Phenolic compounds content in leaf of different varieties of olive and its effect on stability of rapeseed oil

Olive leaf is a source of natural polyphenolic compounds that have antioxidant activity and enrichment of oils with olive leaf extract which contains high amounts of polyphenols and tocopherol can increase its oxidative stability. In this study, the total amount of methanolic extracts of polyphenols of olive leaf (Oleaeurpopeae) in four Iranian varieties of olive was determined and the leaf antioxidant effect on thermal stability of rapeseed oil was studied by rancimat (P<0.05). The amount of tocopherols, fatty acids and polyphenols were determined before and after heating at 180°C. Maximum amount of polyphenols was 80 mg (acid galic in 100 grams of dry leaf) in Taram variety and minimum amount was 52.5mg in Moghan variety. The results showed tocopherols amount were decreased after heating at 180°C. Rancimat results showed that oil fortified with Taram variety extract with induction time of 11.3 hr was stable in comparison with control samples without antioxidants. According to the obtained results, adding olive leaf as a natural and valuable antioxidant to increase stability of oil can be recommended.