Optimization of fermentation conditions for nattokinase production in solid-state fermentation by Bacillus subtilis natto using peanut meal as substrate

The peanut meal was fermented by Bacillus natto to prepare nattokinase. The technological conditions were optimized by single factor and orthogonal experiments with a primary indicator of nattokinase. The results showed that the optimal conditions were as follows: fermentation temperature 37 ℃,inoculum size 10%,the ratio of solid / liquid 1∶ 0.4 g / m L,fermentation time 24 h.Under the optimized conditions,the activity of nattokinase reached3162 U / m L,18% higher than that obtained in one-factor-at-a-time experiments( only 2680 U / m L). And soluble nitrogen reached 5.6 mg / m L. Hydroxyl free radicals scavenging activity of fermentation broth was 74%,and the required absorbance for determining iron reduction capacities was 0.906.