Sensory Evaluation E-Book

Sarah Kemp

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 306

Veröffentlichungsjahr: 2011

Beschreibung

This book is a practical guide to sensory evaluation methods and techniques in the food, cosmetic and household product industries. It explains the suitability of different testing methods for different situations and offers step-by-step instructions on how to perform the various types of tests. Covering a broad range of food and non-food product applications, the book is designed to be used as a practical reference in the testing environment; a training manual for new recruits into sensory science, and a course book for students undertaking industrial training or academic study.

Leseprobe

Contents

Preface

Author biographies

Acknowledgements

1 Introduction

1.1 What is sensory evaluation?

1.2 What is the role of sensory evaluation?

1.3 What drives successful sensory testing?

2 Sensory perception

2.1 The human senses

2.2 Factors affecting sensory measurements

3 Planning your sensory project

3.1 Setting objectives

3.2 Product type

3.3 Budget

3.4 Timings

3.5 Selecting the test method

3.6 Setting action standards

3.7 Experimental design

3.8 Data analysis

4 Requirements for sensory testing

4.1 Professional conduct in sensory testing: health, safety, ethical and legal considerations

4.2 Good working and laboratory practices

4.3 Resources needed for sensory testing

4.4 Samples

4.5 Assessors

4.6 Data capture

5 Sensory test methods

5.1 Selecting the test

5.2 Discrimination tests

5.3 Descriptive analysis tests

5.4 Affective/consumer tests

5.5 Linking consumer, sensory and product data

6 Completing the project

6.1 Reporting

6.2 Documentation and data storage

6.3 Dos and don’ts

7 Appendices

Appendix 1 Examples of Latin Square and Williams Latin Square designs for selected number of samples

Appendix 2 IFST PFSG professional code of conduct for sensory professionals

Appendix 3 Critical values table for triangle test

Appendix 4 Critical values table for duo-trio test and paired comparison test for difference (one tailed)

Appendix 5 ANOVA explained

Appendix 6 Critical values table for chi-squared

Appendix 7 Critical values table for paired comparison and paired difference test (two tailed)

Appendix 8 Critical values table for Friedman test

Appendix 9 Types of scales

Appendix 10 Case study: modified quantitative descriptive analysis of chocolate texture

Appendix 11 R index explained

8 Glossary

9 References

Index

To George, Elizabeth, George and William To Mike, Holly and Socks

To Campbell, Emma and Lara

This edition first published 2009

© 2009 S.E. Kemp, T. Hollowood and J. Hort

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ISBN: 978-1-4051-6210-4

Preface

This book is an affordable sensory science textbook focused on the practical aspects of sensory testing on a broad range of products. It is presented in a simple ‘how to’ style for use by industry and academia as a step-bystep guide on how to carry out a range of sensory tests. It is intended as a companion volume to a larger, more detailed sensory science textbook covering theoretical aspects, advanced techniques and applications of sensory evaluation. The inspiration for this book is the excellent Laboratory Methods for Sensory Evaluation of Food by Elizabeth Larmont first published in 1967 and revised in 1977 and 1991 (Poste et al., 1991). It is now out of print; but at the time of publication, it was popular for its practical, easy-to-read style, coupled with good use of examples and illustrations. The authors have fond memories of using the book during their formative years in sensory science.

Between them, the authors have over 50 years of industrial and academic experience in sensory science and have published widely in the field. All three authors are founder committee members of The Institute of Food Science and Technology’s Professional Food Sensory Group (IFST PFSG).

There are many good sensory textbooks on the market. The generalist sensory science texts are very comprehensive, but are often written in a research style, or with large sections of unbroken text which renders them unsuitable for use as a simple training/teaching aid or as a quick practical guide. They are also expensive/unaffordable in developing countries and difficult to understand for readers who have English as a second language. In addition, more and more specialised sensory texts are now available which tend to focus on theory and application in a narrow field, rather than general practice. There is a tendency for sensory textbooks to focus on food and beverage applications, often to the exclusion of other product categories.

The objectives of this book are as follows:

To provide a practical guide and laboratory manual on how to carry out sensory evaluation techniques.To reach sensory practitioners, as well as sensory scientists, by using a simple, easy-to-read, easy-to-use format.To cover a broad range of product applications, including food, beverages, personal care and household products.To be inexpensive and available to a wide audience who would not usually be able to afford to purchase standard sensory textbooks, including students, technicians and practitioners in developing countries.To cover the IFST PFSG accreditation scheme at foundation and intermediate levels.

The very simple, practical, easy-to-use style of this book, coupled with its affordability, makes it suitable as a training manual, reference text, teaching aid and course book. Key audiences include sensory practitioners, junior sensory staff, sensory students and sensory trainers. It is applicable across a broad range of industries and to those with limited budgets.

The style of the book is easy-to-follow ‘instructions’ with simple explanations of how and why to do testing in a particular way, rather than detailed theory and underlying science of techniques. It is laid out in logical sequence. Examples and illustrations are used throughout. Practical tips and hints in the form of dos and don’ts are included in each section.

The book begins with an introductory chapter that gives an overview of sensory evaluation and a second chapter on sensory perception. The third chapter outlines how to plan a sensory project. The fourth chapter focuses on requirements for sensory testing. Important elements of this chapter are professional conduct and good laboratory practice. These often receive scant coverage, but are becoming increasingly important as novel ingredients and processes continue to be developed (e.g. ingredients from genetically modified origin), and as products are increasingly tested in markets with regulations that are different from those in the markets for which they were designed. No matter how informal the sensory assessment is, it is essential that safe and ethical practices are used. The fifth chapter covers sensory test methods. Methods for statistical analysis are given throughout this chapter, rather than as a stand-alone section, to make the translation to practice easier. Case studies are used to illustrate methods. The sixth chapter covers elements necessary to complete a sensory project. Also included are appendices, glossary, references and index.

The authors hope that you enjoy using this book and that it helps bring success in your sensory endeavours.

Sarah E. Kemp

Tracey Hollowood

Joanne Hort

Author biographies

Sarah Elizabeth Kemp, BSc (Hons), PhD, CSci, FIFST, is a sensory and consumer science professional with more than 20 years of experience in academia and industry. Dr Kemp gained a BSc in Food Technology in 1986 and a PhD in Taste Chemistry in 1989 from the Food Science and Technology Department at Reading University, UK. In 1990, she did a postdoctoral research fellowship on sensory analysis at the Monell Chemical Senses Center in Philadelphia, USA. Dr Kemp has held numerous positions in the industry, including Manager of Sensory Psychology in the Fragrance Division of Givaudan-Roure in New Jersey, USA, Director of European Consumer and Marketing Research in the Fragrance Division at Givaudan-Roure, France, Product Area Leader and Sensory Science Leader in Foods Consumer Science at Unilever Research Colworth, UK, Former Head of Global Sensory and Consumer Guidance at Cadbury Schweppes, UK, and Director of Sensory and Consumer Services at Reading Scientific Services Ltd, UK. Dr Kemp has also set up and run her own consultancy service, Kemps Research Solutions Ltd. She has written numerous scientific articles in the field of sensory evaluation, has provided sensory training courses, including lecturing on the European Masters Course in Food Science, and has worked with bodies developing standards in sensory evaluation, such as the American Society for Testing and Materials. She is a founder member of the Professional Food Sensory Group of the Institute of Food Science and Technology, and a member of several other professional bodies, including the Sensory Evaluation Division of the Institute of Food Technologists, the Consumer and Sensory Research Technical Interest Group of the Society of Chemical Industry and the Association for Chemoreception Sciences.

Tracey Hollowood, BSc (Hons), PhD, MIFST, is currently Associate Director of Sensory and Consumer Research for Sensory Dimensions, UK. She has over 15 years of experience in academia and industry; she worked at Nottingham University for 10 years during which time she achieved her doctorate investigating perceptual taste-texture-aroma interactions. She established the United Kingdom’s first Post Graduate Certificate in Sensory Science, and designed and managed the university’s prestigious Sensory Science Centre. Her research has focused on psychophysical studies, interactions in sensory modalities and fundamental method development. She has over 20 peer-reviewed publications; has given numerous oral presentations and workshops; and has participated in the organisation of seven international symposia, including International Symposium of Taste 2000 and Pangborn Sensory Science Symposium 2005. She is the current Chair of the Institute of Food Science and Technology (IFST), Midland Branch and the Professional Food Sensory Group (PFSG).

Joanne Hort, BEd(Hons), PhD, MIFST, is Associate Professor in Sensory Science in the Division of Food Sciences at the University of Nottingham. Initially, she studied Food Technology and began her career in teaching. However, she returned to the university to receive her doctorate concerning the modelling of the sensory attributes of cheese from analytical and instrumental measures in 1998. As a lecturer at Sheffield Hallam University, she carried out sensory consultancy for local industry, developed a sensory program at undergraduate level and oversaw the installation of new sensory facilities before being appointed as Lecturer in Sensory Science at the University of Nottingham in 2002. She has since established the University of Nottingham Sensory Science Centre, which is renowned for both its sensory training and research into flavour perception. She delivers sensory courses at both undergraduate and postgraduate levels and is the Course Director for the Postgraduate Certificate in Sensory Science. Her research interests focus on the multimodal aspects of flavour perception and she has published several articles in this area, together with oral presentations and posters at international symposia. She is a founder member of the Professional Food Sensory Group of the Institute of Food Science and Technology and was on the organising committee of the 6th International Pangborn Symposium in the United Kingdom in 2005.

Acknowledgements

The authors would like to thank Simon Hails, of Cadbury plc and formally RSSL Ltd, for providing information on the ethical and legal considerations in sensory testing, Emma Louise Hewson for providing the diagram of a sensory testing facility and Rebecca Clark for assistance in compiling the references.

1 Introduction

It is estimated that 75% of new products fail within their first year on the supermarket shelf (Buisson 1995) and that, as a consequence, considerable resource invested in product development is squandered (Deschamps and Nayak 1996). Sensory attributes, whether the flavour of coffee, the smell of an air freshener, the texture of fabric or even the sound of a car door closing, are key determinants of product delivery including quality, functional and emotional benefits. Thus, a considerable proportion of product failure can be attributed to a mismatch between sensory properties and consumer needs or expectations. When integrated within the product development process, sensory and consumer testing allows costeffective delivery of acceptable products to consumers and thus reduces the risk of failure (Lawless and Heymann 1998).

1.1 What is sensory evaluation?

Sensory evaluation is often described using the definition of Institute of Food Technology – a scientific method used to evoke, measure, analyse and interpret those responses to products as perceived through the senses of sight, smell, touch, taste and hearing (Anonymous 1975).

Since its emergence in the 1940s, however, sensory evaluation has developed as an exciting, dynamic, constantly evolving discipline that is now recognised as a scientific field in its own right.

The sensory professional is routinely confronted with problems which call upon an extensive skill set drawn from a range of disciplines, e.g. biological sciences, psychology, experimental design and statistics and will often be required to work with other specialists from these areas. Additional challenges are presented by working with a human ‘measuring instrument’ that is highly variable.

Sensory evaluation can be divided into two categories of testing: objective and subjective. In objective testing, the sensory attributes of a product are evaluated by a selected or trained panel. In subjective testing, the reactions of consumers to the sensory properties of products are measured. The power of sensory evaluation is realised when these two elements are combined to reveal insights into the way in which sensory properties drive consumer acceptance and emotional benefits. Linking sensory properties to physical, chemical, formulation and/or process variables then enables the product to be designed to deliver optimum or appropriate consumer benefits.

1.2 What is the role of sensory evaluation?

The role of sensory evaluation has changed considerably over the years. Initially, it was a service provider supplying data, but now its role is, in partnership with R&D and marketing, to provide insights to help guide development and commercial strategy.

From product conception to post-launch monitoring, sensory professionals can be called upon to inform decision-making during the stages of a product’s life cycle. Sensory and consumer testing can also provide insights into human behaviour and perception at a more fundamental level.

In the early stages of product development, consumer and sensory testing can help identify the important sensory attributes driving acceptability across a product category. It can identify sensory-based target consumer segments, analyse competitor products and evaluate new concepts.

Combining data from sensory and instrumental testing may provide insights into the chemical and physical properties, driving sensory attributes. Where significant correlations exist with sensory data, it may be possible to dispense with the use of a sensory panel, in favour of a more cost-effective instrumental test, e.g. in quality testing.

Sensory testing can determine the impact of scaling up kitchen and/or pilot samples to large-scale production and is invaluable in determining whether raw ingredient changes or modifications to the production process, e.g. for cost reduction or change of supplier, will impact on sensory quality and/or product acceptability.

In terms of quality assurance, it can be used as part of a QA programme on raw materials. In addition, sensory testing can set consumer acceptability limits for sensory specifications used during quality testing. For those products susceptible to taints, sensory testing can ensure substandard products are not released onto the market. For many products, the sensory properties deteriorate ahead of microbial quality and so, in tandem with microbial tests, sensory testing can be used to determine shelf life and product variability through the supply chain.

From a marketing perspective, sensory and consumer testing can inform understanding concerning product preferences and acceptability. It can provide the data to support marketing claims such as ‘best ever’, ‘new creamier’, and ‘most preferred’. It can also ensure that sensory properties work in synergy with brand communication and advertising.

Sensory and consumer testing is widely employed in the research arena. It is used at a more fundamental level to investigate new technologies to aid product development and to understand consumer behaviour. Furthermore, multidisciplinary investigations linking sensory testing with, for example instrumental analyses, brain-imaging techniques, psychophysical tests and genomics provide a wider understanding of the mechanisms involved in sensory perception and the variations that exist within the population.

1.3 What drives successful sensory testing?

Successful sensory testing is driven by setting clear objectives, developing robust experimental strategy and design, applying appropriate statistical techniques, adhering to good ethical practice and successfully delivering actionable insights that are used to inform decision-making. Appropriate training is crucial to ensure that the sensory professional has the necessary technical capability and interpersonal skills.

The aim of this book is to provide new and current sensory professionals with a firm foundation in the above principles in a practical, easy to follow format.

2 Sensory perception

2.1 The human senses

Sensory properties are perceived when our sensory organs interact with stimuli in the world around us. Consequently, it is important for sensory professionals to have some understanding of the biological mechanisms involved in perception. A basic outline of each sensory system is given in the following sections. For more detailed information on the humansenses, see Goldstein (2006).

2.1.1 Vision

The appearance of any object is determined by the sense of vision. Light waves reflected by an object enter the eye and fall on the retina. The retina contains receptor cells, known as rods and cones, which convert this light energy into neural impulses that travel via the optic nerve to the brain. Cones are responsive to different wavelengths of light relating to ‘colour’. Rods respond positively to white light and relay information concerning the lightness of the colour. The brain interprets these signals and we perceive the appearance (colour, shape, size, translucency, surface texture, etc.) of the object.

2.1.2 Gustation

The sense of taste involves the perception of non-volatile substances which, when dissolved in water, oil or saliva, are detected by taste receptors in the taste buds located on the surface of the tongue and other areas of the mouth or throat. The resulting sensations can be divided into five different taste qualities–salty, sweet, sour, bitter and umami. Examples of compounds that elicit particular tastes are given as follows:

Salty substances: sodium chloride, potassium chlorideSweet substances: sucrose, glucose, aspartameSour substances: citric acid, phosphoric acidBitter substances: quinine, caffeineUmami substance: monosodium glutamate.

It is a myth that only certain areas of the tongue are sensitive to particular tastes. In fact, different areas of the tongue can be responsive to all the taste qualities; however, some areas are more sensitive than others.

2.1.3 Olfaction

Volatile molecules are sensed by olfactory receptors on the millions of hair-like cilia that cover the nasal epithelium (located in the roof of the nasal cavity). Consequently, for something to have an odour or aroma, volatile molecules must be transported in air to the nose. Volatile molecules enter the nose orthonasally during breathing/sniffing, or retronasally via the back of the throat during eating. There are around 17,000 different volatile compounds. A particular odour may be made up of several volatile compounds, but sometimes particular volatiles (character-impact compounds) can be associated with a particular smell, e.g. iso-amyl acetate and banana/pear drops. Individuals may perceive and/or describe single compounds differently, e.g. hexenol can be described as grass, green, unripe. Similarly, an odour quality may be perceived and/or described in different compounds, e.g. minty is used to describe both menthol and carvone.

2.1.4 Touch (somesthesis, kinesthesis and chemesthesis)

Somesthesis: The skin, including the lips, tongue and surfaces of the oral cavity, contains many different tactile receptors that can detect sensations related to contact/touch, e.g. force, particle size and heat.

Kinesthesis: Nerve fibres in the muscles, tendons and joints sense tension and relaxation in the muscles, allowing the perception of attributes such as heaviness and hardness.

Chemesthesis: Some chemical substances can stimulate the trigeminal nerves situated in the skin, mouth and nose to give hot, burning, tingling, cooling or astringent sensations, e.g. piperine in pepper, capsaicin in chilli pepper, carbon dioxide in fizzy drinks, coolants in showers gel, warming compounds in muscle rubs and tannins in wine. When sensed in the oral cavity, they form part of what are collectively known as mouth-feel attributes.

Texture perception is complex. Attributes of food texture can be divided into three categories: (i) mechanical, e.g. hardness and chewiness; (ii) geometric, e.g. graininess and crumbliness and (iii) mouth-feel, e.g. oiliness and moistness. These are generally described as being perceived during three phases: Initial phase (first bite), masticatory phase (chewing) and residual phase (after swallowing).

2.1.5 Audition

Sound is sensed by millions of tiny hair cells in the ear that are stimulated by the vibration of air from sound waves. The noise created when touching or stroking objects, e.g. fabric, gives an indication of texture. The noise emitted by food during eating contributes to the perceived texture of a food, e.g. crispness of an apple and fizz of a carbonated drink. When consumers eat food products, the sound waves produced can be conducted by the air and/or bones in the jaw and skull. The latter is known as intra-oral perception.

2.1.6 Multimodal perception

Although distinct sensory organs exist for each of the different senses, it is important to note that information from each of the sensory organs is often integrated in the brain. For example, the perception of flavour results from the interaction between taste, aroma, texture, appearance and sound. Sound can also affect the perception of touch. Similarly, texture perception is a combination of the visual, tactile and chemesthetic properties of the food or object under observation. The sensory professional should, therefore, be aware of how changes in one sensory property can affect others.

2.2 Factors affecting sensory measurements

Unlike instruments, human judgements can easily be affected by psychological or physiological factors. The sensory professional must be aware of these factors and ensure that the chosen procedure and experimental design eliminate or reduce such bias. This section highlights potential sources of error and suggests some strategies for reducing their effects.

2.2.1 Psychological factors

2.2.1.1 Expectation error

Knowledge of experimental objectives, or the samples to be evaluated, can influence an assessor’s judgement. People tend to find what they expect to find. For example, codes such as ‘A’, ‘1’ or round numbers (e.g. 100, 250) can be associated with a higher score. Other numbers can have particular associations, e.g. 999 or 911 and danger.

Do not include people with product knowledge on the panel.

Provide assessors with the minimum amount of information required to perform the test.

Do not disclose information regarding the samples unless it is necessary for ethical procedures, e.g. use of novel ingredients.

Code samples. Use codes such as random three-digit numbers and not letters or colours.

2.2.1.2 Suggestion effect

Comments or noises made out loud, e.g. urghh! or Mmmm! can influence sensory judgements.

Isolate assessors during sample evaluation, e.g. use of sensory booths.

Discourage assessors from discussing samples before or after evaluation unless instructed to do so.

2.2.1.3 Distraction error

Assessors can be easily distracted from the task in hand, either by stimuli in the test environment, e.g. radios and other conversations, or by personal preoccupations, e.g. time pressure or domestic issues.

Ensure test area is quiet.

Create an environment that encourages professionalism amongst the assessors.

Prohibit the use of electronic devices, e.g. mobile phones during testing.

2.2.1.4 Stimulus and logical error

Stimulus error occurs when assessors use additional information to make a judgement about the samples under assessment. When this stimulus is also logically associated with one or more of the characteristics under evaluation, it is called logical error. Some obvious examples are when products of a deeper colour or larger size are presumed to be more flavour intense, or when thinner skin creams are viewed as poorer quality. There are also other less obvious stimuli that may be exploited by assessors, such as cues regarding product branding; running a panel at an unusual time, which may prompt assessors to think there is a production problem; using more luxurious containers may lead assessors to think products are of higher quality.

Ensure sample characteristics are consistent and/or mask irrelevant differences where possible, e.g. use of coloured lighting, blindfolds, nose clips and ear defenders where appropriate.

2.2.1.5 Halo effect and proximity error

Judgements concerning the rating of one attribute may influence the ratings of other attributes when assessors are asked to judge several attributes at once. This is more likely with untrained assessors. For example, a sweeter sample may be rated as softer, or stickier, than it would have, had these ratings been made on separate occasions. Furthermore, when rating several attributes at a time, the ratings of attributes following on from one another tend to be related.

Where possible, evaluate one, or at least a limited number of attributes, at a time.

Where possible and appropriate, use trained assessors.

Where appropriate, randomise the order of attribute evaluation if several attributes have to be rated at once.

2.2.1.6 Attribute dumping

If assessors are not given the opportunity to rate all the attributes they perceive as changing in the products under evaluation, they may still record this observation using the scales available. For example, if products are changing in terms of sweetness but no sweetness scale exists, they may register these changes on a flavour intensity scale such as strawberry flavour. This is known as ‘attribute dumping’.

Enable assessors to score all attributes which vary or indicate that opportunities to rate all varying attributes will be given.

2.2.1.7 Habituation

When assessors score similar products on a regular basis, e.g. on quality panels, they can develop a habit of assigning similar scores each time rather than scores which truly represent the samples.

Vary products or introduce spiked samples from time to time.

2.2.1.8 Order effect

The score assigned to a sample can be influenced by the sensory character of the preceding product. For example, a sample may be rated as less sweet if it follows one of greater intensity. In addition, some sample positions are often favoured, e.g. products in position one are often scored higher in hedonic tests.

Randomise or balance the order of presentation of samples (MacFie et al. 1989).

For affective tests (see Section 5.4), use a dummy sample in position one.

2.2.1.9 Contrast and convergence effects

If two products in the sample set are strikingly different, assessors may exaggerate their ratings of this difference (contrast). If similar products are rated as part of a widely varying sample set, then the difference between them may be rated smaller than it actually is (convergence).

Randomise or balance the order of presentation of samples.

Consider removing outlying samples from the sample set.

2.2.1.10 Central tendency error

When using scales, assessors tend to avoid the extremes and confine their ratings to the middle of the scale. This is more likely to occur with untrained assessors or when assessors are not familiar with the product range.

Train assessors in the use of the scale and expose them to a wide product range where possible.

Use a large enough scale to differentiate between the products, particularly with untrained assessors.

2.2.1.11 Motivation error

A motivated panellist will learn better and, ultimately, perform more reliably. If assessors do not respect the panel leader or product manufacturer, they may rate samples based on how they feel. This can be an issue when using employee panels.

Respect assessors.

Give regular feedback to assessors.

Carry out sessions in a professional manner.

Further information can be found on motivation in Section 4.5.5.

2.2.2 Physiological factors

2.2.2.1 Adaptation

Continued exposure to a stimulus results in a decrease in sensitivity to that stimulus and/or a change in sensitivity to other stimuli. Consequently, assessments of attribute intensity vary depending on the level to which the assessor has adapted to a stimulus. These are known as carry-over effects.

Limit the number of samples presented.

Ensure appropriate time intervals between samples to allow the sensory system to recover; this can be a matter of seconds, minutes or hours, depending on the stimulus, e.g. ‘cooling’ can take 10 minutes to recede.

Ensure assessors take adequate breaks between single and sets of samples; the length of break will vary dependent on sample and test type.

Provide assessors with appropriate palate cleansers, which ensure removal of any sample lingering in the oral cavity, e.g. milk rather than water may be needed for some spicy compounds.

2.2.2.2 Perceptual interactions between stimuli

Certain stimuli can interact to cause the following:

Enhancement (potentiation): The presence of one substance increases the perceived intensity of another, e.g. salt increases perceived intensity of chicken flavour.Synergy: The intensity of a mixture is greater than the intensity of the sum of the individual components, e.g. sweetness and sourness impact on strawberry flavour.Suppression: The presence of one substance decreases the perceived intensity of another, e.g. sourness reduces peach flavour.

Where appropriate, employ careful experimental design to ensure that the effects of combined and individual stimuli are understood.

2.2.2.3 Physical condition

Health and nutritional disorders, together with the drugs prescribed to treat them, can affect sensory performance. Age and stress can also impact on sensory acuity, as can the time of day.

Screen assessors prior to testing or remove assessor data if medical conditions or associated drugs affect the sensory performance.

Instruct assessors to refrain from eating for at least an hour before sensory sessions.

Schedule sessions for around a similar time each day–preferably between 10 and lunch.

Monitor assessor’s performance to highlight changes in sensory ability that may occur due to variation in physical state, e.g. age, hormonal state mood, etc.

2.2.3 Cultural factors

When working with assessors from different cultures or geographical location, the sensory professional needs to be aware of the impact that cultural effects can have on sensory data. For example, in some cultures, particular product codes may have significant connotations; eating in public may be considered as a social taboo; spiritual restrictions may impact on sample selection; group feedback may not be deemed acceptable. In addition, literal translations of questions and scale terminology may result in loss or change of meaning. The use of a scale can vary across cultures, e.g. some tend to score much higher or lower than ‘average’ when using the hedonic scale.

Be sensitive to coding issues.

Clarify translations of sensory scales or questionnaires into other languages, e.g. the use of back translation.

Be aware of cultural tendencies–these will have an impact on many aspects of sensory testing such as products, protocols, scale use and feedback.

Build up information on cultural norms from different cultures or countries.

3 Planning your sensory project

3.1 Setting objectives

It is vital to understand the objectives of a project as these are key factors in determining the test type and, consequently, the experimental design and statistical analysis required to meet these objectives. Commonly asked questions such as ‘are these samples different?’, ‘which is the preferred sample?’, ‘how do these samples compare to the competition in terms of texture?’ and ‘what is the optimum cooking temperature to create the most acceptable golden colour?’ would all require different sensory methods and experimental designs. Often, a client will want to know the answer to all of these questions; however, time and financial constraints may require that the objectives are prioritised. It is imperative that the potential outcomes of different methodologies be highlighted in advance so that clients are aware of any limitations, e.g. a discrimination test identifying the sweetest sample will not allow any conclusions to be drawn about preference or about how sweet it actually is. When working with internal or external clients, the objectives for a project should be documented alongside all other pertinent information (see Chapter 6).

3.2 Product type

When selecting an appropriate methodology to satisfy the desired objectives, it is important to consider the product type as this may have a serious impact on test design. In some instances, products may need to be tested in combination with other foods, e.g. breakfast cereal may be presented with milk, or olive oil may be presented with a neutral carrier such as bread. When the test objective includes some aspects of performance, products may need to be tested in the context of their use, e.g. shampoo, safety razors and skin creams. In this instance, careful consideration needs to be made to other aspects of experimental design (see Section 3.7). For example, some samples have intense carry-over and need to be presented monadically with large breaks in between.

3.3 Budget

Financial constraints have to be considered in any test design. In some instances, the cost associated with the ‘ideal’ design exceeds the budget and appropriate compromises such as reducing the number of products, assessors or replicates are necessary. It is important to understand the consequence of every compromise with regard to the quality of the data and the conclusions that can be drawn.

Reducing the number of assessors from the maximum to the minimum recommended would be acceptable, whereas reducing the number even further may have a deleterious effect on the power of the statistical test (see Section 5.2.4.1) and, therefore, on the likelihood of reporting significant differences between samples. Furthermore, smaller groups of assessors are less representative of their population.

Reducing the number of samples can be an effective way of cutting costs; however, removing replication from the design of certain sensory methodologies, e.g. profiling, can be very dangerous. Furthermore, some methodologies, e.g. preference mapping, require a minimum number of samples and reducing the number below this would render the test invalid.

3.4 Timings

When designing a sensory test, a deadline may affect the decision over which methodology to use. It is important to know in advance if any deadlines exist. In studies that require several test elements, e.g. consumer tests, descriptive analysis, instrumental analysis, shelf life testing, the co-ordination of these elements is crucial for samples whose sensory properties change with time.

3.5 Selecting the test method

There are many sensory tests and a multitude of different situations in which they can be applied. The test employed will depend on the test objective(s). It is imperative that the specific objective of any sensory test is probed and clarified before testing begins.

Often, a series of tests is required to meet the objectives. Careful consideration needs to be given to the order in which different tests are performed. It is futile to carry out large consumer trials concerning the preference for two products without prior sensory information as to whether a significant perceivable difference exists between them.

The most appropriate test may not be the most cost-effective or feasible with the amount of sample or assessors available, and consequently, some form of compromise may need to be reached.

Details of different test methods and their application are given in Chapter 5.

3.6 Setting action standards

Action standards are the criteria that must be met to take a course of action based on test results. They should be set in advance of the test being carried out. Factors to consider include size of the opportunity; business risk and stage of testing, which will determine how strict the criteria are, as well as product type, new or existing product category and communication, e.g. whether a product improvement will be flagged to consumers or not. Action standards may include number and type of consumer, statistical criteria, and elements of the test design (are the products going to be presented simultaneously or sequentially? will the products be branded or unbranded? will the products be presented with a marketing concept?).

A simple example of an action standard to decide whether an optimised product should be substituted for the current product is as follows.

For the optimised product vs. the current project: a ratio of 55:45 in preference in an unbranded product test with heavy product users in the target user group; and at least parity in preference in an unbranded product test with product category users.

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