Odor magnitude

C) Perceived odor component (denoted odor magnitude) of amyl butyrate alone (M), carbon dioxide alone (0), and physical mixtures (O). The low, but nonzero judgments for the odor of the odorless irritant carbon dioxide presumably reflect imperfect perceptual resolution between odor and irritation. The nonmonotonic function formed by the thin dashes depicts how odor magnitude would change in a case where concentration of odorant and irritant changed jointly. Compare this function with that of Subject E in... 

Cain, W. S. Contribution of the trigeminal nerve to perceived odor magnitude. Annals of the New York Academy of Sciences, 1974, 237, 28-34. 

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. 

The threshold limit value for ethyl alcohol vapor in air has been set at 1000 ppm for an 8-h time-weighted exposure by the ACGIH (1989 listing). The minimum identifiable odor of ethyl alcohol has been reported as 350 ppm. Exposure to concentrations of 5,000—10,000 ppm result in irritation of the eyes and mucous membranes of the upper respiratory tract and, if continued for an hour or more, may result in stupor or drowsiness. Concentrations of this latter order of magnitude have an intense odor and are almost intolerable to begin with, but most people can become acclimated to the exposure after a short time. Table 7 gives the effects of exposure to even heavier concentrations. 

Four characteristics of odor are subject to measurement by sensory techniques intensity, detectability, character (quality), and hedonic tone (pleasantness-unpleasantness) (16). Odor intensity is the magnitude of the perceived sensation and is classified by a descriptive scale, e.g., faint-moderate-strong, or a 1-10 numerical scale. The detectability of an odor or threshold limit is not an absolute level but depends on how the odorant is present, e.g., alone or in a mixture. Odor character or qualit) is the characteristic which permits its description or classification by comparison to other odors, i.e., sweet or sour, or like that of a skunk. The last characteristic is the hedonic type, which refers to the acceptability of an odorant. For the infrequent visitor, the smell of a large commercial bread bakery may be of high intensity but pleasant. For the nearby resident, the smell may be less acceptable. 

Other systems such as the oxidation of H2S to SO2 and H2O are also used even though the SO2 produced is still considered a pollutant. The tradeoff occurs because the SO2 is much less toxic and undesirable than the H2S. The odor threshold for H2S is about three orders of magnitude less than that for SO2. for oxidation of HjS to SO2, the usual device is simply an open flare with a fuel gas pilot or auxiliary burner if the H2S is below the stoichiometric concentration. 

The odor threshold for most atmospheric pollutants may be found in the literature (1). By properly applying the diffusion equations, one can calculate the height of a stack necessary to reduce the odor to less than its threshold at the ground or at a nearby structure. A safety factor of two orders of magnitude is suggested if the odorant is particularly objectionable. 

Many odorous compounds may be converted to compounds with higher odor thresholds or to nonodorous substances. An example of conversion to another compound is the oxidation of H2S, odor threshold 0.5 ppb, to SO2, odor threshold 0.5 ppm. The conversion results in another compound with an odor threshold three orders of magnitude greater than that of the original compound. 

Equation (4.20) expresses that the total resistance to mass transfer across the air-water boundary is equal to the sum of the resistances across the liquid film and the gas film. The importance of the magnitude of Henry s constant is, in this respect, evident. For high values of HA, e.g., exemplified by 02, the resistance mainly exists in the water film, and turbulence in a sewer will, therefore, enhance the water-air transfer process. The importance of turbulence in the water phase is reduced for odorous components with a relatively low HA value, and turbulence in the air phase will correspondingly increase the release rate (Table 4.1). As seen from Equations (4.20) and (4.21), these facts also depend on the k1A/k2A ratio that varies according to system characteristics. 

Complementary airflows can be calculated by distracting the odorous and diluting airflow from nasal airflows. Although some notion on the magnitude of the nasal airflow can be... 

Aquatic animals use their chemical senses in all aspects of their lives, from reproductive behavior to feeding, habitat selection, and predator avoidance. The hydrodynamic properties determine the possibilities and limits of chemical communication in water. As a medium, water is as dynamic as air, so that convection and advection are far more important for odor transport than is diffusion. Distribution by currents is even more important in water because compounds of similar molecular weight diffuse four orders of magnitude more slowly than in air (Gleeson, 1978). Diffusion of odorants may be important only in the submillimeter range, while turbulence is typical for water masses above the centimeter range. 

The influence of the sensitivity of the assessors on AEDA has been studied [11], with the result that the differences in the FD factors determined by a group of six panellists amount to not more than two dilution steps (e.g. 64 and 256), implying that the key odorants in a given extract will undoubtedly be detected. However, to avoid falsification of the result by anosmia, AEDA of a sample should be independently performed by at least two assessors. As detailed in [6], odour threshold values of odorants can be determined by AEDA using a sensory internal standard, e.g. ( )-2-decenal. However, as shown in Table 16.6 these odour threshold values may vary by several orders of magnitude [8] owing to different properties of the stationary phases. Consequently, such effects will also influence the results of dilution experiments. Indeed, different FD factors were determined for 2-methyl-3-furanthiol on the stationary phases SE-54 and FFAP 2 and 2 , respectively. In contrast, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone showed higher FD factors on FFAP than on SE-54 2 and 2, respectively. Consequently, FD factors should be determined on suitable GC capillaries [8]. However, the best method to overcome the limitations of GC-O and the dilution experiment is a sensory study of aroma models (Sect. 16.6.3). 

Most patients tend to respond in a positive way to any therapeutic intervention by interested, caring, and enthusiastic medical personnel. The manifestation of this phenomenon in the subject is the placebo response (Latin, "I shall please") and may involve objective physiologic and biochemical changes as well as changes in subjective complaints associated with the disease. The placebo response is usually quantitated by administration of an inert material, with exactly the same physical appearance, odor, consistency, etc, as the active dosage form. The magnitude of the response varies considerably from patient to patient and may also be influenced by the duration of the study. Placebo adverse effects and "toxicity" also occur but usually involve subjective effects stomach upset, insomnia, sedation, and so on. 

A number of investigators (2, 5, 15, 21, 34, 41, 42, 48, 82, 53) have tried to isolate and to characterize the chemical compound or compounds which give rise to irradiation flavor in meat or to correlate irradiation flavor scores with the production of specific compounds or types of compounds during the irradiation of meat or meat fractions (3,4,32,44> 49,50). These investigations have indicated some probable and some improbable sources of irradiation flavor and the order of magnitude of the concentration of the compounds responsible for irradiation flavor. Wick et al. (53) have offered impressive chemical and organoleptic data connecting the 20 2 1 ratio of methional, 1-nonanal, and phenylacetaldehyde found in irradiated beef at the parts per million level with typical irradiation odor. 

If compounds with very low odor thresholds and very small concentrations contribute to a material s odor their detection can be very challenging, especially when only applying routine emission measurements like GC—MS. Such compounds will easily be overlooked, for their detection GC—O can often be the only choice, but so far this method is seldom used in material analysis. Instead concentrations determined by emission measurements are compared with published odor thresholds to decide whether a compound might contribute to the odor or not. One problem is that published odor thresholds can differ quite a lot, even by several orders of magnitude (van Gemert, 2003). The value depends on the method and the panel but also on the purity of the compound used for threshold determination (if small impurities of a substance with a low odor threshold were present in a sample the odor threshold determined would have been too low ). Many factors influence odor threshold determination, therefore many published values are questionable and they are hard to rely on. Some authors (Knudsen et al., 1999 Wolkoff, 1999 Wolkoff et al., 2006) assume that many of the odor thresholds reported in the literature are actually much lower, because if they compare concentrations of compounds emitted and measured with odor thresholds published,... 

Figure 21.1 Air flow is from left. (A) Air moving relative to a solid object (such as the sensory hair shown in cross-section) is slower closer to the surface of the object and is zero at the surface (the no-slip condition). The length and orientation of each arrow represent the magnitude and direction of the air velocity at the point in space at the base of the arrow. (B) Streamlines of the moving fluid are indicated by arrows. The path of a diffusing odorant molecule is pictured crossing the streamlines.

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