Abstract
The effects of fatty acids on the thermal decomposition of tocopherol (Toc) in soybean oil by oxidative products (oxidized fatty acids: fatty substances insoluble in petroleum ether) separated from soybean, corn, olive and coconut oils heated at 180°C for 40h were investigated. Oils containing added oxidized fatty acids and/or several fatty acids (stearic, oleic, linoleic and linolenic acids) were heated in a Pyrex glass tube (2.7×20cm) at 180°C for 0 to 40h uslng an oil bath. Residual Toc was determined by HPLC. Decomposition of Toc in soybean oil was apparently promoted by the addition of oxidized fatty acids during heating. The rate of acceleration of the thermal decomposition of Toc in soybean oil by oxidized fatty acids, which were separated from the heated oil, decreased in the following order: oxidized fatty acids from soybean oil, corn oil, olive oil and coconut oil. Decomposition of Toc in soybean oil was most pronounced following addition of a mixture of oxidized fatty acids and oleic acid than following addition of either oxidized fatty acids or oleic acid alone. Furthermore, the decomposition ratio of Toc increased according to the amount of oleic acid added. The effects of acceleration using stearic, linoleic and linolenic acids on the decomposition of Toc in soybean oil by oxidized fatty acids were similar to that of oleic acid.
