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.