Odorant perception

Odor masking Odor modification Odor perception Odor removal... 

Whatever the physiology of odor perception may be, the sense of smell is keener than that of taste (22). If flavors are classed into odors and tastes as is common practice in science, it can be calculated that there are probably more than 10 possible sensations of odor and only a few, perhaps five, sensations of taste (13,21,35—37). Just as a hereditary or genetic factor may cause taste variations between individuals toward phenylthiourea, a similar factor may be in operation with odor. The odor of the steroid androsterone, found in many foods and human sweat, may eflcit different responses from different individuals. Some are very sensitive to it and find it unpleasant. To others, who are less sensitive to it, it has a musk or sandalwood-like smell. Approximately 50% of the adults tested cannot detect any odor even at extremely high concentrations. It is befleved that this abiUty is genetically determined (38). 

Although the nose houses and protects the cells that perceive odor, it does not direcdy participate in odor perception. The primary function of the nose is to direct a stream of air into the respiratory passages. While this function is occurring, a small fraction of the inhaled air passes over the olfactory epithelium, located 5—8 cm inside the nasal passages. This olfactory area occupies about 6.45 cm (one square inch) of surface in each side of the nose. 

Odor perception and description are highly subjective in nature. Nevertheless, there is a generally agreed-upon odor vocabulary that is used to characterize individual ingredients and finished fragrances. Table 1 shows some commonly used odor descriptors grouped into five general classifications. 

The odor perception threshold for benzene in water is 2 ing/L. The benzene drinking water unit risk is 8.3 x lO L/pg. Calculate the potential benzene intake rate (mg benzene/kg-d) and the cumulative cancer risk from drinking water with benzene concentrations at half of its odor threshold for a 30 year exposure duration. 

With regard to the odor threshold for hydrogen sulfide, it should be noted that although odor can be perceived at 0.5 ppb in air, olfactory fatigue can occur at concentrations of 100 ppm or greater causing a loss of odor perception (Leonardos et al. 1969). 

FIGURE 50-1 A schematic diagram of the olfactory epithelium. The initial events in odor perception occur in the olfactory epithelium of the nasal cavity. Odorants interact with specific odorant receptors on the lumenal cilia of olfactory sensory neurons. The signals generated by the initial binding events are transmitted along olfactory neuron axons to the olfactory bulb of the brain. 

The use of TLV-STELs and ceiling limits may be most appropriate if the objective is to identify effect zones in which the primary concerns include more transient effects, such as sensory irritation or odor perception. In general, persons located outside the zone that is based on these limits can be assumed to be unaffected by the release. 

Consider that the odor perception by human nose is correlated with the odor value, OVj, in the headspace above the liquid. If a specific OVt distribution values is wanted, the perfume composition can be determined with the help of Equation (2). This methodology can facilitate the optimization of perfume compositions, reducing in this way some trial and error time and chemical wastes. Clearly, the problem is determined by structural decisions because the perfume composition depends on the interaction of the different perfume components. 

Hasler, A. D. (1954). Odor perception and orientation in fishes. Journal of the Fisheries Research Board of Canada 11,107-129. 

Although the role of chirality in odor perception is still a rather new area of interest, it was noted that more than 285 enantiomeric pairs are known to exhibit either differing odors or odor intensities. ... 

Interesting examples of single stereoisomers of natural and synthetic odorants, prepared via bioorganic routes, support the statement that our sense of smell is enantioselective. Nowadays, we have enough good quality data to know that sometimes absolute configuration affects odor perception. 

Enantiomeric compounds differ from one another only in two aspects The chiroptical characteristics (optical rotation) and the speed of their reaction with chiral molecules. The human olfactory organ is also capable of distinguishing chiral molecules. The odor quality and potency of enantiomeric compounds may show considerable differences. Thus, distinct differentiation in odor perception could be observed in the pairs of enantiomeric oxygenated monoterpenoid odorants. " However, the... 

Laska M, Liesen A, Teubner P, Enantioselectivity of odor perception in squirrel monkeys and humans, Am J Physiol Regul Integr Comp Physiol 277 (R)1098— (R)1103, 1999. 

Colorless gas pungent suffocating odor human odor perception 0.5 mg/m hquefies by compression at 9.8 atm at 25°C, or without compression at -33.35°C (at 1 atm) sohdifies at -77.7°C critical temperature and pressure, 133°C and 112.5 atm, respectively vapor density 0.59 (air l) density of liquid ammonia 0.677 g/mL at —34°C dielectric constant at —34°C is about 22 extremely soluble in water solution alkaline pKa 9.25 in dilute aqueous solution at 25°C the gas does not support ordinary combustion, but bums with a yellow flame when mixed in air at 16— 27% composition. 

Since fragrance materials differ in volatility, the odor of a perfume composition changes during evaporation and is divided into the top note, the middle notes or body, and the end note or dry out, which consists mainly of less volatile compounds. Odor perception also depends largely on odor intensity. Therefore, the typical note is not determined only by the most volatile compounds. 

Burdach, K.J. and Doty, R.L. 1987. The effects of mouth movements, swallowing, and spitting on retronasal odor perception. Physiol. Behav. 41 353-356. 

RW I represents the concentration of a substance in indoor air for which, when considered individually, there is no evidence at present that even lifelong exposure is expected to have any adverse health impacts. Values exceeding this are associated with an abnormal exposure which is undesirable for health reasons. For precautionary reasons, there is also need for action in the concentration range between RW I and RW II. RW I is derived from RW II through the introduction of an additional factor (usually 10). This factor is a convention. In the case of strong-smelling substances, RW I must be obtained not on the basis of this schematic derivation but on the basis of odor perception (detection threshold) if this results in a lower numerical value. RW I can serve as a target value for clean-up operations. It should be undercut rather than merely complied with. 

Cases with accumulation of complaints/ symptoms or odor perceptions, for example, after major renovation work. 

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. 

This pair of enantiomers represents a good example for chirality and odor perception (89JAFC413,93PF1, 07MI2, 00MI1) ... 

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