Abstract
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-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 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-3. 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.