2.1 ORIGIN
OF AFRICAN YAM BEAN
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.
CULTIVATION
CONDITIONS
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.
2.3 UTILIZATION OF AFRICAN YAM BEAN
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).
2.3.2 USE FOR LIVESTOCK FEED
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.
2.3.3 USE FOR MEDICINE
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).
2.3.4 USE FOR SOIL IMPROVEMENT
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.
2.4 NUTRITIONAL QUALITY OF AFRICAN YAM BEAN
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.).
2.4.1 PROXIMATE COMPOSITION AFRICAN YAM BEAN
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
Component
|
%
|
Crude
protein
|
24-28
|
Fat
|
1.5-2
|
Total
carbohydrate
|
74.1
|
Fibre
|
5.2-5.7
|
Ash
|
2.8-3.2
|
Source:
Kay (1987)
Table
2: Essential Amino Acids Analysis
The
percentage amino acid analysis in seed of four cultivars of African Yam Bean
Component
|
%
|
Aspartic
acid
|
11
|
Threonine
|
4
|
Serine
|
6
|
Glutamic
acid
|
15
|
Proline
|
5
|
Glycine
|
4
|
Alanine
|
4
|
Valine
|
5
|
Methionine
|
1
|
Isoleucine
|
4
|
Leucine
|
7
|
Tyrosine
|
4
|
Phyenylalanine
|
6
|
Histidine
|
5
|
Iysine
|
9
|
Arginine
|
6
|
Cystein
|
2
|
Source:
Evans and Boulter, (1974)
Table
3: The percentage chemical composition
of African yam
Bean
The
percentage chemical composition of African yam bean after drying.
Component
|
%
|
Protein
|
19.5
|
Carbohydrates
|
62.2
|
Fat
|
2.5
|
Ash
content
|
2.8
|
Moisture
|
10.6
|
Source:
Edem et al; (1990).
Table
4: The Percentage Chemical composition of cooked African Yam Bean seed.
Component
|
%
|
Protein
|
19.2
|
Carbohydrate
|
62.0
|
Fat
|
2.3
|
Ash
|
2.7
|
Source:
Edem et al; (1990)
Table
5: Proximate composition of the African yam bean tuber.
Component
|
100g
|
Protein
|
0.6g
|
Total
Carbohydrate
|
85.3g
|
Crude
fibre
|
1.1g
|
Ash
|
2.2g
|
Phosphorus
|
28mg
|
Source:
Duke(1981)
Table
6: The mineral composition of African yam bean
Component
|
100g/mg
|
Potassium
|
43.6
|
Phosphorus
|
27.4
|
Potassium
|
116.4
|
Magnesium
|
43.2
|
Iron
|
12.6
|
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. (en.wikipedia.org/wiki/plant-milk)
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 (en.wikipedia.org/wiki/plant-milk)
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.(en.wikipedia.org/wiki/plant-milk)
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.(en.wikipedia.org/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).