Food Process Engineering and Technology

622 Pages·2008·4.78 MB·English

by  Zeki Berk

FOOD PROCESS ENGINEERING AND TECHNOLOGY
Food Science and Technology
International Series
Series Editor
Steve L. Taylor
University of Nebraska – Lincoln, USA
Advisory Board
Ken Buckle
The University of New South Wales, Australia
Mary Ellen Camire
University of Maine, USA
Roger Clemens
University of Southern California, USA
Hildegarde Heymann
University of California – Davis, USA
Robert Hutkins
University of Nebraska – Lincoln, USA
Ron S. Jackson
Quebec, Canada
Huub Lelieveld
Bilthoven, The Netherlands
Daryl B. Lund
University of Wisconsin, USA
Connie Weaver
Purdue University, USA
Ron Wrolstad
Oregon State University, USA
A complete list of books in this series appears at the end of this volume
Food Process
Engineering and
Technology
Zeki Berk
Professor (Emeritus)
Department of Biotechnology and Food Engineering
TECHNION
Israel Institute of Technology
Israel
AMSTERDAM• BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD
PARIS• SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
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To my students
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First edition 2009
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09 10 11 12 13 10 9 8 7 6 5 4 3 2 1
Contents
Introduction – Food is Life .....................................................................................1
1 Physical properties of food materials .............................................................7
1.1 Introduction ...........................................................................................7
1.2 Mechanical properties ............................................................................8
1.2.1 Defi nitions ..................................................................................8
1.2.2 Rheological models .....................................................................9
1.3 Thermal properties ...............................................................................10
1.4 Electrical properties ..............................................................................11
1.5 Structure ..............................................................................................11
1.6 Water activity .......................................................................................13
1.6.1 The importance of water in foods ...............................................13
1.6.2 Water activity, defi nition and determination ...............................14
1.6.3 Water activity: prediction ...........................................................14
1.6.4 Water vapor sorption isotherms .................................................16
1.6.5 Water activity: effect on food quality and stability .......................19
1.7 Phase transition phenomena in foods ....................................................19
1.7.1 The glassy state in foods ............................................................19
1.7.2 Glass transition temperature ......................................................20
2 Fluid fl ow .....................................................................................................27
2.1 Introduction .........................................................................................27
2.2 Elements of fl uid dynamics ....................................................................27
2.2.1 Viscosity ....................................................................................27
2.2.2 Fluid fl ow regimes ......................................................................28
2.2.3 Typical applications of Newtonian laminar fl ow ..........................30
2.2.3a Laminar fl ow in a cylindrical channel (pipe or tube) ........30
2.2.3b Laminar fl uid fl ow on fl at surfaces and channels .............33
2.2.3c Laminar fl uid fl ow around immersed particles .................34
2.2.3d Fluid fl ow through porous media ....................................36
2.2.4 Turbulent fl uid fl ow ...................................................................36
2.2.4a Turbulent Newtonian fl uid fl ow in a cylindrical channel
(tube or pipe) ............................................................................37
2.2.4b Turbulent fl uid fl ow around immersed particles ..............39
2.3 Flow properties of fl uids ........................................................................40
2.3.1 Types of fl uid fl ow behavior ........................................................40
2.3.2 Non-Newtonian fl uid fl ow in pipes .............................................41
vi Contents
2.4 Transportation of fl uids ........................................................................43
2.4.1 Energy relations, the Bernoulli Equation .....................................43
2.4.2 Pumps: Types and operation ......................................................46
2.4.3 Pump selection ..........................................................................52
2.4.4 Ejectors .....................................................................................55
2.4.5 Piping .......................................................................................56
2.5 Flow of particulate solids (powder fl ow) ................................................56
2.5.1 Introduction ..............................................................................56
2.5.2 Flow properties of particulate solids ...........................................57
2.5.3 Fluidization ...............................................................................62
2.5.4 Pneumatic transport ..................................................................65
3 Heat and mass transfer, basic principles. ......................................................69
3.1 Introduction .........................................................................................69
3.2 Basic relations in transport phenomena .................................................69
3.2.1 Basic laws of transport ..............................................................69
3.2.2 Mechanisms of heat and mass transfer .......................................70
3.3 Conductive heat and mass transfer ........................................................70
3.3.1 The Fourier and Fick laws ...........................................................70
3.3.2 Integration of Fourier’s and Fick’s laws for
steady-state conductive transport ............................................ 71
3.3.3 Thermal conductivity, thermal diffusivity
and molecular diffusivity ............................................................73
3.3.4 Examples of steady-state conductive heat and
mass transfer processes ..............................................................76
3.4 Convective heat and mass transfer .........................................................81
3.4.1 Film (or surface) heat and mass transfer coeffi cients ...................81
3.4.2 Empirical correlations for convection heat and mass
transfer .....................................................................................84
3.4.3 Steady-state interphase mass transfer .........................................87
3.5 Unsteady state heat and mass transfer ...................................................89
3.5.1 The 2 nd Fourier and Fick laws ....................................................89
3.5.2 Solution of Fourier’s second law equation for an
infi nite slab ...............................................................................90
3.5.3 Transient conduction transfer in fi nite solids ...............................92
3.5.4 Transient convective transfer in a semi-infi nite body ....................94
3.5.5 Unsteady state convective transfer ..............................................95
3.6 Heat transfer by radiation .....................................................................96
3.6.1 Interaction between matter and thermal radiation 96
3.6.2 Radiation heat exchange between surfaces ..................................97
3.6.3 Radiation combined with convection ........................................100
3.7 Heat exchangers .................................................................................100
3.7.1 Overall coeffi cient of heat transfer ............................................100
3.7.2 Heat exchange between fl owing fl uids .......................................102
3.7.3 Fouling ...................................................................................104
3 .7.4 H eat exchangers in the food process industry ............................105
3.8 Microwave heating ..............................................................................107
3.8.1 Basic principles of microwave heating .......................................108
Contents vii
3.9 Ohmic heating ....................................................................................109
3.9.1 Introduction ............................................................................109
3.9.2 Basic principles ........................................................................110
3.9.3 Applications and equipment ....................................................112
4 Reaction kinetics ........................................................................................115
4.1 Introduction .......................................................................................115
4.2 Basic concepts ....................................................................................116
4.2.1 Elementary and non-elementary reactions. ................................116
4.2.2 Reaction order ........................................................................116
4.2.3 Effect of temperature on reaction kinetics .................................119
4.3 Kinetics of biological processes ............................................................121
4.3.1 Enzyme-catalyzed reactions ......................................................121
4.3.2 Growth of microorganisms ......................................................122
4.4 Residence time and residence time distribution ....................................123
4.4.1 Reactors in food processing .....................................................123
4.4.2 Residence time distribution ......................................................124
5 Elements of process control .......................................................................129
5.1 Introduction .......................................................................................129
5.2 Basic concepts ....................................................................................129
5.3 Basic control structures .......................................................................131
5.3.1 Feedback control .....................................................................131
5.3.2 Feed-forward control ...............................................................131
5 .3.3 C omparative merits of control strategies ...................................132
5.4 The block diagram ..............................................................................132
5.5 Input, output and process dynamics ....................................................133
5.5.1 First order response .................................................................133
5.5.2 Second order systems ..............................................................135
5.6 Control modes (control algorithms) ....................................................136
5.6.1 On-off (binary) control ............................................................136
5.6.2 Proportional (P) control ..........................................................138
5.6.3 Integral (I) control ...................................................................139
5.6.4 Proportional-integral (PI) control .............................................140
5.6.5 Proportional-integral-differential (PID) control .........................140
5.6.6 Optimization of control ...........................................................141
5.7 The physical elements of the control system .........................................142
5.7.1 The sensors (measuring elements) ............................................142
5.7.2 The controllers ........................................................................149
5.7.3 The actuators ..........................................................................149
6 Size reduction ............................................................................................153
6.1 Introduction .......................................................................................153
6.2 Particle size and particle size distribution .............................................154
6.2.1 Defi ning the size of a single particle ..........................................154
6.2.2 Particle size distribution in a population of particles;
defi ning a ‘ mean particle size ’ ...................................................155
6.2.3 Mathematical models of PSD ...................................................158
6.2.4 A note on particle shape ..........................................................160
viii Contents
6.3 Size reduction of solids, basic principles ...............................................163
6.3.1 Mechanism of size reduction in solids .......................................163
6.3.2 Particle size distribution after size reduction ..............................163
6.3.3 Energy consumption ................................................................163
6.4 Size reduction of solids, equipment and methods .................................165
6.4.1 Impact mills ............................................................................166
6.4.2 Pressure mills ..........................................................................167
6.4.3 Attrition mills ..........................................................................168
6.4.4 Cutters and choppers ..............................................................170
7 Mixing .......................................................................................................175
7.1 Introduction .......................................................................................175
7.2 Mixing of fl uids (blending) ..................................................................175
7.2.1 Types of blenders .....................................................................175
7.2.2 Flow patterns in fl uid mixing ....................................................177
7.2.3 Energy input in fl uid mixing ......................................................178
7.3 Kneading ............................................................................................181
7.4 In-fl ow mixing .....................................................................................184
7.5 Mixing of particulate solids .................................................................184
7.5.1 Mixing and segregation ............................................................184
7.5.2 Quality of mixing, the concept of ‘ mixedness’ ............................184
7.5.3 Equipment for mixing particulate solids ....................................187
7.6 Homogenization .................................................................................189
7.6.1 Basic principles ........................................................................189
7.6.2 Homogenizers .........................................................................191
8 Filtration ...................................................................................................195
8.1 Introduction .......................................................................................195
8.2 Depth fi ltration ..................................................................................196
8.3 Surface (barrier) fi ltration ...................................................................198
8.3.1 Mechanisms ............................................................................198
8.3.2 Rate of fi ltration ......................................................................199
8.3.3 Optimization of the fi ltration cycle ...........................................204
8.3.4 Characteristics of fi ltration cakes ..............................................205
8.3.5 The role of cakes in fi ltration ....................................................206
8.4 Filtration equipment ...........................................................................207
8.4.1 Depth fi lters ............................................................................207
8.4.2 Barrier (surface) fi lters .............................................................207
8.5 Expression ..........................................................................................211
8.5.1 Introduction ............................................................................211
8.5.2 Mechanisms ............................................................................211
8.5.3 Applications and equipment ....................................................213
9 Centrifugation ...........................................................................................217
9.1 Introduction .......................................................................................217
9.2 Basic principles ...................................................................................218
9.2.1 The continuous settling tank ....................................................218
9.2.2 From the settling tank to the tubular centrifuge .........................220
9.2.3 The baffl ed settling tank and the disc-bowl centrifuge ...............223
9.2.4 Liquid–liquid separation ..........................................................224
Contents ix
9.3 Centrifuges .........................................................................................226
9.3.1 Tubular centrifuges ..................................................................227
9.3.2 Disc-bowl centrifuges ...............................................................228
9.3.3 Decanter centrifuges ................................................................230
9.3.4 Basket centrifuges ....................................................................230
9.4 Cyclones. ............................................................................................231
10 Membrane processes .................................................................................233
10.1 Introduction ...................................................................................233
10.2 Tangential fi ltration ........................................................................234
10.3 Mass transfer through MF and UF membranes .................................235
10.3.1 Solvent transport ...............................................................235
10.3.2 Solute transport; sieving coeffi cient and rejection ................237
10.3.3 Concentration polarization and gel polarization ..................238
10.4 Mass transfer in reverse osmosis ......................................................241
10.4.1 Basic concepts ...................................................................241
10.4.2 Solvent transport in reverse osmosis ....................................242
10.5 Membrane systems .........................................................................245
10.5.1 Membrane materials ..........................................................245
10.5.2 Membrane confi gurations ..................................................247
10.6 Membrane processes in the food industry ........................................249
10.6.1 Microfi ltration ...................................................................249
10.6.2 Ultrafi ltration .....................................................................249
10.6.3 Nanofi ltration and reverse osmosis .....................................251
10.7 Electrodialysis .................................................................................253
11 Extraction ..................................................................................................259
11.1 Introduction ...................................................................................259
11.2 Solid–liquid extraction (leaching) ....................................................261
11.2.1 Defi nitions .........................................................................261
11.2.2 Material balance ................................................................262
11.2.3 Equilibrium ........................................................................262
11.2.4 Multistage extraction ..........................................................262
11.2.5 Stage effi ciency ..................................................................266
11.2.6 Solid–liquid extraction systems ...........................................268
11.3 Supercritical fl uid extraction ............................................................271
11.3.1 Basic principles ..................................................................271
11.3.2 Supercritical fl uids as solvents .............................................272
11.3.3 Supercritical extraction systems. ..........................................273
11.3.4 Applications. ......................................................................275
11.4 Liquid–liquid extraction ..................................................................276
11.4.1 Principles ...........................................................................276
11.4.2 Applications. ......................................................................276
12 Adsorption and ion exchange .....................................................................279
12.1 Introduction ...................................................................................279
12.2 Equilibrium conditions ....................................................................280
12.3 Batch adsorption ............................................................................282
12.4 Adsorption in columns ....................................................................287