Spatiotemporal dynamics of volatile flavor compounds and associated functional microbial communities during strong-flavor Daqu fermentation.

Daqu, the essential fermentation starter for Baijiu production, harbors stratified microbial communities that orchestrate flavor formation. This study integrated headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), metagenomics, and PacBio full-length 16S rRNA and ITS sequencing to characterize the spatiotemporal heterogeneity of volatile flavor compounds (VFCs) and functional microbial communities across three layers-the surface (QP), middle (HQ), and core (QX) of strong-flavor Daqu over a 90-day fermentation period. A total of 47 VFCs were identified, with alcohols, aldehydes, and esters as the predominant components. VFCs peaked at 2-4 days, then declined and stabilized, showing a progressive accumulation gradient from QP to QX. Aldehydes and pyrazines were enriched in HQ and QX, while esters and acids were highest in QX. Metagenomic analysis demonstrated that the abundance of flavor-related enzyme genes followed spatiotemporal trends of VFCs. Although filamentous fungi and Lactobacillaceae constituted the primary microbial sources of flavor-related enzyme genes across all layers, their community composition and successional dynamics exhibited pronounced spatiotemporal specificity. Positive microbial interactions increased from QP (71.70%) to HQ (76.73%) to QX (89.95%), indicating stronger cooperation in QX. These findings provide mechanistic insights into the ecological underpinnings of flavor stratification in Daqu and offer a scientific framework for future targeted optimization of strong-flavor Baijiu fermentation.