Journal of Agricultural Science; Vol. 6, No. 1; 2014 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 13 Comparative Antioxidant Activities of Extracts of Vernonia amygdalina and Ocimum gratissimum Leaves Kelly Oriakhi 1 , Ehigbai Igbuan Oikeh 2 , Nkeiruka Ezeugwu 1 , Ogechukwu Anoliefo 1 , Omorede Aguebor 1 & Ehimwenma Sheena Omoregie 2 1 Department of Medical Biochemistry, School of Basic Medical Sciences, University of Benin, Benin City, Nigeria 2 Department of Biochemistry, Faculty of Life Sciences, University of Benin, Benin City, Nigeria Correspondence: Ehigbai Igbuan Oikeh, Department of Biochemistry, Faculty of Life Sciences, University of Benin, Benin City, Nigeria. E-mail: ehigbai.oikeh@uniben.edu Received: September 9, 2013 Accepted: October 27, 2013 Online Published: December 15, 2013 doi:10.5539/jas.v6n1p13 URL: http://dx.doi.org/10.5539/jas.v6n1p13 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 (IC 50 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 Fe 2+ /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 content, flavonoids, DPPH, ferric reducing antioxidant potential (FRAP), lipid peroxidation 1. Introduction The therapeutic effects of several medicinal plants are usually attributed to their antioxidant phytochemicals. There is currently, widespread screening of plants with potential bioactive properties and concomitant isolation and characterization of these bioactive principles for prevention and combating a wide array of diseases (Farombi & Owoeye, 2011; Njan, 2012). Different plant parts used in various treatment regimes include leaves, barks, tubers and root that secrete phytochemicals such as alkaloids, terpenes and phenolic compounds. Their utilization may be in decoction, emulsion, apozems, liniments and powdered forms. Medicinal plants are also exploited in cosmetics, perfumery, pharmaceutical and food industries. Their successful exploitation depends on the identification, isolation and purification of desired phytochemicals (Belewu, Olatunde, & Giwa, 2009). Vernonia amygdalina Del. (Compositae), commonly known as “bitter leaf” in Nigeria because of the bitter taste impacted by the leaves and the stem, is a major vegetable of the celebrated “bitter leaf soup” among the Nigerian people. Vernacular names include “ewuro” among the Yorubas and “onugbu” among the Ibos. It has a long history of use in folk medicine particularly among the people of sub-Saharan Africa. Previous studies have reported that it possess antimicrobial, antidiabetic, antimalarial, antiparasitic, insecticidal, anticancer, anti-inflammatory, antipyretic, analgesic, antihelminthic hepatoprotective, antioxidative and hypolipidaemic effects among others (Atangwho, Ebong, Egbung, & Obi, 2010; Yeap et al., 2010, Danquah, Koffuor, Annan, & Ketor, 2012; Ho et al., 2012).