Chymosin sensitivity of the heat-induced serum protein aggregates isolated from skim milk

The sensitivity of heat-induced milk serum κ-casein/whey protein aggregates to recombinant chymosin was investigated in the serum phase of heated skim milk or on aggregates isolated from it. In both cases, significant amounts of caseinomacropeptide were produced after 1 h-incubation at 37 °C, as assayed by high performance liquid chromatography coupled with mass spectrometry analysis. In milk serum, the aggregates remained stable upon hydrolysis, as opposed to 10 g L−1 suspensions of isolated aggregates in imidazole/Ca2+ buffer where visible flocculation occurred. The results are discussed in terms of variation in chymosin activity between the two systems.