3.6.2 Antioxidant Assays

The DPPH radical scavenging assay measures the ability of a compound to reduce the stable free radical 2,2-diphenyl-1-picrylhydrazyl, observed as a colour...

The DPPH radical scavenging assay measures the ability of a compound to reduce the stable free radical 2,2-diphenyl-1-picrylhydrazyl, observed as a colour change from purple to yellow and quantified by absorbance at 517 nm, with IC50 conventionally benchmarked against ascorbic acid. The ABTS radical scavenging assay operates on an analogous principle using the radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), monitored at 734 nm and benchmarked against the Trolox standard to yield a Trolox equivalent antioxidant capacity (TEAC) value. The FRAP (Ferric Reducing Antioxidant Power) assay measures the reduction of a ferric-TPTZ complex to its blue ferrous form, read at 593 nm, providing an index of total reducing capacity. Nitric oxide scavenging is assessed using the Griess reagent, which reacts with nitrite generated from spontaneous decomposition of sodium nitroprusside (SNP) to form a pink diazonium chromophore measured at 546 nm.