Optimization of microwave-assisted extraction, antioxidant capacity, and characterization of total flavonoids from the leaves of Alpinia oxyphylla Miq.

To optimize the extraction of total flavonoids (TFL) from the leaves of Alpinia oxyphylla Miq. using microwave-assisted method, a orthogonal test was used. The optimal extraction conditions for TFL were determined as follows: ethanol concentration of 50%, solid-liquid ratio of 1:20, temperature of 70 °C, and cycle index of 3. Under these conditions, the extraction yield of TFL was 28.24%. The scavenging rate of TFL against a,a-diphenyl-b-picrylhydrazyl (DPPH), 2,2-azino-bis(3-ethylbenzoth- iazoline-6-sulphonica cid) (ABTS), and superoxide anion radical (O₂^－·) was screened. The results showed that the bioactivity of extracts appeared to be TFL dose-dependent, while it also presented stronger ferric reducing antioxidant power (FRAP). The contents of chrysin and tectochrysin in TFL were quantitatively analyzed by HPLC.