Developing a Rational Basis for Selection of Antioxidant Screening and Testing Methods
Karen M. Schaich
Department of Food Science,
Cook College, Rutgers University, NJ
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, the assay selected was base 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 has been addressed in the First International Congress on Antioxidant Methods held in Orlando, FL, June 2004. Perhaps more importantly, however, the assay 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 of the assays 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 will review mechanisms of the dominant antioxidant assays and relate chemical activity to chemical structure in different solvent and reaction environments in the context of developing a rational approach to selection of antioxidant testing methods.