Determination of antioxidative capacities using an enhanced total oxidant scavenging capacity (TOSC) assay

The antioxidant capacities of nine standard compounds (ascorbic acid, benzoic acid, (+)-catechin, cyanidin-3-glucoside, cyanidin-3-rutinoside, (-)-epicatechin, protocatechuic acid, Trolox and uric acid) towards the three reactive oxygen species (ROS) peroxyl radicals, hydroxyl radicals and peroxynitrite were tested with the total oxidant scavenging capacity (TOSC) assay. The time course of ethylene formation from the reaction of the ROS with !-keto-%-methiolbutyric acid (KMBA) was monitored by automated headspace GC. By this automation and by optimisation of the preparation and storage of the assay solutions, the time- and labour-consumption of the method could be minimised. Based on the experimental data, the relation between concentration and inhibition rate was pointed out by calculating concentrations that corresponded to TOSC values of 20%, 50% and 80%, respectively. Furthermore, the compounds were classified by their reaction mode as fast-acting antioxidants, retardants or pro-oxidants.