Interactions Between Antioxidants: How Useful Are In Vitro Studies for Understanding the Action of Antioxidants in Complex Systems?

Interactions between antioxidants are believed to be fundamental for proper nutrition and health benefits. This review discusses various types of antioxidant interactions in vitro, their mechanisms, and their dependence on assay conditions and evaluates the validity of extrapolations of results obtained from cell-free assays and assays of cellular antioxidant activity to in vivo and food systems. In vitro studies revealed that the type of interaction (additive, antagonistic, or synergistic) depends not only on the identity of compounds but also on their absolute concentrations, concentration ratio, type of assay, reaction medium, and the method of analysis of results. Moreover, reactions of antioxidants in simple model systems, employing synthetic indicators, do not fully reflect their reactivity in food systems and organisms. Although in vitro studies may be a useful and necessary step for explaining the mechanisms of interactions between antioxidants, their importance for explaining the phenomena observed in vivo seems limited, as the organismal effects of compounds referred to as antioxidants depend rather on their actions on specific signaling pathways than on their direct antioxidant action. Nevertheless, they may provide useful information for food preservation, allowing for the reduction of the amounts of antioxidant additives.