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Drying Technologies in Food Processing

De
352 pages
Drying is by far the most useful large scale operation method of keeping solid foods safe for long periods of time, and is of fundamental importance in most sectors of food processing. Drying operations need to be precisely controlled and optimized in order to produce a good quality product that has the highest level of nutrient retention and flavor whilst maintaining microbial safety.


This volume provides an up to date account of all the major drying technologies employed in the food industry and their underlying scientific principles and effects. Various equipment designs are classified and described. The impact of drying on food properties is covered, and the micro-structural changes caused by the process are examined, highlighting their usefulness in process analysis and food design. Key methods for assessing food properties of dried products are described, and pre-concentration and drying control strategies are reviewed. Thermal hazards and fire/explosion detection and prevention for dryers are discussed in a dedicated chapter. Where appropriate, sample calculations are included for engineers and technologists to follow. The book is directed at food scientists and technologists in industry and research, food engineers and drying equipment manufacturers.

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Contents
Contributors Preface Introduction: structural images of some fresh and processed foods XiaoDong Chen
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Food drying fundamentals XiaoDong Chen 1.1 Introduction to food materials 1.2 Drying of food 1.3 Physical properties of foods 1.3.1 The scales of interest 1.3.2 Mechanical properties 1.3.3 Shrinkage and densities 1.3.4 Thermal properties and conventional heating 1.3.5 Colour 1.3.6 Equilibrium isotherms 1.4 Drying rate characteristic curve approach to correlate drying rates – van Meel’s method 1.5 Diffusion theories of drying 1.5.1 Effective Fickian diffusivity 1.5.2 Intuitive understanding of the diffusion theory 1.5.3 Drying of foods simulated using the effective Fickian diffusion law 1.5.4 Alternative effective diffusion theories 1.6 Driers 1.7 Concluding remarks 1.8 Notation Appendix I: Typical mass transfer correlations Appendix II: On the ‘effectiveness’ of the effective moisture diffusivity benchmarked against the Luikov theory Appendix III: Drying of pulped Kiwi fruit layer for making fruit leather References
Water activity in food processing and preservation Bhesh R. Bhandari and Benu P. Adhikari 2.1 Introduction 2.1.1 Thermodynamics of water activity 2.1.2 Definition and significance
xi xiii xv
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1 2 8 8 10 15 20 26 29
30 32 32 34
36 38 42 43 44 46
46 52 52
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2.1.3 Sorption isotherms 2.1.4 Hysteresis in sorption isotherms 2.2 Composition-based water activity predictive models 2.2.1 Raoult’s Law 2.2.2 Norrish model 2.2.3 Ross model 2.2.4 Money–Born equation 2.2.5 Grover model 2.2.6 Salwin equation 2.3 Models for prediction of sorption isotherms 2.3.1 Two-parameter models 2.3.2 Three-parameter isotherms 2.3.3 Effect of temperature on water activity 2.3.4 Water activity above boiling point 2.4 Types of sorption isotherms and hysteresis in isotherms 2.5 Determination of sorption isotherms 2.5.1 Gravimetric method 2.5.2 Manometric method 2.5.3 Hygroscopic methods 2.5.4 Sample preparation and equilibrium time 2.6 Concluding remarks References
Biological changes during food drying processes XiaoDong Chen and Kamlesh C. Patel
3.1 Introduction to drying and food quality 3.2 Post-drying problems 3.3 In-drying problems 3.4 Food bio-deterioration by drying – a sub-cell level approach 3.5 Concluding remarks 3.6 Notation References
Spray drying of food materials – process and product characteristics Bhesh R. Bhandari, Kamlesh C. Patel and XiaoDong Chen 4.1 Introduction 4.2 Basic concepts of spray drying 4.3 Components of a spray drying system 4.3.1 Drying gas supply and heating system 4.3.2 Atomization system 4.3.3 Drying chamber 4.3.4 Powder separators 4.4 Drying of droplets 4.4.1 Fundamentals of droplet drying 4.4.2 Drying kinetics 4.4.3 Residence time
58 58 59 59 60 61 62 63 64 65 65 68 73 75 75 78 78 83 84 84 86 86
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90 91 95 106 108 109 109
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113 114 117 117 118 121 122 125 125 126 129
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4.5 Mass and heat balances over a spray drier 4.5.1 Overall mass balance 4.5.2 Overall heat balance 4.6 Drier efficiency 4.6.1 Thermal efficiency 4.6.2 Evaporative efficiency 4.6.3 Volumetric evaporative capacity 4.7 Powder characterization 4.7.1 Particle micro-structure 4.7.2 Particle morphology 4.7.3 Physical and functional properties of powder 4.7.4 Drying parameters 4.8 Spray drying of various food products 4.8.1 Dairy powders 4.8.2 Micro-encapsulated powders 4.8.3 Sugar-rich products 4.8.4 Egg 4.8.5 Enzymes 4.9 Concluding remarks 4.10 Notation References
Low-pressure superheated steam drying of food products Sakamon Devahastin and Peamsuk Suvarnakuta 5.1 Introduction 5.2 Basic principles of superheated steam drying 5.3 Low-pressure superheated steam drying of foods and biomaterials 5.4 Some advances in LPSSD of foods and biomaterials 5.5 Mathematical modeling of LPSSD of foods and biomaterials 5.6 Concluding remarks 5.7 Notation References
Heat pump-assisted drying Md Raisul Islam and Arun S. Mujumdar 6.1 Introduction 6.2 Classification of heat pump driers 6.3 Fundamentals of heat pump driers 6.4 Heat and mass transfer mechanisms 6.5 Optimum use of heat pumps in drying systems 6.6 Innovative heat pump drying systems 6.6.1 Multi-stage compression heat pump drying 6.6.2 Cascade heat pump drying systems 6.6.3 Heat pump drying systems with multiple evaporators in series and in parallel 6.6.4 Vapor absorption heat pump drier
Contents
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130 130 133 134 134 136 136 137 137 139 141 147 149 149 151 153 154 154 155 155 157
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160 161 163 177 182 186 187 187
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190 191 191 197 210 212 213 214
215 217
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6.7 Closing remarks 6.8 Notation References
Freeze and vacuum drying of foods Cristina Ratti
7.1 Introduction 7.2 States of water 7.3 Food and air properties in relation to vacuum and freeze-drying 7.4 Heat transfer mechanisms at low pressures 7.5 Vacuum drying: principles and dehydration models 7.6 Freeze drying: principles and dehydration models 7.7 Illustrative example 7.8 Advances in vacuum and freeze drying of foods 7.9 Closure 7.10 Notation References
Post-drying aspects for meat and horticultural products Mohammad Shafiur Rahman 8.1 Introduction 8.2 State diagram and stability concepts of dried products 8.3 Controlling quality attributes 8.3.1 Microbial quality 8.3.2 Chemical changes and quality 8.3.3 Physical changes and quality 8.3.4 Vitamins retention 8.4 Conclusion References
Food drier process control Brent R. Young 9.1 Introduction – why process control? 9.1.1 Disturbance variables 9.1.2 Control benefits 9.1.3 Examples 9.1.4 Chapter organization 9.2 What to control (manipulated and controlled variables) 9.2.1 Controlled variables 9.2.2 Manipulated variables 9.3 Where to control (control strategy) 9.3.1 Plant-wide control strategy configuration 9.3.2 Common loops and examples 9.4 When to control (control philosophy) 9.4.1 After something happens – feedback control 9.4.2 As something happens – feed-forward/predictive control
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225 225 227 232 234 236 239 243 245 245 246
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270 270 271 271 272 272 272 273 273 273 274 276 276 278
9.5 How to control (fundamental control methods) 9.5.1 PID feedback control and tuning 9.6 How to do advanced control (advanced control methods) 9.6.1 Model predictive control (MPC) 9.6.2 Adaptive control 9.6.3 Artificial intelligence in control References
10 Fire and explosion protection in food driers XiaoDong Chen 10.1 Introduction – thermal hazards in driers 10.1.1 Conditions for an explosion to occur 10.1.2 How serious is the problem? 10.1.3 What affects the degree of violence of a dust explosion? 10.1.4 How to reduce the risk of dust explosion 10.2 A practical example: milk powder plant safety 10.2.1 Fires 10.2.2 Explosion protection 10.3 Testing for various explosion parameters 10.4 The human factors 10.5 Concluding remarks References
Index
The colour plate section follows page 40
Contents
ix
279 279 292 293 295 295 297
299
299 299 300 300 301 301 302 310 314 314 316 316
319