Mechanism of Formation of Trans Fatty Acids under Heating Conditions in Triolein

Abstract

To elucidate the relationship between heat-induced cis/trans isomerization and reaction temperature and energy in unsaturated lipids, we investigated the molecular mechanism of the heat-induced cis/trans isomerization of 18:1 isomers. Triolein (18:1,9c) was heated at two range temperatures (130, 160, 190, 220 °C and 135, 140, 145, 150, 155 °C) and analyzed by the gas chromatography (GC) method. When the heating temperature increased to 150 °C, the amount of trans 18:1n-9 changed from 0.0897 mg/g oil (1 h) to 0.1700 mg/g oil (3 h). This study shows that the cis to trans isomerization may occur at 150 °C. The formation of fatty acid isomers followed a proton transfer route. All key geometries, transition states, intermediates, and bond dissociation energies (BDE) were optimized at the B3LYP/6-31G* level for the density functional theory (DFT). The zero-point energy corrections of the isomers were carried out using calculations at the B3LYP/6-311++G** level. The calculated energy difference between the cis and trans oleic acid was equal to 7.6 kJ/mol, and the energy barriers of the transition from cis 18:1n-9 to trans 18:1n-9 were 294.5 kJ/mol. The intrinsic reaction coordinates (IRCs) were obtained to be used as an expression of the reaction route and to analyze the transition states and intermediates. The study results suggest that the heating temperature should be kept under 150 °C, to avoid the risk of trans fatty acid (TFA) intake in daily food.

Effect of Frying Temperature and duration on the Formation of Trans Fatty Acids in Selected Fats and Oils

“…This indicates that the structural (positional) isomerization and geometrical isomerization in which the cis isomers of fatty acids in margarine is stable and not affected by applied heat treatment at 120°C. It was reported previously that cis isomerization to trans may occur at 150°C [14]. The results are in accordance with these results where it was found that the amount of elaidic acid in margarine heated at 150, 190 and 250°C varies with time in which there is a cubic nonlinear significant relationship between percentage of elaidic acid and time of heating.…”

Effect of Extruding Full-Fat Soy Flakes on Trans Fat Content

“…Although the change of every type of trans fatty acid was fluctuant, the range of this variation was not very great during extrusion with increasing temperature. Since the cis- to trans -isomerization may occur at 150°C [23], the formation of trans fatty acids was likely exacerbated by the combined effects of pressure and high temperature. A previous study reported that only 1% to 2% of the unsaturated fatty acids were converted to the trans -form during the extrusion of cornmeal [16, 24].…”

Mechanisms of isomerization and oxidation in heated trilinolein by DFT method

“…This paper demonstrates that the temperature of isomerization of linoleic acid is 140 C, and the temperature for oleic acid is 150 C, as was shown by our laboratory previously. 22 This indicates that linoleic acid is more prone to isomerization than oleic acid under heat treatment.…”

“…It has been applied to study the mechanism of trans fatty acids under heating conditions in triolein by our research team. 22 The purpose of this paper is to study the isomerization temperature of linoleic acid and to determine the type and content of trans linoleic acid at various temperatures. The cis/ trans isomers were determined by HPLC and the decomposition products were determined by GC.…”