Dynamics of the microbiome and volatile organic compounds during fermentation and aging of soy sauce

A comprehensive analysis of the microbiome and volatile organic compounds (VOC) in the moromi of soy sauce during fermentation and aging was conducted under industrial production. Microbiome analysis using next-generation sequencing revealed the presence and dynamics of microorganisms other than Aspergillus, Tetragenococcus, Zygosaccharomyces, and Wickerhamiella, which were used as starters. The bacterial community of the moromi on the first day of this process was rich in diversity. Staphylococcus, Bacillus, Kurthia, Acinetobacter, Enterococcus, and Macrococcus that grew during koji making were relatively dominant. However, as the fermentation progressed, only Tetragenococcus became dominant in the bacterial communities. In contrast, the fungal community was simple at the beginning of fermentation and aging, with Aspergillus present almost exclusively. After adding Zygosaccharomyces rouxii on day 42, the fungal community changed significantly. At the end of fermentation and aging, the fungal community diversified, with Millerozyma, Wickerhamiella, Yamadazyma, and Saccharomycopsis becoming dominant. The analysis of VOC showed that the VOC profile changed during fermentation and aging, and that the VOC profile changed significantly after adding Z. rouxii. The correlation analysis between the microbiome and VOC showed that Wickerhamiella, Millerozyma, Debaryomyces, Yamadazyma, and Candida had a significant positive correlation with alcohols, esters, and phenols produced in the later stage of fermentation and aging, indicating that not only Z. rouxii but also various fungi may contribute to the formation of the complex aroma profile of soy sauce.