Concentration-detection functions for the odor of homologous n-acetate esters

Non-monotonic psychometric functions for α-ionone in young adults

The mathematical relationship between the ability to detect an odorant and its concentration appears for some odorants to be non-monotonic, with reversals ("notches") in performance appearing at points along the psychometric function. Like visual adaptation curves that reflect the differential sensitivities of cones and rods, such reversals may provide information about underlying olfactory receptor processes. However, the presence of such reversals is rarely acknowledged, few participants and odorants have been tested, and methodological concerns abound. In this study, we examined in detail the psychometric function for the odorant α-ionone using a sizable number of young participants and 10 log-based concentrations of α-ionone presented in a random fashion. A trial consisted of the counterbalanced presentation of an odorless mineral oil and a concentration of α-ionone in rapid succession using Snap & Sniff® wands. The participants reported which of the two seemed stronger and indicated their confidence on a 9-point scale. In Study 1, 24 participants completed a single 30-minute test session of 60 trials. In Study 2, 600 trials were obtained from each of nine participants over the course of ten 30-minute sessions. In both studies, notches were consistently found in the psychometric function near the 10-5 and 10-3.5 vol/vol concentrations. Participants' trial-by-trial confidence judgments corresponded with their detection performance, but their self-rated sense of smell did not. This research definitively demonstrates the presence of reliable reversals in the human α-ionone psychometric function and begs the question as to whether such reversals reflect the recruitment of receptive elements with differing response profiles.

Indoor Air Quality-An Overview of Methods for Measuring Odor Detection Thresholds of Single Substances

Odor evaluation is an important topic in the field of indoor air quality. Odor detection threshold (ODT) values are used to derive limit values like odor guide values or odor activity value. However, ODT values for the same substance available in compilations or published before 2003 rarely have an accuracy of less than three orders of magnitude. Stimulus preparation, including analytical verification, stimulus presentation, as well as selection and training of test subjects have been identified as major sources of variability. ODT values obtained by validated standardized methods are now considered objective, reliable, and reproducible. They exhibit a variability of one or two orders of magnitude and are lower than traditionally assumed and reported. This review presents the essential criteria for a well-performed ODT determination. It is intended to assist health and safety professionals in assessing whether the methodological approach of a study was appropriate for determining a valid and reliable ODT value.

The Impact of Fermentation Temperature and Cap Management on Selected Volatile Compounds and Temporal Sensory Characteristics of Grenache Wines from the Central Coast of California

Grenache wines from the Central Coast of California were subjected to different alcoholic fermentation temperature regimes (Cold, Cold/Hot, Hot) and cap management protocols, namely, punch down (PD), or no punch down (No PD), to determine the effect of these practices on the color, aroma, and the retronasal and mouthfeel sensory characteristics of the resulting wines. Descriptive analysis (n = 8, line scale rating 0-15) results indicated that the combination of a hot fermentation temperature and no punch downs led to a significantly higher intensity in perceived color saturation (7.89) and purple hue (8.62). A two-way analysis of variance (ANOVA) showed that cap management was significantly more impactful on the perception of orthonasal aromas than fermentation temperature. The reduction aroma was significantly higher in No PD wines (5.02) compared to PD wines (3.50), while rose and hot aromas had significantly higher intensity perception for PD wines (5.18, 6.80) than for No PD wines (6.80, 6.14). Conversely, analysis of selected volatile compounds indicated that fermentation temperature was more impactful than cap management regime. Cold/Hot wines had higher concentrations of important esters such as ethyl hexanoate (650 µg/L) and isoamyl acetate (992 µg/L). Cold wines had a higher concentration of β-damascenone (0.719 µg/L). TCATA evaluation (n = 8) indicated that Cold/Hot PD wines had a significantly higher citation proportion of fruit flavor (1.0) and velvet astringency perception (0.80) without significant reduction flavors. Finally, the present study represents a contribution with the main volatile compounds (e.g., β-damascenone and esters in the Cold and Cold/Hot fermented wines, respectively; hexanol in PD wines, which may be potentially responsible for a hot mouthfeel), and sensory characteristics (red fruit, tropical fruit, white pepper, and rose) of Grenache wines grown in the Mediterranean climate of the Central Coast of California.

The behavioral sensitivity of mice to acetate esters

Measures of behavioral sensitivity provide an important guide for choosing the stimulus concentrations used in functional experiments. This information is particularly valuable in the olfactory system as the neural representation of an odorant changes with concentration. This study focuses on acetate esters because they are commonly used to survey neural activity in a variety of olfactory regions, probe the behavioral limits of odor discrimination, and assess odor structure–activity relationships in mice. Despite their frequent use, the relative sensitivity of these odorants in mice is not available. Thus, we assayed the ability of C57BL/6J mice to detect seven different acetates (propyl acetate, butyl acetate, pentyl acetate, hexyl acetate, octyl acetate, isobutyl acetate, and isoamyl acetate) using a head-fixed Go/No-Go operant conditioning assay combined with highly reproducible stimulus delivery. To aid in the accessibility and applicability of our data, we have estimated the vapor-phase concentrations of these odorants in five different solvents using a photoionization detector-based approach. The resulting liquid-/vapor-phase equilibrium equations successfully corrected for behavioral sensitivity differences observed in animals tested with the same odorant in different solvents. We found that mice are most sensitive to isobutyl acetate and least sensitive to propyl acetate. These updated measures of sensitivity will hopefully guide experimenters in choosing appropriate stimulus concentrations for experiments using these odorants.

Validation of Olfactory Network Based on Brain Structural Connectivity and Its Association With Olfactory Test Scores

Olfactory perception is a complicated process involving multiple cortical and subcortical regions, of which the underlying brain dynamics are still not adequately mapped. Even in the definition of the olfactory primary cortex, there is a large degree of variation in parcellation templates used for investigating olfaction in neuroimaging studies. This complicates comparison between human olfactory neuroimaging studies. The present study aims to validate an olfactory parcellation template derived from both functional and anatomical data that applies structural connectivity (SC) to ensure robust connectivity to key secondary olfactory regions. Furthermore, exploratory analyses investigate if different olfactory parameters are associated with differences in the strength of connectivity of this structural olfactory fingerprint. By combining diffusion data with an anatomical atlas and advanced probabilistic tractography, we found that the olfactory parcellation had a robust SC network to key secondary olfactory regions. Furthermore, the study indicates that higher ratings of olfactory significance were associated with increased intra- and inter-hemispheric SC of the primary olfactory cortex. Taken together, these results suggest that the patterns of SC between the primary olfactory cortex and key secondary olfactory regions has potential to be used for investigating the nature of olfactory significance, hence strengthening the theory that individual differences in olfactory behaviour are encoded in the structural network fingerprint of the olfactory cortex.

Clinical assessment of olfactory function

Approximately 5% of the general population is affected by functional anosmia with approximately additional 15% exhibiting decreased olfactory function. Many of these individuals ask for help. Because the subjective rating of olfactory function is biased, assessment of olfactory function is important. Olfactory measurements are needed for patient counseling and the tracking of changes in the sense of smell over time. The present review provides an overview of frequently used psychophysical tests for olfactory function, discusses differences between threshold and suprathreshold aspects of olfactory function, and gives examples on how to apply psychophysical tests.

The Impact of Indoor Malodor: Historical Perspective, Modern Challenges, Negative Effects, and Approaches for Mitigation

Malodors, odors perceived to be unpleasant or offensive, may elicit negative symptoms via the olfactory system’s connections to cognitive and behavioral systems at levels below the known thresholds for direct adverse events. Publications on harm caused by indoor malodor are fragmented across disciplines and have not been comprehensively summarized to date. This review examines the potential negative effects of indoor malodor on human behavior, performance and health, including individual factors that may govern such responses and identifies gaps in existing research. Reported findings show that indoor malodor may have negative psychological, physical, social, and economic effects. However, further research is needed to understand whether the adverse effects are elicited via an individual’s experience or expectations or through a direct effect on human physiology and well-being. Conversely, mitigating indoor malodor has been reported to have benefits on performance and subjective responses in workers. Eliminating the source of malodor is often not achievable, particularly in low-income communities. Therefore, affordable approaches to mitigate indoor malodor such as air fresheners may hold promise. However, further investigations are needed into the effectiveness of such measures on improving health outcomes such as cognition, mood, and stress levels and their overall impact on indoor air quality.

Occupational exposure to volatile organic compounds and health risks in Colorado nail salons

Nail salon technicians face chronic exposure to volatile organic compounds (VOCs), which can lead to adverse health outcomes including cancer. In this study, indoor levels of formaldehyde, as well as benzene, toluene, ethylbenzene and xylene, were measured in 6 Colorado nail salons. Personal exposure VOC measurements and health questionnaires (n = 20) were also performed; questionnaires included employee demographics, health symptoms experienced, and protective equipment used. Cancer slope factors from the United States Environmental Protection Agency (US EPA) and anthropometric data from the Centers for Disease Control and Prevention were then used to estimate cancer risk for workers, assuming 20-yr exposures to concentrations of benzene and formaldehyde reported here. Results show that 70% of surveyed workers experienced at least one health issue related to their employment, with many reporting multiple related symptoms. Indoor concentrations of formaldehyde ranged from 5.32 to 20.6 μg m^-3, across all 6 salons. Indoor concentrations of toluene ranged from 26.7 to 816 μg m^-3, followed by benzene (3.13-51.8 μg m^-3), xylenes (5.16-34.6 μg m^-3), and ethylbenzene (1.65-9.52 μg m^-3). Formaldehyde levels measured in one salon exceeded the Recommended Exposure Limit from the National Institute for Occupational Safety and Health. Cancer risk estimates from formaldehyde exposure exceeded the US EPA de minimis risk level (1 × 10^-6) for squamous cell carcinoma, nasopharyngeal cancer, Hodgkin's lymphoma, and leukemia; leukemia risk exceeded 1 × 10^-4 in one salon. The average leukemia risk from benzene exposure also exceeded the US EPA de minimis risk level for all demographic categories modeled. In general, concentrations of aromatic compounds measured here were comparable to those measured in studies of oil refinery and auto garage workers. Cancer risk models determined that 20-yr exposure to formaldehyde and benzene concentrations measured in this study will significantly increase worker's risk of developing cancer in their lifetime.

Olfactory Impact of Terpene Alcohol on Terpenes Aroma Expression in Chrysanthemum Essential Oils

The key point of our work was evaluating the impact of terpene alcohols on the aroma expression of terpenes recombination in Chrysanthemum essential oils. Using pure commercial products, various aromatic recombinations were prepared, consisting of terpenes recombination and six terpene alcohols, all the concentrations found in Chrysanthemum essential oils. There were five groups of terpene alcohols mixtures performed very interesting with the addition or omission tests. The “olfactory threshold” of the terpenes recombination had a notable decrease when adding isoborneol, d-Fenchyl alcohol respectively through the Feller’s additive model analysis. Furthermore, the descriptive test indicated that the addition of terpene alcohols mixture had the different effect on fruity, floral, woody, green, and herbal aroma intensity. Specifically, when isoborneol was added to the terpenes recombination in squalane solution, it was revealed that isoborneol had a synergy impact on herbal and green notes of the terpenes recombination and masked the fruity note.

Olfactory impact of esters on rose essential oil floral alcohol aroma expression in model solution

This study focused on the impact of esters on the perception of floral aroma in rose essential oil. Various aromatic reconstitutions were prepared, consisting of 10 alcohols and 9 esters, all the concentrations found in rose essential oil. Sensory analysis by the triangular tests revealed the interesting behavior of certain compounds among the 9 esters following their addition or omission. The results tend to highlight the important role of ethyl octanoate, ethyl tetradecanoate, citronellyl acetate, geranyl acetate, and 2-phenethyl acetate of esters in rose essential oil. The "olfactory threshold" (OT) of the 5 esters, the floral reconstitution and the mixtures of ester and floral reconstitution were evaluated in alkanes solution. Through the Feller's additive model analysis, it was found that the presence of ethyl octanoate, ethyl tetradecanoate, and citronellyl acetate led to a significant in decrease the OT of the mixtures, whereas geranyl acetate raised the OT. The floral reconstitution in alkanes solution was supplemented with the 5 esters at high, medium, and low concentration, then analyzed by quantitative descriptive analysis. It was revealed that ethyl octanoate, ethyl tetradecanoate, and citronellyl acetate adding overall aroma, and geranyl acetate masking the overall aroma perception in a model floral mixture. Sensory profiles highlighted changes in the perception of aroma nuances in the presence of the 5 esters, with specific perceptive interactions, and reported on the graph based on two parameters [σ = f(τ)]. This paper provided a reference for the flavourists.

PLS regression-based chemometric modeling of odorant properties of diverse chemical constituents of black tea and coffee

We investigate the key structural features regulating the odorant properties of constituents present in black tea and coffee, the most attractive non-alcoholic beverages.

Olfactory Sensitivity in Mammalian Species

Olfaction enables most mammalian species to detect and discriminate vast numbers of chemical structures called odorants and pheromones. The perception of such chemical compounds is mediated via two major olfactory systems, the main olfactory system and the vomeronasal system, as well as minor systems, such as the septal organ and the Grueneberg ganglion. Distinct differences exist not only among species but also among individuals in terms of their olfactory sensitivity; however, little is known about the mechanisms that determine these differences. In research on the olfactory sensitivity of mammals, scientists thus depend in most cases on behavioral testing. In this article, we reviewed scientific studies performed on various mammalian species using different methodologies and target chemical substances. Human and non-human primates as well as rodents and dogs are the most frequently studied species. Olfactory threshold studies on other species do not exist with the exception of domestic pigs. Olfactory testing performed on seals, elephants, and bats focused more on discriminative abilities than on sensitivity. An overview of olfactory sensitivity studies as well as olfactory detection ability in most studied mammalian species is presented here, focusing on comparable olfactory detection thresholds. The basics of olfactory perception and olfactory sensitivity factors are also described.

An assessment of air quality reflecting the chemosensory irritation impact of mixtures of volatile organic compounds

We present a method to assess the air quality of an environment based on the chemosensory irritation impact of mixtures of volatile organic compounds (VOCs) present in such environment. We begin by approximating the sigmoid function that characterizes psychometric plots of probability of irritation detection (Q) versus VOC vapor concentration to a linear function. First, we apply an established equation that correlates and predicts human sensory irritation thresholds (SIT) (i.e., nasal and eye irritation) based on the transfer of the VOC from the gas phase to biophases, e.g., nasal mucus and tear film. Second, we expand the equation to include other biological data (e.g., odor detection thresholds) and to include further VOCs that act mainly by "specific" effects rather than by transfer (i.e., "physical") effects as defined in the article. Then we show that, for 72 VOCs in common, Q values based on our calculated SITs are consistent with the Threshold Limit Values (TLVs) listed for those same VOCs on the basis of sensory irritation by the American Conference of Governmental Industrial Hygienists (ACGIH). Third, we set two equations to calculate the probability (Qmix) that a given air sample containing a number of VOCs could elicit chemosensory irritation: one equation based on response addition (Qmix scale: 0.00 to 1.00) and the other based on dose addition (1000*Qmix scale: 0 to 2000). We further validate the applicability of our air quality assessment method by showing that both Qmix scales provide values consistent with the expected sensory irritation burden from VOC mixtures present in a wide variety of indoor and outdoor environments as reported on field studies in the literature. These scales take into account both the concentration of VOCs at a particular site and the propensity of the VOCs to evoke sensory irritation.

Dose-Response Functions for the Olfactory, Nasal Trigeminal, and Ocular Trigeminal Detectability of Airborne Chemicals by Humans

We gathered from the literature 47 odor and 37 trigeminal (nasal and ocular) chemesthetic psychometric (i.e., detectability or dose-response) functions from a group of 41 chemicals. Vapors delivered were quantified by analytical methods. All functions were very well fitted by the sigmoid (logistic) equation: y = 1 / (1 + e({-(x-C)/D})), where parameter C quantifies the detection threshold concentration and parameter D the steepness of the function. Odor and chemesthetic functions showed no concentration overlap: olfactory functions grew along the parts per billion (ppb by volume) range or lower, whereas trigeminal functions grew along the part per million (ppm by volume) range. Although, on average, odor detectability rose from chance detection to perfect detection within 2 orders of magnitude in concentration, chemesthetic detectability did it within one. For 16 compounds having at least 1 odor and 1 chemesthetic function, the average gap between the 2 functions was 4.6 orders of magnitude in concentration. A quantitative structure-activity relationship (QSAR) using 5 chemical descriptors that had previously described stand-alone odor and chemesthetic threshold values, also holds promise to describe, and eventually predict, olfactory and chemesthetic detectability functions, albeit functions from additional compounds are needed to strengthen the QSAR.

[Indoor air guide values for ethyl acetate. Communication of the German Ad Hoc Working Group on Indoor Air Guidelines of the Indoor Air Hygiene Committee and the Supreme State Health Authorities]

The German Ad Hoc Working Group on Indoor Air Guidelines of the Indoor Air Hygiene Committee and the Supreme State Health Authorities issues indoor air guide values to protect public health. No suitable human studies are available for health evaluation of ethyl acetate in indoor air. In a well-documented subchronic inhalation rat study, assessed as reliable, local effects were observed in nasal epithelia. The incidence and severity of degeneration of the nasal olfactory epithelium was dose-dependent. This study leads to a lowest observed adverse effect concentration (LOAEC) of 1280 mg ethyl acetate/m(3) indoor air, corresponding to a LAEC for continuous exposure of 230 mg ethyl acetate/m(3), for the endpoint nasal epithelium degeneration. By applying an interspecies factor of 1, a factor of 10 for interindividual variability and a factor of 2 to account for the higher respiratory rate of children compared to adults, a health hazard guide value (RW II) of 6 mg ethyl acetate/m(3) is obtained. A health precaution guide value (RW I) of 0.6 mg ethyl acetate/m(3) indoor air is recommended.

The relationship between chemical concentration and odor activity value explains the inconsistency in making a comprehensive surrogate scent training tool representative of illicit drugs

This report highlights the importance of an individual chemical's odor impact in the olfactory identification of marijuana, cocaine, and heroin. There are small amounts of highly odorous compounds present in headspace of these drugs, with very low odor detection thresholds, that are more likely responsible for contributing to the overall odor of these drugs. Previous reports of the most abundant compounds in headspace can mislead researchers when dealing with whole odor of these drugs. Surrogate scent formulations, therefore, must match the odor impact of key compounds and not just the chemical abundance of compounds. The objective of this study was to compare odorous volatile organic compounds (VOCs) emitted from illicit drug samples of marijuana, cocaine, and heroin to surrogate smell formulations using simultaneous sensory (via human olfaction) and chemical analyses. Use of solid phase microextraction (SPME) allowed VOCs in drug headspace to be extracted and pre-concentrated on site, and analyzed by multidimensional gas chromatography-mass spectrometry-olfactometry (MDGC-MS-O). Use of MDGC-MS-O allowed for further separation of odorous compounds and simultaneous detection by the human nose of the separate odor parts that make up the total aroma of these drugs. The compounds most abundant in headspace were not the most odor impactful when ranked by odor activity values (OAVs) (defined as ratio of concentration to odor detection threshold, ODT). There were no apparent correlations between concentrations and OAVs. A 1g marijuana surrogate lacked in odor active acids, aldehydes, ethers, hydrocarbons, N-containing, and S-containing VOCs and was overabundant in odor active alcohols and aromatics compared with real marijuana. A 1g cocaine surrogate was overabundant in odor active alcohols, aldehydes, aromatics, esters, ethers, halogenates, hydrocarbons, ketones and N-containing compounds compared with real. A 1g heroin surrogate should contain less odor active acids, alcohols, aromatics, esters, ketones, and N-containing compounds. Drug quantity, age and adulterants can affect VOC emissions and their odor impact. The concept of odor activity value, then, is useful to researchers without access to more sophisticated instrumentation. Odor activity values can be calculated from published odor detection thresholds. More research is warranted to expand the database, and determine odor detection thresholds for compounds of interest. Additional information could be obtained from establishing ODTs of key odorants for canines.

An algorithm for 353 odor detection thresholds in humans

One hundred and ninety three odor detection thresholds, ODTs, obtained by Nagata using the Japanese triangular bag method can be correlated as log (1/ODT) by a linear equation with R(2) = 0.748 and a standard deviation, SD, of 0.830 log units; the latter may be compared with our estimate of 0.66 log units for the self-consistency of Nagata's data. Aldehydes, acids, unsaturated esters, and mercaptans were included in the equation through indicator variables that took into account the higher potency of these compounds. The ODTs obtained by Cometto-Muñiz and Cain, by Cometto-Muñiz and Abraham, and by Hellman and Small could be put on the same scale as those of Nagata to yield a linear equation for 353 ODTs with R(2) = 0.759 and SD = 0.819 log units. The compound descriptors are available for several thousand compounds, and can be calculated from structure, so that further ODT values on the Nagata scale can be predicted for a host of volatile or semivolatile compounds.

The averaging effect of odorant mixing as determined by air dilution sensory tests: a case study on reduced sulfur compounds

To learn more about the effects of mixing different odorants, a series of air dilution sensory (ADS) tests were conducted using four reduced sulfur compounds [RSC: hydrogen sulfide (H₂S), methanethiol (CH₃SH), dimethylsulfide (DMS), and dimethyldisulfide (DMDS)] at varying concentration levels. The tests were initially conducted by analyzing samples containing single individual RSCs at a wide range of concentrations. The resulting data were then evaluated to define the empirical relationship for each RSC between the dilution-to-threshold (D/T) ratio and odor intensity (OI) scaling. Based on the relationships defined for each individual RSC, the D/T ratios were estimated for a synthetic mixture of four RSCs. The effect of mixing was then examined by assessing the relative contribution of each RSC to those estimates with the aid of the actually measured D/T values. This stepwise test confirmed that the odor intensity of the synthetic mixture is not governed by the common theoretical basis (e.g., rule of additivity, synergism, or a stronger component model) but is best represented by the averaged contribution of all RSC components. The overall results of this study thus suggest that the mixing phenomenon between odorants with similar chemical properties (like RSC family) can be characterized by the averaging effect of all participants.

Hydrogen bonding between solutes in solvents octan-1-ol and water

The 1:1 equilibrium constants, K, for the association of hydrogen bond bases and hydrogen bond acids have been determined by using octan-1-ol solvent at 298 K for 30 acid-base combinations. The values of K are much smaller than those found for aprotic, rather nonpolar solvents. It is shown that the log K values can satisfactorily be correlated against α(H)2·β(H)2, where α(H)2 and β(H)2 are the 1:1 hydrogen bond acidities and basicities of solutes. The slope of the plot, 2.938, is much smaller than those for log K values in the nonpolar organic solvents previously studied. An analysis of literature data on 1:1 hydrogen bonding in water yields a negative slope for a plot of log K against α(H)2·β(H)2, thus showing how the use of very strong hydrogen bond acids and bases does not lead to larger values of log K for 1:1 hydrogen bonding in water. It is suggested that for simple 1:1 association between monofunctional solutes in water, log K cannot be larger than about -0.1 log units. Descriptors have been obtained for the complex between 2,2,2-trifluoroethanol and propanone, and used to analyze solvent effects on the two reactants, the complex, and the complexation constant.

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

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.

Time and intensity factors in identification of components of odor mixtures

Identification of odors of compounds introduced into changeable olfactory environments is the essence of olfactory coding, which focuses perception on the latest stimulus with the greatest salience. Effects of stimulus intensity and adapting time on mixture component identification after adapting with one component were each studied in 10 human subjects. Odors of 1 and 5 mM vanillin (vanilla) and phenethyl alcohol (rose) were identified, with adapting time varied by sniffing naturally once or twice, or sniffing 5 times, once every 2 s. Odors of water-adapted single compounds were identified nearly perfectly (94%), self-adapted to 51% but did not cross-adapt (94%), showing the 2 compounds had quickly adapting independent odors. Identifications of the vanilla and rose odors in water-adapted mixtures were reduced to 59% and 79%, respectively. Following single-component adaptation, the average 33% identification of odors of adapted (ambient) mixture components contrasted with the greater average 86% identification of new unadapted (extra) mixture components. Identifications were lower for 1 than 5 mM components when concentrations were not matched, and ambient component identifications were lower after 10-s adaptation than after 1 or 2 sniffs. Rapid selective adaptation and mixture component suppression manipulate effective intensity to promote emergence of characteristic odor qualities in dynamic natural settings.

Determination of odor detection threshold in the Gottingen minipig

The aim of the study was to examine the ability of Göttingen minipigs to acquire an olfaction-based operant conditioning task and to determine the detection threshold for ethyl acetate and ethanol. We used an automated olfactometer developed for rodents to train and test 14 pigs. Odor sampling and reliable responding were obtained after three to fifteen 160-trial sessions. Successful transfer of the task from ethyl acetate to ethanol was achieved in 1–4 sessions. Detection threshold for ethyl acetate varied between 10⁻²% and 10⁻⁶% v/v and for ethanol between 0.1% and 5 × 10⁻⁶% v/v. The results provide evidence that minipigs can successfully acquire 2-odorant discrimination using a food-rewarded instrumental conditioning paradigm for testing olfactory function. This olfactory discrimination paradigm provides reliable measures of olfactory sensitivity and thereby enables detection of changes in olfaction in a porcine model of Alzheimer's disease currently being developed.

Use of a calibration gas generator for irritation threshold assessment and as supplement of dynamic dilution olfactometry

Human odor and mucosal membrane irritation thresholds are used as criteria for assessing air quality in occupational and environmental settings. Unfortunately, reported threshold values still differ by several orders of magnitude rendering most standard compilations of little practical utility. Thus, in view of the need to repeat odor threshold measurements with a reliable methodology, a new technical approach based on original equipment manufacturer integrated solutions is presented. To test applicability, a calibration gas generator was used to continuously generate a fixed odor vapor concentration. Different dilution steps were realized by coupling to a purchasable olfactometer. Comparison with the "standard," that is, odor stimulus supply via sample bags revealed good correspondence. As a second step, the calibration gas generator was used to generate rapid changes in stimulus concentration between consecutive trials. Irritation thresholds were measured with an ascending series of ammonia concentrations generated from an aqueous solution. The obtained thresholds lay within the range previously reported. The introduced technology enables quick and reliable odor stimulus generation and provides flexibility in choosing the optimal start concentration, the step-size between dilutions, and the range of stimulus concentrations. Errors from usage of rotameters or sample bags can be avoided.

Odor detection by humans of lineal aliphatic aldehydes and helional as gauged by dose-response functions

We have measured concentration detection (i.e., psychometric) functions to determine the odor detectability of homologous aliphatic aldehydes (propanal, butanal, hexanal, octanal, and nonanal) and helional. Subjects (16 < or = n < or = 18) used a 3-alternative forced-choice procedure against carbon-filtered air (blanks), under an ascending concentration approach. Generation, delivery, and control of each vapor were achieved via an 8-station vapor delivery device. Gas chromatography served to quantify the concentrations presented. Group and individual functions were modeled by a sigmoid (logistic) equation. Odor detection thresholds (ODTs) were defined as the concentration producing a detectability (P) halfway (P = 0.5) between chance (P = 0.0) and perfect detection (P = 1.0). ODTs decreased with carbon chain length: 2.0, 0.46, 0.33, and 0.17 ppb, respectively, from propanal to octanal, but the threshold increased for nonanal (0.53 ppb), revealing maximum sensitivity for the 8-carbon member. The strong olfactory receptor (OR) ligands octanal and helional (0.14 ppb) showed the lowest thresholds. ODTs fell at the lower end of previously reported values. Interindividual variability (ODT ratios) amounted to a factor ranging from 10 to 50, lower than typically reported, and was highest for octanal and hexanal. The behavioral dose-response functions emerge at concentrations 2-5 orders of magnitude lower than those required for functions tracing the activation of specific human ORs by the same aldehydes in cell/molecular studies, after all functions were expressed as vapor concentrations.

Making scents: dynamic olfactometry for threshold measurement

Data on human odor thresholds show disparities huge enough to marginalize olfactory psychophysics and delegitimize importation of its data into other areas. Variation of orders of magnitude from study to study, much of it systematic, threatens meaningful comparisons with animal species, comparison between in vivo with in vitro studies, the search for molecular determinants of potency, and use of olfactory information for environmental or public health policy. On the premise that good experimental results will flow from use of good tools, this report describes a vapor delivery system and its peripherals that instantiate good tools. The vapor delivery device 8 (VDD8) provides flexibility in range of delivered concentrations, offers definable stability of delivery, accommodates solvent-free delivery below a part per trillion, gives a realistic interface with subjects, has accessible and replaceable components, and adapts to a variety of psychophysical methodologies. The device serves most often for measurement of absolute sensitivity, where its design encourages collection of thousands of judgments per day from subjects tested simultaneously. The results have shown humans to be more sensitive and less variable than has previous testing. The VDD8 can also serve for measurement of differential sensitivity, discrimination of quality, and perception of mixtures and masking. The exposition seeks to transmit general lessons while it proffers some specifics of design to reproduce features of the device in a new or existing system. The principles can apply to devices for animal testing.

Olfactory detectability of homologous n-alkylbenzenes as reflected by concentration-detection functions in humans

As part of our systematic exploration of chemical determinants for the olfactory potency of vapors towards humans, we measured concentration-detection functions for the odor of the homologous n-alkylbenzenes toluene, ethylbenzene, butylbenzene, hexylbenzene, and octylbenzene. A vapor delivery device based on dynamic olfactometry and calibrated by gas chromatography, served to test groups of 16 to 17 participants. Subjects were young adults from both genders, normosmics, and nonsmokers. Odor functions were tightly modeled by a sigmoid (logistic) function, both at the group and the individual level. Odor detection thresholds (ODTs), defined as the concentration producing a detectability halfway between chance and perfect detection, decreased with alkyl chain length from toluene (79 ppb) to butylbenzene (2.5 ppb), and then increased form butyl to octylbenzene (89 ppb). The "U"-shaped trend of ODTs as a function of alkyl chain length indicated a loss of odor potency beyond a certain molecular size, a phenomenon recently described for chemosensory irritation (chemesthesis) and that will need consideration in structure-activity models of chemosensory potency. Interindividual ODTs' variability for any single odorant amounted to one order of magnitude, in agreement with recent studies of other homologous series but quite smaller than commonly depicted.

Olfactory psychometric functions for homologous 2-ketones

We measured concentration-detection (i.e., psychometric) odor functions for the homologous ketones propanone (acetone), 2-pentanone, 2-heptanone, and 2-nonanone. Under a forced-choice procedure, stimuli were presented via an 8-channel air-dilution olfactometer that allowed natural sampling of the odorant and whose output was quantified by gas chromatography. Subjects (17-22 per compound) comprised young adults from both genders, all normosmics and nonsmokers. A sigmoid (logistic) equation tightly fitted group and individual functions. The odor detection threshold (ODT) was the concentration detectable at halfway (P=0.5) between chance (P=0.0) and perfect (P=1.0) detection. Odor sensitivity increased (i.e., thresholds decreased) from acetone to heptanone, remaining constant for nonanone. This relative trend was also observed in previous work and in odor thresholds compilations, but the absolute ODTs obtained here were consistently at the lower end of those reported before. Interindividual variability of ODTs was about 1 order of magnitude. These odor functions measured behaviorally in humans were obtained at vapor concentrations 1000 times lower than functions measured via activation, with similar 2-ketones, of receptor neurons converging into individual olfactory glomeruli of mice, visualized with calcium sensitive dyes. Odorant concentrations presented as vapors (as in behavioral studies) and those presented as liquids (as in cellular/tissue studies) can be rendered equivalent via liquid-vapor partition coefficients and, then, compared in relative olfactory potency. These comparisons can reveal how sensitivity is progressively shaped across levels of the neural pathway.