The effect of liquid fermentation on Nattokinase activity produced by Bacillus natto No.ZN-4 strain was studied. Results showed that the optimal culture conditions were 2% glucose, 1% peptone, 0.6% Na2HPO4, 0.1% NaH2PO4, 0.05% MgSO4, 0.02% CaCl2, pH 7.0, the inoculums size 3% and temperature 35 ℃. Under these conditions, the Nattokinase activities of the strain reached 1903 U/mL in shake-flask, 2210 U/mL for 50 L fermentation, and 1934 U/mL for 500 L fermentation, respectively.
