Antioxidant Potential of Different Types of Tea

Antioxidant Potential of Different Types of Tea.

ABSTRACT

The present study evaluated the phytochemical constituents and in vitro antioxidant potential of different types of tea namely; black tea, un-caffeinated tea, green tea and herbal tea. Radical scavenging capacities of the tea extracts were determined using 2,2-diphenyl-2-picrylhydrazyl (DPPH) assay.

Total antioxidant activity was determined using ferric reducing antioxidant power (FRAP) assay. The results showed that the total flavonoid content (TFC) of green tea (215.61±48.83 QE/mg) wassignificantly (p<0.05) higher than that of un-caffeinated tea (184.32±33.62 QE/mg) and herbal tea (167.25±31.25 QE/mg).

There was no significant (p >0.05) difference between the TFC of un-caffeinated and herbal tea samples. However, the TFC of un-caffeinated and herbal tea samples were found to be significantly (p<0.05) higher than that of black tea (142.32±22.73 QE/mg).

There was no significant (p > 0.05) difference in the total tannin content (TTC) of un-caffeinated tea (411.55±9.21 GAEmg/ml), green tea (406.83±22.71 GAEmg/ml) and herbal tea (402.74±13.2 GAEmg/ml). However, their TTC were found to be significantly (p < 0.05) higher than that of black tea (325.14±108 GAEmg/ml).

The total phenol content (TPC) of green tea (124.81±79.05 GAEmg/ml) was found to be significantly (p < 0.05) higher than that of un-caffeinated tea (63.87±35.76 GAEmg/ml), black tea (51.81±8.90 GAEmg/ml) and herbal tea (15.78±13.02 GAEmg/ml).

The antioxidant activity of black tea and herbal tea was found to be significantly (p < 0.05) higher than that of un-caffeinated tea. Green tea showed the least radical scavenging activity. A correlation between the antioxidant capacity and the phytochemical constituent of the teas was observed.

TABLE OF CONTENTS

Certification i

Dedication ii

Acknowledgements iii

Abstract iv

Table of contents v

List of Figures ix

List of Tables x

List of Abbreviations xi

Abstract xii

CHAPTER ONE: INTRODUCTION 1

1.1 Antioxidants 3

1.1.1 Free Radical Production and Antioxidant Defence Mechanism 3

1.1.2 Endogenous and Exogenous Antioxidants 4

1.1.3 Diet, Antioxidant and Health 4

1.1.3.1 Flavonoids 5

1.1.3.2 Tannins 5

1.1.3.3 Ascorbic Acid 7

1.1.3.4 Carotenoids 8

1.1.3.5 Vitamin E 9

1.2 Mechanism of Action of Antioxidant 11

1.2.1 Antioxidant and Oxidative Stress Biomarkers 12

1.3 Types of Tea and their Chemical Composition 13

1.3.1 Green Tea 13

1.3.2 Green Tea Composition 13

1.3.3 Black Tea 14

1.3.4 Chemical Composition of Black Tea 14

1.3.5 White Tea 15

1.3.6 Pu’erh Tea 15

1.3.7 Rooibos (Aspalathus Linearis) 15

1.3.8Chemical Composition of Rooibos Tea 16

1.3.9 Chamomile Tea 16

1.4 Tea as a Nutraceutical 16

1.5 Tea Production in Nigeria 17

1.6 Bioactivities of Tea 19

1.6.1 Tea and Metabolism, Obesity and Body Fat 19

1.6.2 Role of Tea in Weight Loss 20

1.6.3 Effect of Tea on Absorption of Metal Ion 21

1.6.4 Tea, Diabetes and Blood Sugar Control 21

1.6.5 Effect of Tea on Drug Metabolising Enzymes 22

1.7.1 Role of Tea in Immune Functions 23

1.7.2 Role of Tea in Neurological Health 23

1.7.3 Cognitive Health 24

1.7.4 Cardiovascular Disease Risk Factors 25

1.7.5 Cholesterol Reduction 25

1.7.6 Role of Tea Theaflavin in Cardiac Health 26

1.7.7 Role of Theanine in Stress Management 26

1.7.8 Anticarcinogenic Effect of Tea 27

1.7.8.1 DNA Damage 28

1.7.8.2 Breast Cancer 28

1.7.8.3 Prostate Cancer 28

1.7.8.4 Skin Cancer 29

1.7.8.5 Lung Cancer 29

1.7.8.6 Ovarian Cancer 30

1.7.9 Role of Tea in Oral Health 30

1.8 Adverse Effect of Tea 31

1.9 Aim and Specific Objectives of the Study 32

1.9.1 Aim of the Study 32

1.9.2 Specific Objectives of the Study 32

CHAPTER TWO: MATERIALS AND METHODS 33

2.1 Materials 33

2.1.1 Collection of tea samples 33

2.1.2 Equipment and Instrument 33

2.1.3 Chemicals and Reagent 33

2.2 Methods 34

2.2.1. Preparation of Extract 34

2.2.2 Experimental Design 34

2.2.3 Phytochemical Studies 35

2.2.3.1 Test for Tannins 35

2.2.3.2 Test of Flavonoids 35

2.2.3.3 Test for Total Phenolic Contents 36

2.2.4 Determination of Antioxidant Activity Using DPPH Radical Scavenging Model 36

2.2.5 Ferric Reducing Antioxidant Power Assay 37

2.2.6 Statistical Analysis 37

CHAPTER THREE: RESULTS 34

3.1 Results of Qualitative Phytochemicals of Different Types of Tea 38

3.2 Results of Quantitative Phytochemical Analysis of Different Types of Tea 40

3.2.4 A Comparison of the Mean Values of the Quantity Phytochemicals of the Tea Samples 45

3.3 Results of the Evaluation of Antioxidant Activity of Tea Samples based on DPPH Assay 46

3.3.1 Effects of Black tea on DPPH radical 46

3.3.2 Effects of un-caffeinated tea on DPPH radical 47

3.3.3 Effects of green tea radical on DPPH radical 48

3.3.4Effects of herbal tea radical on DPPH radical 49

3.4 Results of The Evaluation of The Antioxidant Activity of Tea samples by FRAP Assay 50

3.4.1Effect of Black Tea Extracts on Ferric (Fe3+) ions 50

3.4.2 Effect of Un-Caffeinated Tea Extract on Ferric (Fe3+)51

3.4.2 Effect of Green Tea Extracts on Ferric (Fe3+) ions. 52

3.4.3 Effects of herbal tea extracts on Ferric (Fe3+) ions. 53

3.5 A Comparison of the Phytochemicals and Antioxidant Activities of Different Types of Tea 54

3.6 The Correlation of the Phytochemical Constituents with Antioxidant Activities 56

CHAPTER FOUR 58

4.1 DISCUSSION 58

4.2 Conclusion 62

4.3 Recommendation 62

References

INTRODUCTION

Oxygen is an element indispensable for life. When cells use oxygen to generate energy, free radicals are created as a result of cellular redox process which leads to ATP production by the mitochondria (Kabel, 2014). These products are called reactive oxygen species (ROS).

Reactive oxygen species (ROS) is a collective term used for a group of oxygen-centred oxidants, which are either free radicals or molecular species capable of generating free radicals. Free radicals are generated from either endogenous or exogenous sources.

Endogenous free radicals are generated from immune cell activation, inflammation, mental stress, excessive exercise, ischemia, infection, cancer and ageing. Exogenous free radicals result from air and water pollution, cigarette smoking, alcohol, heavy metals, certain drugs (cyclosporine, tacrolimus), industrial solvents, cooking and radiation.

After penetration into the body, these exogenous compounds are decomposed into free radicals (Valko et al., 2007). Under normal physiologic conditions, nearly 2% of the oxygen consumed by the body is converted into reactive oxygen through mitochondrial respiration, phagocytosis, etc.

However, free radicals play a dual role as both toxic and beneficial compound (Kunwar and Priyadesh, 2011). At low or moderate level, ROS exert beneficial effects on cellular responses and immune function. At high concentration, they cause oxidative stress, a deleterious process that can damage all cellular structures (Halliwell, 2007).

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StudentsandScholarship Team.