RESULTS AND DISCUSSION

Effects on Free Fatty Acids

FFA is considered as a weight parameter that is linked to the oxidative stability of vegetable oils. Table 1 shows the various changes in %FFA for all TOs at 95% confidence level (CL). The %FFA of the exposed and unexposed CNO, PKO, and PO were initially 1.32\(\pm 0.01\), 8.42\(\pm 0.01,\) and 3.81\(\pm 0.01,\) respectively. After seven weeks of sunlight exposure, the %FFA in the CNO, PKO, and PO substantially increased to 3.75\(\pm 0.03\), 15.04\(\pm 0.03,\) and 6.59\(\pm 0.03\)respectively. This shows that the effect of sunlight on FFA is significantly different (p < 0.05) for the control and sunlight-exposed TOs. The results presented in Figure 1 indicate that the increase in %FFA is faster in PO than in CNO and PKO. This can be attributed to the differences in the amounts of the saturated FFA present in the TOs. CNO and PKO are characterised by the most representative portion of saturated FFA consisting primarily of lauric acid (54% CNO and 50% PKO). PO is characterised by a substantial level of saturated and monounsaturated FFA, with the prominent constituents being palmitic (52%) and oleic acids (43%)(Kostik, Memeti and Bauer, 2013). Hence, PO is more prone to photooxidation due to its high level of unsaturation compared to CNO and PKO (Maszewska et al. , 2018). Second, the TOs stored away from exposure to the sun recorded the lowest %FFA. After the seven weeks of protection from light, the %FFA increased slightly from 1.30\(\pm 0.01\) to 1.40\(\pm 0.01\) (CNO), 3.81\(\pm 0.01\) to 3.96\(\pm 0.03\) (PKO), and 8.42\(\pm 0.01\) to 8.68\(\pm 0.02\) (PO), among the oils. This increase in %FFA can be attributed to enzymatic or hydrolytic oxidation, which is initiated by the presence of moisture or enzymes remaining in the TOs after processing.
Similar results have already been reported by several researchers and agree well with those of the present study. For instance, Fekarurhobo et al. (2009) investigated the short-term exposure of sunlight on PO and PKO. After eight months of sunlight exposure, they reported an increase in %FFA from 5.0 to 6.0 and 2.5 to 4.1 in PKO and PO, respectively. Henry (2011) also reported variations in the FFA of crude PO when exposed to various light radiations and found that the %FFA in the PO rose from 0.738 to 1.084 after 20 days of sunlight exposure. These results showed an appropriate correlation with the results of Rukmini et al. (2011), who monitored the effects of fluorescent light on virgin coconut oil (VCO). They reported a similar increase in %FFA in various commercial VCOs after exposure to fluorescent light for 5 hrs. The %FFA in several commercial VCOs increased from 0.18 to 0.84, 0.29 to 1.24, 0.48 to 3.11, 0.16 to 1.14, and 0.08 to 0.25 after exposure to light. Figure 1 shows that the higher the degree of the unsaturation in the TO, the faster is the oxidation reaction. Hence, the present study can conclude that the oxidative stability of the TOs decreases in the order: PO < PKO < CNO, due to different degrees of unsaturation. This results in an increase in the %FFA, which decreases the oxidative stability and shelf life of the TOs. Figure 1 shows that the PO with the highest level of unsaturated fats is more prone to photooxidation than CNO and PKO. Thus, the type of FFA present in TOs plays a crucial role in their stability against oxidation. The one-way ANOVA of the mean for the protected and unprotected TOs showed a statistically significant (p > 0.05) difference in %FFA.