Fermentation parameter and partial biochemical characterisation of milk clotting enzyme from Chinese distiller’s yeast

Abstract

A strain F34 producing milk clotting enzyme with high yield was obtained from Chinese distiller’s yeast, using casein plate prescreening and fermentation reselection. The optimum fermentation medium for milk clotting enzyme production was as follows: 5.0% rice flour and bran digest, 5.0% bean flour digest, 0.5% CaCl2, 0.5% KCl, initial pH 4.5. The optimal fermentation parameters was at 34°C for 60h. The enzyme action was optimal at 50°C and at about pH 5.5. In the absence of substrate the enzyme showed good stability at 40°C and pH 3.5. Ca2+, Zn2+, Fe3+ and Fe2+ showed stimulation on the milk clotting activity; K+ and Mg2+ showed weak stimulation; Na+, Cu2+, Co2+ and Li2+ showed inhibition. The results indicate that this milk clotting enzyme may partially substitute calf rennet in the cheese manufacture.