A stoichio-kinetic model for a DPPH^∙ -ferulic acid reaction

Estimates of the activity of antioxidants in the literature often appear inconsistent. In the specific case of the DPPH^∙ test, the diversity of measurements may arise from variations in the protocols followed. This paper proposes an unbiased method which models the reduction mechanism. This method is applied to the reduction of DPPH^∙ by ferulic acid. A scheme with eight coupled reactions is proposed and has been validated on different solvents and using a wide range of DPPH ̇, ferulic acid, and 5,5'-diferulic acid concentrations, and verified using data from the literature on ferulic acid activity. This modeling approach permits a correction to the bias of the 8th reaction (spontaneous reduction of DPPH ̇), because of its sensitivity to solvent, which in most cases is not taken into account. The best experimental strategy to determine the Efficient Concentration of ferulic acid to reduce 20% (EC20) and 50% (EC50) of DPPH^∙ is then detailed in terms of initial DPPH^∙ concentrations and the duration of the experiment.