High throughput sequencing of fermented grains
Here, PacBio single-molecule real-time (SMRT) sequencing and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HP-SPME-GC-MS) were applied to investigate the microbial community succession and volatile flavors formation in glutinous/non-glutinous sorghum-based fermented grains during LFB fermentation process. Results showed that the fermented grains made of glutinous sorghum Liangnuo No.1 (GLN samples) had higher moisture content, while fermented grains prepared with non-glutinous red sorghum (NRS samples) exhibited higher acidity, amino acid nitrogen, total free amino acids, and residual starch. GLN samples had higher bacterial alpha diversity and lower fungal alpha diversity than those with NRS samples (p < 0.05). The most dominant microbial species were S. cerevisiae, Acetobacter, and Lactobacillus, the latter two were the preponderant bacteria at the end of fermentation using GLN and NRS, respectively. Moisture content and reducing sugar had a more significant impact on microorganisms in GLN, while amino acid nitrogen, total free amino acids, and residual starch were the main driving factors for the microbial community succession in NRS. The volatile compounds were more abundant in NRS than that in GLN, especially esters. The correlation network and discriminant analysis indicated that 4-vinylguaiacol, which had a higher content in GLN, showed a significant positive association with significant differential microbial species in GLN. Additionally, the microbial species exhibiting strong co-occurrence or co-exclusion relationships were also identified.