The complex set of data acquired from the S3 sensors response to the volatile organic compounds originating from the EVOO headspace were analyzed through a multivariate analysis PCA and ANN. The measurements were performed in an autosampler HT2800T (HTA srl, Brescia, Italy) . For this, 5mL of olive oil samples were enclosed in 20mL vials and placed randomly in the autosampler. The sample headspace was drawn out from the vial and injected at 1mL/min into a chromatographic air flow (50 sccm). The injection time was 2min and the recovery time was 5min.

Analysis of Volatile Compounds

A sample of 2mL was placed into a 15-mL headspace vial, and 50μL of internal standard solution (5mg/L of ethyl nonanoate) was added. Then, the SPME (solid-phase microextraction) fiber (85μm Carboxen Polydime thylsiloxane, Supelco, St. Louis, MO, USA) was placed in the headspace above the sample, and the vial was incubated for 30min at 40℃. The fiber was subjected to thermal desorption in a gas chromatograph injector at 250℃.

The chromatographic separation was carried out on a Clarus 580 apparatus (PerkinElmer, Waltham,MA, USA) and a Crossbond dimethyl polysiloxane 60 m, 0.25mm, 1.4μm film thickness column. The carrier gas flow (He) was 2mL/min, with the following

temperature program: 35℃, 6min;8℃/min up to 180℃; 12℃/min up to220℃; 25min. The detector and dispenser temperature was 250℃. An HT2800T autosampler (HTA Brescia, Italy) was used,and PerkinElmer Total Chrom 6.3.2 software (PerkinElmer, Waltham, MA, USA) was used to integrate the results.

Analysis of Volatile Compounds

The volatile compounds were determined using a modified Grützman et al. method. A sample of 2mL was placed into a 15mL headspace vial, and 50μL of an internal standard solution (5mg/L of ethyl nonanoate) was added. Then a solid-phase microextraction (SPME) fiber was placed in the headspace above the sample, and the vial was incubated for 30 minutes at 40℃. The fiber was subjected to thermal desorption in a gas chromatographic injector at 250℃.

The chromatographic separation was carried out on a Clarus 580 apparatus equipped with a flame ionization detector (FID) and a Crossbond dimethylpolysiloxane column (60m in length, 0.25 mm of inner diameter, 1.4μm of film thickness). The carrier gas flow (He) was 2mL/min, and the temperature program was: 35℃, 6 min;8℃/min up to 180℃; 12℃/min up to 220℃; 25 min. The inlet and FID temperature was 250℃.

An HT2800T autosampler (HTA Brescia, Italy) was used, and PerkinElmer Total Chrom 6.3.2 software(PerkinElmer, Walthman, MA, USA) was used to integrate the results. Identification was performed based on the retention times compared with those of the standards for the volatile compounds, and quantification was carried out by internal standardization, using 4-methyl-2-pentanol (alcohols) and ethyl nonanoate (esters) as the internal standards. The standard solutions were prepared in synthetic wine (20g/L sucrose, 5g/L tartaric acid, 10% ethanol). All experiments were performed in triplicate.