Olive fruit debittering significantly alters its antioxidant activity as evaluated with multiple free-radical scavenging ability

Raw olive fruits taste bitter and are not edible without debittering. Common debittering process promotes the loss of olive antioxidant activity and the magnitude of loss depends on the debittering reagent used. Antioxidant activity was evaluated as the scavenging ability that was determined with multiple free-radical scavenging (MULTIS) method, where the scavenging abilities against five reactive oxygen species (HO·, O₂⁻·, RO·, t-BuOO·, and ¹O₂) were determined. Significant change in the scavenging activity of debittered olive was found in four debittering methods, i.e., sodium hydroxide, sodium hydrogen carbonate, ethanol, and sodium chloride treatments. Results indicated that the scavenging activities lowered by 60–90% after most debittering processes. Sodium chloride treatment least affected the scavenging activity. Based on the MULTIS measurements for the antioxidant components and debittering reagents, the rate constants of antioxidant compounds with four ROS were determined and the antioxidant activity that depends on the method of debittering is discussed. Oleuropein, olive-related antioxidant compound, showed high scavenging abilities against HO· (k = 6.70 × 10⁹ M⁻¹ s⁻¹), RO· (k = 4.69 × 10⁶ M⁻¹ s⁻¹), and ¹O₂ (k = 1.74 × 10⁷ M⁻¹ s⁻¹). This study suggests that functionality and taste do not always come together. MULTIS method is useful in comparative antioxidant capacity studies in foods.