Screening Of High Exopolysacchrides-producing Lactic Acid Bacteria And Studied Optimization Of Medium

Lactic acid bacterium exopolysaccharides is produced with Lactic acid bacteria growing and penetrates into culture medium.It is amylose compound of sub-metabolism and divided into capsule and mucus amylose.The molecular weight of exopolysaccharides is between 4.0×104 and 6.0×106Da.Lact acid bacteria exopolysaccharides has some characteristics of enhancing yoghurt viscosity and rheology,prohibiting whey loss,improving yoghurt taste and increasing clabber intensity.It is very meaning of theory and practice to studying LAB EPS.twelve strains were obtained bysceening, isolate and identify Lactic acid bacterium from yoghurt and sauerkraut from market.Based on results of the characteristics of morphology,physiology and biochemistry,sugar fermentation,we were ascribed to 2 genus of Lactobacillus,Lactococcus,containing with 5 species. according to Bergy's bacterial identification manual and classified identification of lactic acid bacterium.(2 strains are Lactobacillus delbrueckii subsp.bulgaricus,3 strains are Lactobacillus acidophilus,3 strains are Lactobacillus plantarum);( strains are S. thermophilus,1 strain is Lc. Lactis subsp. Cremoris.)By using the method of Phenol-H2SO4 to detect the amount of exopolysaccharides in culture medium,as well as the viscosity of the medium,we screening out of a higher yield of extracellular polysaccharide strains, namely G1 Test for medium optimization.We studied the carbon, nitrogen, carbon and nitrogen ratio in the medium to influencing the yield of exopolysaccarides of G1 When we optimizate the medium. The strains have a highest yield of EPS about 116.58mg/L , viscosity about 230mPa.s when glucose as the carbon source; the strain Lactobacillus bulgaricus maximum viscosity of fermentation medium about 227.34mPa.s when tryptone as a nitrogen source,as well as the conten of EPS attaint 114.6mg/L; the strains of Lactobacillus bulgaricus extracellular polysaccharide production in the highest, up to 117.24mg / L , viscosity about 213.6mPa.s when Carbon and nitrogen ratio is 3:1.We deployed orthogonal experiment to optimizing the influencing factor of EPS production include temperature,incubation time,initial pH vavule and the amount of glucose in the medium,and to determine the impact of major factors.Result showed: it is the best fermentation conditions for the Lactobacillus bulgaricus to producing EPS that cultivate temperature is 40℃, fermentation 17 hours, the initial pH 6.0, 3% of its adding glucose,a yield of EPS about138.76mg/L ;cultivate temperature is the most impact to producing EPS of Lactobacillus bulgaricus,followed by culturetime,while the amount of glucose had the least impact to yield of EPS.In order to avoid the interaction of cultivate temperature ,time and initial pH,we used Box-Behnken design and response surface analysis to optimization the cultivation condition.The result indicates that temperature cultivate 39.1℃, culture time 14.2h, the initial pH value of 6.9,the yield of EPS of Lactobacillus delbrueckii subsp.bulgaricus is 154.25mg/L ,the yield of EPS elevate 11.2% after optimization.