Green extraction of antioxidant compound (quercetin) from Salix amplexicaulis species using natural deep eutectic solvents

Certain Salix species have been reported to exhibit significant antioxidant activity across various in vitro and in vivo systems. To preserve the environment, reduce humans' negative impact in the field of chemistry, enhance extraction efficiency, and improve the stability of extracted components, this study combined natural deep eutectic solvents (NADESs) with microwave-assisted extraction (MAE) to isolate the highly effective antioxidant quercetin. This study investigated the efficiency of the novel green extraction method, MAE-NADES, to recover the potent antioxidant quercetin from the underexplored leaves and bark of Salix amplexicaulis. Furthermore, the potential of NADES as a sustainable alternative to conventional solvents was assessed by comparing MAE-NADES with MAE-water and traditional ethanol maceration. NADES based on lactic acid-glycerol, lactic acid-glucose, glycerol-glucose, and glycerol-urea were synthesized by heating and stirring. Extracts of Salix amplexicaulis were obtained through forty-eight-hour ethanol maceration and MAE. In MAE, water and NADES were used as solvents, and the extraction was carried out in three cycles, each lasting eight seconds. The quercetin content of extracts was characterized by high-performance liquid chromatography (HPLC). The quercetin content ranged from 0.31 to 1.56 mg/g in crude bark and from 0.30 to 2.04 mg/g in crude leaf. NADESs were superior to water and ethanol extraction, recovering from the bark 4 to 5 times more quercetin than water and 2.5 to 3 more quercetin than ethanol. As for NADES leaf extracts, quercetin amounts were 4.5 to 7 times higher than in aqueous extract and 3.5 to 5 times higher compared to ethanolic extract. Considering the obtained results, MAE-NADES demonstrated significant potential as a sustainable and efficient alternative for quercetin extraction from Salix amplexicaulis, including faster and more cost-effective preparation, high extraction efficiency, and environmentally friendly characteristics.

Acknowledgement: This work was supported by the Provincial Secretariat for Higher Education and Scientific Research, Province of Vojvodina (Grant No. 142-451-3474/2023).