Access of Cellulase to Cellulose and Lignin for Poplar Solids Produced by Leading Pretreatment Technologies

摘要

Adsorption of cellulase on solids resulting from pretreatment of poplar wood by ammonia fiber expansion (AFEX),ammonia recycled percolation (ARP),controlled pH,dilute acid (DA),flowthrough (FT),lime,and sulfur dioxide (SO2) and pure Avicel glucan was measured at 4°C,as were adsorption and desorption of cellulase and adsorption of beta-glucosidase for lignin left after enzymatic digestion of the solids from these pretreatments. From this,Langmuir adsorption parameters,cellulose accessibility to cellulase,and the effectiveness of cellulase adsorbed on poplar solids were estimated,and the effect of delignification on cellulase effectiveness was determined. Furthermore,Avicel hydrolysis inhibition by enzymatic and acid lignin of poplar solids was studied. Flowthrough pre treated solids showed the highest maximum cellulase adsorption capacity (sigma_(solids) = 195 mg/g solid) followed by dilute acid (sigma_(solids)= 170.0 mglg solid) and lime pretreated solids (sigma_(solids)= 150.8 mglg solid),whereas controlled pH pretreated solids had the lowest (sigma_(solids)= 56 mglg solid). Lime pretreated solids also had the highest cellulose accessibility (sigma_(cellulose)= 241 mglg cellulose) followed by FT and DA. AFEX lignin had the lowest cellulase adsorption capacity (sigma_(lignin)= 57 mglg lignin) followed by dilute acid lignin (sigma_(lignin) = 74 mglg lignin). AFEX lignin also had the lowest fi-glucosidase capacity (sigma_(lignin)= 66.6 mglg lignin),while lignin from SO2 (sigma_(lignin)= 320 mglg lignin) followed by dilute acid had the highest (301 mglg lignin). Furthermore,SO2 followed by dilute acid pretreated solids gave the highest cellulase effectiveness,but delignification enhanced cellulase effectiveness more for high pH than low pH pretreatments,suggesting that lignin impedes access of enzymes to xylan more than to glucan,which in turn affects glucan accessibility. In addition,lignin from enzymatic digestion of AFEX and dilute acid pretreated solids inhibited Avicel hydrolysis less than ARP and flowthrough lignin,whereas acid lignin from unpretreated poplar inhibited enzymes the most. Irreversible binding of cellulase to lignin varied with pretreatment type and desorption method.