Paper Title
THE EFFICACY OF DIFFERENT SEASONS ON THE PHENOLIC COMPOUNDS AND ANTIOXIDANT ACTIVITY OF THREE OLIVE (OLEA EUROPAEA L.) CULTIVAR LEAVES

Abstract
Abstract - Olive leaves, an agricultural waste, have great potential as a natural antioxidant.The aim of the present research was to determine total phenolics,total flavonoids, oleuropein andhydroxytyrosolcontent and antioxidant activity of three selected olive cultivarleaves namely ‘Zard’, ‘Roughani’ and ‘Koroneiki’ in different seasons.Total phenolics, total flavnoidsand antioxidant activity were evaluted using Folin-Ciocalteu, Zhishen et al.and 2,2-diphenyl-1-picrylhydrazyl-hydrate (DPPH) free radical scavenging methods, respectively.Also, Oleuropein and hyroxytyrosol were determined by HPLC method.Results revealed that there were significantvariations among the studied cultivars regarding all measured factors (P<0.01). The leaves of ‘Zard’ cultivar had the highest content of total phenolic (26.079 mg g-1DW)in June. ‘Koroneiki’ cultivarshowed highest content of total flavonoids (17.147 mg g-1DW)in June, as well as, Highest antioxidant activity was observed in the leaves of ‘Zard’ cultivar (76.58 %). Regression analysis of the data revealed that there was a positive and significant relation between total phenolic content and antioxidant activity (P<0.01). Among the studied cultivar, observation was made that the highest content of oleuropein (19.334 mg g-1DW)and hydroxytyrosol (0.775mg g-1DW)exists in the leaves of ‘Koroneiki’ cultivar. Findings here, suggest that leaves of some olive cultivars could be good sources of natural antioxidants and valueable flavonoids for food industry. Keywords - Olive leaf, Oleuropein, Hydroxytyrosol, Antioxidant activity, Total phenolic