INHIBITION BY L-ASCORBIC-ACID AND OTHER ANTIOXIDANTS OF THE 2,2'-AZINO-BIS(3-ETHYLBENZTHIAZOLINE-6-SULFONIC ACID) OXIDATION CATALYZED BY PEROXIDASE - A NEW APPROACH FOR DETERMINING TOTAL ANTIOXIDANT STATUS OF FOODS

The accumulation of the 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfoni c acid) (ABTS) radical catalyzed by peroxidase can be inhibited by the presence of L-ascorbic acid in the reaction medium, this inhibition d elaying 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 of L-ascorbic acid in t he reaction medium, The stoichiometry of the system was determined as 1 mol of L-ascorbic acid reducing 2 mol of ABTS radicals. L-Ascorbic a cid is not the only compound to have this ability, since other antioxi dant compounds also react with the ABTS radical. We studied the ABTS/H 2O2/horseradish peroxidase system in the presence of L-ascorbic acid a nd other antioxidant compounds. The influence of such factors as pH, e nzyme concentration, and L-ascorbic acid concentration was studied. A good correlation between the lag time and the L-ascorbic acid present in the medium was observed, and, under optimal conditions, the method could determine as little as 0.65 nmol of L-ascorbic acid. Based on ou r findings, we propose a method to measure the total antioxidant activ ity of different compounds related to L-ascorbic acid and apply this m ethod to determining the total antioxidant activity present in fruit j uices. (C) 1996 Academic Press, Inc.