Antioxidant constituents in Vernonia amygdalina leaves

Vernonia amygdalina Del. ( Asteraceae) is a plant widely used both for nutritional and medicinal purposes throughout the tropical Africa. The health-promoting ability of this plant species might be related to the antioxidative effect of its constituents. In this study, the antioxidant activity of this plant was evaluated by comparing the reducing capacity and the DPPH radical scavenging of two previously isolated sesquiterpene lactones ( vernolide and vernodalol) with the ethanol extract from which the two compounds were isolated. Results indicated that vernolide had a higher reducing power than vernodalol and the ethanol extract. At 0.25 mg/mL, vernolide had an absorbance value of 0.15 while vernolide and the ethanol extract had absorbencies of 0.042 and 0.144, respectively. Catechin ( a standard antioxidant compound), however, exhibited a higher reducing power than all the three samples. In the DPPH radical scavenging, both the sesquiterpene lactones and the ethanol extract exhibited appreciable activity. At 0.25 mg/mL, the activity order was ethanol extract > vernodalol > vernolide. At all concentrations, the ethanol extract had higher radical scavenging activity than the sesquiterpene lactones, suggesting a possible synergistic effect of these and any other antioxidant constituents.