Ultrasound-assisted Extraction of Flavonoids From Lycium barbarum L. using Gemini Ionic Liquid-based Deep Eutectic Solvents

The extraction of bioactive compounds from natural plants has received considerable attention, with deep eutectic solvents (DESs) being considered as a novel kind of green solvent in the extraction processes. To extract bioactive ingredients from natural plants, a series of DESs was synthesized by combining a newly Gemini ionic liquid (IL), C₃(MIM)₂Br₂ with ethylene glycol (EG) in various molar ratios (1:3, 1:4, 1:5, and 1:6). The structure of the C₃(MIM)₂Br₂/EG(1:6) system was characterized using Fourier-transform infrared spectroscopy, as well as ¹H and ¹³C nuclear magnetic resonance spectroscopy. The synthesized DESs were employed for the ultrasonic-assisted extraction (UAE) of flavonoids from Lycium barbarum L., and the flavonoid was quantified using ultraviolet-visible spectroscopy. Key process parameters, including extraction time, temperature, and solid-liquid ratio, were optimized through single-factor analysis and L₉(3³) orthogonal array experiments. The results demonstrated optimal extraction conditions as follows: extraction time of 40 min, extraction temperature of 50°C, and a solid-liquid ratio of 1/50 (g/mL) (the ratio of the mass of the solid material to the volume of the liquid as the extract, g/mL). Statistical analysis revealed that extraction temperature and extraction time had both probability values less than 0.05, indicating a significant impact on the extraction rate, and the extraction yield of flavonoids reached 17.94 mg/g, exceeding that achieved with 60% ethanol. The Gemini IL-based DESs exhibited distinct advantages in flavonoid extraction compared to traditional organic solvents. Additionally, the mechanisms underlying UAE using DESs were investigated through thermogravimetric analysis and scanning electron microscopy. The findings indicate that ultrasonically-assisted incorporation of Gemini ILs holds promise for advancing the extraction of bioactive substances.