## 3 Results
#### 3.3.1 Changes Provoked by in Vitro Digestion, in the Concentration of Linolenic Structures.
Nevertheless, it should be pointed out that the antioxidant efficiency order is not the same regarding the number of moles of the compound required to avoid or reduce oxidation, or if it refers to the amount (expressed in weight or in percentage in weight) of that compound required to reach the same endpoint. If antioxidant efficiency referred to the amount of compound, the hydroxytyrosol acetate would have higher antioxidant efficiency than dodecyl gallate, due to the great difference in the molecular weights of these compounds. For this reason, it is very important to indicate the units by which the antioxidant efficiency is measured. Perhaps a lack of clarity in this respect could be the cause of divergences between studies, regarding the antioxidant efficiency order of some compounds. In Vitro Bioaccessibility of Some Minor Components of Virgin Flaxseed Oil, and Specifically, of Gamma-Tocopherol in the Different Digestates  
As with other vegetable oils, this virgin flaxseed oil contains tocopherols and sterols. Furthermore, this oil also contains terpenes and sesquiterpenes, as has been shown in previous studies [24; 26]. All these compounds have important biological activities, and in some cases, antioxidant abilities. Some of these minor oil components give signals in the \({}^{1}\)H NMR spectra which do not overlap with any others, for which reason their concentrations in the sample before and after in vitro digestion can be estimated. These are (i) of the tocopherols, gamma-tocopherol (singlet signal at 6.36 ppm due to proton aromatic proton C-5, as indicated in Table S5 and shown in Figure 2); and (ii) of the sterols, cycloartenol and 24-methylenedycloartenol free or esterified (two doublet signals overlapping due to the methylene protons on carbon atom C-19 yielding a triplet joint signal centered at 0.33 ppm as is indicated in Table S5, which permits their joint quantification) [36]. They are respectively the main components of the tocopherols and sterols in this oil [26]. Other minor virgin flaxseed oil components such as terpenes and sesquiterpenes can, due to their volatility, be extracted from the headspace of the samples by means of solid phase microextraction (SPME), and can be separated, identified, and semiquantified by means of gas chromatography/mass spectrometry (GC/MS). For this reason, by using these techniques, the in vitro bioaccessibility of these compounds can be estimated. As mentioned, the gamma-tocopherol concentration can be estimated in the different samples before and after in vitro digestion. The in vitro bioaccessibility of this compound can be expressed by its concentration in the digestate [\(\gamma\)T]\({}_{\text{D}}\), given in mmoles, in relation to the concentration of the main components also in the digestate [FA + AG]\({}_{\text{D}}\), given in moles, by the equation \(\text{B}_{\gamma\text{T}}=[\gamma\text{T}]_{\text{D}}/[\text{FA}+\text{AG}]_{ \text{D}}\). This in vitro bioaccessibility definition gives information from a global, quantitative point of view. The values of the thus defined in vitro bioaccessibility of gamma-tocopherol are given in Table 4 for the different samples. It can be observed that during the in vitro digestion of the sample not enriched in phenols, almost the totality of the gamma-tocopherol present in the oil (0.33 mmol/mol(FA + AG)) is degraded. In spite of this, oxidation of the sample took place. In the samples enriched in dodecyl gallate and hydroxytyrosol acetate, a larger amount of gamma-tocopherol remained undegraded than in the unenriched sample. This could indicate that these added di- or tri-phenolic compounds have some protective effect on gamma-tocopherol. It is noteworthy that these samples, in spite of the presence of gamma-tocopherol, were also oxidized, though to a lesser degree than the nonenriched sample. Finally, the amount of this compound that remains undegraded in the samples enriched in gamma-tocopherol after digestion increases according to the enrichment level, as would be expected.