Optimization of Liquid Fermentation Conditions of Nattokinase

Liquid fermentation for nattokinase by Bacillus subitilis natto BSN was investigated.The components of its culture medium including carbon source,nitrogen source,the ratio of carbon source to nitrogen source and ion composition were studied.The results showed that the fermentation conditions included temperature,initial pH value,fermentation time,inoculation quantity and volume of the medium.To fermentative medium,the best carbon source was xylose 1.5%,and the best nitrogen source was soya peptone 2.0%.The components of inorganic salts were MgSO_4 0.05%,CaCl_2 0.02%,and K_2HPO_4/KH_2PO_4 0.1%/0.1%.37℃ was the most suitable temperature for the production of NK.The strain had the biggest speed of growth and the highest yield of NK under pH7.The volume of media was 100 mL/250 mL which was chosen for the most gross production of NK.2% of 18 h-old inoculum was the best condition for NK′s production. After the system optimization,the yield of nattokinase of 1 081 U/mL was obtained at the optimized medium and optimized conditions.