Optimization of Ultrasound-Assisted Extraction Technology of Total Flavonoids from Alpinia oxyphylla Fructus by Response Surface Methodology and Its Antioxidant Activities

The present study aimed to optimize the ultrasound-assisted extraction process of total flavonoids from Alpinia oxyphylla fructus（AOF） and evaluate the antioxidant activities. The single factor experiments were employed to determine the effects of methanol concentrations, ultrasonic time and liquid-to-material ratios on extraction rates of total flavonoids using the yields as indicator, then the Box-Behnken methodology was used to further optimize the ultrasound-assisted extraction conditions of total flavonoids from AOF, subsequently the antioxidant activities were evaluated by the methods of scavenging DPPH and ABTS free radicals, as well as ferric ion reducing antioxidant power（FRAP） assay. Besides, the correlation between total flavonoids contents and antioxidant activities were analyzed. The results showed that, the optimal extraction conditions were as follows: methanol volume fraction of 100%, ultrasound time of 20 min, the liquid-to-material ratio of 25∶1（mL/g） and the extraction rate of total flavonoids reached 0.757%. The IC₅₀ values of scavenging rates on DPPH and ABTS free radicals were0.851 ～3.188 mg/mL and 0.642 ～1.789 mg/mL（equivalent to raw medicine）, respectively. The FRAP value was0.029～0.111 mmol/L. The contents of total flavonoids were positively correlated with the IC₅₀ values of scavenging rates on DPPH free radical and the FRAP values（P＜0.05）. However, there was no significant correlation between the IC₅₀ values of scavenging rates on ABTS free radicals and total flavonoids contents.