Effect of olive leaf on physicochemical parameters, antioxidant potential and phenolics of Ayvalik olive oils at two maturity stages

Ayvalik is an important and widely grown olive cultivar in Turkey. Olive fruits were harvested at two different harvesting periods, early and middle. Olive oils were extracted in an industrial two-phase continuous system with/without olive leaves at 2%, 4%, and 6% (w/w) concentrations. Oils were stored at room temperature and 12 °C in darkness. Basic quality parameters such as free fatty acids (FFA), peroxide value and absorbance values (K232 and K270) conformed to the European extra virgin olive oil standards. Besides, the fatty acid composition of samples was consistent with the values for extra virgin olive oil reported by the European Commission. Leaf addition enriched phenolic compounds, antiradical activity, oxidative stability, color parameters, and sensory characteristics of Ayvalik olive oils. During storage, the losses in phenolic compounds, color and sensory properties of the oils enriched by adding leaves were less than in the control sample. The sensory properties and phenolic composition of the cold-stored olive oils differed from those stored in the dark and at room conditions. Regarding positive sensory properties, the oils stored in the cold have less loss in their desired properties than those stored under room conditions. In addition, the breakdown of complex phenolic substances into simple phenolic substances such as tyrosol and hydroxytyrosol was found to be less in the samples stored at cold conditions. It has been shown that hydrolytic and oxidative changes occur less in cold storage.