Assessment of antioxidant capacity in vitro and in vivo

The role and beneficial effects of antioxidants against various disorders and diseases induced by oxidative stress have received much attention. Many types of antioxidants with different functions play their role in the defense network in vivo. The free radical scavenging antioxidants are one of the important classes of antioxidants and the assessment of their capacity has been the subject of extensive studies and argument. Various methods have been developed and applied in different systems, but many available methods result in inconsistent results. There is no simple universal method by which antioxidant capacity can be assessed accurately and quantitatively. In this review article, the available methods are critically reviewed on the basis of the mechanisms and dynamics of antioxidant action, and the methods are proposed to assess the capacity of radical scavenging and inhibition of lipid peroxidation both in vitro and in vivo. It is emphasized that the prevailing competition methods such as oxygen radical absorption capacity (ORAC) using a reference probe may be useful for assessing the capacity for scavenging free radicals but that such methods do not evaluate the characteristics of antioxidants and do not necessarily show the capacity to suppress the oxidation, that is, antioxidation. It is recommended that the capacity of antioxidant compounds and their mixtures for antioxidation should be assessed from their effect on the levels of plasma lipid peroxidation in vitro and biomarkers of oxidative stress in vivo.