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Structure-activity relationships on the odor detectability of homologous carboxylic acids by humans.

Cometto-Muñiz JE, Abraham MH - Exp Brain Res (2010)

Bottom Line: Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported.No significant effects of gender on odor detectability were observed.We discuss the mechanistic implications of this model for the process of olfactory detection.

View Article: PubMed Central - PubMed

Affiliation: Chemosensory Perception Laboratory, Department of Surgery Otolaryngology, University of California, San Diego, 9500 Gilman Dr, Mail Code 0957, La Jolla, CA 92093-0957, USA. ecometto@ucsd.edu

ABSTRACT
We measured concentration detection functions for the odor detectability of the homologs: formic, acetic, butyric, hexanoic, and octanoic acids. Subjects (14 ≤ n ≤ 18) comprised young (19-37 years), healthy, nonsmoker, and normosmic participants from both genders. Vapors were delivered by air dilution olfactometry, using a three-alternative forced-choice procedure against carbon-filtered air, and an ascending concentration approach. Delivered concentrations were established by gas chromatography (flame ionization detector) in parallel with testing. Group and individual olfactory functions were modeled by a sigmoid (logistic) equation from which two parameters are calculated: C, the odor detection threshold (ODT) and D, the steepness of the function. Thresholds declined with carbon chain length along formic, acetic, and butyric acid where they reached a minimum (ODTs = 514, 5.2, and 0.26 ppb by volume, respectively). Then, they increased for hexanoic (1.0 ppb) and octanoic (0.86 ppb) acid. Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported. No significant effects of gender on odor detectability were observed. The finding of an optimum molecular size for odor potency along homologs confirms a prediction made by a model of ODTs based on a solvation equation. We discuss the mechanistic implications of this model for the process of olfactory detection.

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Left Group detectability functions for the odor of the five carboxylic acids. Each symbol represents the outcome of 630 judgments in the cases of formic and hexanoic acids, 560 judgments in the case of acetic acid, and 490 judgments in the cases of butyric and octanoic acids. Right Plots of group average confidence rating as a function of concentration for each acid. In all cases, bars indicate standard error (SE) of the mean
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Fig1: Left Group detectability functions for the odor of the five carboxylic acids. Each symbol represents the outcome of 630 judgments in the cases of formic and hexanoic acids, 560 judgments in the case of acetic acid, and 490 judgments in the cases of butyric and octanoic acids. Right Plots of group average confidence rating as a function of concentration for each acid. In all cases, bars indicate standard error (SE) of the mean

Mentions: Figure 1 (left) shows the group psychometric functions for the five carboxylic acids. From formic to butyric acid, functions increasingly shifted toward lower concentrations with increasing carbon chain length, reflecting increasing odor potency and lower ODTs. The trend was reversed for hexanoic and octanoic acid, whose functions, close to one another, shifted toward higher concentrations and higher ODTs. The sigmoid Eq. 2 provided a very adequate fit to the group concentration detection data. Table 2 (upper part) quantifies the outcome in terms of ODT (ppb), parameters C (log ODT) and D (steepness of the curve) with their respective standard errors (SE), and the coefficient of determination (R2). In turn, Fig. 1 (right) illustrates how, as expected, confidence ratings closely followed the trend of the respective detectability data for each acid.Fig. 1


Structure-activity relationships on the odor detectability of homologous carboxylic acids by humans.

Cometto-Muñiz JE, Abraham MH - Exp Brain Res (2010)

Left Group detectability functions for the odor of the five carboxylic acids. Each symbol represents the outcome of 630 judgments in the cases of formic and hexanoic acids, 560 judgments in the case of acetic acid, and 490 judgments in the cases of butyric and octanoic acids. Right Plots of group average confidence rating as a function of concentration for each acid. In all cases, bars indicate standard error (SE) of the mean
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2964470&req=5

Fig1: Left Group detectability functions for the odor of the five carboxylic acids. Each symbol represents the outcome of 630 judgments in the cases of formic and hexanoic acids, 560 judgments in the case of acetic acid, and 490 judgments in the cases of butyric and octanoic acids. Right Plots of group average confidence rating as a function of concentration for each acid. In all cases, bars indicate standard error (SE) of the mean
Mentions: Figure 1 (left) shows the group psychometric functions for the five carboxylic acids. From formic to butyric acid, functions increasingly shifted toward lower concentrations with increasing carbon chain length, reflecting increasing odor potency and lower ODTs. The trend was reversed for hexanoic and octanoic acid, whose functions, close to one another, shifted toward higher concentrations and higher ODTs. The sigmoid Eq. 2 provided a very adequate fit to the group concentration detection data. Table 2 (upper part) quantifies the outcome in terms of ODT (ppb), parameters C (log ODT) and D (steepness of the curve) with their respective standard errors (SE), and the coefficient of determination (R2). In turn, Fig. 1 (right) illustrates how, as expected, confidence ratings closely followed the trend of the respective detectability data for each acid.Fig. 1

Bottom Line: Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported.No significant effects of gender on odor detectability were observed.We discuss the mechanistic implications of this model for the process of olfactory detection.

View Article: PubMed Central - PubMed

Affiliation: Chemosensory Perception Laboratory, Department of Surgery Otolaryngology, University of California, San Diego, 9500 Gilman Dr, Mail Code 0957, La Jolla, CA 92093-0957, USA. ecometto@ucsd.edu

ABSTRACT
We measured concentration detection functions for the odor detectability of the homologs: formic, acetic, butyric, hexanoic, and octanoic acids. Subjects (14 ≤ n ≤ 18) comprised young (19-37 years), healthy, nonsmoker, and normosmic participants from both genders. Vapors were delivered by air dilution olfactometry, using a three-alternative forced-choice procedure against carbon-filtered air, and an ascending concentration approach. Delivered concentrations were established by gas chromatography (flame ionization detector) in parallel with testing. Group and individual olfactory functions were modeled by a sigmoid (logistic) equation from which two parameters are calculated: C, the odor detection threshold (ODT) and D, the steepness of the function. Thresholds declined with carbon chain length along formic, acetic, and butyric acid where they reached a minimum (ODTs = 514, 5.2, and 0.26 ppb by volume, respectively). Then, they increased for hexanoic (1.0 ppb) and octanoic (0.86 ppb) acid. Odor thresholds and interindividual differences in olfactory acuity among these young, normosmic participants were lower than traditionally thought and reported. No significant effects of gender on odor detectability were observed. The finding of an optimum molecular size for odor potency along homologs confirms a prediction made by a model of ODTs based on a solvation equation. We discuss the mechanistic implications of this model for the process of olfactory detection.

Show MeSH
Related in: MedlinePlus