## 3 Results and Discussion
### Principal Component Analysis  
In order to differentiate the oils based on their quality parameters, the principal component analysis was applied. The scores for the first two factors of the seven cold-pressed oils are presented in Table 6 and Figure 1. The first two factors amounted to 60.45% of the total variation. According to the scatter plots constructed by Factor 1 and Factor 2 (Figure 1), the oil quality parameters group the oils into three groups according to the similarities of the fatty acid composition, oxidation parameters, and colour. The first group includes CO, PO, and DO, which are similar in terms of monounsaturated acid content and induction time at 120 \({}^{\circ}\)C. The next group includes WCO, FO, and TO; a separate group is BO, which had the shortest induction time.  
PCA analysis also shows a correlation between the analysed quality parameters. Table 6 presents the value of the correlation coefficients between the individual quality factors and the discriminators of the oil stability. The value of the L* parameter and the oxidation coefficient calculated on the basis of fatty acid composition had a great impact on the oil stability (r = 0.88 and r = \(-\)0.87, respectively. This means that the lighter the oil--that is, the smaller amounts of dyes that it contains, the more stable it is, which works well in the case of refined oils. However, the opposite is the case with the COX. The higher value of this parameter, the lower the oil stability.  
The highest correlation was found between the value of the oxidation rate constant and the induction time, but it is related to the calculation of this parameter on the basis of the induction time. The activation energy is the least correlated with the a* parameter of the oil colour and the content of the carotenoid pigments related to it. Along with their content, the activation energy of the oxidation reaction increases, i.e., the initiation of the reaction requires more energy.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Quality Parameter** & **IT at 120 \({}^{\circ}\)C** & **Ea** & \(k\)**at 120 \({}^{\circ}\)C** \\ \hline AV & 0.10 & 0.66 & \(-\)0.16 \\ PV & 0.14 & \(-\)0.08 & \(-\)0.19 \\ \(p\)-AnV & 0.46 & 0.20 & \(-\)0.26 \\ TOTOX & 0.20 & \(-\)0.06 & \(-\)0.22 \\ K232 & 0.22 & \(-\)0.07 & \(-\)0.21 \\ K268 & 0.43 & \(-\)0.11 & \(-\)0.35 \\ Chlorophylls & 0.69 \({}^{\star}\) & \(-\)0.56 & \(-\)0.52 \\ Carotenoids & \(-\)0.08 & 0.78 \({}^{\star}\) & \(-\)0.28 \\ L* & \(-\)0.88 \({}^{\star}\) & 0.02 & 0.85 \({}^{\star}\) \\ a* & \(-\)0.04 & 0.86 \({}^{\star}\) & \(-\)0.35 \\ b* & 0.30 & 0.64 & \(-\)0.65 \\ SFA & \(-\)0.33 & 0.61 & \(-\)0.07 \\ MUFA & 0.63 & 0.17 & \(-\)0.49 \\ PUFA & \(-\)0.61 & \(-\)0.30 & 0.53 \\ COX & \(-\)0.87 \({}^{\star}\) & \(-\)0.14 & 0.77 \({}^{\star}\) \\ AI & \(-\)0.41 & 0.49 & 0.06 \\ TI & 0.17 & \(-\)0.12 & \(-\)0.19 \\ HH & 0.53 & \(-\)0.18 & \(-\)0.18 \\ Ea & \(-\)0.01 & - & - \\ \(k\) at 120 \({}^{\circ}\)C & \(-\)0.89 \({}^{\star}\) & - & - \\ IT at 120 \({}^{\circ}\)C & - & - & - \\ \hline \hline \end{tabular} \({}^{\star}\)statistically significant correlation.  
\end{table}
Table 6: Correlation coefficients between the oxidation parameters and the quality parameters of the tested oils.