Correlation between Dominant Fungi and Variation of Flavor Compounds during High-salt Liquid-state Soy Sauce Fermentation

The variation of fungal community structure and dominant fungi during the fermentation of high-salt liquid-state soy sauce were studied by high-throughput sequencing on the Illumina MiSeq platform, and the changes of reducing sugars, amino acid nitrogen, total acids and volatile flavor compounds were analyzed. The results showed that a total of 44 fungal genera were obtained in soy sauce samples. The dominant genus was Aspergillus (62.62% to 93.85%) during the first two months of fermentation, which promoted the production of reducing sugars and amino acid nitrogen. The content of amino acid nitrogen exceeded 10.45 g/L after three months of fermentation. The dominant genus was Kodamaea (85.64% to 99.50%) from the 3rd to the 5th month, and Zygosaccharomyces (78.12%) in the 6th month. The contents of reducing sugars, amino acid nitrogen and total acid were 17.73, 10.72 and 21.68 g/L after 6 months of fermentation, respectively. A total of 61 volatile flavor compounds were detected in all samples by gas chromatography-mass spectrometry (GC-MS), and the total content of volatile flavor compounds was 12404.15 μg/L at the end of fermentation. The contents of alcohols and acids as major volatile compounds were 8826.2 and 2349.97 μg/L, respectively. Correlation analysis between the dominant fungi and volatile flavor compounds indicated that Aspergillus was significantly positively correlated with 1-octen-3-ol (P < 0.05). Kodamaea was not significantly correlated with any changes in flavor compounds. Zygosaccharomyces was significantly positively correlated with phenethyl alcohol, 3-methyl-1-butanol, 2-methyl-1-butanol, benzaldehyde, and ethyl acetate (P < 0.05). This study has proved that the variation of fungal community structure and the dominant fungi are important factors affecting the formation of flavor compounds, and constructing beneficial fungal flora is beneficial to improve the quality of soy sauce.