Journal of Medicinal Plants Research Vol. 5(31), pp. 6839-6848, 23 December, 2011 Available online at http://www.academicjournals.org/JMPR ISSN 1996-0875 ©2011 Academic Journals DOI: 10.5897/JMPR11.1238 Full Length Research Paper In vitro antioxidant properties of aqueous and ethanolic extracts of walnut (Juglans regia) Ogunmoyole T. 1 *, Kade I. J. 1 and Korodele B. 2 1 Department of Biochemistry, Federal University of Technology, P. M. B. 704, Akure, Ondo State, Nigeria. 2 Department of Biochemistry, Adekunle Ajasin University, P. M. B. 001, Akungba- Akoko, Ondo State, Nigeria. Accepted 1 November, 2011 Walnut has been reported to exhibit several pharmacological properties and widely used in folkloric medicine for the traditional treatment of ailments. Hence, this study sought to investigate the antioxidant properties of the aqueous and ethanolic extract of walnut seed using several antioxidant parameters. Both extracts were tested for free radical scavenging ability against 2, 2 diphenyl-1-picryl hydrazyl (DPPH) radical, ferric reducing and iron (II) chelating ability. Furthermore, the ability of both extracts to offer protective benefit against lipid peroxidation was assessed. Moreover, the phytochemical constituents (total phenolics, flavonoids and vitamin C) of both extracts were measured. Generally, ethanolic extract was found to exhibit a significantly higher antioxidant activity than do aqueous in all parameters determined. Result showed that both extracts demonstrated potent free radical scavenging and ferric reducing ability and iron chelating activity in vitro. Moreover, both extracts demonstrated potent inhibitory effect on proxidant induced oxidative assault against cerebral and hepatic lipid. The phenolic content of Juglans regia was estimated to be 35.22 ± 0.75 mg/g (GAE) for ethanolic and 20.26 ± 0.55 mg/g (GAE) for aqueous extract whereas the flavonoid content was estimated to be 20.02 ± 0.12 mg/g (QE) for ethanolic and 14.82 ± 0.15 mg/g (QE). In addition, the vitamin C contents were 18.22 mg/g and 10.18 mg/g respectively for ethanolic and aqueous extract of dried J. regia. From the foregoing, the wide usage of walnut seed as remedy for ailment in folk medicine may be due to its high phytochemical constituents and potent antioxidant properties in vitro. Hence, information from this study would provide the underlying mechanisms through which walnut seed exhibit its pharmacological properties which when exploited could be helpful in the management of degenerative diseases. Key words: Phytochemical, oxidative assault, proxidant. INTRODUCTION Walnut (Juglans regia L) is a member of Juglandaceae family and one of the finest nuts of temperate regions (Ozcan, 2009) with highly promising economic value for the food industry (Martinez et al., 2008). Its nuts have been reported to exhibit unique organoleptic characteristics (Lopez et al., 1995), hypocholesterolemic (Sabate and Fraser, 1994; Abbey et al., 1994; Savage, 2005; Dogan and Akgulb, 2005; Pereira et al., 2008) and antihypertensive effect (Sabate and Fraser, 1994; Mexis et al., 2008; Arranz et al., 2008). The bark of J. regia is *Corresponding author. E-mail: ogunmoyoledayo@yahoo.com. regularly used as miswaks for teeth and mouth cleaning (Ibrar et al., 2007). Moreover, walnut has been reported to exhibit both antibacterial (Emira et al., 2011) and antifungal properties (Emira et al., 2010). The increasing interest in walnuts may be due to its significant economical value and medicinal importance for human health because of their biochemical composition of polyunsaturated fatty acids, especially (linoleic, oleic acid) and high protein value (Savage et al., 2001). They also contain other beneficial components like plant protein (for example, arginine, leucine), carbohydrates (for example, dietary fibre), vitamins (for example, vitamin A and E), pectic substances, minerals (magnesium, potassium, phosphorus, sulphur, copper and iron), plant