Abstract

The seeds of pistachio Citrullus mucosopermus Fursa much used in the diet in Côte d’Ivoire, were studied to determine their chemical composition and their nutritional potential. The biochemical parameters of the seeds of Citrullus mucosopermus Fursa characterized are dry matter, ash content, moisture content, carbohydrates, fiber, protein, amino and fatty acids. The proximate analysis of the seeds showed dry matter contents 93.6 ± 2.82 %, moisture 6.40 ± 0.14 %, ash 5.18 ± 0.06 %, carbohydrates 24.94 ± 0.18 % , fibre 9.93 ± % and crude protein 28.46 ± 0.04 %. These proteins have two of the essential amino acids with a high level of lysine whereas serine was the limiting essential amino acid. The extraction yield of the lipids (crude fat) of the seeds was 31.49 ± 0.62 %. Unsaturated fatty acids: oleic acid (1.041 ± 0.002 %), linoleic acid (0.998 ± 0.001 %) and arachidonic acid (0.881 ± 0.001) were measured. Results revealed the seeds of pistachio Citrullus mucosopermus to have great nutritional potentials with regard to their chemical composition therefore, their consumption could contribute to fulfill some food deficiencies in Côte d’Ivoire.

1. Introduction

Cucurbits are among the economically most important vegetable crops worldwide and are grown in both temperate and tropical regions ^{1, 2}. Thus, cucurbits (pistachios) have a diverse range of species and are unconventional oil plants. The seeds are widely used around the world in combination with other foods to meet human protein and fat needs. Citrullus mucosopermus Fursa is highly prized for its transformation into a peanut-like paste used to thicken sauces or extract oil ³. The seeds of Citrullus mucosopermus Fursa have an important social and cultural aspect for the populations which consume them ⁴. These seeds are very important from a nutritional point of view given their richness in mineral salts (sulfur, calcium, potassium, phosphorus, iron, magnesium and zinc) ⁵ and in macronutrients. They can contain up to 36 % protein compared to peanuts which only contain 24 % ⁶. They also have a high content of unsaturated and essential fatty acids, in particular linoleic acid ^{7, 8}.

But despite all of this dietary potential, pistachios are still considered marginal crops for nutritional interventions in Africa and are absent from major research and development programs ⁹. These seeds of great potential in nutrients of important use by the ivorian populations deserve to be analyzed from a biochemical point of view to promote an efficient use in the approach to solving nutritional problems in the country. This justifies this study, the general objective of which is to evaluate the biochemical parameters of the seeds of Citrullus mucosopermus Fursa with a view to their valorization in food.

2. Material and Methods

In this study, the biological (plant) material used was oilseeds of the species Citrullus mucosopermus Fursa. These pistachio seeds were purchased in Abidjan (South, Côte d’Ivoire) and transported in plastic bags to Daloa (Central-West, Côte d’Ivoire) (Figure 1).

For the production of the flour, a quantity of one hundred (100) g of Citrullus mucosopermus Fursa seeds were dried in oven at 60°C for 72h and crushed using a blender type MOULINEX (Optiblind 2000). The sieved grind obtained constituted the flour of Citrullus mucosopermus Fursa. This flour was stored in pre-dried jars for further analysis according to the production diagram in Figure 2.

The standard analytical procedures for food analysis were adopted for the determination of the moisture content, crude protein, crude fiber, percentage lipids, carbohydrate, ash and calorific value

The method used is that of AOAC ¹⁰ whose principle is based on the dehydration by drying in the oven of the samples until obtaining a constant mass. A quantity of five (5) grams of the pistachio flour sample was weighed using a balance (Denver, model ABT 320 - 4M) in a crucible of known mass (M0). The crucible + flour of mass M1 was placed in an oven (MEMMERT 854 SCHWABACH, Germany) at 105°C (± 2°C) for 24 hours. After cooling in a desiccator (GLASWERK WERTHEIM, 2 bars), the crucible was weighed again (M2). Three tests were performed and the dry matter content was determined from the following formula:

(1)

M₁: mass of crucible + 5g of sample

M₂: mass of crucible + 5g of sample placed in an oven (105 ± 2°C) for 24h

ME₀: mass of sample (5 g).

The ash content was determined according to the AOAC ¹⁰ method. A quantity of five (5) grams of the flour sample was weighed with a balance (Denver, model ABT 320 - 4M) into a porcelain crucible of known mass (M0). The whole assembly (crucible + product) was heated in a furnace (VELP Scientifica, Spain) at 550 °C (± 2°C) for 24 hours. After cooling in a desiccator (GLASWERK WERTHEIM, 2 bars), the crucible containing the ashes was weighed and noted (M1). The tests were carried out in triplicate. The ash content was determined from the formula :

(2)

M₁: mass of crucible + ash (g) of sample placed in a furnase (550 ± 2°C) for 24h

M₀: mass of empty crucible

ME: mass of sample (5 g)

From the pulverized sample, 3.00 g was used for determining the crude lipid by extracting the lipid from it for 5 h with (60 to 80°C) petroleum ether in a soxhlet extractor ¹¹. Triplicate samples were extracted to obtain triplicate values that were later averaged.

To analyze fatty acids of samples, the HPLC chromatography method was used. The HPLC WATTERS ALLIANCE Chromatography equipped with column C18 or equivalent, wavelength of 262 nm, mobile phase (Methanol/Water (50:50)) and flow rate of 1.2 ml min^-1.

Total protein was determined by the Kjedahl method. 0.5 g of the sample was weighed in triplicate into a filter paper and put into a Kjedahl flask, 8 to 10 cm³ of concentrated H₂SO₄ were added and then digested in a fume cupboard until the solution became colourless. Distillation was carried out with about 10 cm³ of 40 % NaOH solution. The condenser tip was dipped into a conical flask containing 5 cm³ of 4 % boric acid in a mixed indicator till the boric acid solution turned green. Titration was done in the receiver flaskwith 0.01 M HCl until the solution turned red ¹¹. The crude protein was calculated by multiplying the estimated nitrogen by 6.25 and the amount of protein in each sample was obtained. To identify the amino acids after preparation of pistachio and standard solutions prepared, the samples were injected into HPLC WATERS ALLIANCE. The conditions of HPLC was determined as follows: column: C18 or equivalent, Wavelength of 254 nanometer, mobile phase (Methanol/Water (50:50)) and Flow Rate: 1.2 ml min^-1.

From the pounded sample, 3.00 g were used in triplicates for estimating the crude fiber by acid and alkaline digestion methods using 20 % H₂SO₄ and 20 % NaOH solutions ¹¹.

The carbohydrate content was calculated using the following formula: Available carbohydrate (%), = 100 – [protein (%) + Ash (%) + Fibre (%) + Crude Fat (%)] ¹².

The caloric value was calculated in kilocalories per 100 g (kcal/100 g) by multiplying the crude fat, protein and carbohydrate values by Atwater factors of 9, 4 and 4 respectively.

The pH values of the samples were determined by suspending 10 % W/V of the sample in distilled water in each case. It was then thoroughly mixed in a 100 cm³ beaker, stirred and the pH was taken. This was repeated three times and the average calculated ¹³.

All measurements were performed in triplicate. Statistical analyzes of the data were performed using STATISTICA 7 software (Statsoft Inc, Tulsa-USA Headquarters). This software was also used to calculate mean values and standard deviations of the trials.

3. Results and Discussion

Table 1 shows the proximate biochemical composition of pistachio Citrullus mucosopermus seeds which showed that the seeds are good sources of crude fat (31.49 ± 0.62 % dw), protein (28.46 ± 0.04 % dw), fiber (9.93 ± 0.08 % dw) and carbohydrate (24.94 ± 0.18 % dw).

From the same Table 1, the moisture content of the seed was found to be 6.40 ± 0.14 % dw and the ash content was 5.18 ± 0.06 % dw. The pH of Citrullus mucosopermus seed was 6.15 ± 0.07.

Table 2 reveals the amino acid profile (%) of C. mucosopermus. Of the total 4 types of amino acids estimated, the alanine was 0.506 ± 0.004 %, leucine was 0.686 ± 0.005 % , lysine was 9.607 ± 0.012 % and serine 0.189 ± 0.004 % are in the least quantity. Among the four amino acids determined, leucine and lysine are essential aminoacids compare to alanine and serine.

Table 3 highlights the fatty acid profile (%) of C. mucosopermus seeds. Thus, of the total 5 types of fatty acids estimated, the oleic acid (1.041 ± 0.002 %), palmitic acid (1.167 ± 0.012) and stearic acid (1.369 ± 0.011) are the values that are greater than or equal to 1% whereas arachidonic acid (0.881 ± 0.001) and linoleic acid (0.998 ± 0.001) are less than 1 %. It is important to note that arachidonic, linoleic and oleic fatty acids are essential unsaturated fatty acids.

The result obtained from the biochemical analysis carried out on the pistachio C. mucosopermus in this study confirmed that the biochemical, amino acid and fatty acid contents were found to be represented.

In the present study biochemical properties of seeds from fruits of pistachio were analyzed. The crude fat, protein, fiber, carbohydrates and ash contents of seeds were found to be 31.49 %, 28.46 %, 9.93 %, 24.94 %, 5.18 % respectively. The present work showed some what similar data for protein and fat content to those reported by Anwar et al. ¹⁴.

The crude fat was considerably high (31.49 %), a value higher than the 15.48 % reported for Parkia biglobosa seeds ¹⁵, than the 16.01 % reported for Casiatora seeds by Adamu et al. ¹⁶ and than the results reported in Acacia nilotica fruit as reported by Bwai et al. ¹⁷. The high fat content suggests that Citrullus mucosopermus seeds can be classified as an oil-rich seed. Thus, the main fatty acid component found in pistachio kernels was stearic acid, followed by palmitic acid, oleic acid, linoleic acid and arachidonic acid. In addition, the three: arachidonic, oleic and linoleic are unsaturated fatty acids which are considered to have a good nutritional value because it is more reactive and naturally antioxidants in the body ¹⁸. This result is agree with those reported by Atri et al. ¹⁹ and Maftoun et al. ²⁰ in their studies. This gives a nutritional and medicinal importance for these plant seeds. Indeed, linoleic acid has a beneficial role for the human body ²¹. The major saturated fatty acid is the stearic acid. Results show that C. mucosopermus seeds are rich with unsaturated fatty acids. Moreover the monounsaturated fatty acid has an important physiological role ²². These results indicate that C. mucosopermus seed oils could be a good source of table oil. The content of linoleic acid is of particular interest especially in the fight against atherosclerosis ²³. Present results are also similar to that of previous study on Citrullus and Cucurbita pepo seed oil which was found to contain mostly palmitic, stearic, oleic and linoleic acids, with linoleic acid as the most abundant ^{23, 24, 25}.

The protein content was 28.46 %, which was higher than 24.69 and 20 % obtained for unfermented groundnut and sesame seed by Ojokoh and Lawal ²⁶ and Nzikou et al. ²⁷. respectively. This value was also higher than 27.9 % crude protein reported for Parkia biglobosa seeds by Elemo et al. ¹⁵ and the 21.0 % obtained for Pigeon pea ²⁸. This protein value obtained from this study indicates that it can contribute to the daily human protein requirements based on 23 -56g as stipulated ²⁹.

The amino acid profiles of C. mucosopermus seeds flour are presented in Tables 2. The sample contains. The essential and non-essential amino acids for C. mucosopermus determined in this study were 50 % and 50 %, respectively. The C. mucosopermus contained two essential amino acids, with the highest value of lysine (9.607 %) whereas the leucine was in low quantity (0.686 %). The non-essential amino acids include : alanine and serine. The amino acid profile of the studied sample suggests that its protein is of high nutritive value which can be exploited by the feeds industries for feeds formulations.

The carbohydrate content obtained was 24.94 % which was lower compared to 29.72 % reported for Acacia nilotica seeds ³⁰. But this value of carbohydrate was considerably higher than the 8.2 ± 0.32 % reported for Acacia sieberina seeds by Abubakar et al. ³¹. This value of carbohydrate content with protein and fat content obtained make the seeds of Citrullus mucosopermus a better source of energy (497.01 ± 2.75 kCal) than the most of the report seeds. The amount of carbohydrate in pistachios, as in other nuts, is moderate, but pistachios are rich in fiber.

Fiber content is important because epidemiological and clinical studies have consistently demonstrated that fiber intake is associated with weight loss ³², diabetes and some types of cancer ³³. Moreover, pistachios have a low glycaemic index, which contributes to maintaining satiety longer and lowering postprandial blood glucose concentrations ^{34, 35}. As for fibers, which are recognised for their crucial role in the proper functioning of the intestinal transit, they constitute an important fraction of C. mucosopermus. Its consumption represents an asset in a healthy and balanced diet. Kouamé et al. ³⁶ reported that a high-fiber diet reduces the daily insulin requirement of diabetic patients and stabilises their glycaemic profile. Thus the fibre contained in C. mucosopermus could be advised to diabetic patients by decreasing the rate of glucose absorption and/or delaying gastric emptying. It could also contribute to the prevention of colon cancer by binding to the cancer-causing chemicals, driving them away from from the cells lining the colon ³⁷.

The physicochemical composition of the seeds of Citrullus mucosopermus Fursa indicated that the seeds have a low moisture (6.40 ± 0.14 %) content and a high dry matter content (93.60 ± 2.82 %). This moisture valus was low in comparison with that of Casiatora seeds (11.50 %) reported by Adamu et al. ¹⁶. The low moisture content will give long shelf life to C. mucosopermus seed flour. The high dry matter content of C. mucosopermus Fursa seeds could be explained by the fact that they are oilseed cucurbites. Oilseed cucurbites are very rich in fat and protein, but they have a low moisture content in the dried state. Low moisture content does not appear to influence the enzymatic and microbial degradation process. Therefore low moisture content as saw in the sample is an evidence that this specimen may not be more inclined to decay, since nourishments with high dampness substance are more inclined to perishability ³⁸. According to Soro et al. ³⁹, a low moisture content of less than 12 % would allow a better conservation of flours. Therefore, it might be profitable in perspective of the specimen timeframe of realistic usability. Indeed, according to Siddiqui and Chowdhury ⁴⁰ moisture is an important parameter that significantly affects the shelf life and and development of microbial contaminants in flour.

The ash content is 5.18 %. This assumes that these seeds have a good source of important minerals. This ash level is lower than those obtained by N'Dri ⁴¹ in his research on akpi almonds which is 7.32g/100g dw and those of 7.45 % reported for Cucurbita species ⁴². This value was higher than the 2.48 ± 0.18 % reported for Cumis melo variant by Adekunle and Oluwo ⁴³. Ash is a residue of mineral compounds that persists after the incineration of organic substances of animal or vegetable origin.

The pH is a very important factor. Indeed, the pH of the C. mucosopermus Fursa seeds obtained was 6.15 and is higher compared to those reported Citrullus lanatus (5.18) and Cucumis sativus (5.75) by Olayinka and Etejere ⁴⁴. This pH is favourable to the enzymatic activity of these seeds. The slightly acidic pH value showed clear indications that the seeds used for the study were matured.

4. Conclusion

The results of the present study showed that C. mucosopermus Fursa seeds contained appreciable amounts of fiber, protein and crude fat and thus can be consumed for dietary purposes. The oil, extracted from the C. mucosopermus Fursa seeds, revealed the presence of high amount of oleic, palmitic, linoleic and stearic acid as well as it exhibited low levels of saturated fatty acids, suggesting that C. mucosopermus Fursa oil can be used as a diluent with other edible oils to enhance their essential fatty acid content i.e. linoleic acid and make its potential food uses for health benefits. Additional research on the detailed physicochemical and bioactive properties of C. mucosopermus Fursa seed and seed oil is crucial to explore their commercial and functional foods applications.

References