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The effect of γ-tocopherol in proportions between 0.02 and 2% by weight on the accelerated storage process of refined soybean oil is studied by 1H NMR, and compared with that of α-tocopherol. Whereas the lowest γ-tocopherol enrichment level does not affect oil evolution, at higher concentrations both γ- and α-tocopherols initially accelerate acyl groups degradation and hydroperoxides generation, more as higher is the tocopherol concentration, this effect being less marked for γ-tocopherol. However, after this initial stage, the rates of acyl groups degradation and hydroperoxides formation decrease with tocopherol concentration. Furthermore, in the case of γ-tocopherol, the higher the enrichment degree, the later hydroperoxides decomposition occurs, so that, unlike α-tocopherol, γ-tocopherol delays the generation of most secondary oxidation products (aldehydes, (E,E)-keto-dienes, epoxy-keto-enes, (E)-epoxystearates and alcohols) with the exception of some epoxides. Similarly to α-tocopherol, γ-tocopherol modifies the oil oxidation pathway at the highest addition level, promoting the formation of compounds with (Z,E)-isomerism, although less noticeably than α-tocopherol.

European sea bass is very popular in the Mediterranean area, although very little is known about the possible different behaviours of farmed and wild samples during cooking. This study addresses the effect of microwave cooking, salt-crusted and conventional oven baking on the lipids and volatile profile of farmed and wild sea bass. Proton Nuclear Magnetic Resonance did not detect that hydrolysis or oxidation of lipidic components had taken place. However, Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry evidenced that polyunsaturated acyl group oxidation and Maillard-type reactions occurred to a very slight extent, yielding a wide variety of volatile odour-active compounds. Conventional baking enriched fish volatile profile to a higher extent than the other two techniques assayed. In fact, 15 Maillard reaction-derived compounds (pyrroles, alkylpyrazines, alkylthiophenes and 2-ethylpyridine) were only detected in oven-baked samples. Regardless of the cooking method applied, farmed sea bass showed a much richer aromatic profile than did wild samples, having 6-fold higher lipid content than the latter.

The effect of smoking using liquid smoke flavourings on the hydrolysis and oxidation of European sea bass lipids during in vitro digestion was investigated. The techniques used were 1H NMR and SPME-GC/MS. The former proved that liquid smoking does not influence the extent of lipolysis, but prevents those lipid oxidation reactions that occur during in vitro digestion of unsmoked samples, giving rise to cis,trans-conjugated dienes associated with hydroperoxy/hydroxy groups. SPME-GC/MS corroborated the results obtained by 1H NMR in relation to the antioxidant effect of smoking under gastrointestinal conditions. Smoked sea bass digests showed lower abundances of volatile oxidation markers derived from omega-3 and omega-6 lipids than unsmoked ones. Moreover, the lowest values were found in the digests of sea bass samples smoked with the flavouring showing the highest phenolic content. For the first time, the bioaccessibility of smoke flavouring components was evidenced, some of them well-known for displaying antioxidant activity.

Both fresh and slightly oxidized sunflower oils, as models of omega-6 rich lipids, were submitted to in vitro gastrointestinal digestion and studied by 1H NMR and SPME-GC/MS. Changes in lipolysis degree, lipid composition and oxidative level were studied by 1H NMR. Three quantitative approaches were used and several equations were newly developed. In oxidized oil digestates slightly lower hydrolysis and a higher advance of oxidation took place during digestion. This latter was evidenced by a greater decrease of lipid unsaturation degree and enhanced generation of oxidation products (cis,trans-hydroperoxy-octadecadienoates, cis,trans- and trans,trans-hydroxy-octadecadienoates). For the first time, the generation of hydroxy-octadecadienoates during in vitro digestion is reported. Furthermore, SPME-GC/MS study of non-digested and digested samples headspaces confirmed that lipid oxidation occurred: abundances of volatile markers increased (including potentially toxic alpha,beta-unsaturated aldehydes), especially in oxidized oils digestates. Markers of Maillard-type and esterification reactions were also detected in the digestates.

Fillets of farmed gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax) were pan- and microwave-fried using extra-virgin olive and sunflower oils. Moreover, both oils were heated under the same conditions in the absence of food. Proton Nuclear Magnetic Resonance spectroscopy (1H NMR) was employed to study the changes occurring both in the frying oils and in the fish lipids, in terms of main and of some minor components. These results confirm that there is a migration of main and some minor lipidic compounds between oil and fish, this exchange being linked to the proportion of each component in the original lipidic medium. The occurrence of trans-2-alkenals, alkanals, cis,trans- and trans,trans-2,4-alkadienals, trans-9,10-epoxystearate and 1,2-diglycerides in all these systems was quantified. No signals related to primary oxidation compounds were detected. Pan-frying provoked a greater oil thermo-oxidation degree than microwave-frying did. Regarding aldehyde formation, extra-virgin olive oil is safer and more suitable than sunflower oil for shallow-frying.

The performance of commercial non-enriched and lycopene-enriched extra-virgin olive oils (EVOO) during in vitro gastrointestinal digestion was studied in order to elucidate potential benefits of lycopene addition. Samples were analyzed before and after digestion by Proton Nuclear Magnetic Resonance (1H NMR) and Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS). EVOO samples differed in both main (oleic and linoleic acyl groups) and minor components (phenolic and oxidation compounds). Regardless of the presence of lycopene, all the samples reached a high degree of lipolysis and showed high stability towards oxidation under digestion conditions. Rather than oxidation reactions, the hydroperoxides initially present in the oil were reduced to more stable hydroxides. Likewise, hydroxy-diene isomerization from cis,trans to trans,trans occurred. Hence, the presumed antioxidant effect of lycopene was not noticed during in vitro digestion of EVOO. Similar experiments carried out with a more polyunsaturated oil (sunflower oil) indicated that lycopene slowed down the advance of oxidation slightly. However, in the case of EVOO, its initial quality prevailed over the slight antioxidant effect exerted by lycopene at the concentration present in commercial samples, determining the oxidation compound profile of the digests.

Extra virgin olive, soybean and sunflower oils were used in three different series of fourteen experiments to deep-fry three foods of very different lipidic content and composition. The aim of this study was to analyze how much the composition of the frying medium influenced the lipidic composition of the fried food. To achieve this, the compositions both of the frying medium throughout fourteen deep-frying experiments carried out with each kind of oil, as well as that of the unfried food were studied by 1 H NMR. This same technique was used to study the lipidic composition of each fried food. The study focussed on the changes in the molar percentage of the different kinds of acyl groups, sterols and diglycerides as well as on the occurrence of compounds or functional groups coming from lipid degradation, such as aldehydes, epoxy groups and primary and secondary alcohols, all of them determined from 1 H NMR spectral data.

A study of the evolution of the composition of both soybean oil submitted to heating at frying temperature for a prolonged period of time, as well as of soybean oil-frying media used in three different series of deep-frying experiments is carried out by means of 1H nuclear magnetic resonance. The foods involved in the deep-frying processes have very different lipid contents and their lipid composition is also very different. The results obtained allow one to clarify how the nature of the food being fried influences the changes observed in the composition of the soybean oil-frying media throughout the deep-frying process. The study refers both to the evolution of the molar percentage of the different kinds of acyl groups in the frying-media as well as to the nature of the aldehydes formed and the evolution of their concentrations. It is noteworthy that the main aldehydes detected, in both soybean oil and soybean oil-frying media, are the reactive (E,E)-2,4-alkadienals; likewise the genotoxic and cytotoxic 4-hydroxy-(E)-2-alkenals and 4,5-epoxy-2-alkenals are also present. The considerable influence of the food being fried on the occurrence of these reactive and toxic aldehydes in the frying media is shown. Furthermore, the occurrence and evolution of other oxygenated compounds such as alcohols are also addressed, as is the extent of hydrolytic processes. In addition, the evolution of Iodine Value and of the percentage in weight of Polar Compounds is also considered. The influence of the oil nature on all the above mentioned compositional characteristics is also given attention by comparison of these results with those previously obtained using extra virgin olive oil; it is noteworthy that from the toxic aldehyde content point of view the results obtained indicate that the extra virgin olive oil-frying media are much safer than the soybean oil-frying media.

Few in vitro studies have tackled the effect of alpha-tocopherol on lipid oxidation during digestion, and discrepant results have been reported. As a result, the aim of this study was to elucidate whether the addition of alpha-tocopherol enhances or slows down the advance of oxidation that occurs during in vitro gastrointestinal digestion of polyunsaturated lipids. For this purpose, commercial sunflower and flaxseed oils (as models of omega-6 and omega-3 rich lipid systems, respectively) were in vitro digested in the absence or in the presence of this tocol at different concentrations (0.02%, 0.2% and 2%). Proton Nuclear Magnetic Resonance (1H NMR) and Solid Phase Microextraction followed by Gas Chromatography/Mass Spectrometry (SPME-GC/MS) were used to investigate in detail potential differences among the digests regarding lipolysis and oxidation level. Alpha-tocopherol addition did not affect the advance of lipolysis, whereas lipid oxidation was enhanced in a dose-dependent manner. In this regard, the increased degradation of polyunsaturated lipids and greater generation of primary and secondary oxidation products observed at higher concentrations of alpha-tocopherol confirmed this observation. Among the formed oxidation products, hydroperoxy-, hydroxy- and keto-dienes, as well as oxygenated alpha,beta-unsaturated aldehydes are worth mentioning. The in vitro bioaccessibility of added tocopherol was estimated to be very low, suggesting a notable transformation under the assayed conditions. Further in vivo studies are necessary to confirm this prooxidant activity of alpha-tocopherol during gastrointestinal digestion.

The influence of oil composition in the main components and of heating time at frying temperature on the formation of toxic alkylated monoaromatic hydrocarbons in oils is studied. Oils of very different compositions such as extra virgin olive, sunflower and virgin linseed oils were submitted to frying temperature in an industrial fryer for prolonged periods of time and the components of their headspace were periodically extracted by solid phase microextraction and studied by gas chromatography mass spectrometry; simultaneously, the formation of polar compounds was also monitored by means of dielectric constant measures. The results obtained evidence the formation of a very high number of alkylbenzenes with molecular weights ranging from 92 to 190. Evolution, during heating time, of the concentration of these compounds in the headspace of the three oils is reported for the first time. Taking these data into account, the ability of these oils to generate these kinds of compounds is evaluated. The formation of unsaturated alkylbenzenes in edible oils during heating at frying temperature is reported for the first time. Relationships between the nature and concentration of alkylbenzenes found and composition in the main components of the original oils are commented on. Significant increases in the concentrations of these toxic compounds in some of the oils studied, occurring before the oil reaches its permitted limit in polar compounds, suggests the advisability of analysing the safety of this limit, in order to protect public health.

The yield and composition of the volatile fraction of the pentane extracts of leaves, stems and seeds of Foeniculum vulgare Mill, have been studied. The yield obtained from seeds was much higher than that obtained from leaves and stems. The volatile fraction of the pentane extract of the latter two has a higher concentration of terpene hydrocarbons and a smaller concentration of oxygenated terpene hydrocarbons than that of the seeds. Sesquiterpenes have been detected in the leaves, as has petroselinic acid in the seeds. Saturated aliphatic hydrocarbons with 25 or more carbon atoms have been found in all of the parts. The pentane extract of the leaves also contains the antioxidant vitamin E. These extracts from different parts of fennel show not only the proportion of their volatile flavour components, but also the concentration of fatty acids and antioxidant compounds (such as vitamin E), if any.

A new approach is reported, based on Proton Nuclear Magnetic Resonance ( 1 H NMR) spectral data, to study qualitatively and quantitatively the hydrolysis level in complex lipid mixtures. It is based on a detailed study of the spectra of tri-, di-, mono-glycerides and fatty acids. It has been validated by using mixtures of standard compounds which simulate the complex mixtures formed in lipid digestion. To this aim the 1 H NMR spectra of pure compounds, as well as of mixtures containing different known proportions of triglycerides, 1,2-diglycerides, 1,3-diglycerides, 1-monoglycerides, 2-monoglycerides and fatty acids, were acquired. These mixtures cover a very broad range of concentrations and simulate edible oils and fats of vegetable and animal origins, including fish, with different levels of hydrolysis. Equations based on spectral data are proposed to determine the molar percentage of the different kinds of compounds that may be formed in lipid digestion, thus allowing quantification of the advance of lipolysis. To the best of our knowledge, this is the first time that a method based on 1 H NMR spectral data to quantify triglycerides, as well as partial glycerides and fatty acids in complex lipid mixtures coming from lipolysis is proposed. This methodology offers many advantages and is useful not only in the fields of food technology and nutrition, but also in others like enzymology, pharmacology, medicine and petrochemistry, among others.