Evaluation of the effect of repeated heating on commercially available vegetable oils using Raman Spectroscopy
Chemical changes in palm and coconut oil, repeatedly heated for up to 9 times, were evaluated using Raman Spectroscopy. A decreasing trend in band intensities centered at around 1265 cm-1 which corresponds to CH bending in cis double bonds δ(=C-H) was observed, with the trend being more pronounced in palm oil. This is attributed to a decrease in unsaturated fatty acid content as a consequence of oxidation. On the other hand, an increase in band intensities centered at around 1640 cm-1 was observed in palm oil, but not evident in coconut oil. This is attributed to the formation of oxidation products from the breakdown of unsaturated fatty acids. Results suggest that in processes involving repeated heating, coconut oil appears to be more stable against oxidation than palm oil due to the low unsaturated fatty acid content of coconut oil.