ABSTRACT
The aim of this study was to determine the chemical composition of three vegetables (Telfairia occidentalis, Gnetum africanum and Vernonia amygdalina leaves in their fresh and dried states) and the acceptability of soups made with these vegetables through sensory evaluation. The vegetables were washed and processed as traditionally consumed. They were sundried for 3 days and were used for preparing egusi soup and served with garri for the sensory evaluation. Seventy- five gram (75g) of each of the vegetables was used for soup preparation both in the dried and fresh states. Some portion of the vegetables both in fresh and dried states were immediately taken to the laboratory for chemical analysis which was done using standard analytical methods. Drying increased the proximate composition (Protein, Ash, Crude fiber, Carbohydrate) of the vegetables. The ash content was higher in dried bitter leaves (7.62%) than in fresh bitter leaves (2.38%) and higher in dried pumpkin leaves (8.47%) than in the fresh pumpkin leaves (4.83%). The protein content was higher in dried ukazi leaves (17.53%) than in the fresh ukazi, higher in dried pumpkin leaves (16.29%) than in the fresh vegetable and higher in dried bitter leaves (19.61%) than in the fresh bitter leaves. Crude fiber was higher in dried ukazi leaves (15.82%) than in the fresh ukazi leaves, it was higher in dried pumpkin leaves (15.53%) than in the fresh pumpkin leaves and higher in dried bitter leaves (15.19%) than in fresh bitter leaves. Drying increased the mineral content of the vegetables while it reduced the vitamin content of the vegetables. Based on the sensory evaluation, the panelists preferred dried ukazi leaves and fresh pumpkin leaves to other samples of the vegetables. The anti-nutrient values were high in the fresh vegetables than in the dried vegetables, the value of alkaloid in fresh (Telfairia occidentalis) leaves was (0.24mg/100g) and in dried (Telfairia occidentalis leaves) the value was (0.01mg/100g). For the fresh leaves of Gnetum africanum, the value for alkaloid was (0.09mg/100g), while the value for dried Gnetum africanum leaves was (0.08mg/100g). The fresh Vernonia amygdalina leaves had alkaloid values of (0.13mg/100g), while the dried Vernonia amygdalina leaves value (0.08mg/100g). Drying as a processing method, could be used to increase the shelf life of vegetables as well as to increase the nutritive value of vegetables.
TABLE OF CONTENTS
Title Page
Certification
Dedication
Acknowledgements
Table of Contents
List of Tables
List of Figures
Abstract
CHAPTER 1: INTRODUCTION
1.1 Statement of the Problem
2
1.2 Objective of the Study
3
1.2.1
Specific objectives
3
1.3 Significance of the Study
3
CHAPTER 2: LITERATURE REVIEW
2.1.1 Composition and structure of
Vegetables
5
2.2 Nutritional value of Vegetables
6
2.2.1 Energy content of Vegetables
6
2.2.2 Protein content of Vegetables
6
2.2.3 Mineral content of Vegetables 7
2.2.4 Vitamin content of Vegetables
7
2.2.5 Moisture content of Vegetables
7
2.3 Importance of Vegetables in the
Diet
8
2.4 Types of Vegetables 9
2.4.1 Green leafy Vegetables
10
2.5 Post Harvest Handling of
Vegetables
10
2.5.1 Preservation and storage of green leafy
vegetables
11
2.5.2 Different methods used for preserving and
storing green leafy Vegetables
12
2.6 Different Methods Used in Processing Vegetables
14
2.7 Blanching Process
14
2.7.1 Hot water blanching
15
2.7.2 Steam blanching 15
2.8 Drying Process
16
2.8.1 Sun and shade drying
17
2.8.2 Oven drying
18
2.8.3 Solar drying
18
2.8.4 Microwave and cabinet drying
19
2.9 Effects of Processing on
Vegetables
19
2.10 Effects of Drying on the Nutrient and
Sensory Properties of Vegetables
20
2.10.1 Effect of drying on nutrients 20
2.10.2 Effects of drying on sensory quality of
vegetables
21
2.11 Description of Bitter Leaf (Vernonia amygdalina) 21
2.11.1 Major uses and functions of bitter leaf
21
2.11.2 Chemical properties of Vernonia amygdalina 22
2.11.3 Uses of
Vernonia amygdalina
22
2.12 Origin of Telfairia occidentalis
22
2.12.1 Chemical properties of Telfairia occidentalis
23
2.12.2 Uses of
Telfairia occidentalis
23
2.13 Gnetum
africanum (Ukazi)
23
2.13.1 Chemical properties of Gnetum africanum
24
2.13.2 Uses of Gnetum
africanum
24
CHAPTER 3: MATERIALS AND
METHODS
25
3.1 Experimental Design
25
3.2 Sample Collection
25
3.3 Sample Preparation
25
3.3.1 Flow chart for processing of fresh
vegetables
26
3.3.2 Flow chart for processing of dried
vegetables 27
3.4 Soup Preparation 27
3.4.1 Recipe for egusi soup
28
3.4.2 Method of preparing egusi soup using
pumpkin leaves 29
3.4.3 Method of preparing egusi soup using bitter
leaves
29
3.4.4 Method of preparing egusi soup using ukazi
leaves 30
3.5 Packaging and Storage of Samples
30
3.6 Chemical Analysis
30
3.6.1 Proximate composition
30
3.6.1.1 Determination of moisture content 31
3.6.1.2 Determination of fat content
32
3.6.1.3 Determination of ash content
32
3.6.1.4 Determination of protein content
33
3.6.1.5 Determination of carbohydrate content
34
3.6.1.6 Determination of crude fiber content
34
3.6.2 Mineral analysis
35
3.6.2.1 Determination of zinc, iron and magnesium
contents
35
3.6.2.2 Determination of Potassium and Sodium Contents
35
3.6.3 Vitamin analysis
36
3.6.3.1 Determination of vitamin C content
36
3.6.3.2 Determination of niacin content
38
3.6.3.3 Determination of riboflavin content
38
3.6.3.4 Determination of thiamine content 39
3.6.4 Antinutrient analysis
40
3.6.4.1 Alkaloid determination
40
3.6.4.2 Flavonoid determination
41
3.6.4.3 Determination of tannin and oxalate 41
3.7 Sensory Evaluation
42
3.8 Statistical Analysis
43
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Proximate Composition of Fresh and
Dried Vegetables
44
4.2 Vitamin Composition of Fresh and Dried
Vegetables 48
4.3 Mineral Composition of Fresh and Dried
Vegetables
51
4.4 Phytochemical Composition of Fresh and
Dried Vegetables 53
4.5 Sensory Attributes of fresh and Dried
Vegetables
55
CHAPTER
5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 57
5.2 Recommendations
57
References
58
Appendices
LIST OF TABLES
Table
Page
3.4.1 Recipe for egusi
soup
28
4.1 Proximate
composition of fresh and dried vegetables 45 4.2
Vitamin composition of fresh and dried vegetables 49
4.3
Mineral composition of fresh and dried vegetables 53 4.4
Phytochemical composition of fresh and dried vegetables 54 4.5 Sensory attributes of soups prepared
with fresh
and dried
vegetables
56
LIST OF FIGURES
Figure 3. 3.1:
Flow chart for processing of fresh vegetables 26
Figure 3. 3.2:
Flow chart for processing of dried vegetables 27
CHAPTER 1
INTRODUCTION
Vegetables
serve as indispensable constituents of human diet, supplying the body with
minerals, vitamins, protein and energy, and as addition to certain hormone
precursors (Fasuyi, 2006). In Nigeria, as in other tropical countries of Africa
where the daily diets are dominated by starchy foods, vegetables are said to be
cheapest and most readily available sources of important nutrients (David,
2002). They are important low cost foods containing low levels of fat and high
levels of vitamins, minerals, fiber, some calorie and protein (Mepba et al., 2007). Vegetables are also good
sources of carotenes, ascorbic acid, riboflavin, folic acid and minerals like
calcium, iron and phosphorus which have several health benefits including
therapeutic uses such as treatment of scurvy, prevention of cold, correction of
hypertyrosinemia, malformation of bones and anaemia in new born infants ( Fasuji,
2006).
Chemicals
in plant are referred to as phytochemicals. They are naturally occurring
components in fruits and vegetables. They give plants their color, flavor,
smell and are part of the plant natural defense system (disease resistance). According
to Liu (2004), their medical values are based on some phytochemical substances
that they contain, which produce definite physiological actions in the human
body. The most important of these bioactive constituents of vegetables are
alkaloids, tannins, flavonoid and phenolic compounds (Edeoga et al., 2005).
Vegetables
are eaten raw or processed, thus any methods selected for processing vegetables
should be such that does not adversely affect the color, texture, flavor and
nutritional values especially the vitamins and minerals (Edeoga et al., 2006). Fasuyi (2006) reported
that consumption of vegetables helps toward controlling blood pressure and
cholesterol levels, prevent some types of cancer, avoid painful intestinal ailment
called diverticulosis and guard against cataract and muscular degeneration
which are two common causes of vision loss.
The
organoleptic properties of vegetables are due to the composition of the pigment
that they contain. Vegetables contain non-volatile acids such as malice,
citric, oxalic and succinct acid which contribute to their flavor. The color of
vegetables depends on the pigment they contain anthocyanin impart blue, purple
and red color to vegetables such as ripe tomatoes and red cabbage; carotenoids
are responsible for yellow color of carrots, sweet potatoes and maize (Oluwole et al., 2003). Chlorophyll gives
vegetables green color especially leafy ones, green peas and cucumber.
There
are some leafy vegetables that are grown and used in Abia State, whose chemical
and anti–nutrient properties were studied in this work. They are ‘Ukazi’ (Gnetum africanum), ‘Ugu’ (Telfairia occidentalis) and ‘Olugbu’ (Vernonia amygdalina).
1.1
Statement of the problem
Micronutrient
deficiency (hidden hunger) still remains a public health problem in Nigeria
despite the level of efforts made to reduce it. World health organization (WHO, 2002) reported that about 30% of the
population in developing countries suffer from one or more of the multiple forms
of nutritional deficiencies, especially that of micronutrients. Although some
vegetables are scarce and expensive during dry season, during rainy season some people do not still make use of most
vegetables, thus micronutrient deficiency is still high, (Chubike, 2013). These
three vegetables are; ‘Ukazi’ (Gnetum
africanum), ‘Ugu’ (Telfairia
occidentalis) and ‘Olugbu’ (Vernonia
amygdalina), are mostly consumed in the eastern part of Nigeria. These
vegetables are also often dried and sent to Nigerians living abroad too, since they
still enjoy Nigerian dishes in foreign lands. This study aimed at determining the
chemical and organoleptic attributes in both fresh and dried states.
1.2 OBJECTIVES OF THE STUDY
The
general objective of this study was to determine the chemical and organoleptic
attributes of Gnetum africanum, Telfairia occidentalis and Vernonia amygdalina in their fresh and
dried states.
The specific objectives were
to:
1. determine
the chemical content of these vegetables by assessing their proximate,
minerals, vitamins and anti-nutrient composition.
2. assess the acceptability of soups made with
these vegetables using sensory evaluation.
1.3 Significance of the study
1.
The result obtained in this work could provide data on the nutrient content,
especially micronutrient content of the selected vegetables consumed in Abia
State.
2.
Health professionals and other vegetable users (vegetarians) can select
vegetables based on the information provided. It could also enable the
agriculturists to cultivate different vegetables. It could serve as a guide for
individuals, families and even communities to select healthy vegetables for consumption.
3.
The information from the chemical content of these vegetables can form part of
food composition table which can be used by other researchers.
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