STUDIES ON NUTRIENT POTENTIALS OF BLENDS OF TREATED AERIAL YAM (DIOSCOREA BULBIFERA) AND COWPEA (VIGNAUNGUICULATA L. WALP) FED ADULT ALBINO RATS

Abstract

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.

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CHAPTER ONE

INTRODUCTION

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.

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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:

(a)       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;

(b)       Approximately 100,000 Nigerian infants are at increased risk of death in period immediately before or after birth due to severe anemia in mothers;

(c)       An  estimated  11,000  deaths  among  young  Nigerian  women  every  year  in pregnancy and child birth because of severe iron deficiency anemia;

(d)       Over 80,000 children each year died from increased susceptibility to infection due to vitamin A deficiency;

(e)       Approximately  25%  of  Nigerian  children  grow  poorly  due  to  vitamin  A

deficiency coupled with lowered immunity;

(f)       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.

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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

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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.

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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.

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