## 3 Results and Discussion
### Accelerated Storage Trials  
To gain a full understanding of the efficiency of the antioxidants tested, oil samples enriched with 200 mg kg\({}^{-1}\) of each antioxidant were maintained at 65 \({}^{\circ}\)C, for a period of 40 days. Samples were periodically checked for rancidity development, by measuring the onset of peroxide value (PV), which represents the formation of primary lipid oxidation products, and the thiobarbituric acid reactive substances (TBARS), which gives an account of secondary oxidation product formation. For the non-enriched sample (control), PV increased almost 2-fold at 20 days, and 3-fold up to the end of the examination period (40 days), pointing clearly to a gradual peroxide accumulation (Figure 4). On the contrary, for the oil samples enriched with antioxidants, the increases in PV at day 40 were 1.3 to 1.6 times higher than the initial value. Furthermore, it was observed that, after 20 days, the most effective antioxidants were CA and BHT, while at the end of the treatment (day 40), only BHT contributed to  
Figure 3: Correlation between the mean rate (\(R_{\text{m}}\)) of inhibitor (antioxidant) consumption with inhibitor concentration. Assignments: BHT, butylated hydroxytoluene; CA, caffeic acid; CouA, \(p\)-coumaric acid; FA, ferulic acid. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Antioxidant** & **Equation** & \(\mathbf{R^{2}}\) & **Slope** \\ \hline BHT & \(R_{\text{m}}=0.128C+1.089\) & 0.9981 & 0.128 \\ Caffeic acid & \(R_{\text{m}}=0.104C+2.026\) & 0.9999 & 0.104 \\ Ferulic acid & \(R_{\text{m}}=0.150C+0.373\) & 0.9999 & 0.150 \\ \(p\)-Coumaric acid & \(R_{\text{m}}=0.148C+0.656\) & 0.9990 & 0.148 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Linear functions established after plotting the mean rate (\(R_{\text{m}}\)) of inhibitor (antioxidant) consumption with inhibitor concentration. a significantly lower PV. On the other hand, the differences in PV found for oil samples enriched with either CA, FA, and CouA were non-significant. Similarly, the oil sample with no antioxidants added showed a gradual TBARS accumulation over the examination period and, at day 40, the TBARS were increased by approximately 4.5-fold. On the contrary, all antioxidants tested were proven effective in delaying TBARS accumulation. Moreover, measurements at both day 20 and 40 indicated that FA exhibited significantly higher efficacy (\(p<0.05\)) compared to all other compounds (Figure 5). Figure 4: Evolution of peroxide formation upon incubation of OKO at 65 \({}^{\circ}\)C. Assignments: BHT, butylated hydroxytoluene; CA, caffeic acid; CouA, \(p\)-comamaric acid; FA, ferulic acid. Each antioxidant was tested at 200 mg kg\({}^{-1}\) of oil. Bars indicate standard deviation. Columns denoted with different letters (a, b, c, d and e) represent significantly different values (\(p<0.05\)). Figure 5: Evolution of TBARS formation upon incubation of OKO at 65 \({}^{\circ}\)C. Assignments: BHT, butylated hydroxytoluene; CA, caffeic acid; CouA, \(p\)-comamaric acid; FA, ferulic acid. Each antioxidant was tested at 200 mg kg\({}^{-1}\) of oil. Bars indicate standard deviation. Columns denoted with different letters (a, b, c, d, e, f, g and h) represent significantly different values (\(p<0.05\)). Considering both assays, it was evident that all phenolic acids tested were demonstrated to provide significantly enhanced resilience against oxidative rancidity, as this can be manifested by both PV and TBARS. In the case of peroxide accumulation, CA appeared to provide higher stability after 20 days, but not after 40 days of treatment. This finding suggested that, in the long term, the structural features of the phenolic acids tested might not play a pivotal role. Such a phenomenon might be ascribed to the stability of the compounds tested, but also to the fact that peroxides are relatively unstable molecules, and gradually decompose, giving rise to secondary oxidation products [45].