Comprehensive Evaluation of the Nutritional Quality of Stored Watermelon Seed Oils

The appropriate use of food industry by-products such as watermelon seeds could reduce the problem of food waste, following the “zero waste” concept. Research in recent years suggests that these unused waste products could be a source of nutrients and bioactive compounds. Accordingly, the present study aimed to evaluate the nutritional potential and selected quality parameters of watermelon seed oils. Four commercial oils (three unrefined cold-pressed and one refined pressed) and one self-extracted oil were considered. The oils were analyzed over three months of storage after opening/extraction to determine their fatty acid (FA) composition and distribution, hydrolytic and oxidative stability, and selected health indices. Linoleic acid was the predominant FA, ranging from 52.9% (refined oil) to 62.2% (self-extracted oil). Refined oil demonstrated superior oxidative stability, with the lowest acid value (AV) and peroxide value (PV) throughout the storage period, adhering to the Codex Alimentarius standards. Unrefined oils, particularly WO3, showed significantly higher AVs and PVs after storage, indicating greater susceptibility to hydrolytic and oxidative changes. Health indices were favorable for all oils, with self-extracted oil exhibiting the highest health-promoting index (7.07) and hypocholesterolemic/hypercholesterolemic ratio (7.18). Oxidative stability showed that self-extracted oil had significantly higher stability (76.6 min) than other tested oils, despite having the highest PUFA content. In turn, refinement has a significant effect on the AVs and PVs and the oxidative stability of oil, achieving the lowest PUFA level (53.61%). These results emphasize the potential of watermelon seed oil as a health-promoting product and emphasize the role of production and storage conditions in maintaining its quality.