The Effect of Deep Heating on Rheological Behavior of Edible Vegetable Oils

In this study, sunflower, soybean and canola oils were heated by oven in 190˚C, while the oxidation period was passed before in oven with 110˚C.The rheological analyzes were done every 24 hr at 10˚C while measurements were done by viscometer. Temperature was controlled using water bath with precision of 0.1˚C. Measurements were done in different speed ramps (resulting in different shear rates), during heating. The viscosities of samples were investigated as a function of the shear rate and also shear stress as a function of shear rate at 10˚C. The related Herschel?Bulkley Model equations were identified at the specific temperatures. Peroxide index has been determined during investigation. As a result, peroxide reduction during polimerization of the samples,which happen with heating at 190, showed viscosity increase.Deep heating of oils happens in frying process, in which fats and oils are repeatedly used at very high temperatures in the presence of air and moisture. This causes a conversion of fats and oils to dimeric and polymeric, or cyclic and volatile compounds affecting the viscosity of them as well as foods fried in them. Additionally, these undesirable constituents produced may also lead in health hazards. Surprisingly, very few reports have been reported on the rheological behaviors of edible vegetable oils. Besides, they are mostly on temperatures below 100˚C. The present work, therefore, has made an attempt to report the effects of deep temperature and polymerization happening after, on viscosity of sunflower, soybean and canola oils.