Effect Of Extrusion Process Variables On Quality Attributes Of Extrudates From Blends Of Aerial Yam And Soybean Flours - A Response Surface Analysis

ABSTRACT

This study investigated the effect of extrusion process variables on quality attributes of extrudates from blends of aerial yam and soybean flours. Laboratory scale single-screw extruder was used in extruding blends of aerial yam and soybean flours in the ratio of 25% aerial yam: 75% soybean. Response surface methodology based on Box-Behnken design at three factors, five levels of barrel temperature (95, 100, 105, 110, and115 ), screw speed (85, 100, 115, 130, and145 rpm) and feed moisture (31, 33, 35, 37, and 39%) were used in 20 runs. Significant (p< 0.05) regression models, describing the effects of process parameters on the product quality attributes, were employed. Results obtained showed that the proximate compositions varied between 4.03  and 5.90 % ash; 3.10  and 7.02 % moisture content; 2.70  and 4.67 % fibre; 24.57  and 36.79 % protein; 11.39  and 35.35 % lipid; 30.11  and 54.15 % carbohydrate; 398.84  and 529.17 kcal energy value. Anti-nutritional factors of the extrudates ranged between 0.79  and 5.11 /100g HCN, 12.48 and 32.86 /100g phytate; 0.93  and 5.46 /100g tannin; 45.81  and 102.71 /100g oxalate; 0.79  and 2.19  alkaloid. Functional properties varied between 0.4779  and 0.7211 g/cm³ bulk density; 2.52  and 3.89 g/g water absorption; 1.12  and 2.88 g/g oil absorption; 28.51  and 34.85 % emulsion capacity; 3.37  and 4.86 % foaming capacity. Sensory characteristics scores were between 4.38  and 6.02  for texture; 4.68  and 6.78  for taste; 4.58  and 6.97  for colour; 4.45  and 7.00  for aroma; 4.20  and 7.10  for overall acceptability. Barrel temperature, screw speed and feed moisture significantly (p< 0.05) affected the HCN, phytate, tannin and oxalate content of the extrudates. For proximate composition, only barrel temperature affected the ash composition significantly (p< 0.05). Barrel temperature, screw speed and feed moisture showed insignificant (p> 0.05) effect on moisture content, while fibre content was significantly (p< 0.05) affected by barrel temperature and screw speed. Protein, fat and carbohydrates content were significantly (p< 0.05) affected by barrel temperature, screw speed and feed moisture, while barrel temperature and screw speed showed significant effect on caloric value. For functional properties, barrel temperature, screw speed and feed moisture significantly affected the bulk density, water and oil absorption capacity, emulsion and foaming capacity. Sensory characteristics showed that, barrel temperature and screw speed significantly (p< 0.05) affected the texture, while taste was affected significantly by barrel temperature, screw speed and feed moisture. Barrel temperature and feed moisture showed significant effect on colour and overall acceptability of the extrudates, while aroma was significantly affected by barrel temperature. High Regression coefficient, R² ≥ 0.9 were obtained, showing that the models can be used to navigate the design space. Optimization results based on desirability concept indicated that a barrel temperature of 112.83 , screw speed of 127.87 rpm and feed moisture of 32.59% would produce extrudates of preferable anti-nutritional factors; 112.11  barrel temperature, 136.49 rpm screw speed and 34.65% feed moisture would produce extrudates of better proximate composition;112.85  barrel temperature, 144.99 rpm screw speed and 35.12% feed moisture would produce extrudates of preferable functional properties; 114.12  barrel temperature, 100.56 rpm screw speed and 38.02% feed moisture would produce extrudates of preferable sensory characteristics.  

TABLE OF CONTENTS

CHAPTER                                                    TITLE                                                         PAGE

Cover Page                                                                                                                              i

Title Page                                                                                                                                ii

Declaration                                                                                                                              iii

Certification                                                                                                                            iv

Acknowledgement                                                                                                                  v

Table of Contents                                                                                                                   vii                   

List of Tables                                                                                                                          xvi                                                                                                                   

List of Figures                                                                                                                         xx

List of Plates                                                                                                                           xxvi

Abstract                                                                                                                                  xxvii

CHAPTER 1: INTRODUCTION

1.1                    Aerial Yam (Dioscoreabulbifera)                                                                  1

1.2                    Soybean (Glycine max)                                                                                  3

1.3                    Justification of the Study                                                                              5

1.4                    Aim and Objectives of the Study                                                                              6

CHAPTER 2: LITERATURE REVIEW

2.1                     Processing and Utilization of Aerial Yam                                                    7

2.2                     Processing and Utilization of Soybean                                                         9

2.2.1                  Production of Soy Protein Products                                                             11

2.2.2                  Germinated Soy Products                                                                             11

2.2.3                  Soy Oil                                                                                                          12

2.2.4                  Other Traditional Soy Foods                                                                        12                                                                                   

2.2.5                  Progress in Soybean Processing In Nigeria                                       13

2.3                     Food Extrusion Process                                                                                14

2.3.1                  Fundamental Principles of Food Extrusion                                                              16

2.3.2                  Single-Screw Extruders                                                                                18

2.3.3                  Twin-Screw Extruders                                                                                  21

2.3.4                   Comparison of Single- and Twin-Screw Extruders                                     22

2.4                      Effects of Extrusion Process on Proximate Composition of                             

                           Food Products                                                                                             24                                                            

2.4.1                   Dietary Fibre                                                                                                26

2.4.2                   Protein                                                                                                          26

2.4.3                  Carbohydrates                                                                                               28

2.4.4                  Reduction of Lipid Oxidation                                                                      30

2.4.5                  Product Moisture                                                                                          31

2.5                     Effects of Extrusion Process on Functional Properties of

                          Food Products                                                                                              32

2.5.1                  Bulk Density                                                                                                 33

2.5.2                 Water Absorption Index (WAI) and Water Solubility

                          Index (WSI)                                                                                                  35

2.5.3                  Oil Absorption Index                                                                                    37

2.6                     Effects of Extrusion Process on Anti-nutritional Factors in

                          Food Products                                                                                              38

2.6.1                  Reduction of Anti-nutritional factors                                                           38

2.7                     Effect of Extrusion Process on Sensory Properties of

                          Food Products                                                                                              43

2.7.1                  Flavour Formation and Retention during Extrusion                                     43

2.7.2                  Aroma                                                                                                           44

2.7.3                  Colour                                                                                                           45

2.7.4                   Crispness/Hardness/Texture                                                                         46

2.7.5                   Overall Acceptability                                                                                   48

2.8                      Response Surface Methodology (RSM)/Analysis                                       48

CHAPTER 3: MATERIALS AND METHODS

3.1                     Collection of Soybean Seeds and Aerial Yam Bulbs                                   51

3.2                    Sample Preparation                                                                                        51

3.2.1                 Preparation of Aerial Yam Flour                                                                   51

3.2.2                 Preparation of Soybean Flour                                                                        52

3.2.3                  Preparation of Sample Blend                                                                        53

3.2.4                  Extrusion Cooking                                                                                        53

3.4                     Determination of Proximate Composition                                                    54

3.4.1                  Moisture Content                                                                                          54

3.4.2                   Ash Content                                                                                                 55

3.4.3                   Crude Fibre                                                                                                  55

3.4.4                   Crude Protein                                                                                               56

3.4.5                   Crude Fat (Lipid)                                                                                         57

3.4.6                   Carbohydrate Content                                                                                             58

 3.4.7                  Energy Value                                                                                               58

3.5                      Determination of Anti-nutritional Factors                                                   58

3.5.1                   Hydrogencyanide (Cyanogenic Glycosides)                                                           58

3.5.2                   Oxalates                                                                                                                   59

3.5.3                   Phytic acid (Phytates)                                                                                  60

3.5.4                   Tannin                                                                                                          60

3.5.5                   Alkaloids                                                                                                      61

3.6                    Determination of Functional Properties                                                         62

3.6.1                 Bulk Density                                                                                                  62

3.6.2                 Water Absorption Capacity                                                                                       62

3.6.3                 Oil Absorption Capacity                                                                                63

3.6.4                 Emulsion Capacity                                                                                         63

3.6.5                 Foaming Capacity                                                                                          64

3.7                    Determination of Sensory Characteristics                                                     64

3.7.1                 Texture                                                                                                           64

3.7.2                 Taste                                                                                                               64

3.7.3                 Appearance                                                                                                    64

3.7.4                 Aroma                                                                                                            64

3.7.5                 Overall Acceptability                                                                                     64

3.8                    Experimental Design/Response Surface Analysis                                         64

3.9                   Model Selection for Optimization and Validation of Extrusion

                        Process Parameters                                                                                          65

 

CHAPTER 4: RESULTS AND DISCUSSION                                               

4.1                 Proximate Composition of Extruded Aerial Yam and

                Soybean Flour Blend                                                                                                  68

4.1.1                Ash                                                                                                                  68

4.1.2                Moisture Content                                                                                            69

4.1.3                Fibre                                                                                                                69

4.1.4                Protein                                                                                                             70

4.1.5                Crude Fat                                                                                                        70

4.1.6                Carbohydrate                                                                                                  71

4.1.7                 Energy Value                                                                                                 71

4.2                    Model Selection/Equation for Optimization of Extrusion Process

                         Parameters of Proximate Composition of Aerial Yam and

                         Soybean Flour Blends                                                                                    73

                                                        

4.2.1                 Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Ash                                                                                       73

4.2.2                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Moisture Content                                                                  74                          

4.2.3                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Fibre                                                                                      75       

4.2.4                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Protein                                                                                  76                                                                                                        

4.2.5                   Model Selection/Equation for Optimization of Extrusion Process

                           Parameters for Crude Fat                                                                             78

 

4.2.6                   Model Selection/Equation for Optimization of Extrusion Process

                           Parameters for Carbohydrate                                                                       79

 

4.2.7                   Model Selection/ Equation for Optimization of Extrusion Process

                           Parameters for Energy Value                                                                       80                                                                                                 

4.3                      Optimization and Validation of Extrusion Process Parameters for

                           Proximate Composition of Aerial Yam and Soybean Flour Blends            81

                                                              

4.4                      Response Surface Plots for the Proximate Composition of

                           Aerial Yam and Soybean Flour Blends                                                       92

 

4.4.1                   Effect of Extrusion Process Parameters on Ash                                          92

4.4.2                   Effect of Extrusion Process Parameters on Moisture Content                    95

4.4.3                   Effect of Extrusion Process Parameters on Fibre                                        98

4.4.4                   Effect of Extrusion Process Parameters on Protein                                     101

4.4.5                   Effect of Extrusion Process Parameters on Fat                                           104

4.4.6                   Effect of Extrusion Process Parameters on Carbohydrate                          107

4.4.7                  Effect of Extrusion Process Parameters on Energy Value                           110

4.5                     Antinutritional Factors of Extruded Aerial Yam and Soybean

                          Flour Blend                                                                                                   114

 

4.5.1                  Hydrogencyanide (HCN)                                                                             114

4.5.2                  Phytate                                                                                                          115

4.5.3                  Tannin                                                                                                           115

4.5.4                  Oxalates                                                                                                        116

4.5.5                  Alkaloids                                                                                                       116    

4.6                     Model Selection/Equation for Optimization of Extrusion

                          Parameters for Anti-nutritional Factors of Aerial Yam and

                          Soybean Flour Blend                                                                                    118               

4.6.1                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for HCN                                                                                     118

4.6.2                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Phytate                                                                                  119

4.6.3                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Tannin                                                                                   120

4.6.4                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Oxalates                                                                                121

4.6.5                  Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Alkaloids                                                                              122

4.7.                    Optimization and Validation of Extrusion Process Parameters for

                          Anti-nutritional Factors of Aerial Yam and Soybean Flour Blends             124                    

4.7.1                  Numerical Optimization of Extrusion Process Parameters for

                          Anti-nutritional Factors                                                                                124                       

4.8                     Response Surface Plots for the Anti-nutritional Factors of

                          Aerial Yam and Soybean Flour Blends                                                        131              

4.8.1                  Effect of Extrusion Process Parameters on Hydrogencyanide (HCN)        131                                                                                                                    

4.8.2                  Effect of Extrusion Process Parameters on Phytate                                     134

4.8.3                   Effect of Extrusion Process Parameters on Tannin                                     136                                                                   

4.8.4                   Effect of Extrusion Process Parameters on Oxalates                                  140                                                                                                              

4.8.5                    Effect of Extrusion Process Parameters on Alkaloids                                143                                                                       

4.9                       Functional Properties of Extruded Aerial Yam and Soybean

                            Flour Blends                                                                                               147  

4.9.1                    Bulk density                                                                                                147  

4.9.2                    Water Absorption Capacity                                                                        148

4.9.3                    Oil Absorption Capacity                                                                             149   

4.9.4                    Emulsion/Foaming Capacity                                                                       149

                                  

4.10                     Model Selection/Equation for Optimization of Extrusion Process

                            Parameters of Functional Properties of Aerial Yam and

                            Soybean Flour Blends                                                                                 151

4.10.1                  Model Selection/Equation for Optimization of Extrusion Process

                            Parameters for Bulk density                                                                       151                                                    

4.10.2                  Model Selection/Equation for Optimization of Extrusion Process

                            Parameters for Water Absorption Capacity                                                152

4.10.3                  Model Selection/Equation for Optimization of Extrusion Process

                            Parameters for Oil Absorption Capacity                                                     153

4.10.4                  Model Selection/Equation for Optimization of Extrusion Process

                            Parameters for Emulsion Capacity                                                              154

4.10.5                  Model Selection/Equation for Optimization of Extrusion Process

                            Parameters for Foaming Capacity                                                               155

          

4.11                     Optimization and Validation of Extrusion Process Parameters for

                            Functional Properties of Aerial Yam and Soybean Flour

                            Blends                                                                                                         157

4.11.1                  Numerical Optimization of Extrusion Process Parameters for

                            Functional Properties                                                                                  157

4.12                     Response Surface Plots for the Functional Properties of Aerial

                            Yam and Soybean Flour Blends                                                                 165  

                                                                                                             

4.12.1                  Effect of Extrusion Process Parameters on Bulk Density                          165

 

4.12.2                  Effect of Extrusion Process Parameters on Water Absorption Capacity               169                                                                                                   

 

4.12.3                  Effect of Extrusion Process Parameters on Oil Absorption Capacity        172                                                                                                        

 

4.12.4               Effect of Extrusion Process Parameters on Emulsion Capacity                    175                                                                                    

 

4.12.5               Effect of Extrusion Process Parameters on Foaming Capacity                     178                                   

 

4.13                  Sensory Characteristics of Extruded Products from      

                         Aerial Yam and Soybean Flour Blends                                                         182                                     

4.13.1               Texture                                                                                                           182

4.13.2               Taste                                                                                                               183

4.13.3               Appearance                                                                                                    183

4.13.4               Aroma                                                                                                            184

4.13.5               Overall Acceptability                                                                                     184

4.14                  Model Selection/Equation for Optimization Extrusion Process

                         Parameters of Sensory Characteristics of Aerial Yam and

                         Soybean Flour Blends                                                                                    187

                  

4.14.1                Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Texture                                                                                  187                       

4.14.2                Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Taste                                                                                     188

4.14.3                Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Appearance                                                                           189        

4.14.4                Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Aroma                                                                                   190                                

4.14.5                Model Selection/Equation for Optimization of Extrusion Process

                          Parameters for Overall Acceptability                                                            192                                      

4.15                  Optimization and Validation of Extrusion Parameters for

                         Sensory Characteristics                                                                                  193

4.15.1                Numerical optimization of Extrusion Process Parameters for

                          Sensory Characteristics                                                                                 193

4.16                   Response Surface Plots for the Sensory          

                          Characteristics of Aerial Yam and Soybean Flour Blends                           200                                    

 

4.16.1               Effects of Extrusion Parameters on Texture                                                  200

4.16.2               Effects of Extrusion Parameters on Taste                                                     203

4.16. 3              Effects of Extrusion Parameters on Appearance                                           207

4.16.4               Effects of Extrusion Parameters on Aroma                                                   210

4.16.5               Effects of Extrusion Parameters on Overall Acceptability                            214

 

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS

5.1                    Conclusion                                                                                                     218

5.2                    Recommendations                                                                                         220                                  

REFERENCES                                                                                              222

APPENDICES                                                                                                236

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LIST OF TABLES

TABLE                                                                              TITLE                                                                            PAGE                               

 2.1                  Extrusion Cooking Applications                                                                     16

 2.2                  Relative Comparison of Single- and Twin- Screw Extruders                         24

2.3                   Anti-nutrients and Toxins affected by Extrusion Cooking                            40

3.1                   Coded and Actual values of different Experimental Variables                     64

3.2                   Experimental Layout for 3 Variables and 5 Levels Response Surface

                        Experimental Design for the Extrusion of Aerial Yam and Soybean

                        Flour Blend                                                                                                     65      

 

3.3                   Criteria for numerical Optimization of Extrusion Process Parameters

                        for Proximate Composition                                                                             66

 

3.4                   Criteria for Numerical Optimization of Extrusion Process Parameters

                        for Anti-nutritional Factors                                                                             67

 

3.5                   Criteria for Numerical Optimization of Extrusion Process Parameters

                        for Functional Properties                                                                                67

 

3.6                   Criteria for Numerical Optimization of Extrusion Process Parameters

                        for Sensory Characteristics                                                                             67

 

4.1                   Proximate Composition of Extruded Aerial Yam and Soybean

                        Flour Blends                                                                                                   68

 

4.2                   Coefficient of Regression/ANOVA for Proximate Compositions                 72

                                                                                                        

4.3                   Output for Numerical Optimization of Extrusion Process

                        Parameters for Proximate Composition                                                          81

                                                                                                       

4.4                   Optimal Extrusion Process Parameters with Optimum Predicted

                        Responses for Validation of the Proximate Composition                              84

                                                                                                       

4.5                       Analysis of Variance (ANOVA) for Ash at 5% Significance Level                94

 

4.6                   Tests of Between-Subjects Effects of Extrusion Process Parameters

                        on Ash                                                                                                             94

 

4.7                   Analysis of Variance (ANOVA) for Moisture Content at

                        5% Significance Level                                                                                    97

 

 

4.8              Tests of Between-Subjects Effects of Extrusion Process Parameters on

                   Moisture Content                                                                                                 97

 

4.9              Analysis of Variance (ANOVA) for Fibre at 5% Significance Level                 100

 

4.10            Tests of Between-Subjects Effects of Extrusion Process Parameters on

                   Fibre                                                                                                                     100

4.11            Analysis of Variance (ANOVA) for Protein at 5% Significance Level              103

 

4.12            Tests of Between-Subjects Effects of Extrusion Process Parameters on

                    Protein                                                                                                                 103

4.13            Analysis of Variance (ANOVA) for Crude Fat at 5% Significance Level                     106

 

4.14             Tests of Between-Subjects Effects of Extrusion Process Parameters on

                    Crude Fat                                                                                                            106

 

4.15             Analysis of Variance (ANOVA) for Carbohydrate at 5% Significance Level  109

 

4.16             Tests of Between-Subjects effects of Extrusion Process Parameters on

                    Carbohydrate                                                                                                      110

 

4.17            Analysis of Variance (ANOVA) for Energy Value at 5% Significance Level   112

 

4.18            Tests of Between-Subjects Effects of Extrusion Process Parameters on

                   Energy Value                                                                                                       113

 

4.19            Anti-nutritional Factors of Extruded Aerial yam and Soybean Flour Blends     114

                                                    

4.20             Coefficient of Regression/ANOVA for Anti-nutritional Factors                       117

                                             

4.21            Output for Numerical Optimization of Extrusion Process

                   Parameters for Anti-nutritional Factors                                                               124              

 

4.22            Optimal Extrusion Process Parameters with Optimum Predicted

                    Responses for Validation of the Anti-nutritional Factors                                   126

                   

4.23             Analysis of Variance (ANOVA) for HCN at 5% Significance Level                133

4.24            Tests of Between-Subjects Effects of Extrusion Process Parameters

                    on HCN                                                                                                               133

4.25            Analysis of Variance (ANOVA) for Phytate at 5% Significance Level              136

4.26            Tests of Between-Subjects effects of Extrusion Process Parameters

                    on Phytate                                                                                                            136

4.27            Analysis of Variance (ANOVA) for Tannin at 5% Significance Level              139

4.28            Tests of Between-Subjects Effects of Extrusion Process Parameters

                    on Tannin                                                                                                            139

 

4.29             Analysis of Variance (ANOVA) for Oxalates at 5% Significance Level          142

4.30             Tests of Between-Subjects Effects of Extrusion Process Parameters

                    on Oxalates                                                                                                         142

 

4.31             Analysis of Variance (ANOVA) for Alkaloids at 5% Significance Level         145

                                               

4.32             Tests of Between-Subjects effects of Extrusion Process Parameters

                    on Alkaloids                                                                                                        146

                                       

4.33            Functional Properties of Extruded Aerial Yam and Soybean Flour Blends      147                                                                                  

 

4.34             Coefficient of Regression/ANOVA for Functional Properties                          150                                                                           

 

4.35             Output for Numerical Optimization of Extrusion Process

                    Parameters for Functional Properties                                                                  157

                                                                               

4.36             Optimal Extrusion Process Parameters with Optimum

        Predicted Responses for Validation of Functional Properties                            159                                                                   

4.37            Analysis of Variance (ANOVA) for Bulk Density at 5% Significance Level    167                                                                          

4.38             Tests of Between-Subjects Effects of Extrusion Process Parameters

                    on Bulk Density                                                                                                  168

4.39              Analysis of Variance (ANOVA) for Water Absorption Capacity

                    at 5% Significance Level                                                                                    171

4.40              Tests of Between-Subjects Effects of Extrusion Process Parameters

                    on Water Absorption  Capacity                                                                          171         

 

4.41             Analysis of Variance (ANOVA) for Oil Absorption Capacity at 5%

                    Significance Level                                                                                              174

4.42             Tests of Between-Subjects Effects of Extrusion Process Parameters on

                    Oil Absorption Capacity                                                                                    175      

 

4.43             Analysis of Variance (ANOVA) for Emulsion capacity at 5%

                    Significance level                                                                                                177                                                          

4.44             Tests of Between-Subjects Effects of Extrusion Process Parameters on

                    Emulsion Capacity                                                                                              178

                                       

4.45              Analysis of Variance (ANOVA) for Foaming Capacity at 5%

                     Significance Level                                                                                             180       

 

4.46              Tests of Between-Subjects Effects of Extrusion Process Parameters

                     on Foaming Capacity                                                                                         181                    

 

4.47              Sensory Characteristics of Extruded Aerial Yam and Soybean

                     Flour Blends                                                                                                      182

 

4.48                 Coefficient of Regression/ANOVA for Sensory Characteristics                       186

                                                                                                          

4.49              Output for Numerical Optimization of Extrusion Process

                     Parameters for Sensory Characteristics                                                              193

 

4.50              Optimal Extrusion Process Parameters with Optimum Predicted

                     Responses for Validation of the Sensory Characteristics                                  194

                                                                                               

4.51              Analysis of Variance (ANOVA) for Texture at 5% Significance Level           202

 

4.52              Tests of Between-Subjects Effects of Extrusion Process Parameters

                      on Texture                                                                                                         203

 

4.53              Analysis of Variance (ANOVA) for Taste at 5% Significance Level               205                                                                                   

 

4.54              Tests of Between-Subjects Effects of Extrusion Process Parameters

                     on Taste                                                                                                              206

 

4.55               Analysis of Variance (ANOVA) for Appearance at 5%

                      Significance Level                                                                                            209                                                                                            

                                                              

4.56               Tests of Between-Subjects Effects of Extrusion Process Parameters

                      on Appearance                                                                                                  210

 

4.57               Analysis of Variance (ANOVA) for Aroma at 5% Significance Level           212

 

4.58               Tests of Between-Subjects effects of Extrusion Process Parameters

                      on Aroma                                                                                                          213

 

4.59                Analysis of Variance (ANOVA) for Overall Acceptability at 5%

                       Significance Level                                                                                           216

 

4.60                 Tests of Between-Subjects Effects of Extrusion Process Parameters

                         on Overall Acceptability                                                                                216

 

                                                                                            

 

 

LIST OF FIGURES

   

FIGURE                                                                     TITLE                                                                       PAGE

2.1                   A Flow Chart for the Production of Flour from Aerial Yam                         9

2.2                  Conventional Processes for Producing Full-fat and Defatted

                       Soybean Flour/Grits                                                                                         14

 

2.3                  A Cross-section of a Single-Screw Extruder                                                   19

 

4.1                  Ramp for Optimization of Extrusion Process Conditions for

                       Proximate Compositions of Aerial Yam and Soybean Flour Blend                82                                                                            

 

4.2                  Comparison of the Predicted and Experimental Values for Ash                    86

                                                                              

4.3                  Comparison of the Predicted and Experimental Values for

                       Moisture Content                                                                                             86

                                                                                  

4.4                  Comparison of the Predicted and Experimental Values for Fibre                   88

                                                         

4.5                  Comparison of the Predicted and Experimental Values for Protein               88

 

4.6                  Comparison of the Predicted and Experimental Values for Fat                      89

                                                                

 4.7                  Comparison of the Predicted and Experimental Values for

                        Carbohydrate                                                                                                  90

 

 4.8                  Comparison of the Predicted and Experimental Values for

                        Energy Value                                                                                                  91

 

4.9                   Response Surface Plot showing the Effect of Barrel Temperature and

                        Screw Speed on Ash                                                                                       92

                                                                                 

4.10                 Response surface plot showing the effect of Barrel temperature

                        and Feed moisture on Ash                                                                              92

 

4.11                 Response Surface Plot showing the Effect of Screw Speed and

                        Feed Moisture on Ash                                                                                    93

4.12                 Response Surface Plot showing the Effect of Barrel Temperature

                        and Screw Speed on Moisture Content                                                           95                   

 

4.13                 Response Surface Plot showing the Effect of Barrel Temperature

                        and Feed Moisture on Moisture Content                                                         95

 

 

4.14                Response Surface Plot showing the Effect of Screw Speed

                       and Feed Moisture on Moisture Content                                                         96                                  

 

4.15                Response Surface Plots showing the Effect of Barrel Temperature

                        and Screw Speed on Fibre                                                                              98

 

4.16                 Response Surface Plot showing the Effect of Barrel Temperature

                        and Feed Moisture on Fibre                                                                            99

 

4.17                 Response Surface Plot showing the Effect of Screw Speed

                        and Feed Moisture on Fibre                                                                            99

 

4.18                 Response Surface Plots showing the Effect of Barrel Temperature and

                        Screw Speed on Protein                                                                                  101

 

4.19                 Response Surface Plot showing the Effect of Barrel Temperature

                        and Feed Moisture on Protein                                                                        101

 

 4.20                Response Surface Plot showing the Effect of Screw Speed and

                        Feed Moisture on Protein                                                                               102     

 

4.21                  Response Surface Plot showing the Effect of Barrel Temperature

            and Screw Speed on Crude Fat (Lipid)                                                          104            

 

4.22                   Response Surface Plot showing the Effect of Barrel Temperature

             and Feed Moisture on Crude Fat (Lipid)                                                         104

                                         

4.23                   Response Surface Plot showing the Effect of Screw Speed and Feed

              Moisture on Crude Fat (Lipid)                                                                       105

 

4.24                   Response Surface Plots showing the Effect of Barrel Temperature

              and Screw Speed on Carbohydrates                                                             107

 

4.25                  Response Surface Plot showing the Effect of Barrel Temperature and

                         Feed Moisture on Carbohydrate                                                                    107

 

4.26                  Response Surface Plot showing the Effect of Screw Speed and

             Feed Moisture on Carbohydrate                                                                    108

 

4.27                  Response Surface Plot showing the Effect of Barrel Temperature and

             Screw Speed on Energy Value                                                                      111

 

4.28                  Response Surface Plot showing the Effect of Barrel Temperature and

             Feed Moisture on Energy Value                                                                    111

                                                                                                 

4.29                  Response Surface Plot showing the Effect of Screw Speed and

             Feed Moisture on EnergyValue                                                                     112

                                                                                                   

4.30                   Ramp for Optimization of  Extrusion Process Parameters for

              Anti-nutritional Factors of Aerial Yam-Soybean Flour Blends                    125                                                                                

4.31                  Comparison of the Predicted and Experimental Values for HCN                127

                                                                              

4.32                  Comparison of the Predicted and Experimental Values for Phytate             127

                                                                                  

4.33                  Comparison of the Predicted and Experimental Values for Tannin              128

                                                                               

4.34                  Comparison of the Predicted and Experimental Values for Oxalate            128

                                                                           

4.35                  Comparison of the Predicted and Experimental Values for Alkaloid           129

 

4.36                  Response Surface Plots showing the Effect of Barrel Temperature

             and Screw Speed on HCN                                                                            131

                                                                                

4.37                   Response Surface Plot showing the Effect of Barrel Temperature

                          and Feed Moisture on HCN                                                                         132

 

4.38                   Response Surface Plot showing the Effect of Screw Speed and

                          Feed Moisture on HCN                                                                                132

 

4.39                  Response Surface Plot showing the Effect of Barrel Temperature

                         and Screw Speed on Phytate                                                                         134

 

4.40                  Response Surface Plot showing the Effect of Barrel Temperature

                         and Feed Moisture on Phytate                                                                       134

 

4.41                   Response Surface Plot showing the Effect of Screw Speed and

                          Feed Moisture on Phytate                                                                             135

 

4.42                   Response Surface Plot showing the Effect of Barrel Temperature

                          and Screw Speed on Tannin                                                                         137

 

4.43                   Response Surface Plot showing the Effect of Barrel Temperature

                          and Feed Moisture on Tannin                                                                       137

 

4.44                   Response Surface Plot showing the Effect of Screw Speed and

                          Feed Moisture on Tannin                                                                              138

 

4.45                   Response Surface Plot showing the Effect of Barrel Temperature

                           and Screw Speed on Oxalate                                                                       140

 

4.46                   Response Surface Plot showing the Effect of Barrel Temperature

              and Feed Moisture on Oxalate                                                                       140

 

4.47                   Response Surface Plot showing the Effect of Screw Speed and

              Feed Moisture on Oxalate                                                                             141

 

4.48                   Response Surface Plot showing the Effect of Barrel Temperature

              and Screw Speed on Alkaloids                                                                      143

 

4.49                   Response Surface Plot showing the Effect of Barrel Temperature

               and Feed Moisture on Alkaloids                                                                   144

 

4.50                    Response Surface Plot showing the Effect of Screw Speed and

               Feed Moisture on Alkaloids                                                                         144

 

4.51                    Ramp for Optimization of Extrusion Process Parameters for

                           Functional Properties of Aerial Yam and Soybean Flour Blends                158

 

4.52                    Comparison of the Predicted and Experimental Values for

                           Bulk Density                                                                                                160

           

4.53                    Comparison of the Predicted and Experimental Values for Water

                           Absorption Capacity                                                                                    161

                                                                    

4.54                    Comparison of the Predicted and Experimental Values for Oil

                           Absorption Capacity                                                                                    162

 

4.55                    Comparison of the Predicted and Experimental Values for

                           Emulsion Capacity                                                                                       163

                                              

4.56                    Comparison of the Predicted and Experimental Values for

                           Foaming Capacity                                                                                        164

                                                   

4.57                    Response Surface Plot showing the Effect of Barrel Temperature

                           and Screw Speed on Bulk Density                                                              165

 

4.58                     Response Surface Plot showing the Effect of Barrel Temperature

                            and Feed Moisture on Bulk Density                                                           165                                                          

 

4.59                     Response Surface Plot showing the Effect of Screw Speed and

                            Feed Moisture on Bulk Density                                                                  166                                                          

 

4.60                    Response Surface Plot showing the Effect of Barrel Temperature

                           and Screw Speed on Water Absorption Capacity                                                   168                       

4.61                    Response Surface Plot showing the Effect of Barrel Temperature

                            and Feed Moisture on Water Absorption Capacity                                                169                

 

4.62                    Response Surface Plot showing the Effect of Screw Speed and

                           Feed Moisture on Water Absorption                                                                       169

 

4.63                 Response Surface Plots showing the Effect of Barrel Temperature

                        and Screw Speed on Oil Absorption Capacity                                               172                                                

 

4.64                  Response Surface Plot showing the Effect of Barrel Temperature

                         and Feed Moisture on Oil Absorption Capacity                                            172       

 

4.65                  Response Surface Plot showing the Effect of Screw Speed and

                          Feed Moisture on Oil Absorption Capacity                                                  173 

 

4.66                  Response Surface Plot showing the Effect of Barrel Temperature

             and Screw Speed on Emulsion Capacity                                                       175

                      

4.67                   Response Surface Plot showing the Effect of Barrel Temperature

              and Feed Moisture on Emulsion Capacity                                                    176                                              

4.68                    Response Surface Plot showing the Effect of Screw Speed and

               Feed Moisture on Emulsion Capacity                                                          176

                                                                           

4.69                    Response Surface Plot showing the Effect of Barrel Temperature

                           and Screw Speed on Foaming Capacity                                                      170

                                                                                

4.70                     Response Surface Plot showing the Effect of Barrel Temperature

                and Feed Moisture on Foaming Capacity                                                    179

                                                                                        

4.71                     Response Surface Plot showing the Effect of Screw Speed

                Feed Moisture on Foaming Capacity                                                           179

                                                                                          

4.72                     Ramp for Optimization of Extrusion Process Conditions for

                            Sensory Characteristics of Aerial Yam and Soybean Flour Blends           194

                                                                           

4.73                     Comparison of the Predicted and Experimental Values for Texture          195

                                                                        

4.74                      Comparison of the Predicted and Evalues for Taste                                             197

                                                                             

4.75                     Comparison of the Predicted and Experimental Values for

                            Appearance                                                                                                 198

                                                                                

4.76                     Comparison of the Predicted and Experimental Values for Aroma           299

4.77                     Comparison of the Predicted and Experimental Values for

                            Overall Acceptability                                                                                  200

                                                                                    

4.78                     Response Surface Plot showing the Effect of Barrel Temperature

                            and Screw Speed on Texture                                                                      200

 

4.79                Response Surface Plot showing the Effect of Barrel Temperature and

                       Feed Moisture on Texture                                                                                200

 

4.80                Response Surface Plot showing the Effect of Screw Speed and

                       Feed Moisture on Texture                                                                                201

 

4.81                Response Surface plot showing the Effect of Barrel Temperature and

                       Screw Speed on Taste                                                                                      203  

 

4.82                Response Surface Plot showing the Effect of Barrel Temperature and

                       Feed Moisture on Taste                                                                                   204

 

4.83                Response Surface Plot showing the Effect of Screw Speed and

                       Feed Moisture on Taste                                                                                   204

 

4.84                Response Surface Plot showing the Effect of Barrel Temperature and

                       Screw Speed on Appearance                                                                           207

 

4.85                Response Surface Plot showing the Effect of Barrel Temperature and

                       Feed Moisture on Appearance                                                                         207

 

4.86                Response Surface Plot showing the Effect of Screw Speed and

                       Feed Moisture on Appearance                                                                         208

 

4.87                Response Surface Plot showing the Effect of Barrel Temperature and

                       Screw Speed on Aroma                                                                                   210

                       

4.88                Response Surface Plot showing the Effect of Barrel Temperature

                       and Feed Moisture on Aroma                                                                          211

                   

4.89                Response Surface Plot showing the Effect of Screw Speed and

                       Feed Moisture on Aroma                                                                                 211

                        

4.90                Response Surface Plot showing the Effect of Barrel Temperature

                       and Screw Speed on Overall Acceptability                                                     214           

 

4.91                Response Surface Plot showing the Effect of Barrel Temperature

                       and Feed Moisture on Overall Acceptability                                                    214

 

4.92                Response Surface Plot showing the Effect of Screw Speed and

           Feed Moisture on Overall Acceptability                                                           215

 

 

 

 

LIST OF PLATES

 

 

PLATE                                                         TITLE                                                          PAGE

1                 Aerial Yam Plant (Dioscorea bulbifera)                                                              1

2                 Aerial Yam (Dioscorea bulbifera) bulbs                                                              52

3                 Processed Aerial Yam Flour                                                                                52

4                 Processed Soybeans Flour                                                                                   53

5                  Extrudate Sample of Aerial Yam and Soybean Flour Blend                             54