Phytochemical content and antioxidant capacity of water-soluble isolates from peanuts (Arachis hypogaea L.) Christopher E. Duncan a , Daniel W. Gorbet b , Stephen T. Talcott a, * a Department of Food Science and Human Nutrition, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA b University of Florida, North Florida Research and Education Center, Marianna, FL 32344, USA Received 29 November 2005; accepted 22 May 2006 Abstract Numerous polyphenolics have been identified in peanuts, but information relating to their storage stability and contributions to total antioxidant capacity are lacking. This study investigated contributors to the antioxidant capacity of six peanut cultivars by means of fractionation from reversed phase C18 cartridges. Five water-soluble peanut isolates were prepared and subsequently stored at 35 °C and evaluated for individual and total polyphenolics, antioxidant capacity, total reducing equivalents, and total amino acids after 0, 2, 4 and 8 weeks. The relative contribution of each isolate to total antioxidant capacity for each cultivar was additive, with the C18 non-retained fraction containing 100% of the p-coumaric acid and 82% of the total amino acids. During storage relatively small changes were observed for antioxidant activity and total reducing equivalents among cultivars and isolates, indicating the lack of oxidative or condensation reactions among the isolated constituents. Results demonstrated the overall stability and diversity of antioxidant polyphen- olics found in peanuts, information that advances the marketability of the crop. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Peanuts; Antioxidant; Fractionation; Polyphenolics; Storage 1. Introduction Peanuts may be consumed raw, roasted, pureed, or in a variety of other processed forms, and constitute as a multi- million-dollar crop world wide (Yu, Ahmenda, & Goktepe, 2005) with numerous potential dietary benefits. Recently several peanut cultivars were developed with elevated con- centrations of the monounsaturated fatty acid oleic acid, in relation to other highly oxidizable polyunsaturated fatty acids. The high oleic trait provides peanuts with potentially greater health benefits and serves to prolong shelf life char- acteristics (Pattee, Isleib, Moore, Gorbet, & Giesbrecht, 2002; Reed, Sims, Gorbet, & O’Keefe, 2002; Talcott, Dun- can, Del Pozo-Insfran, & Gorbet, 2005). Additionally, pea- nuts were found to lack naturally occurring trans-fatty acids (Sanders, 2001), which have been adversely associated with various diseases (Awad, Chan, Downie, & Fink, 2000; Feld- man, 1999; Peanut-Institute, 2002). Numerous phytochemi- cal compounds are present in peanuts with potential antioxidant capacity including polyphenolics (Talcott, Pass- eretti, Duncan, & Gorbet, 2005), tocopherols (Hashim, Koehler, & Eitenmiller, 1993), and proteins (Bland & Lax, 2000). Other than contributions from these compounds, mature peanut kernels likely possess few other compounds in significant quantities that would impact antioxidant capacity. Up to 15 polyphenolics have been identified in pea- nuts (Duke, 1992) whereas Seo and Morr (1985) identified six from defatted peanut meal where p-coumaric acid was the predominant compound, accounting for 40–68% of the total phenolics present. Fajardo, Waniska, Cuero, and Pettit (1995) reported stress-induced synthesis of free and bound polyphenolics in peanuts with p-coumaric and ferulic acid present in the highest concentrations. Alone, p-coumaric acid has been shown to possess significant radical scaveng- ing activities (Rice-Evans, Miller, & Paganga, 1996; Rice- Evans, Miller, & Paganga, 1997) but its contribution to total 0963-9969/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2006.05.009 * Corresponding author. Tel.: +1 352 392 1991; fax: +1 352 392 9467. E-mail address: sttalcott@mail.ifas.ufl.edu (S.T. Talcott). www.elsevier.com/locate/foodres Food Research International 39 (2006) 898–904