Post harvest technology and food process engineering amalendu chakraverty, r paul singh

Chakraverty
Singh

Food Science & Technology

Postharvest Technology and Food
Process Engineering

This book covers postharvest food preservation and processing methods,
with an emphasis on grains. It is divided into five parts:
•
•
•
•
•

Grain-Properties, Drying and Dryers
Grain Storage
Parboiling and Milling
By-Products/Biomass Utilization
Food Process Engineering

The text covers grain structure and composition, psychrometry, the
theory and methods of grain drying, and design, testing, specification,
and selection of grain dryers. It describes processes such as parboiling,
of grain, hydrothermal treatment of grain, and milling of rice and other
grains and pulses. The text also addresses biomass utilization and
conversion technologies for energy, chemicals, food, and feed. The final
section on food process engineering examines postharvest management
including cooling and packaging, and discusses preservation and
processing, factors that affect deterioration, and various industrial

preservation methods of fruits and vegetables. It also provides an
overview of food chemistry and covers food engineering operations,
including fluid mechanics and heat transfer.

K15262
ISBN: 978-1-4665-5320-0

90000

9 781466 553200

Postharvest Technology and Food Process Engineering

Cereals, legumes, oilseeds, fruits, and vegetables are the most important
food crops in the world, with cereal grains contributing the bulk of food
calories and proteins worldwide. Generally, the supply of grains and other
food can be enhanced by increasing production and by reducing postharvest losses. While food production has increased significantly over the
last few decades, minimizing huge postharvest losses as well as utilizing
their by-products/wastes is the optimal way for a country to become
self-sufficient in food. Postharvest Technology and Food Process
Engineering combines these two subject areas as it covers both the
primary processing of cereals, pulses, fruits, and vegetables and
utilization of by-products/biomass.

Postharvest
Technology
and Food Process
Engineering
Amalendu Chakraverty
R. Paul Singh

Postharvest
Technology
and Food Process
Engineering



Postharvest
Technology
and Food Process
Engineering
Amalendu Chakraverty
R. Paul Singh

Boca Raton London New York

CRC Press is an imprint of the
Taylor & Francis Group, an informa business


CRC Press
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Boca Raton, FL 33487-2742
© 2014 by Taylor & Francis Group, LLC
CRC Press is an imprint of Taylor & Francis Group, an Informa business
No claim to original U.S. Government works
Version Date: 20130111

International Standard Book Number-13: 978-1-4665-5321-7 (eBook - PDF)
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Dedicated to
our parents



Contents
Preface.......................................................................................................... xxv

Introduction���������������������������������������������������������������������������������������������� xxvii

Part I  Grain Properties, Drying, and Dryers
  1 Properties of Grains................................................................................3
Structure.......................................................................................................3
Chemical Composition.................................................................................5
Effects of Temperature on the Quality of Grain.............................................6
Proteins..............................................................................................6
Starch������������������������������������������������������������������������������������������������6
Fats����������������������������������������������������������������������������������������������������6
Vitamins.............................................................................................6
Physical Properties........................................................................................7
Sphericity............................................................................................7
Bulk Density.......................................................................................7
True Density.......................................................................................7
Porosity..............................................................................................8
Coefficient of Friction and Angle of Repose..................................................9
Coefficient of Friction.........................................................................9
Angle of Repose..................................................................................9
Thermal Properties........................................................................................9
Specific Heat.....................................................................................10
Specific Heat Measurement...............................................................10
Thermal Conductivity.......................................................................11
Thermal Conductivity Measurement.................................................12
Aerodynamic Properties..............................................................................13
Resistance of Grain Bed to Airflow..............................................................14
Symbols......................................................................................................15

vii

viii  ◾  Contents

  2 Psychrometry........................................................................................17
Humidity....................................................................................................17
Percentage Humidity...................................................................................18
Relative Humidity.......................................................................................18
Humid Heat...............................................................................................19
Enthalpy.....................................................................................................19
Humid Volume...........................................................................................19
Saturated Volume........................................................................................19
Dew Point...................................................................................................20
Wet Bulb Temperature................................................................................20
Wet Bulb Theory.........................................................................................20
Introduction of Psychrometric Chart..........................................................21
Use of Psychrometric Chart..............................................................22
Problems on Psychrometry..........................................................................24
Solved Problems................................................................................24
Exercises......................................................................................................29
Symbols......................................................................................................29

  3 Theory of Grain Drying........................................................................31

Thin Layer Drying......................................................................................31
Moisture Content.......................................................................................32
Moisture Measurement...............................................................................33
Direct Methods.................................................................................33
Single Stage Method............................................................33
Double Stage Method..........................................................33
Other Methods....................................................................33

Brown–Duvel Distillation Method......................................33
Indirect Methods............................................................................. 34
Electrical Resistance Method.............................................. 34
Dielectric Method.............................................................. 34
Equilibrium Moisture Content.................................................................. 34
Determination of EMC....................................................................35
EMC Models....................................................................................35
Hysteresis..........................................................................................38
Bound Moisture................................................................................38
Unbound Moisture...........................................................................38
Free Moisture....................................................................................39
Constant Rate Period...........................................................39
Falling Rate Period..............................................................43
Drying Equations............................................................................ 44
Determination of Drying Constant.............................................................48


Contents  ◾  ix

Remarks on Thin-Layer Drying Equations..................................................49
Drying Models............................................................................................50
Effects of Different Factors on the Drying Process.......................................50
Effects of Air Temperature................................................................52
Effects of Air Velocity.......................................................................52
Effects of Air Humidity....................................................................53
Effects of Air Exposure Time.............................................................53
Deep Bed Drying........................................................................................53
Time of Advance of Drying Front.....................................................54
Decreasing Rate Period.....................................................................54
Remarks on Deep Bed Drying....................................................................57

Mass and Heat Balance in Grain Drying...........................................57
Mass Balance.......................................................................57
Heat Balance.......................................................................59
Dryer Performance............................................................................59
Thermal Efficiency...............................................................59
Heat Utilization Factor........................................................60
Coefficient of Performance..................................................60
Relationship between HUE and COP.................................60
Effective Heat Efficiency......................................................60
Problems on Moisture Content and Drying................................................61
Solved Problems on Moisture Content..............................................61
Exercises...........................................................................................63
Solved Problems on Drying............................................................. 64
Exercises...........................................................................................71
Symbols......................................................................................................72

  4 Methods of Grain Drying.....................................................................75

Conduction Drying....................................................................................75
Convection Drying.....................................................................................76
Natural Air Drying.......................................................................... 77
Supplemental Heat Drying.............................................................. 77
Heated Air Drying............................................................................78
Radiation Drying........................................................................................78
Sun Drying.......................................................................................78
Infrared Drying.................................................................................79
Solar Drying...............................................................................................79
Integrated Hybrid-Type Solar Grain Dryer.......................................80
Dielectric and Microwave Drying...............................................................80
Chemical Drying........................................................................................81

Sack Prying.................................................................................................81


x  ◾  Contents

  5 Grain Dryers.........................................................................................83
Unheated Air Dryers...................................................................................83
Storage Unit............................................................................................... 84
Round Metal Bin............................................................................. 84
Screen Tunnel Quonset-Type Storage Unit...................................... 84
Aeration System..........................................................................................87
Air Distribution System..............................................................................88
Heated Air Dryers.......................................................................................89
Flat Bed–Type Batch Dryer...............................................................89
Construction.......................................................................89
Operation............................................................................91
Recirculatory Batch Dryer (PHTC Type)..........................................92
Construction.......................................................................92
Operation............................................................................92
Louisiana State University Dryer.................................................................93
Construction....................................................................................93
Rectangular Bin...................................................................96
Air Distribution System.......................................................96
Grain Discharging Mechanism............................................96
Air Heating System.............................................................96
Baffle Dryer.................................................................................................97
Construction....................................................................................97
Operation.........................................................................................98
Rotary Dryer...............................................................................................99
Construction..................................................................................100

Operation.......................................................................................100

  6 Selection, Design, Specifications, and Testing of Grain Dryers..........103

Selection of Dryers....................................................................................103
Preliminary Dryer Selection............................................................103
Comparison of Dryers...............................................................................104
Drying Test.....................................................................................104
Final Selection of Dryer............................................................................105
Design of Grain Dryers.............................................................................105
Size, Shape, and Type of Dryer........................................................106
Calculation of Air, Heat, and Fuel Requirements for Heated Air
Dryers................................................................................107
Drying Air Temperature..................................................................109
Grain Parameters............................................................................109
Airflow Pattern and Air Distribution.........................................................109
Conveying and Handling System..............................................................109
Air Heating System................................................................................... 110
Testing of Grain Dryers............................................................................. 110


Contents  ◾  xi

Simple Method............................................................................... 110
Simple Test Procedure for Continuous Flow Dryer............ 110
Rigorous Method............................................................................ 111
Checking of Construction................................................. 111
Drying Performance Test................................................... 111
Blower Performance Test................................................... 111
Performance of the Control System...................................112

Performance of the Handling Equipment..........................112
Investigation after Disassembling.......................................112
Specifications............................................................................................112
Problems on Dryer Design........................................................................ 117
Solved Problems.............................................................................. 117
Exercises....................................................................................................126
Symbols....................................................................................................127

Part II  Grain Storage
  7 Food Grain Storage.............................................................................131

Grain Storage Principles............................................................................132
General..........................................................................................132
Moisture ..........................................................................132
Temperature......................................................................134
Changes in Food Grains during Storage....................................................134
Chemical Changes..........................................................................134
Physiological Changes.....................................................................136
Respiration........................................................................136
Longevity..........................................................................137
Sprouting..........................................................................137
Heating ..........................................................................138
Biological Changes..........................................................................138
Moisture Migration...........................................................138
Grain Storage Pests and Their Control...............................139
Types of Grain Spoilage.............................................................................139
Reduction in Mass..........................................................................139
Spoilage of Grains by Heating.........................................................140
Reduction in Seed Germination......................................................140
Contamination of Grains by Insects................................................140

Detection of Insect Infestation..................................................................140
Grain Storage Pests....................................................................................140
Important Insect Species........................................................................... 141
Control of Stored Food Grain Pests........................................................... 141
Preventive Measures..................................................................................142


xii  ◾  Contents

Curative Measures.....................................................................................142
Physical Methods............................................................................142
Heating ..........................................................................142
Radiation..........................................................................142
Mechanical Methods.......................................................................143
Chemical Methods..........................................................................143
Biological Methods.........................................................................143
Fumigation...............................................................................................143
Insecticides.....................................................................................143
Principles of Fumigation.................................................................144
Diffusion..........................................................................144
Sorption ..........................................................................144
Penetration........................................................................144
Lethal Effect...................................................................... 145
Applications of Fumigants......................................................................... 145
Rodent Control......................................................................................... 145
Rat and Mice in Stored Grains........................................................ 145
Rodenticides (for Rats and Mice)....................................................146
Food Grain Storage Structures...................................................................146
Rural Storage Structures..................................................................146
Steel Bin ..........................................................................147

Aluminum Bin..................................................................147
RCC Bin..........................................................................147
Bag and Bulk Storage.........................................................148
Stack Plan..........................................................................148
Dunnage..........................................................................149
Silos����������������������������������������������������������������������������������149
Expert System........................................................................................... 151
Optimal Configurations of Silos..................................................... 153
Grain Pressure Theories...................................................................154
Economics of Storage................................................................................ 157
Storage in Godowns........................................................................ 157
Storage in Silos............................................................................... 157
Cost of Storage in Traditional Godowns and Modern Silos............. 157

Part III  Parboiling AND MILLING
  8 Parboiling of Grain............................................................................. 161

Principles..................................................................................................162
Soaking/Hydration.........................................................................163
Soaking Temperature, Duration, and pH........................................163
Pneumatic Pressure and Reduced Pressure.......................................165


Contents  ◾  xiii

Hydration Equations.................................................................................166
Steaming...................................................................................................169
Drying......................................................................................................169
Milling......................................................................................................170
Product Qualities......................................................................................171

Methods of Parboiling...............................................................................171
Traditional Methods.......................................................................171
Single Boiling/Steaming Process........................................172
Double Boiling/Steaming Process......................................172
Improved Methods.........................................................................172
Rice Conversion Process (United Kingdom)......................173
Schule Process (Germany).................................................173
Crystallo Process (Italy).....................................................173
Malek Process (United States)............................................173
Jadavpur University Method (India).................................. 174
CFTRI Method (India)..................................................... 174
Pressure Parboiling Method (India)...................................175

  9 Parboiling of Wheat............................................................................179

Principles of Parboiling of Wheat..............................................................179
Soaking������������������������������������������������������������������������������������������179
Steaming (Cooking)........................................................................ 181
Drying�������������������������������������������������������������������������������������������181
Methods of Parboiling and Production of Bulgur......................................182
Method I: Batch Method................................................................182
Method II: Preheat Treatment Process.............................................183
Method III: Continuous Process.....................................................183
Method IV: Chemical Lye Peeling Process......................................185
Soaking����������������������������������������������������������������������������185
Tempering.........................................................................186
Cooking���������������������������������������������������������������������������186
Lye Treatment....................................................................186
Peeling������������������������������������������������������������������������������186
Acid Treatment..................................................................187

Drying������������������������������������������������������������������������������187

10 General Grain Milling Operations......................................................189
Cleaning/Separation..................................................................................189
Classification of Separation Methods..............................................189
Separation according to Aerodynamic Properties...............190
Separation according to Specific Gravity............................190


xiv  ◾  Contents

Separation according to Magnetic Properties.....................190
Separation according to Electrostatic Properties................. 191
Separation according to Colors (Electronic Separators)...... 191
Separation according to Surface Properties
(Frictional Separators)........................................192
Effectiveness of the Separation........................................................194
Husking/Scouring/Hulling of Grain..........................................................194
Methods of Husking.......................................................................194
Concave-Type Husker.......................................................194
Husking by the Action of Rubber Rolls.............................196
Husking by Under Runner Disk Husker (Disk Sheller).....198
Husking by Scourers and Blade-Type Huskers...................199
Hulling by an Abrasive Drum in a Cylindrical Steel Shell...... 200
Factors Affecting the Effectiveness of Hulling/Husking/Scouring........201
Effectiveness of Hulling/Husking/Scouring.....................................202
Grinding...................................................................................................202
Effectiveness of Grinding................................................................203
Machinery Used in Cereal Grinding.............................................. 204
Grinding of Grain in Roller Mills..................................... 204

Grinding Grain in Hammer Mills.................................... 206
Symbols................................................................................................... 206

11 Hydrothermal Treatment/Conditioning of Cereal Grains..................207
Physicothermal Properties........................................................................ 208
Strength/Hardness......................................................................... 208
Density and Hardness.................................................................... 208
Hysteresis....................................................................................... 208
Thermal Properties......................................................................... 208
Biochemical Properties............................................................................. 208
Physicochemical Properties...................................................................... 208
Effects of Various Factors on the Changes of Different Properties..............209
Effects of Moisture Content............................................................209
Effects of Temperature....................................................................209
Thermal Properties..........................................................................209
Chemical Kinetics...........................................................................210
Coefficient of Expansion.................................................................210
Biochemical Properties....................................................................210
Optimum Conditions.....................................................................210

12 Rice Milling........................................................................................211
Traditional Rice Milling Machinery.......................................................... 211
Single Huller................................................................................... 211


Contents  ◾  xv

Construction..................................................................... 211
Principle���������������������������������������������������������������������������212
Advantages........................................................................212

Disadvantages....................................................................212
Sheller Mill.....................................................................................213
Advantages........................................................................213
Disadvantages....................................................................213
Modern Rice Milling Machinery............................................................... 214
Cleaning......................................................................................... 214
General Principles of Cleaning.......................................... 215
Open Double-Sieve Precleaner.......................................... 215
Single Scalper Drum Cleaner (Japan)................................ 215
Stoner��������������������������������������������������������������������������������������������217
Stoner with Aspirator (Japan)............................................ 217
Paddy Cleaner with Stoner (Japan).................................... 219
Paddy Cleaner (West Germany)........................................ 220
Husking..........................................................................................221
Impact-Type Paddy Husker (Japan)...................................221
Rubber Roll Husker (Japan)..............................................224
Power Transmission System.............................................. 226
Rubber Roll Husker (Europe)........................................... 226
Separation.......................................................................................227
Paddy Separator (Japan)....................................................227
Paddy Separator (Europe)..................................................231
Compartment Separator....................................................231
Whitening......................................................................................233
Vertical Whitening or Pearling Cone (Europe)...................233
Horizontal Rice Whitening Machine (Japan).....................235
Friction-Type Whitening Machine (Japan)........................239
Water Mist Whitening/Polishing.......................................243
Modern Combined Vertical Milling System......................243
Grading�����������������������������������������������������������������������������������������243

13 Milling of Corn, Wheat, Barley, Rye, Oats, Sorghum, and Pulses.....245

Corn Milling.............................................................................................245
Introduction...................................................................................245
Composition and Structure.............................................................245
Corn Dry Milling.......................................................................... 246
Tempering–Degerming Method of Dry Milling............... 246
Description of the Tempering–Degerming System............ 246
Corn Wet Milling...........................................................................249
Cleaning���������������������������������������������������������������������������250
Steeping����������������������������������������������������������������������������250


xvi  ◾  Contents

Germ Recovery..................................................................250
Milling and Fiber Recovery...............................................250
Starch–Gluten Separation..................................................251
Wheat Milling...........................................................................................252
Introduction...................................................................................252
Flour Milling..................................................................................252
Cleaning���������������������������������������������������������������������������252
Conditioning/Hydrothermal Treatment.............................253
Grinding (Milling)............................................................253
Storage of Finished Products..............................................254
Components of a Wheat Mill.........................................................254
Break Roll.........................................................................254
Break Sifting System..........................................................254
Reduction Roll..................................................................254
Reduction Sifting System..................................................255

Scratch System..................................................................255
Barley Processing and Milling...................................................................255
Rye Milling...............................................................................................256
Oat Milling...............................................................................................257
Sorghum Milling.......................................................................................258
Milling of Pulses.......................................................................................259
Introduction...................................................................................259
Varieties, Composition, and Structure.............................................259
Traditional Dry Milling Method (Dhal’s Milling).......................... 260
Cleaning and Grading...................................................... 260
Pitting������������������������������������������������������������������������������260
Pretreatment with Oil....................................................... 260
Conditioning.................................................................... 260
Dehusking and Splitting................................................... 260
Polishing���������������������������������������������������������������������������261
Commercial Milling of Pulses by Traditional Method.....................261
Modern CFTRI Method of Pulses Milling......................................262
Cleaning���������������������������������������������������������������������������262
Preconditioning.................................................................262
Dehusking.........................................................................262
Lump Breaking..................................................................262
Conditioning and Splitting................................................262

Part IV By-Products/Biomass Utilization
14 Rice Bran.............................................................................................265

Effect of Storage Temperature....................................................................270
Effect of Storage Moisture Content of Bran..............................................271

Contents  ◾  xvii

Effect of Relative Humidity.......................................................................271
Particle Size...............................................................................................271
Insect Infestation.......................................................................................271

15 Utilization of Rice Bran......................................................................273

Dry Heat Treatment..................................................................................274
Convection Heating........................................................................274
Conduction Heating.......................................................................274
Infrared Heating.............................................................................274
Frictional Heating...........................................................................274
Wet Heat Treatment..................................................................................274
Rice Bran Stabilizers under Development in India....................................275
Examples of Stabilizer Design....................................................................276
Extraction of Rice Bran Oil...................................................................... 280
Solvent Extraction Method............................................................ 280
Batch Extraction Method................................................................281
Refining of Crude Rice Bran Oil into Edible Grade Oil............................281
Uses of Bran, Bran Oil, and Various Constituents.....................................282
Edible Grade Oil............................................................................282
Industrial Grade Crude Oil.............................................................282
Soap Manufacture.............................................................282
Free Fatty Acid Manufacture.............................................282
Protective Coatings............................................................282
Plasticizers.........................................................................282
Tocopherol........................................................................282
Rice Bran Wax...................................................................282
Uses of Defatted Bran...............................................................................283

Feed�����������������������������������������������������������������������������������������������283
Food����������������������������������������������������������������������������������������������283
Fertilizer.........................................................................................283
Medicinal Use.................................................................................283

16 Biomass Conversion Technologies......................................................285

Biomass.....................................................................................................285
Biomass Conversion Technologies............................................................ 286
Chemical and Biochemical Processing............................................ 286
Silica and Silicon from Rice Husk..................................... 286
Pure Amorphous Silica from Rice Husk.............................289
Ceramics from Rice Husk Ash...........................................290
Paper Production from Cellulosic Biomass........................292
Production of Biodegradable Plastic Films.........................295
Alcoholic Fermentation.....................................................296
By-Products of Fruit and Vegetable Processing...................296


xviii  ◾  Contents

Thermal and Thermochemical Processing........................................299
Pyrolysis���������������������������������������������������������������������������299
Gasification...................................................................... 300
Combustion......................................................................303
Problem on Combustion of Rice Husk..............................309
Problem on the Design of an Inclined Grate Furnace........ 310

Part V  Food Process Engineering
17 Postharvest Management of Fruits and Vegetables.............................315

Respiration Process.................................................................................... 316
Ripening Process.......................................................................................320
Apples��������������������������������������������������������������������������������������������323
Bananas�����������������������������������������������������������������������������������������323
Mangoes.........................................................................................325
Tomatoes........................................................................................325
Cooling of Commodities...........................................................................328
Forced-Air Cooling.........................................................................331
Tunnel Cooling...............................................................................332
Serpentine Cooling.........................................................................332
Cold Wall Cooler............................................................................333
Cooling Rate in Forced-Air Cooling...............................................334
Hydrocooling..................................................................................335
Vacuum Cooling.............................................................................337
Calculating Cooling Time...............................................................338
Packaging of Fruits and Vegetables........................................................... 340
Low-Density Polyethylene..............................................................341
Polypropylene.................................................................................341
Polystyrene..................................................................................... 342
Polyvinyl Chloride......................................................................... 342
Ethyl Vinyl Alcohol....................................................................... 343
Controlled-Atmosphere Storage............................................................... 343
Modified-Atmosphere Packaging.............................................................. 343
Gas Permeability Ratio....................................................................350
Respiratory Quotient...................................................................... 351
Package Design Variables................................................................352
Variable Respiration Rates...............................................................352
Effect of Temperature......................................................................352
Water Condensation on Interior Package Walls...............................354

Holes and Micropores in Package...................................................354
Transient Atmospheric Conditions in Modified-Atmosphere
Packages.............................................................................354


Contents  ◾  xix

18 Food Preservation and Processing of Fruits and Vegetables...............357

Microorganisms and Other Organisms.....................................................358
Heat and Cold................................................................................359
Moisture.........................................................................................359
Enzymes.........................................................................................359
Chemicals/Oxygen..........................................................................359
Light����������������������������������������������������������������������������������������������360
Storage Time.................................................................................. 360
Industrial Preservation Methods............................................................... 360
Food Preservation by Thermal Treatment........................................361
Preservation by Cooling..................................................................361
Preservation by Drying/Dehydration..............................................361
Preservation by Chemicals..............................................................362
Food Preservation by Canning........................................................362
Various Operations in Canning.......................................................363
Grading/Sorting..............................................................................363
Washing......................................................................................... 364
Peeling, Cutting, Slicing.................................................................365
Blanching...................................................................................... 366
Addition of Liquid..........................................................................367
Exhausting and Creating Vacuum...................................................368
Sealing/Double Seaming.................................................................368

Processing.......................................................................................369
Factors Affecting Thermal Processing Conditions............................370
Thermal Processing Time and Temperature.....................................370
Decimal Destruction Time (D Value)................................370
Thermal Death Time.........................................................372
Temperature Dependence (z Value)...................................372
TDT Method (D–z Model)...............................................372
Arrhenius Kinetic K–E Model...........................................374
Lethality/Sterilization Value—F Value...............................375
Thermal Processing Methods and Equipment.................................376
Cookers�����������������������������������������������������������������������������������������376
Retorts�������������������������������������������������������������������������������������������377
Cooling�����������������������������������������������������������������������������������������379
Labeling..........................................................................................379
Spoilage of Canned Foods...............................................................379
Food Preservation by Cooling.........................................................380
Cold Storage...................................................................................380
Freezing of Foods............................................................................381
Food Dehydration..........................................................................382


xx  ◾  Contents

Fruits and Vegetables: Preservation and Processing....................................382
Physiological Changes.....................................................................383
Classification..................................................................................384
Respiration.....................................................................................384
Transpiration/Water Loss................................................................385
Ripening.........................................................................................386
Precooling of Fresh Produce............................................................388

Processing of Fresh Produce............................................................389
Canning of Vegetables.......................................................389
Canning of Peas.................................................................389
Canning of Tomatoes........................................................391
Canning, Bottling, and Freezing of Fruits..........................392
Canning of Apples.............................................................393
Canning of Rhubarb.........................................................393
Bottling����������������������������������������������������������������������������394
Freezing����������������������������������������������������������������������������395
Dehydration of Fruits and Vegetables........................................................395
Dehydration of Vegetables..............................................................396
Mechanical Dehydration...................................................397
Dehydration of Tomatoes...............................................................398
Dehydration of Potatoes................................................................ 400
Dehydration of Fruits.....................................................................402
Sun Drying........................................................................402
Mechanical Drying............................................................402
Dehydration of Grapes for Raisins..................................................403
Quality Parameters of Dehydrated Foods....................................... 404

19 Food Chemistry for Technologists..................................................... 407

Water Activity (aw )..........................................................................407
Glass Transition.............................................................................. 411
Dispersions..................................................................................... 411
Carbohydrates...........................................................................................412
Sugars��������������������������������������������������������������������������������������������413
Starch��������������������������������������������������������������������������������������������415
Gelatinization.................................................................... 415
Proteins..................................................................................................... 417

Chemical Structure......................................................................... 417
Classification.................................................................................. 419
Properties........................................................................................ 419
Denaturation.................................................................................. 419


Contents  ◾  xxi

Gel Formation............................................................................... 420
Essential Amino Acids................................................................... 420
Lipids�������������������������������������������������������������������������������������������������������420
Chemical Structure........................................................................ 420
Rancidity....................................................................................... 422
Vitamins.................................................................................................. 422
Few Chemical Structures............................................................... 423
Color�������������������������������������������������������������������������������������������������������424
Flavor�������������������������������������������������������������������������������������������������������427
Enzymes....................................................................................................429

20 Food Engineering Operations.............................................................431

Fluid Mechanics........................................................................................431
Newtonian Fluid Flow....................................................................431
Introduction......................................................................431
Reynolds Number.............................................................432
Bernoulli Equation........................................................... 434
Laminar Flow....................................................................436
Turbulent Flow..................................................................437
Flat Plate/Slit Flow............................................................441
Non-Newtonian Fluids...................................................................445

Introduction......................................................................445
Velocity Profile of a Power Law Fluid.................................447
Generalized Reynolds Number......................................... 448
Power Law Fluid............................................................... 448
Laminar Flow................................................................... 448
Turbulent Flow..................................................................449
Exercises on Fluid Mechanics..........................................................452
Ideal Gas Laws...................................................................452
Newtonian Fluid...............................................................452
Non-Newtonian Fluid.......................................................453
Heat Transfer............................................................................................454
Conduction....................................................................................454
Steady-State Conduction...................................................454
Unsteady-State Heat Transfer in a Flat Slab.......................458
Biot Number.....................................................................461
Convection.....................................................................................463
Prandtl Number................................................................463
Nusselt Number............................................................... 464
Equivalent Diameter..........................................................465


xxii  ◾  Contents

Film Heat Transfer Coefficient for Laminar Flow Inside
a Pipe................................................................ 466
Film Coefficient in the Turbulent Region Inside a Pipe..... 466
Film Coefficient for Transitional Flow in a Pipe................ 466
Film Coefficient for Non-Newtonian Flow Inside a Pipe...... 468
Convection Inside and Outside of a Pipe and Overall
Heat Transfer Coefficient...................................470

Overall Coefficient through a Series of Multiple
Cylinders........................................................ 472
Forced Convection Heat Transfer Inside Pipes...................472
Wall Temperature, Tw........................................................473
Natural Convection........................................................................473
Grashof Number...............................................................473
Film Coefficient.................................................................474
Boiling�����������������������������������������������������������������������������475
Condensation.................................................................................476
Film-Type Condensation...................................................476
Mass Transfer and Heat Transfer........................................477
Logarithmic Mean Temperature Difference.......................479
Heat Exchangers.............................................................................481
Types of Heat Exchangers..................................................482
Radiation........................................................................................487
Kirchoff’s Law...................................................................487
Emissivity..........................................................................487
Stefan–Boltzman Equation................................................488
Heat Exchange between Two Infinite Parallel
Gray Planes....................................................489
Heat Exchange between Infinite Parallel Gray Planes.........490
Combined Heat Losses by Conduction, Convection, and Black
Body Radiation..................................................................491
Exercises on Heat Transfer..............................................................492
Heat Transfer Coefficient...................................................492
Heat Transfer for Non-Newtonian Fluid............................493
Heat Exchanger.................................................................493
Food Drying and Dryers...........................................................................494
A Few Drying Equations and Some Common Problems.................494
Drying Rate for Constant Drying Conditions...................494

Food Dehydration..........................................................................496
Sun Drying........................................................................496
Mechanical Drying............................................................497


Contents  ◾  xxiii

Fluidized Bed Drying....................................................... 504
Freeze-Drying....................................................................505
Osmotic Drying/Dehydration...........................................505
Exercises on Drying and Dryers..................................................... 506
Appendix.............................................................................................. 511
Bibliography.......................................................................................... 521
Index. ...................................................................................... 535