Background Odors Research Articles

Analysis of Interaction in Binary Odorant Mixtures

An understanding of the olfactory system of any animal must account for how odor mixtures are perceived and processed. The present experiments apply associationist models to the study of how elements are processed in binary odorant mixtures. Using experimental designs for Proboscis Extension Conditioning of honey bees, I show that learning about a pure odorant element is frequently affected by its occurrence in a mixture with a second odorant. Presence of a background odor when an odorant is associated with sucrose reinforcement decreases the rate and/or asymptotic level of associative strength that accumulates to that odorant. This interaction is in part due to synthetic qualities that arise in sensory transduction and initial processing. In addition, it involves an attention-like processing system like that involved in overshadowing. Therefore, a model that includes representations of the component and configural qualities of odorants in mixtures is needed to provide a more complete account of learning about odor mixtures.

Defining Interaction between Electroantennogram Responses of Epiphyas postvittana (lepidoptera: Tortricidae) to Pheromone and Other Volatiles

The potential for electroantennograms (EAGs) to assist in the measurement of atmospheric pheromone concentrations was examined in laboratory and field experiments by using multiple stimuli, the main component of the pheromone of Epiphyas postvittana, ( E)-11-tetradecenyl acetate, its Z-isomer (a behavioral antagonist), and α-terpineol (a representative host-plant odor) were presented to the antenna simultaneously to simulate field conditions. The EAG results were compared with predictions from two models describing responses to combined stimuli. Responses are defined as log-additive if they can be described with the equation [EAG (total) =a (log ([P x]+[B y])+c] and as linear–additive if the EAG follows the equation [EAG (total) =a (log [P x])+c+a′(log [B y])+c′] where [B y] is the concentration of the stimulant background odor and [P x] is the concentration of an additional odor stimulus. The EAGs elicited by the added stimuli were inversely related to the concentration of the volatile in the background. EAGs elicited by all combined stimuli followed the log–additive model. Our laboratory results were validated in field tests; α-terpineol represents the volatiles present in orchard air. In spite of this interaction between the perception of pheromone and plant volatiles, the field EAG can be used for the measurement of atmospheric pheromone concentrations, where background odor concentrations are relatively constant.

A Procedure for Correlation of Chemical and Sensory Data in Drinking Water Samples by Principal Component Factor Analysis

A statistical method utilizing principal component factor analysis (PCFA) was developed for chemical/sensory taste and odor correlation. With this method, specific flavor descriptors can be correlated with specific chromatographic peaks. A background odor mechanism was assumed to explain the odors perceived at or below their odor threshold concentrations. PCFA was applied to a series of simulated data sets and chemical/sensory data obtained from drinking water samples. The simulated data sets were used to evaluate six types of chemical/sensory response equations. The response equation giving satisfactory correlation results was then used to evaluate the drinking water sample data sets. After merger of the chemical/sensory data, the covariance between items was calculated, and PCFA was applied to the covariance structure followed by a target transformation of PCFA factors. Quality assurance evaluations of both sensory and chemical data were an integral part of the correlation procedure. The correlation study using simulated data showed that the PCFA correlation method using linear-additive (e.g., log-additive) data yielded better results (i.e., less type I and II errors) than nonlinear, nonadditive data. The quality of the drinking water sample correlation results was highly dependent on the sensory data quality.

Computational parallels between the biological olfactory pathway and its analogue `The Electronic Nose': Part II. Sensor-based machine olfaction

Over the last fifteen years, we have witnessed a rapid expansion in the development of artificial odour sensing systems, or so called `electronic nose' systems. Whilst the power of this approach to flavour analysis has undoubtedly been demonstrated by its recent application to various complex odours, it will be argued that the original research programme, aimed at developing a comparative model of the biological olfactory pathway, has degenerated into an attempt to obtain an ad hoc workable system, based around readily available sensor and pattern recognition (PARC) technologies. At the time, the first `model' nose system reflected the limited understanding of sensory information processing carried out within the biological olfactory pathway. We are now presented with an opportunity to evaluate and re-assess the architecture for an electronic nose, in view of the recent advances in understanding the key processing principals exploited by the olfactory bulb and cortex in the identification and characterisation of molecular stimuli. In Part II of this paper, we examine the parallels that exist between the biological olfactory system and the electronic nose. It is shown that the two systems share many similarities in their architectures and other properties, such as odour delivery, nonspecific sensor/receptor response, sensor/receptor preprocessing and content addressable memory (CAM) function. Of particular importance, both systems need to overcome similar operating problems, such as sensor/receptor drift, degeneration and poisoning, limited sensor/receptor sensitivity, discrimination of odour quality invariant of intensity and also the identification of particular odour components within a mixture of background odours. Finally, a number of opportunities for improving the biological plausibility of electronic nose systems are suggested that may yield an improvement in performance.

A chemical and sensory study of odour compounds in the Athabasca River, Alberta, Canada

As of early 1993, the Athabasca River received effluent from one bleached kraft pulp mill (Mill A), three chemithermomechanical pulp and paper mills, one oil sands extraction and upgrading plant and a number of municipal effluents. In the latter half of 1993 a second bleached kraft pulp mill (Mill B) began operation midway along the river. An investigation was carried out to characterize the odours in the river water using both chemical and sensory methods, in a pre- and post-operational study of the second bleached kraft mill. Both surveys were carried out under ice during low flow conditions. Samples were analysed by gas chromatography-mass spectrometry after extraction using a closed-loop stripping apparatus (CLSA). In addition, sensory analysis by flavour profile panel and olfactory gas chromatography of the CLSA extracts were performed. In 1993 all analytical methods confirmed that compounds characteristic of bleached kraft mill effluent were detectable for more than 950 km downstream from Mill A and that this effluent was the major source of odour to the Athabasca River. Chemical and sensory results for 1994 samples (collected after Mill B began operation) indicated a decrease in the impact of Mill A compared with the 1993 survey. The Mill B effluent had distinctive odour but its impact on the river was difficult to detect due to dilution and background odour from the Mill A effluent.

How caterpillar-damaged plants protect themselves by attracting parasitic wasps.

Parasitic and predatory arthropods often prevent plants from being severely damaged by killing herbivores as they feed on the plants. Recent studies show that a variety of plants, when injured by herbivores, emit chemical signals that guide natural enemies to the herbivores. It is unlikely that herbivore-damaged plants initiate the production of chemicals solely to attract parasitoids and predators. The signaling role probably evolved secondarily from plant responses that produce toxins and deterrents against herbivores and antibiotics against pathogens. To effectively function as signals for natural enemies, the emitted volatiles should be clearly distinguishable from background odors, specific for prey or host species that feed on the plant, and emitted at times when the natural enemies forage. Our studies on the phenomena of herbivore-induced emissions of volatiles in corn and cotton plants and studies conducted by others indicate that (i) the clarity of the volatile signals is high, as they are unique for herbivore damage, produced in relatively large amounts, and easily distinguishable from background odors; (ii) specificity is limited when different herbivores feed on the same plant species but high as far as odors emitted by different plant species and genotypes are concerned; (iii) the signals are timed so that they are mainly released during the daytime, when natural enemies tend to forage, and they wane slowly after herbivory stops.

A chemical and sensory study of odour compounds in the Athabasca River, Alberta, Canada

As of early 1993, the Athabasca River received effluent from one bleached kraft pulp mill (Mill A), three chemithermomechanical pulp and paper mills, one oil sands extraction and upgrading plant and a number of municipal effluents. In the latter half of 1993 a second bleached kraft pulp mill (Mill B) began operation midway along the river. An investigation was carried out to characterize the odours in the river water using both chemical and sensory methods, in a pre- and post-operational study of the second bleached kraft mill. Both surveys were carried out under ice during low flow conditions. Samples were analysed by gas chromatography-mass spectrometry after extraction using a closed-loop stripping apparatus (CLSA). In addition, sensory analysis by flavour profile panel and olfactory gas chromatography of the CLSA extracts were performed. In 1993 all analytical methods confirmed that compounds characteristic of bleached kraft mill effluent were detectable for more than 950 km downstream from Mill A and that this effluent was the major source of odour to the Athabasca River. Chemical and sensory results for 1994 samples (collected after Mill B began operation) indicated a decrease in the impact of Mill A compared with the 1993 survey. The Mill B effluent had distinctive odour but its impact on the river was difficult to detect due to dilution and background odour from the Mill A effluent.

Partitioning non-linearities in the response of honey bee olfactory receptor neurons to binary odors

In many organisms, of which honey bees are one example, a general (i.e., non-pheromonal) olfactory receptor neuron may respond to some odorants by increasing its firing rate and to others by decreasing its firing rate. In the latter case, this decrease will be with respect to a background firing rate determined by intrinsic (internal noise) and extrinsic (background odors) factors. To analyse receptor neurons of this complexity, we extend Beidler's model of receptor protein activation dynamics to account for the competition between depolarizing and hyperpolarizing pathways and couple the model to a phenomenological description of the non-linear relationship between the proportion of activate membrane receptors and the receptor cell spike generation rates. We then examine the implications of this theory for predicting the response of receptor neurons to odor mixtures based on their response to pure odorants at concentrations matched to the mixture. We derive inequalities that must be satisfied under our normative model, and propose that deviations from the model be designated as synergisms and inhibitions, depending on the direction in which various equalities and inequalities are violated. We then apply our inequalities to identifying synergisms and inhibitions in data analysed in a different way elsewhere (Akers, R.P. and Getz, W.M. Response of olfactory receptor neurons in honey bees to odorants and their binary mixtures. J. Comp. Physiol. (in press)). In these data regarding the response of honey bee placode sensilla to a number of odorants and their binary combinations, we demonstrate the presence of synergisms and inhibitions — that is, elevated or repressed responses that are not due to competitive interactions of mixture component odorants for receptor sites or Beidler (Beidler, L.M., 1962. Taste receptor stimulation. Prog. Biophys. Biophys. Chem. 12, 107–151) saturation mechanisms.

Field investigation of odor intensity and acceptability of tobacco smoke in air-conditioned spaces

This paper presents basic data for estimating the degree of odor in the air obtained from the results of measurement in air-conditioned office spaces. The measurements were made in an office building in Tokyo on 4 and 5 August 1987. The occupants were asked to evaluate odor intensity on scale and acceptability and to answer some questions about odor, while concentration of carbon dioxide and particles in the air, air temperature and relative humidity were measured. The air was sampled four times a day. The air quality was voted on a scale and the acceptability was judged by the panel which consisted of four men and four women. The concentration of the odor was measured by a triangle test with sample bags. Though the concentrations of CO 2 and particles were low, the odor intensity judged by the panel was high. This is possibly due to background odor. The acceptance by the panel was less than 50%. About 30% of the occupants perceived tobacco smoke as a distinct source of odor.

Inhibition of Pheromone Perception by Male Cabbage Loopers 1 and Beet Armyworms: 1 Proximity vs. Atmospheric Permeation 2

( Z,E )-9,l2-tetradecadien-1-ol acetate ( Z,E -9,12-TDDA), ( Z )-9-tetradecen-1-ol acetate ( Z -9-TDA), and ( Z )-9-dodecen-1-ol acetate ( Z -9-DDA) significantly reduced captures of ♂ Trichoplusia ni (Hübner) when these compounds were evaporated separately in the same trap with T. ni sex pheromone, ( Z )-7-dodecen-1-ol acetate. However, when the same compounds were present throughout a small area (81 m 2 ) as a background odor, catches of T. ni males in pheromone traps were not affected. The situation was different with Spodoptera exigua (Hübner). Catches in traps were reduced significantly when Z -9-DDA and Z -9-TDA were evaporated from female-baited pheromone traps and when they were evaporated into the atmosphere surrounding traps. Z,E -9,12-TDDA was also effective in disrupting orientation of S. exigua males to females when it was evaporated into the atmosphere. The reasons for the differences in results obtained with T. ni in the 2 (trapping and atmospheric permeation) tests are obscure.

Enhancement and inhibition of olfactory bulb self-stimulation by odours

Self-stimulation maintained by electrical stimulation of the olfactory bulb was increased at low current intensities, when a background odour of amyl acetate or peppermint was present. No effect was observed at optimal current intensities, nor did the odours enhance self-stimulation at control sites in the zona incerta and ventral premammilary nucleus of the hypothalamus. Malodourous quinoline attenuated self-stimulation at olfactory bulb sites, but had no effect at control sites. These findings are taken as further evidence for the hypothesis that the effects of peripheral reinforcers are mediated by the self-stimulation areas of the brain.

Odor Threshold Determinations of 53 Odorant Chemicals

In order to assist in assessing potential odor problems arising from chemical manufacturing operations, the odor thresholds of 53 commercially important odorant chemicals have been determined using a standardized and defined procedure. The odor threshold data previously available have shown wide variation reflecting the diversity of procedures and techniques used. Factors that may affect the odor threshold measurement include the mode of presentation of the stimulus to the observer, the influence of extraneous odorants in the presentation system, the type of observer used, the definition of the odor response, the treatment of the data obtained, and the chemical purity of the odorant. The experimental approach used has minimized these variations. The odorants were presented to a trained odor panel in a static air system utilizing a low odor background air as the dilution medium. The odor threshold is defined as the first concentration at which all panel members can recognize the odor. The effect of chemica...

An Insect Olfactometer

AbstractAn olfactometer is described in which an attractive zone is established and maintained in a precisely determined location on the floor (or wall) of an observation chamber and also in the air adjacent to it. Insects must therefore manifest their normal behavior in finding their way to it. The attenuation of the attraction by "background odors" can be studied quantitatively.

Threshold Odors of Organic Chemicals

A multiphased study of the problem of taste and odor in water is being sponsored by the Manufacturing Chemists' Association. The first phase of the study involved a critical review of the literature to discover gaps in the technology. Subsequently, recommendations were made for experimental research to fill these gaps. Phase two, a laboratory study, was devoted to an evaluation of the various methods of testing for odor in water and the factors affecting results. The effects on the results reported by a given odor panel member of other persons present and of the chemicals used, of temperature, and background odor have been reported. The application of the reported results to laboratory practice in order to determine the threshold odor levels of 32 various organic chemicals is reported in this article.