Interpretive analysis of the relationship between pseudolignin structure and enzymatic hydrolysis

Dilute acid pretreatment (DAP) produces pseudolignin (PL), causing significant inhibition of cellulase activity. However, the structure of pseudolignin and its effect on enzymatic hydrolysis are not known. In this study, the hydrolysis of hemicellulose and the generation of pseudolignin in poplar fibers were investigated. Treating poplar fibers at 180 °C 30 min 0.8%AC (Acetic acid content 0.8% (v/v%), reaction at holding temperature 180° C for 30 minutes) yielded 32.83% xylo-oligosaccharides, but the accompanying production of pseudolignin reduced the enzymatic hydrolysis efficiency to 26.86%. SEM, FT-IR, XPS, Py-GCMS and 2D-HSQC NMR analyses of 180 °C pseudolignin and 200 °C pseudolignin (180PL and 200 L) indicated that its structure did not change significantly with increasing treatment intensity, but its content increased significantly. The main components of pseudolignin were the furan structure, phenol structure, catechol structure and aliphatic structure with an aldehyde group on the side chain. Then, 180PL and 200PL were treated again using NaOH solution (180PL+NaOH and 200PL+NaOH) to explore the structural changes before and after NaOH treatment. Removal of these structures by NaOH solution treatment increased the enzymatic hydrolysis efficiency of 180HDAP+NaOH (the residue of 180 °C holocellulose diluted acid pretreatment was treated with NaOH solution) from 77.66% to 94.52%, which confirms that furan, phenolic and aliphatic structures in pseudolignin are the main chemical structures inhibiting enzymatic hydrolysis. This study is of great significance for the development of efficient methods.