INTRODUCTORY LECTURE Recent Trends in Food Colloids Research E. Dickinson, 1, 
Adsorbed Layers, 
INVITED LECTURE Structure and Properties of Adsorbed Layers in Emulsions Containing Milk Proteins D. G. Dalgleish, 23, 
INVITED LECTURE Structure of Proteins Adsorbed at an Emulsified Oil Surface M. Sltimizu, 34, 
A Phenomenological Model for the Dynamic Interfacial Behaviour of Adsorbed Protein Layers G. A. van Aken, 43, 
Association of Chymosin with Adsorbed Caseins A, L. de Roos, P. Walstra, and T. J. Geurts, 50, 
Surface Activity and Competitive Adsorption of Milk Component 3 and Porcine Pancreatic Lipase at the Dodecane–Water Interface J.-L. Courthaudon, J.-M. Girardei, C. Chapai, D. Lorient and G. Linden, 58, 
Application of Polymer Scaling Concepts to Purified Gliadins at the Air–Water Interface J- Hargreaves, R. Douillard, and Y. Popineau, 71, 
A Neutron Reflectivity Study of the Adsorption of β-Casein at the Air–Water Interface P. J. Atkinson, E, Dickinson, D. S. Horne, and R. M. Richardson, 77, 
Effect of Temperature on Lipid–Protein Interactions at the Oil–Water Interface J.-L. Gelin. P. Tainturier, L. Poyen, J.-L. Counhaudon, M. Le Meste, and D. Lorient, 81, 
Modification of the Interfacial Properties of Whey by Enzymic Hydrolysis of the Residual Fat C. Blecker, V. Cerne, M. Paquot, G. Lognay, and A. Sensidoni, 85, 
Influence of Charge on the Adsorption of Proteins to Surfaces J. Leaver, D. S. Horne, C. M. Davidson, and D. V. Brooksbank, 90, 
Surface Properties of the Milk Fat Globule Membrane: Competition between Casein and Membrane Material S, Chazelas, H. Razafindralambo, Q. Dumont de Chassart, and M, Paquot, 95, 
Surface-active Properties of Mixed Protein Films Containing Caseinate + Gelatin V. B. Galazka, B. T. O'Kennedy, and M. K. Keogh, 99, 
Protein Adsorption and Protein–Monoglyceride Interactions at Fluid–Fluid Interfaces J, M. Rodriguez Palino and M. R. Rodriguez Niño , 103, 
Destabilization of Monoglyceride Monolayers at the Air–Water Interface: Structure and Stability Relationships J, M. Rodriguez Patino and J. de la Fuente Feria, 109, 
Competitive Adsorption of Spherical Particles of Different Sizes by Molecular Dynamics E. G. Pelan and E. Dickinson, 114, 
Protein Interactions and Functionality, 
INVITED LECTURE Protein–Aroma Interactions S. Langourieux and J. Crouzet, 123, 
Some Changes to the Properties of Milk Protein Caused by High-Pressure Treatment D. E. Johnston and R. J. Murphy, 134, 
Surface Energy at the Ice-Solution Interface for Systems Containing Antifreeze Biopolymers D. S. Reid. W. L. Kerr, J. Zhao, and Y. Wada, 141, 
Studies of Interactions between Casein and Phospholipid Vesicles Y. Fang and D. G. Dalgleish, 146, 
Effect of Protein on the Retention and Transfer of Aroma Compounds at the Lipid–Water Interface B. A. Harvey, C. Druaux, and A. Voilley, 154, 
Emulsifying and Oil-binding Properties of the Enzymic Hydrolysate of Bovine Serum Albumin M. Saito, 164, 
Conformational Stability of Globular Proteins: A Differential Scanning Calorimetry Study of Whey Proteins P. Relkin, A. Muller, and B. Launay, 167, 
Thermal Denaturation and Aggregation of β-Lactoglobulin Studied by Differential Scanning Calorimetry M. A. M. Hoffmann, P. J. J. M. van Mil. and C. G. de Kruif, 171, 
Changes in Molecular Structure and Functionality during Purification and Denaturation of Faba Bean Proteins H. M. Rawel and G. Muschiolik, 178, 
Microstructural, Physico-chemical, and Functional Properties of Commercial Caseinates P. Bastier, E. Dumay, and J.-C. Cheftel, 182, 
Biochemical and Physico-chemical Characteristics of the Protein Constituents of Crab Analogues Prepared by Thermal Gelation or Extrusion Cooking M. Thiebaud, E. Dumay, and J.-C. Cheftel, 189, 
Interactions between Fat Crystals and Proteins at the Oil–Water Interface L. G. Ogden and A. J. Rosenthal, 194, 
Emulsions, 
INVITED LECTURE Surface Structures and Surface-active Components in Food Emulsions B. Bergenstahl. P. Fäldt, and M. Malmsten, 201, 
Ultrasonic Studies of the Creaming of Concentrated Emulsions E. Dickinson, J. G. Ma, V. J. Pinfield, and M. J. W. Povey, 223, 
Formulation and Properties of Protein-Stabilized Water-in-Oil-in-Water Multiple Emulsions J. Evison, E. Dickinson, R. K. Owusu Apenten, and A. Williams, 235, 
Effect of Non-Starch Polysaccharide on the Stability of Model Physiological Emulsions A. Fillery-Travis, L. Foster, S. Moulson, M.Garrood, S.Clark, and M. Robins, 244, 
Investigation of the Function of Wbey Protein Preparations in Oil-in-Water Emulsions G. Muschiolik, S. Dräger, H. M. Rawel, P. Gunning, and D. C. Clark, 248, 
Shear Induced Instability of Oil-in-Water Emulsions A. Williams and E. Dickinson, 252, 
Surfactant–Protein Competitive Adsorption and Electrophoretic Mobility of Oil-in-Water Emulsions J. Chen, J. Evison, and E. Dickinson, 256, 
Osmotic Pressure of Emulsions Containing Polysaccharide + Non-ionic or Anionic Surfactants E. Dickinson, M. I. Goller, and D. J. Wedlock, 261, 
Interfacial and Stability Properties of Emulsions: Influence of Protein Heat Treatment and Emulsifiers E. Dickinson and S.-T. Hong, 269, 
Foams, 
Surface and Bulk Properties in Relation to Bubble Stability in Bread Dough J. J. Kokelaar, T. van Vliet, and A. Prins, 277, 
Comparison of the Foaming and Interfacial Properties of Two Related Lipid-binding Proteins from Wheat in the Presence of a Competing Surfactant F. Husband, P. J. Wilde, D. Marion. and D. C. Clark, 285, 
Reflectance Studies on Ice-Cream Models R. D. Bee and R. J. Birkett, 297, 
Disproportionate in Aerosol Whipped Cream M. E. Wijnen and A. Prins, 309, 
Determination of Protein Foam Stability in the Presence of Polysaccharide E. Izgi and E. Dickinson, 312, 
Bubble Growth on an Active Site: Effect of the Cavity Volume A. F. Zuidberg and A. Prins, 316, 
Mixed Biopolymer Systems, 
INVITED LECTURE Thermal Behaviour of Kappa-Carrageenan + Galactomannan Mixed Systems P. B. Fernandas, M. P. Gonçalves. and J.-L. Doublier, 321, 
Whey Protein + Polysaccharide Mixtures: Polymer Incompatibility and Its Application A, Syrbe, P. B. Fernandes, F. Dannenberg. W. Bauer, and H. Klostermeyer, 328, 
Effect of Sodium Caseinate on Pasting and Gelation Properties of Wheat Starch C. Marzin, J.-L. Doublier, and J. Lefebvre, 340, 
Colloidal Stability and Sedimentation of Pectin-Stabilized Acid Milk Drinks T. P. Kravtchenko, A. Parker, and A. Trespoey, 349, 
Decrease of In Vitro Hydrolysis of Soybean Protein by Sodium Carrageenan J. Mouécoucou, C. Villaume, H. M. Bau A. Schwertz, J. P. Nicolas. and L. Méjean, 356, 
Gels and Networks, 
INVITED LECTURE The Importance of Biopolyniers in Structure Engineering A.-M. Hermansson, 363, 
INVITED LECTURE Physical Chemistry of Heterogeneous and Mixed Gels V. J. Morris and G. J. Brownsey, 376, 
Investigation of Sol–Gel Transitions of β-Lactoglobulin by Rheological and Small-angle Neutron Scattering Measurements D. Renard, M. A. V. Axelos, and J. Lefebvre, 390, 
High Pressure Gelation of Fish Myofibriliar Proteins A. Carlez, J. Borderias, E. Dumay, and J.-C. Cheftel, 400, 
Gelation of Protein Solutions and Emulsions by Transglutaminase Y. Matsumura, Y. Chanyangvorakul, T. Mori, and M. Motoki, 410, 
Sintering of Fat Crystal Networks in Oils D. Johansson, B. Bergenståhl, and E. Lundgren, 418, 
Thermal Gelation of Sunflower Proteins A. C. Sánchez and J. Burgos, 426, 
Binding of Calcium Ions by Pectins and Relationship to Gelation C. Garnier, M. A. V. Axelos, and J.-F. Thibault, 431, 
Heat-induced Denaturation and Aggregation of β-Lactoglobulin: Influence of Sodium Chloride M. Verheul, S. P. F. M. Roefs, and C. G. de Kruif, 437, 
Rheological and Mechanical Properties, 
INVITED LECTURE Mechanical Properties of Concentrated Food Gels T. van Vliet, 447, 
Scaling Behaviour of Shear Moduli during the Formation of Rennet Milk Gels D. S. Horne, 456, 
Sol–Gel Transition of ι-Carrageenan and Gelatin Systems: Dynamic Visco-elastic Characterization C. Michon, G. Cuvelier, B. Launay, and A. Parker, 462, 
Effect of Retrogradation on the Structure and Mechanics of Concentrated Starch Gels C. J. A. M. Keetels, T. van Vliet, and H. Luyten, 472, 
Mechanical Properties of Thermo-reversible Gels in Relation to their Structure and the Conformations of their Macromolecules E. E. Braudo and I. G. Plashchina, 480, 
Effect of Hydrocolloid Concentration on Mechanical Behaviour of Orange Gels S. M. Fiszman, M. C. Trujillo, and L. Durán, 488, 
Effect of Starter Culture on Rheology of Yoghurt H. Rohm, 492, 
Rheology of Mixed Carrageenan Gels: Opposing Effects of Potassium and Iodide Ions A. Parker, 495, 
Rheology of Semi-sweet Biscuit Doughs G. Oliver and S. S. Sahi, 499, 
Bulk and Surface Rheologicai Properties of Wafer Batters G. Oliver and S. S. Sahi, 503, 
Effect of Dry Ultra-fine Size Reduction on Physico-chemical Properties of Pea Starch S. Jacqmin and M. Paquot, 507, 
Influence of Fat Globule Size on the Rheological Properties of a Model Acid Fresh Cheese C. Sanchez, K. Maurer, and J. Hardy, 512, 
Glasses, 
INVITED LECTURE Influence of Macromolecuies on the Glass Transition in Frozen Systems D. Simatos, G. Blond, and F. Martin, 519, 
Phenomenon of Enthalpy Relaxation at the Glass Transition Temperature in Granular Starches C. C. Seow, 534, 
Kinetic Processes in Highly Viscous, Aqueous Carbohydrate Liquids T. R. Noel, R. Parker, and S. G. Ring, 543, 
Calculation of Glass Transition Temperature of Food Proteins and Plasticizer Effects of Different Ingredients Yu. L Malveev, 552, 
Water Adsorption and Plasticization of Amylopectin Glasses K. Jouppila, T. Ahonen, and Y. Roos, 556, 
Influence of Moisture Content on Glass Transition Temperature of the Amorphous Matrix in 'Xixona Turrón' N. Martínez, M. P. Betrán, and A. Chiralt, 560, 
Phase Transitions of Tapioca Starch V. Garcia, A. Buleon, P. Colonna, G. Della Valle, and D. Lourdin, 566, 
CONCLUDING REMARKS D. Lorient, 572, 
Subject Index, 575,

CHAPTER 1

Structures and Properties of Adsorbed Layers in Emulsions Containing Milk Proteins

By Douglas G. Dalgleish

DEPARTMENT OF FOOD SCIENCE, UNIVERSITY OF GUELPH, GUELPH, ONTARIO NIG 2W1, CANADA

1 Introduction

It is probably no exaggeration to say that there are more papers written on the adsorption and surfactant properties of milk proteins than on the same properties of all other food proteins put together. As a result, we understand more of the behaviour of the milk proteins than of most other groups of food proteins. For example, descriptions have been given of systems which contain not only protein and oil but other components such as small molecule surfactants (Tweens, lecithins, glycerol monoesters). Most of this research has been performed in the course of the last 15 years, and has coincided with an increase in the industrial uses of dairy proteins in food emulsions, and a more general interest in the emulsifying properties of proteins.

For the researcher, milk provides a number of proteins of different structures and properties which can be fairly readily separated from one another (in the laboratory, at least). The major proteins in milk, the caseins (αs, β and κ), generally lack large amounts of regular structure; they are considered to be rather flexible molecules, a property which is likely to enhance their surfactant properties. In contrast to the caseins, there are the whey, or serum, proteins, (α-lactalbumin, β-lactoglobulin, bovine serum albumin and immunoglobulins) which are characterized by well defined three-dimensional structures held together by disulfide bridges; these proteins are much more rigid than the caseins. The use of individual proteins, and mixtures of them, to prepare emulsions may potentially allow for the formation of particles having a range of structures and potential functionalities, although this has still to be established in detail.

Most of the research has so far been performed using single purified proteins, or on simple mixtures of them; however, it should be remembered that in milk the caseins naturally form aggregated particles (the casein micelles), and that these can also be used to emulsify fats and oils, as in homogenized milks. Although the latter have received comparatively little research attention relative to other model emulsions, they may become of increased importance, since it is now possible to use microfiltration techniques to isolate a slightly modified micellar fraction from milk; the functional properties, including emulsification, of this fraction therefore need to be established.

This review deals with the properties of the different milk proteins adsorbed to oil–water interfaces. In particular, it contrasts the behaviour of the whey proteins and the caseins in terms of adsorption, and it describes how this may affect the structures of the adsorbed layers of protein at the oil–water interface.

2 Protein Adsorption and Particle Sizes in Emulsions

Both of the major whey proteins, β-lactoglobulin and α-lactalbumin, adsorb to oil–water interfaces and are capable of giving stable emulsions. Indeed, singly or in combination, these proteins are excellent emulsifying agents, and their emulsions are only a little less stable than those produced using caseins. For emulsions prepared under the same conditions (concentrations of oil and protein, pH, homogenization pressure), the droplet sizes in the whey protein emulsions are somewhat greater than those in the casein-stabilized emulsions when the concentration of protein is low (< 1 %), but identical at higher concentrations (Figure 1). This Figure also emphasizes the effect of the concentration of protein on the sizes of the emulsion droplets. It has been known in practice that such a relationship exists, but it has been recently established that the protein concentration affects not only the droplet sizes, but also the protein load (amount of protein per unit area of the oil–water interface); it therefore may also potentially affect the properties of the emulsion droplets.

Figure 2 shows that in emulsions prepared with 20 wt% oil and whey protein in the concentration range 0–3 wt%, the surface concentration (Γ) increases in a series of steps, from 1.5 to 3 mg m-2 as the concentration of protein in the mixture is increased from 0.3 to 3 wt%. It is possible that the last of these steps may arise from multilayer formation, but the others appear to arise from conformational rearrangement of the protein, or different spatial distribution of the protein molecules at the interface. In casein-stabilized emulsions, the surface concentration of protein depends even more strongly on the total concentration of protein in the emulsion. It is possible to make a stable emulsion containing casein when the surface concentration is as little as 1 mg m-2 (Figure 2). That is, if droplets are coated with less than that amount of casein, they will coalesce until the surface area has decreased sufficiently for there to be enough casein to cover it at about this minimum level of Γ. For an emulsion containing 20 wt% oil, the lower limit of the casein concentration is about 0.3%. However, as the amount of casein increases, so does the surface concentration, until an upper limit is reached at about 3 mg m-2, when the casein concentration is about 2%. Unlike the results found for whey proteins, Γ increases smoothly with the concentration of casein, and there are no steps in the function to suggest multilayer formation. The results from both sets of proteins show that, by careful manipulation of the homogenization conditions, and the concentrations of oil and protein, it is possible to produce a range of emulsions with different protein surface concentrations.

3 Competition between Proteins during and after Emulsion Formation

Once the emulsion has been formed, and the proteins have adsorbed, it is generally accepted that the adsorption process is largely irreversible, and that, in the absence of other agents, adsorbed proteins will not wash off the interface. It is possible that β-casein is an exception to this rule: exchange of labelled β-casein between the solution and the interface has been demonstrated. Also, extremely thorough washing of latex particles to which β-casein has adsorbed, by passing them through a long column, reduces the surface concentration from 3 mg m-2 to 1 mg m-2. It is not established whether a similar washing phenomenon occurs when the protein is adsorbed to oil–water interfaces.

(Continues...)

Excerpted from Food Macromolecules and Colloids by E. Dickinson, D. Lorient. Copyright © 1995 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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