Odor detection thresholds

Caution A powerful irritant. Can cause fatal pulmonary edema. Threshold odor detection 0.2-0.4 ppm, cf. Patty s Industrial Hygiene and Toxicology vol. 2B, G. D. Clayton, F. E. Clayton, Eds. (Wiley-lmersclence. New York, 3rd ed., 1981) pp 2954-2965. 

As stated earlier, taste, chemicals that initiate a gustatory response, and smell, chemicals that function as odorant molecules have been extensively studied, first with arthropods and more recently with vertebrates. Since the development of very efficient separation techniques and high sensitive detection systems, we are no longer limited to taste panels and threshold odor detection by humans. Table I shows some examples of the behavior response as shown by certain species for a specific chemical. 

The odor detection-threshold values of organic compounds, water, and mineral oil have been determined by different investigators (Table 2 and 3) and may vary by as much as 1000, depending on the test methods, because human senses are not invariable in their sensitivity. Human senses are subject to adaption, ie, reduced sensitivity after prolonged response to a stimulus, and habituation, ie, reduced attention to monotonous stimulation. The values give approximate magnitudes and are significant when the same techiriques for evaluation are used. Since 1952, the chemistry of odorous materials has been the subject of intense research (43). Many new compounds have been identified in natural products (37—40,42,44—50) and find use in flavors. 

Table 2. Odor Detection Threshold Levels in Water and Mineral Oil, ppm...

Table 3. Odor Detection Thresholds of Organic Compounds ...

The odor threshold for detection of ethyleneimine is 2 ppm. The maximum permissible concentration of ethyleneimine in the air at the place of work is 0.5 ppm (as specified in statutory regulations in the United States (374) and in Germany (375)). Animal experiments have shown ethyleneimine to be both carcinogenic (376) and mutagenic (377) (Table 2). 

Taste and Odor. The measurement of taste and odor is somewhat subjective and depends on the personal judgements of individuals. Panels of not less than five observers, and preferably more than ten, are used. The sample is diluted with odor-free water until a ratio at which the odor is just perceptible is determined this ratio is called the threshold odor number (TON). A similar method is used to detect a distinct taste in water (see Flavor characterization). ... 

Hydrogen cyanide has frequently been associated with the odor of bitter almonds (Ballantyne 1983 Gee 1987). The threshold odor for olfactory detection of atmospheric HCN is 1 mg/L, but the odor may not be detected for various reasons, including the presence of other odors and the fact that only 20 to 40% of those tested could detect a cyanide odor. 

The human taste threshold for PCP in drinking water is about 30 pg/L (USEPA 1980), a level far below the upper safe limit of 1.01 mg/L and near the no-observable-effect level of 21 pg/L (Table 23.7). Odor detection is not as sensitive as taste the odor threshold for PCP ranges from about 857 pg/L at 30°C, to 1600 pg/L at 20 to 22°C, to 12,000 pg/L at 60°C (USEPA 1980). It is not clear whether the determined organoleptic threshold values made the water undesirable or unfit for consumption (USEPA 1980). If fish and wildlife species of concern have PCP organoleptic thresholds that are similar to those of humans, or lower, will they too avoid contaminated habitats or diets ... 

Based on the Stewart et al. (1974) study, the threshold for odor detection in healthy adults is 0.2 ppm, and the threshold for eye irritation is 1.5 ppm, although one of three subjects developed eye irritation during a 2-h exposure at 0.35 ppm. 

Occupational exposures and the study with human volunteers indicate that exposures at low concentrations cause headaches and signs of central nervous system depression. No headaches were reported and no equilibrium disturbances were measured during occupational exposures of healthy workers to Otto Fuel II (measured as PGDN) at concentrations <0.22 ppm (average of approximately 0.06 ppm) for periods of 30-60 min, although subtle changes in eye movements were recorded (Horvath et al. 1981). In a study with healthy but previously unexposed male volunteers, the threshold for odor detection was 0.2 ppm (Stewart et al. 1974). Mild headaches were reported in one of three subjects after a 6-h exposure at 0.1 ppm, in two of three subjects after a 2-h exposure at 0.2 ppm, and in one of three subjects after a 1-h exposure at 0.5 ppm. Severe headaches occurred after an 8-h exposure at 0.2... 

Clear, colorless fuming liquid with an amine-like odor. Turns yellow on exposure to air. Odor detection threshold concentrations ranged from 6.1 to 14 ppmv (Jacobson et al, 1955). 

Clark, L. (1991). Odor detection thresholds in tree swallows and cedar waxwings. Aufe 108, 177-180. 

The threshold of odor detection is approximately 3.3 ppm the repulsive odor is described as rotten eggs, sickly sweet, musty, or foul. ... 

Phosphine has a fishy or garliclike odor detectable at 2 ppm the odor threshold does not provide sufficient warning of dangerous concentrations. 

Experimental studies in humans have attempted to determine the inhalation thresholds for odor detection and eye, nose, and throat irritation. Reports on humans occupationally exposed to isophorone also indicate that isophorone is irritating to the skin, eye, nose, and throat, and may cause symptoms of dizziness, fatigue, and malaise. 

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. 

Furthermore, as an extract of a natural product is concentrated, the number of odorants detected increases indefinitely. Clearly, most of the odorants in a natural product are below their odor threshold, and it is only the most potent compounds that are involved in generating the flavor response. An odorant can be very potent at extremely low concentrations if it has an extremely low odor threshold, (unit go). In practice, early GC/O analysts attempted to concentrate the sample as far as possible to identify as many potential odorants as possible. Compositional studies combined with threshold studies were then used to sort out the important odorants from the ones that did not contribute to the flavor experience. Rothe s odor units (OU = concentration in sample/threshold in sample) were an early attempt to rank odorants by potency. The process of determining OU values for a food required a lot of chemical and psychophysical analysis. Dilution analysis was developed to produce an OU-like value directly from GC/O without the need to know the identity of the odorant. In fact, the real value of dilution analysis is that it can tell the analyst which compounds to identify. 

By way of comparison, the threshold of S02 odor detection is about 0.5 ppm (instantaneous basis), and the U.S. national health standards are 140 ppb for 24 hours and 30 ppb for an annual average. These standards are currently being met in most U.S. locations. 

Odor-active components in cheese flavor, many of which are derived from milk lipids, can be detected using GC-olfactometry (GC-O). GC-0 is defined as a collection of techniques that combine olfactometry, or the use of the human nose, as a detector to assess odor activity in a defined air stream post-separation using a GC (Friedich and Acree, 1988). The data generated by GC-0 are evaluated primarily by aroma extract dilution analysis or Charm analysis. Both involve evaluating the odor activity of individual compounds by sniffing the GC outlet of a series of dilutions of the original aroma extract and therefore both methods are based on the odor detection threshold of compounds. The key odourants in dairy products and in various types of cheese have been reviewed by Friedich and Acree (1988) and Curioni and Bosset (2002). 

Anosmia, the inability to smell, can be divided into two classes. General anosmia, the inability to smell any odors at all, usually is the result of disease or accident. More common is specific anosmia, in which an individual either cannot detect a specific chemical substance that most people can detect or displays a threshold of detection for it which is significantly above the normal range. At one time, specific anosmias were finked to the concept of primary odors (13), but confirmation of the combinatorial mechanism of olfaction has put paid to this concept. Interestingly, it has been demonstrated that exposure to the substance can affect anosmia and individuals can begin to smell materials to which they were previously anosmic. This effect has been demonstrated for androstenone, amyl acetate, geranyl nitrile, and isoborneol (14—18). 

Canola Oil Canola oil is obtained from low erucic acid, low glucosinolate rapeseed. The unique polyunsaturated fatty acid and low saturated composition of canola oil differentiates it from other oils. It has a higher oleic acid (18 1) content (55%) and lower linoleic acid (18 2) content (26%) than most other vegetable oils, but it contains 8-12% of linolenic acid (18 3) (58). Canola oil is most widely used in Canada and is considered a nutritionally balanced oil because of its favorable ratio of near 2 1 for linoleic to linolenic acid content. Unlike most other edible oils, the major breakdown products of canola oil are the cis, trans- and tram, trans-2,4-heptadienals with an odor character generally described as oily, fatty, and putty. Stored canola oil shows a sharp increase in the content of its degradation products, which are well above their odor detection thresholds. The aroma is dominated by cis, tram-, tram, frani-2,4-heptadienals, hexanal, nonanal, and the cis, trans- and... 

The minimum amount of formaldehyde that can be detected by odor varies considerably between individuals and ranges from 0.1 to 1.0 ppm (0.12-1.2 mg/m ), close to the concentration at which minimal irritant effects are felt in the eyes and in the pulmonary airways (3). Thus, the fundamental toxicity of formaldehyde lies in primary irritation to the eyes, nose, and throat when the subject is exposed to concentrations in the range of 1-5 ppm. Concentrations above 2-5 ppm cause irritation of the pharynx, lungs, and eyes, and some erythema of vaporized areas of the skin, such as the face and neck. Acute exposure to concentrations of formaldehyde of the order of three times the maximum threshold of detection of the... 

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