Exploration Of The Germplasm Resources And The Potential Of Probiotics In Fermented Grains Of Fen-Flavor Baijiu

Chinese Fen-flavor Baijiu,as a traditional fermented food,is produced by various microorganisms.There are abundant microbial resources in the fermentation system,and the microbial community structure changes with the fermentation environment during the fermentation process,which makes the microorganisms have good tolerance.Lactic acid bacteria(LAB),yeast and other microbial resources can be used as functional strains.Potential probiotic strains with good physiological characteristics were screened from fermented grains,and their probiotic properties were evaluated in vitro to provide a reference for studying functional microorganisms in fermented grains,especially the development of probiotics.The main research contents are as follows:1.Based on amplicons sequencing,we analyzed the structure and function of microbial communities in Daqu and fermented grains during Fen-flavor Baijiu production.Firmicutes and Ascomycota were the dominant bacteria and fungi in fermented grains.At the genus level,Lactobacillus was the dominant genus in all samples,followed by Pediococcus and Weissella.The primary fungi are yeasts,including Issatchenkia,Candida,and Pichia.At the beginning of fermentation,microbial diversity was highest in fermented grains.As fermentation progressed,the microbial structure in fermented grains tended to be stable.Lactobacillus and Issatchenkia became the dominant genera by inhibiting other bacteria and fungi.2.The microbial composition structures of Daqu and fermented grains at different fermentation stages were constructed based on metagenomic sequencing.The results showed that: Lactic acid bacteria and yeast were the main microorganisms in the fermentation process.At the beginning of fermentation(JP0),the microbial species were similar to Daqu.However,the relative abundance of Lactobacillus was lower than that of Daqu,and the relative abundance of Pichia and Lichtheimia was higher than Daqu.As fermentation progressed,the relative abundance of Lactobacillus,Leuconostoc,and Pediococcus in fermented grains increased and then decreased.The relative abundance of Lactobacillus and Pediococcus reached a maximum at 15 days of fermentation and decreased slightly at the later fermentation stage.Leuconostoc peaked on the seventh day of fermentation and then gradually decreased.The relative abundance of Pichia and Lichtheimia decreased during the early and middle stages of fermentation and increased slightly during the late stage.Saccharomyces showed an increasing trend during the whole fermentation process.In addition,metagenomic sequencing has found that at the species level,Pichia kudriavzevii,Lichtheimia ramosa and Companilactobacillus paralimentarius were the principal strains in the early stage of fermentation.Latilactobacillus curvatus,Loigolactobacillus coryniformis subsp.coryniformis and Lentilactobacillus parabuchneri were the principal strains in the middle stage of fermentation.Lactobacillus＿acetotolerans and Lentilactobacillus parabuchneri were the principal strains in the late stage of fermentation.Spearman correlation analysis showed that lactic acid bacteria inhibited the growth of yeast.The functional annotation found that the critical functions of microorganisms in fermented grains were amino acid metabolism and carbohydrate metabolism.The metabolised carbohydrate enzymes were mainly Glycoside Hydrolases(GH)and Glycosyl Transferases(GT).The three most important functions of protein synthesis by microorganisms are amino acid transport and metabolism,replication,recombination and repair,and carbohydrate transport and metabolism.3.According to the distribution of microorganisms in the sequencing results,29 suspected lactic acid bacteria were screened from the samples of fermented grains by the traditional isolation and culture method.Eleven lactic acid bacteria with good tolerance to the gastrointestinal tract and bile salt were identified by acid resistance,gastrointestinal tract resistance,bile salt resistance tests,and 16 S r DNA sequencing.One strain of Weissella cibaria,one strain of Pediococcus acidilactici,and One strain of Lactiplantibacillus plantarum subsp.plantarum,two strain of Pediococcus pentosaceus,two strains of Levilactobacillus brevis,one strain of Leuconostoc mesenteroides,and three strains of Lentilactobacillus parabuchneri.4.The surface properties(Auto-aggregation,co-aggregation and hydrophobicity),safety(hemolysis and antibiotic sensitivity),antibacterial ability,antioxidant ability and hypoglycemic ability of 11 LAB strains were studied,and the comprehensive evaluation of LAB and its probiotic properties was performed by principal component analysis(PCA).W.cibaria JP001,P.acidilactici JP003,P.pentosaceus JP703,P.pentosaceus JP705 and L.brevis JP718 showed good probiotic properties and high potential,which could be used as potential probiotics for further commercial development.The results also confirmed that fermented grains could be a promising resource bank for probiotics.