As pharmaceutical and nutraceutical interest in natural antioxidants has skyrocketed in the past few years, a plethora of methods have come into common use for screening antioxidant content of natural materials and for comparing antioxidant activity of various classes of compounds. These include ORAC (Oxygen Radical Absorbance Capacity), TEAC (Trolox Equivalent Antioxidant Capacity), FRAP (Ferric Reducing Antioxidant Power), TOSC (Total Oxidant Scavenging Capacity), TRAP (Total Radical-Trapping Antioxidant Parameter), DPPH reactivity, croton bleaching, LDL oxidation, liposome oxidation, and total phenolics analyses. For the most part, assay selection is based on ease of use and availability of instrumentation, and very often there is lack of correlation between is activity assays and phenolic content, between activities determined on the same material by different assays, and between activities determined by the same assay in different laboratories. The need for standardization of procedures is being addressed in a series of International Congresses on Antioxidant Methods. Perhaps more importantly, however, the assays listed above do not all measure the same chemical action. Some assays measure hydrogen atom transfer capability (classical radical quenching), some measure electron transfer propensity, and others measure a variety of other actions. The basic chemistry dominant in the assays and also active in the system of application must be considered as a basis for appropriate application of assays, accurate interpretation of results, and evaluation of antioxidant effectiveness for different end uses. This paper reviews mechanisms and effects of environment on the dominant antioxidant assays and recommends a new integrative approach using a panel of assays and conditions to provide more complete and accurate information during antioxidant testing.
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