OXIDATIVE CHANGES IN REPEATEDLY HEATED VEGETABLE OILS

Thermal oxidation of vegetable oils due to repeat heating is known to exert adverse effects on human health. The oxidative stability of vegetable oils is one of the important factors in determining suitable types of cooking oils and cooking methods. Therefore, the oxidative changes in several types of commonly used vegetable oils, namely: palm olein (POo), soyabean oil (SBO) and corn oil (CNO) were studied. The oil samples were heated repeatedly at 150 degrees C for five rounds. The oxidation level of the oils was assessed by determining their respective changes in fatty acid composition, peroxide value (PV), free fatty acid (FFA) value and p-anisidine value (AV). SBO and CNO contained significantly higher amount of unsaturated fatty acids (84.1% and 86.2%, respectively) compared to POo (56.8%). Consequently, PV, FFA and AV value of the oil samples increased according to their unsaturation level: POo < SBO < CNO. Therefore, POo was shown to have the greatest oxidative stability against thermal oxidation, followed by CNO and SBO.