## 4 Conclusions  
Based on the results obtained in this research, the quality and freshness of commercial VOOs during their storage in market conditions are strongly influenced by photo-oxidation and the initial antioxidant heritage. However, by studying the evolution of parameters that are directly involved in the modification of VOOs' legal, health-promoted, and sensory qualities, the following was found:  
K\({}_{270}\) and \(\Delta\)K extinction indexes and (\(E\))-2-decenal and (\(E\), \(E\))-2,4-decadienal may be useful for monitoring the quality of stored VOOs by determining the time at which they will lose their \"extra\" status. Figure 9: Evolution (reported every two months) of the oleuropein aglycon concentration over 12-month storage with light exposure VOOImp (**A**) and VOOmhp (**B**). VOOImp: Virgin olive oil with low-medium polyphenol content; VOOmhp: Virgin olive oil with medium-high polyphenol content. The rapid increase in the 3_A_-DHPEA-EA-OX contents in the VOOs indicated the immediate and primary involvement of the oleupreein derivatives in inhibiting the oxidation phase. The different wave lengths of absorbance of 3_A_-DHPEA-EA and 3_A_-DHPEA-EA-OX simplify the analytical determination of 3_A_-DHPEA-EA-OX. The results of this study clearly demonstrate the effectiveness of 3_A_-DHPEA-EA-OX as a faster indicator of VOOs' quality and freshness for the first time. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods12152959/s1](https://www.mdpi.com/article/10.3390/foods12152959/s1)]([https://www.mdpi.com/article/10.3390/foods12152959/s1](https://www.mdpi.com/article/10.3390/foods12152959/s1)), Figure S1: Score plot of the first two (at left) and of the first three (at right) components of the PCA space of the D-optimal design model; Figure S2: LC-MS-MS chromatogram (A) and LC-MS-MS spectrum (B) of one of the 20 VOOs (specifically S2) after 12 months of light exposure; Figure S3: Score plot (t1/t2) (A) and loading plot (p1/p2) (B) of the first two principal components of the PCA model built using all the analytical evaluations carried out on the 20 VOOs exposed to light for 12 months. The PCA model explains 70% of the total variance with six significant principal components (27%, 19%, 9%, 7%, 5%, and 3%, respectively). Figure S4: Chromatograms of one of the 20 VOOs (specifically S2) after 12 months of light exposure (A, B); LC-MS extracted ion chromatogram in negative mode (393.11911 \(m/z\)) showing the acidic form of oleupreein aglycone (C); DAD-UV chromatogram absorption at a wavelength of 347 nm and at a retention of at 8.479 min (D). Table S1: Mixing proportions of the 6 \"mother\" samples A, C, D, E, F, and G selected for the preparation of the 20 experimental VOOs S1-S20. Table S2: Values of free acidity, peroxide value, extinction coefficients, 1,2 diacylglyceroliocols, oleic acid, MUFA, PUFA and SFA, of the 20 VOOs at time 0 *. The results are the means of two independent determinations \(\pm\) standard deviation. Legend S: sample; Table S3: volatiles' composition (ug/kg) of the head space of the 20 VOOs at time 0 *. The results are the means of two independent determinations \(\pm\) standard deviation. Legend S: sample; Table S4: Composition in antioxidants (mg/kg), value of OSI time (hour), and content of 3-4-DHPEA-EA-OX (mg/kg) of the 20 VOOs at time 0. The results are the means of two independent determinations \(\pm\) standard deviation. Legend S: sample; OSI: Oxidative Stability Index; 3-4-DPEA-EA-OX: Oxidized form of 3_A_-DHPE-EA; Table S5: Evolution of the extinction coefficient K270 over 12-month storage with light exposure in VOOImp and VOOmhp samples. The results are the means of two independent determinations \(\pm\) standard deviation. Different letters in each row indicate statistically different values at \(p<0.05\).