Pretreatment of tea stem by biocompatible ionic liquids for enhanced enzymatic hydrolysis of cellulose and formation of UV-blocking chitosan film

In this study, novel biocompatible choline-organic carboxylic acid ionic liquids (Ch-OAC-ILs) were developed for pretreatment of tea stems. Among them, the combination of Ch + and levulinate achieved highest cellulose retention and most efficient lignin removal. The pretreatment mechanism were systematically explored using advanced characterization techniques and density functional theory calculations. The Ch-OAC-ILs preferentially targeted β-O-4 and β-5 linkages, yielding regenerated lignin enriched with H units. Both the cation and anion played critical roles in lignin dissolution. Furthermore, the enzyme digestibility of the pretreatment residue was significantly enhanced. The IL-lignin solution obtained after pretreatment was directly incorporated into chitosan films, where the ILs acted as plasticizers and lignin functioned as an active additive. These composite films exhibited superior UV-blocking properties with potential in functional packaging applications. This study highlights the efficacy of Ch-OAC-ILs as a sustainable and efficient method for lignin dissociation, offering a promising strategy for biomass fractionation and valorization.