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SENSORY EVALUATION OF FOOD PRINCIPLES AND PRACTICES
HARRY T. LAWLESS CORNELL UNIVERSITY
HILDEGARDE HEYMANN UNIVERSITY OF MISSOURI
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
The author has made every effort to ensure the accuracy ofthe information herein. However, appropriate information sources should be consulted, especially for new or unfamiliar procedures. lt is the responsibility of every practitioner to evaluate the appropriateness of a particular opinion in in the context of actual clinical situations and with due considerations to new developments. The author, editors, and the publisher cannot be
held responsible for any typographical or other errors found in this book.
Cover design: Will T. Comellas, A.G.T. Inc.
Library of Congress Cataloging-in-Publication Data
Sensory evaluation offood: principles and practices I Lawless, Harry T. and Heymann, Hildegarde. p. cm. (Food science text series)
Includes bibliographical references and index.
ISBN 978-1-4615-7845-1 ISBN 978-1-4615-7843-7 (eBook) DOI 10.1007/978-1-4615-7843-7
I. Food-Sensory evaluation. I. Heymann, Hildegarde. li. Title. lll. Series. TX546.L38 1998
664" .07-dc21
Library of Congress Cataloging-in-Publication Data
A C.I.P. Catalogue record for this book is available from the Library ofCongress.
Copyright© 1998, 1999 by Springer Science+Business Media New York Original1y published by K1uwer Academic/P1enum Publishers, New York in 1999
Softcover reprint of the bardeover 1st edition 1999
All rights reserved. No part of this work may be reproduced, stored in a retrieval system, or transmitred in
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without the written permission from the Publisher, with the exception of any material supplied specifically for
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work.
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Printedon acid-free paper.
5678910
CONTENTS
Preface xii
CHAPTER 1 INTRODUCTION AND 0VERVIEW 1
Definition and Focus 1 Historical Landmarks and the Three Classes of
Test Methods 6 The Central Dogma-Analytic vs. Hedenie Tests 13 Applications: Why Collect Sensory Data? 17 Differences from Other Research Methods 21 Summary and Conclusions 24 Raterences 26
CHAPTER 2 · PHYSIOLOGICAL AND PSYCHOLOGICAL FOUNDATIONS OF SENSORY FUNCTION 28 Classical Sensory Testing and
Psychophysical Methods 28 Anatomy, Physiology, Functions of Taste 39 Anatomy, Physiology, and Functions of Smell 50
vii
yjjj CONTENTS
The Trigeminal Flavor Senses 61 Sensory lnteractions 67 Summary and Conclusions 73 References 74
CHAPTER 3 PRINCIPLES OF Gooo PRACTICE 83 Sensory Testing Environment 85 Test Protocol Considerations 91 Tabulations and Analysis 112 Conclusion 113 References 114
CHAPTER 4 DISCRIMINATION TESTING 116 Types of Discrimination Tests 117 Reputed Strengths and Weaknesses 128 Data Analyses 129 Binomial Distributions and Tables 129 lssues 133 Common Mistakes Made in the Interpretation of
Discrimination Tests 138 References 138
CHAPTER 5 DISCRIMINATION THEORIES AND
ÄDVANCED TOPICS 140 The Theory of Signal Detection 142 Thurstonian Models for Choice Tests 151 Signal Detection Applied to
Feods Using the R-lndex 157 Guessing Models and Discriminator Theory 159 Estimating Sampie Size in Discrimination Tests 164 The Test for Significant Similarity 166 Conclusions: Signal Detection, Thurstonian, and
Guessing Models for Discrimination 170 References 171
CONTENTS ix
CHAPTER 6 MEASUREMENT OF
SENSORY THRESHOLDS 173 lntroduction: The Appeal of Threshold Concepts 173
Empirical Thresholds: Concepts,
lssues, and Problems 176
Practical Methods: Ascending Forced-Choice 181
Alternative Approaches: Rated Difference,
Adaptive Procedures, Signal Detection 191
Dilution Analysis and Odor Units 198
Conclusions 202
References 204
CHAPTER 7 SCALING 208 Practical Applications of Numbers to
Sensory Phenomena 208
Common Methods of Scaling 216
Same Variations-Other Scaling Techniques 230
Comparing Methods: What ls a Good Scale? 241
Practical Guidelines 246
Conclusions 253
Postscript: The 9-Point Scale Revisited-
How They Did lt 254
References 259
CHAPTER 8 TIME-INTENSITY METHODS 265 The Approach and lts Advantages 265 History of lime-lntensity Methods 267
Examples and Applications 270
Data Analysis lssues 283
Problems and Remaining Questions 290
Conclusions 294
References 296
CHAPTER 9 CONTEXT EFFECTS AND
BIASES IN SENSORY JUDGMENT 301 Relative Nature of Rating Scales 301
X CONTENTS
CHAPTER 10
CHAPTER 11
CHAPTER 12
Simple Cantrast and Adaptation Level 306
Range Frequency Theory 315
Poulton's Classification of Biases 319
Halo Effects and False Enhancement from
Response Restrietion 326
Classical Psychological Errors 330
Antidotes 332
Conclusions 335
References 337
0ESCRIPTIVE ANALYSIS 341 Uses of Descriptive Analysis 341
Language and Descriptive Analysis 342
Descriptive Analysis Techniques 346
References 372
TEXTURE EVALUATION 379 Texture Defined 379
Auditory, Visual, and Tactile Texture 383
Sensory Texture Measurements 392
Texture Profile Analysis 392
Instrumental Texture Measurements and
Sensory Cerrelations 395
Conclusions 399
References 400
COLOR AND ÄPPEARANCE 406 What ls Color? 408
Vision 410
Measurement of Appearance and Color Attributes 411
Instrumental Color Measurement 417
Conclusions 428
References 428
CHAPTER 13 ACCEPTANCE AND
PREFERENCE TESTING
Consumer Sensory Evaluation
430 430
CONTENTS xi
Preference Tests 431
Acceptance Tests 450
Variations on Acceptance 457
Oualifying Panelists 470
Conclusions 474
References 475
CHAPTER 14 CONSUMER fiELD TESTS AND 0UESTIONNAIRE DESIGN 480 Objectives: Sensory Testing versus
Concept Testing 480
Testing Scenarios: Central Location. Home Use 484
Practical Conduct of Home Use Tests 489
lnteracting with Field Services 492
Ouestionnaire Design 499
1 0 Rules of Thumb for Question Construction 503
Conclusions 511
References 513
Sampie Consumer Test Ouestionnaire 514
CHAPTER 15 QuALITATIVE CONSUMER RESEARCH METHODS 519 lntroduction 519
Characteristics of Focus Groups 523
Using Focus Groups in Sensory Evaluation 526
Conducting Focus Group Studies 528
lssues in Moderating 533
Analysis and Reporting 536
Alternative Procedures and Variations
of the Group Interview 541
Conclusions 544
References 546
CHAPTER 16 5ENSORY EVALUATION IN 0UALITY CONTROL 548 Objectives and Challenges 548
Program Development and Management lssues 552
xii CoNTENTS
Features of a Sensory OC System 555 Methods for Sensory OC 558 lmportance of Good Practice 574
Summary and Conclusions 577
Postscript: Whither Excellence? 578
References 582
CHAPTER 17 DATA RELATIONSHIPS AND MULTIVARIATE ÄPPLICATIONS 585 lntroduction 585 Overview of Multivariate Statistical Techniques 586 Relating Consumer and Descriptive Data 596 Conclusions 598 References 598
CHAPTER 18 STRATEGIC RESEARCH 602 lntroduction 602 The Category Review 605 Perceptual Mapping and
Opportunity ldentification 606
Consumer Contact 618 Conclusions 620 References 620
CHAPTER 19 0VERVIEW OF SENSORY PRINCIPLES AND PRACTICES 623 General Considerations in Sensory Testing 623 50 (or so) Rules of Thumb for Sensory Testing 625 Flowcharts for Sensory Evaluation Procedures 630 Sensory Evaluation in lndustrial and
Academic Research 640
Conclusions 644
References 646
CoNTENTS xiii
APPENDIX I BASIC STATISTICAL CONCEPTS FOR SENSORY EVALUATION 647 lntroduction 647 Basic Statistical Concepts 650 Hypothesis Testing and Statisticallnterence 658 Variations ot the t-Test 667 Summary: Statistical Hypothesis Testing 674 Postscript: What p-Values Signity and
What They Don't 675 Raterences 678
APPENDIX II NONPARAMETRie AND 81NOMIAL-8ASED 5TATISTICAL METHODS 679 lntroduction to the Nonparametic Tests 679 Binomiai-Based Tests on Proportions 681 Chi-Square 686 McNamar Test 688 Usetul Rank Order Tests 691 Mann Whitney U Test 692 Ranked Data with More Than Two Sampies 694 The Spearman Rank Order Cerrelation 697 Conclusions 698 Raterences 699
APPENDIX 111 ANALYSIS OF VARIANCE 701 lntroduction 701 BasicAnalysis of Variance,Rationale, and
Worked Example 702 An Interlude tor the Contused 707 Multiple Factor Analysis of Variance and the
Concept ot a Linear Model 708 Analysis ot Variance trom Complete Block
Designs and Partitioning ot Panelist Variance 712 Sensory Panelists: Fixed or Randern Ettects 719 Planned Camparisens Between Means
Following ANOVA 722 Two-Way ANOVA trom Randomized
Complete Block Designs 725 Split-Piot or Between-Groups (Nested) Designs 731
xiv CoNTENTS
Epilogue: Other Techniques 735 References 737
APPENDIX IV CORRELATION, REGRESSION, AND
MEASURES OF AsseclATtoN 738 lntroduction 738 Cerrelation 741 Linear Regression 745 Multiple Linear Regression 749 Other Measures of Association 749 References 753
APPENDIX V 5TATISTICAL POWER AND
TEST 5ENSITIVITY 754 I ntroduction 754 Factcrs Affecting the Power of Statistical Tests 757 Worked Examples 767 Power in Simple Difference and Preference Tests 771 Summary and Conclusions 778 References 781
APPENDIX VI 5TATISTICAL TABLES 783
APPENDIX VII BINOMIAL PROBABILITIES FROM
01SCRIMINATION TESTS 795
APPENDIX VIII COMPLETE BLOCK ANALYSIS
OF VARIANCE 797
GLOSSARY OF TERMS 803
INDEX 819
PREFACE
The field of sensory evaluation has matured in the last half century to become a recognized discipline in the food and consumer sciences and an important part of the foods and consumer products industries. Sensory professionals enjoy widespread recognition for the important services they provide in new product development, basic research, ingredient and process modification, cost reduction, quality maintenance, and product optimization. These services enhance the informational support for management decisions, lowering the risk that accompanies the decision-making process. From the consumers' perspective, a sensory testing program in a food or consumer products company helps ensure that products reach the market with not only good concepts but also with desirable sensory attributes that meet their expectations.
Sensory professionals have advanced weil beyond the stage when they were simply called on to execute "taste" tests and to provide statistical summaries of results. They are now frequently asked to partleipale in the decision process itself, to draw reasoned conclusions based on data, and to make recommendations. They arealso expected tobe weil versed in an increasingly sophisticated battery of test methods and statistical procedures, including multivariate analyses. As always, sensory professionals also need to understand people, for people are the measuring instruments that provide the basic sensory data. People are notoriously variable and difficult to calibrate, presenting the sensory specialist with many additional
XV
:xvi PREFACE
measurement problems that are not present in instrumental methods. Sensory science is thus a challenging discipline, every bit as complex and intellectually demanding as other phases offood analysis, food chemistry, and food engineering.
As instructors in sensory evaluation at the university Ievel, we have long feit the need for a comprehensive book on sensory evaluation that could serve as a text for our courses as weil as a reference work for sensory practitioners. Most recent books on sensory evaluation were aimed at serving an audience of practicing sensory scientists. Using such books for university-level courses left. us and other instructors in sensory science (as weil as many students) somewhat frustrated. Furthermore, there has not been a truly comprehensive text since the 1965 publication of Principles oj Sensory Evaluation oj Food by Maynard Amerine, RoseMarie Pangborn, and Edward Roessler. The field of sensory evaluation has seen many developments since that Iandmark text. So with encouragement from other teachers of sensory evaluation, we undertook this work.
We recognize that teachers of sensory evaluation work in a wide range of academic programs with different course orientations and different degrees of depth in their treatment ofthe material. Sensory evaluation may be taught as an entire course or even a multicourse sequence in some programs, while in others it may only be one part of a more general course such as food analysis. For that reason we have arranged the book in chapters, and the chapters in sections, so that instructors can choose to omit sections that they consider more advanced or involved than their students require. For example, Chapter 4 deals with the basics of discrimination testing, while Chapter 5 is devoted to more complex modeling of discrimination. Instructors who want to stress only the fundamentals can assign Chapter 4 alone. Instructors teaching a more advanced-level course may assign both Chapters 4 and 5.
As in the book by Amerine, Pangborn, and Roessler, we have included a section on statistics at the end of the book so as not to digress unnecessarily during the treatment of experimental procedures with full explanations of statistical analyses. We have also added some worked examples in special "boxes" within selected chapters. In the appendices, separate chapters are given on focused topics, so that a student unfamiliar with, say, analysis of variance or nonparametric statistics can go directly to that chapter for information and worked examples. Our goal has been to make statistics understandable through the use of realistic but simple examples.
We are mindful of our predecessors in the field, who brought the science of sensory evaluation from the rudimentary tastings of test kitchens forward into the realm of behavioral experimentation. Without these pioneers and founders, we could not conceive of such a work or even the exis-
PREFACE xvii
tence of the field in its present form. Whether personally known to us or only by their work and publications, they are our mentors. We gratefully acknowledge the assistance and input of many of our colleagues and students in the development of this book, including:
John Horne, Bue Young Imm, Mary Eggeman, Denise Taylor, Doug Holt, JoAnn Lewis, Jackie Craig, Kathy Lyman, Joel Sidel, Edgar Chambers, IV, Gail Civille, and Terry Fowler.
However, any flaws that remain are not their responsibility but ours. Finally we acknowledge with thanks the support of our families during the task of writing this book.
Harry T. Lawless HUdegarde Heymann