Abstract
The preventive effects of catechins (catechin, epigallocatechin, epigallocatechin gallate and catechin mixture) on the thermal decomposition of tocopherol (Toc) in some edible oils were investigated. Samples of hardened rapeseed, olive, soybean and corn oil with or without catechins were each heatedin a Pyrex glass tube (2.7×20cm) at 180°C for 10 or 28 h using an oil bath. After heating of each oil, the residual Toc and oxidative stability were determined by HPLC and the oven test at 60°C, respectively. Catechins suppressed the thermal decomposition of Toc in each oil during heating. The order of suppression of the thermal decomposition of Toc in hardened rapeseed oil was as follows: catechin>epigallocatechin>epigallocatechin gallate>catechin mixture. Thermal decomposition of Toc in hardened rapeseed oil decreased with increasing concentration of catechin. Citric acid in combination with catechin had no synergistic effect on the thermal decomposition of Toc. Catechins improved the oxidative stability of each oil after heating. Upon comparison of catechin with gallic acid, the latter had a more pronounced preventive effect on the thermal decomposition of Toc and produced a higher oxidative stability of heated oils containing it. Decomposition of Toc in oil was apparently promoted by oxidized fatty acids from the heated oil.
