Objective  Extraction process of flavonoids from roots of Acanthopanax senticosus plants was optimized by response surface method, and in vitro antioxidant activity of the extract determined.

  Methods  A single factor Box-Benhnken design experiment was conducted to optimize the flavonoid extraction. The antioxidant activity of the extracted flavonoids was measured against DPPH, ABTS, and hydroxyl free radicals as well as the total reducing capacity and protection of macrophages against oxidative stress.

  Results  The optimized process by a response surface experiment with 4 factors and 3 levels used 55% ethanol at a liquid-solid ratio of 45:1 to extract at 72 ℃ for 73 m. It resulted in a yield of total flavonoids of 24.11±0.17 mg·g⁻¹. The IC₅₀ of the extract on DPPH, ABTS, and hydroxyl free radicals were 28.38 μg·mL⁻¹, 103.77 μg·mL⁻¹, and 228.70 μg·mL⁻¹, respectively. The extract exhibited a capacity in raising the proliferation of RAW264.7 cells and in protecting against the oxidative damage induced by H₂O₂.

  Conclusion  The flavonoids extracted from the roots of A. senticosus exhibited significant in vitro antioxidant activities.