ABSTRACT
Fresh samples were used for moisture content analysis. Standard methods were used to determine in triplicate the proximate, macro minerals, phytochemical and heavy metal levels. Proximate composition of samples revealed that moisture content for all the samples studied was appreciably high and ranged from51.09±0.57% to 92.32±0.06%. Talinum triangulare in Orie-Ugba sample recorded the highest (92.32±0.06%) while Gnetum africanum in Ubani market recorded the lowest (51.09±0.57%). Ash content for the samples was between 1.14±0.07% and 6.53±0.28% with Pterocarpus soyanxii in Ubani market recording the highest while Telfairia occidentalis in Orie-Ugba market gave the least. Crude protein values ranged from 9.24±0.04% in Gnetum africanum in Orie-Ugba market to 24.48±0.02% in Telfairia occidentalis also in Orie-Ugba market. However, crude fibre content was maximum in Pterocarpus soyanxii (12.25±0.06%) obtained from Ubani market and minimum in Talinum triangulare (3.54±0.19%) obtained from Ubani market. A low (
crude lipid composition was observed in the vegetable leaves obtained from the two markets. For carbohydrate content, values ranged from, 56.24±0.23% to 74.69±0.37% with Talinum triangulare in Orie-Ugba market recording the highest and Vernonia amygdalina also in Orie-Ugba market recording the lowest. The result for calorific values of the vegetables revealed that Talinum triangulare from Orie-Ugba market had the highest value (425.95 kcal) although all the other samples also showed a high percentage of energy content. The phytochemical screening results showed amounts of alkaloids (0.63±0.02% - 5.13±0.01%), saponins (1.30±0.02% - 9.13±0.06%), flavonoids (2.51±0.01% to 7.79±0.03%), tannins (0.05±0.01% - 0.14±0.01%) and phenols (0.05±0.00% - 0.26±0.00%) in all the leafy vegetables. The macro mineral analysis showed the leafy vegetables in both markets contain amounts of calcium (0.05±0.00% - 0.26±0.00%), magnesium (0.06±0.00% to 0.55±0.00%), potassium (2.40±0.00% - 10.33±0.00%), sodium (0.29±0.00% - 0.92±0.00%) and phosphorus (2.70±0.00% - 9.40±0.00%). No mercury was detected in any of the leafy vegetables from the two markets while lead, arsenic and chromium levels were below the FAO/WHO limits. Mean cadmium concentrations in Telfairia occidentalis, Gnetum africanum, Pterocarpus soyanxii in Orie-Ugba market and Gnetum africanum, Pterocarpus soyanxii in Ubani market were either above or equal to the limit.
TABLE OF CONTENTS
Title Page i
Certification ii
Declaration iii
Dedication iv
Acknowledgement v
Table of Content vi
List of Tables xi
List of Figure xiii
List of Plate xvi
Abstract xvii
CHAPTER 1: INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement of the Problem 3
1.3 Aim and Objectives 3
1.4 Justification 4
1.5 Scope and Limitations 4
CHAPTER 2: REVIEW OF RELATED LITERATURE 6
2.1 Vegetables 6
2.2 Classification of Vegetables 7
2.3
Leafy Vegetables 7
2.4 Selected Leafy Vegetables 8
2.4.1 Telfaria occidentalis 8
2.4.2 Vernonia amygdalina 9
2.4.3 Gnetum
africanum 10
2.4.4 Talinum
triangulare 11
2.4.5 Pterocarpus soyanxii 12
2.5
Phytochemicals 13
2.6 Some Phytochemicals under Study 14
2.6.1 Alkaloids 15
2.6.2 Flavonoids 17
2.6.3 Phenols 17
2.6.4 Saponins 20
2.6.5 Tannins 21
2.7 Minerals 22
2.8 Heavy metals 24
2.9 Sources of Heavy Metal
Pollution in Vegetables 24
2.10 The Heavy Metals under Study 27
2.10.1 Arsenic (As) 27
2.10.2 Lead (Pb) 27
2.10.3 Cadmium (Cd) 28
2.10.4 Mercury (Hg) 29
2.10.5 Chromium (Cr) 29
2.11 Review of Instrumental Techniques in this
Study
30
2.11.1
Atomic absorption spectroscopy 30
2.11.2 Flame photometry 31
2.11.3
UV-visible spectroscopy 32
2.14.4 Microwave plasma atomic emission spectroscopy 37
CHAPTER
3: MATERIALS AND METHODS 34
3.1 Reagents and Glassware 34
3.3
Reagents and Chemicals 35
3.4
Study Area 35
3.5
Sampling 36
3.6 Sample
Pretreatment and Analysis 37
3.6.1
Proximate analysis 37
3.7 Digestion of Plant Sample 42
3.8
Determination of Minerals 43
3.8.1 Determination of calcium and magnesium 43
3.8.2 Determination of phosphorus 43
3.8.3 Determination of sodium and potassium by
flame photometry 45
3.8.4 Preparation of heavy metals stock solutions 45
3.8.5 Preparation of standard solutions and plotting
of calibration curve 46
3.8.6 Determination of chromium, lead, mercury and
cadmium 47
3.8.7
Determination of arsenic 47
3.9 Determination of Phytochemical 48
3.9.1
Determination of saponins. 48
3.9.2
Determination of tannins 49
3.9.3
Alkaloids determination 50
3.9.4
Determination of phenol 51
3.9.5 Determination of flavonoids 52
3.10 Statistical Analysis 52
CHAPTER 4: RESULTS AND
DISCUSSION
4.1 Proximate Composition 54
4.2 Energy
Value 63
4.3 Phytochemicals 66
4.4 Macro Minerals 74
4.5 Heavy Metals 81
CHAPTER
5: CONCLUSION AND RECOMMENDATIONS 90
5.1 Conclusion 90
5.2 Recommendations
90
References
Appendices
LIST
OF TABLES
2.1 Classification
of Vegetables 7
3.1 Analytical
Conditions for AAS Analysis 47
3.2 Agilent
4200 MP-AES Operating and Method Conditions. 48
4.1 Mean
(±SE) Proximate Compositions (%) of Leafy Vegetable Samples
obtained
from Orie-Ugba Market. 54
4.2 Mean (±SE) Proximate Compositions (%) of
Leafy Vegetable Samples
obtained
from Ubani Market 55
4.3 Mean
(±SE) Energy value (kcal) of Leafy Vegetable Samples
obtained from Orie-Ugba Market 64
4.4 Mean
(±SE) Energy value (kcal) of Leafy Vegetable Samples
obtained from
Ubani Market 64
4.5 Mean (±SE) Phytochemical
Compositions (%) of Leafy
Vegetable Samples obtained from
Orie-Ugba Market 66
4.6 Mean (±SE) Phytochemical Compositions
(%) of Leafy
Vegetable
Samples obtained from Ubani Market. 67
4.7.
Macro Mineral (%) Content
in Leafy Vegetable Samples
obtained
from Orie-Ugba Market. 75
4.8
Macro mineral (%) Content
in Leafy Vegetable Samples obtained
from
Ubani Market. 76
4.9
Heavy Metal
Concentrations (mg/kg) in Leafy Vegetable
Samples
obtained from Orie-Ugba Market. 82
4.10. Heavy Metal
Concentrations (mg/kg) in Leafy Vegetable Samples
obtained
from Ubani Market. 83
LIST OF FIGURES
2.1 Basic structures of some pharmacologically
important plant derived
Alkaloids 16
2.2 Basic structures of some pharmacologically
important plant derived
flavonoids 17
2.3 Basic structures of some pharmacologically important
plant derived
phenols 19
2.4. Basic structures of some pharmacologically
important plant derived
tannins 21
4.1 Bar chart with
error bars comparing the mean moisture content
of some leafy
vegetable samples obtained from two different
markets in umuahia. 58
4.2 Bar chart with
error bars comparing the mean crude ash content
of some leafy
vegetable samples obtained from two different
markets in umuahia 59
4.3 Bar chart with
error bars comparing the mean crude protein content of
some leafy vegetable samples obtained from two
different
markets in umuahia. 60
4.4 Bar chart with
error bars comparing the mean crude fibre content
of some leafy vegetable samples
obtained from two different
markets in umuahia. 61
4.5 Bar chart with error bars comparing the mean crude lipids
content of some leafy
vegetable samples obtained from two
different markets in umuahia. 62
4.6 Bar chart with error bars comparing the mean carbohydrate
content of some leafy vegetable samples
obtained from two
different markets in umuahia. 63
4.7 Bar chart
with error bars comparing the mean energy values
of some leafy vegetable samples obtained from two different
markets in umuahia. 65
4.8 Bar chart with
error bars comparing the mean alkaloids
content of some leafy vegetable samples obtained from two
different markets in umuahia. 70
4.9 Bar chart with
error bars comparing the mean saponins
content of some leafy vegetable samples obtained from two
different markets in umuahia. 71
4.10 Bar chart with error bars comparing the mean
flavonoids
content of some leafy vegetable samples obtained from two
different markets in umuahia.
72
4.11 Bar chart with error
bars comparing the mean tannins
content of some leafy
vegetable samples obtained from two
different markets in
umuahia. 73
4.12 Bar chart with error
bars comparing the mean phenols
content of some leafy vegetable samples obtained from two
different
markets in umuahia. 74
4.13 Bar chart with
error bars comparing the mean calcium
content of
some leafy vegetable samples obtained from two
different markets in umuahia. 78
4.14 Bar chart with
error bars comparing the mean magnesium
content of some leafy vegetable samples obtained from two
different markets in umuahia. 79
4.15 Bar chart with
error bars comparing the mean
potassium content of
some leafy vegetable samples obtained
from two different markets in umuahia. 80
4.16 Bar
chart with error bars comparing the mean sodium
content of
some leafy vegetable samples obtained from two
different markets in umuahia. 80
4.17 Bar chart with error bars comparing the mean phosphorus
content of some leafy
vegetable samples obtained from two different
markets in umuahia. 81
4.18 Bar chart with
error bars comparing the mean cadmium
level of some leafy vegetable samples obtained from two different
markets in umuahia. 86
4.19 Bar chart with
error bars comparing the mean lead level of
some leafy vegetable samples
obtained from two different markets in
umuahia. 87
4.20 Bar chart with
error bars comparing the mean arsenic level of some
leafy vegetable samples obtained from two different markets in
umuahia. 88
4.21 Bar chart with error bars comparing the
mean chromium level of
some leafy vegetable samples
obtained from two different markets in
umuahia. 89
LIST OF PLATES
1. Telfairia occidentalis leaves 9
2. Vernonia amygdalina leaves 10
3. Gnetuma africanum leaves. 11
4. Talinum triangulare leaves. 12
5.
Pterocarpus soyansii leaves 13
6. Google map of umuahia
showing the sample location 36
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
OF THE STUDY
Vegetables are an
important ingredient of human diet that contains essential nutrients and trace
elements (Abdullah and Chmielnicka, 1990). Most vegetables are green and
leaf-like in appearance bearing edible leaves or stems and roots of plants
(Sharma, 2004). Fresh vegetables provide vitamins for the human body (Genderd,
1994).
One
major reason for low exploitation and use of vegetables and fruits in Nigeria
is ascribable to ignorance of the role they play in adequate nutrition
(Kubmarawa et al., 2009; Nnam, 2011a). Throughout the last decade, the
concept of health promotion using vegetables and fruits has become a legitimate
part of health care (Nielsen, 2010). Fruits and Leafy vegetables have a
significant role they play among the food crops as they provide adequate
amounts of essential minerals and vitamins for humans. Vegetables provide rich
source of carotene, ascorbic acid, riboflavin, folic acid and minerals like
calcium, iron and phosphorous (Nnam et
al., 2012). They are crucial protective foods and are highly beneficial for
the maintenance of good health and prevention of diseases (Kubmarawa et al., 2009). Phytochemicals, which are
found in large quantities in vegetables and fruits, are responsible for this
protective effect (Sundarrayanan et al.,
2011). The need for leafy vegetables in man’s diet every period of the year
cannot be overemphasized because they are valuable sources of nutrients
especially in rural areas where they contribute importantly to protein, vitamins,
mineral, fiber and other nutrients which are usually in limited supply in diets
we eat daily (Mepba et al., 2007).
The basic components
in vegetable leave provide alkalizing effects, neutralizing the acidity caused
by other foods of animal origin (Genderd, 1994). Vegetable leaves contain both
toxic and essential metals over a wide range of concentrations, (Radwan and
Salama, 2006). Some metals are essential and their insufficiency results to
biological malfunctions in the human body but when present in excess, they
become toxic (Soylak et al., 2003). The
quality and safety of vegetables should be given utmost consideration due to
the nutritional role they play in human diet. Heavy metal
contamination of food materials is an important consideration in food quality
assurance (Marshall, 2004; Wang et al., 2005; Khan et al., 2008).
Heavy metal pollution is considered a worldwide threat and it is responsible for
environmental contamination because of their persistent nature and high
toxicity in the environment (Khan et al., 2011). The major sources of
these toxic metals are anthropogenic (e.g. sewage sludge, pesticides and fertilizers,
addition of manure). The rate of uptake and accumulation by plants varies with
morpho-physiological nature of the vegetables, although processes that are
natural like straight atmospheric metal deposition on leave surfaces by rain,
air and dust are also possible. Vegetables can accumulate toxic metals in their
edible and non-edible parts. Some of these heavy metals such as Cd, As, Hg, Se
and Pb are not important for growth of plant, as they do not perform any known
physiological function in plants, while others such as Cu, Co, Mn, Fe, Mo, Zn
and Ni are essential elements required for normal plant growth and metabolism,
but these elements can easily cause poisoning when their concentrations are
greater than optimal values (Garrido et
al., 2002; Rascio and Izzo, 2011; Abii et
al., 2012).
1.2 STATEMENT OF THE PROBLEM
Rapid
urbanization with insufficient environmental monitoring planning in Umuahia has
caused an increase in pollution, sufficient to affect food safety. The last
decade, increasing demand for food safety has increased research regarding the
risk associated with consumption of food materials contaminated by heavy
metals, toxins or pesticides (D’Mello, 2003). The contamination of vegetables
with heavy metals due to soil and atmospheric contamination poses a threat to
its quality and safety. Dietary intake of heavy metals also poses a risk to
animals and human health. High concentration of heavy metals heavy metals (Cr,
Cd, As, Hg, and Pb) in vegetables causes cancer (Turkdogan et al., 2003). Metals such as Pb, Cr, Cd, As, and Hg are cumulative
poisons. These metals cause environmental hazards and are toxic (Bahemuka,
1999). Contamination of vegetables with heavy metals may be due to irrigation
with contaminated water, the addition of fertilizers and metal-based
pesticides, industrial emissions, transportation, harvesting process, storage
or during marketing (Khairiah et al.,
2004; Chojnacka et al., 2005). Publicity
regarding the high level of heavy metals in the environment, especially in
Umuahia has created fear in the public as to the presence of heavy metal
residues in their daily food.
1.3 AIM AND OBJECTIVES
The purpose of this work
is to assess the proximate, mineral content, phytochemical and heavy metal
composition of some selected leafy vegetables sold at two major markets in
Umuahia. This aim shall be achieved through the following objectives:
·
To determine the proximate constituents of
the leafy vegetable samples.
·
To determine the levels of macro-nutrients
in the leafy vegetable samples.
·
To assess the heavy metal concentration in
the leafy vegetables.
·
To determine the quantitative
phytochemical composition of the leafy vegetable samples.
·
To compare the levels of heavy metal
obtained in vegetables with internationally allowed limits.
1.4 JUSTIFICATION
Atomic
Absorption Spectroscopy (AAS) and Microwave Plasma Atomic Emission Spectroscopy
(MP-AES) were the analytical methods used for the quantitative determination of
the heavy metals in the leafy vegetables. AAS is cheap and comparatively easy
and simple to manipulate. It is very sensitive such that many elements can be
determined at ppm level or even less. It has high precision and accuracy
obtained by the calibration curves. AAS has absorption signal considerably free
from inter-element interferences and all atoms absorb at a well-defined
wavelength and over a bandwidth, hence isotopes of the same wavelength will not
absorb at each other’s radiation. MP-AES has superior detection limits and
improved dynamic range. It is safer since it eliminates the use of flammable
gases.
1.5 SCOPE AND LIMITATIONS
The scope of the study is
the number of experimental units used to achieve the given objectives. The (5)
different varieties of the leafy vegetables were selected from two major
markets in Umuahia. The leafy vegetables were collected in triplicates. The
analysis for each parameter was done in triplicates. For the determination of
proximate analysis, 21 experimental units were required to determine it. For
the determination of macro-minerals, phytochemicals and heavy metals in each of
the leafy vegetables, 15 experimental units were required respectively to
determine each of the parameters.
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