Oxidation and structural decomposition of fats and oils at elevated temperatures

In the present work a fast and reliable laboratory protocol allowing a holistic statement about thermo‐oxidative structural changes of fats and oils at ambient temperatures, under accelerated conditions using 110°C and under elevated temperature usually used for frying at 170°C is proposed. The results demonstrate that two different routes of degradation may be responsible for fat deterioration at elevated temperatures. Depending on the temperature (at 20, 110, or 170°C) the composition of polar compounds changed. The content of di‐ and polymerized TAGs increased with time at elevated temperature, e.g., frying whereas the formation of oxidized products dominates at 110°C or lower. These different reaction mechanisms may explain the discrepancy between practical experiences during frying and the estimated oxidative resistance of fats and oils using accelerated tests like Rancimat or OSI. Practical applications : Both the amount of total oxidized monomeric TAGs called total oxidized products (TOP) and the amount of di‐ and polymerized TAGs (DPTG) can be used to describe the fat degradation at all stages. These parameters are less dependent on the fat composition but proportional to the heating time and applied temperature. A procedure is proposed to compare thermal and oxidative stability of vegetable oils and effectiveness of oxidative stabilizing agents. Heating apparatus to simulate fat degradation at 110 and 170°C with and without access of oxygen (20 L/h) to monitor oxidation and structural decomposition of fats and oils.