Cellulolytic enzyme-aided extraction of hemicellulose from switchgrass and its characteristics†
The isolation of biomass components with their intact structure is crucial for understanding the characteristics of biomass. Compared to other major biomass components such as cellulose and lignin, hemicellulose remains a challenging component to be isolated from the plant cell wall without significant depolymerization and modification. In this study, a novel cellulolytic enzyme-aided hemicellulose (CEH) isolation method was developed to isolate hemicellulose with a near-native branched structure from switchgrass. The structural characteristics of CEH were investigated and compared with hemicelluloses isolated by conventional alkaline extracted hemicellulose (AEH) and DMSO extracted hemicellulose (DMSOH) methods. Gel permeation chromatography (GPC) analysis indicated that CEH had a weight-average molecular weight of 44 kDa, which was comparable to that of AEH (43 kDa) but higher than that of DMSOH (37 kDa). The chemical composition analysis revealed that CEH retained a higher proportion of glucuronic acid compared to AEH and DMSOH. The 2D 13C–1H heteronuclear single quantum coherence (HSQC) NMR spectra containing the β-(1,4)-linked-D-xylan backbone, non-reducing-end peaks and both α- and β-reducing-end peaks in CEH were comparable to the spectra of the commercial beechwood xylan. CEH showed a highly branched hemicellulose structure, which retained methoxyl groups, O-acetyl groups, and 4-O-methyl-glucuronic acid attached to the xylan backbone.