Isolation of Cellulolytic Enzyme Lignin from Wood Preswollen/Dissolved in Dimethyl Sulfoxide/N-Methylimidazole

Attempts were made to enhance polysaccharide digestibility by crude cellulases in the isolation of cellulolytic enzyme lignin (CEL) by dissolution of ball-milled wood in a dimethyl sulfoxide (DMSO)/N-methylimidazole solvent system as a pretreatment step. Wood regenerated from the DMSO/N-methylimidazole solution was hydrolyzed with crude cellulases for 48 h, removing 73.7 and 66.9% of the original carbohydrate for basswood and loblolly pine, respectively; only 61.7 and 49.2% were hydrolyzed by the crude cellulases without pretreatment. The yields of CEL isolated from regenerated ball-milled wood samples were therefore higher than those directly from ball-milled wood material, presumably via decreasing crystallinity of cellulose. For basswood, the yields of lignin were 45.8 and 36.5% (based on Klason lignin); for loblolly pine, the yields were 35.3 and 30.5%. The isolated lignins were structurally examined using two-dimensional heteronuclear single-quantum coherence (H-1-C-13 HSQC) NMR methods, which showed that the main structural characteristics of the lignin fractions obtained using these two methods are similar except for slightly higher amounts of carbohydrates in the solvent dissolution product.