Optimization of Protease Production Fermentation Conditions by Bacillus subtilis

The response surface methodology(RSM) was used to optimize the immersion fermentation conditions for protease production by Bacillus subtilis.Firstly,dextrin and cornmeal were screened out as the most suitable carbon and nitrogen sources by using single factor experiment.Based on these,the assay Plackett-Burman was designed to evaluate relative factors related to protease production and three statistically significant factors(dextrin,cornmeal and yeast extract) were selected.And then the steepest ascent method was applied to define the optimal response region for these three factors,the RSM was used to optimize the above critical factors,and to find out the optimal concentration levels and the relationships between these factors.By solving the quadratic regression model equation by using appropriate statistic methods,the optimal fermentation concentrations were determined,with dextrin of 11.568g/L,cornmeal of 22.462g/L,yeast extract of 10.202g/L,NaCl of 5g/L,initial pH of 7.0,and 37℃ incubation for 48h.Protease activity after optimization was increased from 2463.95U/mL to 3281.79U/mL,an increase by 33.19%.The experiment data under various conditions have validated the theoretical values.