Do leaf total antioxidant capacities (TAC) reflect specific antioxidant potentials? – A comparison of TAC and reactive oxygen scavenging in tobacco leaf extracts

Two traditional methods of total antioxidant capacity (TAC) assessment, Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP) were applied to water extracts from tobacco leaves at various stages of senescence. Physiological status of the leaves was characterized by the effective photochemical quantum yield of photosynthesis (Y(II)). TAC values were compared to amounts of total phenolics, carotenoid contents and also to reactive oxygen scavenging capacities of the leaf extracts. To this end a new, simple fluorimetric assay was introduced for testing hydroxyl radical neutralizing capacity in leaf extracts. We found that while both TAC values increased with declining photosynthesis and decreasing pigment content, they were not characteristic to specific superoxide or hydroxyl radical scavenging and had limited connection to leaf antioxidant content. Good linear correlations were only found between the following pairs of parameters: Y(II) – total carotenoid, TEAC – total carotenoid, FRAP – total phenolics. Our data show that TEAC and FRAP are not interchangeable in leaf studies and do not represent antioxidant action on ROS.