PROTEOLYSIS OF GOAT BETA-CASEIN BY CALF RENNET UNDER VARIOUS FACTORS AFFECTING THE CHEESE RIPENING PROCESS

The proteolytic activity of calf rennet on goat beta-casein was studie d under various technological parameters which affect cheese ripening (temperature, pH, salt and calf rennet concentrations). Electrophoreti c studies showed that this protein hydrolyzes to give five products; b eta-I-beta-V, in order of appearance and increasing electrophoretic mo bility under alkaline conditions. In an aqueous solution, beta-casein was optimally hydrolyzed to beta-I at pH 6.2, beta-II at pH 3.8, and b eta-III at pH greater than or equal to 5.4. beta-IV products were form ed at all pH values, and beta-V was optimally formed at pH less than o r equal to 5.0. Both beta-IV and beta-V were formed in very small quan tities. Proteolysis of beta-casein by calf rennet is reduced by the ad dition of 5% NaCl, while the addition of 15% NaCl leaves only traces o f beta-I. The polypeptides B-I, B-II, and P-III produced from caprine and bovine beta-caseins gave identical results with PAGE, which sugges ts that the calf rennet attacks the same regions described as suscepti ble to bovine beta-casein cleavage by chymosin.