# Comprehensive Evaluation of the Nutritional Quality of Stored Watermelon Seed Oils
## 3 Results and Discussion
### Determination of Peroxide Value
The differences in the obtained results may be due to variations in the quality of the raw material, different parameters during the extraction process, or different degrees of protection against oxidation after the extraction process was completed. As mentioned earlier, the FA composition of the oil is an important factor influencing the oxidation processes. The determined PUFA contents ranged from about 54% for WO\({}_{\text{ref}}\) to about 62% for WO\({}_{\text{ext}}\). A lower PUFA content may, to some extent, influence the lowest PV observed for WO\({}_{\text{ref}}\). Furthermore, although the storage time negatively affected the PV of all tested oils, the WO\({}_{\text{ref}}\) exhibited the smallest increase, demonstrating greater stability compared to other oils. This suggests that WO\({}_{\text{ref}}\) is less prone to oxidation and could be more suitable for longer storage periods under similar conditions. The initially low PV of the WO\({}_{\text{ref}}\) (1.96 mEq O\({}_{2}\)/kg fat) was probably due to the fact that the refining process removes primary oxidation products. It could also be suggested that the seeds used to produce the oil were probably of good quality and that the conditions and parameters of the pressing process were appropriate. Oxidative Stability, Obtained via Pressure Differential Scanning Calorimetry (PDSC)--Isothermal Measurements  
Lipid oxidation determines the food products' final quality and nutritional properties because it is the main reaction responsible for their degradation. Oxidative stability is an important quality indicator in edible oils and fats [30]. In food chemistry, pressure differential scanning calorimetry (PDSC) is a convenient, reproducible, and fast method that can be used to determine the oxidative stability of fats and oils [57]. The PDSC oxidation time (\(\tau_{\text{max}}\)) is determined based on the maximum oxidation rate. The obtained values for the PDSC oxidation time of individual oils are presented in Figure 4. The results obtained at the beginning of the testing period showed the shortest average \(\tau_{\text{max}}\) of 23.88 min for WO\({}_{1}\) and the longest (76.55 min) for WO\({}_{\text{ext}}\). The same trend was observed during storage. A significant effect of oil type on the PDSC oxidation time was observed. Furthermore, the storage period has an impact on the oxidation time. For  
Figure 3: The peroxide value 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 in the same sample following the storage time 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 \(\alpha=0.05\). WO\({}_{2}\) and WO\({}_{\text{ref}}\), an especially significant difference was observed in the obtained \(\tau_{\text{max}}\) values between the beginning and the end of the testing period. The rate of oxidation is strongly influenced by the quality of the raw material used to produce the oil, since adverse changes in the finished product often begin in the seeds. The high initial oxidation level of oil extracted from low-quality seeds shortens its shelf life. In addition, the processing conditions and parameters play a key role. Factors such as exposure to light and oxygen, and high temperatures during storage, accelerate oxidation [37; 58]. The rate of oxidation is also affected by the composition of the fatty acids and the presence of components of the non-glycerol fraction with pro- and antioxidant properties [43]. Throughout the storage period, self-extracted oil from the 'Sugar Baby' variety showed the longest \(\tau_{\text{max}}\).