An Empirical Test of Olsson's Interaction Model Using Mixtures of Tastants

In 1994, Olsson published a model predicting the intensity andquality of an odor mixture percept on the basis of the intensitiesof the unmixed components. Whether this model can also be usedfor mixtures of dissimilar tasting substances was investigatedfor sucrose/citric acid mixtures. The identification data revealed asymmetrical mixture suppression,which does not support the model. The intensity responses werein accordance with the definitions employed for level independenceand hypo-additivity. However, the intensity judgements suggestdeviations from symmetry and exhibited compromise, which violatestwo other principles. A comparison with previously publisheddata shows that these violations probably occur for other mixturetypes, too. It is concluded that the Olsson interaction modelcannot describe interactions in mixtures of dissimilar tastingcomponents accurately. Chem Senses 21: 283–291, 1996.     

Olfactory Functions in Parkinson's Disease and Alzheimer's Disease

The aim of this investigation was to compare olfactory functionsof patients suffering from Parkinson's disease (PD) and Alzheimer'sdisease (AD). Olfactory threshold, odor identification abilityand odor memory performance were assessed in 21 non-dementedPD patients and in 22 AD patients. Both patient groups wereimpaired in relation to an age-matched control group for themeasure of odor identification. AD patients showed a higherolfactory threshold and poorer odor memory performance. ChemSenses 22: 105–110, 1997.     

Assessment of Conducting Polymer Odour Sensors for Agricultural Malodour Measurements

The major odoriferous components of fresh pig slurry were identifiedusing gas chromatography coupled to mass spectrometry. Fromthe anlaytical data, a standard artificial slurry was reconstituted.The performance of conducting polymer odour sensor arrays wasevaluated using the individual chemical volatile componentsand the artificial slurry itself. Most of the components arediscriminated from each other, when presented singly to thesensor array. The sensors are not poisoned by the chemicalsand give reproducible responses over a 3 month period. The odourcomponents being detected from an artificial alkaline pig slurryappear to be associated with patterns obtained from indole,skatole and ammonia. The intensity of the signal is proportionalto the concentration of the volatiles presented to the sensor.The results indicate that conducting polymer sensor arrays showpromise for measurement of agricultural malodours, and may complementolfactometric techniques. Chem. Senses 21: 495–505, 1996.     

Monitoring growth of the methanogenic archaea Methanobacterium formicicum using an electronic nose

Growth of the methanogenic archaea, Methanobacterium formicicum, in pure culture was monitored by analysing samples from the gas phase with an array of chemical gas sensors (an `electronic nose'). Analyses of the methane and protein formation rates were used as independent parameters of growth, and the data obtained from the electronic nose were evaluated using principal component analysis (PCA). We found that different growth phases can be distinguished with the electronic nose followed by PCA evaluation. The fast response of the sensors in combination with the high correlations with other parameters measuring growth show that the electronic nose can be a useful tool to rapidly determine methanogenic growth.     

Failure to Demonstrate Systematic Changes in Olfactory Perception in the Course of Pregnancy: a Longitudinal Study

Olfactory function was assessed in 20 women during each trimesterof pregnancy and post partum, and compared with that of 20 non-pregnantwomen tested in parallel. In contrast to earlier reports, noconsistent differences in olfactory sensitivity or odor evaluationwere found between the two groups. Chem. Senses 21: 567–571,1996.     

Study of structural and electronic origin of ambergris odor of some compounds

The correlation between structural, stereochemical as well as electronic features and ambergris odor of some tricyclic ethers is established based on quantum chemical calculation method. A definite structural fragment (a “new ambergris triangle”) with certain electronic properties determining the origin of the odor is revealed. The influence of HOMO-LUMO energy gaps and total energies of some ambergris compounds on their odor intensity is investigated.     

Isolation and Chemical Structures of Two New Catechins from Fresh Tea Leaf

A total of 20 volatile organic compounds from the peel of citrus fruit Ohshima no. 1 were identified by gas chromatography-mass spectrometry (GC-MS). The amount of limonene in Ohshima no. 1 was lower than those in the parent cultivars, Miyauchi iyokan and Yoshiura ponkan, whereas those of γ-terpinene, linalool, sabinene, p-cymene, and terpinolene in Ohshima no. 1 were somewhat higher. However, comparing the results, it was found that volatile components from both parent cultivars were present in the peel of Ohshima no. 1. Principal component analysis (PCA) of data obtained with an electronic nose indicated that the odor of Ohshima no. 1 showed a clear upward displacement as compared with those of parent cultivars in PC1. The oils of Miyauchi iyokan and Yoshiura ponkan showed displacement in a negative direction, and a positive one in PC2. By PCA analysis, it was found that the odor quality of Ohshima no. 1 was very different from those of the parent cultivars.     

Central Processing of Odor Concentration is a Temporal Phenomenon as Revealed by Chemosensory Event-Related Potentials (CSERP)

Chemosensory event-related potentials (CSERP) can be used toexamine central nervous odor processing. An important questionfor understanding odor perception is how different concentrationsare processed. In the present study two odors were chosen whichactivate either the olfactory (linalool) or the trigeminal (menthol)system. Both odors were presented to 11 subjects in four differentconcentrations. Four subjects had to attend actively to theodors while the others perceived the odors under passive attention.The results showed that increased concentrations of the olfactorystimulus resulted in shorter latencies of the N1 component butdid not affect the amplitudes of the CSERP. However, the amplitudesof the stimulus dependent, exogenous components (N1, P2) increasedwith higher concentrations of the trigeminal stimulus. The amplitudeof the late positive complex, which reflects endogenous processes,was usually larger when the odorous stimuli had to be attendedto actively. It is concluded that olfactory intensity codingresults in a qualitatively different but not in a stronger neuronalresponse of the human brain. Chem. Senses 22: 9–26, 1997.     

Odor Perception and Beliefs about Risk

Although the perceptual response to environmental odors canbe quite variable, such variation has often been attributedto differences in individual sensitivity. An information-processinganalysis of odor perception, however, treats both the receptionand the subsequent evaluation of odor information as determinantsof the perceptual response. Two experiments investigated whethera factor that influenced the evaluation stage affected the judgementof odor quality and the degree of adaptation to the odor. Peoplewere surveyed in order to measure their tacit perceptions ofthe healthfulness or hazardousness of nine common olfactorystimuli, and the instructional context influenced quality perception.In a second experiment subjects were exposed to an ambient odorunder one of three different conditions, and odorant characterizationinfluenced the degree of adaptation to the odor. Subjects whowere led to believe the odor was a natural, healthy extractshowed adaptation; those told that the odor was potentiallyhazardous showed apparent sensitization; while those told thatthe odor was a common olfactory test odorant showed a mixedpattern: some exhibited adaptation, whereas others showed sensitization.However, detection thresholds obtained before and after exposureshowed adaptation effects that are characteristic of continuousexposure. These findings raise the possibility that cognitivefactors may be modulating the overall sensory perception ofodor exposure (i) for some individuals who exhibit extreme sensitivityto odors and (ii) in situations where adaptation to environmentalodors is expected but does not occur. Chem. Senses 21: 447–458,1996.     

Hybrid neural systems for pattern recognition in artificial noses

This work examines the use of Hybrid Intelligent Systems in the pattern recognition system of an artificial nose. The connectionist approaches Multi-Layer Perceptron and Time Delay Neural Networks, and the hybrid approaches Feature-Weighted Detector and Evolving Neural Fuzzy Networks were investigated. A Wavelet Filter is evaluated as a preprocessing method for odor signals. The signals generated by an artificial nose were composed by an array of conducting polymer sensors and exposed to two different odor databases.     

Evaluating the 'Labeled Magnitude Scale' for Measuring Sensations of Taste and Smell

The Labeled Magnitude Scale (LMS) is a semantic scale of perceptualintensity characterized by a quasi-logarithmic spacing of itsverbal labels. The LMS had previously been shown to yield psychophysicalfunctions equivalent to magnitude estimation (ME) when gustatory,thermal and nociceptive stimuli were presented and rated together,and the upper bound of the LMS was defined as the ‘strongestimaginable oral sensation’. The present study comparedthe LMS to ME within the more limited contexts of taste andsmell. In Experiment 1, subjects used both methods to rate eithertaste intensity produced by sucrose and NaCl or odor intensityproduced by acetic acid and phenyl ethyl alcohol, with the upperbound of the LMS defined as either the ‘strongest imaginabletaste’ or the ‘strongest imaginable odor’.The LMS produced psychophysical functions equivalent to thoseproduced by ME. In Experiment 2 a new group of subjects usedboth methods to rate the intensity of three different tastequalities, with the upper bound of the LMS defined as the ‘strongestimaginable [sweetness, saltiness, or bitterness]’. Inall three cases the LMS produced steeper functions than didME. Experiment 3 tested the hypothesis that the LMS yields datacomparable to ME only when the perceptual domain under studyincludes painful sensations. This hypothesis was supported whenthe LMS again produced steeper functions than ME after subjectshad been explicitly instructed to omit painful sensations (e.g.the ‘burn’ of hot peppers) from the concept of ‘strongestimaginable taste’. We conclude that the LMS can be usedto scale sensations of taste and smell when they are broadlydefined, but that it should be modified for use in scaling specifictaste (and probably odor) qualities. The implications of theseresults for theoretical issues related to ME, category-ratioscales and the size of the perceptual range in different sensorymodalities are discussed. Chem. Senses 21: 323–334, 1996.     

Characteristic vibration patterns of odor compounds from bread-baking volatiles upon protein binding: density functional and ONIOM study and principal component analysis

As the mechanism underlying the sense of smell is unclear, different models have been used to rationalize structure–odor relationships. To gain insight into odorant molecules from bread baking, binding energies and vibration spectra in the gas phase and in the protein environment [7-transmembrane helices (7TMHs) of rhodopsin] were calculated using density functional theory [B3LYP/6-311++G(d,p)] and ONIOM [B3LYP/6-311++G(d,p):PM3] methods. It was found that acetaldehyde (“acid” category) binds strongly in the large cavity inside the receptor, whereas 2-ethyl-3-methylpyrazine (“roasted”) binds weakly. Lys296, Tyr268, Thr118 and Ala117 were identified as key residues in the binding site. More emphasis was placed on how vibrational frequencies are shifted and intensities modified in the receptor protein environment. Principal component analysis (PCA) suggested that the frequency shifts of C–C stretching, CH₃ umbrella, C = O stretching and CH₃ stretching modes have a significant effect on odor quality. In fact, the frequency shifts of the C–C stretching and C = O stretching modes, as well as CH₃ umbrella and CH₃ symmetric stretching modes, exhibit different behaviors in the PCA loadings plot. A large frequency shift in the CH₃ symmetric stretching mode is associated with the sweet-roasted odor category and separates this from the acid odor category. A large frequency shift of the C–C stretching mode describes the roasted and oily-popcorn odor categories, and separates these from the buttery and acid odor categories.     

Pemenone and Androstenone do not Cross-adapt Reciprocally

Explorations of the qualitative and quantitative differencesbetween the odors of pemenone (PEM), androstenone (AND) andisovaleric acid (IVA) show that they share a number of commonperceptual characteristics. Among these are similarities intheir odor quality and relative intensity ratings. PEM is alsoan efficient cross-adaptor and modulator of a subject's ANDsensitivity. Here we evaluate the reciprocal efficacy of ANDadaptation to alter the perceived intensity and quality of PEM,IVA and AND. Twenty-three people, including both those osmicand allosmic (n = 11) for the putrid odor quality of PEM, weretested. Following training in odor quality and intensity ratingtechniques, subjects sampled a selected substance for 2 minto obtain adaptation and then reported quality and intensityratings for the three test stimuli. There was significant self-adaptationby PEM and IVA in all subjects, but self-adaptation by AND wasonly observed in the PEM-osmic subjects. AND did not cross-adaptPEM or IVA to any significant extent. Collectively, these resultscontrast with our earlier study in which PEM was an efficientcross-adaptor of AND. Here, AND was no more efficient than thecontrol as an adapting substance for PEM, despite significantself-adaptation of PEM by itself. This lack of reciprocity inthe effectiveness of PEM and AND as cross-adapters is not relatedto differences in odor intensity, as the PEM and AND concentrationswere adjusted for each subject to elicit comparable intensityreports. These results support the notion that PEM, AND andIVA share certain perceptual characteristics, but interact differentiallywith three or more sets of perceptual channels that are nowthought to result in a putrid odor quality. Chem. Senses 21:711–717, 1996.     

Olfactory Discrimination Ability for Aliphatic Esters in Squirrel Monkeys and Humans

Using a behavioral paradigm designed to simulate olfactory-guidedforaging, the ability of five squirrel monkeys to distinguishiso-amyl acetate from n-and iso-forms of other acetic esters(ethyl acetate to decyl acetate) and from other esters carryingthe iso-amyl group (iso-amyl propionate to iso-amyl capronate)was investigated. We found (i) that all five animals were clearlyable to discriminate between all odor pairs tested; (ii) a significantnegative correlation between discrimination performance andstructural similarity of odorants in terms of differences incarbon chain length of both the aliphatic alcohol group andthe aliphatic acid group of the esters; and (iii) that iso-and n-amyl acetate were perceived as qualitatively similar despitedifferent steric conformation. Using a triple-forced choiceprocedure, 20 human subjects were tested on the same tasks inparallel and showed a very similar pattern of discriminationperformance compared with the squirrel monkeys. Thus, the resultsof this study provide evidence of well-developed olfactory discriminationability in squirrel monkeys for aliphatic esters and supportthe assumption that human and non-human primates may share commonprinciples of odor quality perception. Chem. Senses 22: 457–465,1997.     

Peripheral Mechanisms of Pheromone Reception in Moths

Moths pheromones mostly consist of two or a few chemical componentsin a species-specific ratio. Each component is perceived bya particular type of receptor cell. Some pheromone componentscan inhibit the behavioral responses to other pheromone components.A single pheromone molecule is sufficient to elicit a nerveimpulse. The dose-response curve of single pheromone receptorneurons increases over many decades of stimulus intensity. Pheromonereceptor cells can resolve single stimulus pulses up to a frequencyof 10 pulses/s. Electrophysiological and biochemical studieson perireceptor events suggest that the pheromone moleculesinteract with the receptor cell while bound to a reduced formof the pheromone binding protein. The enzymatic degradationof pheromone found on the antennae is much too slow to accountfor the decline of the receptor potential after end of stimulation.The postulated rapid deactivation of the odor molecules adsorbedmight be performed by an oxidation of the pheromone bindingprotein. Several second messenger systems seem to be involvedin the cellular transduction mechanism (IP₃ diacylglycerol,cGMP, Ca₂₊). It is, however, not excluded that pheromone moleculescan gate single ion channels directly and thus elicit the elementaryreceptor potentials, observed at weak stimulus intensities.Chem. Senses 21: 257–268, 1996.     

Numerical Simulation of Environmental Modulation of Chemical Signal Structure and Odor Dispersal in the Open Ocean

Hydrodynamic models were used to simulate the dispersal of amodel fish pheromone at three characteristic depth regimes (mixedlayer, and 300 and 1000 m) of broad extent in the open oceanat the scale of individual organisms. The models were calibratedto experimental studies of dye dispersal at these depths andthe goldfish pheromone system was used as the model odorant.There are profound differences in the time course and geometryof dispersing odor fields with depth. Below the thermoclineodor fields spread primarily as horizontal patches with dispersalrates about five times slower at 1000 m as compared to 300 m.In the mixed layer, odors disperse rapidly in all directionsand the maximum radial distance of spread of a physiologicallyactive odor patch is less than half of the deep water value.Increases in the threshold sensitivity of olfactory receptorscan greatly increase effective odor field size. Chemical signalsimpact the encounter dynamics among oceanic organisms by affectingthe distance at which the target (emitting) individual is perceived.Perception distances due to olfactory cues can be significantlygreater than for other senses in pelagic oceanic environments.Environment specific modulation of odor fields then affectsthe signal properties and therefore utility of chemoreceptionthat, in turn, bear on encounter probabilities and transferfunctions in oceanic ecosystems. Chem. Senses 21: 121–134,1996.     

Rapid Identification of Rice Samples Using an Electronic Nose

Four rice samples of long grain type were tested using an electronic nose (Cyranose-320).Samples of 5 g of each variety ofrice were placed individually in vials and were analyzed with the electronic nose unit consisting of 32 polymer sensors.TheCyranose-320 was able to differentiate between varieties of rice.The chemical composition of the rice odors for differentiatingrice samples needs to be investigated.The optimum parameter settings should be considered during the Cyranose-320 trainingprocess especially for multiple samples,which are helpful for obtaining an accurate training model to improve identificationcapability.Further,it is necessary to investigate the E-nose sensor selection for obtaining better classification accuracy.A re-duced number of sensors could potentially shorten the data processing time,and could be used to establish an application pro-cedure and reduce the cost for a specific electronic nose.Further research is needed for developing analytical procedures thatadapt the Cyranose-320 as a tool for testing rice quality.