DEVELOPMENT OF LIPID-BASED COATINGS FOR THE QUALITY MAINTENANCE OF FRUIT AND VEGETABLES A Thesis submitted to the • University of New South Wales i as fulfilment of the requirement for the degree of DOCTOR OF PHILOSOPHY by OLABISI ABIOLA AMUDIPE B.Tech (Storage Technol.) FUTA, MAppSc (Food Tech.) UNSW The University of New South Wales Sydney NSW 2052 Australia June, 1996 U N S W 13 OCT 1998 -ARY DECLARATION The candidate, Olabisi Abiola Amudipe, hereby declares that none of the work presented in this thesis has been submitted to any other university or institution for higher degree. O. A. Amudipe CERTIFICATE OF ORIGINALITY of Tcom" ,S ^ ^ Wrk and *»< to ,he be , toy ow^o7h^ZthTXZ",en' °f,hiS ,hesis is ,he Product of °n s,y,e- a~ o.z (Signed) ACKNOWLEDGMENT I wish to express my appreciation and gratitude to my supervisors, Dr J.E. Patton and Dr C.M.C. Yuen, for their patient supervision, guidance and understanding during the conduct of this study and their constructive criticism during the preparation of this manuscript. I am also grateful to Mr. K.J. Scott for his valuable advice and assistance during the course of this study. t I wish to thank Mr P. Chy, Dr M. Forbes-Smith and my other colleagues in the Postharvest Section for making the conduct of this study enjoyable. I am grateful to the Commonwealth Government of Australia for the financial support, The Australian Centre for Industrial and Agricultural Research for the funding of the project and The Federal University of Technology, Akure-Nigeria for granting me a study leave. To my wonderful family and friends who have always had great faith in me, I owe an immeasurable depth of appreciation. And above all, I give God all the glory for the great things He has done. TABLE OF CONTENTS Acknowledgment i Table of contents ii List of tables xi List of figures xv List of plates xviii Abstract xx 1 Introduction 1 2 Literature review * 6 2.1 The fruit and vegetable industry 6 2.1.1 Commercial importance of the fruit and vegetable industry 7 2.1.2 Nutritional importance of fruit and vegetables 9 2.2 Postharvest physiology of fruit and vegetables 10 2.2.1 Classification of produce 12 2.2.2 Respiratory metabolism 16 2.2.3 Ethylene biosynthesis and action 20 2.3 Postharvest handling of fruits and vegetables 22 2.4 Postharvest losses of fruit and vegetables 24 2.4.1 Effect of temperature 25 2.4.2 Effect of humidity 27 2.4.3 Mechanical injury 28 2.4.4 Physiological disorders 28 2.4.4.1 Superficial scald 29 2.4.4.2 Core and flesh browning 31 2.4.4.3 Core flush 31 2.5 Atmosphere modification 32 2.5.1 Controlled atmosphere (CA) storage 33 2.5.2 Modified atmosphere (MA) storage 33 2.5.2.1 Polymeric films 34 2.5.2.2 Commercial coatings 35 2.6 Biochemical and physiological effects of modified atmosphere storage 2.6.1 Effect on respiration 36 2.6.2 Effect on ethylene production and action 38 2.6.3 Effect on compositional changes 40 2.6.3.1 Colour 41 2.6.3.1.1 Chlorophyll degradation 41 2.6.3.1.2 Discolouration 42 2.6.3.2 Texture 43 2.6.3.3 Effect on flavour 44 2.6.4 Effect on physiological disorders 44 2.6.5 Effect on growth and development 46 2.6.6 Effect on decay microorganisms 47 2.7 Edible coatings 47 iii 2.7.1 Principle of edible coatings 47 2.7.2 Historical background 48 2.8 Modified atmosphere effect of edible coatings on fruit and vegetables 50 2.8.1 Water loss 50 2.8.2 Appearance 52 2.8.3 Ripening and quality maintenance 52 2.8.4 Physiological disorders 53 2.8.5 Decay microorganisms 54 2.8.6 Gaseous exchange and/espiration rate 55 2.8.7 Detrimental effect of edible coatings 58 2.9 Development of lipid based edible coatings 59 2.10 Chemistry and properties of lipid coatings 61 2.10.1 Fats and oils 61 2.10.1.1 Chemical properties 62 2.10.1.2 Physical properties 63 2.10.1.2.1 Melting point 63 2.10.1.2.2 Oiliness and viscosity 63 2.10.1.2.3 Surface and interfacial tension 64 2.10.1.2.4 Solubility in water 64 2.10.1.3 Classification, sources and properties 65 2.10.2 Emulsion and emulsifiers 67 2.10.2.1 Definitions 67 2.10.2.2 Types of emulsion 67 2.10.2.3 Emulsifiers 68 2.10.2.4 Types of emulsifiers 69 2.10.2.4.1 Oil and fat derivatives 69 2.10.2.4.2 Hydrocolloids 70 2.10.2.5 Properties and functions of emulsifiers 72 2.10.2.6 Formation of emulsions 73 2.10.2.7 Application of emulsion (wettability) 74 i 2.10.2.8 Wetting of solids 75 2.10.2.9 Nature of wax film 75 2.10.2.10 Thickness of wax film 77 3 Materials and methods 78 3.1 Produce 78 3.2 Coating materials 80 3.3 Preparation and formulation of coatings 81 3.4 Application of coatings 86 3.4.1 Lipid coatings 86 3.4.2 Emulsion 86 3.5 Produce assessment 88 3.5.1 Physico-chemical Analysis 88 3.5.1.1 Weight loss 88 3.5.1.2 Colour assessment 88 3.5.1.3 Measurement of firmness 89 3.5.1.4 Measurement of pH 89 3.5.1.5 Titratable acidity 90 3.5.1.6 Total soluble solids 90 3.5.1.7 Sensory evaluation 90 3.5.1.8 Assessment of physiological disorders 91 3.6 Extraction and analysis of a-farnesene 92 3.7 Extraction and analysis of putrescine 93 3.8 Physiological Measurements ' 95 i 3.8.1 Respiration rate 95 3.8.2 Internal atmosphere 95 3.8.3 Measurement of carbon dioxide and oxygen 98 3.8.4 Measurement of ethylene 98 3.9 Determination of skin permeability 99 3.10 Electron microscopy of coatings 100 3.11 Statistical analysis 100 4 Results 102 4.1 Preliminary studies 102 4.1.1 Non climacteric produce 102 4.1.1.1 Capsicum 102 4.1.1.2 Cucumber 106 4.1.1.3 Carrot 109 VI 4.1.1.4 Zucchini 111 4.1.2 Climacteric produce 114 4.1.2.1 Avocado 114 4.1.2.2 Custard apple 114 4.1.2.3 Mango 115 4.1.3 Summary 117 4.2 Effect of lipid coatings on selected produce 118 4.2.1 Introduction 118 4.2.2 Result , 118 4.2.2.1 Lychee 118 4.2.2.2 Plum 121 4.2.2.3 Nectarine 126 4.2.2.4 Banana 132 4.2.2.5 Apple 138 4.2.2.6 Nashi 147 4.2.2.7 Pear 156 4.3 Formulation trials 166 4.4 Effect of oils and oil emulsions in extending the storage life of produce 4.4.1 Introduction 169 4.4.2 Result 169 4.4.2.1 Cucumber 169 4.4.2.2 Avocado 174 vii 4.4.2.3 Nashi 177 4.4.2.4 Apple 184 4.4.3 Summary 188 4.5 Coating morphology 189 4.5.1 Introduction 189 4.5.2 Result 190 4.5.3 Summary 192 4.6 Effect of oils and oil-based coatings on the permeability of fruit surface to gases and internal composition of Nashi and apple 192 4.6.1 Introduction 192 4.6.2 Result 190 4.6.2.1 Nashi 193 4.6.2.2 Apple 195 4.6.3 Summary 197 4.7 Effect of oils and oil-based emulsions on respiration and internal gas composition of coated fruits 198 4.7.1 Introduction 198 4.7.2 Result 198 4.7.2.1 Avocado 198 4.7.2.2 Nashi 200 4.7.2.3 Apple 204 4.7.3 Summary 208 viii 4.8 Effect of coating on physiological disorders and internal atmosphere of Nashi and apples stored at 0°C 209 4.8.1 Introduction 209 4.8.2 Result 209 4.8.2.1 Nashi 209 4.8.2.2 Apple 215 4.9 Effect of coatings on a-farnesene and putrescine accumulation in Granny Smith apple during storage at 0°C 221 4.9.1 Introduction , 221 4.9.2 Result 221 4.9.3 Summary 223 5 Discussion 224 5.1 Introduction 224 5.2 Effect of coating on storage life 225 5.3 Mechanism of action of coatings 228 5.4 Effect of coatings on permeability of fruit surface to gases 229 5.5 Effect of coatings on sensitivity of fruit to ethylene 231 5.6 Effect of coatings on respiratory metabolism 232 5.7 Effect of coatings on development of physiological disorder 234 6 Conclusion 239 6.1 Commercial potential of coating 240 6.2 Commercial application of coating 240 ix 6.3 Potential problems 242 6.4 Justification 242 6.5 Recommendation 243 Bibliography 245 X LIST OF TABLES Table 1. Percentage of vitamin and mineral intake in the Australian diet contributed by fruit and vegetables (1985 - 1991). Table 2. Classification of some fruits and vegeatbles. Table 3. Production and loss figures in less-developed countries for selected produce. Table 4. Classification of fruit and vegetables according to their tolerance to low oxygen concentrations.