Interaction of Red Cabbage Extract with Exogenous Antioxidants in ORAC Assay

Understanding interactions between antioxidants is crucial since in biological and food matrices, we are dealing with complex multi-component antioxidant systems. This study aimed to quantitatively characterize interactions of antioxidants in anthocyanin-rich aqueous red cabbage extract with several natural (ascorbic acid, gallic acid, and glutathione) and synthetic (Trolox and TEMPOL) antioxidants and to determine their synergistic or antagonistic nature in the ORAC assay. Four parameters derivable from the ORAC assay (extent of fluorescence protection, lag time, fluorescence half-life t_1/2, and maximum rate of fluorescence decay) were analyzed in terms of the integrated interaction coefficient (IIC), reflecting the dependence of the analyzed values on the concentration of antioxidants and the sample interaction coefficient (SIC) derived from interaction at a single set of concentrations. IIC analysis revealed synergistic interactions of Trolox with the red cabbage extract on the basis of fluorescence protection, lag time, and t_1/2. Interactions of TEMPOL with the extract were antagonistic as assessed based on all parameters but the lag time. A correlation between the anodic peak and the lag time and t_1/2 values was observed for the antioxidants studied. The interactions between antioxidants in complex mixtures are important as they affect the measured total antioxidant activity, which, depending on the nature of the interactions, may be lower or higher than the sum of activities of individual components.