Odor perception activity

One precondition of applying the scheme is that the toxicologically based guide values of individual substances are not thereby exceeded. A separate evaluation will however always be required when substances with low odor perception thresholds are involved which even at lower concentrations can be bothersome due to their odor activity or when noticeably high concentrations of individual substances occur. 

For various reasons, it is very difficult to develop an understanding of the chemistry involved in olfaction. The olfactory receptors are found in the membrane of the receptor cells therefore, their active states are not amenable to structural determination by X-ray diffraction or other physical tools. Odor is a mental image rather than a physical property that can be measured and quantified. Odor perception is a multistep process. Olfaction is combinatorial in nature. All of these facts indicate that building of either substrate or receptor models are fraught with significant difficulties. 

ODOR PERCEPTION, PSYCHOLOGICAL EFFECTS AND BIOLOGICAL ACTIVITY... 

In the following section, the odor perception, psychological effects, and biological activity of a variety of essential oils are discussed. It is well known that the odors of naturally derived and chemically synthesized samples of the same compound may be quite different and that it is very difficult to reproduce or imitate the aroma profiles of an essential oil or a constituent natural material. These differences between a natural and a synthetic sample are due primarily to the relative ratios of geometric, chemical and stereochemical isomers constituting what might commonly be referred to as a single compound or material. 

Such descriptors are useful in our attempts to sort out the small number of odor-active compounds present in natural products. However they have little meaning from one laboratory to the next. For example the aroma described in our work as "cotton candy" appears for reasons which will be explained later to be due to the same compound responsible for the strawberry odor detected in the laboratory of Rapp( in Germany. The confusion these non-chemical descriptors create will be minimized once we know the causative agents for odor perception. Then we can use a chemical name to describe that perception. In the meantime we must tolerate to some extent the use of these words in our day-to-day research. 

In all of these examples of regulation of transcription of profiles by allosteric regulation of receptor sites by active profiles THE DUAL NATURE OF ODORIVECTORS manifests itself. This is a new principle postulated to be pertinent in all mixtures of odorivectors. In its most extended scope this principle states that all odorivectors have two functions To display their own intrinsic odor and at the same time act as regulator in the odor perception of a copresent odorivector. The latter is achieved by allosteric regulation in a peripheral process. 

Another powerful technique known as aroma extract dilution analysis is used to determine the most significant odor and flavor compounds in a complex mixture in a food product. This method determines the odor activity of volatile compounds in an extract eluted from a high-resolution capillary GC-SP column (see Table 11.9). The odor activity or impact of a compound is expressed as the flavor dilution factor (FD), which is the ratio of its concentration in the initial extract to its concentration in the most dilute extract in which the odor can be detected by GC-SP. However, the information from this technique may be of limited practical value, because it ignores the significant effect of food matrices on flavor and odor perception of mixtures of flavor and odor compounds. Advanced instrumental techniques have been developed for flavor analysis during food consumption. These techniques permitting direct mass spectrometry at atmospheric pressure are discussed in Chapter 6. 

Another important finding was that a given receptor responds to a variety of odorants (but not all) and a given odorant activates a variety of receptors (17). Thus, we have a combinatorial scheme of odor perception. 

Chiral compounds are frequently foimd among the flavor volatiles of fruits and, like many naturally occurring chiral compounds, one enantiomer usually exists with a greater preponderance when compared with its antipode. Chiral odor compounds may show qualitative and quantitative differences in their odor properties (7). For example, (/ )-(+)-limonene has an orange-like aroma while (5)-(-)-limonene is turpentine-like (5)-(+)-carvone is characteristic of caraway while its enantiomer has a spearmint odor (2). However, other chiral compounds, such as y 6-lactones, show very little enantioselectivity of odor perception (7). The occurrence of chiral flavor compounds in enantiomeric excess provides the analyst with a means of authenticating natural flavorings, essential oils, and other plant extracts. The advent of cyclodextrin-based gas chromatography stationary phases has resulted in considerable activity in the analysis of chiral compounds in flavor extracts of fruits, spices and other plants (i-7). 

Members of the Gs subfamily are activated by hormone receptors, by odor receptors and by taste receptors. Gg-proteins mediate, e.g., signal transmission by adrenaline receptors of type P and by glucagon receptors. During perception of taste, the taste receptors are activated, which then pass the signal on via the olfactory G-protein Gou. Perception of sweet taste is also mediated via a Gs-protein. Transmission of the... 

Physical Properties. The eight optically active menthols differ in their organoleptic properties [77]. (-)-Menthol has a characteristic peppermint odor and also exerts a cooling effect. The other isomers do not possess this cooling effect and are, therefore, not considered to be refreshing. ( )-Menthol occupies an intermediate position the cooling effect of the (-)-menthol present is distinctly perceptible. 

If a spatial olfactory code underlies a subsequent identification of an odor, then we would expect concentration-dependent variations of odor maps to have an impact on the perceived odor quality. Stimulus concentration can indeed influence perception of odor quality and behavior of insects. For example, olfactory responses of the fruit fly, Drosophia melanogaster, shifted from attraction to repulsion as the concentration increased (Siddiqi, 1983 Stensmyr et al., 2003). Future studies should thus involve correlations of behavior with glomerular activity at different concentrations. 

One way to quantify the odor impact of a compound is to determine the aroma value or odor activity value (OAV). This is calculated by dividing the concentration of the compound by its perception threshold. Therefore, the odor impact of a compound increases in proportion to its OAV when this value is >1. Thus, compounds exhibiting higher OAV values are more likely to contribute to the aroma of wine and have an important influence on its sensory characteristics. 

Many materials used for food and beverage packaging have characteristic odors or sensory active compounds (Torri et ah, 2008). The intensity and description of the odor may be affected by the number and type of volatile compounds that are released under environmental conditions at the time of evaluation. Chemical composition of the material and polymer morphology may play a role in the sensory characterization. Sensory descriptors do not define a specific chemical compound but may be related to different compounds, a blend of compounds, and even a limited concentration range of a compound or class of compounds. For example, frans-2-nonenal in water changes in sensory (taste) description from "plastic (0.2 gg/1) to "woody" (0.4-2.0 p.g/1), "fatty" (8-40 pg/1), and "cucumber" (1000 gg/1) (Piringer and Ruter, 2000). Such terms are descriptive of the sensation and perception by human response to the chemical stimuli (Table 2.1). 

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