Abiotic factors modulating metabolic pathways of lactic acid in solid-state fermentation of cereal vinegar

The composition and metabolism of lactic acid bacteria (LAB) is crucial for vinegars fermentation, which are the predominant microorganisms. To reveal the contribution of LAB to Shanxi aged vinegar (SAV) fermentation the metabolic activities of three types of lactic acid pathway, homofermentative, heterofermentative, and facultatively heterofermentative, were simultaneously detected and compared. In particular, the interference from the unviable LAB cells was removed by using PMA-16S rDNA sequencing. The viable to unviable LAB ratio was found to be 1:1.4 during the solid-state fermentation (SSF) of SAV. To investigate LAB and environment interactions, a PMA-qPCR method was developed for quantifying viable LAB and analyzing lactic acid metabolism. During the entire SSF of SAV the main metabolism of lactic acid shifted from facultatively heterofermentative in the early stage to heterofermentative in the mid-stage, then back to facultatively heterofermentative in the late stage. Abiotic factors temperature, ethanol and acetic acid contents had a significant effect on modulating the shift of lactic acid metabolic pathways in SSF of SAV. These findings highlight the complexity of microbial-environment interactions in SSF and underscore the importance of precise environmental control to optimize fermentation processes and enhance vinegar quality. • The viable to unviable LAB ratio was 1:1.4 during the SSF of SAV. • Metabolic activities of three lactic acid pathways were detected and compared. • Ethanol and acetic acid notably affect the lactic acid facultative heterofermentative.