Optimization of the Fermentation Conditions of Poly-γ-Glutamic Acid from Natto by PB Experiment Combined with BBD Response Surface Method

In order to explore the optimal fermentation conditions for the poly-γ-glutamic acid (γ-PGA) production and sensory quality of fermented natto, the comprehensive score of γ-PGA production and sensory evaluation after natto fermentation was used as an index to optimize the natto fermentation process by single factor test, Plackett-Burman test design, steepest climbing test and Box-Behnken response surface method. The optimum fermentation conditions of natto were determined as follows: Soybean soaking pH7.2, fermentation temperature 37.10 ℃, fermentation time 24.20 h, inoculation amount 4.00%, bottling amount 19.90%. Under the optimized conditions, the production of γ-PGA was 3.65 mg/g, the sensory score was 31.67, and the comprehensive score was 10.04. There was no significant difference between the experimental results and the model prediction values, which was stable and reliable.