OBJECTIVE To optimize the ultrasonic-assisted deep eutectic solvent(DES) extraction process of total flavonoids from Puerariae Lobatae Radix residue, investigate its in vitro and in vivo biological activities, and provide an experimental basis for the green and efficient resource utilization of Puerariae Lobatae Radix residue.

METHODS Ultrasound-assisted DES was adopted to extract total flavonoids from Puerariae Lobatae Radix residue. Single-factor experiments and the Box-Behnken design were applied to optimize the extraction process. D101 macroporous adsorption resin was used to recover flavonoid components from the solvent, and experiments on the recovery and reuse of DES were carried out. Liquid film sample preparation was employed to determine the Fourier transform infrared absorption spectra of the three extraction solvents. The in vitro antioxidant activities of total flavonoids from Puerariae Lobatae Radix residue were evaluated by DPPH and ABTS radical scavenging assays. A mouse model of middle cerebral artery occlusion was established, and ELISA was performed to detect the levels of interleukin-1β(IL-1β), interleukin-6(IL-6) and tumor necrosis factor-α(TNF-α) in the cerebral cortex of mice.

RESULTS The optimal extraction conditions for total flavonoids from Puerariae Lobatae Radix residue were as follows: the ratio of choline chloride to ethylene glycol was 1∶3.9, water content was 41.18%, material-to-liquid ratio was 1∶31, and ultrasonic time was 19 min. Under these conditions, the average extraction yield of total flavonoids from Puerariae Lobatae Radix residue reached 4.539 mg·g⁻¹. The recovered DES could be recycled 3 times. The absorption peaks of DES showed a displacement phenomenon in the infrared spectrum. The radical scavenging rate of the DES extract was significantly higher than that of the water extract and ethanol extract(P<0.01). Compared with the model group, the levels of IL-1β, IL-6 and TNF-α in the DES group were significantly decreased(P<0.01).

CONCLUSION Ultrasound-assisted DES can effectively enhance the extraction yield and in vitro/in vivo bioactivities of total flavonoids from Puerariae Lobatae Radix residue, enabling green and efficient utilization, and providing insights for the subsequent development and utilization of Puerariae Lobatae Radix resources in traditional Chinese medicine.