EVALUATION OF MATURITY INDICES OF SELECTED MANGO VARIETIES AND EFFECT ON QUALITY ATTRIBUTES By JACINTA WAIRIMU MUIRURI A56/67250/2013 A Thesis submitted in partial fulfillment of the requirement for the degree of Masters of Science in Horticulture of the University of Nairobi Department of Plant Science and Crop Protection Faculty of Agriculture DECLARATION This thesis is my original work and has not been presented for award of a degree in any other university. Signature ………………………………. Date ……………………… Jacinta Wairimu Muiruri (A56/67250/2013) SUPERVISORS Dr. Jane Ambuko Department of Plant Science and Crop Protection University of Nairobi Signature …………………………………. Date …………………… Dr. Richard Nyankanga Department of Plant Science and Crop Protection, University of Nairobi Signature …………………………………. Date …………………… Prof. Willis O. Owino Department of Food Science and Postharvest Technology Jomo Kenyatta University of Agriculture and Technology Signature …………………………………. Date ……………………… iii DEDICATION I dedicate this work to my children Andrew, Philip and Elizabeth for their endurance during the entire study period. iv ACKNOWLEDGEMENT I thank the Almighty God for His mercy and grace throughout the study period. I express my sincere gratitude to my supervisor Dr Jane Ambuko for her tireless effort towards my success and especially for her guidance in my writing and presentation skills. May the Almighty God reward you. I express my further gratitude to other supervisors; Dr. Richard Nyankanga and Prof. Willis Owino for their support and assistance. I am grateful to Francis for his financial support during the entire study period. I acknowledge Kenya Agricultural Productivity and Agribusiness Project (KAPAP) for sponsoring my entire research work through a research grant awarded to Dr. Jane Ambuko. I sincerely appreciate department of Food Science Technology, Jomo Kenyatta University of Agriculture and Technology (JKUAT) administration for allowing me to conduct the research work in the post harvest laboratory. Special thanks to JKUAT technical staff; Mr. P. Karanja, Mr. David Abuga and Mrs J. Oruka who supported me during the laboratory work. I thank my classmate Esther and the support from Lilian and other friends during the study period. I am grateful to my parents and siblings for their support and encouragement in my education life. God bless you all. v TABLE OF CONTENTS DECLARATION.......................................................................................................................... iii DEDICATION.............................................................................................................................. iv ACKNOWLEDGEMENT ............................................................................................................ v TABLE OF CONTENTS ............................................................................................................ vi LIST OF PLATES AND FIGURES ........................................................................................... ix LIST OF TABLES ........................................................................................................................ x ABBREVIATIONS AND ACRONYMS .................................................................................. xvi ABSTRACT ............................................................................................................................... xvii CHAPTER ONE ........................................................................................................................... 2 1 INTRODUCTION............................................................................................................. 2 1.1 BACKGROUND INFORMATION ................................................................................. 2 1.2 PROBLEM STATEMENT .............................................................................................. 5 1.3 JUSTIFICATION ............................................................................................................. 6 1.4 OBJECTIVES .................................................................................................................. 6 1.4.1 Overall objective: ......................................................................................................... 6 1.4.2 Specific objectives: ....................................................................................................... 7 1.5 HYPOTHESIS ................................................................................................................. 7 CHAPTER TWO .......................................................................................................................... 8 2 LITERATURE REVIEW ................................................................................................ 8 2.1 BOTANY ......................................................................................................................... 8 2.2 MANGO VARIETIES ..................................................................................................... 8 vi 2.2.1 Van dyke ....................................................................................................................... 9 2.2.2 Tommy atkins ............................................................................................................... 9 2.2.3 Kent .............................................................................................................................. 9 2.2.4 Ngowe ........................................................................................................................... 9 2.3 MANGO NUTRITIONAL QUALITY .......................................................................... 10 2.4 MANGO PRODUCTION STATISTICS ....................................................................... 11 2.4.1 Global productions statistics ....................................................................................... 11 2.4.2 Kenya production statistics ......................................................................................... 11 2.5 MANGO FRUIT GROWTH AND MATURATION .................................................... 12 2.5.1 Fruit growth ................................................................................................................ 12 2.5.2 Fruit maturation .......................................................................................................... 12 2.6 FACTORS THAT AFFECT FRUIT GROWTH AND MATURATION ...................... 14 2.6.1 ` Agro-ecological conditions ...................................................................................... 14 2.6.2 Cultural practices ........................................................................................................ 15 2.6.3 Varietal differences ..................................................................................................... 15 2.7 MATURITY INDICES FOR MANGO FRUITS .......................................................... 15 2.7.1 Subjective maturity indices ........................................................................................ 16 2.7.2 Objective maturity indices .......................................................................................... 17 2.8 MANGO RIPENING AND ASSOCIATED CHANGES IN QUALITY ATTRIBUTES 20 2.8.1 Changes in soluble sugars (Sucrose, glucose and fructose) ....................................... 21 2.8.2 Changes in flavor ........................................................................................................ 22 2.8.3 Changes in vitamins.................................................................................................... 22 2.8.4 Changes in β-carotenes ............................................................................................... 22 2.8.5 Changes in mineral nutrients ...................................................................................... 23 2.8.6 Changes in firmness.................................................................................................... 23 2.8.7 Changes in color ......................................................................................................... 23 vii 2.8.8 Changes in acidity ...................................................................................................... 23 2.9 EFFECT OF HARVEST MATURITY ON MANGO FRUIT QUALITY ................... 24 2.9.1 Effect on fresh mango quality .................................................................................... 24 2.9.2 Effect on processed products ...................................................................................... 24 2.9.3 Effect of harvest maturity on dried mango products .................................................. 25 CHAPTER THREE .................................................................................................................... 26 3 MATURITY INDICES OF THREE MANGO VARIETIES PRODUCED IN A MEDIUM ALTITUDE AGRO-ECOLOGICAL ZONE IN KENYA .................................... 26 3.1 ABSTRACT ................................................................................................................... 26 3.2 INTRODUCTION .......................................................................................................... 28 3.3 MATERIALS AND METHODS ................................................................................... 30 3.3.1 Experimental set up .................................................................................................... 30 3.3.2 Determination of maturity indices .............................................................................. 31 3.4 STATISTICAL ANALYSIS .......................................................................................... 33 3.5 RESULTS....................................................................................................................... 34 3.5.1 Computational maturity indices .................................................................................. 34 3.5.2 Physical maturity indices ............................................................................................ 34 3.5.3 Physiological maturity indices .................................................................................... 39 3.5.4 Biochemical maturity indices ..................................................................................... 42 3.6 DISCUSSION ................................................................................................................ 44 CHAPTER FOUR ....................................................................................................................... 48 4 EFFECT OF HARVEST MATURITY ON THE QUALITY ATTRIBUTES OF FRESH AND DRIED MANGO PRODUCTS .......................................................................... 48 4.1 ABSTRACT ................................................................................................................... 48 viii 4.2 INTRODUCTION .......................................................................................................... 49 4.3 MATERIALS AND METHODS ................................................................................... 51 4.3.1 Experimental set up and sampling .............................................................................. 51 4.3.2 Determination of nutritional, physical and sensory quality attributes of fresh mango products 53 4.3.3 Determination of nutritional and physical quality attributes of dried mango products 56 4.4 STATISTICAL ANALYSIS .......................................................................................... 57 4.5 RESULTS....................................................................................................................... 58 4.5.1 Changes in nutritive quality attributes ........................................................................ 58 4.5.2 Nutritional and physical quality attributes of dried mango products ......................... 84 4.6 DISCUSSION .............................................................................................................. 104 CHAPTER FIVE: ..................................................................................................................... 107 5 GENERAL DISCUSSION AND RECOMMENDATIONS ...................................... 107 5.1 GENERAL DISCUSSION ........................................................................................... 107 5.2 RECOMMENDATIONS ............................................................................................. 112 REFERENCES .......................................................................................................................... 113 APPENDICES ........................................................................................................................... 128 LIST OF PLATES AND FIGURES Plate 3.4. Flesh color changes for ‗Kent‘ variety at maturity stages one to four .......................... 39 Plate 3.5. Flesh color changes for ‗Tommy atkins‘ variety at maturity stages one to four .......... 39 Plate 3.6. Flesh color changes for ‗Van dyke‘ variety at maturity stages one to four .................. 39 ix Figure 2.1. ‗Tommy atkins‘, ‗Kent‘, ‗Van dyke‘ and ‗Ngowe‘ mango varieties respectively ..... 10 Figure 4.1. Polythene green house solar drier .............................................................................. 53 Figure 4.2. Hedonic scores for sensory quality attributes of ‗Kent‘ ‗Tommy atkins‘ and ‗Van dyke‘ mango varieties at tree ripe stage. ...................................................................................... 82 Figure 4.3. Hedonic scores for sensory quality attributes of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango variety at maturity stages 3, 4 and tree ripe. .......................................................... 83 LIST OF TABLES Table 2.1. Production of Mangoes in Selected Counties in Kenya, 2012-2014 ........................... 13 Table 3.1. Days after flowering to maturity stages 1 to stage 4 for ‗Van dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango varieties ........................................................................................................... 34 Table 3.2 Size (Length in cm), Density (g/cm3), Peel and Flesh firmness (Newtons) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits varieties harvested at an early and advanced maturity stages in season 1. .......................................................................................................... 35 Table 3.3. Size (Length in cm), Density (g/cm3), Peel and Flesh firmness (Newtons) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits varieties harvested at four stages of maturity; stages 1, 2, 3 and 4 in season 2 ..................................................................................................... 36 Table 3.4. Peel and Flesh hue angle (o) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits harvested during early and late maturities in season 1 ................................................................. 37 Table 3.5. Peel and Flesh hue angle (o) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits harvested at four stages of maturity; stages 1, 2, 3 and 4 in season 2 ........................................... 38 Table 3.6. Physiological maturity indices, including; Ethylene evolution (µl/kg/hr) and Respiration rate (ml/kg/hr) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits harvested at an early and advanced maturity stages in season 1. ...................................................................... 40 x Table 3.7. Physiological maturity indices, including; Ethylene evolution µl/kg/hr and Respiration rate ml/kg/hr of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits harvested at four stages of maturity; stages 1, 2, 3 and 4 in season 2 ................................................................................. 41 Table 3.8. Biochemical maturity indices, including; total soluble solids (o brix), titratable acidity (% citric acid) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits harvested at an early and advanced maturity stages in season 1..................................................................................... 42 Table 3.9. Biochemical maturity indices, including; total soluble solids (o brix), titratable acidity (% citric acid) of ‗Van Dyke‘, ‗Tommy Atkins‘ and ‗Kent‘ mango fruits harvested at four stages of maturity; stages 1, 2, 3 and 4 in season 2 ................................................................................. 43 Table 4.1. Initial and end stage ascorbic acid content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at early and advanced maturity stages in season 1 ................ 58 Table 4.2. Changes in ascorbic acid content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at maturity stages 1, 2, 3 and 4 in season 2 .................................. 59 Table 4.3. Initial and end stage β- carotene content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at early and advanced maturity stages in season 1 ................ 60 Table 4.4. Changes in β - carotene content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at maturity stages 1, 2, 3 and 4 in season 2 ............................................. 61 Table 4.5. Initial and end stage fructose content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at early and advanced maturity stages in season 1 ....................... 62 Table 4.6. Changes in fructose content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at maturity stages 1, 2, 3 and 4 in season 2 ............................................. 63 Table 4.7. Initial and end stage glucose content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at early and advanced maturity stages in season 1 ....................... 64 Table 4.8. Changes in glucose content (mg/100g) of ‗Van dyke‘, ‗Tommy atkins‘ and ‗Kent‘ mango fruits harvested at maturity stages 1, 2, 3 and 4 in season 2 ............................................. 65 xi