Tocopherols Degradation and Polymerized Triacylglycerols Formation during Vegetable Oil Heating
J. Fišnar, Prague/CZ, M. Sabolová, Prague/CZ, Z. Réblová, Prague/CZ, University of Chemistry and Technology Prague, Czech Republic

In this work, tocopherols depletion as a function of the formation of polymerized triacylglycerols was studied during oil heating under frying conditions. Oil samples (olive, palm, peanut, sunflower, soybean, rapeseed, grapeseed, corn and rice bran oil) were heated on a heating plate and oil temperature was 180°C during heating.
The fastest depletion of tocopherols was observed in less unsaturated oils (olive, palm and peanut) and in these oils tocopherols were not presented at the moment when the content of polymerized triacylglycerols was in a range of 2 – 6%. On the contrary, tocopherols in more unsaturated oils (rice bran, sunflower, rapeseed, corn, grapeseed and soybean oil) were presented in a range of 10 – 40% of an initial content at the moment when the content of polymerized triacylyglcerols increased in 12% (i.e. at the end of lifespan of tested oils). The tocopherols depletion as a function of polymerized triacylglycerols was significantly correlated (p < 0.05) with monounsaturated
(R = 0.7600) and polyunsaturated fatty acids (R = -0.8153) and with total antioxidant capacity (R = -0.6907) of unheated (i.e. fresh) vegetable oils. The results of this work showed that the limit for replacement of frying oil (i.e. 12% of polymerized triacylglycerols) should be decreased for some oils (particularly for less unsaturated oils) in relation to the tocopherols content in these oils. It was also observed that the tocopherols depletion as a function of polymerized triacylglycerols is predominantly dependent on two factors, and that is the composition of fatty acids (resp. monounsaturated and polyunsaturated fatty acids) and the amount of antioxidants presented in frying oil.

Financial support from the specific university research (MSMT No 20/2015).