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

Citrullus lanatus and the Cucumis melo seed oils, was the predominant sterol, followed by the 
Δ 5-Avenasterol. The Δ 5-Avenasterol content accounted for 1875.01 mg/kg, 1319.21 mg/kg 
and 1533.11 mg/kg, in pumpkin, watermelon, and melon seed oils, respectively. Thus, β-
sitosterol and Δ 5-Avenasterol were the major sterols and together they made up 78.32%, 
85.98%, and 92.63% of pumpkin, watermelon and melon seed oils. It is note worthy to 
mention that the β-sitosterol was also the sterol marker in Cucurbita maxima var. ’Béjaoui’, 
Cucurbita pepo L., Kalahari melon (Citrullus lanatus), Bittermelon (Momordica Charantia 
L.), Cucumis melo L. and watermelon (Citrullus lanatus (Thunb.) Matsum. &Nakai) seed oils, 
all of which belong to the same botanical family, namely Cucurbitaceae (Veronezi and Jorge, 
2018; Górnaś and Rudzińska, 2016; Rezig et al., 2012; Nyam et al., 2009).The percentages of 
Δ 5- sterols and Δ 7- sterols ranged, respectively, between 30.14% for the Cucumis melo var. 
‘Ananas’ and 39.2% for the Cucurbita pepo var. ‘Essahli’ seed oils, and between 2.95% for 
the Cucumis melo var. ‘Ananas’ and 11.94% for the Cucurbita pepo var. ‘Essahli’ seed oils. 
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The cholesterol content in pumpkin seed oil (7.76 mg/kg) was higher than those observed in 
watermelon and melon seed oils but lower than the one found in pumpkin (Cucurbita maxima 
var. ‘Béjaoui’) seed oil (25.35 mg/100g) (Rezig et al., 2012).
3.6. Phenolic compounds 
Phenolic compounds are part of the unsaponifiable matter and are known as minor oil 
components. These bioactive compounds play a decisive role thanks to their positive features 
such as flavour, shelf life and resistance against oxidation. Table 5 illustrates a list of the 
detected phenolic compounds and their concentrations in the Cucurbitaceae seed oils.
As compared to authentic standards profiles, an HPLC analysis of phenolic 
compounds in the ‘Ananas’ melon seed oil allowed to identify five phenolic compounds. 
There were three phenolic acids (caffeic, vanillic and ferulic), one secoiridoid (oleuropein) 
and one lignan (pinoresinol). The main identified phenolic compounds were phenolic acids 
(139.12 µg/g) followed by lignans (10.88 µg/g) and secoiridoids (2.31 ± 0.22 µg/g). These 
phenolic compounds greatly determine some of the oil’s features and can somehow affect its 
astringency. They also bear some biological properties that account for their antioxidant and 
antiradical scavenging activities (Ahmad et al., 2011). Recent studies have shown that 
polyphenols are being added to foodstuffs, as natural antioxidants, in order to prevent off-
flavour development and to achieve stabilisation (Mallek-Ayadi et al., 2018).
In ‘Essahli’ pumpkin seed oil, phenolic acids (caffeic and vanillic) and lignans 
(pinoresinol) were also identified. Note that pinoresinol was abundant (7.92 
± 0.81 µg/g) then 
quantitatively followed by phenolic acids as 2.33 µg/g.
The ‘Crimson’ watermelon seed oil, however, witnessed the lowest phenolic 
compound content. In fact, only two classes were identified, namely phenolic acids and 
lignans, represented by caffeic acid (1.33 µg/g) and pinoresinol (1.02 µg/g).
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Similarly, three phenolic acids were identified in the ‘Ananas’ melon seed oil, while 
Nyam et al. (2009) recognised other phenolic acids such as gallic acid, protocatechuic acid, p-
hydroxybenzoic acid, syringic acid and p-coumaric acid in the Bittermelon and Kalahari 
melon seed oils. In fact, vanillic acid was the predominant phenolic acid accounting for 0.74 
mg/100g and 0.55 mg/100g respectively in the Bittermelon and Kalahari melon seed oils. 
Apart from caffeic acid, Mallek-Ayadi et al. (2018) identified three other phenolic acids: 
gallic, protocatechuic and rosmarinic acids in the ‘Maazoun’ melon seed oil. Nevertheless, the 
‘Ananas’ melon seed oil witnessed a lower amount of caffeic acid when compared to those 
found by Mallek-Ayadi et al. (2018) and Nyam et al. (2009). It also witnessed a higher 
amount of ferulic acid than that reported by Nyam et al. (2009). The ‘Ananas’ melon seed oil 
also contained oleuropein, which is the major phenolic compound in the olive oil and leaves 
with a high antioxidant capacity (Rodriguez-Morato et al., 2015). Oleuropein was identically 
detected in the ‘Maazoun’ melon seed oil with an amount (1.65 µg/g) lower than that found in 
our study.Attention must be paid to the fact that research papers about phenolic compounds in 
the pumpkin and watermelon oils are very scarce in the literature. In the present study, the 
HPLC analysis identified only two phenolic acids (vanillic and caffeic acids) in ‘Essahli’ 
pumpkin seed oil. These acids were also predominant in the Cucurbita pepo L. seed oil with 
other phenolics such as gallic acid, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, 
p-coumaric acid and ferulic acid (Nyam et al., 2009). In the Cucurbita maxima var. ‘Béjaoui’ 
seed oil, vanillic and caffeic acids were also identified in higher amounts in comparison to 
those found in our study (2.46 mg/100g vs 3.88 mg/100g) with protocatechuic acid, syringic 
acid, p-coumaric acid and ferulic acid. An unidentified peak was detected at a retention time 
of 29.2 min and a M/Z (M-H
-
) of 295.2 (Rezig et al., 2012). 
3.7. Oxidative stability 
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The result of the Rancimat test is illustrated in Table 2. The stability of the pumpkin 
seed oil expressed as the oxidation induction time was about 3.8h, 3.74h and 1.72h 
respectively for the melon, pumpkin and watermelon seed oils. Statistical analyses 
demonstrated significant differences between seed oils samples. The cold-pressed Cucumis