Odor intensity

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. 

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. 

Thresholds may also be determined by extrapolation of dose-response plots. In this approach, the perceived odor intensity is measured at several... 

F.Patte, M.Etcheto, P.Laffort, Selected and Standardized Values of Suprathreshold Odor Intensities for 110 Substances, Chemical Senses and Flavour, 1, 1975, 283-305. 

BARTH, C.L., HILL, D.T. POLKOWSKI, L.B. (1974). Correlating odor intensity index and odorous components in stored dairy manure. Transaction of the American Society of Agricultural Engineers 17 (4), 742-744. 

Patty, F.A. and Yant, W.P. Odor Intensity and Symptoms Produced by Commercial Propane, Butane, Pentane, Hexane and Heptane Vapor, US Bureau of Mines, 1929. 

In general, perceived odor intensity is a power function of the odor concentration. The exponent is below 1, meaning that boosting the perceived intensity requires increasingly more odor production. As odor production becomes more and more costly, fine-tuning of chemoreception (instead of odor production) becomes the more attractive alternative evolutionarily. 

Visual stimuli may influence the perceived odor intensity. An odorous and an odorless solution that were slightly tinted with yellow were more often considered odorous than the corresponding clear solutions with and without odor (Engen, 1972). Based on these findings, Cain (1978) pointed out that in the realm of air pollution the sight of black smoke from a factory may drastically increase the number of odor complaints whether or not the odor is indeed more intense. 

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. ... 

Compounds used in the database were obtained from literature reports of chemical structure and odor quality (7-11). In Table 1, a list of the compounds comprising the database is given. The macrocyclic and nitroaromatic musks are of strong, medium, weak, or unspecified odor intensity the nonmusks are odorless or have an odor other than musk. Information about odor quality and intensity is contained in the activity label associated with each compound. It should be emphasized that a musk compound labeled as weak, medium, or strong refers only to the change in its odor threshold, not to any change in its odor quality. Structural classes present in the dataset are shown in Fig. 1. Natural musks, whose sources include both rare animal and plant species, are... 

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. 

To determine the chemical composition of drinking water, concentration by headspace, extraction, and XAD-2 adsorption were applied to acquire concentrates. Sensory-directed fractionation of these concentrates has led to the identification of odor-intensive compounds of industrial origin. 

Food scientists are interested in the enantiomer distribution of chiral food odorants because enantiomers may have different odors and odor intensities. Determination of enantiomer ratios and their sensory properties can provide information about origin of food aromas and the perceived variations in the taste of foods. These data can be collected only when the enantiomers are separated using enantiose-lective high-resolution gas chromatography, which is the leading method for stereodifferentiation of chiral food odorants. 

The measurement of odor intensity using OAVs is described by Grosch (1993, 1994). It requires the determination of the concentration of each odorant in the sample, and for those present in trace quantities, a stable isotope dilution assay must be used (Guth, 1997). This may make the determination of OAVs very tedious if many values are required. OS Vs are normalized peak areas from an odor chromatogram and represent a more realistic representation of the importance of the odors in a sample as perceived by the nose. Their determination is described by Acree (1997). 

If qualitative data are required, and the enantiomers differ significantly in their odorqual-ity, then acceptable results may be obtained. If odor intensity measurements (OAVs or OSVs) or threshold values are required, then the conditions described above must be obtained if the data is to be of value. Bernreuther et al. (1997) and Koppenhoefer et al. (1994) have published the enantiospecific sensory data for a variety of chiral odorants. 

Reagents and equipment for GC/O with direct sniffing (see Basic Protocol 1), with additional apparatus as needed for desired number of sniffers Cross-modal matching device potentiometer or personal computer with mouse and in-house software for indicating perceived odor intensity... 

Furan derivatives with several functional groups have increased odor intensity as compared with lower homologues. 

Figure 8.1 Non-correlation of TVOC emission and odor intensity of a flooring material.

But research over the past ten years reveals that in most cases there is no direct correlation between VOCs measured by routine emission tests and odor active compounds (Mayer and Breuer, 2000 Knudsen et al., 1999 Salthammer et al., 2004). Figure 8.1 shows an example of the time-dependent TVOC values of a flooring material in comparison to odor intensity scores (see later). 

Odor intensity Hedonic odor tone Perceived air quality (decipol)... 

The relevance of this chemistry is demonstrated by the sensory impressions of linseed-oil based linoleum. Jensen, Wolkoff and Wilkins (1995) studied the autooxidation products emitted from linoleum and identified saturated and unsaturated aldehydes and fatty acids. An odor evaluation of the identified 2-alkenals and the fatty acids as contributing most to odor intensity (Jensen, Wolkoff and Wilkins, 1995), although many odorous products may not be quantified by traditional analytical methods (Knudsen et al., 2007) Knudsen et al. (2007) showed that linseed oil based products exhibited a more negative sensory perception than similar product not containing linseed oil, and that the negative perception persisted for at least a year. 

Considering that at least two studies should have shown effects and that the thresholds should be relevant for the low level indoor exposure range (e.g., below 10mg/m3) then Table 14.5 shows a list of symptoms and thresholds (mg/m3) in relation to M22. Assuming that M22 is a best case, then at exposures below about 2 mg/m3 (TVOC) perceived air quality, odor intensity, irritation of eyes or nose, additional ventilation needed, and cough, are expected to be the most sensitive indicators ofVOC exposures. However, it must be kept in mind that these symptoms are unspecific and may have many other causes. Therefore, the presence or absence of these symptoms cannot infer that VOC concentrations indoors are the responsible agent, only indicate the possibility. 

The Po/w, tbat is, the distribution coefficient between octanol and water, indicates a possible accumulation in fat. Malodorous or odor intense compounds should also be indicated. 

Lansky P and Rospars J.-P (1993) Coding of odor intensity. Biosystems 31, 15-38. Ledent V., Gaillard F., Gautier P, Ghysen A. and Dambly-Chaudiere C. (1998) Expression and function of tap in the gustatory and olfactory organs of Drosophila. Int. J. Dev. Biol. 42, 163-170. 

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