1、Designation: E 679 04Standard Practice forDetermination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits1This standard is issued under the fixed designation E 679; the number immediately following the designation indicates the year oforiginal adoption o
2、r, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe obtaining of odor and taste thresholds requires the sensory responses of
3、a selected group ofindividuals called panelists. These thresholds may be determined in order to note the effect of variousadded substances on the odor and taste of a medium. They may also be determined in order tocharacterize and compare the odor or taste sensitivity of individuals or groups.It is r
4、ecognized that precise threshold values for a given substance do not exist in the same sensethat values of vapor pressure exist. The ability to detect a substance by odor or taste is influenced byphysiological factors and criteria used in producing a response by the panelist. The parameters ofsample
5、 presentation introduce further variations. Thus, the flowrate of a gaseous, odorous sample hasan influence on the detectability of an odor. However, a concentration range exists below which theodor or taste of a substance will not be detectable under any practical circumstances, and above whichindi
6、viduals with a normal sense of smell or taste would readily detect the presence of the substance.The threshold determined by this practice is not the conventional group threshold (the stimulus leveldetectable with a probability of 0.5 by 50 % of the population) as obtained by Practice E 1432, butrat
7、her a best estimate not far therefrom. The bias of the estimate depends on the concentration scalesteps chosen and on the degree to which each panelists threshold is centered within the range ofconcentrations he or she receives. The user also needs to keep in mind the very large degree of randomerro
8、r associated with estimating the probability of detection from only 50 to 100 3-AFC presentations.1. Scope1.1 This practice describes a rapid test for determiningsensory thresholds of any substance in any medium.1.2 It prescribes an overall design of sample preparation anda procedure for calculating
9、 the results.1.3 The threshold may be characterized as being either (a)only detection (awareness) that a very small amount of addedsubstance is present but not necessarily recognizable, or (b)recognition of the nature of the added substance.1.4 The medium may be a gas, such as air, a liquid, such as
10、water or some beverage, or a solid form of matter. The mediummay be odorless or tasteless, or may exhibit a characteristicodor or taste per se.1.5 This practice describes the use of a multiple forced-choice sample presentation method in an ascending concentra-tion series, similar to the method of li
11、mits.1.6 Physical methods of sample presentation for thresholddetermination are not a part of this practice, and will depend onthe physical state, size, shape, availability, and other propertiesof the samples.1.7 It is recognized that the degree of training received by apanel with a particular subst
12、ance may have a profound influ-ence on the threshold obtained with that substance (1).21.8 Thresholds determined by using one physical method ofpresentation are not necessarily equivalent to values obtainedby another method.2. Referenced Documents2.1 ASTM Standards:3D 1292 Test Method for Odor in Wa
13、terE 544 Practice for Referencing Suprathreshold Odor Inten-sity1This practice is under the jurisdiction of ASTM Committee E18 on SensoryEvaluation of Materials and Products and is the direct responsibility of Subcom-mittee E18.04 on Fundamentals of Sensory.Current edition approved April 1, 2004. Pu
14、blished April 2004. Originallyapproved in 1979. Last previous edition approved in 1997 as E 679 91 (1997).2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Serv
15、ice 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.E 1432 Practice for Defining and Calculating
16、 Individual andGroup Sensory Thresholds from Forced-Choice Data Setsof Intermediate Size2.2 CEN Standards:4EN 13725 Air QualityDetermination of Odour Concen-tration Using Dynamic Dilution Olfactometry2.3 ISO Standards:5ISO 13301 Sensory AnalysisMethodologyGeneralGuidance for Measuring Odour, Flavour
17、 and Taste Detec-tion Thresholds by a Three Alternative Forced Choice(3AFC) Procedure3. Terminology3.1 Definitions:3.1.1 samplea material in any form that may or may notexhibit an odor or taste, depending on the amount of odorousor sapid components that it may contain.3.1.2 mediumany material used t
18、o dissolve, disperse, orsorb odorous or sapid material whose threshold is to bemeasured.3.1.3 blank samplea quantity of the medium containingno added odorous or sapid material.3.1.4 test samplethe medium to which an odorous orsapid material has been added at a known concentration.3.1.5 detection thr
19、esholdthe lowest concentration of asubstance in a medium relating to the lowest physical intensityat which a stimulus is detected as determined by the best-estimate criterion.3.1.6 recognition thresholdthe lowest concentration of asubstance in a medium relating to the lowest physical intensityat whi
20、ch a stimulus is recognized as determined by thebest-estimate criterion.3.1.7 best-estimate criterionan interpolated concentrationvalue, but not necessarily the concentration value that wasactually presented. In this practice it is the geometric mean ofthe last missed concentration and the next (adj
21、acent) higherconcentration.3.1.8 panelistsindividuals whose odor or taste thresholdsare being evaluated, or who are utilized to determine the odoror taste threshold of the substance of interest.3.1.9 ascending scale of concentrationsa series of in-creasing concentrations of an odorous or sapid subst
22、ance in achosen medium.3.1.10 scale stepsdiscrete concentration levels of a sub-stance in a medium, with concentrations increased by the samefactor per step throughout the scale.3.1.11 3-alternative forced choice (3-AFC) presentationaset consisting of one test sample and two blank samples (asapplied
23、 to this practice).3.1.12 geometric meanthe nth root of the product ofterms. In this method, the terms are concentration values.4. Summary of Practice4.1 A series of test samples is prepared by dispersing thesubstance whose threshold is to be determined in the mediumof interest. This concentration s
24、cale should increase in geomet-ric increments so that any two adjacent concentration steps areseparated by a constant factor. At each concentration step, twoblank samples consisting of the medium only are madeavailable to the panelist. The blank and test samples areencoded so that there is no visual
25、, audible, tactile, or thermaldifference between the samples other than code designators (2).4.2 The panelist starts at the lowest concentration step,which should be two or three concentration steps below theestimated threshold. Each sample within the set of three iscompared with the other two.4.3 T
26、he panelist indicates which of the three samples isdifferent from the other two. A choice must be made, even if nodifference is noted, so that all data can be utilized.4.4 Individual best-estimate values of threshold are derivedfrom the pattern of correct/incorrect responses produced sepa-rately by
27、each panelist. Group thresholds are derived bygeometrical averaging of the individual best-estimate thresh-olds.5. Significance and Use5.1 Sensory thresholds are used to determine the potential ofsubstances at low concentrations to impart odor, taste, skinfeel,etc. to some form of matter.5.2 Thresho
28、lds are used, for example, in setting limits for airpollution, in noise abatement, in water treatment, and in foodsystems.5.3 Thresholds are used to characterize and compare thesensitivity of individual or groups to given stimuli, for ex-ample, in medicine, in ethnic studies, and in the study ofanim
29、al species.6. Preparation of Concentration Scale6.1 The concentration levels of the test substance in amedium should begin well below the level at which the mostsensitive panelist is able to detect or recognize the addedsubstance, and end at (or above) the concentration at which allpanelists give a
30、correct response.6.2 The increase in concentration of the test substance perscale step should be by a constant factor. It is desirable toobtain a scale step factor that will allow the correct responsesof a group of nine panelists to distribute over three to fourconcentration steps (see Appendix X1-A
31、ppendix X3). This willallow more accuracy in determining the group threshold valuebased on the geometric mean of the individual panelists.6.3 Good judgment is required by the person in charge inorder to determine the appropriate scale step range for aparticular substance. This might involve the prep
32、aration of anapproximate threshold concentration of the odorous or sapidsubstance in the medium of choice. The concentration of thesubstance may be increased two to three times for odorants or1.5 to 2.5 times for sapid substances depending on how theperceived intensity of odor or taste varies with t
33、he concentra-tion of the substance providing the sensory response. For4Available from British Standards Institute (BSI), 389 Chiswick High Rd.,London W4 4AL, U.K.5Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.E679042example, if x represents
34、 an approximate odor threshold con-centration, then a series of concentration steps would appear asfollows if a step factor of “3” were used:. x/27, x/9, x/3, x,3x,9x,27x .6.4 In actual practice, the various concentrations are ob-tained by starting at the highest concentration and dilutingthree time
35、s per step, thus providing a series of dilution factors,“Vi” being the initial volume:.729Vi, 243Vi,81Vi,27Vi,9Vi,3Vi, Vi,.6.5 At each selected concentration or dilution, a 3-AFCsample set consisting of one test and two blank samples ispresented to panelists in indistinguishable fashion (3).Itisdesi
36、rable to have all samples prepared and ready for judgingbefore the evaluation session begins. (Reference (2) containssound practices for coding the samples, rotating the positionsof these test and blank samples as the test proceeds, etc.)6.6 If the samples are arranged in a left-center-right, or ana
37、bove-center-below order, care must be taken that the testsample is presented in one third of the presentations in the left(top) position, one third in the center position, and one third inthe right (bottom) position to eliminate positional bias.6.7 If only one sample at a time is available, the test
38、 andblank samples may be presented one after another in units ofthree presentations, with the test sample being randomized tobe the first, the second, and the third, and requesting theresponse after all three samples in the set have been presented.Better results, however, are obtained if the test an
39、d the twoblank samples are available for a direct comparison, so that thepanelist may sniff or taste back and forth at ease until adecision is reached.7. Judgment Procedure7.1 The panelist begins judging with that set which containsthe test sample with the lowest concentration (highest dilution)of t
40、he odorous or sapid substance, takes the time needed tomake a selection, and proceeds systematically toward thehigher concentrations.7.2 Within each set, the panelist indicates that sample whichis different from the two others (detection threshold) or whichexhibits a recognizable odor or taste of th
41、e substance (recog-nition threshold). If the panelist cannot readily discriminate, aguess must be made so that all data may be utilized.7.3 The judgments are completed when the panelist either(1) completes the evaluation of all sets of the scale, or (2)reaches a set wherein the test sample is correc
42、tly identified,then continues to choose correctly in higher concentration testsample sets.8. Data Evaluation8.1 The series of each panelists judgments may be ex-pressed by writing a sequence containing (0) for an incorrectchoice or (+) for a correct choice arranged in the order ofjudgments of ascend
43、ing concentrations of the added substance.8.2 If the concentration range has been correctly selected,all panelists should judge correctly within the range of con-centration steps provided. Thus, the representation of thepanelists judgments as in 8.1 should terminate with two ormore consecutive pluss
44、es (+).8.3 Because there is a finite probability that a correct answerwill occur by chance alone, it is important that a panelistcontinues to take the test until there is no doubt by that personof the correctness of the choice.8.4 The best-estimate threshold concentration for the pan-elist is then t
45、he geometric mean of that concentration at whichthe last miss (0) occurred and the next higher concentrationdesignated by a (+).8.5 The panel threshold is the geometric mean of thebest-estimate thresholds of the individual panelists. If a moreaccurate threshold value of an individual panelist is des
46、ired, itmay be obtained by calculating the geometric mean of thebest-estimate threshold of all series administered to thatperson.9. Report9.1 Successful completion of the foregoing procedure pro-vides either the detection or recognition threshold of thesubstance in the medium of interest in accordan
47、ce with thispractice.9.2 The threshold value is in concentration or dilution unitsappropriate for the substance tested (4).9.3 For enhanced understanding of the threshold results, thefollowing information is recommended:Threshold of:Procedure: ASTM Practice E 679 (Rapid Method)Presentation:Number of
48、 scale steps:Dilution factor per step:Temperature of samples:Panelist selection:Number of times test given:Type of threshold (detection or recognition):Best-estimate threshold:Individual:Panel:9.4 Refer to Appendix X1-Appendix X3 for examples of thecalculations and reporting requirements.10. Precisi
49、on and Bias10.1 Because sensory threshold values are functions ofsample presentation variables and of individual sensitivities,interlaboratory tests cannot be interpreted statistically in theusual way, and a general statement regarding precision and biasof thresholds obtained by this practice cannot be made.However, certain comparisons made under particular circum-stances are of interest and are detailed below.10.2 When 4 panels of 23 to 35 members evaluated butanolin air (5), the ratio of the highest to the lowest panel thresholdwas 2.7 to 1; when the same panel re
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