Physicochemical Characterization of Detarium microcarpum Seeds from Northern Benin

The objective of this work is to determine the physicochemical characteristics of the Detarium microcarpum seeds from North Benin, specially the proximate composition, colour, minerals, and antinutritional factors using standard analytical methods. The results show that the contents of moisture, protein, total sugars, lipid, crude fiber, and ash ranged, respectively, from 10.85 to 14.69%, from 13.54 to 17.82%, from 19.69 to 32.04%, from 8.68 to 11.90%, from 19.78 to 34.24%, and from 1.5 to 3.49%. The luminance (l∗), red saturation (a∗), and yellow saturation (b∗) have, respectively, ranged from 60.45 to 67.64, from 5.44 to 8.86, and from 8.24 to 9.28. Seeds contain interesting contents of potassium, calcium, magnesium, manganese, sodium, and iron; they have, respectively, varied from 6141.88 to 12305.16 mg/kg, from 1254.47 to 2168.62 mg/kg, from 1298.87 to 2533.06 mg/kg, from 75.18 to 307.23 mg/kg, from 53.52 to 136.19 mg/kg, and from 28.46 to 181.42 mg/kg. The investigation of antinutritional factors indicates the presence of oxalates, phytates, total phenolic compounds, and saponins with contents that have varied, respectively, from 1.01 to 2.36%, from 0.37 to 0.87%, from 3.13 to 7.61%, and from 1.35 to 4.59%. On average, the physicochemical characteristics of the Sudanian and Sudano-Guinean zones are similar, except for total sugar content.


Introduction
In the world, there is an urgent need for new food plants or new sources to meet the nutritional needs of the evergrowing populations. Indeed, according to the Food and Agriculture Organization of the United Nations (FAO), the prevalence rate of undernourishment is 9.9% in the world, 21% in Africa [1], and 7.4% in Benin [2].
Food insecurity persists in most African countries due to the increase in demographic pressure, the insufficiency of basic cereals [3]. The consequences of this situation are mainly hunger, malnutrition, and the increase of foodrelated diseases despite the availability of certain plant resources [4,5]. Therefore, utilizing plant resources that produce edible fruits that are not exploited or not used optimally and available locally for food processing in developing countries can be an approach to achieve food security [6]. Indeed, nontimber forest products (NTFPs) for food provide food security, which contribute to household economic development [7,8]. These are wild or cultivated plants that provide economic and food survival support for local populations [9]. According to the World Health Organization (WHO), wild plants are involved in meeting the health and dietary needs of 80% of people living in developing countries [10]. Detarium microcarpum Guill. & Perr. (Fabaceae-Caesalpinioideae) is one of these plant resources, present in arid regions of West and Central Africa from Senegal and Gambia to Sudan [11], whose fruits are underexploited. The sweet pulp of the fruit is consumed raw at maturity while the seeds are almost unexploited [12,13]. However, the cooked seeds are sometimes used to thicken soup for human consumption [13]. Observations by [14] in Mali show that farmers sell the fruit at a loss, because they are unaware that the seed can also bring in money. The use of local edible materials requires being informed on the physicochemical characteristics of these materials [15], because their better exploitation in the nutritional field depends on it [6].
Physicochemical characterization has been reported on Detarium microcarpum seeds collected in Nigeria [16][17][18][19][20][21]. However, no studies seem to have been conducted on the physicochemical characteristics in relation to the provenance of Detarium microcarpum seeds. The objective of the present work is to determine the physicochemical characteristics of Detarium microcarpum seeds from North Benin and to study the variation of these characteristics according to the origin of the seeds. 2.2. Methods. The collected D. microcarpum fruits were manually peeled with a hammer to separate the seeds from the pericarp. The obtained seeds were then crushed and ground using a Moulinex type of electric grinder. The flour was wrapped in aluminium paper before being submitted to various analyses.

Measurements of the Color of D. microcarpum Seed
Meal. The color was determined according to the standards of the "International Lighting Committee" (CIE) using a Konica Minolta Chromameter in the trichromatic system (CIELAB L * a * b * ) calibrated with a white reference ceramic whose color coordinates are as follows: X = 0:3194, Y = 86:1, and Z = 0:3369. The recorded color parameters are L * (luminance index), a * (red saturation index), and b * (yellow saturation index).

Determination of Mineral and Trace Element
Content of D. microcarpum Seeds. The mineral elements were determined by Atomic Absorption Spectrophotometry (AAS) with a VARIANT type flame equipped with a spectra A110 software. A hollow cathode lamp and standard solutions of each mineral element were used.

Composition of Antinutritional Factors in D.
microcarpum Seeds. Oxalates, phytates, total phenolics, and saponins (saponosides) were determined. The method described in [28] was used to determine the oxalate content. Phytates were determined by the method of [29], and phenolics were determined by the method of Folin-Ciocalteu [30]. As for the saponin content, it was determined by the method of [31] modified by [32].
2.2.5. Statistical Analysis. All determinations were performed in duplicate, and data were processed using Microsoft Excel 2010 and SPSS 25 software. An analysis of variance followed by the Student-Newman-Keuls (SNK) test was performed to compare the samples. To investigate the influence of phytogeographic zone, means were compared using the independent samples t-test.

Proximate Composition of D. microcarpum Seed
Samples. The proximate composition of the seeds is presented in Table 1. The results show that the water and volatile element content of the collected samples varied significantly from 10.85 to 14.69%. These values are higher than 5.9% and 7.2%, reported by [16,20] in Nigeria, respectively, but close to 10.58% and 12.5%, reported by [19,33], respectively. This variation in moisture content in the different studies is believed to be related to environmental factors and sample drying time before analysis, as [34] showed in their study that the moisture content of a sample varies with the drying time of the sample. Furthermore, the moisture contents of D. microcarpum seeds obtained in different studies are lower than the 15% required as a safety limit for the storage of plant foods [35]. Therefore, D. microcarpum seeds can be stored for a long period of time without developing molds. Indeed, [36] showed that high moisture content decreases storage time and impacts seed quality.
As for the protein content of D. microcarpum seeds, it varied significantly (P ≤ 0:05) from 13.54 to 17.82% observed in Tanguiéta and Gogounou, respectively. These values are close to those reported in Nigeria by [16,19,33,20,21] who found 14.8%, 11.11%, 18.6%, 12.54%, and 14.22%, respectively, but lower than 35.94% reported by [18] in Nigeria. The difference between these values could be related to environmental factors, such as the difference in soil nitrogen content [37] and ecological conditions, because water deficit influences the protein content of seeds [38]. Furthermore, the values found in the present study are globally higher than the protein content (14%) of baobab (Adansonia digitata) flour used in Benin as a food supplement [39]. These seeds, having an interesting protein content, can constitute a protein complement in the preparation of soup and could complete the body's need for these nutrients for growth and development. Indeed, protein deficiency leads to stunted growth, muscle wasting, abnormal belly swelling, and fluid accumulation in the body [40].
As for the lipid content of D. microcarpum seeds, it averaged 10.05%. It varied significantly (P ≤ 0:05) from 2 International Journal of Food Science 8.68% to 11.90% obtained, respectively, in the samples from Boukombé and Malanville. The values of lipid content obtained from the seeds in the present study are higher than 7.42%, 7.61%, and 8.43% obtained by [20,41,21] in Nigeria, respectively. However, they are lower than 12%, 15%, and 14.2% as reported by [16,17,19] in Nigeria, respectively. These variations in seed oil content between countries and spatially could be attributed to the environmental and geological conditions of the regions where the seeds were collected [42]. Furthermore, the lipid content (8.68%-11.90%) of D. microcarpum seeds characterized in the present work is lower than that of industrial  International Journal of Food Science oilseeds, for example shea (51.86%) [43]. Thus, D. microcarpum seed cannot be considered an oilseed. However, seeds can be incorporated into food preparations, including the thickening of sauces, without fear of obesity and cardiovascular disease. Indeed, [44] reported that low-fat foods reduce cholesterol levels and obesity.
As for the total sugar content, it averaged 25.54% and ranged from 19.69% to 32.04%. No significant variation (P ≥ 0:05) was observed between the total sugar contents of the D. microcarpum seed samples studied. These values are lower than 42.22%, 54.4%, and 48% obtained by the difference in Nigeria by [16,18,19], respectively. Moreover, since these contents are relatively high, D. microcarpum seeds can be an energy source for the body. Indeed, total sugar is the primary energy source used by the body [45]. Furthermore, seeds can be used in the manufacture of commercial products such as glucose.
The crude fiber content of D. microcarpum seed samples ranged from 19.78% to 34.24% observed in Boukombé and Nikki, respectively. The analysis of variance revealed a significant variability (P ≤ 0:05) within the samples. These values reflect a relative richness in crude fiber compared to the crude fiber content of baobab seeds (Adansonia digitata) which is 21.2% DM as reported by [39]. On the other hand, the values in the present study are higher than 10.7%, 3.42%, and 3.5% reported in Nigeria by [16,18,19], respectively, but lower than 50% reported by [46]. The variations in crude fiber content observed in the present study, between countries, and in space are certainly due to the environmental conditions undergone by the seeds. Crude fiber is a compound that has the properties of providing a satisfactory dietary balance, facilitating intestinal transit, and softening stools, thus preventing constipation. They also reduce cholesterol levels and the risk of diseases such as coronary heart disease, hypertension, and cancer [47].
The average ash content of the D. microcarpum seeds studied was 2.47% DM. It varied significantly (P ≤ 0:05) from 1.5% to 3.49% observed, respectively, in Gogounou and Bassila. Our data are close to those reported in Nigeria by [16,18,19,33] who found 2.2%, 2.77%, 3.2% and 3.49%, respectively. These data reflect a relative richness in mineral elements compared to those of maize, millet, and  [48]. The variations in ash content of D. microcarpum seeds are certainly due to environmental conditions, especially the different nature of the soils. Table 2 shows the color parameters of Detarium microcarpum seeds. It shows that for an average luminance or brightness of 63.98, the red (a * ) and yellow (b * ) saturation of D. microcarpum seeds averaged 7.23 and 8.89, respectively. These seed color parameters varied significantly (P ≤ 0:05) from 60.45 to 67.64 for luminance; from 5.44 to 8.86 for red saturation; and from 8.24 to 9.28 for yellow saturation. The intensities (quantities) of the yellow hues (b * ) are slightly higher than those of the red hues (a * ), and this is true for all samples analyzed (Table 2).

Mineral Elements of D. microcarpum Seed Samples.
The contents of some mineral elements could be determined and are presented in Table 3 below. It was found that potassium was the main mineral element in D. microcarpum seeds with an average content of 8541.85 mg/kg. It varied significantly (P ≤ 0:05) from 6141.88 to 12305.16 mg/kg. The highest value was observed in seeds harvested in Kerou while the lowest was observed in Péhunco. Our data are lower than those reported by [18,21,19] who found 23900 mg/kg, 105000 mg/kg and 35000 mg/kg, respectively, in Nigeria; but [49] in Nigeria found 6260 mg/kg which is between the values in the present study. Since D. microcarpum seeds are rich in potassium, then they can be used to reduce the risk of hypertension. Indeed, [50] showed that a diet rich in potassium reduces the risk of hypertension. In addition, [51] reported that potassium in intracellular and extracellular fluid in humans helps maintain electrolyte balance and membrane fluidity. The calcium content of D. microcarpum seeds is 1802.27 mg/kg and ranges from 1254.47 to 2168.62 mg/kg. The analysis of variance shows us a significant difference (P ≤ 0:05) between the calcium contents of the different samples. The highest content was observed in Malanville while the seeds from Segbana presented the lowest content. These values are lower than those reported by [18,21,19] who found 2700 mg/kg, 23000 mg/kg, and 11500 mg/kg, respectively, in Nigeria; but they are higher than the  [49] in Nigeria. Calcium is a mineral necessary for dentition and ossification.
Regarding the magnesium content of D. microcarpum seeds, it varied significantly (P ≤ 0:05) from 1298.87 to 2533.06 mg/kg observed in Boukombé and Kouandé, respectively. These values are higher than those reported by [18,21,49] who found 700 mg/kg, 220 mg/kg, and 740 mg/kg, respectively, in Nigeria; but they are lower than 10500 mg/ kg reported by [19] in Nigeria. Magnesium is a transmitter of nerve impulses and an activator of coenzymes in carbohydrate and protein metabolism [52].
As for the manganese content of D. microcarpum seeds, it is 135.54 mg/kg on average. The analysis of variance showed a significant variation (P ≤ 0:05) from 75.18 to 307.23 mg/kg obtained, respectively, in Banikoara and Djougou. The value 195 mg/kg reported in Nigeria by [49] is located between the values of the present study. Our values are much higher than those of [21] who found 1.7 mg/kg in Nigeria. Manganese is required for normal bone metabolism, enzymatic reactions, and maintenance of normal nerve, brain, and thyroid functions [53]. In addition, [54] reported that manganese acts as a catalyst and cofactor in many enzymatic processes such as mucopolysaccharide and glycoprotein synthesis, involved in fatty acid and cholesterol synthesis.
The mineral elements investigated in D. microcarpum seeds, sodium, and iron are present in low levels compared to the other elements investigated in the present study. Sodium content varied significantly (P ≤ 0:05) from 53.52 to 136.19 mg/kg as observed in Bembèrèkè and Banikoara, respectively. These values are lower than those reported by [18,19,49] who found 2200 mg/kg, 2380 mg/kg, and 450 mg/kg, respectively, in Nigeria, but higher than 28.29 mg/kg reported by [21] in Nigeria. [51] states that sodium in intracellular and extracellular fluid in humans helps to maintain electrolyte balance and membrane fluidity.
For the iron content, it varied significantly (P ≤ 0:05) from 28.46 to 181.42 mg/kg observed in Boukombé and Copargo, respectively. Our values are lower than those reported in Nigeria by [18,19,49] who found 810 mg/kg, 3120 mg/kg, and 200 mg/kg, respectively; but they are higher than 6 mg/kg reported by [21] in Nigeria. Iron is an   Values with different letters in the same column are significantly different at the 5% level. 6 International Journal of Food Science important element for pregnant women, lactating mothers, and infants to prevent anemia [55]. The variations in the contents of the different mineral elements observed in the present study, between countries, and in space could be related to the different nature of the soils. These values are high compared to those of maize whose calcium, potassium, magnesium, sodium, and iron contents are 145.00, 700.00, 220.00, 175.00, and 27.50 mg/kg DM, respectively [56]. The richness of D. microcarpum seeds in these different minerals gives it a prominent place in human and animal nutrition. Table 4 presents the antinutritional factors sought in D. microcarpum oilcake. These substances are known to reduce the bioavailability of nutrients [48], particularly proteins and minerals [57]. From Table 4, it is clear that the cakes contain total phenols, phytates, oxalates, and saponins with average contents of 4.89%, 0.67%, 1.73%, and 3.08%, respectively. Except for oxalate contents, total phenols, phytates, and saponin contents varied significantly (P ≤ 0:05) from 3.13% to 7.61%, from 0.37% to 0.87%, and from 1.35% to 4.59%, respectively.

Antinutritional Factors of D. microcarpum Seed Samples.
The oxalate (0.16%) and phytate (0.26%) contents reported in Nigeria by [33] are lower than those obtained in the present study. However, our values are lower than 5.57% obtained by [18] in Nigeria. The saponin contents of 0.13% and 0.20% obtained by [18,33], respectively, as well as the total phenol content 0.073% obtained by [16] are lower than the values in the present study. This difference observed between the different results could be due to the environmental conditions experienced by the seeds.
Phytic acid is an antinutritional factor, known as a major inhibitor of the absorption of iron and calcium, zinc, and other minerals [58]. Phytate levels obtained in D. microcarpum seed meals are not negligible. However, the toxicity levels of these antinutrients have not been established [59]. However, treatments such as soaking or fermentation and cooking before consumption of these seeds would be necessary for the improvement of their quality [48,60]. On the other hand, phytic acid can be used as an antioxidant in food products by inhibiting iron-catalyzed oxidative reactions [61]. Oxalates have also been reported to inhibit the absorption of minerals, particularly calcium, magnesium, zinc, and mercury [62]. The calcium oxalate precipitates formed are deposited in the kidneys promoting kidney stones [63]. The maximum tolerable limit of oxalate is between 0.2 and 0.5 g/100 g [64]. This implies that above this value, the adverse effects of oxalate in the human body, namely, limited bioavailability of minerals (Ca, Na, and K), kidney stones (calcium oxalate), and severe irritation of the intestinal wall, will be experienced [65]. The values obtained in the present study are much higher than the maximum tolerable limit. Cooking of D. microcarpum seeds before processing or consumption is essential. Indeed, the high content of oxalate in foodstuffs can be reduced if they are precooked before processing or consumption [66].
Phenolic compounds are known for their antioxidant properties [67], and they allow grain storage because they prevent losses due to premature germination and mold damage [68]. However, they are also substances that have a negative effect on the digestibility of nutrients. Indeed, the chelation property of phenolic compounds contributes to their antioxidant activity but, at the same time, to their inhibiting effect on the bioavailability of minerals [65].
High saponin content causes gastroenteritis manifested by diarrhea and dysentery [59]. However, saponins have cholesterol-lowering properties [69] and play a major role in the treatment of inflamed tissues as well as in cancer prevention [70].
Furthermore, the phenolic compound contents of D. microcarpum seeds obtained in the present study are between 0.2 and 10.3% DM reported by [71] on Sorghum grains.
3.5. Influence of Phytogeographic Zones on the Physicochemical Characteristics of Detarium microcarpum Seed Samples. The physicochemical characteristics of D. microcarpum seeds, evaluated in the present study, were all subjected to the independent samples t-test to estimate the influence of phytogeographic zones on the means of the said characteristics. The results obtained are presented in Table 5 below. It is shown that except the total sugar content, there is no significant difference (P ≥ 0:05) between the means of physicochemical characteristics of seeds from the two phytogeographic zones. Thus, on average, the physicochemical characteristics of the Sudanian and Sudano-Guinean zones are close except the total sugar content. In other words, the phytogeographic zone does not influence the physicochemical characteristics of D. microcarpum seeds except total sugars.

Conclusion
The present study provided scientific data on the proximate composition and antinutritional factors of Detarium microcarpum seeds from Benin. According to the results obtained, Detarium microcarpum seeds can be good sources of total sugars, crude fiber, protein, lipid, and minerals such as

Data Availability
There is no data to support the findings of this study.

Conflicts of Interest
The authors declare that they have no conflicts of interest.