Synthesis and analysis of tocopheryl quinone and tocopherol esters with fatty acids in heated sunflower oil

Abstract

This work focuses on degradation of α‐tocopherol and formation of α‐tocopherol degradation products in sunflower oil heated at frying temperature. We determined the content and measured the kinetics of α‐tocopherol, α‐tocopheryl quinone, α‐tocopheryl fatty acid formation in heated sunflower oil without aeration (So) and in aerated oil (air flow 20 L/h) (SoAir). During 10 h of So oil heating, the α‐tocopherol was depleted and the content of α‐tocopheryl quinone in So grew from 3 to 84 mg/kg, as did the content of tocopherol free fatty acid esters from the initial 5 to 185 mg/kg. In SoAir oil, the rate constants of formation and decomposition of tocopherol degradation products were determined. Accelerated oxidation in SoAir caused depletion of the degradation products of tocopherol after 2 h of heating. The reason for this was significant oxidation and polymerization of fatty acids in SoAir oil. The unique features of this work are the syntheses and spectral analysis of tocopherol oxidation products and the development of a suitable method for quantitative analysis of α‐tocopheryl fatty acids. For the first time, we confirmed formation and degradation of tocopheryl fatty acids during oil heating at frying temperature.Practical applications: All the results presented here, consisting of organic syntheses, qualitative and quantitative analysis of α‐tocopheryl fatty acids as well as oxidation and degradation products of tocopherols and fatty acids, will aid future research focused on the degradation of tocopherols. So far the content of α‐tocopheryl fatty acids has not been determined by GC‐FID or HPLC‐UV. This is why there has been little interest in α‐tocopheryl fatty acids, although they are formed both in culinary treatment of food and in oil refining.Free fatty acids (FFAs), fatty acids (FAs), oxidation [o], products (i) and products (ii) are unspecified products of α‐tocopheryl FAs and α‐TQ degradation. Degradation products of α‐tocopherol were formed in heated sunflower oil and further heating of oil caused decomposition of α‐tocopherol degradation products.