KINETIC AND STOICHIOMETRIC EVALUATION OF FREE RADICALS SCAVENGERS ACTIVITIES BASED ON DIPHENYL-PICRYL HYDRAZYYL (DPPH) CONSUMPTION

ABSTRACT Kinetics and stoichiometric measurements based on the reactions of stable free radicals are among the most employed procedures in the evaluation of antioxidant activities of pure compounds and complex mixtures. In the present work it is shown that initial rates of diphenyl-picryl hydrazyl (DPPH) consumption elicited by cinnamic acid derivatives are closely related to their reactivity towards peroxyl radicals. This implies that kinetic data regarding DPPH bleaching can be useful on the evaluation of antioxidant reactivities. On the other hand, data obtained at a single (long) reaction time are unrelated to the reactivity of the antioxidants and mostly reflect the number of phenol groups present in the tested sample Keywords: Diphenyl-picryl hydrazyl; cinnamic acids; reactivity; stoichiometry . INTRODUCTION Evaluation of the capacity of a given compound (free radical scavenger or antioxidant) to remove biological relevant radicals (ROS or NOS) is a matter of great interest. Similarly, much effort has been devoted to determine in a single assay the total antioxidant capacity (or activity) of complex mixtures (biological fluids, fruits, vegetables, juices, wine, etc.) and a number of reviews has been dedicated to discuss the data and the advantages and limitations of the different methodologies