Odour perception

Observations of smoke plumes, first brief tests and some papers 15, 6/ suggest that the immission concentration is fluctuating in a wide range near the source. Human nose is more sensitive to odour concentration fluctuation than, due to adaption, to constant odour concentration. In fig. 5 it is shown qualitativly that odour perception may occur due to concentration fluctuations although the mean value is far below the odour threshold. In table 1 it is indicated that the distance between agricultural emission sources and receptor is relatively small in relationship to industrial emissions. 

The goal of chemical analysis of odorous compounds in air is to determine all substances, which interact with odour perception cells in our nose, both qualitatively and quantitatively. However, with a few exceptions all compounds with certain vapor pressure have an odour, meaning that their volatilized molecules react with the membrane of odour receptor cells. As will be shown, always hundreds of compounds are present in air this means that the analysis would be very complex. However as was said before, our sense of smell is selective for some products it is very sensitive for other compounds it is much less sensitive. 

For each of the identified osmogenes the relationship between the compounds actual abundance in the mixture and the concentration that represents the odour perception threshold must be evaluated. This is essential to give some indication of the osmogenes perceived intensity and assist in pinpointing which of the odour-intensive species are most significant. 

Olfactometric detection was originally carried out using the same gas chromatograph with a splitting device based on the design by Etzweiler and Neuner-Jehle attached to a locally produced odour port. (9) This approach has been superseded with a Hewlett-Packard 5890A chromatograph equipped with flame ionisation and a low volume (3.5mm) thermal conductivity detector, an extension of which allows odour perception. 

Leffingwell JC, Chirality and Odour Perception, www.leffingwell.com/chirality,... 

Galizia, C. G. and Menzel, R. (2000). Odour perception in honeybees coding information in glomerular patterns. Current Opinion in Neurobiology 10 504-510. 

Visser J. H. (1986) Host odour perception in phytophagous insects. Anna. Rev. Entomol. 31, 121-144. 

Leffingwell Associates, Chirality Odour Perception http //www.leffingwell.com (accessed March 13, 2009). 

Odour perception has been compared with the immune system. But receptor activation in the olfactory system seems to have an instructive rather than a selective role. An instructive role would be in agreement with the large genetic repertoire coding for a receptor for each type of odorant molecule. 

A colourless, heavy liquid of characteristic odour perceptible at great dilutions. It boils at ordinary pressure at 64° to 65° C., with incipient decomposition. 

Chiral discrimination has been recognized as one of the most important principles in biological activity and also odour perception [1-9]. Besides enantioselective biogenesis, the evaluation of chirality in the origin control of flavourings and fragrances has to be discussed with regard to some fundamental conditions. 

We used a similar type of analysis to look for correlations between the odour character of the fragrances (defined by their position on the map) and results obtained from large-scale market research. The market research attributes found to be directly related to the odour perception of the samples are shown on the map in Figure 8.6, with arrows indicating the direction of increasing perception of each attribute. 

The interaction between the study of the mechanism of odour perception and the elaboration of empirical SARs has led to the problem of confusion of the two. It is only too easy to fall into this trap and the lessons which can be learned from the study of odour are, I believe, relevant to most, if not all, branches of science. 

Significant positive associations were observed between the prevalence of each index symptom (headache, nausea, eye and throat irritation) and both frequency of odour perception and degree of worry. Elimination of secondary worry respondents did not affect these relationships. Relationships were strongest for worry rather than odour. In addition to their individual effects, odour and worry exhibited a positive interaction that, in the case of headaches, was almost multiplicative. The authors concluded that worry and odour perception had a potential role in the development of symptoms near hazardous waste sites. 

The two primary aspects of odour are character and intensity. Perfumers are also interested in properties such as tenacity and performance but these are derivative properties combining intensity with physical and chemical properties such as volatility, surface recognition/adhesion, chemical stability in the perfumed medium, Raoult s law deviations and so on. In order to study any phenomenon, it is important to be able to measure it. Unfortunately, both odour character and intensity are very difficult to measure. Odour is a phenomenon that exists only in the higher brain and must therefore be measured using psychological techniques. Moreover, it is highly subjective, even to the point where it would appear that each of us has a unique odour perception of the world around us, as will be explained later. 

Odour did not seem to be a factor that might have biased the results and so the possibihty that increased odour perception of MTBE in gasohne (a suggestion made, with some justification as described earlier, in relation to the original Alaskan observations) is not a valid criticism of this study. In conclusion, the study did not support a simple dose-response relationship for MTBE exposure, although there may be some evidence for a threshold amongst SRSs. 

The difference between the odours of two optical isomers of carvone has been characterised by various authors. Russell and Hills have described that 4S-carvone has the odour of caraway and 4R-carvone has the odour of spearmint. They have stated that these observations lend a definite support to stereochemical considerations of odour perception... 

The biological process by which we perceive odours is not fully understood. However, recent advances in our understanding indicate that the combinatorial nature of the mechanism of odour perception presents serious problems for the design of novel fragrance ingredients. 

A fragrance is a harmonious blend of individual perfume notes, just as a chord is a harmonious blend of individual musical notes. In view of the complexity of odour perception as seen above, it is not surprising that the way in which one perfume ingredient will blend with others is not easily predictable. The only way to find out how well a novel ingredient works in perfume formulae is by experience and so an essential part of the screening of novel ingredients is their use by perfumers in test formulae. 

Albert Einstein said that, The most beautiful thing we can experience is the mysterious. It is the source of all true art and science. The mechanism of odour perception and the nature of interaction of small molecules with biological macromolecules both still hold many mysteries. Perfumery is a blend of art and science, principally chemistry. I agree with Einstein and conclude that perfumery and the design of novel ingredients for it are beautiful and rewarding occupations. 

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