Variations in fungal and bacterial microbiome and chemical composition among fermenting Kishu-Narezushi batches.

Kishu-Narezushi is a spontaneously fermented food comprising fish, rice, and salt. During spontaneous fermentation, the microbiome may differ among batches, even when manufactured in the same way. In addition, analyses of changes in the chemical composition of the product are important for clarifying flavor characteristics. We collected basic information on the microbiome and chemical composition of Kishu-Narezushi using multiple batches of fermentation and evaluated whether the microbiome was homogeneous. The fungal microbiome of Kishu-Narezushi was dominated by Saccharomycetales and Trichosporonales. The bacterial microbiome was diverse, although seven specific genera of lactic acid bacteria were identified. Glutamic acid, histidine, and serine levels decreased after ∼10 days of fermentation. Succinic acid, characteristic of Kishu-Narezushi, accumulated upon the consumption of glutamic acid. Though the microbiome was diverse, the chemical composition was similar among the batches.