A comparative study of the antioxidant profiles of olive fruit and leaf extracts against five reactive oxygen species as measured with a multiple free-radical scavenging method

Abstract: Olive fruits and leaves are recognized to have great potential as natural sources of antioxidants. The major phenolic antioxidant component in these plant tissues is oleuropein. The antioxidant activity of olive fruits and leaves was evaluated in this study using multiple free-radical scavenging (MULTIS) methods, wherein we determined the scavenging abilities of different extracts against five reactive oxygen species (ROS; HO·, O₂⁻·, RO·, t-BuOO·, and ¹O₂). Raw olive fruits taste bitter and are inedible without undergoing a debittering treatment. Following the NaOH-debittering process, the radical scavenging activity of olives decreased by 90%. The MULTIS measurements indicated that oleuropein and hydroxytyrosol are responsible for the radical scavenging activity of olive fruits. Furthermore, we evaluated the radical scavenging profiles of olive leaf extracts against five ROS and found significant seasonal variations in their antioxidant activities. Leaves picked in August possessed greater radical scavenging abilities (180% to 410% for different ROS) than those picked in the cold season (December and February). In roasted olive leaves, we found marked increases (230% to 300% and 180% to 220%) in the antioxidant activities of Maillard reaction products against RO· and t-BuOO·, respectively. This study presented a useful comparative analysis of the antioxidant capacities of food against various types of ROS. Practical Application: In this study, we evaluated the natural antioxidant activity of olive fruits and leaves against five reactive oxygen species (ROS). We found characteristic differences in the antioxidant profiles of different olive tissues, which varied after different treatments (debittering [fruit], drying [leaf], and roasting [leaf]). Comparative studies of the antioxidant capacities of foods against various ROS are useful to improve the functionality of food products.