Enrichment of Sunflower Oil with gamma-Tocopherol. Study by H-1 NMR of Its Effect Under Accelerated Storage Conditions

The effect of the enrichment of sunflower oil with gamma-tocopherol on the evolution of its oxidation is the subject of this study. Sunflower oil and samples of this oil enriched with different gamma-tocopherol concentrations are submitted to accelerated storage conditions and their evolution, until total polymerization is monitored by H-1 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 gamma-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 gamma-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 gamma-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 gamma-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 H-1 NMR spectrum is able to provide information about all the above-mentioned aspects. Sunflower oil enriched with different levels of gamma-tocopherol. Concentrations of primary and secondary oxidation compounds after 4 and 9 days, respectively, under accelerated storage conditions. This work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO AGL 2015-65450-R), the Basque Government (EJ-GV, IT-916-16), and the Agriculture Department of the Basque Government (PA19/02).