Comparative antioxidant activities of carotenoids measured by ferric reducing antioxidant power (FRAP), ABTS bleaching assay (αTEAC), DPPH assay and peroxyl radical scavenging assay

The purpose of this study was to assess the antioxidant activity of carotenes and xanthophylls measured by various methods, compared to α-tocopherol, BHA and BHT. Four assays were selected to achieve a wide range of technical principles. Besides αTEAC, which uses ABTS+ radical cation, ferric reducing activity (measured by using FRAP assay), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assay were used. In addition, a luminol-chemiluminescence based peroxyl radical scavenging capacity (LPSC) assay, was used. Most of the compounds showed significant differences in their activity of scavenging radicals depending on the assay used. Of the 22 compounds tested, only a few such as lutein, zeaxanthin and capsanthin gave comparable results in the various assays. Surprisingly, in contrast to α-tocopherol, BHA and BHT, carotenoids did not show any DPPH scavenging activity. To standardise the relative contribution of the assays used, weighted means of the values obtained in αTEAC, FRAP, DPPH and LPSC assay were calculated. This strategy was used to assess the antioxidant capacity of several juices and oil samples. The highest lipophilic antioxidant capacity in all assays was observed for sea buckthorn berry juice, followed by tomato juice, carrot juice and orange juice. Within the oil samples, the order of antioxidant capacity depended on the assay used.

► Carotenoids did not show DPPH-radical scavenging activity.
► Lycopene was the most effective carotenoid in bleaching the ABTS radical cation.
► Of the carotenes, solely lycopene presented ferric reducing activity.
► Ketocarotenoids were most effective in scavenging peroxyl radicals.
► Weighted averages of antioxidant activities were calculated to summarise effects.