Comparison of ABTS/DPPH assays to measure antioxidant capacity in popular antioxidant-rich US foods

To evaluate the comparability of the two most common radical scavenging assays using 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, the 50 most popular antioxidant-rich fruits, vegetables and beverages in the US diet were identified and analyzed for their antioxidant capacities, total phenolics and flavonoids content. Spearmans-Rho correlation coefficients were calculated in order to characterize the relationship between antioxidant capacities, total phenolics and flavonoids content. Antioxidant capacity showed a strong positive relationship comparing both assays (ρ = 0.949, p < 0.001). Antioxidant capacity detected by ABTS assay was stronger positively associated with the oxygen radical absorbance capacity (ORAC) from USDA database (for ABTS: ρ = 0.593, p < 0.001; for DPPH: ρ = 0.539, p < 0.001, respectively), phenolics (for ABTS: ρ = 0.946, p < 0.001; for DPPH: ρ = 0.897, p < 0.001, respectively) and flavonoids content (for ABTS: ρ = 0.718, p < 0.001; for DPPH: ρ = 0.708, p < 0.001, respectively). Antioxidant capacity detected by ABTS assay was significantly higher for fruits, vegetables and beverages compared to that by DPPH assay. The high-pigmented and hydrophilic antioxidants were better reflected by ABTS assay than DPPH assay. These data suggest that ABTS assay may be more useful than DPPH assay for detecting antioxidant capacity in a variety of foods.