ORAC is the most accurate assay to quantify peroxyl radical scavenging capacity

According to the chemical reactions involved, major antioxidant capacity assays can be roughly divided into two categories: (1) hydrogen atom transfer (HAT) reaction based assays and (2) single electron transfer (ET) reaction based assays. The majority of HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. These assays include inhibition of induced low-density lipoprotein autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced. The degree of color change is correlated with the sample's antioxidant concentration. ET-based assays include the total phenols assay by Folin-Ciocalteu reagent (FCR), Trolox equivalence antioxidant capacity (TEAC), ferric ion reducing antioxidant power (FRAP), "total antioxidant potential" assay using a Cu(II) complex as an oxidant, and DPPH.

ET-based assays measure an antioxidant's reducing capacity, and the HAT-based assays measure the hydrogen atom donating capacity. The hydrogen atom transfer is a key step in the radical chain reaction. Therefore, the HAT-based assays are more relevant to the radical chain-breaking antioxidant capacity. Among all the HAT-based assays, ORAC adopted an AUC (Area Under Curve) technique to quantify antioxidant capacity. The advantage of the AUC approach is that it applies equally well for both antioxidants that exhibit distinct lag phases and those samples that have no lag phases. This approach unifies the lag time method and initial rate method, and it is particularly useful for food samples, which often contain multiple ingredients and have complex reaction kinetics.

Therefore, the ORAC assay has been broadly applied in academics and the food and supplement industry as the method of choice to quantify antioxidant capacity. In fact, an antioxidant database has been generated applying the ORAC assay in combination with the total phenols assay.

Brunswick Laboratories, LLC, is an independent, full-service bio-analytical laboratory specializing in the science of antioxidants and oxidative stress. Brunswick has worked closely with the USDA in the development of the ORAC Assay. Besides the ORAC assay, Brunswick also offers Lipo-ORAC assay to quantify the lipophilic antioxidant, and HORAC (hydroxyl radical scavenging capacity),SORAC (superoxide radical scavenging capacity) and NORAC (Peroxynitrite radical scavenging capacity).

For further information please contact Brunswick Laboratories at 508-291-1830.