Extraction of Flavonoids from Scutellariae Radix using Ultrasound-Assisted Deep Eutectic Solvents and Evaluation of Their Anti-Inflammatory Activities

Deep eutectic solvents (DESs) play important roles in the extraction of active constituents in traditional Chinese medicine. Ultrasound-assisted DES has been used to extract flavonoids from Scutellaria baicalensis. Using the contents of scutellarin, baicalin, baicalein, wogonoside, wogonin, and oroxylin A as quantitative indices, different kinds of DESs have been optimized for extraction and betaine/acetic acid has shown the highest yield. The Box-Behnken response surface method (RSM) was utilized to select the extraction conditions with the highest yields. The optimal extraction conditions were as follows: the molar ratio of betaine/acetic acid was 1:4, the water content was 40%, the solid/liquid ratio was 1:100 g/mL, the extraction temperature was 52 °C, and the extraction time was 23 min. Compared with traditional reflux extraction using 70% ethanol as the solvent, ultrasound-assisted DES has a shorter extraction time and higher yields. Furthermore, anti-inflammatory activities of the two extracts by ultrasound-assisted DES and reflux were compared using RAW264.7 cells and the methyl thiazolyl tetrazolium (MTT) method, and they showed equal anti-inflammatory activities. The results demonstrated that the ultrasound-assisted DES method for extraction of flavonoids from scutellariae radix is simple, green, efficient, and reproducible. This research provides good method guides for the rapid and efficient extraction of flavonoids from natural sources.