Studies on Milk Clotting Enzymes Produced by Basidiomycetes

Abstract

In the previous paper it was reported that three strains of Basidiomycetes, Coriolus consors (Berk.) Imaz., Fomitopsis pinicola (Fr.) Karst. and Irpex lacteus Fr., produced milk clotting enzymes into culture media. These three strains were cultivated in a liquid medium and crude enzymes were obtained from the culture filtrates. Some properties of the crude enzymes thus obtained were investigated. These enzymes are a sort of acid proteases with optimum pH of 2.5 for casein digestion. Different from a calf rennet, the proteolytic activity of the enzymes increased along the prolongation of reaction time. The clotting activity of the enzyme of F. pinicola was much more influenced by pH of milk and Ca ion concentrations in milk than that of the calf rennet. But the enzyme of I. lacteus is very like the calf rennet in these properties. Optimum temperatures of the enzymes lie at 55_??_60°C. When the ratio of milk clotting activity to proteolytic activity (MCA/PA) is measured, the ratio of the calf rennet is remarkably higher than those of microbial rennets tested. Among microbial rennets, Mucor rennet and the enzyme of I. lacteus have rather higher values than others.