of the host. The leucocidins have a high affinity for neutrophils and thus compromise innate immune responses. Secreted enzymes and stoichiometric activators also contribute to tissue damage and disease pathogenesis. Staphylococcus aureus expresses proteases, lipases, a nuclease, and a hyaluronidase. Staphylokinase binds to plasminogen in 1:1 stoichiometry and activates the latent activity of the host plasma protease plasmin, which degrades thrombin. Coagulase binds to and activates prothrombin, which conversely causes fibrinogen to form fibrin clots.
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All strains of S. aureus express at least one of the major enterotoxins A–I (SEA–SEI), which are also potent superantigens. They also have the capacity to express several of the many newly described superantigen-like proteins. The enterotoxins have the ability to trigger emesis at low concentrations, but their importance to the pathogenesis of S. aureus infections lies in their ability to trigger T-cell activation. Toxic shock syndrome toxin-1 is another potent superantigen produced by both human and bovine strains of S. aureus. Superantigens trigger unregulated proliferation of T-helper cells by facilitating the binding of MHC class II molecules of antigen-presenting cells to T-cell receptors in a non-antigen-specific manner. This triggers a large proportion (2–20%) of T cells to become activated and to proliferate. This disrupts the normal immune response. Also, when high levels of toxins are expressed systemically, the massive release of cytokines causes toxic shock. In the rodent house musk shrew emesis model, enterotoxins induce 5-hydroxytryptamine (HT) release in the intestine, rather than in the brain, which is recognized by 5-HT(3) receptors on vagal afferent neurons and is essential for enterotoxin-stimulated emesis.
Biofilm The formation of biofilm was first described in infections associated with indwelling medical devices caused by S. epidermidis, and later by S. aureus. However, it is now thought that the ability to form biofilm is important during S. aureus tissue infection. In vitro studies identified several stages in establishing a biofilm: (1) primary attachment; (2) cell–cell association; and (3) detachment and dispersal. Bacteria can bind to naked plastic or metal or to biomaterial that has been conditioned by host plasma proteins in vivo. The accumulation phase was originally thought to be due to the secretion of a polysaccharide intercellular adhesin PIA, but it is now recognized that cell surface proteins can also cause aggregation. Cells in a biofilm are in a semidormant state, which renders them much more resistant to antibiotics than planktonic cells. Furthermore, the physical structure of the biofilm prevents the immune system from functioning properly to eradicate the bacteria.
Small Colony Variants Bacteriophages Any isolate of S. aureus will be lysogenic for one or more bacteriophages. The phages can contribute to the biology of the host bacterium in several ways. Upon induction of the lysogen, the phage capsid can incorporate fragments of chromosomal DNA or plasmids and introduce them by transduction into a new host. The pathogenicity island S. aureus pathogenicity island-1 (SAPI-1) that encodes toxic shock syndrome (TSST-1) in human strains is transduced at very high frequency by certain phages. Excision of the integrated element is actually stimulated by phage replication. A similar process might occur with a related pathogenicity island (PI) expressed by bovine strains. Some bacteriophages have incorporated genes that contribute to the virulence of the host. The genes are expressed when the phage integrates into the chromosome. CA-MRSA strains are commonly lysogenized with a phage that carries the genes encoding PVL (Figure 1). This could contribute to the enhanced virulence of CA-MRSA strains. About 60% of human S. aureus strains are lysogenized with a phage that carries an immune evasion gene cluster comprising genes encoding CHIPS, SCIN, staphylokinase (SAK), and SEA, or combinations thereof. The site of integration of the phage is within the coding sequence for the -toxin, explaining why the majority of human strains do not express the toxin. In contrast, many bovine strains are -hemolytic because carriage of this type of phage is less common. This could reflect an important role for -toxin in promoting mastitis or the fact that the phage-encoded immune evasion proteins are specific for humans.
Staphylococcus aureus is now regarded as a facultative intracellular pathogen, whereas previously it was thought to be exclusively extracellular. A subpopulation of S. aureus cells called small colony variants (SCVs) have an enhanced ability to enter into and survive within mammalian cells that are not normally phagocytic. SCVs are naturally occurring mutants defective in the biosynthesis of menadione, hemin, or thymidine. This results in reduced tricarboxylic acid metabolism. Phenotypically, SCV bacteria form colonies that are 10-fold smaller than normal colonies and which are nonpigmented and nonhemolytic. The fibronectin binding proteins that promote uptake into mammalian cells are expressed by SCV cells at higher levels than in wild-type bacteria. Once inside the host cell, the SCV can persist because it does not cause cell lysis or trigger apoptosis and the infected cells do not react by synthesizing proinflammatory molecules. Clinically, SCVs are associated with relapsing persistent infections such as osteomyelitis, some foreign body infections, and lung infections in cystic fibrosis patients. SCVs have not been associated with chronic mastitis in cattle, but this might be due to difficulties in the identification of the variants in the laboratory and their instability.
Antibiotic Resistance The ability to treat S. aureus infections has been profoundly compromised by the development of resistance. Shortly after the introduction of penicillin in the late
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1940s, penicillin-resistant bacteria emerged due to acquisition of the ability to express a -lactamase that destroyed the antibiotic. The subsequent introduction of methicillin, a -lactamase-resistant penicillin, was quickly followed by occurrence of methicillin resistance. This was due to acquisition of the mecA gene, which encodes a -lactam-insensitive penicillin binding protein called PBP2a or PBP29, which takes over cell wall biosynthesis in the presence of antibiotic (Figure 1). Methicillin resistance is now widespread in hospital strains and, very recently, highly virulent CA-MRSA strains have emerged and spread in the community at large. It should be emphasized that mecA confers resistance to all classes of -lactam antibiotics including potent broad-spectrum cephalosporins, cephamycins, and monobactams. In addition, S. aureus has developed resistance to all of the antibiotics that are used to treat staphylococcal infections (tetracycline, macrolides, aminoglycosides, quinolones). Wherever these antibiotics have been used to treat bovine mastitis, resistance has also been reported. New antibiotics that are specifically targeted at MRSA have been licensed (Synercid, Zyvox, Cubicin) or are in development (a dehydrofolate reductase inhibitor called iclaprim, a fatty acid biosynthesis inhibitor called platensimycin, and a peptide deformylase inhibitor). The rapid development of resistance is facilitated by horizontal transfer of resistance genes on mobile genetic elements or by mutation. In the case of methicillin resistance, the staphylococcal cassette chromosome (SCC) element can excise from the chromosome of the strain in which it is resident by site-specific recombination (Figure 1). It circularizes and can be transmitted to another strain by transduction or transformation. It then integrates into the chromosome at a specific site promoted by the element-encoded integrases. This process resembles the behavior of lysogenic bacteriophages. There are five major classes of SCCmec element that have transferred into many different strains to form distinct clones of MRSA. There is recent evidence of a specific MRSA type (ST398) infecting intensively reared farm animals, notably pigs. ST398 can be isolated from farm workers and human infections caused by this strain have been reported. The majority of horizontally acquired antibiotic resistance is encoded by genes that are located on conventional plasmids and/or transposons. Resistance is caused by plasmid-encoded enzymes that modify the antibiotic binding site in the ribosome (macrolide lincosamide and streptogramin B resistance), by modification of the drug (aminoglycoside and chloramphenicol resistance), by specific drug efflux (tetracycline), or by displacement of the drug from its target (tetracycline). Resistance to fluoroquinolones occurs by stepwise
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acquisition of mutations that reduce the affinity of two topoisomerase enzymes, which are the inhibitory drug targets, and also by overexpression of the multidrug resistance efflux pump NorA, which reduces the intracellular drug concentration.
Vaccination Recently, there have been several reports of the development and testing of subunit vaccines to combat S. aureus infections in humans. A polysaccharide vaccine comprising the two major serotypes of capsular polysaccharide 5 and 8 has progressed furthest but has shown limited success in human clinical trials. Successful vaccination of laboratory animals with recombinant surface protein antigens (e.g., ClfA and IsdB) has been reported recently. A combination of four of the best performing antigens (IsdA, IsdB, SdrD, SdrE) provided superior protection than each component alone. Vaccination to combat bovine mastitis using bacterins has achieved limited success in trials but has not been developed commercially. The poor performance is likely to be due to the nature of the immunogen, the method of administration, but particularly the difficulty of mounting an effective immune response in the lactating mammary gland. See also: Pathogens in Milk: Staphylococcus aureus – Dairy.
Further Reading Clarke SR and Foster SJ (2006) Surface adhesins of Staphylococcus aureus. Advances in Microbial Physiology 51: 187–224. Diep BA and Otto M (2008) The role of virulence determinants in community-associated MRSA pathogenesis. Trends in Microbiology 16: 361–3699. Fedtke I, Go¨tz F, and Peschel A (2004) Bacterial evasion of innate host defenses – the Staphylococcus aureus lesson. International Journal of Medical Microbiology 294: 189–194. Foster TJ (2004) The Staphylococcus aureus ‘superbug’. Journal of Clinical Investigation 114: 1693–1696. Foster TJ (2005) Immune evasion by staphylococci. Nature Reviews Microbiology 3: 948–958. Gordon RJ and Lowy FD (2008) Pathogenesis of methicillin resistant Staphylococcus aureus infection. Clinical Infectious Diseases 46(5): S350–S359. O’Riordan K and Lee JC (2004) Staphylococcus aureus capsular polysaccharides. Clinical Microbiology Reviews 17: 218–834. Otto M (2008) Staphylococcal biofilms. Current Topics in Microbiology and Immunology 322: 207–228. Rivera J, Vannakambadi G, Ho¨o¨k M, and Speziale P (2007) Fibrinogenbinding proteins of Gram-positive bacteria. Thrombosis and Haemostasis 98: 503–511. Rooijakkers SH, van Kessel KP, and van Strijp JA (2005) Staphylococcal innate immune evasion. Trends in Microbiology 13: 596–601.
110 Pathogens in Milk | Staphylococcus aureus – Molecular Schwarz-Linek U, Ho¨o¨k M, and Potts JR (2006) Fibronectin-binding proteins of Gram-positive cocci. Microbes and Infection 8: 2291–2298. Sendi P and Proctor RA (2009) Staphylococcus aureus as an intracellular pathogen: The role of small colony variants. Trends in Microbiology 17: 54–58.
Shinefield HR and Black S (2005) Prevention of Staphylococcus aureus infections: Advances in vaccine development. Expert Reviews of Vaccines 4: 669–676. Wertheim HF, Melles DC, Vos MC, et al. (2005) The role of nasal carriage in Staphylococcus aureus infections. Lancet Infectious Diseases 5: 751–762.
Staphylococcus aureus – Dairy H Asperger, Veterinary University, Vienna, Austria P Zangerl, Federal Institute of Alpine Dairying BAM, Rotholz, Austria ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2563–2569, ª 2002, Elsevier Ltd.
Introduction Enterotoxin-producing staphylococci, in particular Staphylococcus aureus, are probably the leading cause of foodborne illness throughout the world. The pathogenicity of St. aureus has been recognized for many years since this species causes mastitis and skin diseases in mammals or leads to foodborne intoxication. Milk and milk products can become contaminated if good hygiene practice (including mastitis control) is not exercised on farms and the milk is inadequately pasteurized or not heat-treated. After contamination with enterotoxigenic staphylococci food poisoning may happen when abundant growth and enterotoxin formation is encouraged during production and storage. Staphylococcus aureus is classified in the family Micrococcaceae. The genus Staphylococcus is distinguishable from the morphologically similar members of the genus Micrococcus by biochemical methods such as the ability of growing anaerobically and demonstrating a fermentative metabolism. The two genera differ also in their DNA base, cell wall and enzyme composition. The genus Staphylococcus has been divided into at least 27 species and seven subspecies. The major characteristics of the species St. aureus are coagulase and thermonuclease (TNase) production, but other coagulase- and TNasepositive species, such as St. intermedius and various strains of St. hyicus, are also described. Both species have been reported to produce enterotoxins at low levels.
In broth, growth changes from a uniform turbidity to a fine, easily suspended deposit. Biochemistry and Factors influencing Growth Nutritional requirements are moderate; organic nitrogen sources and group B vitamins are required for growth. Staphylococcus aureus is facultatively anaerobic, but grows best under aerobic conditions. Acid is produced aerobically and anaerobically from glucose, lactose, maltose and mannitol; under anaerobic conditions acid is produced from many other carbohydrates. Major end products of glucose metabolism are acetate and CO2 (aerobic) and lactate (anaerobic). Catalase is produced by cells growing aerobically. Staphylococcus aureus is able to grow between 7 and 48 C (optimum: 37 C) and at pH values between 4 and 10 (optimum pH 6–7). Staphylococcus aureus tolerates lower aw values than other bacteria (aw minimum: 0.83–0.86). The microorganisms grow well at up to 10% NaCl and relatively slowly at 15%. Enterotoxins are produced during all phases of growth, but growth is possible at a wider range of environmental conditions than enterotoxin production. Most strains hydrolyse native animal proteins (e.g. caseins, gelatine, fibrin). Proteases, lipases and esterases are produced. Various lipids, Tweens and phospholipoproteins are hydrolysed with the release of fatty acids. Nearly all strains produce one or a combination of several haemolysins (, , and
); -haemolysin predominates in strains of animal origin. Some strains produce lecithinase.
Characteristics
Serology and Lysotyping
Morphology and Culture
Due to the complex nature of the antigens, serotyping is not used often. However, together with phage typing, where the sensitivity to the lytic action of selected bacteriophages is tested, it is a useful tool in identifying the strain origin in epidemiological studies.
Staphylococcus aureus are Gram-positive, catalase-positive bacteria that do not produce endospores. They are 0.5–1.5 mm in diameter and divide in more than one plane to form irregular, three-dimensional clusters of cells. Colonies are smooth, raised, glistening and circular, and may reach a size of 4–6 mm in diameter on nonselective media. Colony pigmentation is influenced by growth conditions and varies from grey or grey–white with a yellowish tint, through yellow–orange to orange.
Resistance to Antibiotics Antibiotic susceptibility and resistance are of eminent importance for all St. aureus induced illnesses. In
111
112 Pathogens in Milk | Staphylococcus aureus – Dairy Table 1 Penicillin resistance of Staphylococcus aureus isolated from cow’s milk Reference
Number of strains
Resistant (%)
Untermann et al. (1973) Scha¨llibaum and Scha¨ren (1987) Becker et al. (1989) Adesiyun (1995) Honkanen-Buzalski and Myllys (1996)
120 250 387 250 344 (1988) 154 (1995) 182
32.5 33.3 17.0 23.6 31.8 50.7 65.9
Meaney and Flynn (1996)
Sources: Untermann F, Kusch D and Lupke H (1973) Milchwissenschaft 28: 686–688; Scha¨llibaum M and Scha¨ren W (1987) IDF Mastitis News 12: 4; Becker H, Gang-Stiller K and Terplan G (1989) Netherlands Milk and Dairy Journal 43: 355–366; Adesiyun AA (1995) Journal of Veterinary Medicine, Series B 42: 129–139; Honkanen-Buzalski T and Myllys V (1996) IDF Mastitis Newsletter 21: 20–22; Meaney WJ and Flynn J (1996) IDF Mastitis Newsletter 21: 28.
connection with hospitalization, a widespread resistance against many antibiotics is reported. Concerning St. aureus causing mastitis in the udder of lactating cows, antibiotic resistance and susceptibility is most significant. Intramammary infusion of penicillin, which is successful in the treatment of streptococcal mastitis, is often ineffective against St. aureus. Staphylococcal mastitis has reached major importance today, due to the emergence of penicillin-resistant strains (Table 1). Data on the antibiotic resistance of St. aureus as a mastitic pathogen are gathered periodically from various countries by the International Dairy Federation.
Source Infected Udder Staphylococcus aureus is found on the skin, teats and mucous membranes of mammals. The infected mammary gland of cows and other animals used for milk production is the most important reservoir. From here the organisms spread to the udder skin, hands of milking personnel, udder cloth and bedding material, whereby transfer of the pathogens during milking is most important. When the udder is infected, St. aureus is excreted in the milk with high fluctuations in counts ranging from zero to 108 cfu ml1, but a level of 104 cfu ml1 is usual. A characteristic of staphylococcal mastitis is its irregular shedding pattern that complicates diagnosis. Some cows never shed the organisms from the udder or do so infrequently; others shed the staphylococci intermittently at short intervals; and still others show a persistent shedding state, extended over several lactation periods. The frequency of the occurrence of St. aureus in milk is also related to age of the cow. In contrast to reports on the frequency of enterotoxin producers in human strains, the findings with animal strains are very diverse and often apparently
contradictory, depending on the source of strains, and the methods involved. The incidence of enterotoxigenic St. aureus from animal sources is generally lower than from strains in humans and may vary between 5% and 30%, with enterotoxin C predominating; the incidence seems to be higher in strains isolated from mastitic milk. In goats’ milk, more than 30% isolates were enterotoxigenic.
Human Sources Staphylococcus aureus is frequently found on the skin, nose, pharynx, axilla, umbilicus, perineum, gastrointestinal tract and urogenital tract of humans; the major reservoirs are the nails, skin and hair. The nose appears to be the principal site for multiplication. In various surveys, the incidence of human carriers ranged from 4% to 60%. The frequency of enterotoxigenic strains isolated from humans is high, varying between 40% and 60%; enterotoxin A (SEA) producers are most common. The organisms find their way into the food by hands (infected wounds, skin lesions) or by coughing and sneezing. In general, human contamination is the most important factor in staphylococcal food poisoning, because skin lesions are very common and often ignored by food handlers.
Environmental Sources Originating from humans and animals, St. aureus is widespread in nature. The organisms have been isolated sporadically from soil, sand, marine and fresh water, sewage, plant surfaces and products, feeds, poultry and dairy products, and on the surfaces, dust, and air of inhabited areas. While the opportunities for environmental contamination of milk and dairy products are limited, some processes are still vulnerable, e.g. milk powder production.
Pathogens in Milk | Staphylococcus aureus – Dairy 113
Isolation and Identification Numerous methods to isolate and identify staphylococci have appeared in the literature and are standardized by international and national organizations, e.g. International Organization for Standardization (ISO), Comite´ Europe´en de Normalisation (CEN), International Dairy Federation (IDF) and Association of Official Analytical Chemists (AOAC). For the bacteriological examination in mastitis control, nonselective media are used in most cases, where St. aureus is identified by its typical appearance on blood agar, Gram reaction and coagulase activity. For enumeration in foods, Baird–Parker agar (BPA) is recommended because of its high productivity, especially if foods containing stressed cells are analysed. However, the medium is not completely selective and reduction of tellurite and egg yolk reaction are poor diagnostic tools since competing microorganisms are also able to reduce tellurite and less than a half of the strains isolated from milk and dairy products yield a positive egg yolk reaction. Consequently, all black to grey colony types, irrespective of egg yolk reaction, must be examined for coagulase production. This lack of selectivity may lead to unreliable results in foods in which St. aureus is only a minor part of the total flora able to form colonies on the medium. Therefore ISO suggested rabbit plasma fibrinogen agar (RPFA) as an alternative. This medium allows the detection of coagulase directly on the plate due to the formation of fibrin haloes around the colonies, so that further confirmatory tests are not necessary. Plasma media with constant plasma quality are commercially available. For detection of low numbers (<100 g1), enrichment procedures are used followed by streaking a loopful of the incubated media onto BPA or RPFA. Recommended enrichment media are tryptic soya broth containing 10% NaCl and 1% sodium pyruvate, Giolitti– Cantoni broth supplemented with 1% Tween 80 and liquid Baird–Parker medium. The two latter media are incubated anaerobically to enhance selectivity. Identification of suspect colonies is done by the tube coagulase test using rabbit plasma EDTA. The production of thermonuclease may be used for screening purposes. As an alternative to the tube coagulase test, commercially available latex agglutination tests based on clumping factor and protein A detection are in use. Detection of enterotoxins is of great importance in assessing a health hazard of a certain food. They are identified by their reactions with specific antibodies. To date, rapid and very sensitive methods for detecting the enterotoxins A–E based on sandwich enzyme-linked immunosorbent assay (ELISA) procedures are commercially available in test kit form which allows detection of 0.1–1 ng g1 of food. Compared to immunodiffusion assays, ELISA procedures are much more sensitive, but
less specific and may give false positive results. For this reason, positive results, especially weakly positives, should be considered presumptive and confirmed by other tests. Reversed passive latex agglutination (RPLA) kits are also commercially available, but are less sensitive than ELISA and nonspecific agglutination is also possible. Due to their high specificity, immunodiffusion assays are still important for detecting strains of enterotoxigenic staphylococci. Recently, the polymerase chain reaction (PCR) has been introduced as a simple, highly sensitive and specific technique for the detection of enterotoxigenic strains.
Pathogenicity Staphylococcus aureus and Infection Staphylococcus aureus is able to cause acute infections in humans, which may be localized, e.g. pustular, or spread, e.g. septicaemia. These infections are mediated by a wide range of agressins and exotoxins that are chromosomal or plasmid mediated. Diseases due to specific protein toxins are known, e.g. toxic shock syndrome. In animals, St. aureus may cause pustular inflammations of the skin and other organs, of which mastitis is most important. Inflammation of the skin and tissues, especially the mammary gland, is treated by application of antibiotics, taking into account the antibiotic susceptibility and resistance properties of the pathogens involved. Staphylococcus aureus and Intoxication Food is implicated in staphylococcal disease in the case of enterotoxicosis. The agents responsible for staphylococcal food poisoning are a series of toxins described as enterotoxins because of their effects on the intestinal tract. They are labelled enterotoxins A (SEA), B (SEB), C1 (SEC1), C2 (SEC2), C3 (SEC3), D (SED) and E (SEE). Recently, the enterotoxins G, H and I were isolated and characterized, but only limited data about their characteristics exist to date. Staphylococcal enterotoxins are single-chain, low molecular weight (26 000–29 000 Da), heat-stable proteins produced by many strains of St. aureus, but other coagulase-positive and even coagulase-negative staphylococci are also able to produce enterotoxins. Most food poisoning outbreaks involve enterotoxins A and D. Production of enterotoxins is strain-specific, but one strain may produce more than one toxin. The production of enterotoxins B and C is controlled by plasmids and occurs mainly at the end of the stationary phase whereas production of enterotoxins A, D and E is under chromosomal control and occurs throughout the logarithmic growth phase. Depending on temperature, pH, water activity, atmospheric conditions and the presence of other
114 Pathogens in Milk | Staphylococcus aureus – Dairy
microorganisms, they can be produced in food when enterotoxigenic staphylococci are able to proliferate up to a level of at least 106 cfu g1. In most food poisoning outbreaks, counts of 108 cfu g1 food and more, and enterotoxin concentrations of 1–5 mg g1 food were detected. However, in sensitive individuals, 0.1–1 mg enterotoxin is sufficient to produce illness. Enterotoxins are resistant to proteolytic enzymes such as pepsin and trypsin; this makes it possible for them to pass through the digestive tract to the site of action. The common symptoms of staphylococcal enterotoxicosis are nausea, retching, vomiting, abdominal cramps and diarrhoea and they usually develop within 1–6 h after ingestion of the enterotoxin- containing food. In severe cases, headache, muscular cramps, fever and drop of blood pressure may be observed. Deaths of children and elderly people have also been recorded, but they are rare. Recovery takes a few hours to approximately one day, so that a doctor is seldom consulted and consequently most cases are never reported. Effective treatment is not possible, primarily due to the short duration of the disease. In cases where excessive vomiting and diarrhoea occur, administration of fluids may be necessary to restore the salt balance.
Incidence in Milk and Dairy Products Quarter Samples Staphylococcus aureus is the most common pathogen causing both clinical and subclinical mastitis, not only in cows but also in ewes and goats. The organism is responsible for approximately 30% to 40% of all mastitis cases. The occurrence of St. aureus in quarter milk samples varies from 5% to 22%. In foremilk from subclinical cases, St. aureus counts vary from 30 to 380 000 cfu ml1, and in quarter milk from 210 to 78 000 cfu ml1. Bulk Milk The principal source of contamination of raw milk is the infected udder. For this reason, St. aureus is regularly found in bulk milk. However, the counts are related to the mastitis situation of the herd and may range from less than 10 to several thousands per ml milk with occasional counts of 105 ml1. In the EU, criteria for the St. aureus content in raw cows’ milk intended for consumption without heating (n ¼ 5, c ¼ 2, m ¼ 100 ml1, M ¼ 500 ml1) and for the production of raw milk products (n ¼ 5, c ¼ 2, m ¼ 500 ml1, M ¼ 2000 ml1) have been established. In the criteria cited above, n ¼ number of samples analysed; c ¼ maximum allowable number of defective sample units; m ¼ the value of the characteristic separating good quality from marginal quality; M ¼ the
value of the characteristic separating marginal quality from bad quality (m<M). These standards can only be met when effective mastitis control programmes are incorporated on farms and the milk is stored at low temperatures before consumption and manufacture according to the cooling temperatures given in the EU Milk Hygiene Directive 92/46. Dairy Products Liquid products
In liquid milk, the organisms are eliminated by pasteurization. Nevertheless, if recontamination occurs or contaminated additives are added after pasteurization, pasteurized milk is an excellent medium for growth and enterotoxin production due to its optimal nutritional status, water activity, pH value, redox potential and the lack of competing flora. In general, fluid milk is less often involved in food poisoning outbreaks than dried milk or cheese. Dried products
The technology of milk powder production includes several heating procedures, i.e. pasteurization, evaporation and the drying process itself. If contamination occurs, growth and enterotoxin formation during the production process is possible; during the storage of dried milk the organisms surviving the drying process slowly die. Poisoning may happen directly when the milk powder contains enterotoxin and indirectly when contaminating enterotoxigenic staphylococci are able to grow after reconstitution of the powder. Fermented milk products
Fermented milk products may be considered as safe because the raw milk is heated at high temperatures. If recontamination occurs during manufacture the organisms are rapidly inactivated by amensalism and antagonism of the starters used. Actively growing lactic acid bacteria (LAB) inhibit the growth of staphylococci and also kill them off to some extent. If the fermented product itself is contaminated, the contaminants are not able to multiply due the acidic environment even when cooling is unsatisfactory. Cheese
During cheese manufacture, the staphylococci in milk are physically concentrated approximately 10-fold in the curd. Therefore the St. aureus content in the young cheese is directly dependent on the St. aureus counts in milk. Further, the organisms are able to proliferate during the first 24 h (in the vat and during pressing/moulding) until the acids produced by the starters inhibit further growth. If abundant growth of enterotoxigenic strains is possible
Pathogens in Milk | Staphylococcus aureus – Dairy 115
at this stage of production, enterotoxins will be formed. The magnitude of multiplication is strongly dependent on the amount, the activity and the type of the starters used. Growth and enterotoxin production is inhibited primarily due to the low pH and the formation of lactic acid, but during Gouda cheesemaking, inhibition was observed before the pH had dropped below 6.0 and it was concluded that the onset of inhibition of St. aureus may be due to the decrease in redox potential and the formation of antimicrobial compounds excreted by LAB. An increase of 1.5 to 3 log during the first 24 h of cheesemaking may be expected under normal conditions, but, in cheeses with suboptimal acidification, increases up to 5 log have been observed. Low acidification is caused by insufficient starter development due to inhibition of LAB by antibiotic residues in milk or by bacteriophage infection, but the acidification rate is also lowered when inadequate inocula were used or the starters are inactivated due to prolonged storage. In the production of Cheddar cheese, inhibition of LAB is also caused by addition of salt to the curd. A special case is the production of cooked hard cheeses made from raw milk (Emmental cheese, Gruye`re type cheeses, extra hard cheeses), where the curd is cooked at temperatures between 50 and 57 C. Due to these high cooking temperatures, the high temperatures on the press and the acidification with active thermophilic starters, St. aureus is usually inactivated during the first day of manufacture. Although there tend to be large differences between cheese varieties, St. aureus counts decrease during ripening and storage of cheese manufactured with starters of normal activity. However, when acidification is suboptimal, the decline in numbers may not be apparent and less than 1 log cycle. In general, the higher the ripening temperature the higher is the decline in numbers, although the amount of salt present in the cheese may influence this. If enterotoxins were produced during manufacture, they may persist over years in the cheese. Apart from the acidification rate at the beginning of manufacture, the St. aureus content of cheese is primarily dependent on the cheese variety (technology), the kind of milk used for manufacture (raw milk/heat treated milk) and the possibilities of contamination during the manufacturing process (open/closed system). In contrast to cheeses made from pasteurized milk, where St. aureus is usually not detected or present in low numbers, raw milk cheeses are a potential danger, unless contamination of milk is low and acidification is optimal. Therefore, the EU established criteria for cheeses made from raw milk (n ¼ 5, c ¼ 2, m ¼ 1000 g1, M ¼ 10 000 g1), irrespective of the origin of the milk (cow, sheep, goat). If the maximum level M is exceeded, the cheese has to be tested for enterotoxins and also the enterotoxigenicity of the isolated coagulase-positive strains must be determined.
Control General Hygiene Contamination with St. aureus can be effectively controlled by good manufacturing practice (GMP). In recent years, the dairy industry was forced by international and national authorities to introduce the principles of Hazard Analysis Critical Control Point (HACCP) systems according to the EU Milk Hygiene Directive 92/46. This directive provides guidelines for the hygienic design and maintenance of buildings, services and equipment, and also for personal hygiene. Regular training of persons handling food is of eminent importance in preventing human contamination. Further, cleaning and disinfection schedules are necessary for eliminating staphylococci from surfaces. In the production of raw milk cheeses, it must be guaranteed that milk from mastitic cows is not used. This can be achieved by effective mastitis control programmes on farms including the culling of chronic St. aureus cows. Cooling of milk Since St. aureus fails to multiply at temperatures below 7 C, cooling is the most effective means of preventing growth and enterotoxin production. When cheese is produced from raw milk, the milk has to be cooled immediately after production and extended storage must be avoided. In general, raw milk must be processed as soon as possible unless the milk is heat treated. Also preripening in the vat must be as short as possible to prevent undesired growth. Heating of Milk Pasteurization of milk (72 C for 15 s) is effective in the elimination of St. aureus. However, even after applying this temperature/time combination, 0.38% of the staphylococci may survive, but no survivors were detected at 72 C for 35 s. In cheesemaking thermization of milk (57–68 C for at least 15 s) is also applied. The temperature/time combinations at these subpasteurization conditions do not guarantee elimination of St. aureus in every case. Thermal resistance is primarily dependent on the strain, the physiological state of the organisms and the medium. Decimal reduction times may vary between 0.43 and 8 min at 60 C. Unlike the producer organism, staphylococcal enterotoxins are remarkably heat resistant, showing D-values of 3–8 min at 121 C. Interactions with other Microorganisms Since St. aureus is a poor competitor, its growth is inhibited by common spoilage organisms. Bacillus cereus, Proteus
116 Pathogens in Milk | Staphylococcus aureus – Dairy
vulgaris, Escherichia coli, Enterobacter aerogenes and Achromobacter spp. inhibit staphylococci by production of antibiotic substances, while Serratia marcescens and Pseudomonas spp. appeared to inhibit St. aureus by outcompeting it for amino acids. In foods with reduced aw (0.95 or less and salt concentrations of 5.5% and higher), growth of competing flora will be suppressed, whereas St. aureus is able to proliferate under these conditions. In such foods, a hazard can only be minimized by preventing contamination and storage at low temperatures. In the production of fermented milk products, the strong antagonistic activity of LAB is most important. Staphylococcus aureus is inhibited by LAB due to low pH and redox potential, and the formation of acids (especially lactic acid) and antibiotic substances. In the manufacture of raw milk cheeses, sufficient acidification, especially in the early stages of cheesemaking, must be achieved by the use of a sufficient amount of an active starter. Measurement of cheese pH two hours after moulding gives information about the acidification rate.
Conclusions The growing interest concerning the group of ‘new emerging pathogens’ (e.g. Listeria monocytogenes, Campylobacter spp., enterohaemorrhagic E. coli) has overshadowed the interest in St. aureus. Nevertheless, St. aureus remains one of the most important foodborne pathogens, therefore the knowledge of specific characteristics of this species, such as pathogenicity, and of its incidence in milk and dairy products is essential for finding effective ways to control this microorganism in food hygiene and food technology.
See also: Mastitis Pathogens: Environmental Pathogens. Microorganisms Associated with Milk.
Further Reading Ash M (1997) Staphylococcus aureus and staphylococcal enterotoxins. In: Hocking, AD (ed.) Foodborne Microorganisms of Public Health Significance, Australian Institute of Food Science and Technology Sydney, Australia. pp.313–333. Asperger H (1994) Staphylococcus aureus. The Significance of Pathogenic Microorganisms in Raw Milk, IDF, Brussels International Dairy Federation Special Issue no. 9405. Bergdoll MS (1990) Staphylococcal food poisoning. In: Cliver DO (ed.) Foodborne Diseases, San Diego, pp. 85–106. Doyle ME, Steinhart CE, and Cochrane BE (1995) In: Food Safety, New York: Marcel Dekker. Genigeorgis CA (1989) Present state of knowledge on staphylococcal intoxication. International Journal of Food Microbiology 9: 327–360. Halpin-Dohnalek MI and Marth EH (1989) Staphylococcus aureus: production of extracellular compounds and behavior in foods: a review Journal of Food Protection 52: 267–282. IDF (1980) Factors influencing the Bacteriological Quality of Raw Milk, IDF, Brussels International Dairy Federation Bulletin no. 120. IDF (1980). In: Behaviour of Pathogens in Cheese, IDF, Brussels International Dairy Federation Bulletin no. 122. Staphylococci (1990). In: Jones D, Board RG, and Sussman M, (eds.) Journal of Applied Bacteriology 69: pp. 1S–188S. Kloos WE and Schleifer KH (1986) Genus IV Staphylococcus Rosenbach 1884, 18AI (Nom. Cons. Opin. 17 Jud. Comm. 1958, 153. In: Sneath PHA, Mair NS, Sharpe ME, and Holt IG (eds.) Bergey’s Manual of Systematic Bacteriology 2: 1013–1035. Baltimore: Williams & Wilkins. Minor TE and Marth EH (1976) Staphylococci and their Significance in Foods, Amsterdam: Elsevier. Spahr U and Url B (1994) Behaviour of pathogenic bacteria in cheese: a synopsis of experimental data. International Dairy Federation Bulletin: 298: 2–16. Zangerl P and Asperger H (2001) Media used in the detection and enumeration of Staphylococcus aureus. In: Corry JEL, Curtis GDW, and Baird RM (eds.) Culture Media for Food Microbiology: Progress in Industrial Microbiology, Amsterdam: Elsevier.
Yersinia enterocolitica M D Barton, University of South Australia, Adelaide, SA, Australia ª 2011 Elsevier Ltd. All rights reserved.
Characteristics
Laboratory Identification
Taxonomy
Morphology and Appearance in Cultures
The genus Yersinia contains 15 species but only 3 are pathogenic to humans. Yersinia pestis is the cause of plague, Y. pseudotuberculosis is associated with intestinal infections and mesenteric lymphadenitis, and Y. enterocolitica is associated with foodborne intestinal infections. There are a number of species closely related to Y. enterocolitica, which were previously called ‘atypical Y. enterocolitica’ or ‘Y. enterocolitica-like organisms’, but which have now been identified as separate species including Y. intermedia, Y. kristenseniae, Y. frederikseniae, Y. mollaretii, Y. bercovieri, Y. aldovae, and Y. rohdei. These species are widely distributed in the environment and can be isolated from food and water, and from human and animal feces, but there is no evidence linking them with human or animal disease.
Yersinia enterocolitica is a small Gram-negative rod. It is actively motile at 22–25 C but not motile at 37 C. It produces circular, smooth, low, convex colonies of 1–2 mm diameter with an entire or slightly crenulated edge after incubation at 37 C for 24 h. On MacConkey agar, 1.5–2 mm translucent, pale non-lactose fermenting colonies are seen. Some environmental strains do ferment lactose and thus produce bright pink colonies on MacConkey agar. On cefsulodin–irgasan–novobiocin (CIN) agar Y. enterocolitica produces highly characteristic 1.5 mm diameter colonies with a dark pink center and a translucent border (bull’s-eye) colonies.
Biotypes and Serotypes Yersinia enterocolitica is a heterogeneous species that can be divided into a number of groups based on biochemical activity (biotypes) and lipopolysaccharide O-antigens (serotype). Six biotypes are described (Table 1). The strains associated with human disease are most commonly found in biotypes 1B, 2, 3, and 4. Biotype 1A strains were traditionally regarded as environmental but now there is evidence that some strains can cause human disease, and biotype 5 has been isolated only from animals and the environment. At least 60 different serotypes are recognized, with O-antigens shared between Y. enterocolitica and its close relatives. Heat-labile flagella H antigens have been described but are not used in typing. There are strong associations between particular biotypes and serotypes (Table 2) and between bioserotypes, pathogenicity, and geographic distribution. Bioserotype 4, O:3 is the most common human pathogen and is now found worldwide. In northern Europe bioserotypes 2, O:9; 2, O:5,27; and 3, O:5,27 have also been important. However, since 2004 there has been a surge in O:8 cases in northern Europe. Biotype 1B strains (bioserotypes 1B, O:8; 1B, O:13a,13b; 1B, O:20; 1B, O:21), called North American strains, are more pathogenic than the European strains. Information on geographic distribution of bio/serotypes is given in Table 2.
Identification The optimum temperature for growth of Y. enterocolitica is 28 C, and if identification tests are incubated at 37 C confusing results can be obtained. Commonly used identification tests are listed in Table 3. Identification kits such as API 20E (bioMe´rieux SA, France) kit system can be used but should be incubated at 30 C. However, biochemical tests are not particularly reliable as nonpathogenic species can be misidentified as Y. enterocolitica. Increasingly, molecular methods such as 16S rRNA sequencing are used for definitive identification. Molecular typing based on DNA–DNA hybridization and 16S rRNA sequencing can distinguish between biotype 1B (North American pathogenic mouse lethal strains) and the European strains. In addition, PCR for virulence genes such as the plasmid-encoded virF and yadA, and the chromosomally encoded ail, inv, yst, and rfb genes can be used to distinguish Y. enterocolitica from its environmental relatives.
Physiological Properties Yersinia enterocolitica is capable of growth at temperatures ranging from below 0 to 44 C, although its optimum temperature range is 22–28 C. It tolerates a pH range from 4.6 to 9.0 but prefers slightly alkaline conditions. The D values of Y. enterocolitica are approximately 2 min at 55 C, 0.5 min at 60 C, and 2 s at 65 C. The D value for Y. enterocolitica in milk is 0.24–0.96 min at 62.8 C.
117
118 Pathogens in Milk | Yersinia enterocolitica Table 1 Biotypes of Yersinia enterocolitica Biotype Test
1A
1B
2
3
4
5
Lipase (tween esterase) Esculin hydrolysis Indole production Acid from xylose Acid from salicin Acid from trehalose Nitrate reduction Pyrazinamidase -D-Glucosidase Voges–Proskauer Proline peptidase
þ þ/ þ þ þ/ þ þ þ þ þ V
þ þ þ þ þ þ
(þ) þ þ þ þ
þ þ þ þ/#
þ þ þ
V (þ)
, biotype of serotype 0:3 found in Japan; #, some chinchilla isolates may be positive; þ, positive; (þ), delayed positive; , negative; V, variable reaction. Reprinted with permission from Barton MD and Robins-Browne RW (2002) Yersinia enterocolitica. In: Hocking A (ed.) Foodborne Diseases of Public Health Significance, 6th edn. Sydney, NSW: AIFST.
Table 2 Relationship between biotypes and serotypes in Yersinia enterocolitica Species and biotype Y. enterocolitica Biotype 1A
Biotype 1B
Biotype 2 Biotype 3 Biotype 4 Biotype 5
Serotype
Pathogenic in man or animals
Predominant distribution
O:4; O:5a; O:6a; O:6,3a; O:6,30a; O:6,31a; O:7,8a; O:7,13; O:10a; O:10,46a; O:14; O:16; O:17a; O:19a; O:21a; O:22; O:25; O:37; O:41,42a; O:46; O:57; NTa O:8 O:13a,13b; O:20; O:21 O:4,32; O:16;O:18; O:25; O:41; O:42; NT O:8 O:1,2,3; O:3; O:5,27; O:47 O:3; O:15 O:2,3
Some serotypes possibly associated with gastroenteritis Yes Yes No Yes Yes Yes No – animals only
Environment, water, human and animal feces – worldwide Japan, USA, Europe USA Environment Japan, USA, Europe Pigs – Europe, Australia Pigs – worldwide Europe
a
Biotype 1A serotypes with reported epidemiological linkage to cases of gastroenteritis.
Table 3 Biochemical tests used in the identification of Yersinia enterocolitica
Serotyping and Biotyping
Test
Serotyping and biotyping are useful indicators of the potential pathogenicity of isolates of Y. enterocolitica. Antisera to only a few serotypes (O:3, O:8, O:1,2, O:9, and O:5,27) are available commercially.
Catalase Oxidase Motility (25 C) Motility (37 C) Nitrate reduction Fermentation of glucose Fermentation of lactose Fermentation of cellobiose Fermentation of sucrose Fermentation of trehalose Urease Citrate utilization Triple sugar iron agar
Lysine decarboxylase Ornithine decarboxylase Indole Vogues–Proskauer (25 C)
þ þ þ þ V þ þ þ þ Alkaline or acid slope, acid butt, negative gas, negative H2S production þ V þ
Phage Typing Phage typing is carried out in a few specialized laboratories, and thus is not commonly used. Geographic distribution of phage types of bioserotype 4,O:3 is recognized, as is the association of particular phage types of this bioserotype with the development of postinfection sequelae. Phage typing has largely been replaced by molecular typing. Molecular Typing A number of molecular methods have been applied to the identification of Y. enterocolitica and differentiating
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Table 4 Molecular identification and typing of Yersinia enterocolitica
Method
Typability of strains
Reproducibility
Discriminatory power
REAC
All
Poor
Moderate
Ribotyping
All
Good
Good
16S–23S IGS typing
All
Good
RAPD PFGE MLST
All All All
Moderate Good Good
Potentially useful Moderate Good Good
AFLP 16S DNA sequencing
All All
Good Good
Good Good
Comment Some serotype-specific patterns; useful for subtyping O:8 strains Differentiates species; useful for subtyping O:3 strains Only two studies – potential for subtyping Useful in epidemiological studies Best method to date for subtyping Only one study to date – good inter- and intraspecies differentiation Only one study – strong alignment with biotype Species identification – differentiation of pathogenic strains
16S–23S IGS, 16S–23S intergenic spacer typing; AFLP, amplified fragment length polymorphism; MLST, multilocus sequence typing; PFGE, pulsedfield gel electrophoresis; RAPD, randomly amplified polymorphic DNA; REAC, restriction endonuclease analysis of chromosome.
pathogenic from nonpathogenic strains (Table 4). Unfortunately, the high similarity between strains and the predominance of particular genotypes within bioserotypes limit the value of these methods.
Pathogenicity Virulence determinants of Y. enterocolitica are found both on the chromosome and on a 70-kb virulence plasmid. In addition, the North American biotype 1B strains carry a chromosomal pathogenicity island associated with increased virulence for mice and humans. Chromosomal virulence genes include yst, which encodes Yst, a heat-stable enterotoxin; inv, which encodes invasin, a surface protein important in the translocation of Y. enterocolitica across the intestinal epithelium and in the colonization of Peyer’s patches in the mouse model of infection; and ail (found only in pathogenic strains), which encodes a membrane-associated protein that promotes attachment of the organism to eukaryotic cells, has a support role as a secondary invasion factor, and confers resistance to the action of serum complement. Numerous other chromosomal genes contribute to virulence, including a urease gene complex – pathogenic strains of Y. enterocolitica produce urease, which may facilitate survival of the organism in acidic environments such as the stomach. The pYV plasmid of Y. enterocolitica encodes the Yop (Yersinia outer proteins) operon, which is an integrated virulence apparatus. Mouse studies have shown that strains lacking Yop are readily phagocytosed by macrophages and are unable to cause disease. The Yop operon is made up of at least 14 proteins, the majority of which have been shown to be essential for virulence. Another virulence gene carried on the pYV plasmid is yadA, which
encodes YadA, an outer membrane protein expressed only at 37 C and which is responsible for adhesion to intestinal epithelium, serum resistance, and resistance to killing by phagocytic cells. Highly pathogenic biotype 1B strains carry a highpathogenicity island (HPI), which is an iron uptake system that facilitates the growth of these strains under iron-depleted conditions at 37 C. Until recently, biotype 1A strains were regarded as nonpathogenic. They do not carry the pYV plasmid, but are occasionally isolated from humans with gastrointestinal diseases. Serotypes O:5, O:10, and O:6,30 have to date been associated with outbreaks of clinical disease. The infectious dose of Y. enterocolitica is unknown but is estimated to be around 106–107 organisms.
Pathogenesis After ingestion, pathogenic Y. enterocolitica pass through the intestinal tract to the ileum, where they bind to the M cells in Peyer’s patches. This attachment is facilitated by YadA. The organisms penetrate the intestinal mucosa through M cells and colonize the Peyer’s patches from where they can spread to the mesenteric lymph nodes through lymphatic vessels. This phase is facilitated by Yops. In rare cases Y. enterocolitica can spread through the bloodstream to other sites such as liver and spleen. YadA and Ail contribute to resistance to killing by serum complement.
Clinical Disease Yersinia enterocolitica is an enteric pathogen, which in susceptible people can cause extraintestinal disease.
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Enterocolitis is the most common manifestation and is seen principally in young children. Older children and adolescents may develop mesenteric lymphadenitis (mimicking appendicitis). Some cases are subclinical, and in the clinical cases the onset of clinical signs usually occurs within 24–48 h of ingestion of the organism. The illness usually lasts 1–3 days, with diarrhea seen in most cases plus fever, headache, and vomiting in many cases. Involvement of mesenteric lymph nodes leads to severe abdominal pain. The minimum infective dose for humans is not known, and the duration of excretion of the organism ranges from 2 weeks to more than 2 months. Yersinia enterocolitica infection is normally self-limiting but long-term sequelae such as reactive arthritis, erythema nodosum, uveitis, glomerulonephritis, and myocarditis have been reported. Reactive arthritis is associated with the human leukocyte antigen HLA-B27 and certain strains of bioserotype 4, O:3 more common in Nordic countries. Patients with underlying iron metabolism disorders such as siderosis, thalassemia, or hemochromatosis are more susceptible to bacteremia and extraintestinal infections, and transfusion-related septicemia has been reported in patients receiving blood transfusions from asymptomatic blood donors.
Epidemiology and Ecology Most cases of Y. enterocolitica infection are reported from the temperate areas of the world, for example, Scandinavia, northern Europe, and New Zealand. It is widely distributed in the environment and can be isolated from soil and water, and the intestinal tract of many vertebrates and invertebrates. The organism has minimal nutrient requirements at low temperatures and can remain metabolically active at very low temperatures. Most environmental strains belong to the nonpathogenic serotypes, but pathogenic serotypes O:8, O:9, and O:5,27 have been isolated from healthy pigs. The pattern of distribution of serotypes has changed over the years. Originally, serotype O:3 was rare in the United States in comparison with serotype O:8, but in the late 1980s serotype O:3 overtook O:8 and is now the most common serotype worldwide. However, serotype O:8 causes more serious infections.
Sources of Infection Infection with Y. enterocolitica has been linked most clearly to the handling and consumption of raw and undercooked pork, with the same serotypes (principally O:3, O:9, and O:5,27) and genotypes isolated from pigs and affected humans. Yersinia enterocolitica has often been isolated from foods, including animal products (beef, lamb, poultry, as
well as pork), milk, shellfish, and crustaceans. However, most of the isolates belong to nonpathogenic serotypes. Most infections with Y. enterocolitica occur sporadically, where the source of infection is hard to determine. A prospective case–control study in Norway suggested a strong linkage with consumption of raw or rare meat and untreated water. Vegetables and fresh herbs have also been incriminated. Outbreaks of Y. enterocolitica have been reported in a number of countries including the United States, Canada, Japan, Finland, and Czechoslovakia. Incriminated sources include raw and pasteurized milk, chocolate milk, tofu, bean sprouts, and spring and stream water. In many of the outbreaks no source could be identified. Serotypes reported include O:3 (11 of 20 outbreaks); O:8; O:9; O:5,27; and O:13a, 13b. Person-to-person spread in family clusters and direct transmission from animals have been suspected.
Occurrence of Yersinia enterocolitica in Milk and Dairy Products A small number of outbreaks associated with milk and dairy products have been reported from a number of countries (Table 5). No outbreaks have been reported in the literature since 2000. Some serotypes usually regarded as nonpathogenic are alleged to have been the cause of some of these outbreaks. Definitive proof, one way or the other, is difficult to obtain when nonpathogenic environmental strains of Y. enterocolitica are so widely distributed in the environment generally and in milk products specifically, as indicated in Table 6. In general, the microbiological evidence linking even the pathogenic serotypes with the outbreaks is not strong, and the causative linkage is based on epidemiological criteria from investigations such as case–control studies or analysis of food consumption histories. It is interesting to note that many of the outbreaks are associated with pasteurized milk, although Y. enterocolitica is quite heat-sensitive and readily destroyed by pasteurization at concentrations up to 105 organisms ml1. If the milk product is at fault, there must have been postpasteurization contamination. In several of the outbreaks there appears to have been the possibility of postprocessing contamination from pig-related contacts. Yersinia enterocolitica grows well in raw milk but there are few outbreaks linked to this source. The role of milk and dairy products in sporadic cases of Y. enterocolitica infection is not well studied. There are a number of reports of isolation of Y. enterocolitica from raw and pasteurized milk, as indicated in Table 5, and some reports of isolation from milk products such as ice cream and yogurt. Most of
Pathogens in Milk | Yersinia enterocolitica
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Table 5 Outbreaks of Yersinia enterocolitica infection associated epidemiologically with milk and dairy products Product
Number of human infections
Bioserovar
Number of isolates from product
Country (year)
Raw milk Chocolate milk Milk from powder Pasteurized milk Pasteurized milk
138 36 239 172 19
Different serotype 1 ? Nil 1 of each
Canada (1976) USA (1976) USA (1981) USA (1984) UK (1990)
Pasteurized milk
11
O:5,27 O:8 O:8 O:13; O:18a 1,O:10a; 1,O:6,30a O:3; O:6,30a
9 (O:6,30a)
Raw buttermilk Pasteurized milk
25 10
4,O:3 O:8
Nil, 1 from well water 1
Australia (1991) India (1997) USA (2000)
a
Biotype 1A serotypes previously regarded as nonpathogenic. ?, no information provided.
Table 6 Isolation of Yersinia enterocolitica from milk and dairy products Serotype
Countries
Pathogenic
O:21; O:5,27; O:9
Biotype 1A strains some of which may be pathogenic
O:4,32; O:4,33; O:5; O:6,30; O:6,60; O:7,8; O:14; O:15; O:18; O:34; O:41,42; O:46
Canada, France, USA, Ireland, UK, Brazil, Bulgaria, Iran Canada, Australia, France, USA, Italy, UK, Ireland, Brazil
the serotypes reported are those regarded as nonpathogenic, and there appear to be no reports of isolation of O:8 or O:3 or O:9 from raw milk, although there are a number of reports of isolation of O:5,27 (which includes both pathogenic and nonpathogenic strains). Many studies unfortunately do not report the serotypes isolated, and some do not differentiate between Y. enterocolitica and Y. enterocolitica-like species. There are no reports of detection of Y. enterocolitica in ripened hard cheeses and only occasional reports of isolation of the organism from soft cheeses made from raw milk. However, experimental studies have shown that pathogenic serotypes can grow on outer and exposed surfaces of cheese such as Brie at 4, 8, and 20 C, and in Cottage cheese. In most cases where serotyping is reported, the isolates from milk and milk products belong to the nonpathogenic serotypes of biotype 1A (e.g., serovars O:5; O:6,30; and O:7,8) or environmental stains in other biotypes. A number of studies where samples are spiked with microorganisms have reported that Y. enterocolitica does not survive as well as other enteric bacteria in fermented milk products such as yogurt. Yersinia enterocolitica (serotypes not specified) have been isolated from dairy plant environmental samples and equipment in dairy factories.
Isolation and Detection of Yersinia enterocolitica in Food and Environmental Samples The following are the factors that must be considered in approaching the isolation of Y. enterocolitica from food or environmental samples: first, the organism may be present in low numbers, so enrichment is required; second, the presence of the organism could be masked by the presence of large numbers of other bacteria, so a selective step is essential; third, nonpathogenic Y. enterocolitica and Y. enterocolitica-like species are likely to be present, so differentiation of pathogenic from nonpathogenic organisms is required. As a result, in recent years a combination of selective enrichment and molecular methods has been developed. Conventional isolation procedures involve an enrichment procedure followed by plating onto selective media and confirmation of the identity of colonies that have typical colonial morphology. There is no single method of enrichment that will guarantee isolation of all pathogenic Y. enterocolitica serotypes, so the use of more than one approach is often recommended. Enrichment approaches include 1. Cold enrichment at 4 C: This approach takes advantage of the fact that Y. enterocolitica multiplies at 4 C. Simple cold enrichment in phosphate-buffered saline
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(PBS) or tryptone soy broth (TSB) or PBS supplemented with 1% sorbitol and 0.15% bile salts for up to 3 weeks can be used. The method is quite sensitive as Y. enterocolitica multiplies under these conditions while nonpsychrotrophic contaminating organisms die out. However, the method is too slow for routine use. A modification of cold enrichment is to treat the enrichment broth with KOH, as Y. enterocolitica is quite tolerant of alkaline conditions. This is reported to be less effective than other enrichment methods. 2. Single-step enrichment in various selective broths: Selective broths used include modified Rappaport’s medium (MRM) incubated at 22–25 C for 2–4 days, irgasan– ticarcillin–potassium chlorate (ITC) medium incubated at 24 C for 2–3 days, and modified selenite medium. Bioserotype 4, O:3 appears to grow better in MRM and ITC than do other bioserotypes (2, O:9; 2, O:5,27; and IB, O:8). Bile–oxalate–sorbose medium has been reported as suitable for serotype O:8. 3. Two-step enrichment: This method involves preenrichment in a nonselective medium such as PBS or TSB at temperatures between 4 and 25 C for 24 h or longer, followed by inoculation into a selective broth such as MRM. This is reported to allow more sensitive strains of Y. enterocolitica to multiply in the nonselective medium so that a larger inoculum is exposed to the selective medium. A different strategy involving the use of Luria– Bertani–bile salts broth incubated for 24 h at 12 C before the addition of irgasin and a further incubation for 48 h at 12 C has been reported to be particularly successful in the isolation of serotypes O:8, O:5, O:27, and O:3 from spiked samples and in the isolation of bioserotype 4, O:3 from pig samples. 4. Selective isolation media: Yersinia enterocolitica grows readily on a range of media used for the isolation of other enteric organisms such as MacConkey agar, desoxycholate citrate agar, and salmonella–shigella agar. However organisms may be overlooked on such media, particularly if present in low numbers. CIN medium was developed specifically for the isolation of Y. enterocolitica and has the additional advantage that the organism produces the characteristic bull’s-eye colonies on this medium. CIN is considered the most effective medium for the isolation of Y. enterocolitica. A method for direct detection of virulence plasmidcarrying strains of Y. enterocolitica has been described, which involves subculture of Luria–Bertani–irgasan broths onto low-calcium Congo red brain heart infusion agar. Colonies of virulent (plasmid-bearing) Y. enterocolitica produce pinpoint red colonies on this medium. Molecular Detection Methods The traditional cultural methods for the detection of Y. enterocolitica have limitations, especially when
attempting to detect the organism in food or environmental samples. It is clear that detection of Y. enterocolitica in such samples can be improved by the use of polymerase chain reaction (PCR) techniques. Target genes that have been used for PCR include ail, yadA, and yst. Generally speaking, chromosomally located target genes are preferred because the plasmid is unstable and easily lost during subculturing in the laboratory. Single, multiplex, and nested PCR methods have been reported, and, more recently, real-time PCR methods have been described. These have the advantage of greater specificity and require less time to complete than conventional PCR. However, there are some limitations and problems associated with the use of PCR. These include the presence of inhibitory substances in the sample, the inability to differentiate between live and dead organisms, and the low number of organisms in the sample. These problems can be overcome to some extent by using an enrichment step and applying the PCR to the incubated enrichment broth.
Prevention and Control Pasteurization of milk and milk products is a key control measure. However, care has to be taken to ensure that postpasteurization contamination does not occur as Y. enterocolitica can survive and multiply in milk and on the surface of cheeses at refrigeration temperatures. Nonheat methods of treatment such as high-pressure cold pasteurization and pulsed electric field treatments may have a role to play, but their efficacy in killing Y. enterocolitica has not been evaluated. While in the past there may have been concerns about milk as a major source of Y. enterocolitica infections, it is now clear that most infections are directly or indirectly associated with pigs and pig products.
See also: Analytical Methods: DNA-Based Assays; Microbiological. Cheese: Public Health Aspects. Contaminants of Milk and Dairy Products: Environmental Contaminants; Contamination Resulting from Farm and Dairy Practices. Microorganisms Associated with Milk. Psychrotrophic Bacteria: Other Psychrotrophs.
Further Reading Barton MD and Robins-Browne RW (2003) Yersinia enterocolitica. In: Hocking A (ed.) Foodborne Diseases of Public Health Significance, 6th edn. Sydney, NSW: AIFST. Foley SL, Lynne AM, and Nayak R (2009) Molecular typing methodologies for microbial source tracking and epidemiological investigations of Gram-negative bacterial foodborne pathogens. Infection, Genetics and Evolution 9: 430–440.
Pathogens in Milk | Yersinia enterocolitica Robins-Browne RW (2001) Yersinia enterocolitica. In: Doyle MP, Beuchat LR, and Montville TJ (eds.) Food Microbiology: Fundamentals and Frontiers. Washington, DC: ASM Press. Schiemann DA (1987) Yersinia enterocolitica in milk and dairy products. Journal of Dairy Science 70: 383–391. Tennant SM, Grant TH, and Robins-Browne RW (2003) Pathogenicity of Yersinia enterocolitica biotype 1A. FEMS Immunology and Medical Microbiology 38: 127–137.
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Thisted Lambertz S, Nilsson C, Hallanvuo S, and Lindblad M (2008) Real-time PCR method for the detection of pathogenic Yersinia enterocolitica in food. Applied and Environmental Microbiology 74: 6060–6067. Virdi JS and Sachdeva P (2005) Molecular heterogeneity in Yersinia enterocolitica and Y. enterocolitica-like species – implications for epidemiology, typing and taxonomy. FEMS Immunology and Medical Microbiology 45: 1–10.
PLANT AND EQUIPMENT Contents Process and Plant Design Materials and Finishes for Plant and Equipment Flow Equipment: Principles of Pump and Piping Calculations Flow Equipment: Pumps Flow Equipment: Valves Agitators in Milk Processing Plants Centrifuges and Separators: Types and Design Centrifuges and Separators: Applications in the Dairy Industry Heat Exchangers Pasteurizers, Design and Operation Evaporators Milk Dryers: Drying Principles Milk Dryers: Dryer Design Instrumentation and Process Control: Instrumentation Instrumentation and Process Control: Process Control Robots Corrosion Continuous Process Improvement and Optimization Quality Engineering Safety Analysis and Risk Assessment In-Place Cleaning
Process and Plant Design R P Singh, University of California, Davis, CA, USA S E Zorrilla, Instituto de Desarrollo Tecnolo´gico para la Industria Quı´mica (INTEC), Santa Fe, Argentina ª 2011 Elsevier Ltd. All rights reserved.
Introduction The design of a dairy plant and its associated processes is often an open-ended problem with many possible solutions. Each design solution may have a unique impact on production capacity, process control, safety, environment, and economics. In conducting an engineering design project, several requirements relating to the following aspects must be met: 1. Product (raw materials and quality of the end product) 2. Process (plant capacity, equipment, controls, and cleaning) 3. Economics (cost of production) 4. Legal considerations (regulations relevant to process, equipment, and safety).
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Although it is common to seek a compromise between these requirements for a specific application, careful consideration of these characteristics is essential to develop an optimal design. This requires an extensive literature search, knowledge of the food and its material properties, and a description of the equipment, including process flow diagrams. Numerous reference books are available for designing dairy processes and plants (see ‘Further Reading’). Research journals such as Australian Journal of Dairy Technology, Dairy Science & Technology, International Dairy Journal, Journal of Dairy Research, and Journal of Dairy Science, patents, and technical literature available from manufacturers through the World Wide Web are also potential sources of information.
Plant and Equipment | Process and Plant Design
Process Flow Sheet The design process begins with the preparation of a detailed flow sheet, which should clearly indicate the major plant equipment and the flow of product, utilities, and waste materials. Although a simple flow sheet is merely a sequence of processing equipment, it is often necessary to develop a detailed flow sheet with information such as the type of processing equipment, pipes, utility requirements, flow rates, and required instrumentation. It is not uncommon to develop separate flow sheets with more specific information for special purposes, such as for detailing all the control instrumentation. A 3D flow sheet is also generally used for a better visualization of the plant and equipment. A clean-in-place system should be included in the flow sheet for process equipment and pipelines. Each of these items must be labeled clearly. Figure 1 shows the diagram of a multiproduct dairy plant and illustrates a simple flow sheet for a market milk process. This flow sheet may differ depending on different regulatory and marketing requirements. Although pasteurizing whole
125
milk is a simple process line, complexities arise when manufacturing several types of milk products, such as whole milk, milk standardized to various fat contents, and creams with different fat levels. After the flow sheet is completed, the next two steps include conducting mass and energy balances. A mass balance must be comprehensive enough to include all materials flowing through the plant and their composition. The energy balance is conducted to determine the energy requirements of all the operations identified on the flow sheet. After the mass and energy balances have been determined, the next step is to design each unit. At this stage, a preliminary economic appraisal should be conducted based on the data acquired for the mass/energy balances.
Equipment Selection Selection of process equipment requires careful attention to equipment sizing, cost, efficiency, and ease of maintenance. A major emphasis is often placed on the capital as
(a) Fresh milk production
Sterile milk production
Milk powder production
Butter production
Control panel
CIP plant Milk reception Cheese production Whey utilization Yogurt production
(b)
1 7 Cream
2
3
4
Fresh milK 5
Milk reception area
6
(1) Milk tanker (2) Weighing balance (3) Raw milk chiller (4) Raw milk silo (5) Separator (6) Plate heat exchanger (7) Homogenizer (8) Filling line
8
Fresh milk production area
Figure 1 (a) Schematic diagram of a multiproduct dairy plant. (b) A simple flow sheet for a market milk process. Adapted from Spreer E (1998) Milk and Dairy Product Technology. New York: Marcel Dekker.
126 Plant and Equipment | Process and Plant Design
well as operating costs, as these costs influence the profitability of the operation. In food and dairy processing, the ease of cleaning is an important consideration in selecting equipment. Equipment Common to All Dairies Tanks
Tanks of various sizes are essential in dairy processing. Sizes ranging from 100 to 100 000 l are commonly used. Typically, tanks serve two major functions: storage and processing. Storage tanks (silo tanks) constructed of stainless steel range in size from 25 000 to 150 000 l. These storage tanks are often placed outdoors when indoor space is limited. The number and size of silo tanks used are determined by the quantity of milk processed per day and the number of different products manufactured. Furthermore, the frequency of processing days per week, as well as the number of processing hours per day, will determine the size or number of storage tanks. The size of silo tanks in the delivery area is determined by the expected schedule of raw milk delivery to the plant. If the plant is to be operated continuously, then a 7 h supply of raw material should be available. If milk is to be held for more than 8 h in a tank, then refrigerated or insulated tanks are required. In the process line, buffer tanks are used to hold milk for short durations. A general rule of thumb is to have a buffer capacity of a maximum of 1.5 h of normal operation. Heat exchangers
Control of temperature is an essential feature of modern dairy plants. Processing steps require either heating or cooling, processes that are carried out using heat exchangers. For heating purposes, hot water or low-pressure steam is used; however, milk itself is used as a heating medium in a regenerative process. For cooling purposes, chilled water or glycol is used; again, milk is used as a cooling medium in a regenerative process. The three most common types of heat exchangers used in the dairy industry are the plate, tubular, and scraped-surface heat exchangers. Plate heat exchangers are best suited for the treatment of milk, the predominant product in the dairy industry. Heat exchanger design and performance are influenced by product flow rate, temperature and time requirements, cleanability issues, and the properties of the product undergoing heat treatment. Most texts on food engineering address the principles of heat transfer. Pumps
Transport of liquids from one location to another in a dairy processing plant requires energy, which is provided by pumps. For handling milk and dairy products, the construction material used for pumps is typically stainless steel, food grade rubber, or plastic. The pump design should permit easy cleaning-in-place (CIP). The
most common types of pumps used in milk and dairy processing include centrifugal, liquid-ring, and positive displacement pumps. Centrifugal pumps are well-suited for low-viscosity liquids, such as milk. When a liquid contains some amount of air, then liquid-ring pumps are suitable. These pumps are also used for CIP return solutions, which invariably contain air. For higher-viscosity products and those exhibiting non-Newtonian characteristics, such as cream, cultured milk products, and curds, positive displacement pumps are used. Piston pumps are used for metering purposes. A homogenizer is a type of piston pump that is used to break large fat globules into smaller ones (see Homogenization of Milk: Principles and Mechanism of Homogenization, Effects and Assessment of Efficiency: Valve Homogenizers). Pipes, fittings, and valves
Pipes are ubiquitous in a dairy plant; they are used for transporting low- and high-viscosity liquids and gases. Pipes convey not only dairy products but also all the utilities (steam, water, compressed gases) from one processing apparatus to another. The material of construction and design used for pipes depend on the product being conveyed. In designing pipelines for dairies, the important issues of concern include construction material, size, and contact surface, particularly around welded joints. In dimensioning the pipelines, careful attention should be given to the selection of flow rates and velocities. Flow rates in fluid-handling systems are typically in the range of 100–30 000 l h 1, with velocity being limited by the product characteristics. For example, the velocity of raw milk should not be greater than 1.5 m s 1 to avoid damage to the fat globules. For skim milk and buttermilk, the velocity is normally around 2 m s 1. However, because cream has a high viscosity, its velocity would be less than 0.5 m s 1. Utilities are pumped at much higher velocities: steam at around 30 m s 1 and water at 5 m s 1. A variety of fittings are used in the pipelines, such as elbows, tee connections, and connectors. These fittings match the diameter of pipelines and other process equipment. To control the direction and magnitude of flow, a variety of valves are used. Some examples are seating valve, check valve, air blow valve, and regulating valve. Stirring devices
Stirring devices are used for equalizing temperature and/ or concentration in a vessel. The design of stirrers depends on the viscosity of the product. For low-viscosity products (viscosity <1 Pa s), such as whole milk or whey, paddle, curved blade, propeller, or turbine impeller stirrers are used. For medium- to high-viscosity products (viscosity 0.5–5 Pa s), such as condensed milk, yogurt, or cream, cross rod, gate, or blade paddle stirrers are used. For high-viscosity products (viscosity >100 Pa s), such
Plant and Equipment | Process and Plant Design
as quark or processed cheese, anchor, finger, or helical ribbon stirrers are used. Centrifuges
Separating components in a liquid stream is an important process in dairy processing. For purposes of clarification centrifuges are used. Typical centrifuges used in the industry can separate particles of 4–5 mm diameter. Homogenizers
In full-fat milk, the formation of a cream layer occurs during storage due, inter alia, to the large diameter of fat globules. However, if the size of these globules is reduced, creaming is minimized. Homogenizers are used for this process. The degree to which the products should be homogenized depends upon the expected storage time of milk. Because the fat phase in milk must be in liquid state for homogenization to be effective, milk must be heated to a temperature in the range of 55–80 C. A homogenization pressure in the range of 10–25 MPa is selected, depending on the product characteristics. Homogenization of cream with a fat content >12% is difficult owing to the lack of casein to stabilize the newly formed emulsion surface. For adequate levels of homogenization, 0.2 g of casein per gram of fat is necessary. Conventional homogenizers are triple-piston high-pressure pumps. In milk processing, the homogenizer is located after the first regenerative section of a pasteurizer. In the production process of UHT milk, the homogenizer is located in the upstream section when an indirect heat exchanger is used, but on the downstream side when direct heat exchangers are used. When located on the downstream side, the homogenizer must maintain aseptic conditions, requiring special piston seals, packings, and aseptic dampers.
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Standards Specifications for all equipment must be written down carefully. A number of standards are available for writing specifications, such as 3-A Sanitary Standards, 3-A Accepted Practices, International Dairy Federation Documents, and US Department of Agriculture publications. The US Department of Agriculture provides criteria, guidelines, and principles for the sanitary design and fabrication of dairy processing equipment, as well as a list of equipment that are rated as acceptable for use in dairy plants.
Process Control Because processing equipment must have the capacity for trouble-free operation under variable conditions, control equipment is used to maintain desired liquid levels, flow rates, pressures, concentrations, pH levels, and temperatures. The control systems must be simple, rugged, and robust. Careful attention should be paid to maintenance requirements. The level of automation in process control is determined by the type of processing equipment and its interaction with the instrumentation used for automation. The selection of instrumentation depends on how it will interact with the operator and with procedures that manage the information obtained from it, such as how errors will be corrected. Typically, the automation systems use programmable logic controllers. These systems must be flexible, easy to expand, and reliable. These systems should include electronic solutions, with software for diagnostic tests. More recently, simulations have become an attractive part of the software.
Utilities Special Equipment Table 1 lists some of the special items of equipment required for dairy processing operations.
Materials Construction materials that have direct contact with the product must be nontoxic and inert to foods. For hygienic reasons, surfaces that come in contact with dairy materials must be well-ground and polished, or cold-rolled. On the other hand, materials that do not make contact with foods, such as pipelines for utilities, must be corrosion-proof and remain stable. The surfaces of materials used for the construction of manufacturing process equipment must be well-ground and treated with lacquer or undergo a similar procedure.
Dairy operations require a number of utilities such as electricity, steam, hot water, chilled water, compressed air, and refrigeration. Water consumption for a typical dairy plant is 1000–5000 l per 1000 l of milk. Water is transported in stainless-steel pipes with a diameter larger than 6.35 cm or in smaller galvanized-steel pipes. The pipeline system includes valves for shutoff and routing purposes, and pressure gauges. Often, dairy plants rely on their own water supply instead of using municipal water (see Utilities and Effluent Treatment: Water Supply). For most heating applications, steam (140–150 C) is the most commonly used heating medium in the dairy industry. Pipelines convey steam to the locations where it is required. Hot water systems are also used, but heated water must be kept under pressure to avoid boiling,
Table 1 Special equipment required in dairy processing Product
Common steps for the process
Basic equipment required
Comments
Butter
Milk reception Preheating and pasteurization of skim milk Fat separation Cream pasteurization Vacuum deaeration Culture preparation Cream ripening Temperature treatment Churning Buttermilk collection Packaging
Plate heat exchanger Centrifuge Continuous buttermaking machine Packaging system
Capacities of continuous butter-making machines 200–5000 kg h cream; 200–10 000 kg h 1 butter from sweet cream.
Cheesea
Preparation of cheese milk Heat treatment Standardization Preripening process Protein coagulation Curd preparation and treatment Molding Pressing Salting Ripening Packaging
Cheese vat with tools for cheese manufacture Pressing and molding vat Brining system Ripening storeroom
Traditional and partially mechanized processes. Equipment is designed specifically for the type(s) of cheese to be manufactured. Nearly all operations are done manually. Completely mechanized processes. Capacities: 50–100 000 l day 1; completely mechanized processes are economical with higher level of automation.
Ice cream
Preheating Formulation mixing Pasteurization/homogenization/ cooling Aging Freezing Filling/extrusion/molding Hardening Cold storage
Mixing and processing tank Homogenizer Plate heat exchanger Aging tank Continuous freezer Filler
Rapid freezing process is used for the formation of small ice crystals. In a plant with a small capacity, dry ingredients are generally weighed and supplied to the mix tanks manually. Large-scale producers use automatic batching systems. In large production plants, a continuous flow is maintained using mix tanks with a volume corresponding to the hourly capacity of the pasteurizer.
1
butter from sour
Longlife products
Cleaning Fat content standardization Preheating and stabilization Cooling UHTb Homogenization Heat treatment Cooling Storage Filling
Balance tank Plate heat exchanger Nonaseptic homogenizer Aseptic tank Aseptic filling
To improve the texture and physical stability of certain products like cream, an aseptic downstream homogenizer is used.
Milk powder
Milk pretreatment Concentration Homogenization Drying Packaging
Milk concentrate tank Spray-dryer or drum dryer Cyclone Packaging system
Spray-dryers are used to manufacture milk products from concentrates. Drum drying. Typical specific steam consumption is 1.3–1.6 kg per kg of evaporated water, and 4.3–5.0 kg per kg of powder.
Yogurt
Pretreatment of milk: Standardization of levels of fat and dry matter Heat treatment Homogenization Stirred type yogurt:c Incubation Cooling Flavoring Filling Cold storage
Balance tank Plate heat exchanger Evaporator Homogenizer Incubation tanks Plate cooler Buffer tanks Packaging system
Yogurt is a thixotropic non-Newtonian fluid. Its viscosity decreases during processing. A proper optimization of the process is necessary to allow the viscocity to be fully regenerated and syneresis minimized.
a
Cheese of various types is produced in several stages. Each type of cheese has its specific production formula. Some basic stages are shown here. UHT is the most common treatment for preserving liquid food products. c Yogurt is typically classified as follows: set type (incubated and cooled in the package); stirred type (incubated in tanks and cooled before being packed); drinking type (similar to stirred type, but the coagulum is ‘broken down’ to a liquid before being packed); frozen type (incubated in tanks and frozen like ice cream); concentrated (incubated in tanks, concentrated, and cooled before being packed). b
130 Plant and Equipment | Process and Plant Design
because most processing operations require water at around 100 C. Typical steam consumption is around 185–200 kg of steam per 1000 l of raw milk. Refrigeration systems are vital in dairy processing. At elevated and ambient temperatures (see Utilities and Effluent Treatment: Refrigeration), products are prone to microbial and enzymatic degradation. Therefore, rapid cooling to a safe temperature is often a necessity. Generally, the operating cost of the refrigeration system is important in the global cost estimation. For automatic control purposes, especially in damp environments, pneumatically controlled automatic systems are preferred. These control systems require compressed air free from impurities. Compressed air is also used in some processing operations, such as agitation in storage tanks and emptying product from pipelines (see Utilities and Effluent Treatment: Compressed Air). For an electric power demand of 300 kW, dairies take low-voltage supplies of 220–440 V. Many dairies rely on local generation of electricity in the event of power failures or sometimes for continuous operations (see Utilities and Effluent Treatment: Electricity). The typical electric power requirement for a dairy is 15–18 kW per 1000 l of processed raw milk.
Plant Layout A plant layout includes the arrangements of processing, storage, and handling areas, as shown in Figure 2. The layout is developed after the process flow diagrams are completed, and the information is useful in determining construction and manufacturing costs. Several factors influence the plant layout, including the type and quantity of products to be manufactured, process and product
CIP
Lab and quality control
Facilities boiler
Maintenance
Tank room
Office
Sanitary Design In designing any food processing plant, emphasis on proper cleaning and disinfection of equipment and work space is paramount. Disinfection is carried out using chemicals mixed in water: about 1.7 kg of alkali and 0.6 kg of acid are required for each tonne of processed milk. Furthermore, steam is used for high-temperature sterilization. For optimum use of chemical agents, the nature of dirt, the surface characteristics, water quality, and the effectiveness of cleaning and disinfection agents must be clearly understood. According to the terminology used in cleaning, physical cleanliness is removal of all visible dirt from the surfaces; chemical cleanliness is removal of microscopic residues that can be detected by taste or smell; bacteriological cleanliness is obtained by disinfection; and sterile cleanliness is destruction of all microorganisms. In dairy cleaning operations, chemical and bacteriological cleanliness are achieved using chemical agents. Cleaning-in-Place Systems Modern dairy processing plants use CIP systems, which involve circulation of rinsing water and detergent
Packaging material storage
Dry storage Raw ingredient receiving
controls, utilities, building specifications and code requirements, and waste handling and disposal. Equipment should be arranged in such a manner as to minimize capital and operating costs. The actual location of process equipment must permit adequate space for cleaning and maintenance. Similarly, adequate aisle space must be provided for workers in conformity with any building codes. Future plant expansion should be considered.
Cold storage Packaging
Milk processing
Distribution and shipping Specialized packaging
Control room
Break room
Locker
Figure 2 Dairy processing plant layout. Adapted from Hui YH (1993) Dairy Science and Technology Handbook. New York: VCH.
Plant and Equipment | Process and Plant Design
solutions through tanks, pipes, and other process equipment. Because the entire processing system is interconnected, there is no need to dismantle equipment for cleaning. An automated cleaning system requires that all surfaces be accessible to the detergent solution. If the detergent cannot get to any area, such as to the dead ends in a pipe, then the system fails. The installation of pipes and equipment must be done in a manner that promotes easy drainage of cleaning solutions. All components of the equipment that come into contact with chemical detergents must be able to withstand them. Depending on whether heated surfaces are involved in cleaning, a typical dairy CIP program would operate as follows. A CIP program for a pasteurizer involves rinsing with warm water for about 10 min, circulation of an alkaline detergent solution (0.5–1.5%) for about 30 min at 75 C, followed by rinsing out the alkaline detergent with warm water for about 5 min. Then nitric acid solution (0.5–1.5%) is circulated for about 20 min at 70 C, followed by postrinsing with cold water and gradual cooling with cold water for about 8 min. With pipes and tanks, which may be considered as ‘cold components’, the process involves rinsing with warm water for 3 min, circulation of 0.5–1.5% alkaline detergent at 75 C for about 10 min, and again rinsing with warm water for about 10 min. Disinfection with hot water at 90–95 C for 5 min is carried out, which is then followed by gradual cooling with cold tap water for about 10 min. After the process equipment is cleaned, it is sanitized to destroy residual yeasts, molds, bacteria, and bacterial spores. The surfaces must be thoroughly cleaned before sanitizing. Common chemicals used for sanitizing include chlorine compounds, iodophors, quaternary ammonium compounds, and acid-anionic surfactants.
Design Strategy and Optimization In process design, optimization to minimize costs and maximize profitability plays a major role. A number of mathematical procedures are widely available to optimize manufacturing processes. These procedures have the following common elements: design variables, equality and nonequality constraints, feasible solutions, and objective function. Process optimization is increasingly being used in the dairy industry. Typically, the optimization problem is to determine values of independent variables that result in an optimal value of a dependent variable. Commercially available software has made modeling and simulation more user-friendly. These models require reliable information on the physical and thermodynamic properties of foods, preferably in the form of computerized databases. Cost data are also crucial in plant design. Typical data for processing plants manufacturing dairy products are
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shown in Table 2; this is for indicative purposes only, as differential inflation since 1987 will have changed the relative figures significantly.
Safety and Hazard Evaluation In designing plants and processes, the safety of the operating personnel and people living in the vicinity of the plant is of major concern. A safe design involves appropriate steps to protect the life and health of the working population. In the United States, the Occupational Safety and Health Administration (OSHA) promulgates regulations regarding worker safety and health. In Europe, information can be found from EU agencies and national bodies.
Environmental Constraints Since the 1970s, environmental protection has become a primary issue in many industrialized countries. This has resulted in the development of stricter environmental regulations and their enforcement. Dairy processing plants generate large volumes of organic waste, which must be properly discharged and treated. Treatment facilities for waste materials must be designed and constructed in collaboration with local agencies. A large quantity of wastewater in a dairy plant contains milk components, particularly the water used for cleaning equipment and pipelines. Typically, 2 l of water is used for every liter of milk handled. Wastewater from employee washrooms, toilets, etc. amounts to 75 l day 1 per employee. A certain amount of wastewater results from cooling water used for cooling milk. Dairy wastewater is high in organic matter and hence must be diluted by a factor of 150 to 200 (see Utilities and Effluent Treatment: Design and Operation of Dairy Effluent Treatment Plants). As this would be extremely wasteful, dairies use treatment facilities, using either mechanical or biological means. The use of acids and alkaline detergents for cleaning equipment and pipelines results in the pH of wastewater ranging between 2 and 12. Typically, wastewater with a pH higher than 10 or lower than 6 must not be discharged into the sewage system. Effluents from the cleaning systems are usually collected and the pH carefully monitored and adjusted if necessary. Another component of the dairy wastewater is whey. Recently, manufacturing processes have been developed to convert whey into economically attractive by-products such as whey and lactose powders. A variety of separation processes, such as ultrafiltration, reverse osmosis, and electrophoresis, in addition to enzymatic hydrolysis, are used for manufacturing whey products (see Whey Processing: Utilization and Products).
Table 2 Cost data referred to fixed capital and annual operating costs in US dollars Annual operating cost (US$ yr 1)
Fixed capital cost (US$)
Plant
Capacity (109 g yr 1)
Operationg time (h yr 1)
Equipment
Mechanical and electrical
Civil
Materials
Utilities
Labor
Supplementary
Mozzarella cheese plant Ice cream plant Milk powder plant Yogurt plant
1875 4000 12 000 25 000
3000 2000 7200 3125
340 750 1 330 000 2 700 000 3 236 600
65 850 650 000 715 000 878 000
435 000 535 000 585 000 713 000
1 700 000 1 074 860 13 210 000 11 750 000
51 600 143 500 1 088 000 465 375
86 000 271 000 98 000 246 000
10 000 31 000 160 000 111 700
Bartholomai A (1987) Food Factories: Processes, Equipment, Costs. New York: VCH Publishers.
Plant and Equipment | Process and Plant Design
It has become increasingly important for dairy plants to be certified by the ISO13000 series of norms that deal with environmental protection.
Computer-Aided Design Several commercial computer-aided design packages are used in the chemical industry for simulation and design of processes. These simulators are valuable tools for flow sheeting, determining mass and energy balances, sizing the equipment, and analyzing performance. Although the majority of these packages are more suitable for the general chemical industry, some efforts have been made during the last decades to develop materials useful for the dairy and food industry.
See also: Homogenization of Milk: Principles and Mechanism of Homogenization, Effects and Assessment of Efficiency: Valve Homogenizers. Utilities and Effluent Treatment: Compressed Air; Design and Operation of Dairy Effluent Treatment Plants; Electricity; Refrigeration; Water Supply. Whey Processing: Utilization and Products.
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Further Reading Bartholomai A (1987) Food Factories: Processes, Equipment, Costs. New York: VCH Publishers. Bylund G (1995) Dairy Processing Handbook. Lund, Sweden: Tetra Pak Processing System AB. Caudill V (1993) Engineering: Plant design, processing, and packaging. In: Hui YH (ed.) Dairy Science and Technology Handbook. Vol. 3: Applications Science, Technology, and Engineering, pp. 155–294. New York: VCH. Clark JP (1997) Cost and profitability estimation. In: Valentas KJ, Rotstein E, and Singh RP (eds.) Handbook of Food Engineering Practice, pp. 537–557. Boca Raton, FL: CRC Press. Early R (1998) The Technology of Dairy Products. London: Blackie Academic & Professional. Gilmore T and Shell J (1993) Dairy equipment and supplies. In: Hui YH (ed.) Dairy Science and Technology Handbook. Vol. 3: Applications Science, Technology, and Engineering, pp. 155–294. New York: VCH. Hui YH (1993) Dairy Science and Technology Handbook. New York: VCH. Maroulis ZB and Saravacos GD (2003) Food Process Design. New York: Marcel Dekker. Rotstein E, Chu J, and Saguy IS (1997) Simulation and optimization. In: Valentas KJ, Rotstein E, and Singh RP (eds.) Handbook of Food Engineering Practice, pp. 559–580. Boca Raton, FL: CRC Press. Seider WD, Seader JD, and Lewin DR (1999) Process Design Principles. Synthesis, Analysis, and Evaluation. New York: John Wiley. Spreer E (1998) Milk and Dairy Product Technology. New York: Marcel Dekker. Walstra P, Geurts TJ, Noomen A, Jellema A, and van Boekel MAJS (1999) Dairy Technology. New York: Marcel Dekker.
Materials and Finishes for Plant and Equipment K Cronin, University College Cork, Cork, Ireland R Cocker, Ayndo Tree Farm, County Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction
Construction Materials
Hygienic design of processing equipment is a particular requirement for the dairy industry that in general does not apply to the bulk chemical area. The primary intention is to prevent the contamination of product materials during processing. Hygienic design is based on a combination of mechanical, process, and microbiological requirements. Two particular aspects of hygienic design are selection of appropriate materials of construction for equipment and specification of an acceptable surface finish for those materials. Hygienic equipment must be constructed of a durable material that will not compromise the purity of the product, is completely drainable, and has smooth surface finish. If equipment is of poor hygienic design, it will be difficult to clean and difficult to free from microorganisms, which may then survive and multiply in product residues in crevices. It should be noted that hygiene regulations for equipment handling dry product (such as powders) are more relaxed as dry products do not support the growth of microorganisms to the same extent as wet products. There are a number of professional bodies that issue regulations concerning hygienic design. In the United States, the 3-A Sanitary Standards, Inc. (3-A SSI), is a nonprofit association representing equipment manufacturers, processors, regulatory sanitarians, and other public health professionals. This group has established a comprehensive inventory of 3-A Sanitary Standards and 3-A Accepted Practices now known around the world for dairy and food processing equipment and systems. The American Society of Mechanical Engineers (ASME) Bio-Processing Equipment (BPE) Code came into being in the United States in 1998, although it is primarily aimed at the biopharma and biotech sectors rather than the dairy sector. In Europe, the closest equivalent code is the EHEDG Regulations. The European Hygienic Equipment Design Group (EHEDG) is composed of representatives from research institutes, process equipment manufacturers, the food and biopharma industry, and legislative bodies. The objective is to provide specialist advice on hygienic and aseptic design. The EHEDG and both the 3-A and ASME BPE provide suggestions and recommendations but their standards are not mandatory.
At the outset, it must be understood that when discussing the choice of acceptable materials and required surface finish for dairy plant and equipment, the focus is on product holding and processing equipment. In other words, it is equipment that has a product contact surface that is being examined (i.e., the insides of pipes and vessels). For equipment that does not come into direct contact with the dairy product, such as the pumps and pipes for service fluids (steam, water, and air), the conditions determining acceptable materials and surface finish are far less stringent. Likewise, the nonproduct-contact part of dairy processing equipment (such as legs and support features) is not subject to the same scrutiny. In the dairy sector, conditions are in general less exacting than in the chemical industries. Processing temperatures (usually within the range 40 to 140 C) and usual operating pressure ranges (0–10 bar) are limited, and pH does not deviate widely from neutral (a pH of 2 or 3 being a minimum). However, dairy processing operations are unique in that the needs for sanitary design and operation are stringent. In all cases, product contact surfaces must withstand the aggressiveness of the product and processing (temperature, pH, flow velocity, roughness) and must meet special needs of resistance to wear and abrasion and corrosion resistance. The material of construction must also withstand the often greater aggressiveness of the chemicals used for cleaning and sanitation. As a general classification, most dairy products are slightly acidic, and detergents (especially caustic detergents) are alkaline. Sometimes though acids, including hydrochloric and nitric, are used for removing scale from dairy processing equipment and this must be taken into account in material selection. Regulations require that process equipment should be made from a durable, impermeable, and corrosion-resistant material to avoid the contamination of the product and be of such construction as to enable the equipment to be kept clean and disinfected. In Europe, the European Union issues regulations to the member states to this effect. Toxic substances, likely to endanger health (if consumed with the product) or taint the product, must not be used in the construction of equipment if contact with edible material can occur. Some materials are
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Plant and Equipment | Materials and Finishes for Plant and Equipment
slightly soluble, nontoxic, and do not adversely affect the product. Tin and aluminum are in this category. Other materials are toxic and cannot be used for dairy contact surfaces such as lead (solder), zinc (present in galvanized steel), and iron compounds (mild steel). In principle, dairy processing equipment can be built from a wide variety of metals, ceramics, or polymers. However, as stainless steel (particularly the grades 304L and 316L) is so prevalent, it merits the majority of the subsequent discussion.
Stainless Steel Introduction Stainless steel is defined as an alloy of chromium and steel. It has the characteristic of greatly enhanced corrosion resistance over conventional lower alloy and carbon steels. This corrosion resistance derives from the addition of at least 12% chromium, although the most widely used grades contain about 18% of this element. Chromium on its own oxides quickly and produces a stable passive oxide film on exposed surfaces. This property also occurs when chromium is in a solid solution in iron becoming very marked as the amount exceeds 12% in low carbon steels. This corrosion-resistant film protects the underlying metal. This film can be up to 5 nm thick and contains varying amounts of Cr2O3. In an oxidizing media, any defect in the film that arises through abrasion is quickly repaired (i.e., the film is self-healing). However, it must always be remembered that no stainless steel is completely corrosion proof; oxygen is required to maintain passivity. In terms of chemical composition, stainless steel contains the basic elements of steel (iron and carbon) plus chromium. Almost all stainless steels (with the exception of some martensitic steels) have low carbon contents, generally below 0.15%. The main reason is that under certain conditions (e.g., in the heat-affected zone of a weld), carbon can preferentially combine with chromium to form chromium-rich carbon deposits at grain boundaries. This depletes the prevailing chromium levels in this region of the material and makes corrosion possible. Chromium itself is the defining element of stainless steel. It is present in amounts from 12% (a minimum) to 30%, and the most widely used grades contain chromium in contents between 17 and 25%. There are two other elements that can be found in stainless steel, though not all grades of stainless steel contain them. Nickel is added to produce austenitic grades of stainless steel. These steels usually contain 9% nickel and have improved corrosion resistance especially against acids. Stainless steels with 18% chromium and 8% nickel are commonplace (‘18/8 steels’). Finally, molybdenum can be added to improve further corrosion resistance
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in especially aggressive environments such as acids. It is added in amounts of 2% to the 18/8 steels. Types and Classification There are four main types of stainless steel microstructure: ferrite, austenite, martensite, and duplex. These are distinguished from each other by their chemical composition and consequent mechanical and corrosion-resistance properties. Furthermore, within each of these main groups, there is a huge variety of grades depending upon the number and amount of minor alloying elements present and the heat treatment that is carried out. Austenitic steels have excellent toughness (impact resistance) at low temperatures and they are the most readily weldable of the different stainless steel types, which is a very important consideration for a processing plant. One drawback is that the high nickel and chromium content make these alloys expensive. Ferritic stainless steels are cheaper than the austenitic steels and have very good corrosion resistance. Their ductility and toughness is not comparable with that of the austenitic steels. Martensitic stainless steels can have carbon contents ranging from 0.1 to 1%. They have less corrosion resistance than the other steels. The high carbon content makes them very hard, and they are suitable for applications where wear and abrasion resistance is essential. Duplex stainless steels are a newer type of stainless steel with high-strength features. In this stainless steel, the internal structure is an equal mix of face-centered and body-centered crystal structures (austenitic and ferritic). Duplex stainless steels have better toughness than ferritic grades and much higher yield strengths than the austenitics. Most of the above stainless steels are also available as L grades (e.g., 316L). The L designation means the carbon content in the steel is at a particularly low level, usually below 0.03%. This is to diminish further the possibility of chromium carbides being formed at grain boundaries and reducing the protection offered by chromium to the steel. Corrosion The very name ‘stainless steel’ can be misleading; stainless steels are protected by a passive oxide film, and defeat of this film is possible by certain corrosion mechanisms. There are many possible corrosion mechanisms: pitting corrosion, crevice corrosion, stress corrosion cracking, sulfide stress corrosion cracking, intergranular corrosion, galvanic corrosion, contact corrosion, microbial corrosion, and so forth. Stainless steel should be used for corrosion resistance where oxidizing conditions exist. This is to enable the oxide film to regenerate itself constantly. Furthermore, stainless steel is susceptible to corrosion caused by chlorine. Thus,
136 Plant and Equipment | Materials and Finishes for Plant and Equipment
corrosion of stainless steel is especially serious if accompanied by an absence of oxygen or presence of halogens or both. In such a situation, alternative materials of construction such as HastelloyTM or titanium should be specified. Exposure to free chlorine in water droplets (e.g., sea air), brines, or cleaning fluids (hypochlorite bleaches) can cause pitting corrosion in stainless steel depending on factors such as concentration and temperature of the fluid. It is estimated that up to 90% of corrosion failures of stainless steel in the process industries are due to exposure to chloride-containing fluids. It should be mentioned here that chloride attack can lead to the formation of microscopic channels that cannot be detected by dyepenetration testing (only by radiographic methods), yet are significant as channels for bacterial ingress, for example in heat exchangers and water-jackets. Most cleaning solutions may only contain 20 ppm chlorine. However, if they are applied to the steel surface (in a pipe or vessel) and then allowed to dry off rather than being flushed away, the chlorine concentration can rise 10-fold. As a rule of thumb, stainless steel type 304 is liable to corrode when chlorine concentration rises above 200 ppm and type 316 when chlorine concentration is greater than 1000 ppm. The main problem with chlorine-containing cleaning agents is not the cleaning itself; it is not rinsing thoroughly with ordinary water so that chloride levels are allowed to rise to dangerous levels. To maintain the corrosion resistance of stainless steel, a clean, dry surface must be exposed to oxygen (air) so that the passive layer is continually maintained. Poor plant and equipment design or layout can promote corrosion of stainless steel by preventing equipment walls coming in contact with air. When corrosion does occur, remedial action is possible by passivation of stainless steel. Passivation of stainless steel is carried out when the beginnings of rusting are first seen (say inside a liquid holding vessel or pipe network). First, the rust debris contaminant must be removed by rinsing with a 10% nitric acid solution. This is vital because if the rust debris is not removed, corrosion will recommence. Then air is allowed into the pipe and left for a few days (i.e., the pipe is taken out of commission and left idle). The oxygen in the air will regenerate the chromium oxide inert layer and restore corrosion resistance to the pipe. Dairy Plant In summary, stainless steel is the material most widely used for contact surfaces in dairy processing equipment. This metal offers resistance to corrosion, mechanical strength, hardness, and ease of fabrication (weldable). The preferred grades for general process fluid heating, storage, and distribution are AISI type 304 (Deutsches Institut fu¨r Normung (DIN) 1.4301) and 316 (DIN 1.4401).
Type 316 is more expensive but offers greater corrosion resistance due to the inclusion of molybdenum. AISI 304 is nearly always used externally, or for the outer vessel jacket, as it is needed only for protecting the machine from the atmosphere, water, and any spilled liquids. For parts in contact with product, either type can be used though 316 is necessary for acidic products. In very acidic conditions, where the pH falls to 1, type 317 austenitic stainless steel is specified as it has a greater molybdenum content of 4%. For dry solid foods such as dairy powders, wear resistance is also needed in addition to corrosion resistance. The ferritic structural stainless steels offer good flow characteristics for hoppers, chutes, and conveyor lines. High loads on mechanical components or very abrasive conditions may result in the selection of the strong, hard martensitic stainless steels; for example type 410 and 420. These steels can find an application in knives and cutters and mixers and extruders. If chlorides are present, even type 316 is not suitable to prevent localized corrosion (where the oxide film is damaged), and materials such as AL-6XN (a molybdenum-containing super austenitic stainless steel) or titanium may be required. Alternatively in this situation, AISI 410 (DIN 1.4006) or AISI 329 (DIN 1.4406) can be employed.
Other Metals In the rare cases where very extreme corrosion conditions are present, nickel alloys or titanium can be employed. Inconel 600 is a high-nickel alloy (three-quarters nickel) and offers excellent resistance across a broad range of corrosive conditions. It is unsurpassed in caustic conditions. It maintains high strength at elevated temperatures. Its main drawback is the high cost. Hastelloy C276 is a nickel–chromium–molybdenum alloy that has the broadest general resistance to corrosion compared with many other common alloys. It has good resistance to wet chlorine and strong oxidizers and can combat aggressive corrosion conditions that are combined with high temperature and high pressures. Titanium, although very expensive, is sometimes used where extremely high corrosion resistance is required (e.g., to hold liquids containing chlorine ions). It is also used where a brine solution would attack stainless steel. Titanium is an excellent metal for use with oxidizing agents such as nitric acid and mixtures of nitric and hydrochloric acids. It also has good resistance to chloride ions. Inert to nitric acid, it gives acceptable corrosion rates of less than 0.05 mm yr 1 to sulfuric and hydrochloric acids but is attacked by concentrated sulfuric and hydrochloric acids (more than 1.25 mm yr 1). Commercially pure titanium is available in several grades. Grade 2 is suitable for welding. Grade 4 contains traces of iron, has higher strength, but is not suitable for welding.
Plant and Equipment | Materials and Finishes for Plant and Equipment
Aluminum and its alloys have the advantages of being light, easily fabricated, and of reasonably low cost. However, it is so susceptible to corrosion that it is probably safe only for special applications where it can be guaranteed not to encounter alkaline detergents used in cleaning in place (CIP) systems. The low mechanical strength of aluminum can be improved by alloying. Though slightly soluble in many foods, aluminum is not toxic. It may be used in food plants, but as the metal is attacked by both acids and alkalis, great care must be exercised. Aluminum is also attacked by nitric acid, which is a commonly used cleaning agent. As aluminum salts are colorless, tasteless, and claimed to be nontoxic, and the metal is cheap, light, easily cleaned, and has high thermal conductivity, use in food manufacture should be extensive. However, it can impart taints or off-tastes to certain foods. Milk ‘churns’ (cans) are made out of aluminum as its low weight compared with stainless steel is an advantage in handling these containers. Copper and its alloys such as brass (copper–zinc), bronze (copper–tin), and Monel (copper–nickel) should not be used for dairy equipment. Copper alloys do offer ease of fabrication (very advantageous for pipe networks) and display durability in air and water. Alloying is necessary to overcome the lack of strength in pure copper. Copper and its alloys can oxidize food oils and fats and cause flavor and off-taste problems (even at concentration levels as low as 0.1 mg kg–1) especially in food processing at higher temperatures (above 80 C). It should be specifically avoided when handling high-fat foods. Copper is used where its excellent electrical and thermal conductivities are advantageous (e.g., electric conductors and cooling fins). It is also used in nonpotable water distribution circuits such as boiler feed water. Finally, the undesirability of using galvanized steel, for example for motor covers or framework, should be emphasized as this is rapidly corroded by the typical alkaline detergents used in food premises.
Plastics and Rubbers Plastic materials offer certain advantages (being cheap, easy to fabricate, and having low weight and good corrosion resistance) but suffer from low mechanical strength and poor temperature and fatigue resistance. Polymers such as polypropylene, Teflon, silicone, ethylene propylene diene monomer (EPDM), and so forth, can be used. In dairy processing equipment, they must be abrasion resistant and free from constituents that can migrate into foodstuffs especially if they are being used as seals in pipes and process vessels. Food-grade polymers must always be specified. Factors such as reactions with detergents and stability at sterilization temperatures must also be considered (so most polymers are appropriate only for
137
lower temperatures). The relatively strong and heatstable plastics (such as nylon and Teflon) are used in storage vessels, pipework, and pumps. Seals made from elastomeric materials are a common example of the use of plastic and rubbers in dairy processing equipment. Two issues are absorption of materials from the process liquid into the elastomer, which can produce swelling of it and extraction of components from the elastomer seal into the process liquid, which can cause contamination. The perfluoroelastomers behave well with regard to both these issues.
Surface Finish Irrespective of the material chosen, the presence of pits, crevices, and any other surface defects on product contact surfaces are not allowable. These defects can act as harborage sites, trapping and protecting microorganisms from sterilization. Thus, product contact surfaces must be polished (usually by grinding and buffing) to ensure a low surface roughness. Generally speaking, the higher the degree of surface finish, the more cleanable is the surface. All manufactured surfaces will consist of a series of peaks and valleys, varying in both height and spacing. The main measurement parameter of this texture is designated Ra and is the arithmetic average value of the departure of the profile above and below an imaginary centerline throughout the sampling length. Surface quality is generally specified by this surface roughness number, Ra. Food product contact surfaces should have a surface finish of a maximum 0.8 mm Ra. Measurements of contamination levels on a surface after a cleaning regime indicate that the lower the Ra value, the smaller is the contamination level. There are four finishing techniques to reduce surface roughness: 1. Mechanical polishing: Aluminum oxide grit is glued to flat felt disks that are rotated at high speed while being traversed over the surface. 2. Abrasive blasting: The surface to be treated is blasted with high-speed glass beads. 3. Electropolishing: This process involves the electrochemical removal of a surface layer of material. It is the opposite of electroplating. The surface to be treated is dipped into a tank of electrolyte and connected to the positive pole of a current supply. Because peaks of the surface are removed preferentially, a leveling of the surface occurs. 4. Chemical finishing: Chemicals (pickling acids) are applied by brush and left on the surface for a few hours and then rinsed off. Table 1 indicates the roughness level that can be achieved with each method.
138 Plant and Equipment | Materials and Finishes for Plant and Equipment Table 1 Surface treatments of stainless steel and the resulting surface roughness (Ra) Treatment Cold rolling Hot rolling Glass bead blasting Pickling Electropolishing Mechanical polishing
Grit number
Ra (mm) 0.2–0.5 >4 1 0.5–1
60 120 240 500
<3.5 <1.1 <0.5 <0.2
The issue of acceptable surface roughness is particularly important for welds in equipment. The primary purpose of a weld is to provide a permanent joint of sufficient mechanical strength to meet all requirements. However, the weld must also satisfy hygienic requirements. Any excessively rough weld surface promotes adhesion of soil material and is difficult to clean. For a weld to be hygienic, it must have a smooth inner weld bead surface free of crevices, cracks, or pits that would harbor bacteria. Such welds permit sterilization of the equipment to be carried out satisfactorily. A typical series of finishes is the following: flux chipped out and weld wire-brushed, • As-welded: Rough ground: welds are ground with coarse grit, •
scurf: the ground weld scurfed with carborundum • Fine grit, polished: polishing with/without aid of greases, • Bright pickled: application of pickling acids to • Chemically remove weld scale. Stainless steel, available as hot rolled plate, normally has a surface finish of greater than 5 mm Ra. High-quality Tungsten Inert Gas (TIG) welds will leave a finish of between 3 and 8 mm Ra. Thus, polishing is necessary to bring the roughness down to 0.8 mm Ra or less. A grit size of 150 is usually sufficient to give the required surface finish of 0.8 mm Ra.
See also: Milking Machines: Principles and Design. Plant and Equipment: Agitators in Milk Processing Plants; Centrifuges and Separators: Types and Design; Corrosion; Evaporators; Flow Equipment: Pumps; Flow Equipment: Valves; Heat Exchangers; In-Place Cleaning; Pasteurizers, Design and Operation; Process and Plant Design.
Relevant Websites http://www.3-a.org/ – 3-A Sanitary Standards, Incorporated http://www.asme.org/codes – ASME http://ehedg.org – European Hygienic Equipment Design Group
Flow Equipment: Principles of Pump and Piping Calculations J C Oliveira, University College, Cork, Ireland ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 2, pp 1081–1086, ª 2002, Elsevier Ltd.
Principles of Calculation
fluids, the volumetric flow rate (Q) is used, which is equal to the average velocity of the fluid times the cross-sectional area of the pipe (A), and this leads to the so-called continuity equation:
Ideal Flow Conservation of mechanical energy
The basic principle used to describe the flow of liquids in any type of installation is that the total mechanical energy of an element of the fluid at a given position, A, should be maintained while it flows, so that when it reaches another position, B, there may have been conversion of one form of energy to another, but the total should be the same. This analysis is applied at isothermal conditions, so that only mechanical energy needs to be considered (nonisothermal flow will not be addressed). Three forms of energy are involved: pressure, potential energy and kinetic energy. The mathematical expression that translates this principle of conservation of mechanical energy is known as Bernoulli’s equation (the differential form is Euler’s equation), and for isothermal ideal flow of incompressible fluids (liquids), it can be written as: Pa v2 Pb v2 þ ha þ a ¼ þ hb þ b ?g 2g ?g 2g
ð1Þ
where P is pressure, h the height (vertical distance from the ground to the central axis of the pipe), v the average velocity and the subscripts a and b designate the values at locations A and B, respectively. is the specific gravity of the liquid and g the acceleration due to gravity (9.8 ms2). The left-hand side is the sum of energy terms at location A, and the right-hand side at location B. This equation is written so that all terms have units of length (e.g. m), and are known as ‘heads’: the first term is the pressure head, the second is the potential head and the third is the kinetic head. Figure 1 sketches a generic situation where all heads have changed from location A to B, in an example where the potential and kinetic heads have increased at the expense of the pressure head. Conservation of momentum
In addition to Bernoulli’s equation, it can also be stated that there should be a conservation of momentum. For steady flow, this principle reduces to a mathematical expression which simply states that the flow rate must be constant throughout the installation, otherwise there would be an accumulation of liquid. For incompressible
va ?Aa ¼ vb ?Ab
ð2Þ
General design principles
Substituting eqn [2] in eqn [1] and with some basic manipulation, the expression that relates flow rate to the pressure difference between two locations (which is designated P) is obtained: P Q2 1 1 ¼ h þ – 2 ?g Ab 2g A2a
ð3Þ
where P ¼ PaPb ; h ¼ hbha. It should be noted that, by definition, Q ¼ Va?Aa (or Q ¼ Vb?Ab) and that for cylindrical pipes (circular cross-section area), A ¼ (?D2)/4, D being the diameter of the pipe. Equation [3] allows calculation of the pressure difference that must exist to ensure a given flow rate, or by reversing it, to calculate the flow rate that a given pressure difference will imply.
Nonideal Flow Head losses
The analysis above implies that the fluid behaves ideally, i.e. there is no dissipation of mechanical energy. However, this is rarely true and fluids exhibit a resistance to flow which depends on their rheological properties. The concept of viscosity is familiar – a viscous fluid shows greater resistance to flow. Fluids are not rigidly structured materials and flow implies a continuous movement of molecules in relation to one another. Either through viscous shear energy dissipation or by molecular collisions, there is inevitably a loss of mechanical energy, dissipated in the form of heat. It is assumed that this is not so significant that the situation will cease to be isothermal – it is considered that the heat dissipated is transferred easily and lost to the outside and causes no significant rise in temperature. However, while flowing from A to B, part of the mechanical energy is lost. Equation [1] is therefore incorrect, and a term (FA!B) must be inserted to account for all head losses:
139
140 Plant and Equipment | Flow Equipment: Principles of Pump and Piping Calculations
P = 5.0 × 105 Pa h=0m v = 1.0 m/s A
B P = 4.73 × 105 Pa h=0 m v = 1.0 m/s
Figure 1 Conservation of mechanical energy in an ideal system.
Pa v2 Pb v2 þ ha þ a ¼ þ hb þ b þ FA – B ?g 2g ?g 2g
ð4Þ
Hence, the problem can be solved in the same way as if the fluid was ideal, with a minor correction to eqn [3]: P Q2 1 1 ¼ FA – B þ h þ – 2 ?g Ab 2g A2a
molecules and the flow is turbulent. Figure 2 shows how a single drop of dye solution might move along the tube – different drops will move along different paths, as turbulent patterns are unstable (time-dependent). Figure 3 helps to visualize two layers of molecules moving adjacent to each other and at different velocities. Newton’s law states that the shear stress (the force per unit cross-sectional area exerted tangentially to the layers, which is responsible for the velocity difference) should be proportional to the shear rate (the variation of the velocity per unit length), and that proportionality is the viscosity. Hence:
ð5Þ
To deal with this new factor, it is necessary to know more about fluids and their flow behavior. Viscosity and flow regimes
Reynolds performed a simple experiment to visualize how fluid molecules move in the flow of liquids. He injected a dye at a given point in a transparent tube section and noted how the color dispersed in the flow (Figure 2). He found that, for low flow rates, a smooth straight line developed. At different distances from the pipe wall, the velocity of this line was different. He concluded that, at low flow rates, the molecules move in layers and there is no collision between them, but there is friction between adjacent layers, as they move at different velocities (maximum at the centre of the tube, and approaching zero near the walls). He designated this situation as laminar flow. However, when the flow rate is increased, a critical point is reached where turbulence starts to develop and the dye moves unpredictably along the tube. In this case, it is evident that there will be collisions between the
¼
dy dy
where is the shear stress, the viscosity, dv/dy the shear rate, v the velocity and y the height. However, not all fluids obey this law, and those that do not are termed non-Newtonian. Water and milk are Newtonian fluids, while most viscous liquids are nonNewtonian. It makes sense to think that the head losses due to viscous shear energy dissipation in laminar flow, where there are no collisions, should be proportional to the viscosity. This result has been verified empirically and later derived theoretically. The so-called Hagen– Poiseuille equation can be written as: F¼
32?L?v ?g?D2
h1
Injection of coloring at h1
ð7Þ
where L is the length of pipe (distance from A to B) and v is the average velocity (it should be noted that the velocity of a specific layer varies with the distance from the wall), which is given simply by dividing the flow rate by the cross-sectional area. On the other hand, when there is fully turbulent flow, with collisions between molecules causing the loss of so much energy that the effect of viscosity is irrelevant, the head losses should be proportional to the kinetic head. The so-called Darcy–Weisbach equation is applied in this case, stating that:
Injection of coloring at h2
h2
ð6Þ
HIGH FLOW RATE - TURBULENT FLOW
LOW FLOW RATE - LAMINAR FLOW Figure 2 Reynolds experiment and concepts of laminar and turbulent flow.
Plant and Equipment | Flow Equipment: Principles of Pump and Piping Calculations
v2
Δv Δy
lim Δy → 0 Δv Δy
v1 y2
v2 − v1 y2 − y1
y1
dv dy
Figure 3 Concept of viscosity as friction between adjacent layers of fluid moving at different velocities.
F ¼f
L v2 D 2g
ð8Þ
where f is a friction factor that depends on the roughness of the pipe. It has been found that the critical point when laminar flow ceases and eqn [7] is no longer valid occurs for all systems when the so-called Reynolds number reaches a value of 2000. The Reynolds number (Re) is the ratio between kinetic and viscous forces, and its application is based on the principle of dynamic similarity. It is: Re ¼
?v?D
switch from laminar to turbulent, and above that there is a gradual change to fully turbulent flow as Re increases. This is well visualized by plotting the f value of the Darcy–Weisbach equation as a function of the Reynolds number, in what is known as the Moody diagram (Figure 4). In laminar flow, there is a straight line in a log-log graph (f ¼ 64/Re). In fully developed turbulent flow, f is constant, and in between there are the instability and the transition regimes. The point at which fully turbulent flow is reached and f is constant depends on the roughness of the pipe wall. For very smooth tubes, which is the case of stainless steel pipes used in the hygienic design of food-processing installations, fully turbulent flow is not actually reached in regions of practical interest of Re. In transition flow, the Colebrook–White empirical equation can be used to estimate f : 1 k 2:51 pffiffiffi pffiffiffi ¼ – 2?log þ 3:7D Re: f f
!
where k is the roughness factor of the pipe (for perfectly smooth tubes, k ¼ 0) and log is the decimal logarithmic.
Viscus shear energy dissipation
The effect of viscous shear energy dissipation and of collisions between molecules during flow due to turbulence are calculated using eqn [8], with f being given by eqn [10]. However, as this is an implicit equation for f, many people prefer to read the result graphically from Moody’s diagram; a simple version is given in Figure 4.
instability 0.10 0.09 0.08 0.07
transition
fully turbulent
0.06 0.05 f = 64/Re 0.04 f
k/D = 0.01
0.03 k/D = 0.002 0.02
smooth tubes (k = 0) 0.01 103
ð10Þ
ð9Þ
Note from eqns [7], [8] and [9] that it can be concluded that the Darcy–Weisbach equation can be used in laminar flow, provided f is considered as a value which varies with the Reynolds number, with f ¼ 64/Re. However, once laminar flow ceases, fully turbulent flow is not immediately established, where viscosity is irrelevant and eqn [8] applies. Between Re 2000 and 4000 there is an instability regime, where the flow can
laminar
141
104
Re
105
Figure 4 Moody’s diagram (plots of eqn [10] for transition and turbulent regimes).
106
142 Plant and Equipment | Flow Equipment: Principles of Pump and Piping Calculations
Localized head losses
It is evident that any geometric variation in the installation, such as bends, junctions and expansions, will cause collisions between molecules and the pipe walls, and between molecules themselves, resulting in turbulence. Whether the flow regime is laminar or turbulent prior to these geometric effects, there are kinetic losses due to collisions, and hence it is reasonable to assume that these head losses should be proportional to the kinetic head. The simple expression used is similar to eqn [8], but there is no need to individualize the length and diameter of these elements, and a simpler expression can be used: F ¼K
v2 2g
B
pump
A liquid
ð11Þ
where K, the so-called ‘number of velocity head losses’, must be estimated depending on the constriction. Various tables and graphs to estimate K for the various relevant elements that may exist in an installation can be found in the literature, such as bends (where K depends on the curvature), expansions and contractions (where K depends on whether the expansion/contraction is sudden or gradual and on the diameter before and after the element), junctions and flow dividers (where K depends on the type of junction), and valves (where K depends on the type of valve). Except at low Reynolds numbers in some cases, K is usually independent of Re, just like f in fully turbulent flow.
reservoir / feed tank Figure 5 Pump in suction mode from lower reservoir.
(cavitation). Hence, the situation where point B is the entrance of a pump is of particular concern (Figure 5). Available Net Positive Suction Head The net positive suction head (NPSH) in a given point is defined as the pressure head above the vapor pressure head, that is: NPSH ¼
Calculation of head losses in an installation
When calculating the head losses in an installation, eqn [5] is applied and FA!B estimated as the sum of all individual head losses: in each straight section of the pipes there is viscous shear energy dissipation given by eqn [8], and in each element that can cause localized head losses, eqn [11] is used with the corresponding K-value.
Net Positive Suction Head
ð12Þ
where P is the pressure of the liquid at that point and Pv is the vapor pressure (pressure at which the liquid is boiling for the system temperature – for instance, the vapor pressure of water at 100 C is 1 atm, at 20 C it is 0.025 atm). The NPSH available (NPSHa) is the value of the NPSH at the entrance of the pump. It can be calculated by determining the pressure at point B from eqn [3], knowing the pressure at point A, and estimating all relevant head losses using the appropriate eqns [8] and [11]. Mathematically:
Cavitation When point B is located above point A, and with the added effect of head losses contributing to pressure decrease, Bernoulli’s equation indicates that it is eventually possible to reach a pressure low enough to be at the boiling point of the liquid. This would result in the release of gas bubbles. From Bernoulli’s equation, the points to check will be those with smaller cross-sectional area (higher velocity) and located higher in the installation. Gas bubbles are difficult to move, and this could result in severe loss of pumping efficiency. Moreover, the impact of gas bubbles collapsing against a surface moving at high speed is very destructive for centrifugal pumps
P PV – ?g ?g
NPSHa ¼
Pa Q2 1 1 PV – h – FA!B – – – ?g 2g A2b A2a ?g
ð13Þ
It is noted that if the cross-flow areas at A and B are the same, the kinetic flow rate term is zero. Required Net Positive Suction Head In principle, there would be no cavitation if NPSHa is greater than zero. However, in every pump there will be head losses until the fluid starts to build up pressure – there are possibly geometric constrictions at the entrance, collisions with pump parts, etc. Usually, pump manufacturers
Plant and Equipment | Flow Equipment: Principles of Pump and Piping Calculations
will provide this information in terms of an NPSH required (NPSHr), from bench scale tests. Basically, these are the head losses that occur at the pump entrance, until the liquid builds up pressure. Thus, the NPSHr of the pump (or pumps being analyzed) must be checked to ensure that NPSHa>NPSHr. A safety margin of about 0.7–1 m is normally recommended. It is noted that the NPSHr, like all head losses, is obviously a function of the flow rate, and pump manuals usually provide the NPSHr in the form of a graph, as a function of the flow rate or of the Reynolds number.
Pumping Efficiency and Power Requirements Calculation of Pumping Requirements Generically, a pump will be located somewhere between the entrance of an installation (piping line, piece of equipment) and the exit, and must promote a given flow rate. Applying Bernoulli’s equation between the exit of the pump and the exit of the installation gives the pressure head that must exist at the pump exit to ensure the flow rate specified: He ¼
Pg Pout Q2 1 1 ¼ þ h þ Fe!out þ – ?g ?g 2g A2out A2e
ð14Þ
where He is the pressure head at the exit of the pump, and the subscripts e and out indicate values at the exit of the pump and at the end of the installation, respectively. Fe!out is the total head loss from the pump onward. Similarly, the pressure head at the pump inlet can be calculated by applying Bernoulli’s equation between the entrance of the installation and the pump: Hi ¼
Pi Pin Q2 1 1 – – h – Fin!i – – ?g ?g 2g A2in A2i
ð15Þ
Power, Energy and Calculation of Pumping Costs Assuming the usual case of no variation in the potential and kinetic heads at the inlet and outlet of the pump (same cross-flow area and level height), the power provided by the pump to the liquid (W, energy per unit time) to ensure the flow rate, Q, is that required to raise the pressure head from Hi to He: W ¼ ?g?Q ?ðHe – Hi Þ
v¼
W W used
143
ð17Þ
The pump efficiency depends on the type of pump and on the conditions of operation. Generally, there is an optimum efficiency for a given flow rate – operating above or below implies that the pump is under- or overdimensioned for the job, and the consequence is that the pumping efficiency is lower. Hence, engineers must select the pump dimensions according to the specific job, targeting the region of operation of the pump where is maximum, as otherwise Wused, and hence pumping costs, are higher than they could be with an appropriate pump. They may also find that using more than one pump in parallel lines may be more efficient than a single, larger pump. Optimum efficiencies for centrifugal pumps are of the order of 80–90%. This subject is discussed in more detail elsewhere (see Plant and Equipment: Flow Equipment: Pumps).
Pressure Drop in Valves In a certain way, valves are the opposite of pumps. They are the elements that cause a loss of pressure head. From eqn [14], as a valve increases, the head losses, Q, decrease. The head loss caused by a valve is generally described by eqn [11]. The value of K will depend on the type of valve and percentage opening, and is given by manufacturers (otherwise, estimates can be found in the literature for generic valves). Valves and pumps work together: pumps must have some overcapacity and have a valve next to it (the discharge valve) to control the pressure to the desired level. Otherwise, the flow would be subjected to fluctuations due to variations in atmospheric pressure and temperature. Discharge valves and surge valves may also be needed for start-up and/or shutdown procedures. Care should be taken to ensure that the pressure head at the exit of the valve when it is in the lowest opening position (higher K ) does not go below the vapor pressure, which can be checked with Bernoulli’s equation, in a similar manner to NPSHa calculations. See also: Plant and Equipment: Flow Equipment: Pumps; Flow Equipment: Valves; Heat Exchangers; Pasteurizers, Design and Operation; Process and Plant Design.
ð16Þ
To calculate the pumping energy costs, it must be noted that not all power used by the pump from the mains electrical supply will be delivered to the fluid, as there are various energy losses. The pump efficiency () is the ratio between the power delivered to the fluid (W) and that spent from the mains (Wused):
Further Reading Chhabra RP and Richardson JF (1999) Non-Newtonian Flow in the Process Industries. Butterworth-Heinemann, Oxford. Evett JB and Liu C (1989) 2500 Solved Problems in Fluid Mechanics and Hydraulics. McGraw-Hill, New York. Evett JB, Liu C, and Giles RV (1995) Schaum’s Interactive Outline of Fluid Mechanics and Hydraulics. McGraw- Hill, New York.
144 Plant and Equipment | Flow Equipment: Principles of Pump and Piping Calculations Foust AS, Wenzel LA, Clump CW, Maus L, and Andersen LB (1980) Principles of Unit Operations, 2nd edn. John Wiley, New York. Granger RA (1995) Fluid Mechanics. Dover, New York. Mott RL (2000) Applied Fluid Mechanics, 5th edn. Prentice-Hall, New York. Perry R and Chilton C (1984) Perry’s Chemical Engineers’ Handbook, 6th edn. McGraw-Hill, New York.
Rao MA and Rizvi SSH (1995) Engineering Properties of Foods, 2nd edn. Marcel Dekker, New York. Roberson JA and Crowe CT (1996) Engineering Fluid Mechanics, 6th edn. John Wiley, New York. Streeter VL, Wylie EB, and Bedford KW (1998) Fluid Mechanics, 9th edn. McGraw-Hill, New York. White FM (1998) Fluid Mechanics, 4th edn. McGraw-Hill, New York.
Flow Equipment: Pumps J C Oliveira, University College, Cork, Ireland ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 2, pp 1087–1093, ª 2002, Elsevier Ltd.
Introduction Pumps are small pieces of equipment that promote the circulation of liquids between and through pieces of equipment. When selecting a pump, the main factors to consider are: 1. The viscosity of the fluid, and whether it is a clear fluid or contains solid particles in suspension. 2. The sensitivity of the fluid quality characteristics to shearing and viscous shear energy dissipation. 3. The pumping requirements (pressure, flow rate). 4. The hygienic requirements of the process (which are high for dairy products). 5. The cost of the pump and of its maintenance. The main issues are to ensure that: 1. The mechanical action of the pump affects the fluid characteristics to the least extent possible. 2. The pump is operating close to its optimum point. 3. There is no cavitation (the pressure of the fluid cannot go below its vapor pressure anywhere in the pump). 4. The mechanical wear of the elements of the pump (moving parts, seals) is not extensive to the point of causing significant loss of pumping efficiency (a preventive maintenance program would be quite adequate for pumps).
General Classification Pumps force liquids to flow in one of two ways, which gives rise to the major division between pumps: (1) centrifugal, (2) positive displacement. Centrifugal pumps have a rotor that rotates at very high speed (thousands of rotations per minute) and accelerates the fluid. As the fluid leaves the rotor, it is suddenly forced to slow down, pressing against the fluid which is already there. By looking at Bernoulli’s equation, it is evident that the sudden substantial loss of kinetic energy must correspond to a sudden increase in pressure (see eqn [4] in article Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations). Those that provide particularly accurate flow rates are also called metering pumps. A centrifugal pump does not ensure
either a specific flow rate or a specific pressure: both will depend on the piping system after the pump (level differences, head losses, etc.) There is a wide variety of positive displacement pumps, but in general it can be said that they capture a small amount of fluid, cause it to compress in some way, and then deliver the compressed fluid at the outlet. As they deliver a fixed amount of fluid at specific regular intervals, these pumps generally assure a given flow rate, and pressure will be dictated by the piping system and can be estimated by applying Bernoulli’s equation. Centrifugal pumps will obviously cause a substantial amount of kinetic losses due to collisions of molecules with the rotating elements and walls, and between themselves. This can generate a substantial amount of heating and affect thermally sensitive fluids. In addition, the high shearing may also affect molecular networking. Therefore, fluids with delicate macromolecular structures (for instance, a milk coagulum) should not be run through centrifugal pumps. It also follows that very viscous fluids are not suitable, as heat generation would be substantial, and slip is also potentially high (which implies a low pumping efficiency). As a rule of thumb, centrifugal pumps are not generally recommended for fluids with 10 times the viscosity of water or higher. They are obviously not suitable for liquids containing solid particles either. Due to the high velocity of the moving elements, cavitation is a major problem, as it can wear the rotor blades quite extensively and very rapidly (the collapse of a gas bubble when impinging on a moving surface at high speed causes roughly the same type of destruction as the collision with a hard solid particle). In positive displacement pumps, the generation of gas bubbles affects mostly the pumping efficiency, and not so much the actual pump. On the other hand, centrifugal pumps will deliver a steady flow rate. Positive displacement pumps are more prone to pulses and fluctuations in the flow rate, as the cycle capture–compress–deliver repeats itself. It can also be expected that centrifugal pumps will generally have lower pumping costs, as acceleration of a low-viscosity fluid is easy, and pressure is then generated by the fluid slowing down the energy costs are basically those of accelerating the fluid. Positive displacement pumps
145
146 Plant and Equipment | Flow Equipment: Pumps
must supply the totality of pressure by direct mechanical means, and this can be expected to require generally higher energy levels. However, these are not general rules, as there are very different types of positive displacement pumps. In general, it can also be said that the action of positive displacement pumps can be reversed (inlet and outlet may be swapped), which is totally impossible in centrifugal pumps. Not all pumps will be reviewed in this article, only the more common types.
reaches a maximum. The conversion of kinetic energy to pressure is therefore gradual, and it stands to reason that the more gradual it is, the higher the efficiency – a very sudden slow-down implies many collisions between molecules, hence loss of mechanical energy, dissipated in the form of heat. Some pumps have a static ring between the moving rotor and the casing (usually, with channels having the opposite obliquity to the rotor blades), which provides a further gradual step of conversion from kinetic energy to pressure. Figure 2 illustrates this description schematically.
Centrifugal Pumps
Hygienic Requirements
General Design and Principles of Operation
The most obvious hygienic requirement for a centrifugal pump is that it should be easy to disassemble, so that every part can be thoroughly cleaned easily. The blades should be rounded to avoid crevices, and therefore hygienic pumps generally have a lower number of blades (see Figure 2). The pump motor releases much heat, as one would expect from a drive that generates velocities of the order of thousands of rotations per minute. Therefore, the motor casing of normal pumps is corrugated (the higher specific area promotes heat loss). However, this is not satisfactory for hygienic food processing, and food-grade pumps must have a smooth, stainless steel casing. This implies a pump that is built specifically for that, as other means of removing the heat generated by the motor must be improved; if a normal corrugated pump is covered by a smooth casing, it will run the risk of overheating.
Figure 1 shows a centrifugal pump, in front and side view. The fluid enters perpendicular to the axis of rotation of the rotor and will leave tangentially in relation to the rotor blades. As the fluid disperses from the center due to the action of the centrifugal force toward the walls of the rotor casing, it travels in the radial direction through the channel between the blades. It is also accelerated tangentially to the velocity of rotation of the blades. These are constructed in such a way that the distance between blades increases with the radius – therefore, this channel widens as the fluid moves toward the wall. As the continuity equation shows (see eqn [2] in article Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations), the fluid pressure will therefore increase as its kinetic energy decreases, while moving radially between the blades. The fluid then joins the layer moving around the wall toward the exit, pushed by the centrifugal force, which obviously moves slower than the blades, and so the pressure increases again. This layer, close to the casing wall, may also have an increasing flow area as a result of an eccentricity of the axis of the rotor in relation to the center of the casing – again, the reason for this design is to cause a gradual slow-down and respective pressure increase. This eccentricity, and whether it exists or not, depends on the pump design. At the outlet, another slow-down will occur, as the fluid starts moving at the velocity corresponding to the flow rate through the piping system, and pressure
Operating Points and Pumping Efficiency Depending on the piping system to which the pump outlet is connected and on the rotor design and speed, a centrifugal pump will be able to deliver various flow (a)
(b)
(c)
2 1
Motor
Rotor shaft
Outlet
Sharp edges
Inlet
SIDE VIEW
FRONT VIEW
Figure 1 Front and side view of a centrifugal pump.
Figure 2 Rotors of centrifugal pumps. (A) Typical rotor without hygienic design considerations. Note path 1, where the fluid moves toward the wall pushed by the centrifugal force along a channel with increasing cross flow area, thereby increasing pressure; and path 2, where the fluid moves rotationally toward the axis, pushed by the centrifugal force, through a channel of increasing cross flow area due to the eccentricity of the rotor in relation to the casing; (B) rotor encased in a fixed channel distributor; (C) hygienically designed rotor, with smooth edges.
Plant and Equipment | Flow Equipment: Pumps 147
80 76 % 72 % 70 % %
rates at various pressures. The pump characteristic curve indicates all possible operating points of a given pump. Figure 3 shows a typical example. Pump manufacturers usually supply these graphs. Pumping efficiency is not the same along these curves; it is normally maximum around the top right-hand corner and decreases as one approaches the limits of the curve. Therefore, a pump should ideally operate close to the flow rate and pressure combination that gives the maximum efficiency (at the expense of unnecessarily spending more power from the electrical mains to deliver the same amount of energy to the fluid). Lines of constant efficiency are usually drawn on these graphs (see Figure 3). Checking the operating point of a pump in a given piping system is straightforward. Using Bernoulli’s equation, the characteristic curve for the piping system can be constructed by calculating the pressure head at the outlet of a pump for various flow rates. An operating point for a given pump in a given piping system is the intersection of the two characteristic curves (pump and piping system). Figure 3 shows a sketch of a situation where the maximum efficiency is achieved with the intermediate pump configuration, that actually delivers a slightly lower flow rate at a lower pressure than the configuration that gives the maximum flow rate. It should be noted that the characteristic curves of piping systems can be easily modified by operating valves, as they will increase head losses if partially closed. In the example of Figure 3, closing a flow rate control valve would increase head losses and the characteristic curve would be steeper. It would be possible to bring the piping system curve close to the maximum efficiency of the pump only if it would be possible to decrease the head losses.
possible operating points
Pu
Selection of Centrifugal Pumps In order to select a centrifugal pump, one must know: 1. The net positive suction head (NPSH) available at the inlet of the pump (see Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations). 2. The characteristics of the system (cross flow areas, level differences, total length of the piping system, localized head losses). Item (1) is needed only for a verification: the NPSH available must be higher than the NPSH required by the pump chosen, in order to ensure that the vapor pressure is not reached inside the pump, which would cause cavitation and severe wear. Item (2) is needed so as to apply Bernoulli’s equation and determine the characteristic curve of the piping system, from where the operating point and efficiency of the pump can be calculated. The pump, and its operating variables, are chosen that give the maximum efficiency. Manufacturers may provide graphs that indicate which of their makes/models are generally more suitable depending on pressure head and flow rate required. This helps to narrow choice to pumps that are designed for the type of demand in question. Figure 4 shows a typical example.
Positive Displacement Pumps Piston Pumps General design and principles of operation
A typical piston pump, which operates according to a very straightforward principle, is shown in Figure 5. Fluid is admitted to a chamber through the inlet valve, as the piston moves back and sucks the fluid in. The
Pu
p
co
type 1
nf
m
p
igu
ra t
co
ion
nf
igu
ra t
ion
Pu
m
p
2
co
nf
ig
ur at
io
n
3
1
Pressure Head (m)
Pressure Head (m)
m
type 2
type 3 type 4 type 5 type 6 type 7 type 8
type 10 type 9
pressure-flow curve for Flow Rate (m3/s) a given piping system
Figure 3 Typical characteristic curves for a pump in three possible configurations (different rotor design and/or speed), efficiencies and operating points.
Flow Rate (m3/s) Figure 4 Typical chart for selection of the type of centrifugal pump better adapted to a given demand.
148 Plant and Equipment | Flow Equipment: Pumps
valve closes when the piston reaches its back position and then starts moving forward, compressing the fluid trapped in the chamber. When the specified pressure is reached (for incompressible fluids, this is obviously almost instantaneous), the outlet valve opens and the fluid is discharged, as the piston expels it while moving forward. When the piston reaches its forward position, the outlet valve closes, the inlet valve opens and the cycle begins again. A piston pump will therefore deliver a flow rate equal to the volume of the chamber times the number of cycles per unit time. However, it is delivered only when the outlet valve is open, and nothing is delivered during the (a) Piston
Outlet valve
Compression chamber
Inlet valve Seal (Rubber O-ring)
admission part of the cycle. In order to avoid a pulse in the flow, it is normal to use two chambers with the piston of each moving asynchronously, so that when one delivers the other admits and vice versa. Obviously, this can be neatly done by a dual chamber pump, with chambers placed back to back, so that the piston is actually the same. Figure 6 sketches this design.
Hygienic requirements: diaphragm pumps
Piston pumps are not very hygienic because fluid can be trapped in the space between the cylinder side and the chamber wall, at the back (see Figure 5). Diaphragm pumps were built to solve this problem. The piston is not in direct contact with the fluid, but pushes a rubber diaphragm, which fits totally in the chamber geometry. There are pumps commercially available that use compressed air to move the diaphragm. Figure 7 sketches an example of a single-chamber diaphragm pump. For hygienic design, it would be ideal that the pump expels the totality of the fluid in order to avoid stagnated or dead volumes – the design in Figure 7 shows an example which is particularly poor in this respect.
Compression chamber 2
(b)
Stagnated fluid (c)
Piston
Compression chamber 1
Figure 6 Twin-chamber piston pump. Chamber 1 is sucking fluid from the bottom and chamber 2 is delivering compressed fluid to the top. White circles represent open valves and gray cones indicate closed valves.
Compression chamber Piston
Figure 5 Piston pump. (A) Commencement of the admission stage of the cycle; (B) commencement of the compression stage; (C) during the delivery stage. White circles represent open valves and gray cones indicate closed valves.
Diaphragm Figure 7 Diaphragm pump.
Plant and Equipment | Flow Equipment: Pumps 149
Rotary (Gear) Pumps General design and principles of operation
Rotary pumps are also known as gear pumps. They have two rotors and dented wheels moving in such a way that the dents of one wheel fit snugly inside the other. Thus, the fluid is forced toward the outside wall and must move around. The fluid will be trapped inside chambers formed by two dents and the outside casing and is then forced out at the other side. Figure 8 shows this principle of operation. Rotating speeds are about 100 times lower than those of centrifugal pumps. These pumps are therefore more similar to centrifugal than to piston pumps in the sense that they assure a given flow rate rather than a given pressure: the flow rate is simply given by the volume between each pair of dents and the speed at which this volume is transferred to the other side. Pressure is then given by Bernoulli’s equation, as once the flow rate is fixed, the piping system after the pump defines the pressure. Furthermore, while some compression occurs when the fluid is trapped inside the dents, most results from delivering the fluid to the other side and compressing it against the fluid which is already there, a similar situation to that in centrifugal pumps. However, this characteristic makes them the best metering pumps, with the flow rate being quite well controlled, as it is simply proportional to the rotating speed. Hygienic requirements: lobular pumps
Rotary pumps such as that shown in Figure 8 are not hygienic because the dents have sharp edges. Thus, lobular pumps have been developed, with wellrounded lobes, such as those shown in Figure 9. The sealing between the counterrotating rotors is obviously less good than in rotary pumps, as the rounded geometry implies fewer dents and therefore fewer points of contact for sealing at the center. A higher leakage flow between the high-pressure and
Figure 9 Lobular pump with three lobes per rotor.
low-pressure regions through the center is likely, compared to rotary pumps with more dents and more sealing points.
Single-Rotor (Impeller) Pumps Single-rotor pumps are also known as impeller pumps. They seem similar to rotary pumps, having only one rotor. However, their operation is quite different, as they can provide mechanical compression of the fluid in a much better way than rotary or lobular pumps. The blades are either made of rubber so that they can bend against the casing, or are made of metal, but have a spring at the base, so they can be pushed inward while moving against the casing. Figure 10 shows both cases. As the rotor moves, fluid is trapped between two blades. To improve compression, the casing may have a different curvature from the rotor axis, so that the space between them decreases. Therefore, the volume between two blades decreases while the rotor revolves, causing a compression (for relatively incompressible fluids, such as water and milk, this is not so important, while for viscous viscoelastic materials it would be helpful). On reaching the other side, the compressed fluid is expelled. In some pumps with rubber blades, the volume between blades is always the same, and the only compression results from the blades snapping at the inlet and squeezing at the outlet (see Figure 10). Some fluid will certainly remain and proceed to a second turn – potentially, there could be a problem of stagnant fluid. The blades must therefore be designed in a way that helps the expulsion at the outlet, which is better achieved with rubber blades.
Progressing Cavity Pumps Figure 8 Rotary pump.
Also known as monopumps, they have a curious design, with a rotating axis that looks like a twisted worm. It is not really a
150 Plant and Equipment | Flow Equipment: Pumps (a)
These pumps have a good hygienic design, as all fluid is expelled, there is no need for valves, and there are only rounded edges and surfaces.
rubber blades
outlet
inlet
Peristaltic Pumps
steel blades
(b)
inlet
outlet
spring
blade retract pushing against spring
Figure 10 Single-rotor pumps. (A) Pump with rubber blades and no compression in the chambers between blades and outside casing wall; (B) pump with steel blades and with compression caused by decreasing volume between blades.
screw, it is more like a twisted bar which rotates against a rubber casing (the stator), that adapts to the movement of the rotor. The rubber casing has a grooved path of a different shape from the rotor curvature, so that at a given position there is a perfect match between grooves of the rubber casing and curved rotor, while a space exists between each two matching points (for instance, the rotor is a single helix and the casing is a double helix). As the rotor revolves, the points of contact appear to move forward. Hence, the fluid is trapped in a chamber formed by the rubber casing grooves and rotor, sealed at the matching points. The curvature of the rotor (and grooves) may show a decreasing amplitude, so as to reduce volume and hence cause compression (particularly helpful for viscoelastic materials). Figure 11 shows this type of pump.
Peristaltic pumps require a rubber tube through which the fluid flows. A wheel with rollers moves on top of the rubber tube, so that as the rollers move they squeeze the tube. This gentle squeeze causes a compression and therefore the fluid is trapped between two points of roller compression, forced to move forward and delivered at the outlet. Just like rotary pumps, peristaltic pumps basically deliver a fixed flow rate and most of the compression results from forcing the movement of the fluid. Hence, pressure will depend on the piping system, and it is the flow rate that is fixed by the pump operating characteristics. They can therefore provide good metering (flow rate accuracy and control). Figure 12 shows this design. These are obviously the most hygienic pumps of all, as there is no contact between pump parts and fluids. They are also the best for solid particles, as particles are not squeezed. The main limitation is that tubes must be relatively small, as it is not viable to compress very large tubes. Flow rate is therefore more limited than in other pumps. Pumping efficiency is also limited if very large pressures are required. In general, commercial peristaltic pumps can be found for flow rates up to 10 m3 h 1 and pressures up to 1.6 MPa.
Summary of Pump Selection Criteria Table 1 provides an overview of the main selection criteria for pumps. In general practice, centrifugal pumps are used unless the fluid is too viscous, contains solid particles, or is too strongly affected by the high shearing and/or internal energy generation.
Rotor
outlet
outlet
inlet
inlet
Stator (rubber casing) Figure 11 Progressing cavity pump.
Figure 12 Peristaltic pump.
Plant and Equipment | Flow Equipment: Pumps 151 Table 1 Selection criteria for types of pumps Type of pump
Good for
Not good for
Centrifugal
Low-viscosity fluids Clean fluids Steady flow rate
Piston/diaphragm
Viscous fluids Clean fluids High pressures Precise pressure control Viscous fluids Clean fluids Fluids sensitive to shearing Precise flow rate control Viscous fluids Fluids with solid particles Fluids sensitive to shearing Viscous fluids Fluids sensitive to shearing Viscous fluids Fluids with solid particles Fluids sensitive to shearing Flow rate control
Viscous fluids Fluids containing solid particles Fluids sensitive to heat Fluids sensitive to shearing Fluids containing solid particles
Rotary/lobular
Single-rotor
Mono Peristaltic
See also: Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations; Flow Equipment: Valves; Heat Exchangers; Process and Plant Design.
Further Reading Davidson J (1986) Process Pump Selection: A Systems Approach, Institution of Mechanical Engineers, Ipswich. Engineering Equipment Users’ Association, (1972) Guide to the Selection of Rotodynamic Pumps, Engineering Equipment Users’ Association, London.
Fluids containing solid particles
High pressures
High pressures Fluids containing solid particles High pressures High flow rates
Karassik IJ and Krutzsch WC (1986) Pump Handbook, McGraw-Hill, New York. Lobanoff VS and Ross RR (1992) Centrifugal Pumps: Design and Application. Gulf Publishing Co, Houston. McGuire JT (1990) Pumps for Chemical Processing. Marcel Dekker, New York. Perry R and Chilton C (1984) Perry’s Chemical Engineers’ Handbook, (6th edn.), McGraw-Hill, New York. Stepanoff AJ (1992) Centrifugal and Axial Flow Pumps: Theory, Design, and Application. Krieger Publishing Co., Melbourne. Wahren U (1997) Practical Introduction to Pumping Technology: A Basic Guide to Pumps – From Specification to Installation and Operation. Gulf Publishing Co., Houston. Walker R (1977) Pump Selection: A Consulting Engineer’s Manual, Ann Arbor Science Publishers, Ann Arbor. Yedidiah S (1996) Centrifugal Pump User’s Guidebook: Problems and Solutions, Kluwer, Dordrecht, The Netherlands.
Flow Equipment: Valves K Cronin and E Byrne, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by K. Cronin and D. MacCarthy, Volume 2, pp 1093–1099, ª 2002, Elsevier Ltd.
Introduction Valves are devices for controlling the flow of fluids (liquids and gases), and in some cases granular or powdered materials. This article primarily discusses the valves used in product liquid lines in a dairy processing plant although many of the comments are equally applicable to the valves used for service fluids such as steam, refrigerant, compressed air, and process water, which will also be present in a dairy. Broadly speaking, valves can be classified by their function as being either 1. on–off valves or 2. flow regulation valves. On–off valves, which include shutoff, isolation, and changeover valves, have distinct positions, fully open or closed. These valves are used to stop flow or isolate part of a process. Their function is to minimize resistance to flow when fully open and to provide tight shutoff characteristics when fully closed. Regulating valves, on the other hand, have a flow passage, the area of which can be changed gradually. Such valves are used to control flow rates and pressures at various points in the system. Flow control valves can be continuously adjusted from fully open to fully closed in order to govern the flow rate. Pressure control valves determine pressure downstream of the valve, that is, maintain it at some set value irrespective of the flow rate through the valve.
Valve Construction Principles While a wide range of valves are used in industry, there are only a limited number of basic geometries by which an opening in a pipe can be opened or closed. Almost all valves can be classified as belonging to one of three fundamental designs or their variants. These are
• • •
globe valve (Figure 1), butterfly valve (Figure 2), and gate valve (Figure 3).
152
The globe valve (also referred to as a seat valve) consists of a rigid valve body, weir, plug, and spindle. In the closed position, the plug rests on the valve seat in the weir. Linear upward motion of the spindle will raise the plug off the seat and open the valve. This is the most popular type of valve for dairy products. The butterfly valve consists of a flat disc (equal in cross-sectional area to the bore of the pipe), a valve spindle, and an elastomeric or plastic seal ring. It operates on the principle of rotational rather than linear motion. In the closed position, the disc is face-on to the flow area and seals against the seal ring. Turning the spindle rotates the disc through a quarter turn (90 ) and moves it to a side-on orientation with respect to the pipe bore, and thus allowing flow. This valve has low pressure drop characteristics. The gate valve (sometimes known as the slide valve) like the globe valve operates on the principle of linear motion of a spindle. A flat disc is attached to the spindle, and in the closed position, it is fully extended and blocks the flow area of the pipe. Linear upward motion of the spindle will retract the gate into the valve body and permit fluid flow. This type of valve is not found in product lines in the dairy industry as it is unhygienic, although it is used for service fluids.
Valve Flow Design Valve flow design applies the principles of fluid mechanics to determine the flow rate and pressure drop through the valve. Other issues that are of concern include valve flow characteristic and avoidance of water hammer. Pressure Drop All valves cause losses of head (i.e., pressure) in the system due to friction effects. In general, the smaller and more intricate the passage through which the fluid has to pass, the greater the pressure loss. Considering the flow of a
Plant and Equipment | Flow Equipment: Valves
153
diameters is used, this is taken to mean the velocity through the smallest diameter piping). Using the continuity equation, the pressure drop can also be expressed in terms of the volumetric flow rate through the valve: P ¼
8kQ 2 2 D 2
where Q is the volumetric flow rate (m3 s1) and D the valve bore diameter (m). Values of the friction factor k of the valve depend on the exact shape of the flow passage and are generally found from experiments. In some cases, the pressure loss through a valve is expressed in terms of an equivalent length of unobstructed straight piping in which an equal pressure loss would occur:
Figure 1 Globe valve.
P ¼
4fLeq u2 2D
where f is the friction factor (dimensionless). In the above equation, f, u, and D relate to the values associated with the adjacent straight piping and f is the Fanning friction factor, which is equivalent to 16 times the inverse of the Reynolds number in the pipeline where the pipeline flow is laminar. (In the US texts, the Darcy friction factor, which is 4 times larger than the Fanning friction factor, is often substituted for the 4f term in the above equation.) Rather than this equivalent length being given as an absolute measurement in meters, it is more conventional to express it as an integer number, n, times the diameter:
Figure 2 Butterfly valve.
Leq ¼ nD
Table 1 gives approximate values of the friction factor and equivalent lengths for a fully open globe valve and gate valve. It must be stressed that these figures are only rough estimates and many unstated assumptions (such as Reynolds number of flow, valve bore diameter, and pipe roughness) underlie them. Figure 3 Gate valve.
Valve Characteristic turbulent and incompressible liquid (liquid milk for example), the pressure loss through a valve will be proportional to the square of the mean liquid velocity: P ¼ k
u2 2
where P is the pressure loss through the valve (Pa), the density of the liquid (kg m3), u the mean fluid velocity (m s1), and k the friction factor (dimensionless). Note that the mean fluid velocity refers to velocity through the adjacent piping (if piping of various
An important design feature of modulating valves is the valve characteristic. This is the relation between the stem (spindle) position of the valve and the flow through the valve at a constant pressure drop. The valve characteristic determines how a control valve regulates the flow. Two Table 1 Friction losses through valves
Globe valve (wide open) Gate valve (wide open)
k
L/D
10 0.2
340 13
154 Plant and Equipment | Flow Equipment: Valves
characteristics must be evaluated for valve selection: the inherent and installed characteristics. The inherent flow characteristic is the relationship between valve stroke and the resulting fluid flow through the valve for the valve on its own. The installed flow characteristic is the actual relationship between valve stroke and flow when the valve is an element in a particular flow system. Hence the installed flow characteristic incorporates the inherent flow characteristic of the valve itself together with the flow characteristics of the whole line, that is, it depends upon the ratio of the pressure drop through the valve to the total pressure drop across the line and valve. The inherent flow characteristic is the theoretical performance of the valve and is generally either linear or equal percentage. For a valve with a linear characteristic, the flow rate is linearly proportional to spindle position. For a valve with an equal-percentage characteristic, equal increments of spindle movement produce equal percentage changes in flow for a given pressure drop. An equal percentage valve may be combined with a centrifugal pump to provide a linear system. For the control system designer, the aim is to select a valve whose inherent flow characteristic gives an installed flow characteristic that makes the flow controllable over the whole range of valve movement, that is, stem position. Water Hammer Sudden closure of a valve can produce the phenomenon of water hammer in the pipe system. The name is a misnomer; this problem can occur with all liquids. Water hammer occurs when the abrupt deceleration of a liquid in a pipeline, caused by closing a valve too quickly, produces transient pressure shock waves in the liquid. These shock waves in turn can lead to appreciable and damaging levels of pipe vibration. Equipment such as process vessels and heat exchangers connected to the pipe may also be exposed to this vibration. Water hammer must be avoided in the design and selection of the pipe and valve system. Valves should be installed so that valve spring force and fluid pressure force act in opposite directions. Analysis of the phenomenon has been done in greater detail but fundamentally it involves imposing a minimum time limit on the duration of valve closure to avoid decelerating the liquid too rapidly.
Valve Hygienic Design In a dairy, of all the pipe fittings in the product line, valves are probably the most technically complex. For hygiene reasons, all wetted metal parts of the valve are made of stainless steel. These are surfaces that intentionally or unintentionally (e.g., by splashing) come in contact with the product. Two main grades are used, AISI 304 and
AISI 316. The valve body and all the fittings (actuator spindle, springs, flanges, bolts, operating levers, and wheels) will generally be made from 316 stainless steel. Valve seals can be made from a variety of synthetic food grade rubbers; among the most common types are silicone rubber, butyl rubber, nitrile rubber, and EPDM (ethylene propylene diene monomer). The actual choice of rubber is determined by the demand of the particular application of the seal such as required mechanical properties (particularly compression set), temperature regime, and exposure to steam and cleaning/sterilizing agents. Apart from functional performance, the most significant criterion in the selection of valves for milk processing plants is that they must be of a sanitary design and cleanable. Sanitary valves are designed according to the American 3A standards or other relevant hygienic design codes such as EHEDG (European Hygienic Equipment Design Group), Swedish, and German DIN standards. Valves should be self-draining, free of dead spaces, and readily cleanable. They should protect the product from contamination, prevent product leakage, and not allow the ingress of microorganisms. For improved standards of hygiene and cleanability, valves should be connected to pipelines by butt-welding or by sanitary unions. Product contact surfaces should have a surface finish of 0.8 mm Ra or better, and be free of any pits, folds, or crevices. A consequence of hygienic design considerations is that globe valves and butterfly valves are the most prevalent type of valves used in the dairy industry.
Valve Actuation The choice is between manual, pneumatic, hydraulic, or electric drives to control valve position. In general, manually operated valves are now found only in the smaller dairy plants. Automated valves have replaced them in large modern facilities although they are still used occasionally. Pneumatic actuation is generally the first choice in the dairy industry with either a diaphragm or a piston actuator. Spent air can be discharged directly to atmosphere and there are no sparking risks. Because air pressures are generally low (in the region of 7 bar), there are upper limits on the forces that air systems can develop and there is no necessity to resort to impracticably large actuators. However, as valve opening/closing forces in dairy product lines are seldom of large magnitude compared to valve forces found in bulk chemical processing, this limitation is not of great significance. If high valve opening/closing forces need to be generated, hydraulic actuation of the valve is suitable because of the very high oil pressures that can be generated. However, due to the possibility of contamination of the product with the oil, hydraulic actuation is very rare in
Plant and Equipment | Flow Equipment: Valves
the dairy industry. It can be found in applications where there is no possibility of contact with the product. Electric solenoid actuation is not prevalent in the industry due to the fire/explosion risk from electric sparking. Also the damp conditions that can prevail in dairies can lead to problems with electrical connectors. They can be used, however, to control the pneumatic actuation circuits that in turn operate the main process and clean-in-place (CIP) valves. Irrespective of the actuation mechanism chosen, valves can be arranged to be normally open or normally closed according to safe practice. Two arrangements are common:
Globe Valve The globe valve (also called seat valve or poppet valve) is operated by the movement of a valve stem, which raises or lowers a plug on to a valve seat. It can be used as a shutoff valve (Figure 4) or as a changeover or divert valve (Figure 5). When used as a shutoff valve in piping systems, it should close against the flow to reduce the possibility of water hammer. If used as a tank outlet valve, it should be installed so that static liquid pressure helps to keep the valve closed. Depending on system requirements, this valve is available with up to five ports.
closing/spring opening (a normally open valve, • air NO) and • spring closing/air opening (a normally closed valve, NC). Air opening/air closing arrangements are occasionally used. In a system with pneumatic actuation, the usual configuration is that air under pressure is used to move the valve from its default (safe) state to the active state. If the pressurized air is removed, a compressed spring will automatically return the valve to the default state. Hence, occurrences such as electricity failure leading to a loss of compressed air need not have unwanted consequences. As an example, valves on outflow lines from silos or storage tanks will usually have the configuration of air to open and spring to close. This diminishes the possibility of loss of the product due to valve system failure. Figure 4 Seat valve – shutoff.
Valves in Dairy Processing The functions of valves in the dairy processing industry are summarized in Table 2. The different types of valves used in dairy processing are described below. Table 2 Dairy valve functions
1 2 3 4 5 6 7 8
Valve type
Function
Product shutoff Product changeover Product separation Flow regulation One-way flow
Stop and start the flow of the product
Pressure relief Vacuum relief Constant pressure
Divert flow to another pipeline Separate two fluids, for example, product and detergent Adjust the pressure or rate of flow of the product Ensure that the product flows in one direction only Control the maximum pressure of a fluid Admit air to a vessel if vacuum exceeds a preset value Maintain the process liquid at a constant preset pressure
155
Figure 5 Seat valve – changeover.
156 Plant and Equipment | Flow Equipment: Valves
Butterfly Valve The butterfly valve (Figure 6) is designed primarily as a shutoff valve, but is sometimes used for flow regulation.
When fully open, pressure drop is small, which makes the valve suitable for products that require delicate handling with minimum turbulence. It is also suitable for viscous products. The butterfly valve is available in manual or automated formats.
Double-Seat Valve
Figure 6 Butterfly valve.
Figure 7 Double-seat valve.
Situations arise in the dairy industry in which two pipelines must be connected to allow the product to flow from one pipeline to the other, or separated to prevent mixing of two fluids such as product and detergent, and to ensure product integrity by directing any leaks to drain. This function can be achieved by use of three butterfly valves, three on–off globe valves, or one on–off and one changeover valve. It can also be achieved using one double-seat valve (Figure 7), which has two separate seals, one for each pipeline. Between the seals is a chamber, which is connected to atmosphere. Provision is made for in-place cleaning of this leakage chamber. To reduce the risk of a valve seat being lifted by surges in liquid pressure, this valve is available with a hydraulically balanced plug.
Plant and Equipment | Flow Equipment: Valves
Constant-Pressure Valve In the constant-pressure valve (Figure 8), compressed air acting on a diaphragm modulates the flow in the system, in response to changes in product pressure. By this means, product pressure can be maintained constant, for example, for supply to an item of processing equipment.
Modulating Valve The modulating valve (Figure 9), which is conceptually similar to the globe valve, is used to vary product flow rate. It operates by varying the position of the valve in the
157
orifice in the flow weir and flow rate is reduced as the plug is lowered toward the valve seat. It may be operated in conjunction with a flow sensor, which detects product flow rate, and a controller, which adjusts the valve setting to the required flow rate.
One-Way Valve The one-way valve or check valve (Figure 10) uses a spring-loaded seal to allow flow in one direction and to stop flow in the reverse direction. Fluid flow in the desired direction uses the momentum of the fluid to keep the valve open. If the direction of flow is erroneously reversed, the valve closes under the influence of the fluid and the spring, to prevent backflow.
Safety Valves
Figure 8 Constant-pressure valve.
Figure 9 Modulating valve.
Pressure/vacuum relief valves (two possible configurations of a safety valve are shown in Figure 11) are used to ensure safe operation by limiting the maximum pressure/vacuum that can develop in a system. Pressure can be controlled by air pressure or by preset compression of a helical spring. Applications include the use of a pressure relief valve downstream of a positive displacement pump, to avoid damage in the event of a flow shutoff downstream. Since many safety valves are not air actuated, it is difficult to open them for CIP cleaning.
158 Plant and Equipment | Flow Equipment: Valves
Figure 10 Check valve.
(a)
(b)
Valve plug
Spring
Wall of vessel FP Figure 11 Safety valve.
Figure 12 Air blow valve.
Air Blow Valve Before in-place cleaning commences, the product is cleared from pipelines by use of compressed air introduced via an air blow valve (Figure 12). Other valves used in the dairy industry include flow splitters, mixing valves, sampling valves, and plug cocks (for manual operation only). See also: Butter and Other Milk fat Products: The Product and Its Manufacture. Cream: Manufacture.
Dehydrated Dairy Products: Milk Powder: Types and Manufacture. Hazard Analysis and Critical Control Points: Processing Plants. Ice Cream and Desserts: Ice Cream and Frozen Desserts: Manufacture. Milking Machines: Principles and Design. Plant and Equipment: Corrosion; Flow Equipment: Principles of Pump and Piping Calculations; Flow Equipment: Pumps; In-Place Cleaning; Instrumentation and Process Control: Process Control; Materials and Finishes for Plant and Equipment; Pasteurizers, Design and Operation; Process and Plant Design. Utilities and
Plant and Equipment | Flow Equipment: Valves Effluent Treatment: Compressed Air; Design and Operation of Dairy Effluent Treatment Plants; Heat Generation; Refrigeration; Water Supply.
Further Reading Bylund GP (2003) Dairy Processing Handbook. Lund, Sweden: Tetra Pak Processing Systems AB.
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De Nevers N (2005) Fluid Mechanics for Chemical Engineers, 3rd edn. New York: McGraw-Hill. Luyben WL (1990) Process Modeling, Simulation and Control for Chemical Engineers. New York: McGraw-Hill. Pearson GH (1978) Valve Design. London: Mechanical Engineering Publications Limited. Smith P (2004) Valve Selection Handbook: Engineering Fundamentals for Selecting the Right Valve Design for Every Industrial Flow Application. Boston, MA: Gulf Professional Publishing. Timperley DA (1993) Hygienic design of closed equipment for the processing of liquid food. Trends in Food Science & Technology 4(11): 375–379.
Agitators in Milk Processing Plants K Cronin and J J Fitzpatrick, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by D. A. MacCarthy, J. S. Fitzpatrick and K. Cronin, Volume 1, pp 1–6, ª 2002, Elsevier Ltd.
Introduction There are many reasons for the agitation of milk and milk products, including 1. to maintain product uniformity, 2. to promote heat transfer, and 3. to disperse and dissolve solids in water. However, excess agitation is to be avoided, as it can cause product damage by disrupting the fat globule membrane and exposing the fat to the lipase enzyme. Overagitation can also cause the formation of butter granules. This article describes the types of agitators that are commonly used in the dairy industry. The mechanical and hygienic design of such systems is outlined. The issues involved in the selection and sizing of a particular agitation system are presented. Heat transfer in agitated vessels is explained, and finally an overview of the applications of agitation in milk processing is presented.
Types of Agitators Several types of agitators are used in dairy processing and these can be broadly classified based on the viscosity of the product. Propeller Agitators The three-bladed marine impeller (Figure 1(a)) is a high-speed impeller (400–1750 rpm) with a small impellerto-tank diameter ratio (0.2–0.3). It is used for agitating lowviscosity liquids (usually <1 Pa s) whereby the momentum generated by the impeller is easily transferred throughout the liquid. It produces an axial flow pattern (Figure 1(b)), which gives reasonable mixing and good suspension of particles. Turbine Agitators These impellers have an impeller-to-tank diameter ratio in the range of 0.2–0.5, and can be operated at high speeds if required. They are used for agitating low-viscosity liquids (usually <1 Pa s); however, they have also been
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applied for agitating liquids with viscosities as high as 50 Pa s. The basic turbine is a flat-blade design, and one of the most common turbines is the flat-blade impeller with six blades mounted on a disc (Figure 2), which is often used in fermentations. Turbine impellers can induce strong radial flows in addition to axial flows, which impart a much greater mixing capability than imparted by propeller agitators. Pitch-bladed turbines have blades set at an angle less than 90 from the horizontal (Figure 3) and are used in the dairy industry, for example, in lactose crystallization and yogurt manufacture. The smaller the angle, the milder the agitation, as less shear forces are exerted on the liquid and on any particle or droplet within the liquid. Paddle Agitators The basic paddle agitator resembles the basic turbine agitator except that it has a larger impeller-to-tank diameter ratio (>0.5 to <1) and rotates at low speeds, typically 10–150 rpm. Paddle agitators are used in the dairy industry for agitating medium-viscosity liquids (0.5–10 Pa s). Increasing the viscosity will more rapidly dampen the momentum transfer through the liquid, and thus greater contact between the impeller and the liquid is required, which results in larger-diameter impellers with greater contact area. There are many variants of the basic paddle, as illustrated in Figure 4, which give greater contact area. Some of these, such as the gate anchor agitator, can be used with high-viscosity liquids up to around 100 Pa s. High-Shear Agitators High-shear mixers are used for breaking up particles such as in powder reconstitution or emulsion droplet formation. Rotor–stator agitators (Figure 5) are commonly used, in which the product is drawn into a high-speed rotor, with a typical speed of 3000 rpm, positioned in a closely machined stator, in which the solids are subject to milling and intensive hydraulic shear. This may be done batchwise in a mixing vessel, or in-line for continuous blending. Powder-mixing systems are commercially available, incorporating powder hopper, venturi feeder, and in-line mixer.
Plant and Equipment | Agitators in Milk Processing Plants (a)
(b)
(c)
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(d)
Figure 4 Paddle impellers: (a) basic paddle, (b) anchor, (c) gate, (d) anchor gate.
Figure 1 Three-bladed marine propeller showing typical flow pattern for side entry.
Figure 5 High-shear rotor–stator impeller.
Air Agitation Milk in large storage tanks may be agitated by supplying compressed air near the base of the tank. The air bubbles rise, expand, and set up circulation currents in the milk. The air supply is regulated using a level detector, which matches the flow rate of air to the quantity of milk in the tank.
Figure 2 Six-bladed disc turbine impeller showing typical flow pattern for center axial entry.
Mechanical Design The agitation system consists of an electric motor transmitting power through a mechanical drive system. The drive system consists of a power transfer unit (gearbox or belt drive), shaft and impeller, bearings, and seals. Figure 6 illustrates schematically the basic system configuration. Electric Motor and Gearbox/Belt Drive
Figure 3 Pitched three-bladed impeller.
High-Viscosity Agitators Helical and ribbon-type agitators are used for agitating very high-viscosity liquids (up to 1000 Pa s).
Electric motors rotate at an angular velocity (nominally 1500 or 3000 rpm) that is too high for the agitator impeller. Thus, a power transfer unit that allows a reduction in rotational velocity will be needed in the system, as in many cases impeller angular velocity will be less than 100 rpm. In the special case where a power transfer unit is not required, the system is referred to as direct drive. Two of the most common types of power transfer units are the gearbox and the belt drive. Gearboxes have the advantage of high torque transmission capability, high dimensional accuracy, and low friction losses, and they
162 Plant and Equipment | Agitators in Milk Processing Plants
Steam Shroud Reduction Gearbox
Rotating Driveshaft
Electric Motor
Steam in
Spring
Fixed Vessel Top Plate
Ball Bearing Steam Out
Seal Faces
Rotating Collar Fixed to Shaft
Impeller Figure 6 Drive system for top-mounted agitator.
predominate in this application. In many cases, the electric motor and gearbox will be supplied as a single unit. Belt drives are a flexible power transfer unit with the features of quiet running and good vibration damping properties. They are limited by (relatively low) operating temperatures and speeds and are less common in dairy agitation systems.
Drive Shaft The drive shaft transmits mechanical power from the electric motor to the impeller. In tall tanks, it may be necessary to fit more than one impeller at different levels on the stirring shaft in order to obtain the required effect. The number of impellers required is approximately equal to the ratio of tank height to tank diameter. It will be necessary to support this shaft with bearings in order to minimize friction, wear, noise, deflection, and vibration. Bearings can be classified as journal (plain) bearings and rolling bearings, and it is the latter that are generally employed. A variety of arrangements are possible to introduce the impeller shaft into the process vessel. The shaft can enter the vessel from the top (top mounted), from the bottom, or from the side. The shaft can be parallel, perpendicular, or inclined to the longitudinal axis of the vessel. Topmounted vertical agitator drives are most common with the shaft either coaxial or eccentric (off-center) with respect to the vessel axis. Bottom or side entry may be advantageous if more space is needed on top for entry ports and manifolds, or if headspace is limited. The shaft can run the full length of the vessel and be supported by bearings at either end (top and bottom), or can terminate at the impeller and be supported by a bearing at the point of entry into the vessel.
Sealing Satisfactory sealing of the rotating agitator shaft is essential to hygienic operation and yet difficult to achieve. As an example, in top-mounted systems, the dripping of lubricant oil from the gearbox into the tank contents is not acceptable even if a food-grade lubricant oil is specified. Any sealing arrangement must be able to resist the sterilizing temperatures applied. The most common type of dynamic seal is the axially loaded face seal (mechanical seal). Note that O rings should generally be avoided in food contact equipment. A mechanical seal consists of a pair of rings: one stationary and one rotating with the shaft. They are springloaded together, and dynamic sealing takes place between the flat annular surfaces. Mechanical seals can be carbon rings (graphite) rubbing on carbon rings, or silicon carbide on silicon carbide. Silicon carbide is a ceramic material, is harder, and thus gives a longer seal life. For long-life and low-wear seals, tungsten carbide can be chosen. High-temperature, low-friction plastics such as Teflon (PTFE) are also employed. Mechanical seals with silicon carbide/carbon running surfaces are inert under normally encountered operating conditions and are considered safe in food processing. Steam barriers may also be employed to further guarantee containment.
Hygienic Design Hygienic design of the agitator system involves consideration of issues such as materials of construction, cleanability, and surface finish. As food contact surfaces, which must remain inert, impervious, and durable, the shaft and impeller will in all likelihood be built from stainless steel. There are many grades of stainless steel but the austenitic grades AISI 304 and AISI 316 are the most common in dairy applications
Plant and Equipment | Agitators in Milk Processing Plants
(see Plant and Equipment: Materials and Finishes for Plant and Equipment). Cleaning and sterilizing agents (caustic and chlorite bleaches) will generally be more dangerous to the steel than the product itself. It is for this reason that grade 316 may be preferred with its higher resistance to corrosion attack from chloride ions. This also highlights the need for careful water rinsing in the cleaning cycle to ensure that the concentration of chloride ions does not reach dangerous levels in inaccessible places such as any machine crevices. The surface finish of the agitator affects the ability to clean, sanitize, and sterilize the shaft and impeller. Surface finish can be quantitatively measured by the value of the arithmetic mean roughness, Ra, number. Generally, such dairy product contact surfaces should have an Ra of less than 0.8 mm and such a finish is obtainable by mechanicaland electropolishing.
Agitator Selection and Sizing Viscosity Liquid viscosity is the resistance to flow of the liquid. Lowviscosity liquids show little resistance to flow and thus liquid momentum is easily transferred throughout the liquid and low power is required to agitate the liquid. On the other hand, high-viscosity liquids have a high resistance to flow, whereby viscous forces dampen liquid momentum transfer, and require higher power to agitate the liquid. In addition, many dairy liquids are nonNewtonian, and are mainly pseudoplastic, where viscosity decreases with increasing shear rates. This results in higher viscosities in regions of the liquid more remote from the impeller, which may lead to poor mixing in those regions. Some typical values for the viscosity of dairy liquids are presented in Table 1 at specified temperatures, as viscosity is usually a strong function of temperature. Agitator Selection Selection of agitator type is determined by the viscosity of the liquid and the agitation job to be performed, whether it is mixing, heat transfer, particle dispersion, oxygen
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transfer, or a combination of these. Each agitator type has a range of viscosities where it performs best and an agitation duty that it is best suited to, as mentioned above. Equipment suppliers and process design companies have the experience and practical knowledge for selecting an appropriate agitator to perform a specified job.
Agitator Dimensions and Speed Once an agitator type is selected, it then has to be sized in terms of its dimensions. This will depend on the size of the tank and the volume of the product to be processed. For a given impeller type, there are standard geometrical configurations for the impeller and tank, which give guidance to sizing the impeller. For most agitation applications with the exception of heat transfer, there is no well-developed mathematical analysis supported with property data that can be used for evaluating the effect of impeller speed and diameter on agitation performance. In these cases, it is necessary to evaluate on a small/pilot scale how impeller speed and diameter affect agitation performance and then scale up these results. Impeller tip speed is usually constrained in dairy processing because of its effect on product quality.
Agitator Power Requirement There are many power curve correlations available in the literature for estimating the power requirement for specific impeller–tank configurations, and these are usually presented in the form of power number or function versus Reynolds number, as illustrated in Figure 7. Once the impeller speed and diameter, liquid density, and viscosity are known, then the Reynolds number can be calculated. The power number can be read from the power curve for the specific impeller–tank configuration, and the power requirement can be calculated from the power number or function. Separate curves are required for baffled and unbaffled systems due to possible vortex formation in unbaffled systems. As a general guide, the typical mixing power consumption varies from 0.2 kW m3 for
Table 1 Typical viscosities of dairy liquids
Liquid
Temperature ( C)
Viscosity (Pa s)
Low viscosity Water Whole milk Skim-milk concentrate (33% solids)
20 20 25
1103 2103 13103
Medium viscosity Yogurt Milk concentrate (48% solids) Whey concentrate (65% solids)
10 20 10
1–4 1 5
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Transition
Laminar
Turbulent
P
Power Number NP =
ρN 3D 5
102
101
100 100
101
102
103
Reynolds Number NRe =
104
105
ρND 2 µ
Figure 7 Power curve correlation for estimating agitator power requirement.
low-viscosity liquids up to 4 kW m3 for blending materials that have the consistency of pastes and dough.
Vortexing Tangential flow in the direction of rotation of the impeller can lead to vortex formation when agitating lowviscosity liquids by centrally mounted impellers in unbaffled tanks. Vortexing due to increasing rotational speed may lead to air entrainment by exposing the impeller to air. This can also produce large oscillating forces acting on the impeller shaft. Vortexing can be prevented by mounting the impeller off-center or using a horizontal side-entering impeller. There are cases where vortexing is advantageous, for example, powder reconstitution. When powder is added to the surface of water, the vortex can greatly improve powder sinkability by centrifugally spinning the powder into the water, and this becomes even more important as the solids content of the reconstituted mixture increases.
where Nu = hDT/k Re = D2AN/ Pr = Cp/k h = heat transfer coefficient (product) (W m2 K1) k = thermal conductivity (W m1 K1) DT = tank diameter (m) DA = agitator diameter (m) N = rotational speed (s1) = density (kg m3) Cp = specific heat (J kg1 K1) = viscosity (Pa s) W = viscosity at wall temperature (Pa s) Values of a, b, c, and d depend on system geometry. Heat transfer in a jacketed vessel may sometimes be problematic when dealing with medium- and high-viscosity liquids because of low heat transfer rates and formation of deposits on the tank wall. This is overcome by using paddles with small clearances between the impeller and the tank wall so that the blade surfaces sweep the wall of the tank, clearing away any deposits and preventing a stagnant layer at the wall surface.
Heat Transfer in Agitated Vessels Heat transfer coefficients for the heating or cooling of a liquid in a jacketed vessel may be calculated using the correlation b
c
Nu ¼ aRe Pr
W
d
Applications On Farm Following milking, milk is stored in refrigerated tanks pending milk collection and delivery to the dairy. Agitation is required for two purposes: to improve heat transfer while the
Plant and Equipment | Agitators in Milk Processing Plants
milk is being cooled, and to avoid fat separation and facilitate milk sampling for analysis and payment. The typical agitation system used on farm is a paddle agitator, with an approximately 100 W motor geared down to about 30 rpm. The agitator will operate continuously during cooling and intermittently (e.g., 30 s/15 min) during storage.
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Yogurt Yogurt is characterized by a high solids content (about 20%) and a medium to high viscosity depending on whether the yogurt is stirred or set. Gentle agitation is required to avoid damage to product texture. This can be achieved by using a top-mounted agitator with large paddles and speeds of 20–60 rpm.
Milk Intake When milk is received at the dairy, it is stored as raw or pasteurized milk. Agitation is required at this stage to maintain uniform composition for downstream processing and inventory control. Typical agitation systems include (1) topentry agitator with more than one pitched-blade impeller, (2) side-entry agitator, marine propeller, angled down from the horizontal, and (3) air agitation, which is less commonly used because incorporation of air in milk can lead to problems in heat exchangers and centrifuges. In modern installations, provision is made to inactivate the agitator if the product surface reaches the height of the agitator.
Cream Storage Agitation of cream should be gentler than agitation of milk because of the greater possibility of product damage. The typical agitator used is the pitched-blade or paddle impeller, at a speed of 30–60 rpm.
Processed Cheese Processed cheese manufacture is characterized by high viscosity, dispersal of solids, and high heating rates. Agitation is achieved by anchor-type scraped-surface agitators, at speeds of approximately 100 rpm. See also: Butter and Other Milk Fat Products: The Product and Its Manufacture. Cream: Manufacture. Dehydrated Dairy Products: Milk Powder: Types and Manufacture. Hazard Analysis and Critical Control Points: Processing Plants. Ice Cream and Desserts: Ice Cream and Frozen Desserts: Manufacture. Milking Machines: Principles and Design. Plant and Equipment: Corrosion; In-Place Cleaning; Materials and Finishes for Plant and Equipment; Process and Plant Design. Utilities and Effluent Treatment: Design and Operation of Dairy Effluent Treatment Plants.
Further Reading Milk and Whey Concentrates Milk concentrates are produced by evaporation for dehydration, or by the addition of solids for yogurt or ice cream manufacture. These products can be effectively agitated using a marine propeller or pitched-blade agitators at 200–400 rpm.
Powder Dispersion The dispersion of powders in water is required for the manufacture of many dairy products such as ice cream, yogurt, dairy spreads, and dairy desserts. Complete dispersion of the solids in the aqueous phase is required, with no residual lumps and without air incorporation. Particular difficulty is encountered in dispersing stabilizers, for example, guar gum and locust bean gum, and emulsifiers, for example, mono/diglycerides. This is usually achieved using high-shear mixers.
Cowan CT and Thomas CR (1988) Materials of construction in the biological process industries. Process Biochemistry 23: 5–11. Hall CW, Farrall AW, and Rippen AL (1986) Encyclopedia of Food Engineering. Westport, CT: AVI Publishing Company. Harnby N, Edwards MF, and Nienow AW (eds.) (1997) Mixing in the Process Industries. Oxford, UK: Butterworth-Heinemann. Hauser G (1992) Hygienic design of moving parts of machines in the food industry. Transactions of the Institution of Chemical Engineers 70(part C): 138–142. Kessler HG (1981) Food Engineering and Dairy Technology. Freising, Germany: Verlag A. Kessler. Oldshue JY (1990) A Guide to Fluid Mixing. Rochester, NY: Mixing Equipment Company. Paul EL, Atiemo-Obeng VA, and Kresta SM (eds.) (2004) Handbook of Industrial Mixing: Science and Practice. Hoboken, NJ: WileyInterscience. Perry RH and Green DW (2007) Chemical Engineer’s Handbook, 8th edn. New York: McGraw-Hill. Stanbury PF, Whitaker A, and Hall SJ (1995) Principles of Fermentation Technology, 2nd edn. Oxford, UK: Butterworth Heinemann. Tatterson GB, Calabrese RV, and Penney WR (eds.) (1995) Industrial Mixing Fundamentals with Applications. New York, NY: American Institute of Chemical Engineers. Tetra Pak (2003) Dairy Processing Handbook. Lund, Sweden: Tetra Pak.
Centrifuges and Separators: Types and Design B Heymann, GEA Westfalia Separator Process GmbH, Oelde, Germany ª 2011 Elsevier Ltd. All rights reserved.
Introduction Since ancient times it is known that milk tends to separate into cream and skim milk. In static systems this was just a matter of time. During the nineteenth century centrifugal separation was developed for milk skimming before it was introduced to other technologies. Milk separators enabled a very quick skimming of the milk. The first machines were manually driven with a crank handle and mainly used on farms. For increasing the efficiency the original spiral channels were replaced by conical disks. The development of industrial dairies demanded higher capacities, and the machines were equipped with electric motors. Another important step forward was the introduction of self-discharging bowls in the 1970s, which enabled automatic cleaning or cleaning in place (CIP).
The Basics of Centrifugal Separation Centrifugal seperation can be applied on two-phase systems composed of either solid particles dispersed in a liquid or liquid droplets emulsified in another liquid. The individual particles or droplets form a discontinuous phase in the continuous liquid phase. If the density of the particle or droplet is higher than that of the liquid, it will sink down (sedimentation), otherwise it will float up (creaming), as depicted in Figure 1. The velocity of separation is described by Stokes’ law: Vs ¼
d 2 ??g 18?
where Vs is the velocity of sedimentation, d the diameter of particle or droplet, the difference of densities, g the acceleration due to gravity, and the viscosity of the continuous phase. This equation shows that the velocity of sedimentation is to the difference of densities • proportional proportional to the square of the size of the particle or • droplet proportional to the viscosity of the continu• inversely ous phase • proportional to the acceleration due to gravity
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Another important figure is the separating distance. In a slim and tall vat a particle or droplet has to travel a longer distance and needs more time to separate than in a wide flat pan of the same volume. Density and particle or droplet size are product parameters that generally have to be taken as constant values. However, other parameters can be influenced to optimize the process. increasing temperature reduces the viscosity • Usually and thus increases the sedimentation speed. Therefore,
• •
dairy separators are integrated in a pasteurizing process mostly at temperatures of 50–60 C. Centrifugal acceleration in a separator is determined by the bowl diameter and the rotational speed. It can be 8000 times higher than the acceleration due to gravity. Separating distance can be minimized by the geometrical design of the flow path. In modern separators the space between the disks has been reduced to 0.3–0.6 mm.
The increase of the separation effect in a centrifuge is described by the acceleration factor . This figure indicates the centrifugal acceleration as a multiple of the gravitational acceleration. ¼
!2 ?r g
where is the acceleration factor, ! the angular speed (! ¼ 2??n rad min – 1 ¼
2??n rad s – 1 , where n is the 60
bowl speed in rpm), r the radius, and g the acceleration due to gravity (9.806 65 m s2). As the acceleration factor is proportional to the radius of the centrifuge, the centrifugal acceleration is not constant but increases outwardly and decreases inwardly, as sketched in Figure 2. In a static system the gravitational acceleration forces the heavy phase (i.e., solids) downward and the light phase (i.e., cream) upward. In a rotating centrifuge the heavy phase moves outward, and the light phase inward.
Separation in the Disk Stack The feed flow is distributed to the rising channels and then split into a large number of parallel flows in between the conical disks. From here the liquid splits into
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Figure 3 Separation in disk stack. Figure 1 Creaming and sedimentation.
Figure 4 Separator disk stack.
Design Features Separators
Figure 2 Centrifugation.
The most common type of centrifuge in dairy installations is the separator, which is a vertical centrifuge with a stack of conical disks. The size of the flow channels between the disks is defined by spacers welded onto the disks. Phases
the light phase that flows inward and the heavy phase that flows outward. A light fat droplet carried over to the heavy phase will move inward from the main stream until it hits the surface of the disk below. Here the wall speed of the heavy phase flow is close to zero, and the buoyant force is able to move the droplet inward against the main flow until it merges with the light phase. In the light phase the inverse process separates heavy particles and carries them back outward to the heavy phase, as depicted in Figure 3. Figure 4 shows a typical disk stack.
There are two main types of separators. Two-phase separators (Figure 5) provide a solid–liquid separation (clarification), whereas three-phase separators (Figure 6) deal mainly with liquid–liquid separation (skimming). As dairy products always contain a certain amount of solids, such as raw milk impurities or coagulated proteins, in skimming separators there is also a third phase of heavy solids. With regard to the bowl components, the significant difference between two- and three-phase separators is the separating disk. In three-phase separators the heavy liquid
168 Plant and Equipment | Centrifuges and Separators: Types and Design
bowls are equipped with hydraulic sealings (hydrohermetic sealing). In terms of air intake there are no significant differences between the two types. On open bowls the feed and the discharge are usually connected from the top. Due to the additional space requirement of the mechanical seals, the product supply to a closed bowl is preferably connected from below via a hollow spindle. On hermetic separators the mechanical seals are fragile components, and they are prone to wear and tear. An open-bowl separator generates the discharge pressures from the separator drive. On a closed-bowl separator the discharge pressure is largely created by the feed pump, so the machine drive can be smaller, but a bigger feed pump is required. Discharge
Figure 5 Two-phase bowl (clarification).
In the original and the most simple design the liquid phases horizontally overflow from the bowl into collecting channels in the hood. The disadvantages of an opendischarge system are the generation of foam and the need for collecting vats for the discharged liquids. Nowadays, only very small separators feature this type of discharge. Centripetal pumps are fixed devices that use the rotary speed of the liquids to create pressure and forward flow in a closed-discharge system. This system avoids foaming and air intake, and it enables the integration of the separator in a closed-pipe system. The equivalent counterpart to a fixed centripetal pump in open bowls is a rotating impeller on a closed bowl. For some applications, a continuous discharge of major quantities of solids is required, for example, for the production of fresh cheese. Nozzle bowls are equipped with a collar of calibrated nozzles on the circumference of the bowl. To avoid an accumulation of solids between the nozzles, the inside of the bowl has a special shape with conical pockets directing the sedimented solids to the nozzles. Rising channels
Figure 6 Three-phase bowl (skimming).
phase moves outward in the disk stack. It is redirected and flows inward on top of the separating disk to get to the discharge near the center of the bowl. Sealing
Basically, there are two different types of sealing for the feed and discharge connections. Closed bowls use mechanical seals (hermetic sealing), whereas ‘open’
In all cases the product is fed into a distributor that distributes it underneath the disk stack to a number of rising channels. The position (radius) of the rising channels determines the relation between the flow paths of the light and the heavy phases. Channel positions close to the center result in long flow paths for the heavy phase and short flow paths for the light phase. Therefore, there is an improved removal of the light phase from the heavy phase, whereas the removal of the heavy phase from the light phase is less efficient. This is the typical configuration for skimming separators where the efficiency is defined by the residual fat content in the skimmed milk.
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On the other hand, a clarifier needs long flow paths for the light phase to remove as much of the (heavy) solids as possible from the (light) liquid. Therefore, the rising channels are positioned further to the outside of the disk stack. In some cases it is favorable to have no rising channels and the product rises completely outside of the disk stack.
Drive
The development of the drive system has proceeded from gear drive (Figure 7) via flat belt drive (Figure 8) to
Figure 9 Direct drive separator.
Figure 7 Gear drive separator.
direct drive (Figure 9). With fewer changes of direction, the mechanical efficiency factor increases and the noise level reduces. The number of serviceable parts is reduced significantly as well. A limiting factor for the rotary speed is the tensile strength of the bowl material. The admissible bowl speed depends on the bowl diameter and varies within a range of 4800 rpm (>Ø 800 mm) to 11 000 rpm (<Ø 300 mm). Hydraulic system
Figure 8 Belt drive separator.
Until the 1970s all separators had solid wall bowls. They could be operated until the solids holding space was filled up with sediments. After production, they had to be completely dismantled and cleaned manually (‘takedown machines’). One of the most important steps in the development of separators was the introduction of self-discharging bowls. A hydraulic system closes and opens the solids holding space at the bowl perimeter. During production this is used to perform regular discharges of the solids sediment. This enables long production runs without being limited by the solids load. Furthermore, these machines are suitable for automatic cleaning or CIP. Discharges during the recirculation of cleaning solutions remove sedimented solids from the bowl, and at the same time the sudden high velocities in the disk stack effect a mechanical
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cleaning. Besides the cleaning of the machine itself, the integration of a separator in a CIP loop also provides for cleaning of the CIP solutions. The discharged quantity can be controlled to achieve partial discharges during production and total discharges during CIP. A partial discharge ejects a quantity equivalent to approximately the volume of the solids holding space. This can be done without any interruption of the process. A total discharge, however, ejects the complete contents of the bowl. The loss of rotating fluid means a loss of kinetic energy and slowing down of the rotary speed. In order to limit the drop of speed, the feed flow has to be closed during total discharges and has to be kept closed during a recovery time after the discharge.
Figure 11 Decanter with open discharge.
Decanters Unlike separators, decanters have a horizontal axis of rotation (Figure 10). The continuous discharge of sedimented solids is performed by a scroll rotating at a differential speed in relation to the bowl. Generally, decanters are used for the removal of higher solid loads or to achieve a higher dry matter content in the discharged solids. In the dairy industry decanters are used only for a limited range of special applications. Phases
Similar to separators, horizontal centrifuges are available for two-phase or three-phase separations. In dairy applications only two-phase decanters are used. Discharge
The liquid discharge can be executed as an open discharge (Figure 11) or as a closed discharge with a centripetal pump (Figure 12). Depending on the further use of the liquid phase, both versions are used in dairies.
Figure 10 Decanter.
Figure 12 Decanter with centripetal pump.
Drive
A wide range of drive systems is available for decanters. The main classification is into fixed differential speed (selected by exchangeable pulleys, as shown in Figure 13) and variable differential speed (Figure 14). The selection of the drive system is determined mainly by the solids load. If the quantity or quality of the solids is variable, the machine has to cope with it by a variable differential speed.
Figure 13 Decanter drive for fixed differential speed.
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The skimming efficiency achieved is less than that achievable with hot milk skimming, and the milk fat is more crystalline than at hot temperatures. Therefore, the thickness of the flow paths has to be considerably larger. Also viscosities of the cream and skimmed milk are higher. To increase efficiency and/or capacity, the temperature can be gently increased to 20 C.
Whey skimming
Figure 14 Decanter drive for variable differential speed.
Centrifuges for Dairy Applications
Compared to milk (4%), the fat content of whey (0.4%) is much lower. Whey originates mostly from cheesemaking, which is a batch operation; so the operating conditions cannot be kept constant as in a milk pasteurizing line. Cheese whey always contains a certain amount of cheese fines. As a third phase, these particles tend to obstruct the separation process and can cause fouling of the disk surface. For a good skimming efficiency, a proper preclarification is indispensable. Best results are obtained with a clarifying separator rather than by screening.
Skimming Hot milk skimming
Milk skimming is still the most common and most important application for separators today. Worldwide, dairy legislation stipulates pasteurization of raw milk, and in all pasteurizers an important unit is the separator, which is integrated into the process at a temperature of 50–60 C. There are three modes of operation in milk skimming: full skimming (production of skimmed milk and cream), standardizing (production of standardized milk and cream), and back blending (production of whole milk). In all these modes, apart from skimming, the separator also cleans the milk from solid dirt. According to the mass balance, the cream fat content is controlled by adjusting the cream flow rate: Fr – Fs V_c ¼ V_r ? Fc – Fs
where V_ c is the cream flow rate, V_ r the raw milk feed flow rate, Fr the raw milk fat content, Fs the skim milk fat content, and Fc the cream fat content. In the standardizing mode there is no requirement for a high skimming efficiency, so the skimming separator can be operated at a higher capacity than that is possible in the full-skimming mode.
Cold milk skimming
In some cases it is desirable to do the skimming at cold temperatures of 4–15 C. Here, thermal changes are avoided and no heating energy is required at that stage of the process.
Standardizing
Many dairy processes require standardized milk with a specified fat content. The blending of skimmed milk and cream can be done batchwise or continuously, applying different levels of automation. For tank standardizing, the pasteurizer toggles between whole-milk and skimmed-milk production and both qualities are mixed in the right proportion in the pasteurized milk tank. This method is applied in manually operated plants. Continuous standardizing is possible by splitting the cream flow and blending a part of the cream with the skimmed milk. Systems of different automation levels, from manual to fully automatic, are available. Volumetric standardizing systems imply a constant raw milk fat content; they should be recalibrated after a raw milk tank change. Modern high-end systems like the GEA Westfalia Separator standomat continuously measure the fat content of the cream, so that they can compensate for variations in the raw milk composition. The control unit can be equipped with additional features like a continuous density/protein measurement for fat in dry matter or fat/protein standardizing, or proportional dosing of extra cream or other additives. The size of the cream discharge determines a maximum cream flow rate, which corresponds to a minimum cream fat content. The production of low-fat cream is possible with a cream dilution feature in the standardizing unit. Figure 15 shows a typical standardizing unit.
172 Plant and Equipment | Centrifuges and Separators: Types and Design
Figure 15 Standardizing unit.
Butter oil
For the production of butter oil or anhydrous milk fat (AMF) skimming-type separators are used in different ways. concentration: The cream fat content is • Cream increased from 40 to 80%. concentration: After a phase inversion from oil-in• Oil water to water-in-oil in a high-pressure homogenizer,
• •
the fat content can be further increased to over 99%. Oil polishing: Addition of water enables the elimination of concomitant substances. Serum skimming: This is the recovery of the remaining fat in the heavy phases discharged from the abovementioned stages.
Clarification In the dairy industry clarifiers are mostly used for the cleaning of raw milk at an early stage of processing or for the clarification of whey before a whey skimming separator. Recovered cheese fines can be further dewheyed in a decanter and then be used for the production of processed cheese. Bacteria Removal Spore-forming bacteria include Bacillus (aerobic) and Clostridium (anaerobic) species. The spores of these species are dormant bodies that carry all the genetic material
as is found in the vegetative form, but do not have an active metabolism. They are much more resistant against heat, dryness, and other negative ambient conditions than the vegetative form, so they act as a mean of survival during hard times. When the environmental conditions turn favorable, spores germinate to vegetative Bacillus or Clostridium cells. The concentration of spores in milk varies with the conditions of feeding and milking. Wherever the cows are fed with silage in the winter season, there is an important peak in spore count during that time. Owing to the heat resistance of the spores, this imposes specific limitations on the quality of pasteurized milk. On the other hand, spores have a higher dry matter content and a higher density than vegetative cells, so they are easier to remove by centrifugal separation. Removal of bacteria from liquid milk or from cheese milk is usually done in a pasteurizing line immediately before or immediately after the skimming separator. Besides the spores, vegetative bacterial cells and somatic cells from the cow’s udder are also removed. There are two different separation principles that can be applied. Most manufacturers use special clarifying separators to accumulate spores and heavy cells in the solids holding space before they are ejected from the bowl at regular intervals. In contrast to this, GEA Westfalia Separator uses a skimming-type bowl where a small quantity of the heavy phase enriched with respect to bacteria is recirculated to the product feed. This heavy-phase flow acts as a carrier to promote the deposition of the spores and bacteria to the solids holding space and increases efficiency.
Fresh Cheese Production Fresh cheese
Pasteurized cheese milk (skimmed or up to 3% fat) is coagulated by fermentation with or without the addition of rennet. Heating steps before and after coagulation serve to bond the whey proteins to the casein and to increase the yield of coagulated protein. The coagulated protein is separated at 30–50 C as heavy phase and continuously discharged via the nozzles on the perimeter of the bowl (Figure 16). The discharged product quantity is a constant value; therefore, the dry matter of the product is controlled according to the mass balance by adjusting the feed flow. Figure 17 shows a schematic diagram of a fresh cheese bowl. Double-cream fresh cheese
Enriched cheese milk of 8–12% fat content is pasteurized and homogenized before it is coagulated by fermentation. The pretreatment aggregates the protein with the fat, so
Plant and Equipment | Centrifuges and Separators: Types and Design
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Figure 16 Inside shape of a nozzle bowl.
Figure 18 Bowl of double-cream fresh cheese separator.
Process Conditions Satisfactory results are achieved with proper process conditions. discharge pressure determines the (vertical) pro• The duct level in the bowl. The adjustment of pressure to Figure 17 Bowl of fresh cheese separator.
the coagulate constitutes a lighter phase when compared to whey. The separation is performed at 80 C in a specially designed skimming separator that can handle the high viscosity of the cheese. The fat-in-dry matter content is determined by the properties of the cheese milk. The dry matter is controlled during separation by adjusting the discharged whey flow. A schematic of a typical double-cream fresh cheese bowl is shown in Figure 18.
Decanter Decanters are used in some dairy applications where high dry matter content of the solids phase is required: of recovered cheese fines • concentration production of lactose • production of casein • production of high dry matter fresh cheese •
• • •
an appropriate value is fundamental for the functioning of a separator. The process control has to provide constant conditions with regard to temperatures, flow rates, and pressures. Any shearing during the pretreatment of the product tends to reduce the size of fragile particles or droplets and can reduce separation efficiency. An increased air content in the milk, owing to, for example, an inappropriate design of the balance tank, can change the flow pattern in the disk stack and reduce efficiency. However, a certain amount of released air has to be accepted if air-saturated milk is heated from storage temperature to separation temperature.
See also: Plant and Equipment: Centrifuges and Separators: Applications in the Dairy Industry.
Further Reading Buecker FJ, Hoecker J et al. (2009) Separators from GEA Westfalia Separator for the Dairy Industry. GEA Westfalia Separator, Oelde. Renner E (ed.) (1988) Lexikon der Milch. Mu¨nchen: Volkwirtschaftlicher Verlag.
174 Plant and Equipment | Centrifuges and Separators: Types and Design Hinze H, Veer T et al. (2009) Process Lines from GEA Westfalia Separator for the Production of Soft Cheese. GEA Westfalia Separator, Oelde. Pointurier H and Adda J (1969) Beurrerie industrielle. Science et technique de la fabrication du beurre. Paris: La Maison Rustique.
Sienkiewicz T and Riedel C-L (1990) Whey and Whey Utilisation, 2nd revised and extended edn. Gelsenkirchen-Buer, Germany: Verlag Th. Mann. Stahl WH (2004) Fest-Flu¨ssig-Trennung Band 2. IndustrieZentrifugen, Maschinen- und Verfahrenstechnik. Ma¨nnedorf: DRM Press.
Centrifuges and Separators: Applications in the Dairy Industry O J McCarthy, Massey University, Palmerston North, New Zealand ª 2011 Elsevier Ltd. All rights reserved.
Introduction Centrifugal separation is the mechanical fractionation of a fluid mixture of two or more immiscible phases of differing densities by the imposition of a centrifugal acceleration field. Density differences of not less than 3% are required for effective fractionation at respectable throughputs. In the context of the dairy industry, the term centrifugal separation comprises centrifugation and cyclone separation. Centrifugation means separation in centrifuges with power-driven rotating bowls (rotating-boundary machines). Cyclone separation means separation in cyclone separators, in which the mixture to be fractionated, but no part of the machine, rotates; cyclones are stationaryboundary machines. In both cases, it is the rotation of the mixture that generates the centrifugal acceleration field required for fractionation. In dairy processing, the following types of mixtures can successfully be separated centrifugally: (e.g., cream and skim milk) • Liquid–liquid Liquid–solids (e.g., whey and casein curd) • Gas–liquid (e.g., water vapor and heat concentrated • milk) (e.g., dryer outlet air and milk powder) • Gas–solids Liquid–liquid–solids (e.g., cream, skim milk, and sus• pended insoluble matter) Rotation causes separation because, on a per unit volume basis, the higher the density of a component the greater is the centripetal (center-seeking) force that would have to be applied to prevent radial movement away from the axis of rotation. This is a consequence of Newton’s first law of motion. Centrifugal (center-fleeing) force, unlike centripetal force, is a fictitious force when, as is commonly the case, the Earth, rather than the rotating entity, is taken as the inertial frame of reference. However, it is a real force if the rotating entity itself (e.g., a centrifuge bowl) is taken as the inertial frame of reference. In a given case, centripetal force and centrifugal force are numerically equal, but opposite in sign. Centrifugal force is a concept useful in the analysis of a rotating system. Consider the combined separation and clarification of whole milk in a centrifuge. In this context, whole milk can be considered to comprise milk plasma as a continuous phase and milk fat globules and insoluble particles
(impurities) as dispersed phases. The centripetal force required to keep the whole of the centrifuge bowl contents rotating is supplied by the bowl wall. However, no centripetal force acts on the individual insoluble particles or fat globules, because these are free to move in the plasma. The insoluble particles, being denser than the milk plasma, accelerate towards the bowl wall, while the fat globules, being less dense than the milk plasma, are displaced (and decelerate) towards the bowl axis. The following expression for the speed of movement of a dispersed particle (or globule) at a given radius can be derived by taking the rotating centrifuge bowl as the inertial frame of reference and then equating the centrifugal force to the sum of the two opposing forces – the buoyancy force (caused by the displacement by the particle of a volume of plasma equal to the particle’s volume) and the drag force (caused by the movement of the particle through the plasma): 2 d 2 N 30 R v¼ 18
½1
where v is the (radial) separating velocity (m s1), d the particle diameter (m), the density difference between the particle or fat globule and the continuous phase (plasma) (kg m3), N the bowl rotational speed (rpm), R the radial distance from the axis of rotation (m), and the viscosity of the continuous phase (plasma) (Pa s). The net centrifugal force (centrifugal force minus buoyancy force) can be positive or negative, depending on whether the particle is denser or less dense than the continuous phase, but is independent of velocity. The drag force, on the other hand, is directly proportional to velocity (Stoke’s law). Thus, the greater the density difference (eqn [1]), the greater the net centrifugal force and the higher the velocity at which this force comes into balance with the drag force. It is this phenomenon that makes centrifugal separation possible; phases differing in density, because they move radially at different velocities in the centrifugal acceleration field, inevitably become separated as the feed mixture flows through the centrifuge or cyclone separator. and thus v are positive for the insoluble particles in milk (positive net centrifugal force), but negative for fat globules (negative net centrifugal force). The sign of velocity indicates the direction of radial movement during separation. As eqn [1] shows, the separating velocity,
175
176 Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry
in either radial direction, increases with distance, R, from the bowl axis. The dairy separation operations listed above could be achieved using gravitational sedimentation or filtration or both; eqn [1] applies to gravitational separation when 2 N R is replaced the centrifugal acceleration term 30 by the gravitational acceleration, g. However, the rotational speed of a centrifuge bowl (which is limited only by the bowl’s ability to withstand the centrifugal stress of its contents and its own mass) can be high enough to make centrifugal acceleration thousands of times greater than g, resulting in rapid separation. Centrifugal separation is thus far superior to gravitational separation in terms of effectiveness and throughput, and is also superior in terms of controllability, hygienic operation, compactness, and ease of integration into continuous processing systems. In the case of centrifugation, these advantages outweigh the high capital cost and high power consumption of centrifuges. Even though raw milk is routinely in-line filtered to remove impurities with large particle sizes, filtration is generally unsuitable for more demanding solids–liquid separation duties in the dairy industry owing to low efficiency, low throughput, hygiene risks, and other disadvantages. Filtration is, however, effective for solids–gas separation, and is used, for example, for recovering powder particles from dryer outlet air. The main types of centrifugal separators used in the dairy industry are the disk bowl centrifuge, the decanter centrifuge, the scroll-screen centrifuge, and the cyclone separator. Applications of each of these are discussed in turn, with particular emphasis on separating conditions, significant features of machine design, separation control, and separating efficiency.
Applications of Disk Bowl Centrifuges Whole Milk Separation The classical, and still the most important and commonest, application of the disk bowl separator is the separation of whole milk into cream and skim milk. This operation is an early stage in the manufacture of most dairy products. The development of the modern dairy industry began with the introduction of the centrifugal separator, first on individual farms and later at centralized creameries to which farmers brought their milk. Its use enabled the efficient concentration of milk fat, then considered the only milk component of significant value, into the cream stream while minimizing fat loss to the skim milk. The replacement of gravitational separation by centrifugal separation resulted in enormous increases in throughput
and efficiency. The first hand-driven disk bowl separators began to be used on farms in 1893. The capacity of the modern milk separator is around 60 000 l h1 for warm separation (52–55 C) and 50 000 l h1 for cold separation (4–10 C). Fine control of cream fat content is achieved by manual or automatic adjustment of the pressure balance across the separator’s rotating bowl. Usually, the back pressure at the skim milk outlet is kept constant automatically, and cream fat content is controlled by manipulating the back pressure at the cream outlet either manually or automatically. Cream fat content can be adjusted to any desired value up to about 50% without compromising separating efficiency. Separating efficiency, usually called skimming efficiency, is defined either as the percentage of the fat in the whole milk that is separated into the cream stream, or simply as the skim milk fat content. The former definition can be expressed as follows: E¼
fs 1– 100% fw
½2
where E is the skimming efficiency, fs the skim milk fat content (% w/w), and fw the whole milk fat content (% w/w). Equation [2] is derived from a fat mass balance across the separator that incorporates a pragmatic simplification based on the fact that the skim milk fat content is very much lower than that of the whole milk. Separators designed for warm separation, and separators designed for cold separation operating at 20 C, have efficiencies of about 99% (skim milk fat content ¼ 0.05% w/w). In cold separation, efficiency drops with temperature to about 50% (skim milk fat content ¼ 2% w/w) at 5 C if the cold milk separator is operated at its full nominal throughput. The efficiency can be increased to about 94% or more by reducing throughput by half to increase the residence time of the milk in the bowl. This increase compensates for lower fat globule separating velocities, which are a consequence of decreasing and increasing with decreasing temperature (eqn [1]). It is not possible even in warm separation to recover fat globules of less than about 1 mm in diameter because of their very low separating velocities. Separators designed for warm separation can be used for cold separation at temperatures as low as 20–25 C, without an excessive drop in efficiency, provided creams of no more than 15% fat are required. The bowls of dedicated cold milk separators are designed to cope with the very much higher cream viscosity, while avoiding churning of the cream and maximizing skimming efficiency. Cold separation, though not as efficient as warm separation, is useful in some circumstances, and is being more widely applied. Its advantages include better control of the product’s microbiological quality,
Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry 177
improved cream quality (e.g., improved whippability), improved quality of unpasteurized milk cheese, and greater flexibility in the processing of chilled milk on receipt from farms. Separators that can be used for either warm or cold separation are now available, allowing further improvements in flexibility. Separating temperatures above 55 C give negligible improvements in efficiency. Temperatures above 60 C result in a loss of efficiency owing to the deposition of denatured whey protein on to the separator’s disks (which disrupts the smooth two-way flow pattern in the interdisk spaces) and a drastic reduction in the tendency of fat globules to agglomerate; agglomeration is a useful tendency given the d 2 term in eqn [1], and should be preserved. Skimming efficiency is adversely affected by a number of factors besides temperature. As fat globule separating velocity is directly proportional to the square of globule diameter (eqn [1]), pipelines should be designed to avoid damage to fat globules and fat globule agglomerates, and flow rates should be controlled by variable speed drives on pumps rather than by pump throttling. The natural decrease in fat globule size that occurs during lactation, and therefore during the dairy season in countries such as New Zealand and Ireland, can be compensated for by gradually decreasing separator throughput over time. Whole milk to be separated should be deaerated, both to avoid fat globule damage and to avoid loss of efficiency caused directly by the presence of air in the separator itself. Air, being very much less dense than either skim milk or cream, is displaced rapidly to the inner edge of the disk stack, obstructing the flow of cream and in effect throttling the cream outlet. This causes an increase in the fat content and thus in the viscosity of the cream, increasing the throttling effect further. This vicious circle results in excessive fat loss to the skim milk. Milk should ideally be separated when it is fresh, as prolonged storage results in changes in the fat globule membrane that increase fat globule density. This results in a decrease in (eqn [1]), in turn decreasing fat globule separating velocity and thus skimming efficiency. Modern milk separators, which also act as clarifiers (see below) if the whole milk has not been purposely clarified prior to separation, are self-desludging. Sludge, comprising leukocytes, somatic cells, microbial cells and spores, blood and dirt particles, and some milk solids (mostly protein) are ejected at preset intervals. At least one separator manufacturer has introduced a separator bowl modification that almost eliminates loss of milk protein to the sludge. This increases protein yield and reduces sludge production, and reduces water usage by allowing longer intervals between desludges. Equation [1] shows that separator bowl rotational speed, N, has a large influence on separating velocity,
and thus on skimming efficiency; separators should be run at the bowl speed recommended by the manufacturer. Protein streams or concentrated skim milk should not be blended with whole milk prior to separation as this results in an increase in milk plasma viscosity, and thus a reduction in skimming efficiency (eqn [1]). However, badly separated skim milk with an excessive fat content can be blended with the whole milk. This results in an improved overall fat recovery from the blend owing to agglomeration of smaller fat globules.
Partial Homogenization of Milk So-called partial homogenization, mainly applied to retail milk, involves temporarily separating whole milk into skim milk and cream, homogenizing the cream, and then remixing the homogenized cream with the skim milk. Only the cream passes through the homogenizer, significantly reducing the homogenizer’s power consumption, which is directly proportional to volumetric throughput; this is the purpose of the process. As stabilization of the homogenized cream emulsion depends on the presence of at least 0.2 g casein g1 fat, the cream fat content should not exceed 12%. The economics of partial homogenization depend upon the cost of power, and the capital and operating costs of the centrifugal separator and homogenizer.
Milk and Cream Standardization Milk and cream often require standardization of their fat and/or solids-not-fat (SNF) contents for retail sale or, in the case of milk, prior to the manufacture of products such as whole milk powder and cheese. In small-scale dairy processing, standardization can be carried out batchwise by blending whole milk with either cream or skim milk in appropriate proportions. In large-scale operations, so-called direct standardization is used. The first step in direct standardization is centrifugal separation of the whole milk into skim milk and cream. A typical basic system works as follows: The back pressure at the skim milk outlet of the separator is kept constant automatically. The back pressure at the cream outlet is controlled automatically, using continuous inline temperature-compensated sensing of cream density (inversely related to fat content) and cream flow rate, to give a fat-standardized cream. Part of the cream flow and the skim milk flow are remixed (by means of automatic flow rate ratio control using in-line measurements of cream and skim milk flow rates) in proportions that result in a reblended whole milk of the desired standardized fat content. Surplus cream leaves the system as fat-standardized cream. A variation of this system is one in which the fat contents of the standardized cream and
178 Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry
the remixed standardized whole milk are controlled solely on the basis of in-line measurements of density. The accuracy of these systems is unaffected by variations in the flow rate, fat content, or temperature of the whole milk. The capability of simple systems can be extended in a number of ways:
is 50–55 C. As a clarifier has only one outlet, and flow in the bowl is from the outside of the disk stack to the inside, no fat globule separation takes place. The sludge can amount to 0.05–0.1% of the milk volume, and contains 14–16% dry matter comprising nitrogen (6–8%), fat (0.25–0.35%), lactose (4.7%), and nonmilk substances (1.5–3%).
measurement of skim milk density allows fluc• In-line tuations in the SNF content of the feed milk, which
• •
• •
cause density fluctuations unrelated to fat content, to be automatically compensated for. It also allows the fat to SNF ratios of both milk and cream, as well as milk and cream fat contents, to be standardized. Separator size can be reduced by causing part of the feed whole milk flow to bypass the separator, and to be blended in-line with the remixed standardized cream and skim milk from the separator. Part of the skim milk flow from the separator can be made to bypass the skim milk–standardized cream remixing point and rejoin the remixed stream downstream of the homogenizer in the remix line, thus allowing partial homogenization as well as standardization. High-fat standardized milk can be produced by taking off part of the skim milk flow upstream of the cream– skim milk remixing point. Alternatively, cream from a separate source can be remixed with the skim milk along with standardized cream from the separator. Other additive streams, such as concentrated skim milk and whey permeate, can be added to the skim milk from the separator along with the standardized cream, depending on standardization requirements.
As skimming efficiency is of less importance in standardization than it is in separation per se, higher separator throughputs can be used in direct standardization systems. Milk Clarification Self-desludging disk bowl clarifiers are used to remove solid impurities, especially leukocytes and bacterial cells and spores, from (usually raw) whole milk. Listeria cells enveloped by leukocytes, and therefore heat resistant, are removed by clarification, while those not so enveloped are easily killed by subsequent pasteurization. The clarifying efficiency of clarifiers is some 150% higher than that of separators, owing to the greater path length and thus longer residence time of the milk in the disk stack. Clarifiers operate at higher throughputs than separators do, and at low (<8 C) or high temperatures (50–60 C). Lower temperatures result in less loss of milk protein, while higher temperatures result in a greater reduction in total microbial count and allow complete removal of hair and other fibers, which are common contaminants of milk. The optimum temperature range
Bacterial Clarification of Milk When a substantial reduction of the bacterial contamination of milk is required, but without the use of severe heat treatment, purposely designed high rotational speed clarifiers (called ‘bactofuges’ by one separator manufacturer) are used for bacterial clarification prior to pasteurization. Bacterial clarification of standardized cheese milk is carried out mainly to remove spores of a number of (anaerobic) Clostridium species, especially Clostridium tyrobutyricum, which otherwise cause late fermentationinduced gas production (late blowing) in semihard cheese. Their removal enables the use of spore-inhibiting substances such as nitrate to be greatly reduced or eliminated. The numbers of wild lactobacilli are also lowered, resulting in less competition for starter cultures in the manufacture of raw milk cheese. Clarification at 65 C removes 98–99% of anaerobic spores and 95% of aerobic spores (e.g., those of Bacillus cereus). Clarification at 50 C removes 90–92% of lactobacilli. Bacterial clarification of cheese milk is particularly useful in Europe where cows are fed silage during winter; the spore content of milk is directly related to the extent of silage feeding and to the spore content of the silage. Bacterial clarification of consumer milk prior to pasteurization can result in a useful extension, of 3–5 days, in pasteurized milk’s shelf life. It has become more important in regions such as northern Europe where consumers are purchasing pasteurized milk less frequently (but expect it to remain of high quality even after some days of storage) and distribution lines have become longer owing to increasing centralization of milk-processing facilities. Clarification at 50 C reduces the total bacterial count by 86%. The removal of B. cereus spores is of particular significance in this application, as these spores survive pasteurization. The best results are achieved if the milk to be clarified is first separated into cream of 43% fat (to ensure a large density difference between cream and spores) and skim milk. Only the skim milk, which contains virtually all of the spores originally present in the feed milk, is clarified, before being standardized by cream remixing. Bacterial clarification can also be applied to milk and whey for the purpose of improving the bacteriological quality of low-heat milk powders and whey protein concentrate powders, respectively; to milk to be made into fresh cheese to remove ascospores of the molds
Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry 179
Byssochlamys nivea and Byssochlamys fulva; and to skim milk destined for casein manufacture. Two-stage bacterial clarification, using two machines in series, must be employed if one stage is inadequate. The design of bacterial clarifiers varies. The simplest machines separate the milk into a clarified milk stream and either a bacteria-rich milk stream or a sludge stream. In a somewhat more complex design, the milk is separated into a clarified milk stream, a bacteria-rich milk stream, and a sludge stream. In the case of cheese milk, the sludge, the bacteria-rich stream, or both can be UHT sterilized and recombined with the clarified milk. This reduces or obviates loss of milk solids. In another design, used where the total quantity of bacteria-rich material removed from the milk must be minimized, a flow of partially clarified milk (3–5% of the feed flow rate) is continuously recycled from the outer part of the bowl to the bowl feed. This changes flow conditions in the bowl in a way that increases the efficiency of separation of the smallest bacteria, and reduces the amount of sludge produced. Sludge is the only stream removed from the milk in this design.
Cream Processing The main products made from milk fat are butter and anhydrous milk fat (AMF). Centrifugal separation of whole milk to concentrate the fat in cream is the first significant processing step in each case. Butter making
Butter can be made in four ways: batch churning of 25–35% fat cream pro• traditional duced by a single separation step continuous churning of 40–41% fat cream, also • Fritz produced by a single separation step phase inversion of 75–82% fat cream. Milk • continuous is first separated to give 40% fat cream, which is then
•
itself separated in a cream concentrator (a specialized disk bowl separator) to give cream of the required high fat content blending fresh AMF made using the direct-from-cream process (see below) with cream and salt, or with water, milk solids, and salt. The separation steps required in making AMF are described in the following section
Anhydrous milk fat manufacture
AMF can be made from cream or butter. The directfrom-cream process involves the following main separation operations using disk bowl separators: separation of whole milk to give 40% fat cream, concentration of this cream to 75% fat, concentration of the butteroil phase after phase inversion of the concentrated cream, and polishing of the butteroil phase after in-line wash water addition and perhaps neutralization of free fatty acids. Fat
recovery is carried out by centrifugal separation of the heavy phase (secondary skim milk/buttermilk) from the cream concentrator. The heavy phase from the butteroil concentrator can be either recycled to the cream concentrator or centrifugally separated to yield -serum (a phospholipid-rich heavy phase) and a light fat-containing phase (that is recycled). In the manufacture of AMF from sweet cream butter, the melted butter is centrifugally concentrated and then polished in disk bowl separators prior to dehydration. If cultured butter is used, it may be necessary to separate the melted butter in a three-phase decanter centrifuge (see below) because of the butter’s high solids content (which is mainly due to the generation of biomass during cream culturing). The decanter separates the melted butter into butteroil, buttermilk, and solids. Buttermilk separation
Buttermilk has a fat content of 0.5–2.5%, which economically justifies separation to recover fat. As cream for buttermaking is pasteurized at temperatures high enough to denature whey proteins, it may be necessary to centrifugally clarify buttermilk prior to separation to avoid rapid fouling of the separator’s disks. For separating cultured cream buttermilk, the feed rate to the separator should be about 50% of that for milk separation in the same machine, with frequent desludging if prior clarification has not been carried out. Separation is carried out at 40–45 C for sweet buttermilk and at 35 C for cultured cream buttermilk to avoid excessive protein precipitation. The cream produced contains about 25% fat. Fresh Cheese The large-scale production of fresh soft cheeses is made possible by the use of specialized disk bowl machines for separating curd and whey after coagulation. In the case of nonfat or low-fat cheeses made from fresh and recombined whole and skim milks, and buttermilk, the whey is discharged via a centripetal pump (paring disk), while the denser curd is discharged continuously via nozzles at the periphery of the bowl. In the case of double cream cheese, the whey and the less dense curd are both discharged via centripetal pumps. Whey Processing Cheese whey contain curd fines and fat, which can be removed by centrifugal clarification and separation. Such removal is essential where the whey is to be used as an ingredient of, for example, clear drink products, and where it is to be used as a feedstock for the manufacture of whey protein concentrate, whey powder, or lactose. As the fines tend to block the disk spaces of a separator, it is necessary to clarify the whey prior to separation.
180 Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry
(One separator manufacturer used to offer a specialized clarifier separator whose disk stack had a lower preclarifying section and an upper separating section.) Casein whey and casein wash water contain casein fines, which can be recovered with disk bowl clarifiers and recycled, thus increasing the casein yield. Cheese fines recovered as sludge from whey clarifiers and separators can be put through a casein solubilization process. Undissolved denatured casein particles and other impurities are removed from the solution by centrifugal clarification. It can be economically viable to separate whey with a fat content higher than about 0.045% during heat concentration. This is typically done between evaporator stages 2 and 3. Difficulties can be encountered owing to the precipitation of whey protein and adventitious homogenization of fat globules. The dephospholipidation of whey, carried out in the production of whey protein concentrates with very low fat contents, involves treating the whey to cause the lipoproteins to flocculate and then removing the flocculates as sludge by means of centrifugal clarification. The clarifier used has a high rotational speed and nozzle discharge of the sludge, giving a simultaneous bacterial clarification effect. Dephospholipidation improves the performance of ultrafiltration plants and, as a significant proportion of the calcium phosphate in the whey is also separated, allows longer evaporator running times. The fat content of whey protein concentrates made from whey that was itself separated can be reduced by 20–30% by centrifugal separation under optimal conditions. Separator throughput must be about half that of the machine when separating milk, because of the higher viscosity of retentate. Whey can be purposely bacterially clarified, after the initial clarification to remove fines, to reduce the growth of bacteria in ultrafiltration plants, and to enable the production of whey powder suitable for use in baby food. Self-desludging nozzle discharge clarifiers are required in this case. In the basic lactalbumin process, whey is first centrifugally clarified. It is then treated to cause denaturation and precipitation of whey proteins, which are centrifugally recovered as sludge from a second clarifier. This sludge is mixed with water, and the washed protein solids are recovered as sludge (lactalbumin) from a third clarifier. The dry solids content of the lactalbumin is increased from about 16 to 34–35% in a decanter centrifuge (see below) prior to drying. Calcium phosphate is separated from whey permeate to avoid problems caused by precipitated calcium phosphate in evaporator plants and to minimize the salt content of products made from the permeate. Adjustment of pH to 6.6 and suitable heat treatment
cause the formation of calcium phosphate flocculates, which can be separated as sludge using a self-desludging centrifugal clarifier. The sludge from cultured whey that is not pH adjusted is extremely compact and can be continuously discharged from the clarifier via nozzles. Nozzle discharge disk bowl clarifiers are used to separate yeast from fermented serum in the production of ethanol from whey.
Other Applications of the Disk Bowl Separator The use of centrifugal clarifiers to remove cheese solids from brine in the manufacture of brined cheese can sometimes be justified economically. Frequent cleaning in place is required because of the deposition of crystalline fat on the separator’s disks at the low brine temperature, and the parts of the machine coming into contact with brine must be made of corrosion-resistant materials.
Applications of Decanter Centrifuges Centrifugal decanters (also called conveyor bowl centrifuges) are used in solids–liquid separation duties where the solids concentration in the feed and the particle size of the solids are too high to allow the use of disk bowl separators, and where a high dry matter content is required in the separated solids phase. The principal dairy industry applications of the decanter occur in casein and lactose manufacture. These and other applications are described briefly below. The use of decanters in lactalbumin manufacture and in the manufacture of AMF from sour-cream butter has been mentioned above.
Casein Decanters are commonly used to dewhey casein curd, the curd–whey mixture being first put through a dewheying screen to reduce the hydraulic load on the machine. After washing, the curd can be dewatered using decanters. In this operation, the aim is to obtain as dry a curd as possible prior to drying. The scroll-screen (also called the worm-screen) centrifuge is used as an alternative to the decanter for dewatering. It consists of a perforated bowl of truncatedcone shape with an internal corotating helical-flight screw (like that in the decanter). The mixture to be separated is fed to the inside of the narrow end of the bowl, and the solids are conveyed to the wide end during separation. As it approaches the wide end, the layer of solids becomes looser owing to the increasing diameter, and efficient further washing can be achieved by means of water sprays.
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Lactose Decanters are used to separate crystals of so-called edible lactose from the crystal–mother liquor mixture resulting from the crystallization of whey or whey permeate. Two-stage decantation is used in which wash water is added to the solids phase from the first decanter. In the manufacture of refined lactose from edible lactose, decanters are used to recover the lactose after recrystallization.
Concentration of Cheese Fines The fines in the sludge from disk bowl cheese whey clarifiers and separators can be concentrated to 30–50% dry matter by decanting the sludge after dilution to 8–12% dry matter with water and whey. The liquid phase is discharged by means of a centripetal pump.
Cyclone Separators Cyclone separators (used for solids–gas, solids–liquid, and gas–liquid separation tasks), in contrast to centrifuges, are mechanically simple; relatively cheap to purchase, install, and run; are compact compared with noncentrifugal (gravity) separators; and require little maintenance. Cyclone separators are used in the dairy industry for separation, mainly for separating product • gas–solids fines from the air leaving spray dryers and fluidized
•
Effluent The sludge from the flotation and sedimentation steps in the treatment of dairy wastewaters can be concentrated in decanters before disposal, reducing disposal costs.
bed dryers, both to increase yield and to minimize air pollution. This is the commonest application of cyclones. gas–liquid separation, mainly for the in-line deaeration of milk (essential for maintaining the efficiency of downstream centrifugal separators), and for separating the concentrate leaving an effect of a multiple-effect evaporator from the water vapor (steam) evaporated from the product in the effect. In the latter application, clean separation prevents bubbles of steam being retained in the concentrate (ultimately diluting the concentrate when they condense on cooling) and carryover of concentrate into the steam side of the next effect, or into the condenser. solids–liquid separation, one application of which is separating solids from waste streams. Solids–liquid cyclone separators are called hydrocyclones.
Decanter Operating Variables
•
Decanter operating variables are the radial location of the liquid discharge (which determines the thickness or depth of the layer of the separating mixture that rotates with the bowl), the rotational speed of the bowl, the differential speed (the difference between the rotational speeds of the bowl and the screw conveyor), and the feed rate. Liquid discharge at a larger radius gives a dryer solids phase, but increases fines losses, while discharge at a smaller radius has the opposite effects. Thus, in casein dewatering, for example, there must be a trade-off between the dryness of the curd and fines losses to the wash water, although, as mentioned previously, fines can be recovered from wash water (and whey) by means of disk bowl clarifiers. The rotational speed of the bowl must be higher for smaller solids phase particles and/or for a smaller density difference between the particles and the liquid phase. Differential speed must be matched to the rate at which solids are fed to the bowl, to avoid a solids buildup inside the bowl. Feed rate must be matched to the bowl speed, a higher feed rate requiring a higher bowl speed to maintain separating efficiency. The lowest possible bowl speed should be used, to minimize machine wear and power consumption.
Cyclone design is shown in Figure 1. The principles of design and operation can be understood by considering fines recovery from dryer air. The cyclone is a vertical body with a cylindrical upper part and a conical lower part. The solids–air mixture enters tangentially at the top of the cylinder. The linear motion of the mixture is converted to rotational motion by the flow of the air around the curved wall of the cyclone; the cyclone wall provides the centripetal force required to make the air rotate. As soon as the air starts rotating, the fines particles, which are free to move relative to the air, move toward the wall, as there is no centripetal force being applied to them to keep them in orbits about the cyclone’s axis. When they hit the wall, they are separated from the air, and slide to the bottom of the cyclone under the influence of gravity. They are removed via a rotary valve. The centrifugal effect is thus produced by the shape of the cyclone itself, the way the mixture to be separated enters the cyclone, and the velocity of the mixture (which is generated by a fan in the case of dryer air, or by a pump, or by a pressure difference).
182 Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry
relatively large. Separating efficiency can be expressed in terms of the diameter of the limit particle, the smallest particle that can successfully be separated. A simplified analysis of the flow pattern inside the separator, which incorporates eqn [1], leads to the following expression for the limit diameter:
Air out
Feed D
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 18 Q dL ¼ vT2 ðparticle – air Þ2L
S
DT H
L
Separated solids out
vT
Figure 1 Elevation and plan views of a cyclone separator for recovering solids from an airstream.
Separation of the particles in the way described above is not instantaneous; a sufficiently long residence time is attained by the way the air flows through the cyclone. The air moves in a spiral path down the cylindrical part and then the conical part of the cyclone, then flows inward toward the cyclone’s axis, and finally upward into a coaxial tube by which it leaves at the top of the cyclone.
Separating Efficiency The solids (e.g., milk powder particles) in the solids–air mixture entering a cyclone invariably exhibit a particle size distribution; particle size ranges from very small to
½3
where dL is the limit diameter (m), the viscosity of the continuous phase (Pa s), Q the volumetric feed rate (m3 s1), vT the maximum tangential velocity of the particle (m s1), particle the density of the particle (kg m3), and air the density of the continuous phase (kg m3). The maximum tangential velocity occurs at the radial position DT/2 (Figure 1). Equation [3] shows that it is possible to separate even very small particles in a cyclone if the entry velocity, vT, is high; if the cyclone is long (tall); and if it is possible to distribute the flow of feed over a number of smaller cyclones rather than a big one (because dL is directly related to volumetric flow rate, Q). Though the value of the recovered solids (e.g., milk powder fines) has to be balanced against the capital and operating costs of a battery of cyclones, air pollution control may be an overriding factor. In practice, it is often found that the exhaust air contains a small percentage of particles with diameters larger than the limit diameter. The reason for this is probably that small particles impinge on larger ones and push them into the exhaust air. On the other hand, a considerable proportion – often more than 50% – of particles with diameters lower than the limit value are successfully separated in the cyclone. These are particles that have reached the vicinity of the wall shortly after entering the cyclone. From there they are carried down and out by a secondary stream of air produced by frictional forces at the wall. The following geometrical relationships (see Figure 1) have favorable effects on cyclone efficiency: D H S ¼ 2 to 25; ¼ 7 to 8; ¼ 0:8 to 1:3 DT DT DT
As a general rule, the diameter of the exhaust pipe (DT) should be as small as possible, and the entry velocity of the feed mixture as high as possible. The separating efficiency of cyclones falls off dramatically in solids–air separation for particles below about 10 mm in diameter. For this reason, cyclone exhaust streams may need to be bag filtered to ensure that the emission standards aimed at protecting the environment are not exceeded. Cyclones may be entirely replaced by bag filters in milk powder manufacture.
Plant and Equipment | Centrifuges and Separators: Applications in the Dairy Industry 183
Conclusion It is clear from the foregoing that the modern dairy industry could not exist without centrifugal separation. Indeed, as intimated in the introduction, it could never have become established. Arguably, centrifugal separation is the most important unit operation in dairy processing, and the disk bowl centrifuge the single most important item of processing equipment. Centrifuge manufacturers, who are extremely competitive, are continuously improving the performance of their already highly sophisticated machines, by clever design and control innovations. They also put much effort into designing and improving dairy processes in which their machines can be used. It does not seem that the limits of this advanced separation technology, and its application in the manufacture of dairy products, have yet been reached. See also: Cheese: Avoidance of Gas Blowing. Plant and Equipment: Centrifuges and Separators: Types and Design. Standardization of Fat and Protein Content.
Further Reading Anonymous (2003) Dairy Processing Handbook. Lund: Tetra Pak Processing Systems AB. Early R (1998) The Technology of Dairy Products, 3rd edn. London: Blackie Academic and Professional. Kessler HG (2002) Food and Bio Process Engineering. Dairy Technology. Munich: Verlag A. Kessler. Kro¨nchen H-G and Belting M (2001) Centrifuges for milk clarification and bacteria removal. Technical Scientific Documentation No. 12, 3rd edn. Oelde: Westfalia Separator AG. Lehmann H-R, Dolle E, and Bu¨cker H (1997) Processing Lines for the Production of Soft Cheese. Oelde: Westfalia Separator AG. Lehmann H-R, Dolle E, and Uphus A (1991) Processing Lines for the Production of Butteroil. Oelde: Westfalia Separator AG. Lehmann H-R and Zettier K-H (1992) Whey Processing Lines. Oelde: Westfalia Separator AG. McCarthy OJ (2001) Centrifugal separation in food processing. Food Technology in New Zealand 36(7): 23–26, 28–34. Spreer E (1998) Milk and Dairy Product Technology. New York: Dekker. Uphus A (1996) Milk Fat Processing. Butter and Butteroil/AMF (Anhydrous Milk Fat). Oelde: Westfalia Separator AG. Walstra P, Wouters JTM, and Geurts TJ (2006) Dairy Science and Technology. Boca Raton, FL: CRC Press; Taylor & Francis. Zettier K-H and Hanschmann W (2000) Separators for the dairy industry. Technical Scientific Documentation No. 7, 5th edn. Oelde: Westfalia Separator AG. Zettier K-H and Wieking W (1995) Standardizing Systems for the Dairy Industry. Oelde: Westfalia Separator AG.
Heat Exchangers U Bolmstedt, Tetra Pak Processing Components AB, Lund, Sweden ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 3, pp 1313–1321, ª 2002, Elsevier Ltd., with revisions made by the Editor.
Introduction One of the most important requirements of modern dairying is to be able to control the temperature of products at every stage in the process. Heating and cooling are therefore very common operations in the dairy.
Heating Milk is heated by a heating medium such as low-pressure steam (seldom used nowadays) or hot water, so that the temperature of the product rises and that of the water drops correspondingly (see Utilities and Effluent Treatment: Heat Generation).
Cooling On arrival at the dairy, the milk is cooled to 5 C or lower, to limit microbiological growth. After pasteurization, the milk is cooled to about 4 C using chilled water, brine solution, or an alcohol solution such as propylene glycol.
Regenerative Heating and Cooling In many processes, a product must first be heated and then cooled. During pasteurization, milk is heated from, perhaps, 4 C to a pasteurization temperature of 72 C, held at that temperature for 15 s, and then chilled again to 4 C. The heat of the pasteurized milk is utilized to warm the cold milk. The process takes place in a heat exchanger and is called regenerative heat exchange or, more commonly, heat recovery. As much as 94–95% of the heat content of the pasteurized milk can be recycled.
1. Conduction means transfer of thermal energy through solid bodies or through layers of liquid at rest (without physical flow or mixing in the direction of heat transfer). 2. Convection occurs when fluids (gases or liquids) being heated or cooled develop internal mixing currents, either by the temperature-density effect itself (natural convection) or by mechanical agitation or turbulent flow (forced convection). 3. Radiation is the emission of heat from a body that has accumulated thermal energy. The thermal energy is converted to radiant energy, emitted from the body, and absorbed by other bodies, which it strikes. Almost all substances emit radiant energy. Principles Heat transfer in dairies occurs by convection and conduction. Two principles are used: direct and indirect heating. Direct heating
Direct heating means that the heating medium is mixed with the product. This technique is used water (steam is injected directly into the water • toandheat transfers heat to the water); heat products such as curd in the manufacture of • tocertain types of cheese (by mixing hot water with the
•
curd); and to sterilize milk or milk products by steam injection or infusion of the product into steam.
The direct method of heat transfer is efficient for rapid heating. It offers certain advantages, especially in the production of long-life, ultraheat-treated (UHT) milk, where heating is followed by rapid flash-cooling. It does, however, involve mixing of the product with the heating medium, which necessitates certain steps in the subsequent process. It also makes strict demands on the quality of the steam. Direct heating is forbidden by law in some countries on the grounds that it introduces foreign matter into the product.
Heat Transfer Theory Heat can be transferred in three ways: conduction, convection, and radiation.
184
Indirect heating
Indirect heat transfer is therefore the most commonly used method in dairies. In this method, heat is transferred from the heating medium through a partition into the
Plant and Equipment | Heat Exchangers t °C
185
The Heat Exchanger
Heat flow
The heat exchanger is used to transfer heat by the indirect method. The temperature profiles of the heating medium and milk in a typical tubular heat exchanger (THE) are shown in Figure 2.
Dimensioning Data for the Heat Exchanger
Figure 1 Heat transfer from a heating medium to a cold product on the other side of the partition. Courtesy of Tetra Pak.
product (Figure 1). In a plate heat exchanger, the plate is the partition. The velocity of the liquids is reduced by friction to almost zero at the boundary layer in contact with the partition. The velocity increases progressively and is the highest at the center of the channel. The temperature of the hot water is the highest in the middle of the channel. The closer the water is to the partition, the more it is cooled by the cold milk on the other side. Heat is transferred, by convection and conduction, to the boundary layer. Transfer from the boundary layer through the wall to the boundary layer on the other side is almost entirely by conduction, while further transfer to the milk in the central zone of the channel is accomplished by both conduction and convection.
°C
The size and configuration of the heat exchanger depend on many factors. The calculation is intricate and is normally done with the aid of a computer. The factors that must be considered are flow rate • product physical properties of the liquids • temperature program • permitted pressure drop • heat exchanger design • cleanability requirements • running time requirement • The formula for calculating the heat transfer area of the heat exchanger is A¼
Q cp t tm k
ð1Þ
where A is the required heat transfer area, Q the product flow rate, the density of the product, cp the specific heat of the product, t the temperature change of the product, tm the logarithmic mean temperature difference (LMTD), and k the overall heat transfer coefficient. Product flow rate
ti2
The flow rate Q is determined by the planned capacity of the dairy. Other factors being constant, the size of the heat exchanger is directly proportional to the flow rate.
tθ1
Physical properties of the liquids
These include density, , specific heat, cp, and viscosity, . The values depend on product and temperature.
tθ2 ti1
Temperature program Time
tθ1
ti1
Several aspects of the operating temperature must be considered, including the change of temperatures, the differential temperature between the liquids, and the flow direction of the liquids. Temperature change
ti2
tθ2
Figure 2 Temperature profiles for heat transfer in a heat exchanger with countercurrent flow. Courtesy of Tetra Pak.
Inlet and outlet temperatures of the product are determined by the preceding and subsequent process stages. The change of product temperature (t in the general formula above) can be expressed as (Figure 2) t1 ¼ to1 – ti1
ð2Þ
186 Plant and Equipment | Heat Exchangers
The inlet temperature for the service medium is determined by processing conditions. The temperature of the outgoing service medium can be calculated by an energy balance calculation. For a modern heat exchanger, the energy losses to the surrounding air can be neglected. Thus, the heat lost by the hot liquid is equal to the heat gained by the cold liquid. It can be expressed as Q1 1 cp1 t1 ¼ Q2 2 cp2 t2
°C ti2
Δtm tθ2
ð3Þ
tθ1
ti1
Logarithmic mean temperature difference
There must be a difference in temperature between the two media for heat transfer to occur. The differential temperature is the driving force. For sensitive products there are, however, limits to how large a difference can be used. The differential temperature can vary through the heat exchanger. A mean value, LMTD or tm, is used for calculation. ðti2 – to1 Þ – ðto2 – ti1 Þ tm ¼ lnððti2 – to1 Þ=ðto2 – ti1 ÞÞ
Time
tθ1
ti1
ti2
tθ2
ð4Þ
An important factor in determining the mean temperature differential is the direction of flow in the heat exchanger. There are two main options: countercurrent or cocurrent flow. Countercurrent flow
The temperature difference between the two liquids is best utilized if they flow in opposite directions through the heat exchanger (Figure 2). The cold product then meets the cold heating medium at the inlet and a progressively warmer medium as it passes through the heat exchanger. During its passage, the product is gradually heated so that the temperature is always only a few degrees below that of the heating medium at the corresponding point. This type of arrangement is called countercurrent flow. Cocurrent flow
With the opposite arrangement, that is, cocurrent flow (Figure 3), both liquids enter the heat exchanger from the same end and flow in the same direction. In cocurrent flow it is impossible to heat the product to a temperature higher than what would be obtained if the product and the heating medium were mixed. This limitation does not apply in countercurrent flow; the product can be heated to within 2–3 C of the inlet temperature of the heating medium.
Overall heat transfer coefficient
This factor, k, is a measure of the efficiency of the heat transfer. It indicates how much heat passes through 1 m2 of the partition per 1 C of differential temperature. In the
Figure 3 Temperature profiles for heat transfer in a heat exchanger with cocurrent flow. Courtesy of Tetra Pak.
heat exchanger, k should be as high as possible. The heat transfer coefficient depends on the following: pressure drops for the liquids • permitted viscosities of the liquids • shape and thickness of the partition • material of the partition • presence of fouling matter • Permitted pressure drop
To increase the value of k, and improve heat transfer, it is possible to reduce the size of the channel through which the product flows. This reduces the distance over which heat must be transferred from the partition to the center of the channel. At the same time, however, the cross-sectional area of flow is reduced. As a result, the flow velocity through the channel increases, which in turn makes the flow more turbulent and increases the pressure drop. The greater the allowed pressure drops for the product and service medium, the more heat is transferred and the smaller the heat exchanger needed. Products sensitive to mechanical agitation (e.g., milk fat globules) may, however, be damaged by violent treatment. The product pressure before the heat exchanger must be increased to force the product through the narrower channels. It may then be necessary to install a booster pump. In some countries, installation of a booster pump is specified in legal requirements, basically to secure a higher pressure on the product side and thus prevent leakage of unpasteurized product into the pasteurized product.
Plant and Equipment | Heat Exchangers
Heat exchanger design Viscosity of media
The viscosity of the product and the service medium are important determinants of the dimensions of the heat exchanger. A liquid with high viscosity develops less turbulence when it flows through the heat exchanger as compared to a product with lower viscosity. This means that a larger heat exchanger is needed, everything else being constant. Special attention must be paid to products with non-Newtonian flow behavior. For these products, the apparent viscosity depends not only on temperature but also on shear rate. A product that seems rather thick in a tank may flow much more readily when it is pumped through pipes or the heat exchanger. Shape and thickness of the partition
The partition is often corrugated to create a more turbulent flow, which results in better heat transfer (Figure 4). The thickness is also important; the thinner the partition, the better the heat transfer. However, this must be balanced against the need for the partition to be strong (a)
(b)
187
enough to withstand the pressure of the liquids. Modern design and production techniques allow thinner partitions than were possible only a few years ago. Material of the partition
For food processing, the normal material is stainless steel, which has fairly good heat transfer characteristics. Presence of fouling matter
Most dairy products are sensitive to heating, which must therefore be done very carefully to avoid product damage. If the surface is too hot in relation to the product, there is a risk that proteins in the milk will coagulate and be deposited in a thin layer on the partitions. The differential temperature between the heating medium and the product should therefore be as small as possible, normally 2–3 C above the pasteurization temperature. Heat must be transferred through the deposit, reducing the value of the overall heat transfer coefficient, k. The temperature differential between the heating medium and the product will then no longer be sufficient to transfer the same amount of heat (c)
Figure 4 The shape of the partition in a plate heat exchanger may differ depending on the product to be treated and thermal efficiency requirements. (a) and (b) herringbone pattern; (c) washboard pattern. Courtesy of Tetra Pak.
188 Plant and Equipment | Heat Exchangers
as before, and the product outlet temperature will drop. This can be compensated for by increasing the temperature of the heating medium, but this also raises the temperature of the heat transfer surface so that more protein coagulates on the surface, the thickness of the crust increases, and the value of k drops still further. The value of k is also affected by the flow rate through the heat exchanger. Increasing the flow rate makes the flow more turbulent and increases the value of k. Throttling the flow reduces the turbulence and hence also reduces the value of k. In modern pasteurizers and sterilizers the possibility of variable capacity is often included. In addition, multipurpose plants, that is, plants designed for the processing of various products in combination, are common today. As an example, a modern milk sterilizer for 10 000 l h1 of whole milk may be capable of also processing milk-based vanilla pudding at 5000 l h1. In calculating the heat transfer area, the sensitive nature of the product and the process demands must also be considered. Two such factors, not included in the formula, are the requirements for cleanability and running time. Cleanability requirements
The heat exchanger in a dairy must be cleaned at the end of a production cycle, by circulating detergents. To achieve efficient cleaning, while designing the heat exchanger not only the temperature requirements, but also the cleaning requirements must be kept in mind. If some passages in the heat exchanger are very wide, that is, have several parallel channels, the turbulence during cleaning may not be enough to remove fouling deposits effectively. On the other hand, if some passages are very narrow, that is, have few parallel channels, the turbulence may be so high that the pressure drop will be very large. Such a high pressure drop may reduce the flow velocity of the cleaning solution, thereby reducing its effectiveness. The heat exchanger must therefore be designed for effective cleaning.
to increased fouling. Under certain conditions, the running time may also be limited by the growth of microorganisms in the downstream part of the regenerative section of the plate heat exchanger. This is, however, rare; when it occurs it is usually related to the pretreatment of the milk. Hence it is important to allow for cleaning at regular intervals when making production plans for pasteurizers. Regeneration Utilizing the heat of a hot liquid, such as pasteurized milk, to preheat cold incoming milk is called regeneration. The cold milk also serves to cool the hot milk, thus economizing on water and energy. Regeneration efficiencies of up to 94–95% can be achieved in efficient modern pasteurization plants. The percentage of regeneration is calculated as R¼
ðtr – ti Þ 100 tp – ti
ð5Þ
where R is the regenerative efficiency (%), tr the milk temperature ( C) after regeneration, ti the temperature ( C) of raw incoming milk, and tp the pasteurization temperature ( C). Holding Correct heat treatment requires that the milk be held for a specified time at the pasteurization temperature. This is done in an external holding cell, which usually consists of a pipe arranged in a spiral or zigzag pattern and often covered by a metal shroud to protect operators against burns. The length of the pipe and the flow rate are calculated so as to provide the required holding time. Accurate control of the flow rate is essential to achieve the specified holding time. The holding time changes in inverse proportion to the flow rate.
Running time requirement
Some fouling always occurs when milk products are heated to a temperature above 65 C. Hence, the pasteurizer must be stopped periodically for cleaning. The length of the running time is difficult, not to say impossible, to predict, as it is determined by the degree of fouling, which depends on factors such as difference between the product and the • temperature heating medium quality • milk content of the product • air • pressure conditions in the heating section It is especially important to keep the air content as low as possible. Excess air in the product will greatly contribute
Calculation of holding time
The appropriate tube length can be calculated when the hourly capacity and the inner diameter of the holding tube are known. As the velocity profile in the holding tube is not uniform, some milk molecules will move faster than the average. To ensure that even the fastest molecule is pasteurized sufficiently, an efficiency factor, , must be used. This factor depends on the design of the holding tube, but is often in the range 0.8–0.9. The length, L, of the holding cell is calculated as follows: V ¼
Q H dm3 3600
ð6Þ
Plant and Equipment | Heat Exchangers
L¼
V 4 m d 2 10
189
ð7Þ
where Q is the flow rate at pasteurization (l h1), H the holding time (s), L the length (m) of the holding tube, d the inner diameter (dm) of the holding tube, V the volume (l or dm3) of milk, and the efficiency factor, dimensionless. Types of Heat Exchangers The following three types of heat exchangers are most widely used in the dairy industry: heat exchangers • plate tubular heat exchangers • scraped-surface heat exchangers • Plate heat exchangers
Most heat treatments of dairy products are carried out in plate heat exchangers. The plate heat exchanger (often abbreviated PHE) consists of a pack of stainless-steel plates clamped in a frame. The frame may contain several separate plate packs – sections – in which different stages of treatment, such as preheating, final heating, and cooling, take place. The heating medium is hot water and the cooling medium cold water, ice water, or propylene glycol, depending on the required product outlet temperature. The plates are corrugated in a pattern designed for optimum heat transfer. Formerly, the so-called washboard pattern (Figure 4(c)) was predominant, but today the herringbone pattern is normally used for all types of plates, also within the dairy industry (Figures 4(a) and 4(b)). The main advantages with the herringbone pattern are increased thermal efficiency and increased mechanical strength, the latter allowing the plates to be made thinner, which reduces the cost and weight of the plate. The increased thermal efficiency reduces the number of plates necessary, which in turn reduces the cost of the unit and also product hold-up volume. The plate pack is compressed in the frame. Supporting points on the corrugations hold the plates apart so that narrow channels are formed between them. The liquids enter and leave the channels through holes in the corners of the plates. Varying patterns of open and blind holes route the liquids from one channel to the next. Gaskets around the edges of the plates and around the holes form the boundaries of the channels and prevent external leakage and internal mixing. Figure 5 shows a typical arrangement. Flow patterns
The arrangement of the plates is such that the product flows through alternate channels in the plate pack. The service (heating or cooling) medium is introduced at the
Figure 5 Principles of flow and heat transfer in a plate heat exchanger. Courtesy of Tetra Pak.
other end of the section and passes through alternate plate channels. Each product channel consequently has service medium channels on both sides. For efficient heat transfer, the channels between the plates should be as narrow as possible, but both flow velocity and pressure drop will be high if a large volume of product must pass through these narrow channels. Neither of these effects is desirable and, to eliminate them, the passage of the product through the heat exchanger may be divided into a number of parallel flows. In Figure 6, the product flow is divided into two parallel flows, which change direction 4 times in the section. The channels for the heating medium are divided into four parallel flows, which change direction twice. This combination is written as 4 2/2 4, that is, the number of passes multiplied by the number of parallel flows for the product over the number of passes multiplied by the number of parallel flows for the service medium. This is called the grouping of the plates. Tubular heat exchangers
THEs are today normally used for UHT treatment of dairy products. The THE (Figure 7), unlike plate heat exchangers, has no contact points in the product channel and can thus handle products with particles, the maximum particle size depending on the diameter of the tube. The THE can also run longer between cleanings than the plate heat exchanger in UHT treatment. From the standpoint of heat transfer, the THE is less efficient than the plate heat exchanger. THEs
190 Plant and Equipment | Heat Exchangers
Figure 6 The system of parallel flow pattern for both product and heating/cooling medium channels. In this example the combination is written 4 2/2 4. Courtesy of Tetra Pak.
created by helical corrugations on the tubes and shell. The heat transfer surface consists of a bundle of straight corrugated or smooth tubes welded into tube plates at both ends. The tube plates are in turn sealed against the outer shell by a double O-ring construction (floating design). This design allows the product tubes to be taken out of the shell by unscrewing the end bolts, and this makes the unit strippable for inspection. The floating design absorbs thermal expansion, and the product tube bundles in the shell can be changed, allowing different combinations to be used for different applications. The monotube is a version with only one inner tube, which will permit particles with a diameter up to 50 mm to pass. Multi/monotubes are well suited for processes operating at very high pressures and temperatures. Concentric tubes
Figure 7 The tubular heat exchanger tubes are assembled in a compact unit. Courtesy of Tetra Pak.
are available in two fundamentally different types: multi/monotube and concentric tube. Multi/monotubes
The multitube THE operates on the classic shell-andtube principle, with the product flowing through a group of parallel tubes, and the service medium between and around the tubes. Turbulence for efficient heat transfer is
The heat transfer surface of a concentric THE consists of straight tubes of different diameters concentrically located on a common axis, connected by headers at both ends. The product flows in the gap between two concentric tubes and the service medium on both sides of these tubes. The floating design as described above for multi/monotubes is also applied to the concentric tubes. In addition, the multi/monotube inserts and the concentric tube inserts are interchangeable for maximum flexibility. The concentric tube is especially suited for processing viscous products, such as dessert puddings. Due to the thin product layer in the annular channel, very efficient heat transfer is achieved. Also, due to the single product channel design, the risk of maldistribution across parallel tubes for viscous products is eliminated. Scraped-surface heat exchangers
The scraped-surface heat exchanger (Figure 8) is designed for heating and cooling viscous, sticky, or lumpy products, and for crystallization of products. The operating pressures on the product side are high, often as much as 4 MPa. All products that can be pumped can therefore be treated. The scraped-surface heat exchanger consists of a cylinder through which the
Plant and Equipment | Heat Exchangers
and improved thermal performance. The product enters the vertical cylinder through the lower port and continuously flows upward through the cylinder. At process start-up, all the air is completely purged ahead of the product, allowing complete and uniform product coverage of the heating or cooling surface. The rotating blades continually remove the product from the cylinder wall (Figure 9), to ensure uniform heat transfer to the product. In addition, the surface is kept free from deposits. The product exits the cylinder via the upper port. Product flow and rotor speed are varied to suit the properties of the product flowing through the cylinder. At shutdown, thanks to the vertical design, the product can be displaced by water with minimum intermixing, which helps assure product recovery at the end of every run. Following this, complete drainage facilitates cleaning-in-place (CIP) and product changeover. As mentioned above, the rotor and blades are exchangeable, an operation which is possible owing to the automatic hydraulic lift that facilitates raising and lowering of the rotor/blade assembly
Heating or cooling medium
1 Cylinder 2 Rotor 3 Blade 1 2 3
Product Figure 8 Vertical type of the scraped-surface heat exchanger. Courtesy of Tetra Pak.
product is pumped in countercurrent flow to the service medium in the surrounding jacket. Exchangeable rotors of various diameters, from 50.8 to 127 mm, and varying pin–blade configurations allow adaptation to different applications. Smaller-diameter rotors allow larger particles (up to 25 mm) to pass through the cylinder, while larger-diameter rotors result in shorter residence time
1
3
191
2
1 Rotor 2 Blade 3 Cylinder Figure 9 Section through a scraped-surface heat exchanger. Courtesy of Tetra Pak.
Figure 10 Removal of blades from the rotor assembly in lowered position. Courtesy of Tetra Pak.
192 Plant and Equipment | Heat Exchangers
(Figure 10). The typical products treated in the scrapedsurface heat exchanger are ice cream and dairy spread, but fruit preparations, such as yogurt, are also treated. It is also used for fats and oils for crystallization of margarine and shortenings. The scraped-surface heat exchanger is also available in versions designed for aseptic processing. Two or more vertical-type scraped-surface heat exchangers can be linked in series or parallel to give a greater heat transfer surface depending on the processing capacity required. See also: Heat Treatment of Milk: Sterilization of Milk and Other Products; Ultra-High Temperature Treatment (UHT): Heating Systems. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk; Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk); Liquid Milk Products: UHT Sterilized Milks. Plant and
Equipment: Pasteurizers, Design and Operation; Process and Plant Design. Utilities and Effluent Treatment: Heat Generation.
Further Reading Bylund G (1995) Dairy Processing Handbook. Lund, Sweden: Tetra Pak Processing Systems. Coulson JM and Richardson JF (1990) Chemical Engineering, Vol. 1. Oxford: Butterworth–Heinemann. Eastop TD and McConkey A (1993) Applied Thermodynamics for Engineering Technologists. Harlow: Longman. Heldman DR and Lund DB (eds.) (1992) Handbook of Food Engineering. New York: Marcel Dekker. McCabe WL, Smith JC, and Harriott P (2000) Unit Operations of Chemical Engineering, 6th edn. New York: McGraw-Hill Kogakusha Ltd. Sneeden J-BO and Kerr SV (1969) Applied Heat for Engineers, 4th edn. London: Blackie Academic and Professional.
Pasteurizers, Design and Operation A L Kelly and N O’Shea, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction and Historical Development Pasteurization is a heat treatment that inactivates vegetative pathogenic microorganisms so as to render the product safe for consumption if refrigerated, and also prolongs the shelf life of the product. Pasteurized products are not sterile and still harbor low numbers of nonpathogenic psychrotrophic bacteria, which eventually reduce the shelf life. The growth of thermophilic sporeforming bacteria, which survive the relatively mild heat treatment applied, in pasteurized milk is largely controlled by cold storage of the pasteurized milk. Thus, pasteurization is a process that has profound impacts on both the public health implications of milk consumption and the keeping quality of milk and dairy products. The process is named after the French microbiologist Louis Pasteur, who discovered that wine could be preserved by inactivating bacteria by heating at a temperature below boiling. The principle was soon applied to milk, and the first systems for the commercial pasteurization of milk were introduced in about the last decade of the nineteenth century. Early systems relied on heating milk to about 63–65 C and holding for about 30 min in batch heating units, followed by rapid cooling to less than 12 C (i.e., low-temperature–long-time (LTLT) pasteurization). This process is still used by small-scale processors but, since about 1940, such systems have been largely superseded by high-throughput continuous-flow plate heat exchanger (PHE)-based pasteurizers, in which milk is heated to 72–74 C and held for at least 15 s, in a process called high-temperature–short-time (HTST) pasteurization. This remains the most common design of industrial pasteurizers today, and will be the focus of this article. Public health aspects of pasteurization are discussed in Liquid Milk Products: Pasteurization of Liquid Milk Products: Principles, Public Health Aspects.
Heat Treatment Conditions Used for the Pasteurization of Milk In 1980, the International Dairy Federation defined pasteurization as ‘‘a process applied to a product with the object of minimising possible health hazards arising from pathogenic micro-organisms associated with milk by heat treatment which is consistent with minimal chemical, physical and organoleptic changes in the product’’.
The time–temperature conditions selected for the pasteurization of milk were determined, primarily, from the knowledge of the sensitivity of pathogenic microorganisms in milk to heat and, secondarily, from the consideration of the negative impact of heat treatment on the flavor and perceived ‘freshness’ of milk. The most heat-resistant vegetative pathogen in milk was identified originally as Mycobacterium tuberculosis (see Pathogens in Milk: Mycobacterium spp.), and the conditions for LTLT pasteurization were defined to ensure inactivation of this bacterium. The pathogenic rickettsia, Coxiella burnetii, was subsequently recognized as being slightly more heat-resistant, and the need to inactive this species was a key factor in the development of HTST pasteurization conditions (see Pathogens in Milk: Coxiella burnetii). Heat treatments sufficient to thermally inactivate these bacteria kill all less resistant microorganisms, and thus pasteurization should render milk safe for consumption, at least in terms of vegetative bacteria. In recent years, as a result of better understanding of the diversity of the microflora of raw milk and the thermal inactivation kinetics of various bacterial strains, there has been some discussion on modification of pasteurization conditions. For example, use of an extended holding time during HTST pasteurization (to 25–40 s) or a slightly higher pasteurization temperature has been suggested as being required to ensure inactivation of heat-stable strains of Listeria monocytogenes, Escherichia coli, and Campylobacter species (see Liquid Milk Products: Pasteurization of Liquid Milk Products: Principles, Public Health Aspects). Also, in the last 15 years, there has been much debate on the heat sensitivity and public health significance of emerging pathogens in milk, particularly Mycobacterium avium subsp. paratuberculosis (see Pathogens in Milk: Mycobacterium spp.). This bacterium is the causative agent of Johne’s disease, a bowel disease in cattle, and has been linked to a similar syndrome, Crohn’s disease, in humans. Early experiments to determine its heat sensitivity were hampered by the immense difficulty in quantifying this bacterium in milk owing to its extremely slow growth rate in culture and its tendency to grow in clumps due to its rough waxy cell wall. Nevertheless, early studies on the thermal inactivation of this bacterium in milk suggested that conventional HTST treatments were not sufficient to ensure complete inactivation of M. avium subsp. paratuberculosis, leading to an extension
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194 Plant and Equipment | Pasteurizers, Design and Operation
of the holding time and/or use of a higher pasteurization temperature in many countries. However, more recent studies have suggested that, under the extremely turbulent flow conditions in a modern milk pasteurizer, protective clumps of this bacterium are disrupted, enhancing its heat sensitivity and permitting inactivation under conventional HTST conditions.
The surface of the plates displays a corrugated pattern to increase turbulence in the liquid flowing over them and, thus, efficiency of heat transfer (Figure 2). The stainless steel plates are compressed together in the frame, but supporting points on the corrugations hold the plates apart so that thin, rectangular channels are formed between them. Gaskets (made from natural rubber or, more recently, from synthetic elastomers) around the edges of the plates and holes define the boundaries of the channels and prevent leakage. The liquids flowing in the PHE enter and leave these channels by openings at the corners of the plates, and varying patterns of open and blind openings route the liquid from one channel to the next. The flow pattern in alternating plates is illustrated in Figure 3. Milk is introduced through a corner opening into a channel between two plates and flows vertically through the channel; it leaves through the opening at the opposite corner, and bypasses the next channel between plates. In parallel, the heating or cooling medium is introduced at the other end of the section and it passes through the alternating interplate channels in the same manner. Thus, milk has heating or cooling medium, in the respective sections, flowing countercurrent, on either side of it, but separated by the intervening plate wall. For efficient heat transfer, the channels between the plates should be as narrow as possible; however, if a large
Principle of Operation of an HTST Pasteurizer As stated above, in modern dairy processing plants, HTST pasteurization in continuous-flow PHEs is practiced almost exclusively, although on farms or small dairy plants, smaller batch units may still be used (see Plant and Equipment: Heat Exchangers). A typical PHE consists of a vertical stack of many stainless steel plates clamped in a frame. The frame may contain several groups of plates, known as sections, in which different stages of treatment, such as preheating, final heat treatment, and cooling, take place (Figure 1). The heating medium may be steam or hot water, and the cooling medium may be cold water, brine, glycol, or ice water, depending on the desired outlet temperature of the product. The capacity of a milk pasteurizer depends on the size and number of plates, and can be as high as 100 000 l h 1.
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3 Figure 1 A complete pasteurizing plant, including (1) balance tank, (2) feed pump, (3) flow controller, (4) regenerative preheating sections, (5) centrifugal clarifier, (6) heating section, (7) holding tube, (8) booster pump, (9) hot water heating system, (10) regenerative cooling sections, (11) cooling sections, (12) flow diversion valve, and (13) control panel. Reproduced with permission from Tetra Pak A/B, Lund, Sweden.
Plant and Equipment | Pasteurizers, Design and Operation
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Figure 2 Shape and design of typical plate heat exchanger pasteurizer plates. Reproduced with permission from Tetra Pak A/B, Lund, Sweden.
Gap to atmosphere Water Milk Figure 3 Principles of flow and heat transfer in the heating sections of a pasteurizer. Reproduced with permission from Harrison PC (1983) HTST pasteurising plant. In: Green E (ed.) Pasteurising Plant Manual, 3rd edn., pp. 7–36. Huntingdon, UK: Society of Dairy Technology.
volume of product has to pass through these narrow channels, both flow velocity and pressure drop will be high. Neither of these effects is desirable, and to minimize their significance the passage of product through the PHE may be divided into a number of parallel flows. One section of parallel flow is known as a pass, and passes in the PHE change the direction of flow a number of times. Within each section of the pasteurizer, there are many passes, that is, the direction of flow of product or heating/ cooling medium is changed several times. In a pasteurizer, cool raw milk is fed from a silo to a float hopper (balance tank) and pumped at a constant rate to the preheating, or regeneration, section of the pasteurizer, where it is heated to 68–70 C. In this section, milk is heated by absorbing heat from outgoing pasteurized milk through the plates, with the medium being cooled
simultaneously. Similarly, heat from the pasteurized milk is transferred to a cooling medium after reaching the pasteurization temperature. The use of pasteurized milk as a heating medium for incoming cold raw milk results in substantial energy savings, and is called heat regeneration. Raw milk is heated in this manner by pasteurized milk from about 6 C to about 68–70 C and the pasteurized milk is cooled to about 10 C. The temperature of the milk thus preheated must be increased by only about 2–4 C (depending on the pasteurization temperature set point) using steam or hot water in the final heating section, while in the cooling section the pasteurized milk must be cooled by only about 6 C (from 10 to 4 C). With a well-dimensioned regenerative section, it is possible to recover about 94% of the heat from the pasteurized milk.
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Regenerative preheating of raw milk is usually divided over 2–3 sections of the PHE; milk between sections is thus at intermediate temperatures between 6 and 70 C. Milk at around 50–55 C is at the optimum temperature for treatments such as separation (fat removal and/or standardization; see Plant and Equipment: Centrifuges and Separators: Applications in the Dairy Industry), clarification (removal of undesirable solids; see Plant and Equipment: Centrifuges and Separators: Applications in the Dairy Industry), or homogenization (see Homogenization of Milk: Principles and Mechanism of Homogenization, Effects and Assessment of Efficiency: Valve Homogenizers), as milk fat is in a liquid state. Incorporation of such processing steps into the pasteurization line avoids the need to heat milk separately to carry out these operations, making liquid milk processing more economical and reducing the chances of contamination of the milk. Thus, milk is typically routed out of the pasteurizer between regeneration sections for treatments such as homogenization or standardization, before being returned to the PHE for completion of the pasteurization cycle. Milk may, in theory, exit the regeneration section for such parallel processing while being either heated (raw milk) or cooled (pasteurized milk), but the former option is more common, as it avoids the risk of recontamination of pasteurized milk, which otherwise would have to be avoided by use of aseptic
homogenization or separation systems. A complete process line for homogenized market milk is shown in Figure 4. The heating medium in the final heating section is circulated by a pump from a hot water generator, the temperature of which is maintained at 2–7 C above the set point by injecting steam via a steam-regulating valve, which is controlled by an automatic temperature controller (see Utilities and Effluent Treatment: Heat Generation). Both the pasteurization temperature and final milk temperature are generally logged on a chart recorder, which is mounted, along with the flow diversion valve (FDV) (see below) setting control, on a control panel. Correct pasteurization requires that the milk be held for a specified time at the set pasteurization temperature. This can be achieved either in a specific section of plates within the PHE (holding section) or in an external holding tube. No heating or cooling should take place within the holding section or tube; the milk simply flows through a passage, the length of which is determined from the flow rate of the milk and the required residence (holding) time. The control of residence time may be undertaken with greater confidence in a tube than under the turbulent flow conditions encountered in flow between plates. As a fundamental principle, the minimum residence time of milk in the holding section should always exceed the residence time stipulated for the process. An external holding tube
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Figure 4 Production line for market milk with homogenization of cream, showing (1) balance tank, (2) feed pump, (3) flow controller, (4) plate heat exchanger, (5) centrifugal separator, (6) constant pressure valve, (7) flow transmitter, (8) density transmitter, (9) regulating valve, (10) shutoff valve, (11) check valve, (12) homogenizer, (13) holding tube, (14) flow diversion valve, and (15) control panel. Reproduced with permission from Tetra Pak A/B, Lund, Sweden.
Plant and Equipment | Pasteurizers, Design and Operation
typically consists of a length of piping arranged in a spiral or zigzag pattern, and should be insulated. Since the residence time in the holding cell is determined primarily by the flow rate, accurate flow regulation is essential, as changes in flow rate will directly and inversely affect holding time. A resistance thermometer (thermistor) monitors the temperature of milk, generally at the point of exit from the holding section. Less commonly, the thermistor may be located at the start of the holding section. The latter position allows more time for the reaction to drop in temperature, ensuring that no underpasteurized milk can flow downstream for packaging, but does not account for the drop in temperature that can occur in an uninsulated external holding tube. The former position is thus more common, although a drop in temperature in the holding tube may be minimized by insulating the tube or by heating the milk slightly above the set pasteurization temperature in the heating section. However, the latter option implies overheating of milk, with concomitant potential alterations to flavor and properties. The thermistor (which typically operates over the range of 60–80 C) controls the action of a flow diversion device (FDD) or flow diversion valve (FDV), which is located downstream from the thermistor, either at the end of the holding section or, less commonly, after the cooling section of the pasteurizer. The plant shown in Figure 1 shows the FDV located in the latter position, while in Figure 4 the more common configuration is displayed. The function of the FDV is to prevent unpasteurized milk from reaching the packaging unit, by returning milk to the balance tank if the temperature determined by the thermistor drops below the target pasteurization temperature (sometimes referred to as the set point). The default, or fail-safe, position of the FDV of the pasteurizer is the closed or divert position, and the valve opens only if and when the temperature exceeds the set point. During operation, if the temperature of the milk, as measured by the thermistor, falls below the set point, a programmable logic controller (PLC) or similar device detects and records the decrease, often sounds an alarm for operators, and deactivates the FDV, causing the valve to close so that milk is diverted to the balance tank. The principle of operation of a pasteurizer’s FDV is illustrated in Figure 5. If the FDV deactivates and milk is returned to the balance tank, either the plant may stop, necessitating emptying, cleaning, and sanitizing before processing is recommenced, or the milk may be recirculated in the regeneration and cooling sections so as to allow restart when the set-point temperature is reached. In cases where the FDV is located at the outlet from the cooling section of the pasteurizer, the heat exchanger must be emptied, cleaned, and sanitized before restarting operation, if milk temperature decreases below the set point.
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Figure 5 Principle of operation of a flow diversion valve of a high-temperature–short-time pasteurizer. Valves are shown in the (a) open (operating) and (b) divert positions. Indicated are (1) milk inlet from holding section or tube, (2) milk line to regenerative section, and (3) diverted milk line. Reproduced with permission from Tetra Pak A/B, Lund, Sweden.
There is always a possibility of fractures or pinholes occurring in pasteurizer plates, which could lead to recontamination of pasteurized milk. To guard against this possibility, a booster pump may be fitted to the pipeline as it leaves the holding section to increase the milk pressure slightly (by around 0.01–0.02 MPa); should a pinhole then occur, the direction of leakage would be of pasteurized milk into raw milk, thereby precluding postpasteurization contamination. A simpler means of protecting the pasteurized product is to increase the number of passes in the regeneration sections, thereby increasing the back pressure within the pasteurized milk section of the plant. The chilled milk from the pasteurizer flows either to an intermediate storage tank or directly to a packaging unit. It is extremely important to avoid conditions that could introduce microorganisms into pasteurized milk during processing downstream from the pasteurizer; it has been acknowledged that postpasteurization contamination has in the past significantly influenced the shelf life and public health aspects of pasteurized milk. The key operating parameters for an HTST pasteurizer are plant capacity, temperature program, regenerative efficiency, and the temperature of the heating and the cooling medium. During operation, the PHE may be controlled in a feedback loop by monitoring the temperature of the milk in the heating section, milk leaving the cooling section, the heating medium, or the cooling medium. The shelf life of pasteurized milk is dependent on factors such as the microbial quality of the raw milk, the precise processing conditions used, postpasteurization
198 Plant and Equipment | Pasteurizers, Design and Operation
contamination, and refrigeration temperature, but is generally around 10–16 days at 5 C.
Pasteurization of Other Dairy Products Similar processing conditions are generally used for the full range of fat-standardized liquid milk products. However, cream, which contains a higher level of fat, must be heated more severely (e.g., 80 C for 3–5 s), as the fat acts as a thermal insulator, and increases the stability of bacteria (see Cream: Manufacture; Products). Ice cream and dessert mixes, which contain high levels of fat and sugar, are generally pasteurized at about 80 C for 25 s. In some countries, milk or cream heated to around 80 C for a few seconds may be referred to as being ‘flash’ pasteurized.
accuracy, and flow rate (determined by measuring the time to process a known quantity of milk), should be checked on a daily basis. The exterior of the plant should be inspected daily for leaks of all kinds and for general cleanliness. The FDV should be checked regularly for signs of wear or damage, which could impair its operating efficiency. Cleaning procedures for pasteurizers should be designed to prevent the growth of bacteria as biofilms (see Biofilm Formation), which have been shown to have the potential to proliferate on plate surfaces, but which can be removed by use of a cleaning cycle that includes exposure of surfaces to extremes of pH, as in cycled acid and caustic washes. Methods for determining the integrity of PHEs and monitoring the occurrence of pinholes or cracks include differential electrolytic analysis and helium leak detection systems.
Testing and Maintaining Pasteurizers
Testing for Milk Pasteurization
The requirements for the successful operation of a pasteurization plant are shown in Table 1. Pasteurizers should be checked routinely as follows:
The efficiency of pasteurization is generally assessed by using an indicator enzyme, alkaline phosphatase, naturally present in raw milk (see Enzymes Indigenous to Milk: Phosphatases). This enzyme is almost completely inactivated by processing times and temperatures just higher than those required to kill M. tuberculosis, that is, under conditions required for pasteurization. There are simple tests to detect the residual activity of this enzyme in milk and, therefore, if milk has been heated sufficiently strongly to inactivate this enzyme, it is assumed to be free of
calibration of thermometers must be verified; • correct the FDV must be shown to be in correct working order • and functioning as intended; and heating plates should be inspected regularly for leaks. • It is recommended that basic parameters of pasteurizer operation, such as diversion temperature, recorder
Table 1 Critical aspects of control of pasteurizer operation Application of correct heating by the use of Correct control of temperature of heating medium Positive control of flow rate through holding tube Correctly dimensioned holding tube Flow diversion valve Prevention of crosscontamination Positive pressure between raw and pasteurized milk in regenerative section Correct positioning of flow diversion valve Routine inspection of seals for leaks Cleanability High-grade stainless steel used for fabrication Welds, joins, and other parts of highest possible standard All materials compatible with cleaning fluids Limitation of heat damage Minimize temperature difference between heating medium and milk Minimize milk residence time in holding section Ensure efficient cooling Economic operation Ensure efficient regeneration Use a maximum heating surface-to-volume ratio Adopted from Varnam AH and Sutherland JP (1994) Liquid milk and liquid milk products. In: Milk and Milk Products, pp. 42–102. London: Chapman and Hall.
Plant and Equipment | Pasteurizers, Design and Operation
surviving pathogenic bacteria. For many years, tests for the pasteurization of milk were generally based on the production of a colored product from an uncolored substrate by the enzyme (if active). In modern dairy testing laboratories, automated equipment, such as the Fluorophos system, is used to detect and quantify residual phosphatase activity in milk, where a small amount of milk is mixed in a small test tube with a substrate for alkaline phosphatase; if active enzyme is present, it hydrolyzes the substrate, yielding a fluorescent product, which is then measured by the instrument. Incubation, reading, and printing of results take place in a single small, compact unit, with results being produced within 1–3 min. For cream, lactoperoxidase (an enzyme that is considerably more heat stable than alkaline phosphatase; see Enzymes Indigenous to Milk: Lactoperoxidase) is used as the indicator enzyme, rather than alkaline phosphatase, due to the requirements for use of a higher temperature in the pasteurization of cream. Lactoperoxidase activity may also be used to test for excessive heating during pasteurization of liquid milk, as HTST-pasteurized milk should be phosphatase-negative, but lactoperoxidase-positive.
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(ESL) products have a considerably longer shelf life than pasteurized milk, but suffer significantly less undesirable nutritional or sensory effects than ultra-high temperature (UHT)-treated products. ESL-type processes may also be referred to as superpasteurization of milk (see Liquid Milk Products: Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk)). See also: Biofilm Formation. Cream: Manufacture; Products. Enzymes Indigenous to Milk: Phosphatases. Homogenization of Milk: Principles and Mechanism of Homogenization, Effects and Assessment of Efficiency: Valve Homogenizers. Liquid Milk Products: Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk); Pasteurization of Liquid Milk Products: Principles, Public Health Aspects. Milk Protein Products: Membrane-Based Fractionation. Pathogens in Milk: Coxiella burnetii; Mycobacterium spp. Plant and Equipment: Centrifuges and Separators: Applications in the Dairy Industry; Heat Exchangers. Utilities and Effluent Treatment: Heat Generation.
Further Reading Developments in Pasteurization Technology The shelf life of pasteurized milk may be increased significantly by combining pasteurization with technologies that remove bacterial spores such as Bacillus cereus, which would otherwise grow, albeit slowly, during storage and spoil the milk. Approaches to spore removal before heat treatment generally involve either centrifugation (e.g., bactofugation) or microfiltration of skim milk, followed by mixing with strongly heat-treated cream, often followed by aseptic packaging (see Milk Protein Products: Membrane-Based Fractionation). Such extended shelf life
Bylund G (1995) Dairy Processing Handbook. Lund, Sweden: Tetra Pak Processing Systems A/B. Dowman AA and Ratcliffe NM (2000) A study of methods for evaluating the integrity of plate type heat exchangers used in the dairy industry. International Journal of Dairy Technology 53: 13–20. Harrison PC (1983) HTST pasteurising plant. In: Green E (ed.) Pasteurising Plant Manual, 3rd edn., pp. 7–36. Huntingdon, UK: Society of Dairy Technology. Muir DD and Tamime AY (2001) Liquid milk. In: Tamime AY and Law BA (eds.) Automation and Mechanisation in Dairy Technology, pp. 53–94. Sheffield, UK: Sheffield Academic Press. Pearce LE, Truong HT, Crawford RA, Yates GF, Cavaignac S, and de Lisle GW (2001) Effect of turbulent-flow pasteurisation on survival of Mycobacterium avium subsp. paratuberculosis added to raw milk. Applied and Environmental Microbiology 67: 3964–3969. Varnam AH and Sutherland JP (1994) Milk and Milk Products. London: Chapman and Hall.
Evaporators V Gekas, Cyprus University of Technology, Limassol, Cyprus K Antelli, Technical University of Crete, Chania, Greece ª 2011 Elsevier Ltd. All rights reserved.
Introduction An evaporator is a device wherein evaporation occurs, that is, liquid is evaporated from a thin (low-density) feed material in order to produce a denser or thicker product (concentrate). The feed may be a solution, slurry, or suspension of solid materials in a liquid. The heat necessary for the phase change or vaporization is supplied through heat transfer across metallic surfaces by condensing steam. Thus, evaporation as a unit operation involves energy transfer (heat for vaporization and condensation), mass transfer (moisture removal), and fluid flow (feed and vapor flows). In the dairy industry, evaporation is used for concentration of milk or whey. It is also used as a preliminary step to drying. Milk products intended for milk powder are normally concentrated from an initial solids content of 9–13% to a final concentration of 40–50% total solids before the product is pumped to the dryer. Evaporation in the dairy industry involves boiling off part of the water from a solution. To do this, heat must be supplied. The products to be evaporated are normally heat-sensitive and can be destroyed by adding heat. To reduce this heat impact, evaporation is done under vacuum, sometimes at a temperature as low as 40 C. At the same time, the evaporator should be designed for the shortest possible residence time. Most products can be concentrated with good results provided that the evaporator is designed for a low temperature and short holding time. It requires a large amount of energy to boil off water from a solution. This energy is supplied as steam. To reduce the amount of steam needed, the evaporation station is normally designed as a multiple-effect evaporator. Two or more units operate at progressively lower pressures and thus with progressively lower boiling points. In such an arrangement, the vapor produced in the previous effect can be used as a heating medium in the following effect. The result is that the amount of steam needed is approximately equal to the total amount of water evaporated divided by the number of effects. Evaporators with up to seven effects are now used in the dairy industry. Alternatively, electricity can be used as the energy source; in this case, an electrically powered compressor
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or fan is used to recompress the vapor leaving an effect to the pressure needed on the heating side. Although evaporator plants generally work on the same principle, they differ in the details of their design. The tubes that form the partitions between steam and product can be either horizontal or vertical and the steam can be circulated either inside or outside the tubes. In most cases, the product circulates inside vertical tubes while steam is applied on the outside. The tubes can be replaced by plates, cassettes, or lamellae.
Operation Processing Factors The physical and chemical properties of the solution being concentrated and of the vapor being removed have a great effect on the type of evaporator used and on the following characteristics: 1. Concentration of solutes in the liquid: Usually, the liquid feed to an evaporator is relatively dilute, so its viscosity is low, similar to that of water, and relatively high heattransfer coefficients are obtained. As evaporation proceeds, the solution may become very concentrated and quite viscous, causing the heat-transfer coefficient to drop markedly. Adequate circulation and/or turbulence must be present to prevent the coefficient from becoming too low. 2. Solubility: As solutions are heated and the concentration of the solutes increases, the solubility limit of the material in solution may be exceeded and crystals may form. This may limit the maximum concentration in solution which can be obtained by evaporation. 3. Temperature sensitivity of materials: Many products, especially foods and other biological materials, may be temperature-sensitive and degrade at higher temperatures or after prolonged heating. The amount of degradation is a function of temperature and length of time. 4. Foaming or frothing: In some cases, materials composed of caustic solutions, food products such as skim milk, and solutions of fatty acids form foam or froth during boiling. This foam accompanies the vapor phase and entrainment losses occur.
Plant and Equipment | Evaporators
5. Pressure and temperature: The boiling point of the solution is related to the pressure of the system. The higher the operating pressure of the evaporator, the higher the temperature at boiling. Also, as the concentration of the dissolved material in solution is increased by evaporation, the boiling point increases. In order to keep the temperature low in heat-sensitive materials, it is often necessary to operate below atmospheric pressure, that is, under vacuum. 6. Scale deposition and materials of construction: Some solutions deposit solid materials, called scale or fouling, on the heating surfaces. These could be formed by decomposition products or due to insufficient solvent. The result is that the overall heat-transfer coefficient decreases and the evaporator must eventually be cleaned. The materials used in the construction of the evaporator are important to minimize corrosion. Evaporator Types There is no single type of evaporator that is satisfactory for all conditions or all kinds of materials. Heat-transfer properties, energy, and cost factors determine the choice between various types of evaporators for a particular application. Both tubular and plate-type steam-heated heat exchangers have been used. Major manufacturers of evaporators are APV Crepaco, Alfa-Laval, Cook Machinery, Dedert Corp., FMC, GEA Food and Process Systems Corp., Niro Evaporators, Signal Swenson Div., Tito Manzini, and Figi s.p.a. Circulation evaporators Horizontal tube natural circulation evaporator
The horizontal tube natural circulation evaporator is shown in Figure 1(a). The horizontal bundle of heating tubes is similar to the bundle of tubes in a heat exchanger. The steam enters the tubes where it condenses and the condensate leaves at the other end of the tubes. The boiling/liquid solution covers the tubes. The vapor leaves the liquid surface, often goes through some de-entraining device, such as a baffle, to prevent carryover of liquid droplets, and leaves from the top. This type is relatively cheap and is used for nonviscous liquids having a high heat-transfer coefficient and liquids that do not deposit scale. It is unsuitable for viscous liquids because circulation is poor. Vertical-type natural circulation evaporator
In this type of evaporator, vertical rather than horizontal tubes are used; the liquid is inside the tubes and the steam condenses outside the tubes. Because of boiling and decreases in density, the liquid rises in the tubes by
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convection, as shown in Figure 1(b), and flows downward through a large central open space or downcomer. This natural circulation increases the heat-transfer coefficient. This type is often called the short-tube evaporator and is not used for viscous liquids. Circulation evaporators can be used when a low degree of concentration is required or when small quantities of product are processed. In yogurt production, for example, evaporation is used to concentrate milk 1.1- to 1.25-fold, or from 13 to 14.5% or 16.5% solids content, respectively. This treatment simultaneously deaerates the product and removes off-flavors. During the circulation evaporation process, the milk, heated to 90 C, enters the vacuum chamber tangentially at a high velocity and forms a thin, rotating layer on the wall surface, as shown in Figure 2. As it swirls around the wall, some of the water is evaporated and the vapor is drawn off to a condenser. Air and other noncondensable gases are extracted from the condenser by a vacuum pump. The product eventually loses velocity and falls to the inwardly curved bottom, where it is discharged. Part of the product is recirculated by a centrifugal pump to a heat exchanger for temperature adjustment and then to the vacuum chamber for further evaporation. Long tube vertical-type evaporator
Because the heat transfer coefficient on the steam side is very high compared to that on the evaporating liquid side, high liquid velocities are desirable. In a long tube vertical-type evaporator, shown in Figure 1(c), the liquid is inside the tubes. The tubes are 3–10 m long and the formation of vapor bubbles inside the tubes causes a pumping action, giving quite high liquid velocities. Generally, the liquid passes through the tubes only once and is not recirculated. The contact time can be quite low in this type of evaporator. In some cases, as when the ratio of feed to evaporation rate is low, natural recirculation of the product through the evaporator is made possible by including a large pipe connection between the outlet concentrate line and the feed line. This is widely used for the production of condensed milk. Falling film-type evaporator
A variation of the long tube type is the falling film evaporator, wherein the liquid is fed to the top of the tubes and flows down the walls as a thin film. Separation of vapor and liquid usually takes place at the bottom. This type of evaporator is widely used for concentrating heat-sensitive materials because the holdup time is very short (5–10 s or more) and the heat-transfer coefficients are high. It is also the type
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Steam Concentrate Condensate Feed Condensate Concentrate Feed Figure 1 Types of evaporators: (a) horizontal tube type; (b) vertical tube type; (c) long tube vertical type; and (d) forced circulation type.
most often used in the dairy industry. The heating surface may consist of stainless-steel tubes or plates. The plates are stacked together, forming a pack with the product on one side of the plates and steam on the other.
usually shorter in a forced circulation type (Figure 1(d)) than in the long tube type. In other cases, a separate and external horizontal heat exchanger is used. This type is very useful for viscous liquids. Agitated film evaporator
Forced circulation-type evaporator
The liquid-film heat-transfer coefficient can be increased by pumping to cause forced circulation of the liquid inside the tubes. This could be done in the long tube vertical type shown in Figure 1(c) by including a pipe connection with a pump between the outlet concentrate line and the feed line. However, the vertical tubes are
In an evaporator, the main resistance to heat transfer is on the liquid side. One way to increase turbulence in this film, and hence the heat-transfer coefficient, is by mechanical agitation. This is done in a modified falling film evaporator with only a single large jacketed tube containing an internal agitator. This type of evaporator is very useful for highly viscous
Plant and Equipment | Evaporators
Vapor
Product inlet
Concentrated product outlet Figure 2 Product flow in a vacuum chamber. Courtesy of Tetra Pak, Sweden.
materials. However, it is expensive and of small capacity.
Modes of Operation of Evaporators 1. Single-effect evaporators: A simplified diagram of a single-stage (single-effect) evaporator is given in Figure 3. The feed enters at Tf and saturated steam enters the heat-exchange section at Ts. Condensed steam leaves as condensate or drip. Assuming that the solution in the evaporator is perfectly mixed, the concentrated product that exits the evaporator and the solution in the evaporator have the same temperature, which is T1, because of thermal equilibrium with the boiling solution. The pressure is P1, which is the
Vapor
Feed, Tf
P1
T1
To condenser
Heat-exchange tubes
T1 Steam, Ts
Condensate T1
Concentrated product
Figure 3 Simplified diagram of a single-effect evaporator.
203
vapor pressure of the solution at T1. Single-effect evaporators are often used when the required capacity of operation is relatively small and/or the cost of steam is relatively cheap compared to the cost of the evaporator. However, for large-capacity operation, using more than one effect will markedly reduce steam costs. 2. Forward-feed multiple-effect evaporators: A single-effect evaporator, shown in Figure 3, is not energy-efficient because the latent heat of the vapor leaving is not used but discarded. However, much of this latent heat can be recovered and reused by employing a multiple-effect evaporation system, as shown in Figure 4. The first effect operates at a high enough temperature so that the evaporated water serves as the heating medium to the second effect. Here again, the evaporated water can be used as the heating medium to the third effect. Hence, the steam economy, which is kg vapor evaporated per kg steam used, is increased. This also approximately holds for a number of effects over three. However, this increased steam economy of a multiple-effect evaporator is gained at the expense of the original first cost of these evaporators. In forward-feed operation, as shown in Figure 4, the fresh feed is added to the first effect and flows to the next in the same direction as the vapor flow. This method of operation is used when the feed is hot or when the final concentrated product might be damaged at a high temperature. The boiling temperature decreases from effect to effect. 3. Backward-feed multiple-effect evaporators: In the backward-feed operation, shown in Figure 5 for a triple-effect evaporator, the fresh feed enters the last and coldest effect and continues until the concentrated product leaves the first effect. This method of reverse feed is advantageous when the fresh feed is cold, because a smaller amount of liquid must be heated to the higher temperature in the second and first effects. However, liquid pumps are used in each effect, because the flow is from low to high pressure. This method is also used when the concentrated product is highly viscous. The high temperatures in the early effects reduce the viscosity and give reasonable heat-transfer coefficients. 4. Parallel-feed multiple-effect evaporators: Parallel feed in multiple-effect evaporators involves adding fresh feed and withdrawing concentrated product from each effect. The vapor from each effect is then used to heat the next effect. This method of operation is mainly used when the feed is almost saturated and the product is in the form of solid crystals, as in the evaporation of brine to make salt.
204 Plant and Equipment | Evaporators Vapor T1
Feed, Tf
Vapor T2
Vapor T3
(1)
(2)
(3)
T1
T2
T3
To vacuum condenser
Steam, TS Condensate Concentrated from first effect
Concentrated from second effect
Concentrated product
Figure 4 Simplified diagram of a forward-feed triple-effect evaporator.
Vapor (1)
Vapor
Vapor
(2)
(3)
Feed
Steam Condensate Concentrated product Figure 5 Simplified diagram of a backward-feed triple-effect evaporator.
Heat and Material Balances for Evaporators
· T1m V H V
Single-effect evaporators
A single-effect evaporator is shown in Figure 6. The basic equation for solving for its capacity is Q ¼ UA T
where T is the temperature difference between the condensing steam and the boiling liquid in the evaporator, Q is the heat flow, U the overall heat transfer co-efficient and A the contact surface area. In order to solve this equation, the value of Q must be determined by making a heat and material balance on the evaporator shown in Figure 6. The feed to the evaporator is m_ f , having a solids content of wf (mass fraction), temperature Tf, and enthalpy Hf. The concentrated liquid, m, _ from the evaporator has a solids content of w, temperature T1, and enthalpy H. The vapor m_ v is given off as pure solvent having no solids, temperature T1, and enthalpy Hv. Saturated steam entering is m_ s and has temperature Ts and enthalpy Hs. The condensed steam leaving, m_ s , is usually assumed to be at Ts, the saturation temperature, with enthalpy Hc. Total material balance: m_ f ¼ m_ v þ m_
Material balance for the solute (solids):
T1P1
ð1Þ
ð2Þ
· Ts ms Hs
· mHwT1 · Ts ms Hc
m· f H f w f T f Figure 6 Simplified diagram of an evaporator.
m_ f wf ¼ mw _
ð3Þ
m_ f Hf þ m_ s Hs ¼ mH _ þ m_ v Hv þ m_ s Hc
ð4Þ
Heat balance:
Plant and Equipment | Evaporators
The heat Q transferred in the evaporator is Q ¼ m_ s ðHs – Hc Þ
ð5Þ
Selection of Evaporators Evaporator systems are major pieces of process equipment and are often purchased on a total responsibility basis. The purchaser’s task is to define the process, quality, and mechanical limitations accurately to enable the vendor to engineer economical and suitable systems for the intended duty. When selecting an evaporator, one should include the following considerations: 1. compare initial capital cost and operating cost 2. check to see that specifications have been met. Some important specification considerations are operation capacity product viscosity, suspended solids, and density temperature–time profile as related to product quality cooling water temperature steam levels and requirements materials of construction condenser type volatile recovery requirements headroom requirements any special requirements 3. Maintenance considerations manual versus automatic control reliability and simplicity of operation sanitation, ease of cleaning, and cleaning cycle safety requirements 4. Guarantees of after-sale services start-up assistance engineering expertise and response to problems personnel training
• • • • • • • • • • • • • • • • •
205
evaporation. There are three general areas for modifying existing evaporators for energy saving: 1. Fine-tuning existing evaporator: These low-investment improvements do not change the basic evaporator layout. 2. Modifying auxiliary hardware: These moderate-investment changes normally can be authorized at the plant level. 3. Major hardware modifications: These high-investment changes normally require approval at the corporate level. Thermocompression The vapor evolved from the product can be compressed and used as a heating medium. This improves the thermal efficiency of the evaporator. A thermocompressor is used for this purpose. A single evaporator with a thermocompressor is as economical as a twoeffect unit without one. Using thermocompression together with multiple-effect units optimizes thermal efficiency. The main components of an evaporator with thermal vapor recompression (TVR) are shown in Figure 7(a). Mechanical Vapor Compression Unlike a thermocompressor, a mechanical vapor compression system draws all the vapor out of the evaporator and compresses it before returning it to the evaporator. The pressure increase is accomplished by the mechanical energy that drives the compressor. In mechanical vapor compression, the total amount of steam is circulated in the plant. This makes a high degree of heat recovery possible. A three-effect evaporator with mechanical vapor compression can reduce the operating costs by half compared to a seven-effect plant with a thermocompressor. The main components of an evaporator with mechanical vapor recompression (MVR) are shown in Figure 7(b).
Economics Evaporation is one of the high capital cost and energyintensive unit operations. During the era of low energy costs, the major selection criterion was based on the low initial equipment costs. Energy is by far the major cost factor in evaporator operations. As a result, more energy-efficient designs have gained favor for new installations. Methods of Energy Savings Considerable economic benefits can be gained by upgrading existing evaporator systems to reduce energy costs for
Evaporators in the Dairy Industry Milk Evaporators are used during the production of evaporated milk or as a step in the production of dairy powders. As shown in Figure 8, after preheating, the milk is evaporated under vacuum. It is of utmost importance that the evaporator works under optimal hygienic conditions, regardless of the fact that the product is sterilized afterward. All modern milk evaporators are multiple-effect plants, and they almost always use either TVR or MVR.
206 Plant and Equipment | Evaporators Distributor
(a)
Distributor
(b)
Vapor recirculation
Vapor recirculation
Steam ejector
Compressor or fan
Steam Calandria
Condensate
III
Calandria
Separator
III
Condensate
Separator
Feed
Feed
Concentrate
Concentrate
Figure 7 Main components of vapor recompression evaporators: (a) thermal vapor recompression and (b) mechanical vapor recompression.
Standardized milk
Carrrageenan
Stabilizing salts
1
Standardization
Heat treatment
2
3
Evaporation
Storage
Filling
Sterilization
Homogenization/cooling Figure 8 Basic flow diagram for the manufacture of evaporated milk.
As an example of a typical installation, consider a multiple-effect TVR unit. Prior to the milk entering the first effect, it is usually pasteurized.
Whey UF × 18 DF
Whey The whey (typically 6% total solids) is normally evaporated, after pretreatment to remove fat (and/or cheese fines), to between 40 and 60% total solids. The choice of total solids in the final product depends on subsequent processing needs. If the whey concentrate has to be transported, 40% is preferred, to avoid crystallization taking place en route and causing unloading difficulties. Alternatively, when the whey is to be spray-dried (on-site), 60% is better. Both TVR and MVR falling
Dryer
WPC 60–80
Evaporator
Figure 9 Production of whey protein concentrate (WPC). DF, diafiltration; UF, ultrafiltration.
Plant and Equipment | Evaporators
film equipment can be used in this application as well as others, with the latter configuration usually giving better energy economy. An advanced case of application is in the production of whey protein concentrate. As shown in Figure 9, membrane technology and evaporation are combined for protein recovery and the subsequent concentration of the protein solution.
See also: Concentrated Dairy Products: Dulce de Leche; Evaporated Milk; Sweetened Condensed Milk. Plant and Equipment: Corrosion; Flow Equipment: Pumps; Heat Exchangers; Process and
207
Plant Design. Whey Processing: Utilization and Products.
Further Reading Bylund G (ed.) (1995) Dairy Processing Handbook. Lund, Sweden: Tetra Pak. Geankoplis C (1993) Transport Processes and Unit Operations, 3rd edn. New York: Prentice-Hall. Macrae R, Robinson RK, and Sadler MJ (eds.) (1993) Encyclopaedia of Food Science, Food Technology and Nutrition. London: Academic Press. Saravaws G and Kostaropouls A (2002) Handbook of Food Processing Equipment. New York: Kleewer Academic Publishers. Valentas K, Rotstein E, and Singh P (1997) Handbook of Food Engineering Practice. Boca Raton, FL: CRC Press.
Milk Dryers: Drying Principles E Refstrup and J Bonke, GEA Process Engineering – Niro, Søborg, Denmark ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by E. Refstrup, Volume 2, pp 860–871, ª 2002, Elsevier Ltd.
Introduction Drying is defined as the unit operation in which volatile liquids are separated from solids by vaporization to yield (nearly) liquid-free products. A number of different drying processes are in use in the dairy, food, chemical, and pharmaceutical industries, such as drying, • spray fluid bed drying, • drum drying, • batch drying in trays, • freeze drying, • microwave drying, and • superheated steam drying. •
(4) separation of the product from the drying air, and (5) cooling of the powder. The last two points will be discussed elsewhere (see Plant and Equipment: Milk Dryers: Dryer Design). Each of these process stages can be carried out in different ways, depending on the plant design, which in combination with operational conditions and other features, such as integrated and/or external fluid beds and destination of fine powder from powder separators, in turn determine the characteristics and properties of the final powder.
Atomization of the Feed
As the liquid to be removed in the dairy industry is invariably water, only water evaporation into atmospheric air is considered here, although the drying principles involved in the evaporation of nonaqueous, organic solvents into any controlled gaseous atmosphere are the same. From the point of view of drying economy and the final product quality, the processes of major significance in milk powder manufacture are spray drying, fluid bed drying, and drum drying. Spray drying and fluid bed drying are most often used in combination and drum drying is only of limited use. Only spray drying and fluid bed drying processes will be discussed here.
Atomization of the feed, that is, formation of a spray, is the characteristic feature of spray drying. The purpose of atomization is to create a large number of small-diameter droplets. Assuming a completely homogeneous spray, the total droplet surface area is inversely proportional to the droplet diameter, and the number of particles inversely proportional to the square of the droplet diameter. Table 1 shows the number of droplets and the total surface area created by homogeneous atomization of 1 l of concentrate to different droplet sizes. Rotary atomizers and pressure nozzles are in use in the milk powder industry, the former utilizing centrifugal energy and the latter pressure energy in the atomization process. The design of atomization devices is discussed elsewhere (see Plant and Equipment: Milk Dryers: Dryer Design).
Spray Drying
Rotary atomizers (wheel atomization)
The basic principle of spray drying is exposure of a fine dispersion of droplets, created by means of atomization of pre-concentrated milk products, to a hot airstream. The small droplet sizes created, and hence a large total surface area, result in very fast evaporation of water at relatively low temperatures. Hence, heat damage to the product is minimized. The spray drying process for milk drying comprises essentially five subprocess stages: (1) atomization of the feed, (2) mixing of spray and drying air, (3) evaporation,
In rotary atomizers, the feed is accelerated to the applied peripheral speed of the atomizer wheel, which is typically in the range of 150–170 m s1. The feed is introduced centrally around the atomizer shaft via a liquid distribution device. A number of different liquid distributor designs have been developed over the years, which emphasizes the importance of this component for optimum and trouble-free operation of the atomizer (absence of vibrations and product deposits). The efficiency of atomization (droplet size) depends on a number of factors:
208
Plant and Equipment | Milk Dryers: Drying Principles
209
Table 1 Number of droplets and total surface area created by atomization of 1 l of feed Mean droplet diameter (mm)
Number of droplets per liter (106)
Total surface area (m2)
500 250 100 75 50 10
15.3 122.2 1909.9 4527.1 15 278.9 1 909 859.3
12 24 60 80 120 600
peripheral speed, vane height, and number of • higher vanes decrease the mean droplet size; and rate, viscosity, and surface tension of the feed • higher increase the mean droplet size. The power consumption of a rotary atomizer is directly proportional to the feed rate and to the square of the peripheral speed of the wheel. The main advantages of rotary atomizers are the following: flexible with respect to feed rate and feed • very viscosity; feed solids concentrations can be handled, • higher hence higher product capacity and better economy; fouling or blockage problems; • nohigh-capacity units available (up to 200 tonnes h , • although not relevant in the milk powder industry); advantageous for abrasive, crystal-containing feeds like • precrystallized whey or permeate; and different powder properties achievable with different • wheel design. 1
Nozzle atomization
The nozzles used in spray drying are of the centrifugal pressure type, in which pressure energy is converted into kinetic energy of a thin liquid sheet with a partly rotational motion, which causes the spray pattern to be of the ‘hollow cone’ type. Pressures in the range of 180–250 bar are used for most dairy products. However, pressures as high as 500–600 bar have been applied occasionally for highly viscous feeds, such as sodium caseinate. The volumetric flow rate of a nozzle is directly proportional to the square root of the pressure: pffiffiffi Q ¼ ANF p 3 1
ð1Þ
where Q is the flow rate (m h ), A the nozzle capacity factor for water, F the ‘viscosity factor’ (0.9 is used for most milk concentrates), p the nozzle pressure (bar), and N is the number of nozzles. The effects of operating parameters on the efficiency of nozzle atomization (droplet size) are as follows:
1. higher capacity of nozzles, higher viscosity and surface tension of the feed, and larger orifice diameter (other parameters are constant) will increase the droplet size; and 2. higher pressure and wider spray angle will reduce the droplet size. The power consumption of the high-pressure pump is directly proportional to the feed rate and nozzle pressure. The main advantages of nozzle atomization are the following: 1. minimum aeration of the feed during atomization, hence virtually air-free particles and higher particle density. Typical particle densities of whole milk powder with different types of atomization are a. straight vane wheel atomization: 1.14 g cm3, b. curved vane wheel atomization: 1.18 g cm3, c. nozzle atomization: 1.23 g cm3; 2. improved powder flowability; 3. possibility of individual directions of sprays from each nozzle in multinozzle installation, hence improved control of agglomeration; and 4. less fouling of dryers producing ‘difficult’ products. The main disadvantages of nozzle atomization are the following: 1. inflexible to variation in throughput, as it affects the nozzle pressure and hence the atomization efficiency; 2. fairly low feed capacity per nozzle, ideally not more than 2000 kg h1 and preferably lower; 3. multinozzle arrangements required for larger plants, resulting in more complicated plant start/stop procedures; 4. fouling with deposited ‘milk stone’ – particularly at higher feed temperatures – causing a gradual increase in nozzle pressure at a constant throughput; and 5. wear of orifice and swirl chamber/core grooves limiting the lifetime of the components. Depending on the operating conditions and product type, the nozzle insert parts (made of tungsten carbide) should be renewed after 400–800 h of operation.
210 Plant and Equipment | Milk Dryers: Drying Principles
Mixing of Spray and Drying Air The air disperser and the atomizing device are the most vital components in a spray dryer. It has been metaphorically claimed that they are ‘the lungs and the heart’ of a spray dryer. Consequently, the air disperser design has to be in unison with the atomization device and the desired airflow pattern in the drying chamber. Air disperser design and airflow patterns in different types of dryers are discussed elsewhere (see Plant and Equipment: Milk Dryers: Dryer Design). In recent years, the development of computerized fluid dynamics (CFD) software and the emergence of required powerful computers have provided a new tool for the study of airflow, temperature profile, and particle paths in spray dryers. Particularly, the newer three-dimensional (3D) CFD software combined with the specific drying characteristics of the product in question has proven to be a very powerful tool in the design of dryers and in troubleshooting. Figure 1 shows examples of 3D CFD simulations.
pressure, pw (Pa), absolute humidity, x (kg kg1 water vapor in dry air), and total air pressure, ptotal (Pa), is pw ¼ x
ptotal x þ 0:622
ð2Þ
Saturated water vapor pressure
Saturated water vapor pressure is the maximum vapor pressure at a given temperature exhibited by air saturated with water vapor. The extended Antoine equation describes the relation between saturated water vapor pressure (Pa) and temperature ( C): Psat ¼ exp 72:55 –
7206:7 – 7:1385 lnðT þ 273:15Þ T þ 273:15 þ 0:000 004 046 ðT þ 273:15Þ2 ð3Þ ð3Þ
where T is the temperature in C. Relative humidity
Evaporation Similar to the drying air, the product to be dried (the feed) undergoes dramatic changes in its physical properties during the drying process. Before entering into a more detailed discussion of the actual evaporation process, the definition of certain terms is required. Properties of air/water vapor mixture Partial water vapor pressure
Partial water vapor pressure is the pressure the water vapor would exhibit if existing alone in the same volume and at the same temperature. The sum of the partial pressures of all gaseous components is equal to the total pressure of the mixture. The relation between partial
20 15 10 5 0
Relative humidity (RH) is the water vapor content relative to the content at saturation at the same temperature, expressed as %: RH ¼
pw 100 psat
ð4Þ
Properties of the humid air can be shown in a humidity chart (or psychrometric chart, Mollier diagram, I-X diagram) (Figure 2). In the diagram, which is valid only for an atmospheric pressure of 1013 hPa, the water vapor content in g kg1 dry air is plotted on the abscissa and the temperature on the ordinate. The parallel, sloped lines are curves of enthalpy in kcal kg1 dry air and finally the curved lines show the RH. By knowing two of the
20 15 10 5 0 −5 −10
Figure 1 Three-dimensional computerized fluid dynamics simulations of an MSD dryer. Left: Axial air velocities (m s1); right: evaporation rate (g m3 s1).
Plant and Equipment | Milk Dryers: Drying Principles
100 kcal kg−1 DA
211
Properties of the feed
150
Moisture content and solids content
The moisture content of the feed is most often expressed as % (w/w). The solids content equals 100moisture content. However, in drying theory, moisture content on dry basis (DB), which is the weight of moisture per unit weight of solids, is often used:
300 °C 250 50
200
moisture content ðDBÞ ¼
180
150
moisture content ðgÞ solids content ðgÞ
ð5Þ
5 10
Water activity (equilibrium relative humidity)
20
100
100
50
87
50
50
100 %RH
The water activity expresses the moisture content of a product as the RH of the surrounding air with which the product is in equilibrium: aw ¼
0 0 05
40 50
100 g Wv kg−1 DA
Figure 2 Humidity chart showing a spray drying process. Ambient air with 5 g moisture per kg dry air is heated to 180 C. It is assumed that adiabatic drying to a relative humidity (RH) of 10% in the exhaust air, which is assumed to give the required final product moisture content, results in an outlet temperature of 87 C. Wv, water vapor; DA, dry air.
four parameters (for instance, the temperature and RH, which are easily measured), the other two can be found from the diagram. Common drying terms
The moisture in the feed is present as (1) unbound moisture or (2) bound moisture. The physicochemical properties of the product determine the relation between the two types. Bound moisture is bound to the solids by bonds of different strength. Water of crystallization in -lactose monohydrate, ionic bonds in minerals and proteins, and hydrogen bonds in proteins and lactose are examples of different bond strengths. Bound water exerts a water vapor pressure lower than that of pure water. A product containing bound water is said to be hygroscopic. In a nonhygroscopic material, all water is unbound. Equilibrium moisture is the moisture content of the product when it is in equilibrium with the partial water vapor pressure in the surrounding air. Free moisture is the moisture in excess of the equilibrium moisture. A curve showing the relation between moisture content and the RH in the surrounding air at constant temperature is called a sorption isotherm. Figure 3 shows graphically the relationships between the different terms in an ideal case. In practical spray drying, the equilibrium moisture content is never reached due to variations in temperature and humidity inside the drying chamber and limited residence time.
pw psat
ð6Þ
Drying
The drying rate and the droplet temperature during drying depend on whether bound or unbound moisture is being evaporated. As long as unbound moisture is available at the droplet surface, the partial water vapor pressure in the interface between particle and air will be near the saturated vapor pressure at the droplet temperature, the drying will proceed at a near-constant rate, and the droplet temperature will be near the wet-bulb temperature. At the critical moisture content, the diffusion of moisture inside the particles is no longer sufficient to maintain saturated conditions on the particle surface. The result is a gradual decrease in vapor pressure and drying rate and a concomitant increase in the droplet temperature. These drying characteristics are shown in Figure 4. It can be seen that the product temperature never reaches the outlet temperature (T-out) from the dryer and that the residual moisture content is higher than the equilibrium moisture content for the reasons mentioned above. Changes in the state of drying air
The humidity chart is also useful in illustrating the changes that the air undergoes during the spray drying process. Figure 2 shows an example where the ambient air with an absolute humidity of 5 g kg1 is heated to 180 C. If a change of state of the air during drying takes place without any heat exchange with the surroundings, the enthalpy of the system will not change and hence follow a line parallel to the enthalpy lines, and the change is said to be adiabatic. The drying process shown is assumed to be adiabatic. However, in a real situation in a spray dryer, this is not quite the case. Heat will be added to the system with the warm concentrate (T 6¼ 0 C), but on the other hand, heat is also removed from the system
212 Plant and Equipment | Milk Dryers: Drying Principles
Unbound water
Bound water
ϕ 100
Equilibrium moisture
Evaporated (free) moisture
0 kg H2O kg−1 TS Spray particles Figure 3 Sorption isotherm and common drying terms.
Temperature
Constant drying rate T-out
Partial pressure
Partial pressure
Vapor pressure in exhaust air
Temperature % H2O Equilibrium moisture
Feed to dryer
Residual moisture
Figure 4 Temperature and vapor pressur vs. moisture content during drying.
by transmission loss and with the warm powder leaving the dryer. It is assumed that an RH in the exhaust air of 10% results in the required powder moisture content, which corresponds to a T-out of 87 C. Any additional airflow to the dryer, such as air disperser and atomizer cooling air or integrated fluid bed air, will also have an effect, but for the situation in a conventional dryer, the adiabatic change as shown in Figure 2 is a reasonable approximation. If the drying air rate of a plant is known, the evaporative capacity can be estimated under any given drying conditions (ambient humidity, inlet and outlet temperature). In the example in Figure 2, the ambient humidity is 5 g kg1 dry air and the outlet air humidity is 40 g kg1, that is, the evaporation is 35 g kg1 dry air, which multiplied by the air rate yields the evaporative capacity of the
plant. Likewise, the heat input required to increase the temperature from ambient, say 20 C, to the inlet temperature (T-in) can be read. The enthalpy of air at 20 C and absolute moisture content of 5 g kg1 dry air is approximately 8 kcal kg1 dry air. After heating to 180 C, the enthalpy is approximately 47 kcal kg1 dry air, that is, a heat input of 478 ¼ 39 kcal kg1 dry air is required. It can further be calculated that the specific heat consumption is 35/39 1000 1115 kcal kg1 water evaporation.
Change of state of droplets
When pure water is dried, the water droplets will reach the wet-bulb temperature in the initial stage of drying. However, the presence of dissolved and/or dispersed
Plant and Equipment | Milk Dryers: Drying Principles
solids in the droplets causes the water activity (aw) of the drying product to decrease as drying proceeds. The driving force in the drying process is the difference between the partial vapor pressure in the droplet/air interface and the partial vapor pressure in the surrounding air or (roughly) between aw of the product and the RH of the drying air. Any decrease in aw of the particles or increase in RH of the drying air will reduce the driving force. The relation between aw (or equilibrium RH) and moisture content at constant temperature is called a sorption isotherm. As hysteresis effects are quite common, it is important to differentiate between absorption and desorption isotherms in connection with drying. A typical shape of a sorption isotherm is shown in Figure 3. In practice, the minimum outlet temperature from a spray dryer (the highest RH of the outlet air), and the highest capacity and best drying economy without getting excessive deposits, depends mainly on the corresponding aw. If the particle and gas residence time were infinite, equilibrium between the product and drying air would be reached. However, this is obviously not the case and the outlet air RH must be kept well below the product aw to achieve the desired powder moisture content and achieve trouble-free dryer operation. In Figure 2, it can be seen that the RH at a given absolute humidity is highly dependent on temperature, so the lower RH is achieved by operating at increased outlet temperatures. The outlet temperature is a very important process parameter, and to cope with smaller changes in other key parameters and still maintain constant product moisture content, the following guideline can be given: T -out ¼
T -in x-amb þ %TSþ – K H2 O 10 2:8
ð7Þ
whereT-out is the required change in outlet temperature, T-in is the change in inlet temperature, %TS is the change in percent total solids in the concentrate, x-amb is the change in ambient humidity in g kg1 dry air, K is a product-dependent factor, which is about 5 for skimmed milk powder and 6 for whole milk powder, and H2O is the change in powder moisture content. It can be seen that an increase in T-in of 10 C, an increase in %TS of 1%, and an increase in absolute humidity of 2.8 g kg1 should be compensated for with an increased T-out of 1 C.
Fluid Bed Drying A fluid bed is basically a box, divided by a perforated air distributor plate into a lower clean air plenum section and an upper product section. Different types of fluid beds are used:
• back-mix or plug-flow fluid beds;
213
or vibrated fluid beds; and • stationary external fluid • ing chamber. beds or fluid beds integrated in the dryStationary plug-flow beds are used for products that are easily fluidizable at the inlet conditions of the bed. On the other hand, back-mix beds are used for products that are not directly fluidizable, but may be so when mixed and conditioned with the (partly) dry powder already present in the fluid bed. Fluid bed design and technology will be discussed elsewhere (see Plant and Equipment: Milk Dryers: Dryer Design). Originally, the external, vibrating plug-flow fluid beds were implemented for cooling purposes only, but the advantages of using them for the drying of the last amount of moisture as well were soon realized. When the drying takes place in one stage in the drying chamber, the outlet temperature has to be kept fairly high to maintain the required driving force to achieve the desired final moisture content during the fairly short residence time (10–30 s) in the drying chamber. The residence time in fluid beds is typically in the range of 10–20 min, thus allowing the time-dependent diffusion of moisture to the particle surfaces to take place.
Stickiness and Glass Transition Powder buildup on drying chamber walls is a well-known phenomenon, caused by certain product properties described with terms such as stickiness or thermoplasticity. Thermoplasticity is a very descriptive term that implies that the product plasticizes at elevated temperatures. It is well known that increased powder moisture increases the stickiness of the products. The relation between powder moisture and T-out, influenced by other drying parameters as well, is shown in eqn [7]. It shows that increased T-in or %TS – changes that increase the plant capacity – will result in increased powder moisture content and potentially in powder buildup if not compensated for by T-out. Increased ambient air humidity will have the same effect. However, T-out can only be increased within limits, partly for product quality reasons, but also because the powder particles become sticky at a certain T-out due to thermoplastic behavior, even though the moisture content may be quite low. This phenomenon is shown in Figure 5. It should be emphasized that the sticking curve is a product property that depends on product composition, whereas the T-out–moisture relation (and hence T-particle–moisture relation)
214 Plant and Equipment | Milk Dryers: Drying Principles
Models describing Tg in binary systems (one component and a plasticizer) are available. The Gordon–Taylor model [8] has been used extensively, being a generalization of the Couchman–Karasz equation [9].
Temperature (°C)
Sticking curve
Sticking zone
w1 Tg1 þ kw2 Tg2 w1 þ kw2
ð8Þ
w1 Cp1 Tg1 þ w2 Cp2 Tg2 w1 þ w2 Cp2
ð9Þ
Tg ¼ Tg ¼ Nonsticking zone % Residual moisture T-out
T-particle
T-sticking
Figure 5 Empirical sticking curve. Relationship between moisture content, outlet air temperature, particle temperature, and the sticking point temperature.
depends on product properties (composition) as well as drying conditions (T-in, %TS, etc.). The sticking curve approach described above is a rather empirical one. The use of the glass transition concept in the last decade has formed a more theoretical basis for understanding the phenomena. A glass is an amorphous, high-viscous liquid in a nonequilibrium state, exhibiting the mechanical properties of a solid, but with structural characteristics of a liquid, that is, contrary to the crystalline state, a glass is without any ordered molecular arrangement. Due to the non-equilibrium state, a glass is thermodynamically unstable and can undergo phase transitions. The glass transition in amorphous systems is a reversible change in the physical state from a mechanically solid glass to a viscoelastic, rubbery state, which takes place at the characteristic glass transition temperature, Tg. Tg of a product depends on the product composition and in particular on the presence of plasticizers, of which water is very potent, that is the Tg declines drastically at increased moisture content. In spray-dried milk powders, the lactose is usually in an amorphous state because the drying took place so fast that there was no time for the molecular ordering required for crystallization of the lactose. Hence milk powders exhibit glass transition. Although the glass transition temperature of a milk powder is not identical to the ‘sticking temperature’, defined as the temperature at which powder buildup in dryers may occur, there is still a relation between Tg and the sticking temperature. Indications are that the ‘sticking’ temperature is about 20–25 C above the Tg. Glass transition is accompanied by measurable physical changes in viscosity, heat capacity, and other properties. The change in heat capacity can be measured by differential scanning calorimetry.
where wi is the weight fraction of component i, Tgi the glass transition temperature of component i, k is the softening constant, and Cpi the specific heat change of component i across the glass transition. Table 2 shows the glass transition temperature of some food components. It can be seen that lower molecular weight carbohydrates exhibit lower Tg (monosaccharides < disaccharides, and the higher the DE (dextrose equivalent) of maltodextrins, the lower the Tg). The high Tg of starch and low-DE maltodextrins explains why these components are good ‘carriers’ for more difficult components in spray drying. The extremely low Tg of lactic acid also explains the difficulties of drying acid whey. Although the relation between aw of milk powders and Tg is essentially sigmoidal, it has been found to be almost linear in the aw range of 0.2–0.65, Tg ¼ – 143:6aw þ 77:8
ð10Þ
Knowledge of the parameters in eqn [7] for a given product and drying process together with knowledge of the corresponding desorption isotherm and the glass transition temperature as a function of aw can be very helpful in defining optimized but still safe drying conditions.
Table 2 Glass transition temperature of different food components Component
Tg ( C)
Fructose Glucose Galactose Sucrose Maltose Lactose Maltodextrin DE 36 (MW 550) Maltodextrin DE 25 (MW 720) Maltodextrin DE 20 (MW 900) Maltodextrin DE 10 (MW 1800) Maltodextrin DE 5 (MW 3600) Starch Lactic acid Water (amorphous)
5 31 32 62 87 101 100 121 141 160 188 243 60 135
MW, Molecular Weight, g mol1.
Plant and Equipment | Milk Dryers: Drying Principles See also: Plant and Equipment: Milk Dryers: Dryer Design.
Further Reading Carı´c M (1994) Milk Powder: In Concentrated and Dried Dairy Products: General Production. New York: VCH Publishers.
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Masters K (1991) Spray Drying Handbook. Essex, UK: Longman Scientific & Technical. Masters K (2002) Spray Drying in Practice. Denmark: SprayDryConsult International ApS, Charlotlenlund. Pı´secky´ J (1997) Handbook of Milk Powder Manufacture. Copenhagen, Denmark: Niro A/S. Vuataz G (2002) The phase diagram of milk: A new tool for optimising the drying process. Le Lait 82: 485–500. Westergaard V (1994) Milk Powder Technology. Evaporation and Spray Drying. Copenhagen, Denmark: Niro A/S.
Milk Dryers: Dryer Design M Skanderby, GEA Niro A/S, Soeborg, Denmark ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by V. Westergaard, Volume 2, pp 871–889, ª 2002, Elsevier Ltd.
Introduction This article focuses on spray dryers. Although other means of drying are possible, this is by far the most common in the dairy industry. By definition, spray drying is the transformation of a product from a fluid state into a dried form by spraying the liquid feed into a hot drying medium. The feed can be a solution, a suspension, or a paste, depending on the characteristics of the dairy product to be dried. The dried product is a powder consisting of single particles or agglomerates, all depending on the chemical composition and physical properties of the feed as well as on dryer design and operation.
Drying Principles A spray dryer operates in the following way: The feed is pumped from the product feed tank to the atomizing device that is situated in the air disperser at the top of the drying chamber. The drying air is drawn from the atmosphere via a filter by a supply fan and is passed through the air heater to the air disperser. As the atomized droplets meet the hot air, evaporation takes place cooling the air at the same time. After the drying of the atomized feed in the chamber, the majority of the dried product falls to the bottom for further processing. The fines, which are the particles with a small diameter, will remain entrained in the air. Therefore, the air has to pass through powder collectors like cyclones or bag filters. The air passes from the powder collector to the atmosphere via the exhaust fan. The two fractions of powder are collected, for example, in a pneumatic system for conveying and cooling. After separation in a cyclone, the powder is bagged off. A conventional spray dryer consists of the following main components (Figure 1): 1. 2. 3. 4. 5. 6.
Drying chamber Hot air system and air distribution Feed system Atomizing device Powder separation system Pneumatic conveying and cooling system
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7. Integrated fluid bed 8. Fluid bed after-dryer/cooler
Drying Chamber Various designs of the drying chamber are available on the market. The most common one is a cylindrical chamber with a cone of 40–60 , enabling the powder to leave the chamber by gravity. The chamber is also found with a flat bottom in which case a scraper or suction device is needed for removing the powder fraction from the chamber. Horizontal box-type drying chambers are also used, and they, too, operate with a forced (i.e., scraper or screw) powder removal system (Figure 2). Generally, it can be concluded that chambers with a cone for gravity discharge of the powder give the best flexibility for adapting various drying processes like integrated fluid beds or belts to the plant and therefore offer the greatest possibility for drying different products. The tendency in modern designs of drying chamber is to avoid any object inside the chamber that can obstruct the air flow. In the chamber of the TALL FORM, the emphasis has been put on designing a plant with a laminar air flow and a special air outlet system, where the diameter of the cone is bigger than the diameter of the cylindrical part thus forming a ring duct termed ‘bustle’. This minimizes the cyclone fraction by the low velocity of the exhaust air. This chamber is especially suited for infant milk formulae or protein products dried from low-solid content feed. The drying chamber should always be equipped with inspection doors and overpressure vents to withstand a pressure of 1.6 mbar(g). Other safety equipment such as fire extinguishing equipment in the form of water or steam nozzles is always standard in a modern dryer. Drying chambers are usually insulated, either with removable air-filled sandwich panels (see Figure 3) or with 80–100 mm mineral wool covered with a stainlesssteel plate. The advantage of the removable panels is that inspection for cracks in the chamber wall is possible. Furthermore, the risk of having wet insulation material, which can foster bacterial development or cold spots on the chamber wall, is eliminated.
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Ring-formed fluid bed (compact drying chamber) 4
3 1
2
5 6
7
8
Figure 1 Spray drying plant. 1, Drying chamber; 2, Hot air system and air distribution; 3, Feed system; 4, Atomizing device; 5, Powder separation system; 6, Pneumatic conveying and cooling system; 7, Integrated fluid bed; 8, Fluid bed after-dryer/ cooler.
Integrated Static Fluid Bed In an attempt to improve the drying efficiency, a static fluid bed is integrated in the drying chamber. The secondary drying air, typically 25% of the main drying air, is introduced into a plenum chamber below a perforated plate, through which the drying air is distributed. This type of dryer can be operated in such a way that the primary particles reach a moisture level higher than that obtained by using the VIBRO-FLUIDIZER. A specially designed and patented perforated plate, the BUBBLE PLATE (see Figure 4), provides an air– powder mixture that ensures optimal drying without attrition and powder penetration into the clean-air plenum. Furthermore, the BUBBLE PLATE has a more sanitary finish than the other types of perforated plates. The static fluid bed is available in two configurations: fluid bed (compact drying chamber) • Ring-formed Circular fluid bed (multistage drying (MSD) chamber) •
The ring-formed back-mix bed is placed at the bottom of a conventional chamber cone around the exhaust duct placed in the center. The powder is discharged continuously from the static fluid bed by overflowing an adjustable powder weir, thus maintaining a certain level of fluidized powder. When the powder leaves the drying chamber it may be cooled in a pneumatic conveying or VIBRO-FLUIDIZER system. The resulting powder will consist of single particles. For fat-containing products, cooling should be done in a vibrating fluid bed that is also used when agglomerated powders are produced. In this case, the cyclone fraction is returned to the atomizer device for agglomeration (see Figure 5). Circular fluid bed (multistage drying (MSDTM) chamber)
To improve the dryer efficiency and the powder properties even further, the multistage dryer MSD has been designed (see Figure 6). The dryer operates with three drying stages, each adapted to the moisture content prevailing during the drying process. In the preliminary drying stage, the concentrate is atomized by co-current nozzles or a rotary atomizer placed in the hotdrying air duct. Air enters the dryer vertically through the air disperser, ensuring optimal mixing of the atomized droplets with the drying air. The particles reach a moisture content of 6–15%, depending upon the type of product. The fluid bed is supplied with air at a sufficient velocity and temperature for the second-stage drying. The drying air from the preliminary drying stage and the integrated fluid bed leaves the chamber from the top passing through powder separators. This type of dryer offers a perfect choice if the aim is to produce an agglomerated product. Owing to the velocity of the primary drying air, a venturi is formed around the atomizing device, thus sucking in secondary air with powder entrained so that agglomeration is facilitated, that is, attrition between the primary spray particles and the fines powder. When the powder has reached a certain moisture content it is discharged via a rotary valve into a VIBROFLUIDIZER for the final drying and subsequent cooling. The powder exhibits a coarse powder structure originating from the natural agglomeration taking place in the chamber.
Hot Air System and Air Distribution Air Filtration System Until a few years ago, no special requirements were placed on filtration of the process air for the spray drying process. Today, however, very strict requirements are presented by local authorities to ensure a cleaner
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1
2
3 4
5
7
8
6
9
Drying air Cooling air Concentrate/product Fines Figure 2 Different types of drying chambers. 1, TALL FORM dryer type seen in Japan. It is equipped with a low-velocity air disperser, and, although it is used for milk, it is not very suitable for this product; 2, TALL FORM dryer with high-temperature primary drying air. Secondary air is sucked into the drying chamber during the drying operation. The ‘mix’ air temperature is similar to that of a normal spray dryer; 3, Conventional TALL FORM DRYER chamber used predominantly for baby food and protein products; 4, Conventional drying chamber with conical bottom; 5, Box dryer for one-stage drying only – poor economy and normally seen only in the United States; 6, Multistage MSD drying chamber with integrated fluid bed; 7, Conventional COMPACT drying chamber with integrated fluid bed; 8, Flat-bottom spray drying chamber for one-stage drying only. No longer seen on new installations; 9, FILTERMAT drying chamber in a special design for very sticky products.
operation and a higher level of food safety. Common for the different standards are as follows: air should be prefiltered and supplied by a separate • The fan to the fan/filter/heater room, which must be under
•
pressure to avoid the entry of unfiltered air (Figure 7). As an alternative to a fan room, complete ducting of all air flows is fully acceptable. Filtration degree and filter position depend on the final temperature of the process air as follows: – For air to be heated above 120 C only coarse filtration up to 90% (filter class EU7/F7) is needed. The filter should be placed on the pressure side of the fan.
– For air to be heated below 120 C or not heated at all, the filtration must be 95% (filter class EU/F9) or above, and the filter must be placed after the heater/ cooler. Some countries and companies have even stricter requirements demanding a filtration of up to 99.995% (filter class EU13-14/ H13-14).
Air Heating System The drying air can be heated in different ways: indirect (steam/oil/gas/hot oil/electricity) or direct (gas).
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Figure 3 Removable insulation panels for spray drying chambers.
Figure 4 BUBBLE PLATE.
Indirect heating
A steam heater is a simple radiator. The temperature to be obtained depends on the steam pressure available. The air heater consists of rows of finned tubes housed in an insulated metal case. The heat load is calculated from the quantity and specific heat of the air. The heater size depends on the heat transfer properties of the tubes and fins and is usually about 50 kcal C1 h1 m3 for an air velocity of 5 m s1. To avoid corrosion of the tubes in the air heater, use of stainless-steel tubes is recommended. In indirect oil and gas heaters, drying air and combustion gases have separate flow passages. The combustion
gases pass through galvanized tubes, which act as the heat transfer surface for the drying air. The combustion chamber is made of heat-resistant steel. Heaters of this type will have an efficiency of about 85% in the range of 175–250 C (see Figure 8). Hot oil liquid phase air heaters are used either alone or to boost the inlet drying air temperature when the steam pressure is not high enough. The heater system consists of a heater, which can be gas- or oil-fired, and an air heat exchanger. Between these two components, a special food-grade oil or heat transfer fluid, which does not crack at high temperatures, is circulated at high speed.
220 Plant and Equipment | Milk Dryers: Dryer Design
Air
Figure 7 Filtration of process air.
Figure 5 Compact spray dryer with VIBRO-FLUIDIZER as agglomerator/instantizer (CDI).
as boosters instead of, for example, hot oil liquid phase air heaters. Direct heating
Direct gas heaters are used only when the combustion gas can be allowed to come into contact with the product. They are, therefore, not common in the dairy industry. Direct gas heaters are inexpensive, they have a high efficiency, and the obtainable temperature can be as high as 2000 C. When a plant is designed with an air heater with direct combustion, it is necessary to calculate the amount of vapor resulting from the combustion (44 mg kg1 dry air C1), as this will increase the humidity of the drying air. The outlet temperature has therefore to be increased to compensate for this increase in humidity and to maintain the relative humidity. The heater system can be designed with separate heaters for each consumption point or with fewer heaters, of which some supply two or more consumption points. By mixing warm air from the main air heater with cold air, the entire dryer can be run with only one heater. Figure 6 Multistage spray dryer (MSD).
Air Distribution System
The main advantage of a hot oil liquid phase heater is that it is an open, pressureless system. Electrical air heaters have for many years been used mainly for laboratory and pilot plant spray dryers. This heater has low investment costs, but previously the operation costs were considered to be too high for commercial production. However, as the price of electricity in certain parts of the world can be very low during off-peak periods, it is becoming more common to use electrical heaters
Drying-air distribution is one of the most vital functions in a spray dryer. There are various systems depending on the plant design and the type of product. The most common system is where the air disperser is situated on top of the dryer ceiling, and the atomizing device is placed in the middle of the air disperser, thus ensuring an optimal mixing of the air and the atomized droplets. In cylindrical vertical dryers, the whole ceiling may be perforated, thus creating a plug-flow air stream – numerous nozzles are situated in the perforated plate to
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Indirect steam-heated air heater
Cold air in Hot air out
Oil Combustion air
Figure 8 Indirect air heaters.
ensure that the air is cooled by the concentrate. This system, however, operates with a low air velocity, and it makes fines return complicated. It is therefore not suitable for all dairy products. It should be noted that an air disperser should have the ability to guide the air and the atomized droplets in the right direction to avoid deposits in the drying chamber. Two different types of air dispersers are currently used in spray dryers for food and dairy products:
Concentrate
Drying air
Cooling air
Rotary air stream
The air enters tangentially into a spiral-shaped distributor housing (see Figure 9), from where the drying air is
Figure 9 Ceiling air disperser with adjustable guide vanes.
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led radially and downward over a set of guide vanes provided for adjustment of air rotation. This type of air disperser is used for rotary atomizers and nozzle atomizers placed in the center of the air disperser and is used in conventional drying chambers.
7
1
Plug flow air stream
The air enters radially through one side (see Figure 10) and is distributed through a specially designed air guiding arrangement, which ensures a uniform air flow pattern in the entire air disperser area. This enables a very precise, laminar, high-velocity plug flow, which is required in TALL FORM dryers or multistage dryers. This type of air disperser is used for nozzle atomizers only, and has excellent possibilities for nozzle position adjustment and thereby the adjustment of agglomeration structure.
Feed System The feed system (see Figure 11) is the link between the evaporator and the spray dryer, and comprises the following: 1. Feed tanks 2. Water tank
1
4
2
5
6
3 Figure 11 Feed system. 1, Feed tanks; 2, Water tank; 3, Concentrate pump; 4, Preheating system; 5, Filter; 6, Homogenizer/high-pressure pump; 7, Feed line, including return line for CIP.
3. 4. 5. 6. 7.
Concentrate pump Preheating system Filter Homogenizer/high-pressure pump Feed line, including return line for cleaning-in-place (CIP)
Feed Tanks
Fines
Cooling air
Drying air
If feed tanks are used, the use of two tanks is recommended so as to change from one to the other at least once an hour to avoid the risk of bacteria growth. One is therefore in use while the other one is being cleaned. The size of each tank should correspond to 15–30 min of the feed capacity of the dryer. The feed tanks are very often omitted, and the last-stage evaporator is designed as a buffer tank under vacuum. The evaporator then operates as a ‘slave’ to the dryer, because the level switches in the evaporator buffer tank control the inlet feed to the evaporator. Water Tank The water tank is used during the start and stop of the plant, and during the run if there is a sudden shortage of concentrate. It is used only when the evaporator is used as a buffer tank. As an alternative, a direct water supply to the feed line is often used. Concentrate Pump
Concentrate
Figure 10 Plug flow air disperser.
If a rotary atomizer is used, the most common feed pump is the mono type, as it has lower energy consumption and can handle concentrates of high viscosity. In plants equipped with homogenizers for the production of whole milk powder, the homogenizer is used as a feed pump. In plants equipped with high-pressure nozzles, a high-pressure pump is used – often combined with a homogenizer.
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Preheating System Preheating of the concentrate to a higher temperature than that coming from the evaporator is advantageous, not only from a bacteriological point of view. It also produces a decrease in viscosity, which together with the applied calories results in a capacity increase of the spray dryer and an improved solubility of the powder produced. The heating can be either indirect or direct. Indirect preheaters may be of the following types: 1. Spiral-tube heat exchanger 2. Plate heat exchanger 3. Scraped-surface heat exchanger Spiral-tube heat exchanger
The spiral-tube heater (see Figure 12), often with corrugated tubes, is able to heat a concentrate with high solid content to a higher temperature without frequent scaling and cleaning owing to high product velocity and a low T throughout the heater. Furthermore, this type of heater has no moving parts; hence, maintenance costs are minimized.
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temperatures are required. They can operate continuously for 20 h and are cleaned together with the remaining feed system. The disadvantages are high cost of maintenance as well as big variation in holding time. Direct preheaters may be of the following types: steam injection (DSI) • Direct Lenient steam injection (LSI) • Direct steam injection
In the DSI unit, steam is introduced into the milk concentrate via a nozzle, producing relatively big steam bubbles resulting in a superheating of some parts of the concentrate, which leads to protein denaturation. Lenient steam injection
In the LSI unit, steam is mixed into the concentrate by a dynamic mixer. Very small steam bubbles are created, and superheating/denaturation is avoided. Therefore, a much higher steam pressure can be used. The LSI unit can be used in combination with the spiral-tube heat exchanger if temperatures above 80 C are required in the concentrate. Filter
Plate heat exchanger
A plate heat exchanger system is inexpensive, but if the concentrate should be heated to >70 C, if the solid content is >46%, or if a 20 h run is aimed at, it is necessary to have two interchangeable heaters allowing one to be cleaned while the other is being used. Steam or warm water can be used as the heating medium. Scraped-surface heat exchanger
In the scraped-surface heater, the heat transfer surface is continuously scraped off by a fast-rotating scraper made of food-grade synthetic material to avoid any product adherence. The scraped-surface heater is especially suitable for products with high solid content and when high
An in-line filter is always incorporated in the feed system after the heater to avoid lumps, etc., passing to the atomizing device. Homogenizer/High-Pressure Pump If whole milk powder is to be produced, it is recommended that a homogenizer be incorporated to reduce the free-fat content in the final powder. A two-stage homogenizer is preferred; the first stage is operated at 50–100 bar g, and the second stage at 25–50 bar g. Usually the homogenizer and feed pump are combined in one unit. If nozzle atomization is used, then a higher pressure (up to 250 bar g for the nozzles þ 150 bar g for homogenizing) is required, and a combined homogenizer/ high-pressure pump is chosen. Temperatures of 80 C are needed to produce a whole milk powder with a good coffee stability. In view of calcium phosphate precipitation – which is abrasive – the pistons should be made of a ceramic material. Feed Line
Figure 12 Spiral-tube heat exchanger.
The feed pipe should be of stainless steel and, of course, of the high-pressure type if atomization is to be carried out by means of nozzles. The dimensions of the pipe should be such that the feed velocity is 1.5 m s1. In a feed system, a return pipe should also be included for the cleaning solution, so that the entire equipment can be cleaned thoroughly.
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Atomizing Device The aim of atomizing the concentrate is to provide a very large surface from which evaporation can take place. The smaller the droplets, the bigger the surface and the easier the evaporation; and thus a better thermal efficiency of the dryer is obtained. The ideal from the point of view of drying would be a spray of drops of the same size, which would mean that the drying time for all particles would be the same to obtain an equal moisture content. As mentioned previously, air distribution and atomization are the factors key to the successful utilization of the spray dryer. Atomization is directly responsible for many distinctive advantages offered by spray drying: First, the very short drying time of the particles; second, a very short particle retention time in the hot atmosphere and a low particle temperature (wet bulb temperature); and, finally, the transformation of the liquid feed into a powder with long-storage stability ready for packing and transport. In summary, the primary functions of atomization are
5
4 3
a high surface-to-mass ratio resulting in a • tohighcreate evaporation rate create particles of the desired shape, size, and • todensity
2
1. Nozzle body 2. Orifice insert 3. Swirl chamber 4. End plate 5. Screw pin
1 Figure 13 High-pressure nozzle ‘Delavan’.
To comply with these requirements many atomization techniques have been used in spray dryers. However, the most common ones can be summarized as follows:
• • •
pressure nozzles using pressure forces two-fluid nozzles using kinetic forces rotating discs using centrifugal forces
Pressure Nozzle Atomization The basic function of pressure nozzles is to convert the pressure energy supplied by the high-pressure pump into kinetic energy in the form of a thin film, the stability of which is determined by the properties of the liquid such as viscosity, surface tension, density, and quantity per unit of time, and by the medium into which the liquid is sprayed. Most of the commercially available pressure nozzles are designed with a swirl chamber giving the liquid a rotation, so that it will leave the orifice as a hollow cone (see Figure 13). Capacity can usually be assumed to be directly proportional to the square root of pressure retain: Capacity ðkg h – 1 Þ ¼ K
pffiffiffi P
As a rule of thumb, higher viscosity, liquid density, and surface tension, and lower pressure will result in bigger particles. Typically, a feed rate of 1000–1500 kg h1 per
nozzle is used in industrial dryers. The advantages when using high-pressure nozzles are as follows: with a low level of occluded air • Powder with a high bulk density • Powder flowability, especially for whole milk • Improved to form less deposits in the drying chamber • Tendency when difficult products are produced • Ability to produce big particles Two-fluid nozzle or pneumatic atomization
The energy available for atomization in two-fluid atomizers is independent of liquid flow and pressure. The necessary energy (kinetic) is supplied by compressed air. Two-fluid atomization is the only successful nozzle method for producing very small particles, especially from highly viscous liquids. It is not normally used in the drying of milk products. However, it is often used in secondary systems such as lecithin application to the powder. Rotary atomization
In rotary atomizers the liquid is accelerated continuously to the wheel’s edge by the centrifugal forces produced by the rotation of the wheel. The liquid is distributed centrally, then extended over the wheel surface in a thin sheet and discharged at a high speed at the periphery of
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Viscosity of the liquid
Droplet size varies directly with viscosity, and bigger particles are obtained when the viscosity of the feed is higher. To ensure an optimal atomization, the viscosity is therefore normally kept as low and as constant as possible, often by heating the concentrate prior to atomization. Regarding droplet size distribution, it becomes broader with increased viscosity – an effect sometimes used when bulk density of the powder is to be increased. Rotary atomizer has been known and used in the dairy industry for many years; its main advantages are as follows: in throughput • Flexibility Ability to handle quantities • Ability to handle large highly concentrates • Different wheel designsviscous giving different powder • characteristics to handle products containing crystals • Ability Ability handle higher solid content in the feed; • therefore,to better economy
Figure 14 Rotary atomizer with direct drive.
the wheel. The degree of atomization depends upon peripheral speed, properties of the liquid, and feed rate (Figure 14). To select an optimal atomizer wheel, the following factors should be taken into consideration: Liquid feed rate
Droplet size varies directly with feed rate at a constant wheel speed and will increase with increased feed rate. Peripheral speed
The peripheral speed depends on the diameter of the wheel and the wheel speed, and is calculated as follows: Vp ¼
DN 1000 60
where Vp is the peripheral speed (m s1), D the diameter of the wheel (mm), and N the speed of the wheel (rpm). Peripheral speed is widely accepted as the main variable for the adjustment of droplet size. However, it has been shown that droplet size does not necessarily remain constant when equal peripheral speeds are produced in wheel designs of various diameter–speed combinations, as there is a tendency for bigger wheels to produce bigger particles, all other things being equal. However, in the choice of wheel diameter, one should rather look at the reliability of the atomizer, as the differences in spray characteristics are negligible.
To decide whether to use a pressure nozzle or rotary wheel is therefore a question of achieving the demanded properties of the final dried product, given the properties of the feed.
Powder Separation System As the drying air leaving the chamber will contain a small proportion of the powder (10–30%), it is necessary to clean it by separating the powder particles. This powder fraction is usually referred to as the ‘fines’, as they normally represent the smallest particles. The most widely used separators in the milk powder industry are
• Cyclone filter • Bag CIP-able bag filter • Wet scrubber • Combinations of the above • Cyclone Cyclone has some obvious advantages, such as high efficiency, if constructed properly. It is easily maintained, as there are no moving parts. Furthermore, it is easy to clean if the construction is with a fully welded center cyclone. The operation theory is based on a vortex motion where the centrifugal force is acting on each particle and therefore causes the particle to move away from the cyclone axis toward the inner cyclone wall. However, the movement in the radial direction is the result of two opposing forces where the centrifugal force acts to move
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compromise is sought with bigger sizes at the expense of high efficiency. Thus, the cyclones have become bigger and bigger and are now constructed with diameters of up to 4.0 m. When designing a cyclone, various key factors should be taken into account to obtain the highest efficiency. This is achieved if
Air
cyclone diameter 3 exit duct diameter
Air with powder
cyclone height 10 exit duct diameter Inside view of cyclone
Powder
Figure 15 Cyclone.
the particle to the wall, while the drag force of the air acts to carry the particles into the axis. As the centrifugal force is predominant, separation takes place. Powder and air pass tangentially into the cyclone at equal velocities. The mixture swirls in a spiral form down to the base of the cyclone separating the powder out to the cyclone wall. Powder leaves the bottom of the cyclone via a locking device. The clean air spirals upward along the central axis of the cyclone and leaves the cyclone at the top (see Figure 15). The centrifugal force that each particle is exposed to is given by the following equation: C¼
m Vt 2 r
where C is the centrifugal force, m the mass of the particle, Vt the tangential air velocity, and r the radial distance to the wall from any given point. From this equation it can be concluded that the higher the particle mass, the better the efficiency. Also, the shorter distance the particle has to travel, the better the efficiency; that is, the closer the particle is to the wall, the better the efficiency, because the velocity is the highest and the radial distance is short. However, time is required for the particles to travel to the cyclone wall, so a sufficient air residence time should be taken into consideration when designing a cyclone. From the above equation, it is evident that small cyclones (diameter <1 m) will have the highest efficiency, a fact that is generally accepted. However, as the big-tonnage dryers in operation in dairy industry today would require many cyclones, a
Increased air throughput (velocity Vt) and increased pressure drop will also increase the efficiency, but the energy requirement will also increase simultaneously, so in general the upper limit is 175–200 mm WG for skim milk powder. For whole milk, 140–160 mm WG is the maximum so that deposits and final blocking can be avoided. To determine a cyclone’s efficiency, the following terms have to be defined: particle diameter • critical cut size • overall cyclone efficiency • Critical particle diameter is defined as the particle size that will be completely removed from the air flow (100% collection efficiency). However, as there is no sharply defined point where a particle size is 100% separated or 100% lost, the critical particle diameter is not very valuable. Cut size is defined as the size for which 50% collection is obtained and is a much more useful parameter for stating the efficiency of cyclones. To determine a cyclone’s cut size, grade efficiency curves are constructed by systematically operating the cyclone with a uniform particle size dust (see Figure 16). Overall cyclone efficiency is the one obtained when handling a product of definite size distribution. Knowing the grade efficiency curve of the cyclone and the particle size distribution of the powder passing to the cyclone, the overall efficiency can be calculated, that is, the powder loss can be predicted. Another method for determining cyclone efficiency is by a simple powder loss measurement at the exit of the cyclone. A very small fraction of the outgoing air is passed through a high-efficiency minicyclone or through microdust filters. The amount of powder collected is directly proportional to the powder loss, which will mainly be a result of with low solid content or feed containing air • Feed High outlet air temperature • Low particle density (e.g., as a result of the above) • Leaking product on account of old-fashioned • nonadjustable rotaryoutlet valves
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105 D
Theoretical curve E Theoretical critical particle diameter
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Actual critical particle diameter
Actual curve
Cut size
Collection efficiency (%)
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60 80 100 Particle size (µm)
120
60 70 40 50 Particle size (µm)
80
140
Grade efficiency (%)
100 80 60 40 20
0
30
90
100
Figure 16 Critical particle diameter vs. grade efficiency curves for a cyclone.
cyclone • Blocked Changes in drying parameters resulting in a decrease • in mean particle size
blowing compressed air through the filter bags from the inner side. This powder is collected at the bottom via a rotary valve (see Figure 17).
Average powder loss from a normal, high-efficient cyclone should not exceed 250 mg Nm3 when spray drying skim milk.
Wet Scrubbers
Bag Filters However, local authorities in general conclude that 250 mg Nm3 is too high, thus requiring a final cleaning of the air. This is usually done by using bag filters consisting of numerous bags or filters arranged in such a way that all bags receive almost equal quantities of air. The direction of the air is from the outside, through the filter material, to the inner part of the bag from where the cleaned air enters an exhaust manifold. With a correct selection of filter material high efficiencies can be achieved, and collection of 1 m particles has been reported by manufacturers. The collected powder is automatically shaken off by
The wet scrubber is based on the venturi scrubber principle. The droplet separator is designed according to the well-known cyclone principles, however, with a modified outlet, resulting in a minimum liquid level, thereby minimizing bacterial growth, and a design ensuring deaeration, thus avoiding foam building. The principle of venturi wet scrubbers is as follows (see Figure 18). The outlet air from the spray dryer containing powder particles is accelerated to a high velocity in the venturi inlet, where the liquid also is injected through full-cone nozzles. Due to the different velocities of the air/particles and the liquid droplets, they will collide, and the powder will dissolve in the liquid droplets. Passing through the subsequent diffuser this process will continue simultaneously with a certain pressure recovery of the air–droplet mix.
228 Plant and Equipment | Milk Dryers: Dryer Design
Compressed air
Air
Powder Air with powder
Powder
Air with powder
Powder
Figure 17 Bag filter.
Recirculation of water
Air with powder
Air + vapor
Scrubbing liquid recirculation
According to the above description of the principle, water is recycled by means of a centrifugal pump. The flow is controlled by a valve. The level is kept constant in the separator by a tank with an adjustable float simultaneously ensuring addition of water to make up for the evaporation taking place in the scrubber. The evaporation takes place owing to the high temperature of the air from the dryer, which is 90–95 C for example, being cooled to the wet-bulb temperature (45–50 C), at the same time evaporating the water (see Figure 19). As the temperature of the water continues to be around 40–45 C, bacterial growth must be expected after some time, and a CIP-able system is therefore recommended. The scrubbing liquid is used as animal feed.
CIP-Able Bag Filters
Figure 18 Sanitary wet scrubber.
Passing through the separator, the air and the liquid are separated. The air leaves through the central duct and the liquid through the bottom outlet for further processing or recycling depending on the system selected.
Common for all powder separators is the pressure drop across the cyclones, bag filters/scrubbers, or combinations thereof. In a continued effort to comply with the authority’s demand for reduced powder emission and the powder producer’s demand for lower energy consumption figures and reduced space requirements, an optimized powder recovery system has been developed – the CIP-able bag filter – which replaces the cyclones as well as the bag filter.
Plant and Equipment | Milk Dryers: Dryer Design
Air out
Air in
Milk in
Water in
Powder out Figure 19 Wet scrubber recycled with water.
Based on almost 10 years of research, development, and testing of a CIP-able bag filter by GEA Niro, the SANICIP filter has reached a point where it is setting the standard for almost all dryers. The SANICIPTM bag filter
The SANICIPTM bag filter (see Figure 20) is of the reverse-jet type. It consists of a cylindrical bag housing with a spiral-shaped air inlet, a clean-air plenum on top, and a conical bottom with fluidized powder discharge. During operation, the product collected on the outside of the filter material is removed by a compressed-air jet stream from the inside of each bag. The bags are cleanblown individually, resulting in a very even discharge of the powder. The air supply system for the fluidizing bottom has a multiple purpose: During production, the cone of the bag house is first heated by the warm air, which subsequently is used for fluidizing the powder in the bottom. This ensures an even powder flow out of the bag house. During standstill, the air is used for the heating of the cone alone and is in a closed loop. The filter bags are made from a special three-layer gradient polyester material, which is heat-treated to give a special dust-releasing surface. Each bag is supported on a stainless-steel cage and is easily dismountable. In the SANICIP filter, a special reverse-jet air nozzle positioned above each bag (see Figure 21) is
Figure 20 SANICIP CIP-able bag filter.
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230 Plant and Equipment | Milk Dryers: Dryer Design
thereby avoiding discoloring/denaturation. The water is recirculated. 4. The shell CIP is performed by means of standard retractable CIP nozzles. The water is recirculated. Normal acid and caustic are used as CIP agents. The CIP is followed by bag drying. Estimated time for complete CIP and dry out is 10 h. Advantages of the SANICIP filter as follows: pressure loss across the bag filter and, thus, across • Low the entire exhaust system; that is, reduced energy con-
Figure 21 Reverse-jet air nozzle.
used. Compressed air is blown into the bag through this nozzle. A jet is formed that draws into the bag air from the clean-air plenum as well, thereby saving compressed air. The CIP system of the bag house is divided into the following main items: 1. The internal bag CIP system cleans the bag from the inside toward the powder side (outside). Clean water is injected into the inside of the bag through the reversejet nozzle and the water is atomized by compressed air. Powder that has penetrated into the bag material is forced out toward the powder side by the water spray. No recirculation of water in this step. 2. The clean-air plenum CIP cleans the clean-air plenum of the bag filter above the hole plate. No recirculation of water in this step. 3. The hole plate CIP cleans the bottom side of the hole plate and the snap ring area of the bag using a specially designed nozzle, also with a dual purpose: During the process, the nozzle is purged with compressed air to keep the hole plate free of deposits,
• • • • • •
sumption and noise emission Designed for optimum air-to-cloth ratio and powder load (owing to one bag being blown at a time) Higher yield from raw materials owing to the absence of second-grade products Designs with 4 or 6 m bags to suit specific building requirements Reduced space requirements for new installations Easy replacement of cyclones for retrofits without major building changes Short dry-out time, as compared with other CIP-able bag filters
The pros and cons of all the above-mentioned powder recovery tools are listed in Table 1.
Final Drying and Cooling of Powder Pneumatic Conveying and Cooling System A pneumatic conveying system is established when powder has to be conveyed from one place to another. The conveying medium is air, and the quantity is determined by the product. Products with a high fat content require more air (5 times the powder) than that required by skimmed milk (4 times the powder). It is, however, not recommended that powders with
Table 1 Comparison of powder separators
Emission Pressure loss – exhaust system (including ducts, etc.) Auxiliaries Cleaning Hygroscopic products Use of separated product Maintenance
Sanitary conditions
Cyclone
Cyclone þ bag filter
Cyclone þ wet scrubber
SANICIPTM
20–400 mg Nm3 280 mm WG
5–20 mg Nm3 340 mm WG
max. 20 mg Nm3 340 mm WG
5–20 mg Nm3 170 mm WG
None Suitable for CIP Insensitive First grade
Compressed air Difficult Sensitive First and second grade
Liquid circulating system Suitable for CIP Insensitive Not recommended
Compressed air Suitable for CIP Insensitive First grade
Minimal
Servicing of compressed air system and change of bags
Minimal
Good
Relatively good
Less good
Servicing of compressed air system and change of bags Good
Plant and Equipment | Milk Dryers: Dryer Design
a fat content higher than 30% be conveyed, as blocking may occur in the ducts. Air at any temperature may be used, and the powder temperature will naturally follow the air temperature. If hot air is used there will be a drying effect. This will, however, be minimal, as the residence time is short (air velocities of 20 m s1). A pneumatic conveying system is inexpensive and can handle large quantities of powder, but it will destroy any agglomerates, resulting in a powder with maximum bulk density. The powder is separated from the conveying air in a cyclone. Fluid Bed After-Dryer/Cooler In modern dryers, pneumatic conveying and cooling systems are replaced by a VIBRO-FLUIDIZER, which is designed also as an after-dryer, that is, drying is divided into two or more steps. The first step is done in the spray drying chamber transforming the liquid into powder particles and evaporating the main portion of water. The subsequent drying is done in a fluid bed (see Figure 22). The fluid bed drying technology has proved
especially suitable, as the residence time in the fluid bed is so long that the moisture from the center of the particle can reach the surface from where evaporation takes place. The VIBRO-FLUIDIZER is a horizontal box divided into an upper and a lower section by a perforated plate welded to the side wall of the box (see Figure 23). For drying, or alternatively cooling, warm or cold air is introduced into the air plenum chamber, which is distributed evenly over the whole area of the perforated plate. The perforation and amount of air are determined by the air velocity necessary for the fluidizing of the powder; however, special care must be taken to avoid attrition of agglomerates. The temperature and area are determined according to the required evaporation duty. The hole size in the perforated plate is chosen to give an air velocity high enough to fluidize the powder on the plate. The air velocity should be so high that the fines powder becomes airborne and leaves the fluid bed with the air, and is returned to the atomizing zone for agglomeration. The fluid bed can also be designed as a static back-mix bed integrated in the drying chamber.
Powder in
Air out
Drying air in Cooling air in
Powder out
Figure 22 VIBRO-FLUIDIZER.
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232 Plant and Equipment | Milk Dryers: Dryer Design
Figure 23 Construction detail of a sanitary VIBRO-FLUIDIZER.
Fines Return System Agglomeration means getting smaller particles to adhere to each other to form a powder consisting of bigger conglomerates/agglomerates, which are essential for easy reconstitution in water. By means of a fines return system, the cyclone fraction(s) is(are) conveyed back to the atomizer mist, the static fluid bed, or the VIBROFLUIDIZER, depending on the required degree of agglomeration. Fines return systems consist of the following: blowers (the quantity of air is depen• High-pressure dent on the amount of fines – typically, 1 kg of air can convey 3–5 kg of powder)
valves (devices to discharge powder • Blow-through from cyclones and/or bag filters into the conveying
• •
line) Conveying line/diverter valves to convey the fines powder to the desired destination – typically a 76–102 mm (3–4 inch) pipe Fines introduction to the atomization zone
The aim is to bring the fines as close as possible to the atomizer wheel. In modern dryers, fines are introduced from above through the air disperser (FRAD system) via four fines pipes situated just above the atomizer cloud. Deflector plates at the end of each fines pipe ensure a correct introduction and distribution of the fines (see Figure 24).
Cooling air
Fines Concentrate
Figure 24 Fines return for rotary atomizer FRAD.
Fines
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Cooling air Concentrate Fines Fines
Concentrate Cooling air
Drying air
Cooling air
Rotary air steam
Plug flow air steam
Figure 25 Fines return for nozzle atomizer.
For nozzle atomization, the fines return is an integral part of the nozzle unit with the fines duct in the center surrounded by nozzles at the periphery (see Figure 25), provided the dryer is designed for rotary air flow or is with vertical air flow.
See also: Analytical Methods: Sampling; Sensory Evaluation. Dehydrated Dairy Products: Milk Powder: Physical and Functional Properties of Milk Powders; Milk Powder: Types and Manufacture; Infant Formulae. Milk Protein Products: Milk Protein Concentrate; Whey Protein Products. Plant and Equipment: Evaporators; Milk Dryers: Drying Principles. Rheology of Liquid and Semi-Solid Milk Products.
Conclusion Spray drying plants are designed today to fulfill many requirements, including low energy consumption, high final-product quality, reduced space requirements, and a high degree of environmental protection – a challenge taken up by the designers and suppliers of the dryers.
Further Reading Masters K (1991) Spray Drying Handbook. Essex: Longman Scientific & Technical. Pı´secky´ J (1997) Handbook of Milk Powder Manufacture. Copenhagen: Niro A/S. Westergaard V (1994) Milk Powder Technology. Evaporation and Spray Drying. Copenhagen: Niro A/S. www.niro.com.
Instrumentation and Process Control: Instrumentation R Oliveira, New University of Lisbon, Portugal P Georgieva, Bulgarian Academy of Sciences, Sofia, Bulgaria S Feyo de Azevedo, University of Porto, Portugal ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 3, pp 1392–1401, ª 2002, Elsevier Ltd.
Introduction Industrial evolution in the second half of the twentieth century was influenced mostly by four types of interrelated factors: progress in digital technology, advances in science, evolution of societal requirements and demands and, particularly over the last 30 years, evolution of business concepts. Developments in digital technology and in systems theory led to major progress in sensor and information technology and a revolution in the availability of distributed control systems and open software applications. New concepts, particularly knowledge-based measurement and advanced control methodologies, are slowly but steadily being brought into the practice of process operation, performing online and in real time. Societal and economic factors have driven evolution in the same direction. The increasing concern for health, safety and sustainability issues, market quality requirements, economic pressure and the evolution of company strategy from local to global business concepts – the so-called knowledge economy concepts – all together reflected on plant investment decisions, favoring process automation for cleaner and safer operation, higher product quality and improved process efficiency and productivity. Discussing plant automation from a technical point of view means a discussion on instrumentation, control system configurations, data communications and theoretical control structures. This article deals with instrumentation, addressing in particular both basic and advanced concepts concerning sensors and the issue of how to integrate local hardware for automatic control, usually dispersed throughout the plant.
Basics of Plant Automation There are well-established methodological steps for the design and implementation of a control structure: (1) designing and implementing an appropriate, flexible, control
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configuration; (2) performing first-level data acquisition and process monitoring, including record keeping and first-level alarms; (3) performing data interpretation (implementing second-level process monitoring); and (4) designing and implementing optimization and control solutions. In plant-wide distributed control configurations, as illustrated in Figure 1, the backbone of transmission is all digital. Communication protocols (some open, some proprietary) ensure data transmission for centralized data interpretation, for monitoring and for plant scale optimization. Control at sector and unit level is usually performed locally. Local-level signal transmission has for many years been analog only; initially, pneumatic signals and later electric (current or voltage) signals. However, more and more, information also flows digitally between (smart) sensors and controllers. At a local level, process control system instrumentation includes: (1) sensors for measurement of process variables; (2) controllers, for implementing a proper (digital) control structure (e.g. proportional-integral derivative (PID), predictive or adaptive controller, etc.); (3) final control elements for manipulation of process inputs; and (4) support devices such as general signal conditioners of both input and output signals, electric (V/I and I/V) transducers, electric-to-pneumatic transducers and hold elements. The range of instrumentation and control systems is very large today. Nowadays, industrial users are available through the internet information sites of instrumentation manufacturers with very detailed information on all types of instrumentation and control systems configurations, including data communications, related to plant automation. A relevant management decision in the automation of older plants – and most fall into this category – is how to step from existing local control solutions to integrated distributed control. Investment in a complete new solution is high and the tendency is to try to adopt a solution that makes use of available equipment. This is often hard to achieve and leads to a final configuration that mixes too
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235
Server
Network
FP
FP PID
LP
LP
Local unit 1
PID
Local unit N
Figure 1 State-of-the-art instrumentation for process control: devices, signal transmission and information flow. Continuous line-Network line (e.g. Fieldbus protocol/devices); Dashed line-Analog line (0–10 V, 4–20 mA) or Digital serial line (RS232, RS485); PID-Proportional-Integral Derivative; LP-Local Process; FP-FieldPoints.
many different control equipment suppliers, with the related costs of operation and maintenance.
Measurement Instrumentation
to considerable research and manufacturing interest. Basic concepts and the main measurement techniques are reviewed in this section.
Basic Characteristics of Sensors
A key limitation to the application of process control is the lack of appropriate sensors for many process variables. This is so in dairy processes and therefore measuring techniques for online use in the dairy industry are subject
A sensor is composed of a sensing element and a transmitter, as indicated schematically in Figure 2. The sensor output, whether analog or digital, should be a standard signal suitable to be supplied to a controller.
Wiring Physical phenomena (P) Temperature, pressure, flow, density, etc.
V0
Sensor Sensing element
Signal conditioning
Transmitter
V2
V1 Signal conditioning
Multiplexing and ADC
D Final control element
V5
I/P
V4
Signal conditioning
Figure 2 Schematic representation of stages in a digital control system.
V3
DAC & Hold
Digital control system
reference
236 Plant and Equipment | Instrumentation and Process Control: Instrumentation
ef = 2,45 V
2,5
N = 0,12 V
2,3
e = 0.63Δef
2,0 e(V) 1,8 e0 = 1,48 V
1,5
for transmission to standard electronic controllers. These sensors offer the advantage of small size, reduced price and practically no mechanical parts to wear out. Next, measurement techniques and instrumentation for the most important objective properties in the dairy industry are considered. pH
1,3
τ = 570 ms
1,0 0
500 1000 1500 2000 2500 3000 3500 4000 time (ms)
Figure 3 Time response of a pH electrode to a step change in pH (4–7).
Most transmitters respond rapidly. When the sensor element response is also fast, then measurement dynamics can be neglected in view of modeling process dynamics. Such a case is indicated in Figure 3, which shows the time response of a pH electrode to a step change in pH from 4 to 7. The characteristic first-order time constant for the sensor dynamics (the time required for the response change to reach 63% of the step change) is in the order of milliseconds (ffi570 ms). There are, however, cases where the measurement dynamics, particularly time lag, may be significant and ignoring it can lead to control difficulties. Sensors can exhibit linear or non-linear behavior. This is related to and expressed by the relation between the variation of the property value and that of the transmitted signal. Sources of non-linearity usually lie on the sensing element. For a linear sensor, the gain for a given calibration is constant and equal to the ratio between the set span and the range of the sensor output. Nowadays, with digital data acquisition, transducer non-linearities are easily incorporated in the data interpretation software and cause no practical difficulties. Specialized Sensors/Measurement Systems The most important properties of dairy processes subject to measurement that reflect both process operation and product quality are classified as objective or subjective. Examples of the former are pH, temperature, flow rates, pressure and level. Sensors for online measurement of such properties have been available for a long time. Properties such as taste, flavor, color and consistency are considered to be subjective and difficult to measure. Commercial sensors applied in the dairy industry are subject to several quality constraints, such as sanitary, safety and environmental requirements. A trend in new sensor design technologies is the increasing integration of the sensing elements into silicon chip micro-circuits. These new measurement devices directly incorporate all circuitry needed to self-compensate for environmental changes and yield an output that is suitably amplified
pH measurements are of paramount importance for quality control in milk fermentation and related processes. For example, inadequate pH can be a cause of excess free whey and excess or inadequate tartness in fermented products; pH changes are related to the viscoelastic properties of yogurt and they are also correlated to the physiological state of bacteria in the lactic acid fermentation. Also, the final pH value is normally a feature of the final product: fermentation converts lactose to lactic acid, causing a drop in pH to a value in the range of 4.25–4.5; rapid cooling at the correct level of lactic acid then stops bacterial action. pH electrodes can be in direct contact with food, if they meet sanitary requirements. In general terms, pH measurements, particularly in conjunction with electrical conductivity measurements, constitute an important means for continuous, real-time process monitoring. Temperature
In industrial applications, the main measuring devices for low temperatures (below 250 C) are based either on thermoelectric effects (thermocouples) or on resistance changes (e.g. platinum resistance temperature devices (RTD), thermistors). Measurement characteristics, particularly sensitivity and the degree of (non)linearity, favor the use of platinum RTD; the most widely used is the so-called PT100 device. Thermal processing is a key stage in most dairy process operations. As an example, during pasteurization of yogurt the temperature is raised to 85–90 C to destroy undesirable microorganisms and denature the whey to improve viscosity and prevent syneresis. Then, the product is cooled to 40–45 C so that the mix is ready for inoculation. Also, freezing and refrigeration are used to prevent the growth of unwanted microorganisms. In general, these operations and process units require a reliable and accurate temperature-monitoring and control system. Level, density or interface level
Liquid height, density or interface level between two liquids can be measured either by differential pressure (d/p cells) sensors or by measurement of buoyancy force on a displacer suspended in a liquid. An electronic transmitter converts the output of the sensing element to an appropriate analog or digital output signal. Nowadays, instrumentation companies offer the dairy industry a variety of special transmitters for level
Plant and Equipment | Instrumentation and Process Control: Instrumentation
monitoring and control applications in inventory tanks and clean-in-place (CIP) vessels. Pressure
In most process operations, particularly when thermal processing is required, pressure regulation is one of the essential control loops. Pressure sensors are thus among the most commonly used on-line sensors. D/p cell transmitters for either gauge or absolute pressure are the solution which is generally adopted.
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shear viscosity of time-independent non-Newtonian fluids. From the changes in viscosity, the stages of aggregation and gel formation can be described and calculated. The viscosity can finally be used as an objective measure for the control of coagulation processes. In industrial operations involving slurries, pulps, grease or other similar media, consistency, rather than viscosity, is measured by rotation and oscillation rheometers. These devices allow, for example, the continuous online monitoring of the transition of milk fluid into a viscoelastic gel structure.
Thermal conductivity
Thermal conductivity expresses the ability of a substance to conduct heat. The most common thermal conductivity probes consist of an assembly of an electric heated wire and a temperature measurement system (based on thermocouples or thermistors) from where heat fluxes are measured and heat conduction is inferred. Thermal conductivity measurements find wide application in dairy chemistry and biochemistry and in food process engineering. The measurement of thermal conductivity by line heat source probes may be used for in-line determination of the coagulation time of milk for cheese curd and yogurt production and may be helpful for automating these processes, aiming at maximizing the yield of cheese and yogurt. Coagulation time may be detected by the sharp increase in the temperature difference between probe temperature and initial milk temperature.
NIR spectroscopy
Infrared and near-infrared (NIR) spectroscopy can be used to measure the levels of water, fat and protein in liquid milk and related products on-line (and ex situ). This is a commonly used technique for quality control, but may also be used for on-line closed-loop control. Optical density
Optical density (OD) is commonly used to measure biomass concentration on-line and ex situ. The measurement principle is based on the individual or combined use of measurements of transmission, reflection or scattering of light. The interpretation of the signal is complex, but it is normally linearly correlated to biomass concentration in diluted solutions.
Final Control Elements Electrical conductivity
Electrical conductivity (G) expresses the ability of a substance or medium to conduct electricity. It is employed for quality control and further finds on-line use in identifying features of fermentation states. For example, electrical conductivity measurements allow the urease activity and the acidification activity in lactic acid fermentations to be distinguished. For example, electrical conductivity measurements allow the urease activity and the acidification activity in lactic acid fermentations to be distinguished. In a dairy plant where many fermentations are performed, either simultaneously or sequentially, the realtime prediction of fermentation completion time is very important for scheduling raw material supply and energy utilization. Data-driven models (e.g. neural networkbased) relating characteristic properties of the fermentation state (model outputs) to pH and electrical conductivity (model inputs) can be firstly identified (trained) and subsequently used to monitor the fermentation process and to predict fermentation times. Viscosity
The main items of equipment for viscosity measurement are process viscometers. Shear viscosity for Newtonian fluids can be measured by a capillary flow viscometer. Cone and plate viscometers are suitable to determine the
Final control elements (FCE) are devices, driven by controller signals, used to manipulate process control variables. In most cases control actions consist of adjusting flow rates of process input or output streams (solid, liquid or gas) or cooling and heating fluids. The most widely used FCE are flow regulator valves. Designing a valve involves taking decisions on valve size, choice of body material, choice of type of valve (signal-to-close or signal-to-open) and choice of flow versus aperture characteristics (essentially linear or equal percentage valves). Valve sizing (computing the Cv parameter) and the choice of valve flow characteristics require consideration of hydrodynamic aspects, particularly pressure drops along the piping. The choice of material depends on the properties (corrosive, slurry, etc.) of the process fluid. For the dairy industry, stainless-steel valves are most common. The decision on working with normally open or normally closed valves derives directly from answering the safety question of how the valve should stay in an emergency due to energy failure. Regulator valves are typically driven by a pneumatic signal (range 3–15 psig or 0.02–0.1 MPa). Signals are normally transmitted to the FCE as analog current signals (4–20 mA), being converted locally by a
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current-to-pneumatic transducer. Alternatively, a step motor, driven by a digital signal from the controller, can actuate valves. On–off valves normally use electrical or pneumatic actuators. They are used mainly for sequential control and during start-up and shutdown procedures. Other final control elements, namely displacement devices and pumps, are increasingly digitally actuated by step motors.
FieldPoints are modular I/O devices that connect a bank of analog and/or digital I/O modules to an industrial network, being able to perform AD/DA signal conversion. The key feature of a distributed control system is thus that the measurement and control tasks are distributed out into the field. Integrated hierarchical control configurations may be built where high-level tasks, like process supervision and optimization, are fully integrated with the low-level data acquisition and local control tasks.
Digital Control Equipment Digital control instrumentation represents the new standard and indeed has introduced a major change of mindset with respect to control system structures and solutions, with new procedures concerning communications and calibration routines. Digital control instruments offer the computing power required to implement advanced model-based monitoring and control algorithms (software sensors and predictive control) at local level and in real time. They enable the implementation of plant-wide monitoring, optimization and control solutions through the available distributed control architecture. Distributed Control Systems A distributed control system (Figure 1) is simply an arrangement whereby control devices and computer processing power are distributed through a network instead of being centralized. The main devices in a distributed control system are essentially microprocessor-based sub-systems such as programmable logic controllers (PLC), smart sensors, supervisory and engineering stations and other input– output (I/O) devices (e.g. FieldPoints, device integrators, etc.). All devices in the network must be integrated with proper hardware and software for communications. PLC are today’s industrial standard for local digital control. They are reliable special-purpose computers for control in the industrial environment, consisting of a set of I/O modules and a programmable central processing unit. They can perform analog-to-digital (AD) and digital-to-analog (DA) conversion and have special-purpose digital I/O ports (PLCs were originally designed mainly for event control). PLC normally use proprietary programming languages. Smart sensors are devices that through their digital system can be connected to the network, communicating bidirectionally with the other devices. In particular, they accept remote commands for remote calibration. General-purpose computers (PC, workstations) may be interconnected in the control system network to carry out inferential measurement procedures, highlevel data analysis, supervisory duties or more sophisticated dedicated control tasks.
Communication Standards Industrial communications refer to the networking hardware and software, together with the respective communications protocol. A number of industrial network standards, designed to meet different application requirements, are available today: Ethernet, DeviceNet, Foundation Fieldbus, PROFIBUS and controller area network (CAN). Details of these industrial network standards can be found in Table 1. Some specify low-level sensor–controller–actuator communication protocols (like CAN and DeviceNet), whereas others are specially oriented for distributed control systems in the process industries (Fieldbus and PROFIBUS). They differ on communications bus specifications, on velocity of data transfer, on communications protocol used and on the communications model. For distributed control systems in large factories, Fieldbus and PROFIBUS are the two most important standards. Ethernet is the most widely used local area network (LAN) technology. An Ethernet LAN may use coaxial cable, special grades of twisted pair wiring, or fiber optic cable. ‘Bus’ and ‘star’ wiring configurations are supported. Ethernet devices compete for access to the network using a protocol called carrier sense multiple access with collision detection (CSMA/CD). Ethernet conforms to the IEEE 802.3 specifications and runs commonly under the highlevel transfer communication protocol–internet protocol (TCP–IP) (although many others are possible). The Fieldbus standard has adopted a second alternative for the physical layer that is based on Ethernet, thus providing a solution for factory-to-factory communication. Basics of Analog-to-Digital and Digital-toAnalog Signal Conversion All digital control systems contain a data acquisition interface that performs AD/DA conversion. Such tasks are commonly performed by standard computers with AD and DA cards, by FieldPoint modules or by PLC. It is worth examining basic aspects of the data acquisition and control problem, namely the flow of information from the ‘process property’ to the ‘binary word in the
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239
Table 1 Industrial communications standards Standard
Description
General features
Application areas
DeviceNet
Low-level network designed to connect industrial devices (sensors, actuators) to higher-level devices (controllers)
Powered bus consisting of two separate twisted-pair cables Built on CAN protocol Producer–consumer model for data transfer
Mainly manufacturing industries
Foundation Fieldbus
Digital network standard designed specially for distributed process control; expected to substitute for the 4–20 mA analog standard
H1-powered 31.25 kb s1 bus (standards ISA S50.02-1992; IEC 61158-2) or high-speed 10/100 Mb s1 Ethernet (HSE) Fieldbus (communication) protocol (IEC 1158-2)
Mainly process industries
PROFIBUS DP/FMS/ PA
Family of communication standards. Leading open Fieldbus system in Europe; PA is mainly used in the process industries
DP and FMS: RS485 serial line with baud rates up to 12 Mb s1 PA: Fieldbus standard (IEC 1158-2)
Manufacturing and process automation
Ethernet
EtherNet is an industrial standard that defines only the physical layer. Some industrial standards are built on top of Ethernet
CAN
Designed originally for in-vehicle automotive communications
Coaxial cable with BNC connectors or telephone wiring with RJ45 connectors or fiber-optic cable (10–1000 Mb s1) (standard IEEE 802.3) Ethernet does not define itself as the communication protocol. It runs commonly under the TCP–IP
CANbus (serial bus) with CANbus communication protocol
Mainly in LANs for PC-to-PC communication.
Also for process industries
CAN, controller area network; LAN, local area network; PA, process automation; DP, decentralized periphery; FMS, Fieldbus message specifications; BNC, bayonet nut connector; TCP–IP, transfer communication protocol–internet protocol.
computer’ and the feedback from the ‘binary decision variable’ to final control element.
sensor normally delivers an analog electrical sig• The nal (V ), which should be a known function of the 0
process property, P. Assuming, for simplicity, a linear relationship, eqn [1] holds: Data acquisition
The data acquisition chain is represented schematically in Figure 2. The design stage of the data acquisition system should start with a qualitative analysis, addressing the following main considerations: sensor should be chosen with the objective of • The maximizing sensitivity for the desired measurement
• •
interval. This means that calibration should be such that the sensor measurement span should match the measurement interval and be mapped into the full range of the output signal. Industrial analog-to-digital conversions (ADCs) are nowadays standard. A 12-bit AD converter is generally sufficient. The input range is not a problem, assuming that the required signal conditioners are available. Signal conditioning should be such that the sensor output signal V0 is transduced into a signal V2 that exhibits the same range as that of the ADC. This situation maximizes the overall resolution of the acquisition chain.
Still at the design stage, the quantitative analysis must be performed in steps from the process to the computer:
V0 ¼ k0 þ z0
ð1Þ
signal will generally undergo some form of con• This ditioning (transduction, amplification, attenuation, etc.), after the sensor and before the ADC, depending mainly on aspects related to compatibility and range of transmission signals (V1 and V2). These types of transformations can usually be adequately expressed by linear relationships of the form: V1 ¼ k1 V0 þ z1
ð2Þ
V2 ¼ k2 V1 þ z2
ð3Þ
an n-bit ADC, with an input range [V , • Considering V ], the digital word D, corresponding to V , is given min
max
2
by: D ¼ INT
V2 – Vmin n 2 Vmax – Vmin
ð4Þ
The corresponding discretization error is given by 0.5(Vmax Vmin)/2n. For a 12-bit converter this error is well inside industrial requirements, generally lower than all other errors in the chain.
240 Plant and Equipment | Instrumentation and Process Control: Instrumentation
the choice of the sampling time (t) in the imple• For mentation, a simple rule of thumb is often used in
•
industrial applications, adopting a sampling time value of about one-tenth of the process characteristic time constant.The implementation stage of local signal acquisition corresponds to effectively programming the multiplexing, ADC, data reading (binary value D) and data decoding (getting the property P from the binary value D). For each scanning (multiplexing and data reading) of input channels, performed at every time interval t, programming of data decoding is performed by successively computing the values from the binary word D to the property P, by solving eqns [4], [3], [2] and [1] with respect to V2, V1, V0 and P, respectively. V2 ¼ Vmin þ ðD þ 0:5Þ
Vmax – Vmin 2n
ð5Þ
V1 ¼ ðV2 – z2 Þ=k2
ð6Þ
V0 ¼ ðV1 – z1 Þ=k1
ð7Þ
P ¼ ðV0 – z0 Þ=k0
ð8Þ
this stage, process values are available in the data • Atacquisition application for all types of desired actions, namely data interpretation, data plotting, bookkeeping, analysis of alarms and related actions, computing of control actions and output of control commands. Control action
It is outside the scope of this article to analyze control algorithms. Assuming that a control decision has been taken, given by a binary word C, such a command is transmitted from the control system to the final control element through an elementary chain including the digital-to-analog conversion (DAC) (with a hold element), and, in the more general case where the final control element is a valve, a signal conditioner, a power buffer amplifier and a current-to-pneumatic signal transducer (Figure 2). For design purposes, assuming that the DAC is set for a voltage output, eqn [9] represents the DA conversion, where n is the number of conversion bits of the DAC, Vref is the reference voltage (corresponding to an output interval of 0 Vmax, with VmaxffiVref): V3 ¼ Vref C=2n
ð9Þ
The industrial standard for DA converters is normally of 12 bit. Most common ranges of output signals are 0–10 V or 4–20 mA. Finally, referring back to signal conditioning, care must be taken to ensure that wiring is correct, that instruments and source grounds are of good equivalent level (a comment that also applies to wiring in AD lines) and that appropriate buffer amplifiers are used to protect control devices from high currents.
Advanced Topics Two topics closely related to the state of the art in both information technology and systems theory are now discussed: how to make measurable what is not so; and how to integrate information and manage large-scale systems.
Software Sensors In many cases, key process variables and characteristic parameters, namely kinetic and transport parameters, are not available directly on-line and in real time, either because they are really not measurable or simply because measurements may be expensive and/or unreliable. Software sensors are algorithms for the on-line computation of those state variables and parameters that are not measurable in real time, from more easily accessible (accurate and inexpensive) related measurements. The concept is closely related to those of inferential measuring and of state observers, widely discussed in the specialized systems engineering literature. The design and implementation of software sensors provide in some cases a suitable answer to cope with the lack of instrumental sensors. It may require the computational power of a dedicated computer in the distributed control network, a requirement that nowadays represents no technical or economical problem. A software sensor relies on a process (sub-system) model that establishes the relationship between measured and estimated properties. Hence, the key for success (or failure) of a software sensor is the availability of knowledge/information about the relationship between measured and unmeasured properties, i.e. the accuracy and robustness of the underlying model. With respect to and in the context of dairy industries, the kinetics in fermentation tanks are the most difficult part of the process to model. Traditionally, designing adaptive observation/estimation algorithms, of which the most frequently reported technique is the extended Kalman filter, circumvents the problem. This type of method requires a number of simplifying assumptions that are not always acceptable. More recently, knowledge-based software sensors have been reported. They rely on artificial intelligence (AI) models like artificial neural networks (ANN) and fuzzy or hybrid neuro-fuzzy models, combined with mechanistic expressions of process behavior. Though models reported in the literature are excellent in their ability to predict based on minimum information, the requirements of both know-how and computational power for implementation are still substantial. This hinders its industrial application on a wide scale, in the short term.
Plant and Equipment | Instrumentation and Process Control: Instrumentation
Measurement of Subjective Properties Properties such as taste, flavor, and consistency are subjective properties that are extremely important for process operation in food industries. At present operators use their human senses, i.e. smell/aroma, feel, taste, as a gauge for the acceptability of products. Measurement techniques for subjective properties are reported to be under intensive investigations. The electronic nose concept is maybe the best-known example. The electronic nose mimics the human nose to detect specific aromas and smell. This technology is commercially available today. Image analysis is now a well-developed technique. Properties such as material visual aspect can be inferred from these techniques, providing new information for further and new automatic processing.
241
Acknowledgments Dr Petia Georgieva is on leave from the Institute of Control and Systems Research, Bulgarian Academy of Sciences, Sofia, Bulgaria, supported by EU Research Project HPRN-CT-2000-00039. This work was further financed by the Portuguese Foundation for Science and Technology within the activity of the Research Unit Institute for Systems and Robotics– Porto. See also: Hazard Analysis and Critical Control Points: Processing Plants. Plant and Equipment: Flow Equipment: Valves; Instrumentation and Process Control: Process Control; Process and Plant Design.
Factory-to-Factory Automation As a final point, with the internet, it has become clear that the information flow scheme of Figure 1 in an automated factory may move down the hierarchy. As this technology becomes reliable and secure, we may speak of a factoryto-factory (worldwide) automated information flow and distributed processing. Whilst this does not represent a state-ofroutine automation solution, it represents a real management tool in the context of prevailing business concepts.
Conclusions Basic measurement concepts and control instrumentation applied in the dairy industry have been reviewed in this article. The intention was to provide an insight to the main principles and characteristics of classical and more advanced sensor devices and control equipment. The measurement mechanisms considered range from the commercially available sensors for important objective properties of dairy processes to more sophisticated model-based software sensors and new technological solutions for monitoring subjective properties in a variety of food industries. The discussion of digital control system instrumentation is also focused on core items such as final control elements, distributed control systems with respective communications standards and signal conversion required for data acquisition. Though the topics considered are far from being a complete overview of all research and industrial developments in this area, the article provides structured information on the main instrumentation aspects routinely implemented or potentially applicable in the dairy industry.
Further Reading Bentley JP (1995) Principles of Measurement Systems, (3rd edn.), New York: Longman House. Campbell J (1984) The RS-232 Solution. Alameda: Sybex. Carr-Brion K (1986) Moisture Sensors in Process Control. New York: Elsevier Applied Science. Cascetta F and Vigo P (1988) Flowmeters: A Comprehensive Survey and Guide to Selection. North Carolina: Instrument Society of America. Cubberly WH (1988) Comprehensive Dictionary of Instrumentation and Control – Reference Guides for Instrumentation and Control. North Carolina: Instrument Society of America. Doz Y, Santos J, and Williamson P (2001) From Global to Metanational: How Companies Win in the Knowledge Economy. Boston: Harvard Business School Press. Feyo de, Azevedo S, Chora˜o J, Gonc¸alves MJ, and Bento L (1993) On-line monitoring of white sugar crystallization through software sensors. International Sugar Journal 95: 483–488. Feyo de Azevedo S, Chora˜o J, Gonc¸alves MJ, and Bento L (1994) On-line monitoring of white sugar crystallization through software sensors. 2. International Sugar Journal 96: 18–26. Feyo de Azevedo S, Oliveira R, and Sonnleitner B (2001) New methodologies for multiphase bioreactors. 3. Data acquisition, modelling and control. In: Cabral JM, Mota M, and Tramper J (eds.) Multiphase Bioreactor Design, Editors, 2001, pp. 53–83. New York: Taylor & Francis. Fraser RE (2001) Process Measurement and Control: Introduction to Sensors, Communication, Adjustment and Control. Englewood Cliffs: Prentice-Hall. Johnson CD (1997) Process Control Instrumentation Technology. London: Prentice-Hall. Krohn DA (1988) Fiber Optic Sensors: Fundamentals and Applications. North Carolina: Instrument Society of America. Liptak BG and Venczel K (eds.) (1982) Instrument Engineers, Handbook: Process Measurement. Randor: Chilton Book Co., Morris AS (1996) The Essence of Measurement. London: Prentice-Hall. Oliveira R, Ferreira EC, and Feyo de Azevedo S (2002) Stability, dynamics of convergence and tuning of observer-based kinetics estimators. Journal of Process Control 12: 311–323 Article | PDF (297 K) | View Record in Scopus | Cited By in Scopus (14). Twork J and Yacynych AM (eds.) (1990) Sensors in Bioprocess Control. New York: Marcel Dekker.
Instrumentation and Process Control: Process Control P Georgieva, University of Aveiro, Aveiro, Portugal ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by R. Oliveira, P. Georgieva, and S. Feyo de Azevedo, Volume 3, pp 1392–1401, ª 2002, Elsevier Ltd.
Introduction – Dairy Industry, Aims, Trends Dairy processing industries worldwide have undergone rationalization, with a trend toward fewer but larger plants specialized in a limited range of products and operated by fewer people. Plants producing market milk and products with short shelf-life, such as yogurts, creams, and soft cheeses, tend to be located on the fringe of urban centers close to consumer markets. Plants manufacturing items with longer shelf-life, such as butter, milk powders, cheese, and whey powders, tend to be located in rural areas closer to the milk supply. Basic dairy processes have changed little in the past decade. However, changing global needs and the pressure of globalization create contemporary challenges related to rapid development of new, high-value-added products, improvements of production efficiency, and more energyefficient, cost-saving, and environmentally friendly processes. Issues such as pollution prevention and reduction of waste loads and product losses are critical for the dairy industry. To achieve these requirements, an integrated smart production policy is expected based on a holistic plant-wide representation of the production chain from process control level, through plant management, to corporate management. Modern dairy technology consists of a few hierarchical stages: Enterprise resource planning (ERP), which refers to a system that sits at the top of an integrated dairy infrastructure to manage the demands of business, in terms of functions such as sales and distribution, accounting, materials management, asset management, and plant maintenance. Manufacturing execution (ME) refers to a system that centers on the product as it moves through the plant. Supervisory control and data acquisition (SCADA) is a system that provides the operator and other users with access to direct regulatory process control, such as programmable logic controllers (PLCs). The SCADA system works in real time and provides graphical status displays and process monitoring. Though the PLCs form the basis of most traditional process control systems in the dairy industry, the use of more sophisticated control systems, information technology (IT)-based modern control
242
equipment, and new control algorithms are solutions implemented by an increasing number of companies. For example, specialized processes such as ultrafiltration and modern drying processes have increased the opportunity for the recovery of milk solids that were formerly discharged. ME provides a bridge between ERP systems and realtime control supplied by PLC and SCADA systems, for functions such as batch process control and production scheduling. Batch and Semibatch Process Operation Batch or fed-batch mode of operation is a typical production scheme for a large group of dairy processes. It is related to the formulation of control problems in terms of the economic or performance objective at the end of the process; for example, milk powder production quality is evaluated by the total quantity and concentration of solids at the end of the process. The main challenge of batch production is the large batch-to-batch variation of the final characteristics. This lack of process repeatability is an inherent consequence of the variability of raw materials and uncontrolled parameters and not necessarily due to improper control policies, though the latter would greatly enhance the problem. Over the past 10 years, a number of control methods have been researched to cope with process constraints and different objectives derived from economic or environmental considerations with the objective to drive the process to its optimal state of profit maximization and cost minimization. Some of the most typical control paradigms and new model-based control trends are presented in the rest of this article.
Classical Closed-Loop Process Control – Established Control Engineering Practice Any control system in which the output is monitored (measured), compared (subtracted) with the reference (desired) input, and the difference (the error) used to actuate the controller until the output equals the
Plant and Equipment | Instrumentation and Process Control: Process Control
Reference input
+
e(t)
Statistical Process Control
u(t) Controller
Process
–
Measured output
243
Controlled output
Sensor
Figure 1 Closed-loop process control.
reference is called a closed-loop or feedback control system (see Figure 1). The controller design consists of computing the PID parameters Kp ; KI ; Kd such that the closed-loop performance and stability requirements are achieved. Each parameter is related to one of the terms (proportional, integral, or derivative) of the control law. Proportional action. The magnitude of the contribution of the proportional term to the overall control action is determined by proportional gain, Kp . A high proportional gain results in a large change in the output for a given change in the error. If the proportional gain is too high, the system can become unstable. In contrast, a small gain results in a small output response to a large input error and a less responsive (or sensitive) controller. In the absence of disturbances, pure proportional control will not settle at its target value but will retain a steady-state error that is a function of the proportional gain and the process gain. Integral action. The contribution of the integral term is proportional to the error magnitude and error duration. Summing the instantaneous errors over time (integrating the error) gives the accumulated offset. The magnitude of the contribution of the integral term to the overall control action is determined by the integral gain, KI . The integral action (when added to the proportional action – PI controller) accelerates the movement of the process toward the setpoint and eliminates the residual steady-state error that occurs with a proportional-only controller. However, because the integral term responds to accumulated errors from the past, it increases oscillations and overshoots of the setpoint. Derivative action. The rate of change of the process error is calculated by determining the slope of the error over time (its first derivative over time) and multiplying this rate of change by the derivative gain, Kd . The magnitude of the contribution of the derivative action to the overall control action is termed the derivative gain, Kd . The derivative action slows the rate of change of the controller output and thus decreases oscillations and overshoots, an effect that is most noticeable close to the controller setpoint. However, differentiation of a signal amplifies noise, and thus this term in the controller is highly sensitive to noise in the error term and can cause a process to become unstable if the noise and the derivative gain are sufficiently large.
Statistical process control (SPC) is one of the most powerful tools for process improvement. Although SPC is new to the dairy industry, it is not really a new approach. It has been used successfully in manufacturing businesses for more than 60 years. SPC is a set of analytical tools of which the control chart is one of the most important. Control charts are helpful in signaling that a change has occurred. The fundamental concept of control charts is to distinguish between inherent random variation and real changes in output, quality, or measured performance. SPC methods can be used to signal emerging problems and to evaluate the positive or negative impact of a change in a management practice or the implementation of a new product. Next, some of the most commonly used online multivariate SPC techniques are presented briefly.
Empirical Linear Techniques Batch process modeling and monitoring has been always a challenging problem in dairy engineering due to the presence of nonlinear behavior and serial correlation, correlated and/or collinear data, varying batch lengths, and multiproduct production. Current state of the art empirical techniques include the bilinear approaches of multiway principal component analysis (MPCA), the multiway partial least squares (MPLS), and the trilinear methodologies of parallel factor analysis (PARAFAC) and PARAFAC II. Although the above bilinear and trilinear techniques have been applied successfully to batch processes, they experience a number of limitations. For example, they do not incorporate the process dynamics, and with the exception of PARAFAC II, the duration of the batches is assumed to be constant. Moreover, for online monitoring, it is required that the whole batch trajectory is known or is predictable. This requirement results in certain assumptions being made to in-fill the unknown future values of the batch trajectory. Finally, all these techniques are linear and to a greater or lesser extent fail to capture the nonlinear nature of a batch process. Alternative approaches that overcome the issues of data in-filling and unequal batches are presented next.
Moving Window Principal Component Analysis In moving window principal component analysis (MWPCA), typically, measurements from a batch process are arranged in a three-dimensional matrix X (NB NV NT) where NB, NV, and NT are the number of batches, variables, and time instants (Figure 2(a)). The three-dimensional matrix X can be transformed to a bidimensional matrix by unfolding over the batch dimension (NB (NV NT)), as shown in Figure 2.
244 Plant and Equipment | Instrumentation and Process Control: Process Control (a)
NT Time 1 x
Batches NR
⇒
(b)
NV
Variable
t=1
→
t = ti -1
t = ti
1 → NV
1 → NV
→
t = NT
1 ↓
NB 1 → NV
1 → NV
1 → NV
⇒
(c) 1
1→k
→
Pt
2 ∗NV Figure 2 Moving window principal component analysis (MWPCA).
A scaling is usually applied to the unfolded matrix X before an ordinary principal components analysis (PCA). The mean of each column of X is subtracted from each data element of this column. This way of mean centering is very important as it results in the removal of the main nonlinear component in the data. Furthermore, by scaling the variables in each column of X, the differences in the measurement units between variables can be handled to allow equal weight to be given to each variable at each time interval. A PCA model is then developed on a moving window of data. Having selected the length of the moving window (L), MWPCA then develops NTL þ 1 PCA models for each time interval by decomposing the (NB NV) matrix X into a systematic and noisy part: X ¼ Tk PTk þ E
½1
where Tk and Pk are the matrices of the k retained principal component scores and loading respectively, and E is the matrix of the residuals. The number of the retained principal components, k, is usually determined by the means of cross-validation. For the application exemplified, the order of the moving window was selected to be L ¼ 2. For each PCA model, the loading matrix Pk is stored. Having performed a PCA analysis, a set of online monitoring tools can then be developed. Typically, these tools are Hotelling’s T 2 and squared prediction error (SPE) control charts. For instance, considering that a new batch xnew is to be monitored, the Hotelling’s T 2 is calculated using the k retained PCA scores by: tk ¼ xnew Pk
½2
T 2 ¼ tt St– 1 tTt
½3
where tk are the k retained PCA scores and S is their covariance matrix. The SPE is then calculated as follows: SPE ¼ et eTt e ¼ xnew I – Pk PTk
½4 ½5
Batch Dynamic Principal Component Analysis The MWPCA approach does not capture the dynamic behavior within a batch process. The batch dynamic principal component analysis (BDPCA) is an alternative method that uses lagged variables to incorporate process dynamics. More specifically in BDPCA, each batch is isolated from the others (see Figure 3(a)). A matrix Xiv (NT NV) is formed for each iv batch. Then each of the NV variables is lagged d times resulting in a lagged Xiv [(NT d) (NV ? (d þ 1))] matrix (see Figure 3(b)). The covariance matrix of the lagged Xiv matrix, Siv, is then calculated (see Figure 3(c)). The procedure is repeated for all NB batches, resulting in NB Siv covariance matrices. The elements in each of the Siv matrices are a measure of the dynamic relationship between variables in batch iv. Having calculated these dynamic correlations for all NB batches, an average covariance matrix, Savg, is then calculated based on the NB Siv covariance matrices (see Figure 3(d)): ðNT – d – 1Þ Savg ¼
NB P iv¼1
NV ðNT – d Þ
Siv ½6
Plant and Equipment | Instrumentation and Process Control: Process Control
245
Lagged Variables 1 → (K + 1) × NV
Variables 1 → NV 1 ↓ NT
Batch 1
⇒
Xd, 1
⇒
S1
1 ↓ NT
Batch 2
⇒
Xd, 2
⇒
S2
1 ↓ NT
Batch 3
⇒
Xd, 3
⇒
S3
1 ↓ NT
….
⇒
….
⇒
…
1 ↓ NT
Batch NB
⇒
Xd, NV
⇒
SNB
(a)
(c)
(b)
⇒
Savg
(d)
⇒
P
(e)
Figure 3 Batch dynamic principal component analysis (BDPCA).
The average covariance matrix, Savg, expresses the average dynamic relationships between the process measurements. A PCA model is then developed based on Savg (see Figure 3(e)). The resulting BDPCA model is finally used to calculate the T2 and SPE statistics for monitoring purposes. Batch Observation Level The batch observation level (BOL) method considers the problem with unequal batch lengths. In BOL, the original three-way data is unfolded over the variable’s dimension (see Figure 4(a)). A dummy y-variable that can be a time index or a batch maturity index is then specified. Data are scaled and matrix X is transformed into a systematic and Variables 1 → NV
(c) ⇒
⇒
t=1 t=2 t=3 … t = NT 1→k 1→k 1→k 1→k 1→k
1 ↓ NT
Batch 3 (d) …. mean std Batch NB (a)
Figure 4 Batch observation level (BOL).
(b)
½7
where c is the regression vector of y onto the PLS scores Tk (see Figure 4(b)) and f are the PLS model residuals. The number of PLS latent variables to be retained are selected as those that provide an adequate description of both the X and y spaces. For setting up an online monitoring scheme, the PLS scores retained are then rearranged over the batch dimension resulting in an [NB (NT?k)] matrix (see Figure 4(c)) and their mean and standard deviation calculated for each sample point and stored (see Figure 4(d)). In an online situation,
Scores 1→k
Batch 1
Batch 2
y ¼ Tk c þ f
⇒
1 ↓ NT 1 ↓ NT 1 ↓ NT 1 ↓ NT 1 ↓ NT
noisy part as in eqn [1]. Partial least squares (PLS) analysis is then performed between the unfolded matrix X and the dummy y vector:
t=1 t=2 t=3 … t = NT 1→k 1→k 1→k 1→k 1→k
246 Plant and Equipment | Instrumentation and Process Control: Process Control
when a new sample is obtained, the scores are calculated initially and then scaled using the mean and the standard deviation of the corresponding sample point. These scaled scores are plotted against their control limits in univariate score plot charts. Similar to the previous approaches, T2 and SPE charts can also be constructed.
Time-Varying State Space Modeling Time-varying state space (TVSS) modeling is an alternative approach for batch process modeling and monitoring with the following state space model: tt þ1 ¼ Ct tt þ wt
½8
y t ¼ H t tt þ e t
½9
where t is the system states, y is the available process measurements, and w and e are the state and output residuals with covariance matrices Q and R, respectively. Finally, C and H are the state space model matrices, which are assumed to be time-varying as they aim to describe a nonstationary process. To develop the model, the data are initially unfolded and scaled as in MWPCA. The procedure to compute the TVSS matrices C and H then proceeds through the identification of the system states. For a time interval t ¼ k, the past and the future of the system are defined as shown in Figure 5(a). The past (p) of the process is associated with the past process measurements of all batches at time k up to a specific lag (in Figure 5(a), the time lag, K, was set to a value of two): T pt ¼ yt –1 yt –2 yt –K
½10
The future ( f ) of the process is the current and future process measurements of all batches (in Figure 5(a), the future horizon, L, is set up to a value of one): T f t ¼ yt yt þ1 yt þL
½11
Now, by applying any one of either PLS, principal component regression (PCR), or canonical variate analysis (CVA) between the past (eqn [10]) and the future (eqn (a)
t = ti -2
t=1
t = ti -1
t = ti
t = NT
1 ↓ NB
1 → NV
1 → NV 1 → NV 1 → NV
1 → NV
[11]) of the process, new latent variables that provide a reliable approximation of the true system states can be calculated. PCR scores capture the variability between process measurements, while PLS and CVA latent variables are those linear combinations of the past that include the information required to predict process future. The result of applying either a PCR, PLS, or CVA analysis is a weighting matrix Jt , which is used to identify the system states through the past vector pt : tt ¼ Jt pt
½12
Once the system states have been identified, the state space matrices can be computed using a least squares solution.
Intelligent Control The process modeling and monitoring techniques discussed in the section ‘Statistical Process Control’ are the first step toward developing modern computer-based control systems able to collect a large amount of process operational data, store it in databases, and display it to the operator. The next step is the subsequent decision making that still relies mainly on the human operators; however, new concepts and methodologies for automatic analysis and developing a computationally intelligent control (IC) are slowly being introduced in dairy manufacturing. IC deals with the application of data mining, machine learning, and knowledge discovery paradigms, artificial intelligence, expert systems, fuzzy logic, and neural networks for controlling complex physical processes that are difficult to control using conventional methods. The main modules of an IC system are discussed below. Perception Subsystem Information from the plant and the environment is collected and processed into a form suitable for perception. Basic elements of a perception subsystem are arrays – provide raw plant and environmental • Sensor data processing – transforms data into information • Signal and knowledge fusion and pattern recognition – uses multidi• Data mensional and varying nature data spaces to extract underlying patterns describing the plant and the environment
⇒
Cognition Subsystem
(b) Past
↔
Future →
Figure 5 Time-varying state space model (TVSS).
T
In an IC framework, cognition is concerned with the decision-making process under conditions of uncertainty. Basic activities of a cognition subsystem are
Plant and Equipment | Instrumentation and Process Control: Process Control
– using knowledge-based algorithms and • Reasoning fuzzy logic planning – using adaptive search and genetic • Strategic algorithms for optimum policy evaluation and path prediction
– using adaptive supervised (teacher • Learning supported) or unsupervised (self) learning paradigms The Actuator Subsystem The actuators operate using signals from the cognition subsystem to drive the plant to some desired state. In the event of actuator/sensor failure, the IC system has to be able to reconfigure its control strategy. Though milk production is a traditional dairy process for which conventional controllers have been used intensively, IC appears to be quite plausible for such processes. If the temperature drifts during processing, safety can be compromised or the product flavor or texture might be ruined. To perform the delicate balancing act that dairy products demand, plant operators need complete control, including the ability to know precisely what is happening at every moment and to perform urgent changes on time. It is not easy, especially when the product is hidden from sight in tanks and pipes more than 90% of the time. Companies that process the same products day in and day out have experience on their side, but those that change frequently have to be very agile and adaptable. In this sense, fuzzy and model predictive controllers are very good examples for building IC systems that are well accepted generally in the process industry.
membership functions, known as fuzzy sets. Fuzzy set theory provides a means for representing uncertainty. In general, probability theory is the primary tool for analyzing uncertainty and assumes that uncertainty is a random process. However, not all uncertainty is random, and fuzzy set theory is used to model the kind of uncertainty associated with imprecision, vagueness, and lack of information. Conventional set theory distinguishes elements that are members or not members of a set, with very clear, crisp boundaries between them. For example, temperatures between 20 C and 30 C belong to the crisp set ‘medium temperature’, and all temperatures between these boundaries have a membership value of one ( ¼ 1). The central concept of fuzzy set theory is that the membership function can have a value between 0 and 1. The shape of the membership function is also known as the universe of discourse. Among the most typical fuzzy set shapes are symmetrical triangles, trapezoids, and Gaussian or bellshaped curves. Each set is given a linguistic label to identify it; for example, positive big (PB), positive small (PS), about zero (Z), negative big (NB), negative small (NS). The size of the universe of discourse depends on the range of the variable and the number of the sets. The number and shape of fuzzy sets are a trade-off between precision of control action and real-time computational complexity.
Fuzzy Rulebase Module The fuzzy rulebase consists of a set of antecedentconsequent linguistic rules of the form Example: OR IF e is PS AND ce is NS THEN u is PS ½13
Fuzzy Logic Control System The basic structure of a fuzzy logic control system (FLCS) is shown in Figure 6. Fuzzification Module Fuzzification is a process of mapping the input variables to the fuzzy logic controller (FLC) into a set of
where e is the error (process reference – measured value), deðt Þ , and the ce is the rate of change of the error ce ¼ dt objective of the FLC (see Figure 6) is to minimize e and ce. In this example, the FLC input variables are e and ce, the fuzzy logic controller (FLC) output variable is u, and
Data base & Rule base r(t) +
FL controller
e(t)
u(t) Fuzzification
Fuzzy Inference
–
Meaurement system Figure 6 Fuzzy logic (FL) control system.
247
y(t) Defuzzification
Plant
248 Plant and Equipment | Instrumentation and Process Control: Process Control
they all have values defined as fuzzy sets. The fuzzy conditional statement eqn [13] is often called a Mamdani-type rule after Mamdani who first used it to control a steam plant. The rule base is constructed using a priori knowledge from the following sources: laws that govern the plant dynamics. • Physical Data from other controllers. • Imprecise heuristic obtained from experi• • enced plant operatorsknowledge and experts. Fuzzy Inference Module Fuzzy inference is the process of mapping membership values from the input variable(s) through the rulebase to the output variable(s). Example (continued): If at a certain moment the membership values of the input variables are PS ðeÞ ¼ a; NS ðceÞ ¼ b
½14
based on fuzzy set operations and the fuzzy rule eqn [13], the membership value of the control action u is computed as PS ðuÞ ¼ max½minðPS ðeÞ; NS ðceÞÞ
½15
Equation [15] is referred to as the max-min inference process or max-min fuzzy reasoning. Defuzzification Module Defuzzification is the process of mapping from a set of inferred fuzzy control signals belonging to fuzzy sets to a nonfuzzy (crisp) control signal. The center of area is the most well-known defuzzification technique, which can be expressed as n P
C ðAðui ÞÞAðui Þ u ðcrispÞ ¼ i¼1 P n Aðui Þ
½16
i¼1
where Aðui Þ is the area of the ith membership function computed at the previous step (the fuzzy inference), and C ðAðui ÞÞ is the center of the respective area.
Model-Based Predictive Control Modeling Approaches Process modeling strategies can be divided into the following main streams: The analytical approach (white-box models) is concerned • with building the so-called mechanistic model, also known as first-principles model, which is a set of mathematical expressions that reflect the dynamic (differential equations) or static (algebraic equations)
•
behavior of the modeled plant. The mechanistic model is a result of extensive, specially designed experiments and domain knowledge on the physical laws that govern the process at hand. Analytical modeling is time and resource consuming, but it has the main advantage of permitting good generalizations and scale-up. Data-driven alternatives (black-box models) are based on data mining and machine learning techniques and aim at extracting process knowledge from databases collected during the normal operation of the plant. The development of data-driven models usually takes less time and resources; however, their generalization outside the data space used to build the model is poor. One of the most common black-box models is the artificial neural network (ANN) paradigm, which will be described in more detail later. Hybrid modeling (gray-box model) is a combination of the two previous approaches and is also known as knowledge-based hybrid modeling (KBHM). KBHM offers a reasonable compromise between the extensive efforts to obtain a fully parameterized structure and the poor generalization of the data-driven models.
Process modeling for the dairy industry is strongly influenced by the recent trends in building data-based or KBHM models. For example, fouling, the unwanted formation of deposits on heated surfaces, is a major unsolved problem in the dairy industry. A direct consequence of fouling is reduction in the processing efficiency, because the material deposited disturbs both the fluid flow and the heat transfer, which in turn may impair product quality. Additionally, the deposit removal shortens the running time between cleaning cycles and thus increases the costs. As a result, daily cleaning is a common practice in the dairy industry and is necessary for hygienic and product quality requirements. The additional annual costs in the dairy industry caused by fouling are estimated at US$260 million per year. A relevant model of fouling would be a powerful tool for the development of strategies to avoid or reduce this unwanted process. However, due to its very complex nature, milk fouling is only partially understood, and its modeling is a challenging issue. A KBHM model combining parameterized equations (for fluid flow, heat and mass transfer) with qualitative knowledge in fuzzy logic form (for protein and salt deposition) was developed a few years ago. The model describes the fouling behavior with regard to the temperature and the pressure drop in a timedependent manner, and it is not restricted to a certain dairy product or plant configuration. KBHM was successfully used for testing technological improvements
Plant and Equipment | Instrumentation and Process Control: Process Control
in the heat treatment of milk in tubular heat exchangers.
Model Predictive Control – General Formulation The term model predictive control (MPC) does not refer to a particular control method; instead, it corresponds with a general control approach. The MPC concept, introduced in the late 1970s, has evolved to a mature level and has become an attractive control strategy implemented in a variety of process industries and in the dairy industry in particular. The main difference between the MPC configurations is the model used to predict the future behavior of the process or the implemented optimization procedure. First, the MPC based on linear models gained popularity as an industrial alternative to PID control, and later nonlinear cases such as tubular heat exchangers and drying processes were reported as successfully MPC-controlled processes. MPC is an optimizationbased multivariable constrained control technique that uses a dynamic model, from the types described in the previous section, for process output predictions. At each sampling time, the model is updated on the basis of new measurements and state variables estimates. Then, the open-loop optimal manipulated variable moves are computed over a finite (predefined) prediction horizon with respect to some performance index, and the manipulated variables for the subsequent prediction horizon are implemented. The prediction horizon is shifted or shrunk by usually one sampling time into the future, and the previous steps are repeated. Artificial Neural Networks Over the past 20 years, ANNs became a well-established methodology not only as a reliable classifier with countless applications but also as a data-driven modeling framework. The remarkable success of the ANN approach is in great part due to the following features: 1. ANNs are universal approximators. It has been proved that any continuous nonlinear function can be approximated arbitrarily well over a compact set by a multilayer ANNs, which consists of one or more hidden layers. 2. Learning and adaptation. The intelligence of ANNs comes from their generalization ability with respect to unknown data. Online adaptation of the weights is possible. 3. Multivariable systems. ANNs may have many inputs and outputs, which makes it easy to model multivariable systems.
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ANNs have been applied to design robust neural controllers with guaranteed stability and reference tracking. The neural control problem can be approached in a direct or indirect control design framework. Direct ANN control means that the controller has an ANN structure, whereas in the indirect ANN control scheme, first an ANN is used to model the process to be controlled, and this model is then used in a more conventional controller design. The implementation of the first approach is simple, but the design and the tuning are rather challenging. The indirect design is very flexible, the model is typically trained in advance, and the controller is designed online. Moreover, the ANNs appear to be rather convenient numerical models when dealing with nonlinear systems or in general with systems for which data are available but little is known on the physical mechanisms that determine their dynamics. The most popular ANN structures for modeling reasons are feedforward networks (FFNNs) and recurrent networks (RNNs). The RNNs are most suitable for dynamic system modeling, due to the memory introduced by the recurrent (delayed and/or fed back) signals (see Figure 7). Normally, the RNN has two vector inputs (r and p) formed by past values of the process input and the network output, respectively. A linear activation function is often located at the output node (layer 2), and S-shape functions are usually the hidden nodes (layer 1).
ANN Error Tolerant Model Predictive Control MPC controllers proved to be the most promising alternative to the traditional PID control that has the potential to overcome the problem of the lack of repeatability and related product recycling or loss increase. It has been applied successfully in batch dairy processes assuming linear process dynamics. However, online execution of MPC with predictions running on a large number of empirical and analytical nonlinear algebraic differential equations (the process model) make this alternative computationally more demanding or even
Input
Layer 1
Two r (7×1) W1_1 Delays (7×2) (2×1) Σ b1 (7×1) Two p W1_2 (7×1) Delays (7×2) (2×1)
Layer 2
Output
Tansig n1 (7×1)
w2_1 (1×7) b2
(1×1)
Σ
Purelin n2 (1×1)
(1×1)
Figure 7 Recurrent neural network (RNN) architecture.
250 Plant and Equipment | Instrumentation and Process Control: Process Control
unfeasible for dairy processes with fast nonlinear dynamics. Even for processes where the standard control approach (e.g., ladder logic) is not the best solution, the implementation of MPC is impeded due to high computational costs. A recent modification of the classical MPC, termed ANN Error Tolerant (ET) MPC, reduces considerably the average duration of each optimization step and makes the MPC computationally more efficient and attractive for industrial applications (see Figure 8). The ANN model is integrated into the controller, and the optimization procedure is executed only when the error is above a predefined value.
uðt þ kÞ ¼
NN MPC Optimization procedure
ANN process model
Process (KBHM) Figure 8 ANN-based model predictive control (MPC).
The discretized version of the modified performance index is
8 ( Hp Hc X X > > 2 > F ¼ l ð eðt þ kÞ Þ – l ðuðt þ kÞÞ2 ; if EP > u: min > 1 2 < ½uðt þkÞ;uðt þkþ1;...uðt þHc ÞÞ k¼1
> > > > :
k¼1
; PRþ u
1 PHp k ¼ 1 e ðt þ kÞ ;eðt þ kÞ ¼ ref ðt þ kÞ – Hp yp ðt þ kÞ;uðt þ kÞ ¼ uðt þ k – 1Þ – uðt þ k – 2Þ; is the prediction model response. The prediction horizon Hp is the number of time steps over which the prediction errors are minimized, and the control horizon Hc is the number of time steps over which the control increments are minimized. u ðt þ kÞ; u ðt þ k þ 1Þ; . . . u ðt þ Hc Þ are tentative values of the future control signal, which are limited by umin and umax . The controller is denoted as an ET MPC formulation because the optimization is performed only when the error function EP is bigger than a predefined real positive value . To reduce the computational burden when the error is less than , the control action is equal to u , which is the last value of u, computed before the error enters the strip. Note that EP in eqn [17] is defined as the mean value of the future errors, between the predicted output and its reference along the next Hp steps. where EP ¼
Conclusion In new integrated dairy plants, each process is carried out in multiple phases, and there exists strong nonlinear and dynamic effects between the variables. Therefore, modern process control systems have usually a hierarchical architecture including decentralized controllers, remote input and output (I/O) modules, fieldbus systems, local area networks (LANs), and smart sensors and other devices. The huge amount of information flows are stored and used online or off-line for executing the IC alternatives like FLC, ANN MPC, or SPC, all methods described in this article. Interested readers are advised to consult not only the references in the ‘Further Reading’ section but also to
½17
; if EP <
follow publications in the Journal of Food Engineering, Journal of Biotechnology and Bioengineering, and the International Dairy Journal.
Acknowledgment This work was financially supported by the Portuguese Foundation for Science and Technology within the activity of the Institute of Electronic Engineering and Telematics of Aveiro (IEETA). See also: Plant and Equipment: Instrumentation and Process Control: Instrumentation.
Further Reading Braha D (2001) Data Mining for Design and Manufacturing: Methods and Applications (Massive Computing). Dordrecht, Netherlands: Kluwer Academic Publishers. Burns RS (2001) Advanced Control Engineering. Linare House, Jordan Hill, Oxford: Butterworth-Heinemann. Camacho EF and Bordons C (2004) Model Predictive Control in the Process Industry. London: Springer-Verlag. Haykin S (1999) Neural Networks: A Comprehensive Foundation. Upper Saddle River, NJ: Prentice Hall. Nagy ZK and Braatz RD (2003) Robust nonlinear model predictive control of batch processes. AIChE Journal 49: 1776–1786. Norgaard M, Ravn O, Poulsen NK, and Hansen LK (2000) Neural Networks for Modelling and Control of Dynamic Systems. London: Springer-Verlag. Oliveira C, Georgieva P, Rocha F, Ferreira A, and Feyo de Azevedo S (2007) Dynamical model of brushite precipitation. Journal of Crystal Growth 305: 201–210. Oliveira C, Georgieva P, Rocha F, and Feyo de Azevedo S (2008) Artificial neural networks for modeling in reaction process systems. Neural Computing & Applications 18: 15–24.
Plant and Equipment | Instrumentation and Process Control: Process Control Petermeier H, Benning R, Delgado A, and Becker T (2002) Hybrid model of the fouling process in tubular heat exchangers for the dairy industry. Journal of Food Engineering 55: 9–17. Rossiter JA (2003) Model Based Predictive Control. A Practical Approach. New York: CRC Press. Simoglou A, Georgieva P, Martin EB, Morris J, and Feyo de Azevedo S (2005) online monitoring of a sugar crystallization process. Computers & Chemical Engineering 29: 1411–1422.
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Simoglou A, Martin EB, and Morris AJ (2002) Statistical performance monitoring of dynamic multivariate processes using state space modelling. Computers & Chemical Engineering 26: 909–920. Sua´rez LAP, Georgieva P, and Feyo de Azevedo S (2009) Computationally efficient process control with neural network-based predictive models. International Joint Conference on Neural Networks (IJCNN), Atlanta, GA, USA, 14– 9 June. Wang XZ (1999) Data Mining and Knowledge Discovery for Process Monitoring and Control (Advances in Industrial Control). London: Springer.
Robots J C Oliveira, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Robots are electromechanical devices that perform repetitive operations otherwise carried out by humans. In a modern dairy factory, human handling is rare in processing equipment; from liquid milk to packaged product, there are few, if any, manual operations. Even packaging lines have been highly automated, and operators in a modern dairy plant are needed mostly to load/unload some machines, check the controls, and react to production problems. The interest in robots in dairy lies mostly in the two extremes of the process: (1) milking and herd management; (2) final palletizing and stock management. Robots rarely look like humans, as they only need to have the parts that perform the specific action. In essence, an industrial robot must have sensors to detect positions, shapes, and forms, a program that allows it to identify what it will be handling, moving parts with grippers for grabbing and handling, and other sensors directing the moving parts to place what it is handling in the correct position. They may also have valves, pumps, and other devices, depending on the nature of the action they need to perform. Robots must be programmable, so that the actions can be set up by the operator with the required flexibility. This is the main reason why robots are a solution where automation is otherwise not possible. Usually, a period of training of the program will be necessary, so the accuracy of the action can be adjusted to the inputs from the sensors. Dairy offers a good example of the difference between automation and robotics. The latter implies the former, but not the reverse. It is possible to milk a cow using automated systems that collect the milk and even detach the cups from the teats automatically, once they detect that milking should cease. However, it takes a human to place that automated milking device on a cow, because individual animals have their own size and anatomy and teats may be affected by some illness or defect and cannot be handled as if they were all the same. Furthermore, mastitis or any problem with teats or the udder needs to be assessed, and individual animals may need individual attention in feeding or medication. Using robots means that humans are no longer needed for these actions. Simple automation can work only for standardized situations, while robotics can provide the flexibility that the human analysis gives, by mimicking what that analysis does.
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Robots can have several advantages. The most obvious are that they can have much higher productivity and consistency than humans, and that they minimize labor costs. In the food industry, in general, they also have the advantage of high hygienic conditions and ease of sanitizing, compared to humans, therefore ensuring more aseptic conditions. Whether they are a valuable investment or not depends, therefore, on their costs versus labor costs, productivity gains, and lower quality rejection costs. There are other benefits that may accrue in some specific cases, and milking is one of those.
Milking Robots Milking robots have been one of the most popular applications of robotics in agriculture. The first farm to implement such a system in Europe did so in 1992; the first installation in North America was in 1999 (Canada). Interest in the subject rose steadily in the 1990s. In 1997, Computers and Electronics in Agriculture devoted a special issue to robotic milking. In 2000, the European Union commissioned a project on the introduction of automatic milking on dairy farms, under its R&D Framework Programme, which also produced substantial information and analysis (completed in 2003, but the website is still accessible). The Future Dairy project run in Australia also provides comprehensive information and details to assist farmers in evaluating the interest these systems may have for them. In 2006, there were over 4000 farms worldwide reported to use robotic milking. The need to lower farming costs, and particularly labor costs, in developed countries is the most obvious driver for investment. Lack of human resources for farming is also a growing problem in these countries, as the average age of farmers continues to increase, and less people are willing to work as salaried peasants. Robots that facilitate strenuous farm activities have also been claimed to permit farmers to work to a later retirement age, and to be able to take care of themselves better (e.g., cows need to be milked daily even if the farmer needs to be in hospital for a couple of days). Labor issues are therefore a primary reason for a dairy farmer to decide investing in robotic milking, but it should be noted that in farming that is more than just costs. Furthermore, a fully automated milking system (AMS) has other advantages:
Plant and Equipment | Robots
1. The increased sanitization and hygienic conditions from the absence of humans minimize crosscontamination of mastitis and health problems in general (not only between animals, but also between animals and humans), which improves well-being and minimizes health costs. 2. Milking can take place at any time throughout the day, therefore avoiding that animals may need to wait for long times, thus improving their general wellbeing. 3. Animals can be milked more than the conventional 2 times daily. It has been found that increases in milk production of 5 up to 25% typically result from increasing milking from 2 times daily to 3 times daily. 4. Each animal can set the regime that suits it best, instead of a ‘one-size-fits-all’ scheduling of conventional milking (with robotic milking, the animal decides when to be milked). As a result, well-being and production are improved. 5. Feed regimes can be individualized. Typically, animals are attracted to the milking robot by feeding, and so milking robots can also control the feed and nutrient intake, as well as any medication needed. 6. Milking robots can also detect illnesses, such as mastitis, and presence of blood or contaminants in the milk with sensors, besides knowing if the specific animal is going through some medication regime, and automatically divert contaminated milk, thus allowing for an easy management of health-related issues in milk collection. Milking robots cannot be confused with automatic milking systems operated by people, where the animal traffic is controlled by farmers, the animals are placed in position, and automated milking cups are then placed by farmers on the teats for automatic pumping and collection in vats, such as in a rotary dairy parlor. Relatively new dairies may have quite some automation already, such as in-shed computer-managed feeding, automatic cup removal (ACR), teat spraying, and drafting. In fact, one could consider that the only new element of the robot is automatic cup attachment (ACA), so why not add just that one element in an already fairly automated process? Unfortunately, retrofitting a rotary dairy for robotics is not feasible, and in general, any previous automations are made redundant if a farmer invests in milking robots. Typically, robotic milking goes together with free animal traffic, and the animal is motivated to go to the robot, rather than being pushed or forced in some way. Feeding is the usual attraction. As an animal approaches an available robot, its entrance gate opens, the animal goes in to feed, and the gate then closes. The robot detects the individual animal from its collar or tag (if fitted with a relevant device, such as a small radio frequency tag), and may therefore dispense a tailored feed (with eventual
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medication or supplementation needed). The sensors detect the position and size of the animal, and activate an electromechanical arm that reaches under the udder and puts the automated milking cups in place. Teats are brushed first and cups attached one at a time. The robot will also have sensors to detect the flow rate of milk, so it controls the milking amount (thus avoiding overmilking), as well as color, conductivity, and presence of blood. It can therefore divert the milk collection in case of contamination. It may also decide not to collect milk from one of the cups and hence not handle a teat, if there is any reason for the system to do so, such as a health issue. The cups are removed in sequence; as the milk flow rate falls below a given threshold, it removes the quarter teat cup, and so on, until all quarters are milked. Milk collection management by quarter instead of overall udder mix is one of the advantages of AMS, especially if one of the teats has any particular problem. A teat spray is then applied to improve hygiene. All information regarding each individual animal is stored in the system. The animal is released through the exit gate, and the entry gate can then open for the next one. Animal traffic management can be designed to optimize the performance. New animals are trained relatively fast (2–6 milking days have been reported in the literature, with heifers being trained more easily than cows), and adjust their daily cycles to distribute themselves regularly throughout the whole day (and night). Studies showed that cows visit robots an average of 3–4 times a day, and that the number of cows that do not attend a robot for milking over a day, for no apparent reason (thus called ‘lazy cows’), can reach a figure as high as 10%. This was found to relate quite strongly to the palatability of the pelleted concentrate added to the feed, so feed composition plays an important role in motivating the animals to the robot. Ideally, the barn itself should be designed with the implementation of the robots and animal traffic in mind, rather than retrofitting. The design of the infrastructure, farm layout, laneways, ramp, automatic control gates, and strip grazing layouts are very important. Both management and facilities need to be redesigned to integrate AMS successfully. It is not surprising that the herd manager will spend more time servicing the equipment and reading and interpreting the information collected in the system about each individual animal than in actual attending to the animals themselves. The data collected by the sensors will detect estrus, as well as mastitis and other illnesses, and the farmer can plan medication and feeding in the robot, so the health care seems to take place by proxy. On the other hand, the farmer has more time to devote to analyzing the detailed information, which allows for more informed and speedy decisions to maximize efficiency and profitability. The economics of robotic milking are not straightforward. Some analyses indicate that the financial benefits
254 Plant and Equipment | Robots
are clearer for smaller producers, while others point to a break-even level of investment that is about twice that of a conventional parlor milking system and hence a greater financial clout than that of small farms. Cost factors vary from year to year and location to location, and which benefits are more important to individual farmers also vary substantially, depending on various factors such as size of herd, type of management, lifestyle, age, and availability of human resources on the farm. Each farm therefore needs to consider its specific situation to evaluate the feasibility of implementing AMS properly. There may be various reasons for robotic milking to be attractive to one farmer and not to the neighbor. It should be noted that milking robot costs are not just investment. Running costs of a milking robot include maintenance of a sophisticated system and electrical power supply. Typically, a robot will require between 15 and 25 kW per tonne of milk, while being capable of harvesting 2–2.5 tonnes of milk per day. The most important factor to bear in mind is the need for a strategic approach to the whole milking and farming process. The use of electronic tagging and automated gates permits a full herd management approach based on the individuality of each animal, thus including health management to the detail of medication and feeding of individuals, which maximizes the well-being and the benefits. Personalized feeding may prove financially more beneficial than saving labor costs, as the former account typically for 45–50% of the dairy farm costs, compared to 8–15% for labor (approximately half the labor costs are due to milking). The better hygienic handling and more precise health management can also lower health costs. Robotic milking is not only a cost analysis, as gains need to be factored as well, namely the increased milk production resulting from more efficient health and feed management and more frequent milking. The main manufacturers of milking robots are Lely and DeLaval. The former has been on the market for longer and is the market leader. The latter reported selling its 5000th unit in April 2009. Supplier support and training has been considered crucial and therefore a good working relationship between farmers and manufacturers is essential.
several layers in warehouses. All these operations can be robotized. Figures 1–3 show a robotic palletizing solution for 1 l containers. Robots are fed from two fully automated packaging lines for the 1 l containers that begin by forming them out of reels of the packaging material, and fill them volumetrically in one machine. Both lines can then send them individually to the next room, or group them in packs of 10 (or 12) with plastic wrapping in another machine. Conveyors then transport the individual 1 l containers or the packs of 10 or 12 in separate lines from the packaging to the palletizing room, one conveyor line for each robot. Figure 1 shows one of the conveyors delivering the packs of 10 or 12 to robot 1 for palletizing. This robot moves a double gripper that can pick up and then place two packs at a time on one of two palettes. This is the most usual type of palletizing robot, which can also handle other types of boxes, such as yogurt and butter containers. Note in Figure 1 that the packs of 10 were moved so they are not aligned, and that 3 were placed at the base. This will not be a problem for the robot, as its sensors allow it to know exactly where the packs are, when to close the gripper, and to what strength, so that two packs are picked up and placed gently in place. Figure 2 shows the whole palletizing room, and gives a different view of this first robot. It is placing two packs of 10 packages of 1 l at a time on two palettes. In order to improve stability, the stacking patterns are changed from layer to layer. The robot stacks the layers on the palettes
Gripper
Palette 1
Robotic arm
Palette bases
Palette 2
Packs of 1 l
Conveyor 1
Palletizing Robots Once individual containers of any dairy product are bundled in secondary packages (carton boxes, or simple plastic wrapping of individual containers, as with many liquid milk cartons), these must be piled on palettes at the end of the packaging line. These will be stored in warehouses and later loaded onto trucks for sale. The palettes are moved around with forklifts, and often piled on
Figure 1 Palletizing robot with a double gripper. It is picking up two packs of ten 1 l containers at a time and stacking them with varying patterns on two palettes, alternately. The palette (wooden) bases are moved by the robot itself from the stack at the commencement of each palletizing. A conveyor brings the packs to the robot from the packaging room. Photographed by the author, courtesy of Ernesto Morgado S.A.
Plant and Equipment | Robots
2nd robot
255
Robotic arm
Gripper
Conveyor 2 Palette 1
Palette 2
Packs of 10 1 l
Conveyor 1
Figure 2 Example of a robotic palletizing room implemented in a tight space. The robot in Figure 1 is on the right, behind a column. One of the roller conveyors that slide palettes away when ready can be seen at the center. A train line then transports the palettes to the next room. A second robot is on the top left of the figure. Each of the robots in this room is handling over 1000 containers per hour, a rate that is actually controlled by the rate at which conveyors move packs and packages rather than by rate constraints of the robot itself, and could thus be increased further to about 2500 per hour. Photographed by the author, courtesy of Ernesto Morgado S.A.
Robotic arm
Suction line Gripper Carton container
Suction cups Loading tray
Figure 3 Palletizing robot with suction cups. One-liter packages are transported by a conveyor from the packaging room and accumulated as a 6 8 layer of 1 l packs at the bottom plate. The gripper plate, with 48 suction cups, picks up the layer and stacks it on the carton container seen on the right of the picture. When ready, it is slided out to the train line by a roller conveyor, and then moved to the next room. Photographed by the author, courtesy of Ernesto Morgado S.A.
so they will be ready to move on alternately (when one is ready, the other is about half done). When ready, each palette slides with roller conveyors to a train line (near the wall) that will carry the palettes to another room, where they will be automatically wrapped with plastic for extra rigidity, and are then ready for forklifts to carry them to the warehouse. A second robot is also seen on the
left of Figure 2. Note also in this example how robots can be operated in a very tight space, and work around the constraints of an awkward building. Each of the robots in this example is handling over thousand 1 l containers per hour, working at less than 50% of its maximum achievable rate (this is because in these lines the rates are constrained by the rates of the packaging machines).
256 Plant and Equipment | Robots
Achieving these productivities with human handling would require a much bigger room. The second robot can be seen in more detail in Figure 3. It has a different gripping system, so it can handle a whole layer composed of individual 1 l packages into a big carton container. This robot uses a plate with suction cups to pick up a 6 8 layer of individual 1 l packages from the bottom plate, which is fed by the other conveyor coming from the packaging room. These two robotic solutions reflect the client requirements of this particular company. Some clients wish to have packs of 10 or 12 to place on shelves at the point of sale; others prefer to receive a big carton container that is placed like that at the shop floor. From the beginning of forming the 1 l containers to the fully wrapped palettes, the only human intervention in this case is placing the reels of packaging material in the packaging machines and the base of the palettes in the robot stack. In addition to increased productivity and reliability, this has eliminated human intervention, which can be strenuous and prone to employee absence for health reasons, such as ‘bad back’. There are many manufacturers of such systems, such as Robomatic, Robotworx, Kuka, and Yaskawa (Motoman make). The example shown has no more robotic solution, so the forklifts to handle the palettes are still operated by humans. It is however possible to robotize that step also and actually run an entire automated warehouse, with robotic vehicles forklifting and moving the palettes to the warehouse, placing them in locations that its own management program defines, and retrieve them when necessary also according to the store management program of the automated system. Instead of small vehicles, it is also possible to operate the system with hoists and cranes moving around the ceiling, although this would be rather expensive for handling palettes the size of those in Figures 1–3. A robotic warehouse for palettes is rarer, though, because the economic advantages are less significant than those of palletizing. Replacing one or two persons operating forklifts (which is not a strenuous task) by an expensive robotic system likely results in investment costs that are difficult to recoup. Automated warehouses can be found in retailing, where a high turnover of small
items is needed, or in assembly lines using a large amount of small components (as in electronic manufacturing). Some manufacturers who offer these solutions include RMT Robotics and Kiva Systems.
Further Reading Bower-Spence K (2002) Robotic economics: Robots can be profitable for smaller herds, but there are caveats. Dairy Today 18(9): 17–19. Devir S, Maltz E, and Metz J (1997) Strategic management planning and implementation at the milking robot dairy farm. Computers and Electronics in Agriculture 17: 95–110. Dijkhuizen A, Huirne R, Harsh S, and Gardner R (1997) Economics of robot application. Computers and Electronics in Agriculture 17: 111–121. Halachmi I, Adan I, van der Wal J, Heesterbeek J, and van Beek P (2000) The design of robotic dairy barns using closed queuing networks. European Journal of Operational Research 124: 437–446. Hogeveen H (2001) Robotic milking. In: Hogeveen H and Meijering H (eds.) Proceedings of the International Symposium on Robotic Milking. Lelystad, The Netherlands. Wageningen, NL: Wageningen Press. Ipema AH (1997) Integration of robotic milking in dairy housing systems. Review of cow traffic and milking capacity aspects. Computers and Electronics in Agriculture 17: 79–94. Meijering A, van der Vorst Y, and de Koning K (2002) Implications of the introduction of automatic milking on dairy farms: An extended integrated EU project.Proceedings of the First North American Conference on Robotic Milking. Toronto, Canada, March. Wageningen, NL: Wageningen Press. Rodenburg J (2002) Strategies for incorporating robotic milking into North American herd management. Proceedings of the First North American Conference on Robotic Milking. Toronto, Canada, March. Wageningen, NL: Wageningen press. Spahr S and Maltz E (1997) Herd management for robot milking. Computers and Electronics in Agriculture 17: 53–62.
Relevant Websites http://www.automaticmilking.nl – EU-Project Automatic Milking. Website of the EU integrated project on automatic milking. It contains several articles and project results. http://www.lely.com and www.delaval.com – Lely and DeLaval. Websites of the main manufacturers of milking robots. They contain several illustrative pictures of their equipment. http://www.roboticdairy.com – Robotic Dairy. Website of an Australian dairy farm. It has four live cameras at different parts of the farm where the operations can be seen in real time. http://www.futuredairy.com.au – Website of an Australian Project. It covers more than robotic milking, and also contains several articles and analysis on this subject.
Corrosion P D Fox, 90 Old Quarter, Ballincollig, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction
E ¼ E0 –
Corrosion is the deterioration of metals by an oxidation– reduction reaction, usually with loss of the metal to solution. Metals are generally found in their natural state in the Earth as metal oxides or ores. Most metals are more thermodynamically stable as oxides rather than as pure metals, with perhaps the exception of the noble metals, for example, gold and platinum. Mining and refining a metal is therefore an energy-intensive process, that is, there is an input of energy, and corrosion can be seen as the return of the metal to a more thermodynamically stable state. Corrosion causes the loss of billions of dollars per annum, and in industrial nations constitutes a large fraction of the gross national product. These losses are due to replacement of materials and labor costs, as well as plant downtime. Losses due to leaking or contamination of product and heat transfer problems are also significant. Conservation of natural resources is enhanced by the prevention of corrosion. In order to understand corrosion, one needs to be familiar with the basic principles of thermodynamics and electrochemistry.
Thermodynamics and Electrochemistry The change in the Gibbs free energy, G, of a reaction indicates whether or not the reaction will proceed. A reaction is said to be spontaneous if G is negative. At constant temperature and pressure, the maximum amount of work, !max, a system can perform is given by the Gibbs free energy, that is, rG = !max. The Gibbs free energy of a reaction under non-standard conditions can be related to the equilibrium quotient, Q, by the following equation: r G ¼ r G o þ RT ln Q
½1
j ajuj
where Q ¼ and u is the stoichiometric number of the species j. Terms that make up the equilibrium quotient include the activities of metal ions, protons, and gases. In an electric cell, work is due to transfer of charge in the form of electrons across an electrochemical potential, E, between two electrodes. Therefore, the product of charge and potential results in work: r G ¼ !e max ¼ uFE
½2
The Gibbs free energy can be related to electrochemical potential using the Nernst equation:
RT lnQ uF
½3
This equilibrium relates potential to standard potential and the equilibrium under non-standard conditions.
Standard Reduction Potential Electrochemical reactions involve the transfer of electrons resulting in a change of oxidation state: Cu2þ ðaqÞ þ Zn ! Cu þ Zn2þ ðaqÞ
½I
Reaction [I] can be broken down into a combination of two half-cell components, one for reduction (IIa) and one for oxidation (IIb): Cu2þ ðaqÞ þ 2e – ! Cu
½IIa
Zn ! Zn2þ ðaqÞ þ 2e –
½IIb
Half-cell reactions occur at specific potentials. The overall potential of a reaction is the difference between the individual half-cell potentials. However, it is not possible to measure the absolute potential of an electrochemical process; so it is necessary to define a standard half-cell reaction relative to which the potential of all others is measured. For this purpose, by convention, a hydrogen electrode, also known as the standard hydrogen electrode (SHE), was chosen and arbitrarily assigned a value of 0 V: 1 Hþ ðaqÞ þ e – ! H2 ðg Þ; E ðHþ ; H2 Þ ¼ 0V 2
½4
The standard reduction potential of a test electrode is defined by whether it is oxidized or reduced when connected to a standard hydrogen electrode. If electrons flow from the hydrogen electrode to the test electrode, causing reduction of the test electrode, the measured potential is positive. The standard reduction potential is negative if the electrons flow in the opposite direction, that is, from the test electrode to the hydrogen electrode, thus oxidizing the test electrode. Using the standard hydrogen electrode as reference, tables have been constructed for all other electrodes, the reduction potential of which is either positive or negative relative to hydrogen. A partial list is given in Table 1. The same principle applies to any two electrodes when constructing an electrochemical cell. The electrode with the lower standard reduction potential is the
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258 Plant and Equipment | Corrosion
The exact form of the water/oxygen electrode half-cell depends on the chemical environment, which can be acidic or alkaline. In acidic solution:
Table 1 Standard reduction potentials for selected half-cells
Electrode
E V
Au+ + e ! Au O2 + 4H+ + 4e ! 2H2O Ag+ + e ! Ag Fe3+ + e ! Fe2+ Hg2Cl2 + 2e ! 2Hg + 2Cl Cu2+ + 2e ! Cu Co2+ + 2e ! Co 2H+ + 2e ! H2 Fe3+ + 3e ! Fe Fe2+ + 2e ! Fe Zn2+ + 2e ! Zn 2H2O + 2e ! H2 + 2OH Al3+ + 3e ! Al Mg2+ + 2e ! Mg
+1.83 +1.23 +0.80 +0.77 +0.27 +0.34 0.28 0.00 0.04 0.44 0.76 0.83 1.68 2.37
The basic concepts of electrochemistry and half-cells can also be applied to corrosion. In fact, corrosion is the combination of a metal electrode (IIIa) with a water/ oxygen electrode (IIIb). In this section, iron and various grades of stainless steel, due to their extensive use in the dairy industry, will be used to illustrate thermodynamic and kinetic data regarding corrosion: ½IIIa –
2H2 OðlÞ þ O2 ðgÞ þ 4e ! 4OH ðaqÞ
½IIIb
2FeðsÞ þ 2H2 OðlÞ þ O2 ðgÞ ! 2FeðOHÞ2 ðsÞ
½IIIc
V, VI. or VII, therefore as in the previous example, the reaction can be broken down into its individual half-cell components and their corresponding standard reduction potentials as in Table 1: Fe2þ ðaqÞ þ 2e – ! FeðsÞ;E ¼ – 0:44V
4Hþ ðaqÞ þ O2 þ 4e – ! 2H2 OðlÞ;E ¼ þ1:23V
½VI
2H2 Oð1Þ þ O2 þ e – ! 4OH – ðaqÞ;E ¼ þ0:40V
Thermodynamics of Corrosion
–
½V
In alkaline solution:
anode, where oxidation occurs, and that with the higher potential is the cathode, where reduction occurs. The difference in the standard reduction potentials of the two electrodes, that is, cathode potential minus anode potential, is the overall cell potential. Using Table 1 the potential of the cell in eqn [I] is found to be 1.1 V and when substituted into eqn [2], gives a negative Gibbs free energy. The current generated by this cell arises from the spontaneous flow of electrons from the zinc anode to the copper electrode. The flow of electrons from copper to zinc is a non-spontaneous process and requires external energy, as in the recharging of a battery by the electric mains.
2FeðsÞ ! 2Fe2þ ðaqÞ þ 4e –
2Hþ ðaqÞ þ 2e – ! H2 ðgÞ;E ¼ 0V
½IV
½VII
As shown in the previous section, when two electrodes are combined, the electrode with the lower standard reduction potential is the anode and undergoes oxidation. The electrode with the higher standard reduction potential is the cathode and is reduced. Since iron has a lower standard potential (IV) than the half-cells , V, VI or VII, therefore it undergoes oxidation when in contact with water/oxygen. This leads to an overall positive potential and a negative Gibbs free energy, showing that oxidation, that is, corrosion of iron, is a thermodynamically favorable process. A common method for illustrating the thermodynamic data of a metal involves the use of a Pourbaix diagram, which is shown for iron in Figure 1(a). It shows the most stable species of iron as a function of potential and pH. The activities of iron and other ions in solution determine at which pH and potential the transitions between different metal phases occur. Water is stable between the lines a and b (reactions [V] and [VI], respectively). A potential below line a causes the reduction of water to hydrogen, while above line b, water is oxidized and oxygen is evolved. However, the activity of protons in solution is pH dependent. Substitution of a or b into the Nernst equation [3] allows potential to be expressed as a function of proton activity or, more conveniently, as a function of pH: E ¼ 0:00 – 0:059 pH
½5
E ¼ 1:23 – 0:059 pH
½6
The potential for the oxidation and reduction of water, lines a and b, respectively, decreases by 59 mV for every increase of 1 pH unit. In the Pourbaix diagram of iron (Figure 1(a)), the horizontal lines represent equilibrium reactions that are independent of pH, while the vertical lines represent reactions that do not involve the transfer of electrons. Diagonal lines are reactions that involve electron transfer and are pH dependent. The exact position of these lines is determined by the concentration of iron ions or by the presence of other ions in solution. All these reactions can be substituted into the Nernst equation [3] to derive expressions relating potential to standard potential, pH, and ion concentration. For a more complete description of the phase diagrams of
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259
(b)
(a) Fe3+ O2, H+/H2O, b E
E
Corrosion Passivation
H+/H2, a Fe2+
Fe2O3
Corrosion
Fe3O4 Fe 0
Immunity
Fe(OH)–3 7
14
0
7
14
pH
pH
Figure 1 (a) Pourbaix diagram for most stable species of iron in pure water. (b) Pourbaix diagram showing regions of immunity, passivation, and corrosion.
iron, as well as many other electrodes, the reader is referred to the Further Reading section. Figure 1(a) shows that at low pH and potential, iron is stable. Increasing the potential at low pH results in hydrated Fe2+ and Fe3+ and so corrosion occurs. At high pH, iron exists as oxides or hydroxides, with the oxidation number increasing with potential. If the oxide is soluble, further corrosion occurs. However, if the iron oxide is insoluble in water, a thin layer of oxide builds up on the surface. This oxide then protects iron from further oxidation and the metal is said to be ‘passivated’. A similar effect is seen in the formation of green copper oxide, for example, on rooftops where the initial oxidation of copper forms a protective film and prevents further oxidation. Figure 1(b) shows the regions of immunity, corrosion, and passivation for iron.
Kinetics of Corrosion Potential measurements and Pourbaix diagrams indicate whether or not corrosion is thermodynamically favorable. However, thermodynamic data provide no information about the rate of corrosion. Therefore, it is necessary to develop kinetic methods to measure the rate of corrosion. Kinetic information in electrochemistry is usually represented by a Tafel plot. When an electrode is at equilibrium, oxidation and reduction currents of equal magnitude but opposing direction result in zero net current. This equilibrium current is known as the exchange current, i0, and the potential at equilibrium is Eeq. In order to measure i0, a positive or negative polarizing current is applied resulting in an overpotential, . Overpotential is defined as the deviation of potential from Eeq, that is, = EeqE. At high overpotential, a plot of lnji j as a
function of is linear(see Figure 2). Extrapolation back to Eeq gives the value of exchange current: lnji j ¼ lni0 þ
nF RT
½7
The slope gives information about the symmetry, , of the reaction, which relates the reactant and the product to the activated complex along the reaction coordinate. A value of 0.5 means that the structure of the activation complex resembles that of the reactant and product equally. Corrosion is a two-electrode system at equilibrium. The combination of two electrodes results in a mixed potential, known as corrosion potential, Ecorr. Corrosion current, Icorr, is equal to the absolute values of the opposing oxidation and reduction currents. When the Tafel
ln|i |
Eeq
E
Figure 2 Tafel plot for the measurement of exchange current, i0. Transfer coefficient, , is measured from the slope and has a typical value of 0.5.
260 Plant and Equipment | Corrosion
and Equipment). The most popular steel in use in austenitic stainless steel, which contains 18% chromium and 8% nickel and is more commonly known as 18-8 austenitic steel. The carbon content is kept low (0.08%) to ensure that chromium, which is necessary for the prevention of corrosion, is not precipitated as chromium carbide.
+ − i0 (H2 / H +) H2 → 2H + 2e
E
Eeq (H2 /H+)
M → M n+ + ne–
Icorr Ecorr
Eeq (M /M n+)
2H + + 2e– → H2
Types of Corrosion
i0 (M /M n+) M n+ + ne– → M In|i | Figure 3 Tafel plot for corrosion of a metal in water showing equilibrium potential, Eeq, and exchange current, i0, of hydrogen and metal electrodes. Extrapolation of both slopes yields corrosion potential, Ecorr, and corrosion current, Icorr.
plots for both hydrogen and metal are combined (see Figure 3), the point of intersection gives the corrosion potential and corrosion current. The exchange current and equilibrium potential for the individual hydrogen and metal electrodes are also shown in the figure. Stern and Geary derived a simplified version of the Tafel relationship, using empirical values of b, which does not require knowledge of the surface: Icorr ¼
1 ba – jbc j Iappl 2:3 ba þ bc E
½8
where b = 2.3RT/nF. When the potential is varied by not more than 10 mV of Ecorr, it varies linearly with applied current, Iappl. The slope, Iappl/E, is known as polarization conductance, Kcorr. The rate of corrosion, Rcorr, can be related to the corrosion current by Faraday’s law: Rcorr ¼
Icorr Mt nF A
½9
where M is the molecular mass (g mol1), the density (g cm1), A the area (cm2), and n the number of electrons transferred. Integration of this equation for t = 1 year gives the more common expression for corrosion, cm yr1.
Properties and Types of Steel Alloying of iron is an effective approach to increasing mechanical strength and resistance against corrosion. Stainless steel is a chromium–iron–nickel alloy, with a low carbon content, which has good mechanical properties and is resistant to corrosion. There are three different types of steel, martensitic, ferritic, and austenitic, which differ in their crystal structure (see article Plant and Equipment: Materials and Finishes for Plant
There are many types of corrosion. A plant engineer should know the rate of corrosion but should also be aware of the various modes of attack. This information has to be taken into account for plant design. Corrosion of iron or steel is always a result of exposure to air and water. The time span for corrosion can vary dramatically, from hours to years. The amount of damage also depends on the exact form of the corrosion process, which can be influenced by the chemical environment, mechanical stresses, or metallurgical properties. The exact reason for corrosion can be due to any one or a combination of these factors. Pitting and Crevice Corrosion Uniform corrosion of a metal results in an easily measurable loss of metal. However, metal surfaces are rarely homogeneous and are usually covered with a protective layer of oxide or hydroxide. Pitting and crevice corrosion are two forms of localized corrosion where anodic and cathodic areas, that is, regions where oxidation and reduction occur, develop on the metal surface. The anodic area undergoes severe corrosion, whereas the cathodic area is unaffected. Environments containing aggressive species often result in the formation of deep pits on the surface of the metal. This is known as pitting corrosion. The most common cause of pitting is the chloride ion, which is able to penetrate the porous oxide layer (see Figure 4). Pitting generally occurs locally, due to variations in the structure and thickness of the oxide film or due to surface defects, rather than over the entire surface. Chlorides compete with oxygen for adsorption onto metal sites. Once adsorbed on the metal, chloride ions encourage hydration of metal ions and removal from the surface rather than the buildup of a passive oxide layer. Due to a difference in oxygen concentration, a large potential gradient of up to 0.5 V builds up between the anodic area within the developing pit and the cathodic bulk steel, which allows for a considerable current flow between the anodic and cathodic sites. More highly mobile chloride is then attracted into the pitting site in order to balance the charge built up by iron ions. Iron chloride undergoes hydrolysis, further decreasing pH,
Plant and Equipment | Corrosion
O2
Cl–
OH–
Air Solution
Air
Oxide
Oxide
261
Solution O2
OH–
Bolt M n+
ne–
Mn+
Metal
ne– Metal
Figure 4 Schematic illustration of pitting corrosion. Pitting corrosion occurs when the protective oxide layer is breached by chloride. It is an example of localized corrosion on a metal surface, which arises from concentration gradients.
and so pitting corrosion continues in an autocatalytic manner. Therefore, corrosion continues in areas where pitting has been initiated rather than starting at new sites. In this way, the pit can grow very quickly. A Pourbaix diagram for iron modified for a chloride solution shows a region where pitting occurs in addition to areas of passivity, immunity, and corrosion (see Figure 5). Crevice corrosion occurs in areas where movement of electrolyte is likely to be confined, such as between bolts, washers, or gaskets (see Figure 6). The electrolyte within the crevice is stagnant and has different oxygen and metal ion concentrations from bulk surface metal causing a potential gradient. Metal ions released within the crevice cause the local pH to be lowered by up to 6 units. As in pitting corrosion, chloride ions migrate into the crevice to balance the charge. As a result, passivity within the crevice is broken and the potential gradient is increased further, accelerating the rate of corrosion. Another cause of crevice corrosion arises if the protective oxide layer is breached due to a scratch, thereby exposing the metal. A
Pitting E
Corrosion
Passivation
Figure 6 Schematic illustration of crevice corrosion. Crevice corrosion occurs when the electrolyte is stagnant, such as under a bolt. Differing electrolyte composition within the crevice compared to the bulk results in a potential difference and localized corrosion.
potential is again built up between the two sites and crevice corrosion is initiated. The main difference between pitting and crevice corrosion is that pitting starts only when a critical pitting potential is reached, as shown in Figure 5. Crevice corrosion depends on whether passivity due to the oxide layer can be breached within the crevice and can also proceed with ions other than chloride, such as sulfates, nitrates, or acetates.
Intergranular Corrosion Intergranular corrosion is a localized attack at metal grain boundaries, which form during the cooling process in steel production where several nucleation points for crystal growth exist. The orientation of each crystal is random and so when two crystals meet they are often out of phase and a grain boundary is formed. The Gibbs free energy at the boundary is higher than that of the bulk metal and the boundary is preferentially corroded. It is thought that the intergranular corrosion results from improper, or sensitizing, heat treatments of the metal during production or welding. Sensitizing heat treatment of stainless steel depletes the grain boundary of chromium, which precipitates as chromium carbide; chromium is necessary for corrosion protection. Corrosion of this type penetrates the whole boundary, reducing mechanical strength and resulting in failure, even though actual loss of metal is low.
Stress Corrosion Cracking Immunity 0
7
14
pH Figure 5 Pourbaix diagram for iron in salt solution showing four regions: immunity, passivation, corrosion, and pitting.
Stress corrosion cracking results from tensile or residual stress on a metal in a corrosive environment. Without the corrosive environment, the stress would not induce cracking. Stress corrosion cracking can be initiated at metal discontinuities, pits, or intergranular boundaries. Whether propagation of the crack is intergranular or
262 Plant and Equipment | Corrosion
transgranular depends on the exact chemical environment and pretreatment of the metal.
Corrosion Fatigue When subjected to a repeated alternating stress, a metal will fail after a number of cycles; this is known as metal fatigue. In a corrosive environment, the number of cycles required to cause failure is reduced; this is known as corrosion fatigue and is usually generally transgranular and branched. The damage caused by corrosion fatigue is greater than the sum of the individual effects of corrosion and fatigue due to branching.
Cavitation Cavitation occurs under conditions of rapid fluid velocity, where repetitive high- and low-pressure areas are developed and bubbles are formed, which then collapse at the metal–liquid interface. The metal becomes deeply pitted due to mechanical damage and chemical removal of the protective oxide film. Cavitation often occurs on rotors and turbine blades. This is a physical process, not chemical, and it is therefore a form of erosion rather than corrosion proper. It is appropriate, however, to list it as well.
Galvanic/Bimetallic Corrosion Galvanic corrosion occurs when two metals separated by an electrolyte are in close contact. The metal with a lower standard reduction potential is oxidized, whereas the other is reduced. A common source of galvanic corrosion are bolts used to attach a fixture to steel; corrosion then occurs at the joint. Another cause is the welding together of two different grades of steel. Cathodic protection refers to the preferential oxidation of the metal with a lower standard reduction potential over another when two different metals or alloys are in contact with oxygen; the second of the two metals remains unaffected by corrosion. This approach to protection against corrosion is a common practice on ships where a zinc block, which has a lower standard potential than steel, is attached to the hull and is preferentially corroded by seawater while the steel hull remains uncorroded.
Environmental Factors Affecting Corrosion The availability of oxygen is critical for the corrosion process and its availability is affected by a number of interrelated factors. This is the basis of corrosion prevention methods, such as painting, where oxygen availability is suppressed. Steady-state corrosion is dependent on the diffusion rate of oxygen to the metal surface. Therefore, at low oxygen concentrations, corrosion is proportional to the concentration of oxygen. However, above a certain critical concentration, corrosion decreases with increasing oxygen level due to oxide passivation of steel. The critical concentration is increased by increasing salt concentration and/or temperature but is reduced by increasing fluid velocity and pH. Since corrosion is controlled by diffusion of oxygen, its rate increases with temperature. However, at high temperatures, oxygen availability is reduced and the rate of corrosion decreases. Moving liquids supply oxygen to the surface and hence increase the rate of corrosion. At higher flow rates, partial passivity occurs. However, at very high flow rates, mechanical removal of the oxide layer or the prevention of passive oxide layer formation increases the rate of corrosion. Also, in the presence of chlorides, as in brines, oxide layers are not formed and corrosion will continue to increase with flow rate. Increasing the NaCl concentration reduces the solubility of oxygen. However, corrosion increases to a maximum at 3% NaCl, due to Cl, and then declines; this is due to breaching in the passive oxide layer. See also: Plant and Equipment: Materials and Finishes for Plant and Equipment.
Further Reading Evans UR (1960) The Corrosion and Oxidation of Metals: Scientific Principles and Practical Applications. London: Arnold. Korb LJ (1987) Metals Handbook, Vol. 13: Corrosion. Metals Park, OH: ASM International. Lide DR (2000) Handbook of Chemistry and Physics, 81st edn. Boca Raton, FL: CRC Press. MacDonald DD (1978) An impedance interpretation of small amplitude cyclic voltammetry. 1. Theoretical analyses for a resistive–capacitive system. Journal of the Electrochemical Society 125: 1443–1449. Pourbaix M (1966) Atlas of Electrochemical Equilibria in Aqueous Solutions. Oxford: Pergamon Press. Stern M and Geary J (1957) Electrochemical polarization. 1. A theoretical analysis of the shape of polarization curves. Journal of the Electrochemical Society 104: 56. Uhlig H and Revie R (1985) Corrosion and Corrosion Control. New York: Wiley-Interscience.
Continuous Process Improvement and Optimization J C Oliveira, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Origin of the Concept ‘Continuous process improvement’ is a term that emerged from the studies undertaken in American business science on the manufacturing strategies used by the Japanese industries. As such, it is often known by its Japanese term ‘kaizen’. There are many other terms that became popular and are related to managerial and operational strategies from Japanese practice, of which continuous process improvement is one element, such as quality engineering, lean manufacturing, value engineering, manufacturing excellence, and world-class manufacturing, and even six sigma can be related to it. Six sigma is discussed further in the article Plant and Equipment: Quality Engineering. The methodologies developed for continuous process improvement are now regarded as crucial for ensuring competitiveness in a global market, and as such, have been permeating across all sectors of the manufacturing industry. It is worthwhile to understand the origins of the concept. Following World War II, Japanese industry was devastated. In the 1950s, products made were of generally poor quality and the lack of economies of scale and of investment capacity seemed to condemn Japanese industry to a secondary role for a long time, compared to the paradigms of the day, the US industry. However, by the 1970s, American companies began recognizing that the Japanese products were of superior quality and lower price, beating them in their own markets. One of the industrial sectors more strongly affected by the giant leaps of quality and efficiency of the Japanese industry was car manufacturing. It was obvious by then that some time during the 1950s and 1960s Japanese manufacturing was able to find methods to produce high-quality products at a cheaper rate, even though it did not avail (at that time) of the economies of scale that the ‘Detroit giants’ (Ford, Chrysler, and General Motors) had. As the Toyota Motor Company was at the forefront of these developments, and it practiced a notable open philosophy about itself, it became the most widely studied by American business science researchers. Toyota was not the only company developing these approaches in Japan, nor the creator of all the methodologies used, but was one of the pioneers, and became the best
known. In a sense, the fact that various people analyzed various aspects of what was later called the ‘Toyota Production System’ (TPS) and then added their own perspectives and interpretations has ultimately led to the emergence of several ‘westernized’ concepts, such as just-in-time, total quality management, continuous process improvement, and lean manufacturing. However, the Japanese, and Toyota in particular, would not consider any of these concepts as an independent methodology, but as part of a whole. The first studies of TPS brought to global attention a completely different way of organizing production, with just-in-time stock management, a production pull system rather than push system, and a revolutionary approach to the role and intervention of operators in the process, which in itself sparked a new philosophy about teamwork. Studies of the TPS became known as the first paradox (how can quality be achieved with low cost when there are few economies of scale?) after another influential work addressed what it called the second Toyota paradox, which deals with the new product development approach of Toyota (how can a new product development cycle be faster and cheaper by delaying decisions as much as possible?). Another landmark in the dissemination of these practices was the seminal work on lean manufacturing, The Machine That Changed the World.
From Car Manufacturing to Dairy There is a very important conclusion to bear in mind from the historical backgrounds of continuous process improvement and all the TPS-related paraphernalia of modern management best practices and fads: they were not developed and implemented by Toyota, the biggest car manufacturer in the world (that is not what Toyota was then). They were developed and implemented by Toyota, a small company producing low-quality products at a high cost because it had no economies of scale, and therefore had very little financial capacity for investments. What it had was the belief that it could do better, that it could solve the paradox ‘high quality and low cost even without economies of scale’. Toyota did not develop its famous TPS by hiring expensive consultants to design optimum solutions by applying bestin-class principles. It had no financial or human
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264 Plant and Equipment | Continuous Process Improvement and Optimization
resources to do so. It started with months of observation of what happened in the reality of the factory floor, what operators really did and how. Then, considering what was the best in class, how could those efficiencies be emulated? And finally, finding out that they could actually be bettered. It is very informative to know what really happened: Liker provides a historical account that is well worth a read. The relevance of this to modern industries is obvious, as emulating means that abstract principles can be applied across industrial sectors, and there is none that has been immune to the application of the principles of continuous process improvement, lean manufacturing, six sigma, and other improvement programs (see for instance, the list of main clients of the Kaizen Institute – one of the many consultancy groups providing services in this area – at its website). For the dairy industry, see the cover story by Markgraf on an American dairy. It is however crucial to bear in mind the main lesson of Toyota’s origins: if deploying continuous process improvement (or any associated principles) requires an expensive engagement of external experts who will propose an optimum solution from their analysis, then the proposition negates the philosophy right from the start. Continuous process improvement (1) must be a transformation that comes from within (albeit guidance by external experts facilitates commencement, cuts corners, and can thus save time and money), (2) must be ardently desired by the most senior management, and (3) should require few, if any, costs.
United States (and Europe) had been to design an optimum process. This implies defining what the optimum target is, often accepting that the multicriteria nature of ‘optimum’ will require some compromise or trade-off, and from that conceptual definition of what the optimum should be, the process is then designed in one single go to reach that optimum, using sophisticated methods. As the design is complex, it needs advanced knowledge, so the designer is an expert in designing, does so expensively, and is unlikely to be engaged in the actual daily operation of that design. On the other hand, the operators are typically not involved in the design, and are supposed to do exactly as told and exactly as planned in the design. This is, of course, a gross generalization, but the underlying nature of the approach can lead to such extreme dichotomy between the optimum abstract ideal of the design and the practical reality on the factory floor. Therefore, continuous process improvement (kaizen) experts often like to boast of the improvements they were able to extract out of what was supposedly an ‘optimum’ process. Notwithstanding, process optimization methodologies are not to be discarded, some kaizen engineering design methods over rely on simplified approaches, and ‘western’ engineering design has developed some more consistent and comprehensive ones. From a practical point of view, of course, semantics are irrelevant, and what matters is the efficacy of the methods deployed to improve competitiveness.
Continuous Process Improvement or Process Optimization?
Operational Improvements
As the name suggests, continuous process improvement uses methodologies to improve a manufacturing process, so the first question should be what is the target of improvement – costs? productivity? quality? This is a methodology to improve what? The answer is simple: everything. That is one of the reasons for using the word ‘paradox’ in relation to the TPS: How can everything be made better, when reality usually requires compromises and trade-offs? How can costs be reduced and quality improved? The second feature of the term is the word ‘continuous’: process improvement is a neverending journey, the process is to be made better all the time, one improvement after another, because optimum is an ideal, and as such, unreachable. Semantics, therefore, show that the concept implies an incremental approach (one step at a time), where no improvement is too small (summing enough small improvements leads to a big improvement). This, therefore, reveals a fundamental difference between continuous process improvement and the ‘western’ counterpart, process optimization. The practice in the
The first step for improving a manufacturing process is to analyze its operations, from procurement to sales, and not only on the factory floor. Starting with purchase orders (when are ingredients purchased and how, where are they stored and for how long?) and ending with sales (manufacture-to-stock, or manufacture-toorder?) means that stock management strategies are an integral part of process improvement. In relation to the manufacturing process itself, the whole sequence of operations needs to be considered, including not only the actual processing functions, but also its associated functions, such as quality control. In essence, a factory organizes a series of operations, generically, buy ! make ! test ! sell (not necessarily linearly). The first core principle of kaizen is to analyze the operations from the point of view of the flow of the product itself, which already brings in a difference from ‘western’ conventions, where processes tend to be described from the managerial perspective. In order for a process to be improved, this combination of operations must be the most efficient. Redesigning the
Plant and Equipment | Continuous Process Improvement and Optimization
entire set can be associated to the concept of business process reengineering (BPR), a management concept that gave mixed results and was therefore more popular in the 1990s than it is today. BPR considers the ‘western’ approach: that an optimum can be designed from scratch by best principles applications, using sophisticated methods if necessary, and isolated from real practice if need be. A BPR proposes a giant leap to an ideal world. It is not a useless concept, and it can give very good results (and has in reported literature), but obviously, the more reality deviates from ideality, the greater the chance that the giant leap may be toward a big hole. Literature also reports negative experiences of companies with BPR. Incremental approaches therefore have this big advantage: they may be more modest but will always lead to a better situation, and over several incremental steps, the gains will become significant. Critics will contest that incremental solutions may not explore areas of the solution space beyond convention, while advocates prefer to explore without excessive risk in the explorations, and point to practical end results that are equally enviable. It is noted that BPR often shows up associated to the introduction of novel solutions from information technologies (IT) to reorganize business processes. This is a special case of BPR, where it comes associated with the digestion of new IT procedures by company and staff, which in itself (with BPR or not) has its own success and failure factors. Introducing IT may facilitate process improvement, or it may not, and it is not a concern here. IT is a tool; it should be recognized that in fact IT always facilitates kaizen from a conceptual (theoretical) perspective – but how will it work in practice? kaizen in itself is not about a better business concept, it is about a better business reality. Continuous process improvement will suggest starting more modestly than reinventing from scratch, by analyzing all operations and apply what is also known to some extent as value engineering. Of all the business operations involved in manufacturing, some add value to the product and thus to the end client, but some do not. They may well be necessary for some reason, or they would not be there, but if they do not add value, then they are a waste from the point of view of the product and of the client. The Japanese word for wasteful activity (‘muda’) is often cited in this context. A better process will be one where waste is nonexistent, so these operations should, ideally, be eliminated. Therefore, it is logical to start improving a process by eliminating non-value operations (why spend time and resources improving those that are best eliminated altogether?). This analysis is not as straightforward as it looks, because company executives and operators are not used to think from the point of view of the client or of
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the product. A typical example is quality control: from the point of view of the product or the client, it is a wasteful operation. This might seem an excessive comment, but a more detailed analysis shows the philosophy at play here. Quality control is a problem of the manufacturing company, not of the client. The client expects that quality, indeed, he paid for it. If the company is not able to deliver that quality, that is the company’s problem that becomes a client’s waste. From the point of view of the product, being stored somewhere waiting for the results of a quality control test is a waste of time. The product should have quality unless the process is faulty. An improved process should not be faulty, so the product should have quality all the time. This would lead to the concept of quality by design, which is discussed in detail in the article Plant and Equipment: Quality Engineering. A second principle is that the flow of the product must be continuous. From entering the raw materials storehouse to leaving for sale, the product (ingredients/ components, etc.) must not stop; if it does, it is lying idle, and so there is a waste. Hence, storage is a waste, and so the concept of just-in-time, one of the first that was immediately grasped for its financial advantages. The best way to ensure this continuous flow is to pull the product from the end, that is, the last operation sends an order to the before last, and so forth, so the product is pulled from the end. A pull operation (request for a product or part needed) was originally sent with a card in Toyota, or ‘kanban’ in Japanese, a term that endures as synonym of just-in-time operations by a production pull strategy. A good starting point for analysis of the improvements that can be made by eliminating wasteful operations (and hence become ‘lean’) is to apply the lean questionnaire developed by MIT (LESAT – Lean Self Assessment Tool), available for free at the website of the Lean Advancement Initiative of MIT (this site contains plenty of other free tools and studies under the ‘products’ menu). It may help to give a different perspective on what can be classified as waste, and how much waste there is in a normal business operation when it is analyzed from the perspective of the value to the client, or of the product flow. Waste is not confined to operations that should be eliminated because they do not add value; TPS deals with two other types of waste. An obvious waste comes from product variability and consequent loss of quality, which is addressed in the article Plant and Equipment: Quality Engineering, and often referred to by its Japanese term ‘mura’. The third is waste resulting from overcomplexity (‘muri’ in Japanese). This means that every operation and sequence of operations should be as simple and direct as possible. Standardization of simple operations and their straightforward combination
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are the ideal basis to eliminate this type of waste and hence maximize productivity. In some industrial sectors where operations involve manual handling, eliminating muri requires appropriate ergonomic design of the workplace and workstations (the operation should be easy and simple to perform, thus minimizing energy, effort, and time).
Process Engineering Improvements General Approach The operational and managerial implications of kaizen leave a highly flexible, efficient, and productive factory floor, alongside an entire lean supply chain. Operations on the factory floor involve a series of equipment units where the product components are progressively incorporated and turned into the final product. Each of these operations must now be improved. In the context of a process industry such as dairy, the raw materials undergo transformations toward a product of a different nature (e.g., fermentation in yogurts, coagulation in cheese) or that hinder microbial activity to provide shelf life (e.g., ultra-high temperature (UHT) processing, drying). These operations are controlled by a number of variables or control factors, such as temperatures, flow rates, amounts of ingredients, and time of operation. The company decides on the settings (values) of these factors from its knowledge of the system, characteristics of the equipment, recipes, and other things. Each of these control factors can be set at any value within a range of physical interest, and there is an infinite number of combinations of settings of these factors that result in a final product, although not all combinations are possible. Some, however, result in products that are better than others, or in processes that are cheaper, or more productive, or use less energy, and so on (for instance, the objective of reaching a given microbial lethality in the thermal treatment of liquid milk can be achieved equally at a higher or lower temperature, with the processing time being longer the lower the temperature, but the quality characteristics of the product, such as nutrient retention and taste, are better at higher temperature-short time than at low temperature-long time). In this context, process improvement will deploy methods to find a combination of settings of the control factors that will result in a better performance. It may be possible to estimate better combinations of these settings by developing mathematical models that mimic the operation of the equipment by applying first principle equations (laws of conservation of mass, energy and momentum, thermodynamics, kinetics, heat and mass transfer, etc.). However, such models will need to make assumptions that may or may not be good images of
reality, and may also be too complex. The continuous process improvement concept prefers to ‘let the system speak by itself’, and obtain process data from which to infer improvements. Process optimization does the same, only that it assumes that a single giant leap is possible, and that the absolute optimum is identifiable. Kaizen is prepared to move stepwise. The need for process data to infer directions of improvement is an issue in some industrial sectors, such as dairy. If the equipment operates with large quantities of product at any given time, and the business margins are small, there is little room to perform tests with the equipment, each of which could cost many kilograms of product that run the risk of being unsuitable for sale (when the test happens to try settings of the control factors that do not lead to a suitable product). However, process data can also be collected simply from the historical records of the process. This has the huge disadvantages of providing data that have not been planned, with many data points around the same settings, with uncontrolled variabilities, and a scan of the solution space decided by chance and the inaccuracies of the control systems. However, it is ‘free’ data and may reveal useful information about the system, if handled properly. Design of Experiments Kaizen recommends an experimental plan, and as such it starts by giving great importance to the planning of the tests. It is obvious that if each test involves the actual process and equipment, the most information needs to be obtained from the least amount of data, and therefore, it is not surprising that the area of statistics dealing with design of experiments (DoE) must be brought in. The most widely used approach in Japan is due to Genichi Taguchi, and is generally known as the Taguchi method of robust engineering design. The method seeks to achieve improvement of performance and also consistency of performance, and as such it is the foundation of quality engineering too, discussed in the article Plant and Equipment: Quality Engineering. In the context of performance improvement or optimization, it is noted that in order to minimize experimental requirements and take as much information as possible from the data, Taguchi chose designs based on orthogonal arrays (aka Latin squares). They are usually designated as L-4, L-8, L-9, L-12, L-16, L-27, and so on, where L stands for ‘Latin squares’, and the number indicates the number of rows of the array, which is also the number of tests that needs to be performed. When consistency of performance is to be considered as well, the whole set must be repeated a number of times, and therefore, using arrays with as few rows as possible is important. Each array will allow testing
Plant and Equipment | Continuous Process Improvement and Optimization
a number of control factors, which depends on the array, with one factor associated to a column of the array. That column will contain the settings to be used for the factor. Some arrays have only two different settings (two-level design), others have three (three-level design), and other commonly used arrays have four by combining columns of two-level factors (for instance, M-16 or L-16M refers to the L-16 array modified, which tests four different settings of factors, but it can be used for much less factors than the original L-16). There are also some mixed level designs. Table 1 shows an example, the L-8 array, which can be used to test up to seven factors with only two settings used for each. These experimental designs are very good for limiting the number of tests that need to be performed, but come at a cost: the design generates an intricate set of confoundings that may be difficult to separate. ‘Confounding’ is the statistical name given to a combination of terms or factors in the design that results in their effect being indistinguishable. It does not mean that the confounded factors are confounded by nature, it is a consequence of the experimental design that their impact is confounded (pooled together). For instance, if a design tests a system at 20 and 30 C, and also considers a flow rate of 1 or 2 l s1, but in all tests performed the flow rate of 1 l s1 was always used with 20 C and the flow rate of 2 l s1 was used only with 30 C, then when analyzing the data it is not possible to know if the differences were due to (1) the temperature increase, with flow rate change being irrelevant, or (2) the flow rate increase, with the change in temperature being irrelevant, or (3) both changes. Orthogonal arrays do not produce confoundings between factors, but they do between the effects of factors and the effects of their interactions. An ‘interaction’ is a basic feature of nonlinearity in a system. It means that the way that a factor influences a system depends on the actual value of another factor. For instance, if increasing the flow rate has no effect at lower temperature but is important at higher Table 1 L-8 orthogonal array Test no.
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8
1 1 1 1 2 2 2 2
1 1 2 2 1 1 2 2
1 1 2 2 21 2 1 1
1 2 1 2 2 2 1 2
1 2 1 2 1 1 2 1
1 2 2 1 2 2 2 1
1 2 2 1 1 1 2
Control factors are assigned to columns, and the rows indicate the settings of each factor for each of the eight tests that need to be performed. Each factor is tested with only one of two settings. Designs should be replicated, if possible.
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temperature, there is an interaction between flow rate and temperature. For this reason, ‘western’ statisticians prefer other experimental designs that provide a better differentiation between different effects, such as the ‘central composite design’. This design uses five settings for each factor, and tests some combinations of those settings that conform to a particularly well-balanced view of the solution space, which minimizes error regions of mathematical models then used to interpret the data. However, it requires a large amount of data than the orthogonal arrays. Whatever DoE is chosen, it is noted that it can be considered as a plan for tests that will be done (the ideal scenario), or as a filter to be used to collect data from historical records in order to ensure minimum bias of the analysis of those data (even if only a small subset of data are thus collected; this is preferable to overweighing parts of the solution space). Stepwise Approach The Taguchi method advocates a comprehensive approach including meetings, brain-storming, and teamwork, that is not detailed in this text, but it is noted that the first step must be to consider how many factors may influence the system. Usually, this analysis compiles a large number of factors that may be interesting to analyze. If the system should ‘speak for itself’, then one should not curtail the list by rational thought; instead, it is better to rely on Vilfredo Pareto’s famous principle, the 80/20 rule, and use a first experimental plan to zoom in on the 20% of factors that may be causing 80% of the consequences. This is also where analyzing historical records could be helpful, and provide ‘free’ information. A simple twolevel orthogonal array design can be used for this purpose. An L-8 can test up to 7 factors with 8 runs, an L-16 allows one to consider up to 15 factors with only 16 runs, and an L-32 would allow for up to 31 factors with just 32 runs (can, and should, be repeated), and so on, so that the selection can be done quite efficiently. It is noted that the consequences of the confoundings of this design are that some factors that may be considered important in the data analysis could actually be negligible (and this would be because one of the confounded interactive effects was relevant), but if a factor is judged to be negligible, then it is, and so are all effects confounded with it. That means that nothing of importance is lost by analyzing in this way which factors are more crucial for improving the performance. There are possibilities for overlooking important issues with these two-level designs, though: if a factor has an influence that shows a maximum or minimum of its average impact on the performance, it is possible that by a stroke of bad luck the averages at the two extremes used for the settings (low and high, 1 and 2) are similar, and the
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data analysis will then infer that the factor was negligible, while data from a design with three levels would conclude otherwise. Continuous process improvement is however prepared to be incremental – there will always be time to go back into more analysis and improvements. Once two, three, or at most four control factors are chosen for being the most crucial ones, then a design with more levels (three, four, or a central composite design) can be used and the solution space explored in more detail to reveal regions of improved performance. Data Analysis: Identifying Crucial Factors The Taguchi method does not need to fit mathematical models to the data obtained with the orthogonal array design. Instead, it applies an analysis of variance (ANOVA), a statistical method that quantifies the variability of the data collected by its variance, and then determines how much of it can be explained by the fact that each of the factors changed its settings. If the amount of data is sufficient to have enough degrees of freedom with the DoE used, a significance test can also be applied to ascertain which factors have a statistically significant effect. Results can be shown in the form of a pie chart, which gives a very good image of what is more important and what might be neglected in a first approach. A typical result from ANOVA, with the most relevant outcomes in the form of a table and pie chart for a situation where the relevance of seven factors was tested with an L-8, is shown in Figure 1 (case study regarding a particle coating process). In this example, the design was replicated (2 runs for each condition, totaling 16 data points), which gives enough degrees of freedom to test for significance. The pie chart shows not only the relative importance of each factor, but also how much of the variability of the data is unexplained. The unexplained amount of the variance may be due to (1) the relevance of interactions and the consequences of the intricate confounding of the design, (2) the influence of other factors that were not controlled and not considered in the design, and (3) the natural variability, or white noise, which may come from variability in control factors, in the characteristics of the materials or process, and also of the method of analysis of the performance, which is similar to random experimental error. The example shown suggests that changing the settings of three of the factors accounts for a large proportion of the changes that can be achieved in the performance. Data Analysis: Identifying Settings for Improved Performance with the Taguchi Method The estimate of which is the combination of settings of the control factors that gives the best performance is done in the Taguchi method by simply choosing for
each factor the setting that had the best average performance. This has the advantage of not relying on any model fitting, and the disadvantages are that it will suggest settings for all factors from only among those that were used in the experimental design (even if the best combination is not one of those tested), and that it does not account for interactive effects. It is possible to include a correction for the effect of some interactive effects if the DoE has enough degrees of freedom for that, but it is a matter of interpretation which interactive effects are being tested because of the intricate nature of the confoundings. Taguchi recommends the calculation of a severity index to at least evaluate the relative potential importance of all interactions between pairs of control factors, but the extent to which this effectively gives unique results is not clear. Furthermore, when searching for a region of optimum performance, the designs usually have at least three (if not more) settings, and in this case it is virtually impossible to properly account for any interaction, unless one is effectively using a full factorial design (e.g., only two factors in an L-9). Therefore, the best combination of settings obtained by the Taguchi method assumes in practice that interactions between factors are negligible. Taguchi recommends validation tests for the new settings, of course. Figure 2 gives an example of the graphs showing the averages of the data for each setting of each factor, known as the ‘means plots’, for a system where three factors were changed with four levels, according to a modified L-16. The maximum performance in that case is suggested for the combination of settings 3-4-2 of the three factors. The estimated performance of the system for that combination of settings is 99.08, obtained simply by adding to the global average of the data (81.29 in that case) the incremental benefit of choosing the respective setting of each factor, as per the means plots. Estimating performance in this way may lead to physically inconsistent values in some cases (for instance, performance above 100% or losses below 0%), which can be improved by a logarithmic transformation, such as the omega transformation. Data Analysis: Identifying Settings for Improved Performance with Response Surface Method An alternative that has been widely applied in Europe and the United States is the response surface method (RSM; or response surface analysis (RSA)). It can be applied to any design, including the central composite design, and is based on postulating a mathematical model to describe the influence of the factors (and interactions) on the performance. It has the advantage that designs such as the central composite design that have much less confounding issues can be handled, but
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ANOVA table for data FACTORS Torque Rotational speed Temperature Oil viscosity Drip feed rate Drip concentration Coating Error Total
SS 0.000 798 0.001 58 9.51E-05 0.008 145 0.037 733 0.021 098 0.037 153 0.008 633 0.115 234
df 1 1 1 1 1 1 1 8 15 16
Total no. of data points:
VARIENCE 0.000 798 0.001 58 9.51E-05 0.008 145 0.037 733 0.021 098 0.037 153 0.001 079 0.007 682
F 0.739 589 1.464 292 0.088 097 7.548 277 34.96 838 19.551 75 34.430 41
F-limit: 3.457 919 Ne: 2
(a)
Torque 1%
Rotational speed 1%
Error 7%
Temperature 0% Oil viscosity 7%
Coating 32%
Drip feed rate 34%
Drip concentration 18% Figure 1 Example of an analysis of variance (ANOVA) table (a) and pie chart of the corrected sums of squares (b) for a system potentially influenced by seven factors, tested with an L-8 design replicated once. Factors in bold in the ANOVA table have statistical significance at a 90% confidence level. Ne is the effective number of data points, which is equal to the actual number of data points divided by 1+ the sum of degrees of freedom of the factors used to produce the estimate. The table and graph were produced in MS Excel.
the disadvantage is that the results will assume the validity of the mathematical model, and so the lack of fit is added to the overall amount of unexplained variance. The simplest model is a quadratic multifactorial polynomial, that is, the sum of linear, interactive, and quadratic terms. A linear term is proportional to the value of the factor, an interactive term is proportional to the product of the value of one factor and the other, and a quadratic term is proportional to the square of the value of the factor. All values must be normalized between maximum and minimum, which is called ‘coding’ (numerically, 1 and 1 are common, but can also be 0 and 1, or 0 and 100%). While being
useful in terms of all parameters of the model having a very clear meaning, it assumes parabolic curves for all effects, which tends to suggest points of minimum or maximum that do not really exist. Once a model is fitted to the data and its goodness of fit accepted, it can be used to pinpoint the location of the best combination of settings (searching for the point of maximum or minimum within the constraints of the solution space). The goodness of fit is typically quantified by the coefficient of determination (designated R2), which quantifies the percentage of the variance of the data that is explained by the model, and values over 90% are usually desired.
270 Plant and Equipment | Continuous Process Improvement and Optimization Drip feed rate
Drip concentration
Coating
95 90 Best
85
Best
Best 80 75
4
3
tti ng Se
2
tti ng Se
1
tti ng Se
4
tti ng Se
3
tti ng Se
2
tti ng Se
tti ng Se
Se
tti ng
1
4
3 Se
tti ng
tti ng Se
tti ng Se
Se
tti ng
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Figure 2 Example of means plots of the performance of a system affected by three factors changed with four settings each, according to a modified L-16 array. The dotted line indicates the average of all data. For each factor, the data are divided in four subsets according to the setting of that factor and the dots show the four averages. Calculations and plots were produced in MS Excel.
There are two useful plots, Pareto charts and surface plots. The Pareto chart represents the standardized effects as horizontal bars, and as such the limit of statistical significance can also be represented as a vertical line. The bigger the bar, the more important the effect. Standardized effects are the effects divided by the standard errors, and when using a model they are also equal to the parameters of the model divided by their confidence
intervals. An example is shown in Figure 3 (case study of loss of an active ingredient in a pasteurization process, as affected by flow rate, inlet temperature, and length of holding section). Surface plots can only be made for a pair of factors at a time, and they can be represented in three dimension (3D) or two dimension (2D) (Figure 4) to help visualizing the regions of improved performance, as predicted by the model.
P1
9.35 5.98
P11 P2
5.27 4.82
P12 2.89
P22 P3
1.81 0.95
P13 P33
0.71
P23
0.63 0
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Standardized effects
Figure 3 Example of a Pareto chart for a system affected by three factors, which was tested with a central composite design, fitted with a quadratic model. The vertical line represents the limit of significance at a 95% confidence level. The notation 1, 2, or 3 refers to the linear effects (linear terms of the model), 11, 22, and 33 to the quadratic effects, and 12, 13, and 23 to the interactive effects, where 1, 2, and 3 are the generic names of the factors. In this example, factor 3 and all its interactions are not statistically significant. Factor 1 is the most important, and its effect is strongly nonlinear, showing a significant curvature (quadratic effect very relevant) and an influence affected by the settings of factor 2 (interactive effect 1 2 significant). In this case study, the factors were inlet temperature, flow rate, and length of holding section in a pasteurizer. The calculations and graph were produced in MS Excel.
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(a) 46 44 42 40
80 70 60 50 40 30 20 10 0 0 –1 2 3 0 3 8 2 6 2 4 Tb 2 22
38 36 34 32 30 28 26 24 22 20 18
1 1 .2 1.1 .20 5 1 1 .1 5 1.0 .05 0 0 0 20 8 0 .9 0. .90 5 1 8 1 4 0 0.80 85 1 .75
16 14 12 10 8 6 4 2
(b) 32 30 28 26 24 22 20 18 16 14 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25
50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2
Figure 4 (see color plate 89) Examples of three-dimensional (a) and two-dimensional (b) plots of the influence of two factors on the performance of a system predicted by a model (other influential factors are kept at a constant setting). In the example, optimum performance means minimum losses of a valuable active ingredient, and the two factors shown are inlet temperature and flow rate. The plots were made using the Statistica software (Statsoft).
See also: Plant and Equipment: Quality Engineering.
Further Reading Bashein B, Markus M, and Riley P (1994) Preconditions for BPR success – and how to prevent failures. Information System Management 11(2): 7–13. Womack J, Jones D, and Roos D (1990) The Machine That Changed the World – The Story of Lean Manufacturing. New York: McMillan Pub. Co. Liker J (2004) The Toyota Way – Fourteen Management Principles from the World’s Greatest Manufacturer. New York: McGraw-Hill. Markgraf S (1997) Fortified with kaizen: Superior Dairy celebrates its 75th anniversary with a ‘different’ approach to doing business – kaizen business concept. Dairy Foods 1 September 1997.
Monden Y (1981a) What makes the Toyota production system really tick? Industrial Engineering 13(1): 36. Monden Y (1981b) Adaptable kanban system helps Toyota maintain just-in-time production. Industrial Engineering 13(5): 29. Monden Y (1981c) Smoothed production lets Toyota adapt to demand changes and reduce inventory. Industrial Engineering 13(8): 42. Monden Y (1981d) Toyota production smoothing. 2. How Toyota shortened supply lot production time, waiting time and conveyance time. Industrial Engineering 13(9): 22–30. Montgomery D (2009) Design and Analysis of Experiments, 7th edn. Hoboken, NJ: John Wiley & Sons. Ross P (1988) Taguchi Techniques for Quality Engineering. New York: McGraw-Hill. Roy R (2001) Design of Experiments Using the Taguchi Approach – 16 Steps to Product and Process Improvement. New York: Wiley Interscience.
272 Plant and Equipment | Continuous Process Improvement and Optimization Shigeo S and Dillon AP (1989) A Study of the Toyota Production System from an Industrial Engineering Viewpoint. Norwalk, CT: Productivity Press. Sugimori Y, Kusunoki K, Cho F, and Uchikawa S (1977) Toyota production system and kanban system materialization of just-in-time and respect-for-human system. International Journal of Production Research 15(6): 553–564. Taguchi G, Chowdhury S, and Taguchi S (2000) Robust engineering implementation strategy. In: Robust Engineering – Learn How to Boost Quality While Reducing Costs and Time to Market, ch. 2, pp. 10–15. New York: McGraw-Hill.
Ward A, Liker JK, Cristiano JJ, and Sobek DK (1995) The second Toyota paradox: How delaying decisions can make better cars faster. Sloan Management Review 36(3): 43–61.
Relevant Websites http://kaizen.com – Kaizen Institute. http://lean.mit.edu – Lean Advancement Initiative of MIT.
Quality Engineering J C Oliveira, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Quality Engineering and Quality by Design Engineering is the application of scientific and empirical knowledge to create a new good or service. To ‘engineer’ something means to design what it should be, how it should be made, and how the process of making it should operate. ‘Quality engineering’ therefore means that the quality of a product (or service) can be engineered in its production process itself, so that it becomes a characteristic inherent to the product every time it is manufactured in the process. Quality not being a characteristic that is measured, but a consequence of the design of the process and of the way that it operates, leads to the term ‘quality by design’ (QbD) alternatively used to express this concept. Conventional quality control systems act on the end result: products are tested for quality and compared to the desired specifications. Non-conformity of a product to the specifications results in a waste: the product must be discarded or reprocessed, depending on whether something can be done to ensure conformity. Quality control is therefore a waste-generating activity. On the other hand, having no quality control can result in a worse consequence, from simple loss of market image to more serious impact, such as that resulting from inadequately processed foods unsafe for consumption. Quality control therefore implies a lack of trust on the capacity of the process to perform consistently and provide quality products all the time. As the process will certainly have been developed properly, this means that it is subjected to variability in its conditions and/or materials it uses, and that variability may result in non-conformities. Not knowing how these sources of variability can present themselves and what can be done to compensate for them, the only option is to check the result at the end, and pray that it is on target most of the time. Achieving QbD, therefore, implies one of two things: (1) eliminate all sources of variability, controlling obsessively everything so that there is no variation and the system repeats itself exactly the same, time after time; (2) analyze the variabilities of the system inputs, know what their impact will be, and operate the system so that it dampens those variabilities to oscillations within conformity. The first case requires good control systems, and the second needs good process intelligence. The first concept would be hopeless in most food industries because of the natural variability of biological
materials: for instance, in dairy, the composition of milk varies throughout the year, with the lactating cycles of the animals. However, there are sectors where such variability in raw materials does not occur, and one could then envisage that tight control systems would suffice. One should consider, though, whether the cost of such tight control would be an acceptable proposition. In the pharmaceutical industry, there has been a growing deployment of process analytical technologies (PATs), one feature of which may be that more sophisticated sensors measure better aspects of the process so that it may ensure better consistency. Some companies have acquired mass spectrometers for applications such as these. However, some simple calculations should be considered: How much does a mass spectrometer cost to buy and to run? What is the value of the quality gains from the better control? How long does it take for the investment to be recovered? In the pharmaceutical industry, it may well be that the product margins are such that expensive equipment is paid for in some years; in the case of the dairy industry, those margins might point to a few centuries. This has led to a much less interest of the food industry in general for PAT, as deployed in the pharmaceutical sector, which is a pity, because in fact PAT does not necessarily imply that very expensive analytical technologies are used to monitor the process and enable a proactive approach to quality control. It is therefore useful to focus on the second option described above, go back to basics, and work out a better system by using process intelligence to achieve QbD, independent of whether acquiring that intelligence requires expensive analytical technologies or not.
The Principles of the Taguchi Method The pioneering work of Genichi Taguchi was a very influential basis of the modern QbD approach. Appointed to lead the Electronic Communications Laboratory (Nippon Telephone and Telegraph Co.) of Japan in 1950, he was faced with ensuring consistently good communications on resources devastated by war. The problem required solutions to be found fast and there were few resources to help and little money to invest. Taguchi spent the best part of the next 12 years developing methods to improve quality and reliability. One of the companies that took up his concepts early on
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was Toyota, and through it and the Toyota Production System (see Plant and Equipment: Continuous Process Improvement and Optimization), the Taguchi method began permeating US and then European industrial practice in the late 1980s. That such a story is at the origin of QbD is very relevant, as it shows that the essence of the system is all about being able to solve problems without throwing money at them. There are two important concepts at the basis: differentiating between control factors and noise factors, and the loss of quality function. The performance of a system is influenced by factors that are controlled by the operator, probably within tight margins, such as temperatures, flow rates, and pressures. It is, however, also influenced by factors that are not controlled, and these may vary more or less significantly depending on random or non-random effects. For instance, milk composition varies throughout the year and also from producer to producer, as it is influenced by animal feed too, not to mention the genetics of the animals. Although control factors may have a bigger influence on the performance, as they are controlled tightly, the variability of performance may be due more to noise factors than to improper control of the control factors. Therefore, more sophisticated control systems for the control factors may be almost pointless. First and foremost, the sources of variability, and how they influence product variability, must be understood. For instance, a pasteurizer may be set to work at 92 C, and the control system does not give better than 1 C. On the other hand, the pasteurizer was designed considering that ambient temperature was a given constant figure (e.g., 15 C). However, depending on the location, this may vary during the year from anywhere between 20 and 40 C. Even though ambient temperature in itself may be less important than the operating temperature for the design of the equipment, in the operation of the pasteurizer its variability may cause more fluctuations than that of the process temperature. However, it is obvious that controlling ambient temperature tightly is a preposterous idea, so controlling variability may not be an option, and the only possibility may be to find a way to live with it. As an engineer, Taguchi knew that changing the settings of a system influences its inertia and so the way that it amplifies, or dampens, the input oscillations. Therefore, one should look for the settings of the control factors that lead to a system that dampens the input oscillations as much as possible: hence the term robust design. A system has a robust design when it performs consistently in spite of the variability of the inputs. The concept of loss of quality function was another original contribution of Taguchi. Previously, the norm was to consider that a product was either acceptable (within the range of specifications defined) or not acceptable, so there was full acceptance or full loss of a product.
Taguchi considered that every time that the product is not exactly on target, there is a loss, which is bigger the further the result is from the target. Taguchi used a simple parabolic function to quantify the loss of quality as the quality indicator deviates from the target value. In fact, if quality is below expectations, there is loss to the client, which over time becomes loss to the company in terms of market image, market share, and so on. If quality is above expectations, there is loss of opportunity for the company, which could have made use of that better quality to get a better price or greater market share. Furthermore, if that higher quality is presented to a client once, that client will then expect the same higher quality next time, and therefore there can be a greater loss of quality by underperforming to expectations the next time. Therefore, the quality loss function should be minimized, and the process should be steered to the quality indicator value that can be delivered more consistently. This means that one would even prefer a business where the product has a lower average quality but that can be delivered consistently, to one with a greater variability even though on average it may be better. In the long term, the second case is going to pile up client dissatisfaction for one reason or another and hurt the business. It can be argued that the evolution of the world wine markets between French producers and New World producers offers a case in point. In order to improve both average quality and its consistency, Taguchi defined the signal-to-noise ratio (S/N) as the objective of an optimization approach: search for the combination of settings of the control factors that gives the maximum S/N. S/N integrates the two objectives: best average quality and best quality consistency. There are three mathematical definitions of S/N, depending on the type of problem, known as ‘bigger is best’ (the higher the average of the quality indicator, the better), ‘smaller is best’ (the lower the average of the quality indicator, the better), and ‘nominal is best’ (the closest the average of the quality indicator is to a nominal target, the better). In essence, the Taguchi method for robust engineering design consists in deploying an experimental plan and statistical data analysis procedure to identify the combination of settings of the control factors that maximizes S/N (for the methods that Taguchi selected for experimental design and data analysis, see Plant and Equipment: Continuous Process Improvement and Optimization). The Taguchi method does not consist solely of applying statistics to plan and then analyzing a set of tests, but it considers the entire framework of operation, teamwork, and other things. See articles in Further Reading for more information. It is noted that once the ‘process intelligence’ has been gathered in terms of availing of a simple model that relates input variability, control factor settings, and
Plant and Equipment | Quality Engineering
output variability (S/N), it is possible to develop a proactive approach to process control (also known as feed forward; see Plant and Equipment: Instrumentation and Process Control: Process Control). By measuring the input factors and their variability (even if they are not controlled, as noise factors), the model can predict what the outcome will be, and hence correct the settings of the control factors to ensure the robustness of the operation (see Plant and Equipment: Instrumentation and Process Control: Process Control). Recently, Charteris advocated the use of experimental design methods and the Taguchi method in particular for competitive quality systems in the food, and specially dairy, industry. The increasingly extensive application of the method in various companies across industrial sectors is its greatest selling point. Theoretically, the Taguchi approach has been contested, mostly for two reasons: it relies on orthogonal arrays in the experimental design, which leads to intricate confoundings (see Plant and Equipment: Continuous Process Improvement and Optimization), and the S/N ratio concept integrates average and standard deviation, and therefore model predictions bundle them together. It may also be noted that in practice maximizing S/N assumes no interactions between factors (see Plant and Equipment: Continuous Process Improvement and Optimization). However, by giving more and due importance to variability and repeatability, it often leads to good results from a limited amount of data.
Statistical Process Control As Taguchi was beginning his work in Japan, ‘western’ statisticians were also assisting industry to develop methods for improving quality consistency. That a proactive approach to quality control was needed was also concluded early. The process should be monitored at several key moments, the variability must be addressed then, and actions must be taken immediately, as needed. The concepts of statistical process control (SPC) were thus developed (for more details, see Plant and Equipment: Instrumentation and Process Control: Process Control). In this case, the type of variability is categorized between common and special causes. The former are identified primarily due to the randomness of variability, while the latter are pinpointed by a clear pattern in the data that cannot be due to chance. The original practice involved using process charts to identify the sources of variability and progressively eliminate or squeeze them, which an enthusiast of the Taguchi method might regard as too laborious and hence not pro-active enough. It also has the obvious disadvantage of relying on process data, which means that the range of
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values considered for the control factors may be too small and the data excessively biased. SPC is basically very good for ensuring that the oscillations in a given process are minimized, but is not really designed to establish best conditions of operation that offer a more robust operation. It may also lead to the over-zealousness of controlling factors with increasingly expensive methods even if such control results in savings that do not justify the costs. Quality engineers deploying SPC may need to resist the temptation for expensive applications of information technologies (IT) or PAT, unless the benefits are clear upfront. For further details, see articles in Further Reading.
Six Sigma The best practice of modern manufacturing industries is generally regarded to be the six-sigma system, although there is some controversy on this. Its name reveals its primary focus on maximizing consistency and thus eliminating waste, as sigma is the Greek letter used in statistics to denote the standard deviation, a quantitative measure of the spread of a series of data. If the data are normally distributed, then the band defined by the average 6 contains 99.999 998 1% of the data. Bringing some element of reality of process operations, the six-sigma creators discounted 1.5 from this, saying that over time a process becomes more ‘sloppy’ than the original design by this much, that is, a process is said to be 6 when the range of average 4.5 is within the specification range: thus, one would be out of spec only 3.4 times in one million (99.999 66% of the data of a normal distribution within 4.5). In practice, it really means that the process is designed/operated to deliver consistency all the time, or as sometimes stated in business science literature, ‘first time right, every time right’. It is generally accepted that the origin of the system lies in Motorola in the early 1980s, and that it was particularly disseminated by Jack Welch, a charismatic former CEO of General Electric (who famously stated that ‘variation is evil’). In broader terms, six sigma results from giving an American managerial approach and organization to projects aimed at eliminating variation that apply much of the concepts and methods of Japanese manufacturing, with the Taguchi concepts being particularly eminent. Six sigma is a method, or work system, not a tool, and therefore it collects and deploys whatever tools can assist to achieve its objective better. Just like the Taguchi method, it involves a comprehensive approach including teamwork, planning, and other things, and it is data driven, that is, it relies on obtaining and analyzing actual process data. In that respect, six sigma is more an American version of the Taguchi approach than the Taguchi method is a part of six sigma. There is some
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confusion in the literature as to what is a tool and what is a system, and often the Taguchi method is taken as the distillation of its statistical approaches – that, however, is only a part of the whole. Just like Taguchi did, six sigma picks up the tools it finds more useful. Among these are the tools used in the Taguchi method (e.g., design of experiment (DoE), analysis of variance (ANOVA), S/N), but many others as well, such as SPC and lean analysis. When lean thinking is added, it is often denoted as the lean six-sigma approach. As it incorporates both operational and process improvements, it is a proper approach to achieve manufacturing excellence in an organized and systematic manner. Critics contest its novelty, as almost everything it uses existed before, and so are the aspects of its implementation. For someone experienced in the Taguchi method, it also seems to be overcomplex, and could lead to the deployment of different approaches that yield the same end result, with no particular benefit in the redundancy. It is common to summarize the overall approach with acronyms: a project to achieve optimum consistency in an existing process applies a series of steps known broadly as DMAIC (define, measure, analyze, improve, and control), while a project geared at developing a new process or product is composed of a series of steps represented by
DMADV (define, measure, analyze, design and validate, or verify). The latter is also known as DFSS, from design for six sigma, that is, design the new process or product so that it will deliver a six-sigma consistency, which is therefore the same as QbD. See also: Plant and Equipment: Continuous Process Improvement and Optimization; Instrumentation and Process Control: Process Control.
Further Reading Chambers D and Wheeler D (1992) Understanding Statistical Process Control. Knoxville, TN: SPC Press. Charteris W (2007) Taguchi’s system of experimental design and data analysis: A quality engineering technology for the food industry. International Journal of Dairy Technology 45(2): 33–49. Ross P (1988) Taguchi Techniques for Quality Engineering. New York: McGraw-Hill. Roy R (2001) Design of Experiments Using the Taguchi Approach – 16 Steps to Product and Process Improvement. New York: Wiley Interscience. Taguchi G, Chowdhury S, and Taguchi S (2000) Robust Engineering – Learn How to Boost Quality While Reducing Costs and Time to Market. New York: McGraw-Hill. Taguchi G, Chowdhury S, and Yuin W (2004) Taguchi’s Quality Engineering Handbook. New York: Wiley Interscience. Welch J and Welch S (2005) Winning. New York: Harper Collins Publication.
Safety Analysis and Risk Assessment N Hyatt, Dyadem International Ltd, Toronto, ON, Canada ª 2011 Elsevier Ltd. All rights reserved.
Importance of Plant Safety in the Dairy Industry Safety is important in both milk production and dairy processing facilities. Both people and animals can be exposed to a diverse range of hazards. These need to be identified and managed. As an example, people who handle chemicals, antibiotics, vaccines, and veterinary drugs need to be familiar not only with their benefits but also with their potentially hazardous properties. To ensure that these substances are handled safely, the use and distribution of Material Safety Data Sheets (MSDSs) to all involved personnel are a prerequisite. Chemicals, fertilizers, and pesticides can cause environmental damage and possible contamination problems if improperly used or incorrectly handled. Contamination and pollution can also be caused by incorrect handling and storage of manure and dairy wastes. In some instances, asbestos insulation may be present in older farm buildings, which carries the risk of mesothelioma and necessitates a careful and organized program for removal of such insulation by qualified asbestos removal contractors. Dust can also become a health hazard and, if combustible, could lead to fire and/or explosion. Typical job safety hazards are also posed by effluent ponds where drowning can occur and with electrical equipment, often of a temporary and makeshift nature, where electrocution through use of ungrounded electrical equipment, in an aqueous environment, can occur. The use of unguarded prime movers, the temporary removal of guards, and the failure to isolate machinery during maintenance are all sources of hazard and risk: the use of lockout/tagout procedures is essential if maintenance of equipment with moving parts is involved. Also, personnel who work at heights may risk falling and those who engage in manual lifting may sustain injuries. The dairy industry, when compared with many other industries, is not normally associated with high-risk activities. However, large dairy facilities may use a number of hazardous materials that can still pose high risks to both plant personnel and the neighboring communities. As an example, the following substances can present significant risk: 1. Anhydrous ammonia which may be used in refrigeration systems. Release of anhydrous ammonia to the environment, which is normally stored as a liquid
under pressure, can result in a highly toxic subcooled aerosol mist that can hug the ground until it heats up and disperses. Such releases can have quite devastating effects in the path of release. 2. Liquid chlorine which may be stored under pressure and normally used for sanitization purposes. Chlorine gas is heavier than air and is highly toxic: it can cause death even in relatively small amounts. 3. Propane which is stored as a liquefied gas in bullets under pressure. Propane may be used as a heating medium for boilers and heating systems. A number of dangerous incidents have arisen as a result of propane bullets becoming overheated, due to external fires impinging on them and causing Boiling Liquid Expanding Vapor Explosions (BLEVEs). Overall, many different types of hazards are often present at a dairy facility and the failure to be aware of these can lead to accidents and injuries. It therefore follows that potential hazards, in the first instance, need to be formally identified in order for them to be managed. The key steps in safety analysis are (1) the systematic identification of hazards that are present, whether obvious or latent, (2) the prioritization of hazards using a risk matrix approach, and (3) the management of hazards through the introduction of risk control or risk mitigation measures. Usually, these three steps are adequate for the majority of in-plant safety issues. Where greater issues that could pose significant risks not only to in-plant personnel but also to the neighboring communities exist, it may be necessary, in addition, to perform a Quantitative Risk Assessment (QRA).
Formal Safety Analysis A formal safety analysis can be performed using a number of alternative methodologies. These are known collectively as Process Hazards Analysis (PHA). Typically, they proceed as shown in the following six steps: Step 1: Collect engineering drawings such as Process Flow Diagrams (PFDs), Piping and Instrument Diagrams (P&IDs), and documents that specify the nature and operation of the facility in question. In addition, MSDS for all hazardous substances stored or used at the facility should be available for the analysis.
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Step 2: Break down the facility into definable and specific subunits that provide a common function. This is a form of itemizing and is sometimes known as creating ‘nodes’. Step 3: List questions for each subunit or node that can explore and investigate design or operational deviations that might reveal undesirable or possibly hazardous conditions outside the normal range. Step 4: For each question listed in Step 3, record the causes for the deviations and the consequences that might occur or result from such deviations. In addition, the safeguards that may already be in place to either prevent the cause of the deviation or to protect or mitigate the consequences should be recorded. Furthermore, any recommendations should be considered to reduce the risk by providing additional safeguards that are not currently available. Step 5: Proceed throughout the facility so that all subunits or nodes are covered. Step 6: Prepare a detailed report that includes both documentation on the facility as well as details of the PHA. When this stage is reached, it is possible to create a risk management plan to determine what needs to be done to reduce the risk in order to make the facility safer. Also, when the PHA is being undertaken, it is often best to assemble a team of personnel responsible for the design and operation of the facility so that all possible concerns are systematically investigated. There are four different types of PHA that are typically used: 1. Hazard and Operability (HAZOP) analysis, where deviations are created by applying guidewords such as High, Low, Reverse, As Well As, Part Of, and Other Than to properties such as Flow, Level, Pressure, Temperature, Concentration, and pH. This is a popular methodology within the process industries but is really applicable only where the systems involve flowing fluids, often on a continuous basis. HAZOP may also be applied to batch operations where the guidewords also include Sooner and Later to account for time aspects. 2. ‘What if. . .’ analysis, where deviations are created by listing questions that pose design and/or operational problems. This is a relatively simple technique that, although less structured than HAZOP, is applicable to almost any facility or part of any facility regardless of design, function, or operation. Furthermore, it is easy to learn and apply. 3. Failure Mode and Effects Analysis (FMEA), where items of equipment are broken down into components. For each component, the deviations are different possible failure modes for that component. The consequences are the effects of the various types of failure that are identified. FMEA is normally recommended for analyzing equipment failures as opposed to fluid system failures. It can typically be applied to prime movers, instrumentation, and control equipment, and,
in addition, is a useful method for improving reliability through the identification of possible failure modes. 4. Checklist analysis, where a list of questions and concerns is created from either preexisting data or information or based upon previous experience. This technique is less structured than the other three methods described above but is useful prior to commissioning a new system where there are concerns over any residual issues that might have been created or overlooked by construction teams. In addition to these above four methodologies, ‘What if . . .’ analysis and Checklist analysis are often combined as ‘What if/Checklist’. This ensures that an adequate list of questions (i.e., possible deviations) is created. Furthermore, when applying these types of methodologies to occupational safety, the form of analysis used is Job Safety Analysis (JSA) where people’s jobs are specifically analyzed for hazards. All of the above methods are oriented toward the identification of potential hazards and hazardous situations, whether obvious or latent. These analyses normally identify single jeopardy hazards as opposed to double or multiple jeopardy situations. From the standpoint of likelihood, single jeopardy is the most likely and double or multiple jeopardy is far more unlikely.
Definition of Risk While the identification of hazards, including potential hazards, is of paramount importance, the quantification of risk can, in some instances, be desirable. Risk is a measure of the importance of hazards posed and is a function of both the severity of the hazard and the likelihood, or frequency, of the hazard occurring. The technical definition of risk is the product of the consequence, that is, the severity of the hazard and the frequency, that is, the likelihood of the hazard ever occurring. In other words Risk ðRÞ ¼ Consequence ðCÞ Frequency ðF Þ
The consequence may be expressed as the chance of mortality, as financial damage that may be incurred or the loss of revenue that may result from an incident. Typically, when consequence is expressed in terms of mortality or, more specifically, in terms of the probability of fatality, the values provided in Table 1 can be useful. The frequency is often expressed as the number of times per annum that the incident may occur. Hence, for example, if the incident were likely to occur once every year or so, this would be deemed as ‘very likely’ but if it occurred only once in a 1000 years it would be deemed as ‘very unlikely’. It can seem difficult to envision individual risk levels without comparison to known risks experienced on a day-to-day basis. Table 2 provides this comparison.
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Table 1 Value of fatality probability and associated effects Value of fatality probability
Associated effects
1.0 0.1 0.01 0.001
Effects would be fatal for any individual exposed to the hazard With 10 persons exposed to the hazard there would be one fatality With 100 persons exposed to the hazard there would be one fatality With 1000 persons exposed to the hazard there would be one fatality
Table 2 Example of comparative mortality statistics Hazard
Total number of deaths
Individual chance of death per year
Heart disease Cancer Work accidents All accidents Motor vehicles Homicides Falls Drowning Fires, burns Poisoning by solids or liquids Suffocation, ingested objects Firearms, sporting Railroads Civil aviation Water transport Poisoning by gases Pleasure boating Lightning Hurricanes Tornadoes Bites and stings
757 075 351 055 13 400 105 000 46 200 20 465 16 300 8100 6500 3800 2900 2400 1989 1757 1725 1700 1446 124 93 91 48
3.4 103 1.6 103 1.5 104 4.8 104 2.1 104 9.3 105 7.4 105 3.7 105 3.0 105 1.7 105 1.3 105 1.1 105 9.0 106 8.0 106 7.8 106 7.7 106 6.6 106 5.6 107 4.1 107 4.1 107 2.2 107
Data on Mortality Statistics for USA, 1974, and revised, 2000: Chemical Manufacturer’s Association.
In Figure 1, an example of a risk matrix is shown that can be used in conjunction with a PHA to enable members of a risk analysis team to assess first-order estimates of risk associated with an activity or item of plant. When values are in excess of 103 deaths per annum then some additional risk control measures or additional risk mitigation should be considered. Every activity normally carries some level of risk, however small it may be, and most people accept this as part of the day-to-day reality of life. Zero risk for an activity is not usually possible unless the activity ceases altogether.
incidents are high-enough risk to warrant full risk quantification and assessment. Step 2: Model the consequence of the incident as a function of distance from the hazard source. This is done using mathematical models as typically listed in Table 3. Step 3: Model the frequency of the potential incidents. A variety of methods can be used as shown in Table 4. Step 4: Having numerically determined both the consequences, in terms of probability of death per occurrence and frequency of occurrence in times per annum per event, individual risk can be computed as R i ¼ C i Fi
Risk Assessment When incidents involving hazardous materials could cause significant in-plant damage and also threaten neighboring communities, it may be in order to consider performing a QRA for the facility. The following steps are usually undertaken: Step 1: From the PHA already performed and by applying the risk matrix methodology, determine which
where Ri ¼ individual risk, in deaths per annum for a single event, i; Ci ¼ probability of death, dimensionless from the consequence of event, i; and Fi ¼ frequency of single event, expressed in events per annum. The idea behind individual risk is the risk that might be posed to an individual who is in the vicinity and exposed to the hazard in question. Individual risk is also a function of distance from the hazard, which, although not affecting the frequency,
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Figure 1 Matrix showing individual risk in deaths per annum.
Table 3 Listing of consequence models used for risk assessment Hazard
Consequence model
Effects and modeling
Fire
Pool fire Jet fire Fireball Flash fire Vapor Cloud Explosion (VCE) Missiles and shrapnel generation Boiling Liquid Expanding Vapor Explosion (BLEVE)
Thermal radiation generated by fire can cause burns that can be lethal and models can predict exposure levels as a function of distance from source. Probit analysis can predict probability of death as a result of radiation dosage and exposure time. Overpressure and momentum forces can result in lung and ear-drum damage and cause the collapse of buildings leading to death. Probit analysis can predict likely effects and probability of death as a function of overpressure. Simple models for missiles and shrapnel generation exist that indicate likely size, number, and range. BLEVEs are also modeled as fireballs. Vapor dispersion and dilution occur in the atmosphere and can be modeled as a function of distance from the source of the release for both neutrally buoyant and dense gases taking into account meteorological conditions, wind direction, and wind speeds. Probit analysis for specific gases can predict probability of death with dosage and time elapsed.
Explosion
Toxic vapor releases
Vapor dispersion
could increase the consequence if the exposure to the hazard is increased. Since there is often more than one source of risk, it is also relevant to consider total or integrated risk. Thus, the overall integrated risk, considering n events and each event having its own specific consequences and frequency, can be expressed as Roverall ¼
n X ðCi Fi Þ
Step 5: Determine the basis for benchmarking or judging what levels of risk can be considered as acceptable. In judging individual risk criteria, the criteria shown in Table 5 may be considered. Societal risk, as opposed to individual risk, represents the integrated risk that may be posed to a group or multiple individuals located within a specific area or zone. Societal risk may thus be expressed mathematically as
i¼l
where Roverall ¼ integrated individual risk, in deaths per annum for n events in total.
Rsocietal ¼ N
n X ðCi Fi Þ i¼l
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Table 4 Modeling of frequency or likelihood of incidents Method
Basis
Data used
Fault trees
Fault trees model events using a top-down approach to show top event as the undesirable event and all contributory factors and subevents that lead to the top event. Proceeds from left to right starting with initial cause of incident and considers optional outcomes that can be assigned probabilities of occurring or failing to occur. A range of possible final outcomes is the end result.
Available failure rate data, reliability data, and contingent factors analysis where no data are readily available. Original causal event frequency is assigned based on failure rates of piping, gaskets, etc. Subsequent events likelihood use assigned probabilities based on available data, best judgments, and estimates. Recorded data from same, similar facilities and recorded data available on a global basis.
Event trees
Historical data
Use of available databases to provide frequencies of specific types of events.
Table 5 Risk tolerance criteria Individual risk level in deaths/annum >1 103 1 103 1 104 106
Tolerance level Exceeding 1 103 deaths per annum is deemed intolerable Should not exceed 1 103 deaths per annum maximum for workers provided that As Low As Reasonably Practicable (ALARP) measures are in place Should not exceed 1 104 deaths per annum maximum for the public provided that ALARP measures are in place Individual risk criteria are broadly acceptable at 1 106 deaths per annum
Data from ALARP – Guidance on as low as reasonably practicable decisions in COMAH: Health & Safety Executive (HSE), UK.
where N ¼ total number of persons exposed to the individual total risk and where risks vary depending on the numbers in different communities and their locations: Rsocietal overall ¼ Rsocietal overall;1 þ Rsocietal overall;2 þRsocietal overall;3 þ
Although societal risk may be evaluated, the acceptability of criteria is more complex than that of individual risk. FN curves may be used for societal risk where the ordinate represents the cumulative frequency distribution of N or more fatalities and the abscissa represents the consequence (N fatalities). Although there are published data on FN curves, their acceptability has not been widely adopted. Currently of greater interest is the ALARP (As Low As Reasonably Practicable) criteria. This recognizes three regions. The first of these is the ‘unacceptable region’ where the activity is of such a high risk as to render it unacceptable. The second region is the ‘broadly acceptable region’ where the activity has a very low risk and no further measures are needed for risk reduction. The third region is the ‘tolerable region’ where the level of risk falls between ‘unacceptable’ and ‘broadly acceptable’ and has been reduced to the lowest level of risk as considered to be practicable. Step 6: Apply risk management principles. Risk may be managed once the hazards have been identified. If the QRA route has been undertaken, then the calculated overall risk, Roverall or Rsocietal overall should be compared
to what may be deemed as tolerable. Depending on the level of tolerable risk, the decision to accept the risk or take remedial action(s) must be made. If the level of risk is within accepted margins, then no further action may be necessary. If the level of risk is excessive, then actions requiring remediation and costing plant modifications, procedural changes, as well as emergency response planning may be needed.
Risk Reduction and Risk Mitigation Risk reduction is possible only if hazards are identified and then measures are taken to reduce these risks. Although it may be possible to reduce the risk to a level that is considered acceptable, it is rarely possible to eliminate risk altogether. When facilities are designed originally, there may be good opportunities to introduce design features that can minimize risk whereas if safety is addressed as an issue only late in the design it may be extremely costly to incorporate such features. Safety in design is sometimes considered in terms of ‘active’ and ‘passive’ safety features. A passive safety feature requires no form of activation or initiation for the feature to be protective. For example, increased distance and spacing is valuable as a passive safety feature as would also improved road access, dikes around tanks containing flammable materials, and reduced
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inventories of hazardous materials. An active safety feature would be instruments, controls and automated trips, and most safety devices operated electrically, electronically, hydraulically, pneumatically, or even mechanically. Although both active and passive safety features are needed at a facility, passive safety features are much more dependable. On existing facilities, it may be difficult or impossible to add passive safety features and very often only additional active safety features can be incorporated where risk reduction is required.
Qualitative Risk Analysis versus Quantitative Risk Assessment Risk may be analyzed either qualitatively or quantitatively. For the majority of cases where no significant risk is posed to adjoining communities, the qualitative analysis should be adequate. However, where the potential for encroachment by new housing communities is an issue, the quantitative assessment has merit for establishing recommended buffer zones around the facility. It is often difficult to say where an assessment of risks ends and risk control begins or to assess risks without making a number of assumptions; at best, a risk assessment is an order of magnitude estimate and is directional as opposed to being absolute. Unless inputs and assumptions are very similar, the repeatability of risk assessment is hard to achieve. Risk assessment is a tool for extrapolating from statistical, engineering, and scientific data, a value that people will accept as an estimate of the risk attached to a particular facility. There are many techniques for risk estimation, tailored to different applications that cover a wide range of different disciplines, such as toxicology, engineering, statistics, economics, and demography. The true value of risk assessment, through the QRA, lies mainly in comparing overall risk levels both before and after risk remediation is incorporated. For example, suppose an overall level of individual risk is determined to be 104 deaths per annum for a facility and that after remediation it is reduced to 106 deaths per annum. This means that remediation has made the facility 100 times safer. This improvement may be considered to be more important than trying to determine exact levels of risk.
Risk Assessment and Emergency Response Planning A QRA can identify situations where an Emergency Response Plan (ERP) or buffer zones or restrictions should be considered. The output of an analysis, of risk
versus distance from the hazard source, can indicate hazard zones. Depending on these findings, a detailed ERP may be needed. This will also address the Emergency Response Planning Guideline (ERPG) levels 1, 2, and 3 distances. The distance to the ERPG-3 level corresponds to the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for 1 h without experiencing or developing life-threatening health effects. The distance to the ERPG-2 level corresponds to the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for 1 h without experiencing irreversible or other serious health effects or symptoms that could impair their abilities to take protective action. The distance to the ERPG-1 level corresponds to the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for 1 h without experiencing other than mild transient adverse health effects or perceiving a clearly objectionable odor.
See also: Risk Analysis.
Further Reading Center for Chemical Process Safety (CCPS) (1989) Guidelines for Process Equipment Reliability Data, with Data Table. New York, NY: American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS) (1994) Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires and BLEVE’s. New York, NY: American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS) (2000) Guidelines for Chemical Process Quantitative Risk Analysis. New York, NY: American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS) (2008) Guidelines for Hazard Evaluation Procedures. New York, NY: American Institute of Chemical Engineers. Cox AW, Lees FP, and Ang ML (1990) Classification of Hazardous Locations. Rugby, UK: Institution of Chemical Engineers. Hyatt N (2004) Guidelines for Process Hazards Analysis, Hazards Identification & Risk Analysis. Boca Raton, FL: CRC Press. Hyatt N (2006) Incident Investigation and Accident Prevention in the Process and Allied Industries. Boca Raton, FL: CRC Press. Kletz TA (1992) HAZOP and HAZAN. Rugby, UK: Institution of Chemical Engineers. Lees FP (1996) Loss Prevention in the Process Industries, Vol. 1, ch. 2, pp. 10–25. Oxford: Butterworth-Heinemann. Pape RP and Nussey C (1985) A basic approach for the analysis of risks from major toxic hazards. IChemE Symposium Series No.93, pp. 367–388. Rugby, UK: Institution of Chemical Engineers. Parry ST (1986) A Review of Hazard Identification Techniques and Their Application to Major Accident Hazards. SRD R 379. United Kingdom Atomic Energy Authority. SRD R 379. Rijnmond Public Authority (1982) Risk Analysis of Six Potentially Hazardous Industrial Objects in the Rijnmond Area: A Pilot Study. Springer, Hardcover-02-1982, ISBN 90-277-1393–6. Sutton I (2002) Process Hazards Analysis. SW/Sutton & Associates. UK Health & Safety Executive (1980) Quantified Risk Assessment: Its Input to Decision Making. UK Health & Safety Executive (UK HSE).
In-Place Cleaning M Walton, Society of Dairy Technology, Appleby in Westmorland, UK ª 2011 Elsevier Ltd. All rights reserved.
Introduction Cleaning in place (CIP) is a vital discipline within the modern food, dairy, and beverage processing industry. Dairy and beverage have tended to lead the way due to the major products being liquid and the process equipment lending itself to CIP. However, many food or pharmaceutical operations now incorporate CIP and the technology is therefore much more common. In the 1990 edition of the Society of Dairy Technology (SDT) Manual Cleaning In Place, CIP was defined as ‘‘The cleaning of complete items of plant or pipeline circuits without dismantling or opening of the equipment and with little or no manual involvement on the part of the operator. The process involves the jetting or spraying of surfaces or circulation of cleaning solutions through the plant under conditions of increased turbulence and flow velocity.’’ This was taken from the National Dairymens Association (NDA) Chemical Safety Code, 1985, and while the NDA has been superseded, their definition of CIP is still felt to be quite appropriate.
Practice in the Dairy Industry The modern dairy plant, be it for liquid milk or the multitude of other dairy products, will have at least two CIP sets at its heart; it is generally accepted as best practice that raw and finished product should be segregated to avoid cross-contamination. The raw milk CIP set will be responsible for cleaning the raw milk silos and associated milk intake pipe-work along with any in-line coolers and filters including transfer lines to the pasteurizer. It is at this point that the segregation between raw and finished (pasteurized) products is maintained. In many cases the pasteurizer with its associated items of processing equipment such as homogenizer, separator, and standardization unit will be cleaned together. The cleaning operation can be single-stage or two-stage, but the principle of single use remains. In a few sites, a partial recovery system may be used. There are benefits and drawbacks in each type of system and these will be discussed in more detail later. The finished milk CIP set will clean all items of plant that are used to store, process, and pack finished or pasteurized product. It is vital that this cleaning equipment be maintained to the highest
standards in order to ensure good plant hygiene and to avoid product contamination, either physical or microbiological, that would have an adverse effect on final product quality or shelf-life.
Outline of a CIP System The main stages of CIP are similar to any other standard cleaning routine: removal of gross debris (product purge); pre-rinse; detergent (normally acid- or caustic-based); intermediate rinse; second detergent if applicable; intermediate rinse; disinfectant; and final rinse with potable water. The diluted detergents are generally stored in tanks as part of the CIP unit or CIP set and will be built up into a fully operational CIP set with valves, manifolds, and interconnecting pipe-work, including an automated control system. The design of the CIP set will depend on the duty required. Other considerations such as available space and budget constraints do influence the design but making compromises at the design stage is not recommended, as poor CIP performance can have a significant impact on product quality. Figure 1 shows a four-tank partial recovery system with a single channel or CIP route operation. On larger sets, there can be five or six separate channels linked by common inlet and outlet manifolds. Other configurations are possible, with or without a rinse recovery tank. It is quite unusual to find recovered disinfectant storage tanks as these require very close management and can easily become contaminated leading to potentially serious consequences; hence, the tank denoted as ‘utility’ in Figure 1 when used for disinfection is likely to be of single use. Most CIP sets have some degree of automation, the most basic being a set of timers to open and close automatic valves in a particular programmed sequence at specific times. More sophisticated sets incorporate significant levels of field instrumentation with sensors, usually mounted in-line to monitor flow, temperature, pressure, conductivity, turbidity, etc. Control of detergent concentration is usually automated and the most common configuration is a control conductivity probe situated in a recirculation loop to ensure good mixing when extra detergent is added to the solution.
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284 Plant and Equipment | In-Place Cleaning
Alkali Acid Water T
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Figure 1 Single-channel, four-tank partial recovery CIP system.
Detergents and Disinfectants In the dairy industry, the most common type of detergent is a caustic soda-based product, quite often containing a blend of sequestrants, surfactants, and other additives to assist with the cleaning task. The detergent also needs to be compatible with the prevailing water hardness conditions in order to prevent scale deposition, especially during rinsing. The selection of the correct detergent is a specialist activity and needs to take into account factors such as materials of construction, soiling type and levels, and product safety. The effectiveness of the caustic sodabased material is heavily influenced by the specific blend of additives and these are designed to remove dairy soils such as fat, protein, and more complex molecules and structures that are created by the process or simply by heat such as calcium carbonate. In certain circumstances, acidic detergents are used; these are often based on phosphoric or nitric acid or blends of the two and are found to be effective at removing inorganic deposits in dairy processing plants. Disinfectant solutions can generally be divided into oxidizing and non-oxidizing products, the former being more common for CIP use as they tend to be more efficacious and have a lower tendency to foaming that can lead to rinsing difficulties. The traditional dairy disinfectant was sodium hypochlorite, a very cost-effective product for CIP disinfection but with the major drawback for dairy CIP of
being corrosive to stainless steel. It is now more common to utilize an equilibrium mixture of hydrogen peroxide and acetic acid – peracetic acid – and this is commercially available, often supplied at 5 or 15% activity.
Application in Dairy Equipment The four main types of equipment encountered in a typical dairy situation are pipelines, vessels, fillers, and cheesemaking equipment. These are all normally cleaned using CIP and it is important to ensure that each is cleaned in the correct manner, for example, to clean a pipe effectively, turbulent flow should be achieved. As a generally accepted ‘rule of thumb’ the flow rate required to achieve turbulent flow and therefore provide optimal cleaning is around 1.8 ms 1. Fillers and complex items such as cheesemaking equipment will require purpose-built cleaning and spray systems installed within the plant to ensure good coverage. In some cases, there is a requirement to clean internal surfaces via CIP and also to include external surfaces, such as on a liquid milk filler, and utilize a specific, permanently installed foam cleaning system. All tanks and process vessels will include a spray device of some description. Traditionally this was a simple spray ball, which is now being superseded by the use of rotating spray heads that provide a much
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more effective clean and have the added benefit of lower water consumption. See also: Biogenic Amines. Hazard Analysis and Critical Control Points: Processing Plants. Utilities and Effluent Treatment: Design and Operation of Dairy Effluent Treatment Plants.
Further Reading Seiberling DA (ed.) (2007) Clean-in-Place for Biopharmaceutical Processes (Drugs and the Pharmaceutical Sciences), 1st edn. Informa HealthCare. ISBN-13: 978-0849340697. Tamime AY (ed.) (2008) Cleaning-in-Place: Dairy, Food and Beverage Operations, 3rd edn. Wiley-Blackwell in association with the Society of Dairy Technology. ISBN-13:978-14051-5503-8.
POLICY SCHEMES AND TRADE IN DAIRY PRODUCTS
Contents Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy Agricultural Policy Schemes: European Union’s Common Agricultural Policy Agricultural Policy Schemes: United States’ Agricultural System Agricultural Policy Schemes: Other Systems Codex Alimentarius Standards of Identity of Milk and Milk Products Trade in Milk and Dairy Products, International Standards: Harmonized Systems Trade in Milk and Dairy Products, International Standards: World Trade Organization World Trade Organization and Other Factors Shaping the Dairy industry in the Future
Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy H O Hansen, University of Copenhagen, Copenhagen, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction Agricultural support is a very important element in agricultural policy in many countries. Agricultural support is basically an instrument to meet the overall objectives of the agricultural policy – objectives set by society. There are a great number of instruments and ways of intervention in agricultural policy and they have different functions and consequences. Often, price mechanisms are used as support instruments, while direct income support is used in other cases. Choice of support system is of major importance and may have far-reaching consequences.
Objectives and Instruments in Agricultural Policy Intervention through agricultural policy is a very important phenomenon in the agricultural sector in many countries. Often, the intervention takes place through the market, and the aim is to improve or stabilize the economic conditions. Intervention itself is not an objective, but it is an instrument to achieve the overall objectives and aims set by society.
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Before the examination of the different instruments, it will be valuable to expose the underlying factors that legitimize those instruments, including support and price policy, of agricultural policy. There is a close correlation between the objectives and the instruments in agricultural policy. Basically, society has set up a number of objectives, which lay down guidelines and directions for the development of agricultural policy. These objectives, which to a large degree are similar from country to country, explain and set the grounds for the instruments in agricultural policy. There are a number of common features in the objectives that are found in agricultural policy in developed countries. In general, agricultural policy in developed countries aims at improving in agriculture, • income income distribution among farmers, • productivity in agriculture, • efficiency in the and marketing chain, • supply and price processing stability, • demographic situation, • environmental status, and • export, employment, production, added value, and so on. •
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Many different types of instruments can be used to achieve the given objectives, and it is a very complicated relationship. Some instruments can be used to achieve several different objectives, whereas other instruments benefit the achievement of some and limit the achievement of others. Finally, important differences with respect to financing, effect on production and trade, transparency, and other elements are observed. The instruments in agricultural policy can be divided into different groups:
Price Support Support in the form of higher market prices than, for example, on the world market.
Deficiency Payments Transfers from taxpayers to farmers corresponding to the production multiplied by the difference between the world market price and a given target price on the domestic market.
Support Coupled to Input Factors premiums • Area Headage • Financial premiums support • Other supports to reduce costs • Direct Support Coupled with Other Factors
• Extensification of landscape • Protection Support to enhance structural change • Economic development in rural areas • Support Fully Decoupled from Production for the effects of drought and other • Compensation calamities support, lump sum payments • Income Early retirement schemes • Furthermore, one finds a number of other instruments that should not directly be used to achieve the objectives, but should be used to reduce supply and/or costs related to agricultural policy. Quotas and set-aside are examples of such instruments. Price support and deficiency payments are the most important instruments in the agricultural policy of industrialized countries and account for about 75% of the total agricultural support.
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High and Low Price Systems Market price support and deficiency payments are two very important instruments in agricultural policy; however, they belong to two different support regimes or support systems. Market price support operates in the so-called high price system and is financed by consumers, while deficiency payments operate in the so-called low price system and are financed by taxpayers. In the high price system, support is given mainly by means of import regulations, etc., which ensure a relatively high domestic price. In the low price system, support is given by means of direct support, while market prices are left undistorted at, or close to, world market level. The two different support systems have very different implications for agricultural production, financing, markets, and aspects; still, there is an income transfer to agriculture in both systems in the short run. The balance between market price support and direct payments varies greatly from country to country (Figure 1). In countries like the United States, Ukraine, and Australia, agricultural support is granted mainly as direct payments financed by taxpayers, while market price policy, financed mainly by consumers, is predominant in countries like Japan, Korea, and Russia. Figure 1 also shows the total level of agricultural support. Agricultural support includes transfers from consumers and taxpayers to agricultural producers arising from policy measures that support agriculture – producer support estimate (PSE). PSE is here measured as a percentage of gross farm income including support. The figure illustrates that countries like Iceland, Japan, Korea, Norway, and Switzerland have a high agricultural support level. On the other hand, countries like New Zealand, Chile, Brazil, South Africa, and Ukraine have an almost liberalized agriculture. During the recent decades, agricultural support has changed significantly. The level of support has decreased – protectionism has weakened and liberalization has strengthened. At the same time, the composition of agricultural support has changed significantly. Consumer-financed market price support has decreased, and taxpayer-financed direct support has increased (Figure 2).
Structure and Function As shown in Figure 1, countries like Korea and Japan use mainly the high price system in agricultural policy. In this system, support to farmers is given through high market prices maintained by different instruments like import tariffs (variable or fixed) or other import restrictions, export subsidies, and so on. These instruments ensure an artificially high price level compared to the price level that would result from the interaction of supply and demand in an undistorted market.
288 Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy Consumers’ and taxpayers’ share of cost from agricultural support Consumers
Taxpayers
Australia Canada EU-27 Iceland Japan Korea Mexico New Zealand Norway Switzerland Turkey USA Brazil Chile China Russia South Africa Ukraine OECD
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Figure 1 Level and composition of agricultural support (2007). From OECD (2009) producer and consumer support estimates, OECD database 1986–2008.
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Figure 2 Level and composition of agricultural support in OECD (1986–2007). From OECD (2009) producer and consumer support estimates, OECD database 1986–2008.
Support in high price systems is financed by consumers through high consumer prices. Depending on the self-sufficiency rate, public costs and income are also affected. If the country is a net importer, the country will receive a revenue from the import tariff. On the contrary, a net exporting country will have to
pay export subsidies to ensure the price level on the domestic market. The low price system has for decades been the predominant support system in the agricultural policy in the United States. As a result of the recent reforms of the Common Agricultural Policy (CAP) in the European
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Union and as a result of more focus on decoupled support in the World Trade Organization (WTO) negotiations, the European Union has moved toward more low price support and less high price support. Low price support system is now the most important support system in the European Union. In low price systems, market prices are more or less unaffected, and farmers receive prices which in principle correspond to world market prices. Instead, market support payments are given directly to the farmers. These payments can be coupled with production or they can be fully decoupled. Coupled support means that a farmer will receive a payment corresponding to the production multiplied by the difference between the world market price and a given target price on the domestic market. In this case, there is no major difference between a high and a low price system from a farmer’s point of view. If support is more or less decoupled from production, the economic transfer to farmers may have an element of income or social aid. Support can be coupled with the agricultural area or the number of animals belonging to the farm. In this case, support is still decoupled from production. Low price systems are financed by the public budget, indicating that the taxpayers finance this kind of agricultural support in the end. High and low price systems may have different modifications, individual structures, and so on. The income transfer can have various nuances giving different consequences in each case. However, the general structure of high and low price systems is shown in Figure 3. It does not make sense – a priori – to determine whether one system is superior to the other. Support level is independent of the support system, and both systems have advantages and disadvantages. Therefore, it is necessary to compare these pros and cons with the objectives in the agricultural policy. It is evident that the choice of high and low price systems may have profound consequences within and outside the agricultural sector.
High price system
Low price system
Market price
Target price
Price support
World market
World Direct market payments
Figure 3 General structure of high and low price systems.
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Consequences of High and Low Price Systems Conditions and Competition in the (Processing) Food Industry High price systems necessitate border protection of commodities traded internationally. This means that the border protection must comprise processed commodities and not the basic agricultural raw materials. This is the case for milk where border protection must cover the processed and traded goods like butter, cheese, and condensed milk. In this way, the high price system will influence a major part of the food industry and not only the primary agricultural sector. This must be seen in relation to the fact that it is normally only the conditions in the primary agricultural sector that should be improved through the agricultural policy. Especially if the food industry is very concentrated and having great market power, the farmers may not achieve the intended advantages of the high price system. In other fields, a high price policy can be negative for the food industry. At first, the raw materials of the food industry will become more expensive, and unless this cost increase will be fully compensated through other systems, it will lead to worsening of the competitive power. Such distortions of competition conditions in the food industry will not occur in a low price system. Here, a free world market price exists and is created by supply and demand without market intervention, and the food industry will automatically adjust correspondingly to the international comparative advantage of the sector.
Competition Conditions in the Agricultural Sector Another problem with the high price system is that it is often difficult to grant the same subsidies to all products. It is most difficult to implement a uniform subsidy if it is a question about high and low processed products, and also, for some products there is only import protection and for others there may also be supply restrictions. Furthermore, a general price increase for all agricultural products of, for instance, 10% will primarily benefit the crop production whereas gains for animal production will be lower. The explanation is that a major part of the production factors in animal farming consist of crop production, and in this way a general price increase will not have total trenchancy in these production areas. For all industrial countries, there is a clear negative correlation between the grade of self-sufficiency and agricultural subsidy. This means, the higher the grade of self-sufficiency, the lower the agricultural subsidy.
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It is characteristic that some countries often reduce the subsidy level for the products where the degree of selfsufficiency increases considerably to over 100%. With an increasing net export, the nationally financed agricultural subsidy increases, and therefore there will be a distinct incentive to reduce the subsidy. Apart from this, the self-sufficiency objective determines that one in particular protects the products where the grade of self-sufficiency is low. In both cases, there are signs that one in particular protects the products that the agricultural trade already has poor possibilities to produce. On the other hand, the subsidy for the products that have the best natural conditions will be relatively low. It is assumed that a relatively high degree of self-sufficiency all in all is a sign of a comparative advantage. Seen in a global perspective, the subsidy is highest in countries where the degree of self-sufficiency is low. Seen in a national perspective, it applies correspondingly that the subsidy is relatively the highest on products where the grade of self-sufficiency is relatively low. Both factors are part of a blurring of the comparative advantages and the result is welfare economic losses. In the low price system, it can also be difficult to grant the same subsidy to all products; however, it is less complicated than in the high price system. One explanation is that the subsidy is granted directly and past the processing sector and in this way the real agricultural subsidy in the individual production areas is easier to calculate. Apart from that, it is not seen in a low price system that price subsidy for one product has the effect as extra costs in another product area. On the other hand, in a low price system, it can be very difficult to distribute a ‘fair’ subsidy independent of production among the farmers. Historic, structural, or social criteria are often necessary; however, they are rarely logical and they can be very static and not least they can be very difficult to control.
It should also be considered that the above-mentioned costs are calculated with the actual world market prices as reference basis. After both a one-sided and general liberalization, these prices will increase and thereby the consumers’ gains will be smaller than the actual costs calculations show. Even though the prices of agricultural products in a high price system are forced high, it will have far from full trenchancy on the food prices. This is due to the fact that only approximately 25–30% of the consumer price on food in highly developed countries traces back to the agricultural trade. The rest of the costs are wages in the processing industry, transport costs, and so on, and these costs are really independent of the subsidy level in the primary production.
Income Distribution in the Society The choice between the high and low price systems will also influence the income distribution in the society. A high price system, which will cause an increase in the food prices, will after all be the largest burden to the lowest income groups in the society. People with low incomes use a relatively large part of their earnings on food, which means that an increase on these products will limit their consumption possibilities relatively much. Higher prices on food and other necessary products as a result of political or economical measures will in this way have the same effect as a degressive tax. On the other hand, the low price system builds on low prices to producers as well as consumers and that is why this form of protection will be the cheapest solution for the part of the population that have the lowest incomes. The financing of public expenses for income support, supplementary payments, and other supports is normally done by means of income tax, which in most cases is progressive. Contrary to the high price system, the costs of the agricultural policy in this case will be placed on citizens with higher incomes.
The Composition of Consumption The composition of consumption is also affected by the choice between the high and low price systems. In the high price system, the consumers will, through higher food prices, primarily finance the agricultural policy. This means that food prices will increase compared to other products, and in this way the consumption of food will decrease compared to the consumption of other products. The result will be that the consumers’ purchasing power will decrease. At first, the consumers’ loss as a result of the high price policy can seem great, approximately 25% of the agricultural production value is subsidy, and for the European Union 33% of the subsidy is consumer financed.
The State Expenses High and low price systems have a significant impact on public costs and expenses. Market intervention often implies economic support, taxes, levies, and revenues, which means that public expenses will be affected. For a net import country, the revenue of the state will at first increase by imposing a high price system based upon import tax. The state receives customs receipts, and at the domestic market the consumers finance the price subsidy to the agricultural sector. On the other hand, there can be large costs for the state finances with the low price system where direct support to the farmers is a major instrument.
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Finally, any intervention and protection measure will have a negative impact on resource allocation and economic welfare in society. Different measures have different consequences, but in general, coupled price support tends to be the most distorting measure imposing the highest loss of economic welfare in society. The change in agricultural policy during the last decades in OECD countries – decreasing support and increasing role of taxpayer cost – has reduced the total cost, but the taxpayer cost has increased in relative and nominal terms. Direct or Indirect Subsidy The choice between the high and low price systems can also be of great importance as to how direct the subsidy systems are. In a high price system, the agricultural subsidy is given ‘through the market’, and therefore the subsidy is more indirect and invisible. In a low price system, where by means of tax collection the money is directly transferred to the agricultural sector, the transfer is much more obvious. The low price system contains in this way a very direct subsidy to the farmer; however, the effect on international trade is more indirect and invisible. However, in most cases, the effect is the same for agricultural trade, and therefore it is only a pedagogical and comprehension problem. Still, it is certain that a low price subsidy is so visible that there will be a natural pressure from the surroundings (the taxpayers) to reduce the subsidy. Production and Productivity Development The choice between the high and low price systems can also be of great importance to agricultural production and productivity. The high price system gives, at first, the farmers better sales prices, thus better terms of trade, and it will undoubtedly stimulate production. The size of the productivity increase will depend on the size of the supply elasticity. In general, the agricultural production responds relatively weakly to price changes. In the long term – and especially in case of price increases – it is characteristic that the agricultural production to a great extent adjusts itself to the changed price relations. Normally, productivity will be improved through structural and political instruments, where through research, development, education, advising, and other means one can make the production more rational. However, the high price policy will also be able to affect productivity. On the one hand, there will be an incentive to increase production in relation to, for instance, the acreage effort. In this way, there will be an increased yield, and also the yield of the livestock production will increase. This will increase productivity.
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On the other hand, the agricultural policy will also attract input factors which under normal conditions would be used in other sectors or which would not be used at all. For instance, poor soil will be cultivated and this will reduce the average yield. This will also be the case for other input factors, for instance, fertilizers, pesticides, capital, and labor. The low price system has in principle the same consequences for production and productivity development provided that it concerns fully production-coupled subsidies. If, on the other hand, the payments to the farmers are partly or fully decoupled from the size of production, the consequences are crucially different. A totally independent income subsidy means that the farmers receive a relatively low price for their products, and that they have no incentives to increase production. It is only economically optimal to increase production as long as the marginal earnings are larger than the marginal costs, and this point is reached relatively fast with the low market prices. At the same time, the income subsidy is assigned to the farmer regardless of the size of production, which means that production does not increase considerably. However, it must be expected that even a decoupled production income subsidy in a low price system can seem encouraging to production. All agro-political measures will affect the resource allocation in the society, and in this way an income subsidy will maintain resources in the agricultural sector. In this way also the production will be affected to a larger or smaller extent. Decoupled income subsidy will very much limit production development in the agricultural sector. Farmers will not be sufficiently urged (or forced) to introduce new technology or new production methods. At the same time, the more efficient farmers do not benefit sufficiently from the extra effort or risk which they undertake. The high and low price systems can, in this way, have different consequences for production and productivity development in the agricultural sector. One cannot in advance say that one consequence is better than the other.
Market Price Subsidy The market price subsidy – where the market price is kept higher than on the world market – is still a common subsidy measure in the agricultural policies of the Western world (Figure 1). Among others, the European Union has through decades used the market price subsidy as an important instrument in the agricultural policy. The use of the market price subsidy in a high price system demands, naturally, a considerable regulation of the markets. To secure the high price level, the markets are more or less isolated from the surrounding world, as
292 Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Target price Market price Import duty Intervention price
Export subsidy
Expenditure Intervention Revenue World market price
World market price
Domestic market
Figure 4 Instruments in a market price system (high price system).
free import or export will make the system collapse. Furthermore, there can be a need for public buying (intervention) or export support, dependent on the degree of self-sufficiency. There are different types of market price subsidies but the most important one is a price system, where the state in different ways is adjusting the market with the purpose to ensure that the farmers on the market itself are able to obtain the aimed prices. This type of market systems can be schematically illustrated as shown in Figure 4. The target price is the price aimed at for the producers to obtain on the market. The intervention price forms a safety net for the price formation on the market as the product can be sold within the European Union at this price. The actual market price will often be between the target price and the intervention price. If the market price levels drop below the intervention price, some suppliers begin to sell to intervention. This will reduce the supply on the market as the bought-up products will be stocked. This will normally lead to recovery of the market price. The intervention price and the intervention system are, in other words, a central part of the internal regulation of a high price market. However, intervention alone is not enough to secure the price, as there must also be a regulation by import and export. When importing, an import duty is collected, which, in principle, is the difference between the price on the world market and the threshold price. In principle, it can be both a variable and a firm import duty. If the import duty varies, it can continuously be changed according to the world market price, and it therefore increases when the world market price is low and vice versa. In this way, the variable import duty can be a part of securing a constant price level on the internal market. Previously, the variable import duty was often used, but as a result of the WTO agreements a gradual change in the tariffs has taken place. This means that the import
barriers have changed to more firm tariff rates. When exporting, an export restitution (subsidy) is paid, which in principle is the difference between the price on the world market and domestic market price. In the European Union, the market price subsidy works in such a way that the EU farmers have secure higher prices than on the world market. This is still the case for some products where reforms have not yet changed the original support system. This is naturally especially true for products where the market price subsidy is the most important measure and where the subsidy level is high. This applies for, among others, milk, whereas the market price subsidy on the cereal area has decreased considerably as a result of reforms in the EU agricultural policy (Figure 5).
Future Developments Several conditions will influence the future development with regard to the agro-political instruments. The choice between the high and low price systems must not be seen from an economic and social point of view alone. The international negotiations in WTO are also of great importance. The explanation is that the high and low price policy influences the international trade in different ways. First, it is important that the consequences for the size of production are different. All influences on the size of the production will directly influence the foreign trade, as for instance an increase in the production will make the import decrease or the export increase. In this way, these trade-influencing instruments are made objects of negotiations in, for instance, WTO. As mentioned before, all agro-political measures will always influence the resource allocation and production,
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy Wheat
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20 10 0 1980 1985 1990 1995 2000 2005 2010
Figure 5 EU market prices and world market prices for agricultural products. In general, the intervention price system in the European Union has stopped or is diminishing.
and with this, also the foreign trade to a larger or smaller extent. Still, in the international trade negotiations, there is talk about ‘non-trade distortions’, which are instruments with no influence on the trade. It is implied that some agro-political instruments have a less harmful influence on the international trade and that they in this way are more or less legitimate to use. Second, it is important that in a high price system one is forced to introduce trade barriers, which in a very obvious way illustrate protection. The trade barriers can of course be of the same magnitude in a low price system, but here the trade protection is less transparent. Politically seen, the relationship to the trade partners can therefore favor the low price system. The use of import duty, import tax, and especially export subsidy is normally necessary in a high price system, but they very clearly state that one wishes to protect the domestic producers against the surrounding world. This is probably also one of the explanations why the EU agricultural policy was so heavily attacked during the WTO negotiation rounds. It is certain that the WTO rounds were a defeat for the high price system and a victory for the low price system. This fact must be seen in spite of the fact that the low price system does not necessarily create more free trade or greater economical welfare than the high price system.
On the other hand, the results of the WTO rounds, until now, mean that more countries in the future will be prompted to operate an agricultural policy based upon the low price system. Also, more independent experts argue for a gradual change from the high price system to the low price system. The arguments are, for instance, that the subsidy rates will be more transparent and sometimes more trading neutral as well. Also, the instruments and the subsidy level in a low price system can easily be gradually removed and even completely replaced by pure social support arrangements. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: United States’ Agricultural System.
Further Reading European Commission (2009) Agriculture in the European Union – Statistical and Economic Information 2007. http://ec.europa.eu/ agriculture/agrista/2007/table_en/index.htm (accessed 27 March) Hansen HO (2001) Landbrug i et moderne samfund, 438pp. þ XXVIII. Copenhagen, Denmark: Business School Press. Knutson RD, Penn JB, and Boehm WT (1990) Agricultural and Food Policy, 2nd edn., 437pp. Englewood Cliffs, NJ: Prentice-Hall.
294 Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy Nedergaard P, Hansen HO, and Mikkelsen P (1993) EF’s landbrugspolitik og Danmark. Udviklingen frem til a˚r 2000, 398pp. Copenhagen, Denmark: Copenhagen Business School Press. OECD (2008) Agricultural Policies in OECD Countries: At a Glance 2008. Paris: OECD. OECD (2009) Producer and consumer support estimates, OECD database 1986–2008.
Ritson C (1977) Agricultural Economics. Principles and Policy, 409pp. London: Crosby Lockwood Staples. Tracy M (1993) Food and Agriculture in a Market Economy. La Hutte, Belgium: APS Agricultural Policy Studies. Shane M, Roe T, and Gopinath M (1998) U.S. Agricultural Growth and Productivity: An Economy-wide perspective (Agricultural Economic Report No. 758). Washington, Dc: USDA.
Agricultural Policy Schemes: European Union’s Common Agricultural Policy M Keane, University College, Cork, Ireland D O’Connor, Institute of Technology, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by K. W. Rasmussen, Volume 1, pp 15–20, ª 2002, Elsevier Ltd.
Background The Common Agricultural Policy (CAP) was established on the basis of the Treaty of Rome, with effect from 1 January 1958. Article 39 stipulates five fundamental objectives: 1. to increase agricultural productivity by stimulating technical progress and ensuring the rational development of agricultural production and the optimum utilization of factors of production, in particular labor; 2. to ensure a fair standard of living for the farming population, in particular by increasing the earnings of the persons engaged in agriculture; 3. to stabilize markets; 4. to assure the availability of food supplies; and 5. to ensure that supplies reach consumers at reasonable prices. In the following years, the CAP gradually firmed up. It was based initially on the idea of a dual agricultural policy, consisting of structural measures on the one hand and price and market-related measures on the other hand. Eventually, the price and market policy became the overall dominating element of the CAP. The price and market system comprises all the major agricultural products, including milk. In the original form, the policy was based on the following principles: movement of goods within the European Union • free and common prices for the same good; preferences in relation to third countries • common (common import duty system); and financial responsibility for market and price • common policies of the European Community Fund via the European Agricultural Guidance and Guarantee Fund (EAGGF). These principles were adopted at the Stresa Conference in 1958 and meant that the politically fixed prices became the central element of the CAP and the annual price negotiations of the EU Council of Ministers, which took place in April, started attracting great interest. Up to the implementation of the General Agreement on Tariffs and Trade (GATT) in 1995, three prices of
the principal products were fixed at the price negotiations: target prices, intervention prices, and threshold prices. The target price was the price aimed at in the market, but with no guarantee for the producers. The intervention prices for butter and skim milk powder, however, formed the safety net of the price formation in the market, as at worst the products – with various modifications – could be sold to the EU Commission at this price. As dairy produce consists mainly of fat and protein, the safety net really covers all products. Originally, the threshold price was the lowest acceptable import price for third-country products. The threshold price was used to calculate the variable import taxes, which, in principle, formed the difference between the world market price and the threshold price. However, the GATT agreement signed in 1994 meant that import taxes were frozen on 30 June 1995, which is why threshold prices are no longer fixed. The fourth fundamental principle of the EU price and market system is export refunds. Refunds are paid on exports and in principle they form the difference between world market prices and the EU market price. The size of the fixed refunds is the same for all EU Member States, but may be differentiated by destination, if special conditions apply. In connection with the reform of the EU CAP in 1992 (the MacSharry reform), far-reaching changes in price and market policies were introduced, particularly regarding cereals and beef. However, in the milk sector, the old system still applied (Figure 1) as the proposed reform was unacceptable to the EU Council of Ministers. Thus, there were no major changes in the milk regime until the implementation of the CAP Reform in 2003, as discussed later.
Financing of the CAP The CAP system was financed by the EAGGF, which is divided into a guarantee section, financing the price and market policies, and a development section, financing the structural policies. From the start of the European Union, the CAP consumed by far the largest
295
296 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes Target price
Threshold price
EU market price Import tariff Refund
Intervention price income World market price
Expenses EAGGF (European Agricultural Guidance and Guarantee Fund)
Expenses
World market price
Own income Import from world market
EU market
Export to world market
Figure 1 The EU market scheme.
share of the total EU budget. Relatively speaking, the expenses for the agricultural policies have been declining gradually since the 1970s, and now total about 40% of the total EU budget. This decline must be seen in the context of other EU policies and a growing request to stabilize farm expenses. Concurrent with restrictions on farm expenditure, larger funds have gradually been transferred to finance the development of other structural funds, with particular emphasis in recent years on energy, the environment, and new Member States. The EU revenues are based on based on gross national income, • contributions contributions from • tax (VAT) basis, all Member States on a value-added receipts, and • customs various production levies. •
The Price and Intervention Scheme for Milk and Dairy Products The EU basic regulation on milk and dairy products was finally adopted in 1968 (EEC 804/68). The institutional prices for milk and dairy products were fixed for a whole dairy year, running from 1 July to 30 June. The target price was fixed for milk, with 3.7% fat carriage paid at any processing factory. The intervention prices were fixed for skim milk powder and butter and formed a safety net under the milk prices. In this way, the main ingredients, protein and fat, were safeguarded and stored in a form that could be controlled by intervention buying. While intervention prices continue to be fixed as in the past, the levels are now considerably lower following CAP Reform as discussed later. Up to 1987, the
Intervention Boards of the individual Member States were obliged to purchase any product for sale at the fixed intervention price. Subsequently, various modifications have been made.
The System prior to CAP Reform 2003 Skim milk powder and skim milk (EC 1255/99 art. 7, 11, and 12)
During the winter season, from 1 September to 28 February, intervention with regard to skim milk powder is suspended. From 1 March to 31 August, intervention may be suspended; however, private storage of skim milk powder may be subsidized. Only first-class produce meeting the set requirements on age and packaging may be the subject of intervention. As of the market year 1995–96, a minimum protein content of 30% in skim milk powder for intervention was introduced. At a protein content of 34% and above, maximum subsidy is paid, whereas contents between 30 and 34% have 1.75% deducted from the intervention price for each percentage point below 34%. Products subject to intervention, which cannot be sold on normal market terms, may be subject to special stock disposal measures and sold at reduced prices. As for skim milk powder, its use in mixed feedstuffs for calves is subsidized (the most important scheme) as well as its use in mixed feedstuffs for pigs and poultry. Skim milk for processing into casein and caseinates is also subsidized. These products are used as the primary material for processing of various industrial products and foodstuffs, such as processed cheese. Subsidies for casein and caseinates are a production subsidy, as distinct from the price subsidy schemes.
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 297
The intervention system for butter (EC 1255 art. 6 and 13)
From 1987, the intervention system for butter has been a tender procedure. Tenders are submitted every 2 weeks, as the EU Commission fixes a maximum buying-in price. All bids below this price are purchased. Since 1987, the buying-in price has been steady at 90% of the formally fixed intervention price. Like skim milk powder, butter for intervention must meet certain requirements on quality, age, and packaging. When the market situation allows, subsidized butter pursuant to regulations is remarketed on terms that do not damage the competitive position of butter in the market. Butter subject to intervention is remarketed within the European Union under the special scheme for sale of butter at reduced prices, for use in the food industry and for the manufacture of pastry products, ice cream, and other foodstuffs. Analogous to the sale of subsidized butter for food manufacturers, similar subsidies are paid for the use of fresh butter and cream in the food industry. Butter for social institutions and hospitals is also subsidized, as well as for the armed forces. To safeguard the normal market supply and price of butter during winter months, private storage of butter and cream is financially supported. The storage period, fixed by the EU Commission, usually starts on 1 April and ends on 15 August. The stock disposal period is from 16 August to 28 February the following year. The storage period must be a minimum of 4 months. The intervention system for cheese (EC 1255/99 art. 8)
In addition to the general intervention schemes for butter and skim milk powder, private storage of the cheese types Grana Padano, Parmigiano Reggiano, and Provolone may be subsidized in Italy. The special scheme was established as the production of these particular cheese types is a staple element of the Italian dairy industry. Subsidies for sale of liquid milk (EC 1255 art. 14)
To stimulate liquid milk consumption, the European Union contributes to the implementation of the Member States’ special aid schemes to supply milk and selected dairy products for schoolchildren at reduced prices.
the basic period from 1986 to 1988. Moreover, the GATT/ WTO agreement imposes minimum import access quotas at reduced tariff rates, equal to 5% of consumption in the basic period. In addition, the European Union is obliged to give access to butter from New Zealand at a special low rate. This amount represents the average amount exported annually to the United Kingdom by New Zealand under bilateral agreements during the GATT/WTO basic period. Further to GATT/WTO obligations, the European Union has entered a number of bilateral agreements aimed at facilitating market access on a mutual basis. For instance, there are special quotas for the United States, Canada, Norway, Switzerland, South Africa, and others.
Export Schemes for Milk and Dairy Products As a matter of principle, the European Union subsidizes most dairy products for export to balance the price gap between the European Union and the world market, except when this price gap disappears as in the 2007/ 2008 period. Non-Annex I products are subsidized as well; these are processed products containing agricultural produce, such as cereals, sugar, eggs, and milk. After the implementation of the GATT/WTO agreement, the refund system was somewhat restricted. Compared to the basic period of 1986–90, subsidized exports were reduced by 21%, in parallel with a 36% reduction of the refund budgets. The budget restrictions apply only to non-Annex I products. In order to ensure that the restrictions are met, all exports qualifying for refunds are subject to presentation of an export license, prefixing the refund. Export licenses are limited to the permitted quantity, which implies that it is a scarce commodity in times of great demand. The limited opportunity to use refunds means that export refunds for cheese no longer exist for a number of destinations. This generally applies to areas such as the United States, Canada, Australia, Switzerland, and Norway. In other areas, refunds for only selected products have been abolished.
The Milk Quota Scheme The Import System for Milk and Dairy Products Before the introduction of the GATT/World Trade Organization (WTO) agreement on 1 July 1995, thirdcountry imports were subject to variable import levies. Now these levies are tariffed, that is, converted into a fixed tariff rate, payable in Euro per tonne or as a percentage of the import price. Pursuant to the agreement, the rates have been reduced by an average of 36% compared to
As a result of the increasing imbalance between production and demand, the milk quota scheme was introduced in 1984. The purpose of Article 39 of the Treaty of Rome had long been accomplished and the choice was between a reduction of prices and limiting production. Production was chosen and the measures proved effective in limiting surplus production. Each Member State was allocated a national quota (reference quantity) for the quota year 1984–85, which as a rule equaled the total national milk production in 1981 plus 1%. Ireland, Italy, and Northern
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Ireland got a somewhat larger quantity. The Member States were allowed certain latitude to implement the quota scheme in one of two ways, either as direct sales quotas or as dairy quotas. Under the direct sales quota scheme, the national reference quantity was reallocated to individual milk producers. Under the dairy quota scheme, the quota was reallocated to the dairies, which subsequently had to fix quotas for individual producers. In the event of milk production in excess of the quota, a superlevy was collected, totaling 115% of the target price. Regardless of the choice of management scheme, the producers who exceed their quota must pay the superlevy. The dairy quota scheme provides the option to use a net principle, allowing the underuse of quota by some producers to be converted into a deduction for producers who have exceeded their quota. In this way, the quota is fully utilized and the payment of a superlevy reduced.
3. In addition, each Member State would receive financial support by the so-called ‘national envelopes’, which may be allocated according to nationally determined criteria. 4. The total quantity eligible for direct payments in each Member State would be equal to the sum of all individual reference quantities for the 12-month period 1999–2000. 5. A total increase of milk quotas of 2.8 Million tonne (2.4%): in the years 2000–01 to 2001–02, the national quotas were increased for Spain (10%), Italy (6%), Northern Ireland and Ireland (3%) as well as Greece (11%). The increase for the remaining countries was to be 1.5% in the years 2005–06 to 2007–08. 6. The milk quota scheme would continue up to 2008. In 2003, a ‘mid-term review’ would be initiated.
Agenda 2000
CAP Reform (Mid-Term Review) 2003
Following nearly 2 years of discussion, the EU Heads of State finally made the decision to reform the EU CAP, entitled Agenda 2000, at the summit meeting in Berlin in March 1999. Agenda 2000 also embraced the budgetary framework of the European Union for the period 2000–06 and the plans for enlargement by the inclusion of central and east European countries as well as a reform of the structural policy. The fundamental element of the agricultural reform was a reduction of refunds for the most essential agricultural products, as opposed to extended financial aid to producers by premium schemes, only partly related to production. For agricultural produce and beef, the 1992 reform was further expanded, whereas in the case of the milk and dairy sector it is a profound breach of previous policies. The purpose of the reform was to
In 2002, the Mid-Term Review of Agenda 2000 commenced. It concluded in June 2003 with a fundamental reform which provided for the decoupling of direct payments from production in the case of livestock production, milk production, and arable crops, with partial decoupling options for Member States that did not wish to decouple fully. Direct payments (coupled or decoupled) were made conditional on compliance by farmers with a range of food safety, environmental, and animal welfare measures. With regard to the dairy sector specifically, the most important elements were as follows:
the competitiveness of EU agriculture on both • improve domestic and external markets, the progressive integration of new Member • facilitate States, the European Union for the next WTO round, • prepare ensure continuously stable farm incomes, and • integrate environmental goals into the CAP. • The original intention was to implement the reform of the dairy sector in the period 2000–03. However, the final agreement between the Heads of State in Berlin postponed the implementation to 2005–08. The principal elements of the reform that was agreed were as follows: 1. A total 15% reduction in intervention prices for butter and skim milk powder, in three stages from 2005–06 to 2007–08. 2. To compensate for the price cut, milk producers were to be allocated a direct payment per tonne milk quota, fixed at E5.75 in 2005, E11.49 in 2006, and E17.24 in 2007.
1. An asymmetric reduction in intervention price: 25% for butter (from E328.20 to 246.39 per 100 kg) and 15% (from E205.52 to 174.69 per 100 kg) for skim milk powder. The reduction was brought forward to 2004–05, with the butter price reduction spread over 4 years (7, 7, 7, and 4%) and the skim milk powder price reduction in three equal annual steps. 2. Partial compensation for the intervention price cut for dairy farmers: a direct payment of E24.49 per 100 kg of quota and a supplementary payment per Member State equivalent to approximately E11 per 100 kg. Such compensation is paid for the total of national quota as at 1999/2000. Originally, the coupled payments had been programmed in Agenda 2000 at a lower level. The payments were to be decoupled at the latest in 2007. 3. Discouragement of butter intervention: by introducing the possibility to open a tender for intervention buying-in after 30 000 tonnes at fixed prices have been bought in. 4. Expiration of production quotas on 1 April 2015. 5. Postponement by 1 year of the gradual quota increase of 1.5% in three steps of 0.5% for 11 Member States, as
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 299
already foreseen in Agenda 2000. The increase corresponds to 1.4 million tonnes of milk. 6. Reduction of the superlevy: in four steps from E35.63 per 100 kg in 2003/2004 to E27.83 per 100 kg from 2007/2008 onward. Coinciding with the start of the dairy reform in 2004, 10 new Member States joined the European Union. This increased the EU base quota by 18.5 million tonnes and added 80 million consumers. Furthermore, in accordance with the accession agreements, a restructuring reserve of 0.67 million tonnes was established for eight of the new Member States. This additional reserve was added to their national quotas on 1 April 2006. In 2007, a further two new Member States with a total quota of 4 million tonnes joined the European Union, bringing the total amount of quota for the EU-27 to 142 million tonnes. Thus, by 1 April 2008, further to 103 million consumers, 24.5 million tonnes of additional quota will have been added to the EU total since 2003. The aim of the 2003 dairy reform was to increase competitiveness and market orientation. It was intended that by reducing the guaranteed price for butter and SMP, these products would be less attractive to produce and this would give the industry an incentive to produce more value-added products like cheese and fresh dairy products. Increasing the quota at the same time would encourage additional production, facilitate restructuring of the sector, and encourage entrance into the sector of young farmers. It will be recalled that the European Commission’s proposal for the CAP Reform 2003 was to increase quota by 2% on top of the 1.5% increase already agreed in Agenda 2000. In the June 2003 compromise, however, the Council declared that ‘‘No additional quota increase in 2007 and 2008 will be decided now. The Commission will present a market outlook report once the reform is fully implemented on the basis of which a decision will be taken.’’
CAP Health Check 2008 As part of CAP Reform 2003, a mid-term review of policy was completed in 2008, which became known as the CAP Health Check. Agreement was reached among farm ministers in November 2008. The main points related to dairying were as follows: 1. Five annual milk quota increases of 1% each with effect from April 2009, prior to total abolition of the quota system as from 1 April 2015. As is now traditional, when it comes to milk quota, Italy will receive a special derogation that allows it to increase its quota by the full 5% in the first year.
2. The rate of modulation (shifting funds from direct aids to rural development aids) will be raised from 5% at present to 10% by 2012. The increase will be made gradually: 7% in 2009, 8% in 2010, and 9% in 2011. The progressive modulation concept has been watered down; only recipients of more than E300 000 will face a higher modulation rate: 4 percentage points higher than the standard rate. The resulting money will be allocated for ‘new challenges’ – climate change, energy, biodiversity, and water management – but it will also have to fund ‘accompanying measures’ for the dairy sector.
Conclusion The EU CAP is and will remain a fundamental basis of EU cooperation. Financial problems, disputes about GATT/WTO principles as well as problems regarding the enlargement of the European Union have permanently placed reforms of the agricultural system on the EU political agenda. For the first time, the market scheme for milk and dairy products underwent fundamental change in 2003 and further changes may be anticipated in the decade ahead, particularly when milk quotas are finally abolished in April 2015. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: United States’ Agricultural System; Trade in Milk and Dairy Products, International Standards: World Trade Organization.
Further Reading EU Commission (1997a) Agenda 2000, Vol. 1: For a Stronger and Wider Union. Brussels, Belgium: EU Commission. EU Commission (1997b) Agenda 2000, Vol. 2: The Challenge of Enlargement. Brussels, Belgium: EU Commission. EU Commission (2009) Dairy Market Situation 2009, SEC (2009) 1050. Brussels, Belgium: EU Commission. http://caphealthcheck.eu/ health-check-deal (accessed July 2008). European Council Regulations (1999) EEC 804/1968. EC 1255/1999. EC 1256/1999. Brussels, Belgium: EU Council. European Economic Community (1958) Treaty of Rome. Brussels, Belgium: EEC. Nedergaard P (1988) EF’s Landbrugspolitik under Omstilling. Copenhagen, Denmark: DJØF. Organization for Economic Cooperation and Development (2000) Agricultural Policies in OECD Countries: Monitoring and Evaluation 2000. Paris: OECD. Williams RE (1997) The Political Economy of the Common Market in Milk and Dairy Products in the European Union. Rome, Italy: FAO. ZMP (2000) Marktbilanz Milch. Bonn, Germany: ZMP.
Agricultural Policy Schemes: United States’ Agricultural System E Jesse, University of Wisconsin–Madison, Madison, WI, USA ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by D. A. Sumner, J. V. Balagtas, Volume 1, pp 20–25, ª 2002, Elsevier Ltd.
Introduction An active agricultural commodity policy was developed in the United States in the 1930s in response to economic conditions of the Great Depression. Major commodity programs for grains, oilseeds, cotton, peanuts, sugar, tobacco, and dairy that are in place today have their origins in the programs that began nearly 70 years ago. Dairy policy in the United States comprises the following major components: 1. Border measures that create import barriers for most dairy products and export subsidies for a few manufactured dairy products. 2. Federal and state marketing orders that regulate milk prices at the processor and farm levels. 3. Government purchases of manufactured dairy products to support the farm price of milk. 4. Income support to dairy farmers through deficiency payments. Federal, state, and local governments also have longstanding food safety and sanitation regulations for milk and dairy products. In addition, there are myriads of more recent environmental, land use zoning, labor, and other regulations or incentives that influence the dairy industry. This article provides an overview of the key elements of US dairy policy, and provides some statistics to illustrate the economic effects of these programs.
Border Measures for Dairy Products Trade barriers for many dairy products have limited US imports of these products to less than 5% of US consumption (Table 1). Import barriers have traditionally kept the domestic price of dairy products above the price for traded products in world markets, although the gap has narrowed recently (Figure 1). By insulating the domestic dairy economy from foreign supplies of dairy products, the import barriers also make possible the key domestic elements of the dairy program – milk marketing order pricing rules and the price support program (described in the following sections).
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As a part of the Uruguay Round trade agreement that took effect on 1 July 1995, a system of absolute import quotas gave way to a system of tariff rate quotas (TRQs) that set a relatively low tariff on imports up to a determined quantity (the quota) and a relatively high tariff on overquota quantities. Although the quantity of access expanded with the Uruguay Round agreement, the second-tier tariffs applied to over-quota imports remain prohibitively high; therefore, for the present, the effects of the TRQs remain the same as the absolute quotas that were replaced, although at expanded import quantities. Imports of fluid milk, cream, butter, cheese, milk powders, and many other dairy products are subject to TRQs. For those products subject to TRQs, imports accounted for 5% or less of domestic consumption, but for other products, including casein, milk protein concentrate, and some cheeses, imports are not restricted. Not surprisingly, imports of partly or fully unrestricted dairy products represent the bulk of US dairy imports – caseins, milk protein concentrates, and cheeses represented nearly 80% of total import value in 2009. Overall, the United States imports more than $2 billion worth of dairy products each year, and is a substantial importer as well as exporter in the world dairy market. In addition to limiting import access to the domestic market for most dairy products, the US government continues to provide small amounts of direct financial subsidy for US exporters of dairy products. Subsidized exports, along with donations to domestic food programs and international food aid, have long been used to dispose of stocks of dairy products acquired under the price support program. Subsidized exports have been considered a market for US dairy products that does not disrupt domestic commercial sales. In addition to the disposal of government stocks, the Dairy Export Incentive Program (DEIP) has provided explicit price subsidies for commercial dairy product exports since the 1980s. Commodities eligible for DEIP (and annual Uruguay Round WTO maximum subsidized export volumes) are skim milk powder (68 000 tonnes), butter (21 000 tonnes), and cheese (3000 tonnes). With high world market prices for dairy products in recent years, DEIP subsidies have been infrequent. But very low world prices in 2009 triggered DEIP subsidization of 37 200 tonnes of milk powder, 17 400 tonnes of butter, and 1800 tonnes of cheese.
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 301 Table 1 US production, trade, and consumption of select dairy products, 2006–09
All cheese US production (1000 tonnes) US exports (1000 tonnes) US imports (1000 tonnes) Consumptiona (1000 tonnes) Imports/consumption (%) Butter US production (1000 tonnes) US exports (1000 tonnes) US imports (1000 tonnes) Consumptiona (1000 tonnes) Imports/consumption (%) Skim milk powder/nonfat dry milk US production (1000 tonnes) US exports (1000 tonnes) US imports (1000 tonnes) Consumptiona (1000 tonnes) Imports/consumption (%)
2006
2007
2008
2009
4320 71 206 4500 4.6
4433 100 198 4545 4.4
4505 131 170 4600 3.7
4583 108 162 4682 3.5
657 11 32 651
695 41 29 687
746 91 16 778
711 29 19 697
4.9
4.2
2.1
2.7
676 287 2 397 0.5
669 258 2 386 0.5
845 391 1 399 0.2
775 258 1 518 0.2
a Due to storage, consumption does not equal production plus imports minus exports. Government intervention purchases are not included in consumption. Data compiled from US Department of Agriculture, National Agricultural Statistics Service and Foreign Agricultural Service.
3.6 3.4
Butter Cheese Skim milk powder
3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
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Figure 1 Ratio of US market price to Oceania export price for primary dairy export products, 2000–09. Data from the US Department of Agriculture as reported at http://future.aae.wisc.edu/tab/prices.htm#13.
302 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes
Regional Milk Marketing Orders The pricing of nearly all of the milk produced in the United States is regulated by milk marketing orders. In 2010, 10 federal marketing orders regulated the sale of about two-thirds of all milk produced in the country. California, which operates its own marketing order, regulates the sale of another 20% of the country’s milk. Some of the remainder is regulated by other state marketing orders (Maine, Montana, Nevada, Virginia) and some (notably Idaho with 6% of US milk production) is not regulated by any marketing order. State and municipal governments set separate sanitary standards for milk that may be used in fluid products and milk that may be used only in manufactured dairy products. Grade A milk is milk that meets sanitary standards for use in fluid products. Of all milk produced in the United States, 99% is grade A. Grade B milk is eligible for use in only manufactured dairy products and is not regulated by milk marketing orders. Both federal and California milk marketing orders use price discrimination to raise the average price received by producers, setting minimum prices that processors must pay for grade A milk according to its end use (classified pricing). Federal orders distinguish between four end-use classes: fluid products, fresh and frozen products, hard cheeses, and butter and dry milk powder. Each month, federal orders set the minimum prices for milk used in cheese and milk used in butter and dry milk according to formulae that take into account the wholesale prices of these products. The minimum prices for milk used in fluid products (Class I) and soft and frozen products (Class II) are set as a specified differential over the manufacturing-use minimum prices. The differential for Class II is the same across all federal orders, but Class I differentials vary by order. Although the details of the Federal Milk Marketing Order (FMMO) pricing rules have changed over time, the key element of price discrimination remains; the minimum price for milk used in fluid products is set at a premium over the minimum price set for milk used in manufactured dairy products. The California state order distinguishes among five end-use classes, and uses similar formulae to set minimum prices for each class. In addition, each federal marketing order administers a revenue-sharing or ‘pooling’ scheme that distributes revenues from relatively high-priced Class I milk across all grade A milk. Each month, each federal order pools revenues from all end-use classes and announces a uniform, order-wide average price to individual farmers delivering milk to that order, regardless of how any individual producer’s milk was actually used. The weighted average or pool price in any order depends not only on the class prices but also on the utilization rates of milk in the
various end-use classes, which also vary from order to order. California’s revenue-sharing scheme differs from that used in the federal system. In California, a quota program determines how milk revenues from the various end-use classes are distributed among producers. The milk quota program in California does not restrict production or marketing. Rather, for each 100 kg of milk quota owned by an individual producer, the producer receives a fixed payment of $3.75 from the statewide pool of total milk revenues in a month. The remainder of total regulated milk revenues (i.e., what is left over after subtracting total quota payments) is distributed uniformly among all producers in the same way as federal orders. Overall, quotas cover about 22% of all the milk produced in the state. To the extent they raise the average price of milk above what it would be in their absence, both federal and state milk marketing orders encourage milk production. By setting relatively high prices for milk used in fluid products, marketing orders reduce sales of fluid milk. As a result, marketing orders encourage production of manufactured dairy products such as cheese, butter, and milk powder. Each marketing order regulates milk within a geographically defined marketing area. Figure 2 is a map of the 10 federal marketing areas. The relationship of prices among federal orders is determined, in part, by the formulae used to set minimum prices in each order. By formula, the minimum prices for milk used in manufactured dairy products are the same across orders. However, the fluid differentials, and thus the minimum price for milk in fluid uses, are different for each order. Differentials range from a high of $13.23 per 100 kg in parts of Florida, to a low of $3.53 per 100 kg in parts of the Upper Midwest. Table 2 lists the fluid differentials, Class I milk prices, and pool prices that were in effect for the 10 federal orders in 2009. In order to maintain different minimum prices in each marketing order, regulations are in place to discourage the transport of milk across regions. Milk transported freely across marketing order borders would undermine the maintenance of separate fluid milk markets in different orders. Regulations on inter-order milk shipments ensure that there is little economic advantage to arbitrage across prices in different orders. Because marketing orders create separate fluid milk markets in different regions, the benefits and costs of milk marketing orders vary regionally.
Federal Price Supports for Dairy Industry As early as 1935, the federal government was purchasing manufactured dairy products in order to support the farm price of milk. The Agricultural Act of 1949 required the
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 303
Pacific Northwest
Upper Midwest Northeast Mideast
Central
Appalachian Arizona Southeast
Southwest
Florida
Figure 2 Map of the Federal Milk Marketing Order areas as of 1 January 2010. Differences in shading merely serve to differentiate between marketing areas. Reproduced from US Department of Agriculture, Agricultural Marketing Service, Dairy Programs.
Table 2 Federal Milk Marketing Order annual average prices,a 2009 Marketing areaa
Class I differential ($ per 100 kg)
Class I milk price ($ per 100 kg)
Pool priceb ($ per 100 kg)
Northeast (Boston) Appalachian (Charlotte) Southeast (Atlanta) Florida (Tampa) Mideast (Cleveland) Upper Midwest (Chicago) Central (Kansas City) Southwest (Dallas) Arizona (Phoenix) Pacific Northwest (Seattle) Weighted average
7.17 7.50 8.38 11.91 4.41 3.97 4.41 6.62 5.18 4.19 6.34
32.48 32.81 33.69 37.22 29.72 29.28 29.72 31.93 30.50 29.50 31.66
28.62 30.87 31.38 35.61 26.66 25.51 25.75 28.05 26.61 25.91 27.41
a
Prices quoted at ‘principal pricing points’ (in parentheses) within each marketing area. Pool price is the market-wide weighted average of all minimum end-use class prices. Data reproduced from US Department of Agriculture, Agricultural Marketing Service, Dairy Programs. b
US Department of Agriculture (USDA) to continue to support the farm price of milk. Since that time, the USDA has purchased butter, non-fat dry milk, and cheese from processors at administratively determined intervention prices calculated to help ensure that the farm prices of manufacturing milk remain above the legislated support price. In 2008, the dairy price support program was modified to remove the requirement that USDA support a specific milk price, but intervention prices for eligible dairy products remained the same. The name of the support program was changed from the ‘milk’ price support program to the ‘dairy product’ price support program. Table 3 lists the support price for milk and the government purchase prices for eligible dairy products from 2000 through 2009. Note that, on average, market prices exceeded intervention prices, but occasionally fell far
enough below during the year to trigger government purchases. Annual purchases of butter, cheese, and nonfat dry milk are shown in Table 4. Since 1990, dairy price supports have played a minor role and government purchases have been relatively small compared to the 1980s. The 1996 FAIR Act lowered dairy price supports by 33 cents per 100 kg to $21.83 per 100 kg through 1999, at which time the program was scheduled to be terminated. However, the price support program was extended and subsequently reinstated in omnibus farm legislation passed in 2002. While the support price program plays a potentially important role in flooring prices for manufactured dairy products, the current intervention prices provide only the lowest of safety nets. Moreover, added costs of selling to the government (nonstandard packaging, mandatory federal inspection) mean that market prices for cheese often
304 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes Table 3 US market prices and US Department of Agriculture price support and purchase prices, 2000–09 Milk Support
Butter Class III pricea
Support
Year
($ per 100 kg)
($ per kg)
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
21.83 21.83 21.83 21.83 21.83 21.83 21.83 21.83 NA NA
1.45 1.70 1.96 2.32 2.32 2.32 2.32 2.32 2.32 2.32
21.48 28.89 22.97 25.18 33.94 30.97 26.21 39.78 38.45 25.04
Cheese
Nonfat dry milk
Marketb
Support
Marketb
Support
Marketc
2.76 3.86 2.31 2.58 4.05 3.39 2.73 3.10 3.38 2.82
2.45 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.59
2.53 3.17 2.61 2.90 3.64 3.29 2.73 3.88 4.09 2.86
2.23 2.08 1.95 1.76 1.76 1.76 1.76 1.76 1.76 1.83
2.30 2.27 2.08 1.85 1.96 2.15 2.04 4.03 3.00 2.26
a
Federal Milk Marketing Order price for milk used to make cheese. Chicago Mercantile cash market prices. Market and support prices for cheese price are for Cheddar in 40-pound (18.14 kg) blocks. c Wholesale price for western high-heat non-fat dry milk. b
Table 4 US government net purchases of dairy products
Butter Year
(tonnes)
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
4017 0 0 13 182 2971 0 0 0 0 4535
Cheese
Non-fat dry milk
12 711 1749 7179 18 712 2692 907 0 0 0 13 605
328 994 224 878 372 683 301 185 47 816 36 281 31 293 12 245 52 154 62 585
Negative values denote net sales from government stocks. Values include DEIP subsidies in the form of product.
fall below the intervention price without triggering government sales. This further diminishes the ability of the program to provide a price floor.
An annual cap on the amount of milk per farm eligible for payment was initially set at 1.1 million kg, which represented the annual production of about 120 cows. The payment rate was reduced from 45 to 34% on 1 October 2005, but reinstated at 45% in the 2008 Farm Bill. That legislation also provided for an upward adjustment in the MILC target price if dairy feed costs exceed a base level and raised the annual farm production cap to 1.35 million kg. MILC payments since the retroactive inception of the program through 2009 are shown in Figure 3. Payments closely follow milk prices. No payments were made during 2007 and 2008. The crash in milk prices in 2009 combined with a higher target price from the feed price adjuster led to record high payments during the first half of the year. The MILC program has been controversial among producers, mainly because the production cap favors regions with a smaller average herd size. Large western dairies can exceed the production cap in a single month. Their owners argue that they have been forced to bear the brunt of adjusting milk supply to low prices because MILC payments insulate smaller producers.
Direct Deficiency Payments – The Milk Income Loss Contract Program
Final Remarks
The 2002 US ‘Farm Bill’ introduced another dairy subsidy scheme in the form of the Milk Income Loss Contract (MILC) program. MILC is a target price-deficiency payment program that makes payments to all dairy farmers (subject to a production cap) in any month when milk prices fall below a target level. The initial base target price was $37.35 per 100 kg in reference to the Class I milk price announced for Boston. If the Boston Class I price in any month fell below $37.35, then all US milk producers were eligible to receive 45% of the difference.
In the United States, the federal government and several state governments directly and indirectly subsidize milk producers and regulate dairy prices. These programs stimulate additional milk output, raise the price of beverage milk, and shift income from taxpayers and consumers to the dairy industry. Economic research has documented that costs to taxpayers and consumers are significantly larger than gains to producers as a group, but of course, any individual producer gains much more than the system costs a typical dairy consumer or taxpayer.
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 305 0.60 0.55 0.50 Market price
0.45 0.40 Target price $ per kg
0.35 0.30 0.25 0.20 0.15 0.10 0.05
MILC payment
p
ay
Se
M
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ay M
Ja p n '0 8
ay
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M
Ja p n '0 7
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Ja p n '0 5
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Se
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Ja p n '0 3
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Ja n
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Figure 3 Milk Income Loss Contract (MILC) payments. Reproduced from US Department of Agriculture as reported at http:// future.aae.wisc.edu/milc.html.
See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy.
Further Reading Benedict MR (1953) The Farm Policies of the United States 1790–1950. New York: Twentieth Century Fund. California Department of Food and Agriculture (2010) Dairy Programs web page. http://www.cdfa.ca.gov/dairy (accessed 19 February 2010). Chite RM and Shields DA (2008) Dairy policy and the 2008 farm bill. Congressional Research Service, report no. RL34036, 22 January 2009. Washington, DC: Library of Congress. Cox TL and Chavas J-P (2001) An interregional analysis of price discrimination and domestic policy reform in the US dairy sector. American Journal of Agricultural Economics 83: 89–106. FAPRI–UW Alliance (2006) Dairy policy briefs. Food and Agricultural Policy Research Institute and University of Wisconsin–Madison.
http://future.aae.wisc.edu/alliance/DPAA_wCover.pdf (accessed 19 February 2010). Ippolito RA and Masson RT (1978) The social cost of government regulation of milk. Journal of Law Economy 21: 33–65. Jesse EV and Cropp RA (2008) Milk pricing concepts for dairy farmers. Cooperative Extension, University of Wisconsin-Extension, bulletin no. 3738. Jesse EV, Cropp RA, and Gould B (2008) Dairy subtitle: Food, Conservation, and Energy Act of 2008, Marketing and Policy Briefing Paper No. 94. Department of Agricultural and Applied Economics, University of Wisconsin–Madison, and Cooperative Extension, University of Wisconsin-Extension. http://future.aae.wisc.edu/ publications/farm_bill/M&P_Dairy_6-1.pdf (accessed 22 February 2010). Manchester AC (1983) The Public Role in the Dairy Economy: Why and How Governments Intervene in the Milk Business. Boulder, CO: Westview Press. Sumner DA and Wilson N (2000) Creation and distribution of economic rents by regulation: Development and evolution of milk marketing orders in California. Agricultural History 74: 198–210. Sumner DA and Wolf C (2000) Quotas without supply control: Effects of dairy quota policy in California. American Journal of Agricultural Economics 78: 354–366.
Agricultural Policy Schemes: Other Systems P Vavra1, OECD, Paris, France ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by L. Boonekamp, Volume 1, pp 25–31, ª 2002, Elsevier Ltd.
Introduction Milk producers in many countries benefit from government interventions that increase the prices they receive for their raw milk production. In some countries, a system of milk production quota was established to control the growth of surplus production while maintaining the market price support. Below are reviewed the current dairy policies in Canada, Japan, Australia, and New Zealand. The review illustrates the very different policy approaches and the degree of dairy policy interventions. The Organisation for Economic Co-operation and Development (OECD) collects and analyzes information regarding the level of support provided to producers through agricultural policies and calculates some measures of the monetary transfers caused by such policies – the producer support estimate (PSE). Since 2005, the total PSE is no longer broken down for individual commodities, which reflects the gradual shift (in many countries) away from direct commodity-linked supports. Figure 1 shows the change in %PSE for selected countries and the OECD average during the periods 1986–88 and 2002–04. The %PSE expresses the monetary value of the support as a share of gross farm receipts. A notable feature of the %PSE for milk is the reduction in support since the early 1990s, although the reduction varies considerably among countries. Since 2005, a new commodity-based indicator is calculated by the OECD, the so-called single commodity transfers (SCTs), which shows the annual monetary value of gross transfers from policies linked to the production of a single commodity such that the producer must produce the designated commodity in order to receive the transfer. For the countries reviewed below, the change from the commodity-specific PSE to the SCT indicator does not make much difference for New Zealand and Australia, where milk producers are supported either very little or not at all, while in Canada and Japan, a majority of the 1
The author is an agricultural markets and policy analyst at the OECD, Paris. The opinions expressed in this article are those of the author and do not necessarily represent those of the OECD or its member countries.
306
support (more then 90%) has been based on market price support (MPS), which continues to be reported in SCTs. The evolution of the SCT for milk production in the reviewed countries is illustrated in Figure 2 for the period 1986–2008.
Canada Background Since the first dominion dairy commissioner was appointed in 1890, the Canadian Federal Government has played an active role in policymaking for the dairy sector. A milk supply management system was introduced in the early 1970s, and it remains the cornerstone of Canada’s current dairy policy. Import restrictions at the border and milk production quotas are the main instruments allowing for a high level of support to the dairy sector, which continues to be the most heavily supported sector within Canada’s agriculture. In 2004, around 35% of all support to Canadian agriculture (as measured by PSE) went to the dairy sector. Figure 1 also illustrates that Canada’s support to dairy farmers is higher than that in OECD countries on average. When considering the SCT, 33% of the total SCT was attributable to the dairy sector in 2008. Figure 2 shows the relatively stable levels of SCT support, which declined notably after 2006 as international reference prices soared. (In 2009, the SCT level increased significantly following the dramatic price fall on the international dairy markets which has not been transmitted to the domestic market in Canada. The preliminary figures estimated by the OECD indicate an increase of % SCT to a level of 60%.) Canada and Its Milk Supply Management System The milk supply management system, introduced in the early 1970s, is the essence of Canada’s dairy policy. The system is governed by the Canadian Milk Supply Management Committee (CMSMC). The committee is responsible for policy determination and supervision of the national milk marketing plan. The CMSMC annually sets a national production target, the market sharing quota
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Agricultural Policy Schemes: Other Systems 307
OECD United States 2002–04 New Zealand
1986–88
Japan European Union Canada Australia 0
20
40
60
80
100
%PSE Figure 1 Producer support estimates (PSEs) for milk in various countries. Source: OECD.
100 90 80 70 60 %
50 40 30 20 10 0 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 Japan
Canada
Australia
New Zealand
Figure 2 Single commodity transfers (SCTs) for milk over the period 1986–2008 in various countries. Source: OECD.
(MSQ), for industrial milk. The MSQ is set with the goal to achieve a domestic market balance in terms of butterfat, and is assigned to provinces largely on the basis of historical shares. In addition to the MSQ, each province controls its own production quota for fluid milk, and the entire milk quota – industrial and fluid together – is allocated to producers. For the supply management to be effective there is a need to continue the policies of substantial border measures. In other words, a quota system allows a domestic market to be managed only if that market is isolated from external sources of supply. Under the 1994 Uruguay Round Agreement on Agriculture (URAA), the diverse forms of trade measures were converted to tariffs, and market access for sensitive products was provided through a system of tariff rate quotas (TRQs). Under the TRQ system, exporting countries have access to the Canadian dairy market to the tune of 5% of the
domestic consumption. For most products, the final access quota quantities remain below 1000 tonnes (i.e., 1kt), but are 3.2 kt for butter and dry whey, 20.4 kt for cheese, and 64.5 kt for fluid milk. While the in-quota duties are generally low, tariff rates applicable to overquota imports are prohibitively high, ranging from 202% for skim milk powder to 246% for cheese and 299% for butter. A strict control of supplies from domestic production and imports allows prices paid to producers to be supported at levels marginally above the costs of production. The Canadian Dairy Commission annually reviews and establishes a target price for industrial milk. This target price is supported by market intervention for butter and skim milk powder (SMP) at support prices set similarly on an annual basis. The support prices have been increasing steadily over the last decades. In 2009, the support prices for butter and SMP were raised to Can$7102.4 and
308 Policy Schemes and Trade in Dairy Products
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Can$6178.3 per tonne, respectively. For a comparison, the respective prices in 2000 stood at 5540.7 and Can$4684.2 per tonne, which translates to a 28 and 32% increase in the support prices over the 2000–09 period. (Over the same period, 2000–09, in the European Union the butter and SMP intervention prices declined by 25 and 15%, respectively. Using the October 2009 Can$/Euro exchange rate of 0.65, the butter and SMP support prices of Canada in 2009 would amount to E4611 and E4011 per tonne, respectively. The corresponding intervention prices for butter and SMP in the European Union were E2462 and E1764 per tonne, respectively.) In 1995, a supplementary scheme was introduced that provided for the pricing of five classes of milk by virtue of a new permit system. The change allowed dairy processors to purchase surplus milk (over the quota milk) at a discount rate, determined by the government, for the production of dairy products for exports. The United States, joined by New Zealand, claimed that this in fact constituted an export subsidy, that it was in violation of Canada’s commitments under the Uruguay Round, and requested investigation by a World Trade Organization (WTO) compliance panel. In December 2002, the WTO confirmed that Canada’s approach to the export of dairy products constituted an export subsidy. On 9 May 2003, Canada announced that it had entered into an agreement with the United States and New Zealand, and eliminated the subsidies that violated the WTO rules. The supply management system in Canada is sometimes used as an example of a functioning stable system that enables milk producers to receive good prices. Supply management might be considered the second best option in a narrow sense as it alleviates surplus accumulation resulting from a high market price support, but it is unlikely to be the long-term solution in the face of rapid technological and structural developments throughout the world. The problems linked to supply management include the inefficiencies that the system may create, the costs that it imposes on consumers, the difficulties and costs of administration that may arise for governments, the difficulty in setting the quota at a level that would match consumption, the vested interests that it generates (quota rent), and importantly the need to continue the policies of high border measures.
Japan Background Japanese domestic dairy policy focuses mainly on supporting milk destined for the production of dairy products, which procures a lower price than drinking milk and is subject to international competition. Up until 2001, government support was provided mainly
Agricultural Policy Schemes: Other Systems
through three programs: price support, voluntary program to limit supply, and import tariff rate quotas. Price support was administered via a system of deficiency payments on manufacturing-milk introduced in 1966. The deficiency payments, defined as the difference between a guaranteed price and the price paid by dairy plants for milk used in processing (standard transaction price), were limited to an annually fixed quota volume and to designated products such as butter, SMP, and condensed milk. A voluntary production quota for liquid milk was initiated in 1979 in an effort to regulate shipments from Hokkaido – the low-cost production region with over 80% of milk used for manufacturing – to higher-cost production regions. This quota is determined by the Central Council of Dairy Cooperatives and allocated between prefectural cooperatives, who in turn allocate a quota to each farmer. The allocation between prefectures takes into account production of the previous year and planned production for the coming year. Since the voluntary production planning system has no legal binding power, some 5% of dairy farmers choose to operate outside the production guidelines. As measured by the PSE, total transfers to dairy farmers relative to total gross receipts amounted to 73% in the period 2002–04. The support has declined from the levels calculated in the mid-1980s although the Japanese dairy sector remains among the most heavily supported in the world. A Change in Dairy Domestic Policy in 2001 In April 2001, a policy change was introduced to deal with the rigidity of the guaranteed price system, increased budgetary cost, and the additional pressures to reduce domestic support resulting from Japan’s commitments under the Uruguay Round. The policy abolished the guaranteed price and the standard transaction price along with the deficiency payment scheme, and a new direct-payment program was introduced instead; but the annually determined manufacturing-grade milk quotas were kept in place. The move away from a marketintervention system to a payment-based system was designed to improve the market orientation of dairy farms. Producers’ direct payments were to be set annually in light of the unit rate paid in the previous year and the changes in cost of raw milk production. In 2001, in order to ensure a smooth adjustment to the new policy, the direct payments were set equal to deficiency payments of 2000 at ¥10.3 per kg. The amount of manufacturingmilk eligible for payment was set at 2.27 mt. The evolution of deficiency payments and, from 2001, direct payments together with the eligible quantities is illustrated in Figure 3. The move to a more marketoriented system was compensated for by the introduction of emergency measures to protect farmers from
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Agricultural Policy Schemes: Other Systems 309
12
3
Yen Kg–1
2 11 1.5 10.5 1 10
Million tonnes
2.5
11.5
0.5
9.5
0 1993
1995
1997
1999
Unit payment
2001
2003
2005
2007
2009
Eligible volume
Figure 3 The evolution of deficiency and direct payments for milk together with eligible quantities, in Japan. Source: MAFF, Japan. Deficiency payments until 2000; direct payments afterward.
unforeseen fluctuations in the price of manufacturing milk. If the average market price falls, then 80% of the difference between the average market price and the base price (the average transaction price during the previous 3 years) is to be compensated from an income stabilization fund to which producers and the state contribute at the ratio of 1:3. An additional system of direct payments was introduced to provide incentives for environmental conservation under the land using-type dairy farming promotion project and the direct payment system in hilly and mountainous districts. Japan manages imports of dairy products under TRQs by import licensing and state trading. Quantities under import license are allocated by the Ministry of Agriculture, Forestry and Fisheries (MAFF) to private importers based on historical records. The quota access at preferential tariffs for SMP and butter are set at 116 and 1.9 kt, respectively. Typically these quotas remain significantly underfilled. The in-quota ad valorem tariffs are set at 16, 24, and 35% levels for SMP, whole milk powder, and butter respectively. In addition to in-quota tariffs, the government of Japan or its sales agents are able to charge the so-called markup, which can amount to 392, 413, and 594% for SMP, whole milk powder, and butter respectively. The tariffs for out-of-quota imports are set prohibitively high at 210, 316, and 733% levels for SMP, whole milk powder, and butter, respectively (Agricultural Market Access Database (AMAD)). Cheese imports to Japan are not subject to quota. There are various import tariffs for cheese depending on the use of the product, but the average rate is about 31.2%. Although the policy change toward direct payments is in the right direction, the change is relatively small given the design of the policy. The support remains very high and continues to be paid by consumers. The primary
reason for the very modest impact of the new policy is the lack of changes to dairy trade policy, which keeps Japan’s dairy industry highly protected from cheaper imports. Due to very high border measures, the majority of support still falls under the market price support category. In 2008, the market price support stood at 93% of all SCTs.
Australia Background With the Kerin plan in 1986 and the Crean plan in 1992, Australia began a reform process of dairy policies including a gradual reduction in support and a planned elimination of support for manufacturing milk by 1 July 2000. In 1995, a redesigned plan was introduced to ensure that Australia complied with its WTO commitments on export subsidies under the Uruguay Round. The domestic market support (DMS) scheme was restructured so as to ensure that support was provided independently of export sales. In addition to this reform of support policies for manufacturing milk, a regulatory reform process for market milk was initiated in 1995, stipulating that in each state only farm gate price controls would remain in place by January 1999. In July 1999, a review of market milk regulations in Victoria concluded that there was no net public benefit from retaining farm gate price controls. An industry restructuring plan was developed to avoid possible interstate price wars and an industry collapse, which was implemented on 1 July 2000. Following the industry deregulation, support to the Australian dairy sector has declined dramatically and, measured by the PSE, the value of transfers to the dairy industry relative to gross farm receipts fell to 15% in the period 2002–04 (Figure 1). As measured by the SCT, after the
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deregulation, the direct market support to dairy industry has dropped to zero (Figure 2). Policy Reform of the Dairy Industry in 2000 and beyond A new policy reform package was introduced on 1 July 2000, which removed simultaneously the DMS scheme and fresh milk regulations, and allowed the market to determine milk prices. At the same time, a structural adjustment package was introduced through the Dairy Industry Adjustment Act to help producers to cope with the adjustment to lower prices or to choose to leave the industry. The adjustment package was to be funded by a levy of 11 cents (A$) per liter on all domestic sales of fresh milk for 8 years until the package would be fully funded. The individual adjustment programs were called the dairy industry adjustment package, the dairy structural adjustment program, the dairy exit program, and the dairy regional assistance program. Dairy farmers were eligible for dairy structural adjustment program assistance and received a fixed quarterly payment over 8 years, with payments being based on milk production in 1998–99, and subject to income tax. Producers could also opt to leave the dairy industry altogether, and receive an exit payment of up to A$45 000 tax-free under the dairy exit program. The conditions attached to the program prevented the farmers from reentering the industry at a later date. Finally, the dairy regional assistance program was intended to assist dairy-dependent communities in generating alternative employment opportunities and to deal with any social dislocation from deregulation. After the reform, the dairy industry has become fully exposed to world market conditions and emerged as a globally cost-competitive industry. However, following the deregulation, the dairy sector not only had to absorb the reform adjustment pressures but also had to cope with a series of severe droughts that resulted in increased herd contraction. Cow inventories in Australia increased in 2008/09 for the first time in 7 years, however contracted again in 2009/10 and the future industry growth remains sensitive to availability and management of water supply. To address these issues, in 2008 and 2009, the Australian government has strengthened the water policy reforms and environmental programs, and also announced an initiative, Australia’s Farming Future, to help the industry through research and information to manage the impact of climate changes. The Australian Government is also committed to implementing the emissions trading scheme in 2011, which can be expected to impact the dairy sector. Nevertheless, at the same time, a program concentrating on reducing emissions from livestock has been initiated focusing on research into alternative feeds to reduce methane production or genetic approaches to developing low-emitting animals.
Agricultural Policy Schemes: Other Systems
The industry does not use export subsidies to increase its market share of dairy products, although it has a strong focus on export sales. In 2009, the Australian government has announced a reform of the system of export quota allocations to the United States and the European Union. Under tariff rate quotas, certain amounts of Australian dairy products can be exported into the United States and the European Union at reduced or zero tariffs. The old system of distributing fixed shares of quota based on historical entitlements is replaced by a system in which exporters receive a share of quota based on 3-year rolling averages of export performance. Australia has also entered into a number of free trade agreements (FTAs) that have been or are in the process of negotiation. The trade barriers between Australia and New Zealand were fully removed in the Closer Economic Relations Trade Agreement, which came into effect already on 1 January 1983. Australia has FTAs also with Singapore, Thailand, the United States, and Chile. Most recently, the negotiations between ASEAN, Australia, and New Zealand for a free trade agreement (AANZFTA) were concluded on 28 August 2008, and the agreement was signed on 27 February 2009. This was the largest FTA Australia signed to that date. A separate agreement is being negotiated with Malaysia, and there are plans to negotiate an FTA with Indonesia. FTA agreements are also being pursued with China, Japan, and the Gulf Cooperation Council.
New Zealand Background Prior to 1984, the support to farmers in New Zealand went as high as 40% of the farmers’ income. Domestic farm support policies were scaled down dramatically during the 1980s with input subsidies eliminated in 1984 and government involvement in calculation of product prices withdrawn in 1988. The main dairy policy issue following the deregulation of 1984 was related to the export monopoly of the New Zealand Dairy Board (NZDB) and the potential for indirect subsidization of dairy exports. This potential existed as Section 27 of the Dairy Board Act allowed for pooling of revenues from domestic and export markets and, thus, cross-subsidization of lower revenue from export sales by higher revenue from domestic sales. This section was abolished in 1998. The dairy industry is one the most important elements of the New Zealand economy accounting for about one quarter of New Zealand’s total export earnings. Measured by the PSE, total transfers to dairy farmers relative to gross farm receipts were close to zero in 2002–04 (Figure 1). As measured by the SCT, the direct market support to the dairy industry has been zero for more than 20 years (Figure 2).
Policy Schemes and Trade in Dairy Products
Dairy Industry Restructuring Act On 9 April 2001, the New Zealand Government passed the Dairy Industry Restructuring Act (DIRA), which agreed to the formation of a large cooperative Fonterra, originally called GlobalCo, through the merger of most of New Zealand’s cooperative dairy processing companies. The act also stipulated that following the merger, the new company will absorb the activities of the NZDB. The NZDB, established through the Dairy Board Act in 1961, controlled the marketing of all export dairy products and was the largest exporter in New Zealand. An amendment to the Dairy Board Act in 1996 brought the status of NZDB closer to that of a company in which milk processing cooperatives own shares in proportion to their milk deliveries. Nevertheless, the NZDB remained subject to criticism for its export monopoly power. Given the trade agreements and its export power, the NZDB was able to extract quota rents from dairy exports (e.g., to the EU), which were then passed back to individual producers thus increasing the farmers’ marginal returns. The DIRA ended the statutory export monopoly of NZDB and established 11 regulated dairy export markets. On a transitional basis, the act provided Fonterra with exclusive export access to these markets for a fixed period of time. In 2007 the New Zealand Government reviewed the regulated export market established in the DIRA and started the deregulation process to be concluded over the period 2007–10. The DIRA also provided for a regulation that aimed to protect firms from Fonterra’s monopoly pricing. The provision required that 5% of Fonterra’s milk be made available at a predetermined price to other independent processors to allow for a level playing field. The review of this regulation conducted in 2008 concluded that independent processors were able to procure milk at a lower price than what Fonterra paid to its farmers. A new mechanism was proposed under the Dairy Industry Restructuring Bill; this bill (in reading as of October 2009) proposes that the margin be charged from the 2010/2011 dairy season and also provides for raw milk to be allocated through auctions in later years. Government policy in New Zealand affects the dairy industry mainly via policy measures addressing agri– environmental issues. For example, the dairying and clean streams accord, which was agreed between Fonterra and the New Zealand Government in 2003, aims to achieve clean water, including streams, rivers, lakes, and ground water, and wetlands in dairying areas. Moreover, in September 2007, the government released a comprehensive statement on climate change and a range of initiatives across all sectors, including the Emissions Trading Scheme (ETS). Agriculture is likely to be part of the scheme from 2013.
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New Zealand is the largest exporter of butter, SMP, and whole milk powder, and the second largest exporter of cheese in the world. New Zealand achieves this position without relying on production or market subsidies and without protecting the domestic market from overseas competition. In the absence of progress in lowering trade barriers on a multilateral level, New Zealand is seeking trade agreements on a bilateral basis. Apart from New Zealand’s free trade agreement with Australia (already in place since 1983), more recent FTAs were concluded with Singapore, Thailand, the Trans-Pacific Partnership (involving Singapore, Brunei, and Chile), China, and ASEAN (signed in February 2009). Negotiations are currently underway with Malaysia, Hong Kong, and the Gulf Co-operation Council (Saudi Arabia, UAE, Oman, Qatar, Bahrain, and Kuwait). Negotiations are also due to commence for the enlargement of the Trans-Pacific Partnership and bilateral FTAs with Korea and with India. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: European Union’s Common Agricultural Policy.
Further Reading Australian Competition and Consumer Commission (2001) Impact of Farmgate Deregulation on the Australian Milk Industry: Study of Prices, Costs and Profits. Dickson, ACT: ACCC. Campo IS and Beghin JC (2006) Dairy food consumption, supply and policy in Japan. Food Policy 31: 228–237. Federated Farmers of New Zealand (2009) Life After Subsidies. http://www.fedfarm.org.nz/n215.html (accessed August 2010). Japan Dairy Council (2001) Japan Dairy Farming for Yesterday, Today and Tomorrow: Supporting a Healthy Japanese Diet. Tokyo: Japan Dairy Council. Organization for Economic Cooperation and Development (2005) Dairy Policy reform and Trade Liberalisation. Paris: OECD. Organization for Economic Cooperation and Development (2009) Evaluation of Agricultural Policy Reforms in Japan. Paris: OECD. Organization for Economic Cooperation and Development (2009) OECD Agricultural Outlook 2009–2018. Paris: OECD (and earlier issues). Organization for Economic Cooperation and Development (2009) Agricultural Policies in OECD Countries: Monitoring and Evaluation. Paris: OECD (and earlier issues). Obara K, Dyck J, and Stout J (2005) Dairy policies in Japan. Electronic Outlook Report. US Department of Agriculture, Economic Research Service (USDA, ERS). http://gain.fas-usda.gov/pages/Default.aspx USDA (2008) New Zealand, dairy and products. GAIN Report No NZ8026. USDA-FAS. http://gain.fas-usda.gov/pages/Default.aspx Yasaka M (2001) Dairy Farming and the Dairy Industry. Japan’s Livestock Industry: Now and in the Future. Tokyo: Food and Agriculture Policy Research Center.
Relevant Websites http://www.cdc.ca – Canadian Dairy Commission.
Codex Alimentarius C Heggum, Danish Dairy Board, Aarhus, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction Codex Alimentarius is Latin for food code and refers today to the international food code established under the United Nations. It is a collection of internationally adopted food standards that constitute a global reference point for national food legislators and control agencies, the international food trade, and food handlers and consumers. The code has a great impact on the approach to food quality management throughout the world. The code is being developed by the Codex Alimentarius Commission (CAC), which is an international organization run jointly by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO). One hundred and seventy-eight individual countries are members of the CAC (end of 2008). In addition, about 160 other international intergovernmental and international non-governmental organizations contribute to the work. The CAC’s objective is to establish standards, codes of practices, guidelines, and recommendations concerning foods aimed at protecting consumer’s health, ensure fair practices in trade, and facilitate international trade. With the establishment of the World Trade Organization (WTO), the Codex Alimentarius has gained importance due to the fact that two WTO Agreements (the Agreement on the Applications of Sanitary and Phytosanitary Measures (SPS) and the Agreement on Technical Barriers to Trade (TBT)) refer to Codex Alimentarius texts as being the reference for dispute settlements and for application by national legislation.
The Establishment The Need for Harmonization of National Food Regulations The need for international food regulation has developed with international trade. Quality standards for individual commodities have been known since ancient times, but the first general food laws were established in the 1800s. At the beginning of the 1900s, the establishment of international food standards began; it was of growing concern to food traders worldwide that the national standards and regulations developing independently (and sometimes spontaneously) in individual countries started to create trade barriers. As a response to this development,
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trade associations that were formed as a reaction to such barriers pressured governments to harmonize their various food standards so as to facilitate trade in safe foods of a defined quality. One of the earliest such associations was the International Dairy Federation (IDF), founded in 1903. After World War II, there was heightened international concern about the direction being taken in the field of food regulation. Countries were acting independently and there was little, if any, consultation among them with a view to harmonization. In addition, and as a reaction to the food supply situation during the 1940s, many attempts were made to protect and support domestic food production. Food regulations in different countries were conflicting and contradictory, in particular with regard to nomenclature, and much legislation was not based on scientific knowledge. Many efforts have been made to harmonize national food regulations. In the dairy field, the IDF developed during the 1950s a vast number of codes and standards intended to be applied by the dairy sector and to form the basis of national legislation. These efforts resulted in two initiatives being taken at the government level: establishment of the ‘Stresa Convention’ – a multi• the lateral agreement between a number of European
•
countries that governed the naming and composition of a number of individual cheese varieties (see Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products); the establishment of the Joint FAO/WHO Committee of Government Experts on the Code of Principles Concerning Milk and Milk Products (the ‘Milk Committee’) – a worldwide committee established to develop international identity standards for milk products, most of them prepared by IDF, within the framework of the Code of Principles Concerning Milk and Milk Products (see Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products).
Catalyzed by the success of the Milk Committee, the 1961 FAO Conference decided to establish the Codex Alimentarius. The CAC was established in 1962 to govern the work. Due to the importance of the role of WHO in all health aspects of food, the WHO joined in 1963. Since its founding, many food standards, codes of hygienic and technological practice, and maximum
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The Codex Alimentarius • 204 food standards for commodities • 47 codes of hygienic or technological practice • 2930 maximum limits for 218 evaluated pesticides • 1112 maximum levels for 292 evaluated food additives • 441 maximum residue levels for 49 evaluated veterinary drugs • Guidelines for 12 contaminants Figure 1 Standards, codes, and recommendations established by Codex Alimentarius.
residue limits (MRLs) for food contaminants have been established by Codex Alimentarius (Figure 1). The Milk Committee, since its establishment in 1958, was integrated into the Codex Alimentarius system. However, its rules and procedures were different from those of Codex Alimentarius for many years. As late as 1993, the Milk Committee was replaced by the ‘Codex Committee for Milk and Milk Products’ and the rules and procedures were aligned with those applicable for the rest of the Codex system.
The Scientific Basis The Codex Alimentarius is science based. Experts and specialists in a wide range of disciplines contribute to every aspect of the code to ensure that its standards withstand the most rigorous scientific scrutiny. Much work is carried out in the form of collaborative studies between individual scientists, laboratories, institutes and universities, and joint FAO/WHO expert committees and consultations. The membership of expert consultations is of critical importance. The credibility and acceptability of any conclusions and recommendations depend to a very large degree on the impartiality, scientific skill, and overall competence of the members who formulate them. For this reason, care is taken in the selection of experts invited to participate. Those selected must be preeminent in their specialty, have the highest respect of their scientific peers, and be impartial and objective in their judgment. They are appointed in their own personal right – not as government representatives or as spokespeople for organizations. The Joint FAO/WHO Expert Committee on Food Additives (JECFA), the Joint FAO/WHO Meetings on Pesticide Residues (JMPR), and the Joint FAO/WHO Expert Meetings on Microbiological Risk Assessment (JEMRA) have generated a large amount of scientifically based food data.
JMPR was established in 1963 with the task of recommending MRLs for pesticide and environmental contaminants in specific food products. JMPR members are independent scientists who are expert in aspects of pesticides and environmental chemicals and their residues. There is close cooperation between JMPR and the Codex Committee on Pesticide Residues (CCPR). CCPR identifies substances requiring priority evaluation. After JMPR evaluation, CCPR discusses the recommended MRLs and, if they are acceptable, forwards them to the Commission for adoption as Codex MRLs. JECFA was established in 1955 with the task of considering chemical, toxicological, and other aspects of contaminants and residues of veterinary drugs in foods for human consumption. JECFA provides the Commission and other Codex bodies with expert advice relating to food additives, contaminants, and residues of veterinary drugs. The Codex Committee on Food Additives (CCFA), the Codex Committee on Contaminants in Foods (CCCF), and the Codex Committee on Residues of Veterinary Drugs in Foods (CCVDF) identify food additives, contaminants, and veterinary drug residues that should receive priority evaluation and refer them to JECFA for assessment before incorporating them into Codex standards. JEMRA was established in 2000 in response to the increasing need for risk-based scientific advice and information and tools to undertake microbiological risk assessment. The objectives of JEMRA are the development and optimization of the utility of microbiological risk assessment (MRA) as a tool to inform actions and decisions aimed at improving food safety and to make it equally available to both developing and developed countries.
Purpose and Organization The task of creating a food code is immense. Food standards need to mirror the dynamic environment in which they will be applied. Product development, changes in trade and consumption patterns, consumer perception, and scientific progress make creation and review of food standards virtually endless. Furthermore, it requires more effort and resources to create standards that, on the one hand, aim at protecting consumers and ensuring fair practices in the sale of food and, on the other hand, facilitating trade. The need to involve scientific experts from consumers’ organizations, expertise from production and processing industries, and food control administrators and traders is obvious. The finalization of food standards and their compilation into a code that is credible and authoritative requires extensive consultation followed up by confirmation of
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final results and, sometimes, a compromise to satisfy divergent but scientifically sound views. The above comprehensive process makes developments slow. On the other hand, once a standard has been adopted, it reflects worldwide consensus and is therefore useful in practice. Objectives of Codex The objective of Codex is to conduct the Joint FAO/ WHO Food Standards Programme, the purpose of which is (a) to protect the health of the consumers; (b) to ensure fair practices in the food trade; (c) to promote coordination of all food standards work undertaken by international governmental and nongovernmental organizations; (d) to determine priorities and to initiate and guide the preparation of draft standards through and with the aid of appropriate organizations; and (e) to finalize food standards and to publish them in a Codex Alimentarius as either regional or worldwide standards. Structure of Codex The CAC is the supreme body of Codex Alimentarius. It meets every year, alternately at FAO headquarters in Rome and at WHO headquarters in Geneva. Plenary sessions are attended by as many as 800 people. Representation at sessions is on a country basis. Senior officials appointed by their governments lead national delegations. Delegations may, and often do, include representatives of industry, consumers’ organizations, and academic institutes. A number of international governmental and non-governmental organizations also attend in an observer capacity. Although they are ‘observers’, the tradition of the CAC allows such organizations to put forward their points of view at every stage except in the final decision, which is the exclusive prerogative of Member Governments. The Commission is empowered to establish three kinds of subsidiary bodies: 1. Codex Committees, which prepare draft standards for submission to the Commission. These are classed as either General Subject Committees or Commodity Committees. The work of the General Subject Committees has relevance for all foods and applies across the board to all commodities. Therefore, these are sometimes referred to as ‘horizontal committees’. They develop all-embracing concepts and principles applying to foods in general, specific foods, or groups of foods, endorse or
review relevant provisions in Codex commodity standards, and, based on the advice of expert scientific bodies, develop major recommendations pertaining to consumers’ health and safety. Currently, there are 10 General Subject Committees (see Figure 2). Commodity Committees have responsibility for developing standards for specific foods or classes of food. In order to distinguish them from the horizontal committees and recognize their exclusive responsibilities, they are often referred to as ‘vertical committees’. Currently, there are 11 Commodity Committees (see Figure 2). 2. Coordinating Committees, through which regions or groups of countries coordinate food standards activities in the region, including the development of regional standards. Coordinating Committees play an invaluable role in ensuring that the work of the Commission is responsive to regional interests and to the concerns of developing countries. Currently, there are six Coordinating Committees (see Figure 2). 3. Ad Hoc International Governmental Task Forces are established to consider closely defined issues within a time-limited period. Currently, three such Task Forces are operating (see Figure 2). Each worldwide committee and task force is hosted by a member country, which is chiefly responsible for the maintenance and administration cost of the committee and for providing its chairperson. Regional committees have no standing host countries; the Chair is elected at meetings.
The Codex Step Procedure Typically, the Codex work program consists of revision of older, outdated texts and the development of new texts. The latter is usually initiated with the consideration of discussion papers. Once a standard, a code, or a guideline is identified as a potential subject for work, it will be developed in three phases, normally comprising eight formal steps (Figure 3): decision to initiate work (constitutes step 1), result• the ing in the adding of the subject to the work program
•
and allocation of the responsibility to prepare a Proposed Draft Codex Standard, a Proposed Draft Codex Code of Practice, a Proposed Draft Codex Guideline, or another proposed draft Codex recommendation; the process of furnishing a draft text (constitutes steps 2–5), resulting in preparing an almost finalized draft, which is adopted as a Draft Codex Standard, a Draft
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FAO
Executive Committee
Food Additives (China) Contaminants in Foods (Netherlands) Pesticide Residues (China) Methods of Analysis and Sampling (Hungary)
Codex Secretariat
CODEX ALIMENTARIUS COMMISSION
Horizontal committees
Food Import and Export Inspection and Certification (Australia)
WHO
Residues of Veterinary Drugs in Foods (USA) General Principles (France) Food Labelling (Canada) Food Hygiene (USA) Nutrition and Foods for Special Dietary Uses (Germany)
Vertical committees
Cocoa Products and Chocolate (Switzerland)* Natural Mineral Waters (Switzerland)* Vegetable Proteins (Canada)* Cereals, Pulses and Legumes (USA)* Sugars (United Kingdom)* Meat Hygiene (New Zealand)*
Fish and Fishery Products (Norway)
Ad Hoc task forces
Antimicrobial Resistance (Republic of Korea)
Fats and Oils (United Kingdom) Fresh Fruits and Vegetables (Mexico)
Biotechnology (Japan)
Regional committees
Africa
Asia
Europe
Latin America and Caribbean
Processed Fruits and Vegetables (USA)
Near East
Milk and Milk Products (New Zealand)
North America and Southwest Pacific
Figure 2 Organization of the Codex Alimentarius Commission. -Adjourned sine die.
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Codex Code of Practice, a Draft Codex Guideline, or another draft Codex recommendation; and the process of finalizing a text (constitutes steps 6–8), resulting in a Codex Standard, a Codex Code of Practice, a Codex Guideline, or another Codex recommendation.
Initiation of New Work A proposal for a standard or another text can be submitted by any member country or any of the interested international organizations registered. In the dairy field, most proposals derive from the work of the IDF. Prior to the approval of new work a project document that details the purpose and scope, its relevance, main
aspects to be covered, need for any expert scientific advice, and timeline for completion is required. Furthermore, an assessment of the formal criteria for the establishment of work priorities is needed. For commodity standards, these are 1. consumer protection from the point of view of health and fraudulent practices; 2. volume of production and consumption in individual countries and volume and pattern of trade between countries; 3. diversification of national legislation and apparent resultant impediments to international trade; 4. international or regional market potential; 5. amenability of the commodity to standardization; 6. coverage of the main consumer protection and trade issues by existing general standards;
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Steps
1, 2, 3
Decision of the CAC to draft a text (step 1). The CAC allocates the drafting responsibility to a subsidiary body. A proposed draft text is elaborated (step 2) and circulated by Codex to member countries and international organizations for comments (step 3).
The proposed draft text and the comments submitted to it are considered at a meeting of the subsidiary body responsible for the drafting process. The text, as amended by the meeting, is progressed to step 5, kept at step 4 or returned to step 3 for redrafting.
Steps
5, 6
8
Step
7
Step
The proposed draft text, as amended, is considered by the CAC (step 5). The result may be adoption or return to step 3 for reconsideration. If adopted, the proposed draft text becomes a draft codex text and it is circulated to member countries and international organizations for comments (step 6)
The draft text and the comments submitted to it at step 6 are considered at a meeting of the subsidiary body responsible for the drafting process. The text, as amended by the meeting, is either progressed to step 8 or returned to step 6 for recirculation.
Step
4
The CAC adopts the draft text as a Codex text. It is published in the Codex Alimentarius and constitutes a reference text for application by the WTO.
Figure 3 Standard elaboration procedure of Codex texts.
7. number of commodities that would need separate standards indicating whether raw, semiprocessed, or processed; and 8. work already undertaken by other international organizations in this field. The first drafting is normally assigned to the Codex Secretariat, a Member Government, an ad hoc working group established among interested Member Governments and organizations, or, in the case of dairy standards, the IDF. Commodity standards follow a uniform format. The structure of codes of practices and guidelines varies according to the nature of the content and the traditions within the Codex Committee where the draft is developed. A draft Codex text is sent to governments and international organizations a number of times in a stepwise procedure, which, if completed satisfactorily, results in the draft becoming a ‘Codex standard’. In an accelerated procedure, the number of steps required for the development of a standard varies from a maximum of eight to a minimum of five. In many cases, steps are repeated. Most standards take 8 years to develop.
current scientific knowledge. The procedure for revision follows the same procedure as used for the initial preparation of new standards. The Commission can, however, decide to omit any other step or steps of the procedure where an amendment proposed by a Codex Committee is either editorial in nature or consequential to provisions in similar standards adopted.
Application and Role of Codex Texts The Codex Alimentarius has relevance to the international food trade and also to domestic legislation and regulation. With respect to the ever-increasing global market, in particular, the advantages of having universally uniform food standards are self-evident. Texts developed by the CAC are applied in the following contexts: 1. as reference texts for the SPS and TBT Agreements of the WTO; 2. as reference texts and/or foundation for national legislation, regional regulation, and trade agreements; and 3. as reference texts for commercial trading parties.
Revision of Codex Standards The Commission and its subsidiary bodies are committed to revision of Codex standards and related texts as necessary to ensure that they are consistent with and reflect
SPS and TBT Agreements of the WTO Both the SPS and TBT Agreements acknowledge the importance of harmonizing standards internationally so
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as to minimize or eliminate the risk of national legislation and regulation becoming barriers to trade. The SPS Agreement
In its pursuance of harmonization, the SPS Agreement has identified and chosen the standards, guidelines, and recommendations established by the CAC for food additives, residues of veterinary drugs and pesticides, contaminants, methods for analysis and sampling, and codes and guidelines of hygienic practice. In other words, Codex texts are considered scientifically justified and have become an integral part of the legal framework as accepted benchmarks against which national measures and regulations are evaluated (Figure 4). Codex texts have already been used as the benchmark in international trade disputes, and it is expected that they will be used increasingly in this regard. As a consequence, interest in Codex activities and participation at the meetings of governments and international inter- and non-governmental organizations has increased. There are no obligations for a government to use Codex standards, only an encouragement. However, as Codex texts by definition are recognized as being scientifically based, a government need not perform a formal risk assessment (see Risk Analysis) if a Codex recommendation is followed. Thereby, a government can save considerable resources. Otherwise, a government can be faced with the SPS requirement to defend and justify
according to scientific evidence every deviating detail in their national legislation. This possibility to choose Codex standards provides the opportunity for countries with economic limitations to follow Codex recommendations and simultaneously comply with the SPS requirements. In countries where the necessary resources are available, additional risk assessment might be carried out in order to justify desired deviations from Codex. A government can only implement stricter food safety requirements than those recommended by Codex, and if justified. This means that Codex recommendations relating to food safety serve as minimum provisions. The TBT Agreement
The basic principle of the TBT Agreement is that any measure should be enforced only if a so-called legitimate objective exists (e.g., prevention of deceptive practices, meet quality and performance requirements). The legitimate objective should be transparent in order to avoid disguised protection of domestic production and to avoid arbitrary decisions. The TBT Agreement does not make reference to any particular international organization to be used as the ‘benchmark’. With respect to food, however, it is generally recognized that Codex Alimentarius serves this function (Figure 5). It is relatively easy for a government to justify that a particular part of an international standard, for example, a
The SPS Agreement The Agreement on the Application of Sanitary and Phytosanitary Measures acknowledges that governments have the right to take sanitary and phytosanitary measures necessary for the protection of human health. However, the SPS Agreement requires them to apply those measures only to the extent required to protect human health. It does not permit Member Governments to discriminate by applying different requirements to different countries where the same or similar conditions prevail, unless there is sufficient scientific justification for doing so. Article 2.2 of the SPS Agreement states: "Members shall ensure that any sanitary and phytosanitary measure is applied only to the extent necessary to protect human, animal or plant life or health, is based on scientific principles and is not maintained without sufficient scientific evidence ..." Article 3.1 of the SPS Agreement states: "To harmonize sanitary and phytosanitary measures on as wide a basis as possible, Members shall base their sanitary and phytosanitary measures on international standards, guidelines or recommendations, where they exist, except as otherwise provided for in this Agreement." Figure 4 The Agreement on the Applications of Sanitary and Phytosanitary Measures (SPS).
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The TBT Agreement The Agreement on technical barriers to trade seeks to ensure that technical ,regulations and standards, including packaging, marking, and labeling requirements and analytical procedures for assessing conformity with technical regulations and standards do not create unnecessary obstacles to trade. Article 2.4 of the TBT Agreement states “Where technical regulations are required and relevant international standards exist or their completion is imminent, Members shall use them, or the relevant parts of them, as a basis for their technical regulations except when such international standards or relevant parts would be an ineffective or inappropriate means for the fulfilment of the legitimate objective pursued, for instance because of fundamental climatic or geographical factors or fundamental technical problems.” Article 2.5 of the TBT Agreement states “.... Whenever a technical regulation is prepared, adopted or applied for one of the legitimate objectives......., and is in accordance with relevant international standards, it shall be rebuttably presumed not to create an unnecessary obstacle to international trade.” Article 2.6 of the TBT Agreement states "With a view to harmonizing technical regulations on as wide a basis as possible, Members shall play a full part, within the limits of their resources, in the preparation by appropriate international standardizing bodies of international standards for products for which they have either adopted, or expect to adopt, technical regulations." Figure 5 The Agreement on Technical Barriers to Trade (TBT).
labeling requirement, is not appropriate in a particular country or that additional requirements are needed locally. It is allowed to deviate from Codex TBT-related provisions in both stricter and less strict directions, if an appropriate legitimate objective exists. Codex regulations, which are not aiming at protecting human health, are therefore merely to be seen as guidelines. Codex standards may not be the only body that provides reference provisions, as objectives of the TBT Agreement are broader than those of Codex Alimentarius. National Legislation and Regulation The harmonization of food standards is generally viewed as a prerequisite to the protection of consumer health as well as allowing the fullest possible facilitation of international trade. For that reason, both SPS and TBT Agreements encourage the international harmonization of food standards. While the growing world interest in all Codex activities clearly indicates global acceptance of the Codex philosophy – embracing harmonization, consumer protection, and facilitation of international trade – in practice, it is difficult for many countries to accept Codex standards in the statutory sense. Differing legal formats and administrative systems, varying political systems, and sometimes the influence of national attitudes and concepts of sovereign rights impede the progress of
harmonization and deter the acceptance of Codex standards. Most countries have, however, responded by introducing long-overdue or reviewed/aligned existing food legislation and Codex-based national standards and by establishing or strengthening food control agencies.
Regional Regulation and Trade Agreements The Uruguay Round Agreements provide groups of member countries the opportunity to enter into trade agreements among themselves for the purpose of liberalizing trade. So far, three such agreements have been established, all of them having adopted measures consistent with the principles embraced by the SPS and TBT Agreements and which relate to Codex standards: (North American Free Trade Agreement • NAFTA between Canada, the United States, and Mexico)
•
includes two ancillary agreements dealing with sanitary and phytosanitary measures and technical barriers to trade. With regard to SPS measures, Codex standards are cited as basic requirements to be met by the three member countries in terms of health and safety aspects of food products. The Food Commission of MERCOSUR (Treaty of Asuncio´n establishing the Southern Common Market between Argentina, Brazil, Paraguay, and Uruguay)
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recommends a range of Codex standards for adoption by member countries and is using other Codex standards as points of reference in continuing deliberations. APEC (Asia–Pacific Economic Cooperation between 18 Asian and Pacific countries) has drafted a Mutual Recognition Arrangement on Conformity Assessment of Foods and Food Products. This calls for consistency with SPS and TBT requirements as well as with Codex standards.
In addition, the EU (European Union) directives and regulations frequently refer to the Codex Alimentarius as the basis for their requirements. Commercial Trade Besides providing the reference for national legislation, the texts established by the CAC, in particular the commodity standards, are frequently used as references in commercial trade, independent of legislation. Such reference points may be used for price setting and for specifying any deviations agreed.
• • • • • • • •
Coulommiers, Cream Cheese, Camembert, Brie, Extra hard Grating) (2008); whey cheese (2006); fermented milks (2008); evaporated milks (1999); sweetened condensed milks (1999); milk powders and cream powders (1999); edible casein products (2001); whey powders (2006); and lactose (now part of the standards for sugars) (1999).
Revisions have not yet been finalized for named variety processed cheese, processed cheese, and processed cheese preparations. The nonrevised standards date back to the 1960s and 1970s but are still valid as references.
Other Commodity Standards From a dairy perspective, international standards for nondairy foods that contain significant dairy ingredients and/ or are intended to replace dairy products in consumption patterns are of interest. The most important of these commodities regulated by Codex are
Codex Texts Relevant for Dairy Production and Trade
for chocolate, cocoa butter, coconut milk and • standards three standards covering various blends of preserved
The Codex Alimentarius includes general texts applicable across-the board to all foods (general standards, codes of hygienic practices), other codes of practices (technology, control), and commodity-specific texts (commodity standards, commodity-specific codes of practices).
for infant formula, follow-up formula, • standards canned baby foods, and processed cereal-based foods
skimmed milk and vegetable fat;
for infants and young children; and
• vegetable protein products and soy protein products.
Milk Product Standards When Codex decided to adjourn the old Milk Committee in 1993 and replace it with the Codex Committee on Milk and Milk Products, it was agreed that the file of standards established earlier needed extensive revision. This task has almost been accomplished. Updated versions of the milk product standards are as follows (see Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products):
Food Hygiene Food hygiene constitutes the cornerstone in Codex food safety activities. Microbiological hazards constitute the greatest risk for human health. In recent years, focus has been on the development of appropriate tools to assess and manage risks associated with the intake of microbiological hazards through food. New metrics have been identified and described, but they are not implemented as yet. Risk managers including Codex continue using general and specifically targeted good hygienic practices supplemented by the HACCP (Hazard Analysis and Critical Central Point) approach. Of particular interest to the dairy sector are the following Codex hygiene texts that build on well-established concepts:
(2006); • butter dairy fat spreads (2008); • milk fat products (including butter oil, anhydrous milk • fat, and ghee) (2006); and prepared creams; • cream cheese (2008); • unripened cheese, including fresh cheese (2001); • cheese in brine (1999); of Practice of General • individual cheese • Code Hygiene (2003); varieties (Mozzarella, Cheddar, • Danbo, Edam, Gouda, Havarti, Samsø, Emmental, The HACCP • Application (1997);System and Tilsiter, Saint-Paulin, Provolone, Cottage Cheese,
Principles for Food Guidelines for its
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for the Establishment and Application of • Principles Microbiological Criteria (1997); on the Application of General Principles of • Guidelines Food Hygiene to the Control of Listeria monocytogenes in Ready-to-Eat Foods (2007); and
of Hygienic Practice for Powdered Formulae for • Code Infants and Young Children (2008). Other texts that introduce more risk-based approaches for food hygiene management include of Hygienic Practice for Milk and Milk Products • Code (2004); and Guidelines for the Conduct of • Principles Microbiological Risk Management (2007); and for the Validation of Food Safety Control • Guideline Measures (2008). From a dairy perspective, it is also worth noting the existence of the Codex Guidelines for the Preservation of Raw Milk by the Lactoperoxidase System from 1991. The guidelines for this system apply only where the infrastructure does not provide facilities for refrigeration. Food Labeling Labeling constitutes a significant part of most food regulations. A number of standards and guidelines for the labeling of foods, primarily prepackaged foods, have been developed. These standards and guidelines have gained widespread use worldwide and are implemented in the national legislation of most countries. For dairy products, the most relevant are Standard for the Labelling of Prepackaged • General Foods (2008); Guidelines on Claims (1991); • General Guidelines Labelling (2006); and • Guidelines onforNutrition Use of Nutrition and Health Claims • (2008). Among the issues currently being considered are issues related to nutrition labeling and labeling aspects of foods derived from modern biotechnology. The General Standard for the Use of Dairy Terms is especially of interest from the dairy point of view. It provides guidance on where and how to use terms in the labeling and marketing of foods (see Labeling of Dairy Products). Food Additives Codex addresses food additives in horizontal texts as well as in commodity standards. Immense resources have been allocated to the establishment of a comprehensive General Standard for Food Additives. This standard is kept under constant review (see Additives in Dairy
Foods: Consumer Perceptions of Additives in Dairy Products; Emulsifiers; Legislation; Safety; Types and Functions of Additives in Dairy Products). Contaminants Codex addresses contaminants in horizontal texts as well as in commodity standards. A comprehensive General Standard for Contaminants and Toxins in Food is the most important. This standard is kept under constant review. In addition, the Code of Practice for the Reduction of Aflatoxin B1 in Raw Materials and Supplementary Feeding Stuffs for Milk-Producing Animals (1997) and a Code of Practice for the Prevention and Reduction of Dioxin and Dioxin-like PCB Contamination in Food and Feeds (2006) are of interest to the dairy sector. Control of contaminant levels is also addressed in the HACCP System and Guidelines for its Application (see Contaminants of Milk and Dairy Products: Environmental Contaminants; Contamination Resulting from Farm and Dairy Practices; Nitrates and Nitrites as Contaminants). Residues of Veterinary Drugs in Foods Within the veterinary field, Codex has established a database on MRLs for individual foods and categories of foods, including those that specifically relate to milk. Also of specific relevance to the dairy sector are the Guidelines for the Establishment of Regulatory Programme for the Control of Veterinary Drugs in Food and a Code of Practice for Control of the Use of Veterinary Drugs (1993) and a Code of Practice to Minimize and Contain Antimicrobial Resistance. Pesticide Residues Codex has established a huge database on recommended maximum limits for individual foods and categories of foods. Food Import and Export Inspection and Certification Systems The objective of Codex to facilitate the free movement of foods is also pursued through the establishment of recommendations for food control and inspection agencies. For the dairy sector, the most relevant texts developed include for Food Import and Export Certification • Principles (1995); for Design, Production, Issuance and Use of • Guidelines Generic Official Certificates (2007); for Food Import Control Systems (2006); • Guidelines Principles for Traceability/Product Tracing as a Tool • Within a Food Inspection and Certification System (2006);
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Export Certificate for Milk and Milk Products • Model (2008, amended 2010); and for the Judgement of Equivalence of • Guidelines Sanitary Measures Associated with Food Inspection and Certification Systems (2008). Methods of Analysis and Sampling In principle, any criteria specified in an established Codex text need to be followed up by the identification of appropriate and validated methods of sampling and analysis. Codex frequently reviews and updates an inventory of endorsed methods (Analysis of Milk and Dairy Products). See also: Additives in Dairy Foods: Consumer Perceptions of Additives in Dairy Products; Emulsifiers; Legislation; Safety; Types and Functions of Additives in Dairy Products. Contaminants of Milk and Dairy Products: Contamination Resulting from Farm and Dairy Practices; Environmental Contaminants; Nitrates and Nitrites as Contaminants. Labeling of Dairy Products. Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products. Risk Analysis.
Further Reading FAO/WHO (2006) Understanding the Codex Alimentarius, 3rd edn. Rome: Food and Agriculture Organization of the United Nations and World Health Organization. IDF (1996) Codex standards in the context of world trade agreements. Proceedings of the IDF Seminar held in Brussels. November 1995. IDF Bulletin No. 310. Brussels, Belgium: International Dairy Federation. IDF (1997) The influence of Codex standards on international trade in dairy products. Abstracts of the International Symposium. Du¨sseldorf, Germany, 6–7 September 1996. IDF Bulletin No. 319/1997. Brussels, Belgium: International Dairy Federation. IDF (1998) Codex procedures and their importance – the new world for dairy products. Proceedings of the International Symposium. Chicago, IL, USA, 3–4 November 1997. IDF Bulletin No. 331/1998. Brussels, Belgium: International Dairy Federation. IDF (1999) Overcoming barriers to world trade in food and dairy products. Proceedings of the International Symposium. Frankfurt, Germany, 7–8 November. IDF Bulletin No. 349/2000. Brussels, Belgium: International Dairy Federation. Joint FAO/WHO Food Standards Programme (2007) Procedural Manual for the Codex Alimentarius Commission, 17th edn. Rome: Food and Agriculture Organization of the United Nations and World Health Organization. Joint FAO/WHO Food Standards Programme Codex Alimentarius. Rome: Food and Agriculture Organization of the United Nations and World Health Organization. Kozak J (1998) The Influence of Codex Standards on Dairy and the World Trade Organization. IDF Bulletin No. 343/1999. Brussels, Belgium: International Dairy Federation.
Standards of Identity of Milk and Milk Products C Heggum, Danish Dairy Board, Aarhus, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction When compared to other food sectors, the dairy sector has a distinct tradition of regulating production and trade through identity standards. This tradition derives primarily from the cooperative structure of the sector prevailing in the late 1800s and the beginning of the 1900s, and was introduced mainly by exporting countries in support of their trade activities and by countries with a significant domestic competition. Since the mid 1980s, food legislation in general has been subject to substantial changes. General (horizontal) regulation supersedes commodity (vertical) legislation. This change is caused mainly by changed budgetary priorities at national governments level and by the entire focus on food safety issues. The general trend is that vertical legislation decreases, and specific dairy legislation even disappears in some countries. Dairy legislation itself has changed as well. A few decades ago, dairy legislation was, in many countries, characterized by a positive approach (i.e., what is not specified is not permitted), the most significant result being a vast number of identity standards. Today, most dairy legislation has been aligned with the approach used for other food sectors, where everything considered safe and suitable is allowed in principle, and governed primarily by informative labeling. Identity standards fit into the latter approach by providing the specific conditions for referring to a regulated name without by themselves enforcing general restrictions. The dairy trade needs some degree of international regulation to ensure fair practices and to minimize barriers to trade. For the enforcement of the WTO trade agreements, the international trade further needs a sound reference to enable monitoring of whether import restrictions are justified, and if not, to provide the tool for pursuing the goal of avoiding technical barriers to trade. This article focuses mainly on the Codex standards of identity, as these have the greatest potential for widespread use.
Role of Identity Standards Identity standards serve a multifunctional role as follows: 1. As legislative reference texts Nationally, such reference texts may be needed to facilitate understanding and management of other
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regulatory means (e.g., safety limits, additive provisions, inspection practices, certification, statistics, monitoring import/export quotas) Internationally, reference texts are intended to the WTO system to solve trade disputes • enable (Codex standards); governments (and other parties concerned) in • assist the elaboration and implementation of national food legislation in an appropriate manner; and guide international trade. 2. As facilitators of trade International harmonization is a prerequisite for free movement of products, which can be achieved only through international cooperation. The result of harmonization is, as per definition, the minimization of barriers to international trade. The establishment of proper reference texts is a prerequisite for harmonization. If trade is to be facilitated, it is necessary to ensure that such reference texts are kept up-to-date with respect to technological, scientific, and practical knowledge. Otherwise, they may become obstacles to trade. 3. As promoters of fair trade practices The most important objective of an identity standard for milk products is to promote fair trade practices through specifying detailed conditions for the use of specific names reserved for well-defined milk products. International standards also assist in protecting against misleading presentations and practices, for example, a false description of the nature of the product in question. However, achieving international consensus is difficult, mainly because those involved in the process are also commercially competing on the world market. On the other hand, if no difficulties existed, there would be no commercial need for attempting harmonization! With regard to milk and milk products, the most important international text for supporting this objective is the Codex General Standard for the Use of Dairy Terms which reserves, with a few exemptions, names and terms related to dairy products for milk and milk products. Many dairy countries worldwide have established similar regulations.
•
Identity standards normally do not aim specifically at protecting public health, as this objective is typically regulated in more general legislative texts (e.g., Codes of Practices, hygiene rules, MRLs).
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Standard Setting National Standards Several countries do, despite of the general change in the approach to food regulation, retain a significant number of specific identity standards for milk products in their national legislation. This is particularly the case in countries where the dairy industry has played and still plays a significant role in the national economy and retention is generally supported by the domestic dairy industries. On the other hand, very few new identity standards for milk products are being established. Examples of dairy nations that retain a significant number of identity standards for milk products include Canada, Denmark, France, Germany, Greece, Gulf countries, Italy, Japan, MERCUSOR countries (Argentina, Brazil, Uruguay, and Paraguay), South Africa, Spain, Switzerland, and the United States. Certain countries, mainly European, have, in addition to generic identity standards, established systems for reserving certain product names as protected geographical designations. In general, only the basic and the most significant milk products are regulated today by identity standards. Typically, national legislation that includes identity standards for milk products, retain such for drinking milk, traditional fermented milks characterized by specific microorganisms, individual cheese varieties, milk powders, and butter. The cheese varieties most commonly regulated by national identity standards are Brie, Camembert, Cheddar, Cottage Cheese, Cream Cheese, Danbo, Edam, Emmental, Gouda, Mozzarella, Parmesan, Provolone, and Tilsiter. Regional Standards The Stresa Convention
The first international standard-setting body within the dairy sector was the so-called Stresa Convention, named
after the Italian city Stresa. The Stresa Convention, adopted in 1951, lays down a number of standards for individual cheeses and stipulates regulations for the use of these product names. The International Dairy Federation (IDF) played a significant role in its establishment. Originally, eight European countries ratified the Convention. Several of these have now left. For this reason, and since the standards regulated by the Convention have hardly been up-dated since their establishment, the Stresa Convention today plays an insignificant role. However, the principles contained therein have been adopted in other cheese regulations at national, regional, and international levels (Figure 1). EU standards
With the establishment of the European Common Market, a number of regional identity standards have been developed, particularly during the 1970s and 1980s. Identity standards have been established for preserved milk products (milk powder, evaporated milks, sweetened condensed milks), edible casein products, butter, including reduced fat butters, and drinking milk. The EU standards are mandatory in all EU member states. At the beginning of the 1990s, the strategy for establishing regional standards was abandoned and replaced by a system of registering protected designations of origin and certificated products of specific character. Gulf standards
The Gulf Cooperation Council (GCC), established in 1981, develops Gulf standards relating to foodstuffs, intended for adoption by its member states (Saudi Arabia, Kuwait, Bahrain, Qatar, Oman, and the United Arab Emirates). Their influence has become increasingly significant. Most dairy products are currently regulated by the GCC identity standards: raw milk (cow, goat, and
Reservation of four cheese names to be used only by the country in which the names were first developed (Annex A): Rquefort (France), Gorgonzola (Italy), Parmiggiano Romano (Italy), and Pecorino Romano (Italy). Mutual permission to use 30 cheese names on domestic and international markets, on the labels and by reference anywhere, provided adherence to the identity standards subordinated (Annex B): Cheese name: Origin of name: Danablu, Danbo, Elbo, Fynbo, Havarti, Maribo, Denmark Mycella, Samsø, and Tybo Brie, Camembert and Saint Paulin France Gruyere France and Switzerland Asiago, Caciocavallo, Fiore Sardo, Fontina, Italy Provolone Edam, Frisian, Gouda, Leyden The Netherlands Gudbrandsdalsost, Nøkkelost Norway Ädelost, Herregaardsost, Svecia Sweden Emmental, Sbrinz Switzerland Figure 1 Main elements of the Stresa Convention.
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camel), drinking milks (pasteurized, sterilized, UHT, flavored), preserved milk products (dried milk, evaporated milk, sweetened condensed milk, lactose, and caseinates), fermented milk including yogurt (with and without heat treatment after fermentation), cream, butter, milk fat products (anhydrous milk fat, butteroil, and ghee (samn)), processed cheese (including spreadable), cheese, whey cheese, and a number of individual cheese varieties, which besides all varieties standardized by Codex Alimentarius also include Feta, Domiati, Gruyere, Hallom, Kashkaval, and Ras. These standards are subsequently adopted by the GCC member states.
Milk Products in 1993. The new committee has almost completed its work after a thorough revision of all the existing standards as well as elaborating new standards for additional milk products. When the work is fully completed in 2010, approximately 34 specific identity standards for various milk products will have been described. Codex standards are intended as recommendations for adoption by member states and for use by the commercial trade. However, they also serve as international references for application in trade disputes brought to the WTO for settlement (see Policy Schemes and Trade in Dairy Products: Codex Alimentarius).
GMC standards
In 1991, the MERCUSOR (Treaty for the Organization of a Southern Common Market) was established with four countries participating (Argentina, Brazil, Uruguay, and Paraguay). To facilitate trade, harmonized food legislation is being developed by the Common Market Group (GMC). GMC standards are mandatory in all MERCUSOR member states. Identity standards for the following milk products have been established: butter, butteroil, dairy cream, dairy cream for industrial use, UHT milk, fluid milk for industrial use, powdered milk, dulche de leche, food caseinates, food casein, cheese, grated cheese, processed cheese, powdered cheese, and the individual cheese varieties Danbo, Tilsit, Mozzarella, Minas Frescal, Tybo, Cottage Cheese, Tandil, Pategras, Sandwich, and Prato. International Standards Codex Alimentarius
The elaboration of international milk product standards was initiated several years prior to the establishment of Codex Alimentarius. In 1958, on the initiative of the IDF, the FAO established the Joint Committee of Government Experts on the Code of Principles Concerning Milk and Milk Products. The establishment of this ‘Milk Committee’ showed the need for international cooperation in the area of food and triggered the establishment of Codex 4 years later. The Milk Committee was active until 1990, during which period 52 international milk product standards and several other texts related to milk products were developed. However, as the running of the Milk Committee was financed by the FAO, financial priorities resulted in difficulties that hampered the continuation of the work. The Committee was very close to being adjourned at the beginning of the 1990s. In the light of the elaboration of the new WTO trade agreements, however, a FAO/WHO Conference held in 1991 highly recommended the revision of all commodity standards developed by Codex. This was the main reason for establishing the new Codex committee for Milk and
World Customs Organization
The World Customs Organization (WCO) is an independent, inter-governmental organization, the purpose of which is to enhance the effectiveness and efficiency of customs administration on a worldwide basis. The most successful instrument developed by the WCO is the Harmonized Commodity Description and Coding System (Harmonized System). The Harmonized System (HS) is a multipurpose international product nomenclature covering about 5000 commodity groups. Each commodity group is identified by a unique six-digit code and is defined in such a way as to facilitate uniform classification. In many cases, explanatory notes provide identity descriptions of individual commodities. More than 177 countries use the system as a basis for determining customs tariffs and for the collection of international trade statistics. Other uses include the following: the basis for rules of origin; the collection of internal taxes; the basis for trade negotiations (e.g., the WTO schedule for tariff concessions), transport tariffs and statistics, and the monitoring of controlled goods (such as hazardous wastes, narcotics, and chemical weapons). The majority of dairy products are found in Chapter 4 of the Harmonized System. However, Chapter 4 does not cover lactose (Chapter 17), ice cream, and dairy spreads (Chapter 21) or albumins, including concentrates of two or more whey proteins (Chapter 35). The work of the WCO has become increasingly important as world trade in dairy products continues to grow. In particular, product definitions and classification within the Harmonized System greatly influence decisions in product development and marketing. In addition, the Harmonized System is incorporated by individual governments into domestic operating procedures for a variety of purposes. Among these are internal taxes, monitoring of controlled goods, freight tariffs, transport statistics, price monitoring, quota controls, and more. Product definitions developed by the WCO in support of the HS do not necessarily correspond with the
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definitions established in support of food legislation. The individual definitions serve different purposes and are usually developed independently from each other. Consequently, a product labeled with a name in accordance with the food regulation in force may not be classified accordingly by the HS and vice versa.
Codex Milk Product Standards Key Prerequisites for Establishing a Codex Milk Product Standard Consumer protection from the point of view of health and fraudulent practices is one of the key objectives of Codex activities. As health protection alone does not justify the establishment of a commodity standard as such, Codex commodity standards primarily aim at protecting the consumers from fraudulent practices and ensuring fair trade practices. Public health protection is covered by other horizontal and commodity-specific Codex texts concerning hygiene, additives, and contaminants. Whether a risk of fraudulent practice exists depends on the following: degree of consumer’s recognition of the product • The (or designation), expressed as the number of countries
• •
in which the product is manufactured and consumed; The needs of importing-countries to require specific labeling to ensure that adequate consumer information is provided with regard to the nature of the product; and Existing differences in national definitions of the product.
An estimate of the global production may be needed to ensure that drafting resources are not wasted on products that are insignificant in international trade. Production and trade statistics are important tools for evaluating whether an international standard will be justified. Information on the number of countries involved in the trade of the product in question is used for guiding the decision. Local trade between a smaller group of countries (e.g., within one trading block) is not a sufficient justification. It is apparent that the number of countries having established national identity standards and/or industry standards governing the use of a certain product name constitutes a potential for trade problems. Significant deviation between such standards may alone trigger a need to harmonize at international level (Figure 2). Principal Contents of Codex Milk Product Standards Codex milk product standards aim at describing the nature (identity) of the products by addressing the essential
characteristics associated with them. The areas covered by such standards are as follows: characteristics (common understanding of the • Identity meaning of a product name including an end-product
• •
description, principal method(s) of manufacture, compositional requirements, and ingredients) Food additives that are safe and technologically justified Labeling provisions that are needed in addition to general labeling rules and/or that are considered necessary for the correct application of a general labeling principle.
This approach is based on the almost completed revision of the milk product standards developed in the 1960s and 1970s. The former versions contained primarily provisions that aimed at ensuring technical product quality and product identity. Elements that are not justified as essential for the identity of the product cannot be addressed in the standards. Where found appropriate, such material can be provided as information on usual patterns of production in appendices to the standards. The content of an appendix (1) is intended to be applied by commercial trade parties (where found useful), (2) need not be implemented in national legislation, and (3) is not intended to be used by the WTO as reference material. Typical information provided in appendices indicates quality limits on nonhazardous contaminants (e.g., copper); technical quality guidelines; characteristic flavor and taste; nonessential sizes and shapes; and nonessential manufacturing practices. In addition to the principal contents, food safety and general labeling issues are addressed by the Codex milk product standards, mainly by identifying and referring to other relevant Codex texts applicable to the product (e.g., contaminants, hygiene, labeling, and methods of sampling and analysis). General Approach to Codex Milk Product Standards Scope
The Codex milk product standards apply both to retail products sold directly to the consumer and to non-retail products intended for further processing (e.g., as ingredients in other milk products and foods, or for processing into processed cheese, cutting/slicing, drying, fermentation, etc.). Most of the standards do not address addition of nondairy ingredients intended to provide specific non-dairy flavors (such as fruit preparations, meat, vegetables, spices, and sweeteners). The provisions governing such additions are located in the Codex General Standard for the Use of Dairy Terms (GSUDT). According to the GSUDT, such products are identified as ‘composite milk products’ and
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Identification of need
It is concluded that there is a need for a Codex standard for a certain dairy product. Supporting data on production and trade and justification for the work is furnished.. A proposal is submitted for consideration by the Codex Committee for Milk and Milk Products (CCMMP).
If the CCMMP agrees, the proposal is forwarded for approval as new work by the Codex Alimentarius Commission (CAC).
Steps
1, 2, 3
Consideration by the CCMMP
Endorsement of the CAC to establish a standard (step 1). The Proposed Draft Standard, typically prepared by IDF or an ad hoc working group, is circulated by Codex to member countries and international organizations for comments (step 3).
The Proposed Draft Standard and the comments submitted to it are considered at a meeting of the CCMMP. The standard may be amended by the meeting and is either progressed to step 5 or returned to step 3 for redrafting. If returned to step 3, IDF or a new working group is usually requested to redraft it in light of the comments made and the debate and conclusions that took place at the session. The new draft is circulated for comments again at step 3.
Steps
5, 6
8
Step
7
Step
The Proposed Draft Standard, as amended, is considered by the CAC (step 5). The result may be adoption or return to step 3 for reconsideration. If adopted, the Proposed Draft Standard becomes a Draft Codex Standard and it is circulated to member countries and international organizations for comments (step 6). IDF may be requested to redraft the text in light of the comments submitted at this step to provide a further consolidated text for consideration at step 7.
The (further consolidated) Draft standard is considered at a meeting of the CCMMP. The text, as amended by the meeting, is either progressed to step 8 or returned to step 6 for recirculation. If progressed to step 8, the additives provisions are submitted for endorsement by the Codex Committee for Food Additives (CCFA), and the labeling provisions are submitted for endorsement by the Codex Committee for Food Labeling. Endorsements take place at meetings of these horizontal committees.
Step
4
The CAC adopts the Draft standard, eventually with amendments as suggested by the CCFAC and/or the CCFL. It then becomes a Codex Milk Product Standard. It is published in the Codex Alimentarius and constitutes a reference text for application by the WTO.
Figure 2 Typical process of elaboration of a Codex milk product standard.
the milk product names can be used in combined designations of composite milk products, provided that the added nondairy ingredients are not intended to replace any milk constituent(s), in whole or in part. Principal method of manufacture
Milk product designations often originate from descriptive terms that refer to the way in which they are manufactured, for instance, milk powder, evaporated milk, fermented milk, and so on. As a natural consequence, the principal method of manufacturing is reflected in the identity description of many milk products. This approach is often much simpler than attempting to describe all end-product characteristics in full detail. One of the general principles in the WTO Trade Agreements is the principle of equivalence. Since
methods of manufacture applied are not static, and because identity standards should not, unless specifically justified, constitute an obstacle for technological development, most Codex standards for milk products include appropriate wording that, in addition to the principal method of manufacturing, provides for alternative technologies that achieve an equivalent outcome. Raw materials
The general approach is that all milk products derived from any milking animal species can be used as raw material for milk products. This means that milk products can be processed from milk derived from cows, goats, sheep, buffaloes, yaks, camels, reindeer, and so on. Corresponding provisions address whether the dairy species need be labeled (see Labeling of Dairy Products). However, many individual cheese varieties (but not all)
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are characterized by the origin of the milk (texture, color, flavor) wherefore restrictions on type of milk may be imposed. Further, in general, any milk constituents and milk products, including intermediate products, can be used, including those needed for reconstitution and recombination, as long as the compositional criteria and other characteristics of the products are met. There are a few exemptions from this approach (e.g., milk powders). Composition
The minimum and/or maximum requirements for the composition of end products constitute a core part of any identity standards. For all milk product standards established by Codex, such criteria comprise milk fat, and additional criteria as necessary according to the nature and characteristics of the product in question (see Figure 3). The compositional sections of the standards typically specify the reference composition and, in addition, the limits and conditions for modifying the composition of the reference product, by specifying, for example, the range of composition permitted. Therefore, some compositional criteria are absolute (minima or maxima). The Codex General Standard for the Use of Dairy Terms states that products that have been modified in composition beyond the composition of the reference product identified in the relevant standard are only allowed if the following principles are adhered to:
•
That a qualifier that clearly describes the compositional modification made is placed in association with the name of the product
Milk product
Milk fat
Milk protein
Moisture or dry matter
Creams Fermented milks
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Butter Dairy fat spreads Butteroil Evaporated milks Sweetened condensed milks Milk and cream powders Cheese Individual cheese varieties Caseins Caseinates Whey powders
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冑
冑
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the modification is achieved only by the addition • That and/or withdrawal of milk constituents such modification does not alter the basic identity • That of the product and is within the limitations identified in the Codex identity standard concerned. See Figure 4 for examples of modifications covered. In some cases, compositional modification is not desirable, for instance, protein contents below the minima specified and fat reductions below the absolute minima, where such are specified (Figure 4). Food additives
A positive list of justified and permitted groups of additives and/or individual additives is provided. Technological justification for each functional group of additives and for each additive, with a numerical ADI-value listed, is a prerequisite for acceptance by Codex. The IDF provides the information necessary for this purpose.
Labeling
The labeling section makes cross-reference to generally applicable labeling standards and lays down additional labeling provisions as well as practical guidance on the application of general labeling principles (see Labeling of Dairy Products).
Supporting methods of sampling and analysis
Any criteria specified in a Codex standard are to be supported by appropriate analytical methods for verifying compliance. Recognized methods are published in the Codex Alimentarius.
Solidsnot-fat
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Acidity, microorganisms flavoring ingredients 冑
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Ratio of whey protein to casein Variety specific Casein, free acid pH, casein pH
Figure 3 Components regulated by compositional requirements in certain Codex milk product standards.
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Fat-modified products such as high fat, reduced fat (light), low fat, or skimmed/nonfat, Purified products such as demineralized whey powder, lactose-free milk powder, and cholesterol-free butter ; Fortified products such as vitaminized milk powder and calcium enriched yogurt ; Compositionally altered products such as fractionated butter. Figure 4 Examples of compositionally modified milk products.
The Individual Codex Milk Product Standards Drinking milk
Codex has not established, nor does it intend to establish, an identity standard for drinking milk. Although manufactured and marketed in most countries worldwide, drinking milk is primarily sold domestically. Hence, due to significant local differences in consumer perception, attempts to harmonize this area would probably fail. However, some general principles governing drinking milk have been provided in the Codex GSUDT. These principles are targeted national regulations in this area. The GSUDT states that, in general, drinking milk that is modified in composition by the addition and/or withdrawal of milk constituents may be identified with a name using the term ‘milk’, provided that a clear description of the modification to which the milk has been subjected is given in close proximity to the name. However, fat and protein adjustment may be permitted without such description only if milk is sold where such adjustment is permitted in • the the country of retail sale; minimum and maximum limits of fat and/or pro• the tein content (as the case may be) of the adjusted milk
•
are specified in the legislation of the country of retail sale (the protein content shall be within the limits of natural variation within that country); and the adjustment methods permitted by the legislation of the country of retail sale are used. Such methods shall include only the addition and/or withdrawal of milk constituents without altering the whey protein-tocasein ratio (as achieved by traditional ultrafiltration technology).
Creams
The standard for cream addresses ‘cream’ (bulk) and ‘prepared creams’ intended for direct consumption. The standards include a definition of cream and descriptions of recombined and reconstituted cream, respectively. A number of specific consumer products are described, including prepackaged liquid cream, whipping cream, whipped cream, cream packed under pressure, thickened cream, and fermented cream. The standard characterizes creams as milk products comparatively rich in fat (absolute minimum of 10% milk fat), in the form of an emulsion of fat in skimmed milk, obtained by physical separation from milk or by recombination/reconstitution of specified raw materials.
Fermented milks
The standard characterizes fermented milks as milk products obtained by fermentation of milk by the action of specific microorganisms and resulting in a reduction of pH with or without achieving coagulation. These specific microorganisms shall be viable, active, and abundant in the product. In addition, the standard includes specific categories of fermented milks that are additionally characterized by specific microorganism(s) used for the fermentation, which organisms during product shelf life are present in numbers exceeding 107 cfu g 1 (plain part of the end product). Specific categories will include yogurt, kefir, acidophilus milk, and kumys. The products may be heat treated after fermentation, in which case the name shall be ‘heat treated fermented milk’. Reference to the specific names defined by minimum bacterial counts is obviously not relevant in these products. The standard aims also at including fermented milks modified in composition by concentration of the protein to minimum 5.6% – identified as ‘concentrated fermented milks’. This standard (being the only one at that) includes flavored products (i.e., plain fermented milk to which other foods/ingredients, such as fruit, sugar/sweetener, or cereals, have been added to obtain a characteristic nondairy flavor).
Butter and milk fat products
Three milk product standards for yellow milk fats exist: one for butter, one for dairy fat spreads, and a third for milk fat products (covering the names ‘milk fat’, ‘anhydrous milk fat’, ‘butteroil’, ‘anhydrous butteroil’, and ‘ghee’). Butter is, according to the Codex standard, characterized by being a fatty milk product, principally in the form of an emulsion of the water-in-oil type, with minimum 80% milk fat, maximum 16% moisture, and maximum 2% milk solids-not-fat. These compositional criteria are specified as absolute. Unlike many national standards, no upper milk fat limit is specified. Instead, it is stated that fat contents above 95% trigger the use of a qualifier in association with the term ‘butter’; such a qualifier can be, for instance, ‘cooking’. Dairy fat spreads are conceptionally butter with lowered fat contents above 10% and where milk fat constitutes at least two-thirds of the dry matter.
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The milk fat products covered are characterized as fatty milk products obtained by means of processes that result in almost total removal of water and nonfat solids. For ghee, restrictions on milk ingredients as raw material are specified, and the product is further characterized by having a special flavor and physical structure, without further details being provided, however. Preserved milk products
Standards for three categories of traditional preserved milk products have been established: for evaporated milks, for sweetened condensed milks, and for milk powders and cream powder. In common, these products are characterized by being obtained by the partial removal (to various degrees) of water from milk (or cream) by the use of heat or other processes leading to the same composition and characteristics. Milk-based raw materials are restricted. Sweetened condensed milk is further characterized by being preserved with the addition of sugar (sucrose alone or sucrose in combination with other sugars). The adjustment of fat and/or protein is specifically addressed in all three standards, and can be done provided that it is achieved only by addition/withdrawal of milk permeate, milk retentate, and lactose, and provided that the whey protein-to-casein ratio of the milk subjected to adjustment is not altered. Common to all three standards is also that the whole range of fat content is covered by a classification system and that the minimum protein content should be 34% of milk solids-not-fat. Corresponding criteria for milk solids-not-fat content are established for the liquid products, whereas a maximum moisture content of 5% is specified for the powders. These compositional criteria are specified as absolute. Cheese
A general standard for Cheese supplemented by subordinated group standards for cheese in brine and unripened cheeses, respectively, has been established. Cheese is primarily characterized according to the way it is manufactured. Cheese is the ripened or unripened, soft or firm, hard or extra hard, product obtained by (a) coagulating wholly or partly the protein of milk, skimmed milk, partly skimmed milk, cream, whey cream or buttermilk, or any combination of these materials, through the action of rennet or other suitable coagulating agents, and by partially draining the whey resulting from such coagulation, while respecting the principle that cheesemaking results in a concentration of milk protein (in particular, the casein portion), and that consequently, the protein content of the cheese will be distinctly higher than
the protein level of the blend of the above milk materials from which the cheese was made; and/or (b) processing techniques involving coagulation of the protein of milk and/or products obtained from milk which give an end product with similar physical, chemical, and organoleptic characteristics as the product defined under (a). Part (a) reflects the traditional manufacturing method which is still the dominating process used worldwide, and part (b) allows for other processing techniques such as recombination, reconstitution, protein standardization, and membrane filtration in general are covered by subparagraphs. Products complying either to part (a) or to part (b) are equivalent, that is, they are not to be distinguished in any way. Today, the cheese manufacturing process is a combination of (a) and (b). The standard does not specify any compositional criterion but that (1) the protein content is distinctly higher than that of the milk used and that (2) the whey protein-to-casein ratio does not exceed that of the milk used. If the whey protein-to-casein ratio is higher, then the product is to be categorized as ‘whey cheese’. Cheese is generally classified according to principal ripening and firmness as follows: Classification according to principal ripening cheese, which is cheese not ready for • Ripened consumption shortly after manufacture but must be
• • •
held for such time, at such temperature, and under such other conditions as will result in the necessary biochemical and physical changes characterizing the cheese in question; Mold ripened cheese, which is ripened cheese in which the ripening has been accomplished primarily by the development of characteristic mold growth throughout the interior and/or on the surface of the cheese; Cheese in Brine, which is ripened cheese that has been ripened and preserved in brine until delivered to, or prepacked for, the consumer; and Unripened cheese, which is cheese ready for consumption shortly after manufacture.
Classification according to firmness cheese, which is cheese with a content of moisture • Soft on fat-free basis above 67%; (or semihard) cheese, which is cheese with a • Firm content of moisture on fat-free basis between 54 and 69%;
cheese, which is cheese with a content of moist• Hard ure on fat-free basis between 49 and 56%; and hard cheese, which is cheese with a content of • Extra moisture on fat-free basis below 51%. The general cheese standard applies to all cheeses, including individual varieties of cheese.
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Individual cheese varieties
Subordinate to the general cheese standard, 17 standards for individual cheese varieties exist: Cheddar, Danbo, Edam, Gouda, Havarti, Samsø, Emmental, Tilsiter, Saint-Paulin, Provolone, Cottage Cheese, Coulommiers, Cream Cheese, Camembert, Brie, Extra Hard Grating, and Mozzarella. Raw materials for the manufacture of these individual cheese varieties are restricted to milk and milk products derived from cows and buffalos. However, in the case of Extra Hard Grating, the dairy species permitted are goats, ewes, and cows (but not buffaloes), and in the case of Cream Cheese no restrictions in this regard apply. Further, each individual variety will, in addition to the general characteristics applicable to cheeses, be characterized by end-product description including classification according to principal ripening and firmness, as well as color, texture, structure, and ripening characteristics, where appropriate. In certain cases, characteristic elements of the manufacturing methods and dimensions are specified as well. Compositional specifications are unique for each variety and include limitations for compositional modification of the fat content. Specific milk constituents
Two milk product standards regulate whey powders and edible casein products, respectively. A group standard for sugars includes lactose. Whey powders are characterized as being milk products obtained by drying whey or acid whey, where whey means the fluid milk product obtained during the manufacture of cheese, casein, or similar products by separation from the curd after coagulation of milk and/or of products obtained from milk. Reference to ‘whey’ without qualification indicates that coagulation is obtained through the action of rennet-type enzymes, while using the term ‘acid whey’ means that the coagulation is obtained by acidification. Whey powders are further characterized by a reference lactose content, minimum milk protein content, and maximum content of moisture and ash. For whey powder and acid whey powder, the values of these criteria differ slightly. The two powders are principally distinguished by pH. In addition, the standard includes specific reference to demineralization and neutralization as being acceptable compositional modifications. Edible casein products are characterized as being milk products obtained by separating, washing, and drying the coagulum of skimmed milk and/or of other
products obtained from milk. The type of coagulation (acid precipitation or enzymatic coagulation) determines whether the product is classified as acid casein or rennet casein. Differentiation is further supported by specification of ash content (acid casein max. 2.5% and rennet casein min. 7.5% ash; both figures include P2O5). No additives are permitted (enzymes are categorized in milk product standards as ‘ingredients’). Edible caseinate is characterized as being the milk product obtained by the action of edible casein or edible casein curd with neutralizing agents, followed by drying. Caseinates may be manufactured by the use of acidity regulators, including specific neutralizing agents, emulsifiers, bulking agents, and anticaking agents. All casein products are further characterized by criteria for protein content, casein in total milk protein, moisture content, and milk fat content. All compositional criteria specified are absolute. Lactose is characterized as a natural constituent of milk normally obtained from whey with an anhydrous lactose content of not less than 99.0% on a dry basis. Lactose may be anhydrous or may contain one molecule of water of crystallization, or may be a mixture of both forms. No additives are permitted. See also: Labeling of Dairy Products. Policy Schemes and Trade in Dairy Products: Codex Alimentarius.
Further Reading FAO/WHO (2006) Understanding the Codex Alimentarius, 3rd edn. Rome: Food and Agriculture Organization of the United Nations; World Health Organization. IDF (1996) Codex standards in the context of world trade agreements. Proceedings of the IDF Seminar held in Brussels. November 1995. IDF Bulletin No. 310. Brussels: International Dairy Federation. IDF (1997) The influence of Codex standards on international trade in dairy products. Abstracts of the International Symposium. Du¨sseldorf, Germany, 6–7 September 1996. IDF Bulletin No. 319/ 1997. Brussels: International Dairy Federation. IDF (1998) Codex procedures and their importance – the new world for dairy products. Proceedings of the International Symposium. Chicago, IL, USA, 3–4 November 1997. IDF Bulletin No. 331/1998. Brussels: International Dairy Federation. IDF (1999) Overcoming barriers to world trade in food and dairy products. Proceedings of the International Symposium. Frankfurt, Germany, 7–8 November. IDF Bulletin No. 349/2000 Brussels: International Dairy Federation. Joint FAO/WHO Food Standards Programme (2007) Procedural Manual for the Codex Alimentarius Commission, 17th edn. Rome: Food and Agriculture Organization of the United Nations; World Health Organization. Joint FAO/WHO Food Standards Programme (frequently updated) Codex Alimentarius. Rome: Food and Agriculture Organization of the United Nations; World Health Organization.
Trade in Milk and Dairy Products, International Standards: Harmonized Systems K Svendsen, Danish Agriculture and Food Council, Arhus, Denmark ª 2011 Elsevier Ltd. All rights reserved.
The Historical Basis
Nomenclature and Classification
In the aftermath of World War II, several organizations were established to secure, facilitate, and harmonize trade. The General Agreement on Tariffs and Trade (GATT), now the World Trade Organization, is the best known, but other areas have developed their own rules and objectives. In September 1947, the 13 governments represented on the Committee for European Economic Co-operation agreed to set up a study group on the establishment of one or more European Customs Unions based on the principles of GATT. In 1948, the study group, established in Brussels, set up two committees, an Economic Committee and a Customs Committee. The Economic Committee later became the Organization for Economic Cooperation and Development, and the Customs Committee became the Customs Co-operation Council (CCC), created on 15 December 1950, when the convention was signed in Brussels. It took 2 more years before the first session was held on 26 January 1953, a date that 30 years later became known as International Customs Day.
With the growing world trade after World War II, the need for an internationally recognized common nomenclature became more and more obvious. This was discussed in CCC, and the Brussels Convention of 15 December 1950, on Nomenclature for the Classification of Goods in Customs Tariffs laid down the basics. It came into force on 11 September 1959, and was known as the Brussels Tariff Nomenclature (BTN). In 1974, it was renamed Customs Co-operation Council Nomenclature (CCCN). The CCCN was divided into 1241 headings, 96 chapters, and 21 sections, each heading thus being identified by two groups of two digits, one for the chapter and the second for the position in the chapter. The CCCN served only one objective, tariffs, and was purely numerical. At the same time, there were other classifications serving other purposes, the best known of which is the Standard International Trade Classification (SITC) for statistical purposes. During the 1950s and 1960s, great effort was made to correlate these two nomenclatures, but it was still evident that there was a great need for international harmonization, especially concerning commodity description and coding.
Customs Co-Operation Council or the World Customs Organization Harmonized System Committee The aim of this organization is to study all questions relating to customs cooperation and the technical and the economic aspects of customs systems to attain the highest possible degree of harmony and uniformity. This work is done through conventions like the Kyoto Convention on Simplification and Harmonization of Customs Procedures. On the operational level, the work is carried out in technical committees, of which the Harmonized System Committee is central for the topic of this article. In October 1994, the CCC adopted the working name World Customs Organization (WCO), thus mirroring the growing international significance of the organization and the development in world trade.
In 1970, a study group was set up to prepare a Harmonized Commodity Description and Coding system that would handle classification in relation to tariffs, statistics, transport, and production, thus being a multipurpose international products nomenclature. The result of this work was the creation in 1973 of the Harmonized System Committee, which would prepare the Harmonized System (HS) on the background of the CCCN. This resulted in the Harmonized System Convention that entered into force on 1 January 1988. Since that day, an ever-increasing number of countries adhere to this system. According to the WCO, by August 2000 more than 177 countries were using the HS, and 98 countries were contracting parties.
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According to Article 3 of the convention, contracting parties are obliged to ensure that their import customs tariffs and statistical nomenclature for imports and exports are in conformity with the six-digit HS. They are also obliged to make public their import and export statistics at or beyond that level (if at all). The Harmonized System Committee is responsible for the development of the HS and takes care of dispute settlement whenever two contracting parties cannot agree on the nomenclature code for a specific product, a situation that can have substantial economic consequences for the involved parties. The committee meets twice a year to discuss these problems and reach an agreement, eventually by voting on the subject. If one of the contracting parties does not agree with the decision taken by the committee, the party can transfer it to the council. This means that the main tasks of the Harmonized System Committee are to propose amendments to the convention for updating the HS every 4–6 years and to prepare explanatory notes and classification opinions and other advice as guides to the interpretation of the HS and recommendations to secure uniformity in the interpretation and application of the system.
adding another pair of two digits to a total of six digits. In this way, the system lists more than 5000 product lines. The HS as mentioned is dynamic. The latest amendments were decided at the 43rd Session of the Harmonized System Committee in March 2009. They were adopted by the WCO Council at its annual session in June 2009, and the recommendation is now being promulgated under the provisions of Article 16 of the Harmonized System Convention. This implies that HS contracting parties have 6 months during which they can object to a recommended amendment. The amendments will enter into force on 1 January 2012. The Council Recommendation of 26 June 2009, with the HS2012 amendments is the fifth to amend the HS, though it is only the fourth recommendation to make major amendments to the HS since the WCO Council approved the Harmonized System Convention. The main reasons for the latest set of 221 amendments are new environmental and social issues and the use of the HS as the standard for classifying and coding goods of specific importance to food security and early warning data falling within the ambit of the Food Security Information for Action Program of the Food and Agriculture Organization (FAO) of the United Nations.
Harmonized System The HS itself is thus a six-digit products classification system used by most countries in the world to collect tariffs and produce statistics. Some countries still have alternative systems for some uses, like the SIC codes for domestic production in the United States, but more and more the HS is being used for all purposes and by international organizations like the Organisation for Economic Co-operation and Development (OECD) and the World Trade Organization. According to the HS, all goods can be classified in 21 sections but, for more precise classification, sections are divided into chapters. The HS consists of 97 chapters, of which Chapter 77 is reserved for future use. Furthermore, Chapters 98 and 99 are reserved for special uses by adhering countries. To describe a chapter, two digits are always used (e.g., 04 for the chapter containing dairy products and 35 for the chapter containing casein, albumins, and others). The subdivision of chapters is done either by material (e.g., 02 – meat, 03 – fish) or by degree of manufacture or processing (e.g., 01 – live animals, 02 – meat and edible meat offals). Titles in chapters are only guidelines; therefore twodigit chapters are not sufficient. Thus, to clarify and underline the differences between products in the same chapter, most of the chapters are divided into headings (four digits) and even subheadings (six digits), each level
Dairy Products in the Harmonized System Let us take a closer look at the way dairy products are classified. This happens in the first section of the HS, Section I – Live Animal and Animal Products. This section is divided into five chapters: 01. 02. 03. 04.
Live animals Meat and edible meat offal Fish, crustaceans, and other aquatic invertebrates Dairy produce, birds’ eggs, natural honey, edible products of animal origin, not elsewhere specified or included 05. Products of animal origin, not elsewhere specified or included This is followed by the section on vegetable products. In itself, the definition of Chapter 04 tells us that we have to be more specific to find the right code for a product. We therefore have to look at the headings: 04.
Dairy produce, birds’ eggs, natural honey, edible products of animal origin, not elsewhere specified or included 04.01. Milk and cream, not concentrated nor containing added sugar or other sweetening matter 04.02. Milk and cream, concentrated or containing added sugar or other sweetening matter
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04.03. Buttermilk, curdled milk and cream, yogurt, kefir and other fermented or acidified milk and cream, whether or not concentrated or containing added sugar or other sweetening matter or flavored or containing added fruit, nuts, or cocoa 04.04. Whey, whether or not concentrated or containing added sugar or other sweetening matter; products consisting of natural milk constituents, whether or not containing added sugar or other sweetening matter, not elsewhere specified or included 04.05. Butter and other fats and oils derived from milk; dairy spreads 04.06. Cheese and curd 04.07. Birds’ eggs in shell, fresh, preserved, or cooked 04.08. Birds’ eggs, not in shell, and egg yolks, fresh dried, cooked by steaming or by boiling in water, molded, frozen, or otherwise preserved, whether or not containing added sugar or other sweetening matter 04.09. Natural honey 04.10. Edible products of animal origin, not elsewhere specified or included This did bring us one step further, but it did not solve all our problems, as it is evident that, for example, the fat content of different milk powders would qualify for different tariff rates. We therefore have to be even more specific and add a level of subheadings before we can define the right tariff nomenclature code within the HS. 04.
Dairy produce, birds’ eggs, natural honey, edible products of animal origin, not elsewhere specified or included 04.01. Milk and cream, not concentrated nor containing added sugar or other sweetening matter 04.01.10 – Of a fat content, by weight, not exceeding 1% 04.01.20 – Of a fat content, by weight, exceeding 1%, but not exceeding 6% 04.01.30 – Of a fat content, by weight, exceeding 6%. As per 1 January 2012, this last subheading will be replaced by the following: 04.01.40 – Of a fat content, by weight, exceeding 6% but not exceeding 10% 04.01.50 – Of a fat content, by weight, exceeding 10% 04.02. Milk and cream, concentrated or containing added sugar or other sweetening matter 04.02.10 – In powder, granules or other solid forms, of a fat content, by weight, not exceeding 1.5% – In powder, granules or other solid forms, of a fat content, by weight, exceeding 1.5% 04.02.21 – – Not containing added sugar or other sweetening matter 04.02.29 – – Other – Other
04.02.91 – – Not containing added sugar or other sweetening matter 04.02.99 – – Other 04.03. Buttermilk, curdled milk and cream, yogurt, kefir and other fermented or acidified milk and cream, whether or not concentrated or containing added sugar or other sweetening matter or flavored or containing added fruit, nuts, or cocoa 04.03.10 – Yogurt 04.03.90 – Other 04.04. Whey, whether or not concentrated or containing added sugar or other sweetening matter; products consisting of natural milk constituents, whether or not containing added sugar or other sweetening matter, not elsewhere specified or included 04.04.10 – Whey and modified whey, whether or not containing added sugar or other sweetening matter 04.04.90 – Other 04.05. Butter and other fats and oils derived from milk; dairy spreads 04.05.10 – Butter 04.05.20 – Dairy spreads 04.05.90 – Other 04.06. Cheese and curd 04.06.10 – Fresh cheese, including whey cheese, and curd 04.06.20 – Grated or powdered cheese, of all kinds 04.06.30 – Processed cheese, not grated or powdered 04.06.40 – Blue-veined cheese 04.06.90 – Other cheese As exports of dairy products are done by a very limited number of important players, most of the countries using the HS for tariff purposes are importing countries satisfied with this level of specification, as tariff rates in general are rather uniform between these large groups of products. Some countries importing, exporting, and producing a large variety of dairy products do, however, use their right to supplement the six-digit HS codes with their own further subcodes. One example is the US subdivision of Chapter 04.06.20, grated and powdered cheese, into 38 10-digit subheadings according to cheese types, milk used, and tariff quotas.
Classification Principles To classify a given dairy product under the correct HS nomenclature position, one must both consider some general principles and make reference to the explanatory notes given by the Harmonized System Committee. Formally, the descriptions in sections, chapters, and headings cannot be used to classify a product. One must go to the specific subheading texts.
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As the HS is not very specific, this will solve most of the problems. However, when mixing products from different chapters, this may result in a totally different code under a third chapter. If, for example, butterfat is mixed with vegetable oil to make a mixed dairy spread, it will be classified in Chapter 21. This classification is independent of the production process. If vegetable fat is added to a dairy product, according to the explanatory notes it cannot be classified under Chapter 04. In principle, there are then two possible alternatives, Chapter 19 and Chapter 21. A product that needs to be distinguished from a normal dairy product falling under Subheadings 04.01–04.04 will fall under Chapter 19 according to the explanatory notes. This, however, is not the case for dairy spreads or cheeses where the milk fat part has been totally or partly replaced by vegetable fat. In this case, the final products will need to be distinguished from products falling under Subheadings 04.05 and 04.06 of the dairy chapter. Such products according to the explanatory notes must be classified under Chapter 21. In this case, more specific descriptions should come before more general descriptions. This, however, does not mean that one cannot add anything from outside the chapter. If butter or cheese is mixed with small quantities of spices like garlic or cumin, it retains the character of butter or cheese and shall be classified as such. These questions are very delicate as they could be used in an attempt to circumvent high tariff rates or tariff quotas for some products by adding rather neutral or very small quantities of substances that would place the final product in a different chapter with no tariff or unrestricted access. Therefore, this is an important part of the explanatory notes defined by the Harmonized System Committee. Mixing products from within the same chapter is a different matter. If Blue cheese were mixed with processed cheese, the point of departure would be a general rule giving the nomenclature code of the substance with the highest position, in this case, the position of the processed cheese. If the two substances are identifiable, the principle would be to choose the position that makes up more than half of the quantity. However, if one of the substances has a very specific character, like a dominating taste, one should consider using the code for this substance even if it represents less than half of the quantity. The principle of the highest code also applies within a chapter; this means that if a product fits into a subheading, it cannot be placed under a subheading that comes later under the same heading. If, for example, fresh cheeses like Mozzarella, be it the Italian type or the American variety, are grated, the resulting product remains under Subheading 04.06.10 as a fresh cheese and does not fall under Subheading 04.06.20 as a grated cheese.
This, however, does not mean that a fresh cheese cannot be processed with melting salt and classified as a processed cheese under Subheading 04.06.30, as this production process substantially alters the cheese used as raw material, so that this can no longer be identified as such.
Classification Examples With these principles in mind, let us take a closer look at some dairy products and their classification. The author must stress that this relies on his personal opinions and experience and does in no way commit the WCO or the Harmonized System Committee. The official opinions of these bodies are to be found in the relevant texts issued by the WCO. In view of the developments in modern technology, the WCO does also have a website on the Internet (www.wcoomd.org). On this site, HS classification decisions can be found. The decisions will be published as soon as they are approved by the council under the provisions of Article 8.2 of the Harmonized System Convention. This will be about 2 months after the meetings of the Harmonized System Committee at which the decision is taken. The details published will include a complete description of goods, six-digit HS classification, and the legal basis for the classification decision. On the website the user will also find useful information on contracting parties, HS amendments, and amendments to the explanatory notes and a compendium of classification opinions. Heading 04.01 Under Heading 04.01 we find normal fresh drinking milk and cream, with no added sugar. However, we also find Ultra High Temperature (UHT) processed milk and sterilized cream, as these products are in no way concentrated or condensed, and thus cannot fall under Heading 04.02. If any flavor (e.g., chocolate) is added, this milkbased drink no longer falls under Heading 04.01 but under Heading 22.02. Heading 04.02 Take some of the fresh milk or heat-treated products falling under Heading 04.01 and add some sugar, and you have a 04.02.99 product. However, most of the products under Heading 04.02 are either milk powders or condensed milk, which in relation to the HS does not represent big problems. One should, however, bear in mind that lactose in a milk powder is not a sweetening agent. If lactose is added to a milk powder, it will, however, change position to Heading 04.04.90 (see below under Heading 04.04).
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Heading 04.03 All fermented milk products fall under this heading, be it in liquid or solid form. This means that both buttermilk and buttermilk powder will fall under Subheading 04.03.90 in the HS. Heading 04.04 All whey products, except whey butter, will fall under Heading 04.04.10 – as long as the total protein content by weight calculated on the dry matter does not exceed 80%. If it does exceed 80%, it falls under Heading 35.02, which is where you will have to classify whey protein concentrates. In modern dairy production, a lot of products no longer contain the milk constituents in their natural composition. Lactose, whey, permeates, and other constituents are added or deducted. It is even permitted to add small quantities of non-dairy ingredients. These products fall under Heading 04.04.90. This does not mean that all milk powders fall under this heading if their composition is changed, this happens only if they no longer respect the normal natural composition. This problem will have less impact in the future because of the Codex Alimentarius Commission decision to allow protein standardization to a minimum of 34% in milk powders, as this will set a norm for the natural composition and avoid inferior products to be sold as 04.02 products. Heading 04.05 Under this general heading 04.05.10 we find butter, also produced from whey or if recombined. Dairy spreads under 04.05.20 must not contain other fats than butterfat. These products would fall under Heading 21.06 if the butter is mixed with or replaced by vegetable fat. We also find butter oil in this chapter under Heading 04.05.90. Heading 04.06 Here we find all kinds of cheese. As the HS is not very specific, the classification does not represent big problems. We have seen above that all fresh cheeses, also frozen or vacuum-packed Mozzarella, grated or not, will always fall under the Subheading 04.06.10. Subheading 04.06.20 is meant mainly for cheese powder and Subheading 04.06.30 for processed cheese. Here, as was the problem with protein standardization before the Codex decision, the problem is not one of classification but of definition. Another point worth mentioning is the fact that all Blue cheeses fall under Subheading 04.06.40, not only the tasty types like Roquefort and Danish Blue Cheese, but also very mild types and types with mixtures of blue
and white mold. The decisive point is the presence of blue mold. Combined Nomenclature According to Article 3 of the Harmonized System Convention, any contracting party is allowed to establish in its customs tariffs or its statistical nomenclatures subdivisions classifying goods beyond the six-digit level of the HS, provided no changes are made to the HS level. In the European Union, the introduction of the Harmonized System on 1 January 1988, was taken as an opportunity to modernize the European Union nomenclature system. Until that point, customers used the Common Customs Tariff while the statistical instrument was the NIMEXE statistical nomenclature. As per 1 January 1988, the Combined Nomenclature (CN) replaced these two nomenclatures. The CN is, as it should be, based on the HS, but to form the CN one group of two more digits is added to create further subheadings covering some 10 800 eightdigit product groups compared with the approximately 5000 product groups of the HS. For certain import arrangements, the European Union supplements the CN code with a further 2-digit code giving the 10-digit European Union integrated tariff with 14,000 positions.
Dairy Products As shown above, Chapter 04 of the HS contains in total 6 four-digit headings and 20 six-digit subheadings covering dairy products. These are also found in the CN, but at the eight-digit subheading level we now find 153 dairy positions (2009). Within Headings 04.01 and 04.02, the subdivisions mainly take care of packet sizes. In Heading 04.03, the subdivision is made by fat content or sweetening of the product. In Heading 04.04, both fat and protein content and sweetening account for the subdivision. In Heading 04.05, products are at the CN level sorted out by some quality parameters: natural butter, recombined butter, or whey butter, and for the dairy spreads also the fat content. Finally, in Heading 04.06 for cheeses, the subdivision takes care of all the European Union specific varieties. Classifying a product according to the CN is thus more complicated than according to the HS but follows broadly the same principles as mentioned above. Only in this case, the explanatory notes of the HS supplemented with the same notes from the European Union competent authorities on the CN become even more important. Going through all these subheadings is beyond the scope of this article; one example, however, could be shown. As mentioned earlier, the United States is subdividing for import tariff purposes the HS heading 04.06.20,
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grated or powdered cheese of all kinds, into 38 ten-digit subheadings. In the CN, the European Union is only subdividing this heading into 2 eight-digit subheadings: 04.06.20.10 Glarus herb cheese (known as Schabziger), made from skimmed milk and mixed with finely ground herbs 04.06.20.90 Other
be said of an importer’s interest to have the right CN code on imports. It is therefore possible, according to regulation 450/2008 Article 20, to obtain a binding tariff information (BTI) or a binding origin information (BOI) from the customs authorities. With this information, an individual can be sure to use the right classification of his goods, thus knowing his rights or obligations.
Conclusion Refund Nomenclature At the European Union level, one further addition has been made to the CN to make up the Refund Nomenclature (RN). The RN is composed of the eight digits of the CN plus a four-digit extension, thus in total 12 digits. The purpose of the RN is to differentiate the export subsidy according to the real content of milk or milk substances in the final product. During recent years, substantial changes have been made to the RN to exclude positions with no products traded or no subsidy granted. If such a product with no subsidy is exported (e.g., Roquefort cheese), it shall be classified under the relevant CN heading, in this case 04.06.40.10. If we turn once more to the example of the cheese powder chapter, in the RN we find the following subdivision: Ex 04.06.20
–
Ex 04.06.20.90 – – 04.06.20.90.9100 – – –
04.06.20.90.9913 04.06.20.90.9915 04.06.20.90.9917 04.06.20.90.9919 04.06.20.90.9990
Grated or powdered cheese, of all kinds Other Cheeses produced from whey
––– Other – – – – Of a fat content, by weight, exceeding 20%, of a lactose content, by weight, less than 5%, and of a dry matter content, by weight: – – – – – Of 60% or more, but less than 80% – – – – – Of 80% or more, but less than 85% – – – – – Of 85% or more, but less than 95% – – – – – Of 95% or more – – – – Other
The logic here shows us that while the Schabziger cheese must be mentioned in the CN for import purposes – as it is produced in Switzerland – it is not needed in the RN as refunds are granted only on products of European Union origin. Knowing the right position of a product in the RN is of very substantial economic importance to the exporter, as this decides his export subsidy, the refund. The same can
The implementation in international trade of the HS has been of great help to customs officials as well as trading companies all over the world. Problems arising from different interpretations are discussed in a common forum, thus giving more stringent replies. For trading partners, this has led to a higher degree of knowledge of the economic conditions that apply to a specific trade action. The result of this is a general increase in world trade and thus, according to normal economic reasoning, in general welfare worldwide. See also: Policy Schemes and Trade in Dairy Products: Codex Alimentarius; Trade in Milk and Dairy Products, International Standards: World Trade Organization; World Trade Organization and Other Factors Shaping the Dairy Industry in the Future.
Relevant Website On the WCO homepage (www.wcoomd.org), the relevant conventions can be read: *
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Convention establishing a Customs Co-operation Council – signed in Brussels on 15 December, 1950; entered into force on 4 November 1952. Fifteen pages. Convention on the Harmonized Commodity Description and Coding System – entered into force 1 January 1988. Including list of countries, territories, or customs or economic unions applying the HS. 13 pages. International Convention on the Simplification and Harmonization of Customs Procedures (Kyoto Convention) – entered into force 25 September 1974; revised version June 1999. 17 pages.
On the European Union homepage (http://ec.europa.eu/), the relevant regulations can be read: *
*
European Union Combined Nomenclature as expressed in the Annex I to Council Regulation (EEC) 2658/87 last amended by Commission Regulation (EC) No. 948/ 2009 of 30 September 2009, Official Journal L 287, 31/ 10/2009, 897 pages. European Unions Refund Nomenclature as expresseds in Commission Regulation (EC) No. 1298/2009 of 18 December 2009, replacing the Annex to Regulation
Policy Schemes and Trade in Dairy Products | Harmonized Systems 337
*
(EEC) No. 3846/87 establishing an agricultural product nomenclature for export refunds, Official Journal L 343, 31/12/2009, 40 pages. Council Regulation (EEC) No. 450/2008 of 22 April 2008, laying down the Community Customs Code
(Modernized Customs Code), Official Journal L 145, 04/06/2008, 64 pages. http://ec.europa.eu/taxation_customs/customs/procedural_aspects/general/community_code/ index_en.htm
Trade in Milk and Dairy Products, International Standards: World Trade Organization A M Arve, Danish Dairy Board, Aarhus, Denmark ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2752–2758, ª 2002, Elsevier Ltd.
Introduction The World Trade Organization (WTO) is the successor to the former General Agreement on Tariffs and Trade (GATT). The GATT organization was formed in 1948 after World War II as one of three legs in the international economic system; the other legs are the International Monetary Fund (IMF) and the World Bank. The GATT agreement was signed by 23 countries in 1947. In 1995, 123 countries in the multilateral trading system transformed the former GATT into the WTO. Membership by January 2002 is 144. A number of countries are negotiating for membership, amongst them Russia, the only major country of the international economy that is not already a member. China became a member in 2001. Until 1995 the trading system was organized as an agreement, but with the WTO entering into force, the system now consists of a fully fledged international organization with rights and obligations attached to its members. The WTO has its head office in Geneva, Switzerland. The director-general is the former New Zealand minister Mike Moore who took office in 1999. The core functions of the WTO are to ensure a nondiscriminating, smooth, predictable, and free trade between member countries. At the heart of the organization are the following activities: WTO trade agreements • administering for trade negotiations • forum trade disputes • handling national trade policies • monitoring assistance and training for developing • technical countries • cooperation with other international organizations. Both GATT and WTO evolved around trade negotiation rounds. So far there have been eight rounds of negotiations within GATT (Table 1). In 2001, negotiations were in progress on whether to start a new all-encompassing trade round in the WTO or to divide the negotiations into separate subject areas. During the course of time the GATT and now the WTO have increased their agenda according to the developments in the surrounding society. The WTO now covers a wide number of different areas of trade
338
under the three main headings GATT (trade in goods), GATS (trade in services) and TRIPS (trade in intellectual property rights). Within the areas of GATT and GATS there are a number of extra agreements, some of which are listed in Table 2. The decision-making process in the WTO is fundamentally built upon consensus. The top decision-making body is the Ministerial Conference, which consists of the Member Countries’ foreign ministers. This conference convenes at a minimum every second year. On a daily basis, the General Council is the central decision-making forum. All the Member Countries are represented in the Council by their ambassadors or a counterpart. The General Council also acts as Dispute Settlements Body and as Trade Policy Review Body.
Principles of the WTO A number of fundamental principles govern the general agreements and the relations between Member Countries. At the core of these principles is antidiscrimination, amongst trading partners and between domestic and foreign producers of goods. The most important principles are as follows.
Most Favored Nation Status The Most Favored Nation (MFN) clause stipulates that favors such as easier market access (lower duties) given to one country’s produce should be multilateralized and therefore applicable to all member countries. All Member Countries should by this principle be entitled to equal treatment and equal access. The major exception from this rule is free trade areas, customs, economic and political unions that can apply for and under certain conditions be granted exemption.
National Treatment Clause The National Treatment Clause stipulates that imports and domestic or local produce should be equally treated
Policy Schemes and Trade in Dairy Products | World Trade Organization Table 1 GATT trade rounds Year
Name of the round and place
1947 1949 1951 1956 1960–61 1964–67 1973–79 1986–94
Geneva Annecy Torquay Geneva Dillon Round (Geneva) Kennedy Round (Geneva) Tokyo Round (Geneva) Uruguay Round (Geneva)
339
Dispute Settlement Body
upon market entrance of the import products. Duties and import taxes are not regulated by this principle. This rule applies to goods, services, trademarks, copyrights and patents. In practice the National Treatment Clause undermines the possibility of governments giving preferences to nationally produced products over imports and is an important instrument in increasing the transparency of the nontariff barriers to trade.
With the creation of the WTO, the trading system established a much more comprehensive dispute settlement system than was the case under the GATT, led by the Dispute Settlement Body (DSB). This dispute settlement system is based on the rule of law and with the strengthened possibilities of enforcement, the WTO has increased its regulatory and arbitrating powers. The Dispute Settlement Body is one of the cornerstones in the transformation from an international agreement to an international organization. Arbitration between members is a vital task for the WTO in order to secure the adherence by members to different agreements and rules under the WTO, but also to obtain the support of the members for the policies for the development of the international trade regime. The Dispute Settlement Body mainly facilitates the process by which Member Countries obtain legal guidance and counseling to solve bilateral disputes concerning trade issues under coverage of the different agreements under the auspices of WTO. A trade dispute taken to the WTO follows a predetermined structural process with set deadlines and obligations to implement the rulings. This allows for the development of jurisprudence and case law precedent within the WTO, and creates a much more predictable trading system. The different stages of a WTO case are shown in Figure 1. A panel makes first rulings in the WTO; their report is approved unless there is a consensus against this. The panel ruling can on legal grounds be taken to appeal to the appellate body. The appellate body’s decision is final, unless there is a consensus against the decision. This procedure implies that no single country or party to a dispute can veto a final decision and by that hinder a ruling against its interest. Member Countries are compelled to implement rulings of the WTO or to pay compensation to cover the opponent’s losses resulting from the illegal trade practice. The WTO may also allow for retaliation and introduction of sanctions, if a party to a case does not intend to follow the final ruling.
Least-Developed Countries
Non-tariff Barriers
More than 100 of the WTO member countries are developing countries. Within the WTO system there is special treatment for these countries with regard to their potential to fulfill their obligations according to the agreements, rules and regulations. For the group of least-developed countries, there are broad exemptions from the obligations. WTO has set up a system in order to help developing countries to gain knowledge and understanding of the organization and particularly to pass on experience with the trade negotiation system.
In the early days of GATT the focus was on reducing tariffs and import duties in order to enhance trade and reduce protectionism. This goal has largely been achieved for industrial produce during the course of the numerous trade rounds. Tariffs within trade in industrial products have been reduced from approximately 40% to less than 5% in the period from the establishment of GATT to the current implementation of the Uruguay Round. This tariff reduction process is only in an early stage with respect to agricultural and food products.
Source: www.wto.org
Table 2 Agreements within the areas of GATT and GATS The ‘extra’ goods agreements (under GATT)
The GATS annexes (under GATS)
Agriculture
Movement of natural persons Air transport
Health regulations for farm products Textiles and clothing Product standards Investment measures Antidumping measures Customs valuation methods Preshipment inspection Rule of origin Import licensing Subsidies and countermeasures Safeguards
Financial services Shipping Telecommunication
Source: http://www.wto.org
340 Policy Schemes and Trade in Dairy Products | World Trade Organization
The panel process NOTE: some times The various stages a dispute can go through in the WTO. At all stages, countries in dispute are encouraged to consult each are maximum; other in order to settle ‘out of court’. At all stages, the WTO director-general is available to offer his good offices, to mediate some minimum; or to help achieve a conciliation some binding some no!
60 days
by 2nd DSB meeting
0−20 days 20 days (+10 if director-general asked to pick panel)
6 mths from panel’s composition, 3 mths if urgent
up to 9 mths from panel’s establishment
Consultations [Art 4]
Panel established by Dispute Settlement Body (DSB) [Art 6]
During all stages good offices, conciliation or mediation [Art 5]
Terms of reference [Art 7] Composition [Art 8]
Panel examination (Normally 2 meetings with parties [Art 12] 1 meeting with third parties [Art 10]
Expert review group [Art 13; Appendix 4]
Interim review stage Descriptive part of report sent to parties for comment [Art 15.1] Interim report sent to parties for comment [Art 15.2]
Review meeting with panel upon request [Art 15.2]
Panel report issued to parties [Art 12.8; Appendix 3 par 12(i)]
Panel report circulated to DSB [Art 12.9; Appendix 3 par 12(14)] Appellate review [Art 16.4 and 17]
60 days for panel report, unless appealed
‘REASONABLE PERIOD OF TIME’ determined by: member proposes, DSB agrees; or parties in dispute agree; or arbitrator (~ 15 mths if by arbitrator)
30 days after ‘reasonable period’ expires
NOTE: a panel can be composed (i.e. panelists chosen) up to about 50 days after its establishment (i.e. DSB’, decision to have a panel)
DSB adopts panel/appellate report(s) including any changes to panel report made by appellate report [Art 16.1, 16.4 and 17.14]
Implementation report by losing party of proposed implementation within ‘reasonable period of time’ [Art 21.3] In cases of non-implementation parties negotiate compensation pending full implementation [Art 22.22]
Retaliation If no agreement on compensation, DSB authorizes retaliation pending full implementation [Art 22.2 and 22.6] Cross-retaliation: same sector, other sectors, other agreement [Art 22.3]
30 days for appellate report
Possibility of proceedings including referral to the initial panel on proposed implementation [Art 21.5]
max 90 days TOTAL FOR REPORT ADOPTION Usually up to 9 mths (no appeal), or 12 mths (with appeal) from establishment of panel to adoption of report [Art 20]
90 days
Possibility of arbitration on level of suspension procedures and principles of retaliation [Art 22.6 and 22.7]
Figure 1 Flowchart of the dispute settlement process in the WTO. (Reproduced with permission from www.wto.org.)
Policy Schemes and Trade in Dairy Products | World Trade Organization
As duties have diminished, the non-tariff barriers (NTB) have attracted increasing attention as they turn out to be as trade-distorting as flat rate tariffs. Non-tariff barriers consist of a number of different rules, regulations, standards, technical issues, administrative and bureaucratic procedures and other market-related obstacles that exporters meet while trying to gain access to a certain market. The WTO tries to highlight this area with a policy of transparency and information, but also with restrictions on the use of nontariff barriers.
Agreement on Technical Barriers to Trade The Agreement on Technical Barriers to Trade (TBT) is closely tied to the above-mentioned non-tariff barriers. This agreement aims at creating a free flow of international trade by regulating the general use of technical standards in a protectionist way. The agreement installs the principle that technical regulations and standards concerning packaging, marking and labeling, and procedures for assessment of conformity with technical regulations and standards should be used in a nondiscriminative way, both in respect to different trading partners and with regards to domestic versus import products. The agreement encourages the use of internationally recognized standards in national and local laws. At the same time member countries have to enhance transparency and public access with regard to applied and upcoming standards.
Agreement on Sanitary and Phytosanitary Standards The Agreement on the Application of Sanitary and Phytosanitary Standards (SPS) defines and gives opportunities for Member Countries to adopt measures necessary to protect human, animal and plant life and
health and at the same time regulates the use of these measures in order to avoid their discriminative use as barriers to trade. In the SPS agreement the scientific principle prevails. Sanitary and phytosanitary measures restricting trade should at all times have a scientific foundation that is widely recognized. Concurrently, countries are to treat different rules and standards alike, if their ultimate effect is the same for the protection of the human, animal and plant life and health. The Codex Alimentarius is recognized in the SPS agreement as a standard-setting reference point in this area and in the case of disputes among member countries. The objective is to harmonize the basis for sanitary and phytosanitary measures and meanwhile to create transparency and access to information concerning different rules and demands within this area.
Agricultural Agreement With the finalization of the Uruguay Round of trade negotiations agricultural trade fully came under the regulation of the WTO. The Agricultural Agreement is the first real attempt to achieve a common understanding of the trade mechanisms for agricultural and food products and the Agreement implements a number of regulations which in the last half of the 1990s and at the turn of the century set fundamental boundaries and rules for governance and policy-making within agriculture worldwide (Table 3). The major elements of the Agreement fall under three headings: 1. Export subsidies and competition. 2. Market access/imports. 3. Internal/domestic support. Together with the three central parts of the Agricultural Agreement, the Sanitary and Phytosanitary Agreement
Table 3 The outline of the support reductions in the agricultural agreement The main demands for reduced agricultural supports 1995 to 2001 Exports with support
Imports
Internal support
21% reduction in export quantities subject to support 36% reduction in budgetary outlays for export subsidies Base period: 1986–90
All non-tariff barriers converted to tariffs
20% reduction in all trade distorting internal supports based on the AMS calculation Base period: 1986–88
Source: http://www.wto.org
341
Average 36% reduction in tariffs including converted non-tariff barriers, at minimum 15% reduction pre product line Minimum access at reduced tariff rates of 3% increasing to 5% of domestic consumption Base period: 1986–88
342 Policy Schemes and Trade in Dairy Products | World Trade Organization
(see above) constitutes an attempt to formulate an overall framework for agricultural trade and by that the domestic policies concerning production and regulation of food supply. Within the WTO there are a number of different views concerning liberalizing versus protecting agricultural production and trade. The most vocal groupings in the agricultural negotiations are the United States, the EU and the Cairns Group, a number of food exporting countries with Australia and New Zealand at the forefront. The developing countries are with respect to their interests mainly divided into two main groups, net food exporters and net food importers. A number of very important trade disputes concern trade in agricultural produce, such as bananas, hormonetreated beef or milk quotas, to mention just a few. These WTO cases between different Member Countries have been some of the most stringent tests to the dispute settlement system within the WTO. Agricultural and consumer-related issues have proved to be the most politicized cases in the short history of the Dispute Settlement Body of the WTO. But they are also acknowledged as the core challenge to the sustainability of the system and to the Member Countries’ genuine support and acceptance of the WTO rules and governance.
Agricultural Agreement entered into force in 1995 running to 2001, with a peace clause extending it to 2003. The Agreement stipulated that further negotiations were to start in the WTO by 1999 in order to prepare for a new agreement. These negotiations are currently (2002) in process with all the parties outlining their specific interests and suggestions for a new agenda and ultimately an agreement.
Peace Clause It was envisaged in the Blair House Accord that a new agreement might not be reached among the trading partners to take over from the Uruguay Round agreement exactly in 2001. Therefore it was decided to extend the results of the final stage of the implementation – the socalled year 6 (2000/2001) – onward to 2003 to provide some time for negotiations on a new agreement. From 2001 to 2003 no further developments in the levels of subsidies, import tariffs and internal support are anticipated unless a new accord is in place. At the same time, the agreed reductions will not be reversed. The situation for the agreement on agriculture is, however, uncertain if a new deal is not in place by 2003. One option is to agree to extend the peace clause; however, a potential conflict is possible.
Blair House Accord The Blair House Accord between the EU and the United States is named after the presidential official guesthouse in Washington DC where the Agricultural Agreement was finalized. This agreement, reached in November 1992, was a breakthrough in the ongoing Uruguay Round of negotiations in GATT. The accord laid the foundations for the current trade liberalization within agriculture and also facilitated an ending to the very long and at times antagonistic negotiations for a general conclusion to the trade round. The Blair House Accord sets the basic reduction factors both for exports and internal support measured in quantities and budgetary outlays. The accord also sets a 6-year implementation period and the reference periods. Alongside this, the EU and the United States agreed on solving a number of outstanding trade disputes particularly the one on oilseeds. The agricultural breakthrough in the GATT system is widely recognized to rest on the Blair House Accord and hence on the hard-won compromises and common understanding between the EU and the United States. The EU has a mandate to negotiate for all Member Countries of the European Union, which act as one within the WTO. In December 1993, one year after the Blair House Accord, the final GATT agreement was reached and it was signed in Marrakesh in Morocco in April 1994. The
Traffic-Light Model – GATT Boxes and Decoupled Support One of the main objectives of the Agricultural Agreement is to reduce support levels in general; however, support is divided into more and less trade-distorting types. The aim of the Agreement is to target the most distorting support forms which directly influence the international markets for agricultural products, and hence the competition situation between different agricultural producers. Aggregated Measurement of Support The Total Aggregated Measurement of Support (AMS) is a calculation of the total amount of support given to agricultural producers in one country, except for domestic support not subject to reductions, because of their nondistorting or decoupled nature. The AMS calculation is used to facilitate comparisons between countries and to equalize different types of support in order to obtain reductions in all types of distorting supports. Traffic-light model In popular terms the different types of agricultural support are labeled with different colors: red, amber,
Policy Schemes and Trade in Dairy Products | World Trade Organization
green – and blue. The red support forms should be stopped immediately, the amber ones should be phased out and the green ones can be left, as they are not seen as directly distorting. This rule-of-thumb makes for the name ‘traffic-light model’. The different colors also give names to the box scheme, which is another way of describing the different support forms: amber, blue and green boxes.
Export subsidies The export subsidies used by various countries fall into the amber box and must be reduced according to the agreement by 21% for supported export quantities and by 36% in total budgetary outlays. The reduction had to be linear over the implementation period, reaching the final commitments in Year 6, 2001. Developing countries must reduce their support by 14% in quantities and 24% in budgetary outlays with an implementation period of 10 years. Least-developed countries are exempt from this obligation. Member Countries have to keep account of the use of export subsidies for the individual product categories.
Decoupled support and blue box subsidies In order to encompass the American deficiency payments and the EU animal and area premiums of the mid-1990s, the blue color was introduced. Blue color support forms are semi-decoupled, whereas the green ones are decoupled altogether. The term ‘decoupled’ is used to describe the situation where the size and amount of support are not linked to the actual form and size of the agricultural production, as opposed to price support that is directly linked to the production output. Green box types of support are within the areas of research, disease control, government services and many more. Direct income support also falls in this category, as long as it is independent of the production. Semi-decoupled support can take the form of direct payments under production limiting programs with fixed references – area, yield or animal numbers. The blue box supports are not targeted by reduction demands because of their limited trade-distorting nature. The introduction of categorized support forms has allowed for a dynamic agricultural policy reform process in different countries. The major agricultural production and trading countries have undergone a number of reforms since the GATT agreement, all directly related to the WTO policies, in order to enhance competitive powers and allow for a more fair trade with agricultural produce. In most WTO member countries development of agricultural policy instruments is under way in order to avoid potential disputes.
343
Imports and Market Access The import rules in the Agreement specify that tariffs have to be reduced by an average of 36%, with a minimum 15% per product line from 1995 to 2001. Prior to the reduction all non-tariff barriers have to be converted into tariff equivalents to enhance transparency as to the actual level of trade restrictions. This conversion is termed tariffication. It is the overall tariffs (duties, levies, quantitative restrictions, non-tariff barriers and so forth – old and new ones) that are to be reduced by 36%. The tariff rates are listed in the country list for each country with initial and bound rates. Developing countries are only obliged to reduce tariffs by 24%, and they have an extended implementation period, to 2004. Least-developed countries are exempt from the agreement to reduce tariffs.
Minimum import access In order to create some immediate effect for market access it was decided to create a certain minimum access to a preferential tariff far below the general and even reduced tariffs. This minimum quota is set in relation to the consumption in the base period 1986–88. At the beginning of the implementation in 1995 the quota was 3% of base period consumption for the respective products. This amount has gradually increased to 5% at the end of the 6-year implementation period in 2000/2001. Current access opportunities are to be maintained and supplemented with the above-mentioned minimum access in case the actual imports are below the 3–5%.
Trade in Dairy Products It was widely believed that the WTO agreement would increase the international trade in agricultural products, including dairy produce. The actual development does indicate that the total trade is developing; however, what is more noticeable is the change in the trading patterns. Table 4 shows the shift from an EU-dominated international trade in dairy products to a situation where Oceania is the predominant exporter. This situation is reflected in different claims and demands in respect of the ongoing negotiations on a WTO II agreement. It was also expected that the price for dairy products would be affected in an upward trend by the Agricultural Agreement and the increased trade, but this element is harder to deduce from the statistics. However, some signs in the market do indicate a general upward trend in prices for dairy products.
344 Policy Schemes and Trade in Dairy Products | World Trade Organization Table 4 The development in world market shares for dairy products World market share (%) EU USA New Zealand Australia
1990
2000
51 13 27 9
39 2 41 18
Source: Danish Dairy Board.
See also: Office of International Epizooties: Mission, Organization and Animal Health Code. Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: United
States’ Agricultural System; Trade in Milk and Dairy Products, International Standards: Harmonized Systems.
Further Reading Hoekman B and Kostecki M (1995) The Political Economy of the World Trading System, Oxford: Oxford University Press. Jackson JH (1998) The World Trading System, Law and Policy of International Economic Relations, Cambridge: MIT Press. Moon BE (1996) Dilemmas of International Trade, Oxford: Westview Press. Nedergaard P, Hansen HO, and Mikkelsen P (1993) EF’s Landbrugspolitik og Danmark, Copenhagen: Handelshøjskolens Forlag. Ritson C and Harvey DR (1997. In) The Common Agricultural Policy, (2nd edn.. Wallingford: CAB International. World Trading Organization, (1995) The Results of the Uruguay Round of Multilateral Trade Negotiations: The Legal Texts,. Geneva, Switzerland: WTO. World Trade Organization (1998) Trading into the Future, Geneva, Switzerland: WTO.
World Trade Organization and Other Factors Shaping the Dairy Industry in the Future P Vavra1, OECD, Paris, France ª 2011 Elsevier Ltd. All rights reserved.
Introduction How would dairy industry look like after the conclusion of WTO (World Trade Organization) Doha negotiations? Is there going to be a final deal? Is there a need for a Doha deal? Starting with the last question, the answer is ‘yes’. In my view it is not necessary to discuss here the importance of the Doha round and the advantages of a multilateral approach. Bilateral and not even regional agreements cannot match the multilateral system. Issues related to standards or dispute settlements are just two examples that need multilateral consideration. The value of WTO trade negotiations that seek broader consensus has also been underlined in empirical studies. For example, an OECD (Organisation for Economic Co-operation and Development) study pointed to the logical fact that the domestic supply adjustment for dairy sector can be expected to be the highest if a country reforms its dairy policy unilaterally. As more countries join the reform process, adjustments become smaller and would be least in the case of a multilateral reform. As there is a need for a multilateral framework to govern global trade, it could be expected that there will be a final deal. However, in the aftermath of the global economic crises, the question mark after the word ‘When’ is not getting smaller. The answer to the first question is even more complex. It is always difficult to predict how the world would look like after a specific event, and it is not easy to isolate the impact of that particular event from other factors influencing the evolution of the world. In the last decade the dairy industry has been going through remarkably dynamic changes worldwide, becoming truly global in scope. Would this have happened even without the WTO Uruguay Round Agreement on Agriculture? Or, was globalization in fact propelled by numerous border measures protecting domestic markets that provided incentives for foreign companies to circumvent national border measures through investment in protected markets? 1
The author is an agricultural markets and policy analyst at the OECD, Paris. The opinions expressed in this article are those of the author and do not necessarily represent those of the OECD or its member countries.
A Doha deal could be expected to have an impact especially on those domestic markets that have relatively high market price support measures in place. But the actual impact depends on the global market situation and the way countries organize support to agriculture. Moreover, the forces of globalization, underpinned by economic growth, urbanization, and technology transfers, will likely continue to shape the dairy industry, be it preor post-Doha. This article will discuss not only concerns related to Doha but also other issues that are likely to have an impact on dairy markets in the near future.
Doha Round in the Context of WTO Negotiations Established on 1 January 1995, the WTO replaced the GATT (the General Agreement on Tariffs and Trade) as the legal and institutional foundation of the multilateral trading system of its member countries. Although GATT has been providing the multilateral rules governing much of the global trading system since 1948, these rules were largely ineffective in disciplining key aspects of agricultural trade. The Uruguay Round was the first trade round that considered agricultural issues, and it became a turning point in the reform of the agricultural trade system. The Uruguay Round Agriculture Agreement (URAA) has accomplished the development and implementation of a framework to address barriers and distortions to trade in three major policy domains: market access, domestic support, and export subsidies. The diverse forms of trade measures were converted under the URAA to tariffs. Market access for sensitive products was provided through a system of tariff rate quotas (TRQs). The use of export subsidies was reduced by the agreement, while domestic policies that affect production and trade of agricultural products were constrained by a set of rules and bindings. The reduction in domestic support was implemented through a commitment to reduce the total aggregate measurement of support (AMS) for each country. The URAA numerical targets for each policy domain in agriculture are summarized in Table 1. The table indicates that in the developed countries the total AMS support was scheduled to be reduced by 20% over 6 years, while in the developing countries the total AMS
345
346 Policy Schemes and Trade in Dairy Products | World Trade Organization Table 1 Uruguay round numerical targets for agriculture Developed countries
Developing countries
6 years: 1995–2000
10 years: 1995–2004
Tariffs Average cut for all agricultural products Minimum cut per product
36% 15%
24% 10%
Domestic support Total AMS cuts for sector (base period: 1986–88)
20%
13%
Exports Value of subsidies Subsidized quantities (base period: 1986–90)
36% 21%
24% 14%
Source: WTO.
support was scheduled to be reduced by 13% over 10 years. Moreover, the agreement required a reduction of tariffs by 36%, on average, for developed countries, and by 24% for developing countries. It is evident from the table that although the Uruguay Round achieved a historic change, the actual level of agricultural support was reduced only moderately. Nevertheless, the achievement of the Uruguay Round should be seen in the establishment of rules for agricultural support and as a start of the process of long-term objective of substantial reduction in support and protection. This process was to continue in the new round of negotiations. At the Fourth Ministerial Conference in Doha, Qatar, in November 2001, WTO member governments agreed to launch a new round – the so-called Doha round – of negotiations. The round embarked on a very complex agenda with a focus on developing countries, trade facilitation, competition rules, environment, investment, liberalization of trade in services, and liberalization of trade in agriculture, which is likely the single most difficult item. The Doha Ministerial Declaration has set several key dates for the negotiations. The modalities for countries’ commitments were expected by 31 March 2003, and countries’ comprehensive draft commitments by the fifth ministerial conference in September 2003 in Cancu´n, Mexico, with the overall deadline set for 1 January 2005. However, after a failed – the so-called – Harbinson proposal in March 2003, the fifth ministerial conference in September 2003 ended up in a stalemate. Ten months after the Cancu´n deadlock, an agreement on a framework for the modalities on agriculture was reached. The socalled July Framework gave a clearer shape to the modalities for the next phase of the negotiations. The 2004 July Framework Agreement was a starting point toward a draft of the detailed modalities to be agreed at the WTO’s sixth ministerial conference held in Hong Kong, from 13 to 18 December 2005. Rather limited progress was made in reaching an agreement on
precise numerical formulae or targets for liberalizing agricultural trade, the original aim of the Hong Kong Ministerial. Perhaps the most tangible outcome of the Hong Kong Ministerial was the continuing support to eliminate all forms of export subsidies, and disciplines on measures with equivalent effects. The next deadline for reaching agreement on modalities was set for 1 August 2006. As no agreement could be reached, the negotiations had been suspended at the General Council meeting on 27–28 July 2006. In 2007, the negotiations were resumed and a new set of modalities were circulated in July and August 2007. A series of working documents followed, as well as a series of revised draft modalities on 8 February and 19 May 2008, respectively. A revision of the previous versions was circulated on 10 July 2008. But the meeting of ministers in Geneva over 21–30 July did not reach an agreement. The disagreement occurred over the special safeguard mechanism (SSM) for agricultural products in developing countries. Safeguard mechanisms are used to restrict imports in special circumstances such as a sudden surge in imports. The unresolved issue was the size of the trigger allowing to invoke a special safeguard measure. In particular, the disagreement was related to the situation where the SSM raises tariffs above the commitments made by the countries in the 1986–94 Uruguay Round – the pre-Doha Round bound rates. Some commentators viewed the July 2008 failure more as a collapse of negotiations; others noted the progress on issues other than the SSM. It is difficult to estimate what would happen if the questions of the SSM were resolved. In his report to the trade negotiations committee, the chairman of the special session of the committee on agriculture, Ambassador Crawford Falconer, noted that despite the fact that members were prepared to accept compromises it could not be taken for granted that even with the SSM agreement the rest could have fallen into place. There are still unresolved questions related to new tariff quota
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347
Table 2 Overview of GATT and WTO negotiation rounds Name
Start
Duration
Countries
Subjects covered
Geneva Annecy Torquay Geneva II Dillon Kennedy Tokyo Uruguay
April 1947 April 1949 September 1950 January 1956 September 1960 May 1964 September 1973 September 1986
7 months 5 months 8 months 5 months 11 months 37 months 74 months 87 months
23 13 38 26 26 62 102 123
Doha
November 2001
?
141 (November 2001)
Tariffs Tariffs Tariffs Tariffs, admission of Japan Tariffs Tariffs, antidumping Tariffs, nontariff measures, framework agreements Tariffs, nontariff measures, rules, services, intellectual property, dispute settlement, textiles, agriculture, creation of WTO, and so on Tariffs, nontariff measures, agriculture, labor standards, environment, competition, investment, transparency, patents, and so on
?
153 (September 2008)
Adopted from Neary JP (2004) Europe on the road to Doha: Towards a new global trade round? CESifo Economic Studies 50(2): 319–332. ? – not yet known.
creation, tariff simplification, and issues related to cotton. These could be the other deal-breakers. Nevertheless, it was clear from the outset that the agenda is ambitious and that a lot of time and work would be needed to successfully conclude the round. Moreover, the time spent so far on negotiations cannot be considered excessive, despite the slow progress. Table 2 summarizes the time-bound efforts of the previous GATT and WTO rounds.
Implications of the Doha Round for the Dairy Sector The Doha round has not fundamentally changed the rules as agreed by the URAA, but larger reductions (or even elimination) have been considered. Although the actual modalities have not been agreed to and are subject to change, the key factors so far could be described as follows: (1) Elimination of export subsidies in all forms (already agreed in July 2004 Framework) and improved disciplines on all export measures whose effects are equivalent to those of export subsidies. (2) Depending on the base of Overall Trade-Distorting Domestic Support (OTDS), a reduction is envisaged in the range of 50–85% using a tiered formula; the framework also widened the range of support that would be disciplined in the Doha round; Blue Box supports are to be capped at no more than 5% of the value of a country’s agricultural production, in the 1995–2000 period. (3) Tariffs shall be reduced using a tiered formula that requires deeper cuts for higher tariffs. The least developed countries would not be required to make any reduction on domestic support and tariffs. The negotiated framework also provides a number of flexibilities intended to meet specific concerns of
individual or groups of countries. These flexibilities, which are in fact numerous exceptions – such as the designation of sensitive products and special products for developing countries, special agricultural safeguard measures – have substantially increased the complexity of the negotiations and introduced doubts about the effectiveness and success of tariff cuts. What would be the implication of the Doha round for the dairy sector? Dairy markets have traditionally been among the more distorted, and even after the full implementation of the URAA, dairy trade continued to be among the most protected agricultural sectors with high average bound tariffs, low minimum access requirements, a number of special safeguard provisions, complex systems of tariff-rate quotas (TRQs), and large domestic support and export subsidies and other export support measures. In almost all instances, tariffs on dairy products are above the country average for all agri-food products and are among the highest on agricultural products (Table 3). Thus, it could be expected that, after a Doha deal, countries with high tariffs would need to reduce them considerably, but, as noted above, dairy products could be listed as sensitive products falling under the exemption category. Under the current legislation it has been possible to avoid reductions in dairy AMS by adjusting the AMS amounts in other sectors. Such compensation mechanisms are limited in the Doha framework, which specifies product-specific AMS limits and envisages capping of the product-specific funding. The product-specific AMS limits for all developed country WTO Members other than the United States shall be the average of the product-specific AMS during the Uruguay Round implementation period (1995–2000) as notified to the Committee on Agriculture. For the United States, the
348 Policy Schemes and Trade in Dairy Products | World Trade Organization Table 3 Average (scheduled) tariffs in 2000 for main commodities
Coarse grains Wheat Rice Sugar Beef Pig meat Poultry Sheep Butter Cheese Skim milk powder Whole milk powder Whey powder Average of all commodities
In-quota
Out-of-quota
100 73.2 15 15.8 36.3 55.5 39 30.9 48.3 31.8 48.1 79.5 37.8 52.67
217.8 184.4 197.5 126.7 166.9 180.2 171.7 153.3 369.5 121.1 191.6 260.7 545.7 184.18
From OECD (2002) Agriculture and Trade Liberalisation: Extending the Uruguay Round Agreement. Directorate for Food, Agriculture and Fisheries, Committee for Agriculture. Paris: OECD. Average tariff was calculated as an unweighted average of each tariff line for the following countries: Argentina, Australia, Canada, European Union, Hungary, Japan, Korea, Mexico, New Zealand, Poland, United States, Iceland, Norway, and Switzerland.
product-specific AMS limits shall be the resultant of applying proportionately the average product-specific AMS in the 1995–2004 period to the average product-specific total AMS support for the Uruguay Round implementation period (1995–2000) as notified to the Committee on Agriculture. It is not necessary to go through all the details of modalities as these can be found in the original WTO document. However, an important point needs to be made here about the overall process. The WTO negotiations are not about eliminating agricultural policies but about shifting to more effective policies. Hence, countries will be able to implement or keep policies that do not distort trade. It follows that the green box is likely to remain in existence and act as a home for measures that are decoupled from production as far as possible and targeted at specific objectives and beneficiaries. (The green box support measures include those deemed to distort trade only minimally, or not at all, such as some forms of direct payments to producers, decoupled income support, and government financial support for income insurance and income safety net programs.) The simulation results of studies that have analyzed the impact of further trade reforms on the global dairy sector have indicated that, following the reforms, world dairy prices would be lifted while supply would shift toward more efficient areas, although there would not be any significant change in total world milk production. It is however difficult to extrapolate these results in the context of recent developments as the agricultural markets have undergone dramatic changes. This is especially
true of the dairy sector, which has been going through rapid structural changes for some time with several countries also embarking on policy reforms. As a consequence, international dairy markets have slowly shifted from a supply-driven paradigm distorted by price-depressing policies and serving as an outlet for excess supplies, to a more demand-driven paradigm, responsive to market signals and changing consumer preferences. The very recent events on the markets have further refocused attention on food security, availability, and safety. These profound market changes, some of which are believed to be structural and long-term in nature, will have a significant impact on the dairy sector, be it pre- or post-Doha. In order to get a better grasp on global dairy prospects it is essential to understand this shift.
Global Market Changes and Prospects The prices of nearly all agricultural commodities have risen sharply in the 2007–08 period but the prices of dairy products were the first to start the climb. International dairy prices recorded strong gains in the first half of 2007, already peaking in the second half of that year well ahead of similar developments for other commodities (Figure 1). On a year-over-year basis between 2006 and 2007, world butter prices increased by 66% and cheese prices rose by 50%, while prices of milk powders soared by more than 90%. The OECD–FAO Agricultural Outlook report expects that all dairy prices will weaken over the short-term as demand softens and supply, with some lag, reacts to the strong price incentives. Nevertheless, dairy prices in real terms are expected to average 20–30% higher as compared to those of the last decade. The prices in real terms are also expected to resume a modest declining trend, albeit from a much higher level than in the past (Figure 2). However, it is important to note that these projections are conditional on the underlying macroeconomic assumptions, most notably solid economic growths and high crude oil prices. Figure 2, which depicts butter and skim milk powder (SMP) prices in real terms, also illustrates two additional points. First, when viewed from the perspective of last couple of decades, the recent spike of prices in real terms is much less impressive, certainly for butter. Second, over the last several decades the value of milk components on the international market changed considerably and shifted toward non-fat solids away from fat. (The steady decline in milk fat value on world markets could be, to some extent, attributed to the policy decision in heavily protected countries to tilt butter/SMP support prices in favor of butter, which has favored the production of fat for which demand has been stagnating.)
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Figure 1 International monthly commodity prices. Source: OECD–FAO.
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The reasons for expectations of a higher plateau for global dairy prices merit a short consideration. Some of the factors behind the higher prices are related to more structural shifts while others could be considered as transitory. For example, a more permanent change in the markets relates to changes in demand patterns particularly in developing countries where consumers are switching to a more protein-based diet fueled by urbanization, westernization, and growth in per caput income. Consumption of milk and dairy products is rising nearly everywhere, exhibiting the highest growth rates among agricultural food commodities. The rise is particularly marked in rapidly growing economies of the Pacific Rim where an expanding middle-class population is consuming more sophisticated processed foods. Over the medium term, in developing countries, demand growth is expected for all dairy products with whole milk powder
(WMP) consumption showing the strongest growth, followed by butter. Nevertheless, OECD countries continue to dominate cheese consumption and maintain their three-quarter share of the world total (Figure 3). Another important development that slowly changed the usual picture was the decline in the importance of intervention products on world markets, particularly from the European Union and the United States. While in the period 2002–03 the share of EU and US SMP stocks alone amounted to half of the global exports of SMP, in the period 2005–07 this share dropped to below 10%, reducing the buffer against shocks in supply and demand (Figure 4). The lower stock levels have added to market and price volatility, and there is a strong nonlinear relationship of changes in stock levels to the changes in price. When ending stocks are sizable, large
350 Policy Schemes and Trade in Dairy Products | World Trade Organization 25
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Figure 4 Ratio of EU and US stocks of SMP to global exports. Source: OECD.
changes in stock levels may be needed to change prices by a small amount. When stock levels are low, very small changes in stock levels can be associated with major price swings. The tight situation on the market in 2007 was further aggravated by the decline in milk production in Australia and Argentina. Production everywhere was hindered by a strongly increasing cost of production – rising oil and feed prices. Oil, energy, and feed prices are critically important factors in the increased production costs for milk, and a higher plateau of these prices seems to be a more permanent factor that could keep prices above past average levels. The situation on the dairy markets was also to some extent exacerbated by policy decisions in certain countries to tax or ban exports. These ad hoc actions should be considered temporary, and introducing policies that create distortions and that undermine appropriate market responses should be avoided in the future. Finally, an important factor, not unique to the dairy sector, has been the depreciation of the US dollar. Stronger currencies vis-a`-vis the US dollar mitigated the
producer price gains in local currencies and at the same time facilitated higher demand by importers, thus driving world prices higher in terms of US dollars. In general terms, when the dollar is weak, commodity prices tend to be higher, and when the dollar is strong, commodity prices tend to be lower (Figure 5). Nevertheless, in discussing the prospects for the global dairy markets it is important to keep in mind that the most certain thing about the future is that it is uncertain. Weather, economic conditions, and the evolution of policies (induced by Doha deal or not) remain among the key factors influencing the dairy market’s future, with a considerable uncertainty about them. For example, a slowdown in economic growth would moderate international prices. A severe drought in any important dairyproducing region could have a critical impact on the sector in any given year, pushing prices higher. These factors are uncertainties that to some extent form an integral part of the dairy markets. What are the other factors that will likely shape the dairy markets in the near future – be it pre- or post-Doha? Although the choice for the discussion might be subjective, it seems
Policy Schemes and Trade in Dairy Products | World Trade Organization 1.6
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to me that the shifts in the markets will be reinforced by the following mutually inclusive factors: continued globalization, technological progress, and vertical integration of food supply chains. Globalization It is evident that the dairy industry is becoming more global in scope. It could be expected that globalization will continue to reshape the dairy markets in the future and will be fueled by the processes of economic growth, urbanization, technology transfer, and a convergence in consumption patterns. Moreover, the ability to expand, reduce costs, and secure milk supplies will remain additional drivers behind industry consolidation, and the development of discount stores and private labels will quite probably put additional pressure on milk processors, forcing them to look for further cuts in costs. Mergers, strategic alliances, joint ventures with foreign partners, and direct foreign investment and acquisitions will be the main vehicles of the structural change. Competition among dairy firms in well-established developed markets is set to intensify with the focus turning to health and convenience, and increased penetration of foodservice, catering, and restaurant sectors. As a result, many firms will try to enter growing but less established markets in developing countries to source milk and dairy products from multiple locations while the original domestic market will become less relevant. This is also linked to the continued expansion of supermarkets, which will likely contribute to the further weakening of the position of local dairy firms but will help to spread international brands. Thus, for international dairy companies this means that a branded product can be promoted in multiple markets, but perpetuation of local products and catering for local tastes and preferences are to remain important.
Vertical Integration of Food Supply Chains Globalization of the dairy industry goes hand in hand with the expansion of supermarkets and transformation of the agri-food sectors in general. It could be expected that the transition from independent markets toward much more tightly aligned food supply or value chains will continue. The profound changes in the global food system are marked by (1) increase of trade in food, (2) rapid rise of economic concentration of supermarkets, (3) shift to centralized procurement via distribution centers from spot market procurement toward dedicated wholesalers and direct purchase from growers or grower associations, (4) creation of a multiplicity of private standards, often built on top of public standards, (5) rise of third-party certification of food production, (6) development of new technologies, biotechnologies, and process control throughout the entire chain, (7) shift toward nonprice competition among supermarket chains, (8) greater differentiation of food products by class, and (9) the development of new forms of contractual relationships between supplies and buyers. This transition has also been (and will be) accompanied by an increasing use of contracts. The results of several studies indicate an increased use of contracts in most agricultural sectors and dairy is not an exception. However, an increased use of contracts together with a rising upstream concentration in the supply chain could create concerns about the impact of this form of supply chain governance on farmers and issues related to market transparency and market power. The growing market power in the supply chain might have an impact not only on farmers but also on established dairy companies. The growing power of retailers, and in particular the developments of retailers’ private labels, will increasingly represent a challenge for established brands of dairy companies, forcing these firms to continuously innovate.
352 Policy Schemes and Trade in Dairy Products | World Trade Organization
However, the overriding concern for the future seems to be the capability to assure the quality and safety of food. The importance of consumer confidence in the dairy supply chain is ever more evident following one of the largest food safety crises in recent years which spiraled as a result of milk adulteration with melamine in China. The toxic industrial chemical melamine has been added to milk to make it appear higher in protein. A number of babies died and thousands fell ill after drinking melamine-contaminated milk formula. It could be expected that this incidence will irreversibly change dairy markets and the way the milk and dairy production process is monitored and tested. The share of milk and dairy products in consumers’ diets may suffer, so the dairy industry needs to remain proactive and innovative in order to maintain the image of a safe and healthy product. The substitution effect was evident in the recent melamine scare when Chinese consumers sought available alternatives, mainly soy milk. In fact, Starbucks in China announced that all milk used at its cafes in China will be soy-based for the near future. In fact, Starbucks in China announced after the incidence that all milk used at its cafes in China would be soya-based. Technological Progress Technology has been changing the dairy sector for decades, and only a true pessimist would say that the progress has arrived at the end of the road. Given the higher commodity price situation, more attention has been and can be expected to be paid to food production. It follows that private and public money flowing to research and development activities and agricultural extension services could push the technology frontier further. Productivity gains stimulated by increased automation of the production process, improved feed efficiency, improved health and longevity of cattle, and the ability to improve productivity via GM technology could be some of the alternatives. In the milk-processing sector, the availability of ultrafiltration technology has enabled the development of milk component-based markets for milk solids with increasingly broad applications. This trend is expected to continue. Similarly, the growth of demand for dairy products as ingredients in other food products (particularly in pizzas, hamburgers, sandwiches, etc.) will continue. The future will also see a myriad of new dairy-based products. Recent years have already witnessed product developments such as new functional foods; cosmeceutical, nutraceutical, and pharmaceutical products; and new beverages such as omega 3- and calcium-fortified milk. A promising recent development is also the introduction of a new lactose-free dairy drink produced by a special filtration process that removes half of the milk lactose.
Lactose-free milk could be an important factor, driving higher milk consumption, particularly in Asia, where more than half of the population is believed to have some form of lactose intolerance. Finally, in the context of consumer-driven food safety and health concerns, traceability becomes the norm, and this will require the adoption of new technologies and tests for the analysis of residues.
Conclusions In the context of the current global economic situation and the lack of progress in the Doha round negotiations, it is difficult to guesstimate when the final deal of the Doha round could be sealed. It could indeed be expected that the final modalities will impact future dairy markets. However, it is important to keep in mind that the Doha process is not about eliminating agricultural policies but about increasing transparency, fairness, and efficiency of agricultural trade. It follows that adjustment pressure, following the Doha round deal, on producers in developed countries that support domestic agriculture might not be excessive, although those domestic markets that have relatively high market price support measures in place will likely be affected more. But, the actual impact depends on the global market situation and the way countries organize future support to agriculture. Many support policies decoupled from production are already in place and one could expect further shifts toward more effective policies better targeted at specific objectives, possibly including disadvantaged producers or production zones, and delivery of social benefits related to environmental and regional concerns. In fact, good agricultural policies do not need to depend on the WTO negotiations. Moreover, even without a Doha deal it seems that it would become increasingly difficult for governments to continue domestic support based on trade barriers for the traditional dairy products in the face of the rapidly evolving trade in new dairy product and dairy ingredient markets, and globalization of the dairy markets in general. For example, the emergence of a sophisticated ultrafiltration process and expanding markets for milk ingredients have already diminished, to some extent, the importance of increasingly dated dairy support policies. Moreover, the process of globalization is crossing traditional trade barriers and is changing the structure of dairy markets, which have already started to be much more responsive to market signals and changing consumer preferences. Globalization of the dairy sector is set to continue, and international dairy companies will continue to penetrate the less developed markets to satisfy both local and growing export demand. The investments
Policy Schemes and Trade in Dairy Products | World Trade Organization
of multinational dairy processing firms will influence the development of new products and the transfer of technologies that improve market size and reach. The investments of multinational dairy processing firms will influence the development of new products and the transfer of technologies that improve market size and reach. These developments will however need to respect environmental considerations. It could be expected that increasingly important factors which are to influence dairy industry in the future are deterioration of natural grasslands, limited water resources and water pollution. The attention on food security and safety will persist. Safety of milk and dairy products could be expected to become an overriding requirement for producers and dairy supply chain in the future. A related issue for the future dairy sector is the ability of milk and dairy products to keep a good-and-safe image in a broader sense. The industry will need to remain proactive and innovative in order to maintain the share of milk and dairy products in consumers’ diets. Nevertheless, milk is a very unique product that contains very unique components, and it is difficult to see how the dairy industry would not be able to profit from this natural advantage. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: United States’ Agricultural System; Codex Alimentarius; Standards of Identity of Milk and Milk Products; Trade in Milk and Dairy Products, International
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Standards: Harmonized Systems; Trade in Milk and Dairy Products, International Standards: World Trade Organization.
References Busch L (2004) The Changing food system: From markets to network. Paper presented at the XI World Congress of the International Rural Sociological Association. Trondheim, Norway, July. Cox TL and Zhu Y (2004) Assessing world dairy markets and policy reforms: Implications for developing countries. In: Aksoy MA and Beghin JC (eds.) Global Agricultural Trade and Developing Countries., Washington, pp. 161–176. DC: World Bank. Langley S, Somwaru A, and Normile MA (2006) Trade liberalization in international dairy markets: Estimated impact. Economic Research Report Number 16. ERS, USDA. Neary JP (2004) Europe on the road to Doha: Towards a new global trade round? CESifo Economic Studies 50(2): 319–332. OECD (2002) Agriculture and Trade Liberalisation: Extending the Uruguay Round Agreement. Directorate for Food, Agriculture and Fisheries, Committee for Agriculture. Paris: OECD. OECD (2005) Dairy Policy Reform and Trade Liberalisation. Directorate for Food, Agriculture and Fisheries, Committee for Agriculture. Paris: OECD. OECD (2008) Role, Usage and Motivations for Contracting in Agriculture. Paris: OECD. OECD-FAO (2008) OECD-FAO Agricultural Outlook 2008–2017. Paris: OECD. Reardon T and Hopkins R (2006) The supermarket revolution in developing countries: Policies to address emerging tensions among supermarkets, suppliers, and traditional retailers. European Journal of Development Research 18: 4. WTO (2005) Doha work programme. Draft Ministerial Declaration. Ministerial Conference, Sixth Session. Hong Kong, China, 13–18 December, WTO. WTO (2008a) Chairperson’s Report on July 2008 Package Negotiations, with unofficial notes. http://www.wto.org/english/tratop_e/agric_e/ chair_report_11aug08_e.htm WTO (2008b) Revised draft modalities for agriculture. Committee on Agriculture, Special Session, TN/AG/W/4/Rev.3. 10 July.
PREBIOTICS
Contents Types Functions
Types T Sako and R Tanaka, Yakult Europe B.V., Almere, The Netherlands and Yakult Central Institute for Microbiological Research, Tokyo, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction The human gastrointestinal tract becomes inhabited by a huge number of microbes immediately after birth. It has been calculated that in adults this complex open ecosystem, or the intestinal microflora formed in the colon (cecum to proximal and distal colons to rectum), is composed of some 1014 bacteria of hundreds of different species. The microflora as a whole or individual microbes are likely to play pivotal roles in the development of normal gut functions and maturation of mucosal immune system, and in the prevention and/or stimulation of intestinal disorders. The composition and metabolic activity of the gut microflora are influenced by various environmental factors, namely diet, age, stress, health status, and medication. Among all, dietary carbohydrates are the predominant carbon and energy sources for the gut microbes, and hence affect the growth of individual bacterial species in the colon. It has been calculated that 20–60 g of dietary carbohydrates ingested escapes digestion by human digestive enzymes daily, and they become substrates for fermentation in the colon. Among these nonabsorbed carbohydrates, 5–35 g is resistant starch, 10–25 g is nonstarch polysaccharides, and 2–8 g is nondigestible oligosaccharides (for terminology, see below). The diversity and amounts of these carbohydrates influence the composition and metabolic activity of the colonic bacterial ecosystem, which in turn strongly affect human health. The term ‘prebiotics’ was introduced by Gibson and Roberfroid in 1995 to describe the ‘‘nondigestible food ingredients that beneficially affect the host health by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon’’. A characteristic underlying the
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prebiotic concept is to increase ‘indigenous’ beneficial bacteria in the gut by virtue of feeding specific substrates that are preferentially utilized by these bacteria, in contrast to that of ‘probiotics’, which are themselves beneficial bacteria and therefore should directly influence the composition and metabolism of the gut microflora. In the past two decades a substantial number of food ingredients that definitely or possibly exert prebiotic effects have been described. The vast majority of them so far are shortchain carbohydrates that are not absorbed or are poorly digested by human enzymes, and are often called nondigestible oligosaccharides (NDO). In addition, recent extensive studies have revealed that certain nondigestible polysaccharides, which are often referred to as dietary fiber, exert health benefits through being fermented by a limited number of colonic bacteria into short-chain fatty acids, and so are capable of being prebiotics. In this article, the current knowledge of prebiotics especially from a technological and biochemical point of view is summarized.
What Are Prebiotic Effects? The principal effect of prebiotics is to improve the balance of the gut microflora by increasing the numbers of beneficial bacteria and decreasing those of potentially harmful bacteria, as defined above. This is achieved by the preferential utilization of prebiotic carbohydrates by beneficial bacteria such as bifidobacteria and lactobacilli. As a consequence of the alteration of the gut microflora composition, the metabolic activity and the systemic effects of the gut microflora will influence the host health status. In general, toxin production, intestinal
Prebiotics | Types
putrefaction leading to production of harmful and carcinogenic substances, unbalanced immune response, (opportunistic) infection, and the overgrowth of harmful bacteria are suppressed, and the enterocyte activity, bowel movement, and the mucosal immune system are optimized. It is widely accepted that lactobacilli and bifidobacteria are typically beneficial for human health. Primary fermentation products of bifidobacteria and lactobacilli from dietary carbohydrates are acetic and lactic acids. However, the final colonic fermentation products from dietary carbohydrates are short-chain acids (SCA) (mainly acetic, propionic, and butyric), some other organic acids (lactic and succinic), and gases (H2, CO2, and CH4). The proportion of each organic acid in the cecal and fecal contents depends on the composition of the gut microflora and the amounts and forms of supplied carbohydrates. Main players of these diverse fermentation processes are bacteria of clostridia and Eubacterium clusters, which not only directly utilize dietary carbohydrates but also further ferment acetic acid and lactic acid to butyric acid and propionic acid, although the detailed characters of these bacterial groups are not well known yet. There would be some other prebiotic effects based on the production of SCFA and other organic acids, for instance, improvement of mineral absorption in the colon, activation of colonocytes, acidification of cecal and fecal contents, or improvement of lipid metabolism.
Classification and Terminology of Dietary Carbohydrates Carbohydrates are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on the number of monosaccharide units contained in them (which is often referred to as degree of polymerization or DP) (Table 1). Oligosaccharides are defined as carbohydrates with a DP from 2 to 10, according to the IUB–IUPAC nomenclature. However, some authorities recommend using the term disaccharides for those having two monosaccharide units (DP ¼ 2). In fact, most disaccharides fit into simple digestible sugars, while there are some disaccharides that resemble longer oligosaccharides in physiological and biochemical characteristics; for example, they are poorly digested and absorbed in the small intestine, but fermented thoroughly in the colon like a sort of nondigestible oligosaccharides, as will be described later. It is difficult to find chemical, structural, and physiological reasons to fix the definition for oligosaccharides. In this article, oligosaccharides with a DP from 2 to 10 that are not digested by mammalian digestive enzymes in the small intestine are defined as NDO.
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The sources of NDO are diverse. Some are isolated from natural origins (human milk oligosaccharides (HMO), soybean oligosaccharides (SOS), levan-type fructans, etc.) and some can be enzymatically or chemically produced from polysaccharides (maltooligosaccharides and isomaltooligosaccharides (for both, -glucooligosaccharides), oligofructose, xylooligosaccharides, chitin oligosaccharides, etc.) or from mono- and disaccharides (galactooligosaccharides (GOS), fructooligosaccharides (FOS), lactosucrose, gentiooligosaccharides, etc.). Polysaccharides occur naturally and have more complex structures and lengths than oligosaccharides, and can be classified into starch (-glucans) and nonstarch polysaccharides (NSP) (Table 1). In both classes, there are soluble and insoluble polysaccharides. Of the carbohydrates in foods 80–90% are starch consisting of -1,4-linked amylose and -1,4- and -1,6-linked amylopectin, which are both principally hydrolyzed by human -amylase. However, the physical structure and DP of starch are diverse, and thus not all starch molecules consumed are hydrolyzed by human digestive enzymes and absorbed in the upper small intestine. The undigested starch entering the colon is called resistant starch (RS) and provides colonic bacteria with a carbon and energy source. On the other hand, NSP are the sum of non--glucans and -glycans mainly found in plant cell walls such as cellulose, hemicellulose, xylan, arabinoxylan, mannan, pectin, and lignin. Some NSP are intracellular polysaccharides of plant cells such as gums, mucilage, and inulin. All these NSP are poorly digested and absorbed in the small intestine, and hence enter the colon undigested and are readily fermented by colonic bacteria to various extents. Different bacterial groups consume different polysaccharides; bacteroides mainly utilize amylose, amylopectin, and pullulan, which are all -glucan-type RS, while various anaerobic clostridial species utilize NSP. The term ‘dietary fiber’ was originally defined by Trowell, in 1972, as remnants of plant cells remaining after digestion in the mammalian gastrointestinal tract. Nowadays a number of other indigestible carbohydrates of plant and animal origin have been proposed and considered for inclusion in the group of dietary fiber. Hence it is most likely that dietary fiber will be defined as food carbohydrate polymers that are not hydrolyzed by the mammalian digestive enzymes in the small intestine and includes NSP, RS, and NDO. Among these, NDO occupy the most important position in prebiotic substances as they have been extensively studied and shown to be specific substrates for a limited number of colonic bacteria, especially bifidobacteria and/ or lactobacilli, in colonic fermentation, and are more readily assimilated in the colon than NSP and RS. Therefore, NDO’s exertion of the prebiotic effects could be quicker and more tangible than others’ after they enter
Table 1 Classification of dietary carbohydrates Carbohydrate classes (DP)
Subclasses
Examples
Fate in the gastrointestinal tract
Monosaccharides (1)
Sugar
Glucose, fructose, galactose
Disaccharides (2)
Sugar alcohol Digestible sugar
Sorbitol, xylitol, mannitol Sucrose, maltose, trehalose, (lactose)a
Nondigestible disaccharides
(Lactose),a lactulose
Sugar alcohol
Maltitol, lactitol
-Glucans
Maltooligosaccharides (isomaltooligosaccharides)b
Nondigestible oligosaccharides
Soybean oligosaccharides Galactooligosaccharides Fructooligosaccharides Fucosyllactose Sialyllactose Lacto-N-tetraose, etc. Amylose, amylopectin, pullulan
Absorbed in the small intestine Glucose gives rapid glycemic response Absorbed in the small intestine Absorbed in the small intestine Digestible by endogenous hydrolyzing enzymes Rapid glycemic response Not absorbed Nondigestible, but fermented in the large intestine Poorly digested and absorbed in the small intestine Partly or fully fermented in the large intestine Digestible but partly undigested in the small intestine and give rapid glycemic response Nondigestible Fermented in the large intestine No glycemic response Nondigestible Partly fermented in the large intestine
Oligosaccharides (2–10)
Human milk oligosaccharides
Polysaccharides (>10)
Starch (-glucans) Resistant starch (-glucans) Nonstarch polysaccharides ( -glycans)
a
Cellulose, hemicellulose, inulin, guar gum
Lactose may be both a digestible and nondigestible sugar. Isomaltooligosaccharides are less susceptible to digestive enzymes in the small intestine.
b
Digested and absorbed in the small intestine Rapid glycemic response Digestible but undigested in the small intestine Fermented in the large intestine Nondigestible Partly fermented in the large intestine
Prebiotics | Types
Lactose
the colon. The other reasons are that they are easy to handle in food processing and have organoleptic characteristics as mild sweeteners, both of which are important causes for NDO to be widely spread as commercial products.
Lactose (4- -D-galactopyranosyl-D-glucopyranose or -D-Galp-(1 ! 4)-D-Glcp or Gal 1-4Glc) is the primary sugar of mammalian milk. Human milk contains 7% lactose, and cow’s milk 4.8%. Even though lactose is the major carbon source for suckling infants, hydrolysis of lactose is rather a rate-limiting step. In addition, the lactase ( -galactosidase) activity in the small intestine gradually declines as an infant grows: According to a survey of Pima Indians in the United States, lactose malabsorption was seen in 40% by age 3–4 years, 71% by age 4–5 years, and almost 100% by age 8 years. The onset and degree of lactase deficiency are not homogenous among individuals and races. While most Caucasians in Northern European countries, Australia and New Zealand, and North America retain lactase activity, most Africans, Asians, and Native Americans are nonpersistent.
Disaccharides A certain class of disaccharides characterized with a -linkage between the two units could have a role as prebiotics. This class of disaccharides includes lactose, lactulose, lactitol, and several by-products from various oligosaccharide production processes (Figure 1(a)). These disaccharides are poorly or very slowly hydrolyzed by human digestive enzymes. Human studies, as well as in vitro growth analyses, published so far have shown their possible prebiotic effect particularly on stool habits. (a)
O
HOH2C CH2OH
CH2OH
O
O
HO
O
OH
CH2OH
O
O
CH
O
OH
OH
OH
OH
OH
Lactose
HCOH
CH2OH
O
O
O
OH
CH2OH
O OH CH2
CH2 O
O
H2C
O O
OH CH2OH
HO
O
O
HO
CH2OH
OH
O
OH HO
OH
n (n = 1–3)
Isomaltooligosaccharides
CH2OH OH
Soybean oligosaccharides
O
OH
~ OH
OH
O
OH
~ OH
HO OH
HO
~ OH
CH2OH
CH2OH
O
O
O
O
O
HO
HO OH
HO
Stachyose
O OH
O O
OH Raffinose
OH
Fructooligosaccharides
O
CH2OH O
O OH
OH
CH2
OH
O OH
OH
CH2
CH2
CH2 O
OH
HO OH n (n = 0–4)
O
OH
n (n = 0–7) CH2OH
Gentiooligosaccharides
O
OH
O OH
~ OH
OH
HO
CH2OH
~ OH
OH
Galactooligosaccharides (β1,4-type)
OH m OH (m = 0, 1)
O
OH OH
O
OH
CH2OH
O
HO
HO
OH
HO
CH2OH
OH
O
O
OH n (n = 0–5)
CH2OH O
OH
OH
O
CH2OH O
CH2OH
O
O
OH
HO
O
H2C
O
CH2OH
CH2OH O
O
Lactosucrose
CH2OH
HCO
Maltitol
OH
CH2OH
OH
OH
OH
CH2OH
Lactitol
HO CH2OH
CH
O
HO
CH2OH
Lactulose
(b)
HO
HCOH
OH
HCOH HCO
OH
CH2OH
CH2OH
HCOH
O
HO
OH
O
HO
~ OH
OH
CH2OH
CH2OH
HO
CH2OH
357
OH
O
OH
CH2OH O
O
OH
HO OH
OH n (n = 0–5)
Xylooligosaccharides
OH
H3COCNH
H3COCNH
n H3COCNH (n = 0–4)
Chitin oligosaccharides
Figure 1 Chemical structure of major prebiotic disaccharides (a) and oligosaccharides (b). Vertical bars without any formula at the tips of angles indicate a hydroxyl group. Hydrogen atoms on the main frames are not indicated.
358 Prebiotics | Types
Therefore, a substantial number of people are lactose malabsorbers. In these populations lactose behaves like nondigestible carbohydrates especially in lactose maldigesters. While the adverse effects of lactose are extensively studied, few reports concerning the effect on gut microflora are available. Although lactose is utilized preferentially by bifidobacteria and lactobacilli in in vitro fermentation, additional human studies are still needed to elucidate its prebiotic effect. Lactulose Lactulose (Gal 1-4Fru) is a synthetic disaccharide produced from lactose by chemical isomerization under alkaline conditions in the presence of sodium hydroxide and boric acid. Lactulose also naturally appears in heattreated cow’s and human milks. The generation of lactulose during lactose preparation was first reported in 1930. In the history of searching growth-promoting factors for bifidobacteria (bifidus factors) in human milk, Petuely described lactulose as a bifidus factor in 1957. Since then there are a large number of reports published about the effects of lactulose on the gut microflora, stool habits, SCA production, fecal enzyme activity, gut physiology, and so on. Lactulose is not hydrolyzed by human digestive enzymes and is preferentially utilized by bifidobacteria and lactobacilli as well as by bacteroides and some strains of clostridia and Gram-positive cocci inhabiting the human gut. According to these extensive studies, lactulose is now widely used not only as a food additive but also as a drug for constipation, hepatic encephalopathy, and Salmonella infection worldwide.
situations and is also used as a drug for treatment of chronic constipation and hepatic encephalopathy, although it may show a colonic fermentation profile different from that of lactulose.
Oligosaccharides The main and the most important constituents of prebiotics are NDO. Research and application of NDO have attracted much attention since the 1990s as the importance and the role of the gut microflora in human health are becoming more and more documented. As an intrinsic characteristic of NDO, they must escape hydrolysis by human digestive enzymes and be fermented by a limited number of colonic bacteria. Human pancreatic and intestinal digestive enzymes include those hydrolyzing the -glycosidic bonds of various monosaccharide moieties like glucose, galactose, and fructose, except for lactase ( -galactosidase) (EC 3.2.1.108), which mainly hydrolyzes the -linkage of lactose, whereas many colonic bacteria produce a variety of carbohydrate-hydrolyzing enzymes that act on oligo- and polysaccharides with -glycosidic bonds. Therefore, the principal NDO are -glycans (Table 2 and Figure 1(b)). The calorific values of most NDO are about half of those of digestible sugars, namely 2 kcal g1, which are calculated from energy values available by utilization of organic acids produced in the colon after fermentation. Major NDO that are commercially available or of physiological importance are listed in Table 2.
Sugar Alcohol (Polyol) Sugar alcohols are derivatives of mono- and disaccharides obtained by reducing a hexose moiety. Major sugar alcohols available and of commercial interest are the monosaccharide polyols sorbitol, mannitol, and xylitol, and the disaccharide polyols lactitol (Gal 1-4-sorbitol) and maltitol (Glc1-4-sorbitol). In recent years, most of these sugar alcohols have been developed and widely applied for commercial use as noncariogenic sweeteners. They all have less sweetness than sucrose and lower calorific values than normal sugars. While the monosaccharide polyols are all efficiently absorbed from the small intestine, the digestion and thus the absorption of disaccharide polyols, namely, lactitol and maltitol, are much less than those of their parent disaccharides, lactose and maltose, respectively. The average rates of hydrolysis of lactitol and maltitol in human small intestine were shown to be 1.5 and 10% of those of lactose and maltose, respectively. These disaccharide polyols are good substrates for fermentation with colonic bacteria. Lactitol exerts quite similar effects to lactulose in clinical
Production of Nondigestible Oligosaccharides There are three ways to produce NDO: partial hydrolysis of polysaccharides, synthesis by transglycosylation from mono- and disaccharides, and extraction of naturally occurring oligosaccharides. Figure 2 shows the fundamental processes of industrial production of the former two types of NDO. In the industrial transglycosylation process, a high concentration of a substrate solution of mono- or disaccharides at more than 40–50% is used, and more than 50 up to 70% of the crude products are the target oligosaccharides after enzyme reaction. On the other hand, when polysaccharides are used as substrates, oligosaccharides are obtained either by direct endoglycosidase treatment (fructooligosaccharides, xylooligosaccharides, chitin oligosaccharides) or by liquefaction with complete glycolysis followed by transglycosylation (isomaltooligosaccharides, pannose oligomers). The substrates and enzymes used in the production process are indicated in Table 2.
Table 2 Nondigestible oligosaccharides and their structural features Name of NDO
Structures
Sources
Methods of preparation
Lactulose Galactooligosaccharides
-D-Gal-(1 ! 4)-D-Fru [ -D-Gal-(1 ! 4)]n-D-Glc (n ¼ 2 to 6) or[ -D-Gal-(1 ! 6)]n- -D-Gal-(1 ! 4)-DGlc (n ¼ 2 to 5) -D-Glc-[(1 ! 2)- -D-Fru]n (n ¼ 2–4)
Lactose Lactose
Inulin
Raffinose Soybean oligosaccharides Xylooligosaccharides
-D-Glc-(1 $ 2)- -D-Fru-[(1 ! 2)- -D-Fru]n (n ¼ 1 to 8)D-Fru-[(1 ! 2)- -DFru]n (n ¼ 2 to 9) -D-Gal-(1 ! 6)--D-Glc-(1 $ 2)- -D-Fru [-D-Gal-(1 ! 6)]n--D-Glc-(1 $ 2)- -D-Fru (n ¼ 1, 2) -D-Xyl-[(1 ! 4)-D-Xyl]n (n ¼ 1 to 6)
Human milk oligosaccharides Chitin oligosaccharides
-L-Fuc-(1 ! 2)- -D-Gal-(1 ! 4)-D-Glc, -NeuAc-(2 ! 3)- -D-Gal-(1 ! 4)-DGlc, -D-Gal- -GlcNAc-(1 ! 3)- -D-Gal-(1 ! 4)-D-Glc, etc. -D-GlcNAc-[(1 ! 4)-D-GlcNAc]n (n ¼ 1 to 5)
Isomerization in alkali Enzymatic transgalactosylation with galactosidase (EC 3.2.1.23) Enzymatic transfructosylation with -fructosylfuranosidase (EC 3.2.1.26) Partial enzymatic hydrolysis with inulinase (EC 3.2.1.7) Natural product Extraction Partial enzymatic hydrolysis with xylanase (EC 3.2.1.8) Natural products
Lactosucrose
-D-Gal-(1 ! 4)--D-Glc-(1 $ 2)- -D-Fru
Isomaltooligosaccharides (-glucooligosaccharides)
-D-Glc-[(1 ! 6)-D-Glc]n (n ¼ 1 to 3)
Fructooligosaccharides Inulin-type fructans
Gal, galactose; Fru, fructose; Glc, glucose; Xyl, xylose; GlcNAc, N-acetylglucosamine; Fuc, fucose; NeuAc, sialic acid.
Sucrose
Sugar beet Soybean extract Xylan Human milk Chitin Lactose, sucrose Starch
Enzymatic hydrolysis with chitinase (EC 3.2.1.14) or acid hydrolysis Enzymatic transfructosylation with -fructosyltransferase (EC 2.4.1.9) Enzymatic hydrolysis followed by enzymatic transglucosylation with transglucosidase (EC 3.2.1.70)
360 Prebiotics | Types (a)
(b) Substrate (disaccharides or monosaccharides)
Substrate (polysaccharides)
Transglycosylation (batch reactor or immobilized enzyme reactor)
Solubilization and fragmentation (hydrolysis, transglycosylation, endoglycosidation)
Decoloration (activated charcoal filter)
Decoloration (activated charcoal filter)
Demineralization (ion-exchange chromatography)
Demineralization (ion-exchange chromatography)
Sterilization (filtration)
Sterilization (filtration)
Purification (ion-exchange chromatography)
Concentration (ultrafiltration)
Drying (spray dry)
Drying (spray dry)
Syrup-type NDO
Powder-type NDO
Concentration (ultrafiltration)
Drying (spray dry)
Syrup-type NDO
Powder-type NDO
Pure NDO
Purification (ion-exchange chromatography) Drying (spray dry)
Pure NDO
Figure 2 Flowcharts of the synthesis of NDO by transglycosylation using mono- and disaccharides (a) or by hydrolysis/fragmentation of polysaccharides (b).
Galactooligosaccharides GOS are industrially produced from lactose by enzymatic transgalactosylation. -Galactosidase (EC 3.2.1.23) of various origins such as Bacillus circulans, Aspergillus oryzae, and Cryptococcus laurentii is used for the industrial production of GOS. The enzymes from Bifidobacterium strains also have this transgalactosylation activity. The enzyme reaction basically proceeds by the addition of the galactose moiety to the nonreducing end of lactose and transgalactosylated oligomers, resulting in the production of tri-, tetra-, and pentasaccharides, traces of multioligosaccharides, and some disaccharide by-products with different -glycosidic bonds. The products have mainly 1,4- or 1,6-glycosidic bonds between the added galactose moieties (DP from 3 to 6) and a glucose unit at the reducing end of the molecule. GOS are physically stable in various conditions; they were not degraded at 160 C at a neutral pH or at 120 C at pH 3 for 10 min. GOS are not digested by human digestive enzymes at all, but are readily fermented in the colon. From extensive studies of the utilization of GOS, it has been revealed that Bifidobacterium and Bacteroides strains predominantly grow utilizing GOS as the sole carbon source. The prebiotic effect of GOS was first demonstrated by the pioneering work of Tanaka and colleagues in 1983, which showed an increase in indigenous bifidobacteria and a decrease in Bacteroidaceae after a daily intake of 10 g GOS for 2 weeks, in a human study. This was further confirmed by additional human studies. The potential of GOS to
improve defecation in subjects with a tendency toward constipation, to reduce harmful enzyme activities, to reduce the incidence of cancer, to stimulate bone mineralization, and to reduce the production of secondary bile acids in feces has been documented in human and/or animal studies.
Fructooligosaccharides There are two different ways to produce FOS: one is to partially hydrolyze fructose polymers of plant origin, and the other is to transfer the fructose moiety onto sucrose. Fructose polymers occur naturally in a number of vegetables and fruits as -2,1-linked inulin or -2,6-linked levan. Inulin is mainly used for the production of FOS having a DP of 2 to 10 by partial enzymatic hydrolysis using endoinulinase. This type of FOS, sometimes called inulin-type oligofructose, is a mixture of Glc1-2 Fru[12 Fru]n (n ¼ 1 to 8) and Fru[1-2 Fru]n (n ¼ 1 to 9). FOS are also industrially produced from sucrose by enzymatic transfructosylation using Aspergillus niger -fructosylfuranosidase (EC 3.2.1.26). This type of FOS has a DP of 3–5 including an -1,2-linked glucose residue at the terminal of each molecule, and thus is nonreducing. The stability of FOS at neutral pH is as high as that of sucrose, and FOS do not degrade up to 150 C. However, FOS are less stable in acidic conditions; when boiled at pH 3, most FOS molecules degrade into smaller molecules within 15 min.
Table 3 Utilization of NDO by various intestinal bacteria
Bifidobacterium adolescentis Bifidobacterium bifidum Bifidobacterium breve Bifidobacterium infantis Bifidobacterium longum Lactobacillus acidophilus Lactobacillus casei Lactobacillus gasseri Lactobacillus salivarius Bacteroides distasonis Bacteroides fragilis Bacteroides ovatus Bacteroides thetaiotaomicron Bacteroides vulgatus Mitsuokella multiacidus Rikenella microfusus Megamonas hypermegas Clostridium butyricum Clostridium difficile Clostridium innocuum Clostridium perfringens Clostridium ramosum Eubacterium aerofaciens Eubacterium limosum Peptostreptococcus anaerobius Peptostreptococcus prevotii Peptostreptococcus productus Propionibacterium acnes Fusobacterium varium Veillonella alcarescens ssp. dispar Megaphaera elsdenii Enterococcus fecalis ssp. fecalis Enterococcus faecium Escherichia coli
Glucose
Lactose
Lactulose
GOS
FOS
SOSa
XOS
COS
Lactosucrose
þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ
þþþ þþþ þþþ þþþ þþþ þþþ þþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþ þþþ þþ þþþ þþþ þþþ þ þþþ þþþ þþ þþ
þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþ þþþ þþ þþþ þþ þþþ þþþ þ þþ þþþ þþþ þþ þ þþ þþ þ þþþ
þþþ þþþ þþþ þþþ þþþ þþ þþþ þþþ
þþþ þþ þþþ þþþ þþ
þþ þþþ þþþ þþþ þþþ þ þ þþ þþ þþþ þ þþþ þ þþ þþþ þ þ þþ þþ þþþ þþþ þ þþ þ þþ þ þ þþþ þþþ þ þþ þþ
þþþ þ þþþ þþ þþþ
þþ þþ þþ þ þþ þ þþ
þþþ þþþ þþþ þþþ
þ þþ þ þ þþ þþ þ
þþ
þþþ þþþ
þþþ þþþ
þþþ þ þþþ þþþ þþþ þþþ
þþþ
þþþ þþþ
þ þþ
þþ þþþ
þþ
a The data include raffinose. Indication for the growth of bacteria: þþþ, same as that on glucose; þþ, less than that on glucose; þ, slight growth; , no growth; no symbol, no data available. Adapted from Hayakawa Y and Committee for New Materials of Foods (eds.) (1998) New Knowledge of Oligosaccharides. Tokyo (in Japanese): Food Chem. Newspaper Co Ltd.
362 Prebiotics | Types
Bifidogenic effect and other prebiotic effects of FOS such as lowering pH in the colon, reducing potentially harmful bacteria, reducing putrefactive substances, and improving stool habit have been demonstrated in human studies. In addition, beneficial effects of FOS on lipid metabolism and mineral absorption have been suggested in animal studies. While the effect on calcium absorption was further confirmed in several human studies, evidence of beneficial effects on lipid metabolism in humans is not conclusive.
Raffinose, stachyose, and soybean oligosaccharides SOS can be readily isolated from soybean extract and constitute raffinose (Gal1-6Glc1-2 Fru) and stachyose (Gal1-6-raffinose) as oligosaccharides, as well as sucrose, glucose, and fructose. The contents of raffinose and stachyose in SOS are usually 8 and 24%, respectively, whereas the content of sucrose plus glucose and fructose is 55%. Pure raffinose is also commercially produced from beet syrup. Raffinose and stachyose (Figure 1(b)) are not digested in the human upper intestine, but are readily fermented by colonic bacteria, and so are NDO. Most strains of Bifidobacterium species except B. bifidum can grow in a medium containing SOS, raffinose, or stachyose as the sole carbon source, since they usually express -galactosidase activity, which can hydrolyze SOS. The bifidogenic effect of SOS and raffinose has been shown in human studies, where the minimum effective dose could be as low as 0.5 g oligosaccharides equivalent day1. In addition, SOS have the potential to reduce fecal levels of ammonia, p-cresol, and indole, to reduce harmful enzyme activities, and to alleviate constipation at the dose of 1 g oligosaccharides equivalent day1.
Xylooligosaccharides Xylooligosaccharides (XOS) are -1,4-linked xylose oligomers with a DP of 3 to 8, and industrially produced exclusively in Japan from xylan by partial enzymatic hydrolysis using endoxylanase (EC 3.2.1.8). Xylan, a sort of hemicellulose, is usually found in plant cell walls in conjunction with cellulose and pectin. For the commercial production of XOS, plant materials containing large amounts of xylan such as bagasse and cottonseeds are used. XOS is fermented by limited types of colonic bacteria such as Bifidobacterium spp., Lactobacillus spp., Bacteroides vulgatus, and Peptostreptococcus products. Bifidogenic effect in vivo has been shown in a couple of human studies where the effective minimal dose of XOS was as low as 0.4 g day1. Alleviation of constipation and stimulation of
mineral absorption were also documented in human and rat studies, respectively. Chitin Oligosaccharides Chitin oligosaccharides (COS) are N-acetylglucosamine (GlcNAc) oligomers (DP ¼ 2–6) with -1,4-linkages, and are produced from chitin derived from crabs and shrimps by partial acid hydrolysis in a hydrochloride solution. COS can be produced by enzymatic hydrolysis of chitin using bacterial chitinase (EC 3.2.1.14) as well. In addition to the beneficial effects on the gut microflora, attention has been paid to COS due to their immunomodulatory and antimicrobial activities, although the mechanisms behind these effects are mostly obscure. Human Milk Oligosaccharides A French pediatrician, Tissier, observed more than a century ago that bifidobacteria were predominant microbes in the feces of breast-fed infants but not of formula-fed infants, and had an idea that this bifidus flora played a role in the reduced incidence of infection in breast-fed infants. A number of possible substances as bifidogenic factors in human milk have been proposed and utilized to maintain the bifidus flora in formula-fed infants since then. Examples of substances that had been tried include lactose, N-acetylglucosamine-containing oligosaccharides, whey proteins, and vitamins, none of which, however, provided any evidence of modulation of the host gut microflora so far. The composition of HMO is complex. A variety of neutral and acidic oligosaccharides are found in human milk and colostrum. Although the major carbohydrate component of human milk is lactose, the total HMO levels reach up to 20% of the total carbohydrates, or over 12 g l1 in mature milk and 22 g l1 in colostrum, depending on individuals and the stages when the milk/ colostrum is collected. The core carbohydrates in HMO are lactose and lacto-N-tetraose (Gal 1-3GlcNAc 13Gal 1-4Glu), which are usually fucosylated and/or sialylated at nonreducing ends and other sites. Genomic and molecular biology studies have revealed that strains of Bifidobacterium longum ssp. longum, B. longum ssp. infantis, B. bifidum, and B. breve have various combinations of genes coding for enzymes responsible for the utilization of HMO, while HMO are not digested and absorbed in human small intestine. Therefore, HMO are most likely to be the bifidogenic factor in human milk. A certain group of HMO share the structural motifs with the cell surface glycoconjugates (glycoproteins or glycolipids) and mucins to which pathogens adhere at an initial step of infection. Thus, HMO could also be important as absorbers of pathogens to prevent infection during breast-feeding.
Prebiotics | Types
A practical method to produce lacto-N-biose, one of the active bifidobacteria-specific carbon sources derived from lacto-N-tetraose, from sucrose and N-acetylglucosamine with the enzymes sucrose phosphorylase (EC 2.4.1.7), UDP-glucose-hexose-1-phosphate uridylyltransferase (EC 2.7.7.12), UDP-glucose 4-epimerase (EC 5.1.3.2), and lacto-N-biose phosphorylase (EC 2.4.1.211) in large quantities has been established. However, it is still to be confirmed what components in HMO are and to what extent the HMO are responsible for the predominant growth of bifidobacteria in breast-fed infants. Other Oligosaccharides Other commercially available oligosaccharides are maltooligosaccharides (-1,4-linked D-glucose oligomers) and isomaltooligosaccharides (-1,6-linked D-glucose oligomers), both of which are often called -glucooligosaccharides as well, palatinose oligomers (oligomers of 2–4 palatinose (Glc1-6Fru) units), -glucosylsucrose (coupling sugar), lactosucrose, nigerooligosaccharides (-1,4linked D-glucose oligomers with an -1,3-linked D-glucose at the nonreducing end), gentiooligosaccharides ( -1,6linked D-glucose oligomers), chitosanoligosaccharides ( -1,4-linked D-glucosamine oligomers), and so on. Although they have not been necessarily intended to be used as prebiotic food additives, but rather to be used as alternative sweeteners with low calorific values and a low sweetness, evidence is accumulating that some of them have bifidogenic activity. In addition, oligosaccharide fractions obtained from partially hydrolyzed NSP such as guar gum, acacia gum, and wheat bran are possible prebiotic agents.
Polysaccharides Recent studies on dietary polysaccharides have revealed that a variety of dietary polysaccharides have physiological roles, which include significant fermentability by colonic bacteria leading to the production of SCA, influence on colonic microflora, stimulation of mineral absorption, and so on. While numerous studies have shown an increase in SCA production in the colon after the ingestion of RS, NSP, or even starch polysaccharides, an increasing number of studies have shown the effect of dietary polysaccharides on the gut microflora and other physiological parameters in humans or animals. In this section some examples of these polysaccharides are described. Fructans Fructan is the general name of soluble polysaccharides in which one or more fructosyl–fructose links constitute the
363
majority of glycosidic linkages. Two types of fructans have been identified: one is inulin, which is mainly of plant origin and has a 2,1-linkage between fructosyl residues, and the other is levan, which is mainly produced by fungi and bacteria and has a 2,6-linkage. Both types of fructan are neither digested by hydrolases of human origin nor absorbed in the intestines. Inulin has been manufactured, and thus has been studied extensively, and is of industrial importance. The biosynthesis of inulin in plant cells involves two enzymes: sucrose-sucrose fructosyltransferase (EC 2.4.1.99) leading to the formation of 1-kestose (Glc1-2 Fru1-2 Fru) followed by chain elongation by fructan-fructan fructosyltransferase (EC 2.4.1.100) leading to the formation of inulin ( -D-fructofranan). A number of plants contain fructans as storage carbohydrates, some of which we eat as vegetables and fruits; examples are onion, garlic, asparagus, artichoke, chicory, and bananas. Among all, the root of chicory and the tuber of Jerusalem artichoke are the exclusive, if not the only, materials utilized for the industrial production of inulin because of the simplicity of extraction and purification. While native chicory inulin has a DP of 3–70 (average, 35), native inulin preparation from Jerusalem artichoke has a DP of 2 (sucrose) to 15 (average, 7). Inulin shows physiological properties as dietary carbohydrates similarly to the shorter FOS as evidenced in a number of studies published so far. Inulin has a bifidogenic effect like that of FOS, although inulin itself is not fermented by bifidobacteria in in vitro cultivation. This could be because the natural inulin preparation contains shorter oligomers like FOS in addition to longer polymers or because the fructosyl–fructose linkage in polymers may be labile in acidic conditions in the stomach or be digested to oligomers by other colonic bacteria, thereby being preferentially utilized by bifidobacteria. Its bifidogenic effect and fecal bulking with increased water content have been observed in human studies as well as in those using human fecal batch cultures or pure bacterial cultures. Other preliminary physiological effects of fructans reported so far are improved bowel habit, reduced putrefactive fermentation in the large intestine, improved calcium and magnesium absorption, and reduced total serum lipids and cholesterol. All these predictive health effects still await further confirmation in well-designed human trials. Resistant starch RS is a generic term for starches that escape hydrolysis by human digestive enzymes and absorption in the upper gastrointestinal tract. Starches are storage carbohydrates of plant cells consisting of linear 1,4-D-glucan chains (amylose) and those having some additional 1,6-linkages (amylopectin). During food processing, extensive
364 Prebiotics | Types
treatment of starches leads to breakages and conformational changes of starches to various forms, depending on the source and due the amylose-to-amylopectin ratio, resulting in the generation of retrograded starch with a crystalline structure. In addition, there is another type of RS that just escapes digestion in the small intestine due to its physical structure and due to other materials surrounding the starch. Englyst and colleagues, in 1992, classified RS into three groups: retrograded starch, physically indigestible starch, and RS granules. The bifidogenic effect of RS was first suggested by a feeding study on rats, followed by synbiotic (both probiotic and prebiotic) application to pigs, in which concurrent feeding of high-amylose maize starch and bifidobacteria resulted in higher fecal excretion of bifidobacteria. However, this effect needs to be confirmed by human studies. Other polysaccharides It has been reported that germinated barley foodstuff (GBF), which contains low-lignified hemicellulose and cellulose, has the ability to increase the number of bifidobacteria in the gut microflora and to produce more butyrate in the colonic contents. This could be explained as the production of butyrate by the coordinated action of bifidobacteria and Eubacterium, because the batch culture with both B. longum and Eubacterium limosum strains in a medium with GBF as the sole carbon source resulted in the accumulation of butyrate in the medium, whereas no or little butyrate was detected in the single cultures. This indicates that cellulose and hemicellulose, which cousititute a major part of NSP, may have the bifidogenic effect through an indirect supply of fermentable oligosaccharides for bifidobacteria, which are generated by partial breakage of the polysaccharides by Eubacterium. As such, bifidogenic and/or prebiotic effects of various indigestible polysaccharides could be substantiated in the future, as the research in this field will proceed.
Conclusions and Prospects After establishment of the definition of prebiotics in conjunction with that of probiotics, scientific research on food components and additives that influence the composition and function of human gut microflora in health and disease has been accelerated. While the ‘bifidogenic’ effect is recognized as a fundamental for prebiotics, other effects of oligo- and polysaccharides on the host health have been described. However, as it has been defined and revised later, the term ‘prebiotics’ should be used for the food components that have the ability to change the
composition and/or activity of the intestinal microflora to healthier states. Nowadays more than 10 different di- and oligosaccharides are considered as prebiotic agents due to their bifidogenic effect, and the number is still increasing as research and development on dietary carbohydrates proceeds. In addition, the health benefits of prebiotics or dietary carbohydrates are extended wider than previously expected. This is typically explained by the effect on mineral absorption, which may be attributed to the increased production of SCA or to the acidification of the intestinal contents, although the precise mechanism underlying the effect is still to be confirmed. However, there are substantial reports that also describe the stimulating effect of dietary polysaccharides (dietary fiber) on mineral absorption. As such, while a number of different prebiotics with health benefits have been developed, which are composed of a variety of monosaccharide units, with different linkages and lengths, and have different physicochemical properties, the mechanism of action and the outcome of the effects could be similar to each other’s. In this respect, we may need some common biomarkers and analysis procedures with which sound scientific evaluation of each prebiotic agent can be made. See also: Prebiotics: Functions.
Further Reading Cummings JH and Englyst HN (1995) Gastrointestinal effects of food carbohydrates. The American Journal of Clinical Nutrition 75: 733–747. Cummings JH, Roberfroid MB, Andersson H, et al. (1997) A new look at dietary carbohydrates: Chemistry, physiology and health. European Journal of Clinical Nutrition 51: 417–423. Englyst HN, Kingman SM, and Cummings JH (1992) Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition 46: S33–S50. Gibson GR and Roberfroid MB (1995) Dietary modulation of the human colonic microflora: Introducing the concept of prebiotics. The Journal of Nutrition 125: 1401–1412. Grizard D and Barthomeuf C (1999) Non-digestible oligosaccharides used as prebiotic agents: Mode of production and beneficial effects on animal and human health. Reproduction, Nutrition, Development 39: 563–588. Kunz C, Rudloff S, Baier W, Klein N, and Strobel S (2000) Oligosaccharides in human milk: Structural, functional, and metabolic aspects. Annual Review of Nutrition 20: 699–722. Macfarlane GT and Cummings JH (1991) The colonic flora, fermentation and large bowel digestive function. In: Phillips SF, Pemberton JH, and Shorter RG (eds.) The Large Intestine: Physiology, Pathophysiology and Disease, pp. 51–92. New York: Raven Press. Roberfroid MB (2007) Prebiotics: The concept revisited. The Journal of Nutrition 137: 830S–837S. Roberfroid MB and Delzenne NM (1998) Dietary fructans. Annual Review of Nutrition 18: 117–143. Sako T, Matsumoto K, and Tanaka R (1999) Recent progress on research and applications of non-digestible galactooligosaccharides. International Dairy Journal 9: 69–80. Voragen AGJ (1998) Technological aspects of functional food-related carbohydrates. Trends in Food Science & Technology 9: 328–335.
Functions T Sako and R Tanaka, Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction At the end of the nineteenth century, H. Tissier discovered a huge number of specific bacteria, bifidobacteria, in the feces of breast-fed infants. It was believed after his discovery and from the subsequent studies that the bifidobacteria-dominated microflora, called ‘bifidus flora’, played an important role in the reduction of infectious diseases in breast-fed infants. In the same line of evidence E. Metchnikoff speculated in his book The Prolongation of Life published in 1907 that fermented milk with lactic acid-producing bacteria could have a role in keeping the intestines healthy, thus leading to longevity. In addition, there was accumulating evidence indicating that the healthy gut microflora helps the animal to resist infections, which was hence called ‘colonization resistance’ or ‘competitive exclusion’. All these observations in conjunction with practical applications of certain bacteria to treat infections in humans and animals generated an idea that certain beneficial bacteria can modulate the gut microflora to maintain a healthy balance of the flora, thus relieving the adverse effects of disturbed gut microflora and keeping the host animal healthy. R. Fuller proposed in 1989 to call these beneficial bacteria ‘probiotics’, and lactic acid-producing bacteria, namely, lactobacilli and bifidobacteria, have been recognized so far as typical probiotics. Considering the determinants of the composition of the gut microflora, in turn, dietary components of our daily life strongly affect the growth and metabolism of the gut microbes; especially, dietary carbohydrates are the major energy and carbon source for the bacteria inhabiting the colon. Although the colonic bacteria as a whole have glycolytic activities against a variety of carbohydrates consisting of different monosaccharide units with different linkages and different lengths, the individual bacterial species/strains have a different set of enzymes with different substrate specificity. Therefore, the diversity of dietary carbohydrates has a strong influence on the composition of the gut microflora. As scientific evidence showing the effects of various carbohydrates on the composition of microflora accumulates, it has been recognized that certain carbohydrates can stimulate the growth of beneficial bacteria such as lactobacilli and bifidobacteria, and can provide the host with health benefits. Based on these observations, G. Gibson and M. Roberfroid proposed in 1995 the term ‘prebiotic’ for a food component
that beneficially modulates the gut microflora to improve host health. As the research on prebiotics proceeds through the years, the health-promoting effects of prebiotics seem to be wider than initially expected. There have been published reports on a wide variety of dietary carbohydrates with various health benefits. The overall fate of prebiotics in the large intestine and their health benefits are briefly illustrated in Figure 1. In this article the possible health effects of prebiotics are described.
Definition of Prebiotics A prebiotic is defined as ‘‘a nondigestible food ingredient that beneficially affects the host health by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon’’. As prerequisites of a prebiotic agent, the food ingredient must be neither degraded nor absorbed in the upper intestinal tract and be a selective substrate for a limited number of indigenous beneficial bacteria; thus it alters the balance of the gut microflora in favor of a healthier composition. While carbohydrates, proteins, lipids, and other minor components of foods like vitamins and minerals that are supplied unabsorbed through the small intestine could be candidates for prebiotics, only nondigestible carbohydrates of different monosaccharide units with a rather short chain length are recognized and established so far as prebiotic agents. Among dietary carbohydrates, nondigestible oligosaccharides (NDO) including some disaccharides are the main prebiotics, which can either be extracted from natural plants and animals or be manufactured by enzymatic or chemical reactions (for a review, see Prebiotics: Types). Nowadays, a substantial number of NDO with different structures and lengths are commercially available. In addition, fewer differences between the effects of prebiotics and those of indigestible dietary polysaccharides (or dietary fiber) are detected now than in the past, as the research on both NDO and dietary fiber advance. Especially the production of short-chain fatty acids (SCFA) from these compounds and the subsequent physiological effects in response to SCFA are probably common for prebiotics and dietary fibers. In addition, certain indigestible polysaccharides were reported to be bifidogenic, thus being able to be prebiotics. As a conclusion, the bifidogenic effect is a key criterion to
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366 Prebiotics | Functions
Prebiotics
Bifidobacteriapredominated microflora
Lower pH
Lower putrefactive substances
Mineral absorption
Dietary polysaccharides
Butyrate Propionate Acetate
Energy supply
Unfermented fiber
Higher water content
Lower secondary bile acids
Lower putrefactive enzyme activity
Cancer prevention
Stool bulking
Improvement of bowel movement
Lipid metabolism
Figure 1 Flow of metabolism of indigestible carbohydrates in the large intestine and their proposed effects.
distinguish prebiotics from other fibers. However, it is conceivable that this definition may be open for revision in the future.
Composition of the Human Gut Microflora and Health The human gastrointestinal (GI) tract, especially from cecum to rectum, is heavily colonized by microbes, reaching 1012 g1 contents or 1014 in total, with more than 200 species in a person or probably a total of 500–1000 species. This implies that about half of the solid content of the colon or feces is bacteria. After birth, the composition of the gut microflora of a newborn undergoes changes in response to factors such as changes of diet, health status, stress, age, and medication. The fetal GI tract is sterile, but the colonization initiates during birth. It is well understood that during the period of feeding with mother’s milk, the composition of the gut microflora of the infant is rather simple and that the predominant microbes are bifidobacteria. At the weaning period, there is a drastic change in the composition of the gut microflora from the infant type to the adult type, which is characterized by a more complex composition with increased contents of Bacteroides and clostridia, and a wider variety of different species. These commensal bacteria, about 70% of which are still uncultivable or unidentified, not only interact with the host at the mucosal surface but also constitute a complex metabolic machinery that provides the host with a variety of metabolites.
The most numerous microbes isolated from the adult colon are obligate anaerobes such as Bacteroides (1010–1011 g1 wet feces), Eubacterium (1010–1010.5 g1), Peptostreptococcus Bifidobacterium (109–1010.5 g1), 9 10 1 (10 –10 g ), and Clostridium (109–1010 g1). Facultative anaerobes such as Enterobacteriaceae, Enterococcus, and Lactobacillus are also indigenous but less numerous (105–108 g1). Some aerobes such as Bacillus, Staphylococcus, Pseudomonas, and yeasts are occasionally isolated at very low levels (103–105 g1), and are thought to be transient passengers. While the composition and the activity of the gut microflora of healthy persons are relatively stable in individuals, they could be easily disturbed by environmental changes such as illness, medication, stress, and a drastic change of the diet. For instance, antibiotic treatment often causes complete disruption of the composition of the gut microflora and severe diarrhea, and parenteral nutrition also disturbs the gut microflora as well as the gut functions. The intestinal microflora is a complex open ecosystem where the inhabiting microbes in the highly dense microbial community interact with each other and with the host animal, thus constituting the front line of defense against infection or modulating the host mucosal immune system. This could generate a barrier function, which is often called ‘colonization resistance’ or ‘competitive exclusion’, against pathogenic agents. Based on numerous studies, it has been observed that there are beneficial as well as potentially harmful microbes inhabiting the human GI tract. Lactic acid-producing bacteria like Lactobacillus
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and Bifidobacterium are considered beneficial as they produce acids (lactic acid and acetic acid) that contribute to maintain an acidic condition within the intestines, produce vitamins, and potentially modulate the host immune system, whereas some species of Bacteroides, Clostridium, Enterobacteriaceae, and yeasts are potentially harmful as they produce toxins and putrefactive substances, and sometimes become opportunistic infectious agents. Furthermore recent studies have provided indications that some indigenous bacteria and yeasts could have roles in initiating and activating intestinal inflammatory responses. Therefore it is widely accepted that the homeostasis and improvement of the healthy gut microflora in the direction of increasing beneficial bacteria and decreasing potentially harmful bacteria are definitely valuable to keep the host healthy.
Fermentation of Prebiotic Carbohydrates in the Large Intestine Production of Short-Chain Fatty Acids It has been estimated that among the dietary carbohydrates a person consumes everyday, about 20–60 g escape hydrolysis by the intestinal digestive enzymes and become substrates for fermentation in the colon: 5–35 g are resistant starch (RS), 10–25 g nonstarch polysaccharides (NSP), 2– 10 g unabsorbed mono- and disaccharides, and 2–8 g NDO. The pathway of carbohydrate metabolism in the colon is schematically illustrated in Figure 2. Most colonic bacteria have a variety of glycolytic enzymes with different substrate specificity. The major products of microbial fermentation of these carbohydrates in the large intestine are SCFA (mainly acetic, propionic, and butyric acids) and
gases (H2, CO2, and CH4). It is difficult to precisely measure the profile of fermentation of dietary carbohydrates in the colon, especially in human, because most SCFA produced are rapidly absorbed at the site of production. Many researchers have tried to estimate the amounts and available energy values of SCFA by using animal models, isotope-labeled substrates, and in vitro fermentation system, or by indirect calculations. The overall stoichiometry for the hydrolysis of dietary carbohydrates in the intestines can be drawn from G. Liversy and M. Elia’s calculation using the following equation: 58C6 H12 O6 þ 36H2 O ! 60CH3 COOH þ 24CH3 CH2 COOH þ 16 CH3 ðCH2 Þ2 COOH þ 92CO2 þ 256½Hþ
where Hþ will be further accepted by another Hþ or some other molecule, and the total yield of SCFA from 100 g of carbohydrates is calculated to be 64 g. This value is almost the same as that obtained from in vitro fermentation of starch using a human fecal sample. However, the fermentability and the molar ratio of acetic, propionic, and butyric acids produced from carbohydrate substrates vary considerably. Thus the yield of SCFA from mixed carbohydrates is usually between 30 and 50%. In contrast, the contribution of prebiotics in the production of SCFA is different. Considering the predominant utilization of prebiotics by bifidobacteria and/or lactobacilli where the contribution of bifidobacteria is much more than that of lactobacilli due to their numerical advantage, the fermentation profile of prebiotics in the colon will be shifted to a bifidobacteria-driven one. The stoichiometric equation for the hydrolysis of hexoses by bifidobacteria is as follows: 2C6 H12 O6 ! 3CH3 COOH þ 2CH3 CHOHCOOH
Carbohydrates (starch, NSP, NDO)
Hexose Pentose
Nitrogen source
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Pyruvate
Bacterial cell mass
Acetic acid Propionic acid Butyric acid
H2 CO2 CH4
Excretion in feces
Absorption as energy source
Excretion from mouth or anus
Figure 2 The pathway of fermentation of indigestible carbohydrates in the large intestine. NSP = non-starch polysaccharides, NDO = non-digestable oligosaccharides.
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where the available energy value remaining as SCFA (acetic acid) is about 50%, since absorption of lactate in the colon is very slow. In this reaction, gases are not produced as primary fermentation products, although other colonic bacteria such as Megasphaera elsdenii, Eubacterium hallii, and Anaerostipes caccae can further metabolize lactate into butyrate plus hydrogen and carbon dioxide gases. The fermentation pattern by lactobacilli is somewhat different. There are two types of lactobacilli, homofermentative and heterofermentative, which produce only lactate and a mixture of lactate, acetate, and ethanol, respectively, from carbohydrates. The contribution of these lactic fermentations in the physiology of the lower small intestine could be substantial, because lactobacilli are the major inhabitants of that region, although that in the large intestine is probably negligible. Nutritional Values The SCFA produced in the fermentation process are rapidly absorbed from the mucosal surface of the large intestine and used as energy source in various ways. The calorific value of indigestible and fermentable carbohydrates has been a subject of debate due to the difficulty of direct measurement. Considering that the calorific values of digestible carbohydrates absorbed from the small intestine are 4 kcal g 1 (16.8 kJ g1), the yield of SCFA from indigestible carbohydrates that are completely fermented in the colon is approximately 60%, and the efficiency of availability of SCFA in the colon is about 0.85. The practical calorific values of indigestible but easily fermentable carbohydrates like NDO are calculated to be approximately 2 kcal g 1 (8.4 kJ g1) for most of these compounds. The fates of SCFA in the body are distinctive: butyrate is exclusively utilized by the colonocytes, which derive 60–70% of their energy from butyrate; acetate is probably metabolized by skeletal and cardiac muscles and brain, is always detected in the bloodstream at the basal level of 50 mmol l 1, and rises to 100–300 mmol l 1 after meals containing indigestible carbohydrates. Acetate is also utilized for the synthesis of long-chain fatty acids, glutamine, glutamate, and so on. Propionate is a major glucose precursor in ruminants, but the fate of propionate in man is much less known. Probably it is also a substrate for hepatic gluconeogenesis in man, and its effect on the lipid metabolism has been proposed. Modulation of the Gut Microflora A prerequisite characteristic of a prebiotic substance is to be utilized by a limited number of beneficial colonic bacteria. A fermentability profile of a variety of NDO by different colonic bacteria in vitro has revealed that most strains of the genus Bifidobacterium can utilize these carbohydrates efficiently, while the fermentation of NDO
by other major genera inhabiting the colon such as Bacteroides, Clostridium, Eubacterium, and Peptostreptococcus is limited (for details, see Bacteria, Beneficial: Bifidobacterium spp.: Applications in Fermented Milks; Probiotics, Applications in Dairy Products. Prebiotics: Types). In fact, from the cell extracts of bifidobacteria grown in a medium with glucose as a sole carbon source, hydrolyzing activities against -glucosyl, -glucosyl, galactosyl, and -fucosyl bonds have been detected. This is not necessarily achieved by different enzymes. A couple of -galactosidases (EC 3.2.1.23) and -glucosidases (EC 3.2.1.21) with diverse substrate specificity have been identified in various strains of bifidobacteria of human origin. In contrast, animal strains of bifidobacteria analyzed so far except for Bifidobacterium animalis produce fewer glycolytic enzymes, the phenomenon being possibly associated with the presence of complex oligosaccharides in human milk. The production of the enzyme -fructosylfuranosidase (EC 3.2.1.26) responsible for the digestion of fructooligosaccharides (FOS) is induced by FOS in the medium. All these characteristics of bifidobacteria enable the identification of prebiotics as bifidogenic substances. Numerous studies have been conducted to substantiate the bifidogenic effect of prebiotic preparations. Petuely discovered in 1957 that lactulose produced from lactose has a bifidogenic effect in formula-fed infants. Supplementation of lactulose in the cow milk-based formula causes the formation of the so-called bifidus flora and a reduction of fecal pH in formula-fed infants. It also reduces the production and absorption of ammonia in the colon, and hence is approved as a medicine for constipation as well as hepatic encephalopathy. The first oligosaccharide found to exert a bifidogenic effect was galactooligosaccharide (GOS). Tanaka et al. demonstrated that after 1 week of GOS intake at doses of 3–10 g day1, the fecal bifidobacteria increased in a dose-dependent manner, which often accompanies the change of the composition of the gut microflora from a Bacteroidaceaepredominant to a bifidobacteria-predominant one and/or a decrease in Bacteroidaceae. This is also the case for FOS, lactosucrose, xylooligosaccharides (XOS), sucrosyloligosaccharides (SOS), gentiooligosaccharides, and isomaltooligosaccharides (or -GOS). The generation of bifidus flora in breast-fed infants has been confirmed in recent studies with both the authentic plating method and the molecular method, indicating that human milk oligosaccharides (HMO) or certain components in human milk act as prebiotic substances. Effective doses of prebiotics to exert the bifidogenic effect in man have been estimated to be approximately 3–10 g day1 for most NDO. However, XOS has been reported to show the effect at a dose less than 1 g day1, and NDO having -glycosidic linkages like isomaltooligosaccharides usually need
Prebiotics | Functions
more than 10 g day1 to show the effect similar to that of -linked NDO due to their partial digestibility in the upper intestine.
Physiological Effects Improvement of Stool Frequency Beneficial effects of intake of NDO on the nature of feces have been shown in several human studies. NDO improve both the frequency and the consistency of defecation after habitual intake. For example, administration of GOS at a dose of 2.5–5 g day1 for 1 week led to a significant increase in the frequency of defecation in a group of women in a double-blind placebo-controlled trial. The effect was more apparent for subjects who tended to be constipated. The mechanism behind this effect is not precisely known yet. However the intake of prebiotics in addition to normal diet results in an increase in acids especially acetic acid and lactic acid due to the predominant utilization of the substrate GOS by bifidobacteria. In addition, it has been recognized that in some cases succinic acid also accumulates in the cecal and colonic contents after ingestion of GOS in rats with humanized gut microflora and in humans. Unlike the SCFA that are rapidly absorbed from the mucosal surface of the large intestine, lactic acid and succinic acid are less efficiently absorbed, and thus contribute to the decline of the pH of the colon and to the increase in fecal water content. All these alterations of the physiology of the colon could have a role in improving the stool frequency. In contrast, it has been observed that FOS exert an effect to prevent traveler’s diarrhea, which is probably due to the stabilization of bifidobacteria- and lactobacilli-predominated healthy gut microflora. Reduction of Putrefaction The colonic microflora is an agent for the metabolism of various substrates. It provides the host with a variety of enzymes, and the metabolic activity of the gut microflora is estimated to be as high as that of the liver. While dietary carbohydrates are fermented into SCFA and gases, proteins and amino acids that reach the colon are fermented into SCFA as well as branched-chain fatty acids, isobutyrate, isovalerate, and 2-methylbutyrate arising from valine, leucine, and isoleucine, respectively. In addition, proteolysis followed by amino acid catabolism causes an accumulation of ammonia, phenolic compounds, amines, and sulfur compounds, which are all putrefactive substances. These substances are absorbed into the bloodstream, and, either directly or after further metabolization in the liver, show detrimental effects on human health. In a study with rats approximately 40% of blood ammonia was derived from the intestine. It has been
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demonstrated that the amount of urea in rat urine, the final product of ammonia metabolism, is significantly lower in germ-free rats than in normal rats. In a human study with healthy volunteers, the ingestion of GOS not only reduced the fecal ammonia concentration significantly, but also reduced other putrefactive products such as phenol, p-cresol, and indole in the urine. The reduction of blood ammonia concentration by GOS was further confirmed in an additional study using hyperammonemia patients. Lactulose and lactitol have been approved as medicines for hepatic encephalopathy, because they are effective for reducing blood ammonia level of the patients probably due to their effect on intestinal putrefaction. Therefore it is concluded that NDO such as GOS and lactulose can modulate the gut microflora to reduce its putrefactive metabolic activity. Colon Cancer Prevention Several bacterial enzymes such as -glucuronidase, -glucosidase, and nitroreductase derived from the gut microflora can activate precarcinogens to proximal carcinogens. For instance, bile salts secreted from the liver are converted to secondary bile acids by the enzyme glucuronidase derived from bacteria, and the resultant products are potential promoters of colon carcinogenesis. In a couple of studies with human volunteers, a daily intake of GOS at a dose of 10 or 15 g significantly reduced the fecal -glucuronidase activity. In model systems using rats and chemical carcinogens, there are a few reports that have analyzed the suppressive effect of prebiotics on the development of cancer. In a model that monitored the development of colorectal cancer induced by 1,2-dimethylhydrazine (DMH) in rats, fully fermentable GOS appeared to be highly protective, while poorly fermentable cellulose was not effective. In another model, the effect of dietary carbohydrates including FOS and inulin on the development of aberrant crypt foci (ACF), which are recognized as early preneoplastic lesions in the colon, caused by the treatment with azoxymethane (AOM) was analyzed. The formation of AOM-induced ACF was significantly reduced by treatment with inulin, FOS, pectin, or coffee fiber (rich in arabinogalactan). The increase in butyrate concentration in the colon was suggested to be an effective change for the reduction of ACF formation in the colon, because only carbohydrates that resulted in the production of large amounts of butyrate reduced AOM-induced ACF formation. This supposed effect of butyrate on the suppression of cancer development could be explained in part by the inhibitory effect of butyrate on the proliferation of cells including colon tumor cells. In addition, FOS and inulin showed enhanced apoptotic effect in the distal colon of rats after treatment with DMH, where inulin was more effective than FOS. SCFA – acetate, propionate, and butyrate – can in fact induce
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apoptosis in colorectal tumor cell lines at a concentration of 0.5 mmol l1, where butyrate is the most effective agent. All these results imply that SCFA, especially butyrate, produced by the colonic fermentation of dietary carbohydrates may have a role in protecting against the development of cancer in the colon by inducing apoptosis in the injured cells or proliferating cells. However, the enhanced frequency of apoptosis may also imply that the colonic cells become more susceptible to the carcinogen by the increased butyrate concentration or that the activation of the procarcinogen was stimulated by the higher concentration of butyrate. There also appears a conflicting view that fully fermentable carbohydrates such as inulin, as compared with wheat bran, may enhance colon carcinogenesis in the distal colon based on the increased PKC activity and PKC 2 level in response to increased diacylglycerol in the colon in rats fed with a high-fat diet with inulin. Thus, the suppressive effect of prebiotics and dietary carbohydrates on colon carcinogenesis is still inconclusive. Immune Modulation There have been very few reports suggesting modulation of the immune system by prebiotics and dietary carbohydrates. It is not likely that prebiotics directly impact the body’s immune system; however, the improvement of the intestinal environment could enhance the immune system. As described above, prebiotics and dietary carbohydrate supplementation may reduce the development of colonic neoplasia. In general, cells having neoplastic lesions are excluded through the body’s immunological defense mechanism. The fact that the supplementation of FOS, inulin, or GOS in the diet resulted in the reduction of colon carcinogenesis by chemical carcinogens in rats suggests that the immune system involved in this process may be activated by these substances. Stimulation by FOS and inulin of apoptosis of colonocytes induced by treatment with a chemical carcinogen supports this idea. The question remains whether or not, and if so how, prebiotics and dietary carbohydrates directly or indirectly affect the immune system. An alleviation of the symptoms of atopic dermatitis in infants by raffinose has been reported. It could be mediated by the improvement of the colonic microflora; especially a reduction of Candida level in the gut microflora is supposed to be effective in alleviating the symptoms. However, this should be confirmed by additional sound scientific clinical studies. Stimulation of Mineral Absorption Evidence is accumulating showing the enhancing effect of NDO on the absorption of minerals including calcium, magnesium, iron, and zinc. An increasing interest is focused especially on the intake of calcium because of
its role in preventing osteoporosis. From animal and human studies, it has been shown that indigestible polysaccharides, NDO, and other carbohydrate compounds stimulate mineral absorption, and that the major site of action for absorption of minerals is the large intestine. This implies that the large intestine has a significant capacity to absorb minerals. Among NDO, inulin, FOS, GOS, lactulose, isomaltooligosaccharides, and raffinose have been demonstrated to stimulate mineral absorption in animal models. In normal rats, it has been shown that the enhancement of calcium and magnesium absorption was totally dependent on the reduction of cecal pH due to the enhanced production of SCFA by colonic bacteria, since simultaneous addition of neomycin with GOS did not show increased calcium and magnesium absorption. Increased bone mineralization and increased bone strength were also shown by using GOS, FOS, and lactulose in ovariectomized rat models. Unlike the numerous animal studies, however, human studies with clear positive effects of NDO on mineral absorption are not yet available. Ingestion of 15 g day1 of inulin, FOS, or GOS for 3 weeks did not affect mineral (calcium and iron) absorption significantly in 12 healthy young men. Feeding of a larger dose of inulin (40 g day1) significantly increased calcium absorption in nine healthy men. More recently by using postmenopausal women as subjects, it has been shown that feeding of 10 g day1 of FOS significantly increased magnesium absorption. Since there have not been many human trials regarding the effect of NDO or dietary carbohydrates on mineral absorption and bone mineralization, more studies are clearly needed. Modulation of Lipid Metabolism The possibility that prebiotics may have some effects on blood lipid metabolism is an attractive idea. In rats it has been demonstrated that feeding FOS significantly reduced triglycerides in very low-density lipoprotein (VLDL), which is likely to be due to a reduction of lipogenesis in the liver. Regulation of hepatic cholesterol synthesis by SCFA and precipitation of bile acids due to deconjugation and acidification in the intestines have been proposed as likely mechanisms of this effect. However, only very slight effects have been observed in human studies using healthy volunteers, diabetic patients, or hypercholesterolemic persons, which are not yet conclusive. It is still an open question whether or not prebiotics can exert beneficial effects on lipid metabolism and cholesterol lowering.
Conclusion and Perspectives Our daily diet is at the base of our healthy life. We eat a variety of foods derived from animals and plants every day, which basically include all the necessary components
Prebiotics | Functions
of nutrients we need. However, the balance of nutrients is not always sufficient to keep our health. Especially the modern dietary habits often cause the shortage of certain nutrient factors. A typical example is that of formula-fed infants who consume cows’ milk-based foods prior to weaning. It has been demonstrated scientifically that cow’s milk-based formula needs supplementation to fulfill completely the baby’s needs to prevent infection and to keep the infant’s gut microflora healthy. As the role of the gut microflora in human health is recognized more, the importance of management of the intestinal microflora will receive more attention. In the last two decades, a variety of dietary carbohydrates that fulfill the criteria for prebiotics have been developed and have become commercially available. At the same time numerous studies have been conducted in animal models and in humans to show different health effects of prebiotics, thus increasing their health claims. However, we must recognize what the true health benefits of the prebiotics are, and which ones are supported by sound scientific evidence. Unfortunately not every health effect of each of the prebiotics described in this article is sufficiently substantiated in human clinical studies, not even the principal effects of certain established prebiotics. However, these putative effects may counteract any additional physiological effects of prebiotics, and the elucidation of the mechanisms underlying the effects may add a new insight into the field of nutrition. Our knowledge of the composition and the function of the gut microflora is still limited. Recently established molecular identification techniques for bacteria have revealed that a number of bacteria even predominant in the intestinal microflora are still uncultivable. Although a prebiotic is required to be bifidogenic, the influence of the particular prebiotic on the fate of other bacteria is not precisely known. Considering the more than 200 or even 400 different bacteria inhabiting the colon, there may be other beneficial as well as harmful bacteria that
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preferentially utilize the prebiotic in the flora. Individual prebiotics are probably utilized by different sets of bacteria, thereby influencing the gut microflora and physiology in different ways. However, most physiological effects of prebiotics described so far are almost all possessed by every prebiotic uniformly. It may be very difficult to distinguish one prebiotic from another in their physiological characteristics, but when this will be achieved, the era of prebiotics will come. See also: Bacteria, Beneficial: Bifidobacterium spp.: Applications in Fermented Milks; Probiotics, Applications in Dairy Products. Prebiotics: Types.
Further Reading Cummings JH and Englyst HN (1995) Gastrointestinal effects of food carbohydrates. American Journal of Clinical Nutrition 75: 733–747. Cummings JH, et al. (eds.) Physiological and Clinical Aspects of ShortChain Fatty Acids. Cambridge, UK: Cambridge University Press 1995. de Vries M and Schrezenmeir J (2008) Probiotics, prebiotics, and synbiotics. Advances in Biochemical Engineering/Biotechnology 111: 1–66. Gibson GR and Roberfroid MB (1995) Dietary modulation of the human colonic microflora: Introducing the concept of prebiotics. The Journal of Nutrition 125: 1401–1412. Liversey G and Elia M (1988) Estimation of energy expenditure, net carbohydrate utilization, and net fat oxidation and synthesis by indirect calorimetry: Evaluation of errors with special reference to the detailed composition of fuels. American Journal of Clinical Nutrition 47: 608–628. Louis P, et al. (2007) Understanding the effects of diet on bacterial metabolism in the large intestine. Journal of Applied Microbiology 102: 1197–1208. Macfarlane GT, Steed H, and Macfarlane S (2008) Bacterial metabolism and health-related effects of galacto-oligosaccharides and other prebiotics. Journal of Applied Microbiology 104: 305–344. Roberfroid M (1993) Dietary fiber, inulin, and oligofructose: A review comparing their physiological effects. Critical Reviews in Food Science and Nutrition 33: 103–148. Sako T, Matsumoto K, and Tanaka R (1998) Recent progress on research and application of non-digestible galacto-oligosaccharides. International Dairy Journal 9: 69–80.
PSYCHROTROPHIC BACTERIA
Contents Arthrobacter spp. Pseudomonas spp. Other Psychrotrophs
Arthrobacter spp. G Comi, University of Udine, Udine, Italy C Cantoni, University of Milan, Milan, Italy ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by G. Comi, C. Cantoni and L. Cocolin, Volume 1, pp 111–116, ª 2002, Elsevier Ltd.
Introduction The genus Arthrobacter belongs to the ecologically and industrially important class Actinobacteria, family Micrococcaceae, which includes microorganisms that live in soil, subterranean cave silts, sea, glacier silts, sewage, water sludge, aerial surfaces of plants, vegetables, fish, and various animal species. In the environment, they are often the most numerous bacteria because of their versatility. Some species are psychrophilic and psychrotrophic, can use a wide range of organic substrates as sole or principal sources of carbon and energy, and do not require vitamins or other organic growth factors. Aromatic compounds can also be utilized. Arthrobacters are widespread in nature and they readily contaminate raw food, milk and milk products, meat and meat products, and fish and fish products. In food, arthrobacters may be recognized as indicators of sanitation or hygiene quality, or as contaminants of no particular importance. However, they may also grow and be involved in spoilage or ripening of food products. Some Arthrobacter strains have been isolated from human sources and consequently are considered to be opportunistic pathogenic microorganisms. The taxonomy of the genus Arthrobacter has been redefined many times. Great difficulty has been encountered in identifying and classifying Arthrobacter and related coryneforms such as Brevibacterium, Caseobacterium, Cellulomonas, Corynebacterium, Curtobacterium, and Microbacterium. For
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these reasons, sometimes many isolates have been identified as arthrobacters or ‘arthrobacter-like’ simply because they showed the rod–coccus growth cycle (Figure 1) and staining reactions that are characteristic of the genus. Strains of Arthrobacter can be readily recognized in different environments by their morphological properties, although they cannot easily be distinguished from closely related coryneform genera. The development of taxonomy for the genus Arthrobacter is as follows: 1928 – isolation from soil; 1933–38 – similar microorganisms confirmed in soil; 1957 – genus included in the family of Corynebacteriaceae; 1986 – two groups distinguished: A. globiformis/A. citreus and A. nicotianae.
Taxonomy The genus Arthrobacter is closely related to Aureobacterium, Caseobacterium, Cellulomonas, Corynebacterium, Curtobacterium, and Microbacterium and is more distantly related to Brevibacterium. Phylogenetically, it is a member of the high-GC Actinomycetes, and Arthrobacter species could not be separated from members of the genus Micrococcus. These are Gram-positive eubacteria. Only minor differences enable the genus to be distinguished from
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Figure 1 Growth cycles of Arthrobacter globiformis AC 166 starting from coccoid stage, on a rich medium at 25 C. Reproduced from Crombach WHJ (1974) Morphology and physiology of coryneform bacteria. Antonie van Leeuwenhoek 40: 361–376, with kind permission from Kluwer Academic Publishers.
coryneform bacteria. Several tests must be employed simultaneously to classify and identify Arthrobacter spp. and avoid confusion with closely related genera. Molecular and chemotaxonomic techniques are important for the characterization of coryneforms and Arthrobacter spp. because traditional methods based on morphological and physiological features only are insufficient to describe their biodiversity. In recent years, many methods have been developed to classify and identify arthrobacters. Traditional approaches are still used, but must be applied in conjunction with chemotaxonomic and molecular techniques, as the modern taxonomy of bacteria requires a multiphase classification strategy. The following approaches are the most recent and widely used approaches to Arthrobacter taxonomy: 1. Deoxyribonucleic acid (DNA) base composition and DNA–DNA homologies (DNA hybridization). 2. Analysis of particular cell constituents such as peptidoglycans, fatty acids, phospholipids (diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylinositol), and glycolipids, and analysis for the presence or absence of teichoic acids. Numerous studies of the cellular fatty acid composition of coryneform bacteria have been used for their classification. In
many cases, acyl types allow for a more precise characterization. Recently, the identification of cellular fatty acids has enabled the classification into four groups of coryneform bacteria belonging to the genera Arthrobacter, Brevibacterium, Caseobacterium, Caseobacter, Cellulomonas, Corynebacterium, and Curtobacterium. 3. Isoprenoid quinone analysis. It evaluates the presence of dehydrogenated menaquinones with 8 (MK-8), 9 (MK-9), or 10 (MK-10) isoprene units. This is another new method of characterization, but its application has given rise to several problems in distinguishing species and genera. 4. PCR analysis. It is a new method of identifying and classifying Arthrobacter based on the analysis of 16S rRNA by polymerase chain reaction (PCR) and various electrophoresis techniques, such as temperature-gradient gel electrophoresis (TGGE) or denaturing-gradient gel electrophoresis (DGGE). Comparative TGGE is considered more useful in taxonomic studies of coryneform soil bacteria because a high number of strains from the principal species of the genera Aeromicrobium, Agromyces, Arthrobacter, Aureobacterium, Cellulomonas, Curtobacterium, Nocardioides, and Terrabacter can be tested and characterized. In addition, positive results obtained by comparative TGGE can be confirmed by whole-cell fatty acid methyl ester analysis. Finally, PCR amplification of 16S rRNA gene (rDNA analysis), followed by sequencing, allows the identification of new species of Arthrobacter (Figure 2). 5. Biochemical and physiological characteristics. The phenotypic characteristics do not enable differentiation of Arthrobacter species. The multiphase approach has led to the discovery of new species such as A. rhombi sp. nov. (Figure 3), isolated from the Greenland halibut (Reinhardtius hippoglossoides), in addition to A. albus sp. nov. and A. luteolus sp. nov., both isolated from human clinical specimens. It is only by simultaneous employment of several methods (biochemical characteristics, DNA G þ C content, wall murein composition and structure, 16S rRNA gene sequence) that researchers can identify and classify old and new species of Arthrobacter with certainty, and distinguish them from closely related genera.
Morphological and Physiological Characteristics The genus Arthrobacter includes a group of microorganisms with a rod–coccus growth cycle. Initially, the microorganisms grow as rods in a simple medium during the log phase, subsequently becoming shorter in the stationary phase and taking on the appearance of large cocci. In aged cultures, cells may have entirely coccoid conformations, but mixed rod–coccus types are often seen. When aged cells are transferred into fresh broths, they
374 Psychrotrophic Bacteria | Arthrobacter spp. Arthrobacter atrocyaneus Arthrobacter agilis 100 Arthrobacter axydans Arthrobacter polychromogenes Arthrobacter citreus Arthrobacter aurescens Arthrobacter tlicls 82 Arhrobacter ureafactens Arhrobacter histidinolovorans 86 Arhrobacter nicotinovorans Renibacterium salmoninarum Arthrobacter woluwensis Arthrobacter globiformis 86 Arthrobacter pascens Arthrobacter ramosus Arthrobacter sulfureus Arthrobacter creatinolyticus Arthrobacter uratoxydans Arthrobacter protophormiae Arthrobacter nicotianae Brevibacterium ligvefaciens 73 100 Micrococcus hneus Micrococcus lylae Arthrobacter cummensn Nesterenkonia halobia Arthrobacter crystallopoietes Kocuria rosea Stomatococcus mucilaginosus 100 Rothia dentocariosa 2% Figure 2 Phylogenetic relatedness among authentic species of the genus Arthrobacter, which have been subgrouped based on the results of 16S rDNA analysis. Organisms the names of which are displayed in the same color exhibit the same peptidoglycan structure. Numbers within the dendrogram indicate the percentages of occurrence of the branching order in 500 bootstrapped trees (only values of 70 and above are shown). Sequences of the species of the genera of the family Micrococcaceae served as root. The scale bar represents 2 nucleotide substitutions per 100 nucleotides. Reproduced from Stackebrandt E and Schumann P (2006) Introduction to the taxonomy of Actinobacteria. In: Dworkin M, Falkow S, Rosembreg E, Schleifer CK, and Stackebrandt E (eds.) The Prokaryotes: A Handbook on the Biology of Bacteria, 3rd edn., Vol. 3, pp. 297–321. New York: Springer, with kind permission from Springer (New York, USA) and the authors.
become irregular rods, sometimes rudimentarily branched and arranged in V-shaped formations. Cell size is variable and the diameter can be anywhere between 0.6 and 1.2 mm. This life cycle is observed in nonselective media, especially if seeded with food. Many studies have demonstrated that the life cycle matures within 24 h when the cells are isolated from mixed broth food and grown at 25 C. Both conformations are Gram-positive, but on aging, they may be rapidly decolorized and appear Gramnegative. The cell wall mureins contain L-lysine as the main dibasic amino acid. All Arthrobacter strains are non-acid-fast and nonspore-forming. The rods are nonmotile or occasionally motile. They are obligate aerobes, catalase-positive and
oxidase-negative, but a few soil and sea strains have been recognized as oxidase-positive. A large number of arthrobacters are mesophilic, with optimum temperature of 20–30 C. However, some strains are psychrophilic or psychrotrophic and may grow at 4–6 C, or even at close to 5 C (A. glacialis) or 0 C, in some cases. Psychrophilic strains, usually isolated from soil or sea, are characterized by an optimum temperature of 20 C. Mesophilic strains can be adapted to grow at 6 C. Finally, a few strains can grow at 37 C. Temperature seems to have a significant influence on the life cycle. At 25 C, rod–coccus transformation takes place faster than at 15 C. This effect does not seem to be restricted to A. globiformis. In contrast, pigment production appears to be unaffected by temperature. Orange, yellow, and pale red pigments may occur in Arthrobacter. Pigment development seems to depend on various factors such as the strains involved, exposure to light or dark, the growth medium, and the presence or absence of salt in the medium. Nevertheless, many Arthrobacter strains are not pigmented. The cells are rapidly killed by heating at 63 C for 30 min in skimmed milk or in some other nonselective broths. All Arthrobacter strains are chemoorganotrophic and strictly aerobic. Metabolism of carbohydrates and other carbon sources is exclusively respiratory and never fermentative. The most widespread strains of Arthrobacter, especially those from soil, can utilize glucose, saccharose, glycerol, acetate, and citrate. Numerous studies have demonstrated that Arthrobacter strains may utilize more than 90 different carbon sources. Furthermore, Arthrobacter strains seem to have no particular nutritional requirements. Only a few species require biotin, B-vitamins, amino acids, and a siderophore. Many arthrobacters are able to utilize as nitrogen sources either ammonium nitrogen salts or a mix of ammonium nitrogen salts and a single amino acid. In general, it seems that only strains isolated from cheese, sea fish, or food require organic nitrogen. Arthrobacter strains are not inhibited by 3–5% NaCl at pH >6. In contrast, growth slows down at pH <6. Acidic substrates inhibit growth, since pH is a selective factor. The salt tolerance of Arthrobacter strains enables them to grow in salty food such as cheeses and meat products, a parameter that may be used as a selective factor in isolation media. Because of their great nutritional versatility, arthrobacters are frequently isolated from substrates with usual and unusual organic compounds, and have become important in bioremediation and environmental fields. It is known that some arthrobacters are able to dehalogenate 4-chloro-, 4-fluoro-, and 4-bromobenzoate, and to desulfurize heterocyclic organosulfur compounds. These properties mean they can be utilized as starters for the microbial degradation of haloaromatics or other carbon sources in the environment.
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Figure 3 Unrooted tree showing the phylogenetic relationship of Arthrobacter rhombi sp. nov. within the genus Arthrobacter. The tree constructed using the neighbor-joining method was based on a comparison of approximately 1320 nucleotides. Bootstrap values, expressed as a percentage of 200 replications, are given at the branching points. Bar, 1% sequence divergence. With the exception of A. rhombi CCGU 38812, all other strains are type strains; accession numbers are given in parentheses. Reproduced with permission from Osorio CR, Barja JL, Hutson RA, and Collins MD (1999) Arthrobacter rhombi sp. nov., isolated from Greenland halibut (Reinhardtius hippoglossoides). International Journal of Systematic Bacteriology 49(3): 1217–1220.
Hydrolytic activities may also occur in Arthrobacter strains that hydrolyze gelatin, casein, and lipids, but not starch and cellulose. In particular, hydrolytic activities are marked in strains isolated from soil and cheeses; Arthrobacter strains are the major components of smear microflora of cheeses. Extracellular esterases, proteases, and proline iminopeptidases from A. nicotianae strains isolated from smear cheeses have been purified and characterized. The properties of these enzymes demonstrate that arthrobacters may play an important role in casein hydrolysis of smear-ripened cheese. The characteristics of a chitinase enzyme of arthrobacters have also been studied. The aim was to propose an industrial application in the degradation of chitin, an insoluble linear -1,4-linked polymer of N-acetylglucosamine (GlcNAc), which is one of the most common polysaccharides found in nature.
Arthrobacter Species Arthrobacter agilis, A. albus, A. atrocyaneus, A. aurescens, A. citreus, A. creatinolyticus, A. crystallopoietes, A. cumminsii, A. globiformis, A. histidinolovorans, A. ilicis, A. luteolus, A. nicotianae, A. nicotinovorans, A. oxydans, A. pascens,
A. polychromogenes, A. protophormiae, A. ramosus, A. rhombi, A. sulfureus, A. ureafaciens, A. uratoxydans, and A. woluwensis are all included in the genus. The number of species identified may rise or fall. The taxonomy of the genus Arthrobacter and related genera has been redefined many times. It is well known that some strains isolated from cheese, and originally recognized as arthrobacters, have now been identified as Brevibacterium or coryneforms, and vice versa. Almost all species have been isolated from soil, sea, vegetation, pure or sewage water, water sludge, glacier silts, and other natural environments where they play an active role in the degradation of various carbon sources. Recently, new species have been isolated from soil of cold areas, from the marine environment, and monuments. The main new species include A. ardleyensis, A. castelli, A. defluvii, A. flavus, A. gandavensis, A. gangotriensis, A. humicola, A. kerguelensis, A. koreensis, A. monumenti, A. oryzae, A. parietis, A. pigmenti, A. psychrolactophilus, A. psychrophenolicus, A. radiotolerans, A. simplex, A. soli, A. stackebrandtii, A. subterraneus, A. russicus, A. roseus, A. tecti, A. terregens, and A. tumbae. Arthrobacter cumminsii, A. woluwensis, A. creatinolyticus, A. luteolus nov. sp., and A. albus nov. sp. are considered opportunistic pathogens because they have been isolated only from human clinical specimens such as skin, urine,
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and blood culture. Their role in diseases is not proven and their pathological significance has not yet been assessed. Finally, some Arthrobacter species, such as A. aurescens, A. arilaitensis, A. bergerei, A. globiformis, A. variabilis, A. citreus, A. uratoxydans, A. protophormiae, and A. nicotianae, may also be found in food, especially cheeses.
Isolation of Arthrobacter Arthrobacters are usually isolated from different environments by nonselective media, such as plate count agar. Especially where they do not represent the main species, an enrichment culture, containing a variety of organic substrates as sole carbon and energy sources in mineral salts solution, could be used. However, in order to achieve good results in isolation, the media must contain a sufficient amount of organic compounds and mineral constituents. Poor nutriments inhibit the growth of Arthrobacter. To improve the isolation, sometimes antibiotics (nystatin 50 mg ml1, cycloheximide 50 mg ml1) have to be added to the medium in order to suppress fungal growth. The Winogradsky standard salt solution is recommended for their isolation from soil. A mix of soil extract with added yeast extracts, salts, glucose, and peptone is also often used. A selective medium, containing Trypticase soy agar, yeast extract, NaCl, cycloheximide, and methyl red, has been suggested. Cycloheximide (0.01%) inhibits fungal growth, a 2% concentration of NaCl inhibits the majority of Streptomyces, Nocardia, and Gram-negative bacteria, and methyl red (150 mg ml1) acts against other Gram-positive bacteria (bacilli and micrococci). The pH of the medium must be between 5.0 and 8.5, and the presence of Trypticase soy and yeast extract improves the growth of arthrobacters. The cultures can be preserved in soil extract agar or in plate count agar for more than 2 months at 20 C, or for several years if they are frozen on glass beads at 70 C. Lyophilization is suitable for long-term storage.
Arthrobacter in Milk and Dairy Products Arthrobacters contaminate meat and meat products, fish and fish product, fruit, vegetables, and milk and dairy products. Since they are obligate aerobes, arthrobacters grow mainly on the food surface and may result in spoilage, ripening, and colored smear or slime. Growth occurs when the storage temperature is 4–30 C, the pH is over 5.5, and the redox potential is positive. The organic sources of food do not constitute a limiting factor for these microorganisms, which display great nutritional versatility. Antagonistic flora, including lactic acid bacteria, Enterobacteria, Pseudomonas, Micrococcaceae, and
so on, may represent a potential limit. The competition of other microorganisms and the change in pH brought about by the production of lactic acid or other organic acids can inhibit or reduce the growth of arthrobacters. In addition, arthrobacters are rarely found in high concentration in food and never constitute the predominant flora. Where they can rapidly develop on food surfaces, arthrobacters produce colored smears, but they are always present in coculture with coryneforms, micrococci, staphylococci, and yeasts. Arthrobacters may occasionally be isolated from the surfaces of refrigerated fruits, vegetables, and meat and meat products (such as sausages, cooked hams, and airdried hams). The significance of their presence in these foods has not yet been clearly defined and, in some cases, more detailed investigations are required. Arthrobacters are always present in cocultures with strains of lactic acid bacteria, coryneforms, Micrococcaceae, Pseudomonas, Brochothrix thermosphacta, Microbacterium, Moraxella, Acinetobacter, and other psychrotrophic bacteria. On the above-mentioned food products, arthrobacters constitute an insignificant contamination whose growth depends on antagonistic microflora and on the presence of oxygen. Arthrobacters are more frequently isolated from milk and cheese. Several studies have demonstrated that soil- or environment-derived arthrobacters readily contaminate raw milk, where they may survive even if heated at 72 C for 15 s. In milk, Corynebacterium and Arthrobacter strains are recognized as indicators of sanitation or hygiene quality. High numbers of both groups in pasteurized milk are never associated with spoilage, although they do indicate bad sanitation. In fact, Arthrobacter strains are usually considered contaminants of no particular significance. In cheese, they are responsible for either spoilage or ripening. Arthrobacter aurescens, in coculture with Zymomonas mobilis, produces an abnormal yellow discoloration in yogurts and red-orange streaks on the surface of sliced Gorgonzola cheese. Other species, together with strains of Brevibacterium, Rhodococcus, Micrococcus, Staphylococcus, and Corynebacterium, and some yeasts such as Debaryomyces hansenii, Galactomyces geotrichum, Kluyveromyces marxianus, and Pichia membranifaciens play an important role in determining the characteristics and flavor of smear surface-ripened cheeses. Brie de Meaux, Epoisses, Germain, Pont l’E´veˆque, Reblochon, Saint-Nectaire, Tomme de Savoie, Fourme d’Ambert, Pur Brebis, Morbier, Cantal, Comte´, Fromage fermier, Fromage montagne, Domiati, Ras, Edam, Gouda, Gruye`re, Taleggio, Quartirolo, Limburger, Livarot, Rocamadour, Weinka¨se, Harzer, Munster, SaintPaulin, Appenzeller, Brick, Trappist, and Tilsiter are the best-known and most popular smear surface-ripened cheeses. Arthrobacter nicotianae, A. globiformis, and A. arilaitensis sp. nov. seem to be the main strains involved in aroma and color production in red smear cheeses. The ripening process begins with the growth of yeasts, which metabolize lactic
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acid previously synthesized by lactic acid bacteria, causing the pH to increase at the cheese surface. The pH alteration and the presence of growth factors from yeast autolysis stimulate the growth of a mixed population including A. globiformis, A. variabilis, A. citreus, Brevibacterium linens, and Brevibacterium ammoniagenes. This remarkable microflora grows mainly on the cheese surface since it is strictly aerobic, producing colored smears and low-molecularweight compounds that are responsible for the typical aroma of the product. The growth occurs within the first 2 weeks of ripening and then stops until the time of consumption. Thereafter, the aromatic compounds spread from the surface into the cheese, a process that is necessary for the development of the characteristic flavor and taste of the product. More specifically, Arthrobacter and Brevibacterium strains cause casein and lactate breakdown, changes in pH, and the production of ammonia, methanethiol, sulfides, dimethyl disulfide, S-methylthioesters (S-methylthioacetate, S-metylthiobutyrate, S-methylthiopropionate, and S-methylthioisovalerate), other volatile sulfur compounds, and low-molecular-weight nitrogen compounds. The volatile sulfur compounds are products of L-methionine catabolism. The enzymes involved seem to be L-methionine demethiolase, L-methionine aminotransferase, and -keto- -methyl-thiobutyric acid demethiolase. The microorganisms produce orange and reddish brown pigments, owing to their enzymatic activity on casein and amino acids. The proteinases of Arthrobacter spp. may play a significant role in the ripening of smear surface-ripened cheeses. Most notably, proline iminopeptidase seems to have a fundamental activity. Some Arthrobacter species and related genera may also produce antilisterial compounds, an activity that has been demonstrated on solid media. The presence and growth of undesirable microorganisms, such as Listeria monocytogenes, on the surface of smeared cheeses is a severe problem for the dairy industry. Various studies are under way with the goal of selecting strains that are capable of carrying out antagonistic activities on cheese surfaces against pathogenic microorganisms. No starter culture with both ripening and antilisterial activity has been produced yet. Because of high consumer demand for innovative, wellaged, territory-specific tastes, there is likely to be an increasingly widespread use of flavor-enhancing bacteria and yeast strains with a proteolytic enzyme activity. Arthrobacters are being more and more often proposed in cocultures, and also as part of starters, for cheese production. Starters including Staphylococcus and Arthrobacter strains, B. linens, and D. hansenii have been tested to improve the quality of experimental Tilsit, Raclette, and Ku`ssnachter cheeses. Relevant data demonstrate that the starters rapidly predominated on the surfaces and were able to reproduce the characteristic taste, flavor, and color of red smear cheeses. However, in the case of Raclette and Ku`ssnachter cheeses, it seems that Arthrobacter spp. do not necessarily need to be a component
of the starter culture, while B. linens and D. hansenii are essential to produce the typical aroma and the red smear. Conversely, the presence of arthrobacters in Tilsit cheese seems to be necessary for both aroma and color.
Conclusion The Arthrobacter genus is extensive and includes a large number of species that are widespread in nature. Because of their nutritional versatility, arthrobacters are commonly isolated from soil, sewage, food, and several other environments by using nonselective and simple media such as plate count agar. However, selective media and broths are also proposed. Strains with a rod–coccus growth cycle, which are strictly aerobic, and which have lysine as the cell wall diamino acid may be presumably identified as arthrobacters. The genus has great importance in environmental and industrial applications, as different strains are often used in bioremediation and in the degradation of heterocyclic organosulfur compounds, haloaromatics, and other carbon sources (herbicides, pesticides) from the environment. Most notably, A. phenanthrenivorans can break down phenanthrene, A. nitroguajacolicus breaks down 4-nitroguaiacol, and A. defluvii degrades 4-chlorophenol. Some Arthrobacter species may have an important role in phytohormone production, in dinitrogen fixation, and in lysing yeast and mold cells that trigger plant diseases. By chitinase production, some strains can be used as a biological control of Fusarium diseases. Moreover, other Arthrobacter strains are important commercially because they are used to produce glutamic acid, -ketoglutaric acid, and riboflavin. Recently, some Arthrobacter strains have been successfully used as probiotic bacteria to preserve shrimp post-larvae from pathogens such as Vibrio parahaemolyticus and Vibrio nereis. Starter cultures supplemented with Arthrobacter spp. are used to improve the quality of alkaline noodles, a typical food of eastern Asia made with wheat flour, water, sodium chloride, and alkaline salts (sodium and potassium carbonates, bicarbonate, phosphates). The aim is to increase the degree of yellowness of the noodles and prevent the formation of organic acids, which cause a decrease in pH. Arthrobacters also contaminate food, where they may have no significant role or else cause spoilage. Some Arthrobacter strains largely contribute to the production of the typical taste, flavor, and color of smear cheeses. See also: Analytical Methods: DNA-Based Assays. Bacteria, Beneficial: Brevibacterium Linens, Brevibacterium Aurantiacum and Other Smear Microorganisms. Cheese: Secondary Cultures; Smear-Ripened Cheeses. Microorganisms Associated with Milk.
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Further Reading Bockelmann W, Hoppe-Seyler T, Krusch U, Hoffmann W, and Heller KJ (1997) The microflora of Tilsit cheese. Part 2. Development of a surface smear starter culture. Nahrung 41(4): 213–218. Cantoni C and Cozzi M (2004) Pigmented bacteria in cheeses. Industrie Alimentari 42(431): 1247–1249, 1255. Carnio MC, Eppert I, and Scherer S (1999) Analysis of the bacterial surface ripening flora of German and French smeared cheeses with respect to their anti-listerial potential. International Journal of Food Microbiology 47(1/2): 89–97. Cozzi M, Cantoni C, Iacumin L, and Antoniotti G (2006) Pigmented bacteria in industrial purified water for the production of Mozzarella cheese. Archivio Veterinario Italiano 56(6): 261–277. Crombach WHJ (1974) Morphology and physiology of coryneform bacteria. Antonie van Leeuwenhoek 40: 361–376. Eliskases-Lechner F and Ginzinger W (1995) The bacterial flora of surfaceripened cheeses with special regard to coryneforms. Le Lait 75: 571–594. Felske A, Vancanneyt M, Kersters K, and Akkermans ADL (1999) Application of temperature-gradient gel electrophoresis in taxonomy of coryneform bacteria. International Journal of Systematic Bacteriology 49(1): 113–121. Irlinger F, Bimet F, Delettre J, Lefe`vre M, and Grimont PAD (2005) Arthrobacter bergerei sp. nov. and Arthrobacter arilaitensis sp. nov., novel coryneform species isolated from the surfaces of cheeses. International Journal of Systematic and Evolutionary Microbiology 55: 457–462. Jones D and Keddie RM (2006) The genus Arthrobacter. In: Dworkin M, Falkow S, Rosembreg E, Schleifer CK, and Stackebrandt E (eds.) The Prokaryotes: A Handbook on the Biology of Bacteria, 3rd edn., Vol. 3, pp. 945–960. New York: Springer.
Obermayr H and Ginzinger W (1997) Metabolic activity of red smear bacteria. Deutsche Milchwirtschaft 48(11): 396–398. Osorio CR, Barja JL, Hutson RA, and Collins MD (1999) Arthrobacter rhombi sp. nov., isolated from Greenland halibut (Reinhardtius hippoglossoides). International Journal of Systematic Bacteriology 49(3): 1217–1220. Reineke W (1988) Microbial degradation of haloaromatics. Annales Revue Microbiology 42: 263–287. Smacchi E, Gobbetti M, Rossi J, and Fox PF (2000) Purification and characterization of an extracellular esterase from Arthrobacter nicotianae 9458. Le Lait 80: 255–265. Stackebrandt E and Schumann P (2006) Introduction to the taxonomy of Actinobacteria. In: Dworkin M, Falkow S, Rosembreg E, Schleifer CK, and Stackebrandt E (eds.) The Prokaryotes: A Handbook on the Biology of Bacteria, 3rd edn., Vol. 3, pp. 297–321. New York: Springer. Suzuki KI and Komagata K (1983) Taxonomic significance of cellular fatty acid composition in some coryneform bacteria. International Journal of Systematic Bacteriology 33(2): 188–200. Valdes-Stauber N, Scherer S, and Seiler H (1996) Identification of yeasts and coryneform bacteria from the surface microflora of brick cheeses. International Journal of Food Microbiology 34(2): 115–119. Washam CJ, Olson HC, and Vedamuthu ER (1977) Heat-resistant psychrotrophic bacteria isolated from pasteurized milk. Journal of Food Protection 40(2): 101–108. Wauters G, Charlier J, Janssens M, and Delme´e M (2000) Identification of Arthrobacter oxydans, Arthrobacter luteolus sp. nov., and Arthrobacter albus sp. nov., isolated from human clinical specimens. Journal of Clinical Microbiology 38(6): 2412–2415.
Pseudomonas spp. J D McPhee and M W Griffiths, Guelph University, Guelph, ON, Canada ª 2011 Elsevier Ltd. All rights reserved.
Morphology and Characteristics Pseudomonads are Gram-negative, straight or curved rods, which are motile by polar flagella. They are aerobic and their metabolism is never fermentative. They are catalase-positive and the majority of species are oxidasepositive. Pseudomonas fluorescens is found predominantly in soil and water and it produces a diffusible fluorescent pigment, pyoverdin. The taxonomy of the genus Pseudomonas is complex and there is extensive genetic heterogeneity among its members.
Sources of Pseudomonas spp. in Milk
day collection may have little effect on the bacteriological quality of milk rapidly cooled to 4 C or below before addition to the tank, the growth potential of the raw milk microflora is significantly affected. Thus, milk collected on alternate days will contain a greater number of bacteria that are entering the exponential phase of growth when the milk arrives at the processing site, and the amount of time that this milk can be subsequently stored will be reduced. For example, it has been shown that Pseudomonas spp. isolated from milk that had been stored at 7 C for 3 days grew 10 times faster at 7 C, had 1000-fold more proteolytic activity, and were 280-fold more lipolytic than pseudomonads isolated from freshly drawn milk. However, the Pseudomonas counts in the milk increased by only about 1 log cycle during the storage period.
Contamination from Milking and Storage Equipment Significant contamination of milk by pseudomonads occurs due to inadequately sanitized surfaces of milking and milk storage equipment. The organisms grow in milk residues present in crevices, joints, rubber gaskets, and dead ends of badly cleaned milking plants. Although many different bacterial types can be introduced into milk from milk mineral deposits present in milking equipment, the most important of these are the Gram-negative psychrotrophs, which predominate among the microflora that adhere to stainless-steel milk transfer pipelines. Variations in cleaning regimes and levels of contamination from farm to farm lead to differences in the microflora found on milking equipment. The only effective way to limit the introduction of bacteria into the milk supply during milking is to ensure adequate cleaning and disinfection of all the equipment. The effectiveness of sanitation depends to a large extent on the design of the plant and on other factors such as the hardness of the water supply. Generally, farm bulk tanks do not contribute greatly to the bacterial load of raw milk as they are easy to clean and, consequently, have a much lower bacterial content than the milk pipeline. However, ancillary equipment such as agitators, dipsticks, outlet plugs, and cocks can be difficult to clean and these may be a possible source of contamination. Any residual bacteria present have the potential for growth during storage. Milk may be collected from farms on alternate days, or even longer in some instances. Thus, at collection, part of the milk in the bulk tank may be 48 h old or more. Although alternate-
Contamination during Transportation and Storage at the Processing Facility Adequate cleaning of any dairy equipment used for the collection, transport, and storage of refrigerated raw milk must be performed to prevent fouling with milk film, which can support growth of bacteria that then become a source of contamination to subsequent batches of milk. Milk is usually transported in insulated tanks or in refrigerated tankers, and may be transferred to larger vehicles for longer journeys. During transportation, the main cause of increased bacterial count is inadequately cleaned vehicles and growth of bacteria already present in the milk. The latter is dependent on the milk temperature and journey time. A twofold increase in count is common during transportation of milk from the farm to the processing site and this is due primarily to the growth of psychrotrophic bacteria, including pseudomonads. Critical sites in the milk tanker for cleaning have been identified as the air separator, the milk meter, the milk sieve, and the suction hose, and factors that contribute to inadequate cleaning include blockage of the cleaning-in-place (CIP) spray system and low water pressure and flow rate. These can lead to buildup of milk stone on the inner surface of the tanker. Changes in dairy industry practices such as the introduction of a 5-day working week, and milk shortages at certain times of the year due to the adoption of quota systems, have led to milk being stored for longer times before processing. Thus, the temperature at which milk is stored becomes critical. It has been recommended that milk
379
380 Psychrotrophic Bacteria | Pseudomonas spp.
is cooled to, and maintained at, 3 C on receipt at the processing plant before storage. The average psychrotrophic, aerobic bacterial count of silo milk at several dairies in southwest Scotland was 1.3 105 cfu ml 1. The majority of bacteria present were pseudomonads (70.2%) but Enterobacteriaceae (7.7%), Gram-positive bacteria (6.9%), and other Gram-negative, rod-shaped organisms were also isolated. When the milks were stored for a further 48 h at 6 C, the psychrotroph count increased by 2 log cycles to 1.3 107 cfu ml 1. Psychrotrophic growth patterns were independent of whether milks were selected according to their initial counts, and whether they were stored in large air-agitated silos or small, paddle-agitated vats. Growth rates were highest during filling of the silos, due possibly to temperature fluctuation, and final bacterial numbers were dependent on initial counts and storage time, with the latter being the most significant factor affecting milk quality. It has been shown that raw milk stored at low temperatures is spoilt exclusively by Gram-negative bacteria. In earlier studies where identification was primarily performed by phenotypic analysis, Pseudomonas fluorescens biovar I (32.1% of isolates), Ps. fragi (29.6%), Ps. lundensis (19.8%), and Ps. fluorescens biovar III (17.3%) were the most commonly isolated. However, more recent studies conducted in Belgium using molecular methods such as Repetitive sequence-based Polymerase Chain Reaction (REP-PCR) and 16S RNA sequencing identified Ps. lundensis and Ps. fragi as the most common proteolytic psychrotrophs isolated from milk and these two species accounted for 53% of proteolytic strains isolated. The authors of this study concluded that there was an overestimation of the prevalence of Ps. fluorescens in previous studies due to problems with the taxonomy of the genus leading to inappropriate identification methods being used. There seems to be little difference between the types of spoilage microorganisms associated with bovine milk and ovine and caprine milks. Postpasteurization Contamination Although Gram-negative, psychrotrophic bacteria present in raw milk do not survive pasteurization, these organisms are commonly isolated from pasteurized milk and cream, again with Pseudomonas spp. being the most frequently encountered. Thus, the shelf life of pasteurized products is limited by postpasteurization contamination. The microflora of short shelf life milks (i.e., <5 days at 4–6 C) comprise almost entirely of Pseudomonas spp. (approximately 90% of isolates), while those with shelf lives >10 days have a higher proportion of other types of microorganisms. In the latter milks, Pseudomonas spp. account for about 70% of isolates. More recent work using sequence analysis of denaturing gradient gel electrophoresis DGGE
fragments to investigate the microbial ecology of pasteurized milk stored at 4 C revealed high diversity among Pseudomonas spp. in the milk samples. Pseudomonas putida and Ps. migulae grew to high numbers during storage and Ps. fluorescens and Ps. fragi were also found. A variety of sources of contamination by pseudomonads exist in the processing plant. However, personnel and air probably contribute little to the contamination of pasteurized fluid milk products by these organisms. It has been shown that Pseudomonas spp. are able to form biofilms. A likely cause of postpasteurization contamination is shedding of bacteria from biofilms formed on gaskets in pasteurized milk pipelines. Electron microscopy has been used to show that Pseudomonas biofilms can develop on the sides of gaskets, despite operation of CIP systems, and it is well accepted that sanitizer efficacy is greatly reduced against bacteria growing in biofilms. There is substantial evidence that the filling operation has the greatest influence on the potential shelf life of pasteurized milk. Low levels of psychrotrophic bacteria (10–500 cfu l 1) can be introduced into the product at this stage and these can have a profound effect on shelf life. Improvements to the design of fillers have resulted in dramatic effects on the keeping quality of milk. Aseptically packaged milk can be kept for about 48 days when stored at 3 C.
Consequences of Growth of Pseudomonads in Raw Milk In addition to being able to grow rapidly in refrigerated milk, psychrotrophs produce extracellular enzymes that can degrade milk components. Although most psychrotrophs present in milk are not heat resistant, in many cases the extracellular enzymes that they produce can survive pasteurization (70–80 C) and even UHTs (120–140 C). Both proteases and lipases produced by psychrotrophs, representative of a number of genera, retained 60–70% of their activity after heating at 77 C for 17 s and about 30–40% of their activity remained after UHT treatment at 140 C for 5 s. Recent work has shown that proteolytic activity of bacterial origin in milk has a D-value at 75 C of about 360 min and a z-value of about 29 C. The heat stability of these enzymes is influenced by milk proteins, which exert a stabilizing effect. Not all the pseudomonads found in milk are capable of synthesizing these enzymes and, even in those that do, the levels produced are affected by many factors, including growth phase, nutrient supply (such as iron availability), phase variation, and environmental conditions, including temperature and oxygen tension. In a Belgian study, the incidence of proteolytic psychrotrophs was lower in milks collected in winter than in summer but the strains isolated in winter exhibited greater proteolytic activity than their summer counterparts. It has also been
Psychrotrophic Bacteria | Pseudomonas spp. 381
demonstrated that the enzymatic activity of pseudomonads and hence their spoilage potential can be predicted by their ribotype.
Extracellular Enzymes Psychrotrophic bacteria in milk produce many types of extracellular enzymes, including proteases, lipases, phospholipases, exopeptidases, and glycosidases. Proteases and lipases have been better characterized and are thus better understood. Proteases Most of the proteases isolated from pseudomonads are metalloenzymes, containing 1 zinc atom and up to 16 calcium atoms per molecule. There are reports of variable content of zinc and calcium, owing to the diversity of proteases from psychrotrophs. Analysis of the proteaseencoding gene, aprX, showed that pseudomonads expressed proteases with a high degree of heterogeneity. Some strains of Pseudomonas have been found to produce more than one type of protease and strain-to-strain variability is common. Most proteases have milk-clotting activity, and are readily able to degrade -, s1-, and -casein, yet have low activity on nondenatured whey proteins. Isoelectric pH values of proteases from Ps. fluorescens vary from 5.1 to 8.8. The pH optima of proteases fall into two broad categories: neutral proteases with a pH optimum of pH 7 and alkaline proteases with optima at pH 8–9. The molecular weights of most proteases range from 40 to 50 kDa. Temperature optima range from 30 to 50 C; in all cases, activity decreases sharply at temperatures above the optimum but all proteases for which data are available retained activity at 4 C. Pseudomonas fluorescens proteases are extremely heat stable but most are unstable around 60 C. Stability data at high temperatures are not reported for all proteases. This is very important from a spoilage perspective because the presence of proteases following commercial pasteurization (72 C for 12–15 s) and UHT processing (135–148 C for 2–5 s) can lead to quality defects. Lipases and Phospholipases Lipolytic degradation of milk is not as predominant as proteolytic degradation. Lipases of Ps. fluorescens typically form aggregates with lipids, or lipase–polysaccharide complexes. It is generally thought that Pseudomonas produces only one lipase; however, a second lipase has been isolated from Ps. fluorescens. Pseudomonas spp. typically produce a lipase that is active on milk fat. Lipases from Pseudomonas spp. can actively hydrolyze a variety of natural oils and synthetic triglycerides ranging from
tributyrin to triolein. One of the most important enzymes produced by Pseudomonas is lecithinase, a phospholipase, which is able to hydrolyze the protective membrane of milk lipid. The membrane, composed primarily of lecithin, maintains the globular structure of milk lipid. Hydrolysis of the membrane can lead to fat aggregation and render milk lipid susceptible to the action of native milk lipases. Although lipases from Pseudomonas share one or more of the same epitopes, they are structurally diverse, which severely limits the ability to design DNA- or antibody-based probes for their detection. The optimal pH range for lipases from Ps. fluorescens is 7–8; however, activity is maintained from pH 5 to 11. Reported temperature optima range from 22 to 55 C, and activity has been found at 29 C. The pH and temperature optima reported are dependent on the substrate type used for their determination. The molecular weights of most lipases range from 32 to 633 kDa. Lipases appear to be less thermostable than proteases; however, activity has been found at temperatures as high as 130 C. Although strain-to-strain variation prevents generalizing on the thermostability of lipases from Pseudomonas spp., there are several reports indicating that lipases produced by Ps. fluorescens can survive commercial pasteurization and UHT processing and can affect the keeping quality of dairy products. Regulation of Extracellular Enzymes A variety of factors, including quorum sensing, growth phase, and environmental and nutritional factors, are involved in the regulation of synthesis of extracellular enzymes. For example, pH, temperature, oxygen tension, adenosine triphosphate pools, presence of ions, organic nutrients, triglycerides, and many more have been found to influence enzyme synthesis. Surprisingly, the regulation of synthesis of extracellular enzymes by pseudomonads is not unequivocally established, and probably involves a variety of regulatory mechanisms acting in concert. This fact further highlights the complexity and diversity of Pseudomonas extracellular enzymes. Understanding the complex mechanisms that direct enzyme synthesis will provide strategies to target for control. For example, it has been shown that disruption of quorum sensing results in a decreased production of protease by Ps. fluorescens; however, synthesis of the enzyme is not entirely prevented. Heat-based processing methods that are currently employed to curb enzymerelated spoilage are also detrimental toward product quality. One factor responsible for regulation of extracellular enzymes is the phase of growth. Related to this is a growing body of research on cell-to-cell communication termed quorum sensing, dealing specifically with coordinated timing of cellular events according to cell density.
382 Psychrotrophic Bacteria | Pseudomonas spp.
Pseudomonads, like other Gram-negative bacteria, produce an autoinducer, an acyl homoserine lactone derivative. This autoinducer is produced throughout the growth cycle, but it is only when its concentration reaches a threshold level toward the end of the log phase and early stationary phase that it is able to regulate the expression of several genes, including, in part, those responsible for the synthesis of extracellular enzymes of Ps. fluorescens. It has been shown that mutants of Ps. fluorescens that are incapable of producing extracellular proteinase are also incapable of synthesizing the autoinducer molecule.
described as having unacceptable flavor scores and bitter, unclean, or fruity flavors when made from milk having high levels of psychrotrophs. Pseudomonas spp. are also associated with spoilage of Cottage cheese and they are able to oxidize diacetyl to acetoin, a flavorless compound. This results in a product with a bland taste. It is clear that the growth and presence of psychrotrophs in dairy products prior to heat processing can adversely affect the quality of the finished products. Postpasteurization contamination at very low levels by Pseudomonas spp., however, is more detrimental to the keeping quality of pasteurized milk at 4–8 C than the number of psychrotrophic bacteria in raw milk.
Significance in Milk and Dairy Products In general, the overall keeping quality of milk (pasteurized and UHT) and other dairy products is mainly limited by the action of proteases and lipases. When approximately 106 psychrotrophs per ml are present in raw milk before UHT heat treatment, gelation of the product will occur in less than 20 weeks of storage. Psychrotroph counts in the raw milk of about 107 cfu ml 1 will result in gelation after storage of the UHT milk for 2–10 weeks, accompanied by a gradual development of ‘lack of freshness’ and bitter flavors. Pasteurized milk having previously supported growth of psychrotrophs to levels of 5.5 log cfu ml 1 has been described as having an inferior flavor. However, defects in pasteurized milk are not as prevalent as in other dairy products, which may be due to the short period of storage of raw milk prior to processing. The development of flavor defects is dependent on the strain of Pseudomonas and fat content of the milk. Cheese can be affected by both proteases and lipases, with the resultant reduction of yield and flavor defects (such as soapiness, rancidity, and bitterness). It has been suggested that the slight adverse effects of proteases on cheese quality might be due to their removal in whey. However, lipases appear to be retained in cheese, and, for this reason, lipid-associated flavor defects predominate rather than protease-related reduction in cheese yields, although the presence of free fatty acids resulting from controlled lipolysis of milk fat is necessary for the characteristic development of the cheese flavor. Excessive lipolysis of cheese typically results in off-flavors, usually associated with psychrotroph counts in raw milk of about 107–108 cfu ml 1. Butter can also undergo considerable hydrolytic rancidity from heat-resistant lipases. The result is the production of rancid, putrid flavors due primarily to the growth of Pseudomonas spp. in water droplets. By virtue of its high fat content and the tendency of lipase to partition preferentially into the cream phase of milk, cream is very susceptible to lipases from psychrotrophs. Flavor defects are the most common complaint resulting from the growth of lipolytic psychrotrophs in cream. Yogurt and cultured dairy products have been
Control of Pseudomonas spp. and Related Enzymes There is general agreement that it is very difficult to prevent contamination of raw milk by Pseudomonas spp., probably due to their ubiquitous nature. Therefore, approaches involving control of extracellular enzyme production seem to be a more promising solution than methods for prevention. Examples of the wide range of methods currently proposed to control psychrotrophic bacteria and/or their extracellular enzymes include thermization (a heat process of 60–66 C for 5–20 s), additives (CO2, nitrogen), high-pressure treatment, modified atmosphere storage of raw milk, microbial antagonism, activation of the lactoperoxidase system in milk, addition of enzyme inhibitors, addition of bacteriocin-producing lactic acid bacteria, and lowtemperature inactivation of enzymes, to name a few. Only one of the aforementioned processes (low-temperature inactivation of enzymes) specifically targets enzyme synthesis. Most practices currently employed in the industry focus on elimination of the bacteria by heat processing.
Enumeration Two general approaches are used to enumerate psychrotrophic microorganisms. Both apply to enumerating Pseudomonas spp. from dairy products. The traditional method selects specifically for psychrotrophs by incubation of test samples at 7 C for 7 days. Due to the lengthy incubation, it is not very suitable as a quality assurance measure in the dairy processing industry. A second, and more rapid, approach to enumerating psychrotrophs involves incubation at 21 C for 25 h. Most colonies appearing on agar plates using this method will be psychrotrophs since their optimum growth temperatures are typically between 20 and 22 C. The second method is more rapid and correlates very well with the traditional 7-day incubation at 7 C.
Psychrotrophic Bacteria | Pseudomonas spp. 383
Pseudomonas spp. grow well on nonselective media (e.g., plate count agar, tryptic soy agar, Luria-Bertani agar, blood agar, MacConkey agar, eosine methylene blue agar). There exist a variety of media for specifically targeting fluorescent pseudomonads. These media enhance production of the typical green fluorescent pigment, pyoverdin, and therefore allow for easy identification of colonies on agar plates exposed to ultraviolet light. Examples of media found effective for identifying fluorescent pseudomonads include medium B and various media containing penicillin G, novobiocin, and cycloheximide. Considerable interference from other Gram-negative bacteria is encountered when attempting to isolate Pseudomonas spp. on a nonselective medium. One promising selective medium has been developed based on heart infusion agar with addition of the selective agents cephaloridine, fucidin, and cetrimide. This medium effectively suppresses growth of Gram-positive bacteria and inhibits growth of other Gram-negative bacteria. Following inoculation and spread plating, the agar is incubated at 25 C for 48 h. A polymerase chain reaction assay for proteaseproducing pseudomonads, which targets the aprX gene, has been proposed but, due to gene heterogeneity, it failed to detect Ps. lundensis strains.
Pseudomonas aeruginosa Pseudomonas aeruginosa is a Gram-negative, aerobic rod, and is an opportunistic pathogen that causes urinary tract infections, respiratory system infections, dermatitis, softtissue infections, bacteremia, and a variety of systemic infections, particularly in victims of severe burns and in cancer and AIDS patients who are immunosuppressed. Pseudomonas aeruginosa may cause mastitis. The organism can be isolated from soil and water. Pseudomonas aeruginosa isolates may produce three colony types. Natural isolates from soil or water typically produce a small, rough colony. Pseudomonas aeruginosa produces two types of soluble pigments, pyocyanin and (fluorescent) pyoverdin. The latter is produced abundantly in media of low iron content, and could function in iron metabolism in the bacterium. Pseudomonas aeruginosa is primarily a nosocomial pathogen. The organism has an optimal growth temperature of 37 C but is unable to grow at 4 C. This makes Ps. aeruginosa an uncommon contaminant of refrigerated milk.
See also: Milking and Handling of Raw Milk: Effect of Storage and Transport on Milk Quality; Milking Hygiene. Psychrotrophic Bacteria: Arthrobacter spp.; Other Psychrotrophs.
Further Reading Champagne DP, Laing RR, Roy D, Mafu AA, and Griffiths MW (1993) Psychrotrophs in dairy products: Their effect and their control. Critical Reviews in Food Science and Nutrition 34: 1. Dieckelmann M, Johnson LA, and Beacham IR (1998) The diversity of lipases from psychrotrophic strains of Pseudomonas: A novel lipase from a highly lipolytic strain of Pseudomonas fluorescens. Journal of Applied Microbiology 85: 527. Fairbairn DJ and Law BA (1986) Proteinases of psychrotrophic bacteria: Their production, properties, effects and control. Journal of Dairy Research 53: 139. Fox PF, Power P, and Cogan TM (1989) Isolation and molecular characteristics. In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food., pp. 57–120. Boca Raton, FL: CRC Press. Griffiths MW (1989) Effect of temperature and milk fat on extracellular enzyme synthesis by psychrotrophic bacteria during growth in milk. Milchwissenschaft 44: 539. Griffiths MW (2000) Milk and unfermented milk products. In: Lund BM, Baird-Parker AC, and Gould GW (eds.) The Microbiological Safety and Quality of Food, pp. 507–534. Gaithersburg, MD: Aspen. Griffiths MW and Phillips JD (1984) Effect of aeration on extracellular enzyme synthesis by psychrotrophs growing in milk during refrigerated storage. Journal of Food Protection 47: 697. Griffiths MW, Phillips JD, and Muir DD (1981) Thermostability of proteases and lipases from a number of species of psychrotrophic bacteria of dairy origin. Journal of Applied Bacteriology 50: 289. He H, Dong J, Lee CN, and Li Y (2009) Molecular analysis of spoilage-related bacteria in pasteurized milk during refrigeration by PCR and denaturing gradient gel electrophoresis. Journal of Food Protection 72: 572. Law BA and Fairbairn DJ (1982) Influence of nutritional factors on the production of extracellular proteinase by Pseudomonas fluorescens. Journal of Dairy Science 65: 74. Liu M, Gray JM, and Griffiths MW (2006) Occurrence of proteolytic activity and N-acyl-homoserine lactone signals in the spoilage of aerobically chill-stored proteinaceous raw foods. Journal of Food Protection 69: 2729. Marchand S, Heylen K, Messens W, et al. (2009) Seasonal influence on heat resistant proteolytic capacity of P. lundensis and P. fragi, predominant milk spoilers isolated from Belgian raw milk samples. Environmental Microbiology 11: 467. Marchand S, Vandriesche G, Coorevits A, et al. (2009) Heterogeneity of heat-resistant proteases from milk Pseudomonas species. International Journal of Food Microbiology 133: 68. McKellar RC (1982) Factors influencing the production of extracellular proteinase by Pseudomonas fluorescens. Journal of Applied Bacteriology 53: 305. McKellar RC (1989) Regulation and control of synthesis. In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food., pp. 153–172. Boca Raton, FL: CRC Press. Mottar JF (1989) Effect on the quality of dairy products. In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food. Boca Raton, FL: CRC Press. Stepaniak L and Su`rhaug T (1989) Biochemical classification. In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food, pp. 35–56. Boca Raton, FL: CRC Press. Sørhaug T and Stepaniak L (1997) Psychrotrophs and their enzymes in milk and dairy products: Quality aspects. Trends in Food Science and Technology 8: 35.
Other Psychrotrophs L Stepaniak† , Agricultural University, A˚s, Norway ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2345–2351, ª 2002, Elsevier Ltd.
General Considerations Several species of Gram-negative and Gram-positive bacteria which have the capacity to spoil milk and other short shelf-life dairy products and can grow at or below 7 C (Table 1) have been isolated from raw milk and freshly pasteurized milk and cream. Compiled from: Craven HM and Macauley BJ (1992) Australian Journal of Dairy Technology 47: 38–45; Cromie SJ et al. (1989) Australian Journal of Dairy Technology 44: 74–77; Griffiths MW and Phillips JD (1990) Journal of the Society of Dairy Technology 43: 62–66; Suhren G (1989) In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food, pp. 3–34. Boca Raton: CRC Press; Ternstro¨m A et al. (1993) Journal of Applied Bacteriology 75: 25–34. Commercial high-temperature, short-time (HTST) pasteurization (72 C for 15 s) of raw milk of reasonable microbial quality essentially eliminates heat-labile psychrotrophic pseudomonads. Laboratory-pasteurized or pasteurized and aseptically packed milk and cream are free from postpasteurization contaminants but after prolonged cold storage become microbiologically spoiled, even at 1 C (Table 2). Spoilage of such milk is mainly caused by sporeforming psychrotrophic and aerobic Bacillus spp. Unless aseptically drawn, good-quality raw milk contains after milking several thousand bacteria per milliliter, half of which are usually coryneform bacteria and Micrococcus spp. Psychrotrophic Pseudomonas spp. and other heat-labile Gram-negative psychrotrophs, such as Flavobacterium, Alcaligenes and Chromobacterium, are usually reported to be minor components of the microflora of good-quality fresh raw milk. Corynebacteria, Micrococcus, Arthrobacter and Streptococcus are frequently both psychrotrophic and thermoduric. Many of these species, along with spores of Bacillus and Clostridium spp., survive HTST pasteurization. The total number of bacteria that survive HTST pasteurization is often higher than 1000 ml1. The number of spores in raw milk is very variable but rarely exceeds more than 2% of the total microflora. The psychrotrophic Bacillus spp. may represent only a small part of total spore count. Frequently, the number of spores of psychrotrophic Bacillus spp. in freshly pasteurized milk is so low that it can be determined only by the most probable number (MPN) y
Deceased.
384
technique. Spores of Clostridium spp. occur in markedly lower numbers than spores of Bacillus spp. The method recommended for the enumeration of total psychrotrophic count is the same as standard plate count except that plates are incubated at 7 C for 10 days. Short methods with counts after 25 h based on incubation at an elevated temperature have also been developed. A way to obtain the proportion of bacteria present in milk as spores is to conduct viable count of a sample in which the vegetative cells have been killed by heat. Crystal violet or preparations of other selective inhibitors have been used to prevent Gram-positive bacterial growth. Procedures that include biotyping (examination of profile of biochemicals utilized by the cells) have been widely used for identification of dairy isolates of psychrotrophic nonpseudomonads. Many of the isolates have only been identified at the genus level. Computer-aided biotyping using miniaturized commercial kits has been introduced for identification of both Gram-positive and Gram-negative bacteria, including many nonpseudomonad psychrotrophs. Enumeration, detection and typing of Bacillus cereus group isolates from milk have been extensively studied. Biotyping, serotyping, phage typing, nucleic acid-based techniques, immunological methods, electrophoresis of proteins, gas chromatographic analysis of cellular fatty acids and pyrolysis have been used for the identification and/or typing of these microorganisms. Randomly amplified polymorphic DNA procedure which includes polymerase chain reaction (RAPD–PCR) has been used for subtyping of Bac. cereus, Bac. licheniformis and Bac. thuringensis. RAPD–PCR also allowed the tracing of contamination routes of Bac. cereus in dairy processing.
Growth at Refrigeration Temperatures Compared with Pseudomonas spp., available data on the effect of temperature on the growth rate and properties of enzymes produced by other psychrotrophs are limited. Based on the comparison of generation times, it can be generalized that Pseudomonas spp. are more potent psychrotrophs than other genera (Table 1). However, minimum growth temperatures (Tmin) calculated from the Ratkowsky ‘square root’ equation indicate that Alcaligenes spp. and Chromobacterium spp. are as likely to be psychrotrophic as Pseudomonas spp. (Table 3).
Psychrotrophic Bacteria | Other Psychrotrophs
385
Table 1 Generation time of psychrotrophic bacteria in heat-treated milk and frequency of their isolation from raw or pasteurized contaminated milk and cream Frequency of isolation (%) From spoiled pasteurized milk or cream stored at
Generation time (h) at
Gram-negative bacteria Acinetobacter spp. Alcaligenes spp. Achromobacter spp. Enterobacteriaceae Flavobacterium spp. Pseudomonas spp. Gram-positive bacteria Bacillus cereus Bacillus circulans Bacillus polymyxa Bacillus spp. Micrococcus spp.a Psychrotrophic yeasts
3–5 C
7–9 C
From cold stored raw milk
4–5 C
7 C
—
—
—
90
89
14.4 — 9.0 10.3 — 6.5–8 —
— 13 5.5 — 14.1 3.5–4 —
nd–6 nd–1.5 nd–2 8–15 1–14 30–86 —
— 0.4 — 1 2 45–90 5–70
— 1.3 — 1 0.8 50–83 10–55
— — — — 26.2 —
7–48 5–12 22 (at 6 C) — 20.9 —
nd–10 — — — — —
— — — 5–70 — —
— — — 10–55 — 0.7
a
Some can also be Gram-negative. nd, not detected by plate count.
Table 2 Effect of temperature on the shelf-life and growth of thermoduric psychrotrophs in aseptically packed high-temperature, short-time (HTST) pasteurized milk
Temperature ( C)
Shelf-life (days) terminated due to flavor defects
Count (cfu ml1) at the time of spoilage
Days to reach a count of 107 cfu ml1
1 3 7 12
75 52 28 11
5 107 7 107 6 107 2 107
51 34 20 10
Adapted from Dommett (1992).
Both the lag time and the generation time of psychrotrophic Bacillus spp. vary considerably. Bacillus circulans can grow at 1 C and has been found in independent studies to have a shorter lag time and generation time than six other species of psychrotrophic Bacillus spp. Psychrotrophic and thermoduric psychrotrophs may be simply variants of mesophilic organisms, which have adapted to grow at low temperatures. The growth rates and lag times in ultra-heat treated (UHT) milk and pasteurized milk or single and double cream are similar for Gram-negative psychrotrophs as well as Bacillus spp. Tmin for different bacterial cultures are similar in milk and other media. Spores of psychrotrophic Bacillus spp. show maximum germination activity at 15 C, with a possible second maximum peak at 5 C. Increasing the temperature of HTST pasteurization of
milk may actually have an adverse effect on its keeping quality because temperatures higher than 72 C may induce the germination of spores. Spores of Bacillus spp. may germinate and grow rapidly during the first hours of incubation of fermented milks until the pH decreases to a value which is inhibitory to these organisms. Psychrotrophic yeasts and moulds can spoil fermented milks. Psychrotrophic Pathogens Listeria monocytogenes, Yersinia enterocolitica, Bacillus cereus and probably enterohemorrhagic Escherichia coli (see Pathogens in Milk: Bacillus cereus; Escherichia coli; Listeria monocytogenes; Yersinia enterocolitica) are psychrotrophic pathogens that can grow at or below 8 C, but
386 Psychrotrophic Bacteria | Other Psychrotrophs Table 3 Theoretical minimum temperature (Tmin)a for selected bacteria Organism
Tmin (K)
Acinetobacterb spp. 55 Aeromonas hydrophila 1383 Alcaligenes faecalis G2/7 Bacillus cereus (four strains) Bacillus circulans (two strains) Bacillus lentus MRM 305 Bacillus polymyxa MRM 304 Chromobacterium spp. 12 Citrobacter freundii 1197 Coliforms (two strains) Coryneforms (two strains) Enterobacter agglomerans 1498 Micrococcus spp. (two strains) Pseudomonas spp. (five species) Serratia spp. (two species) Streptococcus faecalis NCIB 775
266.6–267.0 269.2–269.4 258.7–259.0 272.9–278.7 262.7–266.1 265.8–267.0 270–272.6 260.2–263.7 268.4–269.8 264–274 275.8–278.5 266.6–267.7 273.6–273.7 260.2–269.8 266.3–274.2 273.6–273.8
p Calculated from Ratkowsky ‘square root’ equation: r ¼ b(T Tmin), p where r is the square root of the growth rate constant, T is temperature (K) and Tmin (or T0) is theoretical (conceptual) temperature of no metabolic significance (conceptual minimum growth temperature). b For single strains, data are from growth in skim and full-fat milk. Compiled from: Phillips JD and Griffiths MW (1987) Food Microbiology 4: 173–185 and Ratkowsky DA et al. (1982) Journal of Bacteriology 149: 1–5. a
only Bac. cereus is a significant determinant of shelf-life of pasteurized milk or fresh dairy products. Proteolytic psychrotrophs may stimulate the growth of pathogens in milk.
Incidence of Genera Other than Pseudomonas in Raw and Pasteurized Milk Psychrotrophs that Survive Pasteurization The incidence of aerobic sporeforming bacteria in milk is highly seasonal. Studies in several countries have shown the highest number of spores during late summer and early autumn. Soiling of the udder during grazing may
be responsible for the high count of sporeforming bacteria. Frequently, the total number of spores reported in raw milk is in the range 1–160 ml1. Occasionally, high numbers (>104 ml1) of spores or vegetative cells of Bacillus spp. have been reported. Both Bac. cereus group, Bac. licheniformis and Bac. coagulans, are the species of sporeforming bacteria predominantly in fresh raw milk. The number of spores in freshly pasteurized milk varies widely between dairy plants and on a daily basis in the same dairy plant. The spoilage potential of thermoduric/sporeforming psychrotrophs has been well demonstrated by incubating milk or cream free from postpasteurization contaminants and therefore free from Pseudomonas spp. and other heatlabile microorganisms. Spoilage may occur at 3 C after approximately 7 weeks of storage (Table 2). The shelflife of pasteurized, noncontaminated milk is approximately three times longer at 7–10 C than the shelf-life of commercially produced milk, which becomes contaminated after pasteurization and stored at 3–5 C (Table 4). Coryneform bacteria dominate freshly pasteurized cream or milk (Table 5). Very often, only 0.05–1 spore of psychrotrophic Bacillus spp. is detected in freshly pasteurized milk or cream by the MPN technique. Vegetative cells of Bacillus spp. can probably be detected on a selective medium such as polymyxin–egg-yolk–mannitol– bromothymol-blue agar in every package of freshly pasteurized milk which has been preincubated at room temperature. Raw milk has been shown to be a markedly more important source of psychrotrophic spores than postpasteurization contamination. Bacillus circulans occurs in both raw and freshly pasteurized milk at lower numbers than Bac. cereus. However, data from different sources show that Bac. circulans dominates spoiled milk or cream, free from postpasteurization contaminants, stored at 3–7 C. At 12 C, a significant proportion of bacteria at the time of spoilage are Bac. cereus, coryneform bacteria, micrococci and streptococci (Table 5).
Table 4 Effect of postpasteurization contamination (PPC) on shelf-life and psychrotrophic count of pasteurized milk or cream. Postpasteurization recontamination was avoided using aseptic packing or laboratory pasteurization Effect on shelf-life
Effect on psychrotroph count Count (cfu ml1) after storage at 6 C
Shelf-life (days) of milk or cream Storage at
PPC-free
Contaminated
Storage of cream for
PPC-free
Contaminated
3–5 C 7–10 C
49–28 35–20
11–6 7–5
6 days 13 days
4 103 7 105
7 105 5 107
Adapted from: Muir, 1996a; Muir, 1996b and Muir, 1996c and Stepaniak, L., 1991. Factors affecting quality and possibilities of predicting shelf-life of pasteurized and ultra-high temperature heated milks. Italian Journal of Food Science 3, pp. 11–26. Stepaniak (1991).
Psychrotrophic Bacteria | Other Psychrotrophs
387
Table 5 Microbial population patterns (% occurrence among isolated bacteria) of aseptically packed fresh and cold stored cream and cold stored concentrated milk
Bacillus circulans Bacillus cereus Other Bacillus spp. Streptococci Micrococci Coryneforms
Fresh cream, pasteurized at
Cream, pasteurized at 72 C for 15 s, by the end of shelf-life at
Concentrated 1:2 milk, pasteurized at 72 C for 15 s, by the end of shelf-life at
72 C for 15 s
80 C for 15 s
3 C
7 C
12 C
3 C
7 C
12 C
nd nd 3 5 22 70
nd 2 5 nd 3 90
100 nd nd nd nd nd
50 2 nd 2 5 41
18 30 5 15 15 17
90 10 nd nd nd nd
95 5 nd nd nd nd
65 35 nd nd nd nd
nd, not detected by plate count. Adapted from Dommett (1992).
Incidence of Psychrotrophs in Commercially Pasteurized Nonaseptically Packed Milk Postpasteurization contamination of commercially pasteurized, nonaseptically packed milk is unavoidable. Recontamination in modern dairy plants can be as low as one bacterial cell per liter, and frequently is in the range of the number of psychrotrophic Bacillus spp. spores in freshly pasteurized milk. Major contaminants are Gram-negative rods, especially Pseudomonas spp., which are the most significant bacteria determining shelf-life of nonaseptically packed milk stored at 7 C or lower. The generation time and the lag time of microflora in pasteurized milks with an initial psychrotrophic count <10 l1 are markedly longer than in milk containing 100 psychrotrophs ml1 after pasteurization. Milk spoiled by coliforms at 7 C has also been reported occasionally. Pasteurized milk containing 1–100 coliforms ml1 after preincubation at 21 C is much more frequently unacceptable after 10 days of storage at 7 C than milk in which coliforms have not been detected. In one study, at 10–12 C, Bacillus spp. and Gram-positive cocci each comprised 32–35% of the total spoilage microflora. The plate count of postpasteurization contaminated milk preincubated at 21 C with a mixture of crystal violet, nisin and penicillin has been used to estimate, within about 48 h, if milk will have satisfactory keeping quality at 6 C. The test correlates well with a standard method, which requires 5 days’ incubation at 6 C. The shelf-life of pasteurized milk, which was free from postpasteurization contaminants, was predictable from the storage time of raw milk. Wide daily fluctuations in the number, growth rate and germination properties of psychrotrophic thermoduric microorganisms and a variable level of postpasteurization contamination have been observed in pasteurized milk from the same processor. Large differences have also been observed between processors. Due to these variations, the correlation between shelf-life of cold
stored pasteurized milk and the total count of microorganisms in raw milk is usually poor. A good index for predicting the shelf-life of contaminated pasteurized milk stored at different temperatures is the average Tmin of its microflora, the value of which is variable and is influenced by the contribution of thermoduric and heat-labile psychrotrophs.
Product Defects Caused by Psychrotrophs and Their Enzymes Milk usually shows flavor defects when the total count of Bacillus spp. and/or Pseudomonas spp. is 2 107–5 107 cfu ml1. Flavor defects occur in pasteurized, aseptically packed milk spoiled by thermoduric and sporeforming bacteria when the number of these microorganisms is >107 cfu ml1 (Table 2). Occasionally, flavor defects are noted at a population of Bacillus spp. <107 cfu ml1. Extracellular enzymes and volatile metabolites have been detected in milk incubated with psychrotrophic Pseudomonas, Alcaligenes, Bacillus or with the indigenous flora, at populations around 106 cfu ml1. The threshold number for some psychrotrophic yeasts required to cause sensory changes in quark varies from 2.4 104 to 4.2 106 cfu g1. The pattern of volatile compounds analysed by gas chromatography or an electronic nose may be characteristic for spoilage organisms and may permit their identification. The production of heat-stable enzymes at low temperatures is not limited to the genus Pseudomonas. At least 5% of extracellular proteolytic activity survives in cellfree supernatants from one or more species of Bacillus, Enterobacter, Serratia, Alcaligenes, Flavobacterium and Achromobacter after exposure to 140 C for 5 s. Lipases with similar heat stability are secreted by Bacillus, Enterobacter, Serratia, Citrobacter, Moraxella and Achromobacter. More than 50% of the lipolytic or proteolytic activity of enzymes secreted by psychrotrophs other
388 Psychrotrophic Bacteria | Other Psychrotrophs
than pseudomonads can survive HTST pasteurization. For comparison, the D-value for Flavobacterium cells determined at 70 C is 0.05 s while the D-value for spores of several Bacillus spp. was between 16.5 and 20.5 min at 85 C. Some strains or species of Bacillus, Flavobacterium, Alcaligenes and Aeromonas also produce heat-stable phospholipase. The secretion of heat-labile proteinases and lipases or phospholipases by strains of the above and other psychrotrophic genera have also been reported. Some strains were only proteolytic or only lipolytic. Some species (Table 6) secrete more than one proteinase. Low-temperature treatment at 55 C, which effectively inactivates proteinases and lipases secreted by Pseudomonas spp., causes little reduction in the activity of proteinases and lipases from other genera of psychrotrophs. Proteinases of Pseudomonas spp., as well as those of other psychrotrophs (both Gram-negative and Grampositive), hydrolyze the major casein fractions with different specificity. Limited proteolysis produces an unclean flavor while advanced proteolysis causes gelation and sweet curdling of milk. Sweet curdling is associated with proteinase from Bacillus spp. Some Bacillus spp. isolated from milk can ferment lactose. Flavor defects caused by different Bacillus spp. grown in milk at 7 C have been described as fruity, sour, yeasty, gassy or unclean. The lipolytic activity of thermoduric psychrotrophs produces rancid and fruity off-flavors in milk products. Lipases from different genera show differences in specificity toward various triglycerides. Phospholipases, proteinases and glycosidases from
Pseudomonas, Citrobacter and Enterobacter may act synergistically in damaging the milk fat globule membrane. The aggregation of fat globules, which produces bitty cream, has been linked to the specific activity of phospholipase from Bac. cereus. The defect is not caused by Gram-negative psychrotrophs and can be substantially reduced if cream is stored below 5 C. Some psychrotrophic nonpseudomonad Gram-negative bacteria may be responsible for the reduction of diacetyl in buttermilk. Spoilage of sterile products by heat-stable enzymes from Pseudomonas spp. has been studied extensively. However, very little is known about the significance of heat-stable enzymes of genera other than Pseudomonas, isolated from cold-stored milk, to the spoilage of UHT-sterilized milk. Enzymes and other metabolites accumulated during the postpasteurization growth of psychrotrophs are likely to be mainly responsible for shortening the shelf-life of pasteurized milk and cream.
Thermoduric Psychrotrophs and Extended Shelf-Life Dairy Products Ongoing centralization of the dairy industry, resulting in the formation of large dairy plants, extends supply lines, while the new habit of consumers to shop less frequently calls for pasteurized milk and other cold-stored perishable dairy products with improved keeping quality. During storage and distribution, dairy products may be exposed to increases in temperature. It is therefore desirable that the products have built-in ‘quality buffers’ to minimize
Table 6 Some properties of proteinases (Pr), lipases (Li) and phospholipases (Ph) from psychrotrophs other than Pseudomonas spp. Molecular massb (kDa)
Optimal temperaturea
Optimal pH a
Microorganism
Pr
Li
Ph
Pr
Li
Ph
Pr
Li
Ph
Pr
Li
Ph
Alcaligenes spp. Achromobacter spp.
— 27 20 — 102 63 420 26, 34 — 75 62 65 — 13 29, 38 70
— — — — 33 — — — — — — — — — 25, 250 —
— — — — 25–35 — — 20, 23 — — — — — — — —
— 50 66 — 37 70 — — — — 45 — 41 42, 50 25, 60 —
50 37 — — — — — — — — — — — — 8.5, 10 —
— — — — — — — 50 — — — — — — — —
— 6.2 — 8.5 7.6 9.3 7.5 6, 7.5 — 5.3 6.2 6.2 8.0 7, 10 7, 10 6, 7.5
9 7 — — 8.5 — — — 6.5 — — — — — — —
— — — — — — — 6.6, 8.0 — — — — — — — —
— S — — M, C M M M — — M — M S M, S —
— — — — — — — — M — — — — — M —
— — — — M — — M — — — — — — — —
Acinetobacter spp. Alteromonas spp. Bacillus coagulans Bacillus spp. Chromobacterium spp. Pr 1 Pr 2 Pr 3 Enterobacter spp. Flavobacterium spp. Micrococcus spp. Vibrio spp. a
Inhibitors
Maximum and minimum values are given when more than one strain was studied. Values for molecular mass are determined by gel permeation chromatography. M, inhibitors of metalloenzymes; S, inhibitors of serine-type enzymes; C, inhibitors of cysteine-type enzymes. Compiled from: Fox PF et al. (1989) In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food, pp. 57–120. Boca Raton: CRC Press.
b
Psychrotrophic Bacteria | Other Psychrotrophs
spoilage at elevated temperatures. In the United States, extended shelf-life (ESL) (see Liquid Milk Products: Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk)) products have become an acronym that refers to the total process which encompasses everything from raw product quality to final distribution. The International Dairy Federation has suggested a target shelf-life of 25–45 days for ESL products. With the improved control of postpasteurization contamination, psychrotrophic sporeforming bacteria have emerged as important causes of spoilage of both normal and ESL milk. A large portion of microflora at the time of spoilage is often represented by Grampositive psychrotrophs. Apart from airborne contamination and contamination from the udder, inadequately cleaned milking equipment, pipelines, farm bulk tanks and product lines in dairy plants may be important sources of spores and thermoduric microorganisms. ESL milk with reduced or zero postpasteurization contamination may often be spoiled by Bacillus spp. only. Elopak and APV have developed the Pure-Lac system that combines heating of milk at 130–140 C for less than 2 s and instant cooling in a special steam infusion chamber with a packing system, which may reduce or completely eliminate postpasteurization contamination. The heating system substantially reduces the number of spores but does not denature much more whey proteins and does not cause more pronounced sensory changes than normal HTST pasteurization. Milk processed by this system is, according to European Union directive, termed as pasteurized at high temperature. Airborne contamination is avoided by surrounding the system with air filtered to remove bacteria and spores. Contamination from the package is eliminated by its sterilization using a solution of hydrogen peroxide at low concentration and UV light. Milk produced by the Pure-Lac system may have a shelf-life of up to 45 days at 10 C. Activation of the lactoperoxidase system, treatment with carbon dioxide, addition of bacteriocin-producing lactic acid bacteria and bacteriocin or antimicrobial peptides derived from lactoferrin may inhibit the growth of all types of psychrotrophs in cold stored milk. Microfiltration (see MEMBRANE SEPARATION) and centrifugation (bactofugation) markedly reduce the number of spores and psychrotrophic bacteria in milk. These techniques, combined with reduction or elimination of postpasteurization contamination, may assure the production of ESL milk and cream of the requisite keeping quality. Contamination with spores of Bacillus spp. and their enzymes produced in raw milk will be increasingly significant for the keeping quality of ESL products. The
389
development of a rapid method for the detection of contamination with psychrotrophic spores or enzymes from thermoduric psychrotrophs is warranted. See also: Bacteriocins. Heat Treatment of Milk: Ultra-High Temperature Treatment (UHT): Aseptic Packaging; Ultra-High Temperature Treatment (UHT): Heating Systems. Liquid Milk Products: Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk). Microorganisms Associated with Milk. Milk Protein Products: Membrane-Based Fractionation. Pathogens in Milk: Bacillus cereus; Escherichia coli; Listeria monocytogenes; Yersinia enterocolitica.
Further Reading Champagne CP, Laing RR, Roy D, Mafu AA, and Griffiths MW (1994) Psychrotrophs in dairy products: their effect and their control. Critical Reviews in Food Science and Nutrition 34: 1–30. Cousin MA (1989) Physical and biochemical effects on milk components. In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food, pp. 205–225. Boca Raton: CRC Press. Dommett TW (1992) Spoilage of aseptically packaged pasteurized liquid dairy products by thermoduric psychrotrophs. Food Australia 44: 459–461. Giffel MC, Beumer RR, Christiansson A, and Griffiths MW (2000) Bacillus cereus in milk and dairy products: advances in detection, typing and epidemiology. International Dairy Federation Bulletin 357: 47–54. Griffiths MW and Phillips JD (1988) Modelling the relation between bacterial growth and storage temperature in pasteurized milks of varying hygienic quality. Journal of the Society of Dairy Technology 41: 96–102. Henyon DK (1999) Extended shelf-life milks in North America: a perspective. International Journal of Dairy Technology 52: 95–101. Mayr R, Eppert I, and Scherer S (1999) Incidence and identification of psychrotrophic (7 C tolerant) Bacillus spp. in German HTST pasteurized milk. Milchwissenschaft 54: 26–29. Meer RR, Baker J, Bodyfelt FW, and Griffiths MW (1991) Psychrotrophic Bacillus spp. in fluid milk products: a review. Journal of Food Protection 54: 969–979. Muir DD (1996a) The shelf-life of dairy products. 1. Factors influencing raw milk and fresh products. Journal of the Society of Dairy Technology 49: 24–32. Muir DD (1996b) The shelf-life of dairy products. 2. Raw milk and fresh products. Journal of the Society of Dairy Technology 49: 44–48. Muir DD (1996c) The shelf-life of dairy products. 3. Factors influencing intermediate and long life dairy products. Journal of the Society of Dairy Technology 49: 67–72. Phillips JD and Griffiths MW (1990) Prediction of the shelf-life of pasteurized milk using dry film medium culture plates (3 M Petrifilm, Hygicult and Millipore Sampler). Journal of the Society of Dairy Technology 43: 45–49. Sørhaug T and Stepaniak L (1991) Microbial enzymes in the spoilage of milk and dairy products. In: Fox PF (ed.) Food Enzymology, vol. 1, pp. 169–219. London: Elsevier Applied Science. Stepaniak L (1991) Factors affecting quality and possibilities of predicting shelf-life of pasteurized and ultra-high temperature heated milks. Italian Journal of Food Science 3: 11–26. Suhren G (1989) Producer microorganisms. In: McKellar RC (ed.) Enzymes of Psychrotrophs in Raw Food, pp. 3–34. Boca Raton: CRC Press. Ternstro¨m A, Linberg AM, and Molin G (1993) Classification of the spoilage flora of raw and pasteurized bovine milk, with special references to Pseudomonas and Bacillus. Journal of Applied Bacteriology 75: 25–34.
R REPLACEMENT MANAGEMENT IN CATTLE Contents Growth Standards and Nutrient Requirements Pre-Ruminant Diets and Weaning Practices Growth Diets Breeding Standards and Pregnancy Management Health Management
Growth Standards and Nutrient Requirements R E James, Virginia Tech, Blacksburg, VA, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The goal of a dairy heifer-rearing program is to provide a regimen that will enable the heifer to develop her full lactation potential at the desired age and at a minimum expense. The optimum age and size at first calving are heavily dependent upon the breed and the genetics for body size of the animal. With increased popularity of crossbreeding of dairy animals, defining optimum body size has become more challenging. Calving heifers at too young or too old an age is associated with reduced production. Studies from a population of US Holsteins found the optimum age of first calving to occur between 22 and 24 months of age. However, for earlier-maturing breeds, such as Jerseys, the optimum age for first calving may be 1 or 2 months lower. Similarly, the optimum age for larger breeds may be higher by 30–60 days. Optimum body size must be defined relative to parturition. Suggestions for desired body weights based upon US genetics of representative breeds are shown in Table 1. This table is not intended to be representative of breeds throughout the world but serves to demonstrate the expected changes in body weight relative to parturition. It should also be noted that genetics within breed has a large impact on body size. As an example, within the US population it is estimated
390
that genetics accounts for approximately 35 kg of the variation in body weight at first calving. In addition to body weight, height at the withers or hips has been used as an indicator of growth. More recently, hip heights have become the more preferred measure of height of the animal as measurements are more repeatable and less influenced by the position of the animal’s head during measurement. Genetics is the major determinant of an animal’s potential for growth in height. However, the feeding program has considerable influence on the animal’s ability to achieve its genetically predetermined potential for growth. As an example, Table 2 shows median, 75th, and 95th percentiles for weight and height of a national sample of US Holsteins. Note the variation observed in height in this population. Ideally, body composition data would provide valuable information, which might be a better indicator of future lactation yield than body weight alone. One would expect heifers with greater lean tissue growth and moderate levels of body fat content to produce the most milk. Unfortunately, the noninvasive techniques utilizing urea space, ultrasound, and electrical conductivity have all proven to provide information of limited value in measuring composition in dairy heifers, partly due to low body fat content of dairy
Replacement Management in Cattle | Growth Standards and Nutrient Requirements Table 1 Desired body weights (kg) at first calving Time of measurement
Breed Ayrshire Brown Swiss Guernsey Holstein Milking Shorthorn Jersey
Before calving
Postcalving
Peak lactation
563 625 534 636 591
509 563 477 572 532
486 536 459 545 509
409
368
352
Adapted from Hoffman PC (2003) Heifer fundamentals. In: PC Hoffman and R Plourd (eds.) Raising Dairy Replacements, ch. 6, pp. 53–56. Ames, IA: Midwest Planning Service.
heifers as compared to the beef breeds. The only reliable method to measure body composition is to sacrifice the animal and measure body fat directly. This technique is costly and eliminates the ability to obtain later milk production information.
Rate of Gain Measurements of body size are not adequate to describe the influence of growth on performance and productive life of the dairy animal. The rate of gain in weight and height, and timing of growth must be considered. About 50% of the total gain in height occurs during the first 6 months of life, 25% from 7 to 12 months and the remaining 25% during the last 12 months. The proportion of body weight to wither height increases linearly
391
and the increase in wither height as a proportion of height at maturity is greatest during the first 6 months. This shows that the young heifer has a propensity for rapid growth if properly nourished. Before proceeding further, it is beneficial to review the biology of heifer and mammary growth. At birth, the mammary gland is rudimentary with both the gland and teat cisterns evident and ducts present close to the gland cistern. From birth to 3 months of age, the gland grows at a rate similar to the rest of the body. However, beginning at approximately 3 months of age, the gland begins an allometric growth phase, where the mammary gland grows at a much faster rate than the rest of the body. This phase continues until puberty when once again the gland assumes the same rate of growth as the rest of the body. Just prior to parturition, the mammary gland once again grows at a rate exceeding the rest of the body. The timing of these shifts in differentiation and growth vary with breed and the hormonal events triggering them have not been fully elucidated. The influence of feeding programs and rates of growth during the first 2 years of life has been the subject of much research. There are indications that a higher rate of growth (over 800 g day1 for large breed heifers) prior to weaning during the milk feeding period has a positive influence on mammary development. Studies have shown that the milk-fed calf is capable of rates of growth exceeding 1.5 kg day1. Using the test day model, Cornell researchers can attribute major positive differences in first lactation milk yield to the rate of gain during the preweaning period of life. However, there is a large body of evidence that indicates that rapid growth (over 950 g day1 for large breeds and less for smaller breeds) after weaning and before puberty may have a negative
Table 2 Median, 75th, and 95th percentile weights and heights indicated for Holstein heifers in the National Animal Health Monitoring System (NAHMS) project Weight (kg)
Height (cm)
Age (months)
Median
75th
95th
Median
75th
95th
1 3 5 7 9 11 13 15 17 19 21 23 24
54 96 141 192 241 290 331 383 423 458 494 522 532
62 106 154 213 271 324 368 423 466 494 541 581 591
65 129 187 246 320 353 415 485 541 581 624 645 702
79 89 96 104 109 117 119 124 127 129 132 135 135
84 91 99 109 114 119 124 129 132 134 137 137 140
84 96 102 114 119 124 129 135 137 137 142 145 145
From Heinrichs AJ and Lammers B (1998) Monitoring Dairy Heifer Growth. University Park, PA: Pennsylvania State University Cooperative Extension.
392 Replacement Management in Cattle | Growth Standards and Nutrient Requirements
impact on mammary development. Heifers fed for more rapid rates of gain postweaning exhibit depressed levels of growth hormone and increased growth of the mammary fat pad. However, the influence of diet on growth of mammary parenchyma is less clear with some studies indicating minimal influence on growth of the secretory tissue. The critical rates of gain that may influence mammary development vary with breed as studies have shown that apparent decreased mammary development occurs at lower rates of gain in Jerseys and Red Danish heifers as compared to Friesians. Rate of gain can also be considered in a stair-step fashion. In this scenario, heifers are reared in alternating periods of slow and rapid rates of gain during the second and third trimesters of gestation, respectively. During the restricted phase, energy is fed to 70% of requirements and during the rapid phase at 130% of National Research Council (NRC) requirements for protein and energy. The rapid phase of growth during the third trimester corresponds to a period of robust mammary parenchymal growth. Growth responses and milk production of control and stair-step-reared animals are shown in Table 3. Table 3 Performance of Holstein dairy heifers reared at a steady rate of gain or in a stair-step manner Item
Control
Stair-step
Initial body wt. (kg) Final body wt. (kg) Daily gain (kg day1) DM intake (kg day1) Overall efficiency Energy (g Mcal1) Protein (%)
281 553 0.68 9.3
278 575 0.98 7.5
32.6 54.2
57.9 96.5
4.3 14.5 730.7
5.6 29.7 628.3
Composition of mammary tissue DNA (mg g1) RNA (mg g1) Lipid (mg g1)
In the stair-step management scheme, heifers grow more efficiently and the composition of the mammary gland reveals more secretory cell numbers and cell activity and less lipid as compared to heifers growing at a uniform rate. The stair-step rearing program shows great promise although it requires a departure from conventional thinking and it may present challenges to implement under practical feeding situations on many growing operations. The challenge of adopting uniform growth standards is that dairy breeds vary widely in their genetic capacity for growth and mature size. The adoption of the targeted growth system recognizes that nutrient requirements are linked to an animal’s rate of gain and current body size relative to mature size. In the 2001 Dairy NRC, target weights for breeding and calving are based upon percentages of mature size. Puberty usually occurs when heifers have reached 45–50% of mature size. Heifers should be pregnant by 55% of mature size and calve by 82% of mature size. Table 4 demonstrates the breeding and calving weight targets for heifers of differing mature size based upon desired age at first calving. Requirements are predicted based upon the expected mature weight of the animal being fed, the desired age at first calving, the current weight of the heifer, and the chemical composition of the feeds and dry matter intake (DMI) of the diet.
Nutrient Requirements for Growing Dairy Heifers Previous predictions for DMI and nutrient requirements for energy and protein have been expressed on a tabular basis. However, more recent research and the development of nutrition models for growth and production have led to the use of equations to predict intake and nutrient requirements based upon a variety of readily available animal, environmental, and dietary measures. The 2001 Nutrient Requirements of Dairy Cattle utilizes the following equation, based upon beef cattle data to predict intake:
P < 0.05 P < 0.01 Control ¼ 750 g average daily gain (ADG). Stair-step ¼ alternating requirements at 70 and 130% of NRC requirements. From Park CS (2000) Personal Communication.
Table 4 Application of the targeted growth system under different management scenarios based upon expected mature weight, current weight at 4 months, and targeted calving at 22–24 months of age Mature body weight (Kg)
Age at first calving (months)
Current age (months)
Current weight (kg)
Target postcalving weight (kg)
Target breeding weight (kg)
Target age at breeding (months)
Target growth rate 4 months calving (kg day1)
450 650 800
22 22 24
4 4 4
100 125 160
375 525 675
250 350 450
13 13 15
0.50 0.73 0.85
Replacement Management in Cattle | Growth Standards and Nutrient Requirements DMI ðkg day–1 Þ ð0:2435NEM – 0:0466NEM 2 – 0:1128Þ ¼ Body weight0:75 NEM
where NEM is net energy maintenance However, another equation using over 5000 observations of DMI in Holstein heifers from various US locations was developed to predict intake that accounted for over 59% of the variation in daily DMI. The simplified model was DMI (kg day1) ¼ 29.86 þ (0.54E-05 body weight) þ (0.157 metabolic body weight) þ (2.090 daily gain) þ (0.118 daily gain2) þ (0.730 TDN (total digestible nutrients)) þ (0.005 TDN2) þ (0.001 body weight daily gain) þ (0.019 TDN daily gain). This equation was subsequently verified with data sets representing multiple locations across the United States and found to be equally successful in predicting intake. This equation is most successful in predicting intake of heifers weighing 100–400 kg. Energy requirements for maintenance are based on Mcal of net energy required to support basal metabolism with adjustments for physical activity and temperature regulation. A dynamic model adopted by the 2001 NRC considers body size, temperature, relative humidity, and hair coat condition in estimating energy requirements for maintenance. Determination of the nutrient requirements for growth of the dairy heifer is based upon targeted growth concept, which is used to estimate body composition at a given stage of growth. Body composition at birth and maturity is relatively predictable. However, younger animals have the capacity to deposit more lean tissue per unit of gain. As animals mature they deposit more fat than lean tissue per unit of gain. This principle is utilized to estimate nutrient requirements regardless of the breed. Since a gram of fat contains more calories than a gram of
lean tissue, nutrient requirements for energy and protein will change as the animals reach maturity. As body weight increases, the energy content of gain increases and protein content of gain decreases because more energy is deposited as fat. Also, as the rate of gain increases, energy content of gain increases (more fat deposition) and protein content of gain decreases. As animals increase in weight, protein required does not decrease as rapidly as expected because the efficiency of protein absorption decreases. The revised nutrient recommendations consider protein requirements of the animal in light of rumen microbial protein synthesis as well as dietary protein, which escapes degradation in the rumen to yield an estimate of metabolizable protein available to support growth and maintenance. The new models developed to estimate amino acid requirements have frequently resulted in recommendations for feeding lower levels of protein in the diet of older animals. Feeding higher levels of protein in diets of growing heifers is not recommended because as dietary protein levels increase the amount excreted via the urine and feces increases. This is not only economically inefficient, but also contributes to environmental pollution. Increasingly, the nutritionist is challenged to provide the amount of nutrients that foster optimal, economical growth with minimal detrimental influence on the environment. Mineral requirements are estimated based upon the factorial method using revised estimates of bioavailability of mineral sources. Vitamins are typically supplemented in the diet without regard to amounts supplied by other dietary ingredients with the exception of fresh forage, which supplies abundant amounts of vitamins. Examples of suggested ration specifications for large breed (Holstein) and small breed (Jersey) replacements are shown in Tables 5 and 6. These tables were
Table 5 Nutrient requirements for small breed heifers at 600 g gain day1 Heifer weight (kg) Item
Unit 1
393
100
150
200
250
300
3.1
4.2
5.2
6.1
7.0
Intake
kg day
Energy TDN ME
% of DM Mcal day1
62.9 7.0
62.9 9.5
62.9 11.8
62.9 14.0
62.9 16.0
Protein CP RUP RDP
% of DM % of DM % of DM
16.3 6.7 9.6
13.9 4.3 9.6
12.6 3.0 9.6
11.8 2.2 9.6
11.3 1.7 9.6
CP, crude protein. DM, dry matter. ME, metabolizable energy. RUP, rumen undegradable protein. It refers to rumen ‘bypass’ protein. RDP, rumen degradable protein. Adapted from National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press.
394 Replacement Management in Cattle | Growth Standards and Nutrient Requirements Table 6 Nutrient requirements for large breed heifers (mature weight ¼ 650 kg) at 800 g gain day1 Heifer weight (kg) Item
Unit
150
200
250
350
400
Intake
kg day1
Energy TDN ME
4.2
5.2
6.2
7.9
8.8
% of DM Mcal day1
63.4 9.6
63.4 11.9
63.4 14.1
63.4 18.2
63.4 20.1
Protein CP RUP RDP
% of DM % of DM % of DM
15.9 6.2 9.7
14.2 4.5 9.7
13.1 3.4 9.7
11.7 2.0 9.7
11.3 1.6 9.7
CP, crude protein. DM, day matter. ME, metabolizable energy. RUP, rumen undegradable protein. It refers to rumen ‘bypass’ protein. RDP, rumen degradable protein. Adapted from National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press.
developed using the dynamic models utilized by the 2001 NRC for Holstein heifers gaining 800 g day1 and Jersey heifers gaining 600 g day1.
Conclusions 1. The concept of targeted growth should be practiced when determining growth standards. This enables one to establish desired rates of gain based upon the expected mature weight of the animal. 2. Rate of gain during the first 2 years influences mature weight and height. a. During the first 6–9 months of life, large breed heifers should be fed to gain between 750 and 900 g of gain per day and small breed heifers should gain approximately 500–700 g per day. b. After puberty, rate of gain is not as critical as long as desired height and weight goals after calving are reached. 3. Growth standards can be applied to dairy heifers regardless of breeding based upon expected mature size. Stated in this fashion: a. Calves should double their birth weight by 56 days of age. b. Puberty can be expected to occur when heifers have achieved approximately 45–50% of mature weight. c. When heifers attain 55–65% of mature weight they should be bred. d. At first calving, heifers should have attained 82–85% of mature weight. e. Body weights at second and third calvings should be 92 and 96% of mature weight, respectively.
4. Desired rates of gain can be calculated by comparing the heifer’s current weight and age with the desired weights at the benchmarks described previously. 5. Target calving ages are 22–24 months for large breed heifers and 22–23 months for small breed heifers. 6. Nutrient levels in the diet must be adjusted according to environment and the ability of the animal to withstand heat and cold stress. See also: Replacement Management in Cattle: Growth Diets.
Further Reading Bovine Alliance on Management and Nutrition (2007) Heifer Growth and Economics: Target Growth. Arlington, VA: American Feed Industry Association. Fox DG and Tylutki TP (1998) Accounting for the effects of environment on the nutrient requirements of dairy cattle. Journal of Dairy Science 81: 3085–3095. Fox DG, Van Amburgh ME, and Tylutki TP (1999) Predicting requirements for growth, maturity, and body reserves in dairy cattle. Journal of Dairy Science 82: 1968–1977. Gill GS and Allaire FR (1976) Relationship of age at first calving, days open, days dry and herdlife to a profit function for dairy cattle. Journal of Dairy Science 59: 1131–1139. Heinrichs AJ and Hargrove GL (1987) Standards of weight and height for Holstein heifers. Journal of Dairy Science 70: 653–660. Heinrichs AJ and Lammers B (1998) Monitoring Dairy Heifer Growth. University Park, PA: Pennsylvania State University Cooperative Extension. Heinrichs AJ and Losinger WC (1997) Growth of Holstein dairy heifers in the United States. Journal of Animal Science 76: 1254–1260. Hoffman PC (1997) Optimum body size of Holstein replacement heifers. Journal of Animal Science 75: 836–845. Hoffman PC (2003) Heifer fundamentals. In: PC Hoffman and R Plourd (eds.) Raising Dairy Replacements, ch. 6, pp. 53–56. Ames, IA: Midwest Planning Service. Hohenboken WD, Foldager J, Jensen J, Madsens P, and Andersen BB (1995) Breed and nutritional effects and interactions on energy
Replacement Management in Cattle | Growth Standards and Nutrient Requirements intake, production and efficiency of nutrient utilization in young bulls, heifers and lactating cows. Acta Agriculturae Scandinavica 45: 92–98. Keown JF and Everett RW (1986) Effect of days carried calf, days dry and weight of 1st calf heifers on yield. Journal of Dairy Science 69: 1891. Lammers BP and Heinrichs AJ (2000) The response of altering the ratio of dietary protein to energy on growth, feed efficiency, and mammary development in rapidly growing prepubertal heifers. Journal of Dairy Science 83: 977–983. Meyer MJ, Capuco AV, Ross DA, Lintault LM, and Van Amburgh ME (2006a) Developmental and nutritional regulation of the prepubertal heifer mammary gland: I. Parenchyma and fat pad mass and composition. Journal of Dairy Science 89: 4289–4297. Meyer MJ, Capuco AV, Ross DA, Lintault LM, and Van Amburgh ME (2006b) Developmental and nutritional regulation of the prepubertal bovine mammary gland: II. Epithelial cell proliferation, parenchymal accretion rate, and allometric growth. Journal of Dairy Science 89: 4298–4304. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press. Park CS (2000) Personal Communication.
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Park CS, Erickson GM, Choi YJ, and Marx GD (1987) Effect of compensatory growth on regulation of growth and lactation: Response of dairy heifers to a stair-step growth pattern. Journal of Animal Science 64: 1751–1758. Quigley JD, III, James RE, and McGilliard ML (1986) Dry matter intake in dairy heifers 2. Equations to predict intake of heifers under intensive management. Journal of Dairy Science 69: 2863–2867. Radcliff RP, VandeHaar MJ, Chapin LT, et al. (1998) Effects of diet and exogenous bST on growth and lactation of dairy heifers. Journal of Dairy Science 81(supplement 1): 227. Soberon F, Raffrenato E, Everett RW, and Van Amburgh ME (2009) Early life management and long term productivity of dairy calves. Journal of Dairy Science 92(supplement 1): 238. Van Amburgh ME, Fox DG, Galton DM, Bauman DE, and Chase LE (1998a) Evaluation of National Research Council and Cornell Net Carbohydrate and Protein Systems for predicting requirements of Holstein heifers. Journal of Dairy Science 81: 509–526. Van Amburgh ME, Galton DM, Bauman DE, et al. (1998b) Effects of three prepubertal body growth rates on performance of Holstein heifers during first lactation. Journal of Dairy Science 81: 527–538.
Pre-Ruminant Diets and Weaning Practices R E James, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The newborn calf is essentially a monogastric animal requiring highly digestible nutrients in the liquid diet, especially during the first month of life. During this time, the young calf has limited development of enzyme systems to digest ingredients supplying protein and energy. This dictates that the calf be fed protein and energy sources closely resembling those contained in milk products which will supply needed amino acids and energy from fat and lactose. However, within weeks, as the calf begins consumption of starch-containing grains, rumen microflora develops, which produces volatile fatty acids that stimulate preferential development of the rumen epithelium. Successful nutritional management of the calf is indicated when the following goals are met: percent of calves born on the farm achieve a • Eighty-five serum immunoglobulin G (IgG) >10 mg ml or serum 1
1
• •
protein >5.5 g dl between 1 and 7 days of age. Ninety percent of calves double their birth weight by 56 days of age. Less than 30% of calves are treated for disease during the first 30 days.
Key factors to consider in the preruminant feeding program include management • colostrum provision of high-quality liquid diets fed in sufficient • quantity to encourage biologically normal growth and
• • •
immunity weaning at a reasonably early age provision of adequate amounts of high-quality water and calf starter grain provision of a favorable rearing environment
Colostrum Management Consumption of adequate quantities of high-quality colostrum early in life is the single most important factor determining health and survival of the calf. The first milk produced by the dam is a rich source of immunoglobulins (Igs), nutrients, and immune cells. As shown in Table 1, the level of Igs declines rapidly over the first three milkings.
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Fortunately, the intestine of the newborn calf is able to absorb these Igs, unchanged for the first 6–24 h of life. Successful absorption is achieved by the consumption of 100–200 g of Ig as soon as possible after birth. Although the level of Ig is variable, good-quality colostrum contains approximately 50 g Ig l 1. The period of time that the calf is able to absorb colostrum Ig is also quite variable. It may cease within 6 h of birth, but generally ceases within 24 h. Reasons for cessation of absorption are unclear, but research indicates that the presence of large quantities of bacteria in the intestine may inhibit absorption of Ig. Feeding contaminated colostrum or a dirty calving environment may accelerate bacterial colonization of the intestine and impair Ig absorption. Thus, successful immunity transfer occurs when the calf consumes 3–4 l of ‘clean’ colostrum within the first 12 h of life. Colostrum may also be involved in the establishment of cellular immunity in the calf. Additional feedings of colostrum beyond the first day result in improved growth of the intestinal epithelium as well as improved absorptive capacity.
Liquid Diets for Calves Many alternatives exist for feeding the neonatal calf after the first day. They include whole saleable milk, waste milk unsuitable for human consumption, and milk replacer. Milk replacers vary widely in nutrient content and ingredient composition. Before selecting an alternative, one should consider the benefits and risks of each alternative feeding program for calves. Whole milk usually fosters the best growth of the calf as it contains high levels of protein (24% on a dry matter (DM) basis) and fat (28.7% on a DM basis) to support calf growth. In addition, it is likely that these nutrients are more highly digestible than those from other sources. However, in nearly all cases, whole milk is more expensive and there is a risk of transmission of disease to calves by feeding raw milk. On most dairies, there is a supply of waste milk from cows that have calved within the past 3 days or from cows that have been treated with antibiotics. Generally, waste milk contains similar levels of protein, fat, and lactose as whole milk. However, fat levels can vary from 2.0 to more than 4% and protein from 2.5 to 4.0%. Field studies with dairies utilizing waste milk for calves indicate that the
Replacement Management in Cattle | Pre-Ruminant Diets and Weaning Practices
397
Table 1 Summary of the composition of colostrum, transition milk, and normal milk Milking number Parameter
1
2
3
Milk
Specific gravitya Solids (%)a Protein (%)a Casein (%)a Immunoglobulin (mg ml 1)a Fat (%)a Lactose (%)a Vitamin A (mg dl 1) Vitamin E (mg g 1 fat)c
1.056 23.9 14.0 4.8 48.0 6.7 2.7 233–400b 45–206
1.040 17.9 8.4 4.3 25.0 5.4 3.9 190a
1.035 14.1 5.1 3.8 15.0 3.9 4.4 113a
1.032 12.9 3.1 2.5 0.6 3.7 5.0 34a–38b
1, Colosrum; 2 and 3, transition milk. a Foley JA and Otterby DE (1978) Availability, storage, treatment, composition, and feeding value of surplus colostrum: A review Journal of Dairy Science 61: 1033–1060. b Franklin ST Sorenson CE and Hammell DC (1998) Influence of vitamin A supplementation in milk on growth, health, concentrations of vitamins in plasma, and immune parameters of calves Journal of Dairy Science 81: 2623–2632. c Weiss WP Todhunter DA Hogan JS Smith KL (1990) Effect of duration of supplementation of selenium and vitamin E on periparturient dairy cows. Journal of Dairy Science 73: 3187–3194.
supply of waste milk varies from 2.5 to 9 kg per calf per day. On many dairies, the supply of waste milk is adequate to meet the needs of less than 50% of the calves prior to weaning. Therefore, feeding programs based upon use of waste milk must make accommodations for supplementation with additional milk solids when the supply of nutrients is inadequate. In addition to challenges with varying supply and nutrient content, waste milk frequently contains antibiotic residues (in the United States) and microorganisms that are potentially harmful to the calf. Fortunately, systems have been developed to effectively pasteurize either whole milk or waste milk, which renders waste milk less likely to cause disease in calves. Successful pasteurization occurs when milk is heated to a sufficient temperature for an adequate time period to destroy 98% of the microorganisms present. Most systems used for pasteurizing waste milk can be described as being batch or high-temperature short-time (HTST) units. Batch systems (Figure 1) are typically simpler and more suitable for feeding smaller number of calves (<100). Batch systems heat a ‘batch’ of milk to a temperature of 62 C for 30 min. The HTST units (Figure 2) utilize either heat exchange plates or tubes to heat milk more quickly to 72 C for 15 s. These systems are more expensive but their operation and cleaning can be more easily automated. Either system can be successful if properly installed, maintained, and operated. Successful pasteurization is generally indicated when the aerobic plate count has been reduced to 20 000 cfu ml 1 or less. Pasteurization does not sterilize milk but reduces bacterial numbers by 98%. Therefore, it is important that waste milk be handled with the same care as that which
is sold for human consumption. If the aerobic plate count prior to pasteurization exceeds 2 000 000 cfu ml 1, then the goal of <20 000 cfu ml 1 after pasteurization may not be achieved. It is also important that all vessels receiving waste milk after pasteurization be thoroughly cleaned
Figure 1 Example of a batch pasteurizer system (Dairy Tech, Windsor, CO).
398 Replacement Management in Cattle | Pre-Ruminant Diets and Weaning Practices
Figure 2 Example of high-temperature short-time pasteurizer (Goodnature, Orchard Park, NY).
and sanitized as microbial growth of pasteurized milk is very rapid when placed in unclean tanks or feeding bottles. Adoption of a pasteurized waste milk-feeding program requires institution of stringent quality control programs to ensure that pasteurization has occurred and to account for variations in supply and nutrient content of waste milk. Samples of waste milk obtained after the last calf has been fed should contain less than 100 000 cfu ml 1. Milk should also be tested for total solids and percentage of fat and protein. Additional milk solids should be added if waste milk contains less than 12.5% solids. Frequency of testing is determined by number of calves fed, but should be no less than once per month.
Milk Replacers Milk replacers enable dairy producers to market more saleable milk. The objective of the formulation of a milk
replacer is to provide nutrition to the calf that results in nearly equal growth and performance as that achieved with whole milk at less cost and with greater biosecurity. Typically, milk replacers are based upon the use of whey proteins, which are by-products of cheese manufacturing. The different whey products used in milk replacers include dried whey, delactosed whey, and whey protein concentrate, which contain progressively higher concentrations of protein. In an effort to further reduce costs, soy, wheat, and plasma proteins have been used as partial substitutes for milk proteins. Soy is treated to concentrate the proteins and reduce undesirable antigenic properties that can cause an allergic reaction in the intestine of the young calf. Milk replacers based upon milk proteins are recommended for calves less than 1 month of age due to their higher digestibility as compared to vegetable proteins. When vegetable proteins are utilized, it is recommended that they substitute for less than 50% of the milk proteins. The acceptability of various ingredients as sources of protein in milk replacers is shown in Table 2. In the United States and most part of the world, lard and tallow are the primary sources of fat used in milk replacers. Due to concern over bovine spongiform encephalopathy (BSE), palm and coconut oil are used as a replacement for animal fats in EU countries. These oils appear to be of high digestibility and are well tolerated by the calf. Lactose is the primary carbohydrate used in milk replacers as it is of the lowest cost and is most efficiently digested by the calf. Milk replacers are marketed as dry powders that contain 10–25% fat and 20–28% protein. In the United States, whole milk on average contains approximately 3.6% fat and 3.1% protein, which on a dry powder basis would equal 28% fat and 24% protein.
Liquid-Feeding Programs There has been a substantial shift in the concept of liquidfeeding management of the dairy calf over the past 10 years. Traditional liquid-feeding programs for calves sought to minimize rearing expenses and encourage early development of the rumen to enable early weaning of the calf. A substantial body of work has demonstrated
Table 2 Ingredients used as sources of protein for milk replacers Recommended
Acceptable
Marginal
Not acceptable
Dried whey protein concentrate Dried skim milk Casein Dried whey Dried whey product
Soy protein isolate Protein-modified soy flour Soy protein concentrate Animal plasma Wheat gluten or isolate
Soy flour
Meat solubles Fish protein concentrate Wheat flour
Bovine Alliance on Management and Nutrition Information Sheet (2008) A guide to calf milk replacers.
Replacement Management in Cattle | Pre-Ruminant Diets and Weaning Practices
that feeding approximately 454 g of solids per day containing 20% protein and 10–20% fat appeared to be the best compromise between desired growth, calf performance, and encouragement of early consumption of dry calf starter grains. Under this traditional model, the calf grew modestly, especially during the first 2–3 weeks of age (<200 g day 1), and began consuming dry grains by the end of the second week. Some rearing programs resulted in consumption of sufficient dry feeds to enable weaning by the end of the fourth week of life or earlier. Although it achieved a low daily feed cost, this practice ignored the influence of body size, environment, and ingredients utilized in the diet on growth and development as well as health of the preweaned calf. The concept of limit-feeding calves liquid diets is a departure from the approach of diet formulation used for older dairy animals, which considers requirements for maintenance, body size and expected growth, or other performance measures such as milk production. Rather the goal with the traditional limit-fed program in preweaned calves is to reduce nutrient intake early in life to stimulate premature intake of dry feeds and reduce cost. Research over the past 10 years has resulted in the determination of nutrient requirements for body weight gain as well as the composition of gain in the growing calf. Using all-milk protein sources it appears that daily protein accretion in the calf plateaus at 28% crude protein (CP) on a DM basis, which is also similar to the protein content of whole milk. These studies have also shown that body fat accretion decreases with increasing protein in the diet and that the protein content of body weight gain increases with increasing protein intake of the diet. Energy intake is derived from lactose, fat, and to a lesser extent from protein. Most milk replacer diets contain 10–20% fat, considerably below that found in milk solids. Research has shown that growth rate is not appreciably influenced by differences in the proportion of energy provided as lactose or fat. However, as the fat intake increases, the
accretion of body fat increases. When diets are formulated with regard to nutrient requirements for growth as well as maintenance, the amounts of solids recommended to be fed to the preweaned calf are considerably higher than 454 g day 1 common to traditional systems. Nutrient requirements can be partitioned into requirements for maintenance and growth. Maintenance requirements are a function of age, body size, environmental temperature and exposure, and disease status. The thermoneutral zone for young adapted calves appears to be 15–25 C. This means that the calf would require additional energy for maintenance when temperatures exceed this zone. Smaller, younger animals would require proportionately more energy to meet energy requirements than older, larger animals because smaller animals have proportionately more body surface area and thus lose body heat more readily. Therefore, during cold weather, both solids intake and fat content of the diet should be increased. Table 3 demonstrates the influence of environmental temperature on maintenance requirements of calves of different body sizes. Note the increase in maintenance requirements and the amount of milk solids required to meet maintenance needs as temperature decreases. The most recent edition of the Nutrient Requirements of Dairy Cattle has used a dynamic approach in determining nutrient requirements of the dairy calf that considers body size as well as temperature. Table 4 demonstrates the influence of environment and composition of the diet upon expected growth of a 55 kg calf. Table 4 demonstrates that limit feeding a 20:20 milk replacer during cold weather has a detrimental influence on calf growth with possible repercussions on health if body fat stores are depleted. Additional research has demonstrated that maintenance requirements of smallbreed calves such as Jerseys may be at least 20% higher than the maintenance requirements of large-breed calves due to increased heat loss from the greater surface area of smaller calves as compared to larger calves. As a result,
Table 3 Influence of environmental temperature and body size on megacalories of net energy maintenance and gram of whole milk required to meet maintenance requirements of calves of different body sizes Environmental temperature (oC) Body weight (kg) 30 50 70
399
15
0
1.25 Mcal 270 g 1.83 Mcal 400 g 2.35 Mcal 510 g
1.7 Mcal 370 g 2.49 Mcal 554 g 3.12 Mcal 690 g
15 2.14 Mcal 460 g 3.14 Mcal 800 g 4.04 Mcal 870 g
Adapted from National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press.
400 Replacement Management in Cattle | Pre-Ruminant Diets and Weaning Practices Table 4 Expected body weight gain of 55 kg calf fed whole milk or two different milk replacers under different environmental temperatures 20 C
0 C
Liquid
per day
Energy allowable gain
Protein allowable gain
Energy allowable gain
Protein allowable gain
Whole milk Whole milk 20% protein:20% fat milk replacer 28% protein:20% fat milk replacer
4l 9l 4 l at 12.5% DM
213 g 1110 g 45 g
345 g 990 g 218 g
Weight loss 852 g Weight loss
Weight loss 990 g Weight loss
6.7 l at 17% DM
1010 g
1150 g
739 g
1150 g
Adapted from National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press.
in milk replacer powders, fat levels of 25% may be warranted during cold stress experienced by small-breed calves. There is a growing body of evidence that restricting calves to consumption of 454 g of milk solids per day may not be advisable. A recent study in the United States revealed that mortality from birth to weaning exceeded 8% in limit-fed calves while that of more liberally fed beef calves was less than 3%. These surveys of US dairy operations indicated that over 40% of calves were considered to be ill or unthrifty and required medication prior to weaning. A predisposition to illness could be caused by feeding calves at or below maintenance. In one study, calves fed 4 l of pasteurized waste milk daily experienced higher daily gains than calves fed a similar volume of milk replacer containing 20% CP and 20% fat reconstituted to 12.5% solids. In addition to better growth, the calves fed pasteurized waste milk experience lower levels of morbidity (12 vs. 32%) and mortality (2.3 vs. 11.6%). Differences in mortality and morbidity were more striking when comparing the influence of season; calves fed milk replacer experienced 21% mortality and 52% morbidity as compared to 2.8% mortality and 20.4% morbidity for calves fed whole milk during the winter season. Improved performance and health of calves fed pasteurized waste milk could be attributed to increased intake of protein and fat as compared to calves fed the milk replacer. Growth rate of the calf prior to weaning may have a profound effect upon mammary development. Calves fed a milk replacer containing 28.5% protein and 15% fat for an average daily gain of 666 g had 32% more mammary parenchymal mass and 47% more parenchymal DNA than calves fed a 20% protein and 20% fat milk replacer for an average daily gain of 379 g at 8 weeks of age. Several studies have demonstrated that calves fed more liberally during the preweaning period produced more milk per day during first and later lactations than limit-fed calves receiving 454 g of milk replacer or an equivalent amount of solids from whole milk. The more liberal feeding programs have been commonly referred to as ‘intensive’ or
‘accelerated’ while ‘more biologically normal’ might be a better terminology as the more liberal feeding program more closely resembles what takes place when the calf is allowed to nurse the dam. Additional responses to more biologically normal feeding rates include indications for improved immune function. Insufficiencies of protein or energy are known to impair health and immune system function in other species. Nutritional insufficiency is likely to be much more problematic in smaller, younger, limit-fed calves during cold or heat stress when maintenance requirements are known to be higher. More liberal feeding programs result in increased lean tissue growth and, when whole milk or milk replacers contain 20% or more fat, increased body fat deposition. In the young calf (less than 3 weeks of age), additional reserves of body fat may be a desirable trait. When calves become ill, intake is frequently decreased. Concurrently, an illness of infectious origin generally results in increased body temperature and increased energy requirements. If young calves are fed whole milk or milk replacers with higher protein and fat at higher intakes, the extra body fat may assist them in recovering from disease.
Practical Management of Milk-Feeding Programs Limit Fed There are numerous studies indicating that calves can be successfully reared when liquid feeding is limited to 4 l of milk or milk replacer containing the equivalent of 454 g of milk solids with 20% protein and 20% fat. The following management strategies increase chances for a positive outcome with this program. The environment needs to be optimal to minimize both cold and heat stress, which increase nutrient requirements for maintenance. During cold weather (<15 C), the proportion of solids should be increased to provide additional energy and protein. Avoid the use of vegetable proteins for the first 3 weeks of life due to their lower digestibility. Outside of the EU countries, plasma proteins are an acceptable, lower cost partial
Replacement Management in Cattle | Pre-Ruminant Diets and Weaning Practices
substitute for milk protein. Due to the lower intake of milk solids, there is a stronger incentive for calves to consume dry starter feeds at an earlier age and there is a trend for early weaning. The greatest limitation to limit-feeding systems is that cost per pound of gain may be higher as significantly more nutrients are required for maintenance with less remaining to support growth. During cold and heat stress, there may be a higher risk of morbidity and mortality. Intensive, Accelerated, or Biologically More Normal Liquid-feeding programs that involve feeding 680–1150 g of milk solids (5.5–7.5 l) per day more closely resemble what takes place when the calves are allowed to nurse their dams. Consequently, their growth and feed efficiencies are more similar to other young farm animals such as piglets or lambs. It is essential that milk-derived proteins be used throughout the liquid-feeding period as a higher intake of less-digestible vegetable proteins may increase the risk of diarrhea. During the first week of life, intake of milk is generally limited to 4 l for small-breed calves and 6 l for large-breed calves. Milk replacers usually contain 26–28% CP and 16–25% fat. Higher fat levels are recommended for small-breed calves, especially during times of cold stress, which can amount to 6 months of the year when ambient temperature is less than 15 C. Milk replacer powders are reconstituted by the addition of warm water to a final solid level of 12.5–17%. The higher level of solids enables use of 3 l nipple bottles for twice-daily feeding. Once calves reach full feed of 5.5–7.5 l day 1, they are maintained at this level until weaning. The feed cost per kilogram of gain may be less with this program as nutritional requirements for maintenance comprise less of the daily nutrient intake leaving more nutrients to support body weight gain. The limitation of this feeding system is that the rearing cost per day is significantly higher. Intake of dry calf starter is delayed by several weeks, but once the calves begin consuming calf starter they generally compensate due to their larger body size at a given age as compared to limit-fed calves. Calf feeders will note that feces from more liberally fed calves are looser and should not be confused with increased diarrhea.
Calf Starters for Preweaned Dairy Calves Calf starters should be formulated and delivered to the calf to encourage intake early in the calf’s life. As they are replacing nutrients provided by the liquid diet, the ingredients should be highly palatable and digestible and encourage development of the rumen epithelium and musculature. Historically, producers believed that early consumption of hay was critical to rumen development.
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However, research has shown that the consumption of grains high in starch is responsible for stimulating exponential growth of rumen epithelium. Consumption of hay prior to weaning is not recommended as it is much lower in energy than grains and will reduce energy intake and possibly delay weaning. In addition, calves frequently waste large portions of the hay that is offered. Ground hay can be included in calf starter grain mixtures in limited amounts (5–10%) provided it is high in energy and protein and low in fiber. Unfortunately, difficulty in handling such ground hay and grain mixtures precludes them from being used in most commercial calf starter mixtures. Calf starters typically contain 18–24% CP on a DM basis. The National Research Council (NRC) recommends 20% CP (DM basis) for calf starter feeds. When calves are limit-fed a 20% CP:20% fat milk replacer, little improvement is observed when higher CP% calf starters are fed. However, calves managed under a more liberal milkfeeding program using whole milk or higher protein milk replacers appear to adjust better to the diet postweaning with higher feed efficiency when a calf starter with up to 24% CP is fed. This is logical when one considers that the calf has received a higher protein liquid feed during the preweaning period. Little benefit accrues from prolonged feeding of higher-protein calf starter mixtures (>20% CP) beyond the first month after weaning. Ingredient composition of calf starter mixtures influences palatability and digestibility. Soybean meal (48% CP) and corn appear to be the most reliable protein and energy sources. It is not uncommon to include crimped oats owing to their palatability. However, oats are lower in energy and starch content and frequently a more expensive ingredient. Various forms of corn have been used in calf starter grains. Research comparing whole, dry-rolled, roasted-rolled, and steam-flaked corn in calf starter mixtures resulted in no difference in weight gains, but feed efficiency and dry feed intake postweaning favored starter grain mixtures containing whole or dryrolled corn. Molasses is commonly added to calf starter grains at 2–5% to improve palatability and reduce dustiness. Higher levels have been shown to reduce gain and solid feed intake. Molasses has a tendency to deteriorate during storage and causes clumping of the mixture thereby making handling of the starter difficult. The addition of nonforage fiber sources such as beet pulp, soy hulls, wheat midds, corn gluten feed, and cottonseed hulls to calf starter diets at low inclusion rates (12– 20%) is common. In most cases, feed intake is either not affected or increased only slightly. Since these feedstuffs contain less energy as corn or other high-starch grains, they commonly result in reduced feed efficiency. Improved gains when high-fiber starters are fed can be attributed to greater rumen fill and not necessarily improved lean tissue growth. If ground hay or nonforage fiber sources are
402 Replacement Management in Cattle | Pre-Ruminant Diets and Weaning Practices
included, they should be limited to 5–10% of the final mixture. Fat is occasionally added to calf starter mixtures to reduce dustiness. Addition to calf starters at levels exceeding 3.5% of the mixture reduces intake and live weight gains. Consistent improvement in live weight gains of calves has been observed when anticoccidial compounds such as decoquinate, lasalocid, or monensin are added to calf starter grains. They aid in controlling some types of coccidia. Lasalocid and monensin have also been shown to improve feed efficiency through an influence on rumen fermentation. The use of microbial probiotics and yeasts has resulted in benefits in some trials, but responses have been highly variable and less conclusive than with lasalocid or monensin.
Water Management Provision of ample supplies of fresh, clean water to calves is essential to successful early consumption of calf starter and early weaning regardless of the liquid-feeding program. Water should be provided in a bucket separate from that used for feeding milk. The water bucket should be located a sufficient distance away from the calf starter bucket so that the calf cannot dampen the starter with water nor foul the water with calf starter.
Successful Weaning Calves can usually be weaned successfully when they are consuming at least 1.5–2.0 kg of dry calf starter grain per day. Exceptions can be made during extremely cold weather when liquid feeding may be prolonged for a week or two longer. Weaning usually occurs at around 6–8 weeks of age. Calves can be encouraged to increase consumption of dry feeds in several ways. Maintaining a constant rate of liquid feeding from birth means that the liquid diet provides progressively less of their daily nutrient requirements as the calves grow larger. During the fifth or sixth week, the amount of nutrients obtained from the liquid diet can be reduced by feeding once daily, or in the case of milk replacers, maintaining liquid intake but providing half of the amount of milk powder in the same volume of water. The latter examples are commonly used and are very successful in stimulating dry calf starter
intake and weaning. Calves should be maintained in their current environment until 1–2 weeks after weaning to minimize social stress. The highest quality dry hay has be to introduced 2–3 weeks after weaning.
Conclusion Calves can be reared successfully with either limitfeeding or biologically more normal systems. However, the most important factor influencing success is obtaining adequate immunity from colostrum. This is achieved by feeding 4 l of colostrum containing at least 50 mg IgG ml–1 within the first 6–12 h of life. Whole milk, pasteurized waste milk, and milk replacers with higher levels of protein and energy can support gains of 500 g or more per day and promote excellent health and development. Early consumption of a digestible and palatable calf starter grain is essential regardless of the liquid-feeding program. Weaning is achieved when starter intake reaches 1.5–2 kg day 1. See also: Husbandry of Dairy Animals: Goat: Replacement Management; Sheep: Replacement Management.
Further Reading Bovine Alliance on Management and Nutrition Information Sheet (2008) A guide to calf milk replacers. Davis CL and Drackley JK (1998) The Development, Nutrition, and Management of the Young Calf. Ames, IA: State University Press. Foley JA and Otterby DE (1978) Availability, storage, treatment, composition, and feeding value of surplus colostrum: A review Journal of Dairy Science 61: 1033–1060. Franklin ST, Sorenson CE, and Hammell DC (1998) Influence of vitamin A supplementation in milk on growth, health, concentrations of vitamins in plasma, and immune parameters of calves Journal of Dairy Science 81: 2623–2632. Garnsworthy PC (ed.) (2005) Calf and Heifer Rearing. Principles of Rearing the Modern Dairy Heifer from Calf to Calving. Nottingham, UK: Nottingham University Press. National Animal Health Monitoring System (2007) Dairy Herd Management Practices Focusing on Preweaned Heifers. Fort Collins, CO: USDA, APHIS, Veterinary Service. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academy Press. Proceedings of Annual Conference of Dairy Calf and Heifer Association. Multiple years. Chesterfield, MO, USA. Weiss WP, Todhunter DA, Hogan JS, and Smith KL (1990) Effect of duration of supplementation of selenium and vitamin E on periparturient dairy cows. Journal of Dairy Science 73: 3187–3194.
Growth Diets R E James, Virginia Tech, Blacksburg, VA, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction Dairy heifers should be fed and managed to achieve 55% of their mature weight at first breeding and 82–85% of their mature weight at first calving. These principles enable the establishment of growth goals regardless of breed. In addition, heifers should have a body condition score after calving of 3.5 and be free of disease. Probably, no factor other than the feeding program influences achievement of these goals. The feeding program also comprises 50–70% of the cost of rearing heifers to first calving. Therefore, profitable heifer-rearing enterprises must concentrate on economical feeding programs. The purpose of this article is not to provide a ‘how to’ description of heifer-feeding programs because available feed resources and facilities vary to a great extent. This article will focus on a discussion of decision-making areas with considerable importance to the financial success of the heifer-feeding programs. Managing the feeding program of the heifer enterprise is not unlike that of any other decision made on the farm. Good heifer managers maximize benefits, control expenses, and manage risk well. This article will concentrate on the major goals the heifer grower needs to achieve during the rearing period: 1. successful weaning from liquid diets to forage- and concentrate-based feeding programs with minimal stress and loss of weight, and transition to group housing management systems; 2. controlling the rate of gain during the prepubertal period to enable early breeding (12–13 months) while assuring desired mammary development; 3. sustained growth after breeding and optimization of economy of feeding; and 4. preparing the heifer for eventual calving. The development of the feeding program should consider that approximately 50% of the total gain in height occurs during the first 6 months of life with 25% occurring from 7 to 12 months and the remaining 25% during the 12 months before calving. Feed cost is generally lowest per unit of gain during the first 6 months of life and then increases at a decreasing rate during the remaining 18 months. The proportion of body weight to wither height increases linearly and the increase in wither height as a proportion of total height is greatest during the first 6 months. This demonstrates that assuring adequate growth during the first 6 months is critical to success in growing
the dairy heifer and is where nutrition and management must be optimal. Poor growth prior to puberty cannot be compensated for later in the rearing period. After puberty and when the heifer has attained early growth goals, opportunities for considerable economy of feeding exist. Profitable heifer management requires labor-efficient systems and the ability to evaluate ration dry matter intake (DMI) and animal performance. Periodic weighing of heifers with comparison to established growth goals is critical to achieving desired performance. Heifer-feeding programs vary widely depending on the environment and available forage resources. In tropical and more temperate areas of the world, pasture-based systems are more popular because they provide nutrients at the lowest cost and promote excellent animal health. In other areas where land resources are more valuable, or the length of the grazing season is limited, confinement systems may be more conducive to economical heifer growth. In many areas of the world, a combination of systems where heifers are raised on pasture during the warmer months and moved to confinement during the winter is commonly practiced. Basic principles of nutritional management using pasture-based and confinement systems will be discussed.
Managing the Transition Calf This stage refers to the time between 2 weeks prior to and 2 weeks after weaning. Success during this phase is dependent upon excellent housing and health programs. Regardless of the rearing system, it is assumed that the calf is consuming adequate amounts of a high-energy calf starter grain prior to weaning. When preweaned calves have been housed individually, it is recommended that calves be placed into small groups of 4–6 calves several weeks after weaning to allow them to adjust to competition for feed. However, when the environment is optimal, the author has observed newly weaned calves reared in groups of 20–30 with great success. Under this scenario, ventilation is outstanding, bedded pens are cleaned frequently, and calf starter grain is fed often to keep the feed fresh. Calves that have been fed their liquid diet in groups from mob or robotic feeders adapt to weaning quite well as there is no social stress associated with adapting to the group housing and feeding environment. Calf starter grains can vary widely, but should be highly palatable and digestible,
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404 Replacement Management in Cattle | Growth Diets Table 1 Desired nutrient levels in a calf starter grain
Nutrient
Amount recommended
Crude protein (% of DM) Fat (% of DM) TDNs (% of DM) Metabolizable energy (Mcal kg Calcium (% of DM) Phosphorus (% of DM) Vitamin A (IU kg 1) Vitamin D (IU kg 1) Vitamin E (IU kg 1)
18.0–22.0 3.0 80 3.1 0.60 0.40 2200 300 24
1
DM)
DM, dry matter; TDNs, total digestible nutrients.
with nutrient concentrations as shown Table 1. Under more intensive liquid-feeding programs for calves, protein levels may be increased to 22% of dry matter (DM). For calves that have been housed individually prior to weaning, Morrill suggests three transition pens after weaning. The first pen has 4–8 calves with 2.8 m2 per calf and a starter the same as they had been receiving prior to weaning. Two weeks later, the calves are moved to a larger pen with more calves and with the same starter and about 15% chopped alfalfa hay added to the ration. In the next transition pen, the amount of chopped alfalfa is increased to 20% of the mixture. By the time the calves are moved to the last transition pen, they can be switched to a more economical grower concentrate mixture, with examples shown in Table 2.
Table 2 Examples of calf starter grain mixtures Feed
Grower 1
Grower 2
Cracked corn Rolled oats Rolled barley Molasses Soybean meal Canola meal Limestone Dicalcium phosphate Salt Trace mineral mix Vitamin E mix Vitamin ADE mix Additives
63.8 9.9
53.23
3.5 20.4 1.2 0.27 0.18 0.09 0.09 0.07 0.50
20.48 2.97 21.33 1.08 0.18 0.09 0.09 0.07 0.46
Values are percentage of total mixture on an as-fed basis. Composition of trace mineral mixture (%): Co, 0.01; Cu, 1; Fe, 5; I, 0.06; Mn, 4; Se, 0.03; Zn, 4. Composition of vitamin ADE mixture, per kg: A, 44 000 KIU; D, 990 KIU; E, 17 600 IU. Vitamin E supplement contains 44 000 IU kg 1. Grower grain mixture should contain coccidiostat or other additive as desired. Reproduced from Morrill J (1999) Proceedings of the Third Conference of the Professional Dairy Heifer Growers Association, p. 26. Minneapolis, MN. Savoy, IL: Professional Dairy Heifer Growers Association.
Workers at North Carolina State University have successfully developed a self-fed calf starter grain utilizing cottonseed hulls to limit intake. Calves are offered the starter from birth through 4–6 months of age. Cottonseed hulls represent a uniform, consistent source of more slowly digested fiber that helps limit intake in the older heifers. Critical to success of the system is maintaining a reliable source of clean cottonseed hulls, keeping the selffeeders clean, and providing plenty of water. Nutrient content of these starter mixtures on a DM basis is 16–18% crude protein (CP), 76% total digestible nutrients (TDNs), 0.66% calcium, and 0.42% phosphorus. The ingredient composition is 493 kg ground corn, 300 kg cottonseed hulls, 184 kg soybean meal, 9 kg calcitic limestone, 5 kg tricalcium phosphate, and 5 kg white salt, ionophore, and a vitamin–trace mineral mixture. Although apparently successful, these starters are lower in energy and require higher intakes to meet the energy requirements for acceptable growth.
Managing Growth of the Heifer from Weaning to Breeding Once the heifer has been successfully weaned and has transitioned to group housing, control of rearing rate is of primary concern. If one assumes that a goal of age at first calving of 22–24 months is desirable, breeding should be initiated at 12–13 months. Animals must be of adequate weight and body condition to accomplish this objective. Table 3 demonstrates the challenges faced in feeding the large-breed heifer prior to breeding. It also demonstrates the difficulty in attaining ages at first calving below 20 months. Based upon these assumptions, it is assumed that rations for the large-breed heifers should foster a gain of 750–900 g day 1. Smaller breed heifers require gains of 500–650 g day 1. Excessive gains may increase the risk for problems with mammary development, particularly if protein is limiting in the ration. Pasture-based systems
In many areas of the world, the greatest forage asset is the availability of abundant, low-cost land suitable for pastures. The best example for pasture systems exists in Table 3 ADG necessary to achieve suggested 360 kg weight at breeding and postcalving body weight of 570 kg at varying ages Age at calving goal (months) Age at breeding goal (months) ADG birth–breeding (g) ADG breeding–calving (g)
20 11 953 884
22 13 800 884
24 15 680 884
Assumes 39 kg birth weight, 45.4 kg loss of weight at calving, and 280 days of gestation. ADG, average daily gain.
Replacement Management in Cattle | Growth Diets
Ireland, New Zealand, southern Chile, and Argentina, and similar climes that have cool temperatures with frequent, moderate rainfall during a large portion of the year. Less desirable examples of grazing systems are range management systems in arid areas, which require extensive land bases exceeding 20 hectares per animal and they support little more than maintenance nutrient requirements. In many areas of the world, the role of pasture in heifer-feeding systems is probably in between these extremes. It is important to evaluate realistically the advantages and liabilities of pasture systems and determine how best to optimize their benefits and minimize the risk of their shortcomings. The biggest challenge faced in the pasture system is reliably estimating the carrying capacity of the land. If land is to be utilized for pasture, its use during the year must be maximized to provide the best compromise of yield of animal growth and forage nutrient yield. Figure 1 shows the effect of grazing pressure on production per animal and per acre. Note that optimal growth per head is not the same as optimal growth per acre. Optimum growth per animal occurs at a point less than optimum for land utilization. When grazing pressure is low to medium, heifers graze on only the best quality forage. When pasture output is optimized at higher stocking rates, heifers are forced to consume some of the less nutritious forage and animal performance declines. This represents a challenge for the heifer grower or dairy producer. Extremes in stocking rate are undesirable. Long periods of low grazing pressure lead to a loss of legumes in a stand and increased growth of weeds and less desirable species. Long periods of high grazing pressure result in temporary or long-term decreases in forage production as nutrient reserves of desirable forage species are depleted and plants become less dominant in the sward. For optimum grazing, one should maintain available forage at
Production
High
Output per head
Output per acre
Medium
Available pasture
Low
Neg
High
Medium
Low
Very low
Low
Medium
High
Very high
Stocking rate
Figure 1 Effect of grazing pressure on production per animal and per acre. Reproduced from Hall MH (2009–2010) The Agronomy Guide. University Park, PA: Department of Crop and Soil Sciences, The Pennsylvania State University.
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approximately 1122–1685 kg DM per hectare. This is the equivalent of a 7–10 cm high stand of bluegrass/ white clover or 15–20 cm of tall grasses and legumes. Continuous or rotational grazing?
Historically, continuous grazing has been the most popular grazing system since it is simple and requires little labor. Grazing pressure is adjusted by adding or subtracting animals or temporarily fencing off areas for hay harvest. However, continuous grazing is a land extensive system, and low production of gain per hectare makes it inefficient. In contrast, rotational grazing can dramatically increase animal performance and forage DM yield per hectare. In heifer feeding systems, intensive rotational grazing systems are probably not as important. Improvements in nutrient quality of forage accrued from more daily movement of fences or shifting heifers to new paddocks daily do not offset the labor and fencing expense and convenient provision of water. Many heifer growing systems include some combination of both continuous and rotational systems. A continuously grazed paddock may be used to house animals during the winter or during periods of drought to enable other areas to recover forage growth. Other paddocks are designed to enable movement of fences on less frequent interval of 3–14 days. Supplemental nutrition of pasture systems
For many areas of the world, dairy heifers cannot be reared without significant nutrient supplementation during some portion of the year. The nutrient variation of grazed forage species represents one of the greatest challenges of grazing, particularly for animals less than 1 year of age. In the more temperate areas of the world, protein concentrations of pasture can vary from 6% to levels exceeding 20%, while the growing dairy heifer may require levels ranging from 12 to 18%. Similarly, energy values will range from those similar to corn silage to levels that more nearly resemble straw. Although heifer rearing regimes might tolerate some variation in growth, in today’s economic climate it is important that heifers calve at an early age and with desired body size and condition. When forage availability is adequate, but quality is lacking, provision of supplemental energy and protein through concentrate feeding is advised. At other times such as winter months or during severe drought, heifers require supplementation with both forages and concentrates. It is beyond the scope of this article to address adequately the supplemental nutrient needs of pasturereared heifers. Pasture-reared heifers require more energy than those in confinement due to their increased activity and exposure to environmental conditions, particularly during the winter. Research at Virginia Tech has shown that
406 Replacement Management in Cattle | Growth Diets
confinement-reared heifers require 12–25% less energy than indicated by National Research Council (NRC). They are also less influenced by severe cold and wet weather. Therefore, managers of pasture-reared heifers must make adjustments in nutritional strategies when environmental conditions are less than perfect. Factors such as cold weather, nonthermal resting areas, wind, rain, and snow increase demand for energy for maintenance thereby reducing that available for growth. Environmental conditions for heifers raised without housing may become so severe that it is not possible to maintain sufficient growth, even with substantial energy and protein supplementation. Supplementation of rations with energy must be based upon observed growth of heifers during inclement weather. Similarly, supplementation can often be reduced at considerable savings when pasture growth and environment are optimal. The greatest challenge of pasture systems lies in the establishment of pastures that enable maximal grazing throughout the season and provisions for supplementation when pasture nutrients are insufficient to promote desired growth. Depending upon the climate and resources, successful growers utilize a mixture of swards containing cool and warm season perennial grasses and legumes. Young calves readily adapt to pasture systems as they provide ample opportunity for exercise, excellent air quality, and when pasture growth is young and rapid, a plentiful supply of energy, protein, mineral, and vitamins. However, it is important to note that calves weighing less than 150 kg require nutrients at least as high as that for the lactating cow (>16% CP and >2 Mcal of metabolizable energy (ME) per kg of DMI). An additional consideration for younger calves is their susceptibility to parasitism. Aggressive parasite control programs are recommended because the young animals have not developed sufficient immunity more common in animals in their second grazing season. By 300 kg body weight, concentration of nutrients is less important as adequate intake (7 kg DM per day) of forage providing 12% protein and 2 Mcal ME per kg DMI is adequate for 700 g of gain per day. It is uncommon to formulate rations for grazing dairy heifers. Rather the manager assesses pasture quality and availability, and heifer growth to determine if supplemental nutrition is needed. Confinement rearing systems
Young heifers, less than 150 kg body weight, require diets of high forage quality to enhance rumen function and promote economical growth. Forages must be free of mold and spoilage to ensure adequate ration intake. Fermented feeds and a wide variety of by-product feeds are readily accepted by heifers more than 150 kg body weight. Forage quality, as defined by nutrient content, becomes less important for the heifer over 150 kg body
weight as intake is usually not the limiting factor in nutrition. Professional heifer growers have been especially aggressive in seeking ways to provide nutrients at the lowest possible costs. This strategy requires the grower to ‘think outside the box’ when it comes to selecting ration components. Rations are presented to demonstrate the possibilities for utilization of by-product feeds. They are based upon those used by several large heifer growers in Colorado and Texas as well as conventional rations used in heifer feeding trials at Virginia Tech. Each ration was evaluated using the Cornell Penn Minor (CPM) program to determine expected gains based on ME and metabolizable protein (MP). Ration I relied heavily on by-products from vegetable processing, wet brewer grains, and low-cost alfalfa silage, which were of insufficient quality for lactating dairy cattle or export. Frequent weighing of heifers revealed growth of 800 g day 1, while the CPM model indicated that ME supplied by the ration should provide for only 690 g of gain per day and sufficient MP for 1.17 kg of gain per day. Ration II used an exceptional array of by-product feeds. Alfalfa was of lower quality, as was the whole cottonseed. Outdated dairy products (ice cream, cottage cheese, yogurt, and other products) were also used as available in this ration. In comparison to ration I, this ration contained an abundance of protein of a very degradable nature. Sufficient ME and MP were present to support gains in excess of 1 kg day 1, which supported observations on the feedlot of rapid gains, and heavy body condition. Ration III represents the traditional ration fed to dairy heifers in Virginia. MP and ME were present in sufficient amounts to support daily gains in excess of 900 g. These rations demonstrate the ability of heifers to grow at rates that support early calving at recommended body sizes at very low ration costs. The greatest limitation involved in the successful use of by-product feeds is personal prejudices and preconceived ideas of what will be successful. Once it has been determined that by-products contain no harmful substances and that product quality is predictable, many by-products serve as economical ingredients for heifer rations (Table 4). Feeding the Breeding Age Heifer and Bred Heifer Growers should not need to increase nutrient levels for the breeding age heifer, since she should already be on a high plane of nutrition promoting 750–900 g of average daily gain (ADG) for large-breed heifers or 500–650 g of ADG for small-breed heifers. Once the heifer is bred, it is important to maintain these growth rates, although it is possible to tolerate some variation as long as goals for growth are attained at calving. As shown earlier, attaining a breeding weight of 363 kg at 13 months of age requires an ADG exceeding 800 g. However, attaining
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407
Table 4 Example rations for growing a 225 kg heifer at an average daily gain of 815 g
Ration I
kg DM
CP (%)
RUP (% of CP)
TDNs (%)
ME (Mcal lb 1)
NDF (%)
Cost ($ day 1)
6.0
11.2
45.4
66
2.2
46
0.72
Ground wheat straw, 1.45 kg; wet brewers’ grain, 2.9 kg; carrots, 1.8 kg; wet beet pulp, 1.8 kg; corn screenings, 1.1 kg; alfalfa silage, 3.6 kg; Rumensin was included in the mix. Ration II
5.85
17.2
29.4
68
2.6
35.91
74
Cotton gin trash, 730 g; rolled corn, 1.27 kg; distillers’ grains, 454 g; whole cottonseed, 363 g; alfalfa hay, 1 kg; wheat midds, 1.63 kg; cottonseed meal, 363 g; sorghum silage, 1.27 kg; waste dairy products, 1.82 kg. Ration III
13.6
12.0
33.9
67
2.44
41.3
90
Corn silage, 6.82 kg; soybean meal, 454 g; ground shelled corn, 1.6 kg; orchard grass hay, 2.27 kg. All rations were fed as total mixed rations for ad libitum intake, with prevailing feed prices as of August 2009. DM, dry matter; CP, crude protein; RUP, rumen-undegradable protein; TDNs, total digestible nutrients; ME, metabolizable energy; NDF, neutral detergent fiber.
the postcalving weight of 570 kg requires heifers to continue to gain 750–900 g day 1. Opportunities to utilize by-product feeds in total mixed rations continue. These heifers can tolerate variations in gain, and rapid compensatory growth prior to calving is well tolerated provided that heifers do not become overconditioned.
Feeding Management Considerations Grouping heifers is a challenging issue to resolve, as it is a compromise between facilities, labor, and nutrient efficiency. Heifers should be placed in as many groups as is efficient from a labor standpoint. Suggested grouping are transition heifers, 4–8 months, 9–12 months, breeding-age heifers, and pregnant heifers. If possible, place heifers in groups within a range of 50 kg. Group heifers by size and body condition, paying close attention to note heifers significantly older within a group that may need to be culled. When multiple breeds are present in a herd, it is important to remember that smaller breeds mature more rapidly than larger breeds. If heifers are grouped by size, smaller breed heifers such as Jerseys will frequently become overconditioned. It is recommended that Jerseys and other earlier-maturing breeds are housed with slightly larger and older large-breed heifers. Provision of sufficient feed bunk space is an important consideration in such situations. Factors influencing growth and feed efficiency of dairy heifers
A common misconception regarding dairy heifer nutrition is that published nutrient requirements provide sufficient nutrients to assure the stated rate of gain under a wide variety of environments. One must
remember that these recommendations are based on the assumption that replacement heifers are clean, dry, fed ad libitum, free of disease and parasites, unbred, and raised at moderate temperatures. A survey of Wisconsin dairy herds showed that much of the variation in gains could be attributed to environment rather than feeding programs. Net energy maintenance requirements were 12–24% higher for fall/spring and winter as compared to summer. Failure to adjust for these added nutrient needs could decrease ADG by 90–180 g or more. Cold stress is especially problematic for smaller heifers or when the animal has lost insulating capacity of its coat due to excess mud or moisture. Temperature has an influence on DMI. However, it was found that although temperature had a statistically significant influence on intake, it is of less importance than for lactating dairy cattle. In heifers, intake does not increase appreciably unless the temperature is less than – 10 C for more than several days. Likewise, heifers are not as prone to experiencing a meaningful depression in daily DMI during hot weather as they delay eating during the day and consume the majority of their ration during the cooler hours of the evening. Housing type has a strong influence on growth and feed efficiency. Heifers housed in well-designed confinement systems are not subjected to wind, rain, snow, or solar radiation. Nutrient expenditures for exercise are also reduced compared to pasture or more open housing systems. Several studies at Virginia Tech conducted in a counter-sloped heifer barn have demonstrated that heifers reared in housing systems with a resting area of 4.2 m2 per head had 10–20% higher feed efficiency than expected according to published nutrient requirements. This is attributed to lower maintenance costs and
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less exercise. Similarly, housing can have a dramatic influence on animal performance in heifers changing from confinement systems to systems that are more extensive, such as might happen when heifers reared in confinement during the winter are moved to a pasture system. Research at Virginia Tech has shown that when Holstein heifers reared in a counter-sloped heifer barn with 4.2 m2 or less per heifer were moved to a pasture system, they lost between 500 and 1000 g day 1 for the first 30 days. This was primarily due to increased activity of the heifers. This experience has demonstrated the need for transition housing under these circumstances and the need for substantial increases in energy in the diet during the transition. The latest version of Nutrient Requirements of Dairy Cattle (2001) has included adjustments for environmental conditions in its estimates of nutrient requirements for growth. In addition to expected growth, the user is requested to enter estimates for previous temperature, coat condition, hair depth, and evidence of heat stress and nighttime cooling. These factors are considered when estimating maintenance requirements for the growing heifer and represent a significant improvement. In addition, the program may be used for grazing animals as it includes distance animals are expected to walk and the topography of the land being grazed in estimating energy requirements. Unlike the high-producing dairy cow, the nutrient requirements of the growing heifer can be met at less than the animal’s intake capacity. Recent research has demonstrated that feeding dairy heifers at less than ad libitum intake results in reduced fecal output and improvements in feed efficiency. Diets are formulated to provide adequate nutrients for the desired rate of gain at 80–90% of ad libitum intake using higher-quality forages and/or more-concentrate-type ingredients. Since these diets are typically consumed within a relatively short period of time, the limit-fed systems require that feeding facilities have sufficient feed bunk space for all animals to eat simultaneously and that the bedding used is not edible. In contrast, the advantages of balancing rations for ad libitum intake are that less expensive by-products and high-fiber feeds can be utilized to reduce ration cost. Growers and producers believe that it also encourages body development, but research has not confirmed this anecdotal observation. The economic advantages of either system depend upon ingredient costs and existence of facilities with sufficient feed bunk space. A significant negative side effect of limit feeding is that heifers become bored quickly and will readily consume fences and housing facilities if they are constructed of wood. Probably one of the most important components of the heifer-feeding program is the implementation of a system to weigh and measure heifers on a routine basis. For the lactating herd, the dairy herd improvement (DHI)
program has provided a valuable decision-making tool for herd management. Similarly, heifer weights and heights are essential to successful heifer growing systems. Scales should be electronic with facilities to enable weighing animals easily with minimal stress to the animal or grower. Such management information is necessary if the grower is to respond in a timely manner to the environmental and health-related factors that might impair heifer growth or lead to overfattening. An excellent example of the effectiveness of routine body weight monitoring is the management system of the New Zealand Grazing Company that has contract raised over 300 000 heifers on pasture-grazing systems. All heifers are weighed (monthly up to 10 months of age and subsequently bimonthly) by a technician using electronic scales. Using an internet management system, the company is able to analyze the performance of each heifer compared to predetermined benchmarks, which means that the data are quickly translated into management information for the grower and enables a meaningful report to the owner of the heifers. This has enabled the New Zealand Grazing Company to guarantee performance of heifers and build a business that raises 5000–10 000 heifers annually. By 2009, the New Zealand dairy industry has widely accepted the principle of regular monitoring and reporting heifer growth performance, and consequently most dairy farmers outsource their dairy replacement growing allowing increased profitability from their dairy herd. Feeding programs for heifers must first achieve the ultimate goal of providing an animal capable of expressing her genetic potential at a reasonable age. Current research indicates that this is somewhere between 22 and 24 months of age and a body weight of 550 kg after calving for Holsteins and 350 kg after calving for Jerseys. Future research may yield ways in which age at calving may be reduced without significant risk to mammary development. At the present time, average ages of first calving below 22 months are not advisable for large-breed heifers. The second requirement for success involves aggressively seeking out low-cost ingredients, which will enable attainment of growth goals. Profitable heifer-growing operations will thrive in locations adjacent to sources of by-products or low-cost pasture, which will enable economical feeding programs. The third requirement for success involves monitoring body weights of the growing heifers. Facilities must be incorporated into heifer management system that enable weighing and measuring animals.
Conclusion Heifer feeding management requires a different mindset than feeding cows. Heifer performance is not monitored well enough and we are not sure of the effects of
Replacement Management in Cattle | Growth Diets
heifer management decisions on the heifer’s ability to lactate. 1. The importance of forage quality declines in importance as the heifer ages. Significant opportunities for economy exist for growers willing to consider unusual by-product feeds and forages of insufficient quality to use in the lactating herd rations. 2. Transition to group housing requires well-designed facilities that permit easy accommodation of outliers from the average. 3. Control of the rate of gain from weaning to onset of puberty is critical. Too much energy and too rapid a rate of gain enhance the onset of puberty, but at the risk of impaired mammary development. Increasing protein avoids overfattening to a point, but still may not result in normal udder growth. Too little energy and protein or poor environmental conditions reduce gains and delay breeding and calving, resulting in significant increases in rearing costs. 4. Bred heifers offer significant opportunities for economizing feeding as nutrient density of rations is more moderate. 5. Feeding systems should be labor efficient, enable monitoring of intake and growth of heifers, and permit documentation of rearing expenses.
See also: Replacement Management in Cattle: Breeding Standards and Pregnancy Management; Growth Standards and Nutrient Requirements; Health Management; Pre-Ruminant Diets and Weaning Practices.
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Further Reading Bethard GL, James RE, and McGilliard ML (1997) Effect of rumenundegradable protein and energy on growth and feed efficiency of growing Holstein heifers. Journal of Dairy Science 80: 2149. Bickert WG (1990) Feed manger and barrier design. In: Dairy Feeding Systems, NRAES-38: Proceedings of the Dairy Feeding Systems Symposium. Harrisburg, PA, USA, 10–12 January. Ithaca, NY: NRAES. Hall MH (2009–2010) The Agronomy Guide. University Park, PA: The Department of Crop and Soil Sciences, Pennsylvania State University. Hoffman PC (1999) Protein requirements of dairy replacement heifers. In: Proceedings of the Four State Applied Nutrition and Management Conference, pp. 97–103. Dubuque, IA, 3–4 August. Hoffman PC, Brehm NM, Howard WT, and Funk DA (1994) The influence of nutrition and environment on growth of Holstein replacement heifers in commercial dairy herds. The Professional Animal Scientist 10: 59. Hoffman PC, Simson CR, and Wattiaux M (2007) Limit feeding of gravid Holstein heifers: Effects of growth, manure nutrient excretion, and subsequent early lactation performance. Journal of Dairy Science 90: 946–954. Kertz AF, Barton BA, and Reutzel LF (1998) Relative efficiencies of wither height and body weight increase from birth until first calving in Holstein cattle. Journal of Dairy Science 81: 1479–1482. Moody ML, Zanton GL, Daubert JM, and Heinrichs AJ (2007) Nutrient utilization of differing forage-to-concentrate ratios by growing Holstein heifers. Journal of Dairy Science 90: 5580–5586. Morrill JL (1999) Managing the calf from weaning through four months of age. In: Proceedings of the Third Annual Conference of the Professional Dairy Heifer Growers Association, pp. 23–30. Savoy, IL: FASS. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th edn. Washington, DC: National Academy Press. Quigley JD, III, James RE, and McGilliard ML (1986) Dry matter intake in dairy heifers: 1. Factors affecting intake of heifers under intensive management. Journal of Dairy Science 69: 2855–2862. Wickham IW (1997) Marketing a custom heifer business. In: Proceedings of the First Conference of the Professional Dairy Heifer Growers Association, pp. 13–22. Savoy, IL: FASS.
Relevant Websites http://www.nzgrazing.co.nz – New Zealand Grazing Company Limited.
Breeding Standards and Pregnancy Management J S Stevenson, Kansas State University, Manhattan, KS, USA A Ahmadzadeh, University of Idaho, Moscow, ID, USA ª 2011 Elsevier Ltd. All rights reserved.
Value of Replacements Heifers give birth to approximately 25–33% of all calves born on a dairy. This percentage can be increased by applying sex-biased semen from a number of superior sires, although conception rates are generally low, reaching about 60–80% of that achieved with conventional semen. Consequently, when using superior proven sires, heifers should represent the most advanced genetics in the herd. The genetic merit of artificial insemination (AI)-sired calves from heifers should be superior to that of AI-sired calves from older cows. Rearing and breeding of replacement heifers is critical to survival of the dairy farm because it represents 15–20% of total farm costs. Age at first calving is the single most important variable influencing the costs of raising heifers. Age at first calving could be defined as total days on feed since birth and is a function of the rate at which breeding weight (age) and conception are achieved. Once pregnancy is established, total days on feed become fixed. Costs associated with age at first calving include feed, labor, housing, interest on investment, breeding and veterinary health, and death loss. To reduce the costs associated with rearing heifers, one must reduce age at first calving or reduce feed costs because they represent approximately 60% of the total rearing costs. Reducing age at first calving is more easily achieved than saving on low-cost feeds given the lack of universal availability of inexpensive feeds to most producers. In a recent survey, the average cost to raise a home-grown heifer was US$100 more than that required to raise the heifer on a custom heifer-rearing operation.
Age at First Calving Lifetime milk yield, 305-day lactation yields, and lifetime profit of replacement heifers are maximized when heifers calve for the first time between 23 and 24 months of age. An evaluation of 6 million US dairy cow records from 1960 to 1982, however, found no appreciable change in calving age for any of six dairy breeds. Mean ages (months) at first calving for 1960 and 1982 were as follows: Ayrshire, 28.4, 28.6; Brown Swiss, 28.2, 27.8; Guernsey, 27.6, 27.4; Holstein, 27.3, 27.8; Milking Shorthorn, 27.7, 27.8; and Jersey, 26.0, 25.9 months, respectively. Since 1980, however, age at first calving has decreased to
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current mean age ranging from 24 months for Jerseys to 28 months for Ayrshires, with the other dairy breeds falling in between these extremes. Holsteins had the smallest standard deviations for age at first calving (21.2–24.8 months) of any breed. Puberty in heifers is dependent on many factors including, but not limited to, breed, age, and body weight. Nonetheless, age at puberty is generally not considered to be a limiting factor for age at first conception and thus age at first calving. Most dairy breeds achieve puberty by 11–12 months of age or sooner as long as they are fed according to the minimum standards suggested by the National Research Council for energy, protein, minerals, and vitamins. Heifers less than 1 year of age should be fed to maximize growth without achieving excess body condition. Increased nutrient intake and average daily gain from 4 to 10 months of age improved feed efficiency and increased structural growth rates with a small increase in body condition of heifers by 10 months of age. Feeding a high-energy diet for a short duration (3 or 6 weeks beginning at 11 weeks of age) altered body growth and fat deposition in a time-dependent linear manner consistent with feeding a high-energy diet for a long duration (12 weeks). Feeding prepubertal heifers a high-energy diet for a longer duration resulted in a linear decrease in both the percentage of mammary epithelial cells that were proliferating and the mass of fat-free mammary parenchyma per unit of carcass. High-energy feeding and excessive prepubertal body gain hastened puberty and reduced the first and later lactation performance attributable to decreased mammary epithelial cell proliferation in areas of active ductal expansion. Because feeding heifers a high-energy diet will likely reduce mammary parenchymal mass at puberty, controlling the rate of body weight gain is likely a key to reducing mammary tissue loss resulting from excess body condition. Feeding dairy heifers a high-concentrate (75%) diet (beginning at 125 kg of body weight and continued for 245 days) did not affect most structural growth characteristics and puberty attainment, and equaled or improved 150-day milk and milk component yield after calving compared with heifers fed a high-forage (75%) diet as long as both diets were fed for equal average daily gains. Little biological rationale exists opposing the use of
Replacement Management in Cattle | Breeding Standards and Pregnancy Management
high-concentrate rations for dairy heifers, provided the daily gain is controlled and feed ingredients can be used to maintain a healthy rumen environment. Heifers on pasture have increased maintenance requirements, and depending on the nutrient quality of the pasture, less pasture nutrients may be available to support growth. If heifers have adequate high-quality forage, supplementing concentrates may not be necessary, particularly in pasture-based dairy systems. Therefore, monitoring and supplementing diets of pastured heifers before anticipated breeding occurs may prevent their underdevelopment before first breeding. Attempts to reduce age at first calving much less than the recommended 23–24 months should be avoided. Unless grown adequately, heifers calving at younger ages (<22 months) are more likely to experience dystocia and are subsequently 3–4 times more likely to have a retained placenta, metritis, reduced reproductive efficiency, and are likely to be culled from the herd. In addition, first lactation milk yields may be compromised.
Reproductive Cycle and Breeding Standards Research indicates that breeding for milk yield is more important than breeding for size because genes that control body size seem to be independent of those for milk yield. Dairy heifers reach puberty as indicated by the regular occurrence of estrus. The period of estrus and a new (or first) estrous cycle usually begins when heifers first stand to be mounted from the rear by another heifer. This period is about 10–18 h in duration and begins each new estrous cycle (day 0 of the cycle). About 90% of cycling heifers show a slightly bloody discharge (bloody Metestrus
tail or metestrual bleeding) from the vulva 1–2 days after estrus whether or not they were inseminated or conceived. This bloody discharge is a sign that they were in estrus. The estrous cycle is about 21 days in duration and normally ranges from 18 to 24 days. The cycle consists of four stages: estrus (estrogen is the dominant hormone and initiates mating behavior), metestrus (time of ovulation and early corpus luteum development), diestrus (progesterone is the dominant hormone as the corpus luteum grows and matures), and proestrus (decreasing progesterone, increasing estrogen, and final follicular maturation). Cycles shorter than 18 days may occur in heifers after they experience their first estrus at puberty. The estrous cycle is cyclical because in the absence of fertile mating or AI during estrus, estrus will recur in approximately 3 weeks. During normal estrous cycles in heifers, follicles grow in either two or three wave-like patterns, with the majority of heifers exhibiting three waves (Figure 1). Follicular waves are induced by increased follicle-stimulating hormone (FSH) secretion. The largest or dominant follicle of the third wave generally matures during proestrus because of increased pulse secretion of luteinizing hormone (LH) and secretes estrogen to induce estrus. A preovulatory surge of LH secretion then causes ovulation. Ovulation occurs approximately 24–32 h after the beginning of estrus and subsequently the oocyte (egg) is released into the oviduct. At the site of ovulation, the ruptured follicle transforms into a corpus luteum. The corpus luteum produces progesterone necessary to prepare the uterus for a potential pregnancy. In the absence of a viable conceptus about days 16–17 of the 21-day cycle, prostaglandin F2 (PGF2) is secreted by the uterus to cause death or regression of the corpus luteum (known
Diestrus
Proestrus
Ovulation
Ovulation
E Estrus
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P LH
LH FSH PGF2α
0
5 10 15 Days of the bovine estrous cycle
21
Figure 1 Characteristics of the bovine estrous cycle. Four stages of the cycle are illustrated (estrus, metestrus, diestrus, and proestrus) in addition to various hormonal changes that occur. Three follicular waves are illustrated (repeating patterns of circles) with the third wave producing the ovulatory follicle. Large dominant follicles of the first two waves become atretic and never ovulate during a normal cycle. E, estradiol or estrogen; FSH, follicle-stimulating hormone; LH, luteinizing hormone; P, progesterone; PGF2, prostaglandin F2.
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as luteolysis). Diestrus ends as luteolysis is initiated and proestrus begins. Otherwise, the conceptus secretes a pregnancy signal (interferon-) to preserve the corpus luteum to allow pregnancy to continue. As the corpus luteum regresses in the absence of pregnancy, the dominant follicle continues to mature and will ovulate just after the heifer goes out of estrus, producing the egg that potentially will form a new conceptus upon fertilization. Thus, the cyclic nature of the estrous cycle continues, only to be interrupted by pregnancy. The recommended age to begin a breeding program with heifers is about 12–14 months, provided the heifers are adequately grown and cycling. Growth rates are important to reach targeted body weights and frame sizes (skeletal growth measured by wither height) by breeding age as well as expected calving at 22–24 months of age (Table 1). Breeding body weight as a percentage of first postcalving body weight should be in the range of 60–65% for most breeds. Hence recommended median body weights and median wither heights at first insemination of replacement heifers are as follows: Ayrshire (318–340 kg and 117–122 cm); Brown Swiss (340–363 kg and 122–130 cm); Guernsey (318–340 kg and 117–124 cm); Holstein (340–363 kg and 122–127 cm); Jersey (238–261 kg and 109–114 cm); and Milking Shorthorn (340–363 kg and 117–122 cm), respectively. If heifers are inseminated too young or before adequate growth occurs, their first lactation yields will be compromised. Furthermore, overconditioned (fat) heifers do not reproduce well and will not produce milk to their genetic potential. Waiting to inseminate heifers when older than 14–15 months negatively affects their lifetime milk production. It is important that heifers calve at or near 2 years of age, which reduces their rearing costs and also results in milk production at an earlier age.
Proper feeding management for adequate growth is necessary to ensure puberty has occurred before breeding age. Adequate growth is even more critical for seasonal breeding systems because the window of opportunity for breeding and hence timely calving is limited. It is needless to say that growth rates of heifers on pasture should be similar to those raised in confinement. Thus, raising cattle on pasture necessitates management decisions about grazing and forage systems and supplementation regimens to support proper growth of dairy heifers. Collectively, in addition to age, body weight of heifers at breeding and immediately before or after calving plays a role in their subsequent lactational performance. Thus, age at first calving is considered to be less than 24 months and postcalving body weights of at least 82% of mature weight is recommended for all breeds. In seasonal breeding dairy systems, calving at the beginning of the calving season is more critical to survivability and economic return than age at first calving.
Management of Breeding Age at first breeding and at first calving may be managed more precisely through the combined management of estrous cycle before AI. Well-managed heifers exhibit greater conception rates than lactating cows, resulting in lesser costs per pregnancy generated and per replacement heifer produced. Therefore, the most effective management strategy to increase genetic progress and maximize profitability on a dairy is to use estrus or ovulation synchronization before AI. This is particularly critical in seasonal, pasture-based dairy systems that require heifers to calve at the beginning of the herd-calving season when forage supplies are optimal. Seasonal breeding requires an efficient and effective use of labor and other resources
Table 1 Recommended median body weights (kg) for dairy heifers by age (months) and by breed Breed Age
Aryshire
Brown Swiss
Guernsey
Holstein
Jersey
Milking Shorthorn
2 4 6 8 10 12 14 16 18 20 22 24
90 130 165 210 225 290 330 375 410 440 485 510
85 120 195 250 310 340 380 450 465 495 550 560
70 120 170 210 260 295 335 385 410 445 485 500
85 125 175 220 265 310 350 395 445 475 515 530
55 100 125 160 195 220 250 280 305 330 350 370
90 135 180 225 275 320 370 410 450 490 520 545
Adapted from Heinrichs J and Lammers B (1998) Monitoring Dairy Heifer Growth. Accessed http://das.psu.edu/dairy/pdf-dairy/ud006.pdf.
Replacement Management in Cattle | Breeding Standards and Pregnancy Management
related to detection of estrus, breeding program, and calving at specific times of the year. Before 1980, a few or no hormonal products were available to synchronize estrus and ovulation in heifers. Therefore, breeding of heifers entirely depended on visually detecting estrus before AI. Today, various products include orally active (feed additive) or intravaginally placed progestins, gonadotropin-releasing hormone (GnRH), and PGF2. Managing the estrous cycle to the convenience of the breeder is now possible even in large heifer developer operations where replacements are raised on contract for individual dairy producers or are raised for sale to other producers. Progestins Feeding melengestrol acetate (MGA: 0.5 mg per heifer per day) for 14 days synchronizes estrus (see (1) in Figure 2). Depending on the stage of the estrous cycle in which any heifer begins the MGA feeding period, a few may have a functional corpus luteum after 14 days of feeding. Most heifers show estrus within 2–6 days after withdrawing MGA from the feed. This estrus is quite infertile in those heifers that began MGA feeding after day 10 of the cycle. Because the identity of the less fertile heifers is unknown, this first estrus after MGA withdrawal is passed over and heifers are given an injection of PGF2 17–19 days after MGA withdrawal. Insemination of heifers based on detected estrus usually occurs between 2 and 5 days after PGF2 administration. It is possible to time inseminate any noninseminated heifers at 72 h after PGF2 administration but conception rates will be approximately 60–75% of those achieved based on observed estrus. Progesterone Inserts Insertion of a progesterone-impregnated intravaginal insert (progesterone-releasing intravaginal device (PRID) or controlled internal drug release (CIDR) insert) in addition to PGF2 effectively synchronizes estrus in a short-term, 5- or 7-day period (see (2) in Figure 2). PGF2 lyses any functional corpus luteum when injected at removal of the insert. Generally, inseminations occur after detected estrus during a 2- to 5-day period after its removal. In an attempt to further control estrus and ovulation, ovulation can be synchronized by inducing synchronous emergence of a new follicular wave in the presence of high blood concentrations of progesterone. This method is similar to the previous method (2); however, the progesterone insert is placed intravaginally in conjunction with a first injection of
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GnRH, and PGF2 is injected with removal of the insert 5 or 7 days later. If timed AI (TAI) is desired, a second injection of GnRH should be administered 48–56 h after PGF2 injection and insert removal, with AI occurring 12–20 h later. Prostaglandin F2 A simpler and less expensive method (see (3) in Figure 2) includes detection of estrus during 6 days and then inseminating any estrual heifers according to the signs of estrus. On the seventh day, PGF2 is injected into any noninseminated heifer to induce luteolysis and estrus for subsequent insemination. The success of this method depends on the accuracy and efficiency of visual detection of estrus. A more complicated method involves administering two injections of PGF2 14 days apart. One can inseminate only estrus-detected heifers after the second of two injections (see (4) in Figure 2) or inseminate after both injections (see (5) in Figure 2) and reduce the number of second injections to all noninseminated heifers. Timing of inseminations without regard to detected estrus at 72–80 h after PGF2 produces lesser conception rates than those made after detected estrus. Prostaglandin F2 þ Gonadotropin-Releasing Hormone Another technique (see (6) in Figure 2) combines injection of GnRH to induce the release of FSH and LH plus injection of PGF2 7 days later followed by visual detection of estrus and AI. The GnRH injection in some heifers better controls follicular development and synchronizes it with luteolysis that follows PGF2. About 10% of heifers show estrus within 24 h of PGF2, and therefore, for optimal results, detection of estrus should begin 24–48 h before PGF2. An alternative (see (7) in Figure 2) to the previous method allows for a single TAI after the injection of PGF2. This protocol (i.e., Ovsynch) synchronizes ovulation (rather than estrus), thereby allowing for AI at a fixed time without detection of estrus. One gives a second injection of GnRH to all heifers at about 48–56 h after PGF2 and then inseminates about 12–20 h later without regard to detected estrus. Of course, if estrus is observed before PGF2 or the second GnRH injection, one may inseminate the heifer based on visual signs and discontinue the remainder of the injections. It is apparent that in all systematic breeding programs, the conception rate at first AI will not reach 100%. First-service conception rates should range from 50 to 70% in heifers. Therefore, some heifers will need additional inseminations in order to become
414 Replacement Management in Cattle | Breeding Standards and Pregnancy Management ±GnRH Feed MGA
PGF2α Watch for estrus and AI
(1) –33
–19
OR TAI at 64–72 h
0
Watch for estrus and AI
CIDR or PRID
(2)
PGF2α OR
–7
OR
GnRH TAI
–5
0
2 3
Watch for estrus and AI
PGF2α (3) –6 PGF2α
0 PGF2α Watch for estrus and AI OR TAI at 64−72 h
(4) –14
0 Watch for estrus and AI
PGF2α
PGF2α
(5) –14
0 GnRH
PGF2α
(6) –7
0 Watch for estrus and AI
GnRH
GnRH PGF2α TAI
(7) –7
0
2 3
Days Figure 2 Seven programs for synchronization of estrus or ovulation are illustrated for dairy heifer replacements. (1) Feeding of melengestrol acetate (MGA) for 14 days and passing over the estrus expressed upon MGA withdrawal followed by an injection of prostaglandin F2 (PGF2) given 17–19 days after MGA. AI, artificial insemination; GnRH, gonadotropin-releasing hormone; TAI, timed AI. (2) Intravaginal insertion of a progesterone-releasing insert (progesterone-releasing intravaginal device (PRID) or controlled internal drug release (CIDR) insert) for 5 or 7 days with PGF2 injection administered at insert removal; or injection of GnRH at insert placement, injection of PGF2 at insert removal, followed by second injection of GnRH given 48–56 h after PGF2 with one TAI 12–20 h later. (3) Visual detection of estrus for 6 days before injecting all noninseminated heifers with PGF2 on the seventh day. (4) Two injections of PGF2 given 14 days apart with inseminations occurring after the second injection or (5) inseminate after either injection. (6) An injection of GnRH 7 days before an injection of PGF2. (7) Same as (6) but a second injection of GnRH is given 48–56 h after PGF2 with one TAI 12–20 h later.
pregnant. Producers should pay close attention 18–24 days after AI to detect heifers that return to estrus. All of these breeding programs only synchronize estrus or ovulation for the first AI. Subsequent estrous periods, however, are fairly well synchronized in those heifers that fail to conceive to the first AI. Estrus detection aids such as tail chalk or tail paint, heat mount detectors, or more sophisticated electronic devices can be used to detect estrus before insemination. Because heifers tend to display very pronounced signs of
estrus, they can be easily detected by consistent twice-daily visual observations. About 5% of heifers eventually fail to conceive for various reasons and must be culled. Early detection of pregnancy allows identification of those heifers that are not pregnant so that prompt reinsemination can occur. Pregnancy can be accurately determined by transrectal ultrasonography as early as day 28 after insemination or by transrectal palpation of the uterine contents by days 35–40. The other available
Replacement Management in Cattle | Breeding Standards and Pregnancy Management
tool is a blood test to measure the presence of a pregnancy-specific protein (pregnancy-specific protein B or other pregnancy-associated glycoproteins (PAGs)). These PAGs are produced by the conceptus and can accurately determine pregnancy status as early as 18–30 days after breeding. The objective of this diagnosis is to find nonpregnant heifers so that they can be treated promptly to induce a new fertile estrus. Treatments utilized on nonpregnant heifers can include any of those short-term hormonal methods described previously. Historically, when transrectal palpation occurs, the heifer is given an injection of PGF2 when a functional corpus luteum is palpated and subsequent behavior is monitored for visual signs of estrus. When synchronization of estrus is performed before first AI, the day of estrus is generally known when palpation occurs. If palpation occurs at 35 days after AI, one is generally correct in assuming that an estrus was not detected at 20–21 days post-AI; hence the heifer is on cycle days 14–15 when pregnancy diagnosis occurs. This is an ideal time to give PGF2 to induce a fertile estrus. Given similar costs of palpation and a PGF2 injection, any nonpregnant heifer is generally given PGF2 and observed for subsequent signs of estrus. Injections of PGF2 cause abortions in pregnant heifers, so caution is warranted.
Management of Pregnancy Once pregnant, replacements should not be forgotten and allocated to pasture or other areas without observation. Some embryonic and fetal losses occur after conception. It is recommended to reconfirm pregnancy by 90–100 days of pregnancy to preclude maintaining an open replacement until she is found not pregnant at her projected calving date. Pregnant heifers should continue to grow at rates recommended by the National Research Council to achieve adequate body weight and size by calving time. Depending on the breed, ration formulations to attain daily gains of 0.50–0.80 kg are usually adequate to achieve desired first-calving weights. Regardless of when first breeding begins in heifers, once pregnant, heifers should be fed to calve in good body condition. Without adequate body reserves of fat, it becomes very difficult to achieve good first-lactation milk yields. Which heifers will use body reserves to maximize milk yield is difficult to predict. Those that consume greater amounts of dry matter tend to be those that produce more milk. Precautions should be taken to prevent disease and injury to gestating heifers. Adequate shade during hot months of the year prevents low birth weights and subsequent poor milk yield and reproductive performance after calving. Furthermore, adequate shelter to eliminate
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windchill during cold months minimizes frostbite to teats when udder and tissue edema occur during late gestation. Immunizations before first breeding and again between 50 and 60 days before expected parturition for prevention of infectious bovine rhinotracheitis (IBR), parainfluenza (PI3), bovine viral diarrhea (BVD), bovine respiratory syncytial virus (BRSV), clostridial spp., leptospirosis (five way), and calf scour pathogens (Escherichia coli, Clostridium perfringens (type C), rotavirus, and coronavirus) are recommended. Reimmunization against calf scour pathogens is recommended at 3 weeks precalving. Depending on the location of heifers (pasture vs. concrete confinement facilities), dewormers (to prevent gastrointestinal roundworms) should be administered at or near calving.
Parturition In addition to milk yield, milk components, and physical type traits, sire selection for heifers is critical for what occurs at calving. It is recommended to choose calvingease sires for heifers. The United States Department of Agriculture (USDA) produces sire summaries with calving-ease information on all sires whose semen is available for purchase from semen-producing organizations or bull studs. The information reported is the percentage of difficult births in heifers as reported by observers attending calvings. Calving difficulty scores assigned at calving range from 1 to 5 (1 ¼ no assistance; 2 ¼ slight problem; 3 ¼ needed assistance; 4 ¼ considerable force; 5 ¼ extreme difficulty). The calving-ease percentage reported for each sire is based on the percentage of births in heifers when the calving difficulty scores were 4 or 5. In the Holstein breed, the average calvingease percentage is about 9%. For heifers, one should use sires with calving-ease percentages that are less than average while not compromising selection for excellent production traits of sires. Preventing calving difficulty or dystocia is important. Dystocia may predispose heifers to placental retention, metritis, breeding inefficiency, and greater culling rates. Most births do not require assistance (82%) and rushing delivery can injure the dam; however, waiting too long, after the water breaks, may deprive the calf of sufficient oxygen and cause death. Heifers should be observed frequently as due dates approach because some heifers may need assistance at calving. Observation of calving can reduce the number of stillborn calves and increase survival rates. The calf is born with no protection from disease or infection; hence, every effort must be made to limit its exposure to pathogens. Passive immunity is bestowed on the newborn by ingesting colostral milk antibodies shortly after birth.
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Calving areas should be clean, dry, well lit, draft free, free of hazards, provide good footing, and spacious to allow the heifer to move about and position herself without pinning herself against an obstruction in the calving area in which the calf has no room to be delivered. When assistance is required for a large calf, twins, or breech births, arms, hands, and instruments should be sanitized. Plenty of lubricant should be used. When a calf jack or obstetrical chains are used, one should only pull when the abdominal muscles of the mother contract, therefore working with her contractions. Applying too much force can injure the heifer and damage the calf. Heifers and calves that experience difficulty need extra attention. The absolutely most important measure and end point of successful reproduction is survival of the calf at birth and at various intervals thereafter. Immediately after birth, proper management of the newborn is critical to its survival. This includes high-quality colostrum (IgG concentrations >60 mg ml1) feeding immediately after birth, navel-dipping (7% tincture of iodine) to prevent navel invasion of microorganisms, immunizations, and other treatments. Delay in colostrum feeding can significantly diminish or preclude immunoglobulin absorption through the gut. Moreover, calves should be immediately identified for good record keeping. It is extremely important to disinfect calving pens between calvings. All contaminated bedding should be removed and the surface cleaned with a disinfectant.
Conclusion Because replacement heifers represent the future genetic investment of any dairy herd, their management is critical to herd survival and longevity. Associated costs and investments in replacements are significant at 15–20% of all farm costs. Timeliness of establishing pregnancy can be significantly improved by using various hormonal schemes to program the estrous cycle to facilitate the use of AI and ensure a greater proportion of heifers calve by 23–24 months of age. The key to efficient reproduction is proper growth and body weight by calving time. Sire selection should emphasize production traits and calving ease to maintain good production but facilitate fewer problems at first parturition. Because heifers are more fertile than their lactating counterparts, the best available proven sires should be used with a much greater cost–benefit ratio. Perhaps, the most effective management strategy to increase genetic progress and maximize profitability on a dairy is to use synchronization of estrus and ovulation before AI in all dairy heifers. Furthermore, using gender-selected semen in replacement heifers available from several of the AI companies is the most
cost-efficient application of this new technology because of the greater fertility in heifers than in lactating dairy cows. However, one can expect a reduction in fertility associated with gender-selected semen of 60–80% of that achieved with conventional semen, with the realization of 85–90% of the resulting calves to be females. See also: Replacement Management in Cattle: Growth Diets; Growth Standards and Nutrient Requirements; Health Management; Pre-Ruminant Diets and Weaning Practices. Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Estrous Cycles: Puberty.
Further Reading Bailey TL and Murphy JM (1999) Dairy heifer development and monitoring. In: Howard JL and Smith RA (eds.) Current Veterinary Therapy, Vol. 4: Food Animal Practice, pp. 86–92. Philadelphia, PA: W.B. Saunders Co. Beal WE (1998) Current estrus synchronization and artificial insemination programs for cattle. Journal of Animal Science 76(supplement 3): 30–38. Davis Rincker LE, Weber Nielsen MS, Chapin LT, Liesman JS, and VandeHaar MJ (2008a) Effects of feeding prepubertal heifers a highenergy diet for three, six, or twelve weeks on feed intake, body growth, and fat deposition. Journal of Dairy Science 91: 1913–1925. Davis Rincker LE, Weber Nielsen MS, Chapin LT, et al. (2008b) Effects of feeding prepubertal heifers a high-energy diet for three, six, or twelve weeks on mammary growth and composition. Journal of Dairy Science 91: 1926–1935. Gill GS and Allaire FR (1976) Relationship of age at first calving, days open, days dry, and herd life to a profit function for dairy cattle. Journal of Dairy Science 59: 1131–1139. Head HH (1992) Heifer performance standards: Rearing systems, growth rates and lactation. In: Van Horn HH and Wilcox CJ (eds.) Large Herd Dairy Management, p.422. Champaign, IL: American Dairy Science Association. Heinrichs AJ (1993) Raising dairy replacements to meet the needs of the 21st century. Journal of Dairy Science 76: 3179–3187. Heinrichs AJ and Losinger WC (1998) Growth of Holstein dairy heifers in the United States. Journal of Animal Science 76: 1254–1260. Heinrichs J and Lammers B (1998) Monitoring Dairy Heifer Growth. http://www.das.psu.edu/research-extension/dairy/nutrition/pdf/ ud006.pdf (accessed 22 June 2010) Hoffman PC (1997) Optimum body size of Holstein replacement heifers. Journal of Animal Science 75: 836–845. Hoffman PC and Funk DA (1992) Applied dynamics of dairy replacement growth and management. Journal of Dairy Science 75: 2504–2516. Keown JF and Everett RW (1986) Effect of days carried calf, days dry, and weight of first calf heifers on yield. Journal of Dairy Science 69: 1891–1896. Lammers BP, Heinrichs AJ, and Kensinger RS (1999) The effects of accelerated growth rates and estrogen implants in prepubertal Holstein heifers on growth, feed efficiency, and blood parameters. Journal of Dairy Science 82: 1746–1752. Lin CY, McAllister AJ, Batra TR, et al. (1986) Production and reproduction of early and late bred dairy heifers. Journal of Dairy Science 69: 760–768. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th revised edn. Washington, DC: National Academic Press.
Health Management S T Franklin and J A Jackson, University of Kentucky, Lexington, KY, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2422–2426, ª 2002, Elsevier Ltd.
Introduction Replacements are the future of the dairy industry. Focusing on improving health management of replacements will yield tremendous returns through decreased losses of animals with the greatest genetic potential on the dairy, decreased costs of medication, improved growth rates, improved feed efficiency and earlier entry into the milking herd.
Precalving and Calving Management Health management of dairy replacements begins before the replacements are born. Several factors, such as nutrition of lactating and dry cows, vaccinations of lactating and dry cows, length of dry periods, cleanliness of the calving environment and disease status of the dams, will ultimately affect disease resistance and health of replacements. It is important to note, however, that cows that are overfed tend to have difficulty calving because of being excessively overconditioned. Cows that are underfed, which results in mineral or vitamin deficiencies or lack of body condition, may produce inferior and low-volume colostrum. They also may experience difficulty calving. Protein deficiency in cows during the dry period may lead to low birth weights, low metabolic rates and poor vigor of calves, resulting in poor survivability. Some research also indicates that inadequate protein and energy nutrition of the dam results in poor absorption of immunoglobulins from colostrum by the calf. Cows that lose condition during the dry period are also at greater risk of experiencing calving difficulty. Calves that experience difficult births require more time before being able to stand, experience an increase in the time to voluntary suckling and have a decreased ability to absorb immunoglobulins. All these problems result in decreased transfer of passive immunity from the dam to the calf and increased risk of disease in calves. As the degree of calving difficulty increases, the risk of mortality for calves increases. Proper nutrition of dairy cows during lactation and the dry period will help decrease disease risks for replacements. Vaccinations of the dams will also impact disease resistance of dairy replacements. Proper vaccination of the dairy herd will increase the concentration of antibodies (immunoglobulins specific for diseases) in colostrum.
Dams may be vaccinated during the dry period against pathogens that are common causes of diarrhea in calves, such as Escherichia coli, rotavirus and coronavirus. Vaccination of the dams increases the concentration of antibodies against these pathogens in colostrum, thus providing increased protection for calves, resulting in decreased incidence or duration of diarrhea. Vaccination of the dams during the dry period is more effective for prevention of disease in calves than vaccination of calves at an early age. The immune system of neonatal calves is unable to respond quickly to a vaccination or an infection because the immune system of the newborn is immature at birth. Both numbers and effectiveness of antibodyproducing cells are lower in calves at birth than in adult cattle. Therefore, it is important for calves to obtain antibodies against common diseases of calves by consumption of colostrum rather than from an attempt to vaccinate calves at an early age. Vaccination of the dams against pneumonia may also help to decrease the incidence or severity of this disease in replacements. Another important factor that may affect the health of replacements is the length of the dry period of the dam. A dry period that is too short, i.e. less than 6 weeks, may not provide enough time for involution of the mammary gland and preparation for the next lactation. Cows with shortened dry periods produce small quantities of colostrum that may also have low concentrations of immunoglobulins. It is important for health of replacements, therefore, that cows have at least a 6-week dry period for production of high-quality colostrum. Management of the calving environment has a tremendous impact on the health of replacements. It is important for calves to be born in a clean, dry environment. Wet, sloppy stalls provide a perfect environment for growth of bacteria. Calving on a grass lot may be the best alternative when the climate is dry and mild. If a maternity barn is used, it is important to clean stalls thoroughly between calvings to prevent transfer of disease. Maternity stalls should only be used for calving and never for housing sick cows. Maternity pens and sick pens should be kept in separate facilities in order to prevent transfer of disease to highly vulnerable neonates and periparturient dairy cows. It is also important for the cows to be as clean as possible at calving in order to prevent calves from contracting disease organisms when suckling or attempting to
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suckle their dams. Preferably, calves should be separated from dams prior to suckling in order to prevent the calf from ingesting pathogens present on the legs, belly, flanks or udder of the cow as the calf attempts to nurse. Separating the calf from the dam and feeding colostrum by bottle also ensures adequate intake of colostrum for transfer of passive immunity from the dam. Finally, it is important to know the disease status of cows prior to calving. Diseases such as Johne’s disease, bovine viral diarrhea (BVD), and bovine leucosis virus (BLV) may be passed in utero or through colostrum. Calves should only be fed colostrum from cows known to be free of these diseases. It is important, therefore, to maintain a supply of frozen, high-quality colostrum from cows free of such diseases.
Care of Young Calves The importance for baby calves of adequate consumption of immunoglobulins from colostrum has been reviewed elsewhere (see Replacement Management in Cattle: Pre-Ruminant Diets and Weaning Practices). Mortality resulting from lack of consumption of adequate amounts of immunoglobulins is commonly greater than 35% and has been reported to be as high as 60%. Others have indicated a 74-fold increased risk of mortality when calves do not consume colostrum. Along with economic losses from high mortality rates as a result of lack of colostrum consumption, there are also increased costs associated with increased medication and poor feed efficiency. Transfer of passive immunity (absorption of immunoglobulins from colostrum) can be determined using commercial kits that measure immunoglobulins in the blood. For adequate protection of calves, blood immunoglobulin concentrations should be at least 10 mg ml 1. Serum protein concentrations in calves are also highly correlated with the concentration of immunoglobulins in blood and can be used to determine adequate transfer of passive immunity. A hand-held refractometer can be used to measure serum protein; levels greater than 5.0 g 100 ml 1 by 24 h of age indicate adequate consumption of colostrum. The use of colostrum substitutes and replacers may help improve disease resistance in calves when high-quality colostrum is not available. The most prevalent health problem of calves on most farms in the United States is diarrhea. Organisms such as Cryptosporidium parvum, rotavirus and coronavirus that cause diarrhea will not respond to antibiotic treatment. For cryptosporidiosis, the only means of prevention is sanitation, which includes controlling flies. For rotavirus and coronavirus, the most effective prevention is vaccination of the dam to increase antibodies in the colostrum against these organisms. Other organisms, such as E. coli and Salmonella sp., may be resistant to many of the
commonly used antibiotics. Producers often give antibiotics to calves during episodes of diarrhea in order to prevent secondary infections; however, this practice often does more damage than good, killing beneficial gut microflora and damaging the gut lining. The first step in caring for calves with diarrhea is to provide fluids for hydration and electrolytes for mineral loss, while continuing to provide milk for protein and energy. An electrolyte solution can be fed from 20 min to 2 h after each feeding of milk or milk replacer until feces return to normal. Secondly, the organism causing diarrhea should be identified to determine whether antibiotic treatment is needed. Pneumonia is the second most prevalent health problem of replacements, especially for replacements raised indoors. Research has shown that calves raised in individual hutches (plastic, fiberglass or wooden structures providing individual housing) perform very well and have fewer health problems, especially pneumonia, than calves raised in closed buildings. Open-front housing for older heifers should also help prevent pneumonia. Adequate, draught-free ventilation is important for prevention of pneumonia. Hutches, pastures and open-front housing for replacements provide optimal ventilation. In addition, hutches can be moved from location to location, giving producers the opportunity easily to remove old bedding and to break disease cycles. No matter what type of housing is used for replacements, cleanliness, dry bedding and adequate ventilation are essential to decrease incidence of disease. Another important factor for controlling disease in replacements is grouping of heifers. Most producers in the United States house young calves individually. In other areas, housing calves in groups and using mob-feeders is an efficient method of rearing calves during the liquid feeding phase. After weaning, calves should be housed in small groups of 10 or fewer until they have successfully made the transition from liquid feed to dry feed and the transition from individual housing to competing for food. Additionally, by housing in small groups (rather than mixing large groups of animals at one time), producers can limit the exposure of calves to disease organisms and match calves more closely by size. As calves age, they can be housed in increasingly larger groups; however, animals should be grouped so there is not more than 50 kg difference in size of animals up to 6 months and not more than 90 kg difference in size for older animals.
Biosecurity All dairy producers must actively institute biosecurity measures to prevent introduction of disease into the herd and to minimize spread of disease within the herd. For replacements, it is extremely important to prevent exposure of younger animals to older animals that may
Replacement Management in Cattle
have Johne’s disease. Exposure is not limited merely to animal-to-animal contact, but also includes articles of transmission, such as manure on hands, clothing and boots of workers, manure from older animals on equipment for feeding and handling replacements, or water that has been contaminated by older animals. In addition, flies can transfer diseases from older to younger animals. Producers must determine whether to have a closed herd or to allow introduction of new animals to the farm. If new animals are brought to a farm, the producer should work closely with a veterinary surgeon to determine which vaccinations animals should receive prior to coming to the farm. Once new animals arrive on the farm, or animals return to the farm from contract-growers or exhibitions, they should be quarantined for at least 30 days. This will allow time to determine if the new animals are likely to become ill and to allow the new animals to be exposed more slowly to any disease organisms currently on the farm. Other potential sources of disease entry into replacements are visitors, vehicles removing dead animals, feeddelivery vehicles, wild and domestic animals, and birds. Within the herd of replacements, diseases can be transferred by using needles on more than one animal or using the same glove to palpate more than one animal. Producers must identify potential sources for transfer of disease-causing organisms within the herd and from outside the herd and institute a management plan to control them.
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Internal Parasites Several types of internal parasites are found in dairy replacements. Perhaps the most common problem is coccidiosis. Coccidiosis causes diarrhea, which may be severe, resulting in weight loss, dehydration and anemia. Animals can be treated with a coccidiostat, such as amprolium, for severe coccidiosis. Coccidiostats such as decoquinate or lasalocid may be included in grain rations or even in milk replacers to help control coccidiosis. Another common internal parasite of calves is Cryptosporidium parvum. This organism causes diarrhea in young calves at 7–10 days of age that lasts approximately a week. There are no cures for cryptosporidiosis and no means of prevention other than sanitation to decrease the pathogen load. Treatment involves electrolyte solutions along with continued milk feeding. Replacement animals are very vulnerable to internal parasites (especially worms) during their first grazing season. Deworming of heifers yields economic returns in growth rates and feed efficiency. Producers should consult their veterinary surgeon to determine the most effective method of treating internal parasites both to decrease the parasite load in the animals and to prevent shedding of eggs onto pastures. Depending on geographical location, different deworming strategies are needed to control internal parasite populations. Producers should be aware that cold temperatures cause larvae to undergo arrest, even when ingested into the host. During this arrested stage, the larvae are resistant to most deworming agents.
Digestive Disorders Digestive disorders can occur in dairy replacements, resulting in problems such as acidosis and overeating diarrhea. Overeating diarrhea is found in replacements during the liquid feeding phase and may be prevalent in systems using accelerated feeding programs. This form of diarrhea can be treated by decreasing the amount of dry matter offered to calves in the liquid diet until the consistency of the feces returns to normal. Care should be taken to determine whether increased fluidity of the feces is caused by overeating or by disease organisms. If caused by disease organisms, treatment should include administration of an electrolyte solution and may require use of antibiotics. Acidosis can occur in replacements if they consume large amounts of grains. Forages comprise the basis for diets for replacements after 3 months of age. Animals that gain access to fields of maize or bags of feed by accident will often suffer acidosis leading to laminitis (founder) or even death. Animals that are affected will generally have severe diarrhea. They can be treated by withholding grain until feces return to normal, followed by gradual reintroduction of grain into the diet.
External Parasites Many external parasites, including various species of flies, affect health and growth of replacements. Several species of blood-sucking flies affect replacements. Horn-flies can be a major problem for cattle. They can cause substantial blood loss, transmit diseases including mastitis to replacements and decrease growth rates. Use of forced back rubs is probably the most effective method of decreasing populations of horn-flies. Additionally, removal of manure, which is the major breeding habitat for horn-flies, helps decrease populations. Another type of fly, the stable-fly, breeds in wet feed. Severe infestations of stable-flies can cause up to a 50% decrease in milk production. Counts of 25 flies per animal cause economically important losses in milk production and growth. Removal of waste feed from under feed troughs and other areas to decrease breeding areas is the most important mechanism for control. Horseflies and deer-flies are also blood-sucking flies and may be responsible for spread of several diseases but are impractical to control.
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Common house-flies are not blood-sucking insects but feed on muzzles, eyes and open wounds. They can be contaminated with more than 30 viruses and 175 bacteria, as well as other disease-causing organisms. The main form of control for common house-flies is sanitation and removal of breeding material because many house-flies are resistant to insecticide sprays. Cattle grubs are another parasite common in North America. The main damage to cattle is caused by the migration of the grubs through host tissues and production of cysts on the animals’ backs. Growth rates can be adversely affected with infestations of cattle grubs. Appropriate insecticide treatment will kill grubs; however, care must be taken not to administer insecticides when large numbers of grubs may have accumulated in the spinal canal. Killing of large numbers of grubs at once can lead to anaphylaxis in cattle. Other external parasites that may affect dairy cattle include fleas, lice, ticks and mites. Itchiness and formation of scabs should be examined by a veterinary surgeon who can prescribe appropriate forms of treatment.
Vaccinations Many disease occurrences can be prevented or at least minimized by appropriate vaccination programs. The program that is appropriate, however, will vary from region to region, and even farm to farm. Establishment of a vaccination program requires knowledge of diseases prevalent in the area, history of diseases on the farm, history of diseases in the herd, vaccinations used previously in the herd and an assessment of the risk of contracting economically important diseases based on management of the herd (open or closed). Producers should, therefore, consult their veterinary surgeon to develop a vaccination program appropriate for their animals, management and location. Timing of vaccinations is important for replacement animals. If the colostrum consumed by the calf contained antibodies against the disease organism present in the vaccine, the vaccine will not generate a sufficient immune response in the replacement animal. Maternal antibodies obtained from colostrum may be present up to 6 months of age, preventing an adequate response to vaccinations. It may be beneficial to wait until 6 months of age or greater for many initial vaccinations in calves in order to avoid interference from maternal antibodies. Additionally, many vaccines are not effective in neonatal calves because their immune system is not sufficiently developed to generate a protective response. Common mistakes made in vaccination programs are lack of booster vaccinations at the appropriate time and lack of frequent vaccinations. If the vaccination protocol calls for an initial vaccination followed by a booster
vaccination within 2 to 3 weeks, maximum protection will not be achieved without the booster vaccination. Essentially, the money spent for the first injection is wasted. The second problem, lack of frequent vaccinations, is seen especially with leptospiral vaccines. Leptospiral vaccines should be administered every 6 months to achieve adequate protection. It is also important for heifers to start receiving leptospiral vaccinations at 6 months of age so that they have received two vaccinations by the time they are used for breeding.
Conclusions Health management of replacements requires attention to many different areas, ranging from nutrition and management of late lactation and dry cows to vaccinations of replacements. Health management of replacements is an area that is often overlooked because producers do not see an immediate return on their efforts and prefer to spend their time improving management of the milking herd. For health management of replacements, however, the old saying that ‘‘an ounce of prevention is worth a pound of cure’’ really holds true. See also: Body Condition: Effects on Health, Milk Production, and Reproduction. Diseases of Dairy Animals: Infectious Diseases: Johne’s Disease; Infectious Diseases: Leptospirosis; Non-Infectious Diseases: Acidosis/Laminitis. Feeds, Ration Formulation: Dry Period Rations in Cattle; Lactation Rations for Dairy Cattle on Dry Lot Systems. Milk: Colostrum. Replacement Management in Cattle: Growth Diets; Pre-Ruminant Diets and Weaning Practices.
Further Reading Bovine Alliance on Management and Nutrition (2000a) An Introduction to Infectious Disease Control on Farms: Biosecurity. Arlington: American Feed Ingredients Association. Bovine Alliance on Management and Nutrition (2000b) Biosecurity on Dairies. Arlington: American Feed Ingredients Association. Bovine Alliance on Management and Nutrition (2001) Biosecurity of Dairy Farm Feedstuffs. Arlington: American Feed Ingredients Association. Butler JF (1992) External parasite control. In: Van Horn HH and Wilcox CJ (eds.) Large Dairy Herd Management, pp. 568–584. Champaign: American Dairy Science Association. Courtney CH (1992) Internal parasites of dairy cattle. In: Van Horn HH and Wilcox CJ (eds.) Large Dairy Herd Management, pp. 564–567. Champaign: American Dairy Science Association. Hjerpe CA (1992) Vaccines and vaccination programs. In: Van Horn HH and Wilcox CJ (eds.) Large Dairy Herd Management, pp. 538–555. Champaign: American Dairy Science Association. Quigley JD III. and Drewry JJ (1998) Nutrient and immunity transfer from cow to calf pre- and postcalving. Journal of Dairy Science 81: 2779–2790.
REPRODUCTION, EVENTS AND MANAGEMENT
Contents Estrous Cycles: Puberty Estrous Cycles: Characteristics Estrous Cycles: Postpartum Cyclicity Estrous Cycles: Seasonal Breeders Control of Estrous Cycles: Synchronization of Estrus Control of Estrous Cycles: Synchronization of Ovulation and Insemination Mating Management: Detection of Estrus Mating Management: Artificial Insemination, Utilization Mating Management: Fertility Pregnancy: Characteristics Pregnancy: Physiology Pregnancy: Parturition Pregnancy: Periparturient Disorders
Estrous Cycles: Puberty K K Schillo, University of Kentucky, Lexington, KY, USA ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2145–2151, ª 2002, Elsevier Ltd.
Introduction The term puberty is derived from the Latin word pubescere, which is translated to mean ‘becoming covered with hair’. Puberty originally referred to the appearance of body hair at the time of sexual maturation in humans. Today, puberty refers collectively to all of the physiological, morphological and behavioral changes that occur in animals as their gonads undergo the transition from the infantile to adult condition. The so-called onset of puberty refers to the time at which an individual gains the capacity to reproduce. Onset of puberty is the result of a series of developmental events that occur within the reproductive endocrine system. This article focuses on sexual development in females with emphasis on the dairy heifer.
Characteristics and Importance Heifers are said to have attained puberty when they first exhibit estrus, followed by a viable ovulation and an estrous cycle of normal length (18–25 days). First estrus
is not accompanied by ovulation. Rather, it is followed by luteinization of an ovarian follicle and a short estrous cycle (<18 days). An accurate determination of puberty onset in heifers requires not only estrus detection, but also examination of the ovaries and/or assessment of circulating concentrations of progesterone to confirm the presence of a corpus luteum. The average age at which heifers attain puberty is 11 months of age. However, average age at puberty varies greatly, ranging from approximately 8 to 24 months (Table 1). In general dairy heifers (e.g. Holstein) attain puberty earlier than beef heifers (e.g. Angus, Hereford). It is not unusual for Holstein heifers to attain puberty at 8–9 months of age, whereas English breeds of beef cattle attain puberty at 10–14 months of age. It is important to emphasize that age at puberty is profoundly influenced by plane of nutrition. For example, in an early study done at Cornell University, Holstein heifers fed a low, medium or high plane of nutrition exhibited first estrus at 20.2, 11.2 and 9.2 months of age, respectively. Age at puberty is an extremely important economic trait in production systems where reproductive
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422 Reproduction, Events and Management | Estrous Cycles: Puberty Table 1 Differences in age at puberty among various breeds of cattle Breed
Age
(months) Jersey Guernsey Holstein Ayrshire Beef (European) Zebu Water buffalo
8 11 11 13 10–15 17–27 15–36
efficiency is a primary goal. One of the greatest costs in dairy production is feed. Generally, feeding animals that are not productive reduces production efficiency. In most intensive dairy production systems, producers strive to have heifers calve by 24 months of age and produce one calf each year thereafter. In order to accomplish this a heifer must become pregnant by 14 months of age, have sufficient body size for pregnancy and dystocia-free parturition and sufficient body energy reserves to return to oestrus following calving. An understanding of mechanisms controlling onset of puberty should facilitate management of heifers to optimize production efficiency.
Review of the Reproductive Endocrinology of the Female The major anatomical components of the reproductive endocrine system of females include the hypothalamus, anterior pituitary gland, ovaries and uterus. These are endocrine organs and therefore produce hormones which permit communication among the various reproductive tissues. To understand the physiological mechanisms governing onset of puberty it is necessary to understand how the hypothalamus, anterior pituitary gland and ovaries interact in an endocrine fashion (Figure 1). Discussions of the role of the uterus in reproduction are included in other articles. The central nervous system, which includes the hypothalamus, plays a pivotal role in regulation of reproductive function. Higher centers of the brain receive neuronal inputs from a variety of sensing systems that monitor internal and external environments (e.g. ambient temperature, day length, nutritional status). Information carried by these systems is integrated in the hypothalamus and transduced into a neuroendocrine signal. A small number of neurons in the hypothalamus produce gonadotropin releasing hormone (GnRH), a decapeptide which is secreted into capillaries located in the median eminence of the hypothalamus. GnRH enters these capillaries and is
CENTRAL NERVOUS SYSTEM
Hypothalamus GnRH
+/–
Anterior pituitary gland FSH
Estradiol
–
LH Ovaries
Progesterone
Figure 1 Endocrine interactions within the hypothalamic– pituitary–ovarian system. Various inputs conveying information about the external and internal environments converge on the hypothalamus. The hypothalamus transduces these neuronal signals into an endocrine signal, i.e. the pattern of GnRH secretion. GnRH regulates release of FSH and LH from the anterior pituitary gland. These gonadotropins regulate ovarian function which includes the synthesis and secretion of the steroid hormones estradiol and progesterone. These steroids feed back to regulate gonadotropin secretion. In prepubertal heifers, low concentrations of estradiol exert a negative feedback effect on pulsatile release of LH. Estradiol also inhibits release of FSH. High concentrations of estradiol (i.e. those present during estrus) induce a preovulatory surge of LH. Progesterone is the major negative feedback hormone controlling LH secretion in the adult female.
carried to the anterior pituitary gland via portal vessels, which drain into another capillary bed. The major action of GnRH is to stimulate release of gonadotropins, i.e. luteinizing hormone (LH) and follicle stimulating hormone (FSH). GnRH is secreted in a pulsatile manner and has been shown to cause the pulsatile release of LH and possibly FSH. The pulsatile pattern of LH release can be demonstrated by measuring circulating concentrations of LH at frequent intervals for several hours. The pulsatile release of GnRH has been documented by measuring concentrations of this hormone in blood collected from the pituitary portal vessels. During pulsatile secretion concentrations of a hormone increase abruptly within minutes. This increase is followed by a slower decrease, which reflects the clearance of the hormone from circulation. Pulsatile secretion is typically characterized by quantifying the frequency of pulses (number of pulses in a given period of time) and the amplitude of pulses (difference between the peak of a pulse and the previous nadir). Figure 2 illustrates pulsatile LH secretion. The gonadotropins, LH and FSH, are released into the general circulation by gonadotropic cells in the anterior
Reproduction, Events and Management | Estrous Cycles: Puberty
regulation of FSH secretion during the prepubertal period. Estradiol and inhibin, a peptide hormone produced by granulosa cells of follicles, appear to regulate FSH release via feedback inhibition. Whereas low levels of estradiol inhibit pulsatile LH secretion in prepubertal heifers, high levels of this steroid (i.e. those present during estrus) facilitate LH secretion. The high levels of estradiol produced by the preovulatory follicle induce an LH surge, which results from enhanced pituitary response to GnRH, as well as an increase in GnRH release.
10 9 8
Peak
7 LH (ng ml–1)
423
6 5 4 3 2 1
Development of the Hypothalamic– Pituitary–Ovarian System
Nadir
0 0
60
120 Time (min)
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Figure 2 Example of pulsatile patterns of LH in a series of blood samples collected at 10-min intervals for 180 min. Each pulse is characterized by a rapid increase in concentrations, followed by a slower decrease. Pulsatile release of LH is typically characterized by quantifying the pulse frequency (number of peaks per unit time) and average pulse amplitude (difference between the peak concentration and preceding nadir).
pituitary gland. These hormones regulate ovarian function. It is generally accepted that the pulsatile release of LH is necessary for the initiation and maintenance of ovarian activity. With respect to onset of puberty, LH plays important roles. First, a high-frequency mode of LH secretion (>1 pulse h1) is necessary for follicle maturation. Second, an LH surge, which accompanies estrus, is necessary for ovulation and formation of the corpus luteum. The role of FSH in onset of puberty is not well defined. It is generally accepted that FSH is important in stimulating early follicle development (prior to maturation to the preovulatory stage). The gonadotropins regulate production of ovarian steroid hormones, which in turn regulate gonadotropin release, uterine function, sexual behavior and expression of secondary sex traits. LH and FSH act together to regulate production of estradiol by granulosa cells of ovarian follicles, whereas LH alone appears to govern progesterone synthesis by the corpus luteum. An appreciation for the regulation of gonadotropin secretion by ovarian steroids is critical to understanding sexual maturation (Figure 1). In prepubertal heifers, oestradiol is the major negative feedback regulator of LH secretion. In postpubertal females, progesterone is responsible for most of the inhibitory effects of the ovary on LH secretion. Estradiol inhibits LH secretion by suppressing pituitary responsiveness to GnRH, and by inhibiting release of GnRH by the hypothalamus. Progesterone appears to act at the level of the hypothalamus to inhibit GnRH release. Little is known about the
An understanding of the mechanisms controlling sexual maturation in heifers has been gained by systematically examining the development of the reproductive endocrine axis. The experimental approach has been to identify the physiological and/or anatomical component(s) that are rate-limiting in terms of the timing of puberty onset. Hypothalamus and Anterior Pituitary Gland It is generally accepted that the hypothalamic–pituitary axis and the capacity of this system to synthesize and secrete GnRH and gonadotropins is fully competent long before onset of puberty. The hypothalamic–pituitary portal vascular system appears to be developed and functional prior to birth. GnRH secretion has not been measured directly in heifers. However, bull calves exhibit GnRH pulses in portal blood by 2 weeks of age. In heifers and bull calves, pulses of LH appear in the peripheral circulation by 2 weeks of age. Collectively, these results support the idea that the neuroendocrine mechanisms controlling the pulsatile release of GnRH/LH are competent by 3–5 weeks of age. This casts doubt on the notion that development of this system is the rate-limiting step in onset of puberty. Ovaries The ovaries of heifers appear to be functionally competent long before the onset of puberty. Vesicular follicles are present by 2–4 weeks of age, and reach a peak in average size by 12–16 weeks of age before declining to an average size that varies little until the peripubertal period. These follicles will respond to exogenous gonadotropins. Treatment with FSH and LH induces ovulation in heifers by 1 month of age, but number of induced ovulations increases between 1 and 5 months of age.
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Ovarian Control of Gonadotrophin Secretion As mentioned previously, the ovaries regulate gonadotropin secretion via steroid hormones. Ovulation is induced by a surge of LH which is caused by elevated concentrations of estradiol. This important positive feedback system appears to be fully developed prior to onset of puberty. In beef heifers, injections of estradiol induce preovulatory-like surges of LH in prepubertal heifers as early as 5 months of age. This suggests that onset of puberty may be limited more by development of events leading up to the LH surge (i.e. elevated levels of estradiol) than by development of the capacity to produce an LH surge. Although dominant, vesicular follicles appear in waves throughout the prepubertal period, they do not produce enough estradiol to induce an LH surge. At this point it is important to reiterate that both the ability of follicles to respond to gonadotropins as well as the ability to elicit an LH surge appear to be fully developed months before onset of puberty. Therefore, the rate-limiting step in sexual maturation appears to be appearance of the endocrine signal that stimulates follicle development to the preovulatory stage. This signal appears to be the highfrequency mode of LH secretion. Examination of LH pulse patterns between birth and puberty reveals that LH pulse frequency increases between birth and 3–5 months of age, but then declines and remains relatively low until a few weeks prior to onset of puberty. The frequency of LH pulses before this peripubertal increase in LH secretion is much lower than that of the follicular phase of the estrous cycle, when LH pulses occur with a frequency of approximately once per hour. This observation begs an important question: why does LH pulse frequency remain low even though the mechanisms necessary for the pulsatile release of LH appear to be fully developed by one month of age?
Pulsatile secretion of LH is regulated by the negative feedback actions of ovarian steroids. In heifers a rise in LH concentrations following ovariectomy has been demonstrated as early as 1 month of age, suggesting that ovarian negative feedback is present at this age. Estradiol appears to be the major negative feedback regulator of LH secretion before the onset of puberty. In ovariectomized heifers, physiological doses of this steroid lower concentrations of LH to preovariectomy levels. The transient increase in pulsatile LH secretion between 3 and 5 months of age may reflect development of the estradiol–LH negative feedback loop. Although the estradiol negative feedback system may be present by 1 month of age, it may not be expressed at this time due to extremely low levels of estradiol. The increase in LH concentrations during the first several months of age may be attributed to ovarian estradiol reaching a threshold for inhibiting LH secretion. By 3–5 months of age, the ovaries produce enough estradiol to suppress LH secretion. However, the ability of estradiol to suppress LH release changes with advancing age in prepubertal heifers. Physiological doses of estradiol suppress concentrations of LH in ovariectomized heifers until the age at which ovary-intact heifers attain puberty (Figure 3). At this time estradiol becomes less effective in suppressing LH pulses, i.e. animals appear to escape estradiol negative feedback. Little is known about the cellular and molecular mechanisms regulating the negative feedback actions of estradiol. It seems likely that such changes are attributed 15 Number of LH pulses per 8h
Between birth and puberty follicles grow in waves, meaning that at regular intervals, dominant follicles emerge from pools of growing follicles, and then regress before reaching the preovulatory stage. The size of the dominant follicle increases with age; the largest dominant follicles are found during the peripubertal period. The dominant follicles of the late prepubertal period produce sufficient estradiol to induce estrous behavior and LH surges. The first of these estrous periods are not necessarily followed by ovulation and a normal estrous cycle. Peripubertal heifers may exhibit oestrus in the absence of a subsequent estrous cycle. First ovulation is normally preceded by one or two LH surges followed by elevations in progesterone that are lower in magnitude and shorter in duration than those expressed during a normal luteal phase. These short luteal phases are attributed to ovarian follicles that become luteinized, but do not ovulate.
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Figure 3 Circulating concentrations of LH in prepubertal beef heifers that were either ovariectomized (OVX) or ovariectomized and treated chronically with physiological concentrations of estradiol (OVX þ E). Ovariectomy results in an immediate increase in LH due to removal of ovarian negative feedback. Replacement with estradiol prevents the postovariectomy increase in LH suggesting that this steroid is the major negative feedback hormone regulating LH secretion in prepubertal heifers. Eventually heifers become less sensitive to this negative feedback and LH concentrations increase. This escape from negative feedback coincides with the onset of puberty in ovaryintact animals. (Based on data from Day et al., 1984.)
Reproduction, Events and Management | Estrous Cycles: Puberty
to changes in GnRH neurons and/or neurons that regulate GnRH neurons. There is evidence to support the idea that changes in response to estradiol negative feedback reflect changes in number of estradiol receptor in neurons that regulate secretory activity of GnRH neurons.
Theory of Puberty Onset The observations discussed above serve as the basis for the widely accepted theory of puberty onset summarized in Figure 4. The central claim of this theory is that a cascade of endocrine events is required for ovulation, i.e. a high-frequency mode of LH secretion which stimulates growth of a dominant follicle to the preovulatory stage, which results in production of enough estradiol to induce estrus and a preovulatory surge of LH. The prepubertal heifer has the capacity to express this cascade by 5–6 months of age, but does not due to a high sensitivity to estradiol negative feedback which maintains a low-frequency mode of LH secretion. Onset of puberty can occur only after the hypothalamic–pituitary axis escapes estradiol negative feedback, or when this negative feedback effect is overridden by administering exogenous GnRH or LH. It is unclear whether the decrease in sensitivity to estradiol negative feedback is strictly a developmental event. Recent evidence suggests that the timing of this change in sensitivity may be more a function of metabolic status than one of age. Restriction of dietary energy delays onset of puberty, apparently by delaying escape from estradiol negative feedback. Moreover,
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precocious puberty in heifers appears to be related to favorable energy status and high growth rates. Preliminary studies suggest that in beef heifers, highenergy intake early in life (birth to 6 months of age) induces transient but cyclic luteal function, suggesting that the estradiol negative feedback system may have been prematurely inactivated. Additional studies are required to test this hypothesis. Nevertheless, these observations reinforce the idea that the hypothalamic– pituitary–ovarian system is functionally mature by 5–6 months of age.
Timing of Puberty Onset Although the endocrine events leading to onset of puberty have been well characterized in heifers, it remains unclear why puberty occurs at a particular age in individual animals. It seems reasonable that timing of puberty onset is a function of genetic and environmental factors, as well as geneticenvironment interactions. Although breed type has been shown to influence age at puberty, there has been no attempt to understand these effects in terms of the endocrine mechanisms controlling puberty onset. In other words, we know little about the effects of breed on the endocrine mechanisms timing onset of puberty. Of the studies that examine effects of environment on sexual development most have focused on the effects of nutrition. A few studies examined the effects of season on sexual development.
Nutrition, Growth and Onset of Puberty
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Figure 4 Summary of the prevailing working hypothesis explaining how nutrition influences timing of puberty onset. According to this hypothesis, various blood-borne signals reflecting nutritional status (e.g., metabolites, metabolic hormones) are detected by sensors in the peripheral and/or central nervous systems. These sensors trigger various neuropathways that converge on the hypothalamus, where they are transduced into signals that regulate pulsatile secretion of GnRH and LH (e.g., response to estradiol negative feedback). In this way, nutritional status influences the timing of the increase in LH pulse frequency that is critical for onset of puberty.
Research in the 1950s and early 1960s established that age at puberty is inversely related to growth rate in dairy heifers. This was later documented in beef heifers. Most studies dealing with growth and puberty focus on the effects of plane of nutrition on age at puberty. For example, beef heifers fed to sustain an average daily gain of 0.23 kg reached puberty later than those fed to sustain an average daily gain of 0.82 kg. In one study, postweaning growth rates were inversely related to age at puberty in heifers fed to gain an average of 0.2 kg day1, but not in heifers fed to gain 0.4 kg day1. This lead to the hypothesis that growth rate has little effect on sexual development above a certain critical body weight, or that puberty onset occurs at a critical body weight. However, the fact that heifers maintained on different planes of nutrition typically attain puberty at different body weights casts doubt on this ‘critical body weight hypothesis’. Nevertheless, it is clear that sexual development is somehow linked to growth and/or nutritional status.
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Mechanisms Linking Onset of Puberty and Nutrition It is beyond the scope of this article to review the voluminous research concerning the possible endocrine mechanisms linking nutrition and sexual development. However, it is generally agreed that nutrition influences sexual development via signals that influence the pulsatile release of LH. A working hypothesis illustrating how nutritional status might influence sexual development is summarized in Figure 5. Using this framework, there appear to be four major areas of focus for research in this area: nutritional signals, peripheral and central systems that sense these signals, neuropathways that transduce these nutritional signals into neuroendocrine signals, and GnRH/LH secretion. In cattle attention has focused primarily on mechanisms controlling LH secretion. In beef heifers, it has been demonstrated that a delay in onset of puberty caused by undernutrition is accompanied by a delay in escape from estradiol negative feedback. Moreover, underfeeding induces a decrease in LH pulse frequency and cessation of estrous cycles in sexually mature heifers suggesting that the effects of nutrition on reproductive activity are not confined to sexual development. Although it can be concluded that undernutrition suppresses the pulsatile secretion of LH in
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Figure 5 Summary of the prevailing theory explaining control of puberty onset in the heifer. During the early infantile period pulsatile LH secretion increases slightly due to limited follicle development and minimal estradiol secretion. This promotes vesicular follicle development and estradiol secretion. Due to a high sensitivity of the hypothalamic–pituitary axis to the negative feedback actions of estradiol, pulsatile LH secretion decreases and remains low throughout the prepubertal period. The end of the prepubertal period is heralded by a decrease in response to estradiol negative feedback, and a resultant increase in LH pulse frequency. The timing of this escape from negative feedback is dependent on nutritional status; heifers on high planes of nutrition escape at an earlier age than those on low planes of nutrition. The increase in LH pulse frequency is critical to onset of puberty because it stimulates follicle development to the preovulatory stage, thereby inducing estrus and a preovulatory surge of LH.
heifers, we know very little about the signals that reflect nutritional status or how these signals are detected and transduced into signals that influence LH secretion. Season and Sexual Development Sexual development in seasonal breeders
Seasonal breeders exhibit a well-defined anestrous period each year. Short-day breeders such as sheep and goats exhibit regular estrous cycles in late summer, when day length is decreasing, and enter a period of anestrus in early spring, when day length is increasing. Extensive research has supported the theory that in these species, photoperiod regulates reproductive activity by affecting the pulsatile release of LH. During the anestrous season, LH pulse frequency is suppressed due to enhanced responsiveness to estradiol negative feedback, as well as a steroid-independent effect on GnRH secretion. This inhibition is lifted during periods of short day lengths. The transition from the anestrous to the breeding season resembles the transition from the prepubertal to pubertal state, i.e. increased frequency of LH pulses, maturation of a dominant follicle, increased production of estradiol, onset of estrus and induction of an LH surge. In temperate climates, lambs are typically born in late winter and early spring and attain puberty in late summer and early autumn. As in heifers, puberty in ewe lambs is the result of an escape from estradiol negative feedback which allows pulsatile LH secretion to increase. As might be expected, season influences onset of puberty in seasonal breeders. For example, ewe lambs born during the autumn attain puberty at 10–12 months of age (during the subsequent autumn), whereas lambs born in the spring reach puberty at 5–6 months of age (during the autumn). Although it is beyond the scope of this article to describe details of how season influences onset of puberty in sheep, a few general comments seem appropriate. First, it seems clear that photoperiod is the major mediator of the effect of season on puberty onset in sheep. In order for puberty to occur at a normal age (5–6 months of age), lambs must experience several months of long day lengths before exposure to short days. Second, the delay in puberty onset experienced by autumn-born lambs is associated with low LH pulse frequency, due to high sensitivity to oestradiol negative feedback. Third, the pineal gland and its pattern of melatonin secretion appear to be important in mediating the effects of day length on sexual development. Effects of season on sexual development in cattle
Cattle are not seasonal breeders. Nonpregnant heifers and cows will exhibit regular estrous cycles throughout the year. However, there is evidence to suggest that season influences sexual development in heifers. Early studies described an effect of season of birth on age at puberty in dairy heifers. Heifers born during the spring and summer
Reproduction, Events and Management | Estrous Cycles: Puberty
were younger at first estrus than those born during autumn and winter. Similar observations were reported for beef heifers; heifers born in the spring were younger at puberty than those born in the winter. Examination of year-round reproductive records in Wisconsin revealed that the winter environment appears to delay onset of puberty in autumn-born heifers. Autumn-born heifers that failed to attain puberty before the subsequent winter did not attain puberty until the subsequent spring and summer. It appears that both season of the first 6 months of life and season of the second 6 months of life influence sexual development. Heifers born near the time of the autumnal equinox (23 September) were younger at puberty than those born near the time of the vernal equinox (21 March). In both autumn- and spring-born heifers, exposure to spring–summer conditions (i.e. increasing day length and temperature) resulted in an earlier onset of puberty compared to autumn–winter conditions (i.e. decreasing day length and temperature). The environmental variable(s) responsible for the seasonal effects on puberty in cattle remain(s) unidentified. Artificially lengthening photoperiod (16L:8D) during the winter months hastens onset of puberty in heifers and bull calves suggesting that day length may be important, as it is in seasonal breeders. Few studies have addressed the physiological mechanisms whereby season influences sexual development in heifers. Based on the importance of pulsatile LH secretion in regulating onset of puberty, it is reasonable to hypothesize that seasonal effects on sexual development are somehow mediated by changes in LH patterns. However, support for this hypothesis remains elusive.
Summary Puberty in dairy heifers is a gradual process involving maturation of the endocrine mechanisms controlling ovarian development. Although puberty does not occur until 8–14 months of age, the hypothalamic–pituitary– ovarian system appears to be functionally competent as early as 5–6 months of age. By this time the estradiol– LH negative feedback loop is established and secretion of estradiol by ovarian follicles is sufficient to maintain pulsatile LH secretion in a low-frequency mode. As long
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as this mode of LH secretion is sustained, follicle development will not progress to the preovulatory stage. When the hypothalamic–pituitary axis escapes this inhibitory effect of estradiol, pulsatile LH secretion enters the high-frequency mode, allowing a dominant follicle to mature and release enough estradiol to induce estrus and a preovulatory surge of LH. It is likely that both genetic and environmental factors influence timing of puberty onset in cattle. We understand very little about genetic variation in the physiological mechanisms that regulate onset of puberty. While the effects of nutrition on puberty onset clearly involve effects on pulsatile LH secretion, the mechanisms mediating the effects of other environmental factors such as season remain unclear. See also: Husbandry of Dairy Animals: Sheep: Reproductive Management. Replacement Management in Cattle: Growth Standards and Nutrient Requirements. Reproduction, Events and Management: Estrous Cycles: Characteristics; Estrous Cycles: Seasonal Breeders.
Further Reading Day ML and Anderson LH (1998) Current concepts on the control of puberty in cattle. Journal of Animal Science 76: 1–15. Day ML, Imakawa K, Garcia-Winder M, et al. (1984) Endocrine mechanisms of puberty in heifers: estradiol negative feedback regulation of luteinizing hormone secretion. Biology of Reproduction 31: 332–341. Foster DL (1994) Puberty in the sheep. In: Knobil E and Neil JD (eds.) The Physiology of Reproduction, 2nd edn., pp. 411–451. New York: Raven Press. Kinder JE, Day ML, and Kittok RJ (1987) Endocrine regulation of puberty in cows and ewes. Journal of Reproduction and Fertility 34: 167–186. Kinder JE, Bergfeld EG, Wehrman ME, Peters KE, and Kojima RN (1995) Endocrine basis for puberty in heifers and ewes. Journal of Reproduction and Fertility 49(supplement): 393–407. Schams D, Schallenberger E, Gombe S, and Karg H (1981) Endocrine patterns associated with puberty in male and female cattle. Journal of Reproduction and Fertility 30(supplement): 103–110. Schillo KK, Hall JB, and Hileman SH (1992) Effects of nutrition and season on the onset of puberty in the beef heifer. Journal of Animal Science 70: 3994–4005. Schillo KK, Hansen PJ, Kamwanja LA, Dierschke DJ, and Hauser ER (1983) Influence of season on sexual development in heifers: age at puberty as related to growth and serum concentrations of gonadotrophins, prolactin, thyroxine and progesterone. Biology of Reproduction 28: 329–341.
Estrous Cycles: Characteristics M A Crowe, University College Dublin, Dublin, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2152–2157, ª 2002, Elsevier Ltd.
Introduction The estrous cycle represents the cyclical nature of ovarian activity that facilitates female animals to go from a period of reproductive receptivity to nonreceptivity ultimately allowing the establishment of pregnancy following mating. The normal estrous cycle in cattle is 18 to 24 days. The cycle consists of two discrete phases: the luteal phase (14 to 18 days) and the follicular phase (4 to 6 days). The luteal phase is the period following ovulation when the corpus luteum (CL) is formed, while the follicular phase is the period following the demise of the corpus luteum (luteolysis) until ovulation. During the follicular phase final maturation and ovulation of the ovulatory follicle occurs which leads to the release of an oocyte (the female gamete) into the oviduct allowing the potential for fertilization. Commencement of regular estrous cycles in cattle occurs at the time of puberty. Heifers reach puberty between 6 and 24 months of age typically at 50% of mature body weight. At the onset of puberty, the first estrous cycle tends to be of a short duration (3 to 12 days) and follows a silent ovulation (that is not associated with expression of behavioral estrus). Estrous cycles cease during pregnancy due to the prolonged presence of elevated progesterone from the CL. Following parturition estrous cycles recommence after a variable period of anestrus and anovulation. Similar to the transition from prepuberty to puberty, the resumption of ovarian cycles postpartum is usually associated with a silent ovulation followed by a short cycle (see Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity).
Behavioral Changes throughout the Estrous Cycle Estrous behavior in cattle is closely related with time of ovulation and allows successful mating to occur prior to ovulation to maximize the chances of conception. During estrus, heifers and cows will stand to be mounted by herd mates or a bull, if present. Estrus is expressed at 18- to 24-day intervals and lasts for 8 to 24 h. Estrus is caused by
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the secretion of the proestrus estradiol surge from the preovulatory dominant follicle. The estrous cycle may be divided into diestrus, proestrus, estrus and metestrus. During diestrus, cyclic animals will not show signs of estrous behavior. During the preovulatory period there is a peak in butting activity and attempted mounting without standing. During estrus heifers will stand to be mounted and also show increased mounting activity. Levels of investigatory behavior (including sniffing, rubbing, licking, chinresting and orientation) occurs at similar intensities both before, during and after the period of standing to be mounted. Standing to be mounted is considered to be the definitive sign of estrus in cattle. A number of other qualitative signs of estrus have been described including: mounting of other cows, ruffling of the rump hair or abrasion of the rump skin, vulval relaxation and moistness, estrous mucus appearing from the vulva, sensitivity to palpation of the rump and general restlessness; however, none of these signs are as definitive as standing to be mounted. Cows or heifers that are in proestrus, estrus or metestrus simultaneously within a herd usually form sexually active groups that will include a bull if present (see Reproduction, Events and Management: Mating Management: Detection of Estrus).
Follicular Growth and Development The growth, development and maturation of ovarian follicles is a fundamental process for effective reproduction in farm animals. Primordial follicles are established in the ovary during embryonic development. A fixed number of primordial follicles are established during fetal development. During the lifetime of the female, primary follicles enter a growing pool. Initial stages of follicle growth occur independently of gonadotrophic hormones; antral follicles then become responsive to and subsequently dependent on follicle stimulating hormone (FSH). The pattern of follicle growth in cattle has been clearly characterized with the use of transrectal ovarian ultrasonography. Several detailed studies have demonstrated that there are either two, three or occasionally four waves of follicle growth during the
Reproduction, Events and Management | Estrous Cycles: Characteristics
normal estrous cycle of cattle. During each wave of follicle growth, a cohort of two to five follicles emerges to grow beyond 4 mm in diameter to medium (5–9 mm) size classes (emergence) (Figure 1). From the pool of medium follicles that emerge a single follicle is selected to become the dominant follicle (selection). Selection is a hypothetical physiological process whereby ‘excess’ follicles are reduced to the ovulatory quota. This determines the species-specific ovulation rate in females thereby playing a major role in determining the number of offspring born per pregnancy. The selected dominant follicle continues to grow in size, while other follicles in the cohort undergo atresia. Dominance is a process that enables the ‘selected’ follicle to suppress further growth of other follicles, escape initial atresia and continue to grow until either atresia (during the luteal phase) or ovulation (during the follicular phase). The preovulatory dominant follicle undergoes a period of final maturation, following CL regression and increased luteinizing hormone (LH) pulse frequency, and it then ovulates. After ovulation, a CL is formed which secretes progesterone throughout the luteal phase of the cycle.
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The number of follicular waves during the estrous cycle is affected by breed and management of animals. In dairy cows two waves of follicular growth per estrous cycle are more common, while in beef heifers up to 70% of ovarian cycles consist of three follicular waves. During the transition from prepuberty to puberty and from anestrus to resumption of ovarian cycles in postpartum cows, the short ovarian cycle that typically occurs is associated with a single follicular wave.
Endocrine Regulation of Ovarian Function Ovarian activity throughout the estrous cycle is controlled by the hypothalamic–pituitary–ovarian–uterine axis (Figure 2). Gonadotropin releasing hormone (GnRH) is secreted in a pulsatile manner by neurons of the hypothalamus into the hypophyseal portal blood system. It is transported to the anterior pituitary where it controls the secretion of LH and FSH, collectively known as the gonadotropins. Pulsatile secretion of GnRH from the hypothalamus is virtually 100% coincident with pulsatile secretion of LH from the anterior pituitary.
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Figure 1 Schematic depiction of the pattern of secretion of follicle stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P4) and estradiol (E2); and the pattern of growth of ovarian follicles during the estrous cycle in cattle. Each wave of follicular growth is preceded by a transient rise in FSH concentrations. Healthy growing follicles are shown as open circles, atretic follicles are shaded. A surge in LH and FSH concentrations occurs at the onset of estrus and induces ovulation. The pattern of secretion of LH pulses during an 8-h window early in the luteal phase (high frequency, low amplitude), the mid-luteal phase (low frequency, low amplitude) and the follicular phase (high frequency, building to the surge) is indicated in the insets in the top panel.
430 Reproduction, Events and Management | Estrous Cycles: Characteristics Hypothalamic nuclei GnRH Anterior pituitary gland Estradiol Negative in luteal phase Positive in follicular phase Inhibin Negative on FSH
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Figure 2 Schematic diagram depicting the endocrine feedback mechanisms of the hypothalamic–pituitary–ovarian– uterine axis regulating the estrous cycle in cows. Luteinizing hormone (LH) and follicle stimulating hormone (FSH) are both secreted from the anterior pituitary gland. LH pulses are tightly associated with pulses of gonadotropin releasing hormone (GnRH) from the hypothalamus. GnRH and hence LH pulse frequency are regulated in a negative feedback mechanism by estradiol and progesterone during the luteal phase, while in the follicular phase there is a positive feedback of estradiol (in the absence of progesterone) from the preovulatory follicle inducing the GnRH, LH and FSH surges. Secretion of FSH requires GnRH pulses, but is regulated by feedback mechanisms of estradiol and inhibins.
Secretion of FSH is also regulated by GnRH and other endocrine and paracrine mechanisms. The gonadotropins when secreted from the anterior pituitary enter general circulation and have their major biological effect at the gonads. In heifers, receptors for LH have been located in the CL, the theca cells of healthy growing follicles and the granulosa cells of large growing follicles (8 mm in diameter). Receptors for FSH are present in the granulosa cells of healthy antral follicles. Follicle stimulating hormone is the main hormone that stimulates follicular growth. Follicle stimulating hormone concentrations are related to follicular growth throughout the estrous cycle in heifers. Associated with each new wave of follicular development, FSH concentrations increase as emergence occurs (Figure 1). This transient rise in FSH concentrations occurs over a period of 1 to 2 days during emergence of each new wave of follicle growth. Thus, in a typical three-wave estrous cycle, recurrent FSH rises occur on days 0.5 to 1.5, 9 to 11, and 13.5 to 15, whereas in a two-wave estrous cycle only the first two recurrent FSH rises occur. During all
physiological states where follicle waves occur (that is, cyclic cattle, postpartum cows during anestrus, and prepubertal heifers), associated transient increases in FSH concentrations coincide with follicle wave emergence. The process of selection of the dominant follicle occurs during a period when FSH returns to nadir concentrations. The physiological mechanisms that allow one follicle to become selected and continue growing while other follicles in the cohort undergo atresia in, the presence of declining FSH concentrations remain to be elucidated. However, early survival factors have been identified and they include development of LH receptors by the granulosa cell layer allowing a switch away from FSH dependency toward LH dependency and an increase in the amounts of bioavailable insulin-like growth factor-I (IGF-I). The increase in bioavailable IGF-I is thought to be mediated through a decrease in insulin-like growth factor binding proteins. Final maturation and either atresia or ovulation of a selected dominant follicle is then dependent on the prevailing LH pulse secretory pattern. The precise pattern of pulsatile LH during each wave of follicle growth has been less clearly described. However, during the early luteal phase low amplitude and high frequency (20–30 pulses 24 h 1) LH pulses occur, in the mid-luteal period LH pulses are high amplitude and low frequency (6–8 pulses 24 h 1) and the preovulatory surge occurs on day 18/19 with high frequency and high amplitude pulses occuring during the surge (Figure 1). The LH pulse frequency is at a minimum during the mid-luteal phase (days 7–13 of the estrous cycle; 2.7 to 3.4 pulses per 12 h window); LH pulse amplitude increases from early (0.5 ng ml 1) to mid-luteal phase (1.04 to 1.3 ng ml 1 on days 8–11); subsequently decreases to 0.7 to 0.8 ng ml 1 on days 12–14; and recovers to about 1.0 ng ml 1 from days 15–19. There also appear to be subtle changes in pulsatile secretion of LH during the different phases of a follicular wave. LH pulse frequency decreases between day 5 (first day of dominance; 7.5 0.4 pulses 12 h 1) and day 8 (end of growth phase of the first dominant follicle; 5.7 0.8 pulses 12 h 1) while LH pulse amplitude increases between day 5 (0.45 0.04 ng ml 1) and day 11 (loss of dominance of the first wave dominant follicle; 1.1 0.2 ng ml 1). Thus, there are good characterizations of the pattern of LH secretion during the estrous cycle. However, the relationship of LH pulse pattern to the stage of the follicle wave has only been characterized for the first wave, so the precise role of LH in controlling follicular dynamics throughout the entire estrous cycle remains somewhat unclear. Nonetheless, it is hypothesized that LH pulse frequency decreases once a follicle is selected to become dominant, with an associated increase in LH pulse amplitude; an increase in LH pulse frequency and a decrease in amplitude occurs when a nonovulatory
Reproduction, Events and Management | Estrous Cycles: Characteristics
dominant follicle undergoes atresia or both frequency and amplitude increase as a dominant follicle proceeds to ovulate during the follicular phase. Further evidence for the role of increased LH pulse frequency at later stages of follicular development is provided by the fact that LH receptors are acquired by granulosa cells of growing ‘selected’ follicles once they reach 8 mm in diameter. This is further supported by the fact that dominant follicles may be maintained for prolonged periods of time following artifical induction of luteal phases using low levels of progesterone (in the absence of endogenous CL) during which an increase in LH pulse frequency occurs. The pattern of secretion of LH at the time when a dominant follicle is selected is responsible for determination of the fate of that dominant follicle. Luteal phase LH pulse frequencies allow dominant follicles to turn over and undergo atresia; whereas, follicular phase LH pulse frequencies are associated with dominant follicles that ovulate. Ovarian steroid secretion is also controlled by LH and FSH. Estradiol is secreted predominantly by the physiologically active dominant follicle. Cyclical changes in estradiol that correspond to the periods of growth of each follicular wave have been reported. Estradiol concentrations in the utero-ovarian vein increase during the follicular phase reaching a peak coincident with the LH surge. This is followed by a second increase in estradiol 3–7 days after the LH surge and a mid-luteal increase in estradiol (days 13–15 of the estrous cycle). These increases in estradiol in the utero-ovarian vein coincide with the first and second dominant follicles that develop during the estrous cycle. Furthermore, estradiol concentrations in plasma collected from the posterior vena cava are pulsatile, throughout the estrous cycle, with each pulse of estradiol following a LH pulse. Androgen secretion occurs in the thecal cells and appears to be controlled by LH in both sheep and cattle. In the granulosa cells, androgens are converted to testosterone which is aromatized to estradiol-17 under the influence of FSH. Serum estradiol concentrations are elevated 1–2 days prior to the LH surge reaching a peak of 9.7 pg ml 1. This increase in estradiol in the follicular phase acts in a positive feedback mechanism (Figures 1 and 2) to induce the LH (and FSH) surge required for ovulation. Once the corpus luteum is formed after ovulation, progesterone secretion from the CL increases and remains elevated throughout the luteal phase of the cycle. Both estradiol and progesterone act in a feedback mechanism to control gonadotropin secretion. Estradiol and high progesterone concentrations during the luteal phase of the cycle act to decrease pulsatile secretion of the gonadotropins. In the presence of low progesterone concentrations during the follicular phase, GnRH and LH pulse frequency increase ultimately reaching a GnRH and LH (and FSH) surge required for ovulation.
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A further hormone family termed inhibins, secreted by the granulosa cells of follicles, is also implicated in the control of gonadotropin secretion. Inhibin has been defined as a hormone which selectively suppresses the synthesis and secretion of FSH. Inhibin is a dimeric glycoprotein consisting of two subunits, termed and , linked by disulfide bridges. Both subunits are secreted as large precursor molecules and can occur in many sizes and combinations. For example, >160, 108, 95, 78, 57, 47, 32 and 29 kDa forms of inhibin have been isolated. However, bioactive inhibin is usually defined as being the 32 kDa form of the – dimer. There is a lot of confusion as to the exact mechanisms by which all the inhibin forms control and affect follicular growth. Evidence exists that inhibins have a local as well as a systemic role in controlling follicular growth.
Corpus Luteum Function The CL forms from the collapsed preovulatory follicle after ovulation. In the cow, the weight and progesterone content of the CL increase rapidly between days 3 and 12 of the estrous cycle and remain relatively constant until day 16. The main function of the CL in cattle is to secrete progesterone. In cattle progesterone and its metabolite -pregnene-20 -ol-3-one are the major progestagens secreted by the CL. Progesterone is secreted both from CL formed during normal estrous cycles and pregnancy. During pregnancy, progesterone plays a similar role in decreasing gonadotropin secretion and prevention of behavioural estrus as occurs during the luteal phase of the estrous cycle. Luteinizing hormone is the major luteotropic hormone in cattle and is responsible for stimulating luteinization of the theca and granulosa cells of the preovulatory follicle into luteal cells. Luteal cells may be classified into small and large cell types both of which secrete progesterone. Small bovine luteal cells appear to secrete progesterone in response to LH stimulation, while large bovine luteal cells produce greater amounts of progesterone under basal conditions and are generally insensitive to exogenous LH stimulation.
Luteolysis of the Corpus Luteum Prostaglandin F2 (PG) is secreted by the uterus in cows. It is the major luteolytic hormone in ruminants. During the late luteal phase of a normal cycle PG is secreted in a pulsatile pattern from the uterus, but during the equivalent period of early pregnancy, pulsatile PG secretion is attenuated. The presence of an embryo prevents luteolysis by suppressing the ability of the uterus to release PG in a pulsatile manner rather than reducing the ability of the
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uterus to synthesize PG. This pulsatile secretion of PG induces luteolysis. Uterine PG reaches the CL through a local mechanism of countercurrent exchange between the uterine vein and the ovarian artery (Figure 3). Oxytocin plays an integral role in induction of PG release required for luteolysis. It stimulates the uterine endometrium to secrete PG in vitro and in vivo. Oxytocin along with estradiol potentiates the release of PG from the uterus; estradiol from the ovulatory dominant follicle appears to stimulate the development or formation of oxytocin receptors in the uterus and enables increased binding of oxytocin, which in turn stimulates PG synthesis from the nonpregnant uterus. Pulsatile PG secretion in ruminants is associated with pulsatile oxytocin secretion. Pulses of oxytocin occur concurrently with PG during luteolysis and most of this oxytocin appears to be luteal in origin. Uterine PG and luteal oxytocin comprise a positive feedback loop, and PG can stimulate luteal oxytocin secretion. The trigger for luteolytic pulses of PG to be secreted from the uterus has not been identified but oxytocin from the posterior pituitary has been suggested by some authors to be involved. In species such as cattle that require PG for luteolysis, oxytocin can only stimulate the uterus to secrete pulsatile PG during the late luteal phase. Thus, one or more components of pulsatile PG release must be absent in the uterine endometrium during the nonresponsive stage of the estrous cycle. Endometrial oxytocin receptors only increase approaching the time of luteolysis and their absence is thus a likely candidate for limiting the responsive period for PG secretion. The control mechanisms of induction of oxytocin receptors in the uterine
Uterine horn PG released into uterine vein
Corpus luteum Oviduct Ovary
Uterine vein
Ovarian pedicle
endometrium and the secretion of PG appear to involve the steroid hormones progesterone and estradiol. In ovariectomized ewes or cows, oxytocin will only stimulate PG secretion after the animal has been exposed for 7–10 days to luteal phase progesterone concentrations. Some of the processes that are required to supply precursors for PG secretion appear to be progesterone-dependent, such as accumulation of lipid droplets and triglycerides in the uterine endometrium. Estradiol administration during the mid-luteal phase of the cycle will induce premature CL regression. In sheep, acute treatment with estradiol on days 9 and 10 of the cycle induces an increase in endometrial oxytocin receptors within 12–24 h and premature luteal regression. Thus, progesterone and estradiol both appear to be necessary in the development of uterine oxytocin receptors. Estradiol appears to have the additional role of enhancing secretion of oxytocin from the posterior pituitary and infusion of low doses of estradiol to ovariectomized ewes results in pulsatile secretion of oxytocin from the posterior pituitary. Thus, the mechanism of luteolysis appears to be initially triggered by increased estradiol from the dominant follicle that increases oxytocin pulse frequency from the posterior pituitary, which in turn will stimulate PG secretion from the uterus during the late luteal phase, i.e. when oxytocin receptors are present on the endometrium. The initial secretion of PG stimulates luteal oxytocin secretion which in turn stimulates further PG secretion from the uterus and causes the uterus to become temporarily refractory to oxytocin for 6–8 h, thus establishing a pulsatile pattern of uterine PG secretion at 6–8 h intervals. In cattle and sheep, the presence of an embryo appears to inhibit the formation of oxytocin receptors in the endometrium, thereby preventing pulsatile release of PG required for luteolysis. The presence of certain proteins from the developing embryo in the uterus, e.g. trophoblast protein-1 (interferon-), prolongs the estrous cycle, presumably because they inhibit pulsatile release of PG by some mechanism. Interferon- is now recognized as the key mediator of maternal recognition of pregnancy in cattle.
PGF
Ovarian artery
PGF into ovarian artery by countercurrent exchange
Figure 3 Schematic diagram illustrating the role of prostaglandin F2 (PG) in controlling luteolysis. Prostaglandin released from the uterine endometrium into the uterine vein is picked up by the ovarian artery through countercurrent exchange and is delivered back to the CL as a local mechanism where it causes luteolysis. (Adapted and reprinted from CD-ROM Learning Reproduction in Farm Animals, with permission of Rodney D. Geisert, Oklahoma State University.)
Conclusions It is concluded that the estrous cycle in cattle is typically 18–24 days in duration, with estrous behavior being expressed for an 8- to 24-h period during the late follicular phase. During the normal estrous cycle there are typically two to three and occasionally four waves of follicular growth each involving a period of emergence and selection followed by either atresia or ovulation of the dominant follicle. The gonadotropin hormones FSH and LH are the main regulators of folliculogenesis and
Reproduction, Events and Management | Estrous Cycles: Characteristics
steroidogenesis with LH being the major luteotropic hormone. LH pulse frequency is the major determinant affecting the ultimate fate of a selected dominant follicle. Pulsatile prostaglandin F2 of uterine origin is the main hormonal signal that induces luteolysis of the corpus luteum and the switch from the luteal to the follicular phase.
See also: Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity; Estrous Cycles: Puberty; Mating Management: Detection of Estrus.
Further Reading Adams GP, Matteri RL, Kastelic JP, et al. (1992) Association between surges of follicle-stimulating hormone and the emergence of follicular waves in heifers. Journal of Reproduction and Fertility 94: 177–188. Bao B, Garverick HA, Smith GW, et al. (1997) Changes in messenger ribonucleic acid encoding luteinizing hormone receptor, cytochrome P450-side chain cleavage, and aromatase are associated with recruitment and selection of bovine ovarian follicles. Biology of Reproduction 56: 1158–1168.
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Campbell BK, Scaramuzzi RJ, and Webb R (1995) Control of antral follicle development and selection in sheep and cattle. Journal of Reproduction and Fertility 49 (supplement): 335–350. Cooke DJ, Crowe MA, Roche JF, et al. (1996) Review: Gonadotrophin heterogeneity and its role in farm animal reproduction. Animal Reproduction Science 41: 77–99. Cooke DJ, Crowe MA, and Roche JF (1997) Circulating FSH isoform patterns during recurrent increases in FSH throughout the oestrus cycle of heifers. Journal of Reproduction and Fertility 110: 339–345. Crowe MA (1999) Gonadotrophic control of terminal follicular growth in cattle. Reproduction in Domestic Animals 34: 157–166. Crowe MA, Kelly P, Driancourt MA, et al. (2001) Effects of folliclestimulating hormone with and without luteinizing hormone on serum hormone concentrations, follicle growth and intra-follicular estradiol and aromatase activity in gonadotrophin releasing hormoneimmunized heifers. Biology of Reproduction 64: 368–374. Ireland JJ and Roche JF (1987) Hypothesis regarding development of dominant follicles during a bovine estrous cycle. In: Roche JF and O’Callaghan D (eds.) Follicular Growth and Ovulation Rate in Farm Animals, pp. 1–18. The Hague: Martinus Nijhoff. McCracken JA, Custer EE, and Lamsa JC (1999) Luteolysis: a neuroendocrine-mediated event. Physiological Reviews 79: 263–324. Roche JF (1996) Control and regulation of folliculogenesis: a symposium in perspective. Reviews of Reproduction 1: 19–27. Savio JD, Keenan L, Boland MP, et al. (1988) Pattern of growth of dominant follicles during the oestrus cycle of heifers. Journal of Reproduction and Fertility 83: 663–671. Sunderland SJ, Crowe MA, Boland MP, et al. (1994) Selection, dominance and atresia of follicles during the oestrus cycle of heifers. Journal of Reproduction and Fertility 101: 547–555.
Estrous Cycles: Postpartum Cyclicity H A Garverick and M C Lucy, University of Missouri, Columbia, MO, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction In dairy cows, the interval from calving to resumption of ovulatory ovarian cycles has increased and fertility has decreased over the past half century as average milk production per cow has increased more than threefold. Understanding the physiological processes that regulate ovarian follicular development and ovulation is a necessary prerequisite for shortening the interval to first ovulation, increasing fertility, and optimizing reproductive management in modern dairy operations. During pregnancy, cows have a corpus luteum (CL) and do not ovulate additional follicles. Nevertheless, follicular growth in waves continues throughout pregnancy. Wave activity decreases as pregnancy progresses and dominant follicles are less prominent. Coincident with the reduction in follicular wave activity during pregnancy is a reduction in the pulsatile release of circulating luteinizing hormone (LH) in blood. Following parturition, ovarian follicular growth and ovulatory follicular cycles must be reinitiated if the subsequent pregnancy is to be established within a reasonable amount of time. The mechanisms associated with the resumption of ovulatory waves postpartum are complex and there is a large variation in the interval from parturition to first ovulation in lactating dairy cows. This article will review the timing of postpartum ovarian cyclicity in dairy cows and the mechanisms associated with normal and abnormal ovarian cycles during the postpartum period. The cellular and molecular mechanisms regulating ovarian follicular development and ovulation as influenced by body condition and energy balance will be discussed.
Ovarian Follicular Dynamics during Estrous Cycles in Cattle The characteristics of estrous cycles in cattle have been reviewed (see Reproduction, Events and Management: Estrous Cycles: Characteristics). However, a brief summary here is pertinent to the discussion of postpartum ovarian activity. The dynamic nature of ovarian follicular growth in cattle was unknown for a considerable period of time. A typical estrous cycle in cattle has two or three waves of follicular growth. The initiation of each follicular wave (recruitment) is characterized by the growth of a cohort (usually 2–6) of small follicles
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from approximately 2–4 to 5 mm in diameter. The initiation of each wave of follicular growth is preceded by a transient increase in circulating follicle-stimulating hormone (FSH). The recruited follicles continue their growth to approximately 7–8 mm in diameter. At this time, one follicle is typically selected (selection) to continue to grow to ovulatory size (14–18 mm in diameter; dominant follicle). The remaining subordinate follicles undergo atresia. If the cow is in the luteal phase of the estrous cycle, the dominant follicle maintains its maximum size for 3–6 days, but undergoes atresia and another wave of follicular growth is initiated. The dominant follicle in the second or third wave will ovulate if luteal regression occurs during the growing phase.
Postpartum Follicular Growth Gonadotropins At parturition, concentrations of LH, but not FSH, are low. In particular, mRNA expression of the subunit of LH is low, and there is little LH in the pituitary or in blood circulation. With increasing time following parturition, synthesis and release of the gonadotropins increase. There is little release of LH following gonadotropinreleasing hormone (GnRH) injection for the first week postpartum, but the mean concentration of LH and the pulsatile release of LH increase thereafter, and a GnRHinduced release of LH capable of inducing ovulation is possible within 2 weeks postpartum. Similar to initiation of follicular waves during normal estrous cycles, a transient increase in FSH precedes initiation of waves of follicular growth postpartum. The first wave of follicular growth is usually initiated within 5–10 days postpartum. Growth of follicles to approximately 9 mm in diameter follows the stimulation of the transient increase of FSH. Growth beyond this size is dependent upon additional stimulation with LH in addition to the FSH. When adequate concentrations of LH are present, follicles continue their growth to ovulatory size. Follicular Growth Waves of follicular growth following calving are similar to those seen in normal estrous cycles and are usually initiated within 10–14 days. With each wave of follicular growth, a cohort of follicles is recruited to grow above
Reproduction, Events and Management | Estrous Cycles: Postpartum Cyclicity
5 mm in diameter and the follicles continue their growth to about 7–8 mm in diameter, whereupon one follicle is selected for further growth. The selected follicle of the first follicular wave follows one of three fates: (1) it continues its growth to ovulatory size and ovulates (cyclic cows); (2) it grows to various sizes but not ovulatory size, stops growth, and undergoes atresia, following which a new wave of follicular growth is initiated (anovulatory anestrous cows); or (3) it surpasses ovulatory size and develops into an ovarian follicular cyst (cystic cows).
Estradiol
Estradiol
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LH Surge
CL
Estradiol
IGF-I LH
Postpartum Ovulatory Follicles Postpartum follicles that ovulate probably do so through the stimulatory effects of normal levels and secretory patterns of FSH and LH. Dairy cows that ovulate the first wave dominant follicle postpartum are generally in good body condition and are not experiencing extreme negative energy balance. Cows in poor body condition, in extreme negative energy balance, or with metabolic or infectious diseases at calving often have delayed initiation of follicular waves, multiple follicular waves before first ovulation, and extended intervals to first postpartum ovulation.
Postpartum Anovulatory Follicles In some cows, the first follicular wave postpartum does not end in ovulation, but instead ends in atresia. In cows that do not ovulate the first wave dominant follicle that occurs following parturition, initiation of follicular growth may occur at the same or at a later time than those that ovulate the first wave dominant follicle. Recurrent follicular waves usually occur in postpartum cows that do not ovulate the dominant follicle (Figure 1). While the processes of recruitment, selection, dominance, and atresia of follicles in anovulatory waves are generally similar to those observed in ovulatory waves, some differences have been noted. Anovulatory follicular waves are usually longer than ovulatory waves, and the maximum size of the selected follicle is usually smaller. The growth rate from recruitment (5 mm in diameter) to selection (7–8 mm in diameter) and to maximum size of the anovulatory dominant follicle is usually similar to that of the ovulatory follicle. Instead of reaching ovulatory size (16 mm in diameter), however, the anovulatory follicle usually stops growing when it is 10–14 mm in diameter. The smaller-sized follicles produce less estradiol than the larger ovulatory follicles, and the amount of estradiol produced is likely less than the threshold amount needed to induce the preovulatory LH surge. The reason that anovulatory follicles stop growing at the smaller size and have decreased synthesis and release of estradiol may be because of decreased LH secretion or decreased
Figure 1 Development of ovulatory follicles in postpartum cows. Ovarian follicles grow in waves during the postpartum period. Successive waves produce larger dominant follicles that secrete greater amounts of estradiol. The luteinizing hormone (LH) surge is induced and the corpus luteum (CL) is formed when estradiol concentrations reach a threshold level. Blood concentrations of insulin-like growth factor I (IGF-I) (dashed line) and LH (pulses) increase during the postpartum period from basal levels (first few days postpartum) to greater levels (3–4 weeks postpartum). The postpartum increase in LH and IGF-I depends on the nutrition and body condition of the cow. The LH and IGF-I synergistically promote follicular growth and development.
responsiveness of follicles to LH support. These mechanisms will be discussed in the following sections. In some dairy cows, the initiation of follicular waves is delayed for extended periods of time after parturition. Cows that do not initiate follicular waves postpartum are usually in extremely poor body condition at calving or have severe metabolic or infectious diseases that cause excessive loss of body condition and poor health. In general, any deleterious postpartum health problem increases the interval to initiation of follicular waves and ovulation, and decreases fertility (Table 1) .
Mechanisms Associated with Ovulatory and Nonovulatory Postpartum Follicles Initiation of postpartum ovarian cyclicity is related to body condition at calving and to negative energy balance following calving, which affects the change in body condition during the postpartum period. Cows should be in good Table 1 Influence of health status on reproductive performance of dairy cows
Days to first estrus Days to first insemination Days to pregnancy Cumulative pregnancy rate (%)
Healthy cows (n ¼ 38)
Cows with major health problems (n ¼ 26)
37.7 58.7
51.2 68.4
71.9 88.9
84.1 63.2
Adapted from Barton, et al. (1996) Journal of Dairy Science 79: 2225–2236.
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body condition at calving (body condition score (BCS) should be 3–3.5 on a 5-point scale, where 5 is obese and 1 is very thin). High-producing dairy cows are usually in a negative energy balance following parturition because there is a dramatic change in energy requirements to meet the energy demands of lactation. There is an immediate shift in metabolism from nutrient partitioning toward body reserves and fetal mass to one of nutrient mobilization of energy and protein stores to meet the demands of lactation. Energy and feed intake are not maximized in lactating dairy cows for a few weeks following parturition. It is during this time that negative energy balance reaches its maximum, and the resumption of postpartum cyclicity is dependent upon the severity of the negative energy balance and body condition of the cow. The effects of various nutritional and environmental factors on postpartum cyclicity are described below. Body Condition Attaining the optimum BCS of 3.0–3.5 during the dry period is important for reestablishment of ovarian cyclicity during the postpartum period. Cows that are overly fat (BCS near 5) have a decreased appetite following parturition compared with more ideally conditioned cows (BCS 3.0–3.5) and, thus, are in a greater negative energy balance and have a much larger change (decrease) in BCS. Cows that have increasingly larger negative changes in BCS during the postpartum period take a longer time to achieve first ovulation postpartum, and fertility is decreased. In addition, some cows calve with less than optimum body condition. Cows calving with BCSs of 1.5 or less have a longer interval to first ovulation than those that calve in better condition. Cows in very poor body condition do not have energy stores available to mobilize for maintenance and lactation requirements. It has long been known that the body diverts energy from reproductive processes when conditions do not meet the needs for maternal survival. Cows that experience the greatest change in body condition after parturition take longer to achieve ovulation than those that have less change in body condition, and conception rates of cows with a greater BCS loss are lower than those of cows with less BCS loss postpartum. Similarly, cows in a lesser negative energy balance or in a positive energy balance have greater conception rates than those with a more negative energy balance. Energy Balance As stated previously, high-producing dairy cows are in a negative energy balance following parturition. The negative energy balance increases for a period of time as milk production increases faster than feed intake. When the amount of negative energy balance decreases, events
leading up to the first ovulation begin. Ovulation of a dominant follicle postpartum is dependent upon stimulation through increasing mean concentration and pulsatile release of LH (Figure 1). Pulsatile release of LH is greater in cows that ovulate a dominant follicle in the postpartum period than in those that have recurrent follicular waves, and the size of the ovulatory dominant follicle is usually larger than the nonovulatory dominant follicles. In most cases, follicles that fail to ovulate do not reach full ovulatory size. Low energy availability decreases LH pulsatility and, thus, follicular stimulation and estradiol synthesis are less. Also the responsiveness of follicles to LH may be decreased because of lower concentrations of circulating insulin-like growth factor I (IGF-I) (Figure 2). The concentrations of circulating IGF-I are directly correlated with energy status. Cows in a greater negative energy balance have lower concentrations of circulating IGF-I. The IGF-I concentrations are greater in cows that are ovulating.
GH LH
Liver –
+
+
Ovary F
F
F Ovarian IGF-I
Blood IGF-I Energy balance Nutrition Disease Aging
Figure 2 Control of follicular growth by luteinizing hormone (LH) and insulin-like growth factor I (IGF-I) secretion in postpartum cows. At parturition, pulses of LH and concentrations of IGF-I in blood are low. Blood growth hormone (GH) concentrations are elevated and GH drives nutrient partitioning for milk synthesis. Most of the IGF-I in blood is derived from the liver and is released in response to GH. In early postpartum cows, the GH–IGF-I axis is uncoupled so that high concentrations of GH do not lead to elevated blood IGF-I. Negative energy balance, undernutrition, disease, and aging increase the amount of uncoupling and reduce IGF-I synthesized and secreted from the liver. The GH–IGF-I axis is recoupled postpartum so that the synthesis and secretion of IGF-I into the blood are increased. Pulses of LH increase postpartum and stimulate follicular growth. The greatest LH pulsatility is found in cows with better body condition and less negative energy balance. The effects of LH on the ovary are synergistic with IGF-I in blood. Greater IGF-I and more LH pulsatility postpartum act in a synergistic manner to increase the growth and development of ovarian follicles. Factors such as negative energy balance may decrease IGF-I by preventing the recoupling of the GH–IGF-I axis. Negative energy balance may also inhibit LH pulses. Collectively, low IGF-I and low LH pulsatility may not provide adequate stimulation for the development of a preovulatory follicle.
Reproduction, Events and Management | Estrous Cycles: Postpartum Cyclicity
Abnormalities of the Puerperium Cows must be healthy for efficient postpartum reproduction. Diseased cows are less fertile and the effects of disease on reproductive performance are greater than any other factor. Both metabolic and reproductive diseases and disorders can negatively affect reproduction. Cows with metabolic and reproductive diseases are usually in poorer general health, lose a greater amount of body condition, and experience delayed postpartum ovarian cyclicity. Thus, cows with abnormal puerperium require additional time to establish ovarian follicular waves and develop ovulatory follicles. In addition, fertility is lower in affected cows than in cows with no abnormalities during the periparturient period. Metabolic disturbances and diseases include dystocia, retained placenta, metritis, pyometra, milk fever, ketosis, acidosis, mastitis, laminitis, brucellosis, and tuberculosis. Several studies have demonstrated the relationship between health and reproduction. For example, healthy cows in one study had a shorter interval to first estrus, shorter days to first insemination, shorter days to pregnancy, and fewer services per conception than cows that needed veterinary assistance for postpartum health problems (Table 2). Mastitis also has a major effect on reproduction in postpartum dairy cows. Cows that develop clinical mastitis have delayed intervals to first insemination, greater services per conception, and greater days open. A regular herd health program for veterinary care can prevent many deleterious effects of postpartum disease on reproduction.
Ovarian Follicular Cysts (Cysts) The third fate of follicles during the postpartum period is the development of cysts. Cysts have been classified as anovulatory ovarian follicular structures of at least 2.5 cm in diameter that persist in the absence of a CL for a period of at least 10 days. This definition may no longer be accurate due to the dynamics of follicular growth and the dynamics outlined in previous sections. Nonetheless, the cystic condition is a serious cause of reproductive inefficiency in dairy cattle because cows are infertile as
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long as the condition persists. It is estimated that 10% of dairy cows develop cysts annually.
Characteristics of Cysts Follicular dynamics in cows with cysts has similarities to follicular dynamics in normal cows. Development of cysts begins when a cohort of follicles less than 4 mm is recruited to grow beyond 5 mm in diameter. At approximately 7–8 mm in diameter, one follicle (sometimes more than one) is selected for continued growth to become dominant over the other follicles as occurs in normal ovulatory follicles. The growth phase to ovulatory size is similar to ovulatory follicles. However, instead of ovulating, the follicle destined to become a cyst continues to grow for several more days and becomes enlarged and is anovulatory. In some cases, more than one follicle continue growth and codominant or multidominant cysts are formed. The size of the cysts may be slightly less than in the classical definition when more than one cystic structure develops. Earlier research suggested that cysts persisted for considerable periods of time if left untreated. More recently, studies using ultrasonography or charcoal marking have shown that cysts do not always persist as previously thought. Three fates of cysts have been shown to occur: 1. Persistence, as originally thought. The percentage of cysts that are persistent is approximately 15–20%. Some cysts persist for longer than 60 days, remain dominant, and inhibit follicular growth during this time. 2. Cyst turnover, whereby the original cyst loses dominance, and a new wave of follicular growth is initiated. One (or more) follicle is selected to become dominant from the cohort of new follicles that are recruited, and develops into a new cyst. Cysts that have lost dominance have morphological and endocrine characteristics of atretic follicles. This condition may continue for repeated waves of cyst development, and the anovulatory condition, but not a single cyst, persists. The period of the waves of cyst growth may be similar in length to normal follicular waves, but is, on
Table 2 Effects of problems occurring during lactation on reproductive traits
Item
Average days to postpartum breeding
Average calving interval (days)
Average services/ conception
No problem Metritis Cystic ovaries Retained placenta Anestrus Aborted
86 99 107 92 141 80
395 433 447 419 480 402
1.8 2.3 2.1 2.0 2.2 2.4
Data are from 2352 observations in dairy herds (HA Garverick, unpublished data).
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the average, twice as long. Cyst turnover is prevalent in most cases (60–65%) of cows with cysts. 3. Turnover with initiation of a new wave of follicular growth whereby the cow self-corrects and ovulates a new dominant follicle. Approximately 20% of cows with cysts self-correct the condition.
Etiology of Cysts A number of factors including endocrine imbalances, heredity, milk production, and seasonality have been associated with the development of cysts. Endocrine imbalances include various abnormalities of the hypothalamic–hypophyseal–ovarian axis. There is an increase in mean circulating and pulse amplitude secretion of LH during cyst development, and pulse frequency is similar to that observed in a normal follicular phase (Figure 3). Both mean concentration and pulse amplitude of LH are nearly twice as high in cows with cysts compared with cows that ovulate. However, there is an absence of the preovulatory LH surge in cows with cysts. Cysts may produce more estradiol than ovulatory follicles, but the LH response to estradiol is absent in cows with cysts. There is no difference in pituitary concentrations of FSH and LH in cows with cysts and cows that ovulate. The concentration of GnRH in the hypothalamus is lower in cows with cysts, but the GnRH content of the median eminence is greater in cows with cysts. Thus, the GnRH content of the median eminence is likely released and caused increased secretion of basal LH.
Cystic follicle >25 mm
16 mm Ovulatory size
High LH pulse frequency no LH surge LH
Figure 3 Formation of ovarian follicular cysts in cows. Cysts form when postpartum luteinizing hormone (LH) secretion is highly pulsatile. A large follicle develops on the ovary and secretes estradiol. Estradiol secretion, however, fails to trigger an LH surge and the cow becomes cystic because the follicle does not ovulate.
Heredity has also been associated with cyst development. However, the estimation of heritability has been difficult because of confounding factors such as nutrition, body condition, and milk production. Increased milk production has also been associated with cyst development. However, it is unclear whether increased milk production produced cysts or whether cows produced more milk because they were cystic and were not pregnant for a longer period of time. Season of the year has also been associated with the development of cysts. However, there are reports that did not find a relationship between cysts and the level of milk production or seasonality. Numerous miscellaneous factors have been linked to cyst development. These include estrogen content of forages, which is consistent with the altered response of the cows with cysts to estradiol as previously mentioned. Abnormal reproductive and metabolic events during the postpartum period have also been linked to development of cysts, suggesting that the increased stress associated with these events contributes to cyst development. Diagnosis and Treatment of Cysts Classical diagnosis of cysts was based on behavioral symptoms of intense sexual desire or nymphomania. Cows exhibiting such behavior exhibited estrus for extended periods of time, sometimes with repeated periods between times of no estrual activity. However, it is now clear that most cows with cysts do not exhibit estrous activity (anestrous). Diagnosis of cysts is usually based upon finding a follicular structure of 2.5 cm in diameter or larger following a single examination via manual palpation per rectum or ovarian ultrasonography. While diagnosis based upon the single examination is efficacious for producers, the diagnosis may not be accurate for several reasons. First, size alone is not an absolute criterion because size is influenced by stage of development, which is difficult to know with one examination. Second, there are often large follicles on the ovaries of cows during a normal estrous cycle as previously described. Thus, the dynamic nature of follicular and cyst growth complicates diagnosis. Third, some CLs developing during the first 5–7 days following estrus exhibit characteristics similar to cysts when diagnosis is by manual palpation. Luteal structures during this period are often soft and contain fluid-filled structures that rupture during manual palpation. Diagnosis with ultrasonography greatly reduces this type of diagnostic error. Cysts are typically treated with GnRH to induce an endogenous LH release, or treated with human chorionic gonadotropin (hCG) that has LH-like activity. In both cases, successful treatment is based upon luteinization of the cystic structure and subsequent production of progesterone in response to the GnRH-induced LH release or the exogenous hCG. Success rates are about 80% with
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these treatments. Response of the cystic structure is dependent upon its state at treatment. Responding cysts are those that are ‘healthy’ in that theca and granulosa cells appear morphologically intact and are producing estradiol. More recently, progesterone implants have been used successfully to treat cysts. Treatment with progesterone must raise blood levels of progesterone to high enough levels to mimic luteal phase concentrations. Success of the aforementioned treatments is dependent upon increased concentrations of circulating progesterone that restore the sensitivity of the hypothalamic– pituitary axis to estradiol. With these treatments, concentrations of LH are inhibited, the cyst(s) undergo atresia, and a new follicular wave follows that results in selection of an ovulatory dominant follicle that secretes estradiol. The sensitivity of the hypothalamic–pituitary axis to estradiol is restored and an LH surge and ovulation of the dominant follicle occur.
Conclusion Initiation of ovulatory ovarian cycles following parturition is a prerequisite for the establishment of pregnancy within an opportune time interval. Following parturition, waves of ovarian follicular growth are usually established within 10–14 days. There are three fates of the first wave dominant follicles. The selected follicle may (1) continue its growth to normal ovulatory size and ovulate, (2) grow to less than ovulatory size, fail to ovulate, and undergo atresia, or (3) surpass ovulatory size and develop into an ovarian follicular cyst. Body condition at calving, negative
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energy balance, and disease determine the fate of ovarian follicles postpartum (ovulation, anovulation, or cystic) by affecting the endocrinology of the postpartum cow (LH, FSH, and IGF-I secretion). See also: Reproduction, Events and Management: Estrous Cycles: Characteristics.
Further Reading Barton BA, Rosario HA, Anderson GW, Grindle BP, and Carroll DJ (1996) Effects of dietary crude protein, breed, parity and health status on the fertility of dairy cows. Journal of Dairy Science 79: 2225–2236. Chagas LM, Bass JJ, Blanche D, et al. (2007) Invited review: New perspectives on the roles of nutrition and metabolic priorities in the subfertility of high-producing dairy cows. Journal of Dairy Science 90: 4022–4032. Garverick HA (1997) Ovarian follicular cysts in dairy cows. Journal of Dairy Science 80: 995–1004. Garverick HA (2007) Ovarian follicular cysts. Current Therapy in Large Animal Theriogenology 2: 379–383. Lucy MC (2003) Mechanisms linking nutrition and reproduction in postpartum cows. Reproduction Supplement 61: 415–427. Lucy MC (2007a) Fertility in high-producing dairy cows: Reasons for decline and corrective strategies for sustainable improvement. Society of Reproduction and Fertility Supplement 64: 237–254. Lucy MC (2007b) The bovine dominant ovarian follicle. Journal of Animal Science 85: E89–E99. Stevenson S (2007) Clinical reproductive physiology of the cow. Current Therapy in Large Animal Theriogenology 2: 258–270. Webb R and Campbell BK (2007) Development of the dominant follicle: Mechanisms of selection and maintenance of oocyte quality. Society of Reproduction and Fertility Supplement 64: 141–163. Wiltbank MC, Gu¨men A, and Sartori R (2002) Physiological classification of anovulatory conditions in cattle. Theriogenology 57: 21–22.
Estrous Cycles: Seasonal Breeders S T Willard, Mississippi State University, Mississippi State, MS, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The effects of seasonal influences on reproduction are directly linked to milk yield, as the production of offspring is required for initiation of lactation, and is important in relation to targeting milk markets. For example, in India and Pakistan, water buffaloes calve primarily between July and December, which can result in excess milk production in the winter months and milk shortages during the summer months. Similarly, dairy sheep producers are particularly cognisant of the effects of seasonality on lambing intervals of ewes and on an ewe’s lifetime lactation yield in light of the strict seasonal nature of some sheep breeds used in intensive dairy sheep operations. While an understanding of seasonality is critical from a production standpoint, from an evolutionary perspective seasonal breeding has evolved as an adaptation to ensure a favorable reproductive rate and the survival of offspring in regions with great variations in climatic, nutritional, and/or other adverse environmental conditions. The reasoning behind the evolution of these strategies in the context of agriculturally important livestock species will be explored herein, in addition to the physiological basis for seasonality and how it might be controlled in a production setting. For comparative purposes, the seasonal nature of several multipurpose livestock species will be indicated, with emphasis on those used worldwide for the production of milk and milk by-products.
Strategies and Theories for the Seasonal Regulation of Reproduction Some species do not exhibit seasonal cycles in reproductive activity (nonseasonal breeders), while others may display ‘clusters’ of reproductive cycles that occur only during a certain season of the year (seasonal breeders). Of the seasonal breeding species, some exhibit reproductive cycles during the short day lengths (autumn; e.g., sheep and goats), while others exhibit reproductive cycles only during the long day lengths (spring; e.g., mare). Patterns of seasonal breeding range from species that have one period of estrus (receptivity and mating) each year (monoestrus), to species that exhibit a series of estrous cycles limited to a portion of the year (seasonally polyestrus). True seasonal breeding patterns are inherent in some species
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(e.g., ewe, doe, and mare), while other species may show seasonal patterns due to environmental or other overriding influences. Of these, climatic, nutritional, and behavioral effects on seasonal cycles will be described below. However, one should be cognisant of the fact that seasonality is a coordinated effort in which multiple exogenous (environmental) and endogenous (hormonal) rhythms may be involved in the integration of seasonal reproductive cycles.
Climatic Climatic events that regulate seasonal reproductive processes encompass primarily the effects of photoperiod and temperature, with climatic variables including drought and precipitation influencing reproduction as related to nutrient availability (nutritional considerations will be described in greater detail below). Of these, photoperiod is seen as a primary mechanism driving the endogenous circannual rhythm that synchronizes mating and birthing seasons. The effects of photoperiodism (photic cues) are translated into reproductive effects via hormonal mediators (e.g., melatonin), which augment or suppress endocrine and neuroendocrine pathways critical to reproductive processes (see ‘Endocrine and Neuroendocrine Regulation of Reproduction in Seasonal Breeders’). The influence of photoperiod on the reproductive system was first observed in relation to the timing of puberty for lambs born at different times of the year. Specifically, spring-born lambs attain puberty in about 30 weeks of age, which they reach during the breeding season, while fall-born lambs reach the pubertal age of 30 weeks during the nonbreeding season, and thus do not exhibit reproductive cycles until the following breeding season at nearly 1 year of age. Such dramatic effects illustrate the prevailing and central role that photoperiod plays in the reproductive lives of strict seasonal breeders. In conjunction with or independently from photoperiod, which changes incrementally during the year, alterations in ambient temperatures (high and low) can contribute to shifts in seasonal breeding activities as well. For dairy cattle bred by natural or artificial means in the southern United States and elsewhere, it has been observed that fertility is lowest in late summer when ambient temperature and humidity are high, and is often followed by a slow recovery time thereafter producing a lag effect into the fall. To this end, heat stress in cattle has
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been the primary focus of research, which has illustrated how severe thermal stress can suppress reproductive processes, negatively impacting livestock production operations – particularly in dairy cattle. Summer heat stress has been shown to lower semen quality in bulls, alter hormonal secretory patterns, suppress estrous behavior, reduce conception rates, and negatively affect embryo quality and survival. Moreover, heat stress during late gestation can adversely affect fetal growth in cattle and sheep, with summer-born calves and lambs being generally smaller than winter-born calves and lambs, and an increased incidence of stillbirths has been observed in swine. Low temperatures (i.e., cold stress) at the time of birth also have implications relative to offspring survival (e.g., Bos indicus calves are more susceptible to cold stress than Bos taurus calves), yet in relation to mating success the effects of cold stress are less well characterized in livestock than the effects of heat stress. This is due to the confounding effects of food intake, which increases during colder periods to facilitate metabolic heat production (i.e., maintenance of thermoneutrality) as part of an adaptive response to low environmental temperatures. Nevertheless, appropriate adaptation periods to low environmental temperatures are required to alleviate both endocrine and exocrine effects on reproductive processes in some breeds. For example, in Brahman bulls translocated to the northern United States, reduced concentrations of testosterone and decreased semen quality have been observed during the winter months (0 to 10 C). When considering both heat and cold stress together, it seems reasonable that seasonal breeding strategies would have evolved, in part, to coordinate breeding periods for an increased probability of mating success and postparturient neonatal survival in relation to annual changes in environmental temperatures. Nutritional Late pregnancy, birth, and lactation require energy and nutrient demands above and beyond what is required for normal body maintenance. This means that conception must occur months earlier in relation to other environmental cues (e.g., photoperiod) to achieve a birthing season that will coincide with the season of greatest abundance in nutrient quantity and quality. When energy and protein, for example, become limiting, a number of reproductive processes may be affected, resulting in delayed puberty, suppressed estrus and ovulation, reduced conception rates, an increased incidence of fetal resorption, and premature or weak offspring. As evident from these examples, the seasonal suppression of puberty or estrous cycles due to nutritional deficiencies could delay transitions into seasonal breeding periods, while deficiencies
later in the year may influence survival of the fetus late in pregnancy or the neonate postpartum. Conversely, an abundance of nutrients may permit animals to exhibit reproductive cycles earlier in the season, and adequate nutritional reserves during pregnancy and lactation would directly benefit offspring survival postpartum. Food in this regard has been described as having a ‘proximate’ and ‘ultimate’ action in relation to seasonal breeding. Specifically, the quantity of nutrients available can have an immediate beneficial or detrimental effect on an animal’s reproduction (a proximate action), and the fact that the presence of nutrient resources can vary seasonally in an animal’s environment is an important factor in the evolution of that animal’s reproductive strategy (an ultimate action). The tendency toward seasonal breeding begins to manifest primarily in regions where nutrient availability varies somewhat, with increases in the severity of this variation leading to stricter and stricter breeding and birthing seasons out of an apparent necessity for nutrient resources. This is, of course, superimposed on other climatic events (photoperiod, temperature, precipitation, etc.) that can influence growing seasons and plant vigor. Social/Behavioral Reproductive processes can be dramatically affected by social cues relayed from one individual to another of the same or opposite sex. This can occur via pheromones, which are chemical substances liberated from one animal (through urine or other secretions) and received by another (olfactory cues), or through visual or tactile cues associated with complex mating rituals. These behavioral or chemical cues have a priming effect that can alter hormonal secretions (primarily luteinizing hormone (LH) and prolactin from the pituitary) and advance the breeding season. In sheep, this is often referred to as the ‘ram effect’, as ram exposure can increase LH pulsatility in the ewe and elicit signs of estrus in the female that would not normally be present in the absence of a ram. Furthermore, introduction of a ram into an ewe flock during the transition from anestrus to estrus can in turn result in a high degree of synchrony in first mating. A similar reaction is achieved in wapiti (North American elk) and red deer, in which vocalizations from the stag during the early rut can hasten seasonal reproductive cyclicity in females. While in today’s livestock management systems such cues have become less vital from a mating strategy standpoint, for animals in the wild with varying social structures (e.g., dominance hierarchies, single-sex groups) and a need to locate receptive mates, such behavioral cues are critical to mating success and genetic survival. While social interactions are not a singular cause for initiating or terminating seasonal reproductive events in most species, they can greatly augment the degree to
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which an animal responds to other environmental cues regulating seasonal processes.
Endocrine and Neuroendocrine Regulation of Reproduction in Seasonal Breeders Seasonal breeders are often referred to as undergoing an annual puberty, in that reproductive cycles must begin anew following a period of anestrus (i.e., no estrus or the absence of heat cycles). The principal mechanism responsible for transitions into and out of periods of sexual activity in strict seasonal breeders is mediated by the retinal-hypothalamo-pituitary pathway (Figure 1). Specifically, photic cues detected by the sensory neurons in the retina of the eye are transmitted via the
suprachiasmatic nucleus of the hypothalamus to excitatory cervical ganglia that can alter the release of the hormone melatonin from the pineal gland and, in turn, influence hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary LH release. The pineal gland is located posterior to the hypothalamus between the hemispheres of the brain, and increased sympathetic activity induced by darkness increases the secretion rate of its primary hormone, melatonin. Exactly how melatonin acts singularly or in a coordinated fashion with other hormones (e.g., norepinephrine) to influence reproductive processes is still unresolved. Nevertheless, in shortday breeders (e.g., sheep and deer), cyclic activity that occurs during the short photoperiods (longer nights) of fall and winter is characterized by greater melatonin release and an active hypothalamic GnRH neurosecretory system, while the long photoperiods (short nights) of
Figure 1 Integration of environmental cues on endocrine and neuroendocrine pathways regulating seasonal reproduction. A multitude of exogenous environmental factors and endogenous hormonal cues coordinate the seasonal reproductive cycle in short- (e.g., sheep) and long- (e.g., horse) day breeders. Central to seasonal regulation is the role of photoperiod (light:dark cycles), which changes annually (see Figure 2c). To this end, photic cues are relayed via the retino-hypothalamo-pituitary pathway using melatonin as a primary regulator of GnRH and LH/FSH release either directly or indirectly by mediating changes in the sensitivity of the hypothalamus and pituitary to the negative feedback effects of gonadal steroids. It has been said that seasonal breeders undergo an annual puberty, with spermatogenesis and estrous cycles beginning anew each breeding season as they make the transition from sexual inactivity into periods of reproductive competence and back again. While strict seasonal breeders are driven principally by photoperiodic cues, other species may exhibit seasonal cycles directed by a variety of climatic, nutritional, and/or behavioral indicators. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone.
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spring and summer are characterized by lower melatonin release, and thus periods of reproductive dormancy. In long-day breeders like the horse, the relationship between melatonin and season remains the same (high during short days and low during long days), but the effects on the reproductive axis are opposite to that seen in short-day breeders (i.e., for the mare, reproductive dormancy during fall and winter and reproductive competence during spring and summer). The role of melatonin in coordinating the seasonal regulation of reproduction has been demonstrated in studies where melatonin has been administered to short-day breeders during long days (thus, increasing melatonin and mimicking the effects of short days) to induce gonadal recrudescence. In sheep, the switch from the breeding season to anestrus, or vice versa, is associated with marked changes in hypothalamic GnRH pulse frequency, which has downstream effects on pituitary LH release, gonadal steroid hormone production, and gamete development. There is conclusive evidence that changes in photoperiod can specifically alter the communicative relationship between the gonads and higher brain centers. Indeed, during seasonal transitions in and out of the breeding season in response to changes in photoperiod, there are marked changes in the sensitivity of hypothalamus (GnRH release) and pituitary (LH release) to the negative feedback effects of gonadal steroid hormones in both males and females. These coordinated activities influence not only gonadal activity, but also related behavioral processes and secondary sex characteristics. Opposite to melatonin, pituitary secretion of prolactin is high when melatonin is low (long days) and vice versa. While prolactin has been implicated as being inhibitory to reproductive function in some short-day breeders and induced (reflex) ovulators (i.e., species that require stimulation of the vagina and/or cervix for ovulation to occur), there is strong evidence that fluctuations in prolactin are not related to the seasonality of mating; however, an endogenous rhythm of prolactin is noted in the ram and stag. Changes in prolactin have been linked specifically to secondary seasonal characteristics, such as coat growth and molt in red deer stags, suggesting that seasonal changes in prolactin may be more related to alterations in temperature. This notion is supported by studies of blind bulls and steers that have shown that photoperiod does not affect prolactin secretion, implicating temperature as the dominant environmental cue regulating prolactin. Thus while photoperiod has been described as being central to the regulation of seasonality, multiple factors can positively or negatively affect the sensitivity and integration of the endocrine and neuroendocrine systems in mediating seasonal cycles and seasonal reproductive transitions (Figure 1).
Artificial Manipulation of Seasonal Breeders Advancement or prolongation of the breeding season in seasonal breeders used in livestock production has been desired in some areas to coordinate breeding seasons with other management-related events (e.g., forage availability). An example specific to the equine racing industry is that foals are routinely assigned a universal birth date of 1 January (northern hemisphere) regardless of when they are born, making advancement of the breeding season beneficial to achieve the birth of foals as early in the year as possible. At present, the primary means to alter circannual rhythms in strict seasonal breeders includes manipulation of photoperiod through exposure of animals to alternate light cycles, and the use of pharmacological (hormonal) means. While these methods will be highlighted in more detail, it should be noted that a variety of other management-related alterations have similarly resulted in a dampening of seasonal influences for some species. For example, seasonal fluctuations in libido and semen quality, estrous activity, and conception rates have been overcome in dairy cattle and water buffalo by providing cooling facilities during heat stress. Additionally, other management practices including early weaning (beef cattle and small ruminants) and increased nutrition (e.g., flushing) have also aided in facilitating early returns to estrus to override any seasonal influences on reproductive function. Finally, behavioral influences should also not be overlooked, as the exposure of ewes to a ram prior to the breeding season can induce early cyclicity (the ‘ram effect’).
Artificial Manipulation of Light–Dark Cycles The artificial manipulation of light–dark cycles is achieved primarily by altering housing strategies. This can be accomplished by blocking natural light from entering stalls or barns for specified periods of time at the beginning and end of each day, or through controlled lighting. In a long-day breeder like the mare, changes in photoperiod to mimic long days (16 h of light:8 h of darkness) during the nonbreeding season (short days) will stimulate reproductive function in anestrous mares. Conversely, periods of seasonal anestrus in the ewe, a short-day breeder, can be altered by changing day length during long days to mimic short days (8 h of light:16 h of darkness). While dairy cattle are not traditionally considered as seasonal breeders, supplemental lighting (16–18 h of light:6–8 h of darkness) has been shown to boost milk production through increased secretion of insulin-like growth factor-1 (IGF-1), which acts on the mammary gland, and concomitant decreases in melatonin secretion. How IGF-1 is regulated in response to reduced
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concentrations of melatonin when day length increases remains unclear. To this end, the manipulation of photoperiod to alter melatonin release may have numerous implications in relation to the reproductive and lactational abilities of animals sensitive to photoperiodic cues.
Pharmacological Control: Exogenous Melatonin and Other Hormonal Means Pharmacological control of seasonal breeding has been achieved in a number of species, and has been implemented as part of routine production management strategies in some areas. As described previously, increasing concentrations of melatonin of pineal origin during short days arouse dormant reproductive processes in short-day breeders. Thus melatonin implants have been inserted in ewes for periods of 30–40 days to advance the breeding season for matings in spring or early summer. However, one problem with using these types of manipulations (melatonin and changes in photoperiod) is that animals can become refractory (i.e., temporarily unresponsive) after a period of time to the stimulatory effects of melatonin and light, thus limiting their use. Moreover, use of melatonin for advancement of the breeding season may not be effective in all seasonal breeding species. For example, in the female goat, melatonin administration has been less successful than in sheep in advancing the breeding season. In addition to melatonin, a whole host of other hormones have been utilized to stimulate reproductive activity during the nonbreeding season or as methods for prolonging the breeding season itself. Specifically, hormonal treatments have included equine chorionic gonadotropin (eCG), human chorionic gonadotropin (hCG), crude pituitary extracts, GnRH, progesterone, and prostaglandins. In camels, GnRH treatment can stimulate sexual activity in males during the nonbreeding season, while in other induced ovulators such as the llama and alpaca, hCG and GnRH have been used to induce ovulation outside of normal periods of sexual receptivity. Taking management strategies a step further, combinations of artificial lighting and pharmacological approaches have also been used with some success. For example, in the mare, initiation of a 16-h photoperiod for 60 days prior to treatment with altrenogest (a synthetic progestin) for 12 days followed by the administration of hCG on day 2 of estrus has been reported to be an effective regime for induction of estrus and ovulation in the mare early in the year outside of the normal breeding period. Such lighting and hormonal combinations and other clinical therapies abound for short-day and longday breeders alike, with the intent to modify periods of sexual activity to meet management constraints, whether environment- (e.g., temperature or forage availability) or industry- (e.g., the equine racing industry) related.
Seasonal Breeding in Domesticated and Semidomesticated Multipurpose (Meat and Dairy) Livestock While not all of the livestock species described herein are used in typical dairy production operations (e.g., swine), for comparative purposes the seasonal nature of reproductive cycles, whether endogenously generated or due to exogenous environmental cues, will be discussed briefly for each species indicated. As described previously, photoperiod, temperature, and a multitude of other climatic and/or nutritional factors are the driving forces regulating the timing of breeding and birthing seasons in most species.
Domestic Cattle: Temperate (Bos taurus) and Tropical (Bos indicus) Cattle are nonseasonal and polyestrous, yet the onset of puberty and postpartum reproduction are often stimulated by exposure to long days. Moreover, seasonal trends emerge in some climates due to adverse environmental conditions. Specifically, heat stress is often implicated as the cause of reduced reproductive performance, particularly in temperate, European-type cattle (B. taurus). Summer heat stress conditions can lower semen quality in the bull, reduce fertilization rates, affect embryo quality and viability, and result in an overall decrease in conception rates. Of all temperate breeds, dairy cattle (e.g., Holstein) in particular show marked seasonal fluctuations in reproductive function due to the effects of environmental heat stress and to meet the metabolic demands of lactation. In the southern United States, cows calving in spring and summer have reduced reproductive performance, with milk production depressed for cows that calve in summer and fall. During heat stress, dairy cows exhibit shorter less intense periods of estrus (as much as 6–8 h less) and a reduced frequency of mounting activity than during cooler seasons. These effects contribute to a lower estrus detection rate, an increased number of artificial breeding services per conception, and an overall decrease in conception rates in production dairy operations during the summer months. Nevertheless, through the implementation of housing strategies to offset environmental extremes (e.g., cooling with fans and sprinklers during heat stress), seasonal influences on fertility in cattle can be markedly reduced. In contrast to heat stress, cold stress has not been implicated in causing seasonal depressions in fertility in cattle, with the exception of when tropically adapted cattle (Zebu; B. indicus) have been translocated to colder environments without appropriate periods for adaptation. To this end, Zebu cattle exhibit the greatest entrainment to seasonal cycles (primarily temperature-
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related) than all other breeds, with the frequency of estrus, ovulation, and conception rates being higher during the summer months than during the winter months in equatorial Africa. Water Buffalo (Bubalus bubalus) Water buffaloes are polyestrous and can breed yearround. However, peaks in calving during the year do occur, which indicates possible seasonal effects on fertility that are most likely the result of temperature, photoperiod, and nutritional interactions. The impact of these effects is seen in buffaloes that calve in winter and spring and do not exhibit postpartum estrous cycles as early as cows that calve in summer and fall. Those calving in winter and spring would be returning to reproductive function during the summer months when high temperatures, increased photoperiods, and elevated prolactin levels might prolong periods of anestrus. Moreover, high temperatures (heat stress) may contribute to reduced sexual activity of male buffaloes during this time. In tropical regions where water buffaloes are maintained, conception rates have been observed to be greatest 2–4 months following the peak in the rainy season. This coincides with cooler temperatures and increasing forage availability. Yak (Bos grunniens) Yaks are considered seasonally polyestrous in their native environments, although female yak showing only a single estrus in a season, even if mating and conception does not occur, is not uncommon. The driving force affecting the onset and end of the breeding season is primarily climatic factors including forage availability and location (latitude). When ambient temperatures and vegetation increase as the winter thaw progresses, females will show an increase in body condition and weight gain, which can initiate cyclicity. The breeding season begins in June and reaches its peak in July and August (in China and upper Mongolia), when temperatures are highest and forage availability is maximal. Estrous activity decreases in frequency and generally stops around November. As the yak is usually found at high altitude, it has been observed that at lower elevations of 1400 m breeding seasons begin earlier (late May), while at higher elevations of 2700 m breeding seasons tend to begin later (late June). Sheep (Ovis aries) and Goats (Capra hircus) In temperate regions, both sheep and goats are seasonally polyestrous. Seasonality is driven by photoperiodism with increased estrous activity during decreasing day lengths. In tropical regions, sheep and goats tend to breed throughout the year. Nevertheless, even in tropical
environments, feed restriction (dry seasons) and high temperatures may cause a suppression of sexual activity, but when rainy seasons resume sexual activity increases. Genetics plays a large role in the breeding seasons of sheep and goats, with some breeds showing longer breeding seasons (sheep: Dorset, Merino, and Rambouillet; goats: Anglo-Nubian) than others with more restrictive breeding seasons (sheep: Southdown, Shropshire, and Hampshire; goats: Toggenburg, Saanen, and French Alpine). Unlike the female, the male is less restrictive with respect to seasonal breeding activity, although sexual activity is greatest in the fall in response to decreasing day length when the secretion of testosterone, testis size, and testicular spermatogenesis increase. As such, melatonin interacts with the neuroendocrine axis mediating the sensitivity of higher brain centers (hypothalamus and pituitary) to the negative feedback effects of steroid hormones in both sheep and goats (see general model depicted in Figure 1). Deer (Cervidae species) The majority of deer are classified as seasonal breeders that are polyestrous, short-day breeders. Nevertheless, 19 species of the 40 or more existing deer species are found in equatorial regions (between 20 N and 20 S latitude) and exhibit nonseasonal breeding capabilities, although peaks in breeding and fawning seasons differ markedly among tropical deer species – some of which inhabit the same ecosystem. In white-tailed deer (Odocoileus virginianus), for example, the distribution of this species extends from 55 N to 18 S latitude, with white-tailed deer in temperate regions breeding strictly seasonally, while those in tropical climates (Caribbean, Central America, and northern part of South America) breeding yearround. In addition to short-day and nonseasonal breeders, one species, Pere´ David’s deer (Elaphurus davidianus), has an advanced onset of the breeding season, which begins mid-summer (3–4 months before typical short-day breeders) when day lengths are long, melatonin is low, and prolactin levels are high. Thus, some have referred to the Pere´ David’s deer as a long-day breeder. While photoperiod is the primary factor that mediates seasonal cycles in most deer, an inherent rhythmicity in metabolism, antler and coat (pelage) growth, and hormonal cycles is evident when photoperiods are altered dramatically or eliminated completely. This suggests entrainment of reproductive and metabolic cycles to an endogenous rhythm that is overlaid on the influence of photoperiodic cues. Even in tropical species of deer (e.g., axis deer; Axis axis), circannual cycles of antler growth, testis size, and body weights are observed, yet estrous cycles, testicular spermatogenesis, breeding, and fawning occur throughout the year. For comparative purposes, the year-round estrous cycle activity of a strict seasonal breeder
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during periods that would favor fawn survival. This is true for all deer, as evidenced by the fact that late-born fawns show lower survival rates due to a shortened lactation (early weaning), low birthweights, and winter death loss, while early-born fawns exhibit similarly low birthweights and may succumb to summer thermal stressors. Thus a window of opportunity exists for fawns born neither too late nor too early, which would favor their survival. For reindeer (Rangifer tarandus) in the arctic, highly variable rates of fertility are noted with reproductive success intimately linked to body fat reserves and the timing of births directed toward snow melt and the emergence of new plant growth. As in sheep and goats, reproductive cyclicity in deer is driven by the myriad of hormonal interactions that occur between melatonin, prolactin, GnRH, gonadotropins, and gonadal steroid hormones in response to photoperiodic, metabolic, and/ or other exogenous and endogenous cues. Camel (Camelus dromedarius)
Figure 2 Serum concentrations of progesterone depicting the estrous cycles of nonseasonal (axis deer (a)) and seasonal (fallow deer (b)) species of farmed deer in relation to photoperiod and ambient temperature (c). The axis deer is a tropical deer species that is a nonseasonal breeder and exhibits continuous estrous cycles irrespective of changes in photoperiod (a). Note the presence of 18 estrous cycles throughout the 346-day sampling period for the axis doe depicted here (serum samples for progesterone analysis were collected twice weekly). In contrast, the seasonally polyestrous fallow doe shown in panel b exhibits only 6–7 estrous cycles annually, which are restricted to the short photoperiods between October and March. Both deer were maintained at the same location at the Texas Agricultural Experiment Station in Overton, Texas (32 169N; ST Willard and RD Randel, unpublished data).
(e.g., fallow deer (Dama dama)) and a nonseasonal breeder (e.g., axis deer) is shown in Figure 2 for axis and fallow does maintained at the same location in Texas. Irrespective of the nonseasonal nature of some deer species, seasonal peaks in the frequency of breeding and fawning are still noted in tropical deer, and are attributed to climatic and/or nutritional cues to achieve fawning
Female camels are typically seasonally polyestrous and are induced ovulators. Decreasing day length appears to be the stimulus for reproduction in most regions, although in equatorial locations when adequate rainfall and nutrients are available year-round breeding can occur. It is well documented that by providing sufficient food, nutrition may override the effects of photoperiod and increase sexual receptivity in the female. Male camels also exhibit seasonal sexual activity, with higher concentrations of testosterone and increased spermatogenesis during cooler months. Nevertheless, spermatogenesis can continue throughout the year in the male, reaching a peak during the rutting period. Increased prolactin (hyperprolactinemia) during the nonbreeding season has been suggested as the cause of reduced fertility and sexual activity via prolactin-induced inhibition of gonadotropin (FSH and LH) secretion, although more research in this area is needed. Llama (Lama glama) and Alpaca (Lama pacos) Like camels, llamas and alpacas are induced ovulators that show rhythmic patterns of follicular development and periods of sexual receptivity. In their native highlands of Peru, llamas and alpacas exhibit seasonal sexual cycles from December to March, which are the warmer summer months for this region. However, in these wild settings, males and females are generally together throughout the year, and when females are separated from males in production management settings and pair-mated monthly, they will exhibit sexual activity year-round. Therefore, seasonal breeding can be directly influenced by the continuous contact of females with males, versus when males and females are managed
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separately. Ovulation rates, fertilization rates, and embryo survival do not appear to be affected by the season in which breeding occurs under these management circumstances. Male llama and alpaca produce fertile ejaculates throughout the year, although the quality of the ejaculate is directly affected by season and nutrient availability, with higher testosterone and greater spermatogenesis during the spring and summer months (the peak breeding periods). The degree to which other environmental cues (visual, olfactory, etc.) may influence reproductive processes in the llama or alpaca is unclear. However, like camels, food availability may directly influence the existence of nonseasonal breeding activity. In North America, llama births are observed throughout the year, reaching a peak during the warmer months of June–November. Horse (Equus caballus) Mares are seasonally polyestrous, long-day breeders. However, considerable variation exists among breeds and with respect to location (latitude). Some mares exhibit a strict breeding season accompanied by estrus and ovulation, while others may have a defined fertile breeding period preceding and followed by a transitory period in which estrous cycles are present but may not be accompanied by ovulation. Still others may show continuous, year-round periods of estrus and ovulation such as for those mares maintained in equatorial regions. It is well accepted that photoperiod is the primary regulatory mechanism controlling seasonal breeding in the mare as mediated by the hormonal interactions of melatonin, prolactin, GnRH, FSH, LH, and estradiol. Unlike the mare, the stallion does not show as defined a breeding season, with fertile ejaculates capable of being collected throughout the year. Nonetheless, seasonal differences in reaction time, mounting frequency, testis size, semen volume, numbers of spermatozoa, and other semen quality characteristics are observed in the stallion, decreasing during short photoperiods and increasing during long photoperiods. Swine (Sus domesticus) Swine are polyestrous and nonseasonal. Nevertheless, fertility (mean litter size) declines sharply when photoperiods are long and temperatures become elevated (summer months). In addition to effects on litter size, increased ambient temperatures can cause sperm output and the motility of spermatozoa in the boar to decrease,
which undoubtedly contribute to a decrease in fertilization rate and subsequently litter size. Unlike dairy cattle, which show a decrease in the duration of estrus during the hotter summer months, periods of estrus in sows and gilts are longest during summer and shortest in winter. Today, any traces of seasonality in swine breeds have been, for the most part, completely controlled or eliminated due to the enclosed housing environments within which most swine are currently maintained. See also: Stress in Dairy Animals: Heat Stress: Effects on Milk Production and Composition; Heat Stress: Effects on Reproduction.
Further Reading Al Eknah MM (2000) Reproduction in Old World camels. Animal Reproduction Science 60–61: 583–592. Amoah EA, Gelaye S, Guthrie P, and Rexroad CE (1996) Breeding season and aspects of reproduction of female goats. Journal of Animal Science 74: 723–728. Bearden HJ, Fuquay JW, and Willard ST (2003) Applied Animal Reproduction, 6th edn. Upper Saddle River, NJ: Prentice-Hall Inc. Bronson FH and Heideman PD (1994) Seasonal regulation of reproduction in mammals. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, 2nd edn. New York: Raven Press Ltd. Chemineau P, Martin GB, Saumande J, and Normant E (1988) Seasonal and hormonal control of pulsatile LH secretion in the dairy goat (Capra hircus). Journal of Reproduction and Fertility 83: 91–98. Commission on International Relations – National Research Council (1981) The Water Buffalo: New Prospects for an Underutilized Animal. Washington, DC: National Academy Press. Foster DL (1994) Puberty in the sheep. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, 2nd edn. New York: Raven Press Ltd. Godfrey RW, Lunstra DD, Jenkins TG, et al. (1990) Effect of season and location on semen quality and serum concentrations of luteinizing hormone and testosterone in Brahman and Hereford bulls. Journal of Animal Science 68: 734–749. Hafez ESE and Hafez B (2000) Reproduction in Farm Animals, 7th edn. Baltimore, MD: Lippincott Williams & Williams. Li C and Wiener G (1995) The Yak. Bangkok, Thailand: Regional Office for Asia and the Pacific of the Food and Agriculture Organisation of the United Nations. McKinnon AO and Voss JL (1995) Equine Reproduction. Hoboken, NJ: John Wiley & Sons, Inc. Ray DE, Halbach TJ, and Armstrong DV (1992) Season and lactation number effects on milk production and reproduction of dairy cattle in Arizona. Journal of Dairy Science 75: 2976–2983. Senger PL (2005) Pathways to Pregnancy and Parturition, 2nd revised edn. Pullman, WA: Current Conceptions, Inc. Thatcher WW (1973) Effects of season, climate and temperature on reproduction and lactation. Journal of Dairy Science 57(3): 360–368. Tucker HA and Petitclerc D (1982) The role of the eye on secretion of prolactin during various photoperiods and seasons in cattle. In: Ortavant R, Pelletier J, and Ravault JP (eds). Photoperiodism and Reproduction in Vertebrates, pp. 147–156. Les Colloques de l’INRA – 6. Nouzilly, France, (Sept. 24-26 1981): INRA Publishing. Turek FW and Van Cauter E (1994) Rhythms in reproduction. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, 2nd edn. New York: Raven Press Ltd.
Control of Estrous Cycles: Synchronization of Estrus Z Z Xu, Livestock Improvement Corporation Ltd., Hamilton, New Zealand ª 2011 Elsevier Ltd. All rights reserved.
Introduction Techniques for synchronizing the onset of estrus in dairy cattle and other species have been available since the 1960s. Research effort to improve the performance of estrus synchronization programs continues to this day and more work is required to make estrus synchronization more acceptable on the farm. The reasons for using estrus control vary between breeds and species and between different farming systems. In dairy cattle, estrus synchronization is often used to aid mating management by improving the efficiency and accuracy of detection of estrus (heat) or by reducing the labor requirement for estrus detection. Estrus synchronization is especially useful in small herds with year-round calving where there may be only one animal in estrus at any given time or in animals, such as nulliparous heifers on pasture, that cannot be easily accessed for estrus detection. Estrus synchronization can also be used to increase the percentage of cattle conceiving within a defined period of time. This is achieved by improving the efficiency and accuracy of estrus detection and by allowing most eligible cattle in a herd to be bred within a few days rather than spread over an entire estrus cycle. Another important usage of estrus synchronization in dairy cattle is to synchronize recipient animals for embryo transfer so that the desired number of recipients at the appropriate stage of the estrous cycle are available. There are other likely benefits from estrus synchronization in dairy cattle, such as facilitating the adoption of treatments or management practices that must be implemented at a specific stage of pregnancy or lactation. A successful estrus synchronization program should have the following features: implementation with minimal distress to animals; • easy applicability to animals of different physiological sta• tus, for example, cyclic versus noncyclic; precise onset of estrus to minimize or eliminate estrus • detection; detrimental effect on reproductive performance • nocompared with that achieved under the current system; cost-effectiveness relative to the objectives to be • achieved. This article discusses the techniques available to synchronize dairy cattle for breeding after detection of estrus. Techniques for synchronizing ovulation so that breeding can be carried out at a fixed time after treatment
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without estrus detection are discussed elsewhere (See Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Ovulation and Insemination). Ovulation synchronization removes the need for estrus detection and is well suited for production systems where accurate estrus detection is difficult and costly. However, a successful ovulation synchronization program usually involves synchronization of follicular wave development, which requires additional treatments with hormones. There may be semen wastage associated with ovulation synchronization because not all treated animals ovulate around the time of artificial insemination (AI).
Principles of Estrus Control During each bovine estrus cycle, there are characteristic changes in sexual behaviors, follicular development, and the circulating profiles of several reproductive hormones (see Reproduction, Events and Management: Estrous Cycles: Characteristics). Among all the reproductive hormones, progesterone can be considered as the main ‘orchestrator’ of events during an estrus cycle. During the luteal phase of the estrus cycle when circulating progesterone concentration is high, no estrous behavior or ovulation occurs. The decrease in circulating progesterone concentration after the onset of luteolysis relieves the reproductive system from the negative feedback control of progesterone and, consequently, estrous behavior and ovulation ensue within a few days. Therefore, estrus control mainly involves manipulating the circulating concentrations of progesterone. This can be achieved either by artificially prolonging the luteal phase of the estrus cycle using exogenous progesterone or a synthetic progestogen or by shortening the luteal phase using prostaglandin F2 (PG) or one of its analogues, or by a combination of both mechanisms.
Estrus Control Using Progestogens For a group of cattle at random stages of the estrus cycle, treatment with progestogen for more than 14 days will produce a synchronized onset of estrus within 2–3 days after cessation of the progestogen treatment. The progestogen treatment prevents cows whose corpora lutea (CLs) undergo spontaneous luteolysis during the treatment
Reproduction, Events and Management | Control of Estrous Cycles: Synchronization of Estrus
period (cows on day 5 or later of the estrus cycle at treatment initiation) from showing estrous behavior and ovulating until after the end of treatment. For animals in the early stage of the estrus cycle (days 0–4), the progestogen treatment either prevents the formation of CLs or shortens the life span of freshly formed CLs. Early studies on estrus synchronization with progestogens involved daily injection of sufficient amounts of progesterone or the feeding of orally active and highly potent progestogens, such as melengestrol acetate (MGA). The development of progestogen application devices, including the norgestomet ear implant, the progesterone-releasing intravaginal device (PRID), and the controlled internal drug release (CIDR) device, has facilitated the use of progestogens for estrus synchronization in dairy cattle. However, a common adverse effect of estrus synchronization with progestogen alone is the reduction in conception rate at the synchronized estrus. The longer the duration of progestogen treatment, the better the synchrony, but the lower the conception rate. It is now known through studies of follicular dynamics using ultrasonography that the reduction in conception rate at the synchronized estrus is due to the development of persistent dominant follicles. The doses of progestogens administered in these programs, while effective in suppressing estrus and ovulation, are ineffective in suppressing the development of persistent dominant follicles in the absence of a functional CLs. Oocytes from persistent dominant follicles can be fertilized, but the resulting embryos have reduced developmental capability. As a result, estrus synchronization programs using progestogens alone are no longer widely used commercially.
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single injection of PG can theoretically show estrus over a 3-day period. Estrous response to PG injections can be lower in Bos indicus than in Bos taurus, which may be related to poor estrus expression in B. indicus rather than luteal responsiveness to PG. Several approaches have been developed to circumvent the problem that not all cows in a group will respond to a single PG treatment (Figure 1). The most widely used approach is to administer two injections of PG 11–14 days apart (Figure 1, program (1)). This treatment program ensures that all animals are at a stage of the estrus cycle when they are capable of responding to the second PG treatment, irrespective of whether they have responded to the first PG treatment or not. A variation of the above program is to treat all cattle with PG and breed on detection of estrus, followed by retreatment 11 days later of those that have not responded to the first PG (Figure 1, program (2)). A third approach is to mate cows for 5–7 days on detection of estrus and then to treat with PG animals that have not been mated (Figure 1, program (3)). Another approach is to treat only cows that are identified, using rectal palpation, ultrasonography, or progesterone measurement, to have responsive CLs. This approach is not often used systematically at the herd level because of errors in, and costs associated with, identifying cows with responsive CLs. Initially, it was hoped that the double-PG program would result in a synchronized onset of estrus that was precise enough for a single fixed-time insemination to achieve an acceptable conception rate. Such a hope has never been realized because the interval from PG injection to onset of estrus is influenced, among other things, by the developmental stage of the dominant follicle at the time of PG treatment. In nonlactating heifers, estrous response rate
Estrus Control Using Prostaglandin The luteolytic property of PG and its analogues was discovered in the early 1970s. This was followed by numerous studies on the use of PG for estrus synchronization. Several PG products are licensed for use on dairy cattle and there does not appear to be significant differences among products in their efficacy for estrus synchronization. A single injection of PG will reliably induce regression of the CLs between days 7 and 18 of the estrus cycle. Regression of the CLs results in a drop in circulating progesterone concentration. This allows the normal sequence of physiological and endocrinological events associated with the follicular phase to proceed, leading to estrus and ovulation. However, PG is not effective at all stages of the estrus cycle. It has no consequence if administered after the spontaneous onset of luteolysis. The developing CLs before day 5 of the estrus cycle are not responsive to PG and young CLs (days 5 and 6) are less responsive to PG than mature CLs. Consequently, about two-thirds of cows treated with a
Figure 1 Diagrammatic illustration of various estrus synchronization programs involving PGF2 or its analogues (PG). AI, artificial insemination; h, hour.
450 Reproduction, Events and Management | Control of Estrous Cycles: Synchronization of Estrus Table 1 Estrous response rate (%) of cyclic lactating cows synchronized with two injections of PG 14 days apart and the effect of progesterone supplementation for 5 days before the second PG Day after second PG
No_progesterone (n ¼ 572)
Progesterone (n ¼ 605)
Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Total over 6 days
7.9 40.6 14.9 9.6 7.3 2.5 82.9
9.9 30.9a 25.1b 12.1 8.1 3.5 89.6a
a p < 0.01 compared with the corresponding value for cows in the no_progesterone group. b p < 0.001 compared with the corresponding value for cows in the no_progesterone group. PG, prostaglandin F2. From Xu ZZ, Burton LJ, and Macmillan KL (1997) Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2 and progesterone. Theriogenology 47: 687–701.
within 7 days after the second PG treatment can exceed 90% with a large peak response (up to 60%) between 48 and 72 h. By contrast, estrous response of lactating dairy cows to the double-PG treatment is inconsistent and less precise compared with that of heifers (Table 1). The percentage of cows that are noncyclic at the time of PG treatment can affect the estrous response. Stage of the estrus cycle at the time of PG treatment can also affect estrous response, with advanced stages of the luteal phase being associated with increased estrous response rate (Table 2). Thus, a 14-day interval between the two PG treatments will result in a higher estrous response rate compared with an 11-day interval due to an increase in the proportion of animals in the middle to late stages of the luteal phase. Progesterone supplementation for 5 days before the second PG injection can affect the pattern of onset of estrus and increase the estrous response rate (Table 1). The increase in estrous response rate mainly occurs in cows in the early to middle stages of the luteal phase (Table 2).
Many studies have found that conception rate after PG treatment is normal or even improved compared with nonsynchronized animals. Some of the improvement in conception rate could be due to improved estrus detection accuracy in synchronized cows. In herds with high estrus detection efficiency and accuracy, estrus synchronization with PG can reduce conception rate. The reduction in conception rate mainly occurs in cows in the early to middle stages of the estrus cycle at the time of the second PG injection. Therefore, it is not the PG treatment per se that reduces conception rate, rather the reduction is probably caused by shortening of the luteal phase, thus reducing the total amount of progesterone the reproductive system is exposed to before ovulation. The reduction in conception rate can be largely eliminated by supplementing progesterone for 5 days before the second PG injection (Table 2). In some countries, PG is the only drug that is licensed for estrus synchronization in lactating dairy cows. Systematic breeding programs based on PG have been developed. Targeted breeding is a systematic breeding program that is advocated by the manufacturer of Lutalyse, Pharmacia-Upjohn (now a division of Pfizer) (Figure 1, program (4)). It consists of three PG injections at 14-day intervals. For simplicity of implementation in nonseasonal herds, PG is usually administered on 1 day of the week to all cows that qualify in that week. To get more cows bred early, the first set-up injection of PG could be given to cows that are between 7 and 14 days before the end of the voluntary waiting period. Cows are not mated after the first set-up injection. The set-up injection ensures that cows will be in a stage of the estrus cycle when the CLs are responsive to the second PG injection. The second PG injection is administered 14 days later and cows are mated after detection of estrus. Those that have not been detected in estrus after the second PG treatment are given a third PG injection 14 days later, and the cycle can continue. For the targeted breeding program, a fixed-time insemination is carried out at 80 h after the third PG injection on cows that have not displayed estrus by that time. Alternatively,
Table 2 Effects of stage of the estrous cycle at second PG and progesterone supplementation for 5 days before second PG on ORR (%) and CR (%) of postpartum lactating cows synchronized with two injections of PG 14 days apart No_progesterone
Progesterone
Stage of estrous cycle
ORR
CR
ORR
CR
Days 5–9 Days 10–13 Days 14–19
75.9 85.5 93.1
52.3 59.3 71.3
86.8a 91.5a 94.3
64.8b 66.2 71.4
a
p < 0.05 compared with the corresponding value for cows in the no_progesterone group. p < 0.1 compared with the corresponding value for cows in the no_progesterone group. CR, conception rate; ORR, estrous response rate; PG, prostaglandin F2. From Xu ZZ, Burton LJ, and Macmillan KL (1997) Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2 and progesterone. Theriogenology 47: 687–701. b
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the first PG injection in the targeted breeding program could be given to those cows that have just passed the voluntary waiting period and cows are mated after detection of estrus. This treatment program will be cheaper due to the reduced total number of PG injections, but the interval from calving to first AI will be longer because only two-thirds of the cows can potentially respond to the first PG injection.
Combination Treatment Programs To improve the precision of synchrony and to reduce the adverse effects on fertility, various treatment programs involving a combination of two or more drugs have been developed. Some of the popular combination programs for synchronizing estrus are discussed here. Progestogen and Prostaglandin Progestogen in combination with PG is a widely used combination treatment program for estrus synchronization. It usually involves a short period (commonly 6–8 days) of progestogen treatment with a PG injection 1–2 days before or at the time of termination of the progestogen treatment (Figure 2, program (5)). This combination program ensures that, at the time of PG injection, animals either do not have functional CLs or have CLs that are responsive to PG. Most treated animals (85% or more) will show estrous behaviors between 2 and 5 days after the end of treatment. The time and the magnitude of the peak estrous response are affected by when PG is administered relative to the termination of progestogen treatment. If PG is injected 1–2 days before the end of progestogen treatment, peak estrous response occurs on the second day after progestogen treatment, whereas it occurs on the third day if PG is injected at termination of progestogen treatment. Conception rate to inseminations at the synchronized estrus has been reported to be normal or slightly reduced, but the reduction is generally less compared with the situation in which long-term progestogen treatment is used for synchronization. Persistent dominant follicles can still develop in some animals that are in the late stage of the estrus cycle at the start of progestogen treatment. Another combination program involving progestogen and prostaglandin is to presynchronize animals with a long-term (e.g., 14 days) progestogen treatment, followed by an injection of PG during the late luteal phase of the synchronized cycle (e.g., 17–18 days after the end of the progestogen treatment) (Figure 2, program (6)). This program takes advantage of the ability of a long-term progestogen treatment to precisely synchronize estrus and the high estrous response and normal fertility when PG is administered in the late luteal phase (Table 2). However, this program requires that progestogen
Figure 2 Diagrammatic illustration of the various estrus synchronization programs involving a combination of two or more hormones. PG, prostaglandin F2 or its analogue; GnRH, gonadotropin-releasing hormone; P4, progesterone or synthetic progestogen; E2, estradiol-17 or its derivatives; AI, artificial insemination.
treatment be initiated more than 30 days before the start of breeding when many postpartum cows may have not resumed ovarian cyclicity. Therefore, this program may not be well suited for postpartum lactating dairy cows.
Estrogen and Progestogen Studies have shown that an injection of progestogen and estrogen at the start of an estrus synchronization program using progestogen can reduce the duration of progestogen treatment from >14 to 9 days. This has formed the basis for the Synchro-Mate-B (SMB) treatment for estrus synchronization in beef cattle and dairy heifers. The SMB program involves a 9-day treatment with an ear implant containing 6 mg of norgestomet plus an injection of 5 mg of estradiol valerate and 3 mg norgestomet at the time of implant insertion. The injection of estradiol valerate and norgestomet serves two functions. First, the injection causes regression of large antral follicles and initiation of a new follicular wave 4–5 days after treatment so that a newly developed dominant follicle is available for ovulation after the 9-day treatment program. Second, the injection, presumably the estradiol valerate in the injection, causes premature luteolysis of CLs during the treatment period, irrespective of the stage of the estrus cycle at the start of
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SMB treatment. Estrogen induces luteolysis by stimulating PG secretion from the uterus. In addition, progestogen treatment during metestrus can also prevent normal CLs development in some animals. Estrous response following SMB treatment is typically greater than 90% and fixedtime insemination between 48 and 54 h after implant removal can achieve acceptable reproductive performance. However, SMB has been withdrawn from the market. Gonadotropin-Releasing Hormone and Prostaglandin Studies, mainly in North America, have shown that treatment with gonadotropin-releasing hormone (GnRH) followed 7 days later by PG can be used for estrus synchronization (Figure 2, program (7)). The dose of GnRH used in this program is typically half of that recommended for treating follicular cysts. The GnRH treatment induces ovulation of existing dominant follicles and the formation of new or accessory CLs. This prevents most animals in the late luteal and follicular phases of the estrus cycle from showing estrus before PG injection. However, between 5 and 10% of treated cows can still show estrus between the GnRH and PG treatment, thus reducing the effectiveness of this program for estrous synchronization. Nevertheless, some studies have shown similar or improved reproductive performance after this program compared with the double-PG program. Progestogen, gonadotropin-releasing hormone, and Prostaglandin Studies in New Zealand and Ireland have investigated synchronization programs that incorporate progesterone treatment between GnRH and PG injections (Figure 2, program (8)). A CIDR device is inserted at the time of GnRH injection and removed at PG injection. The progesterone treatment prevents estrus and ovulation before PG injection and may also improve conception rate at the synchronized estrus by increasing circulating progesterone concentrations in cows without a functional CLs. An estrous response rate of greater than 90% has been obtained and the conception rate at the synchronized estrus is similar to that of nonsynchronized herd mates inseminated at detected estrus. Estrogen, Progestogen, and Prostaglandin Estrogen has been used at the beginning of combination treatment programs involving progestogen and PG (Figure 2, program (9)). The purpose of this estrogen treatment is to regress dominant follicles that are present at the time of estrogen treatment so that freshly developed dominant follicles are ready to ovulate after the program. A gelatin capsule containing 10 mg of estradiol benzoate is
developed for intravaginal use together with the CIDR device or PRID. Injection of 5 mg of estradiol-17 or 2 mg of estradiol benzoate has also been found to improve the precision of synchrony and conception rate compared with no estrogen treatment. Estrogen has also been used after the end of progestogen and PG treatment to increase the precision of onset of estrus. An injection of 1 mg of estradiol benzoate 48 h after the end of progesterone and PG treatment can significantly increase the percentage of cows showing estrus between 48 and 72 h (85 vs. 57%). However, in 2006, the European Union banned the use of estradiol and its derivatives for estrus synchronization in food-producing animals. This has led other countries, such as New Zealand and Australia, to adopt the EU Directive and ban the use of estrogens for estrus synchronization. Consequently, the use of GnRH at the beginning of a progesterone–PG program to increase the precision of onset of estrus and/or after the progesterone–PG program to synchronize ovulation has gained popularity.
Treatment of Noncyclic Cows In a group of cows eligible for breeding, some may be noncyclic. The problem of noncyclic cows at the start of the breeding season is particularly severe in high-producing dairy cows or in seasonal dairy cows grazing on pasture. Therefore, an effective estrus synchronization program should also be able to induce estrus and ovulation in noncyclic cows. In New Zealand, a popular program for treating noncyclic cows involves progesterone treatment in the form of an intravaginal CIDR device for 6–7 days, followed by an injection of 1 mg of estradiol benzoate either 24 or 48 h after CIDR removal. An estrous response rate of close to 90% and conception rate of around 35% have been obtained with this treatment program. However, this program does not work for cyclic cows and special effort is therefore needed to separate cyclic from noncyclic cows. Recent studies have shown that a combination program involving GnRH, progesterone, PG, and estradiol may be used to synchronize all cows in a herd regardless of their cyclic status. Cows are treated with a CIDR device for 7 days, along with GnRH at CIDR insertion and PG at CIDR removal. At 48 h after CIDR removal, 1 mg of estradiol benzoate is injected to cows that have not been detected in estrus by that time. This program has been tested for treating noncyclic cows due to nutritional stress and has been found to result in better estrous response (93 vs. 89%) and conception rate (47 vs. 29%) than the program based on progesterone and estradiol benzoate only. The GnRH and PG used in this program could also be beneficial for treating noncyclic cows due to ovarian cysts and uterine infection.
Reproduction, Events and Management | Control of Estrous Cycles: Synchronization of Estrus
Following the ban on the use of estrogens in foodproducing animals, the available programs for both cyclic and noncyclic cows in New Zealand have been changed to Ovsynch-type programs involving a combination of GnRH and PG, with or without progesterone in the form of the CIDR device. A second GnRH injection around 56 h after PG and fixed-time insemination at 72 h may improve pregnancy rate compared with insemination after detected estrus.
Practical Considerations Despite the aforementioned advantages from using estrus synchronization, it remains a major challenge to make this technique widely accepted by commercial dairy producers. Costs of drugs and labor for implementing an estrus synchronization program are among the first things considered by dairy farmers when deciding whether to use estrus synchronization. Estrus detection can be more difficult in a large group of synchronized cattle because so many animals are in estrus at the same time and it is difficult to identify those that are in genuine estrus. This problem can be solved by developing synchronization programs that allow fixed-time insemination. Herd managers need to have good organizational skills and some technical knowledge of the program in order to implement a successful estrus synchronization program. Good communication and cooperation among herd managers, veterinarians, and AI technicians are essential. Good record keeping is also important because the use of PG on pregnant animals will lead to abortion.
The Future The challenge for future research on estrus synchronization will be to increase the estrous response rate, to improve the precision of synchrony, and at the same time to maintain and increase conception rate at the synchronized estrus. A reduction in conception rate at the synchronized estrus is a common feature following most estrus synchronization programs. Although many studies have reported improved reproductive performance after estrus synchronization compared with nonsynchronized control animals, most of this increase is probably due to improvement in the efficiency and accuracy of estrus detection and not due to improved fertility. The objective is to achieve a conception rate that equals the conception rate to inseminations at correctly detected natural estrus or to natural mating. It is likely that achieving this objective will require the use of multiple drugs. Therefore, the other challenge for research is to develop smart drug delivery systems that simplify the implementation of estrus synchronization
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programs. Furthermore, the development of semen products that allow sperm to survive for several days in the female reproductive tract will eliminate the need for tight synchrony. Finally, the challenge will be even greater to develop estrus synchronization systems that can effectively synchronize the onset of estrus in those animals that return after a synchronized insemination. See also: Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Estrous Cycles: Characteristics; Mating Management: Detection of Estrus.
Further Reading Bo GA, Cutaia L, Peres LC, Pincinato D, Marana D, and Baruselli PS (2007) Technologies for fixed-time artificial insemination and their influence on reproductive performance of Bos indicus cattle. Society of Reproduction and Fertility Supplement 65: 223–236. Ferguson JD and Galligan DT (1993) Prostaglandin synchronization programs in dairy herds – part I. Compendium on Continuing Education for the Practicing Veterinarian 15: 646–655. Gordon I (ed.) (1996) Artificial control of oestrus and ovulation. In: Controlled Reproduction in Cattle and Buffaloes, pp. 133–166. Wallingford, UK: CAB International. Jo¨chle W (1993) Forty years of control of the oestrous cycle in ruminants: Progress made, unresolved problems and the potential impact of sperm encapsulation technology. Reproduction Fertility and Development 5: 587–594. Kesler DJ and Favero RJ (1995) Estrus synchronization in beef females with norgestomet and estradiol valerate. Part 1: Mechanism of action. Agri-Practice 16: 6–11. Lane EA, Austin EJ, and Crowe MA (2008) Oestrous synchronisation in cattle – current options following the EU regulations restricting use of oestrogenic compounds in food-producing animals: A review. Animal Reproduction Science 109: 1–16. Larson LL and Ball PJH (1992) Regulation of estrous cycles in dairy cattle: A review. Theriogenology 38: 255–267. Macmillan KL and Peterson AJ (1993) A new intravaginal progesterone releasing device for cattle (CIDR-B) for oestrous synchronization, increasing pregnancy rates and the treatment of post-partum anoestrus. Animal Reproduction Science 33: 1–25. Nebel RL and Jobst SM (1998) Evaluation of systematic breeding programs for lactating dairy cows: A review. Journal of Dairy Science 81: 1169–1174. Roche JF, Austin EJ, Ryan M, O’Rourke M, Mihm M, and Diskin MG (1999) Regulation of follicle waves to maximize fertility in cattle. Journal of Reproduction and Fertility Supplement 54: 61–71. Twagiramungu H, Guilbault LA, and Dufour JJ (1995) Synchronization of ovarian follicular waves with a gonadotropin-releasing hormone agonist to increase the precision of estrus in cattle: A review. Journal of Animal Science 73: 3141–3151. Watts TL and Fuquay JW (1985) Response and fertility of dairy heifers following injection with prostaglandin F2 during early, middle or late diestrus. Theriogenology 23: 655–661. Xu ZZ, Burton LJ, and Macmillan KL (1997) Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2 and progesterone. Theriogenology 47: 687–701. Xu ZZ, Burton LJ, McDougall S, and Jolly PD (2000) Treatment of anestrous lactating dairy cows with progesterone and estradiol or with progesterone, GnRH, prostaglandin F2 and estradiol. Journal of Dairy Science 83: 464–470. Zimbelman RG, Lauderdale JW, Sokolowski JH, and Schalk TG (1970) Safety and pharmacologic evaluations of melengestrol acetate in cattle and other animals: A review. Journal of the American Veterinary Medical Association 157: 1528–1536.
Control of Estrous Cycles: Synchronization of Ovulation and Insemination W W Thatcher and J E P Santos, University of Florida, Gainesville, FL, USA ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by W. W. Thatcher, Volume 4, pp 2178–2184, ª 2002, Elsevier Ltd.
Introduction Intensive genetic selection for milk production without attention to reproductive performance has contributed to an inverse relationship between milk production and reproduction. Inclusion of productive life and daughter pregnancy rate and, more recently, the availability of sire conception rate, as a measure of phenotypic service-sire fertility, appear to have reduced the rate of decline in fertility in the United States. Reproductive management of the lactating dairy cow has been a challenge because of poor expression of estrus and low fertility to insemination at a detected estrus. The duration of estrus is reduced as milk production increases, and the frequency of double ovulations and subsequent occurrence of twins is also increased in cows with high levels of milk production at the time of the breeding period. The high-producing dairy cow of today expresses estrus for approximately 7 h during which time an average of 6.5 standing events take place with an accumulative period of standing of 20 s (i.e., 3 s per standing event). Pregnancy rate over a 21-day period for the national herd of dairy cows in the United States is approximately 16.2%. The component parts of pregnancy rate are the rate of estrus detection and conception rate. Technology is available for systems to detect estrus accurately, but a major issue is that lactating dairy cows do not display strong symptoms of estrus. Expression of estrus has been affected adversely by high milk production and associated metabolism of hormones, as well as housing facilities (e.g., concrete floors) that reduce the cow’s willingness to be sexually active. An additional challenge is the high occurrence of nonovulatory dairy cows that either have reoccurring follicle waves without ovulation or develop ovarian cysts. A major advance in reproductive management that has addressed how to improve pregnancy rate has been the development of timed artificial insemination (TAI) programs based on the development of systems to control or program optimal development of ovarian follicles, induce ovulation, and develop a corpus luteum (CL) capable of supporting pregnancy. The component pharmaceutical agents available to the dairy industry in many countries for use with dairy cattle are gonadotropin-releasing hormone (GnRH), luteolytic prostaglandins, and intravaginal
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progesterone (using a controlled intravaginal drug release (CIDR) insert, or similar device). These are pharmaceuticals that mimic the actions of the cow’s endogenous hormones, are physiological, and pose no health hazard to the cow. The original TAI protocol is the Ovsynch procedure. This protocol has been in use for approximately 12 years. During this period, both basic and applied research has led to major advancements in optimizing the system. As a consequence, pregnancy responses have increased, the system has been extended to resynchronization of nonpregnant cows, and programs have been developed for TAI in dairy heifers. The dynamics of various cow factors such as body condition score, parity, and health status in the transitional-periparturient period have been shown to influence pregnancy rates in the controlled breeding program. The present objective is to update major advancements that will increase reproductive performance in controlled breeding in dairy cattle.
Lactating Dairy Cattle It is essential that producers and veterinarians understand the physiological reasons why certain components of the reproductive management program are able to improve reproductive performance or conversely why a misunderstanding of the program can lead to catastrophic pregnancy results. No one reproductive breeding program is practical and economically optimal for all dairy production units due to differences in available facilities, size of the unit, labor that places reproduction as a high priority, and a functionally dynamic record system.
Optimizing Stage of the Estrous Cycle at the Onset of Ovsynch The original Ovsynch program involved two injections of GnRH administered 7 days before and 48 h after an injection of prostaglandin F2 (PGF2), and cows were inseminated 16–20 h after the second injection of GnRH. If TAI in the Ovsynch protocol is performed at the same time as the second GnRH injection, then the protocol is referred to as Co-synch.
Reproduction, Events and Management | Control of Estrous Cycles 455
Figure 1 Follicle dynamics and hormonal responses to the Ovsynch protocol. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; PGF2, prostaglandin F2; P4, Progesterone; TAI, timed artificial insemination.
Optimization of stage of the estrous cycle (i.e., days 5–9) at the onset of the Ovsynch protocol is important to achieve a subsequent synchronized ovulation at the second GnRH preceding the TAI (Figure 1). Programming the stage of the estrous cycle at the time the Ovsynch protocol is implemented (e.g., days 5–9 of estrous cycle) ensures there is progesterone availability throughout the period between the first injection of GnRH and injection of PGF2, and that there is a CL to respond to the luteolytic injection of PGF2 (Figure 1). The continual exposure to progesterone is important for sequentially programming the brain, oviduct, and uterus with the appropriate changes in hormones, receptors, and secretions leading to an induced ovulation, fertilization, and development of an embryo capable of maintaining a pregnancy with minimal embryonic and fetal losses. Programming the start of the Ovsynch protocol to occur between days 5 and 9 of the estrous cycle increases the probability that the first injection of GnRH will induce
ovulation of the first wave follicle and recruitment of a new follicle wave (Figure 1), which upon induction of ovulation in response to the second GnRH increases the probability of producing a viable oocyte for fertilization and a robust CL. Indeed ovulation of the first follicle wave results in the presence of both the original CL and an accessory CL, induced by the GnRH injection, which are responsive to the injection of PGF2. The Ovsynch protocol preceded by a PGF2 presynchronization program (Presynch–Ovsynch) has become the nucleus program for reproductive management in the industry. Successful use of such a program is highly dependent upon obtaining good compliance in implementing all component parts of the protocol. The original Presynch–Ovsynch program entailed two injections of PGF2 given 14 days apart with the Ovsynch protocol initiated 12 days after the second injection of PGF2 for presynchronization (Figure 2). This system increased pregnancy rates compared to Ovsynch alone for
Figure 2 Presynch/Ovsynch protocol for TAI at the first postpartum service. GnRH, gonadotropin-releasing hormone; PGF2, prostaglandin F2; TAI, timed artificial insemination.
456 Reproduction, Events and Management | Control of Estrous Cycles Table 1 Pregnancy rates for lactating dairy cows receiving various reproductive management systems for timed insemination
Treatment (n)
Control (n)
Treatment (Percent pregnant to AI)
Control (Percent pregnant to AI)
References
Presynch-12d/Ovsynch (269) Presynch-12d/Ovsynch (304) 11-Day Presynch (410) 33-Day Resynch (180) 38-Day Resynch (GnRH (357)/CIDR (316))
Ovsynch (274) Ovsynch (310) 14-Day Presynch (412) 26-Day Resynch (189) 38-Day Resynch (386)
48.3 46.8 40.5 39.4 33.6/31.3
36.9 37.5 33.5 28.6 24.6
Moreira et al. (2001) El-Zarkouny et al. (2004) Galvao et al. (2007) Sterry et al. (2006) Dewey et al. (2009)
AI, artificial insemination; CIDR, controlled intravaginal drug release; GnRH, gonadotropin-releasing hormone.
the reasons outlined above, when the Ovsynch protocol is initiated in early diestrus (Table 1). Dairy producers were keen to extend the period when Ovsynch was initiated to a 14-day interval such that four of the five sequential hormonal injections would be given on the same day of week. Field experiences indicate that 60% of detected estruses occur on days 3–6 after the second injection of PGF2 of presynchronization. A recent study indicated that an 11-day interval after presynchronization (i.e., cows would be predominately 5–8 days of the estrous cycle) is better than a 14-day interval to begin the TAI protocol. The overall ovulation rate in response to the first injection of GnRH was greater for an 11-day than a 14-day interval (62 vs. 44.7%). This was attributed to GnRH being given at 11 days when the first wave follicle will ovulate whereas the 14-day interval increased the proportion of cows injected early in the second follicle wave at a time the follicle was developed insufficiently to ovulate in response to GnRH. The latter follicle would continue to develop and be slightly more aged and/or dominant compared to the newly recruited follicle from the day 11 injection interval for GnRH. Indeed pregnancy per TAI was 6.6% greater for the 11-day interval (40.1 vs. 33.5% at day 38 after TAI; Table 1). Thus, subtle changes in presynchronization protocols can cause substantial increases in pregnancy rate, and the optimal period to start the Ovsynch protocol is 10–12 days after the second PGF2 injection of presynchronization (Figure 2).
after the injection of GnRH. In contrast, percent pregnant to AI was decreased when inseminations were made at the time of GnRH injection or 28 h later. Producers often favor the convenience of carrying out a TAI at the time of GnRH injection (i.e., referred to as a Co-synch program) to reduce the number of times cows need to be held up. Alternatively, some producers prefer to perform TAI on the following day at approximately 24–28 h after the GnRH injection for convenience. Either option likely will reduce percent pregnant to AI. The importance of the correct timing is indicated by a study completed at the University of Wisconsin. All cows were presynchronized with two injections of PGF2, and the Ovsynch protocol was started 11 days later. The optimal timing program was to inject GnRH 56 h after the injection of PGF2 and inseminate the cows 16 h after the injection of GnRH, which was 72 h after the injection of PGF2 (see Figure 2). Percent pregnant to AI was 36.1% compared to Co-synch 48 h (26.7%) and to 72 h (27.3%) programs. The last two programs injected GnRH and TAI concurrently at 48 or 72 h, respectively. Clearly, subtle changes in the timing of the GnRH injection and time of insemination result in substantial differences in percent pregnant to AI responses. If a Co-synch program is to be followed, one needs to understand the physiology of the injection sequence so that functionally active ovarian follicles are at an optimal stage analogous to a follicle in the close periestrus period when GnRH/TAI is performed.
Interval from PGF2 to Ovulatory Injection of GnRH and Timing of AI
Resynchronization of Nonpregnant Cows Following First Service
It has been well documented that cows should be inseminated 8–16 h after the onset of estrus for an optimal conception rate. The preovulatory surge of luteinizing hormone (LH) occurs very close to the onset of estrus with ovulation occurring approximately 28 h after the LH surge. It is important to recognize that the second injection of GnRH of an Ovsynch program is analogous to the onset of estrus since an LH surge is induced immediately. Indeed maximal rate of pregnancies per artificial insemination (AI) was achieved when a timed insemination was made at 16 h
A reproductive management challenge following first service is to reinseminate cows that did not conceive as quickly as possible. The same principles to optimize the Presynch–Ovsynch program are applicable to development of a resynchronization program. However, a resynchronization system is somewhat constrained in that programming nonpregnant cows to ovulate must be done in a manner that will not interfere with cows that are pregnant to first service. Thus, accurate identification of nonpregnant and pregnant cows is important, and timing
Reproduction, Events and Management | Control of Estrous Cycles 457
of the diagnosis is dependent upon the technology applied (i.e., rectal palpation at 35–42 days, ultrasound diagnosis at 30–32 days, blood pregnancy test at 27–30 days (measurement of PAG)). To some degree, there is a natural presynchronization of nonpregnant cows because those detected in estrus have a median return to estrus interval of 22 days in which 64.3% show estrus within 17–24 days after first service. Thus, initiation of Ovsynch at 30 days after first service would mean most cows would be at approximately day 8 of the cycle. GnRH injection would induce ovulation of a first wave follicle and initiate recruitment of a new follicular wave under a high progesterone environment. At 37 days after first service, a decision can be made to inject PGF2 in cows diagnosed nonpregnant (e.g., rectal palpation). These cows would then be injected with GnRH and TAI at 56 and 72 h after the PGF2 injection, respectively. Several days after first service (days 19, 26, and 33) have been examined to begin resynchronization of nonpregnant cows with Ovsynch. Starting resynchronization on day 33 resulted in the highest pregnancy rate for the second service. Ultrasound technology was used for detection of nonpregnant cows at day 26 or day 33 after first service for the day 19–26 and 33 resynchronization groups, respectively. Hypothetically, the timing of GnRH at day 26 would tend to target the majority of cows too early in their follicle wave (i.e., day 4 of the wave) to induce follicle turnover, whereas at day 33 they would be ovulating potential first or second wave follicles and a sustained progesterone environment would be present for cows potentially returning to estrus between 17 and 24 days after first service. Experimental results clearly document that fertility was increased for the day 33 resynchronization group (i.e., 33.7%) compared to the day 19 and 26 groups (27.1 and 26.6%, respectively). The benefit of the day 33
resynchronization on pregnancy per TAI compared to the day 26 resynchronization group was repeated (39.4 vs. 28.6%; Table 1) with the benefit most apparent in primiparous cows. In the latter study, insertion of a CIDR insert in cows without a CL improved pregnancy rate per TAI in the multiparous cows to a level comparable to that of primiparous with or without a CL. An alternative resynchronization strategy is a more conventional system based solely on pregnancy diagnosis per rectal palpation at day 38 (Figure 3). In this scenario, an Ovsynch 72 h Co-synch (GnRH, 7 days later PGF, and 72 h later GnRH and TAI) was initiated at day 38 after first service in three groups of nonpregnant cows (Group 1: control, GnRH; Group 2: received a GnRH injection on day 31 at 7 days before pregnancy diagnosis; Group 3: received a CIDR insert on day 38 that was removed at the time of PGF2 injection; Figure 3). Pregnancy rate per TAI was greater and tended to be greater for GnRH/Group 2 (33.6%) and Group 3/CIDR (31.3%) cows than Group 1 (24.6%) cows (Table 1). It is likely that presynchronization with a single injection of GnRH at day 31 programmed a new follicle wave and increased the occurrence of a CL at the beginning of the Ovsynch 72 h Co-synch protocol. Insertion of a CIDR insert likely improved the synchronization of ovulation associated with the 72 h Co-synch response because it held ovarian follicles from ovulating prematurely in cows that were in late diestrus at the time the Ovsynch 72 h program was started. It is clear that several alternatives are available for resynchronization of lactating dairy cows. With the acquisition of new technology for a cow side diagnosis of nonpregnant cows early after insemination (e.g., 27, 28, or 30 days), it will be possible to implement even earlier resynchronization systems for TAI within 3 days (e.g., day
Figure 3 Resynchronizations of cows diagnosed nonpregnant at 38 days after first AI. AI, artificial insemination; CIDR insert, controlled intravaginal drug release insert GnRH, gonadotropin-releasing hormone; NP, nonpregnant; PGF2, prostaglandin F2; TAI, timed artificial insemination.
458 Reproduction, Events and Management | Control of Estrous Cycles
30, 31, or 33) after the diagnosis of a nonpregnancy. This would offer a reduction in reinsemination interval of 9.5–17 days compared to the promising systems described above.
Timed Artificial Insemination for Dairy Heifers A major limitation for using AI in dairy replacement heifers is time and effort associated with daily estrus detection. Unfortunately, however, the Ovsynch has resulted in unacceptable pregnancy rates of approximately 38% in dairy heifers (Table 2). Compared to lactating cows, heifers have a faster rate of follicular growth and a higher frequency of three wave follicular cycles. Consequently, approximately 57% of the cycle is comprised of times when follicles are unresponsive to the first injection of GnRH. Furthermore, rapid turnover and growth of follicles lead to asynchrony with heifers expressing estrus during different stages of the protocol prior to the second ovulatory injection of GnRH for TAI. Investigators at Ohio State University working with beef cattle deduced that an increase in percent pregnant per TAI could be achieved by insertion of a CIDR insert at the time of GnRH injection and, after
5 days, withdrawing the CIDR insert and injecting PGF2. An extended proestrus period was achieved by allowing a 3-day interval from the time of PGF2 injection to the time of GnRH injection and a concurrent TAI. The entire protocol takes only 8 days to be accomplished. Since the interval from the first GnRH injection and CIDR insertion to PGF2 injection is 5 days, a second injection of PGF2 was given 12 h after the first PGF2. This program in beef cows resulted in a higher pregnancy rate compared to a 7-day Ovsynch with a CIDR in which the second GnRH and TAI occurred at 60 h. This program has been further modified for use in dairy heifers in which only a single injection of PGF2 is given at the time of CIDR removal (5-day CIDR Co-synch 72 h with one injection of PGF2; Figure 4). Pregnancy rates to first and second services at 32 days after TAI were 60.3 and 52.5%, respectively (Figure 4). Essentially, 81% (337/416) of the heifers were pregnant after two programmed TAIs following a 5-day CIDR Co-synch 72 h with one injection of PGF2. This is an efficient reproductive management program that successfully synchronizes ovulation for TAI and reduces labor costs associated with estrus detection. Indeed all of the TAI procedures described in Table 2 incorporated some degree of estrus
Table 2 TAI in dairy heifers Protocol
n
Percent pregnant to AI
References
Ovsynch Ovsynch Ovsynch 6-Day Co-synch 48 h 6-Day Co-synch 48 h 6-Day Co-synch 48 h + CIDR 6-Day Co-synch 48 h Overall
187 77 113 175 95 94 82 823
45.5 35.1 42.5 34.3 29.5 31.9 45.1 38.3
Schmitt et al. (1996) Pursley et al. (1997) Stevenson et al. (2000) Rivera et al. (2004) Rivera et al. (2005) Rivera et al. (2005) Rivera et al. (2006)
AI, artificial insemination; TAI, timed artificial insemination.
Figure 4 Pregnancy rate of dairy heifers to a 5-day CIDR Co-synch 72 h with one injection of PGF2. AI, artificial insemination; CIDR, controlled intravaginal drug release; GnRH, gonadotropin-releasing hormone; PGF2, prostaglandin F2; TAI, timed artificial insemination.
Reproduction, Events and Management | Control of Estrous Cycles 459
detection that is not necessary with the present program. The concept of a 5-day interval between GnRH and PGF2 (i.e., with or without a CIDR insert) and a subsequent 3-day proestrus period (i.e., 72 h Co-synch) warrants investigation in lactating dairy cows.
Conclusion Tremendous advances have been made in improving milk production, but have in turn resulted in an overall decline in reproductive efficiency for the dairy industry. Problems associated with the cow include inability to properly express estrus and altered hormonal profiles resulting in low conception rates and increased early embryonic death. Coordinated systems of reproductive management offer means to improve herd reproductive performance, and major advances have been made for synchronization of ovulation in both lactating dairy cows and dairy heifers. Such systems are predicated on a greater understanding of the factors controlling follicle development, ovulation, and CL development. The programs as described require the producer, veterinarian, and reproductive management staff to understand the programs and make an effort to obtain a high level of compliance. The platforms used for controlling first service and resynchronized subsequent services in cows that do not conceive provide valuable platforms to implement new technology such as the use of sexed semen, embryo transfer, and cow-side chemical diagnosis of nonpregnant cows. Functional and efficient computer record programs are essential to implement such reproductive management programs. For the research scientist, the reproductive management systems provide the infrastructure to quantify the effects of nutritional, health, and physiological interventions on pregnancy rate. With the advent of new technologies to precisely manipulate reproductive function in lactating dairy cows, dairy producers are presented with a new opportunity. Coordination of management strategies to maximize both milk production and reproductive performance may optimize the economical return of dairy herds, and allow the industry to take complete advantage of the genetic potential to improve milk production through AI. See also: Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Estrous Cycles: Characteristics; Estrous Cycles: Postpartum Cyclicity; Estrous Cycles: Puberty; Estrous Cycles: Seasonal Breeders; Mating Management: Artificial Insemination, Utilization; Mating Management: Detection of Estrus; Mating Management: Fertility; Pregnancy: Characteristics; Pregnancy: Parturition;
Pregnancy: Periparturient Disorders; Pregnancy: Physiology.
Further Reading Bartolome JA, Sozzi A, McHale J, et al. (2005) Resynchronization of ovulation and timed insemination in lactating dairy cows, II: Assigning protocols according to stages of the estrous cycle, or presence of ovarian cysts or anestrus. Theriogenology 63(6): 1628–1642. Bridges GA, Helser LA, Grum DE, Mussard ML, Gasser CL, and Day ML (2008) Decreasing the interval between GnRH and PGF2alpha from 7 to 5 days and lengthening proestrus increases timed-AI pregnancy rates in beef cows. Theriogenology 69(7): 843–851. Brusveen DJ, Cunha AP, Silva CD, et al. (2008) Altering the time of the second gonadotropin-releasing hormone injection and artificial insemination (AI) during Ovsynch affects pregnancies per AI in lactating dairy cows. Journal of Dairy Science 91(3): 1044–1052. Dewey ST, Mendonc¸a LG, Lopes G, Jr., et al. (2009) Resynchronization strategies to improve fertility in lactating dairy cows utilizing a presynchronization injection of GnRH or supplemental progesterone: I. Pregnancy rates and ovarian responses. Journal of Dairy Science 92(supplement 1): 267; Abstract. El-Zarkouny SZ, Cartmill JA, Hensley BA, and Stevenson JS (2004) Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone. Journal of Dairy Science 87(4): 1024–1037. Fricke PM, Caraviello DZ, Weigel KA, and Welle ML (2003) Fertility of dairy cows after resynchronization of ovulation at three intervals following first timed insemination. Journal of Dairy Science 86(12): 3941–3950. Galva˜o KN, Filho MFS, and Santos JEP (2007) Reducing the interval from presynchronization to initiation of timed artificial insemination improves fertility in dairy cows. Journal of Dairy Science 90(9): 4212–4218. Lopez H, Caraviello DZ, Satter LD, Fricke PM, and Wiltbank MC (2005) Relationship between level of milk production and multiple ovulations in lactating dairy cows. Journal of Dairy Science 88(8): 2783–2793. Lopez H, Satter LD, and Wiltbank MC (2004) Relationship between level of milk production and estrous behavior of lactating dairy cows. Animal Reproduction Science 81(3–4): 209–223. Lucy MC (2001) Reproductive loss in high-producing dairy cattle: Where will it end? Journal of Dairy Science 84(6): 1277–1293. Moore K and Thatcher WW (2006) Major advances associated with reproduction in dairy cattle. Journal of Dairy Science 89(4): 1254–1266. Moreira F, Orlandi C, Risco CA, Mattos R, Lopes F, and Thatcher WW (2001) Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. Journal of Dairy Science 84(7): 1646–1659. Norman HD, Wright JR, Hubbard SM, Kuhn MT, and Miller RH (2007) Genetic selection for reproduction: Current reproductive status of the national herd; Application of selection indexes for dairy producers. In: Thatcher WW and Jordan ER (eds.) Proceedings of the Dairy Cattle Reproductive Conference, pp. 69–78. Hartland, WI: Dairy Cattle Reproductive Council. Pursley JR, Kosorok MR, and Wiltbank MC (1997) Reproductive management of lactating dairy cows using synchronization of ovulation. Journal of Dairy Science 80(2): 301–306. Pursley JR, Wiltbank MC, Stevenson JS, Ottobre JS, Garverick HA, and Anderson LL (1997) Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus. Journal of Dairy Science 80(2): 295–300. Rabaglino MB, Risco CA, Thatcher MJ, Kim IH, Santos JEP, and Thatcher WW (2009) Application of one injection of PGF2 in the 5 d Co-Synch + CIDR protocol for estrous synchronization and resynchronization of dairy heifers. Journal of Dairy Science 93(3): 1050–1058.
460 Reproduction, Events and Management | Control of Estrous Cycles Savio JD, Keenan L, Boland MP, and Roche JF (1988) Pattern of growth of dominant follicles during the oestrous cycle of heifers. Journal of Reproduction and Fertility 83(2): 663–671. Schmitt EJ, Diaz T, Drost M, and Thatcher WW (1996) Use of a gonadotropin-releasing hormone agonist or human chorionic gonadotropin for timed insemination in cattle. Journal of Animal Science 74(5): 1084–1091. Silva E, Sterry RA, Kolb D, et al. (2007) Accuracy of a pregnancyassociated glycoprotein ELISA to determine pregnancy status of
lactating dairy cows twenty-seven days after timed artificial insemination. Journal of Dairy Science 90(10): 4612–4622. Sterry RA, Welle ML, and Fricke PM (2006) Effect of interval from timed artificial insemination to initiation of resynchronization of ovulation on fertility of lactating dairy cows. Journal of Dairy Science 89(6): 2099–2109. Stevenson JS, Smith JF, and Hawkins DE (2000) Reproductive outcomes for dairy heifers treated with combinations of prostaglandin F2alpha, norgestomet, and gonadotropin-releasing hormone. Journal of Dairy Science 83(9): 2008–2015.
Mating Management: Detection of Estrus R L Nebel and C M Jones, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA Z Roth, The Hebrew University of Jerusalem, Rehovot, Israel ª 2011 Elsevier Ltd. All rights reserved.
Introduction Estrus detection is one of the key components in fertility management programs on dairy farms. Excellent reproductive performance can be defined as the ability to consistently have 90% or more of the cows in a herd conceive and maintain pregnancies in a timely, economically justified manner. On the other hand, low detection rate is strongly associated with poor fertility, long calving interval, intensive replacement of heifers, and reduced genetic progress, resulting in heavy economic losses. Maintaining a consistently high-performing reproductive program requires a substantial investment in management, labor, and other costs, such as semen and pharmaceuticals. The goal of an estrus detection program should be to identify estrus positively and accurately in all cycling cows and to identify all of the cows that are not cycling or are expressing irregular cyclicity. The ultimate goal should be to predict the time of ovulation, thus allowing for insemination that will maximize the opportunity for conception. Dairy farming is one of the most intensive technologically integrated systems in the world of production agriculture. In general, the market sorts out which technologies offer a competitive advantage and which do not. Most of the aids that have been developed are not reliable or sensitive enough to relieve the farmer from frequent visual observation of the herd. Furthermore, none of the technologies is appropriate for every farm. New approaches are being developed to provide automated systems for estrus detection using remote-sensing technology, but the development of these new tools is in its infancy.
silent ovulation (i.e., ovulation without the expression of estrous behavior), which occurs mostly during the postpartum period. Occasionally, pregnant cows exhibit signs of estrus, particularly during middle to late gestation. Also, cows with ovarian follicular cysts may have a hormonal milieu that leads to estrous behavior similar to that of cyclic cows in estrus. Therefore, estrous behaviors other than ‘standing’ are crucial for accurate identification of estrus coincident with ovulation. Secondary signs of estrus include attempting to mount other cows, clear mucus discharge from the vulva, swelling and reddening of the vulva from increased blood flow, bellowing, restlessness, trailing other cows, chin resting, sniffing the genitalia of other cows, and lip curling. These signs may serve as clues that cows are near estrus so that they can then be observed more intensely for ‘standing’ behavior, but cannot be used as a practical predictor of ovulation. Other characteristics are reduction in food intake followed by reduced milk production during estrus, but these are not overt in all animals. The time of the day and duration of observation are the most important factors for a high detection rate. Traditional management of visual estrus detection is based on a twice-a-day detection regime or observation (20 min each) 3 times a day while taking into account the aforementioned primary and secondary signs of estrous characteristics. Observations are mostly performed in coincidence with each milking. Additional observations are recommended during periods of high activity, such as feeding time or while going to and coming back from the milking parlor. Nevertheless, estrus detection rate in dairy cows is low (<50%) because of limited observation times and the fact that high-yielding dairy cows express shorter duration of estrus.
Behavioral Characteristics of Estrus The expression of estrous behavior is brought about by high systemic concentrations of estradiol-17 produced by the preovulatory follicle, which stimulates behavior coincident with the ovulatory surge of luteinizing hormone. Traditionally, a cow that ‘stands’ to be mounted is the most definitive behavioral sign of estrus, in particular when reproductive management is based only on artificial insemination (AI). However, ‘standing’ cannot be the only distinguishing sign of estrus. This is particularly true for
Automated Systems to Detect Physical Activity Various approaches have been examined to detect the accurate time of estrus. It includes monitoring of electrical resistance, vaginal and core body temperatures, and progesterone level in plasma or milk, but none of them have yet been implemented in practice. Determination of the onset of estrus is only possible with continuous monitoring for behavioral activity. Based on this concept, few
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techniques have been developed. The ideal aid should provide continuous surveillance (24 h day 1) of cows, and accurate and automatic identification of the cows in estrus. Time-Lapse Video Recording Video recording allows continuous monitoring of behavioral activity. Investigations revealed that cows spent considerably more time walking when in estrus, and less time resting and eating, than when they were not in estrus. Studies with advanced video equipment tested the hourly distribution of onset of estrus. Pooled 6-h intervals demonstrated that the highest frequency of onset of estrus occurs at 1200–1800 and 0600–1200 h in primiparous and multiparous groups, respectively. For a large herd, more cameras are needed because of the resolution of the equipment. Recognition of cows can sometimes be problematic. In addition, the time needed to watch video tapes makes this method not very practical. Time-lapse video recording is mostly used for research rather than for estrus detection in farms. Pedometer
Steps h–1
A pedometer is an electronic device attached to the cow’s leg or its neck collar, which measures cow activity (number of steps) in a 24-h day. The potentially useful field application of pedometry is based on the recognition that female mammals display a predictable increase in physical activity when in estrus. Guernsey cows equipped with
mechanically activated pedometers were characterized as exhibiting 218% higher physical activity during estrus than during late diestrus and proestrus or during metestrus. Similarly, pedometer has been found to be a practical tool for estrus detection in dairy cows with an average 393% increase in activity at the time of estrus, or approximately 4 times the activity of cows not in estrus when housed in a freestall barn. Individual cows differ significantly in the amount of activity expressed under the same conditions. A modified pedometer was designed to internally compare the activity change during a specific time interval to the five previous morning or afternoon activity recordings. This modification was implemented to account for the individual activity. Figure 1 represents a typical activity graph for a complete lactation. The aim of most reported applications of pedometers was to improve the rates of estrus detection. It was claimed that 70–80% of cows in estrus are detected by pedometer measurements. Pedometry systems that in addition to efficient and accurate estrus identification allow identification of its onset would increase the usefulness of such technology in animal breeding. However, most current pedometry systems do not use real-time data transfer, thus requiring the activity information to be retrieved by an interrogation device. Since retrieval of activity measurements can be performed 2 or 3 times daily, usually at milking, the effectiveness of determining the timing of insemination is not optimal. An active technology for estrus identification and activity measurements in dairy cows and buffalo was
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Figure 1 Typical activity graph for the first 175 days of lactation. Reproduced with permission from Nebel RL, Altemose DL, Munkittrick TW, Sprecher DJ, and McGilliard ML (1989) Comparisons of eight on-farm milk progesterone tests. Theriogenology 31: 753–764.
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developed in the late 1990s and is already being successfully operated (SCR Engineers Ltd., Israel). The technology is based on an integrated neck tag that includes an acceleration sensor, microprocessor, and memory, which enable the recording of a general activity index, which is stored separately in the tag’s memory for every 2-h period. This separate recording enables monitoring the cow’s activity on a time axis with great accuracy regardless of the time intervals between tag readings. The tag can store data for up to 24 h. The identification unit (‘Heatime’) is based on an infrared communication method that enables reliable communication. A recent study reported reliability of estrus detection in Holstein heifers with 100% efficiency and 83% accuracy at 1.4 times the threshold value for a 7-day reference period by using a novel radiotelemetric leg pedometer (Gyuho, Comtec, Miyazaki, Japan). The pedometer, powered by a replaceable lithium battery, automatically counted the number of signals generated in 1-h intervals using a pendulum switch (MK-060; Yamasa Tokei, Japan) and temporarily stored the data, which were then read by telemetric receiver (reading ability of 150 m distance) and transferred to a desktop computer. Pedometry systems that allow prediction of ovulation in addition to efficient and accurate estrus identification will increase the usefulness of such technologies in animal breeding. A study examining the relationship between estrous behavioral parameters, pedometer recordings, and time of ovulation revealed that the increase in the number of steps preceding ovulation, as recorded by the pedometer, rather than other behavioral signs of estrus, could be used to detect estrus and to predict time of ovulation fairly accurately. Cows were equipped with pedometers (Nedap Agri B.V., Groenlo, The Netherlands) that stored number of steps in a 2-h period. Ovaries were examined rectally using an ultrasound scanner. The average interval between onset of pedometer estrus and ovulation was 29.3 3.9 h and ovulation occurred 19.4 4.4 h after the end of pedometer estrus. The interval between onset of pedometer estrus and time of ovulation did not differ between primiparous and multiparous cows. However, the interval between end of pedometer estrus and time of ovulation was shorter for primiparous cows (16.9 3.0 h) than for multiparous cows (20.6 4.5 h), most likely due to the longer duration of estrus in the former. Since the optimal time of AI was found to be 24–12 h before ovulation, based on the above data, inseminations should be performed 5–17 h after the onset of increased activity. Despite the large variation in times from pedometer estrus to ovulation, the pedometer appears to be a promising tool for practical prediction of ovulation as long as the threshold for increased activity is based on the cows’ individual activity patterns, and hence could be a tool for improving fertilization rate.
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The growing use of computerized dairy management systems and the accurate recording of cow activity by the pedometer system have created new opportunities for the use of cow locomotors as a means of improving the management of both beef and dairy herds. This approach was recently developed by a group of Israeli scientists. Data from serial independent field studies demonstrated that activity data provided by a pedometer system (S.A.E. Tzacham Afikim, Israel) can serve as a predictor of health problems or stress. Significant differences between pedometric activity of sick and healthy cows were reported in the same herd. It was found that during ketosis, left displaced abomasums, and digestive disorders, walking activity declined several days before the decline in milk production or diagnosis by the herd practitioner. This approach is highly relevant for the early detection of lameness. Clinical lameness causes considerable financial losses for the dairy farm, mostly due to decreased production and delayed estrus and conception. Examination of the pedometer’s efficacy at predicting lameness earlier than the appearance of its clinical signs revealed that 46% of the lame cows showed a reduction in pedometric activity (5% or more compared to the average activity recorded through the previous 10 days), 7–10 days prior to the appearance of clinical signs. Given the vast opportunities to improve management routines via the detection of behavior variables, a new behavior sensor has been recently developed by S.A.E. (Tzacham Afikim), which, in addition to activity (number of steps) for estrus detection, also measures cumulative lying time and lying bouts. For example, this sensor enables the identification of behavioral changes that could indicate calving within 24 h. Pressure-Sensing Radiotelemetric System Radiofrequency data communications is the base technology employed by the commercially available pressure-sensing radiotelemetric HeatWatch system (DDx Inc., Denver, CO, USA) shown in Figure 2. A radiotelemetric device attached to each cow consists of a miniaturized radiowave transmitter, powered by a lithium 3-V battery and linked to a pressure sensor enclosed in a hard plastic case that is 5.3 8.1 cm and 1.8 cm in height. Each device is secured in a waterresistant pouch, attached to a saddle-shaped nylon mesh patch that is glued with contact-type adhesive to the hair caudal to the sacral region. Activation of the pressure sensor by weight of a mounting herdmate for a minimum of 2 s produces a radiowave transmission (0.4 km range). Transmitted data consist of sensor identification, date (month, day, and year), time (hour and minute), and duration of sensor activation (seconds). Transmitted signals are sent to a microcomputer via a fixed radio antenna. The remote signal receiver should
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Factors That Affect Estrous Behavior
Transmitter Receiver Repeater
Most of the older studies report a mean duration of estrus around 18 h; however, recent reports indicate a decrease in ‘standing heat’, to as low as 37% with shorter periods of around 13 h and, in some cases, as short as 4 h. While not clear enough, various physiological or management factors and health-related problems should also be taken into account.
Buffer
High Milk Yield
Computer
Figure 2 Configuration of the radiotelemetric HeatWatch system.
be centrally located on each farm to maximize transmission area and situated to minimize transmission interference. Transmitted data from a remote receiver are chronologically stored in a buffer external to the microcomputer and transferred to the microcomputer upon software request. The software generates both fixed management reports and individual cow files, which can be viewed or printed. Using the radiotelemetric system to monitor mounting activity and ultrasonography to determine the time of ovulation, a significant positive relationship between duration of estrus and time of ovulation was reported. A prolonged duration of mounting activity was associated with an extended interval from first mount to ovulation. However, this relationship existed over a relatively brief time interval (25 34 h); therefore, differences in the duration of estrus would have limited importance in the timing of AI and did not have a significant effect on conception rate. Duration of estrus, defined as the time interval from first to last standing event recorded by the radiotelemetric system, averaged 7.1 5.4 h for 2055 estrous periods. The duration of estrus varies greatly not only among cows in the same herd but also among different studies (Table 1). Differences in age, herd size, management conditions, frequency of observation, and definition of onset of estrus may account for most of the variation in the duration of estrus among studies.
An increased level of milk production has been reported to inversely affect the duration and intensity of estrus and has been related to decreased estradiol concentration in the serum. Since estrogen acts by inducing estrus, both reduced estradiol production and metabolic clearance of estradiol related to high production could account for the inverse correlation between milk level and physical expression of estrus. Postpartum Period The postpartum period is critical for efficient reproduction. The occurrence of silent ovulation during the postpartum period is common for the first ovulation following calving. Without progesterone priming, ovulation will occur without clearly expressed behavior. Silent estrus is also related to the extent and duration of negative energy balance and loss of body condition during the transition period or approximately the first 30 days postpartum. Documentation of silent ovulation has been based on endocrine assay and visual observation, including video recording, combined with additional information provided by techniques such as rectal palpation, the use of marker animals, animal activity, and milk–temperature measurements. A recent study using radiotelemetry (HeatWatch System) that allowed continuous monitoring of cow mounting activity to identify mount acceptance by estral animals and frequent blood collection for progesterone analysis characterized 22% of all ovulations during the postpartum period as being silent ovulations. If visual observations for the detection of
Table 1 Characteristics of estrus and conception rates (least square means standard error) for Holstein and Jersey cows and heifers continuously monitored by a rump-mounted pressuresensitive radiotelemetric system Estrous periods (n) Cows Holstein Jersey Helfers Holstein Jersey
Standing events (n)
Estrous duration (h)
Conception rate (%)
845 410
8.8 1.7 123 1.4
7.2 0.31 8.8 0.37
47 1.5 53 1.1
355 166
23.6 1.3 38.8 1.2
10.7 0.39 125 0.51
66 1.11 56 0.9
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estrus were the only criteria for determination, 62% of all ovulations during the postpartum period would have been classified as silent ovulations. However, many ovulations were associated with fewer mounts accepted by the estral cow and were of shorter duration than mounts accepted at the time of subsequent ovulation.
Circadian Rhythm Conflicting data concerning diurnal and nocturnal estral activities are found in the literature. While the factors underlying these discrepancies are probably complex, direct or indirect effects on estral expression may be predominant. If estral activities are light-mediated, then suppression of estrus expression would be expected during the nocturnal period. Using the radiotelemetric system to monitor mounting activity in pasture-fed cows, the onset of estrus and total mounting activity were found to be equally distributed throughout the day when grouped into 6-h periods. However, individual hourly variation did occur, with the greatest number of first mounts or onset of estrus occurring between 1200 and 1500 and between 2100 and 2300 h. Total mounting activity did not parallel the hourly distribution of onset of estrus and was more evenly distributed throughout the day, despite a trend toward more mounting activity in the afternoon.
Management Problems
Conception rate (%)
The simultaneous presence of other animals in estrus affords the opportunity of sharing estrous behavior. As a consequence, behavioral signs of estrus involving interactions between cows, such as standing heat, are affected by the number of cows in estrus at any given time. Total herd size as well as milking herd size is an important factor in mating management. A minimum of two cows near or at estrus is required to identify clear estrous behavior. Having few cows in estrus might have an amplifying effect on mounting activity. Small herds are characterized by a low number of mounts per cow in estrus and lack of standing activity, most likely due to the absence of cow– cow interactions.
When housed in comfort stalls, cows were about 2.76 times more active during estrus, indicating that the type of housing influences the magnitude of the change in physical activity. The type of floor can also influence mounting behavior. For example, slippery, wet, or concrete floors are not conducive to mounting, while a dirt floor or thick straw bedding is preferred. Studies in heifers have shown that detection indices by pedometer systems (Gyuho, Comtec, Miyazaki, Japan) were influenced by the location of pedometer attachment (neck or leg) and rearing condition (grazing, paddock, tie stole) with a high value for leg pedometer in paddock rearing condition. Seasonal variation in ambient temperature, photoperiod, and humidity can influence estrous behavior. Heat stress lengthens the estrous cycle and decreases the duration and the intensity of estrus. Estrus can be 20–30% longer in temperate or moderate climates than in very hot or cold weather. Combinations of different detection systems, including modern cooling systems, have been reported as a better strategy than the use of a single system in order to increase estrus detection and conception rates. When more than one system was used, a higher conception rate was obtained under summer conditions. Therefore, this strategy should be included in dairy herd management programs. It should be noted, however, that stresses other than heat stress can promote a decline in normal forms of estrous behavior. Different daily activities such as walking to the milking parlor, cleaning the resting area, or number of feedings can also affect estrous behavior. Physical discomfort or social stress caused by moving cows from their original groups can result in altered behavior and production performance.
Estrus Detection and Prediction of Ovulation and Time of Insemination Several studies have examined the optimal time for insemination relative to the onset of estrus. In one study, each of 17 farms selected a different interval to inseminate cows identified in estrus during the previous 24 h. Pregnancy status was determined by data for return to
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4–8 8–12 12–16 16–20 Interval from first standing event to Al (h)
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Figure 3 Percentage of pregnant cows by 4-h intervals relative to timing of artificial insemination (AI) from first standing event detected by the radiotelemetric HeatWatch system across 17 herds and 2661 inseminations.
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estrus and palpation of the uterus 35–75 days following insemination. The bar graph shown in Figure 3 represents the proportion of pregnant cows for each 4-h interval from first standing event to insemination. Inseminations performed between 4 and 12 h following onset of estrus achieved a conception rate of approximately 50 versus 30% for inseminations performed after 16 h from onset (Figure 3). From previous studies, nearoptimal conception rates would be expected for cows submitted for insemination 12–18 h after detection of estrus. Mathematical modeling to predict the optimal time for AI using activity pedometers and visual signs of estrus estimated 11.8 h from onset as the optimal time for AI, which coincides with the approximate midpoint of the 5 16 h optimum using the HeatWatch System. Since the chance of fertilization strongly depends on the interval from insemination to ovulation, it is reasonable that insemination time be based on time of ovulation rather than detection of estrus. Pedometer activity systems and pressure sensing to monitor mounting activity appear to be promising tools for predicting ovulation and hence could serve for the improvement of fertilization rate. Use of these systems showed that ovulation takes place 22–32 h after the first increase in activity. Since the optimal insemination time is 24–12 h before ovulation, the optimal time of insemination becomes 4 17 h after the increase in locomotive activity or 0–12 h following the first standing event associated with the onset of estrous behavior.
Conclusion Remote-sensing systems for the detection of estrus are expected to be more efficient but not necessarily more accurate than visual observation. Differences in housing and environmental conditions, in addition to labor, cost, and efficacy, have resulted in variable acceptance of remote-sensing technologies. Detection efficiency and accuracy can be improved by the simultaneous use of more than one technology. Combining technologies for simultaneous measurements of several physiological events associated specifically with the onset of estrus and ovulation time should provide more accurate predictions of the optimal time for insemination. Ultimately, herd management must interpret the information
gathered by these technologies and judge whether and when to inseminate the identified cows based on visual inspection. See also: Body Condition: Effects on Health, Milk Production, and Reproduction. Replacement Management in Cattle: Breeding Standards and Pregnancy Management. Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Estrous Cycles: Characteristics; Mating Management: Artificial Insemination, Utilization; Mating Management: Fertility.
Further Reading Allrich RD (1994) Endocrine and neural control of oestrus in dairy cows. Journal of Dairy Science 7: 2738–2744. Arney DR, Kitwood SE, and Phillips CJC (1994) The increase in activity during oestrus in dairy cows. Applied Animal Behavioral Science 40: 211–218. Dransfield MBG, Nebel RL, Pearson RE, and Warnick LD (1998) Timing of insemination for dairy cows identified in oestrus by a radiotelemetric oestrus detection system. Journal of Dairy Science 81: 1874–1882. Hurnik JF, King GJ, and Robertson HA (1975) Oestrous and related behaviour in postpartum Holstein cows. Applied Animal Ethology 2: 55–68. Klemm WR, Rivard GF, and Clement BA (1994) Blood acetaldehyde fluctuates markedly during bovine oestrous cycle. Animal Reproduction Science 35: 9–26. Lehrer AR, Lewis GS, and Aizinbud E (1992) Oestrus detection in cattle: Recent developments. Animal Reproduction Science 28: 355–361. Maatje K, Loeffler SH, and Engel B (1997) Optimal time of insemination in cows that show visual signs of oestrus by estimating onset of oestrus with pedometers. Journal of Dairy Science 80: 1098–1105. Nebel RL, Altemose DL, Munkittrick TW, Sprecher DJ, and McGilliard ML (1989) Comparisons of eight on-farm milk progesterone tests. Theriogenology 31: 753–764. Roelofs JB, van Eerdenburg FJCM, Soede NM, and Kemp B (2005) Pedometer reading for estrous detection and as a predictor for time of ovulation in dairy cattle. Theriogenology 64: 1690–1703. Senger PL (1994) The oestrus detection problem: New concepts, technologies, and possibilities. Journal of Dairy Science 77: 2745–2753. Shipka MP (2000) A note on silent ovulation identified by using radiotelemetry for estrous detection. Applied Animal Behavior 66: 153–159. Van Eerdenburg FJCM (2008) How to beat the bull: Oestrus detection in dairy cattle. Veterinary Quarterly 30(1): 1–97. Walker WL, Nebel RL, and McGilliard ML (1996) Time of ovulation relative to mounting activity in dairy cattle. Journal of Dairy Science 79: 1555–1561.
Mating Management: Artificial Insemination, Utilization M T Kaproth, Genex Cooperative, Ithaca, NY, USA R H Foote, Cornell University, Ithaca, NY, USA ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by R.H. Foote, Volume 3, pp 1764–1770, ª 2002, Elsevier Ltd.
Introduction Artificial insemination (AI) of cattle represents the most successful sophisticated program of animal breeding ever implemented to improve the quality, productivity, and reproductive health of dairy cattle and other farm animals. This article, in conjunction with other articles on AI (see Gamete and Embryo Technology: Artificial Insemination), provides an overview of the advanced technology developed, the facilities and management required, and the genetic improvement in cattle as a result of the use of AI during the past half century. Other species are considered briefly. Recent advances in genomics, computerized mating programs, gender sorting of semen, and cloning relevant to AI programs are considered.
Components of a Successful Artificial Insemination Program The key to any successful program is capable, welltrained, and dedicated people. Expertise represented by
number of progey per sire per year ¼
the array of people in AI encompasses geneticists to select bulls, expert bull handlers, semen collectors and laboratory technicians, highly trained field staff, skilled inseminators, and superior farm managers. All require appropriate facilities and equipment to conduct a highquality program. The two major factors responsible for the success of AI are (1) improved reproductive health, particularly through the control of venereal diseases, and (2) genetic improvement in productivity and a reduction in lethal genes. All of the components of AI and their relationship can be quantified by two simple equations. A sire’s genetic contribution will depend upon its genetic superiority and the number of progeny produced: genetic impact per sire ¼ ðgenetic superiority of the sireÞ ð number of progeny per sireÞ ð1Þ
The physiology and management that impact on the number of progeny produced per sire are represented by the equation
ðnumber of sperm harvested per sireÞ ðnumber of sperm inseminated per cowÞ
ð2Þ
ðfraction of the semen used for inseminationÞ ðfertility : % of inseminations producing progenyÞ ð2Þ
All of the improvements in harvesting sperm from the bull, preserving sperm with minimal loss, and skillfully placing the right number of sperm in the well-managed cow at the proper time will affect the number of progeny.
Landmarks in the Development of Artificial Insemination Facilities Early in the development of AI for livestock breeding, facilities were very limited, with a modified existing barn to house bulls, an area equipped to serve as a simple laboratory, and a semen collection chute, often outdoors. Originally, developed around a liquid semen program, regionally sited bull studs were needed. Following the
introduction of semen cryopreservation, nationally sited centers were developed. With sophisticated facilities allowing assured health surveillance, international trade became possible. Semen cryopreservation required special equipment for processing, packaging, storing, and transportation of semen. The equipment developed for bull sperm provides the basis for the worldwide cryopreservation of biologics today (see Gamete and Embryo Technology: Artificial Insemination). Modern facilities that were better, larger, and more expensive emerged. Many small bull studs were merged for efficiency, as climate-controlled bull barns, herd health surveillance and isolation facilities, special semen collection areas, animal clinic areas, and modern laboratory facilities were built by consolidated larger AI organizations. Today in the field, supervisors and
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reproductive specialists help AI technicians and herdsmen to manage the on-farm AI program.
Frozen Semen in the Field Equipment and techniques were developed for handling semen stored in liquid nitrogen at 196 C in the laboratory and moving it safely to the field for each inseminator’s storage unit. Today, inseminating technicians are given special training to handle frozen semen into and out of the liquid nitrogen tank, and to retrieve the proper breeding unit for insemination without exposing the remaining units in storage. Proper handling of frozen semen and maintenance of an unbroken chain of cryogenic temperature (less than 130 C) are important. Otherwise, carefully prepared high-quality sperm could be damaged with resultant lowering of fertility. Proper thaw and insemination methods are discussed later in this article. Inseminations today are performed by both professional inseminators and herdsmen who buy semen from a producer. As herd size has increased, many onfarm inseminators have gained proficiency by inseminating several hundred cows, one or more times.
Farm Facilities and Detection of Estrus Upon adoption of AI, a very important task faced by dairy farmers is accurate detection of estrus, so that cows could be inseminated at the proper time. Extensive efforts are made to ensure that all users of AI implement sound programs for estrus detection. This includes proper identification of each animal (highly visible cow ID), turning out cows in stanchions, and watching of cows for estrus for about 30 min each morning and evening. Some herdsmen manage this program better than others. Many aids for detection of estrus have been developed. Several will be listed here because poor detection of estrus is the largest single cause of prolonged, uneconomic calving intervals (see Reproduction, Events and Management: Mating Management: Detection of Estrus). Estrus detection aids include using surgically altered bulls that could not mate with animals, but could mount and roll colored paint on the rump of animals that stood when they were mounted. Alternatively, a colored crayon or especially brittle paint could be used to stripe the tailhead of any animals due to be inseminated. This stripe is smudged or the paint broken up when that cow is mounted. Different types of pressure-sensitive patches, which are easily attached to the rump, were developed that become more visible when pressed hard by a mounting animal. One version uses small digital radio transmitters incorporating a pressure switch in the tailhead patch. The transmitter monitors mounting activity and transmits the data (cow
ID, date and time of mount, duration of the mount) to the herd computer. Electronic probes to measure changes in electrical resistance of cervical mucus are also effective in revealing changes at estrus. Pedometers of various types record walking activity of the animal, indicated on a mechanical component of the pedometer. More advanced types transmit activity electronically, along with the cow identification, to a receiver. To develop effective estrus detection programs and evaluate their efficiency, it was necessary to monitor the estrous cycle of cows. This became possible with the discovery that the cyclic hormone progesterone could be measured in milk. The milk progesterone followed a similar pattern as blood progesterone, so simply collecting small samples of milk 2 or 3 times per week for progesterone determination permitted the cyclic activity of each cow to be tracked. In addition, this monitoring enabled one to determine missed heats, plus cows that were inseminated at the wrong stage of the estrous cycle or when pregnant. Studies in Israel and at Cornell University have shown that the use of some of these technological aids, plus training of the farm managers and the inseminators, can minimize mating at the incorrect time, and thereby maintain an optimal calving interval. Heifers often are housed in open areas with bulls. However, they should be managed to use AI because more genetic progress is made when they are inseminated with conventional or sexed semen from genetically superior bulls.
Procedures for Artificial Insemination Effective care needs to be taken to prevent temperature fluctuations of thawed semen, abrupt cooling of semen (cold shock), and semen or supplies from sun exposure or warming beyond body temperature. Loading the AI gun should take place in a protected area, free of extreme temperatures and close to the cryostorage unit. All AI should be completed within 15 min of straw thawing. The number of straws thawed at one time is dependent on the quantity that can be used within 15 min. In large herds, teams of inseminators work together to prepare AI guns, and perform AI. Unless specified otherwise, semen should be ‘warmwater thawed’. Some organizations produce semen as straws processed by alternative methods that permit straws to be ‘pocket thawed’ as well as ‘warm-water thawed’. Upon retrieval from the cryostorage unit, straws that require warm-water thawing are thawed in water (0.5 l) in an insulated vessel at 33–35 C for a minimum of 40 s. A maximum of four straws at a time can be thawed in the vessel. This prevents the water temperature from cooling to temperatures below specifications. Straws should be agitated slightly to ensure uniform thawing. Straws that are ‘pocket thawed’ are immediately placed in a folded paper towel for protection following
Reproduction, Events and Management | Mating Management: Artificial Insemination, Utilization
retrieval from the cryostorage unit. After this preparation, straw and towel are placed into a thermally protected pocket. A minimum of 2–3 min of thawing time within the pocket is provided before preparing the AI guns. For retrieval of multiple straws, straws are placed into separate towels to ensure uniform thawing. Straw forceps should be used at all times to prevent contact between bare fingers and the straw. If needed, the temperature of the AI gun is tempered by friction and prior placement within the inseminator’s coveralls. Before sliding the thawed straw into the barrel of the AI gun, the temperature should be checked by touch, as a subjective method to avoid temperature extremes. The loaded gun is covered with a paper towel for insulation while cutting the straw end. A sheath is slid over the loaded gun and is secured. The loaded gun is then placed within a clean breeding glove, providing an added layer of thermal protection, and is finally tucked inside the coveralls. The following is a conventional rectovaginal insemination procedure. Generally, the left arm, covered with a disposable glove and lubricated with mineral oil, enters the rectum. Through the thin tract layers, the cervix is located and grasped. Folded paper toweling is used to spread the vulva, allowing clean entrance of the gun into the vestibule of the vagina. Care is taken to gently manipulate the cervical rings of the lumen over the end of the gun until the gun tip reaches just past the anterior cervical ring. Location of the gun tip in the uterine body is determined with an extremely light touch through the uterine body wall. When satisfied with the position, the outside end of the AI gun is braced on the opposing arm and the plunger is pushed to deliver semen to the uterine body in 3–5 s. The gun tip is not extended past the internal uterine bifurcation to avoid the possibility of any injury to the uterine mucosal tissue. Cows that have been bred once, but then exhibit estrus behavior again should be rebred with caution as an abortion can be initiated in a pregnant female. Therefore, the AI gun should be passed completely through the cervix only if the tract is felt to be typical for a female in normal estrus.
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files of sire information, potential mating sires are selected, emphasizing corrections to worst faults for maximum genetic progress. A very important benefit of using computerized mating program is that it is possible to control and restrict the level of inbreeding in the herd. A mating program will ensure that no member of a three-generation pedigree is duplicated in the mating. This is expected to maintain inbreeding below 6.25%. Furthermore, mating programs can be set up so that embryo losses that result from harmful gene interactions can be avoided. Cattle that carry the same lethal recessive gene should not be mated.
Artificial Insemination in Estrus-synchronized Cattle Several programs have been developed to synchronize estrus and ovulation so that a group of cows can be inseminated at a fixed time. These programs involve the injection of prostaglandin F2 or analogues to regress the corpus luteum (the source of progesterone), and an injection of gonadotropin-releasing hormone (GnRH) to stimulate ovulation (see Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination). In viewing 2008–09 data (500 000+ inseminations) from a company providing extensive professional AI service in US herds, AI to synchronized cattle approximates 27% of total inseminations; however, in many herds, AI to synchronized cattle accounts for 80% of inseminations. Of these AIs, Cosynch and Ovsynch accounted for 25 and 75%, respectively. Differences in fertility (as unadjusted nonreturn rate means) between the two synchronization protocols were essentially zero. An inspection of adjusted fertility rates revealed that AI to synchronized cattle approaches, but does not equal, AI to nonsynchronized cattle (1.5% for probability of conception). There is an interaction of bulls and synchronization. That is, while bulls can be ranked with respect to overall fertility, bulls will rerank in a different order when semen is used on synchronized cattle.
Use of Computerized Mating Programs in Artificial Insemination In dairies that utilize computerized mating programs, each cow in a herd is examined and scored in a linear trait evaluation format. Cows are compared to their contemporaries for each trait and the differences are weighted by the heritability of the specific trait. Deviations from contemporaries are adjusted for the herd’s genetic level. Pedigree information is also included. When a mating is planned, the cow’s complete phenotypic evaluation linear score is viewed and from computer
Use and Efficiency of Artificial Insemination in the United States The changes in dairy cow numbers and the use of AI in the United States are summarized in Table 1. Milk production per cow has tripled since 1925 while the number of cows has been reduced by two-thirds. Consequently, the many fewer cows today produce as much milk nationally as was produced in 1925. This production meets demands as milk consumption per capita has decreased.
470 Reproduction, Events and Management | Mating Management: Artificial Insemination, Utilization Table 1 Dairy and beef cow numbers and the percentage inseminated artificially in the United States Dairy cowsa
Beef cows
Year
Number
Artificially inseminated (%)
Number
Artificially inseminated (%)
1925 1950 1975 2000
25 000 000 21 500 000 12 000 000 9 000 000
0 12 57 65
10 000 000 15 000 000 45 000 000 34 000 000
0 <1 4 10
a Dairy cow numbers do not include heifers; a lower percentage of heifers is inseminated artificially. Data indicate trends only, as precise data are not available for all time periods, particularly with many inseminations by on-farm personnel not reported.
This massive increase in the efficiency of milk production, with fewer cows and 99% fewer bulls used through AI, has saved 25 million tonnes of maize otherwise needed for feed. Along with other improvements in management, it has allowed many producers to become so efficient that they have survived the increased costs of doing business. Economic and organizational efficiencies have resulted in the reduction of the number of AI organizations worldwide. In the United States, there were about 100 AI organizations in the 1940s. Most of these organizations have merged or closed. Today, six AI organizations supply most of the semen for dairy cattle AI.
Extent of Artificial Insemination Worldwide In Table 1 it is shown that about 65% of the cows in the United States are enrolled in an AI program. In many European countries, use of AI is as high as, or higher than, 65%. In Czechoslovakia and Hungary, more than 90% of the dairy cows are artificially inseminated, and in Denmark, Israel, and Japan the proportion of cows impregnated by AI is essentially 100%. The various countries comprising the former USSR also use AI extensively. Most countries rely essentially 100% on frozen semen for cattle. Countries with large dairy cow populations are listed in Table 2. In New Zealand, a majority of cows are inseminated during 2–3 months so that cows will calve and initiate lactation during the excellent pasture season. During this short time, mostly liquid semen is used to meet demands, with 2 000 000 sperm per cow giving acceptable fertility. This permits a few top sires to be scheduled to meet the market demands at low costs of semen processing. Frozen semen is banked at other times, with 20 000 000 sperm per breeding unit, providing more than is necessary to compensate for freezing damage.
Sire and Selection Programs and Genetic Progress The modern progeny test system as a useful genetic program for identifying superior sires for extensive use in AI was developed simultaneously by Henderson at Cornell and by Rendel and Robertson in Scotland. A young bull for progeny testing is produced by inseminating a genetically elite dam with semen from an elite sire. The young bull enters the stud through its isolation facility, enters the production herd, matures and produces semen for progeny testing at about 12–15 months. This semen is used in AI to produce daughters, whose subsequent records for production traits contribute to the production proof of the bull. Bulls being progeny tested are returned to service with a progeny test proof at about 4–5 years of age. The genetic progress, along with levels of milk production, is illustrated in Figure 1. Little genetic progress was made before 1955, but by then a few bulls proven in AI through the progeny testing scheme outlined above were available. Progress has been rapid since 1975 when many tested bulls were available. There is no indication yet that a peak is being reached.
Effect of Genomic Evaluations on Artificial Insemination Utilization Genomic information in cattle is increasing rapidly, aided partly by cross-species homologies. Geneticists working with cooperating AI companies used DNA derived from a pooled frozen library of semen from generations of dairy bulls and the resulting daughters’ milk records. They identified DNA segments associated with phenotypic traits, and this genomics approach, with the application of microarray identification of single nucleotide polymorphisms (SNPs), marker-assisted selection, and other reproductive technologies, has increased the intensity of selection and shortened generation intervals with more
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Table 2 Use of frozen semen in countries reporting 1 500 000 cows artificially inseminated Countrya
Number of dairy and beef cows artificially inseminated
Use of frozen semen (%)
Number of sperm per cow (106)b
Australia Brazil Canada China France Germany Italy Japan Korea Netherlands New Zealand Spain United Kingdom United States
1 600 000 2 860 000 1 500 000 10 000 000 4 800 000 5 600 000 2 450 000 1 600 000 1 600 000 1 650 000 3 800 000 1 800 000 2 600 000 10 500 000
100 100 100 100 90 98 100 99 94 100 37b 95 100 100
20 40 15 20 15 18 20 30 20 20 30 20 20
a
Data from the former USSR were not available, but historically it has been a leader in numbers. For bulls in high demand, the insemination dose may be reduced to 10 million sperm, and with the liquid semen program (63%) in New Zealand only 2 million sperm are used per insemination.
b
Milk, kg per cow (thousands)
10
1200 1000
9
900
8
800
7
700
6
600
5
500
4
400
3
300
2
200
1
100
0
1955
1965
1975 Years
1985
1995
Genetic increase in milk (kg per cow)
11
1300
DHI cows All cows Genetic gain
0
Figure 1 Changes in milk production per cow in all herds and those on test in dairy herd improvement (DHI) in the United States, along with the estimated genetic improvement, primarily as a result of superior sires used in AI.
rapid progress in genetics (see Genetics: Selection: Concepts). Positive identification of a variety of alleles present in newborn animals will assist in selecting those with the greatest promise for transmission of genes associated with desired traits. In the United States, more than 30 000 cattle, primarily Holsteins, have been genotyped since December 2007 for important production traits such as milk, fat, protein, somatic cell score (SCS), and daughter pregnancy rate (DPR). While genomic evaluations have a lower reliability, many outstanding bulls have been identified with genomic evaluations, reflecting several years of added
genetic progress. In 2009, young Holstein bulls with genomic-only evaluations began to be utilized for breeding purposes. Due to lower reliability, the pattern of AI usage is changing to limit the amount of semen used from an individual bull and to utilize semen from much larger groups of bulls. In 2009, a large proportion of semen being utilized for AI in the United States is from bulls with genomic-only evaluations.
Selection and Mating Based upon Multiple Traits Selection of Mating Sires Based on ProductionAssociated Evaluations Much information is collected on sires proven in AI in addition to the milk, butterfat, and protein production of their daughters. Daughters are checked for traits such as body size, leg conformation, mammary gland size, udder support and teat placement, and milking speed. This information is published so that those who wish to select semen from sires that produce daughters with particular strengths besides high milk yield can do so. Bulls that produce small calves are identified, and may be selected to minimize calving difficulties when small heifers are inseminated. The broad scope of possibilities among frozen semen available from many bulls through AI gives the producers almost limitless opportunities to plan a program that meets individual desires. However, when selection is made for more than one trait, the genetic gain for each trait is reduced. The most profitable program for commercial dairy producers is to put major emphasis on milk yield.
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Selection of Mating Sires Based on FertilityAssociated Evaluations Fertility of the bull is important, as high reproductive efficiency is a major factor in the success of the dairy enterprise. Bulls with low fertility are in limited demand, even when genetic merit is high. Semen from low-fertility bulls is seldom used to inseminate repeat breeder cows. AI companies with large numbers of professional inseminator staff can utilize breeding receipt and farm records to provide sophisticated fertility evaluations. For many companies, it is more difficult to obtain such records as the proportion of semen sales directly to farms has grown. National evaluations for sire fertility exist in many countries. From the USDA’s use of milk test records, estimations of sire fertility, as sire conception rate (SCR), are available. SCR results are based on confirmed pregnancies. Important factors that are adjusted include year, herd differences, parity, service number, location, season, milk yield, and sire age. Selection of a mating sire based on its DPR is also possible. A calculated DPR includes calving interval and days open in the calculation. Predicted transmitting abilities (PTAs) for cow fertility traits have high reliabilities only after hundreds of daughters are recorded.
Advanced Reproductive Technologies in Artificial Insemination Multiple Ovulation and Embryo Transfer Multiple ovulation and embryo transfer (MOET) herds are an important source (oocytes, sperm) for elite genetics used in cattle AI. With the introduction of genomic evaluations, newborn cattle of either gender produced in MOET herds are quickly evaluated for their genomic estimated production superiority. While conventional AI provides genetic material from superior males, MOET provides a greater influx of genes into the population from superior females. A genetic evaluation based on MOET-derived cattle is possible. Full brother–sister embryos are produced and transferred. As full brothers and sisters are born at the same time, full sisters can be raised in a sib test to provide contemporary production information for the sires. This decreases the generation interval compared with the progeny test system, although the comparative information is a little less reliable than the progeny test. By harvesting oocytes from juvenile females and fertilizing them in vitro to produce embryos, the generation interval can be further reduced (see Gamete and Embryo Technology: Multiple Ovulation and Embryo Transfer). With MOET programs, animals are usually raised in a central facility. This makes it possible to record multiple production information and related
traits. For example, body and udder conformation and milking speed can be recorded. Such a facility could also use sexed sperm to produce embryos of the desired sex by in vitro fertilization. Embryos produced by any method can presently be sexed and in the future can be tested with DNA analysis, allowing genomic evaluation (see Gamete and Embryo Technology: Sexed Offspring). Also, embryos can be split quite easily with 50% more progeny per donor cow. All these techniques can be combined, and each one adds a small increment to the rate of genetic progress. However, the greatest single component of genetic gain is the use of AI-proven sires. Artificial Insemination with Sexed (GenderSorted) Semen The ability to use sexed semen has been an important development in AI. With ample replacement cattle now available, it is viewed as allowing the dairy herds to obtain their heifers from their best maternal lines, increase calving ease, close their herds if desired for biosecurity (growing from within the herd), and provide an ability to absorb increased culling rates, allowing disposal of problem cows. Sexed semen, however, is expected to have a lower fertility rate (see Gamete and Embryo Technology: Sexed Offspring). For this reason, best results are obtained when breeding heifers exhibiting standing heat. Research is ongoing on whether sorted semen can be economically used in cows. Two types of products are available for AI: 90% gender purity and 75% gender purity. While sorting purity can be achieved for either gender, in the dairy industry it is overwhelmingly desired toward producing female offspring. In 2008, 14% of all USDA-AIPL reported heifer breedings in the United States were with sexed semen AI. During the period from 2006 to 2008, AI with conventional semen in heifers and cows achieved a 56 and 30% conception rate, respectively, while AI with sexed semen achieved 39 and 25%, respectively. In viewing current US data gathered in large commercial herds (188 700+ total professional AIs), AI with sexed semen accounted for 16% of AI and in some herds 100% of heifers are bred with sorted semen. In these herds, use of sorted semen, after adjustments for interactions, was found to reduce the probability of conception by 12.7%. Bulls ranked by overall AI fertility may rerank differently when their semen is sorted. Cloned Sires in Artificial Insemination Currently, there are a few cases where semen for AI is currently being processed from sires produced as clones from deceased genetically evaluated individuals. The
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genetic evaluation of the original sire is utilized as the evaluation for the clone. Currently, cloning is inefficient and expensive. If bulls with rare or unique genes are selected and cloned, the resulting clones can be used to inexpensively disseminate desired genes by AI. Tissue appropriate as a source of cloning could be preserved by cryopreservation for use in cloning.
Artificial Insemination in Beef Cattle and Buffaloes AI and embryo transfer played an important role following limited importation of several European breeds of beef cattle into North America. In some breeds, AI usage was as high as 75% initially, but with expansion it has decreased. The overall estimated usage of AI is shown in Table 1. Beef bulls produce approximately the same number of sperm as dairy bulls. The management of beef sires is similar to that of dairy sires, but owners should not let beef bulls get fat, as sperm output and quality are depressed. Testis size and quality should be measured on all sires. The quality of frozen beef semen varies more than the quality of semen from dairy bulls, probably because much of the frozen beef semen is custom collected, with less culling of bulls for semen quality. The major management difference between dairy and beef is in management of the females. Beef cows and heifers for AI must be confined. Animals should be in good condition. Cows suckling calves, and with poor body condition, have low pregnancy rates. High pregnancy rates in beef cattle are much more important than in dairy cattle, as females with no progeny contribute nothing economically to the beef enterprise. Buffaloes are a major source of meat, milk, and work in many Asian countries where 95% of the world’s
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buffaloes exist. Leading countries include India, Pakistan, China, Nepal, and Thailand. Significant numbers are also found in Romania, Egypt, and Italy (see Animals that Produce Dairy Foods: Water Buffalo). Reliable statistics on the percentages of AI use and results are not available.
Use of Artificial Insemination in Species other than Cattle A summary of the technical feasibility of using AI in several species is given in Table 3. The fastest growing use of AI is in swine. Sows are usually confined; they are easily inseminated. Large breeding and production farms can capitalize on inseminating many more sows with semen from superior boars than through natural mating. In China, 10 000 000 sows are inseminated annually, with an estimated 50 000 000 inseminated worldwide. With liquid semen, pregnancy rates and litter sizes are normal. Freezing boar sperm depresses fertility. The poultry industry also depends essentially 100% upon AI in the industrial breeding flocks to produce hatching eggs for turkeys, broilers, and egg-laying hens. Semen is easily collected. Many caged females per male can be inseminated rapidly with fresh semen once a week with high fertility. This permits selection of the best males to produce the next generation of poultry. Tens of millions of sheep and goats are artificially inseminated worldwide, particularly in Russia, Bulgaria, Romania, China, several other Asian countries, and South America. In western Europe, France is the leading country, where 850 000 sheep are inseminated with liquid semen and 580 000 goats with frozen semen. In Australia, 200 000 ewes are artificially inseminated, particularly in flocks producing rams for sale. The number inseminated
Table 3 Technical feasibility of using AI in species other than cattle Fertility of semen a
Species
Liquid
Frozen
Any limitations
Sheep Goats
Good Good
Poorb Fair
Swine
Good
Fair
Horses
Good
Fair
Turkeys, chickens
Good
Poor
Problem with large ranges. Low value per ewe, so AI costs must be very low Detection of estrus in small herds. Insemination is more difficult. Lack of available semen Supply of liquid semen and rapid transportation is required. Improved detection of estrus in gilts. Cost per sow must be kept low, but this is competitive Long estrus. Multiple inseminations needed. Frozen semen conception rates are reduced. Breed restrictions No limitation in breeding flocks. Use of fresh semen is the method of choice
a Note that cattle have an advantage over other species in number of progeny possible per tested sire per year: cattle, 50 000; sheep and goats, 5000; swine, 2000; horses, 750. The successful development of a frozen semen bank is especially advantageous in seasonal breeders such as sheep, goats, and horses. b Frozen semen can be used successfully provided a laparoscope is used with intrauterine inseminations. AI, artificial insemination.
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with frozen semen has been limited by low fertility, unless intrauterine insemination with the aid of a laparoscope is used. Investigation of AI in the early 1900s was directed toward the horse, but declined as the horse populations decreased on farms. In the United States, horse AI has increased to about 300 000 mares inseminated annually, as several breed associations have revised breed codes to permit registration of foals produced by AI. Lighting is often used to alter the seasonal breeding of mares. The smallest animals where AI is used extensively are laboratory rabbits and foxes. The latter are raised for the fur trade in northern Europe. Deer farming is extensive in a few countries. There are many examples of selective AI used for endangered species in zoos where few males are available, or if females refuse to accept the male. See also: Animals that Produce Dairy Foods: Water Buffalo. Gamete and Embryo Technology: Artificial Insemination; Cloning; Multiple Ovulation and Embryo Transfer; Sexed Offspring; Transgenic Animals. Genetics: Selection: Concepts. Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Mating Management: Detection of Estrus.
Further Reading Bearden HJ and Fuquay JW (2000) Applied Animal Reproduction, 5th edn. Upper Saddle River, NJ: Prentice-Hall. Brackett BJ, Seidel GE, Jr., and Seidel SM (eds.) (1981) New Technologies in Animal Breeding. New York: Academic Press. Davies Morel MCG (1999) Equine Artificial Insemination. Wallingford, UK: CAB International. Foote RH (1999) Artificial insemination from its origins up to today. In: Russo V, Dall ’Olio S, and Fontanesi L (eds.) Proceedings of the Spallanzani Institute Symposium, pp. 23–67. Reggio Emilia, Italy. Foote RH (2002) The history of artificial insemination: Selected notes and notables. Journal of Animal Science 80: 1–10. Foote RH (2003) Fertility estimation: A review of past experience and future prospects. Animal Reproductive Science 75(1–2): 119–139. Gordon IR (2005) Reproductive Technologies in Farm Animals. Wallingford, UK: CAB International. Herman AA (1981) Improving Cattle by the Millions. Columbia, MO: University of Missouri Press. Hutchison JL and Norman HD (2009) Characterization and usage of sexed semen from US field data. Theriogenology 71(1): 48. Johnson LA and Seidel GE, Jr. (2000) Proceedings of the current status of sexing mammalian sperm. Theriogenology 52: 1267–1484. Kaproth MT, Parks JE, Grambo GC, Rycroft HE, Hertyl JA and Gro¨hn YT (2002) Effect of preparing and loading multiple insemination guns on conception rate in two large commercial dairy herds. Theriogenology 57: 909–921. Nicholas FW (1996) Genetic improvement through reproductive technology. Animal Reproductive Science 42: 205–214. O’Brien SJ, Menotti-Raymond M, Murphy WJ, et al. (1999) The promise of comparative genomics in mammals. Science 286: 458–481. Salisbury GW, VanDemark NL, and Lodge JR (1978) Physiology of Reproduction and Artificial Insemination of Cattle, 2nd edn. San Francisco, CA: WH Freeman. Weigel KA, de los Campos G, Gonza´lez-Recio O, et al. (2009) Predictive ability of direct genomic values for lifetime net merit of Holstein sires using selected subsets of single nucleotide polymorphism markers. Journal of Dairy Science 92: 5248–5257.
Mating Management: Fertility M G Diskin, Teagasc, Animal & Grassland Research and Innovation Centre, Mellows Campus, County Galway, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction In dairy cows, reproduction has two major functions: to induce the onset of lactation and to provide replacement animals for the current generation of cows. Consequently, reproductive efficiency is a major factor affecting production and economic efficiency. Over the past four decades, milk yield per cow has increased significantly through genetic selection and improved management. Not withstanding these improvements, there has been a steady decline in reproductive performance of dairy cows coincident with the improvement in yield. The focus of this article is to review the components that determine reproductive efficiency of dairy cows, and to investigate how best to use the new information that has emerged over the last few decades to improve the reproductive management of a herd and consequently its production efficiency.
Reproductive Targets Although it is frequently argued that milk production efficiency is at its highest when cows reproduce once every 365 days, the optimal reproduction function that maximizes profit is dependent on numerous factors, including production system, level of milk production, milk prices, and feed cost, among others. Consequently, it is impossible to give a set of specific targets applicable to all systems of production. However, the three measures presented in the following section (see also Table 1) are useful as initial measures of reproductive performance in seasonal and all-year-round calving herds. Using only one measure of reproductive efficiency can be misleading and can mask other important inefficiencies.
Components of Reproductive Efficiency Even though there are numerous factors that affect the reproductive performance of individual cows and consequently herd reproductive performance, these factors can be categorized under the following three broad headings: 1. The interval from calving to resumption of ovulation and regular estrous cycles 2. Estrous detection efficiency and submission rate 3. Conception rate following service
The Interval from Calving to Resumption of Ovulation and Regular Estrous Cycles Generally, about 80% of dairy cows will have ovulated within 28 days of calving and about 10% of cows will not have commenced ovulation by 42 days postcalving. In dairy cows, the main cause of anestrum is prolonged negative energy balance (NEB), which results in low LH pulse frequency, decreased concentration of insulinlike growth factor-I (IGF-I), low estradiol production, and ultimately the failure of the dominant follicle (DF) to ovulate. The number of ovulatory estrous cycles preceding insemination has been shown to beneficially influence subsequent conception rate. Consequently, it is desirable that dairy cows resume ovulation in the first 4 weeks after calving. Following delivery of the calf and fetal membranes, there is a decline in the plasma concentrations of progesterone and estradiol and a corresponding removal of the negative feedback effects of these steroids, particularly estradiol, on gonadotropin synthesis and secretion. Follicle-stimulating hormone (FSH) secretion commences during the first week postpartum, and this stimulates the commencement of ovarian follicle growth and the appearance of a DF on the ovary at about days 12–16 postpartum. The fate of this follicle in terms of whether it ovulates or undergoes atresia appears to be related to whether it produces estradiol, which in turn appears to be associated with exposure to an adequate LH pulse frequency and concentration of IGF-I. NEB in early lactation does not affect the follicle population or the timing of recommencement of DF growth but does affect the ovulatory fate of the first DF. However, energy balance (EB) in early lactation, rather than milk yield per se, appears to be the more important factor affecting resumption of ovulation postcalving, and dry matter intake (DMI) is a more important determinant of EB than milk yield. Positive association between EB in early lactation and the interval from calving to resumption of estrous cycles has been recorded. There is increasing evidence that IGF-I is a potential mediator of nutritional effects on fertility. Increased plasma concentrations of IGF-I during the first 2 weeks postpartum are associated with early resumption of ovulation. It has been demonstrated that feeding dairy cows an insulin-promoting diet increases plasma concentrations of insulin and also shortens the interval from calving to first postpartum
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476 Reproduction, Events and Management | Mating Management: Fertility Table 1 Targets for seasonal and all-year-round calving herds Variable
Seasonal calving herds
All-year-round calving herds
Calving interval Culling for infertility Compactness of calving
365 days <5% 80% calved in 60 days
<420 <10% NA
hasten the onset of estrous cycles postcalving but also to increase conception rates (see later) and shorten calvingto-conception intervals. Increasing dietary intake is restricted by the requirement for inclusion of fiber in the diet to maintain rumen function as well as by the variability in voluntary feed intake by cows during this period.
ovulation in both high- and low-genetic merit dairy cows. Insulin is a potent stimulator of follicle differentiation and steroidogenesis, promotes DF differentiation, and enhances responsiveness to LH and in turn increases estradiol secretion leading to a preovulatory LH surge and ultimately the ovulation of the DF. NEB also causes a decrease in circulating concentrations of IGF-binding proteins (IGFBPs). Because the IGFBPs transport and increase the half-life of IGFs, low blood concentrations of IGFBPs brought about by NEB would therefore limit the availability of IGFs to target cells in the follicle and hence limit their ability to synergize with pituitary gonadotropins to stimulate cell proliferation and steroidogenesis and ultimately ovulation (Figure 1). An objective with dairy cows in early lactation is to achieve a high DMI, as this would be expected not only to
Improving Heat Detection The single most important factor affecting heat detection efficiency is the ability of those responsible for checking for heat to fully understand the signs of heat and their commitment to heat detection for as long as is planned to use artificial insemination (AI). About 10% of the reasons for failure to detect heats can be attributed to cow problems, and 90%, to ‘management’ problems. The latter
Brain NPY and EOP Hypothalamus N GnRH U
Glucose
T Anterior pituitary GH
R Liver
FSH
I
Insulin
LH
T Steroid and protein negative feedback
IGF-I Pancreas DF
I O N
Autocrine and paracrine factors
Figure 1 Possible mechanisms by which nutrition could affect ovarian follicular function. EOP, endogenous opioid peptides; NPY, neuropeptide Y. Reproduced with permission from Diskin MG, Mackey DR, Roche JF, and Sreenan JM (2003) Effects of nutrition and metabolic status on circulating hormones and ovarian follicle development in cattle. Animal Reproduction Science 78: 345–370.
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would include too few observations per day for checking for heat activity, too little time spent observing the cows, and/or observing the cows at the wrong time or in the wrong place, such as feeding time or in the collecting yard at milking time. Another major reason for failure to detect heat is that those involved in heat detection do not understand the signs of heat. Records
Individual animal records are an essential part of good breeding management. All animals must be clearly and permanently identified by one of several methods, such as plastic ear tags, neckbands, or freeze branding. Whichever system is preferred, it is essential that the animal number be clearly legible from a reasonable distance. Breeding records should include (1) animal number, (2) calving date, and other information relevant to calving, (3) prebreeding heat dates, (4) first and repeat service dates, sire used on each date, and inseminator code, (5) date and result of pregnancy diagnosis, and (6) date of expected calving. Good records are not only part of good farm management practice, but also the first essential step in all infertility investigations. Monitoring submission rate
Submission rate is calculated as the proportion of cows calved at the beginning of the breeding season that are intended for rebreeding and submitted for insemination. A submission rate of at least 80% of the eligible cows during a 21-day period is desirable. Submission rate, which is easily calculated, is an excellent measure of heat detection rate and should be calculated at the end of the first 21-day period of the breeding season. A submission rate of less than 80% indicates a problem with heat detection, and diagnosis of this problem at an early stage allows corrective action to be taken before much of the breeding period has elapsed. Technological Aids to Improve Heat Detection The low to moderate heat detection efficiencies achieved on most farms reflect the difficulty of detecting heat in cows. Consequently, it has been and is the goal of many animal science programs to develop more objective systems to overcome some of the problems of heat detection. An ideal system for detecting estrus should have the following characteristics: (1) continuous surveillance of the cow; (2) accurate and automatic identification of the cow in estrus; (3) operation for the productive lifetime of the cow; (4) minimal labor requirements; and (5) high accuracy and efficiency (95%) for identifying the appropriate physiological events that correlate with estrus or ovulation or both. A number of aids and technologies, inexpensive or expensive, are available to meet some, but not all, of these criteria. In any case, use of the various
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technologies to identify the symptoms associated with estrus, ovulation, or both will require the judgment of the herd management, based on common husbandry experience, to verify whether or not the cow seems to be in estrus. Tail-painting
Research from a number of laboratories has shown that applying paint or chalk to the tailhead of cows is effective in indicating standing activity. When such tail-painted cows are mounted from the rear some or all of the chalk or paint is rubbed off indicating that the painted cows possibly stood in estrus while being mounted by a herd mate. When combined with early-morning and late-evening observations, checks for paint loss at milking times should result in a heat detection rate of close to 90%. Vasectomized bulls with chin ball marking harness
Active vasectomized teaser or detector bulls are useful in identifying cows either coming into or on heat. Vasectomy should be carried out 40–60 days prior to introduction to the herd. Many small- to medium-size dairy herds in Ireland are now finding that teaser bulls are particularly useful after the first 3 weeks of the breeding season when fewer cows are in heat each day and when the level of heat-related activity in the herd is reduced as more cows become pregnant. However, considerable variation in libido exists among bulls, and they require the same management as full bulls without conferring any of the advantages. As an alternative to vasectomized bulls, cows or heifers treated with testosterone or estradiol can be useful in detecting cows in estrus. Pressure-activated heat mount detectors
These devices, including the ones marketed as Kamars, Bovine Beacon, and Mate Master, are affixed to the tailhead of the cow and change color when pressure is applied by the weight of the mounting animal. Reported efficiencies of heat detection using such heat mount detectors vary from 56 to 94%, whereas the accuracy of heat detection is reported to vary from 36 to 80%. The relatively low accuracy of heat detection, combined with the difficulties in keeping the devices affixed to the tailhead, limits the potential of this approach. Pedometers
Estrus in cattle is accompanied by increased physical activity. Cows in heat do 2–4 times more walking than a nonestrous cow. Pedometers can be attached to the leg of the cow to measure the amount of her activity over a unit time-span. Early pedometer-aided heat detection systems operated with a reported heat detection efficiency of 60–100% and with an accuracy in the range of 22–100%. The low level of accuracy was related to a
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high proportion of false-positives and to technical problems that led to breakage, malfunction, or loss of the pedometers. New improved pedometric technology has now led to improved information storage systems; improved analytical capabilities to allow comparison of current with previous physical activity; incorporation of internal power supply to operate the electronics; and the development of self-contained devices to interrogate the pedometers in milking parlor and relay and store the information in a personal computer. Some systems have an inbuilt alert system, such as a bleeper or flashing light, which alerts the farmer when a cow is deemed to be in heat. A number of pedometric systems are commercially available in the United States and Europe. Even though scientific information on their operating efficiencies is not yet available, these systems would appear to have significant commercial potential particularly when cows are housed. Radiotelemetric devices
The primary sign of heat is standing to be mounted. A number of research laboratories have attempted to develop pressure-sensitive devices that measure such standing activity. Such a system (HeatWatch II; CowChips Manalapan, NJ, USA) is currently commercially available in the United States and in a number of other countries. This system involves the location of a pressure-sensitive battery-powered transmitter on the cow’s tailhead, which, when activated by the mounting cow, emits a radio signal, which is picked up by either a receiver or a repeater and relayed to a buffer and ultimately to a personal computer where the information is digitized and stored. The time, date, and duration of each mount along with the identity of each cow are recorded. From this information, the time of heat onset is calculated. The HeatWatch software generates management reports and individual cow reports that can be viewed or printed. HeatWatch classifies a standing heat as a cow having three standing events in a 4-h period. A cow with fewer standing events is recorded as a ‘suspect heat’, and such a cow should be checked for secondary signs of heat prior to deciding to inseminate her. Periodically during the day, the farmer checks the computer for a listing of the cows in heat. The data available suggest that HeatWatch operates with both an efficiency and an accuracy of almost 100% in detecting cows in heat. Heat detection patches
Recently, a number of scratch card type patches have come on the market, including Estrus Alert and ESTROTECTTM. These are affixed to the cow’s tailhead. Friction from mounting activity rubs off the silver coating to reveal a bright-colored patch underneath. These devices show significant potential to improve submission rates in dairy herds.
The consistent drawbacks with all of these systems that require the fixing of a device such as a kamar, beacon, or transponder to the tailhead of a cow are the significant amount of effort required to maintain the devices on the cows and the high loss rates. Similarly, tail-paint or chalking must be reapplied to cows at 7–10 day intervals – again requiring handling and time. Conception Rate This is the third major factor affecting reproductive efficiency. The main factors implicated in causing conception failure or embryo death are normally categorized as those of genetic, physiological, endocrine, and environmental origin. Fertilization rate and early embryo loss rates in Cattle
Based on published data, there is little evidence to suggest that fertilization rates are likely to be different in the modern high-producing cow as compared with lowerproducing cows or heifers particularly under temperate climatic conditions. When adequate numbers of spermatozoa are used from bulls of high fertility and cows are correctly inseminated during or shortly after the end of standing estrus, fertilization rates approaching 90% should be expected. Although fertilization rate is apparently similar in high- and moderate-producing cows and is unlikely to be affected by whether the cows are on pasture or high-input total mixed ration (TMR) diets, the average calving rate to a single service, nevertheless, is significantly lower in high-producing cows than in either low-producing cows or heifers. An embryonic and fetal mortality rate (excluding fertilization failure) of 40% is calculated for moderate-producing cows based on a fertilization rate of 90% and an average calving rate of 55%, with an estimated 70–80% of the loss being sustained between day 8 and 16 after insemination. The comparative figure for high-producing dairy cows, based on a fertilization rate of 90% and a calving rate of 40%, would be 56%. Pattern of early embryo loss
Based on published literature, there is some evidence that the pattern of early embryo death in the modern highproducing cow may be different from that observed in heifers and lower-yielding dairy cows. The extent of early embryo loss appears to be larger in the modern highproducing dairy cows, with a much higher proportion of the embryos dying before day 7 following insemination. The expected outcome of 100 inseminations of BritishFriesian and Holstein-Friesian cows is summarized in Figure 2. Because fertilization rate is close to 100%, conception failure is almost synonymous with embryo and fetal loss.
Reproduction, Events and Management | Mating Management: Fertility British Friesian 1980
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With the advent of ultrasound scanning, it has been comparatively easier to accurately establish the extent and timing of late embryo/fetal mortality. A recent study by the Teagasc laboratory, Galway, Ireland, quantified the extent and pattern of embryo/fetal loss from days 28 to 84 of gestation in 1046 lactating dairy cows and 162 dairy heifers managed on pasturebased systems of milk production. The overall embryo/fetal loss rates between days 28 and 84 of gestation were similar for cows (7.2%) producing on average 7247 kg of milk and heifers (6.1%), and the pattern of loss over this period was also similar for cows and heifers. Almost half (47.5%) of the total recorded loss occurred between days 28 and 42 of gestation. There was no significant association between the level of milk production or milk energy output measured up to day 120 of lactation, milk fat concentration, milk protein concentration, or milk lactose concentration and the late embryo/fetal loss rate. The extent and pattern of embryo/fetal loss were not related to either the cow’s or the cow sire’s genetic merit. The author does acknowledge that the extent of late embryo/fetal mortality recorded in the Irish pasture-based studies is much lower than that reported for some US-based studies. However, a clear explanation for the reported differences is not apparent but may be related to the level of milk production, ambient temperature, and/or the breeding of cows following various Ovsynch-based protocols in the United States. Progesterone during the cycle immediately prior to insemination and embryo survival rate
Data from a recent study conducted by the Teagasc laboratory, Galway, Ireland, clearly show that there is a positive linear association between the concentrations of progesterone on the day of PGF-2-induced luteolysis and the subsequent embryo survival rate (Figure 3). Following a literature review, it was concluded that the most probable effect of low concentrations of
Probability of embryo survival
Figure 2 Reproductive outcomes in British-Friesian vs. Holstein-Friesian cows.
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Figure 3 Relationship between plasma concentrations of progesterone on day of induced luteolysis and subsequent embryo survival rate.
progesterone in the cycle preceding estrus on subsequent embryo survival rate is preterm oocyte maturation, which subsequently compromises its ability to continue normal embryo development after its fertilization. Post insemination progesterone and embryo survival rate
Recent studies by the Teagasc laboratory, Galway, Ireland, that have employed logistic regression techniques to model the relationship between the binomially distributed dependent variable (conception/embryo survival rate; yes or no) and the continuously distributed independent variable (progesterone) have established a relationship between circulating progesterone and embryo survival rate. In a study by Stronge et al. (Figure 4) there was a positive linear relationship between milk concentrations of progesterone on days 5, 6, and 7 post insemination and the embryo survival rate, and a quadratic relationship between the rate of change in concentrations of progesterone between days 4 and 7 and the embryo survival rate. Further analysis of this data set reveals that 75, 72, and 56% of dairy cows had concentrations of progesterone that were optimal for conception on days 5, 6, and 7 post insemination, respectively. There is evidence that progesterone supplementation of dairy cows having low endogenous
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Milk progesterone concentration (ng ml–1) Figure 4 Relationship between milk concentrations of progesterone on day 5, 6, and 7 after AI and subsequent embryo survival rate in lactating dairy cows. Reproduced with permission from Stronge AJH, Sreenan JM, Diskin MG, Mee JF, Kenny DA, and Morris DG (2005) Post-insemination milk progesterone concentration and embryo survival in dairy cows. Theriogenology 64: 1212–1224.
concentrations of progesterone, and consequently at risk of suffering embryo death, will have improved embryo survival rates. A series of studies with dairy cows at the University of Wisconsin have shown that peripheral concentrations of both progesterone and estradiol are lowered by increased plane of feed intake owing to increased metabolic clearance rate (MCR) of the steroids, which is related to liver blood flow (LBF). From these studies, it would appear that LBF is elevated in high-producing lactating dairy cows and this in turn would result in a lowering of peripheral concentrations of progesterone thus increasing the risk of embryo death. The reduced progesterone effect may retard the growth and development rate of the embryo by hampering uterine secretion of proteins and growth factors essential for early embryo development. Interferon-, the embryonic signal required for the maintenance of the corpus luteum and the estalishment of pregnancy, has also been shown to be positively correlated with progesterone. Uterine expression of the mRNA for progesterone receptor and estradiol receptor and of the retinol-binding protein mRNA are all sensitive to changes in peripheral concentrations of progesterone during the first week after AI.
Nutrition–Energy Balance Over the past three decades, intensive genetic selection for milk yield has increased the differences between feed intake potential and milk yield potential. This has resulted in dairy cows that have a greater predisposition for mobilizing body reserves and for NEB. It is also clear that even under optimal grazing conditions total DMI is lower than when cows are fed maize-based TMR diets. A pasture DMI of 3.4–3.6% of body weight has been recorded for early-lactation cows grazing high-quality pasture compared to 3.9–4.2% of body weight for cows fed a nutritionally balanced TMR. From this, it is clear that under optimal grazing conditions the actual DMI of cows is significantly lower than the cows’ potential intake, and this is likely to have implications for EB status and subsequent fertility in early lactation, particularly for cows with a high genetic potential for milk production. Energy balance during the early postpartum period and subsequent conception rate
The relationships between EB, DMI, and peripheral concentrations of IGF-I measured during the first 28 days of lactation and subsequent conception rate have recently been explored in a number of Teagasc studies. All three variables were positively associated with first-service
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conception rate, and the results are presented in Figure 5. This is a particularly interesting observation and suggests that there may be long-term carryover effects of nutrition/EB on conception rate. It has also been hypothesized that follicles exposed to adverse conditions such as a negative EB during their initial stages of growth would have impaired development resulting in the production of inferior quality oocytes and dysfunctional corpora lutea. The results of this study strongly emphasize the importance of maximizing feed intake and minimizing NEB in the immediate postcalving period. Energy balance at around the time of insemination and subsequent conception rate
It is clear that DMI is lower for cows grazing pastures than for cows fed maize-based TMR diets. Supplementation of dairy cows at pasture with concentrates increases the total DMI, but its effects on conception rate are equivocal. Following a review of a
number of experiments that examined the effects of supplementation on conception rate, Diskin et al. (2008) concluded that supplementation had little effect on conception rate but that withdrawal of the supplementation during the breeding period may be counterproductive to conception rate. Only a small proportion of the additional feed intake achieved by concentrate supplementation is partitioned toward an improvement in EB, with >80% supporting increased milk production. This clearly highlights the difficulty that improving the EB of the modern dairy cow presents at this stage of lactation when grazed grass is the predominant component of the diet. Based on the Wisconsin study, it is reasonable to hypothesize that the increased milk production resulting from concentrate supplementation may well be associated with a further increase in hepatic blood flow resulting in increased metabolism of progesterone and consequently in lowering of the peripheral concentrations of progesterone, thus predisposing cows to greater risk of embryo death.
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Effect of sudden reductions in feed intake on conception rate
Studies by the Teagasc laboratory, Galway, Ireland, show that sudden reductions in DMI at around the time of insemination adversely affect embryo survival in heifers. When energy intake was reduced from a high level of twice their maintenance requirement to 0.8 times maintenance for 2 weeks immediately after AI, embryo survival rate in heifers was consistently <40%. When heifers were either provided with a constant level of feed intake or changed from a low to a higher level of feed intake, embryo survival was consistently high at 65–71%. In one study where heifers were used, there was no indication of any association between energy intake and systemic progesterone concentration. Unlike the situation in sheep and pigs, there was no change in systemic progesterone following either an increase or a reduction in energy intake. Changes in progesterone metabolism may have been balanced by changes in progesterone production.
of insemination site and inseminator on conception rate. For some inseminators, there was a significant increase (up to þ percentage points) on conception rates following cornual insemination, whereas for others there was no effect. A retrospective analysis of all the data showed that there was an inverse relationship between the improvement in conception rate and conception rate following uterine body insemination. The largest improvements in conception rates were recorded by inseminators with the lowest conception rate following body insemination. These results suggest that conception rates could be improved for individual inseminators by adopting the practice of placing half of the inseminate beyond the curvature of each uterine horn as opposed to body insemination, which is the normal practice. It is clear from many studies that placement of the inseminate in the cervix results in significantly lower conception rates. Therefore, it is critical to at least ensure that the inseminate is placed in uterine body, and for skilled and experienced inseminators, it would appear beneficial to place half of the inseminate in each uterine horn.
Protein nutrition and conception rate
Dairy cows at pasture frequently ingest high quantities of protein, often with a high proportion of the ingested protein being rapidly degradable in the rumen. The effects of high intakes of crude protein on conception rate are equivocal. For example, US data have shown that high-protein intake reduces uterine pH, which has been hypothesized to have a detrimental effect on either the gametes or the developing embryo. High-protein diets elevate plasma urea nitrogen (PUN) levels. PUN in excess of 19 mg dl1 has been associated with a 20% depression in conception rate in dairy cows. However, in an extensive range of studies by the Teagasc laboratory, Galway, Ireland, using beef heifers in positive EB, no effect of a high crude-protein intake on conception in heifers was recorded, irrespective of whether the crude protein was derived from highly nitrogen-fertilized grazed grass or from added urea to a silage-based diet. Furthermore, a retrospective analysis of the data failed to record any association between peripheral concentrations of urea and embryo survival, notwithstanding peripheral concentrations of urea having been elevated up to 25 mmol l1. It is concluded that elevated peripheral concentrations of urea per se are not detrimental to embryo survival. However, it needs to be clarified whether the observed adverse effects of urea on embryo survival are dependent on the energy status of the animal. Insemination technique
The reported effects of the site of placement of semen within the uterus on conception rate are equivocal. In a recent study by the Teagasc laboratory, Galway, Ireland, involving 3546 dairy cows in 51 herds and 8 inseminators, Diskin et al. (2005) recorded a significant effect (P < 0.02)
Time of insemination
Results from a recent large-scale study that utilized the HeatWatch system to detect the onset of standing heat concluded that conception rates were optimum when dairy cows were inseminated 4–16 h after heat onset. Insemination later than 16 h after heat onset results in significantly lower conception rates. However, in most instances the time of heat onset is not accurately determined, and in such situations once-daily AI for cows observed in standing heat is equally effective as inseminating cows in accordance with the long-established a.m.–p.m. guidelines. Calving difficulty
Calving difficulty, besides affecting calf and cow mortality and the milk yield, also decreases cow rebreeding performance. Teagasc data clearly show that as the severity of calving difficulty increases, conception rate to the first and to all services combined also decreases (Figure 6). This reduction in conception rate is owing to the abnormalities directly arising from calving difficulty, including delayed uterine involution and increased uterine infection, damage to the reproductive tract, and the development of uterine and ovarian adhesions. Furthermore, the interval to first heat is often extended after a difficult calving. For optimal reproductive performance, calving difficulty must be minimized. Two factors that greatly influence the incidence of calving difficulty are the age of the cow and the breed of the sire. The incidence of calving difficulty is 4–8 times higher in first-calving heifers than in mature cows and about twice as high in second calvers as in mature cows. The breed of the sire and indeed the individual sire within a breed should be carefully selected for use on
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improvement in conception rate often arises following the introduction of a bull. This apparent improvement is likely to be because of cows being mated at a longer postpartum interval and/or because of inaccuracies in heat detection being eliminated. Where heat detection is accurate, and when insemination is timed and carried out correctly, conception rate is similar following either AI or natural service.
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Figure 6 Relationship between calving difficulty score and conception rate to first services and to all services combined. Difficulty ranges from score 1 (unassisted birth) to score 5 (severe difficulty requiring mechanical extraction of the calf).
heifers and on young cows to minimize the risk of calving difficulty and therefore of subsequent infertility. In some countries, there is a practice of breeding latecalving dairy cows to beef sires. The combined effect of the longer gestation and the increased incidence of calving difficulty makes it even more difficult to achieve a 365-day calving interval in such cows. The wisdom of this practice, especially if the objective is to optimize reproductive performance, is therefore questionable. Bull fertility
Bull reproductive performance is influenced by several factors including testicular development, semen quality, libido, mating ability, and physical soundness. On farms using natural service, the level of bull fertility can have a major impact on pregnancy rate and calving spread. Published data suggest that up to 5% of bulls in natural service may be completely infertile and that a further 30% may be subfertile. Unfortunately, if a bull is infertile, it is not usually discovered until at least one repeat interval has elapsed since joining the herd. Although a veterinary examination combined with a semen evaluation 1 month before the start of the breeding season will help to identify the majority of infertile bulls, it will not identify subfertile bulls. Furthermore, it should be realized that a bull may not remain fertile for all of his working life or even throughout a single mating season. For example, a bull that is ill with a raised temperature for a number of days may have a period of temporary infertility 40–60 days later. Similarly, injury to the penis, sheath, or prepuce, though not necessarily affecting mounting behavior, can prevent mating. Therefore, the bull should be observed regularly for serving ability, and all mating dates recorded. Such recording will help identify infertile or subfertile bulls at an early stage. AI versus natural service
AI is often criticized on the grounds that conception rate is lower than when following natural service. Apparent
Relative Importance of Heat Detection Efficiency and Conception Rate Once estrous cycles have resumed postcalving, then it is the product of heat detection efficiency and conception rate that determines the overall herd reproductive efficiency (Table 2). The clear message from Table 2 is that low or relatively low conception rates can be compensated for by improving heat detection efficiency. Practical and easily adoptable technologies are available to improved heat detection efficiency.
Conclusion It is well established that reproductive performance is critically important, particularly in seasonally calving herds, to maintain compact calving close to the onset of the grazing season. Even though the modern high-genetic merit Holstein-type dairy cow selected solely for milk production is biologically more efficient at converting forage, irrespective of source, to milk, their sustainability in predominately pasture-based systems of production is questionable given their low fertility. Therefore, it is important to develop appropriate supplementation strategies, probably beginning before parturition, to improve fertility in dairy cows on pasture-based systems of production. In the medium to long term it should be possible to develop more balanced breeding strategies with greater emphasis on fertility- and feed intake-related traits, which are critically important to pasture-based systems of milk Table 2 The effect of different heat detection (submission) and conception rates on the percentage of the herd that is pregnant at 90 days after onset of breeding season Conception rate (%)
Heat detection rate (%)
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production. It is clear that sufficient genetic variability exists within the Holstein breed for important fertility and feed intake traits. Alternatively, strains of cows derived from more balanced breeding objectives, such as the New Zealand Friesian, or alternative dairy breeds such as the Jersey or Norwegian Red could also be utilized in such production systems. It is now becoming increasingly clear that EB during the immediate postcalving period affects both the onset of estrous cycles postcalving and the subsequent conception rates. Development of feeding strategies that increase intake without proportionally increasing milk yield, thereby improving EB, is important. Paying more attention to other factors that are predominately under management control, particularly heat detection, can significantly offset some consequences of inherently low fertility traits that exist with the modern dairy cow. Improving heat detection efficiency by 12–15% has the equivalent effect of increasing conception rate by 10 percentage points. Based on numerous published reports, it can be concluded that there is scope in most herds to improve heat detection efficiency by at least 15 percentage points by adopting well-described practices. Conception rate is affected by a range of both cow and management-related factors. Producers should ensure that cows presented for insemination are in heat and are properly inseminated with high-fertility semen. Sudden reductions in feed intake during the breeding season should be avoided.
Further Reading Beam SW and Butler WR (1999) Effects of energy balance on follicular development and first ovulation in postpartum dairy cows. Journal of Reproduction and Fertility Supplement 54: 411–424. Butler WR (1998) Review, effect of protein nutrition on ovarian and uterine physiology in dairy cattle. Journal of Dairy Science 81: 2533–2539. Diskin MG, Kenny DA, Dunne L, and Sreenan JM (2002) Systemic progesterone pre and post AI and early embryo survival in cattle. Proceedings of the Agricultural Research Forum, p. 27. Tullamore, Ireland.
Diskin MG, Mackey DR, Roche JF, and Sreenan JM (2003) Effects of nutrition and metabolic status on circulating hormones and ovarian follicle development in cattle. Animal Reproduction Science 78: 345–370. Diskin MG and Morris DG (2008) Embryonic and early foetal losses in cattle and other ruminants. Reproduction in Domestic Animals 43(2): 260–267. Diskin MG, Murphy JJ, and Sreenan JM (2006) Embryo survival in dairy cows managed under pastoral conditions. Animal Reproduction Science 96: 297–311. Diskin MG, Pursley R, Kenny DA, Mee JF, Corridan D, and Sreenan JM (2005) The effect of deep intrauterine placement of semen on conception rates in dairy cows. Proceedings of the Agricultural Research Forum, p. 29. Tullamore, Ireland. Diskin MG and Sreenan JM (2000) Expression and detection of oestrus in cattle. Reproduction Nutrition Development 40: 481–491. Dunne LD, Diskin MG, Boland MP, O’Farrell KJ, and Sreenan JM (1999) The effects of pre-and post-insemination plane of nutrition on embryo survival in beef heifers. Animal Science 69: 411–417. Gong JG, Lee WJ, Garnsworthy PC, and Webb R (2002) Effect of dietary-induced increases in circulating insulin concentrations during the early postpartum period on reproductive function in dairy cows. Reproduction 123: 419–427. Macmillan KL and Curnow RJ (1977) Tail painting – A simple form of oestrus detection in New Zealand dairy herds. New Zealand Journal of Experimental Agriculture 5: 357–361. McNeill RE, Sreenan JM, Diskin MG, et al. (2006) Effect of progesterone concentration on the expression of progesterone-responsive genes in the bovine endometrium during the early luteal phase. Reproduction, Fertility and Development 18: 573–583. Nebel RL, Walker WL, Kosek CL, and Pandolfi SM (1995) Integration of an electronic pressure sensing system for the detection of estrus into daily reproductive management. Journal of Dairy Science 78(1): 225 (Abstract). Patton J, Kenny DA, Mee JF, et al. (2006) Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows. Journal of Dairy Science 89: 1478–1487. Sangsritavong S, Combs DK, Sartori RF, Armentano LE, and Wiltbank MC (2002) High feed intake increases liver blood flow and metabolism of progesterone and estradiol 17 in dairy cattle. Journal of Dairy Science 85: 2831–2842. Silke V, Diskin MG, Kenny DA, et al. (2001) Extent, pattern and factors associated with late embryonic loss in dairy cows. Animal Reproduction Science 15: 1–12. Stevenson JS (2001) A review of oestrous behaviour and detection in dairy cows. In: Diskin MG (ed.) Proceedings of the BSAS Occasional Publication No. 26. Fertility in the High-Producing Dairy Cow, Vol. 1, pp. 43–62. Galway, Ireland. Stronge AJH, Sreenan JM, Diskin MG, Mee JF, Kenny DA, and Morris DG (2005) Post-insemination milk progesterone concentration and embryo survival in dairy cows. Theriogenology 64: 1212–1224.
Pregnancy: Characteristics H Engelhardt, University of Waterloo, Waterloo, ON, Canada G J King, University of Guelph, Guelph, ON, Canada ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by G. King, Volume 4, pp 2283–2290, ª 2002, Elsevier Ltd.
Introduction Milk, like all consumable products obtained from domestic animals, is acquired through exploitation of reproductive processes. Therefore, dairying will be efficient only if females regularly produce offspring. Both sexes must be involved for the initiation of pregnancy but, with the ejaculation of viable spermatozoa into either a natural or artificial vagina, the male’s role is finished. In contrast, the female’s role has just begun. The mammalian embryo is referred to as a zygote from fertilization through the early cleavage divisions, a morula when a spherical cluster of cells has formed, and a blastocyst once it consists of a hollow sphere and the two cell lineages that will give rise to the embryo proper and the placental membranes. Once organs have formed, the developing offspring is referred to as a fetus. At any stage, it can be referred to as a conceptus, the product of conception. For the purposes of this article, these terms may be used interchangeably. As gestation progresses, the maternal systems are modified to provide an environment that supports development. The process includes remodeling of uterine structure and function to provide nutrients for growth plus suppression of maternal immune responses so that the potentially antigenic conceptus is not rejected. The following text deals with the establishment, progression, duration, and detection of pregnancy. Although most of the world’s milk comes from Bos taurus or Bos indicus cows, information on other species used for dairying will be included when available.
In the Beginning Preattachment Development: Zygote to Expanded Blastocyst Embryos pass through the first few cleavage stages as they travel down the oviduct. All development up to the midblastocyst stage occurs while the embryo is confined within its zona pellucida (Figures 1(a)–1(d)). Because zona-enclosed embryos do not grow larger, as the number of blastomeres doubles at each cleavage their individual size is halved. In cattle, sheep, and goats, embryos enter
the uterus 3–5 days after fertilization, typically at the 8- to 16-cell stage. In the sheep, if two oocytes are released from the same ovary and no ovulation occurs from the other ovary, one embryo commonly migrates down the ipsilateral horn of the uterus, passes through the uterine body, and develops in the contralateral horn (i.e., on the opposite side). In contrast, migration between uterine horns in cattle is rare. If there are two ovulations from the same ovary, both embryos will remain and develop in the adjacent uterine horn. It was thought that uterine capacity might be limiting, such that twins gestated in separate horns would be more likely to survive to term. However, studies have found this to be a problem only with nulliparous heifers. Twinning in cattle, regardless of uterine position, is associated with substantially higher rates of calf mortality, dystocia, and metabolic problems. An additional problem associated with twins in cattle is the possible fusion between the placental membranes of the two conceptuses. This situation leads to exchange of cells and signaling molecules between fetuses. If one fetus is male and the other female, the male will be normal but the female will have abnormal sexual differentiation. Most heifer calves that develop as cotwins with males become sterile freemartins characterized by apparently female external genitalia with variable asexual or phenotypically male internal genitalia. Although some aspects of this centuries-old phenomenon remain a mystery, studies of freemartins in cattle have made fundamental contributions to our understanding of sexual differentiation and immunology. In fact, the groundbreaking work by Medawar (cowinner of Nobel Prize, 1960) on naturally acquired immunological tolerance was initiated by studying transplantation reactions in freemartins. Soon after entering the uterus, the embryo passes through the morula and to the blastocyst stage (Figures 1(e) and 1(f)). Fluid accumulates between some of the cells and these spaces unite to form the blastocoel, a fluid-filled cavity. A cluster of cells give rise to the inner cell mass, which will form the embryo proper, while the remainder surrounding the cavity form the trophectoderm, the precursor of the placental membranes. Embryos
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Figure 1 Development of the conceptus from fertilization to elongation of the chorionic vesicle. (a) Fertilization, the union of spermatozoon and oocyte to form the zygote or embryo; ZP, zona pellucida. (b) First cleavage, occurring about 24 h after fertilization, producing an embryo with two cells or blastomeres still contained within the zona pellucida. (c) Second cleavage, usually within 12 h of first cleavage, producing four blastomeres. (d) Third cleavage, within a few more hours, resulting in eight blastomeres within the zona pellucida. (Blastomere division is not synchronized exactly, so zygotes with intermediate numbers may be observed.) (e) Subsequent cleavages produce the morula with 16–64 blastomeres, still within the zona pellucida. (f) Continued cleavage results in a blastocyst with a distinct inner cell mass (ICM) and a layer of trophectodermal cells (T) surrounding a fluid-filled central blastocoelomic cavity (BC). (g) Outward pressure from the growing blastocyst ruptures the zona pellucida (hatching), so the conceptus can now increase in size. (h) The conceptus grows rapidly into and through the spherical blastocyst stage. At this time, it is a fluid-filled sac with a distinct embryonic disc (ED) on the surface. (i) In most ungulate species, the spherical blastocyst elongates quickly into a filamentous form that grows to fill much of the uterine lumen. The embryonic disc remains as a distinct spot on the surface of this chorionic vesicle. It is the trophectoderm or outer cell layer that interacts with the endometrium to form the placenta.
intended for transfer are typically collected from the uterus at the morula or blastocyst stage. Early in the second week of gestation, the zona pellucida ruptures and the blastocyst is freed or hatched (Figure 1(g)). Cell division continues and, since the blastocyst is no longer confined within the zona, it can now increase in size. By 10 days, the inner cell mass forms an embryonic disc located as a discrete structure at the surface of a hollow sphere (Figure 1(h)). The original cells forming the inner cell mass and trophectoderm
constitute the ectoderm, the first of the three primary germ layers. A sheet of flattened cells, the endoderm, proliferates from the inner cell mass during the second week of gestation and develops into a single cell layer closely associated with the inner surface of the trophectoderm. This proliferation progresses until the endoderm lines the entire inner surface, forming a two-layered or bilaminar membrane surrounding the blastocoel. Shortly after the bilaminar blastocyst forms, further differentiation within the inner cell mass initiates production of mesodermal cells beneath the disc. The mesoderm or the third germ layer proliferates and spreads between the ectodermal and endodermal cells resulting in a trilaminar blastocyst. During subsequent development, the three germ layers interact to produce tissues and organs within the developing embryo/fetus plus the various embryonic membranes. The hatched blastocysts of domestic ruminants remain in the spherical stage (Figure 1(h)) for several days. The trophectoderm, which has now become the outer embryonic membrane or chorion, extends to form an oval shape and quickly stretches into an elongated, sausage casing-like, filamentous structure (Figure 1(i)). Much of this initial increase in length is accomplished through cellular remodeling into greatly stretched configurations rather than by cell proliferation. The embryonic disc begins to develop a neural fold and somites, giving rise to a primitive embryo that is enveloped by an infolding of the rapidly growing membranes. Late in the second or third week of gestation, the filamentous blastocyst, also called a chorionic vesicle, assumes a fixed position within the uterus, stretches to a substantial length, and begins to fuse with the uterine lining. Formation of Embryonic Membranes As a blastocyst elongates and the embryo forms, several other membranes develop. A yolk sac grows out from the middle section of the embryo and proliferates within the chorionic vesicle. The yolk sac quickly develops an extensive vascular bed and extends toward, but never reaches, the chorionic tips. Both the chorion and yolk sac synthesize peptides, proteins, and steroid hormones, some of which serve as signals from the conceptus to the dam, coordinating maternal responses to embryonic requirements. In addition, the yolk sac produces the first embryonic blood cells and serum proteins. The primordial germ cells, which subsequently migrate to the genital ridge and transform this region into a gonad, also originate in the yolk sac. Once the liver and other organs develop and assume their functions, the yolk sac regresses. Another embryonic membrane, the allantois, develops from the hind region of the embryo late in the third week of gestation. It begins as a small sac but soon becomes filled with fluid and expands. In most species, the allantois displaces the yolk sac and, within a few days, lines most of
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the chorionic vesicle. The allantoic and chorionic membranes fuse to form the chorioallantois. This combined membrane rapidly develops an extensive blood vascular system that is connected directly with the embryonic circulation via the umbilical cord. In most mammals, the chorioallantoic membrane constitutes the outermost layer of the embryo/fetal unit that attaches to the uterine lining forming the placenta. As the yolk sac and allantois are developing, the differentiating embryonic disc sinks below the surface of the chorionic vesicle. The embryo is then surrounded or enveloped by infolding chorion that fuses in the middle to form a separate sac, the amnion. This compartment is also filled with fluid and intimately surrounds the embryo/fetus to provide a stable physical environment for growth and a cushion against mechanical shock. Embryos implant in the distal third of the ipsilateral uterine horn, and the chorionic vesicle expands into the contralateral horn. In camelid species, embryos tend to implant in the left horn even though ovulation can occur on either side, with membranes expanding into the opposite horn. Development of the Fetus As the embryonic membranes organize, the ectodermal, mesodermal, and endodermal components of the inner cell mass differentiate and begin forming specific organs. Early in gestation, the embryonic disc region organizes through the primitive streak, neural fold, and somite stages. Around the time when placental attachment commences, the heart forms and vascularization of the embryo and associated membranes begins. At this stage, a head and body region become recognizable but bear little resemblance to the final product. The individual organs, limb buds, and other features appear within a very few weeks, heralding the transition from an embryo to a fetus. During the initial stages of development, there is almost no increase in uterine size. Once the attachment of the chorion to the uterine epithelium is well under way, fluids begin to accumulate in the chorioallantoic and amniotic space and the uterus enlarges (Figures 2(a) and 2(b)). It is this fluid that accounts for much of the increase in size through midgestation. In the later stages, growth of the fetus accelerates so that by term it will account for about half of the total conceptus-uterine weight. In late gestation, the fetal fluids probably account for another quarter, with the placenta and uterus constituting the remainder.
Nutrition of the Conceptus Mammalian oocytes have sufficient stores of yolk material to provide nutrients to support embryonic development through the first few cleavage divisions. However, once cell numbers begin to increase through
Figure 2 (a) Bovine uterus, day 32 of gestation. The embryo/ fetus is located near the middle of the slightly enlarged left (ipsilateral) uterine horn. The right (contralateral) horn is just beginning to enlarge. The corpus luteum on the left ovary is cut open. (b) Bovine uterus, day 61 of gestation. The fetus is located in the substantially enlarged left uterine horn. By this stage, the contralateral horn is also obviously distended.
the morula and blastocyst stages, the embryo must obtain and metabolize materials from the mother. There are two possible ways for the embryo to obtain nutrients. First, material secreted by the epithelial lining of the endometrium (inner layer of uterus) is absorbed by the outer surface of the chorionic vesicle. This mode of transfer, known as histotrophic (histiotrophic) nutrition, is carried out by a uterine lining of tall, columnar cells loosely associated with the fetally derived layer. Uptake is facilitated by areolae, which are pockets of columnar trophoblast cells overlying
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the mouths of uterine glands. In the second route, material diffuses between maternal and fetal circulations through various tissue layers. This mode of nutrient transfer, hemotrophic nutrition, requires a well-vascularized fetal layer and a thinning of the layers separating maternal and fetal vasculature. The placenta provides this situation. All mammalian embryos are dependent on histotrophic nutrition up to the blastocyst stage. These stages are considered to be anaerobic, such that embryos require a supply of nutrients but minimal levels of oxygen. Subsequently, the relative importance of histotrophic nutrition and the timing of the switch to hemotrophic nutrition are highly variable among species. In humans, the period of histotrophic exchange is believed to be very brief, since the embryo invades and implants within the uterus quickly (10 days after fertilization) and the placenta is formed relatively early in pregnancy. In contrast, in all ungulates (hoofed animals), attachment to the uterus is delayed and the placenta is formed later in gestation. Because histotrophic transfer is important throughout the entire gestation, conceptuses in ungulate species typically undergo considerable expansion prior to attachment to occupy a larger surface area of the uterus. Placentation In all mammals, placentation begins when the embryonic vesicle assumes a fixed position within the uterus (apposition), followed by adhesion between chorion and uterine epithelium and the interdigitation of finger-like projections (microvilli) that develop on apposed maternal and embryonic cells. In many mammalian species, attachment is followed by destruction of uterine epithelium, and invasion of endometrium by embryonic cells (e.g., true implantation). However, placentation in ungulates is characterized by simple attachment to the uterine epithelium with little or no destruction of maternal tissues. In essence, the ungulate placenta forms as a result of interaction between the outermost membrane of the embryonic vesicle, the chorion, and the epithelial lining of the uterus. Attachment begins on days 18–19 in cows and goats, and on days 14–15 in sheep. The intimate association between chorion and endometrium constitutes the mature placenta in camelids. In true ruminants (e.g., cattle, goats, sheep), the most obvious features of the placenta are placentomes, which consist of caruncles – raised round or oval areas on the inner uterine lining – interacting with cotyledonary areas of the chorioallantoic membrane (Figure 3(a)). Individual caruncles are composed of dense connective tissue covered by simple columnar epithelium. A distinctive feature of the caruncular endometrium is its lack of glands; the openings of uterine glands are found only on the intercaruncular surface. Although caruncles do not come into play until pregnancy, they begin to develop during
Figure 3 (a) Bovine fetus within the placental membranes showing conspicuous cotyledons at the surface. Note that the largest cotyledons are nearest to the fetus. The gestational age is approximately 6.5 months. (b) Inner endometrial surface of the uterus from a 6-month-old calf. Note the four rows of caruncles in each uterine horn. Modified with permission from Atkinson BA, King GJ, and Amoroso EC (1984) Development of the caruncular and intercaruncular regions in the bovine endometrium. Biology of Reproduction 30: 765, Figure 2(a).
fetal life, and are easily visible in the inner surface of a prepubertal calf uterus (Figure 3(b)). The number of caruncles is highly variable both between and within species, with estimates of 70–142 in cows, 160–180 in goats, and 60–150 in sheep. In both intercaruncular and caruncular regions, apposition and subsequent attachment of the chorion and uterine epithelium commence near the embryonic disc. The union of maternal and fetal surfaces is consolidated by ridging or folding of the interface, which follows almost immediately after attachment begins. In the cow, physical union between these tissues extends over the entire mucosa by day 27. Attachment at placentomes is reinforced by the penetration of chorionic villi into crypts that form within the endometrium (day 33 in the cow). The folding of the maternal–fetal interface together with the progressive branching of the villi and deepening of the maternal crypts provide a vast surface area for exchange. The placentomes are such obvious features that the ruminant placenta is classified as a cotyledonary placenta. This terminology infers that definitive placentation involves only the placentomes. However, interplacentomal regions are also involved in exchange. Indeed, placentomal and interplacentomal regions are
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specialized for hemotrophic and histotrophic nutrition, respectively. The caruncles, with their thin, closely applied covering of trophoblast and extensive vascular bed, are well suited for hemotrophic exchange of gases and small molecules. The glandular interplacentomal regions with their areolar-gland complexes are well suited for histotrophic transfer, and are believed to be primarily involved in the exchange of large molecules. Histotrophic nutrition is of greater significance in ungulates than in any other placental group.
Gestation Length The duration of gestation in mammals is controlled almost entirely by genotype with major differences between species and minor variations among breeds or strains. The age of the dam, sex of the fetus, or season of birth may have slight effects, but these are small in comparison to the interspecies variation. The ranges of gestation lengths for various domestic animals used for milk production are given in Table 1. In cattle, birth weight is correlated positively with gestation length since the longer a fetus remains in utero, the larger it grows. Also, the heavier male calves are usually carried slightly longer than female calves. Equine gestation length is somewhat longer and more variable than that in the ruminant dairy animals. The interval for mares may range from just over 300 days to almost 1 year, but most parturitions probably occur from 330 to 350 days. The differences between breeds and season of foaling are significant. Gestation is longer than normal in mares carrying mules. With the wide ranges reported for the various camelids, one might question how accurately mating was recorded or whether a number of offspring were born prematurely. Table 1 Gestation lengths for species of animals that might be used for dairying
Species
Gestation length (days)
Cow – Bos taurus Cow – Bos indicus Water buffalo – Bubalus bubalis Goat – Capra hircus Sheep – Ovis aries Horse – Equus caballus Arabian camel – Camelus dromedarius Asian camel – Camelus bactrianus Llama – Lama guanicoe¨ glama Alpaca – Lama guanicoe¨ pacos Reindeer – Rangifer tarandus Yak – Bos grunniens
278–290 285–295 302–317 142–154 143–153 330–350 345–395 370–440 320–345 325–366 210–240 250–270
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Pregnancy Diagnosis The main hurdles to successful pregnancy are breeding the female to a fertile male when she is in estrus, conception, and the resulting conceptus attaching to the uterus and developing a placenta. The majority of pregnancy failures are early in gestation (first 2 months in cattle). Thus, mating even during estrus is not a guarantee that females will complete gestation. Because of this uncertainty, managers of both intensive and extensive livestock production units may seek assurance that mated or maleexposed animals are truly pregnant. The ideal pregnancy test would be sensitive enough to detect pregnancy early to allow timely rebreeding of the animal. It would be specific, in that it correctly distinguishes nonpregnant from pregnant animals. Pregnancy tests should be inexpensive and simple to conduct under field conditions. The procedure itself should have no negative impact on pregnancy, involving minimal physical manipulation of the pregnant uterus or stress to the pregnant female. At this point, the pregnancy test for dairy animals that meets all these criteria does not exist. An example of an ideal indicator is the chorionic gonadotropin of higher primates (e.g., human chorionic gonadotropin (hCG) in humans), which can be measured in blood and urine as early as 1 week after conception. Unfortunately, analogous molecules have not yet been identified in dairy species.
Detecting Nonpregnancy by Return to Estrus Although the occasional cow may show weak estrus-like signs during pregnancy, female domestic animals rarely exhibit any signs of sexual behavior at one cycle interval after a fertile mating. Thus, for animals mated on known dates, demonstration of sexual receptivity when the next estrus is due indicates no conception from the previous service. Conversely, the absence of sexual behavior is a strong evidence for pregnancy. When hand mating is practiced, cows, ewes, or does can be tested with males just before and during the period when the next cycle should occur. Animals that show estrus can then be remated or treated hormonally. However, one caveat is that in many dairy herds relying on visual observation of estrus for mating via artificial insemination, estrus detection efficiency may be less than 50%. In such cases, a presumptive diagnosis of pregnancy based on missed estrus cannot be very accurate.
Direct Methods of Pregnancy Detection Ballottement
The increasing size of fetal membranes and associated fluids within the uterus eventually produce abdominal distension. The physical enlargement usually becomes obvious during the later stages of gestation and is too
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late to be of much practical use for management decisions. Palpation of the firm fetal mass through the body wall may be attempted in ewes or does accustomed to being handled enough to relax their abdominal muscles. In cows, it is frequently possible to detect the presence of mid- or late gestation fetuses by ballottement. The open palm or fist is placed against the right flank just above the stifle joint, pressed firmly into the body wall with a short rapid movement, and then held in this position. The pressure wave produced by this movement shifts the fetus within its fluid-filled sac away, then back toward the hand. Once the fetal mass reaches a substantial size, it can be detected as a rebounding bump. Right horn pregnancies are easily detected by ballottement during the last trimester. However, the presence of the rumen between the uterus and left flank often hides fetuses developing on that side. In some instances, left-horn pregnancies may be detected by right-side ballottement. Rectal palpation
Rectal palpation is an extremely useful procedure for pregnancy diagnosis in larger animals such as cattle. The bovine rectum is quite distensible and elastic allowing considerable mobility by the palpating arm and thus complete examination of the reproductive tract. Very early pregnancies can be diagnosed by detecting the very slight bulge of the embryo within its amnion before any obvious swelling of the gravid horn occurs. It is also possible to detect twins by this method. In the fifth or sixth week of gestation, the bovine conceptus enlarges within the uterus and the embryonic membranes thicken, so they can be felt through the uterine wall. The tactile sensation generated as the uterine wall is gently released between thumb and fingers provides the membrane slip test for pregnancy. Later, actual placentomes and fetal parts may be palpated. Around midgestation, the weight of the fetus and placental fluids pull the uterus forward into the abdominal cavity, so it cannot be reached by palpation. At this stage, it is still possible to diagnose pregnancy through examination of the middle uterine arteries and detection of the characteristic fremitus or dynamically vibrating pulse to the gravid uterine horn. By late gestation, the limbs and head are again within reach. Although learning to diagnose pregnancy by rectal examination is not beyond the ability of most people, some expert instruction and considerable practice is necessary to develop this skill. Careless or rough handling, particularly in early gestation, can induce abortions. Thus, the procedure should be left to experienced professionals and even they must be very careful when examining animals before 50 days. Ultrasonography
Several types of ultrasound units are commercially available for pregnancy diagnosis. The most sophisticated and accurate are real-time B-mode ultrasound models
equipped with rectal or surface probes. Although these units are relatively expensive, ultrasound examinations are an integral part of reproductive management programs for a substantial number of dairy practitioners. Experienced technicians can detect pregnancy in cows by the third or fourth week of gestation. Some herd health programs also include a follow-up examination a few weeks later to determine fetal sex. Simpler Doppler or amplitude-depth (A-mode) ultrasound units are also available. The Doppler principle is based on detection of movement – blood flow in uterine or umbilical arteries, fetal heartbeat. A-mode ultrasound detects a fluid-filled uterus, which can occur in situations other than pregnancy. Although these less expensive units cannot be used as early in gestation, or with the same accuracy, as real-time units, they can be reliable in experienced hands. Reports on the reliability of ultrasound for early pregnancy diagnosis in sheep and goats are variable. Using rectal probes in research settings, pregnancy in sheep and goats can be consistently diagnosed by days 20–25. However, in the field, it is generally recommended to scan after day 45 and even later (70–90 days) for information about number of fetuses. While the sensitivity and accuracy of ultrasound methods in all species vary with the skill level of the technician and type of equipment, the results in goats and sheep are influenced by additional factors such as animal position (for rectal) and whether wool is shaved (abdominal probes in sheep). Although rectal probes have the advantage of earlier detection, they may result in rectal damage in small ruminants. Indirect Methods of Pregnancy Detection Indirect methods for pregnancy diagnosis are based on measurements of substances in blood or milk. Antibodybased methods, either radioimmunoassays (RIAs) or enzyme-linked immunosorbent assays (ELISAs), have been developed for detection of these molecules. Because RIA uses radioactively labeled tracers that require expensive detection equipment, the emphasis is now on development of ELISAs that are based on changes in color. Despite many decades of research, options for early pregnancy markers in dairy ruminants are still limited. Elevated concentration of progesterone, a steroid hormone produced by the ovaries, in blood or milk at the time of next expected estrus is the best established biochemical test for pregnancy in dairy animals. Unfortunately, progesterone levels are elevated during both the luteal phase of the nonpregnant cycle and pregnancy, so this test must be interpreted carefully. A more recently developed biochemical test is based on concentrations of pregnancyassociated glycoproteins (PAGs) in maternal blood. Although the functions of PAGs in pregnancy are not clear, the fact that they are produced by the placenta
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suggests that they would make an ideal marker for pregnancy. The limitations of these two approaches will be discussed in more detail below. Milk progesterone concentrations as indicators of nonpregnancy
There are a number of variations but generally milk samples are collected from cows 20–24 days after service. In concept this same method is available in goats and sheep, but blood rather than milk is often used. If the female is pregnant, progesterone concentrations should be elevated. In contrast, luteolysis will occur in cows that were serviced without conception and progesterone concentrations should be very low. The test is very accurate for nonpregnancy but not so reliable for a positive diagnosis. For example, if a female is inseminated not at estrus but during the luteal phase and a sample taken 3 weeks later, she will be in her next luteal phase and could be incorrectly identified as pregnant. An animal with a prolonged luteal phase would also produce a false-positive result. With careful interpretation, milk progesterone tests are a valuable management aid for herdsmen with good estrus detection practices. Researchers in Denmark have developed a mathematical model capable of processing raw progesterone values from milk collected by a robotic milking system into a palatable form, providing the biological interpretation. These innovations, particularly when combined with inline measurement technology, will be of great interest to operators of large herds. Pregnancy-associated glycoproteins in plasma as indicators of pregnancy
The PAGs, including pregnancy-specific protein B (PSPB), are a large family of glycoproteins produced by binucleate cells within the chorion of the ruminant placenta. These unusual cells, which constitute up to 20% of the trophectodermal cells, are present only during pregnancy. However, detectable levels of PAGs have been reported in a proportion of virgin heifers, unbred cows, and even bulls, suggesting an alternate source. For this reason, the cutoff value to discriminate between pregnant and nonpregnant animals must be carefully considered. Another drawback of PAGs is that, typical of heavily glycosylated proteins, they have a long half-life in the circulation. Plasma concentrations rise to very high levels in dairy cows during the last few days of gestation, which carry over into the postpartum period. Residual levels of PAGs that would be considered diagnostic of pregnancy can still be detected up to 3 months postpartum, which limits the use of PAGs for early pregnancy detection. A third drawback of PAGs is that they are not secreted into milk to any appreciable extent, which necessitates collection of a blood sample.
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Development of assays for pregnancy-associated glycoproteins
RIAs utilizing antisera from rabbits immunized with purified or semipurified preparations of bovine cotyledons have been described in the scientific literature beginning in the late 1980s. These assays have also been used to detect PAGs in sheep and goats, using bovine standards and tracer. More recently, RIAs using antisera raised against preparations of ovine and caprine placentomes have been developed. Curiously, when used for screening of cattle, these heterologous RIAs measured higher concentrations than homologous assays using all bovine reagents. Indeed, an RIA using a mixture of rabbit antisera produced with cow, sheep, and goat PAGs as immunogens found greater differences in PAG concentrations in pregnant versus nonpregnant cattle. ELISAs do not require expensive detection equipment or radioactivity, and can be modified to provide qualitative ‘cow-side’ kits for on-farm use. A test based on an ELISA developed at the University of Idaho has been commercially available since 2005 (BioPRYN, BioTracking, Moscow, ID, USA). This test requires that a blood sample be sent to a testing lab. A ‘sandwich’ type of ELISA has been developed at the University of Missouri, Columbia, using a mixture of monoclonal antibodies to trap PAG in the wells and a polyclonal antiserum to detect the bound PAG. The goal was to develop an assay that detected the PAG subset that was expressed during early pregnancy rather than the late gestation forms that persist into the postpartum period. The ELISA outperformed the RIAs in this regard, with the vast majority of cows with undetectable levels by 8 weeks postpartum. A cow-side version of this test is currently under development and may eventually be available for commercial use. One of the challenges in developing these assays is that PAGs are a diverse family of molecules rather than a single molecule. As gestation progresses, differentially glycosylated forms of particular PAGs and even different PAG molecules are expressed. Detection of these different forms is highly dependent on the assay system. PAG secretion may even be affected by parity and level of milk production. Developing robust immunological assays for these molecules clearly presents a different challenge than for a molecule like progesterone, which is biologically identical across all mammals. Management Considerations in Development of Pregnancy Diagnosis Strategies Features of currently available methods for early pregnancy diagnosis in cattle, goats, and sheep are summarized in Table 2. However, dairy producers must recognize that there is one inherent problem that will continue to be associated with even the most reliable pregnancy test. No matter how accurate the procedure, the results are valid only for the time the sample was
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Table 2 Methods for early pregnancy diagnosis in common dairy ruminants Method
Species
Stage
Comments
Nonreturn to estrus
Cow Goat Sheep Cow Goat Sheep Cow
Days 20–24 Days 20–24 Days 16–19 Days 20–24 Days 20–24 Days 16–19 After day 35a
Best to assess nonpregnancy; requires knowledge of breeding dates and behavioral observation Best to assess nonpregnancy; requires knowledge of breeding dates
Cow, rectal Goat and sheep, rectal Abdominal
After day 28 After day 25
Cow Goat and sheep
After day 30 After day 24
Progesterone (milk or blood) Rectal palpation Ultrasound
PAG/PSPB (blood)
After day 35
Some risk to developing fetus; requires considerable expertise Use of rectal probes in small ruminants is associated with risk of rectal damage; thus, animal restraint system must be factored into decision to use this approach At present, no animal-side test available, so samples must be shipped to testing laboratory
a Pregnancy can be diagnosed in heifers as early as days 28–30, but rectal palpation at this early stage is not recommended due to the risk of damage of the very fragile conceptus. PAG, pregnancy-associated glycoprotein; PSPB, pregnancy-specific protein B.
collected or the physical examination was conducted. A substantial number of pregnancies are lost during the first trimester, so any early pregnancy diagnosis should be reconfirmed at a later date. False positives in early assessments and early embryo losses will be detected at a follow-up check. But false negatives (animals incorrectly identified as nonpregnant) are potentially disastrous, in that prostaglandins used to induce estrus for rebreeding would cause abortion in pregnant animals. See also: Gamete and Embryo Technology: Artificial Insemination; Multiple Ovulation and Embryo Transfer. Husbandry of Dairy Animals: Goat: Reproductive Management; Sheep: Reproductive Management. Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Mating Management: Fertility; Pregnancy: Parturition; Pregnancy: Physiology.
Further Reading Atkinson BA, King GJ, and Amoroso EC (1984) Development of the caruncular and intercaruncular regions in the bovine endometrium. Biology of Reproduction 30: 763–774.
Capel B and Coveney D (2004) Frank Lillie’s freemartin: Illuminating the pathway to 21st century reproductive endocrinology. Journal of Experimental Zoology. Part A, Comparative and Experimental Biology 301: 853–856. Carter AM and Enders AC (2004) Comparative aspects of trophoblast development and placentation. Reproductive Biology and Endocrinology 2: 46. Enders AC and Carter AM (2006) Comparative placentation: Some interesting modifications for histotrophic nutrition – A review Placenta 27(supplement 1): S11–S16. Green JA, Parks TE, Avalle MP, et al. (2005) The establishment of an ELISA for the detection of pregnancy-associated glycoproteins (PAGs) in the serum of pregnant cows and heifers. Theriogenology 63: 1481–1503. King GJ (1993) Comparative placentation in ungulates. Journal of Experimental Zoology 266: 588–602. King GJ, Atkinson BA, and Robertson HA (1982) Implantation and early pregnancy in domestic ungulates. Journal of Reproduction and Fertility 31(supplement): 17–30. King GJ and Thatcher WW (1993) Pregnancy. In: King GJ (ed.) World Animal Science, Series B, Vol. 9: Animal Reproduction, pp. 229–270. Amsterdam: Elsevier. Perry JS (1981) The mammalian foetal membranes. Journal of Reproduction and Fertility 62: 321–335. Sousa NM, Ayad A, Beckers JF, and Gajewski Z (2006) Pregnancy-associated glycoproteins (PAG) as pregnancy markers in the ruminants. Journal of Physiology and Pharmacology 57(supplement 8): 153–171. Steven DH (1975) Comparative Placentation. London: Academic Press. Wooding FB, Roberts RM, and Green JA (2005) Light and electron microscope immunocytochemical studies of the distribution of pregnancy associated glycoproteins (PAGs) throughout pregnancy in the cow: possible functional implications. Placenta 26: 807–827.
Pregnancy: Physiology P J Hansen, University of Florida, Gainesville, FL, USA ª 2011 Elsevier Ltd. All rights reserved.
Physiology Pregnancy is a key event in the life of a dairy animal because the hormonal processes that are played out during this period include those that prepare the mammary gland for lactation following parturition. Indeed, perturbations in the placenta, the source of many mammogenic hormones, can conceivably lead to a reduction in the magnitude of milk synthesis in the subsequent lactation. For pregnancy to succeed, the conceptus must be able to successfully progress through a series of preprogrammed developmental steps that transform it from an undifferentiated one-cell organism into a neonatal animal capable of life outside of the womb. Accordingly, the maternal system must be made to serve the nutritional, immunological, and physiological needs of the conceptus. Not surprisingly, then, there is a close coordination of maternal and conceptus physiology that is achieved by the exchange of information between mother and offspring through chemical signals. The complexity of pregnancy makes it susceptible to failure and the newly formed conceptus has only a fair chance of completing development. In many populations of lactating dairy cows, especially those that are intensively managed for high milk production, only about 15–30% of cows that are inseminated carry a fetus to term. Pregnancy failure is most prevalent early in development but can occur throughout gestation (Figure 1). Historical data indicate that pregnancy rate per conception in dairy cattle declined through the last 30–40 years or so of the twentieth century in most developed countries. The reasons for this decline are unclear but likely include the consequences of increased milk yield, changes in animal housing, and increased inbreeding. Understanding the physiology of the processes involved in pregnancy, then, offers the opportunity to increase reproductive function and improve the efficiency of milk production. Unfortunately, a diverse and not always coherent system has arisen for naming organisms during the period of prenatal life. In this article, the term conceptus will be used to refer to all of the products of conception (the embryo or fetus and its associated extraembryonic membranes). Until differentiation of placental tissues, the term embryo can be considered analogous to conceptus. Thereafter, embryo refers to the part of the conceptus that will give rise to the neonate. Once the embryo has
undergone sufficient differentiation to be reasonably identifiable as a member of the species, it is referred to as a fetus. This transition, which is somewhat arbitrary, occurs at about day 45 of gestation in cattle and day 34 in sheep.
Preimplantation Period Pregnancy is initiated at the moment of conception when the newly ovulated oocyte is fertilized by one of the spermatozoa resident in the oviduct following mating. The early preimplantation embryo is distinct from most other cells in that the embryonic genome is largely repressed for the first several cleavage divisions. Rather, the embryo relies on mRNA formed during oocyte growth for direction of the bulk of protein synthesis. In the cow and sheep, major activation of the embryonic genome occurs at the 8- to 16-cell stage. There is limited transcription before these stages, however, and heat shock can induce transcription of genes for heat shock protein 70 as early as the two-cell stage. Activation of the embryonic genome is initiated following the loss of maternally derived mRNA, which is in turn caused by the loss of proteins such as MSY2 that mask mRNA. A schematic illustration of events in early pregnancy is presented in Figure 2 (see Reproduction, Events and Management: Pregnancy: Characteristics). Early stages of development involve a series of cleavage divisions whereby cell number of the embryo increases while size of individual cells (called blastomeres) decreases. Early cells of the embryo are totipotent – a new individual can be derived from a single blastomere appropriately transferred to an empty zona pellucida (the protein coat surrounding the embryo). Differentiation of the preimplantation embryo is first initiated at the morula stage of development (5–6 days after ovulation in cattle and 3–4 days in sheep), which is characterized by a loss in the ability to view individual cell membranes. Morulae are formed through a process called compaction in which embryonic size decreases somewhat and cells become more tightly associated. The underlying basis for compaction is the formation of intercellular junctional complexes between blastomeres at the basolateral regions of the cells. These tight junctions limit fluid movement between cells and lead to the polarization of blastomeres into apical
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100
Number
80 15% fertilization failure
60 40
54% early embryo mortality
15% late embryo mortality
20
10% fetal loss
0 AI
Fertilization
Day 28 Ultrasound
Day 45 Palpation
Term
Figure 1 Pregnancy loss throughout gestation in a hypothetical herd of 100 lactating dairy cows with a calving rate of 30%. The y-axis represents the number of cows. Note that fertilization occurs only in about 85% of inseminated cows. Following fertilization, large numbers of embryos die before pregnancy diagnosis by ultrasound at day 28. Other losses occur between days 28 and 45 (about 15% of pregnancies), when pregnancy is diagnosed by rectal palpation, and day 45 and term (about 10% of pregnancies present at day 45). AI, artificial insemination. The figure is reproduced with permission from Hansen PJ (2007) Hidden factors affecting fertility. WCDS Advances in Dairy Technology 19: 339–349.
regions in contact with the external environment of the embryo and basolateral regions located near the interior of the embryo. The blastocyst is formed from the morula when fluid accumulates in the embryo to form a blastocoelic cavity. Embryos progress from the morula stage to the blastocyst stage at about days 6–8 after ovulation in cattle and days 6–7 in sheep. At the same time, two distinct cell layers can be identified – the trophectoderm, which subsequently gives rise to the extraembryonic membranes, and the inner cell mass, which gives rise to the fetus. Two processes have been implicated in the formation of the blastocoel (Figure 3). The outer layer of blastomeres develop Naþ/Kþ ATPase pumps on the basolateral surface that use movement of ions to direct water into the interior of the embryo. In addition, water channel molecules called aquaporins allow direct movement of water across blastomeres. Emergence of the blastocyst from the zona pellucida follows blastocyst formation. This process, called hatching (at about days 9–10 postovulation in cattle and days 7–8 in sheep), is caused by a combination of proteinases from the
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Figure 2 Schematic diagram of events during early pregnancy in the sheep. Events in the cow are similar except that timing relative to days after mating differs slightly. For example, interferon- (IFN-) secretion starts between days 15 and 17 of pregnancy and the earliest attachments to the uterus are at day 18 of pregnancy. In the bottom panel, progesterone concentrations are represented by blue lines. CL, corpus luteum; ZP, zona pellucida. The figure is reproduced with permission from Spencer TE, Johnson GA, Bazer FW, Burghardt RC, and Palmarini M (2007) Pregnancy recognition and conceptus implantation in domestic ruminants: Roles of progesterone, interferons and endogenous retroviruses. Reproduction, Fertility and Development 19: 65–78. Copyright IETS 2007. Published by CSIRO PUBLISHING, Melbourne, Australia – http://www.publish.csiro.au/nid/45/issue/3364.htm.
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Figure 3 Blastocoel formation in embryos. Formation of a central, fluid-filled cavity is a central event in development, which results in morphological differentiation of the embryo into inner cell mass (from which the fetus will arise) and trophectoderm (from which the extraembryonic membranes arise). Two processes have been implicated in the formation of the blastocoel. The first involves pumping of sodium. The outer layer of blastomeres develop Naþ/Kþ ATPase pumps on the basolateral surface of the cell membrane that pump sodium out of the cell. Other specialized proteins on the apical side of the cell allow sodium to enter the cell and remove potassium that is pumped into the cell. Water flows between cells and into the central cavity of the embryo to maintain osmolarity. The second process involves channel proteins called aquaporins that allow direct movement of water across blastomeres. These proteins are present on the apical and basolateral surfaces of the plasma membrane of trophectoderm cells.
embryo and uterine environment as well as the physical forces applied to the zona pellucida as the blastocoel undergoes periodic contractions and expansions. The process of expansion and contraction is dependent upon embryonic synthesis of prostaglandin E2. Hatching is followed by a process initiated at about day 14 or 15 in cows and day 11 in sheep whereby the trophoblast rapidly expands to transform the embryo into a long filamentous structure. Expansion is rapid – while the day 13 cow embryo is 3 mm in diameter, it reaches a size of 25 cm by day 17 and begins to grow into the opposite uterine horn by day 18. The regulation of the process of trophoblast expansion, which is caused largely by increased cell division, is unknown. However, it is likely that the process requires a uterine signal since the process cannot be mimicked in vitro. One purpose of elongation is to ensure that the conceptus covers much of the endometrium so that secretory molecules regulating endometrial function (particularly those for inhibition of prostaglandin synthesis) are distributed widely throughout the uterine horn in which the embryo resides. Ruminant embryos spend a considerable period of time (16 and 18 days in sheep and cattle, respectively) unattached to the epithelial lining of the reproductive tract. Before attachment, the embryo is dependent upon secretions from the oviduct and endometrium for
nutritional support. The embryo has only a limited ability to utilize glucose as an energy source before compaction and glucose utilization can potentially be inhibitory to embryo development. During this period, pyruvate, lactate, and amino acids are the primary energy source. Many specific amino acids are present in high concentration in the oviduct and these not only serve as an energy source but also help regulate osmotic pressure and pH in the embryo and inhibit deleterious actions of glucose. Beginning at compaction, which represents the first major energy-expensive event in development, glucose uptake increases and glucose becomes the preferred energy substrate. As is apparent from the successful development of embryos produced by in vitro fertilization, there is no absolute requirement of the embryo for macromolecules specific to the reproductive tract environment. However, in vitro-produced embryos have aberrant biochemical and molecular properties compared to embryos produced in vivo and it is likely that macromolecules in oviductal and uterine fluid regulate early embryonic development. Many of the components of oviductal and uterine fluid are derived from transudation from the blood. In addition, both the oviduct and endometrium secrete specific molecules into the lumen of the reproductive tract. Secretion
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of many of these locally produced factors is under the control of progesterone or estrogen. Some molecules, such as oviductal secretory protein-1 and osteopontin, may play a role in fertilization. Many are regulatory molecules that mediate the complex communication between the cells of the reproductive tract and embryo. For example, growth factors and other regulatory molecules produced by cells of the oviduct and endometrium include insulin-like growth factors I and II, basic fibroblast growth factor (bFGF), activin, and leukemiainhibitory factor. Similarly, the embryo produces epidermal growth factor and transforming growth factor-. The reproductive tract also produces proteinase inhibitors such as plasminogen activator inhibitor-1 and tissue inhibitor of metalloproteinase-1 (TIMP-1) that likely prevent degradation of the lining of the female reproductive tract by embryonic proteinases and thereby block implantation of the embryo into the underlying stroma. Most embryonic mortality occurs during the preimplantation period, that is, before day 20 of pregnancy (see Figure 1). Numerous causes of embryonic loss have been identified. These include chromosomal abnormalities, inheritance of specific alleles causing embryonic or fetal death (e.g., allelic variants in fibroblast growth factor 2, STAT5A, and uridine-59-monophosphate in cattle), reduced progesterone concentrations or premature luteolysis in the dam, and defects in the process of development (e.g., inadequate trophoblast development and reduced secretion of interferon-). Oocytes damaged during follicular development can give rise to embryos with reduced developmental competence. Environmental influences that increase embryonic mortality include provision of feed with high levels of rumen-degradable protein, various microbial or viral diseases, and heat stress.
Maintenance of the Corpus Luteum Among the changes in maternal physiological function necessary for the maintenance of the corpus luteum is the rescue of the corpus luteum from luteolysis. In the absence of pregnancy, the corpus luteum regresses beginning around days 15–16 in cattle and days 13–14 in sheep as a result of release of prostaglandin F2 (PGF2) produced by endometrial epithelial cells. Prostaglandin is rapidly metabolized in the lung and other organs; the prostaglandin responsible for luteolysis arrives at the corpus luteum via a local pathway involving movement out of the utero-ovarian vein and into the closely apposed ovarian artery (Figure 4). Some prostaglandin may also reach the ovary through the lymphatic system. PGF2 causes luteolysis by stimulating local luteal synthesis of cytokines, endothelin-1, and nitric oxide, which in turn
Figure 4 Arrangement of the uterine and ovarian vasculature of the sheep. Note that the utero-ovarian vein, which carries blood draining the uterus, is in very close apposition to the highly coiled ovarian artery carrying blood to the ovary. The close anatomical relationship of these two vessels facilitates the countercurrent movement of prostaglandin F2 from the uterus to the ovary during luteolysis. Figure reproduced with permission from Flood PF (1991) The development of the conceptus and its relationship to the uterus. In: Cupps PT (ed.) Reproduction in Domestic Animals, 4th edn., pp. 315–360. San Diego, CA: Academic Press.
initiate functional (loss of progesterone secretion) and structural luteolysis (loss of luteal cells by apoptosis). Endothelin-1, for example, decreases progesterone production by luteal cells while stimulating additional luteal production of PGF2. As shown in Figure 5, the embryo blocks luteolysis by inhibiting PGF2 synthesis. The embryo first acts to inhibit luteolysis between days 15 and 17 of pregnancy in cow and days 12 and 14 in sheep. Removal of the embryo before this time does not affect luteal life span but the life span of the corpus luteum is extended if the embryo is removed afterward. The most important of the antiluteolytic signals produced by the embryo, at least during the initial rescue of the corpus luteum, is a molecule called interferon-. This molecule is a member of the class I interferon family, which also includes
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Figure 5 Concentrations of prostaglandin F2 in utero-ovarian plasma of nonpregnant and pregnant ewes during the time of expected luteolysis. Note the large pulses of prostaglandin F2 in the nonpregnant ewe that are responsible for luteolysis. These pulses are attenuated in the pregnant ewe. Figure is reproduced from Barcikowski B, Carlson JC, Wilson L, and McCracken JA (1974) The effect of endogenous and exogenous estradiol-17 on the release of prostaglandin F2 from the ovine uterus. Endocrinology 95: 1340–1349 with permission of the Endocrine Society.
interferon-, , and !. Interferon- arose in evolution in ruminants via gene duplication about 36 million years ago. While interferon- is similar in many ways to other class I interferons (including binding to class I interferon receptor, signal transduction, antiviral, and immunosuppressive activity), it differs from these interferons in the fact that gene expression is under the control of a trophoblast-specific promoter and expression is not strongly induced by virus. The pattern of expression of interferon- gene is distinct. The protein can be detected in low amounts when the embryo undergoes blastocyst formation. There is then a massive upregulation of gene expression coincident with impending luteolysis so that interferon- becomes the major secretory product of the conceptus from around days 15–20 in cattle and days 13–17 in the sheep. Gene expression is then rapidly turned off so that secretion is low by 25 days in cows and 21 days in sheep. Interferon- acts on endometrial epithelial cells to inhibit PGF2 secretion. Proposed mechanisms by which interferon- inhibits prostaglandin secretion are illustrated in Figure 6. Endometrial PGF2 synthesis is
caused by oxytocin-induced activation of cyclooxygenase-2, the rate-limiting step in the conversion of arachidonic acid to PGF2. Responsiveness of the endometrium to oxytocin is dependent upon estradiol-induced synthesis of oxytocin receptors. There is evidence to suggest that interferon- acts to inhibit expression of oxytocin receptor gene. Inhibition of oxytocin receptors may be due to inhibition of gene expression of estrogen receptors to make the endometrium unresponsive to estradiol induction of oxytocin receptors. This seems to be the case for sheep. In the cow, oxytocin receptors can be inhibited independent of the changes in estrogen receptor. In addition, interferon- increases the fatty acid linoleic acid, at least in cattle, and this molecule acts as an inhibitor of cyclooxygenase. The corpus luteum also becomes more resistant to destruction by PGF2 in early pregnancy. This could be due to interferon- because small amounts of the molecule leave the uterus, due to the actions of another prostaglandin, PGE2, that is produced by uterine endometrium, or due to another unknown molecule. Later in pregnancy, some unidentified molecule is important for
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(4) OTR Oxytocin (1) Figure 6 Proposed mechanism by which interferon- (IFN-) inhibits estradiol- and oxytocin-driven induction of luteolytic prostaglandin F2 (PGF2) release from endometrium. Luteolytic pulses of PGF2 are driven by the release of oxytocin from the corpus luteum (CL) and hypothalamus (1). Oxytocin acts through receptors (OTR) that are synthesized under the control of estradiol to activate the synthesis of PGF2 from arachidonic acid (AA) by cyclooxygenase. IFN- acts through binding to its receptor (IFNR) (2) to cause several changes that lead to inhibition of PGF2 synthesis. Foremost is a reduction in the synthesis of OTR, caused by inhibition of the estrogen receptor (ER) (3), as in the sheep, or by direct inhibition (4), as occurs in the cow. The reduction in OTR makes the endometrium unresponsive to oxytocin. In addition, IFN- increases intracellular concentrations of linoleic acid (Lin. acid), at least in the cow, and this fatty acid acts to inhibit cyclooxygenase (5).
luteal maintenance. This is so because administration of interferon- to nonpregnant animals extends luteal life span for a limited time that is much shorter than the period during which the corpus luteum of pregnancy persists. For example, intrauterine infusion of interferon- extended interestrous interval from an average of 23 days in controls to 32 days in cattle and from 16 days to 32 days in sheep.
Role of Progesterone While progesterone is indispensable for pregnancy in all mammals, the major sources of progesterone vary between species. In both cattle and sheep, progesterone is produced by the placenta, especially the fetal cotyledon. In cattle, however, placental secretion of progesterone is low for most of pregnancy, possibly because of the presence of an endogenous inhibitor of steroidogenesis. Removal of the corpus luteum before day 200 of pregnancy leads to pregnancy loss. Placental progesterone synthesis rises at the end of pregnancy. Pregnancy can continue if the corpus luteum is removed after day 200 although premature parturition is common. In the sheep, in contrast, the placenta becomes a sufficient
source of progesterone earlier in pregnancy, by day 50 of gestation. Progesterone maintains pregnancy by exerting a variety of actions on the uterus. One target is the myometrium – progesterone maintains the quiescence of this muscular layer of the uterus by causing hyperpolarization of myometrial cells. In vitro, progesterone causes increased proliferation of endometrial stromal cells in cattle without affecting epithelial cells. In vivo, however, progesterone causes some increase in the proliferation of luminal endometrial epithelial cells in sheep. It is likely that progesterone’s effects on the epithelium are mediated by growth factors such as hepatocyte growth factor that are secreted by the stroma. Progesterone increases expression of multiple genes in the endometrial lining of the uterus. Use of DNA microarray technology has led to the identification of 140 genes whose expression is higher during the luteal phase of the estrous cycle. Some progesterone-induced genes encode for proteins involved in conceptus nutrition. For example, retinol binding protein, which binds retinol and presumably transports it to the conceptus, is a progesteroneinduced endometrial secretory protein in cattle. It is also likely that the actions of progesterone are required for attachment of the conceptus to the endometrium and for subsequent placentation. Among the genes induced in the
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endometrium by progesterone is osteopontin, which is a glycoprotein component of the extracellular matrix that promotes cell–cell attachment by binding to cell surface integrins. Osteopontin may have an important role in mediating attachment of the trophoblast to the maternal endometrium. Other genes induced by progesterone regulate angiogenesis to increase vascular blood supply to the placenta. Among the genes identified as being upregulated during the luteal phase in cattle were several involved in angiogenesis including angiotensinogen, hypoxia-inducible factor 2-, and ephrin-A1. Exogenous administration of progesterone early in pregnancy hastens the growth of the embryo. Certain cases of infertility may be due to inadequate progesterone secretion because correlations have been made in cattle between the concentrations of progesterone in the blood early in pregnancy (days 4–5) and embryo development, amounts of interferon- in the uterus at day 16 of pregnancy, and pregnancy rate following insemination. The lactating dairy cow, which represents an infertile animal type, often experiences reduced circulating concentrations of ovarian steroids.
Placental Function Placentation is a gradual process in ruminants (see Reproduction, Events and Management: Pregnancy: Characteristics). Invasion of trophoblast cells into the uterine endometrium is limited and the basement membrane of the luminal epithelium of the endometrium remains intact. Attachment to the endometrium is a gradual process that starts with apposition of conceptus and endometrium, adhesion of the two tissues mediated by interdigitation of microvilli, invasion of trophoblast binucleate cells into the endometrial epithelium, and fusion of binucleate cells with endometrial epithelial cells to form a syncytium. In the cow, the first attachments are seen at day 18 and binucleate cell invasion is initiated at day 20. In sheep, the conceptus is adhered to the endometrium by day 16. The adhesion process is facilitated by cell adhesion molecules on the surface of the trophoblast (e.g., integrin) and molecules secreted by the endometrium such as galectin 15 and osteopontin. The anatomy of the definitive placenta, which has differentiated by about day 37 of pregnancy in the cow and day 30 in the sheep, is described elsewhere (see Reproduction, Events and Management: Pregnancy: Characteristics). Most growth in the placenta is completed by midgestation. Growth occurs at a much slower rate after this time in cattle and ceases in sheep. The placenta serves as the sole organ for chemical exchange between fetus and mother. All of the water, oxygen, and nutrients necessary to support life and growth of the developing fetus move through the placenta. In addition,
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the placenta serves as the organ by which fetal waste products including carbon dioxide and by-products of metabolism are removed to the mother for eventual elimination via the maternal respiratory, renal, and digestive systems. In addition to its transport role in fetal respiration, nutrition, and electrolyte balance, the placenta is also an endocrine organ. The hormones it produces alter maternal function to support pregnancy, lead to development of the mammary gland in anticipation of parturition, and participate in the process leading to parturition. Other regulatory molecules secreted by the placenta probably act locally on the uterus to optimize maternal function during pregnancy. The mechanism for transport across the placenta varies depending upon the specific chemical. Some molecules such as oxygen, carbon dioxide, free fatty acids, and some electrolytes passively diffuse across the placenta. The glucose transports GLUT1 and GLUT3 are involved in the transport of glucose. Amino acids are also actively transported a cross the placenta. Fatty acids are poorly transported across the ruminant placenta. As a result, despite being major sources of energy for the adult, fatty acids contribute in only a minor way to the energy needs of the fetus. Movement of some other molecules poorly soluble in water is facilitated by carrier molecules secreted by uterine glands. For example, retinol is carried by retinol binding protein and iron by transferrin. Most of the chemical exchange between mother and fetus occurs at the placentomes, which are formed from the union of specialized protrusions of the chorioallantois called cotyledons with corresponding structures on the maternal endometrium called caruncles (see Reproduction, Events and Management: Pregnancy: Characteristics). As a result, about 94% of fetal blood flowing to the sheep placenta is distributed to the cotyledons and 84% of maternal blood distributed to the uterus is distributed to the caruncles. Nonetheless, some placental exchange occurs in the interplacentomal regions also. In this region, there is a close contact between maternal and fetal epithelia. Moreover, maternal endometrial glands are in the interplacentomal regions and their secretions are released into the fetal–maternal interface. Placental efficiency can be estimated by determining the mass of fetal tissue that a given unit of placenta can support. By this measure, the ruminant placenta is a relatively efficient organ. The ratio of fetal to placental tissue is 13:1 in cattle and 10:1 in sheep and goats. In contrast, each gram of human placenta can support only about 6 g of fetus. The efficiency of the placenta is due largely to the architecture of the maternal blood vessels supplying the placenta relative to the fetal vessels. In ruminants, maternal and fetal blood vessels are arranged so that most blood flow is in a countercurrent or crosscurrent direction (Figure 7).
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Figure 7 Overview of the ruminant placenta. The placenta of the ruminant is characterized by an outer placental membrane formed from the fusion of the chorion and allantois (1). Knob-like projections of the chorion called cotyledons fuse with complementary structures on the maternal endometrium called caruncles to form placentomes. A single placentome is shown in (2) where fetal tissue is white and maternal tissue is stippled. Note the chorionic villi that project into the crypts in the maternal caruncles. As shown in (3), fetal vessels in chorionic villi are in close apposition to the corresponding maternal vessels in the caruncular septa. Basket-like maternal capillaries surround fetal venous capillaries. This arrangement of vessels allows for very efficient exchange of materials between mother and fetus because the pattern of flow is crosscurrent and countercurrent. fa, fetal artery; ma, maternal artery; mv, maternal vein. The figure, which was modified from Leiser R, Krebs C, Ebert B, and Dantzer V (1997) Placental vascular corrosion cast studies: A comparison between ruminants and humans. Microscopy Research and Technique 38: 76–87 and is reproduced with the permission of the publisher, is based on an earlier figure from Dantzer V, Leiser R, Kaufmann P, and Luckhardt M (1988) Comparative morphological aspects of placental vascularization. Trophoblast Research 3: 221–244.
Placental blood flow increases during pregnancy to match the increased demands of the fetus. Increased blood flow is due to vasodilation and angiogenesis. During late pregnancy, endothelial cells in the uterine artery increase synthesis of two vasodilators, prostacyclin and nitric oxide. Angiogenesis is at least in part regulated by growth factors such as vascular endothelial growth factor (VEGF) and bFGF produced by the placenta. These molecules, as well as others such as angiotensin II,
also likely contribute to vasodilation by participating in the regulation of synthesis of prostacyclin and nitric oxide. The placenta is an endocrine organ that produces hormones whose synthesis occurs uniquely in the placenta as well as those also produced by other organs. Among the former is placental lactogen, which is a member of the prolactin/growth hormone family. Synthesis occurs by the binucleate cells that migrate from the trophoblast into the uterine endometrium. Concentrations of placental lactogen in the blood increase as gestation progresses. Placental lactogen is believed to play two roles – increase mammary development in anticipation of the birth of the neonate and act as a metabolic hormone to redirect maternal metabolism to provide nutrients for the fetus. The role of the placenta in progesterone production has already been noted. In addition, the ruminant placenta produces estrogens, androgens, and prostaglandins in increasing amounts toward late pregnancy. Estrone synthesis predominates over estradiol-17 synthesis and most of the circulating estrogens exist in conjugated, inactive form (e.g., estrone sulfate). Estrogen plays at least two roles during late pregnancy. With progesterone, estrogen stimulates growth of the mammary gland. Estrogen also plays a role in parturition by counteracting the effect of progesterone on uterine contractility (causing depolarization of myometrial cells so that the uterine capacity for contractions is increased) and by acting on the fetus to increase adrenocorticotropin, the hormone that acts as the central regulator of the timing of parturition. Unlike some species, ruminant placentas do not produce a chorionic gonadotropin or relaxin. Another secretory product of the placenta is a group of proteins called the pregnancy-associated glycoproteins (PAGs). These proteins, which are members of the aspartic proteinase family, are very unusual in that they are encoded by a large number of genes (perhaps as many as 100). Some PAGs are produced predominately in binucleate cells, while others are produced throughout the chorionic epithelium. It is not clear whether the PAGs are hormones or what function they serve during pregnancy. However, PAG genes have undergone rapid evolution, suggesting that they play an important role in pregnancy. Radioimmunoassay of PAGs (originally called pregnancy-specific protein B) has been utilized as the basis for a pregnancy test in cattle. The long half-life of PAGs in the blood after parturition has limited the usefulness of PAG-based pregnancy tests, however. Maternal stress can lead to a disruption in placental function and compromised fetal development. Since hormones produced by the placenta are involved in mammogenesis, disruptions in placental function can conceivably alter subsequent milk yield. One example is heat stress, which causes a redistribution of blood from the internal organs (including the placenta) to the skin to
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Figure 8 Effect of heat stress on plasma concentrations of estrone sulfate in pregnant cows. Cows during the summer in Florida were housed with or without shade. Note the reduction in estrone sulfate concentrations in cows housed without shade. This reduction represents reduced secretion of estrone sulfate from the placenta. The figure, which is reproduced with the permission of the publisher, was modified slightly from Collier RJ, Doelger SG, Head HH, Thatcher WW, and Wilcox CJ (1982) Effects of heat stress during pregnancy on maternal hormone concentrations, calf birth weight and postpartum milk yield of Holstein cows. Journal of Animal Science 54: 309–319.
increase heat loss to the environment. The resultant decrease in placental perfusion leads to depressed placental growth accompanied by reduced fetal growth and placental hormone secretion (see Figure 8). There is evidence in cattle that failure to cool cows during late parturition can compromise subsequent milk yield. Undernutrition can also have complex effects on placental function. The placenta can adjust somewhat to a reduction in circulating glucose concentrations by increasing the synthesis of glucose transporter GLUT3. However, severe glucose deficiency can lead to reduced placental uptake of glucose and fetal growth retardation. In fat ewes, underfeeding during early and mid-pregnancy can actually lead to increased placental growth while overfeeding during the same period can sometimes reduce placental growth. Nutritional deprivation during fetal life can also have consequences such as altered cardiovascular function that persist into adult life.
Immunology of Pregnancy The conceptus inherits transplantation antigens from its father that could potentially lead to activation of tissue rejection responses against the conceptus by the mother. However, fetal gene expression in the placenta is altered to minimize the antigenicity of the tissue that is in direct contact with maternal tissues. Tissue graft rejection
responses are typically mounted by the host against two classes of proteins called major histocompatibility complex (MHC) antigens. The expression of MHC antigens on the trophoblast is limited. This absence of antigenicity on the placental surface is likely a major cause of survival of the conceptus as a foreign tissue. In sheep, both class I and class II MHC are absent from the surface of the placenta. The same is true in cattle except that there is some expression of MHC class I antigen on the interplacentomal parts of the chorionic epithelium, especially during late pregnancy. Most of these trophoblast MHC class I molecules represent ‘nonclassical’ MHC proteins that have limited genetic polymorphism and which may regulate populations of lymphocytes called natural killer cells that ordinarily kill cells not expressing MHC class I molecules. The conceptus and uterus secrete molecules that regulate the function of maternal lymphocytes. Early in pregnancy, interferon- secreted by the trophoblast of the cow and sheep causes upregulation of a host of immune response genes in the endometrium. Later in pregnancy, molecules that inhibit immune responses predominate. Progesterone is one of the major systemic regulatory molecules produced during pregnancy and it regulates uterine immune function. In fact, progesterone can promote survival of skin grafts and xenografts in the sheep uterus. Progesterone can directly inhibit lymphocyte function at micromolar concentrations. However, it
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is likely that concentrations of progesterone at the fetal– maternal interface do not reach these high concentrations until after placental progesterone synthesis becomes sufficient to maintain pregnancy (i.e., day 50 of gestation in sheep and day 200 in cattle). Rather, it is believed that progesterone regulates uterine immune function primarily by inducing endometrial secretion of molecules that block lymphocyte proliferation. In the ewe, this activity has been ascribed to a progesterone-induced protein of the serpin superfamily of serine protease inhibitors called ovine uterine serpin (also called SERPINA14). Despite the prevalence of immunosuppressive molecules in the uterine environment, some leukocyte populations accumulate in the endometrium during pregnancy and may become activated to play roles in immune regulation, placental growth, parturition, or host defense against uterine pathogens. One such population of cells is the macrophage. Another, at least in the sheep, is a type of lymphocyte called the -T lymphocyte. These granulated cells, which increase in both number and granularity after about day 50 of pregnancy, have been identified as -T lymphocytes. The cells express perforin and may function as lytic cells to facilitate parturition or to lyse virally infected cells. They may also secrete cytokines that promote placental growth. There is some limited evidence that expulsion of the placenta is facilitated if the mother and conceptus have dissimilar MHC class I haplotypes. Perhaps, macrophages, -T cells, or other leukocyte populations are involved in the placental expulsion process. See also: Reproduction, Events and Management: Pregnancy: Characteristics.
Further Reading Barcikowski B, Carlson JC, Wilson L, and McCracken JA (1974) The effect of endogenous and exogenous estradiol-17 on the release of prostaglandin F2 from the ovine uterus. Endocrinology 95: 1340–1349. Bell AW, Hay WW, Jr., and Ehrhardt RA (1999) Placental transport of nutrients and its implications for fetal growth. Journal of Reproduction and Fertility Supplement 54: 401–410.
Blomberg L, Hashizume K, and Viebahn C (2008) Blastocyst elongation, trophoblastic differentiation, and embryonic pattern formation. Reproduction 135: 181–195. Brevini TA, Cillo F, Antonini S, Tosetti V, and Gandolfi F (2007) Temporal and spatial control of gene expression in early embryos of farm animals. Reproduction, Fertility and Development 19: 35–42. Collier RJ, Doelger SG, Head HH, Thatcher WW, and Wilcox CJ (1982) Effects of heat stress during pregnancy on maternal hormone concentrations, calf birth weight and postpartum milk yield of Holstein cows. Journal of Animal Science 54: 309–319. Dantzer V, Leiser R, Kaufmann P, and Luckhardt M (1988) Comparative morphological aspects of placental vascularization. Trophoblast Research 3: 221–244. Eckert JJ and Fleming TP (2008) Tight junction biogenesis during early development. Biochimica et Biophysica Acta 1778: 717–728. Flood PF (1991) The development of the conceptus and its relationship to the uterus. In: Cupps PT (ed.) Reproduction in Domestic Animals, 4th edn., pp. 315–360. San Diego, CA: Academic Press. Gardner DK (1998) Changes in requirements and utilization of nutrients during mammalian preimplantation embryo development and their significance in embryo culture. Theriogenology 49: 83–102. Hansen PJ (2000) Immunology of reproduction. In: Hafez B and Hafez ESE (eds.) Reproduction in Farm Animals, 7th edn., pp. 341–353. Philadelphia, PA: Lippincott Williams and Wilkins. Hansen PJ (2007) Hidden factors affecting fertility WCDS Advances in Dairy Technology 19: 339–349. Khatib H, Maltecca C, Monson RL, Schutzkus V, Wang X, and Rutledge JJ (2008) The fibroblast growth factor 2 gene is associated with embryonic mortality in cattle. Journal of Animal Science 86: 2063–2067. Leiser R, Krebs C, Ebert B, and Dantzer V (1997) Placental vascular corrosion cast studies: A comparison between ruminants and humans. Microscopy Research and Technique 38: 76–87. Mitko K, Ulbrich SE, Wenigerkind H, et al. (2008) Dynamic changes in messenger RNA profiles of bovine endometrium during the oestrous cycle. Reproduction 135: 225–240. Robinson RS, Hammond AJ, Wathes DC, Hunter MG, and Mann GE (2008) Corpus luteum–endometrium–embryo interactions in the dairy cow: Underlying mechanisms and clinical relevance. Reproduction in Domestic Animals 43(supplement 2): 104–112. Skarzynski DJ, Ferreira-Dias G, and Okuda K (2008) Regulation of luteal function and corpus luteum regression in cows: Hormonal control, immune mechanisms and intercellular communication. Reproduction in Domestic Animals 43(supplement 2): 57–65. Spencer TE, Johnson GA, Bazer FW, Burghardt RC, and Palmarini M (2007) Pregnancy recognition and conceptus implantation in domestic ruminants: Roles of progesterone, interferons and endogenous retroviruses. Reproduction, Fertility and Development 19: 65–78. Watson AJ, Natale DR, and Barcroft LC (2004) Molecular regulation of blastocyst formation. Animal Reproduction Science 82–83: 583–592. Wood CE (2005) Estrogen/hypothalamus–pituitary–adrenal axis interactions in the fetus: The interplay between placenta and fetal brain. Journal of the Society for Gynecologic Investigation 12: 67–76.
Pregnancy: Parturition P L Ryan, Mississippi State University, MS, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2299–2309, ª 2002, Elsevier Ltd.
Introduction Parturition in animals, after a normal gestation, is a unique physiological process that signifies the termination of pregnancy and the beginning of extrauterine life of the newborn (neonate). Once parturition is initiated, it must proceed to completion and, as such, is difficult to interrupt or delay. It is a timed event that requires the fetus to have attained a stage of maturity that will enable it to survive extrauterine life. Parturition involves the orchestration of a complex series of physiological events that require the rotation of the fetus into the birth position, which is accompanied by a cascade of endocrine changes that terminates with a successful delivery. When the fetus is in the birth position, the temporal alignment of these endocrine changes is paramount in determining the timing of delivery. Although many of the hormonal cues as well as physiological and anatomical changes that precede delivery are similar among domestic animals, each species seems to have developed its own temporal relationship among events that govern parturition. A great deal of research has been undertaken over the past 25 years, particularly on the endocrine parameters of the fetal hypothalamic– pituitary–adrenal (HPA) axis and endocrine contribution of the fetal membranes, to understand better the mechanisms associated with parturition in humans and domestic animals alike. With the exception of the mouse, the sheep has been the most popular animal model of study and data from this model have contributed significantly to this field of reproductive biology. Parturition in domestic animals is initiated by the fetus but can be postponed temporarily, as in the case of the mare, when disturbed. Feeding can also alter the exact timing of delivery in sheep and cattle. It is now very apparent that both the mother and the fetus contribute significantly to the events associated with parturition and the importance of their individual contributions will be addressed in this article.
Duration of Pregnancy In the western hemisphere the most common dairy breeds of cattle are of European origin. However, other domestic animals, including the goat, sheep and, to a lesser degree, the horse, are used for the harvesting of milk for production
of dairy products. Observations of these domestic breeds have shown that duration of gestation is genetically determined (see Reproduction, Events and Management: Pregnancy: Characteristics). However, factors that can modify length of gestation include age and parity of the dam, sex and size, normality and abnormality, and genotype of the fetus, twinning (in cow and mare) and an array of environmental factors (Figure 1). The average duration of pregnancy in dairy breeds of cattle is approximately 280 days but there are considerable differences between breeds (Table 1). The yak, although not a common species, is an important related species of cattle found in the harsher climates of Asia where it is used as a source of meat and milk. In this species, duration of pregnancy is much shorter (258 days) and this is reflected in the lower birth weight of calves (bull and heifer calves, 14.2 and 12.9 kg, respectively). The camel, an important beast of burden and source of meat and milk in desert environments, displays species variation in duration of gestation. The African dromedary has a gestation length of 385 days (13 months) while the Bactrian camel has a gestation length ranging from 370 to 440 days. There is also a breed-dependent difference in the duration of pregnancy in the horse (pony, light and draft breeds, 330–345 days), sheep (domestic breeds, 144–152 days) and goat (domestic breeds, 145–151 days). Genotype is apparent when cows are crossed with certain breeds of sires. Crossbreeding may result in an increase in length of gestation. Embryo transfer studies have clearly established that the breed of the embryo determines length of gestation (i.e. embryos from breeds with shorter gestation transferred to recipients with longer gestation and vice versa). Gender has also been cited as a factor, with bull calves having a slightly longer gestation (1–2 days) than heifers of the same breed. Size and/or weight of calf may contribute to a longer gestation (Table 1), a factor that may be influenced by season and/or level of nutrition of the dam. Twinning is thought to occur in 1–2% of cattle and is more frequently observed in multiparous or older cows. In sheep, the genotype of the fetus accounts for approximately two-thirds of the variation in length of gestation; male lambs and singletons are carried longer and gestation lengths increase with age of the dam.
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Variations in gestation length
Maternal factors Age of dam Parity of dam Twinning
Fetal factors Size/weight of fetus Fetal gender Pituitary and adrenal function
Genetic factors Breed Fetal genotype
Environmental factors Nutrition Season Temperature
Figure 1 Schematic representation of factors that may influence length of gestation in the cow, goat, sheep and horse. (Reproduced with permission from Jainudeen and Hafez (2000).)
Table 1 Gestation length and birth weights of different breeds of cattle
Breed
Average length of gestation in days (range)
Average birth weight (kg)
Aberdeen Angus Ayrshirea Brown Swissa Charolais Friesian–Holsteina Guernseya Hereford Jerseya Milking Shorthorna Simmental South Devon Yak
280 (273–283) 279 (277–284) 286 (285–287) 287 (285–288) 279 (272–284) 284 (281–286) 286 (280–289) 280 (277–284) 283 288 (285–291) 287 (286–287) 258 (226–283)
28.0 34.0 43.5 43.5 41.0 30.0 32.0 24.5 ? 43.0 44.5 13.0
a Common dairy breeds. Compiled from Noakes (1997)
Presentation of Fetus in Birth Position As parturition approaches, the fetus must rotate into the birth position. For most of gestation, the fetus usually rests on its back with its feet directed upward. After rotation into the birth position, the fetus rests on its abdomen or thorax with its nose resting between the forefeet as they extend toward the uterine aspect of the cervix (Figure 2). Correct positioning of the fetus allows for parturition to proceed more easily while malpresentation of the fetus predisposes to a complicated delivery that may, in severe cases, lead to the loss of both fetus and dam. This is true for the cow, sheep, horse and goat. Abnormal presentation of the fetus occurs in 5% of dairy cows and is observed more frequently with twin pregnancies. Such abnormal presentations may range from one leg to both legs and/or head reflected back to severe breech positions, including tail presentation toward the uterine aspect of the cervix (Figure 3).
Fetal Hypothalamic–Pituitary–Adrenal Axis The initiation of parturition is associated with a spontaneous increase in activity of the fetal HPA, and is completed by a complex interaction of endocrine, neural and mechanical events. The discovery in the 1960s that hypophysectomy of the fetal sheep abolished initiation of parturition in the ewe demonstrated that the fetus played a fundamental role in the process of parturition. Since it is essential that the fetus is born at a time when it is capable of surviving extrauterine life, it is fitting that it plays a role in determining the time of parturition. It is now well established that the fetus initiates parturition and that together the fetal and maternal endocrine environments orchestrate the process of delivery. What drives the activation and maturation of the periparturient fetal HPA axis is unclear. Several lines of evidence have suggested that the increase in activity is a programmed event, and that the rapid growth of
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Figure 2 Normal birth position in cows assumed before labor. After rotation into the birth position, the fetus rests on its abdomen or thorax with its nose resting between its forefeet as they extend forward toward the uterine aspect of the cervix. The horse, sheep and goat adopt a similar birth position. (Adapted from Salisbury GW, Van Demark NL and Lodge JR (1978) Physiology of Reproduction and Artificial Insemination in Cattle, 2nd edn, San Francisco: WH Freeman.)
the fetus in the final weeks of gestation causes the release of endocrine signals from the placenta, leading to the maturation of key organ systems in the fetus, including the HPA axis, and terminating with delivery (Figure 4). Research data suggest that the increase in fetal HPA axis activity at the end of gestation is associated with the increased secretion of estrogen by the placenta. Chronic increases in estradiol and androstenedione, another placental hormone, can advance the day of parturition in the sheep and other species. Others have promoted the hypothesis that release of prostaglandin E2 (PGE2) by the placenta facilitates the maturation of the HPA axis, resulting in increased secretion of adrenal corticotrophic hormone (ACTH) and cortisol. The rapid growth of the fetus toward the end of gestation is thought to be a genetically programmed event stimulating both fetal and maternal sources of PGE2 that facilitate the maturation of the fetus and preparation of the mother for delivery. In the latter stages of gestation, the pituitary source of ACTH is from corticotrophic-releasing hormone (CRH)-sensitive cells that act on the adrenals via type II receptors to increase fetal cortisol production. Placental PGE2 overrides the negative-feedback effects of cortisol on CRH release, thus enhancing fetal adrenal cortisol production. Cortisol enhances prostaglandin endoperoxide H synthase-2 (PGHS-2) expression, leading to an increase in PGE2 production that in turn promotes C17 hydroxylase and cytochrome P-450c17
enzyme activity in the placenta. This elevated enzyme activity increases the amount of C19 steroids for conversion to estrogen, resulting in increased contractionassociated protein (CAP) gene expression (oxytocin and prostaglandin receptors, Naþ and Ca2þ ion channels, gap junction protein connexin-43). The functional expression of these CAP genes leads to increased spontaneous activity of the myometrium and enhanced responsiveness to oxytocin and prostaglandin. In addition to these changes, the coincidental increase in the estrogen-to-progesterone ratio promotes production of both oxytocin and prostaglandin F2 (PGF2). The increase in estrogen synthesis toward the end of pregnancy is a common phenomenon among mammalian species but strategies associated with its production may vary. In the bovine, parturition is initiated by endocrine changes originating from the fetus when it reaches a critical size and stage of maturation. The fetal adrenals become increasingly responsive to ACTH secreted by the fetal pituitary. In turn, there is a corresponding increase in the rate of cortisol secretion from the fetal adrenals that induces placental trophoblast 17-hydroxylase and 17,20-lyase activity. This activity increases the metabolism of progesterone to estrogen, thereby increasing the maternal estrogen-to-progesterone ratio. During pregnancy, progesterone maintains the quiescent state of the uterus that facilitates the growth and development of the fetus. In the cow, the onset of
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Figure 3 Diagrammatic representation of abnormal birth positions that may be observed in cattle. (Adapted from US Department of Agriculture (1942) Diseases of Cattle.)
labor is associated with a switch from a state of progesterone domination to one of enhanced estrogen influence. The decline in circulating progesterone, often referred to as progesterone ‘withdrawal’, together with elevated circulating concentrations of estrogen, stimulates increased prostaglandin production, formation of myometrial gap junctions, sensitization of the uterus to uterotonic agents (prostaglandins, oxytocin), cervical ripening and the commencement of labor. Cortisol is thought to increase prostaglandin synthesis
during labor primarily due to an increase in PGHS-2 (inducible cyclooxygenase, COX-2 gene product) expression and function in uterine and intrauterine tissue. The activity of prostaglandin endoperoxidase synthase in the placenta (cotyledons) increases and mirrors the changes in ACTH concentrations seen in fetal plasma at this time. The prostaglandin cascade is also activated by proinflammatory cytokines (i.e. interleukin1 ) and these effects are modulated by antiinflammatory cytokines (i.e. interleukin-10). Oxytocin, a potent
Reproduction, Events and Management | Pregnancy: Parturition
Fetal genotype
Fetal endocrine pathway
Fetal growth pathway
Hypothalamic–pituitary– adrenal axis
Myometrial stretch
Placental endocrine axis
Contraction-associated protein gene expression
Labor
Figure 4 Schematic representation of factors associated with the onset of events involved in labor in domestic animals.
uterotonic stimulant, is expressed in intrauterine tissue in late pregnancy and stimulates myometrial contractility and fetal expulsion.
Maternal Endocrine Changes and Myometrial Activity Progesterone is the primary hormone responsible for the maintenance of pregnancy. In the pig, goat and cow the presence of functional corpora lutea is essential for the production of progesterone and pregnancy maintenance, while in the ewe and the horse the placenta is the primary source after the luteoplacental shift has occurred. This shift in source of progesterone is completed by approximately day 55 and day 150 of pregnancy in the ewe and mare, respectively. Removal of the ovaries before this date will terminate the pregnancy. Parturition cannot proceed without uterine contraction. At term, there is a dramatic increase in uterine myometrial activity. This activity is facilitated by spontaneous changes in the secretion of estrogen and progesterone at the end of gestation. During pregnancy, progesterone maintains uterine quiescence by hyperpolarizing the myometrial smooth muscle cells. As the rate of production and concentrations of estrogens increases relative to progestagens, the myometrial cells begin to depolarize and increase in contractile activity. This activity is augmented by the release of prostaglandins. In most mammalian species, the increase in estrogen toward the end of gestation seems to be a common theme and the placenta seems to be the source of the
507
estrogen responsible for the increased myometrial activity. However, the strategy in the production of estrogen differs among species. At the end of gestation, the sheep placenta, under the influence of increased fetal cortisol levels, acquires the ability to induce 17 -hydroxylase enzyme activity, which enables the synthesis of placental estrogen. Thus, the maturation of the fetal HPA axis is critical for the initiation of parturition in ruminants. In the horse, the source of estrogen is the fetoplacental unit because the equine placenta alone does not possess an inducible 17-hydroxylase enzyme system. In this instance, the steroid precursors, for example, dihydroepiandrosterone (DHEA), necessary for estrogen synthesis, are derived from the fetal horse gonads. Gonadectomy of the fetal horse results in the interruption of initiation of parturition in this species. Humans and other primates are similar to the horse in that estrogen synthesis is also dependent on a functional fetal–placental unit. However, the source of steroid precursors (i.e. DHEA) is the fetal adrenals since the placenta in these species lacks the cytochrome P-450C17 enzyme system to produce estrogen from cholesterol. Parturition depends on the coordinated rhythmic contraction of the uterine smooth muscle (myometrium) and on involuntary contraction of abdominal muscles. Throughout most of pregnancy the myometrium is nonexcitable and relatively unresponsive to uterotonic agents (prostaglandins, oxytocin). This relative quiescent state of the uterus is due to progesterone or the progesterone ‘block’. Under the influence of progesterone, myometrial activity and coordination of contractions and responsiveness to uterotonic agents are diminished. However, the onset of labor is linked to a transformation in the pattern of contractile activity of the myometrium. The myometrium becomes highly responsive to prostaglandins (PGE2 and PGF2) and oxytocin once the progesterone block has been removed. This increased capacity of the myometrium to develop contractions is referred to as myometrial activation, and once activated it can respond to paracrine and endocrine stimulation from increasing concentrations of uterotonic agents. This concomitant activation and stimulation enable the myometrium to generate intense, high-amplitude and high-frequency contractions that are necessary to dilate the cervix and facilitate fetal expulsion. Also, fetal growth leading to increased tension on the uterine wall and stretching of the myometrium can augment CAP gene expression. It has been suggested that two parallel pathways are initiated by signals within uterine tissues that lead to the development of intense and synchronous myometrial contractions
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that facilitate dilation of the cervix and accommodate delivery of the fetus (Figure 5). During pregnancy and in the face of elevated progesterone, fetal growth stimulates myometrial stretch and hypertrophy which in turn reduces myometrial tension. At term, the increase in the estrogen-to-progesterone ratio terminates the uterine growth response, while increased fetal growth enhances myometrial tension, CAP gene expression and initiation of labor. The rise in estrogen not only increases myometrial activity but also enhances the synthesis and release of prostaglandins and oxytocin during labor. Myometrial smooth muscle contraction is dependent on an increase in intracellular free calcium, which causes formation of a calcium–calmodulin complex. This complex binds to and activates myosin kinase to
interact with actin to cause contraction of the smooth muscle fibers. Oxytocin and PGF2 influence smooth muscle activity by regulating intracellular concentrations of Ca2þ. Prostaglandins increase free calcium by liberating Ca2þ from intracellular binding sites while oxytocin has a direct effect on the rate of Ca2þ influx and also lowers the threshold for initiation of action potential activity. Oxytocin is not effective on myometrial activity until uterine receptors are expressed. This is an estrogen-dependent event in sheep. Similar patterns of myometrial activity exist before parturition in the sheep, goat and cow. Recent information also suggests that the fetal membranes in the sheep and human contribute to the enzyme pathways that facilitate and promote endocrine (prostaglandin) synthesis at parturition.
? Signal E:P
Myometrial transcription factors (c-fos, c-jun, c-myc)
?
Contraction-associated proteins (oxytocin and prostaglandin F2α receptors, gap junctions, Na+ and Ca2+ ion channels)
Increased production and release of uterotonic agonists (oxytocin, prostaglandin F2α)
Myometrial contraction
Myometrial stimulation
Labor
Neonate(s) Figure 5 Proposed scheme for the initiation of parturition. E:P, estrogen-to-progesterone ratio. At term, the uterine environment switches from a progesterone-dominated to an estrogen-dominated environment. The consequence of this shift is the activation of parallel pathways that involve a complex series of molecular, cellular and biochemical events within uterine tissues terminating with the expulsion of the fetus and fetal membranes. (Adapted from Lye SJ (1996) Initiation of parturition. Animal Reproduction Science 42: 495–503.)
Progesterone may regulate myometrial activity by downregulating the synthesis of oxytocin receptors, prostaglandin receptors and gap junction proteins, as well as inhibiting pituitary oxytocin release and suppressing prostaglandin production. Progesterone blocks high-amplitude myometrial cell contractions but low-amplitude, high-frequency contractions persist during pregnancy. However, there are other endocrine factors that regulate myometrial activity. For example, relaxin, a small polypeptide hormone, is capable of inhibiting spontaneous myometrial contractions. Although a bovine relaxin gene and protein have not been identified, there is immunohistochemical evidence for the presence of the protein hormone in the corpora lutea of pregnant cows but little or no activity was found in the placenta. Heterologous radioimmunoassay studies have detected relaxin in plasma of pregnant cows between days 5 and 1 prepartum and this therefore suggests a role for relaxin in preparation of the birth canal for delivery, as in other domestic species. A relaxin-like factor (RLF) gene and protein is expressed by the bovine corpus luteum of pregnancy; however, its role in the corpus luteum is unclear. Moreover, the identification of a third relaxin gene in the human (H3) and the mouse (M3) may prove to be the active relaxin gene in the bovine, although such a gene has yet to be identified in this species. Whether similar expression of RLF and/or a third relaxin gene occurs in the bovine placenta has yet to be determined, and implicating a role during delivery for RLF protein would be speculative. A recent but all-important discovery in the relaxin field is the activation of orphan receptors (heterotrimeric guanine nucleotide-binding protein (G-protein)-coupled receptors) by relaxin via an adenosine 39,59-monophosphate-dependent pathway. This discovery will undoubtedly lead to new studies that will enhance our understanding of the role relaxin plays in parturition. Other inhibitory uterotonins, including prostacyclin and nitric oxide, have an inhibitory effect similar to relaxin. Progesterone, in association with relaxin, nitric oxide and prostacyclin, suppresses spontaneous and stimulated myometrial activity, thus preventing the spontaneous expulsion of the fetus. In summary, parturition is thought to be a linear biochemical and physiological process beginning with fetal maturation, leading to an increase in fetal cortisol, which initiates synthesis and release of uterotonic agents that intensify uterine myometrial contractile activity, leading to delivery. The endocrine events associated with the periparturient period are complex, and summarized in Figures 5 and 6. Enhanced myometrial activity and delivery at term result from the dual activity of increased uterine activation as characterized by increased connexin-43 (gap junction proteins), oxytocin and prostaglandin receptor expression, along with increased concentrations of oxytocin and prostaglandins.
Relative hormone levels
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Fetal cortisol
Progesterone Estrogens Prostaglandin
–10 –8 –6 –4 –3 –2 –1 Days
0
1 2 3 Parturition
4
5
Figure 6 Relative hormone profiles in the cow during the periparturient period. (Adapted from Senger PL (1997) Pathways to Pregnancy and Parturition, p. 243. Pullman: Current Conceptions.)
Cervical Ripening and Expulsion of the Fetus During pregnancy in mammals, the cervix is a relatively firm and inextensible structure that protects the fetus from the external environment and prevents spontaneous delivery. This firmness is due to the highly organized arrangement of collagen fibers in dense parallel bands. As term approaches, the cervix begins to soften and the collagen fibers become dispersed and randomly oriented within an increased proteoglycan extracelluar matrix, accompanied by an increase in the uptake of water. Remodelling of cervical tissue is necessary in order to accommodate normal expulsion of the fetus and fetal membranes at term. This softening or remodeling and increased distensibility of the cervix are regulated hormonally. Several hormones, including estrogen, relaxin, prostaglandin and oxytocin, have been implicated in the stimulation of cervical distensibility. Unlike in the mare and ewe, the ovaries of the cow are essential for the latter stages of pregnancy maintenance and thus may be the primary source of hormones for initiating cervical ripening. Relaxin is an important hormone of pregnancy in many species and is known to facilitate tissue remodelling of the reproductive tract, including the cervix. The effects of relaxin on cervical ripening are particularly important in the mare and the sow since failure of relaxin to facilitate these events can result in increased incidence of dystocia and stillbirths, as is the case in the pig. Interestingly, the placenta is the source of relaxin during pregnancy in the mare, while the corpora lutea of pregnancy are the principal source in the sow. Although the evidence of a bovine relaxin is sketchy, there are
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sufficient physiological data to support the presence of such a hormone in this species. The biochemistry of cervical ripening is a complex process that involves the upregulation of proteolytic factors such as matrix metalloproteinases and the corresponding tissue inhibitors of matrix metalloproteinases. Also, the increased expression of gap junction proteins (connexin-26, -32 and -43) is thought to be important in this process. Connexins are gap junction proteins that belong to an evolutionarily conserved, multigene family of channel-forming proteins which are important for cell–cell communication and are hormonally regulated. In cattle, the ratio of fetal birth weight to maternal weight is high (approximately 11% and may be higher when crossbreeding is practiced), and the pelvic cavity expands rapidly during the last 4 days prepartum to facilitate delivery of the calf. Little is known concerning secretion of relaxin in the cow; however, there is reason to suspect that relaxin may loosen the pelvic ligaments and facilitate softening of the cervix. Treatment of cows with highly purified porcine relaxin a week before their due date resulted in a rapid increase in pelvic height and width similar to the elevation of the tail head seen in prepartum cows. When porcine relaxin was placed in the cervical os of beef heifers 5–7 days before the anticipated day of delivery, a premature increase in the dilation of the cervix occurred within 8–12 h of relaxin treatment. In addition, this relaxin-induced cervical ripening was observed to reduce the incidence of dystocia in the treated heifers. In general, little is known about the hormonal regulation of cervical ripening or distensibility in cattle at parturition. Most of our knowledge of the changes that occur in the cervix before delivery is derived from studies performed in pigs and rodents.
Stages of Labor Labor has been described as occurring in three stages; great variations in the duration of these stages exists among species (Table 2). Stage I involves the initiation of labor by the fetus and the resultant dilation of the
cervix. Uterine contractions begin to occur in a more rhythmic fashion and continue until the cervix is fully dilated and continuous with the vagina. This period is accompanied by increased restlessness of the dam accompanied by elevated body temperature, pulse and respiratory rates. This is more evident in the horse where the mare may break out in a sweat. Changes in the fetal position and posture will also occur at this stage. Stage II is associated with fetal expulsion. During this stage of labor the dam may assume recumbency and commence straining, which results in the rupture of the allantochorion and release of chorionic fluid from the vulva. Moments later, the amnion appears as a whitish fluid-filled bag at the vulva. This is followed by the appearance of the forelimbs and nose of the fetus and is accompanied by strong uterine and abdominal contractions. The expulsion and delivery of the fetus follow rupture of the amnion. This stage of labour is the shortest and is associated with the commencement of strong uterine and abdominal contractions and completion of cervical dilation. The cervix remains in a dilated state until the termination of the delivery of the fetus. In sheep and goats, twin births are usually more rapid than single births, but the interval between the delivery of twins may vary from minutes to a couple of hours. Stage III is the final stage of labor and is associated with the expulsion of the fetal membranes. During this stage of labor the uterine contractions begin to decrease in frequency and amplitude. For successful expulsion of the placenta to occur, loosening of the chorionic villi from the maternal endometrial crypts must take place. The spasmodic contraction of the uterine wall, which abates following the inversion and expulsion of the fetal membranes, facilitates this process. However, the interval between birth of the fetus and expulsion of the fetal membranes varies among species. In the horse, the placenta is shed within 30–60 min after delivery compared to the 6–12 h it typically takes in the cow (Table 2).
Table 2 Average duration of the three stages of labor in different domestic species Stages of labor (h) Animal
I: Dilation of cervix
II: Expulsion of fetus(es)
III: Expulsion of fetal membranes
Cow, buffalo Ewe Goat Mare Sow
2–6 2–6 ? 1–4 2–12
0.5–1.0 0.5–2 ? 0.2–0.5 2.5–3
6–12 0.5–8 ? 1 1–4
Compiled from Jainudeen and Hafez (2000).
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Complications (Dystocia and Retained Placentas)
Table 3 Recommended weight and age of dairy heifers at time of mating, by breed
Complications associated with parturition can impact negatively on postpartum cows in terms of their reproductive efficiency and milk productivity (see Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity; Pregnancy: Periparturient disorders). Dystocia and retained placenta are the most common problems associated with parturition in dairy cattle and are probably linked to a number of interrelated variables. Dystocia is defined as prolonged or difficult delivery and can be due to either fetal or maternal abnormalities. Fetal dystocia refers to an abnormality of the fetus that may lead to incorrect birth positioning while maternal dystocia refers to abnormality of or physical problem of the mother. Such abnormalities of the mother may include poor pelvic confirmation, incomplete ripening of the cervical canal and immaturity. The most common causes of dystocia in cattle include the incompatibility of size of the fetus and the mother’s pelvis and the malpresentation, position or posture of the fetus in utero. In beef cattle, size and birth weight of calves have been determined to be the most common factor contributing to dystocia. Very large calves also tend to have higher perinatal mortality. Other factors that contribute to dystocia are uterine inertia, uterine torsion and failure of the cervix to dilate. In primiparous or first-calf heifers, stricture of the vulva can also be problematic and may lead to dystocia and stillbirth. In addition, the economic need to place heifers into the milking parlor at an earlier age has led to the practice of breeding heifers at under 15 months of age, increasing the risk of dystocia in first-calf heifers. In the yak, the incidence of dystocia is low (3.3%) and twinning is rare (0.5%). In high-yielding dairy cows, reduced blood calcium concentrations at time of parturition can be problematic and increase the risk of dystocia in these animals. This condition is associated with milk fever and the incidence is on the rise as dairy producers genetically select for high-yielding cows. Milk fever is a metabolic disorder of calcium homeostasis and decreased blood calcium reduces the availability of Ca2þ for uterine smooth muscle contraction and, in so doing, increases the risk of a difficult delivery and/or retained placenta (see Diseases of Dairy Animals: Non-Infectious Diseases: Milk Fever). Feeding anionic salts to near-term cows, which mobilizes bone reservoirs of calcium, thereby elevating blood Ca2þ concentrations and availability for uterine muscle tissue, can alleviate this condition. Treatment with opiate antagonists (e.g. naloxone) in low doses has recently been shown to be a safe method to offset the adverse effects of milk fever in cows and thus reduce muscular complications at delivery (dystocia and retained placenta).
Breed
Minimum weight range (kg)
Minimum age (months)
Ayrshire Brown Swiss Friesian–Holstein Guernsey Jersey Milking Shorthorn
308–318 374–397 374–397 308–318 263–272 308–354
14–15 14–15 14–15 14–15 14–15 14–15
Compiled from Gillespie JR (1998) Animal Science, p. 948. New York: Delmar.
Dystocia in horses is also a serious problem and if proper assistance is not given can put both the mare and foal at risk. The incidence of dystocia in horses is breed-dependent, with a rate of 4% in light breeds (thoroughbred, standardbred, walking horse, saddle horse) but increases to 8% in pony breeds (Shetlands, Connemara), with an incidence of 10% in the heavy draft breeds (Shire, Belgian). The causes of dystocia in horses are many but the most common appear to be reflected head and neck and/or forelimbs when the foal is in anterior presentation. Other contributing factors include deformed limbs, oversized fetus and hydrocephalus, being more frequently observed in pony breeds. Dystocia may also affect the future reproductive performance of the cow and is often associated with a delayed postpartum estrus, extended calving interval and an overall reduction in fertility (see Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity). Implementation of two simple rules of thumb may help reduce the incidence of dystocia and resulting stillbirths in a herd. The first is to avoid breeding young heifers when below their optimum breeding weight (Table 3) and the second is to take advantage of the selection of easy-calving bulls that have been identified by breed associations to inseminate heifers. Dairy heifers should attain at least 60% of the mature adult body weight for the breed before being mated. European and Israeli dairy producers have taken advantage of genetic information provided by their dairy breed associations on control of dystocia due to feto-pelvic incompatibility, resulting in approximately a 60% and 40% reduction in the incidence of dystocia and stillbirths, respectively. The bottom line is to select carefully ease-of-calving sires, giving due consideration to maternal traits to avoid producing progeny that may be small of stature as adults and thus confound the dystocia problem. It is important to remember the genetic (breed) and environmental (size, pelvic dimensions, uterine environment) factors that the dam contributes to a pregnancy and the impact they have at delivery. Studies have shown that fetal genotype is the
512 Reproduction, Events and Management | Pregnancy: Parturition
primary factor controlling birth weight in crossbred breeding, but that the maternal uterine environment (size, number of placentomes) could promote or markedly limit the full genetic growth potential of the calf in utero. Implications of hormonal imbalances have been correlated with dystocia. Scientists have looked at blood concentrations of prolactin, progesterone and the various estrogens (estrone, estradiol-17 and -17 ) for an endocrine association with the incidence of dystocia in dairy cows. Estrogen concentrations were markedly depressed in animals experiencing dystocia but in most cases there seemed to be an accompanying anatomical incompatibility. The possibility of other endocrine factors known to be important in parturition, including adrenal corticosteroids, uterine prostaglandins, oxytocin and relaxin release, cannot be overlooked. Placental dystocia refers to the retention or difficult delivery of the placenta and is more commonly referred to as retained placenta or retention of fetal membranes. It is the failure of the chorionic villi (cotyledons) to separate from the caruncles of the uterine endometrial wall and be expelled within a specific timeframe (Table 2). A placenta is usually classified as retained if the cow has not shed the placenta within 24 h of delivery. Retained placentas increase the risk of uterine infections (metritis), predispose the cow to toxemia, diminish milk production and markedly reduce the reproductive efficiency of the animal (see Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity). The incidence of retained placentas in cattle is thought to be 5–15% of the deliveries in healthy herds. In herds where the incidence runs higher than 15%, there is usually an underlying cause contributing to the problem. For example, poor nutrition and lack of essential micronutrients such as vitamin A or selenium can cause a higher than normal incidence of retained placentas in a herd. Also, cases of retained placentas are more frequent after difficult deliveries, induction of parturition, premature deliveries and twins; first-calf heifers are at higher risk than multiparous cows. This may be true in cases where the calving age of heifers is less than 24 months. Retained placenta in the horse is regarded as the most common postpartum problem and may be associated with the failure to shed part or all of the allantochorionic membranes with or without the amniotic membrane. The time it takes to pass the placenta in this species is critical. Although varying times have been given, failure of a mare to pass the placenta within 2 h postpartum is regarded as a retained placenta. As in the cow, failure to shed the placenta is associated with failure of the microvilli (microcotyledons) to separate from the endometrial crypts. Failure to pass the placenta in a timely manner usually predisposes the animal to uterine infection and increases the potential for poor postpartum reproductive efficiency. This is especially problematic in horses and dairy cows.
See also: Diseases of Dairy Animals: Non-Infectious Diseases: Milk Fever. Replacement Management in Cattle: Breeding Standards and Pregnancy Management; Health Management. Reproduction, Events and Management: Pregnancy: Characteristics; Pregnancy: Periparturient disorders; Pregnancy: Physiology; Estrous Cycles: Postpartum Cyclicity.
Further Reading Bathgate R, Balvers M, Hunt N, and Ivell R (1996) Relaxin-like factor gene is highly expressed in the bovine ovary of the cycle and pregnancy: sequence and messenger ribonucleic acid analysis. Biology of Reproduction 55: 1452–1457. Bathgate RAD, Samule CS, Burazin TCD, et al. (2002) Human relaxin gene 3 (H3) and equivalent mouse relaxin (M3) gene: novel members of the relaxin peptide family. Journal of Biological Chemistry 277: 1148–1157. Bazer FW and First NL (1983) Pregnancy and parturition. Journal of Animal Science 57 (supplement 2): 425–460. Bearden HJ and Fuquay JW (2000) Applied Animal Reproduction. Upper Saddle River: Prentice Hall. Card CE and Hillman RB (1993) Parturition. In: McKinnon AO and Voss JL (eds.) Equine Reproduction, pp. 567–573. Philadelphia: Lea & Febiger. Casy ML and Mac Donald PC (1990) Endocrinology of pregnancy. In: Carsten ME and Miller JD (eds.) Uterine Function, pp. 501–517. New York: Plenum Press. Challis JR and Lye S (1994) Parturition. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, pp. 985–1031. New York: Raven Press. Goff JP, Horst DL and Reinhardt TA (1987) The pathophysiology and prevention of milk fever. Veterinary Medicine 82: 943–950. Hauser ER (1994) Importance of genotype environment interactions in reproductive traits of cattle. In: Fields MJ and Sand RS (eds.) Factors Affecting Calf Crop, pp. 213–222. Boca Raton: CRC Press. Hsu SY, Nakabayashi K, Nishi S et al. (2002) Activation of orphan receptors by the hormone relaxin. Science 295: 671–673. Jainudeen MR and Hafez ESE (2000) Gestation, prenatal physiology, and parturition. In: Hafez ESE and Hafez B (eds.) Reproduction in Farm Animals 7th edn, pp. 140–155. New York: Lippincott Williams & Wilkins. Lenhart JA, Ryan PL, Ohleth KM and Bagnell CA (1999) Expression of connexin-26, -32, and -43 gap junction proteins in the porcine cervix and uterus during pregnancy and relaxin-induced growth. Biology of Reproduction 61: 1452–1459. Lenhart JA, Ryan PL, Ohleth KM and Bagnell CA (2001) Relaxin increases secretion of matrix metalloproteinase-2 and matrix metalloproteinase-9 during uterine and cervical growth and remodeling in the pig. Endocrinology 142: 3941–3949. Liggins GC and Thorburn GD (1994) Initiation of parturition. In: Lammming GE (ed.), Marshall’s Physiology of Reproduction, 4th edn, vol. 3, pp 863–1002. London: Chapman & Hall. Liggins GC, Kennedy PC, and Holm LW (1967) Failure of initiation of parturition after electrocoagulation of the pituitary of the fetal lamb. American Journal of Obstetrics Gynecology 98: 1080–1086. Li C and Wiener G (1995) The Yak. Bangkok, Thailand: FAO Regional Office for Asia and the Pacific. Lye SJ (1996) Initiation of parturition. Animal Reproduction Science 42: 495–503. Musah AI, Schwabe C, Willham RL, and Anderson LL (1986) Relaxin on induction of parturition in beef heifers. Endocrinology 118: 1476–1482. Noakes DE (1997) Fertility and obstetrics in cattle. In: Sutton JB and Swift ST (eds.) Library of Veterinary Practice, pp. 37–43. Oxford: Blackwell Science.
Reproduction, Events and Management | Pregnancy: Parturition Price TD and Wiltbank JN (1978) Dystocia in cattle. Theriogenology 9: 195–219. Rice LE (1994) Dystocia-related risk factors. Veterinary Clinics of North America: Food Animal Practice 10: 53–68. Schlafer DH, Fisher PJ, and Davies CJ (2000) The bovine placenta before and after birth: placental development and function in health and disease. Animal Reproduction Science 60–61: 145–160. Sciorsci RL, Dell’Aquila ME, and Minoia P (2001) Effects of naloxone on calcium turnover in cows affected by milk fever. Journal of Dairy Science 84: 1627–1631.
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Senger PL (1997) Pathways to Pregnancy and Parturition. Pullman: Current Conceptions. Sherwood OD (1994) Relaxin. In: Knobill E and Neill JD (eds.), The Physiology of Reproduction, 2nd edn, vol. 1, pp 861–1009. New York: Raven Press. Thorburn GD (1991) The placenta, prostaglandins and parturition: a review. Reproduction Fertility and Development 3: 277–294. Vandeplasscche M (1993) Dystocia. In: McKinnon AO and Voss JL (eds.) Equine Reproduction, pp. 578–587. Philadelphia: Lea & Febiger. Wood CE (1999) Control of parturition in ruminants. Journal of Reproductive Fertility supplement 54: 115–126.
Pregnancy: Periparturient Disorders C A Risco and P Melendez, University of Florida, Gainesville, FL, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2309–2314, ª 2002, Elsevier Ltd.
Introduction
Fetal Growth
The majority of diseases that affect dairy cows occur during the peripartum time, which is defined as parturition, initiation of lactation and the early postpartum period. Parturition and the onset of lactation impose tremendous physiological challenges that may predispose the dairy cow to physiological and infectious disorders. These disorders include parturient paresis (milk fever), calving difficulty (dystocia), retained fetal membranes (fetal membranes retained beyond 24h postpartum), metritis (infection and infammation of the uterus), fatty liver (pathological 2310 PREGNANCY/ Periparturient Disorders fat accumulation of the liver), ketosis (excessive ketone body production) and displacement of abomasum (displacement of the abomasum to the left side of the abdominal cavity). These disorders result in signifcant economic losses to dairy producers by reducing reproductive performance and milk yield during the subsequent lactation, cost of treatments and culling.
Fetal growth occurs exponentially, with over 60% of total fetal growth occurring during the last 2 months of gestation. Maximal growth occurs during the last 6-8 weeks of gestation. This fetal and placental growth results in a nutritional burden of pregnancy to the cow during the dry period. Therefore, inadequate nutrition at this time can result in loss of maternal body reserves in order to sustain fetal and placental development. These losses in body reserves or fat mobilization cause an increase in blood of certain type of fats, called plasma nonesterifed fatty acids (NEFA), which predispose the cow to hepatic fat accumulation or fatty liver.
Dynamics of the Dry Period When dairy cows are 7 months pregnant milking should be discontinued to allow them a 2 month rest period (dry period). The dry period allows lacteal tissue involution and regeneration, which prepares cows for the next lactation. It is generally perceived that during the dry period, the pregnant nonlactating dairy cow is in a quiescent metabolic state. This is an incorrect assumption since the late pregnant cow undergoes a series of complex metabolic changes as parturition approaches. These changes are related to growth of the calf, reduction of feed intake during the end of gestation and the initiation of lactation. Collectively, these events increase the energy and calcium demands during parturition and the initi-ation of lactation. If difficulties occur in making the necessary peripartal energy and calcium adjustments, metabolic disorders such as fatty liver, ketosis and parturient paresis may occur (Figure 1).
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Parturition Parturition occurs as a result of a complex series of hormonal changes in the dam that are initiated by the fetus (Figure 1). When the size of the fetus reaches a certain relation to the mother’s size, corticoidal hormones increase gradually from 3 weeks to 4 days prepartum. This increase in fetal corticoidal hormones during the last month of gestation is responsible for the conversion of placental progesterone and pregnenolone to estrogenic hormones. One week prepartum, in response to the increase in estrogen production, a fatty acid hormone, prostaglandin F2a is released from the uterus. This increase in prostaglandin results in lysis of the corpus luteum of pregnancy and is accompanied by a decline in luteal progesterone. Similar hormonal changes, are also common in other domesticated species and in women.
Lactation Initiation of lactation occurs in concert with the hormones that are involved in the initiation of parturition, which are: an increase in estrogen, a reduction in progesterone and an increase in corticoids. Alteration in these hormones also induces changes in a series of other regulatory hormones (thyroid hormones, insulin, glucagon, growth hormone,
Reproduction, Events and Management | Pregnancy: Periparturient Disorders 515
Starting of transition Period. 21 days prepartum
Rumen adaptation to lactating diet 7–5 days prepartum decrease in feed intake (30%) ↑ Corticoids ↓ Progesterone ↑ Estrogen ↑ Prostaglandins ↑ Growth hormone ↑ Insulin
Parturition
Periparturient Disorders • Milk fever • Retained fetal membranes • Metritis • Fat liver accumulation • Ketosis • Displacement of abomasum • Mastitis • Lameness
Low immunity Low feed intake Lactation
Ending of transition period. 25 days postpartum Figure 1 Dynamics of the transition period in dairy cows.
placental lactogen, prolactin) that promote the production of glucose and ketone bodies and the mobilization of fatty acids. These complex hormonal and metabolic alterations shift the priorities of the cow from tissue and fetal gain to mammary development and copious milk production.
the growing fetus/maternal tissues, during the period of feed intake depression and the endocrine events associated with parturition.
Feed Intake
Energy Status, Body Condition Score and Reproductive Performance
Feed intake decreases 5 to 7 days prior to parturition. This reduction can reach up to 30% under normal feeding management practices. Depression of feed intake before parturition has been considered a major factor in the development of the fatty liver complex. Accumulation of fat in the liver occurs during periods of elevated fat mobilization, especially in cows with excessive fat body reserves at parturition. During the last 2 weeks prepartum, NEFA increases twofold in blood. This increase in plasma NEFA concentration prepartum has been attributed to excessive fat mobilization that provides energy for
Dairy cows reach peak milk production around 8 to 10 weeks post calving. However, feed intake increases slowly after parturition lagging 2 weeks behind the peak of milk production. This lag explains the adipose reserve mobilization experienced by cows, with a typical weight loss during the first one-third of lactation. Because energy output (milk yield) exceeds energy intake via feed consumption, dairy cows undergo a period of negative energy balance in early lactation (Figure 2). Any periparturient disorder that predisposes the cow to reduce feed consumption will exacerbate
516 Reproduction, Events and Management | Pregnancy: Periparturient Disorders 60 Milk yield
Milk yield/feed intake (kg day–1)
50 3.75 40 3.5 30 Feed intake
20
10 2.5
BCS (1−5)
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 200 220 240 260 280 300 Days of lactation Figure 2 Milk production, feed intake and body condition score (BCS) in a typical dairy lactating cow.
the negative energy status already present during the postpartum period. The energy status of the postpartum cow has an effect on integrated reproductive activity during early lactation. Cows losing weight may experience a delay in the resumption of cyclicity. A return toward a positive energy status appears to be important in the initiation of cyclicity. The marked deficit in early energy status for the anestrus cow exerts a negative carryover effect on conception. Body reserves can be measured through a visual evaluation of different anatomical points of the cow. This methodology called body condition scoring (BCS) has been validated through different studies using scales from 1 to 5 or 1 to 9, being 1 a very thin cow and 5 or 9 a very fat cow. Body condition score has been related with the magnitude and severity of negative energy balance. Cows that lose more than 0.5 to 1.0 BCS (scale 1-5) during the frst 60 days postpartum have been shown to have lower conception rates to first insemination. A score of 3.25 to 3.75 at calving is recommended with no more than a 0.5 point loss of body condition during the frst 60 days postpartum (Table 1). Cows that are overconditioned at calving (>3.75) experience less feed intake, more fat mobilization and are at high risk of experiencing calving-related disorders. Consequently, BCS should be monitored specially during the last one-third of lactation and the dry period. Losses of more than 0.25 units should be avoided during the entire dry period. Changing body condition through
Table 1 Target body condition scores (BCS scale 1-5) Stage
Ideal BCS
Range
Dry-off (around 7 month of pregnancy Calving Early lactation Mid-lactation Late lactation Growing Heifers Heifers at calving
3.5
3.25–3.75
3.5 3 3.25 3.5 3 3.5
3.25–3.75 2.5–3.25 2.75–3.25 3.0–3.5 2.75–3.25 3.25–3.5
dietary manipulations requires some strategic planning and careful consideration. Underconditioned cows (thin animals) should be allowed to recover condition during the late lactation period because during this time lactating cows are more efficient in restoring body condition than during the dry period. In addition, the dry period may be too short to fully recover condition needed prior to calving. Cows should not lose weight during the dry period, as the cow must gain 0.45 to 0.68 kg day-1 simply to meet the needs of the rapidly developing fetus.
Periparturient Disorders Milk Fever (Parturient Paresis) During calving or shortly thereafter, the fall of calcium levels in blood (hypocalcemia) is inevitable in the dairy cow and is characterized by a blood calcium concentration
Reproduction, Events and Management | Pregnancy: Periparturient Disorders 517
<1.88 mmol l-1(<7.5 mg dl-1). Hypocalcemia develops as a result of the sudden drain of calcium to colostrum at the onset of lactation, resulting in a tremendous challenge to cows’ ability to maintain normal calcium levels. At parturition, 30 g or more of calcium must be replenished into the calcium pool each day to maintain the normal calcium levels. Clinical hypocalcemia or milk fever develops when blood calcium concentration is below 7.5 mg dl-1. A cow affected with milk fever may present with nervousness, staggering but usually becomes recumbent and is unable to rise (paresis). If blood calcium concentration is not restored quickly death occurs. Ten to fifty percent of cows may develop low calcium levels without symptoms of milk fever (subclinical hypocalcemia) up to 10 days postpartum. Hypocalcemia may affect organs that have smooth muscle function such as the uterus, rumen and the abomasum. Hypocalcemia is a signifcant risk factor for calving difficulty, retained fetal membranes, metritis, uterine eversion or prolapse, displacement of abomasum and clinical ketosis. These disorders have been associated with no estrus or heat expression (anestrus), cyst in the ovaries and metritis, which negatively affect the reproductive performance of dairy cows.
Retained Fetal Membranes (Retained Placenta) Retained fetal membranes (RFM) is defined as the lack of detachment of fetal membranes (cotyledons) from the maternal membranes (caruncles) within the frst 12-24 h after calving. The incidence of retained fetal membranes may range from 1.3% to 39.2%. The cost of a case of RFM ranges between US$106 and $285. Some risk factors for RFM are hypocalcemia, calving difficulty, parity, abnormal gestation length, season and sire of the calf. Retained fetal membranes have been the major factor predisposing cattle to metritis. About 20-25% of cows affected by RFM may develop moderate to severe metritis.
with a uterine infection has been estimated in US$106. Some predisposing factors for metritis are calving difficulty, retained fetal membranes, twins or stillbirths, fat cows at calving and metabolic disorders.
Ketosis and Liver Fat Accumulation (Fatty Liver) Ketosis is defined as a metabolic disorder characterized by high levels of ketone bodies (-OH-butyrate, acetoacetate and acetone) affecting dairy cows in the period from parturition to 6 weeks postpartum. There are two types of ketosis, primary or secondary. A cow with primary clinical ketosis has a decreased appetite and elevated serum, milk, urine or breath ketones in the absence of another concurrent disease. Ketosis may be clinical or subclinical. Subclinical ketosis is defined as a preclinical stage characterized by an elevated ketone body level but not clinical signs, such as loss of appetite, hard feces, or dullness; however reproductive responses might be affected. The incidence of ketosis may range from 1.3% to 18.3%. Economic losses from ketosis have been estimated to total approximately US$145 per case. Feed intake starts to decrease precipitously, and the reduction could reach as high as 30% on day 1 or 2 before calving and does not recover until 1 to 2 days after calving. Glucose availability is an important factor in the pathogenesis of clinical ketosis and liver fat accumulation. When glucose availability is low, ketone bodies formation occurs; when glucose is high, fat deposition is favored. Elevation of plasma fatty acids starts prior to feed intake depression, on day 5 before parturition. Liver fat infltration does not occur until the concentration of plasma fatty acids are maximized on day 1 after calving. Liver fat accumulation can occur very rapidly. Within 48 h, hepatic fat levels can rise up to 25%, under conditions of extreme fat mobilization.
Left Displacement of Abomasum (LDA) Metritis (Puerperal Metritis, Toxic Metritis) Metritis (infection of the uterus) is one of the most frequent disorders affecting dairy cows during the postpartum period. Metritis is a major cause of economic losses to the cattle industry. The condition is characterized by an abnormal uterine discharge, with local or systemic symptomatology. Systemic or toxic metritis is characterized by a foul-smelling, watery uterine discharge usually accompanied by a severe drop in milk production and a fever, and it may be life threatening. The total cost to producers for each lactating dairy cow
In left displacement of the abomasum, the abomasum slides under the rumen and dorsally along the left body wall. The result is a partial impairment of abomasal outfow, leading to abomasal gas accumulation, electrolyte pooling with subsequent systemic alterations, and depressed gastrointestinal motility and appetite. Left displacement of abomasum occurs most commonly 2 weeks prepartum to 8 weeks postpartum. The incidence of LDA may range between 0.3% and 6.3%. This digestive disorder may occur in cows from frst lactation and later. Cows with displacement of the abomasum experience severe losses of milk yield and body weight. They are more likely to have another disease than healthy
518 Reproduction, Events and Management | Pregnancy: Periparturient Disorders Table 2 Summary of periparturient disorders in dairy cattle Disorder
Incidence (%)
Risk factors
Cost per case
Prevention
Hypocalcemia
0.03–22
Parity Milk yield Breed Parity Hypocalcemia Calving difficulty Twins Hypocalcemia RFM Calving difficulty Ketosis Hypocalcemia RFM Displacement of abomasum Parity Metritis Mastitis Milk Yield Fat cows Ketosis RFM Metritis Mastitis Hypocalcemia
$335
Acidic (Anionic) diets prepartum
$285
Adequate feeding and obstetrical management
$106
Avoiding predisposing factors Adequate treatments for RFM
$145
Avoiding risk factors Good feeding management
$340
Good feeding management Avoiding risk factors
Retained fetal membranes (RFM)
1.3–39.2
Metritis
2.2–37.3
Ketosis
1.3–18.3
Displacement of abomasum
0.3–6.3
cows and thus are more likely to be culled than normal cows. Left displacement of abomasum is a multifactorial disease. Hypocalcemia, calving difficulty, ketosis, excessive body condition score at calving and incorrect feeding management practices are risk factors for displacement of abomasum. Prevention and Management of Periparturient Disorders The most common periparturient disorders of dairy cattle are summarized in Table 2. Prevention of these disorders is best accomplished by providing a well-balanced diet to prepartum cows. Enhancing calcium availability during the time of parturition is crucial in preventing milk fever. This may be achieved by feeding a diet low in potassium and selecting feedstuffs with higher chlorine and sulfur contents (anionic diets). These diets induce a mild metabolic acidosis, which increases calcium levels in blood. Thus, the effectiveness of these diets can be tested monitoring the acidity of urine (urine pH). Too much acidity or alkalinity of the urine indicates that the cows are not responding to the anionic diets. Furthermore, prevention of hypocalcemia with oral calcium products have been recommended. These products are administered near calving, as supportive therapy in the management of clinical hypocalcemia in cattle. The most common oral products are calcium chloride and calcium propionate. However, under adequate management of acid diets and low incidence of hypocalcemia, oral products as prevention may not be necessary. Intravenous calcium products are only recommended for treatment purposes.
In order to prevent liver fat accumulation and ketosis, the key is to minimize the increase in fat mobilization from adipose tissue as parturition approaches. This can be accomplished by ensuring that the ration contains the required amount of energy and maintenance of maximum feed intake during the prepartum period (Table 3). Vitamins and minerals should be fed to dry cows at the Table 3 Example of anionic diet for close-up1 prepartum dairy cow1 Nutrient
Close-up dry cows2
Feed Intake (dry matter basis) kg/day NEL,3 Mcal/kg Crude protein(CP), % UIP,4 % Acid detergent fiber (ADF), % Neutral detergent fiber (NDF), % NFC,5% Calcium, % Phosphorus, % Magnesium, % Potassium, % Sulfur, % Sodium, % Chlorine,%
10.1 1.58 12.4 4.5 21.8 37.2 41.6 0.98 0.37 0.38 1.32 0.31 0.15 0.89
1
Table 14-11, NRC (2001) Dry transition cows 21 days before expected calving 3 NEL ¼ Net energy for lactation. 4 UIP ¼ Undegradable intake protein. 5 NFC ¼ Nonfiber carbohydrate, calculated as 100-CF-CP-NDF-Ash. 2
Reproduction, Events and Management | Pregnancy: Periparturient Disorders 519 Table 4 Example trace mineral and vitamin diet for close-up prepartum dairy cow1 Nutrient
Close-up dry cows2
Cobalt, ppm3 Copper, ppm Iodine, ppm Iron, ppm Manganese, ppm Selenium, ppm Zinc, ppm Vitamin A, IU/kg4 Vitamin D, IU/kg Vitamin E, IU/kg
0.11 13 0.4 13 18 0.3 22 7300 1824 132
1
Table 14-11, NRC (2001) Dry transition cows 21 days before expected calving Parts per million 4 International Units/kg 2 3
National Research Council recommendations as shown in Table 4. Good feeding management not only includes the formulation of the diet, but also feed trough space in order to allow maximal feed intake per cow, adequate shade and good quality water and a comfortable environment where cows can lie down. Cows during the prepartum period need to adapt to the new diet, when the cow commences lactation. This challenge requires gradual changes through the prepartum until the early postpartum period and is the art of feeding transition cows.
Conclusions During the postpartum period dairy cows are at a higher risk of developing metabolic diseases that impair milk
production and reproductive performance. Many of these diseases are a result of improper nutritional management during the dry period. Because dry cows do not contribute to the economics of the dairy farm, many producers ignore these animals and their nutritional needs are compromised. We have to convince producers that the dry period is a preparatory phase for the next lactation, and that dry cows must be considered an investment for the next lactation.
See also: Body Condition: Effects on Health, Milk Production, and Reproduction; Measurement Techniques and Data Processing. Diseases of Dairy Animals: Non-Infectious Diseases: Displaced Abomasum; Non-Infectious Diseases: Ketosis; NonInfectious Diseases: Milk Fever. Feed Ingredients: Feed Supplements: Anionic Salts. Feeds, Ration Formulation: Dry Period Rations in Cattle. Mammary Gland: Growth, Development and involution. Reproduction, Events and Management: Pregnancy: Parturition.
Further Reading Howard J and Smith R (eds.) (1999) Food Animal Practice. Current Veterinary Therapy, vol. 4, Philadel-phia: WB Saunders. National Research Council (2001) Nutrient Requirements of Dairy Cattle, 7th edn. Washington, DC: National Academy Press. Radostits OM, Leslie KE, and Fetrow JWB (1994) Herd Health: Food Animal Production Medicine, 2nd edn. Philadelphia: WB Saunders. Van Horn HH and Wilcox CJ (eds.) (1992) Large Dairy Herd Management. Champaign: American Dairy Science Association. Veterinary Clinics of North America (2000) Food Animal Practice. Metabolic Disorders of Ruminants, vol. 16, Philadelphia: WB Saunders.
RHEOLOGY OF LIQUID AND SEMI-SOLID MILK PRODUCTS O J McCarthy, Massey University, Palmerston North, New Zealand ª 2011 Elsevier Ltd. All rights reserved.
Introduction The rheological behavior of milk is, in a general sense, typical of a semi-dilute emulsion/suspension. However, the complex composition and microstructure of milk result in complexities in behavior not exhibited by simple systems of this kind. These complexities become more pronounced when milk is subjected to such treatments as concentration (of fat or of total solids), fractionation, homogenization, heating, renneting, and acidification during its conversion to dairy products. In this article, quantitative descriptions (mathematical models) of the rheological properties of milk, cream, concentrated milks and creams, sweetened condensed milk, ice cream mix, yogurts, buttermilk, and fresh cheeses are presented. The models are of three kinds: those that relate rheological behavior to composition and microstructure, those that quantify objective properties related to texture (texture itself must be measured subjectively), and phenomenological models useful for process engineering design and other technological purposes.
Milks and Creams The rheological behavior of milk and cream is in accord with that of emulsions and suspensions in general. Milk and cream can exhibit Newtonian or non-Newtonian behavior depending on composition, temperature, prior treatment, and measurement conditions. Fresh skim milk, whole milk, and cream can for almost all practical purposes be treated as Newtonian liquids under the following conditions: fat content <40% (w/w), temperature >40 C (milk fat completely molten; no cold agglutination of fat globules), and moderate to high shear rates. Rheological behavior is completely characterized by a temperature-dependent coefficient of viscosity, defined by Newton’s law of viscosity: ¼ _ ðPaÞ
½1 1
where is the shear stress (Pa), _ is the shear rate (s ), and is the coefficient of viscosity (Pa s). The term ‘coefficient of viscosity’ strictly denotes the proportionality constant in eqn [1]. The term ‘viscosity’ is a more
520
general one, meaning the extent to which a fluid resists being sheared. The distinction between the two is irrelevant for Newtonian liquids, though not for nonNewtonian liquids. Representative values, at 20 C, of the coefficient of viscosity of whole milk and fractions derived therefrom, measured under conditions where Newtonian behavior exists, are given in Table 1. Several points can be made on the basis of these data. First, lactose, the major low-molecular-weight milk component, and even the whey proteins influence viscosity to a relatively small extent. Second, the fat content has a major influence. Third, the (micellar) casein content has by far the greatest influence. The viscosity and the rheological behavior of milk (and the semi-liquid products made from it) depend largely upon the state and concentration of the fat and casein, and thus on factors that affect these. The viscosity of whole and skim milk, for conditions under which Newtonian behavior occurs, can be modeled with Eilers’s semi-empirical equation: ¼ 0 1 þ
1:25ði Þ 1 – ði Þ=max
2 ½2
where is the coefficient of viscosity of the milk product (Pa s); 0 is the coefficient of viscosity of the portion of the product consisting of water and low-molecular-weight substances other than lactose (Pa s); i is the volume fraction of a dispersed component with a particle size at least an order of magnitude greater than the size of the water molecule; (i) = fat + cas + wp + L, where fat represents milk fat, cas is casein, wp whey proteins, and L lactose; and max is the assumed value of (i) for maximum packing of all dispersed particles; max depends on the overall size distribution of the dispersed particles and on particle shapes (though not on particle size per se). The volume fraction of an individual component is given by i ¼ Vi cv;i
½3
where Vi is the voluminosity of component i (m3 kg1 of dry component) and cv,i is the volume concentration of the component in the product (kg m3 of product). Representative values of voluminosity are given in Table 2. Voluminosity and volume fraction pertain to
Rheology of Liquid and Semi-Solid Milk Products 521 Table 1 Representative values of the coefficient of viscosity, at 20 C, of whole milk and fractions derived from it Viscosity (mPa s)
Milk fraction Whole milk Skim milk (ffi whole milk minus fat globules) Rennet whey (ffi skim milk minus casein micelles) 5% Lactose solution (ffi whey minus whey proteins) Water (ffi whole milk minus all dissolved and dispersed components)
2.13 1.79 1.25 1.15 1.00
Temperature and Thermal History
From Jenness R and Patton S (1959) Principles of Dairy Chemistry. London: Chapman & Hall.
Table 2 Representative values of the voluminosities of milk components Component
Voluminosity
Fat globules Casein Whey proteins Lactose
1.11 103 m3 kg1 of lipid in fat globules 3.9 103 m3 kg1 of dry casein 1.5 103 m3 kg1 of dry protein 1.0 103 m3 kg1 of lactose
From Walstra P and Jenness R (1984) Dairy Chemistry and Physics. New York: Wiley.
hydrodynamic volume, and thus account for particle shape and water of hydration as well as volume per se. Equation [2], for (i) ! 0, reduces to Einstein’s equation for the viscosity of a very dilute solution of hard spheres: ¼ 0 ð1 þ 2:5Þ
depends, in turn, upon such factors as the concentration of colloidal calcium phosphate, Ca2þ activity, and pH. The viscosity of milk and cream increases with age owing partly to changes in ionic equilibria. The viscosity of milk increases slightly with increasing pH, perhaps owing to swelling of the casein micelles. Conversely, a small decrease in pH reduces viscosity, whereas a large decrease causes micelle aggregation.
½4
Einstein’s equation assumes no particle–particle interaction; Eilers’s equation accounts for both the presence of the dispersed phase(s) and the hydrodynamic interaction between particles during flow. Eilers’s equation does not, however, account for mutual attraction/repulsion between particles. Eilers developed his equation at a time when viscometric techniques were too unsophisticated to detect non-Newtonian behavior at low shear rates. The equation is useful for predicting the effects on viscosity of variations in the composition and concentration of milks and creams. Viscosity increases with %TS (total solids), but, for a given %TS, is inversely related to %fat content (F) because of the lower voluminosity of fat when compared with that of casein in particular. When (i) exceeds 0.6 (which corresponds to /010), viscosity increases steeply with (i), and the rheological behavior becomes non-Newtonian. The volume fraction of the casein (cas) in milk is the main determinant of (i), and thus of viscosity. Large differences in viscosity between different lots of milk are almost certainly attributable to differences in cas, which
Viscosity is inversely related to temperature per se. Cooling of milk results in an increase in viscosity, which is partly the result of an increase in 0 and partly the result of a sharp increase in Vcas and thus in cas. Furthermore, some caseins, especially -casein, dissociate from the micelles at low temperatures; this contributes to an increase in viscosity because dissociated proteins have higher hydrodynamic volumes. Heating of skim milk or whole milk to 65 C, followed by rapid cooling, results in a temporary decrease in viscosity (measured at a lower temperature) because of the increased association of -casein with the micelles that would have occurred at the higher temperature; viscosity recovers exponentially with time as some -casein gradually dissociates again at the lower temperature. Warming of milk to temperatures above ambient causes viscosity to decrease, because 0 decreases and cas decreases moderately. The change in cas is reflected by a decrease in the ratio skim/whey when temperature is increased from 5 to 30 C. The decrease is less marked at temperatures >30 C. During dynamic heating and cooling (e.g., 15 $ 80 C), the viscosity of milk can vary depending on both temperature and temperature history; plots of viscosity versus temperature can display hysteresis. The hysteretic pattern for fresh milk itself depends on temperature history, and this effect is attributable to the reversible melting and crystallization behavior of the milk triglycerides. Different hysteretic patterns are found with aged milk; these are considered to reflect the decreases in the heat stability of proteins with age. The viscosity of whole milk increases with age. The rate of increase is inversely related to the temperature of measurement. Pasteurization, a relatively mild heat treatment, results in no noticeable change in the rheological properties of whole milk. Non-Newtonian Behavior Non-Newtonian behavior manifests itself in raw whole milks and creams under conditions that favor cold agglutination of fat globules (temperatures of <40 C and low shear rate). Shear thinning is the predominant rheological behavior. Aggregates of fat globules contain trapped
522 Rheology of Liquid and Semi-Solid Milk Products
interstitial plasma, and thus together have a high effective volume fraction, especially at low shear rates. As shear rate is increased, shearing forces cause aggregates to become more regular in shape or to break down. The volume fraction and consequently the apparent viscosity then decrease. Apparent viscosity, which is thus shear rate dependent, is defined app ¼
_
½5
As shearing forces become larger compared with the attractive forces holding the globules together, successive increases in shear rate have smaller and smaller effects on apparent viscosity. At sufficiently high shear rates, the behavior becomes Newtonian. At high fat contents, nonNewtonian behavior is more pronounced and persists to higher shear rates. At very low shear rates (_ 30 s1), at ambient temperature, the shear rate dependence of the viscosity of model emulsions made by mixing pasteurized cream with pasteurized skim milk is due only to the skim milk. Skim milk exhibits shear-thinning behavior at shear rates <250 s1 and temperatures <30 C. Lower temperatures enhance cold agglutination. This increases both the apparent viscosity and the nonNewtonian behavior, the latter persisting to higher shear rates. Separation of milk at temperatures 40 C gives cream in which cold agglutination is largely reduced owing to the loss of agglutinin to the skim milk. Conversely, cold separation enhances cold agglutination. Thus, the separation conditions influence the rheology of cream. Cold agglutination in raw cream, and the presence of homogenization clusters in homogenized cream, can result in time-dependent shear thinning (called thixotropy if recovery of viscosity occurs on resting after shearing). The apparent viscosity of raw milk at infinite shear rate (_ ¼ 1 ), at temperatures <40 C, can be related to fat by the following equation: _ ¼ 1 ¼ skim ð1 þ 3:25fat Þ
½6
_ 1, by extraEvaluation of apparent viscosity at ¼ polation, allows the effects of fat content to be separated from the effects of shear rate. The Cross equation, which relates apparent viscosity to shear rate, has been found to describe exactly the pseudoplastic nature of raw cream: app ¼ _ ¼ 1 þ
_ ¼ 0 – _ ¼ 1 1 þ b _ m 1
½7
where app is the apparent viscosity at _ s ; _ ¼ 0 is the apparent viscosity at _ ¼ 0, found by extrapolation; and b and m are constants. The factors _ ¼ 0 , _ ¼ 1 , b, and m are each dependent on temperature and fat content. The applicability of the Cross equation implies that a state of
equilibrium exists during flow between the size and number of fat globule aggregates and shear rate. Shear thickening can be observed in high-fat creams; shearing induces partial coalescence of globules, thereby increasing the effective fat by entrapment of plasma. Cream is viscoelastic; its rheological behavior may be represented by the generalized Maxwell body (a mechanical analog), the relaxation time of which is nearly independent of fat content. Cream, a concentrated emulsion, can in fact exhibit most of the possible types of non-Newtonian behavior depending on conditions and treatment. The viscosity of milks and creams depends on technological treatments as well as on composition, concentration, and shear rate.
Effects of Technological Treatments Homogenization
Homogenization of milk and cream results in an increase in viscosity measured at high shear rates. The increase is inversely related to fat globule size. At low shear rates and ambient temperature, the viscosity of homogenized milk is lower than that of raw milk. This is possibly a consequence of the destruction of agglutinin by homogenization. Homogenization of cream reduces deviation from Newtonian behavior, possibly for the same reason.
Heat treatment, renneting, acidification
The effects of heat treatment, renneting, and acidification on the viscosity of milk, under conditions where coagulation has not (yet) occurred, can be modeled using the socalled adhesive hard sphere (AHS) theory. It has been shown that skim milk behaves rheologically as a semi-dilute colloidal suspension of hard spheres, the casein micelles, in a medium comprising all of the other milk components. For such a suspension, the viscosity (strictly speaking the coefficient of viscosity at _ ! 0) is given by the following theoretical equation (which is a modification of Einstein’s equation [4]): ¼ 0 ð1 þ 2:5 þ kH 2 Þ
½8
where kH (the Huggins constant) accounts for hydrodynamic interactions. For 0.2 (semi-dilute dispersion), in the absence of mutual attraction/repulsion between the micelles (nonadhesive hard spheres), kH is equal to 5.913. Viscosity is then given by ¼ 0 ð1 þ 2:5 þ 5:9132 Þ
½9
Untreated skim milk closely follows this equation. A series development of the semi-empirical Eilers’s equation (with max = 0.74) gives a similar expression: ¼ 0 ð1 þ 2:5 þ 4:942 þ 8:783 þ Þ
½10
Rheology of Liquid and Semi-Solid Milk Products 523
Both eqn [9] and eqn [10] reduce to Einstein’s equation when is small enough to preclude interactions of any kind between the suspended spheres. The Huggins constant is given by the following equation: kH ¼ 5:913 þ
where B is measure of (stickiness). coefficient, suspension:
1:9 B
½11
the Baxter interaction parameter, which is a adhesive interactions between the spheres It is related to the second osmotic virial B2, a property of the casein micelle B2 1 ¼ 4– B VHS
Acidification of milk, for example, that resulting from starter bacterial activity during yogurt manufacture, causes micelle flocculation (eventually leading to coagulation) owing to a loss of the steric stabilization of micelles. Loss of stabilization is due to the loss of the extended conformation of the -casein hairs on the micelle surfaces, and their eventual collapse. The AHS theory accurately quantifies the relationship between viscosity (increasing) and pH (decreasing) during acidification. The AHS theory has been applied mainly to normal skim milk. The effects of other variables such as fat content and calcium concentration on the applicability of the theory are apparently yet to be investigated.
½12
where VHS (¼4/3a2) is the volume of a hard sphere of radius a. For nonadhesive hard spheres (no mutual attraction) B = + 1, and kH ¼ constant ¼ 5.913, as indicated above (eqn [9]). When mutual attraction does exist (adhesive hard spheres), B has a positive finite value. Then, kH > 5.913, and viscosity has a value larger than that predicted by eqn [9]. The adhesive hard-sphere theory is embodied in eqns [8], [11], and [12]. Heat treatment of skim milk severe enough to cause denaturation of -lactoglobulin and its subsequent association with the casein micelles results in an increase in and a decrease in B, the latter change indicating the development of mutual attraction between the casein micelles. This results in a viscosity increase larger than that predicted by either eqn [9] or eqn [10]. A computer-based model utilizing both the AHS theory and the denaturation kinetics of -lactoglobulin has been developed that allows the prediction of the viscosity of skim milk resulting from any combination of heating temperature and heating time. The model shows that viscosity not only depends on the extent of denaturation of -lactoglobulin but, for a given denaturation, also is higher for a higher heating temperature or a higher heating rate. The addition of chymosin to milk at the start of renneting initiates two sequential changes. First, there is a fall in viscosity caused by the enzyme cutting -casein hairs from the surfaces of the casein micelles, with a consequent reduction in cas. Second, the loss of the stabilizing -casein layer causes the micelles to become mutually attractive (adhesive hard spheres). This leads to an increasingly rapid rise in viscosity, which eventually culminates in micelle flocculation. These two effects together are qualitatively and quantitatively modeled well by the AHS theory. The theory can be used to predict coagulation time, defined as the time, after chymosin addition, at which the viscosity recovers its initial value after its temporary fall.
Storage
The viscosity of ultra-high temperature (UHT) sterilized milk can increase gradually during storage. This phenomenon, age thickening, can eventually lead to gelation. It is thought to be the result of the gradual release, from the casein micelles, of -lactoglobulin–-casein complexes formed during the high-temperature heat treatment, and the subsequent cross-linking of the complexes to form a gel network.
Technologically Useful Relationships for Predicting the Rheological Properties of Milks and Creams Successful attempts have been made to establish empirical relationships useful for technological and engineering purposes between the viscosity of Newtonian-fluid milk products and their temperature and composition. A number of these relationships, the development of which ignored any observed (slight) non-Newtonian behavior, are given in Table 3. In the case of non-Newtonian milks and creams, phenomenological relationships between shear stress and shear rate have been developed for practical purposes. (These contrast with expressions for viscosity at zero shear rate, which are valuable for relating rheological behavior to structure and composition in a fundamental way.) The shear-thinning behavior of raw whole milk in the shear-rate range 1–1500 s1 can be modeled well by the power-law (Ostwald–de Waele) equation: ¼ k_ n
½13
Typical values of k and n for raw milk (3.35% fat) at 25 C are 6.14 103 Pa s and 0.798, respectively. Rheological behavior becomes essentially Newtonian at shear rates >800 s1. The shear-thinning behaviors of pasteurized skim milk, whole milk, and cream at low shear rates and
524 Rheology of Liquid and Semi-Solid Milk Products Table 3 Technologically useful relationships between the viscosity of Newtonian milk products, and temperature and composition Product specifications
Relationship
Milk, 8–28 %TS, 0.07–7.4% fat, Fat to solids-not-fat ratio: 0.01–0.4 0–80 C
log ¼ 0:249 – 1:3 10 – 2 þ 5:2 10 – 5 2 þ ð2:549 10 – 2 – 9:8 10 – 5 þ4 10 – 7 2 Þ ð%TSÞ þ ð5:43 10 – 4 – 1:39 10 – 5 þ 1:117 10 – 7 2 Þ ð%TSÞ2
Milk, 0.03–15% fat, 70–135 C
ln ¼ 3:92 10 – 5 2 – 1:951 10 – 2 þ 0:666 þ Fð – 9:53 10 – 6 2 þ 1:674 10 – 3 – 4:37 10 – 2 Þ þ F 2 ð9:75 10 – 7 2 – 1:739 10 – 4 þ 9:83 10 – 3 Þ
Milk of normal composition, 25 C
¼ 0:96 þ 0:058F þ 0:156P
Milk and cream, 0.1–30% fat, 0–30 C
ln ¼
2731:5 þ 0:1F – 8:9 ð273 þ Þ
log ¼ AðF þ F 5=3 Þ þ log 0 where A ¼ 1:287 6 þ 11:07 10 – 4 ;
Milk and cream, 0–40% fat, 40–80 C
103 – 2:437 and 0 ¼ 0:768 7 273 þ
and 0 ¼ viscosity in mPa s, ¼ temperature in C, %TS ¼ % total solids, F ¼ % fat, and P ¼ % protein.
temperatures <40 C, can be modeled satisfactorily by the Bingham equation: ¼ pl _ þ 0
½14
Values of pl (the plastic viscosity) for skim milk and whole milk (3.5% fat) at 25 C are 1.53 103 and 1.81 103 Pa s, respectively. The corresponding values of 0 (the yield stress) are 1.98 102 and 4.6 102 Pa. For cream of 38% fat, at 25 C, the values of pl and 0 are 9.44 103 Pa s and 0.381 Pa, respectively. Raw cream of 60% fat has been found to obey the Bingham equation at constant temperature in the range 15–80 C. When subjected to dynamic heating and cooling in this temperature range, the rheological behavior of the same cream is modeled better by the power-law equation [13]. The values of k and n at a given temperature depends on thermal history, a phenomenon attributed to the interaction between heating/cooling rates and the rates of melting and crystallization of milk triacylglycerols. Cream of 40–55% fat, at 5–20 C, has been shown to obey the Herschel–Bulkley equation: ¼ k_ n þ 0
of cream.The numerical values of the parameters in these phenomenological equations depend on composition, concentration, and temperature.
½15
This equation is a generalized form of the Bingham equation [14]. Values of n have not been reported. (The powerlaw equation [13] and Newton’s equation [1], as well as the Bingham equation, are special cases of eqn [15].) As stated above, the Cross equation [7] accurately models the shear dependence of the apparent viscosity
Non-Newtonian Behavior in Concentrated Milks and Creams When milk is concentrated by heat evaporation or by membrane processes (ultrafiltration, reverse osmosis), (i) increases because of the concentration effect per se and because particle–particle interactions (especially micelle–micelle interactions) increase owing to smaller interparticle distances. These interactions lead to aggregate formation. The effects of aggregate formation on rheological behavior are essentially the same as the effects of concentrating only the fat globules, as in cream: apparent viscosity increases; shear thinning becomes more pronounced; and deviation from Newtonian behavior persists to higher shear rates. Time-dependent shear thinning appears at a sufficiently high concentration or after a sufficiently long storage time (at concentrations and temperatures above certain minima) during which structure development occurs. Such structure development, and the consequent steady viscosity increase, is known as age thickening. Rheologically, there are no fundamental differences between concentrates produced by heat, by reverse osmosis, or by ultrafiltration, or between whole milk and cream concentrates on the one hand and skim milk concentrates on the other. Rather, the differences are of degree. For given conditions, non-Newtonian behavior tends to appear at
Rheology of Liquid and Semi-Solid Milk Products 525
lower %TS in ultrafiltration skim milk concentrates than in evaporated skim milk (because of the preferential concentration of proteins in the former), and at lower %TS in skim milk concentrates than in whole milk concentrates (because the proportion of protein in the dry solids is higher in the former). For the same reasons, viscosity at a given %TS is higher in ultrafiltration skim milk concentrates than in evaporated skim milk, and in skim milk concentrates than in whole milk concentrates. The viscosity of any concentrate under given conditions of %TS, shear rate, temperature, dry solids composition, time after preparation, and other variables such as preheat treatment and pH is directly related to (i). This is discussed first below. Then, phenomenological relationships that have been found useful in describing the non-Newtonian behavior of concentrates as a function of shear rate are reviewed. Last, the phenomenological description of age thickening is presented. Dependence of concentrate viscosity on total volume fraction
It has been shown that the apparent viscosity (at a specified shear rate) of heat-concentrated whole and skim milks is weakly related to %TS but closely related to total volume fraction calculated by ði Þ ¼ cas þ nwp þ dwp þ fat
½16
where nwp and dwp are the volume fractions of native and denatured whey proteins, respectively; the effect on the whey proteins of preheating the milk prior to concentrating is thus automatically taken into account. Volume fractions (i) of individual components were calculated by i ¼ i; milk
TSconc conc TSmilk milk
½17
where is the density (kg m3) and the subscripts ‘milk’ and ‘conc’ refer to the milk prior to evaporation and the concentrated milk, respectively. Concentrates are shear thinning; app;_ ¼ 1 of freshly prepared heat concentrates (no age thickening) is closely predicted by Eilers’s equation [2]. max in the equation, for heat concentrated skim milk, has been shown to be 0.79, by extrapolation of heat gelation time versus protein curves to gelation time ¼ 0. The same value has been found to be satisfactory for whole milk concentrates. o in Eilers’s equation may be calculated for heatevaporated and reverse-osmosis milks by 0 ¼ water þ ðs þ Ls Þ
ð%TSÞconc ð%TSÞunconc
½18
s = water + saltswater = 0.02 water and Ls ¼water + 5%lactosewater. For ultrafiltration concentrated milks, 0 = permeate. Temperature dependence of viscosity can be allowed for by evaluating s, Ls, and permeate at
the required temperature using literature data or direct measurement. The apparent viscosity, the rate of age thickening, and the degree of shear thinning of milk concentrates made by evaporation all increase with both time and %TS. At elevated holding temperatures, for example, 50 C, even _ ¼ 0 increases slightly with holding time (at a given %TS), suggesting a permanent change in concentrate structure that cannot be reversed by shearing. The change in the apparent viscosity with time during age thickening can be predicted by a modified Eilers’s equation: app ¼ 0 1 þ
1:25ði Þð1 þ t :kði Þ =ði ÞÞ 1 – ði Þð1 þ t :kði Þ =ði ÞÞmax Þ
2 ½19
where t is the time, (i) = (i) at t = 0, and k(i) = d((i))/dt. For a given shear rate and temperature, k(i)/(i), the so-called shear-thickening constant, is independent of %TS. The rate of age thickening is somewhat lower for whole milk concentrates than for skim milk concentrates because the fat in the former, while contributing to the overall volume fraction, is inert with respect to the age-thickening process. Phenomenological rheological relationships for concentrated milks and creams
As %TS increases, the rheological behavior of freshly prepared milk concentrates changes from Newtonian to time-independent shear thinning to time-dependent shear thinning. Under conditions where time dependence is absent, flow behavior changes, as %TS is increased, from Newtonian (eqn [1]) to shear thinning with no yield stress (power-law behavior; eqn [13]) to shear thinning with a yield stress (Bingham plastic behavior (eqn [14]) or Herschel–Bulkley behavior (eqn [15])). In fact, because (as pointed out above) the Newtonian, power-law, and Bingham equations are all special cases of the Herschel–Bulkley equation, this last equation can be said to describe adequately the flow curves of timeindependent milk concentrates and the instantaneous flow curves of time-dependent concentrates, under all conditions of temperature, shear rate, and other variables. When 0 ¼ zero and n ¼ 1 in the Herschel–Bulkley equation, k ¼ , the Newtonian coefficient of viscosity. For a given type of concentrate, the constants n and k of the power-law equation [13] tend to be inversely related to one another in ways that are independent of %TS, temperature, and other factors. This reflects the fact that structure development in concentrates that results in greater deviation from Newtonian behavior (lower n) also results in increased viscosity (higher k). The constant k can often be related directly to (i). For example, a unique direct relationship between log10 k (at
526 Rheology of Liquid and Semi-Solid Milk Products
20 C) and concentrate (i) has been demonstrated for ultrafiltration whole milk and cream concentrates. This relationship is linear up to (i) ¼ 0.5, and also linear, but with a higher slope, for (i) > 0.5. For (i) < 0.5, concentrates are Newtonian and the relationship is log10 k ¼ log ¼ 3:82ði Þ – 3:35
½20
where the units of k and are Pa sn and Pa s (i.e., n ¼ 1), respectively. Shear-thinning behavior exists at (i) > 0.5. This critical value of is close to the theoretical maximum value of 0.52 that could exist in an ideal monodisperse suspension in which the suspended particles are in contact with one another but able to move in straight lines in the direction of flow. The dependence of k (at 20 C) on (i) at > 0.5 is higher than that expressed by eqn [20] and has been found to be log10 k ¼ 10:15ði Þ – 6:51
½21
Fresh skim milk heat concentrated 6.22-fold was found to obey the Bingham equation [14]. Yield stress was found to be proportional to (cas)4.1 at cas > 0.3. The value of the exponent is close to the value of 3.85 exhibited by weakly flocculated latex suspensions, implying that concentrated milks are themselves weakly flocculated suspensions. Phenomenological description of time-dependent behavior
Milk concentrates can exhibit two forms of time-dependent rheological behavior: time-dependent shear thinning (a decrease in viscosity with time at constant shear rate) and age thickening (an increase in viscosity with storage time). These can be directly related: age thickening is caused by gradual structure development, which at a certain point starts to result in time-dependent shearthinning behavior – the result of the time-dependent breakdown of the developed structure when the agethickened concentrate is sheared. When concentrates age thicken, the Herschel–Bulkley equation per se or the Bingham equation has been found to describe adequately the instantaneous flow curves. The rate of viscosity increase during age thickening can be quantified in terms of the rate of evolution with time of the flow equation constants or the rate of increase with time in apparent viscosity, which at a given time is a function of these constants.
Sweetened Condensed Milk and Dulce De Leche Sweetened condensed milk (SCM) is essentially a highviscosity suspension of lactose crystals, fat globules, casein, and whey proteins in a saturated solution of lactose and sucrose. Its rheological behavior is complex.
SCM exhibits age thickening, which occurs faster at higher storage temperatures. The structure development is thought to involve not only casein micelles but also the whey proteins (especially if these have suffered a high degree of denaturation during milk preheating) and the fat globules. The viscosity and the rate of age thickening of recombined SCM are significantly influenced by the conditions used during milk powder manufacture. SCM exhibits time-dependent shear thinning. Recovery of structure (and consequently of viscosity) at ambient temperatures is highly retarded by the still-high viscosity that exists after shearing. The rheological properties of shear-thinned SCM can be characterized by the power-law equation [13] or the Herschel–Bulkley equation [15], depending on composition and processing conditions. Deviation from Newtonian behavior is slight immediately after manufacture, but increases with time during storage. The viscoelastic properties of SCM have been described by means of a generalized Maxwell model that incorporates yield stresses. Dulce de leche is an Argentinean dairy product similar to SCM in composition but with even more complex rheological properties. There are three types: standard, low calorie, and confectionery. The last contains a hydrocolloid thickener. Like SCM, dulce de leche is a timedependent shear-thinning material. The properties of shear-thinned samples can be modeled by the powerlaw equation [13], the Herschel–Bulkley equation [15] or the Casson equation, depending mainly on composition. The Casson equation is pffiffiffi pffiffiffiffiffiffiffipffiffiffi pffiffiffiffiffiffiffiffiffiffi ¼ Ca _ þ 0; Ca
½22
where Ca and 0, Ca are the Casson viscosity and the Casson yield stress, respectively. The Herschel–Bulkley and the Casson equations appear to be equally useful models for samples that possess a yield stress. Dulce de leche, like SCM, is viscoelastic, as indicated by the stress overshoot that occurs just after the start of a constant shear rate experiment. Thereafter, the shear stress declines with time as the structure is broken down by shear. The entire shear stress–time data can be modeled well with a generalized form of the Bird–Leider equation: j t _ – 1Þ wj exp – ¼ k_ n 1 þ ðb t j n j ¼1
½23
where k and n are the power-law equation constants, b and are fitting parameters that model the time dependence, and wj is a weighting factor. At long times, this equation converges to the power-law equation [13], which describes the equilibrium flow behavior of many foods.
Rheology of Liquid and Semi-Solid Milk Products 527
At times post the maximum (overshoot) stress, the decay of shear stress during shear thinning can be modeled with the Weltman equation: ¼ A – Blnt
½24
where A is the maximum (overshoot) shear stress, B is the coefficient of time-dependent breakdown, and t is the time. Oscillatory rheometric frequency sweep measurements, at strains within the linear elastic region, of the dynamic elastic modulus G9 and the loss modulus G0 (where G9 þ iG0 ¼ G , the complex elastic modulus) reveal differences in structural characteristics among the three types of dulce de leche. The behavior of all three approaches that of concentrated solutions, especially when presheared. The confectionery type, when unsheared, possesses characteristics intermediate between those of a concentrated solution and a gel, and may thus be termed a weak gel.
This is a consequence of the continuation, on melting, of the fat globule coalescence that takes place during the initial stages of whipping and freezing. The rheological properties of the melt are important with respect to the subjective assessment of ice cream on the palate.
Yogurt Two basic types of yogurt are made commercially: set yogurt and stirred yogurt. Yogurt rheology is complex. Yogurt exhibits viscoelastic behavior (especially the set type) and highly time-dependent shear thinning in flow. The rheological behavior of the final product depends on the concentration, composition, and pretreatment of the milk (especially heat treatment), starter culture and incubation conditions, and post-incubation shearing (stirred type). Measurement of rheological properties is useful in objectively investigating, characterizing, and predicting the effects of these variables on the nature of the final product, especially its texture.
Ice Cream Mix Unfrozen ice cream mix is a dispersion of milk fat and vegetable fat in an aqueous phase containing non-fat milk solids, carbohydrate sweeteners, and a stabilizer (usually a hydrocolloid). The mix commonly contains, in addition, an added emulsifier. The total fat concentration is about 10% (w/w). Ice cream mix is thus essentially a dilute oil-in-water emulsion and in this respect is similar to cream. However, viscosity and rheological behavior are more variable, as they depend on both mix formulation and processing conditions. Ice cream mixes are time-dependent shear-thinning liquids that can exhibit significant viscosity recovery after subjection to high shear. Shear thinning and viscosity recovery can be attributed partly to deflocculation and flocculation, respectively, of fat globules (to the surfaces of which the micellar casein is attached) and to changes with time in the crystalline state of the fat. Age thickening of unsheared mix has been attributed to progressive flocculation of fat globules. Mixes exhibit viscoelastic behavior typical of weak gels, the gel network being the result of interactions involving fat globules, and the proteins and polysaccharides present in the aqueous continuous phase. Ice cream mix flow curves can generally be described adequately by the power-law equation [13]. The values of the constants k and n in the equation are largely influenced by the presence, type, and concentration of the hydrocolloid stabilizer and by processing treatments such as homogenization. Melted ice cream has a much weaker structure, and consequently a lower viscosity and a lower extent of deviation from Newtonian behavior, than had the original mix.
Heat Treatment The development of desirable final rheological properties is highly dependent on there being sufficient interaction between, and flocculation of, the casein micelles during incubation, so that a satisfactory coagulum forms; heat treatment of the milk must be severe enough to cause extensive denaturation of -lactoglobulin, some denaturation of -lactalbumin, and the interaction of both of these whey proteins with the micelles. The effect of heat treatment depends on whether it is carried out before or after homogenization. Fermentation Though acid production by the starter microorganisms is the main cause of micelle flocculation and consequent structure development, the starter strain can be chosen to influence the rheological properties. In particular, strains that produce exopolysaccharides can be used to increase yogurt viscosity and decrease susceptibility to syneresis. Final rheological properties are dependent both on strain and on incubation conditions (time and temperature). Post-Fermentation Shearing The rheological properties of stirred yogurt are greatly influenced by the shearing to which the yogurt is subjected during post-fermentation stirring, cooling, and packaging. The shear history and consequent structure breakdown are related directly to equipment geometry and to process conditions such as temperature and flow rate. The final product is a strongly shear thinning, viscous liquid.
528 Rheology of Liquid and Semi-Solid Milk Products
Solid-like and Viscoelastic Behavior The solid-like behavior of yogurt (especially set yogurt) can be determined very simply by measuring the force required to push a probe into the product under standard conditions. The method is empirical, but simple, rapid, and inexpensive. The result obtained is some function of the elastic, viscous, and breakdown properties of the product. The results can be correlated to texture, and can be used to investigate the relative effects of changes in processing conditions. Objective measurements of the texture-related rheological properties of set-type yogurts can be made using the technique of texture profile analysis, which involves force– distance measurements during compression/decompression tests in suitable rheometers. When measurements are to be made on intact yogurt gels in well-defined rheometer geometries, either during or at the end of fermentation, the fermentation process must, of course, be carried out in the rheometer itself. Fundamental viscoelastic properties of both set and stirred yogurts have been determined using dynamic oscillatory rheometry and stress relaxation measurements. The mechanical spectra (dynamic elastic moduli versus frequency) of the set and the stirred yogurts are similar, with the moduli of the former being 8–10 times higher than those of the latter. In one study (of a stirred yogurt) dynamic measurements showed that at low strain ( < 3%) linear viscoelastic behavior existed: the rigidity modulus G 9 and the loss modulus G 0 were constant and independent of strain. For 3% < < 32%, there existed a non-linear region where G 9 started to decrease but G 0 remained fairly constant, indicating a partial breakdown of the elastic structure. At ¼ 32%, G 0 became larger than G 9, indicating a change from a predominantly solid-like to a predominantly liquid-like behavior. For > 32%, G 0 became increasingly larger than G 9 as the strain was increased. Pre-shearing and then resting resulted in the same behavior, but the values of the moduli in the linear region were 20% lower, indicating a temporary or perhaps permanent loss of structure. Within the linear region, values of G 9 measured dynamically were in good agreement with the values of the relaxation modulus measured in stress relaxation experiments. (Critical values of strain such as those given above would be expected to vary with yogurt and the method of measurement.)
Flow Behavior Rheological behavior in continuous shear can be determined either by empirical tests, in which no attempt is made to generate fundamental shear stress–shear rate data, or by tests in which such data are generated and then modeled phenomenologically.
The rheological characterization of a yogurt by means of a standardized empirical measurement (e.g., the apparent viscosity at a specified spindle rotational speed in a rotary viscometer, or the area of the hysteresis loop on a plot of torque versus rotational speed obtained with the same type of viscometer) can be useful when the manufacturing process itself is highly standardized; in such a process the rheological character of the final product may be predictable from a simple measurement of this kind. Stirred yogurt, in particular, is amenable to more fundamental characterization by means of experiments, usually in rotary viscometers, in which instrument-independent values of shear stress and shear rate can be measured. Three approaches are commonly used: the generation of hysteresis loops by increasing and then decreasing the applied shear rate; the measurement of the shear stress as a function of time at constant shear rate; and the measurement of the effect on viscosity of time and shear rate at constant shear stress.
Flow curves and hysteresis loops
Hysteresis in up–down flow curves is a consequence of the highly time-dependent shear-thinning behavior of yogurt. As the recovery of viscosity (i.e., of shear damaged structure) on post-shear resting is usually slight, this behavior has been called ‘irreversible thixotropy’. Individual flow curves (up, down, or equilibrium) have been modeled with the power-law equation [13], the Bingham equation [14], the Herschel–Bulkley equation [15], and the Casson equation [22]. The Herschel–Bulkley equation has been found particularly useful for characterizing yogurt flow curves. However, one comparative study found that over the complete range of shear rates involved, the following hyperbolic relationship, inspired by the well-known Michaelis–Menten equation, modeled flow curves more accurately: ¼
Q _ þ 0 _ ðR þ Þ
½25
(Q + 0) is the hypothetical asymptotic value of shear stress, , at infinite shear rate, and R is the shear rate at = 0 + Q /2. Values of the parameters in these phenomenological models are highly dependent on the experimental procedure used to obtain the up–down flow curves, as is the area enclosed by the curves. This area is proportional to the degree of time-dependent behavior. The modeling of thixotropic loops can be useful in product formulation. For example, it is found that the addition of pectin to stirred yogurt increases both viscosity and shear stability, whereas the addition of fruit concentrate increases viscosity in a less shear-stable way. Rheological measurements allow rheological properties to
Rheology of Liquid and Semi-Solid Milk Products 529
be manipulated purposely by the addition of these two ingredients in appropriate proportions.
in a somewhat different way by means of the Weltman equation [24], modified as follows:
Constant shear rate experiments
If the initial viscosity of a yogurt (the viscosity at zero time of shearing) can be modeled by a phenomenological equation such as the power-law or the Herschel–Bulkley equation, the decay of shear stress (and thus apparent viscosity) with time at constant shear rate can be modeled by incorporating into the equation a time-dependent structure parameter, . The Herschel–Bulkley equation, for example, is then written as ¼ ðk_ n þ 0 Þ
½26
The value of ranges from unity at the start of shearing ( 0 ¼ 1, corresponding to app, 0) to an equilibrium value,
e, after prolonged shearing that is less than unity and corresponds to an equilibrium viscosity, app, e. The rate of change of with time is given by the following bth-order kinetic equation: –
d ¼ K ð – e Þb for > e dt
½27
where K ¼ a _ d
½28
K is a rate constant, and b, a, and d are empirical constants. A definition of is obtained by combining eqns [5] and [26]:
¼
app _ ð0 þ k_ n Þ
½29
e ¼
app; e _ ð0 þ k_ n Þ
½30
At equilibrium,
By integrating eqn [27] and incorporating the definitions represented by eqns [26], [29], and [30], the dependence of apparent viscosity on time at constant shear rate can be expressed as ¼
n
1 – b app; 0 – 0 _ – 1 þ k_ n – 1 1 – b o1=ð1 – bÞ – Kt ð1 – bÞ 0 _ – 1 þ k_ n – 1 þ 0 _ – 1 þ k_ n – 1
½34
where tmax is the time (e.g., 12 s from the start of a 60 min shearing time) at which is at a maximum (the overshoot shear stress); thus A ¼ max. The value of at zero time, which cannot be expressed by eqn [34], is obtained by a separate linear graphical procedure. This initial shear stress and the parameters A and B in eqn [34] are quantitatively related to shear rate and temperature. Equation [31] and its analogs, and eqn [34], are currently the best quantitative descriptions of the timedependent shear-thinning properties of both stirred and set yogurts. The Cross equation [7] has been used successfully to model the shear rate dependence of the equilibrium apparent viscosity of yogurt. It has been shown that a vane viscometer gives the same results as that of a bobin-cup viscometer. An advantage of the former instrument is that it enables measurements to be carried out on yogurt containing fruit pieces. After fermentation, yogurt must be transported to filling equipment and dispensed into the final containers. The effects of pumping yogurt through pipework and filling heads on the viscosity of the final filled product, which is closely related to texture, can be predicted by a procedure based on straightforward rheological measurements made under controlled shear rate conditions that simulate process conditions. By measuring changes in apparent viscosity over a sequence of shear rates consistent with those existing in different stages of the real process – shear rates being applied for periods of time consistent with yogurt residence times in these stages – the end-of-process viscosity can be predicted. The extent of structural recovery in the filled containers can also be predicted by simple oscillatory tests conducted on the unsheared and sheared yogurt. Constant shear stress experiments
½31
Analogous equations have been developed for yogurt by starting with the power law or with an exponential model modified as in eqn [26]: ¼ k_ n
½32
1 _ ¼ 0 þ _ app; p expð – tp Þ
½33
p¼1
t ¼ A – B log for t tmax tmax
In a study of a commercial stirred yogurt, the decrease in shear stress with time at constant shear rate was modeled
Processing effects can be predicted by an alternative approach, as follows. The time-dependent shear thinning of yogurt can be described by means of a plot of shear rate against time at constant shear stress (measurements being made using a controlled-stress rheometer). The typical plot shows a steep slope initially, which then decreases with time to a constant positive non-zero value. It has been shown, for yogurt that has been sheared (e.g., in processing and filling operations post-fermentation), that the straight line part of the plot can be predicted from the straight-line part of a similar plot determined for an unsheared (unprocessed) sample. This is done by offsetting the latter plot in a negative time direction by a period
530 Rheology of Liquid and Semi-Solid Milk Products
that can be related to the work done on the yogurt per unit volume during processing. This approach, which allows prediction of the effect of process handling on the rheological properties of the yogurt as packaged, was demonstrated to be accurate in the case where the ‘process’ was flow through a straight round pipe (a relatively simple system). It can in principle be applied to (more complex) real processing systems that are amenable to the fluid mechanical analysis required.
Cultured Buttermilk
1 ð0 þ k_ n Þ ð1= 0 e Þ þ K t
½35
Numerical values of the variables in eqn [35], for the particular buttermilk investigated, were as follows:
1 0:4 þ 1:362_ 0:385 ¼ 0:449 þ 1:815 þ 0:0051t
½36
An American study found that both ‘modern’ cultured buttermilk (made directly from low-fat milk, as in the Irish study) and ‘traditional’ cultured buttermilk (made from cultured cream) were time independent at 25 C and could be characterized rheologically by the power-law equation [13]; at 10 C, the modern buttermilk exhibited time-dependent behavior. It is appropriate to mention here that eqn [31] (with b ¼ 2) has been found to describe adequately the timedependent shear thinning of a thickened cream (containing 35% fat, and gelatin as stabilizer). Clearly, this approach to modeling such behavior is especially useful for dairy products.
Fresh Cheeses Low-total solids fresh cheeses have structures similar to that of stirred yogurt. However, the wider ranges of composition and processing technique lead to a correspondingly wider variation in rheological behavior. Some are shear thinning, but time independent. Flow curves can be modeled by the power-law equation [13], or by the following expression for apparent viscosity:
E RT
½37
where = 1, 1 is the hypothetical apparent viscosity (Pa s) at a temperature ( C) of infinity and a shearing time of 1 s; E is the activation energy of flow (J mol1), R is the gas constant (8.314 J K1 mol1), T is the absolute temperature (K), and B is a constant. Some fresh cheeses exhibit time-dependent shear thinning. For a constant D the fall in apparent viscosity with time at constant shear rate has been modeled by the following equation: log app ¼ log ¼ 1; 1 þ
An Irish study showed that eqn [31] could be used to model the time dependence, at 5 C, of cultured buttermilk made directly from skim milk. In this particular case, it was found that b ¼ 2 in eqn [27], and that the dependence of K in the equation on shear rate was relatively slight. The latter finding allowed eqn [27] to be integrated, using an average value of K, to give an equation for shear stress in terms of only shear rate and time: ¼ e þ
log app ¼ log ¼ 1; 1 þ Blog_ þ
E þ Dlogt RT
½38
For such cheeses at 1 C, the relationship between apparent viscosity and time in experiments where the shear rate was oscillated linearly between 0 and 4.5 s1 at a frequency of 0.05 Hz has been modeled for the shear rate range 1–4.5 s1 by the equation app ¼
t i 1h t ¼ 1 þ ðt ¼ – t ¼1 Þ exp – _ P
½39
where P is the time required for app to become equal to _ ðt ¼ 1 þ ðt ¼ 0 – t ¼ 1 Þ=eÞ. ð1=Þ At any given time, the phenomenological relationship between shear stress and shear rate could be modeled well by the Bingham equation [14] for shear rates between 1 and 4.5 s1. Over the whole shear rate range of 0–4.5 s1 the data could be modeled by the power law equation [13] or the Herschel–Bulkley equation [15] or the Casson equation [22]. The power law was the poorest (though still reasonably good) model. The best model was found to be a modified Bingham equation: ¼ 0 þ pl _ –
C _ – _ 0
½40
C=_ is the difference between the shear stress value calculated using the Bingham equation and the value found by fitting the experimental results with eqn [40]. C=_ 0 is the value of C=_ at _ ¼ 0. (The unit of C is Pa s1.) Fresh cheeses are viscoelastic. Such behavior can be investigated conveniently by measuring the dynamic rigidity and loss moduli (G 9 and G 0, respectively) using oscillatory rheometry. Such measurements indicate, for example, that a soft cheese similar to Mozzarella behaves in a way typical of a weak viscoelastic gel. In contrast, for double cream cheese, the frequency dependence of G 9 suggests viscoelastic behavior dominated by a network, whereas the frequency dependence of G 0 is similar to that observed for a nonchemically cross-linked polymer. Measurement of the dynamic moduli is a sensitive way of investigating and interpreting the effects of making changes to cheese milk composition and cheesemaking conditions.
Rheology of Liquid and Semi-Solid Milk Products 531
The Bird–Leider equation (see eqn [23]) has been found to model the combined viscoelastic and timedependent properties of whipped cream cheese, but only moderately well; this is perhaps owing to the absence of yield stress as a variable in this equation, which is one of the limitations of the equation. In spite of this, the equation has been found to be satisfactory for modeling the sensory property ‘thickness’ of whipped cream cheese when shear rate in the equation is replaced by an expression for shear rate in the mouth that incorporates thickness and other relevant variables. It has been possible to model the stress relaxation properties of commercial fresh cheeses using the Avrami equation: n t ¼ t ¼ 0 – ðt ¼ 0 – t ¼ 1 Þexp – R1
½41
where n ¼ exponent of time and R1 ¼ relaxation time after 1 s of stress relaxation. The time-dependent shear thinning, at constant shear rate, of spreadable cheeses made from whole milk preconcentrated by ultrafiltration has been modeled by eqn [31] with b ¼ 2. At a given shear rate, the constant K in eqn [31] changed from one value (K 9) during the early part of the shearing time to a lower value (K 0),which then stayed constant during the remainder of the shearing time. K 9 decreased with increasing shear rate. K 0 was about half the value of K 9. These findings may be evidence for macroscopic shear-induced breakdown initially, followed by slower breakdown at a finer structural level. Empirical rheological measurements made by uniaxially compressing or penetrating the cheese sample can give data of practical usefulness.
Conclusion In spite of the complexity of milk and the semi-solid products made from it, there has been considerable success in quantitatively elucidating the interrelationships between rheological properties and microstructure, and in providing quantitative descriptions of rheological behavior useful in dairy process design and control. These is no doubt that future advances in rheology theory, in computing, and, perhaps especially, in the sophistication of rheometers will lead to a deeper understanding. See also: Cheese: Cheese Rheology. Concentrated Dairy Products: Dulce de Leche; Evaporated Milk; Sweetened Condensed Milk. Fermented Milks:
Buttermilk; Yoghurt: Types and Manufacture. Ice Cream and Desserts: Dairy Desserts. Milk: Physical and Physico-Chemical Properties of Milk. Milk Lipids: Rheological Properties and Their Modification.
Further Reading Adam M, Celba J, Havlı´cˇek Z, et al. (1994) Thermophysical and Rheological Properties of Foods. Milk, Milk Products and Semi-Products. Prague: Institute of Agricultural and Food Information. Anonymous (1996) Physical Properties of Dairy Products. Hamilton, New Zealand: MAF Quality Management. Bakshi AS and Smith DE (1984) Effect of fat content and temperature on viscosity in relation to pumping requirements of fluid milk products. Journal of Dairy Science 67: 1157–1160. Barnes HA, Hutton JF, and Walters K (1989) An Introduction to Rheology. Amsterdam: Elsevier. Bertsch AJ and Cerf O (1983) Dynamic viscosities of milk and cream from 70 to 135 C. Journal of Dairy Research 50: 193–200. De Jong P and van der Linden HJLJ (1998) Polymerization model for prediction of heat-induced protein denaturation and viscosity changes in milk. Journal of Agricultural and Food Chemistry 46: 2136–2142. De Kee D, Code RK, and Turcotte G (1983) Flow properties of time dependent foodstuffs. Journal of Rheology 27: 581–604. de Kruif CG (1993) Milk clotting time as a function of volume fraction of casein micelles. In: Dickinson E and Walstra P (eds.) Food Colloids and Polymers: Stability and Mechanical Properties, pp. 55–65. Cambridge: Royal Society of Chemistry. de Kruif CG (1998) Supra-aggregates of casein micelles as a prelude to coagulation. Journal of Dairy Science 81: 3019–3028. Fernandez-Martin F (1972) Influence of temperature and composition on some physical properties of milk and milk concentrates. II. Viscosity. Journal of Dairy Research 39: 75–82. Hinrichs J (1999) Influence of volume fraction of constituents on rheological properties and heat stability of concentrated milk. Milchwissenschaft 54(8): 450–454. Jaros D and Rohm H (2003) The rheology and textural properties of yoghurt. In: McKenna BM (ed.) Texture in Food, Vol. 1: Semi-Solid Foods, pp. 321–349. Cambridge: Woodhead Publishing Limited. Jenness R and Patton S (1959) Principles of Dairy Chemistry. London: Chapman & Hall. Jeurnink TJM and de Kruif KG (1993) Changes in milk on heating: Viscosity measurements. Journal of Dairy Research 60: 139–150. Korolczuk J (1993) Flow behaviour of low solids fresh cheeses. Journal of Dairy Research 60: 593–601. McCarthy OJ and Singh H (2009) Physico-chemical properties of milk. In: McSweeney PLH and Fox PF (eds.) Advanced Dairy Chemistry, Vol. 3: Lactose, Water, Salts and Minor Constituents, 3rd edn., pp. 691–758. New York: Springer. Phipps LW (1969) The interrelationship of the viscosity, fat content and temperature of cream between 40 and 80 C. Journal of Dairy Research 36: 417–426. Rohm H, Mu¨ller A, and Hend-Milnera I (1996) Effects of composition on raw milk viscosity. Milchwissenschaft 51: 259–261. Snoeren THM, Brinkhuis JA, Damman AJ, and Klok HJ (1984) Viscosity and age-thickening of skim-milk concentrate. Netherlands Milk and Dairy Journal 38: 43–53. Ve´lez-Ruiz JF and Barbosa-Ca´novas GV (1997) Rheological properties of selected dairy products. Critical Reviews in Food Science and Nutrition 37(4): 311–359. Walstra P and Jenness R (1984) Dairy Chemistry and Physics. New York: Wiley.
RISK ANALYSIS C Heggum, Danish Agricultural and Food Council, Aarhus C, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction Risk analysis is a formalized scientifically based approach that is recognized by the World Trade Organization as a tool for addressing food safety issues and which shall establish food safety regulations. When carried out correctly, risk analysis provides a tool for the identification, assessment, management, and communication of risk. In the area of food safety, risk analysis approaches have been applied for many years to assess and manage chemical food hazards (e.g., food additives, veterinary drugs, and pesticides). More recently, risk analysis techniques have been established for addressing microbiological food risks. The application of risk analysis techniques is an emerging discipline. This article attempts to provide an overview of the concept of risk analysis, the individual steps of risk analysis, and the application of risk analysis.
Purpose and Role Traditionally, the approach to food safety control, both by the food industry and by public authorities, has been technical, ad hoc, and mainly reactive, based upon utilization of experience obtained from many years of exposure to various hazards, taking into account local practices, traditions, and technological possibilities. This approach has proven to be insufficient to ensure public health and fair international trade in foods. Analyses of major food safety problems that have occurred through the last decades demonstrate that these are, most of the time, the consequence of organizational deficiencies, reflecting defective global organizations for controlling food safety. Risk analysis provides an opportunity to address these organizational difficulties by systematic integration of scientific understanding of the risks involved and the legitimization of decisions taken. The rationale for utilizing a formal risk analysis approach is multiple: 1. To assist in the control of the multiple foodborne risks in a proactive and cost-effective way. The multiplicity of food safety comprises
532
a. potential microbiological foodborne risks (for instance, from ‘classical’ salmonellosis to emerging pathologies due to protozoa or viruses); b. chemical/toxicological risks, such as naturally and environmentally occurring toxicants and residues of chemicals and drugs used; c. newly emerging areas of concern, such as allergenicity, antimicrobial resistance, genetic engineering, and nanotechnology. 2. To support national food safety regulation by providing a sound, science-based, systematic and target-focused tool that secondarily facilitates fair international trade. The Sanitary and Phytosanitary (SPS) Agreement of the World Trade Organization has established the tenet that ‘‘members shall assure that their sanitary and phytosanitary measures are based on an assessment, as appropriate to the circumstances, of the risk to human, animal or plant life or health, taking into account risk assessment techniques developed by relevant international organizations’’ (Article 5.1). Codex Alimentarius has established international principles and guidelines for risk analysis. 3. To address the increase in the social unacceptability of food risks. As food becomes objectively safer, the remaining and occasional risks are even less tolerated by the public at large, a trend that is enhanced by the general public feeling increasingly alien to food safety control activities (decisions are perceived to be mainly the affair of the food industry and/or the public agencies having jurisdiction). The application of the risk analysis concept has, however, also some disadvantages when used to support national food legislation. Many legislative measures are multifunctional as they address public health issues as well as other issues such as wholesomeness/suitability of foods, environmental protection, and basic animal welfare. Therefore, the challenge for legislators is to achieve sufficient transparency in the objective(s) of reasoning for any such measure to avoid confusion. Risk analysis is usually described as a process consisting of three elements: risk assessment, risk management, and risk communication. It is a decision-oriented process and making decisions is a managerial activity (Box 1).
Risk Analysis
Box 1
Hazards and risks
The meaning of the terms hazards and risks is often confused. This is due mainly to translation problems as, in many languages, these terms are directly translated into the same word. Although often synonymous in everyday life, they have taken different meanings in the technical language used in risk analysis. A hazard is a biological, chemical, or physical agent in, or a condition of, food with the potential to cause an adverse health effect (Codex Alimentarius). A risk is the function of the probability of an adverse health effect and the severity of that effect, consequential to a hazard in food (Codex Alimentarius). In more common words, a risk is the likelihood and severity of a failure causing deaths or illnesses among consumers. For instance, the probability of humans being affected by the survival of a pathogenic microorganism during pasteurization is the risk while the microorganism itself is the hazard. Risk analysis should not be confused with the similar term hazard analysis, the latter constituting the assessment steps of the hazard analysis and critical control point (HACCP) system. Although hazard analysis contains some of the same steps as does risk analysis, it is principally limited to a single type of food from a single processing line (or from the specific food chain it has been following). Hazard analyses of two processing lines/ food chains are independent and may result in different outcomes (HACCP plans), as the objective is to ensure the safety of the specific food lots resulting from the specific process. Risk analysis is principally broader in scope, typically addressing one or more food types (e.g., a whole food category) from multiple manufacturers/food chains, the objective being to protect the health of the population.
Risk Assessment Risk assessment is the scientific part of risk analysis that is initiated and commissioned by risk managers. The purpose is to estimate the severity and likelihood of harm from exposure to a certain hazard by furnishing all scientific data relevant for the evaluation. The output might, for example, be an estimate of the annual rate of illness per 100 000 inhabitants or an estimate of the rate of human illness per eating occurrence. The scientific data needed are both qualitative and quantitative. They concern the nature and sources of the hazard, how it affects human health, and how it behaves under various conditions. In addition, scientifically based information on the potential exposure of humans is needed. The risk assessment process comprises four steps: hazard identification, exposure assessment, hazard characterization, and risk characterization. The information is passed to the risk managers to assist them in continuing the risk management process. Codex Alimentarius has established general principles for the conduct of risk assessments.
533
Hazard Identification Hazard identification is predominately a qualitative process, the purpose of which is to identify the hazards of concern associated with food. Hazards can be identified from relevant data sources. Information on hazards can be obtained from scientific literature, from databases such as those in the food industry and government agencies, and through expert elicitation/consultation. Relevant information includes data in areas such as clinical studies, epidemiological studies and surveillance, laboratory animal studies, investigations of the characteristics of the hazards, the interaction between hazards and their environment through the food chain, and studies on analogous hazards and situations. Exposure Assessment The purpose of exposure assessment is to obtain a quantitative assessment of the actual or anticipated human exposure to a food hazard. It is normally based upon realistic exposure scenarios, including the potential extent of food contamination, and on actual dietary information. Susceptible and high-risk population groups with regard to acute, chronic (including long-term), cumulative, and/or combined adverse health effects should also be brought into consideration. Typical factors considered include the following: 1. the frequency and level of contamination of food over time, which are influenced by a. the characteristics of the hazard, b. the nature/ecology of the food, c. the initial contamination of the raw material, d. the level of process controls, e. the methods of processing, packaging, distribution, and storage of the foods, 2. patterns of consumption, which relate to socioeconomic and cultural backgrounds, ethnicity, seasonality, age differences (population demographics), regional differences, and consumer preferences and behavior. In practice, exposure assessment of foods can be qualitatively categorized according to (1) the likelihood that the foodstuff will or will not be contaminated at its source and (2) whether or not the level of the hazards in the food can increase over time, taking into account the potential for abusive handling. Hazard Characterization The purpose of hazard characterization is to provide a qualitative or quantitative description of the severity and duration of adverse effects that may result from the ingestion of contaminated food. The level of the hazard that
534 Risk Analysis
causes an adverse health effect (dose–response assessment) should be estimated if such data are obtainable. Several important factors that are considered in hazard characterization relate both to the hazard itself and to the human host. Factors related to the hazard:
characterization, where uncertainty and varia• Hazard bility arise when extrapolating from high to low doses
of the hazard to replicate; • potential virulence infectivity of the hazard; • impact ofandinteractions between the host and the • environment; for transfer of genetic material (e.g., antibiotic • potential resistance, virulence factors); • potential for spread through secondary and tertiary • transmission; period (clinical symptoms can be delayed • incubation substantially following exposure); for changed pathogenicity due to the attri• potential butes of a food, for example, fat content. Factors related to the host:
• • • •
genetic factors; increased susceptibility due to the breakdown of physiological barriers; individual host susceptibility characteristics such as age, health and medication status, concurrent infections, immune status, and previous exposure history; population characteristics such as population immunity and population behavior, and persistence of the organism in the population.
Risk Characterization Risk characterization represents the integration of the results of hazard identification, hazard characterization, and exposure assessment, the purpose being to provide qualitative or quantitative estimates of the likelihood and severity of the adverse effects, which could occur in a given population. The data may permit only a qualitative estimate of risk. The degree of confidence in the final estimation of risk depends on the variability, uncertainty, and assumptions made in all previous steps. Variability represents heterogeneity within biological systems and populations, while uncertainty represents a lack of precise knowledge associated either with the data themselves or with the choice of model. Variability and uncertainty arise at all steps of the risk assessment process: identification, where uncertainty or variability • Hazard may arise because of (1) misclassification of the agent, (2) the potential unreliability of the screening method used to identify the hazard, or (3) problems in extrapolating the information provided by the screening test for predicting human hazards.
•
and from one species to another and when considering varying sensitivities within human populations. When models are used, additional uncertainty as to whether they represent actual biological processes is introduced. For instance, the transfer of data from animal studies into estimates relating to humans involves uncertainties. For this reason, a 100-fold safety factor is often applied to account for likely inter-species differences in susceptibility. Exposure assessment, where many uncertainties arise due to the lack of detailed data on, for example, the level of the agent in food products and the frequency, duration, and magnitude of human intake of food products, and changes in the concentration of the chemical or microbiological agent during storage, processing, and preparation of the food product. There is also a great deal of variability in dietary habits. Risk characterization, where uncertainty and variability arise because of the uncertainties and variability involved in its constituent steps and in the model used for constructing the distribution of individual or population risk.
Risk Assessment of Chemical Hazards Chemical risk assessment in one form or another has been applied to the evaluation of various chemical hazards in foods for many years. Assessment of food additives and that of contaminants fundamentally differ because food additives, which are generally of low toxicity, are deliberately added to food, whereas contaminants are unavoidable and generally demonstrate greater potential toxicity. Food additives can be controlled easily, while the elimination of contaminants from foods incurs cost, such as reduction in food availability and/or affordability. JECFA (Joint FAO/WHO Expert Committee on Food Additives) and JMPR (Joint FAO/WHO Meeting on Pesticide Residues) carry out risk assessments of the following substances: additives, resulting in the establishment of accep• food table daily intakes (ADIs); contaminants and naturally occurring toxicants, • food resulting in the establishment of provisional maximum
•
tolerable daily intakes (PMTDIs) or provisional maximum tolerable weekly intakes (PMTWIs) where no observed effect can be identified; in other cases, other outcomes are provided; veterinary drug residues, leading to the establishment of ADIs and, taking into account good practices, the establishment of maximum residue levels (MRLs) in target animal tissues, milk, and egg;
Risk Analysis
residues, resulting in the establishment of • pesticide ADIs and acute reference doses and, taking into account good practices, the establishment of MRLs in foods. The approach is somewhat different from risk assessment, but does have the advantage of preventing problems associated with deciding on an acceptable level of risk. The acceptable or tolerable intake is an indication of both the magnitude and the duration of acceptable intake. The ADI usually represents an acceptable average daily intake for the life span of an individual. Tolerable intakes for contaminants should be compared with intake surveys of appropriate duration. In cases where no threshold is thought to exist, such as aflatoxins, JECFA does not allocate tolerable intake values but recommends that the level of contaminant in food be reduced to as low as reasonably achievable (ALARA). The ALARA level is regarded as the concentration of a substance that cannot be eliminated from a food without having to discard that food or severely compromising the availability of major food supplies.
Microbiological Risk Assessment The risk assessment process was originally developed for chemicals. Extending the practice to microbial pathogens poses significant difficulties. Therefore, most microbial risk assessments currently have a qualitative base. However, in recent years, the interest in qualitative approaches to microbial food safety has increased dramatically and quantitative models for specific pathogen/food combinations are developed in many circles. One difficulty relates to the fact that microbial pathogens can multiply as food moves from the farm to the table, making intake assessment very difficult. In addition, many data gaps exist, limiting the precision necessary for quantitative risk assessments. For example, little information is available to accurately estimate the relationship between the quantity of a biological agent and the frequency and magnitude of adverse human health effects, particularly for susceptible populations. Microbial pathogens multiply and die, and the biological interactions are complex. The contamination levels of the raw material entering the food chain dictate the character of the initial microflora, but this can be modified markedly by subsequent events. Additionally, there are marked differences in the virulence and pathogenicity of animal and environmental strains for humans, and the individual interactions of host and pathogen are very variable. Factors to consider for exposure assessment include the frequency and level of contamination of raw materials, possibilities of post- and cross-contamination, and the level of contamination of the food during the shelf life of the product. The characteristics of the pathogenic agent, the microbiological ecology of the food, the level
535
of basic hygiene, the level of sanitation and process controls, and the methods of processing, packaging, distribution, and storage of the foods impact these factors. Microbial pathogen levels may be kept low, for example, by proper time/temperature controls during food processing, but they can increase substantially with abuse conditions. Therefore, exposure assessment should include different scenarios describing the pathways from production to consumption and should be constructed to predict the range of possible exposures. Construction of scenario trees for all steps from production and processing through to intended end-uses of a food describes the pathway for exposure, and targeted research is often required to accumulate appropriate microbiological data. Predictive modeling plays an important role in this respect. Unfortunately, dose– response data to service the hazard characterization component are currently very limited. Because of the wide variability inherent in much microbial data, Monte Carlo simulation modeling is being used increasingly to generate probabilistic risk estimates that are biologically realistic. FAO and WHO have recently established an expert body system, similar to JECFA and JMPR, the tasks of which are to carry out microbiological risk assessments.
Physical Risk Assessment Risk assessment of physical hazards can be achieved readily. The characteristics of the hazards do not usually change once they have been introduced to the food, and adverse health effects can usually be subjected to simple ranking systems to generate estimates of risk.
Risk Management Risk management is a continuing process and constitutes the managerial and political part of risk analysis. It concerns the transfer of the results of risk assessment into actions in accordance with established political priorities. Risk management sets priorities, commissions risk assessments, and implements, monitors, and reviews the chosen strategies and options. The risk management process comprises four steps: risk evaluation, risk management options assessment, implementation, and monitoring and review.
Risk Evaluation The initial part of the risk management process sets the stage for risk assessment, and evaluates the outcome of the risk assessment process, which should result in a risk estimate.
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Risk profiling
A risk profile is developed when a new food safety problem has been identified or if surveillance information shows an unacceptable increase/level of a disease or a hazard. The food safety problem and its context are described briefly, including the size and nature of the problem, available data, type of foods involved, main sources, the values expected to be placed at risk (e.g., human health, economic concerns), stakeholders perceptions, distribution of risks and benefits, and what immediate action(s) may be necessary, including whether a risk assessment should be carried out. Goal setting/acceptable level of protection
To guide the rest of the decision-making process, the goals for the risk management activity need to be identified as early as possible. However, the results of a subsequent risk assessment process and subsequent steps of risk management may identify needs to modify or redefine the goals. One management goal can be to establish relevant risk-based metrics such as food safety objectives (FSOs) and performance objectives (POs). Any goal should be related to the acceptable level of protection – defined by the SPS Agreement as the level of protection deemed appropriate by the member state to protect human life within its territory and could, for instance, be expressed as the acceptable number of cases of a particular foodborne disease per million inhabitants. Usually, when no significant food-related public health problem exists, the acceptable level of protection is the level obtained from the sanitary measures already practiced. Decisions on acceptable levels of protection should be determined primarily by human health considerations, but other factors may legitimately be taken into account, for example, technological feasibility and economic/political/social concerns (Box 2). Different approaches to acceptable levels include policies, for example, de minimus, ADI; • ‘zero-risk’ risk-balancing • ALARA; policies, for example, cost–benefit, threshold policies, for example, specified levels of • risk risk deemed acceptable; comparison policies, for example, comparison • risk between sources, precedence; approaches, for example, negotiation, con• procedural sensus building.
Box 2
The SPS Agreement
The key point in the Sanitary and Phytosanitary (SPS) Agreement is that any sanitary measure has to be based on science. A government cannot restrict trade or maintain a restriction against scientific evidence. Science can, of course, be misused. Therefore, the Agreement also specifies that the scientific approach applicable is the scientific assessment principles and evaluation procedures established by international organizations such as Codex Alimentarius. The SPS Agreement stipulates government’s rights to decide what they regard as the appropriate level of protection, or in other words, the right to decide on the acceptable level of risk that should be valid on their territory. Therefore, the level of protection may differ between countries, but it shall be determined using harmonized risk analysis procedures. Therefore, the importance of transparency in the risk assessments carried out is obvious. A government must be able to show which factors it has considered and what have been the results of its consideration. This is to ensure that potential differences between the regulations of two countries (e.g., differing maximum limits) are not due to differences in scientific evidence but only due to differences in the politically decided acceptance levels.
Box 3 Examples of risk assessment policies at specific decision points in chemical risk assessment
Reliance on animal models to establish potential human effects.
Using body weight scaling for inter-species comparison.
Assuming that absorption in animals is approximately the same.
Using a 100-fold safety factor to account for likely interand intraspecies differences in susceptibility, with guidelines for deviations that are permitted in specified situations.
and how to deal with uncertainties (e.g., application of safety factors) (Box 3).
Commissioning of risk assessments
Commissioning of the risk assessment process is a risk management activity that aims at ensuring that the needs of the risk managers are addressed and that resources are used in the most effective way. Typically, it includes clear statements of purpose and scope of the assessment addressing the risk management goals.
Risk assessment policy
Risk assessment policy setting serves to protect the essential scientific independence and integrity of the risk assessment. It provides guidelines for value judgments and policy choices that may be needed at specific decision points in the risk assessment process and addresses how to ensure transparency, clarity, and consistency in outcome
Consideration of the result of risk assessment
When the results of the risk assessment are available, a risk estimate is established. Risk estimates should take into account variability, uncertainties, and assumptions made during the risk assessment process.
Risk Analysis
Risk Management Options Assessment Risk management option assessment typically includes four steps: of available management options; • identification of the preferred management option, includ• selection ing consideration of an appropriate level of protection
• •
(ALOP; see above); evaluation of the impact of the preferred management option on other factors; final management decision targeted at appropriate stages throughout the food chain.
Identification of available options
Risk management options include consideration of all general and hazard-specific measures. General risk management measures
or encouraging the development of good • developing agricultural practices (GAPs), good veterinary prac-
• • •
tices (GVPs), good hygienic practices (GHPs), and good manufacturing practices (GMPs); developing, or encouraging the development of, guidelines for the establishment of hazard analysis and critical control point (HACCP) systems, and establishing public inspection schemes and audit procedures; setting up approval and certification procedures; promulgating awareness and developing educational and training programs for consumers and industry.
Measures targeted at the individual commodities/ hazards
risk-based targets for benchmarking purposes, • setting for example, FSOs (or POs at the end of shelf life) for a
• • • •
particular food safety hazard, leaving flexibility to the industry to select appropriate control measures to meet the target; setting maximum limits (e.g., MRLs, microbiological criteria) in support of testing procedures intended to determine the presence (or levels) of specific hazards; establishing specific control measures required to be used by industries that do not have the means to establish appropriate measures themselves or that adopt such control measures; tailoring frequencies of testing and monitoring for each commodity/hazard; requiring export/import certificates.
Selection of options
The SPS Agreement states that sanitary measures must not be more trade restrictive than required to achieve the ALOP, taking into account technical and economic feasibility (Article 5.6). A measure would be more trade
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restrictive than required if another equivalent and reasonably achievable measure is significantly less restrictive. The outcome of the risk management process for a specific hazard will differ in various societies, due to natural or cultural differences. Such difference can be scientifically justified, for instance in relation to the exposure situations in different countries. Differences from the contaminant levels recommended by Codex Alimentarius may, for instance, be justified where the average body weight differs and where relatively little average consumption permits higher threshold levels in a particular food. Also, the prevalence of various foodborne pathogens in the food chain and variation in foodborne disease patterns may justify different risk management outcome. In selecting the preferred option, the consequences of impact on other factors should be estimated, such as on consumption patterns (e.g., nutritional con• impact sequences of restricting food availability), introduction of substitute risks (i.e., increasing • possible another risk by reducing a risk, for instance increasing
•
microbial risks when not allowing a preservative), impact on public acceptability of measures that intervene in cultural patterns and traditions (e.g., requiring that cheeses be made from pasteurized milk).
Examples of socioeconomic and technological factors may be taken into account and these could, for instance, result in the best management option being at the source rather than later in the food chain, • control regulation through detailed GMP rules rather than, for • example, mandatory HACCP systems, food safety verification through end product testing • rather than reliance on HACCP systems (for instance,
•
where the origin of the food is unknown), reliance on labeling, the effectiveness of which has been subject to validation.
Use of risk-based targets
An important element in risk management is the responsibility of competent authorities to specify the level of control that food businesses should achieve, typically in the form of food safety metrics, such as microbiological criteria (for analytical testing purposes), process criteria (e.g., pasteurization temperature), and product criteria (e.g., water content of milk powder). New metrics have been developed by Codex Alimentarius (see Box 4), which are related more directly to public health outcomes through risk assessment processes. FSOs assist in making the ALOP operational, that is, by translating the health risk into food-related targets that can be used readily by food business operations to design their food safety management systems appropriate to location and role within the particular food chain. Conceptually, the FSOs can be viewed as the consumers’
538 Risk Analysis
Box 4
The three new risk-based food safety targets
Food safety objective (FSO), defined as the maximum frequency and/or concentration of a hazard in a food at the time of consumption that provides or contributes to the appropriate level of protection (ALOP). Performance objective (PO), defined as the maximum frequency and/or concentration of a hazard in a food at a specified step in the food chain before the time of consumption that provides or contributes to an FSO or ALOP, as applicable. Performance criterion is the effect in the frequency and/or concentration of a hazard in a food that must be achieved by the application of one or more control measures to provide or contribute to a PO or an FSO.
maximum level of exposure to a hazard that achieves the ALOP. As such, FSOs articulate the overall performances expected of a food chain in order to reach a stated or implied public health goal. POs assist in making the FSOs operational throughout a particular food chain. A PO is a means by which a particular control measure combination can be shown to contribute to achieving an FSO. The PO describes the expected outcome of the food chain up to the point of its application. A performance criterion (PC) is an expression of the target change in the frequency and/or concentration of a hazard in a food that must be obtained by the application of one or more control measures. PC can be expressed, for instance, in terms of a desired reduction (or acceptable increase) in the concentration of a hazard in the course of a particular control measure. Equivalence
Differences in food safety programs inevitably exist between countries. Therefore, determination of the equivalence in the sanitary measures applied in importing and exporting countries is becoming a priority issue in the international trade. The SPS Agreement requires that sanitary measures of other countries are accepted as equivalent, even if they differ from their own or others, if the exporting country objectively demonstrates that its measures achieve the ALOP established by the importing country (Article 4.1). The quantitatively expressed risk-based metrics, FSOs and POs, are also intended to be applied as a means to demonstrate whether different processing lines, plants, or food chains can achieve equivalent outcomes.
Risk Communication Risk communication is the third component of risk analysis, and is a central and integral part of effective food safety management.
Every stage of risk management should rely on an exchange of information and opinions about risk between risk managers, risk assessors, and all other stakeholders concerned about or affected by the problem and the risk management decision. Risk communication and involvement of stakeholders are crucial for open, transparent, and effective decisions. Communication of correct and updated risk assessment information to the food manufacturers is also crucial for obtaining correct hazard analyses and designs of HACCP programs. Risk communication aids in considering the different, and at times conflicting, interpretations about the nature and magnitude of the risk; it offers an opportunity to bridge gaps in understanding, language, values, and perceptions; it ensures that public values are considered; it generates better accepted and more readily implemented risk management decisions. In brief, it supports democratic decision making. Poor risk communication will almost always increase conflict and distrust over risk management decisions. See also: Hazard Analysis and Critical Control Points: HACCP Total Quality Management and Dairy Herd Health; Processing Plants. Policy Schemes and Trade in Dairy Products: Codex Alimentarius; Trade in Milk and Dairy Products, International Standards: World Trade Organization.
Further Reading Codex Alimentarius Commission (1999) Principles and Guidelines for the Conduct of Microbiological Risk Assessment. CAC/GL 30-1999. Rome: FAO. Codex Alimentarius Commission (2007a) Principles and Guidelines for the Conduct of Microbiological Risk Management. CAC/GL 632007. Rome: FAO. Codex Alimentarius Commission (2007b) Procedural Manual, 17th edn., Section III. FAO: Rome. FAO/WHO (1995) Application of risk analysis to food standards issues. Report of the Joint FAO/WHO Expert Consultation. 13–17 March. Geneva, Switzerland: WHO. FAO/WHO (1997) Risk management and food safety Report of a Joint FAO/WHO Expert Consultation. 27–31 January. Rome: FAO. FAO/WHO (1998) Application of risk communication to food standards and safety matters Report of a Joint FAO/WHO Expert Consultation. 2–6 February. Rome: FAO. Hathaway S (1998) General concepts of risk analysis. In: Heggum C (ed.) Proceedings of the 25th International Dairy Congress, vol. V. 21–24 September. Aarhus, Denmark: Danish National Committee of IDF. Heggum C, Sayler A, Christiansson A, Burel D, Cerf O, and Fawcet P (2004) Food Safety Objective (FSO) & Performance Objective (PO) – Concept paper on future development of food safety management. Bulletin of the International Dairy Federation 392: 3–11. Herrman JL and Nakashima N (1999) Assuring science-based decisions: Expert advice and risk analysis – validity of the process and dealing with uncertainty. Report of the FAO/WHO/ WTO Conference on International Food Trade Beyond 2000:
Risk Analysis Science-Based Decisions, Harmonisation and Mutual Recognition. Rome: FAO. Jouve JL (1998) Development of risk analysis in the international framework. In: Heggum C (ed.) Proceedings of the 25th International Dairy Congress, vol. V. 21–24 September. Aarhus, Denmark: Danish National Committee of IDF.
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Schlundt J (1998) Application and acceptance of risk management procedures. In: Heggum C (ed.) Proceedings of the 25th International Dairy Congress, vol. V. 21–24 September. Aarhus, Denmark: Danish National Committee of IDF. Vose D (2000) Risk Analysis – A Quantitative Guide, 2nd edn. London: John Wiley & Sons Ltd.
RODENTS, BIRDS, AND INSECTS K M Keener, Purdue University, West Lafayette, IN, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction Basic pest control in the dairy processing plant is an essential prerequisite for a food safety program. Unfortunately, many processors have never established a systematic, organized pest control program. This article outlines the pests of concern and steps that the dairy processors can take to start a pest control program. All dairy processing facilities, regardless of size, must maintain a hygienic facility, and this requires a sanitation program. One section of the sanitation program should address the exclusion/control of pests: rodents, birds, and invertebrates. Current good manufacturing practices (cGMPs) specified in the Code of Federal Regulations (CFR) clearly state that pests cannot be present in the food-processing environment. To prevent infestation, the processor must take a proactive approach to stopping these pests from threatening the safety and quality of the product. The pest control program is both a stand-alone program and a prerequisite program under hazard analysis and critical control points (HACCP). Most small food plants must decide whether to maintain a pest control program themselves or contract the program to a pest control company. There are positive and negative aspects of each approach. Table 1 illustrates key differences between plant operated programs and contract pest control programs. Many small dairy processing facilities hire a pest control company because the processor lacks the personnel and expertise to run such a program. Such pest control contractors must be reputable and have proper training and experience. A pest control contractor must provide records and reports to the processor, verifying that the program is effective and operating successfully. This verification is usually done through visual inspection for pests and/or evidence of pests in the plant or product. The processor must maintain these records with the plant’s hazard analysis records to prove that the contracted pest control program is effective. The verification records should include evidence of contractor training and certification to apply pesticides in a food manufacturing environment. Many processors choose to develop and maintain a pest control program themselves. An effective program can be developed in-house if the processor understands how to control pests. The program should consist of several written sections and include the following items:
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1. Pest control procedures: The activities performed to control each type of pest. The written procedures should be detailed and include frequency of action. 2. Recordkeeping: The documentation of each performed activity. The records must be accurate, up-to-date, and include inspection for evidence of pests in each plant area. 3. Responsible individuals: The person(s) who are responsible for performing pest control procedures and recordkeeping and the supervisor who is responsible for signing off on reviewed records. 4. Deviation: Evidence of a pest problem is a subjective determination that requires expertise. For example, periodically finding a cockroach under a waste bin may be accepted as evidence of a possible problem, while finding many cockroaches would be a deviation, that is, when an allowable limit has been exceeded. 5. Corrective measures: Written action steps in the plan that will be performed if there is a deviation from the pest control program. Often, they may include increasing control procedures, retraining of employees, cleaning up the area, and other measures. 6. Verification and validation: Written scientific evidence that the procedures are effective in controlling pests. This material is often available from chemical, trap, and pest control equipment makers. Also, verification is documentation of visual inspection for evidence of pests.
Common Pests in Dairy Plants and Ways to Control Them Potential pests in the dairy plant range in size from mammals and birds down to barely visible invertebrates. While problems can arise from almost any animal seeking to take advantage of the food available, including stray dogs and cats, the most common sources of pests are discussed below. Rodents Rodents include rats and mice. They must be controlled in and around a food plant because they carry and transmit disease and because they can cause significant economic loss by damaging food containers, contaminating food with their droppings, and consuming food. Two
Rodents, Birds, and Insects
541
Table 1 Major differences between internal and external pest control programs Plant operated program
Contracted program
Upfront costLower
Higher
Processor time commitment Pest control expertise Recordkeeping Equipment and chemicals Validation materials Overall benefits
High – at least one dedicated employee Minimal – need to periodically meet the contractor Usually low High Plant supported Contractor maintained Plant must obtain Contractor provided Processor obtains/develops Contractor provided Must be evaluated by the processor, taking into account all the factors necessary to develop and maintain the program
major species of rats are found in and around human habitation: the gray or Norway rat (Rattus norvegicus) and the black or roof rat (Rattus rattus). The house mouse (Mus musculus domesticus) is the common mouse species prevalent around human population in the United States and Europe. Both rats and mice reproduce rapidly, with rats having 20 offspring per year and mice up to 35 young per year. Both mammals are primarily nocturnal, but they leave behind several signs of infestation. Signs of rodents are as follows: 1. Droppings: Fecal matter is a sign of the presence of rodents, and the quantity can indicate the extent of infestation. 2. Visual sightings: Seeing rats or mice often indicates a serious and probably well-established infestation, but most experts believe that visual sightings are the least reliable indicators. 3. Noises: Shrill squeaks, gnawing sounds, and scurrying sounds could be caused by rodents. 4. Smudge marks: Rodents emit oily lipid material from their fur and leave greasy smudges at entry points and frequent travel paths. Rat smudge marks are often more noticeable than those left by mice. 5. Tracks: Coating the area around suspected entry points and travel ways with talc, chalk, or flour can detect tracks and tail marks to identify locations for bait station or trap placement. 6. Gnawing: Both rats and mice chew and gnaw materials, which is a sure sign of the presence of rodents. Rats and mice are known to gnaw the insulation of electrical wires, causing fire hazards. Mice are known to cause extensive damage to insulation materials. 7. Urine stains: Both rats and mice leave urine stains, which can be detected with long-wavelength UV light as a yellow-to-blue fluorescent spot. Elimination of harborage is the most effective way to control rodents. This includes removing all general clutter from the food plant and storage areas to eliminate rodent hiding places. Maintain an open, well-kept perimeter around the processing plant to discourage rodent activity; a bare concrete or bitumen surface is ideal. Next, food and water sources must
be eliminated. This would include environmental management to reduce or eliminate free water and food sources. Third, rodents must be denied entry into the food plant. This would include filling all structural cracks, screening fan and vent openings, and installing drain covers to prevent rodent entry. It has been shown that a mouse can squeeze through a 6 mm gap, for instance under a poorly fitting door. Mice and black rats are also exceptional climbers, which means openings should be located and closed at all levels in the facility. Next, a physical control system should be included. Physical control systems would include strategically placed poisons, glue boards, bait boxes, ultrasonic devices, and traps, described in more detail below. 1. Toxic baits and concentrates: Primary types are the anticoagulant baits; they are relatively safe to use, inexpensive, and effective. Single- and multidose anticoagulant products are available, as are products with active ingredients other than anticoagulants. Prebaiting with similar nonpoisonous bait may be effective if the rodents exhibit bait shyness. Regular rotation of brands and formulations of baits may also deter bait shyness. Poisons may be administered in bait blocks, liquid baits, pelletized baits, or treated grain. 2. Toxic tracking powders: Tracking powders are designed to kill the rodents when they groom themselves. These powders are placed along rodent travel ways or in burrows. 3. Trapping: Traps are a safe and effective method of eradication, especially for mice and roof rats. Rodents, especially rats, can become trap shy. Glue traps are also effective, and they may trap cockroaches as well. 4. Ultrasonic devices: There is controversy about the effectiveness of using ultrasounds (above 30 000 Hz) to repel rodents. Some devices alter the wavelength and direction of sound, and most are somewhat effective when placed at openings to food plants. Most rodents become used to ultrasonic devices on exposure. Rodenticides can be used in food-processing plants when placed in secure/tamper-proof stations and restricted to areas where food is not processed (warehouse, storage and service spaces, utility rooms/closets, offices, etc.).
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Normally, three perimeters are established for physical control measures. First, bait stations are positioned at the perimeter of the processing plant fence. Second, the outside wall of the plant should be spotted with bait boxes placed directly against the wall, with entry holes to the boxes parallel to the wall. Boxes should be locked and chained to prevent tampering. Finally, a third perimeter of traps inside the plant should be concentrated at areas of high rodent density and near entrances to the plant. All bait stations should be numbered and inspected once each week. Traps should be inspected daily. The density of bait placements may need to be adjusted upward during the fall when a large number of rodents seek winter harborage inside buildings. Norway rats most often build their nests below ground and may be effectively controlled by baits placed directly in their burrows, if that can be done without risk of exposure to nontarget animals or tampering. Roof rats present special control problems since they typically nest in overhead areas. Solid and liquid baits should be placed in attics or above drop ceilings. Block baits or traps should be attached to rafters, joists, and sills in open overhead spaces. Birds
Several species of birds harbor disease and pose a risk to food plant hygiene. The most common species involved are pigeons (Columba livia), sparrows (Passer domesticus), and starlings (Sturnus vulgaris). Birds pose a threat to the food processor by carrying disease-causing microorganisms, by contaminating product areas with excreta and feathers, or by carrying external parasites such as mites. The most common microorganisms spread by birds are Salmonella spp. Up to 50% of house sparrows were found to contain these microorganisms. Campylobacter jejuni has also been commonly isolated from wild birds. The best and most effective means of controlling birds is to eliminate nesting and feeding sites on the building(s) and in the vicinity. This includes initial construction of window, door, and ledge areas to prevent roosting and nesting. Birds are difficult to eradicate once they frequent a dairy. Once a bird problem develops, an effort should be made to scare and deter birds from roosting areas. There are a number of common bird repellent methods: 1. Scaring devices: Decoys of natural predators, such as owls and hawks, have been used to scare birds but often become ineffective after birds learn to ignore them. 2. Sticky pastes: Pastes can be applied to roosting areas to entangle birds and frighten them away. 3. Electrical wires: Wires that emit a shock to roosting birds can be effective but are difficult to maintain and costly to operate.
4. Netting: Placing netting or chicken wire over nesting sites such as trusses on a loading dock can be very effective. This has been used extensively to prevent pigeons from roosting on older commercial buildings where there are plenty of wide ledges, and on monuments and federal buildings in Washington, DC. 5. Entry barriers: Devices designed to block entry to a building, such as automatic doors, vertical plastic strips, and even high-velocity air curtains, are available. A double barrier system is often needed as some birds, for example, robins, can learn to get around strips by hitching a lift on a forklift truck. 6. Needle strips: Needle strips are applied to ledges, rooflines, and other roosting points. They have been shown to be very effective if installed correctly. Traps can effectively remove bird pests. Starlings are the most easily trapped bird pests. Traps can become expensive, because they must be examined regularly so that accidentally trapped nontarget species are not destroyed. (Bats, for instance, are very heavily protected under European law.) Baiting and poisoning of birds is debatable, and highly contentious. This method is usually a last resort when other means of control have failed. Poisons are indiscriminate, having the potential to harm desirable species of birds as well as pest birds. It is recommended that only professional pest control applicators use toxicants for bird pests. Several chemical control agents are commercially available, and Avitrol is one of the most commonly used chemical. There is a fumigant formulation that is available for use in warehouse areas. As with all chemicals, one should follow the manufacturer’s instructions on application and use. Insects
Insects are the most common source of invertebrate infestation problems and may be divided into those that essentially crawl, for example, cockroaches, and those whose adult forms normally fly. Cockroaches
There is no insect, other than the housefly, that is more easily recognized and detested than the cockroach. Cockroaches have been shown to transmit diseases including those caused by pathogenic foodborne bacteria such as Salmonella spp., Vibrio cholerae, and Staphylococcus aureus by carrying these in their gut and also on the exterior surface of the body. Each species has specific habitat preferences, although any species could be found in a food plant building. A good way to detect cockroaches is to enter a darkened production or storage area, turn on the lights, and quickly look for cockroaches scurrying back into hiding. Cockroaches may also be found by inspecting inside the
Rodents, Birds, and Insects
electrical junction boxes, receptacles, and control panels, or by looking behind objects and in floor drains. Glue traps are often a good monitoring device; some come equipped with a pheromone attractant. The use of flushing gases (a number of pyrethroid aerosol products are very good for this purpose) is a common method of driving them out in the open. These materials are so highly repellent that a single squirt into a suspect crack or crevice can cause the cockroaches to come out into the light. Also, look for droppings and egg cases, which indicate their presence. Control of cockroaches starts with the elimination of debris (especially cardboard boxes that could harbor the insects or their egg cases) and elimination of their harborage. This is done by sealing and filling cracks and crevices and maintaining a sealed, smooth surface throughout the plant in production and nonproduction areas. Seal junction boxes and trunking, receptacles, and control panels. Seal openings around conduits and pipes where they pass through walls and ceilings. Inspect shipments (packaging, ingredients, etc.) and reject infested shipments. Chemical control requires that European Community (EC)- or United States Environmental Protection Agency (USEPA)-permitted insecticides be used in the food plant. These products are generally formulated as sprays, aerosols, or dusts. Dry powders and dusts, such as boric acid and insecticide powders, take advantage of the cockroaches’ habit of preening themselves. It is important to understand that no pesticide can be used in a food-processing plant unless the statutory authority, for example, the EC or EPA, has approved such use. Flying insects
The most common flying insects are the housefly and fruit fly. A single housefly has been estimated to carry up to 3.6 million bacteria. Flies transmit disease by spending part of their life in direct contact with or in close contact with fecal matter or decaying material. Flies must liquefy their food before ingestion, so they secrete salvia (often called vomitus) onto surfaces. Flyspecks are dried vomitus and fecal material. The movement of flies from unwholesome sources to fresh food products, processing equipment, and other surfaces provides many opportunities to transmit disease-causing bacteria. The common housefly is a known carrier of diseases and pathogens, including Listeria spp. and Salmonella spp. It has been estimated that in a 6-month period, a pair of houseflies and their offspring would total 191 000 000 000 000 000 000 if all survived. Removal and elimination of breeding sites is a key to fly control. This primarily involves avoiding the availability of garbage. Garbage must be kept away from doors in sealed/ enclosed containers and removed frequently; in addition, waste disposal areas must be regularly cleaned and properly maintained. Next, flies must be excluded from entering the
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food-processing facility. This includes using air curtains (air screens) and/or doors that close automatically. Electrocution traps with blue fluorescent light traps are effective in reducing flying insects, including flies. One drawback of these electrocution traps is that they can literally cause the fly to explode, throwing an aerosol of fly matter into the air. As these particles can drift down some distance from the trap, it is best to place these traps away from food-handling areas, or well removed from food-handling surfaces in these areas. Blue-lighted sticky traps, baited jug traps and strips, or sticky ribbons are a safer alternative in these areas. Dead flies should be removed from traps at regular intervals. Catch basins of electrocution traps or jug traps, and strips should be cleaned daily. Sticky devices should be replaced at least once a week. Other commercial methods utilize insecticidal sprays or fogs to suppress flies, but exclusion should be the main line of defense.
Pests of Stored Products These are primarily invertebrates that use the food as both nourishment and a habitat. They are usually small insects that infest and destroy foods during all stages of their life cycles. This group includes beetles, weevils, borers, and moths. Stored product pests are not generally associated with disease, as are cockroaches and flies, but they are considered a major food contaminant. As a group, they prefer dry products such as cereal grains and flours, but other foods such as nuts and dried fruits may be infested, as well. Weevils infest stored grain and cause economic losses worldwide. The life cycle of most weevils is 4–5 months, and they can infest nearly every cereal grain. Flour moths lay their eggs in flour or meal, where the larva destroys the product, and they are important grain pests. A variety of beetles can infest foods and food ingredients. These include grain beetles, flour beetles, and others. The purchase of quality, pest-free grain and food ingredients is the first step in the prevention of stored product pests. Regular cleaning of storage areas and processing equipment to remove ingredient spills and accumulated dust is also important. Fumigation of empty storage bins with phosphine, ethylene oxide, or carbonyl sulfide is an effective control option for stored product pests, subject to statutory approval in the country of operation. Similarly, fumigation may be used in facilities when processing operations are over for the day. Traditional cheesemakers and affineurs (those who mature bought-in cheeses) can have significant problems with cheese mites, which feed on the rind of cheeses that are not encapsulated in barrier films or wax.
544 Rodents, Birds, and Insects
Integrated Pest Management Integrated pest management (IPM) is a strategy to manage pest populations safely and economically through a wellbalanced combination of control practices. The small processor should begin a pest control program by determining which activities will best control each pest most effectively. 1. Inspection (monitoring): Thorough inspection of the entire plant by an expert to objectively identify pest problems is recommended. A written analysis should be provided, with details on problem areas within the plant. Inspections should be conducted at a predetermined frequency. For a small processor, it may be costeffective to hire a pest management specialist 2. Physical control: A standard of cleanliness must be established, with direct accountability for cleaning. This includes all areas inside and around the outside of the facility. Exclusion practices combined with routine inspection and repair restrict the ability of pests to enter and move from place to place in the plant. Some examples of these practices would be proper landscaping, adequate door seals, no entrances from outside directly into the processing area, and proper placement of dumpsters. 3. Mechanical control: These are nonchemical means that stop pests or prevent infestations, such as the sticky traps, electronic fly traps, needle strips mentioned earlier. Storage insects can often be controlled by temporarily raising or lowering ingredient temperatures or by reducing the moisture content to levels at which they cannot grow. 4. Chemical control: IPM does not eliminate the need for pesticides, and they should be used when necessary. Only qualified personnel should apply pesticides. Application of restricted-use pesticides requires certification, and it may be practical to hire a professional exterminator. Once the methods of control have been chosen, they must be written down in a concise program with specific instructions, frequency of monitoring, responsible persons, monitoring activities, and reassessment. The program should be available for viewing by government inspectors. Many small processors completely contract out the pest control program to private exterminators who provide all procedures, monitoring, and documentation.
Verification of the Pest Control Program All food safety programs (HACCP, recall, sanitation, pest control) must have validation documentation that demonstrates that the instituted procedures are effective. For example, if the pest control program calls for air
curtains on the loading dock door, is this measure effective at preventing incoming insects? Often, manufacturers of pest control products provide documentation of the effectiveness of their products. This is evidence that the procedures in the program are effective. Most importantly, the pest controls must also be verified by evaluating data collected on pest numbers and frequencies and by visual checks of the processing plant.
Action Steps for Dairy Processors and obtain a copy of regulations pertaining to • Read pest control in dairy plants. whether to create an internal program or hire a • Decide private company. current pest control procedures and define areas • Assess that need correction or addition. the pest control program in concise form • Document with required procedures, recordkeeping materials, verification materials, frequency, and so on.
the individuals responsible for each aspect of the • List program. contact pest control experts who can evalu• Ifateneeded, your plan for completeness and effectiveness. See also: Contaminants of Milk and Dairy Products: Environmental Contaminants. Hazard Analysis and Critical Control Points: HACCP Total Quality Management and Dairy Herd Health. Plant and Equipment: Process and Plant Design; Safety Analysis and Risk Assessment. Risk Analysis.
Further Reading CAC (2004) Code of hygienic practice for milk and milk products. Codex Alimentarius Commission Recommended Code of Practice No. 57. Rome, Italy: Food and Agricultural Organization of the United Nations. Clute M (2009) Food Industry Quality Control Systems. Boca Raton, FL: CRC Press. FDA (2003a) Current good manufacturing practice in manufacturing, packing or holding human food – sanitary operations. CFR Title 21, Part 110.35. Washington, DC: Food and Drug Administration, United States Department of Health and Human Services. FDA (2003b) Current good manufacturing practice in manufacturing, packing or holding human food – plant and grounds. CFR Title 21, Part 110.20. Washington, DC: Food and Drug Administration, United States Department of Health and Human Services. IFST (2007) Food and Drink – Good Manufacturing Practice: A Guide to Its Responsible Management, 5th edn. London: Institute of Food Science and Technology. NCIMS (2008) Overview of the NCIMS Dairy HACCP Program. 16 May. Monticello, IL: National Conference on Interstate Milk Shippers. Shapton DA (1998) Principles and Practices for the Safe Processing of Foods. Cambridge: Woodhead Publishing.
S STANDARDIZATION OF FAT AND PROTEIN CONTENT P Jelen, University of Alberta, Edmonton, AB, Canada ª 2011 Elsevier Ltd. All rights reserved.
Introduction Milk of all mammals (including human milk as well as milk of cows, buffaloes, goats, and sheep) contains, in addition to water, four major types of components: fat, protein, carbohydrate, and minerals. As the cow (genus Bos) is by far the most important provider of the raw material used by the dairy industry worldwide, the following discussion focuses on cows’ milk only, even though most of the information would be applicable to other milk types as well. From an economic standpoint, milk fat has been considered the most valuable component of milk used for manufacturing dairy products for the regular consumers’ market. Indeed, the economic value of milk was (and generally continues to be) directly related to the fat content. Thus, altering the fat content in market milk and other dairy products has been accepted as a widespread practice used by dairy processors for decades. In recent years, the value of milk protein has increased significantly, mainly due to the steadily increasing popularity of cheese (a milk protein-based product) as a major component of Western-style diets. The advances of modern dairy technology make it now possible to manipulate the protein content of fluid milk in a manner similar to that used for fat standardization. Although the technological approaches in the two cases are somewhat different, the reasons for the need to control the content of the two nutritionally as well as economically important milk components in various dairy products (destined for direct consumption or for further industrial use) are similar. The two aspects of the component standardization in milk and dairy products can be compared, focusing on the compositional, technological, nutritional, and economical determinants of the two processes.
Milk Composition and Properties Relevant to Component Standardization It is well known that the fat content of raw milk fluctuates rather widely, depending on the breed, feeding practices, geographical location, and many other factors. The average fat content of cows’ milk is approximately 4% with the range for this value being given in various textbooks as 2.5–5.5% or wider. Less well recognized is the fact that the average protein content of milk (3.3–3.4%) also shows relatively wide natural variations (2.8–4.2%) in international comparisons, with narrower limits (~ 0.5% or less) reported for individual countries. Table 1 illustrates the fluctuation of the protein content of cows’ milk in several main dairy producing countries. Clearly, the wide fluctuations in the contents of the two most valuable components of milk can result in significant nutritional as well as economical and regulatory consequences when no standardization is practiced. The original aim of fat standardization was to divert some of the fat from the ‘rich’ raw milk to the production of cream and butter, considered premium dairy products. At present, however, fat standardization has assumed another important role, that of providing consumers with dairy products perceived by many to be ‘healthier’ because of their low fat content. Most modern dairy products are labeled (some are legally required to be) as to their fat content; thus, accurate fat standardization processes have become an integral part of the modern dairy technology. In contrast to the well-established standardization of fat, protein standardization is still an issue being debated in international dairy circles. The technology enabling the online, continuous protein standardization has not been available until relatively recently, and this is why protein content standardization of milk is not practiced
545
546 Standardization of Fat and Protein Content Table 1 Protein content in cows’ milk in different countries
Country
Protein content (g per 100 g)
Canada Spain Ireland UK Finland Germany New Zealand World (min–max range)
2.75–4.09 2.80–3.25 2.85–3.60 2.96–3.54 3.11–3.40 3.26–3.48 3.16–4.22 2.75–4.22
Adapted with permission from Rattray W and Jelen P (1996) Protein standardization of milk and dairy products: A review. Trends in Food Science and Technology 7: 227–234.
widely, and, in general, only rarely approved by the various regulatory bodies in individual countries or states (e.g., some states in Australia). Technological approaches to both fat and protein standardization are based on the forms in which these components are present in milk and on the physical properties of the system. The milk fat globules, present in the raw milk in diameters of approximately 0.2–10 mm, have a much lower density (~920 kg m 3) than that of the aqueous fat-free fraction of milk (density ~1035 kg m 3). Consequently, separation of the milk fat from the aqueous phase can be easily accomplished by centrifugation based on the density differential. In contrast, the milk proteins are distributed in the nonfat portion of the milk as individual molecules or as molecular clusters (containing up to 104 molecules in the case of casein micelles but only as little as 2–8 molecules in the case of whey proteins). Although the size of the largest micelles (~300 nm) is approaching that of the smallest milk fat globules, the molecular mass of even the smallest free whey protein molecules (~14 000 Da) is still much larger than that of the next molecular species on the milk component spectrum, lactose (molecular mass 342 Da). Differential molecular sizes are the basis for fractionating aqueous solutions using the ‘molecular sieve’ principle of membrane processes. Specifically, the molecular sizes of milk proteins are ideal for the use of ultrafiltration (UF) as the method of choice for separation of milk proteins from other components of the fat-free aqueous phase of milk. As a result, the protein content in skim milk can be standardized either upward by removing a portion of the protein-free UF milk permeate, or, more typically, downward by admixing excess protein-free UF permeate to regular skim milk. In theory, UF does not affect the ratios of the individual water-soluble molecules capable of permeating the UF membrane; thus, the upward or downward standardization of the protein content by adding or removing
relatively small amounts of the UF permeate should not affect the lactose or the mineral compositions of the final product (see Milk Protein Products: Membrane-Based Fractionation). However, as discussed below, this theoretical assumption does not always hold perfectly.
Technological Principles of Fat Standardization Centrifugal separation is a straightforward process. Raw milk entering the continuous dairy centrifuge is subjected to a centrifugal force that causes the heavier nonfat aqueous milk phase to migrate toward the perimeter of the centrifuge bowl and the lighter fat globules are concentrated in the volume toward the center of the bowl. To facilitate this movement, the bowl is filled with a multitude of conical disks. The separation occurring along these disks produces two fractions: the fat-free skim milk of greater density and the more concentrated emulsion of the fat globules in a smaller volume of the nonfat aqueous milk fraction, resulting in the production of cream. Depending on the running conditions of the separator, the fat content of the cream can be adjusted within wide variations of the required final fat content. Because the process does not affect the condition of the fat globules, the final cream structure is the same as in the original milk, that is, cream is still an oil-in-water emulsion (see Plant and Equipment: Centrifuges and Separators: Applications in the Dairy Industry; Centrifuges and Separators: Types and Design). The production of the various low-fat liquid milk products demanded by the market is typically accomplished by reblending some of the cream into the skim milk produced as the high-volume stream emerging from the continuous centrifuge. The reblending may occur online with modern centrifugation equipment, or it can be accomplished in a storage tank by mixing known volumes of skim milk and cream of known composition. Nutritional and sensory quality consequences of the fat standardization have been well documented in the literature and accepted by the market. As milk fat is the principal carrier of delicate dairy flavors, the taste of low-fat or fat-free liquid milk products is more bland and watery. The main nutritional effect of fat downstandardization is lower food energy value and lower content of saturated fat, features considered as positive by many consumers today. However, as some fatty acids are nutritionally indispensable especially for children and adolescents, the exclusive consumption of low-fat and especially skim milk products by these age groups without other adequate sources of the indispensable fatty acids may be a questionable nutritional practice. Downstandardization of fat in other dairy products may
Standardization of Fat and Protein Content
have either positive or negative effects. Dried dairy products containing fat are known to be prone to undesirable oxidation and other chemical changes, resulting in a potential for major quality impairment. On the contrary, reducing the fat content of standard cheeses can lead to major textural and flavor defects in comparison to full-fat products. In other classes of products (e.g., some fermented dairy foods such as yogurt or sour cream, as well as ice cream or dairy desserts), the removal of fat may be compensated for by using suitable fat mimetics, resulting in very minor quality alterations. Because the technology of fat manipulation does not affect other milk components (with the exception of minute quantities of components associated with the milk fat globule membrane), the nutritional consequences are primarily limited to the effects of the presence (or absence) of the fat itself.
Technological Principles of Protein Standardization Similar to the fat standardization procedure, protein standardization may be accomplished online or in a batch mode using the UF membrane process. Typically, the milk is first skimmed, and the standardization of the protein content is then carried out on the skim milk. As shown in Figure 1, the UF plant, similar to the centrifuge in fat standardization, produces two streams: protein-free permeate (analogous to fat-free skim milk) and protein-enriched retentate (akin to the cream in the fat content manipulation process). Depending on the aim of the protein standardization process, one of the streams is then blended in varying ratios with regular fluid milk, which could then undergo additional fat standardization if desired. In a batch arrangement of this process, the permeate obtained by an UF process would be accumulated in a storage tank and then reblended with a batch of skim – or fat-adjusted – milk in a separate blending facility. In industrial practice, the permeate for protein downstandardization of fluid market milk could come from a separate department or factory, most often from a fresh
547
cheese manufacturing plant, as the use of UF for pretreatment of the cheese milk before the cheese manufacturing process is practiced widely in some countries. Such practice could result in additional technological complications; as the transportation of the unconcentrated permeate is costly, a preconcentration could be used but this may result in precipitation of some mineral complexes. In some cases, upstandardization of the protein content may be desired, either to increase the nutritional value of a special product, or to bring the protein content of regular milk to a legal minimum, should such a minimum exist or be agreed upon. Present European Union (EU) legislation specifies that cows’ milk shall contain not less that 2.8% w/v total protein (N 6.38). It is thus conceivable that in some instances of low protein content, upstandardization could be required, especially if there were to be an international agreement on a minimum protein content in fluid milk (a value 3.0% has been proposed at various international discussions). Again, the UF offers the simplest alternative for such upstandardization; in this case, it is the retentate that is used directly as the upward standardized product (e.g., skim milk with increased protein content) or is blended with incoming unstandardized fluid milk (Figure 1). In addition to the direct use of membrane processes, several technological alternatives to the UF-based protein standardization are now practiced by the industry. These include addition of skim milk powder to regular milk to increase the amount of protein and calcium in the market milk (thus also increasing the contents of lactose and other components), or addition of powdered lactose for protein downstandardization as approved by the Codex Alimentarius specifically for adjustments of protein content in milk powders. These two alternatives, together with the UF approach, do not violate the main principle governing the protein standardization considerations – that of maintaining the casein:whey protein ratio of the original milk unchanged. For this reason, using powdered whey or whey protein products for down- or upstandardization of market milk would not be permissible.
Sensory, Nutritional, and Technological Properties of Protein-Standardized Products
Figure 1 Schematic representation of the protein standardization process using ultrafiltration of skim milk. Adapted with permission from Rattray W and Jelen P (1996) Protein standardization of milk and dairy products: A review. Trends in Food Science and Technology 7: 227–234.
In contrast to the well-established sensory effects of milk fat, dairy proteins (both casein and whey proteins) have been shown to have a minimal impact on the flavor of fluid milk. Evidence in the literature confirms that protein standardization within rather wide limits (1.5–6.4% for whole milk, 2.4–6.5% for skim milk) by using UF milk permeate had no effects on the sensory properties of such standardized milk, which was indistinguishable from the
548 Standardization of Fat and Protein Content
nonstandardized controls. Investigations with other types of UF permeates (e.g., from acidified milk or cheese whey) showed that the acidity itself was not detrimental within relatively wide protein standardization limits (2.8–3.4%), but the use of permeates from fermentation-acidified products imparted major sensory changes in virtually all cases. Using other membrane processes (e.g., reverse osmosis) for upstandardization of the protein content produced a noticeable salty-sweet sensation with as little as 0.3% total solids (TSs) (i.e., ~0.1% protein) adjustment. Similarly, addition of as little as 0.5% lactose to fluid milk was shown to result in a detectable increase in sweetness. Addition of some powdered lactose to the protein-standardized fluid milk to increase the low TSs content could be considered in the case that a minimum TSs in protein-standardized fluid milk products is required. The TS content of typical UF milk permeates is approximately 5.2–5.4% TS; thus downstandardization of protein in fluid milk with these permeates could be considered as adulteration, similar to the addition of water. Use of freezing-point measurement as a control technique for adulteration of raw milk with water is widely established; the same method could not be used to detect any ‘dilution effects’ of protein standardization of regular market milk. Considering the relatively wide natural variations in the protein content in milk (Table 1), the nutritional consequences of the slightly lower protein content in the downstandardized milk should be considered of a very minor importance. However, in contrast to the fat standardization, the UF technique used for protein manipulation can have an effect on other nutritionally important milk components, especially calcium. Because of the association of most of the milk calcium with casein micelles under normal milk pH conditions (~6.6), the calcium content in the milk UF permeate (~270 mg kg 1) is much lower than in milk (~1150 mg kg 1); using this permeate for protein downstandardization will thus lower the calcium content of such milk. Published calculations show than within the rather narrow limits of the protein standardization being considered (where less than 10% of the final product milk solids would come from the permeate) the changes in some of the affected micronutrients (in addition to calcium, also zinc and vitamin B12) will be minimal, certainly lower than resulting from natural variability. However, unlike lowering of the fat content, manipulation of the protein content could be viewed negatively by consumers, especially if accompanied by decreases in contents of other valuable nutrients, no matter how small. Use of permeates from UF processing of milk to downstandardize protein in dried skim milk can have small but technologically important effects in such powders. As the profile of the mineral fraction of the standardized milk
may be slightly different and the mineral content slightly increased, this may affect the buffering capacity and ionic strength of the reconstituted milk, resulting in needs for small adjustments in established processes where such milk may be used (e.g., in recombination or evaporation). Also, the total protein profile of the standardized product will be slightly altered by the additional nonproteinnitrogen content of the UF permeate.
Regulatory Aspects and Current Status of Protein and Fat Standardization Although fat standardization and production of low-fat – or even fat-free – dairy products have been the accepted practice for decades, protein standardization is still an issue hotly debated in the regulatory bodies such as Codex Alimentarius, EU, and national agencies. Protein downstandardization in concentrated and dried dairy products has been approved by the Codex Alimentarius; however, similar practice is generally unacceptable for regular market milk. Use of protein downstandardization for specific unregulated products such as UHT milk may have been practiced in the past without labeling the products as protein standardized; such practice is now expressly forbidden in the EU. Published research indicated no unusual sensory quality or technological problems in UHT products that were downstandardized with UF milk permeate to 3.2–2.6% protein. Fluid milk products with a higher-than-normal protein content are now quite common in various countries; their market positioning is as being nutritionally and/or sensorically superior to the corresponding regular products. In California, skim milk or low-fat milk is routinely fortified with skim milk powder to improve the sensory properties; this practice also increases the protein content without the products being labeled as protein standardized. In Australia and other countries, fluid milk products with increased calcium content are being promoted. Such products can be obtained easily by subjecting the regular milk to limited UF, which increases not only the calcium but also the protein content. Protein adjustment (i.e., de facto standardization) in other dairy products and in milk used as a raw material for manufacture of products such as cheese or yogurt is being practiced widely, mostly as upstandardization. The main reasons are technological, increasing the output of specific equipment (e.g., in cheesemaking) or improving the technological and/or sensory properties of final products (e.g., gelling properties of yogurt, overrun control of ice cream). Downstandardization of protein content in certain products (e.g., sour milk, buttermilk) could lower the sometimes undesirable high viscosity of such products, although no published reports of such practices
Standardization of Fat and Protein Content
seem to exist. Fat adjustment in these products is a wellestablished practice with no controversial consequences.
Conclusions and Future Prospects The international dairy community is currently divided on the issue of general protein standardization of milk. Although there are no technological barriers and no real nutritional issues of major consequence (other than the general distrust of the consumers if such a practice were to become common), the major issues concerning widespread downstandardization of protein are economical. It has been calculated that if all fluid milk produced by the EU, the United States, Australia, and New Zealand were to be standardized to 3% protein, the additional amount of protein that would be available for processing into other dairy products (principally cheese) would be over 170 000 tonnes annually, corresponding to more than 500 000 tonnes of cheese. With this extra cheese production, the market could experience similar distortions as used to be common in the days of butter surpluses, resulting in fact from the downstandardization of fat in dairy products. The milk production aspects (with negative consequences for the farmers) could be also severely impacted by protein adjustments, as would be the general credibility of the dairy industry in the eyes of consumers. Downstandardization of milk fat in many dairy products, combined with the nutritionally unfavorable image that butter has been saddled with in recent times on one side, and the continuing practice of rewarding producers for high fat content in their milk on the other, has resulted in difficulties for the dairy industry still searching for new uses for butterfat. Similarly, large surpluses of UF milk permeate, resulting from modern cheese manufacturing practices, are becoming a major industrial problem. Use of at least some of this permeate for slight adjustment of the protein content in milk and other dairy products is a
549
tempting and technologically fully justifiable option. Some consumer research indicates that if several types of fluid milk products with varying protein content (and correspondingly adjusted prices) were to be available on the market, the downstandardization of protein content might be viewed favorably. It can be expected that protein standardization of milk and dairy products will remain one of the highly controversial issues for the dairy industry for the foreseeable future. See also: Milk Proteins: Heterogeneity, Fractionation, and Isolation. Milk Protein Products: Membrane-Based Fractionation. Milk Salts: Macroelements, Nutritional Significance. Plant and Equipment: Centrifuges and Separators: Applications in the Dairy Industry; Centrifuges and Separators: Types and Design.
Further Reading IDF (1991) New application of membrane processes. International Dairy Federation Special Issue No. 9201. Brussels: IDF. IDF (1994) Milk protein definition and milk protein standardization. International Dairy Federation Special Issue No. 9502. Brussels: IDF. IDF (1995) Protein standardization of milk and milk products: Report on responses to three IDF questionnaires. International Dairy Federation Bulletin No. 304. Brussels: IDF. IDF (1996) Advances in membrane technology for better dairy products. International Dairy Federation Bulletin No. 311. Brussels: IDF. IDF (1997) Protein standardization: The case of liquid milks. International Dairy Federation Bulletin No. 319. Brussels: IDF. Rattray W, Gallmann P, and Jelen P (1997) Nutritional, sensory and physicochemical characterization of protein-standardized UHT milk. Le Lait 77: 279–296. Rattray W and Jelen P (1996) Protein standardization of milk and dairy products: A review. Trends in Food Science and Technology 7: 227–234. Spreer E (2005) Technologie der Milchverarbeitung. Hamburg, Germany: B. Behr’s Verlag. Walstra P, Wouters JTM, and Geurts TJ (2006) Dairy Science and Technology. Boca Raton, FL: CRC Press.
STRESS IN DAIRY ANIMALS
Contents Cold Stress: Effects on Nutritional Requirements, Health and Performance Cold Stress: Management Considerations Heat Stress: Effects on Milk Production and Composition Heat Stress: Effects on Reproduction Management Induced Stress in Dairy Cattle: Effects on Reproduction
Cold Stress: Effects on Nutritional Requirements, Health and Performance L E Chase, Cornell University, Ithaca, NY, USA ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2582–2586, ª 2002, Elsevier Ltd.
Introduction Environmental stresses, which include temperature, humidity and wind speed, can alter both nutrient utilization and animal performance. The effects of heat stress have received the majority of attention in research studies. The impact of cold stress on nutrient metabolism and animal performance in ruminant animals has received minimal research attention, the majority of investigations being conducted with beef cattle. The quantity of data relating to the effects of cold stress on dairy cattle is very limited. A primary reason for this dearth of information is the housing systems utilized in dairy production systems. Typically, dairy cattle are housed in barns that minimize the impact of environmental temperature fluctuations on the animal. Pasture systems are used in dairy production systems in many parts of the world. However, these systems are usually limited to the warmer months of the year. It is rare to find dairy cattle housed outside during the winter months in most dairy areas. The result is that very few dairy cattle are actually exposed to cold stress conditions. Dairy replacement heifers may be housed outside during the winter months and could be exposed to cold stress in some situations. There are a number of terms that need to be defined prior to examining the influence of cold stress. These terms include:
550
zone (TMZ), i.e. the range of environ• thermoneutral mental temperatures where normal body temperature
•
is maintained and heat production is at the basal level lower critical temperature (LCT), i.e. the environmental temperature at which an animal needs to increase metabolic heat production to maintain body temperature.
There are a number of factors that determine the LCT for a specific animal. These factors include body surface area (SA), heat production by the animal (HE), retained energy (RE), external insulation (EI), internal insulation (TI), evaporative losses and respiratory losses. The quantity of subcutaneous fat and thickness of the skin are the main factors that determine TI. The primary factors that influence EI are hair coat depth, wind, precipitation and mud on the hair. Thus, there will be a specific LCT for an animal as the above factors vary. The LCT for dairy heifers may range from 10 C to 20 C. The LCT for lactating dairy cows may range from 20 C to 50 C. The lower LCT range for lactating dairy cows is mainly due to the HE of the animal (Table 1).
Heat Loss There are four primary ways in which animals can lose heat to the environment. These are:
Stress in Dairy Animals | Cold Stress: Effects on Nutritional Requirements, Health and Performance
551
Table 1 Estimated lower critical temperatures for dairy animals ( C)a,b Animal type
Body weight (kg)
Average daily gain (kg)
Milk (kg)
LCT–Ac
LCT–Bd
Heifer Heifer Dry cow Milking cow Milking cow
220 440 700 635 635
0.8 0.8 – – –
– – – 45 25
6.7 19.4 9.3 35 21
4.8 9.8 3.8 24 13
a
Heifer LCTs estimated using the 2001 Dairy–NRC program. Dry and milking cow LCTs estimated using the Cornell Net Carbohydrate and Protein System (CNCPS) model, version 4. c Situation A: hair depth, 1.28 cm; wind speed, 1 kph; hair coat, clean and dry; ambient temperature, 20 C. d Situation B: hair depth, 1.28 cm; wind speed, 10 kph; hair coat, wet and matted; ambient temperature, 20 C. b
1. Evaporation. The body heat is used to evaporate water mainly from the skin and hair. 2. Conduction. This is heat loss that occurs as result of direct contact by the animal with items such as bedding or stall surfaces. 3. Radiation. This is the transfer of heat through the air from a warm object. 4. Convection. This loss occurs when air passes over the body. Exposure to wind increases the heat lost by this mechanism.
Metabolic and Physiological Adaptations A number of adjustments take place in animals exposed to cold stress. These can be grouped into the following categories: 1. Increase in response to cold stress: rumination gastrointestinal tract motility rate of passage of feed in both the rumen and total tract liquid passage rate in the rumen protein flow to the small intestine basal metabolic rate
• • • • • •
body oxygen consumption • whole output • cardiac epinephrine, cortisol and growth • circulating hormone levels lipolysis, gluconeogenesis and • increased glycogenolysis hepatic glucose output • increased increased uptake of glucose precursors • (propionate,hepatic glycerol). 2. Decrease in response to cold stress: rumen volume in vivo and in situ cell wall digestion diet dry matter digestibility insulin response to a glucose infusion temperature of skin, ears, legs and extremities.
• • • • •
Nutrient Requirements Research literature has very little data on the effect of cold stress on nutrient requirements. The primary change is an increase in the maintenance energy requirement as environmental temperature decreases. Table 2 contains metabolizable energy (ME) requirements for dairy animals at varying temperatures. These requirements are
Table 2 Maintenance ME multipliers for animals at varying environmental temperaturesa,b Temperature ( C)
Heiferc (220 kg)
Heiferd (440 kg)
Dry cowe (700 kg)
Lactating cowf (635 kg)
20 10 0 10 20 30
1.0 1.05 1.13 1.24 1.57 2.00
1.0 1.05 1.13 1.23 1.36 1.61
1.0 1.05 1.13 1.23 1.37 1.64
1.0 1.05 1.13 1.23 1.37 1.52
a
Simulations carried out with the Cornell Net Carbohydrate and Protein System (CNCPS) model, version 4. Hair depth, 1.28 cm; wind speed, 1 kph; hair coat, clean and dry. Base maintenance ME requirement, 7.9 Mcal day1 (33 MJ day1). d Base maintenance ME requirement, 13.8 Mcal day1 (57.7 MJ day1). e Base maintenance ME requirement, 20.2 Mcal day1 (84.5 MJ day1). f Base maintenance ME requirement, 17.1 Mcal day1 (71.5 MJ day1). b c
other
552 Stress in Dairy Animals | Cold Stress: Effects on Nutritional Requirements, Health and Performance
listed as a multiple of the base maintenance ME requirement for an animal with no stress. The effect of cold stress on requirements for protein, minerals and vitamins has not been defined.
Ration Formulation Programs The challenge for nutritionists is how to account for and incorporate the effects of environmental conditions on nutrient requirements, feed utilization and projected animal performance. The majority of the available ration formulation programs do not contain equations to assist in making these adjustments. There are at least three ration formulation programs that can account for some of these factors: the 2001 Dairy-NRC, CPM Dairy and the Cornell Net Carbohydrate and Protein System (CNCPS) models. All of these programs adjust maintenance requirements for changes in environmental temperature (see Feeds, Ration Formulation: Models in Nutritional Management; Lactation Rations for Dairy Cattle on Dry Lot Systems). None of these programs adjusts feed passage rate or feed digestibility in response to cold stress.
A number of options exist to increase energy intake to maintain average daily gain as the temperature decreases. One option would be to feed a higher quantity of the milk replacer powder each day. This would require about 17% more DM from the milk replacer as the environmental temperature decreases from 20 C to 10 C. A second option would be to formulate a milk replacer with a higher fat content. A third option would be to add a fat supplement to the currently used milk replacer. The addition of 0.1 kg of tallow would provide adequate supplemental energy to maintain average daily gain as the temperature dropped from 20 C to 10 C. It is important to remember that the above calculations are relevant only for calves in a clean, dry and draughtfree environment. These calves are assumed to have a clean, dry hair coat. If calves are exposed to more severe environmental conditions, the maintenance requirement would increase and the projected average daily gain would decrease. One option that has become available in the United States is the use of calf blankets. These coats keep the hair coat dry and decrease the heat loss to the environment from the calf. This would increase the proportion of the daily energy intake available to support weight gain. It is also important to have water available to the calves and to keep it from freezing in cold weather.
Milk-Fed Calves The LCT for newborn calves is estimated to be 10 C; this LCT is for a calf housed under dry conditions with no wind. This temperature decreases to about 0 C by the time the calf is 1 month old. If the calf is subject to wind, precipitation or a wet hair coat, the LCT could be considerably higher. The 2001 Dairy-NRC program was used to estimate the impact of environmental temperature on the ME maintenance requirement and predicted energy allowable gain. A milk replacer containing 20% fat and 20% crude protein was used. The feeding rate was 0.6 kg dry matter (DM) day1. The results of this simulation are given in Table 3. Table 3 Impact of environmental temperature on the ME maintenance requirement and predicted energy allowable gaina,b ME for maintenance
Mcal
MJ
Energy allowable gain (kg day1)
20 10 0 10
1.74 2.21 2.68 3.23
7.28 9.24 11.21 13.51
0.41 0.26 0.09 Weight loss
For a dairy calf with a body weight of 45 kg. Feeding 0.6 kg day1 of dry milk replacer.
b
Environmental conditions will alter both the dry matter intake (DMI) (Table 4) and growth rates (Table 5) of dairy heifers. Table 5 contains model predicted energy allowable gains for dairy heifers exposed to three environmental temperatures, and the effects of wind speed, hair depth and coat condition. The same diet is fed in these examples. However, DMI was predicted to increase at colder temperatures. This would result in an increase in daily energy intake. Note that energy allowable gain decreases by more than 50% in the most severe environmental conditions used in this example. These differences in average daily gain reflect the combined effects of temperature, wind speed and hair coat condition.
Dry Cows
Temperature ( C)
a
Replacement Heifers
The maintenance requirement of dry cows increases as the environmental temperature decreases (Table 2). The data in this table assumes a dry cow with a clean, dry hair coat, a hair depth of 1.28 cm and a wind speed of 1 kph. Cows with mud on the hair coat, a different hair depth or subjected to higher wind speeds would have changes in both the ME maintenance requirement and the predicted LCT.
Stress in Dairy Animals | Cold Stress: Effects on Nutritional Requirements, Health and Performance
553
Table 4 Predicted daily dry matter intake (kg day1)a,b Temperature ( C)
Heifer (220 kg)c
Heifer (440 kg)d
Dry cow (700 kg)e
Milking cow (635 kg)f
20 10 0 10 20
5.7 5.8 6.0 6.3 6.7
11.0 11.3 11.5 11.8 12.7
13.9 14.1 14.6 15.4 16.4
23.2 23.5 24.3 25.6 27.3
a
Heifer dry matter intakes predicted using the 2001 Dairy–NRC program. Dry cow and milking cow dry matter intakes predicted using the Cornell Net Carbohydrate and Protein System (CNCPS) model, version 4.0. c Average daily gain ¼ 1.0 kg day1 at 20 C. d Average daily gain ¼ 0.9 kg day1 at 20 C. e 240 days pregnant. f Milk production ¼ 40 kg day1. b
Table 5 Predicted energy allowable gain and lower critical temperature (LCT) for Holstein heifersa,b Temperature ( C)
Wind speed (kph)
Hair depth (cm)
Coat c
DMI (kg)
Average daily gain (kg)
MEd (Mcal day1)
LCT ( C)
20 20 0 0 20 20 20 20
1 10 1 10 1 1 10 10
1.28 2.54 1.28 2.54 1.28 2.54 1.28 2.54
1 3 1 3 1 1 3 3
11.3 11.3 11.8 11.8 13.3 13.3 13.3 13.3
0.88 0.88 0.82 0.82 0.77 0.77 0.41 0.62
14.3 14.3 16.1 16.1 19.5 19.5 24.1 21.5
18.9 5.8 22.7 8.7 31.2 41.6 10.1 15.3
a
15-month-old heifer, 440 kg body weight. Simulations carried out with the Cornell Net Carbohydrate and Protein System (CNCPS) model, version 4. c Coat condition: 1, clean and dry; 3, mud on lower body. d ME maintenance requirement. b
Milking Cows A series of simulations were run using both the 2001 Dairy-NRC program and the CNCPS 4.0 programs (Table 4). A mature cow weighing 635 kg was used. The food ration contained 2.66 Mcal of ME kg1 of DM (11.1 MJ of ME kg1). Clean, dry hair coats with a hair depth of either 1.28 or 2.54 cm were used. Environmental temperatures ranging from 20 C to 30 C were used with wind speeds of 1 or 10 kph. The maintenance ME requirement changed with decreasing environmental temperature as indicated in Table 1. There was also an increase in the predicted DMI as temperature decreased. The predicted DMI for a cow exposed to an environmental temperature of 30 C was 17% higher than a cow in a 20 C environment. There was no change in the predicted daily milk production of 30 kg day1 as environmental temperature decreased. Previous reviews have indicated a potential for depressed milk production when environmental temperatures are less than 10 C to 15 C. However, as indicated earlier, no adjustments in
either rate of passage or feed digestibility are included in these ration formulation programs. One concern for dairy cattle exposed to cold temperatures is the potential for frostbite or frozen teats. One approach to minimize the risk of frozen teats is to make sure that teats are dry after milking before cows return to the cold environment. A second option is to use some specialized teat dips that contain emollients. Commercial ointments or salves could also be applied to the teats if evidence of chapping becomes visible.
Summary There are a number of metabolic and physiological adaptations that occur in animals exposed to cold environmental temperatures. The basal metabolic rate and maintenance energy requirements increase. Dry matter intake also increases while diet digestibility decreases. There are a number of factors that alter the effects of cold temperatures on animals. These include wind, hair depth
554 Stress in Dairy Animals | Cold Stress: Effects on Nutritional Requirements, Health and Performance
and hair coat condition. An animal with a clean, dry hair coat has a lower LCT at the same environmental temperature than an animal with a wet, matted hair coat. This emphasizes the value of a clean, dry environment for animals exposed to low environmental temperatures. In most dairy production systems, dairy cattle are rarely exposed to environmental temperatures lower than 0 C because of the housing systems used. This temperature is higher than the LCT for milking cows. However, the LCT is higher for calves and heifers versus cows (Table 1). Cows can withstand a colder outside environmental temperature than either heifers or calves. In some cases, replacement heifers may be housed outdoors for the winter months. In this situation, the LCT could be used as an index of the need for a windbreak or housing. This would be true as the environmental temperature approaches or is lower than the LCT. A simple windbreak, increased DMI and a clean, dry hair coat can minimize the decrease in ADG in dairy heifers housed outdoors in the winter months. Management practices have the ability to counteract many of the effects of cold stress on dairy animals. A key component is to keep animals in a clean, dry environment with minimal wind. Maintaining a clean, dry hair coat will also help to decrease the impact of cold stress on dairy animals. One key adjustment to make on the nutrition side is to ensure that animals can consume additional DMI to compensate for the higher maintenance energy requirements of animals exposed to cold stress conditions. See also: Feeds, Ration Formulation: Lactation Rations for Dairy Cattle on Dry Lot Systems; Models in Nutritional
Management; Systems Describing Nutritional Requirements of Dairy Cows. Stress in Dairy Animals: Cold Stress: Management Considerations; Heat Stress: Effects on Milk Production and Composition.
Further Reading Agricultural and Feed Research Council (1993) Energy and Protein Requirements of Ruminants. Wallingford: CAB International. Fox DG and Tylutki TP (1998) Accounting for the effects of environment on the nutrient requirements of dairy cattle. Journal of Dairy Science 81: 3085–3095. Fox DG, Tylutki TP, VanAmburgh ME, et al. (2000) The net carbohydrate and protein system for evaluating herd nutrition and nutrient excretion. Animal Science Department Mimeo 213. Gwazdauskas FC (1985) Effects of climate on reproduction in dairy cattle. Journal of Dairy Science 68: 1568–1578. Kennedy PM, Christopherson RJ, and Milligan LP (1982) Effect of cold exposure on feed protein degradation, microbial protein synthesis and transfer of plasma urea to the rumen of sheep. British Journal of Nutrition 47: 521. Kennedy PM and Milligan LP (1978) Effect of cold exposure on digestion, microbial synthesis and nitrogen transformations in sheep. British Journal of Nutrition 39: 105. National Research Council (1981) Effect of Environment on Nutrient Requirements of Domestic Animals. Washington, DC: National Academy Press. National Research Council (1996) Nutrient Requirements of Beef Cattle, 7th edn. Washington, DC: National Academy Press. National Research Council, (2001) Nutrient Requirements of Dairy Cattle, 7th edn. Washington, DC: National Academy Press. Young BA (1975) Effects of winter acclimation on resting metabolism of beef cows. Canadian Journal of Animal Science 55: 619–625. Young BA (1975) Temperature-induced changes in metabolism and body weight of cattle. Canadian Journal of Physiology and Pharmacology 53: 947–953. Young BA (1986) Food intake of cattle in cold climates. In: Symposium Processings: Feed Intake by Beef Cattle, Animal Science Department, Oklahoma State University, Stillwater, pp. 328–340.
Cold Stress: Management Considerations W G Bickert, Michigan State University, East Lansing, MI, USA ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2587–2592, ª 2002, Elsevier Ltd.
Introduction Providing environments for dairy calves, heifers and cows that permit them to grow, mature, reproduce and maintain health is a primary goal in housing design. While climate in a particular geographic area influences design choice, the barn environment finally provided for the animal must positively influence the animal’s health, welfare and productivity. In winter, outdoor winter air is used to provide the ventilation necessary for barns or other enclosures. Since dairy animals adapt well to cold climates, maintaining indoor air temperature equal to or slightly above outdoor air temperature is quite tolerable to the housed animals. Coincidentally, providing the ventilation rate necessary to maintain this minimum temperature difference leads to good air quality. Protecting the animal from extreme drafts, providing dry lying places that contribute to a dry, fluffy, erect haircoat, meeting the nutritional needs of the animal and allowing the animal sufficient freedom of movement are essential.
Ventilation Ventilation permeates all aspects of the animal environment. Most often associated with respiratory health of animals, ventilation – directly and indirectly – impacts many other aspects of health as well. Good ventilation in the stall area of the lactating cow helps to keep bedding dry, a factor favoring good udder health. Good ventilation along alleys helps to keep walking surfaces dry, contributing to healthy feet. Good ventilation may lead to greater productivity, dry matter intake during hot weather may be maintained as a result of good air movement and more comfortable cows in the area of the feed manger. A comfortable, well-ventilated stall area encourages animals to lie down, an important contribution to many aspects of animal health. Ventilation is bringing outside air into a barn where it collects moisture, heat and other contaminants, all produced by the animals, then exhausting it to the outside. Ventilation is an air exchange process – contaminated air inside the barn is exchanged for fresh outside air. To determine ventilation rates, we focus on the moisture
content of the air, measured by relative humidity. But moisture is only one aspect. Ventilation removes other undesirable contaminants as well. Air Quality Animal health and disease are influenced by air quality. Air quality, in turn, is related to ventilation and the positive result of removing contaminants from the air. Empirical observations and field trials suggest that the aerosol spread of pathogens between animals and the influence of air pollutants on pulmonary defense mechanisms are important, especially to respiratory health. Excess moisture, gases and other contaminants in the air are considered to be problematic as well. But the exact relationship among these factors is not fully understood. The term air quality is not easily defined. With respect to animal spaces, good air quality generally implies that the characteristics of ambient air bear no harmful effects on the animals in the space. Actually, the ambient air itself is not at issue – the contaminants in the air are the source of concern. Ambient air, in itself, begins as a mixture of clean, dry air (a mixture of gases, chiefly nitrogen and oxygen) and varying amounts of water vapor. When moisture in the air in an animal space is considered to be a problem, it is actually the concentration of moisture in the air above some arbitrary level that is of concern. Moisture is considered to be an air contaminant above some concentration. Other contaminants may include pathogens, harmful gases, dust and undesirable odors. But it is the concentration of a contaminant above some predetermined level that is considered a threat to animal health. Dilution Effect of Ventilation Ventilation is truly a process of dilution. Air moved through a barn actually serves to dilute the inside air and, very importantly, to dilute all of its components. Dilution reduces concentrations of moisture and heat. Dilution reduces concentrations of airborne disease organisms, harmful gases and dust, and undesirable odors as well. One air change can theoretically reduce the concentrations of air pollutants by 63.2%.
555
556 Stress in Dairy Animals | Cold Stress: Management Considerations
Conversely, concentrations of air pollutants increase when ventilation is lacking. For example, a 7.8-fold increase in airborne bacteria was observed when the outlet ventilation openings in a 15-stall dairy barn were closed. Odors increase also and, in fact, can be an important indicator of the poor air quality that results from underventilation. Terms like ‘barny’, ‘close’ and ‘stuffy’ are sometimes used to describe the environment inside a barn that is suffering from underventilation and poor air quality. Indeed, concentrations of gases are related to ventilation. In an Alberta study of air quality in six freestall barns, average ventilation rates could, in fact, be estimated by measuring building carbon dioxide concentrations. When ventilation is reduced below the recommended level – usually in a misguided effort to warm the barn using animal heat – less moisture is removed. Sometimes the consequences of the resulting moisture build-up and lack of proper ventilation are masked by: (1) insulating the barn, (2) using a greenhouse effect, (3) providing supplemental heat, or (4) dehumidifying the inside air. For example, adding heat to the air reduces relative humidity, without the need for air exchange. So it is possible to have substantial quantities of moisture added to the air and, if accompanied by heating of the air, have the relative humidity remain in an acceptable range. Thus, air quality may be deemed to be satisfactory if relative humidity is the only measure of air quality. But even though excess moisture may not be apparent, the reduced dilution does indeed result in increased concentrations of airborne disease organisms, harmful gases and dust, and undesirable odors. If these increases are ignored, animal health problems are inevitable. Essential to maintaining a healthy animal is providing an environment that does not needlessly stress or challenge the animal (see Stress in Dairy Animals: Management Induced Stress in Dairy Cattle: Effects on Reproduction). Maintaining good air quality is a fundamental aspect of that healthy environment with ventilation providing the key. But air quality is more than just measuring relative humidity. Through ventilation the air inside the barn is continually diluted, assuring that the air the animal breathes has low concentrations of all contaminants that threaten the animal’s health. If sufficient ventilation is provided for moisture control during the winter, the undesirable effects of other airborne pathogens and noxious gases apparently are minimized.
Relative humidity expresses, as a percentage, the relationship between the amount of moisture present in a quantity of air and the amount of moisture the air is capable of holding. For example, if the air in a room is at 40% relative humidity, 40% of the moisture-holding capacity of the air is occupied (Figure 1). From the standpoint of ventilation and the need to pick up moisture, 60% of the air’s moisture-holding capacity remains. If no air exchange occurs, the air can take on moisture only until its relative humidity reaches 100%. Thus, ventilation requires continuous air exchange and the rate of exchange must be sufficient to maintain relative humidity below 100%. A range of 60% to 75% is preferred for animals. The relative humidity of a quantity of air varies with the air temperature. This fact is useful in controlling the ventilation process (Figure 2). As moist air is warmed, its moisture-holding capacity increases markedly. Although
60
40
Figure 1 An illustrated quantity of air at 21 C and 40% relative humidity. Forty percent of the air’s moisture holding capacity is occupied; 60% remains.
Cold air and moisture
Heat
The Air–Water Vapor Relationship Because ventilation involves moisture in the air, relative humidity – a measure of the concentration of moisture in the air – is of primary interest. Understanding the relationship between relative humidity and ventilation is helpful to comprehending the ventilation process itself.
Figure 2 Heating a quantity of air and raising its temperature reduces its relative humidity and increases its moisture-holding capacity; the change in relative humidity is dependent on the temperature rise.
Stress in Dairy Animals | Cold Stress: Management Considerations 557
the air expands as it is warmed, its moisture content, expressed in absolute terms, does not change; relative humidity therefore drops. This warmed air of lower relative humidity becomes more able to pick up moisture. For example, if typical outside winter air at 18 C and 80% relative humidity is used for ventilation (Figure 3), this air will not be very useful for picking up additional moisture and certainly not for achieving a relative humidity of less than 80%. But if this air is used for ventilating a warm calf barn kept at 7 C, the air will be heated to 7 C as it mixes with inside air and passes through the barn, reducing its relative humidity to about 10%. From the standpoint of ventilation for moisture control, heating the air increases its moisture-holding capacity. What remains is to carefully balance the calves’ moisture production rate, the rate at which heat must be added to the air, and the necessary ventilation rate so the resultant relative humidity in the calf barn is controlled at 60–75% and the desired temperature is maintained. This is the basis for determining the minimum continuous ventilation rate for moisture control. If calves are to be kept in a warm barn, say 10 C, supplemental heat must be provided. Calves simply do not produce enough heat to properly warm the amount of ventilation air that is required to remove the moisture they produce. On the other hand, mature cows do produce substantial amounts of heat in relation to their moisture production. This heat, when used to warm the ventilation air required for moisture removal, allows stanchion and tie stall dairy barns to be kept above freezing in the winter. But there is a limit to the temperature rise that cow heat can impart to the ventilating air. In a well-insulated tie stall barn, filled to capacity with cows, the maximum temperature rise of the ventilating air that can be obtained
Warm moist air
Cold air
8 H2O
H2O
Add heat and moisture Figure 3 Cold outside air with a high relative humidity can pick up large quantities of moisture in a barn if the air is heated. Even a slight temperature rise of 5.5 C to 8.3 C, as can occur in cold dairy barns, is useful.
from cow heat alone is of the order of 20 K. This means that ventilation can proceed without interruption until outdoor temperature falls below about 20 C. Beyond that, the indoor barn temperature would fall below freezing and water lines would freeze, a condition that is avoided by installing a safety thermostat on the fan providing the minimum continuous ventilation. In a cold barn, the temperature rise of the ventilating air is limited to 3–6 K. Even so, the dependence of relative humidity on temperature is beneficial. For example, if the 18 C, 80% relative humidity outdoor air is warmed by only 5.5 K, its relative humidity decreases to less than 50%. Thus even this cold air, warmed just slightly, is useful for picking up moisture. Moreover, the heat produced by the animals themselves can cause this slight temperature rise. Care must be taken, however, to assure sufficient air movement, preferably by natural means, to limit the temperature rise to 3–6 K. This is the basis for cold housing, a preferred alternative for all dairy animals.
Minimum Continuous Winter Ventilation A minimum rate of ventilation is required for removing animal moisture from barns in the winter regardless of outside temperature. This applies to barns designed to be warm barns and cold barns alike in winter. In addition, the minimum ventilation should be continuous. Continuous dilution of inside air acts to maintain concentrations of moisture and contaminants in the air at minimal levels. The minimum rate depends on outside weather design conditions, number and type of animals in the barn, age and size of animals, and whether the barn is intended to be cold or warm. With mechanical ventilation, the capacity of the fan chosen to supply the minimum continuous rate should closely match the rate of ventilation that is calculated for a particular housing situation. Mechanical ventilation is most often associated with warm housing where ventilation must have a high degree of control. With natural ventilation, minimum ventilation is less controlled. Depending upon thermal and wind forces, natural ventilation is most often associated with cold housing. As will be described in later sections, deciding between warm and cold housing is critical to the design and subsequent management of the ventilation system. Understanding the differences between the two types of environments is especially important as related to the need for maintaining the minimum continuous ventilation for winter in either situation that is in the best interest of animal comfort and health.
558 Stress in Dairy Animals | Cold Stress: Management Considerations
Barn Categories and Winter Temperatures Barn environments are often categorized according to temperatures maintained in the barn in winter. The particular environment, based on desired indoor temperature, is the first determination in ventilation system design. In a cold barn, indoor temperatures fluctuate with outdoor temperatures. Ventilation maintains indoor temperatures within 3–6 K of outdoor temperatures in winter. Usually, the barn is not insulated and ventilation is largely unregulated, except to adjust for seasonal changes. Adequate air exchange during cold weather to assure moisture control eliminates the need for insulation. Warm barns are well insulated and, by necessity, have a well-controlled ventilation system. These barns are designed to provide a relatively uniform environment throughout the winter. Tie stall barns, where indoor temperatures are to be maintained at least above freezing, remain the principal example of this type of housing for dairy animals. The key to success is ventilation that is regulated in order to compensate for changing outside climatic conditions. Some barns do not fit into either the warm or cold category. An in-between barn or modified environment barn usually has indoor temperatures in winter above freezing, even though it is substantially colder outdoors. Minimum insulation (perhaps only under the roof) reduces evidence of condensation. Recommended ventilation features include open ridge, eaves and side walls. Unfortunately, ventilation openings may be closed or blocked during extreme weather to keep manure from freezing and for other reasons. This practice can result in inside temperatures rising 10–20 K above the outside temperature, significantly higher than the 3–6 K temperature difference limit considered acceptable for cold barns. This alone can create problems because of excess moisture build-up and a high relative humidity. But, even more seriously, openings that may remain closed or blocked after severe weather conditions have passed restrict airflow during less severe conditions. The result of this mismanagement is underventilation and poor environmental conditions. A properly designed and managed in-between barn is more like a warm barn, in terms of both design and operation. Thus, to avoid problems, the design and management of in-between barns should follow the guidelines for a warm barn.
ventilation system may be reasons that wintertime ventilation is lacking, compromising animal health. Problems are most likely during colder seasons of the year, especially during rainy weather and times of warmer days coupled with cold nights. Underventilation occurs after ventilation is adjusted for the worst case – severe winter weather – and is not readjusted to allow increased ventilation when milder winter weather appears. Cold barns with manually controlled natural ventilation can be a particular problem. Perhaps ventilation openings are closed in anticipation of a windy, cold, blustery night, but are not opened the next day when, although the temperature may still be cold, the wind subsides and the sun shines. Very simply, reduced wind reduces ventilation, reducing air exchange and reducing the positive effects of dilution. In a cold barn, the inside temperature is maintained no more than 3–6 K above the outside temperature in winter. Usually this is accomplished through largely unregulated natural ventilation with appropriately sized ridge and eaves openings along with adjustments in door and wall openings. The danger of mismanaging ventilation in a cold barn in winter increases when insulation is installed under the roof. Insulation suggests that the barn is something other than a cold barn, that an available option is to close or block ventilation openings during extreme weather conditions to restrict ventilation. The most serious deficiency associated with this approach is the lack of automatic control to restore ventilation rates when extreme weather has passed. The consequences of this mismanagement are even more serious if high-producing cows are in the barn because of their higher rates of heat and moisture output. Condensation on the underside of the roof of a cold enclosed barn may, in fact, be considered a management tool, a signal to the farmer that underventilation is present. Condensation is a sign that additional ventilation is needed for a higher rate of air exchange to reduce moisture build-up. The presence of insulation can take away this important indicator resulting in a potentially unfavorable environment. If a barn is to be insulated, it must be designed, constructed and operated more like a warm barn than a cold barn. Adequate insulation, a high level of management and well-regulated ventilation are necessary ingredients.
Barn Ventilation – Construction and Management Consequences of Mismanaged Ventilation in Winter Underventilation in winter is one of the most serious threats to air quality and to the environment of animals. Both improper design and improper management of the
In general, a cold barn with natural ventilation has these minimum characteristics: (1) no insulation, (2) open ridge and eaves, and (3) side walls and end walls that open. Providing an open ridge along with open eaves has long been recognized as a means of utilizing a stack effect to
Stress in Dairy Animals | Cold Stress: Management Considerations 559
cause air exchange, especially for controlling moisture in winter. Indoor temperatures are expected to be a few degrees warmer than outdoor air temperature due to the heat being given off by the animals being housed. Current recommendations call for providing a ridge opening of 5 cm per 3 m of barn width and equivalent open area divided between the two eaves. Raised ridge caps are to be avoided. Their performance has been unpredictable due to local wind patterns, often channeling winds into the structure, thereby increasing the entry of wind-blown snow and rain. Very importantly, the combination of the open ridge and eaves should be viewed as the sole source of ventilation only during the most severe winter weather – during periods when temperatures reach the lowest levels or times when especially windy, stormy conditions are present. During all other times in winter, additional ventilation must be provided. Typically, doorways are left open for this purpose, or portions of the end wall sections of the gable roof may be left uncovered, or side walls away from prevailing winter winds may be left open. Then, as temperatures rise into spring and summer, side walls and end walls are opened fully. As a general rule, too much ventilation is preferred over too little. In winter, air movement through the barn should be sufficient to maintain inside temperature within 3–6 K of outside temperature. Natural ventilation has been used successfully for warm housing. Such barns are temperature controlled in cold weather and guidelines for construction and for sizing chimney and side wall openings must be followed carefully. Moreover, if ventilation openings are not operated automatically, frequent attention to management of the ventilation system is essential to avoiding underventilation and associated consequences. Except for higher initial and operating costs, a wellcontrolled mechanical ventilation system is desirable for a warm barn in order to minimize risks associated with the reduced rate of air dilution that accompanies warm housing.
drying time for wet feet, especially important to a mature cow. Bedded areas, including bedded manure packs, are common in cold climates for housing groups of young animals and dry cows. Bedded pens that are frequently cleaned are recommended for calving as well. However, in most areas today, when barns are provided for lactating cows, these barns are equipped with freestalls. Cleanliness and comfort are two basis prerequisites that must be satisfied in freestall design and construction. Cleanliness relates to clean, dry conditions, especially a clean, dry stall bed in the vicinity of the udder. Comfort means a comfortable bed to allow the cow to lie comfortably in the stall along with roomy dimensions that make it easy for the cow to enter the stall, lie down, rise and exit. In simplest terms, the main purpose of a freestall is to reduce exposure of the teat ends to mastitis-causing organisms. What follows is to make the stall so appealing that a cow chooses no other place but a freestall to lie down 10–14 h day 1. Adequate supplies of feed and water, besides being of suitable quality, must be easily accessed as a result of proper feed manger and waterer space and design. Providing a minimum manger space of 60 cm per cow is recommended. Waterers should provide a space for every 15–20 cows in a group. Two waterer locations per group are recommended. Skid-resistant walking surfaces reduce injuries, improve movement to feed, water and resting areas and enhance estrus detection. As in all aspects of facilities design, a compromise must be reached. On the one hand, the surface should provide enough texture so as to keep the animal from skidding. On the other hand, the surface cannot be so aggressive as to injure the underside of the foot of the cow. Grooves in concrete surfaces, up to 1 cm deep and 1 to 1.5 cm in wide, spaced 8–9 cm in on centre, are an acceptable method.
Summary Other Factors Related to Cow Comfort Besides ventilation, other aspects of housing influence cow comfort. A reasonably clean, dry, resilient bed upon which to lie down helps maintain a dry erect haircoat for the small calf in cold weather as well as providing the larger cow with a clean, comfortable place to lie down for rest and to relieve stress on feet and legs. An animal will lie down for longer periods of time and more total hours per day when provided a dry, comfortable lying place. The outcome is longer resting time, less time for the animal to be standing in wet manure and more
Proper ventilation system design and management is essential to providing an environment that allows dairy animals to grow, mature, reproduce and maintain health during cold weather. Stalls and beds, access to feed and water and walking surfaces must be considered also. Dairy farm profitability relies on sound management and quality animal environment. Both factors depend on the buildings and equipment on the dairy farm. Understanding the sometimes complex interactions involved, such as between cow comfort and barn design or between grouping strategies and the management plan, is essential when building new facilities as well as remodelling existing ones.
560 Stress in Dairy Animals | Cold Stress: Management Considerations See also: Reproduction, Events and Management: Estrous Cycles: Characteristics; Estrous Cycles: Postpartum Cyclicity. Stress in Dairy Animals: Cold Stress: Effects on Nutritional Requirements, Health and Performance; Heat Stress: Effects on Milk Production and Composition; Heat Stress: Effects on Reproduction; Management Induced Stress in Dairy Cattle: Effects on Reproduction.
Further Reading Bickert WG (1994) Designing dairy facilities to assist in management and to enhance animal environment (keynote paper). Proceedings of the 3rd International Dairy Housing Conference, ASAE, St Joseph. Bickert WG, Holmes B, Janni K, et al. (2000) Dairy Freestall Housing and Equipment, 7th edn. Ames: MidWest Plan Service.
Choiniere Y and Munroe JA (1990) Natural Ventilation for Warm Housing. Canada Plan Service Leaflet M-9760. Ottawa, Canada: Canada Plan Service. Choiniere Y, Munroe JA and Suchorski-Tremblay A (1994) Sizing Openings for Naturally Ventilated Barns. Canada Plan Service Leaflet M-9765. Ottawa, Canada: Canada Plan Service. Clark PC and McQuitty JB (1987) Air quality in six Alberta commercial freestall dairy barns. Canadian Agricultural Engineering 29(1): 77–80. Constantine DG (1969) Airborne microorganisms: their relevance to veterinary medicine. In: Dimmick RL et al. (eds.) An Introduction to Experimental Aerobiology, pp. 463–476. New York: Wiley Interscience. Curtis SE (1983) Environmental Management in Animal Agriculture. Ames: Iowa State University Press. Kilburn KH (1967) Cilia and mucus transport as determinants of the response of lung to air pollution. Archives of Environmental Health 14: 77–91. Malecki, J, Gorski, S, Tupaj, C. and Lasoryszczak, M (1993) Effect of gravity ventilation facilities control on the microclimate condition in home stockfarm buildings. Proceedings of the 4th International Livestock Environment Symposium, ASAE, St Joseph.
Heat Stress: Effects on Milk Production and Composition C R Staples and W W Thatcher, University of Florida, Gainesville, FL, USA ª 2011 Elsevier Ltd. All rights reserved.
Heat Stress Defined by Environment and Cow Response Measurements The most productive dairy breeds predominantly used around the world were developed in temperate climes, and are most productive between the temperatures of 5 and 15 C. As temperatures increase from 15 to 25 C, cows experience a small degree of loss in production. However, as temperatures exceed 25 C, dramatic reductions in milk production can occur. As a result, 25 C is usually considered the upper critical temperature for lactating dairy cows. In addition to ambient temperature, relative humidity should be considered when assessing the heat stress effect of the environment on dairy cows. The temperature– humidity index (THI) is a single value combining the air temperature and humidity. It has been developed to better define the environmental conditions under which productivity and the well-being of animals are likely to be compromised. This THI is also called the ‘discomfort index’. It can be calculated for outside cattle using the following equation: THI ¼ ð1:8 dry bulb temperature ðC+ Þ þ32Þ – ðð0:55 – 0:0055 % relative humidityÞ ð1:8 dry bulb temperature – 26ÞÞ
Traditionally, the THI system has been used to describe the expected negative effects of a hot environment on milk production. Milking dairy cows are considered to experience no stress when THI is <72, mild stress when THI is between 73 and 77, significant stress when THI is between 78 and 88, severe stress when THI is between 89 and 99, and possible death when THI is >99. However, recent research conducted at the University of Arizona indicates that milk production by today’s higher producing dairy cows is negatively affected starting at a THI less than 72. In eight separate studies involving 100 Holstein cows housed in environmental chambers and producing at least 35 kg of milk, production of milk was reduced when the daily minimum THI was 65 or when the daily average THI was 68 for more than 17 h per day. For example, when the minimum temperature settles at 19.6 C and 50% humidity (THI ¼ 68), effects of heat stress will start taking a toll. These guidelines may shift somewhat depending on the degree of air movement and direct solar radiation. Current research suggests the need to adjust the THI equation to place more weight on
humidity for hot, humid areas and more weight on ambient temperature for semiarid regions in order to make THI a more accurate tool for predicting heat stress. This is based upon examination of the effects of heat stress on first-parity milk yield by cows managed in the semiarid region of Phoenix, AZ (n ¼ 81 889 cows) and in the hot, humid region of Athens, GA (n ¼ 12 473 cows). Yet recent work from Florida indicates that temperature alone had the greatest influence on predicting comfort of dairy cows managed under subtropical conditions. Although THI is a useful tool to assess the degree of heat stress potential on the cow, her own responses to the hot weather are a more true indicator of her degree of heat stress. Increased breathing and sweating are classified as evaporative cooling techniques and are the primary means of dissipating excess heat under heat stress conditions. A rise in body temperature indicates the cow’s inability to completely dissipate her heat load. Figure 1 plots body temperatures and respiration rates collected from lactating dairy cows (<13.6 kg day1 of milk) housed in chambers at eight different ambient temperatures. Points in each curve at which the measured responses made a dramatic shift upward were at 60 respirations per minute and at 39.2 C rectal temperatures. In 2009, Arizona scientists reported a linear relationship between respiration rates and rectal temperatures of higher producing dairy cows expressed as y ¼ 0.028x þ 37.438. Based on this equation, a rectal temperature of 39.2 C would be accompanied by 63 respirations per minute, values that support Figure 1. These values may be used as reference points to identify cows on the verge of experiencing significant heat stress: points at which the cow will heat up exponentially if exposed to increasing temperature and humidity.
Heat Stress Effects on Cow Performance Studies that have been conducted to evaluate the effects of heat stress on cow performance have utilized three main approaches. Animal performance comparisons have been made between (1) cows milking during cool and hot seasons, (2) cows managed with and without methods of heat stress abatement such as shade, fans, and sprinklers, and (3) cows managed in environmentally controlled chambers.
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Figure 1 Effect of environmental temperature on respiration rates and rectal temperatures of lactating dairy cows. From Regan WM and Richardson GA (1938) Reaction of the dairy cow to changes in environmental temperature. Journal of Dairy Science 21: 73–79.
The Prepartum Period Reducing the effects of heat stress during a cow’s nonlactating, pregnant stage of life has shown benefits. Florida and Israeli workers provided either little or significant relief from heat stress conditions to cows during their last 60 days of pregnancy. Upon calving, both groups were managed the same. Cows provided relief from thermal stress gave birth to heavier calves (3 kg) and produced more milk during the next lactation. Animals exposed to heat stress conditions likely consume less dry matter (DM) (evidenced by greater plasma nonsterified fatty acids (NEFA)), which may limit fetal growth in the last trimester, leading to smaller birth weights of calves and lower milk production. In addition, uptake of glucose and amino acids by the fetus is reduced under heat stress conditions, which contributes to reduced birth weights of calves according to research conducted at Colorado State University. Cooling during the close-up dry period also has improved colostrum quality. Holstein heifers were exposed to (1) a THI of 65 or (2) a THI of 82 from 09.00 to 20.00 h and a THI of 76 from 21.00 to 08.00 h during the last 3 weeks before calving and 36 h postcalving. Concentrations of immunoglobulins G and A were lower in the first four milkings of heifers exposed to greater THI. The Postpartum Period – Milk Production and Dry Matter Intake The production of heat by a cow increases when she is in the metabolic state of lactation. This is due to (1) an increase in feed intake, which increases the heat of fermentation and nutrient metabolism, and (2) the output of a daily renewable product (milk) whose synthesis
generates heat within the body. Both sources of metabolic heat must be dissipated from the body; this is more difficult when the environment has a high THI. At the upper critical temperature of 25.5 C, the cow often begins to eat less feed. Elevations in body temperature may signal the hypothalamus to reduce voluntary intake. As the temperature increases, the amount of energy expended by the cow to maintain homeothermy is increased. It is estimated to be 20% greater at 35 C compared to that at 20 C. In order to cover this additional energy cost, the intake of DM must increase. However, during hot weather, DM intake decreases. Therefore, the energy status of the cow is challenged due to greater energy costs required to maintain homeothermy and less energy consumption. Thus, it is not surprising that milk production goes down because availability of energy for lactation is less. However, the decrease in DM intake may only account for 35–50% of the decrease in milk production. Arizona research suggests that heat-stressed cows partition more nutrients toward other tissues and less toward the mammary gland, contributing to reduced milk production. A review of 12 studies from the scientific literature indicates a simultaneous drop in feed intake and milk production as cows experience heat stress. As rectal body or milk temperatures increased from an average of 38.8 to 39.9 C, average DM intake decreased from 18.4 to 15.6 kg day1 and average milk production decreased from 22.4 to 19.2 kg day1. For the most part, these cows are considered ‘lower producing cows’. To examine whether higher producing cows are more sensitive than lower producing cows to thermal stress, the studies were divided into two groups. Three studies in which cows produced an average of >30 kg milk day1 under thermoneutral conditions were grouped together. A second group of nine studies was composed of cows that produced an average of <25 kg milk day1 at thermoneutral conditions. As the average body temperature of ‘lower’ producing cows increased from 38.9 to 39.9 C, average intake of DM decreased from 17.4 to 15.0 kg day1 and average milk production decreased from 19.0 to 16.3 kg day1. Milk production decreased 2.7 kg day1 per 1 C increase in body temperature. As the average temperature of ‘higher’ producing cows increased from 38.5 to 39.8 C, average intake of DM decreased from 21.3 to 17.5 kg day1 and average milk production decreased from 32.6 to 27.9 kg day1. Milk production decreased 3.6 kg day1 per 1 C increase in body temperature. Based upon limited information, it appears that heat stress is more detrimental to cows of greater milk production. When Holstein cows (summary of 8 studies involving 100 cows) were housed in environmental chambers to control THI, milk production decreased linearly by 2.1 kg day1 for every 1 C increase in body temperature between 38 and 41 C.
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Other studies have implied this same principle. As temperature and humidity rose, milk production decreased to a greater extent for Holstein cows than for Jersey and Brown Swiss breeds. Cows in the early part of lactation experienced a greater depression in feed intake than cows in midlactation during the summer season. The use of bovine somatotropin (bST) as a lactational promotant can increase body temperature as a result of increased milk production. Cows injected with 20 mg day1 of bST were reported to increase their milk production by 4 kg day1 and milk temperature was increased between 0.4 and 0.5 C. As cows are managed to produce more milk, we should be equally dedicated to providing them the means to cope with the additional heat load that comes with this additional milk during hot weather. In a 10-year study, involving 100 purebred Holstein cows in their first lactation in Maryland, cows calving in January and February produced 17% more milk than cows calving in July and August. Major differences in performance took place in the first 50 days of lactation. Environmental conditions, mainly temperature, had a negative effect on appetite. Cows that calved in July and August consumed 14% less feed and produced 21% less milk than cows that calved in winter. As a result, loss of body weight was greater for summer calvers compared to winter calvers. Cows can inadvertently increase the heat load on themselves by consuming much of their ration prior to the hottest part of the day. Peak heat production by the cow occurs about 3–4 h after eating. Therefore, the rising body temperature due to feed intake may coincide with the rising ambient temperature, thus increasing the maximum heat load on the cow. Cows fed in the evening cooled down more quickly after exposure to elevated THI in environmental chambers than cows fed in the morning. The pattern of eating also differs during cool and hot conditions. Under hot conditions, cows often eat more frequent meals of smaller size resulting in a lower intake per day, yet they experience a greater increase in body temperature. Cows may attempt to eat more feed at night than during the day. Under conditions when the THI still
exceeded the upper critical THI of 72, Florida workers reported that the amount of feed consumed at night did not compensate for the greatly depressed intake during the day. The ability of a cow to cope with heat stress may be dependent upon the extent to which she can cool down at night. Very warm evenings (i.e., lack of night cooling) can prevent cows from making up the DM intake they lost during the day. Daily intake of DM began decreasing when the minimum environmental temperature was above 19 C for lactating Holstein cows. Scientists in Arizona documented that milk production of Holstein cows suffered when THI failed to drop below a THI of 65. Loss of milk averaged 2.2 kg per cow per day for cows producing at least 35 kg day1 at thermoneutral temperatures. Jersey cows in Arizona were able to maintain milk production until nighttime THI failed to drop below 75 and then production dropped 2.8 kg day1. Sometimes, it is the intermittent heat waves that are more dangerous than the regular episodic thermal stress. In 1997, more than 100 feedlot cattle died due to extreme THI over a 4-day period. It was the third such heat wave in 3 weeks. What made the third heat wave so lethal may have been an increased DM intake of animals just prior to the third event. Relatively cool weather had come in right after the second heat wave so the animals had compensated for their reduced intake during the second heat wave by eating much more feed. Greater gut fill during the third heat wave increased their metabolic heat load on top of the environmental heat load, which may have prevented the animals from dissipating the heat needed to survive. Without question, water is the nutrient of greatest importance in hot weather. Cows drink more water under heat stress conditions. This undoubtedly aids in cooling the body core of the cow. In addition, the cow loses additional water from the skin and lungs as she works to minimize her increased body temperature. Intake of drinking water by lactating cows increased 29% (16.8 kg day1), and loss of water via the skin and respiration increased 59 and 50%, respectively, when ambient temperature increased from 18 to 30 C (Table 1). Any factor that may inhibit cows from
Table 1 Intake and excretion routes of water by lactating cows at two environmental temperatures Measurement 1
Water drank (kg day ) Feed water (kg day1) Urine volume (kg day1) Fecal water (kg day1) Evaporation Surface (g m2 h1) Respiration (g m2 h1)
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18 C
30 C
57.9 1.6 11.1 17.9
74.7 1.4 12.8 12.0
29.0 14.3 15.0 33.0
94.6 60.6
150.6 90.7
59.3 50.0
Percentage difference
Reproduced with permission from Collier RJ, Beede DK, Thatcher WW, Israel LA, and Wilcox CJ (1982) Influences of environment and its modification on dairy animal health and production. Journal of Dairy Science 65: 2213–2227.
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drinking must be eliminated. If water intake is restricted in hot weather, the drop in milk production will be precipitous. The cows will become hotter than normal, and DM intake will decrease to a greater extent as intake of DM and water are closely linked. Providing cool, clean water in ad libitum amounts is simply good management. The Postpartum Period – Milk Composition Milk fat concentration
In 6 of 14 scientific studies, milk fat percentage decreased significantly (4.05 vs. 3.58%) when heat stress conditions were intensified. All other studies reported no change in milk fat percentage as rectal temperatures increased. An additional study involving nearly 23 000 observations on Florida dairy farms examined the relationships between many variables, including milk composition and environmental temperature. As temperatures increased from 9.4 to 36.1 C, the authors reported that milk fat concentration dropped from 3.85 to 3.31% and milk protein dropped from 3.42 to 2.98%. Milk constituents were not influenced by the degree of relative humidity. The effect of heat stress on milk fat content appears to be influenced by the forage-to-concentrate ratio of the diet. Fat concentration of milk from cows fed a 35% hay diet was lower during hot conditions compared to thermoneutral conditions (3.69 vs. 3.90%). However, milk fat concentration was unchanged by heat stress when cows were fed a diet containing 65% forage. In a separate study, cows were fed diets of 16, 17.9, 19.4, and 21.2% acid detergent fiber during warm (THI between 64 and 77) and hot weather conditions (THI between 72 and 84) (Table 2). Milk fat percentage was unchanged by the diet during the period of warm temperatures. However, under greater heat stress conditions, milk fat content decreased linearly as the fiber content of the diet decreased. The authors speculated that a slight acidosis was corrected with the higher fiber diet, resulting in improved ruminal efficiency and digestion.
It appears that cows subjected to heat stress may be at increased risk to ruminal acidosis. It appears that heatstressed cows can have lower ruminal fluid pH, less ruminating activity, low milk fat percentage, and reduced buffering capability by the saliva. Fistulated Holstein cows were kept at either 18 C and 50% relative humidity or 29 C and 85% relative humidity for 5 weeks. Ruminal fluid was measured 12 times postfeeding for pH and lactic acid concentration. Cows kept in the hotter environment had lower ruminal pH (5.8 vs. 6.3) and greater lactic acid (1.9 vs. 0.45 meq l1). In another study, mean ruminal fluid pH (24 h average) was lower (6.53 vs. 6.66) for Holstein cows denied access to shade. Fecal pH was lower (5.92 vs. 6.08) for unshaded compared to shaded lactating cows. A predisposition to acidosis during heat stress is indicated by the report that elevated environmental temperatures negatively affected ruminal contractions. The number of ruminal contractions decreased from 2.4 to 1.7 per minute when lactating cows were not provided shade (rectal temperatures of 38.7 vs. 39.6 C). Missouri workers kept ruminally fistulated Holstein cows at an ambient temperature of 38 or 18 C for 5 days (rectal temperatures of 40.9 vs. 38.4 C). The hotter cows had less rigorous ruminal contractions as evidenced by a 50% reduction in the average amplitude. The frequency of contractions (2.2 vs. 1.7 per minute) closely followed the pattern reported earlier but was not significant. A lower DM intake by cows at the higher temperatures in the Missouri study was not responsible for the difference in rumen movement because DM intakes were equalized by placing uneaten feed into the rumen via fistula. A decreased number or intensity of ruminal contractions due to heat stress may have a negative effect on saliva production, thereby reducing the buffering activity in the rumen, resulting in a lower ruminal pH. This decreased activity of the rumen musculature of heat-stressed cows may be related to a reduced concentration of volatile fatty acids (VFAs) in
Table 2 Effect of heat stress on milk production (kg day1) and milk fat percentage of cows fed diets differing in ADF concentrations Milk production (kg day1)
Milk fat percentage
Percentage ADF of diet
Warm temperaturesa, b
Hot temperaturesc, d
Warm temperaturesa
Hot temperaturesb, c
16.0 17.9 19.4 21.2
32.3 32.6 31.4 28.9
24.6 25.8 26.4 22.7
3.24 3.49 3.58 3.62
3.21 3.28 3.50 3.69
a
Minimum and maximum values of THI were 64 and 77, respectively. Linear effect. c Minimum and maximum values of THI were 72 and 84, respectively. d Quadratic effect. ADF, acid detergent fiber. Reproduced with permission from West JW, Hill GM, Fernandez FM, Mandebvu P, and Mullinix BG (1999) Nutritional strategies for managing the heat-stressed dairy cow. Journal of Dairy Science 82: 2455–2465. b
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the rumen. That ruminal VFAs may play an essential role in stimulating rumen motility by influencing the neural receptors in the rumen wall may partially explain the reduced motility noted under heat stress conditions. When ruminally fistulated Holstein cows were kept at either 18.2 or 37.7 C, the concentration of VFAs decreased by more than 50% in heat-stressed cows despite maintaining equal intake of DM through placement of uneaten feed into the rumen. Respiratory alkalosis is an additional physiological mechanism operating during heat stress conditions that may contribute to ruminal acidosis and thereby lower the fat content of milk. As cows become heat stressed and respiration rates increase, CO2 is eliminated from the lungs faster than it is produced. This results in decreased blood CO2. In an attempt to keep the CO2-to-bicarbonate (HCO 3 ). ratio constant in the blood, the kidney excretes more HCO .3 . With more CO2 leaving from the lungs and more bicarbonate leaving in the urine, bicarbonate concentration in the blood drops, Hþ concentration in the blood drops as Hþ is used to produce more CO2, and blood pH becomes more alkaline (termed respiratory alkalosis) (Figure 2). This drop may, in turn, reduce the bicarbonate concentration in saliva, thus reducing the buffering activity in the rumen and increasing the risk of ruminal acidosis. A last factor that may contribute to lower milk fat content is the habit of cows to selectively consume concentrates and minimize intake of forages to a greater degree in hot compared to cooler weather, thus predisposing them to acidosis and lower milk fat content.
Milk protein concentration
Lactating cows exposed to heat stress conditions can experience lowered protein concentration in milk. In 5 of 10 studies examining heat stress effects on animal performance, milk protein concentration was significantly reduced by an average of 0.18 units. The solids-not-fat content was reduced due to heat stress in three other studies by 0.2–0.4 units. These decreases in milk protein Panting =
CO2 Exhaled Kidney
Blood [CO2]
Excretion of HCO3– in urine
Production of CO2 in blood H2CO3 CO2 + H2O HCO3– + H+
Respiratory alkalosis
[H+] is reduced so blood pH
Figure 2 Metabolic responses to heat stress work to maintain equilibrium of CO2 and HCO 3 in bloodstream.
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percentage due to heat stress may be due to lowered microbial protein synthesis in the rumen and lowered protein intake due to lowered intake of DM. Milk somatic cell count
In five of six studies, somatic cell counts (SCCs) were higher in the milk of cows exposed to greater heat stress and two of these five studies reported significant increases. The number of white blood cells in plasma was reduced 16% in cows exposed to heat stress conditions using environmental chambers. The immune system of the cow is likely under greater strain during heat stress conditions and therefore the cow is less able to manage subclinical mammary infections. Other milk constituents
The fatty acid profile of milk fat is changed as cows are exposed to greater heat stress conditions. The concentrations of the shorter chain fatty acids (C6–C12) were reduced in the milk of cows housed in chambers kept at 29.4 C and 70% relative humidity compared to those housed in chambers kept at 18.3 C and 50% relative humidity. This is possibly because of lower production of VFAs in the rumen due to lowered feed intake. The proportion of C18:1 in milk fat was also decreased whereas the proportion of C18:0 was increased in hotter conditions. This is thought to be due to lower feed intake that results in slower passage of feed from the rumen, thus allowing a greater degree of biohydrogenation of dietary polyunsaturated fats. The potassium content of milk decreased from 2005 to 1853 ppm when cows were denied access to shade but sodium content was unchanged (521 vs. 543 ppm). Unlike man, the primary electrolyte lost in skin secretions of cattle is K (K2CO3 and KHCO3) rather than Na. As heat stress conditions intensify, the production of secretions by the skin and the concentration of K in the secretions increase resulting in an exponential loss of K. The decreased potassium in milk may reflect a conserving mechanism by the cow for prioritized secretion of potassium from the skin. When exposed to heat stress conditions, milk concentrations of growth hormone increased 38% and prolactin increased 85%. Prolactin may be involved in helping the heat-stressed cow meet increased requirements of water and electrolytes.
Conclusion Lactating dairy cows begin to experience seriously the negative effects of heat stress when rectal temperatures exceed 39.2 C. A respiration rate of >60 per minute is an indication that stress due to heat and
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humidity is becoming excessive. Pregnant cows provided relief from thermal stress during the nonlactating period will have heavier calves at parturition, show improved colostrum quality, and will produce more milk postpartum. Intake of feed is reduced as cows attempt to maintain homeothermy in thermal stress conditions. Intake was reduced 15% in a review of 12 scientific studies as rectal temperatures increased from 38.8 to 39.9 C. As a result, production of milk was reduced 14% as well. Higher producing cows as well as all cows in their first 50 days of lactation are most sensitive to heat stress. Management of feed and water intake is important in helping cows cope with conditions of thermal stress. Cows exposed to significant heat stress are more susceptible to ruminal acidosis. Ruminal pH may be lowered because of reduced buffering of the rumen and a reduction in the number and intensity of ruminal contractions. Percentages of milk fat and protein are often lowered (0.5 and 0.2 percentage units, respectively) during the times of heat stress and during the summer season. The decrease in milk fat percentage may be aggravated by feeding diets that contain borderline concentrations of fiber. There is an increase in SCC, growth hormone, and prolactin and a decrease in potassium content in the milk of cows exposed to greater heat stress.
See also: Stress in Dairy Animals: Cold Stress: Effects on Nutritional Requirements, Health and Performance; Cold Stress: Management Considerations; Heat Stress: Effects on Reproduction; Management Induced Stress in Dairy Cattle: Effects on Reproduction.
Further Reading Armstrong D (1994) Heat stress interaction with shade and cooling. Journal of Dairy Science 77: 2044–2050. Berman A (2005) Estimates of heat stress relief needs for Holstein dairy cows. Journal of Animal Science 83: 1377–1384. Blackshaw JK and Blackshaw AW (1994) Heat stress in cattle and the effect of shade on production and behaviour: A review. Australian Journal of Experimental Agriculture 34: 285–295. Collier RJ, Beede DK, Thatcher WW, Israel LA, and Wilcox CJ (1982) Influences of environment and its modification on dairy animal health and production. Journal of Dairy Science 65: 2213–2227. Hahn GL (1999) Dynamic responses of cattle to thermal heat loads. Journal of Animal Science 77(supplement 2): 10–20. McDowell RE (1972) Improvement of Livestock Production in Warm Climates. San Francisco, CA: WH Freeman. Mishra M, Martz FA, Stanley RW, Johnson HD, Campbell JR, and Hilderbrand E (1970) Effect of diet and ambient temperature–humidity on ruminal pH, oxidation reduction potential, and ammonia and lactic acid in lactating cows. Journal of Animal Science 30: 1023–1028. National Research Council (1971) A Guide to Environmental Research on Animals. Washington, DC: National Academy of Sciences. Regan WM and Richardson GA (1938) Reaction of the dairy cow to changes in environmental temperature. Journal of Dairy Science 21: 73–79. West JW (1999) Nutritional strategies for managing the heat-stressed dairy cow. Journal of Animal Science 77(supplement 2): 21–35.
Heat Stress: Effects on Reproduction P J Hansen, University of Florida, Gainesville, FL, USA J W Fuquay, Mississippi State University, Mississippi State, MS, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction Mammals are homeotherms and regulate heat production and heat loss to maintain a constant and high body temperature. It becomes difficult for mammals to successfully regulate body temperature when heat production increases (such as during vigorous exercise or associated with lactation) or when the environment limits the degree of metabolic heat loss from the animal. Heat stress represents the combination of high air temperature, intense solar radiation, and high humidity that together reduce the flow of heat from the animal so that body temperature increases. The condition of elevated body temperature is known as hyperthermia. Biological and productive functions are compromised by heat stress because the physiological adjustments animals undergo to regulate body temperature can have other deleterious effects on the animal and because hyperthermia itself can alter cellular function. One example of a physiological adjustment to heat stress that can compromise biological function is a reduction in feed intake. About half of the decrease in milk yield in dairy cows exposed to heat stress is caused by reduced appetite and feed intake. An example of alterations in cellular function caused by hyperthermia is the embryonic death that occurs when preimplantation embryos are exposed to temperatures above normal body temperature. All mammals are susceptible to heat stress but lactating cows are particularly so. The large amounts of heat produced as a result of lactation make it difficult for the lactating female to regulate its body temperature. Indeed air temperatures as low as 25–29 C can cause hyperthermia in lactating dairy cows. As a result, heat stress has greater effects on body temperature and reproduction in lactating animals than in nonlactating animals (Figure 1). In addition, cows producing more milk experience a greater decline in reproductive function during heat stress than do cows producing less milk. There are two consequences of the relationship between milk yield and heat stress. First, lactating dairy cows intensely managed to produce large amounts of milk are susceptible to heat stress in most temperature regions of the world and not just in regions considered to have a hot climate. Indeed a reduction in fertility in summer has been reported in Alberta, Canada. Second, further increases in milk yield, due to genetic improvement or
changes in management, are likely to make cows more susceptible to heat stress in the future. This, coupled with the possibility for global climate change, are likely to increase the economic losses and reduce animal comfort associated with heat stress.
Actions of Heat Stress on the Female Expression of Estrus Reduced intensity of estrus limits the use of artificial insemination (AI) and other reproductive management techniques dependent upon visualization of estrus (see Reproduction, Events and Management: Mating Management: Detection of Estrus). The reduction in estrus behavior involves reduced mounting activity and shorter periods of estrus. In a Virginia study, Holsteins in estrus during the summer had about half the number of mounts of cows in estrus during the winter. In another study, the duration of estrus was 20 h for cows maintained in cooled conditions compared to 11 and 14 h for heatstressed cows in temperature control chambers or the natural summer environment, respectively. As a result of a reduction in behavioral estrus, the proportion of cows not detected in estrus can rise to 80% in summer, as has been reported in Florida. Lack of detected estrus in summer is a result of suboptimal estrus behavior rather than because cows become acyclic in the summer. Once established, cyclicity is generally unaffected by heat stress. Fertility Even if lactating cows are detected in estrus, the probability that pregnancy will be established and maintained after mating is low during heat stress. Depending upon the degree of heat stress, first-service conception rates in lactating dairy cows exposed to heat stress can be 10% or less as compared to rates of 25–40% in cows not exposed to heat stress. Fertility is also reduced by heat stress in other mammals used for milk production, including sheep. The reduction in fertility caused by heat stress is due to a combination of reduced fertilization rate and increased embryonic mortality. Changes in oocyte function are responsible for some of the infertility. The early embryo is very susceptible to elevated maternal
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568 Stress in Dairy Animals | Heat Stress: Effects on Reproduction
Rectal temperature ( °C)
40.5 40.0
Cows
39.5 39.0 Heifers 38.5 38.0 18
20
22
24 26 28 30 Air temperature ( °C)
32
34
Figure 1 The relationship between air temperature and rectal temperature for nonlactating heifers and lactating cows. Data were collected in Wisconsin and are from Sartori R, Sartor-Bergfelt R, Mertens SA, Guenther JN, Parrish JJ, and Wiltbank MC (2002) Fertilization and early embryonic development in heifers and lactating cows in summer and lactating and dry cows in winter. The figure was prepared by PJ Hansen and is reproduced with permission of Intervet.
temperature, but resistance increases as development proceeds so that by the morula stage (day 5 after estrus) a single day of heat stress has no effect on embryonic survival. As illustrated in Figure 2, there are three windows in the reproductive life cycle of cows where heat stress
st s lea ru at est e e itiv for ns be e s s at day He 26 – 20
results in reduced pregnancy rate after mating. The first is the period before ovulation. The oocyte that ovulates coincident with estrus is located in a follicle that initiated growth 90–110 days previously, and it is possible that heat stress during some or all of this period of follicular growth can lead to ovulation of an oocyte with reduced competence for fertilization and development. It has been demonstrated experimentally that heat stress 20–26 days before estrus alters follicular function. Studies in Israel indicate that there is a lag in restoration of fertility in autumn and that the length of this lag can be shortened by removing follicles that experienced growth during summer. The second window is the periovulatory period. Experimental heat stress during this time did not decrease fertilization rate, but the ability of the embryos formed after fertilization to develop normally was reduced. The third window is the period of embryonic development. As mentioned above, embryos are initially sensitive to heat stress but become resistant by the morula stage. The reason why embryos acquire thermotolerance during development is not known for certain but probably involves decreased free radical formation and acquisition of biochemical mechanisms to stabilize cells exposed to elevated temperature (e.g., antioxidants such as glutathione and heat shock protein 70). Although embryos become resistant to heat stress by the morula stage, heat stress can cause some embryonic
Ovary
~3 months th takes grow r a l cu Folli
Follicle
Estrus-ovul
Day 1
Cleavage stages Day 2
Day 3
Day 4
Morula Day 5
Day 6
Blastocyst Day 7
Damage caused by heat stress
Day 0
Fert
Figure 2 (see color plate 94) Changing sensitivity of the cow to heat stress. The follicle takes about 3 months to complete growth. Heat stress can disrupt follicular function at least as early as 20–26 days before estrus. Heat stress can also disrupt the oocyte on the day of estrus and inhibit development of the early embryo. By day 3 after breeding, however, heat stress has little effect on embryonic survival, and the morula and blastocyst present beginning at about day 5 after breeding are resistant to elevated temperature. The figure was prepared by PJ Hansen and is reproduced with permission of Intervet.
Stress in Dairy Animals | Heat Stress: Effects on Reproduction
Progesterone (ng ml–1)
15
10
5
0
0
5
10
15
20
25
Estrus cycle (days) Figure 3 Average daily serum concentration of progesterone during spring (*) and summer (). Reproduced with permission from Howell JL, Fuquay JW, and Smith AE (1994) Corpus luteum growth and function in lactating Holstein cows during spring and summer. Journal of Dairy Science 77: 735–739.
loss later in pregnancy. Effects of heat stress that can contribute to pregnancy loss at the morula stage or after are a reduction in circulating concentrations of progesterone (Figure 3), reduced uterine blood flow, and disruptions in the process by which the embryo antiluteolytic signal, interferon-, causes reduced synthesis and release of prostaglandin F2 by the uterus (see Reproduction, Events and Management: Pregnancy: Characteristics; Pregnancy: Physiology).
Fetal Growth Heat stress during the latter half of pregnancy has been implicated in intrauterine growth retardation, resulting in smaller birth weights (Table 1). Intra-uterine growth retardation has been seen in sheep, especially those
carrying twins, and in cattle. One consequence of intrauterine growth retardation caused by heat stress is increased neonatal mortality, especially in sheep. Some effects of heat stress on placental function represent redistribution of blood to the periphery and reduced perfusion of the placental vascular bed. However, placental blood flow per gram of fetus was similar both in the heat-stressed and in the control ewes in one study, and it may be that increased vascular resistance in the placenta caused by aberrant angiogenesis is more important. In addition, placental capacity to transport glucose using the glucose transporter GLUT8 can be reduced by heat stress. Another consequence of heat stress during gestation is a decrease in milk yield after calving. This effect presumably reflects alterations in secretion of placental hormones by the thermally compromised placenta.
Actions of Heat Stress on the Male Semen Quality Summer conditions in most regions of the world are severe enough to lower semen quality. In one study, ambient temperatures above 27 C for as little as 6 h day 1 were sufficient to lower semen quality in Bos taurus bulls. Effects of heat stress include a reduction in sperm concentration and progressive motility as well as an increase in sperm with abnormal morphology (Table 2 and Figure 4). The reason why germ cells are damaged by heat stress is not completely understood but increased oxidative stress in the testis is one cause. Spermatocytes, spermatids, and, to a lesser extent, B spermatogonia are the germ cells most sensitive to heat
Table 1 Spring lambing performance of ewes maintained in three environmental conditions during the last third of pregnancy Ewe treatment Item
Range control
Restricted feed
Hot room
Number of ewes pregnant Ewe conditiona Ewe dispositionb Lamb %, livec Lamb %, total Average birth weight, live (kg) Average birth weight, total (kg) Lamb conditione
15 2.0 0.0 2.0 0.0 167 19 173 18 4.69 0.26 4.57 0.26 1.9 0.2
15 2.1 0.1 2.0 0.1 173 15 173 15 4.16 0.16 4.16 0.16 2.0 0.1
14 2.0 0.0 2.0 0.0 100 26c 150 23 3.26 0.31d 3.18 0.22d 1.5 0.3d
a
1, fat; 2, good; 3, poor. 1, wild; 2, calm. Lambs pregnant ewes 100. d 0, dead; 1, weak; 2, average; 3, strong. e p < 0.01 after the removal of sex and multiple birth effects. Data are from Brown DE, Harrison PC, Hinds FC, Lewis JA, and Wallace MH (1977) Heat stress effects on fetal development during late gestation in the ewe. Journal of Animal Science 44: 442–446. b c
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570 Stress in Dairy Animals | Heat Stress: Effects on Reproduction Table 2 Mean semen characteristics of breeds of bulls before, during, and after heat stress
Initial motility
Abnormal spermatozoa
Spermatozoan concentration
Breeda
Periodb,c
%
% of initial
%
% of initial
106 ml
Holstein
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
53 45 34 42 48 33 46 43 48 35 23 43 49 40 48 51
100 85 64 79 100 69 96 90 100 73 48 90 100 82 98 104
9 13 53 29 11 21 38 23 16 21 33 20 16 12 22 18
100 144 589 467 100 191 345 209 100 131 206 125 100 75 138 113
1194 1303 537 460 1239 2150 1734 903 935 1322 476 523 1126 1291 852 1062
Red Sindhi Holstein
Brown Swiss
Red Sindhi Brown Swiss
1
% of initial 100 112 48 39 100 174 140 73 100 141 51 56 100 115 76 94
a
Crossbred–purebred period of interaction significant (p < 0.05) for all variables. 1, three weeks prior to heat stress (initial); 2, one week of heat stress; 3, one–three weeks after heat stress; 4, seven–nine weeks after heat stress. c Period effects significant (p < 0.01) for all variables. Data are from Johnston JE, Naelapaa H, and Frye Jr. JB (1963) Physiological responses of Holstein, Brown Swiss and Red Sindhi crossbred bulls exposed to high temperatures and humidities. Journal of Animal Science 22: 432–436. b
Motile sperm (%) 60.00 70.00
80.00
90.00
stress. One consequence is that semen characteristics are not immediately affected by heat stress because damaged spermatogenic cells do not enter ejaculates immediately. Similarly, elimination of heat stress does not lead to improved sperm quality until the damaged germ cells have completed spermatogenesis. In the bull, for example, where spermatogenesis takes about 61 days, semen characteristics change about 2 weeks after heat stress and do not return to normal until up to 8 weeks following the end of heat stress. Libido
40.00
50.00
Control Heat stressed
Pre
2 4 6 8 During treatment Weeks
2 4 6 Posttreatment
8
Figure 4 Time course of effects of heat stress on motility of ejaculated spermatozoa in bulls. Control bulls were maintained in a chamber at 23 + 1 C for 16 weeks. Heat-stressed bulls were maintained for 8 weeks in a chamber that was at 31 + 1 C for 8 h and 35 + 1 C for 16 h each day. Thereafter, heat-stressed bulls were returned to an environment of 23 + 1 C for 8 weeks. Reproduced with permission from Meyerhoeffer DC, Wettemann RP, Coleman SW, and Wells ME (1985) Reproductive criteria of beef bulls during and after exposure to increased ambient temperature. Journal of Animal Science 60: 352–357.
It is reasonable to expect that heat stress would decrease libido but the experimental evidence to support this idea does not exist. In addition, changes in testosterone secretion in response to heat stress are transient, with an initial decrease in testosterone secretion after heat stress reversed within 2 weeks.
Management to Reduce the Effects of Heat Stress Environmental Modifications to Reduce the Magnitude of Heat Stress As shown in Figure 5, a wide range of housing systems have been developed to reduce the magnitude of heat
Stress in Dairy Animals | Heat Stress: Effects on Reproduction
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Figure 5 (see color plate 90) Some housing systems to cool dairy cattle during heat stress. The shade structure shown in the upper left panel is insufficient for adequate cooling in lactating cows. The photograph in the lower left shows a barn with sprinklers and fans installed over the feeding area. Such a system can provide significant cooling but often reproduction is still compromised during heat stress. A barn with tunnel ventilation is shown in the upper right photograph. Tunnel ventilation can be an effective system for cooling cows but is also expensive to construct. The photograph in the lower right panel shows cows cooling themselves in a man-made cooling pond. Reproduced from Horizons with permission of Genex Cooperative (2006) 12(3): 12–13.
stress faced by lactating animals (see Dairy Farm Layout and Design: Building and Yard Design, Warm Climates). Provision of fans, sprinklers or misters, shade, and cooling ponds can reduce the magnitude of heat stress affecting the cow, improve the animal’s ability to regulate its body temperature, and enhance milk yield. There can be reproductive benefits also. For example, in a Mississippi study, fan cooling of shaded, lactating Holsteins that were synchronized with two injections of prostaglandin F2 resulted in 71% exhibiting estrus, compared to 33% for shaded cows without fan cooling. Under on-farm conditions, however, seasonal variation in reproductive function persists in most herds even when environmental modifications are present. Recently, the so-called tunnel ventilation barns and cross-ventilation barns have received much attention in popular press as effective structures for cooling cows. In these low-ridged barns, fans are located at one end of the barn to create a wind tunnel-like effect.
Evaporative cooling is by means of misters or evaporative pads through which air is drawn by the fans. A comprehensive study to evaluate reproductive function in tunnel ventilation or cross-ventilation barns has not yet been conducted. Overcoming Poor Detection of Estrus Detection of estrus during heat stress can be improved by various methods, including application of paint to the tailhead, commercial mount detectors, and radiotelemetric pressure transducers, such as the HeatWatchTM system. The advent of hormonal programs to synchronize ovulation for fixed-time insemination can eliminate the need for estrus detection during heat stress (see Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Ovulation and Insemination). In a study in Florida, Holsteins subjected to synchronized ovulation with timed insemination for
572 Stress in Dairy Animals | Heat Stress: Effects on Reproduction
Summer Winter
Natural service (%)
Natural + AI (%)
AI (%)
9.8 18.0
9.3 17.8
8.1 17.9
From De Vries A, Steenholdt C, and Risco CA. (2005) Pregnancy rates and milk production in natural service and artificially inseminated dairy herds in Florida and Georgia. Journal of Dairy Science 88: 948–956. Pregnancy rate was the proportion of cows that became pregnant out of those eligible to be bred in a 21-day period. Herds were designated natural service if 90–100% of cows were bred with bulls, natural + AI if the proportion of matings with bulls was from 11 to 89%, and AI if 0–10% of breedings were with bulls. Season mating system, p < 0.001.
the first insemination had more pregnancies (16.6%) at 90 days postpartum than did controls (9.8%). In another Florida study, pregnancy rates at 90 days were 34.3% for cows given the synchronized ovulation with timed insemination treatment compared to 14.3% in controls. The improvement in the proportion of cows pregnant through the use of a timed AI program is the result of inseminating more cows and not of fertility to service, which remains compromised by heat stress. Some producers utilize natural service to reduce the requirement for estrus detection and AI. A study in Florida indicates that the pregnancy rate (defined as the percentage of cows that become pregnant out of those eligible to be bred in a 21-day period) in summer was slightly higher for herds using bulls or a mix of bulls and AI than for herds using AI alone (Table 3). In winter, pregnancy rates were similar for all three types of herds. Loss of genetic progress and increased feed costs associated with natural service may negate the economic advantage of the higher pregnancy rates achieved with use of bulls.
Improving Embryo Survival One important cause of damage to gametes and the embryo due to heat stress is increased production of free radical species. There is some evidence that feeding the antioxidant -carotene can improve fertility in dairy cows exposed to heat stress; further studies are required to verify this effect. A variety of hormonal treatments has also been used in attempts to improve fertility in lactating dairy cows exposed to heat stress (see Reproduction, Events and Management: Mating Management: Fertility). Among these treatments are bovine somatotropin, human chorionic gonadotropin, and gonadotropin-releasing hormone. Unfortunately, no hormonal treatment that can consistently improve embryo survival has been identified. It is probable that damage to the oocyte before ovulation caused by heat stress leads to a reduction in the oocyte’s competence to be fertilized or to develop into an
embryo and that this damage is not reversible by hormonal treatments given at or after breeding. As mentioned previously, restoration of fertility after the end of the hot season is gradual because follicles that were damaged early in development need to complete folliculogenesis and be cleared from the ovary by atresia or ovulation. Research in Israel indicates that restoration of fertility in autumn can be hastened by ablation of follicles on the ovary by increasing follicular turnover through bovine somatotropin or follicle-stimulating hormone treatment, or by physical ablation of follicles.
Use of Embryo Transfer to Bypass Effects of Heat Stress on the Oocyte and Embryo From an examination of Figure 2, it is apparent that embryos that reach the blastocyst stage at day 7–8 after estrus have already passed through the most thermosensitive periods of development. It follows, therefore, that pregnancy rate for embryo transfer during summer would be higher than pregnancy rate for AI. Indeed, this is often the case, as illustrated in a large-scale study in Brazil in which lactating cows were either inseminated or subjected to embryo transfer. In cool weather, fertility was the same for both groups. However, the decline in fertility in summer seen in cows bred by AI did not occur for cows subjected to embryo transfer (Figure 6). 50 40 Pregnancy rate (%)
Table 3 Seasonal variation in pregnancy rate in dairies in Florida and Georgia as affected by mating system
30 20 10
ET Al
T < 22.5 °C
0 Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec.
Figure 6 Differences in pregnancy rate between embryo transfer recipients and inseminated animals in lactating cows in Brazil. Lactating Holstein cows either were inseminated or received a fresh or frozen-thawed embryo produced by superovulation. Data are either the number pregnant/number inseminated or number pregnant/number receiving an embryo. Months in which the average ambient air temperature was less than 22.5 C are shown with the gray bar. Note that embryo transfer increased pregnancy rate in hot weather but not in cool weather. Data are redrawn from Rodrigues CA, Ayres H, Reis EL, Nichi M, Bo GA, and Baruselli PS (2004) Artificial insemination and embryo transfer pregnancy rates in high production Holsetin breedings under tropical conditions. In: Proceedings of the 15th International Congress on Animal Reproduction, vol.2, p.396. Porto Seguro, Brazil (abstract) with permission.
Stress in Dairy Animals | Heat Stress: Effects on Reproduction
In fact, embryo transfer represents the only consistent method for improving pregnancy success in heatstressed cows. Estrus detection is not a limiting factor in the utilization of embryo transfer during heat stress because embryos can be transferred at a fixed time when ovulations are programmed using hormonal regimens developed for timed AI. One limitation is the high cost of embryo production, especially for embryos produced by superovulation or in vitro after harvesting oocytes via transvaginal ultrasound-guided follicular aspiration (see Gamete and Embryo Technology: In Vitro Fertilization; Multiple Ovulation and Embryo Transfer). The most inexpensive embryo is one produced by in vitro fertilization using oocytes recovered from abattoir material. The genetic merit of cows sent to slaughter is only slightly lower than average, and embryos can be produced inexpensively using semen from bulls of high genetic merit because one straw of semen can fertilize 100 or more oocytes.
Genetic Selection As illustrated in Table 2, there are distinct breed differences in the ability to regulate body temperature during heat stress. In cattle, Bos indicus are better able to regulate body temperature during heat stress than B. taurus, which evolved in temperate climates. Under conditions where feed availability, housing, and veterinary care are low, B. indicus dairy breeds or their crosses with B. taurus may produce a greater economic return than the breeds of B. taurus selected for milk yield. In most cases, however, European dairy breeds outperform B. indicus or B. indicus cross-breeds, even under situations where heat stress is severe. Even among European dairy breeds, however, there are genes that control the regulation of body temperature and selection for body temperature regulation is possible (see Genetics: Selection: Concepts). One gene that has been demonstrated to control body temperature is the ‘slick-hair’ gene. Introduced into Holsteins from Senepol cattle, cows with the slick-hair gene have short hair coats, increased capacity for sweating, and lower body temperatures during heat stress. There is some evidence for genes controlling cellular resistance to elevated temperature. Thus, preimplantation embryos from two thermally adapted breeds, the Brahman and Romosinuano, are more resistant to disruption in development when exposed to elevated culture temperature than embryos from the Angus, Holstein, or Angus Holstein. Identification of the genes responsible for these breed differences could lead to their introduction into thermosensitive breeds.
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Conclusions Lactating animals are among the mammals most sensitive to heat stress because of the metabolic demands of lactation. The result is reduced intensity of behavioral estrus, low fertility, and compromised fetal growth. In males, too, heat stress can affect reproduction with the most noticeable effects being compromised sperm output and increased sperm abnormalities. Prevention of heat stress effects on reproduction is difficult but the magnitude of effects can be reduced by provision of housing that contains shade, sprinklers or misters, and fans, and by using reproductive management tools such as timed AI and embryo transfer. See also: Dairy Farm Layout and Design: Building and Yard Design, Warm Climates. Gamete and Embryo Technology: Artificial Insemination; In Vitro Fertilization; Multiple Ovulation and Embryo Transfer. Genetics: Selection: Concepts. Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Mating Management: Artificial Insemination, Utilization; Mating Management: Detection of Estrus; Mating Management: Fertility; Pregnancy: Characteristics; Pregnancy: Physiology.
Further Reading Brown DE, Harrison PC, Hinds FC, Lewis JA, and Wallace MH (1977) Heat stress effects on fetal development during late gestation in the ewe. Journal of Animal Science 44: 442–446. Collier RJ, Dahl GE, and VanBaale MJ (2006) Major advances associated with environmental effects on dairy cattle. Journal of Dairy Science 89: 1244–1253. De Vries A, Steenholdt C, and Risco CA (2005) Pregnancy rates and milk production in n atural service and artificially inseminated dairy herds in Florida and Georgia. Hansen PJ (2007a) To be or not to be – determinants of embryonic survival following heat shock. Theriogenology 68S: S40–S48. Hansen PJ (2007b) Exploitation of genetic and physiological determinants of embryonic resistance to elevated temperature to improve embryonic survival in dairy cattle during heat stress. Theriogenology 68S: S242–S249. Hansen PJ (2009) Effects of heat stress on mammalian reproduction. Philosophical Transactions of the Royal Society, Series B 364: 3341–3350. Howell JL, Fuquay JW, and Smith AE (1994) Corpus luteum growth and function in lactating Holstein cows during spring and summer. Journal of Dairy Science 77: 735–739. Imtiaz Hussain SM, Fuquay JW, and Younas M (1992) Estrus cyclicity in nonlactating and lactating Holsteins and Jerseys in a Pakistani summer. Journal of Dairy Science 75: 2968–2975. Johnston JE, Naelapaa H, and Frye Jr.JB (1963) Physiological responses of Holstein, Brown Swiss and Red Sindhi crossbred bulls exposed to high temperatures and humidities. Journal of Animal Science 22: 432–436. Meyerhoeffer DC, Wettemann RP, Coleman SW, and Wells ME (1985) Reproductive criteria of beef bulls during and after exposure to increased ambient temperature Journal of Animal Science 60: 352–357. Rensis FD and Scaramuzzi RJ (2003) Heat stress and seasonal effects on reproduction in the dairy cow – a review. Theriogenology 60: 1139–1151.
574 Stress in Dairy Animals | Heat Stress: Effects on Reproduction Rodriques CA, Ayres H, Reis EL, Nichi M, Bo GA, and Baruselli PS (2004) Artificial insemination and embryo transfer pregnancy rates in high production Holstein breedings under tropical conditions. In: Proceedings of the 15th International Congress on Animal Reproduction, Vol. 2, p. 396. Porto Seguro, Brazil (abstract). Roth Z (2008) Heat stress, the follicle, and its enclosed oocyte: Mechanisms and potential strategies to improve fertility in dairy cows. Reproduction in Domestic Animals 43(supplement 2): 238–244. Rutledge JJ (2001) Use of embryo transfer and IVF to bypass effects of heat stress. Theriogenology 55: 105–111.
Sa´nchez JP, Misztal I, Aguilar I, Zumbach B, and Rekaya R (2009) Genetic determination of the onset of heat stress on daily milk production in the US Holstein cattle. Journal of Dairy Science 92: 4035–4045. Sartori R, Sartor-Bergfelt R, Mertens SA, Guenther JN, Parrish JJ, and Wiltbank MC (2002) Fertilization and early embryonic development in heifers and lactating cows in summer and lactating and dry cows in winter. Journal of Dairy Science 85: 2803–2812. Wolfenson D, Roth Z, and Meidan R (2000) Impaired reproduction in heat-stressed cattle: Basic and applied aspects. Animal Reproduction Science 60–61: 535–547.
Management Induced Stress in Dairy Cattle: Effects on Reproduction M C Lucy, H A Garverick, and D E Spiers, University of Missouri, Columbia, MO, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The correct definition of stress is important in any discussion of dairy reproduction. A stress or stressor is a force external to a system which acts to displace the system. A stress condition can be quantified and applied equally across animals. A strain is the animal’s response to stress (the magnitude of the displacement). The strain often represents a cost to the individual animal and the level of strain can vary from animal to animal. Stressors assume a variety of forms including environmental, physical, physiological, and psychological stressors. Environmental stress caused by heat and humidity in the summer is common in dairy cattle and its effects are discussed elsewhere in this encyclopedia. Physical stress involves an acute injury that causes a dramatic physiological response, for example, when a cow sustains a life-threatening injury involving hemorrhage. Physical stress is uncommon in dairy cattle. Physiological stress is common in dairy cattle and includes high milk yield and disease. Psychological stress is also common in dairy cattle. The common forms of psychological stress include social interactions with other farm animals and people. There are many examples of stress and the associated strain on dairy reproduction. For example, when dairy cows have high milk production (a stress), their reproductive efficiency will decrease (a strain that is caused by the high milk production). In this example, the stress is applied equally across animals but the strain will vary because some high-producing cows remain reproductively healthy whereas others become infertile.
Endocrine Pathways Associated with Stress and Reproduction It is impossible to understand the mechanisms linking stress and reproduction without a cursory knowledge of the pituitary gland and the endocrine mechanisms controlling pituitary function. The pituitary is an endocrine gland that synthesizes and secretes hormones that control many aspects of animal physiology. The major hormones synthesized and secreted by the pituitary are
growth hormone, prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), adrenocorticotrophic hormone (ACTH), and thyroid-stimulating hormone (TSH). Hormones of the pituitary play major roles in coordinating growth, reproduction, lactation, and metabolism of animals. They are also involved in the stress response. The pituitary is positioned below a specialized region of the brain called the hypothalamus. Neurons within the hypothalamus synthesize releasing factors that control pituitary hormone synthesis and secretion. Releasing factors are secreted into the median eminence, a region of the hypothalamus that contains the terminals of hypothalamic neurons as well as a capillary bed. Releasing factors enter the capillaries and travel from the median eminence to the pituitary via portal vessels. The portal vessels lead to a second capillary bed within the pituitary. The system of two capillary beds and the connecting blood vessels is called the hypothalamic-pituitary portal system. Binding of releasing factors to endocrine cells within the pituitary causes the secretion of pituitary hormones. The hypothalamus also synthesizes and secretes hormones that inhibit the secretion of hormones by the pituitary. The balance between stimulatory and inhibitory factors determines the level of secretion for individual pituitary hormones.
The Hypothalamic-Pituitary-Gonadal (HPG) Axis The hypothalamic releasing factor responsible for reproduction is gonadotropin-releasing hormone (GnRH). GnRH is released in pulses from the hypothalamus and the pulsatile release of GnRH causes the pulsatile release of LH from pituitary cells called gonadotrophs. The release of FSH from gonadotrophs is also under the control of GnRH but FSH release is less pulsatile because other hormones modify FSH release. Pulses of LH in blood stimulate ovarian follicular growth. A massive release of LH into blood (the LH surge) causes ovulation. FSH will also stimulate follicular growth but in most instances LH and not FSH is the limiting factor that controls reproductive processes in dairy cattle. Collectively, the endocrine system controlling reproduction is called the HPG axis (Figure 1).
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576 Stress in Dairy Animals | Management Induced Stress in Dairy Cattle: Effects on Reproduction
Figure 1 The interaction between the hypothalamic-pituitary-gonadal (HPG) axis and the hypothalamic-pituitary-adrenal (HPA) axis in animals. Neurons within the hypothalamus synthesize and secrete pulses of GnRH. The GnRH travels through the portal vessels into the pituitary where it causes the secretion of LH from pituitary gonadotrophs. Pulses of LH cause follicular growth. A high blood concentration of estradiol from the preovulatory follicle triggers an LH surge that causes ovulation. When the HPA axis is activated, CRH inhibits the activity of GnRH neurons and blocks GnRH release. Thus, follicular growth and ovulation are inhibited. Cortisol is also inhibitory to the reproduction because cortisol decreases the responsiveness of the gonadotrophs to GnRH and decreases the responsiveness of ovarian follicles to LH. Heavy black arrows show pathways for HPG inhibition by an activated HPA axis. The diagramed mechanisms are still under investigation and do not apply to all stresses that affect reproduction.
The Hypothalamic-Pituitary-Adrenal (HPA) Axis A second endocrine axis called the HPA axis is activated in response to stress. The magnitude of HPA axis activation is not an accurate reflection of the degree of stress. Furthermore, not all stressors activate the HPA axis. Nevertheless, there is evidence that the reproductive system can be affected through the HPA axis. Therefore, the HPA axis will be presented here. Neurons within the hypothalamus secrete corticotropin-releasing hormone (CRH) into the median eminence. The CRH travels through the hypothalamic-pituitary portal system and causes the release of ACTH from pituitary corticotroph cells. A second hypothalamic hormone, arginine vasopressin (AVP), can increase the activity of CRH on corticotrophs. ACTH travels through the blood and causes the adrenal gland to synthesize and secrete glucocorticoids. The primary glucocorticoid in dairy cattle is cortisol. Glucocorticoids are initially
permissive to the stress response and improve an animal’s ability to cope with stress. After their initial permissive effects, glucocorticoids are suppressive to the stress response and may play an important role in limiting the potentially damaging effects of stress-activated defense mechanisms.
Control of Reproductive Processes by the HPG axis LH is a critical hormone for the attainment of puberty in heifers and the resumption of normal estrous cycles in postpartum cows. In heifers, ovarian follicles grow and develop throughout the prepubertal period. Follicles grow in cycles (known as follicular waves) and achieve progressively larger sizes until they reach physiological maturity and trigger estrus and ovulation (puberty). Following ovulation, cells within the follicle differentiate
Stress in Dairy Animals | Management Induced Stress in Dairy Cattle: Effects on Reproduction
and form the corpus luteum (CL) that secretes the hormone progesterone that is required for pregnancy. The process is similar (but not identical) in postpartum cows. The maternal ovary is relatively inactive during pregnancy. Ovarian follicles grow and develop but follicles do not ovulate (i.e., release an oocyte for fertilization). This makes physiological sense because ovulation and the potential to establish pregnancy are futile in animals that are already pregnant. Shortly after calving, however, the ovary resumes the cyclical process of ovarian follicular growth. Ovarian follicular development within the first 2 weeks after calving can lead to ovulation (i.e., a follicle grows to ovulatory size and ovulates with subsequent CL formation). However, alternative ovarian follicular development may also occur. These alternative processes represent the strain caused by the stress of pregnancy, calving, disease, and lactation. The first possibility is anestrus. Anestrus occurs when ovarian follicles resume the cyclical process of development but fail to grow to an ovulatory size and fail to ovulate. A short period of postpartum anestrus (3–4 weeks) is normal for dairy cattle. Longer periods of postpartum anestrus lead to infertility because estrus is not expressed and cows do not ovulate. The second possibility is a follicular cyst. Follicles grow to an abnormally large size (a cyst) and fail to ovulate. Estrus may occur with cysts but cysts fail to ovulate resulting in infertility. In heifers, the frequency of LH pulses increases before puberty and stimulates maturation of preovulatory follicles. The same is true for postpartum cows; greater frequency of LH pulses leads to maturation of preovulatory follicles. Preovulatory follicles secrete large quantities of estradiol that cause the hypothalamus to release a surge of GnRH. The estradiol-dependent release of GnRH causes the LH surge. The LH surge is necessary for ovulation and formation of the CL. Stress can cause a strain on reproduction by slowing the pulsatile release of LH or blocking the LH surge.
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neurons decreases the pulsatile LH release and prevents the LH surge. Decreased LH pulsatility leads to a decrease in follicular growth that delays the onset of puberty in heifers and delays the onset of estrous cycles in postpartum cows. Blocking the LH surge prevents ovulation. The increase in cortisol that occurs in response to the increase in ACTH may also affect the endocrine physiology of GnRH and LH. Cortisol inhibits the pituitary release of LH in response to GnRH. Furthermore, cortisol may decrease responsiveness of ovarian follicles to LH. Therefore, GnRH release (through a CRHmediated mechanism), the release of LH in response to GnRH (through a cortisol-mediated mechanism), and the response of ovarian cells to LH (through a cortisolmediated mechanism) may all be inhibited when the HPA axis is activated by stress. Stressors that affect ovarian function in dairy cattle commonly do so by interfering with the normal process of LH release. Not all stressors, however, affect reproduction through the HPA axis. For example, undernutrition in dairy cattle (a stress) will cause a decrease in the frequency of LH pulses (a strain). The decrease in frequency of LH pulses delays puberty in prepubertal animals because LH secretion is inadequate and follicles fail to mature to a preovulatory size. Likewise, in postpartum cows, undernutrition or severe weight loss shortly after calving will decrease the frequency of LH pulses and cause anestrus. The exact mechanisms through which undernutrition slows the frequency of LH pulses are poorly understood but a variety of mechanisms that are acting independently from the HPA axis are probably involved (see later).
Common Stressors and Their Effects on Reproduction in Dairy Cattle Physiological Stressors Nutrition
Mechanisms Linking the HPG and HPA Axes Tentative links have been made between the HPG and the HPA axes. These links remain under scientific investigation and will require additional research. As mentioned above, not all stressors affect the HPA axis. Thus, stress-induced changes in the HPG axis that affect reproduction are not always caused by activation of the HPA axis. The stressors that cause activation of the HPA axis may cause infertility by affecting LH (Figure 1). Some CRH neurons within the hypothalamus terminate on the cell bodies of GnRH neurons. When CRH neurons are stimulated and release CRH, GnRH release from GnRH neurons may be blocked. The inhibition of GnRH
Underfeeding energy or protein or failing to supply adequate amounts of essential vitamins and minerals are stressors that affect reproduction in dairy cattle. Inadequate vitamin and mineral nutrition in dairy cattle is an uncommon stressor that will not be reviewed here. The stress of mineral and vitamin deficiency will have dramatic effects on health and reproductive function of the animal but effects will vary depending on the specific deficiency. Underfeeding energy is an important nutritional stressor because the pulsatility of LH depends on caloric intake. Postpartum cows are fed ad libitum but nonetheless may be ‘undernourished’ because they are producing large quantities of milk and cannot consume enough feed to meet their energy requirements. They reside,
578 Stress in Dairy Animals | Management Induced Stress in Dairy Cattle: Effects on Reproduction
therefore, in a state of negative energy balance for several weeks postpartum (see later). Cattle that are in negative energy balance fail to achieve normal LH pulsatility. In prepubertal heifers, the onset of puberty is caused by an increase in frequency of LH pulses. Undernutrition in heifers delays onset of puberty by delaying the age when the frequency of LH pulses increases. In postpartum cows, negative energy balance delays the onset of ovarian activity after calving through a similar mechanism. Cows that are in negative energy balance fail to resume normal LH secretory pulsatility and do not ovulate. These cows are termed ‘anovulatory’ (failing to ovulate) or ‘anestrus’ (failing to express estrus). Although the psychological stress of a short-term fast may activate the HPA axis, effects of chronic undernutrition on the HPG axis are probably independent of the HPA axis. Mechanisms linking undernutrition or negative energy balance to LH pulsatility are still obscure but may involve metabolic hormones like insulin, leptin, and insulin-like growth factors that are closely tied to nutrition and adipose tissue mass of the animal. Brain hormones like opiod peptides and neuropeptide Y also play a central role in regulating activity of GnRH neurons in response to changes in nutritional status. Once heifers are pubertal or once dairy cows initiate regular postpartum estrous cycles, the effects of undernutrition or negative energy balance are slightly different. Several weeks of severe undernutrition are required to force cattle back into the prepubertal state or back into anestrus (cows). Therefore, even when they are undernourished, cattle will temporarily (several estrous cycles) continue to express estrus and ovulate. Conception rate, however, is decreased in undernourished cattle. The decrease in conception rate may be caused by a decrease in progesterone synthesis by the CL of undernourished animals.
Protein intake also affects reproductive efficiency. Underfeeding protein results in slow growth in heifers and low milk production in lactating cows. Underfeeding protein can therefore delay onset of puberty and may affect interval to estrous cyclicity in postpartum cows. Overfeeding protein is the more common stress in lactating dairy cows. Diets high in crude protein are fed during early lactation so that milk production is increased. Lush springtime grasses can also have high protein content. The stress of high protein feeding causes a strain on reproductive efficiency. Blood concentrations of ammonia and urea are increased. The increase in ammonia and urea does not delay the time of postpartum cyclicity. However, increased ammonia and urea cause a change in uterine pH that alters uterine secretions. These secretory and pH changes create a toxic uterine environment and cause early embryonic death and infertility. High milk yield
Dairy cattle have been genetically selected for greater milk production. Currently, the best dairy cows are capable of producing over 30 000 kg of milk in a single lactation. The ability of dairy cattle to produce large quantities of milk depends on their ability to partition nutrients and body reserves toward milk production and away from other biological processes. In early lactation, the energy requirements for milk production increase rapidly and are greatest during peak lactation (4–6 weeks after calving). The ability of cows to consume feed, however, lags behind their ability to produce milk (Figure 2). Therefore, early postpartum cows must mobilize nutrients stored in the body (primarily adipose tissue) to support milk production during early lactation. Cows that cannot consume adequate feed are in ‘negative energy balance’ because their intake energy is less than the energy required for milk production and maintenance. By selecting for
Figure 2 Conceptual diagram of changes in milk production, dry matter intake, and energy balance in postpartum dairy cattle. Energy balance is negative in early postpartum dairy cattle because milk production increases faster than dry matter intake. Cows reach their energy balance nadir within 1–2 weeks postpartum.
Stress in Dairy Animals | Management Induced Stress in Dairy Cattle: Effects on Reproduction
greater milk production we have created cows that will enter negative energy balance and mobilize adipose tissue to support high milk production during early lactation. We have also created cows that are larger and have the body capacity to consume large quantities of feed. Negative energy balance is a stress that creates a strain on reproduction in dairy cows. Cows in more negative energy balance initiate estrous cycles later postpartum and are more likely to develop cystic ovarian follicles. Anestrus in negative energy balance cows is caused by reduced LH pulsatility. Cows in negative energy balance have fewer LH pulses than cows in positive energy balance. The mechanisms linking energy balance to LH pulsatility may be similar to those that link undernutrition to LH pulsatility. Once the cow becomes cyclic, the strain that high milk production places on fertility is much less. Several large epidemiological studies suggest that high-producing dairy cows are only slightly less fertile than low-producing dairy cows. Postpartum cows with a low body condition score (indicative of inadequate fat mass), however, are susceptible to infertility. The low body condition score during lactation is usually caused by extreme negative energy balance shortly after calving. High-producing as well as low-producing cows are susceptible to infertility caused by low body condition. Disease
The effects of increased milk production or rbST on reproductive performance are relatively minor compared to the effects of disease on reproduction (Figure 3). Diseases that place a strain on reproduction include metabolic diseases (ketosis and fatty liver), uterine and mammary infections (mastitis, metritis, and pyometra), and periparturient disorders (dystocia and retained placenta). The strain is manifested as either anestrus (secondary to a reduction in feed intake and excessive
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body condition loss), cystic ovarian follicles, or a decrease in conception rate following insemination. The mechanisms through which diseases affect reproductive processes vary. Dystocia predisposes cattle to retained placenta and uterine infection (metritis and pyometra). Uterine infections lead to a uterine environment that is not conducive to early embryonic development. Some forms of mastitis generate endotoxins that can activate the HPA axis. Activation of the HPA axis inhibits the reproductive axis by inhibiting the activity of GnRH neurons (see earlier). It is also possible for cytokines (hormones released from activated immune cells) to block GnRH release. The decrease in activity of GnRH neurons reduces LH secretion and can block follicular growth and ovulation. Acute mammary infections can also increase release of prostaglandin F2 from the uterus, which in pregnant cows is especially problematic because prostaglandin F2 can regress the CL and cause abortion. This may explain why dairy cows that contract mastitis within the first 21 days after insemination have a decrease in conception rate. Metabolic diseases (ketosis and fatty liver) are risk factors for infertility in dairy cattle but mechanisms through which their effects are exerted are less clear. Ketosis and fatty liver are sometimes secondary to a displaced abomasum, an inversion of the intestinal tract that blocks normal digestion and decreases feed intake. The drop in feed intake creates excessive mobilization of fatty acids, an excessive loss in body condition, accumulation of fatty acids in liver, and excess metabolism of fatty acids to ketones (ketosis). Displaced abomasum, fatty liver, and ketosis typically occur in early postpartum cows so that the strain on reproduction is initially manifested as anestrus. However, there can be carryover effects of these diseases on conception rates during the breeding period, especially in cows that lose considerable body condition.
Figure 3 Effect of milk yield (first 60-day cumulative yield in kilogram) and disease on hazard ratio for conception in 13 307 New York State Holstein cows. The hazard ratio is the relative risk of conception. A hazard ratio of 1.0 equates to a neutral effect (dashed line). Hazard ratios less than 1 indicate reduced likelihood of conception (i.e., cows experiencing a disease with a hazard ratio of 0.86 are 14% less likely to conceive compared to a healthy cow). p < 0.01. From Gro¨hn YT and Rajala-Schultz PJ (2000) Epidemiology of reproductive performance in dairy cows. Animal Reproduction Science 60–61: 605–614.
580 Stress in Dairy Animals | Management Induced Stress in Dairy Cattle: Effects on Reproduction
Housing and facilities
The consolidation of the dairy industry into larger farms with more cows per farm has necessitated movement of dairy cattle into confinement housing. Confinement housing is different from traditional grass pastures because cows are kept in large barns with concrete floors and open stalls (free stall barns) or in large corrals with concrete or dirt floors. Convenience and productivity of cows in confinement housing has forced the move from grass pastures. Moving cows into confinement housing and managing cows in larger herds are stressors that increase risk of mammary and uterine infections. Increases in mammary and uterine infections create a strain on reproductive efficiency (described earlier). Managing cows in large groups can also cause psychological stress (see later). In addition to disease stress, the stress of concrete floors also creates a strain on reproduction by decreasing estrous activity. Dairymen use mounting behavior to determine when a cow is in estrus and when cows should be inseminated. Duration of estrus, mounting activity, and standing activity are greater on dirt than on concrete. Therefore it is difficult to appropriately time insemination in cows that are housed on concrete floors because it is more difficult to determine when cows are in estrus. Concrete floors also predispose cows to lameness. Thus, poor expression of estrus may be secondary to lameness (a strain) caused by the stress of concrete floors on the feet and legs of cattle.
Psychological Stressors Transportation
Transportation of cattle in a vehicle (trucking) causes immediate activation of the HPA axis. Activation of the HPA axis can potentially inhibit the HPG axis through mechanisms described earlier but the effect is only temporary. Transportation stress is uncommon in lactating
dairy cows because dairy cows are generally not trucked during lactation. Heifers may be purchased and trucked from other locations prior to breeding but there is no evidence that trucking has any long-term effect on reproduction in cattle.
Social interactions with cattle
Cattle are social animals that live in groups with a dominance hierarchy. Mixing groups of cattle inevitability leads to decreased productivity because cows must spend time and energy to reestablish the dominance structure within the group. A recent study of dairy cows showed that dairy cows losing social status during the breeding period had a longer interval from calving to conception and required more inseminations per conception (Figure 4). The mechanisms linking changes in social status to reproductive efficiency are not clear but may involve activation of the HPA axis and subsequent inhibition of the HPG axis in animals that are subjected to aggression from other cows. Establishment of a dominance hierarchy depends on the ability of cattle to recognize one another. Cows may have difficulty recognizing one another when they are penned in large groups. The optimum group size for maintaining a stable social order may be as small as 50–60 cows. Therefore, cows in large dairy herds may be especially susceptible to psychological stress caused by an unstable social structure.
Isolation
Social interactions create stress in cattle (see earlier) but isolation from the herd also creates a stress. Isolation is a stress that activates the HPA axis. Although the effects of isolation on reproduction are unknown, activation of the HPA axis during isolation can potentially affect the HPG axis. Therefore, isolation could potentially create a strain on reproduction in dairy cows.
Figure 4 Calving-to-conception interval and inseminations per conception in dairy cows with increasing or decreasing social status. p < 0.05. From Dobson H and Smith RF (2000) What is stress, and how does it affect reproduction. Animal Reproduction Science 60–61: 742–752.
Stress in Dairy Animals | Management Induced Stress in Dairy Cattle: Effects on Reproduction
Human–cow interaction
Dairy cattle can recognize individual people and have better performance when handled by gentle people compared with aggressive people. For example, cows milked in the presence of an aggressive handler had 70% more residual milk left in the udder following milking. The effects on milk yield may be directly related to a stress response. Cows have an increase in heart rate during milking when an aggressive handler is present. The increase in heart rate is suggestive of epinephrine release and psychological stress caused by the aggressive person. To our knowledge, no studies have evaluated the effects of aggressive versus gentle handling on conception rate. However, there are clearly differences in conception rates across individuals that perform artificial insemination. Part or all of the conception rate differences could be related to handling of the animals before and during insemination.
Conclusions Stress is an everyday part of the lives of dairy cattle. Physiological and psychological stressors generally inhibit the HPG axis and cause a decrease in LH release. The decrease in LH release slows follicular growth and prevents ovulation. Some stressors activate the HPA axis and affect LH through a HPA-dependent mechanism. Other stressors (i.e., negative energy balance or undernutrition) have similar effects on LH but act through pathways that do not involve the HPA axis. A certain amount of management-induced stress is unavoidable in dairy farms. The best reproductive performance, however, will be achieved when management-induced stress is minimized so that the HPG axis can function at its maximal level.
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See also: Body Condition: Effects on Health, Milk Production, and Reproduction. Reproduction, Events and Management: Mating Management: Fertility; Estrous Cycles: Characteristics; Estrous Cycles: Postpartum Cyclicity. Stress in Dairy Animals: Heat Stress: Effects on Reproduction. Welfare of Animals, Political and Management Issues.
Further Reading Chagas LM, Bass JJ, Blache D, et al. (2007) Invited review: New perspectives on the roles of nutrition and metabolic priorities in the subfertility of high-producing dairy cows. Journal of Dairy Science 90: 4022–4032. Dobson H and Smith RF (2000) What is stress, and how does it affect reproduction. Animal Reproduction Science 60–61: 742–752. Dobson H, Smith R, Royal M, Knight Ch, and Sheldon I (2007) The highproducing dairy cow and its reproductive performance. Reproduction in Domestic Animals 42(supplement 2): 17–23. Gro¨hn YT and Rajala-Schultz PJ (2000) Epidemiology of reproductive performance in dairy cows. Animal Reproduction Science 60–61: 605–614. Lucy MC (2001) Reproductive loss in high-producing dairy cattle: Where will it end? Journal of Dairy Science 84: 1277–1293. Lucy MC (2005) Non-lactational traits of importance in dairy cows and applications for emerging biotechnologies. New Zealand Veterinary Journal 53: 406–415. Lucy MC (2007) Fertility in high-producing dairy cows: Reasons for decline and corrective strategies for sustainable improvement. Society for the Study of Reproduction and Fertility Supplement 64: 237–254. Matteri RL, Carroll JA, and Dyer CJ (2000) Neuroendocrine responses to stress. In: Moberg G and Mench J (eds.) The Biology of Animal Stress, pp. 43–76. Wallingford, UK: CAB International. Rushen J, DePassille AMB, and Munksgaard L (1999) Fear of people by cows and effects on milk yield, behavior, and heart rate at milking. Journal of Dairy Science 82: 720–727. Smith RF, Ghuman SP, Evans NP, Karsch FJ, and Dobson H (2003) Stress and the control of LH secretion in the ewe. Reproduction Supplement 61: 267–282. Swanson JC (1995) Farm animal well-being and intensive production systems. Journal of Animal Science 73: 2744–2751. von Borell E, Dobson H, and Prunier A (2007) Stress, behaviour and reproductive performance in female cattle and pigs. Hormones and Behavior 52: 130–138.
U UTILITIES AND EFFLUENT TREATMENT
Contents Water Supply Heat Generation Refrigeration Compressed Air Electricity Dairy Plant Effluents Design and Operation of Dairy Effluent Treatment Plants Reducing the Negative Impact of the Dairy Industry on the Environment
Water Supply F Riedewald, CEL-International, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by B. Creedon, Volume 4, pp 2470–2476, ª 2002, Elsevier Ltd.
Introduction Water is an important utility in the dairy Industry; its uses are numerous and diverse, ranging from product ingredient to cleaning agent. The utilization of water in the dairy industry can be divided into processes in which water has direct contact with the product, and those in which water has indirect contact with the product. To comply with EU legislation, water that comes into direct contact with the product (e.g., steam injection of milk in the production of UHT milk, or when used as a cleaning or rinsing agent) must be of ‘drinking water’ quality as defined by EU legislation (Council Directive 98/83/EC on the quality of water intended for human consumption). For water that has only indirect contact with the product, for example, when used as a coolant, the EU legislation has not stipulated any water quality
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requirements. However, in many dairy plants drinking water is used as the coolant to ensure that accidental leaks of cooling water into the product will not cause contamination. Some special applications such as readymade infant formula require water of higher specification than that of ‘drinking water’. Such applications are beyond the scope of this article. This article examines drinking water generation and distribution in the dairy industry, and also outlines treatment processes required for boiler and cooling waters.
Generating Drinking Water for the Dairy Industry Water of EU-defined ‘drinking water’ quality required in the dairy industry may be delivered to the facility from a municipal water distribution system, or it may be
Utilities and Effluent Treatment | Water Supply
generated onsite using natural water sources such as groundwater or river water.
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treatment processes routinely employed in the production of drinking water: Removal of suspended solids and turbidity
Drinking Water Sourced from Municipal Water Systems Should the water be supplied to the site via a municipal drinking water system, filters are typically installed at the factory boundary to ensure that the intake of water is free from particulate contamination, which might have been picked up en route. Finer-rated filters may be installed closer to delivery points of supplies that feed particularly sensitive processes. EN13445 or similar standards may provide guidance on the selection of filters for drinking water systems (DWSs).
Water from Natural Sources Untreated water from natural sources used for DW generation onsite may contain natural minerals, gases, and possibly some • dissolved other chemicals debris – vegetable and mineral • insoluble microorganisms – living or dead. • Some of these constituents may make the water unsuitable for use in specific applications in the dairy industry (see Table 1). The aim of water treatment is simply to modify these constituents to render the water suitable for a desired application. The following are some water
Table 1 Specific problems caused by common constituents of water Suspended solids
Iron and manganese Microorganisms
Organic compounds Calcium and magnesium
Dissolved gases (O2 and CO2) Other dissolved materials Total dissolved solids (TDS)
Settlement to form deposits on equipment and piping Facilitation of the growth of microorganisms Fouling and staining of equipment and piping Microbiological contamination of equipment surfaces Secondary contamination of products or potable supply Promotion of growth of microorganisms Imparting of taste or odor to product Staining of equipment and piping Scale formation when water is heated or evaporated Increase in detergency requirement (and reduced performance) Increased corrosion of pipework, etc. Contamination of product Increased blowdown requirement in boiler and cooling systems
Suspended solids and turbidity are typically removed by coagulation, flocculation, and settlement, followed by filtration. Chemical coagulants exploit the electrostatic charges on suspended particles, encouraging coalescence to form larger particles. Flocculants provide a chemical bridging between these particles to form yet larger and heavier flocs that may be removed by sedimentation. After flocculation the suspended solids are allowed to settle out. The clear supernatant liquid is removed and filtered. The process of filtration can be achieved by a number of methods, although the traditional method of sand filtration is still the most common. The water is allowed to percolate through appropriately graded sand and suspended materials become trapped within the bed. A backwash process is used to clean and regenerate the sand filters periodically. For filtering smaller amounts of water, disposable or washable cartridge-type filters may be suitable. There are two standard types of cartridge: the depth type (where the solids are trapped within the cartridge itself) and the pleated filter type (which depends on the surface layer to perform the filter duty, similar to filter papers used in the laboratory). Most filter elements are disposable, though washable types are available. Cartridge filters are rated either absolute or nominal, depending on the percentage of suspended solids of a particular size held back by the filter. Water can be filtered up to 5 nm using present technology but, in general, the finer the filtered particle specification, the more expensive the element. Bag filters offer a variation on the cartridge filter and can normally hold a larger quantity of filtered materials between filter changes. The water is fed into the centre of the bag and forced to flow outward through the bag to service. Filtered material trapped within the bag is removed periodically by manual or automatic procedures. Many systems depend on periodic disposal of the bag. The limiting factors for the sizing of filters are the maximum flow rate required, the concentration of suspended solids present, and the desired treated water quality.
Removal of Organic Compounds Organic materials appear occasionally in groundwaters and commonly in surface- and postprocessing waters. The high costs of both water extraction and effluent treatment have led to a renewed interest in techniques for the recovery and reuse of postprocessing waters, for example, the second condensate from milk evaporators, for reuse as process water.
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One method for removing organics in this scenario is dosage of the condensate to a high level with an oxidizing agent. Chlorination at 6–10 mg l 1 or ozonation at 0.1–1.0 mg l 1 per 1 mg l 1 of organic material present would suffice. The contact time required depends on the oxidant used. The treated water is then passed through a carbon filter that destroys residual oxidizing agent and removes excess and oxidized organics by absorption into the carbon matrix. Carbon filters require periodic backwashing and the activated medium requires replacement from time to time. This process combines microbiological disinfection with organic removal. Ultrafiltration is also used to remove organic contaminants from water. These filters comprise molecular pore sizes of 5–10 nm and are used in a cross-flow configuration. Water is split into two streams by the ultrafiltration element. The reject stream, containing the bulk of the solid materials, is diverted to the drain while the product water or permeate becomes the treated water stream. The cross-flow configuration allows the process stream waste constantly and tangentially to wash the upstream surface of the membranes, thereby reducing the risk of fouling. Removal of hardness
Scale formation and degradation of detergents due to the presence of calcium and magnesium salts are widely experienced problems in the dairy industry. The most common method of removing hardness salts is by baseexchange softening. Typically, the water is passed through an ion-exchange resin, held in a pressure vessel fitted with some type of control valve system, usually automatic. Base exchange removes the hardness salts by adsorbing calcium and magnesium ions on to the resin in exchange for the ionic equivalent in sodium ions. Sodium salts rarely form scale. In time the resin will become saturated with the adsorbed hardness metal ions, and regeneration is effected by passing a concentrated sodium solution (NaCl brine) through the resin bed. This solution displaces calcium and magnesium ions and leaves a sodium-rich resin recharged for the next service period. Concentrated hardness salts are washed to the drain during regeneration. The process involves exchange of metals and does not lead to a reduction in the overall dissolved solids. Water softeners should be sized to maximum flow rate, total hardness of the influent, and the required hardness of the effluent, thus determining the quantity of resin and the control-valve design. Reduction in dissolved solids concentration
It is sometimes desirable to reduce the total dissolved solids (TDS) in the water supply. Two processes in the dairy industry requiring low TDS are waters used for boiler makeup or in the manufacture of cream liqueurs. Two systems are commonly in use.
Ion exchange
Ion-exchange systems typically use two resin beds, housed in separate pressure vessels in series. The first stage contains a cation exchange resin that will exchange positively charged metal ions for hydrogen ions. The cation exchanger is normally regenerated (while offline) using hydrochloric acid. The water from the cation exchanger is fed to the anion exchanger unit, which exchanges the negatively charged anionic salts (e.g., chloride, bicarbonate) for hydroxide ions. The anion exchanger is regenerated using a caustic (sodium hydroxide) solution. The resultant hydrogen and hydroxyl ions react to form water. The major factors affecting the size of deionization equipment are flow rate and the quantity of dissolved solids in the raw water. Reverse osmosis
The second method of TDS reduction in common use is reverse osmosis, which uses a membrane system similar to that described for ultrafiltration. However, this membrane has a pore size of 0.1–1.0 nm. By applying upstream pressure higher than the natural osmotic pressure of the feed water, water can be forced to flow through the membrane. This effectively allows the dissolved materials to be concentrated in the reject stream and produces a purer permeate stream with a low dissolved-solid content. Reverse osmosis is particularly cost-effective for waters with very high TDS. Typically, chemical pretreatment is required. Removal of microbial contamination
Disinfection of water is the process of destroying or inactivating the microorganisms present in the water and thereby providing drinking water fit for human consumption. Disinfection of water entering a water distribution system can be relatively easily achieved; however, the subsequent maintenance of the water distribution system itself to maintain water quality within the distribution system offers more challenges. Both will be considered together in the following section.
Disinfection and Sanitization of DWSs Depending on the source of the water, conditions of use, and magnitude and extent of microbiological contamination of the water, in addition to microbiological contamination of the distribution surfaces in the form of a biofilm, disinfection may be needed on a continuous basis or occasionally as shock short-term sanitization (see Table 2) should the microbial contamination in the DWSs exceed some threshold.
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Table 2 Typical concentrations and application times for shock sanitization of some chemicals
Chemical
Normal conc. (mg l 1)
Min. conc. (mg l 1)
Application time (hours)
Hypochlorite Chlordioxide Hydrogen peroxide
50 as Chlorine 5–10 as Chlorine 150
10 as Chlorine 50 as Chlorine 150
8–12 8–12 24
If the presence of a potentially contaminating biofilm is factored in and understood, then the management of the quality of the DWS becomes easier to control (see Biofilm Formation). In low-nutrient DWSs, bacteria can only grow and multiply in the so-called biofilms attached to surfaces; planktonic, or free-floating, bacterial cells released from the biofilm are important for dissemination only. These planktonic bacterial cells are easier to enumerate and destroy than the bacterial cells attached to a surface existing in a community as a biofilm. Because of the structure of the biofilm, with its protective polysaccharide coating and altered phenotype cells, bacteria in biofilms are greatly protected from chemical attack from biocides, drying, and mechanical removal. Bacteria in biofilms may be up to 500 times more resistant to chlorine than in their planktonic state, well exceeding shock concentration limits.
In practice biofilm activity can only be suppressed below a certain level, but not completely reduced. Therefore, only disinfection, not sterilization, of DWS can be achieved in practice. There are three commonly used techniques for the destruction of microorganisms in water. The advantages and disadvantages of these are summarized in Table 3
Oxidizing Agents Oxidizing agents in common use are chlorine and its compounds (e.g., calcium hypochloride, sodium hypochloride), ozone, and chlorine dioxide (bromine normally in cooling systems). All oxidizing agents require an adequate contact time to disinfect properly. Stronger oxidizing agents require lower concentrations and shorter contact times. The water may be treated before the
Table 3 Advantages and disadvantages of most commonly used disinfection methods for water supply Chlorination Advantages
Disadvantages
Very effective; proven in practice Provides residual disinfectant Residual easy to measure
May give the water a chlorine taste Turbidity may reduce the effectiveness of chlorine May require high concentrations of chlorine to kill certain bacteria and viruses Special storage and handling requirements for gaseous chlorine are required May cause corrosion of system components
Chlorine readily available at reasonable cost Can be used for multiple water problems (bacteria, iron, etc.) Appropriate as both primary and secondary disinfectant Ozone Advantages Very effective being a strong oxidant, proven in practice Effective against virtually all bacteria and viruses
Ultraviolet light Advantages No chemical added to the water. Does not change taste or odor of water nor causes corrosion of system components Kills bacteria and viruses almost immediately Simple operation and maintenance for high-quality water Handling and storage of chemicals is not required
Disadvantages Must be generated onsite, as ozone is unstable. Ozone generator is more complex than chlorination generator Relatively high cost May cause corrosion of system components May require a secondary disinfectant (chlorine), as ozone does not maintain adequate disinfection residual Disadvantages Relatively high capital cost High electrical demand Local operation only, may require a secondary disinfectant, as there is no disinfection residual Requires pretreatment of surface water as water must be clear Requires frequent cleaning and installation of new UV lamps
586 Utilities and Effluent Treatment | Water Supply
storage tanks or by installing an inline contact pressure vessel after the dosing point. Ozone is a replacement for chlorine in some applications. As a strong oxidizing agent that does not form trihalogenated methanes (THMs), it is particularly suited for disinfecting waters with a high content of organics or colorants. Ozone naturally decomposes rapidly to oxygen, and for this reason does not provide the extended postprotection offered by other oxidizing compounds. Water treated with ozone may be chlorinated to a low concentration to provide postprotection. All of the above chemicals should be dosed according to the volume of water to be treated, and in continuous processes the chemical flow rate needs to be set in proportion to the water flow rate so that the required concentration is reached. Chemical concentration is often monitored by an online analyzer to allow for automatic control of the chemical flow rate. Ultraviolet Irradiation Ultraviolet (UV) radiation used to control microorganisms has some advantages over chemical methods, which entail inconvenient and potentially dangerous handling. Chemicals may also leave undesirable residual products in the water. The major disadvantage of UV systems lies in the failure to provide postprotection. There is, then, the possibility of water becoming re-infected after treatment. Ideally, UV systems should be used as close to the point of use as possible. Sizing to the particular flow rate is critically important, as is matching to the UV transmittance of the pretreated water.
Nonoxidizing Biocides Nonoxidizing biocides are usually microbiologically toxic organics and find maximum application in the treatment of cooling- and chilled-water systems. Typically, two chemicals are used alternatively to prevent the development of resistant strains. Typically, DWS designed to the latest design standards, for example, EN 806, should not require disinfection. However, should it become necessary, the
system should first be surveyed for problem areas, which should be rectified before disinfection to avoid rapid reoccurrence of microbial contamination. Typically, chemical disinfection is used. Disinfection of DWS itself is best applied by specialist companies. As a guideline as to when it may be necessary to ¨ N B5019 may sanitize a DWS, the Austrian standard O be helpful. Table 4 gives some details.
Guidelines for DWS Design and Operation Drinking water is a valuable resource needing protection from contamination during its distribution from the source to the tap. Therefore, the water must be distributed in a suitable manner preventing contamination. The DWSs designed to the latest standards, for example, EN806, for distributions systems within facilities are not likely to exhibit premature aging (corrosion) or excessive microbial growth. The design and maintenance of drinking water generation and distribution systems requires specialized knowledge. However, some general guidelines can be given as follows: 1. Do not Oversize To avoid the formation of local corrosion nests and excessive microbial contamination in stagnation and areas of low flow, drinking water distribution systems should not be oversized. Correct sizing of hot-water storage is essential to avoid temperature gradients in storage tanks, which may encourage bacteria to grow in some areas of the tank. 2. Avoid Dead Legs Dead legs or rarely used pipe sections where water may remain stagnant for long periods should be avoided. This is particularly important for hotwater systems, as in the stagnant sections the normal hotwater temperature may not be able to be maintained, which in turn may lead to excessive microbial proliferation. In addition, dead legs may reduce the service life of the pipes due to corrosion. 3. Positive Pressure Maintain a positive pressure in the DWS to prevent inward entry of contamination. 4. Insulate Pipes To impede microbial growth the temperature of the water in the cold-water pipes should not exceed 20 C. Insulation of the cold water pipes which
¨ N B5019 Table 4 When is sanitization necessary according to Austrian standard O Legionella cbu/100 ml
Normal conc. (mg l 1)cfu/l
Assessment
Action
>10 000 1001–10 000 101–1000 10–100 <10 Nondetectable
>100 000 10 001–100 000 1001–10 000 100–1000 <100 Nondetectable
Very high concentration High concentration Medium concentration Low concentration Low concentration Legionella not detectable
Stop using system for certain applications, i.e. showers Sanitization is required Sanitization may be required Sanitization may be required No sanitization necessary None
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run close to hot services (steam, condensate, hot water, etc.) may be necessary. 5. Material of Construction Many different materials from plastics (PVC, PP, PE, etc.) to steels (ductile iron, galvanized steel, stainless steel) are used to convey drinking water. While no material of construction can be considered ideal, all materials used for a DWS should be approved for use by an authorized body. A major problem with construction materials is corrosion. Corrosion is a term used to describe deterioration of materials over time. Corrosion may contaminate the DWS with corrosion products, reduce the throughput of the pipes, and lead to a foul taste and to other problems (see Plant and Equipment: Corrosion). Before these symptoms are detected, corrosion may have remained undetected for a long time. The root cause of corrosion in DWS may have many sources: galvanic, microbial influenced, pitting, and crevicing, to name but a few. 6. Backflow Prevention Backflow from non-DWS into the drinking water distribution system may contaminate the drinking water. Therefore all drinking water standards stipulate backflow preventers. The incoming water from the municipal water distribution system must be protected from contamination by a suitable backflow preventer (see EN 1717). Water taps are generally protected from backflow by an air gap of a suitable length (>50 mm). Firewater, boiler water, wastewater, and other services not directly related to a DWS must also be segregated by backflow preventers from the DWS (see EN 1717). 7. Construction, Pressure Testing, and Documentation Install pipes in a hygienic manner to avoid contamination of the pipes, valves, and other DWS components during the construction. Pressure tests should be carried out using either drinking water or oil-free air. Construction debris should be removed using a drinking water rinse. The documentation should as a minimum include all relevant P&IDs, layouts, maintenance records, and certificates on the materials of construction. 8. Regular Inspection and Maintenance Regular inspection and maintenance will help to maintain the availability of the DWS for the lifetime of the plant.
the operating pressure of the boiler, the purer the boiler feed water must be; for details, see standards such as EN 12953. Evaporative cooling systems should also be fitted with automatic blowdown systems for TDS control. Cooling towers are normally dosed with biocides and either a scale or a corrosion inhibitor. Chilled-water systems are typically treated with a corrosion inhibitor only, though microbiological protection may be required in some instances.
Boiler Water and Cooling Water Treatment
Further Reading
Treatment of makeup water for boilers frequently requires special consideration and is therefore often separated from that of the main water supply. Boiler water influent is known as feed water and needs to have minimal dissolved solids and hardness, and low corrosive qualities. As a general rule the higher
Costerton JW (2007) The Biofilm Primer. Berlin, Heidelberg: Springer. Faust SD and Aly OM (1998) Chemistry of Water Treatment, 2nd edn. Washington, DC: American Water Works Association. Flynn D (1988) The Nalco Water Handbook, 2nd edn. New York: McGraw-Hill. Kreysa G and Schutze M (2009) Corrosion Handbook: Drinking Water, Waste Water (Municipal), Waste Water (Industrial), Vol. 4: Corrosive
Appendix A List of Some European Standards EN 806 Parts 1–5: On the conveying of water for human consumption. EN 1717: Protection against pollution of potable water in water installations and general requirements of devices to prevent pollution by backflow. EN 12953-10 Shell boilers – Part 10: Requirements for feedwater and boiler water quality. EN ISO 19458: Water quality – Sampling for microbiological analysis. prEN 14897: Water conditioning equipment inside buildings – Disinfection devices using ultraviolet radiation – Requirements for performances, safety, and testing. EN 13445 Part 1–3: Water conditioning equipment inside buildings – Mechanical filters. EN 14812 Water conditioning equipment inside buildings. Chemical dosing systems. Preset dosing systems. Requirements for performance, safety, and testing. ¨ NORM B5019 (Austrian standard) Hygienic aspects of O planning, construction, operation, maintenance, surveillance, and rehabilitation of central heating installations for drinking water (in German).
See also: Plant and Equipment: Corrosion; Instrumentation and Process Control: Process Control; Process and Plant Design; Utilities and Effluent Treatment: Dairy Plant Effluents; Design and Operation of Dairy Effluent Treatment Plants.
588 Utilities and Effluent Treatment | Water Supply Agents and Their Interaction with Materials, 2nd edn. Weinheim: Wiley VCH. Letterman RD (1999) Water Quality and Treatment Handbook, 5th edn. New York: McGraw-Hill. Mann HT and Williamson D (1982) Water Treatment and Sanitation, 2nd edn. Rugby: ITDG. Meltzer TH (1997) High Purity Water Preparation for the Semiconductor, Pharmaceutical, and Power Industries. Littleton, Colorado: Tall Oaks Books.
Letterman RD (ed.) (1999) Water Quality & Treatment Handbook: A Handbook of Community Water Supplies, 5th edn. New York: McGraw-Hill. US Environmental Protection Agency (2002) Ground Water and Drinking Water, Health Risks from Microbial Growth and Biofilms in Drinking Water Distribution Systems. www.epa.gov/ogwdw/ disinfection/tcr/pdfs/whitepaper_tcr_biofilms.pdf (accessed June 2010) Venkateswarlu KS (1996) Water Chemistry–Industrial and Power Station Water Treatment, 1st edn. Mumbai: New Age International.
Heat Generation O S Mota, University of Porto, Porto, Portugal ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2476–2482, ª 2002, Elsevier Ltd., with revisions made by the Editor.
Introduction Heat generation is a very broad subject and has many applications. These may be classified according to the amount of power involved, e.g. high power values are transferred in power plants where the expansion of water vapor in turbines generates electricity. Low powers are frequent in industrial applications. In the dairy industry, heat generation is a vital service, because many of the processes require heat and vapor. Some examples include pasteurizing milk by heating it to a temperature of about 72 C or above, heating milk with hot water in a heat exchanger, cooking coagulated milk and producing hot water for washing, all of which are processes in the production of cheese and in the manufacture of concentrated, dried or sterilized milk products. Water is abundant in nature and is the preferred working fluid for heat transfer because of its thermodynamic properties.
Properties of Water and Steam The thermodynamic properties of water have been determined experimentally for equilibrium states. A thermodynamic equilibrium state is reached when mechanical, thermal, chemical and phase equilibrium exists. It is characterized by two independent properties. Consider a constant mass of liquid water at pressure P1 ¼ 1 kPa and temperature T1 ¼ 20 C (state 1) contained in a piston-cylinder arrangement (Figure 1). Heating the system with an external heat source will maintain a constant pressure and cause temperature and volume to increase. As can be seen in Figure 2, the system undergoes a change of state, from state 1 to state 2. As long as the temperature (T) is below the saturation temperature (Tsat 100 C), vaporization will not occur. This region is the liquid water region (T < Tsat). Additional heating will take the system to Tsat, bringing the liquid to the saturated state, state 3. Any more heating causes part of the liquid to vaporize. It is observed that, during this process, the temperature and pressure are constant and dependent variables, and the volume increases.
The heat transferred during the liquid–vapor change is known as the latent heat of vaporization, and the mixture of saturated liquid in equilibrium with saturated vapor is called humid vapor. In this region, state 4 for example, the state of the system may be defined by using the fraction relating the saturated vapor mass, mv, to the total mass of the mixture, mv þ ml: x¼
mv mv þ m1
ð1Þ
where ml is the saturated liquid mass. This parameter changes from 0% (saturated liquid) to 100% (saturated vapor). It is used to determine the specific volume of humid vapor, v ¼ V/m (where V/m is the volume of the system divided by its mass): v ¼ v1 þ x ðvv – vl Þ
ð2Þ
where vv is the specific volume of saturated vapor (some authors prefer vg) and vl is the specific volume of saturated liquid (some authors use vf) (see Figure 2). This relationship is valid for other specific properties, such as internal energy, u, enthalpy, H ¼ u þ Pv, and entropy, S. The vaporization process ends at state 5, at the instant when all the liquid is completely vaporized and only saturated vapor is present. Further heating will cause increases in temperature and volume and take the system to a state called the overheated vapor state (T > Tsat), state 6 in Figure 2. If the entire heating process described above is repeated for another pressure, achieved by putting weights on the piston, the lines obtained correspond to P2, P3 etc. in Figure 3. It can be observed from Figure 3 that the horizontal part of the isobar (phase change) tends to be smaller as pressure increases, until it disappears at pressure Pc ¼ 22.1 MPa, the critical point pressure corresponding to Tc ¼ 374.2 C, vc ¼ 0.00318 m3 kg1, where instantaneous vaporization of liquid occurs. Joining the points corresponding to the saturated liquid states in Figure 3 (i.e. a, b and c) results in the saturated liquid line. Linking the saturated vapor points (d, e and f) gives rise to the saturated vapor line. These two lines meet at the critical point (see Figure 4).
589
590 Utilities and Effluent Treatment | Heat Generation T
Critical point Saturated vapor line Saturated liquid line
Water
Liquid
Q
Humid vapor
Over-heated vapor
Figure 1 Piston–cylinder arrangement containing water.
V
v
V L
T (°C)
L
P = 1 bar Figure 4 Representation of the saturated line of water in a diagram of temperature versus specific volume.
6 3
100
5
4
into hot water, or into steam, by burning fuel that releases heat to the working fluid.
2 20
1
ν1
νv
ν (m3 kg–1)
Figure 2 Temperature (T) changes for a specific volume of water during isobaric heating.
PC T (°C)
Critical point P3
TC = 374.2
P2 c b
100
a
P1 =1 bar
d e f
νc = 0.00318
ν (m3 kg–1)
Figure 3 Temperature versus specific volume of water for various pressures.
In problem-solving, the thermodynamic properties of water are frequently obtained from tables: saturated vapor tables represent the saturated line, and overheated vapor tables represent both the overheated vapor and the liquid regions. There are also expressions that establish property relations but these are very awkward to use. In more advanced cases, computer programs generate the property values. In most of the applications, the water temperature lies between freezing point and the critical point. Using water in this range of temperatures takes advantage of the latent heat. Boilers are the equipment used to convert cold water
General Classification of Steam Boilers Boilers are classified according to different characteristics as follows: 1. Location. The boiler may be moveable or installed in a fixed place. 2. Fuel. The fuel may be fossil, such as coal, fuel oil and natural gas, residual, or there may be none at all. In the latter case, flue gases from industrial processes or internal combustion engines heat the working fluid. 3. Working fluid. Water is the usual working fluid but other fluids may be used, such as thermal fluids. Water is treated to remove impurities. The pH must be controlled to prevent corrosion and should be maintained between 9.5 and 10.5, depending on boiler pressure. 4. Pressure level of the working fluid. The fluid undergoes a phase change and the energy required to vaporize the liquid varies with pressure. Therefore, boilers may be classified according to the working fluid pressure as: lowpressure boilers (P < 0.15 MPa), medium-pressure boilers (0.15 MPa < P < 9.0 MPa), high-pressure boilers (9.0 MPa < P < Pcrit (critical point pressure)) and very high-pressure boilers (P > Pcrit – in this case, vaporization is instantaneous). 5. Form of flow promotion. The working fluid may travel through the boiler by natural convection or by forced convection. 6. Flow location. In water-tube boilers, the water flows inside the tubes while the hot gas products of combustion heat the tubes from the exterior. If, instead, the combustion gases flow inside the tubes, heating them internally, and the water surrounds the tubes exteriorly, then the boiler is of the fire tube type.
Utilities and Effluent Treatment | Heat Generation
7. Tubular bank configuration. Tubes may be positioned horizontally, vertically or inclined. The tubes connect to boiler headers that are used to collect steam and water for distribution to other parts of the boiler or users. 8. Furnace position. The boiler is internally fired if the boiler shell contains an internal furnace, or externally fired if the combustion takes place outside the boiler shell and the products of combustion are directed to flow within the tubes inside the shell. 9. Firing arrangements. The firing arrangements may be horizontal (flame travels horizontally into the furnace; used in small- to medium-capacity boilers), vertical (the burner is located at the top of the furnace and the flame travels downward to the bottom of the furnace; used in small-capacity, fire-type tube boilers and also in largecapacity water-tube boilers that burn pulverized coal) or tangential (the furnace has a square or rectangular geometry and, at each of the four corners, the flame travels tangentially to a ‘fire ball’ where all the flames meet, located at the center of the furnace). The great turbulence favors the mixing of the fuel and air. 10. Number of combustion gas passes. The design may include one, two, three or four passes through the boiler. The latter configuration is the most efficient; however, the greater the number of gas passes, the more fan power is required. In the dairy industry, small- to medium-capacity unit boilers are used. They may be water-tube or fire-tube boilers, and are equipped with all the boiler auxiliaries, such as water pumps, fans, burners, fittings, controls, etc. The only exterior connections that need to be made are electrical, water, fuel and stack. Stacks, made of steel or concrete, are used to deliver the flue gases to the atmosphere. In this way, dispersion of particles is simplified and has a low impact on the environment. Prefabricated unit boilers are more advantageous than boilers constructed on site due to ease of installation, compactness of size and lower cost. They are limited to the existing design and produce small steam flow rates, below 250 103 kg h1. The heart of the boiler is the furnace where combustion takes place.
Combustion Combustion is a process of rapid chemical combination of fuel with air that releases the chemical energy of the fuel. Air and fuel are the reactants in the combustion reaction and the by-product is the flue gases (products of combustion) and heat. It may be represented by the following relation:
fuel þ air ! products of combustion þ heat
591 ð3Þ
For this process to occur efficiently, good mixing between the fuel and the air (essentially a mixture of oxygen (O2) and nitrogen (N2)) must be accomplished by intensified turbulence, and the ignition temperature of the fuel must be reached. In addition enough time must be allowed for the fuel to burn in the furnace. Normally, fossil fuels are burnt and these always have in common carbon (C) and hydrogen (H). However, the composition varies greatly with the fuel type: 1. Coal is a solid fuel consisting of carbon, hydrogen, moisture (water), nitrogen, sulfur and ash. It is classified according to the carbon content: anthracite coal has 86–98% carbon (it has a caloric value of approximately 35 MJ kg1, determined experimentally), bituminous coal has 70–86% carbon (and a caloric value of 25–36 MJ kg1), lignite coal has a carbon content up to 70%. Coal needs to be prepared before combustion and its supply to the boiler has to be controlled. It is difficult to burn and produces a high level of ash and sulfur. 2. Fuel oil is a liquid fuel classified according to its ash and moisture content. Its caloric value is the highest of all fossil fuels and may be as high as 46 MJ kg1. Fuel oil has advantages over coal in requiring less storage space, yielding less ash, being easier to control and requiring less equipment. However, it is more expensive because its distribution is not so even around the world. 3. Natural gas is a gaseous fuel with a caloric value of approximately 37 MJ m3. It has advantages over other fossil fuels in requiring the least amount of equipment, being easy to control, mixing well with air and requiring the least amount of excess air, and producing little or no ash (it is the cleanest fuel to burn). Combustion air is supplied to the reaction in a quantity greater than the theoretically least amount of air needed to burn all of the fuel, so that the combustion reaction is not limited by insufficient air. The amount of excess air depends on the fuel type. Relative to the theoretical amounts, the following are medium values for excess air: large coal particles, 30–40%; pulverized coal particles, 15–20%; fuel oil, 10–15%; and natural gas, 5–10%. In theory, the fuel is completely burned if the products of combustion are composed mainly of CO2 and H2O, and no traces of fuel exist in these products. In practice, this ideal situation does not occur and, due to furnace design, insufficient turbulence, or insufficient residence time of the fuel in the furnace, some traces of fuel, such as CO, always remain in the flue gases, causing incomplete combustion. These gases are undesirable since they are poisonous and explosive and the caloric value is half of the value on complete combustion. The combustion process may be measured by the combustion efficiency. Among the several notions that
592 Utilities and Effluent Treatment | Heat Generation
exist for this parameter, a simple one is to consider the conversion of carbon to carbon dioxide, given by c: c ¼
ðXco2 Þ real ðXco2 Þ theoretical
Combustion and stoichiometry affect the global heat transfer from the fuel to the water in the boiler or, in other words, the boiler efficiency.
ð4Þ
where (Xco2)real is the measured CO2 molar fraction and (Xco2)theoretical is the CO2 molar fraction in the off-gas in the case of complete combustion. The theoretical amount of air needed for combustion is determined by the stoichiometry of the reaction.
Calculation of Boiler Efficiency Boiler efficiency, b, is the ratio between the heat power received by the water, Q_ w , and the heat content of the fuel, Q_ f , since the electrical energy that is necessary to drive the boiler’s auxiliary equipment is comparatively much smaller than these values and is normally neglected:
Stoichiometry
b ¼
As mentioned above, normally the fuels burned in boilers are hydrocarbons of the type CxHy. The theoretical amount of air needed to burn this fuel completely is given by the following stoichiometric relation: y Cx Hy þ aðO2 þ 3:76N2 Þ ! xCO2 þ H2 O þ 3:76aN2 2
ð5Þ
where a ¼ x þ y/4. It must be noted that, since air is a mixture of roughly 21% of O2 with 79% N2 by volume (having insignificant traces of other gases), each mole of O2 is mixed with 79/21 ¼ 3.76 moles of N2. From eqn [5] it can be observed that (4.76 a) moles of air are necessary to burn 1 mol of fuel completely. Normally, the stoichiometric air–fuel ratio, (A/F)stoich, represents this relation on a mass basis as: A mair að1 þ 3:76Þ Mair ¼ ¼ F stoich 1 mfuel stoich Mfuel
ð6Þ
where Mair and Mfuel are the molar masses of air and fuel, respectively, Mair ¼ 0.21 MO2 þ 0.79 MN2 ¼ 28.85 g mol1, and Mfuel ¼ xMC þ y MH where x and y are the number of carbon and hydrogen atoms in the fuel molecule, and MC and MH are the atomic mass of carbon and hydrogen, respectively 12.011 g mol1 and 1.00794 g mol1. If a smaller amount of air is supplied, then the reactant mixture is said to be rich in fuel; if excess air is supplied, it is lean in fuel. The equivalence ratio, j, is the ratio between the stoichiometric air–fuel ratio and the real air–fuel ratio, (A/F)real: j¼
A A = F stoich F real
ð7Þ
This parameter allows one to determine whether the combustion is stoichiometric, j ¼ 1, the reaction mixture is lean, j < 1, or the reaction mixture is rich, j > 1, and it is related to the following parameters: the percentage stoichiometric air is given by 100%/j, the percentage excess air is equal to (1 j)/j 100%, and the percentage lack in air is given by (j 1)/j 100%.
Q_w m_ w hw ¼ m_ f LCVf Q_f
ð8Þ
where m_ w and m_ f are, respectively, the water and fuel mass flow rates; hw is the enthalpy difference the water undergoes while it travels through the boiler, and LCVf is the lower caloric value of the fuel (this is the caloric value usually considered since the water leaves the boiler as a vapor). Normally, not all the parameters in eqn [8] are easy to determine, so the boiler efficiency must be calculated, by an indirect approach, from the following equation: b ¼ 100 –
X
Li
ð9Þ
This definition considers that the difference between the input and the output energy of the boiler is due to several energy losses. So, from the flue energy P content, one subtracts the various energy losses, Li, expressed as a percentage of the LCVf value, namely: X
Li ¼ Luf ðunburned fuelÞ þ Lig ðflue gasÞ þ Lp ðpurgesÞ þ Lb ðheat losses to surroundingsÞ
These values may be calculated approximately by the expressions shown in Table 1. The unburned fuel may be present together with the ash, and the energy loss is Lufa (unburned fuel in the ash) because carbon may be carried away by the ash – either the fly-ash, which escapes in the flue gases, and/or the bottom ash, which settles in the boiler. The flue gases may also contain unburned fuel and the energy loss is Luff (unburned fuel in the flue gases) because CO may exist in the products of combustion due to incomplete combustion. The energy loss due to the energy content of the fuel gases, besides unburned fuel, is represented by Lfg (flue gas). It must be noted that the latent heat of the water in the flue gases is not accounted for because it normally leaves the boiler in the vapor phase. Periodic removal of debris from the bottom drums is necessary, as well as the removal of water for pH control purposes. The energy content of the water removed represents a loss designated Lp (purges).
Utilities and Effluent Treatment | Heat Generation
593
Table 1 Boiler energy losses in eqn 9 Energy losses (Li) LufLufa Lutt Lfg Lp Lh
Expression or value (%LCVf)
Parameters in expressions
¼ ACLCVc 100ð1 – CÞLCVf Fð1 – LÞufa COLCVco ¼ LCVf
A ¼ mass of ash kg1 of fuel C ¼ mass of carbon kg1 of ash
¼ ¼
ð1 – Lufa ÞFCpfg ðTfg Tat Þ
CO ¼ CO mass percentage dry basis
LCV1 Wh1 LCV1
¼ 2.0% for Qw 2 MW ¼ 1.6 % for 2MW < Qw < 5 MW ¼ 1.4% for Qw 5 MW
Heat loss to the surroundings, Lh, is very difficult to determine accurately. It is usually obtained by the difference due to all the other losses, so that the energy balance of the boiler is satisfied. Medium values for fire-tube or water-tube boilers at full rate depend on the boiler power, as can be seen from Table 1. By far the most important of the above energy losses is that in the flue gases. For this reason it is usual to recover heat from the flue gases after they leave the boiler, by passing them through economizers (to heat boiler feed water) and air heaters (to preheat combustion air). To attain good boiler efficiency it is necessary to implement a control strategy that acts on several parameters during boiler operation.
Basic Control Techniques Basically, the control strategy is implemented as follows: measuring instrumentation detects physical values, such as temperatures, pressures and flow rates; transducers convert these values into electrical signals and send them to data processing systems; these take a controlling action, by comparing the measured values to their preset ones, and send an electrical signal to control systems, e.g. electro-valves, that actuate on the components and regulate the physical values. By this means it is possible to control the properties of the water vapor produced, the water supply flow and the water level that exists at the boiler’s upper drum, the combustion process (regulating the operation of burners or fans), and also ash-removal systems, when applicable. Obviously, the pressure level of the water vapor produced must be controlled, not only to attain the goal of the boiler, but also to protect it from excessive pressure build-
Cp1g ¼ specific heat of the flue gases F ¼ fuel gas mass kg1 fuel mass LCVc ¼ lower caloric value of carbon LCVco ¼ lower caloric value of carbon monoxide LCV1 ¼ lower caloric value of fuel Qw ¼ heat power transferred to water Tfg ¼ flue gas temperature Tat ¼ atmospheric temperature W ¼ mass of water purged kg1 of fuel h1 ¼ enthalpy different between leaving and entering boiler liquid
up that may cause boiler explosion. By controlling the pressure, the corresponding saturated temperature is fixed automatically (during vaporization, pressure and temperature are dependent variables). Therefore, temperature control acts on the temperature of overheated vapor that is produced in the boiler. One technique, known as attemperation, may be implemented by regeneration of water vapor or by a spray process. Another technique uses an independent energy source at the boiler exit. It is also essential to control the water supply flow and the water level that exists at the upper drum in order to guarantee that water in the liquid state is always present inside the boiler (ready to be vaporized) and to avoid a tube explosion due to an excessively high temperature. The steam produced in the boiler is delivered by a steam piping system (normally made of steel) to the sites where it is used. A return piping system reintroduces the condensed water into the boiler. The design of these piping systems requires great attention because steam leakage losses and hot water losses occurring as a result of deficient design may assume such importance that they may reduce the measures adopted to increase efficiency of the steam generator and of the steam user.
Design of Steam Piping Systems The design of the steam piping system is normally determined on an economy basis. The total cost of the system is equal to the sum of the capital, installation (an important part of the total cost) and operating costs. These costs depend upon the tube’s internal diameter, D, as can be seen in Figure 5 which shows the relationship between cost and D.
594 Utilities and Effluent Treatment | Heat Generation
Cost
Total (a + b + c)
Installation cost (b) Capital cost (a) Operating cost (c) D Figure 5 Cost of piping systems as a function of tube diameter (D).
The dependency of the operating cost on diameter results from the pressure drop due to friction between the steam and the tube’s internal surface. Assuming a given flow rate, V_ , and considering suggested values for the fluid velocity, , saturated steam velocity between 30 and 50 m s1 and overheated steam velocity in the range 50 to 100 m s1, the diameter, D, results from:
4 V_ D v
1=2 ð10Þ
The next step is to select a normalized diameter close to this value, as well as at least two diameter sizes immediately above and immediately below it. The pressure drop, p, is then calculated for each of these diameters from: 2 L X v K p ¼ p f þ D 2
1 pffiffiffi ¼ f
– 2:0log
"=D 2:51 þ pffiffiffi 3:7 Re f
1. The operating pressure may differ from the design pressure; review the capital cost of the steam generator or steam user due to variation of friction losses. 2. Additional operating costs of returned feed water may be incurred due to an increase in operating pressure; the condensed water is collected and reintroduced into the boiler. 3. Heat loss may differ from the design value; steam enthalpy change affects the steam user and the operating costs.
ð11Þ
where is the specific mass given by steam tables (¼1/); f is the friction P factor; L is the tube length (a known quantity); and K is the localized pressure P drop due to accessories (some authors convert K to Leq, i.e. an equivalent straight pipe length of the same diameter having the same pressure drop as the accessories). The friction factor in eqn [11] is given by the Colebrook equation: "
recommended to redesign the piping system by choosing another value for D. The outlined procedure allows calculation of the pressure drop, and hence the operating cost shown in Figure 5, for a range of possible sizes of tube (such that the steam velocity is within admissible values). Based on the economic criterion, the trend is to favor smaller pipe diameters, i.e. high steam velocities. An important aspect not to be neglected is that steam at a high temperature flowing in a pipe loses heat to the surroundings (depending on tube insulation), which may cause superheated steam or saturated steam to condense. To prevent damage by erosion or water hammer, the condensed water should be drained by allowing the tube to have a continuous fall in the direction of flow of at least 4–5 mm in every 1 m, and by providing an adequate number of drain points (e.g. in a straight main pipe one every 20–40 m). During operation, condensed water is removed using steam traps; these automatic valves are able to remove liquid but prevent the escape of steam. The piping system can be optimized using the following parameters:
!# ð12Þ
where Re is the Reynolds number; Re ¼ D/; is the steam dynamic viscosity; " is the tube rugosity; and " ¼ 0.000 05 m/D (m) (for commercial steel tubes). The pressure drop normally adopted is approximately 5% of the value of the pressure in the main steam pipe. Should the calculated value be greater, it is
See also: Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations; Instrumentation and Process Control: Process Control; Process and Plant Design; Utilities and Effluent Treatment: Water Supply.
Further Reading Abrial JR, Bo¨rger E, and Langmaack H (1996) Formal Methods for Industrial Applications: Specifying and Programming the Steam Boiler Control. New York: Springer-Verlag. American Society of Mechanical Engineers (2000) ASME International Steam Tables for Industrial Use: Based on the International Association for the Properties of water and Steam Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam. New York: American Society of Mechanical Engineers. Basu P (2000) Boilers and Burners: Design and Theory. Springer-Verlag: New York. Energy Technology Supply Unit (1998) Coal-fired Commercial Boilers. Harwell: ETSU. Energy Technology Supply Unit (1998) Industrial Boilers. Harwell: ETSU.
Utilities and Effluent Treatment | Heat Generation Goodall PM (1980) The Efficient Use of Steam. Guildford: Westbury House. Granet I (1996) Thermodynamics and Heat Power. Englewood Cliffs: Prentice-Hall. Johnson CD (1982) Process Control Instrumentation Technology. New York: John Wiley.
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Kakac¸ S (1991) Boilers, Evaporators, and Condensers. New York: John Wiley. Payne FW (1985) Efficient Boiler Operations Sourcebook. Atlanta: Fairmont Press. Rhine JM and Tucker RJ (1991) Modelling of Gas-Fired Furnaces and Boilers and Other Industrial Heating Processes. London: British Gas.
Refrigeration A C Oliveira and C F Afonso, University of Porto, Porto, Portugal ª 2011 Elsevier Ltd. All rights reserved.
Vapor Compression Cycle Principles Refrigeration is the most common technology used for the conservation of perishable products. It involves the production and maintenance of a level of temperature in a space or object that is lower than ambient temperature. A consequence of lowering the temperature of perishable products is that the reactions that cause their deterioration, mainly microbial and enzymatic reactions, slow down, enabling the conservation of products for longer periods of time. The lower temperatures needed for conservation of perishable products can be subdivided into two groups: positive temperatures, which are referred to as refrigeration, and negative temperatures, below the freezing point of the product, which are referred to as freezing. Whereas in the former, all water in the product is in the liquid phase, in the latter most can be in solid phase. However, we must bear in mind that the microbial and enzymatic reactions do not cease, they just slow down. As soon as the product is exposed again to ambient temperature, the reactions resume their normal rate. An advantage of freezing is that the products can be stored for much longer periods compared with that for refrigeration. As deteriorative reactions occur in aqueous media, the loss of liquid water to ice substantially reduces water availability, and hence reactions can be severely restricted well beyond the lowering temperature effect. In principle, at temperatures even lower, below the glass transition temperature, all water is in either ice or part of the amorphous vitreous structure, molecular mobility is restricted to mutarotation and vibration, and all reactions cease. Unfortunately, such temperatures depend on water content, and for most foods they are typically well below practical storage applications (20 to 50 C for typical foods). In the old days, refrigeration was understood as natural refrigeration, that is, the lower temperatures were obtained with ice found in nature. Nowadays, it is understood as artificial refrigeration (i.e., the lower temperatures are obtained by mechanical systems, the most common one being the vapor compression system, shown schematically in Figure 1). The basic system shown is composed of four components, namely the evaporator, which is generally located inside the refrigerated space, the compressor, the condenser, and the expansion valve, connected in series by
596
piping. Inside the system there is a flowing fluid, called refrigerant, which exchanges energy in those components. In state 1, the refrigerant is in the liquid phase, either saturated or sub-cooled. From state 1 to state 2 the liquid flows through the expansion valve, a device that controls the refrigerant flow rate to the evaporator, where its pressure and temperature are lowered. As in the expansion valve, the refrigerant does not exchange heat or work with the outside, it maintains its total energy – enthalpy (h). In state 2, due to the pressure drop in the expansion valve, the refrigerant has two phases in equilibrium: saturated liquid and vapor. Then it flows through the evaporator where it absorbs heat from the refrigerated space in which the products are stored, lowering or maintaining its temperature. This refrigerant heat gain in the evaporator (increase in enthalpy) causes the boiling of the liquid so that state 3 corresponds with saturated vapor or even super-heated vapor. This process occurs at constant pressure and at constant temperature if there is no super-heating at the outlet of the evaporator. The vapor then enters the compressor where it is compressed to a higher pressure – the same as in state 1 – and with an increase in temperature, and consequently with an increase in enthalpy, state 4. At this point the vapor flows through the condenser, again in a constant pressure process (ideally). In this component, the refrigerant loses heat to the outside (either ambient air or water, or both) with a decrease in enthalpy, changing phase again – condensation – so that at the outlet it is in the same state referred above as state 1. As can be seen, this cycle operates between two constant pressure levels: a higher one in the condenser and a lower one in the evaporator, the pressure drop and increase being carried out respectively by the expansion valve and by the compressor. To visualize the refrigerant’s evolutions in the vapor compression cycle, different types of thermodynamic diagrams may be used, the most common one in refrigeration being the pressure–enthalpy (p–h) one. Figure 2 shows a typical p–h diagram of the cycle shown in Figure 1. It was considered that no super-heating or sub-cooling exists in the refrigerant at the outlet of the evaporator and condenser. By applying the first law of thermodynamics to the whole cycle and to each of its components and neglecting changes in kinetic and potential energy, it is possible to calculate the different energy fluxes in the cycle: :
Q
:
:
evap
þQ
cond
þW ¼ 0
Utilities and Effluent Treatment | Refrigeration Heat rejection
1 Expansion valve
Condenser
2
Evaporator
4 Electrical energy
Comp
3
Heat from refrigerated space Figure 1 Vapor compression system.
p
1
4
2
3
h Figure 2 Pressure–enthalpy diagram of the cycle shown in Figure 1. :
evaporator – refrigeration effect : Q
evap: :
¼ mðh3 – h2 Þ :
compressor – compression power : W ¼ mðh4 – h3 Þ :
condenser – condensation heat : Q
:
cond
¼ mðh1 – h4 Þ
expansion valve: h2 ¼ h1
where m_ is the refrigerant flow rate, Q is the heat exchanged, W is the energy (work) supplied by the compressor, and hi is the specific enthalpy of the refrigerant at the different points of the cycle. As can be seen, all the energy fluxes can be easily evaluated if the refrigeration cycle is conveniently plotted in a p–h diagram of the refrigerant used. It is only necessary to read the different enthalpy values and make the above calculations. However, nowadays all the calculations can be performed analytically because the equations of state (equation that enables the evaluation of the different properties of the fluid used) of the different refrigerants are well known. Existing software allows these calculations to be performed easily.
Equipment There is a wide range of equipment for each component in the vapor compression cycle. The choice of one or another depends mainly on the purpose of the system.
597
In this text, only a general classification of the equipment will be given. Evaporators are heat exchangers where the refrigerant boils while receiving heat from the surroundings. One possible classification of evaporators is based on their application. In that way, they can be classified as direct expansion or indirect expansion evaporators. In the first type, the coils of the evaporator are in direct contact with the space or body to be refrigerated (i.e., the refrigerant absorbs the heat directly from there). In the second type, the refrigerant takes the latent heat of vaporization from a secondary fluid, usually brine or water. This fluid flows in a closed loop making the connection between the evaporator itself and the objects to be cooled, where it withdraws heat. The evaporators can be classified into two groups: direct expansion and liquid recirculation type. In the first type, the refrigerant coming from the expansion valve boils completely in the tubes of the evaporator, leaving it as a saturated vapor. The second type is designed so that only part of the liquid boils in the coils. At the outlet of the evaporator there are then two phases in equilibrium, liquid and vapor. The vapor flows to the compressor, while the remaining liquid is recirculated back to the evaporator. The compressors can be classified as centrifugal compressors, vane compressors, rotary screw compressors, or reciprocating compressors, with the last types used in most refrigeration applications. When the pressure ratio of the compressor is typically above 10 (ratio between condensation pressure and evaporation pressure), the performance of the compressor falls and it is not possible to use only one compressor if it is of the reciprocating type. In this case, it is necessary to either use more than one compressor or choose another type. Usually, the compressors are coupled with electrical motors that provide the necessary running power. However, it is not unusual to find internal combustion engines instead of electrical motors driving the compressors. Condensers, like evaporators, are heat exchangers, and they are classified as air-cooled, water-cooled, or evaporative. In the first type, the condensing refrigerant loses heat to the ambient air, whereas in the second type the removal of heat is to water that flows in a closed loop, where usually a cooling tower cools the warm water. In the third type, air and water in a packed tower are used in counterflow over the coils of the condenser, inside which the refrigerant condenses. This kind of condenser must be located outside the building and as the refrigerant flows inside it, the length of the pipe carrying it is much longer than the first two types of condensers. Therefore, the pressure drop in the high-pressure part of the system is also higher. Also, as the length of the piping increases, the probability of leakage is increased. As already mentioned, the expansion valve controls the flow of refrigerant into the evaporator. There are different
598 Utilities and Effluent Treatment | Refrigeration
types of expansion valves, namely, the manually operated, automatic low side float valve, automatic high side float valve, automatic valve, thermostatic valve, and the capillary tube, the last two being very common in most applications. The capillary tube is used in small-capacity refrigeration systems, namely refrigerators and small-size air-conditioning equipment, whereas the application of the thermostatic valve is wider. This valve also controls the degree of refrigerant superheating at the outlet of the evaporator, comparing it with some pre-set value.
Heat rejection
Condenser Comp.
Electrical energy
Comp.
Electrical energy
Evaporator
Coefficient of Performance Heat from refrigerated space
The cycle analyzed so far is an inverse thermal machine. It is therefore possible to evaluate its performance, like in any other thermal machine, as the desirable effect of the system divided by what must be paid for this effect. The performance of refrigeration cycles is expressed through the coefficient of performance (COP), which is the ratio of refrigeration effect (desirable effect) divided by the compression power (what must be paid): :
COP ¼
Q
evap: :
W
¼
h3 – h2 h4 – h3
COP values are always positive and usually greater than one, due to the fact that the refrigeration effect is greater than the compression power. Typical values of COP for the vapor compression systems are in the range 2–3. Even if the evaporation temperature is held constant throughout the year, the COP is not constant due to changes in air or water temperature feeding the condenser, which causes changes in the condensing temperature and also in the enthalpies appearing in the COP equation.
Refrigeration Systems
Figure 3 Multistage vapor compression system.
the two compressors, and a higher one at the condenser. Multistage systems usually have higher COP values than basic vapor compression systems. This is due to the fact that there is a decrease in compression work and an increase in the refrigerant effect. There are different ways to implement this technique, one of them being to couple the system with several evaporators, each one with a typical operating temperature. To achieve very low temperatures – much lower than the freezing point of the products – with a good performance, the so-called cascade systems are frequently used. In its simplest form it is composed of two basic vapor compression systems in a way that the evaporator of one cycle is simultaneously the condenser of the second system (see Figure 4).
Heat rejection
Condenser
Vapor Compression Systems The system analyzed so far is the basic vapor compression system that is used in several applications of refrigeration. However, and keeping in mind this basic system, better performances can be achieved if some modifications are introduced. There are several possible modifications that can be implemented, for specific applications. A very common modification is the use of multi-stage compression (i.e., the use of more than one compressor), with inter-cooling of the refrigerant between each pair of compressors. Inter-cooling is carried out with the refrigerant at a lower temperature withdrawn from other parts of the system. This technique reduces the system total work. Figure 3 shows schematically such a system. As can be seen, in this system there are three levels of pressure, a lower one in the evaporator, an intermediate one between
Comp.
Evaporator condenser
Comp.
Evaporator
Heat from refrigerated space Figure 4 Cascade system.
Utilities and Effluent Treatment | Refrigeration
In that way, the evaporator of the upper system absorbs the heat lost in the condenser of the lower system. Usually two different refrigerants are used, one in each cycle. The refrigerant in the lower cycle should have good characteristics at lower temperatures while the other refrigerant should have good characteristics at higher temperatures. It is also possible for each of the subsystems considered to operate as a multistage system. Other Systems One variant of the vapor compression system is the absorption system, also used for refrigeration. This system is as old as the vapor compression system but only recently has its utilization increased, due to the ozone depletion potential of most of the synthetic refrigerants used in the vapor compression system, as will be described later. The absorption system differs from the vapor compression system in that low compression of the refrigerant is carried out, having in common the other three components: the evaporator, the condenser, and the expansion valve. Figure 5 shows only the part of the cycle that is different. In the absorption system, the compression is done using a secondary fluid that has the capacity of absorbing the main refrigerant flowing in the other three components. At the absorber outlet, where heat is lost to the outside in order to carry out the absorption process, there is a homogeneous liquid solution that is pumped to another component, the generator. Here, it is necessary to supply heat to separate the two fluids, a process opposed to the one in the absorber. The work of compression in the absorption system is much lower than in the vapor compression system due to the fact that a liquid solution is pumped instead of a vapor. But in an opposite way, a large quantity of heat at a higher temperature (typically over 100 C) must be supplied to the generator. These two combined effects lower the COP value of the absorption system, compared with that of vapor compression systems, to values below 1.0, typically around 0.7. It is however possible to obtain higher COP values if the heat supply in the generator is waste heat (found in many industrial processes) or is complemented with solar energy. Because of the need to supply heat to carry out the compression process, this part of the system Heat supply Refrigerant for condenser
Generator
Liquid solution (refrigerant + absorbent) Pump
Refrigerant from evaporator
Absorber
Heat rejection Figure 5 Compression in the absorption system.
599
(see Figure 5) is also called a thermal compressor in opposition to the vapor compression system where a mechanical compressor is used. The absorption system is nowadays very common in household and camping refrigerators as well as in air-conditioning equipment. The most common fluids for the absorption system are H2O–LiBr (water as refrigerant and lithium bromide as secondary fluid) and NH3–H2O (ammonia as refrigerant and water as secondary fluid). The first pair of fluids is used for positive temperatures in the evaporator (water freezes below 0 C at ambient pressure) while the second one can also be used for negative temperatures. In spite of a fast increase in use, absorption systems are still more expensive than the classic vapor compression systems and are also larger. Other types of refrigeration systems are available, some already commercially, and some at the development stage. They can either be operated electrically (like the vapor compression system) or thermally (like the absorption system). An example of electrically operated systems is the one using thermoelectric coolers, where direct current is used to produce a cooling effect. There are more examples of thermally operated systems, namely, adsorption, desiccant, or ejector systems. The combination of solar energy with refrigeration/ cooling equipment is a way of reducing energy consumption and harmful emissions to the environment. Solar thermal collectors can be used with thermally operated cooling equipment, and solar photovoltaic (PV) collectors can be used with electrically operated cooling equipment. Solar cooling systems are interesting, due to the fact that cooling demands in summer are associated with high solar energy availability, which allows operation with maximum collector efficiencies.
Refrigerants The first refrigerants used in vapor compression systems were inorganic or natural, and some are still widely used, namely NH3 and H2O. However, new refrigerants were produced synthetically from methane (CH4) and ethane (C2H6) being divided into two groups, depending on whether or not chlorine is in the molecular structure. In the first group there are two different kinds of refrigerants: the chlorofluorocarbons (CFCs), namely R-11, R-12, R-113, R-114, R-115, R-500, and R-502, and the hydrochlorofluorocarbons (HCFCs), namely R-22, R-123, R-141b, and R-142b. The second group is hydrofluorocarbons (HFCs), and some refrigerants belonging to this group are R-32, R-134a, R-143a, and R-152a. Due to the ozone depletion potential (ODP) of CFCs and HCFCs, it was established in 1987 at the Montreal Protocol that the production and use of these refrigerants
Table 1 Characteristics of some synthetic and natural refrigerants
Refrigerant Natural substanceNo ODPa GWPb Toxicity TLVd (ppm, volume) Flammability Critical point temperature ( C) Critical point pressure (bar) Normal boiling point ( C) Maximum refrigeration capacity at 0 C (kJ m3) a
R-12 (CFC)
R-22 (HCFC)
R-134a (HFC)
R-717 (NH3)
No 0.9 3 1000 No 115.5 40.1 30 2733
No 0.05 0.34 500 No 96.2 49.9 40.8 4344
Yes 0 0.29 1000 No 100.6 40.7 26 2864
Yes 0 0 25 Yes 133 114.2 33.3 4360
Ozone depletion potential – compared with R-11. Global warming potential – compared with R-11. Zero effective GWP, because more than sufficient quantities of it can be recovered from waste gases. d Threshold limit value (TLV) for exposure of 8 h day1, 40 h week1, without any adverse effect. e At 100 C. b c
R-744 (CO2)
R-290 (propane)
R-600 (butane)
R-718 (H2O)
Yes 0 0c 5000 No 31.1 73.7 78.4 22 600
Yes 0 <0.03 1000 Yes 96.8 42.6 42.1 3888
Yes 0 <0.03 1000 Yes 152.1 38.0 0.4 1040
Yes 0 0 No No 374.2 221.2 100 1349e
R728 (air)
0 0 No No 140 37.2 No
Utilities and Effluent Treatment | Refrigeration
should cease gradually. This leaves room for HFCs, the most common one nowadays being R-134a, and to inorganic fluids – air and CO2 besides those already mentioned. Another problem regarding refrigerants is its global warming potential (GWP), related to the greenhouse effect. In spite of the null ODP of HFCs, they may have a significant GWP, which makes the choice of the refrigerant to be used not easy when taking into account the two parameters simultaneously. Besides adequate thermodynamic and physical properties, each refrigerant must also have good chemical characteristics. From the safety point of view, these are its flammability and toxicity. Regarding flammability, ammonia is flammable as well as propane and butane, whereas the others are considered as nonflammable. All refrigerants are considered toxic in a small degree,
601
except ammonia, which can be lethal above low concentrations in air. Table 1 provides a comparison between some characteristics of the most common synthetic and natural refrigerants.
Further Reading ASHRAE (1998) Handbook – Refrigeration. USA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers. C¸engel Y and Boles M (1989) Thermodynamics: An Engineering Approach. New York: McGraw-Hill. Gosney W (1982) Principles of Refrigeration. Cambridge: Cambridge University Press. Riffat S, Afonso C, Oliveira A, and Reay D (1997) Natural refrigerants for refrigeration and air conditioning systems. Applied Thermal Engineering 17: 33–47.
Compressed Air O Santos Mota, University of Porto, Porto, Portugal ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2487–2495, ª 2002, Elsevier Ltd., with revisions made by the Editor.
Introduction Compressed air is a utility that consumes an important share of the energy consumption in industry. Great attention must be paid to the production of this form of energy for it is one of the most expensive. The following are some compressed air applications: driving power for some types of equipment, conveying materials such as chemicals, ventilation of buildings, supplying combustion air for boilers, as a power source for air-operated valves and shutters, and as a medium to transmit signals as in instrumentation. Air compressors operate on a source of energy (normally electrical energy but other kinds are possible, e.g., internal combustion engines and vapor or gas turbines). Compressors take in air at atmospheric pressure (101 325 N m2 (100 kPa)) and produce compressed air at a desired pressure. This air is then sent to an air receiver and distributed via a piping system to the final points of use. There are a great variety of compressors and selection depends on the pressure and volumetric flow rate of the compressed air, among other factors.
General Classification of Air Compressors The general classification of compressors, showing their most important characteristics and applications is summarized in Table 1. Air compressors are normally grouped into two classes: positive displacement and dynamic.
In this group, a distinction is made between reciprocating and rotating compressors, depending on the motion of the solid boundary. Reciprocating compressors A crankshaft is used to transfer the power, e.g., from an electric motor to the compressor (Figure 1). A connecting rod joins the crankshaft to the piston, which moves back and forth in the cylinder, with a velocity of between 2 and 4 m s1 at normal crankshaft-rotating velocities. The power received by the air is due to hydrostatic pressure forces acting on a piston during the compression stroke (valves 5a and 5b closed, and the piston moves toward the cylinder head). Consequently, the volume of air decreases and its pressure increases. Regarding the pressure ratio (Pr, delivery air pressure/admission air pressure), for low values, single-stage compression is sufficient: compression takes place in one or more cylinders of identical size. Multistage (two or more stages) are used when a higher pressure ratio is needed: the air is first compressed in a large low-pressure cylinder, then flows to an intercooler (normally a finned tube), where the air temperature drops, before proceeding next to a small high-pressure cylinder where the final pressure is reached. This arrangement consumes over 15% less power than the single-stage type when producing air at the same volume and pressure.
Rotary Compressors Positive-Displacement Compressors These compressors operate intermittently, subjecting the air to non-flow processes. An important limitation is that they can handle a small flow rate compared to the dynamic compressors that operate continuously. The flow proceeds in the same direction as the pressure gradient since these machines have parts that ensure positive admission and delivery of air, preventing undesired reflux.
602
It is worth noting that rotary compressors are also positive-displacement machines because the fluid is prevented from flowing back in the direction of the pressure gradient by solid boundaries. They have lobes (Roots blowers), vanes or screws to reduce the air volume and increase its pressure (Figure 2). Other geometrical configurations exist on the market but, because of their less frequent use in compressed air applications, they are not discussed. The following is a brief reference to these compressors.
Utilities and Effluent Treatment | Compressed Air
603
Table 1 General classification of compressors
Type
Pressure ratio, Pra
Free air delivery, ? V1 (m3 min1)
Positive-Displacement Reciprocatingb
<1000
Small <1 Medium 1–10 High >10
Rotating
The Roots blower
<3
Vane Screw
<10 <4
>3000
<6
>10
<10
<500 000
Dynamic Radial (centrifugal)
Axial
Some applications
Compressed air
Pneumatic transport, vacuum pumps, volumetric flow rate meters Compressed air Compressed air Compressed air Small size – as supercharges Large sizes – gas turbine plants Gas turbine (power plants and aircrafts) Delivery of natural gas in pipelines
a
=(delivery air pressure)/(admission air pressure). It is the only technical solution for high pressure ratios.
b
Vane-type compressors
5b 5a 4
6
2 3
1 7
8
The vane compressor action differs slightly from that of the Roots blower. These compressors are said to have internal compression because of the reduction in volume in the initial phase of the compression process (a feature which is absent from the Roots blower). They have only one rotor, the axis of which is parallel to the stator’s axis and is eccentric to it. The eccentric feature is the essence of the principle of operation. Pressure ratios of up to 10 are common. They do not have valves. The cooling medium can be air or water. Screw-type compressors
Figure 1 Schematic representation of a reciprocating air compressor: 1, cylinder; 2, piston; 3, piston ring; 4, cylinder head; 5a, admission value; 5b, discharge valve; 6, fins; 7, connecting rod; 8, crankshaft.
Lobe-type compressor (Roots blower) The Roots blower is one of the simplest and best-known of the rotary compressors. It does not have valves. A gearing system synchronizes the movement of two symmetric rotors, which rotate in opposite directions in the form of a figure 8. Lubrication is not needed because they do not contact each other. This action forces the air to contact the compressed air that exists in the piping system, where oil-free compressed air is produced. Air is the cooling medium. Compared to the reciprocating compressor, the power required is greater and it has a lower efficiency. For this reason, it is used when low pressure ratios are required, e.g., up to 3 in pneumatic transport, vacuum pumps and volumetric flow rate meters.
These consist of two rotors that move in opposite directions. The rotors have an asymmetric design (made by computer-aided design and manufacture) that makes possible a lower energy consumption, a better gap reduction between rotors and less friction. Practically constant compressed air flow rates are produced. They can be lubricated or oil-free. When lubricated, the oil and air mix together, so this mixture is compressed and three functions are simultaneously fulfilled: sealing, lubricating and cooling. In the case of oil-free compressors, there is no metallic contact between rotors so a gearing system is used to synchronize the rotor movements.
Dynamic Compressors Dynamic compressors, or nonpositive displacement compressors, operate continuously, subjecting the air to steady flow processes. An important advantage is that they can handle large flow rates efficiently, as long as
604 Utilities and Effluent Treatment | Compressed Air (a)
(b) Shaft
Shaft
(c) Shaft
Lobe type
Vane type
Screw type
Figure 2 Schematic representation of some rotary compressors: (A) lobe type, (B) vane type and (C) screw type.
the pressure ratio is kept small in comparison to that of alternating and rotary compressors. These machines have no means of preventing backflow. At a given compressor speed, only a limited range in air flow rate is possible: if it is reduced beyond a certain value, it is impossible to maintain the desired air velocity profile. In this group, distinction is made between axial and radial compressors, depending on the direction of the air flow.
Radial compressors (centrifugal) An external source applies an input torque that drives the rotors, which are constructed with recent technology in order to withstand high velocities between 20 000 and 30 000 rpm, accelerating the air in the radial direction (Figure 3): the work transfer is due to a change in momentum of the air stream. It then flows into the diffuser and volute casing, suffering a decrease in velocity and an increase in pressure. The combination of the inlet nozzle, impeller, diffuser and volute is called a ‘stage’. Pressure ratios of 4–6 are common. For greater pressure ratios, additional stages are needed. They are adequate for the production of oil-free compressed air and have been used extensively, both in small sizes as superchargers and in large sizes as compressors for gas turbine plants.
(a)
Axial Compressors In these compressors, the acceleration of the air takes place in the axial direction (parallel to the shaft) (Figure 3). Each stage consists of a pair of stationary and moving blade rows (like a turbine): the rotating blades, with velocities in the range 10 000–30 000 rpm, increase the pressure and the stator blades act as a diffuser by converting the air velocity into air pressure. Pressure ratios of 10 or more can be obtained. Normally, high flow rates are produced (the minimum flow rate is approximately 900 m3 min1), making them a good choice for power-plant and aircraft gas turbines, as well as for the conveying of natural gas in pipelines.
Ideal versus Real Reciprocating Cycles The reciprocating compressor is the most common type used in air compression, followed by the screw compressor. Since both are of the positive-displacement type, the basic theory of reciprocating compressors is also applicable to screw compressors. The ideal reciprocating compressor cycle is an open cycle that consists of the following evolutions, shown on the P–V diagram in Figure 4 (P being pressure and V being volume):
(b)
Shaft
Shaft Rotor with moving blades Rotor (impeller)
Diffuser
Casing with fixed blades Volute casing
Figure 3 Schematic representation of dynamic compressors: (A) radial type and (B) axial type.
Utilities and Effluent Treatment | Compressed Air
605
(b)
(a) P (Nm–2)
P (Nm–2) d
P2
2 2
2
a
P1
P2
2
d
1
P1
1
0
a
e
0 0
V1
V2
V (m3)
Va
0 Vd
V2
V1 Ve
Admitted volume
V (m3)
Real cycle
Ideal cycle Figure 4 Ideal and real reciprocating compressor cycles: (A) ideal cycle and (B) real cycle.
1. The admission valve opens at a pressure level P1 and admission of atmospheric air at P1 and temperature T1 takes place (state 1). The volume inside the piston cylinder arrangement varies from 0 to V1. 2. The admission valve closes and the entrapped air suffers a frictionless isothermal compression between state 1 and state 2 (at P2, T1). The air volume is reduced from V1 to V2. 3. The discharge valve opens when the pressure level is P2, and the air is discharged to the piping system at state 2. The volume inside the piston cylinder arrangement varies from V2 to 0. The work transfer (W) during each step of the cycle is R given by W ¼ PdV. In terms of the P–V diagram, this is equivalent to the area underneath each evolution, namely: Admission work performed by the incoming air on the piston: Wa–1 ¼ P1V1 (area a, 1, V1, 0, a). Compression work performed by the piston on the air: W1–2. Writing the ideal gas equation in terms of P (P = mRT/V) gives: W1 – 2 ¼ –
ZV2 V1
mRT1 dV ¼ – mRT1 V
ZV2
dV P1 V1 lnðPrÞ V
ð1Þ
V1
(area 1, 2, V2, V1, 1); discharge work performed by the piston on the air: W2–d = P2V2 (area 2, d, 0, V2, 2). The total ideal cycle work (Wi) is given by:
W1 ¼ – P1 V1 þ P1 V1 lnðPrÞ þ P2 V2 ¼ P1 V1 lnðPrÞ
ð2Þ
since P1V1 = P2V2. It can be seen that Wi is equal to the compression evolution work, W12. Ideally, this is the minimum work required to increase the pressure from P1 to P2. The ideal power is obtained by dividing Wi by time: W1 ¼ P1 V1 lnðPr Þ
ð3Þ
The real compressor cycle is also shown in Figure 4. It deviates from the ideal cycle due to a number of differences that cause the flow rate to be smaller and the work/ power absorbed by the compressor to be greater, i.e., the compression evolution is not isothermal, there is a clearance volume, there is a pressure drop in the admission and discharge valves, the air temperature increases during the admission stroke, and there are flow rate losses. These causes are analyzed briefly below.
Compression Evolution If an adiabatic compression is considered (no heat transfer to the surroundings), the compression evolution is characterized by PVk ¼ const, with k ¼ 1.4. Following the same procedure as in the ideal case to calculate the work, the compression work is: W1 – 2 ¼
P2 V 92 – P1 V1 K –1
ð4Þ
606 Utilities and Effluent Treatment | Compressed Air
Wa ¼ kW1 – 20 ¼ k
P2 V 92 – P1 V1 K –1
ð5Þ
This work is equal to the area a, 1, 29, d, a (see Figure 4). Since this area is greater than that corresponding to the ideal cycle work, Wa>Wi. In practice, the compression evolution can be considered polytropic, PVk ¼ const, where normally k ¼ 1.3 for low-speed compressors with good refrigeration, and k ¼ 1.35 for high-speed compressors.
Clearance Volume Not all the air is evacuated from the compressor at the end of the delivery stroke: some remains in the clearance volume, Vd6¼0 in Figure 4. The air at pressure P2 enclosed in this space therefore expands from d to a (Figure 4) until it reaches the pressure P1 when admission commences. At this pressure, it occupies the volume Va so there is a decrease in aspirated volume represented by VaVd. The clearance volume results in a lower flow rate, and also the work is decreased almost proportionally to the flow rate. This influence is more pronounced for higher pressure ratios; Va tends to be greater. This parameter is given as a percentage of the piston displacement (the volume displaced by the piston between the head end and the crank end).
Pressure Drop in the Admission and Discharge Valves Before the discharge stroke begins, the air pressure must be greater than P2, allowing the opening of the discharge valve and overcoming the pressure losses due to the flow from the cylinder through the discharge orifice into the piping system. As a consequence, the work increases and the air temperate rises because of its increased pressure. During the admission stroke, the work increases and the air temperature rises: the air passes isothermally through the admission valve and the pressure depletion that occurs is always greater than that at the end of this stroke. Consequently, the flow rate decreases, causing a decrease in efficiency.
consequently, a temperature rise, in addition to that caused by pressure changes. As the flow rate is measured at the inlet, this temperature increase has an important effect on the compressor efficiency and may justify the differences encountered according to their refrigeration modes.
Flow Rate Losses The effect of these losses on the cycle work is negligible. However, its influence on efficiency must not be ignored because the effective flow rate decreases and the work is fairly constant.
Compressor Efficiency Calculations The above differences between the real and the theoretical cycles result in a decrease in flow rate and in efficiency. The volumetric efficiency (v) accounts for the decrease in flow rate. It is given by the ratio between the free air delivery (V_ 1 , the real volumetric air flow rate produced by the compressor measured at the inlet pressure and temperature) and the piston displacement per unit of time (Figure 4): v ¼
V_1 Vd h 1=k i ¼ 1– Pr – 1 Ve – Vd V_e V_d
ð6Þ
where depends on Pr, the pressure losses at the valves and on the cooling medium (v water-cooled>v air-cooled). An example of the dependency of the volumetric efficiency on clearance volume and pressure ratio is shown in Figure 5. It can be understood based on Figure 4 that, for
100 ηv (%)
and the cycle work, Wa, is given by:
Cle
Cl
aran
ea
ce v
ra n
ce
olum
vo
e=2
%
lum
e=
Air Temperature Rises during the Admission Stroke 0
During compressor operation, the temperature of the cylinder wall will be greater than that of the incoming air. This results in heat transfer to the air and,
0
Pr (–)
8%
10
Figure 5 Volumetric efficiency versus pressure ratio with clearance volume as parameter.
Utilities and Effluent Treatment | Compressed Air
a given clearance volume (Vd), as Pr rises (P>P2), it causes the entrapped air to expand to a greater volume (V>Va), reducing the admitted volume and therefore v; on the other hand, for a given Pr (e.g. P2/P1), if the clearance volume is greater than Vd, the air expands to another volume (V>Va), causing a decrease in v. Normally, v ranges between 60% and 90%. The clearance volume causes the greatest decrease of flow rate loss, up to 20% of the piston displacement per time unit. As mentioned above, another consequence of the differences between the real and theoretical cycles is greater power consumption of the compressor when compared to the ideal power consumption. The compressor efficiency, also referred to as the isothermal efficiency (i), accounts for this effect. It is given by the ratio between the power of a frictionless compressor (with an isothermal evolution) and the shaft power of a real compressor: 1 ¼
W_ i W_ r
ð7Þ
where w_ r is the shaft power. This efficiency defines the global compressor efficiency. In order to analyse the compressor operation, one may divide this efficiency into two factors, namely the indicated isothermal efficiency (ii), and the mechanical efficiency (m): i ¼ ii m ¼
isothermal power indicated power indicated power shaft power ð8Þ
where ii is the losses due to cycle imperfections and m is the friction losses. Therefore, the ratio i/m ¼ (isothermal power/shaft power)(shaft power/indicated power) shows the power loss due to the fact that the compression evolution deviates from the isothermal evolution. Another notion of efficiency related to the compressor operation is the polytropic efficiency (p): P ¼
W_ p W_ I
ð9Þ
where w_ p is the theoretical power of a frictionless compressor undergoing a polytropic evolution such that at the end of the compression the real air temperature is reached. Relative to the isothermal efficiency, the polytropic efficiency includes the additional work converted to heat the air during compression: pi ¼ losses in percentage of the shaft power. The referred efficiencies are not the only criteria by which compressors are compared. It must be stated that their characteristics also come into play, namely the
η i = 100% η i = 70% η i = 60%
100 Pr (–)
607
η i = 50%
η i = 40%
10
Single stage Double stage 1
0
5
10
15 . . Wr V1–1 (kW (m3 min–1)–1)
Figure 6 Characteristics of single- and double-stage reciprocating compressors.
relationship between the delivery air pressure, free air delivery and power. It is the operating conditions that establish the delivery air pressure (which must equal the required pressure plus the line pressure losses), the free air delivery (which must equal the required flow rate plus the line flow rate losses), and the power consumption. The characteristics of reciprocating compressors, Pr versus Wr/V1with i as parameter are shown in Figure 6. The isoefficiency lines results by combining eqns [3] and [7]: ln ðPr Þ ¼
I W_ r PI V_I
ð10Þ
Two superimposed regions on Figure 6 show the characteristics of single- and double-stage compressors.
Basic Control Techniques In general, a flow rate control is necessary because the need for compressed air varies greatly, depending on the number of users connected to the piping system. There are two basic control techniques: motor on/off operation (applied to compressors with shaft power 12 kW), and continuous motor operation (shaft power >12 kW). During the on/off control, the compressor motor operates until the delivery pressure level is reached, turning off at this instant. When the line pressure drops, due to air consumption, below a pre-established value (normally 0.05 MPa below delivery pressure), the compressor turns on again. The maximum number of starts per hour is around 10.
608 Utilities and Effluent Treatment | Compressed Air
In the continuous motor operation control mode, the motor does not have an intermittent operation, which may cause malfunction considering the powers involved. When the required pressure is reached, the admission valve opens and the discharge valve closes. In this way, the air enters and leaves the compressor without being compressed. The power absorbed is 7–20% of the power needed to produce the normal flow rate.
Treatment of Compressed Air From the point of view of compressed air production systems, atmospheric air contains undesired constituents or ‘impurities’, mainly water vapour and dust particles. It is essential to treat the resulting compressed air, which may also contain lubricating vapours resulting from compressor operation. The degree of cleaning depends on applications, especially in the dairy and beverage industries. Several air-intake filters are used before the air enters the compressor:
• viscous filters – as the air passes it impinges on an obstruction that traps the dust • oil-bath filters – the incoming air agitates the oil in a reservoir, causing the impurities to settle in the bath • travelling screen filters – air flows through a screen that rotates continuously; the screen is coated with oil to trap the debris, which is then washed out as the screen moves through an oil bath dry-type filters – utilizing a medium often made of felt or fibreglass.
•
It is common to install a silencer integrated with the air inlet filter to reduce the noise level where this is problematic. Water and lubricant vapours are removed by condensation in cooling systems located at the compressor exit. Purges control the removal of water and oil condensed from the compressed air. For the majority of applications, compressed air has a dewpoint temperature of 2 C (below this temperature, water vapour condensation occurs) and the lubricant vapour concentration is 1 mg m3. The concentration of dust particles in air is roughly 5 mg m3, consisting of particles with an average diameter of 5 mm.
Design of Compressed Air Piping Systems A piping system conveys the compressed air to the consumption points. An advantage of compressed air distribution systems is that no piping system is necessary for the return of the used air because it simply escapes to the atmosphere.
The main distribution system is made of rigid tubes (steel, galvanized iron and plastic are common materials), while flexible tubes join the system to the final users. Dilatation tubes are also used to compensate for temperature differences. Purges must be placed at low-level points (to remove further condensed water and oil), so the slope of the tubes towards these points must be at least 1%. Large tube diameters favour small pressure drops caused by the air flow. The design of the piping system involves choosing all tube diameters on the basis of the admissible pressure drop through the tubes. However, it is suggested that the air flowing through the longest tube length, from the compressor to the furthest consumption point, should undergo a maximum pressure drop of 0.01 MPa. Normally, the flow is turbulent and the pressure drop (p) is proportional to the square of the air velocity (v), i.e., inversely proportional to the fourth power of the internal tube diameter (D): 2 L X 1 p ¼ p f þ K 2 D
ð11Þ
where is the specific mass given by the ideal gas equation ( ¼ P/(RT), R ¼ 287 J/(kg K1)), f is the friction factor, L is the tube length, K is the localized pressure drop due to accessories (some authors convert K to Leq, i.e., an equivalent straight pipe length of internal diameter D having the same pressure drop as the accessories) and v is the air velocity (suggested values for v range from 10 m s1 for the main piping system to 20 m s1 for the flexible pipes). For pressure drop prediction, normally only an order of magnitude is sufficient. A more accurate value requires great calculation effort and it also requires the knowledge of the rugosity (roughness) of the tube’s internal surface and an accurate definition of all the piping system components. In practice, an abacus is used to determine the pressure drop. The example shown in Figure 7 was constructed considering smooth pipes, admission air at P1 ¼ 0.1 MPa and T1 ¼ 293 K (20 C). Following the calculus sequence (follow the line with an arrow in Figure 7):
• •
Assume an internal tube diameter D and a delivery pressure P2. For a given free air delivery V_ 1 , determine the air velocity v ¼ V_ 1 =D2 =4 and f, from the Colebrook equation: " !# 1 "=D 2:51 pffiffiffi – 2:0log þ pffiffiffi 3:7 Re f f
ð12Þ
where Re is the Reynolds number, Re ¼ vD/, ¼ 1.81105 Ns m2 (is the dynamic air viscosity at T1), " is the tube rugosity (" ¼ 0 (smooth tube)).
Utilities and Effluent Treatment | Compressed Air
. V1 3 (m min–1)
1000
100
10
m m .0 m .0 m 100 150 ∞ ∞ D D m 0m 50. D∞ m 0m 25. ∞ D
2.5
1 D∞
1
mm
0.1 1 P1–1 (bar) 8 6 4
10
100
1000 ΔPL–1 (Nm–2 m–1)
609
compressed air deteriorates with use, so higher pressures and flow rates must be considered, respectively between 0.05 and 0.1 MPa (depending on L) and flow rates between 30% and 40% relative to the operating characteristics when new. The piping system design is important for it is responsible for energy losses due to pressure drops (caused by the flow) and due to flow rate losses which occur mainly at the tube joints. The latter are the most important (for pipe lengths below 1000 m it may represent 5–10% of the flow rate) so frequent inspection of the piping system is suggested. To meet the requirements of the piping systems, the choice of the compressor characteristics must be such that it has a small variation in pressure ratio values for a great variation in the flowrate values. See also: Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations; Instrumentation and Process Control: Instrumentation; Instrumentation and Process Control: Process Control; Process and Plant Design. Utilities and Effluent Treatment: Water Supply.
100 00 Figure 7 Abacus for determination of the pressure drop in smooth pipes.
•
Determine the pressure drop per unit tube length, assuming K ¼ 0 (no localized pressure drop):
p f 12 ¼ L D2
ð13Þ
Roughly, one may increase the value of P/L by 30% to account for the rugosity effect. The design is confined to determining D since the other variables are known: P2, the delivery pressure, and V_ 1 are imposed by the users of compressed air and the maximum value suggested for P/L is 0.01 MPa L1. It must be borne in mind that the equipment consuming
Further Reading Anonymous (1982) Compressed Air and Gas Data, 3rd edn. Woodcliff Lake: Ingersoll–Rand. Antony B (1997) Pneumatic Handbook, 8th edn. Oxford: Elsevier Applied Science. Carello M, Ivanov A, and Mazza L (1998) Pressure drop in pipe lines for compressed air: comparison between experimental and theoretical analysis. Advanced Fluid Mechanics 21: 35–44. Gresh MT (1991) Compressor Performance: Selection, Operation, and Testing of Axial and Centrifugal Compressors. London: Butterworth. John D and von Otto B (eds.) (1996) Process Fan and Compressor Selection. London: Mechanical Engineering Publications. Lamit LG (1981) Piping Systems: Drafting and Design. Englewood Cliffs: Prentice-Hall. Matley J (ed.) (1979) Fluid Movers: Pumps, Compressors, Fans and Blowers. New York: McGraw-Hill. O’Neill PA (1993) Industrial Compressors: Theory and Equipment. Oxford: Butterworth-Heinemann. Rollins JP (1989) Compressed Air and Gas Handbook, 5th edn. Englewood Cliffs: Prentice-Hall. Vetter G (ed.) (1995) Leak-Free Pumps and Compressors. Oxford: Elsevier Advanced Technology.
Electricity R Yacamini, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2495–2497, ª 2002, Elsevier Ltd., with revisions made by the Editor.
Introduction A well-designed electricity supply system is fundamental to the operation of all processing plants. It is the electricity supply that provides much of the heat, as well as the power to drive pumps, compressors, refrigeration plant, instrumentation, lighting (both standard and emergency), control systems of all types, and computers and communication systems. It is important, therefore, that dairy scientists and plant operators have at least some understanding of the component parts of the electricity supply system.
Electricity for Power Electricity is generated primarily in large power stations which are powered by coal, gas, oil or nuclear plants. These are often sited on a river or close to a sea coast because cooling water is a primary requirement for operation. Renewable sources of energy, such as wind, wave, solar and others, will become increasingly relevant as countries attempt to cap their greenhouse gas emissions and increase sustainability. The electricity, which is generated using synchronous generators, is transformed to a higher voltage using transformers and fed into an interconnected grid system, usually at a high voltage of 400–800 kV. This allows for the bulk transfer of power, which can be tapped into, using a transformer, to supply electricity to a city, perhaps at 200 kV or so, or downward to what is known as distribution level, for supply to factories or processing plant, often at a voltage around 11 kV or perhaps 6 kV, depending upon the concentration and size of the plant. Unless very large motors or heaters are involved, this voltage is further reduced to perhaps 415 V three-phase or 240 V singlephase. The exact voltage is determined by the standards of the country in which the plant is operating. Another factor which can vary between countries is the frequency of the supply, which can be either 50 Hz or 60 Hz. Users should be cautious when ordering equipment or instrumentation that is designed for use in plant in another country.
610
For larger processing plants, a substation containing primarily transformers, switches and circuit-breakers is a feature of the site, often at the roadside. If there are processes or systems within a plant that could be either commercially sensitive or unsafe if the electricity supply should fail, there might also be a diesel generator or some other standby supply of electricity which can be switched on if there is an emergency loss of power from the supply company. Another feature of processing plant is the existence of a battery room, often associated with an uninterruptible power supply (UPS), which may be used for emergency lighting systems, protection systems, gas alarms, fire alarms, computer networks, or anything that has to be supplied with continuous power in the event of a supply failure. The interaction of these primary and standby power supplies is determined by commercial and safety considerations. A factor which is becoming increasingly important, as electricity suppliers are becoming more competitive and sophisticated post-deregulation, is making use of, for example, standby generators at times when tariffs are very high due to high peak demand, in order to avoid exceeding agreed maximum demand levels.
Energy Management and Usage All energy management is a compromise. Energy costs can be saved by use of insulation to prevent heat loss or by the reprocessing of low-grade heat to higher-grade heat. The level of insulation or recovery depends very much on the size of the plant and also on the operating temperatures of hot liquids and the refrigeration plant. It is also a function of the system involved and the life expectancy of the plant. The larger the plant, the higher the temperature differences, and the greater the life expectancy the more scope there is for energy management. An important factor in the usage of electricity is to minimize costs by planning the optimum use of tariffs. This is a subject which gains in complexity with the size of plant because electricity suppliers, in order to reduce
Utilities and Effluent Treatment | Electricity
their installation and running costs, financially discourage the consumption of power during times of peak demand. It is therefore advisable to carry out periodic energy audits to see whether cost savings can be made by replanning production or by segmentation of plant so that only essential loads are attached during times of peak demand. For smaller systems, the tariffs tend to fall into four categories, depending on location. These are: (1) a flat rate service fee, (2) a fee for electrical usage measured in kW h, (3) a charge (or credit) for running with a power factor outside an agreed limit and (4) peak demand charges. Apart from the power factor charge, these are largely self-explanatory. Loads that are connected in a plant and draw a current which is not in phase with the applied voltage are said to have a poor power factor. This will happen where there is a large induction machine load on the system or when power converters are used to convert three-phase AC into DC for whatever purpose. This poor power factor obliges the supply company to install extra generating capacity and burn extra fuel. The inductive loads can be balanced at plant level by installing power factor-correction capacitors that will pull the wave shape of the current into phase with the voltage. Depending upon the expected lifetime of the plant and the extent of the inductive load, power factor correction often turns out to be a good investment. Another factor which sometimes has to be taken into consideration is the effect that installed plant can have on the power quality. If large numbers of AC-to-DC power converters are used, they may distort the incoming supply. If the supply is distorted beyond a certain level (known as the harmonic content) at the point of common coupling with other users, it may be necessary to fit tuned harmonic filters. These will remove the offending distortion close to the source.
Distribution and Safety Issues The power distributed within a plant is fed from the incoming substation or switching room, primarily using cables. These are normally installed in ducts, using wallor floor-mounted cable trays, or in the wall, floor or ceiling in spaces created during construction. In designing the electrical supply to a plant, safety is paramount. Safety considerations fall into three categories: (1) the prevention of personal accidents due to electric shock or contact with rotating machinery, (2) the prevention of damage to plant and the process and (3) the prevention of fire. The safety of personnel is catered for at several levels. All electrical connections should be covered or positioned inside enclosures to which entry is forbidden
611
except with a permit. All rotating machinery should be fitted with a guard so that it cannot be touched inadvertently and it is impossible to fall onto rotating shafts. Shock prevention at low voltage is enhanced by the use of ‘residual current’ or ‘earth-leakage circuit-breakers’. These trip at very low levels of fault current imbalance and were a major advance when first introduced. Older plant should be retrofitted with such devices during plant maintenance. Damage to plant and the prevention of electrically induced fires are prevented by using circuit-breakers and fuses. These either trip or blow if excess current is generated by a fault in a piece of equipment or if, for example, a cable is inadvertently cut by maintenance personnel or a vehicle within the plant. These will isolate the electrical supply until the fault is corrected.
Electric Motors The problem of selecting the most suitable type of motor was at one time a significant factor in the design of new plant. Recent events have, however, simplified the choice. In the past, processing plant tended to have a mixture of different types of motors, e.g. the DC motor was used widely where a variable shaft speed was required and induction (or asynchronous motors) were used where a fixed speed of operation was deemed necessary. With the development of larger-powered, pulse width modulated (PWM) converters, the induction motor can now be used to power most variable frequency applications as well. The PWM drive, as the combination is known, is widely used for all applications from a small part of a kilowatt (low horsepower) up to the megawatt region. Previously, the choice of motor type, which was based on the detail of the starting torque and speed range required, was a matter of much debate. The various grades of motors are based on the National Electrical Manufacturers Association (NEMA) classification A to F, from which different ratios of maximum torque compared to rated torque can be selected. Increasingly, the Class B general-purpose motor is used for all directly connected and variable-speed applications, making selection easier. In the author’s opinion, variable-speed drives should not be bought as a separate converter and motor because this can lead to coordination problems. There is an exception to this new simplification of the selection process: such motors should not be used in conditions where there is a potential danger of explosions, e.g. in an environment where there are dust particles in the air or where distillation products are
612 Utilities and Effluent Treatment | Electricity
escaping into the air. Under these conditions, it may be desirable to purchase totally enclosed motors of the type developed for mining and offshore oil-platform applications. These can also be found in the NEMA standards. See also: Hazard Analysis and Critical Control Points: Processing Plants. Plant and Equipment: Process and Plant Design. Utilities and Effluent Treatment: Heat Generation.
Further Reading Fink DG and Beatty HW (1993) Standard Handbook for Electrical Engineers, 13th edn. New York: McGraw-Hill. Fitzgerald AE, Kingsley C, and Umans BD (1990) Electric Machinery, 5th edn. New York: McGraw-Hill. McPartland JF (1984) McGraw-Hill’s National Electrical Code Handbook. New York: McGraw-Hill. National Electrical Manufacturers Association (1989) Standard MG-1 Motors and Generators. Rosslyn: NEMA. Slemon GR (1992) Electric Machines and Drives. Boston: Addison-Wesley. Westinghouse Electric Corporation (1964) Electrical Transmission and Distribution Reference Book. East Pittsburgh: Westinghouse Electric Corporation.
Dairy Plant Effluents G Wildbrett, Technical University of Munich, Weihenstephan, Germany ª 2011 Elsevier Ltd. All rights reserved.
Introduction Dairies are considered as a ‘wet industry’ since they consume much water. Water is used for very different purposes (Table 1). Therefore, dairies discharge large volumes of wastewater. Recent mean values vary between 0.5 and 2.0 m3 wastewater per 1 Mg (tonne) treated milk. However, there are large differences according to different production lines: milk and desserts: 1.0–12.9 m3 Mg 1 final product; cheese: 0.5–6.0 m3 Mg 1 final product; and milk powder: 0.9–10.0 m3 Mg 1 final product. Among other things, variations depend on the equipment and its maintenance, the working method, and the environmental engagement of the management in the dairy, but there is no influence of the amount of milk processed. The figures given include the volumes of cooling water. As it is common for the food industry, pollution of the wastewater is the most important contribution to the pollution of the environment from dairies in both quality and quantity; contamination by solid waste and waste gas is less serious. The pollution of wastewater must be considered under the following aspects: and quantity; • kind ecological evaluation; and • means for reduction. •
Analytical Indices for Wastewater Pollution Dairy effluent mainly contains milk components: organic substances are dissolved or suspended in the wastewater; their quantity is determined analytically using summary parameters. Adsorbable organic halogen (AOX) represents an unspecific value for a group of substances similar in chemical composition (Table 2). Important values for quantification of the organic load of dairy effluent are the biochemical oxygen demand (BOD5) and the chemical oxygen demand (COD). The quotient COD/BOD5 indicates the biodegradability of the organic material under aerobic conditions. When the ratio is close to 1, the biodegradability is said to be good. The natural organic constituents of milk are very biodegradable but the aerobic degradation of milk fat requires
much oxygen – for instance, the COD of skim milk is about 90 000 mg l 1 but for cream (30% fat) it is 400 000 mg l 1. Besides milk fat, the wastewater may contain other lipophilic substances, for example, mineral oils or grease, that are less biodegradable. Due to a relatively high protein content in dairy wastewaters, the nitrogen content is often used as a pollution index. When comparing effluent loads from different dairies, the indices referred to are expressed in volumetric percent, as shown in Table 2. Thus, if a dairy discharges cooling water together with polluted wastewater, the indices will decrease. Therefore, low pollution indices do not conclusively indicate diligent working practice. For this purpose, the complete size of contamination must be considered, that is, the concentration of pollutants and the total volume of wastewater. Other pollutants come from the regular hygienic operations; detergents represent the biggest portion of chemicals used in dairies. In some cases, NaOH or an acid alone is used, but mixtures of several chemical substances are advantageous to obtain really clean surfaces; Table 3 lists the most important components of dairy detergents. Besides, many cleaning solutions also contain residues of dairy products or other kinds of soil (Table 1) that have been displaced in the cleaning process. Often, the product residues are altered by the cleaning solution: proteins may be partially hydrolyzed by alkalies or enzymes or may be coagulated in acid solutions. Fats may be emulsified and in strong hot alkalies even soaps may be formed. Soaking alkalies from bottle-washing machines contain dissolved starch or protein glues from removed paper labels. In contrast to most cleaning solutions, disinfecting solutions can be used only once, and then they must be discharged. Commonly, they contain only very small amounts of soil but always a surplus of the active disinfectant and of potential reaction products also, for instance halogenics and AOX. Conditioning of boiler feed water demands some chemicals, that is, complexing agents to sequester the residual hardness of the pretreated water and to give an alkaline pH. Other additives, for instance starch, tannins, or synthetic polymers like polyacrylate or polystyrene derivatives, serve to improve the blowdown of the sludge from the boiler into the wastewater. Furthermore, sodium sulfate may appear in the effluent formed from sodium
613
614 Utilities and Effluent Treatment | Dairy Plant Effluents Table 1 Consumption of water in dairies in view of effluent generation Area of use
Application
Examples
Main effluent pollutants
Production
Manufacture
Hygienic operations
Prerinsing
Washing of butter or cheese curd Electrodialysis of whey Removal of product residues from equipment after use Solutions of detergents or disinfectants Rinsing off residues of cleaning and disinfecting solutions Regeneration of plants for water conditioning Washing the outside of transporters Rinsing of sludge from boilers
Product streams like buttermilk or whey Mineral salts Portions of raw materials or products
Solvent Rinsing Others
Solvent Cleaning Rinsing
Portions of raw materials or products, constituents of detergents and disinfectants Constituents of detergents and disinfectants Ions of chloride, alkali earth metals, or hydrogen Soil, mineral oil, any detergent used Alkali earth metals, organic dispersing agents
Table 2 Most important pollution indices for wastewater Index BOD5
COD
TKN AOX SS
Brief definition
Unit
Biochemical oxygen demand; quantity of oxygen used for aerobic biodegradation of organic matter in the sewage during 5 days Chemical oxygen demand; quantity of oxygen needed for the chemical oxidation of organic matter in the sewage by potassium dichromate Total Kjeldahl nitrogen; mass of bound nitrogen in the sewage, determined by the Kjeldahl method Mass of adsorbable organic halogen compounds in the sewage Volume of sedimentable matter in the sewage
Standard methods
mg O2 l
1
ISO 6060 (1989)
mg O2 l
1
ISO 6060 (1989)
mg N l mg Cl l ml l
1
1
1
ISO 5663 (1984) ISO 95625 (2005) ISO 11926 (1997)
Table 3 Common components of detergents and disinfectants for dairies Range of application
Kind of components
Substances
Cleaning
Alkalies
Sodium hydroxide Sodium carbonate Sodium silicates Trisodium phosphate Nitric acid Phosphoric acid Sulfamic acid Gluconic acid Phosphonates Nitrilotriacetate Ethylenediaminetetraacetate Linear alkylsulfonates (anionic) Alcohol sulfates (anionic) Alcohol ethoxylates (nonionic) Proteasesa Iodophores Sodium hypochlorite Sodium trichloroisocyanurate Chloramine T Quaternary ammonium compounds (cationic) Hydrogen peroxide Peracetic acid
Acids
Complexing agents
Surfactants
Disinfection
Enzymes Halogens
Surfactants Peroxy compounds a
Technical grade, especially for cleaning of membranes.
Utilities and Effluent Treatment | Dairy Plant Effluents
sulfite, which is added to the boiler feed water in order to bind the residual oxygen in the pretreated water.
Quantities of Pollutants
615
Bottle washing has to remove not only product residues from the bottles but also the labels and glue from the outside. The quantity of glue depends on the gluing technology. The additional organic pollution of the soaking lye may be as high as 1–5 kg glue per 10 000 bottles.
Product Losses First of all, product losses into the wastewater and discharged whey cause the organic load of dairy effluent and thus the BOD5 as well as the COD. Compared with other food industries, for example, starch or meat factories, a specific BOD5 not higher than 4.0 kg O2 per Mg processed milk indicates a relatively low organic loading of the wastewater. But the BOD5 of dairy sewage markedly exceeds the average for domestic wastewater (300 mg O2 l 1). In contrast, the dairy wastewater contains a very low quantity of sedimentable substances (Table 4); this is only a small fraction of the common content in domestic sewage. Different equipment and production methods strongly influence the degree of pollution by organic matter and explain the varying indices in Table 4. Even for a single product, like spray-dried milk, BOD5 values between 0.152 and 22.4 kg O2 per Mg final product are reported. Extremely high organic loads are probable from manufacturing specialities like cacao drinks or processed cheese. As a consequence of their viscosity, they leave more residues on each contact surface, which are discharged into the effluent together with soiled cleaning solutions.
Auxiliary Chemicals Little is known about the consumption of chemicals for hygienic operations because exact documentation is lacking; only estimated quantities are available, and the data from 1990 are given in Table 5. Since dairies tend to reduce the chemical pollution of their wastewater, recycling of soiled alkaline solutions is commonly practiced nowadays. Thus, the consumption of alkaline detergents, NaOH included, should have decreased since 1990. In the dairy industry, normally alkaline and less frequently acid solutions are used for cleaning. Therefore, wastewater usually contains a surplus of alkali, which must be neutralized to pH 6–9 before it is discharged into the public sewage system. Only in special cases is there a surplus of acid in the sewage. Therefore, more acid than alkali is needed to neutralize the effluent from cleaning operations (Table 5). Figures for the consumption of auxiliary chemicals for purposes other than hygienic care are hardly available. Thus, it is nearly impossible to give any data on their quantity in dairy wastewater. The demineralization of whey by ion exchange demands NaOH and inorganic acids. Increasing degree of demineralization increases
Table 4 Indices for untreated dairy wastewater Average value (over the day) Indexa
Unit
Doedens1
Bertsch/Doedens2
Quantity of polluted effluent BOD5 load Specific BOD5 COD load Specific COD COD/BOD5 TKN NO3-N BOD5/ total N Total P Lipophilic substances SS pH
m3 Mg 1 kg Mg 1 mg l 1 kg Mg 1 mg l 1 mg l 1 mg l 1 mg l 1 mg l 1 mgl l 1 -
0.8–2.0 0.8–2.0 500–2000 1.5–2.2 30–50 20–130 10–100 20–250 1.0–2.0 9–10.5
1.0–2.0 0.8–4.0 500–2000 0.8–4.0 500–4500 30–250 10–100 3–14 20–250 80–250 1.0–2.0 6–11
a
For abbreviations, see Table 2. Doedens H (2000) Verarbeitung von Milch und Milchprodukten. In: ATV (Abwassertechnische Vereinigung, Hrsg.) (ed.) Industrieabwasser Lebensmittelindustrie, 4. Aufl., pp. 259–277. Berlin: Ernst u. Sohn 2 Bertsch R and Doedens H (2003) Abwasserentsorgung. In: Verband der Deutschen Milchwirtschaft (VDM) (ed.) Richtlinien fu¨r Wasser und Abwasser, pp. 120–213. Berlin: Selfpublisher. 1
616 Utilities and Effluent Treatment | Dairy Plant Effluents Table 5 Specific consumption of cleaning and disinfecting chemicals (kg dry substance per Mg processed milk) in different countries Country
Alkaline detergents (including pure alkalis)
Acid detergents (including pure acids)
Disinfectants
Czechoslovakia Switzerland
0.3–0.8 1.12 (1.23)a 1.13 2.4
0.1–0.3 0.66 (1.08)a 0.71 0.5
0.001–0.7 0.065
Finland Germany
0.07 -
a Including wastewater neutralization. IDF (1993) Environmental influence of chemicals used in the dairy industry that can enter the waste water. Bulletin of the International Dairy Federation, Vol. 288, pp. 17–31. Brussels: IDF.
the required amounts of these chemicals disproportionately and also the chemical load of the sewage. The quantity of chemicals needed for water conditioning depends primarily on the hardness of the available water and on the applied process; generally, demineralization needs more chemicals than softening would require.
Environmental Evaluation General Remarks Dairy effluent often blends with sewage from other industries or from households. This complicates the evaluation of the sewage pollution from dairies. Compared with the effects of product components in dairy wastewater, it is much more difficult to estimate the risks from auxiliary chemicals used. Ecological evaluation has to be based on the knowledge of the concentration of a chemical substance that is expected in the effluent or river. Moreover, fundamental knowledge of the resulting damaging potential is necessary for each applied substance. However, for cleaning and disinfection, dairies often apply mixtures of several chemical agents for increased effectiveness and not a single substance. This complicates environmental evaluation further, because the single components of such a mixture act very differently and may even develop antagonistic or synergistic effects in an aquatic system. The user cannot have the necessary knowledge. Therefore, only the manufacturer is responsible for the selection of suitable components for detergents and/or disinfectants. He has to combine sufficient effectiveness with environmental compatibility in his products as far as possible. But it is the responsibility of the user to apply detergents and disinfectants carefully and to follow the advice of the producer. All these facts explain that the ecological importance of only single chemical substances and not ready-to-use products can be discussed here.
Product Residues If untreated dairy effluent is discharged directly into rivers or lakes, the oxygen consumption by aerobic degradation of product residues would disturb the aquatic ecosystem considerably. Besides, such water is unsuitable for the production of potable water. The higher the organic load of the sewage, the more expensive the treatment in the sewage plant will be and the more sludge that will be produced. Milk proteins contribute to the phosphorus and nitrogen load of the effluent (Table 4) as well as solutions of detergents and some disinfectants (Table 3). Both elements support an unwanted growth of algae in lakes and slowly running waters. For the Federal Republic of Germany, an estimation of phosphorus and nitrogen content of dairy effluents has shown that the mass of nitrogen from product residues and losses and that from chemicals used for hygienic operations are nearly equivalent. But the main sources for phosphorus are detergents. It is possible to eliminate both elements and thus to prevent eutrophic effects (see Utilities and Effluent Treatment: Design and Operation of Dairy Effluent Treatment Plants). Nowadays, more and more effluent plants are equipped with these additional stages.
Auxiliary Chemicals High hygienic standards make the application of chemicals for cleaning and disinfection inevitable. The chemical components in these products show very different effects in sewage, rivers, and lakes. Alkalies and acids strongly change the pH of the wastewater and increase the salt load of running waters, because they pass through the sewage plant unchanged. About one-third of the phosphorus in untreated sewage is used by microorganisms in the biological stage of the effluent plant. The remaining phosphorus, similar to nitrogen, supports the growth of algae, especially in lakes. But nitrogen is not normally as critical as phosphorus because the latter is mostly the limiting factor for the development of algae.
Utilities and Effluent Treatment | Dairy Plant Effluents
Surface-active agents tend to form a foam on the surface of water and thus impede the uptake of oxygen into water or activated sludge systems. As a consequence of a low oxygen concentration in the water, fish may die. Besides, several surfactants or metabolites from these may impede the reproduction of fish by damaging sperm, eggs, or spawn. Other aquatic animals, like daphnia, are inhibited, too. Therefore, surfactants must be biodegradable. This does not mean total demineralization but at least loss of their surface activity by biodegradation in the effluent plant. Special attention must be paid to disinfectants, because generally discharged solutions still contain a considerable portion of the active microbicidal agent. However, they are inactivated by the organic load in dairy wastewater. Only traces of reactive disinfectants may reach the treatment plant and do not inhibit the biodegradation of organic material. But exceptionally high concentrations of a disinfectant as a consequence of an accident or inattentive handling can markedly inhibit biodegradation processes. A more important problem results from the reaction of active chlorine with organic material in the sewage to form undesired AOX. They are persistent, accumulate in the food chain, and are more or less toxic. If there are organic substances with a free amino group, active chlorine in the wastewater may form chloramines, which still have a limited bactericidal effect. Complexing agents can sequester metal ions and some of these compounds can also mobilize undissolved heavy metals from sludge or sediments in rivers or lakes. Especially in the case of ethylenediaminetetraacetate (EDTA), this effect seems dangerous, because it is scarcely biodegradable in contrast to nitrilotriacetate. EDTA passes through the effluent plant unchanged. Therefore, low concentrations of EDTA have been detected in rivers; possible metabolites are aquatoxic. Complexing phosphonates that have substituted for polyphosphates show a ‘threshold effect’: This means that very low quantities are sufficient to sequester alkaline earth ions in hard water; thus, the danger of eutrophication by phosphonates is considerably lower than by phosphates. In addition to the quantities of alkalies and acids from cleaning operations, chemicals used for the regeneration of ion exchange plants increase the salt concentration in dairy sewages. Further pollution by salt results from brine bath overflow in cheese factories.
auxiliary chemicals must be avoided as far as possible. Moreover, the auxiliary chemicals should be used as sparingly as possible. It is the task of management to detect critical points of sewage pollution, to create the technical conditions for reduced pollution, and to consistently motivate the employees to follow the special instructions. The following general remarks may help to reduce effluent pollution or to reduce water consumption. These hints are examples; each dairy has to identify its own weak points and resolve them. Equipment: short routes for flow and transportation of raw • Have materials and products, because it minimizes the
• •
adhering residues after use. Ensure that all plants are easy to clean. Therefore, avoid blind pipes, which need additional volumes of cleaning and disinfecting solutions. Ensure by automatic control of the flow ways that products and fluids for cleaning and disinfection do not contaminate each other.
Production: losses of raw materials, products, additives, and • Avoid auxiliary chemicals into the wastewater by splashing,
• • •
leaking valves or pipe connections, or overflowing containers. Optimize operations aiming to have a minimum of residues on product-contacting surfaces. For instance, preheating for the production of ultra-high temperature milk reduces the deposits on heat exchange surfaces. Try to utilize whey fully. Never discharge solid sludge from centrifugal processing or residues from microfiltration by membranes into the wastewater.
Hygienic operations: product residues from product-contacting • Remove surfaces. For instance, blowing out by filtered com-
• •
Steps Toward a Reduced Effluent Pollution Each dairy should attempt to minimize effluent pollution; it saves costs for internal and public effluent treatment. Thus, losses of raw material, products, and
617
•
pressed air or rinsing with a small volume of water may be useful; rinsing with warmed skimmed milk is advisable for cream residues, because it makes it easier to recover and to utilize the cream rinsed off. Avoid needless dilution of chemical solutions by rinse water; it increases the consumption of detergents or disinfectants. Use mixed detergents instead of pure chemicals. Suitable additives can markedly improve the efficiency of alkalies and acids in many cases. Subsequently, the chemical pollution of the wastewater by used solutions decreases. Regenerate used cleaning solutions by sedimentation, centrifugation, or membrane techniques in order to extend their useful life whenever it promises success.
618 Utilities and Effluent Treatment | Dairy Plant Effluents
• •
The sludge may be disposed or utilized for biogas production. Disinfect closed systems by heating instead of applying chemicals, if it is safe and the consumption of energy seems acceptable. Avoid chemicals that are dangerous for aquatic systems or may disturb wastewater treatment. If there are any doubts, ask the producer or the distributor of the detergent/disinfectant.
Conditioning of water and sewage: the water hardness only as far as necessary for • Reduce the intended use. Water softening should be done by
• •
•
•
•
ion exchange or reverse osmosis. Other physical methods cannot be advised since at present too little is known about their effectiveness. Use as much condensate from evaporators as possible in order to reduce water hardness, but do not overlook possible microbiological risks. Use condensates also for cleaning purposes. The condensates from the production of evaporated milk or milk powder contain only small amounts of organic substances. Therefore, it is not necessary to discharge them into the general wastewater. Condensates may be used for cleaning of floors in uncritical areas, like offices, or for cleaning of cars and trucks. Following pollution with mineral oil or grease, they must be eliminated before this wastewater may be discharged into the general sewage. Condensate that is not used should be discharged with rainwater. Neutralize the surplus of alkalies from cleaning lyes by carbon dioxide or boiler flue gas but not by mineral acids. This reduces inorganic pollution of the wastewater. Further advantages of using boiler flue gas are less exhausted SO2 and low running costs but it needs special installations. Separate the fat from the wastewater. This is normally not necessary for all the wastewater but essential for the part of the sections producing butter or cream. The separation may be done in gravity traps or by flotation. However, the separation will not work in case of emulsified fat. The separation of fat, oil, and grease from the wastewater by the dairy itself not only reduces the BOD5 and COD, but it also prevents deposits in the drain. Moreover, these pollutants can cause severe problems
• •
in the biological wastewater treatment process on-site and in public sewage treatment facilities. Collect and discharge the normally unpolluted rainwater separately from the common wastewater. It saves money and avoids overflow of the wastewater plant in case of heavy rainfall. Further recommendations for minimizing product losses into the wastewater and also for reducing the cost of freshwater production as well as of wastewater treatment are given in the IDF document no. 382 (2003).
See also: Milking and Handling of Raw Milk: Milking Hygiene. Milk Protein Products: Membrane-Based Fractionation. Utilities and Effluent Treatment: Design and Operation of Dairy Effluent Treatment Plants; Water Supply.
Further Reading Bertsch R and Doedens H (2003) Abwasserentsorgung. In: Verband der Deutschen Milchwirtschaft (VDM) (ed.) Richtlinien fu¨r Wasser und Abwasser, pp. 120–213. Berlin: Selfpublisher. Britz TJ and Lamprecht C (2008) Dealing with environmental issues. In: Britz TJ and Robinson R (eds.) Advanced Dairy Science and Technology, pp. 262–293. Oxford, UK: Blackwell Publishing. Britz TJ, van Schalkwyk C, and Hung Y (2006) Treatment of dairy processing wastewaters. In: Wang LK, Hung Y, Lo HH, and Yapijakis C (eds.) Waste Treatment in the Food Processing Industry, pp. 1–28. Boca Raton, FL: Taylor and Francis. Demmel U (1998) Abwasserbehandlung in der Lebensmittel- und Getra¨nkeindustrie im Vergleich. Entsorgungsmagazin 6: 42–47. Doedens H (2000) Verarbeitung von Milch und Milchprodukten. In: ATV (Abwassertechnische Vereinigung, Hrsg.) (ed.) Industrieabwasser Lebensmittelindustrie, 4. Aufl., pp. 259–277. Berlin: Ernst u. Sohn. European Hygienic Engineering and Design Group (ed.) (2004) Hygienic Equipment Design Criteria, Doc. 8, 2nd edn. Brussels: EHEDG. IDF (1979) Control of water and waste water in the dairy industry. B-Doc. 75. Brussels: IDF. IDF (1993) Environmental influence of chemicals used in the dairy industry that can enter the waste water. Bulletin of the International Dairy Federation, Vol. 288, pp. 17–31. Brussels: IDF. IDF (2003) Guide for dairy managers on wastage prevention in dairy plants. Bulletin of the International Dairy Federation, Vol. 382. Brussels: IDF. Kunz P and Frietsch G (1986) Mikrobizide Stoffe in biologischen Kla¨ranlagen. Berlin; Heidelberg; New York; Tokyo: Springer. Noyes R (1993) Pollution Prevention Technology Handbook. Park Ridge, NJ: Noyes Publication. Scho¨berl P (1993) Biologischer Tensidabbau. In: Kosswig K and Stache H (eds.) Die Tenside, pp. 409–464. Mu¨nchen; Wien: Hauser. Wildbrett G (2006) Abwasserfragen. In: Wildbrett G (ed.) Reinigung und Desinfektion in der Lebensmittelindustrie, 2nd edn., pp. 317–341. Hamburg: Behr’s Verlag.
Design and Operation of Dairy Effluent Treatment Plants R J Byrne, Jacobs Engineering, Mahon Industrial Estate, Blackrock, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Glossary Biochemical oxygen demand (BOD) It is an important measure of water quality. It is a measure of the amount of oxygen needed (in mg l1) by bacteria and other microorganisms to fully oxidize the organic matter present in a water sample. It is also called the biological oxygen demand. Chemical oxygen demand (COD) It is defined as the oxygen equivalent of the organic portion of the sample that is susceptible to oxidation by a strong chemical oxidant. COD does not distinguish between refractory and inert organic matter. COD tests require approximately 3 h. Five-day biochemical oxygen demand (BOD5) It is defined as the amount of oxygen required by bacteria to decompose organic matter for a specified time (5 days) under aerobic conditions. The amount of oxygen reported with this method represents only the carbonaceous oxygen demand (CBOD) or the easily
decomposed organic matter. BOD5 is commonly used to measure natural organic pollution. The BOD5 of drinking water should be less than 1, while that of raw sewage may run to several hundreds. The BOD5 of dairy waste may run from several hundreds to hundreds of thousands. Total dissolved solids The weight of solids in solution per unit volume of water, measured by evaporating a known volume of filtered water and weighing the residue. Total solids The weight of all solids, dissolved or suspended, and organic or inorganic, per unit volume of water, measured by evaporating a known volume of water and weighing the residue. Total suspended solids The measure of particulate matter suspended in a sample of water or wastewater. After filtering a sample of a known volume, the filter is dried and weighed to determine the residue retained.
Effluent Characteristics
Discharge Standards
Dairy effluents contain dissolved sugars and proteins, fats, and sometimes the residues of additives used in production. The effluent treatment plant designer is primarily interested in the following characteristics of the effluent: biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total dissolved solids (TDS), phosphorus (P), nitrogen (N), and pH. Table 1 shows typical losses from some of the principal activities in a dairy. The typical characteristics of dairy effluent are given in Table 2. The waste-load equivalents of specific milk constituents are
The design of the treatment plant depends on the discharge standards set by the licensing authority. A British Royal Commission in 1912 determined that where a receiving water body could provide a dilution of 8:1, a discharge standard of 20 mg l 1 BOD and 30 mg l 1 Suspended Solids (SS) was appropriate. However, much higher standards are now frequently required. Table 3 summarizes the license requirements of a number of dairy facilities in Ireland.
1 kg milk ¼ 3 kg COD 1 kg lactose ¼ 1.13 kg COD 1 kg protein ¼ 1.36 kg COD The wastewater may also contain pathogens from contaminated materials, grit or other particulates from truck washing, and paper and other packaging materials.
Prevention and Control of Pollution Given the very high capital and operating costs associated with wastewater treatment, not to mention the cost of water and chemicals and the value of lost product, it makes good sense for producers to initiate and maintain a program of pollution prevention. Prevention practices in the dairy industry include
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620 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants Table 1 Typical losses in milk processing operations (in kg BOD m3 milk)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Operation
Average
Range
Milk reception, churn washing, cleaning up Cooling raw milk, storage, washing tanks and pipelines Washing road tankers Separation, storage of skim milk and cream Separation, storage of skim milk and cream plus cream pasteurization Churning and washing butter Evaporating skim milk to low total solids Evaporating skim milk to high total solids and spray-drying Roller drying Pasteurizing milk and storage, bottling milk, bottle washing Clotted cream Cheesemaking (hard pressed) Cottage cheese (washed curd) Condensing fresh whey (to low total solids) Condensing sweetened separated condensed milk Full-cream evaporated milk, with canning
0.26 0.19 0.25 0.14 0.66 0.46 0.23 0.74 0.53 0.85 1.20 0.89 12.00 0.25 1.40 0.75
0.11–0.66 0.07–0.31 0.10–0.40 0.09–0.24 0.46–1.25 0.25–0.80 0.16–0.30 0.14–1.50 0.25–1.30 0.49–1.70
Table 2 Typical characteristics of dairy effluent BOD
0.8–2.5 kg tonne1 milk
COD TSS TDS Phosphorus Nitrogen pH Flow
1.5 times BOD 100–1000 mg l1 10–100 mg l1 10–100 mg l1 6% of BOD level 2–12 1–2 m3 tonne1 milk
of product losses by better production • reduction control; of disposable packaging (or bulk dispensing of • use milk) in lieu of bottles where feasible; and reuse of waste product (where feasible) • collection in lower-grade products such as animal feeds; of water and chemical use; use of high• optimization pressure nozzles; recirculation of cooling waters; of condensates for cleaning; • use energy and • avoidancerecovery; of phosphorus-based cleaning agents. •
Unit Processes for the Treatment of Dairy Effluent The series of unit processes chosen for the treatment of any particular effluent will depend upon the characteristics of the wastewater, the location and space available, the outlets for residual products, and the final effluent quality required.
0.23–2.00
1.20–1.70 0.50–1.00
and preliminary treatment processes • Pretreatment Coarse and screening • Removal of fine fats, • Grit removal oils, and grease • pH control • Nutrient balancing • Flow and load balancing • treatment processes • Biological sludge process • Activated Biological • Anaerobic filtration •Clarification treatment • Sludge treatment • Solid–liquid separation • Stabilization •
Pretreatment and Preliminary Treatment Processes Coarse and Fine Screening Screening is designed to remove suspended particles from the wastewater, in order to protect the remainder of the treatment plant from damage by gross solids and to protect subsequent treatment stages from solids overload. Usually, the screening process is divided into two stages: screening – to remove solids of nominal size • coarse 20 mm and above; and screening – to remove solids of nominal size • fine 0.25 mm and above. Coarse screens can be either static, comprising inclined bars at a spacing of approximately 25 mm, or mechanically raked. In either case, it is important that the velocity of flow through the chamber is maintained at values between 0.3 and 0.8 m s1 to ensure that grit or other
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Table 3 Comparison of treated effluent discharge standards
Facility
BOD mg l1
SS mg l1
Ptot mg l1
A B C D E F
20 15 20 20 20 25
30 15 30 30 30 35
2
G H J
20 10 40
30 15 40
1 1 2
2 2 2 2
Ammonia as N mg l1
Nitrate mg l1
1 10 0.5 10 2 5
20 10
1 2
Temperature C
Flow m3 day1
15 15 15 15
25 21 25 25 25 25
10 000 900 4000 4500 8900 18000
25 25
1400 9000 2800
15 10 15
detritus does not settle out and that the intercepted screenings are not dislodged and carried forward. Fine screens can be installed directly after the coarse screens, except where the wastewater has a high content of fat or grease. Fine screens can be – parabolic wedge-wire screens – sometimes • static called ‘sidehill’ screens; – where the wastewater is screened through a • brushed curved perforated plate, which is brushed intermit-
•
Ntot mg l1
tently or continuously; a typical rotary brushed fine screen is shown in Figure 1; and rotating drum screens – where the wastewater is led to the center of the drum and flows via wedge wires to the next stage. This type of screen cannot be used where there are high levels of fat in the wastewater.
Provision should always be made for the high-pressure or steam cleaning of fine screens, particularly where the screens are subjected to fatty wastewaters.
Discharge to River Spray irrigation River River Sewer Stream (dilution 6:1) Lake River Estuary
quiescent flow pattern. On small plants it is still not unusual to find static grease traps designed on the basis of flow rate. Typically, a retention period of 30 min or more is provided and the accumulated fat/grease is removed manually. The principal drawback of such systems is the possibility of the accumulated fats being subjected to a higher temperature and becoming emulsified. Recently, however, flotation, particularly dissolved air flotation (DAF), has become the most frequently used process for the removal of fat/grease. In this process, air is dissolved in water under pressure and then the supersaturated air–water mixture is injected into a flotation tank. The process is shown schematically in Figure 2. The air comes out of solution in the form of microbubbles, which attach themselves to suspended matter, including fat/grease, which then float to the surface. The floating material forms a scum on the surface of the tank and is removed intermittently by a mechanical skimmer. Typical design parameters for a DAF unit are flow velocity: up to 7.2 m h ; • upward volumetric time at maximum inflow: 20–30 min; • recycle rate:retention 20–35% of inflow; and • air/solids ratio: 0.005–0.06 kg air kg solids to be • removed. 1
Removal of Fat and Grease Fat and grease will solidify and float to the surface of the liquid given time, temperate ambient conditions, and a Brushes
1
Where the efficiency of the process can be improved by the use of flocculating agents, it has also been found that 50% or more of the COD load can be removed by the DAF process.
Grit Removal Screenings
Pertorated screen
Figure 1 Rotary brushed fine screen.
Grit particles, which can include sand, gravel, clay, and other detritus, generally enter the waste stream from the truck and tanker washing area or through the corrosion of concrete or paved surfaces. If allowed to pass through the process, grit could cause serious damage to pumps and other mechanical equipment in addition to combining with sludge to cause pipe obstructions.
622 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants Scraper belt
Steel with rubber tips
Inlet pipe Air/water
DAF/cell
Float scum
Steel baffles
Outlet to balance tank
Figure 2 Dissolved air flotation.
Grit will settle readily, provided the velocity of flow is reduced to approximately 0.3 m s1. It is quite important that the velocity is not permitted to fall below 0.15 m s1, as this could result in the settlement of organics. Grit settles at about 30 mm s 1, so where the length of the grit channel is 15–20 times the depth, the grit removal efficiency is high. The maintenance of constant velocity in the grit channels is usually achieved either by the formation of parabolic channels or by using a Sutro Weir. This is a special type of weir that ensures that the velocity of flow is directly proportional to depth.
pH Control The influence of pH within a treatment plant is both chemical and biological. Control of pH is necessary to ensure that the wastewater does not damage the structures, equipment, or pipework. Most biological processes operate best within the range 6.5–8.5; however, it has been found that process efficiency can be maintained even where the resulting pH is not optimal, provided the pH is reasonably constant and not subject to sudden change.
Nutrient Balancing Biological treatment processes can be inhibited if the balance of available nutrients is insufficient to ensure that the microbes can break down the organic matter in an efficient manner. Frequently, dairy wastewater may have an excess of phosphorus and a deficiency of nitrogen or potassium. It is generally accepted that the ratio BOD:nitrogen:phosphorus should be 100:5:1 to facilitate microbial breakdown. Nutrient deficiency can be overcome by the addition of urea (or any other source of N) and phosphoric acid. In addition, there are several proprietary products available that can provide nutrients in different proportions to meet the specified demand. It is important to ensure that the
available N and P are measured at the entry to the biological treatment and not prior to other physical/chemical processes. Hydraulic and Load Balancing Biological treatment processes operate best under constant and consistent organic load, with only minimal, gradual variations in the substrate. Most physical and physiochemical processes are flow-dependent, as are pumps, pipework, and other items of mechanical equipment. It is therefore essential that adequate provision be made for balancing both pollution load and flows. Balancing can be effected by a combination of provision of adequate storage capacity and control of the forward flow. The theoretical capacity of a balancing tank can be determined as follows: buffer required to minimize substrate variations þ provision for variations in inflow over day/week/month as appropriate þ provision for equipment malfunction þ freeboard
Provision must be made for mixing the balancing tank contents thoroughly, and consideration should be given to aerating the contents where the potential for biodegradation of the waste exists.
Biological Treatment Processes Biological treatment processes have generally been classified as aerobic (where the degradation takes place in the presence of oxygen) and anaerobic (where oxygen is excluded). Processes classified as aerobic include activated sludge process and biological filtration, although in the case of the latter, both aerobic and anaerobic systems coexist on the surface of the media. Activated Sludge Process The activated sludge process, discovered in the early 1900s, is a biological wastewater treatment method in
Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
which microorganisms are bunched together to form sludge flocs. The flocs develop spontaneously when the wastewater is aerated. The wastewater and the sludge flocs are mixed in the aeration tank. Most of the impurities in the wastewater are suitable nutrients for the bacteria in the flocs; these bacteria take up the nutrients in their cells. An activated sludge floc is a conglomerate of and dead bacterial cells; • living protozoa and higher organisms; • trapped inorganic • precipitated salts. particles and organic fibers; and • The floc is held together by chemical forces and a slime matrix surrounding the cells. The composition of the floc is dynamic, not static, and can be changed through alterations in the process conditions. The general processes that occur are
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The key parameters used in the design of the activated sludge process are (F), usually expressed in kg BOD; • food microbial population, usually expressed as kg mixed • liquor suspended solids (MLSS); it is also referred to as
•
mass (M); and the ratio of food to mass, which is usually called F/M ratio and is a measure of the loading rate.
Typical design data are shown in Figures 4 and 5. Activated sludge is generally categorized based on the F/M ratio as follows: high-rate activated sludge conventional activated sludge extended aeration sludge
F/M ratio in the range 0.6–1.8; F/M ratio in the range 0.2–0.5; and F/M ratio in the range 0.04–0.1.
Several configurations of the aeration tank have become – slow breakdown of adsorbed materials; • stabilization popular in the treatment of dairy wastewaters, including – conversion of nutrients to substances • mineralization like carbon dioxide; flow – the wastewater and sludge are introduced • plug – conversion of nutrients to cell material; into one end of an aeration basin where the ratio • assimilation and length:width is >12:1; respiration – microbial mass converted to the ditch (developed by Paasver in 1953) – • endogenous • the oxidation new cell material for new cells. aeration tank is laid out as a racing track, and The operating principle of the activated sludge process is that wastewater containing biodegradable organics is fed to a reactor containing a wellmixed, well-aerated population of microbes (biomass, in the form of a flocculent suspension). The resulting mixture of biomass and water is separated, with the solids (sludge) being returned to the reactor (Figure 3).
• •
oxygen transfer and mixing are effected by horizontal rotors (Figure 6); the carousel – this is similar to the oxidation ditch; however, the oxygen transfer and mixing duties are frequently split. This configuration allows the establishment of an anoxic zone; and the sequencing batch reactor – aeration and clarification take place in the same tank (Figure 7).
Oxygen
Input Aeration stage
Preaeration stage (optional)
Figure 3 The basic activated sludge process.
Sludge recycle
Sludge separation
Treated effluent
624 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
% BOD removal
100 90 80 70 60 0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
F/M
kg oxygen kg–1 BOD removed
Figure 4 Percentage BOD removal versus food-to-mass (F/M) ratio for the activated sludge process.
2.5 2 1.5 1 0.5 0 0.02
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
F/M 1
Figure 5 Oxygen demand (kg O2 kg
BOD removed) versus food-to-mass (F/M) ratio for the activated sludge process.
Oxidation ditch
Clarifier
Rotor Rotor Excess activated sludge
Return sludge Figure 6 Typical oxidation ditch plant.
Biological Filtration The principle of the biofiltration process is similar to that of the activated sludge process. In this process, the organic matter (food) is brought into contact with high numbers of microbes (film adhering to media) in the presence of oxygen (Figure 8). Biological filters are not normally mechanically aerated, as the heat generated during the microbial degradation process is usually sufficient to maintain a temperature gradient between the wastewater and the surrounding air, ensuring an adequate draught. The most common form of biofilter used in the treatment of dairy wastewater is the high-rate biofilter. The biofilter
media, which are usually in the form of open-textured plastic, can be either random-packed or modular. High-rate biofilters are normally loaded above 0.6 kg BOD m3 and generally remove 50–70% of the applied BOD (Figure 9). The wastewater is distributed over the surface of the media at a minimum irrigation rate of 1.5 m3 per m2 plan area per h, and this ensures that no clogging of the media occurs and discourages insect life (Figure 10). The most critical parameters in the operation of a biofilter are rate – it is essential that the irrigation rate is • irrigation maintained at all times to ensure that the filter media do not become clogged;
Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
625
Wastewater in
Fill 1
Aeration 2
Clarified outflow
Sludge
Settlement 3
Decant and waste sludge 4
Figure 7 Sequencing batch reactor.
– the presence of fats and grease in concen• fats/grease trations above 50 mg l can result in the coating of the
Effluent
1
• Film Media
biological film; this can lead to uncontrolled anaerobic activity and significant odors in extreme cases; and temperature – a reduction in efficiency will occur when the temperature within the biofilter drops below 8 C.
Usually, the outflow from high-rate biological filters, even after settlement, is not of sufficiently high quality to be discharged to watercourses and will require further treatment; activated sludge process is frequently used.
Nutrient Removal Air Figure 8 Activity on biofilter media.
applied – the application of excessive loading • BOD rates (shock loads) can also result in clogging of the
•
media and ponding of the surface; prolonged BOD loading can give rise to odor problems; pH – inadequate control of the pH will reduce the efficiency of the biofilter and may even result in damage to the media and support structures;
Nitrogen
This is a two-stage process: nitrification, which is carried out under strongly aerobic conditions, and denitrification, which is carried out under anoxic conditions. In the nitrification stage, ammonia is converted to nitrite and nitrate. For each kilogram of ammonia oxidized kg O is consumed; • 4.18 14.1 kg as CaCO is destroyed; • 0.15 kg alkalinity of cells is created sludge); and • 0.09 kg of inorganic carbon(extra is consumed. • 2
2
626 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants 100 % BOD removal
90 80 70 60 50 40 1
2
3
4
5
Applied load (kg BOD m–3 day–1) Figure 9 Distribution of wastewater over modular plastic media.
Distribution channel
• Hole in channel floor Splasher bracket
Splasher plate Spacer
•
(SCFA), which are stored in the cell as polyhydroxyl butyrates (PHB); under aerobic conditions, the stored PHB is oxidized and energy is released, allowing the assimilation of soluble orthophosphate; and the orthophosphate is metabolized by the cell and excess quantities are stored in the cell as polyphosphate. The storage of excess phosphorus is known as ‘luxury uptake’ of phosphorus, and it is this ability of the cell that is exploited in the biological phosphorus removal process.
A number of biological processes have been developed, many based on the activated sludge process, that are very effective in the biological removal of nitrogen and phosphorus from wastewater. The A2O process
Flocor module
Figure 10 Biofiltration efficiency.
In the denitrification stage, the nitrate and nitrite are converted to nitrogen gas (N2). For each kilogram of nitrate reduced kg O is recovered; • 2.86 3.0 kg as CaCO is recovered; and • 0.4 kgalkalinity of cells is created (extra sludge). • 2
2
Biological phosphorus removal
Biological phosphorus removal is dependent mainly on the ability of the Acinetobacter spp. to release phosphorus under anaerobic conditions and to absorb it under aerobic conditions. The mechanism can be summarized as follows: anaerobic conditions, readily degradable organic • under matter (BOD) is fermented to short-chain fatty acids
This continuous process (Figure 11), developed in the United States, is a refinement of the activated sludge process and takes advantage of the ability of denitrifying bacteria (abundant in the anoxic denitrification (DN) tanks) to convert the nitrate (which is recirculated from the nitrification (N) tanks) to nitrogen gas and phosphorusaccumulating bacteria in the anaerobic (AN) tanks to take up the available P. This process is capable of producing an effluent with NTOT <10 mg l 1 and PTOT <1.0 mg l 1. The BIODENIPHO process
This process (Figure 12), which was developed in Denmark, is based on the oxidation ditch configuration and utilizes the ability of a special culture of phosphorusaccumulating bacteria, which is cultivated in an anaerobic tank. This process is then incorporated into a nitrification–denitrification system. This process is capable of producing an effluent with NTOT <10 mg l 1 and PTOT <1.0 mg l 1. The BIOSTYR process
The BIOSTYR process (Figure 13) was developed in France and is based on upflow filtration through
Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
Influent
627
Recirculation Clarifier
AN
AN
DN DN DNN DN NNDN
N
Return sludge
N
N
Excess activated sludge
Figure 11 Biological N and P removal.
DN Phase 1
AN
N
N Phase 2
AN
N
N Phase 3
AN
DN
N Phase 4
AN
N Figure 12 Phased oxidation ditch process for biological nitrogen and phosphorus removal.
submerged and floating fine granular media. Air can be injected at the base of the bed or into the media itself. In the latter case, the filter can simultaneously nitrify and denitrify. The BIOSTYR process does not require separate clarification. Special characteristics of the method are processes in one tank, that is, no final settling • three tank; treatment efficiency; • high space-saving unit; • compact, often be built into existing plants; • can temperature dependency; and • low odor nuisances, as the surface water is oxygen• nosaturated, treated water.
recycling of organics within the natural environment. It occurs naturally in river and lake sediments, marshes, and so on, and although it has been used since the nineteenth century, it is only in recent times that the biochemistry and microbiology of the process have been understood. The production of methane – for reuse – is the prime reason for using anaerobic processes in the treatment of dairy wastes. The anaerobic digestion of complex organic waste can be summarized as follows: 1. the breakdown of large molecules such as cellulose, proteins, and fats to simpler molecules such as sugars, alcohols, peptides, amino acids, and other products. This stage is accomplished largely by enzymes released by the microbes (bacteria, fungi, and protozoa); 2. the utilization of simpler molecules by the acidforming bacteria to form volatile acids, carbon dioxide, and hydrogen; and 3. the production of methane from the products of the second stage by methane-generating bacteria. The microbial population within an anaerobic digester comprises many different types of bacteria. 1. Non-methanogenic stage The non-methanogenic bacteria are obligate anaerobes and facultative bacteria. These bacteria feed on the primary substrate and produce a variety of organic acids and alcohols as end products, and are adaptable and could survive in the progressively decreasing pH. 2. Methanogenic stage The methanogenic bacteria are obligate anaerobes and include various methanobacterium, methanosacina, and methanobacilli. These use the acids and alcohols produced in the non-methanogenic stage as their growth substrate and produce a mixture of carbon dioxide and methane: CH3 COOH ¼ CH4 þ CO2
Anaerobic Processes Anaerobic digestion is one of the many microbial processes that have existed since the earliest times for the
If the process is balanced, the production of acids should be equal to the utilization of acids; however, the production of methane is the rate-limiting process. Methanogenic bacteria are very susceptible to pH
628 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
Effluent to further treatment
Backwash water reservoir Floating granular media
Aeration inlet
Wastewater inlet Sludge Figure 13 Upward flow submerged filter.
changes (6.8–7.8), so it is critical that the substrate load to the system be strictly controlled and that the system retains a significant buffering capacity. Buffering Buffering in an anaerobic process is provided largely by the presence of ammonium bicarbonate formed by anaerobiosis:
returned to the aeration tank. Success in meeting the discharge standards is dependent on the efficiency of clarification, which, in turn, is dependent on the settleability of the sludge. In order to ensure that the sludge settles in the clarifier, conservative design parameters should be chosen: surface overflow rate: 21–27 m3 m2 day1 sidewall depth: >2.5 m solids loading rate: 0.25–5 kg m 2 h1 sludge retention time: <1 h
CO2 þ H2 O þ NH3 ¼ NH4 HCO3
If the waste being treated is mainly carbohydrate, with few proteins, it may be necessary to add some nitrogenous material. Temperature Anaerobic digestion generally takes place within two temperature ranges: 30–37 C and • mesophilic thermophilic 52–60 C. •
Sludge Treatment The on-site treatment of the biological sludge generally comprises a number of elements, some focused on solid– liquid separation and others on stabilization. The choice of the process is heavily influenced by the available disposal routes.
Although most anaerobic digestion plants operate in the mesophilic range, the thermophilic range offers the advantages of greater gas production, faster reaction rates, greater breakdown of organics, and, especially, pasteurization of product. The operation and control of thermophilic digesters is much more difficult. For this reason, thermophilic digestion is generally used only where the wastewater is already quite hot and the COD is very high (>5000 mg l 1).
Solid–Liquid Separation Solid–liquid separation usually comprises two distinct elements: thickening (see Table 4) and dewatering (which need not be sequential). Thickening is used to increase the solids content to 3–5% and generally removes the unbound water from the sludge. Dewatering is used to further increase the solids content. Filter belt pressing and centrifugation can increase the solids content to 18–25% (depending on sludge characteristics) and plate presses can increase it to 40%, while drying can produce sludge granules with a moisture content of <10%.
Clarification Stabilization of Sludge An integral part of most biological treatment processes is the clarification of the wastewater to remove the sludge generated. In the activated sludge process, the sludge is generally
Stabilization of sludge is carried out to ensure that the sludge is suitable for long-term storage and ultimate
Table 4 Comparison of thickening processes Method
Advantages
Disadvantages
Picket fence thickener
Simple to operate Low operating cost Low operator attention Minimal power consumption Effective for excess activated sludge Will work without conditioning chemicals Relatively simple equipment components
Odor potential during stirring Thickened sludge concentration low (3–5%) High space requirements
Dissolved air flotation
Centrifuge
Gravity belt thickener
Rotating drum thickener
Low space requirements Effective for excess activated sludge Minimum housekeeping and odor considerations High thickened sludge concentrations Low space requirements Relatively low capital cost Relatively low power consumption requirements High thickened sludge concentrations and solids capture with minimum polymer consumption Low space requirements Low capital cost Relatively low power consumption High solids capture
Relatively high power consumption Thickened solids concentration limited Odor potential due to air-stripping effects Operator attention High space requirements Relatively high capital cost and power consumption Sophisticated maintenance requirements Best suited for continuous operation Housekeeping Polymer dependent Moderate operator attention Odor potential Building corrosion potential, if enclosed Polymer dependent Sensitivity to polymer type Housekeeping Odor potential Moderate operator attention requirements
630 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants Table 5 Comparison of biological stabilization processes
Process
Operating temperature C
Retention period days
Aerobic digestion
20
20–30
ATAD (auto-thermal aerobic digestion)
45–60
<20
Mesophilic anaerobic digestion
36
10–18
Thermophilic anaerobic digestion
55
<6
Composting
60
10–20 þ maturation
Comments Can reduce organic content by up to 40% Kills most viruses and reduces organic matter by 50% Can reduce organic matter by up to 30% and produces about 1 Nm3 of biogas for every kg of matter degraded Can reduce organic matter by up to 30% and produces about 1 Nm3 of biogas for every kg of matter degraded Process can be very unstable and difficult to operate Can be either in windrows with forced ventilation or regular mechanical turning, or in tanks with forced ventilation
Table 6 Comparison of chemical stabilization processes
Process
Operating pH
Lime stabilization
12
N-Viro
>11
Chemfix
11.5–12.5
Retention period
Comments
Min 3–5 days Material normally stored for 20–30 days 3–5 days Material normally stored for 20þ days 1–2 days
Produces a product with a solids content in excess of 50% and highly desirable as an additive on lime-deficient soils
Uses an alkaline admixture (cement kiln dust and quicklime). Produces a granular product with a solids content in excess of 50% and highly desirable as an additive on acidic soils Produces a soil-like, odorless product with 50% dry solids
disposal without having adverse environmental or safety impacts. A well-stabilized sludge will be free of odors and pathogens, and will generally be free of biological activity. Stabilization can be achieved biologically (aerobic or anaerobic digestion, or composting), chemically (using alkaline admixtures), or thermally (drying) (see Tables 5 and 6). Pasteurization is normally required to eliminate pathogens. See also: Utilities and Effluent Treatment: Dairy Plant Effluents.
Further Reading Eckenfelder W and Musterman J (1995) Activated Sludge: Treatment of Industrial Wastewater. Lancaster, PA: Technomic Publishing Company Inc.
Forster CF (1985) Biotechnology and Wastewater Treatment, pp. 61–133. Cambridge: Cambridge University Press. Gerardi MH (2006) Wastewater Bacteria. Hoboken, NJ: John Wiley and Sons Inc. Gray NF (1989) Biology of Wastewater Treatment, pp. 232–479. Oxford: Oxford University Press. Henze M (1997) Basic biological processes. In: Henze M, Harremoe¨s P, la Cour Jansen J, and Arvin E (eds.) Wastewater Treatment – Biological and Chemical Processes, pp. 55–111. Berlin; Heidelberg: Springer-Verlag. Kiely G (1998) Environmental Engineering, pp. 493–622. Maidenhead: McGraw-Hill. Metcalf & Eddy, Inc., Asano T, Burton F, Leverenz H, Tsuchihashi R, and Tchobanoglous G (2007) Water Reuse: Issues, Technologies and Applications. New York: McGraw-Hill. Spellman FR (2008) Handbook of Water and Wastewater Treatment Plant Operations, 2nd edn. Boca Raton, FL: CRC Press. Stephenson RL and Blackburn JB, Jr. (1998) The Industrial Wastewater Systems Handbook, pp. 247–299. Boca Raton, FL; New York: Lewis Publishers. Water Environment Federation (2006) Membrane Systems for Wastewater Treatment. New York: McGraw-Hill.
Reducing the Negative Impact of the Dairy Industry on the Environment V B Alvarez, M Eastridge, and T Ji, The Ohio State University, Columbus, OH, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The dairy industry is important for providing a nutritious food source for millions of people and contributing to a major portion of the economical structure of many communities, states, and countries. Besides providing the livelihood of the family involved at the farm in the production of milk, there is about $2 generated elsewhere in the sector for each $1 earned on the farm and about 2.25 jobs generated elsewhere for every job on a dairy farm. Although the number of dairy farms has decreased (less than 2% of the population today produces food to feed the world), milk production in the United States and worldwide has been increasing. According to the UN Food and Agricultural Organization, the world milk production from cattle expanded by 1.2% from 2007 to 2008 (578 billion tonnes). India produces the most milk in the world, but in terms of total annual milk production from cattle, the United States ranks first, followed by India and China. From 1970 to 2009, the world population increased by about 1.7 times, and the population growth is expected to be about 1.8% per year. For a variety of reasons, the landscape of farms has changed significantly through the years. For example, the number of dairy cows in the United States has declined from about 12 million in 1970 to about 9 million in 2009. However, milk production has increased from 52.5 billion kg in 1970 to 85.8 billion kg in 2009. Thus, the production per cow has substantially increased during the same period from 4432 to 9353 kg cow 1 yr 1, a 2.1-fold increase over a 40-year period. Although the total production and efficiency of milk production has increased, the increase in the world population, number of cows per farm, and farming methods and human population densities has necessitated the development of new best management practices (BMPs) and environmental policies for the production and processing sectors of the dairy industry. Federal and local agencies in several countries, including the United States, closely regulate the environmental practices for dairy farms in order to protect the land, water resources, and air. Although the regulations may be different from country to country or from state to state, farmers employ a wide variety of BMPs to reduce the risk of environmental contamination by manure (animal manure, bedding, and wastewater) and to conserve the quantity of water used.
The manufacturing of fluid milk and other dairy products leads to the production of wastes. The various handling steps include product processing, storage, transportation, and distribution, with each generating waste that has a potential impact on the environment. More than 1000 dairy processing plants in the United States manufacture fluid milk, different types of cheese, butter, yogurt, ice cream, evaporated milk, condensed milk, nonfat dry milk, and other related products. Approaches are being taken in each sector of the dairy industry to minimize the environmental impact of milk production, transport, and processing (Figure 1). This article focuses primarily on practices used to minimize this risk at the production and processing stages. However, it is also important to acknowledge that direct loading of tanker trucks on large farms and the use of ultrafiltration equipment to concentrate milk prior to shipment help to reduce the energy cost of transporting milk from the farm to the processor.
Farm Level Manure Manure consists of animal feces, urine, bedding, and any water coming in contact with these materials. The composition of manure varies depending on the type of bedding material used, types and amounts of feed used, and whether the manure is being mixed with parlor wastewater. Application of manure to land provides valuable nutrients for crop growth; however, it can be detrimental if it enters water resources. One of the fundamental approaches to improving environmental compatibility at the farm level is by reducing the excretion of nitrogen (N) and phosphorus (P) in manure. This is done by improving the diet formulation of these nutrients to meet the animal’s requirements for specific nutrients (i.e., amino acids and P). In addition, management practices and improved facilities for animal comfort have increased production per cow, resulting in greater efficiency of nutrient utilization. The increased milk yield of cows while reducing resource use aids in mitigating the dairy industry’s environmental impact. Adequate storage of manure is essential for facilitating land application at suitable times of the year, depending on weather conditions and cropping system used. At least
631
632 Utilities and Effluent Treatment | Reducing the Negative Impact of the Dairy Industry
Production
• Reduce nutrient excretion • Increase animal efficiency • Provide adequate volume of storage • Improve stabilization of manure during storage • Proper land application of liquid and solid manure
Processing • Reduction in amount of waste water Transport (e.g., ultrafiltration)
• Increased development of valueadded products to reduce waste • Proper disposal of wastewater, including chemicals, and storage containers • Increased energy efficiency of equipment
Figure 1 Approaches to minimize the environmental impact of milk production, transport, and processing.
6 months of storage is needed, but at least 12 months is suggested. Farm manure is generally applied to croplands as a fertilizer, which reduces the dependence on commercial fertilizers. The manure provides nutrients for crops and improves soil quality if applied properly. Land application of manure, especially liquid manure, can cause problems if the land surface cannot absorb the manure or if a major rain event occurs soon after application. In addition, drainage tiles that are buried in fields should be plugged while liquid manure is applied in the event that manure leaches through the soil and enters the drainage tile. Adhering to established setbacks during application, using vegetative buffer zones near waterways, and not applying manure to frozen ground reduce the risk of runoff. In addition, injecting liquid manure and tillage after surface application reduce the risk of runoff, control odor emission, and prevent flies from populating the manure. There are several techniques and treatments available to improve the utilization of manure and reduce the risk of manure contaminating the environment. Solid–liquid manure separation equipment allows for wastewater to be used in flushing feed alleys and for irrigating fields. The solids can be used as animal bedding (composted or air dried) and/or land applied. Other manure storage and treatment systems include lagoons, anaerobic digestion, activated sludge, and constructed wetlands. Lagoons must be constructed in such a manner that they have a very low permeability, or with certain highly permeable soil types an impermeable liner is needed. Lagoons may be constructed to be aerobic or anaerobic in function; a topcrusted, supplemental thatch (e.g., straw) or synthetic covering can help to reduce odors. In some countries, lagoon covers are required. Alternative farm waste treatment techniques, such as anaerobic digestion and activated sludge techniques, have been developed to recycle and reuse organic wastes more efficiently. The anaerobic fermentation of manure to produce methane allows farmers to produce enough electricity not only to run their farm operations but also to produce a surplus that can be sold to the local utility supplier. However, the cost of construction is quite high, and the price provided
by utility companies is often low. The price for excess electricity is higher in some countries and areas within a country than other comparable areas. Constructed wetlands can improve water quality by intercepting the farm wastewater and retaining contaminants and nutrients through a series of vegetative ponds. New practices and innovative technologies to improve manure and odor management are being researched and incorporated in many dairy operations. Some dairy farms are using alternative natural energy sources (e.g., solar and wind). In addition, using plate coolers on dairy farms for heat exchange between the milk and water improves the quality of the milk because the milk is cooled more rapidly. Plate coolers reduce the energy required to operate the refrigerated bulk tank.
Milking Parlor Wastewater Milking parlor wastewater contains cow feces, urine, chemicals, and wash water used in cleaning the milking units, pipelines, receiver, bulk tank, and the floor and wall surfaces. The volume of wastewater generated from cleaning the milking system can be up to 30% of the total farm wastewater. The wastewater from a toilet or employee comfort area in a milk house must, in most cases based on local and state health codes, be handled according to domestic sewage disposal regulations. The parlor wastewater may be stored in a separate containment from manure or in the same vessel (e.g., lagoon). Land application is the most common method for discarding wastewater. Some pre-treatments being used prior to land application include facultative ponds, wetlands, anaerobic ponds, and fabricated reactors. Facultative ponds retain wastewater from 5 to 30 days. This retention time allows for some biological degradation, making the wastewater more suitable for land application. Anaerobic ponds utilize microbes to oxidize organic matter, especially to treat such wastes as oils and greases. Fabricated reactor systems, such as anaerobic reactors and sand filters, are also biological treatments for wastewater. A horizontal flow biofilm reactor can be effective for the removal of carbon and nitrogen from
Utilities and Effluent Treatment | Reducing the Negative Impact of the Dairy Industry 633
wastewater. The treatment process used for wastewater depends on the operating cost and the composition of the wastewater, for example, filtration for ammoniumnitrogen, potassium, and other dissolved solids, precipitation for phosphorus, and nitrification for nitrogen.
Environmental Impact of Dairy Processing
down-flow fixed-film digester, membrane anaerobic reactor system, and separated phase digesters. Specific separation methods that are widely used in the food processing industry have been incorporated into the purification, recycling, and treatment of wastewater. The most commonly used separation methods in the dairy industry are membrane technologies, such as ultrafiltration, nanofiltration, reverse osmosis, and microfiltration.
Processing Wastewater Wastewater from food processing may contain acids or bases, organic chemicals that are toxic and cause depletion of dissolved oxygen, suspended solids, phosphorus, nitrogen, heavy metals (e.g., cadmium, chromium, copper, lead, mercury, nickel, and zinc), cyanide, oily materials, and volatile compounds. Effluents from dairy plants contain dissolved or suspended compounds, such as proteins, fats, sugars, residues of additives, and cleaning and sanitation chemicals. High concentrations of sodium, potassium, calcium, and chloride may also exist. Most of the water consumed in dairy processing plants is for the clean-in-place (CIP) operation, which is responsible for 50–90% of the overall volume of the waste stream. During milk processing, 0.2–11 l of wastewater may be generated per liter of processed milk. The water used for CIP contributes to the high pH (9–11) in wastewater purification stations. Wastewaters from the cleaning of equipment may contain milk or milk products, whey, brines, cleaning agents, and various acid and alkaline detergents, including caustic soda, nitric acid, phosphoric acid, and sodium hypochlorite. Due to the high concentration of dissolved solids (1800 mg l 1), dairy wastewater has a high biological oxygen demand (BOD) (2000 mg l 1). Wastewater from dairy processing has been managed by direct land application, discharging wastewater to a nearby sewage treatment plant, removing semi-solids and special wastes through a waste disposal contractor, or operating an on-site wastewater treatment plant. However, most small dairy plants dispose of their wastewater by irrigation onto land, which causes a potential threat to the environment. Improper treatment and disposal may cause odors produced by biological decomposition of milk-derived organic matter. Biological treatments (aerobic and anaerobic biological systems) are the most promising and cost-effective methods for the removal of organic compounds from dairy processing wastewater compared to other removal systems. Aerobic systems include conventional activated sludge processes, aerobic filter treatment, sequencing batch reactor treatment, rotating biological contactor treatment, lagoons, and the wetland system. Anaerobic biological systems include anaerobic digestion by conventional digester, anaerobic lagoon, completely stirred tank reactors, up-flow anaerobic filter, expanded bed, up-flow anaerobic sludge blanket reactor, fixed-bed digester,
Whey Whey is a liquid by-product generated from cheese manufacturing. It is composed of approximately 0.3% fat, 0.8% protein, 4.9% lactose, and 0.5% minerals. More than 145 106 tonnes of whey wastewater is produced per year worldwide; it is another potential source of environmental contamination. The major components mentioned above can be separated using advanced technologies to reduce the environmental risk of whey. However, approximately half of the world production of whey is not processed, and it is disposed of into waterways or loaded onto land. Whey has high BOD (40–60 g l 1) and chemical oxygen demand (COD) values (50–80 g l 1) due to the concentrations of lactose, proteins, and mineral salts. Approximately 35% of the total production of liquid whey in the United States is converted to whey powder, whey protein for human food, and animal feed. An additional 10–15% of the total liquid whey is converted to other products, such as blends of whey with other protein sources (e.g., casein or soybean), lactose, and partially delactosed whey. The rest of the unprocessed whey is directly utilized for animal feed or mixed with wastewater. Serious waste volume is caused by the mixture of unprocessed whey and wastewater from cleaning and sanitizing in the cheese industry. Whey can be converted through various technologies and processes to different products, such as condensed whey, dry whey, dry modified whey, whey protein concentrate, isolates, and dried lactose. However, separation technologies and storage of whey require high-energy processes that add to the cost and maintenance of cheese plants. Small cheese plants are usually not able to afford such equipment, so they may sell the whey to larger processors. Anaerobic systems are used to treat organic wastewater in the cheese industry, resulting in the production of methane (CH4) gas. Ethanol can be produced by fermentation of lactose in whey. Ireland started producing fuel ethanol from whey in 1985, and New Zealand started using fuel ethanol produced from whey in August 2007. Fats, Oil, and Grease Milk, cheese, butter, whey separation, milk bottling, and plant machinery are the main sources of fats, oil, and grease. These materials in wastewater are a major concern
634 Utilities and Effluent Treatment | Reducing the Negative Impact of the Dairy Industry
in dairy industries when processing the wastewater. These materials may cause clogging of wastewater treatment systems, holding tanks, and septic tanks; cause sludge flotation; cause the formation of films on the surface of reactors; and result in malodorous wastewater. Common pre-treatment systems for removing fats, oil, and grease are gravity traps, air flotation systems, or enzymatic hydrolysis. Gravity traps can remove fats, oil, and grease by trapping within a series of cells when wastewater flows through the cells. Despite their high efficiency, there are some disadvantages as the need for constant cleaning and monitoring to prevent variation in pH. Anaerobic digesters for oil and grease residues increase fat reduction rates in the range of 88–94%. Air flotation systems that apply air bubbles in wastewater at a pressure of 400–600 kPa allow for fat globules to attach to the air bubbles and become suspended. High-density solids are then settled at the bottom of the containment, whereas the bubbles are eliminated through the effluent, possibly improving the efficiency of fat removal by 35–60% in waste streams. Enzymatic hydrolysis, which hydrolyzes fat in dairy processing wastewaters by lipases, results in high COD removal efficiencies. A hydrolytic enzyme pretreatment system in grease traps can produce hydrolysis rates greater than 90% for lipid degradation in wastewater. Another alternative method that facilitates biodegradation of lipid concentrations is the use of surfactants. For example, the application of 500 mg l 1 of a surfactant derived from cactus to wastewater has been observed to improve the anaerobic biodegradability and reduce the COD level. Dairy industry wastewater pretreated with lipases in an up-flow anaerobic sludge blanket reactor may improve oil and grease removal efficiency by 90% of the initial value.
piping, fuel piping, and wires for electric power transmission. Energy losses from boilers vary from 10 to 45%, and are mainly due to equipment aging, type of fuel, and lack of proper maintenance. The largest energy transmission losses are typically 20% in steam pipes. Equipment energy losses are typically 80% compressor, 35–45% pumps and fans, and 5–10% motors. Improving energy efficiency in dairy processing plants reduces the risk to the environment and reduces reliance on natural resources. Therefore, improving energy efficiency also reduces energy use, operating costs, and greenhouse gas emission into the atmosphere. Many practices are currently being used to improve energy efficiency in the dairy processing sector, including solar or wind power; continuous pasteurizers instead of batch pasteurizers; multistage evaporators; insulating the refrigerated area; a centralizing CIP system; installation of more efficient heating, ventilation, and air-conditioning (HVAC) systems; or recovering and reusing waste heat. An example of heat recovery equipment in the dairy processing industry is a plate heat exchanger, commonly used for liquid–liquid heat exchange. Combined heat and power (CHP) system increases energy efficiency through on-site production of thermal energy (typically steam) and electricity from a single fuel source. Replacing or retrofitting existing equipment (e.g., lighting and HVAC) improves energy efficiency for on-site heat or power generation and distribution, and manufacturing processes. A CHP system, commonly operated by coal, natural gas, biomass, and fuel oil, increases energy efficiency 70–90% in providing electricity, hot water, and chilled water. Steam system improvement, such as replacing or relocating the steam systems, stabilizing steam pressure, or improving overall boiler efficiency, may save 10–20% in fuel cost per year.
Energy
Packaging
Operating dairy processing plants requires significant amounts of energy, which contributes to processing costs. The dairy industry uses about 80% of the energy for thermal processing to generate steam and hot water for process applications (e.g., pasteurization, evaporation, and milk drying) and cleaning purposes, and 20% for electricity to operate refrigeration, air compression, ventilation, and lighting. The combustion of wood, gas, fuel oil, diesel, or coal in turbines, boilers, compressors, and other engines to produce power and heat generates gas emission, such as carbon dioxide, nitrogen oxide, and carbon monoxide, which has a negative environmental impact. The US Department of Energy estimates that 67.5% of the external energy is lost by electric power generation, transmission, and distribution, including piping for steam, hot water, chilled water, cooling water, and compressed air, steam condensate return piping, chilled water return
In 2005, dairy packaging demand in the United States was $3.5 billion, resulting from packaging of milk (30%), cheese (23%), frozen products (19%), cultured products (12%), and all other applications (16%). It is anticipated that packaging in the dairy industry will increase 4.1% annually from $2.7 billion in 2000 to $4.3 billion in 2010. The demand for pouches used in cheese, small containers of frozen dairy and cultured dairy products, and bottles with milk and drinkable yogurt is expected to grow. The main packaging materials for dairy products are paper and paper-based products, glass, tin plate, aluminum foil, wood, plastic, and laminates. Most plastic milk bottles are made from high-density polyethylene, which is not biodegradable, taking about 500 years to decompose. Other plastic packaging materials are composed of polystyrene and polyvinyl. Milk containers made from laminated cardboard cartons coated with different layers
Utilities and Effluent Treatment | Reducing the Negative Impact of the Dairy Industry 635
of plastic or aluminum are extremely slow to biodegrade, and thus, this contributes to a negative impact on the environment. The degradation process of polymers depends on different environmental factors, such as sun rays, moisture and humidity, temperature, chemical compounds, bacteria, and mold. In 2008, the United States recycled about 1 billion kg of plastic bottles, a 27% increase since 1990. Current management of packaging wastes include recycling, combustion for energy recovery, and disposal through land filling. New packaging materials and new processes are being developed in the dairy industry to reduce the environmental impact of dairy packaging materials. A modification of plastic’s chemical structure by organic ketones can enhance its biodegradability. Biodegradable polylactic acid produced from renewable resources is a new packaging material developed to replace petroleum-based packaging films for cheese and yogurt. A new bottle system from molded recycled paper and low-density plastic liners has been developed to reduce waste and plastic usage. Manufacture of new bottles for fluid milk, juices, smoothies, and drinkable yogurt consumes about a third of the energy required to make a plastic bottle and has a 48% lower carbon footprint than plastic. Other new technologies include the use of an electron-beam emitter that sterilizes pouches without use of chemicals and water, and dry sterilization that is conducted with vaporized hydrogen peroxide, eliminating water consumption for sterilizing a lightweight polyethylene terephthalate bottle, additionally providing sustainability benefits by virtually eliminating the need for rinse water in this system.
Greenhouse Gas Emission Global warming has been a focus for many years, with the focus especially on carbon dioxide (CO2) and methane (CH4) absorbing and trapping the heat in the atmosphere. Other gases of concern are nitrous oxide, chlorofluorocarbons, and hydrofluorocarbons, which are generated by the dairy processing industry. The contribution of reactive nitrogen to the atmosphere, primarily from ammonia but also from volatile organic compounds (VOCs; ozone concern), nitrous and nitrogen oxides are the focus of environmental regulators. In addition, the malodorous nature of farms, manure, and wastewater continues to generate many complaints from local residents. The most notable odorous compounds detectable on dairy farms are ammonia, hydrogen sulfide and other sulfurous compounds, amines, organic acids, and heterocyclic nitrogenous compounds; however, with the exception of manure storage pits and covered silos, the maximum allowable concentrations are not normally found on or near the farm. Therefore, the most common concern with air
quality in relation to animal agriculture is the nuisance of odors. Odor from manure on dairy farms can be minimized with proper installation of wind breaks and proper storage, handling, and application of manure to soils. Also, building positive relations with neighbors about the practices at the farm and informing them of major manure application events results in fewer complaints. The US Department of Agriculture estimates that dairy waste output per billion kg of milk produced is 7.91 million kg nitrogen, 3.31 million kg phosphorus, 1.91 billion kg manure, 26.8 million kg methane, 230 000 kg nitrous oxygen, and 1.35 billion kg carbon dioxide, including CO2 equivalents from CH4 and N2O. In dairy processing plants, gas emissions originate from the use of electricity (75%) and fuel (23%), and refrigerant leakage (2%). System improvements on steam and boiler systems reduce the equivalent of 616 tonnes of CO2 per year. Optimization of compressed air reduces greenhouse gas emissions to the equivalent of 762 tonnes of CO2 per year. There are several ways to reduce greenhouse gas emissions. For example, optimizing processes with new technologies, better process control systems, and renewable energy sources can reduce CO2 emissions. At the farm level, improvement in the efficiency of microbial fermentation in dairy cattle can lower CH4 production, for example, feeding supplemental fat or an ionophore (e.g., Rumensin, Elanco, Greenfield, Indiana, USA). Alternatives for stabilizing ammonia in manure continue to be investigated, including keeping pH low for a greater concentration of NH4 versus NH3. Manure can be converted into electricity through anaerobic digester technology, providing for a reduction in fossil fuel consumption and maximizing environmental benefits. This technology is currently being used by about 2% of the US dairy farms, but its use will likely increase in the future.
Further Reading Anonymous (2000) Dairy Packaging: US Industry Study with Forecasts to 2010 and 2015. Cleveland, OH: Freedonia Group, Inc. Capper JL, Cady RA, and Bauman DE (2009) The environmental impact of dairy production: 1944 compared with 2007. Journal of Animal Science 87: 2160–2167. Castrillon L, Fernandez-Nava Y, Maranon E, Garcia L, and Berrueta J (2008) Anoxic–aerobic treatment of the liquid fraction of cattle manure. Waste Management 29: 761–766. Clifford E, Rodgers M, and de Paor D (2008) Dairy washwater treatment using a horizontal flow biofilm system. Water Science and Technology 58(9): 1879–1888. FAO (2010) Food and Agriculture Organization of the United Nations. http://www.fao.org (accessed 1 April). Janni KA, Christopherson DR, and Schmidt DR (2009) Milk house wastewater flows and characteristics for small dairy operations. Applied Engineering in Agriculture 25(3): 417–423. Keppler AM and Martin JF (2008) Investigating the performance of a laboratory-scale ecological system to treat dairy wastewater. Transactions of the ASABE 51(5): 1837–1846. James R (2006) Ohio Livestock Manure Management Guide. Bulletin 604. Columbus, OH: Ohio State University Extension.
V VITAMINS Contents General Introduction Vitamin A Vitamin D Vitamin E Vitamin K Vitamin C Vitamin B12 Folates Biotin (Vitamin B7) Niacin Pantothenic Acid Vitamin B6 Thiamine Riboflavin
General Introduction D Nohr, Universita¨t Hohenheim, Stuttgart, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by G. Schaafma, Volume 4, pp 2653–2657, ª 2002, Elsevier Ltd.
Historical Background Vitamin deficiencies are as old as mankind; for example, as early as 3500 years ago people knew about treating night blindness by eating liver. In the centuries that followed, people learned to avoid numerous symptoms of diseases by choosing specific items of food without knowing anything about the vitamins they contained. However, by the end of the nineteenth century, feeding experiments with animals showed that specific deficiency symptoms could be caused by certain diets, which led to the hypothesis that organic micronutrients must be part of a healthy diet. Chemical identifications during investigations on beriberi (a disease caused by vitamin B1 deficiency) disclosed that an amino group must be part of the unknown substance, and therefore,
636
in 1912, Funk proposed the name ‘vitamins’ for these substances. This term is still in use today, although many of the known vitamins now do not contain an amino group. By 1941, all the 13 known vitamins – vitamins A, D, E, K, C, and eight B-vitamins – had been described, and many scientists involved in the research were honored by a Nobel Prize for chemistry or medicine. It became more and more easy to understand vitamin deficiency-derived diseases and to treat these symptoms by optimal nutrition or supplementation. A number of recommendations were published in various countries, and recent investigations aim to understand the preventive effect of specific vitamins on a number of widespread ‘modern’ diseases like coronary heart disease, atherosclerosis, diabetes, and even cancer.
Vitamins | General Introduction
Today, vitamins are defined as organic compounds that cannot (or not in sufficient amounts) be synthesized by an organism but are indispensable for its life. Thus, vitamins have become essential parts of the diet, either as they are or as provitamins that can be converted to the respective vitamins (e.g., -carotene ¼ provitamin A). It must be mentioned that not all vitamins are vitamins for all species as per the above definition, owing to the fact that some vitamins can be synthesized by some species, whereas others cannot. For example, vitamin C cannot be synthesized by humans, monkeys, and guinea pigs; vitamins K and B12 cannot be synthesized by humans but they can be synthesized by microorganisms in the human intestine (though not in amounts sufficient for the respective person). Although vitamins fulfill numerous functions, they are divided into only two groups, not based on their functions but based on their resorption, transport, storage, or excretion: fat-soluble vitamins (A, D, E, K) and water-soluble vitamins (C and B group) (for a brief overview, see
637
Tables 1 and 2; details are given in the respective articles on each vitamin).
Sources of Vitamins Most of the vitamins can be synthesized only by microorganisms or plants; hence, we have to consume them in fruits/vegetables or in animal nutrients (meat, fat, milk, eggs), the latter containing vitamins stored as such or as part of coenzymes. However, the animals in their turn have to obtain these vitamins either from vegetables or by resorption after synthesis by, for example, intestinal microorganisms in ruminants. The latter method is not a real possibility in humans, as in the colon – where most of the bacteria live – only vitamin K can be resorbed in detectable amounts and it is still under debate whether these amounts are adequate. Disturbing the colonic flora by long-lasting treatment with antibiotics leads to vitamin K deficiencies.
Table 1 A brief overview of fat-soluble vitamins, A, D, E, K Vitamin
RDA
Sources
Functions
A (Retinol)
1 mg
Liver, milk, fish, egg yolk, fruits, vegetables
D (Calciferol)
5 mg
E (Tocopherol) K (Phyllochinon)
12 mg 65 mg
Cod liver oil, milk, fish. About 90% are synthesized in the skin under UV light (sun!) Plant oil, germs, nuts Green vegetables, liver, wheat germ
Vision, embryogenesis, cell proliferation and differentiation Ca2þ and P homeostasis, insulin release, inhibition of tumor cell growth, immune functions (?) (Membrane-protective) antioxidants Blood clotting
RDA, recommended dietary allowance.
Table 2 A brief overview of water-soluble vitamins Vitamin
RDA
Sources
Functions
B1 (Thiamin)
1–1.2 mg
B2 (Riboflavin)
1.2–1.4 mg
B3 (Niacin)
13–17 mga
Brewer’s yeast, wheat germ, sunflower seed Brewer’s yeast, liver, almonds, dried whole milk, Camembert Wheat bran, liver, peanuts, salmon, halibut, Limburger, Brie, Camembert
B5 (Pantothenic) acid B6 (Pyridoxine)
6 mg
Coenzyme for enzymes of the intermediary metabolism Enzymes in the metabolism of, e.g., glucose, fatty acids, amino acids, drugs NAD and NADP are coenzymes of dehydrogenases, and hydrogen and electron carriers Numerous functions as coenzyme A
1.2–1.6 mg
B7 (Biotin)
30–60 mg
B9 (Folate)
400 mg
B12 Cobalamine
3 mg
C (Ascorbic acid)
100 mg
a 1 mg niacin-equivalent ¼ 60 mg tryptophan. RDA, recommended dietary allowance.
Liver, pea, soybean, lentils, dried whole milk, Blue cheese Soybean, salmon, liver, maize, Camembert Brewer’s yeast, liver, soybean, peanut, dried whole milk Brewer’s yeast, liver, soybean, egg, Brie Liver, kidney, mackerel, herring, Emmentaler, Camembert Pepper, black currant, green cabbage, kiwi, oranges
Coenzyme for transaminases Carboxylation and decarboxylation processes Cofactor to carry one-carbon units Homocysteine metabolism Antioxidants, collagen synthesis
638 Vitamins | General Introduction
As we do not have any single food that contains all vitamins in optimal concentrations or in optimal relative proportions, we have to rely on a mixed healthy diet containing fruits, vegetables, cereals, dairy products, fish, and also meat to be on the safer side. For special risk groups (e.g., elderly, pregnant women, adolescents, competitive athletes; see below) supplementation of single vitamins might be inevitable. Good sources of the various vitamins and recommended daily allowances are given in Tables 1 and 2 and in more detail in subsequent articles. There are some reasons why vitamin deficiencies can occur even in developed countries; these include malnutrition, undernourishment, extreme diets, or destruction of vitamins while food preparation (e.g., cooking or heat-treatment of dairy products; storage under light). In addition, an insufficient intestinal absorption owing to chronic diarrhea, atrophic intestinal mucosa, or resections of the small intestine also leads to deficiencies, as does an enhanced need because of diseases accompanied by fever or cross-reactions with pharmaceuticals, alcohol, or nicotine, or an enhanced loss due to hemodialysis.
Risk Groups Two of the major risk groups are pregnant women and breast-feeding women. Especially in the second half of pregnancy, large amounts of vitamins are transferred to the fetus via the placenta, in general independent of the vitamin status of the mother; that is, even under developing deficiencies in the mother, the fetus receives the vitamins. Unfortunately, the need for vitamins during pregnancy increases not in parallel with the enhanced energy needs (13%), but can reach levels of up to 50% (folate) or 58% (pyridoxine). In cases of pregnancies with twins or triplets, or short-interval births, the risk of deficiencies is even higher. During breast-feeding, for example, deficiency of vitamin A can occur, and the risk for the neonate is higher than that for the mother, especially in premature babies and babies lacking vitamins from the last weeks or months of pregnancy. In the case of sufficient maternal vitamin stores, no risk exists for the breast-fed suckling, except perhaps of vitamin K deficiency, which therefore is routinely supplemented during the first weeks of life. Strictly vegetarian mothers normally have very low vitamin B12 stores and produce almost vitamin B12-free milk, which can lead to irreversible brain damage of the child. Children and adolescents are other potential risk groups, due to an enhanced demand by the growing body or due to (additional) smoking or malnutrition (e.g., regular intake of fast foods). Also, alcohol and slimming diets can lead to vitamin deficiencies in adolescents as well as in adults.
Elderly people are also at risk of developing vitamin deficiencies due to a reduced food intake on account of reduced energy demand and changes in metabolism and lifestyle. Especially males who live alone have been shown to develop combined deficiencies, as they often use canned food and omit fresh vegetables or fruits. Finally, ill people must be controlled regarding their vitamin status, but this depends on the kind and degree of their illness.
Prevention of Deficiencies For healthy people in developed countries with an average workload and under European climatic conditions, a balanced and mixed diet is regarded as sufficient for supplying the necessary vitamins. However, nutrition organizations have tabulated (see Tables 1 and 2) the recommended daily allowances of vitamins, almost independent of their sources. Recently, it is being debated whether these recommendations are really sufficient or should be enhanced (and if so, by how much) for a better prevention of diseases like coronary heart disease, cancer, metabolic syndrome, and others. Hopefully we will find out from ongoing and future studies how we have to handle our vitamin stores and which recommendations, under which conditions, should be followed.
Fat-Soluble and Water-Soluble Vitamins A brief overview of the most relevant data for the single fat-soluble vitamins and single water-soluble vitamins is given in Tables 1 and 2, respectively. Further details can be found in the respective articles dealing with each of the vitamins. See also: Vitamins: Biotin (Vitamin B7); Folates; Niacin; Pantothenic Acid; Riboflavin; Thiamine; Vitamin A; Vitamin B6; Vitamin B12; Vitamin D; Vitamin E; Vitamin K.
Further Reading Biesalski HK and Grimm P (2005) Pocket Atlas of Nutrition. Stuttgart: Thieme (this book is also available in other languages). Biesalski HK, Ko¨hrle J, and Schu¨mann K (2002) Vitamine, Spurenelemente und Minaralstoffe, pp. 111–116. Stuttgart: Thieme. Linus Pauling Institute (2009) Micronutrient Information Center. Vitamins. http://lpi.oregonstate.edu/infocenter/vitamins.html (accessed May 2009). McSweeney PLH and Fox PF (eds.) (2009) Advanced Dairy Chemistry, Vol. 3, New York: Springer.
Vitamin A P Sauvant, ENITA de Bordeaux, Unite´ de Formation QENS, Gradignan Cedex, France B Graulet and B Martin, INRA, Unite´ de Recherche sur les Herbivores, Saint Gene`s Champanelle, France P Grolier, INRA, Laboratoire PsyNuGen, Universite´ Bordeaux 2, Bordeaux Cedex, France V Azaı¨s-Braesco, VAB-Nutrition, Clermont–Ferrand, France ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. Sauvant, P. Grolier, and V. Azaı¨s-Braesco, Volume 4, pp 2657–2664, ª 2002, Elsevier Ltd.
Introduction Vitamin A is an essential fat-soluble vitamin involved in multiple critical biological functions such as embryonic development, growth, vision, and regulation of gene expression. Because most mammals cannot carry out its synthesis de novo, vitamin A must be provided by the diet. In human nutrition, plant products (like carrots or spinach) provide provitamin A (i.e., provitamin carotenoids, like -carotene, -carotene or -cryptoxanthin), which may, after specific cleavage, yield retinal and then retinol. By contrast, animal products (such as cod liver oil or liver, but also ruminant milk and dairy products) provide retinol or its esters directly, and also serve as provitamin A. In this way, dietary provitamin A carotenoids participate actively in the supply of vitamin A to the organism. Because vitamin A is absolutely necessary for embryonic development, it should be provided to the fetus through the placenta. And because vitamin A is also greatly involved in growth after delivery, it must be provided to the newborn through milk consumption. In the past, studies on the status of -carotene and vitamin A in bovine plasma and milk have focused on the objective of achieving suitable plasma levels during the peripartum period to maintain the cow’s health, to prevent reproductive disorders, and to ensure an adequate vitamin supply to calves via colostrum. More recently, the role of carotenoids and fat-soluble vitamins in the nutritional and sensorial properties (via antioxidant activity or the yellow color of fat) of dairy products and their potential use as biomarkers for the traceability of cows’ feeding management have led to a renewed interest at the INRA research center at Clermont–Ferrand. In order to better characterize how the feed can influence the appearance and nutritional properties of milk and other dairy products, new studies that follow variations in vitamin A, carotenoids, and color in cow’s plasma and milk during lactation have been carried out.
General Features of Vitamin A and Carotenoids Vitamin A or retinoids are generic compounds other than carotenoids, which exhibit biological activities like those of retinol, the main component of this family. The International Union of Pure and Applied Chemistry– International Union of Biochemistry (IU-PAC–IUB) defines retinoids as compounds containing a -ionone ring, substituted with an alkyl chain made of four isoprenoid units ended by a functional group R. The nature of this end-substitution forms the basis of the classification of retinoids (Figure 1). Nowadays, because many chemical compounds not based on this structure have been shown to have a retinol-like activity, a new definition based on the ability of retinoids to bind and activate their nuclear receptors (retinoic acid receptors (RARs) and retinoid X receptors (RXRs)) has been proposed. According to this definition, the retinoid family includes all the natural or synthetic derivatives of retinol in terms of structure or biological functions. It is generally recognized that vitamin A is essential for vision. Retinal acts as the chromophore of vertebrate visual pigment, and vitamin A deficiency results in the loss of structural integrity of photoreceptors, alteration of night vision, and finally blindness. In addition, vitamin A exerts pleiotropic effects on vertebrate development, vitamin A homeostasis, epithelial integrity, gene regulation, and cell differentiation. Recently, it has been shown that these effects are mediated largely through interactions of retinoic acid bound to specific nuclear receptors with retinoic acid response elements (RAREs). Two main classes of receptors were identified: the RARs, which bind both all-trans retinoic acid and its 9-cis isomer, and RXRs, which respond exclusively to 9-cis retinoic acid. Excess of vitamin A supply, dietary or supplementary, can result in embryogenetic defects and fetus malformation. Vitamin A, or more precisely retinyl esters, is present in animal products. Generally, mammals producing milk
639
640 Vitamins | Vitamin A
Main retinoids Retinol and retinyl esters COOR Retinyl ester (R = fatty acid)
+R Retinol
Esterase Hydrolase
CH2OH
Active metabolites of retinol CHO
All-trans retinal COOH
All-trans retinoic acid A provitamin carotenoid β-carotene
A non-provitamin carotenoid found in milk Lutein
OH
HO
Figure 1 Retinoid family and examples of the main carotenoids found in milk (a provitamin A carotenoid: -carotene; a nonprovitamin A carotenoid: lutein).
consumed by humans (cow, goat, etc.) are usually herbivorous. They acquire vitamin A principally by the conversion of carotenoids from the diet into vitamin A. Preformed vitamin A is sometimes added, often together with other vitamins and minerals, as a supplement to the ration to meet the requirements of the animal and to improve the performance of lactating cows. Carotenoid is also a generic term used to describe plant pigments corresponding to the general formula C40H56On. In mammals, only 50–60 carotenoids, of the 700 discovered until now, exhibit a provitamin A activity. To be provitaminic A, these pigments should have at least one nonsubstituted -ionone ring and an alkyl chain containing at least four conjugated double bonds. For example, among the carotenoids frequently found in cows’ milk, lutein (because of its substitution on the two -ionone rings) is not a provitamin A carotenoid, whereas -carotene (the main carotenoid found in milk) exhibits the highest provitamin A activity (Figures 1 and 3). This conversion occurs mainly in the intestine and to a lesser extent in the liver, the corpus luteum, but may also occur in
the mammary gland. The enzyme involved in this conversion, and identified as -carotene 15-159 monooxygenase (E C 1.14.99.36), has been cloned in Drosophila, chicken, mice, and humans. -Carotene is an essential pigment of plants, associated primarily with chloroplasts and chromoplasts. Its primary function is to protect the plant against photooxidation and to contribute along with chlorophylls in collecting light energy. In vertebrates, -carotene, and to a lesser extent, -carotene and -cryptoxanthin, can be converted to vitamin A mainly in the intestine and liver. Thus, -carotene would contribute 40–60% of dietary vitamin A intake in humans and 100% in non-vitamin A-supplemented herbivores. Carotenoids have also been shown to have antioxidant activity through quenching of activated species of oxygen (1O2) and scavenging of free radicals. However, at a high concentration and under a high oxygen pressure, carotenoids can act as prooxidants. They might be active in the inhibition of neoplastic cellular transformation by inducing cell–cell communications. They have also been shown to stimulate the immune system. In cattle, many studies have been focused on the role of -carotene in reproduction, and the suggestion that it may be essential for normal reproduction in cattle is still a matter of debate. Moreover, studying the absorption and metabolism of -carotene in cattle is particularly relevant because -carotene is the main source of vitamin A in milk.
Metabolism of Vitamin A and Carotenoids in Dairy Cattle Cattle differ from most farmed animals in that they have a significant concentration of circulating -carotene in their blood. The concentration of -carotene in blood is dependent on the concentration in feeds, and is particularly high in animals grazing fresh forage. A high blood -carotene concentration results in yellow coloration of both body fat and milk, and this can influence consumer acceptance of the product. Both -carotene and vitamin A are fat-soluble compounds, and consequently, they will be distributed in the lipid globules in milk. When fresh forage is ingested by cattle, about 60% of plant cells are ruptured by chewing (the first step of digestion), releasing cellular contents. Then, the intracellular contents are processed first in the rumen where negligible loss of -carotene (in contrast to vitamin A) occurs during fermentation. Probably, most of the carotenoids consumed will pass unchanged to the acidic conditions of the abomasum. Lipids and -carotene are then emulsified with bile salts in the small intestine to form micelles, and maximum lipid absorption occurs when the pH reaches 6.5. After this step of solubilization,
Vitamins | Vitamin A 641
-carotene is absorbed by enterocytes, and transported with other lipids as -carotene or linked to specific protein carriers (the retinol-binding proteins) as vitamin A. The efficiency of -carotene absorption in the cow has not yet been published. However, considering the respective levels of its ingestion with the diet (0.1 to 3 g day1) and secretion per se in milk (1 to 10 mg day1), the transfer rate of -carotene from diet to milk could be estimated to be 0.1 to 1.2%. However, this value is underestimated since part of the absorbed -carotene is converted to retinol to meet the cow’s requirements for vitamin A, the latter being stored in the liver of the cow, used by the peripheral tissues, or secreted in the milk (3 to 4 mg day1) (Figure 2). Lactating cows producing 10, 20, or 30 l milk day1 are estimated to require, respectively, 300, 500, and 700 mg -carotene day1. These quantities are based on a daily requirement of 100 mg day1 for biological functions and a supplement of 20 mg l1 of produced milk. The mechanism by which -carotene is metabolized to retinaldehyde in the intestinal mucosa, or to a lesser extent in the liver, is well defined in humans and rats. This process involves the enzyme called 15-159- -carotene monooxygenase. Two theories have been proposed to explain the formation of vitamin A (retinol or retinoic acid) from carotenoids: (1) the central cleavage theory and (2) the eccentric cleavage theory.
Small intestine
5 The newly formed vitamin A is then stored in the liver and secreted into blood. Nontransformed β-carotene is directly transferred into blood
6 Vitamin A or intact β-carotene is filtered by the mammary gland from the blood to the milk
The first theory is based on the fact that the addition of one molecule of oxygen at the central double bond of carotenoids can lead to the formation of two molecules of retinaldehyde, which are then processed into molecules of retinol or retinoic acid. The second theory has been developed by Krinsky and Russel, who found apocarotenals after incubation of carotenoids with intestine or liver homogenates of rabbit or ferret. Indeed, the system of conjugated double bonds contained in the carotenoid could lead to a resonance phenomenon in which the central double bond of carotenoids is more stable than the others. Consequently, the eccentric cleavage of carotenoids occurs, leading to the formation of only one molecule of retinaldehyde, which is then processed into only one molecule of retinol or retinoic acid. However, today, most authors favor the central cleavage as the most prevalent physiological mechanism. The eccentric oxidation might be an artifact explained by a chemical and nonspecific degradation (nonenzymatic degradation) of carotenoids (Figure 3). Because retinoic acid, the active metabolite of vitamin A, is a potent regulator of gene expression, its precursor (i.e., retinol) concentration has to be regulated precisely in circulating blood to avoid any deleterious effect due to a high concentration of vitamin A. The main plasma form of vitamin A is retinol, which circulates bound to retinolbinding protein (RBP) and transthyretin (TTR).
4 β-Carotene and lipids are emulsified with bile salts to form micelles, which are absorbed through intestinal mucosa when the pH reaches 6.5
Rumen
1 The main source of vitamin A for the cow is β-carotene, a provitaminic A carotenoid present in forage Abomasum
3 Most of β-carotene will pass unchanged to the acidic conditions of the abomasum
Figure 2 Metabolism of vitamin A and -carotene in cow.
2 The first step of digestion in cow is fermentation occurring in the rumen. During this step, the loss of β-carotene is negligible
642 Vitamins | Vitamin A
β-Carotene or its isomers 12′
15
10′
8′
15′
8 ′Apo-carotenals 10 ′Apo-carotenals 12 ′Apo-carotenals
β-Apocarotenal
Central cleavage CHO
Apocarotenoic acid
Retinal
COOH
CH2OH
Retinoic acid Retinol
Eccentric cleavage Figure 3 Different cleavage pathways for -carotene.
Milk is produced by the mammary gland through filtration of blood. An increase in dietary -tocopherol and -carotene supply has been shown to lead to higher plasma concentrations of these nutrients in lactating cows but not of circulating retinol. However, in the milk of the same animals, -tocopherol concentration increased accordingly, whereas -carotene secretion seemed to saturate near 0.13 mg ml1 and retinol content was stable (0.19 mg ml1). Elsewhere, the quantitative secretion of -tocopherol and -carotene from blood to milk has been shown to follow the Michaelis–Menten kinetics for active transport across membranes (Vmax was, respectively, 32.4 and 2.5 mg day1). These results suggest that the daily secretion of vitamin E and -carotene is limited in quantity. Because retinol concentration is stable in plasma, retinol concentration in milk is also relatively stable.
Factors that Influence the Concentration of Vitamin A and -Carotene in Milk The composition of milk is a key factor in its economical value, as well as a relevant criterion in terms of nutrition. Factors that influence milk composition, especially -carotene concentration, are the breed, the genetics and the age of the animal (mainly parity), the stage of lactation, and the composition of the diet. Channel Island
cows, Jerseys and Guernseys, have a higher -carotene and a lower vitamin A content in the milk fat than other breeds (Friesians). Genetic correlations between carotene yield and the production traits are positive. No significant differences have been observed between mastitic and non-mastitic cows for vitamin A and -carotene levels in milk. The levels of fat-soluble vitamins (A, E, and -carotene) in milk are also very much dependent on the amounts of these compounds consumed by the cow. The highest levels are normally found during spring and summer, when the cows are fed on fresh carotene-rich pasture. In forages, a gradient of -carotene concentration is found from maize silage (1 to 4 mg kg1 DM), hay (5 to 10 mg kg1 DM), haylage (5 to 20 mg kg1 DM), grass silage (25 to 100 mg kg1 DM depending on direct cut or wilting intensity), and fresh grass (up to 400 mg kg1 DM). In milk obtained under experimental conditions, the same trend was observed according to diet composition (from 1 to 2.5 and 2.8 mg g1 fat for -carotene and retinol, respectively, in milk from maize silage-fed cows, to more than 5 mg g1 fat for both in milk from cows at pasture). However, under the real conditions at the farm, animal variability and the effect of the nature of forage are limited due to mixing of individual milks in the tank and to specific vitamin supplementations (A and E) through the feed concentrates. Such is not the case for -carotene for
Vitamins | Vitamin A 643
which lower dietary intakes in winter result in a decrease of milk fat color. Plasma carotene and fat color are generally correlated, with increases in plasma carotene being associated with increases in the concentration of carotene in the milk. In addition, plasma carotene level is well correlated with the amount of ingested carotene. So, -carotene concentration in milk is usually quite low during the period when the cattle are kept in sheds, as compared with the grazing period. At the end of the grazing period (autumn), when the grass turns yellow, the concentration of carotenoids in forage decreases and, as a consequence, the level of -carotene both in the blood serum and in milk decreases. Therefore, there is a clear seasonal effect on milk -carotene content, essentially due to the -carotene concentration in the pasture eaten by the cow. -Carotene concentration in milk has been measured in very few studies (Tables 1 and 2).
Effects of Processing Conditions on Vitamin A and -Carotene Content of Milk and Dairy Products Milk or some of its components are raw materials for a great number of dairy products after various technological processes. These processes are, essentially, designed to improve the stability of milk. To partially or totally eliminate the microorganisms found in raw milk, dairy industries use thermal treatment. Pasteurization (72 to 76 C for 15 s) is a mild treatment, whereas ultra-high temperature (UHT) (130 to 140 C for
3 to 20 s) treatment is more drastic. Under low oxygen tension, retinol is considered to be heat resistant. However, reports on retinol stability are sometimes inconsistent, which may be related to the analytical method used. Several studies in which total vitamin A and total carotenoid levels were measured after different thermal treatments showed that these levels are not affected by heat processing, especially because these treatments are carried out under a closed atmosphere (without removal of air). Nevertheless, using higherresolution techniques, some authors have demonstrated that during heat treatment, isomerization of retinol may occur. Indeed, in raw milk, the main form of vitamin A is all-trans retinol, whereas the level of the 13-cis isomer is increased in heat-treated milk. This cis–trans isomerization can also be promoted directly by exposure to light, the relative amount of different cis isomers depending on the wavelength of the light and the light permeability of the container. A comparison among glass, plastic, and paperboard containers showed no significant loss of alltrans retinol in milk contained in paperboard boxes, while the loss was significantly lower in plastic containers than in glass. From a nutritional point of view, it is fundamental to evaluate the pattern of isomers produced in milk after heating or storage. Hence, isomerization of all-trans retinol reduces its vitamin activity: 13-cis retinol has the highest vitamin A biological activity (75%) relative to all-trans retinol (100%), while 9-cis retinol exhibits a biological activity as low as 19%. The other isomers have even lower vitamin A activity. In order to stop the growth of microorganisms in milk, other thermal treatments, such as chilling and freezing,
Table 1 Influence of technical treatments and fat content on vitamin A and carotenoid concentrations in milk
Influence of technical process
Influence of skimming
Retinol
Carotenoids
Total vitamin A
Fat
Different types of cow’s milk
(g per 100 g of milk)
(g per 100 g of milk)
(g RE per 100 g of milk)
(%)
Consumer milk Ultra-high temperature-heated milk Sterilized milk Condensed milk Milk powder Cow’s milk, reduced fat (1.5 and 1.8%) Skimmed milk Condensed skimmed milk Dried skimmed milk
28 (25–32) 30 (27–34)
17 (13–21) 18 (10–20)
31 (27–36) 33 (29–37)
3.57 (3.50–3.62) 3.78 (3.60–3.88)
30 (27–34) 64 (61–72) 230 (220–240) 13 (11–14)
18 (10–20) 45 (37–51) 140 (nd) 8.0 (6.0–9.0)
33 (29–54) 72 (67–81) 253 (243–263) 14 (12–16)
3.78 (3.60–3.88) 10.1 (10.0–10.3) 26.2 (24.6–26.8) 1.6 (1.50–1.80)
2.4 (1.8–3.0) 1.2 (nd)
– 0.9 (nd)
2.4 (1.8–3.0) 1.4 (nd)
0.07 (0.02–0.12) 0.2 (0.10–0.30)
5.3 (nd)
21 (nd)
8.8 (nd)
0.97 (0.50–1.50)
Retinol equivalent (RE) is based on an old definition with RE ¼ amount (retinol þ ( -carotene/6) þ (other carotenoids/12)). Data are expressed as the average and in parentheses the range of variation is given. nd, not determined. Data are obtained from Souci SW, Fachmann W, and Kraut H (2000) Food Composition and Nutrition Tables, 6th edn. Stuttgart: Medpharm, Scientific Publishers; Boca Raton, FL: CRC Press.
644 Vitamins | Vitamin A Table 2 Influence of fat content on the concentrations of vitamin A and carotenoids in commonly consumed dairy products Retinol
Carotenoids
Total vitamin A
(g per 100 g of products)
(g per 100 g of products)
(g RE per 100 g of products)
Camembert cheese (30% fat content in dry matter)
200 (140–250)
100 (80–150)
217 (153–275)
Camembert cheese (40% fat content in dry matter) Camembert cheese (45% fat content in dry matter) Camembert cheese (50% fat content in dry matter) Camembert cheese (60% fat content in dry matter) Yogurt low fat (max 0.3% fat content) Yogurt reduced fat (max 1.8% fat content) (min 1.5% fat content) Yogurt (min 3.5% fat content) Butter (83.2% fat content) Butterfat (99.5% fat content)
300 (nd)
170 (130–230)
328 (322–338)
330 (240–420)
190 (140–250)
362 (263–462)
380 (280–480)
220 (160–290)
417 (307–528)
503 (nd)
290 (nd)
552 (nd)
0.8 (0.7–0.9)
0.5 (0.4–0.6)
0.8 (0.7–1.00)
13 (11–14)
8.0 (6.0–9.0)
14 (12–16)
29 (26–33) 590 (520–670) 850 (nd)
18 (14–22) 380 (300–460) 200 (nd)
32 (28–37) 653 (570–747) 883 (nd)
Different types of dairy products Influence of fat percentage in cheese
Retinol equivalent (RE) is based on an old definition with RE ¼ amount (retinol þ ( -carotene/6) þ (other carotenoids/12)). Data are expressed as the average and in parentheses the range of variation is given. nd, not determined. Data obtained from Souci SW, Fachmann W, and Kraut H (2000) Food Composition and Nutrition Tables, 6th edn. Stuttgart: Medpharm, Scientific Publishers; Boca Raton, FL: CRC Press.
may be used. These treatments do not modify vitamin A or carotenoid content. Because vitamin A and carotenoids are fat-soluble compounds, their concentration in milk is increased after elimination of water, by concentration (375 IU 100 g–1 of milk) or by dehydration (1150 IU 100 g–1 of milk). These differences observed in the concentration of vitamin A during these treatments are due mainly to the degree of concentration occurring during each treatment (2.5 and 8, respectively, for concentrated and dehydrated milk). Fresh, dehydrated, and condensed milk represent the principal sector (46%) of the world’s trade in dairy products and the most consumed dairy products. In these products, the amounts of vitamin A and carotenoids are not modified when compared to those in whole milk. The other main sectors are cheese (36%), butter (11%), and ice cream, which represent only 4% of the world sales of milk. Because vitamin A and carotenoids are located exclusively in milk fat, their concentrations decrease proportionally with the degree of skimming of milk (see Tables 1 and 2). For cheeses, recent data have shown that the rates of transfer of retinol and -carotene from milk fat to cheese fat average 66 and 95%, respectively, considering four different cheesemaking technologies (three from cow’s milk: Abondance, Tomme de Savoie, and Cantal; one from goat’s milk: Rocamadour) and with the original milk covering a large range of concentration of these
micronutrients. Cow’s milk cheeses were found to be richer in -carotene (3.27 mg kg1 fat) and poorer in retinol (5.17 mg kg1 fat) than goat’s milk cheeses (0 and 6.81 mg kg1 fat, respectively). Moreover, these values did not vary according to the cheesemaking process (acidification level, heating temperature, ripening time) in agreement with previous reports. Elsewhere, large retinol losses have been reported during heating and ripening of Gruye`re cheese, which would result mainly from retinol instability due to exposure to light during cheesemaking technology (photoisomerization into 13-cis isomer).
Nutritional Issues In cows, as in all mammals, vitamin A homeostasis in blood is very well regulated by the liver, avoiding any deleterious effects related to an excess of vitamin A. Inversely, the level of carotenoids in blood is strongly influenced by the nature of the diet. Because milk is the result of a specific synthesis of proteins (caseins, etc.), glucides (lactose, etc.), and lipids (short-chain fatty acids, etc.) and of blood transfusion for vitamin A and carotenoids, the vitamin A content of milk is quite stable, whereas -carotene concentration (the main provitamin A carotenoid in milk) follows the concentration of -carotene in the forage consumed by the cow. Because the concentration in forage is highly dependent on season
Vitamins | Vitamin A 645
and altitude, milk composition also varies according to these conditions. Vitamin A and -carotene are relatively stable during food processing and storage. The main factors that may influence the stability of these compounds are exposure to light and the skimming process. Because milk is stored in opaque containers, their levels are not changed significantly during storage. Because vitamin A and -carotene are fat-soluble, their concentrations are closely related to the fat percentage, and are dependent largely on the skimming process. This consideration is nutritionally important, in view of the recommendation to reduce the consumption of a fat-rich diet in an attempt to reduce the risk of cardiovascular disease. For example, in France, most of the milk consumed is half-skimmed milk, which results in a reduction in the intake of fat-soluble vitamins. When the reduction of fat intake in the whole diet remains limited, the consequent reduction in the level of fat-soluble vitamins generally has little nutritional outcomes, especially for vitamin A, which can be obtained from -carotene from fruits and vegetables. However, some special diets, including the slimming diets, can have a critically low nutritional density and may create infraclinical nutritional deficiencies. This problem is real in some population categories, and restoration (addition of the vitamins unavoidably lost because of the technological process) or enrichment (addition of vitamins above the level contained in the raw materials) is a good means to cope with it. With or without restoration or enrichment, milk and dairy products are excellent sources of vitamin A, a vitamin involved in several key physiological functions in animals and humans. See also: Vitamins: General Introduction.
Further Reading Adrian J (1987) Les vitamines. In: Le Lait Matie`re Premie`re de l’Industrie Laitie`re. Paris: CEPIL-INRA. Alais C (1984) Science du Lait, Principes des Techniques Laitie`res, 4th e´dn. Paris: SEPAIC (Socie´te´ d’Edition et de Promotion Agro-Alimentaires Industrielles et Commerciales). Batra TR, Singh K, Ho SK, and Hidiroglou M (1992) Concentration of plasma and milk vitamin E and plasma -carotene of mastitic and healthy cows. International Journal for Vitamin and Nutrition Research 62: 233–237. Bauernfeind JC (1983) Vitamin A: Technology and applications. World Review of Nutrition and Dietetics 41: 110–199. Calderon F, Chauveau-Duriot B, Martin B, Graulet B, Doreau M, and Noziere P (2007b) Variations in carotenoids, vitamin A and E, and color in cow’s plasma and milk during late pregnancy and the first three months of lactation. Journal of Dairy Science 90: 2335–2346. Calderon F, Chauveau-Duriot B, Pradel P, et al. (2007a) Variations in carotenoids, vitamin A and E, and color in cows plasma and milk
following a shift from hay diet to diets containing increasing levels of carotenoids and vitamin E. Journal of Dairy Science 90: 5651–5664. Gaylord AM, Warthesen JJ, and Smith DE (1986) Influence of milk fat, milk solids, and light intensity on the light stability of vitamin A and riboflavin in low fat milk. Journal of Dairy Science 69: 2779–2784. Goff JP and Stabel JR (1990) Decreased plasma retinol, alpha tocopherol, and zinc concentration during the periparturient period: Effect of milk fever. Journal of Dairy Science 73: 3195–3199. Hartman AM and Dryden LP (1965) Vitamins in Milk and Milk Products. Champaign, IL: American Dairy Science Association. Jensen SK, Johannessen AKB, and Hermansen JE (1999) Quantitative secretion and maximal secretion capacity of retinol -carotene and -tocopherol into cows’ milk. Journal of Dairy Research 66: 511–522. Johnston LA and Chew BP (1984) Peripartum changes of plasma and milk vitamin A and beta-carotene among dairy cows with or without mastitis. Journal of Dairy Science 67: 1832–1840. Lindmark-Mansson H and Akesson B (2000) Antioxidative factors in milk. The British Journal of Nutrition 84: S103–S110. Lucas A, Rock E, Agabriel C, Chilliard Y, and Coulon JB (2008) Relationships between animal species (cow versus goat) and some nutritional constituents in raw milk farmhouse cheeses. Small Ruminant Research 74: 243–248. Lucas A, Rock E, Chamba JF, Verdier-Metz I, Brachet P, and Coulon JB (2006) Respective effects of milk composition and cheese-making process on the cheese composition variability in components of nutritional interest. Le Lait 86: 21–41. Martin BA, Cornu A, Kondjoyan N, et al. (2005) Milk indicators for recognizing the types of forages eaten by dairy cows. In: Hocquette JF and Gigli S (eds.) Indicators of Milk and Beef Quality, pp. 127–136. Waegeningen, The Netherlands: Wageningen Academic Publishers. EAAP Publ no. 112. Michal JJ, Heirman LR, Wong TS, and Chew BP (1994) Modulatory effects of dietary beta-carotene on blood and mammary leukocytes function in periparturient dairy cows. Journal of Dairy Science 77: 1408–1421. Nozie`re P, Graulet B, Lucas A, Martin B, Grolier P, and Doreau M (2006) Carotenoids from forages to dairy products. Animal Feed Science and Technology 131: 418–450. Panfili G, Manzi P, and Pizzoferrato L (1998) Influence of thermal and other manufacturing stresses on retinol isomerization in milk and dairy products. Journal of Dairy Research 65: 253–260. Prache S, Priolo A, Jailler H, Dubroeucq H, Micol D, and Martin B (2002) Traceability of grass-feeding by quantifying the signature of carotenoid pigments in herbivore meat, milk and cheese. Grassland Science in Europe 7: 592–593. Randoin L and Causeret MJ (1958) Evolution de la valeur vitaminique du Gruyere aux divers stades de sa fabrication. Le Lait 38: 43–48. Runner E (1989) Micronutrients in Milk and Milk-Based Products. London: Elsevier. Souci SW, Fachmann W, and Kraut H (2000) Food Composition and Nutrition Tables, 6th edn. Stuttgart: Medpharm, Scientific Publishers; Boca Raton, FL: CRC Press. Weiss WP (1988) Requirements of fat-soluble vitamins for dairy cows: A review. Journal of Dairy Science 81: 2493–2501. Wildi B and Lu¨tz C (1996) Antioxidant composition of selected high alpine plant species from different altitudes. Plant, Cell & Environment 19: 138–146. Winkelman AM, Johnson DL, and Mac Gibbon AK (1999) Estimation of heritabilities and correlations associated with milk color traits. Journal of Dairy Science 82: 215–224. Zahar M, Smith DE, and Martin F (1995) Vitamin A distribution among fat globule core, fat globule membrane, and serum fraction in milk. Journal of Dairy Science 78: 498–505. Zahar M, Smith DE, and Warthesen JJ (1987) Factors related to the light stability of vitamin A in various carriers. Journal of Dairy Science 70: 13–19.
Vitamin D W A van Staveren and L C P M G de Groot, Wageningen University, Wageningen, The Netherlands ª 2011 Elsevier Ltd. All rights reserved.
Introduction Vitamin D is the generic descriptor for all steroids having similar biological activity as cholecalciferol or vitamin D3. Important forms of vitamin D in this context are the following: (vitamin D ): is sparsely present in natural • ergocalciferol sources, but it is the major synthetic form of vitamin D; (vitamin D ): is widely distributed in • cholecalciferol animals, in which its provitamin D form, 7-dehydro2
3
• •
cholesterol, is a normal metabolite, but in contrast it has an extremely limited distribution in plants; calcidiol (25-hydroxyvitamin D (25(OH)D)): is produced in the liver from D2 or D3 and circulating calcidiol is a good indicator of the vitamin D status in humans; calcitriol (1,25-dihydroxyvitamin D (1,25(OH)2D)): is the result of further hydroxylation of calcidiol in the kidney; it is the most active form of vitamin D.
In human beings, the main source of vitamin D is cutaneous formation when the skin is exposed to adequate sunlight. Therefore, vitamin D might be considered a hormone and not a vitamin. Deficiencies of vitamin D lead to structural lesions of bone. The role of vitamin D in the increasing prevalence of osteoporosis and related fractures in elderly people has led to new research in recent decades. The discovery that most tissues and cells have a vitamin D receptor (VDR) and that several possess the enzymes necessary to convert the primary circulating form of vitamin D, 25(OH)D, to the active 1,25(OH)2D has provided new insights into the vitamin. Of great interest is the role it can play in reducing the risk of many chronic illnesses. The results of studies have led to ongoing discussions about daily requirements of vitamin D.
Historical Perspective and Discovery of Vitamin D Vitamin D is a unique vitamin and hormone the origin of which dates back about 750 million years when it was first produced in ocean-dwelling phytoplankton and zooplankton while these were being exposed to sunlight. It is likely that most plants and animals exposed to sunlight have the capacity to produce vitamin D. In the nineteenth century, Bennett (1812–75) of Edinburg recognized the nutritional value of cod liver oil in the treatment of
646
rickets. In the same century, Mellanby showed in experiments with puppies that rickets is a nutritional disease which responded to a fat-soluble vitamin present in cod liver oil. Rickets is a bone disease characterized by deformities of the skeleton, shortened stature, and muscle weakness. The disease was first identified in children living in industrialized cities of northern Europe. The relationship between lack of sunshine and rickets was demonstrated by Sniadecki in Poland in 1822, and McCollum and associates showed that the antirachitic activity of cod liver oil was due to vitamin D rather than vitamin A. In the early twentieth century, Steenbock and Black exposed a variety of foods such as wheat, lettuce, vegetable oils, and animal feed to ultraviolet (UV) radiation. They found that this radiation gave antirachitic activity to these foods. It was in the early 1930s that Askew’s and Windaus’s groups isolated and identified ‘ergocalciferol’ or vitamin D2 by irradiation of ergosterol. A few years later, after a suggestion of Wadell, Windaus’s group also isolated ‘cholecalciferol’ or vitamin D3 by irradiation of 7-dehydrocholesterol. Once the structure of vitamin D was established in the 1960s and a simple process was developed for its synthesis, vitamin D could be used as a supplement and was added directly to milk in the United States. In Europe, other supplementation programs were developed for the prevention of rickets. In the 1970s, intensive research on vitamin D revealed that vitamin D is a hormone rather than a vitamin.
Chemistry Vitamin D is the generic descriptor for all steroids exhibiting qualitatively the biological activity of cholecalciferol. These compounds contain the intact ‘A’, ‘C’, and ‘D’ steroid rings being ultimately derived in vivo by photolysis of the ‘B’ ring of 7-dehydrocholesterol (see Figure 1). These compounds have either of two types of isoprenoid side chains attached to the steroid nucleus at C-17 of the ‘D’ ring. Ergocalciferol and derivatives have one side chain containing nine carbons and a double bond. Cholecalciferol and derivatives have a side chain with eight carbons and no double bond. Cholecalciferol (D3) and ergocalciferol (D2) are white to yellowish powders and are insoluble in water, moderately soluble in fats, oils,
Vitamins | Vitamin D 647 R CH3
R=
CH2 (D2) R=
HO
(D3) Figure 1 Structure of vitamin D (calciferol).
and ethanol, and freely soluble in acetone, ether, and petroleum ether. Each shows a strong UV absorption, with a maximum at 264 nm. Vitamin D is sensitive to oxygen, light, and iodine. Heating and mild acidity can convert it to an inactive form. Whereas the vitamin is stable in dry form, in organic solvents and most plant oils (due to the presence of -tocopherol, which serves as a protective antioxidant), its thermal- and photolability can result in losses during such processes as saponification with refluxing. However, storage and processing of foods in general do not affect vitamin D activity.
Food Sources and Endogenous Synthesis The main food sources of vitamin D are fish and fish products, many of which contain 5–15 mg per 100 g, and foods to which vitamins have been added. Table 1 shows the main sources in Europe. This list does not include dairy products, because the amount is only 0.7–1.0 mg l1 whole milk. Even a high-fat dairy product like butter does not contain more than 0.75 mg per 100 g. Also, human milk does not contain much vitamin D, at least 75% of which is available as
calcidiol (vitamin D2). The total activity in human milk is about 0.4–0.6 mg l1, which does not meet the daily requirement of infants; an extra supply is required either via exposure to sunlight or by vitamin D supplements. Photosynthesis of pre-cholecalciferol occurs in the skin during exposure to sunlight. The high-energy UVB photons with wavelength between 290 and 320 nm penetrate into the skin, where they are absorbed by epidermal and dermal stores of 7-dehydrocholesterol (D3). When the sky is clouded, exposure to this radiation is only 30% and via glass it is reduced to about zero. Only 2 h after pre-cholecalciferol is formed in the skin, it is converted to cholecalciferol. Once formed, cholecalciferol exits the skin into the dermal capillary bed where it is bound to a vitamin D-binding protein (DBP). In 1967, Loomis estimated that the pink cheeks of a European infant (area 20 cm2) can synthesize daily about 10 mg of vitamin D if adequately exposed; this is sufficient to prevent rickets.
Absorption and Metabolism Dietary vitamin D is predominantly in the D3 form and is passively absorbed from the small intestine. The absorption is dependent upon micelle solublization and, hence, the presence of bile salts. Vitamin D enters the lymphatic circulation mainly with chylomicrons and is predominantly associated with the -globulin fraction. The efficiency of this absorption process for vitamin D appears to be about 50%. After absorption, vitamin D is transported first to the liver and converted to 25-hydroxycalciferol (calcidiol), and then it is converted in the kidney to 1,25-dihydroxycalciferol (calcitriol), the metabolically active form of the vitamin.
Table 1 Important dietary sources of vitamin D Source
Vitamin D content
Fish
Wild mushrooms Meat products
Pike, perch Salmon Sardines, canned Tuna, canned Wild chanterelles Liver Chicken
Eggs Margarine Milk
Whole Low fat
The vitamin D content depends on where fish is caught 9–12 mg per portion (150 g) 20 mg per portion (150 g) 2.2 mg per can (70 g fish) 1.2–2.0 mg per can (70 g fish) 13 mg per 100 g The vitamin D content of meat products probably depends on the feed of the animals 1.8–2.7 mg per 100 g 1.7 mg per 100 g 1.4 mg per 110 g Vitamin D is added to margarine in most European countries 0.7–1.0 mg per 100 ml 0
1 mg vitamin D ¼ 40 IU. From European Commission (1999) Report on Osteoporosis in the European Community. Luxemburg: Directorate Employment: Social affairs and Health.
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Vitamin D, like other steroids, is transported in the plasma in association with the protein called DBP. The appearance of vitamin D in the blood is short-lived, as it is either stored in the fat or metabolized in the liver. The half-life of 25(OH)D in the human circulation is approximately 10 days to 3 weeks. It has been suggested that the efficiency of endogenously produced vitamin D3 is greater than that given orally because the former enters the circulation strictly via DBP, whereas the latter enters as complexes with DBP as well as in chylomicrons. This indicates that oral vitamin D remains longer in the liver and is therefore catabolized more quickly to excretory forms. Furthermore, cholecalciferol (D3) is very photolabile and when it does not escape in the circulation after it is formed in sunlight, it will be converted efficiently into nontoxic substances. DBP has a higher affinity for 25(OH)D than for 1,25(OH)2D, most likely because 25(OH)D is present in
the circulation at concentrations about 1000 times higher than that of 1,25(OH)2D, and DBP binds 99% of it.
Metabolic Functions The most clearly elucidated function of vitamin D is the maintenance of homeostasis of Ca2þ and phosphate in the extracellular fluid. Three organ systems are involved in the regulation: intestinal absorption; bone accretion; and mobilization and renal excretion. In these systems, control of the blood levels of Ca2þ, parathyroid hormone (PTH), and calcitonin (CT) is important (see Figure 2). For example, when serum Ca2þ falls below the target level of 10 mg dl1, PTH is secreted by the parathyroid glands, which function to detect hypocalcemia. The kidney responds in two ways to increased PTH level: diuresis of phosphate and stimulation of 25(OH)D-1hydroxylase. The latter effect increases the production of
Vitamin D
25-OH-ase Liver
25-OH-D Pi and other factors Kidney 1 α-OH-ase 1,25(OH)2D
1,25(OH)2D
PTH
Intestine
Bone PTH 2+
Ca
HPO4–
Parathyroid glands
2+ – Ca HPO4
n
atio cific
Cal
Blood calcium and phosphorus
Figure 2 Metabolism of vitamin D and the biological actions of 1,25-dihydroxycholecalciferol (1,25(OH)2D). PTH, parathyroid hormone.
Vitamins | Vitamin D 649
1,25(OH)2D, which will stimulate the enteric absorption of both Ca2þ and phosphate. Also, calcitriol acts jointly with PTH in bone to promote the mobilization of Ca2þ and phosphate. The combined result of these responses is an increase in the concentration of Ca2þ and phosphate in the plasma. Clearly, in the long run, this will lead to demineralization of bone and consequently to an increased risk of fractures. In addition to maintaining homeostasis of Ca2þ and phosphate in the extracellular fluid, 1,25(OH)2D exerts its effects by binding to a specific nuclear receptor (VDR), a ligand-dependent transcription factor that belongs to the superfamily of steroid–thyroid hormone–retinoid nuclear receptors. This VDR when activated switches on the gene that induces synthesis of a calcium transport protein (calbindin) in the epithelium of the small intestine. Until now, the main effects of VDR have been found in the small intestinal epithelium and the cells in the bone, osteoblasts (that form new bone), and osteoclasts (that break down bone). However, VDR appears to be present not only in these target cells, but also in a range of tissues. This observation will lead to promising research on the functional role of vitamin D in areas such as type I diabetes, some cancers, autoimmune disease (e.g., multiple sclerosis), and infectious diseases (e.g., tuberculosis).
Reference Intakes The Institute of Medicine of the US National Academy of Sciences has estimated adequate intakes of vitamin D for those with no sun-mediated synthesis in the skin. For those aged 0–50 years (including pregnant and lactating women), the adequate intake is 5 mg day1; for those 51–70 years of age, 10 mg day1; and for those over 70 years of age, 15 mg day1. The European Community has an ongoing project (EURRECA) to harmonize dietary reference intakes. First results show that the median vitamin D intake recommendations for the European population vary from 5 mg day1 for people aged 5–50 years to 10–15 mg for younger and older age groups and for pregnant and lactating women. But note that the reference intake is already up to 20 mg according to EURRECA. With a few exceptions, in most countries the median recommendations are the same for males and females.
and is mostly by passive absorption. This makes the requirement for vitamin D also lower. The vitamin D requirements mentioned are based on an adequate intake of calcium and other nutrients. Dietary Fiber Studies have shown that increasing dietary fiber in a daily diet from 20 to 40 g shortens the biological half-life of calcidiol by about 30% and therefore may increase the requirements for vitamin D by 40%. Skin Pigmentation Melanin skin pigmentation determines the color of the skin. Increased melanin pigmentation reduces the efficiency of sun-mediated photosynthesis of pre-cholecalciferol. This is particularly important for dark-colored immigrants who live in Northern latitudes and who ingest little dietary vitamin D. Effect of Latitude, Season, and Time of the Day Latitude, season, and time of the day have a dramatic effect on the cutaneous production of vitamin D3. Above and below latitudes of approximately 40 N and 40 S, respectively, vitamin D3 synthesis in the skin is absent during most of the 3–4 winter months. This also holds for the middle of the day, when in summer production of vitamin D via sunlight is highest. Far-Northern and farSouthern latitudes extend this period to 6 months. Sunscreen Use, Clothing, and Glass Sunscreens protect against the damaging effect of highenergy UVB radiation; however, it is this radiation that produces pre-cholecalciferol in the skin. It is therefore not surprising that studies show that young adults covered with a sunscreen with a sun protection factor of 8 or higher are unable to increase circulating vitamin D above baseline after exposure to simulated sunlight. Similarly, clothing absorbs most UV radiation and exposure of the skin to sunlight that has passed through windowpane glass or Plexiglas will not increase circulating calcidiol levels. Aging
Factors Affecting Vitamin D Requirements Availability of Calcium Vitamin D requirement is inversely related to the intake of calcium. Calcium is absorbed by active transport, which is vitamin D-dependent, and passive diffusion, which does not depend on the availability of vitamin D. When the intake of calcium is high, the percentage absorbed is low,
In adults over 65 years, there is a fourfold decrease in the production of vitamin D compared with younger adults aged 20–30 years. This is well documented. It is not known whether the absorption of physiological amounts of vitamin D is altered. However, after the age of 20 years, skin thickness decreases linearly with age. This thickening reduces the synthesis of vitamin D. Nevertheless, it has been shown that 5 min exposure daily to UV light to
650 Vitamins | Vitamin D
0.1 m2 (about hands and face) has the same effect as a daily supplement with 10 mg vitamin D. Clearly, important additional risk factors in elderly people are immobility and protection against sunlight. Since dietary intake for most people will not exceed 5 mg day1, unless sufficiently fortified foods are used, elderly people above the age of 70 (and in some countries even earlier) are advised to use a vitamin D supplement. Obesity Obesity is associated with vitamin D insufficiency and secondary hyperparathyroidism. It has been demonstrated that in obese individuals (body mass index (BMI) >30 kg m2), bioavailability of cutaneously synthesized vitamin D3 is reduced by >50%. Obesity-associated vitamin D insufficiency is most likely due to the deposition of vitamin D3 from cutaneous and dietary sources in body fat compartments. Malabsorption Disorders Patients suffering from various intestinal malabsorption syndromes, such as steatorrhea, sprue, Whipple’s disease, Crohn’s disease, and severe liver failure, often suffer from vitamin D deficiency, due to their inability to absorb vitamin D via the intestine; they should receive vitamin D either via exposure to UV light or intravenously.
Vitamin D Deficiency and the Relationship with Chronic Disease Two forms of bone disease, caused by inadequate mineralization or demineralization of the skeleton, may accompany vitamin D deficiency. Severe deficiency results in rickets in children and osteomalacia in adults. Rickets in children is characterized by widening at the end of the long bones, rachitic rosary, and deformations in the skeleton including frontal bossing and outward or inward deformities of the lower limbs causing bowed legs or knocked knees, respectively. Signs of osteomalacia are more generalized than those of rickets, for example, muscle weakness and bone tenderness, especially in the spine, shoulders, ribs, or pelvis. Patients with osteomalacia are at increased risk to fractures of all types, but particularly to those of the wrist and pelvis. In addition, the secondary hyperparathyroidism associated with vitamin D deficiency enhances mobilization of calcium from the skeleton, resulting in osteoporotic bones. It is one of the causes of osteoporosis, the etiology of which is not fully understood but appears to involve impairment of vitamin D metabolism and/or function associated with decreasing estrogen levels.
Vitamin D deficiency causes muscle weakness. This weakness and the susceptibility to infections in rickets or osteomalacia may reflect roles for VDR in the muscles and the immune system. Causes of a vitamin D-deficient state can be any alteration in the cutaneous production of vitamin D3, absorption in the intestine, or the metabolism of vitamin D to its active form, 1,25(OH)2D. Furthermore, an alteration in the recognition of 1,25(OH)2D by its receptor can also cause vitamin D deficiency, metabolic bone disease, and accompanying biochemical abnormalities. Biochemical characteristics of vitamin D deficiency are plasma calcium and phosphate concentrations, • reduced an elevated level of serum PTH (>30 ng ml ) in • conjunction with a low level of serum 25(OH)D, a serum level of 25(OH)D below 20 ng ml or • 50 nmol l , elevated level of serum alkaline phosphate, and • anurinary of bone collagen by-products and an • increaseexcretion in their level, including hydroxyproline, 1
1
1
pyridinoline, deoxypyridinoline, and N-telopeptide. There is increasing evidence that in addition to osteoporosis, vitamin D deficiency may be associated with other chronic diseases. For instance, in epidemiological surveys, colon, breast, and prostate cancers seem to be less prevalent in people living at sunny (lower) latitudes and so is multiple sclerosis. A likely explanation is that colon, breast, prostate, and other tissues express 25(OH)D-1hydroxylase and produce 1,25(OH)2D locally to control genes that help to prevent cancer by keeping cellular proliferation and differentiation in check. It has been suggested that if a cell becomes malignant, 1,25(OH)2D can induce apoptosis and prevent angiogenesis, thereby reducing the potential for the malignant cell to survive. It has been shown in culture experiments that 1,25(OH)2D modulates T and B lymphocytes. In Finland, a 20-year trial including treatment of children with vitamin D reduced the risk of developing type I diabetes. Furthermore, psoriasis has long been known to improve in the summer and is now treated with 1,25(OH)2 derivates. Currently, a relationship between vitamin D and cardiovascular diseases, mental health, lung function, and other autoimmune diseases has also been found. How these findings will affect vitamin D requirements is not yet known.
Hypervitaminosis D Hypervitaminosis D is characterized by raised circulating 25(OH)D plasma levels up to more than 160 ng ml1, accompanied by thirst, nausea, and anorexia. Hypervitaminosis D involves increased enteric absorption and bone resorption of calcium, producing
Vitamins | Vitamin D 651
hypercalcemia, with attendant decreases in PTH and glomerular filtration rate and, ultimately, loss of calcium homeostasis. The result is calcinosis, expressed in various organ systems including kidney, bone, central nervous system, and cardiovascular system. The upper level of intake per day for adults set by Institute of Medicine of the US National Academy of Sciences is 50 mg and for infants this is 25 mg. For most people, vitamin D intake from food and supplements is unlikely to exceed the tolerable upper intake levels. However, persons who are at the upper end of the ranges for both sources of intake, particularly those who use many supplements and those with high intakes of fish or fortified milk, may be at risk for vitamin D toxicity. Under some conditions, people are more sensitive to vitamin D (e.g., sarcoidosis and a rare condition in infants with elfin facial appearance, Williams syndrome).
Vitamin D and Dairy Fortification As part of a nutrition policy to combat vitamin D deficiency in infants and children, many countries have a vitamin D supplementation program. In some countries, one of the items of this program is fortification of dairy products. Since there is a growing number of elderly people at risk for insufficient vitamin D supply, this might be one of the options to solve this problem. However, since the margin between an adequate vitamin D supply and the upper tolerable level of intake is rather small for elderly people (15–50 mg day1), caution should be taken to avoid an overdose. In the United States and Canada, where fortification is a long-standing practice, studies have demonstrated that the amount of vitamin D added to milk is variable and does not amount to that stated on the label.
Concluding Remarks Vitamin D is considered a hormone rather than a vitamin. Nevertheless, as a dietary component it can prevent deficiency diseases, in concert with other sources such as exposure to sunlight and supplements. Undiagnosed vitamin D deficiency is not uncommon and 25(OH)D is the barometer for vitamin D status. Serum 25(OH)D is not
only a predictor of bone health, but, according to recent research, is also an independent predictor of risk for cancer and other chronic diseases. In the Western world particularly, elderly people are at risk of an insufficient vitamin D supply. Also immigrants and particularly pregnant and lactating women, with a colored skin and who have moved to countries at a greater distance from the equator, are at increased risk for vitamin D deficiency. In these countries, a sensible and reliable supplementation program including fortification of dairy products may contribute to the prevention of vitamin D-related diseases.
Further Reading Boonen S, Lips P, Bouillon R, Bischoff-Ferrari HA, Vanderschueren D, and Haentjens P (2007) Need for additional calcium to reduce the risk of hip fracture with vitamin D supplementation: Evidence from a comparative meta-analysis of randomized controlled trials. The Journal of Clinical Endocrinology and Metabolism 92: 1415–1423. Brannon PM, Yetly EA, and Picciano MF (2008) (eds.) Vitamin D and health in the 21st century: An update. The American Journal of Clinical Nutrition 88(2): 483s–592s. Delucca HF (2004) Vitamin D and health in the 21st century: Bone and beyond. Overview of general physiologic features and functions of vitamin D. The American Journal of Clinical Nutrition 80: 1689s–1696s. Health Council of the Netherlands (2000) Dietary reference values: Calcium, vitamin D, thiamin, riboflavin, pantothenic acid and biotin. Publication no. 2000/12. Den Haag, The Netherlands: Health Council of the Netherlands. Holick MF (2007) Vitamin D deficiency; review article. The New England Journal of Medicine 357: 266–281. Institute of Medicine, Food and Nutrition Board (1997) Dietary Reference Intakes for Calcium Phosphorus, Magnesium, Vitamin D and Fluoride. Washington, DC: National Academy Press. Jackson C, Gaugris S, Sen SS, and Hosking D (2007) The effect of cholecalciferol (vitamin D3) on the risk of fall and fracture: A meta analyses. The Quarterly Journal of Medicine 100: 185–192. Norman AW and Henry HH (2006) Vitamin D. In: Bowman BA and Russell RM (eds.) Present Knowledge in Nutrition, Vol. 1, pp. 198–210. Washington, DC: ILSI. Rock E (2008) Fat soluble vitamins. In: Raats M, de Groot L, and van Staveren W (eds.) Food for the Ageing Population, pp. 374–398. Cambridge: Woodhead Publishing Limited. Vieth R (1999) Vitamin D supplementation, 25-hydroxyvitamin D and safety. The American Journal of Clinical Nutrition 69: 842–856.
Relevant Websites http://www.eurreca.org – European recommendations aligned (EURRECA).
micronutrient
Vitamin E P A Morrissey and T R Hill, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. A. Morrissey and M. Kiely, Volume 4, pp 2670–2677, ª 2002, Elsevier Ltd.
Introduction
Chemistry
In 1922, Evans and Bishop discovered a fat-soluble dietary constituent that was essential for the prevention of fetal death and sterility in rats fed a diet containing rancid lard. This was originally called ‘factor X’ or ‘antisterility factor’, but was later named vitamin E. Subsequently, the multiple nature of the vitamin began to appear when two compounds with vitamin E activity were isolated from wheat germ oil and characterized. These compounds were designated - and -tocopherol, derived from the Greek ‘tokos’ for childbirth, ‘phorein’ meaning to bring forth, and ‘ol’ for the alcohol portion of the molecule. Later, two additional tocopherols, - and -tocopherol, as well as four tocotrienols were isolated from edible plant oils. After the initial discovery, more than 40 years passed before it was proved that vitamin E deficiency could cause disease in humans. Vitamin E has been linked to several distinct clinical problems in humans, including hemolytic anemia in premature infants, reduced erythrocyte stability in patients with cystic fibrosis, and ‘short bowel syndrome’. Other studies demonstrated that vitamin E plays an essential role in maintaining the integrity of neuromuscular systems and retina. Studies on children and adults with specific causes of fat malabsorption and patients with familial isolated vitamin E deficiency syndrome have conclusively shown that neurological dysfunction is associated with vitamin E deficiency and that vitamin E is an essential nutrient for the optimal development and maintenance of the integrity and function of the human nervous system. One of the more significant developments in the history of vitamin E was the identification that it is an effective lipidsoluble scavenger of lipid peroxyl radicals and, while present at very low concentrations, it is extremely efficient in protecting membranes against lipid peroxidation. This article reviews the chemistry of the tocopherols and their dietary sources, absorption, transport, and storage mechanisms, and metabolic function. In addition, the potential role of dietary or supplemental tocopherol intake in the prevention of chronic diseases and possible mechanisms for the observed protective effects are discussed. Finally, a summary of the assessment of tocopherol status in humans, intake requirements, and an overview of the safety of high intakes is provided.
The chemistry of vitamin E is rather complex because there are eight structurally related forms – four tocopherols (, , , and ) and four tocotrienols (, , , and ) – that are produced at various levels and in different combinations by all plant tissues and in some cyanobacteria. All are amphipathic molecules with the general structures shown in Figure 1. The polar head group is derived from aromatic amino acid metabolism and the hydrophobic tail is derived from phytyl-diphosphate (phytyl-DP) or geranylgeranyl diphosphate (GGDP) in tocopherols and tocotrienols, respectively. -Tocopherol is methylated at C-5, C-7, and C-8 on the chromonol ring, whereas the other homologues ( , , and ) differ in the number and positions of the methyl groups on the ring (Figure 1). Tocopherols have a fully saturated 20-carbon phytyl side chain attached at C-2 and have three chiral centers that are in the R configuration at positions C-2, C-41, and C-81 in the naturally occurring form, which are given the prefix 2R, 41R, and 81R (designated RRR). They are more biologically active than their synthetic counterparts, which are mixtures of all eight possible stereoisomers and are given the prefix all-rac. Tocotrienols differ from the corresponding tocopherols in that the 20-carbon isoprenoid side chain at C-31, C-71, and C-111 is unsaturated and they possess one chiral center at C-2 in addition to two sites of geometric isomerism at C-31 and C-71. Natural tocotrienols have the 2R, 31-trans, 71-trans configuration. The phenolic hydroxyl group is critical for the antioxidant activity of vitamin E, as donation of hydrogen from this group stabilizes free radicals. The presence of at least one methyl group on the aromatic ring is also critical. The biological activity of vitamin E is defined in terms of -tocopherol equivalents (-TE) whenever possible. RRR--tocopherol has an activity of 1 mg -tocopherol equivalents (-TE mg1 compound). The activities of RRR- , RRR- , and RRR--tocopherol are 0.5, 0.1, and 0.03, respectively. Synthetic all-rac--tocopheryl acetate has an activity of 0.74 mg -TE mg1. Of the tocotrienols, only -tocotrienol has significant biological activity (0.3 mg -TE mg1). Lengthening or shortening of the side chain results in a progressive loss of vitamin E activity.
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Figure 1 The four major forms of vitamin E (-, -, -, and -tocopherol) differ by the number and position of methyl groups on the chromanol ring. In -tocopherol, the most biologically active form, the chromanol ring is fully methylated. In - and -tocopherol, the ring contains two methyl groups, while in -tocopherol, it is methylated at one position. The corresponding tocotrienols have the same structural arrangement except for the presence of double bonds on the isoprenoid side chain at C-31, C-71, and C-111.
Dietary Sources The composition and content of the different tocopherol components in plant tissue vary considerably, ranging from the extremely low levels found in potato tubers to the high levels found in oil seeds. -Tocopherol is the predominant form in photosynthetic tissues and is localized mainly in plastids. The particular enrichment in the chloroplast membranes is probably related to the ability of tocopherols to quench or scavenge reactive oxygen species (ROS) and lipid peroxy radicals by physical or chemical means. In nonphotosynthetic tissues,
-tocopherol frequently predominates and can be involved in the prevention of autoxidation of polyunsaturated fatty acids (PUFAs). Most of the tocopherol content of wheat germ, sunflower, safflower, canola, and olive oils is in the form of -tocopherol and these oils contain about 1700, 500, 350, 200, and 120 mg -TE kg1, respectively. Vegetable oils such as of corn, cottonseed, palm, soybean, and sesame and nuts such as Brazil nuts, pecans, and peanuts are rich sources of -tocopherol. Corn and soybean oils contain 5–10 times as much -tocopherol as -tocopherol-rich sources and each contains about 200 mg -TE kg1. Because of the widespread use of these plant products,
-tocopherol is considered to represent 70% of the vitamin E consumed in the typical US diet. The level of vitamin E in nuts ranges from 7 mg -TE kg1 in
coconuts to 450 mg -TE kg1 in almonds. Cereals are moderate sources of vitamin E, providing between 6 (barley) and 23 (rye) mg -TE kg1. Fresh fruit and vegetables generally contain about 1–10 mg -TE kg1. Different authors have reported concentrations of -tocopherol between 0.2 and 0.7 mg l1 in bovine milk;
-tocopherol has also been found in addition to the presence of trace amounts of some other vitamers. Colostrum contains about 1.9 mg l1 of -tocopherol, and the level decreases in approximately 4 days to the level in fresh milk (0.3 mg l1). -Tocopherol is also present in small amounts. The concentration of vitamin E in milk appears to be dependent principally on the amount consumed by the cows. Even in the case of human milk, the concentration of vitamin E in colostrum is much higher than that in mature milk. Human colostrum contains 14.4 2.3 mg -TE l1 compared to 3.1 0.5 mg -TE l1 in mature milk. Ingestion of colostrum is therefore important to provide mammalian neonates with an adequate source of vitamin E to protect against oxidative stress and enhance the immune response. Following birth, colostrum intake induces a sharp increase in the circulating and tissue levels of vitamin E in the young. Mean dietary intakes of 6.3–13.0 mg -TE day1 have been reported in various European and American population studies. Data from the Third National Health and Nutrition Examination Survey (NHANES III) (1988–94) in the United States indicate a median total intake
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(including supplements) of -TE of 12.9 mg day1 and a median intake from food only of 11.7 mg day1 in men aged 31–50 years. In women in this age range, the median total intake (including supplements) of -TE was 9.1 mg day1 and the median intake from food only was 8.0 mg day1. In the United States, fats and oils used in spreads and other products contribute 20.2% of the total vitamin E intake; vegetables, 15.1%; meat, poultry, and fish, 12.6%; desserts, 9.9%; breakfast cereals, 9.3%; fruit 5.3%; bread and grain products, 5.3%; dairy products, 4.5%; and mixed main dishes, 4.0%. The North/South Ireland Food Consumption Survey, published in 2001, reported that the median daily intake of vitamin E from all sources was 6.3 mg for men and 6.0 mg for women aged 18–64 years. The largest contributors of vitamin E to the diet were vegetables and vegetable dishes (18.9%) and potatoes and potato products (12.4%), most likely as a result of the oils used in composite dishes. Nutritional supplements contributed 5.5% of the vitamin E intake of men and 11.9% of women overall. In the subgroup that regularly consumed nutritional supplements (23% of total), vitamin E was the nutrient most frequently obtained in supplemental form by men (78%) and women (73%). In these people, supplements made a larger contribution to total vitamin E intake than did food.
Absorption, Metabolism, and Excretion Following ingestion, fats are emulsified into smaller particles, first in the stomach and then in the small intestine, where they are mixed with pancreatic and biliary secretions. Pancreatic esterases convert triglycerides to monoglycerides and free fatty acids, which together with bile acids form micelles into which vitamin E and other hydrophobic molecules become solubilized. Vitamin E is absorbed in the proximal part of the small intestine, where transport across the brush border is thought to occur by passive diffusion. There are no selective differences in absorption between - and -tocopherols, but - and -tocopherols are absorbed poorly and are excreted in the feces. Together with triglycerides, phospholipids, and apolipoproteins, the tocopherols ( and ) are reassembled to chylomicrons by the Golgi of the mucosal cells. The chylomicrons are stored as secretory granula and eventually excreted by exocytosis to the lymphatic compartment from which they reach the bloodstream via the ductus thoracicus. The transfer of vitamin E from chylomicrons is regulated by complex mechanisms that control lipid and lipoprotein metabolism. Chylomicrons are degraded to remnants by lipoprotein lipase (LPL) and some - and
-tocopherols are transferred to peripheral tissues such as muscle, adipose tissue, skin, and brain by this enzyme-
mediated mechanism. The resulting chylomicron remnants are then taken up by the liver, where most of the remaining -tocopherol and only small amounts of
-tocopherol are reincorporated into nascent very lowdensity lipoproteins (VLDLs) by a specific 32-kDa -tocopherol transfer protein (-TTP), which enables further distribution of -tocopherol throughout the body. Approximately 50% of the dietary intake of -tocopherol appears to be degraded in the liver by a cytochrome P450-dependent process and is then excreted primarily in the urine. Catabolism of -tocopherol by this route occurs only when the daily intake of -tocopherol exceeds 150 mg or plasma concentration of -tocopherol is above a threshold of 30–40 mmol l1. Plasma or serum concentrations of -tocopherol are typically around 20–35 mmol l1. -Tocopherol concentrations are approximately 5–15% of those of -tocopherol and generally remain around 1 mmol l1 even after supplementation. The highest concentrations of -tocopherol in the body are in the adipose tissues and adrenal glands. Adipose tissues are also the major stores of the vitamin, followed by liver and skeletal muscle. The rate of uptake and turnover of -tocopherol by different tissues varies greatly. Uptake is most rapid in the lungs, liver, spleen, kidney, and red blood cells (in rats t1/2 < 15 days) and slowest in the brain, adipose tissues, and spinal cord (t1/2 < 30 days). Likewise, depletion of -tocopherol from plasma and liver during times of dietary deficiency is rapid, whereas adipose tissues, brain, spinal cord, and neural tissues are much more difficult to deplete. A considerable, but variable proportion (typically 30–70%) of ingested vitamin E is unabsorbed and therefore excreted in the feces, making this the main route of elimination, and is influenced by experimental conditions and a variety of luminal and physiological factors. When large doses of vitamin E are administered, much of it is secreted in the bile, which may account for the relative safety of vitamin E compared to vitamins A and D. Both bile acids and pancreatic juices are important for the absorption of vitamin E. This has been established clearly in patients where secretion of either, or both, is severely diminished as in patients with cystic fibrosis or pancreatitis. The simultaneous intake of fat is necessary to stimulate bile flow and the secretion of pancreatic enzymes to allow micelle formation. However, the amount of fat necessary to ensure absorption may be small.
Vitamin E as an Antioxidant Under normal physiological conditions, cellular systems are incessantly challenged by stressors arising from both internal and external sources. The most important
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potential stressors are reduced derivatives of oxygen, which are classified as ROS. ROS are toxic as they can oxidize biomolecules, leading to cell death and tissue injury, and are associated with the onset of a variety of chronic disease conditions in humans. ROS include the ? ? superoxide anion (O 2 ), hydroxyl radical ( OH, and oxygen-centered radicals of organic compounds (peroxyl (ROO?) and alkoxyl (RO?)) together with other nonradical reactive compounds, such as hydrogen peroxide (H2O2). In addition, reactive nitrogen species (RNS) such as nitric oxide (NO?), nitrogen dioxide (NO?2), peroxynitrite (ONOO), and hypochlorous acid are involved. Cell systems have evolved a powerful and complex antioxidant defense system to limit inappropriate exposure to these stressors. Much of the work on antioxidant defense has been confined to studies on the chain-breaking antioxidants vitamins C and E and the carotenoids. -Tocopherol is quantitatively the most important antioxidant in plasma and biological membranes. -Tocopherol is an indispensable component of biological membranes and has membrane-stabilizing properties. The molecule is anchored in the highly hydrophobic hydrocarbon part of the membrane layer by the isoprenoid chain (Figure 2). The chromanol nucleus lies at the surface of lipoprotein or at the membrane–water interface, and it is the phenolic group that quenches free radicals (X?) (Figure 2). In this position, the chromanol ring has considerable mobility; it is able to quench peroxyl radicals that partition to the water–membrane interface and can be regenerated by harvesting the
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antioxidant capacity of other lipid-soluble antioxidants (e.g., ubiquinols) and water-soluble reductants, such as ascorbate and glutathione. The overall mechanism of lipid peroxidation and antioxidant protection in biological systems is outlined in Figure 3. Steps a and b show the abstraction of a labile hydrogen from a methylene group adjacent to the double bond of an unsaturated fatty acid (RH) by an oxidizing radical (X?) and subsequent oxygenation to form a peroxyl radical. Step c shows how the peroxyl radical moiety diffuses out of the autooxidizable, nonpolar interior region of the bilayer and into the non-autooxidizable polar membrane–water interface. Step d shows how the proximity to the interface of the anchored phenol on the chromanol ring allows for rapid formation of the lipid hydroperoxide (ROOH) and tocopheroxyl radical (TO?). The TO? can be regenerated, thereby recycling tocopherol. The remarkable antioxidant properties of vitamin E may be explained by its ability to be efficiently re-reduced from its radical form to its native state by ascorbate and other intracellular reductants. The ascorbate radical can be regenerated and the potentially toxic lipid hydroperoxide can be cleaved, detoxified, and repaired. The antioxidant activities of chain-breaking antioxidants are determined primarily by how rapidly they scavenge peroxyl radicals, thereby preventing the propagation of free radical reactions. When the chromanol phenolic group of -tocopherol (TOH) encounters a peroxyl radical (ROO?), it forms hydroperoxide (ROOH), and in the process a tocopheroxyl radical (TO?) is formed:
Figure 2 Schematic representation of the lipid bilayer of a cell membrane, showing the possible positions of the tocopherol and cholesterol molecules. OH?, hydroxyl radical; X?, free radical. Reproduced with permission from Morrissey PA, Buckley DJ, and Galvin K (2000) Vitamin E and the oxidative stability of pork and poultry. In: Decker EA, Faustman C, and Lopez-Bote CJ (eds.) Antioxidants in Muscle Foods: Nutritional Strategies to Improve Quality, pp. 263–287. New York: John Wiley.
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Figure 3 Membranal lipid oxidation. Details on ae are explained in text. RH, unsaturated fatty acid; GSH-Px, glutathione peroxidase; GSH, glutathione; SOD, superoxide dismutase; ASCH, ascorbate monoanion; ASC, ascorbate free radical; X , free radical. Reproduced with permission from Morrissey PA, Buckley DJ, and Galvin K (2000) Vitamin E and the oxidative stability of pork and poultry. In: Decker EA, Faustman C, and Lopez-Bote CJ (eds.) Antioxidants in Muscle Foods: Nutritional Strategies to Improve Quality, pp. 263–287. New York: John Wiley.
k1 TOH þ ROO? ! ROOH þ TO?
The rate constant (k1) for hydrogen abstraction from -tocopherol is 2.35 106 mol l1 s1, which is higher than that for the other tocopherols and related phenols. Because the rate constant (k2) for the chain propagation reaction between ROO? and an unsaturated fatty acid (RH) (ROO? + RH ! ROOH) is much lower than k1, at approximately 102 mol l1 s1, -tocopherol outcompetes the propagation reaction and scavenges the ROO? 104 times faster than RH reacts with ROO?. The concentration of -tocopherol in biological membranes is approximately 1 mol per 1000–2000 mol phospholipids (i.e., 1:103). This effectively means that about 90% of ROO? are scavenged by tocopherol before they can attack another RH. Thus, the kinetic properties of antioxidants, and in particular -tocopherol, require that only relatively low concentrations are required for them to be effective. Because -tocopherol lacks one of the electron-donating methyl groups on the chromonal ring, it is less hydrophobic and is somewhat less potent in donating electrons than -tocopherol, and is, thus, a slightly less powerful antioxidant. However, the unsubstituted C-5 position on -tocopherol allows it to trap lipophilic electrophiles such as RNS. Excessive generation of RNS is associated with chronic inflammation in humans and animals.
Vitamin E Deficiency Vitamin E deficiency is seen rarely in humans. However, there may be a risk of vitamin E deficiency in premature infants because the placenta does not transfer
-tocopherol to the fetus in adequate amounts. When it occurs in older children and adults, it is usually a result of lipoprotein deficiencies or a lipid malabsorption syndrome. Patients with abetalipoproteinemia or homozygous hypobetalipoproteinemia, those with cholestatic disease, and patients receiving total parenteral nutrition suffer from vitamin E deficiency. There is also an extremely rare disorder in which primary vitamin E deficiency occurs in the absence of lipid malabsorption. This disorder is a rare autosomal recessive neurodegenerative disease, and is caused by mutations in the gene for -TTP. This disorder is known as ataxia with vitamin E deficiency (AVED). Patients with AVED have extraordinary low plasma vitamin E concentrations (<5 mg ml1) and have an onset between 4 and 18 years, with progressive development of peripheral neuropathy, spinocerebellar ataxia, dysarthria, absence of deep tendon reflexes, and vibratory and proprioceptive sensory loss. Therapeutic and prophylactic vitamin E supplementation (up to 2000 mg day1) prevents the onset of the disease before irreversible neurological damage develops.
Vitamin E and Low-Density Lipoprotein Modification It is generally accepted that low-density lipoprotein (LDL) undergoes oxidation in vivo when challenged by a variety of ROS and RNS and that oxidized LDL is the component central to the initiation and/or progression of atherogenesis at the molecular and cellular level. The
Vitamins | Vitamin E
typical LDL particle is not only rich in cholesterol, but also contains approximately 1300 molecules of RH, which are very sensitive to oxidation. Vitamin E, mainly as -tocopherol, is quantitatively the most important lipophilic antioxidant present in LDL particles. On average, each LDL particle is protected by 10 mol of -tocopherol (range 3–15 mol), 1 mol of -tocopherol, and smaller amounts of carotenoids. All major cells of the artery wall, such as monocytes– macrophages, endothelial cells, and smooth muscle cells, can modify LDL oxidatively in vitro. Monocytes have been shown to induce peroxidation of lipids such as those in LDL by the generation of reactive species, including superoxide anion, hydrogen peroxide, and hydroxyl radicals. Other oxidants have been implicated, including 15-lipoxygenase, myeloperoxidase-generated hypochlorous acid, and RNS such as peroxynitrite. In vivo, oxidized LDL particles are recognized by macrophage scavenger receptors and taken up by macrophages, forming lipid-laden foam cells in the fatty streak lesions. The free radical oxidation of LDL results in numerous structural changes that all depend on a common event, that is, the peroxidation of PUFAs in the LDL particle. In vitro studies have indicated that increasing the vitamin E content of LDL particles increases LDL resistance to oxidation and decreases their uptake by macrophages. A number of research groups have concluded that vitamin E is the most important variable that determines oxidative resistance of LDL. This mechanism of protecting LDL may be significant when -tocopherol constitutes a major portion of vitamin E intake, as in the United States. It is worth noting that the ability of -tocopherol to attenuate oxidative damage produced by RNS may prevent or delay the progression of other diseases, in which inflammation plays a role, such as cancer, rheumatoid arthritis, inflammatory bowel disease, and neurodegenerative disorders, as well as cardiovascular disease (CVD).
Vitamin E and Other Metabolic Function Vitamin E, in addition to having a protective role in the oxidative modification of LDL, may affect or limit the progression of atherosclerosis and a number of other conditions in ways that are unrelated to its antioxidant activity, as outlined below: 1. Vitamin E acts as a negative regulator of smooth muscle cell proliferation via modulation of protein kinase C activity and by activating protein phosphatase 2A. Protein kinase C is an important element in the signal transduction cascade mediated by growth factors such as platelet-derived growth factors, which are necessary for the progression and completion of the cell proliferation cycle.
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2. Vitamin E may stabilize the atherosclerotic plaque and prevent its rupture and subsequent clot formation. This could be an important contributor to the prevention of ischemic heart disease, because plaque types that are most subject to rupture present the greatest threat. 3. Vitamin E reduces the expression of adhesion molecules that can cause neutrophils to stick to the endothelial cells lining the artery, leading to platelet aggregation. 4. Vitamin E may inhibit vitamin K-dependent clotting factors by the action of vitamin E quinone. 5. Vitamin E supplementation reduces the level of thromboxane A2 in vivo, supporting the role of vitamin E as an antithrombic agent. 6. Vitamin E reduces the uptake of oxidized LDL by endothelial cells, preserves the barrier function, increases the activity of cytosolic phospholipase A2 and cyclooxygenase, and augments the release of prostaglandin I2 by endothelial cells. Thus, vitamin E may act both directly, by affecting the uptake of oxidized LDL by endothelial cells, and indirectly, by modulation of oxidized LDL formation and activity. 7. Vitamin E regulates mitochondrial production of ROS, changes the redox state and/or redox controlling factors, and in turn modulates redox-sensitive signaling pathways and transcriptional factors (e.g., activator protein 1, nuclear factor B, mitogen-activated protein). High levels of ROS are likely to increase the expression of a number of ‘atherogenic’ genes and signal transduction pathways leading to inflammation and vascular dysfunction. At low levels of ROS, ‘atheroprotective’ genes are expressed, antiinflammatory factors are produced, and the vascular system is protected. Thus, by regulating the production of ROS, vitamin E modulates the expression and activation of signal transduction pathways and other redox-sensitive biological modifiers, and thereby may prevent or delay the onset of degenerative diseases.
Vitamin E and Cardiovascular Disease The effects of dietary vitamin E have been examined in several studies, and many have reported a clear association between reduction in the relative risk of CVD and high intakes of vitamin E from foods or supplements of vitamin E, although some have shown no such association. The Vitamin Substudy of the WHO/MONICA Project showed that in European populations whose classical risk factors for CVD were very similar, the sevenfold differences in CVD mortality could be explained at least to about 60% by differences in the plasma level of vitamin E and up to 90% by the combination of vitamins E, A, and C. The Edinburgh Case Control Study and Basel Prospective Study consistently revealed an increased risk of ischemic heart disease and stroke for low plasma level of vitamin E.
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However, other European population studies have not found an association between blood levels of vitamin E and end points of CVD. In the European Community Multicentre Study on Antioxidants, Myocardial Infarction and cancer of the Breast (EURAMIC) study, the adipose levels of vitamin E did not correlate with the relative risk of myocardial infarction. A number of prospective studies examined the association between vitamin E intake and risk of CVD. The Nurses’ Health Study, conducted on 87 245 women, showed a 34% reduction in CVD in women who had consumed vitamin E supplements containing more than 67 mg -TE daily for more than 2 years. However, there was no significant effect of vitamin E obtained from food sources. The Established Populations for Epidemiologic Studies of the Elderly (EPESE) trials showed that the use of vitamin E supplements significantly reduced the risk of all-cause mortality and mortality from heart disease. Another prospective study, performed in Canada, reported a consistent inverse association between CVD and vitamin E supplement usage. The Health Professionals Study, conducted on 39 910 men aged 40–75 years, also showed that dietary intakes of vitamin E were not significantly correlated with reduced risk of CVD or death. A protective effect was seen in those who took 67–160 mg supplemental -TE daily for more than 2 years. In contrast, the Iowa Women’s Health Study reported that dietary vitamin E (mainly -tocopherol) was inversely associated with the risk of death from CVD. This association was particularly striking in the subgroup of women who did not consume vitamin supplements. There was little evidence that the intake of vitamin E from supplements (mainly -tocopherol) was associated with a reduced risk of death from CVD. The reasons for the differences between dietary and supplemental vitamin E are not clear. Other studies point to the potential importance of -tocopherol in preventing heart disease. High dietary intake of nuts, an excellent source of
-tocopherol, lowered serum cholesterol, improved plasma lipid profiles, and was inversely associated with the risk of death from heart disease. -Tocopherol may also function in nitric oxide formation, which suppresses the expression of pro-inflammatory cytokines and maintains the integrity of the arterial wall. Several other human clinical trials have shown an improvement in markers of atherosclerosis by vitamin E supplementation. These findings have been contradicted by several vitamin E supplementation trials. It is important to note that, in general, women develop fewer cardiovascular events than do men. Thus, in studies in which many women are enrolled, the low incidence of CVD may weaken the statistical power of the overall trial. However, overall evidence from cell culture, as well as animal and human clinical and observational studies, strongly supports the contribution of dietary vitamin E in the maintenance of
vascular function and health, in particular when used in combination with other foods containing antioxidants.
Vitamin E and Cancer The capacity of vitamin E, particularly -tocopherol, to quench free radicals damage, induce apoptosis, and impact expression of oncogenes makes it a strong candidate for chemotherapeutic strategies. Clinical and epidemiological data, together with evidence from experimental models, support a role for the involvement of free radicals throughout the cancer process. Several studies of oral, pharyngeal, and cervical cancer found a relationship between vitamin E status and cancer risk. The evidence for stomach and pancreatic cancers has not been consistent, and no association with breast cancer has been found. Evidence for the role of vitamin E in cancer prevention was derived from a study conducted in Linxian, China, in a population with persistently low micronutrient intakes and having one of the world’s highest incidences of esophageal/stomach cancer, where an overall reduction in cancer mortality, particularly mortality from stomach and esophageal cancer, was observed. The efficacy of supplementation with -tocopherol on the prevention of certain cancers in male smokers was investigated in the Finnish ATBC study. There was no decrease in the incidence of lung cancer among men supplemented with synthetic -tocopherol compared to those who were not fed supplements. In contrast, prostate cancer incidence and mortality rates were reduced by 32 and 41%, respectively, among the vitamin E-supplemented group. The overall results of epidemiological studies relating to vitamin E and colon cancer have been inconsistent and mixed. Recent epidemiological experiments and mechanistic evidence suggest that -tocopherol may be a more potent cancer chemopreventive agent than -tocopherol. A nested case–control study examined the association of -tocopherol, -tocopherol, and selenium with the incidence of prostate cancer. The most striking finding was that men in the highest quintile of plasma -tocopherol concentrations had a five-fold reduction in the risk of prostate cancer compared with those in the lowest quintile. Other studies have shown that only the plasma levels of -tocopherol served as a biomarker of CVD and cancer. In summary, inverse associations between dietary and supplemental vitamin E intakes and the incidence of several common chronic diseases have been noted in many observational studies, whereas results from studies using blood concentration of vitamin E have been limited and inconsistent. Randomized trials using supplemental vitamin E have not shown substantial effects on mortality
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end points. Recently, a prospective cohort study of 29 092 Finnish male smokers, aged 50–69 years, who participated in the ATBC study was carried out where the prospective association between circulating concentrations of -tocopherol and total and cause-specific mortality in the group was evaluated. Higher circulating concentrations of -tocopherol within the normal range were associated with significantly lower total and cause-specific mortality in older male smokers. The lower total and causespecific mortality rates in older male smokers were observed as the serum -tocopherol values increased from 9.1 mg l1 (21 mmol l1) up to 13–14 mg l1 (30– 33 mmol l1), after which no further benefit was noted.
Vitamin E and Other Diseases Vitamin E appears to act as an immunosuppressant due to its ability to suppress both humoral and cellular immune responses. Tocopherol supplementation significantly enhances lymphocyte proliferation, interleukin-2 production, and delayed-type hypersensitivity skin response and decreases prostaglandin E2 production by inhibiting cyclooxygenase activity. There appears to be compelling evidence that intervention with dietary antioxidants, such as vitamin E, may help maintain the well-preserved immune function of ‘very healthy’ elderly, restore the age-related decrease in immune function, and reduce the risk of several age-associated chronic diseases. Epidemiological evidence suggests an association between the incidence of cataract and vitamin E status. In a prospective study, the sum of serum - and -tocopherol, but neither tocopherol alone, was inversely associated with the incidence of age-related nuclear cataracts. Among the most common neurological diseases are neurodegenerative disorders, such as Alzheimer’s and Parkinson’s disease, which may be caused by oxidative stress and mitochondrial dysfunction leading to progressive neural death. An increasing number of studies show that antioxidants (vitamin E and polyphenols) can block neuronal death in vitro. In a 2-year, double-blind, placebocontrolled, randomized trial in patients with moderately severe impairment from Alzheimer’s disease, treatment with 1340 mg -TE day1 significantly slowed the progression of the disease. Clinical treatment of Alzheimer’s patients with large doses of vitamin E (670 mg -TE twice daily) is one of the key therapeutic guidelines published by the American Academy of Neurology. In a multicenter, double-blind trial, vitamin E (1340 mg -TE day1) was not beneficial in slowing functional decline or ameliorating the clinical features of Parkinson’s disease. Administration of vitamin E significantly relieved symptoms in patients suffering from several types of acute or chronic inflammatory conditions such as acute arthritis, rheumatoid arthritis, and osteoarthritis.
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Vitamin E Status and Requirements Interest in the role of vitamin E in disease prevention has encouraged the search for reliable indices of vitamin E status. Most studies on human subjects make use of static biomarkers of status, usually -tocopherol concentrations in plasma, serum, erythrocytes, lymphocytes, platelets, lipoproteins, adipose tissues, buccal mucosal cells, and LDL, and the -tocopherol: -tocopherol ratio in serum or plasma. Other markers of vitamin E status include susceptibility of erythrocyte or plasma LDL to oxidation, breath hydrocarbon exhalation, and the concentration of -tocopherol quinone in the cerebrospinal fluid. There is no consensus as to the threshold concentration of plasma or serum -tocopherol at which a person can be defined as having inadequate tocopherol status, but values of <11.6, 11.6–16.2, and >16.2 mmol l1 are normally regarded as indicating a deficient, low, and acceptable vitamin E status, respectively. It is now recommended that plasma or serum -tocopherol concentrations be lipid-corrected (i.e., expressed relative to either the sum of cholesterol and triacylglycerol or cholesterol alone). The -tocopherol (mmol):cholesterol (mmol) ratio is the simplest to obtain and probably the most useful, with values <2.25 indicating a risk or deficiency and values >5.2 optimal values. It has been estimated that an average daily dietary intake of 15–30 mg of -tocopherol would be required to maintain this plasma level, an amount that could be obtained from dietary sources if a concerted effort was made to eat foods rich in vitamin E. The US Institute of Medicine set an estimated average requirement (EAR) of 12 mg of -tocopherol for adults >19 years on the criterion of vitamin E intakes that were sufficient to prevent hydrogen peroxide-induced hemolysis in men. The same value was set for men and women on the basis that although body weight is smaller on average for women than men, fat mass as a percentage of body weight is higher on average for women. As information is not available on the standard deviation of the requirement for vitamin E, the recommended dietary allowance (RDA) was established for men and women as the EAR (12 mg) plus twice the coefficient of variation (assumed to be 10%), rounded up, giving a value of 15 mg day1. The RDA values set by the US Institute of Medicine are estimates that meet the requirements of practically all healthy people and the values differ by life stage (Table 1). In the case of lactation, the average vitamin E secreted in human milk is calculated at 4 mg day1 of -tocopherol. For this reason, 4 mg -tocopherol is added to the RDA for non-lactating women, giving an RDA for lactation of 19 mg day1 of -tocopherol (Table 1). In the case of infants aged 0–12 months, the recommended intakes of vitamin E are based on an adequate intake (AI) that reflects a calculated mean
660 Vitamins | Vitamin E Table 1 Recommended dietary allowance Age (years) Children 1–3 4–8 Boys & Girls 9–13 14–18 Men & Women 19–70 >70 Lactation
RDA
6 7 11 15 15 15 19
RDA, recommended dietary allowance. Institute of Medicine (2000) Dietary Reference Intakes of Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC: National Academic Press.
vitamin E intake of infants fed principally with human milk. In Europe, the Scientific Committee for Food did not set a population reference intake (PRI) for vitamin E on the basis that there is no evidence for deficiency from low intakes, and the frequency of distribution of intakes is skewed to the right, making it difficult to set a PRI that is not inappropriately high, especially for those with a low consumption of PUFAs, whose requirements is lower than those with a high consumption of PUFAs. It has been suggested that the optimum concentration of -tocopherol in plasma for protection against CVD and cancer is >30 mmol l1, given normal plasma lipid levels and in conjunction with a plasma vitamin C concentration >50 mmol l1 and a -carotene level >0.4 mmol l1. This has not been proven in large-scale human intervention trials, but even in the absence of conclusive evidence for a prophylactic effect of vitamin E on the prevention of chronic diseases, some experts believe that a recommendation of a daily intake of 87–100 mg of -tocopherol is justifiable based on the current evidence. Realistically, these levels can be achieved only by using nutritional supplements. The tolerable upper intake level (UL) for vitamin E is 1000 mg day1, based on studies showing hemorrhagic toxicity in rats, in the absence of human dose–response data. The Scientific Committee for Food proposed that the intake should not exceed 2000 mg -TE day1.
See also: Milk Lipids: Lipid Oxidation; Nutritional Significance. Vitamins: Vitamin C.
Further Reading Azzi A and Stocker A (2002) Vitamin E: Non-antioxidant roles. Progress in Lipid Research 39: 231–255. Bramley PM, Elmadfa I, Kafatos A, et al. (2000) Review: Vitamin E. Journal of the Science of Food and Agriculture 80: 913–938. Brigeluis-Flohe R, Kelly FJ, Salonen JT, Neuzil J, Zingg J-M, and Azzi A (2002) The European perspective on vitamin E: Current knowledge and future research. American Journal of Clinical Nutrition 76: 703–716. DellaPenna D and Pogson BJ (2006) Vitamin E synthesis in plants: Tocopherol and carotenoids. Annual Review of Plant Biology 57: 711–738. Esposito E, Rotilio D, and Di Matteo V (2002) A review of specific dietary antioxidants and the effects on biochemical mechanisms related to neurodegenerative processes. Neurobiology of Aging 23: 719–735. Frei B (1994) Natural Antioxidants in Human Health and Disease. London: Academic Press. Institute of Medicine (2000) Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC: National Academy Press. Jiang Q, Christen S, Shigenaga MK, and Ames BN (2001)
-Tocopherol, the major form of vitamin E in the US diet, deserves move attention. American Journal of Clinical Nutrition 74: 712–722. Morrissey PA, Buckley DJ, and Galvin K (2000) Vitamin E and the oxidative stability of pork and poultry. In: Decker EA, Faustman C, and Lopez-Bote CJ (eds.) Antioxidants in Muscle Foods: Nutritional Strategies to Improve Quality, pp. 263–287. New York: John Wiley. Neuzil J, Weber C, and Kontush A (2001) The role of vitamin E in atherogenesis: Linking the chemical, biological and clinical aspects to the disease. Atherosclerosis 157: 257–283. Packer L and Fuchs J (eds.) (1993) Vitamin E in Health and Disease. New York: Marcel Dekker. Pryor WA (2000) Vitamin E and heart disease: Basic science to clinical intervention trials. Free Radical Biology and Medicine 28: 141–164. Rimbach G, Minihane AM, Majewicz J, et al. (2002) Regulation of cell signalling by vitamin E. Proceedings of the Nutrition Society 61: 415–425. Thomas SR and Stocker R (2000) Molecular action of vitamin E in lipoprotein oxidation: Implications for atherosclerosis. Free Radical Biology and Medicine 28: 1795–1805. Traber MG and Sies H (1996) Vitamin E in humans: Demand and delivery. Annual Review of Nutrition 16: 321–347. Tucker JM and Townsend DM (2005) Alpha-tocopherol: Roles in prevention and therapy of human disease. Biomedicine & Pharmacotherapy 59: 380–387. Wagner KH, Kamal-Eldin A, and Elmadfa I (2004) Gamma-tocopherol – an underestimated vitamin? Annals of Nutrition and Metabolism 48: 169–188.
Vitamin K T R Hill and P A Morrissey, University College Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. A. Morrissey, Volume 4, pp 2677–2683, ª 2002, Elsevier Ltd.
Introduction Vitamin K (the coagulation vitamin) was discovered in the 1930s as a result of investigations into the cause of an excessive bleeding disorder in chickens fed on a fat-free diet. Its isolation and structural determination were accomplished in 1939 and its metabolic function was defined only after a new amino acid, -carboxylglutamic acid, was discovered in bovine prothrombin in 1974. Vitamin K is essential for the blood clotting process, where it serves as an essential cofactor for the specific carboxylation of a number of vitamin K-dependent coagulation proteins.
Chemistry The term ‘vitamin K’ is a group name for a number of related compounds that have in common a 2-methyl1,4-naphthoquinone ring system, but differ in the length and degree of saturation of their isoprenoid side chain at the 3-position. Three vitamin K compounds have biological activity (Figure 1). Phylloquinone, vitamin K1 (2-methyl-3-phytyl-1,4naphthoquinone), is found in green leafy vegetables and represents the main dietary source of vitamin K in Western diets. Menaquinones (MKs), vitamin K2 (2-methyl-3-1,4-naphthoquinone), are synthesized by the gut microflora, and have fully or partially unsaturated isoprenoid side chains of various length at the 3-position. The predominant forms of the MK compounds contain between 6 and 10 isoprenoid units, but Makes containing up to 13 units have been isolated. The parent structure of the vitamin K group of compounds is 2-methyl-1,4naphthoquinone, commonly called menadione (vitamin K3). This compound is not found in nature but is a synthetic form that can be metabolized to phylloquinone or MK and thus may be regarded as a provitamin. Menadione is also used as an animal feed supplement and in this way may indirectly enter the human food chain as preformed MK-4. Previous analytical techniques to measure vitamin K compounds, such as the chick bioassay, were cumbersome and tended to overestimate the vitamin K content of foods. However, at present, the method of choice for vitamin K analysis in foodstuffs is high-performance liquid chromatography (HPLC) separation after lipid extraction.
Electrochemical or fluorescence detection (after reduction to the hydroquinone form) offers the sensitivity and selectivity needed for quantification of the small amounts of vitamin K compounds. Food composition data for vitamin K derived from HPLC are generally lower than earlier data derived from the chick bioassay. The use of these HPLC-derived data on the vitamin K content of foods allows for a more accurate determination of the phylloquinone content of a typical Western diet.
Dietary Sources of Vitamin K Green leafy vegetables are the best dietary source of vitamin K (as phylloquinone) (see Table 1). Some plant oils such as soybean oil and rapeseed oil are good dietary sources, containing 173 and 123 mg of phylloquinone per 100 g, respectively. Some vegetable oils, such as peanut, corn, sunflower, and safflower oils, have much lower phylloquinone content (1–10 mg 100 g1). In general, meat, cereals, fish, and milk are poor sources of phylloquinone. MKs seem to have a more restricted distribution in the diet than does phylloquinone. In the Western diet, nutritionally significant amounts of long-chain MKs have been found in animal livers and fermented foods such as cheeses. The Japanese food ‘natto’ (fermented soybeans) has an MK content higher than the content of phylloquinone in green leafy vegetables. Mean dietary phylloquinone intakes were reported for a nationally representative sample of US consumers (n ¼ 3967), aged 13þ years, at levels of 81 and 73 mg day1 in men and women. There are limited data on dietary phylloquinone levels in European populations and, of those that are available, the use of different dietary tools precludes comparison in some cases. For example, mean intake estimates of phylloquinone in the United Kingdom, Ireland, and Norway of 60–85 mg day1 were obtained using food records, while estimates in the Netherlands (250 mg day1) were based on a food frequency questionnaire. Phylloquinone intake decreases with age, especially for adults over the age of 65 years and, more notably, over the age of 85 years. However, consistently higher intakes for older adults (>40 years) than younger adults are reported, most probably due to lower green vegetable consumption by younger adults.
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662 Vitamins | Vitamin K
Figure 1 Structure of vitamin K1 (a), K2 (b), and K3 (c).
Table 1 Vitamin K1 (phylloquinone) concentration in commonly consumed vegetables
Vegetables
Phylloquinone content (g 100g1 raw food)
Kale Spinach Broccoli Brussels Onions Lettuce Cabbage, savoy Cauliflower Celery Carrots Green pepper
816 483 102 139–193 207 23–173 69 16 29 13 7
Source: USDA National Nutrient Database for Standard Reference. http://www.nal.usda.gov/fnic/foodcomp/Data/SR17/wtranks/ sr17a430.pdf
Absorption, Metabolism, and Excretion Dietary vitamin K, mainly as phylloquinone, is absorbed into the lymphatic system from the proximal intestine after solubilization into mixed micelles composed of bile salts and the products of pancreatic lipolysis. In healthy adults, the efficiency of absorption of phylloquinone is about 80%. Intestinal bacteria can synthesize a variety of MKs, which are absorbed to a limited extent from the large intestine, transported into the lymphatic system, cleared by the liver, and released in very low-density
lipoprotein (VLDL). However, it is not fully clear to what extent intestinal MK contributes to the vitamin K requirement. Approximately 50% of vitamin K is carried in the plasma in the form of VLDL, about 25% in lowdensity lipoprotein (LDL), and about 25% in high-density lipoprotein (HDL). Once in the circulation, phylloquinone is cleared rapidly at a rate consistent with its continuing association with chylomicrons. Vitamin K is extensively metabolized in the liver and excreted in the urine and bile. It has been demonstrated in tracer experiments that about 20% of an injected dose of phylloquinone is recovered in urine, whereas about 40–50% is excreted in the feces via the bile and the proportion excreted was the same regardless of whether the injected dose was 1000 or 45 mg. It seems likely, therefore, that about 60–70% of the amount of phylloquinone absorbed from each meal will ultimately be lost to the body by excretion. These results suggest that the body’s stores of phylloquinone are constantly replenished. Vitamin K itself is too lipophilic to be excreted in the bile and is excreted as side chain-shortened carboxylic acid metabolites. There is no evidence that phylloquinone and MK are toxic. However, high intakes of phylloquinone can negate the effects of the anticoagulant warfarin. The synthetic form of vitamin K, menadione, can interfere with the function of glutathione, one of the body’s natural antioxidants, resulting in oxidative damage to cell membranes. Menadione given by injection has been shown to induce liver toxicity, jaundice, and hemolytic anemia (due to the rupture of red blood cells) in infants, and is no longer used for the treatment of vitamin K deficiency. No tolerable upper level (UL) of intake has been established for vitamin K.
Metabolic Function of Vitamin K Vitamin K acts as a cofactor for a specific carboxylation reaction that transforms selective glutamate (Glu) residues to -carboxyglutamate (Gla) residues. The reaction is catalyzed by the microsomal enzyme vitamin K-dependent -glutamyl carboxylase, which, in turn, is linked to a cyclic pathway known as the vitamin K epoxide cycle. The resultant Gla residues are common to all vitamin K-dependent proteins and these have increased affinity for calcium. Prothrombin and other proteins of the blood clotting system, as well as certain bone matrix proteins, contain Gla. The vitamin K epoxide cycle serves to recycle the nutrient via a cyclic interconversion. In this cycle, the vitamin K quinone form is reduced by the FADcontaining enzyme DT-diaphorase (NAD(P)H:quinone oxidoreductase) into the vitamin K hydroquinone (KH2), which then serves as a cofactor for vitamin K carboxylation of Gla proteins and, in so doing, is oxidized
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to vitamin K epoxide. Vitamin K epoxide is then recycled back to the quinone form by the enzyme vitamin K epoxide reductase (VKOR), completing the cycle. At a molecular level, vitamin K epoxide is reduced in two steps: first to the quinone form by VKOR and then to KH2 by DT-diaphorase.
Vitamin K-Dependent Proteins Vitamin K-Dependent Coagulation Proteins There are seven vitamin K-dependent proteins involved in blood coagulation, namely, prothrombin (factor II), factors VII, IX, and X, and proteins C, S, and Z, all of which are synthesized in the liver and contain between 10 and 12 Gla residues (Table 2). The Gla residues enable Ca2þ-mediated binding of the proteins to the negatively charged phospholipid surfaces provided by blood platelets and endothelial cells at the site of injury. Prothrombin and factors VII, IX, and X possess procoagulant activity and participate in the cascade that results in the formation of the fibrin clot. A key element in the formation of fibrin is the conversion of prothrombin to thrombin by activated factor X (which is, in turn, activated by activated factors VII and IX). In contrast, proteins C and S act as anticoagulants. Protein C inhibits coagulation by inactivating activated factors V and VIII and enhancing fibrinolysis, with protein S as a cofactor.
Bone Vitamin K-Dependent Proteins There are two bone matrix proteins that contain Gla: osteocalcin (OC) and matrix Gla protein (MGP) (Table 2). OC is an osteoblast-derived, specific vitamin K-dependent protein that also contains hydroxyproline and is the most abundant of all the noncollagenous bone matrix-bound proteins. It has a molecular mass of 5700 Da and contains three Gla residues, which give this protein a high affinity for hydroxyapatite, in fact much higher than its affinity for calcium. The synthesis of OC is under the regulatory control of the active vitamin D metabolite, 1,25 dihydroxyvitamin D (1,25OHD), and its release into the circulation provides a sensitive index of vitamin D action. While a high proportion of newly synthesized OC is incorporated into bone, approximately 30% of it is released into the circulation and serum levels of the protein are used widely as an indicator of the rate of bone formation. The precise physiological function of OC remains unclear. The less well characterized MGP has a molecular mass of 9600 Da and contains five Gla residues and in contrast to OC, which is exclusively associated to mineralized tissues, MGP is present in cartilage and is expressed at a high rate in many soft tissues (heart, kidney, lungs), in addition to bone.
Vitamin K and Health Deficiency Newborn infants are at serious risk of hemorrhaging because of poor placental transfer of vitamin K, lack of
Table 2 The main vitamin K (Gla)-dependent proteins and their physiological function Gla protein
Tissue
Physiological function
Liver (then plasma)
Procoagulants
Liver (then plasma) Liver (then plasma), endothelium Liver (then Plasma)
Anticoagulant Cofactor for protein C Exact function unknown Unknown, may be a matrix signal for osteoclasts Inhibitor of calcification
Protein S
Bone Bone, cartilage, and most soft tissues Bone
Others Nephrocalcin
Renal tissue
Undetermined, may inhibit the growth of calcium oxalate monohydrate crystals Undetermined
Blood coagulation Prothrombin (factor II), factors VII, IX, and X Protein C Protein S Protein Z Bone Osteocalcin (bone Gla protein) Matrix Gla protein
Plaque Gla protein Growth arrest specific gene 6 (Gas 6) Proline-rich Gla protein 1,2 (PRGP 1,2)
May be present in artherosclerotic plaque Detected in cartilage and numerous soft tissues Broad tissue distribution
Unknown
Cellular growth regulation factor Undetermined
Data from Ferland G (1998) The vitamin K-dependent proteins:an update. Nutrition Reviews 56: 223–230; Shearer MJ and Bolton-Smith C (2000) Food Chemistry 68: 213–218.
664 Vitamins | Vitamin K
intestinal bacteria, and the low vitamin K content in breast milk. For this reason, vitamin K is routinely administered prophylactically at birth in many countries. The risk of bleeding is greatest in prematurely born infants, in breast-fed infants, and in those with gastrointestinal conditions that impair vitamin K absorption. In normal infants, plasma prothrombin concentrations and those of the other vitamin K-dependent factors are approximately 20% of adult values at birth. Normal or near-normal blood coagulation is usually maintained in older children and adults. Several factors protect adults from a lack of vitamin K and these include widespread distribution of vitamin K in plant and animal tissues, the vitamin K cycle, which conserves the vitamin, and the microbiological flora of the normal gut, which synthesizes MKs. The causes of the reduced levels of vitamin K-dependent coagulation factors in adults are largely secondary to diseases such as cystic fibrosis, celiac disease, ulcerative colitis, and short-bowel syndrome. Biliary obstruction and liver disease may also lead to vitamin K deficiency. There are numerous reports of bleeding episodes in patients treated with anticoagulant drugs and broad-spectrum antibiotics. In children and adults, ‘clinical’ vitamin K deficiency in terms of blood coagulation is rare. However, ‘subclinical’ vitamin K deficiency in extrahepatic tissues, particularly in bone, is not uncommon in the adult population. From the multitude of proteins that require carboxylation of Glu to Gla residues for proper functioning, it is clear that poor vitamin K status may contribute to certain chronic vascular and skeletal diseases. Furthermore, it has been suggested that dietary phylloquinone levels that are sufficient to maintain normal blood clotting (which forms the basis of the recommended dietary allowance) may be suboptimal for adult bone health. Vitamin K and Bone Health The identification of -carboxyglutamyl-containing proteins in bone, notably OC and MGP, has generated considerable interest in the role of vitamin K in bone metabolism and bone health. In addition, another functional index of vitamin K status in bone metabolism is the level of undercarboxylated osteocalcin (ucOC). The extent to which OC is uncarboxylated has been assessed with respect to age, bone status, and risk of hip fracture. A high concentration of circulating ucOC has been associated with low bone mineral density and increased risk of hip fracture. The percentage of uncarboxylated OC is high (by 40%) in post-menopausal women compared with pre-menopausal women. The post-menopausal women responded to phylloquinone supplementation with an increase in total and carboxylated OC and a decrease in urinary calcium and hydroxyproline. The
incidence of hip fractures in aged women correlates directly with the increase in ucOC and bone mineral density correlates negatively with the rise in ucOC. The relationship between ucOC and bone health in young growing teenagers has also received attention recently. For example, a significant inverse association has been reported between ucOC and bone mineral content of the total body and lumbar spine in peripubertal Danish girls. Vitamin K intake has been associated with bone health in epidemiological studies. A cohort of elderly men and women from the Framingham Study in the United States showed an association of vitamin K intake with the incidence of hip fracture. In addition, there was evidence that phylloquinone intakes <109 mg day1 are associated with an increased risk of hip fracture in 72 327 women participating in the Nurse’s Health Study in the United States. In addition, among post-menopausal Scottish women, phylloquinone intake has been positively associated with bone mineral density of the femoral neck and lumbar spine as well as biochemical markers of bone turnover. Based on the intervention studies to date that have investigated the effect of phylloquinone supplementation on bone loss in later life (generally >50 years), it appears that phylloquinone supplementation does not protect against loss of bone mineral in some skeletal sites (lumbar spine, total body, mid-distal radius). Furthermore, the evidence base for bone health benefits at the femoral neck from phylloquinone supplementation is mixed and may require further research. In particular, the inconsistent findings in relation to the effects of phylloquinone supplementation on bone mineral density of the hip do not explain the mechanism underpinning the protective effect of high phylloquinone intake/status against hip fracture observed in a number of prospective cohort studies. More research is needed on whether phylloquinone supplementation may be lowering the risk of fractures through other mechanisms such as effects on bone quality parameters. The finding that relatively lowdose phylloquinone supplementation improved bone mineral density of the forearm (ultradistal radius) of post-menopausal women is interesting even though it was investigated in only one study. It has been suggested that ultradistal forearm has a higher metabolic turnover rate than predominantly cortical bone and thus may be more responsive to dietary treatment. Vitamin K and Cardiac Health A role for vitamin K in atherosclerosis was hypothesized when proteins containing Gla residues were isolated from hardened atherosclerotic plaque, which were later identified as OC and MGPs. Increasing evidence is emerging suggesting a role for vitamin K in the calcification of
Vitamins | Vitamin K 665
arteries and atherogenesis. Moreover, the therapeutic potential of vitamin K2 as an antihepatoma drug has been recently highlighted. Results from human observational studies investigating relations between vitamin K intake and cardiovascular diseases are inconsistent. The Nurses’ Health Study showed a modest risk reduction of coronary heart disease (CHD) for high phylloquinone intakes, while no significant associations were observed in the Health Professionals Follow-up Study and the Rotterdam Study. On the other hand, in the Rotterdam Study, a strong inverse association between MK intake and CHD mortality and severe aortic calcification was observed. These inconsistencies may relate to different effects of phylloquinone and MK on coronary calcification. In a large study on 16 057 women, MK intake was inversely associated with coronary events, while phylloquinone intake was not related to CHD. Similarly, in animals, MK-4-but not phylloquinone-appears to inhibit warfarin-induced coronary calcification. The different effects of MK and phylloquinone probably reflect differences in metabolism as a result of different distributions over plasma lipoproteins.
Vitamin K Status and Requirements Defining reliable indicators of vitamin K status has proven to be a difficult task. The serum concentration of ucOC is a more sensitive indicator of vitamin K status than the traditional blood coagulation tests, and a high serum level of ucOC is indicative of low vitamin K status and vice versa. UcOC has been reported to have a negative association with plasma phylloquinone concentrations. The difference between the vitamin K-dependent coagulation factors (all synthesized in the liver) and the bone Gla protein OC suggests that different tissues (at least bone and liver) may have different vitamin K requirements; hence, bone tissue may be more prone to vitamin K deficiency than liver. If this is the case, impaired synthesis of some vitamin K-dependent proteins may be far more prevalent in the human population than coagulation assays previously indicated, potentially resulting in an increase in dietary recommendations for vitamin K, especially for the elderly. A number of clinical trials have shown that high circulating ucOC levels are common in postmenopausal women as well as healthy young and elderly adults but levels are reduced significantly with vitamin K supplementation. Even in healthy newborns, whose vitamin K status is known to be precarious, very low levels of undercarboxylated prothrombin are detectable, whereas all babies tested exhibited high
concentrations of serum ucOC. These data together with other evidence suggest that circulating OC is the most sensitive known marker for vitamin K status. Until recently, the only widely accepted criterion for vitamin K sufficiency was the maintenance of plasma prothrombin concentration. It has been estimated that 0.5–1.0 mg kg1 day1 was required to correct induced clotting changes. In adults, primary vitamin K-deficient states that resulted in bleeding were almost unheard of, except in a hospital setting. This is due to the widespread distribution of vitamin K in foods, the ability of the vitamin K cycle to conserve vitamin K, and endogenous bacterial syntheses of MKs. Therefore, a healthy population is not at risk of dietary vitamin K deficiency as the recommendation for optimal blood clotting is readily achievable. However, recent attention has focused on the importance of vitamin K for optimizing bone health and it has been proposed that vitamin K supplies believed sufficient to maintain normal blood coagulation may be suboptimal for bone health. The Food and Nutrition Board (2001) has recently established an adequate intake (AI) value for vitamin K. The recently discovered indicators sensitive to vitamin K intake, although useful to describe relative diet-induced changes in vitamin K status, were not used for establishing an estimated average requirement (EAR) because of the uncertainty surrounding their true physiological significance and the lack of sufficient dose–response data. Therefore, the AI for adults was based on reported vitamin K dietary intake in apparently healthy populations. A large review, including 11 different studies, reported that phylloquinone intake ranged from 60 to 210 mg day1 with an average intake of approximately 80 mg day1 for younger adults (<45 years) and approximately 150 mg day1 for older adults (>55 years). Healthy individuals with a phylloquinone intake approaching 80 mg day1 have been investigated and showed no signs of deficiency, suggesting that this level is probably adequate for the majority of the adult population. Because dietary assessment methods tend to underestimate the actual daily intake of foods, the highest intake value reported for four adult age groups was used to set the AI for each gender rounding up to the nearest 5 mg. Therefore, the most recent guideline (AI) for vitamin K intake in the United States for adults (aged 19 years and older) is 120 and 90 mg day1, for men and women, respectively. To date, no adverse effect has been reported for individuals consuming greater than the AI for vitamin K. However, the data on adverse effects from high vitamin K intake are not sufficient for a quantitative risk assessment and a tolerable UL of intake has not been established by the Institute of Medicine in the United States or by the Scientific Committee of Food in the European Union.
666 Vitamins | Vitamin K See also: Nutrition and Health: Nutritional and HealthPromoting Properties of Dairy Products: Bone Health; Vitamins: General Introduction.
Further Reading Bentley R and Meganathan R (1982) Biosynthesis of vitamin K (MK) in bacteria. Microbiological Reviews 46: 241–280. Cashman KD (2005) Vitamin K status may be an important determinant of childhood bone health. Nutrition Reviews 63: 284–289. Ferland G (1998) The Vitamin K-dependent proteins: an update. Nutrition Reviews 56: 223–230.
Ferland G (2001) Vitamin K. In: Bowman BA and Russell RM (eds.) Present Knowledge in Nutrition, 8th edn., pp. 164–172. Washington, DC: ILSI Press. Institute of Medicine (2001) Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press. Shea MK and Booth SL (2008) Update on the role of vitamin K in skeletal health. Nutrition Reviews 66: 549–557. Shearer MJ (2000) Role of vitamin K and Gla proteins in the pathophysiology of osteoporosis and vascular calcification. Current Opinion in Clinical Nutrition and Metabolic Care 3: 433–438. Shearer MJ and Bolton-Smith C (2000) The UK food database for vitamin K and why we need it. Food Chemistry 68: 213–218. Suttie JW (1995) The importance of menaquinones in human nutrition. Annual Reviews of Nutrition 15: 399–417.
Vitamin C P A Morrissey and T R Hill, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. A. Morrissey, Volume 4, pp 2683–2690, ª 2002, Elsevier Ltd.
Introduction
Chemistry
Among specific nutritional deficiency diseases, scurvy was the dreaded disease of seamen and explorers forced to subsist for months on diets of dried beef and biscuits. The symptoms of scurvy are rather characteristic and consist of bleeding and rotting gums, swollen and inflamed joints, dark blotches on the skin, and muscle weakness. Scurvy afflicted nineteenth-century populations on land, including armies of the Crimean and United States Civil wars and the California gold rush communities. In 1907, scurvy was produced experimentally in the guinea pig and from 1928 to 1930, Albert Szent-Gyorgy and Glen King independently published their isolation of vitamin C or hexuronic acid. It was later named ascorbic acid for its antiscorbutic properties and its molecular structure was determined in 1933. Ascorbate, also known as ascorbic acid (AA) or vitamin C, is synthesized de novo from glucose in the liver of most adult mammals. D-Glucose is converted into L-ascorbic acid via D-glucuronic acid, L-gulonic acid, L-gulonolactone, and L-gulono- -lactone as intermediates. However, humans and non-human primates, guinea pigs, the Indian fruit bat, several species of birds, and some fish have lost the ability to synthesize ascorbate de novo. As a result of a gene mutation, they lack a key ascorbate-oxidizing enzyme, L-gulono- -lactone oxidase, an essential oxidizing enzyme in the liver for the conversion of L-gulono- -lactone into 2-oxo-L-gulono- -lactone, a tautomer of L-ascorbic acid, which transforms spontaneously into the vitamin. In plants, the biosynthesis of ascorbate is more complicated than in animals. The vitamin is synthesized from guanosine diphosphate (GDP)-mannose, and the pathway shares GDP-sugar intermediates with the synthesis of cell wall polysaccharides and those glycoproteins that contain D-mannose, L-fucose, and L-galactose. Ascorbate is quantitatively the predominant antioxidant in plant cells and is found in all subcellular compartments, including the apoplast, and has an average cellular concentration of 2–25 mmol l1 or more in the chloroplast stroma. This article discusses the chemistry of vitamin C. In addition, the role of vitamin C as a biological antioxidant, specific functions in humans, and role in health and disease are highlighted.
Ascorbic acid is the enolic form of an -ketolactone (2,3-didehydro-L-threo-hexano-1,4-lactone). The molecular structure (Figure 1) contains two ionizable –OH groups at C2 and C3 that give the compound its acidic character, and since pKa1 at C3 is 4.17 and pKa2 at C2 is 11.79, a monoanion is the favored form at physiological pH where 99.95% of AA is present as ascorbate monoanion (AscH), 0.05% as AA (AscH2), and 0.004% as ascorbate dianion (Asc2). Thus, the antioxidant chemistry of vitamin C is the chemistry of AscH. The asymmetric carbon 5 atom allows two enantiomeric forms, of which the L-form is naturally occurring. Oxidation of AA takes place as either two one-electron transfer processes or as a single two-electron reaction without detection of the intermediate ascorbyl radical. In the two one-electron oxidation processes, the first step involves loss of one electron from AscH to form the neutral ascorbyl radical (AscH? ), which is not protonated in biological systems and is present as the resonance-stabilized tricarbonyl ascorbate free radical (Asc – ? ), which is relevant in biology. Asc – ? is a weakly reactive radical, and in vivo it is likely that reducing enzymes are involved in its removal, resulting in the recycling of ascorbate. Loss of an additional electron yields L-dehydroascorbic acid (DHA). The oxidation of AA to DHA is reversible via the same intermediate radical process, and for this reason DHA also exhibits biological activity, since it can be easily converted to AA in the human body. However, DHA is highly unstable because of the susceptibility to hydrolysis of the lactone bridge. DHA has a half-life, in aqueous solutions at 37 C, of approximately 6–20 min as a function of concentration, and catabolism beyond DHA is enhanced by alkaline pH and metals, especially copper and iron. Hydrolysis of DHA irreversibly forms 2,3-diketogulonic acid and leads to the loss of vitamin C activity (Figure 1). Further catabolism leads to the formation of a wide array of other nutritionally inactive products such as L-xylonic acid, L-lyxonic acid, L-xylose, oxalic acid, and L-threonic acid. The rate of oxidative degradation of the vitamin is a nonlinear function of pH because the various ionic forms of AA differ in their susceptibility to
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Figure 1 Ascorbic acid and its oxidation products. Dehydro-L-ascorbate may exist in multiple forms. Formation of 2,3-diketogulonic acid by hydrolytic cleavage is probably irreversible.
oxidation: fully protonated AscH2 < AscH < Asc2. Under conditions relevant to most biological systems, the pH dependence of oxidation is governed mainly by the relative concentrations of AscH2 and AscH species and this, in turn, is governed by pH (pKa1 4.17). The rate of oxidation of ascorbate is generally observed to be first order with respect to the concentration of AscH, molecular oxygen, and the metal ion.
Dietary Sources More than 80% of the vitamin C in western diets comes from fruits and vegetables, with citrus fruits, tomatoes and tomato juice, and potatoes being major contributors. A minor portion comes from enriched or fortified products, meats, fish, poultry, eggs, and dairy products, and essentially none from grains. The mean content of vitamin C is 2.11 mg per 100 g (range 1.65–2.75 mg per 100 g) in cow’s milk, 5.48 mg per 100 g in goat’s milk, 3.9 mg per 100 ml in summer human milk, and 3.02 mg per 100 ml in winter human milk. There is some evidence that the concentration of vitamin C in cow’s and goat’s milk changes with season. It has been observed that in raw milk sampled in March
or August the concentration of vitamin C was higher (2.0–2.7 mg per 100 ml) than in samples collected in October (1.2 mg per 100 ml). The mean concentration of vitamin C in human milk also appears to be affected by the stage of lactation and declines from 6.18 mg per 100 ml in colostrum to 4.68 mg per 100 ml at 9 months. The influence of maternal vitamin C intake and its effect on the vitamin C content of human milk have not been clearly defined. It has been observed that the vitamin C level in human milk did not increase significantly in response to increasing maternal intake (up to 10-fold). It appears that a regulatory mechanism may be present in mammary cells to prevent an elevation in the concentration of vitamin C in milk beyond a certain saturation level. On the other hand, when the intake of vitamin C is low, breast milk levels are sensitive to supplementation. In the United States, the median dietary intake of vitamin C by adult men from 1988 to 1994 was about 105 mg day1 and the median total intake (including supplements) was about 120 mg day1. For women, the median intake was estimated to be 90 mg day1 and median total intake (including supplements) was about 108 mg day1. The average consumption for children was 84 mg day1. The recent North/South Food
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Consumption Survey in Ireland (2001) showed that mean daily intake of vitamin C was not significantly different in men (116 mg) and women (108 mg). The primary sources of vitamin C for the total population were potatoes and potato products (25.9%); fruit juices; nuts and seeds; herbs and spices (25.6%); and vegetable and vegetable products (22.1%). The contribution from supplements was 5.8% for men and 8.6% for women. Ascorbic acid is also added to some processed foods for its antioxidant or functional properties and consequently the mean total vitamin C intake may be considerably higher than indicated above. Ascorbic acid is the nutrient taken most frequently as a supplement, particularly among the elderly population. The Boston Nutritional Status Survey of the Elderly (1992) estimated that 35 and 44% of males and females, respectively, took some form of vitamin supplements, with a median supplemental intake of 300 mg day1. Clinical signs of vitamin C deficiency are rarely seen in developed countries. The content of vitamin C in foods may be reduced significantly because of thermal destruction that occurs during cooking, losses in cooking water, and subsequent holding prior to consumption.
Absorption, Metabolism, and Excretion In rats and hamsters (for which AA is not a vitamin), intestinal absorption is passive. In the case of guinea pigs and humans, both of which have an absolute requirement for exogenous AA in their diet, there is a sensitive sodium-dependent active transport system for AA in the brush border of the duodenum and upper ileum, and another sodium-independent transfer process in the basolateral membrane. There is also a passive transport mechanism, which in humans is predominant only at high intake levels. Ascorbate transport has been specifically shown to require metabolic energy, with a stoichiometry for Naþ from 1.1 to 2.1. Intestinal absorption of AA and its entry into cells are facilitated by conversion to DHA, which is transported across cell membranes more rapidly than ascorbate. Because DHA is structurally similar to glucose, its transport across membranes is facilitated by glucose transporters (GLUTS). Transport of DHA is primarily Naþ-independent in animal and human tissues, and does not require metabolic energy. Upon cell entry, DHA is reduced immediately to AA, which produces an effective gradient of DHA across the membrane. Intracellular reduction of DHA to AA is mediated by two major pathways: chemical reduction by glutathione and enzymatic reduction. The flux of ascorbate in and out of the cell via facilitated diffusion and active transport is mediated by distinct classes of proteins such as facilitative glucose transporters and sodium–vitamin C cotransporters, respectively.
Information on the bioavailability of vitamin C in foods is limited. It is generally agreed that at relatively low intakes (less than 30 mg day1), ascorbate is nearly completely absorbed, and 70–90% of the usual dietary intake of ascorbate (30–180 mg day1) is absorbed. Similar levels of absorption (80%) have been reported for pure ascorbate, ascorbate in orange juice, and ascorbate in cooked broccoli, which suggests that the absorption of vitamin C is almost complete. However, absorption falls to approximately 50% or less with increasing doses above 1.5 g day1. Following absorption, ascorbic acid circulates freely in plasma, leukocytes, and red cells, and enters all tissues, with maximum concentrations of 68–86 mmol l1 plasma being achieved with an oral intake of 90–150 mg day1. Excess is excreted by the kidney, which conserves the vitamin at plasma levels of up to 46–86 mmol l1 by a saturable, sodium-dependent reabsorption process. The upper limit of plasma ascorbic acid concentration is controlled by the gastrointestinal absorption and renal reabsorption mechanisms, and fasting plasma concentration rarely exceeds 100 mmol l1, even with dietary supplementation. Specific proteins mediate the entry and exit of vitamin C in cells by facilitated diffusion or active transport. These cellular transport systems are responsible for high intertissue ascorbate levels found in the pituitary and adrenal glands (30–400 mg per 100 g tissue), followed by the brain, spleen, pancreas, kidney, liver, and tissues of the eye with 10–50 mg per 100 g of tissue. Vitamin C concentration also varies widely in different blood cell types. About 70% of blood-borne ascorbate is in plasma and erythrocytes. The remainder is in white cells, which have a marked ability to concentrate ascorbate; mononuclear leukocytes achieve 80-fold concentration, platelets 40-fold, and granulocytes 25-fold, compared with plasma concentration. Tissuespecific cellular mechanisms of transport and metabolism allow for wide variation of tissue ascorbate concentration in order to enhance its function as an enzyme cofactor and antioxidant. Intracellularly, and in plasma, vitamin C exists predominantly in the free form as AscH. DHA is either not detectable or found at only very low levels in the circulation of healthy people. The total body pool of ascorbate is affected by limited intestinal and renal tubular absorption. It reaches a maximum value of about 20 mg kg1 body weight or about 1500 mg for the average-size man when the ascorbate intake is increased from 30 to 180 mg day1; above this level of intake, excretion of ascorbate in the urine rises rapidly. Unabsorbed ascorbate is degraded in the intestine, a process that may account for the diarrhea and intestinal discomfort sometimes reported by persons ingesting large doses.
670 Vitamins | Vitamin C
Antioxidant Activity of Ascorbic Acid Ascorbate is often called the outstanding antioxidant. In chemical terms, this is simply a reflection of its redox properties as a reducing agent. In physiological terms, this means that ascorbate provides electrons for enzymes, for chemical compounds that are oxidants, or for other electron acceptors in biological systems. In addition to its redox potential, other properties of ascorbate make it an excellent electron donor in biological systems. Ascorbate undergoes two consecutive, reversible, one-electron oxidation processes forming the ascorbate radical (Asc – ? ) as an intermediate. The Asc – ? has an unpaired electron, making it a relatively unreactive free radical, especially with oxygen, and the ascorbate oxidation product, DHA, is reduced by cells to ascorbate, which then becomes available for reuse. These properties make ascorbate an excellent biological donor system. Thus, ascorbate is a reversible biological reductant and, as such, it provides reducing equivalents for a variety of biochemical reactions, is essential as a cofactor for reactions requiring a reduced metal ion (Fe2þ, Cuþ), and serves as a protective antioxidant that operates in the biological aqueous phase and can be regenerated in vivo when required. Ascorbate is thermodynamically close to the bottom of the list of one-electron reducing potentials of oxidizing free radicals (E 9 ¼ þ282 mV). For this reason, ascorbate is considered to be the most important antioxidant in extracellular fluids and is the first line of defense against reactive oxygen species (ROS) and reactive nitrogen species (RNS) (e.g., nitric oxide, NO? , and nitric dioxide, NO?2 ) in plasma. It efficiently scavenges all oxidizing species with a greater one-electron potential (higher E 9 – values), which include the superoxide anion (O2 ? ) and hydroxyl radical (? OH), and oxygen-centered radicals of organic compounds (peroxyl, LOO? , and alkoxyl, LO? ) can be repaired by ascorbate as follows: AscH – þ X? ! Asc – ? þ XH
where X? is any of the oxidizing radicals. Although ascorbate itself forms a radical in the reaction, a potentially very damaging radical (X? ) is replaced by the relatively unreactive Asc? . Overall, ascorbate is reactive enough to affectively interrupt oxidants in the aqueous phase before they can attack and cause detectable oxidative damage to DNA and lipids. In aqueous solutions, ascorbate also scavenges RNS efficiently, preventing nitrosation of target molecules. Consequently, both thermodynamically and kinetically, ascorbate can be considered to be an excellent aqueous antioxidant. Ascorbate may also regenerate -tocopherol (-TOH) from the tocoperoxyl radical (TO? ), which is formed upon inhibition of lipid oxidation by -tocopherol. Ascorbate has a lower redox potential (E 9 ¼ þ282 mV) than
-TOH (E 9 ¼ þ500 mV) and, in addition, the -TO? is at the membrane–water interface, thereby allowing watersoluble ascorbate access to membrane-bound -TO? for the repair reaction and recycling of -tocopherol: 9
– E ¼þ200 mV AscH – þ -TO? ! Asc? þ -TOH
The rate constant for the reaction is 1.5 106 l mol1 s1. Thus, in cellular membranes, ascorbate plays an indirect antioxidant role to reduce the -tocoperoxyl radical (-TO? ) to -tocopherol (-TOH). Recycling of -tocopherol by ascorbate has been demonstrated in liposomes and cellular organelles and may also spare and recycle -tocopherol in erythrocyte membranes and intact erythrocytes (see Vitamins: Vitamin E). The Asc – ? formed in the above reaction dismutates to DHA and is then regenerated to ascorbate at the expense of glutathione, dihydrolipoate, thioredoxin, and other enzyme systems. This process allows for the transportation of a radical load from a lipophilic compartment to an aqueous compartment where it is taken care of by efficient enzymatic defenses. It should be noted that as a reducing agent, ascorbate has the ability to reduce Fe3þ to Fe2þ and Cu2þ to Cuþ, thereby increasing the prooxidant activity of the metals and generating HO? , O2–?, and H2O2 that initiate lipid peroxidation in biological systems. It is considered unlikely that ascorbate shows prooxidant properties in vivo since the concentrations of ‘free’ transition metals in healthy biological systems are very small because they are effectively bound by metal ion storage and transport proteins.
Biological Functions Many of the biological functions of ascorbic acid are based on its ability to provide reducing equivalents for a variety of biochemical reactions. The vitamin can reduce most physiologically relevant reactive species and, as such, functions primarily as a cofactor for reactions requiring a reduced iron or copper metalloenzyme and as a protective antioxidant that operates in the aqueous phase both intra- and extra-cellularly. Ascorbate is known to be a specific electron donor for eight human enzymes; three enzymes participate in collagen hydroxylation, two in carnitine biosynthesis, and three in hormone and amino acid biosynthesis. Evidence also suggests that ascorbate plays a role in or influences collagen gene expression, cellular procollagen secretion, and the biosynthesis of other connective tissue components, including elastin, proteoglycans, bone matrix, and elastin-associated fibrillin. Ascorbate is also involved in the synthesis and modulation of some hormonal components of the nervous system.
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Collagen Formation Scurvy, the classical disease of severe ascorbate deficiency, is characterized by symptoms related to connective tissue defects. Clinically, signs of scurvy are seen when the total body pool of ascorbate is below 300 mg. Clinical features of scurvy include skin bruises, perifollicular hemorrhages, bleeding gums, joint pain and swelling, and fatigue. Oxidative degradation of some blood coagulation factors due to a low concentration of plasma ascorbate may contribute to hemorrhagic symptoms. Ascorbate-dependent aspartate -hydroxylase is known to be required for the postsynthetic modification of protein C, the vitamin K-dependent protease that hydrolyses activated factor V in the blood-clotting cascade. Ascorbic acid affects the biosynthesis of collagen at several levels from collagen transcription, to expression, including the regulation of the processing enzymes. It acts as a cofactor for several metaldependent oxidative reactions, catalyzed by both monooxygenases and dioxygenases. Other cofactors required by the dioxygenases are Fe2þ, -ketoglutarate, and O2, whereas the monooxygenase requires Cuþ and O2 for activity. Ascorbate functions as a reductive cofactor for posttranslational hydroxylation of peptide-bound proline and lysine residues during the formation of collagen. The hydroxyproline is required for normal triple-helical backbone structure and the hydroxylysine cross-linkages are needed for normal collagen fiber formation. The enzyme involved in proline hydroxylation, prolyl hydroxylase, requires molecular oxygen, ascorbic acid, iron, and -ketoglutarate. The first step in the reaction is the attack on peptide-bound proline by oxygen, followed by condensation with -ketoglutarate, the release of the hydroxylated substrate, and decarboxylation to release succinate. During the hydroxylation reaction, the enzyme-bound iron is oxidized to Fe3þ, which is catalytically inactive. The ascorbate is involved in reactivating the enzyme by reduction of Fe3þ back to the loosely bound ferrous form. In an analogous reaction, ascorbate participates as a cofactor in the hydroxylation of lysine residues catalyzed by copper-dependent lysyl hydroxylase. Hydroxylysine cross-linkages are central for normal collagen fiber formation. Prolyl and lysyl hydroxylases are also called dioxygenases, referring to the ability of the enzymes to provide two oxygen atoms to the same or separate substrates. Ascorbate may also serve as a reductant for other metal-dependent polymerization and cross-linking reactions of connective tissue and as a carrier for sulfate groups needed for the production of glycosaminoglycans (e.g., chondroitin).
A deficiency of ascorbate results in a weakening of collagenous structures, causing tooth loss, joint pains, bone and connective tissue disorders, and poor wound-healing, all of which are characteristic of scurvy. This disease is now rare in developed countries, but is occasionally seen in individuals in classes with exceptionally poor or restricted diets, such as low socioeconomic groups and those who have a near total lack of fruit and vegetables, or those who abuse alcohol or drugs. Low ascorbate levels and scurvy are most often noted in men who live alone and eat a diet frequently low in fruit and vegetables. Because breast milk provides adequate ascorbic acid, infantile scurvy is seen more often after weaning, between 6 and 12 months. Modern infant formulae are fortified with sufficient ascorbic acid such that infantile scurvy is now almost nonexistent. Neurotransmitter Synthesis Ascorbic acid appears to be involved in catecholamine metabolism in two mixed-function oxidases, dopamine -hydroxylase and para-hydroxyphenylpyruvate oxidase. Ascorbic acid is required as a cofactor for the coppercontaining dopamine- -monooxygenase enzyme, which catalyzes hydroxylation of the dopamine side chain to form norepinephrine. Ascorbate provided electrons for reduction of molecular oxygen, transferred by copper to dopamine, and hydrogen atoms to reduce the other oxygen to water. The active enzyme contains Cuþ, which is oxidized to Cu2þ during hydroxylation of the substrate: reduction back to Cuþ specifically requires ascorbate, which is oxidized to AscH? . Depression, hypochondria, and mood changes frequently occur during scurvy and could be related to deficient dopamine hydroxylation. Ascorbic acid also appears to be involved in the hydroxylation of tryptophan to form serotonin in the brain and in the degradation of tyrosine by p-hydroxyphenylpyruvate hydroxylase. Carnitine Biosynthesis Carnitine plays a central role in transporting long-chain fatty acids across the mitochondrial membrane wherein -oxidation provides energy to cells, especially for cardiac and skeletal muscles. Esterification with carnitine appears to provide a mechanism for transport, storage, and excretion of long-chain fatty acid acyl groups. The biosynthesis of carnitine involves the methylation of lysine, with methionine as methyl donor, and requires ascorbate, ferrous iron, vitamin B6, and niacin as cofactors for various enzymes of the pathway. The loss of fatty acid-based energy production because of limited carnitine biosynthesis may explain the fatigue and muscle weakness observed in humans with ascorbic acid deficiency.
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Other Functions of Ascorbate
Ascorbate and Cardiovascular Disease
Ascorbate is also involved in the hepatic microsomal hydroxylation of cholesterol in the conversion and excretion of cholesterol as bile acids via 7-hydroxycholesterol. These reactions require the microsomal enzymatic system containing cytochrome P-450 hydroxylase. Impaired cholesterol transformation to bile acids causes cholesterol accumulation in the liver and blood, and atherosclerotic changes in coronary arteries. Hydroxylation and demethylation of aromatic drugs and carcinogens by hepatic cytochrome P-450 appear to be enhanced by reducing agents such as ascorbate. Limited data suggest that ascorbate modulates prostaglandin synthesis and thus exerts bronchodilatory and vasodilatory function as well as anticlotting effects. Vitamin C has been shown to affect various components of the human immune response, including antimicrobial and natural killer cell activity and lymphocyte proliferation. The ability of phagocytes and lymphocytes to concentrate vitamin C at levels up to 100 times higher than in plasma may indicate that the vitamin has a physiological role in these immune cells. Cataracts which appear to be due to oxidation of lens proteins in the eye may also be protected by ascorbate. One report has shown that the use of vitamin C supplements (ranging from 400 to 700 mg day1) for 10 years or more reduced the number of lens opacities by about 80%. Women who consumed vitamin C supplements for less than 10 years were not protected. Data from other studies suggest that dietary measures to increase plasma ascorbate may be an important public health strategy for reducing the prevalence of diabetes. Ascorbic acid is a potent enhancer of nonheme iron absorption, both in its natural form in fruit and vegetables, and when added as the free compound. In addition, ascorbic acid increases the bioavailability of all iron fortification compounds. The mechanism of ascorbate action is believed to involve the reduction of intraluminal iron by ascorbate to the more absorbable ferrous state and/or the formation of soluble iron complexes in the duodenum. Generally, the enhancement of iron absorption is proportional to the amount of ascorbic acid in the meal, although observed differences in the effect of ascorbic acid may result from varying the amounts of substances in the food that promote or inhibit iron absorption. Ascorbate reacts with nitrite and other nitrosating agents, forming nitric oxide and nitrous oxide and thereby preventing the formation of carcinogenic nitrosamines by reaction between nitrites and amines present in foods in the acid conditions in the stomach.
It is generally accepted that the oxidation of low-density lipoprotein (LDL) particles and the accumulation of oxidized LDL in the vessel wall are key early events in the progression of atherosclerosis. Studies have shown that high plasma concentrations of ascorbate not only correlate with lower concentrations of oxidized LDL, but also function to protect endothelial cells against the detrimental effects of oxidized LDL once this is formed. Since ascorbate is water soluble and is not incorporated in LDL particles, it has been proposed that it may prevent oxidation of LDL particles by scavenging aqueous ROS and RNS in the aqueous milieu. Ascorbate is also capable of regenerating -TOH from -TO? , which is formed on inhibition of lipid peroxidation by vitamin E. Ascorbyl radicals formed in this process may be reduced to ascorbate by dismutation, chemical reduction, or enzymatic reduction. Several epidemiological studies have examined the association between vitamin C concentration in blood and the risk of cardiovascular disease. A prospective study of 1605 Finnish men showed that those with increased plasma vitamin C (greater than 11.4 mmol1) had a 60% decreased risk of coronary heart disease. The Basel Prospective Study of 2974 Swiss men reported that plasma vitamin C concentrations greater than 23 mmol1 were associated with nonsignificant reduction in the risk of coronary artery disease and stroke. In a 20-year followup study of elderly adults (n ¼ 730) in Britain, plasma concentrations greater than 28 mmol1 were associated with a 30% decreased risk of death from stroke compared with concentrations less than 12 mmol l1. The Second National Health and Nutrition Examination Survey (NHANES II) reported that the relative risk of coronary heart disease and stroke was reduced by about 26% with serum vitamin C concentrations of 63153 mmol l1 (1.1–2.7 mg dl1) compared with concentrations of 6–23 mmol l1 (0.1–0.4 mg dl1). However, supplementation with vitamin C did not reduce the risk of major cardiovascular events. The EPIC–Norfolk Prospective Study in the United Kingdom showed that plasma ascorbate levels were inversely related to mortality from all causes and from cardiovascular disease and ischemic heart disease in men and women. A 20% fall in the risk of allcause mortality, independent of other risk factors, was associated with a 20 mmol l1 rise in plasma ascorbate, approximately equivalent to a 50 g day1 increase in fruit and vegetable intake. It was also noted that a high plasma concentration of ascorbate was inversely related to various cardiovascular risk factors. Compared with people in the lowest quartile of the ascorbate distribution, those in the highest quartile had a 33% lower risk of coronary artery disease, independent of other known risk factors,
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including age, blood pressure, plasma lipids, cigarette smoking, body mass index, and diabetes. Several prospective cohort studies have shown that vitamin C intakes between 45 and 113 mg day1 are associated with reduced risk of cardiovascular disease. Results from the First US National Health and Nutrition Examination Survey (NHANES I) showed that cardiovascular mortality rates were 50% lower than average among participants with the highest vitamin C intake, defined as 50 mg or more per day from the diet plus regular supplements. A Finnish study on 5000 men and women found that women who consumed more than 91 mg day1 vitamin C had a lower risk of coronary artery disease than those who consumed less than 61 mg day1. However, a similar association was not found for men. The NHANES I Epidemiologic Follow-up Study cohort of more than 11 000 adults showed a reduction in cardiovascular disease of 45% in men and 25% in women whose vitamin C intake from both food and supplements was approximately 300 mg day1. However, in contrast to the above, other studies reported no association between vitamin C intake and risk of cardiovascular disease. It is important to emphasize that much of these data were obtained from well-nourished populations.
Vitamin C and Cancer Early epidemiological evidence indicated that high intakes of vitamin C-rich fruit and vegetables and a high vitamin C concentration in serum are inversely associated with the risk of certain cancers. Of 46 such studies in which a dietary vitamin C intake index was calculated, 33 found a statistically significant protective effect, with high intakes conferring approximately a two-fold protective effect compared with low intakes. The evidence for a risk-reducing role of vitamin C is not as strong as for fruit and vegetables. However, an extremely strong and consistent protective effect of vitamin C was found in 17 of 19 studies of stomach, esophageal, and pharyngeal cancers. The Iowa Women’s Health Study found a 20% decrease in breast cancer risk with greater than 500 mg day1 of vitamin intake from supplements; in contrast, the Nurses’ Health Study, which used the same dietary assessment instrument, found no decreased risk of breast cancer at intake greater than 357 mg day1. In a large case–control study in New York, the data showed that increased intake of vitamin C from food and supplements was associated with a reduced risk of rectal cancers. In contrast, the Iowa Women’s Cohort Study found no association between vitamin C intake from fruit and supplements of approximately 300 mg day1 and colon cancer risks. However, in women who consumed more than 60 mg day1 vitamin C from supplements compared to no supplements, the risk was
reduced by 30%. The association between vitamin C intake and the risk of lung cancer is generally weak, but still in a protective direction in several studies. Epidemiological and experimental evidence has suggested that vitamin C may protect against the development of gastric cancer by several potential mechanisms, including the following: vitamin C reduces gastric mucosal oxidative stress, DNA damage, and gastric inflammation by scavenging ROS; it inhibits gastric nitrosation reaction for the formation of N-nitroso compounds by reducing nitrous acid to nitric oxide and producing dehydroascorbic acid in the stomach; it enhances host immunologic functions; it has a direct effect on Helicobacter pylori growth and virulence; and it inhibits gastric cell proliferation and induces apoptosis. Recent reports on the NHANES II survey in the United States and the EPIC–Norfolk Prospective Survey in the United Kingdom showed that men with a low serum ascorbate concentration may have an increased risk of mortality, probably because of an increased risk of dying from cancer. In contrast, serum ascorbate concentrations were not related to mortality among women. The EPIC–Norfolk report concluded that increases in dietary foods rich in ascorbic acid might have benefits for all-cause mortality in men and women. A report from the World Cancer Research Fund and the American Institute of Cancer Research rated the anticancer effect of ascorbate as ‘probable’ only for stomach; ‘possible’ for prostate, mouth, pharynx, esophagus, lung, pancreas, and cervical cancer; and ‘insufficient data’ for cancers of the colon, rectum, larynx, breast, and bladder.
Vitamin C Status and Requirements In setting values for average population requirements and individual nutrient intakes, the important question is how do we differentiate between preventing deficiency symptoms, ensuring an adequate intake, and promoting optimal intake for the prevention of disease? The recommended dietary allowance (RDA) of 60 mg day1 in the United States, the reference nutrient intake (RNI) of 40 mg day1 in the United Kingdom, and the population reference intake (PRI) of 45 mg day1 in the European Union were aimed at prevention of the clinical deficiency state, scurvy. However, no obvious deficiency does not necessarily indicate adequacy, and subclinical or marginal deficiency of vitamin C owing to insufficient intake and/or to increased utilization may be common in many disease situations. Increased risk of chronic disease, including cancer, cataract, and coronary heart disease, is associated with low intake or plasma concentrations of vitamin C. However, the contribution of high intake or plasma levels of vitamin C to lowered risk of disease is
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difficult to assess, as other health-promoting habits generally accompany high vitamin C intake, and clinical trials have shown inconsistent and inconclusive results. The Institute of Medicine in the United States (2000) established an estimated average requirement (EAR) for vitamin C, which is the nutrient intake value that is estimated to meet the requirements of half of a specific gender and life-stage group and was based on evidence that 75 mg day1 vitamin C can maintain near-maximal neutrophil concentration with minimal urinary loss. Thus, the EAR for men aged 19–50 years is 75 mg day1, with a value of 60 mg day1 for women, based on women having less lean body mass and body water, and a smaller body size than men. There are no data on the distribution of vitamin C requirements in healthy adults; therefore the US RDA for vitamin C, which is the intake value considered to meet the requirements of 97.5% of the relevant life-stage and gender population group, is set at 90 mg day1 for men and at 75 mg day1 for women (RDA ¼ EAR þ 2CV), assuming a coefficient of variation (CV) of 10%. In Japan, Germany, Austria, and Switzerland, an uptake of 100 mg day1 is recommended for both men and women. There is evidence to show that an average intake of 90 mg day1 of vitamin C can maintain a plasma ascorbate concentration at 50 mmol l1 and for this reason a ‘potential protective plasma level’ of 50 mmol l1 has also been proposed. This concentration has been shown to inhibit plasma LDL oxidation in vitro and may have relevance for the prevention of heart disease in vivo. Smokers have been recommended by the United States to consume an additional 35 mg over and above the RDA value, but this recommendation has not been made explicit in other countries. Excessive consumption of vitamin C is unusual, and the upper intake level (UL) set by the United States is 2000 mg day1,
which is achievable only by using chronic megadoses of concentrated vitamin C supplementation. See also: Milk Lipids: Lipid Oxidation. Vitamins: Vitamin E.
Further Reading Benzie IFF (1999) Vitamin C: Prospective functional markers for defining optional nutritional status. Proceedings of the Nutrition Society 58: 469–476. Block G (1991) Vitamin C and cancer prevention: The epidemiologic evidence. American Journal of Clinical Nutrition 53: 270s–282s. Boekholdt SM, Meuwese MC, Day NE, et al. (2006) Plasma concentrations of ascorbic acid and C-reactive protein and risk of future coronary artery disease, in apparently healthy men and women: The EPIC-Norfolk prospective population study. British Journal of Nutrition 96: 516–522. Carr AC and Frei B (1999) Towards a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. American Journal of Clinical Nutrition 69: 1086–1107. Halliwell B (2001) Vitamin C and genomic stability. Mutation Research 475: 29–35. Institute of Medicine (2000) Dietary Reference Intakes for Vitamin C, Vitamin E Selenium and Carotenoids. Washington, DC: National Academy Press. Khaw KT, Bingham S, Welch A, et al. (2001) Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study: A prospective population study. Lancet 357: 657–663. Lee KW, Lee HJ, Surh Y-J, and Lee CY (2003) Vitamin C and cancer prevention. American Journal of Clinical Nutrition 78: 1074–1078. Loria CM, Klag MJ, Caulfield LE, and Whelton PK (2000) Vitamin C status and mortality in US adults. American Journal of Clinical Nutrition 72: 139–145. Packer L and Fuchs J (1997) Vitamin C in Health and Disease. New York: Marcel Dekker, Inc. Rumsey SC and Levine M (1998) Absorption, transport and disposition of ascorbic acid in humans. Journal of Nutritional Biochemistry 9: 116–130. Smirnoff N (2000) Ascorbic acid: Metabolism and functions of a multi-facetted molecule. Current Opinion in Plant Biology 3: 229–235.
Vitamin B12 D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2721–2726, ª 2002, Elsevier Ltd.
Cobalamin or Vitamin B12 The terms vitamin B12 and cobalamin, represent a group of several cobalt-containing corroids. A corrin ring with four reduced pyrrole rings and cobalt as central atom, a nucleotide-like compound, and an additional variable compound are their common features (Figure 1). B12 is the only vitamin containing a metal ion. In biological systems, hydroxo-, aquo-, methyl-, and 59-deoxyadenosylcobalamin occur, while cyanocobalamin is a decomposition product which, however, is used for therapeutic purposes as also is hydroxycobalamin. Only microorganisms are able to synthesize vitamin B12. Thus, some animal species have sufficient supply from their intestinal microorganisms. In humans, however, the synthesizing organisms are localized in the colonic part of the intestine which is too distal from the small intestine (ileum), where vitamin B12 must be taken up. Consequently, humans obtain B12 exclusively from their diet and only animal-derived foods contain sufficient amounts of vitamin B12 (Tables 1 and 2). Another prerequisite for the uptake of vitamin B12 is an intrinsic factor which is secreted from gastric parietal cells and facilitates ileal uptake of cobalamin. While storage has only minor effects on the concentration of cobalamin in milk (30–40% in sterilized milk after 90 days at room temperature) and radiation also has small effects, heat destruction plays a major role. Losses in cow milk caused by heat treatment are, sterilization: 20–100%; evaporation: 50%; boiling: 20%; pasteurization: <10%; ultra-high temperature (UHT): 5–10%. In cheese, an overall loss of 10–50% can be assumed, although there are differences between cheese types, for example, in Gruye`re cobalamin concentration even increases due to vitamin B12-synthesizing microorganisms.
Functions of Cobalamin Adenosylcobalamin (in the cytosol) and methylcobalamin (in the mitochondria) are the coenzyme forms of cobalamin. In humans, these coenzymes are involved in three metabolic reactions (for details see textbooks):
1. Leucine 2,3-amino-mutase reversibly changes -leucine into -leucine (3-aminocaproic acid), thus starting the degradation of this amino acid. 2. Methionine synthetase (N5-methyltetrahydrofolate homocysteine methyltransferase) reaction. Methionine synthetase needs methylcobalamin as a cofactor for the remethylation of homocysteine to methionine. During this process, the methyl group of 5-methyltetrahydrofolate is transferred to homocysteine, resulting in methionine and tetrahydrofolate. The latter is converted to N5,10-methylenetetrahydrofolate, a cofactor of thymidylate synthetase, finally ending up in DNA synthesis. 3. Adenosylcobalamin is needed by methylmalonyl-CoAmutase for the isomerization of methylmalonyl-CoA to succinyl-CoA during the degradation of propionic acid, thus offering the entrance to the citric acid cycle.
Sources of Cobalamin Cobalamin can be synthesized only by microorganisms and does not occur in plant-derived food. Therefore, animal-derived foods containing cobalamin are essential for humans; more or less good sources are listed in Tables 1 and 2. In cow’s milk, the cobalamin content is very constant regarding feed, breed, season, or stage of lactation, except colostrum which has a very high level. In contrast, concentrations in human milk are markedly lower than in cow’s milk and vary depending on the above-mentioned parameters. Concentrations in the milk of cow, human, and other species and in some dairy products are given in Table 2.
Cobalamin Deficiencies Although normally in developed countries the vitamin B12 uptake meets the recommendations (Table 3), cobalamin deficiencies are the most numerous vitamin deficiencies requiring clinical treatment. This is due mainly to a reduced uptake in the intestine that can have various causes. One major prerequisite is a sufficient amount of intrinsic factor
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Vitamin B12 Table 2 Vitamin B12 concentration in milk, dairy products, cheese, and milk from different species
R
Concentration (ng 100 g–1)
Food Emmental cheese (45% fat in dry matter) Camembert (45% fat in dry matter) Brie (50% fat in dry matter) Dried whole milk Condensed milk (min. 10% fat) Cream cheese (min. 60% fat in dry matter) Yogurt (min. 3.5% fat) Consumer milk (min. 3.5% fat) Cream (min. 30% fat) UHT milk Skim milk Buttermilk Sweet whey Sterilized milk
R
Vitamer
–CN
Cyanocobalamin
–OH
Hydroxocobalamin
–5′-Deoxyadenosyl 5′-Deoxyadenosylcobalamin –CH3
Methylcobalamin
–H2O
Aquacobalamin
–NO2
Nitritocobalamin
Milk from Sheep Cow Buffalo Horse Donkey Goat Human
3000 2800 1700 1500 540 530 420 410 400 380 300 200 200 100 510 420 300 300 110 70 50
From Souci et al. (2008).
Table 3 Recommended daily uptake of vitamin B12 Vitamin B12 Figure 1 Structure of the different vitamin B12 vitamers.
Table 1 Vitamin B12 concentration in foods Food
Concentration (ng 100 g–1)
Ox liver Pig liver Ox kidney Kipper Mackerel Herring Beef Red perch Salmon Egg
65 000 39 000 33 000 9700 9000 8500 5000 3800 2900 1900
From Souci et al. (2008).
which is produced by parietal cells of the stomach and binds vitamin B12. This molecule is resistant to intestinal proteolysis and binds under neutral pH conditions to specific mucosal receptors on the microvilli of the enterocytes mostly in the distal ileum to be taken up either as a complex
g MJ–1 (nutrient density)a Age
g day–1
Male
Female
Sucklings <4 monthsb Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnantc women Breast-feedingd women
0.4 0.8 1.0 1.5 1.8 2.0 3.0 3.0 3.0 3.0 3.0 3.5 4.0
0.20 0.27 0.21 0.23 0.22 0.21 0.27 0.28 0.29 0.33 0.36
0.21 0.28 0.23 0.26 0.25 0.24 0.32 0.36 0.38 0.41 0.43 0.38 0.37
a Calculated for adolescents and adults, mostly sedentary (PAL-value 1.4). b Estimated value. c 0.5 mg more for filling up body stores and to maintain nutrient density. d Approximately 0.13 mg vitamin B12 added per 100 ml secreted milk. From Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed May 2009).
Vitamins
or as cobalamin alone. After absorption, cobalamin is bound to transcobalamin and transported to the liver in the portal blood. Reasons for vitamin B12 deficiency can be atrophic gastritis, • chronic defects of the gastric mucosa (loss of parietal cells), • atrophic gastritis (chronic), • gastrectomy (partial total), • malabsorption in theorileum, • intestinal stasis, • sucklings when the mother suffers from vitamin B • deficiency, disturbances of cobalamin metabolism, • congenital intestinal parasites, and • age. •
12
If normal stores in humans are sufficiently filled (2–5 mg) and enterohepatic recirculation occurs, it takes 10–15 years for deficiency symptoms to appear after stopping any B12 intake. Characteristic vitamin B12 symptoms are macrocytic hyperchromic anemia (CAVE: this can also appear due to folic acid deficiency) and funicular myelitis, that is, neurological disorders like symmetrical paraesthesias in feet and fingers, disturbances of proprioception and vibratory senses, spastic ataxia, and degeneration of the spinal cord. Vitamin B12 delays the onset of signs of dementia (and blood abnormalities), provided it is administered before the onset of the first symptoms. Supplementation with cobalamin improves cerebral and cognitive functions in the elderly; it frequently improves the functioning of factors related to the frontal lobe, as well as the language function of those with cognitive disorders. Adolescents who have a borderline level of vitamin B12 develop signs of cognitive changes. Although the homocysteinelowering effect of vitamin B12 and folate supplementation is well known, a protective effect on the development of vascular diseases by this supplementation can be seen as a tendency; however, the final results of some ongoing trials are required before making a final recommendation. While, in former times, the ingestion of about 1 kg of raw liver per week was used to treat vitamin B12 deficiency, nowadays pernicious anemia is treated by a multistep therapy: 1 mg day–1 hydroxycobalamin intramuscularly for 7 days followed by the same dose applied weekly for up to 6 weeks, followed by the same dose every 2 months for life. Funicular myelitis is treated by a 2-week therapy with 250 mg day–1 to replenish stores followed by lifelong monthly injections
|
Vitamin B12
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of 100 mg if a disturbed absorption was the cause of cobalamin deficiency. Elderly people with reduced absorption due to gastric problems (reduced intrinsic factor) should be supplemented with 500 mg of crystalline vitamin B12 daily. Side effects have not been observed, even with pharmacological doses up to 5 mg. An overview of the varying strategies and the discussion of the different methods in different countries can be found in ‘Further reading’. See also: Vitamins: General Introduction; Vitamin B6.
Further Reading Bourre JM (2006) Effects of nutrients (in food) on the structure and function of the nervous system: Update on dietary requirements for brain. Part 1: micronutrients. The Journal of Nutrition, Health & Aging 10: 377–385. Butler CC, Vidal-Alaball J, Cannings-John R, et al. (2006) Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency: A systematic review of randomized controlled trials. Family Practice 23: 279–285. Campos-Gime´nez E, Fontannaz P, Trisconi MJ, Kiline T, Gime´nez C, and Andrieux P (2008) Determination of vitamin B12 in food products by liquid chromatography/UV detection with immunoaffinity extraction: Single laboratory validation. Journal of AOAC International 91: 786–793. Carmel R and Sarrai M (2006) Diagnosis and management of clinical and subclinical cobalamin deficiency: Advances and controversies. Current Hematology Reports 5: 23–33. Clarke R, Lewington S, Sherliker P, and Armitage J (2007) Effects of B-vitamins on plasma homocysteine concentrations and on risk of cardiovascular disease and dementia. Current Opinion in Clinical Nutrition and Metabolic Care 10: 32–39. Cook S and Hess OM (2005) Homocysteine and B vitamins. Handbook of Experimental Pharmacology 170: 325–338. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed May 2009). Herrmann W, Herrmann M, and Obeid R (2007) Hyperhomocysteinaemia: A critical review of old and new aspects. Current Drug Metabolism 8: 17–31 Hvas AM and Nexo E (2006) Diagnosis and treatment of vitamin B12 deficiency – an update. Haematologica 91: 1506–1512. Karademir J, Suleymanoglu S, Ersen A, et al. (2007) Vitamin B12, folate, homocysteine and urinary methylmalonic acid levels in infants. The Journal of International Medical Research 35(3): 384–388. Park S and Johnson MA (2006) What is an adequate dose of oral vitamin B12 in older people with poor vitamin B12 status? Nutrition Reviews 64: 373–378. Reynolds E (2006) Vitamin B12, folic acid, and the nervous system. Lancet Neurology 5: 949–960. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Folates C M Wittho¨ft, Swedish University of Agricultural Sciences, Uppsala, Sweden ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by C. M. Wittho¨ft and M. Ja¨gerstad, Volume 4, pp 2714–2721, ª 2002, Elsevier Ltd.
Introduction Folate is a B-vitamin present inter alia in milk and dairy products. The term folate is generic, referring to a class of compounds having similar chemical and nutritional properties as pteroyl-L-(mono)glutamic acid (folic acid) (Figure 1). Food-borne folates mostly have reduced pteridine moieties as dihydro- and tetrahydrofolates with different C1-substituents linked to the N5 and/or N10 position (Figure 1). Up to seven glutamyl residues are attached, via -peptide linkages, to the para-aminobenzoic group. Especially reduced folates are labile to interconversion and oxidative degradation. The stability is pH-dependent, with the reduced folates being most stable between pH <2 and >8. Oxidative cleavage of the molecule at the C9–N10 bond results in loss of biological activity. For fortification purposes, synthetic fully oxidized folic acid is used, which is not naturally present in foods, but shows higher stability during food processing and storage. For mammals, folate is an essential micronutrient that has to be obtained from the diet. Folates are involved as a cofactor in one-carbon reactions in the cell, for example, during nucleotide synthesis, supplying carbon units for purine and pyrimidine bases (Figure 2). They are also coenzymes in the methylation cycle, for example, for protein methylation and synthesis of neurotransmitters and phospholipids. Therefore, a good folate status is essential for normal cell division, and the requirement for folate is increased during, for example, growth, pregnancy, and lactation. A suboptimal folate status during pregnancy has been shown to increase the risk of birth defects, for example, neural tube defects (NTD). Deficiency leads to megaloblastic anemia, which is nowadays seldom observed in the United States and European countries. Dietary folates occur mainly in their polyglutamate forms and are absorbed at physiological concentrations by an active carrier-mediated process in the small intestine after hydrolysis of the polyglutamate chain by the intestinal brush-border enzyme -glutamyl hydrolase. When present at higher concentrations, folate monoglutamates also pass through the cell membrane by passive diffusion. During transit through the intestinal mucosa cell, folates are reduced and converted to 5-methyl tetrahydrofolate
678
monoglutamate, the transport form of the vitamin, which is released thereafter into the portal vein. It is estimated that, depending on hepatic folate status, during first pass through the liver, up to 20% of the portal folate is retained. The remaining folate is transported via peripheral blood circulation into the body tissues. In tissues or red blood cells, folates are retained as polyglutamates. A good folate status is linked to several health benefits, for example, a reduced risk for NTD and other malformations during pregnancy. Furthermore, folate is assumed to play a key role regarding prevention of coronary heart disease by lowering serum homocysteine concentration, which is suggested as an independent risk factor. Less consistent is the evidence regarding the health-protective role and mechanisms with respect to the prevention of certain cancers. Unclear is, for example, the impact of folate status on initiation, progression, and growth of subclinical cancers, as well as on neuropsychiatric disorders, such as dementia and Alzheimer’s disease. Consequently, this vitamin remains still today in research focus with the demand to further elucidate and evaluate the health-protective role of natural dietary folate as well as folic acid fortificant. In the past, nutrient intake recommendations had the aim to prevent deficiency diseases, while today it is rather focused on health benefits in connection with a good nutritional status. Already a decade ago, the US Food and Nutrition Board included the concept of potential health-protective effects when publishing dietary reference intakes for folate by drastically doubling intake recommendations for adults to 400 mg per day. Similar recommendations were made in many European countries. However, food intake surveys in most Western countries show that the average intake of folate – from natural food sources – ranges between 200 and 300 mg day 1, much below recommendations. Fortification policies were discussed as efficient ways to increase the average folate intake. The United States and Canada in 1989 introduced mandatory fortification of cereal-grain products with synthetic folic acid to reduce prevalence of NTD. This aim was achieved and epidemiologic data state that the US population improved their folate status by an increased average intake of folic acid fortificant.
Vitamins | Folates
679
O H COOH
10
N
C–N–CH–CH2–CH2–COOH
OH CH2
N 5
N
Folic acid (pteroyl-L-glutamic acid) H2N
N
N
N
C --N–CH–CH2–CH2–C--N–C–CH2–CH2–COOH
OH N
5
O H COOH
O H COOH
10
R
H
CH2
N
n
H H H2N
N
N
H
H
Pteridine
p -Aminobenzoyl-
L-Glutamate
Folate form
Abbreviation
Substituent
Position
5-Methyl tetrahydrofolate
5-CH3–H4folate
–CH3
N-5
5-Formyl tetrahydrofolate
5-HCO–H4folate
–HCO
N-5
10-Formyl tetrahydrofolate
10-HCO–H4folate
–HCO
N-10
5-Formimino tetrahydrofolate
5-CHNH–H4folate
–CHNH
N-5
5,10-Methylene tetrahydrofolate
5,10-CH2–H4folate
–CH2–
N-5 and N-10
5,10-Methenyl tetrahydrofolate
5,10-CH+–H4folate
–C+H=
N-5 and N-10
Figure 1 Structure of folic acid and folates.
Folic acid
Cell H2folate
SAM
Methionine
Purine nucieotides 10-CH3-H4 folate
H4folate 1 B12
5,10-CH2-H4 folate
dUMP
2 Activa- SAH ted CH3
Homocysteine
Methylation reactions
5,10-CH3-H4 folate
dTMP
Nucleotide biosynthesis
Figure 2 Some metabolic function of folates in the cell. H2folate – dihydrofolate, H4folate – tetrahydrofolate, –5-CH3-H4folate–5methyl tetrahydrofolate, 5,10-CH2-H4folate – 5,10-methylene tetrahydrofolate, 10-HCO-H4folate – 10-formyl tetrahydrofolate, SAH – Sadenosyl homocysteine, SAM – S-adenosyl methionine, dTMP – thymidine monophosphate, dUMP – uridine monophosphate, 1 – methionine synthase (vitamin B12-dependent), 2 – methylene tetrahydrofolate reductase.
680 Vitamins | Folates
Analysis Folate food composition data derive traditionally from microbiological analyses with Lactobacillus rhamnosus (ATCC7469) (Table 1). The assay principle is based on estimation of growth of the organism, which is dependent on folate with up to three glutamate residues. This assay does not discriminate between the different folate forms and therefore ‘total folate’ is quantified. In order to differentiate between the individual folate forms, HPLC methods are used, for which an important prerequisite is commercially available standards of the numerous folate forms. After chromatographic separation, various detection modes can be used for quantification of folates. In the past, UV spectrophotometric or fluorescence detection was used widely, but in recent years, the use of LC–MS or MS–MS techniques resulted in improved sensitivity and specificity of the determination. For clinical routine purposes, (radio-) protein-binding assays (RPBAs) are used, which are based on the affinity of folate for bovine folate-binding proteins (FBP). RPBAs have also been used by some investigators for food applications. Depending on the chosen method for folate quantification, the sample pretreatment (Figure 3) is more or less laborious, but it is always a crucial step. The extraction is usually carried out, in a stabilizing buffer with antioxidants, by means of heat, for example, in a boiling water bath or by autoclaving. The next step is an enzyme treatment, where samples are incubated with preparations of
-glutamyl hydrolase in order to deconjugate the folate polyglutamate chain. Depending on the method of
quantification, different sources for -glutamyl hydrolase can be chosen. Deconjugation with enzyme preparations from hog kidney or human plasma generates folate monoglutamates as usually required for HPLC quantification because most commercial folate standards are available only in their monoglutamate forms. For microbiological assays, incubation with chicken pancreas enzymes is usual, leading to folate di- and triglutamates. Depending on the food matrix, monoenzyme extraction may not be sufficient to release all folates from the matrix. Di- or trienzyme extraction methods have been developed, using, in variable order, additional enzyme preparations containing thermostable -amylase or protease. The final step is the purification of the food extract, for example, by centrifugation and filtration. Especially in connection with HPLC quantification, solid-phase extraction methods or affinity chromatography using agarose gel immobilized bovine FBP is used. Different approaches for sample preparation were developed, omitting or replacing individual steps, for example, by sonication or microwave treatment. Thorough quality control and documentation during all steps of sample preparation, however, is required.
Folates in Dairy Products Dairy products are considered to be moderate folate sources, but are reported to contribute between 10 and 15% to the dietary folate intake. The folate content of milk and fermented dairy products is in the range of a
Table 1 Common methods for folate analyses – an overview
Method
Microbiological assay
Principle
Estimation of growth of Lactobacillus rhamnosus (ATCC7469), responding almost equally to reduced and oxidized folate mono- to triglutamates Food samples
Application + Advantages – Limitations
+ High sensitivity, high throughput when automated, accredited methods for food analysis – Quantification of total folate, no discrimination of individual folates
Competitive binding assay Competitive binding of the analyte to a protein or antibody, often using radiolabeled standard
Clinical samples + Kit commercially available, high throughput – Not suitable for food samples containing different folate forms due to varying affinity of folate binder
Biosensor
HPLC
Biosensor-based inhibition-immuno assay with monoclonal antibodies (surface plasmon resonance principle) Folic acid-fortified food samples + Kit commercially available, label-free, real-time quantification, suitable for analysis of binding kinetics – Quite expensive, no discrimination of individual folates
Chromatographic separation of folates, identification/ quantification by FLD, DAD, UV, EC, MS, MS-MS Food samples + Determination of individual folates – Dependent on (commercial) availability of folate standards, usually only available as folate monoglutamates
FLD, fluorescence detector; DAD, diode array detector; EC, electrochemical detector; MS, mass spectrometer; MS-MS, tandem mass spectrometer.
Vitamins | Folates Monoenzyme extraction Extraction Autoclaving
Extraction Waterbath
121 °C, 10 min
boiling, 10 min
681
Trienzyme extraction Extraction Waterbath Thermostable boiling, 10 min α -amylase Protease 1–3 h, 37 °C
Deconjugation Chicken pancreas
Deconjugation Hog kidney or rat serum 37 °C, 2 to several hours
37 °C, 2 h overnight
Centrifugation or Filtration Purification Affinity chromatography or SPE MA
HPLC
Figure 3 Principles of sample pretreatment prior to folate quantification. HPLC – high-performance liquid chromatography, MA – microbiological assay, SPE – solid-phase extraction.
few micrograms to around 40 mg per 100 g (Table 2). Typical folate sources, with rich or high folate content, are leafy green vegetables, pulses, liver, yeast, citrus fruits, and some berries, containing up to several 100 mg per 100 g folate. Fermentation of bovine milk with L. rhamnosus (ATCC7469), however, results in a three- to fourfold increase of the initial folate content from 4–8 mg per 100 g to around 20 mg per 100 g. The folate increase during fermentation seems to be dependent on the type of starter culture. Whey products and dairy products containing whey show a slightly higher folate content than milk, for example, up to 30 mg per 100 g folate was found in Cottage cheese. Hard cheeses, for example, Cheddar, Edam, and Gouda, are reported to contain 20–45 mg folate per 100 g and ripened soft cheeses like Brie and Camembert, around 100 mg folate per 100 g and more. The relatively high folate content in cheeses is assumed to be a result of both the reduction of water and biosynthesis of folate by microorganisms during ripening. The folate content of milk seems to undergo minor seasonal variation, which could be caused by feeding with folate-rich green pasture during summer. The dominant folate derivative in milk is reported to be 5-methyl tetrahydrofolate amounting to about 90%, but some other folate forms like 5-formyl tetrahydrofolate and tetrahydrofolate were also found by some investigators using HPLC methods. Bovine milk contains folate in both monoglutamate and polyglutamate forms. Human breast milk contains similar amounts of folate to bovine milk, with around 5 mg per 100 g, while the folate content in goat’s milk is only half as high and in buffalo’s milk, for example, below 1 mg per 100 g.
Fortification Food fortification is defined as the addition of a nutrient to a food above the level that is normally present. This practice is governed differently in countries, and both mandatory and voluntary fortification policies exist, with respect to folates. A prerequisite is the availability of a stable form of the nutrient, which survives food processing and storage and can be synthesized at low cost. For fortification purposes, commonly the synthetic and fully oxidized vitamer folic acid is used. Risk and safety aspects are of importance with respect to fortification, but safety issues focus exclusively on synthetic folic acid, because natural folates ingested via food are considered safe over a wide intake range. The upper safe level for folic acid intake was set by the US Food and Nutritional Board in 1998 at 1 mg day 1. In the United States, folic acid levels in fortified foods of 140 mg per 100 g are far below doses reported to show adverse epileptogenic and neurotoxic effects in animal models. However, a potential risk of folic acid fortification is the masking of an undiagnosed vitamin B12 deficiency. Vitamin B12 deficiency is fairly common in the elderly population due to age-related atrophy of the gastric mucosa and can lead to irreversible neurological dysfunction and pernicious anemia. Due to the metabolic interrelationship of both vitamins, vitamin B12 deficiency can induce a secondary folate deficiency. According to the methylfolate-trap hypothesis, the activity of the vitamin B12-dependent enzyme, methionine synthase, is reduced in B12 deficiency (Figure 2). This results in accumulation of methyl groups in the form of 5-methyl tetrahydrofolate
682 Vitamins | Folates Table 2 Folate content of milk and dairy products Dairy product Milk
Total folate content (mg per 100 g) Pasteurized, bovine UHT, bovine Condensed milk, bovine
Goat Sheep Buffalo Fermented milk
Cottage cheese Soft curd cheese Soft cheese
Hard cheese
Blue cheese Whey products Milk powder Whipping cream
Camel Filmjo¨lk Yogurt Buttermilk, bovine, cultured Plain Average Plain Brie Camembert Feta Average Edam Gouda Emmental Greve´ Herrga˚rd Cheddar Va¨sterbotten Average Kvibille a¨del Whey Whey (cream) cheese Bovine, skimmed Average
4–10 4–8 8–11 1–3 2 1 4 8–11 7–18 2–15 9–12 9–27 4–12 38–150 44–102 18–62 10–45 16–40 43 40 16–18 18–21 16–33 13 24–94 30–50 6 5–50 21–60 4–7
Data given as ranges, as compiled from numerous publications and food composition tables, analyzed by microbiological assay or HPLC.
which is no further converted into tetrahydrofolate. Synthetic folic acid bypasses this reaction and is converted via dihydrofolate into tetrahydrofolate, thereby masking the B12 deficiency and reducing methionine synthase activity. In 1998, the United States and Canada introduced nationwide mandatory fortification of cereal-grain products and ready-to-eat cereals, to reduce the incidence of pregnancies affected by NTD. The folic acid fortification level of 140 mg per 100 g, aiming to provide an additional 100 mg folic acid to the folate intake from the diet, was chosen to increase the average intake of women of childbearing age while preventing excessive intake by other population groups. Folate status of the US population improved in the post-fortification period, resulting in less than 1 and 5% being at risk from too low serum and erythrocyte folate levels, respectively. However, smaller concentrations of (unmetabolized) folic acid were found in peripheral blood of a certain group of the US population in addition to the normal plasma folate form 5-methyl tetrahydrofolate. Also several other countries, for example, Chile and Costa Rica, introduced folic acid fortification of staple
foods with the aim of reducing births complicated by NTD. Most European countries, however, have voluntary fortification policies, as to date no final agreement has been reached regarding potential risks from longterm exposure to folic acid from fortification. An alternative approach to the current fortification practice with folic acid, which was discussed with respect to potential risks of folic acid fortification, is the fortification with synthetic (6S)-5-methyl tetrahydrofolate, a natural food folate form. However, synthesis of the nonracemic (biological) diasteromer (6S)-5-methyl tetrahydrofolate is not cost-efficient and this form of folate is less stable than folic acid fortificant during food processing and storage. While the protective role of folates with respect to the prevention of NTD is commonly accepted, no conclusive recommendations are made regarding the effect of folic acid fortification on initiation, progression, and growth of subclinical cancers. Folic acid-fortified foods are, like in the United States and Canada, staple foods and foods of cereal-grain character. Other fortified products – offered in some countries by voluntary fortification – are beverages (juices, soft
Vitamins | Folates
drinks, and mineral water), snacks, and table salt. Also, dairy products have been considered as vehicles for folic acid fortification.
Processing Food composition data for milk and dairy products are usually presented as total folate content. Only few systematic data are available regarding the pattern of individual folate forms in milk and processed dairy products, but the folate forms, tetrahydrofolate, 5-methyl tetrahydrofolate, 5-formyl tetrahydrofolate, and 10-formyl folic acid, were reported to be present in fermented dairy products and cheese. The chemical reactivity of reduced food folates makes the vitamin one of the most vulnerable with respect to losses during food processing. Following a number of different processes, considerable losses have been reported due to degradation enhanced by oxygen, light, and heat. Folates are also easily lost by leakage into water during processing. Fermentation of milk increases folate content by 40–50%, as reported for yogurt and a Swedish fermented milk product, called filmjo¨lk. The organism of the starter culture seems to have influence on the resulting folate content and pattern, with respect to species and strains. Streptococcus thermophilus species were reported to lead to a three- to fourfold folate increase, while fermentation with Lactobacillus bulgaricus resulted in only a minor increase or even a decrease in folate content in the final product. An increase of folate content was reported after fermentation with S. thermophilus, Lactobacillus acidophilus, Bifidobacterium longum, and L. bulgaricus, which thereafter during storage at 4 C over a 3-week period decreased, suggesting folate utilization by the lactic acid bacteria. The increase of folate content in hard cheeses can be explained mainly by reduction of the water content. The different starter cultures and length of ripening period influence folate concentrations in the final product. Mild heat treatment seems to cause minor losses of milk folate amounting to less than 10%, while folate retention during ultra-high temperature (UHT) treatment is substantially lower. Folate retention is affected not only by the amount of soluble oxygen present in the milk before processing, but also by the amount of protective ascorbic acid. Storage of pasteurized milk in the refrigerator during shelf-life does not affect folate content, while folate retention was lower during storage of UHT milk at ambient room temperature. Inconsistent data are available regarding refrigerated storage of fermented dairy products and cheeses, and most probably effects on folate content are also affected by the lactic acid bacteria strain.
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Bioavailability of Dairy Folates Bioavailability is defined as the absorption and metabolic utilization of a nutrient, thereby referring to the proportion of the ingested nutrient being absorbed and metabolized or stored. A nutrient’s bioavailability is dependent on host-related factors, for example, folate status of body stores, gastrointestinal function, health status, genetic factors, age, and possibly sex. Also extrinsic factors like properties of the ingested folate (oxidation status, substituent, and length of the polyglutamate chain), the food matrix (presence of pro- and antioxidants, fibers, binding proteins), and processing and storage were reported to influence bioavailability. Different methods can be used to assess folate bioavailability (Table 3). In vitro methods, using everted sacs or Caco cell culture models, allow the study of mechanisms during absorption and affecting factors, but do not reflect the complexity of in vivo folate absorption. An advanced computer-controlled in vitro model simulating the gastrointestinal tract is the so-called TNO gastroIntestinal Model, TIM. The TIM model has been applied successfully to study effects of food processing on folate bioaccessibility in dairy products and other foods. Animal models were used to investigate the biological role of folate in growth and reproduction, but how relevant is the information from animal trials to predict folate metabolism in humans is questionable. Human in vivo trials are time- and cost-intensive and limited by ethical restrictions. However, as short-term protocols, they can supply information regarding folate absorption. Intervention trials can be used to study longterm effects on folate status. Several trials have been carried out with the aim of investigating effects of processing and fortification of dairy foods on folate bioavailability (see section ‘Bioavailability Studies with Dairy Products’).
Folate-Binding Proteins Folate in milk is bound to an excess of FBP. At saturation, FBP binds approximately 1 mol of folate per mol protein. The function of FBP is to sequester folate from the blood in order to secure an adequate folate supply to the neonate although the concentration of folate in milk is relatively low. FBP occurs in two forms, whereby the major part exists in a soluble form and a very small amount as particulate FBP. The transport of folate in, for example, serum or milk has been suggested as the physiological function of soluble FBP. Particulate FPB is found in cell membranes and plays a role during membrane transport.
684 Vitamins | Folates Table 3 Models used to study folate bioavailability Model/assay
In vitro
Animal
Human short-term
Human long-term
Example
Everted sacs/ dissected loop/cell culture model TIM Use of human cell culture model (Caco2 cells) to study uptake and transport/ flux Simulation of the human GIT to determine stability and bioaccessibility of nutrient
Chicken, rat, pig, monkey
Investigator-controlled feeding trials
Random-controlled intervention trials (CRT)
Study biological role of folate on growth and reproduction Study effects on tissue folate distribution and concentrations Depletion/repletion models
Random application of supplements, foods, meals (with labeled compounds) as single doses multiple doses. Determination of folate concentrations and metabolites in body fluids, absorption kinetics by plasma AUC. + Information on absorbed folate – Problems with compliance and nonphysiological doses, expensive
Effect of (ideally blind) intervention with supplements, foods, meals on folate status parameters/end points
Principle/studied effect
+ Advantages – Limitations
+ No ethic restrictions – No reflection of complexity of in vivo absorption
+ Information on folate metabolism and deficiency – Limited (quantitative) information due to physiological differences between species
+ Evidence of effect from intervention on status – Problems with compliance, choice of relevant intervention period, expensive
AUC, area under the curve; GIT, gastrointestinal tract; TIM TNO, gastroIntestinal Model.
Pasteurized milk contains between 160 and 250 nmol l 1 FBP. Data regarding survival of FBP in processed dairy products are conflicting; some investigators reported reduction of the FBP content while others observed reduction of the folate-binding capacity. While 80–90% of the initial FBP content of untreated milk survives pasteurization at 72 C, it is almost completely destroyed by intense heat treatment, for example, UHT treatment or heat treatment before fermentation of milk. FBP concentrations of <15 nmol l 1 are found in yogurt, other fermented dairy products, and UHT milk. Skimmed milk powder and Cottage cheese, however, contain up to 2000 nmol k g 1 and 500 nmol l 1 FBP, respectively. During cheese-making, half of the FBP from the milk, around 100 nmol l 1, is recovered in the whey fraction. Hard cheeses contain around 13 nmol k g 1 FBP. FBP was shown to enhance folate stability under certain processing conditions. Initially, FBP was considered to stimulate folate absorption in general, as it could be shown that breastfed babies had a better folate status than bottle-fed babies. This was attributed to the presence of intact FBP in human breast milk, while in infant formula FBP was destroyed by heat treatment. However, most of these studies investigating the effect of FBP on folate bioavailability were animal experiments. FBP was also suggested to prevent folate uptake by intestinal bacteria. Recent
in vitro and in vivo studies, however, indicate reduced folate bioavailability by complex building with FBP. Bioavailability Studies with Dairy Products Only a few bioavailability trials have been carried out on dairy products fortified with synthetic folic acid or the alternative fortificant (6S)-5-methyl tetrahydrofolate. Using the in vitro model TIM, folate bioaccessibility was estimated from pasteurized milk and yogurt samples which were fortified with folic acid or (6S)-5-methyl tetrahydrofolate with and without FBP in equimolar concentrations (ca. 900–1000 nmol l 1). Unexpectedly, folic acid in both milk and yogurt was less bioaccessible in the presence of FBP (Figure 4). For added (6S)5-methyl tetrahydrofolate, the folate form naturally present in dairy products, a decrease of folate bioaccessibility from FBP was observed only in yogurt, but not in milk. Both folate forms were more than 80% bioaccessible in yogurt without added FBP. Yogurt usually contains almost no FBP. A similar negative effect of FBP on short-term folate absorption was observed in human volunteers, who consumed, in random order, pasteurized milk or fermented milk (filmjo¨lk) fortified with (6S)-5-methyl tetrahydrofolate with or without FBP. Absorbed folate was assessed by post-dose plasma concentrations (area under the plasma curve, AUC),
Vitamins | Folates
Yogurt
– FBP
+ FBP
80 60 40 20 0 Folic acid
(6S )-5-Methyl tetrahydrofolate
Folate bioaccessibility (% of intake)
Folate bioaccessibility (% of intake)
Milk 100
685
100
– FBP
+ FBP
80 60 40 20 0 Folic acid
(6S )-5-Methyl tetrahydrofolate
Figure 4 Effect of folate-binding proteins on the bioaccessibility of folate fortificants in dairy products as studied in dynamic in vitro TNO gastroIntestinal Model, TIM. TIM – TNO gastroIntestinal Model, FBP – folate-binding proteins, panels: left – milk, right – yogurt, -FBP (white bars) – no FBP added, +FBP (grey bars) – 1100–1200 nmol l 1 FBP added; added fortificants: 900–1200 nmol l 1 folic acid or 5-methyl tetrahydrofolate. Compiled from Arkba˚ge K, Verwei M, Havenaar R, and Wittho¨ft C (2003) Bioaccessibility of folic acid and (6S)-5-methyltetrahydrofolate decreases after addition of folate-binding protein to yogurt as studied in a dynamic in vitro gastrointestinal model. The Journal of Nutrition 133: 3678–3683.
which were corrected for ingested doses (Figure 5). For seven of nine volunteers, FBP reduced short-term folate absorption, as shown by significantly greater AUCs after consumption of the fermented dairy product without FBP. Median apparent absorption was estimated to be 86% of the ingested dose of the FBP-free fermented milk and 62% and 55% for fermented milk and pasteurized milk containing added FBP, respectively. However, after a 12-week intervention with folic acid-fortified
(400 mg day 1) milk (resolubilized from powder), female volunteers improved their folate status. In a Dutch intervention trial with pasteurized and UHT milk, both fortified with folic acid (200 mg day 1), the folate status of volunteers improved after 4 weeks. The Dutch investigators concluded that milk was a suitable matrix for folic acid fortification, and that the endogenous FBP content in pasteurized milk did not affect the bioavailability of folic acid fortificant significantly.
0.2 0.18
AUC (h*ng ml–1)/dose (µg)
0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 Volunteer 1–9 Figure 5 Relative absorption of (6S)-5-methyl tetrahydrofolate fortificant from dairy products with and without folate-binding protein in nine human volunteers. Relative absorption estimated by the area under the plasma folate concentration curve (dose-corrected AUC) for: light-grey bars – pasteurized milk with 250 mg (6S)-5-methyl tetrahydrofolate and 260 nmol FBP, striped bars – fermented milk with 180–205 mg (6S)-5-methyl tetrahydrofolate and 156–442 nmol FBP, dark grey bars – fermented milk with 187–234 mg (6S)-5-methyl tetrahydrofolate, no FBP. Test foods were ingested after overnight fasting on independent days in random order; blood was collected until 10 h postdose. Compiled from Wittho¨ft CM, Arkba˚ge K, Johansson M, et al. (2006) Folate absorption from folate-fortified and processed foods using a human ileostomy model. British Journal of Nutrition 95: 181–187.
686 Vitamins | Folates
Summary and Future Trends This article summarized data on the folate content of milk and processed dairy products. Systematic studies are, however, not many. Dairy products are ‘moderate sources’ of folate, but they provide between 10 and 15% of the average dietary folate intake in Western populations. Folates have been recognized regarding their health beneficial effects, for example, with respect to their protective role against NTD. With regard to the gap between actual dietary folate intake and nutritional recommendations, mandatory folic acid fortification has been discussed or introduced in several European countries; here, cerealgrain staple foods are targeted. Milk and dairy products, however, were also discussed as suitable matrices for folic acid fortification. In order to develop folate-rich functional foods with benefit for the consumer, more research is required regarding effects of processing on fortified products and their physiological effects on humans. See also: Fermented Milks: Nordic Fermented Milks; Yoghurt: Types and Manufacture.
Further Reading Arkba˚ge K, Verwei M, Havenaar R, and Wittho¨ft C (2003) Bioaccessibility of folic acid and (6S)-5-methyltetrahydrofolate decreases after addition of folate-binding protein to yogurt as studied in a dynamic in vitro gastrointestinal model. The Journal of Nutrition 133: 3678–3683. Bailey LB (ed.) (1995) Folate in Health and Disease. New York; Basel; Hong Kong: Marcel Dekker Inc. Eitenmiller RR and Landen WO (1990) Folate. In: Eitenmiller RR and Landen WO (eds.) Vitamin Analysis for the Health and Food Sciences, pp. 411–466. Boca Raton, FL; London; New York; Washington, DC: CRC Press. Hawkes JG and Villota R (1989) Folates in foods: Reactivity, stability during processing, and nutritional implications. Critical Reviews in Food Science and Nutrition 28: 439–538. Picciano MF, Stokstad ELR, and Gregory JF (eds.) (1990) Folic Acid Metabolism in Health and Disease. New York; Chichester; Brisbane, QLD; Toronto, ON; Singapore: Wiley-Liss Inc. Wittho¨ft CM Analytical methods to assess bioavailability of water-soluble vitamins in food – exemplified by folate. In: Rychlik M (ed.) Fortified Foods with Vitamins – Analytical Concepts to Assure Better and Safer Products. Hoboken, NJ: Wiley & Sons Inc (accepted) Wittho¨ft CM, Arkba˚ge K, Johansson M, et al. (2006) Folate absorption from folate-fortified and processed foods using a human ileostomy model. British Journal of Nutrition 95: 181–187. Wittho¨ft CM, Forsse´n K, Johannesson L, and Ja¨gerstad M (1999) Folates – food sources, analyses, retention and bioavailability. Scandinavian Journal of Food & Nutrition 43: 138–146.
Biotin (Vitamin B7) D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2711–2714, ª 2002, Elsevier Ltd.
Introduction The chemical structure of biotin (hexahydro-2-oxo-1Hthieno (3,4-D) imidazol-4-valeric acid) is shown in Figure 1. Of the eight isomers that exist, only D-(þ)biotin is biologically active and occurs naturally. Although in milk (cow’s as well as human) biotin occurs in the free form, most foods of animal origin or cereals contain it in an enzyme-bound form named biocytin ("-N-biotinyl-L-lysine). Biotin is essential for many microorganisms and numerous animals, including humans, and it can be synthesized by the colonic microflora. Although recent findings demonstrate an uptake of water-soluble vitamins (including biotin) by colonocytes, it remains unclear whether the amount produced is sufficient to fulfill all physiological functions or it is only a kind of fine-tuning of body homeostasis. The loss of biotin during processing or storage of food is generally small or negligible. There was no loss of biotin observed in milk kept in frozen state for some weeks or in dried milk stored at room temperature for 1 year or subjected to 2 h of sunlight or 10 Gray gamma radiation. Even UHT sterilization did not lead to biotin loss, whereas pasteurization and/or sterilization caused a <10% loss. In evaporated, condensed, or dried whole milk, the loss is <15%.
Functions of Biotin Carboxylation and decarboxylation processes are the main reactions in which biotin is involved. It is linked to the enzymes by an amide bond between the amino group of a specific lysyl residue in the active center of the respective apo-carboxylase and its valeric acid side chain. During the (ATP-dependent) carboxylase reaction, a CO2 molecule is attached to biotin at the ureido nitrogen, which is opposite to the side chain. The activated CO is then transferred from carboxybiotin to the substrate. The four representative biotin-dependent enzymes (as a prosthetic group) of the intermediary metabolism are
(catalyzes the first step in • Acetyl-CoA-carboxylase fatty acid synthesis) (catalyzes the carboxyla• Propionyl-CoA-carboxylase tion of propionyl-CoA to form methyl-malonyl-CoA) carboxylase (catalyzes the carboxylation of • Pyruvate pyruvate to form oxaloacetate) (plays an impor• 3-Methylcrotonyl-CoA-carboxylase tant role in the catabolism of leucine) which can be metabolized via alternative pathways as well. Such metabolites detected in urine suggest biotin depletion at the tissue level in individuals without congenital metabolic disorders. Recently, some additional functions of biotin have been found: it induces dermal differentiation and has been used to treat lameness in animals and brittle nails in humans.
Sources of Biotin Tables 1 and 2 give an overview of dietary sources of biotin and its appearance especially in the milks of various species and in dairy products; the recommended daily intake is given in Table 3. In cheese, changes in the concentration of biotin depend on processing procedures or maturation (microbiological synthesis, e.g., in Limburger or Brie); the highest concentrations are often found in the outer layers but can also extend throughout the cheese.
Biotin Deficiencies One outstanding biotin deficiency is egg white injury, caused by extensive consumption of raw egg white, which contains the glycoprotein avidin, which binds biotin and is resistant to intestinal digestion. Symptoms of biotin deficiency are severe dermatitis, hair loss, and neuromuscular dysfunction. In several other species (mouse, rat, hamster), subclinical biotin deficiency has been shown to be teratogenic, and this may be the case also in humans.
687
688 Vitamins | Biotin (Vitamin B7) O Ureido ring HN Tetrahydrothiphene ring
NH
OH C
S
Valeric acid side chain
O Figure 1 Structure of biotin.
Table 1 Biotin concentration in foods
Table 3 Recommended daily uptake of biotin
Food
Concentration (mg 100 g1)
Brewer’s yeast Ox liver Calf liver Soy bean, dry seed Peanut Egg Oat flakes Wheat germ Rice, unpolished Wheat, wholemeal flour
115 100 75 60 34 25 20 17 12 8
From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 6th edn. Stuttgart: Medpharm Scientific Publishers.
Age
Biotin (mg day 1)
Sucklings <4 months Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnant women Breast-feeding women
5 5–10 10–15 10–15 15–20 20–30 25–35 30–60 30–60 30–60 30–60 30–60 30–60
From Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
Table 2 Biotin concentration in milk, dairy products, cheese, and milk from different species
Food
Concentration (mg 100 g1)
Dried whole milk Limburger (40% fat in dry matter) Condensed milk (min. 10% fat) Quark/fresh cheese, from skim milk Brie (50% fat in dry matter) Camembert (45% fat in dry matter) Cream cheese (min. 60% fat in dry matter) Consumer milk (min. 3.5% fat) Sterilized milk UHT milk Yogurt (min. 3.5% fat) Cream (min. 30% fat) Buttermilk Skim milk Sweet whey
24 9 8 7 6 5 4 4 4 4 4 3 2 2 1
Milk from Buffalo Sheep Goat Cow Human
11 9 4 4 1
From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 6th edn. Stuttgart: Medpharm Scientific Publishers.
In humans, biotin deficiency is very rarely detected in industrial countries with an average biotin intake of 35–70 mg day1 which exceeds the recommended daily intake (see Table 3). However, it must be recognized that such recommendations are difficult to calculate, as the sources of biotin (diet, microorganisms, bioavailability) are quite variable. In general, biotin uptake seems to be adaptively regulated and the sodium-dependent multivitamin transporter hSMVT is involved in this regulation. Besides those who consume raw egg white in excessive amounts, persons on long-term parenteral nutrition with insufficient biotin supplementation, people suffering from congenital biotinidase deficiency (‘secondary biotin deficiency’; see below), or patients on a long-term anticonvulsant therapy are at risk of developing biotin deficiency symptoms, although only after biotin deprivation for months or even years. Symptoms like scaly/ seborrheic and red/eczematous skin rash around the eyes, nose, and mouth, and anorexia, and also neurological symptoms like depression, lethargy, hallucinations, and paraesthesiasis of the extremities have been described. In children, generally comparable symptoms appear under parenteral nutrition, but earlier (3–6 months).
Vitamins | Biotin (Vitamin B7) 689
Biotinidase is an enzyme that catalyzes the hydrolysis of biocytine to biotin and lysine in the intestine, making biotin bioavailable; in addition, biotinidase plays a role in biotin recycling. Deficiency of this enzyme is therapeutically treated by a daily supplementation with 50–150 mg of free biotin. In this context, it is interesting to note that in such patients intestinal biotin production is insufficient. See also: Milk Proteins: Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins. Vitamins: General Introduction.
Further Reading Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
Ferreira G, Weiss WP, and Willett LB (2007) Changes in measures of biotin status do not reflect milk yield responses when dairy cows are fed supplemental biotin. Journal of Dairy Science 90: 1452–1459. Mock DM (2005) Marginal biotin deficiency is teratogenic in mice and perhaps humans: A review of biotin deficiency during human pregnancy and effects of biotin deficiency on gene expression and enzyme activities in mouse dam and fetus. The Journal of Nutritional Biochemistry 16: 435–437. Reidling JC, Nobokina SM, and Said HM (2007) Molecular mechanisms involved in the adaptive regulation of human intestinal biotin uptake: A study of the SVMT system. American Journal of Physiology. Gastrointestinal and Liver Physiology 292: G275–G281. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 6th edn. Stuttgart: Medpharm Scientific Publishers. Staggs CG, Sealey WM, McCabe BJ, Teague AM, and Mock DM (2004) Determination of the biotin content of select foods using accurate and sensitive HPLC/avidin binding. Journal of Food Composition and Analysis 17: 767–776. Watanabe T and Endo A (1989) Species and strain differences in teratogenic effects of biotin deficiency in rodents. The Journal of Nutrition 119: 1348–1350.
Niacin D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2703–2707, ª 2002, Elsevier Ltd.
Introduction Niacin is the common name for a group of vitamers with a biological activity associated with nicotinamide. These include nicotinamide itself (pyridine-3-carboxamide), nicotinic acid (pyridine-3-carboxylic acid), and a number of pyridine nucleotide structures. Nicotinamide and nicotinic acid are white, crystalline structures. When dissolved in water, they have a maximum UV-absorbance at 263 nm. Each of these vitamers can be converted to the other; their structures are shown in Figure 1. Two coenzymes also exist, nicotinamide-adenine dinucleotide (NADþ) and nicotinamide-adenine dinucleotide phosphate (NADPþ), and the structures of these are shown in Figure 2. These coenzymes are most prominent in animal food sources and possess a high bioavailability, in contrast to nicotinic acid which has a lower bioavailability and is present in lower concentrations, mainly in plants. Niacin in cereals is found mainly in the outer layer, bound to the protein niacytin and thus having a bioavailability of only 30%. In milk, almost all niacin appears in the free form. Niacin is stable to sunlight, to various storage conditions, and also to heat used in dairy processes. High pressure-low temperature treatment leads to a significant loss from raw milk. Exposing liquid milk to gamma radiation (1 megarad) leads to a loss of about 30%, whereas milk powder resists even higher doses of radiation. During cheese production, most of the niacin passes to the whey, which can partly be compensated by an increase of the niacin content in the outer layers during maturation (10–25-fold).
NADP-dependent coenzymes are involved in cytosolic syntheses (reductive biosynthetic processes), while NAD-dependent enzymes are located in the mitochondria, delivering H2 to the respiratory chain for oxidation and energy metabolism. NADH is used in the respiratory chain and can be delivered by the tricarboxylic acid cycle, glycolysis, the -oxidation of fatty acids, and the degradation of amino acids. NADPH is used for the synthesis of fatty acids, cholesterol, and steroids, and for hydroxylations; it can be delivered from the pentose phosphate pathway, photosynthesis, malic enzyme, and extramitochondrial isocitrate dehydrogenase. In addition, NAD has non-redox functions: the energy provided by breaking the high-energy bond of the glycosidic linkage between nicotinamide and ribose allows the addition of ADP-ribose to quite a number of nucleophilic acceptors. NAD serves also as a substrate in poly(ADPribose) synthesis (important for DNA repair processes) and in mono(ADP-ribosyl)ation reactions (involved in endogenous regulation of various aspects of signal transduction and membrane trafficking in eukaryotic cells). NADP serves as the substrate for the formation of nicotinic acid adenine dinucleotide phosphate (NAADP), which is involved in the regulation of intracellular calcium stores. Recent publications describe additional functions of nicotinic acid, which exhibits vasodilatory and antilipolytic effects, and of niacin, which lowers plasma levels of C-reactive protein (CRP), a general marker for inflammation, which is also involved in cardiovascular disease. The nicotinic acid receptor is also discussed as a target for the development of dyslipidemic drugs for the prevention and treatment of cardiovascular disease.
Functions of Niacin Most important are the roles of NAD and NADP as coenzymes of dehydrogenases. The C4 position on the pyridine ring of the nicotinamide part of the molecule participates in oxidation as well as in reduction reactions by taking up the hydrogen ion. Thus, NADH and NADPH are intermediate hydrogen and electron carriers.
690
Sources for Niacin Tables 1 and 2 give an overview of the dietary sources of niacin and specifically the milks of various species and dairy products.
Vitamins | Niacin
Table 2 Niacin concentration in milk, dairy products, cheese, and milk of different species
O COOH
C NH2
N
N
Nicotinic acid
Nicotinamide
Figure 1 Structure of nicotinic acid and nicotinamide.
Nicotinamide
ADP
O C
NH2 NH2
N
N
N
CH2 O P O P O CH2 OH OH
O
N
O
O
–
O–
691
N
O
Food
Concentration (mg 100 g1)
Limburger (40% fat in dry matter) Brie (50% fat in dry matter) Camembert (45% fat in dry matter) Blue cheese (50% fat in dry matter) Dried whole milk Condensed milk (min. 10% fat) Sweet whey Cream cheese (min. 60% fat in dry matter) Buttermilk Skim milk Consumer milk (min. 3.5% fat) Sterilized milk UHT milk Yogurt (min. 3.5% fat) Cream (min. 30% fat)
1200 1100 1100 870 700 260 190 110 100 95 90 90 90 90 80
Figure 2 Structure of nicotinamide-adenine dinucleotide (NADþ; R ¼ H) and nicotinamide-adenine dinucleotide phosphate (NADPþ; R ¼ PO3H2).
Milk from Sheep Goat Human Horse Cow Buffalo Donkey
Table 1 Niacin concentration in foods
From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
O Ribose
Food Wheat bran Pig’s liver Ox liver Peanuts Coffee, roast Beef Salmon Ox heart Chicken Pig heart Halibut Rice (unpolished) Mushroom Pork Wheat flour (wholemeal) Sunflower seeds Herring Trout
HO
OR
450 320 170 140 90 80 74
Concentration (mg 100 g1) 18 000 16 000 15 000 15 000 14 000 7500 7500 7200 6800 6600 5900 5200 5200 5000 5000 4100 3800 3400
From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Niacin Deficiencies Owing to the coenzymes’ major role in energy metabolism, the requirement is related to energy intake. The recommended dietary allowance in the United
States has been set at 6.6 niacin equivalents (NE; see below) per 1000 kcal per day; the requirements have been established experimentally for adults and were set at a minimum of 8 mg NE day1. However, the overall calculation is difficult because the intestinal utilization rates are unknown and, in addition, NAD can be synthesized from tryptophan when the latter is available in sufficient amounts. Therefore, the niacin content of the diet is often given as niacin equivalents, that is, 1NE ¼ 1 mg niacin ¼ 60 mg tryptophan. The tryptophan content of some selected foods as a percentage of total protein is eggs 1.5%; milk 1.4%; animal products >1.1%; cereals, fruits, and vegetables 1%; and maize 0.6%. A ‘normal, mixed diet’ in industrial countries includes about 13 mg NE day1, thus providing more than the required amount. Milk, for example, is regarded as a good pellagrapreventing food (see below), not because of its niacin concentration, which is relatively low, but because of its high concentration of tryptophan. Other good sources of niacin are shown in Table 1. Niacin content of milk and other dairy products are listed in Table 2. The recommended daily uptake is shown in Table 3.
692 Vitamins | Niacin Table 3 Recommended daily uptake of niacin Niacin (mg-equivalent day1) 1 mg niacin equivalent ¼ 60 mg tryptophan Age
Male
Sucklings <4 months Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnant (>4 month) Breast-feeding
2 (estimated) 5 7 10 12 15 18 17 16 15 13
Female
13 15 13 13 13 13 15 17
From Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
The main disease caused by niacin deficiency is pellagra (pellagrosis; maidism; mal de la rosa, Saint Ignatius itch, erythema endemicum; Jolliffe syndrome). It is characterized by the three Ds dermatitis, diarrhea, and dementia. The name pellagra is derived form pelle agra ¼ rough skin, that is, the prominent symptom is a rough skin in light-exposed areas with a symmetric appearance and with a distinct border to normal skin (glove-like appearance on the hands). Disorders of the gastrointestinal tract (GIT) can include nausea, abdominal pain, increased salivation, soreness of the mouth, inflammation of the mucosa, and diarrhea. Early neurologic disorders are depression, anxiety, and poor concentration; prolonged symptoms are disorientation, confusion, and delirium. The prevalence of pellagra is sporadic in USA and Europe but higher in poor and malnourished people, alcoholics, patients undergoing long-time parenteral nutrition with insufficient niacin supplementation, and also in some psychiatric patients. Pellagra is endemic in a few regions of Africa and Asia where maize (corn) represents a major part of the common food together with very low amounts of meat, fruits, and vegetables. Pellagra-like symptoms can also appear during tryptophan deficiency (cf. Hartnup syndrome). The clinical diagnosis of pellagra is that of the (rough) skin, preferably in context with GIT symptoms. The laboratory diagnosis is still unsatisfactory in terms of a specific measurement to estimate niacin.
Thus, fluorometric assays for urinary metabolites N9-methyl-nicotinamide (NMN) and N9-methyl-2-pyridone-5-carboxamide (2-pyridone) are used. Urinary NMN levels of <0.8 mg or a combined excretion of <1.5 mg per 24 h indicates niacin deficiency. Acute therapy is by oral application of 100–300 mg day1 niacinamide or niacin in three doses, niacinamide having less intense side effects (flushing). Mental changes disappear within 24–48 h, and skin lesions, within several weeks. Concomitant administration of riboflavin and pyridoxine, and a diet rich in calories and protein are reasonable. Nicotinic acid is used as a supplement in the treatment of hyperlipidemia; high doses of up to 5 g day1 resulted in the reduction of total serum cholesterol (20%), serum triglycerides (40%), and high-density lipoprotein (LDL; þ15%). Such high doses ingested over longer periods can lead to some side effects: besides the immediate symptoms (mainly flushing and itching), hepatotoxicity, including elevated liver enzymes and jaundice, appears mostly after long-term treatment (3–9 g day1) for months or years, but has also been reported with 750 mg day1 for 2 months. Nicotinamide potentiates the effects of chemotherapy and radiation treatment fighting tumor cells, perhaps attributable to increased blood flow and oxygenation. Interestingly, supplementation with 2 g day1 led to a decreased insulin sensitivity in adults at high risk of insulin-dependent diabetes.
See also: Milk: Human Milk. Nutrition and Health: Effects of Processing on Protein Quality of Milk and Milk Products; Nutritional and Health-Promoting Properties of Dairy Products: Contribution of Dairy Foods to Nutrient Intake. Vitamins: General Introduction.
Further Reading Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H, Kluthe R, Po¨lert W, Puchstein C, and Sta¨helin HB (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Clarke R, Lewington S, Sherliker P, and Armitage J (2007) Effects of B-vitamins on plasma homocysteine concentrations and on risk of cardiovascular disease and dementia. Current Opinion in Clinical Nutrition and Metabolic Care 10: 32–39. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009). Hegyi J, Schwartz RA, and Hegyi V (2004) Pellagra: Dermatitis, dementia, and diarrhea. International Journal of Dermatology 43: 1–5. Liepa GU, Ireton-Jones C, Basu H, and Baxter CR (2007) B vitamins and wound healing. In: Molnar JA (ed.) Nutrition and Wound Healing, pp. 99–119. Boca Raton, FL: CRC Press. Niehoff ID, Hu¨ther L, and Lebzien P (2008) Niacin for dairy cattle: A review. The British Journal of Nutrition 15: 1–15.
Vitamins | Niacin Nohr D (2009a) Niacin deficiency (pellagra). In: Lang F (ed.) Encyclopedia of Molecular Mechanisms of Disease, 2nd edn, pp. 1475–1476. Berlin; Heidelberg: Springer. Nohr D (2009b) Niacin excess. In: Lang F (ed.) Encyclopedia of Molecular Mechanisms of Disease, 2nd edn, pp.1476–1477. Berlin; Heidelberg: Springer. Offermanns S (2006) The nicotinic acid receptor GPR109A (HM74A or PUMA-G) as a new therapeutic target. Trends in Pharmacological Science 27: 384–390.
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Rabinowitz SS, Reddy S, and Kumaravel R (2008) Pellagra. http://www.emedicine.com/ped/topic1755.htm (accessed April 2009). Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Pantothenic Acid D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved.
Pantothenic Acid or Vitamin B5 The natural form of pantothenic acid (Figure 1) and the only stereoisomer with biological activity is D(þ)-pantothenic acid. However, the alcohol (D)-panthenol can be converted to pantothenic acid, thus having – although indirectly – also biological activity. The major portion of pantothenic acid in the diet occurs as coenzyme A (CoA) or pantetheine (Figure 2). Pantothenic acid is a highly hygroscopic, light-yellowish viscous oil that is soluble in water as well as in ethanol. It is stable to heat and light, but otherwise is unstable; thus in pharmaceutical preparations, the Naþ or Ca2þ salts of panthenol are usually used. About 50–95% of pantothenic acid occurs as CoA or pantetheine (fatty acid synthetase complex) in the overall diet. In milk, about 25% of pantothenic acid is proteinbound, but this value rises to 40–60% in cheese, depending on the type of cheese.
Function of Pantothenic Acid The main physiological activity of pantothenic acid is related to that of CoA, pantetheine being a part of both. The HS group of cysteamine in CoA and pantetheine represents the active site for the binding of acyl or acetyl residues. Furthermore, there is a pantothenate-dependent step in the synthesis of arginine, leucine, and methionine. For the detailed synthesis of pantetheine and CoA and their numerous functions in the intermediate metabolism of animal cells (carbohydrates, fatty acids, nitrogenous compounds), the reader is referred to relevant textbooks on biochemistry or physiology or recent reviews (see Further Reading). In brief, CoA plays a role in of proteins • acylation internal acetylation of proteins • N-terminal acetylation of proteins • transfer of C2-units released of fatty • acids and oxidative degradationinof-oxidation amino acids of C2-units required for fatty acid synthesis • transfer introduction of C2-units in the tricarboxylic acid cycle • transfer of fatty acids required for the synthesis of • triglycerides and phospholipids • synthesis of isoprenoid-derived compounds
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of hemoglobin, cytochromes, acetylcholine, • synthesis taurine, and acetylated sugars In summary, pantothenic acid, especially as part of CoA, plays numerous roles in animal and human cellular metabolism.
Pantothenic Acid Sources Tables 1 and 2 give an overview of dietary sources of pantothenic acid, especially in the milk of various species and in dairy products; the recommended daily intake is given in Table 3. In cheese, amounts of pantothenic acid depend on the degree of proteolysis. While Cheddar and Cottage cheese lose large amounts (mainly of the free form) during manufacture, the concentration in some types of cheese (e.g., Limburger, Camembert, Brie) increases due to microbiological synthesis.
Pantothenic Acid Deficiencies When suffering from a deficiency of pantothenic acid, chickens develop keratitis, dermatitis, degenerations of the spinal cord, and a fatty liver, while rats show retarded growth. For humans, only effects that occur under experimental conditions are known (e.g., application of an antagonist (!-methyl pantothenic acid); severe undernutrition), as pantothenic acid occurs in almost all kinds of food and true requirements are hard to assess. The first symptoms of a deficiency are headache, fatigue, gastrointestinal tract (GIT) disturbances, palpitation of the heart, burning feet syndrome (first described in prisoners during World War II in Burma, Japan, and the Philippines). Prolonged deficiency leads to retarded wound healing, hypotonia, and uncoordinated movements. In general, all symptoms are reversible. Due to large individual variations, both the level in blood and the amount in urine excretion are not good indicators of the vitamin status. However, a blood level between 1 and 4 mg l1 is regarded as sufficient. A daily uptake of 4–6 mg is recommended by several nutritional societies because of epidemiological data: 1 mg day1 does not lead to deficiency symptoms in humans. Interestingly, some intestinal bacteria can synthesize pantothenic acid, but this source seems to be ineffective in humans.
Vitamins | Pantothenic Acid
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Table 2 Concentration of pantothenic acid in milk, dairy products, cheese, and milk of different species
Figure 1 Structure of pantothenic acid.
Food
Concentration (mg per 100 g)
Dried whole milk Blue cheese (50% fat in dry matter) Limburger (40% fat in dry matter) Condensed milk (min. 10% fat) Camembert (45% fat in dry matter) Quark/fresh cheese, from skim milk Brie (50% fat in dry matter) Parmesan Cream cheese (min. 60% fat in dry matter) Consumer milk (min. 3.5% fat) Sterilized milk UHT milk Yogurt (min. 3.5% fat) Sweet whey Buttermilk Cream (min. 30% fat) Skim milk
2700 2000 1200 840 800 740 690 530 440 350 350 350 350 340 300 300 280
Milk from Buffalo Sheep Cow Goat Horse Human Figure 2 Structure of coenzyme A (CoA). ADP, adenosine diphosphate.
370 350 350 310 300 270
UHT, ultra-high temperature treated. From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publishers.
Table 1 Pantothenic acid concentration in foods
Food
Concentration (mg per 100 g)
Ox liver Pig’s liver Ox kidney Pea, dry seed Soybean, dry seed Rice, unpolished Egg Watermelon Lentil, dry seed Rye, whole grain Broccoli Wheat flour, wholemeal Herring Oats Pork
7300 6800 3900 2000 1900 1700 1600 1600 1600 1500 1300 1200 940 710 700
From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publishers.
Pantothenic acid is used therapeutically in doses up to 5 mg day1 to treat burns (sunburn), anal fissures, rhagades, and conjunctival inflammation without any signs of hypervitaminosis. It is required as a supplement by patients on
Table 3 Recommended daily uptake of pantothenic acid
Age Sucklings <4 months 4–12 months Children 1–4 years 4–7 years 7–10 years 10–13 years 13–15 years Adults 15–25 years 25–51 years 51–65 years >65 years Pregnant Breast feeding
Pantothenic acid (mg day1)
2 3 4 4 5 5 6 6 6 6 6 6 6
From DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
696 Vitamins | Pantothenic Acid
total parenteral nutrition or those who regularly undergo dialysis. In addition, administration of pantothenic acid is used to counteract the inhibitory effects of some drugs on respiratory metabolism (e.g., valproic acid). The vitamin leads to improved wound healing following surgery.
See also: Vitamins: General Introduction.
Further Reading Biesalski HK and Hank A (2002) Pantothensa¨ure. In: Biesalski HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Minaralstoffe, pp. 111–116. Stuttgart, Germany: Thieme.
Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/modules.php?name¼ St&file¼w_referenzwerte (accessed April 2009). Leonardi R, Zhang YM, Rock CO, and Jackowski S (2005) Coenzyme A: Back in action. Progress in Lipid Research 44: 125–153. Plesofsky NS (2001) Pantothenic acid. In: Rucker RB, Suttie JW, McCormick DB, and Machlin LJ (eds.) Handbook of Vitamins, pp. 317–337. New York: Marcel Dekker, Inc. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Santschi DE, Berthiaume R, Matte JJ, Mustafa AF, and Girard CL (2005) Fate of supplementary B-vitamins in the gastrointestinal tract of dairy cows. Journal of Dairy Science 88: 2043–2054. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publishers.
Vitamin B6 D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2699–2703, ª 2002, Elsevier Ltd.
Pyridoxine or Vitamin B6 The term vitamin B6 represents a group of substances with vitamin B activity and these substances are derivatives of 3-hydroxy-2-methylpyridine: pyridoxine (PN, alcohol), pyridoxal (PL, aldehyde), and pyridoxamine (PM, amine; Figure 1), and their 59-phosphorylated forms (Figure 2). PN and PM and their phosphorylated forms are the predominant forms in plant-derived foods, while PL and pyridoxal-59-phosphate (PLP) predominate in animalderived foods. In cow’s milk, 14% of vitamin B6 is in the bound form and 86% is in the free form. It is sensitive to light and heat, partly depending on the pH of the medium. PM and PN are more stable than PL, particularly to light. In neutral and alkaline solutions, B6 is destroyed by UV light. PL, PM, and PN are generally heat stable in acidic surroundings but heat sensitive in an alkaline medium. The amount of reported loss differs between different publications, maybe due to different procedures. However, some approximations can be made: Heat treatment leads to a loss: insignificant effects • Drying: Pasteurization: 0–8% • Ultra-high temperature (UHT) treatment: <10% • Boiling: 10% • In-container sterilization: 20–50% • Evaporation: 35–50% • UV light leads to a reduction of 10–45%, depending on the intensity and duration of exposure, and gamma radiation (10 Gy) causes a loss of 90%.
Functions of Vitamin B6 In general, PLP serves mainly as a coenzyme for about 100 enzymes in amino acid metabolism. It is covalently bound to its enzyme by a Schiff base linkage to the "-amino group of lysine in the enzyme. During the enzymatic reaction, the amino group of the substrate and the aldehyde group of PLP form a Schiff base. All subsequent reactions can occur at the -, -, or -C of the respective substrate. In the following, a brief list of common reaction types is given; for further details, the reader is referred to specific literature (see Further Reading):
(transfer of the amino group of one • Transamination amino acid to the keto analogue of another amino acid) (deletion of a CO -group from a • Decarboxylation molecule; e.g., resulting in biogenic amines) (deletion of 2 subsituents from neighbored • Elimination (C-)atoms; e.g., by Serine dehydratase) 2
Pyridoxamine-59-phosphate (PMP) acts exclusively as a coenzyme for transaminases: 1. Transferase a. Serine hydroxymethyl transferase (C1 metabolism) b. D-Aminolevulinate synthase (porphyrin biosynthesis) c. Glycogen phosphorylase (glycogen mobilization) d. Aspartate aminotransferase (transamination) e. Alanine aminotransferase (transamination) 2. Oxidoreductase a. Lysyl oxidase (collagen biosynthesis) 3. Hydrolase a. Kynureninase (niacin biosynthesis) 4. Lyase a. Glutamate decarboxylase (-aminobutyric acid (GABA) synthesis) b. Tyrosine decarboxylase (tyramine biosynthesis) c. Serine dehydratase (-elimination) d. Cystathionine -synthase (methionine metabolism) e. Cystathionine -lyase (-elimination) Due to its role as a coenzyme in amino acid metabolism (see below), vitamin B6 has a broad range of functions in many systems of the body, including the immune system, the nervous system, gluconeogenesis, lipid metabolism, erythrocyte function, hormone modulation, gene expression, and niacin formation. In the immune system, for example, vitamin B6 increases the immune response of critically ill patients and suppresses the nuclear factor-kappa B (NF-B) reaction in lipopolysaccharide (LPS)-stimulated mouse macrophages, a well-established laboratory method to challenge the immune system. In the nervous system, PLP may cause neurological dysfunction, particularly epilepsy. On the other hand, there is no direct evidence for an influence on cognitive functions in people with either normal or impaired cognitive functions. An intensively investigated role is that of vitamin B6 (with B12 and folate) in regulating homocysteine levels, with homocysteine levels playing a major role in
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698 Vitamins | Vitamin B6
Figure 1 Structures of pyridoxine, pyridoxal, and pyridoxamine.
Figure 2 Structure of the coenzymes pyridoxal-59-phosphate (PLP) and pyridoxamine-59-phosphate (PMP).
cardiovascular diseases like atherosclerosis or endothelial dysfunction, and is also associated with the risk of hip fractures in the elderly. The benefits of vitamin B6 supplementation during pregnancy (e.g., higher birth weight or reduced incidence of preeclampsia and preterm birth) could not be confirmed by a meta-analysis. Additional effects of B6 include decarboxylation and transamination, inhibition of DNA polymerases and a couple of steroid receptors, and usefulness as an adjunct in cancer chemotherapy (see Further Reading).
the milk of different species that is used for human consumption. Regarding vitamin B6 in cheese, most of the vitamin passes into the whey and the concentration decreases further during early maturation, while in later phases the concentration increases, especially on the surface (yeast and molds). Cheese types like Camembert and Brie have the highest vitamin B6 concentration, followed by very hard, hard, semi-hard, and soft unripened cheese. Table 3 presents recommended dietary uptakes.
Table 2 Vitamin B6 concentration in milk, dairy products, cheese, and milk from different species
Sources of Vitamin B6 Tables 1 and 2 give an overview of the concentrations of vitamin B6 in selected foods and dairy products, including Table 1 Vitamin B6 concentration in foods Food
Concentration (g per 100 g)
Soybean, dry seed Salmon Oats Ox liver Mackerel Pig’s liver Lentil, dry seed Pork Chickpea, dry seed Millet Wheat germ Wheat, wholemeal flour Herring Maize Rice, unpolished
1000 980 960 877 630 590 575 565 550 519 492 460 450 400 275
From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Food
Concentration (g per 100 g)
Camembert (45% fat in dry matter) Brie (50% fat in dry matter) Dried whole milk Emmental cheese Condensed milk (min. 10% fat) Cream cheese (min. 60% fat in dry matter) Skim milk Yogurt (min. 3.5% fat) Sweet whey UHT milk Buttermilk Consumer milk (min. 3.5% fat) Cream (min. 30% fat) Sterilized milk
250 230 200 111 77 60 50 46 42 41 40 36 36 23
Milk from Cow Horse Goat Buffalo Human
36 30 27 25 14
UHT, ultra-high temperature treated. From Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Vitamins | Vitamin B6 699
Vitamin B6 status is normally measured by
Table 3 Recommended daily uptake of vitamin B6 Vitamin B6 (mg day1) Age
Male
Sucklings <4 months Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnant (>4 months) Breast feeding
0.1 (estimated) 0.3 0.4 0.5 0.7 1 1.4 1.6 1.5 1.5 1.4
Female
1.2 1.2 1.2 1.2 1.9 1.9
From DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2010).
in plasma • PLP 4-Pyridoxic in 24 h urine (short-term) • Assessment ofacidtheexcretion activation • transaminase (long term) coefficient of erythrocyte PN is highly toxic when taken over an extended period of time. A dose of 150 mg day–1 over several months leads to (reversible) peripheral neuropathy with dysreflexia and insensibility. However, therapies with megadoses of vitamin B6 showed high positive potential in the treatment of PN dependency (2–11 mg day–1), cystathioninuria (400 mg day–1), homocystinuria (250–1250 mg day–1), primary oxalosis type I (‘spine syndrome’, 150 mg day–1), and also isoniazid intoxication (1 g PN g–1 isoniazid). In some cases, beneficial effects have been described for carpal tunnel syndrome, premenstrual syndrome, and rheumatic diseases, although for the latter it is still unclear. See also: Vitamins: Folates; Vitamin B12.
Vitamin B6 Deficiencies Further Reading The vitamin is essential for humans, most animals, and some microorganisms. Some recommendations concerning uptake relate the concentration of B6 to protein uptake; the German Society for Nutrition, for example, recommends a minimum intake as shown in Table 3 based on a quotient of 20 mg g–1 recommended protein uptake. Bioavailability is negatively correlated with the amount of glycosylated forms of vitamin B6 in the respective food. The glycosylated form mainly appears in plant-derived foods but not animal-derived foods. As an estimation, the bioavailability of vitamin B6 in a ‘normal, mixed diet’ is about 75%. A specific vitamin B6 deficiency in humans can hardly be detected, as the first symptoms resemble the symptoms of niacin and riboflavin deficiency (stomatitis, dermatitis like pellagra). Sometimes, in children, neurological problems occur, maybe due to changes in neurotransmitter metabolism (PLP functions as a coenzyme of an amino acid decarboxylase). Longer-lasting deficiency might lead to peripheral neuropathy (nerve demyelination and hypochromic anemia that cannot be cured by iron supplementation (vitamin B6 functions in heme synthesis)), and also the risk of dementia is recently under discussion. Some drugs, hydrazines, chelators, antibiotics, oral contraceptives, L-DOPA (L-3,4-dihydroxyphenylalanine), and alcohol, reduce vitamin B6 concentration, especially when they are taken over an extended period of time (then vitamin B6 status should be monitored.
Arkaravichien T, Sattayasai N, Daduang S, and Sattayasai J (2003) Dose-dependent effects of glutamate in pyridoxine-induced neuropathy. Food and Chemical Toxicology 41: 1375–1380. Aufiero E, Stitik TP, Foye PM, and Chen B (2004) Pyridoxine hydrochloride treatment of carpal tunnel syndrome: A review. Nutrition Reviews 62: 96–104. Balk EM, Raman G, Tatsioni A, Chung M, Lau J, and Rosenberg IH (2007) Vitamin B6, B12, and folic acid supplementation and cognitive function: A systematic review of randomized trials. Archives of Internal Medicine 167: 21–30. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Carrero JJ, Fonolla´ J, Marti JL, Jime´nez J, Boza JJ, and Lo´pez-Huertas E (2007) Intake of fish-oil, oleic acid, folic acid, and vitamins B6 and E for 1 year decreases plasma C-reactive protein and reduces coronary heart disease risk factors in male patients in a cardiac rehabilitation program. The Journal of Nutrition 137: 384–390. Cheng CH, Chang SJ, Lee BJ, Lin KL, and Huang YC (2006) Vitamin B6 supplementation increases immune responses in critically ill patients. European Journal of Clinical Nutrition 60: 1207–1213. Chiang EP, Selhub J, Bagley PJ, Dallal G, and Roubenoff R (2005) Pyridoxine supplementation corrects vitamin B6 deficiency but does not improve inflammation in patients with rheumatoid arthritis. Arthritis Research & Therapy 7: R1404–R1411. Clarke R, Lewington S, Sherliker P, and Armitage J (2007) Effects of B-vitamins on plasma homocysteine concentrations and on risk of cardiovascular disease and dementia. Current Opinion in Clinical Nutrition and Metabolic Care 10: 32–39. Clayton PT (2006) B6-responsive disorders: A model of vitamin dependency. Journal of Inherited Metabolic Disease 29: 317–326. Cook S and Hess OM (2005) Homocysteine and B vitamins. Handbook of Experimental Pharmacology 170: 325–338. DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2010). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36.
700 Vitamins | Vitamin B6 Ganji V and Kafai MR (2004) Frequent consumption of milk, yogurt, cold breakfast cereals, peppers, and cruciferous vegetables and intakes of dietary folate and riboflavin but not vitamins B-12 and B -6 are inversely associated with serum total homocysteine concentrations in the US population. The American Journal of Clinical Nutrition 80: 1500–1507. Herrmann W, Herrmann M, and Obeid R (2007) Hyperhomocysteinaemia: A critical review of old and new aspects. Current Drug Metabolism 8: 17–31.
Smith AD (2008) The worldwide challenge of the dementias: A role for B vitamins and homocysteine? Food and Nutrition Bulletin 29: S143–S172. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ. Thaver D, Saeed MA, and Bhutta ZA (2006) Pyridoxine (vitamin B6) supplementation in pregnancy. Cochrane Database of Systematic Reviews 19: CD000179.
Thiamine D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2690–2694, ª 2002, Elsevier Ltd.
Introduction Thiamine or vitamin B1 is a water-soluble vitamin and is unstable and loses its biological activity in alkaline solutions (pH >7) as well as in the presence of oxidants and radiation. The chemical name of thiamine is 3-[(4-amino-2-methyl5-pyrimidinyl)methyl]- 5-(2-hydroxyethyl)-4-methylthiazolium; its coenzyme form is thiamine pyrophosphate (TPP; Figure 1). In pharmaceutical and other preparations, thiamine is used in the form of water-soluble thiazolium salts (thiamine chloride hydrochloride, thiamine mononitrate); synthetic lipophilic derivatives (allithiamins) also exist. The latter can pass through biological membranes more easily and in an almost dose-related manner, thus offering a possibility to develop thiamine stores by supplementation, which are normally low and last for only 4–10 days. In the presence of oxidizing agents and in strongly alkaline solutions, thiamine is converted into thiochrome, a fluorescent substance used to determine the thiamine content of feeds, foods, or pharmaceutical preparations.
Functions of Thiamine A number of enzymes (pyruvate dehydrogenase complex; -ketoglutarate dehydrogenase complex; branched-chain -keto acid dehydrogenase complex) involved in intermediary metabolism and playing a role in the oxidative decarboxylation of -keto acids require TPP as a coenzyme. Thus, metabolites from carbohydrate metabolism and keto analogues from amino and fatty acid metabolism are made available for energy metabolism. In addition, a TPP-dependent transketolase is involved in the formation of NADPH and pentose in the pentose phosphate pathway. Both metabolites play important roles in several other synthetic pathways. There are hints that the above-mentioned enzymes are also involved in neural functions; however, the exact mechanisms of action need to be elucidated further. Interestingly,
a decrease of glutamate uptake in the prefrontal cortex of thiamine-deficient mice is described.
Sources of Thiamine Tables 1 and 2 show the thiamine content of various foods. Table 2 focuses on dairy products, including milk from different species, that are consumed by humans. It has to be taken into account that heat treatment, as well as storage conditions, can lead to losses of the thiamine content of the foods: pasteurization 3–4% • low boiling 4–8% • spray-drying • roller-drying 10% • pasteurization15% • condensed milk9–20% 3–75% • sterilization 20–45% • evaporated milk 20–60% • Fresh milk in dark bottles loses 24% of its initial thiamine content on storage for 24 h at 4 C, 14% on storage at 12 C, and 16% on storage at 20 C. Evaporated milk loses 15–50% over periods >12 months; spray-dried whole milk shows no changes up to 12 months. Thiamine is lost during cheese manufacture mainly during drawing of the first whey; no significant changes occur during maturation. UV light-induced inactivation of thiamine can, under certain conditions (cheese, fresh milk), be counterbalanced by thiamine-synthesizing microorganisms. Modern highpressure-assisted thermal sterilization methods result in almost stable vitamins, although the decay in model solutions (acetate-buffered, pH 5.5) was about 30 times higher than in minced pork. Thus, a general deduction of the test results to routine food preparation needs further investigations. The recommended daily uptake of thiamine given by the DGE (German Nutrition Society) is shown in Table 3.
701
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Figure 1 Structure of thiamine (left) and thiamine pyrophosphate (TPP, right). Table 1 Thiamine concentration in selected foods
Food
Concentration (g 100 g1)
Brewers’ yeast, dried Wheat germ Sunflower seed, dry Soybean, dry Pork Pea seed, dry Oat flakes Wheat, wholemeal flour Hazelnut Pig, kidney or liver Ox, kidney or liver Eel Potato
12 000 2000 1900 999 900 765 590 470 390 310–340 290–300 180 110
Data from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Table 2 Thiamine concentration in dairy products and milk
Food Dried whole milk Condensed milk (min. 10% fat) Camembert (45% fat in dry matter) Cream cheese (min. 60% fat in dry matter) Quark/fresh cheese, from skim milk Skim milk Consumer milk (min. 3.5% fat) Sweet whey Yogurt (min. 3.5% fat) Buttermilk UHT milk Gouda Cottage cheese Cream (min. 30% fat) Sterilized milk Parmesan Milk from Buffalo Goat Sheep Donkey Cow Horse Human
Concentration (g 100 g1) 270 88 45 45 43 38 37 37 37 34 33 30 29 25 24 20 50 49 48 41 37 30 15
UHT, ultra-high temperature. Data from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Table 3 Recommended daily uptake of thiamine Thiamine (mg day1) Age
Male
Sucklings <4 months 4–12 months
0.2 0.4
Children 1–4 years 4–7 years 7–10 years 10–13 years 13–15 years
0.6 0.8 1.0 1.2 1.4
Adults 15–25 years 25–51 years 51–65 years >65 years Pregnant Breast feeding
1.3 1.2 1.1 1.0
Female
1.0 1.1 1.0 1.0 1.0 1.0 1.2 1.4
From DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
Thiamine Deficiencies Because of the relatively small and short-lasting thiamine stores, marginal deficiencies are quite common, but early symptoms are rarely recognized. Symptoms of thiamine deficiency are cardiac failure, muscle weakness, peripheral and central neuropathy, and gastrointestinal malfunction. Reasons for deficiency besides a thiamine-free diet (e.g., parenteral nutrition) might be reduced absorption (gastrointestinal diseases), impaired transport, increased requirements (pregnancy, lactation, infancy, childhood, adolescence, increased physical activity, infections, trauma, surgery), or increased losses and impaired biosynthesis of TPP. Clinically manifest deficiency appears in several forms of an illness called beriberi, which is nowadays mostly a problem in some regions of Southeast Asia, mainly because of the consumption of thiamine-free rice or raw fish (which contains thiaminase) or chewing of betel nuts or fermented tea leaves (which contain ‘antithiaminic’ tannins). Another risk group is chronic alcoholics who often consume low-quality meals, have poor appetite,
Vitamins | Thiamine
and suffer from gastrointestinal problems and malabsorption. One can differentiate infantile beriberi (often lethal in sucklings fed by thiamine-deficient mothers) from two forms of adult beriberi: dry beriberi is characterized by peripheral neuropathy (‘burning feet syndrome’, exaggerated reflexes, diminished sensation, and weakness in all limbs, muscle pain, problems rising from squatting position, and, in severe cases, eventually seizures). Wet beriberi is characterized by cardiovascular symptoms (rapid heart rate, enlargement of the heart, edema, breathing problems, and ultimately congestive heart failure). ‘Cerebral’ beriberi mostly leads to Wernicke’s encephalopathy and Korsakoff’s psychosis, both together appearing as the Wernicke–Korsakoff syndrome, which is, however, not easily diagnosed but can be treated by thiamine supplementation.
Thiamine Supplementation For the therapeutic treatment of diseases of the central (CNS) and the peripheral nervous system (PNS) and of exhaustion and during cytostatic treatment, doses of 50–200 mg thiamine day1 are administered orally. Clinically manifest beriberi is treated by administering 50–100 mg day1 subcutaneously or intravenously for several days, followed by the same dose orally for several weeks. Other than single cases of anaphylactic shock after intravenous application, no side effects of higher doses of thiamine (e.g., up to 200 mg day1) are known.
See also: Vitamins: General Introduction.
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Further Reading Attard O, Dietemann JL, Diemunsch P, Pottecher T, Meyer A, and Calon BL (2006) Wernicke encephalopathy: A complication of parenteral nutrition diagnosed by magnetic resonance imaging. Anesthesiology 105: 847–848. Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H, Kluthe R, Po¨lert W, Puchstein C, and Sta¨helin HB (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart, Germany: Thieme. Bitsch R (2002) Vitamin B1 (thiamin). In: Bieslaksi HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Mineralstoffe, pp. 70–74. Stuttgart, Germany: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. DGE (Deutsche Gesellschaft fu¨ r Erna¨ hrung) (2007) Die Referenzwerte fu¨ r die Na¨ hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36. Harper C (2006) Thiamine (vitamin B1) deficiency and associated brain damage is still common throughout the world and prevention is simple and safe! European Journal of Neurology 13: 1078–1082. Heath ML and Sidbury R (2006) Cutaneous manifestations of nutritional deficiency. Current Opinion in Pediatrics 18: 417–422. Liepa GU, Ireton-Jones C, Basu H, and Baxter CR (2007) B vitamins and wound healing. In: Molnar JA (ed.) Nutrition and Wound Healing, pp. 99–119. Boca Raton, FL: CRC Press. Lonsdale A (2006) A review of the biochemistry, metabolism and clinical benefits of thiamin(e) and its derivatives. Evidence-Based Complementary and Alternative Medicine 3: 49–59. Meier S and Daeppen JB (2005) Prevalence, prophylaxis and treatment of Wernicke encephalopathy. Thiamine, how much and how do we give it? Revue Me´dicale Suisse 1: 1740–1744. Nohr D (2009) Thiamin deficiency. In: Lang F (ed.) Encyclopedia of Molecular Mechanisms of Disease, 2nd edn., pp. 2044–2045. Berlin; Heidelberg, Germany: Springer (in press). Said HM and Mohammed ZM (2006) Intestinal absorption of water-soluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Smith AD (2006) Prevention of dementia: A role for B vitamins? Nutrition and Health 18: 225–226. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Riboflavin D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2694–2699, ª 2002, Elsevier Ltd.
Riboflavin or Vitamin B2 The chemical name for riboflavin is 7,8-dimethyl-10-(19D-ribityl)isoalloxazine; riboflavin exists in an oxidized and a reduced form (Figure 1), from which two coenzymes are formed: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD; Figure 2). The ending ‘flavin’ refers to its yellowish color (in Latin flavus means yellow). Free as well as protein-bound riboflavin occurs in the diet, and milk in general is the best source. In cow’s milk, the free form, with a higher bioavailability, is the major one (61% riboflavin, 26% FAD, 11% hydroxyethyl form, and others), whereas the protein-bound, and thus less bioavailable, form predominates in other foods. In human breast milk, approximately one- to two-thirds of riboflavin occurs as FAD. Riboflavin is very heat stable but it is extremely photosensitive. It is photodegraded to lumiflavin (under alkaline conditions) or lumichrome (under acidic conditions), both of which are biologically inactive. Concentrations are significantly reduced in high-pressure low-temperature treated milk as compared to raw milk. UV light excites riboflavin to a high degree of natural fluorescence, which is used for its detection and determination in yogurt or non-fat dry milk.
Functions of Riboflavin Riboflavin-dependent enzymes are called flavoproteins or flavoenzymes, because of their yellowish appearance. They catalyze hydroxylations, oxidative decarboxylations, dioxygenations, and reduction of oxygen to hydrogen peroxide, serving as electron carriers, mediators of electron transfer from pyridine nucleotides to cytochrome c or to other one-electron acceptors, and as catalysts of electron transfer from a metabolite to molecular oxygen. The two flavoenzymes, FMN and FAD, play major roles in the metabolism of glucose, fatty acids, amino acids, purines, drugs and steroids, folic acid, pyridoxine, vitamin K, niacin, and vitamin D.
704
The FAD-dependent enzyme, glutathione reductase, plays a major role in the antioxidant system by restoring reduced glutathione (GSH) from oxidized glutathione (GSSH). GSH is important in protecting lipids from peroxidation and in stabilizing the structure and function of red blood cells; it is the most important antioxidant in erythrocytes and in keeping lens proteins in solution (thus preventing cataracts). The formation of FMN and FAD is ATP dependent and takes place mainly in the liver, kidney, and heart. All enzymatic steps are under the control of thyroid hormones. riboflavin þ ATP ! r/FMN þ ADP • Flavokinase: FAD pyrophosphorylase: þ ATP ! /FAD þ PP • FAD þ apoenzyme/proteinFMN ! covalently bound flavins •
Sources of Riboflavin Tables 1 and 2 summarize dietary sources of riboflavin and its concentration, especially in the milk of various species and in dairy products. Heat treatment has only negligible effects on riboflavin concentrations, whereas exposure of milk to sunlight results in the loss of 20–80% of riboflavin. Thus, storage in dark bottles, light-tight wax cartons, or special polyethylene terephthalate (PET) bottles is recommended. Photo-degradation of riboflavin catalyzes photochemical oxidation and loss of ascorbic acid. Gamma radiation of 10 Gy destroys about 75% of riboflavin in liquid milk, whereas milk powder shows no losses even at higher doses. Storage influences riboflavin concentration as follows: condensed milk loses 28% (33%) of its initial riboflavin content when stored at 8–12 C for 2 years (10–15 C for 4 years), ice cream loses 5% when stored at –23 C for 7 months. No losses were found in fresh milk stored at 4–8 C for 24 h or in milk powder stored for 16 months. In cheese, most losses (66–88%) of the original riboflavin content of the milk appear to occur during whey
Vitamins | Riboflavin Table 2 Riboflavin in milk, dairy products, and cheese
5′ CH2OH
5′ CH2OH HO
HO Ribitol
OH
OH HO
HO
CH2
CH2 H3C
N
H3 C
N
N
O
H3C
N
H3C
N H
NH
H N
O NH
O
O 7,8-Dimethylisoaloxazine
Figure 1 Structures of oxidized (flavoquinone, left) and reduced (flavohydroquinone, right) forms of riboflavin (vitamin B2).
Adenosine(-5′)-diphosphate NH2 O 5′
CH2 O R
P
–
O
5′ CH2 O
O–
R
N
O
O
P O
P O CH2
O–
O–
O
HO
N
705
N N
OH
Figure 2 Structure of flavin mononucleotide (FMN, left) and flavin adenine dinucleotide (FAD, right). R: riboflavin.
Food
Concentration (g per 100 g)
Dried whole milk Parmigiano Camembert (45% fat in dry matter) Blue cheese (50% fat in dry matter) Condensed milk (min. 10% fat) Limburger (40% fat in dry matter) Quark/fresh cheese (from skim milk) Cream cheese (min. 60% fat in dry matter) Consumer milk (3.5% fat) UHT milk Yogurt (min. 3.5% fat) Skim milk Buttermilk Cream (min. 30% fat) Sweet whey Sterilized milk
1400 620 600 500 480 350 300 230 180 180 180 170 160 150 150 140
Milk from Sheep Cow Goat Buffalo Donkey Human
230 180 150 100 64 38
Reproduced with permission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Table 1 Riboflavin concentration in food Food
Concentration (g per 100 g)
Brewers’ yeast Pig’s liver Ox liver Wheat germ Almonds Wheat bran Soybean, seed, dry Mushroom Egg Mackerel Eel Lentil, seed, dry Beef Pork Herring Maize
3800 3200 2900 720 620 510 460 436 408 360 320 262 260 230 220 200
Reproduced with prermission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
drainage, while ripening has almost no effects. However, in some cheese varieties, the concentration is higher in the outer layers due to microbial synthesis. High-pressure tests for thermal sterilization processes led to different results concerning the decay of the vitamin, depending on the matrix of the food tested.
Riboflavin Deficiency Riboflavin is essential for humans, animals, and some microorganisms. Among humans, seniors and adolescents seem to be at particular risk of deficiency; the recommended uptake is given in Table 3. In some cases, recommended Table 3 Recommended daily uptake of riboflavin Riboflavin (mg day–1) Age
Male
Sucklings <4 months Sucklings 4–12 months Children 1–4 years Children 4–7 years Children 7–10 years Children 10–13 years Children 13–15 years Adults 15–25 years Adults 25–51 years Adults 51–65 years Adults >65 years Pregnant Breast feeding
0.3 0.4 0.7 0.9 1.1 1.4 1.6 1.5 1.4 1.3 1.2
Female
1.2 1.3 1.2 1.2 1.2 1.2 1.5 1.6
Reproduced with permission from Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http:// www.dge.de/modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
706 Vitamins | Riboflavin
uptake is related to energy intake, and 0.6 mg riboflavin per 1000 kcal is considered adequate. Milk and milk products (without butter) can contribute about 30% of the total riboflavin supply. A major portion of riboflavin is bound to proteins and these flavoproteins have to be hydrolyzed before absorption by specialized transporters in the upper gastrointestinal tract. The amount that can be stored depends on the availability of proteins providing binding sites. Although a limited uptake makes sense in preventing accumulation in tissues, it increases the body’s dependence on dietary supply. Under normal conditions, riboflavin stores last for 2–6 weeks, but in cases of protein deficiency, they last significantly shorter. Symptoms of a marginal deficiency are often nonspecific: weakness, fatigue, mouth pain, glossitis, stomatitis, burning and itching of the eyes, and personality changes. Signs of increased deficiency are cheilosis; angular stomatitis; seborrheic dermatitis at the mouth, nasolabial sulcus, and ears (later extending to the trunk and extremities); desquamative dermatitis with itching in genital regions; opacity of the cornea; cataract; and brain dysfunction. The major reasons for riboflavin deficiency are dietary intake by seniors and adolescents • Insufficient (especially girls) abnormalities, insufficient adrenal and thyr• Endocrine oid hormones (psychotropic, anti-depressant, cancer therapeu• Drugs tics, anti-malarial) intake interfering with the digestion and • Alcohol absorption of food flavins that chelate or form complexes with riboflavin • Agents or FMN, affecting their bioavailability: copper, zinc, iron, caffeine, theophylline, saccharine, nicotinamide, ascorbic acid, tryptophan, urea. As riboflavin (via FAD-dependent glutathione reductase) is involved in antioxidant mechanisms, riboflavin deficiency may considerably affect erythrocyte metabolism. However, several studies have reported protective effects of a deficiency against malaria infection. A study in the United States showed that the uptake of yogurt, milk, cereals, and also riboflavin was inversely correlated with homocysteine levels in plasma, which, in turn, seem to be positively correlated with a higher risk of developing atherosclerosis. Assessment of the riboflavin (mainly by HPLC methods) status uses the following parameters: glutathione reductase activity coefficient, • Erythrocyte Excretion in urine (mg g creatinine to assess • short-term effects), and Riboflavin in erythrocytes (mg g hemoglobin). • –1
–1
Concerning supplementation, no case of intoxication has been described. Thus, riboflavin is regarded as safe even at high doses. Supplements are usually given to reverse deficiency symptoms or to support high-risk groups: intake of drugs (e.g., anti-depressants, oral • Regular contraceptive) • Malnutrition after trauma • Patients Malabsorption • Chronic alcoholics • Hyperbilirubinemia can be treated much quicker by phototherapy when 0.5 mg riboflavin per kg of bodyweight is given. Finally, persons with congenital methemoglobinemia might benefit from 20–40 mg day–1. See also: Milk Proteins: Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins. Vitamins: General Introduction.
Further Reading Ahmad I, Fasihullah Q, and Vaid FH (2006) Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution. Journal of Photochemistry and Photobiology. B, Biology 82: 21–27. Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H et al. (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart: Thieme. Bitsch R (2002) Vitamin B2 (riboflavin). In: Bieslaksi HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Mineralstoffe, pp. 95–103. Stuttgart: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/modules.php?name¼St&file¼ w_referenzwerte (accessed April 2009). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36. Ganji V and Kafai MR (2004) Frequent consumption of milk, yogurt, cold breakfast cereals, peppers, and cruciferous vegetables and intakes of dietary folate and riboflavin but not vitamins B-12 and B-6 are inversely associated with serum total homocysteine concentrations in the US population. The American Journal of Clinical Nutrition 80: 1500–1507. LeBlanc JG, Burgess C, Sesma F, Savoy de Giori G, Vansinderen D, and Powers HJ (2003) Riboflavin (vitamin B2) and health. The American Journal of Clinical Nutrition 77: 1352–1360. LeBlanc JG, Rutten G, Bruinenberg P, Sesma F, de Giori GS, and Smid EJ (2006) A novel dairy product fermented with Propionibacterium freudenreichii improves the riboflavin status of deficient rats. Nutrition 22: 645–651. LeBlanc JG, Sesma F, de Giori G, and vanSinderen D (2005) Ingestion of milk fermented by genetically modified Lactococcus lactis improves the riboflavin status of deficient rats. Journal of Dairy Science 88: 3435–3442. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers. Woolf K and Manore MM (2006) B-vitamins and exercise: Does exercise alter requirements? International Journal of Sport Nutrition and Exercise Metabolism 16: 453–484.
W WATER IN DAIRY PRODUCTS
Contents Water in Dairy Products: Significance Analysis and Measurement of Water Activity
Water in Dairy Products: Significance Y H Roos, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Properties of Water and Water Activity Water is a well-characterized compound that exhibits physical and chemical properties that differ significantly from those of other compounds with a corresponding molecular structure. These include relatively high phase transition temperatures, heats of changes in phase, and other thermodynamic quantities. The latent heat of melting of ice at 0 C, Hm, is 334 J g1 (6.012 kJ mol1), the latent heat of vaporization of water, Hv, at 100 C is 2255 J g1 (40.63 kJ mol1), and the heat of sublimation of ice at 0 C is 2826 J g1 (50.91 kJ mol1). The solid, liquid, and gaseous states of water may coexist in equilibrium at the triple point, which is located at 0.0099 C and a pressure of 610.4 Pa. Water may solidify in various forms of ice depending on the pressure. Water may also solidify as an amorphous glass. Vapor-deposited glassy water undergoes the glass transition with onset temperature, Tg, at 138 C. The fundamental physical properties of water in dairy products are the main determinants of energy and temperature requirements as well as economics of all heat treatments and the evaporation and dehydration processes, in particular, in the dairy industry. The purest forms of water in dairy products are crystalline ice and gaseous water vapor. The vapor pressure of
water is lower in solutions as well as in dairy products than the vapor pressure of pure water at the same temperature. In ideal dilute solutions, vapor pressure is defined by Raoult’s law: p ¼ xp0
½1
where p is the vapor pressure of water in the solution, p0 is the vapor pressure of pure water at the same temperature, and x is the mole fraction of water. Raoult’s law defines that water in a solute–solvent system has a lower vapor pressure than that of pure water. This results in a lower freezing temperature and a higher boiling temperature than those of pure water at the same pressure. Real solutions, such as milk, do not obey Raoult’s law, but an ‘effective’ mole fraction for the solutes can be defined. The effective mole fraction of water is often referred to as water activity, aw. Water activity is equal to the equilibrium relative vapor pressure (RVP) of water in the surrounding atmosphere, i.e., aw as the ratio of the vapor pressure in a solution to that of pure water at the same temperature: aw ¼
p p0
½2
Therefore, the equilibrium or steady-state water activity is related to equilibrium relative humidity (ERH)
707
708 Water in Dairy Products | Water in Dairy Products: Significance
corresponding to the equilibrium RVP of the surrounding atmosphere by aw ¼
ERH 100
½3
Although water activity is a measure of water availability, it should be emphasized that water activity is a temperature-dependent property of water in a material, such as food. In most dairy products, temperature and pH are more important factors that control rates of deteriorative changes and the growth of microorganisms than water activity. This is because the average water content of milk is very high, 87.1%, and milk contains only about 8.9% of non-fat solids. The water activity of milk is, therefore, very high, 0.993. The pH of milk is close to neutral, about 6.7, which allows the growth of almost all microorganisms. Thus, in high-water, nonfermented dairy products, temperature is the main variable controlling microbial growth. In fermented milk products and in the water phase of butter, the pH is reduced, for example, to about 4.6 in ripened cream butter, which significantly reduces the growth of spoilage microorganisms. Water activity is, however, an important factor controlling the microbial flora in ripening cheese, and quality changes of some cheeses and dairy powders during storage. The reduction of water activity in these products affects the predominant microbial culture, and, in some cases, an increase in water activity improves shelf life due to reduced availability of water for microbial growth. The water activity of evaporated milk is 0.986 and a relatively rapid removal of water by dehydration or freezing results in supersaturation of soluble compounds. Evaporation of water also reduces the pH of milk to about pH 6, depending on the extent of concentration.
and the surrounding atmosphere is reached. The sorption properties are strongly dependent on temperature. Moreover, sorption properties of low-water solids and desorption of high-water solids may differ resulting in water sorption hysteresis. Sorption isotherms, which show the water content as a function of water activity at a constant temperature, are useful tools in describing the relationships between water content and steady-state RVP. Typical sorption isotherms of dairy powders, such as that of skim milk solids in Figure 1, with amorphous components, and milk and whey proteins are sigmoid curves and exhibit hysteresis. However, the amorphous lactose in dairy powders is unstable and it tends to crystallize during the storage of powder above a critical water content or water activity. Such crystallization is observed from time-dependent loss of sorbed water and a break in the sorption isotherm. The water sorption properties of the nonhygroscopic, crystalline lactose differ significantly from the water sorption properties of amorphous lactose. Therefore, crystallinity and crystalline forms of lactose may greatly affect sorption properties and one of the most significant differences between dairy powders with glassy or precrystallized lactose is the water sorption behavior. Amorphous lactose is very hygroscopic and it may sorb high amounts of water at low relative humidities. Crystalline lactose shows little sorption of water at low humidities and its water sorption becomes significant only at the higher relative humidities as a result of partial solubilization. In addition, differences in salt content may affect water sorption; for example, the presence of salts may increase water sorption by cheese and milk proteins.
Water Sorption Water sorption characteristics, as well as most other interactions of solids with water, are defined by the composition of the non-fat solids of dairy products. The water sorption properties are affected mainly by the component carbohydrates and proteins, which represent most of the non-fat fraction of milk solids, as well as by the physical state. The sorption properties may also be affected by time-dependent phenomena as a result of structural transformations and solute crystallization. Water sorption in low-water dairy products results from the difference between the vapor pressure of water in the material and the vapor pressure of water in the surrounding atmosphere. Water sorption occurs when the solids are exposed to conditions where the vapor pressure of water is higher than that within the solids. Therefore, the solids may sorb water until an equilibrium vapor pressure within the food
Figure 1 Sorption isotherm of skim milk solids (___). The break in the sorption isotherm resulting from crystallization of amorphous lactose is shown schematically (...).
Water in Dairy Products | Water in Dairy Products: Significance
709
Phase and State Transitions Water-soluble milk solids often form amorphous, supercooled liquids or glasses as a result of dehydration or freeze concentration, for example in dairy powders and frozen desserts. The dominant component in defining the physical state is lactose. The formation of the non-crystalline, amorphous state of lactose results either from the rapid removal of solvent water by dehydration or from freeze concentration in freezing of water. In the amorphous solids, water behaves in a manner similar to plasticizers in synthetic polymers. Water plasticization is observed from a softening of the amorphous material, which is accompanied by increasing rates of quality changes. Plasticization may also result from an increase in temperature, or an increase in both temperature and water content. At a sufficient level of plasticization by temperature or water, the amorphous solids exhibit the glass transition. The glass transition occurs over a temperature or water content (water activity) range, and it can be observed from changes in heat capacity, dielectric properties, various mechanical properties, volume, and molecular mobility. The effect of water on the physical state of milk solids can be observed from decreasing glass transition with increasing water content (Figure 2) and structural changes that occur above a critical temperature, water activity, or water content, as the material suffers the glass transition. The temperature–water combinations that support the various states or that result in state or phase transitions of amorphous solids and freeze-concentrated solutions can be described using state diagrams. State diagrams are simplified phase diagrams that describe the concentration dependence of the glass transition of solutes and relationships between ice formation and solute concentration at low temperatures. State diagrams are useful in the characterization of the physical state and physical properties of milk solids at various temperatures
Figure 3 State diagram of lactose showing the decrease of the glass transition temperature, Tg, with increasing water content (___), the glass transition temperature of maximally freezeconcentrated lactose solutions, T9g, and onset temperature for ice melting in the maximally freeze-concentrated state, T9m. C9g shows lactose concentration in the maximally freezeconcentrated, unfrozen solution. The equilibrium ice melting temperature, Tm, curve is shown schematically (---).
and water contents. The state diagram, as shown for lactose in Figure 3, shows the glass transition of the solids and the decrease in the glass transition temperature, Tg, with increasing water content. At sufficiently high water contents, ice formation before vitrification cannot be avoided, separating ice from the material with concurrent freeze concentration of solutes in an unfrozen water-solute phase. Therefore, the state diagrams often show the effect of ice formation on the phase and state behavior. A maximally freezeconcentrated solute has the glass transition at T 9g, which corresponds to a solute concentration of Cg9. Moreover, a full state diagram shows the onset temperature for ice melting in the maximally freeze-concentrated solution, Tm9, equilibrium ice melting temperature, Tm, curve, and the solubility curve. The solute concentration of maximally freeze-concentrated solute matrices, including non-fat milk solids, has been found to be about 80% (w/w).
Water in Milk Solids and Dairy Powders Stickiness and Caking
Figure 2 Glass transition temperature, Tg, of skim milk solids as a function of water content.
Various time-dependent structural transformations or changes in mechanical properties may occur in dairy powders at temperatures or water contents resulting in the glass transition. These transformations include stickiness and caking of powders, plating of particles on amorphous granules, and structural collapse of dehydrated structures, which are related to a rapid
710 Water in Dairy Products | Water in Dairy Products: Significance
decrease in viscosity and increase in flow above the glass transition. The main cause of stickiness is water or thermal plasticization of particle surfaces, which allows a sufficient decrease of surface viscosity for adhesion. Since viscosity is extremely high in the glassy state, the contact time must be very long for the occurrence of stickiness. A dramatic decrease in viscosity above Tg reduces the contact time and causes stickiness that can be related to the timescale of observation. A contact time of 1–10 s is sufficient at a surface viscosity less than 106–108 Pa s to cause stickiness. The decrease in viscosity is orders of magnitude over a fairly narrow water activity range, which results from the transformation of the solid material into the free-flowing liquid state. Obviously, water activity or storage relative humidity is often a more important indicator of stability than water content. The most common caking mechanism in food powders is plasticization due to water sorption and subsequent interparticle fusion. Caking of amorphous powders results from the change of the material from the glassy to the less viscous liquid-like state, which allows liquid flow and the formation of interparticle liquid bridges. The close relationships between collapse phenomena and glass transition suggest that the former occur above Tg with rates that are defined by the temperature difference, T–Tg. Agglomeration is an important step in achieving instant solubility properties for dairy powders. The process is based on controlled thermal and water treatment of fine particles. Common agglomeration methods are based on rewetting of fine powders or on agglomeration during and after spray drying using a straight-through process. The straight-through process is accomplished by producing plasticized particles with a temperature and water content that allow sufficient plasticization of particle surfaces and the formation of interparticle liquid bridges. The plasticized agglomerates enter a vibrating fluidized bed dryer, which completes dehydration and allows sufficient cooling of the product with concurrent solidification and vitrification of the particle surfaces. Agglomeration by both the rewetting and straight-through processes requires that amorphous solids are allowed to exist for a sufficiently long time in the plasticized state at appropriate temperature–humidity conditions allowing controlled stickiness. The proper agglomeration conditions are defined by the Tg of the particles and their water plasticization properties. Lactose Crystallization Drying of milk and whey by spray drying or roller drying produces a glass that is composed of a noncrystalline mixture of - and -lactose. The existence of lactose in
the glassy state and lactose crystallization due to increased molecular mobility have been confirmed by several studies, which have determined the physical state using polarized light microscopy, electron microscopy, differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectroscopy, and X-ray techniques. Crystallization of amorphous lactose in dairy powders may accompany the glass transition due to thermal or water plasticization and the increase in molecular mobility. Such crystallization is often detrimental to powder quality and it may significantly alter rehydration characteristics and reduce shelf life. In general, the crystallization time of amorphous sugars above Tg depends on temperature and water content. The crystallization behavior of amorphous lactose is also temperature dependent. An increase in storage temperature shifts the break in the sorption isotherm, indicating loss of sorbed water, to a lower relative humidity. Typical DSC heating scans of milk powders with amorphous lactose show a glass transition followed by a crystallization exotherm. Lactose crystallization during water sorption may occur either into the anhydrous -form or into -lactose monohydrate. The crystalline form produced depends on relative humidity and temperature. Lactose crystallization occurs into the anhydrous -form at relatively low water activities and the -lactose monohydrate form often crystallizes at water activities above 0.57 aw at room temperature. Crystallization into the anhydrous -lactose crystals releases water associated with the amorphous lactose while the -lactose monohydrate contains 5% water in the crystalline lactose phase. At higher temperatures, crystallization behavior may change according to the stability of the crystalline form at the crystallization temperature. The kinetics of crystallization at a constant temperature above glass transition can be related to water content and water activity, which define the T–Tg. Therefore, lactose crystallization may occur above a critical water content or water activity at a constant temperature with a rate defined by T–Tg. An increasing relative humidity increases water sorption by amorphous lactose, which causes water plasticization and increases the temperature difference, T–Tg. Combined Tg and water sorption data have suggested that a water content of 7.6 g per 100 g non-fat solids depresses the glass transition to room temperature. The corresponding water content for pure lactose is 6.8 g per 100 g solids and the critical aw is 0.37. This water activity or storage relative humidity of 37% RH is empirically known as critical to the stability of dairy powders, including milk and whey powders. Milk powders with lactose hydrolyzed to galactose and glucose show no break in the sorption isotherm. Both the water sorption and crystallization behavior of these sugars differ significantly from that of lactose, and the behavior
Water in Dairy Products | Water in Dairy Products: Significance
of the sugar mixture differs from that of typical skim milk solids. For example, component crystallization in the protein–glucose–galactose mixture is delayed in comparison to lactose crystallization in common dairy powders. Skim milk powders containing hydrolyzed lactose show a glass transition well below that of amorphous lactose. The glass transition of lactose-containing anhydrous skim milk powder has an onset at 92 C. Anhydrous powder produced from skim milk with lactose hydrolyzed to galactose and glucose has the glass transition onset at 49 C, and the critical water content that depresses the glass transition to room temperature is as low as 2.0 g per 100 g. The decrease in the Tg and the low critical water content are responsible for difficulties in the production of lactose-hydrolyzed dairy powders. These powders are extremely sensitive to temperature and water and they show hygroscopicity and stickiness during processing and storage. Chemical Stability Rates of deteriorative changes at reduced water activities are often related to water content and molecular mobility. Water as a plasticizer has a significant effect on molecular mobility above a critical, temperature-dependent water activity or water content. Molecular mobility is governed by the physical state and water plasticization of solids, and rates of several deteriorative changes are probably affected by diffusion. Diffusion below Tg may be assumed to be restricted, and a chemical reaction may become diffusion limited in a glassy matrix. Although diffusion of water occurs in glassy systems, the diffusion of larger reactant molecules is most likely to be affected by the glass transition. A significant increase in a reaction rate may occur as the material is transformed into the supercooled liquid state as a result of the glass transition. The temperature dependence of chemical changes often follows the Arrhenius equation, but kinetics may show deviations from Arrhenius kinetics at reduced water contents due to diffusional limitations. Non-enzymatic browning is one of the most important, water content-related deteriorative reactions in lowmoisture dairy foods. The non-enzymatic browning reaction is a series of condensations, but it may be considered as a bimolecular reaction. Browning rates in non-fat milk powder below the critical water activity (water content) are low, but the rate of browning is dependent on water content and it increases substantially above the critical water activity. In general, non-enzymatic browning occurs very slowly in glassy dairy products. However, above the glass transition, the rate of the reaction increases and a further increase often results from lactose crystallization and release of the sorbed water. Lactose crystallization must be prevented to avoid caking and impaired solubility. The loss of lysine is most rapid at
711
water activities that allow lactose crystallization. It should also be taken into account that crystallization of amorphous lactose in closed containers or packages is more detrimental as the water released from amorphous lactose remains in the system, accelerating deterioration of the noncrystalline solids. Diffusion of reactants is probably the main requirement for the occurrence and increasing rates of chemical reactions above some critical temperature or water content. In some cases, flow through pores may increase reaction rates. Such exceptions include oxidation of free fat in dairy powders. Oxygen may diffuse in the material and enhance oxidation on the pore membranes. Crystallization of lactose coincides with an increase in free fat, which presumably facilitates lipid oxidation. In powders containing amorphous lactose, milk fat is encapsulated within the amorphous lactose–protein matrix and it is protected from oxidation. Exceeding the Tg and subsequent crystallization releases the encapsulated lipids, which become accessible to atmospheric oxygen and undergo oxidation rapidly.
Frozen Dairy Products and Ice Cream The freezing temperature of milk, about 0.53 C, is relatively constant. At the freezing temperature, all ice formed at lower temperatures is melted into water. The initial ice formation in milk, dairy products, and in foods, in general, requires supercooling to below the equilibrium melting temperature and it is followed by further crystallization of water as the temperature is decreased. Freezing behavior of water, for example, in ice cream is significantly affected by the component compounds, and by sugars in particular. The main component affecting freezing behavior is lactose. Ice formation in a lactose solution, provided that no lactose crystallization is taking place, occurs at temperatures above 30 C. At 30 C, the maximum ice formation in the solution can be achieved and a highly viscous, freeze-concentrated lactose solution with approximately 80% lactose and 20% unfrozen water remains unfrozen, as described by the state diagram. During further cooling, this unfrozen solution suffers the glass transition. Such nonequilibrium ice formation is a typical phenomenon of carbohydrate solutions and probably the most common form of ice formation in frozen foods, including frozen dairy products. The viscosity of a freeze-concentrated solute phase is an important factor that may affect time-dependent crystallization phenomena, ice formation and recrystallization, and material properties. At a sufficiently low temperature, the viscosity of a freeze-concentrated solute matrix becomes high enough to retard diffusion and delay ice formation. The ice formation in real time ceases at the T 9g, since the high viscosity of the freeze
712 Water in Dairy Products | Water in Dairy Products: Significance
concentrated solute matrix prevents diffusion of water molecules to the surface of ice crystal lattice and crystal growth. Ice formation and the extent of freeze concentration are dependent on temperature according to the melting temperature depression of water caused by the solute phase. Maximum freeze concentration may occur at temperatures slightly below the onset temperature of ice melting, T 9m, in the maximally freeze-concentrated material. The size of ice crystals that are formed during freezing depends on the freezing method and freezing rate. Rapid freezing at a low temperature produces a large number of small ice crystals, while slow freezing at a higher temperature results in the formation of relatively few large ice crystals. The ice crystals, which form during freezing, are not stable, and recrystallization is common at typical storage temperatures of frozen dairy products. Recrystallization is a temperature-dependent process, which is enhanced by temperature fluctuations. Recrystallization with a decrease in the number of crystals and an increase in the average crystal size is referred to as Ostwald ripening. Recrystallization by fusion of smaller crystals resulting in the formation of large ice crystals is also an important recrystallization mechanism in ice cream. Melt–refreeze crystallization, which involves melting of ice and refreezing of unfrozen water, may occur under fluctuating temperatures, especially at relatively high temperatures. An average ice crystal size of 40 mm with a distance of 6–8 mm between the crystals is acceptable. The critical size, which produces a grainy texture, is 40–55 mm. Recrystallization of ice in ice cream and other products that are consumed in the frozen state produces a coarse, icy, undesirable texture. In addition, solute crystallization in freeze-concentrated products can be retarded by the use of sugar blends and syrups. Evaluation of kinetic data on ice recrystallization should consider the effect of ice melting above T 9m. The viscosity of the unfrozen matrix is increased by stabilizers, which decrease the rate of recrystallization. Recrystallization of ice, as well as lactose crystallization during frozen storage, can be reduced by using hydrocolloids, such as carrageenans, guar gum, or locust bean gum, as stabilizers. Polysaccharide stabilizers do not significantly alter the T 9g of ice cream mixes, but ice crystal growth in stabilized ice cream above T 9g is a function of kinetic properties of the unfrozen solute matrix and the mobility of water within the unfrozen matrix. An increase in the amount of unfrozen water increases the recrystallization rate, but stabilizers reduce the recrystallization rate.
Water and Microbiological Stability Microbial growth requires a minimum amount of water in an environment supporting the growth of microorganisms. In dairy products, the effect of water
on the growth of microorganisms is probably most important in the ripening, texture, and quality of cheeses. Water availability may also be an important factor in controlling mold growth in low-fat dairy spreads and butter. Water activities of milk products vary widely, from 0.1 to 0.3 for dried dairy products to above 0.99 for liquid milk and whey. Sweetened condensed milk with 0.77–0.85 aw has an intermediate water activity, but most other dairy foods have high water activities supporting the growth of bacteria and other microorganisms. The minimum requirement for microbial growth is aw 0.62, which allows the growth of xerophilic yeasts. An increasing aw allows the growth of molds, other yeasts, and finally bacteria at high water activities. The most important water activity value for the safety of food materials is 0.86, which is the limit for the growth of Staphylococcus aureus (Table 1). The water activity of various cheeses and processed cheeses varies between 0.86 and 0.99 (Table 2). There are also critical aw values for the multiplication of bacteria used in cheese manufacture. For example, propionibacteria, which are responsible for eye formation in Swiss cheese, are very Table 1 Minimum water activities (aw) for the growth of selected pathogenic bacteria in dairy products Pathogen
Minimum aw
Bacillus cereus Campylobacter jejuni Clostridium perfringens Escherichia coli Listeria monocytogenes Salmonella spp. Shigella spp. Staphylococcus aureus Vibrio parahaemolyticus Yersinia enterocolitica
0.930 0.990 0.945 0.935 0.920 0.940 0.960 0.860 0.936 0.960
Table 2 Typical water activity (aw) of common cheeses at 25 C Cheese type
Water activity
Appenzeller Brie Blue Camembert Cheddar Cottage cheese Edam Emmentaler Gouda Mozzarella Parmesan Tilsiter
0.96 0.98 0.94 0.98 0.95 0.99 0.96 0.97 0.95 0.99 0.92 0.96
Water in Dairy Products | Water in Dairy Products: Significance
713
Figure 4 Food stability map showing the effect of water activity on the relative rates of various changes in food systems. The critical aw refers to the water activity at which the glass transition occurs at the storage temperature.
sensitive to changes in aw over the range 0.95–0.99. Water activity in cheese ripening may affect growth and CO2 production. Inhibition of the growth of most microbes in salted butter may be accounted for by the high concentration of salts in the water fraction and reduced water activity. The water activity of salted butter is 0.91–0.93, while that of unsalted butter is >0.99. In low-fat dairy spreads, a low pH with a reduced water activity is necessary to prevent the growth of pathogens and molds.
Stability Maps The relative rates of deteriorative changes in food materials are traditionally related to water content and water activity on the assumption that stability at common storage temperatures can be maintained at a low water content. Structural transformations in milk solids may occur at temperatures above the glass transition, which corresponds to a water content that can be quantified. Such transformations include collapse of the physical structure, which reduces diffusion through pores and crystallization of amorphous lactose. Crystallization of amorphous lactose may also release encapsulated fat, which becomes susceptible to oxidation. The effect of water activity on the relative rates of deteriorative changes is often described by stability maps, which are used to show the relative rate of enzymatic changes, non-enzymatic browning, lipid oxidation, microbial growth, and overall stability as a function of water activity (Figure 4). Various reactions rates may also be related to the physical state, molecular mobility, and water plasticization and glass transition of
amorphous food solids. It is obvious that structural transformations, as well as diffusion-limited deteriorative reactions and those affected by lactose crystallization, occur at increasing rates with increasing water activity above the critical aw.
See also: Butter and Other Milk Fat Products: Anhydrous Milk Fat/Butter Oil and Ghee; Fat Replacers; Milk Fat-Based Spreads; Modified Butters; Properties and Analysis; The Product and its Manufacture. Dehydrated Dairy Products: Milk Powder: Physical and Functional Properties of milk Powders; Milk Powder: Types and Manufacture. Ice Cream and Desserts: Dairy Desserts; Ice Cream and Frozen Desserts: Manufacture; Ice Cream and Frozen Desserts: Product Types. Plant and Equipment: Milk Dryers: Dryer Design; Milk Dryers: Drying Principles.
Further Reading Chuy LE and Labuza TP (1994) Caking and stickiness of dairy-based food powders as related to glass transition. Journal of Food Science 59: 43–46. Fox PF and McSweeney PLH (1998) Dairy Chemistry and Biochemistry. London: Blackie Academic & Professional. Haque MK and Roos YH (2004) Water sorption and plasticization behavior of spray-dried lactose/protein mixtures. Journal of Food Science 69: E384–E391. Haque MK and Roos YH (2005) Crystallization and X-ray diffraction of spray-dried and freeze-dried amorphous lactose. Carbohydrate Research 340: 293–301. Haque MK and Roos YH (2006) Differences in the physical state and thermal behavior of spray-dried and freeze-dried lactose and lactose/protein mixtures. Innovative Food Science and Emerging Technologies 7: 62–73. Jouppila K, Kansikas J, and Roos YH (1997) Glass transitions, water plasticization, and lactose crystallization in skim milk powder. Journal of Dairy Science 80: 3152–3160.
714 Water in Dairy Products | Water in Dairy Products: Significance Jouppila K and Roos YH (1994a) Water sorption and time-dependent phenomena of milk powders. Journal of Dairy Science 77: 1798–1808. Jouppila K and Roos YH (1994b) Glass transitions and crystallization in milk powders. Journal of Dairy Science 77: 2907–2915. Roos YH (1995) Phase Transitions in Foods. San Diego, CA: Academic Press. Roos YH (2009) Solid and liquid states of lactose. In: McSweeney PLH and Fox PF (eds.) Advanced Dairy Chemistry Volume 3: Lactose, Water, Salts and Minor Constituents, 3rd edn., pp. 17–33. New York: Springer ScienceþBusiness Media. Roos YH, Jouppila K, and Zielasko B (1996) Nonenzymatic browning induced water plasticization: Glass transition temperature depression and reaction kinetics determination using differential scanning calorimetry. Journal of Thermal Analysis and Calorimetry 47: 1437–1450.
Roos Y and Karel M (1991) Amorphous state and delayed ice formation in sucrose solutions. International Journal of Food Science and Technology 26: 553–566. Roos Y and Karel M (1992) Crystallization of amorphous lactose. Journal of Food Science 57: 775–777. Roos YH, Karel M, and Kokini JL (1996) Glass transitions in low moisture and frozen foods: Effects on shelf life and quality. Food Technology 50(11): 95–108. Shimada Y, Roos Y, and Karel M (1991) Oxidation of methyl linoleate encapsulated in amorphous lactose-based food model. Journal of Agricultural and Food Chemistry 39: 637–641. Vega C and Roos YH (2006) Spray-dried dairy and dairy like emulsions – compositional considerations. Journal of Dairy Science 89: 383–401. Walstra P, Geurts TJ, Noomen A, Jellema A, and van Boekel MAJS (1999) Dairy Technology. New York: Marcel Dekker.
Analysis and Measurement of Water Activity D Simatos, G Roudaut, and D Champion, ENSBANA–Universite´ de Bourgogne, Dijon, France ª 2011 Elsevier Ltd. All rights reserved.
G ¼ w – 0 w ¼ RT ln aw
Definition and Significance of Water Activity Definition Water activity of a system is a way of characterizing the potential energy of the contained water, which is thought to be related to the difficulty to remove it, for example, in drying, and to its availability to allow the functioning of living cells. It can be viewed, for instance, as the difference between the water vapor pressure measured over pure water and that measured over a food product (Figure 1(a)), or as the energy necessary to compensate for the osmotic pressure of a solution (Figure 1(b)). Figures 2 and 3 show schematic views of water activity of dairy products as compared to their water content. The chemical potential (i, J mol–1) of the component i in a mixture is defined as the partial derivative of the free energy, G, when the number of molecules of i (ni) is varied, whereas the temperature, pressure, and total number of molecules in the system are kept constant.
qG qni
¼ i
½1
T ;P;n
If the component considered is water, the subscript w will be used. For a process where the water concentration (expressed as the mole fraction Xw) is changed from X 0w to Xw, the change in free energy, G, is G ¼ w – 0w
½2
where X 0w and 0w concern a state of reference, namely, pure water under the temperature and pressure conditions of the system. As we will see later, G can be calculated for various processes, for example, as the work corresponding to the upward motion of the piston if water is allowed to enter the concentrated solution in the system shown in Figure 1(b), or as the change in free energy as the pressure is changed from pw0 to pw in the system shown in Figure 1(a). If the system is a dilute solution, G is observed to be proportional to the logarithm of the solvent molar fraction (Raoult’s laws and van’t Hoff’s law): G ¼ w – 0w ¼ RT ln Xw
½3
Solutions obeying eqn [3] are called ‘ideal’ solutions. For nonideal systems, Xw is replaced by a new characteristic named ‘water activity’ (aw):
½4
Comparing eqns [3] and [4], aw = Xw for ideal solutions. For nonideal solutions, a parameter, (activity coefficient), was introduced to represent the deviation from ideality: aw ¼ Xw
½5
Water activity is a colligative property; that is, it depends on the number of solute molecules in the solution. The presence of solutes induces a disorder in the water structure, that is, an increase in entropy, which results in a reduced chemical potential. With small solutes, aw is controlled mainly by Xw, that is, by the number of solute molecules. In the presence of macromolecules or hydrophilic surfaces (cell membranes), the mixing entropy plays a minor role in the depression of aw (Xw remains high); low values of w (and, in turn, of aw) are attributed to interactions of the water molecules with the other constituents. When interactions occur between water and solutes (dipole–dipole, ionic interactions, or hydrogen bonds), or when the size of the solute is much larger than the size of the water molecule, < 1. When solute–solute interactions dominate over water–solute interactions, > 1 (remember, however, that aw is always <1). Figure 4 shows some examples of the aw-lowering effect of dairy components. If pure water is contained in a cylindrical capillary space (diameter d), the wall of which is perfectly wetted by water, the difference in chemical potential defined as in eqn [2] can be shown to be (Kelvin’s law) w – 0 w ffi – Vw ln aw ¼ –
4 d
Vw 4 RT d
½6
where Vw and are, respectively, the molar volume and the surface tension of water. For a descending pore diameter range of 100–1 mm (and a surface tension of 35 mN m1 for a caseinate solution–air interface), eqn [6] predicts aw in the range 1–0.999, that is, a very small lowering of aw by capillary effects. If Kelvin’s law can be assumed to be valid for a pore size approaching molecular dimensions (d 10 nm), aw could be lowered to 0.90. In products with intermediate or low water content, it is generally considered that water is retained by adsorption processes. The model most often referred to is the BET multilayer adsorption process, according to which a
715
716 Water in Dairy Products | Analysis and Measurement of Water Activity (b)
(a)
Piston rod Temperature: 25 ⬚C Water P 0w = 3.167 kPa aw = 1
Pw = 2.534 kPa aw = 0.80
Semipermeable piston plate Milk
Water
Sweetened condensed milk
Figure 1 (a) Schematic representation of the difference in water vapor pressure above pure water and above a food product, measured at the same temperature (T). This difference may be known, either from a direct measurement of the partial water vapor pressures (P0 w (T), the saturated water pressure at T, above pure water, and Pw above sweetened condensed milk) or from the relative humidity (RH) in the headspaces. (b) Since the chemical potential of water in the concentrated milk is less than in pure water, there is a Q tendency for water to move into milk through the semipermeable plate. A downward pressure, , on the piston is required to maintain it in place. Reproduced from Simatos D, Champion D, Lorient D, and Roudout G (2009) Water in dairy products. In: McSweeney PLH and Fox PF (eds.) Advanced Dairy Chamistry-3. Lactose, Water Salts and Minor Constituents, 3rd edn. In press.
first layer of sorbate (water) molecules would be formed on the surface of the solid, followed by a multilayer condensation of the sorbate onto the monolayer. The relations between aw and water content are represented by sorption isotherms (SI) for dairy products and components, example of which are shown in Figures 5 and 6. SI have a sigmoid shape for products with a high content of biopolymers. Small-molecular-weight solutes, such as lactose, have a higher aw than biopolymers at low water contents, and a lower aw than biopolymers at high 100 Milk Fermented milk products
90
Water content (% w/w)
80
Condensed milk
70
Frozen desserts
60 50 40
Sweetened condensed milk
30 20
Dry milk products
10
Butter salted/unsalted
0 0
0.2
0.4 0.6 Water activity
0.8
1
Figure 2 Schematic representation of water activity and water content of various dairy products (for cheese, see Figure 3).
water contents. As illustrated in Figures 5 and 6, it is important to remember that important variations in SI may result not only from variations in chemical composition, but also from variations in the conditions of determination such as water content measurement, equilibration time, variations in structure resulting from the drying process, or from evolution during the sorption experiment (crystallization of lactose, physical aging of polymers). SI found in the literature should therefore be used only as a first approximation. One interesting aspect of aw in food science and technology is that chemical potential must be the same in all phases of the system at equilibrium; this is important because food products most often comprise regions with different chemical compositions, physical states, or structures. A particular example of a multiphase system is frozen food products. As will be seen below, in a frozen product aw = pice/psupercooled water and is, therefore, a function of temperature only. For instance, a food product with a water content high enough for the food to contain ice at 20 C has (if at equilibrium) aw = 1.035/ 1.257 = 0.82. It must be remembered, however, that the definition of aw and the derived expressions for its determination assume that the system is in a state of thermodynamic equilibrium. Hence, it is sensible to question the validity of their applicability to food products (Expert Panel, ISOPOW, 2000). Actually, solutions of small solutes, even if concentrated, can be considered to be at thermodynamic equilibrium, whereby the aw concept is valid. For low-moisture or semi-moist solid food products, it is difficult to predict the actual status of the product, which will depend on (1) its position in comparison with glass
Water in Dairy Products | Analysis and Measurement of Water Activity 100
Water content (%)
80
60
1: Bergkase 2: Emmental 3: Gruyere 4: Parmesan 5: Sbrinz 6: Appenzeller 7: Bel Paese 8: Cheddar 9: Edam 10: Fontal 11: Gouda 12: Saint Paulin 13: Tilsit 14: Raclette
15: Belle des Champs 16: Brie Suisse 17: Camembert Suisse 18: Tomme Vaudoise 19: Limburger 20: Munster 21: Vacherin Mont d’Or 22: Cottage cheese 23: Fat white cheese 24: Nonfat white cheese
717
Milk 22
23
F.C. 24
F.C.: Fresh cheese S.C.: Soft cheese P.C.: Pressed cheese H.C.: Hard cheese
19
18
16 20
7
9
10
12
14
40
S.C.
15
21 17
6
11
13 3
4
2
P.C.
8 5
1
H.C. 20 0.88
0.90
0.92
0.94
0.96
0.98
1.00 aw
Figure 3 Water content and aw of cheeses. Reproduced from, Banon S and Hardy J (2002), eau dans les produits laiters. In: LeMeste M, Lorient D, and Simatos D (eds.) L’Eau dans les Aliments. pp. 235–238. Paris: Lavoisier.
1 Skim milk
Lactose
Water activity
0.98
0.96 Lactic acid 0.94 NaCl 0.92
0.9 0
10
20
30
40
50
Solute concentration (% w/w) Figure 4 Water activity versus concentration for some dairy components: – experimental values from freezing point depression: 4 , spray-dried milks (solute concentration as non-fat solids) (Chen P, Chen XD, and Free KW (1996) Measurment and data interpretation of the freezing point depression of milk. Journal of Food Engineering 30: 239–253) ^, lactose and &, NaCl (Lerici CR, Piva M, and Dalla Rosa M (1983) Water activity and freezing point depression of aqueous solutions and liquid foods. Journal of Food Science 48: 1667–1669). – bold lines calculated from Norrish equation: lactose (Miracco JL, Alzamora SM, Chirife J, and Ferro Fontan C (1981) On the water activity of lactose solutions. Journal Food Science 46: 1612–1613); lactic acid (Chirife J and Ferro Fontan C (1980) The prediction of water activity in aqueous solutions in connection with intermediate moisture foods. V. Experimental investigation of the aw lowering behaviour of sodium lactate and some related compounds. Journal of Food Science 45: 802–804). – bold line for NaCl: CRC Handbook of Chemistry and Physics. – dotted lines: values calculated from Raoult’s law. Note that the aw of skim milk is very similar to that of lactose solutions in this aw range. The large depression of aW by NaCl is due to its low molecular weight and due to its dissociation into two ‘active particles’ (ions). Lactic acid has been considered as nondissociated by the authors.
718 Water in Dairy Products | Analysis and Measurement of Water Activity
Water content (g water 100 g −1 dw)
35
Freeze-dried skim milk, ads. GAB Freeze-dried skim milk, ads. (experimental) Yogurt, des. GAB Freeze-dried yogurt, ads. GAB Spray-dried yogurt, ads. GAB Yogurt powder, ads. Halsey
30 25 20 15 10 5 0 0
0.1
0.2
0.3
0.4 0.5 Water activity
0.6
0.7
0.8
0.9
Figure 5 Water sorption isotherms for skim milk powder and yogurts. The experimental data for milk showing that the sorbed water amount remains constant (and even decreases) for aW >0.66 indicate that lactose is crystallizing (crystals of anhydrous lactose are able to adsorb much less water than amorphous lactose). Lines are from GAB or Halsey models, as indicated in the figure. (ads, adsorption; des, desorption). Freeze-dried skim milk: Jouppila K and Roos YH (1994) Glass transitions and crystallization in milk powders. Journal of Dairy Science 77: 2907–2915; yogurt, freeze-dried and spray-dried yogurt: Kim SS and Bhowmik SR (1994) Moisture sorption isotherms of concentrated yogurt and microwave vacuum dried yogurt powder. Journal of Food Engineering 21: 157–175; yogurt powder: Wolf W, Spiess WEL, and Jung G (1973) cited by Iglesias HA and Chirife J (1982) Handbook of Food Isotherms: Water Sorption Parameters for Food and Food Components. New York: Academic Press.
Water content (g water 100 g−1 dw)
35 30 25
Na caseinate Whey protein isolate 1 Whey protein isolate 2 Micellar casein Lactose
20 15 10 5 0 0.0
0.2
0.4
0.6
0.8
1.0
Water activity Figure 6 Water sorption isotherms for lactose (adsorption, 20–38 C, Bronlund J and Paterson T (2004) Moisture sorption isotherms for crystalline, amorphous and predominanthy crystalline lactose powders. International Dairy Journal 14: 247–254), micellar casein and whey protein isolate 2 (adsorption, 4–37 C, Foster KD, Bronlund JE, and Paterson T (2005) The prediction of moisture sorption isotherms for dairy powder. International Dairy Journal 15: 411–418), whey protein isolate 1 (adsorption, 23 C, Zhou P and Labuza TP (2007) Effect of water content on glass transition and protein aggregation of whey protein powders during short-term storage. Food Biophysics 2: 108. DOI: 10.1007/s11483-007-9037-4), and Na caseinate (adsorption, 25 C, Weisser H (1985) Influence of temperature on sorption equilibria. In: Simatos D and Multon J-L (eds.) Properties of Water in Foods, pp. 95–118. Dordrecht: Martinus Nijhoff Publishers). The lines are from the GAB model.
Water in Dairy Products | Analysis and Measurement of Water Activity 100
β Anhydrous
Pasteurization 80
Atomization
Spray-drying
Concentration Homogenization
60 Temperature (⬚C)
719
Solution (emulsion)
40
Ts
Spontaneous nucleation
Viscous state crystal growth α Hydrate Lactose crystals and solution
20 Milk 0
Powder
Delay 10 min 1h
Tm
Eutectic
Rubbery zone β Anhydrous crystallization
Tg
1 day
−20 Ice and solution
−40 −60
Glassy solid state Cg⬘, Tg⬘
0
10
20
30
40
50
60
70
80
90
100
Total solids (%) Figure 7 State diagram for milk, based on lactose (Vuattaz G (2002) The phase diagram of milk: A new tool for optimising the drying process. Lait 82: 485–500). Ts, solubility curve; Tm, freezing point versus concentration; Tg, temperature of glass transition versus concentration. The dry product (with a water content below 5%) is a glass at room temperature. If the ambient temperature is increased, or if Tg is decreased as a consequence of an increase in water content, the product becomes ‘rubbery’. An increase in molecular mobility allows crystallization of lactose. The larger the distance of water content/temperature conditions to Tg, the shorter the delay, as indicated on the graph.
transition, as determined by its temperature and water content and (2) the duration of its stay under these conditions. A food material such as skim milk powder in the dry state is in a glassy state at room temperature (its glass transition temperature Tg is 100 C). When water is sorbed, the material is plasticized, that is, its Tg decreases to 20 C for a critical water content of 8%. For a higher water content, the product is transformed into a viscoelastic material (supercooled liquid or rubber depending on the composition) (Figure 7). In the rubbery state, the product is in a metastable state: amorphous constituents (e.g., lactose) may crystallize; the more distant the product is from its glass transition, the faster the crystallization. In the glassy state, the product is out of equilibrium: it may undergo some evolution of its structure (physical aging); the closer the temperature is to Tg, the faster the evolution, but in practice it is always very slow. In both the rubbery and glassy states, the mobility of water remains rather high, and one may expect that equilibration of aw will be usually accomplished within times of interest to the food technologist, as suggest some observations. In some situations, however, it must be recognized that what is measured is the relative humidity of the atmosphere in contact with the product, at best in a pseudoequilibrium state. Hence it would be safer to use the term ‘apparent water activity’ (Expert Panel, ISOPOW, 2000).
Water Activity versus Bound/Free Water Water activity is a way of measuring the energy status of water in a product. It gets depressed as a result of water structure being perturbed and due to interactions between water and solute molecules. Nevertheless, it does not allow one to define a fraction of bound water. The first point is the broad range of interaction energies between water and solutes: from the van der Waals interactions (1 kJ mol1) to hydrogen bonds (10–40 kJ mol1) and ion–water interactions (50–100 kJ mol1 for univalent ions and even more for multivalent ions). It can be noted that water–water and water–solute interactions that occur through H bonds have strength values of the same order; water molecules cannot therefore be viewed as strongly bound to solutes. Actually, spectroscopic observations and molecular dynamics simulations show that water molecules remain highly mobile, even when in direct contact with solute molecules. In liquid water at room temperature, water molecules tumble about with a reorientation time of 2 ps (2 1012 s). Although the properties (orientation, mobility) of some water molecules belonging to the primary hydration shell of ions are strongly modified, they still exchange with bulk water, albeit more slowly (e.g., lifetime 109 s for Na+). Similarly, molecular dynamics simulations of a sugar molecule in an aqueous solution show water molecules located at specific sites on the sugar molecule; however, within a few picoseconds,
720 Water in Dairy Products | Analysis and Measurement of Water Activity
these molecules escape into the bulk water and are replaced by other water molecules. From spectroscopic methods, the ratio s =bulk of the rotational correlation time of water molecules in direct contact with the surface of solutes and that of bulk water is found to be in the range 1.0–2.5 at room temperature for free amino acids and other small organic molecules. For proteins in solution, only water molecules in direct contact with the protein surface are significantly perturbed, although they are still highly mobile, with mean residence times in the range 10–100 ps and the ratio s =bulk averaging around 5.5. Only water molecules buried within the protein have residence times longer than 1 ns (in the range 108–104 s at room temperature). It is estimated that reduction of the mobility of water molecules in contact with proteins is not due to the interaction with the protein per se but rather due to their physical entrapment within the protein matrix. Even in low-moisture solid products, water molecules appear to have a relatively high freedom of motion. The translational diffusion coefficient of water in a hydrated polysaccharide (pullulan with 20% water) has been estimated at 5 1012 m2 s1 at 0 C, that is, 1000 times lower than in liquid water, whereas the viscosity of the system in this glassy state (50 C below the glass transition temperature) would be 1015 times higher. Based on the multilayer adsorption process, mathematical expressions have been derived to describe sorption isotherms (Table 1). The BET expression correctly describes the experimental curves of food materials for 0.2 < aw < 0.5; the GAB expression, which is derived from the BET expression, can be fitted satisfactorily to experimental data up to aw 0.9. The fitting parameters of these expressions are commonly used to calculate the water content corresponding to the monolayer and sorption energies, which are supposed to give information about the interactions of water with the material components. However, this use of the BET and GAB expressions is very questionable. First, the hysteresis observed between sorption and desorption points to the non-equilibrium character of the isotherms. Moreover, it is increasingly being admitted that the basic assumptions of the BET model are not fulfilled in the case of water sorbed on polar materials (energy equivalence of all sites on the sorbing solid surface). In the end, the plastifying action of water on the solid certainly plays a role in determining the form of the sorption curves. A plausible view would be that the sorption process changes at glass transition: in the glassy state, where the conformation is ‘frozen’, an adsorption model (such as the Freundlich model, assuming a distribution of independent sorption sites with different energies) would be suitable, whereas in the supercooled state, the isotherm could be based on the Flory–Huggins theory of polymer solutions.
Water Activity versus Food Quality and Food Processing Operations In the 1960s, water activity became the favored parameter to characterize the availability of water to control the physical, chemical, or biological evolutions in foods. This originated in observations showing that the aw values of media generally correlated well with the potential for growth and metabolic activity of microorganisms. Stability maps were produced, indicating aw thresholds and aw ranges corresponding to the maximal rates of chemical and biological evolutions. In the late 1980s, the value of aw as a predictive index of food stability was questioned, first because most food products are not in a state of thermodynamic equilibrium, as discussed before; moreover, emphasis was placed on the importance of molecular mobility, namely in connection with the glass transition phenomenon. The respective relevance of both approaches, aw and glass transition, has been discussed vigorously. Currently, a consensus appears to have become established, to recognize that both may have an essential role, in a particular domain, depending on the type of product or the objectives. Microbial cells cannot be considered to behave as true osmometers; other parameters, such as pH, nature of the solutes in the medium, and mobility of the metabolites, must also be taken into account. Glass transition concepts, however, do not provide any better alternatives than aw as a predictor of microbial behavior. Water activity is now generally recognized as an essential parameter for all aspects of microbial activity: germination and growth, and production of toxins and aroma. As regards texture, water content seems a better predictor than aw; for instance, the texture of cheese was found to be better correlated to water content (coefficient of correlation with an extrusion force = 0.867) and fat content than to aw (coefficient of correlation = 0.548). Crystallization (e.g., of lactose in milk powder) is a good example of evolution, the kinetics of which are controlled by water content and temperature, in connection with glass transition. With regard to chemical and biochemical reactions, the implication of water is complex: besides being a reactant for many reactions in foods and being necessary for the establishment of the appropriate conformation of enzymes, it constitutes the usual solvent for reactants and imparts the necessary mobility to reactants and reaction products. Water activity does not seem to be directly involved in the control of reaction kinetics; the observation that a reaction (e.g., non-enzymatic browning) occurs, in various food products, with a maximum rate in a characteristic aw range most likely can be explained by these products having similar sorption isotherms and similar Tg values (e.g., because of a high content of biopolymers). Actually, if mobility is increased in these products, through the addition of a liquid fat or of a
Table 1 Expressions to describe or predict relations between water activity and water content Model Raoult’s law
Norrish
Pitzer
Equation aW ¼ Xw ¼
m=18 m=18 þ ð100=Ms Þ
i n n n n 0:5 M X M X ¼ 1 þ jzM zX jF þ 2 CMX B MX þ 22 n n
i z2i jzM zX j ¼ P i i
Dilute solutions
References (for dairy products)
Nonelectrolyte solutions
Chirife and Ferro Fontan (1980), Miracco et al. (1981)
¼ osmotic coefficient i ¼ molality of ion i ZM, ZX, nM, nX = charges and numbers of ions M and X n ¼ nM + nX I ¼ ionic strength BMX(0), BMX(1), CMX = Pitzer coefficients for the electrolyte MXb
Electrolyte solutions
Ferro Fontan et al. (1980)
2 ¼ volume fraction of the polymer n = number of polymeric segments = fitting interaction parameter
aw > 0:90
n>1
Glassy state
m1B ¼ water content of the « monolayer »
0.2 < aw < 0.5
Ruegg amd Blanc (1979)
m1G ¼ water content of the « monolayer »
0.2 < aw < 0.9
Bronlund and Paterson (2004), Jouppila and Ross (1994), Kim and Bhowmik (1994), Lin et al. (2005), Lomauro et al. (1985), Weisser (1985) Jouppila and Rose (1994)
K ¼ empirical constant for the solutea
i
P
Xw ¼ mole fraction of water
Xs ¼ mole fraction of solute
P
I0:5 F ¼ – 0:392 1 þ 1:2I0:5
Range
Ms ¼ molecular weight of the solute ¼ dissociation constant of electrolyte
aW ¼ Xw exp K Xs2
ln aw ¼ – 0:180 2
Parameters
I ¼ 0:5
P i
i z2i
BMX ¼ BMX ð0Þ þ BMX ð1Þexp – 2l0:5
i
Flory–Huggins
1 ln aw ¼ lnð1 – 2 Þ þ 1 – 2 þ 22 n
Freundlich
1=n m ¼ Ca w
BET
m¼
m1B CB aw ð1 – aw Þ½1 þ ðCB – 1Þaw
GAB
m¼
m1G CG Ka w ð1 – Ka w Þ½1 þ ðCG – 1ÞKaw
Kuhn Halsey Peleg Lewicki
K1 þ K2 ln aw P ln aw ¼ – 1 mP2 n n m ¼ k1 aw1 þ k2 aw2 1 b–1 m ¼ Að – 1Þ aw m¼
Iglesias and Chirife (1982), Kim and Bhowmik (1994), Miracco et al. (1981)
(Continued )
Table 1 (Continued) Model
Equation
Parameters
Ross
awmix ¼ ðaw1 Þ . . . ðawi Þ . . . ðawn Þ
SalwynSlawson
P Mi aw i tani awmix ¼ P Mi tani
awmix ¼ aw of a mixture of n solutes awi = aw of a solution where the solute i would be dissolved in all the water of the mixture awmix = aw of a mixture of n components for which SI are known Mi = dry weight of the component i awi = initial aw of component i tani = average slope of the SI of component i in the range of awi
Additive model
mðaw Þ ¼
a
n P 1
M i miðaw Þ
m=predicted water content at aw Mi = mass fraction of component i (db) Mi(aw) = water content of i at aw
Range
References (for dairy products)
4
K = 10.2 for lactose; K=1.59 for lactic acid. For NaCl, BMX(0)¼0.076 5, NaCl, BMX(1)=0.266 4, CMX¼0.001 27. Bronlund J and Paterson T (2004) Moisture sorption isotherms for crystalline, amorphous and predominantly crystalline lactose powders. International Dairy Journal 14: 247–254. Cheirife J and Ferro Fontan C (1980) The prediction of water activity in aqueous solutions in connection with intermediate moisture foods. V. Experimental investigation of the aw lowering behaviour of sodium lactate and some related compounds. Journal of Food Science 45: 802–804. Ferro Fontan C, Benmergui EA, and Chirife J (1980) The predication of water activity of aqueous solutions in connection with intermediate moisture foods. III: aw prediction in multicomponent strong electrolyte aqueous solutions. Journal of Food Technology 15: 47–58. Foster KD, Bronlund JE, and Paterson AHJ (2005) The prediction of moisture sorption isotherms for dairy powder. Internation Dairy Journal 15: 411–418. Iglesias HA and Chirife J (1982) Handbook of Food Isotherms: Water Sorption Parameters for Food and Food Components. New York: Academic Press. Jouppila K and Roos YH (1994) Glass transitions and crystallization in milk powders. Journal of Dairy Science 77: 2907–2915. Kim SS and Bhowmik SR (1994) Moisture sorption isotherms of concentrated yogurt and microwave vacuum dried yogurt powder. Journal of Food Engineering 21: 157–175. Lin SXQ, Chen XD, and Pearce DL (2005) Desorption isotherm of milk powders at elevated temperatures and over a wide range of relative humidity. Journal of Food Engineering 68: 257–264. Lomauro CJ, Bakshi AS, and Labuza TP (1985) Evalution of food moister sorption isothermm equation. Part II: milk, coffee, tea, nuts, oilseeds, spices and starchy foods. Lebensmittel Wissenschaft und technologie 18: 118–124. Miracco JL, Alzamora SM, Chirife J, and Ferro Fontan C (1981) On the water activity of lactose solutions. Journal of Food Science 46: 1612–1613. Ruegg M and Blanc B (1979) Hydration of casein micelles: kinetics and isotherms of water sorption of micellar casein isolated from fresh and heat - treated milk. Journal of Dairy Research 40: 325–328. Weisser H (1985) In: Simatos D and Multon J-L (eds.) Properties of Water in Food, pp. 95–118. Dordrecht: Martinus Nijhoff Publishers.
b
Water in Dairy Products | Analysis and Measurement of Water Activity
723
Table 2 Water activity of cheese vs. chemical composition
Equation
Range
Std error of estimate
Concentration units
References
aw ¼ 0.94 0.005 6(NPN) 0.005 9(NaCl) 0.001 9(Ash-NaCl) þ 0.015pH aw ¼ 1.004 8 0.038 6(NaCl)
aw > 0.90
0.009
g per 100 g water
Ruegg (1985)
Fresh cheeses (moisture > 40% no proteolysis) Bacterial-ripened cheeses Blue cheeses French Emmental after brining after ripening
0.01
mol kg1 water
Esteban and Marcos (1990)
aw ¼ 1.023 4 0.007 0(Ash) aw ¼ 0.980 8 0.005 8(Ash) aw = 0.99 0 0.936(NaCl) þ 0.951(water)(NaCl) aw = 1.066 0.194(water) 3.490(NaCl) 0.331(NH2) þ 6.509(water)(NaCl) þ 0.571(water)(NH2)
g per 100 g water
0.006 0.006
g per 100 g water kgNaCl kg1 water kgwater kg1 dry solids mol eq glycine kg1 cheese
Saurel et al. (2004)
From Ruegg M (1985) Water in dairy products related to quality, with special reference to cheese. In: Simatos D and Multon J-L (eds.) Properties of water in Foods, pp. 603–625. Dordrecht: Martinus Nijhoff Publishers; Esteban MA and Marcos A (1990) Equations for calculation of water activity in cheese from its chemical composition: A review. Food Chemistry 36: 179–186; Saurel R, Pajonk A, and Andrieu J (2004) Modelling of French Emmental cheese water activity during salting and ripening periods. Journal of Food Engineering 63: 163–170.
plasticizer such as glycerol, the aw range for maximal reaction rate can be shifted widely. However, aw continues to serve as a useful guide for chemical stability because it allows prediction of the water content of the product in a given environment (so long as the specific sorption isotherm of the product is known). More generally, aw is an essential tool in food technology, because it allows description of the gradient that will determine the transfer of water between two compartments having different initial relative vapor pressures in a multidomain food system, or between a food product and its environment during drying or osmotic dehydration, or during storage.
Principles of Measurement Physical Properties to Be Measured Water activity cannot be measured directly, but eqn [4] allows derivation of relations between aw and some
physical properties (Table 3), which lead to measurement methods. Water vapor pressure
When the pressure of water vapor is changed from p0 to p (Figure 1(a)), the change in free energy can be calculated from basic thermodynamics (and assuming that water vapor behaves as a perfect gas) to be G ¼ RT ln p=p0 . Then aw ¼
p p0
½7
100 p/p0 (%) defines the relative humidity (RH) of the atmosphere in equilibrium with the product, and aw can be obtained from the measurement of p by various methods and calculation using the known p0 values at the temperature of measurement. measurement with a manometer: The air must be • Direct evacuated from the apparatus; drying of the sample during this operation must be kept at a negligible
Table 3 Relations between water activity and physical properties (1) Equilibrium relative humidity (2) Freezing point depression
(3) Osmotic pressure
aw ¼
p ERH ¼ p0 100
ln aw ¼
H m T – T0 Cp ðT – T0 Þ2 þ R TT0 2RT 2
V ln aw ¼ – w RT
p ¼ partial water vapor pressure (Pa) p0 ¼ saturated water vapor pressure (Pa) at temperature T ERH ¼ equilibrium relative humidity T0, T ¼ temperature of freezing of pure water and of the sample (K) Hm ¼ melting enthalpy of ice at T0 (¼ 6 kJ mol1) Cp ¼ difference in the specific heat of ice and liquid water (¼ 37.697 J K1 mol1) R ¼ 8.314 J K 1 mol1 Q ¼ osmotic pressure (Pa) V ¼ molar volume (8106 m3 mol1) T ¼ temperature (K) R ¼ 8.314 J K 1 mol1
724 Water in Dairy Products | Analysis and Measurement of Water Activity
Mechanical/electrical properties varying with RH Fan
Unlike the preceding methods, which can be absolute measurements, these methods require calibration of the sensor. The sensor can be a thread-like material (a hair or a synthetic polymer) the length of which, when exposed to a force of given strength, depends on its water content and is measured. The sensor can also be a material the electrical conductivity or dielectric constant of which depends on the water content and which is measured.
Optical sensor Mirror
Infrared sensor
Sample
Sorption isotherms
Figure 8 Schematic diagram of a dew point cell. The mirror is cooled progressively (e.g., via a Peltier device). The optical sensor emits light onto the mirror and detects the reflected light. When condensation occurs, the temperature of the mirror is recorded (giving the value of pW). The temperature of the sample is recorded via the infrared sensor (giving the value of p0 w ). Diagram from Decagon.
•
level, for instance, by freezing it. This method is not suitable for products containing volatiles. Moreover, because of its technical requirements, its use is restricted to the laboratory as a standard method. Dew point temperature: Figure 8 shows the experimental setup for measuring dew point temperature. As the mirror is progressively cooled, condensation occurs when its temperature is that for which the saturated vapor pressure is equal to p. Commercial instruments claim a measurement range of 0.030–1.000 aw with an accuracy of 0.003 aw.
Water activity can be determined from SI of the product after measurement of the water content. In this case, it is more practical to have a mathematical expression of the SI, allowing interpolations. Besides the ones cited before, many expressions have been proposed to describe SI, a few examples of which are given in Table 1. For milk products, as for other foods, GAB expression was shown to be fitted satisfactorily to experimental data up to aw 0.90. To create SI, representative food samples that are initially dried (for adsorption isotherms) or hydrated (for desorption) are placed in controlled humidity chambers at constant temperature and are weighted periodically until a constant weight is reached. In the static desiccators method (Figure 9), different levels of RH are obtained using 1
2
3
4
5
Freezing point
The second equation in Table 3 is derived from thermodynamics. Cp is assumed to be independent of temperature in the range T–T0. This assumption does not result in any significant loss of accuracy. Considering that chemical potential must be equal in both the phases present in a frozen solution, that is, ice and the concentrated solution resulting from the separation of ice, the vapor pressure at equilibrium with the frozen product is pice. The reference vapor pressure (p0) is the vapor pressure of supercooled water at the same temperature (T). Then aw ¼
pice p0
½8
Both expressions give very similar results, confirming the validity of both. The measurement of T, where the first ice crystals are formed, by a classical cryoscopic measurement, gives accurate values of aw (up to 0.001 aw) in the range 0.80–1. Actually, what is measured is aw of the product at T. The differences with aw at 25 C are shown to be not more than 0.01 aw. The values may be corrected to obtain more accurate ones at the desired temperature.
Figure 9 Sorption device as standardized for the COST Project 90 (Wolf W, Spiess WEL, and Jung G (1985) Standardization of isotherm measurement (COST Project 90 and 90 bis). In: Simatos D and Multon J-L (eds.) Properties of Water in Foods, pp. 661–679. Dordrecht: Martinus Nijhoff Publishers). 1. water bath, 2. sorption container (1-l glass jar, with a vapor-tight lid), 3. weighing bottle with a ground-in stopper, 4. Petri dish on trivet, 5. saturated salt solution.
Water in Dairy Products | Analysis and Measurement of Water Activity
saturated salt slurries that have known aw values. Commercial devices control RH by mixing wet and dry gas streams and continuously monitor weight changes of the samples.
Equilibrium The issue of equilibrium has already been mentioned concerning the internal moisture equilibrium of the product; equilibration of water vapor pressure between the sample, headspace of the measurement chamber, and the probe is also an important practical problem. Theoretically, the equilibration process is slowed as vapor pressures come closer, and equilibration time is infinite. Practically, therefore, the rate of change of RH is monitored continuously and the measurement is ended when the rate of change falls below a chosen limit. Equilibration of most products typically requires 45–60 min and can take as long as a couple of hours. Gentle ventilation in the measuring chamber may reduce equilibration time by 50%. For the generation of SI by the desiccators method, reducing the total pressure in the containers also reduces the equilibration time by a factor of 2–3. The volume and geometry of the sample are important parameters. Increasing its surface area (possibly by grinding) will reduce equilibration time; care should also be taken to ensure that the amount of sample is large enough, as compared to the headspace volume of the chamber (and to the surface area of the dew point mirror), so that the water lost by the sample will not significantly decrease its water content. Several commercial instruments designed to generate SI change the controlled RH in a stepwise progression; some another instruments uses only air saturated with
725
water (for adsorption) or dry air (for desorption), and continuously monitor weight changes and RH in the chamber with a dew point sensor. While the SI obtained with the former devices may be considered to represent equilibrium states, the latter are expected to provide information on the evolutions (glass transition, crystallization) occurring in the sample during sorption (Figures 10 and 11).
Temperature Water activity of a product shows only small variations with temperature. For ideal solutions, aw, being identical to Xw, is independent of temperature; even for nonideal systems, changes are small. SI of various dairy powders show no obvious temperature dependence between 4 and 38 C; only at 50 C the amounts of sorbed water are lower. Similarly, the aw measured for six different cheeses between 5 and 30 C showed no significant temperature dependence. The temperature of a sample, however, is an important concern for aw measurements. For methods relying on the measurement of pw (direct measurement of pw, dew point), an error in the sample temperature measurement will result in an error in p0 w and consequently in aw. Between 20 and 25 C, a 1 C error in the sample temperature measurement represents a 6% error in p0 w and aw. Similarly, to achieve an accuracy of 0.003 aw within the range of 0.800–1.000 aw, the temperature of a dew point sensor is to be measured with an accuracy of 0.05 C. Because the temperature dependence of aw is small, the actual temperature need not to be known precisely with apparatus measuring RH, so long as both temperatures of sample and of sensor are the same.
Figure 10 Two dynamic methods of sorption isotherm generation: dynamic vapor sorption (DVS): change in mass (blue) and change in target RH (red) versus time; dynamic dewpoint isotherm (DDI): sample weight (red) and measured RH (blue) versus time. Carter B (Decagon), personal communication.
726 Water in Dairy Products | Analysis and Measurement of Water Activity
Moisture content (% d.b.)
Traditional desiccator 20 18 16 14 12 10 8 6 4 2 0
GAB model fit
DDI method
Dissolution onset Crystallization onset Surface and bulk adsorption Surface adsorption
Glass transition 0
0.2
0.4 0.6 Water activity
0.8
1
Figure 11 Sorption isotherm of milk powder (adsorption) obtained by continuously changing RH above the sample (DDI method), as compared to that obtained with the desiccators method. As water is adsorbed by the dry product, the temperature of glass transition is lowered to the working temperature; the glassy product is plasticized, water is then more easily adsorbed in the bulk of the sample. With the increase in molecular mobility,crystallization of lactose develops. Redrawn from Carter B (Decagon), personal communication.
See also: Cheese: Microbiology of Cheese. Concentrated Dairy Products: Sweetened Condensed Milk. Dehydrated Dairy Products: Milk Powder: Physical and Functional Properties of Milk Powders. Water in Dairy Products: Water in Dairy Products: Significance.
Further Reading Chirife J and Buera MP (1996) Water activity, water glass dynamics and the control of microbiological growth in foods. Critical Review in Food Science and Nutrition 36: 465–513. Fontana AJ (2007) Measurement of water activity, moisture sorption isotherms, and moisture content of foods. In: Barbosa-Canovas GV, Fontana AJ, Schmidt SJ, and Labuza TP (eds.) Water Activity in
Foods: Fundamentals and Applications, pp. 155–171. Ames, IA: Blackwell Publication. Halle B (2004) Protein hydration dynamics in solution: A critical survey. Philosophical Transactions of the Royal Society of London. Series B 359: 1207–1224. Karel M (1999) Food research tasks at the beginning of the new millennium. A personal vision. In: Roos YH, Leslie RB, and Lillford PJ (eds.) Water Management in the Design and Distribution of Quality Foods (ISOPOW VII), pp. 535–559. Lancaster, PA: Technomic. LeMeste M, Champion D, Roudaut G, Blond G, and Simatos D (2002) Glass transition and food technology: A critical appraisal. Journal of Food Science 67: 2444–2458. Simatos D, Champion D, Lorient D, Loupiac C, and Roudaut G (2009) Water in dairy products. In: McSweeney PLH and Fox PF (eds.) Advanced Dairy Chemistry-3. Lactose, Water, Salts and Minor Constituents 3rd edn., 457–526, New York, Springer Science.
WELFARE OF ANIMALS, POLITICAL AND MANAGEMENT ISSUES H D Guither and S E Curtis, University of Illinois–Urbana, Urbana, IL, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2735–2739, ª 2002, Elsevier Ltd.
Introduction Since World War II, a major revolution in social concern with the welfare and moral status of agricultural animals has emerged. The animal rights movement has arisen from old ideas but with new philosophies, emphasizing moral and ethical standards for how human beings should treat animals. Public policy establishing the animal welfare movement began in the United Kingdom with the passage of an act in 1835 to ‘‘consolidate and amend the several laws relating to the cruelty and improper treatment of animals’’. In 1911 the UK Parliament passed the Protection of Animals Act which is still in force. It was established on the principle that, although human beings are free to subjugate animals, it is wrong for people to cause animals to suffer unnecessarily. The cultural and social evolution of animal protection in Europe has led to changes in the United States.
Terms Defined Animal protection refers to all efforts to prevent cruelty, improve humane treatment, reduce stress and monitor research with animals. Animal welfare generally describes the philosophy espoused by those who support the humane treatment of all animals without concern for their ultimate use. An ‘animal welfarist’ believes that human beings have the right to use animals so long as suffering is reduced or eliminated. Those who believe in animal welfare work for the reform of abusive or neglectful situations to alleviate animal suffering. Farmers have historically been perceived as strong supporters of animal welfare because they believed that animals raised under humane conditions and practices would be the most productive and profitable. The animal rights philosophy, encompassing animal liberation, includes some fundamental differences from animal welfarism. It involves the idea that nonhuman animals are sentient beings – that they have the capacity consciously to experience pain and pleasure, among other things. Accompanying this belief is the notion that
animals have certain inalienable moral rights which humans should not violate.
Philosophers, Activists and Political Action Ruth Harrison, an English homemaker, initiated much of the public concern for the welfare of farm animals under modern production methods when her book Animal Machines was published in 1964. Following publication of her book, the UK Parliament called for an investigation. In 1965, the Brambell Committee, a group of scientists and concerned citizens, issued their report calling for certain mandatory standards that would conform to good husbandry in agricultural/animal production systems. The political dimension of the animal rights and animal welfare movements involves individual and group efforts supporting or opposing specific issues. The methods include campaigns to influence legislation through letter-writing and other direct contacts; seminars and media events to influence members of legislative bodies and public opinion; demonstrations to draw public attention to what activists see as improper treatment; inviting sympathetic legislators and government officials to speak or receive awards at meetings and other special events; and securing sponsorship of bills in various legislative bodies. The participating activists may be classified as reformists or abolitionists. Political action by animal rights and animal welfare advocates covers many issues from many different perspectives. However, four phases in these movements to influence political action can be identified: (1) identifying the problems of animal mistreatment; (2) developing appropriate ideology to cover the principles and concerns; (3) understanding how change occurs; and (4) developing explicit standards of ethics for advocating change. Although intensive methods of animal production, which use more capital and less labor than traditional methods do, have improved production efficiency, they have at times put milk and meat producers in defensive positions because animal activists have branded certain
727
728 Welfare of Animals, Political and Management Issues
ones of these contemporary methods as ‘factory farming’. Producers adopted high-technology, intensive production systems because they would allow them to produce more product by substituting capital for labor to achieve lower cost per unit product. Critics, however, see intensive animal agriculture differently because their views are based on philosophical thinking, feelings or opinions, often with little exposure to or understanding of the economics, the science or the actual practice of agricultural/animal production.
Dairy Cattle, Animal Welfare and Management Issues A British report in 1983 identified animal protectionists’ major animal welfare concerns for dairy animals: of quality and quantity of individual atten• reduction tion in larger herds of calves with caustic chemicals with or • dehorning without anesthetic stanchion tying of cows, especially without • prolonged exercise for separation of cow and calf • need neglect of unwanted bull calves • raising replacements in individual hutches rather than • in groups of veal calves in small crates • confinement failure to employ research knowledge • production-relatedwelfare-related susceptibility to disease and meta• bolic disorders • transportation of injured and sick animals to slaughter. All of these issues continue to be mentioned to this day (but much progress has been made in correcting those issues that deserved attention). In addition another issue has come on the scene – docking cows’ tails. Several of these issues have been addressed by scientists and government officials around the western hemisphere in the intervening two decades. The UK Ministry of Agriculture, Fisheries and Food (now the Department of the Environment, Food and Rural Affairs) issued its codes of recommendations for the welfare of cattle emphasizing avoiding discomfort or distress and allowing the animals to fulfil their ‘basic needs’. The recommendations called for these provisions to be considered: comfort and shelter, readily accessible fresh water and a diet to maintain full health and vigor; freedom of movement; company of other animals, particularly of like kind; and opportunity to exercise most normal patterns of behavior. Specific recommendations were identified for buildings, fire and other emergency precautions, ventilation and temperature, lighting, mechanical equipment
and services, space allowance, feed and water and management. Recommended codes of dairy cattle and veal calf husbandry practices also have been published in Canada. Guidelines for the care of dairy cattle and veal calves have been published by dairy-industry stakeholders and scientists in the United States. With respect to some of the issues listed above, much progress has been made, and general consensus currently stands as follows: 1. Cow behavior and care in large groups can be satisfactory. 2. Dehorning is beneficial, and its conduct has been refined to make it more humane. 3. Very few dairy cows are stanchioned for long periods nowadays. 4. Separating calf from cow very soon after birth is justifiable in terms of the dam’s udder health so long as the calf receives an adequate dose of appropriate colostrum the first day after delivery. If a calf is to be weaned early, in terms of minimizing the stress of separation and loss it should be done as soon after birth as possible. 5. Dairy farmers are being educated as to the necessity of ensuring that surplus bull calves (to be finished as veal calves or dairy beef) be cared for just as heifer calves being kept as herd replacements, especially with respect to receiving an adequate dose of colostrum the first day after birth. 6. Individual outdoor hutches – in terms of calf sanitation, health and performance – are preferable to group housing for calves for the first 2 months after birth. This is so, regardless of the nature of the local climate. Benefits of the opportunity to socialize with other calves are outweighed by vices and other practical problems associated with group-rearing of young calves. 7. Although there have been numerous studies in many places seeking a suitable alternative to the conventional veal-calf stall, no alternative has emerged. Applied discovery research continues along this line. 8. There remains in the industry a strong tendency to follow economic dictates rather than ethical ones when the two are in conflict. Some of the reasons for this seem to be that, unfortunately, the correspondence of high animal state-of-being with high animal performance rate has not been adequately demonstrated by scientists, so the whole economic situation in such cases may be neither understood nor considered. Ironically, criticism and charges by animal protection advocates have probably dampened the support resources the industry and the governments of the various nations have devoted to such research, the results of which would probably for the most part be ‘win–win’ for agriculturists and animal protectionists alike.
Welfare of Animals, Political and Management Issues 729
9. Simply put, with modern animal production systems come the smouldering, multifactorial production diseases characterized by long-term, moderate morbidity and low mortality. But on balance the overall health of the animals is roughly the same in intensive production systems as in extensive systems. In the latter systems, the animals are more likely to suffer from parasitic diseases and the acute infectious diseases characterized by short-term, severe morbidity and high mortality. 10. Most abattoirs nowadays refuse to permit nonambulatory animals to be off-loaded at their docks, so most nonambulatory cows (which became nonambulatory at the farm) are not on-loaded and transported in the first place. 11. A consensus regarding tail-docking of dairy cows is now forming. On balance the practice seems to have few, if any, advantages but several disadvantages.
Policy and Legal Aspects Calls for regulation of agricultural/animal care practices have been more successful in western Europe than in North America. The US House of Representatives did conduct hearings on the issues of veal calf husbandry and handling and transportation of nonambulatory animals in the late 1980s and early 1990s, but so far no legislation regulating these matters has been passed and signed into law. Some European countries, however, have set legal standards for animal husbandry on farms, although these standards often differ among nations. In 1986 the European Communities Council issued its directive for protection of animals used for ‘experimental and other scientific purposes’. The directive was designed to provide guidelines for uniform laws in the member countries. The objectives were to reduce the use of animals for experimental purposes to a minimum, ensure that they were adequately cared for, and avoid or minimize pain, suffering, distress and harm. The farm animal welfare policies and regulations in the United Kingdom are developed in line with European Union (EU) directives and have led the way for other European countries. The major issues around which all European animal welfare policies have evolved focus on housing, rearing, feeding, transporting, marketing and killing. In 1996 the EU Commission proposed that French, Italian and Dutch farmers could continue to use crates for raising veal calves until the year 2008, but new crates would be banned after 1998. The UK Department of the Environment, Food and Rural Affairs (DEFRA) recognizes that both ethical and scientific issues play a part in this issue. For advice and counsel on animal welfare matters, DEFRA looks first to the Farm Animal Welfare Council (FAWC), comprised of scientists, educators and producers.
The FAWC is expected to combine the use of appropriate new technology with efficient use of available resources and adequate provision for the welfare and behavioral needs of animals. More practices requiring a veterinary surgeon are spelled out. Citizens who believe a livestock owner is not following the welfare guidelines can file a complaint, and government inspectors then determine whether violations have occurred. In Sweden the 1988 Animal Protection Act established the most detailed and comprehensive laws dealing with animal welfare in any country. Livestock buildings had to have windows and provide space so all animals could lie at once and be able to move freely. Milk cows had to be sent out to pasture in the summer. In Switzerland, veal calves must receive iron and roughage in their rations. Differences within the EU exist on animal welfare policies. The northern countries tend to be more sympathetic to welfare policies than the southern countries. Eastern European countries are in transition, and animal welfare policies have much lower priority than other economic and social concerns. Producer attitudes toward animal welfare regulations in the western hemisphere have changed in recent years. Many now recognize that public opinion cannot be ignored if they are to maintain a market for their products. The development of welfare-oriented regulations for production practices is only part of the evolution of government influence. Along with concerns for the humane treatment of animals is the concern for the quality and safety of products and the environment. Production regulation also involves pollution controls, manure disposal, dead-animal disposal and the use of medicines and feed additives that could affect the safety of the processed animal product. Producers are consulted as new animal welfare regulations are developed, but in their minority position they must accept the final policy decision. Many of the regulatory guidelines simply represent good management practices that any considerate producer would follow. In Europe the policies and regulations established are primarily welfare-oriented, with less noticeable activism for animal rights per se than is observed in the United States. There is a growing consumer interest and awareness in Europe and North America about how food is produced. Although the primary concern is food safety, the humane treatment of animals is second and interest is growing. The rising profile of animal welfare in public awareness is contributing to growing demands for food that is labeled as having been produced under certain standards. The legal framework regarding animals in the United States has focused on concerns that they should be treated humanely. Successful legislative efforts fall into these categories: (1) humane treatment of animals in slaughter plants, in research facilities and in transit; (2) protection of
730 Welfare of Animals, Political and Management Issues
endangered animal species; (3) protection of fish, marine mammals and wildlife; (4) establishment of standards for conducting research with laboratory and other animal species; (5) protection of pets; and (6) control of terrorism. Dairy cattle owners have the most concern with categories (1), (4) and (6). One of the oldest federal laws deals with livestock transportation. The act applies to the transport of animals and requires a respite period unless the vehicle itself provides feed, water and space. In the United States, many bills dealing with animal protection have been introduced but none has been enacted. Those that would target dairy animals included bills attempting to identify humane animal husbandry practices for livestock, to establish a farm animal husbandry committee to investigate all aspects of intensive farm animal husbandry and to mandate diets and accommodations for veal calves. In 1989 the US House of Representatives Agriculture Subcommittee on Livestock, Dairy and Poultry held a hearing on a bill (HR 84) that attempted to prohibit certain practices in raising veal calves. Testimony revealed support for the bill from the Humane Society of the United States, Humane Farming Association and other animal rights/welfare groups. Veal producers, the US Secretary of Agriculture, and members of Congress with major producer constituencies opposed the bill. The bill failed to receive a favorable vote in committee. In the United States, advocates of a humane ethic for animals are gaining momentum based on a philosophy regarding the sacredness of life. Animal-welfare advocates emphasize that animals are sensing, living beings capable of feeling fear and pain and that they must be respected as such. Some members of Congress recognize the emotional commitment of animal-welfare advocates. However, the US animal industry’s strong public support, the close ties between trade associations and government agencies and the rapport between producers, state legislators and members of the US Congress provide major advantages over organizations and individuals’ philosophies that would disrupt the economically sound management practices used on dairy, livestock and poultry farms. See also: Office of International Epizooties: Mission, Organization and Animal Health Code.
Further Reading Albright JL (1983) Status of animal welfare awareness of producers and direction of animal welfare research in the future. Journal of Dairy Science 66: 2208–2226. Albright JL (1987) Dairy animal welfare: current and needed research. Journal of Dairy Science 70: 2711–2731.
Albright JL and Arave CW (1997) The Behaviour of Cattle. Wallingford: CAB International. Arave CW and Albright JL (1997) Animal welfare issues: dairy. In: Reynnells RD Eastwood BR and Editors (eds.) Animal Welfare Issues Compendium. Washington, DC: US Department of Agriculture, Cooperative State Research, Education and Extension Service. Birbeck AL (1991) A European perspective on farm animal welfare. Journal of the American Veterinary Medical Association 198: 1377–1380. Brambell FWR (1974) Report of the Technical Committee to Enquire into the Welfare of Animals Kept under Intensive Livestock Husbandry Systems. London: HMSO. Brown GE Jr (1997) Thirty Years of the Animal Welfare Act. Beltsville: National Agricultural Library. Canadian Agri-Food Council (1998a) Recommended Code of Practice for the Care and Handling of Farm Animals: Dairy Cattle. Ottawa, Canada: CARC. Canadian Agri-Food Council (1998b) Recommended Code of Practice for the Care and Handling of Farm Animals: Veal Calves. Ottawa, Canada: CARC. Curtis SE (1988) Animals in food production: American issues. Applied Animal Behavioral Science 20: 151–157. Curtis SE (1991) The welfare of agricultural animals. In: Blatz CV (ed.) Ethics and Agriculture: An Anthology on Current Issues in World Context, pp. 447–457. Moscow: University of Idaho Press. Curtis SE and Baker FH (eds.) (1997) The Well-Being of Agricultural Animals. Ames: Council for Agricultural Science and Technology. Dairy Quality Assurance Center (1995a) Caring for Dairy Animals: Reference Guide. Stratford: DQAC, Agri-Education. Dairy Quality Assurance Center (1995b) Caring for Dairy Animals: On-Farm Evaluation Guide. Stratford: DQAC, Agri-Education. Federation of Animal Science Societies (1999a) Guidelines for dairy cattle husbandry. In: Mench JA (ed.) Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Savoy: FASS. Federation of Animal Science Societies (1999b) Guidelines for veal calf husbandry. In: Mench JA (ed.) Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Savoy: FASS. Finsen L and Finsen S (1994) The Animal Rights Movement in America. New York: Twayne. Fox MW (1983) Animal welfare and the dairy industry. Journal of Dairy Science 66: 2221–2225. Garner R (1993) Animals, Politics and Morality. Manchester: Manchester University Press. Grandin T (ed.) (2000) Livestock Handling and Transport, 2nd edn. Wallingford: CAB International. Guither HD (1998) Animal Rights: History and Scope of a Radical Social Movement. Carbondale: Southern Illinois University Press. Guither HD and Curtis SE (1983) Animal Welfare: Developments in Europe: A Perspective for the United States. Urbana: University of Illinois at Urbana, Illinois Agriculture Experimental Station. Jasper JM and Nelkin D (1992) The Animal Rights Crusade: The Growth of a Moral Protest. New York: Free Press. Leahy MPT (1991) Against Liberation: Putting Animals in Perspective. London: Routledge. Ministry of Agriculture, Fisheries and Food (1983) Codes of Recommendations for Welfare of Livestock: Cattle. London: MAFF. Marquardt K, Levine HM and LaRochelle M (1993) Animal Scam. Washington, DC: Regnery Gateway. Matthews LR, Phipps A, Verkerk GA et al. (1995) The Effects of Tail Docking and Trimming on Milker Comfort and Dairy Cattle Health, Welfare and Production. Report to Ministry of Agriculture and Food, Animal Behavior and Welfare Research Center. Hamilton, New Zealand: AgResearch Ruakura. Regan T (1983) The Case for Animal Rights. Berkeley: University of California Press. Rollin BE (1981) Animal Rights and Human Morality. Buffalo: Prometheus Books. Van Horn HH and Wilcox CJ (eds.) (1992) Large Dairy Herd Management. Champaign: American Dairy Science Association.
WHEY PROCESSING
Contents Utilization and Products Demineralization
Utilization and Products P Jelen, University of Alberta, Edmonton, AB, Canada ª 2011 Elsevier Ltd. All rights reserved.
Introduction Whey, the greenish translucent liquid obtained from milk after precipitation of casein, has been viewed until recently as one of the major disposal problems of the dairy industry. The biological oxygen demand (BOD) of whey is very high (40 000 mg kg 1 or more), constituting a major ecological burden if disposed off as a waste material. Thus, the disposal practices of the past, including drainage into waste treatment facilities or spraying onto fields, are currently seldom practiced. Use of whey as cattle or pig feed is still one of the significant alternatives to utilization in the human food chain, now being predominantly favored due to the economic opportunities provided by some of the milk nutrients contained in the whey.
Whey Types and Composition There are several types of whey, depending mainly on the processing sequence resulting in casein removal from fluid milk. The type of whey most often encountered originates from the manufacture of cheese or certain industrial casein products, where the processing is based on coagulating the casein by rennet, an industrial casein-clotting preparation containing chymosin or other casein-coagulating enzymes. Since the rennetinduced coagulation of casein and the subsequent whey drainage occur at a pH value of approximately 6.5–6.0, this type of whey is referred to as sweet whey. The second basic whey type, acid whey, results from processes using fermentation or addition of organic or mineral acids to coagulate the casein as in the manufacture of fresh acidcoagulated cheeses (e.g., Cottage cheese or quark) or most industrial acid casein.
The main components of both sweet and acid wheys, after water (which constitutes approximately 93% of the whey on an ‘as is’ basis), are lactose (approximately 70–72% of the total solids), whey proteins (approximately 8–10%), and minerals (approximately 12–15%). Table 1 gives a more detailed breakdown of these components of the two basic whey types. The main differences between the two whey types are in the mineral content, the acidity, and the composition of the whey protein fraction (WPF). Although these differences are relatively minor on an ‘as is’ basis, they can have a profound effect on the technological as well as nutritional properties of the wheys and must be taken into consideration in applications of the various whey processing technologies now available to whey processors. The acid coagulation approach (using conversion of some of the lactose in milk to lactic acid by lactic acid bacteria and/or addition of acidulants such as glucono-lactone or various acids such as sulfuric, phosphoric, hydrochloric, citric, or lactic acid) results in substantially increased acidity (final pH approximately 4.5) necessary for casein precipitation. At this low pH, the colloidal calcium contained in the casein micelles in normal milk is solubilized and partitioned into the whey. On the other hand, rennet clotting produces a fragment of the -casein molecule, termed glycomacropeptide (GMP), which ends up in the whey. Thus, the GMP constitutes approximately 20% of the WPF of sweet, rennet-based wheys but is not found in acid wheys unless use of rennet was included in the fresh cheese manufacturing process (as sometimes happens in the Cottage cheese manufacture for increased firmness) in addition to the acid coagulation. Various technological steps used in the pretreatment of milk before the main processes (such as various thermal treatments before the casein-clotting operation) may also influence the composition of the whey resulting from such
731
732 Whey Processing | Utilization and Products Table 1 Typical composition of sweet and acid whey (g l 1 whey) Component
Sweet whey
Table 2 Typical composition of major types of dried whey products (%, w/w)
Acid whey Product type
Total solids Lactose Protein Calcium Phosphate Lactate Chloride
63.0–70.0 46.0–52.0 6.0–10.0 0.4–0.6 1.0–3.0 2.0 1.1
63.0–70.0 44.0–46.0 6.0–8.0 1.2–1.6 2.0–4.5 6.4 1.1
Illustrative data compiled from various sources.
milk. Typically, the composition of the mineral fraction may be altered slightly and the content of heat-labile whey proteins may be reduced; these changes may result in further alterations in the technological properties of such wheys. New technological alternatives for processing of dairy fluids, including membrane processing by ultrafiltration (UF) of milk in cheese manufacture or fractionation of the various wheys into various whey-based products, produce a whey-like residue termed UF permeate. The main difference between UF permeates and the various whey types is typically the virtual absence of whey proteins from the permeate. Although technically UF permeate does not fit the definition of whey, it is referred to in this article where appropriate, as its processing and utilization often present similar challenges and opportunities as for whey.
Industrial Technologies Used in the Processing of Whey and UF Permeates As a general rule, about 9 l of whey is obtained for every kg of cheese produced; thus, the volume of whey to be processed, originating from just one typical large-scale cheesemaking operation, can exceed 1 106 l day 1. Most of the technological alternatives used in specialized whey-processing plants are thus large-scale operations, some with a capacity to handle up to 107 l of whey daily. The simplest technology for the conversion of whey to industrially valuable products is drying. Typical traditional whey-drying operations consist of evaporation in multistage vacuum evaporators, followed by spray-drying. The equipment used does not differ greatly from other such dairy plant installations but the evaporation and drying conditions must be adjusted to accommodate the specific properties of the whey. In particular, the differences between evaporation or spray-drying of skim milk and whey include the need to precrystallize the lactose in whey before the drying step to minimize the problems of hygroscopicity, as well as careful manipulation of the heat conditions to minimize problems related to heat sensitivity of whey proteins. Dried whey powders can differ rather substantially in composition and
Regular whey powder Demineralized (70%) whey powder Demineralized (90%) whey powder Ultrafiltration permeate powder Whey protein ‘concentrate’ (skim milk replacer) Whey protein concentrate Whey protein isolate
Total protein
Lactose
Minerals
12.5
73.5
8.5
13.7
75.7
3.5
15.0
83.0
1.0
1.0
90.0
9.0
35.0
50.0
7.2
65.0–80.0 88.0–92.0
4.0–21.0 <1
3.0–5.0 2.0–3.0
Illustrative data compiled from various sources including data from manufacturers.
technological properties, depending on various pretreatment operations used to handle the original milk or the original whey. Some of the typical dried whey products are listed in Table 2. Partial (70%) or almost complete (90%) demineralization of the whey is an important pretreatment process differentiating many of the whey powders (see Whey Processing: Demineralization). Dried whey powder can be produced also by roller (drum)-drying; although roller-drying of whey is not easy, the process is much cheaper than spray-drying and the lower quality of the resulting powder may not be detrimental for all applications. Whey, or nowadays more importantly UF permeate from milk or whey, is the principal raw material for the crystallization of lactose (see Lactose and Oligosaccharides: Lactose: Chemistry, Properties; Lactose: Production, Applications); the residual, partially or more substantially delactosed whey (‘mother liquor’) constitutes yet another dried whey product differing in composition from the basic dried unmodified whey. Finally, UF permeates are also being dried with increasing frequency, giving yet another modified dried whey product consisting primarily of lactose and whey minerals but almost devoid of protein. Until recently, spraydrying was the only technique used for the production of dried permeates; however, due to the very low market value of these powders, the spray-drying of permeates is uneconomical. Several novel technological approaches to drying of milk or whey permeates have been described in the literature and are available to the industry. In principle, these technologies are based on the production of concentrates with very high total solids
Whey Processing | Utilization and Products 733
content (about 76%) combined with additional moisture removal by alternative means, for example, by specially designed screw conveyors allowing additional evaporation of water while inducing lactose crystallization. The final drying step is accomplished in a fluidized bed, thus avoiding the need for the costly spray-drying. The levels and forms of whey proteins are important factors differentiating the various dried whey protein products. In contrast to the processes described above, the WPF can be removed (selectively or totally) from raw whey and concentrated by using various membrane processes (see Membrane-based fractionation) giving rise to whey protein concentrate (WPC), whey protein isolate (WPI), or WPF products (see Milk Protein Products: Whey Protein Products). Although products with as little as 35% protein (produced by partial removal of lactose through crystallization or by using simple UF and intended for replacement of skim milk powder in certain applications) are included under the term WPC, the more valuable WPC products have at least 65% protein and the production technology does not involve any step involving lactose precrystallization. The highest quality WPI and WPF products are manufactured using various technologies including diafiltration, electrodialysis, ion exchange, nanofiltration, or their combinations. For the production of almost all whey protein products, the final step is spray-drying, which should be controlled carefully to minimize heat damage of the thermally sensitive whey proteins. Both spray-drying and especially evaporation can cause heat damage resulting in loss of solubility and other functionality defects. Thus, as a preconcentration step, especially for the production of WPC, WPI, and WPF products, reverse osmosis or freeze concentration can be viewed as viable alternatives to traditional thermal evaporation. The use of reverse osmosis to increase the capacity of conventional whey evaporators, or even for preconcentrating large amounts of whey before transportation to a central whey processing facility, is quite common in the whey processing industry.
Utilization of Whey in Industrially Processed Foods The preceding discussion focused on industrial large-scale processes resulting in an array of technological and functional whey ingredients or whey protein products, used commonly in many processed foods such as spreads, sauces, dry soups, beverage and similar mixes, cookies and other bakery products, ice cream, and a myriad of other industrial food items. Dried whey is a very suitable ‘bulking’ food ingredient due to its bland taste compatible with many food processing applications. The heat sensitivity of whey proteins could pose problems in heated liquid food applications, but in most solid foods this is of no concern. Similarly, the limited solubility of lactose must be kept in
mind when using dried whey in applications leading to development of supersaturated lactose solutions, for example, the unfrozen fraction of ice cream. The well known – but nowadays rarely seen – sensory defect called sandiness can occur more readily when dried whey is used as a portion of nonfat milk solids in ice cream formulation. The various higher value dry whey-based products, listed in Table 2, are increasingly being used as nutritionally important components in special dietary products for infant, geriatric, or sport nutrition. Large amounts of whey are being processed for use in the various infant nutrition products, with demineralized whey, lactose, and modified whey protein products being especially important in this application. Some of the unique technological properties of whey protein (in particular the acid solubility, heat-gelling, and foaming) make the various whey-based high-protein products ideal for use in acid beverages, foamed dairy desserts, yogurts, and similar dairy and nondairy products. A heat-denatured whey protein powder termed ‘traditional lactalbumin’ has a very high waterholding capacity and thus has been shown to be preferable to the undenatured whey protein in applications such as protein enrichment of pasta dough. In general, it has been estimated that of about 10 million tonnes of dried whey solids produced annually worldwide, over 50% is being utilized in human foods, with the rest finding less attractive valorization in animal feeds. However, liquid unprocessed whey can also be a raw material for the production of some traditional foods destined for direct consumer markets. Two such product classes, whey cheeses and whey beverages, represent the traditional uses of whey on a small scale, practiced long before the industrial approach became feasible, and are still important in some parts of the world.
Whey Beverages The drinking of whey for therapeutic applications was already advocated in ancient Greece by Hippocrates. This and other similar anecdotal comments concerning the use of whey as a beverage (including even in the rhyme Little Miss Muffet. . .) illustrate one of the most obvious, but least industrially advantageous, uses of whey as a drink, logically paralleling the use of milk, buttermilk, and other fluid milk products as beverages. In general, whey beverages have not been overly successful with the sophisticated modern consumer, save for a few rather exceptional instances. Minimally processed unflavored or modified raw whey is sold in health-food stores in various countries, especially in Europe, where the current organic food movement may result in increased opportunities in this regard. Occasional reports on wheybased beverages marketed for special occasions (e.g., an ‘official Olympic Games drink’ in 1984 in Sarajevo) can
734 Whey Processing | Utilization and Products
be found in the literature. Local markets often feature whey beverages produced by dairy companies looking for new outlets for their surplus whey; unfortunately, these attempts are typically short-lived, often due to the lack of any serious product development effort that is necessary preceding the launch of any such new product. The rather unpleasant flavor of raw whey, the origins of which have never been satisfactorily explained, is a major deterrent limiting the acceptance of these products by contemporary consumers, especially in view of the fierce competition of other flavorful and inexpensive thirst-quenching beverages. The only whey beverage with a record of lasting success is the Swiss product Rivella, which in fact uses highly modified whey as only a minor ingredient at 33% total volume (the remaining 67% being added water). Other locally successful products have existed on some European national markets (Austria, Finland, The Netherlands, and Switzerland) for some time; however, several known international marketing attempts with these products have failed. The most typical approach to whey beverage development is combination with fruit juices, especially citrus fruits, which are most compatible with the flavor characteristic of whey. This is especially true in the case of acid whey, which is more suitable for this application due to its high content of lactic acid and calcium in comparison to sweet whey. Some of the fruit flavors used in commercial whey beverages include mango, passion fruit, grapefruit, lemon, orange, pear, or their combinations. Other approaches documented in the literature include the production of yogurt drinks containing a substantial whey component, or fermentation of liquid WPCs from sweet whey to produce a ‘thin sour milk’, as the stability of the whey protein at low pH does not lead to the clotted appearance of traditional sour milk products. Milk or whey UF permeates are suitable for the production of isotonic sport drinks or beverages destined for replenishment of the mineral balance after vigorous physical activity; several such products have been described in commercial product surveys. Attempts to produce whey beverages with high whey protein content have been recorded in the literature and are often seen in various food trade exhibitions, with little or no indication of commercial viability. It may be that with the presently increasing reputation of whey proteins as nutraceutically important food components, the development of such products will be intensified. The heat sensitivity of whey proteins is one important problem encountered in manufacturing these products with a demand for extended shelf life. However, since the resistance of whey proteins to heat-induced coagulation in the absence of casein increases dramatically at pH below 3.9, it may be possible to formulate high whey protein drinks, even for ultra-high temperature (UHT) processing. Alternatively, various nonthermal processes now being studied actively for various food processing uses can be considered. Whey beverages offered as liquid
concentrates or as dry powders for home reconstitution can be occasionally found on regular market shelves, including even suitably flavored plain dry whey powder. Various ‘‘miracle protein’’ milk shake formulae based on isolated – even hydrolyzed – whey proteins are commonly marketed as products for body builders, active sport enthusiasts, and other health-food applications.
Whey Cheeses Whey cheeses have suffered a somewhat similar lack of international marketing success; however, in a few localities, whey cheeses belong among the most traditional and most important foods. Two types of whey cheeses are recognized in the textbooks and by the International Dairy Federation. The main differences between the production technologies for these two products are illustrated schematically in Figure 1. The more widespread of the two is the Italian-type whey cheese Ricotta; similar products are also popular in Portugal, Turkey, and other localities. These products are essentially a heat–acid-coagulated whey protein paste, sometimes referred to as ‘whey quark’ (see Cheese: Acid- and Acid/Heat Coagulated Cheese). The processing technology is quite simple, consisting of heating whey (often mixed with up to 25% added skim milk) to at least 90 C for a few minutes, resulting in heat-induced coagulation of whey proteins (and any caseins if present due to the added milk); the coagulum is then separated by suitable mechanical means. The traditional batch manufacturing procedures are cumbersome and involve much
Figure 1 Alternative processes for manufacturing whey cheeses.
Whey Processing | Utilization and Products 735
hand labor, in particular in the separation of the heatcoagulated, fragile whey protein curd. Mechanized and automated continuous systems are now in existence and these result in increased economy, improved shelf life, and better sensory qualities of the final product. In contrast to the Ricotta-type whey cheese involving primarily the protein fraction of whey (and thus not offering a solution to the whey disposal problem, which is especially pressing for the small-scale cheese manufacturers), the Norwegian-style whey cheese Mysost utilizes all the whey components and leaves no residue other than water vapor. The principle of the Mysost cheese process is even simpler than that for the manufacture of Ricotta, as Mysost is essentially highly concentrated whey to which some other components (such as milk fat, cream, or goats’ milk in the most traditional version) have been added (Table 3). The main technological problem encountered in the manufacture of Mysost cheese is the crystallization of lactose in the highly concentrated whey-based paste related to the low solubility of lactose. Thus, a ‘controlled crystallization’ step, consisting of rapid cooling of the hot paste with intensive stirring, from about 95 C (the temperature of the last phase of the evaporation process) to below 65 C, is the most essential aspect of the otherwise routine evaporation process carried out in two steps. After preconcentration in traditional dairy evaporators, the final operation involves a special kettle, ‘gryta’, in which batch evaporation is carried out at an elevated temperature needed to reduce the viscosity of the thick paste. This high temperature tends to minimize the uncontrolled crystallization of lactose and is the main reason for the typical brown color of the product due to the pronounced Maillard reaction. The subsequent rapid cooling step in scraped-surface agitators/coolers promotes formation of very small lactose crystals, thus minimizing the development of pronounced grittiness/sandiness of the final product. There are two basic types of Mysost – sliceable or spreadable – available in Norway, its country of origin and still the only significant market for these products; the two main types are differentiated principally by the moisture content and encompass further variations differing in the fat content, inclusion of some goats’ milk for a stronger Table 3 Compositional characteristics of whey cheeses (%, w/w) Cheese Ricotta Whole milk Whey Mysost Sliceable Spread
Moisture
Fat
Protein
72.2 82.5
12.7 0.5
11.2 11.3
3.0 1.5
17.4 26.6
28.3 3.6
11.5 7.7
36.2 46.2
Illustrative data compiled from various sources.
Lactose
taste, intensity of the brown color development, and sometimes inclusion of sweetening agents or other nondairy ingredients such as hazelnuts or chocolate. Because the relatively simple Mysost process technology leaves no residue other than the evaporated water, its principle is much more useful than that of the Ricotta process as a means of whey disposal, particularly for small cheese manufacturers. However, significant product development efforts would be necessary to modify the sensory profiles of the basic Norwegian products to suit the tastes of markets outside Norway, as demonstrated in several consumer studies conducted in Canada and elsewhere.
Utilization of Whey as a Fermentation Substrate for Food or Nonfood Applications Although whey and whey-like UF permeates originate from milk and contain about 50% of valuable milk nutrients, the profitable utilization of these materials for human nutrition continues to be a problem because of the sheer volume of these by-products of conventional or modern cheesemaking. In numerous research reports and several major industrial projects, whey – due to its suitable content of a fermentable carbohydrate, lactose – was used as a medium for the production of various food-grade or nonfood products using microbial fermentations. Among the most successful current uses of whey in this regard are the plants producing foodgrade or industrial alcohol in New Zealand, the United States, Ireland, and possibly other countries; one of the best examples of such use is the Original Bailey’s Cream Liqueur from Ireland or most of the liqueurs produced in New Zealand. In the past, whey was an important substrate for conversion into Torula spp. yeast biomass used in animal feeds, or for other fermentation-based, lactose-derived products such as antibiotics, lactic acid, or other microbial metabolites. The current preoccupation with organically produced foods and natural food ingredients may signal a possible opportunity for revitalization of some of these processes, abandoned in the past due to unfavorable economic feasibility in comparison to direct chemical synthesis or using other fermentable substrates. Use of whey for the propagation of lactic cultures for cheese manufacturing is well established in many countries. Whey can be used also for the generation of biogas; several such installations where biogas is used as an energy source in the same cheese plant at which whey is produced are in operation in Switzerland and possibly other countries. More recently, whey or whey permeates have been shown to be suitable fermentation substrates for the production of
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bacteriocins such as nisin, or for other valuable food ingredients using specific strains of various lactic acid bacteria. Lactose is not fermented by many microorganisms, necessitating careful selection of the cultures for many of the possible fermentation applications. Uses of whey as a raw material for the production of alcoholic beverages, such as whey wine or whey beer, have been described in the literature, but because lactose is not fermented by common yeasts without special pretreatments, as well as other reasons, these attempts at profitable whey utilization have not resulted in lasting success. However, since the key to new approaches to utilization of whey is to find new avenues for conversion or other utilization applications of lactose, the fermentation route will undoubtedly continue to be explored. One of the currently active industrial research topics is the conversion of lactose to oligosaccharides, either by fermentation with whole microorganisms or by applications of crude enzymatic extracts of suitable bacterial cultures. Similarly, production of exopolysaccharides from lactose is increasingly being used in the production of yogurt; it is likely that this route could be explored in large-scale whey fermentations as well.
Nutritional and Nutraceutical Aspects of Whey Utilization The new approach to developing technically and economically feasible uses of whey and whey-like products lies in finding some unique properties of at least some of the main whey components. The current trend in the food field, focusing on the health-promoting aspects of traditional or novel foods, has opened up new possibilities for whey-based products. Whey contains many minor milk components that are known (or thought) to have physiologically important functions. Some of these compounds are found especially among whey proteins; these include minor whey protein components such as lactoferrin or lactoperoxidase, the immunoglobulins, and even major constituents of the WPF such as the GMP or bovine serum albumin. Some of the mineral compounds, especially the calcium phosphate complex, are now also being marketed as ‘natural’ milkbased food ingredients. Even lactose is being reexamined for its unique nutritional properties, including the purported enhancement of calcium absorption or its unique disaccharide composition, thus serving as a raw material for the production of prebiotic compounds such as galacto-oligosaccharides (see Lactose and Oligosaccharides: Lactose: GalactoOligosaccharides) or heterooligosaccharides. The limited sweetness of lactose can be enhanced by hydrolysis into the two lactose monosaccharides,
glucose and galactose. Most of the industrial lactose hydrolysis processes developed for the production of sweetening syrups for food uses (such as in ice cream) using immobilized -galactosidase enzyme reactors have failed mainly because of the high cost of such technology. Alternative low-cost processes, based, for example, on the use of mechanically disrupted common dairy bacteria producing high amounts of -galactosidase, or on other principles, continue to be investigated. In general, the lactose hydrolysis process, which seems to be grossly underutilized by the industry today, could have a major impact on expanding the dairy markets for lactose- intolerant consumers not only for the processing and utilization of whey, but also for uses in other dairy and especially nondairy foods (see Enzymes Exogenous to Milk in Dairy Lactose and Technology: -D-Galactosidase, Oligosaccharides: Lactose: Chemistry, Properties; Lactose: Production, Applications). The main focus of interest regarding the nutritional/ nutraceutical properties of whey is currently centered on the WPF. Today, whey protein products are the main ingredients in most protein formula supplements used by bodybuilders and active athletes worldwide. Whey protein products have been one of the principal ingredients in infant feeding formulae for some time, often requiring additional treatments such as enzymatic hydrolysis to minimize the allergenicity potential of some of the components such as -lactoglobulin. Most recently, whey protein and/or its main fractions have been investigated for many unique health-enhancing or disease-combating properties, including immunopotentiation through increased intracellular glutathione synthesis; role in reducing cancer cell proliferation; counteracting the wasting syndrome in HIV-positive individuals; antimicrobial properties of some of the minor whey proteins; and other effects. WPIs advertised to supply some of these benefits are now being marketed even as dietary supplements at highly inflated prices. Hydrolysates of whey proteins have been shown to contain bioactive peptides effective in blood pressure reduction, and several industrial products are now on the market. Extraction of some functional components from whey has become a major industrial activity for specialized whey processors, although in most cases, the physiological functionality in human subjects still awaits confirmation from well-controlled clinical trials. Of course, manufacture of any such isolated functional product from the liquid whey will not alleviate requirements for further processing of the residual by-product. As many of the components with documented or proposed unique functionalities are present in the whey in very minute amounts, the need to process the bulk of the residual
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whey stream will remain a major challenge accompanying any such novel development. Surprisingly, by far the most abundant whey component, water, seems to have been neglected in the innumerable research attempts to find new profitable uses of whey and/or its components. The only wellknown use of whey water is as a condensate from the evaporators, mainly for rinsing and equipment washing purposes, but not for productive economically advantageous applications. As one potential such use suggested in the past, the adjustment of the mineral content of the whey water by suitable membrane processing could lead to various pharmaceutical uses for cleansing solutions mimicking the human body fluids. The approach to whey processing and utilization has changed in the recent past, from considering whey a bothersome waste to capitalizing on the opportunities that the whey and whey-like products present for the innovative technically advanced processor. However, for traditional cheese manufacturers, the problems of dealing with large volumes of whey or whey permeate continue to pose difficulties, determining the overall success of their main industrial activity. Nowadays, industrial processing of whey is a highly specialized, technologically advanced segment of the dairy industry requiring up-to-date knowledge and focused attention.
See also: Cheese: Acid- and Acid/Heat Coagulated Cheese. Enzymes Exogenous to Milk in Dairy Technology: -D-Galactosidase. Lactose and Oligosaccharides: Lactose: Chemistry, Properties; Lactose: Galacto-Oligosaccharides; Lactose: Production, Applications. Milk Protein Products: Membrane-Based Fractionation; Whey Protein Products. Whey Processing: Demineralization.
Further Reading Anonymous (2001) The importance of whey and whey components in food and nutrition. Proceedings of the International Whey Conference, 411pp. Munich, Germany. Hamburg, Germany: B. Behr’s Verlag. IDF (1998) Whey: Proceedings of the 2nd International Whey Conference, 367pp. Chicago, IL, USA, 27–29 October 1997. Brussels, Belgium: International Dairy Federation. Jelen P (1999) Whey: Composition, properties, processing, and uses. In: Francis FJ (ed.) Encyclopedia of Food Science and Technology, 2nd edn., Vol. 4, pp. 2652–2661. New York: John Wiley. Jelen P (2009) Whey-based functional beverages. In: Paquin P (ed.) Functional and Speciality Beverage Technology, pp. 259–280. Cambridge, UK: Woodhead Publishing Ltd. Modler HW (2000) Milk processing. In: Nakai S and Modler HW (eds.) Food Proteins: Processing Applications, pp. 1–88. New York: Wiley-VCH. Onwulata C and Huth P (2008) Whey Processing, Functionality and Health Benefits, 416pp. Hoboken, NJ: Wiley-Blackwell. Sienkiewicz T and Riedel C-L (1990) Whey and Whey Utilization, 379pp. Gelsenkirchen, Germany: Verlag Th. Mann. Zadow JG (ed.) (1992) Whey and Lactose Processing, 489pp. London: Elsevier Applied Science.
Demineralization G Gernigon, P Schuck, and R Jeantet, UMR 1253 INRA-Agrocampus Ouest, Rennes, France H Burling, Arla Foods amba, Lund, Sweden ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. Burling, Volume 4, pp 2745–2751, ª 2002, Elsevier Ltd.
Introduction In order to make nonhygroscopic whey powder as well as to make whey powder a suitable ingredient for certain foods, a reduction of the mineral content is needed. Typically, whey contains 8–10% minerals on a dry weight basis. This can be problematic when processing whey, especially when concentrating, crystallizing lactose, and spray-drying whey. It is also a problem when using whey and whey powders as food, especially for infant formulas, where a 90–95% reduction in minerals is needed. This is necessary in order to mimic the mineral composition of human milk. Critical ions for the preparation of infant formulas are Naþ, Kþ, Cl, and PO3 4 . For example, for ice cream applications, in order to reduce the salty taste of ordinary whey powder, a 50–70% overall reduction in minerals is often enough. Addition of less demineralized whey powder is always a possibility. It should be remembered that instead of using a specific demineralization process, like ion exchange or electrodialysis, ultrafiltration in combination with pure lactose is an alternative for the manufacture of infant formulas. The necessary composition of macrocomponents can thus be reached in many different ways. This article will focus on three main technologies for whey demineralization, that is, electrodialysis, ion exchange, and nanofiltration (NF). Combination of these processes will also be mentioned.
Electrodialysis Electrodialysis is defined as the transport of ions through semipermeable membranes under the driving force of an electric field caused by an applied direct current (DC) source. The membranes used have both anion and cation exchange functions, making electrodialysis capable of reducing the mineral content of a process liquid, for example seawater or whey. Figure 1 is a schematic representation of an electrodialysis unit. It consists of a number of compartments separated by alternate cation and anion exchange membranes, which are spaced about 1 mm apart. The end compartments contain electrodes. There can be as many as 200 cell pairs between each pair of
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electrodes. The two electrodes at each end of the cell stack have separate rinse channels, through which a separate acidified stream is circulated to protect the electrodes from chemical attack. For whey treatment, the whey feed and acidified brine pass through alternate cells in the stack.
Operating Principle Alternate cells in the electrodialysis stack act as concentration and dilution cells, respectively. Whey is circulated through the dilution cells and a 5% brine carrier solution through the concentration cells. When DC is applied across the cells, cations attempt to migrate to the cathode and anions to the anode, as shown in Figure 1. However, completely free migration between the cells is not possible because the membranes act as barriers to ions of like charge. Anions can pass through an anion membrane but are stopped by a cation membrane. Conversely, cations can pass through a cation membrane but not an anion membrane. The net effect is depletion of ions in the whey (depletion) cells. The whey is thus demineralized, to an extent determined by the ash content of the whey, residence time in the stack, current density, and flow viscosity. The electrodialysis plant can be run either continuously or in batches. A batch system, which is often used for demineralization levels above 70%, can consist of one membrane stack over which the process liquid, for example, whey, is circulated until a certain ash level is reached. This is indicated by the conductivity of the process liquid. The holding time in a batch system can be as long as 5–6 h for 90% demineralization at 30–40 C. Preconcentration of the whey to 20–30% dry matter (DM) is desirable for maximum utilization of installed membrane area and low electric power consumption. The whey concentrate should be clarified before it enters the electrodialysis unit. The high process temperature means that there is a risk of bacterial growth in the product. A bacteriostatic compound such as hydrogen peroxide is therefore often added to the whey, when allowed. The process liquid heats up during the process, so cooling is needed if it is necessary to maintain process temperature. In a
Whey Processing | Demineralization
Figure 1 Schematic layout of an electrodialysis stack.
continuous plant, consisting of, for example, five membrane stacks in series, the holding time can be reduced to 10–40 min. The maximum demineralization level of such a plant is 60–70%. In relation to capacity, the installed membrane area is much larger in a continuous plant than in a batch plant. An electrodialysis plant can easily be automated and furnished with a programmed clean-in-place (CIP) system. The cleaning sequence normally includes water rinse, cleaning with an alkaline solution (maximum pH 9), water rinse, cleaning with hydrochloric acid (pH 1), and a final water rinse. A typical cleaning program takes about 100 min.
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factor shortening the lifetime of the anion membrane. The theoretical background to this problem is as follows. At the normal pH of whey, the main whey proteins are negatively charged (anionic character) and move as such under the influence of the electric field in the stack. These molecules, which are too big to pass through the anion exchange membranes, are deposited as a thin protein layer on the face of the anion exchange membranes in the whey compartments. Techniques such as polarity reversal can be used to dislodge these deposits. Although frequent cleaning at high pH removes most of the deposits, at least in older plants, disassembly of the stack for manual cleaning is recommended at intervals of 2–4 weeks. The processing cost of electrodialysis depends very much on the degree of demineralization. Increasing the demineralization level in steps from 50 to 75 to 90% doubles the processing cost per step, as a rule of thumb. Water treatment, electric power, chemicals, and steam account for the operating costs of a demineralization plant. Wastewater treatment is a particularly expensive item. During production, lactose leaks through the membranes to an extent of as much as 5–8% at 90% demineralization. The phosphate removed from the whey accumulates in the waste stream. The cost of electric power amounts to 10–15% of the processing cost, while the chemicals used in the process, mainly hydrochloric acid, account for 5%. The cost of steam used for preheating the product and cost of cooling for controlling the process temperature are 10–15%, depending on the demineralization level.
Power Supply and Automation
Ion Exchange
DC is used in the electrodialysis plant, which should have facilities for regulating current in the range of 0–185 A and voltage in the range of 0–400 V. Flow rates, temperatures, conductivity, pH of process water and product, product inlet pressure, pressure difference between the stacks, and current and voltage over each membrane stack are monitored and controlled during production.
Industrial application of ion exchange often means pumping the process liquid to be treated through a fixed-bed column filled with polymeric beads loaded with ions that are exchangeable with the ions in the process liquid. The capacity of the process is limited by the amount of ions on the resin in the fixed bed. After the ion exchange capacity has been used up, the adsorbed ions must be removed by regeneration of the column by an appropriate regeneration solution. After that, the flow of process liquid through the column can be resumed. Modern ion exchange resins are macromolecular porous plastic materials formed into beads with a diameter in the range of 0.3–1.2 mm for technical applications. Chemically, they act as insoluble acids or bases, which when converted to salts remain insoluble. The main characteristic of ion exchange resins is their capacity to exchange the mobile ions (counterions) that they contain for ions of the same charge sign contained in the solution to be treated. The exchange reactions are equilibrium reactions governed by a constant. The concentration of ionic species is an important factor for the driving force in the exchange reaction. The functional groups of ion exchange resins for
Limiting Factors in Electrodialysis and Processing Costs A major limiting factor for using electrodialysis in dairy processing is the cost of replacing membranes, spacers, and electrodes, which constitute about 35–40% of the total running costs of the plant. Replacement is necessary due to fouling of the membranes, which in turn is caused by (1) precipitation of calcium phosphate on the cation exchange membrane surfaces and (2) deposition of protein on the anion exchange membrane surfaces. The first problem can be handled by proper flow design over the membrane surface and regular acid cleaning. The second problem, with adsorption of protein, is the main
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demineralization purposes vary. First of all, a distinction between anion exchangers and cation exchange resins can be made and within these groups there are both weak or strong base and acid varieties, respectively. The group to which the specific ion exchange resin belongs depends on the functional group. Strong cation exchange materials often have sulfonic groups bound to the matrix. This group is ionized throughout the pH range 0–14, and therefore active for exchange reactions to take place. The most common weak acid exchange material has a carboxylic acid functionality. This group is ionized at pH values above the isoelectric point, typically above pH 5–6. Strong base functionality is based on quaternary amine groups. These groups are dissociated throughout the pH range. Weak base ion exchange functionality is often based on tertiary amine groups, which are active in the pH range 0–7. From the point of view of ease of regeneration, it is beneficial to use weak resins whenever possible. They can be regenerated with acid or alkali in excess in comparison with the theoretical need of just 10–50%. Strong resins need 200–400% excess of regenerant to be fully converted to the active form. For demineralization according to the classical procedure, a strong cation exchanger in the hydrogen ion form is often combined with a weak base anion exchanger working in the free base (hydroxyl) form. The whey passes through the cation exchange column before the anion exchange column. It is not possible to use a weak acid cation exchange resin instead of a strong one, because of pH and the carboxyl functionality of the weak cation exchange resin. The equilibrium constant for the exchange reaction to occur is unfavorable. Other important characteristics of ion exchangers that are not further discussed are (1) ion exchange capacity, (2) swelling properties, (3) mechanical strength, (4) fluidization during backwashing of the bed, (5) pressure drop,
(6) flow velocity restrictions, and (7) water rinse requirement after regeneration.
Conventional Ion Exchange for Demineralization A simple demineralization plant based on ion exchange is shown in Figure 2. The whey enters the strong cation exchanger, loaded in the hydrogen ion form, and continues to the weak base anion exchanger in its free base form. The ion exchange columns are rinsed and regenerated separately with dilute hydrochloric acid and sodium hydroxide (or ammonia). Once a day, the columns are disinfected by rinsing with water containing active chlorine. The following net reactions take place during demineralization (NaCl is used to illustrate the salts of whey and R represents the insoluble resin exchange site): cation exchange:R-H þ Naþ þ Cl – Ð R-Na þ Hþ þ Cl – anion exchange: R-OH þ Hþ þ Cl – Ð R-Cl þ H2 O
The above reactions illustrate that by the ion exchange process the whey salts are exchanged for water. The flow program in the ion exchange process includes the following steps: 1. exhaustion: 10–15 bed volumes of whey can be treated per regeneration cycle. The bed volume refers to the volume of the cation exchanger; 2. regeneration; 3. displacement of whey from the columns by water; 4. backflushing; 5. contact with regeneration solution; and 6. water rinse. A typical cycle time is about 6 h: 2 h for exhaustion and 4 h for regeneration. The ion exchange vessels are often
Figure 2 Schematic diagram of an automatic whey demineralization plant.
Whey Processing | Demineralization
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made of rubber-lined mild steel to avoid corrosion problems. A conical shape is used specially for the anion exchanger to allow for swelling of the bed during transformation from the free base to the salt form. It is common practice to regenerate the cation column in upflow (countercurrent to exhaustion). This system reduces the consumption of regeneration chemicals by as much as 30–40%. The plant can easily be automated. Two or three parallel ion exchange systems are needed for a continuous flow of whey.
Process Limitations and Costs Whey is a liquid with a high ash content, which means short runs between regenerations with high consumption of regeneration chemicals. These facts lead to a high salt load in the wastewater from both the whey and from the surplus of regeneration chemicals. Consumption of rinse water is also high, especially from washing out excess sodium hydroxide from the weak anion exchange resin. Losses of whey proteins occur due to adsorption phenomena, primarily on the anion exchange resin. Consumption of regeneration chemicals accounts for 60–70% of the operating costs. The process is primarily designed for 90–95% demineralization but any level can be chosen if a bypass system is used.
An Alternative Ion Exchange Process In order to reduce the consumption of regeneration chemicals and thus also create a better waste situation for a demineralization plant, the R&D Department of the Swedish Dairies’ Association, SMR, developed an alternative ion exchange process. In this process, several different unit operations are linked together, namely, ion exchange, evaporation, distillation, and absorption in order to recover the regenerant, NH4HCO3, as illustrated in Figure 3. In this process, the whey is first treated with the anion exchange resin regenerated in the bicarbonate form. During anion exchange, the anions of whey are exchanged for HCO 3 . After this, the whey enters the cation exchange column regenerated in the ammonium form. During the passage of the whey through this column, the cations in the whey are exchanged for NHþ 4 . Thus after the process, the whey salts are exchanged for ammonium bicarbonate, NH4HCO3. The reactions can be summarized as follows: anion exchange: R-HCO3 þ Naþ þ Cl – Ð R-Cl þ Naþ þ HCO3 –
Figure 3 The SMR process for demineralization. A, whey; B, demineralized whey powder; C, condensate with NH3 and CO2; D, new regeneration solution; E, spent regeneration solution; F, whey salts; G, NH3 and CO2; H, precipitate of MgNH4PO4.
cation exchange: R-NH4 þ Naþ þ HCO3 – Ð R-Naþ þ NH4þ þ HCO3 –
NH4HCO3 is a thermolytic salt (sometimes used as baking powder), which decomposes to NH3, CO2, and H2O when heated. This happens during the subsequent evaporation of the whey, offering the possibility of recovering the NH3 and CO2 vaporized from the whey to make new regeneration solution (NH4HCO3). Part of the used regeneration solution after passing the columns, containing surplus of regeneration salt (about 100% of theoretical need is used during regeneration), is collected for vaporization in a distillation tower. Figure 4 shows the industrial layout of the SMR process. The description of the flow arrangement is given below. The whey first enters the anion exchange column regenerated in bicarbonate form and then the cation exchange column in ammonium form. This is in reverse order compared with the classical ion exchange demineralization procedure. In practical design, the ion exchange systems are paired, one working on whey while the other is being regenerated. With two pairs of columns, an uninterrupted flow of whey is obtained. The cycle time is 4 h (2 h for ion exchange and 2 h for regeneration). After passing through the ion exchange unit (1) the cool whey is used for heat recovery in the absorption tower and as cooling medium in the condenser (9). Then, the whey enters the evaporator (3) and finally the demineralized whey concentrate is spray-dried (10). The condensate from evaporator stage 2, which is especially rich in ammonia, is separated from the other condensate streams and continues to the absorption
742 Whey Processing | Demineralization
Figure 4 Flow sheet of a full-scale production plant based on the SMR process. A, whey; B, whey powder; C, condensate; D, CO2 and NH3; E, water; F, disinfectant; G, wastewater; H, phosphate salt; J, CO2 and NH3; 1, ion exchanger; 2, ion exchanger; 3, heat recovery; 4, condenser; 5, evaporator; 6, spray tower; 7, adsorption column; 8, fresh regeneration solution; 9, spent regeneration solution; 10, stripping solution.
tower (4), where it forms the liquid base for the new regeneration solution. The condensates from evaporator stages 1, 3, and 4 are used to rinse off the ion exchangers, giving further recovery of ammonia in these condensates. The recovery of ammonia is 75–80% in the process. Most of the CO2 stripped off during evaporation is recovered in gaseous form from the mechanical vacuum pump of the evaporator. This gas flows directly into the bottom of the absorption tower, where it is almost completely absorbed in the synthesis of NH4HCO3. Overall recovery of CO2 is more than 90%. To compensate for losses of NH3 and CO2 in the process, fresh quantities of NH4HCO3 are injected into the circulation flow of the absorption tower (4). The part of the regeneration solution which is rich in NH4HCO3 is collected in a tank (8), where the phosphate from whey is precipitated by addition of MgCl2. When the precipitate of magnesium ammonium phosphate (MgNH4PO4) has settled, the supernatant liquid is pumped to the top of the distillation tower (9) and at the same time preheated in a plate heat exchanger (not shown in the figure) using the bottom liquid in the distillation tower as the heating medium. About 10% of the liquid is stripped off as vapor, which in turn is condensed by using the whey after ion exchange as cooling medium (2). In summary, the SMR process has the following characteristics: 1. low running costs due to recovery of the regeneration chemicals; 2. low losses of whey solids and only half of the salt discharge compared to the classical ion exchange process; 3. small variations in pH of the whey (6.5–8.2), resulting in minimum losses of denatured whey proteins due to adsorption on the columns; 4. high demineralization efficiency (more than 90%);
5. low operating temperature (4–6 C), enhancing the microbiological status of the end product; 6. high yield of whey solids compared to classical ion exchange and electrodialysis; and 7. optimum heat recovery. Process Limitations and Costs In most cases, depending on the cost of chemicals, the operating cost of the SMR process is 30–70% lower than that of the classical ion exchange process. The equipment for plant design of an SMR plant includes more components than the classical ion exchange process. Therefore, the capital costs are somewhat higher. For optimum profitability, a plant greater than 100 m3 is needed. Nanofiltration An interesting alternative to electrodialysis and ion exchange is NF. NF is a membrane pressure-driven process in between reverse osmosis and ultrafiltration. It is named after the mean pore diameter, which is approximately 1 nm. Thus, the separation area for molecules, especially charged monovalent ions like Naþ, Kþ, and Cl, lies in the molecular range of 100–1000 Da. The normal operating pressure is typically 2–3 MPa. Apart from steric exclusion and considering the low value of pore diameter, the membrane separation characteristic is to a large extent determined by electrostatic forces in the membrane matrix because of the electric charges of its carboxyl groups; this causes ions to avoid regions of low dielectric constant. Moreover, the role of the retention of multivalent co-ions (salts and/or proteins) in the facilitated transmission of monovalent ions has been demonstrated.
Whey Processing | Demineralization
In the case of sweet whey (membrane negatively charged), the retention of polyvalent anions leads to the presence of higher amounts of negative charges in the retentate, which results in an increased transmission of Cl and an increased retention of Naþ and Kþ and Ca2þ in order to maintain the electroneutrality. The demineralization efficiency is thus almost restricted to removal of monovalent ions. For a volume reduction ratio of 4–5 during filtration of whey, an ash removal from whey of 40–60% is obtainable. It corresponds to 70–80% for monovalent co-ions (which are Naþ, Kþ, and Hþ for acid whey and Cl and OH for sweet whey) and 40–70% for monovalent counterions (which are Naþ, Kþ, and Hþ for sweet whey and Cl and OH for acid whey). Divalent ions are reduced in the range of 3–20%. Partial demineralization is often needed in various situations when manufacturing dairy ingredients, for example, various whey protein concentrate products, in order to adjust the mineral composition. Another effect of NF is the concomitant concentration of the whey up to a DM of 20–22%, which helps to economize the evaporation costs. By combining with water dilution of the NF retentate and renewed filtration (diafiltration), the ash reduction can be driven from 35–50 up to 60–70% but at the expense of increased cost, water utilization, and by-product (nanofiltrate) production. In contrast, in newer types of NF membranes, the loss of organic molecules has been improved, especially lactose. Indeed the loss of lactose and the loss of nonprotein N and protein in NF are today lower than those found in electrodialysis or ion exchange, making retentate more valuable and leading to a permeate with lower biological oxygen demand (BOD). Urea does leak quite extensively. Also, organic acids like lactic and acetic acid can pass through the membrane to a large extent, presenting the possibilities of deacidification of acid whey. Corresponding salts of these acids are strongly retained by the membrane. The benefits of NF are low investment costs and simple installations, which are easy to run. Moreover, the amount of effluents is greatly reduced in comparison with the other demineralization processes, and the generated effluents have a lower BOD. Demineralization by electrodialysis and ion exchange is usually known to generate high amounts of effluents. Moreover, it has been demonstrated that the running costs of these demineralization techniques are 25–55% higher than NF, due to their combination with evaporation concentration. NF is a fast-growing technology in the dairy world today for different application purposes.
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Combination of Processes For large demineralization installations, that is, those processing more than 400 m3 day1 of whey, investment in combined technologies may be of interest. The combinations used are electrodialysis or NF in combination with the classical ion exchange process. The benefits are reduced costs of chemicals but the capital costs are higher and more complicated processes are more difficult to run. Many modern demineralization plants are combinations of classical ion exchange with NF. By doing this, the ionic load on the ion exchangers is reduced by about 30% in combination with lower volumes to treat. The size of the columns can be reduced by the same figure, in principle. When electrodialysis and classical ion exchange are combined, the whey first passes the electrodialysis step to about 50% demineralization level. After that, the whey passes on to the ion exchange plant.
See also: Dehydrated Dairy Products: Dairy Ingredients in Non-Dairy Foods; Infant Formulae. Milk Protein Products: Whey Protein Products. Milk Salts: Distribution and Analysis; Interaction with Caseins. Whey Processing: Utilization and Products.
Further Reading Delaney RAM (1976) Demineralization of cheese whey. Australian Journal of Dairy Technology 31: 12–17. Hoppe GK and Higgins JJ (1992) Demineralization. In: Zadow JG (ed.) Whey and Lactose Processing, pp. 91–131. London: Elsevier Applied Science. Houldsworth DW (1980) Demineralization of whey by means of ion exchange and electrodialysis. Journal of the Society of Dairy Technology 33: 45–51. Jeantet R (1995) Nanofiltration de liquides laitiers. The`se de l’ENSAR 95-18-B-65, Agrocampus Quest. Jeantet R, Schuck P, Famelart MH, and Maubois JL (1996) Nanofiltration benefit for production of spray-dried demineralized whey powder. Le Lait 76: 283–301. Jo¨nsson H and Arph SO (1987) Ion exchange for demineralization of cheese whey. International Dairy Federation Bulletin 212: 91–98. Kelly PM, Horton BS, and Burling H (1991) Partial demineralization of whey by nanofiltration. International Dairy Federation Special Issue 9201: 130–140. Rousset F and Reboux P (1997) Nanofiltration and ion exchange for the demineralization of whey. In: Whey, Proceedings of the 2nd International Whey Conference, pp. 93–99. Chicago, IL, October. Brussels, Belgium: International Dairy Federation. Sienkiewicz T and Riedel C-L (1990) Whey and Whey Utilization, 2nd edn. Gelsenkirchen, Germany: Verlag Th. Mann. Vasiljevic T and Jelen P (2000) Comparison of nanofiltration and ultrafiltration of cottage cheese whey and whey permeate. Milchwissenschaft 55: 145–149.
Y YEASTS AND MOLDS Contents Yeasts in Milk and Dairy Products Kluyveromyces spp. Geotrichum candidum Penicillium roqueforti Penicillium camemberti Spoilage Molds in Dairy Products Aspergillus flavus Mycotoxins: Classification, Occurrence and Determination Mycotoxins: Aflatoxins and Related Compounds
Yeasts in Milk and Dairy Products N R Bu¨chl and H Seiler, Technische Universita¨t, Mu¨nchen, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. Seiler, Volume 4, pp 2761–2769, ª 2002, Elsevier Ltd.
Introduction Yeasts are widespread microorganisms that are able to colonize many different types of habitats. Food with high contents of nutrients such as sugar, organic nitrogen sources, minerals, and vitamins in general presents an ideal substrate for yeast growth. However, the influence of yeasts in dairy products can be either beneficial or detrimental. Some species play an important role in the production of traditional fermented milk products and cheese. They generate specific aroma ingredients, for example, ethanol and carbon dioxide in kefir and kumys, and contribute to the growth of bacterial starter cultures on surface-ripened soft cheeses and semihard cheeses. Nevertheless, growth of yeasts is in most instances undesirable in milk and dairy products, because these microorganisms harbor a high risk of spoilage. Yeasts are able to grow in a broad range of pH environments. Hence, they are normally capable of spoilage of dairy products with a low pH fermented by lactic acid bacteria (LAB), whereas the
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frequently occurring organisms in milk, belonging to the bacterial families Bacillaceae, Enterobacteriaceae, and Pseudomonadaceae, cannot proliferate at such conditions. Acid dairy products formed with the addition of fruit mixes, honey, cereals, chocolate, and so on are at maximum risk. These products contain, in addition to lactose and small amounts of galactose, considerable amounts of fructose and sucrose providing excellent conditions for growth and fermentation of many yeast species. Consequently, lactose-utilizing species are not the only yeast species that spoil these products.
Raw and Market Milk During milking, yeast contamination originates in most cases from the floors, litter, feed, and air, and only less frequently from the milking machine or udders affected with mastitis. The total yeast count in raw milk is negligible at 101–103 cfu ml1. The species most often found are
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Candida intermedia, C. parapsilosis, Cryptococcus curvatus, Debaryomyces hansenii, Galactomyces geotrichum, Issatchenkia orientalis, Kluyveromyces marxianus, K. lactis (both sometimes referred to as K. marxianus subsp. marxianus, K. marxianus subsp. lactis, K. marxianus subsp. bulgaricus, Candida kefyr), Pichia farinosa, P. fermentans, P. membranifaciens, P. anomala, Trichosporon beigelii, and Yarrowia lipolytica (Table 1). There is a significant relationship between udder health, and general hygiene during milking, and the yeast count in raw milk (see Liquid Milk Products: Liquid Milk Products: Pasteurized Milk; Pasteurization of Liquid Milk Products: Principles, Public Health Aspects). Even after homogenization at 55–65 C and heat treatment at pasteurization conditions, milk can get recontaminated with yeasts and can develop moldiness, mustiness, and yeast odor. Amino acids and peptides in spoilt milk can stimulate the growth of starter cultures. During fermentation, this can lead to overacidification or to an undesirable population displacement. Also, inhibitory substances can be produced. Consequently, product defects like soft curd, separating and stripping, flavor defect or lack of aroma can occur. During pasteurization of milk, vegetative cells of yeasts, blastospores, chlamydospores of Candida albicans and other species, teliospores, ballistospores, basidiospores, endospores, ascospores of ascosporogenous yeasts, and arthrospores of the Endomycetaceae (e.g., Galactomyces geotrichum) are destroyed. For the most heat-resistant species, Zygosaccharomyces bailii, the following inactivation values were determined: vegetative cells: D56 C ¼ 1 min, z ¼ 4 C; ascospores: D64 C ¼ 1 min, z ¼ 3 C (see Heat Treatment of Milk: Sterilization of Milk and Other Products). Under low water activity (aw) conditions, for example, when yeast cells are pressed in porous gaskets, the heat inactivation can be insufficient. Areas in the processing plant that pose a risk of recontamination are heat exchangers, cooling water, filling equipment, air, and packaging materials. Generally, recontamination with yeasts is less important for the spoilage of pasteurized milk and neutral-pH dairy products. Acinetobacter spp. and many Gram-positive bacteria, including spores of Bacillus spp. and Clostridium spp., survive pasteurization. Moreover, because the filling operation is not sterile, the milk is most frequently recontaminated with Gram-negative organisms. Hence, these bacteria are responsible for the shelf life limit of 7–14 days for pasteurized milk. Various milk products are heat treated at 90–110 C for a short time. Under these conditions, all bacteria as well as ascospores from thermophilic molds are destroyed. But it has no effect on spores of bacilli and clostridia. Hence, these spore-forming bacteria can cause microbiological problems. Only in case of recontamination can yeasts contribute to or cause spoilage. Under high-temperature pasteurization (e.g., 125 C for 5 s) and
sterilization (e.g., 109–115 C for 20–40 min) conditions, all microorganisms except for some heat-resistant bacterial endospores are inactivated. Nevertheless, it has been observed that the occurrence of spoilt milk is connected with the presence of heat-stable proteases and lipases, which originate from the high numbers of microorganisms present in milk before heating (see Microorganisms Associated with Milk). However, these enzymes originate from Pseudomonas spp. as enzymes produced by yeasts are completely inactivated during these heat treatments.
Butter and Natural Buttermilk Butter made in a dairy plant and stored at a low temperature seldom undergoes microbial spoilage within its shelf life. The fine dispersion of water, low pH value (in cultured butter), and low solubility of oxygen in fat hinder the growth of microorganisms. The product surface is exposed to limited hygienic risk. Yeasts can grow there and damage the butter, for instance, by lipolysis or discoloration. Improper production conditions or unsterile storage can facilitate spoilage caused by yeasts. Homemade butter contains many serum droplets with lactose as a convenient nutrient for microorganisms; its hygienic status leaves much to be desired. Here yeasts can reach high counts. Addition of NaCl reduces the risk of spoilage. Natural buttermilk should at the most contain 200 cfu ml1 yeast cells. A large number of microbiological defects can be traced to yeasts, as they can grow even at pH < 3.5 and at 0 C. The spoilage is caused by proteolysis, lipolysis, and carbohydrate fermentation with the formation of gas. Overacidification as well as consistency and sensory problems can arise and packages can blow. The yeast species most often found in industrially produced buttermilk are Debaryomyces hansenii, Candida tropicalis, Galactomyces spp., Geotrichum spp., Issatchenkia spp., Kluyveromyces spp., Pichia anomala, P. kluyveri, Saccharomyces cerevisiae, and Torulaspora delbrueckii. In buttermilk made from traditional Jordanian butter, Saccharomyces cerevisiae, Kluyveromyces marxianus, Pichia kluyveri, Galactomyces geotrichum, Issatchenkia orientalis, Torulaspora delbrueckii, Candida tropicalis, and Trichosporon ovoides were the most prevalent yeast species.
Ice Cream and Frozen Yogurt Milk products marketed in the frozen state cannot be spoiled by yeasts. The growth rate and metabolic activity at temperatures < 0 C are irrelevant. However, the finished product should not be more than very minimally contaminated; the product cannot be permitted to thaw out in between.
746 Yeasts and Molds | Yeasts in Milk and Dairy Products Table 1 Yeast species frequently isolated from milk and dairy products Speciesa
Habitatb,c
Bullera variabilis Candida atmosphaerica Candida auringiensisd Candida boidinii Candida butyri Candida catenulata Candida diddensiae Candida etchellsii Candida ethanolica Candida fennicad Candida glabrata Candida glaebosa Candida haemulonii Candida intermediad Candida lactis-condensi Candida magnoliae Candida parapsilosis Candida peltata Candida rugosa Candida sake Candida santamariae Candida savonica Candida sorbophila Candida tenuisd Candida tropicalis Candida versatilisd Candida vini Candida zeylanoides Citeromyces matritensis (Candida globosa) Clavispora lusitaniae (Candida lusitaniae) Cryptococcus albidus/curvatus/humicolus/laurentiaed Debaryomyces hansenii (Candida famata)d Dekkera anomala (Brettanomyces anomalus)d Dekkera bruxellensis/custersiana (Brettanomyces spp.) Filobasidiella neoformans (Cryptococcus neoformans) Filobasidium floriforme Galactomyces geotrichum (Geotrichum candidum) Geotrichum fragrans/klebahnii Hanseniaspora uvarum (Kloeckera apiculata) Hanseniaspora vineae (Kloeckera africana) Issatchenkia occidentalis (Candida sorbosa)e Issatchenkia orientalis (Candida krusei)e Kloeckera lindneri Kluyveromyces lactis (Candida sphaerica)d Kluyveromyces marxianus (Candida kefyr)d Leucosporidium scottii (Candida scottii) Metschnikowia pulcherrima (Candida pulcherrima) Metschnikowia bicuspidate/reukauffii Pichia angusta Pichia anomala (Candida pelliculosa)e Pichia burtonii (Candida chodati) Pichia cactophila Pichia etchellsii Pichia fabianii (Candida fabianii)e Pichia farinose (Candida cacaoi) Pichia fermentans (Candida lambica) Pichia guilliermondii (Candida guilliermondii) Pichia jadinii (Candida utilis)e Pichia kluyveri Pichia membranifaciens (Candida valida)
en en fr, yo bu ch, en, ma, mi br, bu, en br, yo en, fr, yo fr, yo mi fr, yo br, ch, co, en, fr, yo ch, co, yo fr, yo br, bu, ch, en, fr, ma, yo ma br, bu, ch, en, ke, mi, se bu, ch, en, fr, mi, yo fr, en fr, en en br, ke, ma bm, br, bu, ch, fr, ke, mi, yo br, ch, en, ke, mi bu, ch, se br, ch, se co, fr, mi br, ch, en, fr, ma, yo br, ch, en, fr, mi, yo bm, br, bu, ch, en, fr, ke, mi, re, yo ch, ke ke, mi, yo ma en br, bm, ch, en, ke, mi, yo bm, br, ch, en, mi, yo en, fr, mi, yo en, fr, mi, yo br, bm, ch, en, fr, ke, mi, yo br, bm, ch, en, fr, ke, mi, yo fr, yo br, bm, bu, ch, en, fr, ke, mi, yo br, bm, bu, ch, en, fr, ke, mi, yo en fr, yo fr, yo ch, fr, mi, ma, yo bm, ch, co, en, fr, mi, ma, yo ch, mi, yo bu, fr, yo bu fr, en mi, en bm, ch, ke, mi, yo bm, bu, ch, en, fr, yo br, bm, ch, fr, ma bm ch, fr, ke, yo (Continued )
Yeasts and Molds | Yeasts in Milk and Dairy Products 747 Table 1 (Continued) Speciesa
Habitatb,c
Pichia norvegensis (Candida norvegensis) Pichia pini Pichia pseudocactophila Pichia sorbitophilad Pichia triangularis (Candida polymorpha) Rhodotorula glutinis/graminis/minuta/mucilaginosad Saccharomyces cerevisiae (Candida robusta) Saccharomyces dairensis/kluyveri Saccharomyces exiguus (Candida holmii) Saccharomyces servazzii Saccharomyces unisporus Saccharomyces turicensis Saccharomycodes ludwigii Sporobolomyces roseus/salmonicolor Sterigmatomyces halophilus Torulaspora delbrueckii (Candida colliculosa) Trichosporon asteroids/ovoides/pullulans Trichosporon beigelii/cutaneum Trichosporon capitatum (Geotrichum capitatum) Williopsis californica/saturnuse Yarrowia lipolytica (Candida lipolytica) Zygoascus hellenicus (Candida hellenica)d Zygosaccharomyces rouxii Zygosaccharomyces bailii/bisporus Zygosaccharomyces florentinus/mellis
bu, en, yo fr, yo ch, en, yo br, ch br, bu, ch, en, fr, mi, ma, yo br, bm, ch, en, fr, ke, mi, yo bm, ke bm, ke, yo ke ch, ke ke yo fr, en br br, bm, ch, en, fr, ke, mi, yo bm, bu, ch bm, ch, en, se, mi, yo ch, ma ch, yo br, bu, ch, en, ke, yo ma ch, fr, yo ch, fr, yo ke
a
In parentheseis: imperfect state. Often found in: bu, butter; bm, natural buttermilk; ch, cheese; br, cheese brine; co, condensed milk; en, dairy environment; se, dairy sewage; fr, fruit mix for fruit-supplemented yogurt and quark; ke, kefir; mi, milk; ma, mastitis milk; re, rennet; yo, yogurt. c Bold print: very frequently found. d Lactose assimilation and fermentation. e New classification according to Kurtzman CP (2008): formerly Issatchenkia occidentalis: Pichia occidentalis, formerly Issatchenkia orientalis: Pichia kudriavzevii, formerly Pichia anomala: Wickerhamomyces anomalus, formerly Pichia fabianii: Lindneri fabianii, formerly Pichia jadinii: Lindnera jadinii, formerly Williopsis californica: Barnettozyma californica, formerly Williopsis saturnus: Lindnera saturnus. Data compiled from Barnett JA, Payne RW, and Yarrow D (1990) Yeasts: Characteristics and Identification. Cambridge: Cambridge University Press. b
A health risk from yeasts exists when facultative pathogens appear in food or on food-contaminated equipment. Facultative pathogens are known to cause infections in susceptible individuals such as infants, seniors, immunocompromised persons, persons with AIDS, diabetics, alcoholics, and pregnant women. In young children, oral thrush and nappy rash are not unheard of; allergies can also be involved. Immunosuppressed individuals can suffer from a serious mycosis of the organs. More than 50% of all fungal infections are caused by Candida spp. like C. albicans, C. dubliniensis, C. glabrata, C. krusei (¼Issatchenkia orientalis), C. parapsilosis (group I), C. metapsilosis (formerly C. parapsilosis group III), C. orthopsilosis (formerly C. parapsilosis group II), C. stellatoidea (a taxonomic synonym C. albicans but with differences in the pathogenesis), and C. tropicalis. But also species of other genera that can
appear in food are regarded as facultative pathogens: Filobasidiella neoformans subsp. neoformans, F. neoformans subsp. bacillisporus, and F. neoformans subsp. gattii; Cryptococcus spp.; Debaryomyces hansenii; Pichia guilliermondii; Rhodotorula spp.; Sporobolomyces spp.; and Trichosporon beigelii. An attack by Filobasidiella (teleomorph of Cryptococcus) leads to the dreaded Cryptococcus mycosis of the brain, lungs, bone marrow, kidneys, respiratory tract, digestive tract, eyes, skin, central nervous system, and nails. These yeasts are ubiquitously distributed, but Candida albicans and Filobasidiella neoformans, the species with the highest potential risks, are very seldom found in milk and dairy products. In food, potentially dangerous concentrations of toxins are not produced. Opportunistically pathogenic yeasts are generally found in milk from cows with mastitis.
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Cultured Milk Products Cultured milk products (fermented milk, sour cream, yogurt, drinking yogurt, cottage cheese, cream cheese, etc.) should be free from yeasts. These foods are ideal media for the propagation of yeasts, as they exhibit a low pH of 4–6, which is optimal for yeast growth. The approximate decimal doubling time in fruit yogurt without shaking for Saccharomyces cerevisiae is td ¼ 5 h (30 C), 10 h (20 C), 62 h (10 C), and 84 h (4 C), and for Galactomyces geotrichum is td ¼ 6 h (30 C), 12 h (20 C), 96 h (10 C), and 7 days (4 C). Due to the acidic environment (pH 3.8–4.5), there is limited competition from bacteria in yogurt. Most of those that can still grow alongside the yeasts and molds are LAB (i.e., Lactobacillus, Lactococcus, Weissella, and Leuconostoc spp.), streptococci, enterococci, bifidobacteria, propionic acid bacteria, acetic acid bacteria, Micrococcus kristinae, and Zymomonas mobilis. The enterobacteria, for example, die off quickly in yogurt. Spores of bacilli and of most clostridia cannot germinate. For the acid-tolerant anaerobic Pediococcus spp., Pectinatus cerevisiiphilus, and Megasphaera cerevisiae, this environment contains too much oxygen. Therefore, next to contamination with molds, contamination with yeasts is the largest microbial problem in these types of products. The annual economic losses to the dairy industry are substantial. Fruit-containing fermented milk products spoil quickly, owing to the high fructose and sucrose content of the fruit preparations, which encourage yeast growth and fermentation. A collapse (with nonfermenting yeasts) or swelling (with fermenting yeasts) of the cups, a change in texture, product discoloration, off-flavors, off-tastes, or visible microbial colonies on the product surface are the evidence of this spoilage. The fruit preparations are delivered to the dairy in large containers. As a rule, even negligible contamination with yeasts in these containers can lead to immense losses. An entire day’s yogurt production can be affected. These products cannot be offered for sale. In Germany, for example, such contaminated products are declared as hazardous waste and consequently have to be discharged on a special rendering facility. The risk of damage can be reduced by maintenance of the filling temperature of the fruit mix at < 15 C, consistent chilled storage of the container, avoidance of a stepwise emptying of the container, a high sugar concentration in the fruit preparation, and prompt processing. Large dairies increasingly produce the fruit preparations themselves. This increases the microbiological safety considerably, as the processes of portioning and transport are eliminated. The fruit preparation is pumped directly from the cooking boiler or
tubular heat exchanger through a cooler into the storage tank, from where the portions for the fruit yogurt are drawn directly. In the preparation of heat-treated yogurt, the mixture of fruit preparation and cultured milk is heated to 70–80 C in a scraped-surface or tubular heat exchanger (immediately before filling into the cups). This type of yogurt has a shelf life of 1–5 months longer than yogurt with viable LAB cultures. This product generally does not undergo changes due to the activity of LAB and fruit mix contaminants such as other acid-tolerant bacteria as well as yeasts and molds. With the exception of the ‘white mold’ Galactomyces geotrichum (anamorphic state ¼ Geotrichum candidum; formerly Oidium lactis or Oospora lactis), no fungi that are limited only to the fruit preparations or to the yogurt portion are found. The xerophilic species Zygosaccharomyces spp., Citeromyces matritensis, Candida versatilis, Pichia etchellsii, P. ciferrii, and P. sorbitophila are considerably more common in fruit preparations than in products made only from milk. On the other hand, the typical cheese yeast Debaryomyces hansenii is found more often in milk than in the fruit mix. The fermented milk portion is occasionally sweetened with sucrose syrup. In such cases, it is not possible to distinguish between yeast species originating from the production environment of the dairy and that of the fruit mix processor. In the dairy plant environment (floors, walls, equipment) the yeast species identified most commonly are Debaryomyces hansenii, Clavispora lusitaniae, Rhodotorula spp., Cryptococcus spp., Candida intermedia, C. parapsilosis, C. sorbophila, Kluyveromyces marxianus, Yarrowia lipolytica, Issatchenkia spp., Trichosporon spp., and Galactomyces geotrichum. The dominant yeast species from fruit preparations and contaminated fruit-containing cultured milk products are Saccharomyces cerevisiae, Pichia anomala, P. fabianii, P. membranifaciens, Hansenispora vineae, H. uvarum, Debaryomyces hansenii, Candida parapsilosis, C. tropicalis, C. intermedia, Torulaspora delbrueckii, and Clavispora lusitaniae. The molds Mucor spp. and Aureobasidium spp., as well as the unpigmented algae Prototheca spp., show yeast-like growth at submerged cultivation; hence a risk exists of mistaking them for yeasts. Moreover, Mucor spp. and Prototheca spp. produce large quantities of carbon dioxide and are opportunistic pathogens. Prototheca spp. have a physiological reaction pattern similar to that of Saccharomyces cerevisiae. A yeast-killing toxin designated mycocin HMK (Hansenula mrakii killer strain) produced by Williopsis mrakii (reclassified) was reported to have potential application in controlling yogurt spoilage caused by yeasts (see Fermented Milks: Yoghurt: Types and Manufacture).
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Neutral-pH Fruit-Containing Milk Products In milk products with a pH near neutrality, for example, milk rice, semolina pudding, or milk pudding, with additions based on fruit, cocoa, nuts, vanilla extracts, vitamin mixes, or cereals, yeasts are (next to bacilli and molds) the most common spoilage organisms. All yeast species that can be found in the added preparations, in the dairy-based component, and in the dairy environment are possible contaminants. The spoilage organisms are strictly oxidative as well as fermentative yeasts. The usual appearances of spoilage are blowing or sucking in of containers and a conspicuous change in product consistency or in flavor and taste. In most cases of spoilage, the fault lies with the added preparations, owing to the favorable nutrient conditions (glucose, fructose, sucrose, organic acids) as well as to the occasional long storage time of the product containers at 20 C; in such situations, a considerable increase in yeast count can occur. In addition, underlaid products are often produced, which means that first the fruit preparation is filled in the cup and then the hot dairy portion at a temperature of 70–80 C is added on top. No yeasts appear in the milk portion. Yeasts are also seldom found in toppings made from whipping cream or vegetable oil foams, as these have been heated and there is little possibility for yeasts to multiply.
Fermented Products Containing Yeasts A Japanese patent describes milk fermentation with Bifidobacterium longum together with yeasts under not strictly anaerobic conditions. The growth of these fastidious bacteria is positively influenced by the change in the milk environment brought about by the yeast growth. In Finland, viili is a popular set-curd milk product. It is consumed pure, or sweetened with jam and raisins, or with cereals. The milk is inoculated with a mesophilic, aroma-producing LAB culture and with Galactomyces geotrichum. Taxonomically, the yeast-like fungi Galactomyces spp. and also Geotrichum spp. and Dipodascus spp. are seen to be somewhere between yeasts and molds. Different authors will place the genera in one taxonomic order or the other. Because of the growth of the strictly oxidative white mold on the product–air interface, viili has a matte, velvety, white to light yellow surface. Galactomyces geotrichum works to develop the flavor and also hinders autooxidation of fats as well as contamination of the product surface by wild molds. The strains used are only those that have minimal lipase activity. Galactomyces geotrichum and similar species can produce a nutlike flavor. Similar products are the Norwegian tettemelk and
the Swedish la˚ngfil (see Yeasts and Molds: Geotrichum candidum). Leben is a fermented milk product from Arab countries and is similar to kefir. This product is made from fresh milk using a mesophilic LAB and thermophilic yogurt culture as well as yeasts. Correspondingly, one also finds ethanol, acetoin, and diacetyl in leben. Again Kluyveromyces marxianus becomes dominant within the yeast species. Generally, however, the microflora is not homogeneous, because leben is mostly homemade. Coliform bacteria, black and green molds, and enterococci are also regularly found in this product (see Fermented Milks: Middle Eastern Fermented Milks). Similar yeast-containing products are yaghurt (Middle East); dahi and misti dahi (India); acidophilus yeast milk, busa, kuban, kurunga, prohlada, and salomat (Russia); rob (Egypt); omaere (Africa); skyr (Iceland); samokisselis (Yugoslavia); airan and arsa (Asia); aker (Tibet); airag, khoormog, tschigan, and umdaa (Mongolia); matzoon (Armenia); brano milk (Bulgaria); felisowka (Poland); galazyme (France); cellarmilk (Norway); hooslanka, urda, and zhentitsa (Carpathian Mountains) (see Fermented Milks: Types and Standards of Identity). Kefir and Kumys Kefir is a type of fermented milk produced by a mixed flora consisting of yeasts, various LAB, and acetic acid bacteria (see Fermented Milks: Kefir). This flora forms nodules known as ‘kefir grains’. Typical kefir contains ethanol and predominantly L-(þ)-lactic acid and has effervescence owing to the presence of CO2. Under German regulations, kefir must contain at least 0.05% (w/v) ethanol and CO2 produced by yeast fermentation. According to the Swiss food manual, there should be a minimal yeast count of 105 cfu g1. The International Dairy Federation standard proposes a minimal yeast count of 104 cfu g1, but without being species specific. Kumys (also kumiss, koumyss, koumiss, coomys, kimiz) is a fermented beverage made from mare’s milk (see Fermented Milks: Asia). Its origins are in central Asia. The flora of kumys includes yeasts and various LAB. Owing to a relatively high lactose concentration in mare’s milk, alcohol content in kumys can reach 3.5%.
Cheese and Brine White Cheese The yeast species most frequently isolated from acid-curd cheeses (quark, Gervais, cottage cheese, cream cheese) are Galactomyces geotrichum, Kluyveromyces marxianus, K. lactis, Pichia membranifaciens, P. guilliermondii, Debaryomyces hansenii, Trichosporon beigelii, Issatchenkia
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orientalis, and Yarrowia lipolytica. The yeast count thresholds for defects such as slightly versus strongly ‘yeasty, fermenting, fruity, old, musty, bitter’ are 104–105 and 105–106 cfu ml1, respectively. The effect on sensory profile depends upon the species. The lowest count value to cause a sensory change was shown by Galactomyces geotrichum, followed by Kluyveromyces spp., Pichia membranifaciens, Saccharomyces cerevisiae, Debaryomyces hansenii, Issatchenkia orientalis, Yarrowia lipolytica, and Saccharomyces exiguus. A separator curd that had been initially contaminated with 100 cfu g1 showed the first signs of sensory defects after 5–7 days at 10 C; after 10 days, it was spoiled. Therefore, a good product should have <100 cfu g1 contaminants. The generation times of yeasts in curd at 2, 4, 6, and 10 C are 100, 50, 20, and 10 h, respectively. Yeasts have a direct correlation with the quality of acid-curd cheese, and their absence is an important indicator of good manufacturing practice (GMP). With the presence of yeasts the shelf life of products at 10–6 C is limited to 10–15 days. Soft, Semihard, and Hard Cheese Positive aspects
Yeasts are important in the development of the micoflora of surface-ripened cheese (see Cheese: Smear-Ripened Cheeses). It is commonly known that there exists a synergistic relationship among yeasts, Brevibacterium linens, Microbacterium spp., micrococci, and LAB. The survival of lactobacilli is enhanced by the presence of yeasts. The low pH resulting from the metabolism of the LAB is raised through lactate utilization by yeasts as well as the formation of alkaline products through proteolysis, so that aerobic, acid-sensitive bacteria such as Brevibacterium linens and micrococci can develop. For the growth of this bacterial flora, vitamins and amino acids are provided by yeasts. At the same time, yeasts are a protective culture against undesired enterobacteria, Clostridium tyrobutyricum, Staphylococcus aureus, or wild molds. Through the development of gas in Gorgonzola and other blue cheeses, an open doughy structure is promoted. Aromatic components are formed through lipolysis and proteolysis. Some yeast species or single strains that hydrolyze specific casein fractions have a positive effect on the growth of LAB and Penicillium roqueforti in blueveined cheeses. Aminopeptidases and carboxypeptidases from Galactomyces geotrichum are essential contributors to the breakdown of bitter peptides. Extracellular and intracellular peptidases with varying pH optima are found, respectively, in Yarrowia lipolytica and Candia catenulata, and in Trichosporon beigelii and Debaryomyces hansenii. The concentration of soluble nitrogen increases; glutamate and aspartate as well as tryptophan, leucine, methionine, phenylalanine, and other amino acids are deaminated. Sensorially important alcohols and aldehydes are
produced by utilization of amino acids and carbohydrates. The intracellular enzymes are found after yeast autolysis, that is, in the late stages of ripening. In cheese ripening studies done with aseptic curd slurries, Debaryomyces hansenii produced an acidic, fruity, and cheesy aroma. Other cheese isolates did not reveal similar tendencies. The species Yarrowia lipolytica, Trichosporon beigelii, and Galactomyces geotrichum had a positive influence on the aroma as a result of the breakdown of proteins and peptides. The species Clavispora lusitaniae, Pichia jadinii, and Williopsis californica showed weak proteolytic activity, but caused an increase in pH owing to their ability to utilize lactate. The strongest lipolytic and proteolytic activity was demonstrated by Yarrowia lipolytica. Debaromyces hansenii and other yeast species are able to assimilate the amines cadaverine, histamine, putrescine, and tyramine.
Negative aspects
Strong yeast growth on cheese can lead to defects in aroma and flavor (yeasty, moldy, putrid, overripe, alcoholic, musty, fermented, earthy, spicy, ammonia, pungent, rancid, sweet, and gassy). Sometimes, Pichia jadinii causes blowing in young cheese. The rind can become slimy and even semifluid owing to the growth of Cryptococcus spp., because this genus produces an extracellular starch-like capsule. The yeast species Pichia anomala reduces the growth of Penicillium roqueforti. Some DOPA-positive strains of Debaryomyces hansenii and Yarrowia lipolytica with high levels of metabolic activity produce an undesirable brownish pigment. With acid-curd cheeses, an overdominance of Galactomyces geotrichum is an indicator of spoilage; Yarrowia lipolytica was found to generate the strongest odor, from overripe to putrid, whereas Trichosporon beigelii was judged to produce a rancid odor. In mixed cultures, Issatchenkia orientalis inhibited the growth of Lactococcus lactis, whereas Lactococcus lactis stimulated the growth of Issatchenkia orientalis. In pickled cheese brine, acid-consuming yeasts increased the pH of the brine to a level that enabled the development of Staphylococcus aureus. This indicates the need to monitor yeast contamination in cheeses preserved by a combination of acid and high salt content. In Brick cheese, a low temperature during ripening, a high salt content, or drying of the cheese surface suppresses yeast growth, thereby prolonging the ripening process. Interactions among the various LAB and yeast organisms take place in the overall product formation. Because of this, one must specify the yeast count, species, and strains favorable to the respective cheese type. In some countries, the antifungal agents natamycin (pimaricin), propionate, or sorbate are used to inhibit the growth of yeasts on the surfaces of hard and semihard cheeses.
Yeasts and Molds | Yeasts in Milk and Dairy Products 751
Starter cultures
Yeasts, together with conidia of Penicillium camemberti, can be added as a starter culture directly to the milk (for white surface-ripened cheeses such as Camembert and Brie), or sprayed or brushed onto the rind together with the red smear flora (red cheese, acid-curd cheese, Croute Mixte cheese). Culture suppliers offer preparations with Debaryomyces hansenii and Pichia jadinii for the production of Brick cheese. For manufacturing acidcurd cheeses, a preparation with ‘mycoderma’ species is offered. Mycoderma were previously known as the pellicle-forming fungi Galactomyces geotrichum, Dipodascus capitatus, Geotrichum spp., Trichosporon beigelii, Issatchenkia orientalis, Pichia membranifaciens, and P. fermentans. The cultures contain selected strains with a defined ability to metabolize lactate, citrate, and acetate (deacidifying activity), as well as galactose and lactose (growth rate). They should also have proteinase, peptidase, and esterase activity (flavor, taste), and lipase and phospholipase activity (aroma), and be able to produce CO2 (doughy structure); tolerate anaerobiosis, acid, cold, and NaCl; have a high growth rate; and have an effect on cheese surface appearance, as well as inhibit wild molds (see Cheese: Starter Cultures: Specific Properties. Yeasts and Molds: Geotrichum candidum). Interior of cheeses
In the interior of cheeses made under strict standards of hygiene, the yeast count is low at 101–103 cfu g1. Metabolic products of importance are not expected in these cases. The process of diffusion between the rind and the core brings about deacidification. In the interior of raw-milk cheeses the counts and the diversity of the flora are higher than those in cheeses made from pasteurized milk. The species identified inside the raw-milk cheese Teˆte de Moine were Clavispora lusitaniae, Debaryomyces hansenii, Pichia pseudocactophila, Kluyveromyces marxianus, Rhodotorula mucilaginosa, Debaryomyces capitatus, and Pichia jadinii. Owing to the large differences in the yeast counts of the surface, middle, and core layers of the cheese, distinct variations in the metabolic products are observed. For example, in Taleggio cheese after 35 days of ripening at 3–10 C, the three layers mentioned above had pH values 6.5, 5.5, and 5.2, respectively. In cheeses that should have an adequate yeast flora in the interior to soften the cheese structure through CO2 production, the yeasts have to be added to the milk vat. Here, a naturally high yeast count can be established. The speed of deacidification of the core area will depend upon the size of the cheese and its dry weight. Yeast species and counts on cheese surface
In the first few days of the ripening period the yeast count on the surface increases rapidly and after 8–10 days it reaches a maximum of 106–109 cfu g1 or 108 cfu cm2.
This count decreases slightly during further ripening. The softer the rind, the higher the initial yeast count, and, therefore, the smaller the decrease in viable count. On soft, semihard, and hard cheeses, diverse yeast species are seldom found, but various species of the flora may dominate. The predominant species are Debaryomyces hansenii, Trichosporon beigelii, Yarrowia lipolytica, Kluyveromyces marxianus, Candida zeylanoides, C. catenulata, Torulapsora delbrueckii, and Galactomyces geotrichum. In well-ripened Mozzarella cheese, Saccharomyces cerevisiae and Kluyveromyces spp. were primarily found; in cheeses with a yeasty flavor defect, the species Yarrowia lipolytica, Issatchenkia orientalis, and Candida parapsilosis were found in addition to Saccharomyces cerevisiae and Kluyveromyces spp. On surface-ripened, acid-coagulated skim milk cheeses, Debaryomyces hansenii and Pichia membranifaciens were the predominant yeast species. On Brick cheese, the dominant yeasts were Debaryomyces hansenii and Galactomyces geotrichum. The surfaces of blue-veined cheese overwhelmingly had Debaryomyces hansenii, and on the inside Debaryomyces hansenii, Kluyveromyces marxianus, Saccharomyces cerevisiae, Pichia anomala, Torulaspora delbrueckii, and Galactomyces geotrichum were found. In Harzer cheese, a shift in the flora was observed. At the beginning, those primarily found in dry quark were Kluyveromyces marxianus, Trichosporon beigelii, Issatchenkia orientalis, and Dekkera anomala, while in the early stages of ripening Trichosporon beigelii and Candida catenulata were predominant. At the end, only Yarrowia lipolytica could be identified. Kluyveromyces marxianus, K. lactis, and Saccharomyces cerevisiae contribute to the characteristic open structure of Gorgonzola. In foil-ripened Raclette model cheese, a combined yeast starter culture of Debaryomyces hansenii, Pichia jadinii, Yarrowia lipolytica, and Galactomyces geotrichum was found to be advantageous. In general, different population spectra are observed depending on milk quality, water and salt content of the cheese, production hygiene, possible addition of yeast culture, storage temperature, stage of ripening, competing flora, and location of cheese sampling. Microbial flora is also affected by the geographic region, manufacturer, the range of products made on site, production lot or batch, age of the brine bath, and season of the year, as well as the methods of isolation, enumeration, and identification of yeasts used. As a rule, Debaryomyces hansenii is the prevailing species identified. Its role in the deacidification of surfaceripened cheeses is essential. This is due to its favorable metabolic capacity in the specific environment (fermentation of glucose, galactose, etc.; metabolism of lactose, lactate, citrate, etc.; proteolysis), high rate of sodium expulsion, potassium uptake potential, and its high salt tolerance (aw minimum 0.85). To protect against plasmolysis caused by NaCl and dehydration, osmotolerant yeasts produce large quantities of polyols such as
752 Yeasts and Molds | Yeasts in Milk and Dairy Products
glycerol, arabitol, xylitol, erythritol, and mannitol. Debaromyces hansenii still shows growth to 0.3 OD after 100 h incubation in a broth medium containing yeast extract, malt extract, glucose, and 18% (w/v) NaCl. It is followed by Kluyveromyces marxianus (15% NaCl), Torulaspora delbrueckii (14%), Yarrowia lipolytica (14%), Pichia farinosa (14%), Candida versatilis (14%), Saccharomyces unisporus (14%), Candida zeylanoides (13%), Candida catenulata (13%), Saccharomyces cerevisiae (9%; aw minimum 0.94), Galactomyces geotrichum (2%), and Trichosporon beigelii (2%). For Debaryomyces hansenii, the optimum for growth lies between 0 and 11% NaCl, and the inhibitory concentration of NaCl is 24%. Distinctly lower are the optimum concentrations for Clavispora lusitaniae (0–6%) and Saccharomyces cerevisiae (0–2%). The xerotolerant Zygosaccharomyces spp. and Citeromyces matritensis have a high tolerance to low aw values (minimum 0.650.60) in an environment with high sugar concentrations, yet are relatively sensitive to NaCl. In values of osmotic tolerance reported in the literature the specific test substance is generally named. For example, for a strain of Zygosaccharomyces rouxii the following aw values are given: glucose/fructose 0.71, ammonium sulfate 0.82, xylose 0.89, KCl 0.87, PEG 400 (polyethylene glycol with an average molecular weight of 400) 0.88, NaCl 0.89, PEG 200 (polyethylene glycol with an average molecular weight of 200) 0.95. As a rule, different values are observed depending on whether the strains were cultivated on agar plates (colony-forming capability as the criterion) or in broth (OD as the criterion); whether gas production was used as a parameter (fermentation as the criterion); and whether the ability to bud could be determined under a microscope (initiation of reproduction as the criterion). Also of diagnostic importance is what incubation temperature and time were used, as well as which factor is limiting their ability to grow (OD), ferment (amount of gas), or bud (number of budding cells). These values therefore allow differentiation between various strains of a species on the basis of differing test conditions and defined positive metabolic activities. Because of this, no general values can be given. Strains of the osmotolerant to osmophilic species Candida etchellsii, Sterigmatomyces halophilus, Pichia triangularis, and Candida halonitratophila are more salt tolerant than Debaryomyces hansenii. They do not grow at low NaCl concentrations (optimum is 11–13%) and they generally grow more slowly than Debaryomyces hansenii. Brine
In brines for surface-ripened soft, semihard, and hard cheeses with 12–22% NaCl, the dominant species are Debaryomyces hansenii and Candida versatilis. Also worth mentioning are the species Trichosporon beigelii, Candida
parapsilosis, C. tropicalis, C. polymorpha, C. zeylanoides, C. rugosa, C. intermedia, C. tenuis, Kluyveromyces marxianus, K. lactis, Clavispora lusitaniae, Issatchenkia orientalis, Pichia jadinii, Geotrichum spp., Yarrowia lipolytica, Saccharomyces spp., and Torulaspora delbrueckii. Several other species are less frequently isolated. In the brine of Nabulsi cheese, a Jordanian traditional boiled white cheese usually made from sheep’s milk and kept in brine with 20% NaCl, the halotolerant species Debaryomyces hansenii and Candida parapsilosis, and the halophilic species Pichia triangularis, P. etchellsii, and Sterigmatomyces halophilus were found. The yeast counts were between 102 and 106 cfu ml1. For the determination of halophilic species, one needs an isolation medium with salt (e.g., 15% NaCl). In the brines of Feta made in Germany and Italy, the yeast species found were Debaryomyces hansenii, Pichia membranifaciens, Yarrowia lipolytica, Kluyveromyces marxianus, Zygosaccharomyces bicuspidata, Candida magnoliae, C. zeylanoides, Saccharomyces cerevisiae, and Torulaspora delbrueckii. The yeast counts were mostly between 105 and 107 cfu ml1. Two products were free of yeasts because they had been pasteurized. From the consumer’s point of view, packages should be used up quickly after opening, so that yeasts do not multiply with the introduction of oxygen and develop a musty, yeasty, soapy, or rancid flavor in the product.
See also: Cheese: Smear-Ripened Cheeses; Starter Cultures: Specific Properties. Fermented Milks: Asian Fermented Milks; Kefir; Middle Eastern Fermented Milks; Types and Standards of Identity; Yoghurt: Types and Manufacture. Heat Treatment of Milk: Sterilization of Milk and other Products. Liquid Milk Products: Liquid Milk Products: Pasteurized Milk; Pasteurization of Liquid Milk Products: Principles, Public Health Aspects. Microorganisms Associated with Milk. Yeasts and Molds: Geotrichum candidum; Kluyveromyces spp.
Further Reading Barnett JA, Payne RW, and Yarrow D (1990) Yeasts: Characteristics and Identification. Cambridge: Cambridge University Press. Engel G, Einhoff K, Prokopek D, and Teuber M (1987) Beziehungen zwischen Hefenart, Hefenkeimzahl und hefenbedingten sensorischen Fehlern in Magerquark nach Zugabe definierter Hefenarten. Milk Science International 42: 428–430. Fleet GH (1990) Yeasts in dairy products: A review. Journal of Applied Bacteriology 68: 199–211. Geiges O and Spillmann H (1994) Yeast flora of commercial kefir and kefir cultures. Proceedings of the 24th International Dairy Congress, p. 403. Melbourne, VIC, Australia. Jakobsen M and Narvhus J (1996) Yeasts and their possible beneficial and negative effects on the quality of dairy products. International Dairy Journal 6: 755–768. Kurtzman CP, Robnett CJ, and Basehoar-Powers E (2008) Phylogenetic relationships among species of Pichia, Issatchenkia and Williopsis determined from multigene sequence analysis, and the proposal of Barnettozyma gen. nov., Lindnera gen. nov. and
Yeasts and Molds | Yeasts in Milk and Dairy Products 753 Wickerhamomyces gen. nov. FEMS Yeast Research 8(6): 939–954. Pfaller MA and Diekema DJ (2007) Epidemiology of invasive candidiasis: A persistent public health problem. Clinical Microbiology 20(1): 113–163. Rohm H, Eliskases-Lechner F, and Braeuer M (1992) Diversity of yeasts in selected dairy products. Journal of Applied Bacteriology 72: 370–376.
Rosi J (1978) The kefir (grain beverage) microorganisms: The yeasts (Saccharomyces delbrueckii and Saccharomyces cerevisiae). Scienza e Tecnica Lattiero-Casearia 29: 59–67. Seiler H and Ku¨mmerle M (1997) Die Hefenflora von Handelskefir. Deutsche Milchwirtschaft 48: 438–440. Wyder MT (1998) Identification and Characterization of the Yeast Flora in Kefyr and Smear-Ripened Cheese: Contribution of Selected Yeasts to Cheese Ripening. PhD Thesis, ETH, Zu¨rich, Switzerland.
Kluyveromyces spp. C Belloch and A Querol, Institute of Agrochemistry and Food Technology (IATA), CSIC, Valencia, Spain E Barrio, Cavanilles of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by C. Belloch, M. Hamamoto, F. Eliskases-Lechner, and H. Prillinger, Volume 3, pp 1417–1428, ª 2002, Elsevier Ltd.
Introduction The genus Kluyveromyces is constituted by yeasts isolated from a wide range of environments such as fruit flies, trees, seawater, and dairy products. The ubiquity of the genus has resulted in a high variability in the morphological, physiological, and molecular characteristics of the yeast strains, hence making very difficult the classification of yeast strains in the different species. In the first monograph on the genus Kluyveromyces, 18 species were included in the genus. Presently, a multisequence-based approach has reduced the number of species in the genus to six. Species that are most important for the dairy industry are K. lactis and K. marxianus, whose strains contribute to the ripening process of different cheeses and to the production of kefir. Several studies have exposed the exceptional heterogeneity in the physiology and genetics of these yeasts, which has led to their division into several ecological and geographical ‘populations’. The most interesting population is constituted by the dairy yeast pertaining to the variety K. lactis var. lactis, characterized by the presence of the lactose regulon in their genome. The recent completion of the whole-genome sequence has made K. lactis one of the best-known ‘nonconventional’ yeasts. Despite the taxonomical problems created by the heterogeneity of the Kluyveromyces yeasts, their metabolic diversity has led to numerous biotechnological applications such as production of enzymes, single-cell proteins, bioingredients from cheese whey, and metabolites with biological activity.
Recent History of the Genus Kluyveromyces The last edition of The Yeasts: A Taxonomic Study included 15 species in the genus Kluyveromyces. The diagnosis of the genus and key characters for species delineation were based on several indistinct
754
morphological traits such as cell shape, which may be ovoidal, ellipsoidal, cylindrical to elongate; absence of formation of true mycelium although pseudomycelium may be formed; sexual reproduction by ascus formation preceded or not by conjugation; formation of 1–4 (or more in several species) ascospores per ascus, with the ascospores being smooth, reniform, bacilliform, ellipsoidal, or spheroidal and tending to agglutinate after liberation. Molecular-genetic characterization of the species in the genus Kluyveromyces showed a very heterogeneous portrait of the genus. Karyotype analysis revealed that the species in the genus Kluyveromyces can be divided into two major groups. One group includes the species K. aestuarii, K. blattae, K. dobzhanskii, K. lactis, K. marxianus, K. thermotolerans, K. waltii, and K. wickerhamii, which exhibit chromosomal patterns with less than 10 chromosomes. The second group comprises the species K. africanus, K. bacillisporus, K. delphensis, K. lodderae, K. phaffii, K. polysporus, and K. yarrowii, composing the so-called ‘Saccharomyces-like’ group, because their karyotypes exhibited more than 12 chromosomes resembling that of the Saccharomyces species. This division of the genus Kluyveromyces was in accordance with the position of the species in phylogenetic reconstructions of the family Saccharomycetaceae. In the phylogenetic reconstructions based on the partial sequences of the nuclear 26S rRNA and the mitochondrial COXII genes, the species displaying the Saccharomyces-like karyotype appeared intermixed with species of the genus Saccharomyces, whereas the rest of species in the genus Kluyveromyces constituted a clearly separated monophyletic group (see Figure 1). A more detailed examination of the evolutionary tree of Saccharomycetaceae shows that the Kluyveromyces species are distributed into six clades, demonstrating that the morphological definition of the genus has no phylogenetic basis. Accordingly, a new genus Kluyveromyces based on phylogenetic relationships determined from multigene sequence analysis was proposed.
S. kudriavzevii S. cariocanus S. paradoxus
Saccharomyces
S. mikatae 95
S. bayanus S. pastorianus
98
S. cerevisiae K. viticola K. piceae 70
S. rosinii K. lodderae
Kazachstania
S. spencerorum S. martiniae K. africana S . kunashirensis K. unispora S. servazzii 95 N. castellii
96
Naumovia
N. dairenensis T. globosa T. pretoriensis 96 88
Torulaspora
T. franciscae T. delbrueckii Z. microellipsoides
78
Z. kombuchaensis Z. lentus
98
Zygosaccharomyces
Z. bisporus Z. bailii 99
C. glabrata N. delphensis
Nakaseomyces
N. bacillisporus C. castellii K. blattae
T. phaffii T. iriomotensis
87 83
V. polyspora K. yarrowii 99
Tetrapisispora
T. nanseiensis
99
T. arboricola
Vanderwaltozyma
H H. valbyensis K. lindneri
H. occidentalis
88 81
99
Hanseniaspora
H. vineae H. osmophila 99 L. kluyveri L. cidri L. fermentati
Lachancea
L. thermotolerans L. waltii
97
E. gossypii E. ashbyi 99
E. cymbalariae
Eremothecium
E. coryli E. sinecaudum 77 K. aestuarii
88
K. nonfermentans K. dobzhanskii
99
K. wickerhamii 93 95
Kluyveromyces
K. lactis K. marxianus
S. pombe 0.02 Figure 1 Phylogenetic tree showing the distribution of Kluyveromyces species in several genera of the family Saccharomycetaceae. The neighbor-joining tree is based on 26S rRNA gene sequences. Bootstrap values higher than 70% are given. Schizosaccharomyces pombe is the outgroup species.
756 Yeasts and Molds | Kluyveromyces spp.
Current Status of the Genus Kluyveromyces The new genus Kluyveromyces has been reduced to six species, K. marxianus, K. lactis, K. dobzhanskii, K. aestuarii, K. nonfermentans, and K. wickerhamii. In addition, the species K. lactis is presently divided into the varieties lactis and drosophilarum. The remaining species in the former Kluyveromyces genus have been assigned to the new or revised genera Kazachstania, Nakaseomyces, Tetrapisispora, Vanderwaltozyma, and Lachancea (see Figure 1). The new description of the genus Kluyveromyces is consistent with previous studies regarding ascospore shape and number and the sexual compatibility to form stable hybrids, as well as with genetic studies such as DNA base composition, DNA–DNA relatedness, and
isoenzyme analysis. Furthermore, the six species in the genus Kluyveromyces display similar morphological and physiological characteristics. Sexual reproduction occurs by ascus formation and the asci contain only 1–4 ascospores. Physiological traits common to all species are galactose assimilation and utilization of cadaverine, L-lysine, and ethylamine as nitrogen sources. Physiological key characters for differentiation of the species are presented in Table 1. In contrast, the monophyletic nature of the new genus Kluyveromyces does not conceal the significant genetic heterogeneity within the species when large numbers of strains are compared. Characterization of K. dobzhanskii, K. lactis, and K. marxianus yeasts by means of restriction analysis of their mitochondrial DNA (mtDNA) showed a high level of intraspecific pattern heterogeneity (see Figure 2). Restriction
Table 1 Physiological key characters for identification of species in the genus Kluyveromyces Assimilation Species
GL
Tre
Lac
In
Ce
Xy
Suc
K. aestuarii K. dobzhanskii K. lactis var. lactis K. lactis var. drosophilarum K. marxianus K. nonfermentans K. wickerhamii
þ v v
þ þ v
þ þ v v þ þ
v v þ
þ þ v v v v þ
v þ þ þ
þ þ þ þ v
10649
10585T
10374
10367
10315
1446
m
1442
10390
10669
10366
10356
1961T
1132
m
11211
10197
10194
10189
10182
10187
10180
10177
10148
10161
10147
m
1952T
Abbreviations: GL, -methyl-D-glucoside; Tre, trehalose; Lac, lactose; In, inulin; Ce, cellobiose; Xy, D-xylose; Suc, succinate. Data compiled from Lachance MA (1998) Kluyveromyces van der Walt emend. van der Walt. In: Kurtzman CP and Fell JW (eds.) The Yeasts, a Taxonomic Study, 4th edn. New York: Elsevier; Belloch C, Fernandez-Espinar T, Querol A, Garcia MD, and Querol A (2002) An analysis of inter- and intraspecific genetic variabilities in the Kluyveromyces marxianus group of yeast species for the consideration of the K. lactis taxon. Yeast 19: 257–268; Nagahama T, Hamamoto M, Nakase T, and Horikoshi K (1999) Kluyveromyces nonfermentans sp. nov., a new yeast species isolated from the deep see. International Journal of Systematic Bacteriology 49: 1899–1905.
m
21.2 9.4 6.5 4.9 4.2 3.5
2.3 2.0 1.9 1.6
K. dobzhanskii
K. lactis
K. marxianus
Figure 2 Mitochondrial restriction analysis of Kluyveromyces dobzhanskii, K. lactis, and K. marxianus with the endonuclease HinfI. Lanes m correspond to molecular size markers. Strain numbers are CECT (Spanish Type Culture Collection) numbers. From Belloch C, Barrio E, Uruburu F, Garcia MD, and Querol A (1997) Characterisation of four species of the genus Kluyveromyces by mitochondrial DNA restriction analysis. Systematic and Applied Microbiology 20: 397–408.
Yeasts and Molds | Kluyveromyces spp. 757
analysis of the mtDNA of 46 strains revealed 34 unique restriction patterns and 8 common patterns shared by the remaining 12 strains. mtDNA restriction using the enzyme HinfI revealed the highest genetic variability among strains in all species. Most of the total genetic diversity was attributable to variation among subgroups of strains within K. lactis and K. marxianus, indicating restriction of gene flow due to ecological or biogeographical barriers, asexual reproduction, or self-fertilization.
Intraspecific analysis of chromosomal patterns by pulsed-field gel electrophoresis (PFGE) showed a rich polymorphism in the species K. dobzhanskii, K. lactis, and K. marxianus (see Figure 3). The most common karyotype in the species K. lactis is constituted by six chromosomes distributed in five bands (the second band is a doublet), which is present in all strains in the variety K. lactis var. lactis. The homogeneity in the chromosomal patterns in this variety is in accordance with the heterothallism of the strains. On the contrary, the homothallic strains in the
S.c. 1952 K. dobzhanskii
10147 10180 10187 10189 10194 10197
S.c. 1961 K . l ac t i s
11395 10669
S.c. K. aestuarii K. dobzhanskii K. lacits
11337 K. marxianus 10340 K. wickerhamii 11390
S.c. 1446 1442 K . m ar x i an u s
10584 10585 10668 10649 10369 11232
Figure 3 Chromosomal profiles of strains in the new genus Kluyveromyces after pulsed-field gel electrophoresis (Contour-clamped homogeneous electrical field) under the following conditions: 600–1200 s, 75 V for 48 h; 120–400 s, 80 V for 48 h; and 60–120 s, 100 V for 18 h at 14 C in 0.8% chromosomal grade agarose gel. Lanes S.c. correspond to the karyotype of Saccharomyces cerevisiae. Data extracted from Belloch et al. (1998a; unpublished results).
758 Yeasts and Molds | Kluyveromyces spp.
variety K. lactis var. drosophilarum display very different chromosomal patterns. The electrophoretic karyotype of the strains in the species K. marxianus also shows a common set of eight chromosomes. This species-specific pattern can be recognized in almost all strains. Variations from the basic species-specific pattern include the presence of one or two extra bands with different mobility in some strains. The species showing the most different karyotypes was K. dobzhanskii. The strains analyzed exhibited such different karyotypes that a common chromosomal pattern could not be found. Five different
karyotypes could be distinguished, some of them shared by more than one strain. The intra- and interspecific genetic variability among the species in the new genus Kluyveromyces examined by sequence analysis of the 5.8S rRNA gene and comparisons of the two internal transcribed spacers (5.8S-ITS rRNA) of 59 strains revealed a complex sequence heterogeneity. Figure 4 shows the maximum parsimony (MP) tree, which minimizes the number of nucleotide substitutions required to connect the different 5.8S-ITS sequences from the strains in the genus Kluyveromyces. The highest
K. nonfermentans JCM10227 JCM10230 JCM10231 JCM10232 JCM10234 JCM10236
K. aestuarii 1949T 23
15
(100%)
H 11390 6169, 6170 6171, 6172 6191
42
1
K. wickerhamii (83%)
11398 11399
16
1966T
4
7
6
7 10
A 1446 B
CBS 9818 CBS 9820
B
1122, 10669 10390 C 1 11380,11394 11337 11396, Est86 CBS 9819 4 VKM-831 CBS 9820 1 CBS 9815 CBS 9816 11340 CBS 9817 D F 4
A
1
1 1
1961NT, 1931 1 10356, 10361 11366, 11395, 11397, 11401
1
1 1442, 10315 2 10357, 10368 1043 10374, 10379 10584, 10585T 10668, MG14 D MR12 2 1 1123 10649 1 11389 10369 F E 10367 10370 C
G
E
10177 10180 10187
K. lactis (99%)
6 1952T
K. dobzhanskii (93%)
K. marxianus (99%) Figure 4 Maximum parsimony tree that minimizes the number of nucleotide substitutions (indicated on the branches) required to connect the different 5.8S-ITS sequences of the strains within the circles. The alignment of the 5.8S-ITS sequences showed 120 variable positions out of 642, out of which 78 were phylogenetically informative. Numbers given in parentheses are the percentage of bootstrap values. CBS, Centraalbureau voor Schimmelcultures; JCM, Japanese Culture Collection; VKM, All-Russian Collection of Microorganisms. Strain numbers without collection acronym are CECT (Spanish Type Culture Collection) numbers.
Yeasts and Molds | Kluyveromyces spp. 759
variability in the sequence of the 5.8S-ITS rDNA region was found within the species K. lactis and K. marxianus, both represented by a large number of strains. The species K. aestuarii and K. nonfermentans isolated from marine environments in the United States and Japan appear as sister taxa. The first species to diverge is the type strain of K. wickerhamii isolated from Drosophila montana in the United States. The remaining three species K. lactis, K. dobzhanskii, and K. marxianus appear more closely related than the others although they are clearly separated. The next species to diverge is K. lactis. The most heterogeneous strains, constituting the variety drosophilarum, appear separated into seven different groups. These strains have been isolated from natural environments such as water, insects, and trees or fruits in Europe, Far East, Africa, and North America. The last group of strains appearing at the end of the branch constitute the variety lactis; most of the strains in this group have been isolated from dairy products. Finally, K. dobzhanskii and K. marxianus are the last species to diverge. The strains in the species K. dobzhanskii have been isolated exclusively from insects in Europe and the United States. The species K. marxianus is constituted by strains isolated from very different environments such as plants, beer, wine, clinical sources, and dairy products in Europe, Africa, and the United States. Several groups of strains can also be recognized in the species K. marxianus, but none of them is constituted exclusively by dairy strains. Sequence comparisons of the 5.8S-ITS rDNA established the existence of nucleotide substitutions involving restriction site gains or losses in the sequences of strains belonging to the different species. This was found very useful to formulate strategy for discrimination among the species in the genus Kluyveromyces.
Key to Species in the Genus Kluyveromyces PCR amplification of the 5.8S-ITS rDNA and restriction with specific endonucleases produces different band patterns useful for discrimination of the species in the genus Kluyveromyces (see Table 2). The species K. aestuarii, K. nonfermentans, K. marxianus, K. dobzhanskii, and K. lactis var. lactis produce species-specific patterns after digestion with HinfI. The strains within the variety K. lactis var. drosophilarum yield three different patterns. Pattern I is identical to the pattern of K. lactis var. lactis. In silico restriction of the 5.8SITS sequences generates no discriminative restriction bands. However, strains displaying this pattern can be distinguished easily by their lactose utilization, which is positive in the variety lactis and negative in the variety drosophilarum. Pattern II is identical to the pattern of K. wickerhamii; however, they can be distinguished by their different restriction bands with the enzyme AluI. Pattern III is different from the other two patterns in the variety drosophilarum and it is also different from the rest of restriction patterns displayed by the species of the genus.
Taxonomy of the Dairy Yeast Species Kluyveromyces lactis and Kluyveromyces marxianus The strains in the genus Kluyveromyces inhabit very different environments both natural and man-made; however, strains isolated from dairy products belong only to the species K. marxianus and K. lactis. The ability to use lactose as the sole carbon source as well as the dairy origin of strains within
Table 2 Key for species differentiation in the genus Kluyveromyces Fragment size Species
PCR product
Hinfl
AluI
K. aestuarii K. dobzhanskii K. lactis var. lactis K. lactis var. drosophilarum I II III K. marxianus K. nonfermentans K. wickerhamii
725 725 725 725 725 725 725 725 725
350 þ 170 þ 160 þ 40 240 þ 180 þ 115 þ 100 þ 80 285 þ 180 þ 115 þ 100 þ 60 285 þ 180 þ 115 þ 100 þ 80 240 þ 180 þ 115 þ 80 þ 60 þ 50 240 þ 190 þ 180 þ 60 þ 50 240 þ 180 þ 115 þ 60 þ 60 þ 50 350 þ 170 þ 115 þ 50 þ 40 240 þ 180 þ 115 þ 80 þ 60 þ 50
580 þ 150 395 þ 180 þ 130 395 þ 180 þ 130 395 þ 180 þ 130 395 þ 180 þ 150 395 þ 180 þ 130 395 þ 180 þ 150 500 þ 150 þ 70 520 þ 130 þ 70
Differences in the size of the restriction fragments obtained with the enzymes HinfI and AluI of the 5.8S-ITS PCR product are used for differentiation among the strains in the different species. Data compiled from Belloch C, Barrio E, Garcia MD, and Querol A (1998b) Phylogenetic reconstruction of the genus Kluyveromyces: Restriction map analysis of the 5.8S rRNA gene and the two ribosomal transcribed spacers. Systematic and Applied Microbiology 21: 266–273; Belloch et al., unpublished results.
760 Yeasts and Molds | Kluyveromyces spp.
the species K. lactis was the basis for the division of this species into the varieties K. lactis var. lactis and K. lactis var. drosophilarum. The strains in the variety lactis are homogeneous in their karyotypes and 5.8SITS sequences although they display variability in their sugar assimilation patterns (see Table 3). The strains in the variety drosophilarum are very heterogeneous and combinations of karyotypes, 5.8S-ITS sequences, and assimilation patterns produce no clear groups of strains. However, a specific population of K. lactis var. drosophilarum strains isolated from European natural habitats showed the same karyotypes and 5.8S-ITS sequences as the strains in the variety K. lactis var. lactis. This specific population of strains was named ‘krassilnikovii’. Other populations of strains within the variety drosophilarum separated on the basis of 5.8S-ITS sequencing were named ‘aquatic’, ‘oriental’, ‘drosophilarum’, ‘phaseolosporus’, ‘pseudovanudenii’, ‘vanudenii’, and ‘new’ (see Table 3). Kluyveromyces marxianus is the only inulin-assimilating Kluyveromyces species that does not assimilate or ferment -glucosides and grows well at 37 C. Molecular-genetic studies indicate that the strains in this species are very
heterogeneous in their karyotypes and 5.8S-ITS sequence types. The K. marxianus species was formerly represented by five populations denominated ‘fragilis’, ‘bulgaricus’, ‘cicerisporus’, ‘wikenii’, and ‘marxianus’ on the basis of morphological and physiological characters (see Table 4). However, only the group constituted by the population ‘bulgaricus’ isolated from yogurt (type E in Figure 4) shares similar karyotype profile and 5.8S-ITS sequence.
Recent Advances in Genomic Studies of Kluyveromyces lactis and Kluyveromyces marxianus The complete genome sequencing of a K. lactis strain was achieved by the ‘Genolevures 2’ consortium in 2004. The genome of the K. lactis-type strain has a size of 10.6 Mb distributed into six chromosomes. Comparison of the K. lactis genome with other yeast genomes revealed that K. lactis has a very compact genome (71.6 gene density), with less redundancies than other species, as well as 38 unique open-reading frames (ORFs). Comparison of the K. lactis and Saccharomyces cerevisiae genomes revealed that 78%
Table 3 Summary of assimilation tests, electrophoretic karyotyping, and 5.8S-ITS sequence type displayed by strains in the species Kluyveromyces lactis Assimilation Strain numbers
Lac
Mel
Cell
Sal
Mal
GL
ITS typea
Population of K. lactis
CECT 1121 CECT 1961 CECT 10356 CECT 10361 CECT 10364 CECT 10366 CECT 11401 CECT 1122 CECT 11380 CECT 11394 CECT 11395 CECT 11397 CECT 10669 CECT 10390 CECT 11337 CBS 9821 CECT 11340 CBS 9818 CBS 9815 CECT 11398 CECT 11390
þ þ þ þ þ þ þ
þ þ þ þ þ þ þ þ þ nd nd nd þ þ
þ þ þ þ þ þ þ þ þ þ þ nd nd nd þ
þ þ þ þ þ þ þ þ þ nd nd nd þ
þ þ þ þ þ þ þ þ þ þ þ þ þ
þ þ A þ þ þ þ þ þ þ nd nd nd þ þ
A A A lactis A A A B B B B B B C C C D E F G H
lactis lactis lactis lactis lactis lactis krassilnikovii krassilnikovii krassilnikovii krassilnikovii krassilnikovii vanudenii drosophilarum drosophilarum New phaseolosporus pseudovanudenii Oriental aquaticus aquaticus
a Correspond to the 5.8S-ITS sequence types in Figure 4. Abbreviations: Cell, cellobiose; Lac, lactose; Mal, maltose; Mel, melibiose; nd, not determined; Sal, salicin; GL, -methyl-Dglucoside. Data compiled from Belloch C, Fernandez-Espinar T, Querol A, Garcia MD, and Querol A (2002) An analysis of inter- and intraspecific genetic variabilities in the Kluyveromyces marxianus group of yeast species for the consideration of the K. lactis taxon. Yeast 19: 257–268; CBS, www.cbs.knaw.nl.
Yeasts and Molds | Kluyveromyces spp. 761 Table 4 Summary of assimilation tests and 5.8S-ITS sequence type displayed by strains in the species Kluyveromyces marxianus Assimilation Strain numbers
Lac
Mel
Cell
Suc
Mal
Tre
ITS typea
Population of K. marxianus
CECT 1446 CECT 10585 CECT 1043 CECT 10584 CECT 10668 CECT 10649 CECT 10369
þ þ þ þ þ
þ þ þ þ
þ þ þ þ þ þ
nd
v
A B C B B D E
marxianus marxianus marxianus fragilis cicerisporus wikenii bulgaricus
a Correspond to the 5.8S-ITS sequence types in Figure 4. Abbreviations: Lac, lactose; Mel, melibiose; Cell, cellobiose; Suc, sucrose; Mal, maltose; Tre, trehalose. Belloch et al., unpublished data.
of the genes belonging to clusters of syntenic genes correspond to intermingled series in which one region of the K. lactis genome corresponds to two (and sometimes more) distinct chromosomal regions in S. cerevisiae. Compared with the 56 duplicated blocks scattered throughout the genome map in S. cerevisiae (plus 21 blocks in subtelomeric regions), only 8 blocks (1 tandem) are duplicated in K. lactis. However, none of the eight duplicated blocks in K. lactis coincide with the duplicated blocks in S. cerevisiae, indicating a distinct formation, unrelated to the major duplication event that occurred in an ancestor of S. cerevisiae. Apparently, the eight duplicated blocks observed in K. lactis may have originated from independent segmental duplications because they are too few to indicate massive genome duplications. In addition to the duplication events, the genome of K. lactis lacks five genes, including the genes for sterol uptake, which may explain the lack of anaerobic growth by this yeast. Presently, only a small part (approximately 17%) of genome sequence of K. marxianus is available. The type strain K. marxianus var. marxianus contains 10 chromosomes with an estimated genome size of 14 Mb. Comparison of K. marxianus and S. cerevisiae genomes revealed that several genes that are adjacent in K. marxianus have homologues that are distributed in two different chromosomal regions in S. cerevisiae. Such series of genes may reflect the chromosomal map of the common ancestor of S. cerevisiae and K. marxianus. According to the ‘Genolevures’ sequencing data, an expression microarray for the yeast K. lactis consisting of 482 genes involved in central metabolism facilitated transport, and stress response was developed. Using this partial-genome microarray a comparison of the expression patterns of two dairy strains was achieved. The study revealed unexpected differences in expression of genes involved in the respiratory and fermentative metabolic pathways of
different carbon sources. Presently, a commercial microarray containing ORFs of the whole K. lactis genome has been made available.
Lactose Metabolism, a Salient Characteristic of Kluyveromyces spp. Yeast species that assimilate lactose aerobically are widespread, but those that ferment lactose are very rare. The species K. lactis and K. marxianus include strains that are lactose-fermenting yeasts. Lactose utilization in K. lactis is an inducible system triggered by lactose or galactose. The lactose regulon in K. lactis consists of LAC4 (encoding -galactosidase) and LAC12 (encoding lactose permease) genes. Both genes are contiguously placed in the genome of K. lactis sharing a divergent promoter that might have been cotransferred from external origin. The presence of lactose regulon in K. lactis var. lactis was decisive for its survival in milk products and, therefore, to explain the adaptation of this yeast to manmanipulated environments. The lactose-negative strains within K. lactis var. drosophilarum have also been investigated for the presence of lactose regulon genes. Complementation of strains with functional LAC4 and LAC12 genes produced lactose-negative strains; therefore, the locus containing nonfunctional genes is absent in natural K. lactis var. drosophilarum strains. In the case of K. marxianus, most of nondairy strains are able to assimilate lactose. Similar studies complementing lactose-negative K. marxianus with functional LAC12 genes yielded lactosepositive strains, indicating that these strains are mutant for the permease gene. Furthermore, comparison of LAC4 gene sequences of K. marxianus- and K. lactis var. lactis-type strains revealed a very high sequence similarity. Additionally, these facts indicate that LAC4 gene might have originated from K. marxianus and then transferred to K. lactis var. lactis, while both concur in dairy products.
762 Yeasts and Molds | Kluyveromyces spp.
Role of Kluyveromyces spp. in Dairy Products Kluyveromyces marxianus and K. lactis (Kluyveromyces spp.) are the only lactose-fermenting species regularly found in milk and dairy products. Their main role in dairy products is lactose metabolism, but they also possess weak proteolytic and lipolytic activities. The ability of Kluyveromyces spp. to metabolize milk constituents (lactose, proteins, and fat) makes them very important in cheese ripening and fermented milk products such as kefir, as they contribute to maturation and aroma formation. However, despite the importance of yeasts in dairy products, commercial yeast starters are not commonly used and the yeast flora developing in cheeses and other dairy products appears as a result of spontaneous contamination. The occurrence of yeasts in cheese is not unusual as they tolerate low pH, low water activity (aw) (moisture), elevated salt concentration, and low storage temperatures. Investigation of yeast microbiota of cheese brines, dairy utensils, raw milk, and smear water revealed the presence, among other yeasts, of Kluyveromyces spp. Kluyveromyces marxianus can grow in milk at 25 C, reaching populations of 108 cfu ml1 in 3 days. Salt concentration affects growth rate; at 15% salt concentration, the maximum growth reached was 105 cfu ml1. Temperature affects lactose fermentation rate; lactose utilization at 10 C is 70% of the total utilization at 25 C. Utilization of lactose produces galactose, glucose, ethanol, and glycerol. Proteolytic activity of K. marxianus in milk is of medium importance when compared with other proteolytic yeasts such as Debaryomyces hansenii and Yarrowia lipolytica. Concentration of total free amino acids in milk increased very little after 12 incubation days and the main amino acids present were leucine, valine, alanine, isoleucine, and phenylalanine. Similarly, K. marxianus excretes intermediate levels of lipases in milk. Increase in free fatty acids in milk was significant after 12 days growth at 25 C. However, the different free amino acids and fatty acids produced by the growth of K. marxianus in milk indicate that the proteases and lipases are different from those produced by other dairy yeasts. The lactose-fermenting Kluyveromyces spp. yeasts produce ethanol but also aromatic esters of fatty acids and acetaldehyde. In experimental hard cheeses, the presence of Kluyveromyces spp. increased the production of ethanol, isoamyl alcohol, and ethyl acetate. Sensory analysis of the slurries after incubation at 25 C for 7 days associated the growth of K. marxianus with acidic, cidery, alcoholic, fermented, and fruity flavors as a result of volatile fermentation products such as formic or acetic acid. Kluyveromyces spp. are part of the microbiota of the surface and interior of the cheese, and they play an important role in the ripening process of several cheese
varieties. The growth of Kluyveromyces spp. on the surface of blue-veined cheese contributes to the open structure of the cheese. Production of CO2 due to lactose fermentation generates small holes in the cheese curd, helping the growth of aerobic Penicillium during the ripening process. After the first days of cheese maturation, Kluyveromyces yeasts disappear from the surface but appear in high counts in the cheese interior. The lactose-fermenting ability of Kluyveromyces spp. promotes their growth in the interior of the cheeses, where other dominant yeasts such as D. hansenii and Y. lipolytica are scarce. Kluyveromyces strains are constituents of the yeast microbiota in traditional kefir. The kefir grain is produced by the synergic growth of yeasts such as Kluyveromyces spp. and Saccharomyces spp. and several lactic acid bacteria. Ethanol and CO2 production due to lactose fermentation by Kluyveromyces spp. gives kefir its particular alcoholic aroma. In recent years, several microorganisms have been selected by starter-producing companies for their functionalities in the dairy industry. These microorganisms are mainly lactic acid bacteria, molds, and yeasts. Presently, specific dairy cultures with application for cheese ripening and kefir production containing strains of Kluyveromyces spp. are commercially available.
The Potential Biotechnological Applications of Kluyveromyces Yeasts The broad spectrum of metabolic activities displayed by several strains of Kluyveromyces has led to the investigation of different biotechnological applications of these yeasts. In earlier times, the dairy Kluyveromyces yeasts were mainly investigated for production of -galactosidase. Lactase ( -galactosidase from K. lactis) was produced commercially by several enzyme-producing companies for hydrolyzing lactose into the sweeter-tasting monosaccharides (glucose and galactose) in the manufacture of ice cream, fermented milk, and milk drinks. Presence of lactose in milk makes milk not suitable for the majority of world’s adult population due to lactose intolerance. Problems of lactose intolerance are especially severe in African and Asian populations; therefore, low-lactose milks are very important in food-aid programs. However, lactase usage has not reached its full potential at present because lactase production is expensive and the enzyme can be effective only at low temperatures. Recent studies have reported the easy and cost-effective production of -galactosidase by K. marxianus growing on cheese whey; also the growth of K. marxianus on cheese whey is effective in reducing whey disposal problems. Other enzymes of industrial interest produced by K. marxianus are -glucosidases for hydrolysis of cellulose-containing materials, inulinase for production of
Yeasts and Molds | Kluyveromyces spp. 763
fructose syrups from inulin-containing feed stocks, and polygalacturonases for reduction of viscosity in fruit processing products. One of the major achievements of the biotechnological industry in the 1990s was the use of K. lactis as expression host for production of the milk clotting enzyme bovine chymosin. This protein was the first heterologous enzyme originating from a higher eukaryote that was produced in a microorganism. Presently, more than 40 proteins have been expressed and produced using K. lactis. Some of the recombinant proteins secreted by K. lactis are -amylase, cellulase, endoxylanase, glucoamylase, insulin precursor, interferon, interleukin beta, invertase, lipase, and xylanase. In recent years, Kluyveromyces spp. yeasts have been investigated for their production of peptides derived from whey fermentation with potential bioactive sites. Milk whey contains water-soluble milk proteins such as -lactoglobulin, -lactalbumin, bovine serum albumin, and immunoglobulins IgG, IgA, and IgM. Proteolysis of whey proteins by K. marxianus can result in bioactive peptides with potential applications in food products; short peptides produced during proteolysis of whey proteins are among the most potent pharmacologically active agents. As an example, peptides derived from whey protein proteolysis have been reported to show angiotensin-I-converting enzyme (ACE) inhibitory activity. Furthermore, extensive research has been done on the antitumor activity of kefir and kefir grains due to the ability of specific cultures isolated from kefir to bind to mutagenic substances such as imidazole and indole. Another recent application of Kluyveromyces is the production of oligosaccharides used as components of functional foods or nutraceuticals. These food bioingredients inhibit the growth of pathogenic Gram-negative bacteria and stimulate the growth of Bifidobacterium sp. in the human and animal intestines. Specifically, production of fructooligosaccharides (FOSs) and galactooligosaccharides (GOSs) by Kluyveromyces is presently investigated. Several studies have shown that in the presence of high concentrations of lactose and galactose, the -galactosidase enzyme of the dairy yeasts K. lactis and K. marxianus shows transferase activity and produces galactosyl-oligosaccharides. Similarly, the inulinase activity shown by K. marxianus can be used for production of FOSs. In the next future, products containing bioingredients may play an important role in improving human health and well-being; therefore, current research on the production of metabolites from Kluyveromyces spp. has a promising prospect in the future. See also: Cheese: Microbiology of Cheese. Enzymes Exogenous to Milk in Dairy Technology:
-D-Galactosidase; Fermented Milks: Kefir; Koumiss. Lactose and Oligosaccharides: Lactose: GalactoOligosaccharides. Yeasts and Molds: Yeasts in Milk and Dairy Products.
Further Reading Belem MAF, Gibbs BF, and Lee BH (1998) Proposing sequences for peptides derived from whey fermentation with potential bioactive sites. Journal of Dairy Science 82: 486–493. Belem MA and Lee BH (1998) Production of bioingredients from Kluyveromyces marxianus grown on whey: An alternative. Critical Reviews in Food Science and Nutrition 38(7): 565–598. Belloch C, Barrio E, Garcia MD, and Querol A (1998a) Inter- and intraspecific chromosome pattern variation in the yeast genus Kluyveromyces. Yeast 14: 1341–1354. Belloch C, Barrio E, Garcia MD, and Querol A (1998b) Phylogenetic reconstruction of the genus Kluyveromyces: Restriction map analysis of the 5.8S rRNA gene and the two ribosomal transcribed spacers. Systematic and Applied Microbiology 21: 266–273. Belloch C, Barrio E, Uruburu F, Garcia MD, and Querol A (1997) Characterisation of four species of the genus Kluyveromyces by mitochondrial DNA restriction analysis. Systematic and Applied Microbiology 20: 397–408. Belloch C, Fernandez-Espinar T, Querol A, Garcia MD, and Querol A (2002) An analysis of inter- and intraspecific genetic variabilities in the Kluyveromyces marxianus group of yeast species for the consideration of the K. lactis taxon. Yeast 19: 257–268. Belloch C, Querol A, Garcia MD, and Barrio E (2000) Phylogeny of the genus Kluyveromyces inferred from the mitochondrial cytochrome-c oxidase II gene. International Journal of Systematic and Evolutionary Microbiology 50: 405–416. Bolotin-Fukuhara M, Toffano-Nioche C, Artiguenave F, et al. (2000) Genomic exploration of the hemiascomycetous yeasts. 11. Kluyveromyces lactis. FEBS Letters 487: 66–70. Choisy C, Desmazeaud M, Gripon JC, Lamberet G, Lenoir J, and Tourneur C (1986) Microbiological and biochemical aspects of ripening. In: Eck A (ed.) Cheesemaking: Science and Technology, pp. 62–100. Paris: Lavoisier. Fonseca GG, Hinzle E, Wittmann C, and Gombert AK (2008) The yeast Kluyveromyces marxianus and its biotechnological potential. Applied Microbiology and Biotechnology 79: 339–354. Kurtzman CP (2003) Phylogenetic circumscription of Saccharomyces, Kluyveromyces and other members of the Saccharomycetaceae, and the proposal of the new genera Lachancea, Nakaseomyces, Naumovia, Vanderwaltozyma and Zygotorulaspora. FEMS Yeast Research 4: 233–245. Kurtzman CP and Robnett CJ (1998) Identification and phylogeny of ascomycetous yeasts from analysis of nuclear large subunit (26S) ribosomal DNA partial sequences. Antonie van Leeuwenhoek 73: 331–371. Kurtzman CP and Robnett CJ (2003) Phylogenetic relationships among yeasts of the ‘Saccharomyces complex’ determined from multigene sequence analyses. FEMS Yeast Research 1554: 1–16. Lachance MA (1998) Kluyveromyces van der Walt emend. van der Walt. In: Kurtzman CP and Fell JW (eds.) The Yeasts, a Taxonomic Study, 4th edn., pp. 227–247. New York: Elsevier. Nagahama T, Hamamoto M, Nakase T, and Horikoshi K (1999) Kluyveromyces nonfermentans sp. nov., a new yeast species isolated from the deep see. International Journal of Systematic Bacteriology 49: 1899–1905. Naumov GI, Naumova ES, Barrio E, and Querol A (2006) Genetic and molecular study of the inability of the yeast Kluyveromyces lactis var. drosophilarum to ferment lactose. Microbiology 75(3): 248–252. Naumova ES, Nataliya N, Sukhotina NN, and Naumov GI (2005) Molecular genetic differentiation of the dairy yeast Kluyveromyces lactis and its closest wild relatives. FEMS Yeast Research 5(3): 263–269. Panesar PS (2008) Production of -D-galactosidase from whey using K. marxianus. Research Journal of Microbiology 3(1): 24–29.
764 Yeasts and Molds | Kluyveromyces spp. Roostita R and Fleet G (1996) Growth of yeasts in milk and associated changes to milk composition. International Journal of Food Microbiology 31: 205–219. Seiler H and Busse M (1990) The yeasts of cheese brines. International Journal of Food Microbiology 11: 289–304. Wyder M-T and Puhan Z (1999) Role of selected yeasts in cheese ripening: An evaluation in aseptic cheese curd slurries. International Dairy Journal 9: 117–124.
van Ooyen AJJ, Dekker P, Huang M, et al. (2006) Heterologous protein production in the yeast Kluyveromyces lactis. FEMS Yeast Research 6: 381–392.
Relevant Websites http://www.genolevures.org – Genolevures consortium.
Geotrichum candidum F Eliskases-Lechner, Federal Institute of Alpine Dairying, Jenbach, Austria M Gue´guen and J M Panoff, University of Caen Basse–Normandie, CAEN Cedex, France ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by F. Eliskases-Lechner, Volume 2, pp 1229–1234, ª 2002, Elsevier Ltd.
Introduction Geotrichum candidum is an acid-tolerant, yeast-like fungus, often characterized as an intermediate between molds and yeasts but classified as a yeast for more than 25 years. It is the best-known species of the genus and very common, occurring on moist substrates rich in nutrients. Apart from milk and milk products, the habitat of this worldwidedistributed species encompasses soil, water, air, maize and other cereals, rice grain, grapes, citrus fruits, bananas, tomatoes, cucumber, frozen fruitcake, fruit juices, bread, animals, and humans. Geotrichum candidum is used in dairies as a culture for cheesemaking and in some traditional fermented milks, especially those from northern Europe, but is also frequently recorded as a spoilage organism, called ‘machinery mold’ because the undesired contamination is mainly caused by deficiencies in equipment hygiene. Furthermore, this species is weakly pathogenic for plants, animals, and also humans. The main human disorders caused by G. candidum are bronchial or pulmonary infections known as geotrichosis (see Cheese: Secondary Cultures. Yeasts and Molds: Yeasts in Milk and Dairy Products). The taxonomic position of G. candidum was revised in 2004 by de Hoog and Smith. The current taxonomy for the teleomorphic state (sexual form) is as follows: Ascomycota (phylum), Hemiascomycetes (class), Saccharomycetales (order), Dipodascaceae (family), Galactomyces (genus). For the anamorphic state (asexual form) the taxonomy is Candidaceae (family) and Geotrichum (genus). The genus Geotrichum is composed of 22 species (including 10 sp. nov.). The ecology of the species of the genus Geotrichum shows a rather unexpected degree of consistency given the large phylogenetic distances between the species. For several years, the taxonomic position of G. candidum was unclear. DNA–DNA reassociation experiments with Galactomyces geotrichum and its anamorph G. candidum showed that representative strains were not homogenous. Four groups were found, and all the studied strains originating from dairy products were found to be in the same group, including the type culture of Geotrichum javanense, which is an isolate from yogurt. On the basis of its rDNA
sequences, nDNA–DNA reassociation data, mol% GþC of nDNA, and physiological characters, de Hoog and Smith, in 2004, split up this complex into four species (Table 1). A standardized protocol developed through a series of intra- and interlaboratory trials was proposed by Gente et al. in 2006 to identify G. candidum at the species and strain level. In contrast to the teleomorphic species, the anamorphic species (G. candidum) is commonly found in food products and is an important organism in food technology. It is therefore proposed to conserve the name G. candidum throughout this article.
Morphology and Physiology Two main morphotypes have been described, with differences depending only partly on cultural conditions. The yeast morphotype is characterized by smooth, yeast-like, and cream-colored colonies that produce abundant asexual spores named arthrospores. The mold morphotype corresponds to hairy, felting, and white-colored colonies with a predominance of vegetative hyphae. The hyphae are dichotomously branched (forked) and 7–11 mm across. Arthrospores form by the breaking up of fertile hyphae (Figure 1) and not by budding as in most of the yeasts. They are cylindrical, barrel-shaped, or ellipsoidal, and are mostly 6–12 3–6 mm in size (Figure 2). Formation of blastospores does not occur. Geotrichum candidum grows very rapidly on media that are commonly used. On malt extract agar at 25 C, it forms colonies with a diameter of 7 cm within 7 days. The species grows at temperatures ranging from 5 to 35 C (variable response at 37 C). Among the four species previously mentioned, G. candidum is the only one able to grow at 35 C. The temperature optimum lies at 25 C. Furthermore, a broad range of pH values is tolerated; values between 5.0 and 5.5 are optimal. For the dairy industry, the organism’s low salt tolerance is worth mentioning. Contrary to the case of the majority of other dairy yeasts, the growth of G. candidum is limited by salting. Concentrations of 1% NaCl lead to a slight suppression of
765
766 Yeasts and Molds | Geotrichum candidum Table 1 Teleomorph and anamorph species of the Galactomyces/ Geotrichum complex Teleomorph
Anamorph
Galactomyces candidus sp. nov.a Galactomyces geotrichum Galactomyces pseudocandidus sp. nov. Unknown
Geotrichum candidumb Unnamed Geotrichum species Geotrichum pseudocandidum Geotrichum europaeum sp. nov.
Types: a CBS 178.71 exholotype strain of teleomorph. b CBS 615.84 neotype of anamorph. From de Hoog GS and Smith MTh (2004) Ribosomal gene phylogeny and species delimitation in Geotrichum and its teleomorphs. Studies in Mycology 50: 489–515.
2 1
Figure 1 Microculture of Geotrichum candidum at 25 C for 17 h on malt extract medium. (1) Vegetative hyphae slightly septated. (2) Sporulating hyphae corresponding to future arthrospores. Photograph MILA Laboratory, University of Caen Basse–Normandie, France.
growth. NaCl concentrations of 5–6% have an inhibitory effect. The species of the genus Geotrichum can assimilate only a few carbon compounds. These tests are usually remarkably stable within the species, which can be explained by the rather strict ecological preferences of a number of species. The ability to ferment sugar is rare in G. candidum, except for a weak or delayed fermentation of D-glucose or D-galactose; fermentation of lactose does not occur. Nearly all G. candidum isolates from the cheese environment assimilate glucose, galactose, sorbose, xylose, glycerol, and succinate. Lactate is used as a good carbon and energy source; use of citrate is strain-dependent; and lactose is not metabolized. Like the other three species, G. candidum does not require a supply of exogenic vitamins. Table 2 shows the percentage of assimilation results of selected isolates from milk products compared with the standard description for the species according to de Hoog and Smith (2004).
Physiological Adaptation to Freezing Stress
Figure 2 Arthrospores of Geotrichum candidum formed by breaking up of hyphae after 48 h in YEG broth. Scanning electronic microscopy (scale ¼ 10 mm). Photograph MILA Laboratory and Microscopy Center Applied to Biology, University of Caen Basse–Normandie, France.
Like other microorganisms, G. candidum is able to generate a biotic stress against pathogenic bacteria such as Listeria monocytogenes. Conversely, as a ripening starter, this micromycete is itself subjected to numerous anthropogenic stresses generated by food processing, including cheesemaking. Among those stresses, freezing/thawing has been the focus of many studies. It has been shown that G. candidum can be physiologically adapted to this lethal challenge by homologous (positive cold temperature) or heterologous pretreatment. Heterologous adaptation can be stimulated by osmotic stress agents (NaCl, MgCl2, CaCl2) and by nystatin, an antifungal compound that targets the plasma membrane and can act as a thermomimetic. Currently, freezing stress is considered to be a combination of both osmotic and mechanical stresses, leading to cryoinjury of cellular structures and
Yeasts and Molds | Geotrichum candidum Table 2 Physiological characteristics of G. candidum isolates from milk products compared to the standard description of Galactomyces candidus
D-Glucose D-Galactose L-Sorbose D-Glucosamine D-Ribose D-Xylose L-Arabinose D-Arabinose L-Rhamnose Sucrose Maltose ,-Trehalose Me -D-glucoside Cellobiose Salicin Arbutin Melibiose Lactose Raffinose Melezitose Inulin Sol. starch Glycerol Erythritol Ribitol Xylitol L-Arabinitol D-Glucitol D-Mannitol Galactitol myo-Inositol D-Glucono-1,5-lactone D-Gluconate D-Glucuronate D-Galacturonate DL-Lactate Succinate Citrate Methanol Ethanol Propane-1,2-diol Butane-2,3-diol Nitrate Ethylamine L-Lysine Cadaverine Without vitamins At 25 C At 30 C At 35 C At 37 C At 40 C Mol% G þ C low Mol% G þ C high
Standard descriptiona
% Positive (n ¼ 135)b
þ þ þ þ þ v þ þ þ w þ þ þ v þ þ þ þ þ þ þ þ þ þ v 38.4 41.6
100 100 93 0 4 100 0 0 0 0 0 0 0 0 0 0 0 1 0 0 nd nd 100 0 4 0 0 nd 44 nd nd nd 21 nd nd 99 nd 24 nd nd nd nd 10 60 99 99 86 100 100 49 1 0
þ, positive; , negative; v, variable; w, weak; nd, not determined. a Adapted from de Hoog GS and Smith MTh (2004) Ribosomal gene phylogeny and species delimitation in Geotrichum and its teleomorphs. Studies in Mycology 50: 489–515. b F. Eliskases-Lechner, unpublished results.
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macromolecular damage. The adaptation of G. candidum to freezing stress by pretreatment with osmotic chemicals is in accord with this dichotomous approach. Cryopreservation is an important technology used to produce food starters and to improve the ex situ preservation of microbial biodiversity. Therefore, G. candidum, which is characterized by a significant intraspecies diversity, is an interesting model to examine the relation between morphotype, arthrospore-to-hyphea ratio, and freezing sensitivity. The phenomenon of homologous or heterologous adaptation in G. candidum allows us to consider a substantial development of studies on the adaptation caused by abiotic (physical and chemical) stresses, which may lead to an active response by the cell, in parallel with the usual modifications of physical (cooling and warming rate) and chemical (addition of cryoprotectants and nucleators) freezing parameters, which may lead mainly to a passive response by the cells.
Biochemical Characteristics Geotrichum candidum produces cellulolytic enzymes, glycerol dehydrogenases, gluconases, lipases, proteinases, and peptidases. Proteolytic and lipolytic activities, as well as catabolism of amino acids and free fatty acids, and deacidification activity are of primary importance when selecting suitable strains as a culture for use in cheesemaking (see Cheese: Microbiology of Cheese). Proteolytic Activity Geotrichum candidum plays an important part in the degradation of proteins in many soft cheeses and in some semihard cheeses. It synthesizes extracellular and intracellular proteinases (pH optima 5.5–6.0), which catabolize s1- and -caseins. Peptide degradation to amino acids is achieved through aminopeptidases and carboxypeptidases. Enzyme production varies widely from one strain to another and can be attributed to the strain’s origin. Commercially available cultures have a relatively low proteolytic activity as compared to wild strains isolated from diverse cheese varieties. Lipolytic Activity Fatty acids released by microbial lipases contribute to the flavor of cheeses. In mold-ripened cheeses of the Camembert type, hydrolysis of fat by G. candidum is of particular importance. Geotrichum candidum produces extra- and intracellular lipolytic enzymes, some of these being highly specific with regard to the action and not the position. The particularly high proportion of free oleic acid in Camembert has been attributed to G. candidum lipases, which preferentially release this fatty acid.
Furthermore, G. candidum lipases show specificity for palmitoleic, linoleic, and linolenic acids. The lipolytic activity is strain specific. Strains producing a slight lipolysis are preferentially used as ripening organisms for diverse soft-cheese varieties.
Flavor-Forming Activities Geotrichum candidum produces several enzymes (amino and carboxypeptidases, decarboxylases, deaminases, thiolase, -keto-acyl-decarboxylase) for the degradation of amino acids and fatty acids resulting in important aroma compounds. The catabolism of amino acids by G. candidum leads to many compounds important for cheese flavor development, such as 2-methylpropanol, 3-methylbutanol, and especially sulfur compounds (methanethiol, sulfides, dimethyl disulfide, S-methylthioesters), which are catabolized from L-methionine. From free fatty acids, G. candidum produces various volatile compounds or precursors of aromatic compounds such as methyl ketones (pentan-2-one, heptan-2-one, nonan-2-one, undecan-2-one).
Deacidification Deacidification plays a major role in the cheese ripening process. Lactic acid produced by the starters may be utilized by yeasts. In addition, yeasts produce alkaline metabolic products, which further increase the pH value. The pH first increases at the surface of the cheese, then, later, in the inner part because of the migration of lactic acid toward the surface. Deacidification favors the activity of various ripening enzymes whose pH optima are often close to neutrality and enhances the development of acid-sensitive microflora. A rapid decrease of lactate levels coincides with the growth of the mold cultures and coryneforms. Therefore, the deacidification process is extremely important for the appearance and the organoleptic characteristics of mold- and smear-ripened cheeses (see Cheese: Smear-Ripened Cheeses). The deacidification properties of G. candidum are not only strain-dependent but also vary significantly according to the growth medium and incubation conditions. Geotrichum candidum can neutralize a calcium lactate yeast extract medium within 24 h, producing ammonia values of 290 mg kg1 but without lactate reduction. In contrast, when a cheese medium is used, G. candidum reduces lactic acid from 150 to 5 mmol kg1 within 4 days, while the ammonia values remain stable. Therefore, for the purpose of testing deacidification ability, it is necessary to distinguish between the pH increase due to lactate utilization and that due to ammonia production.
Yeasts and Molds | Geotrichum candidum
Applications Development of G. candidum is typical for quite a large number of cheese varieties. It is a part of the surface flora of mold-ripened soft cheeses from cow’s milk (e.g., Camembert), goat’s milk (e.g., Chabichou), or ewe’s milk (e.g., Perail); smear-ripened soft cheeses (e.g., Livarot); smear-ripened semihard cheeses (e.g., Tilsit); and acidcoagulated cheeses (e.g., Quargel, Harzer), and plays an active part in the formation of the characteristic grayishwhite crust found on the surface of Saint-Nectaire. Depending on the type of cheese, G. candidum appears either only at the very early stages of cheese ripening or during the entire ripening period. A recent application is its use in cow’s milk cheese made without Penicillium camemberti. Knowledge about the direct contribution of G. candidum to cheese ripening continues to grow. Even if little is known about gene expression, DNA sequencing will be completed in the near future. From the controlled production of Camembert-type cheeses inoculated with Kluyveromyces lactis, G. candidum, P. camemberti, and Brevibacterium linens, Leclercq-Perlat et al. (2004) have established relationships between the different microbiological and biochemical changes during cheese ripening. Though the presence of G. candidum has always been desirable in ripened soft cheese manufactured from raw milk, its relevance to the cheese-ripening process is a subject of controversy. Metabolism of lactic acid, which is responsible for the increase in pH as well as for the production of aroma substances and proteolytic and lipolytic enzymes, and the ability to reduce bitterness in cheeses, is one of the main reasons for the use of G. candidum as a culture. Nevertheless, G. candidum is feared by cheesemakers because of the risk of overgrowth, which leads to the ‘slippery rind’ defect, and the appearance of off-flavors due to contamination. These originate from the raw milk, air, utensils, brine, and the smear water during the manufacturing and ripening processes.
Cultures Properties of the strains can vary widely, and different specifications are required depending on the cheese variety. The applications of G. candidum cultures may vary according to the cheese type produced: to milk in the vat is only suitable for cheeses of • addition the Camembert type, where a limited growth of the
•
culture is desired the culture can be sprayed onto the surface of the cheese, for soft cheeses after brining and for acidcoagulated cheeses after molding
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smear-ripened cheeses, the culture should be added • for to the smear water; a single application at the first smearing step may be sufficient Smear-Ripened Cheeses The surface smear is a viscous coating consisting of microorganisms and abraded particles of the cheese surface. On the surface of young, still acidic cheeses, yeasts are dominant and the contribution of G. candidum resembles that of other yeasts. They deacidify the surface and consequently permit the development of acid-sensitive bacteria. Since the bacterial flora is composed of a salttolerant population of coryneforms, salting can be used to control their development. Due to the lower salt tolerance of G. candidum as compared to other yeasts, the relationships within the yeast flora can be influenced by salting, thus preventing the overgrowth of G. candidum. Depending on the cheese variety, the counts normally vary between 106 and 107 cfu g1 if G. candidum is a desired part of the surface flora. This species contributes to the flavor of those cheeses by the production of sulfur compounds, which have very low threshold values. Furthermore, G. candidum influences the texture of the smear. The white film of G. candidum on the cheese surface dries up the cheese surface and thereby reduces the risk of a sticky smear (see Cheese: Smear-Ripened Cheeses). Mold-Ripened Cheeses The formation of aroma substances by G. candidum is of great importance for mold-ripened cheeses. Geotrichum candidum contributes notably to the taste of Camembert, especially that of pasteurized cheeses, and to the production of the typical Camembert aroma. Typical substances produced by G. candidum are secondary alcohols, methylketones, and sulfur compounds. Geotrichum candidum appears at the same time as the other two yeasts (Debaryomyces hansenii, K. lactis) and develops during the first week of ripening. Later, counts remain more or less unchanged until the time of consumption. The rapid growth on the cheese surface leads to growth interactions. While P. camemberti subsp. caseicolum (named P. candidum by cheesemakers) is stimulated, undesirable molds such as Mucor may be suppressed by certain strains. On the other hand, abundant growth of G. candidum hinders the implantation of Penicillium, leading to defective cheeses. This defect is called ‘toad skin’, where the rind of the cheese does not adhere to the inner part. In addition, uncontrolled development of G. candidum produces defects in the appearance of the cheeses and may also affect the taste. Furthermore, G. candidum can contribute to improving the organoleptic properties of cheese by reducing bitterness. Penicillium camemberti plays a leading role in the
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appearance of bitterness in Camembert; an excessive growth of the mycelium can lead to this defect. Because of the high activity of the proteinases of P. camemberti, an accumulation of bitter peptides may occur in the cheese. However, if the growth of Penicillium is limited by the presence of G. candidum or by incubating the cheese in the presence of ammonia, proteolysis is reduced and this defect does not occur. The effect of ammonia can be explained by higher pH values in the cheese rind, which delay the growth of P. camemberti and consequently reduce the intensity of proteolysis. Some strains of G. candidum produce such high amounts of ammonia that a pronounced increase in pH can be attained. Ammonia values as high as 50–300 mg kg1 were reached when G. candidum strains were incubated in a sterile cheese curd medium. Therefore, for the purpose of reducing bitterness in soft cheeses, strains have to be carefully selected according to their ammonia-producing capacity. Since the optimal relationship between P. camemberti and G. candidum is of such great importance, a combined culture of both microorganisms is advisable. The portion of G. candidum in the total inoculum can vary between 0.5 and 5%. The advantage of the G. candidum culture lies in the more rapid covering of the cheese surface, which leads to a suppression of undesired molds. During culture selection, strains that produce the typical aroma combined with a low lipolytic activity should be given preference.
infection due to G. candidum in connection with its technological use and consumption in dairy products is therefore virtually nil.
Geotrichum candidum as a Spoilage Organism As in the case of other yeasts, the presence of G. candidum leads to product spoilage of fermented milks and fresh cheeses, and limits the shelf life of these products. Besides the visually observable change due to colonies on the product surface, degradation of protein or fat results in smell and taste defects in cottage cheese, quark, yogurt, buttermilk, and fermented cream. Further, growth of G. candidum on the surface of butter causes flavor defects and surface discoloration.
Enumeration Detection and identification of fungal contamination in dairy products are important in assessing hygiene practices during the manufacture and distribution of foods. Especially in ripened cheeses, where G. candidum is a part of the ripening flora, other yeasts and molds must be counted separately in order to interpret the results correctly.
Acid-Coagulated Cheeses Acid-coagulated cheeses include some smear-ripened cheeses as well as cheeses without a smear surface. On the surface of the smear-ripened varieties, G. candidum is regarded as a contaminant, whereas it gives all other varieties their typical ammonia odor and characteristic texture. The cultures used have a relatively high lipolytic and proteolytic activity (see Cheese: Acid- and Acid/Heat Coagulated Cheese). Safety Assessment Regarding the safety assessment of G. candidum, only 11 yeasts, which do not include G. candidum, and no filamentous fungi, have obtained the qualified presumption of safety (QPS) status delivered by the European Food Safety Authority (EFSA). Nevertheless, G. candidum infections are very rare, with fewer than 100 cases having been reported between 1842 and 2006. Less than one case per year of disease is possibly caused by G. candidum, and this never includes dairy products or foodborne infections. The species can be unambiguously differentiated from the two species most frequently described in human pathology: Geotrichum clavatum (reclassified Saprochaete clavata) and Geotrichum capitatum (reclassified Magnusiomyces capitatus/Saprochaete capitata). The risk of developing an
Direct Microscopic Method Microscopic examination permits rapid estimation of the G. candidum content when relatively high levels are present. The presence of a fungus with holothallic spore production named arthrospores can also be microscopically determined. In Situ Quantification Polymerase chain reaction (PCR)-based methods can rapidly identify and quantify yeast species in complex microbial ecosystems without isolation. A real-time PCR method was developed by Larpin et al. (2006), to quantify the main yeasts, including G. candidum, that composed the microbial communities of many cheeses. Culture Method Yeast extract-dextrose-chloramphenicol agar and yeast extract-dextrose-oxytetracycline agar were found to be among the most satisfactory media available for the enumeration of G. candidum and the other yeasts in milk products (ISO 6611/IDF94). These media contain chloramphenicol or oxytetracycline as selective substances to suppress the accompanying bacterial flora. Plates are
Yeasts and Molds | Geotrichum candidum
incubated aerobically at 25 C for 5 days; however, G. candidum can be counted after 48–72 h of incubation. The incubation temperature should not exceed 25 C because the growth of some strains is restricted at higher temperatures. For the examination of ripened cheeses that have a mold coat, it may be desirable to split the sample into the surface part and the inner part, depending on the purpose of the investigation. For special purposes, several modifications may lead to better results: 1. Addition of dyes, for example, bromophenol blue (0.01 g l1), is advantageous in distinguishing between G. candidum and colonies of other yeasts and molds. Furthermore, bacteria resistant to chloramphenicol or oxytetracycline are generally easier to distinguish from yeast colonies. 2. Generally, for the quantification of G. candidum, the spread-plate method is preferable to the pour-plate method because higher counts are obtained in the former. In addition, surface plating facilitates the characterization of the morphology of the colonies and their isolation for further investigation. It is also easier to differentiate between G. candidum and the accompanying mold colonies. Whereas the surface colonies of G. candidum can be easily removed from the agar when using a loop, mold colonies are intimately bound within the agar. 3. For certain samples, for example, raw milk or farm house products, lowering the pH to 4.6 may be necessary to suppress the accompanying flora of chloramphenicol- or oxytetracycline-resistant bacteria. The pH value of the medium is lowered by an aseptic addition of tartaric acid, after sterilization. 4. Quantitative analysis of G. candidum can be difficult in cheeses made with mold cultures. Mold cultures usually exceed the G. candidum counts and overgrow the plates. The antibiotic oligomycin is particularly useful in suppressing the mold cultures usually used for cheesemaking. Addition of 0.1 ml oligomycin solution (100 mg oligomycin ml1 ethanol) on the agar surface before plating suppresses mold growth, while growth of G. candidum and other yeasts is not inhibited.
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See also: Cheese: Acid- and Acid/Heat Coagulated Cheese; Microbiology of Cheese; Secondary Cultures; Smear-Ripened Cheeses. Yeasts and Molds: Yeasts in Milk and Dairy Products.
Further Reading Boutrou R and Gue´guen M (2005) Interests in Geotrichum candidum for cheese technology. International Journal of Food Microbiology 102: 1–20. Boutrou R, Kerriou L, and Gassi JY (2006) Contribution of Geotrichum candidum to the proteolysis of soft cheese. International Dairy Journal 16: 775–783. de Hoog GS and Smith MTh (2004) Ribosomal gene phylogeny and species delimitation in Geotrichum and its teleomorphs. Studies in Mycology 50: 489–515. Dieuleveux V, Vanderpyl D, Chataud J, and Gue´guen M (1998) Purification and characterization of anti-Listeria compounds produced by Geotrichum candidum. Applied and Environmental Microbiology 64: 800–803. Dubernet S, Panoff JM, Thammavongs B, and Gue´guen M (2002) Nystatin and osmotica as chemical enhancers of the phenotypic adaptation to freeze-thaw stress in Geotrichum candidum ATCC 204307. International Journal of Food Microbiology 76: 215–221. Gente S, Sohier D, Coton E, Duhamel C, and Gue´guen M (2006) Identification of Geotrichum candidum at the species and strain level: Proposal for a standardized protocol. Journal of Industrial Microbiology and Biotechnology 33: 1019–1031. Hubalek Z (1996) Cryopreservation of Microorganisms, at Ultra-Low Temperatures. Prague: Academia Praha. Larpin S, Mondolini C, Georges S, Vernoux JP, Gue´guen M, and Desmasures N (2006) Geotrichum candidum dominates in yeast population dynamics in Livarot, a French red-smear cheese. FEMS Yeast Research 6: 1243–1253. Leclercq-Perlat MN, Buono F, Lambert D, Latrille E, Spinnler HE, and Corrieu G (2004) Controlled production of Camembert-type cheeses. Part I: Microbiological and physicochemical evolutions. Journal of Dairy Research 71: 346–354. Missous G, Thammavongs B, Dieuleveux V, Gue´guen M, and Panoff JM (2007) Improvement of the cryopreservation of the fungal starter Geotrichum candidum by artificial nucleation and temperature downshift control. Cryobiology 55: 66–71. Pottier I, Gente S, Vernoux JP, and Gue´guen M (2008) Safety assessment of dairy microorganisms: Geotrichum candidum. International Journal of Food Microbiology 126: 327–332. Smith M, Poot GA, and Cock WAM (2000) Re-examination of some species of the genus Geotrichum Link: Fr. Antonie van Leeuwenhoek 77: 71–81. Thammavongs B, Denou E, Missous G, Gue´guen M, and Panoff JM (2008) Response to environmental stress as a global phenomenon in biology: The example of microorganisms. Microbes and Environments 23: 20–23. Thammavongs B, Panoff JM, and Gue´guen M (2000) Phenotypic adaptation to freeze-thaw stress of the yeast-like fungus Geotrichum candidum. International Journal of Food Microbiology 60: 99–105.
Penicillium roqueforti A Abbas and A D W Dobson, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Penicillium roqueforti is a saprophytic fungus that is commonly found in nature and can be isolated from soil or from decaying organic matter. It is used as a fungal starter culture for the production of blue-veined cheeses such as Danablu, Gorgonzola, Roquefort, and Stilton. The mold is primarily responsible for ripening the cheese, involving the production of both proteolytic and lipolytic enzymes. The proteolytic enzymes produced by the fungus act to soften the curd and produce the desired body in the cheese. These proteolytic enzymes involve both extraand intracellular proteinases and peptidases, with the extracellular aspartic proteinases being particularly important for the ripening process. The water-soluble lipases produced by the fungus hydrolyze the milk fat to free fatty acids, such as butyric caprylic, caproic, and capric acids, which contribute to the flavor of Blue cheeses. Other important components of Blue cheese flavor are also produced by the mold, such as the ketone heptan-2-one, which is produced from caprylic acid, as well as other ketones such as pentan-2-one and nonan-2one. In addition, P. roqueforti is also known to reduce methyl ketones to form secondary alcohols such as heptan-2-ol, pentan-2-ol, and nonan-2-ol, which also contribute to cheese flavor. Due to its resistance to organic acids and weak acid preservatives together with an ability to grow at low pH, particularly at water activity (aw) values >0.95, P. roqueforti also commonly spoils processed foods such as bread, beer, olives, and hard cheeses. In addition, it is commonly found in silage and grains stored under microaerophilic conditions.
Morphology Penicillium roqueforti is a rapidly growing fungus and it produces low and velutinous dark green colonies, which on malt extract agar (MEA) grow rapidly to 40–70 mm in diameter. These colonies are characterized by moderate to heavy conidial production with either grayish turquoise or dull green color at the margins of the colony, with olive brown color sometimes being observed in the center of the colony. The reverse of the colony is pale, brown, or green to deep blue green (almost black). Conidiophores are borne from subsurface hyphae with
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stipes (hyphae supporting the fruiting structure, forming the conidiophore) of between 100 and 200 mm long. These stipes have very rough walls, which bear large terminal penicillia, which are rarely biverticillate, typically terverticillate, and occasionally quaterverticillate.
Physiological Factors Affecting Growth of the Fungus Penicillium roqueforti appears to have the lowest oxygen requirements for growth of any Penicillium species. It can grow at only 10% of standard atmospheric O2 partial pressure. In reduced oxygen atmospheres, the fungus is largely unaffected until the oxygen concentration drops below 4.2%. In addition, it is known that growth of the fungus is stimulated by carbon dioxide concentrations of up to 15% in air. In an atmosphere containing 80% CO2, 4.2% O2, and 15.8% N2, growth of P. roqueforti has been reported to be 30% of that in air at 20 C. The fungus has also been reported to grow at lower oxygen concentrations, such as 0.05%, and in the presence of 20% CO2 at 25 C, while growth and sporulation also occur in atmospheres containing 20% O2 and 80% CO2. These properties are the main reason for the dominant growth of this fungus in ripening cheese. Penicillium roqueforti is a psychrophile and grows vigorously at temperatures as low as 4 C, but not above 35 C. It is tolerant to both acid and alkaline conditions and can grow in the pH range of 3–10. Many P. roqueforti strains are known to be very tolerant to weak acid preservatives, being able to grow in the presence of 0.5% acetic acid. This property can be used to selectively grow P. roqueforti as other Penicillium species are unable to grow under these conditions. Penicillium roqueforti is also resistant to sorbate. Sorbate-resistant isolates of the fungus isolated from sorbate-treated cheeses are able to metabolize and grow in the presence of 9000 ppm sorbate. Tolerance to sorbate is accompanied by degradation of the preservative and the development of a ‘kerosene’ taint in cheese, through the formation of 1,3-pentadiene. In addition, at aw values >0.97, growth of P. roqueforti isolates is stimulated by propionate, another commonly used weak acid preservative. This resistance to weak acid preservatives, which are routinely used to prevent fungal spoilage of foods, coupled with its ability to grow at refrigeration
Yeasts and Molds | Penicillium roqueforti
temperatures, makes the fungus a common cause of spoilage in cool-stored preserved commercial and domestic foods. The microenvironment of Blue cheese is characterized by profound NaCl gradients from the core to the surface of the cheese, which reach equilibrium slowly during ripening. These differences are known to affect the growth, germination, and sporulation of P. roqueforti. Penicillium roqueforti has an optimum water activity (aw) value of 0.998 for growth at 25 C, and a colony growth rate of 13.4 mm day1. The lag phase of growth for P. roqueforti is relatively stable at aw > 0.92, but increases for aw < 0.94. This is advantageous for the use of the fungus as a starter culture, as the final aw values of Blue cheeses are in the range of 0.91–0.94, which allows P. roqueforti to germinate quickly and grow through the entire cheese processing and ripening process. The pH and NaCl concentrations of the cheese are also known to influence the proteolytic activity of the fungus, with proteolysis typically being less pronounced in the high salt environment in the outer parts of the cheese. Growth of P. roqueforti strains is stimulated at low salt concentrations, with 1% salt (NaCl) having the highest stimulating effect. In addition, while it is known that P. roqueforti strains can grow at low temperatures, the rate of growth at 10 C is around 2–3 times lower than that at 25 C, the optimum temperature for the species. At 25 C, P. roqueforti strains have been reported to produce around 10% more mycophenolic acid (MPA) at an aw value of 0.97 when compared to that at an aw value of 0.95. This effect does not appear to be significantly affected within the pH range of 4.7–7.4. At aw values >0.97, growth of P. roqueforti is stimulated by propionate, another commonly used weak acid preservative. There are a number of conflicting results reported in the scientific literature with respect to the effects of preservatives on growth and mycotoxin production by P. roqueforti. Some reports appear to indicate that at subinhibitory levels preservatives inhibit mycotoxin production, whereas the opposite has been reported by other groups. Thus, it is likely that the mechanisms of mycotoxin regulation are quite complex and not readily generalized and are most probably not only speciesdependent but also affected by the growth medium and by the concentration of the preservative. In a study involving 30 P. roqueforti strains, the effects of various physiological conditions on both esterase and lipase activities were monitored, using diffusion assays on tributyrin and olive oil agars, and growth at either 10 or 25 C in butterfat emulsions containing up to 7% NaCl was also monitored. This study reported that extracellular lipase production is stimulated at low NaCl concentrations and that lipases show a higher activity against shortchain fatty acids while triolein is hydrolyzed at a much
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lower rate. Mathematical models combining the effects of temperature and salt concentration have been developed to predict their effects on the growth rate of P. roqueforti, in an attempt to prevent food spoilage by the fungus. Other approaches to prevent growth of the fungus have involved the use of an antifungal compound produced by a Bacillus subtilis strain and which has been reported to inhibit the germination of P. roqueforti conidiospores. This iturin-like compound is believed to act by permeabilizing the fungal spores, thereby inhibiting germination. The addition of essential oils has also been shown to inhibit the growth of P. roqueforti, with the addition of eugenol, caryophyllene, p-cymene, and thymol being reported to be particularly effective.
Production of Volatiles A number of methods have been developed to study the volatile compounds produced by Penicillium species, including P. roqueforti. Three popular methods include diffusive sampling from headspace on carbon black adsorbent in glass tubes, purging and trapping of headspace gases with carbon black adsorbent tubes, and simultaneous distillation extraction (SDE) with diethyl ether solvent. The diffusive sampling method is regarded as the most appropriate method because with the purgeand-trap method purge flow significantly determines the quantitative volatile metabolite profile and SDE causes formation of lipid oxidation products. Such an approach has been successfully employed to profile volatile metabolites to allow the differentiation of species from the P. roqueforti group. It has also been shown that P. roqueforti strains that produce PR toxin (7-acetoxy5,6-epoxy-3,5,6,7,8,8a-hexahydrocarboxaldehyde) produce the volatile metabolite (þ)-aristolochene, which is considered a biomarker for P. roqueforti within the Penicillium genus.
Genetics Penicillium roqueforti is quite a heterogeneous species and has recently been divided, based on differences in its internal transcribed spacer (ITS) regions and its secondary metabolite patterns, into three distinct species, namely, P. roqueforti, P. carneum, and P. paneum. While all three species are morphologically very similar, there are marked differences in their ability to produce secondary metabolites. Penicillium roqueforti can produce PR toxin, marcfortines, and fumigaclavine A, P. carneum can produce patulin, MPA, and penitrem A, while P. paneum produces patulin and botryodiploidin. DNA-based molecular techniques have been developed and applied in the detection and identification of
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Penicillium species. Polymerase chain reaction (PCR) primers based on the ITS region have been developed to monitor P. roqueforti in a variety of foods. These PCR primer pairs, which specifically amplify a 300-bp fragment, not only specifically identify all members of Penicillium subgenus Penicillium, but also specifically recognize P. roqueforti and P. carneum. Even though many of the P. roqueforti strains that have been isolated from Blue cheeses are known to produce both PR toxin and roquefortine and these secondary metabolites have been shown to be present in cheese, they are not thought to pose a significant health risk to consumers as they are very unstable in cheese. Notwithstanding this, P. roqueforti strains that do not produce secondary metabolites or mycotoxins would be preferable as starter cultures for cheese manufacture, from a food safety perspective. Thus, several groups have set out to develop DNA-based methods to identify P. roqueforti starter strains that do not produce toxic secondary metabolites. In this respect, Geisen and coworkers targeted the ari1 gene encoding aristolochen synthase, one of the key enzymes in the PR toxin biosynthetic pathway, in a PCR-based approach to screen for PR toxin-free strains of P. roqueforti. Using the ari1-specific PCR primers, a product of the expected length was observed in many of the 21 strains tested. However, some of the strains that were PCR-negative were also toxin producers. These were subsequently shown to be positive following dot-blot hybridization using an ari1-specific gene probe, indicating the presence of ari1 genes in some P. roqueforti strains with altered PCR primer binding sites. Another potential problem with this method was also identified whereby ari1 gene homologues were observed in Penicillium species, such as P. italicum and P. nalgiovense, which are known not to produce PR toxin. Thus the group advise that care should be taken when using a monomeric PCR reaction, which targets only one mycotoxin biosynthetic gene, as the primers may not be sufficiently specific to detect the mycotoxin-producing fungus. More recently, the group have successfully performed random amplified polymorphic DNA (RAPD) analysis, using three primers (ari1 (CTGCTTGGCA CAGTTGGCTTC), nor1 (ACCGCTACGCCGGCAC TCTCGGCAC), and omt1 (GTGGACGGACCTAGT CCGACATCA)), of 76 P. roqueforti starter culture strains and reported a correlation between RAPD patterns and the production of MPA. In addition, they reported on one fungal genotype, which was distinguishable with the ari1 primer, that produced fewer secondary metabolites than other genotypes and which did not produce PR toxin. Thus, this strain may be a good candidate for use as a safe starter culture. The group advocate that before being used as starter cultures in the dairy industry P. roqueforti strains should be checked for their inability to produce toxins in the
cheese, and suggest the approach they employed as a reliable method for achieving this goal.
Mycotoxins Produced by Penicillium roqueforti PR Toxin PR toxin is one of the most acutely toxic metabolites produced by the fungus and is frequently detected in Blue cheese. PR toxin produces acute toxic effects in animals via an increase in capillary permeability and due to direct damage to lungs, heart, liver, and kidneys. PR toxin also inhibits RNA and protein synthesis, DNA polymerase activity as well as mitochondrial respiration and oxidative phosphorylation in animal cells. It has also been reported to result in gene alterations and gene conversions in Saccharomyces cerevisiae and Neurospora crassa strain N24, respectively. A number of P. roqueforti strains have been isolated from Blue cheese, which when grown under different culture medium produce PR toxin, with levels of toxin production being highly dependent on environmental conditions. For example, when P. roqueforti is grown in yeast extract–sucrose medium, which favors the production of PR toxin, levels of between 82 and 770 mg l1 are produced. It has also been reported that toxin production is highest in stationary cultures at temperatures ranging from 20 to 24 C and at pH 4; the addition of octanoic acid to P. roqueforti cultures growing on wheat kernel medium has recently been reported to inhibit PR toxin biosynthesis. However, despite the ability of P. roqueforti strains to produce the toxin, no PR toxin or at most very low levels can be detected in cheese. Researchers believe that the microaerophilic conditions that prevail in most cheeses appear not to favor the production of PR toxin. In addition, the toxin appears to be very unstable in cheese, where it is believed to react with ammonia and free amino acids, which are present in high concentrations in Blue cheese, to form PR, which is unstable and is subsequently degraded to PR acid. Roquefortine This is an indole mycotoxin and is identical to roquefortine C. It has been assigned the structure 10b-(1,1-dimethyl2-propenyl)-3-imidazol-4-methylene-5a,10b,11,11a-tetrahydro-2H-pyrazino-[19,29:1,5]pyrrol[2,3,b]indole-1,4(3H,6H)-dione. Roquefortine is a relatively weak neurotoxin and in studies in ruminants that have consumed contaminated silage, clinical symptoms include muscle weakness and lack of coordination. Roquefortine is also reported to cause convulsive seizures in mice when injected intraperitoneally. Penicillium roqueforti strains
Yeasts and Molds | Penicillium roqueforti
isolated from Blue cheeses have been reported to produce between 0.18 and 8.44 mg l1 of roquefortine in culture medium containing yeast extract, while in experiments in which cheese was inoculated with a toxigenic strain of the fungus, levels of between 2.1 and 2.4, and 2.1 and 3.8 mg kg1 have been reported in cheese ripened at 5 and 12 C, respectively. Roquefortine C levels ranging from 0.05 to 12 mg kg1 have been reported in cheeses, while in a recent study roquefortine at concentrations of 0.8–12 mg kg1was detected in all of the 10 blue mold cheese samples obtained from Finnish supermarkets. Although roquefortine is produced by most strains of P. roqueforti that have been isolated from Blue cheese or which are used as starter cultures, the low levels of the toxin that are present in Blue cheese together with the relatively low toxicity of roquefortine are such that roquefortine is believed not to present a major health hazard to the consumer and make the consumption of Blue cheese safe. Mycophenolic Acid This is a mycotoxin and is reported to be produced by many strains of P. roqueforti that have been tested and by some other Penicillium strains, particularly P. brevicompactum and P. paneum. For example, in a study where 80 P. roqueforti strains were tested, of which 62 of the strains were starter culture strains from western Europe, only 20 were able to produce up to 600 mg of the toxin in 2% yeast extract–5% sucrose broth. MPA has antibiotic activity against bacteria and dermatophytic fungi and is also known to interfere with viral multiplication. For mammals, the toxicity of MPA is low. There are reports of toxicity in rats, with oral administration of daily doses of 30 mg kg1 resulting in anemia and death. Interestingly, MPA is routinely used in the treatment of psoriasis and in addition both MPA and MPA derivatives have been reported to have both antitumor and immunosuppressive effects. MPA is the active
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ingredient in mycophenolate mofetil (MMF), which is widely used to prevent rejection after solid organ transplantation. It acts as a reversible, noncompetitive inhibitor of inosine monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in de novo purine biosynthesis in T and B lymphocytes. Penicillium roqueforti strains isolated from baled grass silage have been reported to produce MPA, and thus subsequent consumption of this silage by livestock should be a concern for livestock producers. In one study, all 16 strains of P. roqueforti isolated from Blue cheeses have been reported to produce MPA, at levels of between 0.8 and 4 mg g1 dry culture, with the highest levels of the toxin being reported following 10 days of incubation of fungal cultures at 15 C. However, the yeast Geotrichum candidum has been reported to inhibit the growth of P. roqueforti when cocultured on agar medium at both 18–25 C and in addition to inhibit the production of MPA. See also: Yeasts and Molds: Penicillium camemberti.
Further Reading Biotechnology Program Under Toxic Substances Control Act (TSCA) (1997) Penicillium roqueforti Final Risk Assessment Attachment I. http://www.epa.gov/oppt/biotech/pubs/fra/fra008.htm (accessed May 2010). Edwards SG, O’Callaghan J, and Dobson ADW (2002) PCR-based detection and quantification of mycotoxigenic fung. Mycological Research 109: 1005–1025. Ernstrom CA and Wong NP (1974) Milk-clotting enzymes and cheese chemistry. In: Webb BH, Johnson AH, and Alford JA (eds.) Fundamentals of Dairy Chemistry, 2nd edn. Westport, CT: AVI Publishing. Karlshoj K and Larsen TO (2005) Differentiation of species from the Penicillium roqueforti group by volatile metabolite profiling. Journal of Agricultural and Food Chemistry 53: 708–715. Pitt JI and Hocking AD (1997) Penicillium and related genera. In: Pitt JI and Hocking AD (eds.) Fungi and Food Spoilage, 2nd edn.,ch.7, pp. 203–338. London: University Press Cambridge.
Penicillium camemberti A Abbas and A D W Dobson, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Penicillium camemberti was first described by Thom and is thought to be a domesticated form of P. commune. A number of synonyms exist for the species including P. rogeri, P. candidum, P. album, and P. caseicolum. The fungus is mainly (almost exclusively) found either on cheese or in the cheese factory environment and is rarely found away from this environment. Penicillium camemberti is used in the production of Camembert and Brie cheeses, on which colonies of the fungus form a white crust. It is also used as a starter culture for fermented meat products and is often found as a spontaneous colonizer of fermented sausages originating from the mycobiota of the production facility. There have been reports on the wider exploitation of P. camemberti especially in the decontamination of softwood bleach effluents, which contain high levels of ecologically undesirable phenolic and chlorinated phenolic compounds. Therefore, P. camemberti, which to date has been predominantly used in the dairy industry, may also find future utility in other nondairy-related areas.
Growth Characteristics of Penicillium camemberti Colony diameter on Czapek yeast extract agar (CYA) is typically 19–27 mm at room temperature (24–26 C) after 10 days. Colonies on CYA appear yellow/orange or green to fawn to pale brown/blue in color. The reverse sides of the colonies on CYA typically appear either yellow/ orange or green brown in color. Colony diameter on malt extract agar (MEA) is typically 12–27 mm. Colonies on MEA also appear yellow/orange or green in color, with the reverse sides of the colonies being red, olive, green, or brown in color depending on the growth medium. The optimum growth temperature range is 20–25 C, with growth being recorded at 5 C but not at 37 C. With respect to pH, growth can take place in the pH range of 3.5–6.5. Penicillium camemberti has similar water activity (aw) limits for growth as P. roqueforti with an optimum aw value of 0.998 for growth at 25 C and an ability to grow in the aw range from 0.91 to 0.94. Thus, from a pH standpoint, P. camemberti is ideal as a starter culture given that the pH of Camembert and related types of cheese reaches about 4.6 during the first 24 h and eventually following maturation increases to around 5.5
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in the center of the cheese and around 7.0 in the outer part of the cheese. Similarly, it is suitable as a starter culture from an aw standpoint given that the aw of the surface and center of Camembert cheese has been recorded as 0.93 and 0.97, respectively. The salt tolerance of the fungus coupled with its ability to grow at an aw of 0.93 results in it growing on the surface of Camembert cheese during the cheese maturation process. However, it is only after 1 week of ripening that P. camemberti is observed, and within 2–3 weeks it covers the entire surface of the cheese. During this process, the fungus also metabolizes lactate to CO2 and H2O at the surface of the cheese to establish a pH gradient, which is a key factor in the maturation process, and results in a higher pH. This effect is pronounced on the surface of the cheese, with a pH gradient becoming established toward the center of the cheese, resulting in lactate migrating toward the surface, where it is assimilated as a carbon source by the fungus. This depletion of lactate in the center of the cheese results in casein being degraded primarily by enzymes from the rennet, the plasmin from the milk, and by enzymes from the lactic acid starter cultures. Ammonia is formed at the surface of the cheese from amino acids, the consequence of which is a further increase in pH. The proteinases from P. camemberti are activated by the increasing pH and they migrate only slowly into the cheese. During ripening, the dynamics of sporulation of P. camemberti is affected by the concentration of CO2 in the atmosphere. For example, the number of P. camemberti spores present in the rind is fairly constant at around 104 cfu g1 during the first 6 days of ripening at 6% CO2. However, at 2% CO2, the fungus is known to sporulate at a faster rate and spore counts can reach levels as high as 106 cfu g1 on the 6th day of growth. After day 11 and until day 40, sporulation remains stationary, close to 106 cfu g1. Regardless of CO2 concentration, the mycelium of P. camemberti begins to grow from day 4 onward with both mycelium and aerial mycelia being visible. Between days 5 and 12, the mycelia grow and uniformly cover the entire cheese surface. From day 10 to 16, if the cheese is wrapped, the rind color remains white and is around 3 mm thick. Increases in CO2 concentration above 2% negatively affect the growth of P. camemberti on cheese. Because in Camembert-type cheese, P. camemberti is generally inoculated in a mixed culture with Geotrichum candidum, CO2 is known to alter the equilibrium between
Yeasts and Molds | Penicillium camemberti
these two strains, with higher CO2 concentrations favoring G. candidum and resulting in poorer development of P. camemberti mycelium.
Enzymes Produced by Penicillium camemberti Penicillium camemberti produces a variety of different proteinases including two extracellular endopeptidases. One of the two extracellular endopeptidases is a metalloprotease and is the principal proteolytic enzyme active at close to neutral pH values (pH 6.5). It is similar to the metalloprotease produced by P. roqueforti. At acidic pH (pH 4.0), P. camemberti produces an acid protease. Other proteolytic enzymes produced by P. camemberti include an aminopeptidase and a carboxypeptidase. These proteolytic enzymes play an important role in cheese ripening. There are some differences between strains with respect to the production of different types of proteinases. There is, however, greater variation between P. camemberti strains in their ability to produce extracellular lipolytic enzymes. The lipase system is active within broad pH (5.5–9.5) and temperature (1–35 C) ranges.
Penicillium camemberti as a Biocontrol Agent in Cheese Starter cultures are known to contribute to the inhibition of the undesirable growth of fungal contaminants and mycotoxin production in fermented foods. When P. camemberti is used as secondary starter culture, it exerts a powerful inhibitory effect on many common cheese contaminants such as Cladosporium herbarum, P. roqueforti, P. caseifulvum, and P. commune. The antagonistic power of P. camemberti is strain dependent in that the growth inhibition of C. herbarum is not affected by the choice of the strain of P. camemberti, whereas the Penicillium contaminants are very sensitive to the choice of strain. The antagonistic activity is much stronger when P. camemberti is used as pure culture, with the inhibitory activity being reduced considerably if the fungus is used in a mixed culture, for example with G. candidum.
Secondary Metabolism in Penicillium camemberti A number of Penicillium toxins have been identified in contaminated cheese, including roquefortin C, isofumigaclavine A, cyclopiazonic acid (CPA), mycophenolic acid, and, much less frequently, ochratoxin A and PR toxin. A few strains of P. camemberti are known to produce a number of secondary metabolites such as cyclopaldic
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acid, rugulovasine A, and rugulovasine B as well as palitantin. However, CPA, which is a neurotoxic and immunosuppressive compound, remains the most significant toxin produced by P. camemberti, particularly at higher storage temperatures. The toxicity of CPA results in a large part from its specific inhibition of calciumdependent ATPase in the sarcoplasmic reticulum, leading to altered cellular (Ca2þ) levels and resulting in increased muscle contractions. CPA is almost exclusively found in the rind but not in the core of the cheese. This is due to the inability of P. camemberti to grow in the cheese core. CPA does not appear to constitute a major threat to the consumer with the highest levels in cheese being reported to date at >2 ppm, which would constitute <4 mg CPA in a portion of the most highly contaminated cheeses. It has also been reported that CPA can be produced by P. camemberti in submerged culture, at levels <4 ppm following a 96 h fermentation. Production of CPA is known to be strainspecific and appears to be unrelated to spore yield. No noticeable mutagenic activity was detected when crude extracts of several strains of P. camemberti containing a pool of metabolites were assessed, suggesting that undesired long-term effects from the consumption of P. camemberti-ripened cheese are unlikely. This may explain the fact that despite many P. camemberti strains possessing the ability to produce CPA, no acute toxicity associated with the consumption of food produced by the fungus has been reported to date. The possibility exists that this may also be due to the fact that many other metabolites are likely to be produced at the same time as CPA and that these metabolites may in some way have an antagonistic effect that could neutralize or negate the toxicity of CPA. However, no clear scientific evidence exists to support this hypothesis and further work is required to substantiate this theory.
Penicillium camemberti and Cheese Flavor The production of numerous flavor compounds in Camembert cheese can be directly attributed to the enzymatic activity of P. camemberti. While the presence of the fungus at the surface of the cheese gives the cheeses their characteristic appearance, it is known that lowmolecular-weight compounds produced by the fungus contribute significantly to taste. Volatile compounds are an important component of these low-molecular-weight molecules, with volatile fatty acids being the most abundant compounds within the volatile fraction. In fact, lipolysis is particularly important in soft cheeses such as Camembert where free fatty acids can reach up to 10% of the total fatty acids present. As previously mentioned, P. camemberti produces a lipase, which is similar to the
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alkaline lipase produced by P. roqueforti, and proteases. Lipase and protease activities are involved in the degradation of short-chain fatty acids and peptides in the cheese. The resulting products are subsequently transformed into important taste and aroma compounds such as ammonia, methyl ketones, primary and secondary alcohols, esters, aldehydes, lactones, and sulfur compounds. The methyl ketones are by far the most abundant neutral compounds in the volatile fraction of mold-ripened cheeses. Such methyl ketones include 2-nonanone, 2-undecanone, 2-heptanone, and 2-pentanone and their corresponding secondary alcohols, and contribute to the musty flavor of the cheese. Due to their typical odors and their low odor thresholds as well as their concentration in cheese, ketones and methyl ketones play a key role in the overall flavor of surface mold-ripened cheeses. The secondary alcohol 1-octen-3-ol in particular is responsible for the characteristic mushroom flavor of Camembert-type cheese. Most esters have floral and fruity notes and are believed to contribute to the overall aroma by minimizing the sharpness and bitterness imparted by fatty acids and amines, respectively.
Types of Cheese Involving Penicillium camemberti Camembert Cheese In the traditional manufacture of the surface moldripened Camembert cheese, whole pasteurized milk is warmed to 29–33 C and ripened using a lactic acid bacteria starter culture. The high acidity of the milk assists in whey drainage and suppresses the growth of undesirable organisms. Coagulating enzyme is added to allow the formation of a firm curd within a 1–2 h period. The resulting curd is then dipped into small, perforated forms and allowed to drain for 1–2 days, with frequent turning. The cheese is then removed and salted, and is typically inoculated with a culture containing both mold and bacteria. The curing of Camembert cheese is quite a complex process and involves not only the uniform and progressive development of certain ripening agents, but also the gradual drying out of the curd. To help achieve this, the curing rooms are usually maintained at temperatures of around 13 C and at a relative humidity of 90%. The creamy, semiliquid interior consistency characteristics of Camembert are largely due to the activity of P. camemberti. The mold can be mixed with the milk, sprinkled on the curd, or rubbed on the cheese along with salt. After 2 weeks, the primary surface of mold growth forms a thin, gray-white, felt-like rind but does not penetrate the cheese. The cheese is then wrapped in parchment and foil, and boxed. The cheese is regarded as being in prime condition after a 4- to 5-week period at which time it should be consumed.
Ammonia, which has a low odor threshold (5 mmol kg1), is associated with a ripened aroma when its concentration is within the accepted limit. However, overripened Camembert cheeses can develop a strong ammonia odor as a result of the intense deamination activity of P. camemberti. Thus, a pronounced aroma of ammonia is indicative of overripening of Camembert. Flavor defects characterized by a typical celluloid flavor originating from the production of styrene by the mold sometimes appear during ripening or storage of mold-ripened cheese. It has recently been shown that P. camemberti can produce styrene from phenylalanine by phenylalanine ammonia lyase activity followed by a decarboxylation reaction catalyzed by a cinnamic acid decarboxylase. Brie Cheese Brie, a cheese that is surface ripened by mold, is very similar to Camembert. Differences exist, however, in the internal ripening and in the characteristic flavor and aroma of the cheeses. The traditional manufacture of Brie cheese involved initially warming the milk to 32 C and then adding coagulating enzyme to initiate curd development within 2–3 h. The curd is then dipped into small forms and hoops and allowed to drain for about 24 h. The hoops are removed, and the cheese is turned and dry-salted. Initial ripening for about 8 days occurs in a well-ventilated drying room maintained at 13–16 C. During this time, the curd softens rapidly and becomes slightly yellow and translucent in color, and a felt-like layer of white mold appears on the surface. The cheese is then moved to a dark, moist room or cellar that is maintained at 11 C and at a relative humidity of 85% for 2–4 weeks. The initial white mold layer formed by P. camemberti eventually changes to a yellow color and is subsequently overgrown with Gram-positive organisms similar to those found on smear-ripened cheese appearing red in color. The cheese becomes less acidic and the curd is yellow and creamy. The surface growth of both P. camemberti and smear organisms during ripening is responsible for the characteristic flavor of Brie. Like Camembert, Brie ripens rapidly, is perishable, and must be consumed soon after ripening.
Penicillium camemberti in Other Food-Related Applications Penicillium camemberti has successfully been used to improve the quality of sausage meat, through the superficial inoculation and growth of an atoxigenic strain of P. camemberti on the surface of the sausage. This has been reported to result in strong proteolysis and lipolysis, which produce an intense increase in the diglyceride,
Yeasts and Molds | Penicillium camemberti
monoglyceride, phospholipid, and free fatty acid concentrations and in volatile compounds and a corresponding decrease in triglyceride levels. Compounds such as branched aldehydes and the corresponding alcohols, acids, and esters, derived from the catabolism of amino acids, are responsible for the ripened flavor. The development of the fungal mycelia on the surface of the sausages not only protects lipids from oxidation, resulting in lower 2-thiobarbituric acid values and lipid oxidation-derived compounds, such as aliphatic aldehydes and alcohols, but also completely eliminates the growth of undesirable naturally occurring mold contaminants. Thus, the use of P. camemberti results not only in the protection of the sausage from fungal contamination but also in an improvement in the odor and flavor of the sausage.
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species and to distinguish between cheese-related fungi. Karlshøj and colleagues analyzed the pool of volatile metabolites produced by several fungi species, including P. camemberti, using the e-nose approach and showed an increasing difference between fungal species throughout time. These authors indicated that P. camemberti can be unambiguously identified after 3 days of growth on yeast extract glucose medium, with no CPA being detected. Thus, they clearly demonstrated the ability of e-nose to identify correctly closely related fungi, grown on given conditions, to a species level. Because these species have also been shown to differ in mycotoxin production, it also demonstrates the potential use of e-nose as a powerful tool for the identification of mycotoxigenic fungi in food and feedstuffs. See also: Yeasts and Molds: Penicillium roqueforti.
Advanced Methods for the Identification of Penicillium camemberti Further Reading Numerous industries are currently employing electronic nose (e-nose)-based detection systems to monitor food quality control, storage, and spoilage by both bacteria and fungi. E-nose involves an analysis of the chemicals contained in an extract using gas chromatography coupled to mass spectrometry (GC–MS) and liquid chromatography coupled to mass spectrometry (LC–MS). A fungal taxon can be identified by the metabolites it produces. Thus, profiling the pool of volatile and nonvolatile metabolites produced by Penicillium species, in defined conditions, can be used as a chemotaxonomic tool to differentiate efficiently even closely related
Brunaa JM, Hierroa EM, de la Hoza L, Mottramb DS, Fernandeza M, and Ordonez JA (2003) Changes in selected biochemical and sensory parameters as affected by the superficial inoculation of Penicillium camemberti on dry fermented sausages. International Journal of Food Microbiology 85: 111–125. Karlshøj K, Nielsen PV, and Larsen TO (2007) Differentiation of closely related fungi by electronic nose analysis. Journal of Food Science 72: 187–192. Le Bars J (1979) Cyclopiazonic acid production by Penicillium camemberti Thom and natural occurrence of this mycotoxin in cheese. Applied and Environmental Microbiology 38: 1052–1055. Nielsen MS, Frisvad JC, and Nielsen PV (1998) Protection by fungal starters against growth and secondary metabolite production of fungal spoilers of cheese. International Journal of Food Microbiology 42: 91–99.
Spoilage Molds in Dairy Products T Sørhaug, Norwegian University of Life Sciences, A˚s, Norway ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by M. A. Cousin, Volume 3, pp 2072–2078, ª 2002, Elsevier Ltd.
Introduction Molds are present in air, water, and soil and are regularly found on production equipment; hence, they can contaminate milk and dairy products. Molds are important in dairy products because they are involved in fermentation, spoilage, and mycotoxin production. Thus, molds may, even in the same product, contribute to desirable flavors or off-flavors, cause cheese coloring or discoloring, result in high-quality product structure or disintegration, and even produce toxins if not controlled. Several types of cheese are manufactured with molds either as veins throughout the cheese or as exterior crusts covering soft-cheese interiors. Some mold genera, dominated by Penicillium and Cladosporium, have species that are involved in the spoilage of cheese, yogurt, and other fermented or concentrated dairy products. Spoilage molds are mainly characterized by growth at low temperature, at low aw, and in atmospheres of low oxygen tension. Some of these molds also have an advantage because they resist some preservatives. Species of mainly Aspergillus and Penicillium can produce low concentrations of mycotoxins or other toxic metabolites on cheese as a result of growth during maturation, distribution, or storage in homes. Overall, the presence of molds in dairy products can be either acceptable or unacceptable depending on why, when, and where the molds have grown. Control of undesirable mold infection and growth in or on dairy products puts emphasis on hygiene, clean air practice, and the use of preservatives and controlled atmosphere packaging.
Molds Involved in the Spoilage of Dairy Products Cheese Although molds can be isolated from many dairy products, spoilage by molds is mainly associated with cheeses. The susceptibility depends on several conditions, namely, sanitation during manufacture and ripening, length and degree of ripening, storage conditions (temperature, relative humidity, type and extent of packaging), water activity (aw), and composition. During
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the ripening of cheese, species from genera such as Penicillium, Cladosporium, as well as Phoma and other minor molds are found on cheeses because they grow in the refrigerator at temperatures as low as 1–5 C. Penicillium species can grow at aw levels that approach 0.80; however, Cladosporium species only grow down to aw of only 0.86. Some Penicillium species, particularly P. roqueforti, can grow in low oxygen (at 1%); however, carbon dioxide at levels of 40% or more can prevent growth. In various surveys of molds in commercial packages of cheese (hard, semihard, semisoft), 50 to > 90% of the isolates were Penicillium species, with P. commune, P. nalgiovense, and P. roqueforti dominating the spoilage microflora and other Penicillium species (P. brevicompactum, P. chrysogenum, P. citrinum, P. cyclopium, P. expansum, P. glabrum, P. granulatum, P. palitans, P. solitum, P. verrucosum, P. viridicatum) being isolated less often. Although exceptions may occur, the above appear to be representative of the results that have been reported internationally from several countries including Australia, New Zealand, South Africa, Argentina, Norway, Turkey, Spain, Italy, Denmark, Greece, France, Germany, Belgium, Japan, the Netherlands, the Czech Republic, Switzerland, Malta, Costa Rica, Azores, the United Kingdom, and the United States. In the literature, many names are used for Penicillium species that are no longer recognized; the currently accepted names are listed in Table 1. In addition, species of Aspergillus (A. versicolor), Cephalosporium, Cladosporium, Geotrichum, Mucor, Scopulariopsis, and Syncephalastrum have been isolated at percentages less than 10% of the total mold isolates. In vacuum-packaged Cheddar cheeses, Cladosporium cladosporioides, C. herbarum, P. commune, P. glabrum, and Phoma species produce a condition termed ‘thread mold’ because these molds grow in the refrigerator and tolerate low levels of oxygen. Shredded cheese is particularly susceptible to spoilage by yeasts and molds. Modified atmosphere packaging in CO2/N2 (e.g., 73%/27%) has been explored and may be necessary to control mold growth. Some molds can produce bitter peptides in surfaceripened or blue-veined cheeses, with strains of P. camemberti, P. roqueforti, and G. candidum being among those identified. In highly acidic Cottage cheese, molds may cause spoilage because many bacteria cannot grow. Besides causing
Yeasts and Molds | Spoilage Molds in Dairy Products 781 Table 1 Names of molds that have been either misidentified in the literature or renamed based on new taxonomic tools Names of molds as cited in the literature
Accepted name of molds
Penicillium candidum, Penicillium caseicolum, Penicillium caseicola Penicillium cyclopium, Penicillium puberulum, Penicillium verrucosum var. cyclopium Penicillium patulum, Penicillium urticae
Penicillium camemberti Penicillium aurantiogriseuma Penicillium griseofulvum
a
Penicillium commune is similar to Penicillium aurantiogriseum and either may be misidentified in the literature citations.
discoloration due to mold spore pigments and ‘fuzzy’ appearance on the surface, molds can produce numerous off-flavors that have been described as bitter, earthy, kerosene, musty, mushroom, plastic, rancid, and related flavors. Resistant species of Penicillium, such as P. roqueforti, decarboxylate the preservative sorbic acid to 1,3-pentadiene, which causes the kerosene off-flavor in chemically preserved cheese spreads. Other Penicillium species reduce sorbic acid to 4-hexanoic acid and 4-hexanol. Molds can grow in cheese because they can overcome several conditions that are unfavorable to other microorganisms, namely, low temperature, low oxygen levels, reduced aw, lack of carbohydrates, and presence of chemical preservatives and free fatty acids.
Other Dairy Products Although molds are normally associated with the spoilage of cheeses, spoilage of yogurt, butter, sweetened condensed milk, cream, and other dairy products is occasionally caused by mold growth. Species of Absidia, Alternaria, Aspergillus, Monilia, Mucor, Penicillium, and Rhizopus can grow on the surface of yogurt; however, mold growth is usually secondary to yeast growth because they grow more slowly than yeasts. Fruit preparations added to yogurts may be a source of molds and yeasts and should be considered; for example, some Mucor species grow well at refrigeration temperatures and also under conditions of very low oxygen tension. Heat-resistant molds may be introduced in the fruit preparations; however, such molds are often not of the psychrotrophic strains and may not grow at all at refrigeration temperatures. Improved sanitation and control of dairy plant air have reduced the level of mold spoilage of butter by lipase-producing species of Aspergillus, Cladosporium, Geotrichum, and Penicillium. Low-salt margarine is a product that invites increased fungal spoilage. Penicillium and Cladosporium species have been observed; these molds are lipolytic and also produce off-flavors including 2-methylisoborneol and geosmin, thus contributing to an undesirable earthy flavor. In sweetened condensed milk, species of Aspergillus and Penicillium can grow on the surface if there is poor sanitation in the processing plant that allows entry of mold spores and a large enough headspace in the can to provide oxygen
for growth. Sometimes, cream that is stored for long periods at temperatures close to 0 C can have Penicillium species growing on the top. Geotrichum candidum and yeasts can grow on cream containing added sucrose for sale to bakeries because they produce lipases. Heat-resistant fungi, which produce ascospores, do not normally spoil dairy products; however, there are reports of Byssochlamys nivea, Eupenicillium brefeldianum, Neosartorya fischeri, and Talaromyces avellaneus causing spoilage in products such as ultra-heat-treated (UHT) custard and cream cheese. In addition, Fusarium oxysporum has been isolated from UHT flavored milks in Australia, possibly due to the production of thickwalled chlamydoconidia and the ability to tolerate low oxygen tensions. Strawberry yogurt may also harbor relatively heat-resistant Talaromyces. Under some conditions, molds can occasionally grow in or on these different dairy products and cause spoilage.
Control of Mold Growth in Dairy Products Several methods can be used to control the growth of molds on dairy products. One important way to prevent contamination of dairy products by molds is to use good practices to clean and sanitize dairy plants and processing equipment to reduce the level of mold spores in the environment. Areas that may be improperly cleaned and allow mold buildup include conveyor belts, pumps, and valves. The choice of sanitizers can be critical because chlorine seems to be more effective against molds than either peracetic acid or peroxides. Molds can grow in moist environments found in dairy plants and establish themselves on ceilings, floors, walls, and even in floor drains if these areas are not properly cleaned and sanitized. Mold spores can also enter the processing plant in raw ingredients, on packaging materials, and on people; therefore, all potential sources of molds need to be considered when determining whether contamination can occur. Another source of contamination by mold spores is the air in the processing, ripening, and packaging areas; therefore, good air-filtration systems are essential in dairy processing plants to reduce the level of mold spores. Recommendations of fewer than 50–100 molds and yeasts per cubic meter have been suggested for cheese
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processing plants. One way to reduce molds in the air is to use high-efficiency particle air (HEPA) filters because they are designed to remove 90–99% of particles 0.3 mm in size, which should help to reduce the level of mold spores in the air. As with all filtration systems, proper maintenance and regular filter replacement are critical for good air quality. In addition, the use of positive air pressure in critical areas, such as rooms for ripening and packaging of cheese, can significantly decrease the level of mold contamination. The air intake and exhaust systems in the plant need to be properly separated from each other to prevent recontaminated air from coming back into the processing plant. In an effort to improve air quality, ‘cleanroom technology’ has been introduced into some cheese processing plants, especially in the ripening rooms. The design of the rooms is carefully monitored to control air filtration and circulation, movement of people who are dressed in cleanroom attire, and microbial contamination by using footbaths and airlocks before entering the area. Generally, cleanrooms have air zones that limit particles >0.5 mm per 0.3 m3 of air, providing a room that is considered to be bacteria-free, because there are <0.1 bacteria per 0.3 m3 of air. The humidifiers in these areas also operate by using sterilized and even demineralized water. In addition to humidity, control of the temperature of the ripening and storage rooms can help to slow down the growth of molds in cheeses. Mold spoilage of cheeses has been considerably reduced by the use of new packaging technologies. Packaging material can be coated with antimycotic agents, such as sorbates, propionates, or natamycin, or, alternatively, antimycotic agents can be incorporated directly into the packaging material. Excluding oxygen
by the use of vacuum and modified atmosphere packaging is also used to limit growth of molds on cheeses sold commercially. Usually, the use of more than 50% carbon dioxide and less than 0.5% oxygen prevents spoilage molds from growing on cheeses in modified atmosphere packages. However, package leakage and pinhole defects can be problems with these types of packages, allowing molds to grow and cause spoilage.
Toxic Metabolites Produced by Molds in Dairy Products Mycotoxins and other toxic metabolites can be produced in cheese; however, many of these metabolites are produced in low concentrations or their toxicity for humans is slight or unknown at the present time. Generally, lower concentrations of mycotoxins are produced in cheese than in laboratory media; therefore, caution needs to be exercised when assessing the importance of these toxic metabolites to human health when reviewing laboratory research. The major fungal metabolites produced in cheese are listed in Table 2. Aspergillus flavus and A. parasiticus, which produce aflatoxins, rarely grow on cheese that is held at a temperature below 10 C because these species have a minimum temperature for growth above 7 C and, for aflatoxin production, usually above 15 C. If aflatoxin M1 is present in the milk, then it may still be present in dairy products made from that milk. A concern about the presence of mycotoxin-producing fungi in cheese is that several fungi reported in the literature have been misidentified; hence, the mycotoxins attributed to them have been inaccurate. One example is that P. viridicatum has been incorrectly identified as
Table 2 Mycotoxins produced in cheese by molds and potential health effects Mycotoxin
Mold producers
Effect on humans
Citrinin
Penicillium citrinum, Penicillium verrucosum
Unknown, may affect kidneys
Cyclopiazonic acid
Penicillium camemberti, Penicillium commune
No current evidence for human toxicity
Ochratoxin A
Penicillium verrucosum,a Aspergillus ochraceus
Kidney disease (Balkan endemic nephropathy)
Patulin
Penicillium expansum, Penicillium roqueforti var. carneum
Low toxicityb
Penitrem A
Penicillium crustosum
Penicillic acid
Penicillium aurantiogriseum, Penicillium cyclopium, Penicillium viridicatum
Potential neurotoxicity in humans not well understood Unknown
Roquefortine C
Penicillium species (P. chrysogenum, P. crustosum, P. roqueforti)
Unknown for humans because of low toxicity
Rugulovasine A and B
Penicillium commune
Unknown
Sterigmatocystinc
Aspergillus versicolor
Potential for liver cancer but 1/150 strength of aflatoxin
a
Penicillium viridicatum has been misidentified as producing ochratoxin A (incorrectly cited in many journal articles). Reports of carcinogenicity have not been documented. c Precursor of aflatoxin. b
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producing ochratoxin A and citations to this still occur in the literature. Although several mycotoxins are listed in Table 2, the ones that may be of importance because of potential human health effects are ochratoxin A and sterigmatocystin. Since P. verrucosum and A. ochraceus, which produce ochratoxin A, are not frequent isolates from cheese, the presence of ochratoxin A may be of minor importance. Aspergillus versicolor produces sterigmatocystin and both the mold and its mycotoxin have been isolated from cheese in temperate climates. Since A. versicolor is a mesophile that does not grow below 10 C and can be controlled by modified atmosphere packaging, both refrigerated ripening and storage of cheese plus packaging to reduce oxygen prevent its growth and toxin production. Molds that produce mycotoxins grow on the surface of cheese. However, studies on the migration of mycotoxins into cheese rarely show greater than a 2 cm movement into the cheese; therefore, cutting more than 2 cm under the moldy portions of the cheese should remove the mycotoxin as well as the mold. Much research has been done on the growth of molds on cheeses and the production of various mycotoxins. When studies have been done to detect mycotoxins in naturally contaminated cheeses, the results have varied from the detection of moderate amounts of the mycotoxins to absence of mycotoxins. The effects of mycotoxins on human health still need to be evaluated. The importance of mycotoxins in cheese also needs further study; however, the use of low ripening and storage temperatures (<10 C) and vacuum or modified atmosphere packaging can greatly reduce the potential for mycotoxin production in cheese.
Enumeration of Molds from Dairy Products The methods for the enumeration of molds from dairy products vary from country to country; however, the International Commission on Food Mycology has made recommendations for enumeration media and techniques over the past two decades. These recommendations are beginning to become the methods of choice in many countries and are now appearing as the standards in some manuals and governmental publications on official microbiological methods. For general mold enumeration in dairy foods with high a w (>0.95), dichloran rose bengal chloramphenicol (DRBC) agar is the medium of choice because the dichloran (2,6-dichloro-4nitroaniline) and rose bengal prevent the spreading of molds and thereby allow easier counting of
colonies and the chloramphenicol inhibits bacterial growth. Spread or surface plates are prepared because molds need plenty of air for growth. The plates are incubated upright at 25 C for 4–5 days for most molds. Additional incubation time may be needed for slower-growing molds. In cheeses where the a w is below 0.95, dichloran 18% glycerol (DG18) agar is recommended because, in this medium, the final a w is 0.955. Most Penicillium and Aspergillus species that are associated with cheese grow on this medium with lowered aw. Chloramphenicol is used as the sole bacterial inhibitor in these media because it can be autoclaved and remains stable in the prepared media. A different medium, creatine sucrose dichloran agar (CREAD), was developed for selection of mold species occurring on foods particularly high in lipids and protein. Molds commonly detected on cheese, Penicillium and Aspergillus species, grow well on this medium; however, certain airborne penicillia, for example, P. brevicompactum, do not thrive on this medium or on the cheese. The use of acidified media is discouraged because acid-sensitive molds can be prevented from growing on the media. Although potato dextrose agar has been used previously for enumeration of molds, this medium is low in nutrients, and this can prevent some species of Penicillium and Aspergillus from growing. The use of plate count agar or similar media does not prevent the spreading of rapidly growing molds, and colonies could be hard to count. The development of selective media for the isolation of toxigenic molds has been done for A. flavus/parasiticus and some toxigenic Penicillium species; however, these media have been mainly used for foods other than dairy products. Newer methods to enumerate and detect molds in foods are being developed using enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and other molecular biological techniques. In the future, there may be rapid and more precise methods for the enumeration and identification of molds in dairy products.
See also: Analytical Methods: DNA-Based Assays; Immunochemical Methods; Microbiological. Cheese: Acid- and Acid/Heat Coagulated Cheese; Starter Cultures: General Aspects; Starter Cultures: Specific Properties. Fermented Milks: Starter Cultures. Nutrition and Health: Effects of Processing on Protein Quality of Milk and Milk Products. Yeasts and Molds: Mycotoxins: Aflatoxins and Related Compounds; Mycotoxins: Classification, Occurrence, and Determination; Penicillium camemberti; Yeasts in Milk and Dairy Products.
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Further Reading Beuchat LR and Cousin MA (2001) Yeasts and molds. In: Downes FP and Ito K (eds.) Compendium of Methods for the Microbiological Examination of Foods, 4th edn., pp. 209–215. Washington, DC: American Public Health Association. Bullerman LB (1981) Public health significance of moulds and mycotoxins in fermented dairy products. Journal of Dairy Science 64: 2439–2452. Filtenborg O, Frisvad JC, and Thrane U (1996) Moulds in food spoilage. International Journal of Food Microbiology 33: 85–102. Fox PF and McSweeney PLH (1998) Dairy Chemistry and Biochemistry. London: Blackie Academic and Professional. Fox PF, McSweeney PLH, Cogan TM, and Guinee TP (eds.) (2004) Cheese: Chemistry, Physics and Microbiology, Vol. 2: Major Cheese Groups, 3rd edn. London: Elsevier Academic Press. Frisvad JC and Thrane U (2004) Mycotoxin production by common filamentous fungi. In: Samson RA, Hoekstra ES, Frisvad JC, and Filtenborg O (eds.) Introduction to Food- and Airborne Fungi, 7th edn., pp. 321–331. Baarn, The Netherlands: Centraalbureau voor Schimmelcultures. Hocking AD (1997) Understanding and controlling mould spoilage in cheese. Australian Journal of Dairy Technology 52: 123–124.
Kure CF, Borch E, Karlson I, Homleid JP, and Langsrud S (2008) Use of the selective agar medium CREAD for monitoring the level of airborne spoilage moulds in cheese production. International Journal of Food Microbiology 122: 29–34. Ledenbach LH and Marshall RT (2009) Microbiological spoilage of dairy products. In: Sperber WH and Doyle MP (eds.) Compendium of the Microbiological Spoilage of Foods and Beverages, pp. 41–67, Doyle MP (series ed.) Food Microbiology and Food Safety Series. New York: Springer. Lund F, Filtenborg O, and Frisvad JC (1995) Associated mycoflora of cheese. Food Microbiology 12: 173–180. Pitt JI and Hocking AD (2009) Fungi and Food Spoilage, 3rd edn. New York: Springer. Robinson RK (ed.) (2005) Dairy Microbiology Handbook: The Microbiology of Milk and Milk Products, 3rd edn. New York: John Wiley & Sons, Inc. Scott PM (1989) Mycotoxigenic fungal contaminants of cheese and other dairy products. In: van Egmond HP (ed.) Mycotoxins in Dairy Products, pp. 193–259. London: Elsevier Applied Science. Walstra P, Geurts TJ, Noomen A, Jellema A, and van Boekel MAJS (1999) Dairy Technology. Principles of Milk Properties and Processes. New York: Marcel Dekker, Inc.
Aspergillus flavus A D W Dobson, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction
Morphology
Aspergillus flavus is a member of the Aspergillus genus, which contains more than 100 recognized species, most of which grow well on common synthetic or semisynthetic media and around 50 of which have been shown to produce toxic metabolites. Aspergillus flavus is a long-established and welldefined species dating from 1806 and can be classified in Aspergillus sect. Flavi. It is closely related to A. parasiticus and to A. oryzae and A. sojae, the latter two species being particularly important in the manufacture of fermented foods in Asia. The taxonomy of Aspergillus has suffered for many decades by the incorrect application of the rule of the International Code of Botanical Nomenclature (ICBN), leading in many cases to the inaccurate identification of many species as A. flavus, when in fact they were A. parasiticus or A. nomius species. Aspergillus flavus and A. parasiticus species, while very similar, can be differentiated on mycotoxin production profiles with A. flavus isolates usually producing B aflatoxins, with fewer than 50% of isolates being toxigenic, while A. parasiticus isolates produce G as well as B aflatoxins and are all invariably toxigenic. Aspergillus nomius morphologically resembles A. flavus, but differs by producing smaller, more elongated sclerotia than those of A. flavus, which are more globose, and by the production of B and G mycotoxins, and in the production of a unique metabolite nominine, which exhibits activity against Helicoverpa zea (corn earworm) larvae in dietary assays at 100 mg g 1. Aflatoxin B1 (AFB1) is a potent human carcinogen that is produced by A. flavus. If AFB1 is ingested by dairy animals in contaminated feedstuffs or forage, the metabolite is biotransformed at the hepatic level by microsomial cytochrome P450 into aflatoxin M1 (AFM1). It has been estimated that approximately 1–3% of the AFB1 initially present in animal feedstuff appears as AFM1 in milk. Given the evidence that AFM1 is a genotoxic carcinogen and that milk has the greatest demonstrated potential for the introduction of AFM1 into the human diet, consumption of AFM1 contaminated infant milk and milk products by infants and young children in particular should be avoided. Thus, very low AFM1 limits have been set (0.01–0.05 mg kg 1) for infant foods, given the relatively high consumption rate of these products by infants, their low body weight, and the potential higher susceptibility of young children to aflatoxins.
Aspergillus flavus can be readily distinguished from other Aspergillus species, by lack of growth at 5 C, by rapid growth at both 25 and 37 C, and by the production of a bright yellow-green conidial color, when cultured on malt extract agar (MEA) or Czapek yeast extract agar (CYA). Colony growth on CYA can vary, from rapid growth reaching around 60–70 mm in diameter to slower growth of 30–40 mm in diameter at room temperature (24–26 C) in 10 days. Colonies usually consist of a thin, close-textured, basal mycelium. Most strains produce abundant conidial structures directly from the mycelium. The sclerotia, which are produced by many strains, particularly in fresh isolates, can dominate the colony appearance. They first appear as white mycelial tufts that are characteristically globose to subglobose, before gradually changing from white through dark reddishbrown to black in color and appearing spherical, from 400 to 800 mm in diameter. Following 42–48 h growth on A. flavus and A. parasiticus agar (AFPA), colonies of A. flavus exhibit a brilliant orange-yellow reverse coloration. Few other colonies produce this coloration on AFPA medium. However, prolonged incubation on AFPA, beyond 4 days, is not recommended, because A. ochraceus and other closely related species may also produce yellow reverse color after this time. This aside, AFPA is recommended for the detection and enumeration of A. flavus strains in nuts, corn, spices, and other commodities. Aspergillus flavus produces conidial heads that are typically radiate and highly variable in both shape and size, usually possessing relatively thin, finely roughened, or, rarely, smooth walls. Conidiophores are borne from either subsurface or surface hyphae. Stipes (hyphae supporting the fruiting structure, forming the conidiophore) can be 400 mm to 1 mm or more in length. The vesicles are spherical to subspheroidal in shape and are usually 20–45 mm in diameter, but can be up to 50 mm in diameter. They usually bear both metulae and phialides, but occasionally in some isolates a fraction or even a majority bear phialides alone. Various isolates of A. flavus appear to have a requirement for 0.2 ng g 1 molybdenum for growth and conidial formation. Molybdenum deficiency appears to depress growth, conidial formation dry weight, soluble protein, and the specific activities of nitrate reductase, succinic dehydrogenase, and aconitase in the fungus.
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Ecology Members of the A. flavus group are distributed widely in nature and have been routinely isolated from soils, particularly in tropical and subtropical areas, and from forage and decaying vegetation. Some of them are pathogenic to insects, and much less commonly to higher animals, including humans. They are commonly isolated from plant materials undergoing microbial decomposition, from grains and stored seeds, and from a variety of different food products. They contribute to the decomposition process at moisture levels above those tolerated by the A. candidus and A. glaucus groups. Aspergillus flavus can invade maize, peanuts, and cottonseed in the field, while in other types of agricultural crops it behaves as other storage fungi do, and does not invade seeds before harvest. Due to the potential aflatoxin problems associated with A. flavus, its presence has been sought in many different types of foodstuffs. This, coupled with the relative ease of identification, has led to A. flavus becoming the most widely reported foodborne fungus. It appears to be particularly prevalent in the tropics with many reports of its growth on oilseeds and nuts, in particular peanuts. In the United Sates and Europe, A. flavus has been reported to occur in a variety of other nuts besides peanuts, from time to time. These include coconut, copra, hazelnuts, kola nuts, pecans, pistachios, and walnuts. Aspergillus flavus is one of the dominant species found on stored products, particularly grains, as it is able to thrive in low-water activity (aw), high-temperature environments. Cereals are also commonly spoiled by the fungus, with maize and maizebased products being particularly susceptible to spoilage. Contamination has also been reported in wheat, wheat flour, and flour products, including bread. Growth on wheat results in the production of methylfuran, 2-methylpropanol, and 3-methylbutanol, and the presence of these compounds is often regarded as an indication of deterioration in grain due to fungal growth. In addition, growth on cotton fibers, for example, results in the production of a bright greenish-yellow fluorescence, thought to be due to kojic acid, which is produced by the fungus and then converted to the fluorescent substance by plant tissue peroxidases. This fluorescence is also visible in maize and other grains in which the fungus has grown. Aspergillus flavus has also been found to contaminate pasta and bran, barley, paddy, milled and parboiled rice and rice bran, sorghum, and pearl millet. Unlike in the case of crops high in oil, spoilage in small-grain cereals is usually a result of poor handling. Interestingly, A. flavus has been shown to produce anti-insectan metabolites. Following the initial observation that the sclerotia of A. flavus were avoided by the common detritivorous beetle Carpophilus hemipterus, an insect that feeds on the conidia and
mycelium of the fungus, a number of secondary metabolites of the sclerotia were isolated and shown to have anti-insect properties. The most potent of these metabolites is also nontoxic to vertebrates at 300 mg kg 1. Some of these compounds have also been shown to be active against Helicoverpa zea. Whether these metabolites are produced as a type of ‘defense mechanism’ by the fungus is open to debate. Aspergillus flavus has also been reported to be present in many different kinds of spices together with green coffee beans and herbal drugs. Other reported sources of the fungus include chickpeas, pigeon peas, soybeans, olives, and rapeseed; and other seeds such as mustard seeds, sesame seeds, amaranth seeds, sunflower seeds, and betel seeds. Aspergillus flavus has been reported to be present in a variety of food products, including processed and smoked meats, bacon, milk, and cheese, particularly in countries where refrigerated storage facilities are not always available. Processed cheese is a very good growth substrate for A. flavus. It has also been isolated from smoked and dried fish, dry-cured hams, and Italian-type salami. Finally, the fungus is also capable of spoiling fruit and vegetables such as citrus, peppers, pineapples, and tomatoes, but spoilage of these particular types of materials is not usually of great economic importance. Interestingly, a green fluorescent protein (GFP) reporter expressing A. flavus strain has recently been developed to monitor fungal growth, mode of entry, colonization of cottonseeds, and production of aflatoxins by the fungus.
Physiological Factors Affecting Growth of the Fungus Water Activity Aspergillus flavus is xerophilic, being capable of growth down to around aw 0.78, with an optimum aw of 0.99. Reported data for growth at various aw values show some variation, from a low of 0.78 at 33 C to 0.84 at 25 C, with other reports of a minimum of 0.82 at 25 C, 0.81 at 30 C, and 0.80 at 37 C. Conidia of A. flavus can germinate at aw of 0.75 aw and 29 C, but do not grow, while at aw less than 0.75 conidia remain dormant but viable. Lag times before germination increase with decreasing aw, where at high water activities (>0.98), lag times vary from a few hours to several days, and they can even extend to several months at lower aw. The salinity and osmotic pressure of the growth medium affect the production of conidia. The vegetative growth of A. flavus increases with an increase in the NaCl content up to 9% NaCl, but at higher salt concentrations inhibitory effects are observed on the production of conidia. However, A. flavus growth and aflatoxin production on processed cheese have been shown to be reduced through the addition of 6% NaCl. The lower limit of moisture for growth
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of A. flavus on cereal grains such as maize, wheat, sorghum, and rice is 18.0–18.5%; for soybeans it is 17–17.5%; and for peanuts, sunflower seeds, and copra it is 11.0–12.0%. Survival of conidia of A. flavus in a variety of dried foods (aw 0.32–0.78) at 21 C is reduced at high aw and low pH. The effect of aw on colony growth rate for each species has been employed to quantify the ‘relatedness’ of four species belonging to Aspergillus sect. Flavi (A. flavus, A. oryzae, A. parasiticus, and A. nomius). A linear model was subsequently proposed in which A. oryzae and A. parasiticus are very close to each other, placed between A. nomius and A. flavus and closer to the latter species. Temperature Aspergillus flavus grows at temperatures as low as 10–12 C and as high as 50–55 C, with optimal growth occurring at temperatures near 33 C. At optimal growth temperatures specific growth rates can reach 500 mm h 1 (or approximately 25 mm day 1). While most storage fungi have a minimum temperature for growth of 0–5 C, optimum of 25–30 C, and a maximum of 40–45 C, A. flavus has been reported to grow on Cheddar cheese at 15, 18, or 25 C and to produce aflatoxin on the cheese at 25 C. Aspergillus flavus can grow vigorously at 50–55 C and can raise the temperature of the materials in which it is growing to that level, maintaining it there for some weeks. The fungus is not very heat resistant, with a D45 value of more than 160 h, a D50 of 16 h, a D52 of 40–45 min, and a D60 of 1 min, at neutral pH and high aw, with z-values from 3.3 to 4.1 C being reported. aw provides a degree of protection. At 52 C, the D-values for conidia increase from 44 to 54 min with increase in level of sucrose from 0 to 60% (aw 0.99–0.89). In addition, high sucrose concentrations reduce the effect of preservatives on D-values. Thus, in general, preservatives act synergistically with heat at low aw values to reduce heat resistance in A. flavus. The combined and independent effects of sucrose, sodium chloride, potassium sorbate, and sodium benzoate on heat inactivation of conidia of A. flavus have shown that increasing concentrations of sucrose results in increased tolerance to heat by the fungus, while low concentrations (3 and 6%) of sodium chloride also protect A. flavus. Potassium sorbate and sodium benzoate acted synergistically with heat to reduce sensitivity to preservatives and reduced aw, whether achieved by the presence of sucrose or sodium chloride, thus demonstrating heat-induced injury. At the same concentration, potassium sorbate is more inhibitory than sodium benzoate to colony formation by A. flavus, and the presence of sucrose and sodium chloride enhances this inhibition. Conidia of A. flavus have been reported to be resistant to freezing in water at 73 C. It is believed that this survival may be partially due to a very low water content such that little or no ice formation occurs, which can affect the integrity of the
spore. Aspergillus flavus is also extremely tolerant to freezing injury, remaining viable for over 20 years in liquid nitrogen vapor. pH Several reports have singled out the importance of pH on mold growth and indicated that the pH effect may vary with mold type, acid, and levels of other variables. Growth of A. flavus is largely unaffected by pH; it can grow over the entire pH range from 2.1 to 11.2, although growth rates are slower at pH <3.5. Some reports have shown complete inhibition at pH <3 and a 50% reduction of mycelium production at pH <4. In six strains of A. flavus that were tested, a pH change from 6.0 to 4.0 reduced the mycelium production by 13%. Preservatives, even at low concentrations, reduce the heat resistance of A. flavus conidia markedly, particularly at low pH, with sodium benzoate being more effective in this regard than potassium sorbate. It has been reported that 1500 mg g 1 vanillin (4-hydroxy-3-methoxybenzaldehyde) is inhibitory at pH 3.5 for A. flavus. In addition, it has been shown that on potato dextrose agar at an aw of 0.98 mold germination times and radial growth rates are affected by vanillin and pH, with increases in lag time being observed with increasing vanillin concentration and reduced pH. Studies on the growth of A. flavus under modified atmosphere packaging (MAP) conditions, where the combined effect of aw, pH, storage temperature, headspace oxygen, and CO2 concentration on the growth of A. flavus on synthethic media using response surface methodology (RSM) were analyzed, indicated that A. flavus can grow in a CO2 enriched atmosphere if headspace oxygen is present. In addition aw, pH, storage temperature, and initial concentration of headspace oxygen in the gas mix are all highly significant factors (p < 0.01) in controlling the growth of the organism on synthetic media. Genetics DNA-based techniques have been developed and applied in the molecular identification and detection of A. flavus, primarily in an effort to distinguish between aflatoxinproducing and nonproducing strains. Research groups have targeted genes that are involved in aflatoxin biosynthesis in A. flavus, such as ver-1, omt-1, and apa-2 and designed PCR (polymerase chain reaction) primers based on these genes. These PCR primers have then been used to detect aflatoxigenic strains of the fungus in grains and foods. Geisen and coworkers, targeting these three genes in a multiplex PCR-based approach, succeeded in differentiating A. flavus from two other Aspergillus species from section Flavi, namely, Aspergillus sojae and Aspergillus oryzae. In addition, they were able to distinguish between
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toxigenic and atoxigenic A. flavus strains. In follow-on studies using sequences of the nor-1 gene, primers have been set up together with a probe for a TaqManTM realtime PCR assay, in which A. flavus has been quantified in contaminated food samples and in cereals. A PCR-based method targeting the aflR gene has also been developed, with specific primers being designed to generate a PCR fragment, and restriction fragment length polymorphism (RFLP) of the PCR product being performed, which allowed the differentiation between A. flavus and A. parasiticus in spiked samples of sterile maize flour. Reverse transcription-polymerase chain reaction (RT-PCR) has been applied to differentiate aflatoxinproducing from aflatoxin-nonproducing strains of A. flavus. Specific primers were employed, which were based on the conserved regions of the nine structural genes, aflD, aflG, aflH, aflI, aflK, aflM, aflO, aflP, and aflQ, and two regulatory genes, aflS and aflR, of the aflatoxin B1 biosynthetic pathway. Expression of the aflD, aflO, and aflP genes in particular was shown consistently to correlate with aflatoxin production by the fungus. Amplified fragment length polymorphism (AFLP-) based techniques have also been employed in an attempt to distinguish A. flavus from other Aspergillus species from section Flavi, but have proven to be problematic. In one study, 500 potentially polymorphic fragments were identified following AFLP analysis involving the use of 12 different primer combinations on 24 of A. sojae, A. parasiticus, A. oryzae, and A. flavus isolates. Subsequent analysis of the AFLP data allowed the separation of the A. sojae/A. parasiticus isolates from the A. oryzae/A. flavus isolates. However, despite the presence of many polymorphisms between isolates within the A. oryzae/A. flavus subgroup, no markers that distinguish between the two species could be identified. Subsequent sequencing of the ribosomal DNA ITSs (internal transcribed spacers) from selected isolates from the A. oryzae/A. flavus subgroup resulted in the identification of some ITS variation between isolates within this subgroup, but did not correlate with the species classification, indicating that it is difficult to use molecular data to separate the two species. Other DNA-based techniques have, however, been successfully employed in the genetic identification of Aspergillus section Flavi fungal isolates. A novel method for heteroduplex panel analysis (HPA), which utilizes fragments of the ITS regions (ITS1-5.8S-ITS2) of the rRNA gene that can be PCR amplified with universal primer has been developed. The method involves formation of heteroduplexes with a set of reference fragments amplified from A. flavus, A. parasiticus, A. tamarii, and A. nomius, and subsequent comparison with speciesspecific standard panels generated by pairwise reannealing among reference fragments. This HPA approach appears to be a useful identification method that may be
particularly suitable for rapid and inexpensive screening of large numbers of A. flavus isolates. In addition, ITSs, inter-simple sequence repeats (ISSRs), and random amplified polymorphic DNA (RAPD) molecular markers have also successfully been used to characterize A. flavus strains genetically. In one study a high degree of genetic diversity was revealed by RAPD and by ISSR, using the primer (GACA)4, which generated ISSR and RAPD profiles that allowed strain identification. Recently, the A. flavus genomics program has been launched with the major objective being the identification of genes involved in aflatoxin biosynthesis and regulation, as well as in pathogenicity. The A. flavus genome has been sequenced and initial annotation has revealed genes that potentially encode for enzymes involved in secondary metabolite production in the fungus. Genome-wide analysis of A. flavus will provide a better understanding of not only the mechanism of aflatoxin formation in the fungus and the factors affecting production of the mycotoxin, but will also allow strategies to be developed to control aflatoxin contamination of preharvest agricultural crops and postharvest grains during storage. Thus, these molecular-based techniques represent significant progress toward the detection and identification of A. flavus strains and in increasing our understanding of the physiological parameters involved in mycotoxin production in the fungus. These techniques will prove useful not only in the detection of aflatoxigenic and nonaflatoxigenic strains in Hazard Analysis Critical Control Point systems, but also in A. flavus species identification, where they will ultimately be employed together with traditional techniques, resulting in a higher efficiency of isolate characterization and in differentiating A. flavus species and strains. Preservatives A large number of both naturally occurring metabolites and chemical preservatives affect the growth of A. flavus.
Naturally Occurring Preservatives Lactococcus lactis subsp. lactis CHD-28.3 has been shown to exert antifungal activity against different A. flavus species. This antifungal activity is due to a proteinaceous compound, and given the generally regarded as safe (GRAS) nature of lactococcal species, this compound may prove useful in the preservation of different milk-based foods. The antifungal properties of extracts from plants and plant parts used as flavoring agents in foods and beverages have been well documented. Citrus oils when added to grapefruit juice or glucose-yeast extract medium at a concentration of 3000–3500 mg kg 1 suppress growth of
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A. flavus, while orange oil added to either medium at concentrations up to 7000 mg kg 1 also results in reduced growth rates. Volatile compounds derived from maize have been found to affect growth and aflatoxin production in A. flavus. Five different concentrations of aqueous extracts of the plants Lupinus albus, Ammi visnaga, and Xanthium pungens (2, 4, 6, 8, and 10 mg ml 1) inhibited the mycelial growth of A. flavus in a chemically defined medium. The inhibitory effect has been shown to be proportional to the applied concentration. Extracts from seven Allium plants (garlic, bakeri garlic, Chinese leek, Chinese chive, scallion, onion bulb, and shallot bulb) also exhibit antifungal activity against A. flavus. With the exception of scallion, the inhibitory effect decreased with increasing incubation and heating temperature (p < 0.05). Acetic acid treatment of the extracts increases the inhibitory effect for all Allium plants against the three fungi than heat treatment alone (p < 0.05). Treatment of the extracts with NaCl, at concentrations of 0.2 and 0.4 mol l 1, does not affect the inhibitory effect of the plant extracts. Thus, a combination of acetic acid plus Allium plants appears to be an effective way to inhibit growth of the fungus. Essential oils and methanol extracts from the plant of Satureja hortensis have recently been reported to have strong antifungal activity against A. flavus, while essential oils extracted from the leaves of Chenopodium ambrosioides Linn. (Chenopodiaceae) have also been reported to inhibit completely the growth of aflatoxigenic strains of the fungus. A number of reports have cited the inhibitory effects of onion extracts on A. flavus growth. Thiopropanal S-oxide, a compound in the ether extract of onion, has been demonstrated to inhibit the growth of A. flavus. The activity is apparently lost, however, by heating, freeze-drying, dehydration, aeration, agitation, and storage. Ethanol extracts of Welsh onion also appear to have an inhibitory effect on A. flavus growth. The mycelial growth of A. flavus cultured on yeast extract-sucrose broth is completely inhibited in the presence of ethanol extracts of the Welsh onions at a concentration of 10 mg ml 1 during 30 days of incubation at 25 C. These extracts showed more pronounced inhibitory effects against A. flavus than did the same added levels of the preservatives sorbate and propionate at pH values near 6.5. The survival of spores of A. flavus depends on both the extract concentration and the exposure time of the spores to the onion extracts. Other reports indicate that natural nontoxic materials including extracts of eugenol and garlic can inhibit the mycelial growth of A. flavus, with garlic extract being particularly effective (approximately 62% growth inhibition). Base-soluble proteins (BSPs) and methanol-soluble polysaccharides (PSs) from A. flavussusceptible (Huffman) genotypes of maize have also been shown to possess antifungal activity, with microgram quantities of the protein and polysaccharides being sufficient to retard fungal growth.
Aqueous extracts from three Egyptian plants, namely, Ammi visnaga (Umbellliferae), Lupinus albus (Leguminosae), and Xanthium pungens (Compositae), at varying concentrations ranging from 2 to 10 mg ml 1, have been shown to inhibit A. flavus growth in a dose-dependent manner. The radial growth of A. flavus in solid culture was inhibited when exposed to atmospheres containing various cotton-leaf-derived volatiles. While 3-methyl-1-butanol and 3-methyl-2-butanol inhibited A. flavus growth by 20%, the most bioactive compounds were the C6–C9 alkenals, which completely inhibited fungal growth. Propolis ethanolic extract (PEE) at 3 and 4 g l 1 and ultragriseofulvin (UG) at 0.75 and 1 g l 1 have been shown to reduce the percentage of conidia germination in A. flavus isolates, with PEE at 1–4 g l 1 decreasing the mycelial dry mass of A. flavus isolates by 11–80% and UG concentrations of 0.25–1 g l 1 reducing the growth of the isolates by 16–88%. At equal concentration, UG is about 4 times more effective than PEE. Essential plant oils and their components have been shown to be effective in protecting maize kernels from infection by A. flavus. Essential oils of Cinnamomum zeylanicum (cinnamon), Mentha piperita (peppermint), Ocimum basilicum (basil), Origanum vulgare (oregano), Teloxys ambrosioides (the flavoring herb epazote), Syzygium aromaticum (clove), and Thymus vulgaris (thyme) are known to cause a total inhibition of A. flavus development on maize kernels. In addition, the plant components thymol and O-methoxycinnamaldehyde have been shown to significantly reduce maize grain contamination. The optimal dosage for protection of maize varies from 3 to 8%, with residual effects in some cases being detected up to 4 weeks after kernel treatment. An essential oil from Cymbopogon citratus has also been shown to exhibit fungitoxicity toward A. flavus with an MIC of 1000 mg l 1. The fungitoxic potency of the oil remains unaltered for 7 months of storage upon introduction of high doses of inoculum of the test fungus. It is thermostable in nature at temperatures ranging between 5 and 100 C. Essential oils and methanol extracts from the plant Satureja hortensis have recently been reported to have strong antifungal activity against A. flavus, while essential oils extracted from the leaves of Chenopodium ambrosioides Linn. (Chenopodiaceae) have also been reported to completely inhibit the growth of aflatoxigenic strains of the fungus. Herbs and spices have been shown to inhibit the growth of A. flavus, with water-soluble extracts of garlic bulbs, green garlic, and green onions showing an inhibitory effect. In some cases, increases in temperature from 60 to 100 C significantly decreased this inhibitory effect, while acid treatments at pH 2, 4, or 6, or salt treatments at concentrations of 0.1, 0.2, 0.3, and 0.4 mol l 1 have no effect. Finally, volatile metabolites of Rhizopus arrhizus, such as ethanol, isobutyl alcohol, and 3-methyl butanol, or of their mixtures when present in the vapor phase at levels
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ranging between 3 and 6% (v/v of headspace), have been shown to inhibit competitively the growth of A. flavus. This growth retardation can be synergistically enhanced by decreases in the aw. The physical state of the alcohols, that is, their partition between solid and gaseous phases, seems to be one of the determinants of their antifungal activity. The mycoparasite Humicola fuscoatra has been reported to produce natural antifungal metabolites, namely, monorden (MIC >28 mg ml 1 of growth medium) and monocillin IV (MIC >56 mg ml 1), and a new monorden analog that is active against A. flavus has been developed. Chemical Preservatives Sorbic acid (1000 mg l 1) and monolaurin (750 mg l 1) reduce the mycelial growth of A. flavus, with monolaurin being 2.4 times more active on a mole-per-mole basis than sorbic acid against the fungus. Formic acid at concentrations of 60 mmol l 1 has been shown to reduce the growth of A. flavus on barley. Polyunsaturated fatty acids have been reported to have sporogenic effects on the development of A. flavus, with the development of cleistothecia and sclerotia in the fungus affected by linoleic acid and light. Linoleic acid specifically induces precocious and increased asexual spore development and alters sclerotium production in A. flavus strains in which sclerotium production decreases in the light but increases in the dark. These sporogenic effects suggest that these factors may be significant environmental signals in the development of the fungus. Sodium diacetate has been shown to inhibit A. flavus at 0.1–0.5% in potato dextrose agar (pH 3.5 and 4.5) and in animal feeds and silage. Diethyl dicarbonate (DEDC), commonly called diethyl pyrocarbonate, has been shown to be fungicidal to A. flavus resulting in a 100% kill at concentrations of 1 g l 1. Phenolics act as antioxidants inhibiting the growth of A. flavus. A number of research groups have reported that butylated hydroxyanisole (BHA) at concentrations ranging from 100 mg l 1 through 200 to –750 mg l 1 results in inhibition of A. flavus growth. However, BHA is less effective in the presence of corn oil. BHA incorporated at 400 mg l 1 in processed cheese spread inhibits the growth of A. flavus, while lower concentrations of 150–200 ppm are effective when BHA is sprayed on the surface of the cheese. The pH of the product may also affect the activity of BHA, and there are reports stating that outgrowth of A. flavus conidia is inhibited to a greater extent at pH 3.5 than at pH 5.5. Phenolic compounds isolated from olive cake are also known to inhibit the growth of A. flavus. Vanillic and caffeic acids at concentrations 0.2 mg ml 1 and hydroxybenzonic, protocatechuic, syringic, para-coumaric acids, and quercetin at concentrations 0.3 mg ml 1
completely inhibit the growth of A. flavus. In addition, four compounds, three of which were phenolic in nature, which were extracted with acetone from cotyledons of freshly harvested peanut seeds, have been reported to inhibit the growth of A. flavus. Benzoic acid derivatives also inhibit A. flavus growth. Benzoic acid (10 mg g 1), sodium benzoate (24 mg g 1), and salicylic acid (2 mg g 1) completely inhibit the mycelial growth of A. flavus in groundnut. In a separate study, methyl benzoate and ethyl benzoate, at concentrations of 2.5 and 5.0 mg per 25 ml of medium, respectively, have also been shown to reduce the mycelial growth of A. flavus. A 96% formulation of gentian violet has been shown to be fungistatic to A. flavus, when incorporated into corn meal agar at 6.5, 12.8, 26.6, 39.0, and 156.0 mg kg 1 of gentian violet. Studies on the effect of chloroperoxidase (EC 1.1.1.10) and hydrogen peroxide on the viabilities of quiescent and germinating conidiospores of A. flavus have shown hydrogen peroxide to be moderately lethal and chloroperoxidase to produce a 30-fold increase in the lethality of hydrogen peroxide to germinating conidia, which were 75-fold more susceptible to chloroperoxidase than were quiescent conidia. Mortality occurs due to oxidation rather than peroxidative chlorination. Fungicides are known to inhibit the growth of A. flavus. In yeast extract-sucrose media, dicloran, iprodione, and vinclozolin fungicides significantly inhibit mycelial growth of A. flavus at 250 mg kg 1. Sensitivity to fungicides increased approximately fivefold in a yeast extractstarch medium with an appreciable reduction in sugar uptake and -amylase activity. In a separate study, pyridazinone herbicides at concentrations of 20, 40, or 60 mg ml 1 herbicide have been shown not to affect mycelium production in A. flavus. Other agents, such as phosphine (insecticide), when added to grain at aw 0.80 or 0.86 reduce growth of A. flavus without affecting survival of conidia. Finally, polyamines appear to play a role as modulators of microcycle conidiation in A. flavus, with putrescine being essential for vegetative growth of the fungus, while spermidine is involved in microcycle conidiation. A low putrescine/ spermidine ratio is important for spore differentiation to microcycle conidiation.
Effects of Physical Agents Near-UV (NUV) irradiation (10 and 20 min) has been shown to stimulate protein synthesis in A. flavus, with concomitant decreases in DNA synthesis, while farUV (FUV) irradiation induces protein synthesis in A. flavus with no effect on DNA synthesis and reversal of RNA synthesis. UV irradiation produces no effect on the process of lipid synthesis. Total soluble
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carbohydrates increase markedly in A. flavus (240 min NUV), with FUV irradiation resulting in an increase in total soluble carbohydrates. Ozone treatments inactivate the fungus, with D-values for conidia of A. flavus exposed to 1.74 mg g 1 ozone in 1 mmol l 1 potassium phosphate buffer (pH 7.0 and 5.5) at 25 C being 1.72 and 1.54 min at pH 5.5 and 7.0, respectively. Microwave energy also affects A. flavus, with germination of fungal spores on slides directly exposed to 6, 9, and 18 kJ for periods of 0–7 min being significantly reduced. Aspergillus flavus is also inactivated by doses of gamma irradiation between 0.6 and 1.7 kGy, with, for example, reports of complete growth inhibition and toxin production in ground beef samples treated with 1.5 kGy.
See also: Contaminants of Milk and Dairy Products: Environmental Contaminants. Yeasts and Molds: Mycotoxins: Aflatoxins and Related Compounds; Mycotoxins: Classification, Occurrence and Determination.
Further Reading Corry JEL (1987) Relationships of water activity and fungal growth. In: Beuchat LR (ed.) Food and Beverage Mycology, 2nd edn., pp. 51–99. London: Van Nostrand Reinhold. Hocking AD (1997) Toxigenic Aspergillus species. In: Doyle MP, Beuchat LR, and Montville TJ (eds.) Food Microbiology, Fundamentals and Frontiers, pp. 393–405. Washington, DC: ASM Press. International Commission on Microbiological Specifications for Foods (1996) Toxigenic fungi: Aspergillus. In: Microorganisms in Foods, Vol. 5: Characteristics of Food Pathogens, pp. 347–381. London: Academic Press. Niessen L (2007) PCR-based diagnosis and quantification of mycotoxin producing fungi. International Journal of Food Microbiology 119: 38–46. Payne GA (1998) Process of contamination by aflatoxin producing fungi and their impact on crops. In: Sinha KK and Bhatnagar D (eds.) Mycotoxins in Agriculture and Food Safety, pp. 279–306. New York: Marcel Dekker. Pitt JI and Hocking AD (1997) Aspergillus and related telemorphs. In: Pitt JI and Hocking AD (eds.) Fungi and Food Spoilage, 2nd edn., pp. 339–416. Sydney, NSW: Academic Press. Sweeney MJ and Dobson ADW (1998) Mycotoxin production by Aspergillus, Fusarium and Penicillium species. International Journal of Food Microbiology 43: 141–158. Yu J, Payne GA, Nierman WC, et al. (2008) Aspergillus flavus genomics as a tool for studying the mechanism of aflatoxin formation. Food Additives and Contaminants 25(9): 1152–1157.
Mycotoxins: Classification, Occurrence and Determination H Fujimoto, Teikyo Heisei University, Chiba, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction Since the discovery of carcinogenic aflatoxins from Aspergillus flavus isolated from the feed was connected to the death of a large number of turkeys (turkey X disease) in Great Britain in 1960, many studies on mycotoxins have been carried out worldwide. Such studies, however, had already begun in the 1950s in Japan, where it had been found that a yellow pigment, ()-luteoskyrin, isolated from Penicillium islandicum grown on rice caused hepatopathy in experimental animals. Today, such toxic fungal metabolites as aflatoxins and ()-luteoskyrin are called ‘carcinogenic mycotoxins’. Many toxic fungal metabolites cause paralysis, tremor, or convulsion in experimental animals. For example, citreoviridin isolated from Penicillium citreoviride, which infects rice, causes paralysis in experimental animals, and fumitremorgins isolated from Aspergillus fumigatus grown on miso (bean paste) causes tremor or convulsion in mice. These fungal metabolites, which have a toxic effect on the nervous system, are called ‘neurotropic mycotoxins’. There are many other mycotoxins, for example, trichothecenes isolated from some Fusarium species cause immunomodulation in experimental animals, and sporidesmins isolated from Pithomyces chartarum cause photohypersensitive eczema in sheep. The important features of mycotoxins may be summarized as follows: 1. Mycotoxins are secondary metabolites of fungi (Fungi Imperfecti and Ascomycetes) that exhibit toxic effects called ‘mycotoxicoses’ when food or feed contaminated with them is ingested by humans or domestic animals. 2. Though mycotoxicoses often spread regionally and seasonally, they are not infectious diseases; therefore, mycotoxicoses are clearly distinguishable from mycoses, which are infectious diseases caused by infectious fungi like Trichophyton spp. 3. Almost all mycotoxicoses are chronic diseases, which result from a prolonged consumption of food or feed contaminated with tiny quantities of mycotoxins, and acute forms of mycotoxicoses are comparatively rare. 4. A large number of mycotoxins showing diversity in structure and in mode of action are known, because of which it is not easy to classify mycotoxins on the basis of their characteristics. In this article, mycotoxins are classified into three categories, carcinogenic, neurotropic, and other mycotoxins.
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5. For qualitative and quantitative analyses and identification of mycotoxins, various chromatographic techniques, including column chromatography (CC), thin-layer chromatography (TLC), gas liquid chromatography (GLC), high-performance liquid chromatography (HPLC), and various spectroscopic techniques such as nuclear magnetic resonance (NMR), infrared (IR), ultraviolet (UV), mass (MS), optical rotation, optical rotatory dispersion (ORD), and circular dichroism (CD) spectroscopy are employed, and various in vitro and in vivo bioassay methods are used on the basis of the biological properties of mycotoxins. 6. Among a large number of mycotoxins, polyketides synthesized through the acetate–malonate pathway, amides and peptides formed through the amino acid pathway, terpenoids formed through the mevalonate pathway, and complex metabolites formed through mixed-type pathways are of major importance (see Yeasts and Molds: Aspergillus flavus).
Carcinogenic Mycotoxins Bisfuranoids: Aflatoxins and Sterigmatocystin Aflatoxins are at present considered to be among the strongest natural carcinogens. These are produced mainly by the three fungi belonging to the A. flavus group, A. flavus, A. parasiticus, and A. nomius, which have been isolated from many types of food and feed, such as peanuts and cereals including maize, spices, nuts, beans, and sugarcanes. There are four congeners of aflatoxins: B1, B2, G1, and G2. Structurally, coumarino dihydro- and tetrahydro-bisfuran, a five-membered , -unsaturated cyclic ketone, is condensed to build up aflatoxins B1 and B2, and the six-membered , -unsaturated lactone is condensed to form aflatoxins G1 and G2 (Figure 1). Biosynthetically, all aflatoxins are formed from decaketide through the acetate–malonate pathway. Aflatoxins cause acute hepatopathy and chronic hepatic cancer in many species of mammals, fowl, and fish (the order of the peroral toxicity against ducklings is: aflatoxin B1 > G1 > B2 > G2). In an in vitro experiment, the dihydrobisfuran moiety in aflatoxin B1 easily formed a covalent by bonded adduct with the base part of nucleic acid by way of an 8,9-epoxide type intermediate, suggesting that the carcinogenicity of aflatoxins B1 and G1 is the result of the dihydrobisfuran
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Figure 1 Structures of aflatoxins B1, B2, G1, and G2, and sterigmatocystin.
moieties in their molecules, which inhibit normal protein biosynthesis by the formation of an adduct with the base part of nucleic acid (Figure 2). Sterigmatocystin was first isolated as a yellow pigment from A. versicolor in 1954, and the structure was established in 1962 (Figure 1). Sterigmatocystin has also been isolated from Aspergillus aurantio-brunneus, Aspergillus amstelodami, Aspergillus chevalieri, A. flavus, Aspergillus multicolor, Aspergillus nidulans, A. parasiticus, Aspergillus quadrilineatus, Aspergillus ruber, Aspergillus unguis, and Aspergillusustus. Sterigmatocystin, the dihydrobisfuran moiety, which has the same configuration as that of aflatoxins, has already been shown to be a natural biosynthetic precursor of aflatoxin produced by A. parasiticus. Although sterigmatocystin has a dihydrobisfuran moiety quite similar to that of aflatoxin B1, the carcinogenicity of sterigmatocystin is only about onehundredth of that of aflatoxin B1 because the solubility of sterigmatocystin is so much lower than those of aflatoxins. Sterigmatocystin has been reported in Gouda and Edam cheese contaminated by A. versicolor (see Yeasts and Molds: Mycotoxins: Aflatoxins and Related Compounds).
Bisanthraquinonoids: ()-Luteoskyrin and (þ)-Rugulosin Rice contaminated with P. islandicum, P. rugulosum, P. citrinum, and P. citreoviride becomes yellow. ()-Luteoskyrin has been isolated as a yellow pigment from rice infected with P. islandicum; it possesses a unique cage-type dimeric bisanthraquinonoid structure and shows levorotatory optical activity (Figure 3). The bisanthraquinonoid structure of ()-luteoskyrin is formed from two molecules of anthraquinone, which are synthesized from octaketide through the acetate–malonate pathway. ()-Luteoskyrin causes hepatopathy, including liver necrosis, fatty degeneration, and hepatic cancer. Hepatoma was induced by ()-luteoskyrin in a dose-dependent manner when administered to mice for 216 days at 16.7, 68.8, and 84.6% at 50, 150 and 500 mg day1, respectively. This tumorigenic effect on the livers of mice was greater in males than in females. Another yellow pigment, (þ)-rugulosin, has been isolated from P. rugulosum. The structure of (þ)-rugulosin is also a cage-type bisanthraquinonoid very similar to that of ()-luteoskyrin, but this compound is dextrorotatory (Figure 3). (þ)-Rugulosin also causes hepatic necrosis, fatty degeneration, and hepatic cancer in mice, but the
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Figure 2 Suggested role of the dihydrobisfuran moiety of aflatoxin B1 in its carcinogenicity.
Figure 3 Structures of ()-luteoskyrin, (þ)-rugulosin, citrinin, and ochratoxin A.
toxicity of this compound is about one half of that of ()luteoskyrin. Citrinin and Ochratoxin A The yellow pigment, citrinin, has been isolated from P. citrinum found on yellow rice called ‘citrinum yellow rice’. Citrinin, which is biosynthesized from a pentaketide
through the acetate–malonate pathway with three C1-sources, causes renal damage in swine. It has also been shown to possess antibacterial, antifungal, and antiprotozoal activity. Citrinin was previously used as an antibiotic, but was later banned because of its nephrotoxicity. Ochratoxin A has been isolated from A. ochraceus, which grows on many types of farm produce. It is an amide formed from a bicyclic carboxylic acid synthesized
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from a pentaketide with a C1-source and L-phenylalanine, and has been shown to cause kidney necrosis and cancer. It is now known that a renal inflammation (nephropathy), which sometimes appears in swine in Northern Europe, results from poisoning by citrinin and ochratoxin A produced by Penicillium viridicatum, which contaminates feed (Figure 3). There is some evidence that ochratoxin A can be produced in cheese contaminated by Penicillium spp. Fumonisins Fumonisins have been isolated from a fungal contaminant of maize, F. verticillioides (formerly Fusarium moniliforme), which occurs worldwide (the teleomorphic state: Gibberella fujikuroi), and Fusarium proliferatum. It has been shown that fumonisins cause leukoencephalomalacia in horses and pulmonary edema in swine. Several congeners of fumonisins, that is, fumonisins A1, A2, B1, B2, B3, and B4, are known (Figure 4). It has been established that fumonisin B1 causes hepatocarcinoma in male rats fed with feed containing 50 mg kg1 for prolonged periods, and also causes nephrosis in male rats fed with 9 mg kg1. Fumonisins, which have a long carbon chain aminoalcohol structure as their basic skeleton, are structurally similar to sphingosines (sphingoids). In fact, it has been demonstrated that fumonisins inhibit sphingolipid metabolism, and consequently, disrupt critical sphingolipid-mediated cell signaling pathways or sphingolipid-dependent physiological functions.
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Other Carcinogenic Mycotoxins A cyclic chlorine-containing pentapeptide named ‘cyclochlorotine’ has been isolated together with ()-luteoskyrin from P. islandicum growing on rice (Figure 4). It has been shown that cyclochlorotine causes hepatopathy in mice, which results in hepatic cancer. Cyclochlorotine also has a cytotoxic effect on cultured cells. Patulin, which has been isolated from P. patulum and Aspergillus clavatus, and penicillic acid, which has been isolated from P. cyclopium, P. puberulum, and many other Penicillium and Aspergillus fungi, are the compounds possessing an , -unsaturated -lactone structure, which is formed via opening of an aromatic ring from tetraketide through the acetate–malonate pathway (Figure 4). Subcutaneous injection of patulin or penicillic acid causes sarcoma in experimental animals. The presence of patulin has been reported in cheese contaminated with Penicillium spp.
Neurotropic Mycotoxins Citreoviridin In 1940, an extract of Penicillium toxicarium (the synonym of P. citreoviride), which contaminated Formosan rice called ‘toxicarium yellowed rice’, was found to cause ascending paralysis, hypothermia, and breathing
Figure 4 Structures of fumonisins, cyclochlorotine, patulin, and penicillic acid.
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Figure 5 Biosynthesis of citreoviridin.
difficulties in mice. These symptoms were thought to be similar to those of cardiac beriberi, which was widespread until about 1925 in Japan and later disappeared. At that time, vitamin B1 was ineffective against cardiac beriberi. In 1947, a yellow pigment named ‘citreoviridin’ was isolated from P. citreoviride, and some time later, this compound was found to be the toxic factor of this fungus. Citreoviridin is formed from 2-pyrone, a conjugated polyene chain, and a tetrahydrofuran moiety is synthesized from nonaketide and C1-sources through the acetate–malonate pathway (Figure 5). Citreoviridin causes neural damage including ascending paralysis in mice, suggesting that the conjugated polyene system in this compound may affect the electron transport system in mice. It is now being suggested that cardiac beriberi, a disease of the past, may have resulted from ingestion of rice contaminated with citreoviridin.
Tremorgenic Dioxopiperazines In 1971, it was discovered that the extract of A. fumigatus grown on miso (bean paste) and rice caused marked tremor in mice and rats. Subsequently, tremorgenic constituents named ‘fumitremorgins A and B’ were isolated from the extract. Fumitremorgins A and B are composed of a basic skeleton of 2,5-dioxopiperazine formed from L-tryptophan and L-proline, with three and two isoprenyl (C5) units in fumitremorgins A and B, respectively (Figure 6). The ED50 values of fumitremorgins A and B needed to cause tremor in mice are 0.18 and 3.5 mg kg1 i.p., respectively. The tremor induced by fumitremorgin A increases with a high level of serotonin, which is an excitatory neurotransmitter in the central nervous system in the brain of mice, and decreases at a high level of
-aminobutyric acid (GABA), which is a suppressive neurotransmitter. Verruculogen isolated from P. verruculosum obtained from peanuts has the structure of fumitremorgin A except that the isopentenyl ether group is replaced with a hydroxyl group in verruculogen (Figure 6). Verruculogen shows tremorgenic activity similar to that of fumitremorgin A. Both fumitremorgin B and verruculogen are produced by Aspergillus caespitosus and Penicillium piscarium. Verruculogen is also produced by Penicillium paraherquei, and both fumitremorgins A and B are produced by Neosartorya fischeri (the teleomorphic state of A. fumigatus). Roquefortine (the synonym: roquefortine C) was isolated in 1976 from P. roqueforti, which is a mold used in the production of blue cheese. Roquefortine, which possesses a dioxopiperazine skeleton composed of tryptophan and histidine with an isopentenyl unit, also exhibits tremorgenic activity (Figure 6). Roquefortine has also been isolated from Penicillium crustosum.
Tremorgenic Indoloditerpenes Paxilline, a tremorgenic compound, was isolated from P. paxilli grown on pecans in 1974, and the structure was determined by X-ray crystallographic analysis in the following year (Figure 7). This was the first tremorgenic indoloditerpene (meaning: indole þ diterpene) to reveal its structure. Paspalinine was isolated from Claviceps paspali as its tremorgenic factor in 1977. Claviceps paspali was suspected to be the causative mold of a neuroataxia of cattle in the United States called ‘paspalum staggers’; its structure was determined in 1980 (Figure 7). Metabolites such as paxilline and paspalinine are thought to be synthesized from
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Figure 6 Structures of fumitremorgins A and B, verruculogen, and roquefortine.
Figure 7 Structures of paxilline, paspalinine, aflatrem, and penitrem A.
tryptophan and geranylgeraniol through the pathway shown in Figure 8. Aflatrem was isolated from A. flavus in 1964 as the tremorgenic agent in this fungus (probably the first tremorgenic metabolite to be isolated from fungi), and its
structure was established in 1980 (Figure 7). In 1968, penitrem A was isolated from P. cyclopium obtained from peanuts implicated in a case of sheep poisoning; it was later also isolated from Penicillium palitans and P. crustosum. The structure of penitrem A was established in 1981
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Figure 8 Suggested biosynthetic route for indoloditerpenes. Adapted from Turner WB and Aldridge DC (1983) Fungal Metabolites II. London: Academic Press.
(Figure 7). It is a derivative of tremorgenic indoloditerpenes; the skeleton of this metabolite is formed from tryptophan, geranylgeraniol, and two further isoprenyl units. This compound is believed to be one of the substances that causes a neuroataxia of cattle named ‘ryegrass staggers’, which occurs in New Zealand and Australia.
including various macrocyclic-type trichothecenes such as verrucarin A isolated from M. verrucaria, are known (Figure 9). These macrocyclic-type trichothecenes are particularly toxic. Various trichothecenes are produced by some species in the genera Fusarium, Trichothecium, Trichoderma, and Myrothecium. Sporidesmins
Other Mycotoxins Trichothecenes Fusarium toxicosis results from toxic metabolites of Fusarium nivale and other Fusarium spp. isolated from wheat and pasture. The causative agents of this toxicosis are nivalenol, deoxynivalenol, T-2 toxin, fusarenon-X, and related compounds, which belong to a sesquiterpene group named ‘trichothecenes’ (Figure 9). Trichothecenes, which possess the unique sesquiterpene skeleton named ‘trichothecane’, cause hemorrhage, vomiting, diarrhea, anorexia, and malfunction of hematopoietic organs, resulting in decreased lymphocyte production and, consequently, immunodeficiency in mice, rats, and swine. The key target cells of trichothecenes are leukocytes, and the toxicity of trichothecenes is complicated because they are immunostimulatory at low doses, but immunosuppressive at high doses. Many compounds belonging to trichothecenes,
In New Zealand, a photohypersensitive exudative eczema called ‘facial eczema’ occurs sometimes in sheep. Sporidesmins have been isolated from the fungus Pithomyces chartarum (the synonym of Sporidesmium bakeri) found in the feed associated with this disease of sheep. This disease is characterized by both photohypersensitive eczema and hepatopathy, which ultimately result in death several weeks later. Sporisdesmins are composed of many congeners, that is, sporidesmin (synonym: sporidesmin A), and sporidesmins B–J. Each sporidesmin possesses a 2,5-dioxopiperazine skeleton formed from tryptophan and alanine as the basic common structure. The dioxopiperazine ring is bridged with a disulfide chain in sporidesmin and sporidesmin B, with a trisulfide chain in sporidesmin E, and with a tetrasulfide chain in sporidesmin G to form epidithio-, epitrithio-, and epitetrathio-dioxopiperazine structures, respectively. These sulfide bridges are eliminated or modified in sporidesmins C, D, and F (see Figure 9). The relative ratio of
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Figure 9 Structures of five trichothecenes, seven sporidesmins, and zearalenone.
cytotoxic activity of di-, tri-, and tetrasulfides against HeLa epithelial cells is 1:4:1. Sporidesmins whose sulfide bridges have been eliminated or modified show no activity. Zearalenone Zearalenone was isolated from Fusarium roseum (F. graminearum, teleomorphic state: Gibberella zeae), which grows on the maize fed to swine. Zearalenone exhibits estrogenic activity, enlarging the uterus and mammary glands, and causing swelling of the vulva (vulvovaginitis) in sows. Hyperestrogenism resulting from zearalenone has also been reported in other animals (and in humans), but swine is perhaps the species most sensitive to this compound. Zearalenone is thought to be synthesized from nonaketide through the acetate–malonate pathway (Figure 9).
from Phomopsis leptostromiformis, which infects the lupin, interferes with tubulin function. Cytochalasins isolated from Helminthosporium dematioideum and chetoglobosins isolated from Chaetomium globosum show inhibition of cytoplasmic cleavage in mammalian cell culture to form large multinuclear cells. For information on the occurrence and significance of mycotoxins in milk and dairy products, see Contaminants of Milk and Dairy Products: Environmental Contaminants.
See also: Contaminants of Milk and Dairy Products: Environmental Contaminants. Yeasts and Molds: Aspergillus flavus; Mycotoxins: Aflatoxins and Related Compounds.
Further Reading Miscellaneous Mycotoxins There are many other important mycotoxins known today. Lysergic acid amides isolated from Claviceps purpurea (ergot), which contaminate rye, are notorious as the causative agents of ergotism. Rubratoxins isolated from Penicillium rubrum obtained from grains and other feedstuffs have a cytotoxic effect. Phomopsin A isolated
Betina V (1984) Zearalenone and brefeldin A. In: Betina V (ed.) Mycotoxins Production, Isolation, Separation and Purification, pp. 237–257. Amsterdam, The Netherlands: Elsevier Science. Bullerman LB (2000) Mycotoxins: Classification. In: Robinson RK, Batt CA, and Patel PD (eds.) Encyclopedia of Food Microbiology, Vol. 2, pp. 1512–1520. London: Academic Press. de Nijs M and Notermans SHW (2000) Mycotoxins: Occurrence. In: Robinson RK, Batt CA, and Patel PD (eds.) Encyclopedia
800 Yeasts and Molds | Mycotoxins: Classification, Occurrence and Determination of Food Microbiology, Vol. 2, pp. 1520–1526. London: Academic Press. Fujimoto H (1991) Chemistry of food-contaminated mycotoxins. Japanese Journal of Food Microbiology 8: 27–35. Iwasaki S (1992) Chemistry and biological activity of the mycotoxins interfering with tubulin function. Proceedings of the Japanese Association of Mycotoxicology 35: 1–6. Kumeda Y (2008) A simple genetic method for identification of mycotoxigenic fungi – Development of heteroduplex panel analysis and its field application. Mycotoxins (Journal of the Japanese Society of Mycotoxicology) 58(1): 29–40. Nagarajan R (1984) Gliotoxin and epipolythiodioxopiperazines. In: Betina V (ed.) Mycotoxins: Production, Isolation, Separation and Purification, pp. 351–385. Amsterdam, The Netherlands: Elsevier Science. Pestka JJ, Zhou H-R, Moon Y, Chung Y, and Islam Z (2004) Molecular mechanisms of trichothecene toxicity. In: Yoshizawa T (ed.) New Horizon of Mycotoxicology for Assuring Food Safety (Proceedings of the International Symposium of Mycotoxicology in Kagawa 2003), pp. 17–31. Tokyo: Japanese Association of Mycotoxicology.
Turner WB and Aldridge DC (1983) Fungal Metabolites II. London: Academic Press. Ueno Y (1984) Trichothecenes: Recent researches and topics. Proceedings of the Japanese Association of Mycotoxicology 19: 2–7. Van Egmond HP (ed.) (1989) Mycotoxins in Dairy Products. London: Elsevier Applied Science. Van Egmond HP, Svensson UK, and Fremy JM (1997) Mycotoxins. In: Residues and Contaminants in Milk and Milk Products, pp. 79–88. International Dairy Federation. Special Issue 9701. Brussels: IDF. Voss KA, Chamberlain WJ, Riley RT, Bacon CW, and Norred WP (1994) In vitro and In vivo effects of fumonisins: Toxicity and mechanism of action. Mycotoxins 39: 1–12. Voss KA, Riley RT, Gelineau-van Waes JB, and Bacon CW (2004) Fumonisins: Toxicology, emerging issues, and prospects for control and detoxification. In: Yoshizawa T (ed.) New Horizon of Mycotoxicology for Assuring Food Safety (Proceedings of the International Symposium of Mycotoxicology in Kagawa 2003), pp. 41–48. Tokyo: Japanese Association of Mycotoxicology. Weidenbo¨rner M (2001) Encyclopedia of Food Mycotoxins. Berlin: Springer-Verlag.
Mycotoxins: Aflatoxins and Related Compounds S Tabata, Tokyo Metropolitan Institute of Public Health, Tokyo, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction Aflatoxins (AFs) are very important mycotoxins due to their extremely high toxicity, carcinogenic activity for animals (including humans), and frequent occurrence in various foods and feedstuffs. AFs found in 1961 in Brazilian groundnut meal were the source of the toxicity associated with ‘turkey X’ disease; more than 100 000 turkeys died in the United Kingdom. Since then, many researchers have vigorously investigated AFs, particularly AFB1, in various fields.
Structure and Chemical Properties More than 10 types of AFs and related compounds have been identified. Among them AFB1, AFB2, AFG1, and AFG2 are especially important because they are highly toxic and often occur in foods and feeds. The structures of the major AFs are shown in Figure 1. AFB1 is representative of the AFs and contains a dihydrobisfuran and coumarin nucleus fused to cyclopentanone. AFB2 is 8,9-dihydro-AFB1. In the AF-G group, sixmembered lactone is substituted by the cyclopentanone of AF-B group. The origins of the names AF-B and AF-G lie with the ‘b’ and ‘g’ of the blue and green fluorescent colors produced under ultraviolet (UV) light on thin-layer chromatography (TLC). AF-M group are 9a-hydroxy derivatives of the AF-B group and are found in cows’ milk as metabolites of the AF-B group in their feeds. Ingested AFB1 is converted to AFM1 in the cows’ liver, and approximately 0.9% of ingested AFB1 is found in the milk as AFM1. AFM1, a major animal metabolite of AFB1, is found in the urine of AFB1-exposed animals at levels of up to 20% of the ingested oral dose. AFB2a and AFG2a are 8-hydroxy AFB1 and AFG1, respectively, formed under acidic conditions (below pH 3) from parent AFs. Aflatoxicol (AFL)-I is a major metabolite of AFB1 formed by microorganisms, and AFL- is the stereoisomer of AFL-I. These are reduced to AFB1; the keto moiety on the terminal cyclopentanone of AFB1 is reduced to a hydroxy group. Most of the other AFs known are hydroxylated metabolites of AFs, such as AFP1 (O-demethylated AFB1), AFQ1 (3-hydroxy AFB1), AFGM1 (10a-hydroxy AFG1), AFL-M1 (9a-hydroxy AFL), and AFL-H1 (3-hydroxy AFL). AFs are slightly soluble in water, insoluble in nonpolar solvents, and soluble in moderately polar or polar organic
solvents such as chloroform, acetonitrile, and methanol. Most AFs have intense blue or green fluorescence (emission wavelength: 420–450 nm) under UV light (excitation wavelength: 350–370 nm).
AF-Producing Fungi AFs are produced in nature only by some strains of Aspergillus flavus, most strains of Aspergillus parasiticus, and Aspergillus nomius. Aspergillus flavus, the origin of the name of aflatoxin, is the main source of AFs, but not all strains produce AFs. It has recently been reported that Aspergillus tamarii also produces the AF-B group. Generally, A. flavus produces only the AF-B group, whereas A. parasiticus and A. nomius produce the AF-B and AF-G groups. In most strains, AFB1 is produced in the largest quantities. AFB2 and AFG2 are produced at one-tenth to one-third of the amount of AFB1 and AFG1, respectively. Aspergillus oryzae, the domesticated form of A. flavus, adapted by centuries of use in fermented food manufacture, never produces AFs.
Condition Favoring Production of AFs The limiting temperature and relative humidity for AF production vary slightly depending on the kind and quality of food. The lower limiting temperature for AF production is approximately 12 C, whereas the upper limiting temperature is 41 C at 99% relative humidity. The limiting relative humidity is approximately 83% or higher at 30 C, varying with the type of growth medium and length of the incubation period. Reducing oxygen concentration generally leads to a reduction in the amount of AF produced, notably so at an oxygen concentration of less than 1%. The presence of certain amino acids, fatty acids, and zinc ions stimulates the formation of AFs.
Biosynthesis The intermediates in the biosynthetic pathway of AFB1, AFB2, AFG1, and AFG2 have been determined, and the synthetic steps were revealed by feeding studies
801
802 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Figure 1 Structures of major aflatoxins.
with radioactive precursors, pathway-blocked mutant strains, and metabolic inhibitors. AFs are formed by head-to-tail condensation of acetyl units to form a cyclized polyketide, which is enzymatically altered through a series of intermediates. At least 18 enzymatic steps are required for conversion of acetyl coenzyme A (acetyl-CoA) and malonyl coenzyme A (malonyl-CoA) to its final product, AFB1. The generally accepted pathway for the production of AFB1 and AFG1 is as follows: acetylCoA þ malonyl-CoA ! hexanoyl-CoA ! norsolorinic acid ! averantin ! 59-hydroxyaverantin ! averufin ! versiconal acetate ! versiconal ! versicolorin B ! versicolorin A ! demethylsterigmatocystin ! sterigmatocystin ! Omethylsterigmatocystin ! AFB1 and AFG1. The enzymatic reactions in the synthesis of AFB2 and AFG2 are the same as AFB1 and AFG1, except for the formation of dihydrodemethylsterigmatocystin from versicolorin B.
Acute Toxicity in Animals AFs are toxic to many forms of life, including animals, birds, and fish. LD50 values of AFB1 are shown in Table 1. The sensitivity toward AFs differs with animal species. Mice and hamsters are relatively resistant to acute AFB1,
whereas ducks, rabbits, and rainbow trout are relatively sensitive. Structure–activity relationship has been studied for four major AFs: AFB1, AFB2, AFG1, and AFG2. Their acute toxicity in rats and ducklings followed the order AFB1 > AFG1 > AFB2 > AFG2. AFs containing an unsaturated terminal furan (AFB1 and AFG1) are much more potent than AFs containing a saturated terminal furan (AFB2 and AFG2). These results indicate that the presence of the double bond in the terminal furan is an important determinant of potential for acute toxicity, and that AFs containing cyclopentanone are more acutely toxic than AFs containing six-membered lactone.
Mutagenicity AFB1 is potently mutagenic for Salmonella strains (TA100 and TA98) at a low dose level (0.1 mg plate1) in the presence of S-9 mix, coenzymes and buffer. It is known that activated AFB1 induces guanine-cytosine to thymine-adenine transistion in genes. The activated K-ras gene detected in AF-induced primary liver tumor contained a guanine to adenine transition in codon 12.
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
803
Table 1 Oral LD50 of aflatoxin B1 Animal
LD50 (mg kg1)
References
Rabbit Duck Cat Dog Pig Horse Rainbow trout Calf Sheep Turkey Guinea pig Monkey Rat Mouse Hamster
0.3–0.4 0.3–0.6 0.5 0.5–1.0 0.6–1.0 0.6–1.0 0.8 1.0–1.5 1.0–2.0 1.4 1.4 2.2–7.8 1.0–17.9 9.0 10.2
Butler (1974), Pier (1992) Butler (1974), Pier (1992), Robens and Richard (1992) Butler (1974) Butler (1974), Robens and Richard (1992) Butler (1974), Pier (1992) Pier (1992) Bauer et al. (1969) Pier (1992) Butler (1974), Pier (1992) Pier (1992) Butler (1974) Campbell and Stoloff (1974) Butler (1974), Robens and Richard (1992) Butler (1974) Butler (1974), Robens and Richard (1992)
Butler WH (1974). Chapter 1 ALFATOXIN In: Purchase IFH (ed.) Mycotoxins, pp. 10–28. Amsterdam – Oxford – New York: Elsevier Scientific Company. Pier AC (1992). Major biological consequences of aflatoxicosis in animal production. Journal of Animal Science 70: 3964–3967. Robens JF and Richard JL (1992). Aflatoxins in animal and human health. Reviews of Environmental Contamination and Toxicology 127: 69–94. Bauer DH, Lee DJ, and Sinnhuber RO (1969). Acute toxicity of aflatoxins B1 and G1 in the rainbow trout (Salmo gairdneri). Toxicology and Applied Pharmacology 15: 415–419. Campbell TC and Stoloff L (1974). Implication of mycotoxins for human health. Journal of Agricultural and Food Chemistry 22: 1006–1015.
Among AFs and related compounds, AFB1 is the most potent, followed by AFL, AFG1, AFM1, AFB2, AFG2, and AFB2a.
classified AFs under group 1 carcinogens, which means that they are carcinogenic to humans.
Metabolism and Mechanism of Toxicity Carcinogenicity AFB1 is one of the most potent carcinogens known. The major target organ of AFB1 is the liver. One hundred percent (12/12) of male rats given 15 mg kg1 dietary AFB1 for 68 weeks, and 100% (13/13) of female rats fed the same diet for 82 weeks developed hepatocellular carcinomas. The carcinogenicity of AFs has been demonstrated in a variety of animals such as ducks, rats, monkeys, and rainbow trout. Other AFs (AFB2, AFG1, AFL, AFM1, and AFQ1) have also been proved to be carcinogenic. The order of carcinogenic potency in rainbow trout was AFB1 > AFL > AFM1 > AFQ1 > AFG1, whereas AFB2 and AFG2 were inactive. Overall, these results indicate that the presence of the double bond in the terminal furan ring is the most important determinant for toxic and carcinogenic activity. The importance of the substitutes on the lactone portion of the molecule is also illustrated by the difference in the potency of AFB1 and AFG1 in all systems studied. The International Agency for Research on Cancer (IARC) evaluated the carcinogenic risk of AFs and
The metabolic pathways for AFB1 in animals are shown in Figure 2. After intake, AF is metabolized by cytochrome p450 in the liver to several compounds; most of them are hydroxylated derivatives, such as AFM1 and AFP1, and are less toxic than AFB1. AFM1 is a major animal metabolite of AFB1. Ingested AFB1 is converted to AFM1 in the cows’ liver, and approximately 0.9% of ingested AFB1 is found in the milk as AFM1. AFM1 is also found in the urine of AFB1-exposed animals at levels of up to 20% of the ingested oral dose. Among the metabolites, AFB1-8,9-epoxide is the source of the potent mutagenicity and carcinogenesis of AFB1. This intermediate binds to cellular macromolecules such as DNA, RNA, and protein (Figure 3) because of which the presence of the double bond in the terminal furan in AFs is such an important determinant of acute toxicity, mutagenicity, and carcinogenicity. The existence of the intermediate, AFB1-8,9-epoxide, was confirmed by the isolation and identification of the absolute structure of 8,9-dihydro-8-(N7-guanyl)9-hydroxy-AFB1 (AFB1-N7-Gua), formed in vitro. It is considered that binding of AFB1 to DNA causes mutation
804 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Figure 2 Metabolic pathways of aflatoxin B1.
in genes, resulting in the activation of ras oncogene and inactivation of p53 tumor suppressor gene.
Effects on Cattle The general effect of AFs in cattle is liver disease. High levels of AF cause acute aflatoxicosis, such as liver
Figure 3 Mechanism of the toxicity of aflatoxin B1.
lesions, reduced feed consumption, weight loss, and reduction in milk production. The chronic effects of low-level consumption of AFs in cattle are reduced reproductivity, immunosuppression, and reduced feed efficiency. Dairy cattle convert ingested AFB1 in their liver to AFM1, which is secreted in milk. When calves consume milk contaminated with AFM1, they may contract aflatoxicosis.
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Effects on Human Acute Toxicity Most of the recorded outbreaks of acute aflatoxicosis have occurred in tropical countries. In India (1974–75), a total of 397 patients were affected, and 106 died. The disease was characterized by jaundice, rapidly developing ascites, portal hypertension, and a high mortality rate and was associated with the consumption of maize contaminated with AF; the AF concentration ranged from 6250 to 15 600 mg kg1, which means the affected people consumed 2–6 mg of AF daily over a month. In Kenya (1981), 12 out of 20 patients died. They ingested maize that contained 12 000 mg kg1 of AFB1. The liver tissue at necropsy showed centrobulbar necrosis and contained up to 89 mg kg1 of AFB1. In 2004, more than 100 people died following consumption of maize highly contaminated with AFs. Reye’s syndrome, manifested by a rapid onset of vomiting, convulsions, coma, and a high mortality rate, was considered to be a kind of aflatoxicosis, because autopsy specimens of the children who died from the syndrome contained AFB1. However, many researchers have recently reported that Reye’s syndrome is caused by other factors, concluding that it is likely to be caused by a combination of factors; AFB1 is probably not an important etiological agent of this disease in the United States.
Cancer In tropical areas, such as Southeast Asia, India, and Africa, the incidence of primary hepatocellular carcinoma (PHC) is high. Epidemiological surveys carried out over the past 25 years in Asia and Africa have revealed a strong statistical association between AF ingestion and PHC incidence. A high rate of mutation at codon 249 of the human p53 tumor suppressor gene has been reported in these tumors.
Exposure to AFB1 and infection with human hepatitis B virus (HBV) are considered to be the major risk factors in the development of PHC. The G to T transversion was found in p53 tumor suppressor gene of hepatocellular carcinomas from patients at high risk of exposure to AFs. The combined experimental and epidemiological evidence has led to designation of AFs as human carcinogens. Collectively, current evidence strongly suggests that PHC is of multifactorial origin, with probable interactions between viral and chemical agents in populations concurrently exposed to both classes of risk factors.
Regulation Because AFs are highly toxic to humans and animals and are frequently found in various foods and feeds, they are of worldwide concern. Regulations concerning AFs have been established in many countries to protect people from the harmful effects of AFs. More than 79 countries regulate the permissible levels of AFs in foods and feeds. The maximum permitted levels have been set for AFB1 alone or total AFs (the sum of AFB1, AFB2, AFG1, and AFG2) (Table 2). The maximum levels range from 1 to 20 mg kg1 for AFB1 and from 0 to 35 mg kg1 for total AFs. More than 60 countries set limits on AFM1 in milk by the end of 2003. The maximum permitted levels are 0 (not detectable) to 15 mg kg1 (Table 3). The levels of the limits for AFM1 in milk are much lower than those for AFB1 in food, because babies or infants are considered to be highly sensitive. AFM1 is a metabolite of AFB1. Therefore, regulation on AFB1 in feed for cattle is most effective for controlling levels of AFM1 in milk. Regulations for AFB1 in feed for dairy cattle exist in at least 39 countries. Although the maximum limits range from 5 to 50 mg kg1, most of these countries set the limit at the level of 5 mg kg1.
Table 2 Regulation for aflatoxins in food Country
Aflatoxin
Limit (mg kg1)
Commodity
Codex EU
B1 þ B2 þ G1 þ G2 B1 B1 þ B2 þ G1 þ G2 B1 þ B2 þ G1 þ G2 B1 þ B2 þ G1 þ G2 B1 B1 B1 þ B2 þ G1 þ G2 B1
15 2–8 4–15 20 20 20 10 20 10
Peanut, raw Foods (nut, cereals, spices, dry fruits)
Mercosur United States China Thailand Japan
805
Peanut, maize and products All foods Maize, peanut (products), rice, edible oil All food products All foods
Extracted from FAO (2004). In: FAO Food and Nutrition Paper 81, Worldwide regulations for mycotoxins in food and feed in 2003. Rome, Italy: FAO.
806 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds Table 3 Regulation for aflatoxin M1 in food 1
Country
Limit (mg kg )
Commodity
Codex EU Mercosur
0.5 0.05 0.5 5 0.5 0.5 5 0.5
Milk Milk Fluid milk Powdered milk Milk Milk and milk products Milk, cheese Milk and milk products
United States China Indonesia Vietnam
Extracted from FAO (2004) Worldwide regulation for mycotoxins in food and feed in 2003. FAO Food and Nutrition Paper 81. Rome, Italy: FAO.
Determination
Purification AFs are purified using an immunoaffinity column, or solid phase extraction, such as florisil or a multifunctional column. The most effective purification is obtained by an immunoaffinity column; the shortcomings of this type of column are high cost and low sample capacity. After purification with an immunoaffinity column, few peaks of ingredient are found in a HPLC (high-performance liquid chromatography) chromatogram. Although multifunctional columns have the same shortcomings as immunoaffinity columns, the process is easy and speedy. With a florisil column, AFs are effectively purified at low cost and high sample capacity. The disadvantage of this column is the necessity to use chloroform.
Standards Standards of AFB1, AFB2, AFG1, AFG2, AFM1, AFM2, AFB2a, AFG2a, AFP1, AFQ1, AFL-A, and AFL-B are commercially available. AFs are unstable in some polar solvents, such as methanol; therefore, the storage solvent system must be carefully selected. AFs are stable in chloroform and benzene:acetonitrile (9:1) in the dark and at low temperatures.
Sampling Sampling is one of the most important steps in AF determination, because the distribution of AFs in naturally contaminated samples is extremely heterogeneous. Usually only a few percentage of kernels in a sample lot are highly contaminated with AFs, whereas other kernels are free of AFs. For example, it was reported that only 0.03% of peanut kernels were contaminated with AFs, the mean concentration was 5 mg kg1, and the content in a single kernel was 1100 mg kg1. Therefore, it is very difficult to collect a sample that actually represents the mean concentration. An inappropriate sampling plan leads to wrong results, even if the analytical method is very precise. Several theoretical distributions for AFs have been reported. Among them negative binomial distribution is usually applied to determine the sample size and sampling procedure.
Extraction Samples are comminuted, and AFs are extracted by shaking or homogenizing with organic solvents, such as methanol–water, acetonitrile–water, or chloroform. Generally, one portion of sample is extracted with 4–5 volumes of solvent. For dry samples, a small amount of water is necessary to extract naturally contaminated AFs, although AFs are rarely dissolved with water.
Detection As AFs have intense fluorescence under UV light, they are determined quantitatively by the measurement of their fluorescence intensity. AFs are usually determined by HPLC or TLC. In HPLC analysis, usually an ODS (octadecyl silane) column and polar mobile phase are used. Generally, the reverse phase mode HPLC is used. The fluorescence of AFB1 and AFG1 is quenched in the polar solvent used as mobile phase; therefore, these AFs cannot be determined without making derivatives with trifluoroacetic acid (TFA) or using a photochemical reactor. It is at times difficult to determine AFs in spice samples such as red pepper, paprika, and white and black pepper by HPLC methods because they contain many impurities, which are difficult to remove by the purification methods. Reliable results are obtained by two-dimensional TLC, with a high-performance TLC (HPTLC) plate and two kinds of developing solvents. Chloroform:acetone (9:1) and diethyl ether:methanol:water (94:4.5:1.5) are commonly used. Because AFs are intensely fluorescent on TLC under UV light, the sensitivities of AFs by TLC method are so high that they enable detection of AFs at the level of 0.1–0.2 ng/spot. The shortcoming of the TLC method is that it needs a densitometer for quantitative analysis. Enzyme-linked immunosorbent assay (ELISA) has been employed for AF screening, but the method should be applied to limited samples because matrices of the samples often give false positive and negative results. Immunochromatography, which is useful for screening for AFs, has been recently developed for AF analysis. Confirmation When AFs are detected, it is necessary to confirm their presence by another analytical method, because some interfering substances remain in the sample solution despite the various purification steps. The comparison
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
of the peak with or without TFA treatment in reverse mode HPLC is not sufficient. The most popular and reliable confirmatory method for AFs with unsaturated terminal furan, such as AFB1, AFG1, and AFM1, is twodimensional TLC following derivatization with TFA. After the first development, a small amount of TFA is dropped on the spot presumed to be AF and developed in the second dimension. The AFs that have a double bond in the terminal furan ring react with TFA to form their hemiacetals (AFB2a, AFG2a, and AFM2a), which have a lower Rf value than their parent AFs on TLC. Presently, AFs are sometimes confirmed by liquid chromatography-tandem mass chromatography (LC/ MS/MS).
Occurrence in Foods and Feedstuffs Many reports about AF contamination in foods and feedstuffs are available. AFs are frequently detected in various foods and feeds produced in hot, humid climates. AF contamination of corn is considered to be the greatest health risk to humans and animals throughout the world because the incidence and level of AF contamination of corn are high, and a large amount of corn is consumed worldwide. AF-contaminated commercial foods and feedstuffs are listed in Table 4. AFs are found in nuts and seeds (e.g., peanut, pistachio nut, Brazil nuts, and sesame), cereals (e.g., corn, rice, buckwheat, and Job’s tears), spices (e.g., nutmeg, red pepper, paprika, and white pepper), beans (butterbean), and dairy products (cheese). AFB1 is the most frequent type present in contaminated samples and is usually found in the greatest quantity. AFB2, AFG1, and AFG2 are never detected in the absence of AFB1.
807
Comparing these results by year, aflatoxin contamination in foods was variable (Figure 4). Aflatoxin M1 in dairy foods is a metabolite of aflatoxin B1 in dairy cattle. Therefore, these results indicated that aflatoxin contamination in feed for dairy cattle decreased after 1985. The reason for this seems to be that the number of countries with legislation controlling aflatoxin in feedstuffs increased from 22 in 1981 to 35 in 1986. Also, the European Community directive was tightened in 1984, when the tolerance for aflatoxin B1 in feedstuffs for dairy cattle was reduced from 20 to 10 mg kg1. Aflatoxin contamination in buckwheat was found in 1982–85. The highest incidence was 46%, found in 1985. Since then, no aflatoxin has been detected, possibly because buckwheat from Brazil has not been imported to Japan after 1985. Until 1992, the incidence of aflatoxins in white pepper was over 30%, but was low in recent years. A high incidence was found in nutmeg throughout the period, reaching over 80% during 1985–90. The contamination level and incidence were then reduced by the efforts of trading companies that collected only good-quality nutmeg from the country of origin. Some causes of the change in AF contamination in commercial food in Japan were factors in the country of origin, including its weather and regulation for mycotoxins. Other causes were factors in Japan such as examination of mycotoxins at port of entry for imported foods, choice of county of origin, and provision of education about mycotoxins to farmers.
AF in Dairy Products AFM1 is sometimes found in dairy products, such as milk and natural cheese (Table 5). The level of AFM1 in dairy products is usually not more than 1 mg kg1.
Table 4 Aflatoxin contamination in commercial foods (Japan) Range (mg kg1) Foods
No. of samples
No. of positive samples
AFB1
AFB2
AFG1
AFG2
AFM1
Peanut Pistachio nut Brazil nut Sesame seed Job’s tears Buckwheat White pepper Red pepper Paprika Nutmeg Natural cheese
459 481 8 47 212 252 220 81 44 257 354
35 9 1 5 48 23 21 31 26 155 44
0.4–21.7 0.8–1380 10.2 0.6–2.4 0.1–14.9 0.1–8.8 0.1–2.3 0.2–27.7 0.2–6.5 0.2–60.3 ND
0.1–5.3 0.1–260 0.8 0.2–0.5 0.1–1.8 0.1–0.9 0.1–0.3 0.1–1.2 0.1–0.3 0.1–6.5 ND
0.3–22.1 306 3.2 ND 0.3–0.7 0.2–0.8 ND 0.1–2.1 ND 0.1–0.4 ND
0.1–6.8 48.3 0.3 ND ND 0.1 ND 0.1–0.2 ND 0.1–0.4 ND
NDa ND ND ND ND ND ND ND ND ND 0.1–1.2
Not detected (detection limit: 0.1 mg kg1). Adopted from Tabata S (1998). Aflatoxin contamination in foods and foodstuffs Mycotoxins; 47: 9–14.
a
808 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Figure 4 Change in the incidence of aflatoxins.
AFM1 in cheese is not produced in the fermentation process because of the AF-contaminated feedstuffs consumed by cows. Ingested AFB1 is converted to AFM1 in the cows’ liver and approximately 0.9% of ingested AFB1 is found in the milk as AFM1. Feedstuffs for cows often contain imported materials. Therefore, AFM1 is also found in dairy products produced in areas not normally associated with AF contamination. AFM1 is stable in the fermentation or heating process in cheesemaking, and its levels are not reduced on storage.
Detoxification or Elimination of AFs from Foods and Feeds For the purpose of reducing the human and animal risk of exposure to AFs, various approaches, including physical, chemical, and biological ones, have been attempted to degrade or eliminate AFs from foods and feeds. It is fairly easy to degrade pure AFs by various methods, such as UV irradiation, heating, boiling, and treatment with chemical reagents. However, AFs in foods are very stable and the mechanisms of their stability are unknown. Cooking processes, such as roasting, boiling, and frying, cannot reduce AFs. To degrade AFs, many procedures have been proposed, such as gamma irradiation, extraction with solvents, and treatment with ozone, hydrogen peroxide, sodium hypochlorite, and alkali. Most procedures are neither practical nor very effective in reducing AFs to safe levels without damaging the quality of the foods. Before AFs are destroyed, foods
are damaged by the treatments. Ammoniated corn may be used for animal feed but not for human food. An exception is the edible oil refining process. In a normal commercial procedure, all AFs in crude oil are removed by washing with water after adding alkali. Attempts at biological degradation of AFs have not been satisfactory. AFB1 is enzymatically converted to AFL, or chemically converted to AFB2a, under acidic conditions of the media by various mycelia. Another biological method, using fungi that do not produce AF to compete with AF-producing fungi, has not succeeded. Detoxification or elimination of AFs in foods without damage to the quality of the product is hardly possible. Therefore, the efforts to avert the occurrence of AFs in foods seem to be the most effective protection against AFs.
Sterigmatocystin Sterigmatocystin is a precursor of AFs in their biosynthesis and is also toxic and carcinogenic. Structure and Chemical Properties Sterigmatocystin consists of a xanthone nucleus attached to a bisfuran structure (Figure 5), similar to AFs. Sterigmatocystin is soluble in acetone, benzene, ethyl acetate, and chloroform, slightly soluble in ethanol, methanol, and diethyl ether, but insoluble in petroleum ether and water.
Table 5 Aflatoxin M1 contamination in dairy products Country
Period of sampling
Type of product
No. of samples
No. of positive samples
Range (ng g1)
Detection limit (mg kg1)
References
USA
1979
209
1
0.3
0.08
Stoloff and Wood (1984)
190
0
0.08
Stoloff and Wood (1984)
1982–85
Cottage cheese Cheddar cheese Nonfat dry milk Ice cream Yogurt Natural cheese
121 328 144 272
0 0 0 44
0.1–1.2
0.4 0.08 0.08 0.1
Stoloff and Wood (1984) Stoloff and Wood (1984) Stoloff and Wood (1984) Tabata et al. (1987)
USA (imported)
1986–96 Before 1985
Natural cheese Cheese
82 118
0 8
0.1–1.0
0.1 0.05
Spain Brazil Japan Taiwan
1985 1992 2001 2005
Milk Milk Milk Milk
47 52 208 144
14 4 207 100
0.02–0.1a 0.073–0.37 0.001–0.029 0.001–0.055
Tabata et al. (1987) Trucksess and Page (1986) Blanco et al. (1988) de Sylos et al. (1996) Nakajima et al. (2004) Peng and Chen (2009)
Japan (imported)
a
0.02a 0.001 0.001
mg/L
Stoloff L and Wood G (1981). Aflatoxin M1 in manufactured dairy products produced in the United States in 1979. J.Dairy Science 64:2426-2430. Tabata S., Kamimura H., Tamura Y., et al. (1987). Investigation of aflatoxins contamination in foods and foodstuffs. J. Food Hygienic Society of Japan 28:395-401. Trucksess MW and Page SW (1986). Examination of imported cheese for aflatoxin M1. J. Food Protection 49:632-633. Blanco JL, Domı´nguez L, Go´mez-Lucı´a E, Garayzabal JF, Garcı´a JA, and Sua´rez G. (1988). Presence of aflatoxin M1 in commercial ultra-high temperature-treated milk. Applied and Environmental Microbiology 54:1622-1623. de Sylos CM, Rodriguez-Amaya DB, and Carvalho PR.(1996). Occurrence of aflatoxin M1 in milk and dairy products commercialized in Campinas, Brazil. Food Additives and Contaminants 13:169-172. Nakajima M, Tabata S, Akiyama H, et al., (2004). Occurrence of aflatoxin M1 in domestic milk in Japan during the winter season. Food Additives and Contaminants 21:472-478. Peng K and Chen C. (2009). Prevalence of aflatoxin M1 in milk and its potential liver cancer risk in Taiwan. J. Food Protection 72:1025-1029.
810 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
occurrence of sterigmatocystin are few. Sterigmatocystin has been found in stored grains or cheese, but not in the field.
See also: Yeasts and Molds: Mycotoxins: Classification, Occurrence and Determination. Figure 5 Structure of sterigmatocystin.
Further Reading Producing Fungi Sterigmatocystin is produced by several species of Aspergillus, including Aspergillus versicolor, Aspergillus nidulans, Aspergillus sydowii, and some species of Bipolaris. Among them, A. versicolor is the major producer of sterigmatocystin, and almost all the isolates produce sterigmatocystin. Toxicity The biological activity of sterigmatocystin is much like that of AFB1, but it is much less toxic than AFB1. The LD50 value of ST for male rats is 60–800 mg kg1, whereas that of AFB1 is 5.5 mg kg1. Sterigmatocystin is a potent mutagen. ST is mutagenic at 10 mg/plate; this potency is 1/100 of AFB1s, which is mutagenic at 0.1 mg/plate. Sterigmatocystin is a primary hepatotoxic agent. All male rats given 150 mg day1/rat of dietary sterigmatocystin for 58 4 weeks developed hepatocellular carcinomas. The heopatotoxigenic activity of sterigmatocystin is approximately 1/10 to 1/1000 of that of AFB1. The IARC classified sterigmatocystin as a group 2B carcinogen, which means that it is possibly carcinogenic to humans. No outbreak of the disease in humans and domestic animals attributed to sterigmatocystin has been reported. Regulation Although sterigmatocystin is highly toxic, no country has set maximum permitted levels for sterigmatocystin owing to the low incidence of natural occurrence. Determination Sterigmatocystin is extracted from ground samples with acetonitrile:4% potassium chloride (9:1). After solvent partition, sterigmatocystin is cleaned up with column chromatography and determined by TLC, HPLC, or LC/MS. Contamination in Foods Although sterigmatocystin-producing fungi are widely distributed in the world, reports concerning natural
Bauer DH, Lee DJ, and Sinnhuber RO (1969) Acute toxicity of aflatoxins B1 and G1 in the rainbow trout (Salmo gairdneri ) Toxicology and Applied Pharmacology 15: 415–419. Blanco JL, Domı´nguez L, Go´mez-Lucı´a E, Garayzabal JF, Garcı´a JA, and Sua´rez G (1988) Presence of aflatoxin M1 in commercial ultrahigh-temperature-treated milk. Applied and Environmental Microbiology 54: 1622–1623. Butler WH (1974) Aflatoxin. In: Purchase IFH (ed.) Mycotoxins, pp. 10–28. Amsterdam-Oxford-New York: ELSEVIER Scientific publishing company. Campbell TC and Stoloff L (1974) Implication of mycotoxins for human health. Journal of Agricultural and Food Chemistry 22: 1006–1015. Chapman HR and Sharp ME (1990) Microbiology of cheese. In: Robinson RK (ed.) Dairy Microbiology, Vol. 2: The Microbiology of Dairy Products, 2nd edn., pp. 280–282. London; New York: Elsevier Applied Science. Cole RJ and Cox RH (1981) Handbook of Toxic Fungal Metabolites. New York; San Francis co CA: Academic Press. Cucullu AF, Lee LS, Mayne RY, and Goldblatt LA (1966) Determination of aflatoxins in individual peanuts and peanut sections. Journal of the American Oil Chemists’ Society 43: 89–92. de Sylos CM, Rodriguez-Amaya DB, and Carvalho PR (1996) Occurrence of aflatoxin M1 in milk and dairy products commercialized in Campinas, Brazil. Food Additives and Contaminants 13: 169–172. FAO (2004) Worldwide regulations for mycotoxins in food and feed in 2003. FAO Food and Nutrition Paper 81. Rome, Italy: FAO. James W, Dickens JW, and Pattee HE (1966) The effects of time, temperature and moisture on aflatoxin production in peanuts inoculated with toxic strain of Aspergillus flavus. Tropical Science VIII: 11–22. Nakajima M, Tabata S, Akiyama H, et al. (2004) Occurrence of aflatoxin M1 in domestic milk in Japan during the winter season. Food Additives and Contaminants 21: 472–478. Peng K and Chen C (2009) Prevalence of aflatoxin M1 in milk and its potential liver cancer risk in Taiwan. Journal of Food Protection 72: 1025–1029. Pier AC (1992) Major biological consequences of aflatoxicosis in animal production. Journal of Animal Science 70: 3964–3967. Pitt JI and Hocking AD (eds.) (1999) Fungi and Food Spoilage, 2nd edn. Frederick, MD: Aspen Publishers. Robens JF and Richard JL (1992) Aflatoxins in animal and human health. Reviews of Environmental Contamination and Toxicology 127: 69–94. Stoloff L, Wood G, and Carter L (1981) Aflatoxin M1 in manufactured dairy products produced in the United States in 1979. Journal of Dairy Science 64: 2426–2430. Tabata S (1998) Aflatoxin contamination in foods and foodstuffs. Mycotoxins 47: 9–14. Tabata S, Kamimura H, Tamura Y, et al. (1987) Investigation of aflatoxins contamination in foods and foodstuffs. Journal of Food Hygienic Society of Japan 28: 395–401. Terao K (1983) Sterigmatocystin – a masked potent carcinogenic mycotoxins. Journal of Toxicology. Toxin Reviews 2: 77–110. Trucksess MW (ed.) (2007) Official Methods of Analysis of AOAC International, 18th edn., ch. 49, pp. 2–50. Gaithersburg, MD: AOAC International. Trucksess MW and Page SW (1986) Examination of imported cheese for aflatoxin M1. Journal of Food Protection 49: 632–633.
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds Van Rensburg SJ (1977) Role of epidemiology in the elucidation of mycotoxin health risks. In: Rodricks JV, Hesseltine CW, and Mehlman MA (eds.) Mycotoxins in Human and Animal Health, pp. 699–711. Park Forest South, IL: Pathotox Publishers Inc. Wang JS and Groopman JD (1999) DNA damage by mycotoxins. Mutation Research 424: 167–181. WHO (2002) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 82, pp. Lyon France: IARC Press. 171–300.
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Wogan GN and Newberne PM (1967) Dose–response characteristics of aflatoxin B1 carcinogenesis in the rat. Cancer Research 27: 2370–2376. Wong JJ and Hsieh DPH (1976) Mutagenicity of aflatoxins related to their metabolism and carcinogenic potential. Proceedings of National Academy of Sciences of the United States of America 73: 2241–2244. Yabe K and Nakajima H (2004) Enzyme reactions and genes in aflatoxin biosynthesis. Applied Microbiology and Biotechnology 64: 745–755.
GLOSSARY
Abomasum The ‘true stomach’ of the ruminant animal with digestive functions similar to the stomach of monogastric species. The abomasum is preceded by the forestomach compartments, the rumen, the reticulum, and the omasum. See also Rumen. Absorption The movement of ions, metabolites or a chemical substance through a body membrane. In the case of magnesium it is the movement of Mg ions from the digestive tract into the bloodstream, either by passive diffusion down a concentration gradient, or active transfer requiring an energy source and usually against a concentration gradient. Acaricide A chemical that kills ticks and mites. It may be mixed with water and put in a dip tank, spray race or used in a knapsack sprayer; there are also pour-on versions available. Acid detergent fiber (ADF) A method for determining the relative digestibility of fibrous feeds. Acidulation The process in which cooked acidprecipitated casein curd and whey are gently agitated in a holding vessel (e.g. a vat) to ‘condition’ the curd. During this period (usually up to 15min), the minerals, especially calcium, in the curd and whey come to equilibrium. Acrosome reaction A change in the membrane at the apical end of the sperm head in a matured spermatozoon which results in release of enzymes needed for the sperm to penetrate the ovum during fertilization. Activation energy (Ea) The minimum energy required for a reaction to occur; expressed in Joules (J). It is independent of temperature or concentrations. Ad libitum A term (literally, ‘according to pleasure’) that refers to the consumption of food at will. In experimental animal studies, ad libitum refers to the provision of food in a manner that allows the animal to consume as much of the food, and at any time, as it desires. Adhesion The surface reaction between a surface and a particle due to intermolecular attraction forces such as van der Waals’ forces or electrostatic forces. Adjunct culture An adventitious non-starter lactic acid bacteria culture consisting mainly of Lactobacillus spp. used in addition to a standard mesophilic starter to improve and to enhance the flavour of cheese. In order to maximize the role of the adjuncts in cheese ripening, the intracellular enzymes must be released
from the cells into the cheese matrix. This fact explains the great deal of attention given to cell autolysis during ripening. It is believed that attenuated adjunct cultures with enhanced autolytic properties provide a more controlled and consistent ripening resulting in flavour and texture improvement, particularly in lower fat cheese. Adjunct cultures are modified or attenuated to enable them to play an appreciable role during cheese ripening without producing excess lactic acid. Physical methods of sublethal treatments such as freeze-shocking, heat-shocking and spray-drying are the most studied techniques for the attenuation of the adjunct cells. These treatments lead to varying levels of the cell viability, modification of the ability to produce acid and intracellular proteinase or esterase activities. Agricultural agreement The agreement within the framework of the World trade organization (WTO). With the establishment of the WTO the regulation of the trade in food and agricultural produce was finally incorporated into the international trading system. This agreement covers export subsidies and competition, market access and imports, and internal/domestic support. All major agricultural trading countries have been forced into changing their agricultural policy according to the agreement. Alkaline phosphatase An indigenous milk enzyme which is denatured by pasteurization. It is used to demonstrate that milk is adequately pasteurized. Allergy An abnormal immune response to an allergen, causing adverse clinical reactions. Allergens may be from the environment, e.g. pollens, or from food, e.g. milk proteins. Symptoms are manifest on the skin (e.g. pruritus and urticaria), or the gastrointestinal (e.g. abdominal pain and diarrhea) or respiratory tracts (e.g. asthma). See also Intolerance. AM system An automated milking machine that can milk cows without human supervision. The AM system has electronic cow identification, robotic teat cleaning and teat-cup attachment systems and a milking machine to milk the cow. The cow visits the AM system voluntarily, with the inducement of the supply of concentrate. Computer controlled sensors are present to detect any abnormalities in the milking process or the milk.
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814 Glossary
Aminopeptidases Enzymes, highly conserved in dairy lactic acid bacteria, that release N-terminal amino acids from dipeptides (except for those containing proline), tripeptides and oligopeptides. Animal model A statistical model used in genetic evaluation in which an animal’s estimated genetic merit is a function of its own performance and the genetic merit of its parents and offspring. All relationships among animals are considered, and males and females can be evaluated simultaneously. Anionic salts Inorganic salts (usually chloride-based) added to close-up dry cow rations to lower urine pH, increase calcium mobilization and raise blood calcium levels to prevent milk fever or hypocalcemia. Anestrus Absence of cyclicity in a mature intact female. The condition can be caused by seasonal factors, severe underfeeding and suckling of offspring. Anestrus, lactational The generalized situation in which an animal that is lactating has diminished, delayed or absent reproductive cyclicity. This is usually exacerbated by decreased energy intake. Anthelmintic A medication used to expel or destroy parasitic worms found in the digestive system. Antibody An immunoglobulin molecule synthesized in response to a foreign substance which provides an animal with means of protection against that substance by combining specifically with it. Artificial insemination The introduction of fresh, chilled or frozen-thawed semen into the female reproductive tract using specific devices. Undiluted or diluted semen can be deposited either into the uterus or the oviduct. Artificial neural network (ANN) A highly interconnected computational structure of elementary processing units (termed neurons) and parameters (termed weights) that are adjusted by an optimization procedure, known as network training. ANNs are implemented for data processing and information storage with its main application in pattern recognition, process modelling, signal filtering and control structure design. Asthma A reaction involving wheezing and breathing difficulty (or sometimes coughing) caused by reversible narrowing of the lung’s airways and often connected with allergic problems. Atopic dermatitis Eczema, an allergic skin reaction, most commonly seen in small children and often affecting the groin, the creases of the elbows and knees, and the hands and face. Atopy A genetic predisposition to produce immunoglobulin E against common antigens in the environment with atopic symptoms, e.g. bronchial asthma, allergic rhinitis and atopic dermatitis. Azadirachtin A compound that exhibits effective insect repellent and sterilization properties. It works on the tick’s hormonal system and does not lead to development of resistance in future generations. Generic name: tetranortriterpenoid.
Bacteriocins Antimicrobial ribosomally synthesized peptides that kill species other than the producer species, bacteriocins usually kill closely related bacteria. The three classes of bacteriocins produced by lactic acid bacteria include the lantibiotics, the small heat-stable peptides not containing lanthionines, and the large heat-labile bacteriocins. Bacteriophage (or phage) A virus that infects a bacterial cell. While the virulent phages usually kill the cells they infect, the temperate phages do not cause cell lysis but exist in a state called lysogeny where most virus genes are not expressed. Bacteriophages are used as a vector for DNA cloning. Phage infection can rapidly destroy the acid-producing activity of starter cultures. Bactofugation A technique in which milk is treated in a type of centrifuge with a continuous separation of a small amount of milk that contains dense particles. This heavy phase contains most of the spores of the anaerobic bacterium Clostridium tyrobutyricum which have a higher density than those of most other bacteria. Bifidus factors Compounds of natural origin able to pass intact to the colon, and which are able to enhance the growth of species of Bifidobacterium spp. Examples are the complex carbohydrates containing N-acetyl glucosamine and L-fucose attached to galacto-oligosaccharide chains in human milk. Other identified bifidus factors include some casein and whey protein digests, lactulose, and cell extracts from Propionibacterium spp. Bioavailability The proportion of a dietary constituent that is utilized for normal body functions. Biochemical oxygen demand (BOD) An important measure of water quality. It is a measure of the amount of oxygen needed (in milligrams per liter) by bacteria and other microorganisms to fully oxidize the organic matter present in a water sample. It is also called the biological oxygen demand. A five-day biochemical oxygen demand (BOD5) is commonly determined. The amount of oxygen reported with this method represents only the carbonaceous oxygen demand (CBOD) or the easily decomposed organic matter. BOD5 is commonly used to measure natural organic pollution. The BOD5 of drinking water should be less than one, while that of raw sewage may run to several hundred. The BOD5 of dairy waste may run from several hundred to hundreds of thousand. See also Chemical oxygen demand (COD). Biofilm A life community based on the capability of microorganisms to adhere to solid surfaces, to proliferate at the surface and to form a microenvironment characterized by the excretion of exopolysaccharides (called glycocalyx). Biofilms growing on stainless steel surfaces, particularly in heat exchangers, can be an important source of contamination of dairy products. Biogas A mixture of gases resulting from anaerobic fermentation of whey, or any other biological matter, and containing methane, carbon dioxide, hydrogen sulfide and other minor gaseous components.
Glossary
Biohydrogenation the process by which unsaturated fatty acids in the diet are converted to trans fatty acids and stearic acid by microorganisms in the rumen. Biopsy A technique in which small amounts of tissue, such as a single cell, can be removed from a tissue or embryo for examination of the genetic makeup of the particular tissue or embryo from which it was derived and/or examination of changes in cell morphology. Biosecurity Management practices designed to prevent transmission of disease agents into, or within, a livestock operation. Biosensor An analytical device including a biological recognition component and a signal transducer. The biological material undergoes a physicochemical change in the presence of the analyte(s). This change is detected by the transducer, amplified and then reported to the operator. Blastocyst An early embryonic stage represented by a spherical mass of cells with a fluid-filled cavity which forms from the cleavage of a fertilized ovum and exists from approximately 8 to 12 days after fertilization in cattle. Blitz therapy An antibiotic therapy technique used against mastitis. All infected cows are treated in all quarters simultaneously in an attempt to maximize treatment success. Bloat A serious and sometimes fatal disorder of ruminants. It is characterized by extreme distension or inflation of the animal’s rumen or first stomach, due to the accumulation of gases. Body condition A general term referring to the relative amount of body fat and muscle on an animal. Body condition score (BCS) A scale for assessing the level of body fat on an animal. It runs from 1 ¼ very thin to 5 ¼ obese, and may be expressed in decimal values, e.g. 3.5. Boiler efficiency (hb) Ratio between the heat received by the water and the heat content of the fuel. The electrical energy that drives the boiler’s auxiliary equipment is comparatively much smaller than these values, and is normally neglected. Bovine lymphocyte antigen (BoLA) genes Genes restricted to the genus Bos that are responsible for tissue compatibility between individuals and function in cell-to-cell signalling between lymphocytes and antigen-expressing cells. Brown mid rib (BMR) A group of mutants in maize, sorghum and millet with higher plant digestibility. Lignin reduces and cellulose and hemicellulose increases BMR. Leaf midrib, stem sheath and pith show a brown coloration in BMR plants. Browse To feed on buds, leaves or twigs, as distinct from grass (grazing). Goats are typical browsing animals. Buttermilk, cultured (fermented) A product made from fresh pasteurized skimmed milk or homogenized, pasteurized low-fat milk by fermentation with flavor-producing mesophilic lactic acid bacteria. Buttermilk, natural (conventional) A byproduct of buttermaking. Depending on the processing con-
815
ditions, either sour cream or sweet cream buttermilk is obtained. Sweet cream buttermilk can be processed further to fermented buttermilk by flavor-producing mesophilic lactic acid bacteria. Traditionally, buttermilk was the fresh serum that was separated during buttermaking on farms after churning cream ripened with naturally occurring lactic acid bacteria. Byproduct feed A feed generated during the production of food and fiber products for human consumption. Usually not of the quality or composition for human use, they provide economical sources of feed for cattle. Calcium-induced precipitation An isoionic precipitation mechanism caused by progressive addition of calcium which decreases the net negative charge of caseins to such an extent that the caseins have little, if any, net charge. Electrostatic repulsive forces are at a minimum and precipitation occurs. Calf hutches Shelters designed to provide individual housing for calves. Hutches can be made of wood, plastic or fiberglass and are intended to provide adequate ventilation. Calving interval The time between calving and reimpregnation of the cow. Calving rate The number of calves born as a percentage of cows mated over a 12-month period. Canonical transformation A procedure commonly used to reduce computational requirements for simultaneous genetic evaluation of more than one trait. Correlated traits are ‘transformed’ to uncorrelated traits, which can be evaluated separately and then retransformed, thus reducing computer processing. CAP genes A group of genes activated at the onset of labor. Contraction-associated protein (CAP) gene expression is increased as estrogen concentration rises at term. CAPs include oxytocin and prostaglandin receptors, Naþ and Ca2þ channels and gap junction proteins (connexin-43), which when activated, increase spontaneous activity of the myometrium. Capillary electrophoresis (CE) A technique that resolves analytes based on net charge, their mass and Stokes’s radius under the infuence of an electric field in a buffer-filled capillary. Capillary electrophoresis is a relatively new technique with the first applications in the early 1980s. One of the major advantages of this technique over traditional electrophoretic techniques is the ease with which quantitative data may be obtained. Casein The acid-insoluble proteins of milk, which occur as large colloidal aggregates called micelles. Casein solubilization (1) The process in which, after casein hydrolysis, the peptides become water soluble. (2) The process in which intact casein molecules become dissociated from casein micelles due to an alteration in pH, electrostatic charge or temperature. Cataract An opacity in the crystalline lens of the eye, which may be partial or complete.
816 Glossary
Cation exchange capacity (CEC) A measure of a soil’s capacity to hold the plant nutrient cations calcium (Ca2þ), potassium (Kþ), sodium (Naþ) and aluminum (Al3þ) to surfaces of negatively charged particles of clay and/or organic matter. Extracts containing ammonium ions displace cations into solution. Individual exchangeable cation concentration is measured in the extract as milliequivalents 100 g1 (meq%) and added to estimate the CEC. Cheese slurry A semi-solid paste containing about 40% solids and possessing the characteristic flavor of the particular cheese used in its preparation. Chemical oxygen demand (COD) The oxygen equivalent (in milligrams of O2 per liter) of the organic portion of the sample that is susceptible to oxidation by a strong chemical oxidant. COD does not distinguish between refractory and ‘inert’ organic matter. COD tests require approximately 3 hours. See also Biochemical oxygen demand (BOD). Chocolate bloom Fat or sugar on the surface of chocolate giving a white ‘mold-like’ appearance. It can be caused by heat damage or by the crystallization of cocoa butter in the wrong form. Chocolate conche A machine for coating the solid particles in the chocolate with fat and at the same time producing the final flavor. The latter is achieved by removing some acidic volatile components and/or developing other flavors by means of heating. Chymosin A milk-clotting enzyme produced in the glandular cells of the ruminant abomasum (fourth stomach). Chymosin is an aspartic (acid) proteinase (EC 3.4.23.4) and has a high specifc milk-clotting activity; it primarily hydrolyzes the peptide bond between Phe105–Met106 in bovine -casein. Chymosin dominates the milk-clotting activity of calf rennets. See also Rennet. Cleanroom A room that is constructed to minimize the introduction of airborne microorganisms or particles and where the concentration of those microorganisms, or particles, is controlled. Closed flock A flock where all female and some male breeding replacements are produced on the same farm as the breeding flock. This system significantly reduces the risk of introducing new diseases into the farm from purchased replacement stock. Coagulant A preparation of milk-clotting enzymes of nonruminant origin. Most often they are milkclotting enzymes derived from different fungi or plants. Coagulants are considered to give a lower yield of cheese and a different cheese flavor compared to calf rennet. Coagulum See also Gel, Coagulum. Celiac disease A disorder caused by a reaction to the gluten of wheat and other cereals in the diet and accompanied by (most notably) bowel disturbances and anemia. Coffee cream A cream product that usually contains 10% or 12% fat and is manufactured for a long shelf-
life either by in-bottle sterilization or, more frequently, by UHT sterilization, followed by aseptic filling. Storage stability (prevention of creaming and sedimentation) and coffee stability (resistance against coagulation or ‘feathering’) are most important for the quality of the product. Cold housing A system of housing for cattle in which barn indoor temperature fluctuates with outdoor temperature. Ventilation maintains indoor temperature within 3–6 C of outdoor temperatures in winter. Usually, the barn is not insulated and ventilation is largely unregulated, except to adjust for seasonal changes. Coliform bacteria Bacteria that produce acid and gas from lactose. Many, but not all, are of enteric origin. They are killed by mild heat, but occasionally recontaminate pasteurized products. Colloid A state of matter in which the particles are in the size range of 10 to 1000 nm. Colloidal particles are approximately of the same size as the wavelength of light and therefore strongly scatter light; they are largely unaffected by gravity. Colloidal calcium phosphate Calcium phosphate that is attached through electrostatic interactions to serine phosphate residues on casein molecules. It is the portion of calcium and (inorganic) phosphate that can potentially be removed from the casein when milk or cheese is acidified. In contrast, the noncolloidal or organic phosphate is directly attached to serine (covalently linked) and can be removed only by enzymatic activity, i.e. phosphatases. Colostrum Mammary secretions during the early period (3-4 days) post-partum. Combustion A rapid chemical combination process of fuel with air that releases the chemical energy of the fuel. Air and fuel are the reactants in the combustion reaction, and the byproducts are the flue gases (products of combustion) and heat. Communal area An area where animals from different herds are communally grazed but may be housed as individual herds at night. Usually, there are no fences in the grazing areas but they may have paddocks. Concentration polarization An increase in the concentration of a component in the boundary layer of a membrane as a result of its rejection. The phenomenon is characterized by a decrease in permeate flux through a membrane to a constant value, irrespective of increasing transmembrane pressure. Conception rate The proportion of cows maintaining pregnancy beyond three weeks. Confocal microscopy A light microscopy technique which greatly reduces out-of-focus blur, enabling optical sectioning of bulk materials. This is particularly useful for shear-sensitive, opaque food materials requiring minimal sample preparation. The most common configuration used in dairy research is the confocal scanning laser microscope. Conjugated linoleic acid A family of 18-carbon fatty acids with conjugated double bonds. These fatty
Glossary
acids are produced in the rumen during biohydrogenation and by action of the 9-desaturase enzyme within the mammary gland. Isomers can have important effects on human health. Consumer nominal assistance coefflicient The ratio of the Consumer support estimate (CSE) to the total value of consumption expenditure on farm commodities produced domestically and valued at world market prices, excluding budgetary support to consumers. Consumer support estimate (CSE) An indicator of the annual monetary value of gross transfers to (from, if negative) consumers of agricultural commodities, arising from policy measures. Contemporary group A group of animals that are subjected to the same environmental influences (e.g. same age, same herd, same calving season, same location). Comparison of an animal with its closest contemporaries allows a more accurate determination of its genetic merit. Continuous ice cream freezer A swept-surface heat exchanger, jacketed with a refrigerant, through which ice cream (or frozen dairy dessert) mix is pumped in order to freeze a portion of its water and incorporate small air bubbles. Cooking of casein Heating of precipitated casein by means of steam injection, or through a heat exchanger, from precipitation temperature to a temperature at which the individual particles of casein agglomerate to form curd of sufficient strength to withstand subsequent wet processing. Copolymer a polymer made up of monomers of two or more types. Corpus luteum An ovarian structure that forms following ovulation. It is responsible for the secretion of progesterone during the luteal phase of the estrous cycle and pregnancy. Luteinizing hormone is the major luteotropic hormone that stimulates luteinization of the theca and granulosa cells of the preovulatory follicle into luteal cells. Cottonseed Seed separated from cotton lint during ginning. It contains a moderate concentration of oil and protein and a high concentration of fiber from lint remaining on hull. Meal is produced from protein and hull as a byproduct when whole seeds are crushed to extract cottonseed oil. Cow comfort A general term that implies that animals are provided with an environment that minimizes stress, illness, mortality, injury and behavioral problems; an environment that permits them to grow, mature, maintain health, reproduce and produce. Cream liqueur A cream product combining the flavor of an alcoholic drink with the texture of cream, and expected to have a shelf-life of several years at ambient temperature. Besides a sufficient amount of alcohol and sugar (for microbiological stability), a very fine milk fat dispersion, non-fat milk solids (from cream), water, sodium caseinate and trisodium citrate are the main ingredients.
817
Cream The part of milk, rich in fat, that can be separated by centrifugation of milk. The fat content of the different liquid and cultured products ranges from 10% to 50%. The special ‘creaminess’ results from the fine dispersion of the fat globules protected by a special membrane against de-emulsification. Cross-flow microfiltration A pressure-driven membrane separation process. It could be described as a more porous form of ultrafiltration where instead of molecular weight cut-off criterion, membranes are defined by their pore size in mm. The selective permeation of protein may be facilitated by choice of membrane and optimization of processing conditions. Cryopreservation A system whereby live cells are preserved using an ultra-low temperature freezing process that allows most of the cells to recover after thawing. Cultured cream A cream product with various applications as an ingredient in sauces or dressings. The fat content of cultured creams ranges from 10% to more than 40%. The manufacturing process is similar to that for other fermented products. Fermentation may take place in retail packages or in a fermentation tank. Cytotoxin A toxin that kills mammalian cells. D value Time in minutes at a defined temperature, required to reduce the microbial population by one log (i.e. to cause destruction of 90% of microorganisms); the temperature is indicated in a subscript, i.e. D70 for 70 C. See also z value. de novo fatty acid synthesis The synthesis of fatty acids within the mammary gland, primarily from acetate. It can also be initiated from b-hydroxybutyrate. Key enzymes include acetyl-CoA carboxylase and fatty acid synthase complex. The resulting fatty acids have an even carbon chain length between 4 and 16 carbon atoms. Dewatering of casein curd The final separation of casein curd and water before the curd is conveyed to the drier. It involves mechanical means for expressing the maximum amount of water from the curd consistent with a friable texture for maximum drying efficiency. Dewheying of casein curd The separation of casein curd and whey before the curd is washed in water. This may be effected by means of inclined stationary screens and/or by mechanical separation, such as a roller press or a decanter centrifuge. Dip tank A long, narrow, deep tank into which acaricide solution is poured and through which cattle are herded. The tank should be deep enough so that cattle have to swim through and become covered in acaracide. Also called plunge dip. Direct government payment A subsidy to producers in the form of transfers from taxpayers rather than through import barriers or government-set minimum prices. Discounts for multiples of maintenance A method used by the US National Research Council (NRC) to account for decreased digestibility as animals
818 Glossary
increase energy intake at multiples above the energy required for maintenance. The NRC system for dairy cattle uses discount factors of approximately 8% at 3 and 12.5% at 4 maintenance. Dispute settlement body A part of the machinery of the WTO. The Dispute Settlement Body and Dispute Settlement System together form the core legal institution within the WTO when solving bilateral disputes concerning trade. Member countries within the WTO are obliged to implement the rulings of the Dispute Settlement Body and no single country has a veto right over the dispute rulings. DNA array A rigid slide or flexible membrane containing a series of up to tens of thousands of single- or double-stranded DNA polymers used to qualitatively or quantitatively evaluate complementary DNA present in a sample using nucleic acid hybridization. Domestication The process of genetic adaptation of a species so that it supplies and receives benefits to and from a human population. Downer cow A cow that lies down and cannot get up. This condition may be due to several causes, such as severe lameness, temporary loss of nerve function after calving, or an acute metabolic disease such as milk fever (calcium deficiency) or magnesium deficiency. Drench To dose an animal orally with a solution using a bottle, syringe or specifically designed drenching apparatus (drench gun). Dry matter (DM) The forage component remaining after water has been removed by oven-drying at a controlled temperature (80 C) until constant weight is attained. Heating to 105 C will remove all water (oven dry). Pasture and crop yield are often reported as kilograms of dry matter per hectare (kg DM ha 1). Dry matter intake (DMI) The weight (kg) of dry matter consumed by an animal each day after feed refusals have been subtracted. Dry period The days during which pregnant cows are not being milked. The recommended dry period is the 60-day period preceding calving. Dynamic compressor A compressor that operates continuously, subjecting air to steady-flow processes. Such a machine has no means of preventing backflow. Distinction is made between axial and radial compressors, depending on the direction of the air flow. Dystocia A prolonged or difficult delivery. It can be due to either fetal factors (size, birth position) or maternal factors (pelvic size). Early embryo loss Loss of embryo during the first three weeks of pregnancy. Edometry The measurement of the physical locomotion of a cow by means of a device attached to its leg. Pedometry is reported to identify 70–80% of the cows in estrus; their activity increases approximately 4 h prior to the onset of standing estrus. The predicted optimum time for artifcial insemination is between 6 and 17 h after increased activity.
Effective fiber Fiber (neutral or acid detergent fiber) provided by plants that are effective at stimulating rumination. Effective population size The size of a population relative to the amount of inbreeding which is expected to accumulate in that population, frequently smaller than the census number of animals in the population. Electrochemical process The process by which chemical change is introduced into a system with electricity, e.g. an electrolytic cell, or by which electricity is produced though a chemical change in a system, e.g. a galvanic cell. Electron microscopy A technique of microscopy in which accelerated electrons, rather than photons, produce images. This offers a much higher resolution than light microscopy. A beam of electrons interacts with the sample to reveal fine structural detail. The two main electron microscopy techniques are scanning electron microscopy (SEM) which reveals topographic features with a high depth of field and transmission electron microscopy (TEM), which is capable of revealing two-dimensional macromolecular structures. Electrophoresis The migration of charged particles under the infuence of an electric field. Electrophoresis is commonly applied for separation, identification, purification and characterization of a variety of proteins and peptides. Electrophoretic mobility (m) The rate of migration of a particle in an electric field. It is dependent on the conditions under which electrophoresis is conducted. Electrophoretic mobility is equal to the vector sum of the driving force and a number of resisting forces. Endocrine A term to describe the secretion of a hormone by an internal gland; the hormone is transported (usually via the blood) and received by a distant gland to exert an effect (i.e. stimulation or inhibition). Enterohemorrhagic Causing hemorrhage in the gastrointestinal tract of the host. Enzyme A protein formed in cells that acts as a catalyst in initiating or speeding up specific chemical reactions. Equine chorionic gonadotropin (eCG) A protein hormone produced by the placenta of pregnant mares from about 40 days post mating until mid-pregnancy. This hormone has biological actions similar to follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Also called pregnant mare serum gonadotropin (PMSG). Equivalence ratio (f) Ratio between the stoichiometric air–fuel ratio and the real air–fuel ratio, A/Freal. This parameter allows one to determine if the combustion is stoichiometric, ¼ 1, if the reaction mixture is lean, < 1, or if it is rich, > 1. Essential amino acids Amino acids that cannot be synthesized by an organism at a sufficient rate and must be supplied in the diet. Estrous behavior The behavior expressed by female animals during the period when they are receptive
Glossary
to mating by males. In heifers and cows, the definitive sign of estrus is standing to be mounted by herdmates or a bull. Estrus typically lasts for 8 to 24 hours in cattle and occurs at 18-to 24-day intervals. Estrus The period of sexual receptivity and behavior in the female brought about by a high systemic concentration of estradiol-17b produced by the preovulatory follicle which stimulates behavior coincident with the ovulatory surge of luteinizing hormone. Ethylene vinyl alcohol (EVOH) A compound formed by reacting ethylene vinyl acetate with methanol in the presence of catalysts. It is a packaging material with high strength, clarity and good odor and oxygen barrier characteristics and is used as an oxygen barrier in multilayer coextruded plastic containers. Eutectic The term used to describe the situation in which two dissimilar materials are blended so that they can combine in such a way that the resulting melting point is lower than the melting point calculated from those of the individual components. Eutherians See also Placental mammals. Evaporative cooling The transfer of heat from the body of an animal to the environment by sweating and/or panting. Export subsidy A government payment conditioned on the export of a commodity that may allow exports even when the domestic market price is higher than the price in export markets. Such subsidies are still used to a small extent by the United States and quite extensively by the EU. Extended shelf-life (ESL) milk A product processed in such a manner that the shelf-life is extended to 60 to 90 days. The milk still must be held at refrigeration temperature (<7 C) throughout distribution and storage and will spoil readily once exposed to the environment. Extensive management Management of animals under range conditions, frequently with migration to seasonal pastures. Extrusion of animal feeds A process used to reduce the degradability of protein in a feed, involving forcing feed through a die using pressure. Heat generated during the process coupled with pressure alters protein structure and susceptibility to degradation by rumen microorganisms. Fat cow syndrome A condition in which a cow enters late pregnancy and early lactation with excessive body fat. This can lead to depressed feed intake, ketosis, displaced abomasum and other metabolic or reproductive problems, as well as reduced milk production. Fatty liver The accumulation of excessive fat in the liver (usually over 10% but can be much higher) which can occur when the rate of lipolysis of adipose tissue exceeds the rate at which peripheral tissues and liver use fatty acids. It can result in diminished functioning of the liver for metabolism of key nutrients.
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Feedback control A control procedure that operates by measuring the controlled process outputs and feeding back this information to the controller. The control action is based on comparing the actual (measured) output with the desired one (the reference signal). This is by far the most widely used process control strategy because the feedback makes the closed-loop system robust against perturbations and noise. Feedforward control A control procedure that operates by measuring important process disturbances (instead of the controlled process outputs) and feeding forward this information to the controller. The control action aims at compensating these measurable disturbances in such a way that process outputs are not affected by them. Feedforward control is usually used in combination with feedback control. Feedwater A blended composite of make-up and returned condensate waters specifc to boiler installations; the quality of boiler water improves as the proportion of the condensate return increases. Fertilization rate The proportion of ovulated oocytes that are fertilized. Final control element (FCE) A device, driven by controller signals, employed to directly manipulate process variables. Usually, the controller output (digital) signal cannot be applied directly to the process. It is first converted by a transducer to a standard (analogue) current signal, which activates the FCE. The most widely used FCEs are flow regulator valves. Flock health plan (sheep) Written preventative health maintenance strategy agreed by the owner and a veterinary adviser. The plan covers the implementation and timing of routine prophylactic interventions such as vaccination, antimicrobial and antiparasitic treatments, footcare and lambing management. It may also extend to cover other issues such as nutrition, housing, shearing and pasture management as necessary. Flow cytometer A device whereby individual cells in suspension flow, in single file, through a beam of light with which they interact individually by emitting a measurable response or florescent signal. A cell sorter has, in addition to the analytical system of the flow cytometer, the ability to vibrate the stream exiting the nozzle of the system to form droplets containing individual cells. This cell sorter system utilizes electronics to charge droplets containing selected cells, either positively or negatively, so that charged droplets can be separated physically from other droplets by the electrical attraction of a plate exhibiting the opposite charge. The charged droplets containing selected cells can be collected into a vessel separate from uncharged droplets or droplets of the opposite charge. Fluazuron The first acarine growth inhibitor to have become commercially available for the control of ticks on cattle. Chemical name: benzoylphenyl urea.
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Foil-ripening Method of ripening in which, after brining, the cheese is packed in a foil practically impermeable to gases and water vapor. It is the opposite of naturally ripening cheese that is covered with a permeable coating layer. As a result, foilripened cheese develops no rind by drying and the ripening of the outer zone is similar to that of the centre. Folate Generic name of a native form of one of the B vitamins (synthetic form; folic acid). Folates carry different one-carbon units (methyl, formyl, methenyl, methylene, formimino), produced from the catabolism of certain amino acids, and used for the biosynthesis of purines and pyrimidines for DNA and RNA. Folates regenerate methionine by methylation of homocysteine. See also Milk folates. Folate deficiency A condition in humans indicated by low concentrations of folates in erythrocytes and plasma. Severe folate deficiency rarely occurs in Western countries. It causes megaloblastic anemia and a decrease in cell replication and growth. Major causes of folate deficiency are malnutrition, malabsorption and increased demands (during pregnancy). Follicle-stimulating hormone (FSH) One of the two gonadotropin hormones secreted by the anterior pituitary gland. Its secretion pattern occurs as recurrent transient increases at 7–10 day intervals that stimulate each wave of ovarian follicle growth. A surge in follicle-stimulating hormone secretion also occurs coinciding with the luteinizing hormone surge in the luteal follicular phase (preovulation). Follow-on formulae Foodstuffs intended for particular nutritional use by infants aged over four months and constituting the principal liquid element in a progressively diversified diet of this category of persons. Foods for special medical purposes A category of foods for particular nutritional uses, specially processed or formulated and intended for the dietary management of patients and to be used under medical supervision. Footrot A bacterial infection of the hoof most frequently caused by Fusobacterium necrophorum with frequent mixed infections resulting from Dichelobacter nodosus, Porphyromonas asaccharolytica and other organisms. Footrot is a leading cause of lameness in sheep, goats, cattle and other even-toed ungulates. Forage quality A general term for forage nutritive value which often includes plant protein, fiber and energy content as well as other intrinsic factors that may affect consumption and animal performance. Free air delivery The real volumetric air flow rate produced by a compressor, measured at the admission pressure and temperature. Freeze-shocking A means for damaging the cell wall and membrane, resulting in cell lysis; it also leads to loss of the ability to produce acid. The range of temperature used has varied from 20 C to 30 C for 20–36 hours.
Functional property A term generally used to describe the physical effects of an ingredient in a food. Functional properties may include water sorption, fat emulsification, viscosity, gelation and texturization, but may also refer to solubility, color, flavour and nutrition. Furosine A relatively stable derivative of the fructoselysine moiety, formed during hydrolysis with concentrated hydrochloric acid. It is an important marker for the early stage of the Maillard reaction of lysine with glucose (fructoselysine), lactose (lactuloselysine) or maltose (maltuloselysine) and for calculation of blocked lysine, especially in milk products. Galacto-oligosaccharides Nondigestible carbohydrates which are resistant to gastrointestinal digestive enzymes, but are fermented by specific colonic bacteria. They are produced commercially by transgalactosylation from lactose using b-galactosidases. They are usually sold as a mixture of tri-, tetra- and pentagalacto-oligosaccharides. Galactose cataract A cataract induced experimentally in animals by an excess of galactose in the diet. Gametes The mature haploid germ cell lines, spermatozoa or ova, capable of transmitting genetic information to the next generation. Gel, coagulum A gel is an ordered network of macromolecules or particles that has solid-like properties (i.e. can support its own weight at rest) and has little tendency to synerese, e.g. heat-coagulated egg white or a gelatin gel. A coagulum is also a network of macromolecules or particles but is less structurally organised and has a greater propensity to synerese than a gel, e.g. yogurt, rennet-coagulated milk. Both a coagulum and a gel exhibit viscoelastic rheological properties, with a preponderence of the elastic (solid-like) modulus. See also Syneresis. Genetic evaluation An estimation of the genetic merit of an animal, usually through the use of statistical models, with results expressed as breeding value or predicted transmitting ability, which is half of breeding value. Glass transition A change between solid and liquid states of a noncrystalline, amorphous substance. For example, sugars can be cooled from melt or dehydrated from solution to noncrystalline solids that exhibit the glass transition. Gluconeogenesis The synthesis of glucose from new sources (genesis of new glucose). Mammals can synthesize glucose only from propionic acid produced by ruminal or hindgut fermentation, or from several amino acids. Glycocalyx Exopolysaccharides synthesized by microorganisms adhering to a surface that form a threedimensional matrix with a sticky character, allowing microorganims to be protected from the environment and to be supplied with nutrients through microchannels and diffusion.
Glossary
Gonadotropin-releasing hormone (GnRH) A decapeptide hormone secreted by the hypothalamus. It is secreted by hypothalamic nuclei into the hypophyseal portal blood system, which carries it to its site of action in the anterior pituitary. It is responsible for stimulating the secretion of luteinizing hormone and follicle-stimulating hormone. Gossypol A polyphenolic compound concentrated in the pigment glands of cottonseed. It is toxic to animals without a functioning rumen or when cottonseed or cottonseed meal is fed in large quantities. Granuloma A mass or nodule of a collection of modified macrophages resembling epithelial cells surrounded by a rim of mainly lymphocytic mononuclear cells and sometimes a center of giant multinucleate cells, either of the Langhan’s (epitheloid) or foreign body type, due to a chronic inflammatory response associated with an infectious disease. Gravimetric analysis Chemical analysis based on the measurement of mass. Growing degree days (GDD) An index of crop maturity which accumulates from sowing and is calculated from daily temperatures. Heat stability (objective) The time elapsed between heating a sample of milk (140 C for unconcentrated milk or 120 C for concentrated milk) and coagulation as denoted by a sharp increase in viscosity or amount of nitrogenous material sedimentable at low gravitational forces. Heat stability (subjective) The time elapsed between heating a sample of milk (140 C for unconcentrated milk or 120 C for concentrated milk) and the flocculation of solid material. Heat-induced acidification Decrease in the pH of milk when heated at an elevated temperature (>100 C) due to thermal oxidation of lactose, precipitation of primary and secondary phosphate as tertiary phosphate. Heat-shocking A means for reducing the acid-producing capability of bacterial cells without a significant decrease in their proteolytic activities, where the optimum heat treatment varies from 56 to 70 C with heating time varying from 15 to 22 seconds. Helminths A broad term that includes many parasitic worms and flukes that are parasites of animals, and thus of veterinary importance, belong to four phyla: (1) Nematoda or roundworms and (2) Platyhelminthes, which include Trematoda (flukes) and Cestoda (tapeworms), (3) Acanthocephala or thorny-headed worms and (4) Annelida or leeches. Phyla (1) and (2) are most important in dairy animals. Heritability The percentage of phenotypic superiority or inferiority of parents transmitted to offspring. Also, the percentage of phenotypic differences that are explained by additive genetic effects, which ranges from 0 (no genetic control) to near 1 for traits unaffected by the environment. Heterofermentative See also Lactic acid bacteria.
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Heterosis The average advantage of crossbred animals in comparison to the average of purebred animals from the component breeds. Also known as ‘hybrid vigour’. High-density polyethylene (HDPE) A compound of which the basic building unit is polymerized ethylene. It is a high molecular weight packaging material of great strength, good gas barrier properties, and low clarity. It is generally of low cost. High-performance liquid chromatography (HPLC) A widely used, highly developed analytical technique for separation of analytes in a complex mixture. The basic theory is the partitioning of the analyte between two phases, one mobile and the other stationary. High-temperature, short-time pasteurization (HTST) A continuous heat treatment process which destroys all pathogenic bacteria and most spoilage bacteria. The heat treatment is sufficient to denature alkaline phosphatase. Products are heated to a minimum of 72 C for at least 15 seconds. Homofermentative See also Lactic acid bacteria. Hydrocyanic or prussic acid (HCN) An acid contained in cyanogenic plants, particularly sorghum species, which causes cyanide poisoning and death of livestock. Glucosides in the plant combine sugar and HCN. Glucoside concentration increases when plant growth is restricted. Enzymes released in plants that are damaged (e.g. by chewing, frost or wilting) break down the glucoside and release HCN. Hydrolytic rancidity Enzymatically catalysed release of free fatty acids from triglycerides. It leads to soapy, goaty or bitter off-flavours in milk. Hydrophilic Term (literally ‘water-loving’) used to describe those segments or parts of a protein molecule that prefer to be in water. Hydrophobic Term (literally ‘water-fearing’) used to describe those segments of a protein molecule that prefer to interact with the oil phase or other hydrophobic groupings. Hyperglycemia Elevated blood glucose concentration. This finding is typical in dairy cows, sheep and goats with milk fever. Hypersensitivity A form of allergy; this term is sometimes also applied to nonimmune-mediated reactions such as intolerance due to an enzyme deficiency. Hypocalcemia (nonparturient) A depression in blood calcium concentration in dairy cows, sheep and goats that does not occur around parturition. Hypocalcemia in these cases is usually secondary to some other disease problem. Hypocalcemia (subclinical) A depression in blood calcium concentration around parturition in dairy cows, sheep and goats that causes no apparent clinical signs. Affected animals are at risk of reduced milk yield, ketosis, retained placenta and displaced abomasum. Hypomagnesemia Decreased blood magnesium concentration. Clinical signs include hyperesthesia and tetany. Also known as grass tetany. Hypomagnesemia can also be a cause of milk fever.
822 Glossary
Hypostome The central mouthpart of a tick which serves as the feeding apparatus. Hypothalamic–pituitary–adrenal axis The endocrine axis that controls the regulation and release of cortisol, which involves the release of hypothalamic (CRH) and pituitary (ACTH) hormones to stimulate the release of cortisol by the adrenal cortex. Hypothalamic–pituitary–gonadal axis The endocrine system controlling reproduction in animals. It comprises gonadotropin releasing hormone neurons in the hypothalamus, gonadotroph cells in the pituitary (responding to gonadotropin releasing hormone by secreting luteinizing hormone and folliclestimulating hormone), and the ovary or testis (responding to luteinizing hormone and folliclestimulating hormone). Ice cream mix A combination of liquid and solid ingredients, including sources of fat, milk solids-not-fat, sugars, stabilizers, emulsifiers and water, that is blended together, pasteurized and homogenized from which ice cream (or frozen dairy dessert) is manufactured by whipping and freezing. Immune system The scattered bodily cells and tissues that react to foreign and potentially harmful agents (such as bacteria and viruses) but can sometimes react inappropriately (and unpleasantly) to harmless substances such as foods or pollens, causing allergic reactions. Immunoglobulins Proteins of the immune system produced by B lymphocytes. They augment phagocytosis and cell-mediated cytotoxic reactions by leucocytes, activate complement system and agglutinate and neutralize microbes and toxins. Immunoglobulins in milk and colostrum protect the offspring against microbial pathogens and toxins and the mammary gland against microbial and viral infections. Immunoglobulins (Ig) occur in five classes: IgM, IgG, IgA, IgD and IgE. Import barrier Any of a set of policy tools that inhibit imports and protect domestic producers. Examples include import tariffs or duties, limits on the quantity of imports or import quotas, and tariff-rate quotas which comprise a combination of tariffs and quotas. In vitro dry matter digestibility (disappearance) (IVDMD) A laboratory estimate of feed digestibility. A mixture of rumen fluid, enzymes and feed is incubated at body temperature (39 C). In a second stage, the incubated mixture is acidifed and digested with pepsin. The residue is dried and weighed. The weight loss is expressed as a percentage of the feed dry matter. In vitro A term (literally, ‘in glass’) that refers to an experiment conducted using isolated tissues, cells or biochemical reactions outside of a living animal. Such experiments can be performed, for example, in cell culture dishes or test tubes. See also In vivo. In vivo A term (literally, ‘in life’) that refers to scientifc experiments performed in a whole, living animal, as
opposed to using isolated tissues or cells. See also In vitro. In-line measurement The set of real-time measurements used in process control. Process control can only be based on the measurement of the quantity of interest. Beside physical quantities (temperature, pressure, etc.), the in-line measurement of chemical quantities (constituent concentrations) becomes more important. Infrared spectroscopy offers the possibility to determine the constituent concentrations directly in the production line. Inbreeding The mating of relatives. Incidence The new cases of a disease in a specifed population of humans or animals. Incidence may be measured as the proportion or percentage of new cases over a particular time interval, or as the rate of new cases as a function of the length of time that each individual in the population is at risk of becoming a new case. Infant formulae Foodstuffs intended for particular nutritional use by infants during the first 4–6 months of life and satisfying by themselves the nutritional requirements of this category of persons. Infrared instrument calibration Procedure for validating infrared absorption data. The infrared absorption measurement is an indirect method, i.e. one has to correlate the measured absorption with the chemically obtained constituent concentration value by using multivariate statistical methods (calibration procedure). Infrared instrument network Any of several networks, having in common the aim of reducing the amount of calibration work, to check the calibration and to harmonize the results. Infrared spectroscopy A technique that excites vibrational states of specifc groups of atoms in molecules. It measures the absorption of infrared radiation as a function of the wavelength. The information is used for identification of the substance or quantitative determination of constituent concentrations in the product. Infusion heating A method of heat transfer in which the target medium is infused into a high temperature steam environment as a fine mist; it effects a rapid increase in temperature with minimal nutrient and flavour degradation. Condensed steam is removed in a subsequent vacuum chamber. See also Injection heating. Injection heating A method of heat transfer wherein the target medium is injected with culinary-quality steam under pressure and at sufficient velocity through a specialized port. It effects a rapid increase in temperature with minimal nutrient and flavour degradation. Condensed steam is removed in a subsequent vacuum chamber. See also Infusion heating. Intensive management Management of animals in a confined area with permanent housing and equipment for feeding, watering, milking and other activities.
Glossary
Intolerance An adverse, reproducible reaction to a food or a food component, which is not mediated by the immune system. Food intolerance may be related to an enzyme deficiency (e.g. lactose intolerance) or may have other underlying mechanisms. See also Allergy. Ion exchange A process by which ions present in a solution (e.g. in milk or whey) are exchanged for ions that are electrostatically bound to an ion exchanger. The molecules bound to the ion exchange resin can be eluted with buffers of different ionic strength, pH or composition. Ion exchange process is often used to soften hard water. See also Water hardness. Ion-selective electrodes (ISEs) Potentiometric analysers that measure the activities of ions in solution. Activity differs from concentration by the activity coefficient and depends on the overall ionic strength of the analyte solution. The most common type is the glass membrane pH electrode. Isoelectric focusing (IEF) A technique involving separation of analytes based on differences in their isoelectric point, exploiting the fact that each protein has a unique isoelectric point. Analytes migrate through a gel medium containing a pH gradient and cease to migrate at a pH value corresponding to their isoelectric point. Kelvin model A model of linear viscoelastic behavior. The Kelvin model comprises a Hookean spring and a Newtonian dashpot connected in parallel. See also Maxwell model. Kishk A dried fermented milk product made from mixed ‘burghol’ (preboiled dried wheat grains) and low-fat yogurt or laban zeer (concentrated fermented buttermilk). The mixture is fermented naturally, shaped into balls or nuggets and sundried or dried in warm shade. It is consumed mainly as a porridgelike product. Knowledge-based hybrid modelling A combination of different modelling techniques based on available process knowledge sources in an integrated hybrid model. The main sources of process knowledge are: (1) classical mechanistic models, (2) heuristic (empirical) knowledge expressed by fuzzy rules and expert systems and (3) data-driven knowledge hidden in the acquired process data. Kraal An enclosure where animals are housed. Also known as corral. Kumys Fermented horse milk, containing at mean 2% alcohol, due to the action of bacteria and yeast species. It is frequently consumed in some parts of Russia, West Asia and Mongolia. Laban kad (rob) A low-fat fermented buttermilk obtained by direct churning of sour milk in goatskin bags called ‘kerbah’. Laban kad is made into either Kariesh cheese or concentrated in earthenware jars (‘zeer’) as laban zeer. Laban rayeb A low-fat fermented milk obtained after removal of the top sour cream layer from naturally fermented milk. Laban rayeb is consumed either
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directly, in salads or used for the manufacture of Kariesh cheese. Labneh A concentrated fermented milk made by straining full cream yogurt or zabady. Addition of table salt (0.2–0.5%) to stirred yogurt before whey removal is optional. Labneh has a soft, smooth, spreadable and creamy texture, with a clean acid taste. Lactase An enzyme occurring in the small intestine of mammals, as well as in some bacteria and yeasts, which hydrolyzes lactose, yielding a mixture of glucose and galactose; also called b-galactosidase. Lactic acid bacteria Bacteria that generate lactic acid as the primary product of fermentation and most are associated with dairy fermentations. They are Grampositive, non-sporeforming and do not produce catalase. They can be either homofermentative (lactic acid makes up over 90% of the end products) or heterofermentive (lactic acid makes up less than 50% of the end products). The main species are from six genera: Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Streptococcus. Lactobacillus, Lactococcus and Streptococcus are typical genera found and used in fermented milk products. Lactoferrin An iron-binding glycoprotein composed of a single-chain polypeptide sequence of about 700 amino acids with a molecular weight of about 78 kDa. Lactoferrin is found at much higher (>10 times) concentrations in human than in bovine colostrum or milk. It has, among other things, antimicrobial and immunomodulatory functions, and may thus play an important role in the natural nonspecifc defense of the body. Lactose A disaccharide present in milk made up of galactose and glucose. Lantibiotic A class of bacterially-derived inhibitory peptides characterized by signifcant posttranslational modifications. In particular, lantibiotics possess internal rings formed by the condensation of a dehydrated hydroxy amino acid and a cysteine to form crosslinking lanthionine residues. See also Bacteriocins. Leptin A recently discovered protein hormone which is made in the adipose tissue and functions in the brain to partially regulate food intake and reproductive function. Defects or mutations in the gene for this hormone, or for its receptor in the brain, result in genetic obesity in rodents and perhaps in humans. Limiting amino acids The essential amino acids in digested protein that are in shortest supply relative to body requirements for absorbed amino acids. The first-limiting amino acid is the essential amino that is provided in shortest supply relative to body need. The second limiting amino acid is the essential amino acid that is in the second shortest supply relative to body need. Lipases enzymes that hydrolyze esters at an oil/water interface. Lipolysis The enzymatic breakdown of triglycerides into mono-and diacylglycerols and free fatty acids. The
824 Glossary
enzymes involved are lipases that act at the fat–water interface and esterases that act on water-soluble acylglycerols. The release of fatty acids from the adipose tissue supplies energy to tissues and milk fat precursors to the mammary gland. It increases during glucose or fat deficit as that associated with early lactation. Lipolytic bacteria Bacteria that are able to produce lipases necessary for splitting fats into partial acylglycerols and fatty acids. Liposomes An assemblage of phospholipids and other lipids sustaining a biomolecular configuration and not requiring mechanical support for their stability; they are now established as a useful model membrane system. Attempts have been made to use enzymes entrapped in liposomes for the acceleration of cheese ripening and the enhancement of cheese flavor. Lodging The falling over of certain forage species due to weak stems. Lodging occurs more frequently as the plants mature and may be precipitated by wind or rain. Low birth weight (LBW) infants Infants born prematurely with a gestational age (GA) of less than 36 weeks or infants born small for GA, i.e. which weigh <2500 g. Infants born with a gestational age of less than 32 weeks are generally referred as ‘very low birth weight’ infants (VLBW) and are generally less than 1000 g. Low-temperature, long-time pasteurization (LTLT) A batch heat treatment process which destroys all pathogenic bacteria and most spoilage bacteria. The heat treatment is sufficient to denature alkaline phosphatase. Products are heated to a minimum of 63 C for at least 30 minutes. Lower caloric value of a fuel (LCVf) The chemical energy content of the fuel, per unit fuel mass, when the products of the combustion reaction contain water in the vapor state. Lower critical temperature (LCT) The temperature at which an animal needs to increase metabolic heat production to maintain body temperature. Luteinizing hormone (LH) One of the two gonadotropin hormones secreted by the anterior pituitary gland. It is secreted in a pulsatile manner and is stimulated by gonadotropin-releasing hormone pulses. It is secreted as a preovulatory surge in the late follicular phase, which is responsible for stimulating ovulation. Its main functions include final maturation and ovulation of ovarian follicles and acting as a luteotropin that stimulates the corpus luteum formation and maintenance. Lysine damage (1) derivatization (mainly fructoselysine) or crosslinking (e.g. lysinoalanine); it results in a loss of bioavailability of lysine and reduced protein digestibility. (2) Complete destruction of lysine by severe heating (total lysine loss). Lysinoalanine A compound formed by the reaction of lysine with dehydroalanine, which itself is produced under alkaline conditions from cystine and especially
phosphoserine (casein). This crosslinking reaction impairs the utilization of the amino acids involved and reduces protein digestibility. Lysogenic bacteriophage A bacterial virus the genome of which is integrated into the host bacterial genome. Lysozyme An enzyme found in egg white, milk and many other sources, which digests the cell wall structure of certain bacteria. Maillard reaction The reaction of free amino groups with reducing sugars forming various compounds that are colorless in the initial and advanced stages and brown-colored in the final stages of the reaction. In proteins, predominantly lysine, with its reactive e-amino group, is involved, thereby losing its bioavailability. Major histocompatibility complex A series of genes found in all mammals that are primarily responsible for the compatibility or rejection of grafted tissues and organs between individuals, and also function in the signalling between lymphocytes and antigenexpressing cells. Make-up water Process water used to replace water losses incurred by overflow or, more especially, evaporation in boilers and cooling systems. Mammals Class of animals that, 1. possess mammary glands (which may secrete milk for the nutrition of the neonate), 2. can control body temperature (homothermic), 3. have hair or wool. Management intensive grazing (MIG) A grazing system characterized by high animal concentration per unit of land area and rapid pasture defoliation (usually within 12–72 h), followed by a prolonged rest period (often 14–28 days) for plant regrowth. Marsupials Mammals with a pouch found in Australasia, South, Central and southern North America. Young are born at a very early stage of development and climb unaided to the pouch where they obtain milk, initially attached to a nipple. The intestine joins the cloaca at its outer end. Mastitis Infammation of the milk gland, usually caused by bacterial or viral infection. Maxwell model A model of simple linear viscoelastic behavior. The Maxwell mechanical model (mechanical analogue) comprises a Hookean spring and a Newtonian dashpot connected in series. More complex models are built up by connecting Maxwell models, Kelvin models and individual springs and dashpots in various configurations. See also Kelvin model. Melatonin A hormone secreted by the pineal gland mainly during darkness that alters gonadotropinreleasing hormone and gonadotropin secretion. Melatonin secretion controls annual photoperiodic changes in mating activity of, among other things, seasonal sheep breeds. Mesophilic starter A starter culture with an optimum growth temperature of approx. 30 C, used for the majority of cheeses.
Glossary
Metabolic disease A general term to describe metabolic disorders such as ketosis, milk fever, fatty liver and others that most frequently occur during late pregnancy or early lactation. These disorders may be caused by a specific nutrient deficiency or by a blockage of a metabolic pathway. Metabolite A substance that is produced by living organisms. Microencapsulation technology A technology recognized as a means for improving the flavor, stability, nutritive value and appearance of foods, offering a means for duplicating some of the protective and selective properties of natural membranes. A more recent application of microencapsulation technology in the dairy industry is the use of enzymes, entrapped with their substrates, for controlled and faster production of flavor compounds in cheese. Micromineral Any of the minerals required in the diet in very small quantities, usually less than 100 mg kg 1 diet. Microstructure A general term describing structuring units, or the visual appearance, of materials of microscopic dimensions, from macromolecules to large phases of up to 500 mm. Microstructures may also be inferred by other physical measurement techniques such as rheometry. Milk fat depression A reduction in milk fat yield with corresponding changes in fatty acid composition of milk fat that is related to dietary conditions with low effective fiber, high fermentable carbohydrate and unsaturated fatty acids. Milk fat composition refects a reduction in de novo fatty acid synthesis with greater proportional use of performed fatty acids. Milk fever An acute drop in blood calcium around the time of parturition in dairy cows, sheep and goats. Clinical signs typically include paralysis and loss of consciousness. Also known as parturient paresis, hypocalcemia, paresis puerperalis and parturient apoplexy. Milk folates The folates found in milk, comprising mainly methyltetrahydrofolates in mono- and polyglutamate forms. In unprocessed and pasteurized milk, the folates are bound to a folate-binding protein (FBP) which is destroyed upon heating above lowtemperature pasteurization. FBP is believed to stabilize the folate and improve folate absorption. See also Folate. Milk marketing order A government-sponsored milkpricing system that sets minimum prices for farm milk delivered within a specifed region in order to raise the average price received by producers of that milk. Milk marketing orders in the United States set minimum prices according to the use of the milk and then specify pooling of revenue across participating producers. Milk protein coprecipitate The product derived from skim milk that has been heat-treated sufficiently to cause interaction between the caseins and the whey proteins. Precipitation of the caseins by acidification
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or by addition of calcium chloride causes most of the whey proteins to coprecipitate with them. Milk protein hydrolysate The products of enzymatic hydrolysis of milk proteins. Modifed environment housing Usually with minimal insulation and manual control of ventilation, this barn type may have less than adequate ventilation in winter as ventilation openings are blocked during extreme weather to keep manure from freezing or for other reasons. Not increasing ventilation during severe weather leads to excess moisture build-up and high relative humidity; unhealthy conditions for animals. Monophyletic Term to describe a group derived from a common ancestor. It is applied to taxomonic groupings that are derived from and include a single founder species. The term monophyletic contrasts with polyphyletic, having origin in several different lines of descent, and paraphyletic, which applies to groups such as reptiles which have evolved from and include a single ancestral species (known or unknown), but do not contain all the descendants of that group. Monotremes The most primitive group of living mammals, found only in Australasia and New Guinea. Embryos develop inside a shelled egg. Once laid, the egg is carried in a pouch (echidnas) or protected in a nest (duck-billed platypus). Young lick milk from mammary glands without nipples. Like reptiles, monotremes have only one opening, the cloaca, for the genital, urinary and digestive tracts. Morula An early embryonic stage represented by a spherical mass of cells which have resulted from cleavage of a fertilized ovum. In cattle, the cell numbers range from approximately 16 cells on day 4 to 64 cells on day 7 after fertilization. Mold A fungus that grows by producing filamentous or threadlike structures. Mold colony A group of fungal hyphae that grow on microbiological media from one spore or cell and appear as velvet, cotton, granular or other textures. Mycotoxin A metabolite produced by molds that is toxic to other organisms, especially vertebrates. Mysost whey cheese A cheeselike product manufactured from a whey base (with added cream and/ or other ingredients) by removal of most of the water through evaporation. N e-carboxymethyllysine (CML) A compound formed by oxidative release of erythronic acid from fructoselysine or lactuloselysine; a useful indicator of advanced heat damage in milk products. Nanofiltration A pressure-driven membrane separation process similar to reverse osmosis, except that its specially formed membranes are also partially permeable to mineral ions and other low molecular weight constituents. Thus, a limited level of product demineralization may be obtained in addition to dewatering/concentration. Natamycin An antimycotic agent produced by Streptomyces natalensis. It is added in small amounts to
826 Glossary
the coating dispersion before application on the outside of cheese in order to inhibit mold and yeast growth. Necrotoxigenic Causing death in host tissue. Nematoda A phylum of worms that are elongate with a cylindrical body pointed at both ends, possessing an alimentary tract; both female and male worms are found. They are an important group of parasites of vertebrates. The most important cattle nematodes are Haemonchus placei, Ostertagia ostertagi (abomasal nematodes), Cooperia oncophora (intestinal nematode) and Dictyocaulus viviparus (lung nematode). Net positive suction head (NPSH) The difference between the pressure head at a given point and the vapor pressure head. Neuro-fuzzy control A control procedure that combines the learning and structural properties of an artificial neural network (ANN) with the rule-based explanations associated with fuzzy systems. Knowledge of the process extracted from experienced process operators is formulated as a set of languagebased fuzzy rules. This knowledge is complemented by an ANN for modeling and state estimation. Neuroendocrine Term to describe the stimulation of sensory neurons that results in the release of a neurohormone which then acts in an endocrine fashion. See also Endocrine. Neutral detergent fiber (NDF) Plant tissue (total cell walls: structural carbohydrates) not soluble in neutral detergent solution (hemicellulose, cellulose, lignin, and a variable portion of pectins). Nondigestible oligosaccharides (NDOs) A term to distinguish those oligosaccharides that are not digested in the stomach and small intestine by acid conditions or by hydrolytic enzymes, and which reach the colon largely intact, from oligosaccharides which are digested such as malto-oligosaccharides. NDOs include galacto-, fructo-and xylo-oligosaccharides. Nonesterified fatty acids (NEFA) Free fatty acids that have been mobilized from adipose tissue and are circulating in the blood. NEFA can be used as a source of energy, ketone bodies, and/or milk fat. Nonfiber carbohydrates (NFC) An element of the diet of cattle consisting primarily of sugars and starch. It is calculated using the following equation: 100% –% neutral detergent fiber –% crude protein –% fatty acids –% ash. Nonstructural carbohydrates (NSC) consist of the same types of carbohydrates but are determined by a wet chemistry method in a laboratory. Nonprotein nitrogen The trichloroacetic acid soluble nitrogen remaining in the supernatant following precipitation of the protein in milk. It contains many components including peptides, urea, uric acid, ammonia, free amino acids, creatine, creatinine, nucleic acids, nucleotides, polyamines, carnitine, choline, amino sugars, hormones and other biologically active compounds such as growth factors. Non-seasonal dairying A commercial dairy production system that employs year-round milking as
opposed to seasonal dairying in which all cows are nonlactating for a portion of the year. Nonstructural carbohydrates See also Nonfiber carbohydrates. Nucleic acid hybridization A process by which two strands of DNA (or DNA and RNA) bind. The complementary nature of nucleic acid bases makes this process exquisitely sensitive to small changes in nucleic acid sequence and thus an extremely accurate measure of the identity of the two strands. Nucleosides N-glycosides of pyrimidines and purines. Nucleotides o-phosphoric acid esters of nucleosides. Oligosaccharides Short chains of monosaccharide units (single sugars) joined together by covalent bonds. Most oligosaccharides that have three or more units do not exist in a free form; rather they are joined as side chains to polypeptides in glycoproteins, proteoglycans or glycolipids. Oocyte The female gamete (egg) that is released into the duct system during ovulation. It has the potential for fertilization through interaction with a spermatozoon resulting in a one-cell embryo. Organoleptic A term which concerns, regarding food use, the senses of taste and smell. Organoleptic properties of foods contribute to the enjoyment of the foods rather than to nutritional or other technological properties such as preservation. Osteoporosis A bone disease characterized by a reduced bone mass, leading to enhanced bone fragility. Ovarian follicle The structure that nurtures the oocyte (female gamete) in the ovary. Follicles grow in response to stimulation by follicle-stimulating hormone and at later stages of development by luteinizing hormone. There are two, three or four recurrent waves of follicle growth during the estrous cycle in heifers and cows. Overrun A measure of the air content of ice cream (or frozen dairy desserts), calculated as the percent increase in the volume of ice cream (or frozen dairy dessert) compared to the initial starting mix. Ovulation The rupture of a mature follicle from the ovary resulting in the release of an oocyte (i.e. female gamete or egg). Palmar A term referring to the caudal or rear aspect or surface of the forelimb. Partial coalescence The agglomeration of emulsifed fat into clusters as a result of applied shear, which forms three-dimensional networks due to the presence of both fat crystals and liquid oil in the emulsion droplets. Partial coalescence is responsible for structure formation in whipped cream and ice cream. Pasteurization See High-temperature, short-time pasteurization (HTST); Low-temperature, longtime pasteurization (LTLT). Pasture A population of herbaceous plants, usually bounded by a fence, considered as a functional unit for grazing. Pasture-based nutrition Nutrition system in which the majority of the forage consumed is from grazed pasture.
Glossary
Pasture utilization The percentage of available forage consumed by cattle and other farm animals. Peak milk The highest level (kg day1) of milk production achieved during the lactation; typically 40 to 60 days after calving. If fat-corrected milk is used to define peak milk, it may occur 2–3 weeks earlier in the lactation. Pedometry The measurement of physical locomotion of a cow by means of a device attached to its leg. Pedometry is reported to identify 70–80% of the cows in estrus, whose activity increases approximately 4 h prior to the onset of standing estrus. The predicted optimum time for artificial insemination is between 6 and 17 h after increased activity. Phenomenological rheology A type of rheology, also called macrorheology or continuum rheology, that treats a material as a continuum, without explicit consideration of microstructure. Placental mammals The largest suborder of living mammals, giving birth to live young. Exchange of gas and nutrients between mother and fetus takes place via the placenta developed at implantation site(s) in the uterus and formed from maternal and fetal tissues. The large intestine, bladder and uterus open separately to the exterior. Plantar A term referring to the caudal or rear aspect of the hindlimb. Plasmids DNA molecules, generally composed of double-stranded, circular or linear DNA, that replicate independently of the bacterial host chromosome, with a size less than 20 times that of the chromosome. Plasmids carry genes that are nonessential for cell survival under non-selective conditions. Many plasmids are used as cloning vectors. Plasmin An alkaline serine proteinase; the major indigenous protease in milk. Plasminogen The inactive form of plasmin, converted to active plasmin by proteolytic action of plasminogen activators. Plasminogen activators (PAs) Serine proteinases that convert plasminogen to plasmin. There are two major types, urokinase-type PA and tissue-type PA. Plasticization The softening of amorphous substances by solvents. For example, amorphous lactose is softened by water. Such plasticization decreases the glass transition to a lower temperature. Pliability The ability of cheese to be bent or deformed. If a cheese can be bent or deformed without breaking or splitting, it is said to have a ‘long body’. This is often used in the context of eye development in Swiss cheese or in the stretch behavior of Mozzarella cheese. Polyacrylamide gel electrophoresis (PAGE) A technique involving the use of a polyacrylamide gel as a medium in which to stabilize the electrophoresis buffer. Early PAGE was performed in long cylindrical (pencil) gels, while slab gel PAGE systems are now used more commonly for separation of proteins.
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Polycarbonate A polyester formed by reacting phosgene and bisphenol A. It is a packaging material with high strength, rigidity, impact resistance and inertness to food components, used in reusable milk bottles. Polyethylene terephthalate (PET) A compound formed by low pressure melt polymerization of ethylene glycol and either dimethyl terephthalate or terephthalic acid. It is a high-clarity packaging material with high strength, and excellent gas barrier properties. Polymerase chain reaction (PCR) An in vitro laboratory procedure for detection of DNA that relies on the specificity of DNA–DNA hybridization with a pair of reagent primers for exponential amplification of product. The procedure can be designed to be extremely specific and sensitive. Polymerization The process by which many molecules are joined together to form a few larger ones. Polyestrous Term to describe a female animal that exhibits multiple estrous cycles continuously throughout the year or seasonally (i.e. seasonally polyestrous). Positive-displacement compressor A compressor that operates intermittently, subjecting the air to flow in the same direction as the pressure gradient since it has members that ensure positive admission and delivery of air, preventing undesired reflux. Distinction is made between reciprocating and rotating compressors, depending on the motion of the solid boundary. Preformed fatty acids Fatty acids in milk fat that originate from dietary lipids absorbed from the digestive tract and from mobilized body fat reserves. These fatty acids are greater than or equal to 16 carbons in length. Pregnancy toxemia A metabolic disorder of advanced pregnancy in ewes due to inadequate supply of glucose. Incomplete oxidation of body fat in the liver results in hyperketonemia and acidosis. Multiparous ewes and ewes carrying multiple fetuses are more susceptible to pregnancy toxemia that often causes death of the pregnant ewe, hence the alternative name ‘twin lamb disease’. Pressure head Pressure expressed in m of fluid height, i.e. the value of pressure in Pa divided by the density of the fluid in kg m3 and the acceleration of gravity (9.8 m s2). Pressure ratio (Pr) The ratio between the delivery air pressure of a compressor and the admission air pressure. Prevalence The existing cases of a disease in a specified population at a given point in time. Prevalence is a function of the incidence of a disease, and the mean duration of disease cases. Price support A government-set minimum producer price for a commodity. In the United States, the government is ready to purchase manufacturing milk products at a stated minimum price, thus
828 Glossary
ensuring that any commercial buyer of the manufactured products must pay a price at least as high as the government purchase price. Primary ripening The term often applied to the hydrolytic breakdown of milk proteins to small peptides and free amino acids and milk lipids free fatty acids. Also included in this term is the fermentation of milk lactose, usually to lactic acid. These compounds form the substrates for secondary ripening reactions. See also Secondary ripening. Probiotics Microorganisms, mostly bacteria, that beneficially infuence the host by improving its microbial balance. Well-documented health-related effects of probiotics are, for instance, alleviating symptoms of lactose intolerance, shortening the duration of rotavirus diarrhea and immune enhancement. Process water Water for general use and circulation within a processing unit. This will normally have been produced by appropriate treatment of ground or surface water (‘raw’ water). Processing adjustment factor (PAF) A factor used in the US National Research Council’s 2001 calculations that accounts for the effect that particle size, heat, and steam have on the digestibility of nonfiber carbohydrates. Producer nominal assistance coefficient The ratio of the Producer support estimate (PSE) and the total value of total gross farm receipts valued at world market prices, excluding budgetary support to producers. Producer support estimate (PSE) An indicator of the annual monetary value of gross transfers from consumers and taxpayers to agricultural producers, arising from policy measures. Progesterone A steroid hormone produced by the corpus luteum during the diestrous stage of the estrus cycle and pregnancy. Progesterone releasing intravaginal device (PRID) A silicon coil containing progesterone that is inserted intravaginally into cows and some other species for the purpose of synchronization of estrus. Protected fat Fat from sources specifically designed to resist biohydrogenation by ruminal microbes and modify fatty acid profile of body tissues and milk. Proteinase Enzyme that catalyses hydrolytic cleavage of the peptide bonds in proteins and large peptides. Proteolysis The enzymatic breakdown of protein to smaller peptides and, eventually, to amino acids. There are many different types of proteolytic enzymes (proteases and peptidases) that have different specificities, presenting difficulties in classification and consistency in nomenclature. Common generic names are proteinases (endopeptidases), aminopeptidases (exopeptidases with specificity for N-terminal residues of proteins and peptides), and carboxy-peptidases (exopeptidases with C-terminal specificity). Proteomics Study of the complete protein profile of cells or secretions.
Protocol A set of rules and formats that govern the way in which devices communicate with each other. Pseudoplastic Term used to describe fluids that exhibit decreasing viscosity with increasing shear rate. The term preferred now is shear-thinning. Psychrotropic bacteria Bacteria that are cold tolerant and can grow at refrigeration temperatures, with an optimum usually between 25 and 30 C and a maximum growth temperature of 35 C. Their growth rate is much reduced as the temperature approaches freezing. Puberty The acquisition of reproductive competence in morphologic, behavioral and endocrine terms such that the animal (individual) is capable of reproducing. Pulsed-field gel electrophoresis (PFGE) A gel electrophoresis method used to separate large DNA fragments (10–100 kb), frequently used to distinguish between bacterial strains. Pump A device that promotes the circulation of liquids between and through pieces of equipment. Pumping efficiency The ratio between the energy absorbed by the fluid in a pump and the energy used by the pump from the electricity supply. QlO value The fold change in a reaction rate with a 10 C alteration in temperature. Quarantine Isolation of newly purchased stock to limit the risk of spreading new diseases to the existing stock on the farm. Quarantined stock will usually have to undergo a series of agreed quarantine treatments set out in the flock health plan before being mixed with existing stock. Radiotelemetry Radio frequency data communications. Random amplified polymorphic DNA (RAPD) A technique that utilizes a single short synthetic primer (about 10 bp) of arbitrary sequence, serving as both forward and reverse primers, in a low stingency amplification reaction by the polymerase chain reaction (PCR) in order to generate anonymous DNA fragments from genomic DNA. Range The interval defined by the upper and lower limit of values of an input variable over which a device can be calibrated. Real-time Term pertaining to a data-processing system that controls an ongoing process and delivers its output or controls its inputs not later than the time these are needed for effective control. Recombined milk products Foods that are made by the rehydration of dry milk products and their subsequent processing with or without milk fat. Reconstitution Term used to describe the process of rehydration of dry milk products into water. Refrigerant The working fluid that flows inside a refrigeration system. Generally, it is designated by the letter, e.g. R, followed by a number, e.g. R-22, R-134a. Refrigeration vapor compression system A system designed to fulfill the aims of refrigeration. It is
Glossary
composed of two heat exchangers (one condenser and one evaporator), a compressor and an expansion valve. Rennet An extract from ruminant abomasa (fourth glandular stomach) containing the milk-clotting enzymes, chymosin and pepsin, in different proportions. Chymosin dominates in extracts from young ruminants (calf rennet). Rennet has been used for the coagulation of milk for cheese since time immemorial and most cheese varieties are produced by use of rennet. See also Chymosin. Reverse osmosis The pressure required to reverse the transport phenomenon (osmosis) that prevails when water migrates across a semipermeable membrane in order to equilibrate the osmotic effect created by solutes present in the solution on the other side of the barrier. Hence, it provides an opportunity to concentrate solutes by means of dewatering. Rheology Science of the flow or deformation of matter. Ribotyping A nucleic acid hybridization based identification system that uses probes complementary to ribosomal genes to identify the species or even provide subspecies strain information. Ricotta cheese A cheeselike product manufactured from whey by heating and separation of the coagulated protein paste from the deproteinated whey residue. Roasting A process used to reduce degradability of protein in a feed, consisting of exposing a feed to heat using a direct or indirect heat source for a fixed time. After heating, the feed is typically steeped for additional time to achieve the desired reduction in protein degradability. Rumen The largest of the forestomach compartments of the ruminant animal. Ingested forages and other feedstuffs enter the rumen from the esophagus and undergo fermentative digestion by the action of bacterial and protozoal enzymes, a process that permits utilization of cellulose which cannot be digested by endogenous digestive enzymes found in mammals. Products of this fermentative digestion are either absorbed by the rumen as volatile fatty acids or transported via the reticulum to the omasum, abomasum, and small intestines where additional digestive action occurs. Rumen degradable protein (RDP) The fraction of ingested protein that is degraded by microbes in the rumen. Rumen undegradable protein (RUP) The fraction of ingested protein that is not degraded in the rumen and passes intact to the abomasum providing amino acids directly from feed for absorption in the lower digestive tract. Rumen-active fat A fat supplement having the potential to interfere with microbial fermentation in the rumen and reduce feed digestibility when fed to dairy cattle or other ruminant species. Rumen-inert fat A commercial fat specifically designed to have little, if any, negative effects on feed digestibility when fed to dairy cattle or other ruminant species. Ruminally protected amino acids Free amino acids that have been encapsulated or coated with materials
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that will allow most of the amino acids to escape ruminal degradation. At present, commercial forms are limited to methionine. Selective use of ruminally protected amino acids and protein supplements allow dairy nutritionists to more adequately match the profile of absorbed amino acids with the profile as required by the animal. This increases the efficiency of use of absorbed amino acids for growth and milk protein production. Salmonellosis A disease caused by infection with Salmonella bacteria that may affect all animal species and humans. Secondary ripening The term often applied to the process by which the products of primary ripening, such as amino acids, fatty acids and lactic acid are converted into flavor compounds by a number of different enzyme (and chemical) reactions. See also Primary ripening. Sensing element Generic name for a device that detects either the absolute value of a physical quantity or a change in value of the quantity and converts the measurement into a useful input signal for an indicating or recording instrument. Also known as a primary detector. Sensitivity (process control) The input signal variation required to produce the minimum detectable output signal of a device. Sensitivity (animal health) The ability of a diagnostic assay to detect true cases of the target disease. An assay with a 65% sensitivity is known to identify a mean of 65% of the truly diseased individuals in a population. Lower assay sensitivities lead to higher probabilities of false-negative assay results. Sensor A generic name for a device composed of a sensing element and a transmitter, also termed measuring device. It is used in acquiring information on the current status of the process output variables. Serovar A strain of bacteria that has a characteristic antigenic structure that differs from other strains of a particular genus of bacteria. (e.g. Leptospira pomona and L. hardjo are serovars of Leptospira interogens). Shelf-life The predicted time at which a product will change from acceptable to unacceptable quality. It is infuenced by such factors as raw ingredient quality, processing conditions, packaging practices, and storage conditions. Typically, shelf-life is determined by a combination of microbial, sensory and chemical methods. Shubat A fermented product made from camels’ milk, produced mainly in Kazakhstan. It is of snow-white color. The fat content reaches 8%. It can be kept for some time without losing its properties. Silent ovulation Ovulation (release of the ovum) without the expression of estrous behavior. Soluble fiber Nonstarch polysaccharides not included with hemicellulose and cellulose in neutral detergent fiber. Not digestible by mammalian enzymes, they are typically readily fermented by microorganisms. Includes pectic substances and mixed linkage b-glucans.
830 Glossary
Soya bean A legume containing moderate concentrations of oil and protein. Meal is a byproduct produced on extraction of soya oil. Protein concentration is standardized through the addition of hulls. Span (in process control) The difference between the highest input value and the minimum input value set for a measurement device within its work range. Specificity of diagnosis The ability of a diagnostic assay to detect individuals that are truly free of the target disease. An assay that has a 60% specifcity will correctly identify a mean of 60% of the disease-free individuals in a population. The remaining mean 40% of disease-free individuals can be expected to have false-positive assay results. Spirochaete A type of long and slender bacterium, usually only a fraction of a micrometre in diameter but 5–500 mm long. They are tightly coiled, and so look like miniature springs or telephone cords. Members of this group are also unusual among bacteria for the arrangement of axial filaments, which are otherwise similar to bacterial flagella. These filaments run along the outside of the protoplasm, but inside an outer sheath; they enable the bacterium to move by rotating in place. Treponema is the only genus to lack the outer sheath. Spoilage Lowering of eating quality of food due to degradation by microbial, chemical or physical means. Spoiled food is generally not harmful to eat, but is of lower eating quality. Spontaneous recovery The ability of an animal to cure herself of an infection without the aid of therapy. Spores Metabolically inactive forms produced by bacteria that allow the cells to survive heat and other stresses. Fungi (yeasts and molds) produce spores as part of their sexual reproduction cycle and provide a means for the microorganism to disseminate in the environment. Fungal spores are not as heat-resistant as bacterial spores. Standardization A process by which a content of a specific component (protein, fat) is kept at a desired predetermined level in a final product, ingredient or material used in further processing. Starter Generally, an inoculum of microorganisms used to initiate (start) fermentation in the manufacture of fermented foods. In the manufacture of fermented milk products, a portion of the previous batch was traditionally used to seed the milk. Today, most large-scale manufacture relies on the use of pure cultures of defined or mixed strains. Either mesophilic (e.g. Lactococcus lactis) or thermophilic (e.g. Streptococcus thermophilus, Lactobacillus helveticus) starter cultures are added to milk, usually at high numbers and primarily to ferment lactose rapidly to lactic acid. See also Lactic acid bacteria. Steric A term used to describe any effect that is caused simply by a group physically getting in the way, rather than by any particular properties of the group.
Stocking rate The number of grazing animals per unit of pasture area. Stoichiometric air–fuel ratio (A/F)stoich Ratio between the theoretical air mass needed to completely burn a fuel and the fuel mass. Strain (in animals) The animal’s response to stress that usually represents a cost to the animal. The level of strain will vary from animal to animal. Infertility is a strain that is caused by the stress of high milk production in dairy cattle. Stressors may be environmental, physical, physiological or psychological. Stress see also Strain. Subsistence management The rearing of a small number of animals (such as goats) for family food. They may be kept in the family dwelling at night and are frequently tethered around the borders of fields, on road banks, or other limited grazing areas. Substitution rate The reduction of herbage intake associated with the intake of 100 g of a supplement (both in terms of dry matter). Subunit vaccines Vaccines generated by biotechnology and genetic engineering. They use only part of a bacterium or virus and produce a potent immune response without stirring up separate and potentially harmful immune reactions to the many antigens carried on a microbe. Sugars Low molecular carbohydrates, including monoand oligosaccharides, soluble in 80% ethanol. Typically rapidly fermented by ruminal microbes, they include glucose, fructose, sucrose, lactose, stachyose and raffinose. Superovulation Ovulation of an abnormally high number of ova as a result of exogenous administration of gonadotropins. Superovulation treatments are conducted mainly as part of embryo transfer programs. Supersaturation Saturation of a solution with a solute beyond the solubility of the solute. Syneresis The process by which a network of macromolecules or particles (gel or coagulum) contracts through the formation of new bonds and/or the rearrangement of existing inter-molecular or interparticle bonds, which results in the expression/exudation of serum, i.e. liquid phase. See also Gel, Coagulum. Taxonomy The study of the classification of organisms according to their similarities and differences. Teat canal keratin Protein deposit formed by the surface cells of the epithelium of the teat canal desquamating continuously. Keratin plays an important role in the prevention of mastitis. Teat-end callosity A change in teat-end tissue as a result of mechanical forces exerted by vacuum and the collapsing liner during machine-milking. Temperature-humidity index (THI) A single numerical rating of an environment based upon the temperature and humidity. It is often used to measure the degree of animal stress due to heat stress conditions. Equation is: THI ¼ (0.81 dry bulb temperature, C) þ (relative humidity (dry bulb temperature 14.4)) þ 46.
Glossary
Temperer A machine for crystallizing the fat in chocolate in the correct form. It operates by cooling to produce several different crystalline states. Heating and intense mixing are then used to remove all but the required stable form. Tempering (in casein manufacture) The process in which, after fluid-bed drying, in particular, the particles of warm casein are transferred between bins for a period of 8–24 h. This allows transfer of moisture from the larger, wetter particles to the smaller, drier particles, producing casein of uniform moisture ready for milling. Tetany A state of increased neuromuscular irritability caused by reduced serum magnesium concentrations and manifested by twitching of the extremities, intermittent muscular spasms, loss of consciousness and convulsions. Tetraploid A plant that contains four sets of individual chromosomes within a cell. This is double the more usual diploid two sets per cell. Tetraploids develop naturally or are induced by treating dividing diploid cells with colchicine. They will breed true, producing tetraploid offspring. Tetraploid cells are larger than diploid cells to accommodate the additional chromosomes. Thermization Process for heating milk with a heat load below pasteurization level before storage. The indigenous enzyme alkaline phosphatase is not fully inactivated but the result is that psychrotropic bacteria are practically killed without substantial denaturation of whey proteins. After storage, the milk is pasteurized before further processing. Thermoduric bacteria Bacteria that can survive exposure to temperatures higher than the maximum temperatures for their growth. In the dairy industry, the term refers to microorganisms that survive pasteurization but do not grow at pasteurization temperatures. Thermoneutral zone (TZ) The range of environmental temperatures in which normal body temperature is maintained and heat production is at the basal level. Thermophilic bacteria Bacteria that grow at elevated temperatures (55 C or higher) with an optimum temperature of about 60 C. Thermophilic starter A starter culture with an optimum temperature above about 40 C used for Swisstype cheeses and for yogurt. Thermophoresis Movement of substances due to a thermal gradient. Thixotropic Term used to describe materials exhibiting time-dependent shear-thinning, i.e. decreasing viscosity with time at a given shear rate. Total dissolved solids (TDS) The weight of solids in solution per unit volume of water, measured by evaporating a known volume of filtered solution and weighing the residue. See also Total solids. Total mixed ration (TMR) A feeding system in which all feed ingredients are blended together in specific proportions or amounts and offered to
831
dairy cattle as one feed resource. Also known as complete diet. Total potentially available nucleosides (TPAN) All potential sources available in milk for the generation of nucleosides via digestion and metabolism. Total solids (TS) The weight of all solids, dissolved or suspended, organic or inorganic, per unit volume of a liquid, measured by evaporating a known volume of the liquid and weighing the residue. See also Total dissolved solids. Total support estimate (TSE) An indicator of the annual monetary value of gross transfers from taxpayers and consumers to the agricultural sector, arising from policy measures that support agriculture. Total suspended solids (TSS) The measure of particulate matter suspended in a sample of water or wastewater. After filtering a sample of a known volume, the filter is dried and weighed to determine the residue retained. Transconjugant A strain that has acquired genetic information (and an associated trait) through the conjugal transfer of a plasmid or a transposon from a donor to a recipient cell. Transducer Any device or component that converts an input signal of one form to an output signal of another form. Devices such as sensing elements, transmitters and signal transducers are considered as transducers. Translucent color A semi-transparent appearance to cheese, i.e. allowing some light to penetrate. It is typically seen in reduced-fat cheeses. If translucent cheese is sliced very thin, shadows of objects can be seen behind the cheese. Transmitter (1) A transducer that responds to a measured variable by means of a sensing element and converts it to a standardized transmission signal, which is a function only of the measurement. (2) A device that converts a variable into a form suitable for transmission to another location. Ultrafiltration A membrane filtration process that separates components on the basis of molecular ‘sieving’. Macromolecular material, such as protein (and fat), is readily recovered as retentate from solutions such as whey, while lower molecular weight material (lactose, minerals, other solutes and water) permeate the membrane. Ultrafiltration operates at a much lower pressure than reverse osmosis and nanofiltration. Upper critical temperature The highest temperature at which the normal body temperature can be maintained without altering basal metabolic rate. Urticaria Hives, the itching weals that can come and go on the limbs and trunk, associated in some cases with allergy and the local release of histamine. Uterotonic agents Hormones that induce uterine (myometrial) contractions. For example, oxytocin is a potent uterotonic stimulant. Vector A living organism that transmits a pathogen and causes a disease.
832 Glossary
Ventilation A process of air exchange, which serves to dilute inside barn air and all of its components, many of which at high concentrations lead to animal health problems. Vernalization The process of exposing plants to low temperature for a defined period. Some plants require exposure to a period of low temperature before they will initiate flowering. Without the temperature stimulus, the plants remain vegetative. For example, winter cereals require vernalization to flower while spring cereals flower without a cold stimulus. Virial coefficients The coefficients in the second and higher-order terms of a virial equation. Such an equation consists of a limiting law as the first term with further terms added to account for effects ignored by the limiting law. For example, the virial equation for osmotic pressure is based on the van’t Hoff equation as the limiting law, and the coeffcient of the second term is called the second osmotic virial coeffcient. Viscoelastic Term used to describe materials exhibiting both liquid-like (viscous) and solid-like (elastic) properties. Vitamin An organic compound found in the nonenergetic part of food. They are essential for the normal functioning of the body. Vitamins are necessary for growth, vitality and general well-being. With few exceptions the body cannot synthesize vitamins, so they must be supplied by the diet. VO2max The level of exercise recorded when maximum oxygen uptake has occurred despite additional increases in exercise; VO2max indicates an individual’s capacity for aerobically resynthesizing ATP. Exercise performed above VO2max can only take place by energy transfer predominantly from anaerobic glycolysis with lactate formation. Voltammetry A group of widely used electrochemical techniques, where the current flowing through an electrochemical cell is measured as a function of the applied potential. Examples of this kind of technique are polarography, amperometry and cyclic voltammetry. Volumetric effciency (hv) A measure of the decrease in compressor flow rate, given by the ratio between the free air delivery and the piston displacement per unit of time. Warm housing A system of housing for cattle in which barns are well insulated and, by necessity, have a well-controlled ventilation system. These barns are designed to provide a relatively uniform environment throughout the winter. Tie-stall dairy barns are an example. Ventilation must be regulated to compensate for changing outside climatic conditions. Water activity (aw) The ratio of water vapor pressure in a system to that of pure water at the same temperature.
Water absorption (farinograph method) The amount of water absorbed during a standard test, using an instrument called farinograph. The product under test (such as milk protein coprecipitate) is added to a standard formula consisting of a standard four and water. Water hardness A term describing the inability of some waters to rinse clean natural fibers of oil and fatty substances. Hardness of water is caused by large concentrations of calcium, magnesium and other multivalent metallic ions. A hard water reduces the effects of detergents, because it forms precipitates with the soap and forms troublesome scales on heating equipment. Wet chemistry (1) Chemistry involving the use of water and/or other solvents. (2) Classical gravimetric, titrimetric or colorimetric analysis. Whey Liquid phase of milk that remains after removal of fat and casein; also, The liquid byproduct of cheesemaking or manufacture of industrial casein products. Whey beverage Any whey-based drink prepared from liquid whey or whey permeate, usually sweetened and containing fruit juices or other compatible ingredients. Whey protein nitrogen index (WPNI) An index used as a means to classify milk powders as low, medium and high heat milk powders, based on the reduction in solubility of whey proteins due to heat denaturation. Whipping cream A typical cream product that has a fat content of 30–40% and is processed without (or with low-pressure) homogenization. Originally, it required no complicated preparation, just careful handling before whipping. The demand for a considerable prolongation of shelf-life may lead to the demands for a premium product with a unique flavour. World trade organization (WTO) An organization established in 1995 as the successor to the General Agreement on Tariffs and Trade (GATT). It aims to ensure the development of a nondiscriminating, smooth, predictable, and free trade between member countries. The WTO evolves around trade negotiations between the 144 member countries. z value the change in temperature (in degrees Celsius) required to bring about a one log (i.e. tenfold) change in the D value. See also D value. Zabady A traditional plain set yogurt, which is made mainly from nonhomogenized buffaloes’ milk. It is characterized by a surface skin high-fat top layer and cooked flavour. Zabady from the previous batch is usually used as starter. Zoonosis An infectious disease of animals that can be transmitted to humans under natural conditions. Also known as zoonotic disease.
INDEX NOTES: Cross-reference terms in italics are general cross-references, or refer to subentry terms within the main entry (the main entry is not repeated to save space). Readers are also advised to refer to the end of each article for additional cross-references – not all of these cross-references have been included in the index cross-references. The index is arranged in set-out style with a maximum of three levels of heading. Major discussion of a subject is indicated by bold page numbers. Page numbers suffixed by t and f refer to Tables and Figures respectively. vs. indicates a comparison. This index is in letter-by-letter order, whereby hyphens and spaces within index headings are ignored in the alphabetization. For example, ‘milk protein’ is alphabetized after ‘milking’. Prefixes and terms in parentheses are excluded from the initial alphabetization. Where index subentries and sub-subentries pertaining to a subject have the same page number, they have been listed to indicate the comprehensiveness of the text. ABBREVIATIONS: HPLC – high-performance liquid chromatography LAB – lactic acid bacteria NMR – nuclear magnetic resonance NSLAB – non-starter lactic acid bacteria PAGE – polyacrylamide gel electrophoresis PCR – polymerase chain reaction
A AACE (amino acid-converting enzymes), Dutch-type cheese, 1: 724 ABBOS peptide, 3: 1047 ABC yogurt, 1: 388 Abomasal displacement see Displaced abomasum Abomasal volvulus (AV) clinical signs, 2: 214 diagnosis, 2: 214 prevalence, 2: 212 shock, 2: 214 see also Displaced abomasum Abomasum, protein digestion, 3: 993 Abondance cattle, 1: 293–294 Abortion bluetongue virus infection, 2: 149–150 brucellosis cattle, 2: 154, 2: 155, 4: 34–35 sheep, 2: 154 Coxiella burnetii infection, 4: 55 goat, 2: 840 leptospirosis, 2: 181–182 listeriosis goats, 2: 186 sheep, 2: 185–186 ‘Abortion storms’, brucellosis, 2: 154 Abortive infection (Abi) bacteriophages, 1: 436 Lactococcus lactis, 3: 135 Abscesses, contagious see Caseous lymphadenitis (CLA) Absolute supersaturation, 3: 185 Absorption laws, spectroscopy, 1: 113 ABT yogurt, 1: 390 AB yogurt, 1: 388 Acaricides, tick-borne diseases, 2: 256–257
Accelerated cheese ripening, 1: 565, 1: 795–798 adjunct cultures, 1: 796 freeze-shocked, 1: 797, 1: 797t heat-shocked, 1: 797, 1: 797t mutants, 1: 797 NSLAB, 1: 796 spray-drying, 1: 797 definition, 1: 795 entrapped enzymes, 1: 796 capsules, 1: 796 cell-free extracts, 1: 796 liposomes, 1: 796 enzyme addition, 1: 796 lipases, 1: 796 method, 1: 796 proteinases, 1: 796 flavor enhancement strategies, 1: 795 elevated ripening temperature, 1: 795 slurry systems, 1: 795 future perspectives, 1: 798 genetically modified lactic cultures, 1: 797 proteinases, 2: 291 pulse electric fields, 1: 797 starter cultures, 1: 565 Accelerated lambing, 2: 71 Accelerated solvent extraction, fatty acids, 3: 698 Acceptable daily intake (ADI), 4: 535 accumulation, 1: 56 additive safety see Food additive safety benchmark dose approach, 1: 56 caseinates, 3: 863 definition, 3: 863 nitrates, 1: 908 nitrites, 1: 908 Accuracy, analytical methods, 3: 742 ACE (angiotensin-converting enzyme), 3: 796–797
Acetaldehyde, 3: 169 antimicrobial properties, 1: 420 flavor formation, 3: 169 ‘green flavor’, 2: 492, 2: 535, 3: 170 Leuconostoc, 3: 141 Acetaldehyde-TPP, 3: 168 Acetate de novo fatty acid synthesis, 3: 655 equine milk, 1: 360 flavor formation, 3: 169 Swiss-type cheese, 1: 408 humans, functions, 4: 368 ketosis, 2: 234 milk fat synthesis, 3: 352–353 Acetic acid Bifidobacterium, 1: 384 cheese preacidification, 1: 550 equine milk, 1: 360 Propionibacterium pathways, 1: 406 Swiss-type cheeses, 1: 408 Acetoin, 3: 169 -Acetolactate, 3: 168 -Acetolactate decarboxylase (ALDB), 3: 170, 3: 171f inactivation, 3: 170 -Acetolactate synthase (ALS), 3: 168 Acetonemia see Ketosis N-Acetyl- -D-glucosaminidase (NAGase) see N-Acetyl- -D-glucosaminidase (NAGase) (under N’s) Acetyl coenzyme A (acetyl-CoA) aflatoxin biosynthesis, 4: 801–802 ketones, 2: 235 N-Acetyl-D-glucosamine-containing saccharides, Bifidobacterium, 1: 384–385 N-Acetylglucosamine, 3: 253f, 3: 258 N-Acetylneuraminic acid see Sialic acid Achondroplasia (bulldog), 2: 676, 2: 676f
833
834 Index Acid–base balance, diet effects, 2: 356 Acid casein acidification, 3: 855 processes, 3: 855, 3: 856f cheese analogues, 1: 817 Codex standard, 3: 861t composition, 3: 858t manufacture, 2: 126, 3: 855 blending, 3: 857 cooking/acidulation, 3: 855, 3: 856f cooling, 3: 857 dewatering, 3: 857 dewheying, 3: 857 drying, 3: 856f, 3: 857 milling, 3: 857 packing, 3: 857 sifting, 3: 857 tempering, 3: 857 washing, 3: 856f, 3: 857 physical properties, 3: 858t Acid-coagulated cheeses, 1: 698–705 byproducts, 1: 705 chemical composition, 1: 700t classification, 1: 540–542 coagulation mechanisms, 1: 698 k-casein, 1: 698 colloidal calcium phosphate, 1: 698 heat treatment, 1: 698–699 rennet addition, 1: 699 flavor, 1: 698 manufacture, 1: 698, 1: 699f rennets, milk coagulation vs., 1: 579 whey incorporation, 1: 698 see also specific cheeses Acid coagulation, whey processing, 4: 731 Acid-curd cheeses, 1: 753 aroma development, 1: 764 deacidification, 1: 761, 1: 761f dry salting, 1: 754 microbiology, 1: 757t, 1: 758 starter cultures, 4: 751 yeasts, 4: 749–750 see also individual cheeses Acid degree value (ADV), raw milk, 3: 645 Acid detergent fiber (ADF), 3: 985 digestible energy estimation, 2: 404, 2: 405t ruminal acidosis, 2: 202 Acid extraction, milk salts, 3: 913–914 Acid/heat-coagulated cheeses, 1: 704 see also individual cheeses Acidification cheese analogues, 1: 815t cheese manufacture see Cheese manufacture control, starter cultures, 1: 440 direct see Direct acidification fast, 3: 911–912 low-moisture part-skim mozzarella (pizza cheese), 1: 737–738, 1: 739f, 1: 739f milk salts equilibria, 3: 911 milks/cream rheology, 4: 523 slow, 3: 911–912 Acidified boiling water, milking hygiene, 3: 634 Acid-induced milk gel, 3: 482 Acidogenic diets, 2: 361t calcium supplementation and, 2: 360 ionized blood calcium, 2: 358 milk fever prevention, 2: 357 Acidophilus milk, 2: 473, 3: 93–94, 3: 94 Acidophilus-yeast milk, 2: 474 Acidosis, 2: 425 dietary carbohydrate, 2: 335, 2: 786 infants, 2: 515 replacements, 4: 419 see also Laminitis; Ruminal acidosis Acid phosphatase (ACP) activity, 2: 317 characterization, 2: 317 isolation, 2: 317
origin, 2: 317 significance, 2: 318 stability in milk, 2: 317 Acid rinse, 3: 634 Acid-soluble nitrogen (ASN), 1: 777–778, 1: 779f Acid stress LAB, 3: 63, 3: 65f Propionibacterium, 1: 407 Acidulation vat, 3: 856–857 Acid whey, 1: 705, 4: 731 composition, 4: 731, 4: 732t definition, 3: 873 Acoustic impedance, 3: 470 Acoustics, 3: 470 Actinomyces, 3: 451 Activated sludge process, 4: 622, 4: 623f aeration tank configurations, 4: 623–624 design parameters, 4: 623, 4: 624f, 4: 624f food:mass (F/M) ratio, 4: 623, 4: 624f operating principles, 4: 623 Active (smart) packaging, 4: 22 Active safety feature, 4: 281–282 Acute carbohydrate engorgement see Ruminal acidosis Acute toxicity tests, additive safety, 1: 58 Additive model, 4: 721t Additives see Food additives Adenosylcobalamin, 3: 1000 Adhesins Enterococcus, 3: 156 Staphylococcus aureus, 4: 105, 4: 106f Adhesive hard-sphere (AHS) theory milks/cream rheology, 4: 522, 4: 523 rennet milk coagulation, 1: 580 Adhesiveness, 1: 265t Adhesive sphere model of rennet-induced gelation, 3: 778 Ad Hoc International Government Task Forces, 4: 314 ADI see Acceptable daily intake (ADI) Adipophilin (ADPH), 3: 374, 3: 680, 3: 688 functions, 3: 688 lactation, 2: 325–326 milk fat globule membrane, 3: 688 milk lipid droplet formation, 3: 374 structure, 3: 686f, 3: 688 Adipose differentiation-related protein (ADRP) see Adipophilin (ADPH) Adipose tissue, somatotropin effects, 3: 26 Adjunct cultures accelerated cheese ripening see Accelerated cheese ripening Enterococcus, 3: 157 flavor-enhancing, 1: 555 low-fat cheese flavor, 1: 840 NSLAB see Non-starter lactic acid bacteria (NSLAB) Pediococcus, 3: 151 Admittance (impedance) spectroscopy, electrical conductivity, 3: 471 Adolescents, vitamin deficiencies, 4: 638 Adrenal corticotrophic hormone (ACTH), 4: 505 -Adrenergic agonists, 1: 893 ADSA see American Dairy Science Association (ADSA) Adsorbable organic halogen (AOX), 4: 613, 4: 614t Adsorption bacteriophages, 1: 433–434 inhibition bacteriophages, 1: 435 lactococci, 3: 135 Adulteration freezing point, 1: 251 milk powder detection, fresh milk, 3: 233 Advanced glycation end products (AGEs) biological role, 3: 1068 3-DG-derived, 3: 1073 lysinoalanine degradation, 3: 1073, 3: 1073t Maillard reaction, 3: 1068 Adventitious non-starter lactic acid bacteria, 3: 161
Aerated emulsions, 1: 71 Aerobic mesophiles,raw milk, 3: 645 Aeromonas, 3: 450 Aerosols, whipping cream, 1: 924 AES (atomic emission spectrometry), 1: 141 AFB1-8,9-epoxide, 4: 803 Affinity column chromatography, milk oligosaccharides, 3: 249 Affymetrix GeneChips, 3: 346–347 Aflatoxicosis, acute cattle, 4: 804 humans, 4: 805 Aflatoxin(s) (AFs), 4: 793, 4: 801–811 acute toxicity, animals, 4: 802, 4: 803t biosensors, 1: 242 biosynthesis, 4: 801 carcinogenicity, 4: 803 carcinogenic potency, 4: 803 cattle, effects on, 4: 804 cheese, 4: 782–783 chemical properties, 4: 801 congeners, 4: 792–793, 4: 793f in dairy products, 4: 807, 4: 809t degradation, 4: 808 lactoperoxidase system, 2: 323 determination, 4: 806 confirmation, 4: 806 detection, 4: 806 extraction, 4: 806 purification, 4: 806 sampling, 4: 806 standards, 4: 806 fluorescence intensity, 4: 806 food, elimination from, 4: 808 food contamination, 4: 807, 4: 807t, 4: 808f dairy products, 4: 807, 4: 809t food detoxification, 4: 808 foodstuff contamination, 4: 807 fungi-producing, 4: 801 humans, effects on, 4: 805 acute toxicity, 4: 805 cancer, 4: 805 hydroxylated metabolites, 4: 801 metabolism, 4: 803, 4: 804f mutagenicity, 4: 802 oxygen concentration, 4: 801 peanut meal, 2: 353 production favoring conditions, 4: 801 raw milk screening, 3: 645 regulation, 4: 805 maximum permitted levels, 4: 805, 4: 805t structure, 4: 801, 4: 802f structure-activity relationship, 4: 802 toxicity mechanism, 4: 803, 4: 804f Aflatoxin B1 (AFB1), 1: 904t, 4: 785 acute toxicity, animals, 4: 802, 4: 803t biosynthesis, 4: 801–802 carcinogenicity, 4: 803 as contaminant, 1: 904 dihydrobisfuran moiety and carcinogenicity, 4: 792–793, 4: 794f food, maximum permitted levels, 4: 805, 4: 806t metabolic pathways, 4: 803, 4: 804f mutagenicity, 4: 802 structure, 4: 792–793, 4: 793f, 4: 801, 4: 804f toxicity mechanism, 4: 803, 4: 804f Aflatoxin B2 (AFB2), 4: 801, 4: 804f Aflatoxin G group, 4: 801 Aflatoxin M1 (AFM1), 1: 904t, 4: 785, 4: 801 as contaminant, 1: 903 in dairy products, 4: 807, 4: 809t immunodetection, 1: 180–182 infant food limits, 4: 785 Aflatoxin M group, 4: 801 Aflatrem, 4: 797f, 4: 797–798 AFLPs (amplified fragment length polymorphisms), 1: 222 AFM (atomic force microscopy), 1: 229, 1: 229f
Index Africa Bos taurus breeds, 1: 298 cattle management see Cattle husbandry (Africa) goats, 1: 322 African elephant milk oligosaccharides, 3: 271t African wild ass (Equus africanus), 3: 518 Afuega’l Pitu cheese, 1: 787 Agar,dairy desserts, 2: 909t Agar dilution reference method, Campylobacter, 4: 43 Agar gel immunodiffusion assay (AGID) bluetongue virus, 2: 150 Johne’s disease, 2: 177 Age at first calving, 4: 410 breed differences, 4: 410 costs associated, 4: 410 definition, 4: 410 optimum, 4: 390 reduction in, 4: 411 future research, 4: 408 Age gelation concentration effects, 1: 231 sterilized milk products see Sterilized milk products sweetened condensed milk, 1: 872 Agenda 2000, 4: 298 Agglomeration, dairy powders, 4: 710 Aggregate genotype definition, 2: 656 economic factors, 2: 658 empirical constraints/changes, 2: 659, 2: 659 practical constraints/changes, 2: 659, 2: 659 trait choice, 2: 656, 2: 657t trait weighting, 2: 656, 2: 657t Aggregate measures of support (AMS), 4: 345 reduction avoidance, 4: 347–348 Aggregation substance (Agg), Enterococcus, 3: 156 AGID see Agar gel immunodiffusion assay (AGID) Agitated film evaporator, 4: 202 Agitation, milk concentrates, 4: 165 Agitators, 4: 160–165 applications, 4: 164 cream storage, 4: 165 on farm, 4: 164 milk intake, 4: 165 powder dispersion, 4: 165 processed cheese, 4: 165 belt drive, 4: 161 construction material, 4: 162–163 dimensions, 4: 163 direct drive system, 4: 161–162 drive shaft, 4: 162 electric motor, 4: 161 gearbox, 4: 161 heat transfer, 4: 164 hygienic design, 4: 162 mechanical design, 4: 161, 4: 162f power requirements, 4: 163, 4: 164f power transfer unit, 4: 161–162 sealing, 4: 162 selection, viscosity and, 4: 163, 4: 163, 4: 163t speed, 4: 163 surface finish, 4: 163 types, 4: 160 vortexing, 4: 164 see also individual types Agreement on Technical Barriers to Trade (TBT), 4: 317, 4: 318f, 4: 341 Agreement on the Application of Sanitary and Phytosanitary Measures (SPS), 4: 316, 4: 317f, 4: 341, 4: 532, 4: 536 acceptable level of protection, 4: 536 Codex Alimentarius as standard-setting reference, 4: 341 government’s rights, 4: 536 Agreement on Trade-Related Aspects of Intellectual Property Rights (TRIPS Agreement), 1: 843 Agribusiness, 2: 4 Agricultural Act (1949), US, 4: 302–303
Agricultural Agreement, 4: 341, 4: 345 aggregated measurement of support, 4: 342, 4: 345 blue box subsidies/supports, 4: 343, 4: 343 decoupled support, 4: 343 export subsidies, 4: 343, 4: 345 imports, 4: 343 market access, 4: 343 minimum import access, 4: 343 numerical targets, 4: 345–346, 4: 346t support reductions, 4: 341t trade disputes, 4: 342 traffic-light model, 4: 342 Agricultural and Food Research Council (AFRC) nutritional requirement models, 2: 424, 2: 427 phosphorus requirement recommendations, 2: 375 Agricultural contaminants see Contaminants Agricultural policy coupled support, 4: 289 decoupled income subsidy, 4: 291 decoupled support, 4: 289 deficiency payments, 4: 287 developed countries, 4: 286 development, 4: 286 direct subsidy, 4: 291 direct support coupled with other factors, 4: 287 future developments, 4: 292 high price systems, 4: 287 agricultural sector competition conditions, 4: 289 border protection, 4: 289 consequences of, 4: 289 consumption composition, 4: 290 food industry competition, 4: 289 food industry conditions, 4: 289 high consumer prices, 4: 288 import tariffs, 4: 287 production, 4: 291 productivity development, 4: 291 sales prices, 4: 291 society income distribution, 4: 290 state expenses, 4: 290 structure, 4: 289f support, 4: 287 indirect subsidy, 4: 291 instruments, 4: 286 groups, 4: 287 low price systems, 4: 287 agricultural sector competition conditions, 4: 289 consumption composition, 4: 290 decoupled payments, 4: 291 production, 4: 291 productivity development, 4: 291 society income distribution, 4: 290 state expenses, 4: 290 structure, 4: 289f support, 4: 287 taxpayers finance, 4: 289 market price support, 4: 287 net import countries, 4: 290 objectives, 4: 286 price support, 4: 287 price systems, 4: 286–294 schemes, 4: 306–311 nongovernmental organizations, 2: 95, 2: 96, 2: 97 see also individual schemes self-sufficiency, 4: 290 support coupled to input factors, 4: 287 support fully decoupled from production, 4: 287 support systems, 4: 286–294 Agricultural Research Council (ARC) nutritional requirement models see Agricultural and Food Research Council (AFRC) Agricultural shows, 2: 799 Agricultural support changes, 4: 287, 4: 288f composition, 4: 288f definition, 4: 286 level, 4: 288f AhrC gene, 3: 63–64
835
AHS see Adhesive hard-sphere (AHS) theory AICs see Artificial insemination centers (AICs) Air compressed see Compressed air moisture-holding capacity, 4: 556–557, 4: 557f quality see Air quality sterile supply, starter culture protection, 1: 441 Airag, 2: 510 Air agitation, 4: 161 Air blow valves, 4: 158, 4: 158f Air compressors admission stroke air temperature rises, 4: 606 admission valve pressure drop, 4: 606 classification, 4: 602, 4: 603t clearance volumes, 4: 605f, 4: 606 continuous motor operation control mode, 4: 608 control techniques, basic, 4: 607 discharge valve pressure drop, 4: 606 energy sources, 4: 602 flow rate control, 4: 607 flow rate losses, 4: 606 on/off control, 4: 607 ‘Air Emissions from Animal Feeding Operations’, 3: 397 Air filters Enterobacter contamination, 4: 79 spoilage mold control, 4: 781–782 Air flotation systems, 4: 634 Air Pollution Control Act (1955), 3: 396 Air puff technique, curd strength measurement, 1: 587 Air quality, 3: 396 agricultural regulation, 3: 397 current focus, 3: 397 definition, 4: 555 issues, 3: 397 future implications, 3: 398 odor, 3: 397 regulatory history, US, 3: 396 relative humidity, 4: 556 Air Quality Act (1967), 3: 396 Air sterilization, starter culture protection, 1: 442–443 Air-water vapor relationship, 4: 556 ALARP (As Low As Reasonably Practicable) criteria, 4: 281 Alcaligenes, 3: 453 Alcohol(s) blood cholesterol levels, 3: 731 blue mold cheese aroma, 1: 772 cheese flavor, 1: 681 heat stability, milk, 2: 746–747 yak milk, 1: 350 see also individual compounds Alcoholic beverages nisin applications, 1: 424 yak milk, 1: 350 Aldehydes aliphatic, milk fat flavor, 3: 652 cheese flavor, 1: 682 see also individual compounds Aldose reductase, 3: 1051 ALF (Association Laitiere Francaise), 2: 103 Alfa Laval, 1: 622–623 Alfa Laval OST I vat, 1: 608 Alfa Laval OST II vat, 1: 608 Alfa Laval OST III vat, 1: 609f Alfa Laval OST IV vat, 1: 608, 1: 609f Alfalfa see Lucerne Alfatoxicol (AFL)-I, 4: 801 Alfomatic cheesemaker, 1: 610f Algebraic reconstruction technique (ART), ultrasound, 1: 213 Alginates applications, 1: 70t dairy desserts, 2: 909t Al-Hmor camels, 1: 352 Alicaligenes flavor defects, 4: 387 growth, refrigeration temperatures, 4: 384, 4: 386t
836 Index Alkaline detergents, milking hygiene, 3: 634 Alkaline phosphatase (ALP) activity, 2: 316 activity determination AOAC methods, 2: 316 International Dairy Federation methods, 2: 316 characterization, 2: 314, 2: 315t heat treatment reactivation, 2: 316 mechanism, 2: 317 isolation, 2: 314, 2: 315t mammalian milk, 2: 314 origin, 2: 314, 2: 315t pasteurization testing, 2: 314, 2: 315, 3: 275, 4: 198–199 automation, 2: 316 limitations, 2: 315, 2: 317 standard determination methods, 2: 316 significance of, 2: 315 study methods, 2: 316 Alkalinization, milk salt equilibria, 3: 912 Al-Khawar camels, 1: 352 Alkoxy radical, 3: 716 Allantois, 4: 486–487 Allergen(s) biosensors, 1: 242 definition, 3: 1041 food, immunochemical detection, 1: 179 Allergenicity, equine milk, 1: 363 Allergic reactions, 3: 1041 Allergic tests, brucellosis, 4: 37 Allergy definition, 3: 1041 ingredient declaration regulations, 3: 5 -lactoglobulin, Maillard reaction enhanced, 3: 234 milk see Milk allergy (MA) see also Lactose intolerance Al-Majaim Al-Arabia camels, 1: 352 Alpaca, 1: 351 colostrum composition, 3: 536t milk, 3: 536 composition, 3: 536t seasonal breeding, 4: 446 species, 3: 536 Alpha Dairy Power Plant, 1: 6 Alpha Tocopherol, Beta Carotene Cancer Prevention Study, saturated fatty acid-coronary heart disease relationship, 3: 1024–1026 Alpine goats, 1: 311t, 1: 312, 1: 313f, 2: 64–65 Alpine yak, 1: 345 Al-Shameya camels, 1: 352 ‘Alternative cheesemaking concepts’, 1: 617 Alternative ligands, biosensors, 1: 236 Alternative pulsation, goat milking, 2: 808–809 Al-Tibawi, 1: 352 Al-Tilal camels, 1: 352 Altrenogest, mares, 4: 444 Aluminum,dairy plant use, 4: 137 Alveoli, mammary gland, 3: 331, 3: 332f, 3: 339f development, 3: 338 epithelial cells, 3: 331–332, 3: 332f involution, 3: 343, 3: 344f lactation, 3: 15, 3: 16f structural changes, 3: 17, 3: 17f mid-gestation, 3: 16–17 Alzheimer’s disease, 4: 659 Amadori compounds enolization derivatives, 3: 223, 3: 224t low-molecular-mass chromophores, 3: 224–225, 3: 225f glycosylamine rearrangement, 3: 217, 3: 219f American Blue cheese, 1: 31 American Dairy Science Association (ADSA), 2: 101 casein nomenclature, 3: 765–766 milk off-flavor categories, 3: 277–278 sensory evaluation, 1: 279–280 American Dietetic Association,fat replacer advice, 1: 528
American Society of Mechanical Engineers (ASME) Bio-Processing Equipment (BPE) Code, 4: 134 Amido black milk protein analysis, 3: 744–745 PAGE, 1: 185–186 Amine(s) cheese flavor, 1: 682 intoxication, 3: 130 see also individual compounds Amino acid(s) absorption, 2: 413 casein effects, 3: 1006–1007 analysis biosensors, 1: 242 ion-exchange chromatography, 1: 170 bioavailability, 3: 816 blue mold cheese aroma, 1: 771–772 catabolism Cheddar cheese ripening, 1: 709 cheese ripening, 1: 673, 1: 673f starter cultures, 1: 562 cysteine-generated off-flavors, 2: 547 dairy cow nutrition, 2: 461–462 deamidation, 3: 1069 degradation, Dutch-type cheeses, 1: 724 digestibility, humans, 3: 816, 3: 817t donkey milk, 1: 368 essential, 2: 389, 2: 390t humans, 3: 818 feeds, 2: 413 fetal requirements, 2: 246–247, 2: 247t goat milk, 3: 486, 3: 487t human milk, 3: 581–582, 3: 582t, 3: 584, 3: 625, 3: 626t, 3: 627t indispensable, 3: 817, 3: 818t LAB requirements, 3: 49 membrane transport, 3: 53 limiting types, 2: 389 milk production requirements, 2: 413 milk protein synthesis limiting, 3: 40 nutritional classification, 3: 818t nutritional descriptive systems, 2: 425, 2: 427 posttranslational modification, 3: 1056–1057 primate milk, 3: 625, 3: 626t, 3: 627t reactions with sugars (Maillard reactions) see Maillard reactions reindeer milk, 1: 377t ruminally protected feed supplements see Ruminally protected amino acids small intestine supply, 2: 413 sources, ruminants, 2: 389 see also specific amino acids Amino acid-based formula, 3: 1043 Amino acid-converting enzymes (AACEs), Dutchtype cheeses, 1: 724 Amino acid lyases, 3: 87–88 Aminopeptidase(s) Brevibacterium linens, 1: 570 enzyme-modified cheese, 1: 802–803 Geotrichum candidum, 1: 568 propionibacteria, 1: 571 Aminopeptidase P (PepP), 3: 87 AminoShare, 2: 392 Aminotransferase, Lactobacillus, 3: 87–88 AMIX process, butter manufacture, 1: 498 Ammonia anhydrous, safety risks, 4: 277 magnesium absorption, 3: 997–998 manure, stabilization, 4: 635 surface mold-ripened cheese ripening, 1: 778, 1: 779f Amnion, 4: 486–487 Amperometry, 1: 194 biosensors, 1: 196 Ampicillin-resistant Enterococcus, 3: 155 Amplified fragment length polymorphisms (AFLPs), 1: 222 AM-PM plan,milk recording, 2: 650
-Amylase, 2: 332 human milk, 2: 332 purification, 2: 332 -Amylase, 2: 333 camel milk, 2: 333 Amylase(s), 2: 332 pancreatic, 3: 991–992 Amyotrophic lateral sclerosis (ALS), 3: 796 Anaerobic digesters grease residues, 4: 634 oil residues, 4: 634 Anaerobic ponds, 4: 632–633 Anaerobic waste lagoons, 3: 393–394 potassium sequestration, 3: 401–402 Analog-to-digital signal conversion, 4: 238 control action, 4: 240 data acquisition, 4: 235f, 4: 239 Analysis of covariance (ANCOVA), 1: 103 Analysis of variance (ANOVA), 4: 268, 4: 269f multivariate statistical tools, 1: 101, 1: 102 Analytical protein chemistry see Proteomic analysis Anaphylactic shock, 3: 1041 ANCOVA (analysis of covariance), 1: 103 Androgens, in milk, 2: 770 Androstenedione, 4: 505 Anestrus, 4: 576–577, 4: 577–578 Angelin cattle, 1: 295–296 Angiogenin(s), 3: 795 osteoclast-mediated bone resorption, 3: 796 Angiogenin 1 (ANG-1), 3: 796, 3: 796t Angiogenin 2 (ANG-2), 3: 796, 3: 796t Angiotensin-converting enzyme (ACE), 3: 796–797 Angiotensin-converting enzyme (ACE) inhibitory peptides, 3: 796, 3: 879–880, 3: 1062 Angiotensin I-converting enzyme (ACEI), 3: 879–880, 3: 1064 Anglo-Nubian goats, 1: 311t, 1: 314, 1: 314f Anhydrous ammonia, 4: 277 Anhydrous milk fat (AMF), 1: 515–521 antioxidant addition, 1: 516–517 applications, 1: 517 cholesterol removal, 3: 736 crystallization, 1: 516, 1: 520 export, 1: 515 fractionation, 1: 516, 1: 520, 1: 520f historical aspects, 1: 15, 1: 515 lipid oxidation, 1: 516–517 lipolytic defects, 3: 724 manufacture, 4: 179 direct-from-cream process, 4: 179 separators, 4: 172 sweet cream butter, 4: 179 manufacture from butter, 1: 519, 1: 520f heating, 1: 519 separation, 1: 519 manufacture from cream, 1: 518, 1: 519f neutralization, 1: 518–519 polishing, 1: 518–519 manufacturing technology, 1: 518, 1: 518f melting point, 1: 516 milk chocolate, 1: 859 olein fraction, 1: 520–521 packaging, 1: 521 product characteristics, 1: 516 rancid flavor, 1: 516 stearin fraction, 1: 520–521 unpleasant off-flavors, 1: 516 see also Ghee Animal(s) domestication, 3: 459 see also individual types of animals Animal experimentation additive safety, 1: 59 type 1 diabetes, 3: 1047 Animal feeds see Feed/feedstuffs Animal identification, 1: 486 collars, 2: 832, 2: 832f ear tags, 2: 649, 2: 832, 2: 832f
Index international, 1: 486, 2: 649 milking parlors, 3: 963 necklaces, 2: 832, 2: 832f permanent, 1: 486 systems, 2: 649 tattooing, 2: 832 temporary, 1: 486 Animal lipases, enzyme-modified cheese, 1: 803 Animal models genetic evaluation, 2: 651 human disease, transgenic animals, 2: 641 Animal products, used in feed, 2: 343, 2: 344t, 2: 345 fatty acid composition, 2: 363, 2: 364t Animal protection, 4: 727 Animal Protection Act (1988), Sweden, 4: 729 Animal rennet, 2: 289 Animal rights philosophy, 4: 727 Animal science programs, 2: 6–7 Animal welfare, 4: 727–730 activists, 4: 727 dairy cattle, 4: 728 definition, 4: 727 legal aspects, 4: 729 management issues, 4: 728 philosophers, 4: 727 policy, 4: 729 political action, 4: 727 phases, 4: 727 public awareness/concerns, 2: 679, 2: 685 predator control resistance, 2: 845–846, 2: 846 public policy, 4: 727 Animal welfarist, 4: 727 Anionic-active emulsifiers, 1: 63 Anionic diet, prepartum dairy cow, 4: 518t Anionic salts, 2: 356–362 oral dosing, 2: 361 standard salts, 2: 359–360 Anion supplementation, 2: 359 dry matter intake reduction, 2: 359 equivalent weights, 2: 359, 2: 359t magnesium and, 2: 360 sources, 2: 359 ANNs see Artificial neural networks (ANNs) Annual forage and pasture crops, 2: 552–562, 2: 563–575 brassicas, 2: 560, 2: 566 antinutritional problems, 2: 574 clovers, 2: 558 cool season grasses, 2: 555, 2: 565, 2: 574 cost-effectiveness and use strategies, 2: 552, 2: 563 farm production planning and analysis, 2: 563 management planning issues, 2: 566 management stages, 2: 566 disease control, 2: 573 establishment, 2: 566 components required for, 2: 568 effectiveness factors, 2: 567 factors to consider before replanting, 2: 569 fertilizer application, 2: 569 land preparation, 2: 567 presowing, 2: 569 replanting decisions, 2: 569 sowing considerations, 2: 567, 2: 568 timing of fertilizer application, 2: 569 fodder antinutritional problems, 2: 573 legumes, 2: 543, 2: 574 warm season grasses, 2: 573 genetically modified, 2: 561 harvesting, 2: 570 grazing management, 2: 570 mechanical (conservation), 2: 571, 2: 572t maintenance, 2: 563–575 aims and options, 2: 570 competition management, 2: 570 established species, 2: 570 fertilizer budgeting, 2: 570 fertilizers, 2: 570 of growth, 2: 570
mixed species sowing, 2: 570 optimizing growth, 2: 570 seedlings, 2: 570 weed competition control, 2: 570 pest control, 2: 573 quality decline with maturity, 2: 557 ryegrasses, 2: 555, 2: 565 small-grain cereals, 2: 556, 2: 565 species/varieties, 2: 94, 2: 552–562 choice criteria, 2: 552 warm season grasses, 2: 553, 2: 564 see also Hay; Silage; individual species; individual varieties Annual statements, 1: 487–488 Annular fold, teat, 3: 333 Anodic stripping voltammetry (ASV), 1: 196 ANOVA (analysis of variance), 1: 101 Anovulatory follicles follicular waves, 4: 435 postpartum, 4: 435, 4: 435f Anoxybacillus biofilms, 1: 446 Anoxybacillus flavithermus, 1: 448 Anterior mammary artery, 3: 334 Anterior pituitary gland development, 4: 423 reproductive function, 4: 422–423 Anthelminitics gastrointestinal nematode infection, 2: 261 lungworm disease, 2: 273, 2: 274, 2: 274t milk yields, 2: 258–259 resistance, 2: 262, 2: 273, 2: 858 Antibiotics bacteriocin combination, 1: 428 bacteriocins vs., 1: 421 biosensor analysis, 1: 240 calves, 4: 418 contaminants, 1: 892 dairy product contamination, 2: 532 ‘dry cow treatment’, 2: 450, 3: 420 historical aspects, 1: 8 immunochemical detection, 1: 180, 1: 182t liquid semen preservation, 2: 605 listeriosis, 2: 187 mastitis, 1: 891–892 vaccination and, 3: 436 nisin, 1: 423–424 organic dairy production, 4: 11t, 4: 12–13, 4: 13 papillomatous digital dermatitis, 2: 171 footbaths, 2: 172 sprays, 2: 171–172 topical, 2: 171, 2: 171f resistance Campylobacter see Campylobacter Enterococcus see Enterococcus Lactobacillus plantarum, 3: 116 Staphylococcus aureus mastitis, 3: 411 subacute clinical mastitis, 3: 437 testing, milk transportation, 1: 544 veterinary use precautions, 2: 803 see also individual drugs Antibodies, 1: 177 biosensor recognition elements, 1: 236 colostrum pathogens, 4: 417 microarrays, 1: 179 see also Immunoglobulin(s) (Ig) Anticancer effects, milk/milk by-products, 3: 1065 Anticarcinogenic effects, milk/milk by-products, 3: 1065 Antigen(s), 1: 177 presentation, 3: 389–390 Antihypertensive action, milk peptides, 3: 1064 Anti-inflammatory products, acute clinical mastitis, 3: 437 Antilisteriolysin O antibodies, 2: 187 Antimicrobial drug contamination, 1: 891 health impact, 1: 892 occurrence, 1: 891
837
sources, 1: 891 technological impact, 1: 892 Antimicrobial peptides, LAB, 1: 420–421 Antimicrobials Bifidobacterium, 1: 391 Brevibacterium linens, 1: 570 Propionibacterium, 1: 409 salmonellosis, 2: 194 Antimycotics, 1: 39 Antioxidants European Union, 1: 37 Maillard reaction products, 3: 227 mastitis, 3: 429–430 milk fat-based spreads, 1: 524 milk lipid oxidation, 3: 718 United States, 1: 39 see also specific antioxidants Antisense RNA, bacteriophage resistance, 1: 437 Antisterility factor see Vitamin E Antithrombotic effects, milk proteins, 3: 1064 Anti-xanthine oxidoreductase antibodies, 2: 326 APCI see Atmospheric pressure chemical ionization (APCI) APEC (Asia–Pacific Economic Cooperation), 4: 318–319 Apellation d’Origine Contrˆol´ee (AOC), 1: 843 Apo--lactalbumin, 3: 780–781 structure, 3: 782 Apo-lactoferrin, 3: 801–802 Apolipoprotein(s), 3: 1031 classes, 3: 727 functions, 3: 727, 3: 729t Apolipoprotein A (apoA), 3: 1031 Apolipoprotein B (apoB), 3: 1031 Apolipoprotein B-48, 3: 712 Apoproteins see Apolipoprotein(s) Apparent digestion, 3: 990 ‘Apparent water activity, 4: 716–719 Appenzeller cheese, 1: 571 Appenzell goats, 1: 311t, 1: 313 Appert, Nicolas, 1: 12 APV SiroCurd process, 3: 851 Cheddar cheese, 1: 621 Aquaporin(s), 3: 379 Aquatic Animal Health Code, 4: 6 Aquatic Animal Health Standards Commission, OIE, 4: 2 Aquatic mammals mammary gland secretion composition, 3: 328–329 milk fat, 3: 323 see also individual mammals Arabian camel see Dromedary (Camelus dromedarius) Arabinose, 1: 386t Arachidonic acid, first-age infant formulae, 2: 141 Archaeocetes, 3: 563 Areolae, 4: 487–488 Argentina, dairy societies, 2: 104 Arginine deiminase, 3: 126 Arginine (Arg) metabolism, LAB stress response, 3: 58, 3: 63–64 Aroma bacteria, 3: 166 Dutch mixed strain starters, 3: 171, 3: 171t Aroma/odor enhancers, dulce de leche, 1: 875 Aromatic amino acids, cheese flavor, 1: 641–642 Arrhenius equation, 2: 715, 2: 720–721 Arrhenius’s law, 3: 187 Arrowleaf clover (Trifolium vesiculosum), 2: 559 Arsenic in milk, 1: 901t, 3: 934, 3: 934t chemical forms, 3: 936 nutritional significance, 3: 939 ART (algebraic reconstruction technique), ultrasound, 1: 213 Arthrobacter, 4: 372–378 aerobic metabolism, 4: 374 antilisterial compounds, 4: 377 cellular fatty acids, 4: 373 cheese, 4: 376–377
838 Index Arthrobacter (continued ) chitinase enzyme, 4: 375 in dairy products, 4: 376 growth, 4: 373f, 4: 376 growth inhibition, 4: 376 hydrolytic activities, 4: 375 isolation, 4: 376 medium, 4: 376 mesophilic strains, 4: 374 in milk, 4: 376 sanitation indicators, 4: 376 morphological characteristics, 4: 373 nutritional requirements, 4: 374 as opportunistic pathogens, 4: 375–376 phylogenetic relatedness, 4: 374f, 4: 375f physiological characteristics, 4: 373 pigment production, 4: 374 psychrophilic strains, 4: 374 salt tolerance, 4: 374 species, 4: 375 new, 4: 375 in starter cultures, 4: 377 taxonomy, 4: 372 development, 4: 372 recent approaches, 4: 373 redefinition, 4: 372 Arthrobacter arilaitensis, 1: 395, 1: 396, 1: 398–399 Arthrobacter aurescens, 4: 376–377 Arthrobacter bergerei, 1: 396 Arthrobacter casei, 1: 759 Arthrobacter globiformis, 4: 373f Arthrobacter nitroguajacolicus, 4: 377 Arthrobacter phenanthrenivorans, 4: 377 Arthrobacter rhombi sp. nov., 4: 373, 4: 375f Artificial gametes, 2: 640 Artificial insemination (AI), 2: 602–609, 2: 610 advanced reproductive technologies, 4: 472 beef cattle, 4: 470t, 4: 473 buffalo, 2: 774, 2: 780–781, 4: 473 bull choice, for superovulatory donor cows, 2: 626–627 bull handling, 2: 603 centers see Artificial insemination centers (AICs) China, 2: 84 cloned sires, 4: 472 competitive fertilization, 2: 604 computerized mating programs, 4: 469 inbreeding control, 4: 469 cryopreservation see Cryopreservation estrus detection, 4: 465, 4: 465f, 4: 468 estrus-synchronized cows, 4: 469 facility development landmarks, 4: 467 farm facilities, 4: 468 fertility measurement, nonreturn rate, 2: 607, 2: 607f freeze-dried sperm, 2: 607 genetic defect carriers, 2: 675 genetic improvement process, 2: 669 genetic progress, 4: 470, 4: 471f goats, 2: 836, 2: 836f historical aspects, 1: 7, 2: 602 discoveries, 2: 602 technique developments, 2: 602–603 insemination timing, 2: 608 liquid semen, preservation, 2: 604, 2: 604f antibiotics, 2: 605 egg yolk based extender media, 2: 605 milk extenders, 2: 605 male fertility prediction, 2: 607 multiple trait-based selection and mating, 4: 471 natural service vs., 4: 483 noncattle species, 2: 608, 4: 473, 4: 473t procedure, 4: 468 progeny per sire, 4: 467 program components, 4: 467 records, database management, 2: 95, 2: 607 semen collection technique, 2: 603 semen quality evaluation, 2: 603
sexing sperm, 2: 607 sex-sorted sperm, 2: 634–635, 4: 472 sheep, 2: 891 frozen semen, 2: 891 melatonin treatment, 2: 890 usage, 4: 473–474 sire selection fertility-associated evaluations, 4: 472 production-associated evaluations, 4: 471 programs, 4: 470 sire’s genetic contribution, 4: 467 sperm quality testing, 2: 604 timed see Timed artificial insemination (TAI) United States, 4: 469, 4: 470t utilization, 4: 467–474 genomic evaluations, 4: 470 worldwide extent, 4: 470, 4: 471t yaks, 1: 345–346 see also Reproductive management Artificial insemination centers (AICs), 1: 468–474 biochemical reference values, 1: 471, 1: 471t dry matter intake, 1: 468 general heath considerations, 1: 471 biochemical reference values, 1: 471, 1: 471t hematologic variables, 1: 471, 1: 471t hooves, 1: 471 upper limbs, 1: 471 health/disease control, 1: 469 bovine leukosis virus, 1: 470 bovine viral diarrhea virus, 1: 470, 1: 470 brucellosis testing, 1: 470 entry isolation interval, 1: 470 gestation, 1: 470 goals, 1: 469 Johne’s disease, 1: 470 resident bull herds, 1: 470 tuberculosis testing, 1: 470 venereal diseases, 1: 470 young bulls, 1: 470 nutrition, 1: 468, 1: 469t calcium/phosphorus ratios, 1: 468–469 recommended weights, 1: 469t weight gains, 1: 469t reproductive health, 1: 472 epididymis pathology, 1: 473 incomplete testicular descent, 1: 472 scrotal circumference, 1: 472, 1: 472t, 1: 472t ‘summer infertility’, 1: 473 testicular degeneration, 1: 473 vesiculitis, 1: 473 semen collection, 1: 473 false mount, 1: 473 negative behavioral factors, 1: 473 records, 1: 474 Artificial insemination gun, 4: 469 ‘Artificiality’, consumer perceptions, 1: 43 Artificial lighting, estrus synchronization, goats, 2: 835 Artificial neural networks (ANNs), 1: 105, 4: 249 direct control, 4: 249 indirect control, 4: 249 Kohonen self-organizing maps, 1: 94t, 1: 98t, 1: 107 multilayer perception, 1: 105 supervised network, 1: 94t supervised networks, 1: 107 Artificial neural network tolerant model predictive control, 4: 249, 4: 250f Artiodactyla see Even-toed ungulates (Artiodactyla) Arvana camels, 1: 352 Arylsulfatase, 2: 282 Aschaffenburg–Rowland procedure, 3: 745 Ascorbate see Vitamin C Ascorbate free radical (Asc*), 4: 667–668, 4: 670 Ascorbate monoanion (AscH), 4: 667–668 Ascorbic acid (AA) see Vitamin C ASDT (Dairy Industry Association of Australia), 2: 104
Aseptic packaging, UHT treatment, 2: 708–713 see also Ultra-high temperature (UHT) treatment Ash content donkey milk, 1: 369 measurement, 1: 77 historical aspects, 1: 20 primate milk, 3: 627–629 Asia Bos taurus breeds, 1: 285t, 1: 298 goats, 1: 318 Southern see Southern Asia Asiago cheese, 1: 729 characteristics, 1: 730t composition, 1: 729t production statistics, 1: 729t ripening, 1: 729–731 Asian (water) buffalo (Bubalus bubalis) see Buffalo Asian elephant milk oligosaccharides, 3: 271t Asian fermented milks, 2: 507–511 historical aspects, 2: 507 starter cultures, 2: 509t see also individual milks Asia–Pacific Economic Cooperation (APEC), 4: 318–319 Asinine milk see Donkey milk As low as reasonably achievable (ALARA), food additives, 4: 535 As Low As Reasonably Practicable (ALARP) criteria, 4: 281 Asociaci´on Nacional de Productores de Leche (ANPL), 2: 105 Aspartate, 1: 714 Aspartic proteases, blue mold cheeses, 1: 769–771 Aspergillus peptidases,enzyme-modified cheese, 1: 802–803 proteinases, enzyme-modified cheese, 1: 802 see also individual species Aspergillus flavus, 4: 785–791 aflatoxins, 4: 792–793, 4: 801 aflatrem, 4: 797–798 anti-insect properties, 4: 786 colonies, 4: 785 culture, 4: 785 ecology, 4: 786 genetics, 4: 787 heat-induced injury, 4: 787 molybdenum deficiency, 4: 785 morphology, 4: 785 physical agent effects, 4: 790 physiological growth-affecting factors, 4: 786 chemical preservatives, 4: 790 naturally occurring preservatives, 4: 788 pH, 4: 787 preservatives, 4: 787, 4: 788 temperature, 4: 787 water activity, 4: 786 stored products, 4: 786 Aspergillus flavus and Aspergillus parasiticus agar (AFPA), 4: 785 Aspergillus niger fermentation-produced chymosin, 1: 576 industrial lactases, 2: 277–278, 2: 279, 2: 280f Aspergillus nomius aflatoxins, 4: 792–793, 4: 801 Aspergillus flavus vs., 4: 785 Aspergillus oryzae, 2: 281 Aspergillus parasiticus aflatoxins, 4: 792–793, 4: 801 Aspergillus flavus vs., 4: 785 Aspergillus versicolor, 4: 783 Assaf sheep, 1: 337, 1: 337f, 2: 72 Assessors, sensory evaluation, 1: 280, 1: 282 Assets, management records, 1: 488 Ass milk, 2: 516 Associac¸ao Brasileira dos Produtores de Leite, 2: 105 Association Laitiere Francaise (ALF), 2: 103
Index Association of Official Analytical Chemists (AOAC) International contaminant hormone analysis, 1: 894 fatty acid analysis (method 996.06), 3: 698 Associations see Dairy science societies/associations Asthma, milk consumption and, 3: 611 ASV (anodic stripping voltammetry), 1: 196 Ataxia with vitamin E deficiency (AVED), 4: 656 Atherosclerosis, 3: 713 cholesterol oxidation products, 3: 719 definition, 3: 727 low-density lipoprotein, 3: 729 vitamin E, 4: 657, 4: 658 vitamin K, 4: 664–665 Atmosphere blue mold cheese microflora, 1: 768 surface mold-ripened cheese ripening, 1: 781, 1: 781 Atmospheric pressure chemical ionization (APCI) cheese flavor assessment, 1: 676, 1: 679 lipid analysis, 1: 204 Atomic emission detector, 1: 678–679 Atomic emission spectrometry (AES), 1: 141 Atomic force microscopy (AFM), 1: 229, 1: 229f Atomic spectrometry, 1: 141–145 analytical performance, 1: 143t applications, 1: 142 instrumentation, 1: 142 method validation, 1: 144 minerals analyzed, 1: 141 sample preparation, 1: 141 techniques, 1: 142 see also specific methods Atomization, 4: 224 Atomizing devices, spray drying, 2: 109, 2: 110f, 2: 117 ATryn, 2: 640–641 Attenuated starter cultures, 1: 565 Attenuation coefficient, 3: 470 Attrition drying, casein curd, 3: 857 A2O process, 4: 626, 4: 627f A-type carboxylic esterases, 2: 304 Aurochs (Bos primigenius; wild ox), 1: 284, 3: 326–327 Austenitic stainless steel, 4: 135, 4: 260 dairy plant use, 4: 136 Australia agricultural policy, 4: 309 background, 4: 309 calving patterns, 2: 30 cereal-based grain concentrate use, 2: 35 cheese definition, 1: 854 cheese legislation, 1: 854 cow breeds, 2: 35 dairy industry deregulation, 2: 30 dairy industry policy reform from 2000, 4: 310 deregulation, 4: 310 export quota allocations, 4: 310 farm gate price controls, 4: 309–310 feed planning, 2: 31 free trade agreements, 4: 310 livestock emission reduction, 4: 310 milk production future trends, 2: 36 patterns, 2: 29 pasture growth, 2: 30, 2: 31f intake, 2: 33 nutritive characteristics, 2: 33, 2: 33f zones, 2: 30 pasture-based systems with seasonal calving, 2: 29–37 processed cheese definition, 1: 854 producer support estimate, 4: 307f, 4: 309–310 single commodity transfers, 4: 307f, 4: 309–310 supplement use, 2: 34 Australian brushtail possum (Trichosurus vulpecula), 2: 197 Australia New Zealand Food Authority (ANZFA), cheese legislation, 1: 854
Australian Friesian Sahiwal cattle, 1: 303, 1: 303t Australian Journal of Dairy Science, 2: 104 Australian Milking Zebu cattle, 1: 303, 1: 303f, 1: 303t Australia’s Farming Future, 4: 310 Austria Fleckvieh cattle, 1: 293 Pingzau cattle, 1: 296 ¨ B5019, water supply Austrian standard ON sanitization, 4: 586t Autoclaves batch, 2: 722, 2: 722f continuously-operating, 2: 722 hydrostatic sterilizer, 2: 722, 2: 723f rotating, 2: 722–723, 2: 723f temperature–time pattern, 2: 720f, 2: 722 Autolysis, cheese flavor, 1: 564 Automated Bactoscan instruments, 3: 899 Automated calf feeding systems, 2: 25 Automated systems body condition scoring, 1: 460 non-seasonal/pasture-based management, 2: 50 starter cultures, 1: 440 Automated warehouses, 4: 256 Automatic cluster removers (ACRs), 3: 947 arm-type units, 3: 962–963 historical aspects, 3: 944 milking parlors, 3: 962–963 sheep, 2: 868 Automatic detachers, 3: 962–963 Automatic feeders, 1: 5 Automatic milking systems (AM systems), 3: 952–958 barn layout, 3: 954 benefits, 3: 952 capacity, 3: 955 daily, 3: 954f, 3: 955, 3: 955t, 3: 956t concentrate dispensers, 3: 954 ‘controlled-traffic’ systems, 3: 954 control system, 3: 953 cow adaptation, 3: 954 database, 3: 953 economic aspects, 3: 956 ‘forced cow traffic’ systems, 3: 954 ‘free cow traffic’ systems, 3: 954 free fatty acid concentrations, milk, 3: 640, 3: 641t milking frequency, 3: 639, 3: 640t, 3: 641 full-time equivalents, 3: 957 handling time, 3: 955 historical aspects, 1: 9 humans vs., 4: 252–253 individual quarter milking, 3: 953–954 labor costs, 3: 956–957 labor requirements, 3: 955 machine-on time, 3: 955 management, 3: 954 milking intervals, 3: 954f, 3: 954–955 milking machine, 3: 953 milking stall, 3: 952 milking visit, 3: 955 milk production, 3: 954 milk quality, 3: 956, 3: 956t free fatty acids, 3: 956 modules, 3: 952 multistall system, 3: 952 one-stall system, 3: 952 daily capacity, 3: 955 premilking udder cleaning, 3: 633 profitable, 3: 957 robotic arm, 3: 953 multibox system, 3: 953 room for investment model, 3: 957, 3: 957f sensors, 3: 953 teat cleaning system, 3: 952 cleaning device efficacy, 3: 953 principles, 3: 953 teat detection system, 3: 953 technical aspects, 3: 952
839
Automatic online detection, abnormal milk, 3: 422–428 decision-making algorithms, 3: 426, 3: 427f mastitis, milk quality standards, 3: 422 objectives, 3: 422 clinical mastitis, 3: 423 subclinical mastitis, 3: 423 test requirements, 3: 422, 3: 425t recent developments, 3: 426 chemical sensors, 3: 426 milk clot sensors, 3: 426 thermal udder cameras, 3: 426 sensor techniques, 3: 423 color, 3: 425 electrical conductivity, 3: 424, 3: 424f L-lactate dehydrogenase biosensor, 3: 425 multiple sensor combinations, 3: 425, 3: 425, 3: 425–426, 3: 427 somatic cell count, 3: 425, 3: 426f visibly abnormal milk, 3: 423 Automatic teat-cup valve, goats, 2: 808, 2: 811, 2: 811f Automation, robotics vs., 4: 252 AV see Abomasal volvulus (AV) Avermectins/milbemycins, 2: 261 Avian tuberculosis, 2: 174 Avoparcin, 1: 650 aw see Water activity (aw) Awassi sheep, 1: 328, 2: 72 distribution, 1: 328 improved see Improved Awassi sheep milk production traits, 1: 328, 1: 328t origins, 1: 328 physical characteristics, 1: 328 reproductive characteristics, 1: 328 Axial compressors, 4: 604, 4: 604f Ayran, Surk cheese, 1: 786 Ayrshire cattle, 1: 285, 1: 286f, 1: 286t historical aspects, 1: 2 milk composition, 2: 53t stability/survival, 1: 290–291
B BA46 see Lactadherin Babcock method, 1: 80 Baboon milk casein:whey protein ratio, 3: 621 free amino acids, 3: 627t -lactoglobulin, 3: 624 lysozyme, 3: 629 pH, 3: 614 proteins, 3: 622t total amino acids, 3: 625 vitamins, 3: 630t whey proteins, 3: 624 Bach Thao goats, 1: 311t, 1: 318, 1: 319f Bacillus biofilms, 1: 446 commercially pasteurized nonaseptically packed milk, 4: 387 flavor defects, 4: 387, 4: 388 growth, refrigeration temperatures, 4: 385 pathogenic, 3: 450 proteinases, enzyme-modified cheese, 1: 802 psychrotrophic, 4: 384 raw milk, 3: 646–647, 4: 386 spoilage, 3: 453 see also individual species Bacillus buchneri see Lactobacillus buchneri Bacillus cereus group, 4: 24–30 biofilms, 4: 28–29, 4: 29f ‘bitty cream defect, 4: 24 carbohydrates utilized, 4: 25 characteristics, 4: 24 cheese, 4: 28 control, 4: 29 at the dairy plant, 4: 29 in dairy products, 4: 29 at the farm, 4: 29
840 Index Bacillus cereus group (continued ) storage temperatures, 4: 29 cultivation, 4: 24 dairy products incidence in, 4: 27 outbreaks, 4: 27, 4: 27t detection, 4: 24–25 enumeration, 4: 24–25 gastroenteritis outbreaks, 3: 312 growth temperatures, 4: 25, 4: 25t milk-borne illness, 4: 26 diarrheal-type outbreak, 4: 26 emetic-type outbreak, 4: 26 morphology, 4: 24 physiology, 4: 25 raw milk, 4: 386 recontamination of milk, 4: 28–29 sources, 4: 28 in dairy plant, 4: 28, 4: 29f at the farm, 4: 28 soil, 4: 28 spores, 4: 25 heat resistance, 4: 26, 4: 28–29 sporulation, 4: 25–26 storage granules, 4: 24–25 strain-typing methods, 4: 28–29 sweet curdling defect, 4: 24 toxins, 4: 26 Bacillus cereus sensu lato see Bacillus cereus group Bacillus circulans, 4: 386 Bacillus coagulans, 4: 386 Bacillus licheniformis, 4: 386 Bacillus mycoides, 4: 24–25 Bacillus pseudomycoides, 4: 24–25 Bacillus sporothermodurans, 2: 703 Bacillus stearothermophilus, 1: 865–866 Bacillus weihenstephanensis, 4: 24–25 dairy product-related outbreaks, 4: 27 growth temperature, 4: 25 Backflushing, mastitis prevention, 3: 413, 3: 433 Back-mix beds, drying, 4: 213 Back-slopped starter cultures, 1: 554t Backyard farming, China, 2: 85 BACTEC MGIT 960 system, 2: 177 Bacteria biosensor analysis, 1: 240 in dairy products intestinal microflora interaction, 2: 483, 2: 485, 2: 486 kefir bacterial species, 2: 519 genome sequences, 3: 966 human intestinal flora, 3: 214 development, 3: 214 nomenclature standards, 3: 47 pathogenic, 3: 447 inactivation temperature, 2: 715–719 kefir products, inhibition by, 2: 523 nonthermal processing resistance, 2: 725–726 receptor binding blockage, 3: 215 sources, 1: 645, 3: 440 pathogen immunosensors, 1: 196 phyogenetic analysis housekeeping genes, 3: 46–47 multilocus sequence typing, 3: 47 single nucleotide polymorphisms, 3: 47 probiotic see Probiotics raw milk, 3: 895t removal, membrane processing, 1: 622, 1: 622f ruminal, 3: 980 smear-ripened cheese defects, 1: 765 species definition, 3: 46, 3: 46 spores see Spores, bacterial surface mold-ripened cheese ripening, 1: 775 taxonomy, polyphasic approach, 3: 46 see also individual species Bacterial clarifiers, 4: 179 Bacterial infections buffalo, 2: 782
lameness, sheep, 2: 857 Bacterial membranes amino acid transport, 3: 53 high-pressure homogenization disruption, 2: 758, 2: 758f peptide transport, 3: 53 pulsed electric field electroporation, 2: 738–739 Bacterial meningitis, 4: 75–76 Bactericidal/permeability increasing-like (BPI-like) proteins, 2: 663–664 Bacteriocins, 1: 410t, 1: 420–429, 1: 422t advantages, 1: 427 inactivation, 1: 427 thermostability, 1: 427 antibiotics vs., 1: 421 applications, 1: 426 bad breath, 1: 426 powdered skim milk, 1: 426 biofilm formation, 1: 449–450 Brevibacterium linens, 1: 570 cheese ripening, 1: 427, 1: 570 Clostridium spore control, 4: 53 deferred antagonism assay, 1: 421, 1: 421f definition, 1: 421, 3: 89 disadvantages, 1: 427 hydrophobicity, 1: 427 new technology resistance, 1: 427–428 toxicity studies, 1: 427–428 future work, 1: 428 antibiotic combination, 1: 428 bioengineering, 1: 428 inactivation, 1: 427 Lactobacillus acidophilus, 3: 93 Lactobacillus helveticus, 3: 106 Lactobacillus plantarum, 3: 114–115 Lactobacillus spp. see Lactobacillus lanthionine-containing see Lantibiotics (lanthionine-containing bacteriocins) non-lanthonide-containing, 1: 421 pathogen control, 1: 646 pediocin-like, 1: 425 as preservatives, 1: 421 production, 1: 428 in vitro fermentation, 1: 428 in product, 1: 428 Propionibacterium, 1: 409 smear-ripened cheeses, 1: 399 tailor-made cultures, 3: 967 target sensitivity, 1: 427 thermostability, 1: 427 Bacteriological cleanliness, 4: 130 Bacteriophage(s), 1: 430–438, 1: 432t actions, 1: 439 characterization, 1: 434 disinfectant resistance, 1: 435 physicochemistry, 1: 434 stress resistance, 1: 434–435 classification, 1: 430 DNA–DNA hybridization, 1: 430 detection of, 1: 438 discovery, 1: 439 Emmental cheese, 1: 407–408 genetics, 1: 434 genome sequences, 1: 434 historical aspects, 1: 31, 1: 430 host resistance mechanisms, 1: 435, 1: 556 abortive infection (Abi), 1: 436 adsorption inhibition, 1: 435 antisense RNA, 1: 437 CRISPRs (clustered regularly interspersed short palindromic repeats), 1: 435, 1: 436 engineered mechanisms, 1: 436 exopolysaccharides, 1: 435 host factor elimination, 1: 437 origin-derived phage-encoded resistance, 1: 436 phage counterdefenses, 1: 438 phage DNA injection inhibition, 1: 435 phage-triggered suicide systems, 1: 437
restriction/modification systems, 1: 435, 1: 556–557 subunit poisoning, 1: 437 superinfection exclusion, 1: 437 Lactobacillus see Lactobacillus life cycle, 1: 433, 1: 433f adsorption, 1: 433–434 host cell lysis, 1: 434 replication, 1: 434 lysogeny, 1: 431 environmental factors, 1: 431 in milk fermentation, 1: 439 failure of, 1: 439–440 morphology, 1: 431, 1: 433f, 1: 439 reproduction, 1: 439 lysogenic cycle, 1: 439 lytic cycle, 1: 439 Scandinavian fermented milks, 2: 499 sensitivity starter culture, 1: 555 starter culture infection, 2: 478–479 sanitation control measures, 1: 441, 1: 442, 2: 480, 2: 532 sources, 2: 480 starter sensitivity, 1: 440 strain specificity, 1: 441, 2: 477 starter culture protection, 1: 441 air sterilization, 1: 442–443 neutralization, 1: 443 phosphate, 1: 443 sterile air supply, 1: 441 sterilization, 1: 442–443 Streptococcus thermophilus see Streptococcus thermophilus technological importance, 1: 439–444 dairy industry, 1: 439, 1: 442, 1: 444 temperate, 1: 431 Bacteriophage-insensitive mutants (BIMs), 1: 436, 3: 135 starter cultures, 1: 442 Bacteriophage-resistant starter cultures, 1: 556 Bacterium lactis see Lactococcus lactis Bacteroides, 1: 383t, 4: 360 Bactocatch process, 1: 622f, 1: 622–623, 2: 113, 2: 113f gas blowing defect prevention, 1: 663 Bactofugation, 2: 729 biogenic amines, 1: 453 cheese manufacture, 1: 545 gas blowing defect prevention, 1: 663 Bactofuges, 4: 178 Bactrian camel (Camelus bactrianus), 1: 351, 3: 512 medium-producing dairy types, 1: 352 Baermann technique, 2: 273 Bag filters spray drying powder separation, 4: 227, 4: 228f suspended solids/turbidity removal, water, 4: 583 Bag-in-box containers, 2: 711, 2: 712f Bag presenters, 1: 611 Baird–Parker agar (BPA), Staphylococcus aureus, 4: 113 Bakers’ cheese, 1: 701 Bakery products anhydrous milk fat use, 1: 517 dairy ingredients, 2: 130 Baladi cattle, 1: 298 Balancing tank, 4: 622 Balansa clover (Trifolium michelianum), 2: 559 Baleen whales, 3: 563 lactation, 3: 564t milk fat levels, 3: 574 Ballottement, pregnancy detection, 4: 489 Ballottement with simultaneous auscultation, displaced abomasum, 2: 215 Bangladesh, milk marketing systems, 2: 96–97 Bang’s disease see Brucellosis Barbari goats, 1: 311t, 1: 318, 1: 319f milk yields, 1: 312t Barbary sheep, 1: 336
Index Barki goats, 1: 311t, 1: 317 milk yields, 1: 312t Barley, 2: 557 Barn(s) categories, winter temperatures and, 4: 558 storage, 1: 5 Barn ventilation construction, 4: 558 management, 4: 558 Barrier teat dips, 3: 433 Basal media, Brucella, 4: 36 Base-exchange softening, 4: 584 Basque-B´earn sheep, 1: 332t Batch dynamic principal component analysis (BDPCA), 4: 244, 4: 245f Batch observation level (BOL) method, 4: 245, 4: 245f Batch pasteurization see Low-temperature–long time (LTLT) pasteurization Batch process operation, 4: 242 Bavaria, Pingzau cattle, 1: 296 BCS see Body condition score (BCS) Bear(s) milk carbohydrates, 3: 550, 3: 551 composition, 3: 566–569, 3: 567t oligosaccharides, 3: 272 as predators, 2: 842, 2: 843–844 Bearded seal milk oligosaccharides, 3: 271t Bedding calving facilities, 2: 28 cold stress, 4: 559 cow comfort, 4: 559 environmental mastitis prevention, 3: 420 mastitis prevention, 3: 433 organic dairies, 4: 14 warm climate calving facilities, 2: 28 Beef cattle, artificial insemination, 4: 470t, 4: 473 Beef production, Bos taurus breeds, 1: 289, 1: 290t, 1: 290t, 1: 291t, 1: 291t Beetal goats, 1: 311t, 1: 318, 1: 318f milk yields, 1: 312t Belgian Red cattle, 1: 296 Bellevue cheese, 1: 786–787 Belt cheddaring systems, 1: 608–610, 1: 610f, 1: 610f Beluga milk oligosaccharides, 3: 271t Benadir camels, 1: 352 Benchmarking, 1: 489 Bending, rheology instrumentation, 1: 274–275 Bentley Somacount system, 3: 896 Benzimidazole-resistant nematodes, 2: 269 Benzoates, 1: 37t Benzoic acid derivatives, 4: 790 Bergamasca sheep, 1: 332, 1: 333f Beriberi, 4: 702–703 Bermuda grass (Cynodon dactylon), 2: 578 Bernoulli’s equation, 4: 139 cavitation, 4: 142 ‘heads’, 4: 139, 4: 140f Berridge method, curd strength, 1: 585 Berseem (Egyptian) clover (Trifolium alexandrinum), 2: 558 Betabacterium breve see Lactobacillus brevis Betacellulin, 3: 596 Betaine, rumen-protected, 3: 1000–1001 BET expression, 4: 720, 4: 721t BET multilayer adsorption process, 4: 715–716 Beverages dairy ingredients, 2: 129 US market, 3: 279, 3: 279t Beyer and Rohde milking machine, 3: 941, 3: 942f Bezoar goat (Capra aegagrus), 2: 814, 3: 326–327 Bias measurement error, 1: 85 measurement process characterization, 1: 87 Biexponential behavior, NMR relaxation studies, 1: 157 Bifidobacterium, 1: 381–387 acetic acid production, 1: 384
N-acetyl-D-glucosamine-containing saccharides, 1: 384–385 acid-resistant strains, 1: 388 adherence properties, 1: 393 anticarcinogenic activity, 1: 392 antimicrobial properties, 1: 391 antimutagenic properties, 1: 392 bile-resistant strains, 1: 388 carbohydrate metabolism, 1: 387 characteristics, 2: 479t classification, 1: 382–383 colonies, 1: 384 fermentation starters, 3: 456 in fermented milk products, 1: 388–394, 1: 389t adherence properties, 1: 393 health effects, 2: 484, 2: 485 Japan, 1: 390 see also Bifidus products fructose-6-phosphate phosphoketolase, 1: 387 galacto-oligosaccharide use, 4: 360 gastrointestinal microflora (human), 1: 382–383, 1: 383, 1: 383t age-relation, 1: 383–384 colon walls, 1: 383 lipoteichoic acids, 1: 383 genetically engineered, tumor treatments, 3: 71 genome, 3: 71–73, 3: 72t, 3: 73t reduction, 3: 76 genomics, 3: 75f, 3: 76 growth bifidus pathway, 1: 385f breast vs. bottle-fed infants, 3: 253 characteristics, 1: 384 in vitro studies, 3: 254 oligosaccharide effects, 3: 253, 3: 253f requirements, 1: 384, 1: 389 temperature range, 1: 384 hexose hydrolysis, 4: 367–368 history, 1: 381 lactose tolerance, 1: 392 lactulose requirements, 1: 384–385, 1: 389 metabolism, 3: 46 morphology, 1: 384 colonies, 1: 384 mucin requirements, 1: 387 mucoid variants, bifidan production, 2: 481 nitrogen source, 1: 387 occurrence, 1: 381 phylogenetic tree, 3: 67, 3: 68f probiotic fermented milk, 2: 473 as probiotics, 3: 67 serum cholesterol effects, 1: 392 species, 1: 382 sugar fermentation patterns, 1: 386t taxonomy, 1: 381, 3: 46 DNA probes, 1: 382 pulsed-field gel electrophoresis, 1: 382 therapeutic properties, 1: 391, 1: 391t uses, 1: 381 vitamin production, 1: 384 see also individual species Bifidobacterium adolescentis, 1: 382t, 1: 387 Bifidobacterium angulatum, 1: 382t Bifidobacterium animalis, 1: 382t, 1: 390–391 Bifidobacterium animalis subsp. lactis, 3: 76 Bifidobacterium asteroides, 1: 382t, 1: 384 Bifidobacterium bifidum, 1: 382t adherence properties, 1: 393 growth requirements, 1: 385–387 lacto-N-biose hypothesis, 3: 253 in yogurt, 1: 390, 1: 390 Bifidobacterium boum, 1: 382t Bifidobacterium breve, 1: 382t adherence properties, 1: 393 in yogurt, 1: 390 Bifidobacterium catenulatum, 1: 382t Bifidobacterium choerinum, 1: 382t Bifidobacterium coryneforme, 1: 382t
841
Bifidobacterium cuniculi, 1: 382t, 1: 387 Bifidobacterium denocolens, 1: 382t Bifidobacterium dentium, 1: 382t Bifidobacterium gallicum, 1: 382t Bifidobacterium gallinarum, 1: 382t Bifidobacterium globosum, 1: 382t Bifidobacterium indicum, 1: 382t, 1: 384 Bifidobacterium infantis, 1: 382t, 1: 383, 1: 393 growth enhancement by casein macropeptide, 3: 1063–1064 Bifidobacterium lactis, 1: 382t Bifidobacterium longum, 1: 382t adherence properties, 1: 393 anticarcinogenic properties, 1: 392 genome, 3: 76 in yogurt, 1: 390, 1: 390 Bifidobacterium longum NCC2705, 3: 76 Bifidobacterium longum subsp. longum, 3: 76 Bifidobacterium longum subsp.infantis genome, 3: 76 glycosidases, 3: 254–255 human milk oligosaccharide effects, 3: 254 Bifidobacterium magnum, 1: 382t Bifidobacterium mericicum, 1: 382t Bifidobacterium minimum, 1: 382t Bifidobacterium pseudocatenulatum, 1: 382t, 1: 390 Bifidobacterium pseudolongum, 1: 382t, 1: 390 Bifidobacterium pullorum, 1: 382t Bifidobacterium ruminatium, 1: 382t Bifidobacterium saeculare, 1: 382t Bifidobacterium subtile, 1: 382t Bifidobacterium suis, 1: 382t nitrogen source, 1: 387 urease, 1: 387 Bifidobacterium thermacidophilum, 1: 382t Bifidobacterium thermophilium, 1: 382t Bifidus, labeling issues, 1: 417 Bifidus pathway, 1: 385f Bifidus products, 1: 388 Bifidobacterium characteristics, 1: 388 acid-resistant strains, 1: 388 bile-resistant strains, 1: 388 peptide micronutrients, 1: 388–389 organisms, 1: 388 yogurt, 1: 388 Bike shift irrigation system, 2: 591 Bile acids, 3: 711 Bile ducts, liver fluke infection, 2: 266 Bile salts cholesterol reduction, 3: 736 Propionibacterium, 1: 407 Bile salts-stimulated lipase (BSSL), 3: 629 Bimetallic corrosion, 4: 262 Binding origin information (BOI), 4: 336 Binding tariff information (BTI), 4: 336 Bingham equation cheese rheology, 4: 530 milks/cream rheology, 4: 523–524 Bingham fluids, 1: 270 Bioactive peptides, 2: 294, 2: 294t, 3: 879–886 anticariogenic properties, 3: 1036 antihypertensive effects, 3: 884 antioxidant properties, 3: 883 beneficial effects, 3: 880t cheese, 3: 884–885 commercial dairy products, 3: 885t definition, 3: 879 donkey milk, 1: 369 enzymatic hydrolysis, 3: 885 enzyme-modified cheese, 1: 799–800 functions, 3: 879, 3: 881t health benefits, 3: 1062 hypocholesterolemic effects, 3: 883 immunomodulation, 3: 883, 3: 1062 interactions, other food components, 3: 885–886 physiological importance, 3: 883 production, 3: 760, 3: 884 release, 2: 293
842 Index Bioactive peptides (continued ) sheep milk, 3: 500 structures, 3: 879, 3: 880t transport systems, 3: 1062–1063 Bioactives definition, 3: 365 intestinal development, 3: 364t, 3: 365 Bioavailability, 2: 384, 4: 683 Biobreeding rat (BB rat), 3: 1047 Biochemical oxygen demand (BOD) definition, 4: 614t, 4: 619 wastewater, 4: 613 Biocytin, 4: 687 BIODENIPHO process, 4: 626, 4: 627f Bioengineering, bacteriocins, 1: 428 Biofilms, 1: 445–450 Anoxybacillus, 1: 446 Bacillus cereus group, 4: 28–29, 4: 29f cheese, 1: 446 Chronobacter, 1: 447 cleaning, 1: 448 clean-in-place system, 1: 448–449 pigging, 1: 449 control of, 1: 448 disruptive technologies, 1: 450 incoming milk quality, 1: 449 plant surface modification, 1: 449 definition, 1: 445 detection, 1: 448 development of, 1: 447, 1: 447f flow rates, 1: 448 heat treatment effects, 1: 447–448 initial attachment, 1: 447 irreversible stage, 1: 445 surface conditions, 1: 445, 1: 446, 1: 448 drinking water systems, 4: 584 Enterobacter, 4: 79 future work, 1: 450 Geobacillus, 1: 446, 1: 448 Lactobacillus, 1: 446 Listeria monocytogenes, 1: 447 milk powder, 1: 446, 1: 446f pathogens, 1: 447 planktonic bacterial cells, 4: 585 problems with, 1: 445 product functional properties, 1: 445 Pseudomonas, 1: 446, 4: 380 raw milk, 1: 446 sanitizing, 1: 448 single species, 1: 445 Staphylococcus aureus, 4: 108 Streptococcus thermophilus, 1: 448, 3: 143, 3: 146, 3: 148f whey, 1: 446 Biogas generation, whey, 4: 735–736 Biogenic amines, 1: 451–456 characteristics, 1: 452t in cheese, 1: 451 influencing factors, 1: 452 poisoning outbreaks, 1: 651 public health aspects, 1: 651 definition, 1: 451 degradation, 1: 452 detection, 1: 455 molecular methods, 1: 455 diamines, 1: 451 enterococci, 1: 451–452, 3: 156 extraction, 1: 455 Gram-negative bacteria, 1: 452 high-pressure treatment, 1: 454 inhibitory bacteria, 1: 453 LAB, 1: 451 Lactobacillus, 1: 451 milk treatment effects, 1: 452, 1: 453t bactofugation, 1: 453 high-pressure homogenization, 1: 453 pasteurization, 1: 452 monoamines, 1: 451
polyamines, 1: 451, 1: 452t proteolytic enzymes, 1: 454 quantification, 1: 455 raw milk cheeses, 1: 658–659 ripening conditions, 1: 454 starter culture effects, 1: 453 strain-dependency production, 1: 455 thermization ineffectiveness, 2: 697 see also specific amines Biohydrogenation theory, milk fat depression, 3: 356, 3: 356f Bioinformatics, 3: 347, 3: 1057–1058 LAB stress genes, 3: 59–60, 3: 61t Biological filtration, effluent, 4: 624, 4: 625f biofilter media, 4: 624, 4: 626f operation parameters, 4: 624–625 efficiency, 4: 624, 4: 626f Biological phosphorus removal, 4: 626 The Biological Standards Commission, OIE, 4: 3 Biopreservatives, Clostridium spore control, 4: 53 Biopsy, fatty liver, 2: 217 Biosecurity, non-seasonal/pasture-based management, 2: 50 Biosensors, 1: 235–247 abnormal milk analysis, 3: 425, 3: 426 advantages, 1: 235 animal management, 1: 245 feed management, 1: 245 recombinant bovine somatotropin, 1: 246 reproductive management, 1: 245 composition measurement, 1: 243 calcium, 1: 244 carbohydrates, 1: 243 casein, 1: 244 choline, 1: 245 fats, 1: 244 fatty acids, 1: 244 folic acid, 1: 245 L-lactic acid, 1: 245 lactose, 1: 244 proteins, 1: 243 riboflavin, 1: 245 vitamin B12, 1: 245 continuous flow analysis, 1: 235 control and automation, 1: 235 dairy product analysis, 3: 750 definition, 1: 235, 3: 750 electrochemical analysis, 1: 196 future work, 1: 246 HACCP programs, 1: 246 milk adulteration, 1: 245 miniaturization, 1: 235 multianalyte detection, 1: 235 product quality/processing, 1: 242 amino acid analysis, 1: 242 heat treatment efficacy, 1: 243 -lactalbumin, 1: 243 lactulose, 1: 243 milk freshness, 1: 242 protein degradation, 1: 243 starter culture characterization, 1: 243 sulfhydryl groups, 1: 243 real-time analysis, 1: 235 recognition elements, 1: 235 alternative ligands, 1: 236 antibodies, 1: 236 catalytic, 1: 235–236, 1: 236f noncatalytic, 1: 235–236, 1: 236f safety assurance, 1: 240 aflatoxins, 1: 242 allergens, 1: 242 antibiotic analysis, 1: 240 bacterial analysis, 1: 240 botulinum toxin, 1: 242 insecticides, 1: 242 mastitis detection, 1: 241 microbial toxins, 1: 241
multipathogen analysis, 1: 241 pathogen-specific, 1: 241 pesticides, 1: 242 staphylococcal enterotoxins, 1: 241 sensitivity, 1: 235 transducers, 1: 236 chemiluminometric, 1: 238 direct detection, 1: 236 electrochemical, 1: 239, 1: 239f field-effect transistors, 1: 238, 1: 238f fluorescent-label based, 1: 238, 1: 238f indirect detection, 1: 238 light-addressable potentiometric sensor, 1: 239, 1: 239f, 1: 241 mechanical, 1: 237, 1: 237f optical transducers, 1: 237, 1: 237f BIOSTYR process, 4: 627, 4: 628f Bioterrorism, raw milk, 3: 647 Biotic stresses, 3: 56 Biotin, 4: 687–689 carboxylation processes, 4: 687 chemical structure, 4: 687, 4: 688f dairy products, 4: 688t decarboxylation processes, 4: 687 deficiencies, 4: 687 symptoms, 4: 688 feed supplementation, 2: 396 hoof health, 2: 396–397 milk production increases, 2: 396–397 strategies, 2: 400–401 functions, 2: 397t, 4: 687 recommended daily intake, 4: 688t ruminal microorganism synthesis, 2: 396–397 sources, 2: 397t, 4: 687, 4: 688t Biotin-dependent enzymes, 4: 687 Biotinidase, 4: 689 Birabish camels, 1: 352 Bird–Leider equation, 4: 531 Birds, 4: 542 baiting, 4: 542 microorganisms spread, 4: 542 poisoning, 4: 542 repellent methods, 4: 542 Birth see Parturition Birth-and-spread model, 3: 189 Birthweight, 2: 826 Biruni, 2: 505 Bisanthraquinonoids, 4: 793 structure, 4: 793, 4: 794f Bisfuranoids, 4: 792 Biting flies, 3: 431 ‘Bitty cream’ defect, 3: 721, 4: 24 Black Bedouin goats see Barki goats Black box models, 4: 248 Blair House Accord, 4: 342 peace clause, 4: 342 Blastocoel, 4: 485–486 formation, 4: 493–494, 4: 495f Blastocoelic cavity, 4: 493–494 Blastocyst, 4: 485, 4: 486f, 4: 493–494 definition, 4: 485 filamentous (chorionic vesicle), 4: 486 freed/hatched, 4: 486, 4: 486f hatching, 4: 494–495 spherical stage, 4: 486, 4: 486f Blastomeres, 4: 493–494 Bleaching agents, 1: 40 Blended fat spreads, 1: 523 Blends, 1: 523 batch churning, 1: 526 cream inversion, 1: 527 Bloat, 2: 206–211 breed susceptibility, 2: 208–209 economic significance, 2: 206 esophageal sphincter inhibition, 2: 206–208 foam hypothesis, 2: 206 antifoaming agents, 2: 208 foamy see Foamy bloat
Index foraging management, 2: 574 free-gas, 2: 206, 2: 206–208 future impacts, 2: 210 in goats, 2: 794–795 legumes, 2: 206 mortality, 2: 206 prevention, 2: 209 severity rating, 2: 206, 2: 207f surgical interventions, 2: 210 tannins, 2: 208, 2: 577, 2: 577, 2: 584–585 treatment, 2: 209 types, 2: 206 weather parameters, 2: 208–209 Blockformer, 1: 611, 1: 612f, 1: 613f Blood pressure fermented milk effects, 2: 486 milk proteins reducing, 3: 1064 Blood serum albumin (BSA), 3: 481 Blue cheese(s) cholesterol-reduced, 3: 738 flavor, 2: 287 Harmonized System, 4: 335 hyperspectral imaging classification, 1: 131 manufacture mechanization, 1: 614 PR toxin, 4: 774 roquefortine, 4: 775 Blue mold cheeses, 1: 767–772 aroma formation, 1: 771 detrimental microbial effects, 1: 769 Geotrichum candidum, 1: 769 Penicillium, 1: 769 lipolysis, 1: 771, 1: 771t manufacture, 1: 767 microflora, 1: 767 atmosphere, 1: 768 microstructure, 1: 767, 1: 768f mold growth, 1: 767 pH, 1: 767 proteolysis, 1: 769, 1: 770f, 1: 770t aspartic proteases, 1: 769–771 enzymes, 1: 770t exopeptidases, 1: 771 metalloproteases, 1: 769–771 NSLAB, 1: 771 pH, 1: 771 yeasts, 1: 771 see also specific cheeses Blue native electrophoresis, 1: 189, 1: 189 Bluetongue (BT), 2: 146–152 causes, 2: 147 control, 2: 151 diagnosis, 2: 150 differential diagnosis, 2: 148–149 disease signs, 2: 148, 2: 148f, 2: 148f, 2: 148f, 2: 149f, 2: 149f edema, 2: 148f, 2: 148f epidemiology, 2: 146–147 male reproductive tract damage, 2: 150 necrotic skin lesions, 2: 148–149, 2: 149f reproductive health, 2: 149–150 treatment, 2: 152 ulcers, 2: 148f, 2: 148–149 Bluetongue virus (BTV), 2: 147 congenital infection, 2: 149–150 control, 2: 151 endemic countries, 2: 147 isolation, 2: 150 seroprevalence, 2: 151 serotypes, 2: 147 sheep, 2: 147 vaccines, 2: 152 vectors, 2: 151 worldwide distribution, 2: 146–147 Blue-veined cheeses homogenization, 1: 549 Kluyveromyces, 4: 762 ripening, Penicillium roqueforti, 1: 568 secondary cultures, 1: 568t
spoilage molds, 4: 780–781 surface yeasts, 4: 751 Blue whale milk, 3: 580 B lymphocytes immunoglobulin production, 3: 811 mammary gland defense, 3: 390, 3: 390t Body condition, 1: 463–467 data processing, 1: 457–462 dry period, 2: 449 ghrelin, 1: 465 importance, 1: 457 leptin, 1: 464–465 measurement techniques, 1: 457–462 see also Body condition score (BCS) Body condition score (BCS), 1: 458 automated system, 1: 460 calving, 1: 464, 1: 464f, 4: 436 data processing, 1: 460 first breeding, 1: 461–462 management decisions, 1: 460–461 nutritional management, 1: 462 reproductive management, 1: 461 development, 1: 458 drylot management systems, 2: 53 dry period, 4: 436 fat cow syndrome, 1: 466 fatty liver, 1: 465 feed intake, 1: 463 5-point system, 1: 458, 1: 459f, 1: 459t automated, 1: 461f tactile appraisal, 1: 459–460 use of, 1: 459 visual appraisal, 1: 459–460 goats, 2: 790, 2: 790, 2: 792, 2: 825 breeding period, 2: 834–835 health indices, 1: 463 historical aspects, 1: 458 ketosis, 1: 465 metabolic diseases, 1: 465 milk fever, 1: 465 milk production effects, 1: 463, 1: 463 postpartum, 4: 515, 4: 516f anovulatory follicles, 4: 435, 4: 435t estrous cyclicity, 4: 436 reproductive disease, 1: 466 fatty acid availability, 1: 466 insulin, 1: 466 insulin-like growth factor-I, 1: 466 luteinizing hormone-releasing hormone, 1: 466 retained placenta, 1: 466 sheep, 2: 888 targets, 4: 516, 4: 516t Body fat, milk production, 1: 464 Body mass index (BMI), blood cholesterol levels, 3: 731 Body weight blood cholesterol levels, 3: 731 leptospirosis, 2: 181 loss, drylot management systems, 2: 53 milk production, 1: 457–458 Boer goats, 1: 311t, 1: 322, 1: 322f milk yields, 1: 312t Boiler(s) return piping systems, 4: 593 water treatment, 4: 587 Boiler efficiency calculation, 4: 592 indirect approach, 4: 592, 4: 593t definition, 4: 592 Boiler feed water, effluent, 4: 613–615 Bone health, 3: 1009–1015 calcium, 3: 1009 dairy product effects controlled trials, 3: 1014 interventional studies, 3: 1014 diet and, 3: 1060 lactose intolerance, 3: 1013 lifetime mass changes, 3: 1009, 3: 1010f
843
Bone loss, phosphorus, 3: 931 Bone mineral density (BMD) periodontal disease, 3: 1039 potassium intake, 3: 1013 Bone proteins, vitamin K-dependent, 4: 663 Bone resorption, milk protein effect, 3: 1065 Bonobo milk oligosaccharides, 3: 617t chemical structures, 3: 271t Booster pump, HTST pasteurizer, 4: 197 Bordaleiro sheep, 1: 332t Boron in milk, 3: 934, 3: 934t chemical forms, 3: 936 nutritional significance, 3: 939 Bos bubalus bubalis see Indian buffalo Bos grunniens see Yak Bos indicus cattle, 1: 300–309, 1: 301t, 2: 99 behavior, 1: 300 Bos taurus vs., 1: 284–285 characteristics, 1: 300 cold stress, 4: 444–445 domestication, 3: 326–327 gestation period, 1: 300 historical aspects, 1: 3 seasonal breeding, 4: 444 yak hybrids, 1: 345–346 see also specific breeds Bos indicus Bos taurus cattle, 1: 302, 1: 306 adaptation traits, 1: 306 characteristics, 1: 303t crossbreeding strategies, 1: 308 F1 system, 1: 308 hybrid bulls, 1: 308 rotational crossing, 1: 308 dairy performance, 1: 307, 1: 307f genetic soundness, 1: 302–303 heterosis, 1: 308 milking traits, 1: 306, 1: 307t production systems, 1: 306 Bos primigenius (auroch; wild ox), 1: 284, 3: 326–327 Bos taurus cattle, 1: 284–292 breed concepts, 1: 285 classification by utility, 1: 285 dairy cattle, 1: 285 Asian breeds, 1: 285t in beef production, 1: 289, 1: 290t, 1: 290t, 1: 291t, 1: 291t European breeds, 1: 286t genetic trends, 1: 290, 1: 291f, 1: 291f, 1: 292f North America, 1: 286t stability/survival, 1: 290 straightbred vs. crossbreeds, 1: 289, 1: 289t, 1: 290t domestication, 1: 284, 3: 326–327 dual-purpose breeds, 1: 293–299 historical aspects, 1: 293 future work, 1: 291 geographical distribution, 1: 285 heat stress, 4: 444–445 minor breeds, 1: 293–299 Africa, 1: 298 Asia, 1: 298 Europe, 1: 297 New World, 1: 298 seasonal breeding, 4: 444 yak hybrids, 1: 345–346 see also specific breeds Bottle-feeding, lambs, 2: 884 ‘Bottle jaw’, 2: 176 Bottlenose dolphin milk oligosaccharides, 3: 271t Bottles glass see Glass bottles plastic, 2: 710 Bottle washing, wastewater production, 4: 615 Bottoming, 2: 590 Botulinum toxins, 4: 47–49 biosensors, 1: 242 detection methods, 4: 52
844 Index Botulism, 4: 47–49 affected cattle, milk safety, 4: 51 dairy foods, 4: 50 recent outbreaks, 4: 50, 4: 50t symptoms, 3: 312 Boulette d’Avesnes, 1: 787 Bound moisture, 4: 211, 4: 212f Bovine genome sequence, 2: 663 human genome sequence vs., 2: 663 sequence variations with/between populations, 2: 664 Bovine Genome Sequencing Project, 3: 966 Bovine leukocyte adhesion deficiency (BLAD), 2: 677 comparative mapping, 2: 677–678 Bovine leukosis virus (BLV), 1: 470 Bovine lymphocyte antigen (BoLA) genes, 3: 429 Bovine milk see Milk Bovine milk lysozyme (BML), 2: 331 Bovine neutrophil cationic proteins, 3: 388 Bovine progressive degenerative myeloencephalopathy (weaver), 2: 676–677 Bovine rennets see Rennet(s) Bovine serum albumin (BSA), 3: 796t, 3: 798 allergic reactions, 3: 799 gelation, 3: 892 mammary tight junction integrity, 3: 798–799 primary structure, 3: 755, 3: 757f type 1 diabetes, 3: 1047 Bovine somatotropin (bST), 3: 32–37 administration, 3: 38 approved formulation, 3: 32 biweekly injection, 3: 33 body temperature increases, 4: 563 buffalo, 3: 36 carbohydrate metabolism, 3: 35 as contaminant, 1: 893–894 direct effects, 3: 33–34 goats, 3: 36 historical aspects, 3: 32 homeorhetic regulation, 3: 36 induced lactation, 3: 21 insulin-like growth factors, effects on, 3: 33–34, 3: 38 insulin responsiveness, 3: 34–35 lactation efficiency, 3: 32–33 lipid metabolism, 3: 34, 3: 35f lipolysis promotion, 3: 35 mammary gland population kinetics, 3: 36 mastitis, 3: 37 milk composition, 3: 33 milk production effects, 3: 32 milk yield, exogenous stimulation, 3: 38 mode of action, 3: 33 metabolic adaptations, 3: 34 negative energy balance, 3: 32–33 protein metabolism, 3: 35–36 reproductive effects, 3: 37 sheep, 3: 36 sustained-release formulation, 3: 33 udder health effects, 3: 37 Bovine spongiform encephalopathy (BSE) resistance, transgenic animals, 2: 643 Bovine tuberculosis, 2: 195–198 airborne infection, 2: 195 causative organism, 2: 195 clinical signs, 2: 195 diagnosis, 2: 196 domestication and, 2: 195 economic impact, 2: 195–196 epidemiology, 2: 195 eradication programs, 2: 49, 4: 91 historical aspects, 1: 26 import testing requirement, 2: 195–196 Mycobacterium bovis, 2: 195 pathogenesis, 2: 195 prevention/control, 2: 197 within herds, 2: 197 obstacles to, 2: 197
regional/national level, 2: 197 public health concerns, 2: 197 surveillance, 2: 197 symptoms, 4: 87–88 treatment, 2: 196 wildlife populations, 2: 197 wildlife reservoirs, 4: 91 Bovine viral diarrhea (BVD), bulls, 1: 479, 1: 479 Bovine viral diarrhea virus (BVDV), 1: 470, 1: 470 Bowl milking units, goats, 2: 811, 2: 811f Bracken fern toxin, 1: 905 Brambell Committee, 4: 727 Branched-chain amino acids (BCAAs), cheese flavor, 1: 641–642, 1: 642 Branched-chain fatty acids, sheep milk, 3: 498 Brassica napus var. napobrassica (swede; rutabaga), 2: 560 Brassica napus var. napus (rape), 2: 560 Brassica oleracea (kale), 2: 560 Brassica rapa var. rapa (turnip), 2: 560 Braunvieh cattle, 1: 286t Brazil dairy cow numbers, 1: 10, 1: 10t dairy industry, 1: 10t dairy societies, 2: 105 Brazilian Milking Hybrid cattle, 1: 303t, 1: 304, 1: 304f Bread, dairy ingredients, 2: 130 Breast cancer milk consumption and, 3: 610, 3: 610f vitamin C, 4: 673 Breast epithelial antigen see Lactadherin Breast milk see Human milk Breed, Robert Stanley, 1: 26–27 Breeding see Reproduction Breed smear, 1: 26–27 Bregott, 1: 523 Brela camels, 1: 352 Brevibacterium aurantiacum, 1: 395, 1: 398 Brevibacterium linens, 1: 395–400 cheese ripening, 1: 569, 4: 750 antimicrobials, 1: 570 bacterial surface-ripened cheeses, 1: 569–570 bacteriocins, 1: 570 commercial cultures, 1: 572 methanethiol, 1: 570 pigments, 1: 570 sulfur compounds, 1: 570 colonies, 1: 396 extracellular aminopeptidases, 1: 570 extracellular proteinases, 1: 570 smear-ripened cheeses, 1: 395, 1: 396, 1: 398, 1: 759, 1: 762, 1: 763 starter cultures, 1: 560t Brewing byproducts, 2: 346 copper toxicity, sheep, 2: 852–853 Brick cheese starter cultures, 4: 751 yeasts, 4: 750, 4: 751 Bridging flocculation, 3: 891 Brie cheese free fatty acids, 1: 771t manufacture, traditional, 4: 778 mechanization, manufacture, 1: 614 Penicillium camemberti, 4: 778 Brie de Meaux cheese, listeriosis outbreaks, 4: 83 Bright field light microscopy, 1: 226 Brin d’Amour, 1: 787 Brine semihard cheese manufacture, mechanization, 1: 613–614, 1: 615f yeasts, 4: 752 Brine-matured cheeses, 1: 790–794 characteristics, 1: 790, 1: 790 color, 1: 790–791 shape, 1: 791 cheese solid removal, 4: 180 color, 1: 790–791 composition, 1: 792
flavor, 1: 793 lipolysis, 1: 793 volatile free fatty acids, 1: 793 manufacture, 1: 791 standardized techniques, 1: 791 microbiology, 1: 793 production statistics, 1: 790 ripening, 1: 793 structure, 1: 794 texture, 1: 794 types, 1: 790, 1: 791t see also Cheese salting; specific cheeses Brine salting, 1: 597–598, 1: 598 brine concentration, 1: 601 cheese geometry, 1: 601 Emmental cheese manufacture, 1: 712 initial moisture content, 1: 601 initial salt content, 1: 601 lactate levels, 1: 605 moisture content, 1: 604–605 pH, 1: 601 salt distribution, 1: 602, 1: 603f salting time, 1: 601 salt uptake/moisture loss, 1: 598, 1: 599f, 1: 600f, 1: 601 temperature effects, 1: 601 British-Friesian cows, 4: 479f British Milksheep, 1: 337 -Bromoergocryptine (CB154), 3: 18 Bromus willdenowii (prairie grass), 2: 576 Broth microdilution test, Campylobacter, 4: 43 Brown Atlas cattle, 1: 298 Brown capuchin colostrum oligosaccharides, 3: 271t milk oligosaccharides, 3: 617t ‘Brown cheese’, 1: 542 Browning, 3: 217 chemical nature of products, 3: 217 enzymic, 3: 217 low-moisture part-skim mozzarella (pizza cheese), 1: 743 nonenzymatic see Nonenzymatic browning oxygen in, 3: 217 Brown midrib (bmr) gene, forage crops, 2: 553–554, 2: 554, 2: 564, 2: 582–583, 2: 585 Brown Swiss cattle, 1: 286, 1: 286t, 1: 287f birth, weaning and postweaning traits, 1: 290t carcass characteristics, 1: 290t historical aspects, 1: 2 Latin American dairy management, 2: 91 milk composition, 2: 53t puberty/pregnancy rates, 1: 291t reproductive/maternal traits, 1: 291t Brucella, 2: 153, 3: 450, 4: 31–39 antibiotic susceptibility, 4: 33, 4: 33t antigenic characteristics, 4: 31, 4: 33t biochemical characteristics, 4: 31, 4: 32t, 4: 33t characteristics, 4: 31 culture, 4: 31, 4: 33t detection, 2: 155 differential characteristics, 4: 32t dye susceptibility, 4: 33, 4: 33t growth characteristics, 4: 31 morphology, 4: 31 phage susceptibility, 4: 32t, 4: 33 resistance, 4: 33 survival, 4: 33, 4: 34t Brucella abortus, 1: 645, 2: 153, 4: 31, 4: 32t Brucella abortus 45/20 vaccine, 2: 158 Brucella abortus biovar 2308 vaccine, 2: 158 Brucella abortus RB51 vaccine, 2: 158 Brucella canis, 4: 31, 4: 32t Brucella ceti, 4: 31, 4: 32t Brucella melitensis, 2: 154, 4: 31, 4: 32t, 4: 35 Brucella melitensis H38 vaccine, 2: 158 Brucella melitensis strain Rev 1 vaccine, 2: 158 Brucella microti, 4: 31, 4: 32t Brucella neotomae, 4: 31, 4: 32t
Index Brucella ovis, 2: 154, 4: 31, 4: 32t Brucella pinnipedialis, 4: 31, 4: 32t Brucella suis, 4: 31, 4: 32t Brucellosis, 2: 153–159, 4: 34 allergic tests, 4: 37 artificial insemination centers, 1: 470 buffalo, Mediterranean region, 2: 782 carrier state, 2: 153 clinical findings, 2: 154 cattle, 2: 154 sheep/goats, 2: 154 congenital infection, 4: 35 control, 2: 157, 4: 37 general measures, 4: 37 laboratory, 4: 38 diagnosis, 2: 154, 4: 36 bacteriological methods, 4: 36 clinical signs, 2: 155 culture, 4: 36 direct bacteriological assessment, 2: 155 serological assays, 2: 155, 2: 156t staining methods, 4: 36 epidemiological surveillance, 4: 38 epidemiology, 2: 153 eradication by test and slaughter, 4: 38 fetal necropsy, 2: 155 history, 2: 155 human, 2: 153, 3: 312–313, 4: 35 chronic, 4: 35–36 complications, 4: 35–36 diagnosis, 4: 35–36 infection routes, 4: 35–36 symptoms, 4: 35–36 treatment, 4: 36 identification, 4: 37 immunization, 4: 38 mammary gland, persistent infection, 4: 35 national eradication schemes, 2: 49 new infection prevention, 2: 157–158 risk factors, 2: 153–154 screening tests, 2: 155 serological diagnosis, 4: 37 shedding, 4: 35 sheep, 2: 857 small ruminants, 4: 35 specimen collection, 4: 36 dairy products, 4: 36 milk, 4: 36 specimen culture dairy products, 4: 36 milk, 4: 36 surveillance, 2: 158 symptoms, 4: 31, 4: 34, 4: 34–35 typing, 4: 37 vaccination, 2: 158 Brydes whale milk oligosaccharides, 3: 271t BSE resistance, transgenic animals, 2: 643 B-type esterases, 2: 304 Bubalus bubalis (water buffalo) see Buffalo BUBBLE PLATE, 4: 217, 4: 219f Buck(s) breeding soundness examination, 2: 837 foot care, 2: 837 general physical examination, 2: 837 genital examination, 2: 837, 2: 837f, 2: 838t scrotal circumference measurement, 2: 837–838, 2: 838f feeding management, 2: 787t, 2: 792, 2: 793t fertility examination, 2: 838 libido assessment, 2: 838 semen quality, 2: 838t, 2: 838–839 health, 2: 801 natural service management, 2: 837 prebreeding nutrition, 2: 837 see also Goat(s) Bucket milking machines, goats, 2: 804 Buck exposure, estrus synchronization, 2: 835 Bucking pressure, teat-cup liners, 3: 948
Buckwheat, aflatoxin contamination, 4: 807 Budget method, additive exposure assessment, 1: 58 Buendner goats, 1: 313 Buffalo, 1: 340–342, 1: 341f artificial insemination, 4: 473 Asia, 2: 772–779 artificial insemination, 2: 774 breeding management, 2: 773 calf feeding, 2: 775 calf mortality, 2: 779 crop residue utilization, 2: 776 crossbreeding, 2: 775 embryo transfer technology, 2: 774 estrous cycle, 2: 773 estrus signs, 2: 773–774 feeding management, 2: 775 fertility, 2: 775 gestation, 2: 774 health management, 2: 778 infectious diseases, 2: 778t, 2: 779 lactating buffalo feeding, 2: 775 lactation length, 2: 776 metabolic disorders, 2: 778t, 2: 779 milk harvesting, 2: 776 milking technique, 2: 776 milk marketing, 2: 777, 2: 777t milk production, 2: 776t milk products, 2: 778 milk yield, 2: 776 nutritional requirements, 2: 775, 2: 776t parturition, 2: 774 population, 2: 772 postpartum period, 2: 775 pregnancy diagnosis, 2: 774 puberty, 2: 773 reproductive management, 2: 775 reproductive parameters, 2: 774t ‘silent estrus’, 2: 775 species, 2: 772 thermal stress, 2: 778 types, 2: 772, 2: 773t bovine somatotropin treatment, 3: 36 crossbreeding, 1: 340 diseases, 1: 341 distribution, 1: 340 domestication, 3: 327 future work, 1: 342 grazing characteristics, 1: 342 heat stress, 4: 445 Mediterranean region, 2: 780–784 artificial insemination, 2: 780–781 breeding management, 2: 780 bull/heifer choice, 2: 780–781 bulls, 2: 780 butter, 2: 783 cheese, 2: 783 cheese-processing plant byproducts, 2: 783 creams, 2: 783 daily milk yield, 2: 781 feeding management, 2: 781, 2: 782t fermented milk, 2: 783 ghee, 2: 783 health management, 2: 782 herd size, 2: 780, 2: 781f housing, 2: 781 lactation, 2: 781, 2: 781f milk products, 2: 783 parasitic infections, 2: 782 phenotypic differences, 2: 780 population, 2: 780 traditional housing, 2: 781 viral infections, 2: 782 productivity, 1: 340 reproduction, 1: 341 seasonal breeding, 4: 444 Buffalo colostrum oligosaccharides, 3: 271t Buffalo milk, 3: 503–511 buffering capacity, 3: 509
845
cholesterol, 3: 506 color, 2: 778, 3: 510 composition, 1: 341t Asia, 2: 777, 2: 777t other species vs., 3: 503, 3: 504t curd tension, 3: 510 dahi, 2: 507 density/specific gravity, 3: 509 electrical conductivity, 3: 472 enzymes, 3: 505, 3: 505t ethanol stability, 3: 509 fat globules and membranes, 3: 507 fatty acid composition, 3: 506, 3: 506t, 3: 506t flavor, 3: 510 freezing point, 3: 509 global production, 3: 503 glyceride structure, 3: 506 heat capacity, 3: 510 heat stability, 2: 749 immunoglobulins, 3: 505 khoa, 1: 882–883 lipids, 3: 505 lipoprotein lipase, 2: 304–305 Mediterranean region, 2: 783 cheese-processing plant byproducts, 2: 783 milk fat minor components, 3: 506 physicochemical properties, 3: 507 mineral salts, 3: 507, 3: 507t nonprotein nitrogen, 3: 508 nutritive value, 2: 777 oxidation–reduction potential/conductivity, 3: 510 pH, 3: 509 phospholipids, 3: 506 physicochemical properties, 3: 508, 3: 508t heat stability and pH, concentrated milk, 3: 509, 3: 509f heat stability and pH effects, 3: 508, 3: 509f thermal expansion/conductance, 3: 510 pigments, 3: 508 processing inherent advantages, 3: 510 problems, 3: 511 products, 3: 510 proteins, 3: 503, 3: 504t cross-reactivity, 3: 1044 rennet stability, 3: 509 storage, 2: 776 surface tension, 3: 510 trace elements, 3: 507 viscosity, 3: 510 vitamins, 3: 508, 3: 508t yogurt Enterobacteriaceae, 4: 69 set see Zabady (buffalo milk set yogurt) Buffered Brucella antigen tests (BBAT), 4: 37 Buffered peptone water (BPW), 2: 193 Buffering capacity, 3: 911–912 Buffering index, 3: 474 Buffering salts, 2: 201–202 Buffer tanks, 4: 126 Buhlri goats, 1: 311t Building design (farm) see Farm design (warm climates) Bujiri goats, 1: 319 Bulgarian buttermilk, 2: 472 Bulk milk bacterial sources, 3: 632 culture cleaning assessment methods, 3: 636 Mycoplasma bovis mastitis, 3: 412 Staphylococcus aureus incidence, 4: 114 Streptococcus agalactiae mastitis, 3: 410–411 Bulk starter cultures, 1: 557 growth units, 1: 557 Bulk tank(s) historical aspects, 1: 6 improper cleaning, 3: 646
846 Index Bulk tank(s) (continued ) Salmonella contamination, 4: 93 spray cleaning, 3: 636 Bulk tank somatic cell count (BTSCC), 3: 897 herd welfare index, 3: 897 Bulk waves, ultrasound, 1: 206, 1: 207f Bull(s) artificial insemination centers handling, 2: 603 nonreturn rate, as success measurement, 2: 607, 2: 607f semen freezing and thawing equipment, 2: 606 brucellosis, 2: 154 fertility, 4: 483 fertility evaluation, 1: 476 coitus examination, 1: 477 epididymis, 1: 476 penis examination, 1: 476 scrotal circumference, 1: 476 scrotal examination, 1: 476 semen examination, 1: 477 testicular examination, 1: 476 health/disease control, 1: 479 health evaluation, 1: 476 infertility, 4: 483 lameness, 1: 479 management, 1: 475–480 mating period, 1: 477 heat stress, 1: 478 number required, 1: 478 nutrition, 1: 478 performance monitoring, 1: 479 selection, 1: 477, 1: 478 nutrition, 1: 475 sexually transmitted disease, 1: 479 vasectomized, heat detection, 4: 477 Bulldog (achondroplasia), 2: 676, 2: 676f The Bulletin, OIE, 4: 5 Bunker silos, 1: 5–6 Buoyancy force, centrifuges, 4: 175 Burger bodies, 1: 689, 1: 689f Burgos, 3: 501 Burton–Cabrera–Frank (BCF) theory, 3: 189 Business goals, 1: 482 Business management analysis, 2: 684t, 2: 685 dairy production protocol, 2: 683, 2: 684f implementation, 1: 481, 1: 484 personal development, 1: 484 resources, 1: 484 staff, 1: 484 training, 1: 484 management roles, 1: 481–485 controlling, 1: 484 finance, 1: 481 marketing, 1: 481 problem solving, 1: 485 production, 1: 481 skills needed, 1: 482 planning, 1: 481, 1: 482 business goals, 1: 482 decision making, 1: 483 definition, 1: 482 long-term (strategic), 1: 482 marketing decisions, 1: 483 market research, 1: 483 past performance evaluation, 1: 483 resource management, 1: 482–483 risk management, 1: 483 sensitivity analysis, 1: 483–484 system diversity, 1: 483 quality management support, 2: 685 records, 2: 684t, 2: 685 Business process reengineering (BPR), 4: 264–265 Butter, 1: 492–499 air content alterations, 3: 708 analysis, 1: 506–514 appearance, 1: 511
autoxidation, 1: 513 batch manufacture, 1: 497 batch vs. continuous manufacture, 3: 708 buffalo milk, Mediterranean region, 2: 783 camel milk, 1: 356 characteristics, 1: 493 cholesterol removal, 1: 503, 3: 737 Christmas, 1: 503 churning, 1: 494 cream pretreatment/cooling, 1: 494, 1: 495t fermentation, 1: 495 Codex standard, 1: 492, 4: 328 color, 1: 511 -carotene, 1: 511 composition, 1: 506 confectionery, 1: 503 confocal scanning laser microscopy, 1: 233–234, 1: 234f consistency, 1: 512 consumption, 1: 506 continuous manufacture, 1: 495, 1: 496f, 3: 708 churning, 1: 495 culturing, 1: 497 packaging, 1: 497 salting, 1: 497 separation, 1: 496 vacuum pretreatment, 1: 497 working, 1: 496 cream aging, 3: 709 E. coli control measures, 4: 65 elevated somatic cell count effects, 3: 905 fat content, 1: 506, 1: 506 chemical composition, 1: 506 seasonal variation, 1: 507 fat globules, 1: 509–510 electron microscopy, 1: 510–511 fatty acid composition, 1: 506, 1: 507f, 1: 507f margarine vs., 1: 507, 1: 507f ‘faultless’, 1: 511 flavor, 1: 511 lipid fraction compounds, 1: 511–512 temperature effects, 1: 511–512 unsaturated fatty acid oxidation, 1: 511–512 flavor defects, 1: 511–512 half-fat, 1: 522 hardness, 3: 704, 3: 705f high-melting fraction triacylglycerol addition, 3: 707 historical aspects, 1: 1, 1: 15 hydrolytic rancidity, Pseudomonas, 4: 382 infrared spectrometry, 1: 119t international prices, 4: 348, 4: 349f iodine value modifications, 3: 706 keeping quality, 1: 513 light-induced oxidation, 3: 718, 4: 21 lipolytic defects, 3: 724 postmanufacture, 3: 724 lipoprotein lipase, 1: 493 low-melting fraction triacylglycerol addition, 3: 707 macromineral contents, 3: 927t macroscopic properties, 1: 511 see also specific properties manufacture, 1: 494, 1: 494f byproducts, 2: 489, 2: 490f citrate fermentation, 3: 172 emulsification, 1: 498, 1: 498f methods, 4: 177 plasticizing treatments, 3: 709, 3: 709f prechilling, 3: 709 traditional process, 1: 526 mechanical agitation, 3: 709 melting behavior, 1: 508, 1: 508f microstructure, 1: 234f, 1: 509, 1: 510f electron microscopy, 1: 510–511, 1: 511f fat crystals, 1: 509–510 fat globules, 1: 509–510 water droplets, 1: 509–510
milk fat, 1: 493 rapid cooling, 3: 708, 3: 709f slow cooling, 3: 708, 3: 708f modified see Modified butters moisture content alterations, 3: 708 moisture determination, 1: 76 moisture droplets, 1: 524 mouthfeel, 1: 508f, 1: 512 nondairy food, 2: 128t off-flavors, 1: 493–494 packaging, 4: 21 phospholipid composition, 1: 506 processing equipment, 4: 128t properties, 1: 506–514 see also specific properties ‘protected fat’ supplements, 3: 659 pseudoplastic flow, 3: 705, 3: 705f raw material quality, 1: 493 recombined/reconstituted products, 3: 319 rheology, 1: 493 sampling, 1: 73 scanning electron microscopy, 1: 233–234 seasonal variability, 3: 704–705 seeding (recycling), 3: 709 setting, 1: 501, 1: 512, 3: 709 sodium dietary source, 3: 928 softness, 3: 549 solids-not-fat, 1: 506 spreadability, 1: 508f, 1: 513 spiced see Spiced butter spoilage, 4: 21 spreadability, 1: 513, 3: 704, 3: 705f, 3: 705f cream ripening, 1: 513 grading, 1: 513 seasonal diet, 1: 513 stability, anhydrous milk fat, 1: 517 starter cultures, historical aspects, 1: 15, 1: 28 storage conditions, 3: 709 summer, 1: 513, 3: 704–705 surfactants, 3: 708 texture, 1: 512 thixotropy, 1: 512–513 trace element content, 3: 935t triacylglycerols composition, 1: 506, 1: 507, 1: 508f recrystallization, 3: 709 type identification, 3: 977 varieties, 1: 492 cultured salted, 1: 492–493 unsalted, 1: 492–493 sweet cream salted, 1: 492–493 unsalted, 1: 492–493 viscoelastic nature, 3: 705 mechanical models, 3: 705 water content, 1: 493, 1: 496t, 1: 502, 1: 506 whipped see Whipped butter winter, 1: 513, 3: 704–705 work softening, 1: 501, 1: 512 world production, 1: 492 yak milk see Yak milk butter yeasts, 4: 745 Butterballs, 1: 544 Butterfat hardness, cow’s ration and, 1: 509f melting behavior, 1: 508, 1: 508f milk chocolate, 1: 857 synthesis, 3: 332 Butterfly valve, 4: 152, 4: 153f dairy processing, 4: 156, 4: 156f Buttermilk, 2: 489–495 acidity, 2: 535, 2: 536f applications, 3: 694 caseins, 3: 693 cheesemaking, 3: 695 commercial production, 2: 489, 2: 489 composition
Index aroma chemicals, 2: 535 chemical components, 2: 489, 2: 490t fermentation changes, 2: 535, 2: 536f, 2: 536f flavor chemicals, 2: 535 standard requirements, 2: 489 consumption, 2: 489, 2: 494 cultured see Cultured buttermilk defects, 2: 493, 2: 535 definition, 2: 489 flavor development, 2: 492, 2: 493, 2: 535 food products uses, 2: 489 fractions, 3: 691–697 as heat stability enhancer, 3: 695 microbiological defects, 4: 745 milk fat globule membrane composition, 3: 691 proteins, 3: 692 natural (conventional), 2: 489, 2: 490f nutritional value, 2: 494, 3: 694t, 3: 695 phospholipids, 3: 671–672, 3: 673t polar lipids, 3: 692 processing technologies, 2: 494 production diacetyl formation, 3: 172 processes, 2: 489, 2: 490f separation, disk bowl centrifuges, 4: 179 starter cultures, 2: 491, 2: 493t technological value, 3: 694, 3: 694t vitamin content, 2: 494, 2: 494t whey see Whey buttermilk yeasts, 4: 745 Buttermilk powder, milk chocolate, 1: 860 Butter oil cholesterol removal, 3: 737 lipolysis, 2: 285–286 production, separators, 4: 172 Butter powder, 1: 502 manufacture, 1: 502 uses, 1: 502 Butylated hydroxyanisole (BHA), 4: 790 Butyrate colon cancer prevention, 3: 1021, 4: 369–370 equine milk, 1: 360 humans, 4: 368 ketosis, 2: 233 Butyric acid analysis, 3: 699 Dutch-type cheese defects, 1: 726 equine milk, 1: 360 fermentation, raw milk cheeses, 1: 659 pregastric esterase-induced release, 2: 285 skeletal structure, 3: 656f Swiss-type cheese defects, 1: 719 Butyric acid bacteria, gas blowing defects, 1: 662 avoidance, 1: 663 bacterial growth inhibition, 1: 663 cheese milk spore removal, 1: 663 milk contamination avoidance/minimization, 1: 663 spore germination inhibition, 1: 663 Butyrophilin lactation, 2: 325–326 nomenclature, 3: 758 Butyrophilin 1A1, 3: 375–377 functions, 3: 687 glycans, 3: 687–688 knockout mice, 3: 687 milk fat globule membrane, 3: 687 structure, 3: 686f, 3: 687 synthesis, 3: 687 Bypass protein, 3: 361 Byproduct feeds see Coproduct feeds
C CA, see Cheese analogues (CA) Ca2+ATPase isoform 2 (PMCA2bw), 3: 379 Cabrales cheese, 3: 501 free fatty acids, 1: 771t
Cacik (lor), Otlu cheese, 1: 783–784 Caciocavallo Podolico, 1: 746 Caciocavallo Pugliese, 1: 746 microbiology, 1: 748 plasmin activity, 1: 749–751 Caciocavallo Ragusano see Ragusano Caciocavallo Silano, 1: 746 lipolysis, 1: 751–752 manufacture, 1: 746 microbiology, 1: 748 related varieties, 1: 746 Cadaverine, 1: 451, 1: 452t Cadmium, 1: 901t Caking, 4: 709 milk powder, 2: 122 plasticization, 4: 710 Calbindin (CaBP), 3: 996–997 Calbindin D9k, 3: 1056 Calcidiol, 4: 646 Calciferol see Vitamin D ‘Calcified liver fluke liver with pipes’, 2: 266, 2: 267f Calcitriol, 4: 646 calcium-phosphate homeostasis, 4: 648–649 Calcium, 2: 371 absorption, 2: 239, 2: 372 dietary influences on, 2: 372 lactose effects, 3: 929–930 from milk products, 2: 484 phosphopeptides, 3: 1063 physiological state, 2: 372 ruminants, 3: 996 small intestine, lactating ruminants, 3: 995 adequate daily intake, 3: 929, 3: 1009 age and, 2: 372 biosensors, 1: 244 bone health, 3: 1009 breed and, 2: 372 cheese, 1: 536, 3: 926, 3: 927t chelatants and, 3: 912–913 colorectal cancer prevention, 3: 1019, 3: 1019t epidemiology, 3: 1018 mechanisms, 3: 1019, 3: 1019f in dairy products, 3: 926t, 3: 926t, 3: 927t, 3: 1011, 3: 1011t bioavailability, 3: 1012 deficient diet, milk fever prevention, 2: 243 dietary availability, 2: 372 dietary sources, 3: 929 displaced abomasum, 2: 213 dry period, 2: 450 equine milk, 3: 526–527 first-age infant formulae, 2: 142 functions, 3: 929 gels, 3: 892–893 heat stability, milk, 2: 745 homeostasis, 2: 371 human milk, 3: 929 imitation milks, 2: 914 induced interactions, rennet milk coagulation, 1: 580–581 ionized, 3: 927 lactase persistence, 3: 239 lactation diets, 2: 373 laminitis, 2: 203–204 low-moisture part-skim mozzarella (pizza cheese), 1: 743 metabolic acidosis effects, 2: 356 in milk, 3: 925, 3: 926t absorption, 2: 484 bioavailability, 3: 929, 3: 1006, 3: 1006, 3: 1012 chemical form, 3: 908, 3: 927 mastitis effects, 3: 904 mean absorption, 3: 929 nutrient intake, contributions to, 3: 1006 nutritional significance, 3: 929 seasonal variations, 3: 601f milk fever, 2: 243 oral dosing, 2: 243
847
negative balance, 2: 372 nondairy sources, 3: 1010, 3: 1011t osteoporosis, 3: 930 primate milk, 3: 627–629, 3: 628t ration requirements, 2: 373 recommended dietary intake, 3: 928t, 3: 929 rennet milk coagulation, 1: 582 requirements, 2: 371 actively growing cattle, 2: 372 lactating cows, 2: 371–372 nonlactating cattle, 2: 371–372 in pregnancy, 2: 372 secretion in milk, 3: 379 sequestration cheese analogues, 1: 818–819 pasteurized processed cheese products, 1: 809 in serum, 3: 919, 3: 920t citrate interactions, 3: 919, 3: 920f sheep milk, 3: 500 starter chelation, phage control, 1: 443 supplements acidogenic diet and, 2: 360 fracture risk reduction, 3: 1009 hypocalcemia prevention, 4: 518 tolerable upper level, 3: 1009 transition cows, pasture-based systems, 2: 467 vitamin D-dependent absorption, 2: 239 Calcium–calmodulin complex, 4: 508 Calcium caseinate gelation, 3: 893 manufacture, 3: 859 viscosity, 3: 889 Calcium-casein ratio, seasonal variations, 3: 601f Calcium chloride milk fever, 2: 243 milk salt equilibria, 3: 913 oral dosing, 2: 361 rennet milk coagulation, 1: 583 Calcium gluconate, 2: 243 Calcium lactate, 3: 913 Calcium phosphate cheese preacidification, 1: 550 low-moisture part-skim mozzarella (pizza cheese), 1: 737–738 Calcium phosphate nanoclusters, 3: 908–910, 3: 921, 3: 923f chemical formula, 3: 921–923 Calcium phosphate salts, 3: 927 alkalinization, 3: 912 cooling, 3: 912 thermal treatment, 3: 912 Calcium:phosphorus ratio, 2: 372–373 artificial insemination center nutrition, 1: 468–469 Calcium propionate, 2: 243 Calcium salts addition to milk, 3: 913 water hardness, 4: 584 Calcium stearoyl lactylate, 1: 66t Calf see Calves Calf area, 3: 959 Calf blankets, 4: 552 Calf crates, 2: 24, 2: 24f Calf hutches, 2: 24 Calf rearing feeding, 1: 9 historical aspects, 1: 8 warm climate farms, 2: 23 Calf starters, 4: 401 contents, 4: 401 grains, 4: 403–404 desired nutrient levels, 4: 404t mixtures, 4: 404t nonforage fiber sources, 4: 401–402 California, revenue-sharing schemes, 4: 302 California Mastitis Test (CMT), 3: 896 camels, 1: 353 historical aspects, 1: 7 Calorimetry, 2: 418–419, 2: 419
848 Index Calpis, 2: 510 health benefits, 2: 510 starter cultures, 2: 509t, 2: 510 Calves antibiotics, 4: 418 blood immunoglobulin concentrations, 4: 418 colostrum management, 4: 396 diarrhea, 4: 418 growth rate, mammary development and, 4: 400 Johne’s disease, 2: 175 limit-feeding, 4: 398–399 mortality rates, 4: 400 practical management, 4: 400 liquid diets, 4: 396 liquid-feeding programs, 4: 398 environmental effects, 4: 399, 4: 399t, 4: 400t growth rates, 4: 399 intensive/accelerated, 4: 400, 4: 401 practical management, 4: 400 traditional, 4: 398–399 maintenance requirements, 4: 399 environmental temperature and, 4: 399t manual feeding systems, 2: 25 multiple sucking feeding systems, 2: 25 parasite control programs, 4: 406 pasture system adaptation, 4: 406 postweaning, Africa, 2: 78 preruminant diets, 4: 396–402 goals, 4: 396 preweaning, African dairy cow management, 2: 77–78, 2: 78f, 2: 78f transition group placement, 4: 403–404 management, 4: 403 transition pens, 4: 404 waste milk vs. liquid-feeding, 4: 400 water management, 4: 402 weaning, successful, 4: 402 xanthine oxidoreductase supplementation, 2: 325 Calving body condition score, 1: 464, 1: 464f, 4: 436 facilities, warm climates, 2: 27 bedding materials, 2: 28 calving pads, 2: 28 first age see Age at first calving desired body weight, 4: 390, 4: 391t weight at, 4: 403 liver triacylglycerol, 2: 217 see also Parturition Calving difficulty age of cow, 4: 482–483 conception rate, 4: 482, 4: 483f heifers, 4: 415 lost maternal condition, 4: 417 sire breed, 4: 482–483 Calving difficulty scores, 4: 415 Calving-ease sires, 4: 415 Calving paddocks, 2: 27 Calving pads, 2: 28 CamDairy nutrition model, 2: 426 Camel(s), 1: 351–357 breeds, 1: 351 calf mortality, 3: 512 chymosin, 1: 577 functional classification, 1: 351 future work, 1: 357 genetic groups, 1: 352 geographical distribution, 1: 351 gonadotropin-releasing hormone treatment, 4: 444 high-producing dairy types, 1: 352 husbandry, 1: 353 lactation length, 3: 512 mastitis, 1: 353 medium-producing dairy types (dual purpose), 1: 352 milk see Camel milk milk harvesting, 1: 354
intense systems, 1: 354 milk yield, 1: 354 pregnancy duration, 4: 503 reproduction, 1: 353, 3: 512 seasonal breeding, 4: 446 males, 4: 446 udder edema, 1: 353 world population, 3: 512 see also Bactrian camel (Camelus bactrianus); Dromedary (Camelus dromedarius) Camel colostrum, 3: 512–513 Camel meat, 3: 512 Camel milk, 3: 512–517 -amylase, 2: 333 casein phosphorylation, 3: 835 cheese, 3: 515, 3: 515f coagulation time, 3: 514, 3: 514, 3: 515f commercialization, 3: 515 components, 3: 513 composition, 1: 355, 1: 355t, 3: 513, 3: 513t creaming, 3: 513–514 enzymatic coagulation, 3: 514, 3: 515f fat, 3: 513 fatty acids, 1: 355, 1: 355t handling techniques, 3: 516 heat effects, 3: 515 heat stability, 2: 749 hygiene, 3: 515 immunoglobulins, 3: 811 lactose, 3: 514 milk allergy sufferers, 3: 1044 minerals, 1: 355, 1: 356t mineral salts, 3: 514 pasteurization, 3: 515 pH, 3: 513 processing, 1: 356 marketing, 1: 356 production, 3: 512 products, 1: 356 butter, 1: 356 cheese, 1: 356 proteins, 3: 513 spoilage, 3: 516 taste, 3: 513 technologically relevant properties, 3: 514 type 1 diabetes, 3: 1048 vitamins, 1: 355, 1: 356t, 3: 514 water, 1: 355 yield estimates, 3: 512, 3: 513t Camel milk lysozyme (CML), 2: 331 Camel-oriented dairy systems, 3: 516 Camelus bactrianus (two-humped camel) see Bactrian camel (Camelus bactrianus) Camelus dromedarius (one-humped camel) see Dromedary (Camelus dromedarius) Camembert cheese ammonia odor, 4: 778 cholesterol-reduced, 3: 738 curing, 4: 778 flavor, 4: 777–778 flavor defects, 4: 778 free fatty acids, 1: 771t Geotrichum candidum, 4: 769 lipolysis, 4: 768, 4: 777–778 manufacture mechanization, 1: 614 membrane processing, 1: 621 milk ultrafiltration, 1: 621 traditional, 4: 778 overripened, 4: 778 Penicillium camemberti, 4: 776, 4: 778 raw milk vs. pasteurized milk, 1: 656t ripening, surface pH increase, 1: 648, 1: 649f secondary cultures, 1: 567 Camembert de Normandie PDO cheese, 1: 656t Camobacteriocin A, 1: 422t Camobacteriocin B, 1: 422t
Campylobacter, 4: 40–46 antibiotic resistance, 4: 43 determination methods, 4: 43 epidemiology, 4: 43 future issues, 4: 46 antibiotic susceptibility, 4: 41 biochemical properties, 4: 41 clinical disease, 4: 43 detection in milk, 4: 40 identification, 4: 41 isolation, 4: 41, 4: 41f disease and, 4: 43 pathogenesis, 4: 44 fermented dairy products, 4: 44, 4: 45 fluoroquinolone resistance, 4: 43 future issues, 4: 46 laboratory techniques, 4: 46 public health burden, 4: 46 growth conditions, 4: 40 historical aspects, 4: 40 macrolide resistance, 4: 43 mammary glands, subclinical infection, 4: 45 milk-associated outbreaks environmental sources, 4: 44 epidemiology, 4: 44 prevalence, 4: 44 milk quality control farming practices, 4: 45 husbandry practices, 4: 45 pasteurization, 4: 45 postharvest phase, 4: 44 postprocess contamination, 4: 45 preharvest phase, 4: 44 molecular characteristics, 4: 42 detection, 4: 42 subtyping approaches, 4: 42 public health concerns, 3: 313–314 public health risk, 4: 40 serology, 4: 41 thermal resistance, 4: 40 Campylobacter coli, 4: 41 Campylobacter enteritis, 4: 43–44 Campylobacter fetus, 4: 41 Campylobacter fetus subsp. venerealis, 1: 470, 1: 479 Campylobacteriosis foodbourne, 4: 44 humans, 4: 40 public health concerns, 3: 311–312 see also Campylobacter Campylobacter jejuni adhesion inhibition, human milk oligosaccharide, 3: 255 antibiotic susceptibility, 4: 41 in cheese, 4: 45 gastroenteritis, 3: 313 human infection, 4: 43–44 identification, 4: 42 in milk, 3: 449 Campylobacter upsaliensis, 4: 41 Canada agricultural policy, 4: 306 butter support price, 4: 307–308 cheese legislation, 1: 852 casein amounts, 1: 852–854 compositional requirements, 1: 853t cheese standards, 1: 852 dairy product exports, 4: 308 dairy societies, 2: 105 industrial milk target price, 4: 307–308 milk supply management system, 4: 306 historical aspects, 4: 306 organic sector, 4: 9 producer support estimate, 4: 307f sheep distribution, 2: 67 single commodity transfers, 4: 306, 4: 307f sires of sons, 2: 671–672 skin milk powder support price, 4: 307–308 substantial border measures, 4: 307
Index supply management problems, 4: 308 tariff rate quotas, 4: 307 Canadian Food and Drug Regulations, 1: 852 cheese legislation, 1: 852 Canadian Institute of Food Science and Technology (CIFST), 2: 105 Canadian Milk Supply Management Committee (CMSMC), 4: 306–307 Canadian Organic Advisory Board Inc. (COAB), 4: 10 Canadienne cattle, 1: 299 Canaria goats, 1: 316 Cancer, 3: 610 aflatoxins, 4: 805 antagonists in milk, 3: 610 bracken fern toxin, 1: 905 vitamin C, 4: 673 vitamin D, 4: 650 vitamin E, 4: 658 see also individual cancers Candida, 4: 747 Candida albicans, 3: 1040 Candida catenulata, 4: 750 Candidate gene, 3: 1059–1060 Candida versatilis, 4: 752 Canestrato Pugliese cheese, 1: 732 characteristics, 1: 730t composition, 1: 729t free fatty acid lipolysis, 1: 736t production statistics, 1: 729t proteolysis, 1: 733 free amino acids, 1: 734t NSLAB, 1: 735 Canned dairy food sampling, 1: 73 Canned foods, nisin applications, 1: 424 Canola, 2: 349 Canola meal, 2: 349, 2: 353 Canola oil blends, 1: 523 Canonical variate analysis (CVA), time varying state space modeling, 4: 246 Cans coated, 4: 19 composite see Composite cans evaporated milk, 1: 865, 4: 19 sweetened condensed milk, 4: 19 yogurt packaging, 4: 21 Cantilever-based biosensors, 1: 237, 1: 237f, 1: 237–238 Cape fur seal involution delay, 3: 783–784 -lactalbumin gene mutation, 3: 783–784 CAP Health Check 2008, 4: 299 Capillary electrophoresis (CE), 1: 190, 1: 190f milk ion quantification, 3: 914t, 3: 915 milk proteins, 3: 746, 3: 748 future trends, 3: 750 Capillary gas chromatography, fatty acid analysis, 3: 698–699 Capital investment, milk powder spray drying, 2: 110 Capra aegagrus (bezoar goat), 2: 814, 3: 326–327 Capra falconeri (markhor), 2: 814 Capra hircus see Goat(s) Capra ibex (ibex/wild goat), 2: 814 CAP Reform 2003, 4: 298 Caprenin (caprocaprylobehenic triacylglycerol), 1: 529 Caprine arthritis-encephalitis (CAE), 2: 798, 2: 825 Caprine milk see Goat milk Caprocaprylobehenic triacylglycerol (caprenin), 1: 529 Caramelization, 3: 217, 3: 224 Carbamate kinase, 3: 126 Carbohydrates analytical techniques, 3: 550 biosensors, 1: 243 blood cholesterol levels, 3: 731 byproduct sources, 2: 342, 2: 343, 2: 346 classification, 4: 355, 4: 356t colonic fermentation, humans, 4: 354
degree of polymerization, 4: 355 digestible energy (DE), 2: 338, 2: 338f, 2: 405 feed particle size, 2: 461 structural fraction, 2: 461 first-age infant formulae, 2: 142 in fodder grass species variations, 2: 584, 2: 584f structural, 2: 579–580 fractions, digestion rates, 2: 461 grassy tetany, 2: 227–228 infant formulae, 2: 136 ion-exchange chromatography, 1: 171, 1: 171f metabolism Bifidobacterium, 1: 387 starter cultures, 1: 560, 1: 561f in milk, 3: 550 nutrient intake, contributions to, 3: 1004 species comparison, 3: 484, 3: 550, 3: 585 processing adjustment factor (PAF), 2: 338 quantification, 3: 550 ration formulation dry lot systems, 2: 461 guidelines, 2: 463 rumen fermentation, 3: 981f, 3: 982, 3: 982f sheep milk, 3: 499 specificity, 3: 550 terminology, 4: 355 see also individual sugars Carbohydrate-type fat replacers, 2: 896 14 C-labeled peptides, dairy cow digestion models, 2: 430 Carbon dioxide, milk shelf life extension, 2: 730 Carbonyl compounds, 3: 717 Carboxyl ester hydrolase, primate milk, 3: 629 Carboxymethyl cellulose applications, 1: 70t as emulsifier, 1: 69t C N -(Carboxymethyl)lysine (CML), Maillard reaction, 3: 1068 Carboxypeptidases, 3: 87 Carcinogenicity tests, additive safety, 1: 57 Cardiac beriberi, 4: 795–796 Cardiovascular disease (CVD) definition, 3: 727 milk consumption, 3: 1005 saturated fatty acids, 3: 1023–1033 vitamin C, 4: 672 vitamin E, 4: 657 see also Coronary heart disease (CHD) Cardiovascular health nutrition, 3: 1060 vitamin K, 4: 664 Caribou, 3: 533 lactation milk yield, 3: 533 milking, 3: 533 see also Reindeer Caries see Dental caries Carnitine biosynthesis, vitamin C in, 4: 671 fatty liver, 2: 221–222 sheep milk, 3: 496 Carnocin U149, 1: 422t Carola cattle, 1: 303t, 1: 305 -Carotene, 4: 639 absorption cattle, 4: 640–641 inhibition, plant sterols, 3: 1001 butter color, 1: 511 cleavage pathways, 4: 641, 4: 642f dietary supply-milk concentration relationship, 4: 642 feed supplements, 2: 399 mastitis resistance, 3: 430–431 forage concentrations, 4: 642–643 function, 4: 640 heat stress, fertility improvement, 4: 572 in milk, 3: 652
849
concentration influencing factors, 4: 642 seasonal effects, 4: 643 optical properties, 3: 472 provitamin A activity, 4: 639–640, 4: 640f, 4: 642f singlet oxygen quenching, 3: 719 15-159- -Carotene monooxygenase, 4: 641 Carotenoids absorption, 3: 1001 antioxidant activity, 4: 640 cheese color, 1: 537 definition, 4: 639–640 general features, 4: 639 metabolism, 4: 640, 4: 641f in milk, 3: 652 nutrient intake, contributions to, 3: 1005 milk concentration influencing factors fat content, 4: 643t, 4: 644, 4: 644t processing conditions, 4: 643 milk lipid oxidation, 3: 719 singlet oxygen quenching, 3: 719 Carousel milking parlors see Rotary (carousel) milking parlors Carpet-woolled (dual purpose) sheep, 2: 875, 2: 876, 2: 878t, 2: 879 Carra cheese, 1: 786 manufacture, 1: 786 Carrageenan applications, 1: 70t dairy desserts, 2: 908, 2: 909t as fat replacer, 1: 531 flavored milk stabilization, 3: 303 dosage, 3: 304 heat treatment, 3: 305 shear, 3: 304 temperature, 3: 304 milk interactions, 2: 910 structure, 3: 303 weak gel formation, 3: 303 k-Carrageenan k-casein interactions, 3: 304, 3: 304f as emulsifier, 1: 69t enzyme entrapment, accelerated cheese ripening, 1: 796 flavored milk stabilization, 3: 303 Carr–Purcell–Meiboom–Gill (CPMG) sequence, NMR, 1: 153–155 Cartons, 2: 709, 2: 710f prefabricated, 2: 710 Cartridge-type filters, drinking water, 4: 583 Caruncles, 4: 488, 4: 488f, 4: 499 -Cas0 mutations, 3: 833, 3: 833 Casein(s), 3: 480, 3: 765–771 acid see Acid casein allergenicity reduction, 3: 1043 amino acid composition, sow vs bovine, 3: 532t antioxidant activity, 3: 719 autosomal genes, 3: 821–822 biological roles, 3: 759 biosensors, 1: 244 buffalo milk, 3: 503, 3: 510 calcium binding, 3: 770–771, 3: 775 calcium-induced precipitation, 3: 775 ‘calcium-sensitive’ genes, 3: 823–824 camel milk, 3: 513, 3: 514f casein-casein interactions, 3: 770 casein-mineral interaction, 3: 770 catabolism, starter cultures, 1: 563f characteristics, 3: 752t charge distribution, 3: 766–767, 3: 767f cheese analogues, 1: 815–816 compositional standards, 3: 855–863 curd strength, 1: 585 dephosphorylation, 3: 912 cheese ripening, 2: 315–316, 2: 318 dried powders, flavor defects, 2: 548 malodorant diagnostic techniques, 2: 548, 2: 549f odor-active chemicals analysis, 2: 548, 2: 549t, 2: 550t
850 Index Casein(s) (continued ) dried powders, malodors, 2: 548 edible uses, 3: 855 equid milk, 3: 519, 3: 522 equine milk, 1: 361–362 evolution, 3: 821 first-age infant formulae, 2: 141 function, 3: 461–462 gastrointestinal digestion, 3: 1062 genes, splicing behavior, 3: 824–825 genetic variants, 3: 752t, 3: 759, 3: 822t null alleles, 3: 833 peptide chain length heterogeneity, 3: 832 glycosylation, 3: 773 interspecies comparison, 3: 835 goat milk, genetic polymorphism, 3: 486–487, 3: 491 heat stability, 3: 1067–1068 heterogeneity, 3: 752 historical aspects, 1: 22 technologically important properties, 1: 24 human milk, 3: 583, 3: 758–759 humans, ingestion, 3: 819 hydration, cheese salting, 1: 597 hydrolysis first-age infant formulae, 2: 141 hard Italian cheeses, 1: 733f, 1: 733–734 hydrolysis in milk fermentation, 2: 513, 2: 517, 3: 54 bioactive peptide products (IPP/VPP), 3: 54 bitter peptide products, 3: 54 proline content and proteolysis resistance, 3: 53 hydrophobicity, 3: 766–767, 3: 767f immunological analysis, 3: 749 industrial production, 3: 855–863 interactions curd syneresis, 1: 592 low-fat cheese pH, 1: 837 interspecies comparison, 3: 821, 3: 822f, 3: 823f gel electrophoresis analysis, 3: 541, 3: 541f hereditary lineage traces, 3: 542–543 primary structure, 3: 825 ion-exchange chromatography, 1: 170 isolation, 3: 765 lactose concentration relationship, 3: 173, 3: 175f low-fat cheeses, 1: 833–834, 1: 836, 1: 837 mammalian milk, 3: 322–323 manufacture, 3: 855 colloid mills, 2: 761–762 skim milk use, 3: 855 marine mammal milk, 3: 574–576 mastitis, 3: 363, 3: 903, 3: 903f micellar structure see Casein micelles microbial transglutaminase, 2: 299 sensitivity, 2: 298 microstructure, 1: 232 milk/cream rheology, 4: 520 molecular diversity cryptic splice site stochastic usage, 3: 830 glutaminyl residue stochastic deletion, 3: 830–831 interspecies variability, 3: 830 polymorphisms and peptide chain length, 3: 832 posttranslational modifications, 3: 833 Q (Gln) insertion/deletion, 3: 831–832 species-specific stochastic exon-skipping, 3: 832 splice variants, 3: 830, 3: 832 molecular properties, 3: 772 molecular structure in solution, 3: 773 adsorption, 3: 773 as amphiphilic molecules, 3: 773, 3: 774f secondary structure, 3: 773 self-association, 3: 774 multiphosphorylated forms, 3: 833, 3: 835 mutagens effects, 3: 234 native states, 3: 768 nitrogen, 3: 742 NMR relaxation studies, 1: 158t nomenclature, 3: 765 historical aspects, 3: 765 nondairy food, 2: 128t
number (casein N/total N ratio), 3: 490–491 phosphorylation, 3: 773 interspecies comparison, 3: 833, 3: 834t multiphosphorylated forms, 3: 833, 3: 835 sites, 3: 766–767, 3: 833, 3: 835, 3: 835 pigment binding, in Maillard reactions, 3: 226 preparation techniques, 2: 125 primate milk, 3: 621, 3: 624 products see Casein products proportions, lactation stage and, 3: 602 rennet see Rennet casein reversed-phase HPLC, 1: 171–172 SDS-PAGE, 1: 186–187 seasonal variations, 3: 601f sequence characteristics, 3: 772 genetic variants, 3: 772–773 sheep milk, 3: 494, 3: 496t standardization, cheese manufacture, 1: 623 steric emulsion stabilization, 1: 64 structure, 3: 766 future developments, 3: 841 primary, 3: 751–752 substitution, cheese analogues, 1: 818 syneresis, 1: 593–594 synthesis, 3: 332, 3: 361, 3: 377 3D structures, 3: 765, 3: 766f types, 3: 359, 3: 360t urea fractionation, 3: 760–761 value-added products, 3: 365 viscosity, 3: 770 weight average molecular weights, 3: 768t see also specific caseins s0-Casein, 3: 752–753 s1-Casein, 3: 480–481, 3: 768 buffalo milk, 3: 503 calcium binding capacity, 3: 775 calcium binding properties, 3: 770–771 casein-casein interactions, 3: 770 chymosin cleavage site, 3: 768 deficiency, micellar diameter, 3: 837 dual-binding model for micelle assembly and structure, 3: 777–778 equine milk, 3: 522 exon-skipping, 3: 825 F variant, 3: 778 genetic variants, 3: 759–760 glutaminyl residue stochastic deletion, 3: 830–831 hydrophilic residues, 3: 774, 3: 774f hydrophobic domains, 3: 825 hydrophobicity, 3: 767f, 3: 768 immunomodulation, 3: 883 micelle size, 3: 775–776 multiple phosphorylation sites, 3: 825 null variant, 3: 772–773 phenotypes, 3: 832 phosphorylation, 3: 773 polymers, 3: 768, 3: 768t polymorphism, 3: 841 primary structure, 3: 752–753, 3: 753f interspecies comparison, 3: 825, 3: 826f self-association, 3: 774–775 sheep milk, 3: 495, 3: 496t 3D model, 3: 766f s2-Casein, 3: 480–481, 3: 768 association studies, 3: 769 buffalo milk, 3: 503 calcium binding capacity, 3: 775 camel milk, 3: 828–830, 3: 835 casein phosphorylation, 3: 835 covalent aggregate formation, 3: 1067–1068 cysteinyl residues, 3: 830 dual-binding model for micelle assembly and structure, 3: 777–778 D variant, 3: 773, 3: 828–830 equine milk, 3: 522 forms, 3: 753–754 gene duplications, 3: 828
tandem repeat, 3: 828 hydrophilic residues, 3: 774, 3: 774f micelle size, 3: 775–776 ovine, 3: 835 phosphorylation, 3: 773 primary structure, 3: 752t, 3: 753f, 3: 753–754 interspecies comparison, 3: 828, 3: 829f sheep milk, 3: 495, 3: 496t 3D model, 3: 766f, 3: 768 s3-Casein, 3: 753–754 s4-Casein, 3: 753–754 s5-Casein, 3: 753–754 s6-Casein, 3: 753–754 -Casein amino acid sequences, 3: 542, 3: 542f cross-reactivity, 3: 1044 exorphins, 3: 879 historical aspects, 1: 22 marsupial milk, 3: 556–558 -Casein, 3: 480–481 adsorption, emulsification, 3: 890 amino acid sequences, 3: 542, 3: 542f ancestral gene, 3: 828 buffalo milk, 3: 504 calcium binding capacity, 3: 775 casein-casein interactions, 3: 770 dual-binding model for micelle assembly and structure, 3: 777–778 equine milk, 3: 523 gene -Cas0 mutations, 3: 833, 3: 833 exon-skipping, 3: 828 transcription factor-binding site, 3: 823–824 historical aspects, 1: 22 human, 3: 754 hydrophilic residues, 3: 774 hydrophobicity, 3: 767f, 3: 769 immunomodulation, 3: 883 lactation stage, 3: 602 marsupial milk, 3: 556–558 micelle size, 3: 775–776 monotreme milk, 3: 558 phosphorylation, 3: 773 plasmin cleavage, 3: 769 polymers, 3: 768t, 3: 769 primary structure, 3: 754, 3: 754f interspecies comparison, 3: 825, 3: 827f self-association, 3: 774f, 3: 774–775 self-consistent field calculations, 3: 774, 3: 774f sheep milk, 3: 495, 3: 496t structure, 3: 766f, 3: 769 type 1 diabetes, 3: 1047 variants, 3: 1047–1048
-Casein buffalo milk, 3: 504 heat stability, milk, 2: 746 lactation stage, 3: 602 sheep milk, 3: 495–496 structure, 3: 754 k-Casein, 3: 480–481 amyloid bodies, 3: 770 buffalo milk, 3: 504 calcium binding capacity, 3: 775 calcium salt interactions, 3: 771 k-carrageenan interaction, 3: 304, 3: 304f casein-casein interactions, 3: 770 chymosin (rennin) cleavage, 3: 543, 3: 766–767 coagulation mechanisms, 1: 698 covalent aggregate formation, 3: 1067–1068 dual-binding model for micelle assembly and structure, 3: 777–778 enzymatic cleavage, 3: 769–770 equine milk, 3: 523 functional duality, 3: 830 genetic variants, 3: 759–760 glycosylation, 3: 754, 3: 773 sheep milk, 3: 835 sites, 3: 835
Index heat stability, milk, 2: 746 historical aspects, 1: 22 hydration loss, 3: 302–303, 3: 303f hydrolysis, curd syneresis, 1: 591 hydrophobicity, 3: 767f, 3: 769–770 hydrophobic residues, 3: 774 intermolecular disulfide bonds, 3: 766–767 -lactoglobulin interactions, 3: 793 micelle size, 3: 775–776 pectin interaction, 3: 302–303, 3: 303f phosphorylation, 3: 835 phosphoseryl cluster lack, 3: 773 platelet aggregation, effect, 3: 1064–1065 primary structure, 3: 753f, 3: 754 interspecies comparison, 3: 830, 3: 831f proteolysis, chymosin, 3: 776 rennet milk coagulation, 1: 579 self-association, 3: 774–775 sheep milk, 3: 495–496 structure, 3: 766f, 3: 769 submicelle model, 3: 776 transgenic cows, 2: 643 Caseinate products annual production, 3: 860, 3: 860t Codex standard, 3: 861t Caseinates, 3: 855–863 acceptable daily intake, 3: 863 extrusion techniques, 3: 858–859 manufacture, 3: 858 milk protein concentrates vs., 3: 848 nondairy food, 2: 128t preparation techniques, 2: 125 roller-dried, 3: 858–859 solubility, 3: 888 Casein-based ingredient production, whey source, 3: 873–874 Casein curd, dewatering equipment, 3: 857 Casein derivatives, anticariogenic properties, 3: 1036 -Casein exorphins, 3: 879 Casein gene locus (CSN), 3: 823 organization, 3: 823, 3: 824f quantitative variability, 3: 823 Casein macropeptide (CMP), 3: 769–770 antimicrobial activities, 3: 1063–1064 antithrombotic effect, 3: 1064–1065 immunomodulating effects, 3: 1064 influenza virus inhibition, 3: 1063–1064 intestinal motility, 3: 1063 MS, 1: 201 rennet milk coagulation, 1: 579 Casein micelles, 3: 359, 3: 481 appearance, 3: 776 dual-binding model, 3: 778 camel milk, 3: 513, 3: 514f curd formation reaction, 3: 776 definition, 3: 765 disintegration, 3: 775 equid milk, 3: 523 equine milk, 3: 521t, 3: 523 formation, 3: 377 heat stability, 3: 891–892 high-pressure homogenization disruption, 2: 757 historical aspects, 1: 23 induced destabilization, 3: 776 instability mechanism, 3: 772 microstructure, 1: 230, 1: 230f milk pH, dual-binding model, 3: 778 models, 3: 772, 3: 776, 3: 821–822 dual-binding model for micelle assembly and structure, 3: 772, 3: 774f, 3: 774f, 3: 777, 3: 777f historical aspects, 1: 23 Holt model, 3: 777 submicelle model, 3: 776 primate milk, 3: 625 properties, 3: 775, 3: 841 rennet milk coagulation, 1: 579 sheep’s milk, 3: 494
size, 3: 775 sodium chloride addition, 3: 913 stability, 3: 776 equid milk, 3: 523 static light scattering, 1: 134–135 structure, 3: 491, 3: 772–779 dynamic, 3: 775 technologically important properties, historical aspects, 1: 23–24 water-binding capacity, 3: 889–890 zinc content, 3: 935 Casein network cheese rheology, 1: 688 curd syneresis, 1: 592–593 k-Caseinoglycopeptide, 3: 835 Caseinomacropeptide (CMP) see Casein macropeptide (CMP) Caseinophosphopeptides (CPPs), 3: 883, 3: 1063 contradictory data, 3: 884 physiological importance, 3: 883–884 Casein phosphopeptide–amorphous calcium phosphate (CPP-ACP) nanocomplexes, anticariogenic properties, 3: 1036 Casein products annual production, 3: 860, 3: 860t historical aspects, 1: 16 regulatory aspects, 3: 860 compositional standards, 3: 860, 3: 861t definition, 3: 860 health aspects, 3: 863 methods of analysis, 3: 860 safety aspects, 3: 862t, 3: 863 specifications, 3: 860, 3: 861t world production, 3: 855 Casein-to-fat ratio lactation stage, 3: 600–602 milk standardization, 1: 546, 1: 546, 1: 548 Casein–whey protein particles, evaporated milk, 1: 867–868 Caseous lymphadenitis (CLA) goats, 2: 798 sheep, 2: 858–859 Caseous necrosis, bovine tuberculosis, 2: 195 s1-CasF mutations, 3: 833 -Cas0 gene mutations, 3: 833, 3: 833 Cash inflows/outflows, 1: 488 Casocidin, 3: 1064 Casocidin-I, 3: 883 -Casomorphin(s), 3: 879, 3: 881t antidiarrheal effects, 3: 1063 effects, 3: 1063 physiological importance, 3: 883–884 -Casomorphin-7 (BCM-7), 3: 1048 Casoplatelins, 3: 880–883, 3: 881t Casoxins, 3: 879, 3: 1063 Casson equation cheese rheology, 4: 530 sweetened condensed milk/dulce de leche, 4: 526, 4: 526 Castelmagno cheese, 1: 732 characteristics, 1: 730t composition, 1: 729t production statistics, 1: 729t proteolysis, 1: 733 NSLAB, 1: 735 Castillana sheep, 1: 332t Catalase, 2: 301, 2: 327, 2: 694–695 Bifidobacterium growth, 1: 384 heat stability, 2: 327 mastitis indicator, 2: 327 purification, 2: 327 Catalytic recognition elements, biosensors, 1: 235–236, 1: 236f Cataracts classical galactosemia, 3: 1053 vitamin C, 4: 672 Categorical analysis, genetic evaluation, 2: 652
851
Cathelicidins bovine vs. human, 2: 663–664, 2: 664f marsupial milk, 3: 558 Catheter devices, 3: 941, 3: 942f Cathodic protection, 4: 262 Cation-exchange chromatography, microbial transglutaminase, 2: 298 Cattle artificial photoperiod changes, 4: 443–444 breeding programs, 3: 463 historical aspects, 1: 7, 2: 610 byproducts, 2: 97 domestication, 3: 326, 3: 459, 3: 941 genetic defects see Genetic defects, cattle genetic improvement, 2: 648 gestation length, 4: 489 health management business operational programs, 2: 683 food production chain integration, 2: 679 health status documentation, 2: 685 risk factor ranking, 2: 684 routine monitoring activities, 2: 684, 2: 684t hybrid breeds, 2: 99 income generation, 2: 97 as plant material converter, 3: 464 twinning problems, 4: 485 Cattle breeds China see China historical aspects, 1: 2 Latin American see Cattle husbandry (Latin America) milk freezing point, 1: 251–252 non-seasonal/pasture-based management, 2: 44, 2: 45t see also Bos taurus cattle; specific breeds Cattle grubs, 4: 420 Cattle husbandry (Africa), 2: 77–82 feeding management, 2: 78 extensive grazing, 2: 79 minimal grazing, 2: 79 total mixed ration, 2: 78–79, 2: 79f zero grazing systems, 2: 78–79, 2: 79f feed types, 2: 78 roughage, 2: 79 water supply, 2: 79 grouping, 2: 77 postweaning calves, 2: 78 preweaning calves, 2: 77–78, 2: 78f, 2: 78f housing, 2: 77 open sheds, 2: 77, 2: 78f labor management, 2: 80 advice access, 2: 81 veterinarians, 2: 81 large-scale, 2: 77, 2: 78f milking management, 2: 80, 2: 80f milk processing, 2: 80 price fixing, 2: 80 production constraints, 2: 81 disease, 2: 81 mastitis, 2: 81 milk as luxury item, 2: 81 small-scale, 2: 77 Cattle husbandry (Latin America), 2: 88–93 cattle breeds, 2: 91 Brown Swiss, 2: 91 Criollo cattle, 2: 91 Gir, 2: 91 Guzerat, 2: 91 Holstein Friesians, 2: 91 Jerseys, 2: 91 production, 2: 91, 2: 91t cool regions, 2: 88 intensive systems, 2: 88, 2: 90 dual-purpose systems, hot lowlands, 2: 89, 2: 89t economic factors, 2: 92 extensive systems, 2: 89 feed resources, 2: 90 cool zone intensive systems, 2: 90
852 Index Cattle husbandry (Latin America) (continued ) lowlands, 2: 90–91 hot lowlands dual-purpose systems, 2: 89, 2: 89t intensive systems, 2: 88 intensive systems cool regions, 2: 88, 2: 90 hot lowlands, 2: 88 marketing, 2: 92 potential, 2: 92, 2: 92t production systems, 2: 88 see also specific production systems semi-intensive systems, 2: 89 breeds, 2: 89–90 tick-borne diseases, 2: 89–90 social factors, 2: 92 Cattle husbandry, China see China Caujen Red cattle, 1: 298 Caustic soda-based products, cleaning, 4: 284 Cavitation, 2: 741, 2: 742, 3: 1034–1035 applied pressure effects, 2: 741 corrosion, 4: 262 net pressure suction head see Net positive suction head (NPSH) CCP see Colloidal calcium phosphate (CCP) CcpA regulatory gene, 3: 64 CD8+ lymphocytes, 3: 390 CD36 see Cluster of differentiation 36 (CD36) Cebreiro cheese, 3: 158 Cebus apella see Brown capuchin Cefquinome, 2: 171 Ceftiofur hydrochloride, 3: 420 Ceftiofur sodium, 2: 171 Celiac artery, 3: 989–990 Cell envelope proteases (CEP, Prt), 2: 290, 3: 49 cheese ripening, 1: 670–671, 1: 671 genetic coding, 3: 53, 3: 107 maturation, 3: 52, 3: 52f specificity, 3: 52–53 structure, 3: 52, 3: 52f Cell lipids, Propionibacterium envelope, 1: 403 Cellobiose, 1: 386t Cell survival factors, galactopoietic effects, 3: 29f, 3: 31 -Cellubiose, monohydrated -lactose crystal growth, 3: 193 Cellulose as fat replacer, 1: 531 rumen fermentation, 3: 983 Cellulose derivatives dairy desserts, 2: 909t heat-stable, 3: 302 Center-fleeing (centrifugal) force, 4: 175 Center of area, 4: 248 Center pivot irrigation system, 2: 591 Center-seeking (centripetal) force, 4: 175 Central cleavage theory, vitamin A formation, 4: 641, 4: 642f Central composite design, 4: 267 Central Council of Dairy Cooperatives, Japan, 4: 308 Central Europe goats, 1: 310 sheep distribution, 2: 67 Central feed wagon alley, 2: 20 Central nervous system infections, Enterobacter, 4: 75 Central obesity, 3: 712 Centrifugal acceleration, 4: 166 acceleration factor, 4: 166 Centrifugal decanters see Decanter centrifuges Centrifugal (center-fleeing) force, 4: 175 Centrifugal pumps, 4: 145, 4: 146 design, 4: 146, 4: 146f energy costs, 4: 145–146 fluid pressure, 4: 146 hygienic requirements, 4: 146 motor, 4: 146 net positive suction head, 4: 147 operating points, 4: 146, 4: 147f
principles of operation, 4: 146, 4: 146f pump characteristic curve, 4: 146–147, 4: 147f pumping efficiency, 4: 146, 4: 146, 4: 147f rotors, 4: 146f selection, 4: 147, 4: 147f, 4: 151t viscosity and, 4: 145 Centrifugal separation creaming, 4: 166, 4: 167f cream manufacture, 1: 913 definition, 4: 175 disk stack separation, 4: 166, 4: 167f, 4: 167f gravitational acceleration, 4: 166 gravitational separation vs., 4: 176 historical aspects, 1: 13 milk fat, 4: 546 principles, 4: 166, 4: 167f sedimentation, 4: 166, 4: 167f separating distance, 4: 166 temperature, 4: 166 two-phas system application, 4: 166, 4: 167f velocity of, 4: 166 Centrifugal separators development, 1: 28 historical aspects, 1: 13 Centrifugation, 2: 729 butter manufacture, 1: 494 definition, 4: 175 microstructure, 1: 230 Centrifuges, 4: 175–183 dairy applications, 4: 171 design, 4: 166–174 fresh cheese production, 4: 172, 4: 173f, 4: 173f future developments, 4: 183 mixed types separated, 4: 175 process conditions, 4: 173 selection, 4: 127 skimming, 4: 171 back blending, 4: 171 cold milk skimming, 4: 171 continuous standardizing, 4: 171 cream fat content, 4: 171 hot milk skimming, 4: 171 standardizing, 4: 171, 4: 172f tank standardizing, 4: 171 whey skimming, 4: 171 sludge thickening, 4: 629t theory, 4: 175 types, 4: 166–174 see also individual types Centripetal (center-seeking) force, 4: 175 Centripetal pumps decanters, 4: 170, 4: 170f separators, 4: 168 Centro de la Industria Lechera (CIL), 2: 104 Ceramic microfiltration membranes, 3: 868 Cereals forage and pasture uses, 2: 556, 2: 565 deficiency problems, 2: 574 spring cereal regimes, 2: 556 toxins, 2: 574 winter regimes, 2: 556 grains see Grains milling byproducts, 2: 342–343, 2: 344t, 2: 345 see also individual types ‘Cerebral’ beriberi, 4: 702–703 Cerebrocortical necrosis (CCN) see Polioencephalomalacia Cerebrosides, 3: 651 Certified milk, salmonellosis outbreaks, 4: 94 Certified Organic Associations of British Columbia (COABC), 4: 10, 4: 11t Ceruloplasmin, 3: 758 mastitis, 3: 430 Cervical ripening, 4: 509 Cervix pregnancy, 4: 509–510 remodeling, 4: 509–510 Cesium, 1: 902
Cetacea see Cetaceans Cetaceans -lactalbumin, 3: 784 lactation, 3: 564t milk, 3: 563 composition, 3: 569, 3: 571t, 3: 574 CFT see Complement fixation test (CFT) Chain Quality Milk (CQM), Netherlands, 2: 680–681 Chakka, 1: 703 Chamba goats, 1: 320 Chamoisee goats, 1: 311t, 1: 313 Changeover (divert) valve, 4: 155, 4: 155f Chapper goats, 1: 311t, 1: 319 milk yields, 1: 312t Checklist analysis, 4: 278 Cheddar cheeses, 1: 706–711 APV-SiroCurd process, 1: 621 aroma, 1: 710 Aspergillus flavus growth, 4: 787 bitterness, 1: 710 cholesterol-reduced, 3: 738 defects, 1: 710 bitterness, 1: 710 color defects, 1: 711 gas production, 1: 711 mold growth, 1: 711 surface deposits, 1: 711 enzyme-modified cheese flavor, 2: 287 free fatty acids, 1: 771t gas blowing defects avoidance, 1: 665 heterofermentative lactobacilli, 1: 664 gas production, 1: 711 lactate crystal formation, 3: 130–131 manufacture, 1: 706, 1: 707f moisture expulsion, 1: 706–707 rennet, 1: 706–707 salting, 1: 706–707 maturation, 1: 708 amino acid catabolism, 1: 709 chymosin, 1: 708 LAB, 1: 709 NSLAB, 1: 640, 1: 708, 1: 709 plasmin, 1: 709 proteolysis, 1: 708 proteolytic starter, 1: 709 microbiology, 1: 706 milk pretreatment, 1: 706 odor, 1: 710 Pediococcus, 3: 151 plasmin activity, 2: 312 probiotic, 3: 102–103 production mechanization, 1: 607 curd cutting, 1: 608 curing, 1: 611 milk protein standardization, 1: 607 milk treatment, 1: 607 milling, 1: 610 packaging, 1: 611 pressing, 1: 611, 1: 612f, 1: 613f ripening, 1: 611 salting, 1: 610 starter culture neutralization, 1: 607 starter culture preparation, 1: 607 storage, 1: 611 texturing, 1: 608, 1: 610f, 1: 610f, 1: 610f vat process, 1: 608 protein standardization, 1: 619–621, 1: 620f redox potential, 1: 553 ripening enzyme-modified cheese use, 1: 799 lactate metabolism, 1: 667 pathogen survival, 1: 647, 1: 647f, 1: 648, 1: 648f proteolysis, 1: 671, 1: 672 salmonellosis outbreaks, 4: 94 salt distribution, 1: 604 salting, 1: 538 sensorial characteristics, 1: 657t
Index ‘short method’ manufacture, 3: 145 slits, Lactobacillus, 3: 130 standardization, 1: 535 starter cultures, 1: 441, 1: 444, 1: 707 direct vat inoculation, 1: 707 direct vat set cultures, 1: 707 mesophiles, 1: 707 thermophiles, 1: 707 sucrose fatty acid polyesters, 1: 529 sulfur compounds, 1: 710 surface deposits, 1: 711 technology, 1: 706 textural characteristics, 1: 710 thread mold, 4: 780 yield, milk protein content standardization and, 3: 851 Cheddaring tower, 1: 608–610, 1: 610f Cheddarmaster hoop system, 1: 611 salting broom, 1: 611 Cheese(s), 1: 534–543 acid/heat coagulated, 1: 539, 1: 540–542 acidity, 1: 629, 1: 646, 1: 647, 1: 647f soft cheese ripening, 1: 648, 1: 649f active packaging, 4: 22 added condiments, 1: 783–789 additives, 1: 36t lipolytic defects, 3: 724 allowable additives, 1: 38 anticariogenic properties, 3: 1035, 3: 1038 antifungal agents, 4: 750 Bacillus cereus, 4: 28 bacterial fingerprint database creation, 1: 634 bacteriology, historical aspects, 1: 30 biofilms, 1: 446 biogenic amines see Biogenic amines biotin, 4: 688t blowing see Gas blowing buffalo milk Asia, 2: 778 Mediterranean region, 2: 783 buttermilk ultrafiltrate, 3: 695 calcium content, 3: 1011, 3: 1011t calcium/sodium ratio, 3: 1012–1013 camel milk, 1: 356, 3: 515, 3: 515f Campylobacter jejuni survival, 4: 45 Chinese dairy management, 2: 87 cholesterol removal, 3: 738 citrate addition, 3: 171–172 classification, 1: 540, 1: 542f composition-based, 1: 540–542 hyperspectral imaging, 1: 131, 1: 131f Codex definition, 1: 844 Codex standards, 1: 845t, 4: 329 compositional criterion, 1: 853t, 4: 329 fat content requirements, 1: 844 firmness, 4: 329 format, 1: 846t individual varieties, 1: 844, 4: 330 international, 1: 843 principle ripening classification, 4: 329 unripened cheese, 1: 844 color, 1: 537 colorants, 1: 537 colorectal cancer, protective effect, 3: 1018 commodity/retail sector, 1: 822 composition cheese rheology, 1: 696 prediction, hyperspectral imaging, 1: 129–130, 1: 130f condensed buttermilk, 3: 695 consumption statistics, 1: 540, 1: 541t cooking properties, 1: 830, 1: 830t different varieties, 1: 831, 1: 832f fat content, 1: 831 fat phase liquefaction, 1: 830–831 functional attribute definitions, 1: 830, 1: 830t
functional attributes, different parameter effects, 1: 831, 1: 831t heat-induced flow (spread), 1: 830–831 heat-induced functionality, 1: 826 stretchability, 1: 830–831 strings/sheets, 1: 831 culture-based study procedures, 1: 632 definition, 1: 534 delivered to consumer, 1: 822 E. coli control, 4: 65 E. coli outbreaks, 4: 61 Enterobacteriaceae, 4: 68 enzyme-modified see Enzyme-modified cheese (EMC) fat on a dry basis, 1: 545 flavor see Cheese flavor flavor defects, Pseudomonas, 4: 382 flow resistance, 1: 831, 1: 832 folate content, 4: 680–681 as food ingredient, 1: 822–832, 1: 823f, 1: 823f applications, 1: 822, 1: 824f, 1: 824f definition, 1: 822 flavor, 1: 828 functional properties, 1: 829, 1: 829t properties, 1: 828 rheological properties, 1: 829t, 1: 830 texture properties, 1: 829, 1: 829t types, 1: 822 widely used varieties, 1: 822 food service sector, 1: 822 with fruit, 1: 42 gas blowing see Gas blowing geographical names, 1: 843, 1: 844t hard see Hard cheese Harmonized System, 4: 335 herbs added, 1: 783–789 common types, 1: 783, 1: 784t manufacture methods, 1: 783 quality of, 1: 783 types of, 1: 783 historical aspects, 1: 1, 1: 534, 1: 534 Middle Ages, 1: 534 Roman Empire, 1: 534 standardization, 1: 535 imitation, 1: 799 industrial ingredients, 1: 823f industrial sector, 1: 822, 1: 824f infrared spectrometry, 1: 119t as ingredient, 1: 540 interior yeasts, 4: 751 Lactobacillus starter cultures, 3: 80t, 3: 84 lactose intolerance, 3: 1011–1012, 3: 1014 legislation, current, 1: 843–855 background, 1: 843 European, 1: 845 European Union, 1: 846 lipolytic defects, 3: 724 Listeria monocytogenes contamination, 4: 84–85 listeriosis outbreaks, 4: 83 low-fat see Low-fat cheeses macromineral contents, 3: 927t making see Cheese manufacture manufacture see Cheese manufacture mastitis effects, 3: 904, 3: 904t, 3: 906t textural problems, 3: 902 yield, 3: 905 maturation see Cheese ripening microbial DNA fingerprinting see Microbial DNA fingerprinting, cheese microbial transglutaminase use, 2: 299 microbiology see Cheese microbiology milk, seasonal changes, 3: 599 milk composition, 3: 600 milk protein upstandardization, 4: 548–549 milk quality effects, 3: 600 psychrotrophic bacteria, 3: 603–604 moisture content, mastitis effects, 3: 905, 3: 905f, 3: 906t
853
NMR relaxation studies, 1: 158 NMR T2 (spin–spin relaxation), 1: 158 NSLAB see Non-starter lactic acid bacteria (NSLAB) packaging, 4: 20 pantothenic acid, 4: 694, 4: 695t pasteurized milk vs. raw milk, 1: 655, 1: 655t, 1: 656t Pediococcus, 3: 151 defects, 3: 151 plasmin system, 2: 312 processed see Processed cheese processing equipment, 4: 128t production see Cheese manufacture proteins, domestic cooking effects, 3: 1072–1073, 3: 1073t public health aspects see Public health aspects, cheese quality lactoperoxidase system, 2: 323 NSLAB see Non-starter lactic acid bacteria (NSLAB) raw milk see Raw milk cheeses reconstituted milk see Reconstituted milk cheese rheology see Cheese rheology riboflavin, 4: 704–705, 4: 705t ripening see Cheese ripening salmonellosis outbreaks, 4: 94 sampling, 1: 74 sheep milk see Sheep milk cheeses size-reduction operations, 1: 829–830 sodium dietary source, 3: 928 spiced see Spiced cheeses Staphylococcus aureus incidence, 4: 114 starter cultures see Starter culture(s) stress treatments, 3: 56 surface yeasts, 4: 751 texture, pH effects, 1: 552 trace element content, 3: 935t transgenic cow milk, 3: 968 variety differentiation, syneresis, 1: 591, 1: 592t vitamin A concentration, 4: 644 vitamin B6, 4: 698, 4: 698t water activity, 4: 707–708, 4: 712t, 4: 712–713, 4: 717f waxing, 4: 20 whey see Whey cheeses yak milk see Yak milk cheese yeasts see Yeast(s) see also individual cheeses Cheese analogues (CA), 1: 814–821 applications, 1: 814 cooking, 1: 821 classification, 1: 814 composition, 1: 814, 1: 815, 1: 815t, 1: 821 acid casein, 1: 817 acidifying agents, 1: 815t calcium sequestration, 1: 818–819 caseins, 1: 815–816 casein substitution, 1: 818 colors, 1: 815t emulsifying salts, 1: 815t, 1: 818 fat, 1: 815t flavors, 1: 815t hydrocolloids, 1: 815t, 1: 818 milk proteins, 1: 815t preservatives, 1: 815t proteins, 1: 815 rennet casein, 1: 817–818 starches, 1: 815t, 1: 818 sweetening agents, 1: 815t vegetable proteins, 1: 815t, 1: 818 definitions, 1: 814, 1: 814 functionality, 1: 821 historical aspects, 1: 814 manufacture, 1: 815 homogenization, 1: 820 ingredient order, 1: 819 premixing, 1: 819 processing, 1: 820
854 Index Cheese analogues (CA) (continued ) milk protein concentrate, 3: 852 properties, 1: 821 technology, 1: 815 types, 1: 814 see also specific types Cheesecakes, 2: 906 Cheese-containing foods, 1: 828 Cheese dips, 1: 799–800 Cheese factories, historical aspects, 1: 14 Cheese-filled coextruded products (CFCPs), 1: 828 Cheese-filled meatballs, 1: 828 Cheese-filled sausages, 1: 828 Cheese flavor, 1: 675–684 alcohols, 1: 681 aldehydes, 1: 682 amines, 1: 682 aroma, 1: 680, 1: 680f, 1: 680f aroma/odor, 1: 680, 1: 680f, 1: 680f assessment, 1: 675 atmospheric pressure chemical ionization, 1: 676, 1: 679 atomic emission detector, 1: 678–679 dynamic methods, 1: 679 expert panels, 1: 679–680 extraction, 1: 676 flame ionization detectors, 1: 678 flame photometric detector, 1: 678–679 FTIR spectrometry, 1: 678 gas chromatography, 1: 676, 1: 678 gas chromatography–mass spectrometry, 1: 675 gas chromatography–olfactometry, 1: 675 global analysis, 1: 679 headspace analysis, 1: 680 mass spectrometry, 1: 678 nitrogen–phosphorus detector, 1: 678–679 olfactory threshold determination, 1: 676 proton transfer reactions, 1: 676, 1: 679 pyrolysis mass spectrometry, 1: 680 quantification, 1: 676 quantitative descriptive analysis, 1: 675–676 saliva sampling, 1: 679 sampling, 1: 676 sniffing ports, 1: 679 sulfur chemiluminescence detector, 1: 678–679 bitterness, 1: 564 casein degradation, 3: 54 compounds, 1: 680 definition, 1: 675 enzyme-modified see Enzyme-modified cheese (EMC) esters, 1: 681 fatty acids, 1: 680 ketones, 1: 681 lactones, 1: 681 NSLAB see Non-starter lactic acid bacteria (NSLAB) pasteurized vs. raw milk, 1: 655–656 pH effects, 1: 552 phosphatases, 2: 315–316, 2: 318 sorbate addition, 2: 541–542, 2: 542f starter culture effects see Starter culture(s) sulfur compounds, 1: 682 taste, 1: 683 thermized milk effects, 2: 696 Cheese ingredient-containing foods, 1: 828 Cheese ingredients, 1: 822, 1: 823f, 1: 824f, 1: 825f manufacture, 1: 826 technology, 1: 826 see also individual types CheeseMaker 3 trommel salter, 1: 611, 1: 611f Cheesemaking see Cheese manufacture Cheese manufacture, 1: 535, 1: 536f acidification, 1: 538 direct addition of acid, 1: 538 LAB, 1: 538 alternative concepts, 1: 617 bacterial flora, 1: 559
bactofugation, 1: 537 coagulation, 1: 539, 1: 552 curd cutting, 1: 591–592 curd generation, 1: 537 curd high-pressure treatment, 2: 737 curd strength see Gel firmness (curd strength) equipment cleaning in place, 4: 284 historical aspects, 1: 14, 1: 534 lipolysis, 3: 721 mechanization, 1: 607–617 advantages, 1: 616 continuous hard cheese process, 1: 612 definition, 1: 607 future trends, 1: 616 hard cheeses, 1: 607 in-process analysis techniques, 1: 616 major developments, 1: 607 pH control automation, 1: 440 semihard cheeses see Semihard cheese soft fresh cheeses, 1: 615 soft ripened cheeses, 1: 614 membrane processing see Membrane processing, cheese manufacture Middle Ages, 1: 534 milk heat treatment, 1: 537, 1: 549 microorganism reduction, 1: 537 milk pasteurization, 1: 537 milk preparation, 1: 544–551 bactofugation, 1: 545 cheese, 2: 759 clarification, 1: 544 composition changes, 1: 547 filtration, 1: 544 high pressure treatment, 2: 736 homogenization, 1: 549 microfiltration, 2: 729 phage infection prevention, 1: 441, 1: 443 preacidification, 1: 550 separation, 1: 545 thermization, 2: 696 transportation, 1: 544 milk protein concentrates, 3: 851 cheese functionality, 3: 851 early problems, 3: 851 gel formation, 3: 851–852 protein content standardization, 3: 851 protein rehydration behavior, 3: 851 rennet coagulation studies, 3: 852 milk protein fractionation, 3: 762–763 milk quality requirement, 3: 599 fat stability, 3: 599–600 intact casein level, 3: 599 milk selection, 1: 535 animal species, 1: 536 milk standardization, 1: 536, 1: 545, 1: 546, 1: 546, 1: 548 bacterial clarification, 4: 178 calcium content, 1: 536 casein (protein)-to-fat ratio, 1: 546, 1: 546, 1: 548 composition variation, 1: 546 diafiltration, 1: 548 economic analysis, 1: 547 fat:casein ratio, 1: 536 fortification, 1: 546 in-line standardization, 1: 548–549 lactose, 1: 548 legislation, 1: 546 microfiltration, 1: 548 pH, 1: 536–537 preacidification, 1: 537 predictive cheese yield formula, 1: 547 protein content, 3: 851 total fat content, 1: 547 total protein content, 1: 547 milk thermization, 1: 537 nitrate addition, 1: 909 pasteurization alternatives, 1: 537
pathogen control, 1: 645, 1: 646f pathogen growth, 1: 645 postcoagulation processes, 1: 539 principles, 3: 599 process stages, 1: 440 proteinases, 2: 291 rennet see Rennet(s) ripening see Cheese ripening Roman Empire, 1: 534 Salmonella control, 4: 96 salting see Cheese salting secondary cultures, 1: 538 specific functions, 1: 538–539 starter cultures, 1: 555, 1: 559, 1: 560t statistics of, 1: 540, 1: 541t thermal evaporation, 1: 539 ultrafiltration, 1: 539 utensils, Salmonella contamination, 4: 96 whey, 1: 539 see also individual cheeses Cheese microbiology, 1: 625–631 analysis techniques, 1: 630 coryneform bacteria, 1: 627 enterococci, 1: 625 growth-controlling factors, 1: 628 nitrate, 1: 629 organic acids, 1: 629 pH, 1: 629 redox potential, 1: 629 salt, 1: 629 temperature, 1: 630 water activity, 1: 628 micrococci, 1: 627 microorganism roles, 1: 625, 1: 626f molds, 1: 628 NSLAB see Non-starter lactic acid bacteria (NSLAB) propionic acid bacteria, 1: 627 secondary surface cultures, smear/mold ripening, 1: 626 spoilage microbes, 1: 630, 4: 780 susceptibility, conditions affecting, 4: 780 staphylococci, 1: 627 starter cultures see Starter culture(s) Cheese mites, 4: 543 Cheese powders (CPs), 1: 825–826 flavor, 1: 826 manufacture, 1: 826, 1: 827f blend constituents, 1: 826 blend processing, 1: 826–827 filling materials, 1: 826 stability, 1: 822–825 uses, 1: 822–825 Cheese production see Cheese manufacture Cheese Regulations 1965, UK, 1: 846 Cheese Regulations 1970, UK, 1: 846 Cheese rheology, 1: 685–697, 4: 530 affecting factors, 1: 696 cheese composition, 1: 696 fat content, 1: 696 moisture content, 1: 697 pH, 1: 697 protein content, 1: 696, 1: 696f ripening, 1: 697 salt content, 1: 697 casein network, 1: 688 composition, 1: 685 creep, 1: 688, 1: 688f elastic deformation, 1: 688–689 viscoelastic deformation, 1: 688–689 viscous deformation, 1: 688–689 definition, 1: 685 eating quality, 1: 685 fat content, 1: 696 fat globules, 1: 688 macrostructure, 1: 685 measurement, 1: 689 compression tests, 1: 690
Index creep, 1: 688f, 1: 691t, 1: 693 cutting tests, 1: 690, 1: 690 deformation uniaxial compression, 1: 695t dynamic low-amplitude strain rheometry, 1: 691t dynamic low-amplitude stress rheometry, 1: 691t fundamental methods, 1: 690, 1: 691t imitative compression tests, 1: 690 instrumental empirical methods, 1: 690 instruments, 1: 691t large strain deformation, 1: 694 large strain sheer, 1: 695 low-strain deformation tests, 1: 690, 1: 693 low-strain oscillation rheometry, 1: 693, 1: 693f penetration tests, 1: 690, 1: 690 recovery creep, 1: 691t sensoric methods, 1: 689 stress relaxation, 1: 691t texturometer, 1: 690 three-point bending, 1: 691t torsion geometry, 1: 691t torsion shear, 1: 695–696 uniaxial compression, 1: 694, 1: 694f uniaxial extension, 1: 691t mechanical models, 1: 689 microstructure, 1: 685 physical behavior, 1: 685 physicochemical state, 1: 685 stress, 1: 688 stress relaxation tests, 1: 689 structure, 1: 687–688, 1: 688f texture, 1: 685 viscocity, 1: 688–689 Cheese ripening, 1: 536–537, 1: 540 accelerated see Accelerated cheese ripening antibiotic effects, 1: 892 Arthrobacter, 4: 376–377 bacteriocins, 1: 427, 1: 570 bioactive peptides, 3: 884–885 biochemical reactions, 1: 540 biochemistry, 1: 667–674 historical aspects, 1: 30 pH, 1: 667, 1: 668 biogenic amines, 1: 454 bitterness, proteolysis, 1: 671 brine-matured cheeses, 1: 793 citrate metabolism, 1: 667, 1: 668 Lactococcus lactis subsp. lactis, 1: 668–669 Leuconostoc, 1: 668–669 commercial cultures, 1: 571 definition, 1: 534, 1: 795 Dutch-type cheeses see Dutch-type cheeses hard Italian cheeses see Hard Italian cheeses Kluyveromyces, 4: 762 lactase catabolism, 1: 540 lactate metabolism, 1: 667, 1: 667 Cheddar cheese, 1: 667 Clostridium, 1: 668 surface mold-ripened cheese, 1: 667 surface smear-ripened cheese, 1: 667 Swiss-type cheese, 1: 668 lactose metabolism, 1: 667, 1: 668f lipolysis, 1: 540, 1: 669, 1: 669f fatty acid catabolism, 1: 669 MRI, 1: 167, 1: 167f NSLAB, 1: 639 pathogen growth control, 1: 646, 1: 648f, 1: 649f Pediococcus, 3: 151 plasmin, 2: 312 proteolysis, 1: 540, 1: 669, 1: 673f agents, 1: 669 amino acid catabolism, 1: 673, 1: 673f bitterness, 1: 671 cell envelope proteinase, 1: 670–671, 1: 671 characterization, 1: 672 coagulant effects, 1: 670 coryneform bacteria, 1: 673 indigenous milk proteinases, 1: 670
LAB, 1: 670, 1: 672 Lactobacillus, 1: 671, 1: 671 Lactococcus, 1: 670–671, 1: 671 NSLAB, 1: 671–672 pepsins, 1: 670 plasmin, 1: 670 rheology, 1: 697 secondary cultures, 1: 567–573 commercial, 1: 571 microorganisms, 1: 568t see also specific microorganisms smear-ripened cheeses see Smear-ripened cheeses surface mold-ripened cheeses see Surface moldripened cheeses temperature, 1: 630, 1: 647 cheese salting, 1: 603 low-fat cheese flavor, 1: 840 pathogen control in cheese, 1: 647 times, 1: 795, 1: 796t low-fat cheese flavor, 1: 840 vegetal rennets, 2: 290–291 Cheese salting, 1: 538, 1: 595–606, 1: 539, 1: 629 brine concentration, 1: 601 brine salting see Brine salting casein hydration, 1: 597 Cheddar cheese manufacture, 1: 706–707 dry salting see Dry salting enzyme activity, 1: 597 flavor, 1: 597 geometry, 1: 601 initial moisture content, 1: 601 initial salt content, 1: 601 low-moisture part-skim mozzarella (pizza cheese), 1: 738–739, 1: 740f, 1: 743 low/reduced-salt cheese, 1: 606 methods, 1: 597 see also specific methods microbiology, 1: 596, 1: 629 Penicillium roqueforti, 1: 596–597 propionibacteria, 1: 596 salt-resistance, 1: 596 moisture loss, 1: 598 mold-ripened cheese manufacture, 1: 773 NSLAB, 1: 596 preservative, 1: 595, 1: 596f pathogen control, 1: 595–596, 1: 646–647 salt-in moisture content (S/M), 1: 595 property effects, 1: 604 composition, 1: 604 lactate levels, 1: 605 moisture content, 1: 604 pH, 1: 605 quality, 1: 605 quality, 1: 605 rheology, 1: 697 role, 1: 595, 1: 604 salt distribution, 1: 602 Cheddar, 1: 604 concentration gradients, 1: 603 fat levels, 1: 603 geometry, 1: 604 milk solids-not-fat, 1: 604 moisture content, 1: 603 protein content, 1: 603 ripening temperature, 1: 603 salt uptake, 1: 598 smear-ripened cheeses see Smear-ripened cheeses starter bacteria control, 1: 596 starter cultures, 1: 564 surface dry salting, 1: 597–598 salt distribution, 1: 602, 1: 603f Chegu goats, 1: 311t, 1: 319 milk yields, 1: 312t Chelatants calcium affinity, 3: 912–913 milk salt equilibria, 3: 912 Chemfix, 4: 630t
855
Chemical acidification, acid casein manufacture, 3: 855 Chemical analyses, 1: 76–82 Chemical cleanliness, 4: 130 Chemical contaminants, immunochemical detection, 1: 180 Chemical hazards, risk assessment, 4: 534 Chemical imaging see Hyperspectral imaging (HSI) Chemical oxygen demand (COD) definition, 4: 614t, 4: 619 wastewater, 4: 613 Chemiluminometric biosensor transducers, 1: 238 Chemometrics, 1: 93 Chemotaxis inhibitory protein (CHIPS), Staphylococcus aureus, 4: 105–106 Chetoglobosins, 4: 799 Chevon (goat meat) growth rate, 2: 814 nutritional values, 2: 815t Chewing endogenous protein source, 2: 389 stimulation, grain feed variations, 2: 338–340, 2: 339t Chhurpi, 1: 350 Chicken pepsin, 1: 576 Chick-type (c) lysozyme, 2: 330–331 Children, vitamin deficiency risk, 4: 638 Children’s cheeses, 1: 42 Chilled-water systems, treatment, 4: 587 Chimeric animals, 2: 639 Chimpanzee milk free amino acids, 3: 627t oligosaccharides, 3: 617t chemical structures, 3: 271t total amino acids, 3: 625, 3: 626t China, 2: 83–87, 2: 87, 2: 87f artificial insemination, 2: 84 backyard farms, 2: 85 cattle breeds/breeding, 2: 83 problems, 2: 86 progeny testing, 2: 84 cattle husbandry, 2: 83–87 dairy cattle introduction, 2: 83 dairy herd improvement program, 2: 84 dairy processing companies, 2: 87, 2: 87f dairy processing industry, 2: 86 dairy production development, 2: 83 historical aspects, 2: 83, 2: 84f dairy products and technology, 2: 86 cheese, 2: 87 fermented products, 2: 86 liquid products, 2: 86 milk powder, 2: 86, 2: 86f development, 2: 83, 2: 84f diseases, 2: 86 feeding systems, 2: 84 grazing-to-shed farms, 2: 85 hotel farms, 2: 84 imports/exports, 2: 87, 2: 87f management systems, 2: 84 melamine-contaminated milk formula, 4: 352 metabolic disorders, 2: 86 milk production, 2: 83 breeding improvement programs, 2: 84, 2: 86 milk quality, 2: 86 milk yields, 2: 83, 2: 84t reindeer, 1: 374 sheep flocks, movement reduction, 2: 880 Simmental cattle, 1: 295 small private farms, 2: 85, 2: 85 state-owned farms, 2: 84 village milking centers, 2: 85 yak milk collection, 1: 346–347 yak milk production, 1: 347 Chin ball marking harness, 4: 477 Chinese Holsteins, 2: 83, 2: 84t
856 Index Chios sheep, 1: 329, 1: 329f, 2: 72 distribution, 1: 329 milk production, 1: 328t, 1: 329 origin, 1: 329 physical traits, 1: 329 reproductive traits, 1: 329 Chip-based electrophoresis, 1: 191 CHIPS (chemotaxis inhibitory protein), Staphylococcus aureus, 4: 105–106 Chitin oligosaccharides (COS), 4: 362 as prebiotics, 4: 361t, 4: 362 structure, 4: 357f, 4: 359t Chlamyvax, 4: 57 Chloramine-T method, 1: 81, 1: 82t Chloride cheese, 3: 925, 3: 927t in dairy products, 3: 926t, 3: 926t, 3: 927t, 3: 927t nutritional significance, 3: 927 deficiency, humans, 3: 928 excess intake, 3: 928–929 infant formula concentration, 3: 928–929 lactose interactions, 3: 917, 3: 918f in milk, 3: 925, 3: 926t chemical form, 3: 926 nutritional significance, 3: 927 minimum requirements, adults, 3: 928 primate milk, 3: 627–629, 3: 628t in serum, 3: 919, 3: 920t Chloride anionic salts, 2: 360 Chloride ions, pitting corrosion, 4: 260–261, 4: 261f Chlorination organic compound removal, drinking water, 4: 584 water supply disinfection, 4: 585t, 4: 585–586 Chlorine, 2: 373 dietary cation-anion difference reduction, 2: 358 liquid, safety risk, 4: 277 milk, mastitis effects, 3: 904 milk concentrations, 2: 373 pregnancy requirements, 2: 373 ration requirements, 2: 373 requirements, 2: 373 secretion in milk, 3: 379 stainless steel corrosion, 4: 135–136 Chlorine sanitizers milking hygiene, 3: 635 premilking, 3: 635 Chloris gayana (Rhodes grass), 2: 578, 2: 600 Chlorocebus pygerythrus milk see Vervet monkey milk Chloroperoxidase, 4: 790 Chocolate anhydrous milk fat use, 1: 517 dairy ingredients, 2: 130 milk-flavored see Milk chocolate Chocolate crumb, 1: 860 Chocolate drink, 3: 300 Chocolate milk, 3: 300 alkalized cocoa powder, 3: 305 cocoa powder and, 3: 305 particle size, 3: 305 cooling, 3: 305–306 filing temperature, 3: 305–306 heat stability, 3: 305 homogenization, 3: 305–306 listeriosis outbreaks, 4: 83 processing, 3: 305 quality criteria, 3: 306 stabilization, k-carrageenan concentration, 3: 304 Cholecalciferol, 4: 646 chemistry, 4: 646–647 discovery, 4: 646 supplements, housed ruminants, 3: 1001–1002 Cholecystokinin, 3: 993 Cholesterol blood level determining factors, 3: 727–733 age, 3: 732 dietary determinants, 3: 730, 3: 730t genetics, 3: 732, 3: 732t dietary, 3: 730
functions, 3: 727 hydroxylation, vitamin C, 4: 672 liver synthesis, 3: 712, 3: 727 metabolism fermented milk effects, 2: 485, 2: 502, 2: 524 milk fat health risks claims, 3: 609 milk, 3: 734, 3: 735t milk fat, 3: 651 milk fat globule membrane, 3: 682 oxidation, 3: 719 pasture effect on content of goat milk, 2: 63t reduced, modified butter, 1: 503 removal see Cholesterol removal saturated fatty acid effects, 3: 1031–1032 serum Bifidobacterium effects, 1: 392 statin drug effects, 3: 1032 transport, 3: 712, 3: 727, 3: 1031 Cholesterol oxidase, 3: 735 milk, 3: 736 Cholesterol oxidation products (COPs), 3: 719 Cholesterol-reduced foods, 3: 739 Cholesterol reductase, 1: 504 cholesterol extraction from butter, 1: 504 Cholesterol removal, 3: 734–740 adsorption, 1: 503–504 biological processes, 3: 734 byproducts, 3: 734–735 cream, 3: 736 enzymes, 3: 735 microorganisms, 3: 734 milk fat, 3: 736 safety, 3: 734–735 cheese, 3: 738 chemical processes, 3: 735 butter, 1: 503, 3: 738 butter oil, 3: 738 complex formation, 3: 736 cream, 3: 737, 3: 738t milk fat, 3: 737 costs, 3: 738–739 dairy applications, 3: 738 distillation and crystallization methods, 3: 735 milk, 3: 736 physical processes, 3: 735 butter, 3: 737 butter oil, 3: 737 cream, 3: 736 milk fat, 3: 736 processes, 3: 734 product functional property changes, 3: 738–739 scientific justification, 3: 739 taste panel evaluations, 3: 739 Cholesterol Treatment Trialist’s Collaborators, statin meta-analysis, 3: 1032 Cholesteryl esters (CEs), 3: 727 Cholesteryl ester transfer protein (CETP), 3: 729 Choline biosensors, 1: 245 fatty liver, 2: 221–222 feed supplements, 2: 397 strategies, 2: 400–401 functions, 2: 397t, 2: 397–398 rumen-protected, 3: 1000–1001 sources, 2: 397t Cholorfluorocarbon (CFC) refrigerants, 4: 599 Chorioallantois, 4: 486–487 Chorion, 4: 486, 4: 486f Chorionic vesicle (filamentous blastocyst), 4: 486 Chorioptes bovis, 2: 250, 2: 251f Chorioptes capre, 2: 250 Chorioptes ovis, 2: 250 Chorioptic mange clinical signs, 2: 251 epidemiology, 2: 250, 2: 251f lesions, 2: 251f treatment, 2: 252 Christian IX cheese, 1: 788
Christmas butter, 1: 503 Chromatographic methods, 1: 169–176 applications, 1: 170t carbohydrate analysis, 3: 550 future work, 1: 176 milk proteins, 3: 761 sample preparation, 1: 169 see also specific methods Chromium absorption, ruminants, 3: 999 feed supplements, 3: 999 chelated, 2: 387 mastitis resistance, 3: 431 in milk, 1: 901t, 3: 934, 3: 934t chemical forms, 3: 935 nutritional significance, 3: 939 recommended dietary intake, 3: 937t stainless steel, 4: 135 Chromium picolinate, 3: 999 Chromobacterium, 4: 384, 4: 386t Chromogenic Shigella plating medium (CSPM), 4: 101 Chromophores definition, 1: 109–110 energy level diagrams, 1: 110f, 1: 110–111 Chronic diseases, milk protein/by-products affecting, 3: 1064 Chronic toxicity tests, additive safety, 1: 57 Chronoamperometry, 1: 196 Churning, butter see Butter Churro sheep, 1: 333, 1: 333f lactation length, 1: 332t milk yield, 1: 332t Chylomicrons (CMs), 3: 712, 3: 727 adipose tissue, 3: 727–728 composition, 3: 728t functions, 3: 728t triacylglycerols, 3: 727–728 vitamin E transfer, 4: 654 Chymosin, 1: 574, 1: 575, 2: 289 active site, 1: 579–580 camel, 3: 515 casein micelle degradation, 3: 772 k-casein proteolysis, 3: 776 catalytic mechanisms, 1: 576 Cheddar cheese ripening, 1: 708 fermentation-produced see Fermentation-produced chymosin (FPC) history, 1: 574 long ripened pasta-filata cheeses, 1: 749–751 milks/cream rheology, 4: 523 pepsin ratio, bovine rennets, 1: 574–575 pH optimum, 1: 575–576 properties, 1: 552 structure, 1: 575 Chymotrypsin, 2: 289–290 CIFST (Canadian Institute of Food Science and Technology), 2: 105 CIP-able bag filters, 4: 228 Circadian rhythm, estrous behavior, 4: 465 Circling disease see Listeriosis Circulation evaporators, 4: 201 Cis-9, trans-11 conjugated linoleic acid see Rumenic acid (RA) Cis-regulator element (CRE), lactic acid bacteria, 3: 64 Citrate(s) cheese ripening see Cheese ripening conversion to pyruvate, 3: 167, 3: 168f dairy products, 3: 166 fermentation, metabolic pathway, 2: 535, 2: 535f heat stability, milk, 2: 745 imitation milks, 2: 914 metabolism LAB see Lactic acid bacteria (LAB) Lactobacillus, 3: 86 Lactobacillus casei, 1: 641 starter cultures, 1: 562
Index in milk, 3: 166 interspecies variation, 3: 918–919 measurement, 3: 915 pasteurized processed cheese products, 1: 811t primate milk, 3: 628t in serum, calcium interactions, 3: 919, 3: 920f sheep milk, 3: 499–500 Citrate lyase, 3: 167 Citreoviridin, 4: 792, 4: 795 biosynthesis, 4: 795–796, 4: 796f Citrinin, 4: 794, 4: 794f Citrobacter, 4: 388 Citrobacter freundii, 4: 68–69 Citrulline, blue mold cheese aroma, 1: 771–772 Citrus oils, Aspergillus flavus growth inhibition, 4: 788–789 CLA see Conjugated linoleic acid (CLA) Cladosporium herbarum, 4: 777 Clarification, cheese manufacture, 1: 544 Clarifiers clarification, 4: 172 rising channel positions, 4: 169 Clarifying separators, bacteria removal, 4: 172 Classical galactosemia see Galactosemia Clavispora lusitaniae, 4: 750 Clean Air Act (1963), 3: 396 Clean Air Act (1970), 3: 396 Cleaning pasteurized processed cheese products, 1: 807 warm climate feed pads, 2: 21 warm climate milking systems, 2: 18 Cleaning in place (CIP), 4: 283–285 automated systems, 4: 130–131 biofilms, 1: 448–449 concept, 4: 283 dairy equipment applications, 4: 284 dairy industry practice, 4: 283 dairy plants, 4: 130 definition, 4: 283 degree of automation, 4: 283 detergents, 4: 284 disinfectants, 4: 284 electrodialysis plant, 4: 739 finished milk CIP set, 4: 283 milking machine piping systems, 3: 950 milking parlors, 3: 633, 3: 634f milk pump capacity, 3: 635 partial recovery system, 4: 283 raw milk, 4: 283 separators, 4: 169–170 set design, 4: 283, 4: 284f stages, 4: 283 system outline, 4: 283 wastewater, 4: 633 Cleaning solutions, regeneration, 4: 617–618 Cleanroom technology, spoilage mold control, 4: 782 Clean Water Act (CWA), 3: 395 Clerget inversion, 1: 81 ClfA, 4: 105, 4: 106 ClfB, 4: 105 Clinical foods, 2: 131–132 ‘Clinically lactose-free formulae’, 3: 853 Clone, 2: 610 Clone-by-clone shotgun sequencing, 2: 663 Cloned embryo, 2: 611 Cloning, 2: 610–615 cell types, 2: 613–614, 2: 614t food safety, 3: 968 future developments, 2: 613 identical twin formation, 2: 610–611 nuclear transfer see Nuclear transfer (NT) separation, 2: 610, 2: 611f, 2: 612f splitting, 2: 611, 2: 611f, 2: 612f steps, 2: 610 Cloning shuttle vectors, Propionibacterium, 1: 405, 1: 405t Closed-loop process control, 4: 242, 4: 243f controller design, 4: 243
derivative action, 4: 243 integral action, 4: 243 proportional action, 4: 243 proportional gain, 4: 243 Close-harvesting, 2: 816–817, 2: 818f Closer Economic Trade Agreement, 4: 310 Close-up dry cows see Transition cows Clostridial diseases, sheep, 2: 858 Clostridium, 4: 47–53 cheese ripening, 1: 668 cheese spoilage, 4: 780 control, 4: 52 good manufacture practices, 4: 52 heat treatment, 4: 52 raw milk spore reduction, 4: 52 refrigerated storage, 4: 53 spore outgrowth prevention, 4: 52 in dairy foods, 4: 49 diseases associated, 4: 50 incidence, 4: 49 technological problems, 4: 49 detection, 4: 51 biochemical tests, 4: 52 enumeration, 4: 51 media, 4: 51 food-borne diseases, 4: 47 gas blowing defects, cheese, 1: 662–663, 4: 49 gastrointestinal microflora (human), 1: 383t genetic studies, 4: 47 histamine production, 4: 49 HTST pasteurization, 4: 384 in milk, 3: 450 morphology, 4: 47 pathogenesis, dairy food contamination, 4: 47 physiology, 4: 47, 4: 48t silage, 4: 50 spoilage, 3: 453 spores, 4: 47 taxonomy, 4: 47 Clostridium beijerinckii, 4: 48t Clostridium botulinum, 4: 48t neurotoxin, 4: 47–49 proteolytic strains, 4: 50 raw milk contamination, 3: 312, 4: 50 spore numbers as sterility standard, 2: 714, 2: 715, 2: 734 Clostridium butyricum, 4: 48t in dairy foods, 4: 49 diseases associated, 4: 51 late gas formation, 1: 630 pathogenesis, 4: 49 Clostridium perfringens, 4: 48t in dairy foods, 4: 49 endotoxins, 2: 794, 2: 797–798 enteritis, 4: 49 dairy product-associated, 4: 51 enterotoxin-producing, 4: 49 goat enterotoxemia, 2: 794, 2: 797–798 Clostridium sporogenes, 4: 48t in dairy foods, 4: 49 late blowing defects, cheese, 4: 50 Swiss-type cheese defects, 1: 719 Clostridium tyrobutyricum, 4: 48t in dairy foods, 4: 49 Dutch-type cheese defects, 1: 726 late blowing defects, 1: 630, 4: 50 Swiss-type cheese defects, 1: 719 Clotted cream, 2: 907 regulations, 1: 921 Clovers (Trifolium), 2: 558 Clumping factor test, 1: 217 Cluster analysis, 1: 101 Cluster assembly, goats, 2: 811, 2: 811f, 2: 811f Cluster dipping, contagious mastitis prevention, 3: 413 Cluster of differentiation 36 (CD36) functions, 3: 687 milk fat globule membrane, 3: 687
857
synthesis, 3: 687 topology, 3: 686f Coaches, dairy production education, 2: 4 Coagulants, 1: 576 analysis, 1: 578 cheese ripening, proteolysis, 1: 670 chicken pepsin, 1: 576 European Union, 1: 36 nomenclature, 1: 576 pH dependency, 1: 552 porcine pepsin, 1: 576 properties, 1: 552 see also specific coagulants Coagulase, Staphylococcus aureus, 4: 107 Coagulase factor test, 1: 217 Coagulation, 3: 482 acid-coagulated cheeses see Acid-coagulated cheeses camel milk, time to, 3: 514, 3: 515f cheese manufacture, 1: 539, 1: 552 Dutch-type cheeses, 1: 721–722 heat-induced, 2: 748 hyperspectral imaging, 1: 128 mold-ripened cheese manufacture, 1: 773 mold-ripened cheeses, 1: 773 rennet(s) see Rennet-induced milk coagulation sheep milk, 3: 500 suspended solids/turbidity removal, water, 4: 583 ultrafiltration effects, 1: 619 Coagulation experts, US, 1: 39 Coagulation proteins, vitamin K-dependent, 4: 663, 4: 663t deficiency, 4: 664 CoAguLite, 1: 589, 1: 589f, 1: 589f Coagulum, 1: 585 firmness, role in cheese making, 1: 585 see also Gel firmness (curd strength) Coal, 4: 591 Coalescence, emulsions see Emulsions Coarse screening dairy effluent treatment, 4: 620 screens, 4: 620–621 Cobalamin see Vitamin B12 Cobalt, 2: 378 absorption, ruminants, 3: 1000 deficiency early signs, 2: 378 ketosis, 2: 232–233 feed supplements, 2: 378, 2: 385 combination supplements, 2: 386t functions, 2: 385, 3: 939 in milk, 3: 934, 3: 934t chemical forms, 3: 936 nutritional significance, 3: 939 requirements, 2: 379t Cobalt carbonate, 2: 378 Cobalt glucoheptonate, 2: 386, 2: 386t Cobalt sulfate, 2: 378 Coccidiosis coccidiostats, 2: 827–828, 2: 830–831 dairy replacements, 4: 419 goats, 2: 830, 2: 830f Cockfoot (orchardgrass, Dactylis glomerata), 2: 576 Cockroaches, 4: 542 control measures, 4: 543 detection, 4: 542–543 Cocoa powder, dairy desserts, 2: 908 Coconut oil milk replacers, 4: 398 Code of Federal Regulations (CFR), US, 1: 850 additive definitions, 1: 51 cheese legislation, 1: 850 food additives, 1: 850–852 identity standards, 1: 850 label declarations, 1: 850 nutrient content claims, 1: 850 cheese varieties, 1: 850, 1: 851t divisions, 1: 850 food use substances, 1: 852
858 Index Code of Federal Regulations (CFR), US (continued ) milk definition, 3: 274 processed cheese, 1: 852t spiced cheese types, 1: 783, 1: 784t Codex Alimentarius, 1: 55, 4: 312–321 additive definitions, 1: 49 additive labeling, 1: 53 blended spread standard, 1: 522 butter definition, 1: 492 butter standard, 4: 328 cheese standards see Cheese(s) commodity standards, 4: 319 cream product legislation, 1: 920 cream standard, 4: 328 dairy fat spread standard, 1: 522, 4: 328 dairy production relevant texts, 4: 319 analysis methods, 4: 321 contaminants, 4: 320 food additives, 4: 320 food hygiene, 4: 319 food labeling, 4: 320 pesticide residues, 4: 320 residues of veterinary drugs in foods, 4: 320 sampling methods, 4: 321 dairy trade relevant texts, 4: 319 certification systems, 4: 320 food import and export inspection, 4: 320 drinking milk standards, 4: 328 fat adjustment, 4: 328 protein adjustment, 4: 328 edible casein products standard, 3: 861t Emmental cheese standards, 1: 712 establishment, 4: 312, 4: 313f evaporated milk composition, 1: 862 expert selection, 4: 313 fermented milk standards, 4: 328 hard Italian cheeses definition, 1: 728 low-fat cheeses, 1: 833 mandatory food labeling requirements, 3: 1, 3: 2 established names, 3: 2 milk products not covered, 3: 3, 3: 3t microbiological hazards, 4: 319–320 milk chocolate, 1: 861 milk fat product standards, 1: 515, 1: 516t, 4: 328 ghee, 1: 517 recommended quality factors, 1: 515, 1: 516t milk product standards, 4: 319, 4: 324, 4: 325 analysis supporting methods, 4: 327 appendix content, 4: 325 composition requirements, 4: 327, 4: 327, 4: 327f, 4: 328f contents, 4: 325 establishment prerequisites, 4: 325, 4: 326f food additives, 4: 327 fraudulent practice risk, 4: 325 general approach to, 4: 325 identity characteristics, 4: 325 individual standards, 4: 328 labeling, 4: 327 labeling provision, 4: 325 principle manufacture method, 4: 326 principle of equivalence, 4: 326 raw materials, 4: 326 revision, 4: 319 sampling supporting methods, 4: 327 scope, 4: 325 milk protein standardization, 4: 548 national food regulations harmonized need, 4: 312 new work initiation, 4: 315 first drafting, 4: 316 project document, 4: 315–316 nutritional intake claims recommendations, 3: 6, 3: 7, 3: 7t objectives, 4: 314 organization, 4: 313 pasteurized processed cheese products, 1: 805–806, 1: 807t preserved milk product standards, 4: 329
processed cheese standards, 1: 844–845 purpose, 4: 313 scientific basis, 4: 313 standards revision, 4: 316 step procedure, 4: 314, 4: 316f structure, 4: 314 text application, 4: 316 commercial trade, 4: 319 national legislation, 4: 318 national regulations, 4: 318 regional regulations, 4: 318 trade agreements, 4: 318 text roles, 4: 316 Codex Alimentarius Commission (CAC), 4: 312, 4: 314 delegations, 4: 314 members, 4: 312 objectives, 4: 312 observer capacity, 4: 314 organization, 4: 315f subsidiary bodies, 4: 314 Codex Committee on Contaminants in Foods (CCCF), 4: 313 Codex Committee on Food Additives (CCFA), 4: 313 Codex Committee on Food Additives and Contaminants (CCFAC), additive approval, 1: 52 Codex Committee on Milk and Milk Products (CCMMP), 1: 843–844, 4: 313, 4: 324, 4: 324 establishment, 4: 312 Codex Committee on Pesticide Residues (CCPR), 4: 313 Codex Committee on Residues of Veterinary Drugs in Foods (CCVDF), 4: 313 Codex Committees, 4: 314 Codex General Standard for the Use of Dairy Terms (GSUDT), 4: 322, 4: 325–326 drinking milk, 4: 328 products with modified composition, 4: 327, 4: 328f Codex General Standards for Cheese, 1: 844 Codex hygiene texts, 4: 319–320 Codex Standard, 4: 316 revision, 4: 316 Codex Standard for Fermented Milks, 2: 474 Codons, 3: 1056–1057 CodY, 3: 60, 3: 64 Coenzyme A (CoA) function, 4: 694 structure, 4: 695f Coeur de Camembert au Calvados, 1: 787 Coffee cream, 1: 913 aggregation, 1: 921–922 characteristics, 1: 913 imitation, 2: 915 infrared spectrometry, 1: 119t manufacture, 1: 912, 1: 913f, 1: 913–914 flow sterilization, 1: 914 homogenization, 1: 914 milk protein concentrate, 3: 853 packaging, 1: 914 quality problems, 1: 921 shelf life, 1: 913 stability, 1: 921 storage-related changes, 1: 914 creaming, 1: 921 sedimentation, 1: 921 Coffee whiteners, 2: 915 manufacture, 2: 915 Coitus examination, bulls, 1: 477 Cokelek, 1: 785f, 1: 786 Cold barn characteristics, 4: 558–559 ridge opening, 4: 558–559 ventilation, 4: 557 mismanagement, 4: 558 winter temperatures, 4: 558 Cold enrichment, Yersinia enterocolitica, 4: 121
Cold-finger molecular distillation, cheese flavor, 1: 677 Cold-pasteurization methods, 3: 310–311 Cold plasma decontamination, 2: 731 Cold-shock protein (CspA), 4: 25 Cold stress, 4: 550–554 Bos indicus cattle, 4: 444–445 calf feeding, 4: 400–401 dry cow, 4: 551t, 4: 552 heat loss, 4: 550 heifers, 4: 407, 4: 552, 4: 553t, 4: 553t LAB, 3: 63 management considerations, 4: 555–560 bedding, 4: 559 ventilation see Ventilation management practices, 4: 554 metabolic adaptations, 4: 551 metabolizable energy requirements, 4: 551t, 4: 551–552 calves, 4: 552, 4: 552t milking cows, 4: 551t, 4: 553 milk-fed calves, 4: 552 milking cows, 4: 553, 4: 553t milk protein synthesis, 3: 362–363 nutritional requirements, 4: 551 physiological adaptations, 4: 551 ration formulation programs, 4: 552 reproductive process suppression, 4: 441 Colebrook equation, 4: 594 Colebrook–White empirical equation, 4: 141 Coliforms acute clinical mastitis, 3: 437 commercially pasteurized nonaseptically packed milk, 4: 387 gas blowing defects, cheese, 1: 661 avoidance, 1: 661 legal standards, 3: 645 mastitis, 3: 419 microbiological analytical methods, 1: 217, 4: 69 milk hygiene practices, 1: 661 morphology, 4: 67 physiology, 4: 67 raw milk testing, 3: 645 spoilage, 3: 453 see also individual bacterial genera Collars, 2: 832, 2: 832f Colloidal calcium phosphate (CCP) acid-coagulated cheeses, 1: 698 historical aspects, 1: 24 low-fat cheese moisture content, 1: 835–836 low-fat cheese pH, 1: 836 low-fat cheeses, 1: 834 Colloid mills, 2: 761, 2: 762f flow rates, 2: 761–762 Colon cancer dairy foods epidemiology, 3: 1017 protective effects, 3: 1017 removal, 3: 1018, 3: 1018t epidemiology, 3: 1017 lactose, 3: 1020 lactulose, 3: 1020 milk proteins, 3: 1020, 3: 1020f, 3: 1021f prevention, 3: 1016–1022 interventional studies, 3: 1018 mechanisms, 3: 1019 sphingomyelin, 3: 1021 surrogate measures, 3: 1018 probiotics, 3: 1019 Colonization resistance (competitive exclusion), 4: 366–367 Colon walls, Bifidobacterium, 1: 383 Color defects see Color defects definitions, 1: 51–52 European Union, 1: 34, 1: 35t milk transportation, 1: 544 United States, 1: 37 see also individual products
Index Colorants, cheese, 1: 537 Color defects Cheddar cheese, 1: 711 dulce de leche defects, 1: 879 khoa, 1: 885 sweetened condensed milk, 1: 872 Colorectal cancer confounding factors, 3: 1016–1017 diet, relevance of, 3: 1016 incidence, 3: 1016 pathogenesis, 3: 1016, 3: 1017f Colorimetry alkaline phosphatase activity, 2: 316 curd strength measurement, 1: 587 mastitis, 3: 425 Colostral antibody preparation, 3: 813, 3: 814t Colostral lipase, 2: 305 Colostral whey-based antibody preparations, 3: 597 Colostrinin, sheep milk, 3: 500–501 Colostrogenesis, 3: 343–344 Colostrum, 3: 591–597 alpaca, composition, 3: 536t antimicrobial activity, 3: 1063 biological function, 3: 591 buffering capacity, 3: 475 calcium requirements, 2: 240 calf management, 4: 396 camels, 3: 512–513 complement system, 3: 592 composition, 3: 591, 3: 592t, 3: 600–602, 4: 397t antibodies, 2: 825, 2: 883, 3: 530 fatty acid composition, 3: 591, 3: 594t formation cellular transport, 2: 766–767 insulin-like growth factor concentrations, 2: 768 goat see Goat colostrum growth factors, 2: 767, 2: 767t, 3: 595 heat stress, 4: 562 heat treatment, disease control, 2: 797, 2: 799, 2: 825 horse see Equine colostrum human see Human colostrum immune protection, 3: 591, 3: 595f, 3: 595t immunoglobulins, 3: 591, 3: 592, 3: 593f, 4: 396 alpaca colostrum, 3: 537 concentrations, 3: 808t, 3: 810 importance to offspring, 3: 812 transfer, primates, 3: 624–625 industrial utilization, 3: 596 lactational changes, 3: 591 lactoferrin, 3: 801 lambs, artificial/supplemental feeding, 2: 883, 2: 885 leukocytes, 3: 592–593 mineral concentrations, 3: 591 newborn survival, 3: 812 nonconsumption, calf mortality risk, 4: 418 pH, 3: 474 protein content, 3: 359, 3: 363 sheep, 3: 271t, 3: 494 supplements, 3: 597 vitamin E, 4: 653 vitamins, 3: 591, 3: 592t whey proteins, 3: 591 yaks, 3: 532t Combined heat and power (CHP) system, 4: 634 Combined nomenclature (CN), Harmonized System, 4: 335 Combustion, 4: 591 air supply, 4: 591 Combustion efficiency, 4: 591–592 Comisana sheep, 1: 333, 1: 334f lactation length, 1: 332t milk yield, 1: 332t Commercial coolers, mastitis prevention, 3: 432 Commercial frozen/freeze-dried starter cultures, 1: 558 Commodity Committees (vertical committees), Codex Alimentarius, 4: 314
Common Agricultural Policy (CAP), 4: 295–299 Agenda 2000, 4: 298 export refunds, 4: 295, 4: 297 financing, 4: 295 historical aspects, 4: 295 intervention price, 4: 295 reductions in, 4: 298–299 liquid milk sale subsidies, 4: 297 low price support, 4: 288–289 milk/dairy products export schemes, 4: 297 import system, 4: 297 milk quota scheme, 4: 297 direct sales, 4: 297–298 new Member States, 4: 299 non-Annex I products, 4: 297 objectives, 4: 295 price and intervention scheme, 4: 296 butter, 4: 297 cheese, 4: 297 milk/dairy products, 4: 296 prior to reform 2003, 4: 296 skim milk, 4: 296 skim milk powder, 4: 296 principles, 4: 295 reforms, 4: 295 mid-term review 2003, 4: 298 superlevy, 4: 297–298 target price, 4: 295 tender procedures, 4: 297 threshold price, 4: 295 Common liver fluke (Fasciola hepatica) see Fasciola hepatica (common liver fluke) Common Market Group (GMC), identity standards, 4: 324 Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), phages, 4: 108, 4: 108–109 Compaction, preimplantation period, 4: 493–494 Company Competencies (South Africa), 2: 8 Company degrees, food technology, 2: 7 Comparative cervical skin test, bovine tuberculosis, 2: 196 Comparative genome hybridization analyses, starter cultures, 1: 565 Comparative mortality statistics, 4: 279t Competitive enzyme-linked immunosorbent assay (C-ELISA), 1: 178, 1: 178f bluetongue virus, 2: 150 brucellosis, 2: 157 Competitive exclusion (colonization resistance), 4: 366–367 Complement colostrum, 3: 592 mammary gland defense, 3: 389 Complementary DNA (cDNA), microarray technology, 3: 346 Complement fixation test (CFT) brucellosis, 2: 156t, 2: 157, 4: 37 Coxiella burnetii, 4: 57 Johne’s disease, 2: 177 Complex lipids, 3: 670 Complex vertebral malformation (CVM), 2: 677 ‘Component balance theory’, 1: 559–560 Composite cans material specifications, 4: 20 powder milk packaging, 4: 20 Composite milk products, 4: 325–326 Compost barn, 2: 57 Composting, dairy effluent treatment, 4: 630t Compound 1080 (sodium monofluoroacetate), 2: 845 Compound light microscopy, 1: 227t Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), 3: 397 Comprehensive nutrient management plans (CNMPs), 3: 395
859
Compressed air, 4: 602–609 air-intake filters, 4: 608 applications, 4: 602 treatment, 4: 608 see also Air compressors Compressed air piping systems delivery pressure, 4: 609 design, 4: 608 energy losses, 4: 609 pressure drop, 4: 608 abacus use, 4: 608–609, 4: 609f tube diameters, 4: 608 Compression evolution, 4: 605, 4: 605f Compression modulus, cheese, 1: 695t Compression tests cheese rheology measurement, 1: 690 rheology instrumentation, 1: 274–275, 1: 275 Compression (longitudinal) waves, ultrasound, 1: 206, 1: 207f Compressor, vapor compression cycle, 4: 596, 4: 597 Compressor (isothermal) efficiency, 4: 605f, 4: 606, 4: 606f Computer-assisted sperm analysis (CASA), 2: 604, 2: 604, 2: 605 Computerized fluid dynamics (CFD), spray drying, 4: 210, 4: 210f Comt´e cheese pathogen status, 1: 659 umami taste, 1: 683 Concentrated animal feeding operations (CAFOs) nutrient management plans, 3: 395 water quality regulations, 3: 395 implications of, 3: 396 Concentrated dairy products, E. coli control measures, 4: 65 Concentrated dispersions, 1: 269f, 1: 270 Concentrated fermented milk, 2: 475 Concentrated milks curd syneresis, 1: 593 macromineral contents, 3: 926t rheology see Rheology, liquids/semisolids trace elements, 3: 934t Concentration gradients, cheese salting, 1: 603 Concentric-cylinder systems, 1: 272–273 Concentric tube tubular heat exchanger, 4: 190 Conception, 4: 493 Conception rate artificial insemination vs. natural service, 4: 483 calving difficulty, 4: 482, 4: 483f energy balance early postpartum period, 4: 480, 4: 481f at insemination, 4: 481 estrus control, progestogens, 4: 449 feed intake, sudden reductions in, 4: 482 heat detection efficiency, 4: 483, 4: 483t insemination technique, 4: 482 insemination timing, 4: 482 protein nutrition, 4: 482 reproductive efficiency, 4: 478 undernutrition, 4: 578 Conceptus definition, 4: 485 nutrition, 4: 487 Concrete floors, reproductive efficiency, 4: 580 Condensates, 4: 617–618 Condensed milk, sweetened see Sweetened condensed milk Condenser(s) air-cooled, 4: 597 evaporative, 4: 597 vapor compression cycle, 4: 596, 4: 597 water-cooled, 4: 597 Condiment cheese, 1: 840 Conduction, 4: 550–551 heat transfer, 4: 184 Conductometric analysis, 1: 194 Cone-and-plate devices, 1: 273 Confectionery butter, 1: 503
860 Index Confectionery products anhydrous milk fat use, 1: 517 dairy ingredients, 2: 130 see also specific products Confinement housing, reproductive efficiency, 4: 580 Confinement rearing historical aspects, 1: 3 predation protection, 2: 843 night confinement drawbacks, 2: 843 temperature, 2: 832t ventilation, 2: 832t Confocal microscopy, 1: 226, 1: 227t whey proteins, 1: 233f Confocal scanning laser microscopy (CSLM), 1: 226–227, 1: 228f butter, 1: 233–234, 1: 234f Conformation (type) traits, 2: 650 ‘Confounding’, 4: 267 Congenital hypolactasia, 3: 236–237 Congenital muscular dystonia type 1 (CDM1), 2: 665–666 Conjugated linoleic acid (CLA), 3: 657, 3: 660–664 analysis, 3: 699 antiatherogenic effects, 3: 663 anticarcinogenic properties, 3: 663, 3: 663t, 3: 714, 3: 1065 biological activity, 3: 662–663, 3: 1062 butter, 1: 507, 1: 507f cheese, 3: 714 colorectal cancer incidence, 3: 1018 contents alteration, dairy products, 3: 661 dietary effects, 3: 661–662 dietary sources, 3: 660, 3: 661f first-age infant formulae, 2: 142 functional food implications, 3: 662 goat milk, 3: 485, 3: 490 feed concentrate effects, 2: 795 health effects, 2: 366, 3: 42, 3: 116, 3: 657, 3: 662–663, 3: 714 isomeric structures, 2: 367, 2: 367f, 3: 42 mammary gland synthesis, 3: 42 milk fat, 3: 714 milk fat depression, 3: 356, 3: 356f milk fat synthesis inhibitor, 3: 356, 3: 357f modified butter, 1: 504 nutritional significance, 3: 714 origins, 3: 660 polyunsaturated fatty acid levels and, 3: 479–480, 3: 661–662 rumen biohydrogenation, 2: 367, 2: 367f sheep milk, 3: 498 structures, 3: 660, 3: 661f Conjugated linoleic acid-enriched products, consumer acceptability, 3: 664 Conjugation, lactic acid bacteria, 3: 68 Conn, Herbert, 1: 28 Connexins, 4: 509–510 Conserved forage feed value, 2: 45 non-seasonal/pasture-based management, 2: 40 supplementation, 2: 46 Consistent milk production system, 3: 598 Constant-pressure valve, 4: 157, 4: 157f Constitutive secretion, 3: 378 Constructed wetlands, 4: 632 Construction materials, drinking water systems, 4: 586–587 Consumer acceptability testing, 1: 281 Consumer evaluations, 1: 44 Consumer perceptions additives, 1: 41–48, 1: 45f, 1: 45t ‘artificial’, 1: 43 E numbers, 1: 43 health aspects, 1: 44, 1: 44f labeling, 1: 44, 1: 45f ‘natural’ foods, 1: 43, 1: 47 product sectors, 1: 44, 1: 46f, 1: 46t Consumption, dairy products see Dairy products
Contact nucleation, 3: 188 Contagious abortion see Brucellosis Contagious abscess see Caseous lymphadenitis (CLA) Contagious ecthyma see Orf Containers bag-in-box, 2: 711, 2: 712f chemical sterilization methods hydrogen peroxide, 2: 709, 2: 709–710, 2: 710 peroxyacetic acid, 2: 709 form-fill-seal cartons, 2: 709, 2: 710f cups, 2: 712 pouches, 2: 711 irradiation ionizing radiation and electron beams, 2: 708, 2: 711 plasma, 2: 708, 2: 731 pulsed light, 2: 708, 2: 730 UV lasers, 2: 708 lay-flat tubing, 2: 711 plastic bottles, 2: 710 prefabricated cartons, 2: 710 preformed plastic cups, 2: 712 sampling, 1: 72 steam heating, 2: 708, 2: 711–712 see also Packaging Contaminants agricultural, 1: 887–897 -adrenergic agonists, 1: 893 genotoxic carcinogens, 1: 887–889 hormones see Hormones infants, 1: 889 melamine, 1: 896 nonsteroidal anti-inflammatory drugs, 1: 892 safety assessment, 1: 887, 1: 888f see also Antimicrobial drug contamination; Pesticides environmental, 1: 898–905 dioxins see Dioxins metals, 1: 901, 1: 901t mycotoxins see Mycotoxins persistent halogenated hydrocarbons, 1: 900 polychlorinated biphenyls see Polychlorinated biphenyls (PCBs) radionuclides see Radionuclide contaminants milk/dairy products, 1: 645, 2: 480 antibiotics, 2: 532 bacterial species, 2: 491, 2: 493 processing sanitizers, bottling lines, 2: 545–546, 2: 546f Contemporary comparison, genetic evaluation, 2: 651 Contifiller system, 1: 614, 1: 616f Continental cheeses new product launches, 1: 42 see also specific cheeses CONTIN package, 1: 136 Continuity equation, 4: 139 Continuous flow analysis, biosensors, 1: 235 Continuous pasteurization see Hightemperature–short time (HTST) pasteurization Continuous process improvement, 4: 263–272 concept origin, 4: 263 car manufacturing to dairy, 4: 263 definition, 4: 263 emulation, 4: 264 flow of the product, 4: 265 historical aspects, 4: 263 incremental solutions, 4: 264–265 information technologies, 4: 264–265 operational improvements, 4: 264 post-World War II Japan, 4: 263 stock management strategies, 4: 264 Continuous separation (CSEP) chromatographic technology, whey protein products, 3: 874 Continuous variables, statistical analysis, 1: 83 Contraction-associated protein (CAP) gene expression, parturition, 4: 505 Control charts, 4: 243
Controlled drainage, warm climate feed pads, 2: 22 Controlled intravaginal drug release (CIDR) inserts Co-synch program, 4: 457 dairy heifers, 4: 458f, 4: 458–459 heifers, 4: 413 Convection, 4: 550–551 heat transfer, 4: 184 Convenience foods enzyme-modified cheese, 1: 799 new product launches, 1: 42–43 trends in, 1: 42 Conventional polymerase chain reaction, 1: 221 Convention of Paris for the Protection of Industrial Property, 1: 843 Conveyor bowl centrifuges see Decanter centrifuges Conveyor pressing system, 1: 613, 1: 615f Cooking, cheese analogues, 1: 821 ‘Cooking pipe’, acid casein manufacture, 3: 856–857 Cooling milk salt equilibria, 3: 912 pasteurized processed cheese products (PCPs), 1: 807 sweetened condensed milk production, 1: 871 Cooling ponds, mastitis prevention, 3: 432 Cooling systems, warm climate housing systems, 2: 22, 2: 23 Cooling water, treatment, 4: 587 Cool season grasses, potassium concentration, 2: 358 Coomassie blue, 1: 185–186 Coomys see Koumiss Cooperative Milk Marketing model, India, 2: 777 Cooperia oncophora, 2: 258 Coordinating Committees, Codex Alimentarius, 4: 314 Copper, 2: 379 absorption ruminants, 3: 999 sulfur and, 2: 379 dairy plant use, 4: 137 in dairy products, 3: 934t, 3: 935t, 3: 935t, 3: 935t deficiency, 2: 379 humans, 3: 938 dietary molybdenum and, 2: 379, 2: 385, 3: 999 feed supplements, 2: 379, 2: 385 combination supplements, 2: 386, 2: 386t functions, 2: 385, 3: 938 laminitis, 2: 203–204 in milk, 3: 933, 3: 934t absorption, 3: 938 chemical forms, 3: 935 nutritional significance, 3: 938 milk lipid oxidation, 3: 718 primate milk, 3: 627–629, 3: 628t protected form supplements, 3: 999 recommended dietary intake, 3: 937t requirements, 2: 379, 2: 379t rumen fermentation, 3: 983 sheep milk, 3: 500 toxicity, 2: 379–380 sheep, byproduct feeding, 2: 852–853 Copper alloys, dairy plant use, 4: 137 Copper lysine, 2: 386, 2: 386t Copper oxide needles, 2: 379 Copper proteinate, 2: 385 Copper sulfate feed supplementation, 2: 385 papillomatous digital dermatitis, 2: 172 Copper sulfide, 3: 999 Coprecipitates, 3: 849 nondairy food, 2: 128t preparation techniques, 2: 125 Coproduct feeds, 2: 342–348 classification, general, 2: 342 compositional analysis, 2: 342, 2: 344t efficiency benefits, 2: 342, 2: 343f energy feeds, 2: 343 fiber sources, 2: 342, 2: 343–344, 2: 345, 2: 346 protein feeds, 2: 345
Index animal sources, 2: 345 essential amino acid content, 2: 390t quality and variability, 2: 345f, 2: 346, 2: 346t contamination, 2: 345, 2: 347 digestibility, 2: 347 mineral levels, 2: 792–793 storage and souring risks, 2: 346, 2: 347 toxins, 2: 345, 2: 347 range of, 2: 342 Copy number variants (CNVs), within/across bovine populations, 2: 664, 2: 665f Coriosis see Laminitis Corn aflatoxin contamination, 4: 807 calf starters, 4: 401 Cornell Net Carbohydrate and Protein System (CNCPS), 2: 419, 2: 426, 2: 437 bacterial growth, 2: 440 bacterial protein, 2: 440 carbohydrate fractions, 2: 439, 2: 439t dietary protein fractionation, 2: 410, 2: 410t fat digestibilities, 2: 441 feed ingredients energy value, 2: 441 metabolic requirements, 2: 441–442 metabolizable (absorbed) protein value, 2: 441 nonfibrous carbohydrates, 2: 439 protein fractions, 2: 438, 2: 438f, 2: 438t fermentability, 2: 439t, 2: 439–440 Cornell procedure, 1: 622 Cornell University nutrient management planning system (CuNMPS), 2: 445t, 2: 446 Corn products see Maize Corn silage expense, 2: 41 historical aspects, 1: 3, 1: 5 non-seasonal/pasture-based management, 2: 40 Coronary heart disease (CHD) apoB:apoA ration, 3: 1031 lipids and, 3: 713 risk factors, 3: 1023 central obesity, 3: 712 serum cholesterol level, 3: 1023 statin drugs, 3: 1032 vascular endothelial dysfunction, 3: 1033 vitamin C, 4: 672–673 see also Cardiovascular disease (CVD) Corpora lutea (CL), 4: 449 Corpus cavernosum, 3: 334 Corpus luteum function, 4: 431 LH receptors, 4: 429–430 luteolysis, 4: 431, 4: 432f maintenance, 4: 496 progesterone secretion, 4: 431, 4: 431 sheep, 2: 887 Corral dairying, historical aspects, 1: 3 Correlation spectroscopy (COSY), 1: 150, 1: 150f Corrosion, 4: 257–262 definition, 4: 257 drinking water systems, 4: 586–587 economic losses, 4: 257 environmental factors in, 4: 262 kinetics, 4: 259 oxygen availability, 4: 262 ‘passivated’ metal, 4: 259 stainless steel see Stainless steel temperature, 4: 262 thermodynamics, 4: 258 acidic solution, 4: 258 alkaline solution, 4: 258 types, 4: 260 Corrosion fatigue, 4: 262 Corsican sheep, 1: 332t Cortical granule migration, 2: 617–618 Corticosteroids as contaminant, 1: 894 ketosis, 2: 237 pregnancy toxemia, 2: 248–249
Corticotropin-releasing hormone (CRH), 4: 576 Cortisol fetal secretion, 4: 505–507 ketosis, 2: 231 lactogenesis, 3: 18 luteinizing hormone inhibition, 4: 577 milk fever, 2: 242 stress, 2: 770 Corynebacterium acid-curd cheeses, 1: 758, 1: 758f smear-ripened cheeses, 1: 764 Corynebacterium ammoniagenes, 1: 759 Corynebacterium bovis mastitis, 3: 410 control, 3: 412 outbreaks, 3: 410 Corynebacterium flavescens, 1: 396 Corynebacterium pseudotuberculosis, 2: 858–859 Corynebacterium variabile, 1: 396 Coryneform bacteria cheese microbiology, 1: 627 cheese ripening, proteolysis, 1: 673 fermentation starters, 3: 455 pasteurized cream, 4: 386, 4: 387t pasteurized milk, 4: 386, 4: 387t smear-ripened cheeses, 1: 395–396 Corynetoxicosis, 2: 574 Cosmetology, equine milk, 1: 364 COSY (correlation spectroscopy), 1: 150, 1: 150f Co-synch procedure/program, 1: 7, 4: 454, 4: 456 nonpregnant cow resynchronization, post-first service, 4: 457, 4: 457f Cottage cheese, 1: 699 citrate metabolism, 3: 86 composition, 1: 700t defects, 1: 701 floating curds, 1: 701 sludge, 1: 701 dried, 1: 826 equipment, 1: 701 flavor, 1: 699–700 ‘fuzzy’ appearance, 4: 780–781 manufacture, 1: 698, 1: 700, 1: 700t direct acidification, 1: 700–701 Lactococcus lactis subsp. cremoris, 1: 700 Lactococcus lactis subsp. lactis, 1: 700 mechanization, 1: 615 nonfat dry milk powder, 1: 700 preservatives, 1: 701 rennet, 1: 700–701 stabilizers, 1: 700–701 Pseudomonas spoilage, 4: 382 sampling, 1: 74 spoilage molds, 4: 780–781 yield, mastitis effects, 3: 905 Cottonseed, 2: 350 calf starters, 4: 404 definition, 2: 349 feed byproducts, 2: 342–343, 2: 344, 2: 344t, 2: 346 chewing stimulation, 2: 338–340 gossypol, 2: 351 whole see Whole cottonseed (WCS) Cottonseed meal, 2: 353 definition, 2: 349 gossypol, 2: 351 protein concentrations, 2: 353 ruminal protein degradability, 2: 353 Cotyledonary placenta, 4: 488–489 Couchmann–Karasz equation, 4: 214 Couette-type viscometers, 1: 274 Coulometric titration for salt, 1: 194 Coulter counters, somatic cell count, 3: 896 Counter-sloped heifer barn, 4: 407–408 Cowpeas (Vigna unguiculata), 2: 558, 2: 565 Cows see entries beginning dairy cow ‘Cow share’ purchasing programs, raw milk, 4: 96–97 Cows’ milk see Milk Cows’ milk protein allergy (CPMA), alternatives, 1: 365
861
Coxevac, 4: 57 Coxiella burnetii, 4: 54–59 airborne infection, 4: 56 characteristics, 4: 54 diagnostics, 4: 57 disease symptoms, 4: 55 genome, 4: 54 genotyping, 4: 54 infection ticks, 4: 56 isolation, 4: 57 large cell variants, 4: 54 mastitis, 4: 55 in milk, 3: 450, 4: 55 oral infection efficiency, 4: 56 zoonotic risk, 4: 56 plasmid types, 4: 54–55 prevention, 4: 57 reservoirs, 4: 56 routes of infection, 4: 56 serology, 4: 57 shedding, 4: 55 small cell variants, 4: 54 spore-like particles, 4: 54 vaccines, 4: 57 see also Q fever Coxiellosis prevention, 4: 57 treatment, 4: 57 CPM Dairy model, nutritional management, 2: 420–421 lipid submodel, 2: 426 Crabeater seal milk oligosaccharides, 3: 271t Cracks, raw milk cheeses, 1: 658–659 Cranial epigastric artery, 3: 334 Cranial mesenteric artery, 3: 989–990 Cranial mesenteric vein, 3: 989–990 C-reactive protein (CRP) isoflavone supplementation, 3: 1060 statin effects, 3: 1032–1033 Cream(s) agitation, 4: 165 Bacillus, 4: 28, 4: 385 buffalo milk, Mediterranean region, 2: 783 cholesterol removal, 3: 736 Codex standard, 4: 328 composition, 1: 920 E. coli control, 4: 64 E. coli outbreaks, 4: 61 feathering, in coffee, 1: 61–62, 1: 68 formation, immunoglobulin effects, 3: 813 Gram-negative psychrotroph growth, 4: 385 infrared spectrometry, 1: 119t macromineral contents, 3: 926t manufacture, 1: 912–919 centrifugal separation, 1: 913 physical separation, 1: 913 principles, 1: 912 worldwide production, 1: 912 oxidized flavor, ascorbic acid, 3: 718–719 pasteurization, 4: 198 historical aspects, 1: 28 testing, 4: 199 pretreatment/cooling, butter churning, 1: 494, 1: 495t products, 1: 920–925 additives, 1: 921 classification, 1: 920 nondairy food, 2: 128t quality problems, 1: 921 regulations, 1: 920 types, 1: 920 see also specific products recombined/reconstituted products, 3: 319 rheology see Milk/cream rheology ripening, butter spreadability, 1: 513 spoilage molds, 4: 781 trace element content, 3: 935t whipping see Whipping cream
862 Index Cream and Cheese Regulations 1995, UK, 1: 847 Cream cheeses, 1: 701 Codex standard, 4: 330 composition, 1: 700t defects, 1: 702 equipment, 1: 702 manufacture, 1: 698, 1: 702 ultrafiltration, 1: 622 packaging, 4: 20 pH, 1: 702 texture, 1: 702 types, 1: 701 Creamed rice, 2: 907 Creaming cluster formation, 3: 676 coffee cream, 1: 921 emulsions see Emulsions heat effects, 3: 676–677 homogenization and, 3: 676–677 immunoglobulins, 3: 676 milk, 3: 676 cream layer depth, 3: 676 rate of, 3: 676 rate, 1: 21 Stokes’ equation, 3: 675–676 Cream liqueur, 1: 917 defects, 1: 924 granular precipitates, 1: 924 manufacture, 1: 917f, 1: 918 single-stage, 1: 918 two-stage, 1: 918 quality problems, 1: 924 regulations, 1: 921 shelf life, 1: 917–918 Cream ripening (tempering), 3: 709 Cream separator, historical aspects, 1: 3 Cream tempering (ripening), 3: 709 Creatine sucrose dichloran agar (CREAD), spoilage mold enumeration, 4: 783 Creep, cheese rheology measurement, 1: 688f, 1: 691t, 1: 693 Crees Lactator, 3: 941, 3: 942f p-Cresol, 2: 282 Creutzfeldt–Jakob disease (CJD), milk supply safety, 3: 314 Crevice corrosion, 4: 260, 4: 261f Crimson clover (Trifolium incarnatum), 2: 558 Criollo cattle, 1: 298 Latin American dairy management, 2: 91 Criollo goats, 1: 311t, 1: 323, 1: 323f milk yields, 1: 312t CRISPRs (clustered regularly interspersed short palindromic repeats), bacteriophage resistance, 1: 435, 1: 436 Critical collapsing pressure difference (CCPD), teatcup liners, 3: 948 Critical control points (CCPs) definition, 2: 690 determination, 2: 688t, 2: 690 Critical management points (CMPs), 2: 681–682 Critical particle diameter, cyclone efficiency, 4: 226, 4: 227f Croatia, Simmental cattle, 1: 294 Crohn’s disease Johne’s disease comparison, 3: 315, 4: 90t Mycobacterium avium paratuberculosis, 2: 174–175, 2: 179, 4: 90 symptoms, 4: 90 Cronobacter, 4: 72 antibiotic susceptibility, 4: 73 bacteremia, 4: 75 bacterial meningitis, 4: 75–76 biofilms, 1: 447 detection methods, 4: 76 milk-based infant formula, 4: 77 dried milk, 4: 68 Enterobacter vs., 4: 77, 4: 78t environments, 4: 73–74
foodborne outbreaks, 4: 74, 4: 74t genetic-based assays, 4: 77 growth, 4: 72 in milk, 3: 451 milk-borne illness, 3: 315 neonatal infection, 4: 72 feed preparation equipment, 4: 79 risk factors, 4: 75 pH, 4: 73 phenotypic identification, 4: 77, 4: 78t powdered infant formula contamination, 4: 74 water activity, 4: 72 Crop failure, weather-related, nutrient carryover, 3: 403 Crop production costs, 1: 487 recovered manure utilization, 3: 402t, 3: 403, 3: 404t Crossbreeding, 2: 653 Bos indicus Bos taurus cattle see Bos indicus Bos taurus cattle buffalo, 1: 340, 2: 775 pregnancy duration, 4: 503 sheep, 2: 73 sheep breeding, 2: 73 Southern Asia, 2: 99, 2: 99–100 Cross equation milk/cream rheology, 4: 522, 4: 524 yogurt rheology, 4: 529 Cross-flow microfiltration (cMF), 3: 865 fouling, 3: 870, 3: 872 native phosphocasein production, 3: 866 skim milk powder, enhanced renneting properties, 3: 866–867 whey protein isolate, 3: 866 Cross-ventilation barns, 1: 4, 2: 58 floors, 2: 58 heat stress, 4: 570–571 Crowd gates, milking parlors, 3: 963 Crude fiber (CF), 3: 985 Crude protein (CP), 2: 410 calf starters, 4: 401 dry cow requirements, 2: 410–411, 2: 411f excess, 2: 411 fodder content, 2: 578–579, 2: 579f, 2: 581 feed digestibility effects, 2: 404, 2: 405 in pastures, optimal digestible intake, 2: 597, 2: 598f urinary energy losses, 2: 406–407 fractions, 2: 461 fresh pasture, 2: 453, 2: 454f lactating dairy cows, 2: 410–411 optimum rumen fermentation, 2: 410 pasture, 2: 33f, 2: 34 predicted milk, 2: 460 ruminally degraded protein fraction, 2: 411 Cryoglobulins see Immunoglobulin(s) (Ig) Cryopreservation ampoules, 2: 606 cryoprotectants, 2: 606 embryos, 2: 628, 2: 630 extenders, 2: 606 pelleted semen, 2: 606 reproductive management, impact on, 2: 605 semen, 2: 605, 4: 467 storage containers, 2: 605f, 2: 605–606 straws, 2: 606 see also Artificial insemination Cryovac packaging, 1: 611 Cryphonectria parasitica proteinase (Parasitica coagulant), 1: 576, 1: 576 Cryptic splice site usage, 3: 830 Cryptococcus, 4: 750 Cryptococcus mycosis, 4: 747 Cryptosporidiosis calves, 4: 418 milk-borne, 3: 314–315 Cryptosporidium, 3: 314–315 Cryptosporidium parvum, 4: 419
Crystal growth, 3: 189 diffusion theory, 3: 189, 3: 190f diffusion stage, 3: 189–190 growth kinetics, 3: 190 integration (surface reaction) stage, 3: 189–190 diffusion transfer constant, 3: 192 dislocation, 3: 189, 3: 190f impurity effects, 3: 191 kinetics stirring, 3: 191 supersaturation, 3: 191 technological parameters, 3: 191 temperature effects, 3: 191 nucleation kinetics interactions, 3: 191 two-dimensional nucleation, 3: 189 Crystallization differential scanning calorimetry, 1: 258, 1: 259f lactose see Lactose crystallization milk fat rheology modification, 3: 707 Crystal networks fat and emulsions, 1: 161, 1: 162f NMR T1 (spin lattice relaxation), 1: 161–162, 1: 162f Crystal orientation, fat and emulsions, 1: 160, 1: 161f Crystal-solution interface, 3: 192 CSLM see Confocal scanning laser microscopy (CSLM) CstA gene, 3: 64 C-type esterases, 2: 304 Culicoides, 2: 151 Culicoides hypersensitivity, 2: 251–252, 2: 252f treatment, 2: 252 Culling goats, 2: 834 sheep, 2: 888 Culture-containing milk products, hypocholesterolemic, 3: 713–714 Cultured buttermilk, 2: 471t, 2: 472, 2: 489, 2: 490, 2: 492f, 2: 500 milk fat globule membrane, 3: 691–692 production processes, 2: 490–491, 2: 492f, 2: 494, 2: 500 rheology, 4: 530 sensory and keeping qualities, 2: 491 flavor chemical changes in storage, 2: 535, 2: 537t supplements, 2: 490t, 2: 490–491 see also Starter culture(s) Cultured cream, 2: 472 flavor development, 2: 492, 2: 493, 2: 537 imitation, 2: 916 normal flavor components, 2: 535 off-flavors, processing equipment-induced, 2: 539, 2: 540f spray-dried powder, 2,4,5-trimethyloxazole contamination, 2: 547, 2: 547f Cultured cream butter, flavor, 1: 512 Cultured cream products, 1: 916 consistency, 1: 917 direct acidification, 1: 924 fat content, 1: 916–917 manufacture, 1: 916f, 1: 916–917 souring, 1: 917 quality problems, 1: 924 regulations, 1: 920–921 Cultured milk products, yeast contamination, 4: 748 Cultured salted butter, 1: 492–493 Cultured unsalted butter, 1: 492–493 Culture techniques, 1: 215 microbiological analysis see Microbiological analytical methods Cumulus–oocyst complexes (COCs), 2: 616, 2: 617f nuclear transfer, 2: 612 Cups form-fill-seal, 2: 712 preformed plastic, 2: 712 Curd drainage, mold-ripened cheese, 1: 773 emulsification, enzyme-modified cheese, 1: 800
Index generation cheese manufacture, 1: 537 hyperspectral imaging, 1: 128 strength see Gel firmness (curd strength) syneresis see Syneresis (curd) Curd-firming rate, seasonal variation, 3: 601f Curd firmness tester (CFT), 1: 588 Curd washing, yeast contamination, 1: 662 Curvacin A, 1: 426 Curvaticin FS47, 1: 422t Custards, 2: 906 Customs Co-operative Council (CCC) see World Customs Organization (WCO) Customs Co-operative Council Nomenclature (CCCN), 4: 331 Cut size cyclone efficiency, 4: 226 definition, 4: 226 Cutting tests cheese rheology, 1: 690 cheese rheology measurement, 1: 690 CuZn-SOD, 2: 328–329 Cyanide, for predator control, 2: 845 Cyanogenetic goitrogens, 2: 380 Cycled air admission, milking equipment cleaning, 3: 636 Cyclic voltammetry, 1: 193 Cyclochlorotine, 4: 795, 4: 795f -Cyclodextrin, cholesterol removal, 3: 736 cream, 3: 737, 3: 738t milk, 3: 736, 3: 737t Cyclones centrifugal force, 4: 226 design, 4: 226 efficiency, 4: 226 determination, 4: 226, 4: 227f operation theory, 4: 225–226, 4: 226f powder loss measurement, 4: 226–227 spray drying, powder separation, 4: 225 Cyclone separation, definition, 4: 175 Cyclone separators, 4: 181 centrifugal effect, 4: 181 dairy applications, 4: 181 design, 4: 181, 4: 182f separating efficiency, 4: 182 geometrical relationships, 4: 182, 4: 182f limit particle diameter, 4: 182 Cyclopiazonic acid (CPA), 1: 904t, 4: 777 Cynara cardunculus, 2: 290–291 Cynodon dactylon (Bermuda grass), 2: 578 Cynomolgus monkey milk -lactoglobulin, 3: 624 proteins, 3: 622t Cyprus, sheep total mixed ration, 2: 855 Cystathionine- -lyase, 3: 129 Lactobacillus, 3: 87–88 Cysteine, 3: 818 Cystic fibrosis, transgenic animal models, 2: 642 Cytochalasins, 4: 799 Cytokines lactoferrin effects, 3: 804–805 mammary gland defense, 3: 389, 3: 389t Cytolysin, 3: 156 Cytoplasm, milk lipid droplet formation, 3: 374 Cytotoxic T lymphocytes, 3: 390 Cytotoxin K (cytK), Bacillus cereus group, 4: 26 Czapek yeast extract agar (CYA), Penicillium camemberti growth, 4: 776 Czech republic, Simmental cattle, 1: 294
D Dactylis glomerata (cocksfoot, orchardgrass), 2: 576 Dadhi see Dahi Dadih, 2: 510 Dahi, 2: 507 mild, 2: 507 sour, 2: 507 starter cultures, 2: 509t
Dahlia ceramic membranes, 3: 868–869 Dairy bacteriology, history, 1: 26–33 Dairy Board Act, New Zealand, 4: 311 Dairy cattle research programs, mathematics in, 2: 429 Dairy chemistry, historical aspects, 1: 18–25 Dairy cow digestion mechanistic modeling, 2: 430 microbial groups, 2: 430–431 Dairy cow metabolism adipose tissue metabolism, 2: 433 mechanistic modeling, 2: 432 early failures, 2: 433 experimental research-modeling interplay, 2: 433–434 liver parameterization, 2: 433 mammary amino acid uptake, 2: 433, 2: 434f mammary gland elements, 2: 433 organ weight-energy expenditure relationship, 2: 432 Dairy cow models digestion, 2: 430f dynamic behavior, 2: 430 metabolism, 2: 430f Dairy cow nutrition models autobalancing rations, 2: 442 feed constraints, 2: 442 linear programming, 2: 442 nonlinear programming, 2: 443 nutritional constraints, 2: 442 calculation submodels, 2: 439 bacterial growth, 2: 440 carbohydrate, 2: 441 fat, 2: 441 feed ingredient energy value, 2: 441 fermentability (degradation), 2: 439 intestine, 2: 440 metabolic requirement, 2: 441 metabolizable (absorbed) protein value, 2: 441 protein, 2: 440 rumen, 2: 439 components, 2: 437 dry matter intake, 2: 439 input submodels, 2: 437 animal descriptors, 2: 437 environment, 2: 437 ration, 2: 437 optimization, 2: 442 ration formulation, 2: 442 see also individual models Dairy desserts, 2: 905–912 aerated (mousses), 2: 907, 2: 907f colors, 2: 908 commercial scene, 2: 905 fat, 2: 908 flavors, 2: 905, 2: 908 formulations, 2: 905 fortification, 2: 908 frozen see Frozen desserts gelling agents, 2: 908 global market, 2: 905 ingredients, 2: 905, 2: 908 manufacturing methods, 2: 911 milk-carrageenan interactions, 2: 910 new product launches, 2: 905, 2: 906f, 2: 906f powdered products, 2: 911 product types/forms, 2: 905 ready-to-eat see Ready-to-eat (RTE) dairy desserts recombined/reconstituted products, 3: 319 thickening agents, 2: 908 types, 2: 905 Dairy effluent treatment anaerobic processes, 4: 619 buffering, 4: 628 methane production, 4: 627 methanogenic bacteria, 4: 627–628 nonmethanogenic bacteria, 4: 627–628 temperature, 4: 628 thermophilic digestion, 4: 628 biological treatment processes, 4: 622, 4: 633
863
aerobic, 4: 622 clarification, 4: 628 nutrient removal, 4: 625 design, 4: 619–630 fat removal, 4: 621 grease removal, 4: 621 grit removal, 4: 621 hydraulic balancing, 4: 622 load balancing, 4: 622 nutrient balancing, 4: 622 nutrient deficiency, 4: 622 operation, 4: 619–630 pH control, 4: 622 preliminary treatment processes, 4: 620 pretreatment processes, 4: 620, 4: 634 sludge solid–liquid separation, 4: 628 dewatering, 4: 628 thickening, 4: 629t sludge stabilization, 4: 630 biological processes, 4: 630t chemical processes, 4: 630t sludge treatment, 4: 628 unit processes, 4: 620 Dairy enzymology, historical aspects, 1: 23 Dairy exit program, Australia, 4: 310 Dairy Export Incentive Program (DEIP), US, 4: 300 Dairy Farmers of Canada (DFC), 2: 105 Dairy farms/farming bull management see Bull(s) computers, 1: 9 design, warm climates see Farm design (warm climates) drylot systems see Drylot management systems health and product quality management, 2: 679–686 concepts, 2: 679, 2: 680t good farming practice (GFP), 2: 680 public/society considerations, 2: 685 record-keeping, 2: 685, 2: 832 standards, 2: 679, 2: 680t total quality management (TQM) integration, 2: 683 historical aspects, 1: 2–11 labor management see Labor management, dairy farms nutrient management constraints, 2: 462 odorous compounds, 4: 635 profitability, nonlactating cows, 3: 20 records see Management records systems, 1: 3 non-seasonal/pasture based see Non-seasonal/ pasture-based management seasonal/pasture based management see Seasonal/pasture based management Dairy fat spreads, 1: 522 Codex standard, 4: 328 definition, 1: 522 historical aspects, 1: 522–523 Dairy forage system model (DAFOSYM), 2: 445, 2: 445t Dairy goat/agroforestry management interaction systems, 2: 823 Dairy herd improvement (DHI) program, China, 2: 84 Dairy industry aims, 4: 242 consumer confidence, 4: 352 dairy firm competition, 4: 351 economics, 4: 631 efficiency, 1: 10, 1: 10t globalization, 4: 352–353 supermarket expansion, 4: 351 milk safety, 4: 353 negative environmental impact reduction, 4: 631–635 approaches to, 4: 632f farm level, 4: 631 manure, 4: 631 milking parlor wastewater, 4: 632
864 Index Dairy industry (continued ) post-Doha world, 4: 345–353 product development, 4: 352 trends, 4: 242 Dairy Industry Adjustment Act, Australia, 4: 310 Dairy industry adjustment package, Australia, 4: 310 Dairy Industry Association of Australia (ASDT), 2: 104 Dairy Industry Association of New Zealand (DIMINZ), 2: 104 Dairy Industry Graduate Training Programme (NZ), food technology, 2: 7 Dairy Industry Restructuring Act (DIRA), New Zealand, 4: 311 Dairy Industry Restructuring Bill, New Zealand, 4: 311 Dairy ingredients see Non-dairy foods (dairy ingredients) Dairy Lo, 1: 530 Dairy nitrogen planner (DNP), 2: 445f, 2: 445t, 2: 446 Dairy nutrition models forms, 2: 436 levels, 2: 436, 2: 437t production models, 2: 436 role, 2: 436 scientific models, 2: 436, 2: 437t assumptions, 2: 436 Dairy nutrition software, 2: 443, 2: 444t Dairy plant(s) automation see Plant automation clarification, 3: 647 construction materials, 4: 134–138 design see Plant design effluent see Dairy plant effluents electricity consumption, 4: 130 energy efficiency improvement, 4: 634 energy losses, 4: 634 energy use, 4: 634 environmental impact, 4: 633 fats, 4: 633 grease, 4: 633 oils, 4: 633 gas emissions, 4: 635 milk processing steps, 3: 647 plastic use, 4: 137 rubber use, 4: 137 separation process, 3: 647 stainless steel use, 4: 136 surface finishes, 4: 137 typical flow pattern, 3: 647 wastewater, 4: 131 water consumption, 4: 127 reduction, 4: 617–618 Dairy plant effluents, 4: 613–618, 4: 633 alkali surplus, 4: 615, 4: 616t characteristics, 4: 619, 4: 620t complexing agents, 4: 617 discharge standards, 4: 619, 4: 621t ecological evaluation, 4: 616 environmental evaluation, 4: 616 auxiliary chemicals, 4: 616 complications, 4: 616 product residues, 4: 616 nitrogen content, 4: 616 phosphorus content, 4: 616 pollutant quantities, 4: 615 auxiliary chemicals, 4: 615, 4: 616t high organic loads, 4: 615 product losses, 4: 615, 4: 615t pollution reduction steps, 4: 617 hygiene operations, 4: 617–618 sewage conditioning, 4: 617–618 water conditioning, 4: 617–618 processing wastewater, 4: 633 constituents, 4: 633 surfactants, 4: 617 treatment see Dairy effluent treatment
Dairy powders agglomeration, 4: 710 free fat oxidation, 4: 711 Dairy processes, historical aspects, 1: 12–17 Dairy processing plants see Dairy plant(s) Dairy production education, 2: 1–5 agribusiness, 2: 4 coaches, 2: 4 current programs, 2: 3 future programs, 2: 3 students, 2: 4 Dairy products anticariogenic properties, 3: 1035 Brucella survival, 4: 34, 4: 34t calcium bioavailability, 3: 1012 calcium content, 3: 1011, 3: 1011t calcium/protein ratio, 3: 1013 calcium/sodium ratio, 3: 1012, 3: 1012t cancer, experimental data, 3: 1017 cholesterol removal see Cholesterol removal citrate content, 3: 166 compositional analysis, 1: 76 conjugated linoleic acid content alteration, 3: 661 consumption, 1: 46 coronary heart disease risk, 3: 1033 demand pattern changes, 4: 349, 4: 350f evolutionary context, 3: 1010 France, 1: 46, 1: 46, 1: 46t Germany, 1: 46, 1: 46, 1: 46t Italy, 1: 46, 1: 46t Netherlands, 1: 46, 1: 46t Pacific Rim economies, 4: 349 prehistoric times, 3: 1010 Spain, 1: 46, 1: 46t stroke risk, 3: 1033 UK, 1: 46, 1: 46, 1: 46t US, 1: 46t diversity, 3: 465t historical aspects, 1: 12–17 imitation see Imitation dairy products labeling see Labeling, dairy products lactose content, 3: 1011t, 3: 1011–1012 lipolytic defects, 3: 723 foaming difficulties, 3: 724 off-flavors, 3: 723–724 mastitis effects, 3: 904, 3: 904t nisin applications, 1: 424 nitrogen determination, 1: 78 nutrient intake, contributions to, 3: 1003–1008 osteoporosis risk factor, 3: 1013 packaging see Packaging periodontal disease prevention, 3: 1039 potassium content, 3: 1012t, 3: 1013 protein determination, 1: 78, 1: 82t sodium content, 3: 1012, 3: 1012t Staphylococcus aureus incidence, 4: 114 trace elements content, 3: 933, 3: 934t, 3: 935t, 3: 935t, 3: 935t nutritional significance, 3: 936 trade in, 4: 343 see also Harmonized System (HS); World Trade Organization (WTO) world market share, 4: 343, 4: 344t yeasts in, 4: 744–753, 4: 746t see also specific products Dairy regional assistance program, Australia, 4: 310 Dairy science historical aspects, 1,1, 3: 462 molecular microbiology, future perspectives, 1: 637 Dairy Science and Technology, 2: 103 Dairy science societies/associations, 2: 101–107 Argentina, 2: 104 Brazil, 2: 105 Canada, 2: 105 Italy, 2: 105 Japan, 2: 104 South America, 2: 104 Spain, 2: 105
Switzerland, 2: 103 Uruguay, 2: 105 see also specific societies Dairy Shorthorn cattle see Milking Shorthorn cattle Dairy spreads see Spreads Dairy structural adjustment program, Australia, 4: 310 Dairy technology, historical aspects, 1,1, 3: 462 Dairy technology education, 2: 6–12 basic science courses, 2: 6 current trends, 2: 6 curriculum development, 2: 7 degree level, 2: 6 animal science programs, 2: 6–7 company level, 2: 7 Dairy Industry Graduate Training Programme (NZ), 2: 7 generic food sciences, 2: 6–7 discipline-driven academic approach, 2: 9, 2: 10t common curriculum, 2: 10 degrees, 2: 10 non-dairy foods, 2: 10 postgraduate education/research, 2: 11 short courses, 2: 11 future work, 2: 11 industry-driven competency approach, 2: 8, 2: 8t Company Competencies (South Africa), 2: 8 definition, 2: 8 Europel (European Dairy Transport), 2: 9 IDF global competencies, 2: 9 implementation, 2: 9 National Dairy Industry Training Standards (Australia), 2: 8 National Vocational Qualifications (NVQs), 2: 8, 2: 9 workplace, 2: 9 International Dairy Federation (IDF), 2: 6 operator training, 2: 7 specialist courses, 2: 6 Dal´en milking machine, 3: 941–942, 3: 943f Dam energy nutrition, 4: 417 inadequate protein, 4: 417 Damani goats, 1: 311t, 1: 320 milk yields, 1: 312t Damascus goats, 1: 311t, 1: 317, 1: 317f milk yields, 1: 312t Dambo cheese, 1: 788 Damietta cattle, 1: 298 Damrow double-O cheese vat, 1: 608, 1: 609f Danablu cheese, 1: 771t Danedar khoa, 1: 881 Danish Red cattle, 1: 286t Danmarks Mejeritekneiste Selsab (Danish Society of Dairy Technology), 2: 103 DAP (degree of antioxidant protection), goats, 2: 62–63, 2: 63f D’Arcy’s law, 3: 870 Darcy–Weisbach equation, 4: 140–141 Data integrity, 1: 87 Data matrices, 1: 98f Data mining, 3: 347 mammary gland development, 3: 347–348 Data transformation, 1: 99 Date marking, 3: 5 Datongy yak, 1: 345 Daughter–dam comparison, genetic evaluation, 2: 651 DC-SIGN, human milk oligosaccharides, 3: 257 DDHE (scraped-surface heat exchanger), khoa manufacture, 1: 881 DDS module, 3: 868 DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) contaminant, 1: 889 New Zealand, 1: 889 Deacidification acid-curd cheeses, 1: 761, 1: 761f Geotrichum candidum, 4: 768 semihard cheeses, 1: 761, 1: 761f semisoft cheeses, 1: 761, 1: 761f
Index smear-ripened cheeses, 1: 395, 1: 761 soft cheeses, 1: 761, 1: 761f Deamidation, 2: 748 Debaryomyces, 1: 570 Debaryomyces hansenii, 4: 748 blue mold cheeses, 1: 768–769 brine, 4: 752 cheese aroma, 4: 750 smear-ripened cheeses, 1: 754, 1: 755, 1: 756 surface mold-ripened cheeses, 1: 775, 4: 751–752 Debilitation, displaced abomasum, 2: 213–214 Decanter centrifuges applications, 4: 180 bowl speed, 4: 181 casein curd dewatering, 3: 857 casein curd dewheying, 4: 180 cheese fine concentration, 4: 181 effluent management, 4: 181 lactose separation, 4: 181 operating variables, 4: 181 Decanters dairy applications, 4: 173 design features, 4: 170, 4: 170f discharge, 4: 170, 4: 170f, 4: 170f drive, 4: 170 fixed differential speed, 4: 170, 4: 170f variable differential speed, 4: 170, 4: 171f open discharge, 4: 170, 4: 170f phases, 4: 170 Decision making, 1: 483 Decree of the President of the Republic No. 1099, Italy, 1: 849 Deep brining system, 1: 613–614, 1: 615f Deep litter systems, 2: 24 Deer lungworm carriers, 2: 272 non-seasonal breeding, 4: 445–446 seasonal breeding, 4: 445 estrous cycles, 4: 445–446, 4: 446f photoperiod cues, 4: 445–446 Defenses see Host defenses Deferoxamine, 3: 431 Deferred antagonism assay, bacteriocins, 1: 421, 1: 421f Deficiency of uridine monophosphate synthase (DUMPS), 2: 677 Define, measure, analyze design, and validate or verify (DMADV), 4: 276 improve, and control (DMAIC), 4: 276 Defined starter cultures, 1: 554, 1: 554t smear-ripened cheese aroma, 1: 764 smear-ripened cheeses, 1: 759 Deformation, 1: 265t rheology, 1: 685–686 Deformation uniaxial compression, 1: 691t Degree of antioxidant protection (DAP), goat production systems, 2: 62–63, 2: 63f Degree of polymerization (DP), carbohydrates, 4: 355 Degrees, 2: 1 food technology education, 2: 10 Dehorning (disbudding), goats, 2: 832 Dehydrated cheese ingredients (DCIs), 1: 822 classification, 1: 825–826 formulated food manufacture, 1: 822–825 natural cheese vs., 1: 822–825 shelf life, 1: 822–825 uses, 1: 822–825, 1: 824f Dehydrated dairy products non-dairy food ingredients casein powder products, 2: 548 off-flavors causes, 2: 546 storage and shelf life skim milk powder, 3: 233, 3: 233 whole milk powder, 3: 232–233 Dehydration hyperspectral imaging, 1: 129 microstructure, 1: 231 milk fat globule membrane, 3: 679
L-Dehydroascorbic acid (DHA), 4: 667–668, 4: 668f transport, 4: 669 Delayed allergic reaction, 3: 1041 Delayed-type hypersensitivity reaction, TB skin test, 2: 196 Delayed-type hypersensitivity (skin) test, Johne’s disease, 2: 177–178 DELIVER, 2: 269 9 D -desaturase (stearoyl-CoA desaturase), 3: 354, 3: 661 Demineralization, whey see Whey Demodectic mange clinical signs, 2: 251 epidemiology, 2: 250 treatment, 2: 252 Demodex bovis, 2: 250 Demodex capre, 2: 250 Demodex ovis, 2: 250 Denaturing gradient gel electrophoresis (DGGE) cheese microbiological analysis, 1: 630–631 NSLAB genomics, 1: 642 PCR, 1: 222 Denaturing high-performance liquid chromatography (DHPLC), cheese microbial fingerprinting, 1: 633, 1: 634f Dendrograms, 1: 100f, 1: 102 Denmark cheese definition, 1: 848, 1: 849 cheese legislation, 1: 848 compositional requirements, 1: 853t fat-in-dry matter content, 1: 849 Density, 1: 250 Density sensors, 4: 236 Dental caries, 3: 1034 fluoride, 3: 1035 pathogenesis, 3: 1034, 3: 1035f dietary sugars, 3: 1035 host factors, 3: 1034–1035 microorganisms, 3: 1034–1035 time effects, 3: 1034–1035 prevalence, 3: 1034 prevention, 3: 1034–1040 dairy derivatives, 3: 1036 dairy peptides, 3: 1036 dairy products, 3: 1035 fortified products, 3: 1037 whole products, 3: 1035 Deoxynivalenol, 4: 798, 4: 799f Deoxyosones, 3: 1073, 3: 1073t Deoxyribonucleic acid (DNA) see DNA Department of the Environment, Food and Rural Affairs (DEFRA) cattle welfare code of recommendations, 4: 728 Dephosphorylation casein(s), 2: 315–316, 2: 318, 3: 912 heat stability, milk, 2: 747–748 Depletion flocculation, milk protein emulsions, 3: 891 Dera Din Panah goats, 1: 311t, 1: 320, 1: 320f milk yields, 1: 312t Derivatization gas chromatography, 1: 175 reversed-phase HPLC, 1: 172, 1: 173f Dermacoccus, 1: 627 smear-ripened cheeses, 1: 396–397 Dermatitis, 2: 250–252 Dermatophytosis see Ringworm Dermatosis, 2: 250–252 Descriptive sensory evaluation see Sensory evaluation Dessert mixes, pasteurization, 4: 198 Detector, light scattering techniques, 1: 133 Detector bulls, 4: 477 Detergents bloat treatment/prevention, 2: 209 cleaning in place, 4: 284 components, 4: 614t wastewater, 4: 613 Developmental abnormalities, nuclear transfer embryos, 2: 614
865
Developmental toxicity tests, additives, 1: 57 Deworming, goats, 2: 840 Dew point temperature, 4: 724, 4: 724f Dexter cattle, 1: 286t Dextransucrase, 3: 140 Dextrins, 1: 531 Dextrose, pregnancy toxemia, 2: 248 Dextrose equivalence (DE), 1: 531 DGGE see Denaturing gradient gel electrophoresis (DGGE) Dhap khoa, 1: 881 Diabetes mellitus human lactation effects, 3: 589 milk/dairy product consumption, 3: 1046–1050 type 1 see Type 1 diabetes type 2 see Type 2 diabetes Diacetyl, 3: 169 antimicrobial properties, 1: 420 buttermilk production, 3: 172 butter production, 3: 172 cheese flavor, 1: 642 Dutch-type cheese flavor, 1: 726 flavor, 3: 169 formation, citrate metabolism, 3: 86, 3: 169 overproducing cultures, 3: 71 Diacetyl synthase, 3: 169 Diacylglycerols butter, 1: 506 as emulsifiers, 1: 65 milk, 3: 651 physical properties, 3: 651 Diafiltration, milk standardization, 1: 548 Diagnostic tap, displaced abomasum, 2: 215 Dialkyl dihexadecylmalonate (DDM), 1: 530 Diamines, 1: 451 Diaphragm pumps, 4: 148, 4: 148f selection criteria, 4: 151t Diaphragm-type regulators, 3: 947 Diarrhea calves, 4: 418 goat kids, 2: 829–830 treatment, Enterococcus faecalis strain SF68, 3: 154 Dichloran 18% glycerol (DG18) agar, mold enumeration, 4: 783 Dichloran rose bengal chloramphenicol (DRBC) agar, mold enumeration, 4: 783 Dicrocoelium dendriticum, 2: 264 Dictyocaulosis see Lungworm disease Die Schweizer Kaesespezialisten, 2: 103 Diestrus behavioral changes, 4: 428 definition, 4: 411 Diet acidogenic see Acidogenic diets bone health, 3: 1060 colorectal cancer, 3: 1016 ketosis, 2: 231 milk protein synthesis, 3: 361 Dietary acidification, response monitoring, 2: 360 Dietary cation–anion difference (DCAD) calcium homeostasis, 2: 373 calculation, 2: 356, 2: 359t, 2: 373 dairy feed ingredients, 2: 358t pasture diets, 2: 357 reduction, 2: 357, 2: 357f chlorine, 2: 358 feed ingredient selection, 2: 358 high-fiber concentrate feed, 2: 358–359 milk fever risk reduction, 2: 356 potassium reduction, 2: 358 transition cows, 2: 451, 2: 452t pasture-based systems, 2: 467 typical diet, 2: 357 urine pH, 2: 451 Dietary fiber definition, 4: 355 donkeys (Equus asinus), 1: 370 Dietary Guidelines for Americans 2005, 3: 1003–1004
866 Index Dietary supplements see Feed supplements Dietetic foods, 2: 131 ‘Diet-heart hypothesis’, 3: 713, 3: 734, 3: 1031–1032 Diethylaminoethyl cellulose (DEAE-cellulose) chromatography caseins, 3: 762 whey proteins, 3: 762 Diethyl dicarbonate (DEDC), 4: 790 Diethyl pyrocarbonate, 4: 790 Differential interference contrast light microscopy, 1: 226, 1: 227f Differential scanning calorimetry (DSC), 1: 229, 1: 256–263 butter consistency, 1: 512 butterfat melting behavior, 1: 508f butter melting behavior, 1: 509 crystallization, 1: 258, 1: 259f fat, 1: 259, 1: 260f heat flux, 1: 256 lactose glass transition, 1: 256, 1: 257f, 1: 258f, 1: 258t lactose melting, 1: 258, 1: 259f milk fat melting thermograms, 3: 544, 3: 549f milk powder glass transition temperature, 2: 123 minerals, 1: 261–262 phase transitions, 1: 256, 1: 257f, 1: 257f, 1: 258f power compensation, 1: 256 protein denaturation, 1: 260 dry milk powder storage, 1: 261, 1: 262f heat processing, 1: 261, 1: 261f hydrolysis, 1: 262, 1: 262f whey proteins, 1: 261 Diffraction, ultrasound, 1: 208 Diffusely adherent E. coli (DAEC), 4: 61 Diffuse reflection, 3: 473 Diffusing wave spectroscopy (DWS), 1: 137 aggregating systems, 1: 138 back-scattering geometry, 1: 137–138 correlation function, 1: 137–138 curd strength measurement, 1: 589 gelling systems, 1: 138 microrheology, 1: 139 limitations, 1: 139 optical fiber use, 1: 138 particle–particle interactions, 1: 138 relaxation time, 1: 138, 1: 138 skim milk acid-induced gelation, 1: 139 Diffusion, NMR, 1: 155 Difiltration, whey protein concentrates, 3: 866 Difucosyllactose, monotreme milk, 3: 556 Digestibility, 3: 399 Digestible energy (DE), feed intake-related, 2: 338 enzymatic digestion (in vitro) estimation, 2: 406 high intake/concentrate diet discount factors, 2: 406 in vivo methods, maintenance intake, 2: 404 Digital dermatitis see Papillomatous digital dermatitis (PDD) Digital-to-analog signal conversion, 4: 238 control action, 4: 240, 4: 235f data acquisition, 4: 239 Digital warts see Papillomatous digital dermatitis (PDD) Digitaria eriantha (pangola grass), 2: 578 Diglycerides as emulsifier, 1: 66t primate milk, 3: 616 1,25-Dihydroxycalciferol, 4: 647 1,25-Dihydroxyvitamin D (1,25(OH)2D) see Calcitriol Dilatation tubes, compressed air piping systems, 4: 608 DIMINZ (Dairy Industry Association of New Zealand), 2: 104 Dioxins, 1: 898 analysis, 1: 899 health impact, 1: 898 occurrence, 1: 898 provisional tolerable monthly intake (PTMI), 1: 899 sources, 1: 898
Dipeptides, transport, 3: 994 Dipeptidyl carboxypeptidase, 3: 879–880, 3: 1064 Diphenylamine (DPA), 1: 889 Dipping sheep, parasitic condition control, 2: 858 teat see Teat dipping Direct acidification cottage cheese manufacture, 1: 700–701 cultured cream products, 1: 924 Direct additives, 1: 51 Direct counting, Clostridium, 4: 51–52 Direct detection, biosensor transducers, 1: 236 Direct drilling, 2: 586 Direct drive separators, 4: 169, 4: 169f Direct enzyme-linked immunosorbent assay, 1: 178, 1: 178f Direct epifluorescent filter technique (DEFT), milk quality, 3: 899 Directly acidified cheeses, pH, 1: 837 Direct microscopic clump counts (DMCCs), 1: 219 Direct microscopic counts (DMCs), 1: 219 raw milk, 3: 642 somatic cells, 3: 896 Direct microscopic somatic cell count (DMSCC), 1: 219 raw milk, 3: 644–645 subclinical mastitis, 1: 219 Direct steam injection (DSI), spray drying, 4: 223 Direct vat inoculation (DVI) Cheddar cheese starter cultures, 1: 707 starter cultures, 1: 558 Direct vat set (DVS) cultures Cheddar cheese starter cultures, 1: 707 starter cultures, 1: 442 Disaccharides classification, 4: 356t as prebiotics, 4: 357, 4: 357f terminology, 4: 355 see also individual sugars Disbudding (dehorning), goat kids, 2: 832 ‘Discomfort index’ see Temperature–humidity index (THI) Discriminant analysis (DA), 1: 101, 1: 103 Discrimination testing see Sensory evaluation Disease(s) African dairy cow management, 2: 81 buffalo, 1: 341 bulls, 1: 479 eradication and control programs, 2: 799, 2: 799t historical aspects, 1: 8 reproductive stress, 4: 579, 4: 579f risk management/prevention, 2: 685 health promotion, 2: 797 nomadic farming systems, 2: 880 routine cleanliness, 2: 797 selection for resistance, 2: 659 transmission, 2: 825, 3: 440, 3: 441f see also individual diseases ‘Diseases of affluence’, 3: 711 Disialyl lacto-N-tetraose (DSLNT), 3: 250 Disinfectants/sanitizers, 1: 895t biofilms, 1: 448 Brucella, 4: 34 cleaning in place, 4: 284 components, 4: 614t contagious mastitis prevention, 3: 413 contamination, 1: 895 analysis, 1: 896 health impact, 1: 895 occurrence, 1: 895 sources, 1: 895 dairy plant effluents, 4: 617 organoleptic thresholds, 1: 896t oxidizing, 4: 284 pollution, 4: 613 resistance, bacteriophage characterization, 1: 435 spoilage mold control, 4: 781 teats see Teat disinfectants/disinfection
Disk bowl centrifuges applications, 4: 176 bacterial clarification, milk, 4: 178 shelf life effects, 4: 178 standardized cheese milk, 4: 178 capacity, 4: 176 cream processing, 4: 179 anhydrous milk manufacture, 4: 179 butter making, 4: 179 buttermilk separation, 4: 179 fresh cheese manufacture, 4: 179 milk and cream standardization, 4: 177 direct standardization, 4: 177–178 high-fat standardized milk, 4: 178 milk clarification, 4: 178 partial homogenization, milk, 4: 177 whey processing, 4: 179 whole milk separation, 4: 176 cold, 4: 176 deaerated milk, 4: 177 milk freshness, 4: 177 self-desludging separator, 4: 177 skimming efficiency, 4: 176 warm, 4: 176 Disodium phosphate (DSP), pasteurized processed cheese products, 1: 810 Dispersability, milk powder, 2: 121 Displaced abomasum, 2: 212–216 biochemical status, 2: 213–214 causes, 2: 212 chronic, 2: 214 clinical signs, 2: 213 diagnosis, 2: 213 differential diagnosis, 2: 215 heredity, 2: 212 infertility risk factor, 4: 579 ketosis, 2: 213–214 laboratory tests, 2: 215 left see Left displaced abomasum (LDA) milk production, 2: 213–214 nutrition, 2: 216 occurrence, 2: 212 prevention, 2: 216 right see Right displaced abomasum (RDA) significance, 2: 212 treatment, 2: 215 nonsurgical, 2: 215–216 surgical, 2: 216 Dispute Settlement Body (DSB), WTO, 4: 339 appellate body, 4: 339 arbitration, 4: 339 process, 4: 339, 4: 340f Disruptive technologies, biofilm control, 1: 450 Dissolved air flotation (DAF) fat/grease removal, 4: 621, 4: 622f sludge thickening, 4: 629t unit design parameters, 4: 621 Distillation, cholesterol removal, 1: 503 Distillers’ grains, 2: 345–346 Distribution evaluation, 1: 88 Divalent metal transporter-1 (DMT-1), 3: 998–999 Divert (changeover) valve, 4: 155, 4: 155f DLS see Dynamic light scattering (DLS) DMADV (define, measure, analyze, design, and validate or verify), 4: 276 DMAIC (define, measure, analyze, improve, and control), 4: 276 DMI see Dry matter intake (DMI) DNA melting domains, 1: 633 sequencing, twenty-first century, 3: 966 structure, 3: 965, 3: 966f DNA-based assays, 1: 221–225 see also specific assays DNA binding proteins (trans- factors), 3: 1056 DNA–DNA hybridization bacteriophage classification, 1: 430 DNA microarrays, 1: 223–224
Index DNA fingerprinting, microbial see Microbial DNA fingerprinting, cheese DNA microarrays, 1: 223 DNA–DNA hybridization, 1: 223–224 DNA–RNA hybridization, 1: 223–224 DNA probes, Bifidobacterium taxonomy, 1: 382 DNA–RNA hybridization, DNA microarrays, 1: 223–224 Docosahexenoic acid (DHA), 3: 731 first-age infant formulae, 2: 141 Dogs flock predation guards, 2: 843 hunting, 2: 845 milk oligosaccharides, 3: 271t Doha Ministerial Declaration, 4: 346 Doha Round, 4: 345 agenda, 4: 346 Blue Box supports, 4: 347 dairy product tariffs, 4: 347, 4: 348t dairy sector implications, 4: 347 deal impact, 4: 345 developed country Members, tariff reductions, 4: 347 developing country Members, tariff reductions, 4: 347, 4: 347 domestic support, 4: 352 export subsidy elimination, 4: 347 green box support measures, 4: 348 least developed countries, tariff reductions, 4: 347 potential time limit, 4: 347 tariff reductions, 4: 347 Domestic buffalo see Buffalo Domestic donkey (Equus asinus) see Donkey(s) Domestic market support (DMS), scheme, Australia, 4: 309–310 Domiati cheese, 1: 792 headspace analysis, 1: 794 production statistics, 1: 790, 1: 790 texture, 1: 794 Dominant follicles late prepubertal period, 4: 424 ovulation failure, 4: 475 Donkey(s), 1: 365–373, 3: 518 feed and nutrition, 1: 370 dietary fiber, 1: 370 milk effects, 1: 370, 1: 371t health issues, 1: 371 husbandry, 1: 369 hygiene, 1: 369 milk see Donkey milk milking facilities, 1: 371f milking strategies, 1: 365 manual, 1: 365 milking machines, 1: 365, 1: 367f milk yield, 1: 365, 1: 366, 1: 367f reproductive behavior, 1: 369–370 estrous cycle, 1: 370 gestational length, 1: 370 water requirements, 3: 518 Donkey milk, 2: 516 amino acids, 1: 368 aromatic compounds, 1: 366–368 ash content, 1: 369 bioactive peptides, 1: 369 casein micelle stability, 3: 523 caseins, 3: 521t characteristics, 1: 366, 1: 368f, 1: 369t aromatics, 1: 366–368 composition, 1: 368f, 3: 459 energy content, 1: 368 fatty acid profile, 3: 524, 3: 524t, 3: 525t human nutrition, 3: 528 -lactalbumin, 3: 519–522 -lactoglobulin, 1: 369, 3: 519 milk fat globules, 1: 366, 1: 368f organoleptic characteristics, 1: 372 proteins, 1: 368, 1: 368f somatic cell count, 1: 369
urea, 1: 368 utilization, 1: 372 elderly people, 1: 372 fermented milk drinks, 1: 372 hypoallergenicity, 1: 372 organoleptic characteristics, 1: 372 whey proteins, 3: 521t Donkey milk lysozyme (DML), 2: 331 Don Olivo, 1: 786–787 Dopamine- -monoxygenase, 4: 671 Doppelrahmfrischk¨ase, 1: 701 Doppler shift meters, 1: 212, 1: 212f Doppler ultrasound, pregnancy detection, 4: 490 Double-chambered teat-cup, 3: 944, 3: 944f, 3: 944f Double-cream fresh cheese production, 4: 172, 4: 173f Double dilution, polarimetry, 1: 253–254 Double-muscling breeds, 2: 642 Double-seat valve, 4: 156, 4: 156f ‘Dough-drying system’, 1: 14 Doxycycline, 4: 36 Drag force, 4: 175 Drainage, warm climate milking sheds, 2: 25 Dried cheese manufacture, 1: 826 Dried dairy products contaminants trihaloanisoles, 2: 548 2,4,5-trimethyloxazole, 2: 547, 2: 547f, 2: 547f E. coli control measures, 4: 65 moisture content, storage stability, 3: 1071–1072 protein glycation, 3: 1071f, 3: 1071–1072 Salmonella contamination, 4: 94, 4: 95 Staphylococcus aureus incidence, 4: 114 Dried distillers’ grains and solubles (DDGS), 2: 345–346 Dried milk cheesemaking property improvement, 1: 623 Enterobacteriaceae, 4: 68 control, 4: 70 permeate use, 4: 548 yak milk, 1: 350 see also Milk powder Drinking water dairy industry generation, 4: 582 municipal water systems, 4: 583 filters, 4: 583 natural sources, 4: 583 dissolved solid concentration reduction, 4: 584 hardness removal, 4: 584 microbial contamination removal, 4: 584 organic compound removal, 4: 583 suspended solid removal, 4: 583 turbidity removal, 4: 583 unsuitable constituents, 4: 583t Drinking water systems (DWSs) biofilms, 4: 584 construction materials, 4: 586–587 corrosion, 4: 586–587 design guidelines, 4: 586 backflow prevention, 4: 586–587 dead leg avoidance, 4: 586–587 disinfection, 4: 584 methods, 4: 585t nonoxidizing biocides, 4: 586 oxidizing agents, 4: 585, 4: 585t ultraviolet irradiation, 4: 585t, 4: 586 documentation, 4: 586–587 operation guidelines, 4: 586 sanitization, 4: 584, 4: 586t Dromedary (Camelus dromedarius), 1: 351, 3: 512 high-producing dairy types, 1: 352, 1: 352f medium-producing dairy types, 1: 352, 1: 352f see also Camel(s) Droplet size, emulsions NMR, 1: 163 pulsed field gradient NMR, 1: 163–164 Drug residues, immunochemical detection, 1: 180
867
Dry ashing, 1: 77 milk salt analysis, 3: 913–914 Dry beriberi, 4: 702–703 Dry cow see Dry period ‘Dry cow treatment’, 2: 450, 3: 420 Dry dairy ingredients, flavors and off-flavors, 2: 546 spray-dried 2,4,5-trimethyloxazole, 2: 547 ‘Dry-ewe therapy’, 2: 863 Dry fractionation, anhydrous milk fat, 1: 520 Drying definition, 4: 208 glass transition, 4: 213 processes, 4: 208 stickiness, 4: 213, 4: 214f terms, 4: 211, 4: 212f UF permeates, 4: 732–733 whey, 4: 732 see also Spray drying Drying chamber, 4: 216 agglomerated product production, 4: 217 circular fluid bed (multistage drying chamber), 4: 217, 4: 220f designs, 4: 216, 4: 218f insulation, 4: 216, 4: 219f integrated static fluid bed, 4: 217 configurations, 4: 217 ring-formed fluid bed (compact chamber), 4: 217, 4: 220f safety equipment, 4: 216 Drylot dairy cow breeds, management see Drylot management systems Drylot management systems, 2: 52–58 compost barn, 2: 57 mastitis, 2: 57 early lactation cows, 2: 54t, 2: 56 facility management, 2: 57 freestall (cubicle) housing, 2: 57 feed management, 2: 52 body condition score, 2: 53 body weight loss, 2: 53 dry matter intake curve, 2: 52, 2: 53t gain curve, 2: 53 milk fat curve, 2: 52, 2: 53t milk production curve, 2: 52 milk protein curve, 2: 52, 2: 53t forage quality, 2: 459 gain curve, 2: 53 herd size, 2: 52, 2: 53t historical aspects, 1: 4 lactation rations, 2: 458–463 carbohydrates, 2: 461 computer models, 2: 462–463 environmental considerations, 2: 462 feedbunk management, 2: 462 mixing, 2: 462 protein, 2: 461 late lactation cows, 2: 54t, 2: 56 midlactation cows, 2: 56 milking management, 2: 57 phase feeding, 2: 53, 2: 54t close-up dry cows, 2: 55 early lactation cows, 2: 54t, 2: 56 far-off dry cows, 2: 54, 2: 54t fresh cows, 2: 55 late lactation cows, 2: 54t, 2: 56 midlactation cows, 2: 54t, 2: 56 water beds, 2: 57 ventilation, 2: 58 Dry manure, off-farm export, 3: 406 Dry matter (DM), animal feed digestibility estimation methods, 2: 405t, 2: 406 grasses and legumes, 2: 579f, 2: 580, 2: 581 pasture dry matter-on-offer, 2: 595, 2: 599 Dry-matter efficiency (DME) definition, 2: 458 milk production rates, 2: 458, 2: 459t valves, 2: 458
868 Index Dry matter intake (DMI), 2: 338, 2: 419, 2: 425, 2: 459 artificial insemination center nutrition, 1: 468 cold stress milking cows, 4: 553 replacement heifers, 4: 552, 4: 553t drylot management systems, 2: 52, 2: 53t forage, 2: 460 guidelines, 2: 463 heat stress, 4: 562 prepartum period, 4: 562 heifers, 4: 393 hot weather, 4: 562 ketosis, 2: 231–232, 2: 232f lactating cows, 4: 475–476 early, 4: 480 milk production and, 2: 459 prediction, 2: 459 transition cows, 2: 451, 2: 451f Dry period body condition, 2: 449, 4: 436 cold stress, 4: 551t, 4: 552 ‘cold turkey’ method, 2: 448 definition, 3: 343 dynamics, 4: 514, 4: 515f feeding see Dry period rations immunoglobulin transfer to milk, 3: 811 length milk yield and, 2: 448, 2: 449f replacement calf health, 4: 417 mastitis, 2: 450 Gram-negative organisms, 3: 416 prior milk production decrease, 2: 448 weight loss, 4: 516 Dry period rations, 2: 448–452 close-up period cows see Transition cows crude protein requirements, 2: 410–411, 2: 411f far-off dry cows, 2: 448 high-forage diets, 2: 449–450 management goals, 2: 448–449 nutrition requirements, 2: 449t sample diets, 2: 450t historical aspects, 1: 5 low-calcium diet, 2: 450 potassium, 2: 450 Dry salting, 1: 597–598, 1: 598, 1: 602 acid-curd cheeses, 1: 754 effects, starter cultures, 1: 564 lactate levels, 1: 605 moisture content, 1: 605 molded pressed curd, 1: 602 salt distribution, 1: 604 salt uptake, 1: 602 smear-ripened cheeses, 1: 754 Dry whey, 3: 873 DSC see Differential scanning calorimetry (DSC) Duarte galactosemia variant, 3: 1054 Dulce de leche, 1: 874–880, 2: 907 available lysine content, 3: 233 consumption, 1: 874, 1: 874 defects, 1: 878 cluster formation, 1: 879 color defects, 1: 879 flavor defects, 1: 879 lactose crystallization, 1: 878 lactose crystallization rate and isomers, 1: 879 mold, 1: 879 rough texture, 1: 879 sandy texture, 1: 879 syneresis, 1: 879 definition, 1: 874 future trends, 1: 880 production, 1: 874, 1: 875 continuous processes, 1: 877, 1: 878f nonenzymatic browning reactions, 1: 878 open kettle process, 1: 876, 1: 877f semicontinuous process, 1: 877 starting mixture, 1: 876 traditional process, 1: 876, 1: 877f
raw materials/additives, 1: 875 aroma enhancers, 1: 875 milk, 1: 875 milk fat, 1: 875 neutralizing products, 1: 875 nutritive sweeteners, 1: 875 preservatives, 1: 875 regulations, 1: 874 rheology, 4: 526 trade statistics, 1: 874, 1: 875t types, 1: 874, 1: 875t Dumas method Kjeldahl method vs., 1: 78–79 protein determination, 1: 78, 3: 743 ‘Dumping stations’, 1: 6 Duodenojejunal flexure, 3: 989, 3: 990f Duodenum fatty acids, 3: 992 lactating ruminants, 3: 989 lipid digestion, humans, 3: 711 protein digestion, 3: 993 Duo-trio discrimination testing, 1: 280–281 Duplex stainless steel, 4: 135 Duplicate diet studies, 1: 58 Dutch Belted cattle, 1: 286t Dutch-type cheeses, 1: 721–727 citrate metabolism, 3: 86 closed rind, 1: 723 composition, 1: 723 defects, 1: 726 bitterness, 1: 727 butyric acid fermentation, 1: 726 Clostridium tyrobutyricum, 1: 726 Lactobacillus brevis, 1: 726 Lactobacillus casei, 1: 726 Lactobacillus plantarum, 1: 726 mesophilic lactobacilli, 1: 726 mold growth, 1: 727 slimy rind, 1: 727 Streptococcus thermophilus, 1: 726–727 texture, 1: 727 flavor, 1: 726 diacetyl, 1: 726 free fatty acids, 1: 726 lactic acid, 1: 726 volatile compounds, 1: 726 lactate metabolism, 1: 667, 1: 668 lactose fermentation, 1: 723 production statistics, 1: 721 ripening, 1: 721, 1: 723, 1: 724 amino acid-converting enzymes (AACEs), 1: 724 amino acid degradation, 1: 724 lactate metabolism, 1: 667, 1: 668 lipolysis, 1: 725 nitrogen-containing fractions, 1: 724f, 1: 724–725 pH, 1: 723, 1: 724f proteolysis, 1: 724 starters, 1: 723 technology, 1: 721, 1: 722f closed rind, 1: 723 coagulation, 1: 721–722 scalding, 1: 722 thermized, 1: 721 washing, 1: 722 whey, 1: 722–723 texture, 1: 725, 1: 725f eye formation, 1: 725, 1: 725, 1: 725f pH, 1: 725 tyrosine crystals, 1: 725 washing, 1: 722 see also specific cheeses DVI see Direct vat inoculation (DVI) DVS see Direct vat set (DVS) cultures Dye-binding methods, 1: 79, 3: 744 Dye reduction methods, 3: 899 Dynamic (nondisplacement) compressors, 4: 603 Dynamic light scattering (DLS), 1: 135, 1: 229 applications, 1: 136
correlation functions, 1: 135, 1: 135f, 1: 136 angular dependence, 1: 136 cumulants analysis, 1: 136–137 correlation procedure, 1: 135, 1: 135f curd strength measurement, 1: 589 dilute suspension, 1: 136 intensity correlation function, 1: 135 logarithm plot, 1: 136 particle size, 1: 136–137 rotational movements, 1: 136 spherical particles, 1: 136 theoretical background, 1: 135, 1: 135f viscosity and, 1: 136 Dynamic low-amplitude strain rheometry, 1: 691t Dynamic low-amplitude stress rheometry, 1: 691t Dynamic methods cheese flavor assessment, 1: 679 rheology instrumentation see Rheology instrumentation Dynamic strain-controlled rheometers, 1: 276f, 1: 276–277 Dysentery colonic ulcers, 4: 99 complications, 4: 100 outbreaks, 4: 100 dairy product-related, 4: 100–101 seasonal trends, 4: 100 severity, 4: 100 symptoms, 4: 100 see also Shigella Dystocia, 1: 464, 4: 511 definition, 4: 511 first-calf heifers, 4: 511 hormonal imbalances, 4: 512 horses, 4: 511 incidence reduction, 4: 511–512 heifer breeding weights, 4: 511t, 4: 511–512 milk fever, 4: 511 sire selection, 4: 511–512 yaks, 4: 511
E E. coli see Escherichia coli Early-lactation protein (ELP) gene expression, marsupials, 3: 556–558 Ear tags, 2: 649, 2: 832, 2: 832f ‘Earth-leakage’ circuit breakers, 4: 611 East Anatolian Black cattle, 1: 298 East Anatolian Red cattle, 1: 298 East Friesian sheep, 1: 326, 1: 326f, 2: 72 distribution, 1: 326 milk production traits, 1: 326, 1: 327t origin, 1: 326 physical characteristics, 1: 326 reproductive characteristics, 1: 326 Eccentric cleavage theory, vitamin A formation, 4: 641, 4: 642f Echidna, lactation length, 3: 553 Echidna milk composition, 3: 555 immune-related proteins, 3: 558–559 oligosaccharides, 3: 271t Economics analysis, milk standardization, 1: 547 breeding objectives, effects on, 2: 656, 2: 658 economic merit indexes, industry acceptance, 2: 660 gastrointestinal nematodes, 2: 258 Latin American dairy management, 2: 92 lifetime profit estimates, 2: 660 population pressure, developing countries, 2: 880 Economic trait loci (ETLs), 2: 654 Ectoderm, 4: 486 Ectoparasiticides, 1: 890 Edam cheese, 1: 721 Edible caseinate, Codex standard, 4: 330 Edible casein products, Codex standard, 4: 330 Edible oil refining process, aflatoxins, 4: 808
Index Edosensuu, 2: 510 Edrin, 1: 889 Education current trends, 2: 1 dairy production, 2: 1–5 see also Dairy production education food/dairy technology see Dairy technology education graduate careers, 2: 3, 2: 3t industry changes, 2: 2, 2: 2t internships, 2: 3 North American Intercollegiate Dairy Challenge, 2: 4 skills/experience needed, 2: 2, 2: 3t work experience, 2: 3 see also Training ‘Effective fiber’, 3: 985 definition, 3: 985–986 pasture-based system limitations, 3: 986 rumen function optimization, 2: 338–340, 2: 368–369 Effective neutral detergent fiber (eNDF) see ‘Effective fiber’ Effective reserve definition, 2: 807 goats, 2: 807, 2: 809f, 2: 809t Effluent limitations guidelines (ELGs), US, 3: 395 Effluent management, farms see Manure/effluent management Effluent treatment see Dairy effluent treatment Egg lecithin, 1: 66t Egg white injury, 4: 687 Egyptian (Berseem) clover (Trifolium alexandrinum), 2: 558 Egyptian Journal of Dairy Science, 2: 104 Egyptian Nubian (Zaraibi) goats, 1: 311t, 1: 317 Egyptian Society of Dairy Sciences, 2: 104 Eicosapentaenoic acid (EPA), blood cholesterol levels, 3: 731 80/20 rule, 4: 267 Eiler’s equation, 4: 520, 4: 525 Elastase, 2: 289–290 Elastic bodies, 1: 269f Elastic deformation, 1: 688–689 Elasticity, 1: 265t low-moisture part-skim mozzarella (pizza cheese), 1: 742–743 Elastic (compression) modulus, cheese, 1: 695t Elastic theory, 1: 268 Elderly people donkey milk, 1: 372 vitamin deficiency risk, 4: 638 Electrical air heaters, spray drying, 4: 220 Electrical conductivity (EC), 3: 471 abnormal milk, 3: 424 buffalo milk, 3: 472 cream, 3: 471–472 curd strength measurement, 1: 587 definition, 3: 471 mastitis, 3: 424, 3: 424f, 3: 471 clinical, 3: 424 subclinical, 3: 424 measurement, 3: 471, 4: 237 evaluation, 3: 424, 3: 425t milk, 2: 739, 3: 424, 3: 424f, 3: 471 calcium ions, 3: 471 fat content, 3: 471–472 milk quality, 3: 896 udder health measurement, 3: 898 Electrical equipment, safety hazards, 4: 277 Electrical fencing, 2: 27 Electrical resistivity see Electrical conductivity (EC) Electrical substations, 4: 610 Electrical tube heating (ETH), 2: 704, 2: 705t brand names, 2: 704 heating profiles, 2: 702f, 2: 704 indirectly heated UHT milk vs., 2: 704 Electrical wires, bird repellents, 4: 542
Electricity, 4: 610–612 distribution, 4: 611 distribution level, 4: 610 energy management, 4: 610 insulation, 4: 610 fire prevention, 4: 611 for power, 4: 610 power factor, 4: 611 safety issues, 4: 611 personnel safety, 4: 611 standby supply, 4: 610 tariffs, 4: 610–611 usage, 4: 610 Electric motors, 4: 611 grades, 4: 611 Electrochemical analysis, 1: 193–197, 4: 257 amperometric analysis, 1: 194 applications, 1: 194 anodic stripping voltammetry, 1: 196 biosensors, 1: 196 coulometric titration for salt, 1: 194 electrophoresis, 1: 195 gas-sensing electrodes, 1: 195 glass electrodes, 1: 195 ion-selective electrodes, 1: 194 Karl Fischer titrations, 1: 194 liquid membrane electrodes, 1: 195 polarography, 1: 197 solid-state electrodes, 1: 195 conductometric analysis, 1: 194 cyclic voltammetry, 1: 193 polarography, 1: 193 potentiometric analysis, 1: 193 voltammetric analysis, 1: 193 Electrochemical biosensor transducers, 1: 239, 1: 239f Electrocution traps, flying insect control, 4: 543 Electrodialysis (ED), 3: 865, 4: 738 bacteriostatic compound addition, 4: 738–739 batch plant system, 4: 738 clean-in-place system, 4: 739 DC application, 4: 738, 4: 739f definition, 4: 738 limiting factors, 4: 739 manual cleaning, 4: 739 operating costs, 4: 739 operating principles, 4: 738 plant automation, 4: 739 power supply, 4: 739 processing costs, 4: 739 replacement parts, 4: 739 protein adsorption, 4: 739 unit, 4: 738, 4: 739f whey recovery processes, 2: 127f, 2: 127–128 Electromagnetic spectrum, 1: 109, 1: 110f Electronic ID reading systems, 3: 952 Electronic nose see E-nose Electronic pulsator, 3: 950 Electron microscopy, 1: 227 butter microstructure, 1: 510–511, 1: 511f see also specific types Electrophoresis, 1: 185–192, 1: 195 capillary see Capillary electrophoresis (CE) chip-based, 1: 191 definition, 1: 185 free-flow, 1: 189 gel-based see Gel electrophoresis milk proteins, 3: 746 historical aspects, 1: 22–23 see also Polyacrylamide gel electrophoresis (PAGE); Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) Electropolishing, 4: 137 Electroporation, LAB, 3: 67–68 Electrospray ionization (ESI) MS, 1: 198, 1: 199 triacylglycerol analysis, 3: 702
869
Electrothermal atomic absorption spectrometry (ETAAS), 1: 144 analytical performance, 1: 143t Elepharus davidianus (Per´e David’s deer), 4: 445–446 Elimination–challenge test, milk allergy, 3: 1042 -Elimination reaction, milk proteins, 3: 1068, 3: 1069f ELISA see Enzyme-linked immunosorbent assay (ELISA) El Tambo, 2: 105 Embden goose egg whites lysozyme, 2: 331 Embden–Meyerhof pathway, lactate dehydrogenase, 2: 327 Embryo(s) antiluteolytic signals, 4: 496–497 cloned, 2: 611 genome activation, 4: 493 heat stress, 4: 568 loss, causes of, 4: 494f, 4: 496 luteolysis blockage, 4: 496–497, 4: 497f nutritional support, preimplantation period, 4: 495 thermotolerance, 4: 568 transfer see Embryo transfer (ET) Embryonic discs, 4: 486, 4: 486f Embryonic membrane formation, 4: 486 Embryonic stem cells (ESCs), transgenic, 2: 639 Embryo transfer (ET), 2: 610 buffalo, 2: 774 costs, 4: 573 donor selection, 2: 629 embryo recovery and evaluation, 2: 627 abnormality rate, 2: 627–628 embryo quality criteria, 2: 627 nonsurgical procedures, 2: 627 embryo sexing, PCR, 2: 633 facilities, 2: 630 goats, 2: 836 nonsurgical technique, 2: 610 recipient selection, 2: 629 storage, 2: 628 cryopreservation, 2: 629 media and conditions, 2: 628–629 temporary in vitro storage and viability, 2: 628 summer months, heat stress management, 4: 572, 4: 572f transfer methods, 2: 629 see also Multiple ovulation and embryo transfer (MOET) EMC see Enzyme-modified cheese (EMC) Emergency caesarean section, pregnancy toxemia, 2: 248–249 Emergency Planning and Community Right-toKnow Act (EPCRA), 3: 397 Emergency Response Plan (ERP), 4: 282 Emergency Response Planning Guideline (ERPG) levels, 4: 282 Emetic toxin, Bacillus cereus group, 4: 26–27 Emmental cheese appearance, 1: 713f bacteriophages, 1: 407–408 butyric acid bacteria-induced gas blowing defects, 1: 663 calcium content, 3: 1011 characteristics, 1: 712 Codex Alimentarius standards, 1: 712 composition, 1: 712–713, 1: 713t, 1: 714t flavor, 1: 719t compounds, 1: 683 Propionibacterium, 1: 408 as food ingredient, 1: 830 manufacture brining, 1: 712 raw milk, 1: 712 raw milk vs. pasteurized milk, 1: 655t ripening, 1: 716, 1: 717t propionibacteria, 1: 403, 1: 407, 1: 571 Emmentaler PDO cheese alkaline phosphatase activity measurement, 1: 653f
870 Index Emmentaler PDO cheese (continued ) generic Emmental vs., 1: 655t pathogen status, 1: 659 Empirical models, 2: 429–430 Emulsification butter manufacture, 1: 498, 1: 498f enzyme-modified cheese, 1: 800 NMR see Nuclear magnetic resonance (NMR) pasteurized processed cheese products, 1: 810 Emulsifiers, 1: 61–71, 2: 900 anionic-active, 1: 63 applications, 1: 64, 1: 66t, 1: 67, 1: 71t destabilising agents, 1: 68 emulsion stability, 1: 68 choice of, 1: 71 dairy product uses, 1: 67, 1: 71t European Union, 1: 35 hydrocolloids see Hydrocolloids ice cream, 2: 900 legal status, 1: 66t naturally occurring, 1: 64 glycolipids, 1: 64 hydrocolloids, 1: 67 lecithins, 1: 64, 1: 65f phospholipids, 1: 64, 1: 65f proteins, 1: 62f, 1: 64 synthetic, 1: 64, 1: 68f diacylglycerols, 1: 65 identity numbers, 1: 66t lactic acid fatty acid esters, 1: 67 monoacylglycerol organic acid esters, 1: 67 monoacylglycerols, 1: 65 polyol acyl esters, 1: 67 sorbitan esters, 1: 67 United States, 1: 39 see also specific emulsifiers Emulsifying activity index (EAI), 3: 891 Emulsifying capacity (EC), 3: 891 Emulsifying salts (ES) cheese analogues, 1: 815t, 1: 818 enzyme-modified cheese, 1: 800 pasteurized processed cheese products (PCPs) see Pasteurized processed cheese products Emulsions, 1: 61 aerated, 1: 71 coalescence, 1: 63, 3: 890–891 oil-in-water, 1: 63 water-in-oil, 1: 63 creaming, 1: 62, 3: 890–891 density difference, 1: 62–63 particle size, 1: 62 viscocity, 1: 63 creaming rate, 1: 62 creation, 1: 61 definition, 1: 61 destabilization, 1: 68 droplet size NMR, 1: 163 pulsed field gradient NMR (PFG NMR), 1: 163–164 flocculation, 1: 61, 1: 62f, 3: 675, 3: 890–891 pH, 1: 62 ice cream mix, aging process, 2: 901 instability, 3: 890–891 interfacial films, 1: 63 components, 1: 63 milk lipid globule membranes, 1: 63 models, 1: 63, 1: 64f kinetic stability, 1: 61 microbial transglutaminase, 2: 299, 2: 299f milk protein concentrate, 3: 850 oil-in-water see Oil-in-water (O/W) emulsions particle size distribution, 1: 61 physical properties, 1: 61 see also specific properties stability, 1: 68 water-in-oil see Water-in-oil (W/O) emulsions Emulsion stability (ES), 3: 891
Encephalitic listeriosis cattle, 2: 186 differential diagnosis, 2: 186–187 goats, 2: 186 histopathology, 2: 187 pathogenesis, 2: 185 sheep, 2: 185 Encephalization quotient (EQ), primates, 3: 614 Endocarditis, Enterobacter, 4: 76 Endocrine factors see Hormones Endocrine organs, reproductive, 4: 422 Endoderm, 4: 486 Endometrium, preimplantation period secretions, 4: 495–496 Endoparasiticide contaminants, 1: 890 Endopeptidases enzyme-modified cheese, 1: 802–803 LAB, 3: 87 Endoplasmic reticulum (ER), milk lipid droplet formation, 3: 373 Endosome, 3: 374f, 3: 378 Endotoxemia, mastitis, 3: 415 Endotoxin, mastitis, 3: 437 Energy balance negative see Negative energy balance (NEB) postpartum estrous cycling, 4: 436 Energy flow, metabolic see Metabolic energy flow Energy level diagrams, chromophores, 1: 110f, 1: 110–111 Energy status, postpartum, 4: 515, 4: 516f Engineering, 4: 273 Engineering design projects requirements, 4: 124 Engineering stress, 1: 275 Engorgement, ticks, 2: 253 E-nose, 2: 546 concept, 4: 241 mutivariate analysis, with SPME–MS system, 2: 546 Penicillium camemberti detection, 4: 779 strengths, 2: 546 weaknesses, 2: 546 Enteric methane production modeling, 2: 431 Enteritis, Clostridium perfringens type A, 4: 49, 4: 51 Enteroaggregative Escherichia coli (EAEC), 4: 61 cheese-related outbreaks, 4: 61–62 Enterobacter, 4: 72–80 antibiotic susceptibility, 4: 73 bacteremia, 4: 75 biofilms, 4: 79 bloodstream infections, 4: 75 central nervous system infections, 4: 75 classification, 4: 72, 4: 73t clinical relevance, 4: 75 consumer information, 4: 79 control, 4: 79 hygiene standards, 4: 79 manufacture, 4: 79 Cronobacter vs., 4: 77, 4: 78t detection methods, 4: 76 distribution, 4: 73 environment, 4: 73 foodborne outbreaks, 4: 74, 4: 74t food contamination, 4: 74 as food hygiene indicators, 4: 76 future perspectives, 4: 79 gastrointestinal microflora (human), 1: 383t growth, 4: 72 host reservoirs, 4: 73 identification, 4: 76 immunocompromised patients, 4: 75 isolation, 4: 76 milk fat globule membrane damage, 4: 388 molecular identification, 4: 77 nonsocomial pneumonias, 4: 76 phenotypic identification, 4: 77, 4: 78t physiology, 4: 72 prevalence, 4: 73 prevention, 4: 79
resistance, 4: 72 pH, 4: 73 skin infections, 4: 76 soft tissue infections, 4: 76 subtyping, 4: 76 methods, 4: 77 thermal inactivation, 4: 73 water activity, 4: 72 Enterobacter aerogenes bacteremia, 4: 75 bacterial meningitis, 4: 75–76 cheese, public health aspects, 1: 648, 1: 649f cheese spoilage, 4: 68–69 clinical relevance, 4: 75 Enterobacter cloacae bacteremia, 4: 75 bacterial meningitis, 4: 75–76 Enterobacter cloacae complex, 4: 72 antibiotic susceptibility, 4: 73 clinical relevance, 4: 75 food contamination, 4: 74 host reservoirs, 4: 73–74 Enterobacter hormaechei, 4: 73 Enterobacteriaceae, 4: 67–71 amine formation, 4: 69 cheese, 4: 68 control, 4: 69 dairy products, 4: 67 dried milk, 4: 68 enumeration, 4: 69 fecal milk contamination, 4: 67 fermentation types, 4: 67 in milk, 4: 68 morphology, 4: 67 motility, 4: 67 physiology, 4: 67 sources, 4: 69 Enterobacterial repetitive intragenic consensus (ERIC) fingerprinting, PCR, 1: 222 Enterobacter sakazakii see Cronobacter Enterobacter sepsis, 4: 75 Enterocin 1146/A, 1: 422t Enterocin A, 1: 426 Enterococcus, 3: 153–159 antibiotic resistance, 3: 155 in dairy products, 3: 155–156 gene source, 3: 155–156 biogenic amines, 1: 451–452, 3: 156 characteristics, 3: 153 characterization, 3: 158 cheese, 1: 625, 3: 157 as adjuncts, 3: 157 hygiene status preservation, 3: 158 listeria inhibition, 3: 158 public health aspects, 1: 648, 1: 648f, 1: 649 as starters, 3: 157 citrate metabolism, 3: 153 in dairy products, 3: 157 product spoilage, 3: 157 enterocin genes, 3: 154 enterocins as biopreservatives, 3: 154 classification, 3: 154 production, 3: 154 targets, 3: 154 enumeration, 3: 158 environmental mastitis, 3: 416–417 esterolytic activity, 3: 153 ester synthesis, 3: 153–154 flavor, 3: 153 growth requirements, 3: 158 -hemolytic strains, 3: 156 identification, 3: 417 isolation, 3: 158 lipolytic activity, 3: 153 Mediterranean area cheeses, 3: 157 nonsocomial infections, 3: 155 pasteurization resistance, 3: 157
Index pathogenesis, 3: 155 probiotic properties, 3: 154 safety, 3: 155 proteolytic activity, 3: 153 selective media, 3: 158 spoilage, 3: 454 starter cultures, 1: 560t streptococcal species differentiation, 3: 417 vancomycin-resistant, 3: 155 isolation, 3: 159 virulence factors, 3: 156 virulence gene expression, 3: 156 Enterococcus durans brine-matured cheeses, 1: 793 lipolytic activity, 3: 153 Enterococcus faecalis antibiotic resistance, 3: 155 brine-matured cheeses, 1: 793 characteristics, 3: 153 cheese starter, 3: 158 growth in cheese, 1: 648f host tissue colonization, 3: 156 lipolytic activity, 3: 153 probiotic properties, 3: 154 starter cultures, 1: 560t virulence factors, 3: 156 Enterococcus faecalis strain SF68, 3: 154 Enterococcus faecalis subsp. liquefaciens, 3: 153 Enterococcus faecium brine-matured cheeses, 1: 793 characteristics, 3: 153 cheese starter, 1: 560t, 3: 158 host tissue colonization, 3: 156 lipolytic activity, 3: 153 probiotic properties, 3: 154 vancomycin-resistant, 3: 155 virulence factors, 3: 156 Enterococcus faecium PR88, 3: 155 Enterococcus faecium strain CRL13, 3: 155 Enterocytes, fatty acid absorption, 3: 712 Enterohemorrhagic Escherichia coli (EHEC), 1: 650, 4: 60 cheese-related outbreaks, 4: 62 cytotoxins, 4: 60 dairy-related illnesses, 3: 313 human infection, 4: 60–61 raw milk-related outbreaks, 4: 61 Enteroinvasive Escherichia coli (EIEC), 1: 650, 4: 61 cheese-related outbreaks, 4: 61–62 dairy-related illnesses, 3: 313 virulence plasmid, 4: 99–100 Enteropathogenic Escherichia coli (EPEC), 1: 650, 4: 61 Enterotoxemia, goats, 2: 790, 2: 794, 2: 797–798 kids, 2: 831 Enterotoxigenic Escherichia coli (ETEC), 1: 650, 4: 61 dairy-related illnesses, 3: 313 heat-labile (LT) toxins, 4: 61 heat-stable (ST) toxins, 4: 61 infection symptoms, 4: 61 Enterotoxins Bacillus cereus group, 4: 26 staphylococcal poisoning, 3: 314 Staphylococcus aureus, 4: 108 Enterprise resource planning (ERP), 4: 242 E numbers, 1: 53 consumer perceptions, 1: 43 Environment non-seasonal/pasture-based management, 2: 50 sensory evaluation, 1: 282 warm climate feed pads, 2: 20 Environmental contaminants see Contaminants Environmental Protection Agency (EPA), water quality regulations, 3: 395 Environmental temperature lactation, effects on, 2: 99, 3: 42–43 pasture leaf growth, 2: 598 traditional multipurpose breed adaptability, 2: 876, 2: 876–879
Environmental water monitoring, nitrate/nitrite analysis, 1: 910 Enzymatic hydrolysis, processing wastewaters, 4: 634 Enzymatic treatment, milk protein allergenicity reduction, 3: 1043 Enzyme(s) accelerated cheese ripening see Accelerated cheese ripening activity, cheese salting, 1: 597 blue mold cheese proteolysis, 1: 770t exogenous dairy applications, 2: 301 directed (artificial) evolution, 3: 212–213 extraction, 2: 314, 2: 317 heat treatment survival, 2: 541, 2: 542f, 3: 283 temperature-dependent kinetic data, 2: 718t HPLC, 1: 173 immunochemical detection, 1: 180 milk see Milk enzymes milk lipid oxidation, 3: 719 purification, 2: 314, 2: 317 see also individual enzymes Enzyme-linked immunosorbent assay (ELISA), 1: 177 accuracy, 1: 178 aflatoxins, 4: 806 brucellosis, 2: 157 caseins, 1: 244, 3: 749 competitive, 1: 178, 1: 178f Coxiella burnetii, 4: 57 direct, 1: 178, 1: 178f foot-and-mouth disease, 2: 164 indirect, 1: 178, 1: 178f bluetongue virus, 2: 150 infant formulae analysis, 2: 136 Johne’s disease, 2: 177 liver flukes, 2: 267 lungworm disease diagnosis, 2: 273 milk allergy, 3: 1042 milk bacteria determination, 3: 900 Ostertagia ostertagi, 2: 260, 2: 261f, 2: 262 precision, 1: 178 pregnancy-associated glycoproteins, 4: 491 pregnancy detection, 4: 490 quantitative, 1: 178 sandwich, 1: 178f somatic cell count, 3: 896–897 Staphylococcus aureus, 4: 113 types, 1: 178, 1: 178f see also specific types whey proteins, 3: 749–750 Enzyme-modified cheese (EMC), 1: 799–804 advantages, 1: 799 applications, 1: 799, 1: 799 as bioactive peptides, 1: 799–800 bitterness, 1: 802 combinations, 1: 799–800 compositional requirements, 1: 801 definition, 1: 799, 1: 827 dried, 1: 825–826 enzymes in, 1: 802 flavor, 2: 287 flavor development, 1: 799, 1: 802 free amino acids, 1: 802 lipolysis, 1: 802 proteolysis, 1: 802 flavor potentiators, 1: 802 ingredients, 2: 291–292 lipases, 1: 803 manufacture, 1: 827 component approach, 1: 800, 1: 801f curd substrate emulsification, 1: 800 emulsifying salts, 1: 800 enzymatic hydrolysis, 1: 800–801 heat treatment, 1: 800–801 single-step approach, 1: 800f technology, 1: 800 two-stage process, 1: 801
871
natural cheese vs., 1: 825–826 off-flavors, 1: 802 paste, 1: 828 peptidases, 1: 802 powder, 1: 828 proteinases, 1: 802, 2: 291 ripening acceleration, 1: 799 starter cultures, 1: 803 technology, 1: 800f, 1: 827 single-step approach, 1: 800 testing, 1: 800–801 usage, 1: 799 Eosinophilia, lungworm disease, 2: 273 Epidermal growth factor (EGF) colostrum, 3: 596 in vitro maturation, 2: 618–619 lactogenesis, 3: 18 mammary gland development, 3: 341 Epididymis bull management, 1: 476 pathology, artificial insemination centers, 1: 473 Epifluorescence, light microscopy, 1: 226 Epimerase-deficient galactosemia, 3: 1054 Epirus sheep, 1: 336 Epsilometer test (E-test), 4: 43 Equid milk, 3: 518–529 caseins, 3: 522 composition, 3: 518, 3: 521t fat globules, 3: 526 fatty acid profile, 3: 524, 3: 525t human nutrition, 3: 528 immunoglobulins, 3: 521t, 3: 522 indigenous enzymes, 3: 523 -lactoglobulin, 3: 519 lactose, 3: 518 lipids, 3: 524, 3: 524t minerals, 3: 526, 3: 527t physical properties, 3: 527, 3: 528t proteins, 3: 519 whey protein denaturation, 3: 522 Equid species, 3: 518, 3: 520f Equilibrium moisture, 4: 211, 4: 212f Equilibrium relative humidity, 4: 211, 4: 723t Equilibrium vapor pressure, 1: 77 Equine chorionic gonadotropin (eCG), ovine artificial estrous synchronization, 2: 890 Equine colostrum, 3: 518 density, 3: 527–528 immunoglobulins, 3: 811 oligosaccharides, 3: 519, 3: 521t chemical structures, 3: 271t physical properties, 3: 528t refractive index, 3: 527–528 Equine milk, 2: 512, 2: 517 allergenicity, 1: 363 ash content, 3: 521t, 3: 526–527 beneficial effects, 1: 363 casein micelle stability, 3: 523 caseins, 1: 361–362, 3: 519, 3: 521t, 3: 522 -casein variant, 3: 824–825 composition, 1: 359f, 1: 360, 1: 360, 1: 361t, 3: 459, 3: 539t feeding effects, 1: 362 cosmetology, 1: 364 dual-binding model for micelle assembly and structure, 3: 778 ethanol stability, 3: 523 fat globules, 1: 361 fat melting point, 3: 526 fatty acids, 1: 361, 1: 361t, 3: 524, 3: 524t, 3: 525t harvesting, 1: 358 heat coagulation time, 3: 523 heat stability, 2: 749 human nutrition, 3: 528 -lactalbumin, 3: 519–522, 3: 522 lactoferrin, 3: 522 -lactoglobulin, 3: 519, 3: 522, 3: 758–759, 3: 792 lipids, 3: 524, 3: 524t
872 Index Equine milk (continued ) nonprotein nitrogen, 1: 361 physical properties, 3: 528t powdered, 3: 528–529 products, 1: 362 proteins, 2: 507 quality, 1: 360, 1: 362 trace elements, 3: 527, 3: 527t triglyceride structure, 3: 526 utilization, 1: 363 human consumption, 1: 363 vitamin C, 1: 360–361 vitamins, 3: 526, 3: 527t whey proteins, 1: 361t, 1: 361–362, 3: 519, 3: 521t denaturation, 3: 522 Equine milk lysozyme (EML), 2: 331 Equus africanus (African wild ass), 3: 518 Equus asinus see Donkey Equus caballus see Horse Equus ferus, 3: 327 Equus ferus przewalski (Przewalski’s horse), 3: 327 Ergastoplasm, 3: 331–332 Ergocalciferol, 4: 646 chemistry, 4: 646–647 discovery, 4: 646 structure, 4: 646–647 Ergosterol, 3: 1001–1002 Ergot alkaloids, galactopoietic effects, 3: 28 Erythema endemicum see Pellagra Erythromycin papillomatous digital dermatitis, 2: 172 resistance, Campylobacter, 4: 43, 4: 43 ES see Emulsifying salts (ES) Escherichia coli, 4: 60–66 appendages, 4: 60 buffalo, Mediterranean region, 2: 782 characteristics, 3: 419, 4: 60 cheese, public health aspects, 1: 650 clinical syndromes, 4: 60 control, 4: 64 equipment sanitation, 4: 64 good hygiene practices, 4: 64 dairy products incidence in, 4: 62, 4: 63t outbreaks from, 4: 61 enteroaggregative see Enteroaggregative Escherichia coli (EAEC) enterohemorrhagic see Enterohemorrhagic Escherichia coli (EHEC) enteroinvasive see Enteroinvasive Escherichia coli (EIEC) enteropathogenic, 1: 650, 4: 61 enterotoxigenic see Enterotoxigenic Escherichia coli (ETEC) -galactosidase, 2: 276 growth, 4: 62 in cheese, 1: 648f optimal temperature, 4: 62 pH, 4: 62–64 water activity, 4: 64 H/flagella antigens, 4: 60 identification, 3: 419 intramammary infections, 3: 415–416 K antigens, 4: 60 mammary infection, 3: 895 mastitis, 2: 48–49, 3: 419 microbiological analytical methods, 1: 217 in milk, 3: 449 control, 4: 64 fecal contamination, 4: 62 incidence in, 4: 62, 4: 63t outbreaks from, 4: 61 O antigens, 4: 60 pathogenic types, 4: 60 postpasteurization contamination, 3: 313 raw milk cheeses, 1: 659 Shiga-toxin producing see Shiga toxin-producing E. coli (STEC)
survival, 4: 62 see also individual types Escherichia coli O104:H21, 4: 61 Escherichia coli O119, 3: 256 Escherichia coli O157, 4: 61 Escherichia coli O157:H7, 1: 645, 3: 311–312, 3: 313 ESI (electrospray ionization), MS, 1: 198, 1: 199 Esophageal sphincter inhibition, bloat, 2: 206–208 Espa˜nola de Licenciados y Doctores enCienda y Tecnologı´a de los Alimentos (ALCYTA), 2: 105 Essential amino acid index, 2: 412t, 2: 414 Essential oils, 4: 788–789 Established Populations for Epidemiologic Studies of the Elderly (EPESE) trials, cardiovascular disease-vitamin E relationship, 4: 658 Esterase(s) definition, 1: 562 indigenous to milk, 2: 304–307 starter cultures, 1: 562 Esterified propoxylated glycerols (EPGs), 1: 530 Esterolysis, propionibacteria, 1: 571 Esters, cheese flavor, 1: 681 Estimated breeding values (EBVs), 3: 968–969 sheep flocks, 2: 882 Estonia, red cattle breeds, 1: 296 Estradiol(s) corpus luteum luteolysis, 4: 432 estrous cycle, 4: 429f, 4: 430f, 4: 431 induced lactation, 3: 20 plasma levels, 3: 20–21 lactogenesis, 3: 18 LH inhibition, 4: 422f, 4: 423 ovarian follicular cysts, 4: 438f parturition, 4: 505 postpartum anovulatory follicles, 4: 435 prepubertal heifers, 4: 424 Estradiol benzoate, estrus synchronization, 4: 452 noncyclic cow treatment, 4: 452 Estradiol–LH negative feedback loop, 4: 424 Estradiol valerate, 4: 451–452 Estrogen(s) bone density, 3: 1009 estrus synchronization ban on, 4: 452 progestogen and, 4: 451, 4: 451f, 4: 452 prostaglandin and, 4: 451f, 4: 452 galactopoietic effects, 3: 30 mammary gland development, 3: 339–340 metabolism in gastrointestinal tract, 2: 769–770 in milk, 2: 769 induced lactation, 3: 23 milk fever, 2: 240 parturition, 4: 507 placental secretion, 4: 500, 4: 505, 4: 507 pregnancy variations, 2: 769 Estrogen receptor- (ER ) gene, 3: 1060 Estrous cycle behavioral changes, 4: 428 characteristics, 4: 428–433 donkey, 1: 370 first, 4: 411 follicular development, 4: 428 follicular dynamics, 4: 434 follicular growth, 4: 428 follicular phase, 4: 428 heifers, 4: 411, 4: 411f luteal phase, 4: 428 luteinizing hormone, 4: 430–431 luteinizing hormone, 4: 430 ovarian function, endocrine regulation, 4: 429, 4: 430f postcalving, 4: 475 postpartum cyclicity, 4: 434–439 body condition, 4: 436 energy balance, 4: 436 mechanisms associated, 4: 435 puerperium abnormalities, 4: 437 seasonal breeders see Seasonal breeders
stages, 4: 411 Estrous synchronization, 1: 7 Estrus behavior, 4: 428, 4: 461 heat stress, 4: 567 induced lactation, 3: 21–22 behavior-affecting factors, 4: 464 seasonal variations, 4: 465 detection see Estrus detection first, 4: 421 heat stress effects, 4: 567 heifers, 4: 411 high milk yield, 4: 464 hormone treatment timing, 2: 624, 2: 625 management problems, 4: 465 physical activity increases, 4: 462 postpartum period, 4: 464 prepubertal heifers, 4: 424 return to, nonpregnancy detection, 4: 489 secondary signs, 4: 461 sheep, 2: 887 signs, 4: 428 silent, 4: 464–465 ‘standing’, 4: 461 synchronization see Estrus synchronization Estrus detection, 4: 461–466 aids, 4: 468 heifers, 4: 413–414 artificial insemination, 2: 608, 4: 465, 4: 465f, 4: 468 heat stress, 4: 571 ovulation prediction, 4: 465 physical activity detection, automated systems, 4: 461 program goals, 4: 461 visual observation, 4: 461 see also individual aids/devices Estrus synchronization, 4: 448–453 artificial insemination, 4: 469 combination treatment programs, 4: 451 future developments, 4: 453 heifers, 4: 412–413, 4: 414f noncyclic cow treatment, 4: 452 practical considerations, 4: 453 principles, 4: 448 progestogens see Progestogen(s) program features, 4: 448 prostaglandin see Prostaglandin sex-sorted sperm, 2: 635 regimens, 2: 635 sheep, 2: 874 uses, 4: 448 ETAAS see Electrothermal atomic absorption spectrometry (ETAAS) Etazon Lord Lily, 2: 672 Ethanol, lactose-derived, 3: 179, 3: 371 Ethernet, 4: 238 7-Ethoxyacridine-3,9-diamine test, brucellosis, 2: 157 Ethylenediamine dihydroiodide (EDDI), 2: 380 Ethylenediaminetetraacetate (EDTA), 4: 617 Ethyl esters, 3: 161–162 EU see European Union (EU) Eubacterium, 4: 355 EU Milk Hygiene Directive 92/46 Hazard Analysis Critical Control Point system, 4: 115 somatic cell counts, 3: 897 Eurasian badgers (Meles meles), bovine tuberculosis, 2: 197 Europe artificial insemination use, 4: 470 Bos taurus breeds, 1: 286t, 1: 297 chlorine sanitizers, 3: 635 food fortification, folates, 4: 682 Northern see Northern Europe sheep extensive production systems, 2: 71 European Agricultural Guidance and Guarantee Fund (EAGGF), 4: 295–296
Index European Communities Council, animal welfare directives, 4: 729 European Community, cheese legislation, 1: 845 European Dairy Association (EDA), 2: 105 European Food Safety Authority (EFSA), genetically modified organisms, 3: 968 European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies, whole dairy product-dental caries relationship ruling, 3: 1036 European Hygienic Equipment Design Group (EHEDG) Regulations, 4: 134 European Union (EU) additives, 1: 34 antioxidants, 1: 37 approval, 1: 52 coagulation agents, 1: 36 colors, 1: 34, 1: 35t definitions, 1: 49 emulsifiers, 1: 35 labeling, 1: 53 preservatives, 1: 36 stabilizers, 1: 35 sweeteners, 1: 34, 1: 35t thickeners, 1: 35 animal welfare policies, 4: 729 cheese legislation, 1: 846 colors, 1: 34 Common Agricultural Policy see Common Agricultural Policy (CAP) Harmonized System introduction, 4: 335 herby cheeses, 1: 786 Identification Mark, 4: 335 identification system, 2: 649 identity standards, 4: 323 legislation milk protein content, 4: 547 milk protein standardization, 4: 548 water supply, 4: 582 market price subsidy, 4: 292, 4: 293f milk quotas, impacts of, 1: 10, 1: 11t organic standards, 4: 10 skim milk powder, stock:global export ratio, 4: 348, 4: 350f spiced cheeses, 1: 786 spreadable fat standards, 1: 522, 1: 523t Europel (European Dairy Transport), 2: 9 Eutheria (true placental mammals), 3: 460 Eutrophication, 3: 394–395 Evaluation model, 2: 651 convergence criteria, 2: 652 iteration, 2: 652 random effects, 2: 651–652 unknown-parent groups, 2: 652 Evaporated milk, 1: 862–868 age gelatation, 1: 867 Codex standards, 4: 329 composition, 1: 862 creaming, 1: 866, 1: 867f crystalline sediment, 1: 868 definition, 1: 862 as drinking milk, 1: 863 ‘filled’, 1: 862–863 heat stability control, 1: 863 pH dependent, 1: 866 problems, 1: 866, 1: 866f historical aspects, 1: 12, 1: 24, 2: 744 imitation/filled, 2: 915 in-container heating, 1: 865 infrared spectrometry, 1: 119t manufacture methods, 1: 863, 1: 864f, 2: 721, 2: 721f, 4: 205, 4: 206f cold storage, 1: 865 concentration, 1: 863 cooling, 1: 865 homogenization, 1: 863 preheating, 1: 863
stability test, 1: 864 microbiological problems, 1: 865 packaging, 1: 865, 4: 19 problems, 1: 865 product description, 1: 862 recombined see Recombined evaporated milk reconstituted products, 3: 317 sterilization, 1: 865 storage defects, 1: 866 color, 1: 867, 1: 867f flavor, 1: 867 UHT-sterilized, 1: 865, 1: 867 ‘use-by-date’, 1: 866 uses, 1: 863 viscosity, 1: 866 water activity, 4: 707–708 Evaporation heat loss, 4: 550–551 whey, 4: 732 yogurt production, 4: 201 Evaporative capacity, 4: 211f, 4: 212 Evaporative cooling techniques, 4: 561 Evaporative light scattering, HPLC, 1: 174 Evaporators, 4: 200–207 backward-feed multiple-effect, 4: 203, 4: 204f construction materials, 4: 201 crystallizing, 3: 198 nucleation point control, 3: 200 dairy industry uses, 4: 205 definition, 4: 200 direct expansion, 4: 597 economics, 4: 205 energy saving methods, 4: 205 forward-feed multiple-effect, 4: 203, 4: 204f fouling, 3: 199 heat balance, 4: 204 indirect expansion, 4: 597 liquid recirculation type, 4: 597 manufacturers, 4: 201 material balance, 4: 204 multiple-effect, 4: 200 operating pressure-temperature relationship, 4: 201 operation, 4: 200 modes of, 4: 203 parallel-feed multiple-effect, 4: 203 processing factors, 4: 200 foaming/frothing, 4: 200 material temperature sensitivity, 4: 200 solubility, 4: 200 solute concentration, 4: 200 scale deposition, 4: 201 selection, 4: 205 single-effect, 4: 203f, 4: 203–204 heat balance, 4: 204, 4: 204f material balance, 4: 204 steam use, 4: 200 thermocompression, 4: 205, 4: 206f types, 4: 201 use in whey permeate concentration, 3: 197 vapor compression cycle, 4: 596, 4: 597 see also individual types Even-toed ungulates (Artiodactyla), 3: 324, 3: 518, 3: 563 cetacean relationship, 3: 324 INO locus, 3: 324, 3: 326f, 3: 326f milk composition, 3: 571t suborders, 3: 324 Ewe(s) artificial photoperiod changes, 4: 443–444 lactating, health management, 2: 861 lambing health-care, 2: 861 hygiene precautions, 2: 861 training, 2: 861 milk see Sheep milk milk yield, prepubertal weight gains, 2: 884, 2: 884t replacement management, 2: 882–886 first mating, 2: 885
873
milk replacer, 2: 883 nursing lambs, 2: 883 prepartum (pregnant ewes), 2: 882 prepubertal, feeding, 2: 884 as proportion of total flock, 2: 882 selection criteria, 2: 882 yearlings, lactation, 2: 885 replacements, health management, 2: 863 see also Sheep Ewe’s milk see Sheep milk Exchange current, 4: 259 Excipients, lactose particles, 2: 132 Exocellular polysaccharides (EPS), 2: 481, 2: 497 bacterial sources, 2: 481, 2: 496, 2: 498t bifidan, 2: 481 kefiran, 2: 520 biosynthesis determinants, 3: 115 cell surface proteins, 2: 498 growth limiting factors, 2: 498 lipoteichoic acid, 2: 498 plasmid DNA, 2: 497 slime production instability, 2: 498 composition, 2: 497, 2: 498t dairy product properties, effects on, 2: 481, 2: 481, 2: 501, 2: 531 dietary intake, metabolic effects immune system stimulation, 2: 523 intestinal absorption, 2: 485 functions (for bacteria), 2: 481 Streptococcus thermophilus, 3: 145 Exocytosis compound, 3: 377–378 simple, 3: 377–378 Exons, 3: 1056 Exopeptidases, 1: 771 Exopolysaccharides (EPS) bacteriophage resistance, 1: 435 LAB, 3: 136 screening, 3: 136 Lactobacillus delbrueckii group, 3: 122 lactococci, 3: 136 Pediococcus, 3: 150 tailor-made cultures, 3: 967, 3: 967f Exorphins, 3: 879 Expansion valve capillary tube, 4: 597–598 vapor compression cycle, 4: 596, 4: 597–598 Expert panels, cheese flavor assessment, 1: 679–680 Exploratory celiotomy, 2: 215 Exponentially weighted moving average (EWMA), 1: 89 Expression proteomics, 3: 843 Expression vectors, Propionibacterium, 1: 405 Extended Antoine equation, 4: 210 Extended shelf-life (ESL) dairy products in France, 3: 308 target shelf-life, 4: 388–389 thermoduric psychrotrophs, 4: 388 Extended shelf life (ESL) milk, 3: 281–287 appearance defects, 3: 282 consumer acceptance, 3: 283, 3: 283f flavor defects, 3: 281 strategies to minimize, 3: 281–282 nonthermal production technologies, 2: 725, 3: 286, 3: 307 high-pressure homogenizer and microfluidizers, 2: 726–729 microfiltration, 2: 729, 3: 286, 3: 307–309 pulsed electric fields, 2: 738, 2: 740, 3: 286 pasteurized milk vs., 3: 279 product requirement/definition, 3: 281, 3: 283 safe/absolute shelf life, 3: 282 shelf life limiting factors, 3: 281, 3: 282 contamination, postpasteurization, 3: 283 light-induced degradation, 3: 283 raw (preprocessing) milk quality, 3: 282 storage temperature, 3: 282 thermal treatment parameters, 3: 282
874 Index Extended shelf life (ESL) milk (continued ) texture defects, 3: 282 thermal production technologies, 3: 284 aseptic packaging and filling, 3: 285 direct steam heating systems, 3: 284, 3: 284f equipment sanitation, 3: 285 indirect heat exchange systems, 3: 284, 3: 285f see also UHT milk Extensive grazing, Africa, 2: 79 Extensively hydrolyzed formula (EHF), 3: 1043 Extensive systems goat production, 2: 60–61 Latin American dairy management, 2: 89 sheep see Sheep External holding tube, HTST pasteurizer, 4: 196–197 External insulation, animals, 4: 550 External parasites, 2: 254t External pudendal artery, 3: 334 External pudendal vein, 3: 335 Extracellular adherence protein (Eap), 4: 105–106 Extra Hard Grating cheese Codex standard, 4: 330 Extrusion, 2: 349 Exudate gums, dairy desserts, 2: 909t Eyes defects, 1: 719 Dutch-type cheeses, 1: 725, 1: 725f Swiss-type cheeses see Swiss-type cheeses Ezo brown bear milk oligosaccharides, 3: 271t
F F1 system, Bos indicus Bos taurus cattle, 1: 308 FAAS see Flame atomic absorption spectrometry (FAAS) Fabricated reactor systems, 4: 632–633 Facial eczema, 4: 798–799 Facilitated diffusion, calcium absorption, 3: 996–997 Facilities management, drylot systems, 2: 52 reproductive efficiency, 4: 580 Factor analysis, 1: 99 Factor X see Vitamin E ‘Factory farming’, 4: 727–728 Facultatively heterofermentative lactobacilli, Swisstype cheeses, 1: 714 Facultative pathogens, 4: 747 Facultative ponds, 4: 632–633 FAES see Flame atomic emission spectrometry (FAES) Failure Mode and Effects Analysis (FMEA), 4: 278 Fakhreya camels, 1: 352 Falling film-type evaporator, 4: 201 Fallow grazing, Southern Asia, 2: 94, 2: 94 False mount, semen collection, 1: 473 Familial adenomatous polyposis (FAP), 3: 1016 Familial hypercholesterolemia, 3: 732 Fan cooling, heat stress, 4: 570–571 Fanning friction factor, 4: 153 Far-infrared spectroscopy, 1: 113 Farm Animal Welfare Council, UK, 4: 729 Farm Bill (2002), US, 4: 304 Farm design paddock arrangement, controlled grazing, 2: 598 risk asssessment decomposition diagram, 2: 681, 2: 682f Farm design (warm climates), 2: 13–28 calf feeding systems, 2: 25 automated systems, 2: 25 manual milk feeding systems, 2: 25 multiple sucking, 2: 25 calf housing, 2: 23 calf crates, 2: 24, 2: 24f calf hutches, 2: 24 deep litter systems, 2: 24 paddocks, 2: 23 calf rearing facilities, 2: 23 feed pads, 2: 19 advantages, 2: 19 central feed wagon alley, 2: 20
cleaning, 2: 21 controlled drainage, 2: 22 environmental protection, 2: 20 flood (flush) cleaning, 2: 21 geotextile pads, 2: 21 heat stress, 2: 19 high cost, 2: 20 hosing, 2: 21 liquid waste management, 2: 21 loafing areas, 2: 20 low cost, 2: 20 manure seal, 2: 22 mechanical scraping, 2: 21 medium cost, 2: 20 orientation, 2: 22 pasture damage, 2: 19 reduced feed wastage, 2: 19 runoff collection ponds, 2: 22 troughs, 2: 20 types, 2: 20 see also specific types udder cleanliness, 2: 19 heat stress management, 2: 19 herd management, 2: 19 shade provision, 2: 19 ventilation, 2: 19 water sprinklers, 2: 19 hospital facilities, 2: 28 intensive farms, 2: 28 pasture farms, 2: 28 housing systems, 2: 22 cooling systems, 2: 22, 2: 23 feeding alleys, 2: 22 freestall barns, 2: 23, 2: 23f hot dry environments, 2: 22 humid environments, 2: 23 shade, 2: 22 milking shed site selection, 2: 25 access, 2: 25 aspect, 2: 25 drainage, 2: 25 effluent disposal, 2: 25 power supply, 2: 26 site approval, 2: 26 water supply, 2: 26 milking systems, 2: 13 comfortable environment, 2: 17 effluent management, 2: 18 herringbones, 2: 13, 2: 14f, 2: 15f, 2: 16f, 2: 16f holding yards, 2: 18 machine cleaning, 2: 18 rotaries, 2: 15, 2: 17f stray voltage, 2: 17 walkthroughs, 2: 13, 2: 14f pasture farm subdivision, 2: 25 electrical fencing, 2: 27 irrigation, 2: 27 lane ways, 2: 26, 2: 26f permanent fencing, 2: 27 subdivision/fencing, 2: 27 whole farm plan, 2: 27 riparian areas, 2: 27 general environmental health, 2: 27 stream bank stability, 2: 27 water quality, 2: 27 weed populations, 2: 27 Farm Pilot Project Coordination (FPPC), 3: 394 Far-off dry cows drylot management systems, 2: 54, 2: 54t ration see Dry period rations Far-UV (FUV) irradiation, Aspergillus flavus, 4: 790–791 Fasciola gigantica (tropical liver fluke), 2: 265f drug resistance, 2: 269 geographical distribution, 2: 264 life cycle, 2: 266
Fasciola hepatica (common liver fluke), 2: 265f drug resistance, 2: 269 eggs, 2: 264, 2: 265, 2: 266f geographical distribution, 2: 264 life cycle, 2: 265f within host, 2: 265 outside host, 2: 264, 2: 265f metacercaria, 2: 264–265 uptake prevention measures, 2: 268 Fascioloides magna, 2: 264 Fasciolosis, acute, 2: 266 FAST (fluorescence of advanced Maillard products and soluble tryptophan) index, 3: 227–228, 3: 231 Fat(s) absorption, 3: 712 biosensors, 1: 244 calf starters, 4: 402 cheese analogues, 1: 815t cheese salting, 1: 603 dairy processing, environmental impact, 4: 633 definition, 1: 79–80 dietary, blood lipoproteins, 3: 730 differential scanning calorimetry, 1: 259, 1: 260f digestibility, 3: 712 imitation dairy products, 2: 913 ketosis management, 2: 236 milk see Milk fat milk replacers, 4: 398 ration formulations, guidelines, 2: 463 rumen interactions, 2: 366 amino acid feed supplement protection, 2: 391, 2: 392, 2: 392 antimicrobial effects, 2: 342, 2: 345, 2: 366 fatty acid transformations, 2: 366, 2: 367f, 2: 367f fiber digestibility, 2: 342, 2: 345, 2: 366 supplements see Fat supplements transport, 3: 712 see also Fatty acid(s); Lipid(s); specific fats Fatal, 2: 672 Fatality probability, 4: 279t Fat bloom, milk chocolate, 1: 859 Fat cow syndrome, 2: 217 body condition score, 1: 466 Fat crystals butter microstructure, 1: 509–510 NMR T1 (spin lattice relaxation), 1: 161, 1: 161f Fat globules butter microstructure, 1: 509–510 cheese rheology, 1: 688 microstructure, 1: 230 static light scattering, 1: 134–135 ‘Fat heifers’, 1: 8 Fat mimetics, 1: 530 carbohydrate-based, 1: 530 characteristics, 1: 529 low-fat cheeses, 1: 838 protein-based, 1: 530 microparticulated, 1: 530 see also Fat replacers Fat on a dry basis (FDB) cheese, 1: 545 full-fat cheese, 1: 545 hard Italian cheeses, 1: 728 Fat replacers, 1: 528–532, 2: 896 low-fat cheeses, 1: 838 types, 1: 528 see also Fat mimetics Fat-soluble vitamins see Vitamin(s) Fat substitutes, 1: 529 characteristics, 1: 528–529 see also individual types Fat supplements, 2: 363–370 classification, 2: 367 composition definitions, 2: 363 content, 2: 363 dairy rations use, 2: 363, 2: 786, 2: 791–792 ether extract components, 2: 363
Index feed content descriptive accuracy, 2: 347 feeding recommendations, 2: 368 fiber intake with, 2: 368–369 protein intake with, 2: 368–369 quantity limits, 2: 343, 2: 344, 2: 368 timing, 2: 368 milk fatty acid compositions, 3: 658, 3: 659t nutritional value, 2: 364 energy (caloric) benefits, 2: 364, 2: 365t metabolizable efficiency, 2: 406–407 milk yield effects, 2: 369, 2: 369f noncaloric benefits, 2: 365, 2: 365t polyunsaturated fatty acids, 3: 490 protected fats, 2: 368 rumen-active fats, 2: 368 rumen-inert fats, 2: 363, 2: 367 terminology, 2: 367 Fat-tailed (and fat-rumped) sheep, 2: 875, 2: 876, 2: 878t, 2: 879 Fatty acid(s) analysis, historical aspects, 1: 20 biosensors, 1: 244 blood lipoproteins, 3: 730 body condition score, 1: 466 bovine somatotropin treatment, 3: 33 buffalo milk, 3: 506, 3: 506t, 3: 506t butter, 1: 506, 1: 507f, 1: 507f camel milk, 1: 355, 1: 355t catabolism, cheese ripening, 1: 669 cheese flavor, 1: 680 colostrum, 3: 591, 3: 594t equine milk, 1: 361, 1: 361t flavor precursors, 2: 284 free see Free fatty acids (FFA) goat milk, 2: 62t goat production systems, 2: 61–62, 2: 62t mammary cell sources, 3: 543 de novo synthesis, 3: 543 dietary, 3: 543 elongation and desaturation, 3: 543–544 mammary gland development, 3: 341 milk, 3: 655–659 analysis, 3: 698 alkaline digestion method, 3: 698 methods, 3: 698 response factors, 3: 699 results evaluation, 3: 699 total extraction, 3: 698 branched-chain, 3: 657 composition goat vs. cow, 3: 485, 3: 486t interspecies comparison, 3: 543 composition variations, 3: 657 dietary fat supplementation, 3: 658, 3: 659t feeding regimes, 3: 657 lactation, 3: 658 seasonal effects, 3: 658, 3: 658t de novo synthesis, 3: 655 dietary fat supplementation, 3: 658 dietary effects, 3: 655 empirical classification, 3: 655 heat stress, 4: 565 major, 3: 655, 3: 656t minor, 3: 657 odd-numbered, 3: 657 origins, 3: 655, 3: 656f plasma lipids, 3: 655 profile alteration, consumer benefits, 2: 366, 3: 489–490 ruminant vs. non-ruminant, 3: 655–656 short-chain, 3: 656–657 types, 3: 656 in milk see Fatty acid(s), milk musk ox milk, 3: 535 nonesterified see Nonesterified fatty acids (NEFA) phylogeny-related chain length, 3: 545t carnivores, 3: 544 elephants, 3: 544
insectivorous, 3: 544 Lagomorpha, 3: 544 marine mammals, 3: 544 Perissodactyla, 3: 544 primates, 3: 544 rodents, 3: 544 ruminants, 3: 544 polyunsaturated see Polyunsaturated fatty acids (PUFAs) primate milk see Primate milk profile, 3: 461 proportions, 3: 479–480 reindeer milk, 3: 534 rumen fermentation, 3: 984 saturated see Saturated fatty acids (SFAs) sheep milk, 3: 497, 3: 497t feed supplement effects, 3: 497 short chain see Short-chain fatty acids sow milk, 3: 531 Swiss-type cheeses, 1: 408 yak milk, 3: 532–533 Fatty acid-binding protein (FABP), 3: 686f, 3: 689 Fatty acid hydroperoxides, 3: 716 Fatty acid methyl esters (FAME) analysis, milk phospholipids, 3: 673 formation, gas chromatography, 3: 698 Olestra manufacture, 1: 529 preparation standards, 3: 698 separation, 3: 699 Fatty acid polyglycerol esters as emulsifier, 1: 66t structure, 1: 68f Fatty acid propylene glycerol esters as emulsifier, 1: 66t structure, 1: 68f Fatty acid radical, 3: 716 Fatty acid sucrose esters, 1: 66t Fatty acid synthase (FASN), 3: 352–353 Fatty liver, 2: 217–223, 4: 517 body condition score, 1: 465 causes, 2: 218 consequences, 2: 219 diagnosis, 2: 217 fatty acid profile, 2: 222 feeding practices, 2: 221 genetic component, 2: 219 genomics, 2: 222–223 gluconeogenic capacity decreases, 2: 220–221 hepatic structure changes, 2: 220 hormonal interventions, 2: 222 infertility risk factor, 4: 579 ketosis, 2: 218 metabolomics, 2: 222–223 moderate to severe, 2: 218 new directions, 2: 222 prepartum feed intake, 4: 515 prevalence, 2: 218 prevention, 2: 221, 4: 518–519 energy intake, 2: 221 proteomic analysis, 2: 222–223 risks associated, 2: 219 treatment, 2: 221 Fc receptor, 3: 811 Feathering, coffee creams, 2: 915 Fed-batch operation, 4: 242 Federacion Panamericana de Lecheria, 2: 105 Federal Food, Drug and Cosmetics Act (FFDCA) additive definitions, 1: 51 additives, 1: 37 Federal Milk Marketing Order (FMMO) annual average prices, 4: 303t areas, 4: 302, 4: 303f pricing rules, 4: 302 Federation of American Societies for Experimental Biology, casein health aspects, 3: 863 Feed see Feed/feedstuffs Feedback control system see Closed-loop process control
875
Feedback inhibitor of lactation (FIL), 3: 30–31 marsupial milk, 3: 561 Feedbunk management, 2: 462 Feed/feedstuffs additives ketosis management, 2: 236 transition cows, pasture-based systems, 2: 467 aflatoxin contamination, 4: 807 aflatoxin elimination, 4: 808 arid environments, marginal nutrition, 2: 876, 2: 879, 2: 880 body condition score, 1: 463 byproducts see Coproduct feeds calcium absorption, 3: 997 cereal grains see Grains chemical composition, 2: 41 composition analysis for ration balancing, 2: 789, 2: 800 concentrated, historical aspects, 1: 4 costs, milk production and, 2: 458, 2: 459t descriptive systems, 2: 418–428 energy prediction, 2: 403–408 see also Digestible energy (DE), feed intakerelated; Metabolic energy flow energy values, 2: 460 goats see Goat(s) intake, milk flavor effects, 2: 542 management Africa see Cattle husbandry (Africa) biosensors, 1: 245 China, 2: 84 drylot management systems see Drylot management systems equine milk composition, 1: 362 goat production systems see Goat production systems non-seasonal/pasture-based management, 2: 41 practices, historical aspects, 1: 4 prepartum intake, 4: 515 processing adjustment factor, 2: 338 proteins, 2: 409–417 sheep see Sheep storage, historical aspects, 1: 5 unsaturated triacylglycerol increases, milk fat changes, 3: 706–707 see also Forage; Grazing management; Pasture(s); Total mixed ration (TMR); individual feeds Feed industry, historical aspects, 1: 5 Feeding alleys, 2: 22 Feeding regime effects, bovine rennets, 1: 574–575, 1: 575t Feeding units, calves, 1: 9 Feed Into Milk (FIM), 2004 review, 2: 419, 2: 425 Feedlot (grain) bloat, 2: 206 Feed pads, warm climate farms see Farm design (warm climates) Feed storage bags, 1: 5–6 Feedstuffs see Feed/feedstuffs Feed supplements bioavailability, 2: 392 associative effects, 2: 404 blood response approaches, 2: 393 factorial approaches, 2: 393 production responses, 2: 393 protein content responses, 2: 393 bloat treatment/prevention, 2: 210 deficiency correction, trace minerals, 2: 789 fats see Fat supplements goat production systems, 2: 61, 2: 62t microminerals, 2: 378–383 pregnancy toxemia prevention, 2: 248 ruminally protected amino acids see Ruminally protected amino acids sheep extensive production systems, 2: 70–71 sheep intensive production systems, 2: 71 trace mineralized salt, 2: 792–793
876 Index Feed troughs, 2: 20 Feed wastage, warm climate feed pads, 2: 19 Feed water treatment, 4: 587 Fencing cost, related to stocking rate, 2: 844 electrical, 2: 27 permanent, 2: 27 predator exclusion, 2: 844, 2: 844 FEPALE (Pan American Dairy Federation), 2: 105 Fermentation butter churning, 1: 495 immunoglobulins, 3: 813 Fermentation-produced chymosin (FPC), 1: 574, 1: 576, 2: 290 Aspergillus niger, 1: 576 camel chymosin, 1: 577 Kluyveromyces lactis, 1: 576 Fermented dairy products Campylobacter, 4: 44, 4: 45 citrate metabolism, 3: 166 flavor development, 2: 534 folate content, 4: 680–681 Listeria monocytogenes, 4: 85, 4: 85t Staphylococcus aureus incidence, 4: 114 Fermented milks aroma compounds, 2: 492, 2: 493, 2: 534 Asian see Asian fermented milks Bacillus cereus, 4: 28 Bifidobacterium see Bifidobacterium bioactive peptides, 3: 883–884 buffalo, Mediterranean region, 2: 783 Chinese dairy management, 2: 86 Codex standards, 4: 328 colon cancer risk, 3: 1017 concentrated, 2: 475 dairy product formation, 1: 440 definition, 4: 328 donkey milk drinks, 1: 372 E. coli control, 4: 65 equine milk modification, 2: 515–516 fermentation parameters, 2: 492t, 2: 493 microbiological groups, 2: 513f flavor compounds, 2: 492, 2: 493, 2: 534 flavored, 2: 475 folate content, 4: 683 fruit-containing, yeast growth, 4: 748 general features, 2: 470 Harmonized System, 4: 335 health effects, 2: 483–488, 2: 484f, 2: 487f, 2: 501, 2: 522 anticarcinogenesis, 2: 486, 2: 523 cancer cell growth suppression, 2: 487, 2: 523 intestinal microflora effects, 2: 486 mutagenic activity decrease, 2: 486, 2: 502 heat treated, 4: 328 historical aspects, 1: 1, 1: 15, 1: 31, 2: 507 infrared spectrometry, 1: 119t lactic fermentation, 2: 471 Lactobacillus casei group, 3: 102 Lactobacillus starter cultures, 3: 80t, 3: 83 lactose-intolerant consumers, 2: 281 local names, 2: 499t, 2: 503 mesophilic fermentations, 2: 472 microbial transglutaminase, 2: 299, 2: 299f Middle Eastern see Middle Eastern fermented milks milk preparation and treatments concentration, 2: 494 heat treatment, 2: 491t minimum composition types, 2: 474, 2: 475t Nordic see Nordic fermented milks Pediococcus, 3: 151 phage-induced failures, 1: 439 recombined see Recombined fermented milks standards of identity, 2: 474, 2: 475t starter microorganisms, 2: 470, 2: 471t viable count, 2: 474–475 technologically important properties, historical aspects, 1: 24
thermophilic fermentations, 2: 472 types, 2: 470–476, 2: 471t yeast containing, 4: 749 yeast-lactic fermentations, 2: 473 see also Yogurt; individual types Ferritic stainless steel, 4: 135, 4: 136 Ferritin, marsupial milk, 3: 558 Fertility, 4: 475–484 bulls, 4: 483 heat stress, 4: 567, 4: 568f mating management, 4: 475–484 multipurpose sheep, 2: 876–879, 2: 879t trait importance, 2: 658, 2: 658–659 recent decline in dairy herds, 2: 659 Fertilization competitive, 2: 604 rates, 4: 478 Fertilizer agronomic recommended application, 3: 403, 3: 404t application rates, 3: 403, 3: 404t nitrogen addition, 3: 406 Festuca arundinacea (tall fescue), 2: 576 Feta cheese, 1: 790, 3: 501 brine, 4: 752 cast, 1: 791 milk protein concentrate, 3: 851–852 cast Feta cheese, 1: 791 Enterococcus use, 3: 158 headspace analysis, 1: 794 manufacture large-scale production, 1: 791 milks, 1: 791 ultrafiltration, 1: 791 milk ultrafiltration, 1: 621 production statistics, 1: 790, 1: 790 protected designation, 1: 846 structured Feta cheese, 1: 792 texture, 1: 794 Fetal dystocia, 4: 511 Fetal growth, 4: 514 heat stress, 4: 569, 4: 569t Fetus abnormal presentation, 4: 504, 4: 506f birth position presentation, 4: 504, 4: 505f definition, 4: 485 development, 4: 487 expulsion, 4: 509, 4: 510 hypothalamic–pituitary–adrenal axis, 4: 504, 4: 507f nutrient requirements, 2: 246, 2: 247t see also Pregnancy FFDCA see Federal Food, Drug and Cosmetics Act (FFDCA) Fiber blood cholesterol levels, 3: 731 degradation-pH relationship, 2: 431–432 forage quality variations, 2: 579f, 2: 579–580 goats, 2: 786, 2: 790 milk fat depression correction of, 2: 795 in vitro (rumen fluid) digestibility, 2: 406 rumen function, 3: 985 rumen motility, 3: 985 ruminal acidosis prevention, 2: 201 ruminal digestion, 3: 991 soluble, 2: 342 Fibronectin binding proteins, Staphylococcus aureus, 4: 105 FIDs see Flame ionization detector (FID) Field-effect transistors, 1: 238, 1: 238f FieldPoints, 4: 238 ‘Filled’ evaporated milk, 1: 862–863 Filled milks see Imitation milks Fillers, cleaning in place, 4: 284 Filmj¨olk, 2: 472 folate content, 4: 683 FILMTEC NF 45 membranes, 3: 868 Filtration biological see Biological filtration, effluent
cheese manufacture, 1: 544 suspended solids/turbidity removal, water, 4: 583 Final control elements (FCE), 4: 237 Finance business management, 1: 481 management records, 1: 488 Fines, spray drying, 4: 225 Fine screening dairy effluent treatment, 4: 620 screens, 4: 621, 4: 621f ‘Fine-stranded’ gels, 3: 892 Finger test, curd strength measurement, 1: 585 Finnish Mental Health Study, saturated fatty acidcoronary heart disease relationship, 3: 1026 Fin whale milk, 3: 580 Fiore Sardo cheese, 1: 731 characteristics, 1: 730t composition, 1: 729t production statistics, 1: 729t proteolysis, NSLAB, 1: 735 Fire-tube boilers, 4: 590 Firmness, 1: 265t First-age infant formulae see Infant formulae First breeding body condition scoring, 1: 461–462 immunizations prior to, 4: 415 recommended age, 4: 412 weight at, 4: 403, 4: 412, 4: 412t First principles model, 4: 248 First US National Health and Nutrition Examination Survey (NHANES I), vitamin C findings, 4: 673 Fish, microbial transglutaminase, 2: 300 Fishbone milking parlors see Herringbone (fishbone) milking parlors Fish meal, 2: 414 Fish oil modified butters, 1: 504 supplementation, plasma metabolic changes, 3: 1058–1059 Fish products dairy ingredients, 2: 131 nisin applications, 1: 424 Fittings, plant design, 4: 126 5-point system, body condition scoring (BCS) see Body condition score (BCS) Five-day biochemical oxygen demand (BOD5), 4: 619 Fixed-bed ionic exchange, whey, 2: 127f, 2: 128 Fjord, N.J., 1: 13 FlaA restriction fragment length polymorphism (flaARFLP), Campylobacter, 4: 42 Flaccid paralysis, 2: 240 Flamande cattle, 1: 286t Flame atomic absorption spectrometry (FAAS), 1: 142 analytical performance, 1: 143t Flame atomic emission spectrometry (FAES), 1: 142 analytical performance, 1: 143t Flame ionization detector (FID) cheese flavor assessment, 1: 678 fatty acid analysis, 3: 698 gas chromatography, 1: 175 Flame photometric detector (FPD), 1: 678–679 ‘Flash’ pasteurization, 4: 198 ‘Flash pasteurizers’, 1: 13 Flat belt drive separators, 4: 169, 4: 169f Flat-blade impeller, 4: 160, 4: 161f Flavin adenine dinucleotide (FAD), 4: 704 formation, 4: 704 structure, 4: 705f Flavin-dependent SOx (QSOx1), 2: 330 Flavin mononucleotide (FMN), 4: 704 formation, 4: 704 structure, 4: 705f Flavobacterium, 3: 453 Flavoenzymes (flavoproteins), 4: 704 Flavonoids, goat milk, 2: 63, 2: 64t Flavoproteins (flavoenzymes), 4: 704
Index Flavor analytical techniques, 2: 543 electronic nose instruments, 2: 546 technology improvement prospects, 2: 550 dairy foods, 2: 533–551 see also individual products Flavor defects see individual products Flavored milks, 3: 301–306 acidic, milk protein stabilization, 3: 302 additional ingredients, 3: 301–302 definition, 3: 301 fat content, 3: 301–302 importance of, 3: 301 ionic strength, 3: 302 markets, 3: 301 particle stabilization, 3: 305 pH stabilization, 3: 302 popular flavors, 3: 301–302 protein stabilization, 3: 305 sales, 3: 278–279 stabilization, carrageenan, 3: 303 thickeners, 3: 305 total production, 3: 301 worldwide consumption, 3: 301, 3: 302t Fleckvieh cattle Austria, 1: 293 Germany, 1: 293 Flemish milksheep, 1: 332t Fleur du Marquis cheese, 1: 787 Floating curds, 1: 701 Flocculation bridging, 3: 891 emulsions see Emulsions water, suspended solids/turbidity removal, 4: 583 Flood (flush) cleaning, 2: 21 Floors, cross ventilate barn, 2: 58 Florina sheep, 1: 336t Flour moths, 4: 543 Flowability, milk powder, 2: 119 Flow behavior, yogurt rheology, 4: 528 Flow control valves, 4: 152 Flow curves, yogurt rheology, 4: 528 Flow cytometry somatic cell count, 3: 896 udder health measurement, 3: 898 Flow diversion device (FDD) see Flow diversion valve (FDV) Flow diversion valve (FDV) configuration, 4: 194f, 4: 196f, 4: 197 HTST pasteurizer, 3: 275–276, 4: 197, 4: 197f Flow equipment ideal flow, 4: 139 general design principles, 4: 139 ‘heads’, 4: 139 mechanical energy conservation, 4: 139, 4: 140f milking machines, milkline systems effects and causes of vacuum fluctuations, 3: 440 vacuum stability, 3: 440 momentum conservation, 4: 139 nonideal flow, 4: 139 head losses, 4: 139 heat dissipation, 4: 139–140 installation head loss calculation, 4: 142 localized head losses, 4: 142 non-Newtonian fluids, 4: 140 number of velocity head losses calculation, 4: 142 turbulence, 4: 140 viscosity, 4: 139–140, 4: 141f viscosity and flow regimes, 4: 140, 4: 140f viscus shear energy dissipation, 4: 141, 4: 141f piping calculation principles, 4: 139–144 pump calculation principles, 4: 139–144 Flow measurement, ultrasound see Ultrasound Flow phenomena, 1: 268 Flow regulator valves, 4: 237 Flow sterilization, coffee cream manufacture, 1: 914 Flow-time measurements, rheology, 1: 277
Fluazuron, 2: 256 Flue gases, boilers, 4: 592 Fluid bed after-dryer/cooler, 4: 231 Fluid bed drying, 4: 213 types, 4: 213 Fluid milk, packaging, 4: 17 Fluid milk filling room, 4: 17f Flukicides, 2: 268, 2: 268t Fluorescence, 1: 111 Fluorescence of advanced Maillard products and soluble tryptophan (FAST) index, 3: 227–228, 3: 231 Fluorescence polarization assay (FPA), brucellosis, 2: 157 Fluorescent in situ hybridization (FISH), Lactobacillus, 3: 82 Fluorescent-label based biosensors, 1: 238, 1: 238f Fluoridated milk, 3: 1037 Fluoride in milk, 3: 934, 3: 934t chemical forms, 3: 935 nutritional significance, 3: 939 probiotics and, 3: 1038 recommended dietary intake, 3: 937t Fluorimetry, 3: 231 FAST assay, 3: 231 front-face fluorescence spectroscopy, 3: 231 HPLC, 1: 174 milk quality assessment, 3: 231 2-Fluoroethanol, 3: 206–207 Fluorophos system, 4: 198–199 Fluoroquinolones biosensor analysis, 1: 240 resistant-Campylobacter, 4: 43 Flushing, goats, 2: 834–835 Flushing gas, cockroach control, 4: 542–543 Flying insects, control, 4: 543 Fly strike, sheep, 2: 858 FMD see Foot-and-mouth disease (FMD) FMDV see Foot-and-mouth disease virus (FMDV) FMEA (Failure Mode and Effects Analysis), 4: 278 ‘Foam cells’, 3: 713 Foams/foaming destabilization, 1: 68 homogenized milk, 3: 678 ice cream manufacture, 2: 901, 2: 904 partial coalescence, 1: 63, 1: 63 whey protein concentrate, 3: 891 Foamy bloat causes, 2: 206 foam-stabilizing agents, 2: 208 Folate(s), 4: 678–686 absorption, 4: 678 analysis, 4: 680, 4: 682t sample pretreatment, 4: 680, 4: 681f bioavailability, dairy products, 4: 683 assessment methods, 4: 683, 4: 684t studies, 4: 684, 4: 685f, 4: 685f in dairy products, 4: 680, 4: 682t processing effects, 4: 683 feed supplements, 2: 398 milk yield and, 3: 1000–1001 food fortification, 4: 681 Europe, 4: 682 policies, 4: 678 safety issues, 4: 681 United States, 4: 682 voluntary, 4: 682–683 functions, 4: 678, 4: 679f future trends, 4: 686 health benefits, 4: 678 intake recommendations, humans, 4: 678 in milk, contributions to nutrient intake, 3: 1005 structure, 4: 678, 4: 679f Folate-binding protein(s), 3: 796t, 3: 798, 4: 683 bioavailability studies, 4: 684–685, 4: 685f, 4: 685f Folic acid biosensors, 1: 245
877
feed supplements, 2: 398 functions, 2: 397t, 2: 398 sources, 2: 397t sterilized milk, oxygen levels, 3: 294–295, 3: 295 structure, 4: 679f supplementation, metabolic protein expression, 3: 1058 Follicle-stimulating hormone (FSH) embryo transfer, goats, 2: 836 estrous cycle, 4: 429f, 4: 430 follicular growth, 4: 429f, 4: 430 function, 4: 422–423 injection, for superovulation response, 2: 624 normal action, 2: 623–624 ovarian follicular dynamics, 4: 434 parturition, 4: 434 postpartum, 4: 434, 4: 475 puberty, 4: 422–423 Follicular growth estrous cycle, 4: 428 heat stress, 4: 568 pattern, 4: 428–429 postpartum, 4: 434 waves, 4: 428–429, 4: 429f heifers, 4: 411–412 number of, 4: 429 Follow-on (second-age) formulae see Infant formulae Fonterra, 4: 311 Food additives, 1: 34–40 approval for, 1: 52 Codex Committee on Food Additives and Contaminants, 1: 52 European Union, 1: 52 Japan, 1: 53 Joint Expert Committee on Food Additives, 1: 52 USA, 1: 53 cheese, 1: 36t Codex milk product standards, 4: 327 consumer perceptions see Consumer perceptions cream products, 1: 921 dairy products coloring, 2: 901 emulsifiers see Emulsifiers flavoring, 2: 901 labeling regulations, 3: 5, 3: 8 preservatives, 2: 301 stabilizers, 2: 526, 2: 899–900 sweeteners, 2: 899 definitions, 1: 49 Codex Alimentarius, 1: 49 direct, 1: 51 European Union, 1: 49 indirect, 1: 51 Japan, 1: 52 secondary, 1: 51 USA, 1: 51 key trends, 1: 41 labeling, 1: 53 Codex Alimentarius, 1: 53 European Union, 1: 53 Japan, 1: 54 USA, 1: 54 legislation, 1: 49–54 future work, 1: 54 milk, 1: 36t preservatives, 1: 36t, 1: 55 processing aids vs., 1: 50 risk assessment, 4: 534 safety see Food additive safety United States, 1: 37 antimycotics, 1: 39 antioxidants, 1: 39 bleaching agents, 1: 40 coagulation experts, 1: 39 colors, 1: 37 emulsifiers, 1: 39 preservatives, 1: 39 stabilizers, 1: 39
878 Index Food additives (continued ) sweeteners, 1: 38 thickeners, 1: 39 see also specific additives Food additive safety, 1: 55–60 acceptable daily intake, 1: 55, 1: 55 accumulation, 1: 56 benchmark dose approach, 1: 56 derivation, 1: 56 interspecies variability, 1: 56 Joint FAO/WHO Expert Committee on Food Additives, 1: 55 no observed adverse effect level, 1: 56 safety margins, 1: 56 toxicity studies, 1: 56 core toxicity tests, 1: 57 acute toxicity tests, 1: 58 carcinogenicity tests, 1: 57 chronic toxicity tests, 1: 57 developmental toxicity tests, 1: 57 genotoxicity tests, 1: 57 metabolism tests, 1: 57 reproduction tests, 1: 57 subchronic toxicity tests, 1: 57 toxicokinetic tests, 1: 57 emerging issues, 1: 59 animal experimentation, 1: 59 exposure assessment, 1: 58 budget method, 1: 58 duplicate diet studies, 1: 58 maximum permitted level, 1: 58 point estimate (deterministic) approach, 1: 58 probabilistic approach, 1: 58–59 total diet studies, 1: 58 risk assessment, 1: 55 toxological assessment, 1: 57 Food adulteration analysis, MS, 1: 201 Food and Agriculture Organization (FAO) cream product legislation, 1: 920 genetic superiority trial, 2: 669 Food and Drug Administration (FDA) Campylobacter isolation procedure, 4: 41, 4: 41f food additives, 1: 37 status list, 1: 852 genetically modified organisms, food safety, 3: 968 lowered fat content foods, labeling requirements, 2: 896 Olestra approval, 1: 529 Food and Nutrition Board, vitamin K adequate intake value, 4: 665 Food-borne botulism, 4: 47–49 Food fortification, 4: 681 Food Improvement Agents Package (FIAP), 1: 49 (UK) Food Labelling Regulations 1996 cheese composition, 1: 847, 1: 847t cheese definition, 1: 847 Food microbiology, recent trends, 1: 632 Food regulations see Regulations, dairy products Food safety objective (FSO), 4: 537–538 Food Standards Agency (FSA), cattle botulism guidelines, 4: 51 Food Standards Australia New Zealand (FSANZ), cheese standards, 1: 854 Food Standards Code 2000, Australia New Zealand, 1: 854 Food supply chains contract use, 4: 351 market power, 4: 351 vertical integration, 4: 351 Food technology education see Dairy technology education Food texture, 1: 264 butter consistency, 1: 512 Cheddar cheese, 1: 710 cheese rheology, 1: 685 defects, Dutch-type cheeses, 1: 727 definition, 1: 264 khoa defects, 1: 885
principles and significance, 1: 264–271 property classification, 1: 264, 1: 265t quality, 1: 264, 1: 266, 1: 266f within quality complex, 1: 266, 1: 267f quality effects, 1: 264, 1: 266, 1: 266f sensation aspects, 1: 267, 1: 268f sensory context, 1: 264 types, 1: 265t see also individual products Foot-and-mouth disease (FMD), 2: 160–167 airborne infection, 2: 162 carrier animals, 2: 162–163 diagnosis, 2: 165 clinical signs, 2: 163 cattle, 2: 163, 2: 163f, 2: 163f, 2: 164f goats, 2: 163 pigs, 2: 163 sheep, 2: 163 vesicles, 2: 163 control measures, 2: 166 costs, 2: 165–166 disinfection, 2: 166 slaughter, 2: 166 differential diagnosis, 2: 164t economy, 2: 165 direct costs, 2: 165 indirect costs, 2: 165 outbreak costs, 2: 165 emergency vaccination, 2: 166–167 epidemiology, 2: 160 hosts and, 2: 161 historical aspects, 1: 8 laboratory diagnosis, 2: 163–164 surveillance zones, 2: 166 transmission, 2: 162 United Kingdom outbreak, 2: 160 vaccination, 2: 166 websites, 2: 167t Foot-and-mouth disease virus (FMDV), 2: 160 characteristics, 2: 160 excretion, 2: 162 high-risk period, 2: 166 inactivation, 2: 161 reproductive ratio, 2: 166 serotypes, 2: 161, 2: 161t structure, 2: 160–161 surveillance, 2: 167 ‘topotypes’, 2: 161, 2: 162f vaccination cessation, Europe, 2: 160 virus pools, 2: 161, 2: 162f Foot-powered Mehring milker, 3: 942–943, 3: 943f Foot warts see Papillomatous digital dermatitis (PDD) Forage annual see Annual forage and pasture crops availability, non-seasonal/pasture-based management, 2: 40 calcium absorption, 2: 372 conservation systems, non-seasonal/pasture-based management, 2: 45 conserved see Conserved forage digestibility, 2: 460 dry matter intake calculation, 2: 460 high-quality, 2: 459–460 lignin content calculation, 2: 460 non-seasonal/pasture-based management, 2: 46 nutritional content analysis, 2: 789 nutritive value, non-seasonal/pasture-based management, 2: 40 particle size, 2: 460 perennial see Perennial forage and pasture crops quality calculation, 2: 463 dry lot systems, 2: 459 milk production predictions, 2: 460, 2: 460t sheep nutrition, 2: 68–70 winter, 2: 850 toxins fungal endophytes, 2: 574, 2: 583–584
infective agents, 2: 542, 2: 574, 2: 574, 2: 574 plant poisons, 2: 573, 2: 574 see also Pasture(s) Forage:concentrate ratio, heat stress-induced milk fat changes, 4: 564, 4: 564t Forage particle separators, 2: 462 Forced circulation-type evaporator, 4: 202, 4: 203f Forestomach, protein degradation, 2: 411 Forestripping, mastitis prevention, 3: 432 Formagraph, 1: 586 Formalin, 2: 172 Formate, 1: 642 Formic acid, 4: 790 Formulae, hand-reared captive primates, 3: 629–630 Fortification, milk, 2: 515–516, 2: 526 vitamin C, storage problems, 3: 227–228 vitamin D see Vitamin D-fortified milk vitamin D regulations, 3: 609 Fortified products, anticariogenic properties, 3: 1037 Forward sequential quadratic programming, 2: 443 Fossa cheese, 1: 732 characteristics, 1: 730t composition, 1: 729t lipolysis, free fatty acids, 1: 736t production statistics, 1: 729t proteolysis, 1: 734 free amino acids, 1: 734t NSLAB, 1: 735 Fossil fuels composition, 4: 591 theoretical amount of air needed to burn, 4: 592 Fossomatic systems, somatic cell count, 3: 896 Fouling evaporators, 3: 199 knowledge-based hybrid modeling, 4: 248–249 membrane-based fractionation see Membranebased fractionation reverse osmosis, 3: 870 ultrafiltration, 3: 870, 3: 870f, 3: 872 Fourier transform infrared (FT-IR) spectroscopy, 1: 112, 1: 115, 1: 229 cheese flavor assessment, 1: 678 Fourier transform mid-infrared (FT-MIR) spectroscopy, 1: 116, 1: 117f absorbance spectra, 1: 117f Fourier transform near-infrared (FT-NIR) spectroscopy, 1: 116, 1: 149 absorbance spectra, 1: 116, 1: 117f FPC see Fermentation-produced chymosin (FPC) Fractal aggregation theory, 1: 581–582 Fractional passage rate modeling, 2: 432 Fractionation milk fat rheology modification, 3: 707 modified butter, 1: 500 protein, application to different species, 3: 538 Fracture strain, cheese, 1: 695t Fracture stress see Gel firmness (curd strength) Framingham study, 3: 1023 France cheese definition, 1: 847 cheese legislation, 1: 847 compositional requirements, 1: 853t fat content, 1: 848 dairy product consumption, 1: 46, 1: 46, 1: 46t herby cheeses, 1: 786 listeriosis outbreaks, 4: 83 processed cheese definition, 1: 848 processed cheese specialty definition, 1: 848 sheep distribution, 2: 67 Simmental cattle, 1: 293–294 spiced cheeses, 1: 786 Francisella tularensis, 1: 241 Free amino acids enzyme-modified cheese flavor, 1: 802 hard Italian cheeses, 1: 734, 1: 734t Swiss-type cheese flavor, 1: 718 Swiss-type cheese ripening, 1: 716
Index Free fatty acids (FFA), 3: 638–641, 3: 651 automatic milking systems, 3: 956 butter, 1: 506 cheese flavor, 1: 680–681 Dutch-type cheese flavor, 1: 726 hard Italian cheeses, 1: 735–736, 1: 736t lipolysis product, 3: 721 mastitis, 3: 902–903 milking systems, effects on, 3: 638 air intake, 3: 638 different system types, 3: 640, 3: 641t milk cooling, 3: 639, 3: 639f milking frequency, 3: 639, 3: 640t pumping, 3: 639 temperature, 3: 639 milk quality requirements, cheese manufacture, 3: 599–600 milk tank cool storage, 3: 640 cooling, 3: 640 stirring, 3: 640 triglyceride crystallization, 3: 640 physical properties, 3: 651 primate milk, 3: 616 rancid flavor, 3: 638, 3: 651, 3: 652 surface mold-ripened cheese ripening, 1: 778, 1: 780t Swiss-type cheeses, 1: 408 Free-flow electrophoresis (FFE), 1: 189 Free-gas bloat, 2: 206, 2: 206–208 Free induction decay (FID), 1: 147 Free induction delay (FID), NMR, 1: 153–155 Freemartins, 4: 485 Free moisture, 4: 212f definition, 4: 211 Freestall housing drylot management systems, 2: 57 feeding practices, 1: 4 historical aspects, 1: 3 warm climate housing systems, 2: 23, 2: 23f Free trade agreements (FTAs) Australia, 4: 310 New Zealand, 4: 311 Freeze-dried cheeses, 1: 826 Freeze-dried sperm, 2: 607 Freezers batch scale of use, 2: 902–903 semi-continuous, for soft-serve desserts, 2: 903 continuous barrel structure, 2: 901–902, 2: 902f rotating action, 2: 902, 2: 903f screw extrusion, 2: 902 frozen product storage, 2: 903–904 hardening chambers, 2: 903 Freeze-shocking, 1: 797, 1: 797t Freezing definition, 4: 596 microstructure, 1: 231 milk fat globule membrane, 3: 679 Freezing point, 1: 251 adulteration, 1: 251 measurement, 4: 723t, 4: 724 titratable acidity, 1: 252 French ice cream, 2: 896 French soft cheeses, 1: 757t Fresh cheese manufacture centrifuges, 4: 172, 4: 173f, 4: 173f disk bowl centrifuges, 4: 179 Fresh cows, drylots, 2: 55 Friability, 1: 265t Friesian cattle see Holstein Friesian cattle Frisarta sheep, 1: 338 Frisonarta sheep, 1: 338 Fromage frais, 1: 703 composition, 1: 700t Front-face fluorescence spectroscopy (FFFS), 3: 231 Frozen custard, 2: 896
Frozen dairy products Listeria monocytogenes contamination, 4: 84 water, 4: 711 water activity, 4: 716 Frozen desserts, 2: 893–898 E. coli control measures, 4: 65 fancy-molded products, 2: 898 flavor defects, 2: 538–539, 2: 539f handheld, 2: 898 hard-frozen, 2: 893–894 homogenization, 2: 901 impulse, 2: 898 ingredients, 2: 893–894 low glycemic index products, 2: 896 manufacture, 2: 893–894, 2: 899–904 aerated emulsions, fat globule matrix, 1: 71, 2: 904, 2: 904f dynamic freezing, 2: 901 freezing processes, 2: 901 hardening, 2: 903 ingredients, 2: 899 mix blending and preparation, 2: 900 process steps, 2: 899, 2: 900f nonfat products, 2: 896 fat replacers, 2: 896 no-sugar added, 2: 896 ‘novelty’, 2: 898 product types, 2: 894 reduced-fat products, 2: 896 composition, 2: 895t, 2: 896 soft-frozen, 2: 893–894, 2: 897 sugar-free, 2: 896 see also Ice cream Frozen food sampling, 1: 73 Frozen semen in the field, 4: 468 handling, 4: 468 historical aspects, 1: 7 pocket thawed, 4: 468–469 sheep, 2: 891 warm-water thawed, 4: 468 Frozen yogurt, 2: 895t, 2: 897 yeast spoilage, 4: 745 Fructans, 4: 363 as prebiotics, 4: 363 sources, 4: 363 Fructansucrases, 3: 204–205 Fructooligosaccharides (FOS), 4: 360 bifidogenic effect, 4: 368 mineral absorption stimulation, 4: 370 as prebiotics, 4: 361t, 4: 362 production, 4: 360 Kluyveromyces, 4: 763 structure, 4: 357f, 4: 359t traveler’s diarrhea prevention, 4: 369 Fructose, Bifidobacterium, 1: 386t Fructose-6-phosphate phosphoketolase (F6PPK), 1: 387 Fruit preparations, spoilage molds, 4: 781 Fruit yogurt, yeast growth, 4: 748 FSL sheep, 1: 338 FtsH, 3: 64 Fucose, monotreme milk, 3: 556 -1-2-Fucosylated compounds, humans, 3: 249 Fucosyl-lactose, monotreme milk, 3: 556 29 Fucosyllactose, phocid seal milk, 3: 576 Fucosyl oligosaccharides mammalian species differences, 3: 272 seals, 3: 272 1-2-Fucosyltransferase, humans, 3: 249 Fuel oil, 4: 591 Full-fat cheese, fat on a dry basis, 1: 545 Fumitremorgin(s), 4: 792, 4: 796 Fumitremorgin A, 4: 796, 4: 797f Fumitremorgin B, 4: 796, 4: 797f Fumonisin(s), 4: 795 structure, 4: 795f Fumonisin B1, 1: 904t, 4: 795
879
Functional foods dairy ingredients, 2: 132, 2: 133 definition, 3: 662 Functional ingredients, 1: 41 Fungi aflatoxin-producing, 4: 801 inhibition, lactoperoxidase system, 2: 323 ruminal, 3: 980 Fungicides, 4: 790 Fungus see Fungi Funicular myelitis, 4: 677 Furosine (FUR) heat treatment marker, 3: 1069–1070, 3: 1070t infant formula, 3: 1071–1072, 3: 1072f milk heat treatment marker, domestic cooking, 3: 1072–1073, 3: 1073t protein glycation marker, 3: 1071f, 3: 1071–1072 UHT milk, 2: 706t, 2: 706–707, 3: 1071–1072, 3: 1072f Fur seal -lactalbumin lack, 3: 838 milk composition, foraging trip length, 3: 566, 3: 570–574 fat content, 3: 564t, 3: 570–574 F¨urstenberg’s rosette, 3: 333 Fusarenon-X, 4: 798, 4: 799f Fusarium proliferatum, 4: 795 Fusarium toxicosis, 4: 798 Fusarium verticillioides, 4: 795 Fushing, sheep, 2: 888 Fusobacterium, 1: 383t Future Dairy project, milking robots, 4: 252 Fuzzy logic controller (FLC), 4: 247 Fuzzy logic control system (FLCS), 4: 247, 4: 247f defuzzification module, 4: 248 fuzzification module, 4: 247 fuzzy inference module, 4: 248 fuzzy rulebase module, 4: 247, 4: 247f Fuzzy set, 4: 247 Fuzzy set theory, 4: 247
G GAB expression, 4: 720, 4: 721t Gaddi goats, 1: 311t, 1: 320 milk yields, 1: 312t Galactitol, 3: 1053 Galactokinase (GALK)-deficient galactosemia, 3: 1054 Galactomyces geotrichum, 4: 748 cheese, 4: 750 viili, 4: 749 Galactonic acid, 3: 1051 Galacto-oligosaccharides (GOS), 3: 209–216, 3: 210t bifidogenic effect, 3: 215, 4: 368 biological activity, 3: 213 bacterial utilization, 3: 214 pathogen adhesion, 3: 215 colon cancer prevention, 4: 369 digestibility, 3: 214 enzymatic synthesis, 3: 209, 3: 211f enzyme immobilization and engineering, 3: 212 industrial production optimization, 3: 211 product inhibition, 3: 212 reaction conditions, 3: 212 substrate inhibition, 3: 212 temperature effects, 3: 212 food-grade, synthesis, 3: 213 health benefits, 3: 214, 3: 215t industrial production, 4: 360 intestinal fermentation, 3: 214, 3: 214–215, 3: 215t mineral absorption stimulation, 4: 370 occurrence, 3: 209 as prebiotics, 3: 214, 3: 215t, 4: 360, 4: 361t production Kluyveromyces, 4: 763 lactase-induced, 2: 281 putrefaction reduction, 4: 369
880 Index Galacto-oligosaccharides (GOS) (continued ) stool frequency improvements, 4: 369 structure, 3: 209, 3: 211f, 4: 357f, 4: 359t sweetness, 3: 214 terminology, 3: 209, 3: 210t Galactopoiesis, 3: 38–44 bovine somatotropin effects see Bovine somatotropin (bST) cell survival factors, 3: 29f, 3: 31 definition, 3: 26, 3: 38 economic benefit, 3: 38 enhancement methods, 3: 38 growth factor effects, 3: 26–31 hormonal effects, 3: 26–31 lactose synthesis, 3: 41 management methods, 3: 38 increased milking frequency, 3: 39 photoperiod manipulation, 3: 39 milk component-influencing factors, 3: 40 milk fat levels, 3: 41 conjugated linoleic acid synthesis, 3: 42 modulation, 3: 41 milk protein yield, 3: 40 modulation, 3: 40 milk removal, 3: 30 mitogens, 3: 29f, 3: 31 pregnancy hormones, 3: 30 seasonal effects, 3: 42, 3: 43f 4- -D-Galactopyranosyl-D-glucopyranose see Lactose Galactose dietary sources, 3: 1051 endogenous production, 3: 1053 Lactobacillus casei metabolism, 1: 641 metabolism, humans, 3: 1051 Isselbacher pathway, 3: 1051 Leloir pathway, 3: 1051, 3: 1052f monohydrated -lactose crystal growth, 3: 193 Galactose-1-Puridyl transferase (GALT) deficiency see Galactosemia, classical Galactose-free diet, classical galactosemia, 3: 1052 Galactosemia, 3: 1051–1055 classical, 3: 1052 cataracts, 3: 1053 genetics, 3: 1054 newborn screening, 3: 1053 occurrence, 3: 1052 ovarian failure, 3: 1053 prenatal diagnosis, 3: 1053 symptoms, 3: 1052 treatment, 3: 1052 epimerase-deficient, 3: 1054 galactokinase (GALK)-deficient, 3: 1054 in utero effects, 3: 1053 mutations, 3: 1051–1052, 3: 1054 -Galactosidase(s), 2: 276–283, 3: 209, 4: 360 action, 3: 209–211, 3: 211f bacterial sources, 3: 211 biochemical properties, 2: 279, 2: 280f deficiency see -Galactosidase deficiency galactose metabolism, 3: 1051 galactosyl acceptors, 3: 206, 3: 207t hydrolysis mechanism, 2: 278, 2: 279f industrial/commercial use, 3: 212 Lactobacillus, 3: 85 Leuconostoc, 3: 140 marsupial milk, 3: 556–558 oligosaccharide production, 3: 179 recombinant engineering, 3: 212–213 research interests, 2: 276 starter cultures, 1: 560 structure, 2: 278, 2: 278f surface immobilization, 3: 212 thermostability, 3: 212, 3: 212–213 transglycosylation reaction, 2: 279 see also Lactase(s) -Galactosidase deficiency calcium absorption, 3: 929 osteoporosis, 3: 1014
prevalence, 3: 1013–1014 Galactosyl-acetylpyrrole (GALP), 3: 1073 Galactosyl- -pyranone (GAP), 3: 1073 -49 Galactosylfructose see Lactulose -49 Galactosylglucuronic acid see Lactobionic acid -39-Galactosyllactose, 3: 251 -49-Galactosyllactose, 3: 251 -49 Galactosylsorbitol see Lactitol -49 Galactosylsucrose see Lactosucrose -1,4-Galactosyltransferase (Gal-T1), 2: 329 Galactosyltransferase(s), 2: 329, 3: 368–369 marsupial milk, 3: 555–556 4-Galactosyltransferase-1 catalytic domain, 3: 784–785, 3: 785f lactose synthesis, 3: 782 reactions catalyzed, 3: 783f Galactosyltransferase-1, lactose synthesis, 3: 782 Galaxtosyl-isomaltol (GAI), 3: 1073 Gal 1-4Fru see Lactulose Gal 1-4Glc see Lactose Gall bladder, lactating ruminants, 3: 989 -D-Galp-(1!4)-D-Glcp see Lactose GALT deficiency see Galactosemia, classical Galvanic corrosion, 4: 262 Gametes, artificial, 2: 640 Gamma-glutamyltransferase see Gammaglutamyltranspeptidase (GGT) Gamma-glutamyltranspeptidase (GGT), 2: 332 activity, 2: 332 colostrum quality marker, 2: 332 heat resistance, 2: 332 purification, 2: 332 Gamma irradiation, Aspergillus flavus, 4: 790–791 Gangliosides, 3: 651 milk, 3: 670 structure, 3: 670, 3: 672f Garfagnana sheep, 1: 332t Garganica goats, 1: 315, 1: 316f Gariss, 2: 504 Gas blowing, 1: 661 avoidance, 1: 661–666 cell and spore removal, 2: 729, 2: 729 brine-salted cheese, 1: 665 avoidance, 1: 665 early gas defects, 1: 661 cheese spoilage, 1: 630 raw milk cheeses, 1: 658 heterofermentative lactobacilli-induced defects avoidance, 1: 665 Cheddar cheese, 1: 664 late, 1: 661, 1: 662 cheese spoilage, 1: 630 Clostridium, 4: 49 Clostridium butyricum, 1: 630 Clostridium tyrobutyricum, 1: 630 prevention, Lactobacillus bacteriocins, 3: 89 raw milk cheeses, 1: 658 silage feeding, 4: 50 Swiss-type cheese eye formation, 1: 715, 1: 715f Gas chromatography (GC), 1: 169, 1: 174 applications, 1: 175t butter fatty acids, 1: 506 cheese flavor assessment, 1: 676, 1: 678 derivatization, 1: 175 development, 1: 20 dioxin analysis, 1: 899 fatty acid analysis, 3: 698 acid catalyst, 3: 698 method, 3: 698, 3: 702 flame ionization detection, infant formulae, 2: 136 flavor volatile sample preparation, 2: 543, 2: 548 headspace analysis, 1: 174–175 lipolysis analysis, 3: 725 MS, 1: 198, 1: 199 solid-phase microextraction, 1: 174–175 solvent-assisted flavor evaporation, 1: 174–175 triacylglycerol analysis, 3: 700, 3: 700f see also individual methods
Gas chromatography–mass spectrometry (GC-MS), cheese flavor, 1: 675 Gas chromatography–olfactometry (GC-O), 1: 282–283, 2: 533, 2: 533, 2: 537, 2: 543 cheese flavor assessment, 1: 675 Gas formation see Gas blowing Gas-sensing electrodes, 1: 195 Gastric cancers, 4: 673 Gastricisin, 1: 574 Gastroenteritis Campylobacter jejuni, 3: 313 outbreaks, 3: 312 Gastroesophageal reflux, infant formulae, 2: 143 Gastrointestinal microflora, 1: 412, 1: 413t Bifidobacterium see Bifidobacterium function, 1: 412–413 harmful effects, 1: 413 harmful microbes, 4: 366–367 humans, 1: 383t, 4: 354 microbe types, 4: 366 microflora composition, 4: 366 newborn, 1: 413 Gastrointestinal nematodes, 2: 258–263 anthelmintic-resistant, 2: 262 control, dairy cattle, 2: 261 economic importance, 2: 258–259 grazing management, 2: 262 herd health management, 2: 260 immunity maintenance, 2: 260 importance, 2: 258 infection monitoring, 2: 260 life cycle, 2: 258, 2: 259f milk production, 2: 258, 2: 258–259 parasites of concern, 2: 258 pathophysiology, 2: 259 phosphorus absorption, 3: 997 reproductive performance, 2: 259 sheep, 2: 858 sodium absorption, 3: 998 subclinical parasitism, lactating cows, 2: 258 treatment threshold level determination, 2: 260 timing, 2: 261–262 see also individual species Gate valve, 4: 152, 4: 153f Gauge pressure, 3: 945 Gauge R&R studies, 1: 89 Gaulin, Auguste, 1: 13–14 Gaulin Micro-Gap homogenizing valve assembly, 2: 753, 2: 753f Gaulin type homogenizing valve assembly, 2: 752, 2: 752f, 2: 753f Gaymar, 2: 783 GC see Gas chromatography (GC) Gear drive separators, 4: 169, 4: 169f Gear pumps see Rotary pumps Gel(s), 1: 585 firmness, and measurement see Gel firmness (curd strength) (below) water diffusion, 1: 162, 1: 163f Gelatin applications, 1: 70t dairy desserts, 2: 909t as emulsifier, 1: 69t Gelatinase, Enterococcus, 3: 156 Gelation milk proteins, 3: 892 sterilized milk see Sterilized milk products Gel-based proteomics, 3: 843 Gelbvieh (Yellow) cattle, 1: 298 Gel electrophoresis, 1: 185 milk proteins, historical aspects, 1: 22–23 see also Polyacrylamide gel electrophoresis (PAGE) Gel filtration chromatography, milk proteins, 3: 761–762 Gel firmness (curd strength), 1: 585–590 casein changes, 1: 585
Index definition, 1: 585 determination for cutting into curd grains, 1: 585 measurement (objective), 1: 585, 1: 585 air puff technique, 1: 587 Berridge method, 1: 585 colorimetry, 1: 587 electrical conductivity, 1: 587 finger test, 1: 585 infrared light methods, 1: 587 knife test, 1: 585 microscopic analysis, 1: 586 near-infrared reflectance, 1: 587 rolling metal ball, 1: 587 small-amplitude dynamic rheology, 1: 586 ultrasonic systems, 1: 587 viscosity-based techniques, 1: 586 visible light methods, 1: 587 online measurement techniques, 1: 587 diffusing wave spectroscopy, 1: 589 dynamic light scattering, 1: 589 hot wire probe, 1: 588 infrared light methods, 1: 589 mechanical systems, 1: 587 near infrared spectroscopy, 1: 589, 1: 589f optical systems, 1: 589 vibrational systems, 1: 588 visible light methods, 1: 589 rheological quantities of cheese, 1: 695t role of, 1: 585 Gel-free proteomics, 3: 843 Gellan gum accelerated cheese ripening, 1: 796 dairy desserts, 2: 909t Gel permeation chromatography, 1: 169 microbial transglutaminase, 2: 298 Gene(s), 3: 965 definition, 3: 965 international flow, 2: 669–674 changes in, 2: 670 databases, research possibilities, 2: 670 direction of genetic flow, 2: 670 global merit shift, 2: 672, 2: 673t information flow management, 2: 672 source selection, 2: 669 Gene-assisted (marker-assisted) selection, 2: 666, 3: 969 Gene expression cis-acting regulatory elements, 3: 1056 mechanism, 3: 1056, 3: 1057f nutrition effects, 3: 1056 regulation, 3: 1056 trans-factors (DNA binding proteins), 3: 1056 Gene mutations, 2: 675 General Agreement on Tariffs and Trade (GATT) see World Trade Organization (WTO) General Council, WTO, 4: 338 Generally recognized as safe (GRAS), additive definitions, 1: 51 General Standard for Contaminants and Toxins in Food, 4: 320 General Standard for the Use of Dairy Terms, 4: 320 General Subject Committees (horizontal committees), Codex Alimentarius, 4: 314 Generator, absorption refrigeration system, 4: 599 Generic food sciences, education, 2: 6–7 Genetically-modified lactic cultures, accelerated cheese ripening, 1: 797 Genetically modified organisms (GMOs), public concerns, 3: 968 Genetically-modified starter cultures, 1: 557 Genetic base, 2: 653 Genetic defects, cattle, 2: 675–678 carriers, 2: 675 detection, 2: 677 comparative mapping, 2: 677–678 definition, 2: 675 inheritance, 2: 675 types, 2: 675
Genetic disorders, blood cholesterol levels, 3: 732, 3: 732t Genetic engineering, 3: 965 Genetic evaluation systems, 2: 651 categorical analysis, 2: 652 economic indices, 2: 656–662 aggregate genotype changes, 2: 659 breeding objective definiton, 2: 656, 2: 657t data availability, 2: 659 economic value of traits, 2: 658 estimated breeding values (EBV), sheep flocks, 2: 882 index creation, 2: 660 mating systems, 2: 661 selection index usefulness, 2: 659 evaluation model see Evaluation model flow of data, 2: 654f geographical differences, 2: 651 goals/aims, 2: 651 heterogeneous variance adjustment, 2: 653 joint, 2: 651 longevity analysis, 2: 653 multitrait analysis, 2: 652 production evaluation models, evolution, 2: 651 survival analysis, 2: 653 Genetic mouse models, 2: 641–642 Genetic resistance phages, 1: 442 Genetics conversion equations, 2: 669–670 improvements, sheep breeding, 2: 73 polymorphisms, goat caseins, 3: 486–487 quantitative, 3: 968–969 selection see Genetic selection sequencing, used in bacterial taxonomy, 3: 46–47 trait categories, 2: 656–657 conformation traits, 2: 656–657, 2: 658 fertility and udder health, 2: 658 genetic correlations, 2: 659–660 longevity, 2: 656–657 milk production, 2: 657, 2: 882 Genetic selection, 2: 646–648 accuracy, 2: 646 sib performance-based, 2: 623 additive genetic inheritance, 2: 647 breeding strategies, 2: 647 crossbreeding, 2: 647 dairy cattle objectives, 2: 647 embryo transfer, 2: 629 inbreeding management, 2: 647, 2: 661 concepts, 2: 646–648 DNA technology, 2: 654 dominant alleles, 2: 647 evaluation systems see Genetic evaluation systems female superior trait techniques, 2: 623 genetic change prediction, 2: 646 genetic evaluation indexes, 2: 656–662 genetic gain computation, 2: 647 pathway comparisons, 2: 648, 2: 648t goals, 2: 649 historical knowledge/practices, 2: 646 identification systems, 2: 649 international evaluation, 2: 653 male superior trait techniques, 2: 623 mastitis resistance, 3: 429 methods, 2: 649–655 multiple trait improvement programs, 2: 880–881 recessive alleles, 2: 647 traits, 2: 650 fitness, 2: 650 functional, 2: 650 Genetic variants/polymorphism identification, MS, 1: 201 Gene-Trak, 1: 217 Gene transcription, 3: 1056 Genome 10K, 3: 966 Genome sequences bacteriophages, 1: 434 NSLAB, 1: 643t
881
starter cultures, 1: 565 Genomic estimated breeding values (GEBVs), 2: 666–667 accuracy, 2: 667, 2: 667t Genomic evaluations, 2: 659, 2: 661 Genomics, 2: 663–668 fatty liver, 2: 222–223 future developments, 2: 668 starter cultures, 1: 565 Genomic selection, 2: 666, 3: 969 dairy breeding program timelines, 2: 667, 2: 667t inbreeding, 2: 667 Genootschap ter Bevordering van Melkkunde (Netherlands Association for the Advancement of Dairy Science), 2: 102 Genotoxic carcinogens, 1: 887–889 Genotoxicity tests, 1: 57 Gentamicin-resistant Enterococcus, 3: 155 Geobacillus biofilms, 1: 446, 1: 448 Geological time scale, 3: 321t Geometry,cheese salting, 1: 604 Geotextile pads, 2: 21 Geotrichum, taxonomy, 4: 765, 4: 766t Geotrichum candidum, 1: 567, 1: 627, 4: 765–771 amino acid catabolism, 4: 768 ammonia production, 4: 769–770 applications, 4: 769 acid-coagulated cheeses, 4: 770 cultures, 4: 769 mold-ripened cheeses, 4: 769 safety assessment, 4: 770 arthrospores, 4: 765, 4: 766f biochemical characteristics, 4: 768 deacidification, 4: 768 flavor-forming activities, 4: 768 lipolytic activity, 4: 768 proteolytic activity, 4: 768 cheese ripening, 1: 567, 4: 769 surface-ripened cheeses, 1: 567–568 culture method, 4: 770 media, 4: 770–771 enumeration, 4: 770 direct microscopic method, 4: 770 in situ quantification, 4: 770 extracellular aminopeptidases, 1: 568 extracellular proteinases, 1: 568 freezing stress. physiological adaptation, 4: 766 osmotic chemical pretreatment, 4: 766–768 habitat, 4: 765 hyphae, 4: 765, 4: 766f infection, 4: 770 isolate assimilation, 4: 766, 4: 767t lipase A, 1: 568 lipase B, 1: 568 mold morphotype, 4: 765 mold-ripened cheeses, 1: 773 morphology, 4: 765 overgrowth prevention, salting, 4: 769 Penicillium camemberti growth inhibition, 4: 769–770 Penicillium camemberti mixed culture, 4: 776–777 Penicillium roqueforti inhibition, 4: 775 physiology, 4: 765 salt tolerance, 4: 765–766 ‘slippery rind’ defect, 4: 769 smear-ripened cheeses, 1: 395, 1: 398–399, 1: 755, 1: 756, 4: 769 as spoilage organism, 4: 770 surface mold-ripened cheeses, 1: 775, 1: 776f aroma production, 1: 779–781 blue mold cheeses, 1: 769 cheese ripening, 1: 567–568 lipolysis, 1: 778 taxonomy, 4: 765 yeast morphotype, 4: 765 Geotrichum javanense, 4: 765 Gerber method, 1: 80, 1: 81t, 1: 82t German Butter Regulation, 3: 977–978
882 Index Germany cheese legislation, 1: 848 fat-in-dry matter content, 1: 848 dairy industry, 1: 10, 1: 10t, 1: 11t dairy products consumption, 1: 46, 1: 46, 1: 46t Fleckvieh cattle, 1: 293 Germ cells, heat stress, 4: 569–570 Germicidal teat disinfectants environmental mastitis prevention, 3: 419–420 teat dipping, 3: 433 Germinal vesicle (GV), 2: 617 Germinated barley foodstuff (GBF), as prebiotic, 4: 364 Gesellschaft f¨ur Milchwissenschaft (Society of Milk Science), 2: 103 Gestation, 4: 489 artificial insemination centers, 1: 470 Bos indicus cattle, 1: 300 buffalo, 2: 774 cattle, 4: 489 domestic animals, 4: 489t donkeys, 1: 370 end, progesterone and, 4: 507 horse, 4: 489 Ghee, 1: 517 applications, 1: 518 buffalo milk, 2: 778, 2: 783 color, 1: 518 definition, 1: 515 flavor, 1: 517–518 historical aspects, 1: 15 lactones, 1: 517–518 manufacturing technology, 1: 521 packaging, 1: 521 product characteristics, 1: 517 shelf life, 1: 518 texture, 1: 518 traditional manufacture, 1: 517 see also Anhydrous milk fat (AMF) Ghrelin, 1: 465 Giant anteater milk oligosaccharides, 3: 271t Giant panda milk oligosaccharides, 3: 271t Gibb free energy, 4: 257 Gingivitis, 3: 1038–1039 Gir cattle, 1: 300, 1: 301f, 1: 301t Latin American dairy management, 2: 91 Girgentana goats, 1: 315 ricotta cheese composition, 2: 65t Girolando cattle, 1: 303t, 1: 305, 1: 305f Glace aux oeufs, 2: 896 Gland cisterns, mammary gland, 3: 333 Glass bottles fluid milk, 4: 17 pasteurized milk, 3: 277 probiotic dairy foods, 4: 21 yogurt packaging, 4: 21 Glass electrodes, 1: 195 Glass transition, 4: 213 amorphous systems, 4: 214 food components, 4: 214t temperature, milk powder see Milk powder GLEWS (Global Early Warning System for Animal Disease including Zoonoses), 4: 4 Global Early Warning System for Animal Disease including Zoonoses (GLEWS), 4: 4 Global markets changes, 4: 348 commodity prices, 4: 348, 4: 349f future uncertainty, 4: 350–351 prospects, 4: 348 Globe valve, 4: 152, 4: 153f dairy processing, 4: 155, 4: 155f, 4: 155f Globotriose, 3: 251 Glucagon fatty liver, 2: 222 ketosis, 2: 231 milk protein synthesis, 3: 362 1,4--D-Glucan glucanohydrolase see -Amylase
1,4--D-Glucan maltohydrolase see -Amylase Glucansucrases, 3: 206 Glucocorticoids galactopoietic effects, 3: 30 induced lactation, 3: 21 ketosis, 2: 231 lactogenesis, 3: 17 in milk, 2: 770 stress response, 4: 576 Gluconeogenesis fatty liver, 2: 220–221 ketosis see Ketosis precursors, 2: 234 pregnancy, 2: 247 -Glucosamine hydrochlorate, 3: 193 Glucose active transport system, 3: 367 in blood, starch digestion, 3: 992 fetal requirements, 2: 246–247, 2: 247t as prebiotic, 4: 361t pregnancy toxemia, 2: 248 Glucose–galactose syrups, 3: 178 Glucose isomerase (GI), 2: 302 Glucose oxidase (GO) catalytic activity, 2: 301 in food products bactericidal hydrogen peroxide generation, 2: 302 oxygen scavenging activity, 2: 302, 2: 302 trace glucose removal, 2: 302, 2: 302, 3: 212 yogurt acidification, 2: 302 Glucose transporters (GLUTs), 3: 367 -Glucosidase, Cronobacter, 4: 76 Glucosyllactose, 3: 206 Glutamate dehydrogenase (GDH), Lactobacillus, 3: 87–88 Glutamic acid, 1: 771–772, 3: 625–627 Glutamyl aminopeptidase (PepA) enzyme-modified cheese, 1: 802–803 LAB, 3: 87 Glutamyl endopeptidase (GE), 2: 293 Glutathione colon cancer risk, 3: 1020, 3: 1020f, 3: 1021f, 3: 1065 depletion, whey protein effect, 3: 1065 Glutathione reductase, 4: 704 Glycation, MS, 1: 201 Glycerol as cryoprotectant, frozen gametes/embryos, 2: 606, 2: 629 structure, 3: 665, 3: 666f Glycerol phospholipids, 3: 670 Glycerophospholipids, 3: 650 fatty acid composition, 3: 672 Glycine max see Soybean(s) Glycocalyx see Exocellular polysaccharides (EPS) Glycoceramides see Glycosphingolipids Glycodelin, 3: 791t, 3: 791–792, 3: 836–837 Glycolactin, 3: 758 Glycolipids biological functions, 3: 670 as emulsifiers, 1: 64 structure, 3: 670, 3: 672f Glycomacropeptide (GMP), 3: 769–770, 4: 731 whey protein isolates, 3: 875, 3: 876t whey protein products, 3: 876, 3: 876t Glycosphingolipids, 3: 651 anticancer properties, 3: 1062 first-age infant formulae, 2: 141 health benefits, 3: 695 milk fat globule membrane, 3: 681t, 3: 682 structure, 3: 670, 3: 672f Glycosylation, MS, 1: 201 Glycosylhydrolases, 3: 206 -Glycosyltransferase humans, 3: 251 tammar wallaby, 3: 251 Glycosyltransferase(s), 3: 206 humans, 3: 251
Goat(s), 1: 310–324 abortion, 2: 840 acidosis, 2: 793–794 Africa, 1: 322 agricultural waste fodder, 2: 824 Alpine breed, milk ejection kinetic curves, 2: 807, 2: 807f artificial insemination usage, 4: 473–474 Asia, 1: 318 barn milking, 2: 804, 2: 805f biological advantages, 2: 816 bovine somatotropin treatment, 3: 36 breeding management, 2: 834 adult doe management, 2: 834 age at puberty, 2: 834 culling, 2: 834 estrus synchronization, 2: 835, 2: 835t nutrition, 2: 834 replacement doe management, 2: 834 breeding period, 2: 839 dairy breeds, 1: 310, 1: 311t dual purpose breeds, 1: 311t Swiss breeds, 1: 313 see also specific breeds brucellosis, 2: 154 control, 2: 158 -casein null allele, 3: 833 Central Europe, 1: 310 chorioptic mange, 2: 251 cisternal milk, 2: 807 classification, 2: 814 clusters, 2: 808 s1-Cn0 allele, 3: 758–759 crude protein requirements, 2: 410 dairy breeds, 1: 310, 1: 311t dietary imbalance disorders, 2: 793, 2: 800 distribution, 1: 310, 2: 785, 2: 814 domestication, 2: 814, 3: 326, 3: 459 dual purpose breeds, 1: 311t economic contribution, 2: 814, 2: 815t embryo transfer, 2: 836 estrous cycle, 4: 426 extensive production systems, with sheep, 2: 70 feeding habits, 2: 816, 2: 817f, 2: 817f, 2: 817f, 2: 817f feeding management, 2: 785–796 bucks, 2: 787t, 2: 792, 2: 793t feedstuffs, 2: 789, 2: 792, 2: 792, 2: 792t lactating animals, 2: 791, 2: 792t life cycle feeding, does, 2: 787t, 2: 790, 2: 791t, 2: 793t milk composition effects, 2: 795, 3: 489 nutrient requirement affecting factors, 2: 789 nutrients, 2: 785 nutritional adequacy assessment, 2: 789 pregnancy, 2: 790–791 young animal growth, 2: 790, 2: 828, 2: 829t, 2: 830t field milking, 2: 804 foot-and-mouth disease, 2: 163 as future investment insurance, 2: 818–819 gestation management, 2: 839 health management, 2: 797–803 biosecurity program development, 2: 797 buck health, 2: 801 drug residues, avoidance in products, 2: 802 economically serious diseases, 2: 797 reproductive manipulation (for winter milk), 2: 801 routine health practices, 2: 797 specific pathogen prevention programs, 2: 799, 2: 799t transmission biosecurity, 2: 800 husbandry-affecting factors, 2: 822 family status, 2: 823 farmer socioeconomic conditions, 2: 823 flock size, 2: 819t, 2: 823 housing, 2: 823 labor requirements, 2: 823
Index land holding size, 2: 822 husbandry systems (Europe), 2: 59 Johne’s disease, 2: 798–799 ketosis, 2: 794, 2: 800–801 lactation feeding requirements concentrates, 2: 791, 2: 792, 2: 792t nutritional intake, 2: 791t, 2: 791–792 listeriosis, control, 2: 188 management objectives, 2: 818 meat, fiber and milk, 2: 818 meat and fiber, 2: 818 milk, 2: 818, 2: 818f management systems, 2: 819, 2: 819t breed and, 2: 820t extensive system, 2: 822, 2: 823 hobby goat-keepers, 2: 819 intensive system, 2: 819 semi-intensive system, 2: 822 subsistence, 2: 817f, 2: 819 mastitis, 2: 802 mating management, 2: 839 meat see Chevon Mediterranean region, 1: 315 migration, 2: 822 migration stress, 2: 822 milk see Goat milk milk fever, 2: 242 milking ability, 2: 806 milking machine requirements, 2: 807 air lines, 2: 810 automatic cluster removal systems, 2: 812, 2: 812f cluster assembly, 2: 811, 2: 811f, 2: 811f effective reserve, 2: 807, 2: 809f, 2: 809t milklines, 2: 810, 2: 811f, 2: 811t pulsation characteristics, 2: 808, 2: 809t sizing pipes, 2: 810 vacuum levels, 2: 809, 2: 810t vacuum pump capacity, 2: 808 milking parlors see Milking parlors milking routine, 2: 812 milk installations size, 2: 804 types, 2: 804, 2: 805t multipurpose management, 2: 814–824 North America, 1: 314 Northern Europe, 1: 310 nutrition-related diseases, 2: 793, 2: 800 Oceania, 1: 318 origins, 2: 814 as pack animals, 2: 818–819 predation susceptibility, 2: 841 predator control see Predator control, goats and sheep pregnancy detection, 2: 839, 2: 839t ultrasound, 4: 490 pregnancy losses, 2: 840 prepurchase procedures, 2: 799 product consumption, 2: 785 production systems see Goat production systems profitability, 2: 816 protein metabolism, 2: 786 quarantine procedures, 2: 799 religious rituals, 2: 818–819 replacement management, 2: 825–833 bucklings, raising, 2: 828 doelings, feeding, 2: 790, 2: 828, 2: 830t feeding neonates, 2: 826 housing environment, 2: 831 internal parasites, 2: 831 kid health, 2: 801, 2: 828 kid management practices, 2: 832, 2: 832f, 2: 832f neonatal care, 2: 825 prenatal care, 2: 825 reproduction, fundamental concepts, 2: 834 reproductive health program, 2: 840 reproductive management, 2: 834–840 reproductive nutritional requirements, 2: 789 dry period, 2: 790
pregnant ewes, under/overfeeding, 2: 882 transition period, 2: 790 seasonal breeding, 4: 445 genetics, 4: 445 shelters, 2: 815f, 2: 815–816, 2: 816f, 2: 816f, 2: 816f soil-plant-goat relationship, 2: 817 sphincter tonicity, 2: 809–810 stall-feeding breed suitability, 2: 819 flock size, 2: 821 stocking rates, 2: 817 vaccination see Vaccine/vaccination zoonotic diseases, 2: 802, 2: 803t see also Buck(s); Kid(s); specific breeds Goat colostrum oligosaccharides, 3: 258 chemical structures, 3: 271t Goat–farmer/management interaction, 2: 823 Goat-herd, semi-intensive management systems, 2: 822 Goat-keeping, economics, 2: 815 Goat milk, 3: 484–493 amino acids, 3: 486, 3: 487t aroma, 3: 485, 3: 491, 3: 491 breed variation, 3: 490, 3: 490t carbohydrates, 3: 484 s1-casein genetic polymorphism, 3: 832, 3: 837f s1-casein phenotypes, 3: 832 cheeses see Goat milk cheeses composition, 2: 795, 2: 815, 2: 815t, 3: 484, 3: 485t dual-binding model for micelle assembly and structure, 3: 778 Enterobacteriaceae, 4: 68 enzymes, 3: 488 fatty acids, 2: 62t flavor, 3: 485, 3: 491, 3: 491, 3: 491 heat stability, 2: 749 khoa, 1: 882–883 lactoperoxidase, 2: 322 lipids, 3: 485, 3: 486t lipoprotein lipase distribution, 2: 305 management, 2: 804–813 milk allergy, 3: 365, 3: 1042–1043, 3: 1044 milk protein cross-reactivity, 3: 1044 minerals, 3: 488, 3: 488t monoterpene composition, 2: 62t nonprotein nitrogen compounds, 3: 488 nucleosides, 3: 973, 3: 973t off-flavors, diet-related, 2: 795 oligosaccharides, 3: 271t physical properties, 3: 484, 3: 485t proteins, 3: 486, 3: 487t, 3: 488 raw, salmonellosis outbreaks, 4: 94 sesquiterpene composition, 2: 62t terpene composition, 2: 61t therapeutic properties, 3: 491 variability, 3: 489 breed, 3: 490, 3: 490t diet, 3: 489 genotype, 3: 491 lactation, 3: 489, 3: 489f, 3: 489f vitamins, 3: 488t, 3: 489 volatile organic compounds, 2: 65, 2: 65t worldwide production, 2: 804, 3: 484, 3: 485t xanthine oxidoreductase, 2: 326 yields, 1: 312t influencing factors, 3: 489 Goat milk cheeses, 3: 491, 3: 492t salmonellosis outbreaks, 4: 94 volatile organic compounds, 2: 61t Goat production systems, 2: 59–66 breeds, 2: 64 intensive models, 2: 64–65, 2: 65t feeding system, 2: 60 degree of antioxidant protection (DAP), 2: 62–63, 2: 63f extensive, 2: 60–61 fatty acids, 2: 61–62, 2: 62t flavonoids, 2: 63, 2: 64t
883
plant metabolites in, 2: 63, 2: 64t pollutants, 2: 63–64, 2: 64t quercitins, 2: 63, 2: 64t sedentary/confined, 2: 60–61 supplements, 2: 61, 2: 62t terpene contamination, 2: 60–61, 2: 61t vitamins, 2: 62–63, 2: 63t volatile organic compound contamination, 2: 61, 2: 61t feeding systems, -tocopherol and cholesterol content, 2: 63t historical aspects, 2: 59 intensive models, 2: 59–60 breeds, 2: 64–65, 2: 65t grazing behavior, 2: 65 management, 2: 60 objectives and regulations, 2: 60 pastoral models, 2: 59–60 types of system, 2: 60 see also specific systems Goiter, 2: 380, 3: 939 Golden timothy (setaria, Setaria sphacelata), 2: 577 Gold’n Flow process, 3: 708, 3: 708f Golgi apparatus, milk protein secretion, 3: 377 Gonadotropin(s) ovarian secretion control development, 4: 424 postpartum, 4: 434 superovulation response treatment, 2: 624 reference estrus timing, 2: 625 Gonadotropin-releasing hormone (GnRH) estrous cycle, 4: 429–430 estrus synchronization heifers, 4: 413, 4: 414f noncyclic cow treatment, 4: 452 progestogens and, 4: 451f, 4: 452 prostaglandin and, 4: 413, 4: 414f, 4: 451f, 4: 452 function, 4: 422 ovarian follicular cysts, 4: 438–439 Ovsynch procedure, 4: 454 pulsatile release, 4: 422 seasonal breeders, 4: 442–443 secretion, 4: 575 Good farming practice (GFP), 2: 680 Dutch quality assurance program (CQM), 2: 680–681 on-farm and farm-related application, 2: 681 Goose-type (g) lysozyme, 2: 331 Gordon–Taylor model, 4: 214 Gorgonzola, surface yeasts, 4: 751 Gorilla colostrum oligosaccharides, 3: 271t Gorilla milk oligosaccharides, 3: 615–616, 3: 617t chemical structures, 3: 271t proteins, 3: 622t Gossypol, 2: 349 Gouda cheese, 1: 721 ripening, 1: 724 starter cultures, 1: 555 Gouda-type enzyme modified cheese, 2: 287 Government regulations, management records, 1: 491 Graduate careers, 2: 3, 2: 3t Grain (feedlot) bloat, 2: 206 Grain milks, 2: 914 Grains, 2: 335–341 composition, 2: 336, 2: 337t, 2: 389, 2: 390t livestock production significance, 2: 335 processing, 2: 335–336, 2: 338, 2: 338f production, 2: 336, 2: 337t ruminant nutritional utilization, 2: 338, 2: 339t uses, 2: 336, 2: 337t Gram-negative bacteria biofilms, 1: 446–447 biogenic amines, 1: 452 lactoferrin, bacteriostatic effects, 3: 803 Gram-negative organism mastitis, 3: 418 dry period, 3: 416 ‘Grana’ cheeses, 1: 728 cattle nutrition, 1: 728–729
884 Index ‘Grana’ cheeses (continued ) milk fat content, 1: 728–729 natural starter, 1: 728–729 ripening, 1: 728–729 see also Grana Padano; Parmigiano Reggiano Granadina goats, 2: 64–65 Grana Padano cheese, 1: 728 characteristics, 1: 730t composition, 1: 729t lipolysis, 1: 735–736 lysozyme addition, 1: 728–729 production statistics, 1: 729t Granuloma (tubercles), 2: 195 Grass(es) choice of cultivar differences, 2: 582–583, 2: 583f environmental adaptations, 2: 581–582, 2: 582t as forage, 1: 3 growth characteristics cool season annuals/short-rotation types, 2: 555, 2: 565 temperate pasture perennials, 2: 576 tropical pasture perennials, 2: 577, 2: 599 warm season annual crops, 2: 553, 2: 564 tiller density, in pastures, 2: 598–599 Grass–clover pasture, nitrogen responsiveness, 2: 588 Grassland yak, 1: 345 Grass staggers see Grassy tetany Grassy tetany, 2: 224–229, 2: 589, 3: 997–998 clinical symptoms, 2: 224 etiology, 2: 224 reduced magnesium absorption, 2: 225 sodium deficiency, 2: 227 forage quality control, 2: 574 goats, 2: 795 magnesium absorption impairment, 2: 225 dietary factors, 2: 226 magnesium deficiency, 2: 225 magnesium supplements, 2: 457 nitrogen, effects of, 2: 227 occurrence, 2: 224 pasture potassium levels, 2: 595, 2: 597–598 prevention, 2: 228 treatment, 2: 228 Gravimetric solvent extraction methods, 1: 80 Gravitational separation, centrifugal separation vs., 4: 176 Gravity belt thickener, 4: 629t Gravity creaming, 3: 677 Gravity traps, 4: 634 Gray box model (hybrid modeling) see Knowledgebased hybrid modeling (KBHM) Grazing buffaloes, 1: 342 clover-dominant swards, 2: 32 management see Grazing management milk yields, 2: 32 non-seasonal/pasture-based management, 2: 47 efficiency, 2: 47 pasture allowance-herbage intake relationship, 2: 32, 2: 32f rotational see Rotational grazing ryegrass-dominant swards, 2: 32 waste management, 3: 394 yaks, 1: 344 Grazing management, 2: 594–601 annual forages, 2: 570 farming decisions, 2: 600 global variation, 2: 594 developing countries, multipurpose sheep, 2: 880 pastoral systems comparison, 2: 879, 2: 880t transhumance and nomadic livestock farming, 2: 879 pasture plants growth, 2: 594 survival, 2: 594 unbalanced use effects, 2: 879 temperate C3 pastures, 2: 594
controlled (intermittent) grazing, 2: 595 grazing regime comparison, 2: 599 pasture growth monitoring methods, 2: 599 set (continuous) stocking, 2: 594 tropical C4 pastures, 2: 599, 2: 600f controlled grazing, 2: 599 water-soluble carbohydrate reserves, 2: 596, 2: 596f immediately after grazing, 2: 596 maximum grazing interval, 2: 597, 2: 598f minimum grazing interval, 2: 596, 2: 597f regrowth, vulnerable stage, 2: 596 zero grazing, North America, 2: 594 Grazing-to-shed farms, China, 2: 85 Grease, environmental impact, 4: 633 Great Apes milk fat content, 3: 616 gross composition, 3: 613–614, 3: 615t -lactoglobulin, 3: 624 proteins, 3: 621 Greek Native goats, 1: 317 Greek-style yogurts, 1: 47 ‘Green apple-like’ flavor defect, 3: 141 Green chopping (fodder crops), 2: 571 Green (acetaldehyde) flavor, 2: 492, 2: 535, 3: 170 Green forage, buffalos, 2: 781–782 Greenhouse gas emissions, 4: 635 reduction methods, 4: 635 Green panic (slender guinea grass), 2: 577 Grey Alpine cattle, 1: 297 milk records, 1: 297t Grey cattle, 1: 297 milk records, 1: 297t see also specific breeds Grimwade, T.S., 1: 14 Ground water contamination, manure, 3: 393 Group-specific protein (vitamin D-binding protein), 3: 796t, 3: 798, 4: 648 Growing-up milks, 2: 143 Growth factors colostrum, 2: 767, 2: 767t, 3: 595 in milk, 2: 767, 2: 767t molecular binding proteins, 2: 767–768 synthesis and secretion, mammary cells, 2: 766–767 Growth hormone see Somatotropin Gruy`ere cheese free fatty acids, 1: 771t pathogen status, 1: 659 ripening, propionibacteria, 1: 571 starter cultures, 1: 555 Gryta kettle, 4: 735 Guanaco (Lama guanicoe), 1: 351 Guanosine diphosphate (GDP)-mannose, 4: 667 Guar gums applications, 1: 70t as emulsifier, 1: 69t as fat replacer, 1: 531 flavored milks, 3: 305 Gubbeen cheese microbiology, 1: 396, 1: 397t yeasts, 1: 398t Guelma cattle, 1: 298 Guernsey cattle, 1: 286t, 1: 287, 1: 287f historical aspects, 1: 2 milk composition, 2: 53t stability/survival, 1: 290–291 Guidelines for the Production, Processing, Labeling and Marketing of Organically Produced Foods, 4: 10, 4: 11t Guillain–Barr´e syndrome, 4: 43–44 Guinea grass (Panicum), 2: 577 Gulf Cooperation Council (GCC), identity standards, 4: 323 Gulf standards, 4: 323 Gums see Hydrocolloids Gut microbiota see Gastrointestinal microflora Guzera cattle, 1: 301, 1: 301t, 1: 302f Latin America, 2: 91
H H2O2:H2O2 oxidoreductase see Catalase HACCP see Hazard Analysis and Critical Control Points (HACCP) technique Haflinger horses, 1: 358 Hafnia alvei, 1: 648, 1: 649f, 3: 451 Hagen–Poiseuille equation, 4: 140 Hairy heel warts see Papillomatous digital dermatitis (PDD) Half-fat butter, 1: 522 Halloumi cheese, 1: 792, 3: 501 HAMLET (Human -lactalbumin made lethal to tumor cells), 3: 782–783, 3: 838 Hammer, Bernard, 1: 31 Hand disinfection, mastitis prevention, 3: 432 Handkaese cheese, 1: 703 Hand milking historical aspects, 1: 6 sheep, 2: 871 yaks, 1: 347, 1: 347f Hand move irrigation system, 2: 591 Hand-operated water pump, 3: 942–943, 3: 943f Hand-powered pressure device, 3: 941, 3: 943f Haptocorrin (vitamin B12-binding protein), 3: 796t, 3: 798 Harbinson proposal, 4: 346 Harbor seal milk oligosaccharides, 3: 271t Hard cheese(s) classification, 1: 540–542 Enterobacteriaceae inhibition, 4: 70 folate content, 4: 680–681, 4: 683 as food ingredient, 1: 830 Italian see Hard Italian cheeses pathogens, 1: 648, 1: 648f yeasts, 4: 750 negative aspects, 4: 750 positive aspects, 4: 750 on surface, 4: 751 see also specific cheeses Hard-cooked cheeses, flavor, 1: 656–658 Hard Italian cheeses, 1: 728–736 characteristics, 1: 730t chemical features, 1: 728 Codex Alimentarius definition, 1: 728 composition, 1: 729t fat on dry matter basis, 1: 728 moisture on fat-free basis, 1: 728 lipolysis, 1: 735 exogenous lipases, 1: 735–736 free fatty acids, 1: 735–736, 1: 736t production statistics, 1: 728, 1: 729t proteolysis, 1: 733 casein hydrolysis, 1: 733f, 1: 733–734 free amino acids, 1: 734, 1: 734t ketones, 1: 734–735 molds, 1: 733 NSLAB, 1: 735 ripening, 1: 732 sodium chloride gradient, 1: 732 temperature, 1: 732 thermophilic LAB, 1: 733 starter cultures, 3: 108 technology, 1: 728 water-soluble nitrogen to total nitrogen, 1: 733f, 1: 733–734 see also specific cheeses ‘Hard (slow) milkers’, 3: 334, 3: 383 ‘Hardship groove’, laminitis, 2: 203 Harmonic filters, 4: 611 Harmonized Commodity Description and Coding System see Harmonized System (HS) Harmonized System (HS), 4: 324, 4: 331–337, 4: 331 alternative systems, 4: 332 amendments, 4: 332 chapters, 4: 332 combined nomenclature, 4: 335 dairy products, 4: 332 classification examples, 4: 334
Index classification principles, 4: 333 Heading 04.01, 4: 334 Heading 04.02, 4: 334 Heading 04.03, 4: 335 Heading 04.04, 4: 335 Heading 04.05, 4: 335, 4: 335 highest code principle, 4: 334 mixed products, 4: 334 subdivisions, 4: 335 tariff nomenclature code, 4: 333 Harmonized Commodity Description and Coding system, 4: 331 historical basis, 4: 331 structure, 4: 332 tariff purposes, 4: 333 Harmonized System Committee, 4: 331 43rd Session, 4: 332 responsibilities, 4: 332 Harmonized System Convention, 4: 331 Harp seal milk, 3: 580 Harrison, Ruth, 4: 727 Harzer cheese, 1: 703 microbiology, 1: 756, 4: 751 Hastelloy C276, 4: 136 Hay contribution to milk flavor, 2: 542 feedstuffs for goat kids, 2: 827–828, 2: 829t, 2: 830t harvesting, 2: 571 nitrogen removal, 2: 590 phosphorus removal, 2: 590 potassium removal, 2: 590 preweaning consumption, 4: 401 Hay balers, 1: 5 Hazard, 4: 532 Hazard analysis, 4: 532 Hazard Analysis and Critical Control Points (HACCP) technique biosensors, 1: 246 control measures, 2: 688 corrective measures and monitoring, 2: 683 critical control point determination, 2: 682f, 2: 688t, 2: 690 dairy farms, 2: 681 dairy processing applications, 2: 687 decomposition diagram, 2: 681 documentation, 2: 692 effective process control development, 2: 691 cause and effect analysis, 2: 691 corrective actions, 2: 691 critical limits, 2: 691 preventative system, 2: 691 verification procedures, 2: 691–692 hazard identification, 2: 681, 2: 688 historical aspects, 2: 687 pathogen control in cheese, 1: 649 pest control programs, 4: 540 process design identification, 2: 688 process flow chart (PFC), 2: 687, 2: 688f symbols, 2: 689f processing plants, 2: 687–692 product specification, 2: 687 epidemiological data, 2: 688 hazard identification, 2: 688 intended product usage, 2: 688–690 raw milk cheese production, 1: 659–660 risk assessment, 2: 690 consequence severity scores, 2: 690t occurrence frequency scores, 2: 690t seven principles, 2: 687 steps, 2: 687 system description documents, 2: 687 team selection, 2: 688 total assessed risk, 2: 690 matrix, 2: 691t worksheet, 2: 688t Hazard and Operability (HAZOP) analysis, 2: 688, 4: 278 Hazel approach, genetic evalution, 2: 656
HCB (hexachlorobenzene) contaminant, 1: 889 Headspace analysis cheese flavor assessment, 1: 677–678, 1: 680 Domiati cheese, 1: 794 Feta cheese, 1: 794 gas chromatography, 1: 174–175 ‘‘Health and wellness’’, trends in, 1: 41 Health aspects consumer perceptions, 1: 44, 1: 44f milk see Milk new product launches, 1: 42, 1: 42 Health indices, body condition score, 1: 463 Health Professionals Study, cardiovascular diseasevitamin E relationship, 4: 658 Heart attack, 3: 713 Heart disease, milk xanthine oxidoreductase, 2: 326 Heat abatement systems, 1: 4 Heat-coagulated cheeses, 1: 540–542 Heat coagulation temperature, 2: 744–745 Heat coagulation time (HCT), 2: 744–745, 2: 745f equine milk, 3: 523 Heat detection conception rate, 4: 483, 4: 483t historical aspects, 1: 7 improvement, 4: 476 records, 4: 477 submission rate monitoring, 4: 477 technological aids, 4: 477 Heat detection patches, 4: 478 Heat exchangers, 3: 284, 3: 285f, 4: 184–192 batch swept-surface, 2: 902–903 booster pumps, 4: 186 continuous flow sterilization, 2: 721–722 design, 4: 187 media viscosity, 4: 187 partition material, 4: 187 partition shape, 4: 187, 4: 187f partition thickness, 4: 187 dimensioning data, 4: 185 cleanability requirements, 4: 188 liquid physical properties, 4: 185 permitted pressure drop, 4: 186 product flow rate, 4: 185 running time requirements, 4: 188 temperature change, 4: 185, 4: 185f temperature program, 4: 185 external holding cell, 4: 188 length, 4: 188–189 heat transfer area calculation, 4: 185 heat transfer coefficient, 4: 186 flow rates, 4: 188 fouling matter presence, 4: 187 holding, 4: 188 time calculation, 4: 188 logarithmic mean temperature difference, 4: 186 low-temperature screw extruders, 2: 902 plate systems, 3: 284–285, 3: 285f regeneration, 4: 188 percentage, 4: 188 scraped surface, in ice cream making equipment structure, 2: 901–902, 2: 902f operation, 2: 902, 2: 903f principles and objectives, 2: 901, 2: 903 selection, 4: 126 temperature differential, 4: 186 cocurrent flow, 4: 186, 4: 186f countercurrent flow, 4: 185f, 4: 186 temperature profile, 4: 185f temperature–time pattern, 2: 720f, 2: 721 thermization uses, 2: 693, 2: 697 tubular systems, 3: 285, 3: 285f types, 4: 126, 4: 189 see also individual types Heat generation, 4: 589–595 control techniques, 4: 592 attemperation, 4: 593 water vapor pressure, 4: 593 cow performance effects
885
postpartum period, 4: 562 prepartum period, 4: 562 stolchlometry, 4: 592 ‘Heatime’, 4: 462–463 Heat-induced coagulation, 2: 748 Heat loss, 4: 550 Heat processing, protein denaturation, 1: 261, 1: 261f Heat recovery, 4: 184 Heat shock adjunct cultures, 1: 797 LAB, 3: 62–63 Heat stability, milk, 2: 744–749 additives, 2: 746 assessment, 2: 744 compositional factor effects, 2: 745 composition dependence, 3: 482 heat-induced changes, 2: 747 historical aspects, 2: 744 homogenization, 2: 746–747 interspecies comparison, 2: 749 macro-components, 2: 745–746, 2: 746f milk powder, 2: 122 milk salts, 2: 745 pH, 2: 745, 2: 746f, 2: 748 preheating, 2: 746–747 processing factor effects, 2: 746 seasonal variations, 3: 605 temperature-dependent kinetic data, 2: 719t viscosity, 2: 744–745 Heat-stable cellulose derivatives, 3: 302 Heat stress adaptation, multipurpose sheep, 2: 876, 2: 876–879 Bos taurus cattle, 4: 444–445 breed differences, 4: 567, 4: 569t bull management, 1: 478 cow performance effects, 4: 561 postpartum period, 4: 562 prepartum period, 4: 562 cow response measurement, 4: 561 dry matter intake, 4: 562 early lactation, feed intake, 4: 563 environment defined, 4: 561 estrous behavior, 4: 465 estrus detection, 4: 571 estrus expression, 4: 567 evaluation, by temperature humidity index (THI), 3: 42–43 feeding patterns, 4: 563 feed intake decreases, 4: 567 fertility, 4: 567, 4: 568f periovulatory period, 4: 568 restoration, 4: 572 fetal growth, 4: 569, 4: 569t LAB, 3: 63, 3: 65f libido, 4: 570 management, 4: 570 environmental modifications, 4: 570, 4: 571f herd management, 2: 19 housing systems, 4: 570–571, 4: 571f warm climate farms see Farm design (warm climates) metabolic responses, 4: 561, 4: 565f milk composition effects, 4: 561–566 fatty acids, 4: 565 milk fat concentration, 4: 564, 4: 564t milk protein concentration, 4: 565 potassium content, 4: 565 milk production effects, 4: 561–566, 4: 564t milk protein synthesis, 3: 362–363 milk yield, 4: 567 post-calving, 4: 569 night cooling and, 4: 563 peak heat production, 4: 563 placental dysfunction, 4: 500–501, 4: 501f placental function, 4: 569 Propionibacterium, 1: 407 rectal temperature, 4: 561, 4: 562f reproductive effects, 4: 567–574
886 Index Heat stress (continued ) embryo survival improvements, 4: 572 female, 4: 567 genetic selection, 4: 573 lactating vs. nonlactating animals, 4: 567, 4: 568f males, 4: 569 reproductive process suppression, 4: 440–441 respiratory alkalosis, 4: 565 respiratory rate, 4: 561, 4: 562f ruminal acidosis, 4: 564 ruminal contractions, 4: 564–565 semen quality, 4: 569, 4: 570f, 4: 570t somatic cell count, 4: 565 synchronized ovulation, 4: 571–572 warm climate feed pads, 2: 19 water buffalo, 4: 445 water consumption, 4: 563t, 4: 563–564 Heat transfer, 4: 184 direct, 4: 184 indirect, 4: 184, 4: 185f principles, 4: 184 theory, 4: 184 Heat treated fermented milks, 4: 328 Heat treatment acid-coagulated cheeses, 1: 698–699 biofilm development, 1: 447–448 cheese manufacture, 1: 549 curd syneresis, 1: 593 efficacy, biosensors, 1: 243 enzyme-modified cheese, 1: 800–801 khoa, 1: 883 low-fat cheese moisture content, 1: 834–835 milk, 2: 480–481, 3: 307 acceptance, 2: 725, 2: 725 flavors, 3: 281 lysozyme inactivation, 2: 515–516 nutritional value loss, 2: 719–720 off-flavors, 3: 281 processing condition optimization, 2: 715 process types, 3: 310 quality assay methods, 3: 231, 3: 232 reliability, 2: 725, 2: 725 safety assay methods, 3: 231, 3: 232 thermization see Thermization milk/cream rheology, 4: 522 milk powder manufacture, 2: 110–111 milk protein allergenicity reduction, 3: 1043 outcomes, lines of equal effects, 2: 719–720, 2: 720f rennet milk coagulation, 1: 583 yogurt rheology, 4: 527 HeatWatch software, 4: 478 HeatWatch system, 4: 463–464, 4: 464f silent ovulation, 4: 464–465 Heat waves, heat stress, 4: 563 Heel warts see Papillomatous digital dermatitis (PDD) Heifer(s) ad libitum intake, 4: 408 average daily gain, 4: 406–407 body weight:wither height proportions, 4: 391–392 breeding body weight, 4: 412 breeding management, 4: 412 conception rates, 4: 413–414 breeding program, recommended age, 4: 412 breeding standards, 4: 410–416 milk yield, 4: 411 breeding systems, seasonal, 4: 412 cold stress, 4: 407, 4: 552, 4: 553t, 4: 553t confinement rearing systems, 4: 406 byproduct feeds, 4: 406, 4: 407t deworming, 4: 419 dry matter intake, 4: 393 temperature effects, 4: 407 estrous cycle, 4: 411, 4: 411f estrus, 4: 411 feed efficiency, 4: 407 housing type, 4: 407–408 feeding programs bred age heifer, 4: 406
breeding age heifer, 4: 406 confinement systems, 4: 403 development, 4: 403 management considerations, 4: 407 tropical/temperate areas, 4: 403 grouping, 4: 407, 4: 418 growth diets, 4: 403–409 growth-influencing factors, 4: 407 environmental, 4: 407 growth management large breeds, 4: 404 small breeds, 4: 404 weaning to breeding, 4: 404, 4: 404t growth measurement, 4: 408 growth standards, 4: 390–395 body composition, 4: 390–391 height percentiles, 4: 391t uniform, adoption of, 4: 392 weight percentiles, 4: 391t mammary parenchyma growth, 3: 342 mastitis see Heifer mastitis nutrient requirements, 4: 390–395 dynamic model, 4: 393 energy, 4: 393 growth, 4: 392 large breeds, 4: 394t minerals, 4: 393 protein, 4: 393 small breeds, 4: 393t targeted growth concept, 4: 393 vitamins, 4: 393 overconditioned (fat), 4: 412 parturition, 4: 415 assistance, 4: 416 pasture-based systems, 4: 404 continuous vs. rotational grazing, 4: 405 energy requirements, 4: 405–406 environmental effects, 4: 405–406 land carrying capacity, 4: 405, 4: 405f parasite control programs, 4: 406 supplemental nutrition, 4: 405 pregnancy detection, 4: 414–415 pregnancy management, 4: 415 grow rates, 4: 415 profitable management, 4: 403 range management systems, 4: 404–405 rate of growth, 4: 392 mammary development, 4: 391–392, 4: 410–411 stair-step fashion, 4: 392, 4: 392t rearing program goal, 4: 390 reproductive cycle, 4: 411 weight measurement, 4: 408 weight target, 4: 392, 4: 392t weight targets, 4: 412, 4: 412t Heifer growers, 1: 8 rearing period goals, 4: 403 Heifer mastitis, 3: 438 dry cow treatment, 3: 438–439 prepartum therapy, 3: 438–439 treatment procedures, 3: 439 Heifer rearing, historical aspects, 1: 8 Helical agitators, 4: 160 Helicase-dependent amplification (HDA), isothermal PCR, 1: 223, 1: 223f Helicobacter pylori inhibition human milk oligosaccharide, 3: 255 milk fat globule membrane, 3: 695 Hemicellulose, rumen fermentation, 3: 983 Hemoglobin, yak, 1: 344 Hemolysin BL (HBL), 4: 26 Hemolytic–uremic syndrome (HUS), 4: 60–61 Hemorragic septicemia, buffalo, 2: 782 Hemotrophic nutrition, 4: 487–488 Hencky strain, 1: 275f, 1: 275–276 Henderson–Hasselbalch equation, 3: 474 Hen egg white lysozyme (HEWL), 2: 330–331 Heparin affin regulatory peptide (HARP), 3: 796t, 3: 797
Heparin-binding growth-associated molecule, 3: 796t, 3: 797 Heparin-binding growth factor 8, 3: 796t, 3: 797 Heparin-binding neurite-promoting factor, 3: 796t, 3: 797 Hepatic encephalopathy (HE), 3: 204 Hepatic ketogenesis, 2: 235 Hepatic steatosis see Fatty liver Hepatocytes, 2: 219f, 2: 219–220, 2: 220f Herbage, mechanical removal, 2: 590 Herbicide, direct drilling, 2: 586 Herbs Aspergillus flavus growth inhibition, 4: 789 butter, 1: 502–503 cheese see Cheese(s) definition, 1: 783 quality, 1: 783 spiced butter, 1: 502–503 Herd environments, environmental mastitis prevention, 3: 420 Herders (for flock protection), 2: 843 Herd health and production management (HHPM) programs, 2: 683, 2: 684f Herd health facilities, milking center, 3: 959 Herdlife (longevity) trait, 2: 650 Herdmate comparison, genetic evaluation, 2: 651 Herd size average, 3: 392 drylot management systems, 2: 52, 2: 53t Hereditary nonpolyposis colorectal cancer (HNPCC), 3: 1016 Hereford–Angus cattle birth, weaning and postweaning traits, 1: 290t carcass characteristics, 1: 290t puberty/pregnancy rates, 1: 291t reproductive/maternal traits, 1: 291t Herens cattle, 1: 298 Heritability, 2: 647 continuous marker estimates, 3: 430t definition, 3: 969–970 Herringbone (fishbone) milking parlors, 3: 960f, 3: 960–961 goats, 2: 804, 2: 805f historical aspects, 1: 6 Herringbones, warm climates, 2: 13, 2: 14f, 2: 15f, 2: 16f, 2: 16f Herschel–Bulkley equation cheese rheology, 4: 530 milks/cream rheology, 4: 524, 4: 525 sweetened condensed milk/dulce de leche, 4: 526, 4: 526 yogurt rheology, 4: 528, 4: 529 HETCOR (heteronuclear correlation spectroscopy), 1: 151 Heteroduplex panel analysis (HPA), Aspergillus flavus, 4: 788 Heterofermentative pathway, Leuconostoc, 3: 140 Heteronuclear correlation spectroscopy (HETCOR), 1: 151 Heteronuclear multiple-quantum coherence (HMQC), 1: 150, 1: 151f Heterooligosaccharides, 3: 202, 3: 209, 3: 211f Heterosis, 2: 647 Bos indicus Bos taurus cattle, 1: 308 Hexachlorobenzene (HCB), as contaminant, 1: 889 Hexamethylenetetramine (HMT), 4: 52–53 Hexanoic acids, 1: 772 Hexose oxidase, 2: 302 HFK-131 six-inch module, 3: 868 HIC (hydrophobic interaction chromatography), 1: 173 Hierarchical clustering (HCA) see Multivariate statistical tools High-concentrate, low-roughage diets, displaced abomasum, 2: 213 High-density lipoproteins (HDL), 3: 729 cholesterol content, 3: 1031 coronary heart disease risk, 3: 1031
Index low levels, 3: 713 functions, 3: 728t, 3: 729 metabolism defects, 3: 732 High-density lipoproteins (HDL)-cholesterol, premenopausal state, 3: 732 High-density polyethylene (HDPE) blow-molded bottles fluid milk, 4: 17 linear aseptic filler, 4: 22–23, 4: 23f pasteurized milk, 3: 277 High-density SNP arrays, 2: 664 High-efficiency particle air (HEPA) filters bulk starter tanks, 1: 441 spoilage mold control, 4: 781–782 High-ester pectin, 1: 69t High-fat powders, milk chocolate, 1: 860 High Heat Infusion system, 2: 702f, 2: 703 High-heat treatment, cheesemaking milk, 1: 549 High-methoxy pectin, flavored milks, 3: 302 High-moisture Mozzarella, 1: 745 functional characteristics, 1: 747 microbiology, 1: 748 High-moisture silage, 1: 3 High-performance liquid chromatography (HPLC), 1: 169, 1: 197 biogenic amine detection, 1: 455 butter fatty acids, 1: 506 casein, 3: 766, 3: 766f detection techniques, 1: 173 enzymes, 1: 173 folate analysis, 4: 680, 4: 682t infant formulae analysis, 2: 136 milk oligosaccharides, 3: 249 milk proteins, 3: 762 MS, 1: 199 lipid analysis, 1: 204 mycotoxin analysis, 1: 904–905 separation principles, 1: 170t triacylglycerol analysis, 3: 701 High-performance liquid chromatography and electro-spray ionization mass spectrometry (HPLC-ESI-MS), milk fat triacylglycerols, 3: 668 High-pH anion exchange chromatography with pulsed amperometric detection (HPEAC-PAD), milk oligosaccharides, 3: 249 High pipeline milking systems, milk free fatty acids, 3: 641, 3: 641t High-pressure food processing, 2: 732–737 benefits, heat treatment vs., 2: 732 chemical effects, 2: 734 commercial development, 2: 732 dairy products and processes, 2: 736 acid-set gels, 2: 736 cheese, 2: 736 infant milk whey proteolysis, 2: 737 yogurt, 2: 736 equipment and operation, 2: 733 fat components, effects on, 2: 736 microbiological effects bacterial spores, 2: 733 impact on milk shelf life, 2: 734 vegetative organisms, 2: 733 milk pasteurization, 3: 279 milk proteins, effects on casein, 2: 735 enzymes, 2: 735 whey proteins, 2: 735 process principles, 2: 732 water-related properties, effects on, 2: 734 High-pressure homogenization (HPH), 2: 726, 2: 755–760 biogenic amines, 1: 453 conventional valve equipment and operation, 2: 755, 2: 756f enzymes, effects on, 2: 757 equipment capacity, current, 2: 726, 2: 726, 2: 755 microfluidizers, 2: 726–729
milk proteins, effects on, 2: 757 physical phenomena of process, 2: 755 product microbiology, 2: 758, 2: 758f temperature increase, 2: 755, 2: 756–757 High-pressure homogenizers, 2: 751, 2: 751f High-pressure treatment biogenic amines, 1: 454 microstructure, 1: 232 High-producing cows, early embryo loss, 4: 478 High-shear agitators, 4: 160, 4: 161f High-speed blending and mixing devices, 2: 761 High-temperature–short time (HTST) pasteurization historical aspects, 1: 13 immunoglobulin activity, 3: 813 method, 3: 275 milk fat globule membrane, 3: 678–679 milk shelf-life, 4: 385t Mycobacterium avium paratuberculosis, 4: 90 pasteurizers see HTST pasteurizer principles, 3: 310–311 psychrotroph growth, 4: 384, 4: 385t safety, 3: 275–276 time–temperature conditions, 4: 193 waste milk pasteurization, 4: 397–398, 4: 398f High temperature short time system, 1: 441 High-vacuum distillation techniques, cheese flavor, 1: 676–677, 1: 677f High-viscosity agitators, 4: 160 High viscosity fluids, 1: 273–274 HILIC (hydrophilic interaction liquid chromatography), 1: 173 Hinterwald cattle, 1: 295 Hip height, as growth indicator, 4: 390 Hispanic cheeses, 1: 704 Histamine, 1: 451 characteristics, 1: 452t raw milk cheeses, 1: 658–659 Histiotrophic (histotrophic) nutrition, 4: 487–488, 4: 489 Histotrophic (histiotrophic) nutrition, 4: 487–488, 4: 489 HMB (2-hydroxy-4-(methylthio)butanoic acid) see Methionine hydroxy analog HMQC (heteronuclear multiple-quantum coherence), 1: 150, 1: 151f Holding yards, 2: 18 Holland see Netherlands Holo-lactoferrin, 3: 801–802 Holstein cattle, North American, 2: 669 Holstein Friesian cattle, 1: 286t, 1: 287, 1: 288f Australia, 2: 35 birth, weaning and postweaning traits, 1: 290t carcass characteristics, 1: 290t historical aspects, 1: 2 Latin American dairy management, 2: 91 majority use, 1: 290–291, 1: 291 milk composition, 2: 53t milk protein content, 3: 363 New Zealand, 2: 35 puberty/pregnancy rates, 1: 291t reproductive/maternal traits, 1: 291t reproductive outcomes, 4: 479f Holter equation, 1: 582 curd strength, 1: 588–589 Homeorhesis, 2: 427 Hominy feed, 2: 344 Homocysteine methyltransferase, 3: 87–88 Homogenization, 2: 750–754, 3: 678 applications, 2: 753 blue-veined cheeses, 1: 549 cheese analogues, 1: 820 cheese manufacture, 1: 549, 2: 759 chocolate milk, 3: 305–306 coffee cream manufacture, 1: 914 creaming, effects on, 3: 676–677 down-stream, 2: 754 efficiency, 2: 754 frozen desserts, 2: 901
887
heat stability, milk, 2: 746–747 high-pressure see High-pressure homogenization (HPH) historical aspects, 1: 13 ice cream, 2: 901 low-fat cheeses, 1: 834–835, 1: 838 microstructure, 1: 230 milk/cream rheology, 4: 522 milk fat globule membrane, 3: 678, 3: 692, 3: 692t milk property changes, 3: 678 milk surface tension, 3: 470 objectives, 2: 721–722, 2: 755 pasteurized processed cheese products, 1: 807 principal effect, 3: 678 principles, 2: 750 droplet particle size, 2: 755, 2: 756f emulsion energy density, 1: 61 significance of, 2: 753 sterilized products, 2: 721 sweetened condensed milk production, 1: 871 temperature, 2: 751 ultrasonic see Ultrasonic homogenization ultrasonication, 2: 742 whipping cream manufacture, 1: 915, 1: 915, 1: 923–924 yogurt, 2: 526, 2: 759, 2: 759 Homogenization index, 2: 754 Homogenized milk cholesterol reduction, 3: 736 foaming characteristics, 3: 678 Homogenized whole milk, 3: 611 Homogenizer pump, 2: 751 leakage, 2: 753 Homogenizers alternative technologies, 2: 761–764 design, 2: 751 location, 4: 127 pump pistons, 2: 751–752 selection, 4: 127 valves, 2: 751, 2: 752f see also individual types Homogenizing valve assembly, 2: 752, 2: 752f, 2: 753f Hong Kong Ministerial, 4: 346 Honolulu Heart Program, 3: 1024 Hooded seal lactation length, 3: 321 milk fat content, 3: 569–570 oligosaccharides, 3: 271t vitamins, 3: 580 Hoof artificial insemination centers, 1: 471 keratinization process, 2: 204–205 laminitis, 2: 203 Hoof health biotin supplementation, 2: 396–397 zinc supplements, 2: 384 Hoof injury, laminitis, 2: 204 Hooke models, 1: 268 Hooves see Hoof Hor (Godir) camels, 1: 352 Horizontal cheese vat, 1: 608, 1: 610f Horizontal committees (General Subject Committees), Codex Alimentarius, 4: 314 Horizontal tube natural circulation evaporator, 4: 201, 4: 202f Hormonal treatments, heat stress, 4: 572 Hormones contamination, 1: 893 analysis, 1: 894 natural hormones, 1: 893 occurrences, 1: 893 semisynthetic hormones, 1: 894 sources, 1: 893 synthetic hormones, 1: 894 human milk, 3: 583, 3: 584t immunochemical detection, 1: 180 mammogenic, 3: 339
888 Index Hormones (continued ) in milk, 2: 765–771 androgens, 2: 770 delivery mechanisms, 2: 766, 2: 766f discovery, 2: 765 estrogens, 2: 769 glucocorticoids, 2: 770 identification, 2: 765 peptide regulatory factors, 2: 767, 2: 767t physiological functions, 2: 765 progesterone, 2: 770 steroids, 2: 766–767, 2: 768, 2: 769t Horn-flies, 4: 419 Horns, kid disbudding, 2: 832 Horse(s), 1: 358–364 artificial insemination usage, 4: 474 breeds, 1: 358 milking, 2: 512 see also specific breeds colostrum see Equine colostrum digestive system, 3: 518 estrogen secretion, fetoplacental unit, 4: 507 feeding, 1: 359 geographic distribution, 1: 358 gestation length, 4: 489 husbandry, 1: 359 milk see Equine milk milking methods, traditional, 2: 515, 2: 515f milk production, 2: 512 seasonal breeding, 4: 447 photoperiod in, 4: 447 see also entries beginning equine Hortvet cryoscope, 1: 252 Hosing, warm climate feed pads, 2: 21 Hospital area, milking center, 3: 959 Hospital facilities, warm climate farms see Farm design (warm climates) Host cell lysis, bacteriophages, 1: 434 Host defenses enhanced by milk/colostrum, 3: 1063 see also Immunoglobulin(s) (Ig); Mammary gland Host factor elimination, bacteriophage resistance, 1: 437 Host resistance mechanisms, bacteriophages see Bacteriophage(s) Hotel farms, China, 2: 84 Hotelling’s T2 control charts, 4: 244 Hot oil liquid phase air heaters, spray drying, 4: 219–220 ‘Hot wells’, evaporated milk, 1: 863 Hot wire probe, 1: 588 Housefly, 4: 543 dairy replacements, 4: 420 Housing African dairy cow management see Cattle husbandry (Africa) cow comfort, 4: 559 environmental mastitis prevention, 3: 420 estrous behavior, 4: 465 heat stress management, 4: 570–571, 4: 571f non-seasonal/pasture-based management, 2: 45 reproductive efficiency, 4: 580 warm climate farms see Farm design (warm climates) see also individual housing types HPH see High-pressure homogenization (HPH) HPLC see High-performance liquid chromatography (HPLC) HPLC-Chip/MS technology, 3: 249 HR-3 test, raw milk, 3: 645 HTST pasteurization see High-temperature–short time (HTST) pasteurization HTST pasteurizer, 4: 194f flow patterns, 4: 194, 4: 195f holding section, 4: 196–197 homogenization, 4: 196, 4: 196f operation principles, 4: 194 parallel processing, 4: 196
passes, 4: 194–195 postpasteurization contamination, 4: 197 preheating/regeneration section, 4: 195 steam injection, 4: 196 Human(s) s1-casein transcripts, 3: 832 colostrum see Human colostrum encephalization quotient, 3: 614 milk see Human milk Human -lactalbumin made lethal to tumor cells (HAMLET), 3: 782–783 Human chorionic gonadotropin (hCG) mares, 4: 444 ovarian follicular cysts, 4: 438–439 Human colostrum cellular components, 3: 587, 3: 588t, 3: 588–589 composition, 3: 581, 3: 582t fatty acid composition, 3: 586, 3: 586t immunoglobulins, 3: 811 lactoperoxidase, 2: 320 lipids, 3: 585, 3: 586t minerals, 3: 586, 3: 587t nitrogen compounds, 3: 582–583, 3: 583, 3: 583t oligosaccharides, 3: 250 proteins, 3: 582–583, 3: 583, 3: 583t, 3: 591 secretory IgA, 3: 812 vitamins, 3: 586, 3: 587t Human–cow interaction, reproductive effects, 4: 581 Human degenerative photoreceptor disease, 2: 642 Human genome, 3: 1059 bovine genome sequence vs., 2: 663 Human Genome Project (HGP), 3: 966 Human intestinal epithelial cells (HIECs), 3: 257 Human milk, 3: 581–590 amino acids, 3: 581–582, 3: 582t, 3: 584 banking, 3: 590 benefits, 3: 581 bioactive factors and cells, 3: 581–582, 3: 587, 3: 588t, 3: 588t carbohydrates, 3: 209, 3: 213–214, 3: 585, 3: 585t caseins, 3: 624, 3: 758–759 components, 3: 581, 3: 582t composition, factors affecting, 3: 588 changes during feed/day, 3: 589 exercise, 3: 589 infant prematurity, 3: 588 maternal diet, 3: 589 nationality, age and parity, 3: 589 stage of lactation, 3: 581, 3: 582t, 3: 588 enzymes, 3: 583, 3: 584t, 3: 629 fatty acid composition, 3: 586, 3: 586t folate-binding proteins, 4: 684 folate content, 4: 680–681 free amino acids, 3: 625–627, 3: 627t heat stability, 2: 749 hormones, 3: 583, 3: 584t illness/metabolic disorder effects, 3: 589 drug use, 3: 589 immunoglobulins, 3: 811 lactoferrin, 3: 801, 3: 936 lipids, 3: 585, 3: 586t lysozyme, 3: 629 mammalian milks vs., 3: 583, 3: 585, 3: 587 mastitis effects, 3: 589 micronutrients, 3: 586, 3: 587t nonprotein nitrogen, 3: 583, 3: 583t nucleosides, 3: 973t total potentially available, 3: 974t, 3: 974–975 nucleotides, 3: 974, 3: 974t oligoosaccharides see Human milk oligosaccharides (HMOs) proteins, 3: 581, 3: 583t, 3: 622t, 3: 1043 alternatives, 3: 1043 composition, 3: 816, 3: 817t interspecies comparison, 3: 583, 3: 584 ribonucleosides, 3: 975 total amino acids, 3: 625, 3: 626t type 1 diabetes, 3: 589, 3: 1049
variability, 3: 581 vitamin A deficiency, 4: 638 vitamin C, 4: 668 vitamin E, 4: 653 vitamins, 3: 586, 3: 587t volume-influencing factors, 3: 588 xanthine oxidoreductase, 2: 326 Human milk lysozyme (HML), 2: 331 Human milk oligosaccharides (HMOs), 3: 173–174, 3: 615–616, 3: 617t, 4: 362 acidic, 3: 250, 3: 251t intestinal cell growth inhibition, 3: 257 P-selectin ligand binding reductions, 3: 256–257 structures, 3: 248t antiadhesion phenomena, 3: 255 antipathogenic effects, 3: 255 apoptosis, 3: 257 Bifidobacterium growth effects, 3: 253, 3: 253f in vitro studies, 3: 254 biosynthesis, 3: 251 brain stimulating activity, 3: 252 chemical structures, 3: 241, 3: 248t colonic fermentation, 3: 252 colostrum, 3: 250 composition, 4: 362 cord blood T cell activation, 3: 257 core units, 3: 241, 3: 248f cytokine production, 3: 257 degradation, 3: 254 first-age infant formulae, 2: 142 gastrointestinal absorption, 3: 251 intact, 3: 252 gastrointestinal digestion, 3: 251 immunomodulating effects, 3: 256 intestinal cell growth inhibition, 3: 257 lactation stage and, 3: 250–251 mature milk, 3: 250 neutral, 3: 250, 3: 250t intestinal cell growth inhibition, 3: 257 structures, 3: 248t nonhuman ape milk vs., 3: 616 prebiotic effects, 4: 362 quantitative aspects, 3: 249 respiratory disease prevention, 3: 256 selectin resembling, 3: 256–257 type I, 3: 241–249 Human ribonucleases (HmRNase) purification, 2: 333 Humicola fuscoatra, 4: 789–790 Humidity surface mold-ripened cheese ripening, 1: 781 Swiss-type cheese ripening, 1: 716 Humidity chart, spray drying, 4: 210, 4: 211f Humid vapor, 4: 589 specific volume, 4: 589, 4: 590f Hungary, Simmental cattle, 1: 294 Husbandry ancient systems, 2: 875, 2: 875 camels, 1: 353 donkeys, 1: 369 horses, 1: 359 intensification, 2: 880, 2: 881 nomadic pastoralism, 2: 876, 2: 876–879, 2: 879 predator control, goats and sheep, 2: 841–847 see also Confinement rearing; individual animals H-Y antigen detection, 2: 631 Hybrid bulls, 1: 308 Hybrid modeling (gray box model) see Knowledgebased hybrid modeling (KBHM) Hybrid ryegrass (Lolium perenne L. multiflorum), 2: 556 Hydranencephaly, bluetongue virus infection, 2: 149–150, 2: 150f Hydrochlorofluorocarbon (HCFC) refrigerants, 4: 599 Hydrocolloids (gums), 1: 67, 1: 69t, 1: 70t as additives, 1: 35 cheese analogues, 1: 815t, 1: 818 creaming rate reduction, 1: 63, 1: 67 dairy applications, 1: 67, 1: 70t
Index dairy desserts, 2: 908, 2: 909t as fat replacer, 1: 531 heat stability, milk, 2: 746–747 ice recrystallization, 4: 712 properties, 1: 67, 1: 69t sources, 1: 67, 1: 69t Hydrofluorocarbon (HFC) refrigerants, 4: 599 Hydrogenated fats, infant formulae, 2: 914 Hydrogenation, milk fat rheology modification, 3: 707–708 Hydrogen peroxide antimicrobial properties, 1: 420 Aspergillus flavus growth inhibition, 4: 790 lactoperoxidase system, 2: 321 Hydrolytic rancidity, 3: 677 definition, 3: 721 homogenized milk, 3: 678 Hydroperoxides lipid oxidation, 3: 716 measurement, 3: 720 Hydrophilic colloid see Hydrocolloids Hydrophilic interaction liquid chromatography (HILIC), 1: 173 Hydrophobic grid membrane filter technique (HGMF), 1: 216 coliform enumeration, 4: 69 Hydrophobic interaction chromatography (HIC), 1: 173 Hydrophobic interaction high-performance liquid chromatography (HI-HPLC), milk proteins, 3: 762 Hydroxamate method, microbial transglutaminase analysis, 2: 298 4-Hydroxy acid, 3: 652–653 5-Hydroxy acid, 3: 652–653 Hydroxyapatite column chromatography, milk proteins, 3: 762 -Hydroxybutyrate fetal requirements, 2: 246–247, 2: 247f milk fat synthesis, 3: 352–353 25-Hydroxycalciferol, 4: 647 Hydroxymethylfurfural (HMF) fluorescence and color parameters correlation, 3: 231, 3: 231 khoa, 1: 885 lysine availability loss indicator, 3: 228, 3: 228–229, 3: 232 Maillard reaction production pathways, 3: 219, 3: 219–220, 3: 232 -Hydroxypropanaldehyde see Reuterin Hydroxy radical, 3: 716 25-hydroxyvitamin D (25(OH)D), 4: 646 Hygiene donkeys, 1: 369 milking see Milking hygiene pathogen control in cheese, 1: 649 smear-ripened cheeses, 1: 399 Swiss-type cheeses, 1: 720 Hygienic design processing equipment, 4: 134 regulations, 4: 134 Hygroscopicity, milk powder, 2: 121 Hylobates lar (white-handed gibbon) milk, 3: 622t Hyperacute rejection (HAR), xenotransplantation, 2: 641 Hypercholesterolemia, 3: 610 nondietary causes, 3: 1032 Hypercubes, 1: 125, 1: 126f band interleaved by line (BIL) format, 1: 125 band interleaved by pixel (BIP) format, 1: 125 band sequential (BSQ) format, 1: 125 construction methods, 1: 125 staring image configuration, 1: 125, 1: 126f Hyperesthesia, 2: 240 Hyperfiltration see Reverse osmosis (RO) Hyperimmune colostral preparations, 3: 813 Hyperkeratosis, 3: 442 Hyperlipidemia, 4: 692
Hyperspectral imaging (HSI), 1: 125–132 acousto-optic tunable filters, 1: 126–127 applications, 1: 128, 1: 128f dairy product applications, 1: 128 blending, 1: 129 classification, 1: 131 compositional analysis, 1: 129, 1: 130f curd formation, 1: 128 dehydration, 1: 129 milk coagulation, 1: 128 physical property prediction, 1: 130 process monitoring, 1: 128 data acquisition, 1: 127 data storage, 1: 127 image acquisition, 1: 125 image analysis, 1: 127 classification, 1: 127 regression, 1: 127 spatial preprocessing, 1: 127 spectral preprocessing, 1: 127 image calibration, 1: 127 image processing, 1: 128 images see Hypercubes instrumentation, 1: 125, 1: 126f line-mapping instrument, 1: 125 liquid crystal tunable filters, 1: 126–127 pixel spectrum, 1: 125 point and acquire mode, 1: 125 pushbroom acquisition, 1: 125 regression model development, 1: 128 visible-near-infrared systems, 1: 127 Hypertension, milk peptide action against, 3: 1064 Hyperthermia, 4: 567 Hypervitaminosis D, 4: 650 Hypoallergenicity donkey milk, 1: 372 infant formulae, 2: 143 Hypocalcemia clinical see Milk fever magnesium deficiency, 2: 372–373 post-calving, 4: 516–517 subclinical, 4: 516–517 Hypomagnesemia milk fever, 2: 228, 2: 240 weather conditions and, 2: 375 without clinical signs, 2: 224 Hypomagnesemic tetany see Grassy tetany Hypophysectomy, milk production, 3: 26, 3: 27f Hypothalamic–pituitary–adrenal (HPA) axis fetal, 4: 504, 4: 507f HPG axis linking mechanisms, 4: 576f, 4: 577 isolation stress, 4: 580 stress response, 4: 576 Hypothalamic–pituitary–gonadal (HPG) axis, 4: 575, 4: 576f HPA axis linking mechanisms, 4: 577 reproductive process control, 4: 576 Hypothalamic–pituitary–ovarian system, 4: 422, 4: 422f development, 4: 423 Hypothalamic–pituitary–ovarian–uterine axis, estrous cycle, 4: 429–430, 4: 430f Hypothalamic–pituitary portal system, 4: 575 Hypothalamus, 4: 575 development, 4: 423 releasing factors, 4: 575 reproductive function, 4: 422 Hypothermia lambs, 2: 861–863 newborn goats, 2: 826 Hysteresis loops, yogurt rheology, 4: 528
I Ibex (wild goat; Capra ibex), 2: 814 Ice crystal size, 4: 712 formation nonequilibrium, 4: 711 viscosity effects, 4: 711–712
889
microstructure effects, 1: 231 recrystallization, 4: 712 kinetic data, 4: 712 Ice cream, 2: 893–898, 2: 894 aeration , maximum amounts, 2: 895 anhydrous milk fat use, 1: 517 composition standards, 2: 894 dairy fats, 2: 899 E. coli control measures, 4: 65 E. coli outbreaks, 4: 62 economy, 2: 895 flavor defects, 2: 538–539, 2: 539f flavoring, 2: 895–896, 2: 896t freezing curve, 2: 899, 2: 900f, 2: 903 global per caput consumption, 2: 894, 2: 894t global value, 2: 894 historical aspects, 1: 16 homogenization, 2: 901 infrared spectrometry, 1: 119t ingredients, 2: 899 lactose reduction, 2: 281 Listeria monocytogenes contamination, 4: 84 macromineral contents, 3: 927t manufacture, 2: 899–904 aerated emulsions, 1: 71, 2: 904, 2: 904f dynamic freezing, 2: 901 freezing processes, 2: 901 hardening, 2: 903 mix blending and preparation, 2: 900 process steps, 2: 899, 2: 900f milk protein concentrate, 3: 852 new products, 2: 894 non-dairy fats, 2: 899 overrun, 2: 895 packaging, 4: 20 pasteurization, 4: 198 per caput consumption, 1: 16 perceived additives, 1: 46f point of manufacture/consumption market share, 2: 894, 2: 894t processing equipment, 4: 128t product quality, 2: 895, 2: 895t regular, 2: 893–894 rheology, 4: 527 soft-frozen, 2: 897 superpremium products, 2: 895 trace element content, 3: 935t variations, 2: 893–894 water, 4: 711 yeast spoilage, 4: 745 see also Frozen desserts Iclaprim, 4: 109 ICPAES see Inductivity coupled atomic absorption spectrometry (ICPAES) ICRP (International Commission on Radiological Protection), 1: 903 ICTV (International Committee on Taxonomy of Viruses), bacteriophage classification, 1: 430 ID 32 E kit, 4: 77 Ideal elastic solids, 1: 685, 1: 686f, 1: 687f ‘Ideal’ solution, 4: 715 Identity marking and registration see Animal identification Identity standards, 4: 322–330 fair trade practice promoters, 4: 322 international standards, 4: 324 as legislative reference texts, 4: 322 national standards, 4: 323 cheese, 4: 323 regional standards, 4: 323 role, 4: 322 standard setting, 4: 323 trade facilitators, 4: 322 IDF see International Dairy Federation (IDF) Idiazabal, 3: 501 IDRI (Indian Dairy Science Association), 2: 103 IFT (Institute of Food Technology), 2: 106 IgA see Immunoglobulin A (IgA)
890 Index IgG see Immunoglobulin G (IgG) IgM see Immunoglobulin M (IgM) Ileal-cecal fold, 3: 989 Ile-Pro-Pro, antihypertensive effects, 3: 884 Ileum, 3: 989 endogenous protein losses, 3: 993–994 Johne’s disease, 2: 175, 2: 175f protein digestion, 3: 993 Illawara cattle, 1: 285t, 1: 299 Imitation cheese, 1: 799 Imitation coffee creams, 2: 915 Imitation dairy products, 2: 913–916 consumer appeal, 2: 913 definition, 2: 913 descriptive designations, 3: 2, 3: 2, 3: 3t flavor, 3: 300 formulation, emulsifier/protein balance, 1: 71 ingredients, 2: 913, 3: 300 nonstandardized substitutes, 3: 316 product types, 2: 913 Imitation evaporated milk, 2: 915 Imitation milk powders, 2: 914 manufacture, 2: 914 Imitation milks, 2: 913, 3: 300 nutritional status, 2: 914 skim milk powder, 2: 913–914 sterilization, 2: 913 Imitation sour cream, 2: 916 Imitation sweetened condensed milk, 2: 915 Imitation whipped creams, 2: 915 destabilizing emulsifier, 2: 916 manufacture, 2: 916 Imitation yogurt, 2: 916 Imitative compression tests, cheese, 1: 690 Immediate allergic reaction, 3: 1041 Immobilin, 3: 844 Immune milk preparations, 3: 597 Immune product (IP), 3: 1038 Immunization brucellosis, 4: 38 mastitis, 3: 420 see also Vaccine/vaccination Immunoblotting, 1: 179 Immunochemical assays, 1: 177–184 antibiotics, 1: 180, 1: 182t applications, 1: 177, 1: 179 see also specific applications chemical contaminants, 1: 180 definition, 1: 177 drug residues, 1: 180 enzymes, 1: 180 hormones, 1: 180 pathogens, 1: 180, 1: 182t proteins, 1: 179, 3: 745t, 3: 748 caseins, 3: 749 cow’s milk substitution, 1: 179, 1: 181t food allergens, 1: 179 future trends, 3: 750 quantitative techniques, 1: 179 reproducibility, 3: 748 sandwich immunoassays, 1: 179 sensitivity, 1: 180 specificity, 1: 180 whey proteins, 1: 180, 3: 749 sensitivity, 1: 177 speed, 1: 177 terminology, 1: 177 toxins, 1: 180 see also specific methods Immunochemical detection, quantitative techniques, 1: 179 Immunofluorescent assay (IFA), Coxiella burnetii, 4: 57 Immunoglobulin(s) (Ig), 3: 480, 3: 807–815 absorption calves, 4: 396 ruminal neonates, 3: 807 antigen binding, 3: 810 biological roles, 3: 759, 3: 807
colostrum, 3: 591, 3: 591–592, 3: 593f, 4: 396 concentrations, milk, 3: 807, 3: 808t, 3: 810 creaming process, 3: 676 diversity, 3: 807–810 equid milk, 3: 522 functions, 3: 810 heterogeneity, 3: 755–756 importance to offspring, 3: 812 antibody digestion, 3: 812 microbial infection protection, 3: 812 in utero transfer, primates, 3: 624–625 leukocyte binding, 3: 810 mammary gland defense, 3: 391, 3: 391t microbe adhesion prevention, 3: 810 milk, 3: 481 primate milk, 3: 624 properties, 3: 808t structure, 3: 751–752, 3: 755–756, 3: 807, 3: 809f light chains, 3: 807 technological properties, 3: 813 thermal processes, 3: 813 transcytosis, 3: 378–379 transfer, 3: 811 gastrointestinal tract to blood, 3: 812 in utero, 3: 811 lacteal, 3: 811 main pathways, 3: 811 placental, 3: 811 transport mechanisms, 3: 811 serum to milk, 3: 807 transfer to milk, 3: 811 utilization, 3: 813 commercial, 3: 813 Immunoglobulin A (IgA) colostrum, 3: 808t, 3: 810 primates, 3: 624–625 functions, 3: 810 in milk, 3: 808t, 3: 810 proteolytic degradation, 3: 812 secretory see Secretory immunoglobulin A structure, 3: 807, 3: 809f transcytosis, 3: 378–379 transfer to milk, 3: 811 Immunoglobulin-enriched milk, 3: 298 Immunoglobulin G (IgG) camel milk, 3: 811 colostrum, 3: 591, 3: 592, 3: 593f, 3: 808t, 3: 810 equine milk, 3: 522 heat inactivation, 3: 813 induced lactation, 3: 23, 3: 23f in milk, 3: 808t, 3: 810 placental transfer, 3: 592 proteolytic degradation, 3: 812 serum, 3: 808t, 3: 810 structure, 3: 807, 3: 809f subclasses, 3: 807 transcytosis, 3: 378–379 transfer to milk, 3: 811 Immunoglobulin M (IgM) colostrum, 3: 808t, 3: 810 functions, 3: 810 human milk, 3: 807 in milk, 3: 808t, 3: 810 proteolytic degradation, 3: 812 structure, 3: 807, 3: 809f transfer to milk, 3: 811 Immunological function fermented milk effects, 2: 488, 2: 501 infants, protection from milk, 3: 587 protection for infant from milk, 3: 587 stress depression, 2: 830 Immunological memory, 3: 389–390 colostrum, 3: 593 Immunomagnetic-hybridization technique, Campylobacter jejuni, 4: 42 Immunomagnetic separation, PCR, 1: 221 Immunomodulation, milk peptides action, 3: 1064 Immunoprecipitation, 1: 178
Immunosensors, 1: 179 pathogenic bacteria, 1: 196 Imokilly Regato, 1: 850 Impedance (admittance) spectroscopy, electrical conductivity, 3: 471 Impeller pumps see Single-rotor pumps Improved Awassi sheep, 1: 327, 1: 327f distribution, 1: 327 milk production traits, 1: 327 origin, 1: 327 physical characteristics, 1: 327 reproductive characteristics, 1: 327 Inappetence, gastrointestinal nematode infection, 2: 259–260 In-between barn ventilation mismanagement, 4: 558 winter temperatures, 4: 558 Inbreeding, 2: 647, 2: 661, 2: 675 control, 2: 653 computerized mating programs, 4: 469 genomic selection, 2: 667 Holstein breed, 2: 676t international flow of genes, 2: 671 Income, management records, 1: 488 Income over feed costs (IOFC), milk production and, 2: 458, 2: 459t Incomplete testicular descent, 1: 472 Inconel 600, 4: 136 Indexing stalls, milking parlors, 3: 962 India dairy cow numbers, 1: 10, 1: 10t dairy industry, 1: 10t Indian buffalo colostrum immunoglobulins, 3: 811 milk immunoglobulins, 3: 811 Indian Dairy Science Association (IDRI), 2: 103 Indian Journal of Dairy Science, 2: 103 Indirect additives, 1: 51 Individual risk, 4: 279 Induced lactation, 3: 20–25 appetite during, 3: 22 applications, 3: 24 behavioral estrus activity, 3: 21–22 cow injuries, 3: 22, 3: 23 cow’s value, 3: 23 health concerns, 3: 23 in heifers, 3: 22 lactation curve, 3: 22, 3: 22f mammary gland gross appearance, 3: 21 histology, 3: 21 methodology, 3: 20 milk composition, 3: 22, 3: 23f milk production, 3: 22 physiological responses, 3: 21 plasma hormone levels, 3: 20–21 seasonal effects, 3: 21 technological value, 3: 22 udder area, 3: 21, 3: 22f Induced pluripotent stem cells (iPSCs), 2: 639 Induction time, 3: 186, 3: 186f primary nucleation, 3: 188 supersaturation, 3: 188 Inductivity coupled atomic absorption spectrometry (ICPAES), 1: 144 analytical performance, 1: 143t Inductivity coupled plasma mass spectrometry (ICPMS), 1: 144 analytical performance, 1: 143t Industrial communication standards, 4: 238, 4: 239t Industrial evolution, 4: 234 Industrial Revolution, 1: 3 feed storage, 1: 5 Industrias L´acteas Espa˜nolas, 2: 105 Infant(s) agricultural contaminants, 1: 889 Bifidobacterium longum subsp. infantilis activity, 3: 213–214, 3: 214
Index Infant formulae, 2: 131, 2: 135–145, 2: 914 analysis, 2: 135 carbohydrates, 2: 136 ELISA, 2: 136 gas chromatography with flame ionization detection, 2: 136 HPLC, 2: 136 lipids, 2: 136 minerals, 2: 137 protein, 2: 136 SDS-PAGE, 2: 136 surface plasmon resonance, 2: 136 ultrahigh performance liquid chromatography (UPLC), 2: 136 vitamins, 2: 136–137 classification, 3: 1043 Clostridium botulinum contaminated, 4: 50–51 cow milk substitute, milk allergy, 3: 1043 first-age infant formulae, 2: 137, 2: 137t arachidonic acid, 2: 141 calcium, 2: 142 carbohydrates, 2: 142 casein, 2: 141 casein hydrolysis products, 2: 141 classification, 2: 139t conjugated linoleic acid, 2: 142 docosahexaenoic acid, 2: 141 glycosphingolipids, 2: 141 human milk oligosaccharides, 2: 142 iron, 2: 143 -lactalbumin, 2: 138 lactoferrin, 2: 141 lipids, 2: 141 long-chain polyunsaturated fatty acids, 2: 141 micronutrients, 2: 142 minerals, 2: 142 obesity, 2: 138 phospholipids, 2: 141 proteins, 2: 137 vitamin D, 2: 142 vitamin E, 2: 142 vitamins, 2: 142 follow-on (second-age) formulae, 2: 143 classification, 2: 139t composition, 2: 138t future work, 2: 144 galacto-oligosaccharide inclusion, 3: 215 growing-up milks, 2: 143 historical aspects, 1: 15 human milk vs., 3: 196, 3: 581 hydrogenated fats, 2: 914 lactoferrin supplementation, 3: 804 low-birthweight (LBW) formulae, 2: 144 classification, 2: 140t new product category, 2: 144 Maillard reaction-induced deterioration, 3: 229, 3: 230, 3: 233 manufacture, 2: 135, 2: 136f new developments, 3: 976 nonprotein nitrogen addition, 3: 584, 3: 585t nucleotide supplements, 3: 976, 3: 977f packaging, 2: 135 postdischarge formulae (PDF), 2: 140t premature infants, 2: 144 regulations, 2: 135 special medical purposes, 2: 143 classification, 2: 140t gastroesophageal reflux, 2: 143 hydrolyzed proteins, 2: 143 hypoallergenic, 2: 143 nonnutritive additions, 2: 143 nutrient-dense formulae, 2: 143 partial hydrolysate-based formulae, 2: 143 soy-based, 2: 143 whey protein products, 4: 736 Infant nutrition products lipids, 3: 714 whey utilization, 4: 733
Infection(s) bacterial see Bacterial infections protection, transgenic animals, 2: 643 testing methods, 2: 825 tick transmission see Tick(s) see also individual infections; individual infectious agents Infectious abortion see Brucellosis Infectious bovine rhinotracheitis (IBR/IPV), 2: 49–50 Infective dose, 1: 645 Inferential methods, statistics, 1: 102, 1: 104f Infertility bulls, 4: 483 displaced abomasum, 4: 579 metabolic disease, 4: 579 non-seasonal/pasture-based management, 2: 49 sheep, 2: 857 ‘summer’, 1: 473 Inflection point (touch point pressure difference), teat-cup liners, 3: 948 Influenza virus, inhibition by casein macropeptide (CMP), 3: 1063–1064 Information technology (IT) continuous process improvement, 4: 264–265 historical aspects, 1: 9 Infrared (IR) absorption, historical aspects, 1: 18 Infrared (IR) light methods, curd strength, 1: 587, 1: 589 Infrared (IR) spectrometry, 1: 111, 1: 111f, 1: 115–124 acceptable errors, 1: 121 advantages, 1: 115, 1: 120–121 applications, 1: 118, 1: 119t compositional analysis, 1: 118–119 quantitative analysis, 1: 118 calibration models, 1: 119 calibration performance, 1: 121 composition analysis, 1: 118–119 data processing, 1: 118 equipment, 1: 116f Fourier transform infrared spectroscopy, 1: 115 Fourier transform mid-infrared spectroscopy, 1: 116, 1: 117f Fourier transform near-infrared spectroscopy, 1: 116 butter manufacture, 1: 497 good laboratory practices, 1: 121 acceptable errors, 1: 121 calibration performance, 1: 121 sample preparation, 1: 121 harmonization networks, 1: 123 known standards, 1: 119–120 limitations, 1: 121 mechanism of action, 1: 115 milk proteins, 3: 743 networks, 1: 122 harmonization networks, 1: 123 service networks, 1: 122, 1: 122f surveillance networks, 1: 122 prediction models, 1: 121 process monitoring, 1: 120 product monitoring, 1: 120 quantitative analysis, 1: 118, 1: 119 known standards, 1: 119–120 microorganisms, 1: 120 soft independent modeling of class analogy, 1: 120, 1: 120f real-time analysis on-line, 1: 120–121 reflectance spectra, 1: 117–118 sampling techniques, 1: 117 standardization, 1: 118 statistical analysis, 1: 118 calibration models, 1: 119 partial least squares regression, 1: 118–119, 1: 119f Ingredients listing, food labels, 3: 5 Inguinal nerves, 3: 336 Inhalers, lactose particles, 2: 132 Inhibins bioactive, 4: 431
891
estrous cycle, 4: 431 In-line milk (ILM) sampler, 3: 646 Innovative steam injection (ISI), 2: 699 Inositol, marine mammal milk, 3: 579 In-place cleaning see Cleaning in place (CIP) INRAtion software, 2: 854–855, 2: 855t Insect control, 4: 542 Insecticides biosensors, 1: 242 tick infestations, 2: 256t Insemination energy balance-conception rate relationship, 4: 481 ovulation synchronization and, 4: 454–460 sex-sorted sperm, 2: 635 technique, conception rate and, 4: 482 see also Artificial insemination (AI) Insolubility index (IDI), milk powder solubility, 2: 121 Instantization, milk powder see Milk powder Institute of Food Science and Technology, 2: 106 Institute of Food Technology (IFT), 2: 106 Institut National de la Recherche Agronomique (INRA) feed evaluation model, 2: 419, 2: 426 Instrumentation, 4: 234–241 atomic spectrometry, 1: 142 digital control equipment, 4: 238 distributed control systems, 4: 235f, 4: 238 factory-to-factory automation, 4: 241 subjective property measurement, 4: 241 Insulin body condition score, 1: 466 bovine somatotropin effects, 3: 34–35 functions, 3: 34–35 galactopoietic effects, 3: 29 ketosis, 2: 231 mammary development, 3: 341 milk protein synthesis, 3: 362, 3: 362f type 1 diabetes, 3: 1048 Insulin-dependent diabetes mellitus (IDDM) see Type 1 diabetes Insulin-like growth factor(s) (IGFs), 2: 766–767, 2: 768 bovine somatotropin effects, 3: 33–34 galactopoietic effects, 3: 29 lactogenesis, 3: 17 in milk, 2: 768 Insulin-like growth factor-I (IGF-I) body condition score, 1: 466 bovine somatotropin effects, 3: 34 colostrum, 3: 596 estrous cycle, 4: 430 follicular growth, 4: 436, 4: 436f galactopoietic effects, 3: 29 in vitro maturation, 2: 618–619 lactogenesis, 3: 18 mammary apoptosis, 3: 29 mammary gland growth, 3: 341 prepubertal period, 3: 342 mammary gland involution, 3: 343 melatonin reduction, 4: 443–444 postpartum ovulation resumption, 4: 475–476 prolactin interactions, 3: 29 synthesis, thyroid hormone effects, 3: 28 Insulin-like growth factor 2 (IGF-II), colostrum, 3: 596 Insulin-like growth factor binding protein(s) (IGFBPs), 2: 768, 3: 343 Insulin-like growth factor binding protein-5 (IGFBP5), 3: 29 Insulin-like growth factor(s) (IGFs) system, 2: 768 Integrated pest management (IPM), 4: 544 Integrated (total) risk, 4: 279–280 Intelligent control (IC), 4: 246 actuator subsystem, 4: 247 cognition subsystem, 4: 246 perception subsystem, 4: 246 Intensifier pump, microfluidization, 2: 762 Intensive camel dairying, 3: 516
892 Index Intensive grazing management, waste management, 3: 394 Intensive production systems goat production systems see Goat production systems hospital facilities, 2: 28 sheep see Sheep Interbull formation, 2: 669 genetic conversion equations, 2: 669–670 genetic merit advertising guidelines, 2: 672 international rankings, 2: 653 non-North American bull sires, 2: 670–671, 2: 671t, 2: 671t nonparticipating countries, 2: 672 North American bull sires, 2: 671t Interbull Centre, 2: 653, 2: 670 Interdigital dermatitis see Papillomatous digital dermatitis (PDD) Interdigital papillomatosis see Papillomatous digital dermatitis (PDD) Interesterification, modified butter, 1: 501 Interface level sensors, 4: 236 Interfacial films, emulsions see Emulsions Interferometry, ultrasonic, 1: 211 Interferon- test bovine tuberculosis, 2: 196 Johne’s disease, 2: 177–178 Interferon-T, 4: 496–497 oxytocin receptor gene inhibition, 4: 497 progesterone levels, 4: 480 prostaglandin secretion inhibition, 4: 497, 4: 498f Intergenic transcribed spacer (ITS) region, bacterial, 1: 634 Intergranular corrosion, 4: 261 Interlobular duct, mammary gland, 3: 333 Internal insulation, 4: 550 International Agency for Research on Cancer (IARC), aflatoxin carcinogenic risk, 4: 803 International Bull Evaluation Service (Interbull) see Interbull International Commission on Food Mycology, mold enumeration recommendations, 4: 783 International Commission on Microbiological Specifications for Food (ICMSF), udder flora, 3: 645 International Commission on Radiological Protection (ICRP), 1: 903 International Committee on Taxonomy of Viruses (ICTV), bacteriophage classification, 1: 430 International Dairy Federation (IDF), 2: 106 fatty acid analysis method, 3: 698 fermented milk standards of identity, 2: 474 food technology education, 2: 6 foundation, 4: 312 global competencies, food technology education, 2: 9 international agreement on terminology need, 1: 843–844 pasteurization definition, 3: 275, 4: 193 rennet standards, 1: 577, 1: 578 report on alternatives to heat treatment, 2: 725 sensory evaluation, 1: 279–280 Standard 80, butter composition, 1: 506 International dairy markets, changes, 4: 348 International Embryo Transfer Society, 2: 623, 2: 627 International Federation of Organic Agriculture Movements (IFOAM), standards, 4: 10, 4: 11t International food standards, establishment, 4: 312 International Journal of Dairy Technology, 2: 102 International Organic Accreditation Services (IOAS), 4: 10 International Vocabulary of Metrology - Basic and General Concepts and Associated Terms, 1: 83, 1: 84t Internships, 2: 3 Interspecies variability, acceptable daily intake (ADI), 1: 56 Interstitial air, milk powder, 2: 119, 2: 119t
Intestinal microflora see Gastrointestinal microflora Intestinal toxemia botulism, 4: 47–49 infant formula, 4: 50–51 Intestine see Small intestine Intralobular duct, mammary gland, 3: 333 Intramammary infections (IMIs) E. coli, 3: 415–416 Streptococcus dysgalactiae spp. dysgalactiae, 3: 418 Streptococcus uberis, 3: 418 Intrauterine growth retardation, heat stress, 4: 569, 4: 569t Intravaginal sponges, induced lactation, 3: 20 Intrinsic factor (IF), 3: 1000, 4: 675, 4: 675–677 Introns, 3: 1056 Inulin biosynthesis, 4: 363 colon cancer prevention, 4: 369–370 fructooligosaccharide production, 4: 360 mineral absorption stimulation, 4: 370 as prebiotic, 4: 363 prebiotic-fortified milk, 3: 298–299 Inulin-type oligofructose, 4: 360 Inulosucrase, 3: 204–205 In vitro disappearance (IVD) digestibility estimates, 2: 406 in vitro fertilization (IVF), 2: 619 buffalo, Asia, 2: 774 extent, in cattle breeding, 2: 623, 2: 624t male effect, 2: 619–620 sex-sorted sperm, 2: 636 sperm capacitation, 2: 619 sperm concentrations, 2: 619 in vitro maturation (IVM), 2: 618 culture media, 2: 618 cumulus cell expansion, 2: 618, 2: 619f hormones, 2: 618–619 in vitro production (IVP), 2: 616–622 developmental abnormalities, 2: 621–622 embryo cryoresistance, 2: 620 embryo development, 2: 620 culture media, 2: 620 facilities, 2: 620 impact of, 2: 621 laboratory, 2: 621 limitations, 2: 621–622 oocyst collection, 2: 616 facilities, 2: 620 slaughterhouse collection, 2: 616 oocyst maturation, 2: 616 cytoplasmic maturation, 2: 617 nuclear maturation, 2: 616 potential, 2: 621 pregnancy rates, 2: 620 steps, 2: 616, 2: 617f success rate, 2: 618, 2: 618f techniques, 2: 616 Involution see Mammary gland involution Iodide, 2: 380 feed supplementation, 2: 387 Iodine, 2: 380 absorption, ruminants, 3: 1000 as contaminant, 1: 895, 1: 902 in dairy products, 3: 934t, 3: 935t deficiency, 2: 380 humans, 3: 939 excess, humans, 3: 939 in milk, 3: 933, 3: 934t chemical forms, 3: 935 iodophor use, 3: 934, 3: 939 nutritional significance, 3: 939 recommended dietary intake, 3: 937t requirements, 2: 379t, 2: 380 supplemental sources, 2: 380 131 Iodine, as contaminant, 1: 902 Iodophores, as sanitizers, 1: 895 Ion analysis, capillary electrophoresis (CE), 1: 190 Ion exchange (IE), 4: 739 alternative process, 4: 741, 4: 741f
anion exchanger, 4: 740 capacity, 4: 739 cation exchanger, 4: 740 demineralization, conventional, 4: 740, 4: 740f costs, 4: 741 process limitations, 4: 741 -lactoglobulin, 3: 788, 3: 788f permeate preconcentration, 3: 865 resins, 4: 739–740 Swedish Dairies Association (SMR) demineralization process, 4: 741, 4: 741f characteristics, 4: 742 costs, 4: 742 flow arrangement, 4: 741–742 industrial layout, 4: 742f process limitations, 4: 742 total dissolved solid reduction, water, 4: 584 vessels, 4: 740–741 Ion-exchange chromatography (IEC), 1: 169 ‘amino acid analyzer’, 1: 170 carbohydrates, 1: 171, 1: 171f caseins, 1: 170, 3: 766 lactoferrin, 1: 170–171 lactoperoxidase, 1: 170–171 milk proteins, 3: 748, 3: 762 proteins, 1: 170, 1: 171f pulsed amperometric detection (PAD), 1: 171 resins, 1: 170 whey protein isolates, 3: 875 Ionica goats, 1: 315 Ionic chromatography, milk ions, 3: 914t, 3: 915 Ionic concentration, 1: 232 Ionophores fatty liver, 2: 221 ketosis management, 2: 236 Ion-selective electrodes, 1: 194 milk ion quantification, 3: 915 Ion-sensitive field-effect transistors (ISFETs), 1: 195–196, 1: 238, 1: 238f Iota carrageenan, 1: 69t Iowa Women’s Health Study, 4: 658 Ireland, cheese legislation, 1: 850 Iron, 2: 380 absorption from milk, 3: 805–806 ruminants, 3: 999 vitamin C, 4: 672 chelated forms, 3: 999–1000 copper absorption, 3: 999 in dairy products, 3: 934t, 3: 935t, 3: 935t, 3: 935t deficiency, 2: 380 humans, 3: 936 infants, 3: 936 ruminants, 3: 999–1000 first-age infant formulae, 2: 143 functions, 2: 380, 3: 936 human milk, bioavailability, 3: 936 low pH, 4: 259 in milk, 3: 933, 3: 934t, 3: 1006 bioavailability, 3: 936 chemical forms, 3: 935 nutritional significance, 3: 936 milk lipid oxidation, 3: 718 oxidation, 4: 258 primate milk, 3: 627–629, 3: 628t recommended daily allowances, 3: 936, 3: 937t requirements, 2: 379t, 2: 380 sheep milk, 3: 500 toxicity, 2: 380–381 Iron-fortified cow’s milk-based formulae, 3: 936 Irrigation, pasture, 2: 590 farm subdivision, 2: 27 interval, 2: 591, 2: 591f schedule, 2: 591 watering rates, 2: 591t see also individual methods Ischemic heart disease milk xanthine oxidoreductase, 2: 326
Index vitamin C, 4: 672–673 vitamin E, 4: 657–658 ISFETs (ion-sensitive field-effect transistors), 1: 195–196, 1: 238, 1: 238f ISO 6785:2001 method, Salmonella detection, 4: 93 Isoelectric focusing (IEF), 1: 188, 1: 188f milk proteins, 3: 747, 3: 761 historical aspects, 1: 22–23 two-dimensional electrophoresis, 1: 189 Isoelectric point, proteins, 3: 887–888 Isoflavone supplementation, 3: 1060 ISOFLUX ceramic membrane, 3: 871 Isofumigaclavine A, 1: 904t Isoglobotriose, 3: 251 Isolactosucrose, 3: 206 Isolation stress, reproductive effects, 4: 580 Isomerases, 2: 301–303 Isoprenoid quinone analysis, Arthrobacter, 4: 373 Isothermal (compressor) efficiency, 4: 605f, 4: 606, 4: 606f Isothermal polymerase chain reaction see Polymerase chain reaction (PCR) Isracidin, 3: 884, 3: 1064 Israel dairy industry, 1: 10, 1: 11t sheep total mixed ration, 2: 855 Issatchenkia orientalis, 4: 750 Italian ryegrass (Lolium multiflorum), 2: 556, 2: 850 Italy cheese definition, 1: 849 cheese legislation, 1: 849 dairy product consumption, 1: 46, 1: 46t dairy societies, 2: 105 hard cheeses see Hard Italian cheeses herby cheeses, 1: 787, 1: 788f sheep, total mixed ration, 2: 855t spiced cheeses, 1: 787 Ivermectin, 2: 252 I-X (humidity) chart, spray drying, 4: 210, 4: 211f
J Jablu goats, 1: 319 Jakhrana goats, 1: 312t, 1: 320 Jamaica Hope cattle, 1: 303t, 1: 305 Jamnapari goats, 1: 311t, 1: 318, 1: 318f milk yields, 1: 312t Japan additives approval, 1: 53 definitions, 1: 52 labeling, 1: 54 agricultural policy, 4: 308 background, 4: 308 dairy domestic policy changes, 2001, 4: 308 income stabilization fund, 4: 308–309 dairy farm number, 1: 10 dairy industry, 1: 10t dairy societies, 2: 104 deficiency payments, 4: 308, 4: 309f direct payments, 4: 308, 4: 309f environmental conservation incentives, 4: 308–309 fermented milk products, 1: 390 import licensing, 4: 309 organic standards, 4: 10 out-of-quota imports, 4: 309 price support, 4: 308 producer support estimate, 4: 308 voluntary production quota, 4: 308 Japanese black bear milk oligosaccharides, 3: 271t Japanese Dairy Science Association, 2: 104 Japanese Society of Animal Science, 2: 104 Japanese Standards for Use of Food Additives, 1: 52 Jarakhell goats, 1: 311t, 1: 320 Jattan goats, 1: 311t, 1: 320 Javanese cattle, 1: 285t Jejunum, 3: 989 lipid digestion, 3: 992–993 protein digestion, 3: 993
Jenseniin G, 1: 410t Jenseniin P, 1: 410t Jersey cattle, 1: 286t, 1: 288, 1: 288f Australia, 2: 35 birth, weaning and postweaning traits, 1: 290t carcass characteristics, 1: 290t Chinese dairy management, 2: 84 heifer housing, 4: 407 historical aspects, 1: 2 Latin American dairy management, 2: 91 milk composition, 2: 53t milk protein content, 3: 363 New Zealand, 2: 35 puberty/pregnancy rates, 1: 291t reproductive/maternal traits, 1: 291t Job Safety Analysis (JSA), 4: 278 Job safety hazards, 4: 277 Johne’s disease, 2: 174–180 artificial insemination centers, 1: 470 calf infection, 2: 175 causative agent, 2: 174, 4: 89 cell-mediated inflammatory response, 2: 175–176 clinical signs, 2: 176, 2: 176f control, 2: 178 calf exposure reduction, 2: 178 purchased animals, 2: 178–179 state/national level programs, 2: 179 Crohn’s disease comparison, 3: 315, 4: 90t diagnosis, 2: 177 economic impact, 2: 176 goats, 2: 798–799 herd screening, 2: 178 lymph nodes, 2: 175–176 national eradication schemes, 2: 49 pathogenesis, 2: 175 prevalence, dairy cattle, 2: 175 sheep, 2: 858 symptoms, 4: 90 treatment, 2: 178 vaccination, 2: 179 zoonotic concerns, 2: 179 Joint FAO/WHO Committee of Government Experts on the Code of Principles Concerning Milk and Milk Products see Codex Committee on Milk and Milk Products (CCMMP) Joint FAO/WHO Expert Committee on Food Additives (JECFA) acceptable daily intake, 1: 55 additive approval, 1: 52 establishment, 4: 313 risk assessments, 4: 534–535 Joint FAO/WHO Expert Meetings on Microbiological Risk Assessment (JEMRA), 4: 313 Joint FAO/WHO Meeting on Pesticide Residues (JMPR) establishment, 4: 313 risk assessments, 4: 534–535 Joint United Animal Feeding Operation Strategy, 3: 395 Jolliffe syndrome see Pellagra Journal of Dairy Science (JDS), 2: 102, 2: 102 Journal of Food Technology in Africa, 2: 104 Journal of the Canadian Institute of Food Sciences and Technology (JCIFST), 2: 105 Journals, 2: 106 see also specific journals 2004 July Framework Agreement, 4: 346 Just-in-time operations, 4: 265 Juvenile-onset diabetes see Type 1 diabetes
K Kacchan goats, 1: 311t, 1: 321, 1: 321f Kachkaval, 3: 501 Kaizen see Continuous process improvement Kajli goats, 1: 311t, 1: 321 Kale (Brassica oleracea), 2: 560
893
Kamori goats, 1: 311t, 1: 321, 1: 321f milk yields, 1: 312t Kan box, 2: 815f, 2: 815–816 Kankrej cattle, 1: 301, 1: 301t, 1: 302f Kanterkaas cheese, 1: 787 Kanterkomijnekaas, 1: 787 Kanternagelkaas, 1: 787 Karagouniko sheep, 1: 336t lactation length, 1: 332t Karaman sheep, 1: 334 Karish cheese, 1: 788 Karl Fischer reagent, 1: 76–77 Karl Fischer titrations, 1: 76, 1: 194 Karranzana sheep, 1: 332t Karranzona sheep, 1: 332t Karyotyping, embryo sexing, 2: 631 K¨aseverordnung (cheese order), 1: 848 Kashkaval, 1: 746 manufacture, 1: 746–747 ripening, 1: 749–751 varieties, 1: 746–747 Kashmiri goats, 1: 320 Kazakh horses, 1: 358 K-Blazer, 1: 530 Kefir, 2: 473, 2: 518–524, 4: 749 alternative names, 2: 518 characteristics, 2: 518, 2: 519f bioactive components, 2: 523 commercial production, 2: 521 direct-to-vat cultures, 2: 522, 2: 522f grain fermentation, 2: 521, 2: 521f methods, 2: 521, 2: 522f fermentation products in, 2: 518 microbial composition, 2: 518, 2: 519t analytical methods, 2: 518–519 bacteria, 2: 519 bacteria–yeast interactions, 2: 520 contaminants, 2: 520 liquid vs. grains, 2: 518 yeasts, 2: 520 probiotic effects, 2: 522 anticancer activities, 2: 523 bacterial inhibition, 2: 523 cholesterol reduction, 2: 524 gut microflora impact, 2: 523 lactose toleration, 2: 524 starter cultures, 2: 509t substrates for, 2: 518 traditional production, 2: 518, 2: 520 grains, 2: 520 vitamin content, 2: 494t Kefir grains, 2: 473–474, 2: 520, 4: 749 Leuconostoc, 3: 140 Kelvin bodies, 1: 689 Kelvin’s law, pure water, 4: 715 KERASEP ceramic membranes, 3: 868 Keratin, 3: 381 Keratin intermediate filaments, lipid droplet transit, 3: 375 Keshan disease, 3: 938 -Keto acids, 3: 87–88 -Keto acids, 3: 652–653 -Ketoglutarate cheesemaking, 1: 562 Lactobacillus casei group, 3: 102 Ketones acetyl-CoA supply, 2: 235 cheese flavor, 1: 681 hard Italian cheeses, 1: 734–735 origin of, 2: 233 uses, 2: 235 Ketosis, 2: 230–238, 4: 517, 4: 518t biochemistry, 2: 231 body condition score, 1: 465 body weight, 2: 233f clinical, 2: 230, 4: 517 presentation, 2: 230–231 clinical presentation, 2: 230
894 Index Ketosis (continued ) definition, 2: 230, 4: 517 diet, 2: 231 displaced abomasum, 2: 213–214 dry matter intake, 2: 231–232, 2: 232f endogenous ketogenic precursors, 2: 234 energy balance, 2: 233f epidemiology, 2: 230 exogenous ketogenic precursors, 2: 233 fatty liver, 2: 218 feed, 2: 231 free fatty acid concentrations, 2: 232f gluconeogenic precursors, 2: 234 goats, 2: 794, 2: 800–801 herd presentation, 2: 235 heritability, 2: 230 infertility risk factor, 4: 579 lactose biosynthesis, 3: 371 mineral inputs, 2: 232–233 oxaloacetate precursors, 2: 234 periparturient period, 2: 230 physiology, 2: 231 prevalence, 2: 230 prevention, 2: 235, 4: 518–519 body condition management, 2: 236 fats, 2: 236 feed additives, 2: 236 herd management, 2: 236 primary clinical, 2: 230 risk factors, 2: 230 secondary, 2: 230, 2: 232 subclinical, 2: 230, 4: 517 treatments, 2: 237 Khather, 2: 783 Khava see Khoa Khoa, 1: 881–886 acidity, 1: 884 applications, 1: 885 batch manufacture, 1: 881 defects, 1: 885 appearance, 1: 885 body, 1: 885 color, 1: 885 flavor, 1: 885 texture, 1: 885 definition, 1: 881 heat treatment, 1: 883 manufacture, 1: 881 batch method, 1: 881 mechanized methods, 1: 881 milk pretreatment, 1: 883 stirring rates, 1: 883 technique effects, 1: 883 traditional methods, 1: 881 milk quality, 1: 882 milk quantity, 1: 883 milk types, 1: 881, 1: 882 packaging, 1: 883 physiological changes, 1: 882 powder, 1: 885 quality effects, 1: 882 shelf life, 1: 883 storage, 1: 883 storage changes, 1: 884 acidity, 1: 884 hydroxymethyl furfural, 1: 885 lactose, 1: 884 lipolysis, 1: 884 microbiology, 1: 885 moisture, 1: 884 proteolysis, 1: 884 uses, 1: 881 yield, 1: 883 Khoya see Khoa Khurasani goats, 1: 311t, 1: 321 Kid(s) doe weight gain objectives, 2: 828, 2: 830t
feeding management, 2: 787t, 2: 790, 2: 793t, 2: 828, 2: 829t health, 2: 801, 2: 828 housing and shelter requirements, 2: 831 neonatal, colostrum feeding, 2: 825–826 space requirements, 2: 828–829, 2: 831, 2: 831t see also Goat(s) Kikuyu, 2: 577, 2: 599, 2: 600f irrigation interval, 2: 591f nitrogen responsiveness, 2: 588 Kilis goats, 1: 311t, 1: 318 milk yields, 1: 312t King Christian cheese, 1: 788 Kininogen, 3: 796t, 3: 797 Kishk composition, 2: 506 manufacture, 2: 505 microbiological quality, 2: 506 nutritional value, 2: 506 uses, 2: 505 variants, 2: 505 Kivircik (Thrace) sheep, 1: 337 Kjeldahl method, 1: 82t dairy product proteins, 1: 78 Dumas method vs., 1: 78–79 historical aspects, 1: 19 inaccuracy, 1: 78 milk proteins, 3: 743 Klebsiella characteristics, 3: 419 mastitis, 3: 419 Klebsiella oxytoca, 3: 419 Klebsiella pneumoniae, 3: 419, 3: 451 Kluyveromyces, 4: 754–764 bioactive peptide production, 4: 763 biotechnological applications, 4: 762 cheese ripening, 1: 570, 4: 762 chromosomal profiles, 4: 757f, 4: 757–758 in dairy products, 4: 762 ethanol production, 4: 762 -galactosidase production, 4: 762 genus current status, 4: 755f, 4: 756 recent history, 4: 754, 4: 755f industrial lactases, 2: 277 biochemical properties, 2: 279, 2: 280f kefir, 4: 762 lactose metabolism, 4: 761 maximum parsimony tree, 4: 758f, 4: 758–759 mitochondrial DNA analysis, 4: 756f, 4: 756–757 oligosaccharide production, 4: 763 physiological traits, 4: 756, 4: 756t species differentiation, 4: 759, 4: 759t see also individual species Kluyveromyces dobzhanskii karyotype, 4: 757–758 mitochondrial DNA analysis, 4: 756f, 4: 756–757 Kluyveromyces lactis, 4: 754 bovine chymosin production, 4: 763 fermentation-produced chymosin, 1: 576 genomic studies, 4: 760 Saccharomyces cerevisiae comparison, 4: 760–761 karyotype, 4: 757–758 lactose regulon, 4: 761 mitochondrial DNA analysis, 4: 756f, 4: 756–757 strains, 4: 759–760, 4: 760t surface mold-ripened cheeses, 1: 775 aroma production, 1: 779–781 taxonomy, 4: 759 Kluyveromyces lactis var. drosophilarum, 4: 759 Kluyveromyces marxianus, 4: 754 acid-curd cheeses, 1: 760 genomic studies, 4: 760 Saccharomyces cerevisiae comparison, 4: 761 karyotype, 4: 757–758 Leben, 4: 749 mitochondrial DNA analysis, 4: 756f, 4: 756–757 proteolytic activity, 4: 762
strains, 4: 760, 4: 761t surface mold-ripened cheeses, 1: 775, 1: 776f taxonomy, 4: 759 Knife test, curd strength measurement, 1: 585 Knowledge-based hybrid modeling (KBHM), 4: 248 fouling, 4: 248–249 Knowledge economy concepts, 4: 234 Koch, Robert, 1: 26 Kocuria, 1: 627 smear-ripened cheeses, 1: 396–397 Koesler number, mastitis, 3: 174–175 Koh-i-Ghizer goats, 1: 311t, 1: 321 Kohistani goats, 1: 319 Kohonen self-organizing maps (KSOMs), 1: 94t, 1: 98t, 1: 107 Kojic acid, galactosylation, 3: 206–207 Kolmogorow’s equation, 1: 61 Konjac flour, dairy desserts, 2: 909t Koumiss, 1: 363, 1: 363, 2: 473, 2: 512–517, 2: 507, 3: 528, 4: 749 commercial manufacture, 2: 515, 2: 516f product categories, 2: 515, 2: 516t technological advances, 2: 515 consumption, 2: 512, 2: 517 cow’s milk, 2: 508 equine milk, 2: 507, 2: 512 biochemical products, 2: 513 health benefits, 2: 512, 2: 513 history, 2: 512, 2: 514, 2: 517 lactose intolerance, 3: 518 medium-flavored, 2: 508 mild-flavored, 2: 508 non-equine milk products, 2: 516 modified bovine milk, 2: 517 starter cultures, 2: 474, 2: 507, 2: 509t strong-flavored, 2: 508 traditional production, 2: 515, 2: 515f Koumyss see Koumiss Kremis, 2: 896 K2O, fertilizer, 3: 403 Kuminost, 1: 788 Kumis see Koumiss Kumiss see Koumiss Kumys see Koumiss Kunitz family of protease inhibitors, 3: 560 Kuri cattle, 1: 298 Kurri goats, 1: 321 ‘Kurut’, 4: 69 Kvarg, 1: 703 Kymi sheep, 1: 332t Kytococcus, 1: 396–397
L LAB see Lactic acid bacteria (LAB) Laban, 2: 783 Laban kad (rob), 2: 504, 2: 505 Laban rayeb, 2: 504 Laban zeer, 2: 505, 2: 506 Labeling, dairy products, 3: 1–8 Codex milk product standards, 4: 327 conditional requirements, 3: 6 claims, 3: 7, 3: 7t nutrient declaration, 3: 6, 3: 6t consumer perceptions, 1: 44, 1: 45f country of origin, 3: 5, 3: 491–492 customer demands, 1: 47 food origins, 3: 5 ingredient listing, 3: 5 quantitative ingredient declaration (QUID), for special ingredients, 3: 5 milk products, 3: 3, 3: 6 naming, mandatory requirements, 3: 2 composite milk products, 3: 4 descriptive designations, 3: 2, 3: 3t milk, definition, 3: 3 modified milk products, 3: 3 reconstitution/recombination, 3: 4 supplementary names, 3: 4, 3: 4t
Index technology references, 3: 4 optional, 3: 6 claims, 3: 7, 3: 7t nutrient declaration, 3: 6, 3: 6t principles/standards, 3: 1 misleading descriptions, 3: 2, 3: 2t, 3: 3t regulations historical development, 3: 1 trends, 3: 8 shelf life, 3: 5 storage instructions, 3: 5 Lablab (Lablab purpureus), 2: 558, 2: 565 Lablab purpureus (lablab), 2: 558, 2: 565 Labneh, 2: 504 characteristics, 2: 505 chemical composition, 2: 505 manufacture, 2: 504 microbiology, 2: 505 milk solids content, 2: 525, 2: 527–528 Labor, stages of, 4: 510, 4: 510t Laboratories Commission, 4: 3 Laboratory pasteurization count (LPC), raw milk, 3: 645 Labor management, dairy farms, 3: 9–14 African systems see Cattle husbandry (Africa) communication, 3: 11 feedback, 3: 12 model, 3: 11 communication barriers, 3: 12 feedback, lack of, 3: 12 interruptions, 3: 13 language, 3: 12 muddled messages, 3: 12 physical distractions, 3: 13 poor listening skills, 3: 12 stereotyping, 3: 12 wrong channel, 3: 12 employee motivation, 3: 13 job enjoyment, 3: 13 model, 3: 13 rewards, 3: 13 employee satisfaction, 3: 13 hiring, 3: 9 applicant pool, 3: 9 application review, 3: 10 ‘‘help wanted’’ ads, 3: 9–10 interview, 3: 10 interview candidate selection, 3: 10 job description development, 3: 9 labor need determination, 3: 9 reference checks, 3: 10 selection, 3: 10 word of mouth, 3: 9 orienting new employees, 3: 11 team building, 3: 14 training, 3: 11 teaching method, 3: 11 Labri goats, 1: 311t, 1: 322 Lacaune sheep, 1: 330, 1: 330f distribution, 1: 330 farming systems, 2: 848–849 milk production, 1: 328t, 1: 330 origin, 1: 330 physical characteristics, 1: 330 reproductive characteristics, 1: 330 Lacha sheep, 1: 332t Lacho (Manech) sheep, 1: 334, 1: 334f Lactacin F, 1: 422t Lactadherin (PAS 6/7 glycoprotein), 3: 688, 3: 688–689, 3: 797–798 functions, 3: 688–689 SDS-polyacrylamide gel, 3: 683f, 3: 688 structure, 3: 686f, 3: 688 -Lactalbumin, 3: 481, 3: 780–786, 3: 838 A allele, 3: 841 alternative structures, 3: 782 apoptosis, 3: 561, 3: 782, 3: 838 bactericidal properties, 3: 797
B allele, 3: 841 biological roles, 3: 759 biosensors, 1: 243 buffalo milk, 3: 505 calcium binding, 3: 780–781 biological significance, 3: 781–782 primary site, 3: 781f, 3: 781–782 secondary site, 3: 781–782 colostrum, 3: 591, 3: 593f equid milk, 3: 519 equine milk, 3: 522 evolution, 3: 543, 3: 550, 3: 780 lysozyme relationships, 3: 780 first-age infant formulae, 2: 138 galactose transfer competitive inhibitor, 3: 784–785 Gal-T1 modification, 2: 329–330 gene structure conserved, 3: 840 genetic variants, 3: 752t, 3: 840 heat stability, milk, 2: 746 homology, 3: 543 homology-based modeling, 3: 780 interspecies comparison, 3: 838 lactogenesis, 3: 16 -lactoglobulin interactions, 3: 793 lactose concentration relationship, 3: 173 lactose synthesis, 3: 555, 3: 782, 3: 783f molecular basis, 3: 784 lactose synthetase, 3: 368–369 mammary involution, 3: 782 mammary secretion, 3: 782 marsupial milk, 3: 556–558 metal binding, 3: 780 molten globule state, 3: 780–781 partially folded states, 3: 780–781 primate milk, 3: 624 sheep milk, 3: 496 structure, 3: 780, 3: 781f primary, 3: 755, 3: 756f synthesis, 3: 377, 3: 780 whey protein products, 3: 875–876, 3: 876t -Lactams, biosensor analysis, 1: 240 Lactase(s), 2: 277 applications, 2: 276–277, 2: 280 bacterial, 2: 277 cheese ripening, 1: 540 deficiency, 3: 371–372 dietary supplements, 2: 281 expression, 3: 238 galacto-oligosaccharide production, 2: 281 industrial acid, 2: 277 biochemical properties, 2: 279, 2: 280f immobilized enzyme use, 2: 281 metal ions, effects of, 2: 280 neutral, 2: 277 new developments, 2: 281 off-flavor development prevention, 2: 282 sources, 2: 277 sweetness reduction, 2: 282 temperature effects, 2: 279–280, 2: 280f intestinal location, 2: 277, 3: 236, 3: 237f lack of, 3: 1004 persistence see Lactase persistence structure, 2: 278 evolutionary relationship, 2: 278, 2: 278f yeast, 2: 277 Lactase-negative mutants, accelerated cheese ripening, 1: 797 Lactase nonpersistent, 3: 236 Lactase persistence calcium, 3: 239 causes, 3: 237 ‘cultural historical hypothesis’, 3: 239 cultural practice and, 3: 237, 3: 238f definition, 3: 236 evolutionary considerations, 3: 238 evolutionary forces, 3: 239 genetics, 3: 237
895
health considerations, 3: 239 medical considerations, 3: 239 milk dependence, 3: 238–239 status determination, 3: 236 vitamin D, 3: 239 worldwide distribution, 3: 237, 3: 237f Lactase-phlorizin hydrolase (LPH), 2: 277 Lactate oxidation, starter cultures, 1: 553 reduction from pyruvate, 3: 168 L-Lactate, racemization, 3: 85–86 Lactate dehydrogenase (LDH), 2: 327 activity, 2: 328t in colostrum, 2: 328 distribution in milk, 2: 328t Embden–Meyerhof pathway, 2: 327 starter cultures, 1: 561–562 structure, 2: 328 L-Lactate dehydrogenase (L-LDH), 3: 85–86 (S)-Lactate:NAD+ oxidoreductase see Lactate dehydrogenase (LDH) Lactating dairy cows body temperature-respiratory rate relationship, 4: 561, 4: 565f metabolic responses to heat stress, 4: 561, 4: 565f metabolism models, 2: 431–432 ovulation and insemination synchronization, 4: 454 upper critical temperature, 4: 561 Lactation, 4: 514 average yield, 2: 458 calcium outflow, 2: 240 calcium requirements, 3: 996–997 early, energy balance, 4: 475–476, 4: 480–481, 4: 481f endocrine factor levels growth factors, 2: 768 steroid hormones, 2: 769, 2: 770 environmental mastitis, 3: 416 environmental temperature effects, 2: 99, 3: 42–43 evolution, 3: 553 fat supplement effects, 2: 365, 2: 368 heat production, 4: 562 homeorhetic changes, 2: 231 induced see Induced lactation mammary gland development, 3: 343 medical mastitis therapy, 3: 435 milk composition changes fatty acids, 3: 658 goats, 3: 489, 3: 489f, 3: 489f humans, 3: 588 ruminants (cows), 3: 530, 3: 531f sows, 3: 530, 3: 531f ungulates (reindeer), 3: 533, 3: 534f milk production, 4: 515–516, 4: 516f milk production efficiency from nutrients, 2: 426 acetate/propionate precursors, 2: 427t fatty acid/glucose precursors, 2: 427t net energy calculation systems, 2: 407 protein requirement and yield, 2: 424f, 3: 40 milk productivity grass and legume forages, 2: 580, 2: 580f multipurpose sheep, 2: 879, 2: 879t milk protein synthesis, 3: 363 milk yield changes goats, 3: 489, 3: 489f, 3: 489f humans, 3: 588 ruminants (cows), 3: 531f sows, 3: 530, 3: 531f ungulates (reindeer), 3: 533, 3: 534f performance records, 2: 657 persistency, genetic evaluation, 2: 651 sheep, health management, 2: 863 somatic cell count, 3: 603 teat canal keratin changes, 3: 381–382 underconditioned cows, 4: 516 see also Mammary gland; individual animals
896 Index Lactic acid antimicrobial properties, 1: 391–392, 1: 420 biosensor analysis, 1: 245 cheese preacidification, 1: 550 cheese salting, 1: 605, 1: 605 dry salting, 1: 605 Dutch-type cheese flavor, 1: 726 human milk, 3: 589 isomers bacterial, 2: 516t metabolism differences, 2: 515 metabolism cheese ripening see Cheese ripening starter cultures, 1: 553 surface mold-ripened cheese ripening, 1: 777, 1: 778f NSLAB metabolism, 1: 641 Penicillium camemberti, 1: 568–569 as preservative, 1: 37 production, starter cultures, 1: 552, 1: 625 The Lactic Acid Bacteria, 1: 28 Lactic acid bacteria (LAB), 1: 401–402 acid stress, 3: 63, 3: 65f aldehyde generation, 3: 162 antibiotic resistance genes, 3: 69 antimicrobial factors, 1: 420 see also Bacteriocins arginine catabolism, 3: 162–163 aromatic amino acid metabolism, 3: 162 aspartate catabolism, 3: 162–163 bacteriophage-insensitive strains, 1: 442 biodiversity, 3: 45–48 biogenic amines, 1: 451 blue mold cheeses, 1: 768 carbohydrate limitation, 3: 163–164 casein hydrolysis, 3: 54 cell envelope protease, 3: 49 chaperone proteins, 3: 63 Cheddar cheese ripening, 1: 709 cheese acidification, 1: 538 stress conditions, 3: 60 citrate fermentation, 3: 166–172 application aspects, 3: 170 butter production, 3: 172 cheese manufacture, 3: 171 flavor formation, 3: 169 flavor formation engineering, 3: 170, 3: 171f rate increasing strategies, 3: 171–172 starter composition, 3: 170 citrate metabolism, 3: 166 citrate transport, 3: 167 energetics, 3: 167, 3: 167f genetics, 3: 168 metabolic pathways, 3: 167, 3: 168f Clostridium spore control, 4: 53 cold stress, 3: 63 dairy impacts, 3: 45 defining characteristics, 3: 45 definition, 1: 639 diacetyl production improvement, 3: 170 endopeptidases, 3: 87 exopolysaccharide production, 3: 136 expression vectors, 3: 68–69, 3: 69t fermentation challenges, 3: 163–164 as ‘finishers’, 3: 161 flavor development, 3: 160–165 from amino acids, 3: 162 ‘background flavors’, 3: 162 from carbohydrates, 3: 161 coculture, 3: 163 contextualization, 3: 160 future developments, 3: 163 genetic manipulation, 3: 164 Maillard reaction, 3: 162 milk diversity, 3: 161 from milk fat, 3: 163 odor descriptors, 3: 163
processing parameters and, 3: 160 ripening parameters and, 3: 160 as flavor factories, 3: 161 food-grade cloning vectors, 3: 70t food-grade selection markers, 3: 69 food preservation, 3: 114, 3: 115 genetic analysis, 3: 67 genetic engineering, 3: 67–77 accelerated cheese ripening, 1: 797–798 accomplishments, 3: 68 gene transfer, 3: 67 genome reduction, 3: 71–73 genomes mobile elements, 3: 58–59 stress gene comparison, 3: 59–60, 3: 61t genomics, 3: 71, 3: 73t projects, 3: 71–73, 3: 72t glutamate catabolism, 3: 162–163 glycine generation, 3: 162 heat response, 3: 62–63 heat shock, 3: 62–63 heat stress, 3: 65f heterofermentative, pyruvate accumulation, 3: 168 heterologous gene expression, 3: 71 homofermentative, pyruvate accumulation, 3: 168 ketone generation, 3: 162 lactoperoxidase system effects, 2: 322–323 lactose metabolism, 1: 560, 1: 561f lysine catabolism, 3: 162–163 metabolic engineering, 3: 69 aroma compound overproduction, 3: 71 conditional functioning plasmid replicons, 3: 70 DNA fragment insertion, 3: 69–70 flavor overproduction, 3: 71 introns, 3: 71 nonreplicated plasmids, 3: 69–70 site-directed mutagenesis, 3: 71 milk inoculation, acid casein manufacture, 3: 855 nitrogen nutrition, 3: 49 nutrient stress, 3: 60 osmotic stress, 3: 64, 3: 65f oxidative stress, 3: 64 peptidase activities, cheese bitterness, 1: 564 pH stress, 3: 63 phylogenetic relationships, 3: 46f, 3: 46–47, 3: 67, 3: 68f physiology, 3: 56–66 plasmids, 1: 565–566, 3: 67 as probiotics, 3: 67, 3: 115 safety, 1: 417 processing-associated stresses, 3: 56 Propionibacterium interactions, 1: 408 proteolytic activities, 2: 290 cheese ripening, 1: 670, 1: 672 proteolytic system, importance, 3: 49 proteolytic systems, 3: 49–55, 3: 50t abnormal protein degradation, 3: 54 amino acid requirements, 3: 49 amino acid transport, 3: 53 CAAX proteases, 3: 54, 3: 55 extracellular and cell envelope proteolysis, 3: 49, 3: 52f genetic regulation, 3: 54 intracellular proteolysis, 3: 53 peptide transport, 3: 53 peptidoglycans, 3: 55 pheromone regulation, 3: 55 protein maturation and secretion, 3: 54 species involved, 3: 49 see also Cell envelope proteases (CEP, Prt) regulatory genes, 3: 60 representative cloning vectors, 3: 67, 3: 68t salting effects, 1: 564 species delineation, 3: 46 spoilage agents, dairy products, 3: 453 stability impacts, 3: 115 Staphylococcus aureus interactions, 4: 116 stress resistance, 3: 56–66
stress response genetic composition, 3: 56–57 genome plasticity, 3: 58–59, 3: 59f genomic evolution, 3: 58 microbial gene sequences, 3: 57–58 phylogenomic relatedness, 3: 59f study techniques, 3: 56 systemwide study tools, 3: 57, 3: 57f sugar starvation, 3: 64 surface mold-ripened cheeses, 1: 775 Swiss-type cheeses, 1: 713 synergistic relationships, yeast, 4: 750 taxonomy, 3: 45–48 genus groupings, 3: 47, 3: 47f revisions, 3: 47 temperature stress, 3: 60 textural impacts, 3: 115 thermophilic, hard Italian cheese ripening, 1: 733 volatile sulfur compound production, 3: 163 whey protein degradation, 3: 162 see also individual species; Non-starter lactic acid bacteria (NSLAB) Lactic Acid Bacteria Genome Consortium (LABGC), 3: 71–73 Lactic acid dehydrogenase see Lactate dehydrogenase (LDH) Lactic cultures, microbiological analytical methods, 1: 218 Lactic fermentation electrical conductivity measurement, 4: 237 historical aspects, 1: 27 milk, 2: 471 mold in, 2: 474 Swiss-type cheese ripening, 1: 716 Lacticin(s), 1: 422t Lacticin 481, 1: 422t Lacticin 3147, 1: 422t, 1: 423f, 1: 425, 3: 135–136 anticariogenic effects, 3: 1038 Lacticin S, 1: 422t Lactitol, 3: 178, 3: 204 commercial applications, 3: 204t commercial production, 3: 203f hepatic encephalopathy, 3: 204 laxative effects, 3: 204 as prebiotic, 4: 358 putrefaction reduction, 4: 369 structure, 4: 357f Lactobacillus, 1: 401, 3: 78–90, 3: 125–131 as adjuncts, 3: 83 analytical methods, 1: 218 applications, 3: 67 arginine metabolism, 3: 126 bacteriocin-producing species, 3: 128–129 bacteriocins autolysis rates, 3: 89 cheese manufacture applications, 3: 89 lanthionine-containing (lantibiotics), 3: 89 non-lanthionine-containing, 3: 89 production, 3: 89 undesirable microbe control, 3: 89 bacteriophages, 1: 430, 1: 430–431, 3: 84 genome sequences, 1: 434 morphology, 1: 431 biodiversity, 3: 47, 3: 47f, 3: 111 biofilms, 1: 446 carbohydrate digestibilities, 3: 214 cell envelope-associated proteinases, 3: 86 cheese, 3: 80t, 3: 125 flavor defects, 3: 130 odor defects, 3: 130 ripening, 1: 671, 1: 671 culture conditions, preferred, 3: 92 dairy products antimicrobial effects, 3: 128 biogenic amines, 3: 130 desirable effects, 3: 128 flavor production, 3: 129 gas production defects, 3: 130
Index undesirable effects, 3: 130 differentiation, 3: 99t enumeration, 3: 79 esterases, 3: 88 facultative heterofermentative, 3: 78, 3: 126 fermentation patterns, human gut, 4: 367–368 fermentation starters, 3: 455 fermented milk starters, 3: 80t, 3: 83 characteristics, 2: 479t consumer longevity effects, 2: 483, 2: 484f pure cultures, koumiss manufacture, 2: 515 flavor development, 3: 85 citrate metabolism, 3: 86 free amino acid catabolism, 3: 86f, 3: 87 lactate metabolism, 3: 85 lactose metabolism, 3: 85 lipolysis, 3: 88 proteolysis, 3: 86, 3: 86f undesirable flavors, 3: 87–88 gas blowing defects, cheese, 1: 664 brine-salted cheeses, 1: 665 gastrointestinal microflora (human), 1: 383t generally regarded as safe status, 3: 78 genomics, 3: 73, 3: 75f metabolic pathways, 3: 74f groups, 3: 78–79, 3: 79f, 3: 80t, 3: 125 growth media, 3: 79–82 health effects, 3: 88–89 historical aspects, 1: 30 identification methods, 3: 82 genotyping, 3: 82 molecular biology, 3: 82, 3: 83f phenotypic, 3: 82 intracellular peptidases, 3: 86 isolation, 3: 79 lactate crystal formation, 3: 130 lactic acid fermentation, 3: 126 lipases, 3: 88 natural milk inhibitors, 3: 84 non-starter, 3: 125 as NSLAB, 1: 626, 3: 84, 3: 84f obligate heterofermentative, 3: 78, 3: 126 obligate homofermentative, 3: 78 phage resistance mechanisms, 3: 84 phylogenetic tree, 3: 78, 3: 79f, 3: 125 plasmids, 1: 565–566 probiotic effects, 3: 67, 3: 80t, 3: 88, 3: 129 proteolysis, 3: 125 species descriptions, 3: 126 as spoilage microorganisms, 3: 453 as starter cultures, 1: 559, 1: 560t, 3: 83 activity inhibitors, 3: 84 cheese, 3: 80t, 3: 84 Streptococcus thermophilus symbiotic relationship, 3: 145 taxonomy, 3: 47, 3: 47f, 3: 78, 3: 111 reclassification, 3: 78–79 thermophilic, Swiss-type cheese ripening, 1: 716 see also individual species; individual species/groups Lactobacillus acidophilus, 3: 80t, 3: 91–95 acidophilus milk, 2: 473 bacteriocin production, 3: 93 bifidus products, 1: 388 characteristics, 3: 92 metabolism, 3: 92, 3: 92t, 3: 92t classification and taxonomy, 3: 91 phylogenetic relationships, 3: 91 species definition, 3: 91 enumeration, 3: 93 fermented dairy products, 3: 93 fermented milk starter culture, 3: 83 genome, 3: 74f human health benefits, 3: 94 specific strains, 3: 94 identification accuracy, 3: 92 isolation and selective media, 3: 92 metabolic pathways, 3: 74f morphology
cellular, 3: 91 colony growth, 3: 91 occurrence, 3: 91 optimal growth conditions, 3: 91 starter cultures, 1: 560t storage, 3: 93 as yogurt starter cultures, 3: 93 Lactobacillus brevis, 3: 126 biogenic amine production, 3: 130 blue mold cheeses, 1: 769 brine-matured cheeses, 1: 793 cheese flavor, 1: 642 Dutch-type cheese defects, 1: 726 gas production defects, 3: 130 genome, 1: 643t, 3: 74f lactate racemization, 3: 130–131 lactic acid fermentation, 3: 126 metabolic pathways, 3: 74f as NSLAB, 1: 626 probiotic effects, 3: 129 Lactobacillus buchneri, 3: 127 arginine metabolism, 3: 126 biogenic amine production, 3: 130 genome sequence, 1: 643t Lactobacillus buchneri group, 3: 78–79 Lactobacillus bulgaricus, 3: 1038 Lactobacillus casei, 3: 97 anticariogenic effects, 3: 1038 bifidus products, 1: 388 blue mold cheeses, 1: 769 brine-matured cheeses, 1: 793 carbohydrate fermentation, 3: 98t differentiation, 3: 96 Dutch-type cheese defects, 1: 726 genome sequence, 1: 643, 1: 643t lactose starvation, 3: 163–164 metabolism, 1: 641 as NSLAB, 1: 626 flavor compound production, 3: 87–88 population dynamics, 1: 639–640 Swiss-cheese starter culture, 1: 714 Lactobacillus casei group, 3: 78–79, 3: 96–104 bacteriocin production, 3: 100 characteristics, 3: 96 cheese, 3: 97 adjuncts, 3: 100 amino acid metabolism, 3: 102 curd contamination, 3: 98–100 flavor development, 3: 101 growth in, 3: 100 growth substrates, 3: 101, 3: 101–102 NSLAB, 3: 97 peptidases, 3: 101 probiotic effects, 3: 102–103 proteolytic activities, 3: 101 ripening effects, 3: 101, 3: 101 ripening temperature, 3: 100 sources, 3: 97 conjugated linoleic acid formation, 3: 102 differentiation, 3: 96 distinguishing features, 3: 97 division, 3: 96 fermented milks, 3: 102 identification, 3: 97, 3: 99t isolation, 3: 97 lactate racemization, 3: 101–102 as NSLAB, 3: 84–85 probiotic foods, 3: 102 see also individual species Lactobacillus casei spp. casei AB16-65, 3: 734 Lactobacillus casei subsp. casei see Lactobacillus casei Lactobacillus casei subsp. rhamnosus see Lactobacillus rhamnosus Lactobacillus.casei subsp. shirota fermented milks, 2: 514 probiotic effects, 3: 102 Lactobacillus curvatus, 3: 128 gas production defects, 3: 130
897
population dynamics, 1: 639–640 Lactobacillus delbrueckii group, 3: 78–79, 3: 119–124 associative growth, 3: 122 bacteriocins, 3: 122 bacteriophages, 3: 121 in cheese, 3: 122 acid production, 3: 122 flavor development, 3: 123 enumeration, 3: 119 exopolysaccharide production, 3: 122 flavor production, 3: 122 functional properties, 3: 123 general characteristics, 3: 119 genotyping, 3: 119 growth in milk, 3: 122 identification, 3: 119, 3: 120t isolation, 3: 119 lactose fermentation, 3: 121 low-moisture part-skim mozzarella (pizza cheese), 1: 740–741 as starter cultures, 3: 119 subspecies, 3: 119 Lactobacillus delbrueckii subsp. bulgaricus, 3: 80t, 3: 119, 3: 120t amino acid catabolism, 3: 123 associative growth, 3: 122 bacteriocins, 3: 122 bacteriophages, 3: 121 bifidus products, 1: 388 blue mold cheeses, 1: 768 brine-matured cheeses, 1: 793 characteristics, 2: 531 cheese starter culture, 3: 84 exopolysaccharide production, 3: 122 fermented milk starter culture, 3: 83 functional properties, 3: 123 ‘Grana’ cheeses, 1: 728–729 growth inhibition, 3: 122–123 lactose fermentation, 3: 121 lipolyzed cream products, 2: 286 low-moisture part-skim mozzarella (pizza cheese), 1: 740 milk antibiotics, 3: 122 Mozzarella cheese, 3: 123 probiotic supporter strain, 1: 415 as starter culture, 3: 122 starter cultures, 1: 560t yogurt, 2: 472, 2: 525, 2: 527, 2: 529, 2: 531, 3: 121, 3: 145 fermentation time, 1: 390 flavor production, 3: 122 yogurt-like products, 3: 121 Lactobacillus delbrueckii subsp. delbrueckii, 3: 120t, 3: 121 Lactobacillus delbrueckii subsp. indicus, 3: 120t, 3: 121 Lactobacillus delbrueckii subsp. lactis, 3: 80t, 3: 120t, 3: 121 bacteriocins, 3: 122 bacteriophages, 3: 121 cheese starter culture, 3: 84 ‘Grana’ cheeses, 1: 728–729 lactose fermentation, 3: 121 as starter culture, 3: 122 starter cultures, 1: 560t Swiss-cheese starter culture, 1: 408, 1: 713, 1: 714–715 Lactobacillus durianis, 3: 78–79 Lactobacillus fermentum, 3: 127 bacteriocins, 3: 128–129 blue mold cheeses, 1: 769 flavor production, 3: 129 gas production defects, 3: 130 genome sequence, 1: 643t ‘Grana’ cheeses, 1: 728–729 lactate racemization, 3: 130–131 lactic acid fermentation, 3: 126 as NSLAB, 1: 626 Parmigiano Reggiano cheese, 3: 129 Lactobacillus fermentum type II see Lactobacillus reuteri
898 Index Lactobacillus helveticus, 3: 80t, 3: 105–110 accelerated cheese ripening, 1: 797 ACE inhibitory peptide production, 3: 884–885 as adjunct starter, 3: 109 amino acid transamination, 3: 109 bacteriocins, 3: 106 bacteriophage susceptibility, 3: 107 bioactive compound synthesis, 3: 106 health-promoting effects, 3: 109 cheese flavor development, 3: 107, 3: 109 cheese ripening, 3: 108 cheese starter culture, 3: 84 dairy uses, 3: 105 cheesemaking, 3: 108 fermented milks, 3: 108 distinguishing characteristics, 3: 105, 3: 105 enumeration and isolation media, 3: 106 exopolysaccharides, 3: 106–107 fermentation pathways, 3: 106 genetics, 3: 105 genome sequencing, 3: 105 ‘Grana’ cheeses, 1: 728–729 health-promoting effects, 3: 109 hypotensive effects, 2: 486 identification and genetic typing, 3: 106 low-moisture part-skim mozzarella (pizza cheese), 1: 740, 1: 740–741 protemics, 3: 105 proteolytic enzymes, 3: 107 ripening role as starter, 3: 108 starter cultures, 1: 560t as starter in hard/extrahard cheeses, 3: 108 as starter in Swiss type cheese, 3: 108 as starter in yogurts, 3: 108 Swiss-cheese starter culture, 1: 408, 1: 713, 1: 714–715 transamination, 3: 87–88 Lactobacillus kefiri, 3: 128 flavor production, 3: 129 Lactobacillus maltaromicus, 3: 734 Lactobacillus paracasei blue mold cheeses, 1: 769 fermented milk starter culture, 3: 83 lactose-6-phosphate metabolism, 3: 85 as NSLAB, 1: 626 population dynamics, 1: 639–640 starter cultures, 1: 560t Lactobacillus paracasei subsp. paracasei, 3: 80t, 3: 97 brine-matured cheeses, 1: 793 carbohydrate fermentation, 3: 98t as cheese adjunct, 3: 100 citrate degradation, 3: 101–102 dairy uses, 3: 96 differentiation, 3: 96 fermented milk starter culture, 3: 83 free amino acid catabolism, 3: 87–88 proteinases, 3: 101 yakult, 2: 508 Lactobacillus paracasei subsp. tolerans, 3: 97 carbohydrate fermentation, 3: 98t differentiation, 3: 96 heat resistance, 3: 98, 3: 100f as NSLAB, 3: 98 proteinases, 3: 101 Lactobacillus plantarum, 3: 80t, 3: 111–118 amino acid biosynthesis, 3: 114 antibiotic resistance, 3: 116 antifungal compounds, 3: 115 antimicrobial products, 3: 114 bacteriocins, 3: 114–115 blue mold cheeses, 1: 769 brine-matured cheeses, 1: 793 characteristics, 3: 111 dairy product uses, 3: 116 Dutch-type cheese defects, 1: 726 enzymes, 3: 112 esterases, 3: 114 exopolysaccharides, 3: 115
fermentation pathways, 3: 112, 3: 113f fermented milk starter culture, 3: 83 food quality products, 3: 114 functional activities, 3: 115 genome, 1: 643t, 3: 73–74, 3: 111 health benefits, 3: 115 human health benefits, intestinal pathogens protection, 3: 115–116 identification, 3: 111, 3: 112f lipases, 3: 114 Listeria monocytogenes inhibition, 3: 89 metabolism, 3: 112 milk uses, 3: 116 as NSLAB, flavor compound production, 3: 87–88 plantaricin-producing strains, 3: 89 population dynamics, 1: 639–640 proteolytic activity, 3: 114 recent research, 3: 116 antinutritional factor toxicity reduction, 3: 116 conjugated linoleic acid production, 3: 116 live mucosal vaccine, 3: 116 sorbitol production, 3: 71 taxonomy, 3: 111, 3: 112f relationships, 3: 111 Lactobacillus plantarum group, 3: 78–79 Lactobacillus reuteri, 3: 80t, 3: 127 anticariogenic effects, 3: 1038 bacteriocins, 3: 128–129 fermented milk starter culture, 3: 83 flavor production, 3: 129 genome, 3: 74, 3: 127–128 probiotic effects, 3: 129 Lactobacillus reuteri group, 3: 78–79 Lactobacillus rhamnosus, 3: 80t, 3: 97, 3: 128 carbohydrate fermentation, 3: 128 cell envelope proteinase, 3: 125–126 classification, 3: 96 dairy uses, 3: 96 fermented milk starter culture, 3: 83 flavor production, 3: 130 genome, 1: 643t, 3: 128 heat resistance, 3: 98 as NSLAB, 3: 98 population dynamics, 1: 639–640 probiotic effects, 3: 102, 3: 129 proteinases, 3: 101 starter cultures, 1: 560t Swiss-cheese starter culture, 1: 714 Lactobacillus rhamnosus GG (LGG), 3: 1037–1038 Lactobacillus rhamnosus LC705, 3: 1038 Lactobacillus sakei genome, 3: 73–74 Lactobacillus sakei group, 3: 78–79 Lactobacillus salivarius, 3: 73–74 Lactobacillus salivarius group, 3: 78–79 Lactobacillus vaccinostercus, 3: 78–79 Lactobionic acid, 3: 178, 3: 202 commercial applications, 3: 202, 3: 204t pharmaceutical uses, 3: 202 production, 3: 203f Lactococcin A, 1: 422t Lactococcin B, 1: 422t Lactococcin M, 1: 422t Lactococcus, 1: 401 acid stress, 3: 63–64 analytical methods, 1: 218 applications, 3: 67 cheese ripening, proteolysis, 1: 670–671, 1: 671 citrate metabolism energy generation, 3: 167 genetics, 3: 168 dairy-associated genes, 3: 58 gas blowing defects, cheese, 1: 662 avoidance, 1: 662 genomic relatedness, Streptococcus thermophilus, 3: 59, 3: 60f genomics, 3: 74, 3: 75f peptidases, enzyme-modified cheese, 1: 802–803 as spoilage microorganisms, 3: 454
starter cultures, 1: 559, 1: 560t, 3: 455 see also individual species Lactococcus lactis, 2: 489, 2: 491, 3: 132–137 amino acid/peptide metabolism and transport, 3: 49, 3: 53 antigen delivery vehicle, 3: 967–968 bacteriocin production, 3: 135 bacteriophage (phage) resistance, 3: 135 exopolysaccharides, 3: 136 screening, 3: 135 casein breakdown, 3: 134 cell morphology, 3: 132, 3: 133f classification, 3: 132 discovery, 1: 27–28 Dutch-type cheeses, 1: 723 exopolysaccharide production, 3: 136 flavor production, amino acids, 3: 134 genetic typing methods, 3: 132 genomes, 3: 71–73, 3: 74–75, 3: 132 sequence, 1: 643 genomics, 3: 132 habitat, 3: 132 identification, 3: 134 industrially significant properties, 3: 134 lactose utilization, 3: 134 nitrogen metabolism regulation genetic, 3: 54 regulatory intra-membrane proteolysis, 3: 55 signal peptides, 3: 54–55 plasmid encoded traits, 3: 68 plasmidosome, 3: 134 plasmids, 1: 565–566, 3: 132 proteolytic enzymes, 3: 50t, 3: 52, 3: 52f proteolytic system, 3: 134–135 slime encapsulated strains, 2: 496, 2: 497f starter cultures, 1: 554–555 subspecies characteristics, 2: 478t subspecies differentiation, 3: 132 surface mold-ripened cheeses, 1: 775 Lactococcus lactis subsp. cremoris, 3: 132 blue mold cheeses, 1: 768 butter manufacture, 1: 495 Cheddar cheese starter cultures, 1: 707 cottage cheese manufacture, 1: 700 cultured cream products, 1: 917 Dutch-type cheeses, 1: 723 historical aspects, 1: 28 Quarg manufacture, 1: 703 starter cultures, 1: 554–555, 1: 560t, 1: 625 Lactococcus lactis subsp. cremoris MG1363, 3: 71–73, 3: 132–133 Lactococcus lactis subsp. cremoris SK11, 3: 71–73, 3: 132–133 Lactococcus lactis subsp. lactis, 3: 132 blue mold cheeses, 1: 768 brine-matured cheeses, 1: 793 butter manufacture, 1: 495 Cheddar cheese starter cultures, 1: 707 cheese ripening, 1: 668–669 cottage cheese manufacture, 1: 700 cultured cream products, 1: 917 Dutch-type cheeses, 1: 723 historical aspects, 1: 28 nisin, 1: 422–423 Quarg manufacture, 1: 703 starter cultures, 1: 560t, 1: 625 Lactococcus lactis subsp. lactis biovar diacetylactis, 3: 132 citrate metabolism, 3: 168f Dutch-type cheeses, 1: 723 flavor formation, 3: 170 oxaloacetate decarboxylase, 3: 167 Lactococcus lactis subsp. lactis CHD-28.3, 4: 788–789 Lactococcus lactis subsp. lactis IL1403, 3: 71–73, 3: 132–133 Lactoferoxin, 3: 1063 Lactoferricin, 3: 803–804 antiangiogenic properties, 3: 796 antibacterial activities, 3: 1064
Index anticancer effects, 3: 805 antimicrobial activity, 3: 881t, 3: 883 Lactoferrin (LF), 3: 801–806 antibacterial properties, 3: 388–389 anticarcinogenic activity, 3: 805, 3: 1065 antifungal properties, 3: 804 antimicrobial effects, 3: 801, 3: 802, 3: 883, 3: 1064 mechanisms, 3: 802 protease-like, 3: 804 antithrombotic effect, 3: 1064–1065 antiviral effects, 3: 802 applications, 3: 806 bacteriostatic properties, 3: 388–389 iron deprivation, 3: 802–803 bioactivity, 2: 133 biochemical properties, 3: 801 biological importance, 3: 802, 3: 803t biological roles, 3: 759 in biological secretions, 3: 801, 3: 802t buffalo milk, 3: 505 coding sequences, 3: 840 colostrum, 3: 593–594, 3: 595t, 3: 596 cytokine production, 3: 804–805 equid milk, 3: 522 feed supplementation, 3: 804 first-age infant formulae, 2: 141 functions, 3: 801 gene structure, 3: 840 growth factor-like effects, 3: 805 immunomodulation, 3: 797, 3: 804, 3: 883, 3: 1064 infant formulae, 3: 804 inflammatory response, 3: 804 interspecies comparison, 3: 840 in vivo activities, 3: 802, 3: 803t ion-exchange chromatography, 1: 170–171 iron-binding affinity, 3: 801–802 isolation, 3: 806 lymphocyte proliferation, 3: 804 marsupial milk, 3: 556–558 molecular surface, 3: 840 nutritional significance, 3: 805 primate milk, 3: 625 protective effects, 3: 840 safety aspects, 3: 806 structure, 3: 758, 3: 801 synthesis, 3: 801 technological properties, 3: 802 thermal stability, 3: 802 whey protein products, 3: 876, 3: 876t Lactoferrin gene, 3: 801, 3: 840 complete coding regions, 3: 840 Lactofil, 2: 472 Lactogenesis, 3: 15–19 control, 3: 17 mammary structures, 3: 15, 3: 16f secretory cell differentiation, 3: 16 stages, 3: 15–16 -Lactoglobulin, 3: 481, 3: 787–794, 3: 836 allergenicity, 3: 793 allergies, 3: 365 amino acid substitutions, 3: 836–837, 3: 837 A variant, 3: 787–788, 3: 789, 3: 790f, 3: 793 biological roles, 3: 759 buffalo milk, 3: 504 B variant, 3: 787–788, 3: 789, 3: 790f, 3: 793 k-casein reactions, 3: 793 colostrum, 3: 591, 3: 593f commercial vs. laboratory prepared, 3: 788, 3: 789f C variant, 3: 789, 3: 790f, 3: 793 dimers, 3: 789 donkey milk, 1: 369 duplicated gene, 3: 837 emulsion stability, microbial transglutaminase, 2: 299 equid milk, 3: 519 equine milk, 3: 522, 3: 792 fibril self-assembly, 3: 793
function, in milk, 3: 791 gelation, 3: 892 genetic variants, 3: 752t, 3: 759–760, 3: 822t, 3: 837 cheesemaking properties, 3: 837 milk composition, 3: 837 genomic organization, 3: 837 heat stability, milk, 2: 746, 2: 746f heat treatment effects, 3: 792 high pressure hydrolysis, 2: 737 hydrolysis, 3: 793 interprotein reactions, 3: 792 interspecies comparison, 3: 758–759, 3: 836, 3: 836f, 3: 837f intraprotein reactions, 3: 792 isolation, 3: 788 -lactalbumin interactions, 3: 793 lactose, reaction with, 3: 793 ligand binding, 3: 790, 3: 791t, 3: 836–837 Maillard reaction, 3: 219, 3: 227, 3: 793 marine mammal milk, 3: 574–576 marsupial milk, 3: 556–558 milk allergy, 3: 1042–1043 monotreme milk, 3: 558 nomenclature, 3: 787 polymer formation, 3: 792 porcine, 3: 792 primary structure, 3: 755, 3: 756f primate milk, 3: 621, 3: 624 processing-induced structural changes, 3: 792 purification, 3: 788 reindeer, 3: 791–792 separation, 3: 788, 3: 788f sheep milk, 3: 496, 3: 496t, 3: 791–792 species distribution, 3: 792 structure, 3: 787, 3: 788, 3: 790f in milk, 3: 790f, 3: 791, 3: 791t primary, 3: 788 quaternary, 3: 789 secondary, 3: 789 tertiary, 3: 789 synthesis, 3: 377 Tanford transition, 3: 787, 3: 790 UHT milk, 2: 706t, 2: 706–707 variants, 3: 787, 3: 789, 3: 790f -Lactoglobulin gene, 3: 835, 3: 837 Lactollin, 3: 758 Lactometers, 1: 82t, 1: 251 milk solids-not-fat (MSNF), 1: 251 Lacto-N-biose hypothesis, 3: 253, 3: 253f Lactones cheese flavor, 1: 681 ghee, 1: 517–518 milk fat flavor, 3: 652–653 off-flavors cause, 2: 540, 2: 541f, 3: 486 Lactoperoxidase (LPO), 2: 319–323 activity in milk, 2: 322 bactericidal effect, 2: 322 bacteriostatic effect, 2: 322 maximum, 2: 320 as antioxidant, 2: 319 bioactivity, 2: 133 calcium binding, 2: 319–320 colostrum, 3: 594, 3: 595t cream pasteurization testing, 4: 199 functions, 2: 319 historical aspects, 1: 23 inactivation, 2: 320 intermediates, 2: 319 ion-exchange chromatography, 1: 170–171 isolation, 2: 319–320 mastitis infection index, 2: 322 milk preservation, 2: 322 pH effects, 2: 320 physicochemical properties, 2: 319 sheep milk, 3: 500 structure, 2: 319–320 thermal stability, 2: 320
899
Lactoperoxidase system (LPS), 2: 320 antifungal action, 2: 323 antimicrobial action, 2: 321 inhibition, 2: 321–322 antiviral action, 2: 323 applications, 2: 320 camel milk, 3: 516 Lactorphins, 3: 1063 Lactose, 3: 196–201, 3: 367–372, 3: 478 amorphous, spray-drying, 3: 182 anomeric forms, 3: 184f, 3: 184–185 applications, 3: 178, 3: 196, 3: 197f ash concentration relationship, 3: 174–175, 3: 176f bakery ingredient, 3: 196 Bifidobacterium fermentation patterns, 1: 386t biosensors, 1: 244 biosynthesis, 3: 173, 3: 367 enzyme-mediated steps, 3: 368–369 glucose supply, 3: 367 secretory vesicles, 3: 369 calcium intestinal absorption, 3: 929–930 camel milk, 3: 514 casein concentration and, 3: 173, 3: 175f characterization, historical aspects, 1: 20 chemical analysis, 1: 80, 1: 82t enzymatic methods, 1: 81, 1: 82t historical aspects, 1: 20 polarimeter method, 1: 81, 1: 82t chemistry, 3: 173–181 Codex standard, 4: 330 colon cancer risk, 3: 1020 commercial preparation, 3: 178 commercial sourcing and price, 3: 196, 3: 197f concentration, milk, 3: 173, 3: 462, 3: 478 species differences, 3: 367, 3: 368t, 3: 550 confectionary ingredient, 3: 196 crystallization see Lactose crystallization dairy products, 3: 1011t, 3: 1011–1012 derivatives see Lactose derivatives digestibility, 2: 484, 3: 610 edible grade, production process, 3: 197, 3: 198f crystallization, 3: 197 crystal separation and washing, 3: 198 drying and packing, 3: 198 whey permeate concentration, 3: 197 equid milk, 3: 518 feedback inhibitory protein, putative, 3: 370 fermentation, Dutch-type cheeses, 1: 723 fermentation products, 3: 179, 3: 179f, 3: 371 frozen milk, 3: 180 functions in milk, 3: 174 galacto-oligosaccharide synthesis substrate, 3: 196, 3: 209 competitive inhibition, 3: 212 pH, 3: 212 reaction mechanism, 3: 209–211, 3: 211f water activity, 3: 212 genetic engineering, 3: 177 glass transition, differential scanning calorimetry, 1: 256, 1: 257f, 1: 258f, 1: 258t health considerations, 3: 371 heat stability, milk, 2: 745–746, 2: 746f heterolactic fermentation, 3: 161–162 citrate fermentation and, 3: 161–162 historical aspects, 1: 17 homolactic fermentation, 3: 161–162 hydrolysis, 3: 180 ice formation, 4: 711 industrial hydrolysis processes, 4: 736 infant formula supplementation, 3: 196 intolerance see Lactose intolerance isolation, historical aspects, 1: 20 khoa, 1: 884 -lactoglobulin, reactions with, 3: 793 low-fat cheese moisture content, 1: 835 Maillard reaction, 3: 176, 3: 180 malabsorption see Lactose malabsorption/ malabsorbers
900 Index Lactose (continued ) maldigestion see Lactose maldigestion mammary synthesis control, 3: 41, 3: 550 market applications, 3: 196, 3: 197f marsupial milk, 3: 322 mastitis, 3: 904 metabolism cheese ripening, 1: 667, 1: 668f starter cultures, 1: 563 surface mold-ripened cheese ripening, 1: 777, 1: 778f milk chocolate, 1: 858, 1: 860 milk content reduction, 3: 369 gene knockout experiments, 3: 369, 3: 369t milk fat concentration and, 3: 173, 3: 174f milking frequency and, 3: 370, 3: 371f milk osmolarity, 3: 174, 3: 175f milk powder solubility, 2: 122 milk salt interactions, 3: 917, 3: 918f milk standardization, cheese manufacture, 1: 548 molecular formula, 3: 184f monotreme milk, 3: 556 as nondigestible carbohydrate, 4: 357–358 nutrient intake, contributions to, 3: 1004 nutritional problems, 3: 178 paracellular pathway, 3: 370 as pharmaceutical component, 3: 196–197 pharmaceutical derivatives, 2: 132f, 2: 132–133 pharmaceutical grade production, 3: 199, 3: 199f physiological stress, 3: 370 as prebiotic, 4: 357, 4: 361t primate milk, 3: 613–614, 3: 615 production, 3: 178 production problems, 3: 199 caking, 3: 198–199, 3: 200 evaporator fouling, 3: 199 fines generation in crystallizers, 3: 200 whey fermentation, 3: 200 properties, 3: 176 quantitative determination, 3: 176 reindeer milk, 1: 376–377, 1: 377 removal, whey recovery processes, 2: 127, 2: 127f seasonal variations, 3: 601f secretion, 3: 367 sheep milk, 3: 499 significance, dairy products, 3: 180 solubility, 3: 177, 3: 177f, 3: 184, 3: 212 pH changes, 3: 184 temperature effects, 3: 184–185 solubility curve, 3: 185f cooling, 3: 186, 3: 186f source, 3: 196 sterilized milk, 3: 289 structure, 3: 174f, 4: 357f historical aspects, 1: 20 sweetness, 3: 177, 3: 199 synthesis, 3: 332 enzyme-mediated steps, 3: 368t lactogenesis, 3: 16 synthesis-effecting factors, 3: 370 diet, 3: 370 environmental effects, 3: 370 temperature effects, 3: 370 transfructosyllation, 3: 204–205, 3: 205f transglucosylation, 3: 205f uses, 3: 178, 3: 371 -Lactose, solubility, 3: 177, 3: 177f -Lactose anomer, 3: 184f, 3: 192 solubility, 3: 177, 3: 177f Lactose crystallization, 3: 182–195, 4: 710 concentration effects, 1: 231 critical points, 3: 182 dulce de leche defects, 1: 878 growth stage, 3: 190–191, 3: 191f impurity effects, 3: 191 inhibitory capacity, 3: 193–194 macrominerals, 3: 192
similar additives, 3: 192 industrial level, 3: 194 kinetics, 4: 710 lactose phosphate impurities, 3: 193 -monohydrated form, 3: 183 mutarotation very fast, 3: 185 very slow, 3: 185 nucleation see Nucleation riboflavin, 3: 193 from solution, 3: 183 supersaturation, 3: 185, 3: 186t mutarotation kinetics, 3: 185 sweetened condensed milk, 1: 872 temperature effects, 3: 197–198, 4: 710 ‘tomahawk’ morphology, 3: 191f, 3: 192, 3: 192f water sorption, 4: 710 Lactose derivatives, 3: 178, 3: 202–208, 3: 201, 3: 204t chemical production processes, 3: 203f commercially produced, 3: 202 enzymatic production processes, 3: 203f experimental, 3: 206 food applications, 3: 202 lactose transglucosylation, 3: 205f, 3: 206 naturally occurring, 3: 202 as prebiotic carbohydrates, 3: 202 transgalactosylation produced, 3: 206, 3: 207t prebiotic properties, 3: 206 see also individual derivatives Lactose-derived ethanol, 3: 179, 3: 371 Lactose digesters, 3: 236 Lactose-free milk, 3: 299 Asian market, 4: 352 properties, 3: 233, 3: 233 storage conditions, 3: 233, 3: 233 Lactose-free products, 2: 281 market growth rates, 2: 281 off-flavor development, 2: 282 Lactose intolerance, 2: 277, 3: 178, 3: 236–240, 3: 610 alleviation strategies, 3: 610 probiotics, 2: 484 Bifidobacterium, 1: 392 bone health, 3: 1013 colon cancer risk, 3: 1020–1021 definition, 3: 1004 dietary calcium intake, 3: 1013–1014 ethnic incidence, 3: 610 Mongolian, and koumiss consumption, 2: 514 galactose absorption, 3: 1051 -D-galactosidase deficiency, 1: 392–393 research, historical aspects, 1: 20 secondary, 3: 236 symptoms, 3: 236, 3: 371–372 tolerance of kefir, 2: 524 see also Lactase persistence Lactose malabsorption/malabsorbers, 4: 357–358 gastrointestinal symptom variability, 3: 1013–1014 osteoporosis, 3: 1013–1014 severity, 2: 277 Lactose maldigestion, 3: 236 milk consumption, 3: 1004 prevalence, 2: 277 Lactose phosphate, 3: 193 Lactose-reduced milk, 3: 299 Lactose synthase, 3: 173 marine mammal milk, 3: 576 reactions catalyzed, 3: 783f regulation, -lactalbumin, 3: 782 Lactose synthetase, 3: 368–369 Lactose tolerance test, 3: 236 Lactostatin, 3: 883 Lactosucrose, 3: 204 commercial applications, 3: 204t prebiotic effect, 3: 205–206 prebiotic effects, 4: 361t production, 3: 203f, 3: 204–205, 3: 205f structure, 4: 357f, 4: 359t Lactotransferrin see Lactoferrin
Lactra, 4: 22, 4: 22f Lactulose, 3: 178, 3: 204, 3: 371 Bifidobacterium growth requirements, 1: 384–385, 1: 389 bifidogenic effect, 4: 368 biosensors, 1: 243 colon cancer risk, 3: 1020 commercial applications, 3: 204t commercial production, 3: 203f, 3: 204 hepatic encephalopathy, 3: 204 as prebiotic, 3: 204, 4: 358, 4: 361t putrefaction reduction, 4: 369 structure, 4: 357f, 4: 359t UHT milk, 2: 706t, 2: 706–707 Lactulosyl lysine (LL), Maillard reaction, 3: 1068 marker, 3: 1069–1070 Lacune sheep, 2: 74 Lagoons, 4: 632 LALBA see -Lactalbumin Lama glama see Llama Lama guanicoe (guanaco), 1: 351 LaMancha goats, 1: 314, 1: 315f Lama pacos see Alpaca Lama vicugna (vicuna), 1: 351 Lambing, accelerated, 2: 71 Lambing pens, 2: 861 Lambs, artificial/supplemental colostrum feeding, 2: 883, 2: 885 Lamellar plates, mammary suspensory ligaments, 3: 331 Lameness bulls, 1: 479 detection, pedometers, 4: 463 laminitis, 2: 203 non-seasonal/pasture-based management, 2: 49 papillomatous digital dermatitis, 2: 169 rams, 2: 864 sheep, 2: 857 Laminates fluid milk packaging, 4: 17 powder milk packaging, 4: 19 Laminitis, 2: 203 causes, 2: 203 clinical features, 2: 203, 2: 203f, 2: 204f, 2: 204f condition features, 2: 203 definition, 2: 199 flooring surface, 2: 205 goats, 2: 800–801 metabolic causes, 2: 203–204 prevention, 2: 204 ruminal acidosis link, 2: 199, 2: 203 treatment, 2: 205 see also Acidosis Land application, milking parlor wastewater, 4: 632–633 Land irrigation, processing wastewater, 4: 633 Lane ways, 2: 26, 2: 26f Langevin equation, 1: 139 L˚angfil (t¨atmj¨olk), 2: 472, 2: 499, 4: 749 Langhe sheep, 1: 334, 1: 334f milk yield, 1: 332t Lantibiotics (lanthionine-containing bacteriocins), 1: 421, 1: 423f lactococci, 3: 135–136 Laplace principle, 3: 675 LAPS (light-addressable potentiometric sensor), 1: 239, 1: 239f, 1: 241 Large-calf syndrome, 2: 621–622 Large intestine, prebiotic carbohydrate fermentation, 4: 367, 4: 367f Large round baler, 1: 5 Large-scale setups, Africa, 2: 78f, 2: 80 Large strain deformation, 1: 694 Large strain sheer, 1: 695 Lasalocid, calf starters, 4: 402 Laser, light scattering, 1: 133 Laser Doppler electrophoresis, 1: 137 Late blowing see Gas blowing
Index Late-lactation protein-A (LLP-A), 3: 556–558 Late-lactation protein-B (LLP-B), 3: 556–558 Latent heat of vaporization, 4: 589 Lateral suspensory ligament, mammary gland, 3: 329, 3: 330–331, 3: 331f Latin America, dairy management see Cattle husbandry (Latin America) L¨att & lagom, 1: 523, 1: 524–525 Latxa sheep, 1: 332t, 1: 335 Laude mold, 1: 613, 1: 615f Lauric acid, 3: 730–731 Lauric fats, imitation whipped creams, 2: 916 Law for the Protection of the Place of Origin, France, 1: 843 Lawrence–Kennedy machine, 3: 943–944, 3: 944f ‘Lazy cows’, 4: 253 LCPUFAs (long-chain polyunsaturated fatty acids), first-age infant formulae, 2: 141 LCT gene, 3: 238 Lead, in milk, 1: 901t Lead feeding, 2: 792 Lead zirconate titanate (PZT), 1: 209–210 Leaf area index (LAI), 2: 595 Leaf cytoplasmic protein, bloat, 2: 208 Leaky RO see Nanofiltration (NF) Leaky (patent) teats, 3: 334 Lean Self Assessment Tool (LESAT), 4: 265 Leben, 4: 749 flavor, artisanal vs. industrial manufacture, 3: 164 Lecithin(s), 3: 992–993 composition, 1: 66t as emulsifiers, 1: 64, 1: 65f, 1: 66t milk chocolate, 1: 856–857, 1: 858f structures, 1: 65f Lecithinase, 4: 381 Lecithin cholesterol acyl transferase (LCAT), 3: 729 Leco N analyser, 1: 78–79 LECT2, 3: 558–559 Left displaced abomasum (LDA), 4: 517, 4: 518t chronic, 2: 214 clinical signs, 2: 213–214 diagnosis, 2: 214 incidence, 4: 517–518 prevalence, 2: 212 Left paralumbar fossa abomasopexy, 2: 216 Legal records, 1: 491 Legislation additives, 1: 49–54 dairy, changes in, 4: 322 food development, 1: 843 historical aspects, 4: 322 milk standardization, cheese manufacture, 1: 546 see also individual countries Legume bloat, 2: 206 Legumes annuals, 2: 557 annually resown, 2: 558 cool season crops, 2: 558 feed qualities, 2: 565, 2: 566 self-regenerating, 2: 559 specific situations, 2: 558, 2: 560 subtropical, 2: 557 tropical use, 2: 557 warm season crops, 2: 557 perennials temperate pasture, 2: 576 trees used as fodder (Thailand), 2: 95 tropical, 2: 578, 2: 600 sward management, 2: 593 see also individual species Leite Brazil, 2: 104 Length heterogeneity-polymerase chain reaction (LH-PCR), 1: 634 Lenient steam injection (LSI), spray drying, 4: 223 Lentivirus vectors, 2: 638 Leptin, body condition, 1: 464–465 Leptospira, 3: 451
Leptospira interrogans, 2: 181 culture, 2: 182 serovars, 2: 181 Leptospiral vaccines, 4: 420 Leptospirosis, 2: 181–183 buffalo, Mediterranean region, 2: 782 control measures, 2: 183 diagnostic procedures, 2: 182 humans, 2: 183 reduced breeding efficiency, 2: 182 serovars involved, 2: 181 shedding, 2: 182 symptoms, 2: 181 cattle, 2: 181–182 mares, 2: 182 sows, 2: 182 transmission methods, 2: 182 vaccination, 2: 183 vectors, 2: 182 Le Roule, 1: 787 LESAT (Lean Self Assessment Tool), 4: 265 Leucine human requirements, 3: 818 protein synthesis, 3: 819 Leucobacter komagatae, 1: 396 Leucocidins, 4: 107 Leucocin A, 1: 426 Leucocin A-UAL-187, 1: 422t Leuconostoc, 3: 138–142 acetaldehyde use, 3: 141 amino acid biosynthesis, 3: 141 amino acid requirements, 3: 138 bacteriocin production, 3: 141 bacteriophages, 3: 141 blue mold cheeses, 1: 768, 1: 769 carbohydrate metabolism, 1: 562 characteristics, 3: 138, 3: 139t cheese eye formation, 3: 140 cheese ripening, 1: 668–669 citrate fermentation, 3: 140 citrate metabolism, 3: 168f energy generation, 3: 167 genetics, 3: 168–169, 3: 169f citric acid metabolism, 1: 562 dairy cultures, 3: 139 gas blowing defects, cheese, 1: 662 avoidance, 1: 662 genome, 3: 141 genomics, 3: 73t, 3: 74f, 3: 75 human infections, 3: 138 plasmids, 1: 565–566, 3: 142 primary fermentations, 3: 140 products used in, 3: 139 proteolytic activity, 3: 140–141 Quarg manufacture, 1: 703 secondary fermentations, 3: 141 starter cultures, 1: 560t, 3: 138, 3: 455 historical aspects, 1: 28–29 taxonomy, 3: 138, 3: 139t changes, 3: 138 revisions, 3: 47 see also individual species Leuconostoc dextranicum, 1: 28–29 Leuconostoc lactis, 1: 723 Leuconostoc mesenteroides, 2: 489, 2: 491, 2: 494 subspecies characteristics, 2: 478t surface mold-ripened cheeses, 1: 775 Leuconostoc mesenteroides subsp. cremoris butter manufacture, 1: 495 dairy uses, 3: 140 discovery, 1: 28–29 Dutch-type cheeses, 1: 723 starter culture use, 1: 560t, 3: 138 Leuconostoc mesenteroides subsp. dextranicum, 3: 141 Leuconostoc mesenteroides subsp. mesenteroides, 3: 141 Leuconostoc paramesenteroides, 3: 168–169, 3: 169f Leucyl-aminopeptidase (PepL), 3: 87
901
Leukocytes colostrum, 3: 592–593 mammary gland, 3: 387 Levan, 4: 363 Levansucrase, 3: 204–205, 3: 205f Level sensing, ultrasound, 1: 211, 1: 211f Level sensors, 4: 236 Lewis antigen glycans, 3: 256 Lewis (a+b-) individuals, milk oligosaccharides, 3: 249 LH surge, 4: 575 prevention, 4: 577 stress response, 4: 577 undernutrition and, 4: 577 Libido, heat stress, 4: 570 Lice infestation, 2: 251–252 treatment, 2: 252 ‘‘Lifestyle and ethics’’, trends in, 1: 42 Ligases, 3: 965 Light-activated flavor (LAF) mechanism, 2: 538f Light-addressable potentiometric sensor (LAPS), 1: 239, 1: 239f, 1: 241 Light-induced off-flavors, 2: 537 lipid oxidation, 2: 538 methionine and light-activated flavor mechanism, 2: 537, 2: 538f vanilla ice cream, dimethyl disulfide, 2: 538–539, 2: 539f Light microscopy, 1: 226 bright field, 1: 226 compound, 1: 227t differential interference contrast, 1: 226, 1: 227f epifluorescence, 1: 226 homogenization efficiency assessment, 2: 754 phase contrast, 1: 226 polarized light, 1: 226, 1: 227f Light scattering techniques, 1: 133–140 dynamic see Dynamic light scattering historical aspects, 1: 18 light sources, 1: 133 opaque concentrated dispersions, 1: 137 principles, 1: 133 static see Static light scattering see also specific methods Lignins, 3: 984 Limber leg, 2: 677 Limburger cheese microbiology, 1: 396, 1: 397t, 1: 397–398, 1: 757t yeasts, 1: 398t Lime stabilization, 4: 630t Limit of detection, 3: 742 Lincomycin, 2: 172 L’Industria del Latte, 2: 105 Linear discriminant analysis (LDA), 1: 94t, 1: 98t, 1: 103, 1: 103–104 Linear models, 1: 103 Linear moves irrigation system, 2: 593 Linear Programming (LP), 2: 854 Lingual lipases see Pregastric esterases Linkage disequilibrium, 2: 665, 2: 666f genomic selection, 3: 969 whole-genome association studies, 2: 665 Linoleic acid, 3: 657 Aspergillus flavus growth inhibition, 4: 790 cheese flavor, 1: 681 conjugated see Conjugated linoleic acid (CLA) equine milk, 3: 524 infant nutrition, 3: 714 ruminal biohydrogenation, 3: 355, 3: 355f, 3: 660, 3: 662f altered, 3: 356f structure, 3: 660, 3: 661f Linolenic acid(s) cheese flavor, 1: 681 infant nutrition, 3: 714 microbial biohydrogenation, 3: 355, 3: 355f ruminal biohydrogenation, 3: 660, 3: 662f Lior serotyping scheme, Campylobacter, 4: 41
902 Index Lipase(s) accelerated cheese ripening, 1: 796 bacterial, 3: 721 butter, postmanufacture defects, 3: 724 heat stability, 3: 723 lipolysis, 3: 723 off-flavors, cheese, 3: 604 definition, 1: 562 enzymatic interesterification, 1: 501 exogenous, 2: 284–288 homogenized milk, 2: 757, 2: 759 indigenous to milk, 2: 304–307 lower-chain fatty acid release, 2: 285, 2: 285t, 2: 286t low-fat cheese flavor, 1: 839 microbial, 2: 284–285, 3: 638 enzyme-modified cheese, 1: 803 thermal destruction, 2: 285, 2: 285t milk, 3: 721 inactivation, 3: 721 pH sensitivity, 2: 284 properties, 2: 284 sources, 2: 284 starter cultures, 1: 562 Lipase A, 1: 568 Lipase B, 1: 568 Lipid(s) classification, 3: 670 definition, 3: 649, 3: 711 digestion, 3: 711 small intestine, lactating ruminants, 3: 992, 3: 992t first-age infant formulae, 2: 141 hydrolysis see Lipolysis infant formulae, 2: 136 infant nutrition, 3: 714 metabolism, 3: 711 milk see Milk lipids MS see Mass spectrometry (MS) obesity, 3: 712 oxidation see Lipid oxidation postruminal digestibility, 3: 992t, 3: 992–993 rumen fermentation, 3: 983 ruminal hydrolysis, 3: 660 Western diet, 3: 711 see also Fat(s) ‘Lipid hypothesis’, 3: 713, 3: 734, 3: 1031–1032 Lipid oxidation, 3: 716–720 influencing factors, 3: 716 lag phase, 3: 717 measurement, 3: 720 mechanism, 3: 716 initiation, 3: 716 propagation, 3: 716 termination, 3: 716 Lipid supplementation, rumen-protected, 3: 355 Lipid transfer proteins, 3: 729 Lipocalins, 3: 787 Lipolysis, 3: 638, 3: 721–726 analytical methods, 3: 725 free fatty acid extraction methods, 3: 725 free fatty acid measurement, 3: 725 lipase activity, 3: 725 bacterial lipases, 3: 723 blue mold cheeses, 1: 771, 1: 771t brine-matured cheese flavor, 1: 793 cheese ripening see Cheese ripening desirable effects, 3: 721 Dutch-type cheeses, 1: 725 enzyme-modified cheese, 1: 802 hard Italian cheeses see Hard Italian cheeses induced vs. spontaneous, 3: 638 khoa, 1: 884 microorganisms Penicillium camemberti, 1: 569 Penicillium roqueforti, 1: 569 propionibacteria, 1: 571 milk induced, 3: 604
lactation stage effects, 3: 604 seasonal variations, 3: 604 spontaneous, 3: 604 temperature-activated, 3: 604 milk fat, 3: 654 milk lipase system, 3: 721 agitation effects, 3: 722 induced lipolysis, 3: 722 temperature manipulation, 3: 723 milk steam-foaming capacity, 3: 724 products, 3: 721 rancidity, whipping cream, 1: 922 spontaneous lipolysis, 3: 722 lipase activator-inhibitor imbalance, 3: 722 mastitis, 3: 722 MFGM susceptibility, 3: 722 starter cultures, 1: 562 surface mold-ripened cheese ripening, 1: 778 Lipolytic microorganisms, analytical methods, 1: 219 Lipolyzed cream products, 2: 285 patents, 2: 285–286, 2: 286t uses, 2: 286–287 Lipolyzed products production, 2: 285 uses, 2: 285 Lipopolysaccharide (LPS), Shigella, 4: 102 Lipoprotein(a), 3: 1032 Lipoprotein(s), 3: 727, 3: 1031 blood levels, dietary determinants, 3: 730t classification, 3: 1031 composition, 3: 728t functions, 3: 712, 3: 728t genetic polymorphisms, 3: 1032 properties, 3: 728t, 3: 1031 saturated fatty acid action, 3: 1031 types, 3: 727 see also individual lipoproteins Lipoprotein lipase (LPL), 3: 629, 3: 712 action, 3: 353–354 bovine somatotropin treatment effects, 3: 34–35 butter, 1: 493 milk activity, 2: 305, 3: 638 activity quantification, 2: 306 catalyzed reactions, 2: 306 characterization, 2: 305 concentrations, 2: 304–305 cream phase, 2: 305 homogenization, 2: 753 inhibition, 2: 305 isolation, 2: 305 origin, 2: 305 rancidity production, 2: 306, 3: 638 skim milk fraction, 2: 305 synthesis, 2: 305 technological significance, 2: 306 raw milk cheeses, 1: 659 Liposomes, 1: 796 Lipoteichoic acids, 1: 383 Liptaeur cheese, 1: 788 Liquid chromatography future trends, 3: 750 milk proteins, 3: 748 MS, 1: 198 nitrate/nitrite analysis, 1: 910 Liquid dairy food sampling, 1: 72 Liquid membrane electrodes, 1: 195 Liquid precheese production, 1: 621 Liquid unprocessed whey uses, 4: 733 Liquid waste management, 2: 21 Lister, Joseph, 1: 27 Listeria, 2: 184 characteristics, 4: 81 control, 4: 85 differentiation, 2: 184–185 in milk, 3: 449 reservoirs, 4: 84 Listeria innocua, 4: 81
Listeria ivanovii, 2: 184, 4: 81 Listeria monocytogenes, 1: 650, 2: 184, 4: 81–86 biofilms, 1: 447 characteristics, 2: 184, 4: 81 in cheese see Public health aspects, cheese control, 4: 85–86 culture, 2: 187 in dairy products, 4: 84 detection, 2: 184–185 genetics, 2: 185 identification, 4: 81 infection see Listeriosis infective dose, 1: 645 inhibition, enterocins, 3: 154 Lactobacillus plantarum, inhibition, 3: 89 mastitis, 2: 186 in milk, 4: 84 pathogenesis, 2: 185 postpateurization contamination, 4: 84, 4: 85–86 public health concerns, 3: 313 raw milk cheeses, 1: 659 raw milk outbreaks, 3: 646 serotypes, 2: 184, 4: 81–82 shedding, 4: 84 smear-ripened cheese defects, 1: 765 smear-ripened cheeses, 1: 399, 1: 755–756 sources, 4: 84 thermal tolerance, 4: 84 virulence genes, 2: 185 Listeria-related product recalls, 4: 81 Listeriosis, 2: 184–189 bacterial culture, 2: 187 buffalo, Mediterranean region, 2: 782 causative agent, 2: 184 cheese-borne, 1: 650, 3: 311–312 clinical signs, 2: 185, 3: 313 cattle, 2: 186 goats, 2: 186 sheep, 2: 185 control, 2: 188 goats, 2: 188 dairy-related outbreaks, 4: 81, 4: 82, 4: 82t diagnosis, 2: 186 encephalitic see Encephalitic listeriosis histopathology, 2: 187 human, 2: 184 immunocompromised adults, 4: 82 immunoprophylaxis, 2: 188 mortality rate, 4: 82 outbreaks, 3: 313 pathology, 2: 187 pregnancy women, 4: 82 prevention, 2: 188 feed preparation, 2: 188 quarantine, 2: 188 seasonal, 2: 188 serology, 2: 187 stages, 2: 185 symptoms, 4: 82, 4: 84 transmission, 2: 185 treatment, 2: 187, 4: 82 vaccination, 2: 188 Litmus milk, 1: 218 Livarot cheese microbiology, 1: 396, 1: 397t yeasts, 1: 398t Liver anatomy, 2: 219f, 2: 219–220, 2: 220f fat accumulation see Fatty liver fatty see Fatty liver fibrosis, liver fluke infection, 2: 266 somatotropin effects, 3: 26 Liver blood flow (LBF), progesterone levels, 4: 480 Liver flukes, 2: 264–269 clinical signs, 2: 266 control, in host, 2: 268 diagnosis, 2: 266 post-slaughter, 2: 267 drug resistance, 2: 269
Index eggs, 2: 267 epidemiology, 2: 264 genetic resistance, 2: 269 geographical distribution, 2: 264 immunity against, 2: 266 infection control, 2: 267 infection forecasts, 2: 268 life cycle, 2: 264, 2: 265f migrating young stages, 2: 266 pasture management, 2: 268 pathogenesis, 2: 266, 2: 267f serology, 2: 267 sheep, 2: 266 systematics, 2: 264 vaccination, 2: 268 see also individual flukes Livestock protecting collars (LPCs), 2: 845 Livestock records, 1: 487 Ljungstr¨om milking device, 3: 941–942 Llama, 1: 351 milk, 3: 535 composition, 3: 536 production/yield, 3: 535 zinc content, 3: 536 seasonal breeding, 4: 446 LMMCA see Low-moisture Mozzarella cheese analogue (LMMCA) LNFP I, 3: 254 Loafing areas, 2: 20 Lobe-type compressor, 4: 603, 4: 604f Lobe-type vacuum pump, 3: 946, 3: 946f Lobular pumps, 4: 149, 4: 149f selection criteria, 4: 151t Lobule, mammary gland, 3: 333, 3: 338, 3: 339f Lobuloalveolar unit, 3: 338, 3: 339f development, pregnancy, 3: 341 Local Indian Dairy cattle, 1: 285t Localized surface plasmon resonance (LSPR), 1: 244 Local network (LAN) technology, 4: 238 LO Colvin hand-operated vacuum milker, 3: 942–943, 3: 943f Locust bean gum applications, 1: 70t as emulsifier, 1: 69t Lolium multiflorum (Italian ryegrass), 2: 556, 2: 850 Lolium.multiflorum. var. westerwoldicum (Westerwolds ryegrass), 2: 556 Lolium perenne see Perennial ryegrass (Lolium perenne) Lolium perenne L. multiflorum (hybrid ryegrass), 2: 556 Lolium rigidum see Wimmera ryegrass (Lolium rigidum) Long-chain fatty acids, ketosis, 2: 234 Long-chain polyunsaturated fatty acids (LCPUFAs), first-age infant formulae, 2: 141 Long-chain polyunsaturated n-3 fatty acids, modified butter, 1: 504 Longevity productive life definitions, 2: 656–657 selection using correlated traits, 2: 659 Longevity analysis, 2: 653 Longevity (herdlife) trait, 2: 650 Longitudinal (compression) waves, ultrasound, 1: 206, 1: 207f Long lateral irrigation system, 2: 591 Long life milk see Extended shelf life (ESL) milk Long-life products, processing equipment, 4: 128t Long-term planning, 1: 482 Long tube vertical-type evaporator, 4: 201, 4: 202f Loop-mediated isothermal amplification (LAMP), embryo sexing, 2: 633 Loose housing facilities, feeding practices, 1: 4 Loose RO see Nanofiltration (NF) Lor (cacik), Otlu cheese, 1: 783–784 Loss of quality function concept, 4: 274 Lotus major (Lotus pedunculatus), 2: 577 Lotus pedunculatus (lotus major), 2: 577 Low-birthweight (LBW) formulae see Infant formulae Low-density lipoprotein (LDL), 3: 729 cholesterol content, 3: 1031
composition, 3: 728t coronary heart disease risk, 3: 1031 functions, 3: 728t high levels, coronary heart disease risk factor, 3: 713 metabolism defects, 3: 732 modification, vitamin E, 4: 656 oxidative resistance, 4: 657 oxidized, 4: 672 particle size, 3: 1031 properties, 3: 728t statin effects, 3: 1032 Low-density lipoprotein receptor complex, 3: 729 Lower critical temperature (LCT), 4: 550, 4: 551t determining factors, 4: 550 newborn calves, 4: 552 replacement heifers, 4: 553t ‘Lower producing cows’, heat stress, 4: 562 Low-ester pectin, 1: 69t Low-fat cheeses, 1: 833–842 applications, 1: 841 as ingredient, 1: 841 melt characteristics, 1: 841 body characteristics, 1: 836 casein, 1: 836 composition, 1: 836 pH, 1: 836 chemistry, 1: 834 color, 1: 837 casein, 1: 837 milk fat globules, 1: 837–838 titanium dioxide effect, 1: 837–838 composition, 1: 834 condiment cheese, 1: 840 definition, 1: 833 Codex Alimentarius, 1: 833 flavor enhancement, 1: 839 adjunct bacteria, 1: 840 environmental effects, 1: 839 lipase addition, 1: 839 pH, 1: 840 ripening temperatures, 1: 840 ripening times, 1: 840 starters, 1: 840 future work, 1: 841 homogenization, 1: 549 ingredient cheese, 1: 841 manufacture, preacidification, 1: 550 moisture content, 1: 834 colloidal calcium phosphate, 1: 835–836 heat treatment, 1: 834–835 homogenization, 1: 834–835 lactose content, 1: 835 microbiological ecology, 1: 835 pH, 1: 835 non-traditional approaches, 1: 838 fat replacers/mimetics, 1: 838 homogenization, 1: 838 melting salts, 1: 838 surfactants, 1: 838 pH, 1: 836, 1: 836 casein interactions, 1: 837 colloidal calcium phosphate, 1: 836 directly acidified cheeses, 1: 837 hydrophobic interactions, 1: 837 process cheese, 1: 841 table cheese, 1: 840 traditional techniques, 1: 833 casein addition, 1: 833–834 colloidal calcium phosphate, 1: 834 fat removal, 1: 833–834 milk standardization, 1: 833 nonfat dry milk, 1: 833–834 types, 1: 840 Low-lactose dairy products, 2: 277 Low-lactose milk, 2: 280 lactases, 2: 280 production methods, 2: 280–281
903
Low-moisture Mozzarella amino acids, 1: 749t casein hydrolysis, 1: 748–749 flavor development, 1: 749–751 functional characteristics, 1: 747–748 manufacture, 1: 745 microbiology, 1: 748 ripening, 1: 748–749 textural defects, 1: 747–748 Low-moisture Mozzarella cheese analogue (LMMCA), 1: 814 formulation, 1: 815, 1: 817t, 1: 817t, 1: 820t, 1: 821, 1: 821 effects, 1: 819f functionality, 1: 821 Low-moisture part-skim mozzarella (pizza cheese), 1: 737–744 cultures, 1: 740 definition, 1: 737 flavor, 1: 740 as food ingredient, 1: 830 functionality, 1: 737, 1: 742 browning, 1: 743 calcium, 1: 743 elasticity, 1: 742–743 meltability, 1: 742–743 pH, 1: 743 salt, 1: 743 manufacture, 1: 737 acidification and syneresis, 1: 737–738, 1: 739f, 1: 739f calcium phosphate, 1: 737–738 milk, 1: 737, 1: 738f, 1: 738f molding, 1: 738, 1: 740f rennet, 1: 737, 1: 739f, 1: 739f salting, 1: 738–739, 1: 740f stretching, 1: 738, 1: 739f proteolysis, 1: 740 stretching effects, 1: 741 ripening, 1: 740 water absorption, 1: 741, 1: 741f structure, 1: 741, 1: 742f, 1: 742f storage, 1: 741–742, 1: 742f sweet buttermilk use, 3: 695 yield, milk protein concentrates, 3: 851 Low/reduced-salt cheese, 1: 606 Low-resolution nuclear magnetic resonance butterfat melting behavior, 1: 508f, 1: 509 butter melting behavior, 1: 509 Low-salt margarine, spoilage molds, 4: 781 Low-strain deformation tests, 1: 690, 1: 693 Low-strain oscillation rheometry, 1: 693, 1: 693f Low-temperature–long time (LTLT) pasteurization, 4: 193 historical aspects, 3: 310–311 process, 3: 275 time–temperature conditions, 4: 193 waste milk pasteurization, 4: 397, 4: 397f LSPR (localized surface plasmon resonance), casein detection, 1: 244 L (laboratory) starters, 1: 440–441 Lucerne, 2: 577, 2: 596 bloat, 2: 208 seedling vigor, 2: 587 sward management, 2: 593 Luciferase reaction, 1: 239 Lungworm(s) fecal larval output patterns, 2: 272, 2: 272f high-prevalence regions, 2: 271 life cycle, 2: 270 overwintering on pasture, 2: 271 Lungworm disease, 2: 270–275 carriers, 2: 270, 2: 272 clinical signs, 2: 270 diagnosis, 2: 273 epidemiology, 2: 271 grazing management, 2: 274 immunity development, 2: 271
904 Index Lungworm disease (continued ) outbreak causes, 2: 272, 2: 272f phases, 2: 270 prevalence, 2: 271 prevention, 2: 274 general, 2: 274 primary infection sources, 2: 271 reinfection, 2: 270–271, 2: 272 serology, 2: 273 stable infections, 2: 272 treatment, 2: 273 vaccination, 2: 271, 2: 274 vigilance and treatment, 2: 275 weather conditions, 2: 273 Luteal cells, 4: 431 Luteinizing hormone (LH) estrous cycle, 4: 430 follicular growth, 4: 429f, 4: 430, 4: 436, 4: 436f functions, 4: 422–423 heifers, 4: 411–412 ovarian follicular cysts, 4: 438, 4: 438f parturition, 4: 434 postpartum, 4: 434 postpartum anovulatory follicles, 4: 435 preovulatory surge, 4: 456 puberty, 4: 422–423 nutritional effects, 4: 426 pulsatile release, 4: 422, 4: 423f pulse patterns, prepubertal, 4: 424, 4: 424f seasonal breeders, 4: 443 secretion regulation, 4: 422f, 4: 423 surge see LH surge Luteinizing hormone-releasing hormone, 1: 466 Luteolysis, 4: 411–412 (–)-Luteoskyrin, 4: 792, 4: 793 structure, 4: 793, 4: 794f Lybian Shorthorn cattle, 1: 298 Lymnaea, 2: 264, 2: 265f Lymph nodes, Johne’s disease, 2: 175–176 Lymphocytes, mammary gland defense, 3: 390, 3: 390t Lynch syndrome, 3: 1016 LYS-50, 2: 392 Lysergic acid amides, 4: 799 Lysine bioavailability loss, Maillard reactions, 3: 228 extent, 3: 228, 3: 229t quantitative analysis, 3: 228, 3: 228f milk protein output, 3: 361–362 supplementation, 2: 413, 2: 415t RUP, 2: 415t Lysinoalanine (LAL) in caseinates, 3: 1070–1071 degradation, 3: 1073, 3: 1073t function, 3: 1068–1069 infant formula, 3: 1071–1072, 3: 1072f milk heat treatment marker, 3: 1070t, 3: 1070–1071 domestic cooking, 3: 1072–1073, 3: 1073t UHT milk, 3: 1071–1072, 3: 1072f Lysogeny bacteriophage reproduction, 1: 439 bacteriophages see Bacteriophage(s) Lysophospholipids, 3: 670 Lysozyme, 2: 330 antibacterial activity, 2: 330–331 bioactivity, 2: 133 biological roles, 3: 759 Clostridium spore control, 4: 53 colostrum, 3: 595, 3: 595t equine milk, 3: 521t, 3: 522, 3: 523–524 evolutionary relationships, -lactalbumin, 3: 780 gas blowing defect prevention, 1: 664 heat stability, 2: 331 human milk, 3: 629 interspecies comparison, 3: 840 pH stability, 2: 331 primate milk, 3: 629 purification, 2: 331 renaturation rates, 2: 331
species differences, 2: 331, 2: 331t Lysylpyrrolaldehyde (LPA), 3: 1073 Lytic cycle, bacteriophages, 1: 439
M Macaca fascicularis milk see Cynomolgus monkey milk Macaca mulatta see Rhesus monkey Macaque monkey milk immunoglobulins, 3: 625 oligosaccharides, 3: 615–616 Machine milking see Milking machines Machinery, safety hazards, 4: 277 Machinery mold, 4: 765 Macrocyclic lactones, 2: 261 Macroelements see Macrominerals Macrolide resistance, Campylobacter, 4: 43 Macrominerals, 2: 371–377 absorption, 3: 996 optimization, 3: 996 chemical forms, 3: 926 in dairy products, 3: 925 content, 3: 925, 3: 926t goat requirements, 2: 786–789, 2: 787t, 2: 791t, 2: 792–793 interactions, 3: 925 in milk, 3: 925, 3: 926t nutritional significance, 3: 925–932, 3: 926t recommended dietary intake, 3: 928t transition cows, pasture-based systems, 2: 467 see also individual minerals Macronutrients in milk, contributions to nutrient intake, 3: 1004 minerals vs., 3: 996 vitamins vs., 3: 996 Macrophages mammary gland defense, 3: 387, 3: 390t pregnancy, 4: 502 MacSharry reform, 4: 295 Mad cow disease, transgenic animals, 2: 643 Magnesium, 2: 373 absorption, 2: 374 cattle, 3: 997–998 digestible magnesium, 2: 225 gastrointestinal tract, 2: 225 impairment, 2: 225 postruminal, 2: 374 potassium effects, 2: 226, 2: 227t, 2: 374, 2: 375, 2: 376 reduced, 2: 225 ruminal, 2: 225, 2: 226f ruminal pH effects, 3: 997–998 ruminants, 3: 997 site of, 2: 225 sodium deficiency, 2: 227 absorption coefficient, 2: 374 active transport mechanisms, 2: 374 anion supplementation and, 2: 360 availability, 2: 374 blood concentration, milk fever, 2: 242 cheese, 3: 926, 3: 927t colostrum, 3: 926 in dairy products, 3: 926t, 3: 926t, 3: 927t nutritional significance, 3: 931 deficiency, 2: 225, 2: 374–375 humans, 3: 931 hypocalcemia, 2: 372–373 plants, 2: 589 dietary supplementation grassy tetany prevention, 2: 227t, 2: 228 milk fever prevention, 2: 244 pasture-based cows, 2: 457 functions, 2: 373, 3: 931 heat stability, milk, 2: 745 homeostasis kidneys in, 2: 228 regulation, 2: 224 ketosis, 2: 232–233 metabolism, genetic effects, 2: 374
in milk, 3: 925, 3: 926t bioavailability, 3: 931 chemical form, 3: 927 nutrient intake, contributions to, 3: 1006 nutritional significance, 3: 931 pasture-based cows, 2: 374 nitrogen effects, 2: 375 PD-dependent/K-sensitive uptake, 2: 225–226 PD-independent/K-insensitive uptake, 2: 226 primate milk, 3: 627–629, 3: 628t ration requirements, 2: 374 recommended dietary intake, 3: 928t requirements, 2: 374 in serum, 3: 919, 3: 920t solubility, 2: 374 transition cows, pasture-based systems, 2: 467, 2: 468 Magnesium caseinate, 3: 859 Magnesium chloride, 2: 360 Magnesium fertilizer, 2: 589 Magnesium limestone, 2: 589 Magnesium propionate, 2: 237 Magnesium salts, water hardness, 4: 584 Magnesium sulfate supplementation, 2: 360 transition cows, pasture-based systems, 2: 467 Magnetic resonance imaging (MRI), 1: 153, 1: 164 fat–water content distribution, 1: 164, 1: 166f macrostructure information, 1: 164, 1: 166f microstructure, 1: 165 ripening, 1: 167, 1: 167f molecular structure, 1: 165 techniques, 1: 155 Maidism see Pellagra Maillard reactions, 3: 217–235, 3: 1068 amino acids, 3: 217, 3: 229f colored products, structure, 3: 225, 3: 225f Strecker degradation, 3: 221 chemical markers, 3: 1069–1070 chemical stages (Hodge’s scheme), 3: 217, 3: 218f aldehyde–amine condensation, 3: 222 aldol condensation, 3: 222 Amadori rearrangement, 3: 217, 3: 219f sugar–amine condensation, 3: 217 sugar dehydration, 3: 219, 3: 220f sugar fragmentation, 3: 220, 3: 221f early stages, 3: 1068 enzyme (oxidase) addition, 2: 302, 2: 302 final stages, 3: 1068 galactose-negative LAB, 3: 162 -lactoglobulin, 3: 793 lactose, 3: 176, 3: 180 product quality effects, 3: 218t, 3: 224 antioxidant activity, 3: 227 carbon dioxide loss, 3: 227 color, 3: 224, 3: 225f lysine bioavailability loss, 3: 228 metal chelation, 3: 230 pH, 3: 227 solubility loss, 3: 227 toxicity, 3: 231, 3: 234 vitamin C loss, 3: 227 volatile compounds, 3: 226, 3: 226t water activity, 3: 227 prolonged heating, 2: 748 quality monitoring applications chemical indicator methods, 3: 232 color parameters, 3: 231 fluorescence, 3: 231, 3: 234 storage headspace volatiles, 3: 232 sweetened condensed milk, 1: 872 volatile products, 3: 222 pyrazines, 3: 227, 3: 227f storage headspace monitored, 3: 232 see also Browning Mainzer cheese, 1: 703 Maize, 2: 553, 2: 564 byproducts, feed uses, 2: 344t, 2: 345, 2: 347f gluten feed and meal, 2: 345
Index replanting decision, 2: 569 value as feed source, 2: 336, 2: 553, 2: 564, 2: 573 high-oil varieties, 2: 336 waxy hybrids, 2: 336 varietal characteristics, 2: 553 Maize lecithin, 1: 66t Maize silage, 2: 46 Majd goats, 1: 312t Major histocompatiblity complex (MHC) antigen, placenta, 4: 501 Malabar goats, 1: 311t, 1: 322, 1: 322f milk yields, 1: 312t Malaguena goats, 1: 311t, 1: 316, 1: 316f Mal de la rosa see Pellagra ‘Male effect’, goats, 2: 835 MælkeprodukthekendtgØrelsen, 1: 848 Malonyl coenzyme A (malonyl-CoA), 2: 234 aflatoxin biosynthesis, 4: 801–802 milk fat synthesis, 3: 352–353 Malta fever see Brucellosis Maltese goats, 1: 311t, 1: 316, 1: 316f ricotta cheese composition, 2: 65t Malt extract agar (MEA), Penicillium camemberti growth, 4: 776 Maltitol monohydrated -lactose crystal growth, 3: 193 as prebiotic, 4: 358 structure, 4: 357f Maltodextrins, 1: 531 Maltose, Bifidobacterium fermentation patterns, 1: 386t Mamber goats, 1: 312t Mambi cattle, 1: 303t Mamdani type rule, 4: 247–248 Mammals, 3: 320–327 characteristics, 3: 320 classification, 3: 459 definition, 3: 320 domestication, 3: 326 evolution, 3: 320, 3: 459–460 milk nutritive value, 3: 607 milk production, 3: 320 fossils, 3: 320 groups, 3: 320 hair, 3: 320–321 lactation as adaptive character, 3: 321 fasting, 3: 321 length, 3: 321 marine see Marine mammal(s) milk casein sequences, 3: 542–543 milk functions, 3: 607 minor domesticated species milk, 3: 530–537 compositional features, variation, 3: 530, 3: 530, 3: 531t information accuracy, 3: 530 information extent, 3: 530 production, 3: 530 placental see Placental mammals skeletal characteristics, 3: 320 wild (non-dairy land) animal milks, 3: 538–552 comparative milk composition, 3: 530, 3: 538, 3: 539t data availability, 3: 538 domestic species vs., 3: 530, 3: 551 environmental adaptation, 3: 538 uniqueness, 3: 551 see also individual animals Mammary artery, 3: 334 Mammary band, 3: 341–342 Mammary buds, 3: 341–342 Mammary-derived growth inhibition, 3: 759 Mammary-derived growth inhibitor (MDGI), 3: 686f, 3: 689 Mammary ducts, 3: 15, 3: 16f Mammary fat pad, 3: 338 connective tissue sheets, 3: 338–339, 3: 340f gene expression profile, 3: 349–350, 3: 350f histology, 3: 338, 3: 340f
Mammary gland acquired (specific) immunity, 3: 386, 3: 389 cellular defenses, 3: 390, 3: 390t soluble defenses, 3: 391, 3: 391t anatomy, 3: 328–337 arterial supply, 3: 334, 3: 334f at birth, 4: 391–392 capillary ion permeability, 3: 424, 3: 424f cleanliness, warm climate feed pads, 2: 19 development see Mammary gland development endogenous defenses, 3: 386–391 future research needs, 3: 386–391 energy requirements, 3: 461 gross anatomy, 3: 328, 3: 329t growth, 3: 338–345 tissue components, 3: 338 growth stimulation by frequent milking, 3: 39 health, 3: 442 evaluation method comparison, 3: 899 historical aspects, 1: 7 milking machine effects, 3: 443, 3: 444t milk processing characteristics, 3: 902–907 somatic cell count see Somatic cell count (SCC) test methods, 3: 894–901, 3: 900t heifer vs. adult, 3: 438f hormones, 2: 765 leakage and transport, cell junctions, 2: 766–767 infection susceptible, 3: 384 inflammation, 3: 389, 3: 389t inflation, milk fever, 2: 243 innate immunity, 3: 386, 3: 387t cellular defenses, 3: 387 physiological factors, 3: 388, 3: 388t interspecies variations, 3: 460 involution see Mammary gland involution location, 3: 329t long-chain fatty acid uptake, 3: 353–354 lymphatic system, 3: 335, 3: 335f microscopic anatomy, 3: 331, 3: 338 secretory tissues, 3: 331 synthetic tissues, 3: 331 milk biosynthesis and secretion amino acid uptake, 3: 40 epithelial cell number and activity, 3: 38 immunological protection, 3: 587 lipogenesis inhibition, 3: 490 milk constituents secretion of, 2: 766f, 2: 766–767 milk fat, 3: 543 milk fat synthesis gene network, 3: 347–348, 3: 349f milk flow patterns, 3: 330 milk storage, 3: 15, 3: 16f nervous system, 3: 336, 3: 336f number of, 3: 329t pendulous, 3: 329 premilking cleaning, 3: 632, 3: 633t premilking disinfection, 3: 632 quarters, 3: 329, 3: 330f structure, 3: 460 supporting structures, 3: 330 surface epidermis, 3: 330 suspensory ligaments, 3: 329, 3: 330–331 transgenic animals, 2: 640–641 vascular system, 3: 334 venous drainage, 3: 335, 3: 335f Mammary gland development, 3: 338–345, 3: 460 allometric growth phase, 4: 391–392 calf growth rate, 4: 400 data mining, 3: 347–348 feeding program influence, 4: 391–392 fetal, 3: 341 functional genomics, 3: 344, 3: 347 limitations, 3: 347 microarray analysis, 3: 347 pregnancy through lactation, 3: 347 prepubertal development, 3: 349 transcript profiles, 3: 347, 3: 348f gene networks, 3: 346–351 analysis, 3: 347–348
905
growth factors, 3: 339 growth rates and, 3: 342, 4: 391–392 high-energy diet, 4: 410 hormones, 3: 339 lactation, 3: 343 nutritional effects, 3: 342, 3: 350–351 phases, 3: 341 postnatal, 3: 342 postpuberty, 3: 340f, 3: 342 pregnancy, 3: 342 Mammary gland edema, camels, 1: 353 Mammary gland involution, 3: 343 active, 3: 343 apoptosis, 3: 343 colostrum formation, 3: 343–344 explant culture model, 3: 561 forced, 3: 349 gene expression, 3: 344 gene networks, 3: 348 histological changes, 3: 343, 3: 344f, 3: 348 -lactalbumin, 3: 782 microarray analysis, 3: 348 milk’s role in, 3: 561 prevention, marine mammals, 3: 576 proteolysis, 3: 603 steady-state phase, 3: 343–344 Mammary resistance mechanisms anatomical, 3: 381–385, 3: 382f factors affecting, 3: 383 hereditary factors, 3: 384 endogenous, 3: 386–391 Mammary veins, 3: 335 Mammocytes, 3: 460–461 Mammogenic hormones, 3: 339 Management induced stress, reproductive effects, 4: 575–581 endocrine pathways, 4: 575 physiological stressors, 4: 577 psychological stressors, 4: 580 Management-intensive grazing (MIG) system, 2: 38–40 Management records, 1: 486–491 animal identification see Animal identification benchmarking, 1: 489 financial information, 1: 487 annual statements, 1: 487–488 assets, 1: 488 cash inflows/outflows, 1: 488 financing/debt-related flows, 1: 488 income, 1: 488 investing flows, 1: 488 net worth, 1: 487, 1: 488 operating flows, 1: 488 profitability measures, 1: 488 record-keeping system, 1: 487 government regulations, 1: 491 legal records, 1: 491 market information, 1: 490 production information, 1: 486 crop production costs, 1: 487 livestock records, 1: 487 record keeping, 1: 489 analysis, 1: 490 collection, 1: 490 summarization, 1: 490 system choice, 1: 490 specification compliance, 1: 491 Manatee(s) lactation, 3: 563 milk composition, 3: 569, 3: 573t milk lipids, 3: 574 Manchega sheep, 1: 335, 1: 335f, 2: 72 lactation length, 1: 332t milk yield, 1: 332t Manchego, 3: 501 Manganese, 2: 381 absorption, ruminants, 3: 999 chelated forms, 3: 999–1000
906 Index Manganese (continued ) in colostrum, 3: 933 in dairy products, 3: 934t, 3: 935t, 3: 935t, 3: 935t deficiency, 2: 381 cattle, 2: 386 feed supplementation, 2: 385 functions, 2: 386, 3: 938 in milk, 3: 933, 3: 934t bioavailability, 3: 938 chemical forms, 3: 935 nutritional significance, 3: 938 primate milk, 3: 628t recommended dietary intake, 3: 937t, 3: 938 requirements, 2: 379t, 2: 381 sheep milk, 3: 500 supplementation, 2: 381 toxicity, 2: 381 Manganese methionine, 2: 386 Mange, 2: 250–252 clinical signs, 2: 250 diagnosis, 2: 250 differential diagnosis, 2: 251–252 epidemiology, 2: 250 prevention, 2: 252 reporting, 2: 250 treatment, 2: 252 see also individual types Manger space, 4: 559 Mannose, Bifidobacterium fermentation patterns, 1: 386t Manometer, 4: 723–724 MANOVA, 1: 94t Manual calf feeding systems, 2: 25 Manual cleaning, milking equipment, 3: 635 Manual milking donkeys, 1: 365 see also Hand milking Manual of Diagnostic Tests and Vaccines for Aquatic Animals, 4: 7 Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (Terrestrial Manual), 4: 7 Manufacturing execution (ME), 4: 242 Manure ammonia stabilization, 4: 635 anaerobic fermentation, 4: 632 anaerobic treatment, 3: 393 application pasture budget, 3: 405 phosphorus budget, 3: 405 phosphorus vs. nitrogen, 3: 405 rate per hectare, 3: 400t, 3: 405–406 collection area, percentage time in, 3: 405–406 collection method, 3: 392 environmental impact routes, 3: 393, 3: 393f land application, environmental problems, 4: 631–632 management see Manure/effluent management negative environmental impact reduction, 4: 631 nitrogen/phosphorous ratio, 3: 393–394 odor minimization, 4: 635 organic dairies, 4: 14 organic matter content calculation, 3: 399–400 recovered nutrients, budgeting use, 3: 402t, 3: 403 storage, 4: 631–632 Manure/effluent management alternative treatment techniques, 4: 632 collection methods, 3: 392 government regulation, 3: 392–398 air quality, 3: 397 water quality, 3: 395 proprietary additives, 3: 394 system design, 3: 392–398 changing trends, 3: 393 warm climate milking systems, 2: 18 disposal, 2: 25 water quality see Water quality Manure management see Manure/effluent management Manure seal, 2: 22
Map (MHC class II analog protein), 4: 105–106 Maradi goats, 1: 312t Mare(s) altrenogest treatment, seasonal breeding manipulation, 4: 444 artificial photoperiod changes, 4: 443–444 leptospirosis, 2: 182 milk see Equine milk see also entries beginning equine; Horse(s) Margarine fat content, butter vs., 1: 507, 1: 507f microstructure, 1: 510f Marine mammal(s) energy content, 3: 563 lactation, 3: 564t duration, 3: 563–566 evolution, 3: 563 origins, 3: 563 lineages, 3: 563 Marine mammal milk, 3: 563–580 calcium:phosphorus ratio, 3: 579t, 3: 579–580 carbohydrates, 3: 567t, 3: 571t, 3: 576 composition, 3: 538, 3: 539t, 3: 563–566, 3: 567t, 3: 571t absence of lactose, 3: 550, 3: 550 closest living relative comparison, 3: 566 factors influencing, 3: 566 lactation stage, 3: 566, 3: 570f proximate, 3: 566, 3: 567t, 3: 571t, 3: 573t, 3: 575t constituents, 3: 574 energy content, 3: 566 fat content, 3: 563, 3: 566 lipids, 3: 567t, 3: 571t, 3: 574 fatty acid composition, 3: 544, 3: 545t, 3: 549, 3: 574, 3: 575t mineral elements, 3: 579, 3: 579t seawater contamination, 3: 579 oligosaccharides, 3: 576, 3: 577t peak lactation, 3: 566 protein content, 3: 566, 3: 574 terrestrial mammal comparisons, 3: 574, 3: 576f sample collection, 3: 566, 3: 569f seawater contamination, 3: 566 vitamins, 3: 580 see also individual species Marker-assisted (gene-assisted) selection (MAS), 2: 666, 3: 969 Market information, 1: 490 Marketing business management, 1: 481 business management planning, 1: 483 Latin American dairy management, 2: 92 Marketing systems, producers’ cooperatives, 2: 95, 2: 96, 2: 97 Market price subsidy, 4: 288f, 4: 291 actual market price, 4: 292 EU, 4: 292, 4: 293f export restitution, 4: 292 import duty, 4: 292 intervention price, 4: 292 target price, 4: 292 types, 4: 292, 4: 292f variable import duty, 4: 292 Market research, 1: 483 Markhor (Capra falconeri), 2: 814 Marrecha camels, 1: 352 Marsupial(s), 3: 460 lactation length, 3: 321, 3: 553–554 lactation strategy, 3: 553, 3: 555f reproductive strategy, 3: 553, 3: 554f Marsupial milk, 3: 553–562 autocrine factors, 3: 561 biological activity, 3: 559 forestomach tissue morphology changes, 3: 559 carbohydrates, 3: 555 casein structure, 3: 542, 3: 542f composition, 3: 539t, 3: 554 forestomach maturation, 3: 559
lactation stage and, 3: 554–555, 3: 555f fatty acids, 3: 544 immune-related proteins, 3: 558 lactose, 3: 209, 3: 213, 3: 550, 3: 551 lipids, 3: 556 oligosaccharides, 3: 209, 3: 213, 3: 271–272, 3: 550, 3: 551, 3: 555–556 proteins, 3: 556 casein types, 3: 542, 3: 542f lactation stage and, 3: 556–558 total solids, 3: 554–555 Martensitic stainless steel, 4: 135, 4: 136 Marwari goats, 1: 312t Maryute cattle, 1: 298 Mascarpone cheese, 1: 704, 2: 783 composition, 1: 700t Maslow’s Hierarchy of Needs, 3: 13 Massese sheep, 1: 335, 1: 335f lactation length, 1: 332t milk yield, 1: 332t Mass spectrometry (MS), 1: 198–205 analysis strategies, 1: 199 bottom-up approach, 1: 199 top-up approach, 1: 200 applications, 1: 198 cheese flavor assessment, 1: 678 trace elements, 1: 204 capillary electrophoresis, 1: 190 as chemical sensor for e-noses, 2: 546 coupled with gas chromatography, 2: 533, 2: 543, 2: 546 electrospray ionization, 1: 198, 1: 199 gas chromatography, 1: 175, 1: 198, 1: 199 HPLC, 1: 174, 1: 199 lipids, 1: 202 atmospheric pressure chemical ionization, 1: 204 HPLC coupling, 1: 204 triple quadrupole tandem mass spectrometry, 1: 204 liquid chromatography, 1: 198 matrix-assisted laser desorption/ionization, 1: 198, 1: 198 preparative gel, 3: 845 protein identification, 3: 845 protein modification, 1: 200 glycosylation, 1: 201 phosphorylation, 1: 200 posttranslational modification, 1: 200 proteins, 1: 172, 1: 200 casein macropeptide, 1: 201 degradation, 1: 202 food adulteration analysis, 1: 201 genetic variants/polymorphism identification, 1: 201 glycation, 1: 201 milk fat globule membrane proteome, 1: 200, 1: 201 milk proteome, 1: 200 oxidation, 1: 202 polymerization, 1: 202 protein damage analysis, 1: 201 quadrupole time-of-flight, 1: 198 triacylglycerol analysis, 3: 702 two-dimensional electrophoresis with, 1: 198 Mastitis, 3: 422 acute clinical, 3: 415 infectious organisms, 3: 437 symptoms, 3: 437 therapy, 3: 437 African dairy cow management, 2: 81 anatomical defense mechanisms, 3: 429, 3: 430t antibiotic therapy, 1: 891–892 automatic online detection see Automatic online detection, abnormal milk bacterial spread, 3: 408 biochemical susceptibility markers, 3: 429 bovine somatotropin, 3: 37 buffalo, 2: 779
Index camels, 1: 353 causative organisms, 2: 48–49 causes, 3: 415 chronic, 3: 408 definition, 3: 895 clinical, definition, 3: 895 contagious pathogens, 3: 408–414, 3: 415 backflushing, 3: 413 control, 3: 410 purchased replacements, 3: 413 segregation, 3: 413 control programs, 3: 415 historical aspects, 1: 7 Coxiella burnetii, 4: 55 dairy products, effects on, 3: 904, 3: 904t definition, 3: 415 detection, biosensors, 1: 241 dry cow therapy, 3: 420, 3: 438 drylot management systems, 2: 57 dry period, 2: 450 economic costs, 3: 415 endotoxemia, 3: 415 environmental antibiotic dry cow therapy, 3: 420 herd characteristics, 3: 415 lactation, 3: 416 nutrition and, 3: 420 pathogenesis, 3: 415 prevention, 3: 419 therapy, 3: 419 environmental hygiene, 3: 433 environmental pathogens, 3: 408, 3: 415–421, 3: 416t control, 3: 419 detection, 3: 417 streptococcal-enterococcal species differentiation, 3: 417 Streptococcus species, 3: 416, 3: 416t esterase activity, 2: 304 genetic selection, 3: 429 goats, 2: 802 Gram-negative organisms, 3: 418 dry period, 3: 416 heifers see Heifer mastitis historical aspects, 1: 7 HPA axis activation, 4: 579 humans, milk composition effects, 3: 589 inflammatory response, 3: 423 Koesler number, 3: 174–175 lactose, 3: 904 listerial, 2: 186 lysostaphin secreting transgenic cows, 2: 643, 3: 968 machine milking, 3: 440–446, 3: 441t bacterial transfer, 3: 440, 3: 441f frequency/degree of udder evacuation, 3: 441 infection mechanisms, 3: 440, 3: 441t milk letdown flow, 3: 441 teat health and damage, 3: 442 teat penetration by bacteria, 3: 440 teat resistance to bacteria, 3: 442 management control options, 3: 429–434 hygiene, 3: 432 medical therapy options, 3: 435–439 dry-off period, 3: 438 during lactation, 3: 435 milk bacterial contamination, 3: 904 milk composition, 3: 363 affecting mechanisms, 3: 902 milk electrical conductivity, 3: 471 milk fat, 3: 902 milk pH, 3: 904 milk proteins, 3: 903, 3: 903f synthesis, 3: 363 milk quality standards, 3: 422 milk yield, 3: 902 disease resistance relationship, 3: 429 non-seasonal/pasture-based management, 2: 42, 2: 48
nontuberculous mycobacteria, 4: 90 nutrition, 3: 429 opportunistic microorganisms, 3: 408 pathogen categories, 3: 408 pathogenic agents causing, 1: 891 pathology, 1: 891 plasmin levels, 3: 903 postpartum reproduction, 4: 437, 4: 437t postsecretory milk breakdown, 3: 902 predictors, 3: 899 raw milk composition, 3: 902, 3: 903t reproductive stress, 4: 579 risk definition and control programs, 2: 682 seasonality, 3: 431 sheep see Sheep mastitis somatic cell count, 3: 429 somatic cells, 3: 895 somatic cell score, 2: 658, 2: 659 spontaneous lipolysis, 3: 722 stress, 3: 431 management, 3: 431 shade provision, 3: 431 subacute clinical causative organism identification, 3: 437–438 therapy, 3: 437 subclinical definition, 3: 895 diagnosis, 3: 895–896 thermal stress, cooling, 3: 432 transition cows, 2: 451 vaccines, 3: 420 vitamin C supplementation, 2: 399 Material Data Safety Sheets (MSDS), 4: 277 Maternal dystocia, 4: 511 Maternity area, 3: 959 Ma T’ou goats, 1: 311t, 1: 322 Matrix-assisted laser desorption/ionization (MALDI), MS, 1: 198, 1: 198 Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, 3: 845 high-abundance milk proteins, 3: 846 low-abundance milk proteins, 3: 846 Matrix Gla protein (MGP), 4: 663, 4: 663t Mawa see Khoa Maxilact LG, 2: 282 Maxilact LGX, 2: 282 Maximum permitted level (MPL), additives, 1: 58 Maxwell bodies, 1: 689 Maxwell model, 1: 270 M blood group system, mastitis, 3: 429 MDS (multidimensional scaling), 1: 101 Measurement error, statistical analysis see Statistical analysis Measurement instrumentation, 4: 235 specialized, 4: 236 Measurement process characterization instrumental procedure, 1: 87 statistical analysis see Statistical analysis Meat Brucella survival, 4: 34 goat see Chevon (goat meat) microbial transglutaminase, 2: 300 Meat products dairy ingredients, 2: 131 nisin applications, 1: 424 Mechanical biosensor transducers, 1: 237, 1: 237f Mechanical reciprocating chip mills, Cheddar manufacture, 1: 610–611 Mechanical releasers, milking machines, 3: 946 Mechanical scraping, warm climate feed pads, 2: 21 Mechanical seal, 4: 162 agitators, 4: 162 Mechanical vapor compression (MVR), 4: 205, 4: 206f Mechanistic modeling calculus, 2: 429 dairy cow digestion, 2: 430 dairy cow metabolism see Dairy cow metabolism digestion, 2: 429, 2: 430f
907
future developments, 2: 434–435 hierarchy, 2: 429 organization levels, 2: 429, 2: 434f metabolism, 2: 429, 2: 430f process control, 4: 248 Media, bulk starter cultures, 1: 557 Medial suspensory ligament, mammary gland see Median suspensory ligament, mammary gland Median suspensory ligament, mammary gland elasticity, 3: 331 gross anatomy, 3: 329, 3: 330–331, 3: 331f Medicago sativa see Lucerne Medical foods, 2: 131–132 Medics (Medicago spp.), 2: 559 Mediterranean pastures, dairy sheep, 2: 850 grass-legume balance, 2: 850 sward height, 2: 850, 2: 850f Mediterranean region goats, 1: 315 sheep breeds, 1: 325 sheep management, 2: 73–74 sheep numbers and milk production, 2: 69t Medium-concentration retentates, membrane processing, 1: 621 Medium-shear mixer/blender, blended spread production, 1: 527 MEGAMINE-L, 2: 392 Mehraban sheep, 1: 335, 1: 335f Melamine, 1: 896 contaminated milk in China, 4: 352 Melanoidins chemical production mechanisms, 3: 218f, 3: 219–220, 3: 220f, 3: 222 Maillard reaction, 3: 1068 milk properties, effects on, 3: 227, 3: 230–231 sterilized milk products, 3: 293 structure, 3: 222, 3: 223t yield, 3: 222, 3: 223t Melatonin exogenous, 4: 444 goats, 4: 445 horse, 4: 442–443 seasonal breeders, 4: 442–443 sheep, 4: 445 short-day breeders, 4: 442–443 Melatonin implants, 4: 444 Melengestrol acetate (MGA), 4: 413, 4: 414f Meleshin process, 1: 498 Meles meles (Eurasian badgers), bovine TB, 2: 197 Mellibiose, 1: 386t Melt characteristics butter see Butter low-fat cheeses, 1: 841 low-moisture part-skim mozzarella (pizza cheese), 1: 742–743 Melting salts, low-fat cheeses, 1: 838 Melt–refreeze crystallization, 4: 712 Membrane-based fractionation, 3: 864–872 applications, 3: 865 concentration polarization, 3: 870 definition, 3: 870 film model, 3: 871 gel model, 3: 871 membrane/module design approaches, 3: 871 osmotic pressure model, 3: 871 designs, 3: 867 dynamic membrane systems, 3: 869 emerging systems, 3: 869 fouling, 3: 870, 3: 870f calcium, 3: 871 calcium phosphate precipitation, 3: 872 feed parameters, 3: 871 inorganic membranes, 3: 872 membrane hydrophobicity, 3: 871–872 protein adsorption, 3: 871 whey, 3: 871
908 Index Membrane-based fractionation (continued ) low pressure immersed membrane technology, 3: 869 membrane module configuration, 3: 869 multistage recycle basis, 3: 869, 3: 869f membranes, 3: 867 asymmetric structure, 3: 867 composite, 3: 867 hollow fiber, 3: 868 performance, 3: 869 skinless, 3: 867 tubular-inorganic, 3: 868 tubular-organic, 3: 867 milk protein standardization, 3: 866 milk shelf life extension, 3: 867 modules, 3: 867 plate-and-frame, 3: 868 spiral-wound, 3: 868 native phosphocasein, 3: 866 partial demineralization, whey, 3: 865 skim milk powder, enhanced renneting properties, 3: 866 transmembrane pressure, 3: 870 whey preconcentration, 3: 865 Membrane dialysis fermenters, 2: 494 Membrane emulsification, 2: 763, 2: 763f Membrane filtration, milk protein fractionation, 3: 763 Membrane insertion, nisin, 1: 422–423 Membrane-processed milk, 3: 286, 3: 307–309, 3: 647 bacterial removal, 3: 307 commercial products, 3: 308, 3: 308f fat permeation, 2: 729, 3: 309 microfiltration techniques, 2: 729, 3: 307–308 in France, 3: 308 tangential, 3: 307–308 see also Microfiltration; Nanofiltration (NF); Reverse osmosis (RO); Ultrafiltration (UF) Membrane processing cheese manufacture, 1: 618–624, 1: 620f benefits, 1: 618 future potential, 1: 623 liquid precheese production, 1: 621 microfiltration see Microfiltration MMV process, 1: 618–619 nanofiltration, 1: 618, 1: 623 protein standardization, 1: 619 reverse osmosis, 1: 618, 1: 619t ultrafiltration see Ultrafiltration; Ultrafiltration, milk whey recovery processes, 2: 126–127, 2: 127f Membranes, bacterial see Bacterial membranes Membrane technology, historical aspects, 1: 24 Menadione, 4: 661 structure, 4: 662f toxicity, 4: 662 Menaquinones (vitamin K2), 4: 661, 4: 662f Menopause, blood cholesterol levels, 3: 732 MEN (multiple-earthed-neutral) systems, milking systems, 2: 17 Mental stress, hypercholesterolemia, 3: 1032 Menthionine, laminitis, 2: 203–204 Mepron, 2: 391, 2: 393 2-Mercaptoethanol (2-ME) test, 2: 156t, 2: 157 Mercury, in milk, 1: 901t MERCUSOR (Treaty for the Organization of a Southern Common Market), 4: 324 Mesenterocin 52B, 1: 422t Mesenterocin Y105, 1: 422t Mesoderm, 4: 486 Mesophiles Cheddar cheese starter cultures, 1: 707 starter cultures, 1: 554 Mesophilic fermentations, 2: 472 Mesophilic lactobacilli, Dutch-type cheese defects, 1: 726 Mesophilic starter cultures, 1: 625 Messenger RNA (mRNA), 3: 360, 3: 1056–1057
Metabolic acidosis calcium metabolism, 2: 356 definition, 2: 356 Metabolic alkalosis milk fever, 2: 240 parathyroid hormone, 2: 356 Metabolic diseases/disorders body condition score, 1: 465 China, 2: 86 infertility risk factors, 4: 579 sheep, 2: 857 byproduct feeding, 2: 852–853 see also specific diseases/disorders Metabolic energy flow, 2: 403–408, 2: 419, 2: 420f diet formulation, feed energy content, 2: 403, 2: 786 energetic efficiency variation, 2: 426, 2: 427t, 2: 427t dietary ingredients, 2: 403–404, 2: 406–407 fat and cereal supplements, 2: 364 energy partitioning, definitions, 2: 403, 2: 404f mass-based digestibility measures, 2: 403 model accuracy and improvements, 2: 408 Metabolic reconstruction, 3: 56–57 Metabolic status, puberty onset, 4: 425 Metabolic syndrome, 3: 1046, 3: 1049 dairy consumption, 3: 712 Metabolism, additive safety, 1: 57 Metabolite study, LAB stress response, 3: 58 Metabolizable energy (ME), 2: 406, 2: 407t lactation rations, 2: 460–461, 2: 463 pasture-based systems, 2: 453, 2: 454f Metabolizable protein (MP), 2: 413, 2: 461 dairy animal requirement determination, 2: 413 Metabolome, 3: 1057 Metabolomic fingerprints, 1: 151–152 Metabolomics definition, 3: 1057 fatty liver, 2: 222–223 LAB stress response, 3: 58 limitations, 3: 1059 NMR use, 1: 151–152 nutritional research advancement, 3: 1058 Metal cans, powder milk packaging, 4: 19 Metal fatigue, 4: 262 Metallic flavor, buttermilk, 2: 493 Metalloenzymes, Pseudomonas, 4: 381 Metalloproteases, blue mold cheeses, 1: 769–771 Metals environmental contaminants, 1: 901, 1: 901t see also specific metals MetaSmart, 2: 392, 2: 393 Metastability, 3: 186 nucleation and, 3: 187 Metastable zones, 3: 186 Metatheria see Marsupial(s) Metchnikoff, Ilya Ilyich (Elie), 1: 16, 1: 31 Metchnikoff’s longevity hypothesis, 2: 483, 2: 513–514 Metering pumps, 4: 145 Metestrus, 4: 411 Methane losses, feed energy efficiency-related, 2: 406–407 production animal production facilities, 3: 397 ruminal, 3: 982 Methanethiol Brevibacterium linens, 1: 570 cheese flavor, 1: 641–642 cheese ripening, 1: 570 Methicillin resistant Staphylococcus aureus, 4: 106f, 4: 108–109 community-associated (CA-MRSA), phages, 4: 108, 4: 108–109 Methionine analogues, commercial sources, 2: 392 cheese flavor, 1: 641–642 human requirements, 3: 818 metabolism, Lactobacillus casei group, 3: 102 microbial protein, 2: 415t milk production output, 2: 413–414
milk protein output, 3: 361–362 protein supplement, 2: 415t RUP, 2: 415t smear-ripened cheese ripening, 1: 399 transamination, starter cultures, 1: 562 Methionine hydroxy analog (MHA/HMB), 2: 391, 2: 392, 2: 394 bioavailability estimation, 2: 393 isopropyl ester (HMBi), 2: 391, 2: 392 METHIOPLUS, 2: 392 Method of Mohr, milk ion quantification, 3: 915 2-Methyl-1,4-naphthoquinone see Menadione 2-Methyl-3-1,4-naphthoquinone (menaquinones), 4: 661, 4: 662f 2-Methyl-3-phytyl1,4-naphthoquinone see Phylloquinone Methylcobalamin, 3: 1000 Methylene blue test, 1: 26–27 Methylfolate-trap hypothesis, 4: 679f, 4: 681–682 Methyl ketones blue mold cheese aroma, 1: 772 Penicillium camemberti, 4: 777–778 Methylmalonyl-CoA, 2: 234 Methyltransferase (MTase), bacteriophage resistance, 1: 435–436 Met-Plus, 2: 392 Metritis, 4: 517, 4: 518t buffalo, Asia, 2: 779 systemic/toxic, 4: 517 Mexican-style cheese listeriosis outbreaks, 4: 83 salmonellosis outbreaks, 4: 94 MFFB (moisture on fat-free basis), hard Italian cheeses, 1: 728 MHC class II analog protein (Map), 4: 104 Micellar calcium phosphate (MCP), 3: 908, 3: 921 acidification, 3: 911–912 chemical nature, 3: 908–910 cooling, 3: 912 ‘experimental’, 3: 908–910 NMR relaxation studies, 1: 156–157 structure, 3: 908–910 Micellar casein composition, 3: 858t manufacture, 3: 859 physical properties, 3: 858t Michaelis–Menten type equations, dairy cow metabolism modeling, 2: 433–434 Microarray analysis limitations, 3: 1059 mammary gland involution, 3: 348 Microarray ‘chips’, 3: 346 Microarray technology, 3: 346 mammary gland development, 3: 347 platform types, 3: 346–347 reference sample experiment design, 3: 346 Microbacterium gubbeenese, 1: 762 Microbial crude protein (MCP), quantity produced, 2: 461 Microbial DNA fingerprinting, cheese, 1: 632–638 accessory microbiota studies, 1: 635–636 artisanal vs. industrial cheese, 1: 636, 1: 637f culturable microbial species identification without isolation, 1: 636 culture-independent analysis, 1: 633, 1: 634f future perspectives, 1: 637 geographical origin assessment, 1: 636 information obtained, 1: 635 microbial diversity assessment, 1: 635 microbial isolate identification, 1: 637 microbial population monitoring, 1: 635 production mode assessment, 1: 636 ripening microbial population monitoring, 1: 635 starter cultures, 1: 635–636, 1: 636f Microbial lipases, enzyme-modified cheese, 1: 803 Microbial protein, rumen duodenal flow, 2: 409 importance of, 2: 409
Index Microbial toxins, biosensors, 1: 241 Microbial transglutaminase (mTGase), 2: 297 analysis, 2: 298 applications, 2: 297 catalytic reaction, 2: 297, 2: 298f characteristics, 2: 297 cheesemaking, 2: 299 covalent cross-link formation, 2: 297, 2: 298f dairy industry applications, 2: 299 fermented milk, 2: 299, 2: 299f fish, 2: 300 inhibitors, 2: 298 meat, 2: 300 mechanism, 2: 297 milk proteins in emulsions, 2: 299 nondairy products, 2: 300 nonfood product applications, 2: 300 plant protein-based foods, 2: 300 safety regulations, 2: 299 structure, 2: 297, 2: 298f substrate specificity, 2: 298 caseins, 2: 298 Microbiological analytical methods, 1: 215–220 microscopic techniques, 1: 219 plating techniques, 1: 216 dry dehydrated films, 1: 216 rapid methods, 1: 219 recent trends, 1: 632 sample size, 1: 215 sampling, 1: 74, 1: 215 serial dilutions, 1: 216 specific group enumeration, 1: 217 spoilage groups, 1: 218 statistical sampling plans, 1: 215 see also individual methods Microbiology blue mold cheeses see Blue mold cheeses cheese ripening, 1: 568t cheese salting see Cheese salting infrared spectrometry, 1: 120 khoa, 1: 885 smear-ripened cheeses see Smear-ripened cheeses see also individual species Micrococcus, 1: 627, 3: 456 brine-matured cheeses, 1: 793 cheese microbiology, 1: 627 smear-ripened cheeses, 1: 396–397 as spoilage microorganisms, 3: 454 Microcrystalline cellulose (MCC), 1: 531 applications, 1: 70t Microfiltration, 2: 729, 3: 307–309 cheese manufacture, 1: 618, 1: 618, 1: 618, 1: 622, 1: 623 bacteria removal, 1: 622, 1: 622f casein standardization, 1: 623 dried milk products, 3: 1071–1072 extended shelf life milk, 2: 729, 3: 286 micellar casein, 3: 859–860 milk fat globule membrane, 3: 693 milk in France, 3: 308 milk pasteurization, 3: 279 milk protein fractionation, 3: 763 milk standardization, cheese manufacture, 1: 548 small pore diameter, 3: 308 somatic cell removal, 3: 309 Microfluidics, 1: 191 Microfluidization, 2: 762 Microfluidizers, 2: 726–729 -Microglobulin, 3: 758 2-Microglobulin, 3: 796t, 3: 797 Micromanipulators, embryo biopsy, 2: 631 Microminerals see Trace elements (minerals) Micronutrients first-age infant formulae, 2: 142 in milk, nutrient intake, contributions to, 3: 1005 Microorganisms dental caries, 3: 1034–1035 milk-associated, 3: 447–457
contamination sources, 3: 447, 3: 448f fermentation starters (beneficial), 3: 454 heat treatment inactivation kinetics, data, 2: 716t heat treatment survival curves, 2: 715, 2: 719f high pressure treatment effects, 2: 733, 2: 758 molds see Mold(s) numbers, 3: 447, 3: 448f population dynamics, 3: 456 protozoa, 3: 452 removal, membrane microfiltration, 3: 307–308 thermization success, effect on, 2: 695, 2: 696t type groupings, 3: 447, 3: 448f yeasts see Yeast(s) spoilage see Spoilage microorganisms thermal inactivation, 3: 310–311 see also individual species Microparticle-enhanced nephelometric immunoassay (MENI), caseins, 3: 749, 3: 749t Microrheology, diffusing wave spectroscopy, 1: 139 Microscopy, 1: 226–234, 1: 227t Brucella detection, 2: 155 curd strength measurement, 1: 586 see also specific techniques Microsomal triglyceride transfer protein (MTP), 2: 218 Microstructure, 1: 226–234 butter, 1: 234f centrifugation, 1: 230 cheese rheology, 1: 685 concentration, 1: 231 dairy spreads, 1: 233, 1: 234f definition, 1: 226 dehydration, 1: 231 examples, 1: 232 see also specific products freezing, 1: 231 heating, 1: 230 high-pressure treatment, 1: 232 homogenization, 1: 230 ionic concentration, 1: 232 mechanical effects, 1: 232 milk, 1: 229 mozzarella, 1: 233 MRI, 1: 165 pH, 1: 232, 1: 232f processing effects, 1: 229 proteins, 1: 229f, 1: 232 rennet, 1: 232 whey proteins, 1: 232 whipped cream, 1: 232 yogurt, 1: 233, 1: 233f Microtubules, lipid droplet transit, 3: 375 Microwave spectroscopy, 1: 113 Middle Ages, cheese, 1: 534 Middle East sheep breeds, 1: 325 sheep numbers and milk production, 2: 69t Middle Eastern fermented milks, 2: 503–506 concentrated, 2: 504 dried (kishk and related products), 2: 505 historical aspects, 2: 503 normal milk composition, 2: 503 traditional use and history, 2: 503 Mid-infrared (MIR) analysis citric acid, 3: 743–744, 3: 744f milk proteins, 3: 743, 3: 743f, 3: 744f near-infrared analysis vs., 3: 743 nonprotein nitrogens, 3: 743–744, 3: 744f Midlactation cows, drylot management systems, 2: 54t Miehei coagulant (Rhizomucor miehei proteinase), 1: 576, 1: 576 Mie theory, 1: 134 Milchwissenschaft, 2: 103 Milk, 3: 458–466, 3: 478–483 acid-base equilibria, 3: 474 buffering action, 3: 474, 3: 474t concentration, 3: 476 dilution, 3: 476
909
freezing, 3: 475 heating, 3: 475 treatment effects, 3: 475 acidification, heat-induced, 2: 747–748 acidophilus, 2: 473 acoustic properties, 3: 470 additives, 1: 36t, 1: 39 adulteration, biosensors, 1: 245 alcohol stability, seasonal variations, 3: 605 anticariogenic properties, 3: 1035 Bacillus cereus, 4: 28 bacterial contamination, mastitis, 3: 904 biotin, 4: 688t boiling point, 3: 473 Brucella abortis contamination, 1: 645 buffalo see Buffalo milk buffering constituents, 3: 474 calcium see Calcium calcium/protein ratio, 3: 1013 camel see Camel milk cancer and, 3: 610, 3: 610f carbohydrate fraction separation, 3: 249 carrageenan interactions, 2: 910 cholesterol, 3: 734, 3: 735t cholesterol removal, 3: 736 citrate, 3: 166 coagulation see Coagulation colligative properties, 3: 473 color, 3: 462, 3: 480 completeness, as food, 3: 608 composition, 1: 248, 2: 481, 3: 530, 3: 608, 3: 608t amino acids, 3: 530–531, 3: 532t component standardization, 4: 545 determination, historical aspects, 1: 18 early lactation, 3: 600–602 end of lactation, 3: 600–602 interspecies variations, 2: 508t, 3: 458–459, 3: 459t, 3: 460, 3: 513t intraspecies variations, 3: 462 lactation changes, 3: 598 nutritional effects, 3: 602 seasonal changes, 3: 600, 3: 601f, 3: 601f stage of lactation, 3: 600 yak colostrum comparison, 3: 532t yak milk comparison, 3: 533 constituents, 3: 461 categories, 3: 461, 3: 478 characterization, historical aspects, 1: 20 isolation, historical aspects, 1: 20 waste-load equivalents, 4: 619 constituent secretion, 3: 373–380 exocytosis, 3: 377 minerals, 3: 379 pathways, 3: 373, 3: 374f water, 3: 379 consumption coronary heart disease risk, 3: 1033 stroke risk, 3: 1033 contaminants see Contaminants cooling, 4: 184 creaming, historical aspects, 1: 21 definition, 3: 310 as delivery system, 3: 1006 density, 3: 467, 3: 468t dispersed gas, 3: 468 fat content, 3: 468 prediction, 3: 468 dielectric loss factor, 3: 472 dielectric properties, 3: 472 donkeys see Donkey milk dry matter, 3: 462 dulce de leche, 1: 875 as dynamic system, 3: 462 E. coli outbreaks, 4: 61 economic value, 4: 545 electrical properties, 2: 739, 3: 471 Enterobacteriaceae, 4: 68 enthalpy, 3: 468
910 Index Milk (continued ) change prediction, 3: 469 equine see Equine milk evaporated see Evaporated milk evolution and, 3: 607 extended shelf life (ESL) see Extended shelf life (ESL) milk fat see Milk fat fat globules see Milk fat globule(s) fermented see Fermented milks Feta cheese manufacture, 1: 791 flavor/aroma compounds responsible, 2: 533, 2: 534f, 2: 534t consumer responses, 3: 609 flavor compounds, desirable, 2: 533, 2: 534f, 2: 534t raw vs. pasteurized milk, 2: 533 species differences, 2: 533 foot-and-mouth disease infected animals, 2: 165 fractionation, 3: 464 freezing point, 3: 473, 4: 711 freshness, biosensors, 1: 242 gelation induction, 3: 599 global production, 3: 463 goat see Goat milk health and see Milk, nutritional value and human health heat-induced changes, 2: 747 heating, 4: 184 heat stability see Heat stability, milk heat treatment see Heat treatment hormones see Hormones horses see Equine milk human see Human milk for human consumption, 3: 607, 3: 607, 3: 608 indigenous enzymes see Milk enzymes infant nutrition, 3: 463–464 infrared spectrometry, 1: 119t intake, colorectal cancer risk, 3: 1018 as intestinal regulator, 3: 1006 K+/Na+ ratio, 3: 379 lactose-free see Lactose-free milk lactose-reduced, 3: 299 light penetration, 3: 473 light scattering properties, 3: 473 lipids see Milk lipids lipolytic defects, 3: 723 low-moisture part-skim mozzarella (pizza cheese) manufacture, 1: 737, 1: 738f, 1: 738f macromineral content, 3: 925, 3: 926t mechanical damage, 3: 604 mechanical separation, 3: 677 centrifugal, 3: 677 efficiency, 3: 677 membrane-processed see Membrane-processed milk microbiological contamination sources, 3: 632 microorganisms in see Microorganisms microstructure, 1: 229 Mycobacterium infected cattle, 4: 91 myths and facts about, 3: 609 naming regulations (for marketing), 3: 3 consumer demands, 3: 611 native proteinase systems, 3: 603 Newtonian behavior, 3: 467 non-Newtonian behavior, 3: 467 nutritional value and human health, 2: 483, 3: 607–612 lactose digestibility, 2: 484, 3: 610 nutrient deficiencies, 3: 608 quality, 3: 607 stability, 3: 607 off-flavors, oxidation products, 3: 717 on-farm storage, historical aspects, 1: 6 optical properties, 3: 472 infrared region, 3: 473 UV region, 3: 472–473 visible region, 3: 472 osmotic pressure, 3: 473
oxidation–reduction equilibria (redox potential), 1: 250, 3: 476 bacterial activity, 3: 476 heat treatment, 3: 476 pasteurized see Pasteurized milk pathogens common, 1: 217 source, historical aspects, 1: 26 see also individual pathogens perishability, 3: 464 permittivity, 3: 472 pH, 3: 474 mastitis effects, 3: 904 photooxidation, 3: 476 physical properties, 1: 249t, 3: 467–477 definition, 3: 467 physicochemical properties, 3: 467–477 definition, 3: 467 physiological functions, 3: 458–459 plasmin system see Plasmin system, milk powdered see Milk powder pressure stability, 2: 735 pretreatment Cheddar cheese, 1: 706 khoa, 1: 883 processing future considerations, 3: 647 industrialization, 1: 1 processing operations, typical losses, 4: 620t processing properties definition, 3: 598–599 seasonal effects, 3: 598–606 production see Milk production proteins see Milk protein(s) proteomics, 3: 843 quality see Milk quality raw see Raw milk as raw material, attractive features, 3: 464 recording see Milk recording refractive index, 3: 473 renal solute load, 3: 928–929 rennet coagulability, 3: 482 rheology see Milk/cream rheology salts see Milk salt(s) shear thinning, 3: 467 sheep see Sheep milk skim see Skim milk specific gravity (relative density), 1: 77, 3: 467 definition, 3: 467 specific heat capacity, 3: 468 spoilage microorganisms, 2: 539, 3: 282, 3: 282 keeping quality, 3: 894 spontaneous oxidation, 3: 717 Staphylococcus aureus incidence, 4: 114 storage temperature, bacterial growth, 4: 379–380 sugars, 3: 461 super-pasteurised see Extended shelf life (ESL) milk surface tension, 3: 470 fat content, 3: 470 heat treatment effects, 3: 470 technological properties, 3: 482 thermal conductivity, 3: 469, 3: 469t prediction, 3: 469 thermal diffusivity, 3: 469 thermal properties, 3: 468 thermization see Thermization thixotropy, 3: 467 titratable acidity, 3: 475 titration curves, 3: 475, 3: 475f, 3: 475f trace element content see Trace elements (minerals) trade in see Harmonized System (HS); World Trade Organization (WTO) traditional products, 3: 464 transgenic cows, 3: 968 transportation, bacterial growth, 4: 379 triacylglycerols see Triacylglycerol(s)
two-dimensional electrophoresis see Twodimensional electrophoresis, milk unpasteurized see Raw milk utilization, 3: 463 variability, 3: 461 viruses in, 3: 451 viscosity, 3: 467 vitamin D content, 3: 609, 3: 1012 vitamin E, 4: 653 water activity, 4: 707–708 whole see Whole milk world production, 4: 631 xanthine oxidoreductase, 2: 326 yak see Yak milk yeasts in, 4: 744–753, 4: 746t Milk allergy (MA), 3: 607, 3: 1041–1045 allergen types, 3: 1042 alteration, 3: 1043 clinical manifestations, 3: 1041, 3: 1042f diagnosis, 3: 1041, 3: 1042f equid milk substitutes, 3: 528 incidence, 3: 1041 milk protein intolerance vs., 3: 1041 Milk cake, yak milk, 1: 349 Milk chocolate, 1: 856–861 composition, 1: 856, 1: 857f lecithin, 1: 856–857, 1: 858f fat bloom, 1: 859 flavor, 1: 858 lactose, 1: 858 milk fat, 1: 858 future work, 1: 861 history, 1: 856 ingredients, 1: 860 buttermilk powder, 1: 860 chocolate crumb, 1: 860 high-fat powders, 1: 860 lactose, 1: 860 skim milk powder, 1: 860 whey powder, 1: 860 whole milk powder, 1: 860 legislation, 1: 861 Codex Alimentarius, 1: 861 liquid flow properties, 1: 857 butterfat, 1: 857 milk powders, 1: 858 proteins, 1: 858 surface-active agents, 1: 857, 1: 858f viscosity, 1: 857 milk fat effects, 1: 858 anhydrous milk fat, 1: 859 eutectic effects, 1: 859, 1: 859f temperature range, 1: 858, 1: 859f mouthfeel, 1: 856, 1: 858 white crumb lipid breakdown products, 3: 232 ‘Milk Committee’ see Codex Committee on Milk and Milk Products (CCMMP) Milk/cream rheology, 3: 467, 4: 520, 4: 521t acidification effects, 4: 522 casein content, 4: 520 components, 4: 521t Cross equation, 4: 522 Eiler’s semiempirical equation, 4: 520 fat content, 4: 520 heat treatment effects, 4: 522 homogenization effects, 4: 522 Newtonian behavior, 4: 520 non-Newtonian behavior, 4: 520, 4: 521 property prediction, 4: 523, 4: 524t renneting effects, 4: 522 shear thinning, 4: 521–522 storage effects, 4: 523 temperature/thermal history, 4: 521 Milk drinks, 3: 299 additives, 3: 299 processing steps, 3: 300 Milk dryers design, 4: 216–233
Index drying principles, 4: 208–215 Milk enzymes, 3: 751–752 allergic reactions, 3: 1042–1043 heterogeneity, 3: 756 indigenous, 2: 327–334 heat treatment vs.pulsed electric field inactivation, 2: 740, 2: 740t historical aspects, 1: 23 phosphatases see Phosphatases temperature-dependent kinetic data, 2: 718t as thermization indices, 2: 693 ultrasound effects, 2: 742 nomenclature, 3: 756–758 sheep milk, 3: 500 see also individual enzymes Milk extraction principles, 3: 941 Milk fat, 3: 352–358, 3: 353t anhydrous see Anhydrous milk fat (AMF) autooxidation, 3: 717 average content, 4: 545 biosynthesis, 3: 352, 3: 353f de novo synthesis, 3: 352 preformed fatty acids, 3: 353 triacylglycerol synthesis, 3: 354 blending, 3: 706, 3: 706f butter, 1: 493 camel milk, 3: 513 centrifugal separation, 4: 546 cholesterol removal, 3: 736 climate considerations, 3: 357 cold stress, 3: 357–358 composition, 3: 649 diet effects, 3: 355 as conductor, 3: 654 crystallization, 3: 653 high pressure effects, 2: 736 curve, drylot management systems, 2: 52, 2: 53t density, 3: 654 deteriorative reactions, 3: 654 determination methods, 1: 79, 1: 82t historical aspects, 1: 18 dropping point, 3: 704, 3: 705f dulce de leche, 1: 875 economic value, 4: 545 emulsion stability, 3: 675 environmental effects, 3: 355 fatty acids, 3: 354, 3: 354t flavor compounds, 3: 652 folate content, 4: 680–681, 4: 682t fractionation, 1: 500 olein fraction, 1: 500–501 stearin fraction, 1: 500–501 hardness, 3: 704, 3: 705f hardness index, 3: 706f health benefits, 3: 1005 heat stress effects, 3: 357–358, 4: 564, 4: 564t hydrolysis, seasonal variations, 3: 604 interesterification, 3: 707, 3: 707f, 3: 707f lactose concentration relationship, 3: 173, 3: 174f latent heat, 3: 653 lipid classes, 3: 650, 3: 650t lipid-soluble hormones, 2: 766–767, 2: 768, 2: 770 lipolysis, 3: 654 mammalian milk, 3: 323 mastitis effects, 3: 902 melting profile, 3: 653, 3: 653f melting properties, 3: 544, 3: 653 calorimetry, melting thermogram curves, 3: 544, 3: 549f melting peaks-fatty acid composition relationship, 3: 549 melting points, 3: 549 technological implications, 3: 549 milk chocolate see Milk chocolate milk chocolate flavor, 1: 858 nutrient intake, contributions to, 3: 1004 oxidation, 3: 654 percentage, diet effects, 3: 355
physical properties, 3: 653 products see Milk fat products protection of microorganisms against electric pulse, 2: 739 refractive index, 3: 654 reindeer milk, 1: 376–377, 1: 377 seasonal effects, 3: 357, 3: 601f specific heat, 3: 653 standardization see Milk fat standardization temperature effects, 3: 357–358 transgenic cows, 2: 643 viscoelastic nature, 3: 705, 3: 706f, 3: 706f viscosity, 2: 736, 3: 654 yak milk, 1: 347–348 see also Emulsions Milk fat-based spreads, 1: 522–527 antioxidants in, 1: 524 churning technology, 1: 526 batch churning, 1: 526 continuous churning, 1: 527 flavor, 1: 524 food legislation and, 1: 522 manufacturing technology, 1: 524 cream inversion, 1: 527 margarine-based production method, 1: 524, 1: 525f aqueous phase preparation, 1: 524–525 crystallization, 1: 525, 1: 526f, 1: 526f, 1: 526f emulsifiers, 1: 524–525 emulsion, 1: 525 fat phase, 1: 524 mechanical kneading, 1: 525–526 resting cylinders, 1: 526 stabilizers, 1: 524–525 microstructure, 1: 523–524 moisture droplets, 1: 524 product characteristics, 1: 523 products, 1: 522 specifications, 1: 522 taste, 1: 524 Milk fat-canola oil interesterification, 3: 707, 3: 707f Milk fat depression (MFD) causes, 2: 795, 3: 41 diet-induced biohydrogenation theory, 3: 356, 3: 356f etiology, 3: 355–356 investigation, 3: 355–356 induced, 3: 357 insights gained from, 3: 357 Milk fat globule(s), 3: 675–679 breed differences, 3: 675 diameter, 3: 675 dietary effects, 3: 639 donkey milk, 1: 366, 1: 368f equine milk, 1: 361 interfacial area, 3: 675 low-fat cheese color, 1: 837–838 oil-in-water emulsion, 3: 675 particle size distribution, 2: 755, 2: 756f raw milk, 3: 691 sheep milk, 3: 496–497 size distribution homogenization effects, 2: 755, 2: 756f, 2: 901 interspecies variation, 3: 486 synthesis, 3: 680 Milk fat globule EGF factor 8 (MFG-E8) see Lactadherin Milk fat globule membrane (MFGM), 3: 680–690 analysis, 1: 244 antimicrobial properties, 3: 1062 buttermilk, emulsifying properties, 3: 694 casein separation, 3: 693 composition, 3: 691 ‘crescents’, 3: 680, 3: 681f damage induced lipolysis, 3: 722 psychrotrophs, 4: 388 dehydration, 3: 679 emulsion interfacial films, 1: 63
911
enzymes, 3: 683t, 3: 689 formation, 2: 324, 2: 325f, 3: 354, 3: 375–377 fractions, 3: 691–697 antibacterial activity, 3: 695–696 freezing, 3: 679 gross composition, 3: 681, 3: 681t health benefits, 3: 695 heat treatment effects, 3: 678, 3: 692–693 Helicobacter pylori inhibition, 3: 695 homogenization, 3: 678, 3: 692, 3: 692t isolation, 3: 680, 3: 693 commercial-scale, 3: 693 compositional changes, 3: 681 fat globule disruption, 3: 693 lipase permeability, 3: 721 lipid arrangement, 3: 691 lipid composition, 1: 64, 3: 486, 3: 681t, 3: 682, 3: 682t lipid oxidation, 3: 719 lipoprotein lipase, 2: 305, 3: 638 mechanical agitation, 3: 693 milking damage, 3: 677 molecular organization, 3: 689 interactions, 3: 690 MS, 1: 200, 1: 201 mucins, 3: 480 nutritional value, 3: 694t, 3: 695 origins, 3: 680 pathogen adhesion inhibition, 3: 695 phosphatases, membrane-associated, 2: 314, 2: 317 phospholipids, 3: 671 primate milk, 3: 621 processing-related changes, 3: 677, 3: 692 proteins see Milk fat globule membrane (MFGM) proteins RNA, 3: 681–682 stability, air mixing, 3: 638–639 storage effects, 3: 692 structure, 1: 63, 3: 680, 3: 681f supernatant, 3: 681 supramolecular structure, 3: 692 technological value, 3: 694, 3: 694t thermal concentration, 3: 679 tocopherols, 3: 718 volatile sulfur compound release, 3: 692–693 xanthine oxidoreductase, 2: 324, 3: 480 Milk fat globule membrane (MFGM) proteins, 3: 692, 3: 751–752, 3: 758 classification, 3: 758 composition, 3: 681t, 3: 682, 3: 683t nomenclature, 3: 682–683 layer structure, 3: 680 stabilization, 1: 61–62, 1: 64 emulsifier interactions, 1: 63, 1: 64f 2D electrophoresis, 3: 846–847 Milk fat products, 1: 515 Codex standard, 4: 328 manufacturing technology, 1: 518 recommended quality factors, 1: 515, 1: 516t specifications, 1: 515, 1: 516t see also individual products Milk fat standardization, 4: 545–549 aims, 4: 545 current status, 4: 548 downstandardization nutritional effect, 4: 546–547 positive/negative effects, 4: 546–547 future prospects, 4: 549 regulatory aspects, 4: 548 technological approaches, 4: 546 technological principles, 4: 546 cream fat content, 4: 546 reblending, 4: 546 sensory quality, 4: 546–547 Milk-fed calves, cold stress, 4: 552 Milk fever, 2: 239–245, 3: 996–997, 4: 516, 4: 518t age effects, 2: 372 blood ionized calcium concentration, 2: 242
912 Index Milk fever (continued ) body condition score, 1: 465 breed effects, 2: 372 breed predilection, 2: 239 clinical pathology, 2: 242 clinical presentation, 2: 240, 2: 241t dietary cation-anion difference, 2: 356 differential diagnosis, 2: 242 dystocia, 4: 511 economic losses, 2: 239 etiology, 2: 239 goats, 2: 242, 2: 794, 2: 801 hypocalcemic relapse, 2: 243 hypomagnesemia, 2: 228, 2: 240 low-calcium diet, 2: 450 metabolic alkalosis, 2: 240 nonparturient cases, 2: 242 occurrence, 2: 239 cattle, 2: 239 goats, 2: 239 pathogenesis, 2: 239 phosphorus, 2: 240, 2: 242 prevention, 2: 243, 3: 996–997, 4: 518 acidification through diet, 2: 244 acidogenic diet creation, 2: 357 calcium binding with zeolite A, 2: 244 dietary calcium restriction, 2: 243 prophylactic calcium, 2: 244 risk factors, 2: 239 secondary problems, 2: 241 stage I, 2: 241, 2: 241t treatment, 2: 243 stage II, 2: 241, 2: 241t stage III, 2: 241, 2: 241t treatment, 2: 243 Milk fluoridation programs, 3: 1037 Milk fortification see Fortification, milk Milk glycoconjugates, brain stimulating activity, 3: 252 Milk harvesting, historical aspects, 1: 6 Milk Income Loss Contract (MILC) program, 4: 304 payments, 4: 304, 4: 305f Milking African dairy cow management, 2: 80, 2: 80f drylot management systems, 2: 57 environmental mastitis prevention, 3: 419–420 equine, horse milk, 1: 358 feed concentrates, 2: 41 frequency, influence on yield, 3: 39 by hand see Hand milking hygiene see Milking hygiene milk flow patterns, 3: 330 quality, critical management points, 2: 682 warm climate farms see Farm design (warm climates) yaks, 1: 347 Milking center design, 3: 959 Milking equipment cleaning, 3: 633, 3: 634f disinfection, 3: 633 see also Milking machines Milking hygiene, 3: 632–637 bacterial transfer control, 3: 440 chemical concentration, 3: 634 cleaning assessment methods, 3: 636 ATP measurement, 3: 636 bulk milk culture, 3: 636 visual assessment, 3: 636 environmental issues, 3: 636 mechanical cleaning action, 3: 635 flooded flow, 3: 635 herd size and, 3: 636 microbiological contamination sources, 3: 632 Salmonella control, 4: 96 sheep, 2: 871 temperature, 3: 634 Milking machines automatic milking systems, 3: 953
bacteria transferred by, 3: 440 basic function, 3: 945, 3: 945f partial vacuum functions, 3: 945, 3: 945 closure/rest phase, 3: 945, 3: 945f design, 3: 941–951 donkeys, 1: 365, 1: 367f historical aspects, 1: 6, 3: 941 horses, 1: 358–359 incomplete/omitted milking, 3: 441 liners see Teat-cup liners liquid level control system, 3: 950 mastitis transfer, 3: 384 see also Mastitis mechanical releasers, 3: 946 milking cluster, 3: 947, 3: 947f airflow allowance, 3: 946 attachment and removal, 3: 440 clawpiece, 3: 947 clawpiece capacity, 3: 947 milking endpoint determination, 3: 947–948 milking phase, 3: 945, 3: 945f milking recording, 3: 950 milk meters, 3: 950 milk pumps, 3: 946 online mastitis detection, 3: 423, 3: 423, 3: 425–426, 3: 426f operating vacuum, 3: 945–946 overmilking, 3: 441 patents, 1: 6 pipeline systems, 3: 950, 3: 950t premilking lag-time, 3: 441 principles, 3: 941–951 catheter principle, 3: 941, 3: 942f, 3: 942f pressure principle, 3: 941, 3: 942f, 3: 942f, 3: 943f vacuum principle, 3: 942, 3: 943f, 3: 943f, 3: 943f, 3: 944f, 3: 944f, 3: 944f, 3: 944f pulsators see Pulsators regulators, 3: 947 releaser/sanitary milk pump, 3: 950 robotic equipment, 3: 950 sanitary measures (predipping, cup flushing), 3: 440 supplementary equipment, 3: 950 teat-cup shells, 3: 948, 3: 948f unit adjustment, mastitis prevention/control, 3: 433 vacuum measurement, 3: 945 vacuum pumps see Vacuum pumps Milking parlors, 3: 959–964 animal identification, 3: 963 basements, 3: 960 cleaning, 3: 964 construction methods, 3: 960 crowd gates, 3: 963 data collection/records systems, 3: 963 design considerations, 3: 959 design elements, 3: 962 donkeys, 1: 371f electrical systems, 3: 960 entrance/exit gates, 3: 962 environmental control, 3: 960 flat, 3: 962, 3: 963f flushing systems, 3: 964 goats, 2: 804 costs, 2: 806 throughputs, 2: 805, 2: 806t hygiene, 3: 964 indexing stalls, 3: 962 instrumentation, 1: 9 labor efficiency, 3: 963 milkline positioning, 3: 959–960 sheep, 2: 75, 2: 868 feeding, 2: 870 high-line, 2: 868 platform height, 2: 868, 2: 868f restraints, 2: 868 standing platforms, 2: 869f, 2: 870f support equipment, 3: 962 types, 3: 960, 3: 964 ventilation systems, 3: 960
wastewater negative environmental impact reduction, 4: 632 storage, 4: 632–633 working posture, 3: 963–964 work routines, 3: 963 see also individual designs Milking robots, 4: 252 economics, 4: 253–254 farm design and, 4: 253 manufacturers, 4: 254 milking process, 4: 253 personalized feeding, 4: 254 running costs, 4: 254 see also Automatic milking systems (AM systems) Milking Shorthorn cattle, 1: 288 historical aspects, 1: 2 milk composition, 2: 53t stability/survival, 1: 290–291 Milking stall, automatic milking systems, 3: 952 Milking traits, Bos indicus x Bos taurus cattle, 1: 306, 1: 307t Milk ion quantification, atomic spectroscopic methods, 3: 914t, 3: 915 Milk ketone test, 2: 236 Milklines, goat milking, 2: 810, 2: 811f, 2: 811t Milk lipase see Lipase(s) Milk lipids, 3: 479, 3: 649–654, 3: 543 analytical methods, 3: 698–703 historical aspects, 1: 20 breed variations, 3: 479 classes, 3: 650, 3: 650t components, 1: 64, 1: 65t fatty acids, 2: 366, 2: 368, 3: 543 triacylglycerides, 3: 485–486, 3: 486t droplet expansion mechanisms, 3: 374–375 droplet formation, 3: 373 droplet fusion, 3: 374–375 enzymatic off-flavor development, 2: 540f human colostrum, 3: 585, 3: 586t human milk, 3: 585, 3: 586t malnutrition, 3: 479 melting behavior, 3: 704 nutritional significance, 3: 711–715 oxidation affecting factors, 3: 717 antioxidant effects, 3: 718 high-pressure homogenized milk, 2: 758–759 light, 3: 718 light-induced, flavor effects, 2: 538 metal contact, acceleration by, 2: 539, 2: 540f metals, 3: 718 milk fat globule membrane, 3: 719 oxygen, 3: 717 primate milk, 3: 615t, 3: 616 rheological properties, 3: 704–710 composition, 3: 704 composition-related modifications, 3: 706 modifications, 3: 706 process-related modifications, 3: 708 sampling, point during milking effects, 3: 479 seasonal variability, 3: 704 secretion, 3: 373, 3: 374f, 3: 376f droplet membrane coating, 3: 375, 3: 376f droplet transit, 3: 375 secretory vesicles, 3: 375 spreadability, 3: 704 types, 1: 64, 1: 65t Milk peptides anticariogenic properties, 3: 1036 biofunctionality, 2: 293 Milk powder analysis, 2: 115 infrared spectrometry, 1: 119t NMR, 1: 162 applications, 2: 115 as ingredient, 2: 115 reconstitution, 2: 115 Bacillus cereus, 4: 28
Index control, 4: 29 EC regulations, 4: 28 biofilms, 1: 446, 1: 446f bulk density, 2: 118, 2: 119f nozzle atomization, 2: 118 Chinese dairy management, 2: 86, 2: 86f Codex standards, 4: 329 dietary supplementation, postmenopausal women, 3: 1014 emulsifying properties, 2: 122 Enterobacter control, 4: 79 functional properties, 2: 117–124 cakiness, 2: 122 dispersability, 2: 121 emulsifying properties, 2: 122 flowability, 2: 119 heat stability, 2: 122 hygroscopicity, 2: 121 interstitial air, 2: 119, 2: 119t occluded air, 2: 119, 2: 119t particle density, 2: 118 particle size distribution, 2: 118 sinkability, 2: 120 stickiness, 2: 122 water activity, 2: 122 wettability, 2: 120 glass transition temperature, 2: 122 differential scanning calorimetry, 2: 123 historical aspects, 1: 14 instantization, 2: 113, 2: 113f rewetting process, 2: 113f, 2: 113–114 straight through process, 2: 113–114, 2: 114f structural effects, 2: 117 lipolytic defects, 3: 724 manufacture, 2: 108–116, 2: 112f concentration, 2: 110–111 heat pretreatment, 2: 110–111 roller drying, 2: 109, 2: 109f milk chocolate, 1: 858 packaging, 2: 115, 4: 19 particle density, 2: 118 physical properties, 2: 117–124 see also specific properties physical property prediction, hyperspectral imaging, 1: 130–131 processing equipment, 4: 128t raw milk, 2: 110–111 rehydration, 2: 120 sampling, 1: 74 scorched particles, 2: 120 skimmed see Skim milk powder (SMP) solubility, 2: 121 insolubility index, 2: 121 lactose form, 2: 122 spray drying see Spray drying storage, 2: 115 differential scanning calorimetry, 1: 261, 1: 262f structure, 2: 117, 2: 118f drying technique effects, 2: 117 types, 2: 108–116 whole see Whole milk powder Milk production, 3: 463 Awassi sheep, 1: 328, 1: 328t body condition score, 1: 463, 1: 463 body fat, 1: 464 body weight, 1: 457–458 bovine somatotropin effects, 3: 32 Chios sheep, 1: 328t, 1: 329 curve, drylot management systems, 2: 52 decreases, leptospirosis, 2: 181 displaced abomasum, 2: 213–214 dry matter intake in, 2: 459 East Friesian sheep, 1: 326, 1: 327t feed costs, 2: 458, 2: 459t gastrointestinal nematodes, 2: 258–259 Improved Awassi sheep, 1: 327 income over feed costs, 2: 458, 2: 459t increases, profitability, 2: 458
Lacaune sheep, 1: 328t, 1: 330 nutrient intake percentages, 2: 458, 2: 459t Sardinian (Sarda) sheep, 1: 331 traits, 2: 650 transgenic cows, 2: 642–643 Milk products common pathogens, 1: 217 phospholipids, 3: 671–672, 3: 673t Milk protein(s), 3: 359–366, 3: 480, 3: 751–764, 3: 538 allergenicity reduction, 3: 1043 allergens, 3: 1042 allergies, 3: 365 amino acid delivery rates, 3: 818 amino acid residue racemization, 3: 1069 analytical methods, 3: 219, 3: 741–750 analytical performances, 3: 745, 3: 745t, 3: 745t biological properties, 3: 741 chemical characteristic measurements, 3: 741, 3: 742f dye-binding methods, 3: 744 future trends, 3: 750 general criteria, 3: 742 historical aspects, 1: 22 individual proteins, 3: 746 major nitrogen fractions, 3: 745 nitrogen determination, 3: 743 PAGE, 3: 541, 3: 541f physical properties, 3: 741 reference protein preparation, 3: 746 seasonal variations, 3: 745–746, 3: 746t structural characteristic measurements, 3: 741, 3: 742f total proteins, 3: 742 average content, 4: 545, 4: 546t bioactive, 3: 364t, 3: 365 biological roles, 3: 759 biosynthesis, 3: 359, 3: 360f breed differences, 3: 363 diet, 3: 361 endocrine control, 3: 362, 3: 362f factors affecting, 3: 361 mastitis, 3: 363 temperature in, 3: 362 blood-derived, 3: 359 bovine somatotropin treatment, 3: 33 breeding for, 3: 760 buffalo milk, 2: 778 camel milk, 3: 513 casein:whey protein ratio, 3: 480, 3: 758 characteristics, 3: 752t cheese analogues, 1: 815t classification, 3: 751 colon cancer risk, 3: 1020, 3: 1020f, 3: 1021f composition, 3: 359, 3: 360t, 3: 816, 3: 817t concentration variability, 3: 758 constituents, 3: 538 covalent modifications, 3: 1067 cross-reactivity, 3: 1044, 3: 1044f damage causes, 3: 1073–1074 definition, 3: 742 denaturation, 3: 1067 determination, historical aspects, 1: 19 digestibility, 2: 483, 3: 1067–1068 humans, 3: 816, 3: 817t domestic cooking effects, 3: 1072–1073, 3: 1073t donkey milk, 1: 368, 1: 368f drylot management systems, 2: 52, 2: 53t -elimination reaction, 3: 1068, 3: 1069f emulsification, 3: 890 droplet size distribution, 3: 890 microbial transglutaminase, 2: 299, 2: 299f surface protein coverage, 3: 890 fractionation, 3: 751, 3: 760 analysis, 1: 79, 1: 79f industrial, 3: 762 methods, 3: 760 functional products, 3: 888f functional properties, 3: 887–893, 3: 888t, 3: 893t
913
classification, 3: 887 definition, 3: 887 foaming, 3: 891 gelation, 3: 892 hydration, 3: 889 intrinsic properties, 3: 887 solubility, 3: 887 viscosity, 3: 889 water-binding capacity, 3: 889 whipping, 3: 891 genetic polymorphism, 3: 752t, 3: 759, 3: 822t cheese manufacture, 1: 535 health disorders, 3: 365 heat-induced coagulation, 2: 747–748 heat-induced nonenzymatic modifications, 3: 1067, 3: 1068t heat stability, 2: 746, 2: 746f, 3: 891 measurement, 3: 892 heat stress, 4: 565 heterogeneity, 3: 751, 3: 752 future developments, 3: 763 high pressure treatment effects, 2: 735, 2: 757 whey protein denaturation, 2: 757 homology, 3: 758 human milk see Human milk hydrolysis see Milk proteolysis immune-related, 3: 359 indispensable amino acids, 3: 818, 3: 819t induced lactation, 3: 22–23 interspecies comparison, 3: 538, 3: 821–842, 3: 822f buffalo vs. cow, 3: 503, 3: 504, 3: 504t concentration, 3: 758 goat vs. cow, 3: 486–487 primates, 3: 542 quantitative variability and molecular diversity, 3: 821–842 ruminants, 3: 541 whey protein:casein ratio, 3: 538 intraspecies variability, concentration, 3: 758 isolation, 3: 751, 3: 760 methods, 3: 760 lactation stage, 3: 363 mammary-derived, 3: 359, 3: 360t marsupial milk see Marsupial milk mastitis effects, 3: 903, 3: 903f milking frequency, 3: 363 milk lipid oxidation, 3: 719 minor, 3: 795–800, 3: 796t immune defense system, 3: 797 vascular system control, 3: 795 vascular system development, 3: 795 neonate developmental programming, 3: 795 nomenclature, 3: 751 nutrient intake, contributions to, 3: 1004 nutritional quality, 3: 816–820 output, dietary manipulation, 3: 361–362 plasmin digestion, during involution, 3: 41 primate milk, 3: 621 quality processing effects, 3: 1067–1074 storage effects, 3: 1067 reindeer milk, 1: 376–377, 1: 377, 3: 534 seasonal variation, 3: 600 secretion, 3: 359, 3: 374f, 3: 377 exocytosis, 3: 374f, 3: 377 simple exocytosis, 3: 377–378 transcytosis, 3: 374f, 3: 378 sheep milk, 3: 494 standardization see Milk protein standardization synthesis, 3: 332 technologically important properties, historical aspects, 1: 23 total concentration, 3: 461–462 transporter-binding proteins, 3: 798 types, 3: 843 yak milk, 3: 533, 3: 533 see also individual proteins
914 Index Milk protein concentrate (MPC), 3: 848–854 analogue cheese, 3: 852 applications, 3: 850 caseinates vs., 3: 848 cheesemaking see Cheese manufacture coffee cream, 3: 853 disulfide-linked protein aggregates, 3: 850 drying, 3: 850 food emulsions, 3: 850 functionality variability, 3: 850 high-quality milk use, 3: 849 ice cream, 3: 852 insoluble materials in, 3: 850 lactosylation, 3: 850 manufacture, 3: 849f thermal evaporation, 3: 849–850 ultrafiltration-based, 3: 848, 3: 849, 3: 849f, 3: 866 milk-based drinks, 3: 853 nondairy food, 2: 128t nutritional products, 3: 853 particle size, 3: 850 pectin addition, 3: 853 preparation techniques, 2: 125 processed cheese, 3: 852 protein content denotation, 3: 848, 3: 849t protein dissociation, 3: 850 protein-polysaccharide interactions, 3: 853 quality, processing condition effects, 3: 850 selenium-enriched, 3: 853 solubility, 3: 888 spreads, 3: 853 therapeutic products, 3: 853 whipping cream, 3: 853 yogurt, 3: 852 Milk protein-derived peptides, 3: 1062 anticarcinogenic activity, 3: 1065 antihypertensive effects, 3: 1064 antimicrobial activities, 3: 1063 antithrombotic effect, 3: 1064 body defense enhancement, 3: 1063 bone resorption, 3: 1065 chronic disease protection, 3: 1064 gastrointestinal digestion, 3: 1062 gastrointestinal process control, 3: 1063 immunomodulating effects, 3: 1064 intestinal motility regulation, 3: 1063 metabolic processes, 3: 1063 mineral absorption, 3: 1063 see also Bioactive peptides Milk protein hydrolysates, 2: 292 bitterness defects, 2: 295 emulsification, 2: 293 enzyme-induced gels, 2: 292 foaming, 2: 293 food development, specific populations, 2: 295 future developments, 2: 295 hypoallergenic formulas, 2: 295 solubility, 2: 292t, 2: 293 technofunctionality, 2: 292, 2: 292t water-holding capacity, 2: 293 Milk protein intolerance (MPI), milk allergy vs., 3: 1041 Milk protein isolate (MPI), 3: 848 manufacture, 3: 866 Milk protein products historical aspects, 1: 16 plasmin system, 2: 312 Milk protein standardization, 4: 545–549 cheese manufacture, 1: 619 current status, 4: 548 downstandardization calcium content, 4: 548 permeate use, 4: 548 powdered lactose addition, 4: 547 future prospects, 4: 549 legal status, 3: 308–309 nutritional properties, 4: 547 permeate use, 4: 549
regulatory aspects, 4: 548 sensory properties, 4: 547 technological approaches, 4: 546 technological principles, 4: 547 ultrafiltration, 4: 547, 4: 547f technological properties, 4: 547 upstandardization, 4: 547 product sweetness, 4: 548 skim milk powder addition, 4: 547 Milk proteolysis lactation stage, effects of, 3: 603 pathways, 3: 603 psychrotrophic microorganisms, 3: 603 seasonal effects, 3: 603 Milk proteome, 1: 200 Milk pumps, 3: 946 Milk quality biofilm control, 1: 449 Chinese dairy management, 2: 86 microbiological determination, 3: 899 specific bacteria measurement, 3: 900 pH, 1: 248–249 seasonal effects, 3: 603 standards, 3: 894–901 storage effects, 3: 642–648 test methods, 3: 894–901 transport effects, 3: 642–648 Milk quality traits, 2: 650 Milk recording, 2: 650 historical standard, 2: 650 international standard, 2: 650 regional computing centers, 2: 650 yield on test day, 2: 650 Milk removal frequent, benefits of, 3: 31 galactopoietic effects, 3: 30 Milk replacers, 2: 826, 2: 883, 4: 396, 4: 398 calf cold stress, 4: 552 ingredients, 4: 398, 4: 398t Milk residue, yak milk, 1: 349 Milk ring test (MRT), brucellosis, 2: 155–157, 2: 156t, 4: 37 Milk room, 3: 959 Milk salt(s), 3: 481, 3: 908–916 analysis, 3: 913 methods, 3: 914, 3: 914t in aqueous phase, 3: 908, 3: 909t, 3: 910t cation-anion interactions, 3: 910t camel milk, 3: 514 casein interactions, 3: 917–924 colloidal concentrations, 3: 921 interspecies differences, 3: 919t, 3: 920t, 3: 921 multivalent ion interrelationships, 3: 921, 3: 922f distribution, 3: 908–916, 3: 909t, 3: 909t historical aspects, 1: 24 interspecies comparison, 3: 910, 3: 910t lactose interactions, 3: 917, 3: 918f nondairy food, 2: 128t primate milk, 3: 627, 3: 628t sample preparation, 3: 913 aqueous ion concentration determination, 3: 914 total ion content determination, 3: 913 secretory mechanisms, 3: 917 monovalent ion interactions, 3: 917 paracellular routes, 3: 917 transcellular routes, 3: 917 serum concentrations, 3: 919 interspecies differences, 3: 919 intraspecies differences, 3: 919, 3: 920t multiple ion equilibria, 3: 919, 3: 920f, 3: 921f, 3: 921t multivalent ion interactions, 3: 919, 3: 920f total concentrations, 3: 918 cows’ milk variations, 3: 919, 3: 919t interspecies variation, 3: 918, 3: 919t whey recovery processes, 2: 128
Milk salt equilibria, 3: 909f, 3: 910 acidification, 3: 911 alkalinization, 3: 912 calcium addition, 3: 913 chelatant addition, 3: 912 cooling, 3: 912 definition, 3: 908 physico-chemical conditions, 3: 909f, 3: 910 sodium chloride addition, 3: 913 theoretical calculation, 3: 915 thermal treatments, 3: 912 variations in, 3: 910 Milk Science, 2: 104 Milkshakes, 2: 897 perceived additives, 1: 46f Milk solids-not-fat (MSNF) cheese salting, 1: 604 components, 2: 899 dairy desserts, 2: 908 lactometers, 1: 251 Milk substitution, immunochemical detection, 1: 179, 1: 181t Milk sugars, 3: 173–174 Milk tanker, critical cleaning sites, 4: 379 ‘Milk tea’, 1: 348 Milk transfer line, flooded flow cleaning, 3: 635 Milk tube with slide valve, 3: 941, 3: 942f Milk veins (subcutaneous abdominal veins), 3: 335 Milk yields camels, 1: 354 donkey, 1: 365, 1: 366, 1: 367f goats, 1: 312t high estrous behavior, 4: 464 negative energy balance, 4: 578–579 reproductive stress, 4: 578, 4: 578f mastitis effects, 3: 902 non-seasonal/pasture-based management, 2: 38–40 see also other specific animals Millets, 2: 555, 2: 565 feed value, 2: 555, 2: 573 Japanese, 2: 555 Milling byproducts, 2: 342–343, 2: 344t, 2: 345, 2: 347f Mineral acids, 2: 360 Mineral-fortified milk, 3: 297 Minerals absorption milk protein-derived peptide effects, 3: 1063 ruminants, 3: 996–1002 small intestine, lactating ruminants, 3: 994 atomic spectrometry, 1: 141 camel milk, 1: 355, 1: 356t dairy cattle requirements, 2: 420 forage quality, 2: 579f, 2: 580, 2: 581, 2: 582t deficiency diagnosis, 2: 789–790 differential scanning calorimetry, 1: 261–262 endogenous secretion, 3: 995 essential for human diet, 3: 925 fetal growth requirements, 2: 789 first-age infant formulae, 2: 142 goat vs. cow milk, 3: 488, 3: 488t heifer growth, 4: 393 human milk, 3: 586, 3: 587t infant formulae, 2: 137 llama milk, 3: 536, 3: 536 macronutrients vs., 3: 996 major see Macrominerals mammary gland secretion, 3: 379 milk mastitis effects, 3: 903t, 3: 904 nutrient intake, contributions to, 3: 1006 pregnancy requirements, 2: 789 prepartum dairy cow supplement, 4: 519t primate milk, 3: 628t reindeer milk, 3: 534 rumen fermentation, 3: 983 transition cows, pasture-based systems, 2: 467 see also Trace elements (minerals)
Index Mingrelian Red cattle, 1: 298 Miniaturization, biosensors, 1: 235 Minimum tiling path, 2: 663 Ministerial Conference, WTO, 4: 338 Ministry of Agriculture, Forestry and Fisheries (MAFF), Japan, in-quota tariffs, 4: 309 Minke whale milk oligosaccharides, 3: 271t Mink seal milk oligosaccharides, 3: 271t Miracidium, Fasciola hepatica, 2: 264–265 ‘Miracle protein’ milk shake formula, 4: 734 Mirandesa cattle, 1: 298 Miscarriage, Coxiella burnetii, 4: 55 ‘Missing heritability’, 3: 969–970 Mites, 2: 250 Mitogens, galactopoietic effects, 3: 29f, 3: 31 Mixed suspension mixed product removal (MSMPR), 3: 189 MMV process, 1: 618–619 cheese manufacture, 1: 618–619 Mobile bag technique, 2: 440–441 Mobile elements, LAB, 3: 58–59 Mobile milking equipment, goats, 2: 804 Mob stocking see Rotational grazing Model-based predictive control, 4: 248 modeling approaches, 4: 248 analytical approach (white box models), 4: 248 data-driven alternatives (black box models), 4: 248 hybrid modeling (gray box model) see Knowledge-based hybrid modeling (KBHM) Model predictive control (MPC), 4: 249 Models calibration, 1: 91t nutritional management, 2: 421, 2: 423t, 2: 426 CamDairy, 2: 426 CNCPS, 2: 419, 2: 426 CPM Dairy, 2: 420–421, 2: 426 FIM, 2: 419, 2: 425, 2: 427 INRA, 2: 419, 2: 426 NRC, 2: 419, 2: 425 rennet milk coagulation, 1: 581 see also individual models Modified butters, 1: 500–505 flavor modification, 1: 502 functionality modifications, 1: 500 milk fat composition changes, 1: 500 cattle nutrition, 1: 500 fractionation, 1: 500 interesterification, 1: 500, 1: 501 nutritional modification, 1: 503 conjugated linoleic acid, 1: 504 omega-3 fatty acids, 1: 504 reduced cholesterol, 1: 503 physical structure, 1: 501 storage, 1: 501 whipping, 1: 501 work softening, 1: 501 Modified environment barn see In-between barn Modified milks, 3: 297–300 definition, 3: 297 products, 3: 297 Modulating valve, 4: 157, 4: 157f Moisture brine salting, 1: 604–605 cheese rheology, 1: 697 cheese salting, 1: 603, 1: 604 content determination, 1: 76 historical aspects, 1: 19 dry salting, 1: 605 khoa, 1: 884 low-fat cheeses see Low-fat cheeses pathogen control in cheese, 1: 646–647 Moisture loss Cheddar cheese manufacture, 1: 706–707 cheese salting, 1: 598 Moisture on fat-free basis (MFFB), hard Italian cheeses, 1: 728
Mojonnier flask, 1: 80, 1: 80f Mojonnier method, 1: 254 Molasses, calf starters, 4: 401 Mold(s) Cheddar cheese, 1: 711 cheese microbiology, 1: 628 dulce de leche defects, 1: 879 Dutch-type cheese defects, 1: 727 fermentation starters, 3: 456 hard Italian cheeses, 1: 733 historical aspects, 1: 27 mold-ripened cheeses, 1: 628 pathogens, 3: 451 smear-ripened cheese defects, 1: 765 spoilage see Spoilage molds see also individual species Mold counts, 1: 219 Molded pressed curd, dry salting, 1: 602 Mold-ripened cheeses definition, 1: 773 manufacture, 1: 773 curd drainage, 1: 773 milk coagulation, 1: 773 salting, 1: 773 molds, 1: 628 pH, pathogen control, 1: 647 yeasts, 1: 627 see also Surface mold-ripened cheeses Molecular genetics, 3: 965–970 animal breeding, 3: 968–969 future requirements, 3: 969 definition, 3: 965 within farm gate, 3: 968 food processing, future requirements, 3: 969 ‘ideal genotype’, 3: 969 ‘missing heritability’, 3: 969–970 outside farm gate, 3: 966 personalized nutrition, 3: 970 Molecular sieving chromatography, milk proteins, 3: 761–762 Mollier diagram, 4: 210, 4: 211f Molluscicides, 2: 268 Molybdenum, 2: 381 copper metabolism, effects on, 2: 379, 2: 385, 3: 999 deficiency, 2: 381 Aspergillus flavus, 4: 785 feed supplements, 2: 381 functions, 3: 939 in milk, 3: 934, 3: 934t chemical forms, 3: 935 nutritional significance, 3: 939 recommended dietary intake, 3: 937t rumen fermentation, 3: 983 stainless steel, 4: 135 toxicity, 2: 381 Monensin bloat treatment/prevention, 2: 209–210 calf starters, 4: 402 intraruminal controlled-release capsules, 2: 209–210, 2: 210f bloat, 2: 209–210, 2: 210f ketosis management, 2: 236 Mongolian fermented milks, 2: 510 Monoacylglycerol acetic acid esters, 1: 68f Monoacylglycerol diacetyl tartaric acid exters, 1: 68f Monoacylglycerol lactic acid ester, 1: 68f Monoacylglycerol organic acid esters, 1: 67 Monoacylglycerols (MAG), 3: 651 butter, 1: 506 as emulsifiers, 1: 65 flavor effects, 1: 68 organic acid ester derivatives, 1: 67 physical properties, 3: 651 production (glycerolysis), 1: 65 structure, 1: 68f Monoamines, 1: 451 Monoestrus, 4: 440
915
Monoglycerides, as emulsifier, 1: 66t Monolaurin, 4: 790 Mononuclear model, crystal growth, 3: 189 Monopumps see Progressing cavity pumps Monosaccharides, marsupial milk, 3: 556 Monoterpenes, goat milk, 2: 62t Monotreme(s), 3: 460 egg proteins, 3: 559 eggs, 3: 553 genera, 3: 553 lactation strategy, 3: 553 mammary glands, 3: 553 reproductive strategy, 3: 553, 3: 554f see also individual species Monotreme milk, 3: 553–562 autocrine factors, 3: 561 biological activity, 3: 559 carbohydrates, 3: 555 casein structure, 3: 542, 3: 542f composition, 3: 539t, 3: 554 lactation stage and, 3: 554–555 fatty acids, 3: 544 immune-related proteins, 3: 558–559 lactose, 3: 209, 3: 213, 3: 550, 3: 551 lipids, 3: 556 oligosaccharides, 3: 209, 3: 213, 3: 271–272, 3: 550, 3: 551 proteins, 3: 558 total solids, 3: 554–555 Monotube tubular heat exchanger, 4: 190 Monounsaturated fatty acids (MUFA) blood cholesterol levels, 3: 713, 3: 731 coronary heart disease risk, 3: 1029t equid milk, 3: 524, 3: 524t human milk, 3: 714 sheep milk, 3: 498 Montasio cheese, 1: 731 characteristics, 1: 730t composition, 1: 729t production statistics, 1: 729t Montb´eliard cattle, 1: 286t, 1: 293–294 Moody diagram, 4: 141, 4: 141f Morbier, 1: 787 Mortellaro disease see Papillomatous digital dermatitis (PDD) Morula, 4: 485–486, 4: 486f, 4: 493–494 compaction, 4: 493–494 definition, 4: 485 heat stress, 4: 568–569 Mosaic animals, 2: 637 Moscia Leccese sheep, 1: 336t Most Favored Nation (MFN), WTO, 4: 338 Most probable number (MPN) technique, 1: 216 Clostridium, 4: 51–52 development, 1: 27–28 Mouflon (Ovis musimon), 3: 326–327 Mousses, 2: 907, 2: 907f Moutardier, 1: 786–787 Moving boundary electrophoresis, milk proteins, 3: 760–761 Moving window principal component analysis (MWPCA), 4: 243, 4: 244f Mowing pregrazing, 2: 590 Mozzarella cheese analogue, milk protein concentrate, 3: 852 buffalo milk, 2: 783 free fatty acids, 1: 771t furosine content, 3: 233 high-moisture see High-moisture Mozzarella Lactobacillus delbrueckii subsp. bulgaricus, 3: 123 low-moisture see Low-moisture Mozzarella manufacture, commercial process, 1: 617 microstructure, 1: 233 natural, whey-less production process, 3: 851 starter cultures, 1: 555 surface yeasts, 4: 751 whey protein-depleted skim milk powder production, 2: 112f, 2: 113
916 Index Mozzarella di Bufala Campana, 1: 745 manufacture, 1: 745 MPCs (multiprotein complexes), blue native electrophoresis, 1: 189 MRI see Magnetic resonance imaging (MRI) MS see Mass spectrometry (MS) MSNF see Milk solids-not-fat (MSNF) MTase (methyltransferase), bacteriophage resistance, 1: 435–436 mTGase see Microbial transglutaminase (mTGase) MUC-1, 3: 685, 3: 796t, 3: 799 carbohydrate content, 3: 685 functions, 3: 685 milk fat globule membrane, 3: 685 structure, 3: 685, 3: 686f MUC-15, 3: 686, 3: 796t, 3: 799 milk fat globule membrane, 3: 686 structure, 3: 686f, 3: 686–687 Mucin(s), 3: 799 Bifidobacterium growth requirements, 1: 387 equine milk, 3: 621 human milk, 3: 621 primate milk, 3: 621 see also individual types Mucor, 4: 781 Mulchers, 2: 590 Mulching, 2: 590 Mulefoot (syndactylism), 2: 676, 2: 676f Multianalyte detection, biosensors, 1: 235 Multidimensional relaxation, NMR, 1: 164, 1: 165f Multidimensional scaling (MDS), 1: 94t, 1: 98t, 1: 101 Multilocus sequence analysis (MLSA), Enterobacter, 4: 77 Multilocus sequence typing (MLST), 4: 102 bacteria, 3: 47 Campylobacter subtyping, 4: 42 Staphylococcus aureus, 4: 104 Multipathogen analysis, biosensors, 1: 241 Multiple-earthed-neutral (MEN) systems, milking systems, 2: 17 Multiple effect spray dryer, 2: 109, 2: 110f Multiple linear regression (MLR), 1: 94t, 1: 101, 1: 103 Multiple loci variable number of tandem repeat analysis (MLVA), Coxiella burnetii, 4: 54 Multiple ovulation see Superovulation Multiple ovulation and embryo transfer (MOET), 2: 623–630, 2: 625f, 4: 472 genetic evaluation, 4: 472 genetic gain computation, 2: 623 impact and potential, 2: 630 selection and genetic gains, 2: 623 technology development and success, 2: 623, 2: 624t Multiple-strain systems, starter cultures, 1: 442 Multiple-trait across-country evaluation (MACE), 2: 670 Multiplex polymerase chain reaction, 1: 221 Multiprotein complexes (MPCs), blue native electrophoresis, 1: 189, 1: 189 Multistage drying (MSD) chamber, 4: 217, 4: 220f Multitrait analysis, genetic evaluation, 2: 652 Multitube tubular heat exchanger, 4: 190 Multivariate analysis of variance, 1: 103 Multivariate calibration, 1: 92 Multivariate statistical tools, 1: 93–108 analysis of covariance, 1: 103 analysis of variance, 1: 101, 1: 102 artificial neural networks see Artificial neural networks (ANNs) categorical variables, 1: 93 CCA, 1: 94t cluster analysis, 1: 101 CoA, 1: 94t CTs, 1: 94t data, 1: 93 categorical variables, 1: 93 quantitative variables, 1: 93 data matrices, 1: 98f data processing, 1: 93
data transformation, 1: 99 discriminant analysis, 1: 101, 1: 103 EFA, 1: 94t factor analysis, 1: 99 hierarchical clustering, 1: 94t, 1: 98t, 1: 102 dendrograms, 1: 100f, 1: 102 inferential methods, 1: 102, 1: 104f linear discriminant analysis, 1: 94t, 1: 98t, 1: 103, 1: 103–104 linear models, 1: 103 see also specific methods LL, 1: 94t LR, 1: 94t MANOVA, 1: 94t methods, 1: 94t see also specific methods MLP, 1: 98t multidimensional scaling, 1: 94t, 1: 98t, 1: 101 multiple linear regression, 1: 94t, 1: 101, 1: 103 multivariate analysis of variance, 1: 103 nonhierarchical clustering, 1: 94t, 1: 98t, 1: 102 partial least square regression, 1: 94t, 1: 105, 1: 106f PLS1, 1: 98t PLS2, 1: 98t principal component regression (PCR), 1: 94t, 1: 103 principal component analysis, 1: 94t, 1: 98t, 1: 99, 1: 101 process sensors, 1: 93 QDA, 1: 94t quantitative variables, 1: 93 SA, 1: 94t software, 1: 107 Neurosolutions, 1: 108 R, 1: 107 SAS, 1: 108 SPSS, 1: 108 STATISTICA, 1: 108 Sysat, 1: 108 Unscrambler, 1: 108 workflow, 1: 100f Multiway partial least squares (MPLS), 4: 243 Multiway principal component analysis (MPCA), 4: 243 Munster, 1: 787 Muramidase see Lysozyme Murchland teat-cup, 3: 942–943, 3: 944f Murciana-Granadina goats, 1: 311t, 1: 316, 1: 317f Murine typhoid model, salmonellosis, 2: 192–193 Musk oxen, 3: 535 species, 3: 535 Musk ox milk, 3: 535 composition, 3: 535, 3: 535, 3: 535t Mycobacteria other than tuberculosis (MOTT) see Nontuberculous mycobacteria (NTM) Mycobacterium, 3: 450, 4: 87–92 acid-fast staining procedures, 4: 87, 4: 88f farming policy, 4: 91 fast-growing, 4: 87 heat resistance, 2: 314 human infection, contaminated dairy supplies, 4: 91 infection within the herd, 4: 91 milk contamination, 4: 90 oral infection, 4: 91 prevalence in herds, 4: 91 respiratory infection, 4: 91 sheep infections, 2: 858 slow-growing, 4: 87 see also individual species Mycobacterium africanum, 2: 195, 4: 88 Mycobacterium avium complex (MAC), 4: 89 AIDS patients, 4: 89 infection symptoms, 4: 89 Mycobacterium avium paratuberculosis (MAP) see Mycobacterium avium subsp. paratuberculosis Mycobacterium avium silvaticum, 4: 90
Mycobacterium avium subsp. avium, 2: 174 Mycobacterium avium subsp. paratuberculosis vs., 2: 174 Mycobacterium avium subsp. paratuberculosis, 2: 174, 2: 175f, 4: 89 Crohn’s disease links, 2: 174–175, 4: 90 culture, 2: 177 detection, 2: 177 ecology, 2: 174 heat resistance, 2: 174–175 Johne’s disease, 3: 315, 4: 89 land contamination, 2: 798–799 Mycobacterium avium subsp. avium vs., 2: 174 pasteurization and, 4: 90 shedding, 4: 89–90 survival, 2: 798–799 thermal inactivation, 4: 193–194 transmission, 4: 89–90 see also Johne’s disease Mycobacterium bovis, 4: 87 human infections, 2: 197, 4: 87–88 infection see Tuberculosis (TB) wildlife reservoirs, 4: 91 zoonotic potential, 2: 197 Mycobacterium canetti, 4: 88 Mycobacterium caprae, 4: 88 Mycobacterium microti, 2: 195, 4: 88 Mycobacterium paratuberculosis see Mycobacterium avium subsp. paratuberculosis Mycobacterium tuberculosis, 4: 88 cattle infection, 2: 197 intestinal infection, 4: 88 tuberculosis, 2: 195 historical aspects, 1: 26 Mycobacterium tuberculosis complex (MTC), 4: 87 latent infection, 4: 88 members, 4: 87 pathogenesis, 4: 88 Mycoderma, acid-curd cheeses, 4: 751 Mycophenolate mofetil (MMF), 4: 775 Mycophenolic acid, 1: 904t Penicillium roqueforti, 4: 775 toxicity, 4: 775 Mycoplasma bovis mastitis, 3: 409 control, 3: 412 milking hygiene, 3: 412 purchased heifers, 3: 412 symptoms, 3: 412 Mycoplasma mastitis, 2: 48–49 Mycoplasma mycoides mycoides (Mmm) disease, goats, 2: 798 Mycotoxicoses, 4: 792 Mycotoxins, 1: 903, 1: 904t, 4: 792–800 analysis, 1: 904 carcinogenic, 4: 792 classification, 4: 792–800 determination, 4: 792–800 features, 4: 792 health impact, 1: 904 historical aspects, 4: 792 neurotropic, 4: 792, 4: 795 occurrence, 1: 903, 4: 792–800 sources, 1: 903 spoilage molds, 4: 782t, 4: 782–783 see also individual mycotoxins Myocardial infarction, 2: 326 Myococin HMK, 4: 748 Myoepithelial cells, mammary gland, 3: 331 Myometrial activation, 4: 507–508 Myometrium, progesterone effects, 4: 498 Myristic acid, 3: 730–731 Mysost, 4: 735 compositional characteristics, 4: 735t controlled crystallization, 4: 735 types, 4: 735 Mysticetes see Baleen whales
Index
N Nabulsi cheese, 4: 752 N-Acetyl- -D-glucosaminidase (NAGase) clinical mastitis, 3: 899 udder health measurement, 3: 898 N-Acetylglucosamine, 3: 258 N-Acetylglucosamine (NAG), 3: 253f, 3: 258 NAFTA (National American Free Trade Agreement), 4: 318–319 Na+–K+–Cl cotransporter, 3: 379 Na/Mg exchange, 2: 226, 2: 226f Nanofiltration (NF), 3: 864, 3: 865f cheese manufacture, 1: 618, 1: 623 definition, 4: 742 lactose losses, 3: 864 membranes, 3: 864 whey demineralization, 4: 742 benefits, 4: 743 partial, 3: 865, 4: 743 urea leakage, 4: 743 N-(1-Naphthyl)ethylenediamine (NED), 1: 909–910 National Air Emissions Study, 3: 397 National Ambient Air Quality Standards (NAAQS), 3: 396 National American Free Trade Agreement (NAFTA), 4: 318–319 National Dairy Industry Training Standards (Australia), food technology education, 2: 8 National Electrical Manufacturers Association (NEMA), electric motor grades, 4: 611 National Organic Program (NOP), US, 4: 10, 4: 11t antibiotic use, 4: 12–13 National Pollutant Discharge Elimination System (NPDES) permits, 3: 395 National Research Council (NRC), US dairy cow model 2001, 2: 436 bacterial protein, 2: 440 bacterial yield, 2: 440 carbohydrate fractions, 2: 439 endogenous protein, 2: 441 fat digestibilities, 2: 441 feed ingredients energy value, 2: 441 fermentability, 2: 439–440 metabolic requirements, 2: 441–442 metabolizable (absorbed) protein value, 2: 441 protein fractions, 2: 439 dairy nutritional models, 2: 419, 2: 425 nutrient requirements, fat categories energy values, 2: 364–365, 2: 365t ether extract value listing, 2: 363 phosphorus ration requirements, 2: 375–376 National Vocational Qualifications (NVQs), food technology, 2: 8, 2: 9 Native milk fat globule membrane (NMFGM), pasteurized processed cheese products, 1: 808 ‘Native’ polyacrylamide gel electrophoresis, 1: 187 ‘Natural’ foods, consumer perceptions, 1: 43, 1: 47 Natural gas, 4: 591 Natural killer (NK) cells, 3: 387 ‘‘Natural’’ starter cultures, 1: 554t N’Dama cattle, 1: 298 Near-infrared (NIR) analysis, milk proteins, 3: 744 mid-infrared analysis vs., 3: 743 Near-infrared (NIR) reflectance, curd strength, 1: 587 Near-infrared (NIR) spectroscopy, 4: 237 curd strength measurement, 1: 589, 1: 589f Near-UV (NUV) irradiation, Aspergillus flavus, 4: 790–791 Neck chains, 2: 649 Necklaces, 2: 832, 2: 832f Necrotizing enterocolitis (NEC), 4: 75 bactericidal/permeability-increasing protein, 4: 75 breast vs. formula fed infants, 3: 257 Clostridium butyricum, 4: 49 Cronobacter, 4: 75 NEFA see Nonesterified fatty acids (NEFA) Negative energy balance (NEB) anestrum, 4: 475
displaced abomasum, 2: 213 LH pulsatility, 4: 577–578 metabolic disorder predisposition, 2: 464 preconditioning, 2: 465 transition cows, 2: 464 Nematodes, gastrointestinal see Gastrointestinal nematodes Nematodirus helvetianus, 2: 258 Neonatal Fc receptor (FcRn), 3: 378–379 Neonatal tetany, 3: 930–931 Neonates feeding requirements, 2: 826, 2: 827f, 2: 829t automatic feeders, 2: 827, 2: 827f, 2: 828f, 2: 884 bucket feeders, 2: 827, 2: 827f, 2: 828f, 2: 884 colostrum, 2: 825–826, 2: 883 intake limitation methods, 2: 826, 2: 827f maternal access, 2: 826, 2: 883 milk replacers see Milk replacers immunity, 2: 825 millk component protection, 3: 583 milk growth factors/hormones, 2: 765, 3: 587, 3: 588t survival risks, 2: 825 weaning feeds, 2: 827–828, 2: 883, 2: 883t see also Calves; Kid(s); Newborn Nepal, yak milk production, 1: 347 Nernst equation, 4: 257 Nesterenkonia, 1: 396–397 Net centrifugal force, 4: 175 Net energy (NE), 2: 407 Netherlands dairy product consumption, 1: 46, 1: 46t herby cheeses, 1: 787 spiced cheeses, 1: 787 Netherlands Association for the Advancement of Dairy Science (Genootschap ter Bevordering van Melkkunde), 2: 102 Netherlands Institute for Dairy Research (NIZO), 1: 440–441 Netherlands Milk and Dairy Journal, 2: 102–103 Net Merit index (United States) background to weights, 2: 660 breed society alternatives (TPI, JPI), 2: 661 composite components, 2: 658 net economic value calculation, 2: 658 Relative Net Income (RNI) estimates vs., 2: 660–661 trait weighting, changes over time, 2: 656–657, 2: 657t, 2: 660 Net positive suction head (NPSH), 4: 142 available (NPSHa), 4: 142 cavitation, 4: 142, 4: 142f gas bubbles, 4: 142 definition, 4: 142 required (NPSHr), 4: 142 Net postprandial protein utilization (NPPU), 3: 817 humans, 3: 817t Net protein utilization (NPU), 3: 817 Netting, bird repellents, 4: 542 Net worth, 1: 487 management records, 1: 488 Neufchˆatel, geographical differences, 1: 843 Neufchatel cheese, 1: 701 composition, 1: 700t, 1: 702 Neural tube defects (NTD), 4: 682 Neurological disorders, vitamin B12 deficiency, 4: 677 Neurosolutions, 1: 108 Neutraceuticals, milk, 3: 1062–1066 Neutral detergent fiber (NDF), 2: 336 assay, 3: 985 digestibility, 2: 405 determination, 2: 460 pasture concentration, 2: 33f, 2: 34 proportion, in ruminant diet, 2: 338–340 Neutralization, starter culture protection, 1: 443 Neutralizing products, dulce de leche, 1: 875 Neutral-pH fruit-containing milk products, yeast spoilage, 4: 749
917
Neutrophil extracellular trap (NET) formation, 3: 387 Neutrophils mammary gland defense, 3: 387 oxygen-dependent killing mechanism, 3: 388, 3: 388t oxygen-independent killing mechanism, 3: 388, 3: 388t Newborn gut microflora composition, 4: 366 management, 4: 416 vitamin K, 4: 663–664 see also Neonates New product launches, 1: 42 cheese with fruit, 1: 42 children’s cheeses, 1: 42 continental cheeses, 1: 42 convenience foods, 1: 42–43 fruit/flavor origins, 1: 42 health aspects, 1: 42, 1: 42 provenance, 1: 42 Newtonian models milk/cream rheology, 4: 520 rheology, 1: 268, 1: 269f, 1: 269–270 Newton’s law, 4: 140 New variant Creutzfeldt–Jakob disease (nvCJD), milk supply safety, 3: 311–312, 3: 314 New World, Bos taurus breeds, 1: 298 New Zealand agricultural policy, 4: 310 background, 4: 310 artificial insemination use, 4: 470 cheese definition, 1: 854 cheese legislation, 1: 854 chlorine sanitizers, 3: 635 cow breeds, 2: 35 dairy exports, 4: 311 market regulation, 4: 311 dairy industry, 1: 10t DDT (1,1,1-trichloro-2,2-bis(4chlorophenyl)ethane), 1: 889 free trade agreements, 4: 311 milk fatty acid composition, seasonal effects, 3: 658, 3: 658t milk production, 1: 10, 1: 10t future trends, 2: 36 patterns, 2: 29 organic standards, 4: 10 pasture-based dairy production systems with seasonal calving, 2: 29–37 pasture growth, 2: 30, 2: 31f pasture stocking rates, 2: 594 pasture zones, 2: 30 processed cheese definition, 1: 854 producer support estimate, 4: 307f, 4: 310 single commodity transfers, 4: 307f, 4: 310 supplement use, 2: 34 New Zealand Dairy Board (NZDB), 4: 310 New Zealand Grazing Company, heifer management system, 4: 408 NFDM see Nonfat dry milk powder (NFDM) Niacin, 4: 690–693 absorption, ruminants, 3: 1000–1001 cellular energy pathways, 2: 398 dairy process effects, 4: 690 deficiencies, 4: 691 fatty liver, 2: 221 feed supplements, 2: 396–397, 2: 398 strategies, 2: 400–401 functions, 2: 397t, 4: 690 ketosis management, 2: 237 in milk, nutrient intake, contributions to, 3: 1005 recommended daily uptake, 4: 692t ruminal metabolism, 2: 398 sources, 2: 397t dairy products, 4: 691t dietary, 4: 691t toxicity, 4: 692 Niacin equivalents (NE), 4: 691
918 Index Nickel in milk, 1: 901t, 3: 934, 3: 934t chemical forms, 3: 936 nutritional significance, 3: 939 stainless steel, 4: 135 Nickel alloys, 4: 136 Nicotinamide, 4: 690 biological effects, 4: 692 structure, 4: 691f Nicotinamide-adenine dinucleotide (NAD+), 4: 690 functions, 4: 690 nonredox functions, 4: 690 structure, 4: 691f Nicotinamide-adenine dinucleotide phosphate (NADP+), 4: 690 functions, 4: 690 structure, 4: 691f Nicotinic acid, 4: 691f functions, 4: 690 structure, 4: 691f supplementation, 4: 692 Nicotinic acid adenosine dinucleotide phosphate (NAADP), 4: 690 Ni–Cu–P–PTFE coating, biofilm formation, 1: 449–450 Nigerian Dwarf goats, 1: 311t, 1: 315 Nisin, 1: 422t, 1: 426 as antibiotic, 1: 423–424 applications, 1: 424 alcoholic beverages, 1: 424 canned foods, 1: 424 dairy products, 1: 424 meat and fish, 1: 424 Clostridium spore control, 4: 53 gas blowing defect prevention, 1: 664 Lactococcus lactis subsp. lactis, 1: 422–423 membrane insertion, 1: 422–423 mode of action, 1: 422–423 resistance, 1: 423–424 tailor-made cultures, 3: 967 Nisin-controlled expression vectors, 3: 967 Nitrate(s) acceptable daily intake, 1: 908 analysis, 1: 909 cheese microbiology, 1: 629 Clostridium control, 4: 52–53 as contaminants, 1: 906–911 amounts, 1: 910t daily intake, 1: 908 dairy product sources, 1: 909 postsecretory, 1: 909 presecretory, 1: 909 fodder poisoning, 2: 573, 2: 597 gas blowing prevention butyric acid bacteria inhibition, 1: 664 coliform inhibition, 1: 662 groundwater contamination, 3: 394–395 occurrence, 1: 906 physiological role, 1: 906, 1: 907f soil, 2: 588 Nitric oxide, 1: 906 Nitrites acceptable daily intake, 1: 908 analysis, 1: 909 as contaminants, 1: 906–911 amounts, 1: 910t daily intake, 1: 908 dairy product sources, 1: 909 physiological role, 1: 906, 1: 907f toxicity, 1: 908 Nitrogen, 1: 906 amounts recovered for fertilizer, 3: 401, 3: 401t budgeting uses, 3: 402t, 3: 403 value calculation, 3: 403 animal production facility production, 3: 397 Bifidobacterium, 1: 387 dairy farm flow, 2: 444 dairy plant effluents, 4: 616
deficiency, pasture, 2: 588 endogenous secretion, humans, 3: 816 excess plants, 2: 588 stock, 2: 588 excretion estimates, 3: 399, 3: 400t excretion reduction, 4: 631 grass response to, 2: 587f, 2: 588 grassy tetany, 2: 227 leaching, 2: 588 manure, degradation rates, 3: 403 mineralization, 2: 587 ration formulation, excess to requirements, 2: 462 recycling, ruminal, 3: 983 removal, dairy effluents, 4: 625 denitrification stage, 4: 625–626 nitrification stage, 4: 625–626 removal in silage/hay, 2: 590 requirements, humans, 3: 817 retention, 3: 816 determination, 3: 816 volatilization losses, 3: 401–402 Nitrogen-15 spectroscopy, 1: 151–152 Nitrogen balance, 3: 816 Nitrogen-based fertilizers, 1: 906, 2: 587, 2: 587f application-grazing interval interactions, 2: 588 non-seasonal/pasture-based management, 2: 47 Nitrogen-containing fractions, Dutch-type cheeses, 1: 724f, 1: 724–725 Nitrogen cycle, 1: 906, 1: 907f Nitrogen fixation, 2: 587 15 N-labeled ammonia, dairy cow digestion models, 2: 430 Nitrogen–phosphorus detector (NPD) cheese flavor assessment, 1: 678–679 gas chromatography (GC), 1: 175 Nitrogen recycling, ruminal, 3: 983 Nitrogen:sulfur ratio, grass, 2: 589 Nitrosamines as contaminants, amounts, 1: 910t mutagenicity, 1: 392 toxicity, 1: 908, 1: 908 Nivalenol, 4: 798, 4: 799f NIZO butter process, 3: 172 NMR see Nuclear magnetic resonance (NMR) NOAEL (no observed adverse effect level), 1: 56 Nocardia labegensis, 3: 734 ‘No discharge certification’, 3: 395 NOD mouse (non-obese diabetic mouse), 3: 1047 Nokkelost, 1: 788 Nomadic husbandry, reindeer, 1: 375 Nomadism lamb mortality, 2: 876–879 related to climatic conditions, 2: 876, 2: 879 Nominal properties, statistical analysis, 1: 83 Noncatalytic recognition elements, biosensors, 1: 235–236, 1: 236f Non-dairy foods (dairy ingredients), 2: 125–134 applications, 2: 129, 2: 129f, 2: 129t bakery products, 2: 130 beverages, 2: 129 bread, 2: 130 chocolate, 2: 130 confectionery products, 2: 130 dietetic foods, 2: 131 fish products, 2: 131 functional foods, 2: 132, 2: 133 meat products, 2: 131 nutraceuticals, 2: 133 nutritional whey drinks, 2: 129 pharmaceuticals, 2: 132 puff pastry, 2: 130 Rivella, 2: 129 whey protein concentrates, 2: 129 composition, 2: 128, 2: 128t butter, 2: 128t casein, 2: 128t caseinates, 2: 128t
coprecipitates, 2: 128t cream, 2: 128t milk salts, 2: 128t MPC, 2: 128t skim milk, 2: 128, 2: 128t whey, 2: 128t, 2: 129 whey protein isolate, 2: 128t whole milk, 2: 128, 2: 128t WPC-35, 2: 128t WPC-60, 2: 128t WPC-80, 2: 128t food technology education, 2: 10 future work, 2: 133 preparation techniques, 2: 125 acid casein, 2: 126 casein, 2: 125 caseinates, 2: 125 coprecipitate, 2: 125 milk protein concentrates, 2: 125 separation techniques, 2: 125, 2: 126f skim milk, 2: 125 ultrafiltration, 2: 125 whole milk, 2: 125 whey recovery processes, 2: 126, 2: 127f demineralization, 2: 127, 2: 127f electrodialysis, 2: 127f, 2: 127–128 fixed-bed ionic exchange, 2: 127f, 2: 128 lactose removal, 2: 127, 2: 127f membrane processes, 2: 126–127, 2: 127f milk salts, 2: 128 protein fractionation, 2: 128 stirred-bed ionic exchange, 2: 127f, 2: 128 Nondigestible oligosaccharides (NDO), 4: 359t, 4: 365–366 calorific values, 4: 358 definition, 4: 355 fermentation, 4: 368 industrial transglycosylation, 4: 358, 4: 360f mineral absorption stimulation, 4: 370 as prebiotics, 4: 355–357, 4: 358 production, 4: 358, 4: 360f sources, 4: 355 stool frequency improvements, 4: 369 structural features, 4: 357f, 4: 359t see also individual types Nondisplacement (dynamic) compressors, 4: 603 Nonenzymatic browning, 3: 217 ascorbic acid oxidation, 3: 224 caramelization, 3: 224 dulce de leche production, 1: 878 milk powder, 4: 711 symptoms, 3: 217, 3: 218t see also Maillard reactions Nonesterified fatty acids (NEFA) fatty liver, 2: 218 mammary uptake, 3: 353–354 prepartum increases, 4: 515 Nonfat dry milk powder (NFDM) cottage cheese manufacture, 1: 700 low-fat cheeses, 1: 833–834 plasmin system, 2: 313 Nonfiber carbohydrate (NFC) cereal grains, 2: 335, 2: 336 definition, 2: 461 Nonhemolytic enterotoxin (NHE), 4: 26 Nonhierarchical clustering (NHCA), 1: 94t, 1: 98t, 1: 102 Non-insulin-dependent diabetes mellitus (NIDDM) see Type 2 diabetes Non-lactic acid bacteria, cheese manufacture, 1: 538–539 Non-lanthionine-containing bacteriocins, 1: 421 lactococci, 3: 135–136 Nonlinear models, calibration, 1: 91 Non-Newtonian behavior, milk/cream rheology, 4: 520, 4: 521 Nonnutritive additions, infant formulae, 2: 143 Nonnutritive sweeteners, 1: 38
Index Non-obese diabetic mouse (NOD mouse), 3: 1047 Nonparasitic skin diseases, sheep, 2: 858 Nonprotein nitrogen (NPN) definition, 3: 742 equid milk, 3: 523 equine milk, 1: 361, 3: 521t, 3: 523 sheep milk, 3: 496 Nonruminants, dietary protein digestion, 3: 361 Non-seasonal/pasture-based management, 2: 38–43, 2: 44–51 animal health, 2: 48 biosecurity, 2: 50 infertility, 2: 49 lameness, 2: 49 mastitis, 2: 48 national eradication schemes, 2: 49 automation, 2: 50 conserved forage supplementation, 2: 40 dairy cow breeds, 2: 44, 2: 45t definition, 2: 44 efficiency studies, 2: 38 environmental issues, 2: 50 feed management, 2: 41 forage availability, 2: 40 forage nutritive value, 2: 40 grass intake, 2: 47 health, 2: 42 indoor/winter housing, 2: 45 forage conservation systems, 2: 45 forage feeding systems, 2: 46 housing systems, 2: 45 management-intensive grazing (MIG) system, 2: 38–40 milk yield, 2: 38–40 national eradication schemes, 2: 49 numbers, 2: 38 pasture management, 2: 46 grass intake, 2: 47 grazing efficiency, 2: 47 grazing systems, 2: 47 pasture supplementation, 2: 48, 2: 48t pasture quality, 2: 40 performance characteristics, 2: 39t Nonstarch polysaccharides (NSP), 4: 355, 4: 356t Non-starter lactic acid bacteria (NSLAB), 1: 626, 1: 639–644, 3: 116 accelerated cheese ripening, 1: 796 adjunct cheese quality, 1: 640–641 definition, 3: 161 adventitious, 3: 161 biofilms, 1: 446 blue mold cheeses, 1: 769, 1: 771 Cheddar cheese, 1: 708, 1: 709 cheese curd recycling, 3: 84–85 flavor defects, 3: 84–85 microbiology, 3: 116 significance in, 3: 84 cheese flavor, 1: 626, 1: 639, 1: 640, 1: 641, 3: 107, 3: 117, 3: 117 aromatic amino acids, 1: 641–642 branched-chain amino acids, 1: 641–642, 1: 642 development, 3: 84–85 diacetyl, 1: 642 formate, 1: 642 methanethiol, 1: 641–642 methionine, 1: 641–642 phenethanol, 1: 642 phenylacetaldehyde, 1: 642 succinate, 1: 642 cheese manufacture, 1: 538–539 secondary cultures, 1: 538–539 cheese quality, 1: 640 adjunct culture, 1: 640–641 defects, 1: 640 cheese ripening, 1: 639 proteolysis, 1: 671–672
cheese salting, 1: 596 definition, 1: 639, 3: 125–126 esterase activity, 3: 117 fermentation activity, 3: 117 gas blowing defects, 1: 664 genomics, 1: 642, 1: 643t denaturing gradient gel electrophoresis, 1: 642 hard Italian cheeses, 1: 735 historical aspects, 1: 31 initial numbers, 1: 626, 1: 626f Lactobacillus, 3: 84, 3: 84f, 3: 116–117 Lactobacillus casei group, 3: 97 lipase activity, 3: 117 metabolism, 1: 641 lactate, 1: 641 pH, 1: 641 substrates, 1: 641 surface, 1: 641 temperature effects, 1: 641 pasta-filata cheeses, 1: 748 Pediococcus, 3: 151 population dynamics, 1: 639, 1: 640f quality defects, 1: 640 species, 1: 626 stress resistance, 3: 56 see also individual species Nonsteroidal anti-inflammatory drugs (NSAIDs), as contaminant, 1: 892 Nonstructural carbohydrates (NSC), 2: 461 Nontariff barriers (NTB), WTO, 4: 339 Nonthermal dairy technologies, 2: 725–731 adoption barriers, 2: 725 applications, 2: 726, 2: 727t carbon dioxide techniques, 2: 730 cold plasma techniques, 2: 708, 2: 731 continuous UV light irradiation, 2: 730 current status, 2: 725 research motivation, 2: 725 see also individual techniques Non-trade distortions, 4: 289 Nontuberculous mycobacteria (NTM), 4: 88 dairy production, 4: 90 members, 4: 89 No observed adverse effect level (NOAEL), 1: 56 Nordic fermented milks, 2: 472, 2: 496–502 characteristics, 2: 496 consumption, 2: 496, 2: 502 glycocalyx, 2: 497 formation determinants, 2: 497 health-related effects, 2: 501 antibacterial effects, 2: 502 microorganisms, 2: 496, 2: 496, 2: 498t bacteriophage attack, 2: 499 starter cultures, 2: 477 product nutritional composition, 2: 501 shelf life, 2: 501 types and production, 2: 499, 2: 499t buttermilks, 2: 500 concentrated fermented milks, 2: 500 cultured creams, 2: 500 cultured milks, 2: 500 see also individual milks Nordic goats, 1: 311t, 1: 314 Norgestomet, 4: 451–452 Normal distributions, 1: 86, 1: 86f Normal-phase chromatography (NPC), 1: 173 Normande cattle, 1: 296, 1: 297 North Africa sheep distribution, 2: 67 see also specific countries North America Bos taurus breeds, 1: 286t goats, 1: 314 yaks, 1: 345 see also Canada; United States (US) North American Intercollegiate Dairy Challenge (NAIDC), 2: 4
919
Northern Europe goats, 1: 310 milk fatty acid composition, seasonal effects, 3: 658, 3: 658t sheep distribution, 2: 67 see also specific countries Norwegian Red cattle, 1: 286t, 1: 289 Nozzle atomization, 4: 209 advantages, 4: 209 disadvantages, 4: 209–210 efficiency, 4: 209 fines return, 4: 233, 4: 233f milk powder bulk density, 2: 118 plug flow air stream, 4: 222 volumetric flow rate, 4: 209 Nozzle bowls, separators, 4: 168 NPD see Nitrogen–phosphorus detector (NPD) NSLAB see Non-starter lactic acid bacteria (NSLAB) Nubian goats, 2: 64–65 milk yields, 1: 312t Nuclear cloning, 2: 610 Nuclear magnetic resonance (NMR), 1: 153–168, 1: 229, 1: 146–152 active atoms, 1: 146 butter consistency, 1: 508f, 1: 512 carbon-13, 1: 149 ppm scale, 1: 149 Carr–Purcell–Meiboom–Gill sequence, 1: 153–155 dairy powders, 1: 162 diffusion, 1: 155 electron magnetic field, 1: 146–147 ethanol 13 C spectrum, 1: 150, 1: 150f 1 H spectrum, 1: 149, 1: 149f fat and emulsions, 1: 160 crystal networks, 1: 161, 1: 162f crystal orientation, 1: 160, 1: 161f liquid phase, 1: 161 polymorphism, 1: 160 solid-fat content, 1: 160 food science applications, 1: 151 isotopomers, 1: 151 novel/new compounds, 1: 151 free induction delay, 1: 153–155 future work, 1: 167 1 H nuclei, 1: 148 information obtained, 1: 147 magic angle spinning, 1: 151 metabolomics, 1: 151–152 milk oligosaccharides, 3: 249 multidimensional relaxation, 1: 164, 1: 165f multidimensional spectra, 1: 150 nuclear spin, 1: 146 parameters, 1: 153 ppm scale, 1: 148 practical requirements, 1: 147 probes, 1: 147 radiofrequency waves, 1: 146 relaxation studies, 1: 155 biexponential behavior, 1: 157 casein concentrates, 1: 158t cheeses, 1: 158 dairy protein, 1: 155 gel formation, 1: 157 micellar calcium and phosphorus, 1: 156–157 pH effects, 1: 158–159, 1: 159f sensitivity, 1: 156f, 1: 156–157 skimmed milk, 1: 155 syneresis, 1: 157–158, 1: 158f water relaxation time, 1: 159, 1: 159f sample preparation, 1: 147 sample spectra, 1: 149 sensitivity, 1: 147–148 shimming, 1: 147 spectrometer, 1: 147, 1: 147f splitting constants, 1: 148 splitting intensities, 1: 148 splitting patterns, 1: 148
920 Index Nuclear magnetic resonance (NMR) (continued ) T1 (spin lattice relaxation), 1: 153, 1: 153, 1: 154f, 1: 156 crystal networks, 1: 161–162, 1: 162f fat crystal orientation, 1: 161, 1: 161f T2 (spin–spin relaxation), 1: 153, 1: 153–155, 1: 154f, 1: 156 cheese, 1: 158 protein structure, 1: 157 water holding capacity, 1: 160 water relaxation time, 1: 159, 1: 159f techniques, 1: 153 theory, 1: 146 uses, 1: 147 water diffusion, 1: 162 droplet size in emulsions, 1: 163 suspensions and gels, 1: 162, 1: 163f see also Magnetic resonance imaging (MRI) Nuclear magnetic resonance (NMR) spectroscopy, 1: 113, 1: 153 uses, 1: 146 Nuclear Overhauser enhancement (NOE), 1: 148–149 Nuclear transfer (NT), 2: 611, 2: 613f, 2: 638 complications, 2: 639 developmental abnormalities, 2: 614 donor cells, 2: 612 artificial activation, 2: 613 culturing, 2: 612 direct injection incorporation method, 2: 612 embryonic cells, 2: 612 embryo transfer, 2: 613 fusion incorporation method, 2: 612 in vitro culture, 2: 613 preimplantation stage embryos, 2: 612, 2: 613f somatic cells, 2: 612 embryos, genetic composition, 2: 614 enucleation, 2: 612 mitochondria, 2: 614 protein loss, 2: 614–615 recipient oocytes, 2: 612 Nucleation heterogeneous primary, 3: 188 kinetics, 3: 188 homogenous primary, 3: 187, 3: 187f enthalpic variation, 3: 187, 3: 187f kinetics/frequency, 3: 187 metastability and, 3: 187 primary, 3: 187 secondary, 3: 187, 3: 188 kinetics, 3: 188 monohydrated -lactose, 3: 189 Nucleic acid sequence-based amplification, isothermal PCR, 1: 223 Nucleoproteins, 3: 975 Nucleosides, milk, 3: 971–979 abbreviations, 3: 971 biofunctional properties, 3: 975 breast-fed infants immune response, 3: 975 butter type identification, 3: 977 colostrum, 3: 971–973, 3: 973t compositional aspects, 3: 971 concentration vs. time postpartum, 3: 971–973, 3: 973t Dimroth rearrangement, 3: 976–977, 3: 978t functional aspects, 3: 975 goat milk, 3: 973, 3: 973t heat-induced changes, 3: 976 high-pressure-induced changes, 3: 978 human cell culture systems, 3: 972f, 3: 975–976 human milk, 3: 973t nomenclature, 3: 971 sheep milk, 3: 973, 3: 973t structural aspects, 3: 971, 3: 972f technofunctional properties, 3: 976 Nucleotide, definition, 3: 965 Nucleotides, milk, 3: 971–979 biofunctional properties, 3: 975 breast-fed infants immune response, 3: 975
compositional aspects, 3: 971 concentration vs. time postpartum, 3: 974, 3: 974t developmental effects, 3: 975 enterocyte proliferation, 3: 975–976 functional aspects, 3: 975 goat milk, 3: 484, 3: 488 heat-induced changes, 3: 976 high-pressure-induced changes, 3: 978 human cell culture systems, 3: 972f, 3: 975–976 human milk, 3: 584–585, 3: 585t, 3: 974, 3: 974t infant formula, 3: 584–585, 3: 585t sterilization, 3: 976 structural aspects, 3: 971 technofunctional properties, 3: 976 Nurses’ Health Study cardiovascular disease-vitamin E relationship, 4: 658 saturated fatty acid-coronary heart disease relationship, 3: 1024–1026 Nut(s), aflatoxins, 4: 807 Nut milks, 2: 914 Nutraceuticals dairy ingredients, 2: 133 from milk, 3: 1062–1066 see also Milk protein-derived peptides; Whey protein(s) production, Propionibacterium, 1: 409 Nutrient(s) off-farm exports, 3: 406 overfeeding reduction, 2: 462 Nutrient budget, 2: 587, 2: 587t Nutrient composition equations, 2: 404 multiple regression models, 2: 404–405, 2: 405t using fiber concentration (single component regression), 2: 404, 2: 405t Nutrient-dense formulae, 2: 143 Nutrient excretions amounts recovered for fertilizer, 3: 401, 3: 401t dietary-based approach, 3: 399 gain calculations, 3: 399–400, 3: 400t Nutrient management, whole-farm see Whole-farm nutrient management Nutrient management plan (NMP), 3: 396 concentrated animal feeding operations, 3: 395 goals, 3: 396 Nutrient recycling, 3: 399–407 management impact, 2: 589 milking time, 2: 590 night paddocks, 2: 589 paddock size, 2: 589 removal in silage/hay, 2: 590 strip grazing, 2: 590 pastures, 2: 587 preliminary budget analysis, 3: 402t, 3: 405 Nutrient removal, dairy effluent, 4: 625 Nutrient Requirements of Dairy Cattle calf nutrient requirements, 4: 398t, 4: 399 dry matter intake prediction, 4: 392–393 heifers, environmental condition adjustments, 4: 408 Nutrigenetics, 3: 1056–1061 definition, 3: 1059 Nutrigenomics, 3: 1056–1061 definition, 3: 1057 Nutrition artificial insemination centers (AICs) see Artificial insemination centers (AICs) body condition scoring, 1: 462 bull management, 1: 475, 1: 478 displaced abomasum prevention, 2: 216 environmental mastitis prevention, 3: 420 gene expression, 3: 1056 mammary gland development, 3: 342 gene expression profiling, 3: 350–351 mastitis, 3: 429 milk composition, 3: 602 early lactation, 3: 602 late lactation, 3: 602
mid-lactation, 3: 602 modified butter, effects on, 1: 500 ovarian follicular function, 4: 475–476, 4: 476f reproductive stress, 4: 577 sheep see Sheep Swiss-type cheese defects, 1: 719 Nutritionally balanced milk, 3: 299 ingredients, 3: 299 Nutritional management models, 2: 436–447 Nutritional program goals, 2: 458 Nutritional requirement-describing systems, 2: 418–428 aims, 2: 418 amino acid requirements, 2: 420 computer model systems, 2: 423t, 2: 426 CamDairy, 2: 426 Cornell models (CNCPS/CPM Dairy), 2: 419, 2: 426 criteria, 2: 418 energy flow components, 2: 403, 2: 404f, 2: 419, 2: 420f feed intake prediction, 2: 419 model adjustment, high intake/concentrate diets, 2: 406 goat nutrient calculator, 2: 792 historical development, 2: 403, 2: 418 limitations/improvement potential, 2: 408, 2: 426, 2: 428 amino acid composition, 2: 427 energetic efficiency variation, 2: 426 homeorhesis, 2: 427 mineral requirements, 2: 420 protein requirements, 2: 420 published, 2: 421, 2: 423t ARC (AFRC) systems, 2: 424, 2: 427 INRA system, 2: 426 NRC systems, 2: 425 vitamin requirement, 2: 420 Nutritional research models, 2: 429–435 historical aspects, 2: 429 Nutritional systems biology, 3: 1058 Nutritional whey drinks, 2: 129 Nutrition declarations, labels, 3: 6 international reference levels (NRVs), 3: 8 Nutrition-energy balance, fertility, 4: 480 Nutritive sweeteners, 1: 38 dulce de leche, 1: 875 N-Viro, 4: 630t NVQs (National Vocational Qualifications), food technology education, 2: 8, 2: 9 NZ Journal of Dairy Science and Technology, 2: 104
O Oat(s), 2: 557 Oat milks, 2: 914 Oatrim, 1: 531 Oberhasli goats, 1: 312, 1: 313f Obesity blood cholesterol levels, 3: 731 first-age infant formulae, 2: 138 lipids and, 3: 712 reproductive effects, 1: 463 Occluded air, milk powder, 2: 119, 2: 119t Oceania, goats, 1: 318 Ochratoxin A, 1: 904t, 4: 794, 4: 794f cheese, 4: 783 as contaminant, 1: 904 OCs see Organochlorines (OCs) Octanoic acids, blue mold cheese aroma, 1: 772 1-Octen-3-ol, Camembert flavor, 4: 777–778 Odd-toed ungulates (Perissodactyla), 3: 324 molecular studies, 3: 325 phylogenetically related families, 3: 518, 3: 519f Odobenidae evolution, 3: 563–566 lactation, 3: 564t Odocoileus virginianus (white-tailed deer), seasonal breeding, 4: 445–446
Index Odontocetes, 3: 563 lactation, 3: 564t milk composition, 3: 574 Odor, air quality, 3: 397 OECD-FAO Agricultural Outlook report, 4: 348, 4: 349f Oenococcus, 3: 73t, 3: 75, 3: 75f Oesophagostomum radiatum, 2: 258 Oestrogen see Estrogen(s) Off-flavors, 2: 533–551 analytical technique, 2: 543 causes, 2: 537, 3: 609 animal feed, 2: 542, 2: 795–796 light, 2: 537, 2: 726 microbial metabolites, 2: 539, 2: 548 multiple mechanisms, 2: 540, 2: 540f, 2: 541f packaging, 2: 543 prooxidant metal contact, 2: 539 in dry dairy ingredients, 2: 546 feed-related, 2: 542 light-induced, 2: 537 microbial, 2: 539 milk, electronic nose for measuring, 2: 546 oxidized, prooxidant metal contact, 2: 539 packaging-related, 2: 543 see also individual products and off-flavors Office International des Epizooties see OIE (World Organization for Animal Health) OIE (World Organization for Animal Health), 4: 1–8 activities, 4: 7 ad hoc working groups, 4: 3 animal identification, 4: 6 animal production food safety, 4: 5 animal traceability, 4: 6 animal welfare, 4: 6 bovine tuberculosis free country definition, 2: 197 collaborating centers, 4: 3 communication, 4: 7 companion groups and supports, 4: 2 Council, 4: 2 disease information, 4: 4 member countries’ obligations, 4: 4 transparency tools, 4: 4 disease notification, 4: 4 disease tracking, 4: 4 financial resources, 4: 1 global public good, 4: 7 guidelines, 4: 7 headquarters, 4: 2 history, 4: 1 international animal health codes, 4: 6 updating procedures, 4: 7 international solidarity, 4: 5 international trade in animal/animal products, 4: 5 laboratory twinning, 4: 3 mandate, 4: 3 name change, 4: 1 permanent working groups, 4: 3 reference expert, 4: 3 reference laboratories, 4: 3 regional commissions, 4: 2 regional representations, 4: 2 sheep disease outbreak monitoring, 2: 859 specialized commissions, 4: 2 standards, 4: 7 standard setting procedures, 4: 6 structure, 4: 2 subregional representations, 4: 2 veterinary education, 4: 7 veterinary scientific information, 4: 4 technical publications, 4: 5 veterinary service strengthening, 4: 6 World Assembly of Delegates, 4: 2 see also individual commissions OIE list of diseases, 4: 4, 4: 7 Oil(s) bloat treatment/prevention, 2: 209 dairy processing, environmental impact, 4: 633
extraction byproducts, 2: 346 imitation dairy products, 2: 913 Oil-in-water (O/W) emulsions, 1: 61 coalescence, 1: 63 rheology, 1: 63, 1: 68 creaming, 1: 62 flocculation, 1: 61, 1: 62f Oilseed(s), 2: 349–355, 2: 368 chemical composition, 2: 350t milk fat changes, butter spreadability and, 1: 500 Oilseed meals, 2: 352, 2: 368 chemical composition, 2: 350t protein content, 2: 352–353 Oleic acid, 3: 656t, 3: 657 analysis, 3: 699 blood cholesterol levels, 3: 713 skeletal structure, 3: 656f Olestra, 1: 529 gastrointestinal side effects, 1: 529 Olfactometry air quality testing, 3: 397 CharmAnalysis dilution method, 2: 533 detection frequency aromagrams, 2: 537 Osme cross-modal matching, 2: 533 Olfactory threshold determination, cheese flavor assessment, 1: 676 Oligofructose (FOS), prebiotic-fortified milk, 3: 298–299 Oligomycin, Geotrichum candidum, 4: 771 Oligonucleotide probes, Enterobacter, 4: 77 Oligosaccharide:lactose ratio, milk, 3: 241 Oligosaccharides, 3: 479, 4: 358 antipathogenic action, 3: 484, 3: 551, 3: 551 biological functions, 3: 213, 3: 241, 3: 550 characterization methods, 3: 249 classification, 4: 355, 4: 356t definition, 4: 355 goat milk, 3: 258 human milk see Human milk oligosaccharides (HMOs) indigenous in milk, 3: 241–273 biosynthesis, 3: 251 chemical structures, 3: 258, 3: 271t core units, 3: 258 features, 3: 258 gastrointestinal absorption, 3: 251 gastrointestinal digestion, 3: 251 neutral, 3: 258 mammalian species, 3: 258, 3: 271t concentration-postpartum time relationship, 3: 258–271 mammary gland synthesis mechanism, 3: 550 marine mammal milk, 3: 576, 3: 577t marsupial milk, 3: 555–556 nutrient intake, contributions to, 3: 1004 phylogenetic relationships molecular structures, 3: 550–551 specific types in human milk, 3: 551, 3: 585, 3: 585t variation in amounts, 3: 550 as prebiotics, 3: 214, 3: 484, 3: 551, 3: 551, 4: 358 primate milk, 3: 615–616, 3: 617t production, Kluyveromyces, 4: 763 sheep milk, 3: 258, 3: 499 see also individual types Olive oil blends, 1: 523 Omega-3 fatty acids, modified butters, 1: 504 Omega fatty acids, dairy cattle feed, 2: 365, 2: 365t ‘Omic’ technologies LAB stress response, 3: 57–58 limitations, 3: 1059 -13907*G, lactase persistence, 3: 238 -13910*T, lactase persistence, 3: 237, 3: 238 -13915*G, lactase persistence, 3: 238 -14010*C, lactase persistence, 3: 238 One-dimensional polyacrylamide gel electrophoresis, 1: 185 One-hump camel see Dromedary (Camelus dromedarius)
921
One-way valve, 4: 157, 4: 158f Onion extracts, 4: 789 Online cell counter (OCC), somatic cell count, 3: 896 Oocytes, heat stress, 4: 567–568 Opaque concentrated dispersions, 1: 137 Open-bowl separators, 4: 168 Open kettle process, dulce de leche production, 1: 876, 1: 877f Open sheds, Africa, 2: 77, 2: 78f Operating flows, 1: 488 Operator training, 2: 7 Opioid milk peptides, 3: 879 biological activity, 3: 1063 Opsonophagocytic assay, Enterococcus, 3: 159 Optical density measurement, 4: 237 Optical systems, curd strength measurement, 1: 589 Optical transducers, 1: 237, 1: 237f Oral health, 3: 1034–1040 Orangutan colostrum oligosaccharides, 3: 271t milk oligosaccharides, 3: 617t Orchardgrass (cocksfoot, Dactylis glomerata), 2: 576 Orf sheep, 2: 859 vaccination, lambs, 2: 861–863, 2: 862t Organic acids cheese microbiology, 1: 629 rumen fermentation, 3: 983 Organic-chelated minerals, 2: 384–388 Organic dairy production, 4: 9–15 animal health care, 4: 13 antibiotic use, 4: 11t, 4: 12–13, 4: 13 farmland, 4: 13 future developments, 4: 14 growth promotion hormones, 4: 13 historical aspects, 4: 9 international standards comparison, 4: 10 livestock living conditions, 4: 14 market trends, 4: 9 nitrogen self-sufficiency, 4: 14 organic system plan, 4: 14 papillomatous digital dermatitis, nonantibiotic treatments, 2: 172 parasiticides use, 4: 11t, 4: 13 record keeping, 4: 13 water resources, 4: 14 Organic Food Production Act (OFPA), 4: 10 Organic milk, 3: 278 Organic Product Exporters of NZ Inc. (OPENZ), 4: 9 Organic solvents, cholesterol extraction, 1: 503 Organisation for Economic Co-operation and Development (OECD), 4: 306 historical aspects, 4: 331 Organochlorines (OCs) as contaminants, 1: 889, 1: 900 metabolites, 1: 889 Organophosphate pesticides, labile residues, 1: 889 Organophosphorus pesticide residues, polarography, 1: 197 Orientation, warm climate feed pads, 2: 22 Original Bailey’s Cream Liqueur, 4: 735–736 Origin-derived phage-encoded resistance, 1: 436 Orla-Jensen, Sigurd, 1: 28 Ornithine, 1: 771–772 Ornithine transcarbamylase, 3: 126 Orotic acid, 3: 974 Orthophosphates caseins, effects on, 3: 771 pasteurized processed cheese products, 1: 811t in serum, 3: 919, 3: 920t Oscillation rheometer, 4: 237 Osmosis, 3: 864 water secretion, 3: 379 Osmotic pressure, 4: 723t Osmotic stress LAB, 3: 64, 3: 65f Propionibacterium, 1: 407 Osteocalcin (OC), 4: 663, 4: 663t
922 Index Osteomalacia, 4: 650 Osteopontin, 3: 796t, 3: 797 inflammation, 3: 797 mammary involution, 3: 797–798 trophoblast attachment, 4: 498–499 Osteoporosis candidate genes, 3: 1059–1060, 3: 1060t -galactosidase deficiency, 3: 1014 inadequate calcium intake, 3: 930 incidence, 3: 930, 3: 1009 lactose malabsorption, 3: 1013–1014 risk factors, dairy product consumption, 3: 1013 vitamin D deficiency, 4: 650 Ostertagia ostertagi, 2: 258 Ostertagia ostertagi ELISA, 2: 260, 2: 261f, 2: 262 Ostertagia ostertagi-specific antibody, 2: 260 Ostwald–de Waele equation, 4: 523 Otariidae, 3: 563–566 lactation, 3: 564t feast-famine–feast pattern, 3: 570–574 milk composition, 3: 567t, 3: 569 lactose lack, 3: 576–579 see also individual species Otlu Cacik, 1: 785 manufacture, 1: 785–786 Otlu cheese, 1: 783, 1: 785f herbs added, 1: 784, 1: 785t, 1: 786f manufacture, 1: 783–784 types, 1: 785 Otlu Lor, 1: 786 Otobius megnini (spinose ear tick), 2: 253 Ould Sidi al-Sheikh camels, 1: 352 Ovarian failure, classical galactosemia, 3: 1053 Ovarian follicles dominance, 4: 428–429 function, nutrition and, 4: 475–476, 4: 476f growth see Follicular growth normal development, 4: 576–577 selection, 4: 428–429, 4: 430 stress responses, 4: 576–577 Ovarian follicular cysts, 4: 437 behavioral symptoms, 4: 438 characteristics, 4: 437 definition, 4: 437 development, 4: 437, 4: 438f diagnosis, 4: 438 endocrine imbalances, 4: 438 etiology, 4: 438 examination, 4: 438 heredity, 4: 438 increased milk production, 4: 438 persistence, 4: 437–438 seasonality, 4: 438 self-correction, 4: 437–438 treatment, 4: 438 turnover, 4: 437–438 Ovaries development, 4: 423 gonadotropin secretion control, development of, 4: 424 Oven drying, conventional, 1: 76, 1: 82t pre-evaporation step, 1: 76 Overall Trade-Distorting Domestic Support (OTDS), 4: 347 Overeating diarrhea, replacements, 4: 419 Overheated vapor state, 4: 589, 4: 590f Overpotential, 4: 259, 4: 259f Oviduct secretions, preimplantation period, 4: 495–496 Ovine milk see Sheep milk Ovis aries see Sheep Ovis musimon (mouflon), 3: 326–327 Ovostatin-2 (OVOS2), monotremes, 3: 559 Ovsynch procedure/protocol, 1: 7, 4: 454 follicle dynamics, 4: 455, 4: 455f heifers, 4: 413 hormonal responses, 4: 455, 4: 455f
nonpregnant cow resynchronization, 4: 457, 4: 457f optimizing stage of estrous cycle, 4: 454 Ovulation follicular growth, 2: 623–624, 2: 627f insemination synchronization, 4: 454–460 postcalving, 4: 475 sheep, 2: 887 silent, 4: 464–465 undernutrition effects, 2: 626 see also Superovulation Ovulation synchronization, 4: 448 heat stress, 4: 571–572 heifers, 4: 412–413, 4: 414f Ovulatory follicles, postpartum, 4: 435, 4: 435f mechanisms associated, 4: 435 Ovum pickup (OPU) technique, 2: 616, 2: 621f facilities, 2: 620 genetic potential, 2: 621 Oxaloacetate, decarboxylation, 3: 167 Oxaloacetate decarboxylase, 3: 167 Oxidation milk fat, 3: 654 milk lipids see Milk lipids proteins, MS, 1: 202 Oxidation ditch plant, 4: 623–624, 4: 624f Oxidation–reduction potential, 1: 249 cheese, 1: 629 milk, 1: 250 Oxidoreductases, 2: 301–303 Oxygen, food browning, 3: 217 Oxytetracycline listeriosis, 2: 187–188 papillomatous digital dermatitis, 2: 172 pasteurellosis, sheep, 2: 858 Oxytocin acute clinical mastitis, 3: 437 applications, 1: 893 as contaminant, 1: 893 corpus luteum luteolysis, 4: 432 myometrial activation, 4: 507–508 myometrial contraction, 4: 505–507 release, machine milking, 3: 330 Oxytocin receptors, 4: 432 Ozonation, drinking water, 4: 584 Ozone treatments Aspergillus flavus, 4: 790–791 water supply disinfection, 4: 585t, 4: 586
P P2O5, fertilizer, 3: 403 Paar Physica Rheoswing, 1: 588 PAB see Propionic acid bacteria (PAB) Packaging, 2: 708–713, 4: 16–23 air exclusion, 3: 283 anhydrous milk fat, 1: 521 aseptic filling techniques, 2: 721, 3: 285 commercial and consumer requirements, 2: 709 continuous web carton forming and filling, 2: 710, 2: 710f preformed containers, decontamination and filling, 2: 711, 2: 711 sterile blown bottles, 2: 711, 2: 711 aseptic systems, 2: 709 biodegradability, 4: 634–635 coffee cream, 1: 914 continuous butter manufacture, 1: 497 dairy products, 4: 17 fluid milk, 4: 17 historical aspects, 2: 708, 4: 16 infant formulae, 2: 135 integrity testing, 2: 712 nondestructive methods, 2: 713 khoa, 1: 883 light exclusion, 3: 283 materials, 4: 18t, 4: 634–635 cup systems, 2: 712 plastic bottles, 2: 710 vitamin C oxidation, effects on, 3: 227–228
milk powder, 2: 115 negative environmental impact reduction, 4: 634 new concepts, 4: 21 off-flavors causes, 2: 543 plastic additives, 2: 543 residual manufacturing solvents, 2: 543, 2: 544f pasteurized milk, historical aspects, 1: 13 pouch systems, 2: 711, 2: 712f, 2: 712f purpose of, 4: 16 sachet systems, 2: 711, 2: 712f, 2: 712f spoilage mold control, 4: 782 sterilization methods, 2: 708 chemical treatment, 2: 709 heat, 2: 708 irradiation, 2: 708 sweetened condensed milk production, 1: 871 trends, 4: 21 whipping cream, 1: 915–916 yogurt see Yogurt see also Containers; Labeling, dairy products PAD (pulsed amperometric detection), ion-exchange chromatography, 1: 171 Paddle agitators, 4: 160, 4: 161f on farm applications, 4: 164–165 uses, 4: 160 Paddocks calving, 2: 23 warm climate farms, 2: 23 Paenibacillus lactis, 2: 703 PAGE see Polyacrylamide gel electrophoresis (PAGE) Pahari goats, 1: 321 Paint, estrus detection, 4: 468 Paired comparison, discrimination testing, 1: 280–281 Palghoa see Khoa Palletizing robots, 4: 254, 4: 254f, 4: 255f, 4: 255f suction cups, 4: 255f, 4: 256 working space, 4: 254–256 PallSep Vibrating Membrane Filter (VMF), 3: 869 Palmitic acid analysis, 3: 699 blood cholesterol levels, 3: 730–731 Palm oil milk replacers, 4: 398 PAMP (protease-activated antimicrobial peptide), 1: 410t Pan American Dairy Federation (FEPALE), 2: 105 Pancreas, 3: 989 Pancreatic co-lipase, humans, 3: 711 Pancreatic enzymes, 3: 989 Pancreatic lipase, humans, 3: 711 Paneer cheese, 1: 700t, 1: 704 Pangola grass (Digitaria eriantha), 2: 578 Panicum (guinea grass), 2: 577 Pantetheine, 4: 694 Panton and Valentine leucocidin, Staphylococcus aureus, 4: 107 Pantothenic acid, 4: 694–696 dairy sources, 4: 695t deficiencies, 4: 694 dietary sources, 4: 694, 4: 695t function, 4: 694 recommended daily intake, 4: 695t status indicators, 4: 694 structure, 4: 694, 4: 695f therapeutic uses, 4: 695–696 Pan troglodytes milk see Chimpanzee milk Paperboard packaging, 2: 709, 2: 709f ice cream, 4: 20 pasteurized milk, 3: 277 Papillary arteries of the teats, 3: 334 Papillary veins of the teats, 3: 335 Papillomatous digital dermatitis (PDD), 2: 168–173 clinical signs, 2: 169 control, 2: 171 economic loss, 2: 168 etiology, 2: 168 bacteria, 2: 168 footbathing, 2: 171, 2: 172
Index herd epidemiology, 2: 170 histological description, 2: 170 immunity, 2: 173 lesions, 2: 168, 2: 169, 2: 170f, 2: 170f nutrition, 2: 172 prevalence, 2: 168 recurrence, 2: 171, 2: 173 risk factors, 2: 169 treatment, 2: 171 nonantibiotic, 2: 172 response to, 2: 172 Papio cynocephalus anubis milk see Baboon milk Parabone milking parlors, 3: 961, 3: 961f PARAFAC, 4: 243 PARAFAC II, 4: 243 Parallel milking parlors see Side-by-side (parallel) milking parlors Parallel-plate devices, 1: 273–274 Parasites/parasitic conditions buffalo, Mediterranean region, 2: 782 external, 2: 254t, 2: 858 control measures, 2: 831 replacement cattle, 4: 419 internal goats, 2: 831, 2: 831–832 replacement cattle, 4: 419 sheep, 2: 858 control, 2: 858 treatment, 2: 858 see also specific parasites and infestations Parasitica coagulant (Cryphonectria parasitica proteinase), 1: 576, 1: 576 Parasitic gastroenteritis (PGE), sheep, 2: 858 Parathyroid hormone (PTH) calcium homeostasis, 2: 239, 2: 371 calcium-phosphate homeostasis, 4: 648f, 4: 648–649 intestinal calcium absorption, 3: 995 metabolic alkalosis, 2: 356 Paratuberculosis see Johne’s disease Parenchyma, mammary gland, 3: 331, 3: 338 development, 3: 340f gene expression profile, 3: 349–350, 3: 350f heifer calf, 3: 342 early postnatal period, 3: 339 Paresis puerperalis see Milk fever Pareto chart, 4: 270, 4: 270f Paris Conference, 4: 1 Parkinson’s disease, vitamin E, 4: 659 Parmesan drying, 1: 826 as food ingredient, 1: 830 Parmigiano Reggiano cheese, 1: 728 characteristics, 1: 730t composition, 1: 729t free fatty acids, 1: 771t Lactobacillus fermentum, 3: 129 lipolysis, 1: 735–736 free fatty acids, 1: 736t pathogen status, 1: 659 production statistics, 1: 729t protected designation, 1: 846 proteolysis free amino acids, 1: 734t NSLAB, 1: 735 Partial air vapor pressure, 4: 210 Partial GALT deficiency, 3: 1053–1054 Partial hydrolysate-based formulae, 2: 143 Partial least squares regression (PLSR) infrared spectrometry, 1: 118–119, 1: 119f multivariate statistical tools, 1: 94t, 1: 105, 1: 106f Particle concentration fluorescence immunoassay (PCFIA), brucellosis, 2: 157 Particle size distribution, milk powder, 2: 118 emulsion creaming, 1: 62 ‘Particulated’ gels, 3: 892 Parturient apoplexy see Milk fever Parturient paresis see Milk fever
Parturition, 4: 503–513, 4: 514, 4: 515f complications, 4: 511 displaced abomasum, 2: 213 fetal expulsion, 4: 509, 4: 510 fetal hypothalamic–pituitary–adrenal axis, 4: 507f fetal membrane expulsion, 4: 510 heifers, 4: 415 initiation, 4: 508f maternal endocrine changes, 4: 507, 4: 508f, 4: 509f myometrial activity, 4: 507 sheep model, 4: 503 PAS 6/7 glycoprotein see Lactadherin Pascal, 3: 945 PAS III see MUC-15 Paspalinine, 4: 796–797, 4: 797f Paspalum (Paspalum dilatatum), 2: 577 Paspalum dilatatum (paspalum), 2: 577 Paspalum staggers, 4: 796–797 Passive safety feature, 4: 281–282 Pasta-filata cheeses, 1: 737–744 chemical composition, 1: 746t manufacture mechanization, 1: 616 stretchability, 1: 832 stretching operation, mechanization, 1: 616 traditional, 1: 745–752 amino acid concentrations, 1: 749t casein-associated calcium, 1: 747 fatty acid concentrations, 1: 750t flavor development, 1: 749–751 functional characteristics, 1: 747 lipolysis, 1: 751–752 long-ripened, 1: 749–751 microbial acidification, 1: 748 microbiology, 1: 748 proteolysis, 1: 749–751 ripening, 1: 748 secondary proteolysis, 1: 748 stretching process, 1: 747 textural defects, 1: 747–748 texture, 1: 747 types, 1: 745 see also Low-moisture part-skim mozzarella (pizza cheese); specific cheeses Pasteur, Louis, 1: 13, 3: 310 lactic fermentation, 1: 27 Pasteurella multicida, 2: 782 Pasteurellosis, sheep, 2: 858 Pasteurization, 3: 310–315 aims, 3: 310 alkaline phosphatase activity measurement, 1: 652–653 alternative technologies, 3: 279 batch vs. continuous, 3: 275 biogenic amines, 1: 452 camel milk, 3: 515 Campylobacter control, 4: 45 cheese making milk, 1: 549 cheese pathogen control, 1: 645–646 definitions, 1: 652, 3: 274 E. coli control, 4: 64 effects, 1: 655, 3: 276 enzymatic, 3: 276 microbial, 3: 276 nutritional, 3: 276 efficacy, Mycobacterium avium subsp. paratuberculosis, 2: 174–175 Enterobacteriaceae control, 4: 70 heat treatment conditions, 4: 193 high-temperature–short time see Hightemperature–short time (HTST) pasteurization historical aspects, 1: 13, 2: 744, 3: 274, 3: 310, 4: 193 low-temperature–long time see Lowtemperature–long time (LTLT) pasteurization objectives, 3: 274 principles, 3: 310 process types, 3: 310–311
923
public health aspects, 3: 311 concerns, 3: 312, 3: 312t emerging concerns, 3: 314 historical aspects, 3: 311, 3: 312t uncommon concerns, 3: 314 purpose, 3: 310 ready-to-eat dairy desserts, 2: 911 regulations, 3: 274 Salmonella control, 4: 96 sampling, 1: 73 spore removal, 4: 199 starter culture protection, 1: 441 technological developments, 4: 199 temperature-time relationships, 3: 275t testing, 3: 275, 4: 198 time–temperature conditions, 4: 193 vitamin loss, 3: 276, 3: 277t Pasteurized cream, allowable additives, 1: 39 Pasteurized milk, 3: 274–280 Bacillus growth, 4: 385 consumption, 3: 278f extended shelf life milk vs., 3: 279 flavor, 3: 277 flavor defects, 3: 277 Pseudomonas, 4: 382 fluid milk processing, 3: 275 folate-binding proteins, 4: 684 folate bioavailability studies, 4: 684–685, 4: 685f, 4: 685f Gram-negative psychrotrophs growth, 4: 385 induced lipolysis, 3: 723–724 lipolytic defects, 3: 723 listeriosis outbreaks, 4: 83 microfiltered milk vs., 3: 307–308 microorganisms, effect on, 3: 457 nutritive losses, 3: 611 packaging, 3: 276 postpasteurization contamination, 3: 277 production line, 3: 276f psychrotrophs, 4: 386 shelf-life prediction, 4: 387 quality, previously thermized milk, 2: 695–696 Salmonella contamination, 4: 93–94 shelf life, 3: 277, 3: 457, 4: 197–198 mastitis effects, 3: 905–906 types, 3: 274, 3: 278 yeast contamination, 4: 745 Pasteurized Milk Ordinance (PMO), pasteurization definition, 3: 275, 3: 275t Pasteurized processed cheese products (PCPs), 1: 805–813, 1: 806t, 1: 822, 1: 823f applications, 1: 813 batch cooking, 1: 807 blending, 1: 806 blend processing, 1: 807, 1: 808 P-Casein dispersion, 1: 809, 1: 809f composition, 1: 807–808 defects, 1: 808–809 definitions, 1: 805, 1: 805 Codex Alimentarius, 1: 805–806, 1: 807t regulations, 1: 805–806 emulsifying salts, 1: 808, 1: 811t calcium sequestration, 1: 809 casein/P-casein dispersion, 1: 809, 1: 809f citrates, 1: 811t disodium phosphate, 1: 810 effects, 1: 809 fat emulsification, 1: 810 native milk fat globule membrane, 1: 808 orthophosphates, 1: 811t pH stabilization, 1: 809 polyphosphates, 1: 811t properties, 1: 810 pyrophosphates, 1: 811t sodium aluminum phosphate, 1: 810 structure formation, 1: 810 tetrasodium pyrophosphate, 1: 810 trisodium citrate, 1: 810
924 Index Pasteurized processed cheese products (PCPs) (continued ) water-soluble protein, 1: 809f ingredients, 1: 806t, 1: 807t, 1: 812 manufacture, 1: 806 batch cooking, 1: 807 blending, 1: 806 blend processing, 1: 807, 1: 808 cheese composition, 1: 807–808 cleaning, 1: 807 cooling/storage, 1: 807 formulation, 1: 806 homogenization, 1: 807 shredding, 1: 806 temperature–time treatment, 1: 808 properties, 1: 810, 1: 812t pH, 1: 810 processing conditions, 1: 812–813 types, 1: 805 water-soluble protein (WSP), 1: 809f Pasteurizers cleaning in place (CIP) systems, 4: 131 design, 4: 193–199 high-temperature–short time see HTST pasteurizer historical aspects, 1: 13 historical development, 4: 193 ice cream manufacture, 2: 901 maintenance, 4: 198 operation, 4: 193–199 operation control, 4: 198t Streptococcus thermophilus biofilms, 3: 147 testing, 4: 198 Pastoral models, goats, 2: 59–60 Past performance evaluation, 1: 483 Pasture(s) crops annual see Annual forage and pasture crops maintenance, 2: 586–593 dairy sheep, 2: 849 damage, warm climate feed pads, 2: 19 digestibility, 2: 33f, 2: 33–34 establishment, 2: 586–593, 2: 586 seedbed preparation, 2: 586 seed rate, 2: 586 shading prevention, 2: 586 sown grass tillering, 2: 587 weed potential, 2: 586–587 for feeding see Pasture-based systems fertilizers application, 2: 587 application timing, 2: 569 nitrogen, during growth, 2: 570, 2: 595 soil tests, for needs assessment, 2: 569 high-digestibility-rumen pH relationship, 2: 34, 2: 34f land preparation soil preparation aims, 2: 567 tillage methods, 2: 567 leaf growth, environmental temperature effects, 2: 598 Mediterranean see Mediterranean pastures nutrient recycling, 2: 587 nutritional content analysis, 2: 789 nutritive characteristics, 2: 33, 2: 33f sowing seeding rate, 2: 568 seed placement, 2: 568 sowing methods, 2: 568 timing, annuals, 2: 567 supplements interactions, 2: 35, 2: 36f non-seasonal/pasture-based management, 2: 48, 2: 48t temperate see Temperate pastures weeds see Weed(s) Pasture-based systems chewing thresholds, 3: 986 energy content, 2: 454, 2: 455t
pregrazing pasture mass, 2: 455 previous grazing’s postgrazing mass, 2: 455 total amount per hectare, 2: 455 fiber digestibility, 2: 453, 2: 454f fiber digestion, 3: 985–988 green leafy material production, 2: 456 heifers see Heifer(s) lactation rations, cows, 2: 453–457 nutrient requirements, 2: 453, 2: 455t land carrying capacity, 4: 405, 4: 405f milk yields, 2: 453 mineral supplementation, 2: 457 non-seasonal/pasture-based management see Non-seasonal/pasture-based management nutrient supply, 2: 453, 2: 454f optimum grazing, 4: 405 postgrazing residuals, 2: 456 protein supplementation, 2: 456 with seasonal calving, 2: 29–37 cow breeds, 2: 35 feed planning, 2: 31 grazing management, 2: 31 pasture-supplement interactions, 2: 35, 2: 36f rotational grazing, 2: 31 strip grazing, 2: 31 supplement use, 2: 34 seasonal/pasture based management see Seasonal/ pasture based management supplementary fiber, 3: 987 rumen pH, 3: 987 supplementation, 2: 456 energy, 2: 456 supply-demand relationship, 2: 454f transition cows see Transition cows vitamin supplementation, 2: 457 Pasture dusting, grassy tetany, 2: 228 Pasture farms hospital facilities, 2: 28 subdivision, 2: 27 Pasture intake, 2: 32 ‘Patent/leaky teats, 3: 334, 3: 383 Pateri goats, 1: 311t, 1: 322 Pathogen-associated molecular patterns (PAMPs), 3: 387–388 Pathogens, immunochemical detection, 1: 180, 1: 182t Pathogen-specific biosensors, 1: 241 Patulin, 1: 904t, 4: 795, 4: 795f Paxilline, 4: 796–797, 4: 797f PCA (principal component analysis), 1: 94t, 1: 98t, 1: 99, 1: 101 PCBs see Polychlorinated biphenyls (PCBs) PCDDs (polychlorinated dibenzo-p-dioxins), 1: 898, 1: 899f PCDFs (polychlorinated dibenzofurans), 1: 898, 1: 899f PCPs see Pasteurized processed cheese products (PCPs) PCR see Polymerase chain reaction (PCR) PDD see Papillomatous digital dermatitis (PDD) PDF (postdischarge infant formulae), 2: 140t Peanut meal, 2: 353 aflatoxin risk, 2: 353 definition, 2: 349 Pearl millets, 2: 555 Pecorino cheese, 3: 501 E. coli outbreaks, 4: 61–62 Pecorino Romano cheese, 1: 731 characteristics, 1: 730t composition, 1: 729t lipolysis, 1: 735–736 free fatty acids, 1: 736t production statistics, 1: 729t proteolysis, 1: 733–734 NSLAB, 1: 735 Pecorino Sardo cheese, 1: 731 characteristics, 1: 730t composition, 1: 729t lipolysis, 1: 735–736
production statistics, 1: 729t Pecorino Siciliano cheese, 1: 731 characteristics, 1: 730t composition, 1: 729t lipolysis, 1: 735–736 production statistics, 1: 729t Pectin(s) applications, 1: 70t casein micelle interactions, 3: 302–303, 3: 303f dairy desserts, 2: 909t flavored milks, 3: 302 milk protein concentrate, 3: 853 rumen fermentation, 3: 983 Pediculosis see Lice infestation PediCuRx Complete, 2: 172 Pediocin-like bacteriocins, 1: 425 Pediocin PA-1, 1: 422t Pediococcus, 3: 149–152 as adventitious bacteria, 3: 151 bacteriocin (pediocin) production, 3: 150 dairy industry uses, 3: 150 blue mold cheeses, 1: 769 cheese, 3: 151 cheese adjuncts, 3: 151 cheese ripening, 3: 151 enumeration, 3: 149 selective, 3: 149–150 exopolysaccharides, 3: 150 fermentation starters, 3: 456 fermented milks, 3: 151 genomics, 3: 73t, 3: 74f, 3: 75 growth media, 3: 149 isolation, 3: 149 lactate racemization, 3: 151 as NSLAB, 1: 626 phenotypic differentiation, 3: 149, 3: 150t probiotic properties, 3: 150 taxonomy, 3: 149 Pediococcus acidilactici, 3: 149 fermented milks, 3: 151 Pediococcus parvulus exopolysaccharide production, 3: 150 probiotic properties, 3: 150–151 Pediococcus pentosaceus, 3: 149 exopolysaccharide production, 3: 150 genome sequence, 1: 643t oxidative activity, 3: 151 Pedometer estrus detection, 4: 462, 4: 462f, 4: 468 information retrieval, 4: 462 health prediction, 4: 463 heat detection, 1: 9, 4: 477 lameness detection, 4: 463 ovulation prediction, 4: 463 stress prediction, 4: 463 Pefloxacin, 4: 57 Pellagra, 4: 692 acute therapy, 4: 692 clinical diagnosis, 4: 692 Pellagrosis see Pellagra Pendulous udders, mastitis, 3: 429 Penetration tests, 1: 277 cheese rheology measurement, 1: 690, 1: 690 Penicillic acid, 1: 904t, 4: 795, 4: 795f Penicillin, Staphylococcus aureus resistant strains, 4: 111–112, 4: 112t Penicillium blue mold cheeses, 1: 769 cheese ripening, commercial cultures, 1: 572 cheese spoilage, 4: 780 condensed milk spoilage, 4: 781 currently accepted names, 4: 781t margarine spoilage, 4: 781 Penicillium album see Penicillium camemberti Penicillium camemberti, 1: 628, 4: 776–779 applications, 4: 776 non-dairy foods, 4: 779 Brie cheese, 4: 778
Index Camembert cheese, 4: 778 cheese biological control agent, 4: 777 cheese flavor, 4: 777 bitterness, 4: 769–770 cheese maturation, 4: 776 cheese ripening, 1: 567, 1: 568, 1: 568, 1: 568 mold surface-ripened cheeses, 1: 568 cheeses used in, 4: 778 enzymes produced, 4: 777 extracellular endopeptidases, 4: 777 Geotrichum candidum mixed culture, 4: 776–777 growth characteristics, 4: 776 atmospheric carbon dioxide, 4: 776 pH, 4: 776 identification, advanced methods, 4: 779 lactate utilization, 1: 568–569 lipases, 4: 777, 4: 777–778 lipolysis, 1: 569 mold-ripened cheeses, 1: 773 mycotoxin contamination, 1: 903 proteolysis, 1: 569 proteolytic enzymes, 4: 777 sausage meat, 4: 778–779 secondary metabolism, 4: 777 as starter culture, 4: 776 strain variation, 1: 569 surface mold-ripened cheeses, 1: 774–775, 1: 775, 1: 776f, 1: 778 lactose and lactate metabolism, 1: 777 lipolysis, 1: 778 water activity, 4: 776 Penicillium candidum see Penicillium camemberti Penicillium carneum, 4: 773 Penicillium caseicolum see Penicillium camemberti Penicillium paneum, 4: 773 Penicillium rogeri see Penicillium camemberti Penicillium roqueforti, 1: 628, 4: 772–775 Blue cheese flavor, 4: 772 blue mold cheeses, 1: 767, 1: 768 cheese ripening, 1: 568 blue-veined cheeses, 1: 568 cheese salting, 1: 596–597 extracellular lipase production, 4: 773 food spoilage, 4: 772, 4: 772–773 genetics, 4: 773 growth inhibition, 4: 773 Geotrichum candidum, 4: 775 kerosene off-flavor, 4: 780–781 lipases, 4: 772 lipolysis, 1: 569 morphology, 4: 772 mycotoxin contamination, 1: 903 mycotoxins, 1: 769, 4: 774 oxygen requirements, 4: 772 pH range, 4: 772–773 physiological growth-affecting factors, 4: 772 carbon dioxide concentrations, 4: 772 salt concentrations, 4: 773 propionate-stimulated growth, 4: 773 proteolysis, 1: 569, 4: 772 sorbate resistance, 4: 772–773 strain variation, 1: 569, 1: 569f volatile production, 4: 773 water activity, 4: 773 Penis examination, bulls, 1: 476 Penitrem A, 4: 797f, 4: 797–798 Penner serotyping scheme, Campylobacter, 4: 41 Pennisetum clandestinum see Kikuyu Penn State separator, 2: 462 Pentosidine (PTD), 3: 1073 Pepato cheeses, 1: 787 PepC, 3: 87 PepE, 3: 87 PepF, 3: 87 PepI (proline iminopeptidase), 3: 87 PepN, 3: 87 PepO, 3: 87
PEP-PTS (phosphoenolpyruvate phosphotransferase system), starter cultures, 1: 560 PepQ (prolidase) (PepQ), 3: 87 PepR (prolinase), 3: 87 Pepsin(s), 2: 289–290 cheese ripening, proteolysis, 1: 670 as coagulating agent, 1: 574 milk protein allergenicity reduction, 3: 1043 (5-glutamyl)-Peptide:amino acid 5glutamyltransferase see Gammaglutamyltranspeptidase (GGT) Peptide regulatory factors see Growth factors Peptides absorption, 2: 413 Bifidobacterium, bifidus products, 1: 388–389 milk see Milk peptides reversed-phase HPLC, 1: 172 Swiss-type cheese flavor, 1: 718 Peptidoglycan N-acetylmuramoyl hydrolase see Lysozyme Peptidoglycans, Propionibacterium envelope, 1: 403 Peptococcus, 1: 383t Peracetic acid disinfectants, 4: 284 Perceived food quality, 1: 266 Per´e David’s deer (Elepharus davidianus), 4: 445–446 Perennial forage and pasture crops, 2: 576–585 C3 metabolism, 2: 576 C4 metabolism, 2: 576 cultivar differences, 2: 581, 2: 582t, 2: 583f establishment, 2: 586–593, 2: 599 forage quality, 2: 578 breeding aims, 2: 584 grasses vs. legumes, 2: 578, 2: 579f palatability, 2: 583, 2: 584 forbs, 2: 578, 2: 585 herbs, 2: 578, 2: 585 maintenance, 2: 586–593, 2: 599 ryegrass see Perennial ryegrass (Lolium perenne) species, 2: 576–585 quality differences, 2: 581, 2: 582t, 2: 583f temperate species, tropical species vs., 2: 580, 2: 582t tropical species, 2: 577 mineral deficiencies, 2: 581 temperate species vs., 2: 580, 2: 582t varieties, 2: 576–585 see also individual crops Perennial ryegrass (Lolium perenne), 2: 576 cultivar ploidy and forage quality, 2: 583 mineral nutrient levels, 2: 597, 2: 597–598, 2: 598f optimum sward height, 2: 594 plant survival, grazing management-related, 2: 597, 2: 597t stocking density, 2: 594, 2: 597f tiller grazing rate, 2: 594, 2: 597f Performance criterion (PC), 4: 538 Performance monitoring, bulls, 1: 479 Performance objectives (POs), 4: 538 Pericentral hepatocytes, 2: 219–220 Perinatal septicemia, 4: 82 Perineal artery, 3: 334 Periodontal disease, 3: 1038 bacteria associated, 3: 1038–1039 prevalence, 3: 1034 prevention, 3: 1038–1039 dairy derivatives, 3: 1039 dairy products, 3: 1039 whole products, 3: 1039 Periodontitis, 3: 1038–1039 Peripartum time, 4: 514 Periparturient disorders, 4: 514–519 Periparturient periods, environmental mastitis, 3: 416 Periportal hepatocytes, 2: 219–220 Perissodactyla see Odd-toed ungulates Peristaltic pumps, 4: 150, 4: 150f selection criteria, 4: 151t Permanent animal identification, 1: 486
925
Permanent Animal Welfare Working Group, OIE, 4: 6 Permeases citrate metabolism, 3: 167 as exchanger, 3: 167, 3: 167f Lactococcus lactis, 3: 134 Peroxidase enzymes, 2: 319 Peroxy radical, 3: 716 Persian (shaftal) clover (Trifolium resupinatum), 2: 559 Persistent halogenated hydrocarbons, 1: 900 Personal development, 1: 484 ‘Personalized nutrition’, 3: 1059, 3: 1060 Pest control, 4: 540–544 action steps, 4: 544 annual forage and pasture crops, 2: 573 common pests, 4: 540 contractors vs. in-house programs, 4: 541t in-house program, 4: 540 integrated pest management, 4: 544 methods, 4: 540 program verification, 4: 544 stored products, 4: 543 see also individual pests Pest control contractors, 4: 540 in-house program vs., 4: 541t verification records, 4: 540 Pesticides biosensors, 1: 242 contamination, 1: 889, 1: 890t analysis, 1: 891 health impact, 1: 890 occurrences, 1: 889 sources, 1: 889 see also specific pesticides Peyer’s patches, 2: 175 salmonellosis, 2: 192 Yersinia enterocolitica, 4: 119 PFGE see Pulsed field gel electrophoresis (PFGE) PGA (propylene glycol alginate), 1: 36 PGhost vectors, 3: 70 pH blue mold cheese microstructure, 1: 767 blue mold cheese proteolysis, 1: 771 brine salting, 1: 601 changes starter cultures, 1: 552 surface mold-ripened cheese ripening, 1: 777 cheese flavor, 1: 552 cheese microbiology, 1: 629 cheese rheology, 1: 697 cheese ripening, 1: 667 cheese salting, 1: 605 cheese texture, 1: 552 cream cheeses, 1: 702 curd syneresis, 1: 593, 1: 593f dependency, coagulants, 1: 552 Dutch-type cheeses, 1: 723, 1: 724f, 1: 725 heat stability, milk, 2: 745, 2: 746f, 2: 748 low-fat cheeses see Low-fat cheeses low-moisture part-skim mozzarella (pizza cheese), 1: 743 measurement, 1: 248 microstructure, 1: 232, 1: 232f NMR relaxation studies, 1: 158–159, 1: 159f NSLAB metabolism, 1: 641 optima, chymosin, 1: 575–576 pasteurized processed cheese products, 1: 810 stabilization, 1: 809 pathogen control in cheese, 1: 647 rennet milk coagulation, 1: 582, 1: 583 smear-ripened cheeses, 1: 396f urinary, dietary acidification response monitoring, 2: 360 Phage inhibitory media (PIM), 1: 443 Phages see Bacteriophage(s) Phagocytosis, 3: 387 Phagolysosome, 3: 387 Phalaris (Phalaris aquatica), 2: 576
926 Index Pharmaceuticals, dairy ingredients, 2: 132 Pharming, 2: 640, 2: 641t definition, 2: 640–641 Phase contrast light microscopy, 1: 226 Phase feeding, drylots see Drylot management systems Phase transitions, differential scanning calorimetry, 1: 256, 1: 257f, 1: 257f, 1: 258f pH electrodes, 4: 236 time response, 4: 236, 4: 236f Phenethanol, 1: 642 Phenolics, Aspergillus flavus growth inhibition, 4: 790 Phenylacetaldehyde, 1: 642 Phenylethylamine, 1: 451 characteristics, 1: 452t Phenylketonuria (PKU) hypoallergenic formula, 2: 295 Pheromones, 4: 441–442 Phleum pratense (timothy), 2: 576 Phocidae (true seals), 3: 563–566 lactation, 3: 564t milk composition, 3: 567t, 3: 569 Phomopsin A, 4: 799 Phosphatases, 2: 314–318 acid see Acid phosphatase (ACP) alkaline see Alkaline phosphatase cheese flavor, 2: 315–316, 2: 318 high-pressure homogenization inactivation, 2: 758 Phosphates as additives, 1: 36 heat stability, milk, 2: 745 starter culture protection, 1: 443 Phosphatidic acid, 1: 65f, 3: 670, 3: 671f Phosphatidylcholine, 3: 650, 3: 650f fatty acid composition, 3: 672 fatty liver, 2: 221–222 structure, 1: 65f, 3: 670, 3: 671f Phosphatidylethanolamine, 3: 651 structure, 1: 65f, 3: 670, 3: 671f unsaturated fatty acids, 3: 672 Phosphatidylinositol, 1: 65f Phosphatidylserine, 1: 65f Phospho- -galactosidase, 3: 134 Phosphocaseinate see Micellar casein Phosphoenolpyruvate phosphotransferase system (PEP-PTS), 1: 560, 1: 561f starter cultures, 1: 560 Phosphoketolase pathway, Leuconostoc, 3: 140 Phospholipases, ‘bitty cream’ defect, 3: 721 Phospholipids, 3: 670–674 butter, 1: 506 buttermilk, 3: 691 chemical structure, 1: 64, 1: 65f colon cancer prevention, 3: 1021 as emulsifiers, 1: 64, 1: 65f commercial sources, 1: 64, 1: 66t features, 3: 670 first-age infant formulae, 2: 141 ionization constants, 3: 670, 3: 672t milk, 3: 650 analysis, 3: 672 chemical properties, 3: 672 composition, 3: 650t fatty acid composition, 3: 672, 3: 673t features, 3: 673 health effects, 3: 674, 3: 695–696 importance/functions, 3: 673–674 lactation stage, 3: 671 milk fat globule membrane, 3: 682, 3: 682t as prooxidants, 3: 673–674 sources, 3: 671 sheep milk, 3: 499 structure, 3: 670, 3: 671f Phosphopeptides, 3: 930, 3: 1063 Phosphorus, 2: 375 absorption, 2: 375 revised estimates, 3: 406 ruminants, 3: 997 small intestine, lactating ruminants, 3: 994–995
amounts recovered for fertilizer, 3: 401 budgeting uses, 3: 402t, 3: 403 value calculation, 3: 403 availability, 2: 375 biological removal, dairy effluents, 4: 626 bone loss, 3: 931 budgets, 3: 406 amounts exported, 3: 406 cheese, 3: 926, 3: 927t colon cancer prevention dietary reduction studies, 3: 1018–1019 mechanisms, 3: 1019f dairy farm flow, 2: 444 dairy plant effluents, 4: 616 in dairy products, 3: 926t, 3: 926t, 3: 927t nutritional significance, 3: 930 dietary reduction, 3: 406 environmental considerations, 2: 376 equine milk, 3: 526–527 excretion estimates, 3: 399, 3: 400t excretion reduction, 4: 631 functions, 3: 930 laminitis, 2: 203–204 ‘luxury uptake’, 4: 626 in milk, 3: 925, 3: 926t chemical form, 3: 927 inorganic, 3: 927 nutrient intake, contributions to, 3: 1006 nutritional significance, 3: 930 milk fever, 2: 240, 2: 242 neonatal tetany, 3: 930–931 pregnancy requirements, 2: 375 primate milk, 3: 627–629, 3: 628t ration formulation, excess to requirements, 2: 462 ration requirements, 2: 375 recommended dietary intake, 3: 928t removal silage/hay, 2: 590 soil, 2: 587t, 2: 588–589 reproductive performance, 2: 375–376 requirements, 2: 375 sheep milk, 3: 500 Phosphorus fertilizer, 2: 588 sources, 2: 589 Phosphorus index, 3: 405 Phosphorylation, MS, 1: 200 Photoperiod artificial cattle, 4: 443–444 ewes, 4: 443–444 galactopoiesis, 3: 39 mares, 4: 443–444, 4: 447 seasonal breeders, 4: 440 sheep, 2: 889, 4: 426 Phylloquinone, 4: 661 structure, 4: 662f supplementation, 4: 664 Physical activity, blood cholesterol levels, 3: 731 Physical analysis, 1: 248–255 density, 1: 250 freezing point, 1: 251 oxidation–reduction potential, 1: 249 pH measurement, 1: 248 polarimetry, 1: 253 titratable acidity, 1: 248 total solid determination, 1: 254 Physical cleanliness, 4: 130 Physically effective neutral detergent fiber (peNDF), 2: 460, 3: 986 estimation difficulty, 3: 986 ruminal effects, 3: 986 Physicochemistry bacteriophage characterization, 1: 434 surface mold-ripened cheese ripening, 1: 777 Phytate, dietary, 3: 997 Phytoestrogens, 2: 889 Piacentinu Ennese cheese, 1: 787 Pichia jadinii, 4: 750
Picket fence thickener, 4: 629t Picston Shottle, 2: 672 Pig(s) colostrum immunoglobulins, 3: 811 domestication, 3: 326 foot-and-mouth disease, 2: 163 milk see Sow milk transgenic, 2: 642 Pigging, biofilms, 1: 449 Pindi khoa, 1: 881 Pineal gland, 4: 442–443 Pingzau cattle, 1: 296 Austria, 1: 296 Bavaria, 1: 296 milk records, 1: 296t Slovakia, 1: 296 Transylvannian, 1: 297 Pink milk, 2: 873 Pinnipeds evolution, 3: 563–566 milk, 3: 569 energy source, 3: 550 Pinzirta sheep, 1: 332t Pipe(s) cleaning in place, 4: 284 selection, 4: 126 Pipe-line milking machine, goats, 2: 804 Pipelines, dairies design, 4: 126 dimensioning, 4: 126 Piping, calculation principles, 4: 139–144 Piping and Instrumentation Diagram (P&ID), 2: 687, 2: 689f Pirenaica cattle, 1: 298 Pirlimycin hydrochloride, 3: 436 Piscicolin 126, 1: 422t Pishin camels, 1: 352 Piston pumps, 4: 147 design, 4: 147, 4: 148f hygienic requirements, 4: 148 principles of operation, 4: 147 selection criteria, 4: 151t twin-chamber, 4: 148, 4: 148f Pitch-bladed turbines, 4: 160, 4: 161f Pitting corrosion, 4: 260, 4: 261f chloride ions/, 4: 260–261 Pituitary gland, 4: 575 hormones, 4: 575 Pizza cheese see Low-moisture part-skim mozzarella (pizza cheese) Pizzle rot (posthitis), 2: 795 Placenta angiogenesis, 4: 500 efficiency, 4: 499, 4: 500f as endocrine organ, 4: 499 function, 4: 499 disruption, 4: 500–501 maternal stress, 4: 500–501 growth, 4: 499 heat stress effects, 4: 569 retained see Placenta transport mechanisms, 4: 499 Placental cotyledons, 4: 499, 4: 500f Placental dystocia see Retained placenta Placental growth, 4: 514 Placental lactogens, 4: 500 galactopoietic effects, 3: 30 mammary development, 3: 341 Placental mammals, 3: 460 classification, 3: 323 cladistic taxonomy, 3: 324, 3: 325f milk used by humans, 3: 324 principles, 3: 323 evolutionary divergence, 3: 323, 3: 323f K-selecting species, 3: 322 milk composition, 3: 322, 3: 322t r-selecting species, 3: 322
Index Placentation, 4: 488 ruminants, 4: 488, 4: 488f ungulates, 4: 488 Placentomes, 4: 488, 4: 499, 4: 500f Plantaricin A, 1: 426 Plantaricin T, 1: 426 Plant automation, 4: 234 communication protocols, 4: 234 control structure, 4: 234, 4: 235f older plants, 4: 234–235 process control system instrumentation, 4: 234 Plant design, 4: 124–133 cleaning in place (CIP) systems, 4: 130 computer-aided, 4: 133 cost data, 4: 131, 4: 132t environmental constraints, 4: 131 equipment selection, 4: 125 common to all dairies, 4: 126 materials, 4: 127 special equipment, 4: 128t standards, 4: 127 information sources, 4: 124 layout, 4: 130, 4: 130f refrigeration systems, 4: 130 safety and hazard evaluation, 4: 131 sanitary design, 4: 130 disinfection, 4: 130 strategy, 4: 131 utilities, 4: 127 Plant extracts, Aspergillus flavus growth inhibition, 4: 788–789 Plant metabolites, in goat milk, 2: 63, 2: 64t Plants, dairy see Dairy plant(s) Plant safety, importance of, 4: 277 Plant sterols see Sterols Plant surface modification, biofilm control, 1: 449 Plaque, dental, 3: 1034–1035 Plasma proteins, calf feeding, 4: 400–401 Plasma urea nitrogen (PUN), 4: 482 Plasmids, starter cultures, 1: 565 Plasmin, 2: 308 activity, 3: 603 -casein breakdown, 2: 309f casein micelle associations, 2: 309 caseinolytic capacity, 3: 904 Cheddar cheese ripening, 1: 709 cheese ripening, 1: 552, 2: 312 proteolysis, 1: 670 heat treatment, 2: 310 isolation, 2: 311 long ripened pasta-filata cheeses, 1: 749–751 mastitis effects, 3: 903 microbial proteases and, 2: 311 milk cold storage, 2: 311 milk fat globule membrane association, 2: 757–758 milk pH, 2: 310 milk protein products, 2: 312–313 nonfat dry milk, 2: 313 pasteurization, 3: 276 room temperature storage, 2: 311 system, milk see Plasmin system, milk udder health measurement, 3: 898 UHT milk gelation, 2: 312 whey protein interactions, 2: 310 Plasmin inhibitor (PI), 2: 309 Plasminogen, 2: 309 activity, 3: 603 denaturation, 2: 310 heat treatment, 2: 310 isolation, 2: 311 microbial proteases and, 2: 311 milk pH, 2: 310 nonfat dry milk, 2: 313 Plasminogen activator inhibitor (PAI), 2: 309 inactivation, pasteurization, 2: 310 Plasminogen activator inhibitor-1, 4: 495–496 Plasminogen activators (PAs), 2: 309, 2: 309f heat stability, 2: 310
mastitis, 3: 904 milk cold storage, 2: 311 nonfat dry milk, 2: 313 Plasmin system, milk, 2: 308–313 applications, 2: 312 casein micelle associations, 2: 309 cheeses, 2: 312 components, 2: 308, 2: 309f future trends, 2: 313 inhibitors, 2: 309 isolation, 2: 311 isolation, 2: 311 milk protein products, 2: 312 nonfat dry milk, 2: 313 proteolysis-affecting factors, 2: 310 cold storage, 2: 311 heat treatment, 2: 310 microbial proteases, 2: 311 milk pH, 2: 310 room temperature storage, 2: 311 significance, 2: 312 UHT milk products, 2: 312 Plastein reaction, 2: 293 Plastic packaging bottle materials, 2: 710 ice cream, 4: 20 probiotic dairy foods, 4: 21 Plastics, dairy plant use, 4: 137 Plateau yak, 1: 345 Plate detection, cheese, 1: 630–631 Plate heat exchangers (PHE), 4: 189, 4: 189f, 4: 194 butter manufacture, 1: 494 flow patterns, 4: 189, 4: 190f frame, 4: 189 grouping of the plates, 4: 189 herringbone pattern, 4: 187f, 4: 189 plate design, 4: 195f plate patterns, 4: 187f, 4: 189 plate shape, 4: 194, 4: 195f spray drying, 4: 223 UHT, 2: 700 washboard patterns, 4: 187f, 4: 189 Platelet aggregation, k-casein effect, 3: 1064–1065 Platensimycin, 4: 109 Platypus casein gene locus, 3: 823 lactation length, 3: 553 milk oligosaccharides, 3: 272 chemical structures, 3: 271t Pleiade membrane, 3: 868 Pleiotrophin, 3: 796t, 3: 797 PLSR see Partial least squares regression (PLSR) Plug flow tank, 4: 623–624 Pluripotent stem cell-mediated transgenesis, 2: 639 cell versatility, 2: 640f Pneumatic (two-fluid nozzle) atomization, 4: 224 Pneumatic pulsator, 3: 950 Pneumatic ring dryer, casein curd drying, 3: 857 Pneumonia, 2: 828–829 replacements, 4: 418 sheep, 2: 858 Poephagus grunniens see Yak(s) Point estimate (deterministic) approach, additive exposure assessment, 1: 58 Poitevine goats, 1: 311t, 1: 314 Poland, Simmental cattle, 1: 294 Polar bear milk composition, 3: 566–569, 3: 567t fat content, 3: 566 -39-galactosyllactose, 3: 576 isoglobotriose, 3: 576 oligosaccharides, 3: 271t Polarimeter, 1: 82t Polarimetry, 1: 253 double dilution, 1: 253–254 Polarized light microscopy, 1: 226, 1: 227f Polar lipids, 3: 670 abbreviations, 3: 672t
927
milk, 3: 671, 3: 673t Polarography, 1: 193, 1: 197 Polioencephalomalacia, 2: 398, 3: 1000–1001 in goats, 2: 785, 2: 794 Pollutants goat production systems, 2: 63–64, 2: 64t see also specific pollutants Pollution control, 4: 619 prevention, 4: 619 Polyacrylamide gel electrophoresis (PAGE), 1: 185 blue native, 1: 189, 1: 189 cheese proteolysis, 1: 673 fixing solutions, 1: 185–186 isoelectric focusing see Isoelectric focusing (IEF) milk proteins, 3: 541, 3: 541f, 3: 746, 3: 761 historical aspects, 1: 22–23 ‘native’, 1: 187 one-dimensional, 1: 185 sample preparation, 1: 185 SDS-PAGE, 1: 186 staining, 1: 185–186 tris/glycine–SDS-PAGE, 1: 186, 1: 187f tris/tricine–SDS-PAGE, 1: 187, 1: 188f two-dimensional, 1: 189 urea–PAGE, 1: 188, 1: 189 see also Sodium dodecyl–sulfate polyacrylamide gel electrophoresis (SDS-PAGE) Polyamines, 1: 451, 1: 452t Polychlorinated biphenyls (PCBs), 1: 899 analysis, 1: 900 health impact, 1: 900 occurrence, 1: 900 sources, 1: 900 structure, 1: 899f Polychlorinated dibenzofurans (PCDFs), 1: 898, 1: 899f Polychlorinated dibenzo-p-dioxins (PCDDs), 1: 898, 1: 899f Polydextrose, as fat replacer, 1: 531 Polyethylene glycol (PEG)-based phases, fatty acid analysis, 3: 698–699, 3: 699f Polyethylene terephthalate (PET), 3: 277 Polyglycerol, 1: 67 Polyglycerol polyricinolate, 1: 66t Polylactic acid (PLA) packaging, 4: 22 biodegradability, 4: 635 ultrasonic sealing, 4: 22 Polymerase chain reaction (PCR), 1: 221 amplified fragment length polymorphisms, 1: 222 Arthrobacter, 4: 373 biogenic amine detection, 1: 455 bluetongue virus, 2: 150 Brucella, 2: 155, 4: 37 Campylobacter, 4: 42 cheese microbiological analysis, 1: 631 Clostridium, 4: 52 conventional, 1: 221 Coxiella burnetii, 4: 57 denaturing gradient gel electrophoresis, 1: 222 embryo sexing see Sexed offspring Enterobacter, 4: 77 enterobacterial repetitive intragenic consensus fingerprinting, 1: 222 Geotrichum candidum, 4: 770 immunomagnetic separation, 1: 221 isothermal, 1: 222 helicase-dependent amplification, 1: 223, 1: 223f nucleic acid sequence-based amplification, 1: 223 Kluyveromyces, 4: 759, 4: 759t LAB stress response, 3: 57–58 Lactobacillus, 3: 82 Listeria monocytogenes, 2: 184–185 milk bacteria determination, 3: 900 multiplex, 1: 221 Mycobacterium avium subsp. paratuberculosis, 2: 177 Penicillium roqueforti, 4: 773–774 Pseudomonas, 4: 383
928 Index Polymerase chain reaction (PCR) (continued ) randomly amplified polymorphic DNAs, 1: 222 real-time, 1: 221 repeated extragenic palindrome, 1: 222 restriction fragment length polymorphisms, 1: 222 Salmonella detection, 4: 93 Shigella, 4: 102 temperature gradient gel electrophoresis, 1: 222 toxic secondary metabolites, 4: 773–774 Yersinia enterocolitica, 4: 117, 4: 122 Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) cheese microbial fingerprinting, 1: 633 dominant species identification, 1: 636–637 Polymeric immunoglobulin receptor (PIGR), echidna milk, 3: 558–559 Polymerization, proteins, 1: 202 Polymorphonuclear neutrophils (PMNs) mastitis milk, 3: 896–897 milk composition effects, 3: 906 Polymyxin, 4: 51–52 Polynuclear model, crystal growth, 3: 189 Polyol (sugar alcohols), as prebiotics, 4: 358 Polyphosphates Clostridium spore control, 4: 53 pasteurized processed cheese products, 1: 811t Polysaccharides classification, 4: 355, 4: 356t as prebiotics, 4: 363 Polysorbate 60, 1: 66t Polysorbate 65, 1: 66t Polysorbate 80, 1: 66t Polystyrene, cream cheese packaging, 4: 20 Polytropic efficiency, air compressors, 4: 607 Polyunsaturated fatty acids (PUFAs) Aspergillus flavus growth inhibition, 4: 790 blood cholesterol levels, 3: 713, 3: 731 coronary heart disease risk, 3: 1024, 3: 1026, 3: 1027t, 3: 1029t equid milk, 3: 524t human milk, 3: 714 ‘liver X receptor’ signaling, 3: 1058 milk, soybean supplementation effects, 3: 658–659, 3: 659t primate milk, 3: 616 ruminant milk, 3: 479–480 Polyvinylidene fluoride (PVDF) ultrasound transducers, 1: 209–210 Ponded systems, 2: 18 Pongo pygmaeus see Orangutan ´ eque cheese, listeriosis outbreaks, 4: 83 Pont l’Evˆ Population dynamics, NSLAB, 1: 639, 1: 640f Porcine pepsin, 1: 576 PORI vectors, 3: 70–71 Portal-drained viscera (PDV), 3: 989–990 Positive-displacement compressors, 4: 602, 4: 603t Positive displacement pumps, 4: 145, 4: 147 energy costs, 4: 145–146 HTST pasteurizer, 3: 275–276 Postdischarge infant formulae (PDF), 2: 140t Posterior mammary artery, 3: 334 Postgraduate education/research, food technology, 2: 11 Posthitis (pizzle rot), 2: 795 Postmenopausal women bone density, 3: 1009 milk powder supplements, 3: 1014 Postpartum period energy balance-conception rate relationship, 4: 480, 4: 481f estrous behavior, 4: 464 Postprandial hyperaminoacidemia, 3: 818 Potassium, 2: 376 absorption, ruminants, 3: 998 amounts recovered for fertilizer, 3: 401, 3: 401t budgeting uses, 3: 402t, 3: 403 value calculation, 3: 403 bone density, 3: 1013
cheese, 3: 925, 3: 927t dairy feed ingredients, 2: 358t in dairy products, 3: 926t, 3: 926t, 3: 927t, 3: 1012t, 3: 1013 nutritional significance, 3: 927 deficiency humans, 3: 928 pastures, 2: 589 dry period rations, 2: 450 excess intake, 3: 928–929 excretion estimates, 3: 399, 3: 400t extracellular, 3: 927–928 grazing animal considerations, 2: 376 infant formula concentration, 3: 928–929 lactose interactions, 3: 917, 3: 918f magnesium absorption and, 2: 226, 2: 227t, 2: 374, 2: 375, 2: 376 maintenance requirements, 2: 376 marine mammal milk, 3: 579t, 3: 580 in milk, 3: 925, 3: 926t chemical form, 3: 908, 3: 926 heat stress effects, 4: 565 nutrient intake, contributions to, 3: 1006 nutritional significance, 3: 927 secretion, 3: 917 minimum requirements, adults, 3: 928 primate milk, 3: 627–629, 3: 628t ration requirements, 2: 376 reduction, dietary cation-anion difference, 2: 358 removal silage/hay, 2: 590 soil, 2: 587t, 2: 588–589 requirements, 2: 376 sequestered, anaerobic lagoons, 3: 401–402 in serum, 3: 919, 3: 920t sheep milk, 3: 500 soil, high levels, 2: 358 transition cows, pasture-based systems, 2: 467 warm season grasses, 2: 358 Potassium fertilizer, 2: 589 Potassium phosphate, 3: 184 Pot cheese see Cottage cheese Potentiometry, 1: 193 HPLC, 1: 174 Poultry industry, artificial insemination, 4: 473 Pourbaix diagram, 4: 258, 4: 259f pitting corrosion, 4: 260–261, 4: 261f Pour plate technique, 1: 216 Powder dispersion, agitators, 4: 165 Powdered infant formula (PIF), Cronobacter contamination, 4: 74 Powdered whipped toppings, 2: 915 Powder milk see Milk powder Powder recovery systems, milk powder spray drying, 2: 109, 2: 110f Powered skim milk see Skim milk powder (SMP) Power stations, 4: 610 Power supply, warm climate milking sheds, 2: 26 Prairie grass (Bromus willdenowii), 2: 576 Preacidification, cheese manufacture, 1: 537, 1: 550 Pr´ealpes du Sud sheep, 1: 332t Prebiotic-fortified milk, 3: 298 benefits, 3: 298–299 Prebiotics, 1: 412–413, 2: 133 carbohydrates gut microflora modulation, 4: 368 large intestine fermentation, 4: 367, 4: 367f nutritional values, 4: 368 short-chain fatty acid production, 4: 367, 4: 367f defining criteria, 3: 298–299 definition, 4: 354, 4: 365 effects, 4: 354 fate of, 4: 366f functions, 4: 365–371 future prospects, 4: 364, 4: 371 health benefits, 4: 366f historical aspects, 4: 365 immune modulation, 4: 370
lipid metabolism modulation, 4: 370 physiological effects, 4: 369 colon cancer prevention, 4: 369 mineral absorption stimulation, 4: 370 putrefaction reduction, 4: 369 stool frequency improvements, 4: 369 types, 4: 354–364 Precheese, 1: 539–540 ultrafiltration, 3: 868 Pre-cholecalciferol, 4: 647 Precision analytical methods, 3: 742 ELISA, 1: 178 Predator control, goats and sheep, 2: 841–847 policy issues, 2: 846 scale of organization, 2: 846, 2: 847 predation reduction management, 2: 843 confinement, 2: 843 early weaning, 2: 844 fencing, 2: 844 guard animals, 2: 843 herding, 2: 843 night confinement, 2: 843 predator removal methods, 2: 845 denning, 2: 846 hunting dogs, 2: 845 repellants and sterilants, 2: 846 shooting, 2: 845 snares, 2: 845 toxins, 2: 845 traps, 2: 845 predator species, 2: 841, 2: 842t attack methods, 2: 842–843 attack time, 2: 842–843 bears, 2: 842 serious loss causes, 2: 842 threat extent, 2: 841–842, 2: 843 threat impact, 2: 841, 2: 841–842 Predicted transmitting abilities (PTA), US scale, 2: 672, 2: 673t Prediction models, infrared spectrometry, 1: 121 Predictive cheese yield formula, 1: 547 ‘Preference mapping’, 1: 283 Pregastric esterases (PGEs), 2: 284 commercial preparations, 2: 284 enzyme-modified cheese, 1: 803 lipid digestion, 3: 711 Pregnancy, 4: 485–492 calcium requirements, 3: 996–997 characteristics, 4: 485–492 conceptus nutrition, 4: 487 diagnosis, 4: 489, 4: 492t direct methods, 4: 489 false negatives, 4: 491–492 false positives, 4: 491–492 heifers, 4: 414–415 indirect methods, 4: 490 strategy development, management considerations, 4: 491 timed artificial insemination, 4: 456–457 duration, 4: 503, 4: 504t calf weight effects, 4: 503, 4: 504t crossbreeding effects, 4: 503 modifying factors, 4: 503, 4: 504f embryonic membranes formation, 4: 486 failure, 4: 493, 4: 494f fetal development, 4: 487 fetal growth, 4: 514 follicular wave activity, 4: 434 free fatty acid changes, 2: 246–247, 2: 247f gluconeogenesis, 2: 247 glucose changes, 2: 247f immunology, 4: 501 mammary gland development, 3: 342 nonpregnancy detection, estrus return, 4: 489 physiology, 2: 769, 2: 770, 4: 493–502 placental function, 4: 499 preattachment development, 4: 486
Index preimplantation period, 4: 493, 4: 494f progesterone, 4: 498 rates see Pregnancy rates sheep, 2: 887 uterine enlargement, 4: 487, 4: 487f vitamin requirements, 4: 638 xanthine oxidoreductase expression, 2: 325–326 Pregnancy-associated glycoproteins (PAGs), 4: 500 assay development, 4: 491 pregnancy detection, 4: 490–491, 4: 491 heifers, 4: 414–415 Pregnancy disease see Pregnancy toxemia Pregnancy hormones, galactopoietic effects, 3: 30 Pregnancy rates, 4: 454 seasonal variations, 4: 572, 4: 572t timed insemination reproductive management system, 4: 455–456, 4: 456t Pregnancy-specific protein B, heifers, 4: 414–415 Pregnancy test, ideal, 4: 489 Pregnancy toxemia, 2: 246–249 clinical pathology, 2: 247 clinical signs, 2: 246 diagnosis, 2: 247 differential diagnosis, 2: 247–248 epidemiology, 2: 246 goats, 2: 789, 2: 794, 2: 800–801 hormonal treatments, 2: 249 necropsy, 2: 247 neurological signs, 2: 246 pathogenesis, 2: 246 prevention, 2: 248 feed supplements, 2: 248 prognosis, 2: 248 sheep, 2: 889 treatment, 2: 248 Pregnant mare’s serum gonadotropin (PMSG), ovine artificial estrous synchronization, 2: 890 Preimplantation stage embryo, 2: 611f Premating examination, dairy ewes, 2: 863 Premature infants, infant formulae, 2: 144 Premelanoidins, Maillard reaction, 3: 1068 Premiumizatin and indulgence, trends in, 1: 41–42 Prepartum period, heat stress, 4: 562 Prepressing vats, semihard cheese manufacture, 1: 612–613, 1: 614f Preservatives, 1: 36t bacteriocins, 1: 421 cheese analogues, 1: 815t cottage cheese manufacture, 1: 701 dulce de leche, 1: 875 European Union, 1: 36 United States, 1: 39 see also specific preservatives Preserved milk products, Codex standards, 4: 329 Pressure-activated heat mount detectors, 4: 477 Pressure-assisted thermal sterilization/processing (PATS/P), 2: 734 Pressure control valves, 4: 152 Pressure nozzle atomization, 4: 224, 4: 224f advantages, 4: 224 Pressure relief valves, 4: 157, 4: 158f Pressure-sensing radiotelemetric systems estrus detection, 4: 463, 4: 464f estrus duration, 4: 464, 4: 464t Pressure-sensitive patches, estrus detection, 4: 468 Pressure sensors, 4: 237 Presynch–Ovsynch protocol, 4: 455f, 4: 455–456 Price fixing, Africa, 2: 80 Primary hepatocellular carcinoma (HPC), aflatoxins, 4: 805 Primary parasitic pneumonia, 2: 270 Primary sprout, 3: 341–342 Primary stocks, starter cultures, 1: 557 Primate(s) encephalization quotient, 3: 614 lactation length, 3: 321 phylogenetic tree, 3: 614f
Primate milk, 3: 613–631 body weight effects, 3: 613–614 casein:whey protein ratio, 3: 621 composition, 3: 539t dietary influences, 3: 613 fatty acids, 3: 616, 3: 619t, 3: 629–630 n–6 to n–3 fatty acids ratio, 3: 616–621, 3: 619t profile, 3: 544, 3: 545t stereospecific positions, 3: 616 free amino acids, 3: 627t gross composition, 3: 613, 3: 615t immunoglobulins, 3: 624 indigenous enzymes, 3: 629 information lack, 3: 613 lactoferrin, 3: 625 lactose, 3: 613–614, 3: 615 lipids, 3: 615t, 3: 616 milk fat globule membrane, 3: 621 milk salts, 3: 627, 3: 628t nursing style, 3: 613–614 oligosaccharide:lactose ratio, 3: 615–616 oligosaccharides, 3: 615–616, 3: 617t proteins, 3: 542, 3: 621, 3: 622t, 3: 624f future prospects, 3: 629–630 gross energy from, 3: 614, 3: 616t interspecies comparison, 3: 542 saccharides, 3: 615 species studied, 3: 613 total amino acids, 3: 625, 3: 626t vitamins, 3: 629, 3: 630t see also individual species Primates order, 3: 613 Primordial follicles, 4: 428–429 Principal component regression (PCR) multivariate statistical tools, 1: 94t, 1: 103 time varying state space modeling, 4: 246 Principal component analysis (PCA), 4: 244 hyperspectral imaging, 1: 127–128 multivariate statistical tools, 1: 94t, 1: 98t, 1: 99, 1: 101 Priopionate, 2: 234 Probiotic dairy foods, packaging, 4: 21 Probiotic fermented milk, 2: 473 Probiotic milk products, US standards, 3: 278 Probiotics, 1: 412–419, 2: 133, 2: 483–488, 2: 513–514, 2: 514f analytical methods, 1: 218 anticariogenic properties, 2: 486, 2: 523, 3: 1037 applications, 1: 412–419 buffering capacity, 1: 416t buttermilk products, 2: 494 Candida albicans control, 3: 1040 colon cancer prevention, 3: 1019 concepts, 1: 414 definition, 3: 93, 3: 115 definitions, 1: 412, 1: 414, 3: 1037 efficacy, 1: 415, 1: 416t, 1: 416t fluoride and, anticariogenic properties, 3: 1038 frozen yogurt, 2: 897 future prospects, 1: 418 gastrointestinal tract transit kinetics, 1: 414–415 generally regarded as safe status, 1: 417 health benefits, 3: 1037 historical aspects, 1: 413, 4: 365 hypertension lowering, 2: 486, 2: 487f immunological function effects, 1: 415, 2: 488 intestinal health control, 2: 485, 2: 523, 3: 115–116 kefir health benefits, 2: 522 labeling issues, 1: 417 mechanism of action, 1: 415, 1: 416t nutritional function, 2: 483 lactose intolerance alleviation, 2: 484, 2: 524 mineral absorption enhancement, 2: 484 protein digestibility improvement, 2: 483, 3: 116 opportunistic infections, 1: 417 physiological effects, 2: 485 Propionibacterium, 1: 409 safety, 1: 417
929
recommendations, 1: 418t selection criteria, 1: 414t serum cholesterol, lowering, 2: 485, 2: 524, 3: 115–116 significance, 3: 93, 3: 115 species used, 1: 415, 1: 415t strain properties, 1: 416t, 1: 417 strain selection, 1: 414, 1: 414t supporter strains, 1: 415 technological properties, 1: 415 see also Prebiotics Problem solving, 1: 485 Proboscidea, 3: 573t Procaine penicillin, 2: 171 Process analytical technologies (PATs), 4: 273 Process cheese, 1: 841 Process control, 4: 242–251 automation level, 4: 127 design, 4: 127 enzyme-modified cheese, 1: 801 safety and hazard evaluation, 4: 131 Process design, 4: 124–133 energy balance, 4: 125 mass balance, 4: 125 Processed cheese agitation, 4: 165 Codex standards, 1: 844–845 historical aspects, 1: 14 milk protein concentrate, 3: 852 perceived additives, 1: 46f products, 1: 540 UK legislation, 1: 847 Processed euchema seaweed (PES), 1: 36 Processed milk products, heat damage indicators, 3: 1069 Process engineering improvements, 4: 266 control factors, 4: 266 data analysis crucial factor identification, 4: 268 improved performance settings identification, 4: 268 experimental design, 4: 266 general approach, 4: 266 process data, 4: 266 stepwise approach, 4: 267 Process flow sheet, 4: 125, 4: 125f Process Hazards Analysis (PHA), 4: 277–278 creating ‘nodes’, 4: 278 steps, 4: 277–278 types, 4: 278 Processing adjustment factor (PAF), 2: 338 Processing aids, additives vs., 1: 50 Processing equipment construction materials, 4: 134–138 metals, 4: 136 product contact surfaces, 4: 134–135 toxicity, 4: 134–135 hygienic design, 4: 134 surface finishes, 4: 137 Processing plant see Dairy plant(s) ‘Process intelligence’, 4: 274–275 Process optimization, 4: 131, 4: 264 see also Continuous process improvement Process sensors, 1: 93 Process viscometers, 4: 237 Producer support estimate (PSE), 4: 287, 4: 306, 4: 307f Australia, 4: 307f, 4: 309–310 Canada, 4: 306, 4: 307f Japan, 4: 308 New Zealand, 4: 307f, 4: 310 Production business management, 1: 481 education see Dairy production education management records see Management records Production medicine, 1: 8 Product lauches see New product launches Product residues, wastewater, 4: 613
930 Index Product sectors, consumer perceptions, 1: 44, 1: 46f, 1: 46t Proestrus, 4: 411 Profitability measures, 1: 488 Progeny testing, 4: 470 Chinese dairy management, 2: 84 Progesterone estrous cycle, 4: 431, 4: 431 galactopoietic effects, 3: 30 gestation end, 4: 507 heat stress, 4: 568–569, 4: 569f inadequate secretion, infertility, 4: 499 induced lactation, 3: 20 plasma levels, 3: 20–21 interferon- relationship, 4: 480 lactogenesis, 3: 18 LH inhibition, 4: 423 liver blood flow, 4: 480 mammary gland development, 3: 340–341 in milk, 2: 770 estrus detection, 4: 468 induced lactation, 3: 23 nonpregnancy indicator, 4: 491 milk protein synthesis, 3: 362 placental secretion, 4: 498 post insemination, embryo survival rate, 4: 479, 4: 480f pregnancy, 4: 498 pregnancy detection, 4: 490–491 goat, 2: 839t, 2: 839–840 sheep, 2: 891–892 preinsemination, embryo survival rate, 4: 479, 4: 479f uterine endometrial lining gene expression, 4: 498–499 uterine immune function regulation, 4: 501–502 Progesterone ‘block’, 4: 507–508 Progesterone ELISA pregnancy testing, 2: 95 Progesterone implants, ovarian follicular cysts, 4: 438–439 Progesterone inserts, heifers, 4: 413, 4: 414f Progesterone-releasing intravaginal device (PRID), heifers, 4: 413 Progesterone ‘withdrawal’, 4: 505–507 Progestins, heifers, 4: 413 Progestogen(s) application devices, 4: 449 estrus synchronization, 4: 448 estrogen and, 4: 451, 4: 451f, 4: 452 goats, 2: 835 gonadotropin-releasing hormone and, 4: 451f, 4: 452 long-term treatment, 4: 451 noncyclic cow treatment, 4: 452 prostaglandin and, 4: 449–450, 4: 450t, 4: 451, 4: 451f, 4: 452 sheep, 2: 890 Programmable logic controllers (PLC), 4: 238, 4: 242 Progressing cavity pumps, 4: 149, 4: 150f selection criteria, 4: 151t Prolactin camel, seasonal breeding, 4: 446 galactopoietic effects, 3: 28 heat stress, 4: 565 hypophysectomized goats, 3: 27f, 3: 28 induced lactation, plasma levels, 3: 20–21 insulin-like growth factor-I interactions, 3: 29 lactational persistence promotion, 3: 29, 3: 29f lactogenesis, 3: 17, 3: 17 mammary apoptosis, 3: 29 mammogenic effects, 3: 341 milk protein synthesis, 3: 362–363 secondary seasonal characteristics, 4: 443 triiodothyronine interactions, 3: 27 Prolactin receptors, 3: 28 Prolidase (PepQ), 3: 87 Prolinase (PepR), 3: 87 Proline iminopeptidase (PepI), 3: 87
Proline-specific peptidases, actic acid bacteria, 3: 87 Pronuclear microinjection, 2: 637 Proosdij cheese, 1: 726 Propane, safety risks, 4: 277 Propeller agitators, 4: 160, 4: 161f Property classification, food texture, 1: 264, 1: 265t Propionate, 4: 368 Propionibacterium, 1: 403–411 antimicrobial activity, 1: 409 applications cheese flavor, 1: 408 cheese ripening, 1: 403 Emmental cheese ripening, 1: 407 nutraceutical production, 1: 409 occurrence in dairy products, 1: 407 bacteriocin production, 1: 409 characteristics, 1: 404t cheese ripening, 1: 571 aminopeptidase, 1: 571 proteinases, 1: 571 Swiss-type cheeses, 1: 571 cheese salting, 1: 596 classification, 1: 403 envelope capsular polysaccharides, 1: 403 envelope composition, 1: 403 capsular polysaccharides, 1: 403 cell lipids, 1: 403 peptidoglycans, 1: 403 esterolysis, 1: 571 fermentation starters, 3: 455 genetics, 1: 404 cloning shuttle vectors, 1: 405, 1: 405t as expression vectors, 1: 405 genome size, 1: 404 site mutagenesis, 1: 405 transformation efficiency, 1: 404–405 genome size, 1: 404 growth conditions, 1: 404 organic nitrogen sources, 1: 404 yeast extract–peptone–lactate (yel) media, 1: 404 identification, 1: 403 isolation, 1: 404 LAB interactions, 1: 408 lipolysis, 1: 571 metabolism, 1: 406 end products, 1: 406 metabolic pathways, 1: 406, 1: 406f substrates, 1: 406 Wood–Werkman (WW) cycle, 1: 406, 1: 406f, 1: 406–407 morphology, 1: 403 organic nitrogen sources, 1: 404 probiotics, 1: 409 raw milk cheeses, 1: 658 as spoilage microorganisms, 3: 454 stress adaptations, 1: 407 acid stress, 1: 407 bile salts, 1: 407 heat stress, 1: 407 osmotic stress, 1: 407 Swiss-type cheese ripening, 1: 715, 1: 716–717 transformation efficiency, 1: 404–405 see also individual species Propionibacterium acidipropionici, 1: 403 characteristics, 1: 404t starter cultures, 1: 560t Propionibacterium cyclohexanicum, 1: 403, 1: 404t Propionibacterium freudenreichii, 1: 403 characteristics, 1: 404t eye formation, 1: 627 overexpression vectors, 1: 405t Swiss-cheese starter culture, 1: 713–714 Swiss-type cheeses, 1: 407, 1: 408 Propionibacterium freudenreichii subsp. shermanii, 1: 560t Propionibacterium jensenii, 1: 403, 1: 404t Propionibacterium microaerophilium, 1: 403, 1: 404t Propionibacterium thoenii, 1: 403, 1: 404t
Propionic acid Lactobacillus, 3: 128 Propionibacterium pathways, 1: 406 Swiss-type cheeses, 1: 408 The Propionic Acid Bacteria, 1: 30–31 Propionic acid bacteria (PAB) cheese microbiology, 1: 627 cheese ripening, 1: 627 discovery, 1: 30 gas blowing defects, 1: 665 Swiss-type cheeses, 1: 713 see also individual species Propionicin F, 1: 410t Propionicin PLG-1, 1: 410t Propionicin SM-1, 1: 410t Propionicin SM-2, 1: 410t Propionicin T-1, 1: 410t Propolis ethanolic extract (PEE), 4: 789 Propylene glycol fatty liver, 2: 221 ketosis, 2: 237 Propylene glycol alginate (PGA), 1: 36 Propylene glycol monostearate, 1: 67 Prostaglandin(s) as contaminant, 1: 894 estrus synchronization, 4: 449, 4: 449f conception rate, 4: 450 double treatment program, 4: 449, 4: 449f estrogen and, 4: 451f, 4: 452 estrus cycle stage, 4: 449–450, 4: 450t goats, 2: 835 gonadotropin-releasing hormone and, 4: 451f, 4: 452, 4: 452 noncyclic cow treatment, 4: 452 progesterone and, 4: 451, 4: 451f, 4: 452 progesterone supplement, 4: 449–450, 4: 450t response rate, 4: 449–450, 4: 450t luteolysis, 4: 496, 4: 496f Prostaglandin E2 (PGE2) embryonic synthesis, 4: 494–495 fetal HPA axis maturation, 4: 505 Prostaglandin endoperoxide H synthase-2 (PGHS-2), 4: 505 Prostaglandin F2 (PGF2) corpus luteum luteolysis, 4: 431–432, 4: 432f estrous cycle, 4: 431–432 estrus synchronization gonadotropin-releasing hormone and, 4: 413, 4: 414f heifers, 4: 413, 4: 414f Ovsynch procedure, 4: 454 Presynch–Ovsynch protocol, 4: 455f, 4: 455–456 Proteases, bacterial, 3: 49–55 Protected designation of origin (PDO), 1: 845–846 Italian recognition, 1: 849 raw milk cheeses, 1: 653, 1: 654f Protected fat supplements, 2: 363–370 ‘Protected fat’ supplements, 3: 659, 3: 659t Protection of Animals Act, UK, 4: 727 Protection of geographical indications (PGI), 1: 845–846 Protein(s) biosensors, 1: 243 blood cholesterol levels, 3: 731 cheese analogues, 1: 815 content cheese rheology, 1: 696, 1: 696f cheese salting, 1: 603 crude see Crude protein (CP) damage analysis, MS, 1: 201 degradation biosensors, 1: 243 starter cultures, 1: 562, 1: 563f dietary digestion, ruminants vs. nonruminants, 3: 361 fractionation, 2: 410 digestion, 3: 993 as emulsifiers, 1: 64
Index first-age infant formulae, 2: 137 fractionation, whey recovery processes, 2: 128 gluconeogenic potentials, 2: 234 growing heifers, 4: 393 immunochemical detection see Immunochemical assays infant formulae, 2: 136 intake laminitis, 2: 203–204 muscle mass, 3: 1013 renal calcium excretion, 3: 1013 reproductive efficiency, 4: 578 ion-exchange chromatography, 1: 170, 1: 171f isoelectric point, 3: 844 mass spectroscopy (MS), 1: 172 microstructure, 1: 229f, 1: 232 milk see Milk protein(s) milk chocolate, 1: 858 modification, MS see Mass spectrometry (MS) MS see Mass spectrometry (MS) net charge, 3: 844 NMR relaxation studies, 1: 155 ration formulation programs dry lot systems, 2: 461 guidelines, 2: 463 reversed-phase HPLC, 1: 172, 1: 172f rumen fermentation, 3: 993 ruminant metabolism, 2: 420 components, 2: 421f requirement calculation systems, 2: 421, 2: 422t, 2: 424f, 2: 424f sources, 2: 389 supply, 2: 389 SDS-PAGE, 1: 186–187, 1: 187f sources characterization, 2: 414 high in ruminally degraded proteins, 2: 414 high in RUP, 2: 414 lactation performance, 2: 414t, 2: 415t, 2: 416 RUP supplementation, 2: 416 protein fraction flow to small intestine, 2: 414, 2: 415t standardization by ultrafiltration of milk, 3: 308 structure ‘New View’, 3: 767–768 NMR T2 (spin–spin relaxation), 1: 157 supplementation, pasture-based systems, 2: 456 synthesis, 3: 360, 3: 360f, 3: 965 see also specific proteins Protein A (Spa), 4: 105 Proteinases, 2: 289–296 accelerated cheese ripening, 1: 796 cheese processing, 2: 291 classification, 2: 289, 2: 290t dairy industry applications, 2: 291 definition, 2: 289 entrapped, accelerated cheese ripening, 1: 796 enzyme-modified cheese see Enzyme-modified cheese exogenous, 2: 289–296 extracellular Brevibacterium linens, 1: 570 Geotrichum candidum, 1: 568 indigenous to milk, cheese ripening, 1: 670 molds, 1: 628 propionibacteria, 1: 571 sheep milk, 3: 500 sources, 2: 289, 2: 290t animal, 2: 289 microbial, 2: 290 plants, 2: 290 see also specific types Protein digestibility corrected amino acid score (PDCAAS), 3: 817, 3: 817t Protein dispersibility index (PDI), soybeans, 2: 352 Protein-enriched milk, 3: 298 Protein fractionation robot, 3: 763 Protein-free diet, 3: 816
Protein hydrolysis, 1: 262, 1: 262f infant formulae, 2: 143 Protein kinase C modulation, vitamin E, 4: 657 Protein-losing enteropathy, Johne’s disease, 2: 176 Proteins, milk see Milk protein(s) Protein-to-fat ratio (PFR), milk, seasonal variations, 3: 600, 3: 600f Protein-type fat replacers, 2: 896 Proteolysis blue mold cheeses see Blue mold cheeses Canestrato Pugliese cheese see Canestrato Pugliese cheese Castelmagno cheese see Castelmagno cheese Cheddar cheese ripening, 1: 708 cheese ripening see Cheese ripening Dutch-type cheeses, 1: 724 enzyme-modified cheese, 1: 802 enzyme-modified cheese flavor, 1: 802 Fossa cheese see Fossa cheese hard Italian cheeses see Hard Italian cheeses khoa, 1: 884 milk see Milk proteolysis Parmigiano Reggiano cheese see Parmigiano Reggiano cheese pasta-filata cheeses, 1: 749–751 Penicillium camemberti, 1: 569 Penicillium roqueforti, 1: 569, 4: 772 raw milk cheeses, 1: 656, 1: 657t surface mold-ripened cheese ripening, 1: 777 UHT-sterilized milk age gelation, 3: 292 Proteolytic enzymes, biogenic amines, 1: 454 Proteolytic microorganisms, analytical methods, 1: 218 Proteolytic starters, Cheddar cheese ripening, 1: 709 Proteolytic systems, lactic acid bacteria see Lactic acid bacteria (LAB) Proteome, 3: 843, 3: 1057 Proteomic analysis definition, 3: 843 fatty liver, 2: 222–223 Proteomics, 3: 843–847 definition, 3: 843, 3: 1057 future developments, 3: 847 gel-free, 3: 843 LAB stress response, 3: 58 milk, 3: 843 nutritional research advancement, 3: 1058 see also individual techniques Proteose-peptone (PP), buffalo milk, 3: 504 Proteose peptone 3, 3: 796t, 3: 798 Proteus, 3: 451 Proton transfer reactions (PTRs), 1: 676, 1: 679 Protoplasts(spheroplasts), 2: 291 Prototheria, 3: 460 Protozoa, ruminal, 3: 980 Protozoal metabolism, modeling, 2: 431 Provenance, new product launches, 1: 42 Provisional tolerable monthly intake (PTMI), dioxins, 1: 899 Provitamin A see -Carotene Provolone cheese, 1: 771t Provolone del Monaco, 1: 747 ripening, 1: 748 Provolone Valpadana, 1: 747 manufacture, 1: 747 related varieties, 1: 747 PR toxin, 1: 904t Penicillium roqueforti, 4: 774 Przewalski’s horse (Equus ferus przewalski), 3: 327 P-selectin, 3: 256–257 Pseudomonas, 4: 379–383 autoinducer production, 4: 381–382 biofilms, 1: 446, 4: 380 characteristics, 4: 379 commercially pasteurized nonaseptically packed milk, 4: 387 control, 4: 382 in dairy products, 4: 382
931
enumeration, 4: 382 Gram-negative bacteria interference, 4: 383 media, 4: 383 extracellular enzymes, 4: 380–381, 4: 381 growth phase and, 4: 381–382 quorum sensing, 4: 381 regulation, 4: 381 flavor defects, 4: 387 growth, refrigeration temperatures, 2: 695, 4: 384, 4: 385t HTST pasteurization, 4: 384 lipases, 4: 381 thermostability, 4: 381 mastitis, 3: 419 in milk, 4: 382 proteolytic activity, 4: 380–381 milk fat globule membrane damage, 4: 388 morphology, 4: 379 phospholipases, 4: 381 proteases, 4: 381 heat-stability, 3: 645–646 raw milk, growth in, 4: 380 sources in milk, 4: 379 collection time and, 4: 379 milking equipment contamination, 4: 379 postpasteurization contamination, 4: 380 processing facility storage, 4: 379 processing plant contamination, 4: 380 storage equipment contamination, 4: 379 transportation-related contamination, 4: 379 Pseudomonas aeruginosa, 4: 383 pigment production, 4: 383 pyoverdin production, 4: 383 Pseudomonas fluorescens, 4: 379 lipases, 2: 287, 4: 381 lipolysis, 3: 723 proteases, 4: 381 heat-stability, 3: 645–646 Pseudomonas fragi, 4: 380 Pseudomonas lundensis, 4: 380 Psorergatic mange clinical signs, 2: 251 epidemiology, 2: 250 treatment, 2: 252 Psoroptic mange clinical signs, 2: 250 epidemiology, 2: 250 treatment, 2: 252 P (practice) starters, 1: 440–441 Psychological stress, 4: 575 Psychrometric (humidity) chart, 4: 210, 4: 211f Psychrophiles, historical aspects, 1: 27 Psychrotrophs, 4: 384–389 biotyping, 4: 384 commercially pasteurized nonaseptically packed milk, 4: 387 enumeration, 4: 384 enzymes, 4: 387 post-sterilization survival, 2: 714 extended shelf-life dairy products, 4: 388 flavor defects, 4: 385t, 4: 387 generation time, 4: 385t growth patterns, 4: 379–380 refrigeration temperatures, 4: 384, 4: 385t, 4: 386t heat stable proteases, 3: 645–646 historical aspects, 1: 27 isolation frequency, dairy products, 4: 385t lipolytic activity, 4: 387–388, 4: 388t pasteurization survivors, 4: 386, 4: 387t pasteurized milk, 4: 386 pathogens, 4: 385 phospholipases, 4: 388, 4: 388t postpasteurization contamination, 2: 539, 4: 386, 4: 386t prepasteurization contaminants, 2: 541 product defects, 4: 387 proteolytic activity, 4: 387–388, 4: 388t
932 Index Psychrotrophs (continued ) raw milk, 3: 645–646, 4: 386 spoilage potential, 3: 452, 4: 385t, 4: 386 stored milk, 3: 646 thermization control, 2: 693, 2: 695, 2: 695 thermoduric, 4: 388 see also Spoilage microorganisms; individual species PT (ptaquiloside), bracken fern toxin, 1: 905 Ptaquiloside (PT), bracken fern toxin, 1: 905 PTMP-1, marsupial milk, 3: 558 PTMP-2-GlyCAM, marsupial milk, 3: 558 PTRs (proton transfer reactions), cheese flavor assessment, 1: 676, 1: 679 Puberty, 4: 421–427 age at, heifers, 4: 410 annual, seasonal breeders, 4: 442–443 average age, 4: 421, 4: 422t buffalo, Asia, 2: 773 characteristics, 4: 421 definition, 4: 421 as economic trait, 4: 421–422 importance, 4: 421 onset, 4: 421, 4: 428 growth rate and, 4: 425 nutrition and, 4: 426, 4: 426f theory of, 4: 425, 4: 425f timing, 4: 425 reproductive endocrinology, female, 4: 422 seasonal effects, 4: 426 cattle, 4: 426 seasonal breeders, 4: 426 sheep, 2: 887, 4: 426 seasonal effects, 4: 426 silent ovulation, 4: 428 Public health aspects, cheese, 1: 645–651 biogenic amines, 1: 651 Enterobacter aerogenes, 1: 648, 1: 649f enterococci, 1: 648, 1: 648f, 1: 649 Hafnia alvei, 1: 648, 1: 649f hard cheese, 1: 648, 1: 648f infective dose, 1: 645 Listeria monocytogenes, 1: 648, 1: 648–649, 1: 649f, 1: 650 growth profile, 1: 646, 1: 646f pathogen control, 1: 649 pathogen growth in manufacture, 1: 645 in ripening, 1: 646 pathogenic Escherichia coli, 1: 648, 1: 648, 1: 648f, 1: 648–649, 1: 649f, 1: 650 growth profile, 1: 646f pathogen source, 1: 645 raw milk cheese, 1: 645–646, 1: 648 Salmonella, 1: 648, 1: 648f, 1: 651 semihard cheese, 1: 648, 1: 648f semisoft cheese, 1: 648, 1: 649f soft cheese, 1: 648, 1: 649f Staphylococcus aureus, 1: 645, 1: 648, 1: 648f, 1: 648–649, 1: 650 growth profile, 1: 646f Public health concerns bovine tuberculosis, 2: 197 cardiovascular disease and milk fatty acids, 3: 609 cheese see Public health aspects, cheese consumer attitudes, milk consumption demand history, 3: 607 health risk claims, 3: 609 processing issues, 3: 611 production issues, 3: 611 drug residues in dairy products, 2: 802 food labeling claims, regulation, 3: 7 hormone effects, dairy consumption, 2: 765 adverse steroid effect claims, 2: 768 growth factor consumption, 2: 768 survey data quality, 2: 765–766 Maillard product detrimental effects lysine, loss of nutritional availability, 3: 228 toxicity, 3: 231
zinc retention, 3: 230–231 pasteurization see Pasteurization Puddings, 2: 906 Puerperal metritis see Metritis Puerperium abnormalities, postpartum reproduction, 4: 437, 4: 437t Puff pastry, 2: 130 Pulsation, 3: 945 Pulsators, 3: 949 alternating pulsation, 3: 949 historical aspects, 3: 943–944 ratio, 3: 948f, 3: 949 simultaneous pulsation, 3: 949 waveform, 3: 949f, 3: 949–950 Pulsed amperometric detection (PAD), ion-exchange chromatography, 1: 171 Pulsed electric field (PEF) technologies, 2: 738–743, 3: 286 bactericidal effects, 2: 738 bacterial endospores, 2: 739 damage factors, vegetative microorganisms, 2: 739 benefits, 2: 738 dairy processing applications, 2: 740 sensory and nutritional quality effects, 2: 741 dairy product shelf life, 2: 740 enzymes, effects on, 2: 740, 2: 740t suggested mechanisms, 2: 740 equipment, 2: 726, 2: 738 electric pulse parameters, 2: 739 extended shelf life milk, 2: 738, 2: 740, 3: 286 milk pasteurization, 3: 279 potential, 2: 738 related technologies, 2: 738 see also Ultrasonication Pulsed energy technologies, 2: 708, 2: 738–743, 2: 730 high-intensity light, 2: 730 Pulsed field gel electrophoresis (PFGE), 1: 223, 1: 224f Bifidobacterium taxonomy, 1: 382 Coxiella burnetii, 4: 54 Enterobacter, 4: 77–79 Enterococcus, 3: 159 Kluyveromyces, chromosomal profiles, 4: 757f, 4: 757–758 Lactococcus lactis identification, 3: 134 Salmonella detection, 4: 93 Pulsed field gradient NMR (PFG NMR), 1: 155 droplet size in emulsions, 1: 163–164 Pulse-echo ultrasound, 1: 210, 1: 210f Pulse rate, 3: 949 Pulse repetition frequency (PRF), ultrasound, 1: 210 Pumps, 4: 145–151 calculation principles, 4: 139–144 classification, 4: 145 cost calculation, 4: 143 definition, 4: 145 efficiency calculations, 4: 143 energy cost calculation, 4: 143 issues, 4: 145 net positive suction head see Net positive suction head (NPSH) power calculation, 4: 143 requirement calculation, 4: 143 selection, 4: 126, 4: 145 selection criteria, 4: 150, 4: 151t types, 4: 126 see also individual types Pure-Lac system, 4: 389 Purines, 3: 994 Pusillus coagulant (Rhizomucor pusillus proteinase), 1: 576, 1: 576 Putrescine, 1: 451, 1: 452t PVDF (polyvinylidene fluoride) ultrasound transducers, 1: 209–210 PVS tool, OIE, 4: 6 Pyridazinone herbicides, 4: 790 Pyridoxal (PL), 4: 697, 4: 698f
see also Vitamin B6 Pyridoxal-59-phosphate (PLP), 4: 697 structure, 4: 697, 4: 698f Pyridoxamine (PM), 4: 697, 4: 698f see also Vitamin B6 Pyridoxamine-59-phosphate (PMP), 4: 697, 4: 698f Pyridoxine (PN), 4: 697, 4: 698f toxicity, 4: 699 see also Vitamin B6 Pyrolysis mass spectrometry, cheese flavor, 1: 680 Pyrophosphates, 1: 811t Pyruvate Propionibacterium pathways, 1: 406 rumen fermentation, 3: 982 starter cultures, 1: 553 Pyruvate formate lyase, 1: 561–562
Q QDA see Quantitative Descriptive Analysis (QDA) Q fever animals, 4: 55 diagnosis, 4: 57 humans acute, 4: 55 chronic, 4: 55 hygiene management measures, 4: 58 outbreaks, 4: 58 prevention, 4: 57 symptoms, 4: 55 treatment, 4: 57 vaccines, 4: 57 see also Coxiella burnetii Q fever fatigue syndrome, 4: 55 Quadrupole time-of-flight (Q-TOF), mass spectrometry, 1: 198 Quality by design (QbD) see Quality engineering Quality control, 4: 265 Quality control standards, 2: 680, 2: 680t Good Practice codes (GXP), 2: 680 hazard analysis and critical control points (HACCP) concept, 2: 680 International Standardization Organization (ISO) systems, 2: 680 total quality management (TQM), 2: 680 Quality control systems conventional, 4: 273 variability sources, 4: 273 Quality engineering, 4: 273–276 achievement, 4: 273 definitions, 4: 273 Quality scoring, sensory evaluation see Sensory evaluation Quantitative Descriptive Analysis (QDA) cheese flavor assessment, 1: 675–676 descriptive sensory evaluation, 1: 281 multivariate statistical tools, 1: 94t Quantitative enzyme-linked immunosorbent assay, 1: 178 Quantitative flavor profiling, 1: 281 Quantitative genetics, 3: 968–969 Quantitative ingredient declaration (QUID), 3: 5 Quantitative polymerase chain reaction, biogenic amines, 1: 455–456 Quantitative Risk Assessment (QRA), 4: 279 Quantitative trait loci (QTLs) genetic selection, 2: 654 whole-genome association studies, 2: 664–665 Quarantine goats, 2: 799 listeriosis, 2: 188 new arrivals, 4: 418–419 procedures, 2: 799–800 sheep, 2: 860, 2: 861t Quarg, 1: 703 citrate metabolism, 3: 86 composition, 1: 700t equipment, 1: 703
Index flavor, 1: 703 manufacture, 1: 698, 1: 703 properties, 1: 703 types, 1: 703 Quargel cheese, 1: 756 Quark manufacture mechanization, 1: 615 ultrafiltration, 1: 622 spoilage prevention, 2: 697, 2: 697, 2: 697t ultrafiltration, 1: 622 Quarter samples, Staphylococcus aureus incidence, 4: 114 QuEChERS contaminant hormone analysis, 1: 894–895 pesticide contaminant analysis, 1: 891 Quercitins, goats, 2: 63, 2: 64t Queshta mosakhana, 2: 783 Queso Blanco cheese, 1: 700t, 1: 704 Quiescin-sulfhydryl oxidases (QSOx), 2: 330 Quinolones, Q fever, 4: 57 Quishada, 2: 783 Q-Vax, 4: 57
R Rabbit plasma fibrinogen agar (RPFA), 4: 113 Raclette, 1: 787 surface yeasts, 4: 751 Radial compressors, 4: 604, 4: 604f Radiation heat loss, 4: 550–551 heat transfer, 4: 184 Radioallergosorbent test (RAST), milk allergy, 3: 1042 Radiofrequency identification devices, 2: 649 Radioimmunoassays (RIAs), 1: 178 HPLC, 1: 174 pregnancy-associated glycoproteins, 4: 491 pregnancy detection, 4: 490 Radionuclide contaminants, 1: 901 analysis, 1: 903 health impact, 1: 902 occurrence, 1: 901 partitioning, 1: 902 sources, 1: 901 see also specific radionuclides (Radio-) protein-binding assays (RPBAs), folate analysis, 4: 680 Radiotelemetric devices, heat detection, 4: 478 Raffinose atopic dermatitis, 4: 370 as prebiotic, 4: 361t, 4: 362 structural features, 4: 359t Ragusano, 1: 746 manufacture, 1: 746 ripening, 1: 749–751 Raha, 2: 783 Rahmfrischk¨ase, 1: 701 Ram(s) bluetongue, 2: 150 brucellosis, 2: 154 health-care, 2: 864 infertility, 2: 857 lameness, 2: 864 nutritional status, reproductive effects, 2: 889 premating examination, 2: 864 quarantine, purchased/borrowed animals, 2: 864 reproductive activity seasonality, 2: 889 vaccinations, 2: 862t, 2: 864 see also Sheep Raman spectroscopy, 1: 112, 1: 123 Ram effect, 4: 441–442 Randomized controlled trials (RCT), saturated fatty acid-coronary heart disease relationship, 3: 1026, 3: 1030t Randomly amplified polymorphic DNAs (RAPDs) cheese microbiological analysis, 1: 631 PCR, 1: 222
Penicillium roqueforti, 4: 773–774 Rangifer tarandus see Reindeer Ranking tests, discrimination testing, 1: 280–281 Rannie Liquid Whirling valve, 2: 753, 2: 753f Raoult’s law, 3: 473, 4: 707 RAPDs see Randomly amplified polymorphic DNAs (RAPDs) Rape (Brassica napus var. napus), 2: 560 Rapeseed lecithin, 1: 66t Rapid cooling tunnel, Cheddar manufacture, 1: 611, 1: 614f Rapid exit parlors, 1: 6 Rashaida camels, 1: 352 Rate:state formalism, 2: 429–430 Rath cattle, 1: 301t, 1: 302 Ration formulation programs cold stress, 4: 552 computerization, 1: 9 Rat milk oligosaccharides, 3: 271t Raw milk, 3: 611 biofilms, 1: 446 bioterrorism, 3: 647 Campylobacter outbreaks, 4: 44 cheeses see Raw milk cheeses composition, mastitis effects, 3: 902, 3: 903t consumption, disease outbreaks, 3: 311 dairy farm to processing plant flow, 3: 642, 3: 643f definition, 1: 652 E. coli outbreaks, 4: 61 Emmental cheese manufacture, 1: 712 fat globules, 3: 691 fat measurement, 3: 645 flavors, 3: 644 freezing point tests, 3: 644 handling, 3: 642 homogenization, lipolysis, 3: 722 induced lipolysis, 2: 306 listeriosis outbreaks, 4: 82–83 maximum holding time, 3: 645–646 microbiology, 3: 645, 3: 895t Gram-negative pathogens, 3: 646 Gram-positive pathogens, 3: 646 milk powder, 2: 110–111 odors, 3: 644 off-flavors, 3: 644, 3: 644t off-odor checks, 3: 644 pathogens, 1: 645 pathogens of concern, 3: 312 pre-World War II, 3: 312 protein content measurement, 3: 645 psychrotrophs, 4: 386 purchase, 4: 96–97 Q fever, 4: 56 quality, 3: 642 historical aspects, 1: 26 Salmonella, 4: 93 salmonellosis, 4: 68 prevention measures, 4: 96 spore-forming bacteria, 3: 646–647 removal, 4: 172 taste, 3: 644 temperature measurement, 3: 642 testing, 3: 642 post-unloading/troubleshooting tests, 3: 642, 3: 644t prior to unloading, 3: 642, 3: 643t see also individual tests total solid content measurement, 3: 645 transport, 3: 642 yaks, 1: 348 yeast contamination, 4: 744 Raw milk cheeses, 1: 652–660, 1: 654f alkaline phosphatase activity measurement, 1: 652–653, 1: 653f biogenic amines, 1: 658–659 cracks, 1: 658–659 defects, 1: 658 definition, 1: 652
933
E. coli control, 4: 65 flavor, 1: 656, 1: 657t food safety aspects, 1: 659 gas blowing, 1: 658 hydrogen peroxide addition, 3: 64 labeling, 1: 659–660, 1: 660f lipolysis, 1: 656, 1: 657t long cold storage, 2: 696 milk processing, 1: 654–655 milk quality, 1: 654–655 milk thermization, 1: 652–653 NSLAB, 1: 31 optimum age of consumption, 1: 658 pasteurized milk cheese vs., 1: 655, 1: 655t, 1: 656t pathogens, 1: 645–646, 1: 648, 1: 659 production requirements, 1: 654 hygiene practices, 1: 654–655 propionibacteria, 1: 658 protected designation of origin, 1: 653, 1: 654f proteolysis, 1: 656, 1: 657t pungency, 1: 656 rancid flavor, 1: 659 sensorial characteristics, 1: 656, 1: 657t slits, 1: 658–659 Staphylococcus aureus incidence, 4: 115 texture, 1: 656, 1: 657t thermization, 2: 696 traditions, 1: 653 volatile compounds, 1: 657t Rayat, 2: 783 Rayleigh ratio, 1: 133–134 Rayleigh scattering, 1: 112 RB51 vaccine, 4: 38 rBST see Recombinant bovine somatotropin (rBST) Reaction kinetics, 2: 714 chemical reaction mathematical descriptions, 2: 714–715 equipment influences, 2: 720 heating method influences, 2: 720 heat sterilization-relevant parameters D value (microbe population size reduction), 2: 715 Q10 value (reaction rate for increased temperature), 2: 715 z value (required time reduction), 2: 715 lines of equal effects calculation, 2: 715–719, 2: 720f pressure-induced reactions, 2: 732 reported temperature-dependent data enzyme inactivation, 2: 718t heat resistant spore-forming bacteria, inactivation, 2: 716t milk constituent reactions, 2: 719t Reaction rate constant (Arrhenius equation), 2: 715 Reactive arthritis, Yersinia enterocolitica, 4: 120 Reactive nitrogen species (RNS), 4: 654–655 xanthine oxidoreductase and, 2: 324–325 Reactive oxygen species (ROS), 4: 654–655 digestive tract, 2: 324 mitochrondrial production regulation, vitamin E, 4: 657 vasculature, 2: 324 Ready-to-eat (RTE) dairy desserts cold filling, 2: 911 creamy, 2: 905, 2: 907f gelled, 2: 905 hot filling, 2: 911 manufacturing methods, 2: 911 pasteurization, 2: 911 popularity, 2: 905 retort sterilization, 2: 911 ultra-high-temperature–short-time processing, 2: 911 Real Decreto 1113/2006, Spain, 1: 849 Real-time analysis biosensors, 1: 235 on-line infrared spectrometry, 1: 120–121
934 Index Real-time polymerase chain reaction (RT-PCR), 1: 221 bacteriophage detection, 1: 438 Rebaudioside, 2: 908 Reblochon cheese, 1: 396, 1: 397t, 1: 398t Recaldent, 3: 1036 Recessive alleles carriers, 2: 675 inheritance, 2: 675, 2: 676f Reciprocating compressors, 4: 602, 4: 603f double-stage, 4: 607f ideal gas equation, 4: 605 ideal power, 4: 605 ideal vs. real cycles, 4: 604 single-stage, 4: 607f total ideal cycle work, 4: 605 work transfer, 4: 605 Recirculation systems, milking machine cleaning, 2: 18 Recombinant bovine somatotropin (rBST) biosensors, 1: 246 as contaminant, 1: 894 Recombined dairy products see Recombined/ reconstituted dairy products Recombined evaporated milk, 3: 317, 3: 317 filling, 3: 317 formulation, 3: 317 ingredient qualities, 3: 317 preheating, 1: 863 product description, 1: 862 production methods, 1: 865f Recombined fermented milks, 3: 318 ingredients, 3: 319 manufacturing processes, 3: 319 Recombined milk, 3: 316–319 anhydrous milk fat, 1: 517 Recombined/reconstituted dairy products, 3: 316–319 demand, 3: 316 labeling requirements, 3: 4 production, 3: 316 Recombined yogurt, 3: 318 ingredients, 3: 319 manufacturing processes, 3: 319 Reconstituted dairy products see Recombined/ reconstituted dairy products Reconstituted milk, 3: 316–319 Reconstituted milk cheese, 3: 318 cheesemaking process modification, 3: 318 preferred milk powder qualities, 3: 318 Records, 1: 487 semen collection, 1: 474 see also Management records Recovery creep, 1: 691t Rectal cancers, vitamin C, 4: 673 Rectal palpation, pregnancy detection, 4: 490 Rectal temperature, heat stress, 4: 561, 4: 562f Rectovaginal constrictions (RVC), 2: 677 Rectovaginal insemination procedure, 4: 469 Recurrent networks (RNNs), 4: 249, 4: 249f Red cattle breeds, 1: 295 Estonia, 1: 296 milk records, 1: 295t Ukraine, 1: 296 see also specific breeds Red clover (Trifolium pratense), 2: 577 Red Dane cattle, 1: 295 Red Flemish cattle, 1: 296 Red Highland cattle, 1: 296 Redox balance, Propionibacterium pathways, 1: 406–407 Redox potential cheese microbiology, 1: 629 pathogen control in cheese, 1: 647 starter cultures, 1: 553 Red protein see Lactoferrin Red Sindhi cattle, 1: 285t, 1: 301t, 1: 302 Red smear cheeses, Arthrobacter, 4: 376–377 Red smear flora, 4: 751
Red Sokoto goats, 1: 311t, 1: 323 Reduced-fat cheeses see Low-fat cheeses Reduced-lactose milks, 3: 278 Reference powders, rennet analysis, 1: 578 Reference standards calibration, 1: 91, 1: 91t Reflectance spectra, infrared spectrometry, 1: 117–118 Reflection, ultrasound, 1: 207, 1: 208f Refraction, ultrasound, 1: 207, 1: 208f Refractometry, HPLC, 1: 174 Refrigerant(s), 4: 599 characteristics, 4: 600t flammability, 4: 601 global warming potential, 4: 599–601 toxicity, 4: 601 vapor compression system, 4: 596 Refrigeration, 4: 596–601 absorption system, 4: 599 compression, 4: 599, 4: 599f compression coefficient of performance, 4: 599 cascade system, 4: 598, 4: 598f coefficient of performance, 4: 598 definition, 4: 596 historical aspects, 1: 16 solar energy, 4: 599 systems, 4: 598 vapor compression cycle see Vapor compression cycle vapor compression systems, 4: 598 multistage, 4: 598, 4: 598f Refund Nomenclature (RN), 4: 336 export subsidy, 4: 336 Regenerative heating and cooling, 4: 184 Regulated secretion, 3: 378 Regulation (EC) 1331/2008, 1: 49 Regulation (EC) 1332/2008, 1: 49 Regulation (EC) 1333/2008, 1: 49, 1: 50, 1: 50 Regulation (EC) 1334/2008, 1: 49 Regulations, dairy products abnormal milk discarding, 3: 422 consumer attitudes and concerns, 2: 679 cream products, 1: 920 dulce de leche, 1: 874 identity (E, FDA) numbers, permitted emulsifiers, 1: 66t marketing claims, 3: 7 comparative, 3: 7 health, 3: 7 nutritional, 3: 6t, 3: 7, 3: 7t quality properties, 3: 8 pasteurized processed cheese products, 1: 805–806 quality standards, regional variation, 1: 71 see also Labeling, dairy products; Legislation Rehydration, milk powder, 2: 120 Reindeer, 1: 374–380, 3: 533 commercial milking, 1: 379 domestication, 1: 374 future work, 1: 379 geographic distribution, 1: 374, 1: 374, 3: 533 China, 1: 374 Saami, 1: 374–375 historical aspects, 1: 374 husbandry, 3: 533, 3: 533 lactation, 1: 376 life history, 1: 376 maternal control, 1: 376 suckling patterns, 1: 376 lactation milk yield, 3: 533, 3: 534f management practice, 1: 375 nomadic husbandry, 1: 375 migration, 3: 533 milk, 3: 533, 3: 534t utilization, 3: 534 milk composition, 1: 375, 1: 376, 1: 377t, 3: 534, 3: 534t, 3: 535t amino acids, 1: 377t fat, 1: 376–377, 1: 377, 3: 534 fatty acids, 1: 378t, 3: 534
lactose, 1: 376–377, 1: 377 minerals, 1: 377, 3: 534 protein, 1: 376–377, 1: 377, 3: 534 vitamins, 1: 378 milking, 3: 533, 3: 533 timing and seasons, 3: 533 milk products, 3: 534, 3: 534, 3: 535t milk yield, 1: 376f, 1: 378, 1: 379f, 3: 533, 3: 534f actual yields, 1: 378 energy content vs., 1: 378 limitations, 1: 376 potential yield, 1: 378 products, 1: 375 seasonal breeding, 4: 445–446 Reinfection syndrome, 2: 270–271, 2: 271 Reiter’s syndrome, 4: 100 RelA gene, 3: 63 Relative humidity (RH), 4: 723–724 air quality and, 4: 556 air temperature, 4: 556f, 4: 556–557 animal welfare, 1: 4 definition, 4: 210, 4: 556, 4: 556f electrical varying properties, 4: 724 mechanical varying properties, 4: 724 rate of change, 4: 725 Relative supersaturation, 3: 185 Relaxin cervical ripening, 4: 509–510 myometrial contraction inhibition, 4: 509 pelvic ligament loosening, 4: 510 Relaxin-like factor (RLF) gene, 4: 509 Renewable sources of energy, 4: 610 Rennet(s), 1: 574–578 analysis, 1: 577 IDF standards, 1: 577, 1: 578 reference powders, 1: 578 rennet (Berridge) unit (RU), 1: 577 Soxhlet units, 1: 574, 1: 577 animal, 2: 289 bovine, 1: 574 chymosin/pepsin ratio, 1: 574–575 feeding regime effects, 1: 574–575, 1: 575t production, 1: 575 see also Chymosin history, 1: 574 microstructure, 1: 232 milk coagulation see Rennet-induced milk coagulation milk/cream rheology, 4: 522 substitutes see Coagulants see also specific types Rennet casein cheese analogues, 1: 817–818 Codex standard, 3: 861t composition, 3: 858, 3: 858t manufacture, 3: 858 cooking, 3: 858 proteolytic enzyme use, 3: 858 skim milk clotting, 3: 858 vat cooking technique, 3: 858 physical properties, 3: 858t Rennet clotting time (RCT), 1: 586 Rennet-coagulated cheeses, 1: 540–542 Rennet-coagulated curds, 1: 534 ripening, 1: 540 Rennet coagulation time (RCT), seasonal variation, 3: 601f Rennet-curd cheese, 1: 831 Rennet-induced milk coagulation, 1: 579–584, 1: 580f acid-coagulated cheeses, 1: 699 acid coagulation vs., 1: 579 affecting factors, 1: 582 calcium, 1: 582 calcium chloride, 1: 583 enzyme concentration, 1: 582 milk heat treatment, 1: 583 pH, 1: 582, 1: 583 postcoagulation processing operations, 1: 583
Index sodium chloride, 1: 583 temperature, 1: 582 total solids, 1: 583 Cheddar cheese manufacture, 1: 706–707 cottage cheese manufacture, 1: 700–701 enhanced, milk characteristics, 3: 599 high-pressure homogenization effects, 2: 759 historical aspects, 1: 24 human milk, 3: 625 immunoglobulin effects, 3: 813 late-lactation milk, 3: 600 low-moisture part-skim mozzarella (pizza cheese), 1: 737, 1: 739f, 1: 739f milk aqueous ion determination, 3: 914 primary (enzymatic) phase, 1: 579, 1: 579, 1: 580f adhesive hard sphere (AHS) theory, 1: 580 k-casein, 1: 579 casein micelles, 1: 579 caseinomacropeptide (CMP), 1: 579 kinetics, 1: 580 primate milk, 3: 625 secondary (aggregation) phase, 1: 579, 1: 580, 1: 580f attractive sources, 1: 581 calcium-induced interactions, 1: 580–581 fractal aggregation theory, 1: 581–582 modeling, 1: 581 temperature, 1: 581 viscosity, 1: 581, 1: 581f smear-ripened cheeses, 1: 753 temperature effects, 1: 581, 1: 582 Rennet substitutes, 2: 290 Rennet (Berridge) unit (RU), 1: 577 REP (repeated extragenic palindrome), PCR, 1: 222 Repeatability analytical methods, 3: 742 measurement error, 1: 85 milk protein analysis, 3: 745, 3: 745t Repeated extragenic palindrome (REP), PCR, 1: 222 Replacements biosecurity, 4: 418 booster vaccinations, 4: 420 digestive disorders, 4: 419 disease entry sources, 4: 419 external parasites, 4: 419 goats see Goat(s), replacement management health management, 4: 417–420 calf care, 4: 418 calving environment, 4: 417–418 calving management, 4: 417 dam disease status, 4: 418 dam vaccinations, 4: 417 precalving, 4: 417 historical aspects, 1: 8 internal parasites, 4: 419 sheep see Ewe(s) vaccinations, 4: 420 timing, 4: 420 value of, 4: 410 see also Calves; Heifer(s) Replicates, measurement error, 1: 85 Reproducibility analytical methods, 3: 742 measurement error, 1: 85 milk protein analysis, 3: 745, 3: 745t Reproduction breeding season manipulation cows, 3: 39 goats, 2: 795 buffalo, 1: 341 camels, 1: 353 heat stress effects see Heat stress historical aspects, 1: 7 management see Reproductive management obesity, 1: 463 seasonal regulation see Seasonal breeders stress and disease, 4: 579, 4: 579f
endocrine pathways, 4: 575 physiological stressors, 4: 577 psychological stressors, 4: 580 Reproduction tests, additive safety, 1: 57 Reproductive efficiency calving-resumption of ovulation/estrus cycles interval, 4: 475 components, 4: 475 conception rate, 4: 478 early embryo loss patterns, 4: 478, 4: 479f rates, 4: 478 fertilization rates, 4: 478 health status, 4: 437t heat detection see Heat detection sheep, 2: 887 Reproductive management biosensors, 1: 245 body condition scoring, 1: 461 estrous cycles synchronization control, 2: 625–626, 2: 629 timing of insemination, 2: 608 fat supplements for improved performance additional energy, 2: 365 essential unsaturated fatty acid supply, 2: 365 hormonal action, 2: 366 mating management artificial insemination, consequences, 2: 647, 2: 647 fertility, 2: 604 mate assignment decisions, 2: 661 for superovulated embryo donor cows, 2: 626 pregnancy diagnosis, 2: 95, 2: 96t Reproductive performance, postpartum, 4: 515 Reproductive targets, 4: 475, 4: 476t Reserpine, induced lactation, 3: 21 Resistance thermometer, HTST pasteurizer, 4: 197 Resistant starch (RS), 4: 355, 4: 363 prebiotic effects, 4: 364 Resonant crystal biosensors, 1: 237, 1: 237f Respiratory alkalosis, heat stress, 4: 565 Respiratory burst, 3: 388 Respiratory infections, sheep, 2: 858 Respiratory rate, heat stress effect, 4: 561, 4: 562f Response surface analysis (RSA) see Response surface method (RSM) Response surface method (RSM), 4: 268 coding, 4: 268–269 disadvantages, 4: 268–269 goodness of fit, 4: 269 standardized effects, 4: 270 Restraints, sheep milking hand-milking, 2: 871 machine-milking, 2: 868 Restriction endonucleases, 3: 965 bacteriophage resistance, 1: 435–436 Restriction fragment length polymorphisms (RFLPs) cheese microbiological analysis, 1: 630–631 PCR, 1: 222 Restriction modification (R/M) systems bacteriophage resistance, 1: 435, 1: 556–557 phage resistance, 3: 135 Retained fetal membranes (RFM) see Retained placenta Retained placenta, 4: 511, 4: 517, 4: 518t body condition score, 1: 466 horse, 4: 512 incidence, 4: 512 risk factors, 4: 517 Retention of fetal membranes see Retained placenta Reticulorumen, water, 3: 981–982 Retinal-hypothalamo-pituitary pathway, seasonal breeders, 4: 442f, 4: 442–443 Retinitis pigmentosa, 2: 642 Retinoic acid receptors (RARs), 4: 639 Retinoids see Vitamin A Retinoid X receptors (RXRs), 4: 639 Retinol, 4: 641
935
Retinol binding protein, 4: 498–499 Retrovirus vectors, 2: 638 Reuterin, 3: 74, 3: 128–129 antimicrobial properties, 1: 420 Reverse cholesterol transport, 3: 729 Reversed-phase high-performance liquid chromatography (RP-HPLC), 1: 171 casein, 1: 171–172, 3: 766 cheese proteolysis, 1: 672–673 derivatization, 1: 172, 1: 173f milk proteins, 3: 762 peptides, 1: 172 proteins, 1: 172, 1: 172f small organic molecules, 1: 172 triacylglycerol analysis, 3: 701, 3: 701f elution order, 3: 701 Reverse flow cleaning, milking machines, 2: 18 Reverse osmosis (RO), 3: 307, 3: 864 cheese manufacture, 1: 618, 1: 619t evaporated milk, 1: 863 fouling, 3: 870 milk, 1: 618, 1: 619t milk processing, 3: 647 milk protein fractionation, 3: 763 milk protein standardization, 4: 548 osmotic pressure, 3: 864 total dissolved solid reduction, water, 4: 584 whey protein products, 4: 733 Reverse-phase chromatography caseins, 3: 748 milk proteins, 3: 748 Reverse-phase HPLC microbial transglutaminase, 2: 298 milk oligosaccharides, 3: 249 Reverse transcriptase polymerase chain reaction (RT-PCR) Aspergillus flavus, 4: 788 foot-and-mouth disease, 2: 164 Revista Argentina de Lactologı´a, 2: 104 Rewetting process, milk powder instantization, 2: 113f, 2: 113–114 Reye’s syndrome, 4: 805 Reynold’s number, 4: 141 RFLPs see Restriction fragment length polymorphisms (RFLPs) Rheology, 1: 229, 1: 264–271, 1: 268 cheese see Cheese rheology concentrated dispersions, 1: 269f, 1: 270 concentrated milks/creams, 4: 524 phenomenological relationships, 4: 525 time-dependent behavior, 4: 526 total volume fraction, 4: 525 definitions, 1: 685 deformation, 1: 685–686 ideal elastic solids, 1: 685, 1: 686f, 1: 687f elastic bodies, 1: 269f elastic theory, 1: 268 flow phenomena, 1: 268 historical aspects, 1: 21 Hooke models, 1: 268 instruments see Rheology instrumentation liquids/semisolids, 4: 520–531 Bingham fluids, 1: 270 butter, 1: 493 cultured buttermilk, 4: 530 fresh cheeses, 4: 530 ice cream mix, 4: 527 sweetened condensed milk/dulce de leche, 4: 526 viscoelastic liquid (Maxwell element), 1: 269f Maxwell model, 1: 270 milk see Milk/cream rheology Newtonian models, 1: 268, 1: 269f, 1: 269–270 principles and significance of, 1: 264–271 property classification, 1: 269 shear–shear rate profiles, 1: 269f shear-thinning fluid systems, 1: 270 small deformation properties, 1: 269
936 Index Rheology (continued ) thixotropic materials, 1: 270 viscoelastic solids, 1: 269f yogurt see Yogurt see also Food texture Rheology instrumentation, 1: 272–278, 1: 273t, 1: 275f dynamic methods, 1: 273f, 1: 276 dynamic strain-controlled rheometers, 1: 276f, 1: 276–277 transient methods, 1: 277 viscoelastic behavior, 1: 277 empirical measurements+, 1: 277 mechanical measurements, 1: 274 bending, 1: 274–275 compression, 1: 274–275, 1: 275 engineering stress, 1: 275, 1: 275f Hencky strain, 1: 275f, 1: 275–276 tension, 1: 274–275 true (corrected) stress, 1: 275f, 1: 275–276 uniaxial compression, 1: 274f, 1: 275 universal testing machines, 1: 274, 1: 274f one-point measurements, 1: 277 flow-time measurements, 1: 277 penetration tests, 1: 277 viscosity see Viscosity Rhesus monkey milk free amino acids, 3: 627t gross composition, 3: 614 -lactoglobulin, 3: 624 offspring gender influences, 3: 614 proteins, 3: 622t total amino acids, 3: 625 neonate IgG levels, 3: 625 Rhizomucor, 1: 802–803 Rhizomucor miehei proteinase (Miehei coagulant), 1: 576, 1: 576 Rhizomucor pusillus proteinase (Pusillus coagulant), 1: 576, 1: 576 Rhizopus arrhizus, 4: 789–790 Rhodes grass (Chloris gayana), 2: 578, 2: 600 Rhodococcus equi, 3: 735 RIAs see Radioimmunoassays (RIAs) Ribbon-type agitators, 4: 160 Riboflavin, 4: 704–706 absorption, 3: 1000–1001 biosensors, 1: 245 cheese, 4: 704–705, 4: 705t dairy sources, 4: 705t deficiency, 4: 705 causes, 4: 706 symptoms, 4: 706 functions, 4: 704 lactose crystallization, 3: 193 in milk, contributions to nutrient intake, 3: 1005 photosensitivity, 4: 704, 4: 704 recommended daily intake, 4: 705t redox potential, 3: 476 sources, 4: 704, 4: 705t status assessment, 4: 706 storage effects, 4: 704 structure, 4: 704, 4: 705f supplementation, 4: 706 visible region, 3: 472 Riboflavin-binding protein (Rfbp), 3: 796t, 3: 798 Ribonucleases (RNase), 2: 333 function, 2: 333 heat stability, 2: 333 purification, 2: 333 Ribonucleosides, human milk, 3: 975 Ribose, 1: 386t Ribotyping, 1: 223 Ribulose bisphosphate carboxylase, bloat, 2: 206–208 Rickets calcium intake, 3: 1009 dairy cows, 2: 399 humans, 4: 646, 4: 650
Ricotta cheese, 1: 704, 4: 734–735 composition, 1: 700t, 4: 735t ultrafiltration, 1: 622 Ricottone cheese, 1: 700t, 1: 704 Rideau sheep, 1: 338, 1: 338f Rifampicin, 4: 57 Rifampin, 4: 36 Right displaced abomasum (RDA) clinical signs, 2: 213–214 diagnosis, 2: 214 prevalence, 2: 212 Right paralumbar fossa omentopexy, 2: 216 Right paramedian abomasopexy, 2: 216 Ringworm, 2: 251–252 sheep, 2: 858–859 treatment, 2: 252 Riparian areas, warm climate farms see Farm design (warm climates) Ripening see Cheese ripening Risk consequence, 4: 278 definition, 4: 278, 4: 532 frequency, 4: 278, 4: 279t management see Risk management Risk analysis, 4: 532–539 definition, 4: 532 elements, 4: 532 purpose, 4: 532 role, 4: 532 utilization rational, 4: 532 see also Hazard Analysis and Critical Control Points (HACCP) technique Risk assessment, 4: 279, 4: 533 additive safety, 1: 55 chemical hazards, 4: 534 commissioning, 4: 536 consequence models, 4: 279, 4: 280t dairy farms, 2: 681 emergency response planning, 4: 282 exposure assessment, 4: 533 consumption patterns, 4: 533 microbiological, 4: 535 purpose, 4: 533 uncertainty, 4: 534 HACCP see Hazard Analysis and Critical Control Points (HACCP) technique hazard characterization, 4: 533 hazard-related factors, 4: 534 host-related factors, 4: 534 uncertainty, 4: 534 variability, 4: 534 hazard identification, 4: 533 variability, 4: 534 incident frequency modeling, 4: 279, 4: 281t microbiological, 4: 535 difficulties, 4: 535 scenario trees, 4: 535 physical hazards, 4: 535 policy, 4: 536 purpose, 4: 533 qualitative vs. quantitative, 4: 282 results consideration, 4: 536 risk characterization, 4: 534 uncertainty, 4: 534 variability, 4: 534 scientific data used, 4: 533 steps, 4: 533 transparency, 4: 536 Risk communication, 4: 538 Risk management, 4: 535 business management planning, 1: 483 options assessment, 4: 537 available option identification, 4: 537 general risk management measures, 4: 537 individual commodity/hazard-targeted measures, 4: 537 steps, 4: 537 option selection, 4: 537
equivalence, 4: 538 risk-based targets, 4: 537 society/cultural differences, 4: 537 risk evaluation, 4: 535 acceptable levels of protection, 4: 536 goal setting, 4: 536 steps, 4: 535 Risk management plan, 4: 278 Risk matrix, 4: 279, 4: 280f Risk mitigation, 4: 281 Risk profiling, 4: 536 Risk reduction, 4: 281 Risk tolerance criteria, 4: 280, 4: 281t Rivella, 2: 129, 4: 734 River buffalo, 1: 340 River-type buffalo Asia, 2: 772, 2: 773f characteristics, 2: 773t lactation period, 2: 772 RNA interference (RNAi) mechanisms, 2: 643 Roadside grazing, Southern Asia, 2: 94, 2: 94 Roasting, 2: 349 Robbins device, 1: 448 Robotic milker, 1: 9 Robotic milking see Automatic milking systems (AM systems) Robotics, automation vs., 4: 252 Robots, 4: 252–256 advantages over humans, 4: 252 definition, 4: 252 milking see Milking robots palletizing see Palletizing robots Robust design, 4: 274 Rocket immunoelectrophoresis, caseins, 3: 749 Rodent(s), 4: 540 harborage elimination, 4: 541 physical control systems, 4: 541 perimeter establishment, 4: 541–542 signs of, 4: 540–541 Rodenticides, 4: 541–542 Roller drying historical aspects, 1: 14 khoa manufacture, 1: 881 milk powder manufacture, 2: 109, 2: 109f whey, 4: 732–733 Roller press, 3: 857 Rolling procedures, displaced abomasum, 2: 215–216 Romano drying, 1: 826 as food ingredient, 1: 830 Room for investment (RFI) model automatic milking systems, 3: 957, 3: 957f calculation, 3: 955t Roots blower, 4: 603, 4: 604f Roquefort cheese, 1: 771t, 3: 501 Roquefortine, 1: 904t, 4: 796, 4: 797f Penicillium roqueforti, 4: 774 Roquefortine C, 4: 775 Rose bengal test (RBT), brucellosis, 2: 156t, 2: 157 Rose clover (Trifolium hirtum), 2: 559 Rose–Gottlieb method, 1: 18, 1: 80, 1: 82t Rotaries, warm climate milking systems, 2: 15, 2: 17f Rotary atomization/atomizers, 4: 208, 4: 224, 4: 225f advantages, 4: 209, 4: 225 concentrate pump, 4: 222 efficiency, 4: 208–209 FRAD system, 4: 231, 4: 232f liquid distributor, 4: 208 liquid feed rate, 4: 225 liquid viscosity, 4: 225 milk powder spray drying, 2: 117 peripheral speed, 4: 225 wheel selection, 4: 225 Rotary brushed fine screen, 4: 621, 4: 621f Rotary compressors, 4: 602, 4: 604f Rotary (carousel) milking parlors, 3: 961–962, 3: 962f goats, 2: 805, 2: 805f, 2: 806 historical aspects, 1: 6
Index sheep, 2: 868, 2: 868f Rotary pumps, 4: 149 design, 4: 149 hygienic requirements, 4: 149 operation principles, 4: 149, 4: 149f selection criteria, 4: 151t Rotary vane vacuum pump, 3: 946, 3: 946f Rotating disk filters, dynamic membrane systems, 3: 869 Rotating drum screens, 4: 621 Rotating drum thickener, 4: 629t Rotational crossing, Bos indicus x Bos taurus cattle, 1: 308 Rotational grazing, 2: 595 timing criteria, 2: 595–596 tropical grass pastures, 2: 599 Rotational viscometers, 1: 274 Rotation rheometer, 4: 237 Rotation-symmetric geometries, 1: 272–273, 1: 273f Rotor–stator agitators, 4: 160, 4: 161f Rotor–stator system, high-speed blending/mixing, 2: 761 RotoTherm, 2: 704 Rouge de l’Ouest sheep, 1: 337 Roughage, African dairy cow management, 2: 79 Roumloukian sheep, 1: 336t Roundworms, 2: 831, 2: 831–832 RP-HPLC see Reversed-phase high-performance liquid chromatography (RP-HPLC) rRNA technology,Lactobacillus, 3: 82 RT-PCR see Real-time polymerase chain reaction (RT-PCR) Rubbers, dairy plant use, 4: 137 Rubratoxins, 4: 799 (+)-Rugulosin, 4: 793, 4: 794f Rumen dietary fat processing, 3: 355, 3: 355f fermentation see Rumen fermentation function disruption, high fatty acid levels, 2: 365–366, 2: 366, 2: 368 function evaluation models, 2: 420, 2: 425, 2: 426 healthy, 2: 199 lipid hydrolysis, 3: 660 microbial biohydrogenation, 3: 355, 3: 355f, 3: 660 microbial ecosystem, 3: 980 genomic sequencing, 2: 668 microbial fat transformation, 2: 366 biohydrogenation, 2: 367, 2: 367f, 3: 41, 3: 543 desaturation, 3: 543–544 lipolysis, 2: 366–367 microbial protein synthesis, 2: 340, 2: 389 limiting amino acids, 2: 389, 2: 390t mucosal mass, 2: 199 pH maintenance, 2: 200 protein degradation, 2: 411, 2: 412t chemically treated feed, 2: 412, 2: 412f protein solubility and, 2: 411, 2: 412f rumen retention time, 2: 412 steps, 2: 411 Rumen defaunation, sulfur absorption, 3: 998 Rumen fermentation, 2: 409, 3: 980–984, 3: 981f anaerobic, 3: 980 benefits, 3: 980 carbohydrates, 3: 981f, 3: 982, 3: 982f fatty acid synthesis metabolites, 3: 543 cellulose, 3: 983 hemicellulose, 3: 983 lignins, 3: 984 lipids, 3: 983 microbe total number, 2: 409 minerals, 3: 983 model, 3: 981 nitrogenous compounds, 3: 983 organic acids, 3: 983 pectins, 3: 983 proteins, 3: 993 starches, 2: 338, 3: 982 sugars, 3: 983
‘the inside out concept’, 2: 409–410 water, 3: 981 Rumenic acid (RA), 3: 714 anticarcinogenic properties, 3: 663, 3: 663t contents alteration in dairy products, 3: 661–662 genetic variation, 3: 662 health benefits, 3: 356–357, 3: 662–663 origin of, 3: 660 physiological factors, 3: 662 plasma cholesterol levels, 3: 663f, 3: 663–664 structure, 3: 661f synthesis, 3: 355f, 3: 356–357, 3: 661 Rumen mycotic plaques, 2: 200f Rumenotomy, ruminal acidosis, 2: 202 Rumen overload see Ruminal acidosis Rumen-protected choline, fatty liver, 2: 221–222 Rumen-protected fatty acids, 3: 355 Rumen ulcers, 2: 201f Rumen-undegradable feed protein (RUP), 2: 389 duodenal feed protein flow, 2: 414–416 high levels, 2: 414 sources and composition, 2: 389, 2: 394 Rumen wall puncture, 2: 210 Ruminal acidosis, 2: 199–205 acute clinical, 2: 199–200 basic condition, 2: 199 buffering salts, 2: 201–202 definition, 2: 199 economic costs, 2: 202 goats, 2: 793–794 heat stress, 4: 564 laminitis link, 2: 199, 2: 203 prevention, 2: 199, 2: 201 diet changes, 2: 202 feeding practices, 2: 202 secondary problems, 2: 200, 2: 200f, 2: 201f, 2: 201f subacute see Subacute ruminal acidosis (SARA) subclinical, 2: 200 treatment, 2: 202 Ruminal contractions, heat stress, 4: 564–565 Ruminal lactic acidosis see Ruminal acidosis Ruminally protected amino acids, 2: 389–395 benefits, 2: 394, 2: 394 efficacy (bioavailability estimates), 2: 392 historical aspects, 2: 390 lysine, commercial products, 2: 392, 2: 394 methionine, commercial products, 2: 391 methionine analogs, 2: 391, 2: 392, 2: 394 methionine derivatives, 2: 391 polymer coating, 2: 391, 2: 392 product comparisons, 2: 393 usage constraints, 2: 394 Ruminant(s) dietary protein digestion, 3: 361 digestive function models, 2: 431–432 fiber assessment, 3: 985 glucose metabolism, 3: 367 glucose-sparing strategies, 3: 367 milk, variation between species, 3: 539t fatty acid profile, 3: 544, 3: 545t proteins, 3: 541, 3: 541f placentation, 4: 488, 4: 488f roughage intake, milk fat content effecrs, 3: 530 Rumination time, pasture-fed cows, 3: 986 Ruminitis, 2: 200 Runoff collection ponds, 2: 22 Russia, Simmental cattle, 1: 294 Russian Black Pied cattle, 1: 286t Rutabaga (swede, Brassica.napus var. napobrassica), 2: 560 Rye, 2: 557 Ryegrass annual, 2: 555, 2: 565 cropping regimes, 2: 555, 2: 556, 2: 565 self-regenerating, 2: 556 antinutritional factor problems, 2: 574 grass tetany (hypomagnesia), 2: 574, 2: 597–598 irrigation interval, 2: 591, 2: 591f
937
perennial see Perennial ryegrass (Lolium perenne) topping, 2: 590 Ryegrass staggers, 2: 574, 4: 797–798
S Saami, reindeer (Rangifer tarandus), 1: 374–375 Saanen goats, 1: 311, 1: 311t, 1: 312f, 2: 64–65 milk ejection kinetic curves, 2: 807 Sable goats, 1: 311t, 1: 315 Saccharides, primate milk, 3: 615 Saccharimeters, 1: 253 Saccharomyces, 1: 570 Saccharomyces cerevisiae, 4: 760–761 Sachet desserts, 2: 906 SAFE (solvent-assisted flavor evaporation) see Solvent-assisted flavor evaporation (SAFE) Safety analysis, 4: 277–282 agricultural contaminants, 1: 887, 1: 888f formal, 4: 277 key steps, 4: 277 Safety margins, acceptable daily intake (ADI), 1: 56 Safety valves, 4: 157, 4: 158f Sagi hook, 2: 871 misshapen udders, 2: 865, 2: 872 Sahel goats, 1: 311t, 1: 323 Sahiwal cattle, 1: 285t, 1: 301t, 1: 302, 1: 302f Saidi cattle, 1: 298 Saint Ignatius itch see Pellagra Sakacin A, 1: 422t Sakacin P, 1: 422t, 1: 426 Salatrim (short and long acyl triglyceride molecule), 1: 530 Saliva phosphorus recycling, 3: 997 sampling, cheese flavor assessment, 1: 679 Salmonella, 4: 93–98 antimicrobial resistance, 2: 194 carrier animals, 4: 95 cheese, 1: 651, 4: 68 growth, 1: 648f public health aspects, 1: 648, 1: 648f, 1: 651 control measures, 4: 96 culture, 2: 193, 4: 93 in dairy products, 4: 93 farmer/farm worker infection, 4: 95 feed stuff contamination, 2: 190 flagellar/H antigens, 2: 190 host-specific serovars, 2: 190, 2: 191t identification, 4: 93 microbiological analytical methods, 1: 217 in milk, 3: 449 excretion into, 4: 95 fecal contamination, 4: 94–95 incidence, 4: 93 sources, 4: 95 milking equipment contamination, 4: 95 public health concerns, 3: 313–314 raw milk, 3: 646 raw milk cheeses, 1: 659 serovars, 2: 190 somatic/O antigens, 2: 190 subspecies, 2: 190 terminology, 2: 190 see also individual species Salmonella Dublin, 2: 190–191 Salmonella ealing, 4: 68 Salmonella enteritidis, 3: 313–314 Salmonella fyris, 3: 256 Salmonella heidelberg, 1: 645 Salmonella pathogenicity islands (SPIs), 2: 192–193 Salmonella plasmid virulence (spv) genes, 2: 192–193 Salmonella Typhimurium, 2: 190–191 antimicrobial resistance, 2: 193–194 biosensor detection, 1: 241 calves, 2: 192 phagetyping, 2: 193–194 virulence genes, 2: 192–193
938 Index Salmonellosis, 2: 190–194 acute, 2: 193 calves, 2: 191–192, 2: 193 carrier animals, 2: 190, 2: 191 causative organisms, 2: 190 cheese-borne, 4: 68 clinical symptoms, 2: 193 control, 2: 194 diagnosis, 2: 193 epidemiology, 2: 191 histopathological examination, 2: 192 humans, 4: 96 causes, 4: 96–97 dried milk consumption, 4: 68 illness severity, 4: 97 outbreaks, 3: 313–314, 4: 68 susceptibility, 4: 97 symptoms, 4: 97 infection rates, 2: 191 morbidity rate, 2: 193 mortality rates, 2: 193 outbreak causes, 2: 191–192 pasteurized milk consumption, 4: 68 pasture contamination, 2: 192 pathogenesis, 2: 192 predisposing factors, 2: 192 prevention, 2: 194 public health aspects, 2: 194 raw milk consumption, 4: 68 serology, 2: 193 subacute, 2: 193 treatment, 2: 194 vaccination, 2: 194 Salt see Sodium chloride Salted butter, water activity, 4: 712–713 Salt effect, 3: 184 Salting see Cheese salting Salting broom, Cheddar manufacture, 1: 611 Salting of cheese see Cheese salting Salt-in-moisture (SIM) cheese salting, 1: 595 lactose metabolism, 1: 625, 1: 626f Salt-tolerant lactobacilli, gas blowing defects, 1: 665 avoidance, 1: 665 Sampling, 1: 72–75 artifacts, 2: 543 butter, 1: 73 canned dairy foods, 1: 73 cheese, 1: 74 cheese flavor assessment, 1: 676 containers, 1: 72 cottage cheese, 1: 74 extraction and concentration methods, 2: 543–544, 2: 548 frozen foods, 1: 73 infrared spectrometry, 1: 117 liquid dairy foods, 1: 72 microbiological analysis see Microbiological analytical methods milk powder, 1: 74 milk transportation, 1: 544 pasteurized foods, 1: 73 sample preparation atomic spectrometry, 1: 141 chromatographic methods, 1: 169 infrared spectrometry, 1: 121 PAGE, 1: 185 titratable acidity, 1: 249 sample size, 1: 72 sensory evaluation, 1: 74 whey powder, 1: 74 Sand, as bedding material, 3: 392–393 Sand filtration, 4: 583 Sandiness defect, dried whey, 4: 733 Sandwich enzyme-linked immunosorbent assay, 1: 178f Sandwich immunoassays, proteins, 1: 179 Sandy texture, dulce de leche defects, 1: 879
Sanhe cattle, 2: 83 SANICIP bag filter, 4: 229, 4: 229f advantages, 4: 230 CIP system, 4: 230 reverse-jet air nozzles, 4: 229–230, 4: 230f Sanitary and Phytosanitary (SPS) Agreement see Agreement on the Application of Sanitary and Phytosanitary Measures (SPS) Sanitizers see Disinfectants/sanitizers San Simon cheese, 1: 787 Saponins, cholesterol reduction, 3: 736 homogenized milk, 3: 736 Saprophytes, 3: 452 Sap Sago, 1: 786–787 Sarcoptes scabiei, 2: 250 Sarcoptic mange clinical signs, 2: 251 epidemiology, 2: 250 treatment, 2: 252 Sarda goats, 1: 316 Sarda sheep see Sardinian (Sarda) sheep Sardinian (Sarda) sheep, 1: 330, 1: 331f, 2: 72 distribution, 1: 330 farming systems, 2: 848–849 milk production, 1: 328t, 1: 331 milk yield, 1: 332t origin, 1: 330 physical characteristics, 1: 331 reproductive characteristics, 1: 331 Saturated air vapor pressure, 4: 210 Saturated fatty acids (SFAs) blood cholesterol levels, 3: 713, 3: 730 cardiovascular disease, 3: 1023–1033 coronary heart disease risk autopsy studies, 3: 1026 case–control studies, 3: 1024, 3: 1025t ecological studies, 3: 1024 epidemiology evidence, 3: 1024 multifactor intervention studies, 3: 1031 multiple regression models, 3: 1024, 3: 1029t negative association, 3: 1024–1026 prospective (cohort) studies, 3: 1024, 3: 1027t randomized controlled trials, 3: 1026, 3: 1030t relative risk measurement, 3: 1024, 3: 1026t early history, 3: 1023 in fats, 2: 363, 2: 364t lipoproteins, 3: 1031 ‘liver X receptor’ signaling, 3: 1058 medium-chain length, 3: 1023–1024 milk, 3: 656, 3: 656t in oils, 2: 363, 2: 364t plant material sources, 3: 543 serum cholesterol levels, 3: 1005, 3: 1023 short-chain length, 3: 1023–1024 structures, 2: 363, 2: 364f Saturation, 3: 183 Saurmichquark, 1: 703 Sausage meat, Penicillium camemberti, 4: 778–779 Savory butter see Spiced butter Scandinavian fermented milks see Nordic fermented milks Scanning electron microscopy (SEM), 1: 227t, 1: 227–228, 1: 228, 1: 228f butter, 1: 233–234 yogurt, 1: 233f Scaring devices, bird repellents, 4: 542 Scarlet fever, milk-borne, 3: 311–312 Scatterer, 1: 133 Schmidt–Bondzynski–Ratzlaff method, 1: 80 Schweizerischer Milchwirtschaftlicher, 2: 103 Science courses, basic, 2: 6 The Scientific and Technical Review, OIE, 4: 5 The Scientific Commission for Animal Diseases, OIE, 4: 3 SCM see Sweetened condensed milk (SCM) Scour, newborn calf, 3: 812
Scraped-surface heat exchangers, 1: 525, 1: 526f, 1: 526f, 4: 190, 4: 191f blade removal, 4: 191f, 4: 191–192 design, 4: 190–191, 4: 191f, 4: 191f khoa manufacture, 1: 881 products treated, 4: 191–192 rotors, 4: 190–191 spray drying, 4: 223 UHT treatment, 2: 703 Scraper systems, manure collection, 3: 393 Scrapie, 2: 859 control, 2: 859 goats, 2: 802 Screw-type compressors, 4: 603 Scroll-screen centrifuge, 4: 180 Scrotal circumference artificial insemination centers, 1: 472, 1: 472t, 1: 472t bucks, 2: 837–838, 2: 838f bull management, 1: 476 Scrotal examination, bulls, 1: 476 Scurvy, 4: 667, 4: 671 SDE (simultaneous steam distillation extraction), cheese flavor assessment, 1: 676–677 SDS-PAGE see Sodium dodecyl–sulfate polyacrylamide gel electrophoresis (SDS-PAGE) Sea lion milk composition, foraging trip length and, 3: 566 fat content, 3: 564t, 3: 570–574 Seals dairy plants, 4: 137 oligosaccharides, 3: 272 valves, 4: 154 Sea otter milk, 3: 566–569, 3: 567t Searle-type viscometers, 1: 274 Seasonal breeders, 4: 440–447 annual puberty, 4: 442–443 artificial manipulation, 4: 443 exogenous melatonin, 4: 444 housing strategies, 4: 443–444 light-dark cycles, 4: 443 pharmacological control, 4: 444 climatic events, 4: 440 ambient temperature, 4: 440–441 domestic livestock, 4: 444 endocrine regulation, 4: 442 low temperature, 4: 441 milk yield, 4: 440 neuroendocrine regulation, 4: 442, 4: 442f patterns, 4: 440 pheromones, 4: 441–442 photoperiod, 4: 440 proximate action, food, 4: 441 reproductive strategies, 4: 440 semidomestic multipurpose livestock, 4: 444 sexual development, 4: 426 theories for, 4: 440 behavioral, 4: 441 nutritional effects, 4: 441 social, 4: 441 ultimate action, food, 4: 441 Seasonal diet, butter spreadability and, 1: 513 Seasonally polyestrus, 4: 440 Seasonal milk production system, 3: 598 Seasonal/pasture based management (Australia), 2: 13 Seasonal/pasture based management (New Zealand), 2: 13 Seasonal/pasture based management, definition, 2: 44 Seat valve see Globe valve Secondary additives, 1: 51 Secondary cultures, cheese manufacture see Cheese manufacture Secondary sprout, 3: 341–342 Secretory calcium-binding phosphoprotein family, 3: 772 Secretory immunoglobulin A (sIgA) functions, 3: 810
Index human, 3: 807 human colostrum, 3: 812 proteolytic degradation, 3: 812 structure, 3: 807, 3: 809f Secretory vesicles, milk proteins, 3: 376f, 3: 377 Sedentary/confined goat production systems, 2: 60–61 Sedimentation, coffee cream, 1: 921 Sediment test, raw milk, 3: 644 Seed broadcasting, 2: 586 Seed gums, dairy desserts, 2: 909t Seeding, sweetened condensed milk production, 1: 871 Seedling vigor, 2: 587 Seifdar camels, 1: 352 Sei whale milk oligosaccharides, 3: 271t P-Selectin, 3: 256–257 Selectins, 3: 256–257 Selection see Genetic selection Selective media Brucella, 4: 36 Yersinia enterocolitica, 4: 122 Selenate, 3: 1000 Selenite, 3: 1000 Selenium, 2: 381 absorption, ruminants, 3: 1000 breast milk, 3: 939 in dairy products, 3: 934t, 3: 935t, 3: 935t, 3: 935t daily dietary intake, 3: 939 deficiency, 2: 381–382, 2: 386 geographical areas, 2: 789 humans, 3: 938 sheep, byproduct feeding, 2: 852–853 deficiency disorder (white muscle disease), 2: 794 feed supplements, 2: 381, 2: 386 environmental mastitis prevention, 3: 420 mastitis resistance, 3: 430, 3: 430t functions, 3: 938 in milk, 3: 933, 3: 934t chemical forms, 3: 935 nutrient intake, contributions to, 3: 1006 nutritional significance, 3: 938 recommended dietary intake, 3: 937t requirements, 2: 379t, 2: 382 toxicity, 2: 382 vitamin E interactions, 2: 786 Selenium-cysteine, 3: 1000 Selenomethionine (SeMet) absorption, 3: 1000 supplementation, 3: 1000 Seligman, Dr Richard, 1: 13 Selonomethionine, 2: 382 feed supplementation, 2: 386–387 SEM see Scanning electron microscopy (SEM) Semen collection artificial insemination centers see Artificial insemination centers (AICs) negative behavioral factors, 1: 473 technique, 2: 603 cryopreservation, 4: 467 examination, 1: 477 frozen see Frozen semen quality evaluation, 2: 603 heat stress effects, 4: 569, 4: 570f, 4: 570t see also Sperm Semibatch process operation, 4: 242 Semihard cheese manufacture mechanization, 1: 612 brining, 1: 613–614, 1: 615f packaging, 1: 614 pressing, 1: 612 ripening, 1: 614 salting, 1: 613 storage, 1: 614 vat process, 1: 612 whey strainers, 1: 612
public health aspects, 1: 648, 1: 648f raw milk contamination, 1: 659 yeasts, 4: 750 negative aspects, 4: 750 positive aspects, 4: 750 on surface, 4: 751 see also specific cheeses Semiskimmed milk homogenization, 2: 753 Semi-soft cheeses biogenic amines, 1: 454 as food ingredient, 1: 830 public health aspects, 1: 648, 1: 649f see also specific cheeses Semisynthetic hormones, 1: 894 Sensation aspects, food texture, 1: 267, 1: 268f Sensitivity analytical methods, 1: 483–484, 3: 742 immunochemical methods, 1: 177, 1: 180 Sensor(s) basic characteristics, 4: 235, 4: 235f linear behavior, 4: 236 nonlinear behavior, 4: 236 specialized, 4: 236 Sensoric methods, cheese rheology, 1: 689 Sensory context, food texture, 1: 264 Sensory evaluation, 1: 279–283 consumer acceptability testing, 1: 281 definitions, 1: 279 descriptive sensory evaluation, 1: 281 quantification, 1: 281 Quantitative Descriptive Analysis, 1: 281 quantitative flavor profiling, 1: 281 Spectrum method, 1: 281 discrimination testing, 1: 280 duo-trio, 1: 280–281 paired comparison, 1: 280–281 ranking tests, 1: 280–281 triangular tests, 1: 280–281 influence of mouthfeel, 2: 533 measurements, 1: 83 other analyses vs., 1: 282 gas chromatography–olfactometry, 1: 282–283 ‘preference mapping’, 1: 283 quality scoring, 1: 279 American Dairy Science Association, 1: 279–280 assessors, 1: 280 defects, 1: 280 definitions, 1: 279 International Dairy Federation, 1: 279–280 sampling, 1: 74 sensory laboratories, 1: 282 assessor selection, 1: 282 environment, 1: 282 taste panel analysis, 2: 547, 2: 550 see also Olfactometry Sensory laboratories see Sensory evaluation Sensory panels, 1: 44 trained assessors, 1: 44 Separation techniques cheese manufacture, 1: 545 continuous butter manufacture, 1: 496 nondairy food dairy ingredients, 2: 125, 2: 126f see also specific methods Separators, 4: 175–183 bacterial removal, 4: 172 butter oil production, 4: 172 clarification, 4: 167, 4: 168f design features, 4: 167 discharge, 4: 168 quantity, 4: 170 double-cream fresh cheese production, 4: 172, 4: 173f drive, 4: 169, 4: 169f, 4: 169f, 4: 169f historical aspects, 4: 166 hydraulic system, 4: 169 phases, 4: 167 rising channels, 4: 168 positions, 4: 168
939
sealing, 4: 168 hydraulic (hydrohermetic), 4: 168 mechanical (hermetic), 4: 168 self-discharging bowls, 4: 169 separating disk, 4: 167–168 skimming, 4: 167, 4: 168f ‘takedown machines’, 4: 169 Septicemia, listeriosis cattle, 2: 186 goats, 2: 186 sheep, 2: 185–186 Sequencing batch reactor, 4: 623–624, 4: 625f Serbia, Simmental cattle, 1: 294 Serorphin, 3: 1063 Serra da Estrela sheep, 1: 336 lactation length, 1: 332t Serrai sheep, 1: 337 Serrana goats, 1: 317 Serratia, 3: 451 mastitis, 3: 419 Serum agglutination tests (SATs) brucellosis, 2: 156t, 2: 157 leptospirosis, 2: 182 Serum albumin, 3: 759 Service networks, infrared spectrometry, 1: 122, 1: 122f Sesquiterpenes, goat milk, 2: 62t Setaria (golden timothy, Setaria sphacelata), 2: 577 Setaria sphacelata (golden timothy, setaria), 2: 577 Set sprinklers, 2: 593 Set theory, 4: 247 Setting, butter consistency, 1: 512 7-day estrogen–progesterone treatment, induced lactation, 3: 20 Sexed offspring, 2: 631–636 biopsy handling, 2: 632 embryo biopsy, 2: 631, 2: 632f aspiration, 2: 632 freezing, 2: 633 manual, 2: 631 transfer, 2: 633 embryo transfer techniques, 2: 630 non-PCR methods, 2: 633 PCR techniques, 2: 631 analysis, 2: 632, 2: 632f, 2: 632f Y-chromosome-specific DNA amplification, 2: 632 Sexed sperm calving results, 2: 635 embryonic deaths, 2: 635–636 historical aspects, 1: 7 insemination, 2: 635 in vitro fertilization, 2: 636 pregnancy rates, 2: 635 Sex preselection, flow sorted sperm, 2: 633, 2: 634f Sex-sorting sperm, 2: 633, 2: 634f, 2: 634f, 2: 635f packaging, 2: 634 Sexual development seasonal breeders, 4: 426 season and, 4: 426 Sexually transmitted diseases, bulls, 1: 479 Sfakia sheep, 1: 332t Shade heat stress management, 2: 19 mastitis, 3: 431 warm climate housing systems, 2: 22 Shaftal (Persian) clover (Trifolium resupinatum), 2: 559 Shankalish cheese, 1: 788 Shear, homogenization, 2: 750–751 Shearing, 2: 863–864 Shear–shear rate profiles, rheology, 1: 269f Shear-thinning fluid systems, rheology, 1: 270 milk/cream, 4: 521–522 Shear (transverse) waves, ultrasound, 1: 206 Sheep, 2: 67–76 accelerated lambing, 2: 71 admission treatments, 2: 860, 2: 861t age at first mating, 2: 887
940 Index Sheep (continued ) artificial insemination see Artificial insemination (AI) artificial pastures, 2: 849 bovine somatotropin treatment, 3: 36 breeding, 2: 68–70, 2: 72 crossbreeding, 2: 73 genetic improvements, 2: 73 udder morphology, 2: 73 breeding management, 2: 890 controlled mating, 2: 890–891 hand-mating, 2: 890–891 ram-to-ewe ratio, 2: 890 uncontrolled mating, 2: 890–891 breeds see Sheep breeds brucellosis, 2: 154 control, 2: 158 s2-casein multiphosphorylation, 3: 835, 3: 835 s1-casein phosphorylation, 3: 833–835 s1-casein variants, 3: 833–835 chorioptic mange, 2: 251 closed flocks, inbreeding risk reduction, 2: 860 colostrum see Sheep colostrum as ‘concentrate selectors’, 2: 848 confined byproduct misuse, 2: 852 byproduct use, 2: 852, 2: 852t feeding, 2: 852 feedstuffs, 2: 852 copper, protected form supplements, 3: 999 crude protein, dietary requirements, 2: 410 dairy breeds, 2: 865 dairying, 2: 865 diseases, 2: 857 major plagues, 2: 859 distribution, 2: 68, 2: 68t, 2: 69t Canada, 2: 67 Central Europe, 2: 67 France, 2: 67 North Africa, 2: 67 Northern Europe, 2: 67 domestication, 3: 326, 3: 459 dry matter intake, 2: 853–854 embryo losses, 2: 887–888 estrous cycle, 4: 426 estrus, 2: 887 expected yield, 2: 873 extensive production systems, 2: 70 dietary supplements, 2: 70–71 Europe, 2: 71 with goats, 2: 70 feeding management, 2: 848–856 intensification suitability, 2: 848 milk fatty acid composition, 2: 856 product quality implications, 2: 855 protein nutrition monitoring, 2: 855–856 stocking rates, 2: 855 feed supplements, 2: 849 concentrate, 2: 850, 2: 851t grazing dairy ewes, 2: 850, 2: 851t lactating animals, 2: 885 milk yield responses, 2: 850–852 flock health planning, 2: 859 effective recording systems, 2: 859–860 veterinary visits, 2: 859 written plan, 2: 859 foot-and-mouth disease, 2: 163 future prospects, 2: 75 hand-milking, 2: 871 hand vs. machine-milking, 2: 867 health management, 2: 857–864 animal purchase, 2: 860, 2: 860t lactating dairy ewes, 2: 861 nonlactating dairy stock, 2: 863 premating, 2: 862t, 2: 863 historical aspects, 2: 67 husbandry program, 2: 861, 2: 862t infertility, 2: 857
intensive production systems, 2: 70, 2: 71, 2: 848 dietary supplements, 2: 71 features, 2: 849t grazing-based, 2: 848 seasonal production, 2: 848–849 zero grazing-based, 2: 849 intrauterine insemination, 2: 891 lactation curve, 2: 867 lactation length, 2: 867 listeriosis, 2: 185 machine-milking, 2: 868 air bleed, 2: 871 cups, 2: 871 equipment, 2: 870 equipment cleaning, 2: 872 feeding during, 2: 870 milk recording, 2: 870 pulsation, 2: 871 vacuum levels, 2: 871 magnesium absorption, 3: 997–998 management, 2: 73 Mediterranean region, 2: 73–74 traditional, 2: 68 mastitis see Sheep mastitis mechanized milking, 2: 74, 2: 74–75, 2: 75 milking parlors, 2: 75 metabolic disorders, 2: 857 milk see Sheep milk milk hygiene testing see Sheep milk milking, 2: 74 production variation, 2: 74 milking frequency, 2: 873 milking hygiene, 2: 871 milking management, 2: 865–874 cup attachment, 2: 872 cups, maximum attachment time, 2: 872 foremilk taking, 2: 872 future prospects, 2: 874 hand stripping, 2: 872 lambing, 2: 874 machine stripping, 2: 872 milking technique, 2: 872 udder washing, 2: 872 unit size, 2: 865 year-round milking, 2: 874 milking suitability, 2: 865 milk urea, protein nutrition monitoring, 2: 855–856 multipurpose breeds, 2: 875, 2: 878t multipurpose management, 2: 875–881 adaptation, 2: 876 developing countries, 2: 880 environmental conditions, 2: 876 history, 2: 875 husbandry systems, 2: 879 productive performance, 2: 876, 2: 879t nutrition, 2: 70 forage, 2: 68–70 nutritional disorders, 2: 857 ovulation, 2: 887 pasture, 2: 849 see also individual pasture types placental estrogen secretion, 4: 507 postpartum anestrus, 2: 888 predation susceptibility, 2: 841 predator control see Predator control, goats and sheep pregnancy, 2: 887 detection, 4: 490 duration, fetal genotype effect, 4: 503 health-care, 2: 863 supplementary feeding, 2: 863 testing, 2: 891 vaccinations, 2: 862t, 2: 863 production, 2: 68 puberty, 2: 887, 4: 426 quarantine, 2: 860, 2: 861t raw milk handling, 2: 872 raw milk storage, 2: 872
replacement management see Ewe(s), replacement management reproduction dynamic nutritional effects, 2: 888 genetics, 2: 892 immediate nutritional effects, 2: 888 milk yields, effects of, 2: 888, 2: 888f nutrition and, 2: 888 phytoestrogen effects, 2: 889 static nutritional effects, 2: 888 reproductive efficiency, 2: 887 reproductive events, 2: 887 reproductive management, 2: 887–892 estrous synchronization, 2: 890 hormonal synchronization, 2: 890 patterns, 2: 887, 2: 888f prolific breed use, 2: 892 ram effect, 2: 890 seasonal breeding, 2: 889, 4: 445 breed differences, 2: 889 genetics, 4: 445 melatonin secretion, 2: 889 photoperiod effect, 2: 889, 4: 426 rams, 2: 889 superovulation, 2: 890 ‘third profit’, 2: 867 total mixed ration composition, 2: 853t composition-sheep requirement matching, 2: 853, 2: 854t practical formulation, 2: 854, 2: 854t, 2: 855t practical implementation, 2: 853 residues, 2: 853, 2: 853t transgenic, wool production, 2: 643 udder, ideal, 3: 330 udder morphology, 2: 866f udder shape, 2: 865, 2: 866f udder volume to milk yield, 3: 330 vaccines/vaccinations, 2: 862t boosters, 2: 863–864 see also Ewe(s); Ram(s) Sheep breeds, 1: 325–339, 2: 875, 2: 876f, 2: 878t classification, 1: 325 comparative studies, 1: 326 distribution, 1: 325, 2: 875, 2: 876f, 2: 878t Mediterranean, 1: 325 Middle East, 1: 325 future work, 1: 339 high milk production, 1: 328 milk yields, 1: 328t low milk production, 1: 336, 1: 336t moderate milk production, 1: 331 lactation length, 1: 332t milk yield, 1: 332t, 1: 332t newly developed breeds, 1: 337 suckling duration, 1: 325–326 superior milk production, 1: 326 see also specific breeds Sheep colostrum, 3: 494 oligosaccharides, 3: 271t Sheep mastitis, 2: 857 detection, 2: 873 foremilk examination, 2: 873 hand feel, 2: 873 milking hygiene procedures, 2: 863 stress-induced, 2: 874 testing, 2: 863 treatment, 2: 873 Sheep milk, 3: 494–502 annual production, 3: 494 bioactive compounds, 3: 500 carbohydrates, 3: 499 s1-casein phenotypes, 3: 832 s2-casein stochastic alternative splicing, 3: 832 cheeses see Sheep milk cheeses chemical composition, 3: 494, 3: 495t breed differences, 3: 494 lactation stage, 3: 494
Index coagulation, 3: 500 Enterobacteriaceae, 4: 68 enzymes, 3: 500 frozen storage, 2: 872 heat stability, 2: 749 hygiene, 2: 873 lipid fraction, 3: 496 lipoprotein lipase concentration, 2: 304–305 milk allergy, 3: 1044 mineral elements, 3: 499, 3: 499t nonprotein nitrogen, 3: 496 nucleosides, 3: 973, 3: 973t physical properties, 3: 494, 3: 495t production statistics, 2: 68t, 2: 69t proteins, 3: 494 cross-reactivity, 3: 1044 raw milk handling, 2: 872 raw milk storage, 2: 872 renneting properties, 3: 500 storage, 2: 872 unsaponifiable lipids, 3: 499 vitamins, 3: 499t xanthine oxidoreductase, 2: 326 yields, 2: 867, 2: 867t expected vs. actual, 2: 873 see also Sheep, milking Sheep milk cheeses, 3: 501, 3: 501t categories, 3: 501 products, 1: 536 Spanish, 3: 501 Sheep ranching, protein production, 2: 879, 2: 880t Sheep scab, 2: 858 Shelf life barotolerant pathogens, 2: 734 coffee cream, 1: 913 cream liqueur, 1: 917–918 definition, 3: 281 high-pressure treatment, 2: 734 khoa, 1: 883 Maillard deterioration chemical markers, 3: 229f carboxymethyllysine, 3: 230 furosine, 3: 228, 3: 230, 3: 233 lactulose, 3: 230 pyralline, 3: 230 nonthermal extension technologies, 3: 286 carbon dioxide addition, 2: 730–731 microfiltered milk, 3: 308 pathogenic bacteria standards, 2: 714 storage instructions, food labels, 3: 5 whipping cream, 1: 915, 1: 922 Sherbets, 2: 895t, 2: 897 Shewanella putrefaciens, 3: 452 Shiga toxin-producing E. coli (STEC), 4: 60 serovars, 4: 61 Shigella, 4: 99–103 bacteriology, 4: 99 biochemical characteristics, 4: 101–102 cell invasion, 4: 99 cell-to-cell spreading, 4: 99 detection, 4: 101 enterotoxins, 4: 99–100 enumeration, 4: 101 growth media, 4: 101 identification methods, 4: 101 genetics, 4: 102 immunological, 4: 102 microbiological safety, 4: 101 natural hosts, 4: 99 occurrence in milk, 4: 100 ‘omics’, 4: 102 outbreaks, 4: 100 pathogenesis, 4: 99 serovars, 4: 99 thermal treatment, 4: 101 virulence, genetic determinants, 4: 99 virulence plasmid, 4: 99–100 Shigella boydii, 4: 99 dysentery, 4: 100
Shigella dysenteriae, 4: 99 dysentery, 4: 100 Shigella flexneri, 4: 99 dysentery, 4: 100 Shigella-like organisms, 4: 102 Shigella sonnei, 4: 99 dysentery, 4: 100 Shigellosis see Dysentery Shimming, NMR, 1: 147 Shock, abomasal volvulus, 2: 214 Shock sanitization, 4: 584, 4: 585t Short and long acyl triglyceride molecule (salatrim), 1: 530 Short-chain acids (SCA), prebiotic effects, 4: 355 Short-chain fatty acids apoptosis induction, 4: 369–370 butter, 1: 507 colon cancer prevention, 4: 369–370 infant nutrition, 3: 714 prebiotics, 4: 367 Short courses, food technology education, 2: 11 Shorthorn cattle, 1: 286t Shower-and-fanning station, mastitis prevention, 3: 432 Shows, agricultural, 2: 799 Shredded cheese, spoilage molds, 4: 780 Shukoff flask method butterfat melting behavior, 1: 508f, 1: 509 butter melting behavior, 1: 508f, 1: 509 Shurri goats, 1: 311t, 1: 322 Shutoff valve, 4: 155, 4: 155f Sialic acid brain stimulating activity, 3: 252 colostrum, 3: 596 human milk vs. infant formula, 3: 252 whey protein products, 3: 876 Sialylated oligosaccharides, 3: 255 Sialyllactose, 3: 252 Sialyl milk oligosaccharides, 3: 252 Siamang (Symphalangus syndactylus) milk oligosaccharides, 3: 271t, 3: 617t Siboney cattle, 1: 303t, 1: 305 Side-by-side (parallel) milking parlors, 3: 961, 3: 961f goats, 2: 804, 2: 805f Side-opening (tandem) milking parlor, 3: 961, 3: 962f historical aspects, 1: 6 Side role irrigation system, 2: 591 SIgA see Secretory immunoglobulin A (sIgA) Signal-to-noise ratio (S/N), 4: 274 Silage gas blowing defects, cheese, 1: 663 ketosis, 2: 236 Listeria monocytogenes source, 2: 188 mechanical harvesting, 2: 572 musty fermentation, contamination problems, 2: 542 paddy straw preservation, Vietnam, 2: 95–96 Penicillium roqueforti, 4: 775 Silent estrus, 4: 464–465 Silent ovulation, 4: 464–465 Silicon in milk, 3: 934, 3: 934t chemical forms, 3: 936 nutritional significance, 3: 939 Silos, historical aspects, 1: 5 Silo tanks see Storage tanks Simmental cattle, 1: 293 China, 1: 295 Croatia, 1: 294 Czech republic, 1: 294 France, 1: 293–294 Hungary, 1: 294 milk records, 1: 294t Poland, 1: 294 Russia, 1: 294 Serbia, 1: 294 Slovenia, 1: 294 South Africa, 1: 295 subpopulations, 1: 293, 1: 294t
941
Simple lipids, 3: 670 Simplesse, 1: 530 Simulated milk products see Imitation dairy products Simultaneous iterative reconstruction technique (SIRT), 1: 213 Simultaneous percussion and auscultation, displaced abomasum, 2: 214 Simultaneous pulsation, goat milking, 2: 808–809 Simultaneous steam distillation extraction (SDE), cheese flavor assessment, 1: 676–677 Single commodity transfers (SCT), 4: 306, 4: 307f Australia, 4: 307f, 4: 309–310 Canada, 4: 306, 4: 307f New Zealand, 4: 307f, 4: 310 Single nucleotide polymorphisms (SNPs), 3: 1059 bacterial phyogenetic analysis, 3: 47 genetic defects, carrier detection, 2: 677 genetic selection, 2: 654 -lactalbumin, 3: 840 marker-assisted selection, 3: 969 within/across bovine populations, 2: 664, 2: 665f Single radial immunodiffusion (SRID), 1: 178–179 Single-rotor pumps, 4: 149, 4: 150f compression, 4: 149 selection criteria, 4: 151t Single-strand conformation polymorphism (SSCP) cheese microbial fingerprinting, 1: 633–634, 1: 634f cheese microbiological analysis, 1: 630–631 Lactobacillus, 3: 82 Single-trait linear model, 2: 651 Single-tube screening test, Shigella, 4: 101 Sinkability, milk powder, 2: 120 Sire conception rate (SCR), 4: 472 Sire model, genetic evaluation, 2: 651 Sirenia lactation, 3: 563, 3: 564t milk composition, 3: 573t Siriana goats, 2: 65t Sirohi goats, 1: 312t SIRT (simultaneous iterative reconstruction technique), 1: 213 Sirtawi camels, 1: 352 Site approval, warm climate milking sheds, 2: 26 Site mutagenesis, Propionibacterium, 1: 405 Site-specific natural isotope fractionation (SNIF) nuclear magnetic resonance, 1: 151 Sitosterolemia, 3: 732 Six sigma, 4: 275 critics, 4: 276 Skim milk homogenization, 2: 746–747 indirect acidification, 3: 855 NMR relaxation studies, 1: 155 nondairy food, 2: 128, 2: 128t permittivity, 3: 472 preparation techniques, 2: 125 specific heat capacity, 3: 469 ultrasonic properties, 3: 470 Skim milk powder (SMP) bacteriocins, 1: 426 classification, 2: 112, 2: 112t heat classification, 2: 112t dairy desserts, 2: 908 enhanced renneting properties, 3: 866 EU stock:global export ratio, 4: 349–350, 4: 350f imitation milk powders, 2: 914 imitation milks, 2: 913–914 international prices, 4: 348, 4: 349f manufacture, 2: 111, 2: 112f Bactocatch process, 2: 113, 2: 113f -lactoglobulin removal method, 2: 112–113 milk chocolate, 1: 860 US stock:global export ratio, 4: 349–350, 4: 350f Skimming efficiency, 4: 176 Skimming separators, 4: 168 Skin-delayed-type hypersensitivity (SDTH) test, brucellosis, 2: 157 Skin milk agar (SMA) plating, 1: 218
942 Index Skin prick test (SPT), milk allergy, 3: 1042 Skopelos sheep, 1: 336 lactation length, 1: 332t Slab gel electrophoresis, milk proteins, 3: 746 Slashing, herbage, 2: 590 Slaughterhouses, ovary collection, 2: 616 Slender guinea grass (green panic), 2: 577 ‘Slick-hair’ gene, 4: 573 Slide valve, 4: 152, 4: 153f Slimming foods, 2: 131 Slimy rind, Dutch-type cheese defects, 1: 727 Slits, raw milk cheeses, 1: 658–659 Slovakia, Pingzau cattle, 1: 296 Slovenia, Simmental cattle, 1: 294 ‘Slow (hard) milkers’, 3: 334, 3: 383 Sludge, cottage cheese defects, 1: 701 Sludge flocs, 4: 622–623 Slug flow milking equipment cleaning, 3: 636 milklines, 2: 810 Slurry systems, accelerated cheese ripening, 1: 795 Small-amplitude dynamic rheology, 1: 586 Small colony variants (SCVs), Staphylococcus aureus, 4: 108 Small deformation properties, 1: 269 Small ducts, mammary gland, 3: 333 Small intestine lactating ruminants, 3: 989–995 amino acid digestibility, 3: 993, 3: 994f amino acid net uptake measurement, 3: 990–991 anatomy, 3: 989, 3: 990f, 3: 990f blood supply, 3: 989–990, 3: 990f carbohydrate digestion, 3: 991, 3: 991f digesta flow, 3: 989 digesta pH, 3: 989 digestion quantification, 3: 990 energy production, 3: 993 glucose net uptake measurement, 3: 990–991 lipid digestion, 3: 992, 3: 992t mineral absorption, 3: 994 nonruminants vs., 3: 989 nutrients absorbed, 3: 989 physiology, 3: 989 protein digestion, 3: 993 starch digestion, 3: 991, 3: 991f permeability, breast-fed vs. formula-fed infants, 3: 257 protein degradation, 2: 412, 2: 412t protein quality and, 2: 412–413 protein fraction flow, 2: 414, 2: 415t Small organic molecules, reversed-phase HPLC, 1: 172 Small private farms, China, 2: 85 Small-scale setup, Africa, 2: 77 Smartamine, 2: 392, 2: 393 Smart (active) packaging, 4: 22 Smart sensors, 4: 238 Smear-ripened cheeses, 1: 753–766, 1: 754f acid-curd see Acid-curd cheeses aroma development, 1: 763 defined starter cultures, 1: 764 sulfur compounds, 1: 764 classification, 1: 395, 1: 758 color development, 1: 762, 1: 763f commercial surface starter cultures, 1: 759 deacidification, 1: 395 defects, 1: 765 bacterial contamination, 1: 765 Listeria monocytogenes infection, 1: 755–756, 1: 765 mold contamination, 1: 765 examples, 1: 754t microbiology, 1: 395, 1: 395, 1: 397t, 1: 755, 1: 756, 1: 757t brine microflora, 1: 754 commercial surface starter cultures, 1: 759 coryneform bacteria, 1: 395–396, 1: 627 defined starter cultures, 1: 759 enumeration, 1: 399
hygiene, 1: 399 Listeria monocytogenes, 1: 399 micrococci, 1: 627 pathogens, 1: 395 pH effects, 1: 396f recovery of, 1: 398 ripening role, 1: 399 semisoft cheeses, 1: 756 soft cheeses, 1: 756 staphylococci, 1: 627 starter functionality, 1: 760 yeasts, 1: 398t molds, 1: 628 production statistics, 1: 753 rennet, 1: 753 ripening, 1: 753, 1: 760 color development, 1: 762, 1: 763f deacidification, 1: 761 development, 1: 761 methionine metabolism, 1: 399 salting, 1: 754, 1: 755f dry salting, 1: 754 salt tolerance, 1: 398–399 semihard cheeses deacidification, 1: 761, 1: 761f microbiology, 1: 757t semisoft cheeses deacidification, 1: 761, 1: 761f microbiology, 1: 756, 1: 759, 1: 760t smearing/spraying technology, 1: 755 old–young cheeses, 1: 755, 1: 765 soft cheeses deacidification, 1: 761, 1: 761f microbiology, 1: 756, 1: 759–760 surface-ripening cultures, 1: 756 surface-ripening lactate metabolism, 1: 667 technology, 1: 753 yeasts, 1: 627 see also specific cheeses Smoking blood cholesterol levels, 3: 731 coronary heart disease risk, 3: 731–732 Smoothies, 2: 897 SNAREs, milk protein secretion, 3: 377 Snell’s law, 1: 207 Sniffing ports, 1: 679 Social interaction stress, reproductive effects, 4: 580, 4: 580f Societal risk, 4: 280–281 Societies see Dairy science societies/associations Society of Dairy Technology (SDT), 2: 102 Sodium, 2: 376 absorption, 2: 376–377 ruminants, 3: 998 cheese, 3: 925, 3: 927t dairy feed ingredients, 2: 358t in dairy products, 3: 926t, 3: 926t, 3: 927t, 3: 927t, 3: 1012, 3: 1012t nutritional significance, 3: 927 deficiency grassy tetany, 2: 227 humans, 3: 928 drinking water, 2: 377 excess intake, 3: 928–929 extracellular fluid volume regulation, 3: 927–928 growth requirements, 2: 377 infant formula concentration, 3: 928–929 lactose interactions, 3: 917, 3: 918f magnesium uptake and, 2: 226, 2: 226f marine mammal milk, 3: 579t, 3: 580 in milk, 3: 925, 3: 926t chemical form, 3: 908, 3: 926 mastitis effects, 3: 904 measurement, 3: 915 nutritional significance, 3: 927 secretion, 3: 917 pregnancy requirements, 2: 377 primate milk, 3: 627–629, 3: 628t
ration requirements, 2: 377 requirements, 2: 377 in serum, 3: 919, 3: 920t sheep milk, 3: 500 Sodium alginate as emulsifier, 1: 69t flavored milks, 3: 305 Sodium aluminum phosphate (SALP), 1: 810 Sodium biphosphate, flavored milks, 3: 302 Sodium caseinate coffee whiteners, 2: 915 composition, 3: 858t, 3: 859 food processing applications, 3: 770 manufacture, 3: 858–859, 3: 859f microbial transglutaminase substrate, 2: 298 physical properties, 3: 858t solution viscosity, 3: 889 spray-dried, 3: 858–859 Sodium chloride blue mold cheese microflora, 1: 768 in butter, influence on ALP activity, 2: 315 cheese pathogen growth prevention, 1: 646–647 distribution brine salting, 1: 602, 1: 603f cheese salting see Cheese salting dry salting, 1: 604 surface dry salting, 1: 602, 1: 603f gradients, hard Italian cheese ripening, 1: 732 milk salt equilibria, 3: 913 rennet milk coagulation, 1: 583 uptake cheese salting, 1: 598 dry salting, 1: 602 moisture loss, brine salting, 1: 598, 1: 599f, 1: 600f, 1: 601 Sodium diacetate, 4: 790 Sodium dodecyl sulfate (SDS), two-dimensional electrophoresis, 3: 844–845 Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE), 1: 186, 1: 196, 3: 845 infant formulae analysis, 2: 136 milk fat globule membrane, 3: 682–683, 3: 683f milk proteins, 3: 747, 3: 747f PAS 6/7, 3: 683f, 3: 688 Sodium/glucose cotransporters (SGLT), 3: 367 Sodium hydroxide flavored milks, 3: 302 starter culture neutralization, 1: 607 Sodium lick stones, 2: 228 Sodium phosphate, flavored milks, 3: 302 Sodium propionate, ketosis, 2: 237 Sodium stearoyl lactylates as emulsifiers, 1: 66t, 1: 67 structure, 1: 68f Soft cheeses fresh, manufacture mechanization, 1: 615 public health aspects, 1: 648, 1: 649f yeasts, 4: 750 negative aspects, 4: 750 positive aspects, 4: 750 on surface, 4: 751 Yersinia enterocolitica, 4: 121 see also specific cheeses Soft independent modeling of class analogy (SIMCA), infrared spectrometry, 1: 120, 1: 120f Soft Mexican-style cheese, listeriosis outbreaks, 4: 83–84 Soft ripened cheeses continuous vat stage, 1: 615 curd production, mechanization, 1: 614, 1: 616f manufacture, mechanization, 1: 614 Software multivariate statistical tools see Multivariate statistical tools statistical analysis, 1: 92
Index Software sensors, 4: 240 measured-unmeasured property relationships, 4: 240 Soil Association, 4: 10 organic standards, 4: 11t Soil moisture, status determining devices, 2: 592t Soil-plant-goat relationship, 2: 817 Solar cooling systems, 4: 599 Solar energy, refrigeration, 4: 599 Solid-fat content (SFC), fat and emulsions, 1: 160 Solid-liquid extraction, cholesterol removal, 3: 735 Solid-liquid manure separation, 4: 632 Solid-phase microextraction (SPME) capability, 2: 545 cheese flavor assessment, 1: 678 fiber specificity, 2: 544–545 gas chromatography, 1: 174–175 headspace sampling technique, 2: 544 needle assembly and holder, 2: 544, 2: 545f volatiles, extraction/concentration, 2: 544, 2: 545f Solid samples, atomic spectrometry, 1: 141 Solids-not-fat (SNF), butter, 1: 506 Solid-state electrodes, 1: 195 Solubility, 3: 183 definition, 3: 183, 3: 887–888 influencing factors, 3: 183–184 milk powder see Milk powder milk protein hydrolysates see Milk protein hydrolysates milk proteins, 3: 887 solvent nature, 3: 183–184 temperature effects, 3: 183–184 unit types, 3: 183 Soluble CD14 receptors (sCD14), colostrum, 3: 594 ‘Soluble Food for Babies’, 1: 15 Solvent-assisted flavor evaporation (SAFE) gas chromatography (GC), 1: 174–175 volatiles, extraction/concentration, 2: 548 Somatic cell(s) mastitis, 3: 895 milk, 3: 309, 3: 895 seasonal variation, 3: 43 proteinase source, 3: 603 removal by microfiltration, 3: 309 Somatic cell count (SCC) automatic milking systems, 3: 956 ‘background’, 3: 898 cell type effects, 3: 906 differential counting, 3: 896 donkey milk, 1: 369 electric conductivity measurement, 3: 896 financial incentives, 3: 897–898 healthy mammary gland, 3: 387 heat stress, 4: 565 high levels, 3: 897 historical aspects, 1: 7 individual cow, 3: 897 individual cow samples, 3: 894 infected quarter levels, 3: 899 international standards, 3: 897, 3: 897t mastitis, 3: 425, 3: 426f, 3: 429 measurement, 3: 896 milk product suitability, 3: 899 milk samples analyzed, 3: 894 Mycoplasma bovis mastitis, 3: 412 noninfected quarters, 3: 895 producer bonuses, 3: 897 producer penalties, 3: 897 sheep, 2: 873–874 standards, 3: 897 Streptococcus agalactiae mastitis, 3: 409 threshold affecting dairy products, 3: 906 total counting, 3: 896 bulk milk instrumental systems, 3: 896 on-farm, 3: 896 udder health indicator, 3: 902 units, 3: 894 Somatic cell nuclear transfer (SCNT), 2: 611, 2: 638
Somatic cell score (SCC), mastitis, 3: 429 Somatotropin bovine see Bovine somatotropin (bST) colostrum, 3: 596 fatty liver, 2: 222 galactopoietic effects, 3: 26, 3: 27f heat stress, 4: 565 in vitro maturation, 2: 618–619 ketosis, 2: 231, 2: 237 mammary gland growth, 3: 341 thyroid hormone interactions, 3: 28 transgenic animals, 2: 642 see also Recombinant bovine somatotropin (rBST) Somosierra sheep, 1: 337 Sorbates, 1: 37t Sorbic acid, 4: 790 Sorbitan esters, 1: 67 Sorbitan monostearate as emulsifier, 1: 66t structure, 1: 68f Sorbitan tristearate, 1: 66t Sorbitol Bifidobacterium fermentation patterns, 1: 386t frozen desserts, 2: 896–897 Sorghum, 2: 554, 2: 564 antinutritional compounds, management, 2: 336, 2: 573 grain sorghum, 2: 336–338, 2: 554, 2: 564 hybrid forage types, 2: 554, 2: 564 mineral deficiencies, 2: 573 sweet, 2: 554, 2: 564 Sorption isotherms (SI), 4: 212f, 4: 213, 4: 708, 4: 708f, 4: 716 generation, 4: 725, 4: 725f, 4: 726f lactose, 4: 718f crystalline vs. amorphous, 4: 708 mathematical expressions, 4: 720, 4: 721t measurement, 1: 77, 4: 724, 4: 724f skim milk powder, 4: 718f yogurt, 4: 718f Sour buttermilk see Cultured buttermilk Sour cream see Cultured cream Sour milk, yak, 1: 349 South Africa, Simmental cattle, 1: 295 South African Journal of Animal Science, 2: 104 South African Society of Dairy Technology, 2: 104 South America dairy societies, 2: 104 see also specific countries Southern Asia, 2: 94–100 cattle breeds, 2: 99 crossbreeding programs, 2: 99, 2: 99–100 native breeds, 2: 99, 2: 99–100 thermal stress and milk yield, 2: 99 cattle management, 2: 95 health management, 2: 95–96 reproductive management, 2: 95, 2: 96t small dairy farm cooperatives, 2: 95 feed supplement concentrates, 2: 94, 2: 94, 2: 95 fodder availability, 2: 94 livestock and product marketing, 2: 96–97 livestock feed resources, 2: 94 crop residues, 2: 94, 2: 97 fodder crops, 2: 94 Indian subcontinent, 2: 94 livestock use, sustainability and development, 2: 97 milk marketing, 2: 96 consumption levels, 2: 96, 2: 97f prices/marketing systems, 2: 96 production levels, 2: 96, 2: 97f production goals, 2: 98 demand predictions, 2: 98, 2: 98t output improving farming strategies, 2: 98 per caput milk availability, 2: 98, 2: 99f see also Buffalo milk Sow(s) leptospirosis, 2: 182 see also Pig(s)
943
Sow milk, 3: 530, 3: 531f casein, amino acid composition, 3: 530–531, 3: 532t s1-casein phenotypes, 3: 832 s2-casein phosphorylation, 3: 835 cholesterol and somatic cell counts, 3: 531 fatty acid composition, 3: 531 heat stability, 2: 749 -lactoglobulin, 3: 758–759 lipoprotein lipase concentration, 2: 304–305 Soxhlet method, 1: 18 Soxhlet units, 1: 574, 1: 577 Soy, milk replacers, 4: 398 Soy-based infant formulae, 2: 143 Soybean(s), 2: 351, 2: 558, 2: 566 definition, 2: 349 extruding processes, 2: 352 ground, 2: 351–352 micronizing, 2: 352 milk fat effects, 2: 352 milk protein effects, 2: 352 milk yield effects, 2: 352 nonenzymatic browning, 2: 352 protein, 2: 349–350, 2: 352 raw, 2: 351 roasting, 2: 352 rolled, 2: 351–352 supplements, milk fatty acid changes, 3: 658–659, 3: 659t Soybean lecithin, 1: 66t Soybean meal, 2: 353 calf starters, 4: 401 chemically treated, 2: 354 protein degradation, 2: 412, 2: 412f definition, 2: 349 essential amino acid index, 2: 412t, 2: 414 forms, 2: 353 heat-treated, 2: 354 milk yield effects, 2: 354 protein fraction flow, 2: 414, 2: 415t sunflower meal vs., 2: 354 Soybean oligosaccharides, 4: 362 as prebiotic, 4: 361t, 4: 362 structure, 4: 357f, 4: 359t Soy formula, 3: 1043 Soy milks, 2: 914 Spain cheese definition, 1: 849 cheese legislation, 1: 849 fat level descriptors, 1: 849 ingredients, 1: 849 dairy product consumption, 1: 46, 1: 46t dairy societies, 2: 105 herby cheeses, 1: 787 processed cheese legislation, 1: 849–850 spiced cheeses, 1: 787 Spartan, 1: 9 Specialist courses, food technology, 2: 6 Special safeguard mechanism (SSM), agricultural products, 4: 346 Specification compliance records, 1: 491 Specific gravity (SG), 1: 250 Spectrophotometric methods HPLC, 1: 173 milk ion quantification, 3: 914t, 3: 915 Spectroscopic imaging see Hyperspectral imaging (HSI) Spectroscopy, 1: 109–114 absorption laws, 1: 113 electromagnetic spectrum, 1: 109, 1: 110f electronic transitions, 1: 109 far-infrared, 1: 113 instruments, 1: 110 microwave, 1: 113 NMR, 1: 113 see also specific methods Spectrum method, 1: 281 Speisequark, 1: 703
944 Index Sperm analysis computer-assisted, 2: 604, 2: 604, 2: 605 motility, microscopic assessment, 2: 604 sex sorting, 2: 607 staining techniques, 2: 604 viability characteristics/markers, 2: 607 number, potential progeny and, 2: 603, 2: 603t quality testing, 2: 604 sexed see Sexed sperm Spermatogonial stem cells (SSCs), 2: 638 transplantation, 2: 638 Spermidine, 1: 451, 1: 452t Spermine, 1: 451, 1: 452t Sperm-mediated transgenesis, 2: 638 Sperm surface protein P47 see Lactadherin Spheroplasts (protoplasts), 2: 291 Sphingolipids, 3: 651 colon cancer prevention, 3: 1021 Sphingomyelin, 3: 651 colon cancer prevention, 3: 1021 fatty acid composition, 3: 672 structure, 3: 670, 3: 671f Sphingosine, 3: 1021 Spice(s) Aspergillus flavus growth inhibition, 4: 789 definition, 1: 783 microbial quality, 1: 783 quality, 1: 783 Spiced butter, 1: 502 commercial products, 1: 503 keeping quality, 1: 503 manufacture, 1: 502–503 Spiced cheeses, 1: 783–789 manufacture methods, 1: 783 quality, 1: 783 spices added, 1: 783, 1: 784t types, 1: 783, 1: 784t Spin, nuclei, 1: 146 Spinal muscular atrophy (SMA), 2: 677 Spin lattice relaxation see Nuclear magnetic resonance (NMR) Spinose ear tick (Otobius megnini), 2: 253 Spin–spin relaxation see Nuclear magnetic resonance (NMR) Spiral plater, 1: 216 Spiral plate technique, 1: 216 Spiral-tube heat exchangers, spray drying, 4: 223, 4: 223f Spirochetes, papillomatous digital dermatitis, 2: 168–169 Spliceosome, 3: 824–825 SPME see Solid-phase microextraction (SPME) Spoilage microorganisms cheese, 1: 630 effects, 3: 452 family Moraxellaceae, 3: 452 heat resistant spores, 2: 719–720 milk, 2: 539, 3: 282, 3: 282, 3: 452 Gram-negative rod-shaped bacteria, 3: 452 LAB, 3: 453 off-flavor generation, 2: 539 spore-forming, Gram-positive rods, 3: 282, 3: 453 thermal inactivation conditions, 2: 715–719 molds see Spoilage molds species, 3: 452 yogurt, 2: 528 Spoilage molds, 3: 454, 4: 780–784 cheese, 4: 780 dairy product enumeration, 4: 783 media, 4: 783 molecular biological techniques, 4: 783 in dairy products control, 4: 781 spoilage, 4: 780 toxic metabolites, 4: 782, 4: 782t yogurt, 4: 781 Spontaneous milk, 3: 717
‘Spontaneous souring’, 1: 28 Spores, bacterial centrifugal removal, 2: 729 germination activation, 2: 695, 2: 740 heat resistance, 2: 719–720, 2: 725 nonthermal technologies, destructive effectiveness, 2: 725, 2: 726 Sporidesmins, 4: 798, 4: 799f Sports drinks functional requirements, 3: 873 whey protein ingredients, 3: 873 Sports nutritional foods, 2: 132 Spotted hyena milk oligosaccharides, 3: 271t SPR see Surface plasmon resonance (SPR) Spray cleaning, milking equipment, 3: 636 Spray drying, 4: 208 2,4,5-trimethyloxazole problems, 2: 547 adjunct cultures, 1: 797 advantages, 4: 224 air disperser, 4: 210 air distribution, 4: 217 air distribution system, 4: 220 plug flow air stream, 4: 222, 4: 222f rotary air stream, 4: 221, 4: 221f air filtration system, 4: 217, 4: 220f local authority requirements, 4: 217–218 air heating system, 4: 218 direct heating, 4: 220 indirect heating, 4: 219, 4: 221f air prefiltration, 4: 217–218, 4: 220f air/water vapor mixture properties, 4: 210 atomization of the feed, 4: 208, 4: 209t atomizing device, 4: 210, 4: 224 components, 4: 216, 4: 217f definition, 4: 216 droplet state changes, 4: 212 drying air state changes, 4: 211, 4: 211f adiabatic, 4: 211–212 drying characteristics, 4: 211, 4: 212f evaporation, 4: 210 feed properties, 4: 211 moisture content, 4: 211 solid content, 4: 211 water activity, 4: 211 feed system, 4: 222, 4: 222f components, 4: 222 concentrate pump, 4: 222 direct preheaters, 4: 223 feed line, 4: 223 feed tanks, 4: 222 filter, 4: 223 homogenizer/high-pressure pump, 4: 223 indirect preheating system, 4: 223 preheating system, 4: 223 water tank, 4: 222 final drying, 4: 230 fines return system, 4: 232, 4: 232f glass transition, 4: 214 historical aspects, 1: 14–15 hot air system, 4: 217 humidity chart, 4: 210, 4: 211f milk powder, 2: 109 advantages, 2: 109–110 atomizing device, 2: 109, 2: 110f, 2: 117 capital investment, 2: 110 energy consumption, 2: 110, 2: 111t, 2: 117 kinetics, 2: 109 multiple effect spray dryer, 2: 109, 2: 110f parameter determination, 2: 114 powder recovery systems, 2: 109, 2: 110f rotary atomizers, 2: 117 single-stage, 2: 110 three-stage, 2: 110 two-stage, 2: 110 minimum outlet temperature, 4: 211f, 4: 213 operation, 4: 216 partial vapor pressure, 4: 212–213 pneumatic conveying and cooling system, 4: 230
powder cooling, 4: 230 powder separation system, 4: 225, 4: 230t cyclone, 4: 225 principles, 4: 208, 4: 216 spray-drying air mixing, 4: 210 stickiness, 3: 182, 4: 213, 4: 214f straight-through process, 4: 710 subprocess stages, 4: 208 whey, 3: 182, 4: 732 Spreadability butter see Butter definition, 3: 704 Spread-plate method, Geotrichum candidum, 4: 771 Spreads, 1: 522 historical aspects, 1: 15 microstructure, 1: 233, 1: 234f milk fat-based see Milk fat-based spreads milk protein concentrate, 3: 853 Spread-type processed cheese, 3: 852 Spring-loaded regulators, 3: 947 Sputum examination, lungworms, 2: 273 Squared prediction error (SPE) control charts, 4: 244 Square/round (squround) container, ice cream, 4: 20 SRID (single radial immunodiffusion), 1: 178–179 SSCP (single-stranded conformation polymorphism), cheese, 1: 630–631 Stability maps, water activity, 4: 713, 4: 713f Stabilizers cottage cheese manufacture, 1: 700–701 European Union, 1: 35 United States, 1: 39 Stable-fly, 4: 419 Stachyose, 4: 359t, 4: 362 Staff business management, 1: 484 see also Labor management, dairy farms Stainless steel, 4: 135 agitators, 4: 162–163 chemical composition, 4: 135 classification, 4: 135 corrosion, 4: 135 chlorine-induced, 4: 135–136 pitting, 4: 136 resistance, 4: 135 definition, 4: 135 surface finishes, 4: 138t types, 4: 135, 4: 260 see also individual types Stall gate mechanisms, herringbone milking systems, 2: 13–15, 2: 16f Stanchion feeding practices, 1: 4 historical aspects, 1: 3 Standard hydrogen electrode (SHE), 4: 257 Standard International Trade Classification (SITC), 4: 331 Standardizing unit, 4: 171, 4: 172f Standard plate count (SPC) see Total bacterial count (TBC) Standard reduction potential, 4: 257 cell potential, 4: 257–258 half-cell reactions, 4: 257, 4: 258t ‘Standing’, estrus, 4: 461 STANDOMAT, 4: 171 Staphylococcal cassette chromosome, 4: 109 Staphylococcal enterotoxins (SET) biosensors, 1: 241 raw milk cheeses, 1: 659 Staphylococcal poisoning, 3: 314 Staphylococcal superantigen-like proteins, 4: 105–106 Staphylococcus cheese microbiology, 1: 627 gastrointestinal microflora (human), 1: 383t in milk, 3: 447 see also individual species Staphylococcus aureus, 1: 650, 4: 104–110, 4: 111–116 adhesins, 4: 105, 4: 106f antibiotic resistance, 4: 108, 4: 111, 4: 112t
Index methicillin resistance development, 4: 106f, 4: 108–109 bacteriophages, 4: 108 biochemistry, 4: 111 biofilm, 4: 108 bovine clone, 4: 104 bulk milk, 4: 114 carriers, 4: 104–105 characteristics, 4: 111 cheese, 4: 114 growth in, 1: 648f public health aspects, 1: 645, 1: 648, 1: 648f, 1: 648–649, 1: 650 classification, 4: 111 colonization bacterial factors, 4: 104 host factors, 4: 104 humans, 4: 104 control, 4: 115 general hygiene, 4: 115 milk cooling, 4: 115 milk heating, 4: 115 culture, 4: 111 dairy products, incidence in, 4: 114 dried milk products, 4: 114 enterotoxins, 4: 108, 4: 113–114 detection, 4: 113 evasins, 4: 105, 4: 107f fermented milk products, 4: 114 growth-influencing factors, 4: 111 identification, 4: 113 infection, 4: 113 infection risk, 4: 104 intoxication, 4: 113 isolation, 4: 113 liquid milk, incidence in, 4: 114 liquid products, 4: 114 lysotyping, 4: 111 mastitis see Staphylococcus aureus mastitis methicillin resistance development, 4: 106f, 4: 108–109 microbiological analytical methods, 1: 217 microorganism interactions, 4: 115 milk, incidence in, 4: 114 molecular typing methods, 4: 104 morphology, 4: 111 opsonophagocytosis, 4: 106 pasteurization, 4: 115 pathogenicity, 4: 113 population structure, 4: 104 putative surface proteins, 4: 105 quarter samples, 4: 114 raw milk cheeses, 1: 659 serology, 4: 111 small colony variants, 4: 108 somatic cell count, 3: 895 sources, 4: 112 animal, 4: 112 environmental, 4: 112 human, 4: 112 infected udders, 4: 112 squamous cell adherence, 4: 105 toxins, 4: 106f, 4: 107 vaccination, 4: 109 virulence factors, 4: 105 wall teichoic acid, 4: 106f Staphylococcus aureus enterotoxicosis agents, 4: 113 symptoms, 4: 114 Staphylococcus aureus mastitis, 4: 104 acute clinical infections, 3: 409 antibiotic resistance, 4: 111–112 antibiotic therapy, 3: 411 antibiotic therapy-vaccination combination, 3: 436 chronic infections, 3: 409 contagious organisms, 3: 409 control, 3: 411 dry cow treatment, 3: 411
extended therapy, 3: 436 heifers, 3: 409, 3: 412 incidence at calving reduction, 3: 412 medical therapy, 3: 435 combination therapy, 3: 436 intramuscular injections, 3: 436 poor response to, 3: 436, 3: 436f milking hygiene practices, 3: 411 shedding patterns, 4: 112 subclinical infections, 3: 409 transmission, 3: 409 vaccination, 3: 411–412, 4: 109 Staphylococcus equorum, 1: 754 Staphylococcus equorum subsp. linens, 1: 396 Staphylococcus succinus subsp. casei, 1: 396 Staphylokinase, 4: 107 Stara Zagora sheep, 1: 332t Starch(es) amylopectin/amylose content of grains, 2: 336 cheese analogues, 1: 815t, 1: 818 dairy desserts, 2: 908, 2: 909t digestibility (DE), 2: 338, 2: 338f, 2: 339t, 2: 340 enzymatic (in vitro) digestion vs., 2: 406 digestion, 3: 991, 3: 991f endosperm granules, species variation, 2: 336–338 as fat mimetic, 1: 531 feed supplements grazing dairy cows, 2: 456 milk composition changes, 2: 456 fermentation estimates, 2: 431–432 rumen fermentation, 2: 338, 3: 982 steam gelatinization, 2: 338 structure, 4: 355 ‘Star-glazing’ posture, 2: 246 Start codon, 3: 1056–1057 Starter culture(s), 1: 440, 1: 552–558, 1: 559–566, 1: 625, 2: 477–482 accelerated cheese ripening, 1: 565 acidification control, 1: 440 activity-affecting physiological factors, 1: 563 lactose metabolism, 1: 563 salting effects, 1: 564 setting temperature, 1: 563 activity and viability, 2: 480 inhibiting factors, 2: 480, 2: 532 performance criteria, 2: 477 species protocooperation, 2: 531, 3: 53, 3: 94 adjunct starter species, for improved properties, 3: 106–107, 3: 109 adventitious organism control, 1: 553 coliforms, 1: 661–662 aroma compound production, 1: 553 artisan multiple-strain blends, 1: 440 Asian fermented milks, 2: 509t attenuated, 1: 565 automated plants, 1: 440 back-slopped starter, 1: 554t bacteria, 1: 625 bacterial numbers, 1: 625 bacteriophage resistance bacteriophage insensitive mutants (BIM), 1: 442 genetic resistance, 1: 442 bacteriophage sensitivity, 1: 555 biochemistry, 1: 559 intracellular enzyme release, 1: 625 biogenic amines, 1: 453 bulk, 1: 557 butter, historical aspects, 1: 28, 1: 29f buttermilk, 2: 491, 2: 493t carbohydrate metabolism, 1: 560, 1: 561f characterization, biosensors, 1: 243 Cheddar cheese see Cheddar cheeses cheese, 1: 440, 1: 625 historical aspects, 1: 30 cheese flavor, 1: 559–560, 1: 564 autolysis, 1: 564 bitterness, 1: 564 cheese salting, 1: 596
945
choice of, 1: 555, 1: 556f bacteriophage-resistant cultures, 1: 556 cheesemaking characteristics, 1: 555 specific properties, 2: 516, 2: 517 chromosome sizes, 1: 565 citrate fermentation, 3: 170 bacterial enumeration techniques, 3: 170–171 citric acid metabolism, 1: 562 classification, 1: 553–554 commercial, 1: 442 frozen cultures, 1: 558 defined see Defined starter cultures delivery systems, 1: 557 commercial frozen/freeze-dried cultures, 1: 558 primary stocks, 1: 557 size of, 1: 557 direct vat inoculation, 1: 558 direct vat set (DVS) concentrates, 1: 442, 1: 444 DL-type, 1: 553, 1: 664 DNA rearrangements, 1: 566 E. coli control, 4: 65 enzyme-modified cheese, 1: 803 exopolysaccharide formation, 2: 481 fermented milk, 2: 470, 2: 471t product folate content, 4: 683 flavor-enhancing adjunct cultures, 1: 555 flavor production, 1: 553 freeze-dried cultures, 1: 558 functions, 1: 536–537, 1: 552, 1: 559 water activity, 1: 553 gas blowing defects, 1: 662 avoidance, 1: 663–664, 1: 664 genetically-modified strains, 1: 557 genetic improvements, 1: 566 genetics/genomics, 1: 565 chromosome sizes, 1: 565 comparative genome hybridization analyses, 1: 565 genetic improvements, 1: 566 genome sequences, 1: 565 hard Italian cheeses, 3: 108 historical aspects, 1: 440, 1: 552, 1: 559 inferred genes, 1: 565 inoculation systems, 1: 443 intracellular enzyme release, 1: 625 koumiss, 2: 474, 2: 507, 2: 509t lactate metabolism, 1: 553 lactic acid production, 1: 538, 1: 552, 1: 625 lactose transport, 1: 560 lipolysis, 1: 562 low-fat cheese flavor, 1: 840 L (laboratory) starters, 1: 440–441 L-type, 1: 553, 1: 663–664 manufacture, 2: 478 bulk tank sterilization measures, 1: 441, 1: 442–443 frozen and freeze-dried concentrates, 1: 442, 2: 479–480 traditional, 1: 440, 2: 478–479, 2: 481, 2: 515 mesophilic cultures, 1: 554, 1: 625, 2: 477, 2: 478t, 2: 491 mesophilic mixed-strain cultures, 3: 139–140 microbial DNA fingerprinting, 1: 635–636, 1: 636f mixed, 1: 556 multiple-strain systems, 1: 442 ‘‘natural’’, 1: 554t neutralization, 1: 607 optimal pH, 1: 563–564 paired single strains, 1: 441–442 phage inhibitory media, 1: 443 phage resistance, 3: 56 phage-resistant variant selection, 1: 556 genetic factors, 1: 556–557 pH changes, 1: 552 pH control methods, 1: 443 plasmids, 1: 565 product matching, 1: 555 properties, 1: 559–566
946 Index Starter culture(s) (continued ) protein degradation, 1: 562, 1: 563f P (practice) starters, 1: 440–441 quality control, 1: 443–444 rapid-growth, pathogen control in cheese, 1: 646 redox potential, 1: 553 rotation, 1: 556 rotation strategy, 3: 135 setting temperature, 1: 563 species, 1: 559, 1: 559, 1: 560t storage, 1: 557 strain combination, 1: 441 strain isolation, 1: 441, 2: 477, 2: 529 strain selection, 1: 441, 2: 477, 2: 529 Swiss-type cheese, 3: 108 thermophilic cultures, 1: 554, 1: 625, 2: 477, 2: 479t traditional mixed (undefined) blends, 1: 440, 1: 441 traditional preparations, 1: 554 types, 1: 553, 1: 554t, 2: 477, 2: 478t undefined, 1: 554, 1: 554t whey cultures, 1: 554t yeasts, 4: 751 yogurt see Yogurt see also specific bacteria Starter feed, pelleted ewe lambs, 2: 883, 2: 883t goat kids, 2: 826–827, 2: 827–828, 2: 829t State diagrams, 4: 709, 4: 709f ice formation, 4: 709 milk, 4: 716–719, 4: 719f State-owned farms,China, 2: 84 Static grease traps, 4: 621 Static light scattering, 1: 133 caveats, 1: 134 contrast matching, 1: 134 optical constant, 1: 134 principles, 1: 133 Rayleigh–Gans–Debye form factor/scattering factor, 1: 134 size distribution, 1: 134–135 Statin drugs, 3: 1032 atherosclerosis modulation, 3: 1032–1033 mechanism of action, 3: 1032 pleiotropic effects, 3: 1032–1033 serum cholesterol, 3: 1032 Stationary plug-flow beds, 4: 213 STATISTICA, 1: 108 Statistical analysis, 1: 83–92 calibration, 1: 91 models, 1: 91t multivariate calibration, 1: 92 nonlinear models, 1: 91 reference standards, 1: 91, 1: 91t univariate calibration, 1: 92 check standard methodology, 1: 87 distribution evaluation, 1: 88 exponentially weighted moving average (EWMA), 1: 89 s control charts, 1: 88–89, 1: 89f x-bar charts, 1: 88, 1: 89f, 1: 89f gauge R&R studies, 1: 89 infrared spectrometry see Infrared (IR) spectrometry measurement error, 1: 85, 1: 85f bias, 1: 85 normal distributions, 1: 86, 1: 86f repeatability, 1: 85 replicates, 1: 85 reproducibility, 1: 85 measurement process characterization, 1: 87 biases, 1: 87 data integrity, 1: 87 instrumental procedure, 1: 87 measurements, 1: 83 continuous variables, 1: 83 nominal properties, 1: 83 sensory evaluation, 1: 83 multivariate see Multivariate statistical tools
software, 1: 92 variables, 1: 83 Statistical process control (SPC), 4: 243, 4: 275 empirical linear techniques, 4: 243 Steady air admission, milking equipment cleaning, 3: 635 Steam, 4: 589 Steam boilers classification, 4: 590 firing arrangements, 4: 591 pressure level, 4: 590 working fluid, 4: 590 Steam heaters, 4: 219 Steam infusion/injection treatments, 2: 714, 2: 721–722, 3: 284, 3: 284f Steam piping systems design, 4: 593 cost-tube diameter relationship, 4: 593, 4: 594f erosion prevention, 4: 594 pressure drop calculations, 4: 594 optimization, 4: 594 Steam-stripping technology, 3: 735 Stearic acid production, 3: 660, 3: 662f skeletal structure, 3: 656f Stearoyl-CoA desaturase (D9-desaturase), 3: 354, 3: 661 Steatorrhea, 3: 712 Steel properties, 4: 260 stainless see Stainless steel types, 4: 260 Stejneger’s beaked whale milk, 3: 576–579 Stereomicroscopy, 1: 227t Sterigmatocystin, 1: 904t, 4: 793, 4: 808 cheese, 4: 783 chemical properties, 4: 808 determination, 4: 810 dihydrobisfuran moiety, 4: 793 food contamination, 4: 810 as mutagen, 4: 810 producing fungi, 4: 810 regulation, 4: 810 structure, 4: 793f, 4: 808, 4: 810f toxicity, 4: 810 Sterilization containers see Containers definition, 3: 310 milk and dairy products, 2: 714–724 principles kinetics, 2: 714 objectives, 2: 714 process optimization, 2: 715 sterility standards and conditions, 2: 714 processes and equipment, 2: 721 continuous-flow, 2: 721 in-container batch autoclaves, 2: 722, 2: 722f continuous operation, 2: 722, 2: 723f, 2: 723f starter culture protection, 1: 442–443 temperature- time profiles, 2: 720, 2: 720f, 2: 721 Sterilized (UHT) milk, 2: 714–724 Sterilized milk products age gelation, 3: 290 additive effects, 3: 291, 3: 291f, 3: 291t casein micelle modifications, 3: 292 heat treatment severity, 3: 290 homogenization, 3: 290–291 mechanistic aspects, 3: 292 minerals in, 3: 291 non-enzymatic proteolysis mechanisms, 3: 292–293 non-fat constituents, 3: 290–291, 3: 292f processing variables, 3: 290, 3: 290t proteins, 3: 289t, 3: 291 proteolysis, 3: 292 storage conditions, 3: 290, 3: 291f, 3: 292f, 3: 292f storage temperature, 3: 291, 3: 292f
browning reaction, 3: 293 color, 3: 293 flavor, 3: 293, 3: 293t acceptability, 3: 293–294 bitterness, 3: 294 lipolysis, 3: 293 proteolysis, 3: 293 storage effects, 3: 293 gelation, 3: 282 recombined products, 3: 317 gelation-free storage time, 3: 290–291 milk microbiological load, 3: 290–291 melanoidins, 3: 293 nutritional values, 3: 294 light effects, 3: 295 oxygen levels, 3: 295 physicochemical changes, 3: 288, 3: 289t quality-affecting factors, 3: 288, 3: 289t lactose, 3: 289, 3: 289t minimization, 3: 296 vitamin loss, 3: 294–295, 3: 295f, 3: 295t Sterilized recombined milk products, 3: 316 fat sources, 3: 317 milk powder, 3: 317 production protocol, 3: 316 Sterols butter, 1: 506 LDL-cholesterol levels, 3: 731 milk, 3: 651 sheep milk, 3: 499 structure, 3: 651, 3: 651f vitamin absorption inhibition, 3: 1001 Stickiness, milk powder, 2: 122 Sticking curve, 4: 213–214, 4: 214f Stir bar sorptive extraction (SBSE), 2: 548 sequential, 2: 548, 2: 549f volatiles, extraction/concentration, 2: 548, 2: 549f Stirred-bed ionic exchange, whey, 2: 127f, 2: 128 Stirred crystallizers, 3: 188 Stirrers, 2: 761 Stirring device selection, 4: 126 Stocking rate, ecosystems and, 2: 879 Stokes–Einstein relation, 1: 136 Stokes’ equation, creaming, 1: 21, 3: 675–676 Stokes’ law, 2: 750 emulsion creaming rate, 1: 62 velocity of separation, 4: 166 Stolchlometry, hydrocarbon burning, 4: 592 Storage buffalo milk, 2: 776 butter, 3: 709 coffee cream changes, 1: 914 defects, evaporated milk see Evaporated milk khoa, 1: 883 labeling instructions, 3: 5 lactose-free milk, 3: 233, 3: 233 liquid food samples, 1: 73 manure, 4: 631–632 milk/cream rheology, 4: 523 milk powder, 2: 115 milk quality, effects on, 3: 642–648 pasteurized processed cheese products, 1: 807 riboflavin, effects on, 4: 704 sheep milk, 2: 872 sweet whey powder, 3: 231–232 temperature, microstructure effects, 1: 231 whey protein isolate, 3: 234 Storage relative humidity, 4: 710 Storage tanks raw milk storage, 3: 642 selection, 4: 126 Storch, Vilhelm, 1: 28 Straight through process, milk powder instantization, 2: 113–114, 2: 114f Strain, 4: 575 fracture, cheese, 1: 695t Strategic planning, 1: 482 Stratified flow, milklines, 2: 810
Index Strawberry clover (Trifolium fragiferum), 2: 577 Strawberry foot rot see Papillomatous digital dermatitis (PDD) Strawberry yogurt, spoilage molds, 4: 781 Straw supplements, pasture-based cows, 3: 987 Stray voltage, 2: 17 Stream bank stability, riparian areas, 2: 27 Strecker degradation, 3: 221, 3: 222, 3: 227, 3: 232 Streptococcus biofilms, 1: 446 environmental species detection, 3: 417 mastitis, 3: 416, 3: 416t fermentation starters, 3: 455 gas blowing defects, cheese, 1: 665 gastrointestinal microflora (human), 1: 383t genome, 3: 75 in milk, 3: 449 starter cultures, 1: 559, 1: 560t see also individual species Streptococcus agalactiae mastitis antibiotic therapy, 3: 410 ‘blitz’ therapy, 3: 435 contagious infections, 3: 408 control, 3: 410 medical therapy, 3: 435 prevention, 3: 410–411 shedding, 3: 409 reservoirs, 3: 408–409 Streptococcus canis, 3: 417 Streptococcus dysgalactiae, 3: 417 Streptococcus dysgalactiae spp. dysgalactiae characteristics, 3: 418 identification, 3: 417 intramammary infections, 3: 418 summer mastitis, 3: 418 Streptococcus macedonicus, 3: 143 Streptococcus mutans, 3: 1034–1035 Streptococcus parauberis, 3: 417–418 Streptococcus pneumoniae, 3: 255 Streptococcus thermophilus, 1: 401, 3: 143–148 associative growth, 3: 122 bacteriocins, 3: 144 bacteriophages, 1: 431, 3: 146 genome sequences, 1: 434 geographical diversity, 3: 146 morphology, 1: 431 yogurt vs. cheese plants, 3: 146 bifidus products, 1: 388 biofilms, 1: 448, 3: 143, 3: 146, 3: 148f blue mold cheeses, 1: 768 brine-matured cheeses, 1: 793 characteristics, 2: 479t, 2: 530, 3: 143 cheese starter, 3: 145 classification, 3: 143 closely related species, 3: 143 dairy product significance, 3: 145 Dutch-type cheese defects, 1: 726–727 exocellular polysaccharide production, 3: 145 fermented milk starter, 3: 83 galactose-using strains, 3: 144 genetics, 3: 144 genome, 3: 75, 3: 75f genomic relatedness, Lactococcus, 3: 59, 3: 60f growth, 3: 144 free amino acid requirements, 3: 144 habitats, 3: 143 historical aspects, 1: 30 lactobacilli symbiotic relationship, 3: 145 lactose fermentation, 3: 144 low-moisture part-skim mozzarella (pizza cheese), 1: 740, 1: 740–741 metabolism, 3: 144 metabolites, 3: 144 pasteurization, 3: 146, 3: 147f wild-type strains, 3: 147f peptidase systems, 3: 144
plasmids, 3: 145 polymers, 3: 145–146 as probiotics, 3: 144 probiotic supporter strain, 1: 415 raw milk, 3: 143 starter cultures, 1: 625 Swiss-cheese starter culture, 1: 713, 1: 714–715 temperate phage, 3: 146 thermization, 3: 146 traditional use, 3: 143 yogurt, 2: 472, 2: 525, 2: 527, 2: 530, 3: 145 Streptococcus uberis characteristics, 3: 417 genotypes, 3: 417–418 identification, 3: 417 intramammary infections, 3: 418 mastitis, 2: 48–49, 3: 418 Streptococcus parauberis vs., 3: 417–418 virulence factors, 3: 418 Streptococcus uberis adhesion molecule (SUAM), 3: 418 Streptomyces mobaraensis, 2: 297 Streptomycin, biosensor analysis, 1: 240 Stresa Convention, 4: 312, 4: 323, 4: 323f cheese legislation, 1: 843 Stress cheese rheology, 1: 688 cold see Cold stress definition, 4: 575 estrous behavior, 4: 465 fracture, cheese, 1: 695t heat see Heat stress immunity effects, 2: 828–829, 2: 830 management, 3: 431 mastitis, 3: 431 milk cortisol concentration, 2: 770 reproduction and, endocrine pathways, 4: 575 Stress-controlled rheometers, 1: 274 Stress corrosion cracking, 4: 261 Stressor, 4: 575 Stress relaxation, cheese rheology, 1: 689, 1: 691t Stretching low-moisture part-skim mozzarella (pizza cheese), 1: 738 pasta-filata cheeses, 1: 616, 1: 747 Stroke vitamin C, 4: 672–673 vitamin E, 4: 657–658 Stroma, mammary gland, 3: 338 Strontium, 1: 902 Structural carbohydrate:nonstructural carbohydrate ratio, pasture-based transition cows, 2: 466 papillae development, 2: 466 subsequent milk yield, 2: 466f, 2: 466–467 Structured Feta cheese, 1: 792 Structured lipids, 1: 529 Strychnine, 2: 845 Students, 2: 4 Styrene, 4: 778 Subacute ruminal acidosis (SARA) prevention, 2: 201 rumen pH, 2: 199–200 transition diet, 2: 199 treatment, 2: 202 Subchronic toxicity tests, additive safety, 1: 57 Subclinical hypocalcemia, 2: 239 Subcutaneous abdominal artery, 3: 334 Subcutaneous abdominal veins (milk veins), 3: 335 Subjective heat stability assay, 2: 744–745 Subterranean clover (Trifolium subterraneum), 2: 559 Subterranean lines, irrigation, 2: 593 Subunit poisoning, bacteriophage resistance, 1: 437 Subunit vaccines, Johne’s disease, 2: 179 Succinic acid cheese flavor, 1: 642 Propionibacterium pathways, 1: 406 Swiss-type cheese flavor, 1: 714 Sucrose,Bifidobacterium fermentation patterns, 1: 386t Sucrose fatty acid polyesters, 1: 529
947
Sudanese Nubian goats, 1: 311t Sudan grass, 2: 554, 2: 564 Sudden drying-off, sheep, 2: 873 Sudden infant death syndrome (SIDS), 4: 49 Sugar(s) fermentation patterns, Bifidobacterium growth requirements, 1: 386t fragmentation (dealdolization), 3: 220, 3: 221f products, reactivity, 3: 221, 3: 222t reactions with amines (Maillard reactions), 3: 217 furfural formation, 3: 219–220 reductone formation, 3: 220 rumen fermentation, 3: 983 see also individual sugars; Lactose Sugar alcohols (polyol), as prebiotics, 4: 358 Sugar-based supplements grazing dairy cows, 2: 456 milk composition changes, 2: 456 Sugarcane, 2: 555 Sugar-free frozen desserts, 2: 896 Sulfamethazine (SMZ), 1: 240 Sulfanilamide, nitrate/nitrite analysis, 1: 909–910 Sulfate absorption, 3: 998 Sulfhydryl groups, biosensors, 1: 243 Sulfhydryl oxidase (SOx), 2: 330 functions, 2: 330 heat stability, 2: 330 purification, 2: 330 Sulfide absorption, 3: 998 Sulfonamide, 2: 194 Sulfur, 2: 377 absorption, ruminants, 3: 998 deficiency, plants, 2: 589 dietary supplementation, milk fever prevention, 2: 244 requirements, 2: 377 rumen fermentation, 3: 983 ruminal microbe requirements, 2: 377 Sulfur chemiluminescence detector (SCD), 1: 678–679 Sulfur compounds Brevibacterium linens, 1: 570 Cheddar cheese taste, 1: 710 cheese flavor, 1: 682 smear-ripened cheese aroma, 1: 764 Sulfur fertilizer, 2: 589 Summer butter, 1: 513, 3: 704–705 ‘Summer infertility’, 1: 473 Summer mastitis, 3: 418 Summer milk, 3: 718 Sunandini cattle, 1: 303t, 1: 306 Sun-dried milk, 1: 14 Sunflower meal, 2: 352 definition, 2: 349 dehulled, 2: 354 solvent-extracted, 2: 354 soybean meal vs., 2: 354 Sunflower seed, 2: 352 definition, 2: 349 high oleic acid varieties, 2: 352 lecithin composition, 1: 66t milk fat percentage and, 2: 352 Sunlight-oxided flavor, homogenized milk, 3: 678 Supercritical fluid extraction cholesterol removal, 3: 735 butter, 3: 737 butter oil, 3: 737–738 milk fat globule membrane, 3: 693 Superinfection exclusion, bacteriophage resistance, 1: 437 Superovulation, 2: 610 donor variation, 2: 624, 2: 626f hormonal stimulation methods, 2: 623, 2: 627f insemination, 2: 626 response-influencing factors, 2: 625 donor age, 2: 625–626 donor fertility, 2: 625–626 nutrition status, 2: 626
948 Index Superovulation (continued ) timing related to estrus, 2: 625 sheep, 2: 890 see also Embryo transfer (ET) Superoxide dismutase (SOD), 2: 328 activity in milk, 2: 329 assays, 2: 329 biological function, 2: 328 heat stability, 2: 329 isoenzyme types, 2: 328 purification, 2: 329 Superoxide:superoxide oxidoreductase see Superoxide dismutase (SOD) Superpasteurized milk see Extended shelf life (ESL) milk Supersaturation change of state, 3: 185 crystal growth kinetics, 3: 191 definition, 3: 185 induction time, 3: 188 Supervised networks, 1: 107 Supervisory control and data acquisition (SCADA), 4: 242 Supplements see Feed supplements Suppressor T lymphocytes, 3: 390 Supramammary lymph nodes, 3: 335 Surface-active agents, milk chocolate, 1: 857, 1: 858f Surface conditions, biofilm development and, 1: 445, 1: 446, 1: 448 Surface dry salting see Cheese salting Surface finishes, 4: 137 agitators, 4: 163 finishing technique, 4: 137 Surface light scattering, 3: 473 Surface mold-ripened cheeses, 1: 773–782 aroma production, 1: 779 microbiology, 1: 780t classification, 1: 773, 1: 774t future work, 1: 781 microbiology, 1: 774, 1: 776f, 1: 776t, 1: 777t LAB starter, 1: 775 Penicillium camemberti, 1: 774–775, 1: 775, 1: 776f, 1: 778 surface bacteria, 1: 775 yeasts, 1: 775 ripening, 1: 773, 1: 774 acid-soluble nitrogen, 1: 777–778, 1: 779f ammonia production, 1: 778, 1: 779f atmospheric conditions, 1: 781, 1: 781 bacterial flora changes, 1: 775 biochemistry, 1: 777 free fatty acids, 1: 778, 1: 780t humidity effects, 1: 781 lactate metabolism, 1: 667, 1: 777, 1: 778f lactose metabolism, 1: 777, 1: 778f lipolysis, 1: 778 Penicillium camemberti, 1: 568 pH changes, 1: 777 physicochemistry, 1: 777 proteolysis, 1: 777 temperature effects, 1: 781 secondary cultures, 1: 568t see also specific cheese types Surface plasmon resonance (SPR), 1: 237, 1: 237f HPLC, 1: 174 infant formulae analysis, 2: 136 Surface plots, 4: 270, 4: 271f Surface quality, 4: 137 Surface-ripened cheeses pH, pathogen control, 1: 647 ripening Brevibacterium linens, 1: 569–570 Geotrichum candidum, 1: 567–568 secondary cultures, 1: 568t spoilage molds, 4: 780–781 yeasts, 1: 627 see also specific cheeses; Surface mold-ripened cheeses
Surface roughness, 4: 138t welds, 4: 138 Surfactants dairy plant effluents, 4: 617 low-fat cheeses, 1: 838 processing wastewaters, 4: 634 Surge Milker, 1: 6 Surk cheese, 1: 785f, 1: 786 Surveillance networks, infrared spectrometry, 1: 122 Survival analysis, 2: 653 Sus domesticus see Swine Suspensions, water diffusion, 1: 162, 1: 163f Sutro Weir, 4: 622 Swabs, biofilm detection, 1: 448 Swamp buffalo, 1: 340 Swamp type buffalo, 2: 772–773, 2: 773t Swede (rutabaga; Brassica napus var. napobrassica), 2: 560 Swedish Red and White (SRB) cattle, 1: 295 Sweet buttermilk, 2: 489, 2: 489 cheese yield, pizza cheesemaking, 3: 695 Sweet cream salted butter, 1: 492–493 unsalted butter, 1: 492–493 Sweet cream buttermilk, evaporated milk, 1: 862 Sweetened condensed milk (SCM), 1: 869–873, 2: 128 Codex standards, 4: 329 description, 1: 869 historical aspects, 1: 12, 1: 869 market share, 1: 869 microbiology, 1: 872 milk solids, 1: 869 packaging, 4: 19 problems, 1: 872 age gelation, 1: 872 color defects, 1: 872 flavor defects, 1: 872 lactose crystallization, 1: 872 microbiology, 1: 872 production, 1: 869, 1: 870f, 1: 871f concentration, 1: 870 cooling, 1: 871 homogenization, 1: 871 packing, 1: 871 preheating, 1: 870, 1: 873 seeding, 1: 871 sugar addition, 1: 869, 1: 873f recombined products, 3: 317 ingredients, 3: 318 recombination process, 3: 317 viscosity, 3: 318 reconstituted products, 3: 317 regulations, 1: 869 rheology, 4: 526 spoilage molds, 4: 781 uses, 1: 869 Sweeteners, 2: 899 cheese analogues, 1: 815t European Union, 1: 34, 1: 35t frozen desserts, 2: 896–897 natural, dairy desserts, 2: 908 nonnutritive, 1: 38 nutritive, 1: 38 United States, 1: 38 see also individual sweeteners Sweet whey, 4: 731 composition, 4: 731, 4: 732t definition, 3: 873 nanofiltration, 4: 743 Sweet whey powder (SWP) browning deterioration, 3: 231–232 shelf life, 3: 231–232 storage, 3: 231–232 Swine artificial insemination, 4: 473 seasonal breeding, 4: 447 ‘Swinging vacuum’ machine, 3: 943–944
Swing-over milking parlors, 3: 962, 3: 963f Swissalp Panorama cheese, 1: 786–787 Swiss cheese, microfiltration bacteria removal, 1: 623 Swiss Emmentaler PDO cheese, 1: 652–653 Swiss goat breeds, 1: 313 Swiss-type cheeses, 1: 712–720 cultures, 1: 713, 1: 714 facultatively heterofermentative lactobacilli, 1: 714 LAB, 1: 713 propionic acid bacteria, 1: 713 defects, 1: 719 animal nutrition, 1: 719 butyric acid, 1: 719 Clostridium sporogenes, 1: 719 Clostridium tyrobutyricum, 1: 719 eye formation, 1: 719 taste, 1: 719 eye formation, 1: 408, 1: 715 gas production, 1: 715, 1: 715f propionibacteria, 1: 715 flavor characteristics, 1: 718 aspartate, 1: 714 fatty acids, 1: 408 free amino acids, 1: 718 free fatty acids, 1: 408 nonvolatile compounds, 1: 718, 1: 718t off-flavors, 1: 718 peptides, 1: 718 propionate, 1: 408 ripening changes, 1: 719t succinate, 1: 714 volatile compounds, 1: 718 gas blowing defects, 1: 666 avoidance, 1: 666 hygienic safety, 1: 720 plasmin activity, 2: 312 production, 1: 712 proline content, 1: 571 Propionibacterium freudenreichii, 1: 407, 1: 408 ripening, 1: 716, 1: 717f, 1: 717t, 1: 719t free amino acids, 1: 716 humidity, 1: 716 lactate metabolism, 1: 668 lactic acid fermentation, 1: 716 propionibacteria, 1: 571, 1: 716–717 thermophilic lactobacilli, 1: 716 trichloroacetic acid-soluble nitrogen, 1: 716 water-soluble nitrogen, 1: 716 secondary cultures, 1: 568t starter culture Lactobacillus delbrueckii subsp. lactis, 1: 408 Lactobacillus helveticus, 1: 408 starter cultures, 3: 108 technology, 1: 712 texture, 1: 717, 1: 718f yak milk, 1: 350, 3: 533 see also specific cheeses Switzerland dairy societies, 2: 103 herby cheeses, 1: 786 spiced cheeses, 1: 786 Symphalangus syndactylus (siamang) milk oligosaccharides, 3: 271t, 3: 617t Synchro-Mate-B (SMB) treatment, 4: 451–452 Synchronized estrus see Estrus synchronization Synchronized ovulation see Ovulation synchronization Syndactylism (mulefoot), 2: 676, 2: 676f Syneresis (curd), 1: 591–594 cheese ripening, 1: 538, 1: 539 cheese variety differentiation, 1: 591, 1: 592t definition, 1: 591 dulce de leche defects, 1: 879 factors affecting, 1: 593 casein proteolysis, 1: 593–594 coagulation/cooking temperatures, 1: 593 concentrated milks, 1: 593
Index heat treatment, 1: 593 pH, 1: 593, 1: 593f time relationship, 1: 593f low-moisture part-skim mozzarella (pizza cheese), 1: 737–738, 1: 739f, 1: 739f measurement, 1: 591, 1: 592t mechanisms, 1: 591 k-casein hydrolysis, 1: 591 casein interactions, 1: 592 casein network, 1: 592–593 environmental changes, 1: 592 modeling, 1: 591 NMR relaxation studies, 1: 157–158, 1: 158f pH effects, 1: 552, 1: 552 ‘Syneresis tube’, acid casein manufacture, 3: 856–857 Synthetic emulsifiers see Emulsifiers Synthetic hormones as contaminants, 1: 894 see also specific hormones ‘Synthetic milk adjusted’ (SMA), historical aspects, 1: 15 Synthetic milk sheep, 1: 339 Synthetic oviduct fluid (SOF), 2: 620 Synthetic UHT flavor, 3: 293–294 Sysat, 1: 108 ‘System casse’ milking parlor, sheep, 2: 868, 2: 869f, 2: 869f System diversity, 1: 483 Systems biology, 3: 966
T T1 (spin lattice relaxation) see Nuclear magnetic resonance (NMR) T2 (spin–spin relaxation) see Nuclear magnetic resonance (NMR) T-2 toxin, 4: 798, 4: 799f Table cheese, 1: 840 Tactile appraisal, 5-point body condition scoring, 1: 459–460 Tafel plot, 4: 259, 4: 259f metal corrosion in water, 4: 259–260, 4: 260f Tagatose, 3: 178–179, 3: 201 Taguchi, Genichi, 4: 273–274 Taguchi method, 4: 266–267 control factors, 4: 274 data analysis, 4: 268, 4: 269f improved performance settings identification, 4: 268 interaction, 4: 267 Latin squares, 4: 266–267, 4: 267t means plot, 4: 268, 4: 270f principles, 4: 273 severity index, 4: 268 Tahirova sheep, 1: 338 Tail docking, 4: 729 ‘Tailor-made’ additives, lactose crystallization, 3: 192 Tailor-made cultures, 3: 966 phage resistance mechanisms, 3: 967 Tail-painting, heat detection, 4: 477 Taleggio cheese, 4: 751 Tall fescue (Festuca arundinacea), 2: 576 TALL FORM drying chamber, 4: 216 Tammar wallaby lactation phases, 3: 554, 3: 555f milk bioactive identification, 3: 559 composition, 3: 555, 3: 555f oligosaccharides, 3: 271t, 3: 272 protein composition, 3: 556–558, 3: 557f milk protein gene expression, 3: 556–558, 3: 557f reproductive strategy, 3: 553–554, 3: 554f WAP-like protein, 3: 840 Tandem milking parlors see Side-opening (tandem) milking parlor Tank(s) cleaning in place, 4: 284–285 selection, 4: 126 Tank trucks, cleaning, 3: 642
Tannins, bloat, 2: 208, 2: 577, 2: 577, 2: 584–585 Tapeworms, goats, 2: 831 Tarag, 2: 510 Tarantaise cattle, 1: 297–298 Targeted breeding, 4: 449f, 4: 450–451 Tariffication, 4: 343 Tariff rate quotas (TRQs), 4: 300 Taste see Flavor T¨atmj¨olk (l˚angfil), 2: 472, 2: 499, 4: 749 Tattoos, 2: 832 Taurine primate milk, 3: 625–627 sheep milk, 3: 496 Taylor, Michael, 1: 26 TB complex, 2: 195 TB skin test, 2: 196 false-positive results, 2: 196 TCDD (2,3,7,8-Tetrachlorodibenzo-p-dioxin), 1: 898, 1: 899f Teaser bulls, heat detection, 4: 477 Teat(s) arterial supply, 3: 334 bacterial penetration, 3: 440 bacterial resistance, 3: 442 bluetongue, 2: 148–149, 2: 149f canal see Teat canal condition, 3: 442 contamination, housed vs. at pasture cows, 3: 633t development, 3: 341–342 diameter, intramammary infection susceptible, 3: 384 dipping see Teat dipping disinfection see Teat disinfectants/disinfection end see Teat end frozen, 4: 553 gross anatomy, 3: 331 hereditary factors, intramammary infection susceptible, 3: 384 length, hereditary factors, 3: 384 lesions, 3: 442 machine milking-related factors, 3: 443, 3: 444t liner pressure, 3: 445, 3: 445f pulsation, 3: 445 vacuum setting, 3: 445 microscopic anatomy, 3: 333, 3: 333f milking-induced congestion/edema, 3: 382 orifice lesions, mastitis risk, 3: 383–384 orifice openness, 3: 442 ‘patent/leaky’, 3: 383 postdipping, mastitis prevention/control, 3: 433 predipping mastitis prevention, 3: 432 procedure, 3: 432 premilking preparation, 3: 440 scoring, target criteria, 3: 443, 3: 443t shape, hereditary factors, 3: 384 skin, 3: 331 mammary resistance mechanisms, 3: 381 supernumerary, 3: 331 swelling, 3: 442 vascular damage, 3: 442 venous drainage, 3: 335 Teat canal antibiotic treatment syringe insertion full insertion, 3: 333–334, 3: 439 partial insertion, 3: 333–334, 3: 383, 3: 384f, 3: 439 tissue trauma, 3: 333–334, 3: 383, 3: 439 cross section, 3: 381, 3: 382f diameter, mastitis, 3: 429 keratin, 3: 333, 3: 443 drying off, 3: 382, 3: 382f lactation-induced changes, 3: 381–382 loss, pulsationless vs. pulsation milking, 3: 382, 3: 382f mammary resistance mechanisms, 3: 381 length, mastitis, 3: 429 microscopic anatomy, 3: 333
949
smooth muscle fibers, 3: 334 sphincter muscle, resistance mechanisms, 3: 382 Teat cistern, 3: 333 Teat-cup double-chambered, 3: 944, 3: 944f, 3: 944f removal, mastitis prevention, 3: 433 Teat cup crawl, 3: 383–384 Teat-cup liners, 3: 445, 3: 445f, 3: 948 buckling pressure/critical collapsing pressure difference, 3: 948 closure/rest phase, 3: 945, 3: 945f designs, 3: 948 disinfection, mastitis prevention, 3: 433 historical aspects, 3: 944–945, 3: 945f life span, 3: 949 milking phase, 3: 945, 3: 945f mouthpiece chamber vacuum, 3: 948–949 pulsation, 3: 948 slippage, 3: 948 slips, 3: 433 touch point pressure difference, 3: 948 Teat-cup shells, 3: 948, 3: 948f Teat dipping germicidal, 3: 383, 3: 433 postmilking, Corynebacterium bovis mastitis, 3: 412–413 Staphylococcus aureus mastitis, 3: 411 Teat disinfectants/disinfection disinfectants used, 3: 632 environmental mastitis prevention, 3: 419–420 mastitis prevention, 3: 432 postmilking, 3: 632 premilking, 3: 632 Teat duct keratin antibacterial activity, 3: 386 bacteriostatic fatty acids, 3: 386 as physical barrier, 3: 386 Teat end callosity, 3: 442, 3: 443f, 3: 443f classification systems, 3: 442, 3: 443f defenses, 3: 386 milking-induced thickness changes, 3: 382 shape, intramammary infection susceptible, 3: 384–385 sphincter muscles, 3: 386 Teat sealing, mastitis, 3: 438 Teat spraying, mastitis prevention/control, 3: 433 Technology, training on see Dairy technology education Teleme cheese, 1: 794, 3: 501 Teleonomic models, 2: 429–430 TEM (transmission electron microscopy), 1: 227t, 1: 227–228, 1: 228, 1: 228f Temperate grasses, seedling vigor, 2: 587 Temperate pasture, perennials legumes, 2: 576 Temperate pastures dairy sheep, 2: 849 residual stubble height, 2: 849–850 sward height, 2: 849 grazing management see Grazing management plant types, 2: 849 Temperature-gradient gel electrophoresis (TGGE) Arthrobacter, 4: 373 PCR, 1: 222 Temperature–humidity index (THI), 4: 561 animal welfare, 1: 4 stress, 4: 561 Temperature lipolysis, 3: 604 Temperature sensors, 4: 236 Temperature–time treatment, pasteurized processed cheese products, 1: 808 Temporal temperature gradient gel electrophoresis (TTGE) cheese microbial fingerprinting, 1: 633 cheese microbiological analysis, 1: 630–631 Temporary animal identification, 1: 486 Tension, rheology, 1: 274–275
950 Index Terminal ductule lobular units (TDLUs), 3: 338, 3: 339f Terminal-restriction fragment length polymorphism (T-RFLP) cheese microbial fingerprinting, 1: 634, 1: 634f Lactobacillus, 3: 82 Terpenes goat milk, 2: 61t goat production systems, 2: 60–61, 2: 61t Terrestrial Animal Health Code, 4: 6 Terrestrial Animal Health Standards Commission, OIE, 4: 2 Terrestrial Manual (Manual of Diagnostic Tests and Vaccines for Terrestrial Animals), 4: 7 Tertiary sprout, 3: 341–342 Test and slaughter program, brucellosis, 2: 158 Test-day model, genetic evaluation, 2: 651 Testi see Carra cheese Testicular examination, bulls, 1: 476 Tetany grassy see Grassy tetany milk fever, 2: 240 winter see Winter tetany Tˆete de Moine, 4: 751 Tetra Alex valve, 2: 753, 2: 753f 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), 1: 898, 1: 899f Tetracycline, 4: 57 Tetramethyl silane (TMS), 1: 148 Tetra Pak Casomatic, 1: 613, 1: 615f Tetrasodium pyrophosphate (TSPP) milk protein concentrate, 3: 852 pasteurized processed cheese products, 1: 810 Tetra Tebel OST vat, 1: 608 Tetra Therm Aseptic Plus 2 system, 2: 702f, 2: 703 Tetra Therm ESL system, 3: 867 Tettemelk, 2: 499, 4: 749 Texture see Food texture Texture profile analysis (TPA), 1: 265, 1: 265t definitions, 1: 265, 1: 265t principles and significance, 1: 264–271 rating scales, 1: 265 Texturometer, 1: 690 T4-59-deiodinase (59D), 3: 27–28 TGGE (temperature gradient gel electrophoresis), PCR, 1: 222 Tharparkar cattle, 1: 301t, 1: 302 T helper lymphocytes, 3: 390 Theria, 3: 460 Thermal compressor, absorption refrigeration system, 4: 599 Thermal conductivity measurement, 4: 237 Thermalizers, Streptococcus thermophilus biofilms, 3: 147 Thermal stress Enterobacteriaceae control, 4: 70 mastitis, 3: 431 see also Heat stress Thermal vapor recompression (TVR), 4: 205, 4: 206f Thermistor, HTST pasteurizer, 4: 197 Thermization, 2: 693–698 cheese making milk, 1: 549–550 cheese quality effects, 2: 696 cheese yield, 2: 696 definition, 3: 310 development, 2: 693 Dutch-type cheeses, 1: 721 enzyme inactivation, 2: 695 enzymes surviving, 2: 679 indigenous enzyme activity (used as tests), 2: 693 milk components, effects on, 2: 694t microbial quality, 2: 695, 2: 695t spore activation, 2: 695 spoilage prevention, cultured dairy products, 2: 693, 2: 697 temperature, 2: 696t uses, 2: 693 Thermoduric bacteria historical aspects, 1: 27
raw milk, 3: 645 Thermodynamic equilibrium, 4: 716–719 Thermodynamics, 4: 257 Thermoneutral zone (TMZ), 4: 550 Thermophiles biofilms, 1: 446, 1: 446f historical aspects, 1: 27 Thermophilic fermentations, 2: 472 Thermophilic starter cultures, 1: 554, 1: 625 Cheddar cheese, 1: 707 pasta-filata cheeses, 1: 748 Thiaminases, 3: 1000–1001 Thiamine, 4: 701–703 deficiencies, 4: 702 goats, 2: 794 symptoms, 4: 702 feed supplements, 2: 398 functions, 2: 397t, 4: 701 loss from food heat treatment, 4: 701 storage, 4: 701 in milk, contributions to nutrient intake, 3: 1005 recommended daily uptake, 4: 702t sources, 2: 397t dairy products, 4: 702t dietary, 4: 702t structure, 4: 702f supplementation, 4: 703 UV light-induced inactivation, 4: 701 Thiamine pyrophosphate (TPP), 3: 168, 4: 701, 4: 701, 4: 702f Thickeners European Union, 1: 35 United States, 1: 39 Thin film composite membranes, 3: 867 Thin-layer chromatography (TLC), 1: 169 Thiobarbituric acid (TBA), milk lipid oxidation, 3: 720 Thiochrome, 4: 701 Thiocyanate (SCN), 2: 321 Thiols, 3: 719 Thiouracil goitrogens, 2: 380 Thixotropic materials, rheology, 1: 270 Thixotropy butter consistency, 1: 512–513 gels, 3: 304 Thoenilicin 447, 1: 410t 3-A Sanitary Standards, Inc. (3-A SSI), hygienic design regulations, 4: 134 Three-phase separators, 4: 167, 4: 168f Three-point bending, cheese, 1: 691t Three-quarter-fat butter, 1: 522 Three-stage spray drying, 2: 110 Threonine, 3: 818 Threonine aldolase, 3: 122 Through-transmission ultrasound, 1: 210f, 1: 211 Thyroid hormones euthyroid state, mammary gland, 3: 27–28 galactopoietic effects, 3: 26 somatotropin interactions, 3: 28 supplementation, 3: 26–27 see also individual hormones Thyrotropin-releasing hormone, 3: 21 Thyroxine (T4), 3: 26–27, 3: 36 Tick(s) adult stage, 2: 254f Argasidae family (soft ticks), 2: 253 worldwide distribution, 2: 255 Coxiella burnetii vector, 4: 56 diseases transmitted see Tick-borne diseases families, 2: 253 Ixodidae family (hard ticks), 2: 253 worldwide distribution, 2: 254 life cycle, 2: 253, 2: 255f vegetation ecotypes, 2: 253, 2: 254t worldwide distribution, 2: 254 see also specific ticks
Tick-borne diseases, 2: 255 control, 2: 256–257 diagnostics improvement, 2: 257 epidemiology surveys, 2: 257 Latin American dairy management, 2: 89–90 pathogen interactions, 2: 256t socioeconomic surveys, 2: 257 Tick development inhibitors, 2: 256 Tickicides cost, 2: 255 tick species, 2: 255 Tick infestations, 2: 253–257 control, 2: 255 future trends, 2: 257 life cycle stage, 2: 256 diary cattle, effects on, 2: 255 economic impacts, 2: 255 pathogen interactions, 2: 256t treatment, 2: 256, 2: 256t vaccine elaboration, 2: 257 Tie-stall barns feeding practices, 1: 4 historical aspects, 1: 3 winter temperatures, 4: 558 Tiger heart disease, 2: 163 Tilset cheese microbiology, 1: 396, 1: 397t, 1: 756, 1: 757t yeasts, 1: 398t Timed artificial insemination (TAI) dairy heifers, 4: 458, 4: 458t goats, 2: 835 lactating cows, 4: 454 nonpregnant cow resynchronization, post-first service, 4: 456, 4: 457f PGF2-GnRH injections interval, 4: 456 pharmaceutical agents, 4: 454 programs, 4: 454 Time-lapse video recording, estrus detection, 4: 462 Time varying state space modeling (TVSS), 4: 246, 4: 246f Timothy (Phleum pratense), 2: 576 Tinned can see Cans TISAB (total ionic strength adjustment buffer), 1: 195 Tissue inhibitor of metalloproteinase-1 (TIMP-1), 4: 495–496 Tissue-type plasminogen activator (t-PA), 2: 309 Titanium, dairy plant use, 4: 136 Titanium dioxide, 1: 837–838 Titratable acidity, 1: 248 determination, 1: 81 freezing point, 1: 252 sample preparation, 1: 249 Titration, milk ion quantification, 3: 914t, 3: 915 TLC (thin-layer chromatography), 1: 169
-T lymphocytes, 3: 390, 4: 502 T lymphocytes, mammary gland defense, 3: 390, 3: 390t TMR see Total mixed ration (TMR) TNO gastroIntestinal Model (TIM), folate bioavailability, 4: 683 ‘Toad skin’ defect, 4: 769 -Tocopherol see Vitamin E -Tocopherol historical aspects, 4: 652 structure, 4: 652, 4: 653f see also Vitamin E -Tocopherol historical aspects, 4: 652 structure, 4: 652, 4: 653f see also Vitamin E
-Tocopherol as chemopreventive agent, 4: 658 dietary sources, 4: 653 historical aspects, 4: 652 plasma/serum concentrations, 4: 654 structure, 4: 652, 4: 653f see also Vitamin E
Index Tocopherol(s) absorption, ruminants, 3: 1002 milk content influencing factors, 3: 718 milk lipid oxidation, 3: 718 -Tocopherol:cholesterol ratio, 4: 659 -Tocopherol equivalents (-TE), 4: 652 Tocopheroxyl radical (TO’), 4: 655 Tocotrienols, 4: 652 TOCSY (total correlation spectroscopy), 1: 151 Toffee, yak milk, 1: 349 Toggenburg goats, 1: 311t, 1: 313, 1: 313f Tolerable risk, 4: 281 Toll-like receptors (TLRs), mammary gland defense, 3: 387–388 Tooth surface loss, 3: 1039 prevalence, 3: 1034 Topping, 2: 590 Torsional vibration, curd strength, 1: 588 Torsion geometry, 1: 691t Torsion shear, 1: 695–696 Total Aggregated Measure of Support (AMS), 4: 342 Total bacterial count (TBC), 1: 215–216 automatic milking systems, 3: 956 bulk tank milk, 3: 899–900 camel milk, 3: 516 mastitis, 3: 899–900 milk quality, 3: 894, 3: 899 raw milk, 3: 644 Total blood calcium, milk fever, 2: 242 Total correlation spectroscopy (TOCSY), 1: 151 Total diet studies, additives, 1: 58 Total dissolved solids (TSD) definition, 4: 619 water supply, 4: 583t Total ionic strength adjustment buffer (TISAB), 1: 195 Total liver lipid, 2: 217 Total liver triacylglycerol, 2: 217 Total mixed ration (TMR) African dairy cow management, 2: 78–79, 2: 79f early lactating cows, 4: 480 historical aspects, 1: 4–5 roughage, 3: 985–986 ruminal acidosis prevention, 2: 201 sheep see Sheep Total potentially available nucleosides (TPAN), human milk, 3: 974t, 3: 974–975 Total psychrotrophic count, 4: 384 Total quality management (TQM), 2: 683, 2: 683f Total (integrated) risk, 4: 279–280 Total solids definition, 4: 619 determination, 1: 76, 1: 82t, 1: 254 crypscopic methods, 1: 77 densitometric methods, 1: 77 historical aspects, 1: 19 rennet milk coagulation, 1: 583 Total suspended solids, 4: 619 Total viable colony count (TVC) see Total bacterial count (TBC) Touch point pressure difference (TPPD; inflection point), teat-cup liners, 3: 948 Toxic baits, rodent control, 4: 541 Toxicity nitrites, 1: 908 nitrosamines, 1: 908, 1: 908 Toxicity studies acceptable daily intake (ADI), 1: 56 additive safety, 1: 57 bacteriocins, 1: 427–428 Toxicokinetic tests, additive safety, 1: 57 Toxic shock syndrome toxin-1, 4: 108 Toxic tracking powders, rodent control, 4: 541 Toxins immunochemical detection, 1: 180 see also specific toxins Toyota Production System (TPS), 4: 263 first paradox, 4: 263
studies, 4: 263 waste, 4: 265–266 TPA see Texture profile analysis (TPA) Trace elements (minerals) absorption chelated forms, 3: 998–999 ruminants, 3: 998 bioavailability, 2: 378, 2: 384 buffalo milk, 3: 507 chemical forms, 3: 934 in dairy products, 3: 933, 3: 934t, 3: 935t, 3: 935t, 3: 935t deficiency, 2: 378 equine milk, 3: 527, 3: 527t essential in human diet, 3: 933 feed supplements, 2: 378–383 goat requirements, 2: 789, 2: 792–793, 2: 793t interactions, 3: 933 milk, 3: 933, 3: 934t bioavailability, 3: 940 chemical forms, 3: 934 nutritional significance, 3: 936 MS, 1: 204 nutritional significance, 3: 933–940 organic, 2: 384, 2: 385t inorganic feed supplements vs., 2: 387 primary deficiency, 2: 378 primate milk, 3: 628t recommended daily intakes, 3: 937t requirements, 2: 378, 2: 379t secondary deficiency, 2: 378 transition cows, pasture-based systems, 2: 468 see also Minerals Trade see Cleaning in place (CIP) Trade, in milk and dairy products see Harmonized System (HS); World Trade Organization (WTO) ‘Traditional lactalbumin’, 4: 733 Traditional Speciality Guaranteed (TSG), 1: 845–846 Training business management, 1: 484 dairy technology see Dairy technology education see also Education Trans-10, cis-10 conjugated linoleic acid, 3: 356, 3: 357f Trans-18:1 fatty acids (TFAs), 3: 356, 3: 356f Transcription, 3: 965, 3: 966f Transcriptome, 3: 1057 Transcriptomics definition, 3: 1057 nutritional research advancement, 3: 1058 human intervention study, 3: 1058 Transducers biosensors see Biosensors ultrasound see Ultrasonic transducers Trans fatty acids, blood cholesterol levels, 3: 730 Transferrin, marsupial milk, 3: 558 Transformers, 4: 610 Transforming growth factor- (TGF-) colostrum, 3: 596 mammary gland development, 3: 341 Transforming growth factor- (TGF- ) colostrum, 3: 596 mammary gland development, 3: 341 Transgenesis pluripotent stem cell-mediated, 2: 639 sperm-mediated, 2: 638 viral-mediated, 2: 638 Transgenic animals, 2: 637–645, 3: 968 animal health/welfare concerns, 2: 644 improvements, 2: 643 applications, 2: 640 agricultural, 2: 641t, 2: 642 animal models, human disease, 2: 641 biomedical, 2: 640, 2: 641t environmental impact, 2: 643 production traits, 2: 642
951
commercially valuable protein production, induced lactation, 3: 24 continual technological advances, 2: 637 ethical issues, 2: 644 generation methodology, 2: 637 public acceptance, 2: 644 regulatory issues, 2: 644 xenotransplantation, 2: 641 Transgenic cows lysostaphin secreting, 2: 643, 3: 968 milk fat improvement, 2: 643 milk production improvement, 2: 642–643 Transgenic mice, 2: 637 Transgenic pigs, 2: 642 Transglutaminase(s), 2: 297–300 characteristics, 2: 297 historical aspects, 2: 297 industrial applications, 2: 297 microbial see Microbial transglutaminase (mTGase) nonfood product applications, 2: 300 Transhumance decline, in Europe, 2: 879 protein productivity, 2: 879 Transient methods, rheology, 1: 277 Transition calf see Calves Transition cows drylot management systems, 2: 55 fatty liver, 2: 217 feeding management strategies, 2: 221 feed intake depression, 2: 451, 2: 451f lead-feeding, 2: 451 mastitis, 2: 451 pasture-based systems, 2: 464–469 available fetal nutrients, 2: 466 carbohydrate type importance, 2: 465 dry matter intake, 2: 464 feed additives, 2: 467 gluconeogenic precursor inclusion, 2: 465–466 macromineral supplements, 2: 467 micromineral supplements, 2: 468 microorganism carbohydrate acclimatization, 2: 466 minerals, 2: 467 precalving DMI maintenance, 2: 464, 2: 465f precalving DMI requirements, 2: 464 precalving negative energy balance, 2: 465 ruminal papillae development, 2: 466 subsequent milk yield, 2: 466, 2: 466f rations, 2: 449t, 2: 451 anionic salts, 2: 451 Transition-metal ions absorption, 1: 110 Transition milk, 4: 397t Transition period, 2: 464 Translation, 3: 965, 3: 966f, 3: 1056–1057 nutrition effects, 3: 1056–1057 Transmissible spongiform encephalopathies (TSEs), sheep, 2: 859 Transmission electron microscopy (TEM), 1: 227t, 1: 227–228, 1: 228, 1: 228f Transportation stress, reproductive effects, 4: 580 Transporter-binding proteins, 3: 798 Transverse (shear) waves, ultrasound, 1: 206, 1: 207f Transylvannian Pingzau cattle, 1: 297 Traps bird repellents, 4: 542 predator control, goats and sheep, 2: 845 rodent control, 4: 541 Traveling irrigators, 2: 591 Treaty for the Organization of a Southern Common Market (MERCUSOR), 4: 324 Tremorgenic dioxopiperazines, 4: 796 structures, 4: 796, 4: 797f Tremorgenic indoloditerpenes, 4: 796 biosynthetic route, 4: 798f Treponema, 2: 168–169, 2: 169f papillomatous digital dermatitis, 2: 168–169 Treponema denticola, 2: 168–169 Treponema phagedenis, 2: 168–169
952 Index Triacylglycerides, fish oil supplements, 3: 1058–1059 Triacylglycerol(s) (TAG), 3: 650, 3: 665–669 acyl carbon number, 3: 700 analysis, 3: 700 gas chromatography, 3: 700, 3: 700f high-performance liquid chromatography, 3: 701 mass spectroscopy, 3: 702 butter, 1: 506, 1: 507, 1: 508f, 3: 709 crystallization, 3: 653, 3: 668 fatty acid composition and, 3: 668–669 degradation, mastitis, 3: 902–903 fatty acid positional distribution, 3: 650, 3: 665–666, 3: 667t restricted diet, 3: 666, 3: 667t fatty acids, 3: 655 high-melting fraction, 3: 707 low-melting fraction, 3: 707 low-molecular weight, 3: 666 mammary gland synthesis, 3: 665 melting behavior, 3: 653, 3: 668 seasonal variations, 3: 669 middle-melting fraction, 3: 707 in milk, 1: 259 composition, 3: 665, 3: 666, 3: 666t, 3: 667t milk fat, 1: 500–501, 3: 650, 3: 650t major types, 3: 668, 3: 668f milk fat globule membrane, 3: 681–682, 3: 682 molecule, 3: 665, 3: 666f plasma, mammary uptake, 3: 353–354 regiospecific analysis, 3: 702 rumen fermentation, 3: 983–984 saturated, 3: 666 sheep milk, 3: 495t, 3: 497, 3: 498 molecular weights, 3: 498–499 sn-3 position, 3: 665, 3: 666–667 stereospecific analysis, 3: 702, 3: 702f chiral chromatography, 3: 703 structure, 2: 306, 2: 306f, 3: 650f, 3: 665 transport, 3: 727 see also Triglycerides (TGs) Triangular tests, discrimination testing, 1: 280–281 1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane see DDT (1,1,1-trichloro-2,2-bis(4chlorophenyl)ethane) Trichloroacetic acid-soluble nitrogen (TCA-SN), 1: 716 Trichomonas fetus, 1: 479 Trichophyton verrucosum, 2: 858–859 Trichosporon beigelii, 4: 750 odor production, 4: 750 Trichostrongylus, 2: 258 Trichosurus vulpecula (Australian brushtail possum), 2: 197 Trichothecane, 4: 798 Trichothecenes, 4: 798, 4: 799f Triclabendazole, liver flukes, 2: 268 resistance, 2: 269 Trifolium (clovers), 2: 558 Trifolium alexandrinum (Berseem; Egyptian clover), 2: 558 Trifolium fragiferum (strawberry clover), 2: 577 Trifolium hirtum (rose clover), 2: 559 Trifolium incarnatum (crimson clover), 2: 558 Trifolium michelianum (Balansa clover), 2: 559 Trifolium pratense (red clover), 2: 577 Trifolium repens (white clover), 2: 576 Trifolium resupinatum (Persian; shaftal clover), 2: 559 Trifolium subterraneum (subterranean clover), 2: 559 Trifolium vesiculosum (arrowleaf clover), 2: 559 Triglycerides (TGs) analysis, historical aspects, 1: 21 energy value, 3: 712 equid milk, 3: 526 equine milk, 3: 524 liver synthesis, 3: 712 primate milk, 3: 616 see also Triacylglycerol(s) (TAG) Trihaloanisoles, problems in casein powders, 2: 548
Triiodothyronine (T3), 3: 27 Trimethoprim, 2: 194 2,4,5-Trimethyloxazole, problem in spray-dried dairy products, 2: 547 Tripeptidases (PepT), 3: 87 Tripeptide transport, 3: 994 Triple quadrupole tandem mass spectrometry, lipid analysis, 1: 204 Tris/glycine–SDS-PAGE, 1: 186, 1: 187f Trisodium citrate (TSC), pasteurized processed cheese products, 1: 810 Tris/tricine–SDS-PAGE, 1: 187, 1: 188f Triticale, 2: 557 Tritrichomonas foetus, 1: 470 Trommel salter, Cheddar manufacture, 1: 611, 1: 611f Trophectoderm, 4: 485–486, 4: 493–494 Trophoblast endometrial attachment, 4: 499 expansion, 4: 494–495 Tropical grasses, topping, 2: 590 Tropical legumes, seedling vigor, 2: 587 Tropical liver fluke (Fasciola gigantica) see Fasciola gigantica (tropical liver fluke) TruDefender, 1: 123, 1: 123f True digestion, 3: 990 Trueness analytical methods, 3: 742 milk protein analysis, 3: 745, 3: 745t True (corrected) stress, rheology, 1: 275f, 1: 275–276 Trypsin, 2: 289–290 milk protein allergenicity reduction, 3: 1043 Tryptamine, 1: 451 characteristics, 1: 452t Tryptophan, 4: 691 human requirements, 3: 818 TSC (trisodium citrate), pasteurized processed cheese products (PCPs), 1: 810 Tsege, 2: 510 Tselingato (cooperative flock management), 2: 875, 2: 879 Tsigai sheep, 1: 336t TSPP see Tetrasodium pyrophosphate (TSPP) TTGE see Temporal temperature gradient gel electrophoresis (TTGE) Tubercles (granuloma), 2: 195 Tuberculosis (TB), 4: 87 avian, 2: 174 bovine see Bovine tuberculosis buffalo, Mediterranean region, 2: 782 causitive organism see Mycobacterium bovis historical aspects, 1: 8 sheep, 2: 858 testing, artificial insemination centers, 1: 470 Tubular heat exchanger (THE), 4: 189, 4: 190f types, 4: 189–190 UHT, 2: 700 Tubulo-alvelolar gland, 3: 333 Tunnel milking parlors, goats, 2: 805, 2: 806f Tunnel ventilation, 1: 4 Tunnel ventilation barns, heat stress, 4: 570–571 Turbine agitators, 4: 160, 4: 161f, 4: 161f Turbulence, homogenization, 2: 750–751 Turkey X disease, 4: 792, 4: 801 Turkish cheeses, 1: 783 spice-containing, 1: 786 Turnip (Brassica rapa var. rapa), 2: 560 Turnstile rotaries, 2: 16–17, 2: 17f Tvarog, 1: 703 Twarog, 1: 703 Twin disease see Pregnancy toxemia Twin lamb disease see Pregnancy toxemia Twirog, 1: 703 Two-dimensional electrophoresis, milk, 3: 843 gel staining, 3: 845 high-abundance proteins, 3: 846, 3: 846f image analysis, 3: 845 isoelectric focusing of proteins, 3: 844 limitations, 3: 1059
low-abundance proteins, 3: 846 milk proteins, 3: 748 posttranslational modification analysis, 3: 846f, 3: 847 protein solubilization, 3: 843 SDS-PAGE, 3: 845 solubilization buffers, 3: 844 strip equilibration, 3: 843 Two-dimensional polyacrylamide gel electrophoresis, 1: 189 with MS, 1: 198 Two-Factor Theory of Motivation, 3: 13 Two-fluid nozzle (pneumatic) atomization, 4: 224 Two-humped camel see Bactrian camel (Camelus bactrianus) Two-phase separators, 4: 167, 4: 168f Two-stage spray drying, milk powder, 2: 110 Two-step enrichment, Yersinia enterocolitica, 4: 122 Tympanitis see Bloat Type 1 diabetes, 3: 1046 animal feeding experiments, 3: 1047 milk protein effects, 3: 1047 camel milk, 3: 1048 cause, 3: 1046 cows’ milk hypothesis, 3: 1046 antibodies, 3: 1046–1047 epidemiological evidence, 3: 1046 environmental triggers, 3: 1046 human milk absence, 3: 1049 milk protein involvement, 3: 1047 triggering mechanisms, 3: 1048 bioactive peptides, 3: 1048 molecular mimicry, 3: 1048 oral tolerance, 3: 1048 vitamin D intake, 4: 650 Type 2 diabetes, 3: 1049 calcium effects, 3: 1049 dairy product consumption, 3: 1049 diet and, 3: 1049 environmental triggers, 3: 1046 insulin resistance, 3: 1046 vitamin D effects, 3: 1049 Type (conformation) traits, 2: 650 Typhoid fever, milk-borne, 3: 311–312 historical aspects, 1: 26 Tyramine, 1: 451 characteristics, 1: 452t raw milk cheeses, 1: 658–659 Tyrol Grey cattle, 1: 297 milk records, 1: 297t Tyrosine crystals, Dutch-type cheeses, 1: 725
U Udder see Mammary gland UDP-galactose:N-acetylglucosamine galactosyltransferase, 2: 329 UDP-galactosyl transferase, 3: 173 UHT milk aseptic packaging, 2: 708–713, 4: 22 Bacillus growth, 4: 385 buffalo milk, 2: 778 flavored, spoilage molds, 4: 781 galactosyl- -pyranone, 3: 1073 Gram-negative psychrotrophs growth, 4: 385 historical aspects, 1: 16 lipolytic defects, 3: 724 microfiltered products vs., 3: 308 microfiltration pretreatment, 3: 308 oxygen content, 2: 706 plasmin system, 2: 312 processing equipment, 2: 721 protein digestibility, 3: 1067–1068 storage gelation, 4: 382 thermization post-treatment, 2: 693, 2: 695 see also Sterilization UHT-sterilized milk, 3: 288–296 age gelation, proteolysis, 3: 292 free -SH groups, 3: 293–294
Index ‘heated flavor’, 3: 293–294 keeping quality, 3: 288 sediment formation, 3: 289 typical flavor, 3: 293–294 vitamin loss, 3: 294–295, 3: 295f, 3: 295t UHT-treated milk drinks particle stability, 3: 305 protein stability, 3: 305 UHT treatment see Ultra-high temperature (UHT) treatment UK see United Kingdom (UK) Ukraine, red cattle breeds, 1: 296 Ultracentrifugation, 3: 914 Ultra-fast liquid chromatography (UFLC), fatty acid analysis, 3: 698 Ultrafiltration (UF), 1: 618, 1: 618, 3: 213, 3: 308–309, 3: 864 aqueous ions in milk determination, 3: 914 buffering capacity, 1: 619 cheese characteristics, 1: 622 cheese manufacture, 1: 539 cheese milk preconcentration, 3: 866 concentration polarization, 3: 871 dried milk products, 3: 1071–1072 Feta cheese manufacture, 1: 791 fouling, 3: 870, 3: 870f, 3: 872 fresh cheeses, 1: 622 liquid precheese production, 1: 621 yield potential, 1: 621 low pressure immersed membrane technology, 3: 869 medium-concentration retentates, 1: 621 methods, 1: 618–619 milk composition, 1: 619t milk processing, 3: 647 milk protein fractionation, 3: 763 isolate, 3: 866 separation, 4: 546 standardization, 4: 547, 4: 547f milk protein concentrates, 3: 848, 3: 849, 3: 849f, 3: 866 milk viscosity, 1: 619 nondairy food dairy ingredients, 2: 125 on-farm milk, 1: 621 organic compound removal, water, 4: 584 permeate stream, 1: 618 pH, 1: 619, 1: 619f physicochemical milk properties, 1: 619 polymeric membranes, 3: 864–865 precheese concept (high pressure), 1: 618–619 pre-cheese preparation, 3: 868 processing temperature, 3: 870 protein-enriched milk, 3: 298 protein standardization (low-concentration retentates), 1: 619 advantages, 1: 619 equipment, 1: 619, 1: 620f protein standardization by, 3: 308 rennet coagulation, 1: 619 retentate (concentrate), 1: 618 skim milk powder, enhanced renneting properties, 3: 866–867 spiral-wound modules, 3: 868 whey ‘cold filtration’ processing, 3: 866 whey protein concentrates, 3: 865–866 Ultrafiltration (UF) permeate, 4: 732 processing technologies, 4: 732 Ultragriseofulvin (UG), 4: 789 Ultrahigh performance liquid chromatography (UPLC), infant formulae, 2: 136 Ultra-high temperature (UHT) milk see UHT milk Ultra-high-temperature–short-time processing (UHTST), ready-to-eat dairy desserts, 2: 911 Ultra-high temperature (UHT) treatment aseptic packaging, 2: 708–713 camel milk, 3: 515 casein micelle rearrangement, 3: 288–289
chemical changes, 2: 704–706, 2: 706t chemical indices, 2: 706t, 2: 706–707 combination direct-indirect heating systems, 2: 701, 2: 705t temperature profiles, 2: 702f, 2: 703 direct heating systems, 2: 699, 2: 700, 2: 705t heating profile, 2: 701, 2: 702f homogenization, 2: 701 steam infusion, 2: 700–701, 2: 703f steam injection, 2: 700–701, 2: 703f Enterobacteriaceae control, 4: 70 folate retention, 4: 683 heating systems, 2: 699–707 bacteriological index, 2: 706, 2: 706t comparison, 2: 704, 2: 705t steam-based, 2: 700, 2: 700f viscous products, 2: 699 historical aspects, 1: 16 homogenization, 2: 699 immunoglobulins, 3: 813 indirect heating systems, 2: 699, 2: 700, 2: 705t flow diagram, 2: 700, 2: 701f fouling/deposit formation, 2: 700 heating profile, 2: 702f milk shelf life, 3: 1070 p0075, 2: 702f preheat holding section, 2: 700, 2: 701f principles, 2: 699, 3: 310–311 scraped-surface heat exchanger systems, 2: 703 sterilization process, 2: 714–724 time–temperature combinations, 2: 699 tubular heat exchangers, 4: 189–190 whipping cream manufacture, 1: 914, 1: 915, 1: 922 Ultra-OSMOSIS see Nanofiltration (NF) Ultra-performance liquid chromatography (UPLC), fatty acids, 3: 698 Ultrasonication, 2: 741 bactericidal effects, 2: 742 free radicals, 2: 742 heat enhancement, 2: 742 pressure enhancement, 2: 742 dairy processing applications, 2: 742 enzymes, effects on, 2: 742 equipment, 2: 741 homogenization, 2: 742 treatment principles and mechanisms, 2: 741 cavitation, 2: 741 free radical production, 2: 741 heating effect, 2: 741 microstreaming, 2: 741 Ultrasonic cross-correlation meters, 1: 212f, 1: 213 Ultrasonic devices, rodent control, 4: 541 Ultrasonic flow meter, 1: 212, 1: 212f Ultrasonic homogenization, 2: 762 industrial scale, 2: 763 laboratory-scale, 2: 762–763 microbial count reduction, 2: 763 Ultrasonic spectrometry, 1: 211 Ultrasonic tomography, 1: 213, 1: 213f algorithms, 1: 213 Ultrasonic transducers, 1: 209, 1: 209f element, 1: 209 flow meters, 1: 213 frequencies, 1: 209 solid media, 1: 210 structure, 1: 209, 1: 209f ultrasonic homogenization, 2: 762–763 Ultrasonic velocity, 3: 470 Ultrasonic waves definition, 2: 762 types, 1: 206, 1: 207f Ultrasound, 1: 206–214, 1: 229 applications, 1: 213 attenuation, 1: 208 bulk waves, 1: 206, 1: 207f creaming profiles, 3: 471 C-scanning, 1: 211 definition, 1: 206
953
diffraction, 1: 208, 1: 209f fatty liver, 2: 217 flow measurement, 1: 212, 1: 212f cross-correlation meters, 1: 212f, 1: 213 Doppler shift, 1: 213 vortex shedding meters, 1: 212f, 1: 213 inclusion detection, 1: 211 level sensing, 1: 211, 1: 211f material properties, 3: 470 measuring systems, 1: 210 pulse-echo configuration, 1: 210, 1: 210f through-transmission (pitch-catch) method, 1: 210, 1: 210f milk composition measurement, 3: 471 milk enzymes, effects on, 2: 742 mode conversion, 1: 208, 1: 208f near-field distance, 1: 208 pregnancy detection, 4: 490 goats, 2: 839, 2: 840f, 4: 490 sheep, 2: 863, 2: 891, 2: 892f, 4: 490 propagation time measurement, 1: 210 properties, 1: 206 property measurement, 1: 210 curd strength measurement, 1: 587 reflection, 1: 207, 1: 208f refraction, 1: 207, 1: 208f speed of sound, 1: 206 gases, 1: 206 liquids, 1: 206 multiphase media, 1: 206–207 techniques, 1: 206–214 tomography, 1: 213, 1: 213f void detection, 1: 211 Ultraviolet (UV) absorption capillary electrophoresis, 1: 190 HPLC, 1: 173 Ultraviolet (UV) irradiation vitamin D production, ruminants, 3: 1001–1002 water supply disinfection, 4: 585t, 4: 586 Ultraviolet (UV) light sterilization continuous, 2: 730 germicidal wavelength, 2: 730 milk/dairy liquid methods, 2: 730 pulsed, 2: 730 Ultraviolet spectroscopy, 1: 109–110 Undefined starter cultures, 1: 554, 1: 554t Undercarboxylated osteocalcin (ucOC), vitamin K, 4: 664, 4: 665 Undernutrition conception rate, 4: 578 LH surge, 4: 577–578 placental function, 4: 500–501 puberty onset delay, 4: 577–578 Undulant fever see Brucellosis Uniaxial compression cheese rheology measurement, 1: 694, 1: 694f rheology instrumentation, 1: 274f, 1: 275 Uniaxial extension, cheese rheology, 1: 691t Uniform transmembrane pressure control (UTMP), 3: 867, 3: 867f Uninterruptible power supply (UPS), 4: 610 Unipro 50, 3: 853 United Kingdom (UK) cheese legislation, 1: 846 compositional requirements, 1: 853t dairy product consumption, 1: 46, 1: 46, 1: 46t United Kingdom Register of Organic Food Standards (UKROFS), 4: 10 United States (US) additives approval, 1: 53 definitions, 1: 51 labeling, 1: 54 agricultural policy, low price system, 4: 288–289 agricultural system, 4: 300–305 animal welfare policy, 4: 729 artificial insemination efficiency, 4: 469
954 Index United States (US) (continued ) usage, 4: 469, 4: 470t cheese legislation, 1: 850 compositional requirements, 1: 853t chlorine sanitizers, 3: 635 dairy cow numbers, 4: 631 dairy industry, 1: 10, 1: 10t, 1: 11t dairy policy, components, 4: 300 dairy product border measures, 4: 300 dairy products consumption, 1: 46t, 4: 301t governmental net purchases, 4: 304t production, 4: 301t trade, 4: 301t direct deficiency payments, 4: 304 federal price supports, dairy industry, 4: 302 food fortification, folates, 4: 682 foreign sires, impact of, 2: 671–672 herb-containing cheeses, 1: 787 import barriers, 4: 300, 4: 301f milk production, 4: 631 milk sanitary standards, 4: 302 milk support price, 4: 303, 4: 304t organic sector, 4: 9 organic standards, 4: 10 pasteurization, historical aspects, 1: 13 product-specific AMS limit, 4: 348 raw milk cheese regulations, 1: 659–660 regional milk marketing orders, 4: 302 end-use classes, 4: 302 revenue-sharing/pooling schemes, 4: 302 sires, non-North American, 2: 670–671, 2: 671t, 2: 671t spiced cheeses, 1: 787 subsidized exports, 4: 300 United States of America (USA) see United States (US) Univariate calibration, 1: 92 Universal stress protein (UspA), 3: 60 Universal testing machines, rheology, 1: 274, 1: 274f Unpasteurized milk see Raw milk Unsaturated fatty acids in fats, 2: 363, 2: 364t milk, 3: 657 cis vs.trans, 3: 656f, 3: 657 in oils, 2: 363, 2: 364t oxidation, butter flavor, 1: 511–512 plant material sources, 3: 543 structures, 2: 363, 2: 364f Unscrambler, 1: 108 Unsupervised artificial neural networks (ANNs), 1: 107 UPLC (ultrahigh performance liquid chromatography), infant formulae analysis, 2: 136 Urea donkey milk, 1: 368 heat stability, milk, 2: 746 primate milk, 3: 625–627 sheep milk, 3: 496 Urea fractionation, casein, 3: 760–761 Urea–molasses–mineral block (UMMB), buffalo, 2: 776 Urea-polyacrylamide gel electrophoresis (urea-PAGE), 1: 188, 1: 189 long ripened pasta-filata cheeses, 1: 749–751, 1: 751f primate milk proteins, 3: 621, 3: 624f Urease, Bifidobacterium suis, 1: 387 Uric acid, sheep milk, 3: 496 Urick’s equation, speed of sound, 1: 206–207 Urinary calculi (urolithiasis), goats, 2: 795, 2: 800, 2: 828 Urinary pH, dietary acidification response monitoring, 2: 360 Urinary tract infections (UTIs), 4: 76 Urokinase-type plasminogen activator (u-PA), 2: 309
Urolithiasis (urinary calculi), goats, 2: 795, 2: 800, 2: 828 Uruguay, dairy societies, 2: 105 Uruguay Round, 4: 345 achievements, 4: 346 trade agreement, 4: 300 Uruguay Round Agreements, 4: 318–319 The Uruguay Round Agricultural Agreement (URAA) see Agricultural Agreement US see United States (US) USA see United States (US) US Department of Agriculture (USDA), milk farm price, 4: 302–303 US dollar, depreciation, 4: 350, 4: 351f US Pasteurized Milk Ordinance (2003), 3: 897 Uterine body insemination, conception rate, 4: 482 Uterine contraction, 4: 507 Uterine infection, reproductive efficiency, 4: 579 UV irradiation see Ultraviolet (UV) irradiation
V Vaccenic acid, 3: 656t, 3: 657 structure, 3: 656f, 3: 661f Vaccine/vaccination bluetongue virus, 2: 152 brucellosis, 2: 158, 4: 38 Coxiella burnetii, 4: 57 dairy replacements, 4: 420 dams, calf disease resistance, 4: 417 foot-and-mouth disease, 2: 166 goats, 2: 797, 2: 798, 2: 799 does, pre-kidding, 2: 825, 2: 831 enterotoxemia, 2: 797–798 reproductive health program, 2: 840 Johne’s disease, 2: 179 leptospirosis, 2: 183 listeriosis, 2: 188 liver flukes, 2: 268 lungworm disease, 2: 271, 2: 274 mastitis, 3: 420 antibiotic therapy and, 3: 436 orf, 2: 861–863, 2: 862t programs, historical aspects, 1: 8 Q fever, 4: 57 rams, 2: 862t, 2: 864 salmonellosis, 2: 194 sheep see Sheep Staphylococcus aureus, 4: 109 mastitis, 3: 411–412, 4: 109 Vacherin Mont d’Or, 4: 83 Vacuum evaporators, 1: 12 Vacuum oven, 1: 76 Vacuum pumps goat milking, capacity, 2: 808 milking machines, 3: 946, 3: 946f, 3: 946f capacity, 3: 946 falloff, 3: 946 functions, 3: 945, 3: 945 variable-frequency drive systems, 3: 946 Vacuum relief valves, 4: 157, 4: 158f Valais Blackneck goats, 1: 313–314, 1: 314f Valle de Belice sheep, 1: 332t Valley yak, 1: 345 Val-Pro-Pro, antihypertensive effects, 3: 884 Value engineering, 4: 265 Valve(s), 4: 152–159 actuation, 4: 154 electric solenoid, 4: 155 hydraulic, 4: 154–155 manual, 4: 154 pneumatic, 4: 154 classification, 4: 152 construction principles, 4: 152 dairy processing, 4: 155, 4: 155t definition, 4: 152 equal-percentage characteristic, 4: 154 flow design, 4: 152 friction factor, 4: 153, 4: 153t
pressure drop, 4: 152 hygienic design, 4: 154 inherent flow characteristic, 4: 153–154 installed flow characteristic, 4: 153–154 on–off, 4: 152 pressure drop calculation, 4: 143 regulating, 4: 152 sanitary, 4: 154 seals, 4: 154 selection, 4: 126 valve characteristic, 4: 153 water hammer, 4: 154 see also individual types Valve homogenizers, 2: 750–754 fluid velocity, 2: 755 historical aspects, 1: 13–14 Vancomycin-resistant enterococci (VRE), 1: 650, 3: 155 Vane-type compressors, 4: 603, 4: 604f Vanillin, 4: 787 Vapor compression cycle, 4: 596, 4: 597f coefficient of performance, 4: 598 energy fluxes, 4: 596–597 equipment, 4: 597 pressure–enthalpy thermodynamic diagram, 4: 596, 4: 597f pressure levels, 4: 596 principles, 4: 596 system components, 4: 596 Variable-frequency drive (VFD) systems milk pumps, 3: 946 vacuum pumps, 3: 946 Variable-number tandem-repeat (VNTR) analysis, Shigella, 4: 102 Variables, statistical analysis, 1: 83 Variacin, 1: 422t Vascular endothelial dysfunction, 3: 1033 Vat(s) cheese types made, 1: 608 types, 1: 608, 1: 609f, 1: 609f, 1: 610f Vatimer, 1: 588 Vat systems enclosed, 1: 608 equipment choice, 1: 608 Veal-calf stall, 4: 728 Vegetable oil blends, 1: 523 vitamin E, 4: 653 Vegetable proteins, cheese analogues, 1: 815t, 1: 818 Vegetal rennets, 2: 290–291 Vegetarian cheese, rennet, 2: 290–291 Veillonella, 1: 383t Venereal diseases, 2: 602, 2: 605 artificial insemination centers, 1: 470 Ventilation, 4: 555 air contaminants, 4: 555 air quality, 4: 555 cold barn, 4: 557 dilution effect, 4: 555 drylot management systems, 2: 58 heat stress management, 2: 19 minimum continuous winter ventilation, 4: 557 mechanical, 4: 557 natural, 4: 557 mismanagement, winter, 4: 558 moisture control, 4: 557, 4: 557f pneumonia prevention, 4: 418 underventilation, 4: 558 warm barn, 4: 557 Vereinigung Schweizer Milchindustrie (VMI), 2: 103 Verotoxigenic E. coli (VTEC) see Shiga toxinproducing E. coli (STEC) Verrucous dermatitis see Papillomatous digital dermatitis (PDD) Verruculogen, 4: 796, 4: 797f Vertical committees (Commodity Committees), Codex Alimentarius, 4: 314
Index Vertical-type natural circulation evaporator, 4: 201, 4: 202f vacuum chamber, 4: 201, 4: 203f Vervet monkey milk -lactoglobulin, 3: 624 proteins, 3: 622t Very low-density lipoproteins (VLDLs), 3: 728 composition, 3: 728t coronary heart disease risk, 3: 1031 fatty liver, 2: 218 functions, 3: 728t liver (VLDLLIVER), 3: 728–729 mammary uptake, 3: 353–354 small intestine (VLDLINT), 3: 728–729 synthesis, 2: 218 Verzasca goats, 1: 313 Vesicles, milk protein secretion, 3: 377 Vesicular follicle development, 4: 423 Vesiculitis, 1: 473 Veterinarians African dairy cow management, 2: 81 antibiotics use precautions, 2: 803 sheep flock health, 2: 859 Vibrating fluid-bed dryer, 3: 856f, 3: 857 Vibrational spectroscopy, 1: 111 temperature effects, 1: 112 Vibrational systems, curd strength measurement, 1: 588 Vibratory Shear Enhanced Process (VSEP), 3: 869 Vibrio cholerae, 3: 256 VIBRO-FLUIDIZER, 4: 231, 4: 231f compact drying chamber, 4: 217, 4: 220f construction detail, 4: 231, 4: 232f Victoria blue B-tributyrin agar, 1: 219 Vicuna (Lama vicugna), 1: 351 Vigna unguiculata (cowpeas), 2: 558, 2: 565 Viili, 2: 474, 2: 499, 4: 749 Village milking centers (VMCs), China, 2: 85 Villal´on, 3: 501 Viral-mediated transgenesis, 2: 638 Virus(es) buffalo infections, 2: 782 in milk, 3: 451 Virus neutralization test bluetongue virus, 2: 150 foot-and-mouth disease, 2: 164–165 Viscoelastic behavior cheese rheology, 1: 688–689 rheology instrumentation, 1: 277 yogurt rheology, 4: 528 Viscoelastic liquid (Maxwell element), 1: 269f Viscoelastic solids, 1: 269f Viscometers, 3: 889 Viscoprocess, 1: 586 Viscosity, 1: 272 curd strength measurement, 1: 586 dairy liquids, 4: 163t measuring devices, 1: 272 classification, 1: 274 concentric-cylinder systems, 1: 272–273 cone-and-plate devices, 1: 273 Couette-type viscometers, 1: 274 high viscosity fluids, 1: 273–274 parallel-plate devices, 1: 273–274 rotational viscometers, 1: 274 rotation-symmetric geometries, 1: 272–273, 1: 273f Searle-type viscometers, 1: 274 stress-controlled rheometers, 1: 274 rennet milk coagulation, 1: 581, 1: 581f see also individual products Viscosity sensors, 4: 237 Visible light methods, curd strength measurement, 1: 587, 1: 589 Visible light spectroscopy, absorption, 1: 109–110 Visual appraisal, body condition scoring, 1: 459–460 Vitamin(s), 4: 636–638 absorption, 3: 996–1002
Bifidobacterium , production by, 1: 384 buffalo milk, 3: 508, 3: 508t buttermilk, 2: 494, 2: 494t camel milk, 1: 355, 1: 356t, 3: 514 colostrum, 3: 591, 3: 592t in dairy products, 2: 494t deficiencies, 2: 396 prevention, 4: 638 risk factors, 4: 638 definition, 4: 637 equid milk, 3: 526, 3: 527t fat-soluble, 4: 637t absorption, 3: 1001 feed supplements, 2: 399 functions, 2: 397t in milk, 3: 652 requirements, cattle, 2: 400t sources, 2: 397t supplementation strategies, 2: 400 feed supplements, 2: 396–402 prepartum dairy cow, 4: 519t strategies, 2: 400 first-age infant formulae, 2: 142 functions, 2: 396 goat milk, 3: 488t, 3: 489 goat production systems, 2: 62–63, 2: 63t goats, dietary requirements, 2: 786, 2: 787t, 2: 791t heifer growth, 4: 393 historical background, 4: 636 human colostrum, 3: 586, 3: 587t human milk, 3: 586, 3: 587t infant formulae, 2: 136–137 loss light-induced degradation, 2: 711, 3: 283 pasteurization-induced, 3: 276, 3: 277t UHT-sterilized milk, 3: 294–295, 3: 295f, 3: 295t macronutrients vs., 3: 996 marine mammal milk, 3: 580 in milk, contribution to nutrient intake, 3: 1005, 3: 1005 pregnancy, 4: 638 primate milk, 3: 629, 3: 630t raw vs. fermented milks, 2: 500, 2: 513, 2: 513t recommended daily allowances, 4: 637t, 4: 637t, 4: 638 reindeer milk, 1: 378 risk groups, 4: 638 sheep milk, 3: 499t sources, 4: 637, 4: 637t, 4: 637t toxicity, 2: 400 water-soluble, 4: 637t feed supplements, 2: 396 functions, 2: 397t ruminal absorption, 3: 1000 ruminal microorganism catabolization, 2: 396 ruminal microorganism synthesis, 2: 396–397 sources, 2: 397t supplementation strategies, 2: 400 synthesis, 3: 1000–1001 UHT milk storage, 3: 295 see also individual vitamins Vitamin A, 4: 639–645 absorption, ruminants, 3: 1001 cheese, 4: 644 classification, 4: 639, 4: 640f deficiency, 4: 639 breast-feeding, 4: 638 definition, 4: 639 feed supplements, 2: 399 mastitis resistance, 3: 430–431 strategies, 2: 401 formation theories, 4: 641 functions, 2: 397t general features, 4: 639 metabolism, 4: 640, 4: 641f milk concentration influencing factors, 4: 642 dehydration, 4: 643–644 diet, 4: 642–643
955
fat content, 4: 643t, 4: 644, 4: 644t processing conditions, 4: 643, 4: 643t skimming, 4: 643t, 4: 644t thermal treatments, 4: 643 milk containers, 4: 643 milk fat, 3: 652 milk fortification, 3: 297–298, 3: 1005 nutrient intake, contributions to, 3: 1005 nutritional issues, 4: 644 skimming, 4: 645 periparturient period, 2: 401, 2: 401f sources, 2: 397t Vitamin B milk, contribution to nutrient intake, 3: 1005 ruminal microorganism synthesis, 2: 396–397 Vitamin B1 see Thiamine Vitamin B2 see Riboflavin Vitamin B5 see Pantothenic acid Vitamin B6, 4: 697–700 bioavailability, 4: 699 dairy sources, 4: 698t deficiencies, 4: 699 neurological problems, 4: 699 dietary sources, 4: 698, 4: 698t functions, 4: 697 immunological, 4: 697–698 nervous system, 4: 697–698 heat stability, 4: 697 in milk, 4: 698t pregnancy, 4: 697–698 recommended daily intake, 4: 699t status measurement, 4: 699 structures, 4: 697, 4: 698f toxicity, 4: 699 Vitamin B7 see Biotin Vitamin B12, 4: 675–677 biosensors, 1: 245 cobalt requirements, 2: 378 coenzyme forms, 4: 675 deficiencies, 4: 675 causes, 4: 675–677 secondary folate deficiency, 4: 681–682 symptoms, 4: 677 treatment, 4: 677 dietary sources, 4: 675, 4: 676t for cattle, 2: 397t milk/dairy products, 4: 676t feed supplements, 2: 398 milk yield, 3: 1000–1001 strategies, 2: 400–401 functions, 2: 397t, 4: 675 metabolic reactions, 4: 675 in milk, nutrient intake, contributions to, 3: 1005 recommended daily uptake, 4: 676t sterilized milk, 3: 294–295 oxygen levels, 3: 295 structure, 4: 675, 4: 676f supplementation, humans, 4: 677 Vitamin B12-binding protein (haptocorrin), 3: 796t, 3: 798 Vitamin C, 4: 667–674 absorption, 4: 669 ruminants, 3: 1000–1001 active transport, 4: 669 antioxidant activity, 4: 670 bioavailability, 4: 669 biological functions, 4: 670 camel milk, 3: 514 cancer, 4: 673 cardiovascular disease, 4: 672 carnitine biosynthesis, 4: 671 chemistry, 4: 667 cholesterol hydroxylation, 4: 672 collagen formation, 4: 671 degradation, 4: 669 de novo synthesis, 4: 667 dietary sources, 4: 668 equine milk, 1: 360–361
956 Index Vitamin C (continued ) estimated average requirements, 4: 673–674 excretion, 4: 669 facilitated diffusion, 4: 669 fortified milk storage problems, 3: 227–228 functions, 2: 397t goat milk, 4: 668 human immune response, 4: 672 human milk, 4: 668 intake recommendations, 4: 668–669 iron absorption, 4: 672 lysine hydroxylation, 4: 671 mastitis, 2: 399 metabolism, 4: 669 in milk, 4: 668 nutrient intake, contributions to, 3: 1005 storage loss, 3: 227 milk fortification, 3: 298 milk lipid oxidation, 3: 718 molecular structure, 4: 667–668, 4: 668f neurotransmitter synthesis, 4: 671 oxidation, 4: 667–668, 4: 668f packaging effects, 3: 227–228 oxidation browning, 3: 217, 3: 224 proline hydroxylation, 4: 671 recommended dietary allowance, 4: 673–674 redox potential, 4: 670 as reducing agent, 4: 670 requirements, 4: 673 sources, 2: 397t status, 4: 673 sterilized milk, 3: 294–295 oxygen levels, 3: 295 supplements feed, 2: 399 humans, 4: 669 vitamin E regeneration, 4: 670 Vitamin D, 4: 646–651 absorption, 4: 647 ruminants, 3: 1001 bone density, 3: 1060 calcium-phosphate homeostasis, 4: 648, 4: 648f cancer, 4: 650 chemistry, 4: 646 colorectal cancer prevention dietary reduction, 3: 1018–1019 epidemiology, 3: 1018 mechanisms, 3: 1019 dairy fortification, 4: 651 dairy products, 4: 647 deficiencies, 4: 646, 4: 650 biochemical characteristics, 4: 650 chronic disease relationship, 4: 650 secondary hyperparathyroidism, 4: 650 discovery, 4: 646 endogenous synthesis, 4: 647 feed supplements, 2: 399 first-age infant formulae, 2: 142 food sources, 4: 647, 4: 647t functions, 2: 397t health benefits, 3: 609 historical perspective, 4: 646 human milk, 4: 647 intestinal calcium absorption, 3: 1010–1011 lactase persistence, 3: 239 metabolic functions, 4: 648 metabolism, 4: 647 in milk, 3: 609 nutrient intake, contributions to, 3: 1005 milk fat, 3: 652 milk fever prevention, 2: 244 milk fortification see Vitamin D-fortified milk recommended intake, 3: 609 reference intakes, 4: 649 requirement-affecting factors, 4: 649 aging, 4: 649 calcium availability, 4: 649 clothing, 4: 649
dietary fiber, 4: 649 glass, 4: 649 latitude effects, 4: 649 malabsorption disorders, 4: 650 obesity, 4: 650 seasonal effects, 4: 649 skin pigmentation, 4: 649 sunscreen use, 4: 649 time of day, 4: 649 sources, 2: 397t, 4: 646 structure, 4: 646, 4: 647f type 1 diabetes, 4: 650 type 2 diabetes, 3: 1049 Vitamin D2 see Ergocalciferol Vitamin D3 see Cholecalciferol Vitamin D-binding protein (DBP), 3: 796t, 3: 798, 4: 648 Vitamin D-fortified milk, 3: 278, 3: 297, 3: 1003–1004, 3: 1005, 3: 1012 levels, 3: 609 regulations, 3: 609 Vitamin D receptor (VDR), 4: 646 calcium absorption, 3: 996–997 effects, 4: 649 Vitamin E, 4: 652–660 absorption, 4: 654 inhibition, plant sterols, 3: 1001 ruminants, 3: 1002 Alzheimer’s disease, 4: 659 as antioxidant, 4: 654, 4: 655, 4: 655f, 4: 656f active packaging release, 4: 22 atherosclerosis, 4: 657, 4: 658 in biological membranes, 4: 656 cancer, 4: 658 cardiovascular disease, 4: 657 prevention, 4: 660 catabolism, 4: 654 chemistry, 4: 652 colostrum, 4: 653 deficiency, 4: 652, 4: 656 dietary sources, 4: 653, 4: 653 dietary supply-milk concentration relationship, 4: 642 estimated average requirement, 4: 659–660 excretion, 4: 654 first-age infant formulae, 2: 142 functions, 2: 397t humans, 4: 652 goat milk, pasture effect on content of, 2: 63t historical aspects, 4: 652 human milk, 4: 653 as immunosuppressant, 4: 659 low-density lipoprotein modification, 4: 656 mean dietary intakes, 4: 653–654 median total intake, 4: 653–654 metabolic functions, 4: 657 metabolism, 4: 654 in milk, 4: 653 nutrient intake, contributions to, 3: 1005 milk fat, 3: 652 Parkinson’s disease, 4: 659 periparturient period, 2: 401, 2: 401f plasma/serum concentrations, 4: 654 recommended dietary allowance, 4: 659–660, 4: 660t requirements, 4: 659 selenium status and, 2: 399–400 smokers, 4: 658–659 sources, 2: 397t status, 4: 659 markers, 4: 659 structure, 4: 652, 4: 653f supplementation cancer prevention, 4: 658, 4: 660 environmental mastitis prevention, 3: 420 feed, 2: 399, 2: 401 mastitis, 3: 430, 3: 430t vitamin C regeneration, 4: 670
Vitamin-enriched milk, 3: 297 Vitamin K, 4: 661–666 absorption, 4: 662 ruminants, 3: 1002 adequate intake value, 4: 665 bone health, 4: 664 cardiac health, 4: 664 chemistry, 4: 661 compounds, 4: 661 deficiency, 4: 663 subclinical, 4: 664 dietary sources, 4: 661, 4: 662t discovery, 4: 661 excretion, 4: 662 feed supplements, 2: 400 foodstuff analysis, 4: 661 functions, 2: 397t health and, 4: 663 indicators, 4: 665 metabolic function, 4: 662 metabolism, 4: 662 in milk, 3: 652 nutrient intake, contributions to, 3: 1005 newborn infants, 4: 663–664 protein posttranslational activation, 3: 1056–1057 requirements, 4: 665 sources, 2: 397t status, 4: 665 structure, 4: 662f Vitamin K1 see Phylloquinone Vitamin K2 (menaquinones), 4: 661, 4: 662f Vitamin K3 see Menadione Vitamin K-dependent proteins, 4: 663 bone proteins, 4: 663 coagulation proteins, 4: 663, 4: 663t Vitamin K epoxide cycle, 4: 662 Vitamin K epoxide reductase (VKOR), 4: 662–663 Vitex, Shigella identification, 4: 101–102 Vitrification, 2: 606–607, 2: 629 Vlakhiko sheep, 1: 336t VMI (Vereinigung Schweizer Milchindustrie), 2: 103 VOCs see Volatile organic compounds (VOCs) Void detection, ultrasound, 1: 211 Volatile compounds Dutch-type cheese flavor, 1: 726 Penicillium camemberti, 4: 777–778 Swiss-type cheese flavor, 1: 718 Volatile fatty acids (VFAs) algebraic rumen balance model, 2: 431, 2: 432t ruminal, heat stress, 4: 564–565 Volatile free fatty acids (VFFA), brine-matured cheese flavor, 1: 793 Volatile organic compounds (VOCs) contamination, goat production systems, 2: 61, 2: 61t goat’s cheese, 2: 61t goat’s milk, 2: 65, 2: 65t Volatiles, extraction/concentration, 2: 543 Volatile sulfur compounds (VSCs) Arthrobacter, 4: 376–377 LAB, 3: 163 Lactobacillus, 3: 87–88 Voltammetric analysis, 1: 193 Volumetric efficiency, air compressors, 4: 605f, 4: 606 Volumetric methods. fat analysis, 1: 80 Von Liebeg, Justus, 1: 15 Vortex shedding meters flow measurement, 1: 212f, 1: 213 ultrasound flow measurement, 1: 212f, 1: 213 Vosges (Vosgienne) cattle, 1: 295 VSEP (Vibratory Shear Enhanced Process), 3: 869
W WAHID (World Animal Health Information Database), 4: 4 WAHIS (World Animal Health Information System), 4: 4 Walking surface, skid-resistant, 4: 559
Index Walkthroughs, warm climate milking systems, 2: 13, 2: 14f Walrus milk, 3: 576–579 Warehouses, automated, 4: 256 Warm barn natural ventilation, 4: 558–559 ventilation, 4: 557 winter temperatures, 4: 558 Warm climate milking sheds access, 2: 25 aspect, 2: 25 Warm climates, farm design see Farm design (warm climates) Wash/drip pens, milking center, 3: 959 Washed-rind cheese, 1: 27 Waste handling systems, design, 3: 392 Waste management, byproduct feeding, 2: 342, 2: 343f Waste milk calf liquid diet, 4: 396–397 quality control, 4: 398 pasteurization, 4: 397 Wastewater analytical pollution indices, 4: 613, 4: 614t dairy plants, 4: 131 volumes, 4: 613 fat separation, 4: 617–618 see also Dairy plant effluents Water butter composition, 1: 506 camel milk, 1: 355 change of state, 4: 589, 4: 590f, 4: 590f conditioning, 4: 617–618 consumption, heat stress, 4: 563t, 4: 563–564 dairy plant uses, 4: 613, 4: 614t dairy products, 4: 707–714, 4: 709 caking, 4: 709 stickiness, 4: 709 effective mole fraction see Water activity (aw) frozen dairy products, 4: 711 grass transition, 4: 709, 4: 709f diffusion in, 4: 711 ice cream, 4: 711 ice formation, 4: 709 mammary gland secretion, 3: 379 microbiological stability, 4: 712 milk solids, 4: 709 phase transitions, 4: 709 plasticization, 4: 709 pressure, 4: 707 changes, 4: 589, 4: 590f properties, 4: 589, 4: 707 quality see Water quality rumen fermentation, 3: 981 state transitions, 4: 709 temperature changes, 4: 589, 4: 590f thermodynamic properties, 4: 589, 4: 590f, 4: 590f, 4: 590f critical point, 4: 589, 4: 590f translational diffusion coefficient, 4: 720 triple point, 4: 707 Water activity (aw), 4: 707 analysis, 4: 715–726 bound/free water, 4: 719 cheese, 1: 646–647, 4: 707–708, 4: 712t, 4: 712–713, 4: 717f cheese microbiology, 1: 628 cheese texture, 4: 720–723, 4: 723t chemical stability, 4: 711 in dairy products, 4: 716f definition, 1: 77, 4: 715, 4: 716f edible grade lactose, caking avoidance, 3: 200f, 3: 200–201 food processing operation vs., 4: 720 food quality vs., 4: 720 food stability predictor, 4: 720 free energy change, 4: 715 frozen dairy products, 4: 716 Maillard reaction effects, 3: 227
measurement, 1: 77, 4: 715–726 equilibrium, 4: 725 physical properties measured, 4: 723, 4: 723t principles, 4: 723 temperature effects, 4: 725 microbial behavior predictor, 4: 720–723 microbial growth, 4: 712t, 4: 712–713 milk, 4: 707–708 milk powder, 2: 122 milk products, 4: 712 molecular mobility, 4: 711 salted butter, 4: 712–713 significance, 4: 715 solute number, 4: 715, 4: 718f stability maps, 4: 713, 4: 713f starter cultures, 1: 553 temperature-dependence, 4: 707–708 water molecule mobility, 4: 719–720 Zygosaccharomyces rouxii, 4: 752 Water buffalo (Bubalus bubalis) see Buffalo Water disinfection, 4: 584 Water fluoridation, 3: 1035 Water flushing, manure collection, 3: 392–393 Water hammer, valves, 4: 154 Water-holding capacity, NMR T2 (spin–spin relaxation), 1: 160 Water-in-oil (W/O) emulsions, 1: 61 coalescence, 1: 63 emulsifier use, 1: 61, 1: 66t manufacture, 1: 61, 1: 61 properties, 1: 61, 1: 63 Water quality, 3: 394 current regulations, 3: 395 dairy manure management, 3: 394 regulatory history, 3: 395 riparian areas, 2: 27 Water relaxation time, NMR, 1: 159, 1: 159f Water rinses, milking hygiene, 3: 634 Water softening, 4: 617–618 Water-soluble carbohydrate (WSC), grasses and legumes, 2: 579, 2: 581, 2: 596, 2: 596f Water-soluble extracts (WSE), 1: 678 Water-soluble nitrogen (WSN), 1: 716 Water-soluble vitamins see Vitamin(s) Water sorption, 4: 708 lactose crystallization, 4: 710 low-water dairy products, 4: 708 Water sprinklers, heat stress, 2: 19 Water supply, 4: 582–588 African dairy cow management, 2: 79 EU legislation, 4: 582 goat management drinking water quality, 2: 785 requirements, 2: 785 use efficiency, 2: 785 warm climate milking sheds, 2: 26 see also Drinking water Water-tube boilers, 4: 590 Water vapor pressure, 4: 716f, 4: 723 Waxing, cheese, 4: 20 Weaning calves, 4: 402 early, to avoid predation, 2: 844 feeds, 2: 827–828, 2: 883, 2: 883t goats, 2: 826–827, 2: 827–828, 2: 831 lambs, 2: 883 milk compostion changes, 3: 588 Weaver (bovine progressive degenerative myeloencephalopathy), 2: 676–677 Weddell seal, 3: 564f Weed(s) competition control, 2: 570 control at crop seeding time, 2: 567 in established crops, 2: 570 potential for growth, 2: 586–587 riparian areas, 2: 27 Weende assay technique, 3: 985
957
Weevils, 4: 543 Weibull–Berntrop method, 1: 80 Weight see Body weight Weighted-type regulators, 3: 947 Welds, 4: 138 Welfare, animal see Animal welfare Wenicke–Korsakoff syndrome, 4: 702–703 West African Shorthorn cattle, 1: 298 Western Agricultural Economics Association, organic milk sales, 4: 9 Western diet, fat sources, 1: 528 Westerwolds ryegrass (Lolium.multiflorum. var. westerwoldicum), 2: 556 Westfalia separators, 4: 172 West Indian manatee milk, 3: 571t, 3: 576–579 Wet ashing, 1: 78 milk salt analysis, 3: 913–914 Wet beriberi, 4: 702–703 Wet scrubbers spray drying powder separation, 4: 227, 4: 228f water recirculation, 4: 228, 4: 229f Wettability, milk powder, 2: 120 WFDC2/HE4 protein, 3: 838 ‘What if...’ analysis, 4: 278 What if/Checklist analysis, 4: 278 Wheat, 2: 557 byproduct fibrous feeds, 2: 342–343 chewing/digestion, 2: 338–340 Wheel atomization see Rotary atomization/atomizers Whey acid see Acid whey acid-coagulated cheese incorporation, 1: 698 alcohol production, 4: 633, 4: 735–736 animal feed, 4: 633, 4: 731 bacterial clarification, 4: 180 biofilms, 1: 446 biogas generation, 4: 735–736 biological oxygen demand, 4: 731 composition, 4: 633, 4: 731 milk pretreatment, 4: 731–732 dairy plants wastewater, 4: 131 definition, 3: 873 demineralization, 2: 127, 2: 127f, 4: 738–743 combination process, 4: 743 electrodialysis see Electrodialysis ion exchange see Ion exchange nanofiltration see Nanofiltration (NF) dephospholipidation, 4: 180 Dutch-type cheeses, 1: 722–723 environmental impact, 4: 633 evaporation, 4: 206, 4: 206f lactic culture propagation, 4: 735–736 mineral content, 4: 738 nondairy food, 2: 128t, 2: 129 partial demineralization, 3: 865 processing disk bowl centrifuges, 4: 179 technologies, 4: 732 products, 4: 731–737 Harmonized System, 4: 335 see also individual products recovery processes, 2: 126, 2: 127f skimming, centrifuges, 4: 171 spray-drying, 3: 182 treatment industry, 3: 182 types, 4: 731 utilization, 4: 731–737 fermentation substrate, 4: 735 industrially processed foods, 4: 733 nutraceutical aspects, 4: 736 nutritional aspects, 4: 736 yak milk, 1: 350 Whey acidic protein (WAP), 3: 758–759, 3: 837 amino acid sequence, 3: 838 functional differences, 3: 560f gene expression eutherian, 3: 838, 3: 838 marsupials, 3: 556–558, 3: 838, 3: 839f
958 Index Whey acidic protein (WAP) (continued ) gene structure, 3: 838, 3: 839f interspecies comparison, 3: 835, 3: 836f, 3: 837 mammary gland development, 3: 560 marsupial milk, 3: 559–560 monotreme milk, 3: 559–560 overexpression, 3: 560 ruminant sequences, 3: 837–838 structural differences, 3: 560, 3: 560f Whey antibody preparation, 3: 813, 3: 814t Whey beer, 4: 736 Whey beverages, 4: 733 fruit juice combinations, 4: 734 high whey protein content, 4: 734 unpleasant flavor, 4: 733–734 Whey buttermilk composition, 3: 691–692 emulsifying properties, 3: 694 Whey cheeses, 4: 734 Codex standard, 4: 329 manufacture methods, 4: 734f sheep milk, 3: 501–502 Whey concentrates, agitation, 4: 165 Whey permeate, 3: 878 concentration, 3: 197 galacto-oligosaccharide synthesis, 3: 213 production process, 3: 197 Whey permeate agar with calcium lactate and casiton (WACCA), 3: 170–171 Whey powder(s) ‘bulking’ food ingredient, 4: 733 Codex standard, 4: 330 composition, 4: 732, 4: 735t milk chocolate, 1: 860 production, 3: 182, 3: 183f worldwide, 3: 873, 3: 874t sampling, 1: 74 uses, 4: 633 Whey protein(s), 3: 481 ACE inhibitory peptides, 3: 879–880 allergenicity reduction, 3: 1043 analysis, historical aspects, 1: 23 anticarcinogenic activity, 3: 1065 bone resorption, 3: 1065 camel milk, 3: 513 capillary electrophoresis, 1: 190, 1: 191f characteristics, 3: 752t cheese flow resistance, 1: 831 colon cancer risk, 3: 1020, 3: 1065 colostrum, 3: 591 confocal microscopy, 1: 233f covalent aggregate formation, 3: 1067–1068 dairy desserts, 2: 908, 2: 909t degradation, LAB, 3: 162 denaturation, heat treated, 3: 288–289, 3: 289f differential scanning calorimetry (DSC), 1: 261 equid milk, 3: 519, 3: 521t equine milk, 1: 361t, 1: 361–362 fractionation, 3: 761 functions, 3: 461–462 gastrointestinal digestion, 3: 1062 gels, salts and, 3: 892–893 goat milk, 3: 488 heat-induced gelation, 3: 892 heat stability, 3: 891–892, 3: 1067–1068 heterogeneity, 3: 755 human milk, 3: 583 immunochemical analysis, 3: 749 immunochemical detection, 1: 180 ingestion, humans, 3: 819 interspecies comparison, 3: 835 lactation stage and, 3: 602 marine mammal milk, 3: 574–576 mastitis effects, 3: 903 microbial transglutaminase substrate, 2: 298 microstructure, 1: 232 milk replacers, 4: 398 nitrogen, 3: 742
nondairy foods applications, 2: 130–131, 2: 131f primary structure, 3: 751–752 primate milk, 3: 621, 3: 624 SDS-PAGE, 1: 187 sheep milk, 3: 496 solubility, 3: 888 types, 3: 359, 3: 360t value-added products, 3: 365 viscosity, 3: 889 water-binding capacity, 3: 889 Whey protein concentrates (WPCs), 3: 874 added active yogurt cultures, 3: 875 composition, 3: 875, 3: 875t dairy ingredients, 2: 129 definition, 3: 874 80% protein, 3: 875 extruded, 3: 875 foaming, 3: 891 historical aspects, 1: 17 manufacture, 3: 865, 3: 874, 4: 733 nondairy food, 2: 128t protein components, 3: 876t uses, 3: 873, 3: 875 Whey protein fraction (WPF), 3: 875, 3: 876t concentration, 4: 733 nutraceutical properties, 4: 736 nutritional properties, 4: 736 product manufacture, 4: 733 removal, 4: 733 Whey protein hydrolysates, 3: 877 bioactive peptides, 4: 736 composition, 3: 877t gelation, 2: 293 nutritional applications, 3: 877 peptide composition, 3: 878t thermal stability, 3: 877 Whey protein ingredients definition, 3: 873 functionality, 3: 873 specialty, 3: 877t Whey protein isolate (WPI), 3: 875 composition, 3: 875, 3: 875t historical aspects, 1: 17 manufacture, 3: 865, 3: 874, 4: 733 nondairy food, 2: 128t protein components, 3: 876t shelf life, 3: 234 storage, 3: 234 uses, 3: 873, 3: 875 Whey protein products, 3: 873–878 future growth, 3: 873 historical aspects, 1: 17 Maillard reaction volatiles, 3: 232 processing methods, 3: 874 production, 3: 183f thermal processing, 3: 874 ultrasonication effects, 2: 742–743 Whey quark, 4: 734–735 Whey starter cultures, 1: 554t Whey water, 4: 737 Whey wine, 4: 736 Whipped butter, 1: 501, 3: 708 appearance, 1: 502 manufacture, 1: 501–502 uses, 1: 502 Whipped cream imitation see Imitation whipped creams microstructure, 1: 232 Whipped products, emulsifier adsorption, 1: 63, 1: 68 Whipping cream, 1: 914 aerosols, 1: 924 analysis, 1: 922–923 lipolytic rancidity, 1: 922 manufacture, 1: 912, 1: 914, 1: 914f air incorporation, 1: 915 homogenization, 1: 915, 1: 915, 1: 923–924 initial stage (adsorption), 1: 923 temperature treatment, 1: 915
UHT treatment, 1: 914, 1: 915, 1: 922 milk protein concentrate, 3: 853 packaging, 1: 915–916 quality problems, 1: 922 regulations, 1: 920 shelf life, 1: 915, 1: 922 structure development, 1: 923, 1: 923f White box models, 4: 248 White-brined cheeses, 3: 851 White cheese, yeasts, 4: 749 White clover (Trifolium repens), 2: 576 White-handed gibbon (Hylobates lar) milk, 3: 622t White-line separation disease, 2: 203f White muscle disease, 2: 381–382 goats, 2: 794 sheep, 2: 852–853 White-nosed coati milk oligosaccharides, 3: 271t White-tailed deer (Odocoileus virginianus), seasonal breeding, 4: 445–446 ‘White’ whey, 3: 865 Whole cottonseed (WCS), 2: 350 amino acids, 2: 350–351 delinted, 2: 350 fiber, 2: 350 gelatinized corn starch coating, 2: 351 gossypol, 2: 351 mechanically delinted, 2: 350–351 milk yield, 2: 350 processing methods, 2: 350–351 ration dry matter, 2: 350 roasting, 2: 350–351 Whole-farm nutrient management, 2: 444 nutrient flow, 2: 444, 2: 445f nutrient management approaches, 2: 444 nutrient management models, 2: 444, 2: 445t Whole-genome association (WGA) studies, 2: 664 Australian Holstein–Friesian population, 2: 665, 2: 666f Whole-genome microarray analysis, Campylobacter, 4: 42 Whole-genome shotgun sequencing, 2: 663 Whole milk calf liquid diet, 4: 396 consumption, 3: 278, 3: 278f nondairy food, 2: 128, 2: 128t preparation techniques, 2: 125 Whole milk powder milk chocolate, 1: 860 oxidative stability, 3: 717 Wild goat (ibex; Capra ibex), 2: 814 Wild ox (Bos primigenius; auroch), 1: 284, 3: 326–327 Wild yak, 1: 345 Williopsis californica, 4: 750 Wimmera ryegrass (Lolium rigidum), 2: 556, 2: 565 corynetoxicosis, 2: 574 Winter-active cultivars, 2: 593 Winter butter, 1: 513, 3: 704–705 Winter forages, sheep, 2: 850 Winter tetany energy intake, 2: 227–228 etiology, 2: 225 Wisconsin mastitis test (WMT), 3: 896 Wood–Werkman (WW) cycle Propionibacterium, 1: 406f Propionibacterium pathways, 1: 406, 1: 406–407 Wool production, transgenic sheep, 2: 643 Work experience, 2: 3 Work softening butter consistency, 1: 512 butter spreadability, 1: 513 modified butter, 1: 501 World Animal Health, 4: 4, 4: 5 World Animal Health and Welfare Fund, 4: 2 World Animal Health Information Database (WAHID), 4: 4 World Animal Health Information System (WAHIS), 4: 4
Index World Cancer Research Fund and American Institute for Cancer Research report, colon cancer-dairy product relationship, 3: 1016–1017 World Customs Organization (WCO), 4: 331 historical aspects, 4: 331 identity standards, 4: 324 product definitions, 4: 324–325 website, 4: 334 World Health Organization (WHO), nitrate toxicity, 1: 908 World Organization for Animal Health (OIE) see OIE (World Organization for Animal Health) World Trade Organization (WTO), 4: 295, 4: 338–344 Agricultural Agreement see Agricultural Agreement Codex Alimentarius texts as reference, 4: 316 decision-making process, 4: 338 extra agreements, 4: 338, 4: 339t formation, 4: 338 functions, 4: 338 membership, 4: 338 Most Favored Nation, 4: 338 negotiation rounds, 4: 338, 4: 339t time-bound efforts, 4: 347, 4: 347t principles, 4: 338 least developed countries, 4: 339 National Treatment Clause, 4: 338 nontariff barriers, 4: 339 Sanitary and Phytosanitary (SPS) Agreement see Agreement on the Application of Sanitary and Phytosanitary Measures (SPS) sanitary and phytosanitary (SPS) measures, 4: 1 Worm-screen centrifuge, 4: 180
X Xanthan gum, 1: 67 applications, 1: 70t dairy desserts, 2: 909t as emulsifier, 1: 69t Xanthine dehydrogenase (XDH), 2: 324 Xanthine dehydrogenase/oxidase (XDH/XO), 3: 375–377, 3: 685 dehydrogenase form, 3: 685–686 enzymatic activity, 3: 685–686, 3: 689 functions, 3: 686 milk fat globule membrane, 3: 681f, 3: 685 oxidase form, 3: 685–686 Xanthine oxidase (XO), 2: 324 milk lipid oxidation, 3: 719 Xanthine oxidoreductase (XOR), 2: 324–326 equine milk, 3: 523–524 forms, 2: 324 gene targeted disruption, 2: 326 ischemia–reperfusion injury pathogenesis, 2: 324 milk antimicrobial activity, 2: 325 heart disease and, 2: 326 species variation, 2: 326 milk fat globule membrane, 3: 480 milk secretion, 2: 325 reactive nitrogen species and, 2: 324–325 reactive oxygen species source, 2: 324 spore inhibition, 1: 664 structure, 2: 324 Xanthomonas maltophilia, 3: 451 Xenotransplantation, 2: 641 Xinjiang Brown cattle, 1: 285t, 1: 298 X-linked enzyme quantification, embryo sexing, 2: 631 X-prolyl dipeptidyl aminopeptidase (PepX), 3: 87 X-ray diffraction, 1: 229 Xylooligosaccharides (XOS), 4: 362 bifidogenic effect, 4: 368–369 as prebiotics, 4: 361t, 4: 362 production, 4: 362 structure, 4: 357f, 4: 359t Xylose, 1: 386t
Y Yak(s), 1: 343–350, 1: 344f, 3: 531, 3: 532t, 3: 533 adaptation, 1: 344 artificial insemination, 1: 345–346 breeds, 1: 345, 3: 532 Chauri, 3: 532 Jom, 3: 532 characteristics, 1: 343 cheese see Yak milk cheese colostrum, 3: 532t composition, 3: 532t distribution, 1: 343, 3: 531 dystocia, 4: 511 environment, 1: 343 feed shortages, 1: 343–344 functions, 1: 346 transport, 1: 344 grazing, 1: 344, 1: 344f hemoglobin, 1: 344 hybrids, 1: 345 milk yield, 1: 347 milk, 1: 346 collection methods, 1: 346f, 1: 346–347 composition, 1: 347, 1: 348t, 3: 532, 3: 532t consumption and uses, 3: 533 fatty acids, 3: 532–533 importance of, 1: 346 products, 1: 350, 3: 533 protein and solids in, 3: 533 proteins, bovine milk comparison, 3: 533 quality variation, 1: 346 ‘thick’/‘rich’ quality, 3: 532 traditional uses, 1: 348 utilization, 1: 348 milk cake, 3: 533 milk curd and milk whey, 3: 533 milk fat, 1: 347–348, 3: 532–533 milking, 1: 347, 1: 347f milk production, 1: 347, 3: 532 national, 1: 347 milk residue, 1: 349 milk yield, 1: 347, 3: 532 North America, 1: 345 origin, 3: 531 as pack animal, 1: 344 pregnancy duration, 4: 503 raw milk, 1: 348 seasonal body weight changes, 1: 343–344 seasonal breeding, 4: 445 size, 1: 345 types, 1: 345 uses, 1: 346 whey, 1: 350 wild, 1: 345 wild–domestic crosses, 1: 345 Yak milk butter, 1: 348, 3: 533 manufacture, 1: 348 milk separator, 1: 349 uses, 1: 349 Yak milk cheese, 1: 350, 3: 533 chemical composition, 1: 350 economics, 1: 350 processing, 1: 350 Yakult, 2: 473, 2: 508 first commercial production, 2: 513–514 starter cultures, 2: 509t Yard design, warm climates see Farm design (warm climates) Yarrowia lipolytica, 4: 750 Yeast(s) acid dairy products, 4: 744 blue mold cheeses, 1: 768–769, 1: 771 brine, 4: 752 butter, 4: 745 buttermilk, 4: 745 cheese, 1: 627, 4: 749 defects, 1: 628, 4: 750 ripening, 1: 570
species, 1: 627 surface, 1: 627, 4: 751 cultured milk products, 4: 748 in dairy products, 4: 744–753 spoilage, 4: 744 definition, 1: 662 fermentation starters, 3: 456 fermented milk products, 4: 749 frozen yogurt, 4: 745 gas blowing defects, cheese, 1: 662 avoidance, 1: 662 growth requirements, 4: 744 Gubbeen cheese, 1: 398t hard cheeses see Hard cheese(s) historical aspects, 1: 27 ice cream, 4: 745 inhibition, lactoperoxidase system, 2: 323 kefir grain, 2: 520 koumiss, 2: 515 Limburger cheese, 1: 398t Livarot cheese, 1: 398t market milk, 4: 744 milk, 4: 744–753 pathogens, 3: 451 mold-ripened cheeses, 1: 627, 1: 775 smear-ripened cheeses, 1: 398t spoilage agents, 3: 454 starter cultures, 4: 751 see also individual species Yeast counts, 1: 219 acid-curd cheeses, 4: 749–750 cheese inferior, 4: 751 cheese surface, 4: 751 Yeast extract–peptone–lactate (yel) media, Propionibacterium, 1: 404 Yeast-lactic fermentations, 2: 473 Yersinia pathogens, 3: 449 taxonomy, 4: 117 Yersinia enterocolitica, 4: 117–123 bioserotypes, 4: 117 biotypes, 4: 117, 4: 118t serotypes relationships, 4: 118t biotyping, 4: 118 characteristics, 4: 117 chromosomal virulence genes, 4: 119 clinical disease, 4: 119 long-term sequelae, 4: 120 control, 4: 122 culture appearance, 4: 117 in dairy products, 4: 120, 4: 121t ecology, 4: 120 epidemiology, 4: 120 food-borne pathogen, 3: 314 infection sources, 4: 120 isolation/detection enrichment procedures, 4: 121 environmental samples, 4: 121 food samples, 4: 121 molecular, 4: 122 laboratory identification, 4: 117 biochemical tests, 4: 117, 4: 118t in milk, 4: 68, 4: 120, 4: 121t postpateurization contamination, 4: 120 molecular identification, 4: 117, 4: 119t molecular typing, 4: 118, 4: 119t morphology, 4: 117 outbreaks, 4: 120 dairy-related, 4: 120, 4: 121t milk-related, 3: 314, 3: 646, 4: 68 pathogenesis, 4: 119 pathogenicity, 4: 119 phage typing, 4: 118 physiological properties, 4: 117 prevention, 4: 122 serotypes, 4: 117 biotype associations, 4: 118t distribution patterns, 4: 120
959
960 Index Yersinia enterocolitica (continued ) serotyping, 4: 118 Ymer, 2: 472 Yogurt, 2: 472, 2: 525–528 acidity, 2: 527, 2: 528 agitation, 4: 165 buffalo milk, Mediterranean region, 2: 783 concentrated, 2: 527 consumer demands, 2: 525, 2: 529 denatured whey proteins, 3: 1067–1068 E. coli outbreaks, 4: 62 elevated somatic cell count effects, 3: 905 flavor development, 2: 530, 2: 531, 2: 535 LAB, 3: 161 folate bioavailability studies, 4: 684–685, 4: 685f, 4: 685f food safety, 2: 528 frozen, 2: 895t, 2: 897 Greek-style, 1: 47 heat treated, 4: 748 homogenization, 2: 526, 2: 759 imitation, 2: 916 infrared spectrometry, 1: 119t lactose, 2: 484 lactose-free, 2: 281 lactose intolerance, 3: 1014 lactose malabsorption, 3: 1011–1012 lipolytic defects, 3: 724 macromineral contents, 3: 927t manufacture, 2: 525 acidification, glucose oxidase, 2: 302 evaporation, 4: 201 fermentation, 2: 527 high pressure processing, 2: 736 homogenization and heat treatment, 2: 526, 2: 759 microbial inoculation, 2: 527, 2: 530 pressure-treated products, 2: 736 processing, final cooling stage, 2: 527 sonication, 2: 743 microbiological analysis, 2: 530 microstructure, 1: 233, 1: 233f milk fortification, 2: 526 additive ingredients, 2: 526 milk solids, 2: 526 milk protein concentrate, 3: 852 milk protein upstandardization, 4: 548–549 minimum composition types, 2: 475t US, 2: 475t naming, 2: 525 origins, 2: 525, 2: 529 packaging, 2: 527, 4: 21 flexible containers, 4: 21 rigid containers, 4: 21
semirigid containers, 4: 21 perceived additives, 1: 46f processing equipment, 4: 128t Pseudomonas, 4: 382 quality considerations, 2: 528 thermization effects/desirability, 2: 697, 2: 697t recombined products see Recombined yogurt rheology, 4: 527 constant-shear rate experiments, 4: 529 constant-shear stress experiments, 4: 529 fermentation, 4: 527 flow behavior, 4: 528 flow curves, 4: 528 heat treatment, 4: 527 hysteresis loops, 4: 528 postfermentation shearing, 4: 527 solid-like behavior, 4: 528 viscoelastic behavior, 4: 528 scanning electron microscopy, 1: 233f shelf life, 2: 528 spoilage microorganisms, 2: 528, 4: 781 starter cultures, 2: 472, 2: 529–532 bacterial exopolysaccharides, 2: 481, 2: 531 fermentation processes, 2: 531 flavor and aroma, 2: 531, 2: 535 inhibitors, 2: 532 microbial strain selection, 2: 529 regulations, 2: 529 species used, 2: 530 standard specifications, 2: 529 see also individual species synonyms, 2: 472, 2: 473t texture microbial transglutaminase, 2: 299, 2: 299f properties, 2: 759 trace element content, 3: 935t types, 2: 525 vitamins, 2: 494t volatile flavor components, 2: 535, 2: 538t yak milk, 1: 349 see also individual types Yogurt drinks, 4: 734 Yolk sac, 4: 486
Z Zabady (buffalo milk set yogurt), 2: 503 chemical composition, 2: 503 microbiology, 2: 503 prepartion, classical yogurt vs., 2: 503, 2: 504t Zakinthos sheep, 1: 332t Zanba, 1: 348
Zaraibi (Egyptian Nubian) goats, 1: 311t, 1: 317 Zearalenone, 4: 799, 4: 799f Zebu cattle see Bos indicus cattle Zeolite A, 2: 244 Zero grazing systems, Africa, 2: 78–79, 2: 79f Zero risk, 4: 279 Zigaja sheep, 1: 332t Zinc, 2: 382 absorption, 2: 382, 3: 999 antagonists, 2: 384 chelated forms, 3: 999–1000 in dairy products, 3: 934t, 3: 935t, 3: 935t, 3: 935t deficiency, 2: 382 fat-soluble vitamin absorption, 3: 1001 humans, 3: 936 feed supplements, 2: 382, 2: 384 benefits, 2: 384, 2: 385t combination supplements, 2: 386, 2: 386t mastitis resistance, 3: 431 functions, 3: 936 human milk, bioavailability, 3: 938 laminitis, 2: 203–204 llama milk, 3: 536 in milk, 3: 933, 3: 934t bioavailability, 3: 938 chemical forms, 3: 935 nutrient intake, contributions to, 3: 1006 nutritional significance, 3: 936 primate milk, 3: 627–629, 3: 628t recommended daily allowance, 3: 936, 3: 937t reproductive traits, 2: 384 requirements, 2: 379t, 2: 382 sheep milk, 3: 500 toxicity, 2: 383 Zinc chloride, 2: 387 Zinc lysine, 2: 384 Zinc methionine milk yield effects, 2: 384, 2: 385t supplementation, 2: 384, 2: 386, 2: 386t mastitis resistance, 3: 431 Zinc oxide, 2: 384 Zinc proteinate, 2: 385 Zinc sulfate, 2: 384 Zona pellucida, 2: 617, 4: 485, 4: 486f blastocyst hatching, 4: 494–495 Zone electrophoresis milk proteins, 3: 761 historical aspects, 1: 22–23 primate milk proteins, 3: 621 Zoonotic diseases, goats, 2: 802, 2: 803t Zygosaccharomyces rouxii, 4: 752 Zygote, 4: 485, 4: 485