Heat-induced aggregation of whey proteins is enhanced by addition of thiolated beta-casein

Bovine beta-casein has been chemically thiolated by reaction with thiolactone. The purified product was found to contain a variable number of free thiol groups in addition to a number of disulfide bridges. Gel electrophoresis under nonreducing conditions showed the presence of monomeric, dimeric, and tetrameric forms of the protein. Heating whey protein concentrate in the presence of this thiolated casein resulted in a significant increase in the rate of aggregation of all of the whey proteins with the exception of alpha-lactalbumin, where in general the rate of aggregation decreased. This enhancement of the heat-induced aggregation was found to vary with the concentration of thiolated casein. The results are discussed with relevance to decreasing the costs of manufacture of whey protein concentrate.