Trigeminal Chemesthesis

In the present chapter we will summarize some important functional properties of the human trigeminal chemosensory system in the nasal, ocular and oral mucosae. Among others, we will address issues related to candidate molecular receptors for trigeminal chemesthesis, chemesthetic sensitivity (i.e., detection thresholds), structure-activity relationships, detection of chemical mixtures, and temporal properties of trigeminal chemesthetic sensations

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

Experimental Demonstration of Masking Phenomena between Competing Odorants via an Air Dilution Sensory Test

To simulate the occurrence of masking phenomena with the aid of an air dilution sensory (ADS) test, two types of odorant mixtures were prepared: (1) M2 with two individual odorants [H2S and acetaldehyde (AA)] and (2) M6 with six individual odorants (H2S and five aldehydes). The test results derived for samples containing single individual odorants at a wide range of concentrations are initially used to define the empirical relationship between the dilution-to-threshold (D/T) ratio and odor intensity (OI) scaling. Based on these relationships, the D/T ratios were estimated for each odorant with the same intensity as the synthetic mixture. The relative contribution of each odorant to such mixture is then assessed by comparing the estimated and measured D/T values. This stepwise test confirmed the dominance of certain compounds at a given OI rating. In the case of M2, H2S showed sensitive detection at high OI range, while AA did so at low end. The pattern of a competing relationship is also seen consistently from M6 between AA (low) and iso-valeraldehyde (IA: high OI range). The overall results thus suggest that the masking phenomena between strong odorants should proceed under competing relationships, if released at the same time

Determination of solvation descriptors for terpene hydrocarbons from chromatographic measurements

This article discusses the determination of solvation descriptors for terpene hydrocarbons from chromatographic measurements

Determination of solvation descriptors for terpene hydrocarbons from chromatographic measurements

This article discusses the determination of solvation descriptors for terpene hydrocarbons from chromatographic measurements