In vitro antioxidant activities of extracts of Vernonia amygdalina and Ocimum gratissimum leaves

Abstract

Vernonia amygdalina and Ocimum gratissimum occupy prominent positions in the diets of several Nigerian ethnic groups. This study therefore compared the phenolic content and some antioxidative activities of the ethanolic leaf extracts of these two plants. Ethanolic extracts of freshly plucked leaves were obtained using standard procedures. The phenolic content and antioxidant capacity of the vegetables were quantified in vitro. The results show that O. gratissimum contains higher amounts of total phenolics (168.5 ± 5.50 and 97.0 ± 0.01 mg gallic acid equivalents/g extract respectively) and flavonoids (126.7 ± 1.00 and 65.4 ± 4.42 mg quercetin equivalents/g extract respectively) than V. amygdalina. A dose-dependent increase in flavonol content was observed for both extracts with higher contents obtained in the O. gratissimum extract. O. gratissimum also has higher DPPH radical scavenging activity (IC₅₀ values of 105.7 and 111.8 μg/ml respectively) and ferric reducing antioxidant potential (FRAP) (110.0 ± 0.02 and 85.0 ± 0.01 mg Fe²⁺/g extract). O. gratissimum also had higher reducing power than V. amygdalina at the concentrations studied. Standard ascorbic acid however had higher antioxidant activity values for the DPPH, FRAP and reducing power assays. Both plant extracts reasonably inhibit lipid peroxidation at 31.4 ± 0.15% for V. amygdalina and 42.8 ± 1.00% for O. gratissimum. The results further substantiate the medicinal value of these vegetables. Consumption of these vegetables is encouraged to help militate against deleterious effects of reactive species.

Keywords: Phenolic; Flavonoids; DPPH; Ferric Reducing Antioxidant Potential (FRAP); Lipid peroxidation