Enzyme-driven synthesis and metabolic mechanism of ferulic acid in strong-flavor Daqu: pathway elucidation and microbial drivers.

Ferulic acid (FA) is a bioactive phenolic compound in strong-flavor Baijiu with important health functions. Its microbial synthesis and metabolic mechanisms in strong-flavor Daqu remain unclear, limiting the understanding of its production. This study explored FA synthesis and metabolic dynamics during Daqu fermentation from D0-D90 using physicochemical detection, feruloyl esterases (FAEs) activity assay, and metagenomic sequencing. Results indicated that FA content fluctuated dynamically throughout fermentation, reaching a final level of 4.39 ± 0.17 mg/kg, and FAEs activity was significantly positively correlated with FA content. Genera significantly associated with FA dynamics were identified. High-abundance genera including Lichtheimia, Saccharopolyspora, Aspergillus, Byssochlamys and Rasamsonia exhibited significantly positive correlations with FA accumulation at respective fermentation stages. This phenomenon may be attributed to their capacity to secrete FAEs, thereby promoting the release of FA. The dynamic change of free FA content was also associated with the expression of ferulic acid decarboxylase, a key enzyme potentially involved in free FA degradation. A comprehensive FA metabolic network in Daqu was constructed, including the cell wall release pathway and the shikimate biosynthesis pathway. A metabolic association model was established based on the phasic succession of fungal and bacterial communities and their coupling with FA metabolic enzyme systems, which suggested a potential division of labor. Fungi are likely to participate in free FA release through secretion of FAEs and auxiliary degrading enzymes, while bacteria may mainly participate in the metabolic turnover and consumption of free FA. This study expands the current understanding of phenolic acid metabolism in strong-flavor Daqu, and provides a theoretical basis for interpreting FA metabolic characteristics during Daqu fermentation.