Effect of antioxidant potential in the oxygen radical absorption capacity (ORAC) assay

Bisby, RH; Brooke, R; Navaratnam, S

Abstract

The "Oxygen Radical Absorption Capacity” (ORAC) assay (Ou, B., Hampsch-Woodill, M., Prior, R.L. (2001). Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe. Journal of Agricultural and Food Chemistry 49, 4619–4626) is widely employed to determine antioxidant content of foods and uses fluorescein as a probe for oxidation by peroxyl radicals. Kinetic modeling of the ORAC assay suggests that the lag phase for loss of fluorescence results from equilibrium between antioxidant and fluorescein radicals and the value of the equilibrium constant determines the shape of the lag phase. For an efficient antioxidant this constitutes a "repair" reaction for fluoresceinyl radicals and produces a well defined lag phase. The lag phase becomes less marked with increasing oxidation potential of the antioxidant. Pulse radiolysis confirms that fluoresceinyl radicals are rapidly (k 10^9 dm3 mol-1 s-1) reduced by Trolox C, a water soluble vitamin E analogue. ORAC assays of phenols with varying oxidation potentials suggest that it might be employed to obtain an estimate of the redox potential of antioxidants within food materials.

Citation

Bisby, R., Brooke, R., & Navaratnam, S. (2008). Effect of antioxidant potential in the oxygen radical absorption capacity (ORAC) assay. Food Chemistry, 108(3), 1002-1007. https://doi.org/10.1016/j.foodchem.2007.12.012

• Journal Article Type: Article
• Publication Date: Jan 1, 2008
• Deposit Date: Sep 28, 2011
• Journal: Food Chemistry
• Print ISSN: 0308-8146
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 108
• Issue: 3
• Pages: 1002-1007
• DOI: https://doi.org/10.1016/j.foodchem.2007.12.012
• Keywords: Antioxidant, fluorescein, oxygen, radical, ORAC, pulse radiolysis, reduction potential
• Publisher URL: http://dx.doi.org/ 10.1016/j.foodchem.2007.12.012