Diol-Induced Lignin Stabilization Facilitates Softwood Saccharification

Lignocellulose pretreatments for enhancing the cellulose accessibility have been widely investigated, and most of them pursue high delignification and hemicellulose removal at elevated conditions, which at the same time cause severe nonproductive adsorption between the enzyme and the condensed residual lignin, this is especially common for softwood. In this study, the highly lignified softwood was selected as the feedstock, and a series of diol-assisted deep eutectic solvent (DES) systems were established to modify the lignin structure and alleviate the inhibition of lignin on enzymatic saccharification process. Compared with conventional organic acid DES, the residual lignin in the diol-DES solid showed abundant etherified tails in the lignin sidechains, leading to reduced lignin adsorption to enzyme. The mechanism for the lignin modification and saccharification enhancement was elucidated by GPC, 2D HSQC NMR, ³¹P NMR, hydrophobicity, and the Langmuir adsorption isotherm. The diol-modified residual lignin in the recovered solid possessed a specific β-O-4 structure (24.9-36.4/100Ar) with higher aliphatic OH content and lower hydrophobicity, which reduced its nonproductive adsorption to cellulase, thus significantly enhancing Pinus massoniana's cellulose saccharification from 31.2% to 90.0%.