DEVELOPMENTS IN DAIRY CHEMISTRY-2. Lipids

Transcription

1 DEVELOPMENTS IN DAIRY CHEMISTRY-2 Lipids

2 CONTENTS OF VOLUME 1 Volume 1: Proteins 1. Chemistry of Milk Protein. HAROLD E. SWAISGOOD 2. Association of Caseins and Casein Micelle Structure. D. G. SCHMIDT 3. Inter-species Comparison of Milk Proteins. ROBERT JENNESS 4. Biosynthesis of Milk Proteins. T. B. MEPHAM, P. GAYE andj. C. MERCIER 5. The Enzymatic Coagulation of Milk. D. G. DALGLEISH 6. Heat-induced Coagulation of Milk. P. F. Fox 7. Age Gelation of Sterilized Milks. V. R. HARWALKAR 8. Changes in the Proteins of Raw Milk During Storage. ERNST H. REIMERDES 9. Nutritional Aspects of Milk Proteins. LEIF HAMBRAEUS 10. Manufacture of Casein, Caseinates and Co-precipitates. L. L. MULLER 11. Industrial Isolation of Milk Proteins: Whey Proteins. K. R. MARSHALL 12. Functional Properties of Milk Proteins and their Use as Food Ingredients. C. V. MORR

3 DEVELOPMENTS IN DAIRY CHEMISTRY-2 Lipids Edited by P. F. FOX Department of Dairy and Food Chemistry, University College, Cork, Republic of Ireland APPLIED SCIENCE PUBLISHERS LONDON and NEW YORK

4 APPLIED SCIENCE PUBLISHERS LID Ripple Road, Barking, Essex, England Sole Distributor in the USA and Canada ELSEVIER SCIENCE PUBLISHING t,o., INC. 52 Vanderbilt Avenue, New York, NY 10017, USA British Library Cataloguing in Publication Data Developments in dairy chemistry.-(the developments series) 2: Lipids 1. Dairy products--analysis and examination 1. Fox, P. F. II. Series 636'.01'543 SF253 ISBN ISBN (ebook) / WITH 42 TABLES AND 88 ILLUSTRATIONS APPLIED SCIENCE PUBLISHERS LID 1983 Softcover reprint of the hardcover lst edition 1983 The selection and presentation of material and the opinions expressed in this publication are the sole responsibility of the authors concerned. All rights reserved. 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 copyright owner, Applied Science Publishers Ltd, Ripple Road, Barking, Essex, England Typeset in Great Britain by Keyset Composition, Colchester

5 PREFACE Many of the desirable flavour and textural attributes of dairy products are due to their lipid components; consequently, milk lipids have, traditionally, been highly valued, in fact to the exclusion of other milk components in many cases. Today, milk is a major source of dietary lipids in western diets and although consumption of milk fat in the form of butter has declined in some countries, this has been offset in many cases by increasing consumption of cheese and fermented liquid dairy products. This text on milk lipids is the second in a series entitled Developments in Dairy Chemistry, the first being devoted to milk proteins. The series is produced as a co-ordinated treatise on dairy chemistry with the objective of providing an authoritative reference source for lecturers, researchers and advanced students. The biosynthesis, chemical, physical and nutritional properties of milk lipids have been reviewed in eight chapters by world experts. However, space does not permit consideration of the more product-related aspects of milk lipids which play major functional roles in several dairy products, especially cheese, dehydrated milks and butter. Arising from the mechanism of fatty acid biosynthesis and export of fat globules from the secretory cells, the fat of ruminant milks is particularly complex, containing members of all the major lipid classes and as many as 400 distinct fatty acids. The composition and structure of the lipids of bovine milk are described in Chapter 1, with limited comparison with non-bovine milk fats. Since the fatty acid profile of milk fat, especially in monogastric animals, may be modified by diet and other environmental factors, the biosynthesis of milk lipids is reviewed in Chapter 2 with the objective of indicating means by which the fatty acid profile, and hence the v

6 VI PREFACE functional properties of the lipids, might be modified. Lipids in foods are normally present as an emulsion, stabilized by a layer of protein adsorbed at the oil-water interface. The fat in milk and cream exists as an oil-inwater emulsion with a unique stabilizing lipoprotein membrane, referred to as the milk fat globule membrane (MFGM). The inner layers of the MFGM are formed within the secretory cell and are relatively stable; however, the outer layers, which are acquired as the fat globule is exported through the apical membrane of the secretory cells, are unstable. Damage to the MFGM leads to chemical and physical instability of the fat phase in milk and hence the structure of the membrane has been the subject of considerable research, the results of which are reviewed in Chapter 3. Lipids strongly influence, for good or evil, the flavour and texture of foods, especially high-fat products such as butter. The influence of various colloidal features of milk fat on the properties of milk and cream is considered in Chapter 4, while the crystallization of milk fat and how this may be controlled, modified and measured are reviewed in Chapter 5. Unfortunately, lipids are subject to chemical and enzymatic alterations which can cause flavour defects referred to as oxidative and hydrolytic rancidity, respectively. The storage stability of high-fat foods, especially mildly flavoured foods like milk, cream and butter, is strongly influenced by these changes which have been reviewed in Chapters 6 and 7. Dietary lipids play many diverse nutritional roles, some of which are essential. However, dietary lipids, especially saturated lipids of animal origin, have been the subject of much controversy in recent years, particularly in regard to their possible role in atherosclerosis. Various aspects of the nutritional significance of lipids are discussed in Chapter 8. Finally, I wish to thank sincerely the 14 authors who have contributed to this text and whose co-operation has made my task as editor a pleasure. P.F.Fox

7 CONTENTS Preface List of Contributors v IX 1. The Composition and Structure of Milk Lipids. 1 WILLIAM W. CHRISTIE 2. Influence of Nutritional Factors on the Yield, Composition and Physical Properties of Milk Fat 37 J. C. HAWKE and M. W. TAYLOR 3. Origin of Milk Fat Globules and the Nature of the Milk Fat Globule Membrane 83 T. W. KEENAN, DANIEL P. DYLEWSKI, TERRY A. WOODFORD and ROSEMARY H. FORD 4. Physical Chemistry of Milk Fat Globules 119 P. WALSTRA 5. Physical Properties and Modification of Milk Fat. 159 B. K. MORTENSEN 6. Lipolytic Enzymes and Hydrolytic Rancidity in Milk and Milk Products 195 H. C. DEETH and C. H. FITZ-GERALD vii

8 viii CONTENTS 7. Lipid Oxidation. 241 T. RICHARDSON and M. KORYCKA-DAHL 8. The Nutritional Significance of Lipids. 365 M.1. GURR Index 419

9 LIST OF CONTRIBUTORS WILLIAM W. CHRISTIE Department of Lipid Biochemistry and Enzymology, Hannah Research Institute, Ayr KA65HL, UK H. C. DEETH Otto Madsen Dairy Research Laboratory, Queensland Department of Primary Industries, Hamilton, Queensland 4007, Australia DANIEL P. DYLEWSKI Department of Biochemistry and Nutrition, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA C. H. FITZ-GERALD Otto Madsen Research Laboratory, Queensland Department of Primary Industries, Hamilton, Queensland 4007, Australia ROSEMARY H. FORD Department of Biochemistry and Nutrition, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA M. I. GURR Nutrition Department, National Institute for Research in Dairying, University of Reading, Shinfield, Reading RG2 9AT, UK IX

10 x LIST OF CONTRIBUTORS J. C. HAWKE Department of Chemistry, Biochemistry and Biophysics, Massey University, Palmerston North, New Zealand T. W. KEENAN Department of Biochemistry and Nutrition, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA M. KORYCKA-DAHL Department of Food Science, University of Wisconsin, Madison, Wisconsin 53706, USA B. K. MORTENSEN Danish Government Research Institute for Dairy Industry, Roskildevej 56, DK-3400 HillenJd, Denmark T. RICHARDSON Department of Food Science, University of Wisconsin, Madison, Wisconsin 53706, USA M. W. TAYLOR Department of Food Technology, Massey University, Palmerston North, New Zealand P. WALSTRA Department of Food Science, Agricultural University, Wageningen, The Netherlands TERRY A. WOODFORD Department of Biochemistry and Nutrition, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA