Overproduction of organic acids affects the microbial community succession and flavor metabolism during Baijiu fermentation

Overproduction of organic acids will negatively affect the quality and output of Baijiu. This study investigated how variations in acid levels affect the microbial community structure and metabolism. The organic acid content of fermented grains ranged from 42.35 to 56.90 g/kg, and the high-acidity group's average levels of citric acid and succinic acid were around 4.60 and 2.70 times higher, respectively, than those of the control group. In high-acidity settings, volatile component concentrations were reduced by nearly two times, as was starch utilization in fermented grains. Mantel test and linear regression analysis revealed that citric acid and succinic acid significantly ( P < 0.05) influenced the microbial community structure of fermented grains, particularly bacterial community, with decreased diversity as acidity increased. The complexity of microbial ecological networks decreased and robustness increased under high acidity stress. Spearman correlation analysis demonstrated that high-acidity environments altered the relationship between microorganisms and flavor substances, indicating that microbial metabolism was affected. Furthermore, in raw Baijiu, the high-acidity group's acids, aldehydes, and ketones were much greater than those in the control, but alcohols and pyrazines were significantly lower. These findings are valuable for improving quality management and solving abnormal fermentation during the Baijiu production process. • High acidity decreased starch utilization and volatile contents. • The high-acidity group had significantly greater levels of succinic and citric acids. • Succinic and citric acids were significantly associated with bacterial succession. • Network complexity reduced and robustness enhanced under high-acidity environments. • High acidity during fermentation significantly altered raw Baijiu flavor compounds.