AN END-POINT METHOD FOR ESTIMATION OF THE TOTAL ANTIOXIDANT ACTIVITY IN PLANT-MATERIAL

The 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) rad ical can be generated by the enzymatic system formed by hydrogen perox ide and horseradish peroxidase, This ABTS radical (ABTS(.+)), a chromo gen, is stable at room temperature but is unstable above 35 degrees C and/or at pH values of above 7.5. Nevertheless, the most important fac tor in its stability is the ABTS/ABTS(.+) concentration ratio in the m edium. The radical reacts with the antioxidant, L-ascorbic acid, with a high rate constant, the stoichiometry of the reaction being 1 mol of L-ascorbic acid per 2 mol of ABTS(.+) reduced. Based on these conside rations, a spectrophotometric end-point method has been developed to e valuate L-ascorbic acid in aqueous media, and this represents an impro vement over the lag-method previously reported. Under optimal conditio ns of temperature, pH and reagent concentration, the end-point method was capable of determining L-ascorbic acid with a limit of quantificat ion of 0.38 nmol. In the assay described here, this ability is used to evaluate the total antioxidant activity of commercial citrus juices, in which ascorbic acid is a principal component. In our opinion this p rocedure can quickly provide useful information on the antioxidant con tent of foods and plant extracts. (C) 1998 John Wiley & Sons, Ltd.