Comprehensive Utilization Of Sugarcane Bagasse For Preparation Of Xyliooligosaccharides And Cellulosic Ethanol

Sugarcane bagasse (SCB) is an easily available agricultural waste in sugarindustry and contains high content of cellulose and hemicellulose. In order to improvethe additional value of SCB, in this present study, hemicellulose was fractionatedfrom sugarcane bagasse by using NaOH. Subsequetely, the extracted hemicellulosewas used as feedstock to produce xylooligosaccharides (XOS) by enzymatichydrolysis. The NaOH extracted residue was fermented into ethanol by severalfermentation modes by using low loading of cellulase. Utilization of sugarcanebagasse for preparation of XOS and fuel ethanol may increase the additional value ofSCB and further promote the practical value for society.Effects of NaOH concentrations, solid to liquid ratio, and extraction time on therelative yield of xylan were studied. Based on the single factor results, the extractionprocess was optimized by using response surface methods. The optimal conditions forobtaining higher yield of xylan were12%(w/v) sodium hydroxide, solid to liquidratio of2.78:50, and extraction time of5.1h. The maximum yield of xylan was94.5%under the optimal conditions.Xylooligosaccharides were produced from the extracted xylan by usingrecombinant xylanase from engineered Pichia pastoris X33. The effects of enzymeloading, pH, and incubation time on the composition of XOS were investigated. Theresults showed that the main products were xylobiose and xylotriose. Furtheroptimization by using response surface method resulted in the highest yield ofxylobiose of0.59mg/mL with enzyme loading of2.51U/g, incubation time of6.96h,45℃, and pH5.18. The highest yield of xylotriose was0.34mg/mL under optimalconditions which were enzyme loading of2.60U/g, incubation time of6.64h,50℃,and pH6.0.Ethanol was produced from NaOH extracted residue by using different cellulaseloadings. The results showed that higher enzymatic efficiency could be obtained withincreasing cellulase loading. However, increasing initial solid loading depressed theenzymatic convertibility. Under the cellulase loading7.5FPU, the celluloseconvertibility was89.27%and75.06%when the solid loading was1.9%and10%,respectively. However, the glucose yield raised from12.69g/L to55.8g/L. Based onthose results, four fermentation strategies including simultaneous saccharification and fermentation (SSF), Semi-SSF (SS), Fed-batch SSF (FBS), Fed-batch SSF withpresaccharification (FBSP) for ethanol production from NaOH extracted residue athigh solid loading with decreased cellulase loading were investigated. The resultsshowed that increasing initial solid loading reduced the fermentation efficiency. Thefermentation efficiency was74.2%and61.39%with solid loading of14.62%and20%, respctively. The final concentration of ethanol was more than40g/L for all thefermentations and reached the minimum industrial distillation requirment. Asenzymatic hydrolysis of NaOH extracted residue with the lower cellulase loading hadmany advantages including cellulose digestibility, fermentation efficiency, glucoseyield and ethanol yield and so on, it seems that sugarcane bagasse pretreated withsodium hydroxide is a high-efficiency method for comprehensive rational use ofsugarcane bagasse.