Spontaneous and Laccase-Assisted Adsorption of Hemicelluloses Rendering Colloidal Stability of Lignin Nanoparticles at Low pH

Functionalizing lignin nanoparticles (LNPs) is an attractive strategy to improve their properties and expand their range of applications. However, conventional approaches to achieve such modifications are done using environmentally and energy-demanding methods. Here, a green synthetic approach through spontaneous adsorption and laccase-induced reactions to functionalize LNPs with hemicelluloses is introduced. Structurally varying lignin and hemicellulose grades isolated from different sources and several fungal laccases are systematically compared. Specifically, the residual lignin content in hemicelluloses is hypothesized to determine their adsorption efficacy on LNPs. Results reveal that the LNPs can be coated with hemicelluloses by physical adsorption, which greatly increases their colloidal stability at acidic pH, compared to plain LNPs. Furthermore, fungal laccases can play an active role in attaching lignin moieties of the hemicelluloses at the LNP surface, confirmed by the enriched lignin-derived compounds and monosaccharide composition of the laccase-treated hybrid LNPs, compared to the physical adsorption of hemicellulose on the LNP surface. Overall, this study provides new insights on the mechanism of laccase-assisted functionalization of LNPs with other ligands (e.g., hemicelluloses). Furthermore, the increased colloidal stability of LNPs can greatly increase the application of such hemicellulose-lignin hybrid nanosystems for different areas, such as health sciences.