Nutritional and Phytochemical Composition of Bambara Groundnut ( Vigna subterranea [L.] Verdc) Landraces in Kenya

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Introduction
Bambara groundnut (Vigna subterranea) is an underutilized legume in the Fabaceae family, mostly cultivated in Africa and Asia [1]. Te crop is believed to have its origin in a place known as 'Bambara' in Central Mali in West Africa [2]. Te sufx 'groundnut' is due to the fact that pod formation is similar to that of groundnut hence the popular name 'Bambara groundnut' [3]. Cameroon, Niger, and Burkina Faso are the major producers of Bambara groundnut. Tey contribute approximately 74% of the total world production [4]. In Kenya, Bambara groundnut is known by diferent local names including nzugu mawe (Giriama), njugu mawe (Swahili), and tsimbande (Luhya) [5]. It is mostly cultivated in western and coastal regions and some parts of Nyanza and less known in other parts of Kenya [6].
Bambara groundnut is normally referred as a "poor man's crop" or "women's crop" grown primarily to supply the family with sufcient food [7]. However, the crop was lately recognized as one of the crops for the new millennium [8] due to its nutritional value, drought tolerance traits, and its capacity to grow and yield in poor soils [1]. Bambara groundnut is among the list of climate-smart crops that needs to be promoted especially in drought prone areas. It is also a pest-and disease-tolerant crop and has a natural ability to fx nitrogen from the air which enriches the soil and reduce the use of inorganic nitrogenous fertilizers [9]. Te crop is thus very valuable in areas with nutrient depleted soils and saves the poor-resource farmers from spending too much on fertilizers. Majola et al. [4] documented that the production of this crop in Sub-Saharan Africa ranges between 0.65 and 0.78 tonnes per hectare but with a potential of producing over 3 tonnes per hectare [10]. Te use of lowyielding varieties, poor-quality seeds and poor agricultural practices are major production constrains of Bambara groundnut [4].
Changes in eating habits and the realization of the importance of locally available crops have led to the rise in utilization of underutilized crops as source of food for humans [11]. Bambara groundnut is basically cultivated for domestic use and is at times referred as "complete food" as it contains adequate macronutrients [1]. Te crop contains 6.5% fat, 5.5% fber, 64.4% carbohydrate, and 23.6% protein and appreciable levels of several minerals including Ca (360 mg), Na (75.25 mg), Fe (3.6 mg), and K (1723.25 mg) per 100 g of dry sample weight [12]. In developing countries, there is habitual consumption of carbohydrate-based diets by large proportion of population because of scarcity of afordable vitamins, minerals, and protein-based food [5]. Legumes and pulses such as Bambara groundnut are lowcost source of protein as compared to animal sources [13]. It is recommended that 60 to 100 g of Bambara groundnut seeds should be consumed by humans for at least 3-4 times per week to obtain the required amount of plant-based protein [14]. Bambara groundnut which is lysine-rich and methionine-poor makes it a good blend to cereals like maize that often have sufcient methionine but low lysine content [15]. Terefore, consumption of Bambara groundnut alongside other protein sources plays a major role in reducing malnourishment in less-developed areas [16].
Bambara groundnut is primarily consumed by humans [17] as a snack after boiling or roasting when fresh [18] and eaten as confectionery [19], or crushed and used with or without condiments to make soup [20]. Bambara groundnut seeds are very caloric and their four can be used to make a thick porridge [21]. Due to their toughness, dehydrated seeds are difcult to crush into powder, but when crushed, delicious bread and fat cakes can be made [22]. Powdered beans can also be used to make slurry which can be brewed into a gel known as Okpa [23]. Immature seeds can also be cooked or eaten while fresh [24]. Te legume can be utilized as fodder to feed livestock [25]. In addition, Bambara groundnut has several medicinal uses. In South Africa, raw seeds of Bambara groundnut are chewed and swallowed by pregnant women to treat morning sickness as it is thought to be a remedy to vomiting and nausea [26]. Te grains are often chewed to relieve a swelling jaw [27] while four is used to treat skin rashes [4]. Green leaves are eaten to prevent vomiting [28]. In Senegal, sap from Bambara groundnut leaves is used in treatment of epilepsy, infected wounds, and eyes while seed powder can be mixed with water and used to treat cataracts [5]. Water from steamed seeds of Bambara groundnut is used to treat diarrhea by Kenyan Luo tribe [29].
Approximately, 36% of Kenyans are reportedly sufering from malnutrition [30] and 4-8% are in need of food-related emergency assistance at any given time particularly in arid and semiarid areas where farming activities are constrained [31]. Tis realization prompted the Kenyan government to put into action some coping strategies including the launch of National Food and Nutrition Security Policy (FNSP) [32] and the Big Four Agenda whose one of the pillars is anchored on food and nutritional security. Despite the nutritional and medicinal value of Bambara groundnuts, their utilization is limited by presence of phytochemicals including saponins, condensed tannins, phytic acids, and favonoids, which have also been found to possess some antinutritional factors [33]. Tese phytochemicals have been reported to reduce the absorption of nutrients by the body [34]. However, most of these phytochemicals have been reported to have some medicinal values hence promoting good health [35]. Other phytochemicals such as saponins play an important role in plant defense mechanism [36]. Te testa color of Bambara groundnut has been linked to tannin concentration and may also be used as a phenotypic marker for drought tolerance traits in that the dark variant seeds have been reported to germinate faster than light variant seeds under drought due to the presence of tannins [37]. Tis paper outlines the nutritional and phytochemical compositions of Bambara groundnut and its potential in mitigating food and nutritional insecurity.

Bambara Groundnut Seeds Collection.
Te study assessed seventeen Bambara groundnut landraces that were randomly collected from farmers in Kisumu, Vihiga, Busia, Bungoma, and Kakamega Counties in Western Kenya region (Table 1) where the crop is mainly cultivated.

Description of Experimental Site.
Field experiments were set up in a farm in Ishiara location, in Mbeere North Sub-County in Embu County, Kenya. Te area lies in the lower midland 4 (LM4) agroecological zone within the coordinates 0.4548°S, 37.7849°E at an elevation of 853 m above sea level [44]. Te area is characterized by hot, semiarid conditions with a mean temperature of 23°C and receives an average rainfall of 800 mm per annum, which is usually bimodal [45]. Long rains (LRs) are experienced from March to May while short rains (SRs) are experienced from mid-October to December, thus two cropping seasons is possible [45]. Long rains (LRs) defne the cropping season characterized by less interannual variability [46] and heavy rains that last for a longer period [47]. Short rains (SRs) season on the other hand takes shorter period and shows more interannual variability [46]. Te site has reddish brown and blackish grey sandy soils [48].  International Journal of Agronomy groundnut seeds were sown per hill at a depth of 3 cm and later thinned to one seedling two weeks after germination. Di-ammonium phosphate (DAP) fertilizer was applied at the rate of 50 kg·ha −1 at planting and mixed thoroughly with soil before the seeds were sown. Hand weeding was done twice in every season that is, at the third and sixth week after planting. Harvesting was done after all the foliage in the plants had dried up which coincided with 15 th to 19 th week after planting. Mature pods were harvested manually by digging out the entire crop and picking the individual pods and thereafter sun-dried and threshed.

Seeds Preparation and Laboratory Analysis.
Harvested seeds were sorted and cleaned manually to remove foreign materials and damaged seeds and thereafter dry-milled to a fne powder using high-speed universal disintegrator (FW 80−1). Te fne powder was stored in airtight containers in a cool and dry place in the laboratory prior to analysis following the procedure of Olaleye et al. [49]. Te biochemical and nutritional analysis was carried out in triplicates using 100 g ground seed samples. Alkaloids were determined using the method described by Dike et al. [50]. Saponins determination was done according to the procedure described by Obadoni and Ochuko [51]. Tannin was determined using the Folin-Ciocalteu method as described by Wabali et al. [52] while favonoid levels were quantifed as described by Olaleye et al. [49]. Te unit of measure was mg/100 g except for tannin which was quantifed in mg·g −1 .
Proximate analysis was determined using the Association of Ofcial Analytical Chemists (AOAC) methods for moisture content [53], total ash content [54], and crude fat [55]. Te protein content was determined by micro Kjeldahl method by frst quantifying the nitrogen content and then multiplying it by 6.25 to get the protein content [56]. Te approximate values obtained from the analysis were reported in g/100 g of sample. Minerals were determined following the methods described by Olaleye et al. [49]. Sodium and potassium were determined using fame photometry model FP640; zinc was determined using atomic absorption spectrometer (AAS)-PG-990; iron was determined using UV spectrophotometer model ME 801. Te unit of measure for all the minerals was mg/100 g.

Data Analysis.
Te biochemical and nutritional data collected were subjected to analysis of variance (ANOVA) using XLSTAT software version 2022. Te means that were signifcantly diferent were separated using Tukey's Honest Signifcant Diference (HSD) at 95% level of confdence. Data were also subjected to cluster analysis using Agglomerative Hierarchical Clustering (AHC) to determine the diversity among the landraces on the basis of their biochemical and nutritional composition. Pearson correlation analysis was conducted to determine the association between the biochemical and nutritional components.

Proximate and Nutritional Composition of the Bambara
Groundnut Landraces. Te proximate and nutritional composition of the Bambara groundnut landraces used in this study is shown in Table 2. Tere was signifcant difference (P ≤ 0.05) in all the nutritional and phytochemical traits evaluated in the combined data for both seasons. Te results from the frst and second cropping seasons analyzed separately had no signifcant diference at (P ≤ 0.05) levels of confdence. Te moisture content ranged from 3.467% in landrace LU-123 to 6.238% in landrace BG-125. Te total ash content ranged from 3.171% in BS-141 to 4.694% in BS-114. Te landrace BS-114 also had the highest mean value of crude protein (26.002%) while KS-116 had the lowest mean value of crude protein (21.178%). Te fat content ranged from 4.563% in BS-114 to 6.930% in KS-116. Terefore, BS-114 had the highest protein and total ash content but the lowest fat content. Te landrace BG-125 had the highest iron content of 5.125 mg/100 g while BG-112 had the lowest iron content of 4.068 mg/100 g. Zinc content ranged between 0.057 mg/100 g and 0.422 mg/100 g in landraces BS-104 and BG-125, respectively. Potassium ranged from 819.335 mg/ 100 in landrace BS-103 to 1,134.80 mg/100 g in landrace BS-145. Te highest sodium content was obtained in landrace LU-123 with 129.663 mg/100 g while landrace MU-137 had the lowest value of 25.140 mg/100 g .

Antinutrient Composition of the Bambara Groundnut
Landraces. Te results for antinutrient components are presented in Table 3. Tere were signifcant (P ≤ 0.05) differences between the landraces for their antinutrient components. Te composition of tannins ranged from 0.011 mg·g −1 in landrace KS-108 to 0.037 mg·g −1 in landrace BS-114. Saponins composition ranged between 0.815 mg/ 100 g in landrace KS-108 and 1.057 mg/100 g in landrace MU-137. Te alkaloids content ranged from 0.011 mg/100 g in landrace BG-109 to 0.116 mg/100 g in landrace BS-103. Among the test landraces, BS-104 had the highest mean composition of favonoids (4.067 mg/100 g) while KS-108 had the lowest mean value (8.450 mg/100 g). Tere were signifcant diferences (P ≤ 0.05) between seasons for tannins, favonoids and saponins concentrations but no signifcant diference (P ≤ 0.05) between the two seasons for alkaloid content in the tested landraces. Landrace × season interactions were not signifcant (P ≤ 0.05) for all the tested biochemical components.

Cluster Analysis.
Cluster analysis based on the nutritional and phytochemical components was used to estimate the degree of similarity and diversity among the diferent Bambara groundnut landraces used in this study. Te 17 landraces were grouped into fve (5) supported clusters ( Figure 1) with a diversity of 94.02% between clusters and 5.98% within clusters. Cluster 1 was a singleton of landrace

Principal Component Analysis.
Te principal component analysis (PCA) was used to show the relationship between the Bambara groundnut landraces and the nutritional and phytochemical traits evaluated (Figure 2

Pearson Correlation of the Nutritional and Phytochemical
Components. Pearson correlation of the nutritional and phytochemical components of Bambara groundnut landraces is presented in Table 4. Te saponins were found to be positively correlated to tannins and favonoids. Tere was signifcant negative correlation between the alkaloids and potassium content while the favonoid content was positively correlated to iron content but negatively correlated to the sodium content (Table 4). Te protein content was negatively correlated to the fat content but positively correlated to the sodium content which was negatively correlated to the iron content.

Discussion
Te study showed signifcant variation in proximate, mineral, and antinutrient contents of Bambara groundnuts that were evaluated. Results showed that moisture content of the landraces ranged from 3.467% to 6.238%. Tis was lower than the one reported by Olaleye et al. [49] that ranged between 5.23 and 9.23 g/100 g. Yao et al. [57] reported moisture content of Bambara groundnut to be 11.7%. Te seeds with signifcantly lower moisture content such as for LU-123, LU-124 and KS-116 are likely to have a longer postharvest life since they are less susceptible to pest attack [58]. On the other hand, the ash content observed among the tested landraces in this study was comparable to the values reported in similar previous studies [5,24,59]. Te low ash content of Bambara groundnut seeds indicated low level of inorganic substances in the sample with minerals being the main components [60].  International Journal of Agronomy Bambara groundnut is known to be rich in high quality protein compared to other legumes such as cowpea, soybean, and groundnut [61]. Te crude protein observed in this study were comparable to those observed in velvet bean by Vadivel and Janardhanan [62] which contained 20.2 to 29.3%. However, the genotypes in this study had relatively higher crude protein content than the documented content for Bambara groundnuts [63]. Variation in the protein composition among diferent studies could be attributed to environmental conditions, genetics [64], and also the differences in techniques of estimations for instance nitrogen conversion factor [18]. Like other legumes, Bambara groundnuts is lysine-rich and methionine-poor, making it a good blend to cereals like maize that often have sufcient methionine but low lysine content [65].
Te content of crude fat in the tested Bambara groundnut landraces was relatively higher than those found in cereals though may not be adequate to be utilized as oil source [15]. However, Mabhaudhi et al. [11] reported that a tribe in Congo was successfully extracting oil from Bambara seeds. Even so, the levels of crude fat reported in Bambara groundnut would not make them to be classifed together with other oil rich legumes such as soybeans with around 19.5% and groundnut with 25% fat content [66]. Te results from the present study showed that the landrace, BS-114, with dark colored seeds had the highest protein content but the lowest fat content. Nti [59] also observed highest levels of crude protein and lowest levels of fat in dark variants (red and black) of Bambara groundnut and concluded that protein levels are negatively correlated to fat content [59].
Further characterization of the nutritional components showed that all the landraces had considerable amount of minerals higher than the mineral levels reported in other legumes that are mostly consumed such as mung beans [67]. According to Olaleye et al. [49], potassium, iron, zinc,  International Journal of Agronomy phosphorus and magnesium are the most dominant mineral elements found in Bambara groundnut seeds. Tese nutrients are important especially in economically developing nations where there is habitual consumption of cereals hence Bambara groundnut is a super candidate for such areas. Genetic origin, level of soil fertility and geographical source of landraces are the factors that cause diferences in mineral composition in plants of the same species [68]. Te observed levels of potassium were lower than what was reported in other Bambara groundnut genotypes by Chandra et al. [12] and Dansi et al. [69] but higher that what is contained in most consumed legumes such as mung beans [67]. Potassium helps in maintaining the balance of alkaline-acid in the body [70] and also reduces vasoconstriction and blood pressure and acts as vasodilator [68]. Te levels of zinc in the Bambara groundnut seeds in this study were relatively lower than what was reported by Murevanhema and Jideani [5] but higher than what was reported by Olaleye et al. [49] in other Bambara groundnuts. Iron is an important element especially in synthesis of haemoglobin in the blood [68]. Te results of further showed that sodium content was highly variable among the tested landraces as it ranged from 25.16 to 129.67 mg/100 g. Chandra et al. [12] reported a value of 75.25 mg of sodium in Bambara groundnut grown in India. It is recommended that adults should consume not more than 6 g of sodium in a day [71] and high levels of sodium in the body is a health risk as it may cause problems such as cardiovascular diseases [12]. Terefore, the sodium content in Bambara groundnut is low enough to cause health risks.
Te mean value of tannins between 0.011 mg/g and 0.037 mg/g observed in this study was comparable with 0.039 mg/g and 0.046 mg/g reported by Ijarotimi and Esho [72] and Mazahib et al. [73] among Bambara seeds cultivated in Nigeria and Sudan, respectively but lower than 4.5 and 15 mg CE g−1 reported by Nti [59]. Although tannins are important in defense to seeds grown in unfavorable environments [74], they lower the palatability of the crops by causing bitter taste in plants [75]. Low tannins ensure absorption of essential micronutrients and digestion of protein [76]. Te favonoids content observed among the Bambara groundnut landraces in our study was much lower than what was reported by Olaleye et al. [49] but the saponins content in our study corroborated the fndings of Olaleye et al. [49]. Alkaloids content observed in our study was comparable to what was reported by Mbagwu et al. [77] in Bambara groundnut in Eastern Nigeria. Alkaloids have been reported to have anti-cancer activity [78], anti-malarial activity [79] and helps to prevent stroke [80].
Te diversity among the 17 genotypes was further assessed using cluster analysis based on their nutritional and phytochemical composition. Te high percentage of diversity observed between diferent clusters and the low diversity observed within clusters was a good indication that the nutritional and phytochemical components can be successfully used to discriminate between diferent Bambara groundnut genotypes. Te cluster analysis did not group the landraces based on their place of origin indicating that the landraces may have a wider environmental adaptability hence can be widely exploited by the farmers based on the nutritional and phytochemical preferences. Tis observation was also supported by the principal component analysis (PCA) where the genotypes were separated based on the components that captured the largest share of explained variance. Te PCA also uses factor loading to show which features correlate with the most important components. Terefore, both cluster analysis and PCA are useful tools in selecting landraces with desirable traits that can be exploited in a plant breeding program.
Correlation analysis helps in determining the relationship between traits and it's useful in assessing trait combinations during selection. Te study showed that saponins were positively correlated to tannins and favonoids. Positive correlation between the phytochemical is especially important when the objective is to improve the pharmaceutical properties of the genotypes. A negative correlation was observed between the alkaloids and potassium content as well as between favonoids and sodium content. Tis means that lowering the level of alkaloids would increase the level of potassium and increasing the level of favonoids would lower the content of sodium and vice-versa. Te favonoid content was found to positively correlated to iron indicating that the two traits may cosegregate hence enabling their combined selection. Tis may also be possible when targeting a high protein content with low fat content since the two traits were found to be negatively correlated. However, the protein content was positively correlated to the sodium content indicating that improvement of the protein content using conventional breeding methods without increasing sodium content would be difcult unlike for iron which was negatively correlated to sodium. Lack of signifcant correlation between various traits was an indication that such traits may not be linked hence their selection should be considered on single trait basis.

Conclusion and Recommendations
Tis study confrmed that the Bambara groundnut is a good source of nutrients mainly protein and minerals. Te observed diversity in the proximate, nutritional and phytochemical composition of the tested landraces provides the basis for selection for enhanced nutritional and phytochemical composition of this high value legume. Te landraces with high nutritional value such as BG-125, BS-148, and BS-145, among others, are recommended to plant breeders for production of certifed seeds to facilitate their adoption by the farmers for enhanced food and nutritional security. Although the landraces LU-123, BS-114, and KS-108 have high nutritional value, their nutritional composition should be improved by reducing the sodium content before seed multiplication. Te landraces with high levels of phytochemicals are also recommended to plant breeders for production of certifed seeds targeting their utilization by pharmaceutical and nutraceutical industries. 8 International Journal of Agronomy Tese may include BS-104 for favonoids and MU-137 for saponins. All the selections should also be promoted to the farmers for adoption through various extension programs.

Data Availability
Some of the data used to support the fndings of this study are included in the article. Additional data are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that there are no conficts of interest regarding the publication of this paper.