Purification and characterisation of milk‐clotting and caseinolytic activities of pepsin isolated from adult sheep abomasa

Ovine pepsin was isolated and assessed for its milk‐clotting properties and caseinolytic activity in comparison with commercial chymosin. Ovine pepsin showed similar responses to variations in pH, temperature and CaCl₂ concentration of milk compared with chymosin, although its pH sensitivity was higher. SDS‐PAGE electrophoretic analysis of the casein fractions treated with ovine pepsin showed that alpha‐casein was more susceptible to proteolysis than beta‐casein, in contrast to chymosin. Curd‐firming properties of skim milk gels obtained with ovine pepsin and chymosin were evaluated by Gelograph under the same conditions. Curd produced using ovine pepsin was less firm than that made with chymosin.