Abstract
Daqu is an important saccharifying starter in the fermentation of Nongxiangxing Baijiu in China. Vanillin is a health and flavor factor in Baijiu. However, only a few research studies on the vanillin content of Daqu are currently not systematic. In order to investigate the metabolic mechanism of vanillin in the fermentation process of Daqu, we analyzed the changes in microorganisms, influencing factors, and enzymes related to vanillin in Daqu. This research found that there were differences between bacterial and fungal genera in each sample, and the abundance of bacteria was greater than that of fungi. Among the microbial genera, Klebsiella, Escherichia, Acinetobacter, Saccharopolyspora, Aerococcus, and Puccinia were positively correlated with vanillin. Meanwhile, we also found that moisture and reducing sugar were the main physicochemical factors affecting the formation of vanillin. The functional annotation results indicate that carbohydrate metabolism and energy metabolism were important microbial metabolic pathways that impacted vanillin production in solid-state fermentation. The feruloyl-CoA hydratase/lyase (EC 4.1.2.61) and acylamidase (EC 3.5.1.4) were positively correlated with vanillin content (p ≤ 0.05) and promote the increase in vanillin content. These findings contribute to furthering our understanding of the functional microorganisms, physicochemical factors, and enzymes related to the change in vanillin content during the fermentation of Daqu and can help to further explore the flavor substances in Baijiu fermentation in the future.