Analysis of microbial diversity and volatile metabolites across different types of pit mud in sauce-flavored Baijiu based on nanopore sequencing and metabolomics

Abstract

The quality of Jiaomian liquor and Jiaodi liquor in sauce-flavored Baijiu is closely related to pit mud. However, little is known about the pit mud of sauce-flavored Baijiu. This study aimed to investigate the microbiota and volatile compounds in different types of pit mud using nanopore sequencing, digital PCR, and headspace-solid-phase microextraction-gas chromatography-mass spectrometry. The results revealed that bacterial biomass exceeded fungal biomass. The predominant bacteria in new sealing pit mud (NPM) and high-quality sealing pit mud (HPM) were Rhodopseudomonas, Bradyrhizobium, and unclassified_f_Bradyrhizobiaceae. The major fungi in NPM included Colletotrichum and Malassezia, whereas HPM mainly contained Fusarium, Pochonia, Aspergillus, and Talaromyces. Medium-quality sealing pit mud (MPM) and bottom pit mud (BPM) were dominated by Clostridium, Bacillus, unclassified_f_Ruminococcaceae, Aspergillus, and Talaromyces. Acinetobacter and Sugiyamaella predominated in low-quality sealing pit mud (LPM). Hexanoic acid and ethyl hexanoate were the main aroma components, showing the highest contents in MPM and BPM. Ethyl octanoate, 3-methylindole, and p-cresol also significantly contributed to the flavor. Furthermore, the microflora was influenced by urease, AK, AP, AAN, and TC, and the correlations between microbes and volatile flavors were explored. These findings provide valuable insights for improving the quality of pit mud and enhancing the flavor of sauce-flavored Baijiu.