Drying Technologies in Food Processing

by Chen, Xiao Dong; Mujumdar, Arun S.

• ISBN13: 9781405157636
• ISBN10: 1405157631
• Edition: 1st
• Format: Hardcover
• Copyright: 2008-08-04
• Publisher: Wiley-Blackwell

Summary

Drying is of fundamental importance in most sectors of food processing. 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. 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.

Author Biography

Professor Xiao Dong Chen, Department of Chemical Engineering, Monash University, Victoria, Australia

Professor Arun S. Mujumdar, Department of Mechanical Engineering, National University of Singapore, Singapore

Table of Contents

Contributors	p. xi
Preface	p. xiii
Introduction: structural images of some fresh and processed foods	p. xv
Food drying fundamentals	p. 1
Introduction to food materials	p. 1
Drying of food	p. 2
Physical properties of foods	p. 8
The scales of interest	p. 8
Mechanical properties	p. 10
Shrinkage and densities	p. 15
Thermal properties and conventional heating	p. 20
Colour	p. 26
Equilibrium isotherms	p. 29
Drying rate characteristic curve approach to correlate drying rates - van Meel's method	p. 30
Diffusion theories of drying	p. 32
Effective Fickian diffusivity	p. 32
Intuitive understanding of the diffusion theory	p. 32
Drying of foods simulated using the effective Fickian diffusion law	p. 36
Alternative effective diffusion theories	p. 38
Driers	p. 42
Concluding remarks	p. 43
Notation	p. 44
Typical mass transfer correlations	p. 46
On the 'effectiveness' of the effective moisture diffusivity benchmarked against the Luikov theory	p. 46
Drying of pulped Kiwi fruit layer for making fruit leather	p. 52
References	p. 52
Water activity in food processing and preservation	p. 55
Introduction	p. 55
Thermodynamics of water activity	p. 56
Definition and significance	p. 57
Sorption isotherms	p. 58
Hysteresis in sorption isotherms	p. 58
Composition-based water activity predictive models	p. 59
Raoult's Law	p. 59
Norrish model	p. 60
Ross model	p. 61
Money-Born equation	p. 62
Grover model	p. 63
Salwin equation	p. 64
Models for prediction of sorption isotherms	p. 65
Two-parameter models	p. 65
Three-parameter isotherms	p. 68
Effect of temperature on water activity	p. 73
Water activity above boiling point	p. 75
Types of sorption isotherms and hysteresis in isotherms	p. 75
Determination of sorption isotherms	p. 78
Gravimetric method	p. 78
Manometric method	p. 83
Hygroscopic methods	p. 84
Sample preparation and equilibrium time	p. 84
Concluding remarks	p. 86
References	p. 86
Biological changes during food drying processes	p. 90
Introduction to drying and food quality	p. 90
Post-drying problems	p. 91
In-drying problems	p. 95
Food bio-deterioration by drying - a sub-cell level approach	p. 106
Concluding remarks	p. 108
Notation	p. 109
References	p. 109
Spray drying of food materials - process and product characteristics	p. 113
Introduction	p. 113
Basic concepts of spray drying	p. 114
Components of a spray drying system	p. 117
Drying gas supply and heating system	p. 117
Atomization system	p. 118
Drying chamber	p. 121
Powder separators	p. 122
Drying of droplets	p. 125
Fundamentals of droplet drying	p. 125
Drying kinetics	p. 126
Residence time	p. 129
Mass and heat balances over a spray drier	p. 130
Overall mass balance	p. 130
Overall heat balance	p. 133
Drier efficiency	p. 134
Thermal efficiency	p. 134
Evaporative efficiency	p. 136
Volumetric evaporative capacity	p. 136
Powder characterization	p. 137
Particle micro-structure	p. 137
Particle morphology	p. 139
Physical and functional properties of powder	p. 141
Drying parameters	p. 147
Spray drying of various food products	p. 149
Dairy powders	p. 149
Micro-encapsulated powders	p. 151
Sugar-rich products	p. 153
Egg	p. 154
Enzymes	p. 154
Concluding remarks	p. 155
Notation	p. 155
References	p. 157
Low-pressure superheated steam drying of food products	p. 160
Introduction	p. 160
Basic principles of superheated steam drying	p. 161
Low-pressure superheated steam drying of foods and biomaterials	p. 163
Some advances in LPSSD of foods and biomaterials	p. 177
Mathematical modeling of LPSSD of foods and biomaterials	p. 182
Concluding remarks	p. 186
Notation	p. 187
References	p. 187
Heat pump-assisted drying	p. 190
Introduction	p. 190
Classification of heat pump driers	p. 191
Fundamentals of heat pump driers	p. 191
Heat and mass transfer mechanisms	p. 197
Optimum use of heat pumps in drying systems	p. 210
Innovative heat pump drying systems	p. 212
Multi-stage compression heat pump drying	p. 213
Cascade heat pump drying systems	p. 214
Heat pump drying systems with multiple evaporators in series and in parallel	p. 215
Vapor absorption heat pump drier	p. 217
Closing remarks	p. 221
Notation	p. 222
References	p. 223
Freeze and vacuum drying of foods	p. 225
Introduction	p. 225
States of water	p. 225
Food and air properties in relation to vacuum and freeze-drying	p. 227
Heat transfer mechanisms at low pressures	p. 232
Vacuum drying: principles and dehydration models	p. 234
Freeze drying: principles and dehydration models	p. 236
Illustrative example	p. 239
Advances in vacuum and freeze drying of foods	p. 243
Closure	p. 245
Notation	p. 245
References	p. 246
Post-drying aspects for meat and horticultural products	p. 252
Introduction	p. 252
State diagram and stability concepts of dried products	p. 252
Controlling quality attributes	p. 255
Microbial quality	p. 255
Chemical changes and quality	p. 257
Physical changes and quality	p. 260
Vitamins retention	p. 265
Conclusion	p. 265
References	p. 265
Food drier process control	p. 270
Introduction - why process control?	p. 270
Disturbance variables	p. 270
Control benefits	p. 271
Examples	p. 271
Chapter organization	p. 272
What to control (manipulated and controlled variables)	p. 272
Controlled variables	p. 272
Manipulated variables	p. 273
Where to control (control strategy)	p. 273
Plant-wide control strategy configuration	p. 273
Common loops and examples	p. 274
When to control (control philosophy)	p. 276
After something happens - feedback control	p. 276
As something happens - feed-forward/predictive control	p. 278
How to control (fundamental control methods)	p. 279
PID feedback control and tuning	p. 279
How to do advanced control (advanced control methods)	p. 292
Model predictive control (MPC)	p. 293
Adaptive control	p. 295
Artificial intelligence in control	p. 295
References	p. 297
Fire and explosion protection in food driers	p. 299
Introduction - thermal hazards in driers	p. 299
Conditions for an explosion to occur	p. 299
How serious is the problem?	p. 300
What affects the degree of violence of a dust explosion?	p. 300
How to reduce the risk of dust explosion	p. 301
A practical example: milk powder plant safety	p. 301
Fires	p. 302
Explosion protection	p. 310
Testing for various explosion parameters	p. 314
The human factors	p. 314
Concluding remarks	p. 316
References	p. 316
Index	p. 319
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