Research And Mechanism Of Lignin Complex On Enzymatic Hydrolysis Kinetics Of Sugarcane Bagasse

Increasingly serious environmental contamination brought by the fossil energy has emphasized the need to develop clean and renewable energy alternatives.Lignocellulose,the most abundant biomass resources on earth,can be transformed into chemical by biotransformation technology,which is an effective way to ease the problem of environmental contamination.Sugacane bagasse(SCB)has been reccieved interest due to its natural abundance and high carbohydrate content.However,SCB has the resistance to the attack of microorganism and degrading enzyme outside;Moreover,the lignin can irreversiblely adsorb cellulase,which cause the decrease of cellulose hydrolysis efficiency,therefore it is important to research the effective pretreatment technology which can be used to remove lignin and destroy the advanced structure of lignocellulose;In addition it will provide the basis for improving the efficiency of enzymatic hydrolysis to explore lignin adsorption mechanism of cellulase.SCB was ptrtreated by Soda Green liquor(GL)combined with ethanol(Soda GL-ethanol)and sulfite(Soda GL-sulfite),the effect of pretreatment conditions on lignin removal,glucose yield at 72 h and cellulose accessibility,and the relationship among them were researched.The influence of pH increase on cellulase adsorption isotherm of pretreated SCB was discussed.The protease treatment lignin(PTL)was extracted from Soda GL-ethanol substrates,and its effect on cellulase adsorption isotherm of PTL,cellulose accessibility and enzymatic hydrolysis of microcrystalline cellulose(MCC)were determined.Surfactant and its complex with soluble lignin were selected to improve enzymatic hydrolysis efficiency;their influences on enzymatic hydrolysis kinetics of pretreated SCB and kinetics of cellulase adsorption and desorption onto and from PTLwere studied.Soda Green liquor(GL)combined with ethanol(Soda GL-ethanol)and sulfite(Soda GL-sulfite)were selected to pretreat SCB.Maximum lignin removal was 85.2%and 85.5%at 160℃ and a GL loading of 1.5 mL/g-dry substrate.The lignin removal increased with increased pretreatment temperature from 100℃ to 160℃,and glucose yield at 72 h was similar to the changing way of cellulose accessibility of the pretreated SCB.The isotherms of cellulase onto Soda pretreated SCB could be fitted by different models.The result showed that the maximum adsorption and strength of cellulase onto substrate pretreated by Soda GL-ethanol decreased with the increasing of pH from 4.8 to 9.0,but that of substrate pretreated by Soda GL-sulfite did not change remarkably.The effect of protease treated lignin(PTL)of Soda GL-ethanol SCB on the cellulose accessibility and hydrolysis efficiency of microcrystalline cellulose(MCC)was studied.The weight average molecular weight(Mw)and number average molecular weight(Mn)of PTLs(PTL 100/1.5,PTL 120/1.5,PTL 140/1.5 and PTL 160/1.5)increased with the increasing of pretreatment tempreture.The cellulose accessibility of MCC swelled by sodium hydroxide decreased as the molecular weight of PTLs increased.The enzymatic hydrolysis efficiency was decreased by addition of PTLs.The activity of cellobiase was decreased by PTLs.The cellobiase activity could be recovered by zwitterionic surfactant CHAPS.The synergism degree(DS)between the cellulase components was reduced by PTL100/1.5 and PTL 120/1.5,and was improved by the employment of nonionic surfactant TritonX-100.The cellulase adsorption isotherms of the four PTLs indicated that the celluase adsorption onto PTL was physical and spontaneous process.The effect of complex LE140/1.5-Triton X-100 on glucose yield of Soda GL-pretreated SCB was studied at high substrate and low enzyme loading.The glucose concentration in the enzymatic hydrolysis system of Soda GL-ethanol substrate was increased from 23.6 g/L to 63.5 g/L by addition of the complex LE140/1.5-Triton X-100 at a substrate loading of 20%and a enzyme loading of 9 FPU/g-cellulose,while that in the system of Soda GL-suifite substrate rose from 19.7 g/L to 33.6 g/L at a substrate loading of 15%and the same enzyme loading.The fractal kinetics model was employed to fit the time course of enzymatic hydrolysis of Soda GL-ethanol substrate.The result showed that the rate constants K for glucose yield were increased,but was decreased for xylose yield by the assistance of LE140/1.5-Triton X-100,while the fractal exponent h was decreased for the both.When the complex was added to the enzymatic system of Soda GL-sulfite substrate,the rate constants K for glucose yield was increased,but only the fractal exponent h at 5 FPU/g-cellulose was decreased.The time course of cellulse CTec2 adsorption onto PTL 100/1.5 was fitted by different models in the systems of sodium acetate,TritonX-100 and LE140/1.5-TritonX-100.The result showed that the rate constant of the pseudo-first-order and the maximum adsorption capacity were the lowest in the system of LE140/1.5-Triton X-100.The adsorption and desorption competition parameter y was<1 in the system of sodium acetate and Triton X-100,but it was>1 in LE140/1.5-Triton X-100 system.The rate of binding KB was also the minmum value in the LE140/1.5-Triton X-100 system.The time course of cellulase desorption from PTL 100/1.5 saturated by enzyme was fitted in three kinds of system above.The desorption rate constant Koff,the rate of desorption KD,cellulase recyclability parameter R0 and the cellulase-binding reversibility parameter Rb were the highest in the LE140/1.5-Triton X-100 system.Cellobiohydrolase activity of enzyme desorbed from saturated PTL 100/1.5 was measured,and was the highest in the LE140/1.5-Triton X-100 system.