Metagenomic analysis of the relationship between microorganisms and flavor development during soy sauce fermentation

Multispecies microbial mixed fermentation is crucial for the formation of flavors in soy sauce. The present study applied metagenomic strategies to uncover the metabolic network for flavors formation in the non-Cantonese soy sauce in China. Twenty-nine major flavor compounds were identified by GC-MS and HPLC, representing the typical flavor compounds of the non-Cantonese soy sauce, including 3 organic acids, 8 amino acids, and 18 volatile compounds. Metagenomic sequencing and KEGG enrichment analysis revealed the specific functional microbiome, which constituted seven major flavor compounds associated genera, namely Leuconostoc, Staphylococcus, Tetragenococcus, Weissella, Aspergillus, Wickerhamycesa, and Zygosaccharomyces. Aspergillus was primarily responsible for the degradation of raw materials in the early fermentation stage, including the degradation of cellulose and lecithin. It also played an irreplaceable role in the formation of 1-octene-3-ol. Weissella, Staphylococcus, and Leuconostoc played essential metabolic roles in the whole fermentation process, particularly in the metabolism of amino acids and the formation of alcohols. Staphylococcus also participated in the degradation of nitrite/nitrate. Tetragenococcus became the dominant bacteria with the highest relative abundance in the late fermentation stage, which was mainly responsible for the synthesis of acetic acid, lactic acid, and other acids. Additionally, Wickerhamycesa and Zygosaccharomyces also contributed to the formation of alcohols, acids, and aldehydes during the late fermentation stage. This study provides a deeper understanding of the diverse roles in the flavor formation of microorganisms during the traditional condiment soy sauce fermentation process.