The Oxygen Radical Antioxidant Capacity (ORAC) Assay is a classic tool for measuring the antioxidant capacity of biomolecules from a variety of samples. The ORAC Activity Assay is based on the oxidation of a fluorescent probe by peroxyl radicals by way of a hydrogen atom transfer (HAT) process. Peroxyl radicals are produced by a free radical initiator, which quenches the fluorescent probe over time. Antioxidants present in the assay work to block the peroxyl radical oxidation of the fluorescent probe until the antioxidant activity in the sample is depleted. The remaining peroxyl radicals destroy the fluorescence of the fluorescent probe. Cell Biolabs’ OxiSelect™ ORAC Activity Assay is a fast and reliable kit for the direct measurement of ORAC antioxidant capacity from cell lysate, plasma, serum, tissue homogenates, and food extracts. Each kit provides sufficient reagents to perform up to 192 assays, including blanks, antioxidant standards and unknown samples.