Christos Ritzoulis Translated by Jonathan Rhoades INTRODUCTION TO THE PHYSICAL CHEMISTRY of FOODS CRC Press Taylor & Francis Croup Boca Raton London NewYork CRC Press is an imprint of the Taylor & Francis Croup, an informa business
Contents Introduction to the Greek edition Preface to the English edition About the author ix xi xiii Chapter 1 The physical basis of chemistry 1 1.1 Thermodynamic systems 1 1.2 Temperature 2 1.3 Deviations from ideal behavior: Compressibility 4 1.3.1 van der Waals equation 6 1.3.2 Virial equation 9 Chapter 2 Chemical thermodynamics 13 2.1 A step beyond temperature 13 2.2 Thermochemistry 16 2.3 Entropy 17 2.4 Phase transitions 21 2.5 Crystallization 27 2.6 Application of phase transitions: Melting, solidifying, and crystallization of fats 27 2.6.1 Chocolate: The example of cocoa butter 30 2.7 Chemical potential 31 Chapter 3 The thermodynamics of solutions 35 3.1 From ideal gases to ideal solutions 35 3.2 Fractional distillation 38 3.3 Chemical equilibrium 41 3.4 Chemical equilibrium in solutions 44 3.5 Ideal solutions: The chemical potential approach 46 3.6 Depression of the freezing point and elevation of the boiling point 47 3.7 Osmotic pressure 48 3.8 Polarity and dipole moment 50 3.8.1 Polarity and structure: Application to proteins 51 v
vi Contents 3.9 Real solutions: Activity and ionic strength 52 3.10 On ph: Acids, bases, and buffer solutions 53 3.11 Macromolecules in solution 57 3.12 Enter a polymer 58 3.13 Is it necessary to study macromolecules in food and biological systems in general? 59 3.13.1 Intrinsic viscosity 60 3.14 Flory-Huggins theory of polymer solutions 60 3.14.1 Conformational entropy and entropy of mixing 61 3.14.2 Enthalpy of mixing 66 3.14.3 Gibbs free energy of mixing 67 3.15 Osmotic pressure of solutions of macromolecules 68 3.15.1 The Donnan effect 68 3.16 Concentrated polymer solutions 69 3.17 Phase separation 70 3.17.1 Phase separation in two-solute systems 72 Chapter 4 Surface activity 77 4.1 Surface tension 77 4.2 Interface tension 79 4.2.1 A special extended case 80 4.3 Geometry of the liquid surface: Capillary effects 81 4.4 Definition of the interface 82 4.5 Surface activity 83 4.6 Adsorption 85 4.6.1 Thermodynamic basis of adsorption 85 4.6.2 Adsorption isotherms 85 4.7 Surfactants 90 Chapter 5 Surface-active materials 93 5.1 What are they, and where are they found? 93 5.2 Micelles 94 5.3 Hydrophilic-lipophilic balance (HLB), critical micelle concentration (cmc), and Krafft point 96 5.4 Deviations from the spherical micelle 98 5.5 The thermodynamics of self-assembly 100 5.6 Structures resulting from self-assembly 104 5.6.1 Spherical micelles 107 5.6.2 Cylindrical micelles 107 5.6.3 Lamellae: Membranes 108 5.6.4 Hollow micelles 109 5.6.5 Inverse structures 110 5.7 Phase diagrams 112
Contents vii 5.8 Self-assembly of macromolecules: The example of proteins 112 5.8.1 Why are all proteins not compact spheres with their few nonpolar amino acids on the inside? 114 5.8.2 How do proteins behave in solution? 114 5.8.3 A protein folding on its own: The Levinthal paradox 116 5.8.4 What happens when proteins are heated? 117 5.8.5 What is the effect of a solvent on a protein? 118 5.8.6 What are the effects of a protein on its solvent? 119 5.8.7 Protein denaturation: An overview 120 5.8.8 Casein: Structure, self-assembly, and adsorption 121 5.8.9 Adsorption and self-assembly at an interface: A complex example 122 5.8.10 To what extent does the above model apply to the adsorption of a typical spherical protein? 123 5.8.11 Under what conditions does a protein adsorb to a surface, and how easily does it stay adsorbed there? 124 Chapter 6 Emulsions and foams 127 6.1 Colloidal systems 127 6.1.1 Emulsions and foams nomenclature 128 6.2 Thermodynamic considerations 130 6.3 A brief guide to atom-scale interactions 131 6.3.1 van der Waals forces 131 6.3.2 Hydrogen bonds 133 6.3.3 Electrostatic interactions 134 6.3.4 DLVO theory: Electrostatic stabilization of colloids 135 6.3.5 Solvation interactions 137 6.3.6 Stereochemical interactions: Excluded volume forces 138 6.4 Emulsification 141 6.4.1 Detergents: The archetypal emulsifiers 144 6.5 Foaming 145 6.6 Light scattering from colloids 146 6.7 Destabilization of emulsions and foams 147 6.7.1 Gravitational separation: Creaming 148 6.7.2 Aggregation and flocculation 150 6.7.3 Coalescence 152 6.7.4 Phase inversion 153 6.7.5 Disproportionation and Ostwald ripening 153 Chapter 7 Rheology 157 7.1 Does everything flow? 157 7.2 Elastic behavior: Hooke's law 159 7.3 Viscous behavior: Newtonian flow 161
viii Contents 7A Non-Newtonian flow 162 7.4.1 Time-independent non-newtonian flow 162 7.4.2 Time-dependent non-newtonian flow 164 7.5 Complex rheological behaviors 165 7.5.1 Application of non-newtonian flow: Rheology of emulsions and foams 165 7.6 How does a gel flow? (Viscoelasticity) 168 7.7 Methods for determining viscoelasticity 168 7.7.1 Creep 168 7.7.2 Relaxation 169 7.7.3 Dynamic measurements: Oscillation 169 Chapter 8 Elements of chemical kinetics 173 8.1 Diamonds are forever? 173 8.2 Concerning velocity 174 8.3 Reaction laws 174 8.4 Zero-order reactions 176 8.5 First-order reactions 177 8.5.1 Inversion of sucrose 178 8.6 Second- and higher-order reactions 180 8.7 Dependence of velocity on temperature 182 8.8 Catalysis 183 8.9 Biocatalysts: Enzymes 184 8.10 The kinetics of enzymic reactions 185 8.10.1 Lineweaver-Burk and Eadie-Hofstee graphs 187 Bibliography 191 Index 195