*2.3. Volatile Compound Analysis*

The virgin olive oil samples (5 g) were introduced into glass screw top vials, with laminated Teflon-rubber disks in the caps. The vials were left in a water bath at 40 ◦C for 10 min to equilibrate the volatile compounds in the headspace. Then, a solid-phase microextraction (SPME) needle was inserted through the disk, and a 1-cm 50/30 μm thickness DVB/Carboxen/PDMS fibre (Supelco, Bellefonte, PA, USA) was exposed to the headspace for 40 min while the vial was kept in the 40 ◦C-water bath. Later, the fibre was transferred to the gas-chromatograph inlet (splitless mode, 250 ◦C).

The chromatographic separation of the compounds was carried out using a HB-5 (50 m × 0.32 mm i.d, 1.05 μm) column (Agilent, Avondale, AZ, USA) placed into a gas-chromatograph (Agilent 6890 series) equipped with a mass spectrum detector (Agilent 5973). The oven temperature was held at 40 ◦C for 10 min and risen at 3 ◦C min−<sup>1</sup> to a temperature of 160 ◦C, and then at 15 ◦C min−<sup>1</sup> to a final temperature of 220 ◦C, where it was held for 10 min (total run time: 64 min). Mass spectra were generated by electronic impact at 70 eV, with a multiplier voltage of 1756 V. Data were collected at a rate of 1 scan s−<sup>1</sup> over the 30–300 *m*/*z* range. The transfer line to the mass spectrometer was maintained at 280 ◦C. The Agilent MSD Chemstation software was used. *n*-alkanes (C5-C18) were analysed under the same conditions to calculate the linear retention indices (LRI).

The identification was performed by matching mass spectra (MS) and LRI with those of reference compounds analysed under the same conditions (a total of 62 Sigma-Aldrich reference compounds were used), or with those included in the Flavornet (www.flavornet.org) or NIST [19] databases. Two samples of each oil batch were analysed, and results were expressed as total area counts.

#### *2.4. Data Analyses*

A three-way (organic production, harvesting method, and harvesting time) Analysis of Variance (ANOVA) was performed on the data. When a significant effect was found, the Tukey test was carried out to compare the means. A Principal Component Analysis was performed on the mean values for each sample to evaluate the relations among variables and samples [20]. The statistical analyses were performed by means of the SPSS version 22.0.
