*3.1. Oil-Extraction Yield*

First, for a clearer idea about oil yield, it is important to consider seed parts that do not contain a significant composition in oil, which may contribute to reducing the yield value. In this sense, seed peel is mainly composed of carbohydrates, especially fiber [10]. The melon-seed peel constitutes about 30–40/100 g of seed weight. Significant differences were found between cultivars (Table 1). Cv. Piel de Sapo grown under conventional production (not organic) showed the lowest proportion of seed peel (30.65/100 g) followed by the organic Piel de Sapo. Cv. Piel de Sapo grown under PGI conditions showed one of the highest proportions of seed peel (39.00/100 g).


**Table 1.** Proportion of seed peels and oil-extraction yields obtained with screw press in selected melon cultivars.PGI,ProtectedGeographicalIndication.

Mean ± standard deviation; a–g different letters in same column represent significant differences, *p* < 0.05 between samples.

Melon seeds were identified as a good source of oil, with percentages of lipids about 30.7%–32.3% [8–10]. Oil yields from melon seeds were high enough to encourage their use for oil-production purposes when a

screw press is used (Table 1). Obtained yields using the screw press were statistically different depending on the considered cultivar. Cvs. Piñonet and Piel de Sapo PGI showed the highest values, 29.90 and 26.23 g per 100 g, respectively. The lowest values were reported in the Arizo cultivar (16.95/100 g seeds). Negative but not statistically significant (*r* = −0.576, *p* = 0.64) correlation was found between peel proportion and oil yield obtained with the screw press.

### *3.2. Oil-Extraction Methods, Oil Quality, and Color*

To evaluate the di fferences regarding extraction systems, seeds from cv. Piel de Sapo PGI were subjected to oil extraction with two presses, a hydraulic and a screw press. Extraction with the hydraulic press was performed under room temperature, while extraction with the screw press requires previous heating to obtain optimal performance. The data regarding oil yield, regulated quality (acidity and peroxide index) and color of the oils obtained are shown in Table 2. The pressure system selected for oil extraction had significant influence on oil quality and yield. Oil extraction in cv. Piel de Sapo PGI using the screw press resulted in an oil yield of 26.23/100 g, while extraction with the hydraulic press was almost four times smaller (6.80/100 g). This low yield makes the hydraulic press unsuitable for obtaining an economic benefit. Therefore, for analysis of the profile of fatty acids and vitamin E for the rest of the cultivars, only oils extracted with the screw press were used, since this could be the most appropriate method for obtaining commercial oils in the industry.

**Table 2.** Oil yield, parameters of regulated quality, and color of melon-seed oils (cv. Piel de Sapo PGI) according to extraction method.


Mean ± standard deviation; a,b different letters in the same line represent significant differences *p* < 0.05 between samples.

Regarding oil quality, Codex Alimentarius [26] does not have specific regulation for melon-oil quality standards. Results showed that oils obtained with the hydraulic press were of slightly better quality than that of oils obtained with the screw press. In all cases, the values in oils obtained using pressure systems were significantly lower than the values reported for melon-seed oils obtained using solvent extraction [7,11].

Melon oils show a light yellow color. Nevertheless, CIELAB color parameters showed di fferences attending to the used extraction method. Oils obtained with the screw press showed more intense yellow colors, with higher values for the b\* parameter (Table 2). Oil extraction using the screw press requires high temperatures applied on the barrel to ensure proper oil extraction [27]. The processing temperature of screw press compared to room temperature used in hydraulic extraction may a ffect oil pigment content [28]. Previous studies on plant oils showed that lutein, which provides the yellow color to oils, is more resistant to high temperatures than other pigments are, such as chlorophylls [29]. Furthermore, some studies even reported an increase in the content of lutein after the thermal processing of food products due to the inactivation of enzymes responsible for oxidizing carotenoids [30]. Although the total content of carotenoids in melon oil was reported to be low [9], the balance of carotenoids in melon oil could be the reason for the observed change of color in melon oils depending on the extraction method.
