The optimization of total flavonoids from rhizoma drynariae by response surface methodology and the metal ion chelation activity assay

Rhizoma Drynariae, the dried rhizome of Drynaria fortunei (Kunze), is rich in flavonoids and has varieties of pharmacological activities. To optimize the extract conditions for bioactive flavonoids, a response surface methodology (RSM) was utilized to assess the effects of three independent variables (liquid-to-solid ratio (mL/g), extract temperature (°C) and ethanol concentration (%) on the total flavonoids content (TFC). To test the chelation with metal ion, the UV-visible spectrophotometer was used to detect metal ion chelation of extracted flavonoids. Regression analysis displayed a good fit of the experimental data. The optimal condition was liquid-to-solid ratio with 50:1, extract temperature with 80 °C and ethanol concentration with 40.22%. The total flavonoids had a better chelation with metal ions Cu²⁺, Fe²⁺, Fe³⁺ than Zn²⁺. These results suggested that the model employed is suitable and the application of RSM in optimizing the extract conditions is successful. The experimental values were in fine agreement (the yield 24.05±0.69mg/g) with predicted values. The total flavonoids from the extract presented good chelation against four metal ions (Cu²⁺, Zn²⁺, Fe²⁺ and Fe³⁺), which provided a good evidence for Alzheimer's disease treatments.