Structural Features of Lignin and Lignin-Carbohydrate Complexes from Bamboo (Phyllostachys pubescens Mazel)

Understanding the structural features of lignin (L) and lignin-carbohydrate complexes (LCC) in bamboo (Phyllostachys pubescens Mazel) is important in order to expand the use of bamboo biomass. In this study, L and LCC were isolated from four-year-old mature bamboo using an organic solvent as an extractant. The structural features of L and LCC were characterized via UV-vis, FT-IR, NMR, sugar composition analysis, and alkaline nitrobenzene oxidation. L and LCC contained almost the same structural units: guaiacyl (G), syringyl (S), p-hydroxybenzoate substructures (PB), β-O-4' substructures (A), 3-O-acetyl-(1>4)-linked-B-D-xylopyranosyl (βXyl3), (1>4)-linked-α(β)-D-xylopyranosyl (α(β)Xyl), and 4-O-methyl-α-D-glucuronic acid (MeGlcA(1>4)). The contents of the units varied between L and LCC. Carbohydrates linked with lignin in L and LCC mainly consisted of xylans. The sugar units of carbohydrates linked with lignin in LCC were determined to be of xylose (76.98%), arabinose (4.08%), glucose (6.47%), mannose (6.34%), altrose (3.69%), galactose (1.75%), and ribose (0.69%). The S (75.80%) and G (24.20%) units with a high S/G ratio of 3.13 were the main structural elements of lignin associated with carbohydrates in LCC.