Assessing the effects of Sunlight on the Photooxidation of Tropical Oils

This study aims to investigate the influence of sunlight on the photooxidation of tropical oils (TOs). Coconut oil (CNO), palm oil (PO), and palm kernel oil (PKO) were chosen for determining the indicators of photooxidation when exposed to and in the absence of sunlight for seven weeks. The results showed a significant (p < 0.05) increase in free fatty acid (FFA) levels and peroxide value (PV) when the TOs were exposed to sunlight. The iodine value (IV) and colour content decreased significantly (p < 0.05) due to the decomposition of unsaturated FFAs owing to the breaking-down of the π-bonds and the degradation of colour pigments during photooxidation. FTIR analysis showed strong vibrational absorptions at 1721 and 3505 cm, 1720 and 3560 cm, and 1721 and 3554 cm for the CNO, PO, and PKO samples exposed to sunlight, respectively. These bands can be attributed to the presence of secondary oxidation products, which were absent in the TOs that were not exposed to sunlight. A simulation was performed to support the FTIR results, which also indicated peaks from the secondary oxidation products at 1744 and 3660 cm. The study also revealed that the rate of photooxidation was different for each TOs. The rate of oxidation followed the order PO > PKO > CNO. In contrast, no notable changes were observed in the TOs kept away from the sunlight. These results suggest that exposing TOs to sunlight influences their oxidation stability and quality.