Initial acidity regulates microbial sulfur metabolism in the spontaneous fermentation of sesame flavor-type baijiu

Volatile sulfur compounds play a crucial role in fermented foods, however, their metabolism during spontaneous food fermentation remains underexplored. With 3-(methylthio)-1-propanal as a case, we revealed the effect of initial acidity on the sulfur metabolism during sesame flavor-type baijiu fermentation. Results showed that the content of 3-(methylthio)-1-propanal reached 383.29 μg/kg with 1.8 mmol/10 g of the initial acidity, and it decreased to 320.54 μg/kg when the initial acidity increased to 2.4 mmol/10 g. Metagenomic analysis identified 11 core microbes associated with sulfur metabolism, characterized by gene abundance (> 0.5 %) and catalytic enzyme distribution frequency (> 10 %). Saccharomyces was the main producer of sulfur compounds. Lactobacillus was an important player in the methyl cycle pathway of sulfur metabolism. Low initial acidity increased the abundance of Lactobacillus and the content of genes associated with the methyl cycle pathway (P < 0.05). This resulted in a significant increase of methionine (253.26 mg/kg) (P < 0.05) and 3-(methylthio)-1-propanal contents (383.29 μg/kg) (P < 0.05). In simulated fermentation, the content of 3-(methylthio)-1-propanal significantly increased by 2.91 folds when Saccharomyces cerevisiae was cocultured with Lactobacillus acetotolerans (P < 0.05), and the transcription of genes related to sulfur metabolism significantly increased by 33.71 folds (P < 0.05). Results indicated that low initial acidity increased the abundance of Lactobacillus, which mediates the methyl cycle pathway in the sulfur metabolism, thereby increasing the contents of methionine and volatile sulfur compounds. This work provided insight into the regulation of metabolic mechanisms of volatile sulfur compounds in baijiu fermentation.