Efficient Pretreatment of Burdock Straw with Ternary Deep Eutectic Solvents under Mild Conditions Improves Saccharification Efficiency.

Ternary deep eutectic solvents (T-DESs) show considerable potential for biomass refining. In this study, a novel T-DES pretreatment solvent, BE: Gly: UR (2:1:1), composed of betaine (BE), glycerol (Gly), and urea (UR), was developed for high solid loading. It was applied to pretreat burdock straw (BS) under mild conditions (70 °C for 20 min) at a solid-to-liquid ratio of 20%. The BE: Gly: UR system successfully removed 89.4% of lignin while retaining 95.8% of glucan. It also improved the yield of reducing sugars to 97.1% and increased enzymatic hydrolysis efficiency to 89.2%. After pretreatment, cellulose accessibility increased to 537.6 mg/g, whereas the specific surface area of lignin decreased to 145.8 m²/g. These structural and surface modifications collectively improved enzymatic hydrolysis. Molecular dynamics simulations and density functional theory (DFT) calculations revealed that van der Waals and dispersion interactions govern the interaction between BE: Gly: UR and lignin, thereby elucidating the molecular-level mechanisms of lignocellulose deconstruction. Overall, the BE: Gly: UR pretreatment system effectively disrupted the compact structure of BS, promoted lignin and hemicellulose removal, and improved enzymatic hydrolysis. This system offers a novel approach for the high-value utilization of biomass resources.