Study on koji-making conditions optimization of Hongqu rice wine grains and enzyme production conditions of Aspergillus oryzae

Using Hongqu rice wine grains as the raw material, Aspergillus oryzae MJY2-5 as the fermentation strain, the finished koji was prepared by solid-state fermentation. With neutral protease and glutaminase activities as the evaluation indexes, the koji-making conditions were optimized by single factor and orthogonal experiments. Using enzymatic hydrolysis rate as the index, the optimum enzyme production conditions of A. oryzae MJY2-5 were studied. The results showed that the optimal conditions for koji-making with solid-state fermentation by A. oryzae MJY2-5 were as follows: mass ratio of Hongqu rice wine grains and bran 4:6, fermentation temperature 32 ℃, time 72 h, and initial pH 6.7. Under the optimized conditions, the activities of neutral protease and glutaminase produced by A. oryzae MJY2-5 were (1 891.79±6.34) U/g and (19.96±0.44) U/g, respectively. The optimum conditions for enzyme produced by A. oryzae MJY2-5 were initial pH 5.5, enzymolysis temperature 47 ℃ and time 6 h. Under the optimal conditions, the enzymatic hydrolysis rate was (63.42±0.98)%.