Oil composition and characterisation of phenolic compounds of Opuntia ficus-indica seeds
Highlights
► The oils of the Opuntia ficus-indica seeds presented high level of unsaturated fatty acids. ► Three isomers of feruloyl-sucrose and a putative sinapoyl-diglycoside were identified. ► The defatted seed wastes still contain components constituting a source for natural foods. ► Seeds of the orange variety are significantly better sources of these bioactive molecules.
Introduction
Opuntia ficus-indica (OFI) belongs to the Opuntiodeae subfamily among the Cactaceae. Several cultivars are found in the Mediterranean basin. They grow also throughout Algeria where they are used mainly for human food, exclusively as fresh fruit, but also for livestock forage and planted as ornamentals or for fencing.
The literature contains much information concerning the cactus pear, describing the chemical composition of the pulp, peel and seeds (El Kossori et al., 1998, Felker et al., 2002, Matsuhiro et al., 2006, Ramadan and Mörsel, 2003a, Ramadan and Mörsel, 2003b), the antioxidant, anti-inflammatory and anti-ulcerogenic properties of the pulp (Ahmed et al., 2005, Galati et al., 2001, Livrea and Tesoriere, 2006, Maataoui et al., 2006) and, more generally, the nutritional significance of Opuntia sp. (Stintzing, Schieber, & Carle, 1999). However, among all this literature, seed has been the less studied part.
The edible part of the fruit contains a relatively large number of seeds, which amount can vary from 30% to 40% on a dry weight basis. These seeds are usually discarded while proper utilisation of these waste products could lead to an important new source of oil and meal (Habibi, Heux, Mahrouz, & Vignon, 2008). OFI seeds were effectively demonstrated to be rich in the health-promoting polyunsaturated fatty acids and vitamins and may potentially be included in animal and human diets (Ramadan & Mörsel, 2003a). Hence, developing high value methods for utilising the by-products seeds are of great importance.
Recently, the research has been directed towards natural antioxidants in the seeds. Indeed, seeds from Opuntia sp. were shown to be rich in polyphenols, flavonoids and tannins, the concentrations of those molecules being always higher than in the fruit pulp (Cardador-Martínez et al., 2011, Morales et al., 2012).
Phenolic compounds are a large group of ubiquitous molecules synthesised by plants under different environmental factors and stress conditions (Boudet, 2007). They form a diverse group that includes phenolic acids, flavonoids and tannins. Phenolic compounds may arise in food plants as glycosides or esters with other natural compounds such as sterols, alcohols, glucosides and hydroxyl fatty acids (Ghasemzadeh & Ghasemzadeh, 2011).
The interest in plant materials containing phenolic compounds are increasing due to their high antioxidant potency, which may offer protection against cancer through the inhibition of oxidative damage, known to be a potential cause of mutation (Khomdram & Singh, 2011). The antioxidative properties of phenolic compounds are a predominant feature of their radical-scavenging capacity (Cotelle, 2001). This activity is attributed to their ability to scavenge free-radical and to chelate metal ions involved in their production. To our knowledge, the phenolic composition of OFI seeds is very badly documented, studies being often limited to global phenolic measurements. To date, only one study identified individual phenolic acids and flavonoids in Opuntia seeds by using HPLC separation coupled to retention time comparison with standards (Tounsi-Saidani et al., 2011). This approach allowed notably to identify catechin, rutin and syringic acid, but was however limited to the identification of molecules for which a commercial standard was available. Determining the phenolic profile of OFI seeds could serve as a basis for their further utilisation in addition to the oil extraction.
This work was carried out on seeds of four OFI varieties (green, yellow, orange and red) growing in Algeria. The main objectives of this comparative study were (i) to determine the fatty acid composition of these seeds, (ii) to quantify phenolic contents and (iii) to characterise the phenolic composition in defatted seeds. For the third point a combined approach of LC–MSn and LC–NMR was used. In addition, this study was also designed to evaluate the antioxidant and reducing power of the defatted seed extracts. This study goes within the framework of the valorization of the OFI of local origin and the findings will provide more details on bioactive substances from cactus seeds which are considered as by-products.
Section snippets
Plant material
The study was conducted on four varieties of OFI chosen according to the presence or the absence of spins, the colour and the shape of the fruits. They have been picked on august 2008 from Bejaia (Algeria). For each variety, a representative sample comprised of 10 ripe berries has been taken.
Fruit preparation
The fruits were washed with running water to remove glochids and impurities, air-dried and hand-peeled. The seeds were separated from the juicy pulp, washed abundantly with distiled water then dried at room
Physico-chemical analysis
The comparative physical parameters of the four OFI fruits analysed in this study are shown in Table 1.
The four OFI fruits were easily distinguished by their colour (green, yellow, orange, red) and also by their shape and the presence of spins.
The fruit properties differed significantly (p ⩽ 0.05) among the varieties. The green variety comprised higher fruit and edible portion (106 and 57 g respectively) followed by the orange and red ones, while the yellow variety produced the smallest fruits (64
Conclusion
This investigation showed that the seeds of the studied varieties had an appreciable amount of oil with high level of unsaturated fatty acids which are healthy benefic. The oil rate and composition varied slightly among the four varieties. The defatted seeds contained total phenolic, flavonoid and tannin levels comparable to already published contents on OFI seeds. The LC–NMR indicated a high complexity in the seed phenolic composition and allowed the identification of hydroxycinnamic acids
Acknowledgement
We thank Cedric Paris for helping with the analyses with LC–MS Orbitrap and Mustapha Bachirbey for his assistance.
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