Studies On Biological Properties Of Dextran-Producing Leuconostoc And Fermentation Condition Of Dextran

In this study, Lactococci separated from milk products in Inner Mongolia were gram-positive, heterofermentature, cell occurring singly, in pairs or in short chains. Dextran formation of lactococci was screened by the formative broth of dextran from sucrose. The biological properties and tolerance of acid and bile salt of strains were studied. The production of dextran was analyzed by phenol-sulphoacid method. Primary fermentational condition of dextran were analyzed by response surface method.According to their characteristics of morphology,physiology and biochemistry, AY1-2-1,AY1-2-2,AY2-5-1,AY2-5-2,QH38-5,QH31-3-2,WZ4-3 were identified to Leuconostoc mesenteroides subsp. dextranicum, DM1-2-1,DM1-2-2 were identified to Leuconostoc mesenteroides subsp. mesenteroides.To study the acid and bile salt tolerance of 9 Leuconostoc mesenteroides strains, the results showed that 9 Leuconostoc mesenteroides strains were able to grow at pH 3～3.5 and had the best antagonistic properties in best salt. AY1-2-1, AY1-2-2, AY2-5-1, AY2-5-2, DM1-2-1, DM1-2-2, WZ4-3 were able to grow in 0.8 % bile salt.The effect of carbon source,nitrogen source and salt on the production of dextran were analyzed. Yeast extract, sucrose, sodium citrate and sodium acetate could remarkably increase the production of dextran. The culture medium of Leuconostoc mesenteroides DM1-2-2 was optimized by orthogonal experiment. The result was as follows: yeast extract 20 g/L, sucrose 200 g/L, sodium citrate 3 g/L and sodium acetate 1 g/L. The yield of dextran was 4.12±0.15 g/L and improved 1.4 fold under the optimum culture medium.The effect of inoculum concentration, incubation temperature and initial pH on dextran produced were studied by single factor analysis. Optimal parameters of the fermenting process of dextran were analyzed by response surface method. The result was as follows: inoculum concentration 3.5 %, incubation temperature 26.0℃, initial pH 8.00. The production of dxtran was 5.76±0.87 g/L under the optimum culture medium and fermenting conditions.Leuc.mesenteroides DM1-2-2 separated from milk products were able to product dextran, and the production of dextran was higher. Therefore, it has more values and potential development.