Response surface methodology to optimize the Bacillus subtilis var. sojae semen praeparatum liquid fermentation process for the production of fibrinolytic enzyme

Previously, during the Sojae Semen Praeparatum (SSP, Dandouchi in China) concoction process, three types of fibrinolytic enzyme-producing bacteria were screened and identified: Bacillus subtilis, Stenotrophomonas maltophilia and Micrococcus. The fibrin plate approach was used to measure the fibrinolytic enzyme activity of pure fermentation broth, it was found that fibrinolytic enzyme produced by Stenotrophomonas maltophilia has the highest enzyme activity, followed by Bacillus subtilis and Micrococcus is the lowest. In this study, in order to improve enzyme activity and yield, the response surface method was used to optimize the fermentation conditions, including 6 factors such as nitrogen source, carbon source, initial pH, inoculum amount, loading volume and fermentation temperature. Then, the results showed that: the optional fermentation temperature was determined as 28 ℃, 6% inoculum amount, 30.42 h fermentation time and 20 mL of loading volume in 100 mL erlenmeyer flask. Ultimately, under optimal fermentation conditions, enzyme activity produced by Bacillus subtilis var. SSP was 360.82 IU/mL, which was an increase of 109.68% (1.10 folds) compared to before optimization.