## 3 Results and Discussion
### Evolution of VOOs' Overall Quality during 12 Months of Light Exposure  
The whole data set of the results obtained analyzing the 20 experimental blends each month was firstly elaborated by building a PCA (Principal Component Analysis, Figure S3),showed a clear discrimination of the samples according to the time to the light exposure, along the first component (from the left to the right of the score, Figure S3A). Successively, an orthogonal-partial least square (OPLS, Figure 1) of latent variables analysis was carried out to observe a potential correlation between the evolution of the VOOs' quality and the duration of storage to light exposure. The score plot (Figure 1A) confirmed the distribution of the samples according to the time of storage, with those VOOs characterized by the longest period of conservation (from 7 to 12 months), positioned to the right and to the top side of the score plot, and the VOOs with the earliest period of conservation (from 0 to 6 months), to the left and to the lower side of the score (Figure 1A). The relative loading plot (Figure 1B) highlighted that the latent dependent variable Y (time to the light exposure), was positively correlated, particularly with the extinction coefficients K\({}_{270}\) and \(\Delta\)K, C\({}_{7}\)-C\({}_{10}\) aldehydes (\(E\))-decenal and (\(E\), \(E\))-2,4-decadienal, and DHPEA-EA-OX. On the contrary, negative correlations between Y and all the antioxidant compounds, especially with the oleuppein derivatives oleacein (3,4-DHPEA-EDA) and 3,4-DHPEA-EA, were demonstrated. Furthermore, we observed that K\({}_{232}\) and the ligtroside derivatives oleocanthal (\(p\)-HPEA-EDA) and \(p\)-HPEA-EA, as well as lignans, together with volatile compounds such as hexanal, nonanal, decanal and propionic acid, occupying the center of the loading plot, did not show correlation with time (Figure 1B). This general exploration allowed us to conclude that, among all the chemical substances evaluated on the 20 VOOs over the storage to the light exposure evolution of K\({}_{270}\) and \(\Delta\)K, aldehydes (\(E\), \(E\))-2,4-decadienal and (\(E\))-2-decenal, the phenolic composition and in particular the oleuppein derivatives, like 3,4-DHPEA and 3,4-DHPEA-EA-OX, were strongly correlated to the quality/freshness evolution of the VOOs. Those data were very similar to those published by [PERSON] et al. (2017) [7], where PCA and PLS models showed the same positive correlations with the time to exposure to the light of different VOOs and parameters like K\({}_{270}\), C\({}_{7}\)-C\({}_{11}\) aldehydes, and the oxidative products of polyphenols [7]. However, in this research, besides K\({}_{270}\), \(\Delta\)K and the aldehydes (\(E\), \(E\))-2,4-decadienal and (\(E\))-2-decenal also appeared more positively correlated to the time of conservation of the VOOs. Figure 1: _Cont._  
Using the previous separation of the 20 samples into two groups, according to the initial low-medium and high concentration of polyphenols (VOOImp and VOOmhp groups, respectively), we followed the evolution of those parameters that more significantly influenced the quality evolution of the VOO, according to the PLS model. Evolution of Extinction Indexes K\({}_{270}\) and \(\Delta\)K during 12 Months of Light Exposure  
In this study, the evolution of K\({}_{270}\) showed a general tendency to increase during the storage period (Figure 2; Table S5) for all the samples analyzed with strong differences in terms of the number of months in which the samples remained in the extra-virgin category (limit of 0.20) [34], according to the initial concentration of polyphenols. In fact, Figure 2A,B highlighted that in those VOOImp, the legal limit [34] was reached by S12 and S2 within the first four months; by S11, S19, and S20 within 6 months; and by the rest of the VOOImp samples (S13 and S17) within the 10 months of storage to the light exposure. On the contrary, S7 and S18 remained under 0.20 until the end of the experimentation.