## 3 Results
### Oxidative Stability
Hexanal, octanal, and nonanal are the typical volatile compounds of oleic acid oxidation, in particular, from 8-O\({}^{\bullet}\), 10-O\({}^{\bullet}\), and 11-O\({}^{\bullet}\)[34; 35; 36]. Figure 5: Aldehyde content (area %, mean value \(\pm\) SD) in FFA and IFA series during the thermal treatment. S, saturated; M, monounsaturated; P, polyunsaturated. Among saturated compounds, hexanal was particularly represented in the IFA series, but also in the FFA series. [PERSON] et al. (1997) [PERSON] et al. (1997) reported that the hexanal:nonanal ratio could be an appropriate way to detect the beginning of oxidation and its evolution; they found that the ratio changed quickly from the highest values for high-quality extra-virgin olive oil to the lowest for oxidized oils. In this paper, as an interesting result, the hexanal:nonanal ratio decreased for the FFA series, whereas it increased for the IFA series (data not shown), indicating a better protection of IFA with respect to FFA. As an example, Figure 6a-c shows the trend of octanal, _trans_-2-octanel, and _trans_, _trans_-2,4-heptadien during heating, showing lower percentage contents in IFA samples compared to the FFA series. _trans_-2-Octanel was formed from the decomposition of linoleic acid 11-hydroperoxide. [PERSON] et al. (2017) [PERSON] et al. (2017) reported, for example, that _trans_-2-octanel percentage content increased with oxidation in soybean and peanut oils, although it was not found in the rapeseed and linseed oils. This difference was linked to the different FA composition; in fact, linoleic acid was more abundant in soybean and peanut oils, with respect to the other two edible oils. _trans_, _trans_-2,4-heptadien was formed by the decomposition of \(\alpha\)-linolenic acid 12-hydroperoxide. It has been reported that its content increased with oxidation in linseed and rapeseed oils, in particular, for linseed oil where \(\alpha\)-linolenic acid is the main FA [PERSON] et al. (2017). Regarding alkylfurans, 2-pentylfuran was the main alkylfuran detected in FFA, whereas 2-ethylfuran was the main for IFA. High amounts of 2-pentylfuran were detected in edible oils with relatively high linoleic acid [PERSON] et al. (2017). For further investigation, HRGC-FID analysis was performed in order to evaluate the FA percentage composition during the thermal treatment of IFA and FFA series, and the results are reported in Figure 7.  
Figure 6: _Cont._  
Regarding the FFA series, the FA percentage contents of oleic, linoleic and \(\alpha\)-linolenic acids were fairly constant for the first 21 days; after that, linoleic and \(\alpha\)-linolenic acid percentage contents decreased, reaching values of 21.5% and 7.5%, respectively, after 42 days. Clearly, the increase in oleic acid percentage content is a consequence of the percentage decrease in linoleic and \(\alpha\)-linolenic acids. The trend observed for the FFA mixture was expected because it is known that the unsaturation degree is inversely related to the oxidative stability of FA. Very interesting results were obtained for the IFA mixture during the heating; in fact, minimal changes in the FA percentage content were observed. In particular, after 42 days of thermal treatment, the linoleic acid percentage content was almost similar to the initial value. Regarding the percentage content of \(\alpha\)-linolenic acid, only a slight decrease was observed, and it explains the slight increase in oleic acid percentage content. These results indicate that intercalation could represent a valid approach to protect unsaturated FAs from oxidative processes. Figure 6: Content (area percentage, mean value \(\pm\) SD) of octanal (**a**), _trans_-2-ocretal (**b**), and _trans_, _trans_-2,4-heptdaienal (**c**) in FFA and IFA series during heating. Figure 7: Fatty acid composition (area percentage, mean value \(\pm\) SD) of FFA and IFA series during the thermal treatment.