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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