This work evaluated the nutrient and antinutrient content and nutritive value of a lesser-known high yielding crop (aerial yam) and well-known high yielding legume cowpea. Aerial yam and cowpea used in this work were obtained from a family farm in Ovoko, Igbo-Eze South Local Government Area, Enugu state, Nigeria. Four kilogrammes of both foods were harvested. Aerial yam was cleaned, washed, allowed to dry, and divided into three equal portions. Cowpea was also cleaned, washed, allowed to dry and divided into three equal portions. The first portion of aerial yam was peeled, cut into small round sizes, spread out in a wide wooden basket and sun-dried, milled, packaged in cellophane bags, name labelled and stored in a cool place until used. The other two portions were soaked in tap water in a ratio of 1:3 (w/v), drained, spread on a wet jute bag, covered well with another wet jute bag, allowed to germinate, and divided into two portions after germination. The first portion was treated as the first ungerminated sample. The third portion was soaked in a container in tap water in a ratio of 1:3 (w/v) and left for fermentation by inherent microflora enzymes. After fermentation, the samples were dried, milled and packaged as others. Cowpea first portion was spread in a wooden mesh, sun dried, milled and packaged and stored safely until used. The other portion was germinated as aerial yam and treated the same. The last portion was treated as aerial yam and stored for analysis. Various nutrients and antinutrients were estimated using standard techniques. The flours were used to formulate rat diets containing 1.6g N or 10% protein (nitrogen basis). Twenty adult albino rats (100-200)g were allotted to 4 diets based on these two foods (aerial yam and cowpea). Other nutrients, eg. Oil, mineral and vitamins were added to produce four adequate diets for the rats. Both germination and fermentation increased nutrient contents of the two foods and equally reduced their antinutrients.  The protein and mineral bioavailablity of these flours was high as judged by the result of nitrogen balance and liver composition of adult rats based on composites of the flours. Both germination and fermentation increased moisture from 7.68 to 8.63% in aerial yam and 7.78 to 8.24% in cowpea. These processes either single or combination of the two increased protein from 17.76 vs 19.26% in cowpea.  Combination of the two processes caused increase in fibre only, in aerial yam (3.18 vs 3.97%) when compared with the control.  Both processes decreased carbohydrates in aerial yam (65.37 to 62.21 and 60.10%) and cowpea (67.85 to 63.85 and 62.80%) in both flours. Both treatments increased zinc, iron, calcium and phosphorous.  Phytate and tannins decreased due to the processes, except for that of germinated cowpea (4.87 vs 4.79 and 4.32% for aerial yam and 4.61 vs 3.97% for cowpea).  Haemaglutinin and oxalate were decreased by the treatment.  On the other hand, they increased saponins (0.048 vs 0.07 and 0.11% in aerial yam, 0.01 vs 0.09 and 0.12% in cowpea).  Nitrogen solubility, fat absorption capacity, water absorption capacity and foam absorption capacity increased as against their controls (35.48 vs 37.78 and 39.15%, 34.22 vs 36.60 and 38.26mg) for aerial yam and cowpea respectively.  Both germination and fermentation increased mineral and protein bioavailability of the diet and liver composition of adult rats fed these diets.



1.1 Background of the study

Among the basic needs of man, food is considered the most important because it sustains life.  Bamila (2005), described food as any substance which when taken into the body builds new tissues, repairs or maintains old tissues, provides energy and regulates body processes.

No nation succeeds without enough food to feed her populace all year round.  When the foods are available, consumption pattern becomes a problem. Shortage or unavailability of enough food to feed the population of a country is a big political problem.  This is because malnutrition affects the intellectual capacity of the country’s citizens.

Malnutrition is a problem that affects all age groups and different sectors of the population in different ways.  However, pre-school children, pregnant and lactating mothers are the most vulnerable (FAO, 2002).`

It is an accepted fact that over two (2) billion people worldwide suffer from micronutrient malnutrition.  About 100 to 140 million children suffer from Vitamin A deficiency.  Some 20 million people are handicapped because of iron deficiency disorder (IDD).  Iron deficiency anemia accounts for 20% of maternal deaths in Asia and Africa (FAO, 2002).

Maizya-Dixon, Akinyele, Oguntona, Nokoe, Sanusi, and Harris (2004) observed that micronutrient deficiency in Nigeria is approximately 36.3% of children under the age of 5 years.  These children are at different stages of iron deficiency and 29.5% had Vitamin A deficiency.

The food consumption pattern of an individual influences his health and nutritional status.  Adequate nutrients intake maintains good health and increases resistance or protects against ill health.

The ability to diversify foods and inclusion of fruits and vegetables in our diets would effectively protect against micronutrient deficiency diseases in Nigeria.

Some micronutrients were singled out because of their obvious health implications.  Consumption of adequate diets protects against the adverse of vitamins and minerals deficiencies in Nigeria. Some statistics show that:

  • Approximately 40% – 60% of children aged 6 – 24 months are at a risk of death in period immediately before or after birth due to iron deficiency;
  • Approximately 100,000 Nigerian infants are at increased risk of death in period immediately before or after birth due to severe anemia in mothers;
  • An estimated 11,000 deaths among young Nigerian women every year in pregnancy and child birth because of severe iron deficiency anemia;
  • Over 80,000 children each year died from increased susceptibility to infection due to vitamin A deficiency;
  • Approximately 25% of Nigerian children grow poorly due to vitamin A deficiency coupled with lowered immunity;
  • An estimated 350,000 Nigerian babies are born each year with intellectual impairment due to iodine deficiency in pregnancy and others(FAO/WHO, 1996)

These nutrient deficiencies were a function of poor nutrition education and failure to grow foods in home gardens to adequately address these nutritional problems in Nigeria.  Some foods are rarely consumed in Nigerian homes.  However, the cause of inadequate consumption of these foods is because of ignorance of foods and inadequate preparation, etc.  Many of these foods are available due to their high yield.  Aerial yam or adu in lgbo language,  ewuraesi in Yoruba and doyarbisa in Hausa languages and cowpea which is agwa in lgbo, ewa in Yoruba and wanke in Hausa languages are among these food crops.  Combination of these food crops and their consumption may provide adequate nutrients to maintain good health. Seasonality precipitates micronutrient and general nutrient deficiencies.

1.2 Statement of problem

Nigeria as a nation has many food crops, which if carefully processed would add to the nutritional status of her citizens.  Some of these food crops have limited consumption in Nigerian homes.  This is because of inadequate processing and methods of preparation for consumption.  Aerial yam (Dioscorea bulbifera) and cowpea (Vigna unguiculata) are among the high yielding crops in Nigeria.  Nigeria literature on the food potentials of combinations of aerial yam and cowpea are scarce.  Not much study had been undertaken on aerial yam as a food crop despite its high yield.  One would regard this food crop as a lesser-known tuber, especially in Nigeria.  Cowpea is a crop that yields much, locally produced and once dried it is available all the year round.  Aerial yam also has high yield and could keep long all the year round. Both aerial yam and cowpea can contribute to food security.  There are no studies on nutrient content of blend of aerial yam and cowpea subjected to various food processing techniques in Nigeria literature. 

The thrust of this study is to germinate and ferment these two crops, produce their flours and determine the nutrient content of these flours as well as evaluate the biological value of their blends in adult albino rats.

1.3 Objective of the study

The general objective of the study was to determine the chemical composition and nutritive value of blends of processed aerial yam (Discorea bulbefra) and cowpea (Vigna unguiculata).

Specific objectives were

  1. Subject aerial yam (Dioscorea bulbifera) and cowpea (Vigna unguiculata) to food processing techniques of germination and fermentation to produce flours;
  2. determine the nutrient composition of the flours, especially micro-nutrients (iron, zinc, calsuim and phosphorus);
  3. determine the anti-nutrients and food toxicants (tannins, phytate, oxalate saponins and haemaglutinin);
  4. determine the functional properties of the flours (fat absorption capacity, water absorption capacity, nitrogen solubility and foam capacity)
  5. evaluate the nutritive value (mineral and nitrogen) of the blends of germinated and fermented aerial yam and cowpea flours as sole sources of protein in diets fed adult albino rats.

1.4 Significance of study

The result of this study would provide basic information on the nutritional quality of a locally available and lesser-known food crop (aerial yam) whose nutrient composition has not been adequately documented in Nigeria literature.  The results also would serve as baseline information for nutritionists, dieticians, community health workers and other related professionals.  The results would help promote dietary diversification for children and adults.



2.1       Introduction

Nutrition is a vital issue in human development. However, it is taken for granted by the generality of people. The poor state of health in Nigeria is evidence of the persistence prevalence of malnutrition and under-nutrition.  In Nigeria, protein-energy malnutrition is common. Presently it is endemic and the situation is complicated by inflation and economic recession. Legumes are relatively minor crops despite the fact that they play a good role as a source of protein and oil in the diet of people (Onyechi and Nwachi, 2008)  Ideally, good nutrition should be assured of varied diet, rich in protein, carbohydrates, fats and minerals. As a source of protein, carbohydrates and mineral blends of aerial yam and cowpea are good because leguminous proteins are rich in lysine and when combined in adequate proportion with aerial yam, it is assumed that they are going to be good supply of protein.

In Nigeria, many nutritious foods are produced from cowpea. The popularity of many varieties of cowpea in different localities has tended to obscure the importance of other legumes (Obizoba, 1990). Legumes are known to contain anti-nutritional factors that limit their nutritional quality, especially nutrient digestibility. The blends of aerial yam and cowpea flours may help to improve digestibility. Aerial yam as a food crop is grown in the tropics and sub-tropical regions. However, its consumption is minimal when compared to its yield : 2008).

The consumption of aerial yam is not popular in Nigeria. This is because it does not play a significant role in the life of the Nigerian populace as a food crop. Aerial yam yields much. It is now one of the Nigerian food crops that do not benefit the nation. The major reason why the food crop is not beneficial is because of the monotony in its preparation.

            Cowpea (Vigna unguiculata) is widely grown in Nigeria. It is highly acceptable as excellent source of protein. Moreover, it is used to improve root base yam and some cereals diets. Aerial yam is usually boiled whole and consumed. Some communities use the leaves when it is still fresh as a source of green leafy vegetables. Cowpea is the most economically and nutritionally important indigenous African legume. It is a dynamic crop that adds versatility to the diet. It provides carbohydrate, moderate protein and low fat from foliage as well as seeds for a vegetarian’s diet (Bubenhiem, Mitchell and Nielson, 1990).

            Aerial yam is not adequately consumed, the only consumption is done by boiling, peeling and addition of oil and salt to taste. It is a high yielding crop and a good economic crop that is much more beneficial to mankind if it is properly utilized. Cowpea is usually consumed alone or combined with other foods – cereals and other yams apart from ariel yam.

The fight against protein malnutrition all over the world is based on bridging the gap between protein needs and supplies. The development and testing of diets based on commonly consumed foodstuffs have received considerable attention in the laboratory (Nzomiwu and Obizoba, 1998).

            Cowpea (Vigna unguculata L. Walp) and aerial yam (Dioscorea bulbifera) were processed using germination, fermentation and grinding into flour. Cowpea is going to be used in combination with aerial yam as sole source of protein. The blends would be used to feed adult albino rats (100 – 200g).

2.1       Aerial yam

2. 1.1   Botany of aerial yam

Aerial yam is from the family of Discorea speicies. It has  scientific or botanical name of Dioscorea bulbifera which is a twining or climbing or seldom erect herb with large or small basal tubers. The stems are about 20m (16ft.) or more in length (Langelande and Craddock Burks, 1998). It is freely branching above internodes bound or slightly angled in cross-section. Aerial tubers (bulbils) are freely formed in leaf axils usually roundish, to 12cm with smooth surfaces. The leaves are long petiole alternating blades 20cm or more in length, broadly heart shaped with basal lobes usually rounded.  All the leaf veins arise from the leaf base (Langelande and Craddock Burks, 2003) Aerial yam is a climber, new species are made from the bulbils. The aerial stems die in the harmattan and re-sprouting occurs from the bulbils (http://plantations, 2008).  Aerial yam is a food crop that yields much with minimal consumption. Aerial yam is grayish and somewhat irregular when peeled. The seeds are whitish green or golden brown. The skin of the edible core is thick and corky. This is why it is impossible to penetrate them with fingernails (Langelande and Stocher, 2001).

2.1.2 Cultivation

            Aerial yam is cultivated by planting the yam whole or by cutting the bulbs into two or more depending on the size, each of which has the power to shoot out a stem. (Langelande and Stocker, 2001). They are planted in mounds or ridges. They are propped up with hand stick to their twigging (Uguru, 1996). Aerial yam is cultivated more in Nigeria, especially in Igbo speaking areas. The tubers when planted give rise to the stem. The stem quickly grows, often to about 70 feet. They produce aerial tubers that are attached to the stem. Aerial yam has been in cultivation for several years in both Asia and Africa. Africa consumes it the more (Quinin and Mayer, 2002).  When the stem and leaves begin to die, the crop is harvested. Aerial yam generally matures eight months from the time of planting. Aerial yam can be plucked or allowed to drop by themselves (Langelande and Stocher, 2001).

2.1.3 Food uses

Aerial yam serves as food sources for consumption and commercial distribution (Bhandari and Kawabaka, 2005).  Africa and Asia are the principal culinary and commercial cultivars of bulbifera. These provide palatable food for the people. (Webster and Ternai, 1984). Various preparation techniques are used to prepare aerial yam in other countries such as boiling, steaming or baking over coals of fire after peeling or before peeling (Bhandari and Kawabaka, 2005). 

Aerial yams are used as food in emergencies such as during famine and drought where it is applicable. Tubers from Africa, Australia, and Thailand are documented to have well textured flesh and a little bitter taste in contrast to the softer flesh and sweeter taste of tubers produced by the varieties cultivated in Asia (Webster and Ternai, 1984). Various preparation techniques are used to lessen or fully eliminate the bitterness where applicable. The process of detoxification involves pounding the tubers with lime or sand or roasting or repeated pounding with wood ash and steeping in water to clean (Webster et al, 1984).

2.1.4 Medicinal value of aerial yam

            Aerial yam has bitter taste. The bitterness is useful in treatment of worms, stopping vomiting and per-oxidation of blood lipids. This lowers the level of triglycerides. It is good for treating cardiovascular diseases (Bhandari and Kawabaka, 2003). Bulbifera was used in folk medicines in the plants’ natural range. (Martin, 1994).  Among the many documented medicinal folk uses of the plant, some of the most well known include the use of bulbils for external treatment of sores and the internal treatment of hemorrhoids in India. The use of a paste created from the bulbils to treat swelling as a cure for snake bites and scorpion stings in Africa and central Asia. In China, it is used for the treatment of sore throat and struma and remedy diabetes. In Japan, it is used for treatment of leprosy and tumors (Martin, 1994).  In various parts of Africa and on the island of Java, aerial tubers are used as fish poison (Langeland, Cherry, Mccormick and Craddock, 2008). The poison released by the grated tubers placed in a stream acts as to stun fish at a fairly long distance. Varieties of the plant are used by farmers to confuse thieves through the planting of unpalatable varieties within the main crop variety (Langland, Cherry, Mccormick and Cradock, 2008).