Isolation And Identification Of The Lactic Acid Bacteria In Kefir Grains And Study Of The Starter For Yogurt

In recent years,demand for fermented health drinks in china has skyrocketed.And dairy industry has developed rapidly,and then the competition among fermented dairy products is becoming more and more intense.However,most of lactic acid bacteria starters in China rely on import,which is expensive and single variety.Therefore,it has great application value of screening good lactic acid bacteria and developing new fermentation agents with independent intellectual property rights.The kefir grain is very complex and contains many different types and different characteristics of lactic acid bacteria.So it is an important source of high quality lactic acid bacteria.The aim of this study is to isolate and select lactic acid bacteria with excellent fermentation characteristics and suitable for combination from kefir grains and study new fermented starter.And the best fermentation conditions were studied based on single factor experiments and Response surface design(RSD).1?11 strains of Lactobacillus were isolated from one Kefir grains.The phylogenetic tree was constructed using 16S rDNA sequence analysis sequence 11strains which were isolated and 25 strains which were kept in laboratory.In the meantime,The phylogenetic tree was constructed,and strains were identified based on genetic relationship.There were 31 strains of bacillus,including 23 Lactobacillus kefiri strains,5 Lactobacillus paracasei strains,1 Lactobacillus mali strain,and 1Lactobacillus hilgardii strain,1 Lactobacillus ghanensis strain;5 cocci,including 3Leuconostoc mesenteroides strains,and 2 Leuconostoc pseudomesenteroides strains.Lactobacillus mali and Lactobacillus ghanensis have not been reported in studies of kefir grains previously.2?The 36 strains of lactic acid bacteria were screened,including primary screening and secondary screening.After the primary screening,13 strains were obtained which were genetically stable with proper acidity,a high water-holding rate and a good sensory evaluation.Through the secondary screening,one strain of Lactobacillus kefiri,one strain of Lactobacillus casei,and one strain of Leuconostoc mesenteroides can be used for compounding a starter.Among them,the fermentation performance of Lactobacillus kefir E4 performed well in all aspects.The Lactobacillus casei T1 had excellent sensory evaluation and good other fermentation performance.The Leuconostoc mesenteroides A1 had high viscosity and low degree of acidification.so E4,T1 and A1 were selected as complex starter strains.3?The response surface experiment was designed based on the single factor experiment to optimize the fermentation conditions.The four factors were inoculation amount,strain ratio,fermentation temperature and sucrose addition amount.The sensory evaluation score was the response value.The final optimal conditions were:3.92×10~7 CFU/m L inoculum size,bacillus(Lactobacillus kefiri:Lactobacillus casei=1:2):Coccus(Leuconostoc mesenteroides)=1.41:1,fermentation temperature36.57°C,sucrose addition amount 7.02%.The sensory evaluation score of fermented milk prepared under this condition was 82.03.the acidity was 92.76°T,the water retention rate was 72.35%,the viscosity was 1972.4 mPa·s.And the fermented milk had a increase in volatile components compared with the single bacteria fermentation.