Measuring Antioxidant Capacity Using the ORAC and TOSC Assays

Recent epidemiological studies have shown that there may be a link between oxidative stress and the development of several types of chronic diseases. Studies have also shown that diets rich in fruits and vegetables may decrease the incidence of cancer and other chronic diseases. The antioxidant activity of the phytochemicals these foods contain may be partially responsible for the decreased incidence of these diseases in people who regularly consume them. While there are several assays currently used to assess the antioxidant activity of phytochemicals and other antioxidant compounds, two are reviewed here in detail. The first is the oxygen radical absorbance capacity (ORAC) assay, which measures the decrease in fluorescence decay caused by antioxidants, and the second is the total oxyradical scavenging capacity (TOSC) assay, which measures the decrease in ethylene gas production caused by the inhibition of the thermal hydrolysis of ABAP (2,2′-Azobis(2-methyl-(propionamidine) dihydrochloride) by KMBA (α-keto-γ-(methylthio)butyric acid sodium salt) in the presence of antioxidant compounds. These two assays are discussed here, with an in depth review of their methodology and correlation.