Optimization of Extraction of Polyphenols From Vietnamese Zingiber Officinale Rhizome

Zingiber officinale is a popular herb in Vietnam, used as a spice and a traditional medicinal plant, especially its rhizome. The main chemical components are polyphenols. This study was conducted to optimize the extraction of polyphenols from Vietnamese Zingiber officinale rhizome using the magnetic-stirring assisted extraction method and response surface methodology. The solvent used in this study was ethanol 96%. The highest polyphenol content of (12.36±0.04) mg GAE/g dried material was obtained after triplicate repetition of extraction at the optimal conditions of the extraction process as follows: the solvent/dried material ratio (mL/g) of 35/1, the extraction time of 19 minutes, the stirring speed of 400 rpm at the room temperature. In addition, the study also determined the total flavonoid content in the extract by colorimetric method with aluminum chloride reagent and the antioxidant capacity through the DPPH (2,2-diphenyl-1-picryl hydrazyl radical) free radical scavenging method. The results showed that the total flavonoid content was (0.800.06) mg QE/g dried material, and 1 mL of the obtained extract inhibited (96.84  0.26)% of DPPH free radical.