# Comprehensive Evaluation of the Nutritional Quality of Stored Watermelon Seed Oils
###### Abstract  
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 WO\({}_{3}\), 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/hypercholesterolric 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. w +
Footnote †: journal: applied sciences  
0000-0001-6000-0000]B. A.  
Watermelon is typically consumed as fresh fruit or processed into other products, such as juices, nects, jellies, concentrates, and jams, while the seeds and rind are usually discarded as waste. By utilizing these by-products, both environmental and economic benefits can be achieved, promoting sustainable practices and a circular economy in line with the concept of \"zero\" or \"less\" waste [4]. Consequently, an increasing amount of research is focusing on the valuable properties of watermelon seeds and rind and their potential for further use. Studies suggest that watermelon rind may be a source of bioactive compounds, such as phenolic acids, lycopene, and citruline [5; 6], or a source of pectin [7]. The literature indicates that watermelon seeds are highly nutritious. They are a source of protein, unsaturated fatty acids, vitamins C and B, and significant amounts of minerals, primarily phosphorus, magnesium, manganese, and zinc, as well as potassium and calcium [8; 9; 10]. They also contain bioactive compounds such as phenolic compounds and flavonoids [10; 11]. Moreover, studies highlight their antimicrobial, antifungal, antidiabetic, and antihyperlipidemic properties [1; 12; 13]. The nutritional value of watermelon seeds is further enhanced by their favorable amino acid profile. Among the amino acids, watermelon seed proteins contain the highest amounts of glutamic acid and arginine and are also a source of tryptophan and lysine [14; 15]. In Arab and Asian regions, roasted and salted watermelon seeds are consumed as snacks [16]. They are also used as a topping for bread, cakes, confectionery, sweets, and snacks [17]. Fermented seeds have also been used as a flavor enhancer in sauces and soups [18]. Watermelon seed oil is amber, and its taste and aroma are described as distinctive, resembling that of nuts [19]. It is a good source of essential fatty acids, thiamine, riboflavin, vitamins A and E, and minerals, mainly iron, magnesium, copper, phosphorus, potassium, and manganese [20]. Additionally, it contains antioxidants, including tocopherools, polyphenic compounds, and carotenoids [21].