1、Designation: E1909 11Standard Guide forTime-Intensity Evaluation of Sensory Attributes1This standard is issued under the fixed designation E1909; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number i
2、n parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers procedures for conducting and ana-lyzing time-intensity (T-I) evaluations of products or othersensory stimuli. Time-intensity
3、 is the measurement of theintensity of a single sensory sensation over time in response toa single exposure to a product or other sensory stimulus.Simultaneous evaluations of multiple sensory attributes arepossible, although are outside of the scope of this document.See bibliography for more informa
4、tion.1.2 This guide utilizes a specially trained panel to measurethe intensity of a single continuous sensation during the timefrom initial exposure:1.2.1 To its extinction,1.2.2 To a specified intensity, or1.2.3 To a predetermined limit of time.1.3 Applications not covered in this guide include mea
5、sur-ing:1.3.1 Multiple sensations,1.3.2 Multiple exposures within a single measurement, and1.3.3 Qualitative or hedonic changes in the perceived sen-sation.1.4 This guide includes protocols for the selection andtraining of judges, descriptions and use of physical datacollection devices, and methods
6、of data handling, summariza-tion, and statistical analysis. Illustration of two different datahandling and analysis approaches are included in the appen-dixes.1.5 This guide is not applicable to measure product shelf lifeor stability that require evaluations at discrete time intervals.1.6 This stand
7、ard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 AS
8、TM Standards:2E253 Terminology Relating to Sensory Evaluation of Ma-terials and Products3. Terminology3.1 Definitions of Terms Specific to This Standard: See Fig.1.3.1.1 area after Imaxpost-peak area under the curve.3.1.2 area before Imaxpre-peak area under the curve.3.1.3 AUCarea under the curve.3.
9、1.4 Imaxor peak intensitymaximum observed intensityduring the time of measurement.3.1.5 perimetermeasured distance of perimeter of areadelineated by T-I curve.3.1.6 plateau timeduration of peak intensity.3.1.7 rate of increaserate of intensity increase beforepeak intensity (slope).3.1.8 rate of decr
10、easerate of intensity decrease after peakintensity (slope).3.1.9 Tduror duration timetime from onset of sensationuntil it can no longer be perceived (TextTonset).3.1.10 Textor time to extinctiontime from initial exposureto the stimulus (Tinit) until it can no longer be perceived.3.1.11 Tinittime of
11、initial exposure to the stimulus, typi-cally when the clock starts.3.1.12 Tmaxtime to reach maximum intensity of the sen-sation after exposure to the stimulus.3.1.13 Tonsettime point when the stimulus is first per-ceived after initial exposure to the stimulus.3.1.14 Ttrunor truncated timetime until
12、a specified mini-mum intensity or until a pre-determined time point has beenreached.3.2 The graphical illustration of a typical time-intensitycurve is shown in Fig. 1. The time increment may be seconds,1This guide is under the jurisdiction of ASTM Committee E18 on SensoryEvaluation and is the direct
13、 responsibility of Subcommittee E18.03 on SensoryTheory and Statistics.Current edition approved April 1, 2011. Published May 2011. Originallyapproved in 1997. Last previous edition approved in 2003 as E1909 97 (2003).DOI: 10.1520/E1909-11.2For referenced ASTM standards, visit the ASTM website, www.a
14、stm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.minutes
15、, hours, etc., depending upon the characteristic of theparticular material under study.4. Summary of Guide4.1 This guide describes procedures utilizing speciallytrained panelists to measure the intensity of a single sensorysensation as it changes with time and the possible approachesto collect and a
16、nalyze such data. Details on specific proceduresare given in Sections 6-9 of this guide. Examples of time-related evaluations are included in the Appendixes.5. Significance and Use5.1 The purpose of time-intensity measurements is to estab-lish the pattern of development and decline of a particularse
17、nsory characteristic under study. T-I evaluations are appli-cable when measurements at a single time point (an averagingprocess) are not sufficient to distinguish products that havevery different temporal characteristics. As pointed out by Leeand Pangborn (1)3, “This averaging process results in the
18、masking or complete loss of important information such as rateof onset of stimulation, time and duration of maximumintensity, rate of decay of perceived intensity, time of extinc-tion, and total duration of the entire process.”5.2 Products rated similarly using traditional single pointtechniques of
19、product profiling may provide very differenttemporal sensory experiences to the consumer.Acceptability ofthe product may be affected, and traditional descriptive meth-odology does not reflect the changes in an attributes intensityover time.5.3 T-I has applications for a variety of products. Examples
20、include: food products, ranging from short-term sweetness in abeverage to long-term elasticity in chewing gum; personal careproducts, measuring the development and longevity of sham-poo lather and the residual skin feel of a skin cream; householdcare products, monitoring the intensity of scents over
21、 time;pharmaceuticals, monitoring skin cooling after application of atopical analgesic. Auditory signals or visual changes in prod-ucts can also be evaluated by the T-I technique.6. Time-Intensity Panel Selection and Training6.1 Screening and Selection of Panelists6.1.1 Time-Intensity evaluation is
22、a specialized type ofdescriptive analysis. Therefore, use of randomly selected,naive panelists is neither appropriate nor recommended. Pan-elists selected for Time-Intensity studies are screened asrecommended for other descriptive methods (see STP 758 (2).Use of panelists with previous descriptive t
23、raining facilitatesthe T-I training because these panelists are competent in bothrecognizing and intensity scaling an attribute.6.1.2 The goal of the selection process is to identifypanelists who have the ability to:6.1.2.1 Continually focus on a single sensory attribute,6.1.2.2 Accurately identify
24、and quantify a single sensoryattribute within a simple or complex sample,6.1.2.3 Accurately record changes in sensations as theyoccur,6.1.2.4 Perform consistently,6.1.2.5 Perform all test procedures with appropriate motorskills (for example, ability to chew gum while manipulating theinput device to
25、indicate the intensity of the mint flavor).6.1.3 Compared to other descriptive methods, T-I panelistsrequire more skills to complete the time-intensity task. Due tothe complexity of the method and techniques involved, finalselection of panelists may not occur until after completion ofthe training.6.
26、2 Time-Intensity Panel Training:6.2.1 The purpose of T-I training is to demonstrate how toperform the physical, mental and psychological tasks associ-ated with temporal profile method. Training begins with anorientation to the T-I method. Orientation to the methodinvolves explanation and demonstrati
27、on of the temporal natureof sensory properties, utilizing products having diverse tempo-ral profiles. General time-intensity concepts may be illustratedby showing examples from alternate sensory modalities.Sound, light, odor, taste, touch/pressure or texture may alldisplay temporal properties.6.2.2
28、During training, panelists are thoroughly familiarizedwith all testing equipment and procedures.6.2.3 The purpose of training samples is to demonstratedifferent onset, plateau, or duration characteristics. These areoften best presented in contrasting pairs or sets. One exampleis a set of chewing gum
29、s, one with a fast flavor onset, anotherwith a slower onset. Another example is a series of margarineproducts that demonstrate different textural properties, such asrate of melt.6.2.4 References are samples that demonstrate an attributeat a given intensity. Use of references to calibrate intensityra
30、tings occurs prior to the test. This is critical because in T-Ianalysis, attribute intensity is recorded without interruptionduring the test.6.3 Panel Performance Monitoring and Feedback6.3.1 Monitor panelist performance during the training andevaluation sessions. At the start of the study, determin
31、e an3The boldface numbers given in parentheses refer to a list of references at theend of the text.NOTE 1Based on a figure from Ref (15).FIG. 1 Representative Time-Intensity Curve with SelectedParameters LabeledE1909 112acceptable level of individual and group performance. This caninclude deviation
32、around a scale value at a specified time pointor similar indicator. STP 758 (2) provides statistical proceduressuitable for monitoring panelist performance.6.3.2 Panelists should be able to demonstrate consistency intheir evaluations. One approach is to measure reproducibilityin selected curve param
33、eters, for example, Imax,Tmax,Text,oftheir individual T-I curves. However, consistency with otherpanelists is less likely than with general descriptive analysis, aseach panelist tends to produce distinctive curve shapes. In T-Ianalysis, within-panelist consistency, particularly in their abil-ity to
34、communicate relative differences among samples, ismore important than panelist-to-panelist agreement. See dis-cussion in Section 9.6.3.3 One parameter that should show some degree ofagreement among the panelists is Imax, particularly if referencestandards for intensity are being utilized. The Imaxva
35、lue can beused to compare panelist performance with an appropriatemeans-separation test, percent standard deviation, or otheranalysis methods commonly used in monitoring descriptiveevaluations.7. Panel Protocol7.1 Specifics of the actual management of a time-intensitypanel are highly dependent upon
36、study objectives. The follow-ing topics represent major steps or considerations in the designand execution of time-intensity panels. It is assumed that basicpanel training on the product of interest and selection of theappropriate data collection device have been completed (seeSections 6 and 8, resp
37、ectively).7.1.1 Design ConsiderationsBefore the panel is con-ducted, the following sample, experimental design, and set-upissues are resolved:7.1.1.1 The first consideration in designing a time-intensitypanel is to determine the length of time for data collection. Itcan be relatively short, like the
38、 meltdown of a pat of butterwhen placed in the mouth, or relatively long, like the longevityof mint flavor in a chewing gum.7.1.1.2 Knowing the expected duration, and designing thestudy to cover critical changes in a product is prerequisite toother design considerations. The number of sampling point
39、sand the time interval between points is set to capture thechanges in an attribute at the time it occurs. Factors which mayaffect the duration of the attribute to be measured include:sample form (crystalline versus dilute solution of sugar),sample size (larger amount of sample versus smaller amount
40、ofsample), evaluation technique (dissolving versus chewing ahard candy), other materials (water hardness for soaps andshampoos).7.1.2 The number of samples evaluated in a panel session isprimarily dependent upon the duration of the time-intensitysensation. If the evaluation of a chewing gum is desig
41、ned tomeasure mint flavor intensity changes over a 20 min period,one to two samples may be the maximum number panelists canevaluate without excessive physical or mental fatigue. Con-versely, 5 to 6 potato chips may be evaluated for duration ofcrisp/crunchy attributes before fatigue sets in.7.1.3 If
42、the test is designed to measure the perception of anattribute to extinction, there is generally no need for lengthywaiting periods between samples. However, a longer waitingperiod is required when the perception of an attribute isaffected by a preceding sample. Examples include: allowingmouth temper
43、ature to return to normal after ice cream evalu-ations, and recovery from numbing effects due to menthol orspices.7.1.4 Sample presentation order may be randomized, fixed,balanced, or presented as an incomplete block, depending onstudy objectives. Typically, samples are presented in a bal-anced orde
44、r to minimize position bias, context effects, etc. asrecommended for most sensory evaluations. During training,samples may be presented in fixed order (that is, all panelistssee the same samples in the same order of presentation), tofacilitate discussion and learning.7.2 Data Collection Consideratio
45、nsIn any time-intensityexperiment, regardless of the type of data collection deviceused, the rate at which information is collected must bedetermined. Data recording intervals are set to capturemaximum/critical change on a products profile, with intensityratings collected at various time points depe
46、nding on the studyobjective (see Sections 8 and 9).7.3 Sample PreparationAs with any sensory evaluation,sample preparation and presentation for T-I analysis need to becontrolled to eliminate extraneous effects. Recommendedguidelines are to be followed (Manual 26)(3).7.3.1 Reference SamplesIf appropr
47、iate in the test design,use of reference samples is recommended. References areevaluated prior to test samples, so that test sample evaluation isconducted without interruption. References are evaluated bythe same technique as the test samples and may be used tospecify an attributes intensity at a sp
48、ecific point in time.7.3.2 Conditioning SampleUse of a conditioning sample,presented prior to the actual test sample, can be used tocalibrate panelists to the same sensation, and to some extent, tocontrol first position bias or context effects. Considerationshould be given to adaptation, carryover,
49、and fatigue indeciding whether or not to use a conditioning sample.7.3.3 Inter-Stimulus ProceduresSpecify whether panelistsare to rinse, re-taste reference standards, or use a palatecleanser such as a cracker, celery, etc. between samples.7.4 Evaluation Procedures:7.4.1 Evaluation begins as soon as the stimulus is intro-duced to the panelist, for example, when the sample is applied,tasted, or smelled. The evaluation is completed upon reachinga predetermined time limit, intensity, or extinction of thesensation.7.4.2 Standardized evaluation procedures such as
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