Elucidation of the relationship between lignin structure and its inhibitory effect on enzymatic hydrolysis

In this work, milled wood lignin (MWL) was isolated from three distinct raw materials, including reed, poplar and pine. The research focused on investigating the adsorption of lignin onto cellulase and its subsequent impact on enzymatic hydrolysis. Analysis revealed that reed lignin consisted of three structural units: syringal (S), guaiacyl (G), and p-hydroxyphenyl (H), with a G/(G + S + H) molar ratio of 0.26; Poplar lignin contained S and G, with a G/(G + S + H) molar ratio of 0.63, while pine lignin only contained G. Quartz crystal microbalance with dissipation (QCM-D) results demonstrated that lignin with different types of structural units had varying adsorption capacity for cellulase. Specifically, lignin from coniferous wood (pine) displayed stronger adsorption with cellulase compared to lignin derived from grasses (reed) and broad-leaved wood (poplar). Atomic force microscope (AFM) analysis further indicated that G units promoted the adsorption between cellulase and lignin. These findings underscored a strong correlation between the structure of lignin and its interaction with cellulase, with the proportion of G units playing a pivotal role. Notably, a lower proportion of G units in lignin was beneficial in reducing lignin adsorption onto cellulase, thereby enhancing the saccharification rate.