L-Lactic Acid-Enriched Wheat Bran Qu Containing Bacillus cereus Regulates L-Lactic Acid and Ester Formation in Light-Flavor Baijiu Fermentation

Lactic acid is a key metabolite in Baijiu fermentation and plays an important role in ester formation and overall flavor development. However, D-lactic acid commonly accumulates in Baijiu and often exceeds L-lactic acid, resulting in low L/D ratios that may negatively affect fermentation performance and sensory quality. Therefore, regulating the optical composition of lactic acid is of significant importance. In this study, an L-lactic acid-enriched wheat bran Qu was developed by inoculating Bacillus cereus B12 and applied in light-flavor Baijiu fermentation. The preparation conditions were optimized using single-factor experiments and orthogonal experimental design. The optimal conditions were an inoculation level of 3%, moisture content of 55%, cultivation temperature of 37 °C, and cultivation time of 60 h, under which the microbial biomass reached 2.02 × 1010 CFU/g. The L-lactic acid-enriched wheat bran Qu influenced fermentation characteristics, including substrate utilization and physicochemical parameters. Notably, it significantly increased lactic acid production, particularly L-lactic acid, thereby improving the optical composition of lactic acid. Meanwhile, the concentrations of key ester compounds, including ethyl lactate and ethyl acetate, were significantly enhanced (p < 0.05). Microbial community analysis revealed shifts in bacterial composition with enrichment of lactic acid-related genera. These findings demonstrate that L-lactic acid-enriched wheat bran Qu can regulate lactic acid production and promote ester formation, providing a potential strategy for improving flavor quality in light-flavor Baijiu fermentation.