ABSTRACT

This study evaluated the physicochemical, antioxidant activity, glycemic index and glycemic load of mixed fruit juice produced from Monkey kola (Cola lepidota) and Golden apple (Spondias dulcis). Fresh juices extracted from monkey kola and golden apple fruits were mixed at different proportions (100:0, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 0:100). Both fruits and mixed juice samples were subjected to analyses (proximate analysis, physicochemical properties, antioxidant activity, glycaemic index and load, and sensory evaluation). Completely randomization design was the experimental design used for this study, while t-test and one-way statistical tools were used to determine significant different between and among the fruits and mixed juices respectively at p<0.05. The result of the analyses showed that there was significant difference in the proximate composition of the fruits except in fibre (p>0.05). The proximate composition of the mixed juices showed that the moisture content ranged from 87.23 to 94.52%, ash (0.15 to 0.25%), fibre (0.00 to 0.33%), protein (0.09 to 0.31%), fat (5.02 to 9.21%), and carbohydrate (0.09 to 2.89%). The result of the physicochemical composition showed that the total soluble solid ranged from 43.50 to 87.00 brix^o, total titratable acidity (0.03 to 0.22%), and pH (3.79 to 6.92). The result of the antioxidant composition of the fruits showed that there was significant difference (p<0.05) in the total carotenoid, total flavonoid and total phenolic contents of the fruits. The antioxidant composition of the mixed juices showed that total carotenoid ranged from 0.21 to 0.51 mg/100g, total flavonoid (0.74 to 2.82 mg/100g), total phenol (9.11 to 13.16 mg/100g), and ascorbic acid (6.19 to 10.79 mg/100g). The result of the antioxidant activity of the fruits showed that there was significant difference (p<0.05) in the free radical scavenging activity (ABTS), but there was no significant difference (p>0.05) in the ferric reducing power (FRAP). The antioxidant activity of the mixed juices showed that the percentage free radical scavenging activity ranged from 33.00 to 50.29%, while the percentage ferric reducing power ranged from 21.67 to 39.86%. Furthermore, the result of the glycaemic index (GI) and glycaemic load (GL) of the fruits showed that both fruits had low GI at p<0.05. Monkey kola has low GL, while golden apple has moderate GL. The mixed juices also had low GI and low GL at p<0.05. The result of the sensory evaluation of the mixed juices showed that mixed juices with higher proportions of golden apple juice were the most preferred in terms of appearance, taste, aroma, consistency and general acceptability than others. Thus, inclusion of the golden apple juice increased the consumers’ acceptability of the mixed fruit juices. Therefore, this study showed positive synergistic effects of the mixed fruit juices on the nutritional value, improved antioxidant activity and as well as glycaemic index and glycaemic load. The mixed fruit juices are therefore recommended for these functional attributes in modern food systems.

                                                   TABLE OF CONTENTS                                PAGE

Title page                                                                                                                    i

Declaration                                                                                                                  ii

Certification                                                                                                                iii

Dedication                                                                                                                  iv

Acknowledgements                                                                                                    v

Table of Contents                                                                                                       vi

List of Tables                                                                                                              x

List of Figures                                                                                                             xi

List of Plates                                                                                                               xii

Abstract                                                                                                                      xiii

CHAPTER 1: INTRODUCTION

1.1 Background of the Study                                                                                     1

1.2 Statement of Problems                                                                                          3

1.3 Justification                                                                                                           5

1.4 Objectives of the Study                                                                                        6

CHAPTER 2: LITERATURE REVIEW

2.1 Fruits                                                                                                                     7

2.1.1 Fruit juices                                                                                                         8

2.1.2 Physicochemical characteristics of fruit juices                                                   9

2.2 Monkey Kola (Cola lepidota)                                                                               10

2.2.1 Chemical composition of monkey kola                                                              11

2.2.2 Health benefits of monkey kola                                                                         12

2.3 Golden Apple (Spondias dulcis)                                                                           13

2.3.1 Chemical composition of golden apple                                                              14

2.3.2 Health benefits of golden apple                                                                         14

2.4 Antioxidants                                                                                                         14

2.4.1 Importance of antioxidants                                                                                16

2.4.2 Classification of antioxidants                                                                            17

2.4.3 Common antioxidants in fruits                                                                          18

2.5 Glycemic Index (GI)                                                                                            20

2.5.1 Measurement of glycemic index                                                                        21

2.5.2 Factors that affect the glycemic index of a food                                              21

2.6 Glycaemic Load (GL)                                                                                           25

2.7 Role of Glycemic Index (GI) and Glycemic Load (GL) in preventing

      diseases                                                                                                                 26

2.7.1 Diabetes                                                                                                             27

2.7.1.1 Relationship between diabetes and obesity                                                    28

2.7.2 Type 2 diabetes mellitus                                                                                    29

2.7.3 Obesity                                                                                                               31

2.7.4 Cardiovascular disease                                                                                       33

2.7.5 Cancer                                                                                                                35

2.7.6 Gallbladder disease                                                                                            36

CHAPTER 3: MATERIALS AND METHODS

3.1 Sources of Raw Materials                                                                                     38

3.2 Preparation of Samples                                                                                         38

3.2.1 Extraction of monkey kola juice                                                                        38

3.2.2 Extraction of golden apple juice                                                                        40

3.3 Formulation of Mixed Fruit Juices                                                                       40

3.4 Proximate Analyses of the Fruits and Mixed Juices                                             43

3.4.1 Determination of moisture content                                                                    43

3.4.2 Determination of ash content                                                                            44

3.4.3 Determination of fat content                                                                             44

3.4.4 Determination of crude fibre content                                                                45       

3.4.5 Determination of crude protein content                                                            45

3.4.6 Determination of carbohydrate content                                                             46

3.5 Physicochemical Analyses of the Mixed Fruits Juices                                         46

3.5.1 Total soluble solid (TSS)                                                                                    47

3.5.2 Titratable acidity                                                                                                47

3.5.3 pH                                                                                                                      47

3.5.4 Ascorbic acid (AA)                                                                                            47

3.6 Antioxidants Analyses of the Fruits and Mixed Juices                                        48

3.6.1 Total carotenoid content (TCC)                                                                         48

3.6.2 Total flavonoid content (TFC)                                                                           48

3.6.3 Total phenolic content (TPC)                                                                             49

3.7 Antioxidant Activity of the Fruits and Mixed Juices                                           49

3.7.1 Free radical scavenging activity (ABTS)                                                           49

3.7.2 Ferric reducing antioxidant power (FRAP)                                                       50

3.8 Determination of Glycemic Index (GI) and Glycemic Load (GL)                      51

3.9 Sensory Analysis                                                                                                   52

3.10 Experimental Design                                                                                           53

3.11 Statistical Analysis                                                                                              53

CHAPTER 4: RESULTS AND DISCUSSION

4.1 Pictorial Representation of the Juice Samples                                                      54

4.2 Proximate Composition of the Fruits                                                                    56

4.3 Proximate Composition of the Mixed Fruit Juices                                               59

4.4 Physicochemical Composition of the Mixed Fruit Juices                                     64

4.5 Antioxidant Content of the Fruits                                                                                    67

4.6 Antioxidant Content of the Mixed Fruit Juices                                                   70

4.7 Antioxidant Activity of the Fruits                                                                                    73

4.8 Antioxidant Activity of the Mixed Fruit Juices                                                   75

4.9 Glycemic Index (GI) and Glycemic Load (GL) of the Fruits                              78

4.10 Glycemic Index (GI) and Glycemic Load (GL) of the Mixed  

        Fruit Juices                                                                                                          80

4.11 Sensory Evaluation of the Mixed Fruit Juices                                                    82

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion                                                                                                            87

5.2 Recommendations                                                                                                            88

5.3 Contribution to Knowledge                                                                                  88

References                                                                                                                  89

Appendices                                                                                                              

LIST OF TABLES

2.1: Proximate composition of endocarp and exocarp of Cola lepidota                     11

2.2: Energy and proximate composition of monkey kola (C. parchycarpa

       and C. lepidota) juice                                                                                           12

2.3: GI and GL of some common fruits                                                                     36

2.4: GI and GL of some common fruit juices                                                             37

3.1: Formulation of mixed fruit juice                                                                          41

4.1: Proximate composition of the mixed fruit juices                                                 60

4.2: Physicochemical Composition of the Mixed Fruit Juices                                    65

4.3: Antioxidant content of the mixed fruit juices                                                     71

4.4: Antioxidant activity of the mixed fruit juices                                                     76

4.5: Glycemic index (GI) and glycaemic load (GL) of the fruits                               79

4.6: Glycemic index (GI) and glycaemic load (GL) of the mixed

        fruit juices                                                                                                           81

4.7: Sensory evaluation of the mixed fruit juices                                                       83

LIST OF FIGURES

3.1: Flow chart for the preparation of mixed fruit juice                                 42

4.1: Proximate composition of the fruits                                                        57

4.2: Antioxidant content of the fruits                                                             68

4.3: Antioxidant activity of the fruits                                                             74