Abstract:[Objective] This study aims to explore the physicochemical indicators, microbial diversity, and volatile substances in the Qupi (surface) and Quxin (core) of high-temperature Daqu.[Method] High-throughput sequencing and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) were employed to compare the microbial diversity, volatile substances, and physicochemical indicators between Qupi and Quxin of three types of Daqu.[Result] The moisture mass fraction in Qupi of the three types of Daqu was lower than that in Quxin (P<0.05), and the moisture mass fraction was the lowest in the Qupi of white Daqu (WP) and the highest in the Quxin of yellow Daqu (YX). The acidity of Qupi and Quxin were in the order of Quxin of black Daqu (BX) > YX > Qupi of black Daqu (BP) > Quxin of white Daqu (WX) > Qupi of yellow Daqu (YP) > WP. High-throughput sequencing results showed that Firmicutes and Proteobacteria were the dominant bacterial phyla, and Ascomycota was the dominant fungal phylum in Daqu. At the genus level, Pseudomonas_E was the dominant bacterial phyla in BP, BX, and YX; Blastococus was the dominant bacterial phyla in WP; and Scopulibacillus was the dominant bacterial phyla in WX. Thermomyces was the dominant fungal genus in all the samples, while its relative abundance varied among samples. In addition, the microbial diversity in Qupi of Jiangxiangxing high-temperature Daqu was higher than that in Quxin. The redundancy analysis (RDA) results indicated that moisture content and temperature were positively correlated with WP, and YX and BX were positively correlated with acidity. The microbial community structure difference between Qupi and Quxin was mainly attributed to the micro-ecosystem difference. The quantitative analysis results of 76 volatile substances in Qupi and Quxin showed that among esters, the mass fraction of ethyl acetate in WP was relatively high; among aldehydes, the mass fraction of benzaldehyde in BX was relatively high; among acids, isovaleric acid has the highest mass fraction in WX; among pyrazines, tetramethyl pyrazine has the highest mass fraction in WX. The results indicated the mass fractions of volatile substances were different in Qupi and Quxin of different types of Daqu.[Conclusion] This study provides a theoretical foundation for further research on the evolution of microbial communities and the mechanism of volatile substances in Jiangxiangxing high-temperature Daqu.
