Olfactory sensitivity detection thresholds

Odors are characterized by quaUty and intensity. Descriptive quaUties such as sour, sweet, pungent, fishy, and spicy are commonly used. Intensity is deterrnined by how much the concentration of the odoriferous substance exceeds its detection threshold (the concentration at which most people can detect an odor). Odor intensity is approximately proportional to the logarithm of the concentration. However, several factors affect the abiUty of an individual to detect an odor the sensitivity of a subject s olfactory system, the presence of other masking odors, and olfactory fatigue (ie, reduced olfactory sensitivity during continued exposure to the odorous substance). In addition, the average person s sensitivity to odor decreases with age. 

Eels, Anguilla anguilla, are extremely sensitive to odors. Their detection threshold for /3-phenylethyl alcohol lies at the unbelievable concentration of 3 X 10 mol/l. This corresponds to 1ml of this alcohol diluted in 58 times the volume of Lake Constance (80km long) in southern Germany where these experiments were performed. It has been calculated that only three molecules are in the olfactory sac at any one time (Teichmann, 1957, 1959). Coho salmon... 

The most celebrated mammalian olfactory detector is the dog s nose. As a predator, the dog locates its prey by air scenting (following a gradient of airborne odors) and tracking. Practitioners are familiar with the extreme olfactory sensitivity of the dog. The detection threshold for butyric acid has been determined as 9 x 10 molecules/cm air (Neuhaus, 1953). Considering that... 

Thresholds can vary between and within individuals, with the estrus cycle, and with the chemical background. Some benchmarks will be given here. In laboratory (Wistar) rats, the olfactory detection threshold for ethyl acetate was measured as 7.3 x 10 vol% in subadults, while adult rats were more sensitive (1.4 X 10 vol%) (Apfelbach etah, 1990). (By comparison, among insects the gypsy moth is 10 times as sensitive. The threshold for bombykol, defined as... 

Odor thresholds in humans appear to be more influenced by the environment than genetics. The detection thresholds for acetic acid, isobutyric acid, and cyclohexanone varied as much in monozygotic twins as in fraternal twins. Instead, smoking and diabetes were related to lower olfactory sensitivity, and body fatness and alcohol consumption to greater sensitivity to the latter two compounds (Hubert eta/., 1980). 

The human being is exceptionally sensitive to some volatiles (e.g., 2-isobutyl-3-methoxypyrazine has an odor detection threshold in water of 0.002 ppb [49] and 0.015 ppb in wine [50] but insensitive to many other volatiles (e.g., ethanol has an odor threshold of 100,000 ppb in water and a taste threshold of 52,000 ppb in water) [49]. A person s ability to detect odors is also influenced by many other factors such as genetic variability, olfactory fatigue, and naturally occurring and unpredictable factors such as temperature and humidity. The complexity of food aromas and sensitivity required plus the fact that the olfactory system must be able to respond to unknown odorants (it cannot be learned response) make this a most complex phenomenon. 

In addition to health risks there may be an issue on many sites with odours from vapours or trace gasses. In these cases the risk assessment should take account of the threshold concentration at which the vapour or gas can be detected. Many compounds have a very wide range of reported odour thresholds which can make the assessment difficult (e.g. for benzene reported detection values are in the range 0.78-160 ppm). However, the variations that are reported are probably caused in part by each individual s different olfactory sensitivity to these compounds. Therefore it is always wise to use a value from the lower end of the range to take account of the most sensitive people who are likely to be exposed to the vapour. 

The odor threshold of carbon disulfide is about 1 ppm in air but varies widely depending on individual sensitivity and purity of the carbon disulfide. However, using the sense of smell to detect excessive concentrations of carbon disulfide is unreHable because of the frequent co-presence of hydrogen sulfide that dulls the olfactory sense. 

The antennal olfactory receptor system in several phytophagous insects is very sensitive in the detection of the green odour components. In the Colorado beetle Leptinotarsa decemlineata, the threshold of response for trans-2-hexen-1-ol is circa 10b molecules per ml of air (17). In comparison, at 760 mm Hg and 20 C, 1 ml of air contains about 1019 molecules. The insects tested i.e., the migratory locust Locusta migratoria, the carrot fly Psila rosae (18), the cereal aphid Sitobion avenae (19), the Colorado beetle L. decemlineata (17), Leptinotarsa... 

ODOR. An important property of many substances, manifested by a physiological sensation caused by contact of their molecules with the olfactory nervous system. Odor and flavor are closely related, and both are profoundly affected by submicrogram amounts of volatile compounds. Attempts to correlate odor with chemical structure have produced no definitive results, Objective measurement techniques involving chromatography are under development. Even potent odors must be present in a concentration of 1,7 x I07 molecules/cc to be detected. It has been authentically stated that the nose is 100 times as sensitive in detection of threshold odor values as the best analytical apparatus. 

For both olfaction and chemesthesis, sensitivity, and any differences in sensitivity, where they exist, can be determined in populations of interest. Furthermore, by establishing olfactory detection and chemesthetic localization thresholds, one can then know when an odorant becomes an irritant. These quantitative measures then allow discrimination between eognitive and sensory irritation. 

This first study highlights several points that need to be taken into account in any sensory analysis based on olfactory tasks. Thus gender is shown to be able to influence scores in threshold and identification tasks. Cultural origin may influence scores in suprathreshold detection and identification tasks. Scores in identification tasks may also be influenced by healthy aging when corrected by detection measures. Thus it appears to be important (a) to assess and to check panelists olfactory capabilities regularly and (b) to integrate certain parameters in sensory data processing that reflect the panelists sensory sensitivity and could account for interindividual variance. For this purpose, we developed the European Test of Olfactory Capabilities. 

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