Ultrasound-assisted deep eutectic solvent extraction of flavonoids from Hippophae plants: Optimization and α-glucosidase inhibition studies

Abstract

To make full use of Hippophae plant resources, we use the green extraction method of deep eutectic solvent (DES) combined with ultrasonication to extract flavonoids. HPLC was used to measure four flavonoids (isorhamnetin-3-O-glucoside-7-O-rhamnoside, rutin, isorhamnetin-3-O-rutinoside, and isorhamnetin) in fruit samples and five flavonoids (quercetin-7-O-glucoside, isorhamnetin-3-O-glucoside-7-O-rhamnoside, rutin, guaijaverin, and kaempferol-3-O-rutinoside) in leaf samples. The best solvent was chosen from 12 kinds of DES. With betaine/acetic acid (molar ratio of 1:2) as the extraction solvent, a liquid-solid ratio of 21:1 (mL/g), an extraction temperature of 37 °C, and an extraction time of 22 min, the total content of four flavonoids in the fruit was 10.547 mg/g. With L-proline/levulinic acid (molar ratio of 1:2) as the extraction solvent, a liquid-solid ratio of 31:1 (mL/g), an extraction temperature of 49 °C, and an extraction time of 22 min, the yield of five flavonoids in the leaves was 17.921 mg/g. The extraction efficiency of this method was significantly better than that of hot reflux extraction and 60 % ethanol extraction (p < 0.05). The flavonoids obtained by further purification of the extracts from the fruit and leaves exhibited inhibitory ability to α-glucosidase in vitro, IC₅₀ = 28.189 and 19.675 μg/mL, respectively. Above all, the use of optimized DES could efficiently extract flavonoids from Hippophae plants, which have promising applications in the regulation of blood glucose.