Seasonal variations in physicochemical properties, volatile compounds, and microbial community structure of Dajiang fermented using a semi-controlled method

The semi-controlled fermentation method is the primary approach used in the commercial fermentation of Dajiang, where only the Koji is controlled, and no additional control is applied to the fermentation process. As a result, the fermentation of Dajiang is influenced by environmental conditions, exhibiting seasonal differences. This study analyzed the physicochemical properties, volatile compound content, and microbial community structure of Dajiang fermented in different seasons. It was found that Dajiang produced in Summer had significantly higher total free amino acid content, total acid content, and volatile compound levels. Staphylococcus, Tetragenococcus, Aspergillus, Zygosaccharomyces, and Millerozyma were identified as the differential microorganisms in Dajiang across different seasons. However, the relative abundance of Aspergillus was significantly lower in Winter Dajiang compared to other seasons, while the relative abundance of Staphylococcus was significantly lower in Spring and Winter Dajiang compared to other seasons. Temperature and humidity were identified as the primary drivers of seasonal microbial community differences. Additionally, 4-guaiacol and guaiacol were correlated with seasonal changes in microbial community structure, suggesting that these two volatile compounds may have a potential regulatory effect to mediate microbial activity during Dajiang fermentation.