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 were 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 different amounts of whey protein had been added, information on the mechanisms that determine the heat-induced protein-protein interactions in milk was derived. The ratio of alpha-lactalbumin and beta-lactoglobulin to kappa-casein and the ratio of alpha-lactalbumin to beta-lactoglobulin found in the micellar pellet were used as indices of these heat-induced reactions occurring in milk. The results suggested that at these low temperature (70-90 degrees C) with batch heating conditions, whey proteins form soluble complexes which act as intermediates in the heat-induced association of alpha-lactalbumin and beta-lactoglobulin with the micelles. The presence of beta-lactoglobulin was necessary for any association of whey protein with casein micelles to occur; furthermore, the amount of beta-lactoglobulin found in the micellar pellet after heating seemed to be limited by a discrete number of binding sites available on the micelles. (C) 1999 Elsevier Science Ltd. All rights reserved.