The African yam bean (AYB) originated in Ethiopia. Both wild and cultivated types now occur in tropical Africa as far as Zimbabwe, throughout West Africa from Guinea to southern Nigeria, being especially common in the latter and in Togo and the Ivory coast, and in East Africa from northern Ethiopia (Eritrea) to Mozambique, including Tanzania and Zanzibar. The centre of diversity of African yam bean is only in Africa. Nigeria has the highest production of African yam bean (Potters, 1992; Abbey and Berezi; 1988).

2.2       Description
            A vigorous, herbaceous, climbing vine reaching 1.5m-2m in height with trifoliate leaves. The leaflets being up to 14cm in length and 5cm broad. The conspicuous flowers are mauvish-pink, purple or greenish white in colour, about 2.5cm in length and borne on stout auxiliary peduncles. The glabrous seedspod are linear, flat with both margins raised, 25-30 cm long and 1-1.5cm broad, containing 20-30 seeds which may be ellipsoid rounded or truncated and show consideration variation in size and colour, the largest are usually about I cm long and 0.7cm wide-seed colour may vary from creamy white, black, Brown, grey and speckled grey. This plant produces small spindle-shaped tubers about 5-7cm long. There is some evidence that yields of seeds and tubers are inversely related.

Small-scale cultivations are practiced throughout tropical Africa. The plant is especially suited to lowland conditions; though it can be grown up to 1800m. Climates ranging from savannah to rainforest are tolerated provided there is a combination of adequate rainfall (100cm or more during the growing season) and reasonably good drainage. It is often planted along with yams and beans, using the same stakes as the yam support, though sometimes left to trail on the ground. It is sometimes stated that plants perform better when interplanted than when grown alone.
            African yam bean is grown primarily for its dry seed.
2.3.1   USE FOR FOOD
African yam bean is used extensively in various dietary preparations; it can supplement the protein requirement of many families throughout the year. The Igbos extensively explored the crop as a good source of dietary protein in feeding the displaced and the severely malnourished refugees during the Nigeria civil war of 1967-1970 (Nwokolo,1996). Some people in different places eat it in different forms; some mill dry seeds into flour, which is processed into a paste with water and some other condiments. This is then wrapped into plantain leaves and boiled and then eaten as turban just like “Okpa”. Some also mix the flour with flour form cassava and cooked into a paste eaten with soup or sauces. Some others boil the dry seeds for about three hours (3) replacing the water intermittently. The cooked bean seed are made into sauce and eaten with garri, a roasted cassava product. The water drained after boiling the beans may be taken by lactating mothers to increase their milk production.
Some other people in the Avatime tradition area of the Ho west district, add the matured fresh seeds to soup as a protein supplement, some others like people from Enugu state and Ebonyi state in Nigeria roast the seed and eat it with maize, palm kernel and other things or without ;others cooks it as cowpea pottage (Pottage bean). The matured green beans are also boiled in the pods, shelled and eaten. The tuberous roots of African yam bean is used as a source of carbohydrate in West Africa (Okigbo, 1973; Anon, 1979; Ezueh, 1984; Ene-Obong, 1992; Potteer, 1992.
The seed can be produced into milk and further fermented to produce yoghurt (Amakoromo et al; 2012).
            Incorporating AYB in the feed of some livestock has been attempted (Agunbiade and Longe; 1999; Akinmutimi et al; 2006). Akimutimi et al; (2006) specifically remarked that AYB would be good alternative protein source for livestock and poultry. The percentage of the hull from the whole seed of AYB according to Agunbiade and Longe (1999) was 7.3%. They revealed the composition of the hull of AYB as follow: Crude protein (11.4%), crude fat (2.6%), phytic acid (82mg/100g) and phytin phosphours (23mg/100g). Potassium and minerals are the major minerals in the hull. The hull is rich in cell well polysaccharides, with the cellulose content of 35.4%. The crude protein in the hull was 11.4%; almost double that in horse bean (Cering et al; 1975, cited in Agunbiade and Longe, 1998) and  more than twice that in bambara groundnut (Mahala and Mohamed; 2010). Major minerals in AYB hull in the order of magnitude are calcium, potassium, phosphorus, magnesium, sodium and iron, other elements are in trace. The experimentation of the AYB hull on rat feeding (Agunbiada and Longe, 1999), showed increased weight and higher feed conversion efficiency compared with cellulose free and pure cellulose meal. This infers that AYB hull could be a good source of dietary fibre. A low quantity of AYB in the meal of weaner Rabbit could substantially substitute for soybean (Akinmutimi et al, 2006). The leaves and stovers (Asara. 1984), the grains and the hull of AYB (Agunbiade and Longe, 1998, Akimutimi et al; 2006) have been employed to substitute for the common livestock feeds. However there is a report in literature on the experimentation of the AYB tuber in animal feed yet. Since the tuber of AYB does not form part of the meal of the West Africans its incorporation in animal feeds as based or concentrates could be a good research attempt.

            In Togo, Ghana and Nigeria, there are pharmacological evidence of the use of AYB in treating some ailments (Asuzu, 1986), the paste made from the seed is used to cure stomach ache and when the paste is mixed with water, it is traditionally used for the treatment of acute drunkenness (Asusu, 1986).

African yam bean serves as a rich source of leaf litter for improvement of soil characteristic. The crop also nodulates profusely and probably has high nitrogen-fixing ability, thereby helping to replenish soil nitrogen.

            The nutrition quality of the grains and tubers of AYB are immense. The African yam bean (AYB) (Sphenostylis stenocarpa) provides two consumable products- the tuber which grows as  the root source and actual yam bean which develop in pods above ground. The protein in both tuber and seed is comparatively higher than what could be obtained in most tuberous legumes and tubers. The protein in the tuber of AYB is more than twice that in sweet potatoes (Ipomeas batatas or Irish (Solanum tuberosum) potatoes (National Research council (NRC, 1979) and very much higher than those in yam and cassava (Amoatey et al; 2006). The proportion of the essential amino acid in the protein of AYB is over 32% with lysine and leucine being predominant (Onyenekwe et al, 2000). Crude protein content is up to 19% in the tuber. The crude protein in AYB seed is lower than in soybeen. However, the amino acid spectrum indicates that most of the essential amino acids especially lysine and methionine levels in AYB are higher than those in other legumes including soybean (NRC, 1979), Evans and Haismer, 1979; Abbey and Berezi, 1988; Ihekoronye and Ngoddy 1985; Kay, 1987.
 As reported by Ekpo (2006), the amino acid profile in AYB compares favourably with the whole chicken’s egg and meets the daily requirement prescribed by food and Agriculture organization (FAO) and World Health Organization (WHO). The protein concentrations are used in fortification of starchy food like maize, cassava and Akamu flour (Eneche, 2005.).

            Kay (1987) documented the proximate analysis details of the seeds of AYB and revealed that the dry matter component of the seed was about 90.5%.
TABLE 1:   Dry Matter Composition
Crude protein
Total carbohydrate
Source: Kay (1987)

Table 2: Essential Amino Acids Analysis
The percentage amino acid analysis in seed of four cultivars of African Yam Bean
Aspartic acid
Glutamic acid
Source: Evans and Boulter, (1974)

Table 3:  The percentage chemical composition of African yam
The percentage chemical composition of African yam bean after drying.
Ash content
Source: Edem et al; (1990).
Table 4: The Percentage Chemical composition of cooked African Yam Bean seed.
Source: Edem et al; (1990)

Table 5: Proximate composition of the African yam bean tuber.
Total Carbohydrate
Crude fibre
Source: Duke(1981)

Table 6: The mineral composition of African yam bean
Source: Klne, Eka and Aremu (1999)

2.4.2   Anti-nutritional factors in African yam bean
            Anti-nutritional factors (ANF) in food legumes are chemical substances present in products; although non-toxic but generate adverse physiological responses in animal that consumes them. In most cases, ANF interferes with the utilization of nutrition’s in legumes products (Nwokolo, 1996), their presence could cause flatulence. Some workers (Asuzu and Undie, 1986; Okeola and Machuka, 2001; Ajibade et al; 2005) have identified the presence of some ANF such as alkaloids, flavinoids, phytate, Oxalate, saponins, lectin and trypsin inhibitors in the seed of AYB. List of the anti-nutritional factors in the rawbean of AYB includes; trypsin inhibitors, haemagglatinating, tannic acid (tannins), phytic acid, oxalate (Apata and Ologhobo, 1997). In addition to the above list of ANF are α-Galactosides (Stachyose) and Lectin (Oboh et al; 1998). Nwinuka et al, (1997) identified some flatulent factor to include; sucrose, raffinose and stachyose. From the record of Betche et al; (2005), the notable anti nutrients in AYB includes. α-amylase inhibitor (6-13 Ug-1), saponin (2-4mgkg-1),  trypsin inhibitor (0.7-3.0TIUmg-1), total and soluble oxalate (21-35 and 3-6mg 100g-1,respectively), tannin (0.9-20mgg-1), phytic acid (4.5-7.3mgg-1) and β-galactosides (2.3-3.4g 100g-1). They remarked that cynogenic glycoside was higher in the white seeds of AYB compared to those with other seed coat colours.
            Most of the ANF is present in the albumin fraction of the protein of AYB seeds (Machuka and Okeola, 2000). The low acceptability, adoption and utilization of the AYB as human food may have been due to the anti metabolic effect of the protein such as protease inhibitors, chitinase pathogenesis-related proteins and lectin present in the seed of AYB (Machuka and Okelo, 2000).
2.5       Milk Analogues
            These are milk derived from a plant source. (
Vegetable Milk
            Vegetable milk is made based on a seed or cereal soaked in water, ground and fittered. Types of vegetable milk includes; Extracted from legumes; African yam Bean Milk, soymilk which is the most common among the vegetable milk. Extracted from cereals, milk rice, oat or quinoa (

2.5.1   Benefits of vegetable milk
            The main advantage is that it does not contain lactose of animal fat, element that have great amount in cow milk. This makes a prefect substitute for those people who are lactose intolerance and milk allergy. Also for religious/spiritual reasons and for veganism and ovo-vegetarianism, and health condition such as PKU- a rare genetic disorder requiring a low-phenlalanine diet that makes digestion of animal  protein especially case in found in dairy difficult or impossible.  Vegetable milk is a sweet taste and creamy consistency. Moreover, it is rich in protein of good quality.(

2.6       Moi Moi
            Moi moi or moyi-moyi is a Nigeria steamed bean pudding made form a mixture of washed and peeled black-eyed beans, onions and fresh ground-pepper (usual a combination of bell pepper and chilli or scotch bonnet). It is a protein-rich food that is a staple in Nigeria. It originates form south west Nigeria. Moi-moi is prepared by first soaking the beans in cold water until they are soft enough to remove the fine outer covering or peel. Then they are ground or blended (using a blender) until a fine paste is achieved. Moi moi usually comes in a slanted pyramid shape or a clylindrical shape, owing to the mold it is poured into prior to cooking. The pyramid shape come form the traditional broad “ewe eran” (Thaumatococcus daniellii) or banana leaves fashioned into a cone in one’s palm, then the seasoned and garnished liquid is poured into the leaves which is then folded. They cylindrical shapes come from empty cans of tomatoes sauce used in preparation of other dishes. Once placed in its mold, it is placed in a large pot about a tenth filled with water. The water is the source of steam that cooks the moi moi.(

2.6.1   Nutritional Benefits of moi-moi
            Moi-moil is low in cholesterol. Moi-moi is a good source of protein, dietary fibre, iron and calcium.

2.7       Processing of African Yam Bean
            Many food researchers (Njoku et al; 1989; Wokoma and Aziagba, 2000; Aminigo and Meizger, 2005) have employed various processing methods including soaking, blanching, dehulling, heating, soaking with potash etc to attain satisfactory cooking, reduce the ANF content, overcome the harden of the seed coat and improve (by shortening) the cooking time of the seeds. Maximum hydration of the seed was attained at 12 hours of soaking in water. Cooking time could be lowered with 12hours pre-soaked treatment, moreover, a dramatic 50% reduction in cooking time was attained for seeds pre-soaked treatment, with 1% potash or 4% sodium chloride (Njoku et al; 1989). Food processing techniques provides alternative means of improving the quality of foods (Agboola, 2007) and the digestibility of protein in leguminous grains (Abbey and Berezi, 1988). Long time cooking givesS the highest digestibility value in AYB; the thermal process destroys protease inhibitors and opens the protein structure through denaturation (Abbey and Berezi, 1988), breaks down ANF, denatures the protein/enzymes and gelatinized the starch for adequate digestibility (Agunbiade and Longe, 1999). In essence, long cooking using moist heat treatment is a way to rid AYB seeds from ANF (Abbey and Berezi, 1999; Aputa and Ologhobo; 1997; Agunbiada and Longe, 1999, Fasoyiro et al; 2006).
Dehulling of the seeds significantly improved the digestibility of AYB protein compared to whole seed (Abbey and Berezi, 1988). Roasting the bean at 160oC for 30 minutes and the pre-soaking treatment in water alkali, brine and alkali-brine water solution for 24hours (Agunbiad a and Longe, 1999), followed by autocleaving was optimally effective and non-vulnerable to the protein quality of AYB (Nwinuka et al; 1997; Afunbiade and Longe 1999). Although the various processing techniques positively influence the physiochemical properties of AYB; such that the processed meal were of significant nutritional superiority over the unprocessed ones (Agunbiada and Longe, 1996), nevertheless most of the techniques significantly caused high loss in protein, calcium, phosphorus compound (e.g phytin-phosphorus) and phytic acid.
            Fermentation can substantially improve the nutritional quality of AYB (Betche et al; 2005; Agboola, 2007) and reduce loses (due to thermal influences) of most food values. The bacteria encountered during natural fermentation of AYB seeds include; Lactobacillus jensenii, Bacillus coagulans, Aerococcus vindans, pediococcus cereviae.
Naturally, the seeds of AYB were found to contain Lactobacillus jensenii, Bacillus coagulans, Acrococcus viridans, Canadida mycoderm. The high aerobic count might be due to high protein content is AYB. These bacteria produced enzyme which degrade and build up nutrients in AYB with organoleptic quality as condiments (Agboola, 2007). The level of effectiveness of these bacteria during fermentation varies (Berche et al; 2005). The activities of the other ANFs such as trypsin inhibitors, α-amylase inhibitors, tannin and phytic acid were drastically reduced by the two bacteria species. Fermentation slightly increased in vitro protein, digestibility and lowered dietary fibre (Betche et al; 2005; Agboola, 2007).

2.7.1   African Yam Bean Flour
            African yam bean flour can be obtained from the seed by the preparative method described by Eneche (2006). This composite flour with reduced gluten content is limiting in sulphur containing amino acids, methonine and cystine and rich in lysine and tryptophan. (Ene-obong and Carrovale, 1992). African yam bean flour are suitable for breads, cakes and biscuits incorporating the flour into wheat-based products make the foods useful protein and energy sources with good nutritive value. The supplementation of cereal based weaning foods with adequately processed African yam bean flour would help to improve their protein content and quality. The flour of African yam bean can be fortified with other flour sample to produce a good quality bakery products; the flour gives a better colour than other samples dues to the ability of African yam bean products to retain some of the colour pigments found naturally in their seeds on exposure to heat during processing (Banigo et al., 2004).         

2.7.2     Limitations in the Utilization of African Yam Bean
            Some negative conditions have influenced the production and acceptability of African yam bean among cultivators, research scientists and consumers. The potential constraints include;
(i)        The seed contains anti nutritional factors (ANF) or secondary metabolites (Machuka, 2009; Akinmtimi et al; 2006).
(ii)       The agronomic demand for stakes, the long maturation period (National research council, 1979).
(iii)     The characteristic hardness of the seed coat raise high demand on the cost and time of cooking (Oshodi et al; 1995 and Ene-Obony et al; 1993).

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