Total Antioxidant Capacity of Some Commercial Fruit Juices: Electrochemical and Spectrophotometrical Approaches

The aim of this paper was to assess the total antioxidant capacity of some commercial fruit juices (namely citrus), spectrophotometrically and by the biamperometric method, using the redox couple DPPH center dot (2,2-diphenyl-1-picrylhydrazyl)/DPPH (2,2-diphenyl-1-picrylhydrazine). Trolox (R) was chosen as a standard antioxidant. In the case of the spectrophometric method, the absorbance decrease of the DPPH center dot solution was followed. For the biamperometric method, the influence of some parameters like the potential diference, Delta E, DPPH center dot concentration, and Trolox (R) concentration was investigated. The calibration graph obtained for Trolox (R) presents linearity between 5 and 30 mu M, (y = 0.059 x + 0.0564, where y represents the value of current intensity, expressed as mu A and x the value of Trolox (R) concentration, expressed as mu M; r(2) = 0.9944). The R.S.D. value for the biamperometric method was 1.29% (n = 10, c = 15 mu M Trolox (R)). In the case of the spectrophotometric method, the calibration graph obtained for Trolox (R) presents linearity between 0.01 and 0.125 mM (y = -9.5789 x+ 1.4533, where y represents the value of absorbance and x, the value of Trolox (R) concentration, expressed as mM; r(2) = 0.9963). The R.S.D. value for the spectrophotometric method was 2.05%. Both methods were applied to total antioxidant activity determination in real samples (natural juices and soft drinks) and the results were in good agreement.