Copper(II)-Bathocuproine reagent-based dual mode sensing of total antioxidant capacity in food extracts

As food antioxidants are known deactivators of reactive species that may cause oxidative hazard, antioxidant capacity determination has gained importance in biochemistry, medicine and food science. In this study, a simple and sensitive dual-mode system based on spectrophotometric (SP) and spectrofluorometric (SF) determination of food antioxidants was developed using the Cu(II) complex of fluorescent bathocuproine sulfonate disodium salt (BCDS). In the proposed SF assay of total antioxidant capacity (TAC), a linear decrease in fluorescence occurs related to the formation of non-fluorescent Cu(I)-BCDS chelate depending on antioxidant concentration. At the same time in the SP method, the chemical reduction of Cu(II)-BCDS complex by antioxidants reflected in the absorbance increase of the formed Cu(I)-BCDS complex is monitored. By optimizing the optimal experimental conditions of the developed methods and applying them to standard antioxidant compounds separately, calibration equations were obtained and Trolox Equivalent Antioxidant Capacity (TEAC) values were calculated. The LOD values for Trolox obtained by SP and SF methods were found to be 0.16 and 5.08 μmolL^-1, respectively. The sensitivity and accuracy of these two systems were examined by spiking known amounts of antioxidants to complex sample matrices. Both methods were successfully applied to the determination of TAC in food extracts. This dual sensing system is novel in view of the fact that the same probe (Cu(II)-BCDS) is used in the simple, rapid and sensitive determination of the same analyte (TAC) in two different (SP and SF) modes.