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Summary: Principles of Sensory Science
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HNE-30506: Principles of Sensory ScienceA summary of “Sensory Evaluation of Food: Principles & Practices” by Lawless & Heymann
(2nd Edition), the lectures, knowledge clips and e-modules.
BOOK
Chapter 1: Introduction
Sensory evaluation comprises a set of techniques for accurate measurement of human
responses to foods and minimizes the potentially biasing effects of brand identity and other
information influences on consumer perception. As such, it attempts to isolate the sensory
properties of foods themselves and provides important and useful information to product
developers, food scientists, and managers about the sensory characteristics of their
products.
Sensory evaluation has been defined as 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. Furthermore, it gives guidelines for the preparation and
serving of samples under controlled conditions, so that biasing effects are minimized.
Sensory evaluation is a quantitative science in which numerical data are collected to
establish lawful and specific relationships between product characteristics and human
perception. Sensory methods draw heavily from the techniques of behavioural research in
observing and quantifying human responses. Techniques of behavioural research and
experimental psychology offer guidelines as to how such measurements techniques should
be employed and what their potential pitfalls and liabilities may be.
Proper analysis of the data is a critical part of sensory testing. Data generated from human
observers are often highly variable. Hand-in-hand with using appropriate statistical analyses
is the concern of using good experimental design, so that the variables of interest are
investigated in a way that allows sensible conclusions to be drawn.
Conclusions involve consideration of the method, the limitations of the experiment, and the
background and contextual framework of the study.
Precision is the similar to the concept in the behavioural sciences of reliability. In any test
procedure, we would like to be able to get the same result when a test is repeated. The
sensory response is isolated to the factors of interest, minimizing the extraneous influences,
controlling sample preparation and presentation.
Accuracy is the ability of a test instrument to produce a value that is close to the “true” value,
a defined by independent measurement from another instrument or set of instruments that
have been appropriately calibrated. In sensory testing, the test results should reflect the
perceptions and opinions of consumers that might buy the product. The results of the
sensory test should generalize to larger populations.
A good sensory test will minimize errors in measurements and errors in conclusions and
decisions. Whether the test results reflects the true state of the world is an important
question, especially when error and uncontrolled variability are inherent in the measure
process. A test should not often miss important differences that are present. To keep
sensitivity high, we must minimize error variance wherever possible by careful experimental
controls and by selection and training of panellists where appropriate.
The common procedures of interferential statistics provide assurance that we have limited
our possibility of finding a difference where one does not really exist. Statistical procedures
reduce this risk to some comfortable level, usually with a ceiling of 5% of all test we conduct.
Sensory testing is equally concerned with not missing true differences and with avoiding false
positive results.
We can view the outcome of sensory testing as a way to reduce risk and uncertainty in
decision making. In order to know whether it is different or equivalent to some standard
product, or whether it has certain desirable attributes, data are needed to answer the
question.
,The simple sensory tests merely attempt to answer whether any perceptible difference exists
between two types of products. A triangle test judges are asked to pick to odd sample from
among the three. In the duo-trio test, a reference sample was given and then two test
samples. One of the test samples matched the reference, while the other was from a different
product, bath or process. The participant would try to match the correct sample to the
reference, with a chance probability of one-half (50%). In the paired comparison, participants
would be asked to choose which of two products was stronger or more intense in a given
attribute. Typically, a discrimination test will be conducted with 25-40 participants who have
been screened for sensory acuity to common product differences and who are familiar with
the test procedures. Statistical tables derived from the binomial distribution give the minimum
number of correct responses needed to conclude statistical significance as a function of the
number of participants.
The second major class of sensory test methods is those that quantify the perceived
intensities of the sensory characteristics of a product; descriptive analyses. Descriptive
analysis has proven to be the most comprehensive and informative sensory evaluation tool.
It is applicable to the characterization of a wide variety of product changes and research
questions in food product development. The information can be related to consumer
acceptance information and to instrumental measures by means statistical techniques, such
as regression and correlation.
The third major class of sensory tests is those that attempt to quantify the degree of liking or
disliking of a product, called hedonic or affective test methods.
The problem with choice tests is that they are not very informative about the magnitude of
liking or disliking from respondents.
A balanced 9-point scale for liking has a centred neutral category. There was an attempt to
produce scale point labels with adverbs that represented psychologically equal steps or
changes in hedonic tones. Here, we can apply the familiar parametric statistics appropriate to
normally distributed and continuous data, such as means, standard deviations, t-tests,
analysis of variance.
Typically, a hedonic test today would involve a sample of 75 – 150 consumers who were
regular users of the product. The larger panel size of an affective test arises due to the high
variability of individual preferences and, thus, a need to compensate with increased numbers
of people to insure statistical power and test sensitivity.
Sensory test design involves not only the selection of an appropriate method, but also the
selection of appropriate participants and statistical analyses.
For the analytical tests, panellists are selected based on having average to good sensory
acuity for the critical characteristics of products to be evaluated. They are familiarized with
the test procedures and may undergo greater or lesser amounts of training, depending upon
the method.
Consumers are effective at rendering impressions based on the integrated pattern of
perceptions. Participants should be frequent users of the product, since they are most likely
to form the target market and will be familiar with similar products.
It is unwise to ask trained panellists about their preferences or whether they like or dislike a
product. They have not necessarily been selected to be frequent users of the product, so
they are not part of the target population to which one would like to generalize hedonic
results. Conversely, problems arise when consumers are asked to furnish very specific
information about product attributes. Individuals often differ markedly in their interpretations
of sensory attribute words on a questionnaire.
Analytic tests in the lab with specially screened and trained judges are more reliable and
lower in random error than consumer tests.
In type I sensory evaluation, reliability and sensitivity are key factors, and the participant is
viewed much like an analytical instrument used to detect and measure changes in a food
, product. In type II sensory evaluation, participants are chosen to be representative of the
consuming population, and they may evaluate their food under more naturalistic conditions.
Their emphasis here is on prediction of consumer response.
Only human sensory data provide the best models for how consumers are likely to perceive
and react to food products in real life. Changes in products arise from ingredient, processes,
packaging, (and shelf life). Ingredient changes arise to improve product quality, to reduce
costs of production, or simply because a certain supply of raw materials has become
unavailable. Process changes are likewise to arise from the attempt to improve quality in
terms of sensory, nutritional, microbiological stability factors, to reduce costs or to improve
manufacturing productivity. Packaging changes arises from considerations of product
stability, or other quality factors.
In the industrial setting, sensory evaluation provides a conduit for information that is useful in
management business decisions about directions for product development and product
changes. These decisions are based on lower uncertainty and lower risk, once the sensory
information is provided. It may be quite useful or even necessary to include sensory analyses
in quality control (QC) or quality assurance.
There are recurrent themes and enduring problems in sensory science:
1. Sensory methods research: This is aimed at increasing reliability and efficiency,
including research into procedural details and the use of different experimental
designs.
2. Problem solving and trouble shooting
3. Establishing test specifications: This can be important to suppliers and vendors, and
also for quality control in multi-plant manufacturing situations, as well as international
product development and the problem of multiple sensory testing sites and panels.
4. Environmental and biochemical factors
5. Resolving discrepancies between laboratory and field studies
6. Individual differences
7. Relating sensory differences to product variables
8. Sensory interactions
9. Sensory education
Sensory tests are almost always conducted on a blind-labelled basis. In contrast, marketing
research tests often deliver explicit concepts about a product – label, claims, advertising
imagery, nutritional information, or any other information that may enter into the mix designed
to make the product conceptually appealing. In a sensory test all these potentially biasing
factors are stripped away in order to isolate the opinion based on sensory properties only.
Participants often like to please the experimenter and give results consistent with what they
think the person wants.
Different information is provided by the two test types and both are very important. Sensory
evaluation is conducted to inform product developers about whether they have met their
sensory and performance targets in terms of perception of product characteristics.
Chapter 3, Paragraph 5: Panellist Considerations
Sensory panellist should not expect automatic agreement of a person when they are asked
to be on a panel and should be realistic about the benefits for that person. A guideline for
motivation participation is the concept of the token incentive; the incentive should be just
enough to get the person to participate in the evaluation, but not so much that it is the sole
reason for the participation. Common token incentives include snacks or “treats”. This can
serve as a social or coffee-break time for employees or staff and the opportunity for social
interaction may itself become a motivation factor. Small gifts for repeated testing and free
company products are also common incentives.
One of the most important incentives for participation is management recognition. When
management acknowledges participation in sensory panels as an important contribution to
the research effort, recruiting becomes a great deal easier. Support for sensory evaluation
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