he cellular antioxidant activity (CAA) assay quantifies the antioxidant activity of phytochemicals, food extracts, and dietary supplements. Dichlorofluorescin is easily oxidized for fluorescent dichlorofluorescein; the test measures the ability of antioxidants to prevent this oxidation in human hepatocarcinoma HepG2 cells. This method of measuring antioxidant activity differs from other methods, because it accounts for some aspects of uptake, metabolism, and location of antioxidant compounds within cells.