Microbial spatiotemporal succession and metabolic difference in multidimensional pit mud used for the production of Luzhou-flavor baijiu

Pit mud (PM) prokaryotic community is essential for the solid-fermentation of Luzhou-flavor baijiu. In this study, the multidimensional (four vertical positions) microbial communities of different PMs were investigated. Microbial communities were significantly different in multidimensional PMs (p = 0.001). Horizontally speaking, the relative abundance of Longilinea at the position 1 (bottom of the cellar) was highest in 30-year PMs (16.19%) and decreased gradually in 100- (11.95%) and 300-year (0.27%) PMs. Methanobrevibacter had the highest relative abundance at the position 3 (up the huangshui fluid) in 100-year PMs (18.98%), and decreased in 300-year PMs (8.73%), at the position 4 (top site of the cellar), Clostridium had the highest abundance in 100-year PMs (8.24%). Vertically speaking, Petrimonas had the highest abundance (17.4%) at the position 3 in 100-year PMs, while for the 300-year PMs, Lactobacillus and Caproiciproducens had the highest abundance at the position 1. RDA analysis indicated that lactic, caproic, butyric, and acetic acids were the four key physicochemical factors. Amino acids, peptides, fatty acids, and conjugates were the main metabolites of PMs, and S-Acetyldihydrolipoamide-E, succinic acid, aspartic acid, asparagine and valine were key differential metabolites. Based on OPLS-DA analysis, 20 differential flavor compounds were identified, mainly including esters such as hexanoic acid methyl ester, ethyl acetate, hexanoic acid ethyl ester, butanoic acid hexyl ester and acids such as hexanoic acid, butanoic acid and heptanoic acid. Moreover, hexanoic, octanoic acid and their corresponding esters were concentrated on 300-year PMs. This study provides theoretical support for improving the quality of PM.