Some effects of heat on the competitive adsorption of caseins and whey proteins in oil-in-water emulsions

It is common industrially to subject food emulsions to heat treatments of different severity. This may be important when both caseins and whey proteins are present in the emulsion system, because the whey alpha-lactalbumin and beta-lactoglobulin denature when they are heated at temperatures greater than about 70 degrees C and may interact with kappa-casein and alpha(s2)-caseins. At room temperature and neutral pH, caseins and whey proteins do not exchange readily between the interfaces of emulsion droplets and the bulk solution. Even at elevated temperatures (85 degrees C), caseins cannot displace whey proteins adsorbed to the emulsion surface, nor do they interact with the adsorbed whey proteins. The caseins may however co-adsorb if the layer of adsorbed whey proteins is not saturated. Conversely, when whey proteins are added to an emulsion stabilized by caseinate, heating of the mixture causes the whey proteins to adsorb to the interface and to displace the alpha(s1)- and beta-casein fractions, despite the fact that the latter are generally considered more hydrophobic. This is evidence that processing operations may profoundly change the structure and perhaps the properties of food emulsions stabilized by proteins. (C) 1999 Elsevier Science Ltd. All rights reserved.