Efficient extraction of flavonoids from Polygonatum sibiricum using a deep eutectic solvent as a green extraction solvent

Deep eutectic solvents (DESs) are becoming eco-friendly alternatives for extracting biologically-active substances from natural products. In this study, a DES is used as an eco-friendly solvent to extract flavonoids from Polygonatum sibiricum with the assistance of ultrasound. The antioxidant activity of the extracts was then investigated and the recyclability and reusability of the DES evaluated. Optimizing the DES extraction process produced the following optimum conditions: a betaine–acetic acid molar ratio of 1:4, water content of 30%, solid–liquid ratio of 1: 100 g mL−1, extraction temperature of 50 °C, and extraction time of 30 min. The yield of extracted flavonoids reached 25.4 mg g−1, which is about eight times that achieved using ethanol extraction. Furthermore, the antioxidant ability of the DES extract was more potent than that of the extract obtained using ethanol. Used DES can be efficiently recovered using ultrahigh capacitance porous activated carbon (the recovery yield of DES was around 92% of that of the original DES after ten reuses). In conclusion, DESs can be used to establish green ultrasound-assisted extraction methods for efficient extraction of plant flavonoids.