Enzymatic Preparation,Oxidative Modification Of Low Molecular Weight Dextran And Its Applicability In Iron Chelation

Dextran is a kind of biological polysaccharide formed by the dehydration condensation of glucose.It is widely used in many fields such as food,medicine,chemical industry,sewage treatment and other fields,and plays an important role in these fields.One of the derivatives of dextran,the iron dextran is a kind of iron supplement with high clinical value.Based on the enzymatic preparation and obtaining low molecular weight dextran T5,this subject obtained oxidized dextran through oxidation reaction,and then selected the appropriate oxidized dextran to prepare iron dextran and optimizes the synthesis process.At the same time,the physical and chemical properties of oxidized dextran and iron dextran were studied and analyzed.The research content and analysis results were as follows:1.This subject further optimized the process of producing dextranase from recombinant Pichia pastoris.Then,studied the thermal stability of the enzyme and the process of preparing low molecular weight dextran by enzyme method.The optimal process conditions for producing dextranase were to add 0.25%sorbitol and 0.62%methanol every 24h,and the pH value is 5.08.In the experiment of exploring the influence of incubation temperature on the half-life of dextranase activity,it was found that the temperature condition of 30℃ is more suitable for the long-term catalytic reaction of dextranase.In the experiment to explore the effect of incubation temperature on the half-life of dextranase activity,it was found that the temperature condition of 30℃ was more suitable for the long-term catalytic reaction of dextranase.By studying the effect of substrate concentration,enzyme concentration and reaction time on the catalysis of dextranase to degrade high molecular weight dextran,it was found that excessive substrate concentration was not conducive to this enzyme-catalyzed reaction.The increase of the enzyme concentration accelerated the substrate degradation rate.Although the extension of the reaction time caused the substrate to degrade more,the degradation rate decreased accordingly.The affinity of dextranase for dextran decreased as its molecular weight decreased.The 5%substrate solution plus 7.5U/mL dextranase was reacted for 7h.This reaction system prepared dextran T5 in a relatively short time,and its recovery rate was high.2.NaClO/NaBr and H2O2 were used to oxidize dextran to generate oxidized dextran DOB and DOP,respectively.The research results showed that with the increase of the concentration of the input oxidant,the increase of DOB carboxyl content was greater than that of DOP.Both DOB and DOP degraded slightly,but the degradation degree of DOB was lighter than that of DOP.In a certain oxidant concentration range,the iron(Ⅲ)chelating capacity of DOP(H2O2 4g/100g)was weaker than that of DOB(active chlorine 2g/100g).The oxidation reaction would transform the structure of the crystalline region of dextran to amorphous.The oxidation of DOB mainly occurred at the active hydroxyl group at the C-1 position.The oxidation of DOP would break the bond between C-1 and C-2 after the hydroxyl group at C-1 position was oxidized to carboxyl,and then oxidized the hydroxyl group at the C-2 position to a carboxyl group.3.Through the single factor test,the preparation process of iron dextran(DOBIC)was optimized,and analyzed the physical and chemical properties of DOBIC.The results showed that the optimal conditions for DOBIC complexation reaction was ferric chloride input 20g,pH 9,reaction temperature 90℃,and reaction time 2h.The surface of DOBIC was smoother and firmer than that of the original dextran and DOB.The thermal stability of DOBIC and DOB was better than that of the original dextran.DOBIC had better thermal stability in the temperature range of 30℃-203℃.The complex of DOB and iron(Ⅲ)ions formed an iron core β-FeOOH structure.The hydroxyl and carboxyl groups in DOB participated in the complexation reaction.DOBIC had poor crystallinity and was amorphous.The molecular weight of DOBIC was 70kDa,it was easily soluble in water,and its free iron content was less than 0.2%.