# Antioxidants
## Results
### Evaluation of the Oxidative Stability of Bulk Oil
#### Volatile Compounds  
The volatile compounds were determined as related to bulk oils and storage time (detailed in Tables S9, S10, and S11, Supplementary Materials); however, on the basis of the literature, hexanal was selected as a lipid secondary oxidation marker and its quantification was carried out. The kinetics of hexanal levels in CO, HO, and EO is shown in Figure 5. The starting values of hexanal in fresh bulk oils ranged from \(3.57\pm 0.60\) to \(8.71\pm 0.13\) mmol/kg oil without significant differences up to day 1 (all the hexanal contents are shown in detail in Table S8, Supplementary Materials). At day 1, hexanal in CO was significantly higher (\(p<0.01\)) than in HO and EO and, from this point forward, drastically increased during the whole storage treatment, displaying each day the highest value among the three bulk oils. Hexanal in EO increased after 3 days of storage (\(p<0.01\)) (Table S8, Supplementary Materials) and reached its highest value of \(26.53\pm 0.54\) mmol/kg oil after 7 days. On the contrary, HO exhibited different kinetics from the two other oils. In fact, hexanal content in HO displayed no significant changes in abundance (\(p>0.05\)) (Table S8, Supplementary Materials), keeping low values throughout the whole storage treatment.  
In order to better define the impact of lipid oxidation on bulk oils, principal component analysis (PCA) of all volatile compounds during the whole experiment was carried out. PCA was able to explain \(73.90\%\) of the total variance in two principal components, highlighting the presence of different clusters. In the first principal component (PC1), which explains \(59.60\%\) of variance, the terpen except for 3-carene, l-fenchone, and \(p\)-xylene were separated from 1-hexanol, 6 methyl-5-hepten-2-one, and butanoic acid. The second principal component (PC2; 13.80\(\%\) of total variance) visibly separated hexanal and 2,4-nonadiene from nonanal, emphasizing their inverse correlation. A third cluster comprising formic acid, 2-butenal, \(\alpha\)-pinene, and decane was observed, while \(\beta\)-pinene was disjointed from the remaining terpenoid compounds.  
As reported in Figure 6, a clear oxidation trend was found for both CO and EO samples as related to time of storage, while the HO samples displayed a different behavior showing the impact of hemp extract in counteracting the lipid oxidation.  
Figure 5: Kinetics of hexanal content (mmol/kg oil) in stripped linseed oil without antioxidants (CO), with hemp extract (HO), and with \(\alpha\)-tocopherol (EO) and results of ANOVA with Duncan’s test. Each point represents the mean \(\pm\) standard deviation of three independent replicates (\(n=3\)). Different letters a–c within the same day are significantly different at \(p<0.05\). n.s. = not significant.  
Again, when all volatile compounds were considered, including terpenoid compounds, two main clusters were exhibited. PC1 divided the HO samples from both CO and EO, which were mainly separated in relation to the time of storage by PC2. The clustering of HO samples was characterized by terpenes and, as mentioned above, no significant effects of VOCs originating from lipid oxidation were implicated, confirming the capacity of hemp extract to counteract the lipid oxidation in the tested bulk oil (Figure S1, Supplementary Materials).