Antioxidant Activity Evaluation

Antioxidant activity is among the most commonly evaluated properties of herbal extracts, reflecting both the intrinsic radical-scavenging chemistry of polyphenolic phytoconstituents and the mechanistic link between oxidative stress and numerous chronic disease processes. The DPPH radical scavenging assay, the most widely used first-line antioxidant screen, measures the ability of a test extract to reduce the stable purple DPPH radical to its yellow reduced form, monitored by absorbance at 517 nm, with results expressed as an IC50 and benchmarked against ascorbic acid or quercetin reference standards. The ABTS radical scavenging assay operates on an analogous principle using the blue-green ABTS radical cation, with results expressed as a Trolox Equivalent Antioxidant Capacity (TEAC) value. The FRAP (Ferric Reducing Antioxidant Power) assay instead measures a sample's ability to reduce a ferric-TPTZ complex to its blue ferrous form, providing a measure of overall reducing power rather than radical-scavenging capacity specifically. Complementary mechanistic assays include the hydroxyl radical and superoxide radical scavenging assays, which probe activity against biologically generated reactive oxygen species directly relevant to cellular oxidative damage, and the Oxygen Radical Absorbance Capacity (ORAC) assay, regarded by many researchers as the gold-standard antioxidant method owing to its use of a biologically relevant peroxyl radical generator and its capacity for full automation.