## 3 Results
#### 3.3.1 Changes Provoked by in Vitro Digestion, in the Concentration of Linolenic Structures.
The detection and quantification of these can be carried out by means of \({}^{1}\)H Nuclear Magnetic Resonance spectroscopy using both the standard and NOESYGPPS experiments, and by means of Solid Phase Microextraction (SPME) followed by Gas Chromatography (GC/MS). The first technique views the sample as a whole and allows one to detect and quantify compounds of the same family having protons with similar electronic environments in a global way, without the previous steps of sample separation and without causing chemical changes in it. The second technique extracts the headspace components of the sample, among which, if the sample has undergone oxidation, there are volatile oxidation markers. (a) Oxidation Compounds Detected in the Different Digestates by \({}^{1}\)H NMR. Effect of the Enrichment in Phenolic Compounds  
Two kinds of oxidation compounds were detected by this technique in the lipid extracts of the digestates, evidencing that oxidation took place during in vitro digestion. These are hydroperoxides supported on chains having \(Z\),\(E\) conjugated dienic systems (HPO-c(\(Z\),\(E\))-dEs) derived from octadecatrienoic groups, which are primary oxidation compounds (multiplet signal at 6.58 ppm in the \({}^{1}\)H NMR spectrum indicated in Table S4), and n-alkanals, which are secondary oxidation compounds (singlet at 9.75 ppm signal in the \({}^{1}\)H NMR spectrum indicated also in Table S4). The concentrations of both kinds of compounds were determined using the aforementioned approach. They are given in Table 2 and are in agreement with the previous discussion relating to the degradation of linolenic structures. In general, the higher the degradation of linolenic structures, the higher the concentration of both kinds of oxidation compounds; likewise, the greater the enrichment in phenolic compounds in the sample, the lower the concentration of oxidation compounds in the digestates. Finally, it has again been demonstrated that, under in vitro digestion conditions, dodecyl gallate shows higher antioxidant efficiency than hydroxytrosol acetate and gamma-tocopherol. To reduce the same oxidation level during in vitro digestion, measured by the concentration of hydroperoxides and n-alkanals, requires a level of enrichment with hydroxytrosol acetate (or with gamma-tocopherol) that is approximately two times (or ten times) higher than with dodecyl gallate. Likewise, to reduce the same level of oxidation, measured by the aforementioned markers, requires a much higher concentration of gamma-tocopherol than of hydroxytrosol acetate, which indicates that the efficiency of the latter as an antioxidant is higher than that of the former. Although hydroperoxides cannot be detected in the digestates of the more enriched in gamma-tocopherol samples, the presence of n-alkanals indicates that oxidation took place, which is in agreement with data of linolenic degradation and with data of volatile markers that will be discussed later. As the rate of oxidation of fatty acids is much higher than that of the corresponding acyl groups, it could be thought that the first are lipid compounds that have been oxidized, incorporating hydroperoxy groups and conjugated dienic systems into their molecules, and also giving rise to the formation of aldehydes. This suggests that the newly-formed compounds could also be bioaccessible in the concentrations indicated in Table 2, i.e., the bioaccessibility of HPO-c(\(Z\),\(E\))-dEs (or of n-alkanals) will range between zero (or between 0.04 mmol/mol(FA+AG)) in the digestates of the samples which are more enriched in gamma-tocopherol, and nearly 0.4 (or to near 0.09 mmol/mol(FA+AG)) in the unenriched sample or in the sample having the lowest enrichment in gamma-tocopherol. Furthermore, a smaller concentration of oxidation compounds in the enriched samples indicates that a lower level of degradation of fatty acids has taken place during digestion.