Effectively increase the L(+)-isomer proportion of ethyl lactate in Baijiu by isolating and applying L(+)-lactic acid-producing bacteria

Lactic acid (LA) is a significant byproduct in Baijiu fermentation, with both isomers of LA and ethyl lactate (EL) being present in strong-aroma Baijiu . D(-)-isomers cannot be metabolized by humans, and their excessive accumulation can be harmful. This study aims to enhance the proportion of the beneficial L(+)-isomer in Baijiu . We analyzed 106 commercially available strong-aroma Baijiu samples, along with fermented grains ( Zaopei ), yellow water ( Huangshui ), and Baijiu samples from 10 Baijiu factories, confirming the coexistence of D(-)-LA and L(+)-LA in fermentation products. Notably, a strong correlation was found between L(+)-LA in Zaopei and L(+)-EL in Baijiu . Microbial community analysis revealed that Lactobacillus and Bacillus were the dominant bacterial groups, with a succession of microbial communities throughout fermentation. We isolated two strains from Zaopei with high selectivity for L(+)-LA production: Bacillus licheniformis (A6) and Bacillus cereus (B12). Incorporating these strains into both liquid- and solid-state fermentation systems markedly increased the proportion of L(+)-EL relative to total ethyl lactate in Baijiu . This study successfully isolated and applied L(+)-LA-producing strains to fermentation models, offering a practical strategy for increasing L(+)-LA content in Baijiu . • Both isomers of lactate and ethyl lactate were present in strong-aroma Baijiu. • L(+)-isomers of lactic acid and ethyl lactate show a strong correlation. • Two bacteria with high selectivity for L(+)-lactic acid production were isolated. • The strains significantly increase the L(+)-ethyl lactate ratio in Baijiu.