Optimized Production And Application Of Exopolysaccharides Produced By Lactobacillus Pentosus In Fermented Milks

Some lactic acid bacteria produce exo-polysaccharides on the cell surface to form capsules,or secrete into their surrounding medium.Exopolysaccharides by lactic acid bacteria plays an important role in the rheological properties,consistency and texture,as well as the mouth-feel of the end-products,in addition to biologically activities like suppression of cancer cells,immuno-modulation and cholesterol lowering.The objectives of the present study were to:(1) optimize the production conditions of EPS by Lactobacillus pentosus strains Ind-1 and Ind-3,isolates obtained from a traditional Chinese cheese product collected from Xinjiang Region of China;and(2) to examine.the roles of EPS by two strains in improving the quality of fermented milks.The following are main results:1.For strain Ind-1,the optimized parameters for EPS production were incubation temperature at 30℃,fermentation time of 16h,initial pH of 6.0,5%glucose,glucose vs. lactose of 1:1 as carbon sources,and animal peptone vs.soybean peptone of 1:1 as nitrogen sources.EPS formed by strain Ind-1 reached 346.86mg/L after 16h-incubation at 30℃.For strain Ind-3,the optimal conditions were fermentation temperature at,37℃,fermentation time of 24 h,initial pH at:7.0,4%glucose,glucose vs.maltose of 1:1 used as carbon source,and animal peptone vs.soybean peptone of 1:1 used as nitrogen source,with an EPS yield of 315.86mg/L.2.Combination of isoelectric point and TCA method to remove protein,through ethanol precipitation,dialysis desalting,extraction and preliminary purification of Lactobacillus pentosus EPS is feasible.Using of 20%TCA easily removed the protein interference from fermented liquor,thus increasing EPS yields extracted and decreasing the use of organic solvents in EPS production by L.pentosus strains.EPS yielded by two strains averaged to 1.03%after a primary purification with the help of Sephacryl S-300.3.Application of the two EPS-forming strains to fermented milk improved the water-holding capacity of yoghurt and the survival of beneficial lactic bacteria,and thus significantly lowered whey separation.The amount of whey separated from refrigerated yogurts was only 2.3g/10g after 48h storage.The live cell counts of strains Ind-1 and Ind-3 decreased slowly over a 30-day refrigerated storage at 4℃,but were higher than 10~6 cfu/mL...