## 3 Results and Discussion
### Oxidative Stability of Sea Buckthorn and Rose Hip Oils  
The PDSC induction times recorded for sea buckthorn and rosehip oils are shown in Table 2. Rosehip oil R1 was characterized by a statistically longer induction time at each measurement temperature than rosehip oil R2. In the case of R2 rosehip oil, which contained over 20 percentage points less \(\alpha\)-linoleic acid, a shorter induction time was recorded in comparison to R1 oil. The longer induction time of rosehip oil R1 corresponded to the level of the peroxide value, which determined the content of primary oxidation products. The peroxide value was determined at a lower level in the case of R1 oil (2.04 meq O\({}_{2}\)/kg) compared to R2 oil (3.21 meq O\({}_{2}\)/kg) (Table 2), but in general, in both oils, it did not exceed the value of 15 meq O\({}_{2}\)/kg, as specified in Codex Alimentarius for cold-pressed oils [38]. [PERSON] et al. [39] recorded the peroxide value in rosehip oil at the level of 1.24 meq O\({}_{2}\)/kg, which indicated that this oil was characterized by a lower content of primary oxidation products than the analyzed R1 and R2 oils. The lower induction time of R2 oil could also be influenced by the content of free fatty acids, measured by the acid value. Free fatty acid values were obtained for the R2 oil. Figure 3: DSC melting profile of rosehip oils. Figure 2: DSC melting profile of sea buckthorn oils. acids formed during the hydrolysis of ester bonds in triacylglycerglycerol molecules may induce oxidation reactions [40] because they oxidize faster than acylated fatty acids due to the prooxidant effect of free carboxylic groups [5]. Rosehip R2 oil was characterized by an acid value almost 11 times higher than R1 oil (Table 2). In the case of sea buckthorn oil, the influence of polyunsaturated fatty acid content on oxidative stability has been found. Sea buckthorn oil B2, with a lower content of polyunsaturatedarted fatty acids, was characterized by longer induction times at each measurement temperature compared to sea buckthorn oil B1, with shorter induction times (Table 2) and a higher content of polyunsaturated fatty acids. The degree of hydrolysis of ester bonds in the analyzed sea buckthorn oils did not affect the induction times because sea buckthorn oils were characterized by similar levels of acid value (no statistically significant differences were found) (Table 2). The peroxide value for sea buckthorn oil B1 was about 1.3 times higher than for oil B2 (Table 2). In both B1 and B2 oils, the peroxide value did not exceed the value of 15 meq O\({}_{2}\)/kg specified by Codex Alimentarius [38]. The oxidative stability of sea buckthorn oils may be influenced by the content of bioactive compounds such as flavonoids, carotenoids, and polyphenols [27]. According to [PERSON] et al. [26], sea buckthorn oil obtained from fruit pulp contained more flavonoids, carotenoids, and polyphenols than oil obtained from seeds. The authors determined the content of flavonoids in the sea buckthorn pulp oil and seeds oil at the level of 9.54-14.18 mg quercetin equivalents/100 g and 4.11-4.58 mg QE/100 g, respectively. The carotenoid content reached 70.2-104.6 mg/100g for sea buckthorn pulp oil and 15.1-15.4 mg/100g for sea buckthorn seeds oil, and the total polyphenols--129.3-170.1 mg GAE/kg oil for sea buckthorn pulp oil and 86.9-90.1 mg GAE/kg oil for sea buckthorn seeds oil. Differences in the content of these compounds may explain the higher oxidative stability of B2 oil pressed from pulp compared to B1 oil pressed from seeds. [PERSON] et al. also reported that pulp oils showed better oxidative stability than seed oils [26]. Based on the induction times recorded at five measurement temperatures (100, 110, 120, 130, and 140 \({}^{\circ}\)C), the activation energy of the oxidation reactions of the tested rosehip and sea buckthorn oils was determined. Based on the kinetic parameters of the oxidation reaction, it was possible to determine the processing suitability of oils.