Influence of milk protein concentration on the gelling activity of chymosin and bovine pepsin

Abstract

Summary Two stages of gelling by the milk-clotting enzymes chymosin and pepsin were studied at different milk protein concentrations, using milk retentates. In each case, enzymic velocity versus protein concentration described a standard hyperbola. According to the experimental conditions such as pH and type of enzyme, which changed the enzyme concentration used, either the quasi-linear part of the hyperbola was observed, or the velocity hardly increased and tended to a limiting value. Gelling occurred with a lower degree of proteolysis of κ-casein when the protein concentration increased but a minimum proteolysis (1% of total nitrogenous matter content) was required for aggregation to take place. Gelling time varied with the protein concentration, the pH and the enzyme concentration. The final degree of proteolysis of κ-casein was the same whatever the substrate concentration used.