Heat-induced interactions and gelation of mixtures of beta-lactoglobulin and alpha-lactalbumin

The changes in protein aggregation and storage modulus of mixtures of beta-lactoglobulin and alpha-lactalbumin were measured, by gel electrophoresis and dynamic rheology, respectively, during 60 min of heating at 75 or 80 degrees C in a buffer simulating the whey protein concentrate environment. The results were consistent with the formation of heat-induced hydrophobically bonded aggregates involving both alpha-lactalbumin and beta-lactoglobulin that under go disulfide bond interchange reactions within the aggregate as the basis for the generation of gel strands and gels. The apparent difference in response to heat treatment at 75 degrees C between mixtures of bovine serum albumin (BSA) and beta-lactoglobulin and mixtures of alpha-lactalbumin and beta-lactoglobulin is likely to be based on at least three factors: the different thermal transition temperatures of the three proteins; the possibility of self-initiation of thiol-disulfide interchange reactions for BSA and beta-lactoglobulin, but not alpha-lactalbumin; and the ability of alpha-lactalbumin to form interprotein aggregates with each of the other two proteins prior to disulfide bond interchange and gelation.