## 3 Results and Discussion
### Oxidative Stability and Antioxidant Capacity
This variety is characterized by a high content of PUFAs, particularly C18:2, which is nearly twice that of the other tested varieties. Notably, the PUFA levels were not significantly affected by the FTT treatment (Table S5). However, heating during FTT treatment led to a significant reduction in tyrosol and ligstroside aglycone levels (Table 2), as well as \(\alpha\)-tocopherol content (Table 3). The thermally induced decrease in antioxidants, particularly \(\alpha\)-tocopherol which plays a key role in protecting C18:2 against oxidation [100], resulted in a significant reduction in the induction period. A reduction in IP, linked to the loss of phenolic compounds after rapid preheating of olive paste at 38 \({}^{\circ}\)C, was also observed by [PERSON] et al. [52]. Although Oblica exhibited higher antioxidant capacity than Levantinka, applying FTT at all temperatures except 20 \({}^{\circ}\)C caused a statistically significant decline in antioxidant activity. Given the observed influence of PUFAs, phenolic compounds and \(\alpha\)-tocopherol on the induction period and antioxidant capacity of the Oblica variety, we aimed to evaluate the extent to which these and other bioactive components in VOO from the three tested varieties, subjected to FTT, contribute to overall oxidative stability and antioxidant potential. To this end, partial least squares (PLS) regression analysis was applied to investigate the influence of specific oil constituents on oxidative stability and antioxidant capacity. For the oxidative stability model (measured by the induction period, IP), predictor variables included the fatty acid composition and the quantified bioactive compounds. The resulting model is presented in Equation (3):  
\[ \begin{split}\text{IP}&=-31.515+2.716\times\text{ SFA}+1.430*\text{MUFA}-1.992*\text{PUFA}-0.056*\alpha\text{-TOCO}\\ &+0.4801*\text{HTY}-0.115*\text{OLEA}+0.39*\text{OLEU}\text{ AGL}+0.929*\text{TY}+0.135*\\ \text{OLEC}+0.681*\text{MH}\text{OLEC}+0.096*\text{LIG}\text{ AGL}-0.652*\text{pA}+0.023*\text{TPC}\end{split}  \tag{3}\]  
The abbreviations in the equation stand for: SFA--sum of saturated fatty acids, MUFA--sum of monounsaturated fatty acids, MUFA--sum of monounsaturated fatty acids, \(\alpha\)-TOCO--\(\alpha\)-tocopherol, HTY--hydroxytrosol, TY--tyrosol, OLEA--oleacein, OLEC--oleacenthal, OLEU AGL--sum of oleuppein aglycones, LIG AGL--sum of ligstroside aglycones, MH OLEC--methyl hemiacetal of oleocanthal, \(p\)-CA--\(p\)-coumaric acid, TPC--total phenols. The model demonstrated strong predictive power, with a coefficient of determination (R\({}^{2}\)) of 0.788 and a cross-validated R\({}^{2}\) (Q\({}^{2}\)) of 0.733, indicating that approximately 78.8% of the variability in oxidative stability could be explained by the included predictors. Variable Importance in Projection (VIP) scores (Figure 1a) identified key contributors, with PUFA, hydroxyytrosol, oleuppein aglycones, tyrosol, ligstroside aglycones, TPC, \(\alpha\)-tocopherol, and MUFA all exhibiting VIP > 1.0. The predicted vs. observed plot (Figure 1b) confirmed the model's robustness, with most data points aligning closely with the 1:1 reference line. Model predictions indicate that oxidative stability is positively influenced by the presence of MUFA, as well as hydroxyytrosol, tyrosol, oleuppein and ligstroside aglycones, and total phenolic content. Conversely, the IP is negatively affected by elevated concentrations of PUFAs, due to their high susceptibility to oxidation, as well as by \(\alpha\)-tocopherol and oleacein. Similarly, [PERSON] et al. [101] reported a strong positive effect of C18:1 and oleuppein aglycones on IP, while C18:2 and oleacein exhibited a negative impact. For antioxidant capacity (AC), only bioactive compounds (\(\alpha\)-tocopherol and phenolics) were considered. The corresponding PLS model is shown in Equation (4):  
\[