Individual and Joint Effect of Alpha-Tocopherol and Hydroxytyrosol Acetate on the Oxidation of Sunflower Oil Submitted to Oxidative Conditions: A Study by Proton Nuclear Magnetic Resonance.

This study tackles the individual and joint effect of alpha-tocopherol and hydroxytyrosol acetate on the oxidation of sunflower oil submitted to accelerated storage conditions at intermediate temperature, in order to deepen the understanding of antioxidant-prooxidant behaviour. This was accomplished by 1H Nuclear Magnetic Resonance. For this purpose, the evolution of the degradation of both the main components of the oil and the aforementioned added compounds was monitored by this technique throughout the storage time. Furthermore, the formation of a very large number of oxylipins and the evolution of their concentration up to a very advanced stage of oil oxidation, as well as the occurrence of lipolysis, were also simultaneously studied. The results obtained show very clearly and thoroughly that in the oxidation process of the oil enriched in binary mixtures, interactions occur between alpha-tocopherol and hydroxytyrosol acetate that notably reduce the antioxidant effect of the latter compound with the corresponding negative consequences that this entails. The methodology used here has proved to be very efficient to evaluate the antioxidant power of mixtures of compounds.

Alpha-Tocopherol, a Powerful Molecule, Leads to the Formation of Oxylipins in Polyunsaturated Oils Differently to the Temperature Increase: A Detailed Study by Proton Nuclear Magnetic Resonance of Walnut Oil Oxidation.

Lipid oxidation causes food degradation and the formation of toxic compounds. Therefore, the addition to foods of compounds able to avoid, delay or minimize this degradative process is a commonly used strategy. Nevertheless, neither the identity of most of the formed compounds in this complex process nor the way in which their formation is affected by the strategy used are well known. In this context, the effect the temperature increase and the enrichment level in alpha-tocopherol on the evolution of the walnut oil oxidation, as a model of an oil rich in polyunsaturated omega-6 acyl groups, submitted to storage conditions, are tackled by 1H NMR. The study has allowed knowing the degradation kinetic of both the oil acyl groups and alpha-tocopherol, the identification of a very high number of oxylipins and the kinetic of their formation. The temperature increase accelerates the formation of all oxylipins, favouring the formation of hydroperoxy conjugated E,E-dienes and related derivatives versus that of the Z,E-isomers. The enrichment in alpha-tocopherol accelerates the formation of hydroperoxy conjugated Z,E-dienes and related derivatives, and delays in relation to the formation of the former that of the E,E-isomers and related derivatives, hindering, to a certain extent, the formation of the latter in line with the enrichment level.

Influence of Hydroxytyrosol Acetate Enrichment of an Oil Rich in Omega-6 Groups on the Evolution of Its Oxidation and Oxylipin Formation When Subjected to Accelerated Storage. A Global Study by Proton Nuclear Magnetic Resonance.

Sunflower oil samples, both unenriched and enriched with four different concentrations of hydroxytyrosol acetate, were subjected to accelerated storage at 70 °C until a very advanced oxidation stage and the process was monitored by 1H NMR spectroscopy. The aim of the study is to know the effect that the presence of this antioxidant has on the oxidation process of sunflower oil under the aforementioned conditions, as well as on the formation and evolution of the concentration of a significant number of oxylipins. The oxidation process was studied globally by monitoring, during storage time, the degradation of both the linoleic acyl group of sunflower oil, which is the main component of sunflower oil, and the added hydroxytyrosol acetate. Simultaneously, the identification of up to twenty-six different types of oxylipins formed in the oxidation process and the monitoring of the evolution of their concentration over the storage time were carried out. In this way, essential information about the effect that hydroxytyrosol acetate provokes on the oxidation of this oil rich in omega-6 polyunsaturated acyl groups, has been obtained. It has also been shown that the enrichment of sunflower oil with this antioxidant under the conditions tested does not prevent the oxidation process but slows it down, affecting the entire oxidation process.

1H NMR Study of the In Vitro Digestion of Highly Oxidized Soybean Oil and the Effect of the Presence of Ovalbumin.

Oxidized lipids containing a wide variety of potentially toxic compounds can be ingested through diet. However, their transformations during digestion are little known, despite this knowledge being essential in understanding their impact on human health. Considering this, the in vitro digestion process of highly oxidized soybean oil, containing compounds bearing hydroperoxy, aldehyde, epoxy, keto- and hydroxy groups, among others, is studied by 1H nuclear magnetic resonance. Lipolysis extent, oxidation occurrence and the fate of oxidation products both present in the undigested oil and formed during digestion are analyzed. Furthermore, the effect during digestion of two different ovalbumin proportions on all the aforementioned issues is also addressed. It is proved that polyunsaturated group bioaccessibility is affected by both a decrease in lipolysis and oxidation occurrence during digestion. While hydroperoxide level declines throughout this process, epoxy-compounds, keto-dienes, hydroxy-compounds, furan-derivatives and n-alkanals persist to a great extent or even increase. Conversely, α,ß-unsaturated aldehydes, especially the very reactive and toxic oxygenated ones, diminish, although part of them remains in the digestates. While a low ovalbumin proportion hardly affects oil evolution during digestion, at a high level it diminishes oxidation and reduces the concentration of potentially bioaccessible toxic oxidation compounds.

Different Effects of Vitamin C-Based Supplements on the Advance of Linseed Oil Component Oxidation and Lipolysis during In Vitro Gastrointestinal Digestion.

Although widely consumed, dietary supplements based on Vitamin C contain high doses of this compound, whose impact on lipid oxidation during digestion needs to be addressed. Therefore, the effect of seven commercial supplements and of pure l-ascorbic acid and ascorbyl palmitate on linseed oil during in vitro gastrointestinal digestion was tackled. The advance of lipid oxidation was studied through the generation of oxidation compounds, the degradation of polyunsaturated fatty acyl chains and of gamma-tocopherol, by employing Proton Nuclear Magnetic Resonance. Supplements containing exclusively l-ascorbic acid enhanced the advance of linseed oil oxidation during digestion. This was evidenced by increased formation of linolenic-derived conjugated hydroxy-dienes and alkanals and by the generation of conjugated keto-dienes and reactive alpha,beta-unsaturated aldehydes, such as 4,5-epoxy-2-alkenals; moreover, gamma-tocopherol was completely degraded. Conversely, supplements composed of mixtures of ascorbic acid/salt with citric acid and carotenes, and of ascorbyl palmitate, protected linseed oil against oxidation and reduced gamma-tocopherol degradation. The study through Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry of the volatile compounds of the digests corroborated these findings. Furthermore, a decreased lipid bioaccessibility was noticed in the presence of the highest dose of l-ascorbic acid. Both the chemical form of Vitamin C and the presence of other ingredients in dietary supplements have shown to be of great relevance regarding oxidation and hydrolysis reactions occurring during lipid digestion.

Assessment of Soybean Oil Oxidative Stability from Rapid Analysis of its Minor Component Profile.

The minor components of vegetable oils are important for their oxidative stability. In order to know to what extent they can influence oil behaviour under oxidative conditions, two commercial soybean oils, one virgin and the other refined, both with very similar compositions in acyl groups but differing in their minor component profiles, were subjected to accelerated storage conditions. They were characterized by 1H nuclear magnetic resonance (NMR) and direct immersion solid-phase microextraction coupled to gas chromatography/mass spectrometry (DI-SPME-GC/MS), while oil oxidation was monitored by 1H-NMR. The lower levels of tocols and sterols in the virgin oil, together with its higher free fatty acid content when compared to the refined one, result in a lower oxidative stability. This is deduced from faster degradation of acyl groups and earlier generation of hydroperoxides, epoxides, and aldehydes in the virgin oil. These findings reveal that commercial virgin soybean oil quality is not necessarily higher than that of the refined type, and that a simple and rapid analysis of oil minor components by DI-SPME-GC/MS would enable one to establish quality levels within oils originating from the same plant species and similar unsaturation level regarding composition in potentially bioactive compounds and oxidative stability.

Study of the In Vitro Digestion of Olive Oil Enriched or Not with Antioxidant Phenolic Compounds. Relationships between Bioaccessibility of Main Components of Different Oils and Their Composition.

The changes provoked by in vitro digestion in the lipids of olive oil enriched or not with different phenolic compounds were studied by proton nuclear magnetic resonance (1H NMR) and solid phase microextraction followed by gas chromatography/mass spectrometry (SPME-GC/MS). These changes were compared with those provoked in the lipids of corn oil and of virgin flaxseed oil submitted to the same digestive conditions. Lipolysis and oxidation were the two reactions under consideration. The bioaccessibility of main and minor components of olive oil, of phenolic compounds added, and of compounds formed as consequence of the oxidation, if any, were matters of attention. Enrichment of olive oil with antioxidant phenolic compounds does not affect the extent of lipolysis, but reduces the oxidation degree to minimum values or avoids it almost entirely. The in vitro bioaccessibility of nutritional and bioactive compounds was greater in the olive oil digestate than in those of other oils, whereas that of compounds formed in oxidation was minimal, if any. Very close quantitative relationships were found between the composition of the oils in main components and their in vitro bioaccessibility. These relationships, some of which have predictive value, can help to design lipid diets for different nutritional purposes.

Oxylipins Associated to Current Diseases Detected for the First Time in the Oxidation of Corn Oil as a Model System of Oils Rich in Omega-6 Polyunsaturated Groups. A Global, Broad and in-Depth Study by 1H NMR Spectroscopy.

For the first time, an important number of oxylipins have been identified and quantified in corn oil submitted to mild oxidative conditions at each time of their oxidation process. This oil can be considered as a model system of edible oils rich in polyunsaturated omega-6 groups. The study was carried out using 1H nuclear magnetic resonance spectroscopy (1H NMR), which does not require chemical modification of the sample. These newly detected oxylipins include dihydroperoxy-non-conjugated-dienes, hydroperoxy-epoxy-, hydroxy-epoxy- and keto-epoxy-monoenes as well as E-epoxy-monoenes, some of which have been associated with several diseases. Furthermore, the formation of other functional groups such as poly-formates, poly-hydroxy and poly-ether groups has also been proven. These are responsible for the polymerization and increased viscosity of the oil. Simultaneously, monitoring of the formation of well-known oxylipins, such as hydroperoxy-, hydroxy-, and keto-dienes, and of different kinds of oxygenated-alpha,beta-unsaturated aldehydes such as 4-hydroperoxy-, 4-hydroxy-, 4-oxo-2E-nonenal and 4,5-epoxy-2E-decenal, which are also related to different degenerative diseases, has been carried out. The provided data regarding the compounds identification and their sequence and kinetics of formation constitute valuable information for future studies in which lipid oxidation is involved, both in food and in other scientific fields.

A Global Study by 1H NMR Spectroscopy and SPME-GC/MS of the in Vitro Digestion of Virgin Flaxseed Oil Enriched or not with Mono-, Di- or Tri-Phenolic Derivatives. Antioxidant Efficiency of These Compounds.

The effect of enriching virgin flaxseed oil with dodecyl gallate, hydroxytyrosol acetate or gamma-tocopherol on its in vitro digestion is studied by means of proton nuclear magnetic resonance and solid phase microextraction followed by gas chromatography/mass spectrometry. The extent and pattern of the lipolysis reached in each sample is analyzed, as is the bioaccessibility of the main oil components. None of the phenolic compounds provokes inhibition of the lipase activity and all of them reduce the lipid oxidation degree caused by the in vitro digestion and the bioaccessibility of oxidation compounds. The antioxidant efficiency of the three tested phenols is in line with the number of phenolic groups in its molecule, and is dose-dependent. The concentration of some minor oil components such as terpenes, sesquiterpenes, cycloartenol and 24-methylenecycloartenol is not modified by in vitro digestion. Contrarily, gamma-tocopherol shows very low in vitro bioaccessibility, probably due to its antioxidant behavior, although this increases with enrichment of the phenolic compounds. Oxidation is produced during in vitro digestion even in the presence of a high concentration of gamma-tocopherol, which remains bioaccessible after digestion in the enriched samples of this compound.

Oxidative stability of extra-virgin olive oil enriched or not with lycopene. Importance of the initial quality of the oil for its performance during in vitro gastrointestinal digestion.

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.

Effect of the Enrichment of Corn Oil with alpha- or gamma-Tocopherol on Its in Vitro Digestion Studied by 1H NMR and SPME-GC/MS; Formation of Hydroperoxy-, Hydroxy-, Keto-Dienes and Keto-E-epoxy-E-Monoenes in the more alpha-Tocopherol Enriched Samples.

The aim of this study is the analysis of the in vitro digestion of corn oil, and of the effect of its enrichment with three levels of gamma- and alpha-tocopherol, by using, for the first time, 1H nuclear magnetic resonance (1H NMR) and a solid phase microextraction followed by gas chromatography/mass spectrometry (SPME-GC/MS). The attention is focused on the hydrolysis degree, the degradation of oil's main components, the occurrence of oxidation reactions and main compounds formed, as well as on the bioaccessibility of oil's main components, of compounds formed in the oxidation, and, of gamma- and alpha-tocopherol. The lipolysis levels reached are high and show a similar pattern in all cases. The oxidation of corn oil components during in vitro digestion is proven, as is the action of gamma-tocopherol as an antioxidant and alpha-tocopherol as a prooxidant. In the more alpha-tocopherol enriched samples, hydroperoxy-, hydroxy-, and keto-dienes, as well as keto-epoxy-monoenes and aldehydes, are generated. The bioaccessibility of the oil's main components is high. The compounds formed in the oxidation process during in vitro digestion can also be considered bioaccessible. The bioaccessibility of alpha-tocopherol is smaller than that of gamma-tocopherol. The concentration of this latter compound remains unchanged during the in vitro digestion of the more alpha-tocopherol enriched oil samples.

Changes provoked by nixtamalization and tortilla making in the lipids of two corn varieties. A study by 1H NMR.

The aim of this study is to analyze in depth, by means of proton nuclear magnetic resonance, 1H NMR, the changes caused by nixtamalization and tortilla making in the lipid composition of two corn varieties. This technique permits the characterization of not only main but also minor lipid components of both corn and tortilla. Ferulates have been found for the first time among the minor components of these lipids. It has been proved that this processing affects the lipids of both corn varieties in a similar way. The total loss of fatty acids occurs as does partial loss of minor components. Furthermore, a slight oxidation is provoked during this processing as well as a small reduction in the unsaturation degree of the lipids. In spite of this a similar distribution of the different kinds of acyl groups has been found in corn and tortilla within each variety.

Food lipid oxidation under gastrointestinal digestion conditions: A review.

Unravelling the relationship between food and health requires a more in-depth knowledge of the various changes occurring in the gastrointestinal tract during digestion and which may ultimately affect the nutritional quality and safety of ingested food lipids before absorption into the bloodstream. In this context, this review deals with the oxidation process of food lipids under digestive conditions and the studies carried out on this topic using different digestion models: in vitro, in vivo or ex vivo, static or dynamic, and including one, two and/or three digestive phases (oral, gastric and duodenal). These studies have contributed to clarifying the occurrence and extent of lipid degradation under such a particular environment, many of them also highlighting the factors affecting the advance or delay of the oxidation of dietary lipids during digestion, like: food lipid content, unsaturation degree and initial oxidative status; the presence in the food bolus of compounds showing antioxidant activity (polyphenols, tocopherols…) either added or naturally present; the presence in the food bolus of proteins (including iron or not); food technological or culinary processings (salting, smoking, cooking…), among others. Likewise, the methodologies employed to study lipid oxidation under digestive conditions are also summarized and future research perspectives are discussed.

Effect of adding alpha-tocopherol on the oxidation advance during in vitro gastrointestinal digestion of sunflower and flaxseed oils.

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.

A Dual Perspective of the Action of Lysine on Soybean Oil Oxidation Process Obtained by Combining 1H NMR and LC-MS: Antioxidant Effect and Generation of Lysine-Aldehyde Adducts.

Little is still known about both the effect of amino acids on the oxidation course of edible oils and the modifications that the former may undergo during this process. Bearing this in mind, the objective of this work was to study the evolution of a system consisting of soybean oil with 2% of l-lysine under heating at 70 °C and stirring conditions, analyzing how the co-oxidation of the oil and of the amino acid affects their respective evolutions, and trying to obtain information about the action mechanism of lysine on soybean oil oxidation. The study of the oil progress by 1H Nuclear Magnetic Resonance (1H NMR) showed that the presence of lysine noticeably delays oil degradation and oxidation products generation in comparison with a reference oil without lysine. Regarding lysine evolution, the analysis by 1H NMR and Liquid Chromatography-Mass Spectrometry of a series of aqueous extracts obtained from the oil containing lysine over time revealed the formation of lysine adducts, most of them at the position, with n-alkanals, malondialdehyde, (E)-2-alkenals, and toxic oxygenated α ß-unsaturated aldehydes. However, this latter finding does not seem enough to explain the antioxidant action of lysine.

Influence of minor components on lipid bioaccessibility and oxidation during in vitro digestion of soybean oil.

BACKGROUND: Minor components of edible oils could influence their evolution during in vitro digestion. This might affect the bioaccessibility of lipid nutrients and the safety of the ingested food. Bearing this in mind, the evolution of virgin and refined soybean oils, which are very similar in acyl group composition, has been studied throughout in vitro digestion using 1 H nuclear magnetic resonance (NMR) and solid-phase microextraction-gas chromatography /mass spectrometry, focusing on lipolysis and oxidation reactions. The fate of γ-tocopherol, the main antioxidant present in soybean oil, has also been analyzed with 1 H NMR. RESULTS: There were no noticeable differences in lipolysis between the two oils that were studied. The extent of oxidation during digestion, which was very low in both cases, was slightly higher in the virgin type, which showed lower tocopherols and squalene concentrations than the refined one, together with a considerable abundance of free fatty acids. This can be deduced both from the appearance after digestion of conjugated hydroperoxy- and hydroxy-dienes only in the virgin oil, and from its higher levels of volatile aldehydes and 2-pentyl-furan. Under in vitro digestion conditions, the formation of epoxides seemed to be favored over other oxidation products. Finally, although some soybean oil essential nutrients like polyunsaturated fatty acids exhibited no significant degradation after digestion, γ-tocopherol concentration diminished during this process, especially in the virgin oil. CONCLUSION: Although the minor component composition of the soybean oils did not affect lipolysis during in vitro digestion, it influenced the extent of their oxidation and γ-tocopherol bioaccessibility. © 2019 Society of Chemical Industry.

Monitoring of minor compounds in corn oil oxidation by direct immersion-solid phase microextraction-gas chromatography/mass spectrometry. New oil oxidation markers.

The aim of this study is to shed light on the evolution of the minor compounds in the corn oil oxidation process, through the information provided by direct immersion-microextraction in solid phase followed by gas chromatography/mass spectrometry (DI-SPME-GC/MS). This methodology enables one, in a single run, to establish the identity and abundance both of original oil minor components, some with antioxidant capacity, and of other compounds coming from both main and minor oil components oxidation. For the first time, some of the compounds formed from oil minor components degradation are proposed as new markers of oil incipient oxidation. Although the study refers to corn oil, the methodology can be applied to any other edible oil and constitutes a new approach to characterizing the oxidation state of edible oils.

A thorough insight into the complex effect of gamma-tocopherol on the oxidation process of soybean oil by means of 1H Nuclear Magnetic Resonance. Comparison with alpha-tocopherol.

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.

Effects of different cooking methods on the lipids and volatile components of farmed and wild European sea bass (Dicentrarchus labrax).

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.

Prooxidant effect of α-tocopherol on soybean oil. Global monitoring of its oxidation process under accelerated storage conditions by 1H nuclear magnetic resonance.

The effect of adding α-tocopherol in proportions ranging from 0.002 to 5% in weight on the oxidative stability of soybean oil was studied. For the first time, the oxidation process under accelerated storage conditions including evolution of the molar percentages of the several types of oil acyl groups, and formation and evolution of various kinds of oxidation products comprising hydroperoxides, hydroxy-dienes and other alcohols, epoxides, aldehydes and keto-dienes, was followed by 1H nuclear magnetic resonance. It is proved that, except in the lowest proportion, α-tocopherol not only exerts a prooxidant effect on soybean oil but also modifies its oxidation pathway, affecting the oxidation products generation rate, their nature, relative proportions and concentrations. It is noticeable that the highest α-tocopherol concentrations induce the generation of some toxic compounds at earlier stages of the thermoxidation process and sometimes in higher concentration, such as certain oxygenated α,ß-unsaturated aldehydes and monoepoxides derived from linoleic groups.