Magnetic resonance imaging in food science (1998)

MAGNETIC RESONANCE IMAGING IN FOOD SCIENCE BRIAN HILLS Institute of Food Research Norwich Research Park Colney, Norwich United Kingdom A Wiley-Interscience Publication JOHN WILEY & SONS, INC New York • Chichester • Weinheim • Brisbane • Singapore • Toronto This book is printed on acid-free paper © Copyright © 1998 by John Wiley & Sons, Inc All rights reserved Published simultaneously in Canada 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, scanning or otherwise, except as permitted under Sections 107 ot 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744 Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue, New York, NY 10158-0012, (212) 850-6011, fax (212) 850-6008, E-Mail: PERMREQ WILEYCOM Library of Congress Cataloging-in-Publication Data: Hills, Brian, 1949Magnetic resonance imaging in food science / Brian Hills p cm "A Wiley-Interscience publication." Includes bibliographical references and index ISBN 0-471-17087-9 (cloth : alk paper) Food—Analysis Magnetic resonance imaging I Title TP372.5.H55 1998 664'.07—dc21 97-37413 Printed in the United States of America 10 PREFACE I have written this book in the belief that magnetic resonance imaging (MRI) has the potential of revolutionizing food manufacturing science The word potential has to be emphasized, because most applications of MRI to foods at the time of writing are little more than feasibility exercises This, to my mind, is not a disadvantage but rather an exciting opportunity for future research, so that throughout the book I have tried to direct the reader to these opportunities Of course, the magnitude of the scientific and technical challenges to be overcome in fully realizing the potential of MRI in food science should not be underestimated Food displays an enormous range of structural and compositional complexity The spatial heterogeneity in many foods can extend over distance scales ranging from the molecular to the macroscopic and contains hints of fractal geometry, self-similarity, and spatial chaos Moreover, there is an intimate relationship between this structural complexity and the dynamic changes associated with food processing and storage From the perspective of an NMR spectroscopist, having at his or her disposal an almost endless variety of pulse sequences for measuring spin density, relaxation, diffusion, flow, and high-resolution solid or liquid spectra, this structural and dynamic complexity presents a lifetime of research possibilities Fortunately, finding the motive to continue this research effort is not difficult Besides the purely scientific motivation, there are many compelling pragmatic reasons for seeking to maximize the potential of MRI in food science Providing safe and nutritious food for the ever-increasing human population is a daunting global challenge and one that has immediate importance to hungry sections of the world population The technical challenges in achieving this objective remain considerable, and include the optimization of all stages of food production This involves the procurement of the best crop strains by selection and genetic manipulation, optimization of the crop yield, and optimization of postharvest processing for improved food quality, safety, and energy efficiency It also entails the discovery of the best choice of storage and transportation conditions so as to be able to market safe, high-quality food as cheaply and efficiently as possible In writing this book I have had to speculate somewhat about future research possibilities and have not shied away from presenting topics that are still under development This entails the risk that the shortsightedness of my speculations will be revealed by future developments Nevertheless, if my speculations serve to inspire other research workers, this is a risk I gladly embrace To keep the book reasonably concise, I have had to assume that the reader is familiar with the basic ideas of NMR and MRI and have simply summarized some of the major concepts in the introductory chapter This, I trust, is not unreasonable since there are already many excellent textbooks on NMR and MRI, including the wonderful treatise entitled The Principles of Nuclear Magnetism by Abragam, who by delving into the depths of spin physics, appears to have encompassed most of the well-charted and it often seems, even uncharted oceans of NMR The principles of MRI have been explained lucidly in an excellent book by Callaghan entitled, The Principles of NMR Microscopy, and during the preparation of this book, all eight volumes of the encyclopedia of NMR and MRI have appeared in print I therefore refer the reader to these excellent works for details of pulse sequences and NMR concepts However, the emphasis of these texts is on the principles of NMR and MRI rather than their application to food science, so I not hesitate to offer this new book to the reader Throughout I have attempted to incorporate more recent MRI developments, such as STRAFI, gradient-echo imaging, and functional imaging, and point out their relevance in food science Key references to the original literature have been included, but these citations make no claim to completeness and I apologize beforehand to any researcher who feels aggrieved because his or her work is not mentioned They need only send me a reprint, and if there is ever a future edition, I will endeavor to amend my oversight Because "food" is such a diverse and complex collection of biological materials, some rational organization of this book is essential if the reader (and author) are not to get hopelessly confused The book is therefore divided into three parts according to the distance scale being probed by the MRI studies Part One deals with the macroscopic distance scale, Part Two with the microscopic, and Part Three with the (macro-)molecular, although the boundaries between these scales is necessarily somewhat blurred At each distance scale I have attempted to classify each MRI study according to the dynamic changes being investigated This reflects my belief that using MRI simply to look at a static, unchanging food structure is to underuse the technology and risks competition with other techniques that can provide far better spatial resolution, such as optical and electron microscopy, or in the case of the macroscopic distance scale, with a knife and the human eye! Having organized the material by exploiting the space and time dimensions, I have, wherever appropriate, included mathematical models of the dynamic process being imaged, because, ultimately, most of the processes being imaged find their explanation in the (bio-)physics of heat, mass, and momentum transport This book should be of value to all food scientists and technologists who seek a better understanding of the present and future role of MRI in their discipline, and conversely, to NMR and MRI specialists who wish to explore the potential of this wonderful technique in the arena of foods Chapters 7, Whole Plant Functional Imaging, and 9, Macroimaging and NMR Microscopy, will also be of interest to plant physiologists and Chapter 4, Flow Imaging and Food Rheology, to fluid hydrodynamicists BRIAN HILLS Norwich, United Kingdom Contents Preface vii Part Macroscopic Distance Scale 1 Résumé of MRI Methodology 1.1 Introduction 1.2 Phase Coherence and Fourier Conjugate Variables in NMR Higher-Order Combinations of Fourier Conjugates 10 1.4 Modulus and Phase Images 14 1.5 Statistical Aspects of MRI 15 1.6 Fourier Transformation of the RadioFrequency Waveform: Slice Selection 17 Fourier Transformation of the Gradient Modulation: Motional Spectra and FD-MG-NMR 20 Spin and Gradient Echoes: Contrast in kSpace Imaging 22 Fast Imaging Methods 26 1.10 Chemical Shift Imaging 31 MRI and Food Processing: Mapping Mass Transport and Phase Behavior 35 1.3 1.7 1.8 1.9 2.1 Introduction 35 2.2 MRI and Process Optimization 36 2.3 Drying 38 2.4 Rehydration 55 2.5 Freezing and Freeze-Thawing 60 This page has been reformatted by Knovel to provide easier navigation iii iv Contents 2.6 Freeze-Drying 68 2.7 MRI and Miscellaneous Processing Operations 73 MRI and New Processing Technologies 74 MRI and Food Processing: Mapping Temperature and Quality 76 2.8 3.1 MRI and Temperature Mapping 76 3.2 MRI and Food Quality Factors 87 Flow Imaging and Food Rheology 102 4.1 Introduction 102 4.2 Principles of Flow Imaging 103 4.3 Basic Rheology 105 4.4 MRI and Tube Viscometers 108 4.5 MRI and Rotational Viscometers 111 4.6 Solid Suspensions 114 4.7 MRI and Computational Fluid Dynamics 116 4.8 Flow and Quality Assurance 117 4.9 Extrusion 118 4.10 Flow in Bioreactors 121 4.11 Mixing and Turbulence 123 4.12 Velocity Distributions 127 4.13 Displacement Imaging of Complex Flows 128 Solid-Imaging Techniques 134 5.1 Solid Linewidths 134 5.2 Solid Imaging and Food Science 135 5.3 Stray-Field Imaging 137 5.4 Phase-Encoding Solid Imaging 143 5.5 Sinusoidal Gradient-Echo Imaging 148 On-Line MRI for Process Control and Quality Assurance 152 6.1 Introduction 152 6.2 Constraints Imposed by Spin Physics 153 This page has been reformatted by Knovel to provide easier navigation Contents v 6.3 Nonspatially Resolved On-Line NMR 156 6.4 Spatially Resolved On-Line NMR 157 Whole-Plant Functional Imaging 160 7.1 Introduction 160 7.2 Functional Root Imaging 162 7.3 Transport in Intact Plants 162 7.4 Functional Brain Imaging and Consumer Science 164 Unconventional MRI Techniques 166 8.1 Introduction 166 8.2 Rotating-Frame Imaging 166 8.3 Multinuclear Imaging 170 8.4 NMR Force Microscopy 173 Part Microscopic Distance Scale 177 Microimaging and NMR Microscopy 179 9.1 Introduction 179 9.2 Applications of NMR Microimaging to Cellular Tissue 179 9.3 Microimaging Processing Effects in Tissue 188 9.4 Intracellular Microimaging 196 9.5 Microscopic Transport Models for Cellular Tissue 202 10 Microstructure and Relaxometry 205 10.1 Introduction 205 10.2 Water Proton Relaxation in Microscopically Heterogeneous Systems 205 10.3 Relaxation Effects of Internal Field Gradients 234 10.4 Microstructure and the Microbial Safety of Foods 239 11 Probing Microstructure with Diffusion 242 11.1 Introduction 242 11.2 Diffusion-Weighted Pulse Sequences 242 This page has been reformatted by Knovel to provide easier navigation vi Contents 11.3 Diffusion Propagator and Microstructure 244 11.4 Susceptibility Effects on Diffusion Measurements 251 11.5 Coupled Relaxation and Diffusion 252 11.6 Diffusion in Multicompartment Systems 253 11.7 Anomalous Diffusion 254 11.8 Microstructure-Weighted k-Space Imaging 255 11.9 Constant-Gradient CPMG and StimulatedEcho Studies 256 11.10 Microstructural Determination in Food Matrices 259 Part Molecular Distance Scale 265 12 Molecular Origins of Relaxation Contrast 267 12.1 Introduction 267 12.2 Relaxation in a Single Proton Pool 267 12.3 Water Proton Transverse Relaxation 270 12.4 Water Proton Longitudinal Relaxation 284 12.5 Water Proton Rotating-Frame Relaxation 288 12.6 Low-Water-Content Homogeneous Systems 290 Appendix A 298 Appendix B 299 13 Molecular Factors Influencing the Diffusion and Transfer of Water Magnetization 301 13.1 Introduction 301 13.2 Molecular Factors Influencing Diffusion Contrast 301 13.3 Magnetization Transfer 305 13.4 Multistate Theory of Water Relations in Foods 308 References 316 Index 334 This page has been reformatted by Knovel to provide easier navigation PART ONE MACROSCOPIC DISTANCE SCALE 342 Index terms Links Fruit (Continued) blueberry 188 cherries 157 gooseberry 197 grape 183 kiwi 197 mango 192 papaya 194 pear 203 and quality factors 197 strawberry 183 Frying 74 FTIR 292 Functional imaging 160 Funicular state 226 G Gelatin gel 292 gel microstructure 262 Gellan gum, microstructure Gelling agents 191 96 raspberry thickening agent 186 97 261 97 Gels amylopectin 294 carrageenan 282 dextran 261 gelatin, see Gelatin gellan gum 261 guar gum 261 low water content 292 microstructure by diffusion 259 This page has been reformatted by Knovel to provide easier navigation 185 343 Index terms Links Gels (Continued) protein, microstructure 262 proton exchange in 279 starch 261 294 Glassy state and case hardening and diffusion and rehydration 40 304 56 and starch retrogradation 294 water dynamics in 298 Glucose 273 Glutenin 292 290 Goldman-Shen and glassy states 298 and pore connectivity 225 pulse sequence 207 Gooseberry 197 Gradient echo 22 Gradient modulation 20 Grain, see Cereals Grapes 183 Guar gum, microstructure 261 H Hahn echo 23 See also Spin echo Hartmann-Hahn cross polarization 172 Heisenberg uncertainty principle Herschel-Bulkey model High electric field pulsing (HELP) Histology, of plants 108 74 180 This page has been reformatted by Knovel to provide easier navigation 191 344 Index terms Links Hydration multilayer water 292 and multistate theory 308 preferential 296 I Ice crystal size distribution 73 Image analysis 181 Image contrast and microstructure 256 234 In-line MRI, see On-line MRI Infection (in strawberries) 182 Intercellular air gaps, in apple 238 Internal field gradients 234 See also Susceptibility effects Intracellular microimaging Inverse Abel transform 180 196 29 61 43 110 J JEPHI 146 K k-wavevector Kiwi 197 L Laminaran 279 Lipids See also Fat in avocado 157 in chocolate 87 in coffee beans 193 in emulsions 90 263 in meat 96 156 This page has been reformatted by Knovel to provide easier navigation 345 Index terms Liver tissue, and anomalous diffusion Links 255 Longitudinal relaxation, see T1 Lorentzian lineshape M Magic angle spin locking 290 Magic echoes 146 Magnetization density 207 Magnetization transfer 305 Magnetization transfer contrast imaging 305 Maize 163 Maltose glasses 298 Mango 192 183 Maximum entropy method (MEM) 61 210 Mayonnaise 92 Meat 94 156 Meerwall-Ferguson model 185 260 Membrane permeability 185 208 231 MEPSI 146 Methanol 270 Microbial safety, and microstructure 239 314 Microbial spoilage, and relaxometry 239 314 Microimaging 179 Microstructure and diffusometry 242 and drying 216 and freezing 218 and relaxometry 205 and surface relaxation 219 Milk fat 88 Milk 92 This page has been reformatted by Knovel to provide easier navigation 346 Index terms Links Millet 163 Mixing 124 Modulus and phase images 14 Moisture distribution and drying 38 in process optimization 37 and rehydration 56 Monte Carlo method 204 210 Motional narrowing 268 Multinuclear imaging 170 N Neurons 200 New crop syndrome 190 Newtonian fluids 107 NMR force microscope 173 NMR microscopy 179 Nucleation, in colloids 90 O Obstruction effects, on diffusion 302 Olives, pitting 157 On-line MRI 152 of avocado oil content 157 of fat content in meat 156 inside-out magnets 155 and pitting cherries 157 polarization 153 Onion 197 This page has been reformatted by Knovel to provide easier navigation 208 213 347 Index terms Links P Papaya 194 Parenchyma tissue 180 Pasta 43 55 61 Patterson functions 17 Pear, thermal conductivity of 203 Pendular state 226 Percolation backbone 130 Percolation cluster effects on diffusion 303 Permeability coefficient, in gels 261 Permeability, see Membrane permeability Phase coherence Phase-encoding solid imaging (PSI) 143 Plant development 160 180 See also Functional imaging of plants Plant tissue, relaxometry of 230 Plasmalemma membrane 230 Plasmolysis 198 Poiseuille flow 108 Pore connectivity 219 225 248 Pore equilibration 249 Pore geometry 252 Pore size distribution 219 Pore size, in gels 260 Potato drying 46 freeze-drying 70 freezing rehydration 233 60 This page has been reformatted by Knovel to provide easier navigation 220 237 348 Index terms Links Potato (Continued) temperature mapping Power law fluids 80 107 Processing curing of meat and diffusometry drying extrusion 95 262 38 118 and food quality 37 freeze-drying 68 freezing 60 miscellaneous processing operations 73 and moisture distribution 37 and new processing technologies 74 and parameter maps 36 process optimization 36 rehydration 55 and temperature mapping 37 Protein aerogels 262 bovine serum albumin 301 cereal 292 fibrin gel 287 gelatin 281 292 301 globular 281 307 Proton exchange in biopolymer systems 277 in carrageenan gels 283 in carrot tissue 273 and freezing/drying 275 in methanol-water mixtures 270 in monosaccharide solutions 273 This page has been reformatted by Knovel to provide easier navigation 277 349 Index terms Proton exchange-cross relaxation theory Links 284 PSI, see Solid imaging Pulsed gradient stimulated echo pulse sequence 244 Q q-space microscopy 243 246 Quality factors 37 181 87 29 55 43 61 R Radial imaging see also Fast imaging Radiofrequency pulses 17 Raspberry 197 Rayleigh-Benard convection 105 Recycle delay 23 Rehydration beans 59 cereal grains 59 glassy-state rehydration kinetics 56 pasta 55 plant tissue 189 potato 60 and radial imaging 55 starch 55 Relaxation contrast, molecular origins of 267 Relaxation, see T2, T1, or T1p coupled to diffusion 252 in fractal systems 239 in low water content systems 290 Relaxometry of plant tissue 230 This page has been reformatted by Knovel to provide easier navigation 350 Index terms Links Resolution, diffusion limited 209 Restricted diffusion and susceptibility effects 235 Retrogradation imaging 99 and PSI 145 theory of 294 Rheology 102 105 of butter 113 and computational fluid dynamics 116 of cornflower 111 of egg white 111 and flow curves 106 of particulate suspensions 114 of pureed fruit 117 and shear-induced particle migration 114 and shear-induced transitions 113 of tomato juice 111 of xanthan gum 109 113 108 113 Rheomalaxis Ripening of barley seeds 184 of cherries 186 degree of 181 of strawberries 185 of tomatoes 186 in wheat grains 163 Root imaging 162 Rotating frame chemical shift imaging 169 Rotating frame imaging 166 Rotating frame multipulse imaging 169 Rotating frame relaxation, see T1p Rotational viscometer 111 This page has been reformatted by Knovel to provide easier navigation 112 351 Index terms Links S Salad cream 92 Salmonella typhimurium 240 SAXS 292 Schleroglucan gels 279 Seed viability 180 Seeding algorithms 182 Selective excitation, in contrast imaging 305 SEPSI 146 Shear thickening 107 Shear thinning 107 Shear viscosity, and diffusion 303 Shear-induced particle migration 114 Shear-induced phase transitions 113 Shelf-life, and microbial safety 239 Side-line MRI, see On-line MRI Single cell imaging 198 Single point imaging in the rotating frame 168 Single point imaging, See Solid imaging Sinusoidal gradient-echo imaging Slice selection 148 17 Slip boundary conditions 108 SLOAFI 169 23 Sodium ( Na) imaging 171 Soil imaging 162 Sol-gel transition 281 Solid imaging and baking 136 and cryopreservation 136 and glass transitions 137 and MAS 135 multipulse line narrowing 135 This page has been reformatted by Knovel to provide easier navigation 315 352 Index terms Links Solid imaging (Continued) PSI 143 sinusoidal gradient-echo imaging 148 STRAFI 136 Solid-liquid ratios 137 87 Sorption isotherm multistate theory of 310 and preferential hydration 296 and relaxometry 310 Soybeans 189 Spaghetti 43 61 Specific heat 65 Spectral density 268 Spectrum Spin echo 22 Spin locking Spin warp imaging 55 167 22 77 Staling, see Retrogradation Stalk end rot 183 Starch gel microstructure 261 relaxometry of 227 retrogradation 99 thickening agent 97 Starling flow 121 Static structure factor 246 Statistical aspects of MRI 15 Stejskal-Tanner pulse sequence 242 Stem imaging 160 Stick boundary conditions 108 Stimulated echo and displacement imaging 132 This page has been reformatted by Knovel to provide easier navigation 294 353 Index terms Stokes law STRAFI Links 92 303 136 See also Solid imaging Strawberries, ripening of Stress cracking 183 185 73 Stretched exponentials 254 Surface coils 157 161 Surface heat transfer 65 86 Surface mass transfer 86 Surface relaxation 207 220 Surface rendering 182 Surface-to-volume ratio 250 Susceptibility effects 23 and diffusometry 251 in plants 181 and pore geometry 221 and relaxometry 235 Susceptibility matching Swelling pressure 219 257 197 57 T T1 T1-null method frequency dispersions image contrast proton exchange-cross relaxation theory of 32 286 24 284 relaxation time 23 and temperature mapping 80 T1p frequency dispersions 288 and magic angle spin locking 290 proton exchange-cross relaxation theory of 289 This page has been reformatted by Knovel to provide easier navigation 263 354 Index terms Links T1p (Continued) rotating frame relaxation in porous media 221 rotating frame relaxation time 167 268 32 263 T1-null method T1-null microscopy 188 T2 frequency dispersions image contrast 212 271 24 214 mapping in plants 181 multiple exponential relaxation 210 and radial imaging 55 and rehydration 55 relaxation time wavevector dependence of Taylor-Couette flow 23 257 128 Temperature and FLASH 77 mapping by chemical shift 84 mapping by diffusion 77 mapping by T1 80 and process optimization 37 Tempering, of cereal grains 190 Ten Brinke equation 295 Thermal conductivity 65 203 192 194 Thermal processing of plant tissue Thickening agents Thixotropy 97 113 Thomas-Windle rehydration model 56 Time reversed FID 27 Tobacco 163 Tomato 186 Tonoplast 230 This page has been reformatted by Knovel to provide easier navigation 231 355 Index terms Torque plasticorder Links 118 Transverse relaxation See T2 Tube viscometer 108 Turbulence 126 Two-dimensional spectroscopy 10 U Unit-cell model of pore connectivity 220 V Vacuoles 230 Vascular tissue 180 Vegetables carrot 82 corn 49 263 courgette 214 onion 197 potato 46 60 70 232 80 quality factors in 96 relaxometry in 230 tomato 186 Velocity distributions Velocity exchange spectroscopy, VEXSY 127 13 Viscoelastic fluids 113 Voronoi tessellation 202 W Water, see Moisture distribution and Processing Water activity 311 See also Sorption isotherm Water relations, multistate theory of 308 This page has been reformatted by Knovel to provide easier navigation 231 356 Index terms Links Wheat grains 163 Whole plant functional imaging 160 Wiener-Khintin theorem Williams-Landel-Ferry (WLF) equation 16 295 303 109 113 X Xanthangum Z Z-spectroscopy 308 This page has been reformatted by Knovel to provide easier navigation ... Solid Linewidths 134 5.2 Solid Imaging and Food Science 135 5.3 Stray-Field Imaging 137 5.4 Phase-Encoding Solid Imaging 143 5.5 Sinusoidal Gradient-Echo Imaging 148 On-Line... 194 9Magnetic resonance imaging in food science / Brian Hills p cm "A Wiley-Interscience publication." Includes bibliographical references and index ISBN 0-471-17087-9 (cloth : alk paper) Food Analysis Magnetic. .. shall see in Section 5.5 that sinusoidally varying gradients have an important role to play in imaging solids Velocity phase-encoding imaging (or flow imaging) is seen, by the derivation in equations