Exchange reactions between whey proteins and caseins in heated soya oil-in-water emulsion systems - behavior of individual proteins

Further studies of the details of the heat-induced displacement of caseins by whey proteins from emulsion surfaces have been made using specific purified protein fractions. It is demonstrated that the main agent for displacing caseins from an emulsion interface is beta-lactoglobulin, and that alpha-lactalbumin simply tends to adsorb but without having the capacity to displace caseins. This behavior was illustrated for emulsions containing whole sodium caseinate, and purified alpha(s1)- and beta-casein fractions. There are significant differences between the whole caseinate and the purified fractions, emphasizing the importance of the presence of minor caseins in defining the interfacial structures of the emulsions. beta-Lactoglobulin bound strongly to emulsions made using purified kappa-casein, which in its turn was not displaced. It is evident that although the formation of disulphide bonds between proteins is not essential for the displacement reactions to occur, this reaction may define the types of complexes that are formed on the emulsion interface. Some general aspects of the exchange reactions are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.