HYDROLYSIS OF BOVINE BETA-CASEIN-C BY PLASMIN

The frequency of the C genetic variant of bovine beta-casein (beta-CnC ) may vary from 0 to 17%, depending on the breed. Its content in milk is very important in determining some cheese flavour characteristics. According to some authors, during cheesemaking beta-CnC does not under go hydrolysis in the presence of plasmin enzyme, remaining, for some k inds of cheese, practically with the same amino acid configuration. In this paper it was demonstrated that beta-CnC, as well beta-casein A(1 ) (beta-CnA(1)), undergo hydrolysis by plasmin, giving the same kind, but different ratios of peptide products. Hydrolysis was practically c ompleted within 2 hours for beta-CnA(1), and within 3 hours for beta-C nC. Nine peptides from beta-CnC and 6 from beta-CnA(1) were separated and identified according to their C- and N-terminal sequences and amin o acid composition. Eleven peptide bonds (10 Lys-X type and 1 Arg-X ty pe) were sensitive to plasmin in beta-CnC, and 9 (8 Lys-X type and 1 A rg-X type) in beta-CnA(1).