Optimization of Fermentation Process of Natto by Broad Bean and Its Enzymatic Properties

In order to develop new broad bean products and increase the added value of broad bean, this study was based on broad bean as main material. The single-factor experiment and orthogonal experiment were used to optimize the best process of natto by broad bean and then the enzymatic properties of nattokinase were studied. The results showed that the optimal process conditions were as follows:The broad bean were soaked in 48 h and steamed under atmospheric pressure for 20 min, the inoculation of 6% and fermented at 40℃for 72 h. Under these conditions, the enzyme activity reached (4860.13±470.02) U·g^-1, and the sensory score was (95.67±0.71) points. Enzymatic properties analysis showed that the nattokinase had a better thermal stability at 25℃ to 40℃.Meanwhile, the nattokinase had good stability at a pH range from 6 to 9, and the relative enzyme activity was kept over 89.05%.The metal ions of Mg²⁺ and Ca²⁺ had an effect on promoting the activity of nattokinase, and the metal ions of Cu²⁺ and Fe³⁺ had an obvious effect on inhibiting nattokinase. However, the metal ions of Zn²⁺ had no obvious effect. This study could provide a reference for the development of broad bean products and the industrial production of broad bean natto.