Effect of steaming on the functional compounds and antioxidant activity of Fijian taro (Colocasia esculenta L. Schott) corms

We investigated the effects of steaming Fijian taro (Colocasia esculenta L. Schott) corms on their functional compound contents and antioxidant activities by comparison with those of un-steamed Fijian taro corms. Taro corms from Fiji were washed, peeled, cut, then either steamed or left un-steamed, and freeze-dried. Ten gram of each freeze-dried taro corm sample was extracted with water, methanol, and ethanol. The total phenolic content (TPC) and total flavonoid content (TFC) of the taro corms were determined using the Folin-Ciocalteu's colorimetric and the aluminum chloride colorimetric methods, respectively. The antioxidant activity was determined using the 2,2-diphenyl- 1-picrylhydrazyl (DPPH) radical scavenging activity, ferric reducing antioxidant power (FRAP), and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity. The water-extracted steamed Fijian taro corm showed the greatest extraction yield of 11.58±1.20%, whereas the ethanol-extracted un-steamed Fijian taro corm exhibited the lowest extraction yield of 4.24±0.77%. The TPC (42.77±3.39 mg gallic acid equivalents/g dry weight) and TFC (12.68±4.85 mg catechin equivalents/g dry weight) of the methanol-extracted steamed Fijian taro corms were significantly larger than those of the other extracts (p<0.05). The steamed Fijian taro corms extracted with methanol significantly demonstrated greatest activities in DPPH radical scavenging activity (34.82±2.91%), FRAP (339.08±20.50 mM Trolox equivalents), and ABTS radical scavenging activity (56.34±3.54%) (p<0.05). This study provides the basis for developing a healthy snack food based on steamed Fijian taro.