ABSTRACT
Macrominerals and microminerals serve as electrolytes, metabolic regulators and also have a structural function in the human body. Deficiency of essential elements may lead to a list of healthy complications which includes growth impairments, birth defects, reduced fertility, weak bones and affected metabolism of lipid, proteins and carbohydrates. Copper is an essential cofactor for collagen and extracellular matrix formation. Zinc plays a critical role in cell division, growth and protein synthesis hence it is important for infants and pregnant women. Delayed wound healing, impaired taste sensitivity; severe deficiency: retarded growth and sexual development and dwarfism are traded some of the signs of zinc deficiencies. Potassium is essential for normal muscular and digestive function, proper functioning of tissues and cells in the human body and also plays a crucial role in heart function, skeletal and smooth muscle contraction. Potassium deficiency in the human body can lead to electrolyte imbalance. Manganese which is a Cofactor of large number of enzymes acts as an antioxidant during normal brain function and animal reproduction. Tea infusions may be a rich source of some macrominerals and microminerals which are essential to human health. Though in trace amounts, these elements are known to play critical roles in various body mechanisms though too much of this elements may also be a health hazard. The tea plant is a perennial evergreen plant with three species i.e. Camellia sinensis, Camellia assamica and Camellia Cambodiensis which is believed to have been dispersed either naturally or by human agencies into tropical and subtropical regions. Tea leaf which is the raw material for tea infusions is composed of different chemical compounds which comprises of caffeine, catechins, volatile compounds, amino acids, trace elements, proteins, and minerals. The aim of this study was to determine the levels of manganese, potassium, zinc and copper elements in tea leaves. Black tea, green tea and purple tea which are the centre of this research are products of the leaves of Camellia Sinensis. During processing of black tea, tea leaves are fully oxidised before being dried. Green tea is a non- fermented product of the leaves from the tea plant and purple tea is a variety that is rich in some specific nutrients. In this study, 24 samples of tea leaves were randomly purchased from selected supermarkets, hawkers and shops in Nairobi Central Business District. The samples were analysed for total potassium, zinc, manganese and copper using Atomic Absorption Spectroscopy (AAS) and Inductively coupled plasma mass Spectrometry (ICP- MS) techniques. The data obtained was interpreted/analysed using the one-way analysis of variance (ANOVA) tool and Kruskal Wallis test under the Statistical Package (STATA) software. The levels of potassium ions in all the tea leaves and their respective tea infusions was significantly higher compared to the levels of manganese, copper and zinc. Levels of copper, manganese, potassium and zinc metal ions in the tea leaves ranged from 41.20 ± 12.47 µg/g to 48.50 ± 19.40 µg/g, 913.6 ± 471.95 µg/g to 1342.10 ± 310.26 µg/g, 12716.30 ± 2541.56 µg/g to 12837.90 ± 3517.60 µg/g and from 111.10 ± 29.98 µg/g to 116.60 ± 20.25 µg/g respectively. Levels of copper, manganese, potassium and zinc metal ions in the tea infusions ranged from 15.1 ± 4.1 µg/g to 43.3 ± 19.9 µg/g, 231.7 ± 3.8 µg/g to 938.2 ± 96.4 µg/g, 5715.4 ± 64.2 µg/g to 16628.7 ± 246.2 µg/g and from 50.6 ± 8.5 µg/g to 144.2 ± 5.9 µg/g respectively. The levels of metal elements in the tea leaves and tea infusions analyzed arranged in the following order: K>Mn>Zn>Cu hence all the three types of tea leaves are reliable sources of potassium and manganese. There was a significant statistical difference in the manganese levels in the three types of tea.
TABLE OF CONTENTS
DECLARATION ii
ACKNOWLEDGEMENT iii
ABSTRACT iv
DEDICATION v
LIST OF TABLES ix
LIST OF FIGURES x
LIST OF ABBREVIATIONS AND ACRONYMS xi
UNITS OF MEASUREMENT xii
CHAPTER ONE
INTRODUCTION
1.1 : Background of the study 1
1.2 : The origin of the tea plant 2
1.3 Tea infusion 2
1.4 : Food fortification and supplementation 3
1.5 : Counties growing tea in Kenya 3
1.6 : Fertilizers used in tea production 4
1.7 : Diseases affecting tea production 4
1.8 : Pest affecting tea production 5
1.9 : Statement of the problem 5
1.10 : General objective of the study 6
1.10.1 : Specific objectives 6
1.11 : Justification of the study 6
1.12 : Significance of the study 6
CHAPTER TWO
LITERATURE REVIEW
2.1 : Sources of potassium, zinc, copper and manganese 7
2.2 : Macrominerals and microminerals 8
2.3 : Major minerals and trace minerals 8
2.3.1 : Trace minerals 8
2.3.2 : Major minerals 8
2.4 : Inorganic nutrients 9
2.5 : Tea production and processing 11
2.6 : Tea types 12
2.6.1 : Black tea 12
2.6.2 : Green tea 12
2.6.3 : Purple tea 13
2.7 : Problems affecting Tea production 13
2.7.1 : High cost of production 13
2.7.2 : Diseases affecting tea plants 13
2.8 : Spectroscopic methods for metal determination 14
2.8.1 : Atomic absorption spectroscopy (AAS) 14
2.8.1.1 : Detector 15
CHAPTER THREE
MATERIALS AND METHODS
3.1 : Study area 17
3.2 : Chemicals and reagents 18
3.3 : Instrumental and apparatus 19
3.4 : Tea leaves samples 20
3.5 : Laboratory sample storage, preparation and analysis 21
3.5.1 : Sample preparation (tea leaves) 21
3.6 : Standard solutions preparation 23
3.7 : The analytical process 24
3.7.1 : Atomisation process during determination of zinc 24
3.8 : Quality assurance 25
3.9 : Instrument conditions 25
CHAPTER FOUR
RESULTS AND DISCUSSION
4.3 : Metal ions in black, green and purple tea leaves. 29
4.3.1 : The metal elements levels in black tea leaves brand 30
4.3.2 : Levels of metal ions in green tea leaves 32
4.3.3 : Levels of metal ions in purple tea leaves 32
4.3.4 : Comparison of metal element levels in green, black and purple tea leaves 33
4.3.5 : Comparison of the manganese levels in green, black and purple tea leaves 34
4.3.6 : Comparison of the potassium levels in green, black and purple tea leaves samples 36
4.3.7 : Comparison of the zinc levels in green, black and purple tea leaves 37
4.3.8 : Comparison of the mean metal ions levels in green, black and purple tea leaves 38
4.3.9 : Kruskal Wallis H test 40
4.3.10 : Analysis of variance (One-way ANOVA test) 41
4.4 : Copper, manganese, potassium and zinc element levels in tea infusions 41
4.4.1 : Limits of detection and product moment correlation coefficient for the analytes 41
4.4.2 : Copper, manganese, potassium and zinc ions levels in black tea infusions 42
4.4.3 : Copper, manganese, potassium and zinc ions levels in green tea infusions 43
4.4.4 : Copper, manganese, potassium and zinc ions levels in purple tea infusions 43
4.4.5 : Comparison of copper, manganese, potassium and zinc levels in tea infusions 44
4.4.6 : Comparison of the mean metal ions levels in green, black and purple tea infusions 48
4.4.7 : Kruskal Wallis test 50
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
REFERENCES 56
APPENDICES 61
LIST OF TABLES
Table 3.1: Different types of tea samples purchased from different out lets 21
Table 3.2: Absorption radiation wavelengths and gases used during analysis 24
Table 3.3: Absorption radiation wavelength and gas used during analysis 25
Table 4.1: Limits of detection and correlation coefficient for metal analystes 28
Table 4.2: Metal ions levels in black, green and purple tea leaves 30
Table 4.3: Copper, manganese, potassium and zinc metal ions levels in black tea brands 30
Table 4.4: Metal ions specifications 31
Table 4.5: Levels of copper, manganese, potassium and zinc metal ions in green leaves 32
Table 4.6: Copper, manganese, potassium and zinc levels in purple tea leaves brands 33
Table 4.7: Mean metal nutrients levels (µg/g) in purple, black and green tea leaves 39
Table 4.8: Results of the Kruskal Wallis H rank test 41
Table 4.9: One way ANOVA test results 41
Table 4.10: Limits of detection and correlation coefficient for metal analytes 42
Table 4.11: Levels of metal ions in black tea infusions 42
Table 4.12: Metal ions levels in green tea infusions 43
Table 4.13: Metal ions level in purple tea infusions 44
Table 4.14: Mean metal nutrient levels in black, green purple tea infusion 49
Table 4.15: Results of the Kruskal Wallis of population rank test 51
Table 4.16: Results of the One way ANOVA test 51
LIST OF FIGURES
Figure 2.1: ContrAA 700 High Resolution Continuum Source (AAS) machine 15
Figure 3.1: Sampling sites 18
Figure 3.2: Basic illustration of Inductively coupled plasma mass spectrometer 20
Figure 3.3: Analytical process for samples preparation and analysis 22
Figure 3.4: Basic illustration of atomic absorption spectrometer 22
Figure 4.1: Comparison of copper levels in purple, black and green tea leaves samples 34
Figure 4.2: Comparison of manganese levels in purple, black and green tea leaves 35
Figure 4.4: Comparison of zinc metal nutrient levels in purple, black and green tea leaves 38
Figure 4.5: Mean metal nutrients levels in purple, black and green tea leaves 40
Figure 4.6: Levels of metal nutrients in purple, black and green tea leaves 40
Figure 4.7: Comparison of copper levels in purple, black and green tea infusions 45
Figure 4.8: Comparison of manganese levels in purple, black and green tea infusions 46
Figure 4.9: Comparison of potassium levels in purple, black and green tea infusions 47
Figure 4.10: Comparison of zinc metal nutrient levels in purple, black and green tea infusions 48
Figure 4.11: Mean Levels of metal nutrient in purple, black and green tea infusions 50
LIST OF ABBREVIATIONS AND ACRONYMS
AAS Atomic Absorption Spectroscopy
CAN Calcium Ammonium Nitrate
DAP Diammonium Phosphate
FAO Food and Agriculture organisation
ICP-MS Inductively coupled plasma mass spectrometry
KEBS Kenya Bureau of Standards
NPK Nitrogen, Phosphorus Potassium
SSP Single Super Phosphate
WHO World Health Organisation
UNITS OF MEASUREMENT
g Gram
mg/Kg milligram per Kilogram
mL Millilitre
µg/g microgram per gram
ppm Parts per million
CHAPTER ONE
INTRODUCTION
1.1 : Background of the study
United Nations has set an agenda of transforming the world by the year 2030 and in order to achieve this, agenda sustainable development goals have been set (Walker et al., 2019). Good health and well-being for all is one of the goals so as to ensure a productive work force. Public health experts have realized that micronutrient malnutrition is the cause of many non-specific physiological impairments, leading to low immunity and metabolism difficulties. Foods products processed from plants contain almost all the mineral nutrients required for numerous body processes in humans (Organization and FAO, 2004). Micronutrient malnutrition has been identified as a leading contributor to the global burden of disease. Ensuring good health and promotion of well-being is required in enabling sustainable development all over the world. Recently, nutritional science has not only focused on the discovery of vitamins but it has also focused on description of mineral deficiency diseases and as a result there has been efforts to fortify foods that are commonly consumed by humans with vitamins and minerals (Zimmermann, 2011). There are two major categories of minerals i.e. macro minerals which are also known as major minerals; examples include magnesium, nitrogen, potassium, sulphur, calcium and sodium and micro minerals also known as trace minerals, examples consisting of boron, copper, iron, iodine, manganese, and zinc (Medeiros and Wildman, 2013). With an aim of ensuring that the food consumed by the world population meets the dietary requirements for specific micronutrients, product specifications have been established with guidance from FAO (Ottaway, 2008) and WHO (Fortin, 2016).
The African Union’s Agenda 2063 recognises technical solutions in healthcare as one of key requirements for its realization (Vickers, 2017). Nutritive levels of mostly consumed foods in the African region is an information that the public health experts require in the process of policy development. Tea is consumed by two-thirds of the people in the world as a refreshing healthy drink (Khan & Mukhtar, 2013). Originally tea consumers used to chop the tea leaves as vegetable, chewed the leaves but eventually learned how to prepare a drink by extracting nutrients from the leaves using boiling water (Driem, 1957). Tea drinking is a constituent part of Chinese culture and in some countries tea is drunk in social events. Though there are various legends in relation to where tea originated, tea is believed to have been discovered by Shen Nung in 2737 BC who was an expositor of curative properties of plants. Tea leaves are still used in traditional Chinese medicine in China. According to the legend, a tea leaf which was hanging from a wild tea tree fell into the water which Shen Nung was boiling in a pot in the garden. The leave coloured the water brown but Shen Nung went ahead and drunk the accidentally prepared drink. He was surprised when he discovered that the drink had pleasing flavour and aroma (Weinberg et al., 2001). The many different kinds of tea products throughout the world depend on the variety of the tea plant from which the unprocessed tea leaves are harvested from, the curing and processing of the leaves, and the grade of the leaves (Ho et al., 2008). In India, tea remains the beverage of choice for most people across all walks of life.
1.2 : The origin of the tea plant
Tea is believed to have dispersed either naturally or by human agencies into tropical and subtropical parts, covering tropical rain forest, tropical savannah and summer rain areas ( Han et al., 2021). Tea is usually grown in acidic soils with pH values ranging between 5.00 and 5.60. The acidic conditions of the soils favours the solubility/availability of most metals ions (Zhen, 2002). Tea leaves contains elements Ca, k, mg, F, Al and Mn in levels of milligram per gram. Tea leaves contain Cr, Fe, Co, Ni, Zn, Cd, Pb, As and Hg in levels of nanograms per gram ((Guardia and Garrigues, 2015). Tea plant is always green and remains productive throughout the year. The tree has three species i.e. Camellia sinensis, Camellia assamica and Cambodiensis (Driem, 2019). The different tea leaves for human consumption are produced from the buds and young leaves of Camellia sinensis species. The plant is indigenous throughout the forests of south-east Asia and though the tea plant is maintained as a shrub, it has the potential of developing into a tree between 30 and 40 feet (Willson and Clifford, 2012). As a practice, tea plant is pruned and maintained at a height of about 3-5 feet in order to make tea picking easier and increase the yield of the plant. The soils on which tea grows also vary widely hence tea has a wide range of distribution. Though tea has ability to grow under relatively diverse set of environmental conditions, it’s cultivation requires certain definite criteria for optimal productivity (Ahuja et al., 2013).
1.3 Tea infusion
Tea drink is the infusion of the leaves of Camellia Sinensis and it is undoubtedly among the best- loved drinks, it is known to have a unique aroma and flavour. It is the oldest non-alcoholic beverage in the world (Kurian and Peter, 2007). Tea infusions are thought to contain a mixture of organic and inorganic compounds (Justino, 2020). It has been established that tea infusions contain volatile products, flavonoids, proteins, carbohydrates, alkaloids, trace elements, minerals and other compounds which are yet to be identified (Guardia and Garrigues, 2015).
Tea leaves manufacturers use young tea leaves which are composed of two leaves and a bud to produce commercial tea. Trace elements distribution in various types of commercial teas from around the world are highly variable. Tea has been recognized as a useful source of some essential elements in the human diet, hence moderate consumption of tea is unlikely to have any harmful effects to healthy humans (Preedy, 2013).
Most of the time tea consumers are after the stimulating effect of tea but are rarely interested with the nutritional value of tea especially the minerals which are equally of importance (Driem, 2019).
1.4 : Food fortification and supplementation
Activities of food fortification and supplementation has existed since 1824 when native Indians of South America and Columbia used to treat goitre using a particular type of salt. It was later established that the salt contained high levels of iodine ions (Ottaway, 2008). The objective of fortification programs is to raise the level of micronutrients foods that are mostly consumed by many people. The exercise can involve fortification of several foods or fortification of a single element e.g. the iodization of table salt. Vulnerable population groups mostly in developing countries may not be in a position to access food that meet all the micronutrients requirements (WHO and FAO, 2004). Though cereals are poor dietary sources of micronutrients, they are usually fortified with minerals like iron, copper, manganese and zinc (Szefer and Nriagu, 2006). Food fortification play important role in developing countries in helping them to achieve their health policies and ensure the nutritional health of their citizens (Ottaway, 2008).
1.5 : Counties growing tea in Kenya
Tea is currently grown in many countries in the world including China, India, Kenya, Sri lanka, Turkey and Vietnam (Christenhusz et al., 2017). Originally tea in China was consumed as a medicinal drink, hence the Chinese regarded tea as an integral part of their health and well-being (Jain and Priyadarshan, 2008). China produces the largest amounts of tea in comparison to other countries in the world. India comes second after China followed by Kenya. In Kenya small scale holder’s tea accounts for two-thirds of Kenya’s crop and the other fraction is grown on the large estates (Driem, 2019). The small scale tea growers cultivate tea on smallholdings of about 10-12 hectares. Kenya Tea Growers’ Association (KTGA) is an organisation formed by several large plantations tea farmers and they provide a significant amount of tea. Nandi, Kericho and the Great Rift Valley; Mt Kenya, the Nyambene Hills and the Aberdares in the Central Kenya; the Cherangani Hills and the Mau escarpment are areas where the tea plantations are situated. Counties where tea is grown lying in the East of Rift Valley include; Kilifi, Laikipia, Nakuru, Nyeri, Kiambu, Meru, Murang’a, Kirinyaga and Embu. Those in the West of the Rift Valley include; Kericho, Nandi, Trans-Nzoia, Kakamega and Kisii (Ali, 1997).
1.6 : Fertilizers used in tea production
Just like other plants, tea plants require nutrients for growth. Required nutrients include primary plant food elements, secondary plant food elements and micronutrients (Han et al., 2018). The tea plant requires potassium, phosphorus and nitrogen (NPK) as nutrients for growth. The tea plant also requires zinc, calcium, sulphur, magnesium, and other micronutrients (Ahuja et al., 2013). Fertilizers are some of the sources of the elements and hence most tea farmers apply fertilizers so as to raise tea production (Han et al., 2018). Such fertilizers include, Calcium ammonium Nitrate (CAN), NPK, single super phosphate (SSP) and diammonium phosphate (DAP) (Willson and Clifford, 2012). Use of fertilizers though continually practised by most tea growers raises cost of production but most farmers have no choice than to hope that the extra costs in production will be offset by the profits they make (Han et al., 2018).
1.7 : Diseases affecting tea production
There are several diseases which usually affect the roots, stems or even leaves of the tea plant, these include; Blister Blight, Red Rust, Armillaria root rot diseases. Management of these diseases by use of chemicals is practiced in order to ensure that high yields are obtained (Rangaswami and Mahadevan, 1998). In controlling Blister Blight disease, the affected plants are sprayed with fungicides such as Cuprous Oxide or Copper Oxychloride (Gour and Purohit, 2004). Red Rust is also a disease known to appear in the form of minute rusty spots on the leaves of the tea plant (Driem, 2019). Through studies, it has been established that healthy leaves of the plant contain more nitrogen and potassium carbonate in relation to infected leaves (Mehrotra, 2013). In this regard, application of potassium carbonate, foliar spray with Copper hydroxide and Carbendazin are the methods mostly used to control the disease (Mehrotra, 2013). The tea plant is also affected by a root and stump disease known as Armillaria root rot disease (Ahuja et al., 2013). Once diagnosed, it is advisable to remove the stumps of infected trees followed by fumigation of the tea fields with Chloropicrin, carbon disulphide, and methyl bromide ( Han et al., 2018).
1.8 : Pest affecting tea production
The tea plant can be infested by different types of pests e.g. anthropods, including insects and mites (Hall, 2000). The eriophyid mites, Calacarus carinatus and Acaphylla theae and the tenuipalpid, Brevipalpus phoenicis usually infest the tea plants at the same time (Willson and Clifford, 2012). Red rust which is an algal disease is another threat to the tea plant attacking the leaves of the plant and mostly appears in the form of minute rusty spots on the leaves. The pathogen which causes this disease in tea is Cephaleuros Parasiticus Karst (Mehrotra, 2013). Factors favouring the algae include inadequate shade, waterlogging, drought, poor fertility and lack of aeration of the soil (Mehrotra, 2013).
1.9 : Statement of the problem
Tea infusions may be a rich source of some macrominerals and microminerals which are essential to human health. Though in trace amounts, these elements are known to play critical roles in various body mechanisms though too much of this elements may also be a health hazard. Consumption of herbal infusions has greatly increased in the recent years due to their alleged health benefits. Tea infusion is an example of these herbal infusions and is consumed by a large part of the Kenya’s population. The infusion contain volatile products, flavonoids, proteins, carbohydrates, alkaloids, trace elements, major minerals and compounds which are yet to be identified as stipulated by Guardia and Garrigues, (2015). Most of these components play critical role in human health hence they are recognized as essential by various researchers (Ho et al., 2008).
Deficiency of essential elements may lead to a list of healthy complications which includes growth impairments, birth defects, reduced fertility, weak bones and affected metabolism of lipid, proteins and carbohydrates (Erkekoglu and Kocer-Gumusel, 2016). In some cases, supplement consumption is usually recommended to people having deficiencies in these major nutrients. The aim of this study was to determine the levels of manganese, potassium, zinc and copper ions in tea leaves. These metal ions are required in small amounts by humans and too much of these ions is also a health hazard (Reilly, 2008). The study was important considering the increasing habit of consuming tea infusions as a non-alcoholic drink among most of the population so as to determine the safety and the nutritional value of the beverage.
1.10 : General objective of the study
The general objective of the study was to assess levels of copper, manganese, potassium and zinc elements in different types of tea leaves and tea infusions.
1.10.1 : Specific objectives
The specific objectives of the study were to:
i. Determine levels of copper, manganese, potassium and zinc elements levels in black, green and purple tea leaves.
ii. Determine levels of metal nutrients; copper, manganese, potassium and zinc elements in black, green and purple tea infusions.
iii. Compare the levels of copper, manganese, potassium and zinc elements in black, green and purple tea leaves.
1.11 Justification of the study
Though in trace amounts, some trace elements are known to play critical roles in various body mechanisms though too much of this ions may also be a health hazard. Examples of major inorganic nutrients elements that have been detected in tea leaves include iron, copper, zinc, potassium, sodium, manganese, nickel, and magnesium (Justino, 2020). The findings of this research will inform policy makers, Public health experts, the academia, food traders and consumers of tea products.
1.12 : Significance of the study
Though some elements found in tea infusions play critical roles in various body mechanisms, Countries, regions and health organisations have specified levels of most elements in food products (Fortin, 2016). This is meant to ensure safety of the consumer hence traders are expected to ensure that the foods they trade in meet the set specifications. This study therefore sought to determine whether the levels of potassium, copper, manganese and zinc in packed tea leaves marketed in Nairobi County meets the regulators specifications in the tested parameters.
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