Efficient pretreatment of passion fruit husks using choline chloride based deep eutectic solvents

Substituting renewable lignocellulose for fossil fuels is crucial for economic development and environmental protection. Deep eutectic solvents (DESs) demonstrate efficacy in facilitating the fractionation of high-purity lignin and cellulose during lignocellulose pretreatment. In this study, agricultural by-product passion fruit husks underwent pretreatment using DESs comprised of choline chloride (ChCl) and organic acids, aiming to efficiently separate cellulose and lignin. Among the various DESs tested, ChCl combined with lactic acid (LA) exhibited optimal performance in the pretreatment process. This combination demonstrated a remarkable synergistic effect in breaking down the lignin-carbohydrate complex bonds and deconstructing passion fruit husks. Characterizations of the cellulose rich solid residues were performed using FTIR, SEM, and XRD techniques, confirming the effectiveness of lignin removal and cellulose retention through the pretreatment. The regenerated lignin exhibited homogeneous distribution and well-preserved structure, as evidenced by 2D-HSQC analysis. Furthermore, it displayed notable antioxidant activity and antibacterial property. The mechanism underlying the pretreatment was elucidated through density functional theory (DFT) calculations, confirming hydrogen-bond interactions between DESs and lignin, which positively contributed to lignin dissolution. Additionally, hydrogen-bond properties between DESs and lignin were also revealed.