The Effect of Olive Leaf Addition on Antioxidant Content and Antioxidant Activity of “Memecik” Olive Oils at Two Maturity Stages

Abstract

AbstractIn this study, the effects of leaf addition, maturity stage and storage on the antioxidant content and activity of olive oils (cv. Memecik) were investigated in the 2008/09 and 2009/10 crop seasons. Olive fruits were harvested at two different maturity stages (early and late), and the leaves of the same cultivar were added at different rates (0, 1, and 3 %) prior to oil extraction. After extraction, the oil samples were stored for 18 months and total chlorophyll, α‐tocopherol, total phenolic content and the antioxidant activity [DPPH· (2,2‐diphenyl‐1‐picrylhydrazyl) and ABTS·+ (2,2‐azino‐bis(3‐ethylbenzothiazoline)‐6‐sulfonic acid) radical scavenging] were determined at 6 month‐intervals. Olive leaf addition induced a significant increase in total chlorophyll, α‐tocopherol, total phenolic content, and antioxidant activities in both years (P < 0.001). During the storage period antioxidant content and antioxidant activities in the oils significantly decreased in both years (P < 0.001). However, the oils to which leaf material was added had higher antioxidant contents and activities than those without leaf material addition at the end of the 18‐month storage period. After storage, the antioxidant content and DPPH· radical scavenging activity of control (0 %) samples were lower than those in the leaf added samples (3 %). The data obtained from this study suggested that the addition of olive leaf to oils allowed more functional olive oils with higher antioxidant contents.