Effects of Soya Lecithin with Different Degrees of Hydrogenation on the Coloring and Decomposition of Tocopherol in Heated Oils

Abstract

Different types of vegetable oil (soybean, cotton seed, olive, rapeseed and hardened rapeseed) with or without soya lecithin with different degrees of hydrogenation, iron (ferric chloride) and lecithin-iron mixture, were heated in Pyrex glass tubes (2.7×20cm) at 180°C for 10 or 15 hr using an oil bath. After heating of each oil, the residual tocopherol (Toc), coloring and oxidative stability were determined by HPLC, Lovibond colorimeter and the oven test at 60°C, respectively.
Lecithin suppressed the decomposition of Toc in each oil during heating. Hydrogenated lecithin (over 60%) showed a greater protective effect against the decomposition of Toc in olive oil than unhydrogenated lecithin. Iron accelerated not only the thermal oxidation of each oil but also the decomposition of Toc in soybean oil. However, lecithin-iron mixture did not show any accelerative reaction on oxidation or decomposition. A browning reaction of the oil due to heating was most pronounced in the mixture containing iron-hydrogenated (100%) lecithin than in those containing only iron, only hydrogenated (100%) lecithin or iron-unhydrogenated lecithin.