## 3 Results and Discussion
### Tocopherol Quantification in Food Matrices  
In this study, vitamin E content was analyzed in five different food matrices: high oleic sunflower oil, spinach, almond, mackerel fillet, and avocado pulp (Table 2), which are usually considered rich sources of tocopherols according to the USDA Nutrient Database [33]. All samples, except sunflower oil, were subjected to lipid extraction either by the Folch method or with \(n\)-hexane before the chromatographic analysis, and the lipid extraction yields are depicted in Figure 3. Chromatograms of tocopherol analyses in all food matrices considering lipids extracted with the Folch method or with \(n\)-hexane are shown in Figures S1-S5. It was found that \(\alpha\)-tocopherol was the predominant isoform of vitamin E in all cases; sunflower oil was the sample with the highest amount of \(\alpha\)-tocopherol (163.5 mg/100 g), and spinach showed the lowest amount (<0.20 mg/100 g). \(\gamma\)-Tocopherol was also found in lower proportions in all samples except sunflower oil. The presence of \(\beta\)- and \(\delta\)-tocopherol was not detected in any matrix. The \(\alpha\)-tocopherol content in sunflower oil used in this work was higher than that reported by other authors and higher than data available in \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Compound** & **Regression** & **Linearity** & **LOD** & **LOQ** & **Intra-Day** & **Inter-Day** \\  & **Equation** & **Coefficient (R\({}^{2}\))** & **(ppm)** & **(ppm)** & **Precision (RSD\%)** & **Precision (RSD\%)** \\ \hline \multirow{2}{*}{\(\alpha\)-tocopherol} & \multirow{2}{*}{y = 7.549\(\mathrm{x}-61.183\)} & \multirow{2}{*}{0.9988} & \multirow{2}{*}{0.38} & \multirow{2}{*}{1.28} & 1.79 (at 10 ppm) & 3.06 (at 10 ppm) \\  & & & & & 1.50 (at 100 ppm) & 1.81 (at 100 ppm) \\  & & & & & 1.87 (at 250 ppm) & 1.54 (at 250 ppm) \\ \hline \multirow{2}{*}{\(\beta\)-tocopherol} & \multirow{2}{*}{y = 4.206\(\mathrm{x}-34.324\)} & \multirow{2}{*}{0.9985} & \multirow{2}{*}{0.32} & \multirow{2}{*}{1.08} & 2.84 (at 10 ppm) & 4.43 (at 10 ppm) \\  & & & & & 2.59 (at 100 ppm) & 2.51 (at 100 ppm) \\  & & & & & 1.66 (at 250 ppm) & 4.32 (at 250 ppm) \\ \hline \multirow{2}{*}{\(\gamma\)-tocopherol} & \multirow{2}{*}{y = 8.144\(\mathrm{x}-75.855\)} & \multirow{2}{*}{0.9984} & \multirow{2}{*}{0.62} & \multirow{2}{*}{2.06} & 2.56 (at 10 ppm) & 7.80 (at 10 ppm) \\  & & & & & 2.82 (at 100 ppm) & 7.77 (at 100 ppm) \\  & & & & & 1.44 (at 250 ppm) & 5.05 (at 250 ppm) \\ \hline \multirow{2}{*}{\(\delta\)-tocopherol} & \multirow{2}{*}{y = 6.361\(\mathrm{x}-56.739\)} & \multirow{2}{*}{0.9988} & \multirow{2}{*}{0.63} & \multirow{2}{*}{2.11} & 3.63 (at 10 ppm) & 7.51(at 10 ppm) \\  & & & & 1.39 (at 100 ppm) & 7.40 (at 100 ppm) \\ \multicolumn{2}{c}{} & \multirow{2}{*}{2.15 (at 250 ppm)} & \multirow{2}{*}{6.05 (at 250 ppm)} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Method validation parameters for the analysis of tocopherol isoforms. food databases (-60-90 mg/100 g) [34; 35; 36]. It could be due to a fortification of the oil with \(\alpha\)-tocopherol, which is sometimes carried out with unsaturated vegetable oils to prevent lipid oxidation and increase their shelf life [37]. for lipid extraction such as Soxhlet or those involving a saponification step, which are more time-consuming, require larger volumes of solvent, and are developed at higher temperatures, thus increasing the possibility of tocopherol degradation. The lipid extraction yield was significantly higher using Folch extraction in mackerel fillet, almond, and spinach, but not in avocado pulp, where the values were close with both methods (Figure 3). However, despite the higher amount of extracted lipids from mackerel using the Folch method, the \(n\)-hexane extraction led to higher concentrations of \(\alpha\)- and \(\gamma\)-tocopherol (1.33 and 0.61 mg/100 g, respectively) than Folch extraction (0.79 mg \(\alpha\)-tocopherol/100 g).