**2. Materials and Methods**

#### *2.1. Experimental Design and Samples*

Olive fruits (*Olea europaea* L., Verdial de Badajoz cultivar) were collected from unirrigated trees grown in either organic or conventional orchards in the Lácara region (Badajoz, Spain). In the conventional production system, the fertiliser was a nitrogen-phosphorus-potassium-boron complex (20-8-14-0.1 B), as it is common practice in the region. In the organic production, the fertiliser was made up of weeds cut in springtime added to composted olive mill and pruning waste and hay. When mature (maturity index in the orchard ranging between 1 (fruits with green yellowish skin)

and 5 (fruits with black skin and <50% purple flesh)), the fruits from the organic orchards were collected from the trees (Organic), whereas the ones from the conventional orchards were collected either from the trees (Conventional) or from the ground (Ground). They were mechanically processed, separately (in different days after proper cleaning to avoid cross-contamination), into oil under the same conditions in a local factory over the harvesting session. The organic production was subjected to the official control established in Spain according to Regulation 834/2007. Oil samples were taken from a tank filled during a week (20.000 L) for the Organic and Conventional oils, or directly from the production line for the Ground oil (which was produced once per week) once a week from the beginning of November to mid-January. Then, the eighteen (three types of oil x six weeks) virgin olive oils were kept at 6 ◦C and analysed.
