Food Process Engineering and Technology 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 Bihkoven, 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 an Technology Zeki Berk Professor (Emeritus) Department of Biotechnology and Food Engineering TECHNION Israel Institute ofTechnology Israel nunc UN THOKG m-munEn j «H HOC NflWg KGfllff (M »0l' S^SWgara AMSTERDAM • BOSTON • HEIDELBERG * LONDON • NEW YORK • OXFORD aAgBfliM PARIS ' SAN DIEC0 ' SAN FRANCISCO * SINGAPORE • SYDNEY • TOKYO ELSEVIER Academic Press is an imprint of Elsevier To my students Academic Press is an imprint of Elsevier 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA 32Jamescown Road. London NW1 7BY, UK 525 B Street, Suite 1900, San Diego, CA 92101-4495, USA 360 Park Avenue South, New York, NY 1001 0-1 710, USA First edition 2009 Copyright © 2009 Elsevier I nc All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier's Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email; permissions^elsevier.com. Alternatively visit the Science and Technology Books website at www elsevierdirect.com/rights for further information Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-373660-4 For information on all Academic Press publications visit our web site at www.elsevierdirect.com Typeset by Charon Tec Ltd., A Macmillan Company, (www.macmillansolutions.com) Printed and bound in the United States of America 09 10 11 12 13 1098765432 Working I together to grow libraries in developing countries www.clscvicr.com | www.bookaid.org www.sabre.org ELSEVIER ?„?™„^° Sabre Foundation 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 Definitions 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, definition 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 flow 27 2.1 Introduction 27 2.2 Elements of fluid dynamics 27 2.2.1 Viscosity 27 2.2.2 Fluid flow regimes 28 2.2.3 Typical applications of Newtonian laminar flow 30 2.2.3a Laminar flow in a cylindrical channel (pipe or tube) 30 2.2.3b Laminar fluid flow on flat surfaces and channels 33 2.2.3c Laminar fluid flow around immersed particles 34 2.2.3d Fluid flow through porous media 36 2.2.4 Turbulent fluid flow 36 2.2.4a Turbulent Newtonian fluid flow in a cylindrical channel (tube or pipe) 37 2.2.4b Turbulent fluid flow around immersed particles 39 2.3 Flow properties of fluids 40 2.3.1 Types of fluid flow behavior 40 2.3.2 Non-Newtonian fluid flow in pipes 41 vi Contents 2.4 Transportation of fluids 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 flow) 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 coefficients 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 2nd Fourier and Fick laws 89 3.5.2 Solution of Fourier's second law equation for an infinite slab 90 3.5.3 Transient conduction transfer in finite solids 92 3.5.4 Transient convective transfer in a semi-infinite 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 coefficient of heat transfer 1 00 3.7.2 Heat exchange between flowing fluids 102 3.7.3 Fouling 104 3.7.4 Heat exchangers in the food process industry 1 05 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 1 22 4.4 Residence time and residence time distribution 123 4.4.1 Reactors in food processing 123 4.4.2 Residence time distribution 1 24 5 Elements of process control 1 29 5.1 Introduction 1 29 5.2 Basic concepts 1 29 5.3 Basic control structures 131 5.3.1 Feedback control 131 5.3.2 Feed-forward control 131 5.3.3 Comparative merits of control strategies 1 32 5.4 The blockdiagram 132 5.5 Input, output and process dynamics 133 5.5.1 First order response 133 5.5.2 Second order systems 1 35 5.6 Control modes (control algorithms) 1 36 5.6.1 On-off (binary) control 1 36 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 Defining the size of a single particle 154 6.2.2 Particle size distribution in a population of particles; defining a 'mean particle size' 1 55 6.2.3 Mathematical models ofPSD 158 6.2.4 A note on particle shape 1 60 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 1 66 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 1 75 7.2 Mixing of fluids (blending) 175 7.2.1 Types of blenders 175 7.2.2 Flow patterns in fluid mixing 177 7.2.3 Energy input in fluid mixing 1 78 7.3 Kneading 181 7.4 In-flow mixing 1 84 7.5 Mixing of particulate solids 1 84 7.5.1 Mixing and segregation 1 84 7.5.2 Quality of mixing, the concept of'mixed ness' 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 filtration 196 8.3 Surface (barrier) filtration 198 8.3.1 Mechanisms 198 8.3.2 Rate offiltration 199 8.3.3 Optimization of the filtration cycle 204 8.3.4 Characteristics offiltration cakes 205 8.3.5 The role of cakes in filtration 206 8.4 Filtration equipment 207 8.4.1 Depth filters 207 8.4.2 Barrier (surface) filters 207 8.5 Expression 211 8.5.1 Introduction 211 8.5.2 Mechanisms 211 8.5.3 Applications and equipment 213 9 Centrifugation 21 7 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 baffled settling tank and the disc-bowl centrifuge 223 9.2.4 Liquid-liquid separation 224 Contents i> 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 filtration 234 10.3 Mass transfer through MF and UF membranes 235 1 0.3.1 Solvent transport 235 1 0.3.2 Solute transport; sieving coefficient and rejection 237 1 0.3.3 Concentration polarization and gel polarization 238 1 0.4 Mass transfer in reverse osmosis 241 10.4.1 Basic concepts 241 1 0.4.2 Solvent transport in reverse osmosis 242 1 0.5 Membrane systems 245 10.5.1 Membrane materials 245 10.5.2 Membrane configurations 247 10.6 Membrane processes in the food industry 249 10.6.1 Microfiltration 249 10.6.2 Ultrafiltration 249 10.6.3 Nanofikration 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 Definitions 261 11.2.2 Material balance 262 11.2.3 Equilibrium 262 1 1.2.4 Multistage extraction 262 11.2.5 Stage efficiency 266 11.2.6 Solid-liquid extraction systems 268 11.3 Supercritical fluid extraction 271 11.3.1 Basic principles 271 11.3.2 Supercritical fluids 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 1 2.1 Introduction 279 12.2 Equilibrium conditions 280 12.3 Batch adsorption 282 12.4 Adsorption in columns 287