Odour intensity

Ethyl Laurinate.—The laurinic ester of ethyl alcohol has also, quite recently, come into KOgue in synthetic perfumery. It is an oil of peculiar fruity odour, intensely strong, having the constitution... 

During the CEC-seminar in Bad Zwischenahn, Kowalewsky (1) concluded that NH3 is suitable for use as a main component. He defined a main component as a compound whose concentration correlates with the sensory evaluation of odour intensity. 

CORMACK, D., T.A.DORLING and B.W.J.LYNCH (1974). Comparison of techniques for organoleptic odour-intensity assessment. Chem.Ind. (London) no. 2, 857-861. 

Assessment and Effects of Odours—Intensity and Hedonic Tone... 

Since it is the object of olfactometry to give an indication of the perceived intensity of the odours in the environment, a general warning should be given as to the use of the concept of odour units/m. Even if the number of odour units/m is determined correctly, it does not give a direct indication of the perceived intensity as was already pointed out by Frijters (4). The slope of the curve which relates perceived odour intensity to the odour concentration may vary considerably from odour to odour. A schematic example is given in figure 2 for two substances A and B. 

According to Stevens law the logarithm of the perceived intensity is linearly related to the logarithm of the odour intensity. In the figure this relationship is given for two substances, one with a slope of 1.00 and one with a slope of. 67. As can be seen from the figure, this means that an odour concentration of 100 odour units/m3 is related to very different perceived odour intensities for the two substances. This means that odour concentrations computed in odour units/m3 should not be used as an indication of perceived odour intensity, but can only be used in relative measurements where the effects of measures taken to reduce odour pollution are compared, or in studies where dispersion models are used to find the distance to the source at which threshold is reached. 

The most important dates to get comparable results are odour intensity as dilution level Z50 (1), ventilation air flow rate V and number of livestock units LU. The comparable emission level per livestock unit EL from each stall compartment will be ... 

Veiy important differences between different stall compartments could be figured out. We found special differences between different ventilation control systems. The extremely high odour production in some flat decks are only peaks, because the fans are switched on and off. During the off-time the odour intensity in the stall increases and in the beginning of the on-time there will be a peak of odour. 

Physical factors were the cause of differing odour intensity results obtained when 3 commercial olfactometers were compared with the ASTM D1391-57 batch dilution method (1). The variables considered to have the greatest effect were the flow rates and/or velocity of the diluted air at the nose/olfactometer interface. A further physical factor of critical importance, however, is whether the expected dilution factors are actually achieved. 

Fig. 4. Layout of field experiments with observers determining the odour intensity on different distances from the manured field.

Fig. 5. a. Perceived odour intensity as a function of time for two spreading alternatives subsurface injection and spreading on the surface,... 

The principle of scrubbing noxiuous or odour-intensive substances of the process waste air has been applied in industry for many years. It refers to relatively large devices in which the air is scmbbed. After that the scmbbed substances are generally neutralized by chemicals. 

The waste gas, charged with odour-intensive substances (room waste air and process waste air) is purified in a two-stage counter-flow sembber (1). The sembbing fluid for the first stage is weakly acidic (A) and for the second stage, weakly alkaline (B). Both sembbing fluids contain activated sludge which is adapted to the medium concerned. 

Water Reclamation Works by their very nature can, at times be the source of unpleasant odorous emission. The odour-intensive compounds (osmogenes) which make up these emissions are believed to arise mainly as the decomposition products of carbohydrates and proteins. The breakdown of this waste material proceeds by aerobic and anaerobic processes at various stages of the treatment plant. Atmospheric pollution of this nature frequently results in complaints from members of the public either resident, or perhaps employed in the vicinity of such works. In order to confirm or deny that a reclamation works is responsible for a particular nuisance and, if possible to identify the causal agents it was decided that the Authority should have the capability of analysing for odorous and other polluting constituents of the atmosphere. This paper describes the progress made towards this objective and summarises the experience gained with a procedure in use. There are two principle approaches available for the analytical classification of odorous emissions -... 

The only odour-intensive species conclusively identified in the odorous emission of water reclamation works were dimethyl -disulphide, -trisulphide and -tetrasulphide. 

The odour-intensive species which make up the emission under investigation must be identified. The resulting table of osmogenes should be as complete as possible. It is, of course vital that no important osmogenes are overlooked at this stage. 

For each of the identified osmogenes the relationship between the compounds actual abundance in the mixture and the concentration that represents the odour perception threshold must be evaluated. This is essential to give some indication of the osmogenes perceived intensity and assist in pinpointing which of the odour-intensive species are most significant. 

It provides a detection system for gas chromatography which is both sensitive and selective for odour intensive compounds. 

Not all odour-intensive species present in a sample will necessarily be perceived at the... 

The results obtained with this procedure are similar to those previously reported in the literature by Hangartner, Hagenguth et al and Zeman et al (4, 2, 5, 6). The major exception, being the complete lack of alkylated pyrazines and alkylated thiophenes. These odour-intensive compounds arise from the thermal decomposition of proteins and sulphur containing amino acids. They also develop in the thermally induced reaction of proteins with carbohydrates (Maillard reaction). The authors indicated above have demonstrated that these compounds are invariably produced during the thermal treatment of sludge, a process which is not used in this Authority. 

The malodorous emission in this case appears to be dominated by volatile fatty acids and cresol. It is interesting to note in passing that cresol is one of the few odour-intensive species found in almost all odorous emission so far encountered. This osmogene is usually present in sufficient quantities to be clearly detectable of the odour port. Cresol and phenol (only found occasionally) is reported to be formed by the decomposition ol lignin. 

Odour nuisance is a combination of odour intensity and odour quality. Odour intensity is a function of the number of times odourous air must be diluted with odour-free air (i.e. a dilution factor) for 50% of an odour panel to just detect the odour (8 9). It can also be measured by using a panel of people and a scale of intensity on which the strength of the odour is indicated (16). Large panels of people are needed for these measurements, since differences in sensitivity of individuals are known to be large (10, 11 12). 

The concentrations of several specific odorants found in piggery slurry,in particular volatile fatty acids, hydrogen sulphide, ammonia and p-cresol, have been correlated with odour intensity (13, 14, 15 16). 

EARTH, C.L., HILL, D.T. POLKOWSKI, L.B. 1974 Correlating odour intensity index and odorous components in stored dairy manure. Transactions of the American Society of Agricultural Engineers 17(4), 742-4, 747. 

The highest OAVs were found for 4-hydroxy-2,5-dimethyl-3(2H)-fura-none, followed by ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, methyl 2-methylbutanoate and ( ,Z)-l,3,5-undecatriene. It is assumed that these odorants contribute strongly to the aroma of pineapples [50]. However, FD factors and OAVs are functions of the odorants concentrations in the extract, and are not psychophysical measures for perceived odour intensity [71,72]. To take this criticism into account, aroma models are prepared on the basis of the results of the quantitative analysis (reviewed in [9]) and in addition omission experiments are performed [9]. 

VDI (1992) 3882 Part 1, Olfactometry, Determination of Odour Intensity, Beuth Verlag, Berlin, Germany. 

In contrast, odour intensity of other components related to off flavours ( herbal , sawdust , greasy , and cucumber ) can be seen to decrease with toasting. The same happened with the intensity of fruity and floral aromas of linalool oxide, p-damascenone, or 2-phenylethanol, and the oak lactones odour descriptors. 

Compounds that decreased their odour intensity with oak wood toasting Odour descriptors obtained by GC-sniffing Compounds that increased their odour intensity with oak wood toasting Odour descriptors obtained by GC-Sniffing... 

Pet ka, J., Ferreira, V, and Cacho, J. (2005). Posterior evaluation of odour intensity in gas chromatography-olfactometry comparison of methods for calculation of panel intensity and their consequences. Flavour Frag. J., 20, 278-287. 

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