Composition and antioxidant activity of the essential oil from Curcuma zedoaria

Curcuma zedoaria (Berg.) Rosc. (Zingiberaceae) has long been used as a folk medicine. The essential oil of its dried rhizome was isolated using simultaneous steam-distillation and solvent-extraction apparatus and its fractions were prepared by silica gel column chromatography. Totally, 36 compounds were identified in the essential oil, including 17 terpenes, 13 alcohols and 6 ketones. The yields of Fractions 2 and 3 were 83.66 and 10.71%, respectively. Epicurzerenone and curzerene were found in the first and second highest amounts (24.1 and 10.4%). At 20 mg ml−1, the essential oil of C. zedoaria was moderate to good in antioxidant activities by three different methods, good in reducing power and excellent in scavenging effect on 1,1-diphenyl-2-picrylhydrazyl radical but low in chelating effect on ferrous ion. However, after fractionation, with regard to all antioxidant properties assayed, fraction 4 showed consistently better effects than the essential oil did. The compound in fraction 4 responsible for better antioxidant properties might be 5-isopropylidene-3,8-dimethyl-1(5H)-azulenone.