Hydrothermal Treatment Of Bamboo (Dendrocalamus Giganteus Munro) For The Production Of Xylo-Oligosaccharides And Their Enzymatic Hydrolysis

Bamboo,a carbohydrate-rich grass plant with enormous potential for industrial applications,is widely distributed in tropical and subtropical areas.It attracts much attention as biomass due to the advantages of rapid growth,good performance,huge production and rich resources.Xylo-oligosaccharides(XOS)derived from carbohydrate-rich lignocellulose show wide applications in chemical,food,nutraceutical and pharmaceutical industries.Bamboo is mainly composed of three carbon-based natural polymers:cellulose,hemicelluloses and lignin,which are tightly bonded by chemical and physical interactions.In order to provide a technical support and a theoretical basis for the high-value use,bamboo was hydrothermally treated with water to generate xylo-oligosaccharides,and the solid residues obtained by hydrothermal pretreatment were further hydrolyzed by enzyme to produce glucose.Bamboo culm(Dendrocalamus giganteus Munro)was treated with hot water in non-isothermal conditions(140,160,180 and 200℃)for various reaction times(10,30,60 and 120 min)to generate xylo-oligosaccharides in a batch reactor at a solid to liquor ratio of 1:10 g/g.After the treatment,the influence of reaction conditions on yields,compositions and characteristics of the products were evaluated.The maximum yield of xylo-oligosaccharides of 47.49%was achieved at 180℃ for 30 min with a relatively low level of xylose(4.73%)and other products(arabinose 0.20 g/L,galactose 0.19 g/L,HMF 0.15 g/L,furfural 0.36 g/L,acetic acid 0.64 g/L and formic acid 0.26 g/L).The degree of polymerization(DP)of xylo-oligosaccharides depended on the temperature and time.The maximum yield of xylo-oligosaccharides was obtained with 11.19%xylobiose,8.12%xylotriose,7.46%xylotetraose,13.58%xylopentaose,5.56%xylohexaose and 54.09%high-DP xylo-oligosacch arides(DP>6).Higher temperature and/or longer reaction time reduced the yield of oligosaccharides,produced more low-DP xylo-oligosaccharides,and enhanced concentrations of monosaccharides and byproducts.The result demonstrated that the yield of xylo-oligosaccharides obtained by hydrothermal treatment depends on the reaction temperature and time.The solid residues were oven dried and analyzed after the hydrothermal treatment to investigate the effects of pretreatment conditions on the degradation of carbohydrates,cellulose crystallinity,partial removal/relocation of lignin,morphologic change of the feedstock,and glucose yield during the enzymatic hydrolysis were investigated.The effective removal of amorphous cellulose and hemicelluloses led to the increase of crystalline index of the residues.In comparison with the raw material,the surface of the pretreated samples was irregular and numerous lignin droplets appeared on the cellulose bundle surface under the intense pretreatment conditions.Commercial cellulase was employed at the activity of 14.5 FPU/g substrate for all samples.The glucose conversion increased with the raise of pretreatment temperature and the prolongation of time,and the maximum conversion of 75.7%was achieved for the sample pretreated at 200℃ for 120 min,whereas the untreated sample was only 15.7%.The result illustrated that hydrothermal pretreatment affected the composition of bamboo,and remarkably enhanced the enzymatic hydrolysis efficiency.