Kinetic modeling of ultrasound-assisted extraction of dieckol from Ecklonia cava using a choline chloride-based natural deep eutectic solvent

Natural deep eutectic solvents (NADES) are promising green and sustainable solvents for efficient extraction of bioactive compounds. We employed ultrasound-assisted extraction (UAE) to extract dieckol from Ecklonia cava (EC) using choline chloride-based NADES. Eight different NADES (comprising sugars, alcohols, and organic acids) and a conventional solvent were screened to select the best eutectic solvent for dieckol extraction. Among the organic acid-based NADES, choline chloride–acetic acid (CCAC; 1:1 molar ratio with a 50% [v/v] water content) exhibited a higher dieckol content (31.45 mg/g) than other NADES and ethanol. Second-order kinetic modeling was applied using CCAC with varying water content (40–80%, v/v) to confirm the extraction efficiency and underlying mechanism. The kinetic model showed that CCAC with 40% water content (v/v) exhibited the highest capacity (Ce=29.67 mg/g), while CCAC with 60% water content (v/v) yielded a superior extraction rate constant (k=0.12 mg/g min). Moreover, the dieckol extract displayed potent DPPH and ABTS+ antioxidant activities. Furthermore, structural and viscosity changes between the synthesized CCAC with and without water addition were compared. Our study proposes an eco-friendly and efficient extraction alternative for the extraction of dieckol from EC using NADES.