Reduction Of Xylan Inhibition In Enzymatic Hydrolysis Of Cellulose

Biomass is the most abundant and sustainable raw materials for the production of biofuels. However, high cost of the conversion process significantly limits the application of biofuels. Part reason for the uneconomic cost is the complex structure of the lignocellulose materials. In biomass, hemicelluloses and lignin closely associate with cellulose and block the interaction of cellulases and cellulose. In order to overcome the negative effect caused by hemicelluloses in enzymatic hydrolysis of lignocellulosic materials, original location hemicelluloses should be converted into isolated form and degraded to oligosaccharides. However, the isolated xylan and oligosaccharides may inhibit cellulases activities to some extent.In this work, Avicel and corn stover after pretreatment with aqueous ammonia were used as materials, the effects of xylan, the major hemicelluloses in hard wood and annual plants, on the hydrolysis of cellulose by cellulases, especially cellobiohydrolases was investigated. The results indicated that xylan and xylo-oligosaccharides inhibited the hydrolytic efficiency of cellulases, especially cellobiohydrolases. It was found that the end product xylose had a weaker inhibitory effect on cellulose hydrolysis as compared with xylan or xylo-oligosaccharides.Supplementation of xylanase to reduce the inhibitory effects was investigated. It was observed that the addition of endoxylanase and β-xylosidase clearly relieved the inhibitory effect of xylan and xylo-oligosaccharides. In the hydrolysis of Avicel by cellobiohydrolase, the addition of 5 mg/ml xylan and xylo-oligosaccharides decreased the hydrolysis yields from 10% to 1.7% and 4.6%, however, after the addition of endoxylanase and β-xylosidase, the hydrolysis yields clearly increased to 9.1% and 8.4%. Endoxylanase hydrolyzed the xylan that adsorbed onto the surface of cellulose to xylo-oligosaccharides and xylose, and reduced the adsorption of xylan to cellulose, therefore increased the surface of cellulases and cellulose. The addition of β-xylosidase converted xylo-oligosaccharides to less inhibitory xylose, which further decreased the inhibitory effect of xylan.It was found that BSA, Tween 80, and PEG 6000 could increase the hydrolysis efficiency of cellulases, and was the activators of cellobiohydrolases. The addition of the additives reduced the non-specific adsorption of cellobiohydrolase I and endoglucanase II on Avicel and enhanced the hydrolytic action of cellulases. The results indicated that addition of Tween 80 clearly reduced the inhibitory effect of xylan and xylo-oligosaccharides on cellulose hydrolysis, increased the hydrolysis yields of cellulose.The results in this work indicated that optimized the composition of the enzymes had s positive effect in reduction the inhibitory effect of xylan. The results would offer a basic information for the efficient conversion of xylan-containing biomass to fermentable sugars.