Study On The Preparation、Hydrolysis And Purification Of Dextran

Dextran is a bacterial polysaccharide produced by fermentation by bacteria such as LEUCONOSTOC Mesenteroides and streptococcus mutans.Because of its non-toxic,high viscosity and good water solubility,it is widely used in the fields of medicine,daily chemical industry and oil production,in particular,low,low molecular weight Dextran in the pharmaceutical industry is more commonly used as a substitute for plasma medicine,plasma products such as applications.The traditional production process of Dextran is that sucrose is used as raw material to produce macromolecular Dextran by fermentation of LEUCONOSTOC Mesenteroides,and different molecular weight Dextran are obtained by alcohol precipitation,acid hydrolysis and alcohol precipitation.This paper studies the following aspects:1.Taking Leuconostocmesenteroides CICC-23614 as the producing strain,based on the single factor experiment,the concentrations of sucrose,bacterial peptone,Na₂HPO₄·12H₂Oand KH₂PO₄were taken as the influencing factors,and the sucrose conversion rate was taken as the response value,the composition and concentration of culture medium were optimized by Box-Behnken experiment,and the optimal culture medium was determined by Response Surface Analysis:Sucrose 101.31 g/L,bacterial peptone 5.66 g/L,Na₂HPO₄·12H₂O 1.11 g/L and KH₂PO₄0.15 g/L.Under the optimum fermentation conditions,the experimental results show that the design conditions are accurate and reliable.After fermentation for 24 hours,the sucrose conversion rate reached91.9%,which was 1.6 times as high as that of the original medium.2.Compare the acid hydrolysis and enzymolysis products of Dextran.The structure of the Dextran was analyzed by GPC,FTIR and chemical analysis.The linkage between monomers was-glycosidic bond,in which 91.4%-1→6,6.5%-1→3 and a little-1→2,-1→4were connected.The end products of acid hydrolysis were glucose,and the end products of enzymatic hydrolysis were Dextran and isomaltooligosaccharide.The cell structure was not changed by enzymatic hydrolysis or acid hydrolysis.The loss of Dextran is less than that of enzymatic hydrolysis,and the Molecular Weight Distribution Coefficient is lower than that of Dextran.3.The enzymatic hydrolysis of Dextran was studied and the conditions of enzymatic hydrolysis were optimized.The molecular weight of Dextran produced by the traditional Dextran fermentation process is so large that the glycosidic bond of Dextran is hydrolyzed by acid hydrolysis,thus the molecular weight of Dextran is reduced.In this study,dextranhydrase was added to the solution of Dextran,and the conditions of enzymatic hydrolysis were optimized to obtain the target molecular weight Dextran.The optimal conditions of enzymatic hydrolysis were as follows:Temperature 60℃,PH 5.5,substrate concentration 9%and enzyme concentration 6 U/ml.The effect of enzyme concentration on the molecular weight of Dextran is obvious.The effect of enzyme concentration on the molecular weight of Dextran was obvious.The 40KDa molecular weight of Dextran could be obtained within 60-80 min.The separation and purification of Dextran by ethanol fractionation precipitation and membrane separation were compared.The purification effects of different pore size membrane materials on dextran-containing enzymatic hydrolysate were compared in order to provide data for the development of a better separation and purification technology.The separation and purification effects of ethanol fractionation precipitation and membrane separation were compared for Dextran.The filtrate was filtered by a membrane with a pore size of 100 KDA to remove the bacteria and substances with molecular weight greater than100 KDA.The filtrate was then dialyzed and concentrated by a membrane with a pore size of 30 KDA.The concentrated solution was then spray dried to obtain a solid sample.The average molecular weight of the spray-dried samples was about 40KDa.