Automatic method for determination of total antioxidant capacity using 2,2-diphenyl-1-picrylhydrazyl assay

In the present work, an automatic method based on multi-syringe flow injection analysis (MSFIA) was developed for the determination of total antioxidant capacity, measured as the cumulative capacity of the compounds present in the sample to scavenge free radicals, using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) reaction. The determination is based on the colour disappearance due to the scavenging of DPPH by antioxidant compounds monitored spectrophotometrically at 517 nm.The influence of initial DPPH concentration and sample dilution in the present methodology was studied. It was verified that the amount of DPPH consumed by antioxidant standards (ascorbic and caffeic acids) was independent of the initial concentration of radical except for situations where DPPH/antioxidant molar ratio was lower than the stoichiometric value. Furthermore, the sample dilution factor plays an important role for achieving results comparable to those from end-point batch method since the exhausting of scavenging ability of the sample should take place during the period of absorbance measurement.The proposed method was applied to several food products and the total antioxidant capacity was expressed as Vitamin C equivalent antioxidant capacity (VCEAC). The results obtained by the proposed method ranged from 1.1 to 318 mg of ascorbic acid/100 ml and they were statistically comparable to those provided by the batch method. The detection limit was 0.34 mg of ascorbic acid/100 ml and the determination frequency was about 13 h−1 with an excellent repeatability (R.S.D. < 1%, n = 10).