Changesin Peroxide value of Oil samples at different frying Time and constantTemperature The initial Peroxide values of Palm oil, shea butterand blend were 1.80 ± 0.
02, 0.92 ± 0.01 and 1.20 ± 0.03, respectively (Table2). Experimental results in Table 4 shows that Peroxide value of the three oilssamples are significantly (P ? 0.05) increased with frying time. Higherperoxide values were observed in palm oil and the highest (6.
20) after 12hoursof frying circle with initial peroxide value of 1.80±0.20. Shea butter was morestable than other samples with the initial peroxide value of 0.
92±0.01 andrecorded 3.20±0.01 after the frying period of 12hours, peroxide value of blendrange between 1.20±0.03 to 3.
43±0.04 throughout the frying cycle of 12hours. The results recorded for the peroxide value of theseoil samples are similar to those obtained by Tiwari, Tiwari and Toliwal (2014)while frying potato chips at 1800C in palm oil, sesame oil and apalm-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) thatreported increase in rate of degradation of peroxide value in Sorrel (H.sabdariffa) seed oil as the temperature increases. This is an indicationthat prolonged heating of this oil made it to experience thermal degradation,resulting in oxidative rancidity and formation of hydro-peroxides and otherproducts of degradation that can release spontaneous compounds Figure 2 shows the results of the kinetic study of thechange in Peroxide value of the Palm oil, shea butter and blend during repeateddeep frying of cheese for 12hour. It can be seen from the graph that kineticdeterioration (k) concentrationincreased with time.
palm oil and shea butter recorded equal kinetic andhighest constant rate of 0.003min-1 while shea butter recorded thelowest value of 0.0028min-1, this result shows palm oil and sheabutter deteriorate faster than blend.
The first-order kinetic model gave a goodfit in describing the changes in the peroxide value of the oil samples as shownby the high R2 (R2<0.8) of the model (Figure2). 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 blendalso similar to the report of Piedrahita, Penaloza, Cogollo and Rojano (2015)for choibá fruit oil and Sathivel, Huang and Prinyawiwatkul (2008) for Pollockoil.
The Arrhenius equation was used to describe thetemperature dependence of k of the oil samples. Non-linear regressionswere 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 Eavalues for PV are in line with earlier findings that the Ea required forthe formation and accumulation of lipid peroxides and hydroperoxides is verylow since peroxyl radicals’ formation and decomposition take placesimultaneously during thermal processing of oils (Laguerre et al.
, 2007). low Eavalues implies that the reaction takes place very quickly as the buildup ofaldehydes and carbonyls soon dominates (Anio?owska et al., 2016). This resultis 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 ofPiedrahita, Penaloza, Cogollo and Rojano, who polyunsaturated oil, choibá fruitoil, 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 activationenergies Ea (kJ/mol).
This confirmed that the rate of formation ofperoxide 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 strengthas saturation level increased and synergistic radical scavenging activity ofboth natural and synthetic antioxidants (Firestone (2009 and Goburdhun 1995).