SENSORY EVALUATION OF FOOD - pdfs.semanticscholar.org · sensory evaluation of food principles and practices harry t. lawless cornell university hildegarde heymann university of missouri

SENSORY EVALUATION OF FOOD PRINCIPLES AND PRACTICES

HARRY T. LAWLESS CORNELL UNIVERSITY

HILDEGARDE HEYMANN UNIVERSITY OF MISSOURI

A Chapman & Hall Food Science Book

An Aspen Publication® Aspen Publishers, Inc.

Gaithersburg, Maryland 1999

CONTENTS

Preface XII

CHAPTER 1 INTRODUCTION AND OVERVIEW 1

Definition and Focus 1

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 2 8

Classical Sensory Testing and

Psychophysical Methods 28

Anatomy, Physiology, Functions of Taste 39

Anatomy, Physiology, and Functions of Smell 50

VI I

viii CONTENTS

CHAPTER 3

CHAPTER 4

CHAPTER 5

The Trigeminal Flavor Senses

Sensory Interactions

Summary and Conclusions

References

PRINCIPLES OF GOOD PRACTICE

Sensory Testing Environment

Test Protocol Considerations

Tabulations and Analysis

Conclusion

References

DISCRIMINATION TESTING

Types of Discrimination Tests

Reputed Strengths and Weaknesses

Data Analyses

Binomial Distributions and Tables

Issues

Common Mistakes Made in the Interpretation of

Discrimination Tests

References

DISCRIMINATION THEORIES AND

ADVANCED TOPICS The Theory of Signal Detection

Thurstonian Models for Choice Tests

Signal Detection Applied to

Foods Using the R-Index

Guessing Models and Discriminator Theory

Estimating Sample Size in Discrimination Tests

The Test for Significant Similarity

Conclusions: Signal Detection, Thurstonian, and

Guessing Models for Discrimination

References

61

67

73

74

83 85

91

112

113

114

116 117

128

129

129

133

138

138

140 142

151

157

159

164

166

170

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 2 0 8

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 The Approach and Its Advantages

History of Time-Intensity Methods

Examples and Applications

Data Analysis Issues

Problems and Remaining Questions

Conclusions

References

265 265

267

270

283

290

294

296

CHAPTER 9 CONTEXT EFFECTS AND

BIASES IN SENSORY JUDGMENT Relative Nature of Rating Scales

301 301

x CONTENTS

CHAPTER 1 0

CHAPTER 11

Simple Contrast and Adaptation Level

Range Frequency Theory

Poulton's Classification of Biases

Halo Effects and False Enhancement from

Response Restriction

Classical Psychological Errors

Antidotes

Conclusions

References

DESCRIPTIVE ANALYSIS

Uses of Descriptive Analysis

Language and Descriptive Analysis

Descriptive Analysis Techniques

References

TEXTURE EVALUATION

Texture Defined

Auditory, Visual, and Tactile Texture

Sensory Texture Measurements

Texture Profile Analysis

Instrumental Texture Measurements and

Sensory Correlations

Conclusions

References

306

315

319

326

330

332

335

337

341 341

342

346

372

379 379

383

392 392

395

399

400

CHAPTER 1 2 COLOR AND APPEARANCE 4 0 6

What Is Color? 408

Vision 410

Measurement of Appearance and Color Attributes 411

Instrumental Color Measurement 417

Conclusions 428

References 428

CHAPTER 1 3 ACCEPTANCE AND

PREFERENCE TESTING Consumer Sensory Evaluation

430 430

CONTENTS xi

Preference Tests

Acceptance Tests

Variations on Acceptance

Qualifying Panelists

Conclusions

References

431

450

457

470

474

475

CHAPTER 1 4

CHAPTER 1 5

CONSUMER FlELD TESTS AND

QUESTIONNAIRE DESIGN

Objectives: Sensory Testing versus

480

Concept Testing

Testing Scenarios: Central Location, Home Use

Practical Conduct of Home Use Tests

Interacting with Field Services

Questionnaire Design

10 Rules of Thumb for Question Construction

Conclusions

References

Sample Consumer Test Questionnaire

QUALITATIVE CONSUMER RESEARCH METHODS

Introduction

Characteristics of Focus Groups Using Focus Groups in Sensory Evaluation

Conducting Focus Group Studies

Issues in Moderating

Analysis and Reporting

Alternative Procedures and Variations

of the Group Interview

Conclusions

References

480

484

489

492

499

503

511

513

514

519 519 523

526

528

533

536

541

544

546

CHAPTER 1 6 SENSORY EVALUATION IN QUALITY CONTROL 548 Objectives and Challenges 548

Program Development and Management Issues 552

xii CONTENTS

Features of a Sensory QC System

Methods for Sensory QC

Importance of Good Practice

Summary and Conclusions

Postscript: Whither Excellence?

References

555

558

574

577

578

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 1 8 STRATEGIC RESEARCH

Introduction

The Category Review

Perceptual Mapping and

Opportunity Identification

Consumer Contact

Conclusions

References

602 602

605

606

618

620

620

CHAPTER 1 9 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 III 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

APPENDIX IV

Epilogue: Other Techniques References

CORRELATION, REGRESSION, AND MEASURES OF ASSOCIATION Introduction Correlation

Linear Regression Multiple Linear Regression

Other Measures of Association References

735 737

738 738 741 745 749 749 753

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

APPENDIX VII

APPENDIX VIII

STATISTICAL TABLES

BlNOMIAL PROBABILITIES FROM DISCRIMINATION TESTS

COMPLETE BLOCK ANALYSIS

OF VARIANCE

GLOSSARY OF TERMS

INDEX

783

795

797

803

819