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 undergo hydrolysis in the presence of plasmin enzyme, remaining, for some kinds 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 completed within 2 hours for beta-CnA(1), and within 3 hours for beta-CnC. Nine peptides from beta-CnC and 6 from beta-CnA(1) were separated and identified according to their C- and N-terminal sequences and amino acid composition. Eleven peptide bonds (10 Lys-X type and 1 Arg-X type) were sensitive to plasmin in beta-CnC, and 9 (8 Lys-X type and 1 Arg-X type) in beta-CnA(1).