Analysis of the oxidation products of cis- and trans-octadecenoate methyl esters by capillary gas chromatography-ion-trap mass spectrometry. I. Epoxide and dimeric compounds

The oxidative behavior of methyl oleate (MeOl) and methyl elaidate (MeEl) was compared by hyphenated chromatographic techniques. MeOl and MeEl were separately oxidized (200 degrees C/30 min) and subjected to solid-phase extraction, in order to isolate the low polarity compounds. The two isomeric 9,10-epoxystearic methyl esters formed in both MeOl and MeEl at different threolerythro ratios (2.3 and 6.2%, respectively). The dimeric products produced in the thermoxidized MeOl and MeEl (1.4 and 1.6%, respectively), showed similar gas chromatographic characteristics and mass spectra, suggesting similar molecular structures and formation mechanisms. A positional and probably configurational mixture of symmetric and asymmetric dehydrodimers was detected, whereas the occurrence of MeEl or MeOl dimeric ethers is to be confirmed.

Chemical and biological properties related to toxicity of heated fats

Heating of fats brings about measurable changes in their chemical and physical characteristics. Heat is applied in processing for food manufacture, such as during hydrogenation of oils with a catalyst, and in frying for meal preparation. Partially hydrogenated products generally contain substantial quantities of geometric and positional isomers of the original unsaturated fatty acids. During deep-fat frying, when the fat is used repeatedly, oxidative and thermal effects result in the formation of many volatile and nonvolatile products, some of which are potentially toxic, depending on the level of intake. Because of concern about the types of changes that take place in fats during oxidative and thermal deterioration and the effects the derivatives could have on the consumer, many chemical and biological studies have been carried out. Experimental findings indicate that any potential danger to the consumer is relative to the severity of the overall treatment of the fat. In some studies we evaluated biological effects on rats of trans fatty acid in the diet and of concentrates of fatty acid derivatives produced in thermally oxidized fats. trans-Octadecenoic acid changed the concentrations of the phospholipid classes in the liver lipids, and interfered with conversion of the essential n - 6 series of fatty acids to higher members. Compared to oleic acid, elaidic acid was preferentially incorporated into the phospholipids instead of the triacylglycerols and was also concentrated in the lipoprotein fractions. Administration of non-urea-adductable concentrates from thermally oxidized fats produced cellular damage in hearts, livers, and kidneys of the animals. Since even practical processing and frying conditions can produce some nutritionally undesirable products, a concerted effort should be made to minimize substantial accumulation of these in our dietary fats.