Seasonal influence on the microbial diversity and flavor substances in the strong flavor Daqu fermentation.

Baijiu is highly dependent on open Daqu fermentation, which is easily affected by seasonal fluctuations. This study systematically analyzed winter (WID) and summer (SUD) strong flavor Daqu by integrating physicochemical analysis, microbial community detection, volatile component determination, and metabolomics technology. Results showed SUD had significantly higher starch consumption and acidity than WID, directly attributed to enhanced microbial activity and enzymatic efficiency. Metagenomic studies have identified key enzymes including α-amylase (EC:3.2.1.1) and carboxylic esterase (EC:3.1.1.1), as well as CAZy families such as GH65 and GH73. Based on this finding, the dominant microbes in SUD, such as Lactobacillus, Weissella, and Thermoactinomyces, can not only increase community diversity but also play a promoting role in starch saccharification and ester synthesis. Metabolomics detected 1034 differential metabolites, with SUD enriched in acetic/lactic acids and lipids that are critical flavor precursors. Redundancy analysis confirmed temperature as the core factor driving microbial succession and metabolic pathways. Thermoascus is enriched in high-temperature environments, and the affected metabolic pathways include cofactor biosynthesis and amino acid metabolism. This study clarified seasonal impacts on Daqu quality via microbe-enzyme-metabolite synergy, providing a theoretical and technical basis for stabilizing Baijiu production through microbial regulation and precise fermentation parameter control.