Analytical, Nutritional and Clinical Methods Section A critical appraisal of the use of the antioxidant capacity (TEAC) assay in defining optimal antioxidant structures Mariken J.T.J. Arts*, J. Sebastiaan Dallinga, Hans-Peter Voss, Guido R.M.M. Haenen, Aalt Bast Department of Pharmacology and Toxicology, Faculty of Medicine, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands Received 23 March 2002; received in revised form 8 October 2002; accepted 8 October 2002 Abstract In the Trolox Equivalent Antioxidant Capacity (TEAC) assay, i.e. the capacity of a compound to scavenge the ABTS radical (ABTS  ), is assessed. The aim of the present study is to evaluate the applicability of the TEAC assay to predict the antioxidant effectivity of a compound. For this purpose the TEAC assay is compared with other screening assays, such as superoxide scaven- ging, peroxynitrite scavenging and lipid peroxidation. Of the structurally related compounds, catechol, resorcinol and hydro- quinone, resorcinol has the highest TEAC. In contrast, resorcinol appears to have a much lower antioxidant activity than catechol and hydroquinone in other in vitro assays. Similar discrepancies were observed with the flavonoids, chrysin and galangin. The TEAC values of chrysin and galangin are comparable, whereas galangin appears to be a much better antioxidant in other assays. The relatively high TEAC values of chrysin and resorcinol are due to the ability of the reaction products, formed by the reaction of the parent compound with ABTS  , to further react with ABTS  . With catechol, hydroquinone and galangin, these reaction pro- ducts do not react with ABTS  and therefore make no contribution to the TEAC. The possible contribution of reaction products to the TEAC of a compound hampers the use of the TEAC assay for constructing structure–activity relationships (SAR). # 2002 Elsevier Science Ltd. All rights reserved. Keywords: SAR; TEAC; Antioxidant; ABTS radical; Flavonoid 1. Introduction Oxidative stress is involved in the pathogenesis of various chronic diseases, such as cardiovascular disease and cancer (Halliwell & Gutteridge, 1999). Antioxidants protect against free radicals and are therefore important in obtaining and preserving good health. In this respect, much attention has been given to the flavonoids, a class of polyphenols with strong antioxidant activities. Within the wide range of methods used to screen antioxidants, the Trolox Equivalent Antioxidant Capa- city (TEAC) assay is very popular. This assay is based on the scavenging of the relatively stable blue/green ABTS radical (ABTS  ), converting it into a colourless product. The degree of this decolorization reflects the amount of ABTS  that has been scavenged and can be determined spectrophotometrically. The TEAC value is assigned by comparing the scavenging capacity of an antioxidant to that of trolox. The TEAC assay is evaluated using three structurally related compounds. The TEAC values of these com- pounds are compared to their antioxidant activities in several antioxidant assays. Based on the results, the applicability of the TEAC assay for predicting the anti- oxidant effectivity of a compound is discussed. 2. Materials and methods 2.1. Chemicals 2,2 0 -Azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), 6-hydroxy-2, 5,7,8-tetramethylchroman-2-car- boxylic acid (trolox), resorcinol, hydroquinone, catechol, xanthine, xanthine oxidase, Nitro Blue Tetrazolium 0308-8146/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(02)00468-5 Food Chemistry 80 (2003) 409–414 www.elsevier.com/locate/foodchem * Corresponding author. Tel.: +31-43-3881340/417; fax: +31-43- 3884149. E-mail address: mariken.arts@farmaco.unimaas.nl (M.J.T.J. Arts).