The mechanisms of the heat-induced interaction of whey proteins with casein micelles in milk

The heat-induced interactions between whey proteins and casein micelles wer e investigated by defining the final product of the reaction when milk was heated at temperatures up to 90 degrees C. By looking at the changes of the interactions in skim milk and in resuspended casein micelles, to which dif ferent amounts of whey protein had been added, information on the mechanism s that determine the heat-induced protein-protein interactions in milk was derived. The ratio of alpha-lactalbumin and beta-lactoglobulin to kappa-cas ein and the ratio of alpha-lactalbumin to beta-lactoglobulin found in the m icellar pellet were used as indices of these heat-induced reactions occurri ng in milk. The results suggested that at these low temperature (70-90 degr ees C) with batch heating conditions, whey proteins form soluble complexes which act as intermediates in the heat-induced association of alpha-lactalb umin and beta-lactoglobulin with the micelles. The presence of beta-lactogl obulin was necessary for any association of whey protein with casein micell es to occur; furthermore, the amount of beta-lactoglobulin found in the mic ellar pellet after heating seemed to be limited by a discrete number of bin ding sites available on the micelles. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.