Olfactory perception

Masking. Masking can be defined as the reduction of olfactory perception of a defined odor stimulus by means of presentation of another odorous substance without the physical removal or chemical alteration of the defined stimulus from the environment. Masking is therefore hyperadditive it raises the total odor level, possibly creating an overpowering sensation, and maybe defined as a reodorant, rather than a deodorant. Its end result can be explained by the simple equation of 1 + 1 = >2 (Fig. 2a). 

Heth G., Nevo E., Ikan R., Weinstein Y., et ai. (1992). Differential olfactory perception of enantiomeric compounds by blind subterranean mole rats (Spalax ehrenbergi). Experientia 48, 897-902. 

Olfaction, research in, 18 383-384 Olfactory membrane, 11 567 Olfactory perceptions, 11 510-511 Olfactory receptors, 18 383-384 Olfactory response, 11 566-567 01igo(2-propenyloxy)methyloxyirane, sulfonation of, 23 720 Oligocyclic lattice host inclusion compounds, 14 177-179 Oligocyclic lattice hosts, 14 177 01igo(y-caprolactone)dimethylacrylate, in shape- memory polymer networks, 22 364... 

Brett, J. R. and MacKinnon, D. (1954). Some aspects of olfactory perception in migrating adult coho and spring salmon. Journal of the Fisheries Research Board of Canada 11,310-318. 

Idler, D. E., Fagerland, V. H. M., and Mayoh, H. (1956). Olfactory perception in migrating salmon. I. L-Serine, a salmon repellent in mammalian skin. Journal of General Physiology 39,889-892. 

Olfactory perception translates abstract chemical features of odorants into meaningful neural information to elicit appropriate behavioral responses (Shepherd, 1994 Buck, 1996). Specialized bipolar olfactory sensory neurons (OSNs) are responsible for the initial events in odor recognition. These have ciliated dendrites exposed to the environment, and a single axon that extends into the brain and forms synapses with second order projection neurons (PNs) (Shepherd, 1994 Buck, 1996). In arthropods and mammals, the first olfactory synapse is organized into glomeruli, spherical structures in which afferent olfactory neuron axons synapse with projection neuron dendrites (Hildebrand and Shepherd, 1997). 

Acebes A. and Ferrus A. (2001) Increasing the number of synapses modifies olfactory perception in Drosophila. J. Neurosci. 21, 6264-6273. 

Another promising avenue for research that Is unquestionably at the frontier of science concerns development of an understanding of processes Involved In olfactory perception. We know from our research on the sex pheromones that male moths possess a phenomenal ability to perceive and respond behavlorally to Incredibly minute quantities of pheromonal compounds In the air. The chemoreceptive sensitivity of this detector system Is certainly unrivaled by any organic-chemical detector system devised by man. 

Axel R. Scents and sensibility a molecular logic of olfactory perception (Nobel lecture). Angew. Chem. Int. Ed. 2005 44 6111-6127. 

Axel R (2005). Scents and sensibility A molecular logic of olfactory perception (Nobel lectui e). Angew Chem Int Ed Engl 44 6110-6127. Becher B, Prat A, An tel JP (2000). Brain-immune connection Immuno-regulatory properties of CNS-resident cells. Glia 29 293—304. 

During the preparation of this review, a Nobel Lecture describing the latest advances about olfactory perception and existence of odorant receptor genes as well as the role of the vomeronasal organ in the detection of odorants has recently been published by R. Axel [285] and L.B. Buck [286] Nobel Prize winners in Physiology or Medicine 2004). 

The olfactory perception can be reinforced by sniffing i.e. by swirling the air intermittently over the ethmoid bone below the olfactory epithelium. The swirling effect causes the active components producing the smell to flow past the olfactory epithelium several times (instead of just once), thereby reinforcing the effect (particularly important in quality testing in the case of weak samples or samples with only very minor differences between them). 

The agonists and antagonists displayed a wide range of potencies, with the rank order of both similar to that found for the octopamine-2 receptors in the locust extensor tibiae muscle. The results support the proposed role of octopamine as an endogenous neuromodulator of moth olfactory perception. 

In a review, Dufosse et al. (1994) mentioned the flavor thresholds of some lactones, particularly the olfactory perception after dispersion in water and the perception in mouth after dispersion in aqueous or deodorized oily solution. They also insist on the different sensory properties of y-lactone enantiomers isolated by Mosandl and Gunther (1989). Guichard et al. (1990) studied the lactones in apricot cultivars and found that the (7 )-enantiomer is always predominant for the y-Q, to y-C)2 lactones (Q, C9 and Go lactones have been identified in green coffee). Certainly because of the small amount present, no study has been conducted in coffee, to our knowledge, on the enantiomeric distribution of the lactones. 

Pheromone production and perception form a very common means of chemical communication between different individuals of a society, and it is especially developed for well defined molecules among insects. In this case the molecular mechanism of transduction is not very different from that of olfactory perception. On the other hand, chemical signals also exist between microorganism, and chemotaxis is a widespread phenomenon leading to cell motion. Especially bacterial chemotaxis is an important mechanism in the nutrition of mobile bacteria and their protection from toxic substances. Hence the effector substances are not as specialized as pheromones, but rather are molecules of more general availability [19]. 

Source-to-source odor variation in a population of odor-producing objects may be an important statistical feature affecting olfactory perception and behavior. Another recent study showed that variability in the major-histocompatability-complex (MHC) odor signal and the amount of scent marking by individuals affected scent use by female mice when they were selecting mates.They showed that a... 

The olfactory perception threshold of ethyl acetate is approximately 160 mg/1. Even below this value, while it may not be identifiable, it may spoil the bouquet with an unpleasant, pungent tang. It is, however, possible that at very low doses (50-80 mg/1) ethyl acetate contributes to a wine s olfactory complexity and thus has a positive impact on quality. 

Furthermore, ethyl acetate affects wine flavor. At relatively high concentrations (above 120 mg/1) that are still below the olfactory perception threshold, it gives red wines a hot flavor which reinforces the impression of bitterness on the aftertaste. Ethyl acetate contributes to harshness and hardness in red wines. An acetic acid concentration of at least 0.90 g/1 (a volatile acidity of 0.95 g/1 expressed in H2SO4) is required to produce a noticeable bitter, sour aftertaste. Even at these high levels, however, it does not have a strong odor, whereas ethyl acetate is perceptible at much lower concentrations. 

Wine aromas are made up of several hundreds of volatile compounds, at concentrations ranging from several mg/1 to a few ng/1, or even less. The olfactory perception thresholds of these compounds also vary quite considerably. Consequently, the olfactory impact of the volatile compounds in wine depends both on concentration and type. Certain compounds, present in trace amounts, on the order of ng/1, may play a major role in aroma, whereas other, much more plentiful, compounds may make only a slight contribution. Furthermore, the impact of each component on the... 

About forty terpene compounds have been identified in grapes. Some of the monoterpene alcohols are among the most odoriferous, especially linalol, a-terpineol nerol, geraniol, citronellol and ho-trienol, which has a floral aroma reminiscent of rose essence (Figure 7.1). The olfactory perception thresholds of these compounds are rather low, as little as a few hundred micrograms per liter (Table 7.1). The most odoriferous are citronellol and linalol. Furthermore, the olfactory impact of terpene compounds is synergistic. They play a... 

Monoterpene Olfactory description Olfactory perception threshold Org/l-) Concentration (p.g/1) in wines made from ... 

Olfactory perception thresholds have been determined in wine by the following. Boidron (unpublished work). 

Megastigmanes (Figure 7.4) are oxygenated Ci3-norisoprenoids, with skeletons oxygenated on carbon 7 (damascone series) or carbon 9 (ionone series). Among these compounds, j6-damascenone, with a complex smell of flowers, tropical fruit and stewed apple, has a very low olfactory perception threshold in water (3-4 ng/1) and a relatively... 

Table 7.5. Descriptions and olfactory perception thresholds of the main methoxypyrazines...

Pyrazine Olfactory perception threshold in water (ng/1) Description... 

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