Production of milk-clotting enzyme by Bacillus subtilis B1 from wheat bran
Three strains, Bacillus subtilis B1, B. subtilis B18 and Bacillus thuringiensis B12, were screened from wheat bran to produce milk-clotting enzyme. Among them, B. subtilis B1 exhibited considerable milkclotting activity with low proteolytic activity. After response surface methodology optimization, milkclotting activity was improved from 782 SU ml-1 to 1129.05 ± 74.55 SU mL-1 with a small inoculum size (0.130%, v/v). The optimized medium contained glucose (16.2 gL-1), wheat bran (30 gL-1), NaCl (5 gL-1), MgSO4.7H2O (5 gL-1), KH2PO4 (2 gL-1) and CaCO3 (3 gL-1). The milk-clotting enzyme from B. subtilis B1 has the optimum pH 5.5 and CaCl2 concentration 50 mmol L-1. It is completely inactivated after 5 min at 70°C. The result showed that B. subtilis B1 was a promising strain for industrial milk-clotting enzyme production.
Key words: Milk-clotting enzyme, Bacillus subtilis, submerged fermentation, wheat bran.