Microbial Community Analysis And Fermentation Characteristics Of Fermented Soya-bean Milk

Fermented soya-bean milk is fermented from mung beans,a characteristic traditional local food in Beijing.But the research of it was still in its infancy.To protect,find out and further use such food resources with traditional local characteristics,this research analyzed the microbial diversity of fermented soya-bean milk in an all-round manner with 16S rDNA sequencing technology;optimized its fermentation technology based on sensory scoring;and studied the characteristics and safety of the related fermentation process by identification of an isolated strain.With such efforts,this paper aimed to further support development and research of this famous traditional snack in Beijing.The main results are as follows:(1)The dominant bacteria in fermented soya-bean milk were studied by 16S rDNA sequencing in six representative fermented soya-bean milk shops in different urban areas of Beijing.The results showed that Lactobacillus was the dominant bacteria in fermented soya-bean milk,and the proportion of Lactobacillales was more than 95.80%.The dominant strains were Weissella cibaria and Lactobacillus sakei.The function of Lactobacillales in fermented soya-bean milk was predicted and analyzed.It was speculated that the flavor substances in fermented soya-bean milk originated from amino acid metabolism.The production of beta-galacto-oligosaccharides and GOS during fermentation was beneficial to the health of intestinal flora.(2)The parameters of fermented soya-bean milk in the fermentation process were screened by response surface test using sensory evaluation as an indicator.In order to overcome the subjectivity and one-sidedness of sensory evaluation which may influence the result,check analysis was further conducted using fuzzy mathematics.The identification of 16S rDNA was conducted on the strain obtained after fermentation of fermented soya-bean milk.The result revealed Enterococcus Faecium isolate could be found in fermented soya-bean milk;the optimum technological parameters of fermented soya-bean milk fermentation were as follows:fermentation for 24 h at 37? with liquid-to-material ratio of 8:1.(3)16S rDNA sequencing technology was used to analyze the microbial diversity of fermented soya-bean milk in different stages of natural fermentation and determine its protein content.The results showed that there was a competitive relationship between Enterobacteriaceae and lactobacilli in the natural fermentation of fermented soya-bean milk.In the early stage of fermentation,Enterobacteriaceae was the dominant genus,while Enterococcus was transformed into the dominant genus;the results of functional prediction analysis were similar to those of fermented soya-bean milk on the market;there was no microorganism capable of producing protein during the fermentation of fermented soy a-bean milk.(4)The features of growth curve,acid-producing capacity,viscosity-producing capacity and stimulated human gastrointestinal tolerance of Enterococcus faecium DZ from fermented soya-bean milk were studied.Its safety was explored using indole test,hemolysis test and nitrate reductase assay,and the safety of its fermented product was further investigated.The results showed that the colony growth of Enterococcus faecium DZ was rapid in 1 h?4 h.It could survive in simulated gastric juice with pH of 3.0,and then enter the intestine for proliferation.The acidity of fermented soya-bean milk by bacterial inoculation for 16 h was 43.69±1.07°T.The acidity of fermented soya-bean milk by bacterial inoculation presented a significant difference(P<0.01).When fermentation for 16 h,the viscosity was 5.50±0.10 mPa·s and its difference was extremely significant(P<0.01).In the exploration of safety,nitrate reductase assay showed negative results.Indole test presented negative results.Hemolysis test showed that Enterococcus faecium DZ was y-hemolysis.The results demonstrate that Enterococcus faecium DZ has the capacity to survive at very low pH,good acid-producing capacity,and certain viscosity-producing capacity;it does not decompose tryptophan,does not hemolyze,and its metabolites does not contain nitrate reductase,which has certain safety.