Abstract
The accumulation of the 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical catalyzed by peroxidase can be inhibited by the presence ofL-ascorbic acid in the reaction medium, this inhibition delaying the accumulation of the ABTS radical and giving rise to a lag time. A kinetic approach to explain this lag time is presented, which also makes it possible to determine the amount ofL-ascorbic acid in the reaction medium. The stoichiometry of the system was determined as 1 mol ofL-ascorbic acid reducing 2 mol of ABTS radicals.L-Ascorbic acid is not the only compound to have this ability, since other antioxidant compounds also react with the ABTS radical. We studied the ABTS/H2O2/horseradish peroxidase system in the presence ofL-ascorbic acid and other antioxidant compounds. The influence of such factors as pH, enzyme concentration, andL-ascorbic acid concentration was studied. A good correlation between the lag time and theL-ascorbic acid present in the medium was observed, and, under optimal conditions, the method could determine as little as 0.65 nmol ofL-ascorbic acid. Based on our findings, we propose a method to measure the total antioxidant activity of different compounds related toL-ascorbic acid and apply this method to determining the total antioxidant activity present in fruit juices.
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