Flavonoid glycosides in the shoot system of Okinawa Taumu (Colocasia esculenta S.)

Six C-glycosylflavonoids and one O-glycosylflavonoid have been isolated from the shoot system of Taumu (Colocasia esculenta S.). They were identified as schaftoside, isoschaftoside, orientin, isovitexin, isoorientin, vitexin and luteolin 7-O-sophoroside. The presence of catechol moiety in the B-ring of isoorientin, orientin and luteolin 7-O-sophoroside showed strong antioxidant activity with different mechanisms of action in DPPH radical scavenging, β-carotene bleaching and superoxide radical inhibition assays. The amount of dry weight matter extract of water was higher than methanol for both the leaf and the stem parts. Isovitexin was the main compound in water and methanol extracts of the leaf while schaftoside was the main compound of the water extract of the stem. Methanol extract of the leaf showed higher DPPH radical scavenging activity than water extract while the opposite was observed for the stem. The results of this experiment suggest the potential of the leaf of Taumu as a source of dietary antioxidant.