Determination of Fry-life of two formulated frying oils produced in pilot scale

Frying oils undergo quality changes due to long term heating at high temperature in the presence of oxygen and moisture.The aim of this study was determination of fry-life of two formulated frying oils produced in pilot scale. After determination of physical and chemical characteristics of primary oils, two formulations, i.e. formula 1 or F1(palmolein and sunflower oils 50:50)and formula2 or F2(palmolein, sunflower and cottonseed oils 50:25:25) were prepared by blending, then TBHQ(100ppm) and citric acid(100ppm) were added to them.For determination of fry-life potato slices(Agria variety) were fried at a rate of 200g/30 min(180 °C) in a 40-litter fryer, until one of the characteristics(peroxide value or PV, acid value or AV, smoke point, total polar compounds or TPC,Fritest and Rancimat) reached the discard point for frying oil. PV were variable due to decomposition in high temperature and reproducing during cooling of the oils. AV and TPC were increased during frying. The increasing of AV was higher in control, reversely two formulated frying oil,s TPC were more than control. A sample of partial hydrogenated frying oil produced by an Iranian factory was used as control. Oxidative stability of two formulated frying oils and control were determined by Rancimat in 110°C. Oxidative stability of frying oils were reduced during frying as well as smoke point, although this reduction was faster in control,and after 25hrs frying reached the discard point (178 °C). The results of Fritest were not similar to TPC in the last steps. Statistical analysis did not show a significant difference(P<0.05) in the fry-life of F1 and F2(TPC of F1 and F2 were 21 and 20.5 hours, respectively) but there was a significant difference between two formulated frying oils and control(P<0.05). The control was discarded after 26.5 hrs frying. Regarding the frylife, nutritional value(especially trans fatty acid content) and economical aspects(cost of hydrogenation), F1 was the best frying oil(F1>F2>control)and could be suggested as a substitute for hydrogenated frying oils.