The catalytic and kinetic characterization of Bacillus subtilis MK775302 milk clotting enzyme: comparison with calf rennet as a coagulant in white soft cheese manufacture

Abstract

Background: Calf rennet is considered the traditional source of milk clotting enzyme (MCE). However, increasing cheese consumption with decreasing the calf rennet supply had encouraged the quest for new rennet alternatives. The purpose of this study is to acquire more information about the catalytic and kinetic properties of partially purified Bacillus subtilis MK775302 MCE and to assess the role of enzyme in cheese manufacture. Results: B. subtilis MK775302 MCE was partially purified by 50% acetone precipitation with 5.6-fold purification. The optimum temperature and pH of the partially purified MCE were 70 °C and 5.0, respectively. The activation energy was calculated as 47.7 kJ/mol. The calculated Km and Vmax values were 36 mg/ml and 833 U/ml, respectively. The enzyme retained full activity at NaCl concentration of 2%. Compared to the commercial calf rennet, the ultra-filtrated white soft cheese produced from the partially purified B. subtilis MK775302 MCE exhibited higher total acidity, higher volatile fatty acids, and improved sensorial properties. Conclusions: The partially purified MCE obtained in this study is a promising milk coagulant that can replace calf rennet at a commercial scale to produce better-quality cheese with improved texture and flavor.