Chemical composition and bioactive compounds of Cucurbitaceae seeds: Potential sources for new trends of plant oils

melo var.’ Ananas’ seed oil exhibited the highest oxidation induction time when compared to 
the two other seed oil samples. The Cucurbita pepo var. ’Essahli’ seed oil showed an 
oxidation induction time within the range found by Rezig et al. (2018) for the cold pressed 
Cucurbita maxima var. ’Béjaoui’ seed oil. However, the results are lower than those reported 
for the Mashahadi melon (Cucumis melo var. Iranians cv. Mashhadi), Iranian watermelon 
(Citrullus lanatus cv. Fire Fon), and pumpkin (Cucurbita pepo subsp. pepo var. Stryriaca) 
seed oils, which exhibited an oxidative stability ranging between 6h and 9h (Hashemi et al., 
2017). According to Delfan-Hosseini et al. (2017), a high oil stability might be attributed to 
the high values of total polyphenol contents andanti-oxidant activities. 
3.8. Cucurbitaceae seed oils’ free radical scavenging activity 
The antiradical activity by hydrogen-donating antioxidants model is widely used to 
evaluate the antioxidant properties in a relatively short time (Guegouri et al., 2017). To assess 
this ability, the DPPH free radical scavenging assay was used. IC
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of the different 
Cucurbitaceae seed oils were of 52.55 µg/g for the Cucumis melo var. ‘Ananas’ seed oil, 
64.71 µg/g for the Cucurbita pepo var. ‘Essahli’ seed oil and 159.64 µg/g for the Citrullus 
lanatus var. ’Crimson’. The Cucumis melo seed oil showed the highest antioxidant activity, 
followed in descending order by Cucurbita pepo and Citrullus lanatus seed oils. It is fair to 
say that there is a linear correlation between the antioxidant activity of Cucurbitaceae seed 
oils and the stability oil index. The Cucumis melo seed oil, exhibiting the highest antioxidant 
activity, was the most stable against oxidation, followed by Cucurbita pepo and Citrullus 
lanatus seed oils. Similarly, Hashemi et al. (2017) reported the highest antioxidant activity for 
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the pumpkin seed oil ( ̴ 90%) followed by those of Mashhadi melon (between 80% and 90%) 
and Iranian watermelon seed oils ( ̴ 80%). According to Górnaś et al. (2014, 2015), 
watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) and canary melon (Cucumis melo 
L.) seeds and seed oils are a rich source of tocochromanols (tocopherols and tocotrienols) 
amounting to 33.46 ± 1.4 mg/100g and 20.47 ± 0.65 mg/100g for seeds, and 117.87 ± 0.9 
mg/100g oil and 72.10 ± 1.44 mg/100g for seed oils, respectively. The DPPH radical 
scavenging activity mainly depended on the concentration of tocochromanols in these seed 
oils. In fact, according to Górnaś et al. (2015), a significant correlation (r = 0.994) was found 
between the total content of tocochromanols in the seed oils and the DPPH radical scavenging 
activity. Such a result demonstrates that different tocopherol and tocotrienol homologues are 
quenching the DPPH free radicals with similar intensity. It also demonstrates that the 
investigated oils have different tocochromanol compositions and that these components play a 
predominant role in determining the antioxidant characteristics of the seed oils. 
3.9. Thermal behaviour 
The melting curves of the Cucurbitaceae seed oils are illustrated in Fig. 1. When 
heated from - 50°C to 90°C, Cucurbita pepo var. ‘Essahli’ seed oil showed two shoulder 
merging peaks that occurred at -42.27°C and -33.87°C. Yet, the first endothermic transition 
was observed at -38.27°C for the ‘Crismson’ Citrullus lanatus seed oil variety. These 
endothermic transitions were reportedly attributed to the melting of the lowest stability 
polymorphic forms of triacylglycerols (TAG) (e.g., α-TAG). A distinct sharp narrow peak 
occurred at -21.22°C and -26.57°C for the pumpkin and melon seed oils, respectively. 
Melting enthalpy associated with this peak was of 50.23 J/g and 30.57 J/g respectively for 
melon and pumpkin seed oils. However, the watermelon seed oil exhibited a shoulder 
merging peak at -17°C which was referred to a lower melting enthalpy (16.13 J/g) when 
compared to the other seed oil samples. Note that the watermelon seed oil showed a 
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discernible melting thermogram that exhibited a second narrow shoulder peak at -7.15°C. The 
pumpkin and melon seed oils’ melting thermograms exhibited other endothermic transitions 
as well. In fact, the pumpkin seed oil witnessed three endothermic transitions that occurred at 
-15.78°C, -1.35°C, and 2.74°C. For the melon seed oil, only two endothermic transitions 
occurred at -17.8°C and -10°C. A same temperature range (the range of the transition can be 
calculated as temperature difference between T
on
and T
off
) was recorded for the last two 
endothermic transitions with regard to the watermelon seed oil, and for all endothermic 
transitions occurring beyond the typical distinct sharp peak observed in pumpkin and melon 
seed oils. The last transitions could be associated with the melting of the highest stability 
polymorphic forms of TAG, mainly monosaturatedtriacylglycerols (MSTAG). Yet, the 
disaturatedtriacylglycerols (DSTAG) could not be excluded. Nyam et al. (2009) reported that 
vegetable oils with high content of saturated fatty acids (SFA) experienced DSC melting 
profiles at higher regions as compared to oils with a high content of unsaturated fatty acids 
(UFA). The complex endothermic events occurring at higher temperatures were attributed to 
the melting of crystallized lipids and were characterized by multiple overlapping contributions 
as previously observed in vegetable (Tan and Che Man, 2000; Tan and Che Man, 2002) and 
olive oils (Chiavaro et al., 2008; Jiménez Márquez and Beltrán Maza, 2003; Tan and Che 
Man, 2002). No endothermic phenomena were recorded beyond 10°C. Such a feature might 
well confirm the liquid state of the Cucurbitaceae seed oils at room temperature (25°C), and 
the absence of crystals. 
3.10. CIE L*a*b* coordinates 
Cielab coordinates values (L*, a*, b*) of cold pressed Cucurbitaceae seed oils are 
illustrated in Table 6. The Citrullus lanatus var. ‘Crimson’ showed the highest L* value 
(90.93). This proves that the latter is lighter in colour than the melon (Cucumis melo var. 
‘Ananas’) and the pumpkin (Cucurbita pepo var.’Essahli’) seed oils. The Cielab (L*, a*,b*) 
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values of other vegetable oils, such as palm, soybean, sunflower, olive, and corn ranged from 
63.4 to 69.5, 3.8 to 4.4 and 9.2 to 10.4, respectively (Hsu and Yu, 2002). Consequently, the 
Cucurbita pepo and Cucumis melo seed oils’ b* values were higher than those of other 
vegetable oils. This indicates the presence of yellow pigments such as carotenoids.