**1. Introduction**

The melon fruit (*Cucumis melo* L.) belongs to the *Cucurbitaceae* family, and it is grown in tropical and subtropical regions of the world. Global melon production has continuously risen in the last decade, reaching the current annual production of about 31.2 × 10<sup>6</sup> tons. Melon processing in the industry generates large quantities of by-products that are usually discarded. Within those by-products, melon seeds account for 10% of total melon weight [1]. However, melon seeds are not considered as waste in all regions of the world. In some Arabian countries, they are roasted and directly consumed [2], and in India they are dried and used to add flavor to traditional dishes and desserts [3]. This traditional use of seeds is not applied to melon production in Europe, where melon seeds are rarely used in the food chain.

Previous studies carried out mainly on melons grown in some developing countries confirmed the interest in melon seeds as a possible functional ingredient [3–5]. In this regard, the nutritional composition of melon-seed cultivars grown in di fferent countries, including Egypt [6], Brazil [7–9], Tunisia [10], and China [11], was studied. With regard to its nutritional content, melon seeds were

found to be a rich source of proteins (14.9–27.4%), lipids (25.7–30.8%), fiber (19.0–25.3%), carbohydrates (20.8–24.8%), and ashes (3.2–4.8%) [5,8,10]. Within proteins, melon seeds contain essential amino acids such as phenylalanine, isoleucine, and leucine [7,8]. However, results show important di fferences in the proximate and chemical composition of seeds depending on the studied melon cultivar. This is the case of Chinese hybrid ChunLi, which shows protein percentages of up to 29.9% and small concentrations of carbohydrates (5.6%) [11].

The oil content of melon seeds and the current demand for new vegetable oils have led to an excellent opportunity for the industrial production of vegetable oil from melon seeds. The selection of an appropriate extraction method is crucial for producing high-quality oils. Most previous research studied melon-seed oils extracted using solvents [5,7,9–12]. However, the use of solvents, mainly hexane, reduces oil quality and avoid their classification as virgin oils. On the other hand, the most modern method for seed-oil extraction consists of the use of supercritical fluids [3], but the production costs of this method are high, reducing its viability for industrial production. Within this framework, cold extraction based on the use of mechanical presses for oil extraction from seeds and nuts has resulted in the production of high-quality oils at a ffordable prices, encouraging its use for commercial purposes [13–16].

Oils from melon seeds are mainly composed of unsaturated fatty acids, where linoleic and oleic acids are predominant. Most studies reported a content of linoleic acid ranging from 64.1% to 69.0%, and oleic acid from 13.7% to 19.4% [8,10,17]. However, these percentages may di ffer in some cultivars whit lower levels in linoleic acid and higher in oleic acid, like those reported by da Silva and Jorge [9], where 59.0% of linoleic acid and 26.4% of oleic acid were found in an undetermined cultivar, or those obtained by De Mello, Bora, and Narain [7], where similar percentages were found in the Daimiel cultivar (cv.). Regarding saturated fatty acids, melon-seed oil generally shows low percentages, ranging from 8.7% to 10.2% [7–10,17], although in some cultivars like ChunLi, a concentration of palmitic acid of up to 23.9% was reported [11].

Beyond the well-known beneficial e ffects of polyunsaturated oils for human health [18], analysis of bioactive compounds in oils is crucial. Within minor components, significant amounts of tocopherols were reported in melon-seed oils. Tocopherols and tocotrienols are part of vitamin E, a potent antioxidant that was reported to protect against cancer and bone, cardiovascular, eye, nephrological, and neurological diseases [19]. In previous studies, the average total tocopherol content in melon-seed oils was variable, with amounts between 270 and 720 mg/kg [9,10,20]. γ-tocopherol was the main tocopherol isoform described in melon oils, while δ-tocopherol was reported in the Canary melon and in cv. Maazoun, but not in other cultivars [9]. For α-tocopherol, which is the most active homologous in humans, minor concentrations (22.0–68.8 mg/kg) were reported [9,10]. With regard to tocotrienols, little information exists, as they account for roughly 1% of the total studies on vitamin E [21]. The only information about tocotrienols in melon oil was provided by Górna´s, Soliven, and Segli n, a [20], who reported a total concentration of 13.7 mg/kg, with the dominance of γ-tocotrienol.

Considering the high variability of the results described in the di fferent analyzed cultivars, further analysis of the main melon cultivars grown in Europe is needed, encouraging the return of these agroindustrial residues into the food chain. In this study, nine di fferent *C. melo* cultivars, including three types of traditional Spanish cultivar Piel de Sapo, are evaluated. Furthermore, two pressure-extraction methods were used, and the obtained results were compared regarding their availability for the industrial extraction of high-quality oils.

### **2. Materials and Methods**
