[Extraction of flavonoids in Prunella vulgaris based on deep eutectic solvent method：application of new green solvent].

Flavonoids have attracted much attention due to their good anti-inflammatory, anti-oxidation and anti-tumor effects. At present, the extraction of flavonoids is mainly based on organic solvent, while the researches on the use of green and safe solvents are quite limited. Therefore, in the present study, different types of deep eutectic solvents (DESs) were applied to investigate their effect on extraction of flavonoids and optimize the process, also investigate the recovery efficiency of DESs and evaluate the recovery method for total flavonoids. The extraction yield of the total flavonoids acted as the comprehensive evaluation indexes, and a central composite design (CCD) of response surface methodology (RSM) was employed to further optimize the alcohol-based DES extraction conditions. The results showed that the optimized extraction conditions were as follows: water-DES ratio of 27%, solid-liquid ratio of 15 mL·g⁻¹, extraction temperature of 83 °C and extraction time of 42 min in ChCl-glycerol at 1:4 ratio. Under these conditions, the mean experimental value of the extraction yield (75.05 mg·g⁻¹) corresponded well with the predicted value (77.86 mg·g⁻¹). Moreover, these experimental results showed more advantages such as in higher efficiency, economy and environmental protection as compared with previously reported conventional extraction methods. In addition，the recovery yield of the total flavonoids from the DESs extraction solution achieved 97.88% by using AB-8 macroporous resin, and 88.12% desorption ratio can be achieved by 100% ethanol with 5 times resin content. After the above treated DESs were collected, the extraction yield with the same method reached 95.23%, indicating that the method of macroporous resin can be used for efficient and simple recovery and reuse. This study suggests that DESs can be used as a kind of sustainable and efficient natural extraction solvents for extraction of flavonoids from Prunella vulgaris.