Effects of a ternary deep eutectic solvent on the enrichment, structure, and functional properties of okara cellulose: Insights into the underlying molecular mechanisms

To enhance cellulose enrichment and functional properties of okara insoluble dietary fiber (ISF), a ternary deep eutectic solvent (DES) composed of choline chloride, oxalic acid, and ethylene glycol (ChCl/OA/EG, denoted as COE) was developed. The effects of different OA/EG ratios on the composition, structure, and functionality of okara ISF were systematically investigated. DES treatment effectively removed proteins, hemicellulose, and lignin, leading to significant cellulose enrichment. Among the tested systems, COE-4, with a ChCl:OA:EG molar ratio of 1:1.5:1.5, showed the best performance, with cellulose content increasing from 56.3% to 80.33%. The treatment preserved the cellulose Iβ crystalline structure while promoting fiber bundle disintegration, reducing particle size, increasing the absolute ζ-potential, and generating a more porous structure. Consequently, the water-holding, swelling, and oil-holding capacities, as well as glucose adsorption, cation exchange, and cholesterol binding capacities, were markedly improved, whereas nitrite adsorption showed limited enhancement. Molecular dynamics simulations qualitatively suggested that an appropriate OA/EG ratio facilitated preferential enrichment of OA at key cellulose sites and disrupted the hydrogen-bonding network through competitive interactions, together with enhanced interfacial mass transfer. Overall, this study presents a ratio-controlled ChCl/OA/EG ternary DES treatment for okara cellulose, identifying COE-4 as the optimal formulation and linking its functional enhancement with molecular-level mechanistic interpretation.