Free Radical Scavenging Activity and Reducing Capacity of Five Southern Thai Indigenous Vegetable Extracts

The phenolic compounds of five southern Thai indigenous vegetables including Mon-pu (Glochidion wallichianum Muell Arg), Cha-plu (Piper sarmentosum Roxb.), white popinac (Leucaena leucocephala de Wit.), djenkol tree (Archidendrom jiringa I. C. Nielsen.) and stink bean (Parkia speciosa Hassk.) were extracted using different solvents (50 % acetone, 80 % methanol and distilled water) at a ratio of sample to extracting medium of 1:25 (w/v). The extracts were analyzed for total phenolic content using the Folin-Ciocalteu procedure, free radical scavenging capacity by using 2’,2’-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) methods, and reducing capacity by using a ferric reducing antioxidant power (FRAP) assay. The acetone extracts of all plants possessed the highest total phenolic content followed by the methanolic and distilled water extracts, respectively. The highest total phenolic content was found in the acetone extracts of Mon-pu and white popinac (p < 0.05). The acetone extracts of all plants showed higher free radical scavenging capacity and reducing capacity than those of their methanolic and water extracts counterparts, respectively (p < 0.05). Among all plants tested, the extracts of Mon-pu extracted with all extracting media exhibited the highest free radical scavenging and reducing abilities (p < 0.05). The present study suggested that the acetone extract of Mon-pu was a potential source of natural antioxidants.