Study on Solid Fermentation and Antioxidant Function of Natto

[Objectives] To study the optimum conditions of solid fermentation of natto with antioxidant function as an index. [Methods] Single factor experiment and orthogonal experiment were designed to study the effects of temperature, time, initial pH and inoculum amount on the antioxidant activity of natto solid fermentation. The optimum conditions of natto solid fermentation were determined and the antioxidant activity of natto extract was compared. [Results] The optimal fermentation conditions were as follows: temperature 32 ℃, initial pH 7.0, inoculation amount 8%, fermentation time 32 h. The hydroxyl radical scavenging rate of natto solid fermentation crude extract was the highest, which was 82.7%. The optimized natto fermentation extract showed stronger scavenging ability for ·OH and and showed obvious dose-effect relationship. IC50 was 3.63 and 4.24 mg/mL, respectively, and the scavenging efficiency was 1.3 and 1.9 times higher than that of the unoptimized fermentation extract, respectively. [Conclusions] Natto is rich in nattokinase and other functional factors, and its antioxidant activity can be improved by optimizing fermentation technology, so that natto products can be widely used, including cosmetic raw materials, natto skin care soap, health food and medicine, etc., and have a broader development prospect.