CHEMICAL COMPOSITION OF PROCESSED TENDER LEAVES AND HUSKS OF COWPEA AND ORGANOLEPTIC ATTRIBUTES OF THEIR SOUPS AS CONSUMED IN TIV COMMUNITIES, BENUE STATE, NIGERIA

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TABLE OF CONTENTS

TITLE PAGE             –        –           –           –           –           –           –           i

APPROVAL PAGE   –       –           –           –           –           –           –           ii

CERTIFICATION     –             –           –           –           –           –           –           iii

DEDICATION           –          –           –           –           –           –           –           iv

ACKNOWLEDGEMENTS           –           –           –           –           –           –           v

LIST OF TABLES          –           –           –           –           –           –           vii

LIST OF FIGURES             –           –           –           –           –           –           viii

ABSTRACT           –           –           –           –           –           –           –           ix

CHAPTER ONE:  INTRODUCTION       –           –           –           –   1         

1.1       Background of study  –          –           –           –           –           –           1

1.2       Statement of the problem     –           –           –           –           –           2

1.3       Objectives of study     –               –           –           –           –           –           3

1.3.1    General objective        –          –           –           –           –           –           3

1.3.2    Specific objective        –           –           –           –           –           –           3

1.4       Significance of the study         –           –           –           –           –           3

CHAPTER TWO: REVIEW OF RELATED LITERATURE –                  –           4

2.1       Legumes          –           –           –           –           –           –           –           4

2.2       Cowpea           –           –           –           –           –           –           –           4

2.3       Cowpea leaves and husks (vegetables)      –           –           –           9         

2.3.1    Chemical composition of cowpea leaves        –           –           –           10

2.4       Vegetables and their uses       –              –           –           –           11

2.5       Nutrient composition of green leafy vegetables         –           –           12

2.5.1    Moisture content         –        –           –           –           –           –           12

2.5.2    Protein             –           –           –           –           –           –           –           12

2.5.3    Ether extract (fat)             –           –           –           –           –           –           13

2.5.4    Vitamins          –           –  –           –           –           –           –           –           13

2.5.5    Anti nutrient content  –            –           –           –           –           –           13

2.6       Food processing          –           –           –           –           –           –           16

2.6.1    Processing of vegetables          –           –           –           –           –           16

2.6.2    Blanching        –           –       –           –           –           –           –           17

2.6.3    Drying –           –                –           –           –           –           –           17

2.6.4    Effects of processing on nutrient content of leafy vegetables           18

CHAPTER THREE: MATERAILS AND METHODS – –                –           20

3.1       Study area       –           –            –           –           –           –           20

3.2       Sampling procedures   –                  –           –           –           –           21

3.3       Focus group discussion           –           –           –           –           –           22

3.4       Processing of samples –               –           –           –           –           –           22

3.4.1    Cowpea leaves            –                   –           –           –           –           –           22

3.4.2    Cowpea husks             –               –           –           –           –           –           22       

3.5       Purchase of foods       –           –        –           –           –           –           –           26

3.5.1    Pounded yam preparation                 –           –           –           –           26

3.6       soup preparation          –                 –           –           –           –           –           26

3.7       Chemical analysis        –           –  –           –           –           –           –           28

3.7.1    Proximate analysis      –           –        –           –           –           –           –           28

3.7.1.1 Moisture          –           –               –           –           –           –           –           28

3.7.1.2 Protein             –           –              –           –           –           –           –           29

3.7.1.3 Fat                   –           –                –           –           –           –           –           30

3.7.1.4 Ash      –           –           –     –           –           –           –           –           30

3.7.1.5 Crude fiber      –             –           –           –           –           –           –           30

3.7.1.6 carbohydrate   –               –           –           –           –           –           31

3.7.2    Mineral determination –      –           –           –           –           –           31

3.7.3    Vitamins (antioxidants) determination     –           –           –           -31

3.7.3.1 Beta carotene (retinol)    –           –           –           –           –           –           31

3.7.3.2 Vitamin C              –           –           –           –           –           –           32

3.7.4    Phytochemical screening             –           –           –           –           –           33

3.7.4.1 Flavonoids        –           –           –           –           –           –           –           33

3.7.4.2 Saponins        –           –           –           –           –           –           –           33

3.7.4.3 Tannins                –           –           –           –           –           –           33

3.7.5    Anti nutrients  –              –           –           –           –           –           –           34

3.7.5.1 Oxalate determination        –           –           –           –           –           –           34

3.7.5.2 Phytate determination – –           –           –           –           –           –           34

3.7.5.3 Haemaglutinin –         –           –           –           –           –           –           35

3.8       Sensory evaluation                –           –           –           –           –           36

3.9       Statistical analysis            –           –           –           –           –           –           36

CHAPTER FOUR:  RESULTS       –           –           –           –           –           37

4.1.1    Protein –                    –           –           –           –           –           –           –           37

4.1.2    Fat       –           —           –           –           –           –           –           –           37

4.1.3    Ash      –          —          –           –           –           –           –           –           37

4.1.4    Fiber    –                –           –           –           –           –           –           –           37

4.1.5    Carbohydrate  –           –           –           –           –           –           –           37

4.2.1    Iron     –                     –           –           –           –           –           –           –           38

4.2.2    Zinc     –           –     –           –           –           –           –           –           –           38

4.2.3    Iodine  –           –         –           –           –           –           –           –           –           38

4.2.4    Calcium           –        –           –           –           –           –           –           –           39

4.2.5    Phosphorus    –           –           –           –           –           –           –           –           39

4.2.6    Bet carotene        –           –           –           –           –           –           –           39

4.2.7    Vitamin           –       –           –           –           –           –           –           –           39

4.3.1    Tannins            –    –           –           –           –           –           –           –           40

4.3.2    Saponins            –           –           –           –           –           –           –           40

4.3.3    Flavonoids                –           –           –           –           –           –           40

4.3.4    Polyphenols     –           –           –           –           –           –           –           41

4.4.1    Phytate            –              –           –           –           –           –           –           41

4.4.2    Oxalate            –                 –           –           –           –           –           –           41

4.4.3    Haemagglutinin    –           –           –           –           –           –           –           42

4.5.1    Protein –           –             –           –           –           –           –           –           42

4.5.2    Fat       –           –               –           –           –           –           –           –           42

4.5.3    Ash      –           –    –           –           –           –           –           –           –           43

4.5.4    Fibre    –     –           –           –           –           –           –           –           43

4.5.5    Carbohydrate  –  –           –           –           –           –           –           –           43

4.6.1    Iron     –           –  –           –           –           –           –           –           –           43

4.6.2    Zinc     –         –           –           –           –           –           –           –           44

4.6.3    Calcium              –           –           –           –           –           –           –           44

4.6.4    Iodine  –           –      –           –           –           –           –           –           44

4.6.5    Phosphorus        –           –           –           –           –           –           –           44

4.6.6    β- carotene      –   –           –           –           –           –           –           –           44

4.6.7    Vitamin C       –             –           –           –           –           –           –           44

4.7.1    Tannins                     –           –           –           –           –           –           45

4.7.2    Saponins          –           –           –           –           –           –           –           45

4.7.3    Polyphenols and flavonoids    –      –           –           –           –           –           45

4.8.1    Phytate, oxalate and haemagglutinin  –   –           –           –           46

4.9.1    Colour –           –              –           –           –           –           —          –           47

4.9.2    Taste    –           –        –           –           –           –           –           –           47

4.9.3    Consistency     –         –           –           –           –           –           –           47

4.9.4    General acceptability  –         –           –           –           –           –           47

CHAPTER FIVE:  DISCUSSIONS, CONCLUSION AND RECOMMENDATIONS -48

5.1.2    Cowpea leaves and husks samples-    –                   –           –             48

5.1.3    Cowpea leaves and husks soup             –           –           –           –             51

5.1       Conclusion      –           –           –           –           –           –           –           52

5.2       Recommendation       –           –           –           –           –           –           52

REFERENCES        –                      –           –           –           –           –           –           53

APPENDIX   –           –   –           –           –           —          –           –           –           58

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.

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 elucidate information on the effect of processing on the chemical composition of these cowpea leaves and husks and their soups.

Most Nigerian diets are based on starchy roots, tubers and cereals pounded to produce paste or dried and ground to get fine flour. The flour is stirred with hot water to produce paste. These are consumed with the soups as accompaniment. Nigeria uses food composition tables from American and European countries to calculate nutrient needs of patients in hospitals or public health settings. The information on the processing, preparation, recipe and nutrient content of this local specie of Vigna unguiculata (Adengee) will be very useful in this regard.

1.3       Objectives of the study

1.3.1    General objective

This study focused on the food potentials of fresh and processed tender cowpea leaves, husks and organoleptic attributes of their traditional soup meals.

1.3.2    Specific Objectives

The specific objectives of this study were to:

i. collect information on processing, preparation and utilization of cowpea leaves and husks in soup meals;

ii. process cowpea leaves and husks using parboiling and sun drying;

iii. determine chemical composition of both the fresh and processed leaves and husks;

iv. prepare soups with these samples and determine their nutrient composition; and

v. assess the organoleptic attributes of the soups and their accompaniment (pounded yam).

1.4    Significance of the Study.

The result from this study would provide base-line data for compiling nutrient content of Nigerian foods and dishes in the food composition table. This would provide for dietitians an easy tool to calculate nutrient needs for patients in hospitals and clinics. The information from this work would also enable public health nutritionists and dietitians to know how best to use these soups for improvement of feeding habits and diversify diets. This information would assist plant breeders in targeting attributes and characteristics of this cowpea specie for improvement. It would support the identification of traits of local importance, which are crucial for site- specific / local breeding approaches by the public sector both within National Agricultural Research Systems (NARS) and international research institutions.

CHAPTER TWO

2.0                               REVIEW OF RELATED LITERATURE

2.1       Legumes.

Grain legumes occupy an important place in human nutrition, especially in the dietary pattern of low-income group of people in developing countries. Legumes are plants of the beans and pea family. They are rich in protein as compared with other plant foods (Asanke, Adu-dapaah & Acheampong,2010 ). Legumes, considered as poor man’s meat are generally good sources of carbohydrates that are released slowly (Mbah, 2000).

Tharanathan and Mahadevamma (2005) reported that, legumes are normally consumed after processing. This, not only improves palatability of foods but also increases the bioavailability of nutrients, by inactivating trypsin, growth inhibitors and haemaglutinins. Starch is the major biopolymetric constituent of legumes.  Processing partially modifies the resistant starch (RS). The latter, is a man made functional dietary fibre, a unique ingredient that can yield high faecal bulk and butyrate production. These are the putative markers of colonic health of humans (Tharanathan & Mahadevamma, 2005). The slow and reduced digestibility of legume starch has been attributed to its amylose, which is considerably branched and has high molecular weight (Barret,1990).

Dietary fibre is a heterogeneous mixture of several types of polysaccharides. Polysaccharide content is high in legumes, especially the husk fraction. It is beneficial because it has therapeutic effects on health (Barret, 1990).

2.2       Cowpea

Cowpea (Vigna unguiculata L.Walp) is an annual legume commonly referred to a black eyed pea, crowder pea, lubia and southern pea. It originated in Africa, and is widely grown (Davis et al., 1971). There are three basic subgroups of cowpea; the common cowpea, the catjang and the yard-long bean (Larkin, 2002).

Cowpea has many cultivars. Each is popular in the localities it is produced. For example Potiskum, Kabanji, Gauzua, Alouka, Kano white, Maiduguri brown and Ife brown. It is found in various parts of Nigeria (Ihekeronye & Ngoddy,1985). The cultivar under study is a local specie that is prostrate (trailing) with coiled pods referred to as Adengee in Tiv and Oraludi in Igbo. The fresh seeds are green and golden brown when dried. The dried seeds are relatively small in size as compared to the common beans.

Cowpea is warm-season, annual, herbaceous legume well adapted to many areas of the humid tropics and temperate zone. The plant tolerates drought, performs well in a wide variety of soils. Cowpea replenishes low fertility soils when the roots are left to decay (Uguru, 1996; Hartmann, 2010)

 Hallensleben et al. (2009) reported that, cowpea is an important food legume and its use as a leafy vegetable is essential in many African countries. Drought tolerance, short growing period and its multi purpose use make cowpea a very attractive alternative for 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. This confirms the view of Cheya and Eyzaguirre(1999) who reported that, the multi –purpose use of cowpea has a unique advantage within the African farming systems.

CHEMICAL COMPOSITION OF PROCESSED TENDER LEAVES AND HUSKS OF COWPEA AND ORGANOLEPTIC ATTRIBUTES OF THEIR SOUPS AS CONSUMED IN TIV COMMUNITIES, BENUE STATE, NIGERIA