Mechanism Investigation On Sulfonated Lignin Improving Enzymatic Saccharification Of Lignocellulosic Biomass

Nonspecific adsorption of lignin in lignocellulosic biomass is the main inhibition for the enzymatic hydrolysis.Aiming at solving the various problems during the saccharification of cellulose,sulfonated lignin(SL)was added to enhance digestibility of lignocelluloses using cellulase(CTec2).The main factors of lignocelluloses saccharification was proposed during enzymatic hydrolysis with SL addition.Mechanism of SL promoting enzyme hydrolysis was carried out.The main contents are as follows:1.Effect of SL on the enzymatic hydrolysis of different lignocellulosic biomass.SL has no obvious influence on the enzymatic saccharification of untreated(microcrystalline cellulose)and different chemical(bleaching,acid bisulfite and acid chlorite)pretreated lignocellulosic biomass.Using acid bisulfite(AS)-and green liquor(GL)-pretreated poplar as substrates,the sugar conversions of AS-and GL-pretreated poplar went up and then kept stable or leveled off with SL charges from 0 to 0.3 g/g-substrate The highest total sugar conversions was 83.5%(SL 0.3 g/g-substrate)and 90.9%(SL 0.2 g/g-substrate)for AS-and GL-pretreated poplar,respectively.The results demonstrated that the effect of SL on enzymatic hydrolysis varies with the property of lignin and particle size of substrate in materials.2.Effect of hydrolysis pH on the enzymatic hydrolysis of AS-and GL-pretreated poplar with/without SL.The optimal pH of AS-and GL-pretreated poplar was 4.8 without SL addition and the optimal pH of AS-pretreated poplar moved to 5.4,while that of GL-pretreated poplar showed no significant change with SL addition.3.The effect of different ways of addition of SL on enzymatic saccharification of AS pretreated poplar as substrate.The total sugar conversions of AS pretreated poplar was the highest after SL mixing for 0.5 h with cellulase at 4°C,0 r·min-1.4.The effect of SL on concentration of free enzyme using AS pretreated poplar as substrate and the relationship of the mechnism of SL promoting enzymatic hydrolysis and pH.The percentage of the initial concentration increased from 12.2% to 25.6% at 48 h.This suggested the positive effect of SL on enzymatic hydrolysis was related to the effect of SL on enzyme adsorption.In addition,when pH increased from 5.0 to 5.7,the enzymatic digestibility of AS pretreated poplar decreased with SL addition and the surface charges of SL decreased from-0.63 mmol/g to-0.38 mmol/g.This demonstrated that elevated pH may weaken the electrostatic interaction between cellulase and SL.5.The study on the effects of different concentration of SL on different concentration of cellulase adsorption onto substrate demonstrated the interaction between SL and cellulase formed SL-CTec2 complex,which resulted in the absorbance of cellulase decreased with addition of SL with Bradford method measured.When the concentration of SL is 2 mg·m L-1,the absorbance of SL-CTec2 complex was obtain minimum.Therefore,SL may reduce nonspecific binding of cellulase onto substrate through interacting with cellulase,which was related with its concentration.6.Quartz crystal microbalance with dissipation(QCM-D)and atomic force microscope(AFM)were applied to evaluate the effect of SL on the cellulase adsorption on AS and GL thin films.Adding to CTec2 solution prior to adding SL solution into the flow-cell,the maximum adsorption amount of cellulase on the substrate increased significantly.AFM figure showed the adsorption spherical particles on thin films surface became larger.It showed that SL interacted with cellulase.When adding mixture of SL and CTec2,the maximum adsorption amount from decreased obviously,AFM figure showed the thin films surface also has changed dramatically and the slope of ?D-?F curve increased significantly and remain unchange.It showed that the adsorbed layers of cellulase on the substrate became more flexible with celluase mixing with SL.Adsorbed cellulase on the substrate will be more easily from stripping off the lignin in substrates.It means that the interaction between SL and cellulose reduces the nonspecfic adsorbtion of cellulase on the substrate.