Chemical composition of virgin olive oils from Koroneiki cultivar grown in Tunisia with regard to fruit ripening and irrigation regimes

The impact of different irrigation regimes based on two ripeness index, on the quantity and quality of virgin olive oil from the introduced olive cultivar Olea europaea L. Koroneiki grown at a high-density olive orchard in northern Tunisia, was assessed. Olive trees were subjected to three treatments (T1, T2 and T3) that received a seasonal water amount equivalent to 50%, 75% and 100% of the estimated local evaporative demand by a drip irrigation system and olives were collected in two different ripeness index. The olive oil content decreased when the water applied was increased but rose during ripening. The quality indexes and fatty acid composition were less affected by the irrigation schedule but most significantly by the maturity of olives. Moreover, phenol contents increased according to fruit ripening whereas no clear cut differences or consistent effects were observed by irrigation. α-tocopherol decreased slightly in the oils as ripening progressed while insignificant differences between the irrigation treatments studied were obtained. Consequently, a restitution of 75% of crop evapotranspiration (ETc.) was sufficient to achieve good minor compounds; however, higher water volumes (100% ETc.) gave little additional α-tocopherol and phenols increases. © 2011 The Authors. International Journal of Food Science and Technology.