MECHANISMS OF SUNFLOWER OIL TRANSFORMING INTO FORCED THERMAL OXIDATION PROCESSES

Abstract

This article investigates the processes that take place during the forced thermooxidation of sunflower oil. The results obtained in the study showed a major impact of thermo-oxidation. (90 ± 2 °C. supplied air with a speed of 8 ÷ 10 L·h-1 for 50 hours), on the physico-chemical indicators of the studied oil. The acidity index of fresh sunflower oil increased 13.7 times, with a value of 2.46 mg KOH·g-1 of fat for the thermo-oxidized oil compared to the initial value of 0.180 mg KOH·g-1 of fat. The thermo-oxidation of sunflower oil caused a significant decrease of the saponification index, which indicates a significant degree of polymerization and leads to viscosity increase of the studied sunflower oil. In order to highlight the impact of heat treatments, the analysis was performed by IR spectroscopy and the possible mechanisms of unsaturated fatty acids forced oxidation under the influence of thermal factor were analyzed. It was established that the applied treatment favoured both the formation of carbonyl secondary compounds and the simultaneous formation of hydroperoxides and triglycerides containing hydroxylated groups. The accumulation of hydroperoxides and triacylglycerides that have hydroxyl functions have facilitated the course of polymerization reactions, which are to increase the viscosity of thermo-oxidized studied sunflower oil. The formation during thermo-oxidation of the trans-isomers of poly-unsaturated acids led to the appearance of the =CH group deformation vibration band at 966 cm-1 in the spectrum of thermo-oxidized oil, simultaneous to a slight reduction in the intensity of the =CH group deformation vibration band at 1098 cm-1 at the respective cis-isomer of polyunsaturated acids.

Keywords

• sunflower oil
• thermal oxidation
• ir spectroscopy
• peroxide index
• acidity index
• epoxides
• trans- and cis- fatty acid isomers