Fractionation And Depolymerization Of Enzymatic Hydrolysis Lignin And Theirs Effect On Antioxidant Activities

With the exhaustion of fossil energy and the more serious problems caused by the warming and environmental pollution,the exploration and utilization of new energy resources have an important influence on the development of the society.More and more researchers have turned to look for green,efficient and friendly resources.Lignocellulosic biomass which is abundant and renewable attracted much attention.Lignin,one of the three main components of plant cell wall,is the only renewable aromatic polymer in nature,and it is the third largest in reserve following cellulose and chitin.With the development of pulping and papermaking industry and biorefinery,the utilization of lignin becomes more and more important.The enzymatic residue which was derived from the process of steam explosion pretreatment and enzymatic saccharification simultaneous fermentation of corn stover was chosen as the research object.The enzymatic residue was purified,fractionated,and depolymerized.The results showed:(1)Enzymatic hydrolysis lignin was obtained by extraction using neutral 1,4-dioxane solution.The purity of lignin was increased,and the content of carbohydrate and protein was decreased,in addition,the structure was no significant change.Compared with that of enzymatic residue,the antioxidant activity of enzymatic hydrolysis lignin was improved.(2)Enzymatic hydrolysis lignin was fractioned by continuous extraction using different polar organic solvents.The different molecular weight lignin was obtained.13.42±0.96%of enzymatic hydrolysis lignin was dissolved in dichloromethane solvent,and this lignin fraction which has the lowest molecular weight and the highest content of phenolic hydroxyl group showed the excellent antioxidant activity.In addition,with the increasing of polar of organic solvent,the lignin fractions showed the higher molecular weight,the lower content of phenolic hydroxyl group and the poorer antioxidant activity.(3)The high molecular weight lignin obtained from fractionation was depolymerized via acid-ethanol catalysis and the depolymerized products were characterized by GPC,FT-IR,13C NMR,HSQC and Py-GC/MS.The results showed the disruption of ?-O-4 linkages,the destruction of phenylcoumarin structures and the dissolving of p-coumaric acid units,and these results further led to the decreasing in the molecular weight and the increasing in the solubility.The number-average molecular weight of D-200(depolymerized products at 200?)was decreased to 2856 g/mol,and the content of phenolic hydroxyl group was increased to 167.0±3.6 mg GAE/g,meanwhile,its IC50 value(IC50=66.0±2.6?g/mL)from DPPH(1,1-diphenyl-2-picrylhydrazyl)free radical scavenging capacity was close to that(IC50=53.3±4.5 ?g/mL)of the commercial antioxidant BHT(butylated hydroxytoluene).It indicated that the ethanol-acid catalyzed depolymerization could cause the reduction in the molecular weight of lignin,the increasing in the content of phenolic hydroxyl group and the enhancement in the antioxidant activity of lignin.