Regulatory Effects of Tannin Supplementation on Microbial Succession and Flavor Formation During Xiaoqu Light-Flavor Baijiu Fermentation

Sorghum tannins have been suggested to influence microbial ecology and flavor formation in Xiaoqu light-flavor Baijiu (XLB), but their specific contribution is difficult to distinguish from confounding, cultivar-dependent variations in macromolecular components. To address this limitation, a controlled fermentation system was established using a uniform, low-tannin substrate. Based on preliminary gradient trials, a 1.0% tannin supplementation level was selected, and high-throughput sequencing combined with HS-SPME-GC-MS was employed to investigate tannin-related microbial and volatile changes. Compared with the group without tannin supplementation, 1.0% tannin supplementation altered bacterial and fungal community succession during the fermentation, reducing the relative abundances of Saccharomyces and Weissella, and enriching taxa including Cyberlindnera and Pantoea. The tannin-supplemented group exhibited a more complex and stable microbial co-occurrence network. Furthermore, PICRUSt2 predictions suggested enhanced metabolic potentials primarily related to carbohydrate and amino acid pathways. FUNGuild analysis further suggested that tannin supplementation shifted fungal trophic-mode composition, particularly saprotrophic and saprotroph-containing groups. At the end of fermentation, total volatile compounds increased from 4.208 μg/g to 4.983 μg/g, total esters and acids increased by 27.0% and 112.3%, respectively, whereas total alcohols decreased by 13.3%. Spearman correlation analysis revealed that the enriched non-Saccharomyces fungi and acid-producing bacteria in the tannin-supplemented group were positively associated with the accumulation of acids and esters, whereas the control microbiota was mainly linked to an alcohol-oriented profile. These findings may provide process-level evidence for tannin-related microbial and volatile changes during XLB fermentation.