Isolation, screening and identification of high protease-producing strains

In order to degrade the macromolecular protein of soybean meal to soybean peptide, casein-plate method was adopted as a screening model in this study. Firstly, high protease-producing strains were isolated and screened from soil, and the strains possessed bigger ratio of hydrolytic circle and colony diameter were selected. After liquid fermentation, protease activity and peptide conversion rate of the strain were measured. Finally, strain B1 was chosen with 111.8 U/mL in enzyme activity and 37.2% in peptide conversion rate. Judged by morphological, physiological and biochemical characteristics, the strain was identified as Bacillus sp.