Odour threshold value

Published odour threshold values vary widely from source to source. 

Table I Odour threshold values (ppb) of some organics...

Compilation of Odour Threshold Values in Air and Water, Ed. L. J.Van Gemert, A.H.Nettenbreijer, RID, Voorburg, CIVO Zeist, Netherlands, 1977. 

Table 1. Odour threshold values for untreated swine manure spread and buried in different ways. Odour threshold ED-50 (from Lindvall, T. et al. 1972)...

Methods have been developed to characterise odours according to strength (1) and offensiveness (2) using experienced panellists. Measures of offensiveness are necessarily subjective and odour strength (threshold dilution) will depend upon the odour threshold value as well as the concentration. For routine assessment these methods incur the cost of panel time and the problems inherent in the transport and storage of samples. 

National Institute for Water Supply, Netherlands. Compilation of odour threshold values in air and water Central Institute for Nutrition and Food Research TNO Netherlands June 1977. 

The investigations of dust from piggeries show that both VFA and phenols/indoles are present in a considerable amount. However, compared to the air-borne emissions calculated on the base of the results of LOGTENBERG and STORK (38) less than the tenth part (1/10) of phenols/indoles and about the hundredth part (1/100) of VFA are emitted by the dust, only. Table VII compares the dust-borne and air-borne emissions of VFA and phenols from piggeries. The total amounts are given in addition to the amounts of butyric acid and p-cresol which are both known as intensively smelling compounds. The recognition odour threshold values of these two components are included, as well. Under the assumption of a dust concentration of 10 mg/m3 (7) one cubic meter of air... 

However, although this equation was effective in modelling the odour thresholds of the disubstituted pyrazines, two main weaknesses have been identified (72) the first was that it was difficult to dmw physical meaning from the descriptor AA J, since it was not clear which aspects of die molecular structure determined the odour threshold. The second we ess was discovered when pyrazine itself and thirteen mono-substituted pyrazines were added to the original set. The calculated and observed odour threshold values were no longer in agreement. This result indicated diat the model was insufficient for more heterogeneous data sets. 

The most difficult problem in flavour research is to interpret the results of the volatile analysis, which gives information on the identity and the quantity of the volatile compounds collected from a given product. Many volatile compounds are not flavour-active, i.e. they cannot be detected in the olfactory system, while others may even in trace amounts have significant effects on flavour owing to their low odour-threshold values that is defined as the minimum concentration needed to produce an olfactory response. Consequently, the most abundant volatiles are not necessarily the most important contributors to flavour. Much... 

Table 10.1 Odour quality, odour threshold value in water and/or ethanol solution, and concentration range of single volatile compounds in distilled spirits produced during alcoholic fermentation from carbohydrates by yeasts and other microorganisms ...

Most cooked foods contain thiazoles. Simple alkyl-substituted thiazoles generally have odour threshold values in the range 1-1,000 pg/kg. Odour descriptions include green, vegetable-like, cocoa, nutty, and some are claimed to have meaty characteristics [22]. Although most alkylthiazoles result from thermal... 

A number of furans with thiol, sulphide or disulphide substitution have been reported as aroma volatiles, and these are particularly important in meat and coffee. In the early 1970s, it was shown that furans and thiophenes with a thiol group in the 3-position possess strong meat-like aromas and exceptionally low odour threshold values [50] however, it was over 15 years before such compounds were reported in meat itself In 1986,2-methyl-3-(methylthio)furan was identified in cooked beef and it was reported to have a low odour threshold value (0.05 pg/kg) and a meaty aroma at levels below 1 pg/kg [51]. Gasser and Grosch [52] identified 2-methyl-3-furanthiol and the corresponding disulphide, bis(2-methyl-3-furanyl) disulphide, as major contributors to the meaty aroma of cooked beef. The odour threshold value of this disulphide has been reported as 0.02 ng/kg, one of the lowest known threshold values [53]. Other thiols which may contribute to meaty aromas include mercaptoketones, such as 2-mercapto-pentan-3-one. 2-Furylmethanethiol (2-furfurylmercaptan) has also been found in meat, but is more likely to contribute to roasted rather than meaty aromas. Disulphides have also been found, either as symmetrical disulphides derived from two molecules of the same thiol or as mixed disulphides from two different thiols [54]. 

The chemical is used both in flavours and fragrances, but owing to its very strong smell and low odour threshold value the volume is limited. 

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). 

Table 16.6 Odour threshold values (ng/L air) of some odorants of the gas chromatograph capillary [8] as affected by the stationary phase ...

OAVs are calculated on the basis of odour threshold values which have been estimated in a medium that predominates in the food, e.g. water, oil or starch. As an example, the OAVs of the odorants of pineapples are listed in Table 16.7. 

The first attempt to apply odour threshold values to rationalise the extensive information obtained by the analysis of the volatile products of Maillard reactions... 

Flavourings consist of a blend of flavouring substances, which can be classified as lipophilic or hydrophilic. Fat or oil serves as carrier of lipophilic, and water as carrier of hydrophilic substances. Tab. 5.4 shows the variation in odour threshold values of selected flavouring substances when placed in water vs. oil. Due to these great variations, reduction in fat levels of foods will affect not only the intensity of the flavour but also its balance, since only little or no carrier system is available for lipophilic flavour components in water. The lipophilic part of the flavour cannot be retained in the food matrix and is released immediately. Fat-reduced or fat-free foods show high flavour impact initially which dissipates quickly, while full fat products gradually build up intensity and dissipate more slowly (schematically depicted in Fig. 5.25). 

To approach the situation in food, OAVs are calculated on the basis of odour threshold values which have been estimated in a medium that predominates in the food, e.g. water, oil, starch. As an example the OAVs of the key odorants of baguette crust are listed in Table 6.26. The highest OAVs were found for the roasty smelling 2-acetyl-1-pyrroline (no. 7), followed by furaneol (no. 20), 2,3-butanedione (no. 2), (E)-2-nonenal (no. 13), l-octen-3-one (no. 9) and methional (no. 6). It is assumed that these odorants contribute strongly to the aroma of baguette crust. 

The odorants of black pepper are listed in Table 6.47. Their OAVs are calculated on the basis of odour threshold values in starch because at app. 45% it is the major component of the kernel [83]. As a result of its low odour threshold, linalool (no. 11) shows the highest OAV, followed by limonenes nos. 9a and 9b, (-)-P-pinene (no. 6a) and (S)-a-phellandrene (no. 8b). 

Another labelling scheme is the indoor climate labelling scheme, in which building products are tested for their emission of VOCs and by a sensory evaluation of the emissions as a safety measure [62]. The parameter used for evaluation and as a criterion is the time required for the emission of VOCs of concern to decay to the point where their (modelled) room concentrations are below their indoor relevant values. These are based on 50% of either odour-threshold values or airway-irritation estimates. 

Van Gemert, L. J. Nettenbreijer, A. H. Compilation of Odour Threshold Values in Air and Water. National Institute for Water Supply, Central Institute for Food and Nutrition Research Voorburg, Netherlands. 1977. Wick, E. L. Murray, E. Mizutani, J. Koshika, M. Radiation Preservation of Foods, Advances in Chemistry Series, American Chemical Society, Washington, DC, 1967 pp 12-25. 

Abbreviated designation Structure Systematic name Common name Melting point (°C) Odour threshold value (mg kg" )... 

Van Gemert, L.J. and Nettenbreijer, A.H. Compilation of odour threshold values in air and water. Central Institute for Nutrition and Food Research, TNG, Zeist, The Netherlands, 1977. Punter, P.H. Measurements of human olfactory thresholds for several groups of structurally related compounds. 

Determining the odour threshold value for a water (or waste water) is always "subjective". It is nevertheless by no means worthless. 

The odour threshold value is defined as the degree of dilution obtained in the water to be examined, using absolutely odourless water produced by filtration through activated carbon. 

G = the non-dimensional figure for the odour threshold value (dilution factor)... 

A pretest determines initially the approximate range of the odour threshold value, by filling 200 ml, 20 ml, 2 ml and 0.2 ml of the sample each into a test flask and topping up the three latter measures to 200 ml. Beginning with the diluting water, the flask is shaken, the stopper opened, the contents sniffed and the flask immediately resealed. The analogous process is applied to the remaining samples. 

The ability to perceive the odour of a particular substance also depends on its odour threshold (aroma, fiavour) value, which is the concentration of a substance detectable by the sense of smeU. The odour detection threshold value is the lowest concentration of a stimulus (odoriferous substance), which can be detected in comparison with an environment that does not contain this substance. The odour recognition threshold value is the concentration at which a substance can not only be detected, but also recognised. It corresponds to a concentration that allows identification of the odour quality of a substance, which is usually higher than the odour detection threshold. Both values are measures of the odour intensity, but depend considerably on the environment, solubility, partition coefficients between air and water (oil) and some other factors. For example, values measured in air are typically several orders of magnitude lower than the values measured above aqueous solutions. The substance with a high odour threshold value must be present in foods in higher concentrations than substance with a low odour threshold value, otherwise its smell is imperceptible. The measure of whether the substance acts as an odour-active substance is its odour unit, its actual concentration divided by odour threshold concentration. 

The presence of lipids, proteins, carbohydrates and other substances significantly influences the retention of aromatic compounds in foods and has an effect on their odour intensity and quality (e.g. the odour threshold values of non-polar substances measured in water are usually lower than the values measured in... 

Table 8.33 displays the odour threshold values of some intensely odoriferous substances. The odour threshold values of selected common odoriferous substances are Hsted in Table 8.34 and Table 8.35. 

Table 2.2 Odour threshold value of selected trace gases (Guidance of Landfill Gas Flaring, 2002).

Compound Odour threshold value [pg m ] Compound Odour threshold value Qrg m ]... 

Changes in odour and taste are frequently more irksome than minor health disorders. Industrial odour immissions by toluene, xylenes and styrene have been referred to earlier [42]. Odours from combustion processes, such as for example from diesel fuels, are unpleasant. Comparative odour threshold values have been given for benzene of 4.7 ppm, for toluene of 2.1 ppm, for xylene of 0.5 ppm, for chlorobenzene of 0.2 ppm, for styrene of 0.05 ppm, and for nitrobenzene of 0.005 ppm [11]. Slightly lower odour thresholds are reported by other scientists 0.9-1.6 ppm for benzene, 0.03-0.5 ppm for toluene, and 0.15-0.18 ppm for xylene [12]. In water, quantities higher than 6.8 mg/m naphthalene, 37 mg/m styrene and 140 mg/m ethylbenzene cause unpleasant odours [13]. The following compounds may cause... 

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