Antioxidant capacity of reaction products limits the applicability of the Trolox Equivalent Antioxidant Capacity (TEAC) assay

The Trolox Equivalent Antioxidant Capacity (TEAC) assay is based on the scavenging of the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical (ABTS(*)) converting it into a colorless product. The degree of decolorization induced by a compound is related to that induced by trolox, giving the TEAC value. The assay is frequently used for constructing structure activity relationships (SARs). HPLC analysis of the reaction mixture, obtained after scavenging of ABTS(*) by the flavonoid chrysin, shows that a product is formed that also reacts with ABTS(*). The product has a higher antioxidant capacity and reacts faster with ABTS(*) than the parent compound, chrysin. In contrast to the reaction product of chrysin, the reaction product of trolox, which is formed during scavenging of ABTS(*), i.e. trolox quinone, does not react with ABTS(*). The experiments show that the TEAC is the antioxidant capacity of the parent compound plus the potential antioxidant capacity of the reaction product(s). This means that the TEAC assay does not necessarily reflect the antioxidant effect of only one structure. This hampers the applicability of the assay for the construction of SARs and for ranking antioxidants

Masking of antioxidant capacity by the interaction of flavonoids with protein.

: Food Chem Toxicol 2001 Aug;39(8):787-91 Related Articles, Books, LinkOut Masking of antioxidant capacity by the interaction of flavonoids with protein. Arts MJ, Haenen GR, Voss HP, Bast A. Department of Pharmacology and Toxicology, Faculty of Medicine, Maastricht University, PO Box 616, 6200 MD, Maastricht, The Netherlands. [email protected] The effect of antioxidants is often executed in complex biological mixtures where various interactions may take place. Therefore, the antioxidant capacity of antioxidants in blood plasma is examined. The assay used is the trolox equivalent antioxidant capacity (TEAC). This method gives the antioxidant capacity of a compound by measuring spectrophotometrically the disappearance of the blue/green stable ABTS [2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] radical, caused by scavenging. The results show that the antioxidant capacity of quercetin, rutin, catechin or 7-monohydroxyethylrutoside (monoHER) and blood plasma is not additive. This is partly due to interactions between the antioxidant and plasma proteins. However, the antioxidant capacity of alpha-tocopherol, which also binds to protein, is not affected by the interaction. This means that besides the antioxidant capacity of the compound itself, the environment in which the antioxidant has to execute his function is important

A critical appraisal of the use of the antioxidant capacity (TEAC) assay in defining optimal structures

In the Trolox Equivalent Antioxidant Capacity (TEAC) assay, i.e. the capacity of a compound to scavenge the ABTS radical (ABTS(circle)), 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 scavenging, peroxynitrite scavenging and lipid peroxidation. Of the structurally related compounds, catechol, resorcinol and hydroquinone, 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(circle), to further react with ABTS(circle). With catechol, hydroquinone and galangin, these reaction products do not react with ABTS(circle) 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)

A new approach to assess the total antioxidant capacity using the TEAC assay

The trolox, equivalent antioxidant capacity (TEAC) assay is a popular method for assessing the capacity of a compound to scavenge ABTS radicals (ABTS(.)). Under the conditions in which the assay is performed, the reaction between most antioxidants and ABTS(.) does not reach completion within the time span applied. This leads to an underestimation of the TEAC of these antioxidants. In the present study, incubations with different concentrations of ABTS(.) and a fixed concentration of antioxidant were performed. The decrease in ABTS(.) concentration in 6 min was plotted against the initial concentration of ABTS(.) and fitted by an exponential function. Extrapolation of the fit to an infinite excess of ABTS(.) gives the maximal concentration of ABTS(.) that can be scavenged by the antioxidant at the concentration employed. This can be used to determine the actual TEAC of antioxidants, i.e. the total antioxidant capacity

Interactions between flavonoids and proteins: effect on the total antioxidant capacity

Interactions between flavonoids and proteins: effect on the total antioxidant capacity. Arts MJ, Haenen GR, Wilms LC, Beetstra SA, Heijnen CG, Voss HP, Bast A. Department of Pharmacology and Toxicology, Faculty of Medicine, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands. [email protected] Flavonoids are potent antioxidants. It is also known that flavonoids bind to proteins. The effect of the interaction between tea flavonoids and proteins on the antioxidant capacity was examined. Their separate and combined antioxidant capacities were measured with the Trolox equivalent antioxidant capacity (TEAC) assay. It was observed that the antioxidant capacity of several components of green and black tea with alpha-, beta-, and kappa-casein or albumin is not additive; that is, a part of the total antioxidant capacity is masked by the interaction. This masking depends on both the protein and the flavonoid used. Components in green and black tea, which show the highest masking in combination with beta-casein, are epigallocatechin gallate and gallic acid. The results demonstrate that the matrix influences the efficacy of an antioxidan