Abstract:Compared to natto, the fermented soybean milk produced by Bacillus natto fermentation is convenient to consume. However, it suffers from disadvantages such as low nattokinase activity and poor flavor. In this study, we first investigated the effect of adding different grains (tartary buckwheat, brown rice, coix seed, quinoa, oat flour) to enhance the ability of Bacillus natto to produce nattokinase. Results showed that tartary buckwheat was the most effective additive, increasing liquid enzyme activity from 5 803.12 U/mL to 23 326.23 U/mL when added at a 3% mass fraction. Then we evaluated the effects of tartary buckwheat powder on nattokinase activity, flavor and antioxidant activity of fermented soybean milk by Bacillus natto. Results showed that when the amount of tartary buckwheat was added at 50% mass of soybeans, the nattokinase activity, volatile base nitrogen mass concentration and total antioxidant capacity of the fermented soybean milk were 4 460.28 U/mL, 3.45 mg/dL and 16.34 mmol/L, respectively, and accounting for 161.42%, 79.84% and 196.39% of fermented soybean milk from pure soybean fermentation, respectively. Addition of tartary buckwheat significantly enhanced nattokinase activity, improved flavor, and increased antioxidant capacity of fermented soybean milk. This research provides valuable references for the development of nattokinase-enriched and convenient-to-consume natto products.
