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The evolution of the composition of three sunflower oils submitted to frying temperatures over a prolonged period of time was carried out by means of ¹H nuclear magnetic resonance. Using the same technique, the evolutionof the composition of three sunflower oils derived frying media, formed through out 14 deep-frying experiments of three different foods, was also studied. The foods involved in the deep-frying processes differ in bothamount andnature of their lipids. The occurrence ofmigrationof food lipids, thermo-oxidation, and hydrolytic processes in the sunflower oil frying media can be studied simultaneously by this technique. Changes in the evolution of the molar percentage of the different kinds of acyl groups, as well as of the concentration and nature of the aldehydes and alcohols formed were addressed. It is noteworthy that the main aldehydes detected, inboth sunflower oils and sunflower oil fryingmedia,were the reactive (E,E)-2,4- alkadienals, likewise the genotoxic and cytotoxic 4-hydroxy-(E)-2-alkenals and 4,5-epoxy-2-alkenals were also present. In addition, the extent of hydrolytic processes, and, both, the evolution of iodine value and percentage in weight of polar compounds, were also studied. Practical applications: The used technique provides, in only one run and without chemical modification of the sample, a great deal of information related to the quality and safety of the sunflower frying media used in repeated deep frying episodes. The fact that during frying the sunflower oil generates toxic aldehydes with concentrations in line with the heating time and number of fryings should be taken into account at both industrial and culinary levels. It has been shown that the migration of food lipids during frying influences importantly on parameters such as iodine value and percentage in weight of polar compounds, which can mask the degradation level reached by the oil. This study provides useful information about the behavior in deep frying of sunflower, soybean, and extra virgin olive oils, which can be taken into account for the selection of the most suitable oil for frying each kind of food. [ABSTRACT FROM AUTHOR]

This review summarizes present-day knowledge provided by proton nuclear magnetic resonance (1H NMR) concerning food lipid thermo-oxidative degradation. The food lipids considered include edible oils and fats of animal and vegetable origin. The thermo-oxidation processes of food lipids of very different composition, occurring at low, intermediate, or high temperatures, with different food lipid surfaces exposed to oxygen, are reviewed. Mention is made of the influence of both food lipid nature and degradative conditions on the thermo-oxidation process. Interest is focused not only on the evolution of the compounds that degrade, but also on the intermediate or primary oxidation compounds formed, as well as on the secondary ones, from both qualitative and quantitative points of view. Very valuable qualitative and quantitative information is provided by 1H NMR, which can be useful for metabolomic and lipidomic studies. The chemical shift assignments of spectral signals of protons of primary (hydroperoxides and hydroxides associated with conjugated dienes) and secondary, or further (aldehydes, epoxides, among which 9,10-epoxy-12-octadecenoate [leukotoxin] can be cited, alcohols, ketones) oxidation compounds is summarized. It is worth noting the ability of 1H NMR to detect toxic oxygenated α, β-unsaturated aldehydes, like 4-hydroperoxy-, 4,5-epoxy-, and 4-hydroxy-2-alkenals, which can be generated in the degradation of food lipids having omega-3 and omega-6 polyunsaturated groups in both biological systems and foodstuffs. They are considered as genotoxic and cytotoxic, and are potential causative agents of cancer, atherosclerosis, and Parkinson's and Alzheimer's diseases. [ABSTRACT FROM AUTHOR]

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 1H 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 1H NMR spectral data. [ABSTRACT FROM AUTHOR]

Highlights: [•] Extra virgin olive oil is used in three series of deep-frying experiments. [•] Three foods of very different content and nature of lipids are submitted to frying. [•] The evolution of the frying medium composition is studied by 1H NMR spectroscopy. [•] Acyl groups, aldehydes, epoxides, alcohols and diglycerides are determined. [•] The influence of the food nature on the frying medium composition is addressed. [ABSTRACT FROM AUTHOR]

The effect of the enrichment of sunflower oil with γ‐tocopherol on the evolution of its oxidation is the subject of this study. Sunflower oil and samples of this oil enriched with different γ‐tocopherol concentrations are submitted to accelerated storage conditions and their evolution, until total polymerization is monitored by 1H NMR spectroscopy. The concentrations of linoleic acyl groups, of primary and of a great number of secondary oxidation compounds are determined throughout the process. These concentrations, and the times at which the main changes in them occur are analyzed to elucidate if they are valid markers of the global effect of γ‐tocopherol enrichment. It is proved for the first time that certain comparisons between concentrations of some of the compounds formed in oxidation can lead to erroneous conclusions about the effect of this enrichment. It is shown that, during a first short period of time under accelerated storage conditions, the higher the concentration of γ‐tocopherol the faster the degradation of linoleic acyl groups and the higher the concentration of hydroperoxides; after this first period this relationship is more complex. Generally, the higher the γ‐tocopherol concentration the slower the degradation of the oil, except in the first period. Practical Applications: This study provides very valuable information about the effect caused by enrichment with γ‐tocopherol on sunflower oil oxidative stability and oxidation across a very broad range of concentrations. In addition, the amount of information obtained can be of great importance from several points of view because the oxidation process has been monitored globally. This may be of interest not only to researchers involved in the analysis of oxidation mechanisms but also to those in the field of technology and edible oil legislation, and even to those worried about edible oil safety and its effect on nutrition and health. Another important feature of this study, from the practical point of view, is the methodology used because it does not involve the chemical modification of the sample and the same 1H NMR spectrum is able to provide information about all the above‐mentioned aspects. Sunflower oil enriched with different levels of γ‐tocopherol. Concentrations of primary and secondary oxidation compounds after 4 and 9 days, respectively, under accelerated storage conditions. [ABSTRACT FROM AUTHOR]