Oxidative stability, thermal decomposition, and oxidation onset prediction of carrot, flax, hemp, and canola seed oils in relation to oil composition and positional distribution of fatty acids

Triacylglyceride positional distribution of fatty acids in flax, hemp, and canola seed oils were determined using Novozyme 435 and high performance liquid chromatography (HPLC) compared with the less convenient standard method using pancreatic lipase and thin layer chromatography (TLC). SFA were exclusively incorporated into the sn-1,3 position and PUFA were higher at the sn-2 position as expected. Thermogravimetic analysis (TGA) was used to predict onset of oxidation of carrot, flax, hemp, and canola seed oils and could replace conventional oxidation prediction methods due to its simplicity and time-saving nature. Carrot seed oil exhibited higher oxidative stability and longer oxidation onset time compared with the other three oils in the isothermal heating trials due to having the lowest polyunsaturated fatty acids (PUFA) content. Thermal decomposition was influenced by the fatty acids in the oils. Flax, hemp, and canola seed oils contained higher levels of natural antioxidants due to their extraction methods although the effect of natural antioxidants on the maximum temperature of thermal decomposition was masked because of the significant differences in their unsaturated fatty acid compositions, as temperature increased. The decomposition for carrot seed oil commenced earlier compared with the seed oils containing more antioxidants, despite having low PUFA content, once natural antioxidants had been exhausted. Practical applications: This research illustrates the advantage of using novozyme 435, HPLC, and ESI-MS for positional distribution analysis compared to the traditional method employing pancreatic lipase and thin layer chromatography followed by gas chromatographic analysis. Further, the use of thermogravimetry for determination of oxidative stability, shelf life determination and thermal decompositional analysis is illustrated. Results demonstrate influence of fatty acid type and antioxidant content on stability and positional distribution of fatty acids in the oil triglycerides.