Effects And Mechanisms Of Quaternary Ammonium Lignin Carboxylate And Modified ?-glucosidase On The Enzymatic Hydrolysis Of Lignocellulose

As the most abundant renewable physical resource in nature,lignocellulose can be used as a raw material for the production of biofuels and other sugar platform chemicals,and the enzymatic hydrolysis of lignocellulose is considered to be a promising technology due to its green and safety.However,the industial development of enzymatic hydrolysis is still limited by low hydrolysis efficiency,high cost of cellulase,and the difficulties in high-value utilization of enzymatic residue.Numerous studies have shown that the addition of lignin-based surfactants in enzymatic hydrolysis process,as well as the optimization of cellulase are effective ways to improve the efficiency of enzymatic hydrolysis,reducing the cost of enzymatic hydrolysis.Nonetheless,the synthesis and application of lignin-based enzymatic auxiliaries still lack systematic theoretical guidance,while the optimization of cellulase lacks innovative and feasible ideas.Therefore,the enhancements of lignocellulose enzymatic hydrolysis by adding quaternary ammonium lignin carboxylate with different isoelectric points as well as the modification of ?-glucosidase were studied in this paper as follows:Firstly,to study the effect and mechanism of the isoelectric point of lignin-based surfactant on the enzymatic hydrolysis of lignocellulose,lignin carboxylate(LC)and quaternary ammonium lignin carboxylates(LCQ-x,x% was the mass radio of quaternizing agent to enzymatic hydrolysis lignin)with different isoelectric points(pIs)were synthesized by carboxymethylation modification and quaternization of enzymatic hydrolysis lignin(EHL).The results showed that with the increase of isoelectric point(pI)of the products,the enzymatic hydrolysis enhancement of lignocellulose increased first and then decreased,and the product with the isoelectric point around 4.8 had the best promoting effect.Adding 2 g/L LC,LCQ-40 and LCQ-100 increased the enzymatic digestibility of pretreated eucalyptus from 35.2% to 53.4%,95.3% and 60.4% respectively.As for the mechanism,LC or LCQ-x with pI significantly lower or higher than 4.8 reduced the non-productive adsorption of cellulase on lignin,but for the significant inhibitory effect on cellulase activity,their enhancements on the enzymatic hydrolysis of lignocellulose were not remarkable.However,LCQ-x with pI around 4.8 preserved the cellulase activity,and significantly reduced the non-productive adsorption of cellulase,therefore remarkably enhanced the enzymatic hydrolysis.Secondly,according to the previous studies of the interactions between lignin and cellulase,and based on the phenomenon that the adsorption on lignin has no significant inhibitory effect on the catalytic activity of ?-glucosidase,the idea of improving the overall catalytic efficiency of cellulase by the pro-lignin modification of ?-glucosidase was designed.The commercial ?-glucosidase Novozyme 188 was selected as the research object,and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride(EDC.HCl)and N-hydroxysuccinimide(NHS)were used to activate the carboxyl group on betaine,to modify Novozyme 188.The optimization conditions of this modification for 1 g Novozyme 188 were as follows: activation time was 10 min,betaine dosage was 0.2 g,and reaction temperature was 25°C.The results showed that the modified Novozyme 188 could reduce the non-productive adsorption of the other cellulase components on lignin by competitive adsorption,thereby improving the enzymatic hydrolysis efficiency of lignocellulose to some extent.Compaired with Novozyme 188,50 CBU/g glucan modified Novozyme 188 increased the enzymatic hydrolysis efficiency of corn cob from 43.1% to 53.5%.By correlating the adsorption rate of Novozyme 188 on lignin and its promoting effect on enzymatic hydrolysis,the feasibility of the pro-lignin modification of ?-glucosidase to enhance enzymatic hydrolysis of lignocellulose was preliminarily verified,providing new idea and foundation for the further research on cellulase modification.In this paper,enzymatic hydrolysis efficiency of lignocellulose was improved by the addition of lignin-based surfactants as well as the optimization of enzyme preparations,which provided new ideas and theoretical guidances for further improving the enzymatic hydrolysis efficiency and the industrial production of cellulosic ethanol.