# Comprehensive Evaluation of the Nutritional Quality of Stored Watermelon Seed Oils
## 3 Results and Discussion
### Determination of Peroxide Value
During the storage process, the value of the average \(\tau_{\text{max}}\) for this oil decreased slightly. This indicates very good stability regarding the oxidation of the given oil. Comparing the results obtained for unrefined pressed oils, quite large differences could be noted. The WO\({}_{3}\) was characterized by a fairly long oxidation induction time of 49.59 min in the first month of the tests. The average \(\tau_{\text{max}}\) for WO\({}_{2}\) was 36.36 min, while for the WO\({}_{1}\), this value was only 23.88 min. Of the cold-pressed oils, WO\({}_{3}\) showed the best oxidative stability. WO\({}_{\text{ref}}\) also had a relatively long \(\tau_{\text{max}}\), comparable to that of WO\({}_{3}\). This prolonged oxidation induction time may be due to the removal of pro-oxidant compounds during refinement or the low initial oxidation level of the refined oil. The high PUFA contents (above 50%) explain the oxidation processes occurring in the tested oils and the decreasing values of \(\tau_{\text{max}}\). Additionally, linoleic acid was located in the external position of the TAGs, which is in accordance with the literature reports indicating that PUFAs located in the _sn_-1,3 TAG position reduce the oxidative stability of oils [59]. There is a lack of data in the literature regarding the PDSC oxidation time of watermelon seed oil. [PERSON] et al. [60] analyzed self-extracted blackberry, chokeberry, and raspberry seed oils. The high-pressure differential scanning colorimetry method deter  
Figure 4: The PDSC oxidation time of tested watermelon seed oils before their storage and after one, two, and three months of storage at 4 \({}^{\circ}\)C, where WO\({}_{1}\)–WO\({}_{3}\) represent unrefined commercial oils, WO\({}_{\text{ref}}\) represents refined commercial oil, and WO\({}_{\text{ext}}\) represents self-extracted oil. Different lower-case letters (a–d) indicate statistically significant differences within the same sample at varying storage times, at the level of \(\alpha\) = 0.05. Different capital letters (A–E) indicate statistically significant differences between different samples for the same storage period, at the level of \(\alpha\) = 0.05.  
mined the oxidative stability of these oils. The same conditions were used for determination as were used for the oils tested in this paper, i.e., a temperature of 120 \({}^{\circ}\)C and a pressure of 1400 kPa. The average \(\tau_{\text{max}}\) for the tested cold-pressed oils was 41.20 min for chokeberry seed oil and 56.02 min for raspberry seed oil. The highest value of 90.29 min was reported for blackberry seed oil. The studied self-extracted watermelon seed oil is not as oxidatively stable as blackberry seed oil but is more stable than chokeberry seed and raspberry seed oils. The tested commercial cold-pressed watermelon seed oils have a higher \(\tau_{\text{max}}\) than the fruit seed oils mentioned above. They may be considered more stable at 120 \({}^{\circ}\)C than the pomegranate seed oils studied by [PERSON] et al. [30], with an induction time below 2.5 min but lower than that of the pumpkin seed oil examined in the research of [PERSON] et al. [61]. In contrast, the \(\tau_{\text{max}}\) of commercial cold-pressed pumpkin seed oil (under similar conditions) was, on average, 71.05 min. The similar oxidation induction times of commercial watermelon and pumpkin seed oils may be because watermelon and pumpkin come from the same family--_Cucurbitaceae._