Effect of antioxidant on thermal stability of vegetable oils by using ultrasonic studies.
The effect of repeated heating process on edible oils namely, sesame oil (SO), sunflower oil (SFO) and palm oil (PO) with and without antioxidant, tertiary butyl hydroquinone (TBHQ) have been evaluated using ultrasonic velocity. The changes in physico-chemical properties of edible oils has been studied during repeated heating at 180 ± 5oC for 4 hrs/day and for 4 days. The effect of antioxidant, in edible oils on the thermal oxidation behavior has been studied for repeated heating process. The thermal degradation of oils have been evaluated for physical properties such as ultrasonic velocity, viscosity, density and secondary parameters like adiabatic compressibility, intermolecular free length, relaxation time and acoustic impedance. Chemical changes were studied by free fatty acid, total polar compounds and the changes in the unsaturation level of fatty acids were confirmed by gas chromatographic (GC) analysis. The repeated heating process had effect on the physical properties of oil, which is due to the decrease in unsaturated fatty acid composition and other chemical changes. It is observed that all three control oils properties significantly deteriorate on repeated heating. The oils with TBHQ don’t cause significant changes on the physico-chemical properties and ultrasonic properties. This result clearly indicates that oils with 200 ppm TBHQ are found to be more thermally stable.