Microbial and environmental determinants of 1-propanol biosynthesis in Jiang-flavor Baijiu fermentation

1-Propanol is a crucial flavor compound in Jiang-flavor Baijiu, yet the key microbial pathways and environmental factors controlling its synthesis have not been systematically investigated. Using an integrated approach of metagenomics and culture-dependent techniques, this study identified the key microbes, pathways, and factors controlling 1-propanol synthesis. The highest 1-propanol level was detected in first-round base Baijiu, with rapid accumulation during early pit fermentation. Metagenomics revealed the propanoate pathway as the dominant route, primarily contributed by Limosilactobacillus, while Pichia and Saccharomyces were key providers of pyruvate decarboxylase in the citramalate and threonine pathways. Pure-culture validation confirmed that L. panis MR32 predominantly utilizes 1,2-propanediol as the precursor, while yeasts such as P. kudriavzevii 2J2 and S. cerevisiae LB7A prefer the 2-ketobutyrate pathway. Environmental tests revealed optimal 1-propanol production by L. panis MR32 at pH 5.5 and increasing yields with temperature (25-45 °C). In contrast, most yeasts produced the most 1-propanol at 30 °C, beyond which yields declined, with only P. kudriavzevii 2J2 and I. orientalis IO tolerating high lactic acid. Our findings clarify the microbial division of labor and environmental drivers of 1-propanol formation, enabling targeted fermentation control.