Tailoring lignin surface properties for enhanced enzymatic hydrolysis: Comparative insights from pine and eucalyptus

Milled wood lignin (MWL) was isolated from pine and eucalyptus before and after hydrothermal treatment, and its effects on enzymatic hydrolysis were evaluated. Hydrothermal treatment primarily decomposed hemicellulose and induced structural changes in lignin for both species. With increasing treatment severity, the hydrophobicity and lignin surface area decreased, the zeta potential became more negative, aliphatic hydroxyl group content decreased, and β-O-4 linkages were cleaved. These changes influenced enzymatic hydrolysis, with the highest glucan to glucose conversion observed in pretreated eucalyptus (HT60). Correlation analysis indicated that enzymatic hydrolysis efficiency in pine was most strongly influenced by cellulose content, phenolic hydroxyl group in lignin, and zeta potential, while in eucalyptus, the key factors were cellulose content, aliphatic hydroxyl group content, and zeta potential. The role of lignin hydroxyl group in enzyme adsorption was further examined through MWL acetylation, which demonstrated that acetylated MWL exhibited reduced enzyme adsorption compared to unmodified MWL.