Effect of different koji-making processes on the post-fermentation process and product quality of rapid Yongchuan Douchi

Abstract:

[Objective] Due to the difference in production process, conventional Yongchuan Douchi (fermented soybean product) and rapid Yongchuan Douchi are remarkably different in flavor quality. We explored the effect of koji-making process on the quality of Douchi. [Methods] Yongchuan Douchi was prepared with the rapid process but different koji-making methods (conventional natural process and artificial inoculation of Aspergillus oryzae, respectively). Then we compared the physicochemical properties and microbial community of the products. [Results] The Douchi prepared with the natural koji-making process had higher content of amino acid nitrogen and darker color (P<0.05), lower content of reducing sugar (P<0.05), and higher microbial richness and diversity (P<0.05) than the product prepared with the artificial inoculation of A. oryzae. The two products showed no significant difference in the titratable acid content (P>0.05). The dominant bacterial genera of the Douchi prepared with the natural koji-making process were Mucor, Bacillus, Enterobacter, Enterococcus, Pseudomonas, Staphylococcus, Wickerhamomyces, Penicillium, and those of the Douchi prepared with the artificial inoculation of A. oryzae were Bacillus, Corynebacterium, Aspergillus, and Candida. In addition, a small number of Debaryomyces sp. was found on both of the two products. [Conclusion] The koji-making process had significant influence on the physicochemical properties and microbial community structure of rapid Yongchuan Douchi. The key physicochemical indexes of Douchi prepared with the natural koji-making process were significantly better than those of the Douchi prepared with artificial inoculation of A. oryzae.