in Peroxide value of Oil samples at different frying Time and constant
The initial Peroxide values of Palm oil, shea butter
and blend were 1.80 ± 0.02, 0.92 ± 0.01 and 1.20 ± 0.03, respectively (Table
2). Experimental results in Table 4 shows that Peroxide value of the three oils
samples are significantly (P ? 0.05) increased with frying time. Higher
peroxide values were observed in palm oil and the highest (6.20) after 12hours
of frying circle with initial peroxide value of 1.80±0.20. Shea butter was more
stable than other samples with the initial peroxide value of 0.92±0.01 and
recorded 3.20±0.01 after the frying period of 12hours, peroxide value of blend
range between 1.20±0.03 to 3.43±0.04 throughout the frying cycle of 12hours.
The results recorded for the peroxide value of these
oil samples are similar to those obtained by Tiwari, Tiwari and Toliwal (2014)
while frying potato chips at 1800C in palm oil, sesame oil and a
palm-sesame oil blend. This trend was also reported for unrefined pollock oil
(2007) and choibá oil containing antioxidants from Rosmarinus officinalis (Piedrahita et al., 2015).
Also similar to those of Tunde F. A, Abiodun A. and Olawale O. (2013) that
reported increase in rate of degradation of peroxide value in Sorrel (H.
sabdariffa) seed oil as the temperature increases. This is an indication
that prolonged heating of this oil made it to experience thermal degradation,
resulting in oxidative rancidity and formation of hydro-peroxides and other
products of degradation that can release spontaneous compounds
Figure 2 shows the results of the kinetic study of the
change in Peroxide value of the Palm oil, shea butter and blend during repeated
deep frying of cheese for 12hour. It can be seen from the graph that kinetic
deterioration (k) concentration
increased with time. palm oil and shea butter recorded equal kinetic and
highest constant rate of 0.003min-1 while shea butter recorded the
lowest value of 0.0028min-1, this result shows palm oil and shea
butter deteriorate faster than blend. The first-order kinetic model gave a good
fit in describing the changes in the peroxide value of the oil samples as shown
by the high R2 (R2<0.8) of the model (Figure 2). The same order of reaction for lipid peroxidation was reported by Ogan Mba, Ngandi and Marie jose Dunmot (2016) for Palm oil, canola oil and their blend also similar to the report of Piedrahita, Penaloza, Cogollo and Rojano (2015) for choibá fruit oil and Sathivel, Huang and Prinyawiwatkul (2008) for Pollock oil. The Arrhenius equation was used to describe the temperature dependence of k of the oil samples. Non-linear regressions were performed, and the values obtained for the Ea values (kJ/mol) were 4.95, 7.14 and 5.82 for palm oil, shea butter and blend, respectively. The Ea values for PV are in line with earlier findings that the Ea required for the formation and accumulation of lipid peroxides and hydroperoxides is very low since peroxyl radicals' formation and decomposition take place simultaneously during thermal processing of oils (Laguerre et al., 2007). low Ea values implies that the reaction takes place very quickly as the buildup of aldehydes and carbonyls soon dominates (Anio?owska et al., 2016). This result is supported by the finding of Ogan Mba, Ngandi and Marie jose Dunmot (2016) for Palm oil, canola oil and their blend also agreed with the report of Piedrahita, Penaloza, Cogollo and Rojano, who polyunsaturated oil, choibá fruit oil, was reported to have shown PV Ea range of 4.6–7.4 kJ/mol (Piedrahita et al., 2015). The shea butter and blend oil sample had the highest activation energies Ea (kJ/mol). This confirmed that the rate of formation of peroxide radicals in the shea butter and blend was slow compare with palm oil. This can be attributed to the combined effect of reduced double bond strength as saturation level increased and synergistic radical scavenging activity of both natural and synthetic antioxidants (Firestone (2009 and Goburdhun 1995).