## 3 Results
#### 3.3.1 Changes Provoked by in Vitro Digestion, in the Concentration of Linolenic Structures. Antioxidant Efficiency of the Added Phenolic Compounds  
In virgin flaxseed oil, linolenic acyl groups are the main ones, as indicated in the experimental section. Furthermore, the linolenic acyl group and linolenic fatty acid tend to oxidize more than any others due to their low oxidative stability. For this reason, if oxidation reactions take place during digestion, linolenic structures will be clearly affected, diminishing their concentrations in the sample. For this reason, they are the subject of this monitoring. \({}^{1}\)H NMR spectroscopy allowed us to determine the concentration of linolenic structures in relation to the all fatty acids plus acyl groups in the sample subject of study. Table 2 gives the concentration of these structures in the oil before digestion and in the digestates of each of the samples. It can be observed that in vitro digestion of oil F causes a significant diminution in the concentration of linolenic structures. In other words, this group undergoes degradation which provokes a reduction in the molar percentage in relation to the total moles of all kinds of fatty acids plus acyl groups (AG+FA) from 55.7 % in F to 47.9% in DF. The addition of different concentrations of phenolic compounds negates degradation during digestion to a certain extent, even at the lower enrichment level assayed. This indicates that the three compounds act as antioxidants. Nevertheless, their efficiency at avoiding the degradation of linolenic structures, or in other words, their oxidation, is not the same for the three antioxidants tested. From a comparison of data in Table 2, it is evident that in the range of enrichment levels studied, dodecyl gallate is the most efficient antioxidant of the three compounds. It can be observed that approximately half of the enrichment with dodecyl gallate is required (0.14 or 1.35 mmol/mol (AG + FA)) compared to that of hydroxytyrosol acetate (0.24 or 2.65 mmol/mol (AG + FA)) to reach the same reduction in the degradation of linolenic groups. Likewise, the higher antioxidant efficiency of dodecyl gallate than that of gamma-tocopherol is also evident because with similar enrichment levels of both compounds (see Table 2), the former avoids the degradation of linolenic groups to a greater extent than the latter. Finally, also taking data from Table 2, it is evident that hydroxytyrosol acetate is a more efficient antioxidant than gamma-tocopherol, because a concentration about five times greater of the latter is required to avoid a similar degree of oxidation. These results demonstrate that during in vitro digestion of virgin flaxseed oil, the antioxidant efficiency of dodecyl gallate is greater than that of hydroxytyrosol acetate, which is, in turn, greater than that of gamma-tocopherol. This is also in agreement with the general idea that a greater number of phenolic groups in the molecule indicates a higher antioxidant ability, as described by some authors [6]. In the case of the enrichment with gamma-tocopherol and due to the availability of sufficient experimental data, it was possible to look for quantitative relationships between enrichment degree in the oil and linolenic structures concentration, expressed in molar percentage in relation to the total (AG+FA) moles in the corresponding sample, which is inversely related with oxidation level reached during in vitro digestion. It was found that the molar percentage of linolenic structures in the digestate [Ln] and enrichment level in gamma-tocopherol in the oil sample [YT], given in mmol/mol(AG + FA)O, fit the equation [Ln] = 51.06 + 1.16 Ln [YT], \(R\) = 0.9931, where Ln is the Napierian logarithm. This relationship is represented in Figure S1. According to this equation, the relationship between the molar percentage of linolenic structures, which is higher the higher the antioxidant efficiency, is directly related with gamma-tocopherol enrichment through the logarithmic relation given above.