Proteolysis of goat casein by calf rennet

The proteolytic activity of calf rennet on goat casein (CN) was studied under various conditions which affect cheesemaking and ripening processes (pH, salt, calf rennet concentration and α(s1)-CN polymorphism). Electrophoretic studies showed that goat casein was hydrolysed to give characteristic breakdown products derived from individual caseins (β-I to β-V from β-CN, primary hydrolysis product from α(s1)-CN, para-κ-CN from κ-CN and other degradation products from α(s2)-CN). Both goat β-CN and α(s1)-CN were more sensitive to hydrolysis than their bovine counterparts under the same conditions. The pH did not influence the proteolytic specificity of rennet on β-CN, but rennet activity was highly dependent on the pH. However, in the case of α(s1)-CN, the rate of proteolysis and the nature of breakdown products were pH-dependent. NaCl affected only the rate of proteolysis. After prolonged incubation times, the electrophoretic patterns of hydrolysates produced from whole goat casein by rennet were similar to those produced from isolated β-CN, showing that β-CN and its degradation products are quite resistant to proteolysis compared with α(s1)-CN and its primary hydrolysis product. Rennet hydrolysates of goat casein, containing different α(s1)-CN genetic variants, showed slight differences in the electrophoretic profiles which tended to disappear as hydrolysis advanced.