ASTM E1909-97(2003)
(Guide)Standard Guide for Time-Intensity Evaluation of Sensory Attributes
Standard Guide for Time-Intensity Evaluation of Sensory Attributes
SIGNIFICANCE AND USE
The purpose of time-intensity measurements is to establish the pattern of development and decline of a particular sensory characteristic under study. T-I evaluations are applicable when measurements at a single time point (an averaging process) are not sufficient to distinguish products that have very different temporal characteristics. As pointed out by Lee and Pangborn (1)3 , “This averaging process results in the masking or complete loss of important information such as rate of onset of stimulation, time and duration of maximum intensity, rate of decay of perceived intensity, time of extinction, and total duration of the entire process.”
Products rated similarly using traditional single point techniques of product profiling may provide very different temporal sensory experiences to the consumer. Acceptability of the product may be affected, and traditional descriptive methodology does not reflect the changes in an attribute’intensity over time.
T-I has applications for a variety of products. Examples include: food products, ranging from short-term sweetness in a beverage to long-term elasticity in chewing gum; personal care products, measuring the development and longevity of shampoo lather and the residual skin feel of a skin cream; household care products, monitoring the intensity of scents over time; pharmaceuticals, monitoring skin cooling after application of a topical analgesic. Auditory signals or visual changes in products can also be evaluated by the T-I technique.
SCOPE
1.1 This guide covers procedures for conducting and analyzing time-intensity (T-I) evaluations of products or other sensory stimuli. Time-intensity is the measurement of the intensity of a single sensory sensation over time in response to a single exposure to a product or other sensory stimulus.
1.2 This guide utilizes a specially trained panel to measure the intensity of a single continuous sensation during the time from initial exposure:
1.2.1 To its extinction,
1.2.2 To a specified intensity, or
1.2.3 To a predetermined limit of time.
1.3 Applications not covered in this guide include measuring:
1.3.1 Multiple sensations,
1.3.2 Multiple exposures within a single measurement, and
1.3.3 Qualitative or hedonic changes in the perceived sensation.
1.4 This guide includes protocols for the selection and training of judges, descriptions and use of physical data collection devices, and methods of data handling, summarization, and statistical analysis. Illustration of two different data handling and analysis approaches are included in the appendixes.
1.5 This guide is not applicable to measure product shelf life or stability that require evaluations at discrete time intervals.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E1909 – 97 (Reapproved 2003)
Standard Guide for
Time-Intensity Evaluation of Sensory Attributes
This standard is issued under the fixed designation E1909; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E253 Terminology Relating to Sensory Evaluation of Ma-
terials and Products
1.1 This guide covers procedures for conducting and ana-
lyzing time-intensity (T-I) evaluations of products or other
3. Terminology
sensory stimuli. Time-intensity is the measurement of the
3.1 Definitions of Terms Specific to This Standard: See Fig.
intensity of a single sensory sensation over time in response to
1.
a single exposure to a product or other sensory stimulus.
3.1.1 area after I —post-peak area under the curve.
max
1.2 This guide utilizes a specially trained panel to measure
3.1.2 area before I —pre-peak area under the curve.
max
the intensity of a single continuous sensation during the time
3.1.3 AUC—area under the curve.
from initial exposure:
3.1.4 I or peak intensity—maximum observed intensity
max
1.2.1 To its extinction,
during the time of measurement.
1.2.2 To a specified intensity, or
3.1.5 perimeter—measured distance of perimeter of area
1.2.3 To a predetermined limit of time.
delineated by T-I curve.
1.3 Applications not covered in this guide include measur-
3.1.6 plateau time—duration of peak intensity.
ing:
3.1.7 rate of increase—rate of intensity increase before
1.3.1 Multiple sensations,
peak intensity (slope).
1.3.2 Multiple exposures within a single measurement, and
3.1.8 rate of decrease—rate of intensity decrease after peak
1.3.3 Qualitative or hedonic changes in the perceived sen-
intensity (slope).
sation.
3.1.9 T or duration time—time from onset of sensation
dur
1.4 This guide includes protocols for the selection and
until it can no longer be perceived (T –T ).
ext onset
training of judges, descriptions and use of physical data
3.1.10 T or time to extinction—time from initial exposure
ext
collection devices, and methods of data handling, summariza-
to the stimulus (T ) until it can no longer be perceived.
init
tion, and statistical analysis. Illustration of two different data
3.1.11 T —time of initial exposure to the stimulus, typi-
init
handling and analysis approaches are included in the appen-
cally when the clock starts.
dixes.
3.1.12 T —time to reach maximum intensity of the sen-
max
1.5 Thisguideisnotapplicabletomeasureproductshelflife
sation after exposure to the stimulus.
or stability that require evaluations at discrete time intervals.
3.1.13 T —time point when the stimulus is first per-
onset
1.6 This standard does not purport to address all of the
ceived after initial exposure to the stimulus.
safety concerns, if any, associated with its use. It is the
3.1.14 T or truncated time—time until a specified mini-
trun
responsibility of the user of this standard to establish appro-
mum intensity or until a pre-determined time point has been
priate safety and health practices and determine the applica-
reached.
bility of regulatory limitations prior to use.
3.2 The graphical illustration of a typical time-intensity
2. Referenced Documents curve is shown in Fig. 1. The time increment may be seconds,
minutes, hours, etc., depending upon the characteristic of the
2.1 ASTM Standards:
particular material under study.
4. Summary of Guide
This guide is under the jurisdiction of ASTM Committee E18 on Sensory
Evaluation of Materials and Products and is the direct responsibility of Subcom-
4.1 This guide describes procedures utilizing specially
mittee E18.03 on Sensory Theory and Statistics.
trained panelists to measure the intensity of a single sensory
Current edition approved April 10, 2003. Published July 2003. Originally
approved in 1997. Last previous edition approved in 1997 as E1909–97. DOI:
sensation as it changes with time and the possible approaches
10.1520/E1909-97R03.
to collect and analyze such data. Details on specific procedures
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
are given in Sections 6-9 of this guide. Examples of time-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
related evaluations are included in the Appendixes.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1909 – 97 (2003)
recommended for other descriptive methods (see STP758 (2)).
Use of panelists with previous descriptive training facilitates
the T-I training because these panelists are competent in both
recognizing and intensity scaling an attribute.
6.1.2 The goal of the selection process is to identify
panelists who have the ability to:
6.1.2.1 Continually focus on a single sensory attribute,
6.1.2.2 Accurately identify and quantify a single sensory
attribute within a simple or complex sample,
6.1.2.3 Accurately record changes in sensations as they
occur,
6.1.2.4 Perform consistently,
6.1.2.5 Perform all test procedures with appropriate motor
skills(forexample,abilitytochewgumwhilemanipulatingthe
input device to indicate the intensity of the mint flavor).
6.1.3 Compared to other descriptive methods, T-I panelists
require more skills to complete the time-intensity task. Due to
NOTE 1—Based on a figure from Ref (15).
the complexity of the method and techniques involved, final
FIG. 1 Representative Time-Intensity Curve with Selected
selection of panelists may not occur until after completion of
Parameters Labeled
the training.
6.2 Time-Intensity Panel Training:
5. Significance and Use
6.2.1 The purpose of T-I training is to demonstrate how to
5.1 The purpose of time-intensity measurements is to estab- perform the physical, mental and psychological tasks associ-
lish the pattern of development and decline of a particular ated with temporal profile method. Training begins with an
sensory characteristic under study. T-I evaluations are appli- orientation to the T-I method. Orientation to the method
cable when measurements at a single time point (an averaging involves explanation and demonstration of the temporal nature
process) are not sufficient to distinguish products that have of sensory properties, utilizing products having diverse tempo-
very different temporal characteristics. As pointed out by Lee ral profiles. General time-intensity concepts may be illustrated
and Pangborn (1) , “This averaging process results in the by showing examples from alternate sensory modalities.
maskingorcompletelossofimportantinformationsuchasrate Sound, light, odor, taste, touch/pressure or texture may all
of onset of stimulation, time and duration of maximum display temporal properties.
intensity, rate of decay of perceived intensity, time of extinc- 6.2.2 During training, panelists are thoroughly familiarized
tion, and total duration of the entire process.”
with all testing equipment and procedures.
5.2 Products rated similarly using traditional single point
6.2.3 The purpose of training samples is to demonstrate
techniques of product profiling may provide very different
different onset, plateau, or duration characteristics. These are
temporalsensoryexperiencestotheconsumer.Acceptabilityof
often best presented in contrasting pairs or sets. One example
the product may be affected, and traditional descriptive meth-
is a set of chewing gums, one with a fast flavor onset, another
odology does not reflect the changes in an attribute’s intensity
with a slower onset. Another example is a series of margarine
over time.
products that demonstrate different textural properties, such as
5.3 T-I has applications for a variety of products. Examples
rate of melt.
include: food products, ranging from short-term sweetness in a
6.2.4 References are samples that demonstrate an attribute
beverage to long-term elasticity in chewing gum; personal care
at a given intensity. Use of references to calibrate intensity
products, measuring the development and longevity of sham-
ratings occurs prior to the test. This is critical because in T-I
poolatherandtheresidualskinfeelofaskincream;household
analysis, attribute intensity is recorded without interruption
care products, monitoring the intensity of scents over time;
during the test.
pharmaceuticals, monitoring skin cooling after application of a
6.3 Panel Performance Monitoring and Feedback
topical analgesic. Auditory signals or visual changes in prod-
6.3.1 Monitor panelist performance during the training and
ucts can also be evaluated by the T-I technique.
evaluation sessions. At the start of the study, determine an
acceptablelevelofindividualandgroupperformance.Thiscan
6. Time-Intensity Panel Selection and Training
include deviation around a scale value at a specified time point
6.1 Screening and Selection of Panelists
orsimilarindicator.STP758(2)providesstatisticalprocedures
6.1.1 Time-Intensity evaluation is a specialized type of
suitable for monitoring panelist performance.
descriptive analysis. Therefore, use of randomly selected,
6.3.2 Panelists should be able to demonstrate consistency in
naive panelists is neither appropriate nor recommended. Pan-
their evaluations. One approach is to measure reproducibility
elists selected for Time-Intensity studies are screened as
in selected curve parameters, for example, I ,T ,T ,of
max max ext
their individual T-I curves. However, consistency with other
panelistsislesslikelythanwithgeneraldescriptiveanalysis,as
The boldface numbers given in parentheses refer to a list of references at the
end of the text. each panelist tends to produce distinctive curve shapes. In T-I
E1909 – 97 (2003)
analysis, within-panelist consistency, particularly in their abil- recommended for most sensory evaluations. During training,
ity to communicate relative differences among samples, is samples may be presented in fixed order (that is, all panelists
more important than panelist-to-panelist agreement. See dis- see the same samples in the same order of presentation), to
cussion in Section 9. facilitate discussion and learning.
6.3.3 One parameter that should show some degree of 7.2 Data Collection Considerations—In any time-intensity
agreement among the panelists is I , particularly if reference experiment, regardless of the type of data collection device
max
standards for intensity are being utilized.The I value can be used, the rate at which information is collected must be
max
used to compare panelist performance with an appropriate determined. Data recording intervals are set to capture
means-separation test, percent standard deviation, or other maximum/critical change on a product’s profile, with intensity
analysis methods commonly used in monitoring descriptive ratings collected at various time points depending on the study
evaluations. objective (see Sections 8 and 9).
7.3 Sample Preparation—As with any sensory evaluation,
7. Panel Protocol
sample preparation and presentation forT-I analysis need to be
7.1 Specifics of the actual management of a time-intensity
controlled to eliminate extraneous effects. Recommended
panel are highly dependent upon study objectives. The follow-
guidelines are to be followed (Manual 26)(3).
ing topics represent major steps or considerations in the design
7.3.1 Reference Samples—If appropriate in the test design,
and execution of time-intensity panels. It is assumed that basic
use of reference samples is recommended. References are
panel training on the product of interest and selection of the
evaluatedpriortotestsamples,sothattestsampleevaluationis
appropriate data collection device have been completed (see
conducted without interruption. References are evaluated by
Sections 6 and 8, respectively).
the same technique as the test samples and may be used to
7.1.1 Design Considerations—Before the panel is con-
specify an attribute’s intensity at a specific point in time.
ducted, the following sample, experimental design, and set-up
7.3.2 Conditioning Sample—Use of a conditioning sample,
issues are resolved:
presented prior to the actual test sample, can be used to
7.1.1.1 The first consideration in designing a time-intensity
calibratepaneliststothesamesensation,andtosomeextent,to
panel is to determine the length of time for data collection. It
control first position bias or context effects. Consideration
can be relatively short, like the meltdown of a pat of butter
should be given to adaptation, carryover, and fatigue in
when placed in the mouth, or relatively long, like the longevity
deciding whether or not to use a conditioning sample.
of mint flavor in a chewing gum.
7.3.3 Inter-Stimulus Procedures—Specify whether panelists
7.1.1.2 Knowing the expected duration, and designing the
are to rinse, re-taste reference standards, or use a palate
study to cover critical changes in a product is prerequisite to
cleanser such as a cracker, celery, etc. between samples.
other design considerations. The number of sampling points
7.4 Evaluation Procedures:
and the time interval between points is set to capture the
7.4.1 Evaluation begins as soon as the stimulus is intro-
changes in an attribute at the time it occurs. Factors which may
duced to the panelist, for example, when the sample is applied,
affect the duration of the attribute to be measured include:
tasted, or smelled. The evaluation is completed upon reaching
sample form (crystalline versus dilute solution of sugar),
a predetermined time limit, intensity, or extinction of the
samplesize(largeramountofsampleversussmalleramountof
sensation.
sample), evaluation technique (dissolving versus chewing a
7.4.2 Standardized evaluation procedures such as the force
hard candy), other materials (water hardness for soaps and
and frequency of manipulations (for example, chews per
shampoos).
second of a cookie, rubs of a hand lotion, or whether to
7.1.2 The number of samples evaluated in a panel session is
expectorate or swallow) must be specified and incorporated
primarily dependent upon the duration of the time-intensity
into the panel training and test procedures to assure all
sensation. If the evaluation of a chewing gum is designed to
panelists receive the same sample stimulus.
measure mint flavor intensity changes over a 20 min period,
7.5 Other Panel Protocol Considerations:
onetotwosamplesmaybethemaximumnumberpanelistscan
7.5.1 Testing Environment—Follow recommended guide-
evaluate without excessive physical or mental fatigue. Con-
lines for physical testing facil
...
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