## 3 Results and Discussion
### Oxidative Stability  
Adverse changes in oils may already begin in the seeds and kernels of oil plants but are inevitable in the oil production process. The intensity of the oil oxidation processes also depends on the proportion of saturated and unsaturated fatty acids and the content of pro- and antioxidant ingredients [19]. The analyzed apricot kernel oils were characterized by significantly different oxidative stability. For the A1 oil at each measurement temperature (100, 110, 120, 130, and 140 \({}^{\circ}\)C), a significantly longer maximum oxidation time was recorded than for the A2 oil (from 705 to 31.14 min for the A1 oil and 187.70-6.35 min for the A2 oil) (Table 2). The longer oxidation time of apricot kernel oil A1 was associated with a significantly lower peroxide value, which for this oil reached 0.87 meq O\({}_{2}\)/kg fat, while, for the A2 oil, 2.19 meq O\({}_{2}\)/kg fat (Figure 3). Moreover, the A2 oil was characterized by a higher acid value than the A1 oil (0.57 and 3.14 mg KOH/g fat for the A1 and A2 oil, respectively) (Figure 3). Due to the pro-oxidant effect of free carboxyl groups, free fatty acids are oxidized faster than those esterified in triacylglycerols, and they can induce oxidative processes [43]. The increase in the oxidative stability of the oil is also attributed to the high content of oleic acid, which oxidizes more slowly than polyunsaturated acids [19]. The A1 oil was characterized by a two-times-lower share of linoleic acid than the A2 oil and an over 22 percentage points higher share of oleic acid than the A2 oil. In the case of the peach kernel oils, significant differences were also found in the maximum oxidation time, but not as high as in the case of the apricot kernel oils (Table 2). For the P1 oil, the maximum oxidation time, depending on the reaction temperature, ranged from 356 to 22.36 min, while, for the P2 oil, it was 254-16.90 min. Generally, the peach kernel oils were characterized by similar peroxide values of 1.91 and 2.32 meq O\({}_{2}\)/kg fat and acid values \(-\)1.58 and 2.04 mg KOH/g fat for the P1 and P2 oils, respectively (Figure 3). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Temperature**} & \multicolumn{4}{c}{**Type of Oil**} \\ \cline{2-5}  & **A1** & **A2** & **P1** & **P2** \\ \hline
100 \({}^{\circ}\)C & 705.00 \(\pm\) 7.07 \({}^{\mathrm{d}}\) & 187.70 \(\pm\) 17.14 \({}^{\mathrm{a}}\) & 356.00 \(\pm\) 8.49 \({}^{\mathrm{c}}\) & 254.00 \(\pm\) 2.83 \({}^{\mathrm{b}}\) \\
110 \({}^{\circ}\)C & 342.53 \(\pm\) 3.59 \({}^{\mathrm{d}}\) & 78.00 \(\pm\) 0.83 \({}^{\mathrm{a}}\) & 203.59 \(\pm\) 3.74 \({}^{\mathrm{c}}\) & 137.03 \(\pm\) 4.50 \({}^{\mathrm{b}}\) \\
120 \({}^{\circ}\)C & 160.28 \(\pm\) 12.09 \({}^{\mathrm{d}}\) & 33.74 \(\pm\) 0.04 \({}^{\mathrm{a}}\) & 118.52 \(\pm\) 4.02 \({}^{\mathrm{c}}\) & 78.80 \(\pm\) 2.57 \({}^{\mathrm{b}}\) \\
130 \({}^{\circ}\)C & 65.24 \(\pm\) 6.70 \({}^{\mathrm{d}}\) & 20.01 \(\pm\) 8.82 \({}^{\mathrm{a}}\) & 51.84 \(\pm\) 1.14 \({}^{\mathrm{c}}\) & 40.78 \(\pm\) 2.17 \({}^{\mathrm{b}}\) \\
140 \({}^{\circ}\)C & 31.14 \(\pm\) 1.46 \({}^{\mathrm{d}}\) & 6.35 \(\pm\) 0.13 \({}^{\mathrm{a}}\) & 22.36 \(\pm\) 0.73 \({}^{\mathrm{c}}\) & 16.90 \(\pm\) 1.93 \({}^{\mathrm{b}}\) \\ \hline \hline \end{tabular} Data denoted by the different letters are statistically different (\(\alpha\) = 0.05) in terms of temperature of measurement.  
\end{table} 
Table 2: Maximum oxidation times [min] at temperatures 100, 110, 120, 130, and 140 \({}^{\circ}\)C of peach and apricot kernel oils. Figure 3: Acid values (AVs) and peroxide values (PVs) of peach and apricot kernel oil. Data denoted by the same lowercase letters are not statistically different (\(\alpha\) = 0.05) in terms of acid value, and data denoted by capital letters are not different in terms of peroxide value. Additionally, there were no significant differences in the shares of oleic and linoleic acid in the peach kernel oils. [PERSON] et al.