# Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives
## 3 Results and Discussion
### Chemical Determination of Oils
The mean AV differed between the analyzed oils (Table 3). The lowest AV was shown by the flax seed oil (0.51 mg KOH/g). A substantially higher AV was exhibited by the hemp seed oil (1.69 mg KOH/g), whereas the black cumin seed oil had the highest AV (2.36 mg KOH/g). As indicated by the PV, the highest amounts of peroxides and hydroperoxides were detected in the black cumin seed oil with a PV of 3.36 mmol O\({}_{2}\)/kg, while the PV of the flax seed oil was only 0.74 mmol O\({}_{2}\)/kg. This confirms that the oils met the quality requirements in terms of AV and PV (AV \(\leq\) 4 mg KOH/g, PV \(\leq\) 10 mmol O\({}_{2}\)/kg) as specified in the Codex Alimentarius [34]. The contents of free fatty acids as well as peroxides and hydroperoxides varied between the analyzed oils (Table 3). The lowest amount of these compounds was detected in the flax seed oil. The AV obtained in the present study differed substantially from the values reported by other researchers. [PERSON] et al. [33] showed an AV of 2.12 mg KOH/g for the oil extracted from flax seeds with moisture content of 6.7% and a PV of 0.72 mmol O\({}_{2}\)/kg, which was similar to that determined in the present study. [PERSON] et al. [35] analyzed flax and black cumin seed oils and reported AV of 0.07 and 1.62 mg KOH/g, respectively, which were substantially lower than the values determined in the present study. The PV reported by these authors was 2.9 and 34.7 mg O\({}_{2}\)/kg in flax and black cumin seed oils, respectively, whereas the values in the present study were 0.74 and 3.36 mmol O\({}_{2}\)/kg, respectively. The AV (Table 3) was similar to the value reported by [PERSON] et al. [24], who analyzed oil from seeds of the same variety harvested in 2014. In contrast, a considerably higher PV (8.8 mmol O\({}_{2}\)/kg) was reported by the authors than that obtained in the present study (1.40 mmol O\({}_{2}\)/kg). The antioxidant mechanism of capsaicin present in chili peppers has also been described by [PERSON] et al. [36], wherein they showed that capsaicin delayed the lipid oxidation of soybean oil during the frying process at 200 \({}^{\circ}\)C. [PERSON] et al. [37] showed that the oxidation process takes place at 140 \({}^{\circ}\)C, but it is not as effective as that at 100 \({}^{\circ}\)C [38]. Oxidative stability is a very important indicator of the quality of cold-pressed oils. The Rancimat accelerated oxidation test is usually applied to determine the oxidative stability and the shelf life of oils [34]. The test results showed that the hemp seed oil was characterized by the lowest value of this parameter (1.75 h), followed by the flax seed oil \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type of Oil**} & **Extraction** & **AV (\(\pm\) SD)** & **PV (\(\pm\) SD)** & **Induction Time** \\  & **Yield [\%]** & **[mg KOH/g]** & **[mmol O\({}_{2}\)/kg]** & **(\(\pm\) SD) [h]** \\ \hline Flax seed oil & 81.43 \({}^{\text{a}}\),* & 0.51 \(\pm\) 0.08 \({}^{\text{a}}\) & 0.74 \(\pm\) 0.08 \({}^{\text{a}}\) & 2.59 \(\pm\) 0.09 \({}^{\text{a}}\) \\ Hemp seed oil & 72.81 \({}^{\text{b}}\) & 1.69 \(\pm\) 0.09 \({}^{\text{b}}\) & 1.40 \(\pm\) 0.08 \({}^{\text{b}}\) & 1.75 \(\pm\) 0.07 \({}^{\text{b}}\) \\ Black cumin seed oil & 56.13 \({}^{\text{c}}\) & 2.36 \(\pm\) 0.07 \({}^{\text{c}}\) & 3.36 \(\pm\) 0.09 \({}^{\text{c}}\) & 5.80 \(\pm\) 0.08 \({}^{\text{c}}\) \\ \hline \hline \end{tabular} \({}^{\text{a}}\) Values designated by the different small letters in the column are significantly different (\(\alpha\) = 0.05).  
\end{table} 
Table 3: Extraction yield and chemical properties of fresh cold-pressed oils. (2.59 h) (Table 3). The black cumin seed oil was most resistant to oxidation, as its induction time was 5.8 h.  
The Rancimat test results showed the lowest stability of the hemp seed oil, slightly higher stability of the flax seed oil, and the highest value of the parameter in the black cumin seed oil (Table 3). The induction time determined by [PERSON] et al.