Optimisation of semi-solid-state fermentation conditions for soybean meal to improve protease production of Bacillus subtilis N6 by response surface methodology

Abstract

Soybean meal is a major protein source in the animal diet owing to its excellent amino acid components. However, soybean meal still contains some proteins (glycinin and β-conglycinin) that cause allergies for young animals. These proteins have the high heat-stable ability, digestive enzyme resistance, which leads to the increase in immunological responses, intestinal peristalsis, and diarrhea and the decrease in nutrition absorption. This research focuses on the optimisation of the semi-solidstate fermentation conditions to improve the protease production of B. subtilis N6 in the soybean meal medium. The factors that affected the protease production of B. subtilis N6 would be screened by the Plackett-Burman design. Out of five screened factors, three factors that have the great effects were temperature, substrate thickness, and fermentation time (p<0.05). Optimisation experiment was designed by the response surface methodology. The results showed that, the optimised temperature, soybean thickness, and fermentation time were 35o C, 1 cm, and 35h, respectively. These optimum conditions resulted in the enhancement in protease yield to 632 U/g with 1.65 fold increase