Impact of high temperature processing and heating duration on fatty acid composition and trans fatty acid formation in seven cold‐pressed and five refined vegetable oils

Edible oils are essential dietary constituents that contribute as energy source, fatty acids and medium for fat‐soluble vitamins. High temperature during frying induces changes in the fatty acid profile of edible oils. The primary aim of this study is to investigate the influence of high temperature (230 ± 5°C) and duration of heating (0, 1, 2 and 4 h) on the stability and compositional changes of fatty acids, with emphasis on trans fatty acid formation in both cold pressed oils and refined edible oils. Thermal treatment caused progressive increase in saturated fatty acid content in both cold‐pressed and refined oils. Mono‐unsaturated fatty acid levels generally increased with duration, with oil‐specific variation, wherein, cold‐pressed palm oil (from 41.31% to 40.64%), refined palm oil (44.99% to 42.60%) and cold‐pressed coconut oil (from 7.71% to 0.62%) demonstrated a substantial decline. Polyunsaturated fatty acids (PUFA) were highly heat‐labile, wherein mustard and soybean oils showed the most significant depletion, from 30.64% to 17.31% and 61.20% to 40.65%, respectively. Cold‐pressed and refined sunflower oil, rice bran oil showed relatively better retention of PUFA with high temperature treatment. In raw non‐heated state, the trans fatty acids content of refined oils (0.16% to 1.22%) was relatively higher than that of cold‐pressed oils. In refined soybean and cold‐pressed sesame oils, trans ‐fatty acids increased with heating up to a maximum of 5.88% and 4.05%, respectively. TFA levels in cold‐pressed and refined sunflower oil, palm oil and cold‐pressed mustard oil remained stable during heating. Fatty acid composition changed significantly after a 2 h heating in refined oils, whereas the changes were very significant after 4 h in cold‐pressed oils.