Radical scavenging ability of polyphenolic compounds towards DPPH free radical

Free radical scavenging activity of different polyphenolic compounds commonly present in wine has been evaluated using DPPH method. The experiments were performed with different amounts of phenols within the linear interval of response and with an excess of DPPH in all cases. In these conditions, for most of the compounds tested, the reaction was biphasic. Total stoichiometry values n confirm the implication of more than one step in the process. Flavan-3-ol compounds showed the highest values, especially procyanidins B1 (9.8) and B2 (9.1). In this family, n values coincide with the number of hydroxyl groups available. EC(50) and TEC(50) parameters have been calculated. EC(50) values are extremely diverse, being the procyanidins B1 and B2 the most potent scavenging compounds and resveratrol the less one. TEC(50) considers the rate of reaction towards the free radical. (+)-Catechin and (-)-epicatechin are the phenolic compounds that need more time to react. In contrast, caftaric and caffeic acids are the phenolic acids that react more rapidly. Antioxidant efficacy (AE) is a parameter that combines both factors. Compounds as kaempferol, with a high EC(50) value, could be considered as an antioxidant with low relevance, but instead shows the highest AE value of the phenolic compounds tested, due to its fast rate of reaction, what is of great biological importance.