Effects of pit mud on the spatial heterogeneity of bacterial communities and volatile metabolites in Jiupei: Insights from volatile metabolomics and microbial community analysis

The spatial heterogeneity of microbial communities and metabolites within fermentation cellars plays a critical role in determining the quality of Nongxiangxing Baijiu (NX-Baijiu), yet remains insufficiently understood. To address this, we systematically characterized the spatial dynamics of microbial communities and their metabolic functions in the NX-Baijiu fermentation system by comparing pit mud (PM) and Jiupei (JP) from new and old cellars. Samples were collected from 1-year and 10-year cellars across multiple vertical and horizontal positions. Physicochemical properties, organic acids, volatile organic compounds (VOCs), and bacterial communities were systematically analyzed. The results demonstrated that cellar age exerted a stronger effect than spatial position on physicochemical properties and microbial composition. Old PM exhibited higher nutrient levels, greater microbial diversity, and more pronounced spatial heterogeneity than new PM. A clear spatial gradient was observed in JP, with microbial diversity, organic acids, and VOCs varying with distance from PM. Notably, Lactobacillus acetotolerans and Acetilactobacillus jinshanensis dominated JP, showing opposite distribution trends along the PM distance gradient. VOC analysis revealed that esters were the predominant compounds in all samples, while acids contributed more significantly in old cellars. Partial least squares path modeling (PLS-PM) analysis indicated that the spatial distribution of VOCs in JP may be associated with PM physicochemical properties and microbial community structure. Overall, this study suggests that PM is associated with the spatial heterogeneity of microbial communities and metabolites in JP, ultimately shaping flavor formation in NX-Baijiu. These findings provide new insights into the microecological patterns and potential mechanisms of Baijiu fermentation and offer a theoretical basis for improving product quality through targeted regulation of cellar environments.