Sensory Evaluation

A Practical Handbook

Sarah E. Kemp, Tracey Hollowood, Joanne Hort

• Publisher: Wiley-Blackwell
• Year: 2011
• ISBN:
  9781444360516
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

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.

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 human senses, 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 chloride
• Sweet substances: sucrose, glucose, aspartame
• Sour substances: citric acid, phosphoric acid
• Bitter substances: quinine, caffeine
• Umami 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 t...

Table of contents

• Cover
• Dedication
• Title page
• Copyright
• Preface
• Author biographies
• Acknowledgements
• 1: Introduction
• 2: Sensory perception
• 3: Planning your sensory project
• 4: Requirements for sensory testing
• 5: Sensory test methods
• 6: Completing the project
• 7: Appendices
• 8: Glossary
• 9: References
• Index