Oil content and main constituents of cactus seed oils Opuntia Ficus Indica of different origin in Morocco

2.1Sample collection

Cactus seeds were collected in 2012 from five areas of cactus plantation in Morocco (Skour Rhamna (32 °35.777428; 55-7 °50.3976), Chtouka Aït Baha (30 °48.7378; 9-9 °10.7454), Tiznit (29 °55.640441,-9°4337.2714), Ait Baamran(30 °48, 7378; 9-9 °10.7454) and Guelmim (28 °36.871858; 3-10 °38.6274).

2.2Sample preparation

Harvesting was done randomly at each site. Fruits were brushed under water, then divided into three lots and peeled by hand. The seeds were separated from the pulp with a juice sieve lower than 1 mm diameter. The two separated fractions were weighed and then the seeds were washed under water and dried in an oven at 40°C for 12 hours. Each batch of seeds was weighted and the size of the seeds ordered by decreasing sieves, type ASM200, from 3.15 mm, 2.00 mm to 1.00 mm, by vibrating the entire column of sieves. The seed weight retained by each sieve was measured.

2.3Oil yield

Determination of oil yield was performed following method DIN EN ISO 659. Twenty grams of ground seeds were placed in a Soxhlet apparatus and extracted with hexane for 8 h. The organic phase was then concentrated under vacuum and dried for 5 min in an oven at 105°C. After determination of the extraction yield, the oil was used for the other analyses.

2.4Analytical methods

Fatty acid composition was determined using method ISO 5508:1990 [9]. Fatty acids were converted to fatty acid methyl esters before analysis by shaking a solution of 60 mg of oil and 3 mL of hexane with 0.3 mL of 2 N methanolic potassium hydroxide. The fatty acids were analyzed by gas chromatograph (Varian CP-3800, Varian Inc.) equipped with a FID. The column used was a CP-Wax 52CB column (30 m×0.25 mm i.d.; Varian Inc., Middelburg, The Netherlands). The carrier gas was helium, and the total gas flow rate was 1 ml/min. The initial column temperature was 170°C, the final temperature 230°C, and the temperature was increased by steps of 4°C/min. The injector and detector temperature was 230°C. Data were processed using Varian Star Workstation v 6.30 (Varian Inc., Walnut Creek, CA, USA). The results were expressed as the relative percentage of each individual fatty acid (FA) present in the sample.

Sterol composition was determined using method ISO 6799:1991 [10]. Sterol composition was determined after trimethylsilylation of the crude sterol fraction using a Varian 3800 instrument equipped with a VF-1 ms column (30 m & 0.25 mm i.d.) and using helium (flow rate 1.6 mL/min) as carrier gas. Column temperature was isothermal at 270°C, injector and detector temperature were 300°C. Injected quantity was 1 uL for each analysis. Data were processed using Varian Star Workstation v 6.30 (Varian Inc., Walnut Creek, CA, USA).

Tocopherol composition was determined using method ISO 9936:2006 [11]. Analysis of tocopherol contents was performed by high performance liquid chromatography (HPLC), using a solution of 250 mg of oil in 25 ml of n-heptane. A Shimadzu CR8A instruments (Champ sur Marne, France) equipped with a C18-Varian column (25 cm×4 mm; Varian Inc., Middelburg, The Netherlands) was used. Detection was performed using a fluorescence detector (excitation wavelength 290 nm, detection wavelength 330 nm). Eluent used was 99:1 isooctane/isopropanol (V/V), flow rate of 1.2 ml/min.

2.5Statistical analysis

Values reported in tables and figures are the means ± SE of three replications. The significance level was set at P = 0.05. Separation of means was performed by Tukey’s test at the 0.05 significance level.

3.1Influence of seed size on oil yield

For studying the influence of the seed size on the oil yield, seed samples from only one origin (Chtouka Aït Baha) were used. Table 1 shows the amount of oil as a function of the seed size. The results reveal a significant (P = 0.05) influence of the seed size on the oil yield during extraction of the seeds. The amount of oil extracted from the seeds ranged 0.3 g/100 g (seed size >1.25 mm) to 9 g/100 g (seed size >2.25 mm). This is the first time that this feature is referred to our knowledge in the case of prickly pear.

3.2Oil content

The economic value of oilseeds is dependent on its oil content. The oil content of 17 samples of cactus seeds from different locations in Morocco is given in Table 2. A relatively small range from 5.4 g/100 g (Skhour Rhamna-1) to 9.9 g/100 g (Chtouka Aït Baha- 6), with a mean value of 7.8% was observed. This is in good agreement with results reported by El Finti et al. [12]. In general, the oil content of the cultivars were found within the range reported for cactus seed cultivars grown in various parts of the world, such as varieties grown in Turkey (5–14.4 g/100 g) [8]. The differences between the oil content of cactus seeds from different locations can be explained by different growing, climatic, and environmental conditions and differences between different papers are also due to different analytical conditions and localities [8]. The oil yield of cactus seeds is much lower than reported for other well-known oilseeds such as argan kernels (50 g/100 g), sesame seeds (54 g/100 g), nigella seeds (34 g/100 g), sunflower (44 g/100 g), soybean seeds (19 g/100 g) and olive fruits (20 g/100 g) [13–15]. This comparison shows that the use of cactus seeds for oil production is not useful from an economical point of view for a large scale industrial processing, but against the background of a meaningful use of the seeds from juice production the oil content of the cactus seeds is interesting for a small scale processing.

3.3Fatty acid composition

The fatty acid (FA) composition of the oil is an essential indicator for its nutritional value [16, 17]. Table 3 shows the fatty acid composition of the 17 cactus oil samples. The main fatty acids of the cactus oil are palmitic acid (11.6–12.4 g/100 g), oleic acid (18.2–22.3 g/100 g) and linoleic acid (60.2–64.6 g/100 g). They represent 95% of all the fatty acids. The variation of the three main fatty acids of the seeds from different locations was relatively low indicating that the location has only a small influence on the composition of the fatty acids. These results differ from those reported by Ramadan and Mörsel [6], Coskuner and Tekin [5] who showed that the fatty acid composition of cactus plants grown at different locations were significantly different from each other. It is well known that the fatty acid composition of cactus seeds is strongly influenced by climatic factors, soil type in which they are grown [6]. Similarly, genetic factors may be involved.

With respect to the fatty acid composition cactus seed oil belongs to the oleic-linoleic acid group. Unsaturated fatty acids amount to about 83.0% , also with a relatively low variation. Linolenic acid is only a minor component with a concentration less than 0.3 g/100 g. The small content of linolenic acid can be used to detect adulteration of cactus oil with other oils rich in linolenic acid such as rapeseed oil and soybean oil.

Other fatty acids such as palmitoleic acid (C16:1), arachidic acid (C20:0), gadoleic acid and behenic acid (C22:0) were found only in small amounts.

3.4Phytosterol composition

Phytosterols are structurally similar to cholesterol and they are found naturally in plant seeds. The composition and the content of these compounds are very useful parameters for detecting adulterations or to proof authenticity, since it can be considered as a fingerprint of the oil. Besides, phytosterols are of major interest due to their antioxidant activity and impact on health [16, 18]. No significant difference was observed as result of the different geographic origin of the cactus seeds (Table 4). The main phytosterol of catus seed oil is β-sitosterol representing 79.1% of the total sterol fraction. Indeed, this phytosterol can also be found in many other vegetable oils, such as soybean oil, sunflower oil or olive oil [13, 19]. It is interesting to note that cactus seed oil is rich in β-sitosterol which has been shown to inhibit the absorption of dietary cholesterol [20]. Other sterols with some importance for human health [21] are campesterol (10.0% of the total sterols), delta-5-avenasterol (5.1%), and stigmasterol (2.5%). The variation of the total amount and the individual sterols is small. Minor sterols were cholesterol (1%), delta-7-stigmasterol (0.8%), and delta-7-avenasterol (0.6%).

3.5Tocopherol composition

Tocopherols are natural occurring antioxidants with some biological activity [22, 23]. A specificity of cactus seed oil is the high content of total tocopherols [8, 13, 24]. The major tocopherol of cactus oil is gamma-tocopherol, representing an average of 90% of total tocopherols, compared with delta-tocopherol (9%) and alpha-tocopherol (1.8%). beta-tocopherol was not found (Table 5). These results are in agreement with the findings of other authors [8]. Cactus seed oil, argan oil and sesame oil are the richest source of γ-tocopherol [25, 26], while alpha-tocopherol is the major compound in olive oil [27, 28]. Tocopherol compounds are also used in food, cosmetics and pharmaceutical industries [29]. Alpha-tocopherol is recommended for human and animal consumption because it has a higher biological activity than other tocopherols, but gamma-tocopherol shows a higher antioxidant capacity as compared to alpha-tocopherol [28].