Study On Formation Mechanism Of Elaidic Acid Under High Temperature Conditions

Trans fatty acids exist in various types of processed foods, excessive intake may lead to diseases such as coronary heart disease (CHD). So it is imperative to study the detection and the of reaction mechanism of trans fatty acids. The molecular mechanisms of the thermally induced cis/trans isomerization of the oleic acids (C18:1) were investigated in a combined the related structures and energy calculation of C18:1isomers and the detection of the changes of fatty acid in practical samples.Triolein (18:1-9c) was heated at two range temperatures (130,160,190,220℃and135,140,145,150,155℃) were analyzed by gas chromatography (GC) method. When the heating temperature increased to150℃, the amount of trans18:1n-9was from0.0897±0.0102mg/g oil (1h) to0.1700±0.0173mg/g oil (3h). This study show that the cis to trans isomerization may occur at150℃. The isomerization schemes via the proton transfer paths were developed. All key geometries, transition states, intermediates and bond dissociation energies (BDE) were optimized at B3LYP/6-31G*level for the density functional theory (DFT). The calculations of zero-point energy corrections of the isomers were carried out at B3LYP/6-311++G**level. The calculated energy difference between the cis and trans oleic acid was equal to7.6kJ/mol and the energy barriers of the transition from cis18:1n-9to trans18:1n-9was equal to294.5kJ/mol. The intrinsic reaction coordinate (IRC) were obtained to be used as a expression of the minimum energy path and affirmed the relationship among reactants, transition states, intermediates and products. The DFT calculations indicated that the developed isomerization mechanism can explaine the experiment data well. The study results suggested the oil frying temperature should be kept under150℃to avoid the risk of TFA (trans fatty acid) intake in the diet.This work also studied the reaction of forming the aldehyde carbonyl compounds by heating triolein under high temperature conditions. Through detecting the changes of volatile aldehyde carbonyl compounds and the non-volatile aldehyde carbonyl compound by HPLC and ESI-MS, and making use of the DFT method of quantum chemistry to calculate the related C-H bond dissociation enthalpy (BDE) of oleic acid, the triolein autoxidation mechanism of forming aldehyde carbonyl compound was deduced, and the rationality of mechanism was verified from the experiment results.