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In this paper, we report on a method to evaluate the activity of water soluble and H-atom donor antioxidants as peroxyl radical scavengers in a micelle system reproducing the conditions occurring in the upper small intestine in humans, during digestion and absorption of lipids. This method, which overcomes some of the problems of the total radical trapping antioxidant parameter (TRAP) assays, measures the peroxyl radical trapping capacity (n) and the peroxyl radical trapping efficiency IC 50 − 1 of antioxidants, that is the number “n” of peroxyl radicals trapped by one molecule of the studied antioxidant and the reciprocal of the antioxidant concentration that halves the steady-state concentration of peroxyl radicals, respectively. These two fundamental parameters characterizing the radical chain breaking of many water soluble antioxidants, among which dietary polyphenols, can be obtained with relatively good precision from a single experiment, on the basis of a rigorous treatment of the kinetic data.

The inhibitory effect of anthocyanins has been investigated in the peroxidation of linoleic acid in micelles in the presence and in the absence of (+)-catechin. The peroxidation was initiated by thermal decomposition of 2,2(')-azobis[2-(2-imidazolin-2-yl)propane], and the kinetics of peroxidation were followed by measuring the rate of oxygen consumption and the rate of disappearance of the antioxidant. The analysis of the antioxidant effect of various anthocyanins, alone or in the presence of catechin, demonstrates that catechin, which is relatively inefficient at inhibiting linoleic acid oxidation, regenerates the highly efficient antioxidant malvidin 3-glucoside and, at a lower extent, peonidin 3-glucoside. The malvidin 3-glucoside recycling by catechin strongly increases the antioxidant efficiency of these two antioxidants. This protective mechanism appears specific for malvidin and peonidin 3-glucosides. The high unpaired spin density of the phenolic O atoms in the radicals generated by these anthocyanins, calculated by the semiempirical quantum chemical AM1 method, may explain the observed behavior.