Effect of storage process on the quality of Strong-flavor Daqu

Daqu is an important saccharification initiator in Chinese baijiu production, which includes a wealth of enzymes and microorganisms. The quality of Daqu affects the yield and quality of liquor fermentation to a certain extent. Although there have been extensive studies on microorganisms, physicochemicals, and enzymology in Daqu, the dynamics of microbial communities and physicochemical enzymes during the storage period of Strong -flavor Daqu are unknown. To address this gap, we performed physical and chemical and enzymatic tests on the samples of two kinds of Strong-flavor Daqu during the storage period of 8 months, and studied the changes of microbial community during storage by high-throughput sequencing. The results showed that the values of moisture and starch did not change much during storage. The saccharifing activity of traditional Daqu during storage is higher than that of mechanical Daqu, and the esterifying activity of mechanical Daqu is generally higher than that of traditional Daqu. A total of 16 dominant microorganisms were found in two kinds of Daqu: Citrobacter, Weissella, Lactobacillus, Pediococcus, Staphylococcus, Pseudomonas, Acinetobacter, Acetobacter, Bacillus, Pantoea, Lactococcus, Staphylococcus, Corynebacterium, Pichia, Thermoascus, Rhizopus, Aspergillus, Wickerhamomyces, unclassified_Dipodascaceae, Rasamsonia, unclassified_Saccharomycetales and Clavispora. Among them, Weissella, Lactobacillus, Pediococcus, Bacillus and Acetobacter were the common bacterial microorganisms in the two Daqu. Citrobacter dominated the first 6 months of the mechanical Daqu storage period, while Lactobacillus and Weissella were the traditional Daqu which were the leading prokaryotes during storage. Pichia and Thermoascus were the two major eukaryotes in Daqu. Interestingly, the relative abundance of Rhizopus and Aspergillus was higher in the mechanical Daqu while the unclassified_Saccharomycetales in traditional Daqu. Rasamsonia was a peculiar eukaryotic genus in the traditional Daqu. In general, the traditional Daqu presented a more stable microbial succession than the mechanical Daqu. The different trends of the physiochemical and enzymatic indexes of the two Daqu marked the time difference between the maturation time and the quality degradation of the two Daqu.