Bisby Roger H, Brooke Rachel, Navaratnam Suppiah
Biomedical Sciences Research Institute, University of Salford, Salford M5 4WT, UK.
Biomedical Sciences Research Institute, University of Salford, Salford M5 4WT, UK.
Food Chem. 2008 Jun 1;108(3):1002-7. doi: 10.1016/j.foodchem.2007.12.012. Epub 2007 Dec 14.
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)dm(3)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.
“氧自由基吸收能力”（ORAC）测定法（Ou, B., Hampsch-Woodill, M., Prior, R.L.（2001年）。使用荧光素作为荧光探针改进的氧自由基吸收能力测定法的开发与验证。《农业与食品化学杂志》49卷，4619 - 4626页）被广泛用于测定食品中的抗氧化剂含量，并使用荧光素作为过氧自由基氧化的探针。ORAC测定法的动力学模型表明，荧光损失的滞后阶段源于抗氧化剂与荧光素自由基之间的平衡，平衡常数的值决定了滞后阶段的形状。对于一种有效的抗氧化剂，这构成了荧光素自由基的“修复”反应，并产生一个明确的滞后阶段。随着抗氧化剂氧化电位的增加，滞后阶段变得不那么明显。脉冲辐解证实，水溶性维生素E类似物Trolox C能迅速（k∼10(9)dm(3)mol(-1)s(-1)）还原荧光素自由基。对具有不同氧化电位的酚类进行的ORAC测定表明，它可用于估计食品原料中抗氧化剂的氧化还原电位。
