# Comprehensive Evaluation of the Nutritional Quality of Stored Watermelon Seed Oils
## 3 Results and Discussion
### Determination of Peroxide Value  
The peroxide value (PV) indicates the degree of the fat's rancidity, determines the degree of oxidative changes occurring in fats, and is proportional to the content of the primary fat oxidation products, i.e., peroxides. The fatty acid composition plays a crucial role in determining the rate of oxidative changes in oils, as oils with a high PUFA content oxidize more rapidly [51]. Internal factors affecting the rate of oxidation include the presence of natural pro-oxidants and antioxidants in the oil, while external factors that are important to the oxidation process include the conditions and parameters of the technological processes used, access to oxygen and light, and the storage temperature of the finished product [37; 52]. The Codex Alimentarius informs that the maximum PV of cold-pressed vegetable oils is 15 mEq O\({}_{2}\)/kg fat. In contrast, for refined vegetable oils, this result should not exceed 10 mEq O\({}_{2}\)/kg fat [53]. The average PV of the studied oils, obtained during the three-month storage period, met the requirements specified by the Codex Alimentarius (Figure 3), except for WO\({}_{3}\), which met the requirement only at the beginning of the experimental period. WO\({}_{3}\), with the highest PV among the tested oils (16.64 mEq O\({}_{2}\)/kg fat), was probably obtained from damaged or poor-quality seeds, or the pressing process was carried out in inappropriate conditions. The fat in damaged seeds oxidizes much faster [31], which may explain the high PV for this oil obtained in the first month of the study. The increase in the PV of cold-pressed oils may also result from the presence of pro-oxidant substances in the oils [43]. For commercial oils, the first determinations were made immediately after purchase. However, we do not know how long the oil was stored from the moment of production to the moment of purchase. In the case of oil extracted from watermelon seeds of the 'Sugar Baby' variety, the first determinations of PV were made for freshly obtained oil. It might seem that the initially determined PV would be very low. However, the results obtained for WO\({}_{\text{ext}}\) were very similar to those obtained for WO\({}_{1}\) and WO\({}_{2}\). The increased PV may be due to the effect of oxidation processes related to extraction or may result from a lack of sufficient protection against oxidation immediately after the extraction process [54]. It could also be assumed that the seeds used for the extraction process were not of the best quality. [PERSON] et al. [47] obtained watermelon seed oil in laboratory conditions using the cold-pressing method and reported a PV of 2.98 mEq O\({}_{2}\)/kg fat. [PERSON] et al. [20] determined the PV for cold-pressed watermelon seed oil derived from two varieties, finding values of 3.8 and 4.0 mEq O\({}_{2}\)/kg fat. [PERSON] et al. [32] analyzed cold-pressed watermelon seed oil purchased from a grocery store, reporting a PV of 10.7 mEq O\({}_{2}\)/kg fat. In the present study, cold-pressed oils from unrefined watermelon seeds had PVs ranging from 5.39 to 12.41 mEq O\({}_{2}\)/kg fat immediately after purchase. Comparing the above results, it can be seen that the values determined for directly pressed oils under laboratory conditions are lower than those determined for commercially pressed oils. This can be explained by the fact that, during the storage process, oxidative changes occur in commercial oils. The differences in the obtained results may also be a consequence of variations in seed quality, which strongly affect the properties of the oils. [PERSON] et al. [55] used the Soxhlet extraction method with petroleum ether as the solvent, obtaining a PV of 2.8 mEq O\({}_{2}\)/kg fat for tested watermelon seed oil, much lower than the values reported by [PERSON] et al. [56], who used hexane and reported \(\sim\)12 mEq O\({}_{2}\)/kg fat. The PV of WO\({}_{\text{ext}}\) (6.24 meq O\({}_{2}\)/kg fat) was higher than the value obtained by [PERSON] et al. [56], but lower than that obtained by [PERSON] et al. [55].