SENSORY EVALUATION OF FOOD PRINCIPLES AND PRACTICES

SENSORY EVALUATION OF FOOD PRINCIPLES AND PRACTICES

HARRY T. lAWLESS CORNELL UNIVERSITY

HILDEGARDE HEYMANN UNIVERSITY OF MISSOURI

SPRINGER SCIENCE+BUSINESS MEDIA, LLC 1999

The author has made every effort to ensure the accuracy of the information herein. However, appropriate information sources should be consulted, especially for new or unfamiliar procedures. It 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.

Aspen Publishers, Inc., is not affiliated with the American Society of Parenteral and Enteral Nutrition Cover design: Will T. Comellas, A.G.T. Inc.

Library of Congress Cataloging-in-Publication Data

Sensory evaluation of food: principles and practices I Lawless, Harry T. and Heymann, Hildegarde. p. em. (Food science text series)

Includes bibliographical references and index.

ISBN 978-1-4757-6499-4 ISBN 978-1-4419-7452-5 (eBook) DOI 10.1007/978-1-4419-7452-5

1. Food-Sensory evaluation. I. Heymann, Hildegarde. II. Title. Ill. Series. TX546.L38 1998

664'.07-dc21 97-3311

CIP

Copyright© 1998, 1999 by Springer Science+ Business Media New York Originally published by Aspen Publishers, Inc. in 1999

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Editorial Services: Ruth Bloom Library of Congress Catalog Card Number: 97-3311

ISBN 978-1-4757-6499-4

4 5

To

Dave Peryam

Pickle and Chutney

Thanks,

JoAnna Turtletaub

CONTENTS

Preface xii

CHAPTER 1 INTRODUCTION AND OVERVIEW 1

Definition and Focus

Historical Landmarks and the Three Classes of

Test Methods 6

The Central Dogma-Analytic vs. Hedonic Tests 13 Applications: Why Collect Sensory Data? 17 Differences from Other Research Methods 21 Summary and Conclusions 24 References 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

viii CONTENTS

The Trigeminal Flavor Senses 61 Sensory Interactions 67 Summary and Conclusions 73 References 74

CHAPTER 3 PRINCIPLES OF GOOD 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 Issues 133 Common Mistakes Made in the Interpretation of

Discrimination Tests 138 References 138

CHAPTER 5 DISCRIMINATION THEORIES AND

ADVANCED TOPICS 140 The Theory of Signal Detection 142 Thurstonian Models for Choice Tests 151 Signal Detection Applied to

Foods Using the R-lndex 157 Guessing Models and Discriminator Theory 159 Estimating Sample 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 Introduction: The Appeal of Threshold Concepts 173

Empirical Thresholds: Concepts,

Issues, 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

Some Variations-Other Scaling Techniques 230

Comparing Methods: What Is a Good Scale? 241

Practical Guidelines 246

Conclusions 253

Postscript: The 9-Point Scale Revisited-

How They Did It 254

References 259

CHAPTER 8 TIME-INTENSITY METHODS 265 The Approach and Its Advantages 265

History of Time-Intensity Methods 267

Examples and Applications 270

Data Analysis Issues 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 Contrast and Adaptation Level 306

Range Frequency Theory 315

Poulton's Classification of Biases 319

Halo Effects and False Enhancement from

Response Restriction 326

Classical Psychological Errors 330

Antidotes 332

Conclusions 335

References 337

DESCRIPTIVE 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 Correlations 395

Conclusions 399 References 400

COLOR AND APPEARANCE 406 What Is 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

Qualifying Panelists 470

Conclusions 474

References 475

CHAPTER 14 CONSUMER FIELD TESTS AND

QuESTIONNAIRE DESIGN 480 Objectives: Sensory Testing versus

Concept Testing 480

Testing Scenarios: Central Location, Home Use 484

Practical Conduct of Home Use Tests 489

Interacting with Field Services 492

Questionnaire Design 499

1 0 Rules of Thumb for Question Construction 503

Conclusions 511

References 513

Sample Consumer Test Questionnaire 514

CHAPTER 15 QuALITATIVE CONSUMER RESEARCH METHODS 519 Introduction 519

Characteristics of Focus Groups 523

Using Focus Groups in Sensory Evaluation 526

Conducting Focus Group Studies 528

Issues in Moderating 533

Analysis and Reporting 536

Alternative Procedures and Variations

of the Group Interview 541

Conclusions 544

References 546

CHAPTER 16 SENSORY EVALUATION IN QuALITY CONTROL 548 Objectives and Challenges 548

Program Development and Management Issues 552

xii CONTENTS

Features of a Sensory OC System 555

Methods for Sensory QC 558

Importance of Good Practice 574

Summary and Conclusions 577

Postscript Whither Excellence? 578

References 582

CHAPTER 17 DATA RELATIONSHIPS AND MULTIVARIATE APPLICATIONS 585 Introduction 585

Overview of Multivariate Statistical Techniques 586

Relating Consumer and Descriptive Data 596

Conclusions 598

References 598

CHAPTER 18 STRATEGIC RESEARCH 602 Introduction 602

The Category Review 605

Perceptual Mapping and

Opportunity Identification 606

Consumer Contact 618

Conclusions 620

References 620

CHAPTER 19 OVERVIEW 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 Industrial and

Academic Research 640

Conclusions 644

References 646

CONTENTS xiii

APPENDIX I BASIC STATISTICAL CONCEPTS FOR SENSORY EVALUATION 647 Introduction 647 Basic Statistical Concepts 650 Hypothesis Testing and Statistical Inference 658 Variations of the t-Test 667 Summary: Statistical Hypothesis Testing 674 Postscript: What p-Values Signify and

What They Don't 675 References 678

APPENDIX II NONPARAMETRIC AND BINOMIAL-BASED STATISTICAL METHODS 679 Introduction to the Nonparametic Tests 679 Binomial-Based Tests on Proportions 681 Chi-Square 686 McNamar Test 688 Useful Rank Order Tests 691 Mann Whitney U Test 692 Ranked Data with More Than Two Samples 694 The Spearman Rank Order Correlation 697 Conclusions 698 References 699

APPENDIX Ill ANALYSIS OF VARIANCE 701 Introduction 701 Basic Analysis of Variance, Rationale, and

Worked Example 702 An Interlude for the Confused 707 Multiple Factor Analysis of Variance and the

Concept of a Linear Model 708 Analysis of Variance from Complete Block

Designs and Partitioning of Panelist Variance 712 Sensory Panelists: Fixed or Random Effects 719 Planned Comparisons Between Means

Following ANOVA 722 Two-Way ANOVA from Randomized

Complete Block Designs 725 Split-Plot or Between-Groups (Nested) Designs 731

xiv CONTENTS

Epilogue: Other Techniques 735 References 737

APPENDIX IV CORRELATION, REGRESSION, AND

MEASURES OF AsSOCIATION 738 Introduction 738 Correlation 741 Linear Regression 745 Multiple Linear Regression 749 Other Measures of Association 749 References 753

APPENDIX V STATISTICAL POWER AND

TEST SENSITIVITY 754 Introduction 754 Factors 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 STATISTICAL TABLES 783

APPENDIX VII BINOMIAL PROBABILITIES FROM

DISCRIMINATION 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 well 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 participate in the decision process itself, to draw reasoned conclusions based on data, and to make recommendations. They are also expected to be well 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 of food analysis, food chemistry, and food engineering.

As instructors in sensory evaluation at the university level, we have long felt the need for a comprehensive book on sensory evaluation that could serve as a text for our courses as well 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 well as many students) somewhat frustrated. Furthermore, there has not been a truly comprehensive text since the 1965 publication of Principles of Sensory Evaluation of Food by Maynard Amerine, RoseMarie Pangborn, and Edward Roessler. The field of sensory evaluation has seen many devel­opments since that landmark 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 of the 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 Hildegarde Heymann

SENSORY EVALUATION OF FOOD PRINCIPLES AND PRACTICES