## 3 Results and Discussion
### Acid Value, Peroxide Value, and Oxidative Stability
\begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Sample**} & **Acid Value** & **Peroxide Value** & **Oxidative Stability** \\  & **[mg KOH/g]** & **[mmol O\({}_{2}\)/kg]** & **[h]** \\ \hline
**FO** & 0.15 \(\pm\) 0.01 d & 8.51 \(\pm\) 0.12 a & 0.18 \(\pm\) 0.01 e \\
**PO** & 1.95 \(\pm\) 0.05 b & 5.43 \(\pm\) 0.02 c & 0.58 \(\pm\) 0.05 d \\
**MTO** & 2.49 \(\pm\) 0.08 a & 2.27 \(\pm\) 0.04 e & 1.94 \(\pm\) 0.05 b \\
**GO** & 0.32 \(\pm\) 0.03 c & 5.94 \(\pm\) 0.04 b & 2.05 \(\pm\) 0.06 a \\
**WO** & 0.11 \(\pm\) 0.01 d & 2.64 \(\pm\) 0.23 d & 1.09 \(\pm\) 0.02 c \\ \hline \end{tabular}  
* Mean \(\pm\) standard deviation; different letters in a column denote mean values that statistically differ from one another; h—hours; FO—flax seed oil; PO—poppy seed oil; MTO—milk thistle seed oil; GO—grape seed oil; WO—walnut oil.  
\end{table} 
Table 1: Results of acid value, peroxide value, and oxidative stability of analysed oils. 11.39 \(\pm\) 2.26 mmol O\({}_{2}\)/kg in cold-pressed milk thistle oil from Turkey; this was higher compared to the value determined in our sample. In a study by [PERSON] et al. [25], walnut kernel cold-pressed oil showed a peroxide value of 1.95 mmol O\({}_{2}\)/kg. This was lower compared to our observations for walnut oil--2.64 mmol O\({}_{2}\)/kg. According to [PERSON] et al. [23], peroxide values in fresh oils are below 10 mmol O\({}_{2}\)/kg, whereas oils that have spoiled and gone rancid show results that exceed 30 mmol O\({}_{2}\)/kg. Notably, peroxide values that reach 100 mmol O\({}_{2}\)/kg have been associated with cases of food poisoning. Oxidation resistance is one of the most crucial quality parameters for edible oils. It determines their usefulness in technological processes and shelf life. Storage tests are the most reliable, but they are time-consuming. The possibility of determining oil stability in a short time is therefore valued [26]. In our study, the oxidative stability values ranged from 0.18 h (flax seed oil) to 2.05 h (grape seed oil) (Table 1). The stability of oils was generally shorter, which is not surprising because the tested cold-pressed oils contained high levels of polyunsaturated fatty acids. The poppy seed oil and flax seed oil were the most susceptible to oxidation. A similar tendency was observed by [PERSON] [27], who tested the oxidative stability of cold-pressed poppy seed oil using the Rancimat instrument at temperatures of 110, 120, 130, and 140 \({}^{\circ}\)C. The induction time was the lowest at 140 \({}^{\circ}\)C--0.61 h, while at 120 \({}^{\circ}\)C it was 2.73 h. This value was higher compared to the one determined for poppy seed oil in our study in the same conditions (120 \({}^{\circ}\)C). Due to the dominancy of \(\alpha\)-linolenic acid, poppy seed and flax seed oils are prone to oxidation. The shelf life of oils can be prolonged by antioxidants. In a study by [PERSON] et al. [22], flax seed oil containing 80 mg/kg topcopherol, 40 mg/kg ascorbyl palmit, 40 mg/kg phytic acid, and 240 mg/kg tea polyphenol palmit was determined to be very resistant to oxidation. The shelf life of this oil was 3.22-fold longer than that of the control flax seed oil. The addition of the right mix of antioxidants can, thus, result in obtaining oil products with enhanced oxidative stability that are suitable for commercialization. In our study, grape seed oil was found to be the most resistant to oxidation (2.05 h). This result is comparable with the findings of [PERSON] et al. [26], who reported the value of 2.4 h for this type of oil.