Microbial Diversity And Optimization Of Production Technology Of Fermented Milk

Traditional fermented milk contains a variety of beneficial microorganisms such as lactic acid bacteria and yeasts.It is important to study the microbial community structure of traditional fermented milk,to clarify the interaction of different microorganisms in the fermentation process,to reveal the flavor function and physiological activity of microbial strains,which is of great significance for exploring microbial resources and promoting the industrial production and standardization of traditional fermented milk.In this study,samples of four fermented milk,Eedem(ED),Tarag(TR),Airag(AR),and Chige(CG),were collected from Xilin Gol,Inner Mongolia,and the microbial community structure and diversity of different fermented milk were determined by high-throughput sequencing.The results showed that the lactic acid bacteria strains with potential prebiotics were isolated and identified by acid and salt resistance.The fermentation characteristics of lactic acid bacteria were analyzed.And yeast strains were obtained by using lactose to obtain ethanol and identified by culture method.On the basis of this,the fermentation conditions of fermented milk were optimized by the combination fermentation of lactic acid bacteria and yeast,and metabolites and sensory tests as indicators.The results of the study are as follows:1.Microbial diversity of traditional fermented milk in Inner Mongolia(1)Bacterial diversity of traditional fermented milk in Inner Mongolia.The bacterial diversity of AR and CG in fermented milk samples was higher than that of fermented milk samples ED and TR,and the bacterial colony structure of ED samples and TR samples was compared single.The dominant species in the four samples were lactic acid bacteria,and the lactic acid bacteria of Lactobacillus were the dominant species in samples AR,CG and TR,and their abundance accounted for 60%,90%and 50%respectively.While the dominant species in the sample ED is Streptococcus,which accounts for more than 50%abundance and Lactobacillus is the least.Streptococcus also occupies a considerable proportion of the sample TR,close to 50%.In addition,other lactic acid bacteria,such as Leuconostoc,Enterococcus and Melissocossus,were also detected in the four fermented milk samples,but the abundance of these species in the sample was small.The diversity of fungi in traditional fermented milk of Inner Mongolia was higher than that of samples ED and CG,and the distribution of microbes was relatively uniform.The accuracy of the fungal sequence is not as good as that of bacteria.The dominant fungi in the sample CG are 70%of the species that are not identified,and the abundance of Kazachstania is more than 10%.The dominant species in the sample AR were Saccharomycetales(20%),and the abundance of Trichosporon and Issatchenkia were abOTU 20%and 10%,respectively.The dominant bacteria in the sample ED were Saccharomycetales,with an abundance of abOTU 80%.TR in the dominant bacteria for the classification of the location of the Incertae sedis(nearly 20%),not identified to belong to the Archaeorhizomycetaceae(abOTU 10%).2.Screening of probiotics in traditional fermented milk of InnerIn this study,800 strains of lactic acid bacteria were isolated from four kinds of fermented milk samples(AR,TR,CG,ED),and the fermentation of milk was carried OTU.The results showed that the lactic acid bacteria with good probiotic properties and good milk fermentation performance were screened The The isolates were identified by 16S rRNA gene homology analysis.The results showed that the acid-resistant and bile salts were isolated from the CG samples,and the acid-resistant and bile salts were isolated from the Lactobacillus diolivorans,Enterococcus durans,Acetobacter,Lactobacillus kefiri,Lactococcus,Lactis and AR samples.Lactococcus Lactis was isolated from Acetobacter pasteurianus,Lactobacillus paracasei and ED samples of fermented milk candidate strains and was resistant to bile salts and could be used for fermented milk candidate strains.3.Screening of Ethanol Fermentation Yeast in Traditional Fermented Milk of InnerThrough the pure culture method,6 yeast strains which can utilize lactose were screened from the samples of traditional fermented dairy products in Inner Mongolia,and the fermentation experiments were carried OTU with the fermentation experiments with lactic acid bacteria.The comprehensive metabolites were analyzed and the sensory evaluation was carried OTU.Ethanol and fermented milk sensory effect of good yeast strain CG-30-3.The morphological characteristics,physiological and biochemical characteristics,ecological characteristics and genetic characteristics of the isolated yeast were determined.The classification attributes were Kluyveromyces and named Kluyveromyces sp.CG-30-3.4.Study on the Production Technology of Fermented MilkIn this study,the combination of two kinds of lactic acid bacteria(Lactobacillus delbrueckii subsp.Bulgaricus KJ101,Streptococcus thermophiles KP220)and one yeast(Kluyveromyces sp.CG-30-3)was determined by pre-experiment.Firstly,the main factors affecting the fermentation process and sensory effect of fermented milk were determined by single factor experiment:inoculation amount,lactose concentration,lactose concentration,fermentation time and fermentation temperature.The optimal fermentation conditions of fermented milk were determined by orthogonal experiment design,such as pH value,lactose residue,ethanol concentration and sensory evaluation score of fermented milk.The content of lactose was 72 g/L,inoculation ratio of 1:1,inoculation amount of 107 cfu/mL,culture time 36h,temperature at 30 ℃,shaking speed 100rpm.Under the optimized fermentation conditions,the fermented milk was obtained with a new lactic acid content of 8.71g/L(pH value 3.91),ethanol concentration of 28.81g/L and good taste.