Relationship between polymerised triacylglycerols formation and tocopherols degradation was studied during heating of four commercially accessible vegetable oils (rapeseed oil, classical sunflower oil, soybean oil and olive oil) on the heating plate with temperature 180°C. The content of polymerised triacylglycerols 6% (i.e. half of maximum acceptable content) was achieved after 5.3, 4.2, 4.1, and 2.6 hours of heating for olive oil, soybean oil, rapeseed oil and sunflower oil, respectively, while decrease in content of total tocopherols to 50% of the original content was achieved after 3.4, 1.6, 1.3, and 0.5 hours of heating for soybean oil, rapeseed oil, sunflower oil and olive oil, respectively. Because of the high degradation rate of tocopherols, decrease in content of total tocopherols to 50% of the original content was achieved at content of polymerised triacylglycerols 0.6%, 1.9%, 2.8% and 4.9% for olive oil, rapeseed oil, sunflower oil and soybean oil, respectively, i.e. markedly previous to the frying oil should be replaced.
GC-MS and HPLC-DAD analysis of fatty acid profile and functional phytochemicals in fifty cold-pressed plant oils in Thailand
