Natural green deep eutectic solvents-based eco-friendly and efficient extraction of flavonoids from Selaginella moellendorffii: Process optimization, composition identification and biological activity

In this study, ultrasound-assisted natural deep eutectic solvents (DES) were applied to extract total flavonoids (TF) efficiently and eco-friendly from Selaginella moellendorffii. Thirty natural DESs were prepared, of which choline chloride-lactic acid (ChCl-Lac) was selected as the optimal DES. Response surface methodology (RSM) was adopted to obtain the highest TF content from Selaginella moellendorffii by applying ChCl-Lac. A TF content of 5.72 ± 0.13 mg/g was obtained with water content of 24%, extraction power of 260 W, liquid/solid ratio of 24:1 mL/g and extraction time of 43 min. Compared with the ionic liquid extraction and traditional methods, DES-UAE was not only able to save time, but also increased TF content by nearly 2–3 times. Meanwhile, sixteen compounds in S. moellendorffii were identified through UPLC-Q-TOF-MS, and eight compounds were newly discovered. In addition, five biflavonoids in the TF extract were determined simultaneously adopting HPLC under optimal extraction conditions. The results of exploring in vitro biological activities of the TF extract using four antioxidant experiments indicated that the TF extract of S. moellendorffii exhibited potent antioxidant activities. Furthermore, the extract displayed antimicrobial activity against six bacteria, including Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, Proteus, Brucella and Shigella sonnei. For A549, HCT-116, HT-29, sw1990, HepG2 and HeLa cancer cells, the S. moellendorffii extract possessed apparent inhibition effects on the growth rate. All the results indicated that the DES, as an eco-friendly and efficient solvent, was suitable for extracting total flavonoids from S. moellendorffii.