Synthesizing Of Dextran By Biology Transforming

Dextran is a kind of polymerization composing by glucose dehydrating,is of innocuity,is the first microbiology polysaccharid produced in industry, is the substitute of blood plama used at first,is used widely in medicament, food and petroleum.In this subject, Leuconostoc mesenteroides 20074 bought from CICC is choosed,preparing dextran by fermenting when sucrose is used as substrate.The culture condition,precipitating condition of dextran in fermenting culture medium, method of measuring molecular weight of dextran and fermenting condition are investigated, research of preparing dextran by immobilizing Leuconostoc mesenteroides 20074 is done primarily.The optimal composition of Leuconostoc mesenteroides 20074 culture medium is: sucrose 10%, peptone 0.2%, Na₂HPO₄ 0.2%, KH₂PO₄ 0.03%, yeast extract 0.5%.The best technology condition: fermenting time of Leuconstoc Mesenteroides 20074 10-12h, transferring content 10%, pH of culture medium 7.0-7.5, culturing temperature 28℃, vibrator speed 50r/min, fermenting time 24h, consistency of substrate 15%, vitamine E and Mn²⁺ is available for dextran forming and content of vitamine E and Mn²⁺ with certain consistency is 8mL/L. The molecular weight of dextran producd by fermenting is more than 400,000 measured by HPGPC, and the IR spectrum of dextran is accordant with the IR spectrum of standard sample.Active carbon is a better carrier,the best technology condition of immobilizing Leuconostoc mesenteroides 20074 on active carbon is: pH of culture 7.1, transferring content 10%,immobilizing time 10-13h, vibrator speed 150r/min,immobilizing temperature 25℃.The molecular weight and structure of dextran is accordant with dextran preparing by fermenting, and the yield rate of dextran decreases.