Microbial succession and flavor-related metabolic potential during industrial eight-round mechanized stacking fermentation of Maotai-flavor Baijiu.

Abstract

Mechanized production of Maotai-flavor Baijiu (MFB) is increasingly adopted in the Baijiu industry; however, microbial succession and flavor-related metabolic potential throughout the complete eight-round mechanized stacking fermentation (SF) process remain insufficiently understood. In this study, microbial communities, functional genes, physicochemical properties, and volatile compounds during SF were investigated using metagenomic sequencing and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC/MS). A total of 168 volatile compounds were detected, of which 41 representative compounds were selected for further analysis. Among them, 15 differential volatiles were identified by PLS-DA, with furfural showing the highest abundance. Microbial profiling revealed pronounced community differentiation and continuous succession across fermentation rounds. Acidity, starch, and reducing sugars were significantly associated with microbial community variation, with acidity and starch exhibiting the strongest associations. In the initial round (R1), microbial communities were mainly derived from raw materials and Daqu. Bacterial communities shifted from lactic-acid-bacteria-enriched communities to those characterized by Kroppenstedtia and Bacillus, whereas fungal communities transitioned from yeast-enriched stages to mold-enriched and mold-yeast coexistence stages. Metagenome-inferred functional annotation, co-occurrence network, and correlation analyses suggested potential links between microbial succession and flavor-related metabolic pathways. Yeasts were mainly associated with ethanol- and organic-acid-related metabolism during the early stage, whereas Bacillus and Kroppenstedtia were linked to predicted starch-degradation and organic-acid-related pathways during the middle and late stages. Overall, this study provides a comprehensive characterization of microbial succession and metagenome-inferred flavor-related metabolic potential during mechanized SF and offers reference data for process monitoring and quality management in MFB production.