Unmasking the structural features and property of lignin from bamboo

In this study, a simple method based on DMSO/NMI (dimethylsulfoxide/N-methylimidazole) dissolved system for the isolation of dissolved lignin (DL) from bamboo was presented. The lignin extracted was studied as compared to milled wood lignin (MWL) and alkali lignin (AL). Quantitative 13C and 2D-HSQC NMR analysis indicated that all lignin preparations are HGS-type and partially acylated (below 12%) at the γ-carbon of the side chain by p-coumarate. In addition, some LCC linkages and acetylated β-d-xylopyranoside were distinguished from HSQC spectra in the specific lignin preparations. The abundances (Ar/100Ar) of β-O-4, β-β, and β-5, S/G ratios, acylation degree, phenolic hydroxyl, aliphatic hydroxyl and methoxy groups (mmol/g) were also observed in the lignin preparations. Furthermore, the amount of β-O-4 coupling and molecular weight of the lignin decreased in the order of DL < MWL < AL. The in vitro antioxidant activity results showed that the radical scavenging index (RSI) is correlated to the phenolic hydroxyl groups (Ar-OH) involved in the lignin preparations.