Physical chemistry of foods 2003 dekker

Physical Chemistry
of Foods
Pieter Walstra
Wageningen University
Wageningen, The Netherlands

Marcel Dekker, Inc.
TM

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.

New York • Basel


ISBN: 0-8247-9355-2
This book is printed on acid-free paper.
Headquarters
Marcel Dekker, Inc.
270 Madison Avenue, New York, NY 10016
tel: 212-696-9000; fax: 212-685-4540
Eastern Hemisphere Distribution
Marcel Dekker AG
Hutgasse 4, Postfach 812, CH-4001 Basel, Switzerland
tel: 41-61-260-6300; fax: 41-61-260-6333
World Wide Web

The publisher offers discounts on this book when ordered in bulk quantities. For more
information, write to Special Sales/Professional Marketing at the headquarters address
above.
Copyright # 2003 by Marcel Dekker, Inc. All Rights Reserved.
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 and retrieval system, without permission in writing from the
publisher.
Current printing (last digit):
10 9 8 7 6 5 4 3 2 1
PRINTED IN THE UNITED STATES OF AMERICA
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


FOOD SCIENCE AND TECHNOLOGY
A Series of Monographs, Textbooks, and Reference Books
EDITORIAL BOARD

Senior Editors
Owen R. Fennema University of Wisconsin–Madison
Y.H. Hui Science Technology System
Marcus Karel Rutgers University (emeritus)
Pieter Walstra Wageningen University
John R. Whitaker University of California–Davis
Additives P. Michael Davidson University of Tennessee–Knoxville
Dairy science James L. Steele University of Wisconsin–Madison
Flavor chemistry and sensory analysis John H. Thorngate III University
of California–Davis
Food engineering Daryl B. Lund University of Wisconsin–Madison

Food proteins/food chemistry

Rickey Y. Yada

University of Guelph

Health and disease Seppo Salminen University of Turku, Finland
Nutrition and nutraceuticals Mark Dreher Mead Johnson Nutritionals
Phase transition/food microstructure Richard W. Hartel University of
Wisconsin–Madison
Processing and preservation Gustavo V. Barbosa-Cánovas Washington
State University–Pullman
Safety and toxicology Sanford Miller University of Texas–Austin

1. Flavor Research: Principles and Techniques, R. Teranishi, I. Hornstein, P. Issenberg, and E. L. Wick
2. Principles of Enzymology for the Food Sciences, John R. Whitaker
3. Low-Temperature Preservation of Foods and Living Matter, Owen R.
Fennema, William D. Powrie, and Elmer H. Marth
4. Principles of Food Science
Part I: Food Chemistry, edited by Owen R. Fennema
Part II: Physical Methods of Food Preservation, Marcus Karel, Owen
R. Fennema, and Daryl B. Lund
5. Food Emulsions, edited by Stig E. Friberg
6. Nutritional and Safety Aspects of Food Processing, edited by Steven
R. Tannenbaum
7. Flavor Research: Recent Advances, edited by R. Teranishi, Robert A.
Flath, and Hiroshi Sugisawa
8. Computer-Aided Techniques in Food Technology, edited by Israel
Saguy
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


9. Handbook of Tropical Foods, edited by Harvey T. Chan
10. Antimicrobials in Foods, edited by Alfred Larry Branen and P. Michael
Davidson

11. Food Constituents and Food Residues: Their Chromatographic
Determination, edited by James F. Lawrence
12. Aspartame: Physiology and Biochemistry, edited by Lewis D. Stegink
and L. J. Filer, Jr.
13. Handbook of Vitamins: Nutritional, Biochemical, and Clinical Aspects,
edited by Lawrence J. Machlin
14. Starch Conversion Technology, edited by G. M. A. van Beynum and J.
A. Roels
15. Food Chemistry: Second Edition, Revised and Expanded, edited by
Owen R. Fennema
16. Sensory Evaluation of Food: Statistical Methods and Procedures, Michael O'Mahony
17. Alternative Sweeteners, edited by Lyn O'Brien Nabors and Robert C.
Gelardi
18. Citrus Fruits and Their Products: Analysis and Technology, S. V. Ting
and Russell L. Rouseff
19. Engineering Properties of Foods, edited by M. A. Rao and S. S. H.
Rizvi
20. Umami: A Basic Taste, edited by Yojiro Kawamura and Morley R.
Kare
21. Food Biotechnology, edited by Dietrich Knorr
22. Food Texture: Instrumental and Sensory Measurement, edited by
Howard R. Moskowitz
23. Seafoods and Fish Oils in Human Health and Disease, John E.
Kinsella
24. Postharvest Physiology of Vegetables, edited by J. Weichmann
25. Handbook of Dietary Fiber: An Applied Approach, Mark L. Dreher
26. Food Toxicology, Parts A and B, Jose M. Concon
27. Modern Carbohydrate Chemistry, Roger W. Binkley
28. Trace Minerals in Foods, edited by Kenneth T. Smith
29. Protein Quality and the Effects of Processing, edited by R. Dixon

Phillips and John W. Finley
30. Adulteration of Fruit Juice Beverages, edited by Steven Nagy, John A.
Attaway, and Martha E. Rhodes
31. Foodborne Bacterial Pathogens, edited by Michael P. Doyle
32. Legumes: Chemistry, Technology, and Human Nutrition, edited by
Ruth H. Matthews
33. Industrialization of Indigenous Fermented Foods, edited by Keith H.
Steinkraus
34. International Food Regulation Handbook: Policy · Science · Law,
edited by Roger D. Middlekauff and Philippe Shubik
35. Food Additives, edited by A. Larry Branen, P. Michael Davidson, and
Seppo Salminen
36. Safety of Irradiated Foods, J. F. Diehl
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


37. Omega-3 Fatty Acids in Health and Disease, edited by Robert S. Lees
and Marcus Karel
38. Food Emulsions: Second Edition, Revised and Expanded, edited by
Kåre Larsson and Stig E. Friberg
39. Seafood: Effects of Technology on Nutrition, George M. Pigott and
Barbee W. Tucker
40. Handbook of Vitamins: Second Edition, Revised and Expanded,
edited by Lawrence J. Machlin
41. Handbook of Cereal Science and Technology, Klaus J. Lorenz and
Karel Kulp
42. Food Processing Operations and Scale-Up, Kenneth J. Valentas,
Leon Levine, and J. Peter Clark
43. Fish Quality Control by Computer Vision, edited by L. F. Pau and R.
Olafsson

44. Volatile Compounds in Foods and Beverages, edited by Henk Maarse
45. Instrumental Methods for Quality Assurance in Foods, edited by
Daniel Y. C. Fung and Richard F. Matthews
46. Listeria, Listeriosis, and Food Safety, Elliot T. Ryser and Elmer H.
Marth
47. Acesulfame-K, edited by D. G. Mayer and F. H. Kemper
48. Alternative Sweeteners: Second Edition, Revised and Expanded, edited by Lyn O'Brien Nabors and Robert C. Gelardi
49. Food Extrusion Science and Technology, edited by Jozef L. Kokini,
Chi-Tang Ho, and Mukund V. Karwe
50. Surimi Technology, edited by Tyre C. Lanier and Chong M. Lee
51. Handbook of Food Engineering, edited by Dennis R. Heldman and
Daryl B. Lund
52. Food Analysis by HPLC, edited by Leo M. L. Nollet
53. Fatty Acids in Foods and Their Health Implications, edited by Ching
Kuang Chow
54. Clostridium botulinum: Ecology and Control in Foods, edited by
Andreas H. W. Hauschild and Karen L. Dodds
55. Cereals in Breadmaking: A Molecular Colloidal Approach,
Ann-Charlotte Eliasson and Kåre Larsson
56. Low-Calorie Foods Handbook, edited by Aaron M. Altschul
57. Antimicrobials in Foods: Second Edition, Revised and Expanded,
edited by P. Michael Davidson and Alfred Larry Branen
58. Lactic Acid Bacteria, edited by Seppo Salminen and Atte von Wright
59. Rice Science and Technology, edited by Wayne E. Marshall and
James I. Wadsworth
60. Food Biosensor Analysis, edited by Gabriele Wagner and George G.
Guilbault
61. Principles of Enzymology for the Food Sciences: Second Edition, John
R. Whitaker
62. Carbohydrate Polyesters as Fat Substitutes, edited by Casimir C.

Akoh and Barry G. Swanson
63. Engineering Properties of Foods: Second Edition, Revised and
Expanded, edited by M. A. Rao and S. S. H. Rizvi
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


64. Handbook of Brewing, edited by William A. Hardwick
65. Analyzing Food for Nutrition Labeling and Hazardous Contaminants,
edited by Ike J. Jeon and William G. Ikins
66. Ingredient Interactions: Effects on Food Quality, edited by Anilkumar
G. Gaonkar
67. Food Polysaccharides and Their Applications, edited by Alistair M.
Stephen
68. Safety of Irradiated Foods: Second Edition, Revised and Expanded, J.
F. Diehl
69. Nutrition Labeling Handbook, edited by Ralph Shapiro
70. Handbook of Fruit Science and Technology: Production, Composition,
Storage, and Processing, edited by D. K. Salunkhe and S. S. Kadam
71. Food Antioxidants: Technological, Toxicological, and Health Perspectives, edited by D. L. Madhavi, S. S. Deshpande, and D. K. Salunkhe
72. Freezing Effects on Food Quality, edited by Lester E. Jeremiah
73. Handbook of Indigenous Fermented Foods: Second Edition, Revised
and Expanded, edited by Keith H. Steinkraus
74. Carbohydrates in Food, edited by Ann-Charlotte Eliasson
75. Baked Goods Freshness: Technology, Evaluation, and Inhibition of
Staling, edited by Ronald E. Hebeda and Henry F. Zobel
76. Food Chemistry: Third Edition, edited by Owen R. Fennema
77. Handbook of Food Analysis: Volumes 1 and 2, edited by Leo M. L.
Nollet
78. Computerized Control Systems in the Food Industry, edited by Gauri
S. Mittal

79. Techniques for Analyzing Food Aroma, edited by Ray Marsili
80. Food Proteins and Their Applications, edited by Srinivasan Damodaran and Alain Paraf
81. Food Emulsions: Third Edition, Revised and Expanded, edited by Stig
E. Friberg and Kåre Larsson
82. Nonthermal Preservation of Foods, Gustavo V. Barbosa-Cánovas,
Usha R. Pothakamury, Enrique Palou, and Barry G. Swanson
83. Milk and Dairy Product Technology, Edgar Spreer
84. Applied Dairy Microbiology, edited by Elmer H. Marth and James L.
Steele
85. Lactic Acid Bacteria: Microbiology and Functional Aspects: Second
Edition, Revised and Expanded, edited by Seppo Salminen and Atte
von Wright
86. Handbook of Vegetable Science and Technology: Production,
Composition, Storage, and Processing, edited by D. K. Salunkhe and
S. S. Kadam
87. Polysaccharide Association Structures in Food, edited by Reginald H.
Walter
88. Food Lipids: Chemistry, Nutrition, and Biotechnology, edited by
Casimir C. Akoh and David B. Min
89. Spice Science and Technology, Kenji Hirasa and Mitsuo Takemasa

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


90. Dairy Technology: Principles of Milk Properties and Processes, P.
Walstra, T. J. Geurts, A. Noomen, A. Jellema, and M. A. J. S. van
Boekel
91. Coloring of Food, Drugs, and Cosmetics, Gisbert Otterstätter
92. Listeria, Listeriosis, and Food Safety: Second Edition, Revised and
Expanded, edited by Elliot T. Ryser and Elmer H. Marth

93. Complex Carbohydrates in Foods, edited by Susan Sungsoo Cho,
Leon Prosky, and Mark Dreher
94. Handbook of Food Preservation, edited by M. Shafiur Rahman
95. International Food Safety Handbook: Science, International Regulation, and Control, edited by Kees van der Heijden, Maged Younes,
Lawrence Fishbein, and Sanford Miller
96. Fatty Acids in Foods and Their Health Implications: Second Edition,
Revised and Expanded, edited by Ching Kuang Chow
97. Seafood Enzymes: Utilization and Influence on Postharvest Seafood
Quality, edited by Norman F. Haard and Benjamin K. Simpson
98. Safe Handling of Foods, edited by Jeffrey M. Farber and Ewen C. D.
Todd
99. Handbook of Cereal Science and Technology: Second Edition, Revised and Expanded, edited by Karel Kulp and Joseph G. Ponte, Jr.
100. Food Analysis by HPLC: Second Edition, Revised and Expanded,
edited by Leo M. L. Nollet
101. Surimi and Surimi Seafood, edited by Jae W. Park
102. Drug Residues in Foods: Pharmacology, Food Safety, and Analysis,
Nickos A. Botsoglou and Dimitrios J. Fletouris
103. Seafood and Freshwater Toxins: Pharmacology, Physiology, and
Detection, edited by Luis M. Botana
104. Handbook of Nutrition and Diet, Babasaheb B. Desai
105. Nondestructive Food Evaluation: Techniques to Analyze Properties
and Quality, edited by Sundaram Gunasekaran
106. Green Tea: Health Benefits and Applications, Yukihiko Hara
107. Food Processing Operations Modeling: Design and Analysis, edited
by Joseph Irudayaraj
108. Wine Microbiology: Science and Technology, Claudio Delfini and
Joseph V. Formica
109. Handbook of Microwave Technology for Food Applications, edited by
Ashim K. Datta and Ramaswamy C. Anantheswaran
110. Applied Dairy Microbiology: Second Edition, Revised and Expanded,

edited by Elmer H. Marth and James L. Steele
111. Transport Properties of Foods, George D. Saravacos and Zacharias
B. Maroulis
112. Alternative Sweeteners: Third Edition, Revised and Expanded, edited
by Lyn O’Brien Nabors
113. Handbook of Dietary Fiber, edited by Susan Sungsoo Cho and Mark
L. Dreher
114. Control of Foodborne Microorganisms, edited by Vijay K. Juneja and
John N. Sofos
115. Flavor, Fragrance, and Odor Analysis, edited by Ray Marsili
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


116. Food Additives: Second Edition, Revised and Expanded, edited by A.
Larry Branen, P. Michael Davidson, Seppo Salminen, and John H.
Thorngate, III
117. Food Lipids: Chemistry, Nutrition, and Biotechnology: Second Edition,
Revised and Expanded, edited by Casimir C. Akoh and David B. Min
118. Food Protein Analysis: Quantitative Effects on Processing, R. K.
Owusu-Apenten
119. Handbook of Food Toxicology, S. S. Deshpande
120. Food Plant Sanitation, edited by Y. H. Hui, Bernard L. Bruinsma, J.
Richard Gorham, Wai-Kit Nip, Phillip S. Tong, and Phil Ventresca
121. Physical Chemistry of Foods, Pieter Walstra
122. Handbook of Food Enzymology, edited by John R. Whitaker, Alphons
G. J. Voragen, and Dominic W. S. Wong
123. Postharvest Physiology and Pathology of Vegetables: Second Edition,
Revised and Expanded, edited by Jerry A. Bartz and Jeffrey K. Brecht
124. Characterization of Cereals and Flours: Properties, Analysis, and Applications, edited by Gönül Kaletunç and Kenneth J. Breslauer
125. International Handbook of Foodborne Pathogens, edited by Marianne

D. Miliotis and Jeffrey W. Bier

Additional Volumes in Preparation
Handbook of Dough Fermentations, edited by Karel Kulp and Klaus
Lorenz
Extraction Optimization in Food Engineering, edited by Constantina
Tzia and George Liadakis
Physical Principles of Food Preservation: Second Edition, Revised
and Expanded, Marcus Karel and Daryl B. Lund
Handbook of Vegetable Preservation and Processing, edited by Y. H.
Hui, Sue Ghazala, Dee M. Graham, K. D. Murrell, and Wai-Kit Nip
Food Process Design, Zacharias B. Maroulis and George D.
Saravacos

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


Foreword

Knowledge of physical chemistry is of great importance to anyone who is
interested in understanding the properties of food, improving its quality and
storage stability, and controlling its behavior during handling. Yet, curricula
in food science often do not contain a course in food physical chemistry,
especially at the undergraduate level, and failure to acquire skills in this
important area can hinder a food scientist’s success in scientific endeavors.
Some believe that an introductory course in physical chemistry offered by a
department of chemistry will fill this void, but I disagree. If possible, an
introductory course in physical chemistry should be a prerequisite for a
course in food physical chemistry—the former providing a sound background in the principles of physical chemistry and the latter focusing on
application of the principles most relevant to food.

Failure of many food science departments to offer a course on food
physical chemistry is attributable mainly to the lack of an appropriate
textbook. Whereas instructors in food science can select from several good
textbooks on food microbiology, food engineering, food chemistry, and
other more specialized topics, choices in food physical chemistry are severely
limited. The publication of Pieter Walstra’s excellent textbook on food
physical chemistry is therefore an event of major importance to the field of
food science. This book will stimulate universities that do not offer this

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


subject to do so, and will improve the quality of instruction in universities
that do. It will also be of great value to food researchers.
Professor Walstra is eminently qualified to write a book on food
physical chemistry because of his in-depth knowledge of the subject and his
understanding of, expertise in, and dedication to food science education.
This book provides comprehensive coverage of food physical chemistry at a
depth suitable for students in food science, and will serve as an excellent
reference source for food researchers. I congratulate Professor Walstra for
this fine accomplishment.
Owen Fennema
Professor
Department of Food Science
University of Wisconsin–Madison
Madison, Wisconsin

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.

Preface

The scientific basis needed to understand and predict food properties and
changes occurring in foods during processing, storage and use has been
enormously expanded over the past half-century. This has caused a
revolutionary change in the teaching of food science and technology,
especially by application of the disciplines of organic chemistry, biochemistry, and microbiology. With the possible exception of rheology, application of the more physical disciplines has lagged behind. Many years’
experience in food research and teaching has convinced me—although I am
not a physical chemist—of the importance of physical chemistry and related
theories for food science and technology. Moreover, great progress has been
made during the past two decades in the study of physicochemical
phenomena in foods; yet these aspects often remain greatly underexposed.
The main reason for this deficiency is, in my opinion, that the teaching
of physical chemistry for food science majors is often inadequate. In most
universities, students have one introductory course in basic physical
chemistry; this is unsatisfactory for the following reasons:
1. Many of the subjects are of little or no importance for foods or are
treated in too much theoretical detail (e.g., quantum mechanics,
statistical thermodynamics, much of spectroscopy).

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


2. Many subjects of great importance to foods are not included. In
order to keep the theory simple, the treatment is often restricted to
gases and crystals and dilute, homogeneous, ideal solutions,
whereas most foods are concentrated, inhomogeneous, highly
nonideal systems. In particular, coverage of colloid and surface
science is insufficient.
3. In most cases, the course is taken at the wrong time, that is, before

the student is able to see the relevance of the various subjects for
foods.
The primary aim of this book is to help in remedying this situation. It
can be used as the basis of a course for food science majors at a not-tooearly stage in the curriculum (some universities may prefer a graduate
course). Hence it is written as a textbook. A second aim is its use as a
reference book, since basic aspects of physical chemistry are not always
taken into account in food research or process development. Therefore, I
have tried to cover all subjects of importance that are not treated in most
courses in food chemistry or food processing/engineering.
The selection of topics—including theories, phenomena, systems, and
examples—is naturally colored by my experience and opinions. This means
that the treatment is to some extent biased. In my view this is unavoidable,
but I would like to hear from readers who feel that a topic has been omitted
or overemphasized. Remarks about errors and unclear explanations are also
welcome.

ACKNOWLEDGMENTS
The idea for this book was born when I was asked to give a course on the
physical chemistry of foods in the Department of Food Science at the
University of Guelph, Ontario, Canada, in 1993. This course was based
largely on courses in food physics given at Wageningen University,
developed in cooperation with my colleagues Dr. Ton van Vliet and Dr.
Albert Prins. I also want to mention that Dr. Owen Fennema of the
University of Wisconsin has greatly encouraged me in writing this text.
Several colleagues have made valuable suggestions, which have greatly
improved the quality of this book. I am especially indebted to Dr. Eric
Dickinson, Professor of Food Colloids at the University of Leeds, England,
with whom I discussed plans and who has read and commented on virtually
all my drafts. His contributions have been invaluable. Furthermore, several
colleagues have scrutinized one or more draft chapters: Dr. C. van den Berg,

Dr. B. H. Bijsterbosch, Dr. M. A. J. S. van Boekel, Dr. O. R. Fennema,
Dr. G. J. Fleer, Dr. G. Frens, Dr. H. D. Goff, Dr. H. H. J. de Jongh,
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


Dr. J. Lucassen, Dr. E. H. Lucassen-Reynders, Dr. J. Lyklema, Dr. E. R.
Morris, Dr. W. Norde, Dr. J. H. J. van Opheusden, Dr. L. van der Plas,
Dr. M. J. W. Povey, Dr. J. Verhagen, and Dr. T. van Vliet. I express my
gratitude to all these friends and colleagues.
Pieter Walstra

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


Contents

Foreword
Preface
1 INTRODUCTION
1.1 Physical Chemistry in Food Science and Technology
1.2 About this Book
Bibliography
2 ASPECTS OF THERMODYNAMICS
2.1 Concepts
2.2 Solutions
2.3 Electrolyte Solutions
2.4 Recapitulation
Bibliography
3 BONDS AND INTERACTION FORCES
3.1 Types of Bonds

3.2 Solvation
3.3 Recapitulation
Bibliography
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


4 REACTION KINETICS
4.1 Reaction Order
4.2 Chemical Equilibrium
4.3 Rate Theories
4.4 Further Complications
4.5 Recapitulation
Bibliography
5 TRANSPORT PHENOMENA
5.1 Flow and Viscosity
5.2 Diffusion
5.3 Transport in Composite Materials
5.4 Recapitulation
Bibliography
6 POLYMERS
6.1 Introduction
6.2 Very Dilute Solutions
6.3 Polyelectrolytes
6.4 More Concentrated Solutions
6.5 Phase Separation
6.6 Starch
6.7 Recapitulation
Bibliography
7 PROTEINS
7.1 Description

7.2 Conformational Stability and Denaturation
7.3 Solubility
7.4 Recapitulation
Bibliography
8 WATER RELATIONS
8.1 Water Activity
8.2 Sorption Isotherms
8.3 ‘‘Water Binding’’
8.4 Reaction Rates and Water Content
8.5 Recapitulation
Bibliography
9 DISPERSED SYSTEMS
9.1 Structure
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


9.2
9.3
9.4

Importance of Scale
Particle Size Distributions
Recapitulation
Bibliography

10 SURFACE PHENOMENA
10.1 Surface Tension
10.2 Adsorption
10.3 Surfactants
10.4 Time Effects

10.5 Curved Interfaces
10.6 Contact Angles and Wetting
10.7 Interfacial Tension Gradients
10.8 Interfacial Rheology
10.9 Recapitulation
Bibliography
11 FORMATION OF EMULSIONS AND FOAMS
11.1 Introduction
11.2 Foam Formation and Properties
11.3 Breakup of Drops and Bubbles
11.4 Role of Surfactant
11.5 Recapitulation
Bibliography
12 COLLOIDAL INTERACTIONS
12.1 General Introduction
12.2 DLVO Theory
12.3 Role of Polymers
12.4 Other Interactions
12.5 Recapitulation
Bibliography
13 CHANGES IN DISPERSITY
13.1 Overview
13.2 Aggregation
13.3 Sedimentation
13.4 Coalescence
13.5 Partial Coalescence
13.6 Ostwald Ripening
13.7 Recapitulation
Bibliography
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.

14 NUCLEATION
14.1 Phase Transitions
14.2 Nucleation Theory
14.3 Nucleation in a Finely Dispersed Material
14.4 Formation of a Gas Phase
14.5 Recapitulation
Bibliography
15 CRYSTALLIZATION
15.1 The Crystalline State
15.2 Crystal Growth
15.3 Crystallization from Aqueous Solutions
15.4 Fat Crystallization
15.5 Recapitulation
Bibliography
16 GLASS TRANSITIONS AND FREEZING
16.1 The Glassy State
16.2 The Special Glass Transition
16.3 Freezing of Foods
16.4 Recapitulation
Bibliography
17 SOFT SOLIDS
17.1 Rheology and Fracture
17.2 Gels
17.3 Plastic Fats
17.4 Closely Packed Systems
17.5 Cellular Systems
17.6 Recapitulation
Bibliography

APPENDIX A: Frequently Used Symbols for Physical
Quantities
APPENDIX B: Some Frequently Used Abbreviations
APPENDIX C: Some Mathematical Symbols
APPENDIX D: SI Rules for Notation
APPENDIX E: The SI Units System
APPENDIX F: Some Conversion Factors
APPENDIX G: Recalculation of Concentrations
APPENDIX H: Physical Properties of Water at 0–1008C
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


APPENDIX I: Thermodynamic and Physical Properties of
Water and Ice
APPENDIX J: Some Values of the Error Function

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


1
Introduction

1.1 PHYSICAL CHEMISTRY IN FOOD SCIENCE
AND TECHNOLOGY
Food science and technology are concerned with a wide variety of problems
and questions, and some will be exemplified below. For instance, food
scientists want to understand and predict changes occurring in a food during
processing, storage, and handling, since such changes affect food quality.
Examples are

The rates of chemical reactions in a food can depend on many
variables, notably on temperature and water content. However, the
relations between reaction rates and the magnitude of these
variables vary widely. Moreover, the composition of the mixture
of reaction products may change significantly with temperature.
How is this explained and how can this knowledge be exploited?
How is it possible that of two nonsterilized intermediate-moisture foods
of about the same type, of the same water activity, and at the same
temperature, one shows bacterial spoilage and the other does not?
Two plastic fats are stored at room temperature. The firmness of the
one increases, that of the other decreases during storage. How is this
possible?

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


Bread tends to stale—i.e., obtain a harder and shorter texture—during
storage at room temperature. Keeping the bread in a refrigerator
enhances staling rate, but storage in a freezer greatly reduces staling.
How is this explained?
The physical stability of a certain oil-in-water emulsion is observed to
depend greatly on temperature. At 408C it remains stable, after
cooling to 258C also, but after cooling to 108C and then warming to
258C small clumps are formed; stirring greatly enhances clump
formation. What are the mechanisms involved and how is the
dependence on temperature history explained?
Another emulsion shows undesirable creaming. To reduce creaming
rate a small amount of a thickener, i.e., a polysaccharide, is added.
However, it increases the creaming rate. How?
Food technologists have to design and improve processes to make

foods having specific qualities in an efficient way. Examples of problems are
Many foods can spoil by enzyme action, and the enzymes involved
should thus be inactivated, which is generally achieved by heat
denaturation. For several enzymes the dependence of the extent of
inactivation on heating time and temperature is simple, but for
others it is intricate. Understanding of the effects involved is needed
to optimize processing: there must be sufficient inactivation of the
enzymes without causing undesirable heat damage.
It is often needed to make liquid foods with specific rheological
properties, such as a given viscosity or yield stress, for instance to
ensure physical stability or a desirable eating quality. This can be
achieved in several ways, by adding polysaccharides, or proteins, or
small particles. Moreover, processing can greatly affect the result. A
detailed understanding of the mechanisms involved and of the
influence of process variables is needed to optimize formulation and
processing.
Similar remarks can be made about the manufacture of dispersions of
given properties, such as particle size and stability. This greatly
depends on the type of dispersion (suspension, emulsion, or foam)
and on the specific properties desired.
How can denaturation and loss of solubility of proteins during
industrial isolation be prevented? This is of great importance for the
retention of the protein’s functional properties and for the economy
of the process.
How can one manufacture or modify a powdered food, e.g., spraydried milk or dry soup, in such a manner that it is readily
dispersable in cold water?
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


How does one make an oil-in-water emulsion that is stable during

storage but that can be whipped into a topping? The first question
then is: what happens during a whipping process that results in a
suitable topping? Several product and process variables affect the
result.
All of these examples have in common that knowledge of physical
chemistry is needed to understand what happens and to solve the problem.
Physical chemistry provides quantitative relations for a great number
of phenomena encountered in chemistry, based on well-defined and
measurable properties. Its theories are for the most part of a physical
nature and comprise little true chemistry, since electron transfer is
generally not involved. Experience has shown that physicochemical aspects
are also of great importance in foods and food processing. This does not
mean that all of the phenomena involved are of a physical nature: it is
seen from the examples given that food chemistry, engineering, and even
microbiology can be involved as well. Numerous other examples are given
in this book.
The problems encountered in food science and technology are
generally quite complex, and this also holds for physicochemical problems.
In the first place, nearly all foods have a very wide and complex
composition; a chemist might call them dirty systems. Anyway, they are far
removed from the much purer and dilute systems discussed in elementary
textbooks. This means that the food is not in thermodynamic equilibrium
and tends to change in composition. Moreover, several changes may occur
simultaneously, often influencing each other. Application of physicochemical theory may also be difficult, since many food systems do not comply
with the basic assumptions underlying the theory needed.
In the second place, most foods are inhomogeneous systems.
Consequently, various components can be in different compartments,
greatly enhancing complexity. This means that the system is even farther
removed from thermodynamic equilibrium than are most homogeneous
systems. Moreover, several new phenomena come into play, especially

involving colloidal interactions and surface forces. These occur on a larger
than molecular scale. Fortunately, the study of mesoscopic physics—which
involves phenomena occurring on a scale that is larger than that of
molecules but (far) smaller than can be seen with the naked eye—has made
great progress in recent times.
In the third place, a student of the physical chemistry of foods has to
become acquainted with theories derived from a range of disciplines, as a
look at the table of contents will show. Moreover, knowledge of the system
studied is essential: although basic theory should have universal validity, the
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


particulars of the system determine the boundary conditions for application
of a theory and thereby the final result.
All of this might lead to the opinion that many of the problems
encountered in food science and technology are so intricate that application
of sound physical chemistry would hardly be possible and that quantitative
prediction of results would often be impossible. Nevertheless, making use of
the basic science involved can be quite fruitful, as has been shown for a wide
variety of problems. Reasons for this are
Understanding of basic principles may in itself be useful. A fortunate
characteristic of human nature is the desire to explain phenomena
observed and to create a framework that appears to fit the
observations. However, if such theorizing is not based on sound
principles it will often lead to wrong conclusions, which readily lead
to further problems when proceeding on the conceived ideas with
research or process development. Basic knowledge is a great help in
(a) identifying and explaining mechanisms involved in a process and
(b) establishing (semi-)quantitative relations.
Even semiquantitative answers, such as giving the order of magnitude,

can be very helpful. Mere qualitative reasoning can be quite
misleading. For instance, a certain reaction proceeds much faster at
a higher temperature and it is assumed that this is because the
viscosity is lower at a higher temperature. This may be true, but only
if (a) the reaction rate is diffusion controlled, and (b) the relative
increase of rate is about equal to the relative decrease in viscosity.
When the rate increases by a factor of 50 and the viscosity decreases
by a factor of 2, the assumption is clearly wrong.
Foods are intricate systems and also have to meet a great number of
widely different specifications. This means that process and product
development will always involve trial and error. However, basic
understanding and semiquantitative relations may greatly reduce
the number of trials that will lead to error.
The possibilities for establishing quantitative relations are rapidly
increasing. This is due to further development of theory and
especially to the greatly increased power of computer systems used
for mathematical modeling of various kinds. In other words, several
processes occurring in such complex systems as foods—or in model
systems that contain all the essential elements—can now be modeled
or simulated.
Altogether, in the author’s opinion, application of physical chemistry
and mesoscopic physics in the realm of food science and technology is often
needed—besides food chemistry, food process engineering, and food
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


microbiology—to solve problems and to predict changes that will occur
during manufacture, storage, and use of foods.

1.2 ABOUT THIS BOOK

1.2.1 What Is Treated
The book is aimed at providing understanding, hence it primarily gives
principles and theory. Moreover, facts and practical aspects are included,
because knowledge of the system considered is needed to apply theory
usefully, and also because the text would otherwise be as dry as dust. Basic
theory is given insofar as it is relevant in food science and technology. This
implies that several physicochemical theories are left out or are only
summarily discussed. It also means that many aspects will be treated that are
not covered in standard texts on physical chemistry, which generally restrict
the discussion to relatively simple systems. Since most foods are complicated
systems and show nonideal behavior, treatment of the ensuing complexities
cannot be avoided if the aim is to understand the phenomena and processes
involved.
As mentioned, molecular and mesoscopic approaches will be needed.
The first part of the book mainly considers molecules. We start with some
basic thermodynamics, interaction forces, and chemical kinetics (Chapters
2–4). The next chapter is also concerned with kinetic aspects: it covers
various transport phenomena (which means that a few mesoscopic aspects
are involved) and includes some basic fluid rheology. Chapters 6 and 7 treat
macromolecules: Chapter 6 gives general aspects of polymers and discusses
food polysaccharides in particular, with a largish section on starch; Chapter
7 separately discusses proteins, highly intricate food polymers with several
specific properties. Chapter 8 treats the interactions between water and food
components and the consequences for food properties and processes.
Then mesoscopic aspects are treated. Chapter 9 gives a general
introduction on disperse or particulate systems. It concerns properties that
originate from the division of a material over different compartments, and
from the presence of a large phase surface. Two chapters give basic theory.
Chapter 10 is on surface phenomena, where the forces involved primarily act
in the direction of the surface. Chapter 12 treats colloidal interactions,

which primarily act in a direction perpendicular to the surface. Two
chapters are concerned with application of these basic aspects in disperse
systems: Chapter 11 with emulsion and foam formation, Chapter 13 with
the various instabilities encountered in the various dispersions: foams,
emulsions, and suspensions.
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


Next we come to phase transitions. Chapter 14 mentions the various
phase transitions that may occur, such as crystallization, gas bubble
formation, or separation of a polymer solution in two layers; it then treats
the nucleation phenomena that often initiate phase transitions. Chapter 15
discusses crystallization, a complicated phase transition of great importance
in foods. It includes sections on crystallization of water, sugars, and
triacylglycerols. Chapter 16 introduces glass transitions and the various
changes that can occur upon freezing of aqueous systems.
Finally, Chapter 17 is about soft solids, a term that applies to the
majority of foods. It gives an introduction into solids rheology and fracture
mechanics, but otherwise it makes use of many of the theories treated in
earlier chapters to explain properties of the various types of soft solids
encountered in foods.

1.2.2 What Is Not Treated
Some aspects are not covered. This includes analytical and other
experimental techniques. A discussion of these is to be found in specialized
books. Basic principles of some methods will be given, since this can help the
reader in understanding what the results do represent. Possible pitfalls in the
interpretation of results are occasionally pointed out.
Aspects that are generally treated in texts on food chemistry are for the
most part left out; an example is the mechanism and kinetics of enzymecatalyzed reactions. Some subjects are not fully treated, such as rheological

and other mechanical properties, since this would take very much space, and
several books on the subject exist.
Basic theory is treated where needed, but it does not go very deep:
giving too much may cause more confusion than enlightenment. We will
generally not go to atomic scales, which implies that quantum mechanics
and electron orbitals are left out. We also will not go into statistical
thermodynamics. Even classical chemical thermodynamics is restricted to a
minimum. Theories that involve mathematical modeling or simulation, such
as Brownian dynamics, are not discussed either. Equations will be derived
only if it helps to understand the theory, and if the derivation is relatively
simple.

1.2.3 For Whom It Is Intended
The book is written as a text, with clear and full explanations; illustration of
trends rather than giving precise research results; not too many details,
although details cannot always be left out; numerous cross-references in the
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.


text; no full account of literature sources, but a discussion of selected
references at the end of each chapter. Worked out examples and questions
are also given.
The questions not only serve to let the reader test whether he or she
can make use of what has been treated but also serve as further illustrations.
To that end, most questions are followed by worked out answers. By the
nature of food science and technology, the questions often involve a number
of different aspects, and the reader may not be familiar with all of them.
Hence do not worry when you cannot immediately find a full answer, so
long as you can understand the reasoning given.
The readers are assumed to be familiar with elementary mathematics

(up to simple calculus) and with the basics of chemistry, and to have
attended (introductory) courses in food chemistry and food engineering (or
food processing).
The book tries to treat all physicochemical aspects of importance
for foods and food processing. On the one hand, this means that it gives
more than most teachers will want to treat in a course, so that a selection
should be made. On the other hand, it makes the book also suitable as a
work of reference. Some additional factual information is given in the
appendix.

1.2.4 Equations
As mentioned, physical chemistry is a quantitative science, which implies
that equations will frequently be given. It may be useful to point out that
equations can be of various types. Some equations define a property, like
‘‘pressure equals force over area.’’ Such an equation is by definition exact.
Generally, the sign for ‘‘is defined as’’ (:) is used rather than ‘‘is equal to’’
(¼).
Most equations are meant to be predictive. According to their validity
we can distinguish those that are assumed to be
Generally valid. For instance ‘‘force ¼ mass 6 acceleration’’
(although even this one breaks down in quantum mechanics).
Of restricted validity. The restriction is sometimes added to the
equation, by indications like ‘‘for x > 1’’ or ‘‘if z?0.’’ Another
variant is that a ‘‘constant’’ in the equation has restricted validity.
Approximate. Then the & sign is used.
A scaling relation, which means that only a proportionality can be
given. This is done by using the ! sign (some use the * sign), or by
putting an ‘‘unknown constant’’ after the ¼ sign.
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.