Dairy processing improving quality

Dairy processing
Improving quality
Edited by
Gerrit Smit


Published by Woodhead Publishing Limited
Abington Hall, Abington
Cambridge CB1 6AH
England
www.woodhead-publishing.com
Published in North America by CRC Press LLC
2000 Corporate Blvd, NW
Boca Raton FL 33431
USA
First published 2003, Woodhead Publishing Limited and CRC Press LLC
ß 2003, Woodhead Publishing Limited
The authors have asserted their moral rights.
This book contains information obtained from authentic and highly regarded sources.
Reprinted material is quoted with permission, and sources are indicated. Reasonable
efforts have been made to publish reliable data and information, but the authors and
the publishers cannot assume responsibility for the validity of all materials. Neither the
authors nor the publishers, nor anyone else associated with this publication, shall be
liable for any loss, damage or liability directly or indirectly caused or alleged to be
caused by this book.
Neither this book nor any part may be reproduced or transmitted in any form or by
any means, electronic or mechanical, including photocopying, microfilming and
recording, or by any information storage or retrieval system, without permission in
writing from the publishers.
The consent of Woodhead Publishing Limited and CRC Press LLC does not extend
to copying for general distribution, for promotion, for creating new works, or for

resale. Specific permission must be obtained in writing from Woodhead Publishing
Limited or CRC Press LLC for such copying.
Trademark notice: Product or corporate names may be trademarks or registered
trademarks, and are used only for identification and explanation, without intent to
infringe.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library.
Library of Congress Cataloging-in-Publication Data
A catalog record for this book is available from the Library of Congress.
Woodhead Publishing Limited ISBN 1 85573 676 4 (book); 1 85573 707 8 (e-book)
CRC Press ISBN 0-8493-1758-4
CRC Press order number: WP1758
Cover design by The ColourStudio
Project managed by Macfarlane Production Services, Markyate, Hertfordshire
(e-mail: )
Typeset by MHL Typesetting Limited, Coventry, Warwickshire
Printed by TJ International Ltd, Padstow, Cornwall, England


Contributor contact details

Chapter 1
Professor Gerrit Smit
Manager of the Department of
Flavour, Nutrition and Ingredients
NIZO Food Research
Kernhemseweg 2
PO Box 20
6710 BA Ede
The Netherlands

Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
Direct call: +31 (0) 318 659538
E-mail:

Tel: +353 21 490 2362
Fax: +353 21 427 0001
E-mail:

Chapter 3
Dr Mike Boland
Executive Manager Science
Fonterra Research Centre
Palmerston North
New Zealand
Tel: +64 (0) 6 350 4664
Fax: +64 (0) 6 350 6320
Mobile: +64 21338049
E-mail:

Chapter 2
Professor P. F. Fox
Department of Food and Nutritional
Sciences
University College
Cork
Ireland

Chapter 4
Dr ir Meike C. te Giffel

Department of Processing, Quality
and Safety
NIZO Food Research
Kernhemseweg 2


xiv

Contributor contact details

6710 BA Ede
The Netherlands
Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
Direct call: +31 (0) 318 659590
E-mail:


Chapter 5
Dr Mike Lewis
Department of Food Science and
Technology
The University of Reading
PO Box 226
Reading
RG6 6AP
UK
Tel: +44 (0) 1734 318700
Fax: +44 (0) 1734 310080
E-mail:

Chapter 6
Dr R. C. McKellar
Food Research Program
Agriculture and Agri-Food Canada
93 Stone Road West
Guelph
Ontario N1G 5C9
Canada
E-mail:

Chapter 7
Dr A. E. M. Boelrijk
Department of Flavour, Nutrition and
Ingredients
NIZO Food Research
Kernhemseweg 2
PO Box 20
6710 BA Ede
The Netherlands
Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
Direct call: +31 (0) 318 659638
E-mail:


Chapter 8
Dr D. Jaros and Professor H. Rohm
Institute of Food Technology and

Bioprocess Engineering
Dresden University of Technology
D-01062 Dresden
Germany
E-mail:



Chapter 9
Professor Donald Muir
Hannah Research Institute
Hannah Research Park
Ayr
KA6 5HL
Scotland
Tel: +44 (0) 1292 670170
Fax: +44 (0) 1292 670180
E-mail:



Contributors contact details

Chapter 10

Chapter 13

Professor Franz Ulberth
Department of Dairy Research and
Bacteriology

University of Agricultural Sciences
Gregor Mendel Str. 33
A-1180 Vienna
Austria

Dr Geert Ellen
NIZO Food Research
Kernhemseweg 2
PO Box 20
6710 BA Ede
The Netherlands

E-mail:

xv

Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
E-mail:

Chapter 11
Dr Maija Saxelin
Valio Ltd
Meijerite 4 A
PO Box 30
00039 Helsinki
Finland
E-mail:

Chapter 12

Chapter 14
Dr Aziz Amine
Faculte´ de Sciences et Techniques
Universite´ Hassan II-Mohammedia
20650 Mohammedia
Morocco
Tel: +212.23.314705; /315352/
314708
Fax: +212.23.315353
E-mail:

Dr J. Snel
Department of Flavour, Nutrition and
Ingredients
NIZO Food Research
Kernhemseweg 2
PO Box 20
6710 BA Ede
The Netherlands

Dr Laura Micheli, Dr Danila Moscone
and Professor Giuseppe Palleschi
Dipartmente di Scienze e Tecnologie
Chimiche
Universita` di Roma ‘Tor Vergata’
Via della Ricerca Scientifica
Rome
Italy

Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
Direct call: +31 (0) 318 659549
E-mail:

Tel: +39 06 7259 4423
Fax: +39 06 7259 4328
E-mail:



xvi

Contributor contact details

Chapter 15

Chapter 18

Dr J. Van Camp
Department of Food Technology and
Nutrition
Faculty of Agricultural and Applied
Biological Sciences
Ghent University
Coupure Links 653
B-9000 Ghent
Belgium

C. R. Loss and Dr J. H. Hotchkiss

Department of Food Science
Cornell University
Stocking Hall
Ithaca
NY 14853
USA

Tel: +32 9 2646208
Fax: +32 9 2646218
E-mail:

Chapter 19

Chapter 16
Ir R.E.M. Verdurmen
Department of Processing, Quality
and Safety
NIZO Food Research
Kernhemseweg 2
PO Box 20
6710 BA Ede
The Netherlands
Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
Direct call: +31 (0) 318 659563
E-mail:

Chapter 17
Ir Gerrald Bargeman
NIZO Food Research

Kernhemseweg 2
PO Box 20
6710 BA Ede
The Netherlands
Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
E-mail:


Dr P. L. H. McSweeney
Department of Food and Nutritional
Sciences
University College
Cork
Ireland
Tel: +353 21 490 2011 (direct line)
Fax: +353 21 427 0001
E-mail:

Mr V. K. Upadhyay
Department of Food and Nutritional
Sciences
University College
Cork
Ireland

Chapter 20
Dr Tom Beresford
Dairy Products Research Centre
Moorepark

Fermoy
Co Cork
Ireland
Tel: +353 025 42222
Fax: +353 025 42340
E-mail:



Contributors contact details

Chapter 21
Dr W. Bockelmann
Institut fu¨r Mikrobiologie
Bundesanstalt fu¨r Milchforschung
Postfach 6069
D-24121 Kiel
Germany
Tel: +49 (0) 431 609 2438
Fax: +49 (0) 431 609 2306
E-mail:

PO Box 20
6710 BA Ede
The Netherlands
Tel: +31 (0) 318 659511
Fax: +31 (0) 318 650400
Direct call: +31 (0) 318 659532
E-mail:

Chapter 23
Chapter 22
Dr W. J. M. Engels
Department of Flavour, Nutrition and
Ingredients
NIZO Food Research
Kernhemseweg 2

D. Givens and K. Shingfield
The University of Reading
Reading RG6 6AR
UK
E-mail:

xvii


Contents

Contributor contact details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xiii

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
G. Smit, NIZO Food Research, The Netherlands

1

Part I

Dairy product safety and quality . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

2 The major constituents of milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
P. F. Fox, University College Cork, Ireland
2.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2
Lactose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3
Lipids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4
Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5
Minor proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6
Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

3 Influences on raw milk quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M. Boland, Fonterra Research Centre, New Zealand
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2
Breed, genetics and milk quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.3
Cow diet and milk quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4
Other aspects of animal husbandry and milk quality . . . . . . . . .
3.5
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6
Sources of further information and advice . . . . . . . . . . . . . . . . . . .
3.7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5
7
12
18
26
36
38
42
42
45
52
55
59
61
62
62

vi

Contents

4 Good
M. C.
4.1
4.2
4.3
4.4
4.5
4.6

hygienic practice in milk processing . . . . . . . . . . . . . . . . . . . . . . . .
te Giffel, NIZO Food Research, The Netherlands
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The principal hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Good hygienic practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sources of further information and advice . . . . . . . . . . . . . . . . . . .
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Improvements in the pasteurisation and sterilisation of milk . . . .
M. J. Lewis, The University of Reading, UK
5.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2
Kinetic parameters in heat inactivation . . . . . . . . . . . . . . . . . . . . . .
5.3

Thermisation and tyndallisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4
Pasteurisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.5
Factors affecting the effectiveness of pasteurisation . . . . . . . . . .
5.6
Extended shelf-life milks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.7
Sterilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.8
Ultra-high temperature (UHT) sterilisation . . . . . . . . . . . . . . . . . . .
5.9
Aseptic packaging and storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Modelling the effectiveness of pasteurisation . . . . . . . . . . . . . . . . . . . . . .
R. C. McKellar, Agriculture and Agri-Food Canada
6.1
Introduction: the role of predictive modelling . . . . . . . . . . . . . . . .
6.2
The development of thermal models . . . . . . . . . . . . . . . . . . . . . . . . .
6.3
Key steps in model development . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.4
Models for key enzymes and pathogens . . . . . . . . . . . . . . . . . . . . .
6.5
Modelling and risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.6
Risk assessment and pasteurisation . . . . . . . . . . . . . . . . . . . . . . . . . .
6.7
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6.8
Sources of further information and advice . . . . . . . . . . . . . . . . . . .
6.9
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Flavour generation in dairy products . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. E. M. Boelrijk, C. de Jong and G. Smit, NIZO Food Research,
The Netherlands
7.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2
Raw and heat-treated milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3
Yoghurt and buttermilk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.4
Conclusion and future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

68
68
69
72
77
79
79
81
81
82

83
85
86
92
92
95
100
100
104
104
105
110
115
117
121
124
125
126
130

130
134
142
147
148
148


Contents
8 Controlling the texture of fermented dairy products:

the case of yoghurt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Jaros and H. Rohm, Dresden University of Technology, Germany
8.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2
The manufacture of yoghurt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3
Factors affecting yoghurt texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.4
Measuring the rheological and textural properties of yoghurt
8.5
Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.6
Sources of further information and advice . . . . . . . . . . . . . . . . . . .
8.7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

vii

155
155
155
160
166
174
176
176

9 Factors affecting the shelf-life of milk and milk products . . . . . . . .
D. D. Muir and J. M. Banks, Hannah Research Institute, UK

9.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2
Chemical composition and principal reactions of milk . . . . . . .
9.3
Bacteria in milk and related enzyme activity . . . . . . . . . . . . . . . .
9.4
Raw milk enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.5
Control of the quality of short shelf-life products . . . . . . . . . . . .
9.6
Yoghurt and fermented milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.7
Factors affecting the stability of long shelf-life products . . . . .
9.8
Control of the stability of long-life milk products . . . . . . . . . . .
9.9
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.10 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.11 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185
186
190
193
194
197
198
200
206

206
206

10

208

11

Testing the authenticity of milk and milk products . . . . . . . . . . . . .
F. Ulberth, University of Agricultural Sciences, Austria
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.2 Detecting and quantifying foreign fats . . . . . . . . . . . . . . . . . . . . . . .
10.3 Detecting milk of different species . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.4 Detection of non-milk proteins, watering of milk and
alteration of casein/whey protein ratio . . . . . . . . . . . . . . . . . . . . . . .
10.5 Measuring heat load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.6 Identifying geographical origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional dairy products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
M. Saxelin, R. Korpela and A. Ma¨yra¨-Ma¨kinen, Valio Ltd, Finland
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.2 Composition of milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.3 Fermented milk products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.4 What do we mean by functional dairy products? . . . . . . . . . . . .
11.5 Examples of functional dairy products: gastrointestinal
health and general well-being . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185

208
210
214
218
220
221
222
223
229
229
229
231
233
234


viii

Contents

11.6
11.7

Examples of functional dairy products: cardiovascular health
Examples of functional dairy products: osteoporosis and
other conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.8 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.9 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
11.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12

Developing and approving health claims for functional dairy
products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J. Snel and R. van der Meer, NIZO Food Research, The Netherlands
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2 The body’s defence mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3 In vitro studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.4 Animal studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.5 Human studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.6 Making health claims . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.7 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.8 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
12.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Part II
13

14

238
241
242
243
244

246
246
247
249

251
252
254
255
256
257

New technologies to improve quality . . . . . . . . . . . . . . . . . . . . . . .

261

On-line measurement of product quality in dairy processing . .
G. Ellen and A. J. Tudos, NIZO Food Research, The Netherlands
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2 On-line measurement of physical parameters . . . . . . . . . . . . . . . .
13.3 Measuring product composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.4 On-line microbiological testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.5 Monitoring fouling and cleaning-in-place . . . . . . . . . . . . . . . . . . . .
13.6 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.7 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
13.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

263

Rapid on-line analysis to ensure the safety of milk . . . . . . . . . . . . .
A. Amine, Universite´ Hassan II-Mahammedia, Morocco and
L. Micheli, D. Moscone and G. Palleschi, Universita` di Roma
`Tor Vergata’, Italy
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2 Monitoring contamination during milking: faecal

contamination and mycotoxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3 Measuring the effectiveness of heat treatment . . . . . . . . . . . . . . .
14.4 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

263
265
269
279
280
283
287
288
292

292
294
299
306
306


Contents
15

16

17

18

High-pressure processing to improve dairy product quality . . .
W. Messens, Agricultural Research Centre Ghent, Belgium and
J. Van Camp and K. Dewettinck, Ghent University, Belgium
15.1 Introduction: high-pressure principles and technologies . . . . . .
15.2 The effects of high pressure on nutritional and
other qualities in milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3 The effects of high pressure on bacteria and enzymes . . . . . . .
15.4 The effects of high pressure on milk proteins . . . . . . . . . . . . . . . .
15.5 The effects on other properties of milk . . . . . . . . . . . . . . . . . . . . . .
15.6 The effects on cheese and yoghurt-making properties of milk
15.7 High-pressure treatment of cheese . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.8 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.9 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
5.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Optimising product quality and process control for
powdered dairy products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
R. E. M. Verdurmen and P. de Jong, NIZO Food Research, The
Netherlands
16.1 Introduction: evaporation and drying processes . . . . . . . . . . . . . .
16.2 Quality criteria for dairy-based powders . . . . . . . . . . . . . . . . . . . . .
16.3 Modelling quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4 Process and product control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5 Ensuring process safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
16.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Separation technologies to produce dairy ingredients . . . . . . . . . .
G. Bargeman, Akzo Nobel Chemicals bv, The Netherlands
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.2 Separation technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17.3 Isolation of ingredients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17.4 Developments in separation technology . . . . . . . . . . . . . . . . . . . . . .
17.5 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
17.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The use of dissolved carbon dioxide to extend the
shelf-life of dairy products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. R. Loss and J. H. Hotchkiss, Cornell University, USA
18.1 Introduction: factors limiting the shelf-life of dairy
products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.2 The effects of CO2 on bacterial growth . . . . . . . . . . . . . . . . . . . . . .
18.3 The effects of CO2 on raw milk quality . . . . . . . . . . . . . . . . . . . . .
18.4 The effects of CO2 on dairy product quality . . . . . . . . . . . . . . . . .

ix
310

310
311
314
316
317
319
321
325
325
326

333

333

340
347
353
359
362
363
366
366
368
374
385
387
387

391

391
391
396
399


x

Contents
18.5

Bactericidal and sporicidal effects of dissolved CO2 during
thermal processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

406
410
410

Part III Cheese manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

417

19

419

18.6
18.7

20

21

Acceleration of cheese ripening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V. K. Upadhyay and P. L. H. McSweeney, University College Cork,
Ireland
19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2 Accelerating cheese ripening: elevated temperature . . . . . . . . . .
19.3 Addition of exogenous enzymes or attenuated starters . . . . . . .
19.4 Use of adjunct cultures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.5 Genetic modification of starter bacteria . . . . . . . . . . . . . . . . . . . . . .
19.6 High-pressure technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19.7 Enzyme-modified cheeses as flavourings . . . . . . . . . . . . . . . . . . . .
19.8 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.9 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.10 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
19.11 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Non-starter lactic acid bacteria (NSLAB) and cheese quality . .
T. P. Beresford, Dairy Products Research Centre, Ireland
20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.2 Bacteria comprising the NSLAB complex . . . . . . . . . . . . . . . . . . .
20.3 NSLAB in different cheese varieties . . . . . . . . . . . . . . . . . . . . . . . . .
20.4 The source of NSLAB in cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.5 The growth of NSLAB in cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.6 The influence of NSLAB on cheese quality . . . . . . . . . . . . . . . . . .
20.7 Selection of NSLAB adjuncts for quality improvement
of cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The production of smear cheeses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
W. Bockelmann, BafM, Germany
21.1 Introduction: smear-ripened cheese varieties . . . . . . . . . . . . . . . . .
21.2 Production and ripening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21.3 Developing ripening cultures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21.4 Conclusions and future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21.5 Sources of further information and advice . . . . . . . . . . . . . . . . . . .
21.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

419
421
422
431

433
434
437
440
441
441
441
448
448
450
452
454
455
457
461
463
463
470
470
472
477
488
489
489


Contents
22

Flavour formation in cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

W. J. M. Engels, J. E. T. van Hylckama Vlieg and G. Smit,
NIZO Food Research, The Netherlands
22.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22.2 Amino acid conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22.3 Amino acid catabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22.4 Methionine catabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22.5 Branched-chain and aromatic amino acid conversion . . . . . . . .
22.6 Conversion of other amino acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22.7 Natural biodiversity and tailor-made starter cultures . . . . . . . . .
22.8 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Part IV

xi
492

492
493
496
499
501
503
504
505
507

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

513

Improving the nutritional quality of milk . . . . . . . . . . . . . . . . . . . . . . .
D. I. Givens and K. J. Shingfield, The University of Reading, UK
23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.2 Factors affecting milk protein content . . . . . . . . . . . . . . . . . . . . . . .
23.3 Factors affecting milk fat content . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.4 Future trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

515
515
516
518
526
527

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

532

23


1
Introduction
G. Smit, NIZO Food Research, The Netherlands

Milk and the range of dairy products derived from milk have long been central
to diet in both developed and developing countries. Some dairy processing
technologies such as fermentation have been used for thousands of years.

Building on this long lasting foundation, the dairy processing industry continues
to be at the forefront of innovation in the food industry. This important new
collection sums up some of the most important recent developments.
Part I considers key aspects of safety and quality. Chapter 2 provides a
foundation by summarising current knowledge about the major constituents of
milk. The following chapter discusses how factors such as breed and husbandry
practices on the farm influence milk composition. The next three chapters focus
on safety, covering hygienic practices on the farm, developments in
pasteurisation and sterilisation technologies, and the growing use of modelling
to improve these techniques whilst retaining milk quality. A final group of
chapters in Part I consider key aspects of dairy product quality. There are
discussions of the latest research on the control of flavour in milk and other
dairy products, improving texture in fermented dairy products, controlling
stability and shelf-life, and testing the authenticity of milk and milk products.
Building on the traditional nutritional importance of milk, the final two chapters
consider the new generation of functional dairy products.
The second part of the book reviews the range of new technologies that
have emerged recently to improve dairy product quality. The first two chapters
look at on-line techniques to monitor and control various aspects of milk safety
and quality. They are then followed by chapters on extending the shelf-life of
dairy products through such techniques as high pressure processing, the


2

Dairy processing

production of powdered dairy products and the use of carbon dioxide. There is
also a chapter on developments in separation techniques to maximise returns
by producing a wide range of dairy ingredients. The final part of the book

considers key developments in improving flavour and other qualities in cheese
manufacture.
The quality of dairy products, e.g. taste, texture, health and safety, as perceived
by the consumer should be the prime and ultimate driver for the dairy industry. The
new developments described in this book will certainly add to their achievement.


Part I
Dairy product safety and quality


2
The major constituents of milk
P. F. Fox, University College Cork, Ireland

2.1

Introduction

Milk and dairy products are major components of the human diet in Western
countries, providing about 30% of dietary proteins and lipids and about 80% of
dietary calcium. Current annual production of milk is % 600 Â 106 tonnes, of
which %85%, 11%, 2% and 2% are bovine, buffalo, caprine and ovine,
respectively. Although some raw milk is still consumed, the vast majority of
milk is processed to at least some extent. Liquid (beverage) milk is a major food
item in all developed dairying countries, representing %40% of total milk
production. The remainder is processed into one of several thousand products –
the dairy industry is probably the most diverse and flexible sector of the food
industry. The flexibility of milk as a raw material resides in the chemical and
physico-chemical properties of its constituents, many of which are unique. The

principal constituents of milk can be modified by enzymatic, chemical and/or
physical methods, permitting the production of new products. However, the
concentrations and properties of milk constituents are variable and hence the
processability of milk and the properties of dairy products are inconsistent,
although much of this variability can be eliminated by modern technology,
which exploits certain features of milk constituents. Today, most milk is
processed in large, highly mechanized and automated factories, where
consistency in processing properties is essential. The resulting products are
distributed through large wholesale and retail outlets, where consistency is,
again, paramount. Consumers expect consistency also. The consistency expected
by the processor, distributor and consumer can be achieved only if the properties
of milk constituents are understood at the molecular level. This chapter will
describe the principal chemical and physico-chemical properties of the major


6

Dairy processing

constituents of milk, i.e., lactose, lipids, proteins and salts, and variations in the
concentrations and properties of these constituents.
The natural function of milk is to supply the neonatal mammal, of which there
are %4500 species, with its complete nutritional and some of its physiological
requirements. Because the nutritional requirements are species-specific and
change as the neonate matures, the composition of milk shows very large interspecies differences, e.g., the concentrations of fat, protein and lactose range from
1 to 50%, 1 to 20% and 0 to 10%, respectively, and the concentration of each
changes during lactation. Inter-species differences in the concentrations of many
of the minor constituents are even greater than those of the macro-constituents.
Milk from domesticated animals has been used by humans since at least 8000
BC. Although sheep and goats were the first domesticated dairy animals, because

they are more easily managed than cattle, the latter, especially certain breeds of
Bos taurus, are now the dominant dairy animals. Total recorded world milk
production is % 600 Â 106 tonnes per annum, of which %85% is bovine, 11% is
buffalo and 2% each is from sheep and goats. Small amounts of milk are
produced from camels, mares, reindeer and yaks in certain regions with specific
cultural and/or climatic conditions. This chapter will concentrate on the
constituents and properties of bovine milk. Although the constituents of the milk
of the other main dairy species are generally similar to those of bovine milk,
they differ in detail and the technological properties of the milk of these species
differ significantly.
Milk is a very flexible raw material from which several thousand types of
dairy products are produced around the world in a great diversity of flavours and
forms, including %1000 varieties of cheese. The proportions of total world milk
production used for the principal dairy products are: liquid (beverage) milk,
%39%; cheese, %33%; butter, %32%; whole milk powder, %6%; skimmed milk
powder, %9%; concentrated milk products, %2%; fermented milk products,
%2%; casein, %2%; and infant formulae, %0.3%. (The sum value exceeds
100%; this is due to ‘double accounting’, e.g., butter and skim milk powder, and
the standardization of fat content, e.g., for liquid milk, cheese, etc.) This
flexibility and diversity are a result of the properties, many of them unique, of
the constituents of milk, the principal of which are easily isolated from milk,
permitting the production of valuable food ingredients. Milk is free of offflavours, pigments and toxins, which is a very important feature of milk as a raw
material for food ingredients.
The processability and functionality of milk and milk products are
determined by the properties and concentrations of its principal constituents:
proteins, lipids, lactose and salts. Many of the principal problems encountered
during the processing of milk are caused by variability in the concentrations and
properties of these constituents arising from several factors, including breed,
individuality of the animal, stage of lactation, health of the animal, especially
mastitis, and nutritional status. Synchronized calving, as practised in New

Zealand, Australia and Ireland to avail of cheap grass, has a very marked effect
on the composition and properties of milk (see O’Brien et al., 1999a, 1999b,


The major constituents of milk

7

1999c; Mehra et al., 1999). Much of the variability can be offset by standardizing the composition of milk or by modifying the process technology. Genetic
polymorphism of milk proteins has a significant effect on the concentration and
type of protein in milk. The chemical and physical properties of the principal
constituents of milk are well characterized and described, including in the
following textbooks: Walstra and Jenness (1984), Wong (1988), Fox (1992,
1995, 1997), Jensen (1995), Fox and McSweeney (1998, 2003) and Walstra et
al. (1998).

2.2

Lactose

Bovine milk contains about 4.8% lactose. Because lactose is responsible for
$50% of the osmotic pressure of milk, which is equal to that of blood and is
nearly constant, the concentration of lactose in milk is independent of breed,
individuality and nutritional factors but decreases as lactation advances and
especially during mastitic infection, in both cases due to the influx of NaCl from
the blood.
Chemical and physico-chemical properties of lactose
Lactose is a reducing disaccharide comprised of glucose and galactose, linked
by a 1-4-O-glycosidic bond. Among sugars, lactose has a number of distinctive
characteristics, some of which cause problems in milk products during

processing and storage; however, some of its characteristics are exploited to
advantage.
• The aldehyde group on the C-1 of the glucose moiety exists mainly in the
hemiacetal form and, consequently, C-1 is a chiral, asymmetric carbon.
Therefore, like all reducing sugars, lactose exists as two anomers,  and ,
which have markedly different properties. From a functional viewpoint, the
most important of these are differences in solubility and crystallization
characteristics: -lactose crystallizes as a monohydrate while crystals of lactose are anhydrous.
• The solubility of - and -lactose in water at 20ºC is %7 g and %50 g per
100 ml, respectively. The solubility of -lactose is much more temperature
dependent than that of -lactose and the solubility curves intersect at
%93.5ºC.
• At equilibrium in aqueous solution, lactose exists as a mixture of  and 
anomers in the approximate ratio 37:63. When an excess of -lactose is
added to water, %7 g per 100 ml dissolve immediately, some of which
mutarotates to give an : ratio of 37:63, leaving the solution unsaturated
with respect to both - and -lactose. Further -lactose dissolves, some of
which mutarotates to -lactose. Solubilization and mutarotation continue
until two conditions exist, i.e., %7 g of dissolved -lactose per 100 ml and an
: ratio of 37:63, giving a final solubility of %18.2 g per 100 ml.


8

Dairy processing

• When -lactose is added to water, %50 g per 100 ml dissolve initially but
%18.5 g of this mutarotate to -lactose, which exceeds its solubility and
therefore some -lactose crystallizes. This upsets the : ratio and more lactose mutarotates to -lactose, which crystallizes. Mutarotation of lactose and crystallization of -lactose continue until %7 g and %11.2 g of
- and -lactose, respectively, are in solution.

• Although lactose has low solubility in comparison with other sugars, once
dissolved, it crystallizes with difficulty and forms a supersaturated solution.
-Lactose crystallizes spontaneously from highly supersaturated solutions,
but if the solution is only slightly supersaturated, it crysallizes slowly as
sharp, tomahawk-shaped crystals. If the dimensions of the crystals exceed
%15 "m, they are detectable on the tongue and palate. Crystals of -lactose
are smaller and monoclinical in shape. In the metastable zone, crystallization
of lactose is induced by seeding with finely powdered lactose.
• Since -lactose is less soluble than the  anomer below 93.5ºC, it is the
normal commercial form.
• When concentrated milk is spray-dried, there is not sufficient time for lactose
to crystallize and an amorphous glass is formed. If the moisture content of the
powder is kept low, the lactose glass is stable, but if the moisture content
increases to about 6%, e.g., on exposure of the powder to a high humidity
atmosphere, the lactose will crystallize as -lactose monohydrate. If
extensive crystallization occurs, an interlocking mass of crystals is formed,
resulting in ‘caking’, which is a particularly serious problem in whey
powders owing to their high content of lactose (%70%). The problem is
avoided by extensive crystallization of lactose before drying, induced by
seeding the solution with finely powdered lactose.
• Spray-dried milk powder has poor wettability because the small particles
swell on contact with water, blocking the channels between particles. The
wettability (often incorrectly referred to as ‘solubility’) of spray-dried milk
powder may be improved by modifying the drying process to produce milk
powder with coarser, more easily wetted particles. This is achieved by
agglomerating the fine powder particles, in effect by controlling lactoseinduced caking; such powders are said to be ‘instantized’.
• The crystallization of lactose in frozen milk products results in destabilization
of the casein, which aggregates when the product is thawed. In this case, the
effect of lactose is indirect. When milk is frozen, pure water freezes and the
concentration of solutes in the unfrozen water is increased. Since milk is

supersaturated with respect to calcium phosphate (%66% and %57% of the Ca
and PO4, respectively, are insoluble and occur in the casein micelles as
colloidal calcium phosphate; see Section 2.6), when the amount of water
becomes limiting, soluble Ca(H 2 PO 4 ) 2 and CaHPO 4 crystallize as
(Ca)3(PO4)2, with the concomitant release of H+ and a decrease in pH to
%5.8. Unless the temperature is maintained below À30ºC, lactose will
crystallize as  monohydrate during frozen storage, thus reducing the amount
of solvent water and aggravating the problems of calcium phosphate solubility


The major constituents of milk

9

and pH decline. Thorough crystallization of lactose before freezing alleviates,
but does not eliminate, the problem. Pre-heating milk prior to freezing also
alleviates the problem, but pre-hydrolysis of lactose to the more soluble
glucose and galactose using -galactosidase appears to be the best solution.
• Although lactose is hygroscopic when it crystallizes, properly crystallized
lactose has very low hygroscopicity and, consequently, it is a very useful
component of icing sugar.
• Lactose has low sweetness (16% as sweet as sucrose as a 1% solution). This
limits its usefulness as a sweetener (the principal function of sugars in foods)
but makes it is a very useful diluent, e.g., for food colours, flavours, enzymes,
etc., when concomitant sweetness is undesirable.
• Being a reducing sugar, lactose can participitate in the Maillard reaction, with
very undesirable consequences in all dairy products, e.g., brown colour, offflavours, reduced solubility and reduced nutritional value.
Food applications of lactose
The amount of whey produced annually as a by-product of the manufacture of
cheese and casein contains %8 Â 106 tonnes of lactose. About 400 000 tonnes of

lactose are produced per annum. In addition, %2 000 000 tonnes of whey
permeate powder, which serves as a source of lactose for certain applications,
e.g., infant formulae, are produced annually.
Owing to many of its properties, especially low sweetness, the market for
lactose is limited; it is, therefore, often regarded as a waste product and in the
past caused disposal problems. However, some of the properties of lactose make
it a valuable ingredient for pharmaceutical and food applications. Lactose is
most valuable when used in the pharmaceutical industry where it is widely used
as a diluent in pelleting operations.
The principal application of lactose in the food industry is in the
humanization of infant formulae – human milk contains %7% lactose in
comparison with %4.8% in bovine milk. Demineralized whey powder (DWP) is
very suitable for this purpose – it is cheaper than lactose and in addition to
supplying lactose, DWP supplies whey proteins and adjusts the casein:whey
protein ratio to a value closer to that in bovine milk (40:60 compared to 80:20 in
bovine milk). It is necessary to demineralize bovine whey since it contains
approximately four times as much minerals as human milk.
Lactose is also used as an agglomerating/free-flowing agent in foods, in the
confectionery industry to improve the functionality of shortenings, as an anticaking agent at high relative humidity, in icing mixtures or as a reducing sugar if
Maillard browning is required. The low sweetness of lactose is an advantage in
many of these applications. Lactose absorbs compounds and may be used as a
diluent for food flavours or pigments or to trap food flavours.
Lactose derivatives
A number of more useful and more valuable products may be produced from
lactose. The most significant are:


10

Dairy processing

• Lactulose (galactose 1-4 fructose): this sugar, which does not occur in
nature, is produced from lactose by heating, especially under slightly alkaline
conditions. It is not hydrolysed by intestinal -galactosidase and enters the
large intestine where it promotes the growth of Bifidobacterium spp. It is a
mild laxative and is used fairly widely for this purpose. More than 20 000
tonnes are produced annually.
• Glucose–galactose syrups, produced by acid or enzymatic (-galactosidase)
hydrolysis: the technology for the production of such hydrolysates has been
developed but the product is not cost-competitive with other sugars (sucrose,
glucose, glucose–fructose).
• Galactooligosaccharides: -galactosidase has transferase as well as
hydrolytic activity and under certain conditions, the former predominates,
leading to the formation of galactooligosaccharides, which have bifidogenic
properties and are considered to have promising food applications.
• Ethanol is produced commercially by the fermentation of lactose by
Kluyveromyces lactis.
• Other derivatives which have limited but potentially important applications
include lactitol, lactobionic acid, lactic acid, acetic acid, propionic acid,
lactosyl urea and single-cell proteins.
Nutritional aspects of lactose
Lactose is involved in two enzyme-deficiency syndromes: lactose intolerance and
galactosemia. The former is due to a deficiency of intestinal -galactosidase which is
rare in infants but common in adults except north-west Europeans and a few African
tribes. Since humans are unable to absorb disaccharides from the small intestine,
unhydrolysed lactose enters the large intestine where it is fermented by bacteria,
leading to flatulence and cramp, and to the absorption of water from the intestinal
mucosa, causing diarrhoea. These conditions cause discomfort and may be fatal.
Individuals suffering from lactose intolerance avoid the consumption of milk and
lactose-containing dairy products. Hydrolysis of lactose by -galactosidase renders

such products suitable for lactose-intolerant individuals. Hydrolysis may be
performed at the dairy using soluble or immobilized -galactosidase or by the
consumer at home. Lactose-hydrolysed products enjoy limited commercial success
in western countries but have not resulted in a substantial increase in the
consumption of dairy products in Asia, which is a very large potential market for
dairy products but where lactose intolerance is very widespread.
Galactosemia is caused by the inability to catabolize galactose owing to a
deficiency of either of two enzymes, galactokinase or galactose-1P:uridyl
transferase. A deficiency of galactokinase leads to the accumulation of galactose
which is catabolized via alternative routes, one of which leads to the accumulation of galactitol in various tissues, including the eye, where it causes cataract. A
deficiency of galactose-1P:uridyl transferase leads to abnormalities in membranes of the brain and to mental retardation unless galactose is excluded from
the diet within a few weeks post partum. Both forms of galactosemia occur at a
frequency of 1 per %50 000 births.


The major constituents of milk

11

Lactose in fermented dairy products
The fermentation of lactose to lactic acid by lactic acid bacteria (LAB) is a
critical step in the manufacture of all fermented dairy products. The
fermentation pathways are well established (see Cogan and Hill, 1993). Lactose
is not a limiting factor in the manufacture of fermented dairy products – only
%20% of the lactose is fermented in the production of fermented milks.
Individuals suffering from lactose intolerance may be able to consume
fermented milk products without ill-effects, possibly because LAB produce galactosidase and emptying of the stomach is slower than for fresh milk
products, thus delaying the release of lactose into the small intestine.
In the manufacture of cheese, most (96–98%) of the lactose is removed in the
whey. The concentration of lactose in fresh curd depends on its concentration in

the milk and on the moisture content of the curd and varies from %1%, w/w, in
fresh Cheddar curd to %2.5%, w/w, in fresh Camembert. The metabolism of
residual lactose in the curd to lactic acid has a major effect on the quality of
mature cheese (see Fox et al., 1990, 2002). The resultant lactic acid may be
catabolized to other compounds, e.g., carbon dioxide and water by the surface
mould in Camembert, or to propionic acid, acetic acid and carbon dioxide in
Emmental-type cheeses. Excessive lactic acid in cheese curd leads to a low pH,
a strong, acidic, harsh taste, and a brittle texture. In Cheddar and related
varieties, the L-lactic acid produced by the starter bacteria is racemized to DLlactic acid; Ca-D-lactate is less soluble than Ca-L-lactate and if its concentration
is too high, it will crystallize on the surface of the cheese, giving it an
undesirable appearance. Excess residual lactose may also be fermented by
heterofermentative lactobacilli, with the production of carbon dioxide, leading to
an open texture.
In the manufacture of some cheese varieties, e.g., Dutch cheeses, the curds
are washed to reduce their lactose content and thereby regulate the pH of the
pressed curd to %5.3. In most other varieties, e.g., Cheddar and Emmental, the
level of lactose, and hence of lactic acid, in the curd is not controlled by
washing. Hence, changes in the concentration of lactose in milk may affect the
quality of such cheeses. The concentration of lactose in milk decreases
throughout lactation, e.g., from %4.8% to <4.0%. When synchronized calving is
practised, there is a marked seasonal change in the lactose content of milk and
hence of cheese, which may have a significant effect on quality. To overcome
seasonal variations in the lactose content of milk, the level of wash water used
for Dutch-type cheeses is varied according to the concentrations of lactose and
casein in the milk. Ideally, the lactose-to-protein ratio should be standardized,
e.g., by washing the curds, to minimize variations in the level of lactic acid, the
pH and the quality of cheese.
The curds for acid-curd cheeses are washed free of lactose to improve their
keeping quality. Thus, acid-coagulated and mature rennet-coagulated cheeses
may be consumed by lactose-intolerant individuals without ill-effects.

12

2.3

Dairy processing

Lipids

Definition and variability
Lipids are defined as those compounds in foods and tissues that are soluble in
apolar solvents (ethyl/petroleum ether or chloroform/methanol). The lipid
fraction of milk is comprised mainly of triglycerides (98%), with %1%
phospholipids and small amounts of diglycerides, monoglycerides, cholesterol,
cholesteryl esters and traces of fat-soluble vitamins and other lipids. The lipids
occur as globules, 0.1–20 "m in diameter, surrounded by the milk fat globule
membrane (MFGM), which serves as an emulsifier. The concentration of lipids
varies with species, breed, individual animal, stage of lactation, mastitic
infection, plane of nutrition, interval between milkings, and point during milking
when the sample is taken. Among the principal dairy breeds, Friesian/Holsteins
produce milk with the lowest fat content (%3.5%) and Jersey/Guernsey the
highest (%6%). The fat content varies considerably throughout lactation; when
synchronized calving is practised, the fat content of bulk milk varies from %3%
in early lactation to >4.5% in late lactation. Such large variations in lipid content
obviously affect the economics of milk production and the composition of milk
products but can be modified readily by natural creaming or centrifugal
separation or addition of cream and hence need not affect product quality. Milk
lipids exhibit variability in fatty acid composition and in the size and stability of
the globules. These variations, especially of the fatty acid profile, are essentially

impossible to standardize and hence are responsible for considerable variations
in the rheological properties, colour, chemical stability and nutritional properties
of fat-containing dairy products.
Fatty acid profile
Ruminant milk fat contains a wider range of fatty acids than any other lipid
system – up to 400 fatty acids have been reported in bovine milk fat; the
principal fatty acids are the homologous series of saturated fatty acids, C4:0–
C18:0 and C18:1 (see Fox, 1995). The outstanding features of the fatty acids in
bovine milk fat are a high concentration of short and medium chain acids
(ruminant milk fats are the only natural lipids that contain butanoic acid) and a
low concentration of polyunsaturated fatty acids (PUFA).
In ruminants, the fatty acids for the synthesis of milk lipids are obtained from
triglycerides in chylomicrons in the blood or synthesized de novo in the mammary gland from acetate or -hydroxybutyrate produced by microorganisms in
the rumen. The triglycerides in chylomicrons are derived from the animal’s feed
or synthesized in the liver. Butanoic acid (C4:0) is produced by the reduction of
-hydroxybutyrate which is synthesized from dietary roughage by bacteria in
the rumen and therefore varies substantially with the animal’s diet. All C6:0–
C14:0 and 50% of C16:0 are synthesized in the mammary gland via the malonylCoA pathway from acetyl-CoA produced from acetate synthesized in the rumen.
Essentially 100% of C18:0, C18:1, C18:2 and C18:3 and 50% of C16:0 are derived
from blood lipids (chylomicrons) and represent %50% of total fatty acids in