Correlation Between Bacterial Diversity and Flavor Compounds in Hengshui Laobaigan Baijiu

The fermentation cycle critically influences flavor formation in Laobaigan Baijiu, but its effect on the bacterial community–flavor compound correlation remains unclear. This study investigated the co-variation between bacterial community turnover and flavor changes across distinct fermentation rounds of Hengshui Laobaigan Baijiu. Bacterial community structure was characterized via high-throughput sequencing (HTS), while volatile flavor compounds were profiled using headspace solid-phase microextraction combined with gas chromatography–mass spectrometry (HS-SPME–GC–MS). Partial least squares regression (PLSR) revealed their correlation. The analysis revealed 45 volatile compounds in total, with the D-2–D-3 stages serving as the peak production period and stages E-5–E-6 as the key formation period for esters. Lactobacillus dominated the early Dacha (first batch) fermentation, whereas Pseudomonas, Chryseobacterium, and Delftia became dominant after Jiuqu addition in Ercha (second batch). Sphingomonas and Pseudomonas were the major flavor contributors, showing very strong correlations with 9 and 6 compounds, respectively. Sphingomonas was positively correlated with nine compounds (e.g., isoamyl acetate, ethyl pentanoate, acids, benzaldehyde), while Pseudomonas was positively correlated with six esters (e.g., ethyl acetate, ethyl butyrate). Delftia, Pantoea, and Lactobacillus also played important roles in volatile formation. This study establishes a correlation network between bacterial communities and flavor compounds in a multi-round solid-state fermentation system, offering a methodological reference for flavor regulation not only in Laobaigan Baijiu but potentially in other traditional fermented foods with similar batch fermentation processes. This study provides theoretical support for the optimization of Laobaigan Baijiu fermentation and the enhancement of final Baijiu quality.