Comparative characterization of physicochemical properties, microbial communities, and volatile flavor compounds during the fermentation of high-temperature Daqu produced from two different wheat raw materials.

Soft wheat (Sy) and mixed wheat (My; a 7:3 blend of soft and hard wheat) are used to produce high-temperature Daqu (HTD) for reducing production costs in certain baijiu enterprises. However, the differences between single-wheat HTD (S-HTD) and mixed-wheat HTD (M-HTD) remain unclear. This study aimed to compare the physicochemical properties, microbial succession, and flavor metabolism during fermentation of HTD produced from two different wheat raw materials. Although all monitored properties followed the same trends, differences existed between the two types of HTD during fermentation. At the end of fermentation, M-HTD had higher relative contents of key aroma contributors, such as pyrazines, esters, and acids. Metagenomic sequencing revealed Bacillus, Saccharopolyspora, and Kroppenstedtia (bacteria) and Aspergillus, Lichtheimia, Paecilomyces, and Monascus (fungi) as the dominant genera. Different HTD exhibited distinct patterns of microbial relative abundance during fermentation. The correlations of dominant microorganisms with differential flavor compounds were also illustrated. Moreover, microbial functional prediction revealed a higher relative abundance of many enzymes related to flavor production in M-HTD. Gene function prediction also confirmed immense potential for metabolism in M-HTD. These results indicated that HTD produced from the mixed wheat was associated with higher relative contents of key flavor compounds. Our findings may help enterprises select wheat raw materials and provide a theoretical basis for promoting the high-quality production of HTD.