Synergy and antagonism are controversial characteristic behaviors of very diverse systems. Despite their importance, the common characterization of these phenomena in the context of the antioxidant action is often questionable due to some problematic definitions and the type of data used. In this paper, a methodological procedure has been developed for the joint action of several pairs of antioxidants, which enables the determination and quantification of the synergistic and antagonistic interactive effects. Well-established ideas from different existing fields are used to replace the current simplistic procedures to quantify the effects of joint responses. One of the common hypotheses for describing the combined effects is established for SET assays. A dose dependent mathematical model representative of that hypothesis, based on probability functions with meaningful parameters, is applied. The interactive effects between antioxidants are introduced into the model with simple auxiliary functions that describe the variations induced by each antioxidant in the parameters that define the effects of the other. Finally, a comprehensive index to summarize the complex parametric responses in one single value is proposed. Although the approach was experimentally demonstrated just in two classical SET assays (DPPH and ABTS), the results are directly expandable to other types of classical SET assays. Statistically consistent responses of null, synergy and antagonism effects were found when characterizing the interactions between several pairs of individual and complex mixtures of chemical antioxidant agents.
Two types of antioxidant samples, individual chemical entities and complex mixtures, covering as much as possible the range of possible responses, were used to test the rapid methodology proposed here. The results showed that the AC of the extracts was more similar compared to some of the commercial standards in terms of potential maximum capacity, while others showed lower values. The proposed generalized procedures for the joint action of several well-known antioxidants produced consistent results in all cases.
Afterwards, we determined and quantified the null/synergistic/antagonistic interactions between binary combinations of those types of antioxidants using the developed methodological procedure. Therefore, in the assessment of the possible interactive effects in binary mixtures of antioxidants, the new procedure represents a powerful informative tool, which is effectively designed for defining the important aspects of very complex responses. Although the proposed approach is a little more complicated than some relatively common solutions, we believe that it is free from the most controversial aspects of such approaches.