Analysis Of Intestinal Bacterial Diversity Of Young People In Yinchuan And Enshi And Application Of Lactic Acid Bacteria In Fermented Milk

Intestinal flora has a far-reaching influence on human metabolism and health.Therefore,the establishment of intestinal microecology is essential for human health.Lactic acid bacteria is an important probiotic in the human intestine,and also the main starter for preparing fermented milk.Fermented milk prepared by different lactic acid bacteria has different flavors and tastes,so it is especially important to screen lactic acid bacteria strains with excellent fermentation quality.In this study,27 young volunteers,aged 17-22,with BMI value of 19-24,were recruited from a university in Yinchuan City,Ningxia Hui Autonomous Region and a university in Enshi Tujia and Miao Autonomous Prefecture,Hubei Province,who were in good health and did not take probiotics or any drugs for two weeks before sampling,and their intestinal bacterial diversity and differences were analyzed,and the lactic acid bacteria in the intestinal tract of adolescents in two regions were isolated and identified,and then the lactic acid bacteria strains that can be used for food were screened out to prepare fermented milk.According to the physical and chemical indexes,the number of lactic acid bacteria,flavor characteristics and taste characteristics,the quality of fermented milk was evaluated,and the lactic acid bacteria strains with excellent fermentation quality were screened out,and then they were mixed with commercial starters to study their fermentation characteristics during the storage.The concrete research results are as follows:1.Illumina MiSeq high-throughput sequencing technique was used to explore the diversity and differences of intestinal bacteria among young people in Yinchuan,Ningxia and Enshi,Hubei areas in this study.The results showed that the dominant bacteria genera in young people’s intestines in two areas were Bacteroides(20.08%),Prevotella(19.09%),Faecalibacterium(6.13%),Roseburia(5.41%)and Megamonas(5.33%).There are significant differences in the abundance of four bacterial genera.The abundance of Alistipes and Phascolarctobacterium in the intestines of young people in Enshi is higher,and the abundance of Megamonas and Clostridium in young people in Yinchuan is higher.The intestinal bacteria of young people in the two places have high functions such as carbohydrate transport and metabolism,replication,recombination and repair,translation,ribosome structure and biogenesis,cell wall/membrane/envelope biogenesis,etc.,while the tolerance of intestinal bacteria in Yinchuan is obviously higher than that in Enshi(P<0.05).2.171 strains of lactic acid bacteria were isolated from young people’s intestines in Yinchuan,Ningxia and Enshi,Hubei areas by pure culture in this study.They belong to Enterococcus,Lactobacillus,Limosilactobacillu,Ligilactobacillus,Lactiplantibacillus,Leuconostoc,Lactococcus,Pediococcus,Streptococcus and Weissella.23 strains of lactic acid bacteria which can be used in food were selected to prepare fermented milk,and their quality was analyzed.It was found that there were significant differences in viscosity,apparent viscosity,aroma compounds,nitrogen oxides,terpenes,sour taste,astringency and salty taste,among which the fermented milk prepared by strain L.plantarum YC8-8 had higher content of aromatic substances and more prominent flavor.3.The fermentation characteristics of L.plantarum YC8-8 mixed with commercial starter were analyzed.It was found that L.plantarum YC8-8 could increase the acidity,the number of lactic acid bacteria,viscosity,hardness,consistency,cohesiveness and apparent viscosity of fermented milk,and reduce the dehydration shrinkage sensitivity and pH value of fermented milk.During storage at 4℃ for 28 d,the number of viable lactic acid bacteria in fermented milk samples was all more than 107 cfu/g.During storage,the flavor differences of fermented milk samples prepared by the compound fermentation of L.plantarum YC8-8 with commercial starter and the single fermentation of commercial starter are mainly reflected in terpenoids.The flavor quality of fermented milk samples fermented by L.plantarum YC8-8 and commercial starter was the best after 14 d storage.