Development of Novel Antioxidant Evaluation Method Based on the Electrochemical Study of the Formation of the Copper(II) Neocuproine Complex

Considering the importance of antioxidants in food and medical industries, the accurate evaluation of their reactivity is of capital importance. In this work, a new electrochemical approach based on the cupric reducing antioxidant capacity (CUPRAC) is proposed for the accurate evaluation of antioxidant properties. The electrochemical behavior of the complex ([Cu(Nc) 2 ] 2+ ) obtained from the reaction between copper(II) and neocuproine (Nc) used in the CUPRAC method was studied to identify the ideal Cu/Nc molar ratio. The Cu/Nc ratio of 4/3, usually used in the CUPRAC method, was not suitable because of the partial reaction of Nc with Cu(II). A more appropriate Cu/Nc molar ratio of 1/7 was experimentally determined by voltammetry at a stationary or rotating electrode. With this molar ratio, [Cu(Nc) 2 ] 2+ presents a fast and monoelectronic system controlled by diffusion. This allowed antioxidant properties determination by chronoamperometry, by following the [Cu(Nc) 2 ] 2+ reduction current as a function of the tested antioxidant. Ascorbic acid and Trolox used in this study as model antioxidants showed inhibition concentrations values (IC 50 ) very close to the expected theoretical values. These results are proof that the developed electrochemical method is accurate and allows a fast and efficient evaluation of antioxidant properties while minimizing interferences encountered using spectrophotometric methods.