Screening of nattokinase high-yielded in different Bacillus Subtilis and optimization of fermentation conditions

This study was based on soybeans as main material,added different auxiliary material and handled with different treatments. Three Bacillus Subtilis fermentation characteristics were compared and the optimal strain was selected with the index of enzyme activity. The optimal process conditions were determined by solid-state fermentation experiments with the optimal strain. The result showed as follows:among three testing strains,BS21076 had the optimal fermentation characteristics,higher viable count and nattokinase activity. The optimal conditions of solid fermentation were baked at 90℃ for 5min,crushed degree four,3% konjac power,the inoculation of 8% and fermented at 37℃ for 24 h. Under these conditions,the enzyme activity reached(3582.48±83.13)U/g,which compared with traditional fermentation NK activity increased significantly(p<0.01).