Application of a New Area Under Curve Method for Antioxidant Capacity Assays of Some Thiosemicarbazone Compounds

Aims&Objectives: The area under curve (AUC) method is the first quantitative method measuring antioxidant protection against lipid oxidation, with a slightly different order of antioxidative effectiveness from reductive assays because of interfacial effects. In this study, peroxidation of copper (II) -induced linoleic acid (LA) emulsion was investigated using a new method of ‘area under curve’ (AUC) approximation based on iron thiocyanate colorimetry. Materials and Methods: The formation of hydroperoxides in the linoleic acid emulsion was carried out at 37 ° C and in an aerated incubation at pH 7. The peroxidation of LA followed by pseudo first order kinetics, and the increases of absorbance obtained as a function of the incubation period gave sigmoidal curves. When the maximum absorbance of the oxidation products is close to 1.0, the area under the kinetic curve (AUC) and the net AUC, i.e. (AUCsample – AUCblank) calculations, the calibration curve plotted with the net AUC versus the concentration for gallic acid. Results: Gallic acid equivalents (GAE) for 5-Methoxyisatin-3-(N-4chlorophenyl) thiosemicarbazone (H25MI3ClPT) and 5-Methoxyisatin-3-(N-phenyl) thiosemicarbazone (H25MI3PT) compounds were calculated using standard curves. As a result, the gallic acid equivalents (GAE) of antioxidant compounds followed the order of BHT (3,5-Di-tert-4-butylhydroxytoluene) > (H25MI3PT) > (H25MI3ClPT) with the use of this new AUC approach.