Assessing the Effects of Sunlight on the Photooxidation of Tropical Oils with Experimental and Computational Approaches

This study aims to investigate the influence of high-intensity sunlight radiation on the photooxidation of tropical oils (TO). 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 7 weeks. The results showed a significant (P < 0.05) increase in free fatty acid (FFA) levels and peroxide value (PV) when the TO were exposed to sunlight. The iodine value and color content decreased significantly (P < 0.05) due to the decomposition of unsaturated FFA owing to the breaking down of the pi-bonds and the degradation of color pigments during photooxidation. Fourier transform infrared spectroscopy (FTIR) analysis showed strong vibrational absorptions at 1721 and 3505 cm(-3), 1720 and 3560 cm(-3), and 1721 and 3554 cm(-3) 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 TO 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(-3). The study also revealed that the rate of photooxidation was different for each TO. The rate of oxidation followed the order PO > PKO > CNO. In contrast, no notable changes were observed in the TO kept away from sunlight. These results suggest that exposing TO to sunlight influences their oxidation stability and quality.