Heat-Induced Interactions between Serum Albumin, Immunoglobulin, and .kappa.-Casein Inhibit the Primary Phase of Renneting

Skimmed bovine milk and casein micelles (in the presence and absence of various concentrations of individual whey proteins) were heated at 80 degrees C for 30 min. Cloned chymosin was added to the cooled preparations and the enzyme-catalyzed hydrolysis of kappa-casein determined by measuring the formation of caseinomacropeptide. All of the whey proteins tested caused an inhibition of the enzymatic reaction. Heating micelles with individual whey proteins at temperatures as low as 60 degrees C also inhibited both the rate and the extent of the kappa-casein hydrolysis. The results show that interactions between kappa-casein and immunoglobulin G and serum albumin, in addition to the well-documented interaction with beta-lactoglobulin, inhibit the primary phase of the renneting reaction.