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 d ifferent severity. This may be important when both caseins and whey protein s are present in the emulsion system, because the whey alpha-lactalbumin an d beta-lactoglobulin denature when they are heated at temperatures greater than about 70 degrees C and may interact with kappa-casein and alpha(s2)-ca seins. 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 disp lace whey proteins adsorbed to the emulsion surface, nor do they interact w ith the adsorbed whey proteins. The caseins may however co-adsorb if the la yer of adsorbed whey proteins is not saturated. Conversely, when whey prote ins are added to an emulsion stabilized by caseinate, heating of the mixtur e causes the whey proteins to adsorb to the interface and to displace the a lpha(s1)- and beta-casein fractions, despite the fact that the latter are g enerally considered more hydrophobic. This is evidence that processing oper ations may profoundly change the structure and perhaps the properties of fo od emulsions stabilized by proteins. (C) 1999 Elsevier Science Ltd. All rig hts reserved.