ABSTRACT
The study examined the chemical composition of fresh,
sundried tender leaves and husks of cowpea ‘Adengee’ (Vigna
unguiculata) and organoleptic attributes of their traditional soups.
Information on processing, preparation and utilization of soup meals based on cowpea
leaves and husks were obtained during the focus group discussion. The tender
leaves and husks were parboiled and sundried. Proximate, micronutrients,
phytochemicals and antinutrient levels were determined using standard
procedures. The soups based on fresh and sundried leaves and husks were
analysed prior to sensory evaluation. The data collected were statistically
analysed using means, standard deviation and standard error. All values were
based on residual moisture. Protein for dried leaves was higher (p<0.05)
(39.24 vs. 21.98 and 13.95%) than those of fresh leaves and dried husks. Dried
leaves and husks had lower fat than the control (1.31 and 0.75 vs. 9.10%)
(p<0.05). Sun drying increased ash in both dried leaves and husks (14.74 and
10.86 vs. 4.82%). The lower value for fibre in the dry samples was rather
surprising (14.20 and 20.42 vs.25.13%) (p<0.05). Carbohydrate significantly
increased more in dried husks than in dried leaves. (53.76 Vs. 30.22%)
(p<0.05).The micronutrients in both dried leaves and husks were reduced due
to their volatile nature. Tannins, saponins, flavonoids and polyphenols
decreased significantly (p<0.05) in processed samples due to drying. Soups
based on dried leaves (DS) had higher protein (p<0.05) relative to the soup
based on dried husks (HS) and fresh leaves (FS) (34.40 vs.34.10 and 33.30%).
Similarly, husks based soups had higher fat (34.10 vs.34.05 and
31.44%)(p<0.05) Ash was higher in dried leaves based soup(7.83%) and fresh
leaves soup (7.20%). Fibre for the husks based soup was higher (p<0.05)
relative to fresh and dried leaves based soups (6.13 vs.5.58 and 6.11%,
respectively). The carbohydrate levels were generally appreciable. All soups
had appreciable levels of calcium, phosphorus and iron. These minerals varied
significantly amongst the soups (p<0.05). Zinc and iodine also differed
(p<0.05).β-carotene content of soup based on fresh leaves was higher
(p<0.05) relative to those based on dried leaves and husks (6.08 vs.5.07 and
5.46RE).Vitamin C varied significantly (0.90 to 1.10mg) in soups based on fresh
leaves and dried husks. Tannins, saponins, polyphenols and flavonoids in soups
based on fresh leaves and dried husks were comparable. Anti nutrients levels in
all soups were generally low. Scores for all organoleptic attributes of the
three soups were more than half (6.17 to 7.70) of the 9-point scale. The soups
were generally acceptable. As judged by the results, cowpea leaves, husks and
their soups have high nutrient potentials to justify its cultivation, consumption
promotion and diversification. Consumption related information such as
nutritional properties should be packaged and extensively promoted to broaden
the knowledge of health and nutritional benefits of consuming cowpea leaves and
husks. The results demonstrate that, there is a potential in developing
multi-purpose varieties with good performance, which are well-yielding in both
leaves and seeds. Therefore, production related information, such as variety,
yields and cultivation practices as well as processing should be packaged and
made available to extension personnel and governmental agricultural research
institutes that often have a good outreach to farmers.
TABLE OF CONTENTS
TITLE PAGE
LIST OF TABLES
LIST OF FIGURES
ABSTRACT
CHAPTER ONE: INRODUCTION
1.1 Background of study
1.2 Statement of the problem
1.3 Objectives of study
1.3.1 General objective
1.3.2 Specific objective
1.4 Significance of the study
CHAPTER TWO: REVIEW OF RELATED LITERATURE
2.1 Legumes
2.2 Cowpea
2.3 Cowpea leaves and husks (vegetables)
2.3.1 Chemical composition of cowpea leaves
2.4 Vegetables and their uses
2.5 Nutrient composition of green leafy vegetables
2.5.1 Moisture content
2.5.2 Protein
2.5.3 Ether extract (fat)
2.5.4 Vitamins
2.5.5 Anti nutrient content
2.6 Food processing
2.6.1 Processing of vegetables
2.6.2 Blanching
2.6.3 Drying
2.6.4 Effects of processing on nutrient content of leafy vegetables
CHAPTER THREE: MATERAILS AND METHODS
3.1 Study area
3.2 Sampling procedures
3.3 Focus group discussion
3.4 Processing of samples
3.4.1 Cowpea leaves
3.4.2 Cowpea husks
3.5 Purchase of foods
3.5.1 Pounded yam preparation
3.6 soup preparation
3.7 Chemical analysis
3.7.1 Proximate analysis
3.7.1.1 Moisture
3.7.1.2 Protein
3.7.1.3 Fat
3.7.1.4 Ash
3.7.1.5 Crude fiber
3.7.1.6 carbohydrate
3.7.2 Mineral determination
3.7.3 Vitamins (antioxidants) determination
3.7.3.1 Beta carotene (retinol)
3.7.3.2 Vitamin C
3.7.4 Phytochemical screening
3.7.4.1 Flavonoids
3.7.4.2 Saponins
3.7.4.3 Tannins
3.7.5 Anti nutrients
3.7.5.1 Oxalate determination
3.7.5.2 Phytate determination
3.7.5.3 Haemaglutinin
3.8 Sensory evaluation
3.9 Statistical analysis
CHAPTER FOUR: RESULTS
4.1.1 Protein
4.1.2 Fat
4.1.3 Ash
4.1.4 Fiber
4.1.5 Carbohydrate
4.2.1 Iron
4.2.2 Zinc
4.2.3 Iodine
4.2.4 Calcium
4.2.5 Phosphorus
4.2.6 Bet carotene
4.2.7 Vitamin
4.3.1 Tannins
4.3.2 Saponins
4.3.3 Flavonoids
4.3.4 Polyphenols
4.4.1 Phytate
4.4.2 Oxalate
4.4.3 Haemagglutinin
4.5.1 Protein
4.5.2 Fat
4.5.3 Ash
4.5.4 Fibre
4.5.5 Carbohydrate
4.6.1 Iron
4.6.2 Zinc
4.6.3 Calcium
4.6.4 Iodine
4.6.5 Phosphorus
4.6.6 β- carotene
4.6.7 Vitamin C
4.7.1 Tannins
4.7.2 Saponins
4.7.3 Polyphenols and flavonoids
4.8.1 Phytate, oxalate and haemagglutinin
4.9.1 Colour
4.9.2 Taste
4.9.3 Consistency
4.9.4 General acceptability
CHAPTER FIVE: DISCUSSIONS, CONCLUSION AND RECOMMENDATIONS
5.1.2 Cowpea leaves and husks samples
5.1.3 Cowpea leaves and husks soup
5.1 Conclusion
5.2 Recommendation
REFERENCES
APPENDIX
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the study
The scarcity of documented information on the nutrient potentials of most of the foods consumed in Nigeria has greatly contributed towards the ineffectiveness of nutrition education programmes to meet the nutrient needs of a vast segment of the Nigerian population. This lack of documented nutrition information has precipitated wrong choices of foods, low nutrients intake and delay in embracing food diversification. The knowledge of the influence of processing on the chemical composition of foods is also necessary for optimizing nutrient reiteration during handling and processing of our local food materials (Ibok,Ellis & Owusu,2008).
Recently, researchers have become convinced that nutrients found in fruits and vegetables do more than just prevent diseases such as beriberi or rickets. The most publicized finding reveals that certain vitamins or vitamin precursors, notably vitamin C; beta-carotene as well as polyphenols are powerful antioxidants (Consumer Report on Health, 1998). Antioxidants prevent molecular damage caused by oxidation in that, the protection offered may fend off many diseases and muscular degeneration (Islam et al., 2002).
Cowpea (Vigna unguiculata L. Walp), an annual herbaceous legume originated in Africa and is wildly grown. Drought tolerance; short growing period and its multi-purpose use make cowpea a very attractive crop to farmers who cultivate in marginal, drought-prone areas with low rainfall and less developed irrigation systems where infrastructure, food security and diminishing malnutrition are major challenges (Hallensleben, Polrech, Heller &, Maass, 2009). Lawrence and Whitbread (2006) described cowpea as one of the most important tropical dual-purpose legumes, being used as leafy vegetable, grain, as fresh cut-and-carry foliage, and for hay and silage.
Cowpea has much variability within the species. The specie under study is local specie with coiled
pods (Adengee in Tiv,). The fresh seeds are greenish but golden brown when dried and relatively
small in size compared with the common black eyed beans. This crop can be used at all stages of
growth as a vegetable crop. The tender green leaves are an important food source in Tiv communities
in Benue State. The green leaves serve as an ingredient in egusi (melon) soup just like spinach is used
in egusi soup; or the leaves are blanched and sun dried for with egusi soups all year round. The
immature pods are boiled, the boiled seeds are eaten as vegetable and the husks are sun dried, prepared as egusi soup.
1.2 Statement of the problem
Cowpea leaves and husks have not received the needed research-based attention in Nigeria. Despite the abundance of this vegetable crop in the Nigerian communities, particularly in Tiv land, information on their processing for preservation, uses in preparation of traditional soups and their nutrient composition is scanty in Nigeria literature. Although lately, some researches were carried out on African indigenous vegetables, especially leafy ones, cowpea research continued to focus on improvement of the grain and/or the entire herbage for animal feed (Singh, Ajeigbe, Tarawali, Fernandez-rivera & Musa, 2003). According to Hallensleben et al. (2009), cowpea is an important food legume and its use as a leafy vegetable is essential. Utilization of cowpea as a leafy vegetable and grain crop may provide nutritional and harvest versatility not available with purely vegetable crops such lettuce or monocarpic crops such as wheat (Bubenheim, Mitchell and Nielson,1990). The populace unaware of the high nutrient potentials of this vegetable grows cowpea, wait for the harvest of the matured dry seeds, and discard the leaves. However, it is the leaves of some legumes, including cowpea, that showed much promise for providing part of the vastly increased supplies of nutrients that the world population needs(Bubenheim, Mitchell and Nielson,1990). The need remains to further intensively research on these vegetable and their health benefits. It is, therefore, imperative to....
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