Extraction of natural active ingredients from Eucommia ulmoides leaves by natural deep eutectic solvent-based surfactant-free microemulsion: Experimental and mechanism study

Abstract

This study presented the development of a nanoscale, tunable surfactant-free microemulsion (SFME) formulated with natural deep eutectic solvents (NaDES) for the efficient extraction of phytochemicals. The NaDES-SFME, composed of octanol, thymol, ethanol and water, was characterized using a ternary phase diagram, conductivity measurements and UV absorption spectroscopy. The optimal NaDES-SFME composition (15 % v/v NADES, 45 % v/v ethanol and 40 % v/v water) demonstrated superior extraction performance compared to conventional solvents, achieving extraction yields of seven phytochemicals from Eucommia ulmoides leaves that were 1.15–3.55 times higher. FT-IR, dynamic light scattering (DLS) and fluorescence microscopy revealed a reverse W/O structure at 46.7 nm, mimicking cell membranes to penetrate plant matrices and dissolve compounds. Ultrasound-assisted extraction, optimized via response surface methodology, achieved a maximum total yield of 9.763 mg/g under the conditions of 50 °C, 41 min and a solid–liquid ratio of 31 mg/mL. The Pareto plot indicated that the extraction time was the main factor affecting the extraction efficiency and the secondary kinetic model could better fit the dissolution pattern of the phytochemicals. Density functional theory (DFT) analysis confirmed hydrogen bonding as the key mechanism for the high extraction yield. Finally, the combination of ethanol addition and rotary evaporation allowed for a high recovery of the phytochemicals, with a recovery rate of more than 96 %. This green, cost-effective and high-yield microemulsion holds promise for industrial-scale phytochemical extraction and utilization.