# Changes in Selected Properties of Cold-Pressed Oils Induced by Natural Plant Additives
## 3 Results and Discussion
### Chemical Determinations of Supplemented Oils  
Figure 1 shows changes in the values of the quality determinants in the oils supplemented with garlic and chili pepper. The results reveal a significant effect of both storage time and the additives used on the analyzed parameters. During the storage of the oils at 10 \(\pm\) 1 \({}^{\circ}\)C, an increase in AV and PV was observed in the sample without the additives as compared to those in the freshly pressed oils, with the greatest differences noted after 6 weeks (Figures 1 and 2). The oxidative stability of the oils also changed, i.e., the values decreased with the storage time. The black cumin seed oil exhibited the greatest differences from the freshly pressed oil, as its induction time decreased by 26.7% (Figure 3). The present study showed that the additives reduced the AV and PV of the oils and extended their induction time. The comparison of the effects of the additives revealed that garlic was more effective than chili pepper. As shown by the statistical analysis, for the flax and hemp seed oils, only the addition of garlic had a significant effect on the AV after 2, 4, and 6 weeks of storage of the samples. A significant effect of both the tested additives on changes in the value of this parameter relative to the control sample was noted in the black cumin seed oil. The addition of garlic to the flax seed oil caused significant changes in PV after 2 and 4 weeks of storage, while significant changes were caused by this additive in the hemp seed oil only after 4 weeks. For the black cumin seed oil, both garlic and chili pepper additives significantly reduced the PV as compared to that for the control sample after 2, 4, and 6 weeks of storage. The analysis of the changes in the induction time showed that the garlic-supplemented oil had the longest induction time after 6 weeks of storage. The Rancimat test results showed that the addition of garlic to the flax and hemp seed oil produced significant changes in the induction time after 4 weeks and after 4 and 6 weeks of storage, respectively. Statistically significant changes in this parameter were induced in the black cumin seed oil by both additives after each storage period. Figures 1-3 show the effect of the additives used on the chemical parameters that are the determinants of oil quality. The analyses revealed a decrease in the AV and PV and extension of the induction time in the supplemented samples as compared to those for the control sample. A comparison of the effectiveness of the additives showed that garlic had a better effect on the oils than chili pepper. Similar conclusions were reported by [PERSON] et al. [40] in their study of the effect of substances changing the flavor and aroma of extra virgin olive oil. The authors found an increase in the content of primary oxidation products of approximately 11 and 14 mmol O\({}_{2}\)/kg in garlic- and chili-pepper-supplemented samples, respectively. The authors also investigated changes in the content of tocopherols, which are natural antioxidants. Their study showed a higher amount of these compounds in garlic oil than in chili pepper oil. As reported by [PERSON] et al. [41], the addition of a mixture of garlic, bay leaf, and majoram to olive oil with canned dried  
Figure 3: _Cont._  
Figure 2: Effect of additives on the peroxide value of stored oils: (**a**)—flax seed oil; (**b**)—hemp seed oil; (**c**)—black cumin seed oil. The values designated by the different small letters are significantly different (\(\alpha\) = 0.05). The effects of various additives on the quality and stability of cold-pressed oils were also investigated by other scientists. [PERSON] et al. [42] and [PERSON] et al. [43] analyzed the effect of turmeric and rosemary supplementation on changes in AV, PV, and induction time in poppy seed oil and the impact of oregano addition on the same parameters in rapeseed oil. The authors showed that the additives exhibited antioxidant properties and effectively reduced oxidative changes occurring during oil storage.