Preparation Of Corn Stover Hydrolysate With High Concentration Sugars Based On Steam-Explosion Pretreatment And Its Biotransformation For Succinic Acid Production

Succinic acid is a widely used platform compound.The chemical synthesis method in succinic acid is subject to pressure from all sides with the spread of the global energy crisis and the development of low carbon economy mode in China.In recent years,a lot of research pay close attention to biosynthesis method about succinic acid,especially we used fiber hydrolysate as raw materials to produce succinic acid.At present,the strains of Actinobacillus succinogenes ATCC 55618 which attracts huge concern has the most industrial value,but some studies on this strain is mainly concentrated on its metabolism and pure sugar fermentation.There is a little study on use fiber hydrolysate as materials to ferment succinic acid,especially optimizing the fermentation conditions.In this paper,the high concentration of sugar and fermentation conditions about succinic acid was obtained by steam explosion pretreated corn straw.The yield of succinic acid was improved by optimizating the fermentation medium components,combined the single factor with the response surface methodology.In this study,high-concentration sugars were produced from pretreated corn stover by enzymatic hydrolysis and obtained the optimal schemes of enzymolysis,based on fed-batch process.This enzymatic hydrolysis system was added cellulose 20 FPU/g DM and xylanase 200 U/g DM in 2000 ml triangle flask,according to the ratio of 1:8(W/V)with a substrate concentration of 12% dry matter(DM)steam explosion corn stover,under the condition of 4.8±0.2(p H)for 108 h.The reaction vessels were constantly agitated in airbath shaker at 150 rpm and 48?.5.56% solids were fed to the enzymatic hydrolysis at 12 h,24h,36 h,48h and 60 h.After108 h,the final concentrations of reducing sugar,glucose,and xylose reached147.84 g/L,97.74 g/L and 26.84 g/L,respectively.The final total biomass conversion was 56.18% in fed-batch process.Before RSM was applied,the approximate medium composition for cultivation of A.succinogenes was determined by varying one factor at a time while keeping allother factors constant.The medium components(carbon,nitrogen,and metal ions)were selected for maximum succinic acid production for the fermentation.The nutritional factors were optimized by changing one factor at a time and keeping other variables constant.The purpose of using Plackett-Burman design(PBD)was to identify the key medium components for succinic acid production.The optimum point in the optimal range,which used Steepest ascent(SA)design move rapidly towards the neighborhood of the optimum response based on PBD results,was used as the center point for optimization using a central composite design.Box-Behnken design(BBD)are response surface designs especially constructed to require only 3 levels.The levels are formed by combining 2-level factorial designs with incomplete block designs.The experimental data were fitted using a second-order polynomial model equation,which indicated that the concentrations of corn stalk hydrolysate(65 g/L),yeast extract(14 g/L),and Mg CO3(47.3 g/L)resulted in a maximum succinic acid concentration(32.71 g/L).and the average concentration determined by experiment was 32.81±1.42 g/L.The good correlation between the predicted and experimental values after optimization justified the validity of the response model and the existence of an optimum point.The fermentation compositions and concentration of medium was as follow: corn stalk hydrolysate65g/L,yeast extract 14g/L,corn steep liquor(CSL)10 g/L,K2HPO4 3 g/L,KH2PO4 3 g/L,Na Cl 1g/L,Mg Cl2 0.6 g/L,Ca Cl2 0.9g/L,Mg CO3 47.3 g/L.The advantage of this study was used renewable corn straw as raw materials,optimization of fermentation medium for corn stalk hydrolysis.If we can achieve succinic acid in industrialization using this model,it will be able to reduce the dependence on fossil fuels effectively,meanwhile it can reduce the food fight with the situation.The resistant ability of the bacteria about toxic substances was weak,so we hope to increase the resistant ability through domestication and genetic engineering means.