Evaluating composition of fatty acids in commonly used edible oils and fats on repeated frying for its nutritional quality implications

Continuous frying of many food items in the same vegetable oils or partially hydrogenated vegetable oils (fats) by homemakers and commercial vendors has become a routine practice in many developing countries of Asia. The present study evaluated the composition of fatty acids (FAs) in commonly used edible oils (canola oil, sunflower oil, corn oil, and linseed oil) and fats (Utility ghee, Kisan ghee, Shama ghee, and Dalda ghee). Further, it quantified changes in the composition of their FAs, especially regarding transformation of cis-FAs to trans FAs, during repeated frying for 0, 1, 3, 6, 12, and 24 h at 180°C. A large variability (p < 0.001) was observed in composition of FAs among unheated fats and oils. Compared to oils, the fats had higher (p < 0.05) contents of saturated FAs (SFAs) and trans FAs, and lower (p < 0.05) contents of cis-unsaturated FAs (cis-UFAs). Repeated frying for 24 h consistently decreased (p < 0.05) the contents of cis-UFAs and increased (p < 0.05) the contents of SFAs and trans FAs in all fats and oils. The SFA–cis-UFA ratio of all fats and oils increased (p < 0.05) during 24 h of heating, reflecting deterioration in their nutritional quality. In conclusion, repeated frying of fats and oils induces cis–trans conversion and increases SFA–cis-UFA ratio.