Abstract:Wheat ground to different degrees was fermented in high-temperature Daqu (HT-Daqu) to evaluate the effects of grinding on fermentation and the maturity ratio. After fermentation, the microbial community structures and functional characteristics of three categories (black, yellow, and white) of HT-Daqu were analyzed via metagenomic sequencing. The temperature of the low-grinding-degree group reached 60 ℃ in the shortest time, with time gaps observed in three temperature rises with no prolonged overheating. Yellow Daqu accounted for 82.37% of the mature Daqu in this group, which was the highest ratio among the three groups with different grinding degrees. The total relative abundance of major bacteria in black and yellow Daqu of the high-grinding-degree group was more than 28.95%, which was higher than that in the other two groups. Aspergillus, Rasamsonia, Paecilomyces, and Talaromyces dominated the microbial community in the medium- and low-grinding-degree groups, accounting for more than 73.95% of the total, significantly higher than the highgrinding-degree group. The genes of glycoside hydrolases in black and yellow Daqu were mainly contributed by Eurotiales including Rasamsonia, Aspergillus, and Paecilomyces (46.78%~62.33%), while those in white Daqu were found to be mainly derived from Saccharopolyspora. These results demonstrate the importance of the grinding degree of wheat on the quality of Daqu and identifies the microbial sources of genes encoding different carbohydrate-active enzymes. The findings have a practical significance for understanding the fermentation of HT-Daqu comprehensively and guiding the production of HTDaqu scientifically.
