Odor suprathreshold

ASTM E544, "Recommended Practice for Odor Suprathreshold Intensity Referencing", Am. Soc. Test. Materials, Philadelphia, PA (1975). 

F.Patte, M.Etcheto, P.Laffort, Selected and Standardized Values of Suprathreshold Odor Intensities for 110 Substances, Chemical Senses and Flavour, 1, 1975, 283-305. 

Determining the threshold value is difficult because subthreshold levels of one compound may affect the threshold levels of another. Also, the flavor quality of a compound may be different at threshold level and at suprathreshold levels. The total range of perception can be divided into units that represent the smallest additional amount that can be perceived. This amount is called just noticeable difference (JND). The whole intensity scale of odor perception covers about 25 JNDs this is similar to the number of JNDs that comprise the scale of taste intensity. Flavor thresholds for some compounds depend on the medium in which the compound is dispersed or dissolved. Patton (1964) found large differences in the threshold values of saturated fatty acids dissolved in water and in oil. 

American Society for Testing and Materials Standard No. E544-75. "Standard Recommended Practices for Referencing Suprathreshold of Odor Intensity", published by ASTM, 1916 Race Street, Philadelphia, Pa. 19103 (1975). 

In still another study Dravnieks (6) correlated 1 1 structural features with odor threshold and suprathreshold data. More recently Dravnieks correlated odor intensity equivalent to 87 ppm (Vol/vol) of 1-butanol with 20 structural features represMted by Wiswesser line notation. The molecular weight term, (log mw), was reported to be the most statistically significant term. 

The use of computer techniques in the correlation of biological activity with substrate physical-chemical properties has received much attention in the area of medicinal chemistry. The use of these techniques, denoted Quantitative Structure Activity Relationships (QSAR), were developed mostly by Hansch and his coworkers eind have been reviewed by Tute te), Purcell et. al. (9) and Dunn (10). These techniques were utilized by Greenberg (1 l) ln the correlation of odor threshold and suprathreshold data with Log P, the log (n-octanol/water partition coefficient). In the same study it was reported that steric and polar effects as measured by the Taft Steric and Polar Constants poorly correlated with odor intensity data. 

Suprathreshold odor intensity data from Dravnieks (7) equating odor intensity equivalent to 87 ppm (vol./vol.) of n-butanol was used since it eliminated errors between laboratories which occur for threshold measurements and the n-butanol reference scale has been approved by the ASTM (24) as a standard method of measuring odor intensity. 

The alcohol data indicates that the bulkiness of the substituents on the carbinol moiety does not determine the level of odor intensity. The suprathreshold data also indicates that the polar effects of the groups bonded to the carbinol moiety did not effect the level of odor intensity. 

Aldehyde and ketone suprathreshold odor intensity correlated well with log P and HB as shown in Table II. No significant relationship between steric or electronic parameters with aldehyde-ketone suprathreshold data was found with the exception of the Sterimol parameter L which was highly correlated to log P (R=0.95). Aldehyde threshold data weis found to be linearly related to log P as shown in equations 10 eind 13. The same data was poorly correlated with E andvas shown in Table II (eq. 12, 15 and 16). Note that two different aldehyde threshold data sets from two different sources produced very similar equations having slopes, intercepts, correlation coefficients and standard deviations which are not statistically different at the 95% level of confidence (eq. 10 and 13). 

The equations in Table I indicate that for alcohols odor intensity is paraboliccilly dependent upon log P for threshold values determined in air (Eq. no. 11,19) and in water (Eq. no. 20) and linearly dependent upon log P for suprathreshold values in air (Eq. no. 1). The alcohol odor intensity also could be parabolically dependent upon log P for the suprathreshold values in... 

The use of the QSAR technique known as the Hansch Approach in the investigation of odor intensity and odorant physico-chemical properties has indicated that hydrophobic properties of homologous series of compounds, not steric or polar properties, are highly correlated to the level of odor intensity. This was shown to be the case for literature odor threshold and suprathreshold data determined at different laboratories using various media. The poor correlation between odor intensity and the steric properties of molecules (Taft Steric Constant) which had been reported earlier by this author (11) have been further verified by the use of Charton and Verloop Sterimol steric parameters. 

In a dendritic river system, the patterns of odor distribution are complex but exist in two general forms which have particular importance in the homeward migration of salmon. Downstream from a source, odors are distributed fully across the width of the stream. They may not be present in uniform concentrations owing to discontinuous mixing, but are, nevertheless, present at suprathreshold concentrations. A second pattern of distribution exists at the confluence of two streams. The stream carrying the odor of interest is scented from bank to bank, while the other tributary does not carry any of this scent. Where these two channels unite, there exists for a distance downstream, two discrete plumes, one with odor and one without. As these plumes of water move downstream they become mixed. This pattern of distribution and mixing is repeated throughout the river system as the water flows to the ocean. 

Flavomet database [20, 21]. Flavomet is a compilation of aroma compotmds foimd in human odor space, meaning at suprathreshold concentrations where they are likely to stimulate human olfactory receptor neurons [22]. Access to the online database (sponsored by DATU, Inc.) is freely available in the public domain. 

Many psychophysical approaches have been proposed to obtain quantitative estimates of individual percepts. Some studies focus on measurements of threshold sensitivity [29] others focus on the use of suprathreshold stimuli [30] both can be important in determining overall impact. Interests also lie in hedonic evaluations, odor quality and odor (aroma) acceptance in the academic (understanding the workings of the brain), marketing (understanding how to influence and motivate the consumer), and corporate... 

As mentioned, at suprathreshold levels subjects differ greatly both in the kind and in the number of verbal descriptors they apply to a given odor [78,79,81]. Some differences probably stem from the way subjects use labels, but some may reflect true individual differences in perceived quahty [126]. To determine exactly how the odor spaces of two subjects might differ, some test of performance (a task based on discrimination) might serve best [69]. 

The Lyon Clinical Olfactory Test is based on thresholds, suprathres-hold detection, and identification tasks. The LCOT includes two threshold measurements, one for R-(+)-carvone and the other for tetrahydrothio-phene (THT). The same threshold determination procedure is used for both compounds. Five concentration levels are presented in increasing order with a 4-AFC paradigm. In the suprathreshold detection task 16 odors, presented at a suprathreshold level, have to be detected by following a 4-AFC procedure. The identification task consists of 16 odors to be identified, following a 4-AFC procedure and using verbal alternatives. 

The only source of variation in suprathreshold detection scores was found to be the country. This country effect is not yet very well understood but would seem to be due to the Dutch panel as such, although not directly connected to age. In fact, even if suprathreshold detection is an easy and short procedure and seems a priori to be closely related to olfactory sensitivity, our results did not find any significant effect of healthy aging on scores. However, it is to be noted that there is a high ceiling effect on scores in this task as used in the LCOT. On average, panelists detected 15.5 odors of 16, a very high mean score that could explain the poor discrimination power of the task. 

On the basis of the results obtained in Study 1, our team developed the European Test of Olfaetory Capabilities [28]. This test is based on a combination of a suprathreshold deteetion task and an identification task. To construct the test, some of the transeultural odors previously selected in study 1 (vanilla, clove, apple, euealyptus, dimamon, garlic, anise, orange, lemon, and mint) were used [29]. Odor intensity was adjusted to increase the level of difficulty, especially in the detection task. Alternative odor names were also carefully selected in the identification protocol, so as to adjust the difficulty of identification [30]. The test was validated in six European... 

HT Lawless, CJ Corrigan, M Johnston. Variation in odor thresholds for 1-carvone and cineole and correlations with suprathreshold intensity ratings. Chem Senses 20 9-17, 1995. 

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