Isolation And Key Technology Of Direct-Vat-Set Cultures(DVS) In Higher Yield Of Exopolysaccharide Lactic Acid Bacteria Strains

In this study,the T-RFLP technique and traditional training methods combined with 16 Sr DNA homologous sequences analysis were used to study the lactic acid bacteria diversity which was collected from Xinjiang Minfeng. Use the texture detection measured the fermentation characteristics of separated lactic acid bacteria strains, Phenol-sulfuric acid method was used to detect extracellular polysaccharide contence of fermented milk, the results obtained a yield of extracellular polysaccharide lactic acid bacteria; and then choose the best lyoprotectant and high-density culture conditions optimization for this lactic acid bacteria strain, provide an experimental basis for the development of probiotics and lactic acid bacteria DVS.(1) Diversity of lactobacillusUse T-RFLP technique analyze the four traditional fermented yogurt samples which were collected from Minfeng. The results showed that: In this four samples,(AY188354) Streptococcus subsp.thermophilus and(DQ411813) Enterococcus thailandicus were dominant bacteria.The traditional cultured techniques was used to isolated 54 lactic acid bacteria strain, including 23 Enterococcus faecium strains, 29 Streptococcus subsp.themophilus strains, 1 Lactobacillus paracasei subsp.tolerans strains, 1 Enterococcus thailandicus strains. These results indicate that the dominant bacteria which were obtained by T-RFLP techniques and traditional culture techniques was coincide.(2) Isolation of lactobacillus with higher yield of exopolysaccharideThe lactic acid bacteria strain which was isolated by traditional culture technique was fermented in 9% reconstituted milk. By measuring texture and polysaccharide, the lactic acid bacteria strains of high levels extracellular polysaccharide was selected. According to the results of its texture measurement and polysaccharide, the extracellular polysaccharide production of lactic acid bacteria strains 5-6 and M5-5 was higher than other strains(P <0.05). It can take as the probiotics strains in future.(3) Optimization the condition for high density culture of selected high-yielding exopolysaccharides strainStudy The impact of culture conditions(temperature, inoculum size, initial pH) and medium composition(nitrogen source, carbon source, growth factors) were studied on its growth. The results showed that the optimal growth conditions for the lactic acid bacteria strain were initial pH 6.4, incubation temperature 40 ℃. And inoculum had no significant effect(P>0.05) on lactic acid bacteria biomass. The best component of medium was casein peptone 2.5%, maltose 2%, yeast extract 1.5%. In this medium, the final biomass was 2.40 g / L, 1.86 times higher than before.(4) The selection of the best lyoprotectants for M5-5The effection on cell viability and integrity was studied in different lyoprotectants. The results showed that the bacterial survival rates were: 43.7%, 47.7% and 40.9% when use trehalose, glycerin and skim milk as lyoprotectants(P> 0.05).The bacterial survival rates under other six lyoprotectants is much lower than these three lyoprotectants(P <0.05). The concentration of orthogonal experiment about trehalose, glycerol, skim milk and sodium glutamate were studied, Obtain the best component of lyoprotectant was obtained such as trehalose 6%, sodium glutamate 2%, glycerol 2%, skim milk 15%.