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.

1. Introduction

In the world, there is an urgent need for new food plants or new sources to meet the nutritional needs of the ever-growing 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 food-related 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 [16-21]. 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. Materials and Methods

2.1. Plant Material

The fruits of Detarium microcarpum were collected in twenty-two (22) localities in North Benin (Figure 1). They were transported to the “Research Unit in Enzymatic and Food Engineering (URGEA) of the Laboratory of Study and Research in Applied Chemistry” (LERCA) of the “Ecole Polytechnique d'Abomey-Calavi” (EPAC) of Abomey-Calavi University (UAC) for pretreatment and analysis.

Figure 1

Map of Benin showing Detarium microcarpum seed harvesting sites.

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.

2.2.1. Proximate Composition of D. microcarpum Seeds

The content of water and volatile elements, oil, total ash, total sugars (expressed as glucose), protein, and crude fiber were determined, respectively, according to the French standard NF V03-921 of the French Association for Standardization (AFNOR) [22], the Soxhlet method [23] using petroleum ether, AACC 08-01 standard [24], the phenol-sulfuric colorimetric method developed by [25], the Kjeldhal method [26], and the filter bag technique (ANKOM200) [27].

2.2.2. 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).

2.2.3. 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.

2.2.4. 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.

3. Results and Discussion

3.1. 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.

Table 1

Proximate composition of Detarium microcarpum seeds in North Benin.

Areas	Municipalities	Water and volatile matter content (%)	Protein (% DM)	Total sugar content (% DM)	Lipid content (% DM)	Raw fibers (% DM)	Ash content (% DM)
Sudanian	Banikoara	13.40 ± 0.20de	15.66 ± 0.25b	24.43 ± 0.65a	10.60 ± 0.12c	30.93 ± 1.75bc	2.52 ± 0.18abc
	Kandi	12.40 ± 0.43bc	15.57 ± 0.12b	26.8 ± 3.08a	10.15 ± 0.19bc	28.68 ± 3.07bc	2.18 ± 1.17abc
	Malanville	12.24 ± 0.19bc	15.05 ± 0.62ab	22.83 ± 1.23a	11.90 ± 0.74d	31.79 ± 0.87bc	2.08 ± 1.03abc
	Karimama	13.01 ± 0.06cd	15.14 ± 0.27ab	21.925 ± 1.59a	9.01 ± 0.08ab	26.49 ± 0.64bc	2.57 ± 0.04abc
	Ségbana	10.85 ± 0.04a	15.44 ± 0.10ab	27.73 ± 2.33a	10.33 ± 0.07c	31.29 ± 0.46bc	2.73 ± 0.25abc
	Gogounou	12.51 ± 0.14bcd	17.82 ± 0.21b	22.12 ± 1.67a	8.76 ± 0.29a	29.32 ± 2.93bc	1.50 ± 0.01a
	Kérou	12.31 ± 0.29bc	15.43 ± 0.52ab	21.62 ± 2.21a	10.24 ± 0.23bc	31.14 ± 0.18bc	2.95 ± 0.08bc
	Kouandé	12.65 ± 0.22bcd	14.42 ± 0.02ab	19.69 ± 2.92a	9.79 ± 0.23abc	31.54 ± 4.85bc	2.35 ± 0.07abc
	Péhunco	13.46 ± 0.54de	14.03 ± 0.01ab	23.98 ± 2.31a	9.85 ± 0.32abc	27.86 ± 4.65bc	2.35 ± 0.35abc
	Tanguiéta	12.03 ± 0.26bc	13.54 ± 0.44a	25.17 ± 1.63a	9.82 ± 0.28abc	31.51 ± 1.61bc	2.57 ± 0.10abc
	Boukombé	14.69 ± 0.42f	15.41 ± 0.83ab	26.86 ± 1.05a	8.68 ± 0.02a	19.78 ± 1.13a	2.92 ± 0.04abc
	Bembèrèkè	11.78 ± 0.15b	15.29 ± 0.33ab	23.48 ± 4.86a	10.12 ± 0.10bc	31.99 ± 0.98bc	2.27 ± 0.18abc
	Sinendé	12.75 ± 0.50bcd	15.72 ± 0.34b	26.65 ± 2.38a	9.65 ± 0.01abc	32.22 ± 1.17bc	2.32 ± 0.18abc
	Djougou	13.85 ± 0.14e	14.86 ± 0.92ab	23.82 ± 5.78a	10.40 ± 0.07c	30.04 ± 1.31bc	3.17 ± 0.11bc
	Copargo	12.63 ± 0.06bcd	14.42 ± 0.92ab	24.95 ± 0.95a	10.17 ± 0.10bc	28.97 ± 4.58bc	1.76 ± 0.01ab
Sudanese-Guinean	N'Dali	12.68 ± 0.19bcd	15.08 ± 0.22ab	30.41 ± 5.59a	10.44 ± 0.21c	30.62 ± 1.22bc	2.33 ± 0.04abc
	Parakou	11.83 ± 0.42b	14.87 ± 0.93ab	27.14 ± 2.69a	9.43 ± 0.08abc	27.31 ± 2.42bc	2.35 ± 0.14abc
	Pèrèrè	12.31 ± 0.40bc	14.66 ± 0.04ab	27.96 ± 4.16a	10.12 ± 0.41bc	32.71 ± 0.54bc	2.85 ± 0.15abc
	Kalalé	12.85 ± 0.16bcd	14.22 ± 0.61ab	25.68 ± 4.55a	10.22 ± 0.78bc	32.59 ± 3.22bc	2.17 ± 0.11abc
	Tchaourou	12.80 ± 0.25bcd	15.68 ± 0.04b	32.04 ± 2.96a	9.75 ± 0.30abc	32.03 ± 4.33bc	2.58 ± 0.04abc
	Nikki	12.14 ± 0.21bc	15.07 ± 0.59ab	27.41 ± 3.59a	11.63 ± 0.69d	34.24 ± 0.59c	2.32 ± 0.24abc
	Bassila	13.83 ± 0.04e	15.63 ± 0.37b	29.32 ± 2.96a	10.15 ± 0.52bc	22.785 ± 2.29ab	3.49 ± 0.08c
	Total	12.68 ± 0.84	15.14 ± 0.90	25.54 ± 3.75	10.05 ± 0.79	29.81 ± 3.79	2.47 ± 0.51

Values with different letters in the same column are significantly different at the 5% level.

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 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 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 sorghum with contents of 1.50%, 1.90%, and 1.60% MS, respectively [48]. The variations in ash content of D. microcarpum seeds are certainly due to environmental conditions, especially the different nature of the soils.

3.2. Color Parameters of D. microcarpum Seed Samples

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).

Table 2

Color parameters of Detarium microcarpum seeds.

Areas	Municipalities	l∗	a∗	b∗
Sudanian	Banikoara	64.38 ± 0.01h	6.74 ± 0.06c	8.71 ± 0.06bc
	Kandi	62.88 ± 0.26d	7.58 ± 0.03f	9.28 ± 0.01f
	Malanville	63.43 ± 0.01e	7.52 ± 0.05f	8.82 ± 0.04cd
	Karimama	62.54 ± 0.12c	8.25 ± 0.06i	8.89 ± 0.06de
	Ségbana	64.31 ± 0.02h	7.55 ± 0.04f	9.00 ± 0.03e
	Gogounou	60.45 ± 0.04a	8.86 ± 0.07j	9.15 ± 0.06f
	Kérou	62.61 ± 0.01c	7.73 ± 0.05g	9.18 ± 0.07f
	Kouandé	61.95 ± 0.00b	7.44 ± 0.03f	8.89 ± 0.03de
	Péhunco	62.64 ± 0.01c	7.44 ± 0.08f	8.89 ± 0.01de
	Tanguiéta	62.68 ± 0.02c	7.73 ± 0.09g	8.24 ± 0.00a
	Boukombé	65.77 ± 0.00k	6.05 ± 0.04b	8.64 ± 0.03b
	Bembèrèkè	62.46 ± 0.01c	7.91 ± 0.07h	9.25 ± 0.06f
	Sinendé	67.64 ± 0.03m	6.79 ± 0.02c	8.97 ± 0.04e
	Djougou	64.02 ± 0.13g	6.67 ± 0.08c	8.29 ± 0.03a
	Copargo	65.57 ± 0.04j	6.96 ± 0.02d	8.78 ± 0.03cd
Sudanese-Guinean	N'Dali	63.80 ± 0.01f	6.94 ± 0.01d	8.77 ± 0.02cd
	Parakou	64.41 ± 0.13h	7.16 ± 0.01e	8.70 ± 0.04bc
	Pèrèrè	65.86 ± 0.09k	6.60 ± 0.01c	8.72 ± 0.03bc
	Kalalé	64.38 ± 0.04h	7.14 ± 0.01e	8.61 ± 0.03b
	Tchaourou	64.53 ± 0.12h	7.58 ± 0.03f	9.28 ± 0.01f
	Nikki	64.80 ± 0.00i	7.10 ± 0.06e	9.22 ± 0.06f
	Bassila	66.49 ± 0.05l	5.44 ± 0.04a	9.27 ± 0.05f
	Total	63.98 ± 1.65	7.23 ± 0.72	8.89 ± 0.30

Values with different letters in the same column are significantly different at the 5% level.

3.3. 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.

Table 3

Contents of some mineral elements in Detarium microcarpum seeds.

Areas	Municipalities	Sodium (Na), mg/kg	Potassium (K), mg/kg	Manganese (Mn), mg/kg	Calcium (Ca), mg/kg	Magnesium (mg), mg/kg	Iron (Fe), mg/kg
Sudanian	Banikoara	136.19 ± 0.01v	7117.31 ± 0.07e	75.18 ± 0.01b	1590.55 ± 0.01e	1708.35 ± 0.02l	57.54 ± 0.04q
	Kandi	64.56 ± 0.01f	8420.44 ± 0.04n	78.94 ± 0.01c	1254.48 ± 0.01a	1577.07 ± 0.01h	48.87 ± 0.04j
	Malanville	76.67 ± 0.04l	6913.85 ± 0.06d	82.08 ± 0.02g	2168.62 ± 0.02u	1602.65 ± 0.03j	88.75 ± 0.03u
	Karimama	56.94 ± 0.04b	8146.73 ± 0.03l	153.26 ± 0.04s	1274.47 ± 0.05b	1924.62 ± 0.01q	37.17 ± 0.01e
	Ségbana	66.94 ± 0.04h	8446.73 ± 0.03p	133.26 ± 0.04n	1254.47 ± 0.05a	1524.62 ± 0.01g	47.17 ± 0.01h
	Gogounou	70.42 ± 0.01j	8100.84 ± 0.03k	79.79 ± 0.01d	1890.04 ± 0.03p	1672.48 ± 0.03k	54.51 ± 0.01m
	Kérou	66.23 ± 0.01g	12505.46 ± 0.07v	81.64 ± 0.01f	1963.67 ± 0.01q	1745.16 ± 0.01o	36.63 ± 0.01d
	Kouandé	61.83 ± 0.01d	12305.16 ± 0.01u	113.85 ± 0.03j	1650.63 ± 0.01j	2533.06 ± 0.05v	55.33 ± 0.04o
	Péhunco	83.85 ± 0.05o	6141.88 ± 0.02a	142.57 ± 0.03r	1750.65 ± 0.04l	1444.15 ± 0.06e	88.53 ± 0.01t
	Tanguiéta	98.42 ± 0.01s	7193.23 ± 0.04f	100.43 ± 0.01i	1748.56 ± 0.04k	1722.96 ± 0.03m	81.07 ± 0.01s
	Boukombé	83.07 ± 0.01n	8408.14 ± 0.04m	195.07 ± 0.04u	1606.83 ± 0.03h	1298.87 ± 0.03a	28.46 ± 0.01a
	Bembèrèkè	53.52 ± 0.03a	7214.06 ± 0.04g	94.69 ± 0.01h	1759.06 ± 0.04m	1498.87 ± 0.01f	36.12 ± 0.03c
	Sinendé	80.27 ± 0.03m	10110.66 ± 0.02r	131.04 ± 0.01m	1800.17 ± 0.01n	1982.27 ± 0.03r	55.19 ± 0.01n
	Djougou	69.52 ± 0.01i	6699.53 ± 0.02c	307.23 ± 0.01v	1983.29 ± 0.01r	1358.64 ± 0.02b	53.23 ± 0.04l
	Copargo	62.34 ± 0.03e	7783.16 ± 0.01h	138.74 ± 0.01q	2024.23 ± 0.03s	1365.25 ± 0.01c	181.42 ± 0.01v
Sudanese-Guinean	N'Dali	57.12 ± 0.01c	7993.36 ± 0.02i	81.44 ± 0.01e	2099.92 ± 0.03t	1369.28 ± 0.02d	61.44 ± 0.01r
	Parakou	84.16 ± 0.05p	10115.96 ± 0.02s	135.54 ± 0.01o	1802.27 ± 0.01o	1987.27 ± 0.03s	50.16 ± 0.04k
	Pèrèrè	88.94 ± 0.01r	6408.83 ± 0.01b	161.26 ± 0.02t	1649.82 ± 0.01i	1780.64 ± 0.04p	56.06 ± 0.02p
	Kalalé	84.98 ± 0.04q	8443.15 ± 0.06o	137.54 ± 0.01p	1477.60 ± 0.01d	1592.64 ± 0.04h	39.72 ± 0.01f
	Tchaourou	117.85 ± 0.01u	11684.26 ± 0.01t	122.24 ± 0.01l	1605.83 ± 0.03g	2030.35 ± 0.01t	40.54 ± 0.03g
	Nikki	112.47 ± 0.03t	9768.63 ± 0.03q	64.23 ± 0.04a	1593.46 ± 0.02f	1741.86 ± 0.01n	47.84 ± 0.01i
	Bassila	72.75 ± 0.00k	7999.47 ± 0.04j	119.98 ± 0.04k	1354.58 ± 0.01c	2266.51 ± 0.01u	33.64 ± 0.04b
	Total	79.50 ± 20.89	8541.85 ± 1800.90	124.09 ± 52.26	1695.60 ± 263.40	1714.89 ± 306.15	58.15 ± 31.66

Values with different letters in the same column are significantly different at the 5% level.

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 680 mg/kg reported by [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 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.

3.4. Antinutritional Factors of D. microcarpum Seed Samples

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.

Table 4

Antinutritional factors of Detarium microcarpum cake.

Areas	Municipalities	Oxalate (%)	Phytate (%)	Total phenols (%)	Saponin (%)
Sudanian	Banikoara	1.68 ± 0.48a	0.37 ± 0.03a	4.93 ± 0.11bcde	4.59 ± 0.12e
	Kandi	1.67 ± 0.47a	0.87 ± 0.06e	6.62 ± 0.09f	2.41 ± 0.13ab
	Malanville	1.67 ± 0.47a	0.76 ± 0.13cde	4.70 ± 0.03abcde	1.35 ± 0.21a
	Karimama	1.34 ± 0.00a	0.76 ± 0.05cde	5.78 ± 0.66def	3.55 ± 0.83cde
	Ségbana	1.01 ± 0.47a	0.51 ± 0.07abc	5.01 ± 0.04cde	4.01 ± 0.08cde
	Gogounou	2.03 ± 0.01a	0.60 ± 0.21abcde	7.61 ± 0.54g	3.53 ± 0.04cde
	Kérou	1.34 ± 0.95a	0.79 ± 0.04cde	3.43 ± 0.02abc	1.44 ± 0.37a
	Kouandé	2.03 ± 0.95a	0.64 ± 0.01bcde	5.04 ± 0.20de	1.81 ± 0.29a
	Péhunco	1.69 ± 0.47a	0.83 ± 0.01de	3.38 ± 0.02ab	3.48 ± 0.74cde
	Tanguiéta	1.34 ± 0.95a	0.72 ± 0.06bcde	5.77 ± 0.35def	4.11 ± 0.02de
	Boukombé	1.69 ± 0.47a	0.57 ± 0.06abcd	3.13 ± 0.11a	2.91 ± 0.06bc
	Bembèrèkè	1.68 ± 0.47a	0.53 ± 0.01abc	5.73 ± 0.37def	4.47 ± 0.47e
	Sinendé	1.69 ± 0.47a	0.60 ± 1.11abcde	5.00 ± 0.28cde	3.11 ± 0.01bcd
	Djougou	2.36 ± 0.47a	0.76 ± 0.05cde	3.33 ± 0.09a	2.40 ± 0.00ab
	Copargo	1.69 ± 0.48a	0.70 ± 0.04bcde	4.52 ± 0.17abcde	3.75 ± 0.35cde
Sudanese-Guinean	N'Dali	2.02 ± 0.95a	0.73 ± 0.08cde	4.11 ± 0.59abcd	3.70 ± 0.42cde
	Parakou	2.01 ± 0.00a	0.72 ± 0.06bcde	4.65 ± 0.49abcde	2.29 ± 0.12ab
	Pèrèrè	1.68 ± 0.48a	0.77 ± 0.10cde	4.13 ± 0.11abcd	4.05 ± 0.07de
	Kalalé	2.02 ± 0.00a	0.82 ± 0.04de	5.77 ± 0.13def	4.14 ± 0.04de
	Tchaourou	1.35 ± 0.95a	0.58 ± 0.04abcd	4.52 ± 1.10abcde	2.40 ± 0.01ab
	Nikki	1.68 ± 0.47a	0.78 ± 0.11cde	5.99 ± 0.44ef	2.92 ± 0.07bc
	Bassila	2.35 ± 0.48a	0.46 ± 0.00ab	4.52 ± 0.00abcde	1.45 ± 0.36a
	Total	1.73 ± 0.49	0.67 ± 0.14	4.89 ± 1.15	3.08 ± 1.03

Values with different letters in the same column are significantly different at the 5% level.

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.

Table 5

Influence of phytogeographical zones on the physicochemical characteristics of Detarium microcarpum seeds.

		Sudanian	Sudanese-Guinean
Proximate composition	Moisture	12.70 ± 0.91a	12.63 ± 0.64a
	Protein	15.19 ± 0.97a	15.03 ± 0.52a
	Total sugar	21.09 ± 2.01a	24.76 ± 2.01b
	Lipid content	9.96 ± 0.79a	10.25 ± 0.69a
	Raw fibers	27.80 ± 4.88a	28.96 ± 7.77a
	Ash content	2.41 ± 0.44a	2.58 ± 0.46a
Color settings	L∗	63.55 ± 1.78a	64.89 ± 0.94a
	a∗	7.41 ± 0.70a	6.85 ± 0.69a
	b∗	8.86 ± 0.31a	8.94 ± 0.30a
Mineral components	Na	75.38 ± 20.51a	88.32 ± 21.21a
	K	8367.14 ± 1894.72a	8916.23 ± 1733.54a
	Mn	127.18 ± 60.63a	117.46 ± 33.69a
	Ca	1714.65 ± 283.73a	1654.78 ± 240.69a
	Mg	1663.93 ± 311.53a	1824.08 ± 298.32a
	Fe	63.33 ± 37.52a	47.05 ± 9.78a
Antinutrients	Oxalate	1.66 ± 0.33a	1.87 ± 0.33a
	Phytate	0.67 ± 0.14a	0.69 ± 0.13a
	Total phenols	4.93 ± 1.28a	4.81 ± 0.76a
	Saponin	3.13 ± 1.05a	2.99 ± 1.02a

Values with different letters in the same line are significantly different at the 5% level.

4. 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 potassium, calcium, magnesium, and manganese. The obtained oxalate and phytate contents can reduce the bioavailability of nutrients, especially minerals contained in the seeds. On average, the physicochemical characteristics of the Sudanian and Sudano-Guinean zones are close except the total sugar content.