EFFECTS OF PROCESSING METHODS ON NUTRIENTS CONTENT OF BITTER LEAF (VERNONIA AMYGDALINA)

ABSTRACT

The aim of this study was to determine the effect of processing methods on the nutrient, mineral, vitamin and anti-nutrient content of Vernonia amygdalina. The vegetable was harvested from National Root and Crop Research Institute (NRCRI) staff quarters. The vegetable was divided into 5 portions A, B, C, D, and E. Portion A was kept fresh, B was squeeze-washed and boiled, C was squeeze- washed with salt, D was squeeze-washed with oil and E was squeeze-washed and then sundried. The fresh sample of the vegetable served as control. All the samples were analyzed for various nutrients and anti-nutrient on wet and dry weight basis using AOAC methods. Data generated were statistically analyzed. The means were separated and compared. Boiling only increased the moisture content but decreased the content of the other nutrients. The addition of salt while squeeze-washing reduced all the nutrient content except for dry matter, ash, crude fiber, fat, protein, carbohydrate, sodium and flavonoid. There was no significant difference (P>0.05) between the ash content of the fresh and the boiled sample (4.49±0.01% and 4.36±0.00%). For the crude fiber content, the bitter leaf washed with salt, washed with oil and the fresh sample had comparable values (P>0.05) (3.26±0.00%, 3.34±0.85% and 3.24±0.00% respectively). The use of palm oil while squeeze-washing increased the fat, β carotene and vitamin E content of the sample but reduced the content of the other nutrient, vitamin and mineral content. For the fat content, the fresh, boiled and squeezed washed with salt sample had comparable values (2.46%, 2.40% and 2.51% respectively). There was no significance difference (P>0.05) in the zinc content of the fresh and sundried sample (1.67±0.03mg/100g and 1.63±0.00mg/100g) and also no significance difference (P>0.05) in the sundried sample and the sample washed with salt (1.63±0.00mg/100g and 1.61±0.02mg/100g). Sun drying increased the bitter leaf’s dry matter, ash, fiber, fat, protein, carbohydrate content but decreased the content of the other nutrients. There was no significance different (P>0.05) between calcium content of the fresh and the sundried sample (19.61±0.01mg/100g and 19.60±0.00mg/100g). As judged by the result all the processing methods reduced the anti- nutrient content of the vegetable. The addition of salt and palm oil on the overall appears to be the best method that maintained and conserved nutrients, minerals and vitamins composition. Boiling after squeeze washing and sun drying after squeeze washing were of best methods of reducing the anti-nutritional factors of bitter leaf.

TABLE OF CONTENT

Title page i

Certification ii

Dedication iii

Acknowledgement iv

Table of content v

List of tables vii

List of figures viii

Abstract ix

CHAPTER 1

 INTRODUCTION 1

1.1 Statement of the problem 3

1.2 Objectives of the study 4

1.3 Significance of the study 5

CHAPTER 2

LITERATURE REVIEW 6

2.1 Nutritional benefits of bitter leaf 7

2.2 Antinutrient content 9

2.3 Processing methods of Vernonia amygdalina 10

2.3.1 Drying and boiling methods of bitter leaf 11

CHAPTER   3

MATERIALS AND METHOD 15

3.1 Study design 15

3.2 Sample collection 15

3.3 Sample preparation 15

3.4 Chemical analysis 20

3.4.1 Nutrient composition   20

3.4.2 Vitamin analysis 25

3.4.3 Mineral analysis 30

3.4.4 Antinutrient analysis 34

3.5 Statistical analysis 39

CHAPTER 4

RESULTS AND DISCUSSION 40

4.1 Chemical properties of the sample 40

4.1.1 Nutrient composition of processed an unprocessed bitter leaf 40

4.1.2    Mineral contents of processed and unprocessed bitter leaf 46

4.1.3   Vitamin content of processed and unprocessed bitter leaf 50

4.1.4   Antinutritional factors in the unprocessed and processed sample of Vernonia amygdalina 53

CHAPTER 5

CONCLUSION 57

5.1 Conclusion 57

5.2 Recommendations 58

References

LIST OF TABLES

Table 4.1 Nutrient composition of unprocessed (fresh) and

processed Vernonia amygdalina (%) 45

Table 4.2 Mineral content of unprocessed (fresh) and

processed Vernonia amygdalina (mg/100g) 49

Table 4.3 Vitamin content of unprocessed (fresh) and

processed Vernonia amygdalina (mg/100g) 52

Table 4.4 Antinutritional factors in unprocessed (fresh)

and processed Vernonia amygdalina (mg/100g) 56

LIST OF FIGURES

Fig 1: Flow chart of squeeze-washing bitter leaf and boiling 16

Fig 2: Flow chart of squeeze-washing bitter leaf and sun drying 17               

Fig 3: Flow chart of squeeze-washing bitter leaf with salt 18

Fig 4: Flow chart of squeeze-washing bitter leaf with oil 19

CHAPTER 1

INTRODUCTION

According to Adegunwa et al. (2011) nutritional importance of vegetables cannot be neglected in our daily meals. Vegetables are edible parts of the plants, which are usually cooked and salted before consumption with other foods. Fresh vegetables are important foods both from an economic and nutritional point of view and vegetable of all types are valuable part of our diet. They play an important part in maintaining general good health owing to the presence of mineral element and vitamin. Nwanekezie and Obiakor- Okeke (2014) reported that leafy vegetables are consumed as cooked complements to the major staples like cassava, cocoyam, guinea corn, maize, millet, rice and plantain. The high biological value of leafy vegetables depends on the pronounced content of the minerals compound especially, calcium, magnesium, phosphorus and iron. Munaya (2013) emphasized that Vernonia amygdalina commonly called bitter leaf is the most widely cultivated species of the genus Vernonia which has about 1,000 species of shrubs. It belongs to the family Astaraceae. It is vegetatively cultivated by stem cutting at an angle of 45° and popular in most of West Africa countries including Nigeria, Cameroon, Gabon and Congo Democratic Republic. It was named after an English Botanist William Vernon. According to Ibrahim et al. (2010) it can adapt to a variety of climates unlike other plants that are native to certain areas. It is grown in many countries, in savannah zones and cultivated fields. It is also referred to as ironweed. Schiffers (2000) stressed that Vernonia amygdalina is frequently found in gardens. Although most popularly used for food, it has also, been traditionally used for its medicinal properties (Swee et al., 2010). Abosi and Raseroka (2003) emphasized that true to its name, bitter leaf is bitter to taste but surprisingly delicious in meals. Ikeh et al. (2014) stressed that bitter leaf is called Omjunso in East Africa especially Tanzania, Onugbo in Igbo-Eastern Nigeria and Orugbo among the Itsekiri and Urhobo tribes in Nigeria, Ewuro (Yoruba), Etidot (Ibibio and Efik), Ityuna (Tiv), Oriwo (Edo), Chusa-doki Shiwaka (Hausa). According to Remison (2005), Vernonia amygdalina is drought tolerant though it grows better in a humid environment. It is used to a large extent in tropical Africa for its culinary and medicinal purposes.  The leaves are eaten, after crushing and washing thoroughly to remove the bitterness. According to Gill (1992) all parts of the plant are pharmacologically useful. Both the roots and leaves are used in phyto-medicine to treat fever, hiccups, kidney disease and stomach discomfort, among others. Antihelmitic and antimalarial properties (Abosi and Raserika, 2003) as well as antitumourigenic properties (Izevbigie et al., 2004); have also been reported for extracts from the plant. According to Alabi et al. (2005) it is also used in the traditional treatment of diabetes, diarrhea, veneral disease, hepatitis, gastrointestinal problems, skin disorders, cough, and constipation and in the treatment of wounds. According to Munaya (2013) it attains the height of 2.5m with leaf of about 6mm in diameter that is elliptic in shape. The branches are brittle and break off easily.  It has grey or brown colored bark; the bark has a rough texture and is flaked. The leaves are elliptical and up to 20cm long. The leaves have soft hairs on the underside. The bark is green or brownish dark with rough surface. The leaves are green with characteristic odor and bitter taste. The flowers are white, small, tiny and clustered. The small fruits have slightly hairy small nuts inside. It can reach 23ft in height when fully grown.

However, the plant pass through different processing method such as boiling, squeeze-washing, and sun drying before consumption which may result in nutrient lost and it is difficult to assess the nutritional values of the final product in this regard (Adegunwa et al., 2011). It is in the light of this that the present study is designed to evaluate the effect of different processing methods on the nutrient content   of Vernonia amygdalina. It is hoped that the data generated from this study will help in establishing the best processing method with higher nutrient retention for Vernonia amygdalina.

1.4 STATEMENT OF THE PROBLEM

The loss of certain nutrients during food processing is inevitable. Food processing is an important aspect of agricultural production and marketing, it adds value, removes anti-nutritional components, and increases the nutritional value of foods thereby converting them into a form that is more acceptable. The major consideration in evaluating food processing from nutritional point of view is the balance between increased food availability and the effects that each of the various processing methods has on nutrients and food quality. Some people don’t care while some others don’t really know the best processing method that can be used in other to retain the nutrient content of Vernonia amygdalina after processing. This research work will help to educate people on the best method to use while processing Vernonia amygdalina.

1.5 OBJECTIVES OF THE STUDY

General objective:

The general objective of this study is to determine the effects of processing methods on the nutrient content of bitter leaf (Vernonia amygdalina)

Specific objectives:

The specific objectives are to:

1. process bitter leaf using different methods

2. determine the effect of processing on the nutrient composition of bitter leaf (Vernonia amygdalina)

3. determine the effect of processing on the mineral composition of bitter leaf  (Vernonia amygdalina)

4. evaluate the effect of processing on the vitamins composition of bitter leaf (Vernonia amygdalina)

5. determine the effect of processing on the anti-nutrients of bitter leaf

1.6 SIGNIFICANCE OF THE STUDY

The findings of this study will be very useful to everybody in rural and urban areas. Both men and women, old and young will benefit from this research as it will give them the knowledge of how to process this vegetable (bitter leaf) without losing its nutrients.  

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