To explore the effects of fermentation methods on the microbial communities and metabolites in dry fermented mutton sausages, the differences in the microbial communities and metabolites in naturally fermented and starter culture-fermented mutton sausages were analyzed by high-throughput sequencing and metabolomics, and the correlation between microbial communities and significantly differential metabolites (SDM) was investigated. The results showed that inoculated fermentation had obvious effect on the microbial community of mutton sausages. At the genus level, Leuconostoc, Rahnella, Brochothrix and Debaryomyces were dominant during natural fermentation, and Leuconostoc, Brochothrix, Psychrobacter, Pediococcus, Debaryomyces and Penicillium were dominant during inoculated fermentation. Inoculate fermentation increased the types and contents of flavor substances, especially esters and amino acids. Based on multivariate statistical analysis, 29 volatile metabolites and 16 non-volatile metabolites that significantly differed between the natural and inoculated fermentation groups were identified (fold change (FC) > 2, variable importance in the projection (VIP) > 1, P < 0.05). Besides, correlation analysis showed that seven bacterial genera (Leuconostoc, Brochothrix, Pediococcus, Psychrobacter, Enterococcus, Rahnella and Staphylococcus) and seven fungal genera (Debaryomyces, Penicillium, Aspergillus, unspecified_Aspergillaceae, unspecified_Capnodiales, unspecified_Capnodiales, Rhizopus and unspecified_Basidiomycota) were regarded as core microorganisms (| r | > 0.8, P < 0.05).

In this study, the structure and diversity of microbial community in Jiang-flavor Daqu processed using highland barley, purple wheat or pure wheat as raw material under the same conditions were analyzed using the Illumina platform, and intergroup separation was investigated and marker microorganisms were identified by multivariate statistical analysis. The results showed that Ascomycetes, Firmicutes, and Actinomycetes were the absolute dominant phyla in each of the three Daqu samples. The bacterial community in pure wheat Daqu (XMQ) was dominated by the genera Kroppenstedtia, Virgibacillus, Lactobacillus, and Weissella. The bacterial community in purple wheat Daqu (ZMQ) was dominated by the genera Kroppenstedtia, Virgibacillus, uncultured_bacterium_f_Bacillaceae, Bacillus, and Scopulibacillus. The bacterial community in QKQ was dominated by Lactobacillus, Weissella, and Thermoactinomyces. Thermoascus and Debaryomyces were dominant fungal genera in all samples. Meanwhile, Byssochlamys, Monascus, Kazachstania, and Torulaspora were dominant fungal genera in XMQ. Monascus, Aspergillus, and Rasamsonia were dominant fungal genera in ZMQ. Kazachstania, Torulaspora, and Thermomyces were dominant fungal genera in QKQ. In addition, principal component analysis (PCA), hierarchical cluster analysis (HCA), and orthogonal partial least squares discriminant analysis (OPLS-DA) revealed a clear separation between the three Daqu samples, and out of the dominant genera, 10 significantly differential bacterial genera and nine significantly differential fungal genera were obtained by linear discriminant analysis as key biomarkers to discriminate among Daqu produced from different raw materials. The results of this study lay a theoretical foundation for the quality improvement of Jiang-flavor Daqu.

The changes of microbial diversity and volatile flavor compounds in fermented bamboo shoots with chopped pepper during post-ripening were determined by high-throughput sequencing and headspace solid phase micro-extraction (HS-SPME) couple to gas chromatography-mass spectroscopy (GC-MS), and the correlation between them was analyzed. The results showed that Colletotrichum, Penicillium, Xanthomonas, Erwinia, Ralstonia, Pseudomonas, Pediococcus and Enterobacter were dominated in fermented bamboo shoots with chopped pepper during post-ripening. A total of 71 volatile compounds were detected, and the total content of volatile compounds increased from 406.57 to 900.08 μg/kg over the ripening period. The results of principal component analysis (PCA) showed obvious separation between samples at the early and late ripening stages. Based on variable importance in projection (VIP) greater than 1 from orthogonal partial least squares-discriminant analysis (OPLS-DA), 28 important metabolites were identified. The Pearson correlation coefficient showed that bacteria had a greater impact on flavor compounds than fungi, and the dominant bacteria were positively correlated with most flavor substances. This study will provide a theoretical basis for improving the flavor quality of fermented pepper products during post-ripening.