## 3 Results
### Spme-Gc-Ms Results  
A total of 41 VOCs belonging to several chemical classes from different origins (LOX pathway, degradation of amino acids, sugar fermentation, lipid oxidation, etc.) were tentatively identified and quantified according to [PERSON] et al., 2023 (Table S1) [40]. The score plot of the first two PCs (28.56%, and 26.39%) obtained by the PCA is shown in Figure 5. The fresh olive oils, represented in green, are placed in the area of the plot characterized by negative values of the two main principal components. Samples stored for 1 year, in orange, clustered on the opposite side in the area characterized by positive values of principal components. The samples stored for 6 months were distributed between these  
Figure 4: Score plots obtained from the PCA of VOOs analyzed by HS-GC–IMS at time 0 (T0) and at 6 (T6) and 12 (T12) months of storage. The sample sensory classified as VOO after one year of storage is highlighted by a red arrow. two clusters. Furthermore, the PCA results indicated that there are no relevant variations caused by the different types of packaging [41]. Similarly, when considering the time of harvest and the agronomic system employed, no clustering patterns were observed as a function of storage time. From the loading plot analysis (Figure 6), it was possible to evaluate which variables contribute most to the sample separation. In particular, three volatile molecules colored in green and located at the bottom of the graph (4,8-dimethyl-1,7-nonadiene, (\(Z\))-3-hexenal, and (\(Z\))-3-hexenyl acetate) were the most important for explaining the clustering of fresh oil, considering \"freshness\" as the quality condition of the oil at \"time zero\", i.e., immediately after milling and filtration. On the other hand, the 7 molecules in red (at the top of the graph, pentanal, hexanal, (\(E\))-2-heptenal, nonanal, (\(E\),\(E\))-2,4-heptal, formic acid, and propanoic acid) were common in samples stored for 1 year and placed in the 1 st quadrant of the graph and thus are reasonably markers of oxidation. For PC1, the greater contribution is due to the three markers of freshness. Specifically, (\(Z\))-3-hexenal and (\(Z\))-3-hexenyl acetate belong to the broader group called green leaf volatiles, consisting of molecules formed by the enzymatic oxidation of linoleic and \(\alpha\)-linolenic acid through the action of the LOX pathway to produce aldehydes, alcohols, and esters that are responsible for the positive sensory characteristics of VOOs [42; 43]. In particular, (\(Z\))-3-hexen-1-ol, along with (\(Z\))-3-hexenyl acetate, are the main analytes formed by (\(Z\))-3-hexenal by alcohol dehydrogenase and alcohol acetyltransferase [44]. From the loading plot shown in Figure 6, it can be seen that (\(Z\))-3-hexenal and (\(Z\))-3-hexenyl acetate contribute to the discrimination of  
Figure 5: Score plot resulting from PCA of the concentrations of 41 VOCs analyzed using SPME-GC–MS in olive oils stored for 0 (T0), 6 (T6), and 12 months (T12). The sample classified as VOO after one year of storage is highlighted by a red arrow. fresh samples, confirming what has been observed in a previous study on Brazilian EVOOs during an 8-month storage period [45]. In contrast, PC2 was strongly influenced by pentanal, hexanal, (_E_)-2-heptenal, nonanal, (_E_,_E_)-2-4-heptaional, formic acid, and propanoic acid. Figure 7 shows the decreasing trends of the sum of the 3 markers of \"freshness\" and the increase in the sum of the 7 markers of lipid oxidation during storage, selected in agreement with the literature [46]. This visual representation underscores the temporal relationship between the markers of \"freshness\" and those indicative of lipid oxidation [47].