Analysis of plasma antioxidant capacity by competition kinetics.

A competition kinetics procedure for measuring plasma antioxidant capacity is described. This procedure is based on the "crocin bleaching test" (Bors, W., et al. Biochim. Biophys. Acta 796:312-319; 1984) modified for analyzing the antioxidant capacity of complex mixtures (Tubaro, F., et al. J. Am. Oil Chem. Soc. 73:173-179; 1996). The information produced by this test is similar to that of the popular "total radical trapping antioxidant potential" (TRAP) analysis. However, the adopted kinetic approach is, in principle, more precise, taking into account both the concentration of antioxidants and their rate constant for the reaction with peroxy radical, which is overlooked in TRAP tests, as implied by the theory of the approach and confirmed by dynamic modeling. The kinetic analysis has also the advantage of accounting for the average between antioxidant effect (reduction of peroxy radicals) and possible prooxidant effect (oxidation by the radical of the antioxidant of the target supposed to be protected) if any. Thus, the result of this analysis provides a more precise evaluation of the efficiency of antioxidant defense. The intraassay variation resulted in less than 8% and, in young healthy subjects, the plasma antioxidant capacity, expressed as mM equivalents of a reference antioxidant (Trolox C), gave 1.59 +/- 0.28. The validated procedure has been used to show that plasma antioxidant capacity is deeply influenced by the consumption of wine.