## 2 Results and Discussion
### Chemical Changes during the Storage Experiment
The PCA results show that the selected compounds that originated from the lipoxygenase pathway (Table 2), such as (_E_)-2-hexenal and (_Z_)-2-hexen-1-ol and the median of fruity attribute were plotted in the same quadrant in VOO1, VOO3 and VOO4. In the case of VOO2, however, the median of the fruity attribute appears to be only associated to (_Z_)-2-hexen-1-ol and (_Z_)-3-hexen-1-ol, but not with the rest of these compounds, which can be explained by the slight change in their concentrations in this oil during the storage time instead of a reduction in their concentration as in the other oils (Table 2). Furthermore, other compounds, such as butanal and butanal-1-ol, were associated to the median of the fruity attribute in all VOOs, due to their concentration decrease during the storage, except for butanal-1-ol in VOO2. This compound contributes with an aroma that is closer to the negative attributes (fatty and medicine for butanal-1-ol) [43]. Other compounds contributing with negative attributes were plotted near the median of the fruity attribute, which is explained by the fact that their concentrations also decreased over time: methyl acetate in both VOO2 and VOO4, octan-2-one and 1-octen-3-one in VOO1 and nonanoic acid in VOO3. Regarding the median of defect value, the PCA plots show an association of this median with the concentrations of octane, (_E_)-2-heptenal and (_E_)-2-decenal in all cases, these compounds being related with sensory defects and the two latter contributing with oxidized and fatty notes [1]. Moreover, nonanal and the median of defect were plotted in the same quadrant in VOO1, VOO2 and VOO3, which points out that the autooxidation process takes place during the storage experiment. However, this association was not observed in the PCA for VOO4, in which nonanal and median of defect were plotted in different quadrants despite this oil was the first one that downgraded to  
Figure 5: Principal component analysis plots (PCA) of volatile compounds that showed significant changes (_p_ < 0.05) and RSD% > 50% in the storage experiment, the median of the fruity attribute (Mf) and the median of defect (Md) for the storage time. An individual plot was performed for each virgin olive oil (VOO). Note. Codes are indicated in Table 2.  
lampante at the end of the storage. These results may point out that the relationship of nonanal concentration and median of defect is more evident at earlier stages of oxidation as it is the case in VOO1, VOO2 and VOO3. On the other hand, a strong association was found for heptanal and the median of defect in VOO2, VOO3 and VOO4. In VOO1, this association was not found in the PCA plot, probably due to the fact that it was the oil that underwent the oxidation at lower extent in the first half of the storage experiment and the downgrading of category (from \"extra virgin olive oil\" to \"virgin olive oil\") took place the latest (month 15) (Figure 2). Finally, the PCA plots showed that the hexanoic acid is related to the median of defect in the cases of VOO2 and VOO4. In a second PCA, only the concentrations of the same volatile compounds (Table 3) were studied without including the medians of the fruity attribute and the defect in the data set. The objective was to check the score plot (samples) to study the changes of the volatile profile of the oils during the storage experiment with a multivariate perspective. Thus, Figure S1 shows a score plot per each VOO stored, in which the samples collected every month are represented against the factors. The score plot of VOO1 shows a change in the distribution of the samples from month 15 (VOO1-15m), which is the moment when this sample downgraded to \"virgin olive oil\" category (Figure 2). The score plot for VOO2 pointed out a change in the distribution of the monthly collected samples in the month 8 (VOO2-8m) when the assessors identified an incipient rancidity in this oil for the first time (Figure 2).