The physicochemical properties of five vegetable oils exposed at high temperature for a short-time-interval

The objective of this study was to evaluate the physicochemical characteristics of five vegetable oils exposed to high temperatures for a short time interval. Sunflower, rapeseed, maize, palm, and coconut oils, which are largely used for food thermal preparation, were heated for 30 min at 180 °C and analyzed before and after heating in terms of viscosity, Acid value, Peroxide value, density, and fatty acids profile. The rheological measurements showed raised values for the viscosity, shear rates, and densities after the heat exposure for all investigated samples. Moreover, thermo-oxidative modifications considering the Acid value and Peroxide content showed increased values above the recommended limits (0.6 mg KOH/g oil and 10 mEqO2/kg oil) for the investigated oils, excepting the rapeseed oil which was within the limits of the Acid values (0.26 mg KOH/g rapeseed oil). The percentage of the unsaturated fatty acids was influenced by the heat exposure in all samples. The formation of trans fatty acids was visible in all samples (by FTIR at 962 cm-1) excepting the coconut oil. In conclusion, short-time exposure at high temperatures can impact negatively the physicochemical properties of sunflower, rapeseed, maize, palm, and coconut oils.