Coproduction Of Fermentable Saccharides By The Synergistic Hydrolysis Of Spartina Using Xylan-degrading Enzymes And Cellulase

Cellulose,hemicellulose and lignin are three main components in lignocellulosic biomass.Delignification and hydrolysis of cellulose and hemicellulose to monosacchrides(glucose and xylose)or high value-added products(xylooligosaccharide,arabinose,ferulic acid etc.)is of great significance for biological utilization of lignocellulosic biomass.At present,accessibility of hemicellulase to substrate is low because of structural barrier of cellulose and lignin,and which imposes restrictions on the conversion of hemicelluloses to xylooligosaccharide and xylose effectively.In this paper,alkali pretreatment is used to delignify,then hydrolyzing pretreated spartina using recombinant xylan-degrading enzymes and commercial cellulase step by step.In addition to hemicellulose,the glucose in cellulose is also fully hydrolyzed.The main results are as follows:(1)Hydrolyzing sodium hydroxide pretreated-spartina by recombinant endo-?-1,4-xylanases(AnXyn10C),taking reducing sugar concentration as standard to find optimal pretreatment condition by response surface methodology(RSM):1.35%(w/v)sodium hydroxide,72 min and 61? with the solid-to-liquid ratio of 1:10.Under the condition,the content of lignin decreases from 25.73%to 20.72%,the content of cellulose increases from 34.04%to 48.40%,and the content of hemicellulose increases from 26.45%to 28.56%.The effects of ammonia/hydrogen peroxide combined ball milling on the composition,structure and subsequent synergistic enzymatic hydrolysis of Spartina are also investigated.The result also demonstrates that ammonia/hydrogen peroxide pretreatment has good delignification effect on Spartina.Ball milling can destroy the crystalline zone of cellulose.Both of pretreatments promotes the efficiency of subsequent xylanase hydrolysis.(2)Hydrolyzing spartina that is pretreated by optimal alkali pretreatment condition by recombinant endo-?-1,4-xylanases and ?-L-arabinofuranosidases(AnAxh62A).Hydrolysate is analyzed by HPLC:the digestibility of xylan is 35.82%,xylobiose(X2),xylose(Xyl),xylotriose(X3)and arabinose(AX)are 63.93%,13.49%,10.22%and 12.37%respectively in hydrolysate.MALDI-TOF-MS identifies further that a small amount of xylotetraose(X4),xylopentaose(X5)and arabinoxylobiose(AX2),arabinoxylotriose(AX3)and arabinoxylotetraose(AX4)were also detected in hydrolysate.(3)The residue from xylan-degrading enzymes synergistic hydrolysis is hydrolyzed by commercial cellulase further.The hydrolysate components analyzed by HPLC can demonstrate that the digestibility of cellulose was 93.74%.In addition to cellulose,there is 25.82%hemicellulose is hydrolyzed to xylose.(4)The effects of two-step hydrolysis and one-step hydrolysis on xylooligosaccharide and glucose production from pretreated-biomass are explored and compared preliminarily.It is proved that the advantages of two-step hydrolysis are obtaining relatively pure xylooligosaccharides and to aviod the inhibition of xylooligosaccharide on cellulase activity.Two-step hydrolysis is good to subsequent fermentation and utilization.In summary,alkali pretreatment is used to increase accessibility of xylan-degrading enzymes;obtaining high value-added xylooligosaccharides by xylan-degrading enzymes synergistic hydrolysis;taking advantage of cellulose and hemicellulose in Spartina in form of glucose by two-step hydrolysis method which combined cellulase with xylan-degrading enzymes in this paper.