# Filtration Scheduling: Quality Changes in Freshly Produced Virgin Olive Oil
## 2 Materials and Methods
### Chemical Analyses  
According to the official European Union method and following amendments [5; 6], the legal quality characteristics, such as peroxide value (meq O\({}_{2}\) kg\({}^{-1}\)); acidity (% oleic acid); and UV spectroscopic indexes (K232, K270, and \(\Delta\)K), were measured [29].  
Volatile compound contents were measured as described in [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] (2017) [30], using the HS-SPME-GC-MS technique. Compounds were identified and quantified (mg/kg) by comparison of their mass spectra and retention times with those of the internal standard mixture (ISTD MIX), consisting of the following 11 compounds: 4-methyl-2-pentanol, 3,4-dimethylphenol, 1-butanol-d10, hexanoic acid-d11, ethyl hexanoate-d11, ethyl acetate-d8, toluene-d8, 6-chloro-2-hexanone, acetic acid-2,2,2-d3, 3-octanone, and trimethylacetaldehyde.  
Briefly, the analyses were carried out by weighing, into 20-mL screw cap vials fitted with a PTFE/silicone septa, 4.3 g of an oil sample and 0.1 g of an internal standard mixture. After 5 min equilibrium at 60 \({}^{\circ}\)C, a SPME fibre (50/30-\(\upmu\)m DVB/CAR/PDMS by Supelco, St. Louis, UK) wasexposed for 20 min in the vial headspace under orbital shaking (500 rpm). Then, the fibre was immediately desorbed for 2 min in a gas chromatograph injection port operating in splitless mode at 260 \({}^{\circ}\)C. The identification of volatile compounds was performed by gas chromatography coupled to quadrupole-mass spectrometry using an Agilent GC-MS 7890B-5977E, equipped with an Innovax capillary column (50 m \(\times\) 0.4 id \(\times\) 0.4 um ds). Initial column temperature was held at 40 \({}^{\circ}\)C for 10 min, then increased to 200 \({}^{\circ}\)C at 5 \({}^{\circ}\)C/min, then to 260 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min, and finally, to 250 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min, with a hold time of 4 min. Helium was used as the carrier gas at 1.2-mL/min constant flow. The temperature of the source was 230 \({}^{\circ}\)C, while the transfer line was 250 \({}^{\circ}\)C. The mass detector was operated in scan mode within a 29-330-Th mass range at 1500 Th/s, with an IE energy of 70 eV. Volatile compounds quantified with this method were: heptane, octane, methyl acetate, 2-butanone, ethyl acetate, methyl propanoate, 2-methyl batanal, isovaleraldehyde, ethyl propanoate, 3-pentanone, valeraldehyde, ethyl vinyl ketone, 2-butanol, ethyl butanoate, propanol, butyl acetate, hexanal, isobutanol, 2-pentanol, 2-pentenal, Z-3-hexenal, 1-penten-3-ol, 1-penten-3-one, 2-heptanone, heptanal, limonene, 2-methyl-1-butanol + 3-methyl-1-butanol, 2-methyl-1-butanal + 3-methyl-1-butanol E-2-hexenal, ocimene, pentanol, hexyl acetate, 2-octanone, octanal, 1-octen-3-one, E-2-penten-1-ol, Z-3-hexenyl-acetate, E-2-heptenal, 2-heptanol, Z-2-pentenol, E-2-hexenyl-acetate, 5-hepten-2-one-6-methyl, 1-hexanol, E-3-hexen-1-ol, Z-3-hexen-1-ol, 2-nonanone, nonanal, 2,4-hexadienal, E-2-hexenol, Z-2-hexenol, 2-octanol, E-2-octenal, 1-octen-3-ol, heptanol, 2,4-heptadienal, decanal, benzaldehyde, E-2-nonenal, propanoic acid, octanol, butanoic acid, E-2-decenal, nonanol, 2,4-nonadienal, pentanoic acid, 2,4-decadienal, hexanoic acid, guaiacol, phenyl ethanol, phenol, 4-ethylguaiacol, 4-ethyl-phenol, phenol-4-ethyl-2-methoxy, and phenol-2-mehoxy.