## Materials and Methods  
### Sampling  
Three different locations where oleaster (_O. europaea_ L. ssp. _sylvestris_ ([PERSON]) Lehr synonym of _O. europaea_ L. ssp. _oleaster_ ([PERSON] and [PERSON]) plants exist were chosen, being located in three municipalities of the northeast of Portugal, namely: Moncorvo (Foz do Sabor, N 41\({}^{\circ}\)11\({}^{\prime}\)57.498\({}^{\prime\prime}\); W 7\({}^{\circ}\)5\({}^{\prime}\)46.302\({}^{\prime\prime}\)), Vila Nova de Foz Coa (VNFC) (Pocinho, N 41\({}^{\circ}\)8\({}^{\prime}\)6.058\({}^{\prime\prime}\); W 7\({}^{\circ}\)7\({}^{\prime}\)54.005\({}^{\prime\prime}\)) and Alijo (Romaneira, N 41\({}^{\circ}\)12\({}^{\prime}\)7.045\({}^{\prime\prime}\); W 7\({}^{\circ}\)29\({}^{\prime}\)25.444\({}^{\prime\prime}\)). In each location, four adult oleaster plants with frutification were randomly selected considering each plant as an independent tree. In November 2016, from each plant, roughly two kilograms of fruits were manually picked. To overcome the influence of the maturation stage on oil composition, drupes were harvested when the fruit epidermis changed from purple in more than half the olive (ripening stage- R.S. 3.0) to completely purple and white pulp (R.S. 4.0). Fruits were visually examined, being discarded damaged fruits or those that had been attacked by pests or diseases. From each olive sample, a sub-sample of 40 fruits was taken for morphological characterization and the remaining fruits were processed for oil extraction. All fruit samples were evaluated at a morphological level, using biometric parameters of the fruit and the endocarp of the same fruit according to International Union for the Protection of New Varieties of Plants (UPOV) guidelines for _Olea europaea_[13]. The following parameters were evaluated: weight (g), length (mm), maximum diameter (mm), shape, symmetry in A and B positions, position of maximum transverse diameter at B position, apex in A position, base, nipple, number and dimension of the lenticules, colour at full maturity, rugosity of the surface, number of grooves on basal end and distribution of grooves on basal end. Fruit shape was calculated from the ratio between the maximum length/width, which may lead to a classification of the fruit shape as spherical (length/width ratio \(<\) 1.25), ovoid (1.25 \(\leq\) length/width ratio \(\leq\) 1.45) or elongated (length/width ratio \(>\) 1.45).  
Oil was extracted from fruits during the first 24 h after harvest, in a pilot plant with an Abencor analyzer (Comerical Abengoa S.A., Seville, Spain), which included a mill, a thermobateer where malaxation takes place at a controlled temperature, and a centrifuge. Fruits were milled, then around 700 g of homogenized paste was transferred to the thermobeater unit (20 min) for malaxation, which was heated using a thermostatic water bath at 25 \({}^{\circ}\)C. During the last 5 min of each malaxation, 100 mL of water at 25 \({}^{\circ}\)C were added to enhance the oil separation. The mixture was centrifuged, decanted, and the oil collected. After that, the oils were filtered ([PERSON] paper no. 4) over anhydrous sodium sulphate to remove the solid particles and residual water. The oils then were stored in 100 mL dark glass bottles and protected from light exposition, at room temperature. All the assays were performed in triplicate within two months after extraction.