Abstract
Thermal decomposition of added tocopherol (Toc) by fatty acids and their methyl esters differing in their numbers of carbon atoms and degree of unsaturation, and the preventive effect of gallic and thiodipropionic acids were investigated. Test samples were heated in a Pyrex glass tube (2.7×20cm) at 180°C, and residual Toc, anisidine and carbonyl values were determined. Thermal decomposition of Toc by methyl esters of saturated fatty acids occurred in the order of stearate>laurate>caprylate. The oxidation products (Toc dimer and trimer etc.) of Toc in methyl stearate increased with the heating time. In the case of unsaturated fatty acids and their methyl esters, Toc in oleic acid (or ester) was more extensively decomposed by oleic acid (or its ester) than by linoleic and linolenic acids (or their esters), but the anisidine and carbonyl values with oleic acid (or its ester) were markedly low. The degree of Toc loss after heating was also much greater with methyl stearate than with methyl esters of unsaturated fatty acid. In comparison with oleic acid, monoolein and triolein, Toc was greatly decreased by oleic acid. On the other hand, the amount of residual Toc was higher with monoolein. Gallic and thiodipropionic acids suppressed the thermal decomposition of Toc by methyl stearate and oleate.
