Odour olfactometry

CEN (1999), Air quality — determination of odour concentration measurement by dynamic olfactometry, European Committee for Standardisation, draft prEN 13725. 

GILLARD, F. (1984). Measurement of odours by dynamic olfactometry. Application to the steel and carbonization industries. Proc.Int.Symp., Soc. Beige de Filtr. (eds.), 25-27 April 1984, Louvain-La-Neuve, Belgium, pp. 53-86. 

Olfactometry—Odour Threshold Determination—Olfactometers Types 1158 and TO-4... 

Olfactometry—Odour Threshold Determination—Instruction for Application and Performance Characteristics... 

In order to assist the industry in establishing suitable odour reducing processes, odour measurements are performed at our institute. Olfactometry is useful for objective evaluation of odour levels and for characterization of certain odours, often in combination with gas chromatography. 

Each case may provide features which influence the olfactometric measurements, often demanding special sampling techniques and interpretations. In the following some of the problems and experiences will be pointed out by means of examples from sewage treatment and fish meal plants, showing the use of olfactometry for obtaining satisfactory odour reducing results. 

Measure of odour reducing efficiency in iron oxide filtersu is another esample of how olfactometry may contribute to the optimization of an odour reducing method. 

The use of the human subject as a sensor in olfactometry leads to a number of physical, methodological and panel composition requirements. Olactometers used in odour pollution assessment should be able to deliver ranges of concentrations varying in dilution from 1 to 10° at volumes between 1.8 and 3.6 m3/h without changing the pressure at the nose entrance more than 5 mbar. 

The last set of requirements in olfactometry is concerned with the differences between panel members. People vary widely in their sensitivity. A factor of a 100 between the thresholds of two subjects for the same substance is not uncommon. For a number of substances, specific anosmia s or specific hyposmia s are found. In such cases a person has no sensitivity at all or a very high threshold for the given substance, but normal sensitivity to other substances (1). This is an illustration of the fact that sensitivity to odours is specific rather than general. This is also demonstrated by Punter (2, 3) who determined the thresholds of 69 odorous substances for the same group of subjects and calculated the correlations between these thresholds (see figure 2). 

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. 

Measurement of the strength of odours by dynamic dilution olfactometry and observers is a complex task. The observers require adequate training and sound psychophysical procedures are needed to maximise the validity of the measurements. 

The concept of Odour Potential has already shown its usefulness in assessing the right time to spread sludge, and incomparing various sludge stabilisation methods. These results have been achieved without the manpower requirements of an extensive site survey and without the necessity of transporting equipment for olfactometry and makes good use of people expert in odour measurement. 

GILLARD, F. Measurements of odours by dynamic olfactometry application to the steel and carbonisation industries. Paper presented at intemation symposium Characterisation and control of odoriferous pollutants in process industries, Belgian Filtration Society, Louvain-La-Neuve, April 1984. 

Although knowledge on the correlation of odorous compounds concentration and odour impression is still limited, it is used in all types of olfactometry. Indeed diluting this concentration by adding pure air is a general practice. Also many investigations were performed where chemicals are added to air and used in psychophysical experiments. Many speakers in this workshop will present data in this field. Here only chemical analysis will be dealt with. 

DRAVNIEKS, A. JAKE, F. 1980 Odour threshold measurements by dynamic olfactometry significant operational variables J.Air Poll, Control Assoc. 30 (12) 1284-1289. 

The aroma of foods is caused by volatile compounds which are perceived by the human nose. Many studies (reviews in [1, 2]) have indicated that only a small fraction of the hundreds of volatiles occurring in a food sample contribute to its aroma. To detect these compounds, a method proposed by Fuller et al. [3] is used. In this procedure, which is designated gas chromatography-olfactometry (GC-O), the effluent from a gas chromatography column is sniffed by an expert who marks in the chromatogram each position at which an odour impression is perceived. 

DIN EN (2003) 13725. Air Quality -Determination of Odour Concentration by Dynamic Olfactometry, Beuth Verlag, Berlin, Germany. 

Mayer, F. and Breuer, K. (2004b) Human olfactometry and odour analysis as a tool for the development of TPO materials with reduced odour for the automotive industry. Proceedings of the tenth international conference TPOs in Automotive 2004 , Barcelona, Spain. 

The volatiles of fresh leaves, buds, flowers and fruits were isolated by solvent extraction and analysed by capillary gas chromatography-mass spectrometry. Their odour quality was characterized by gas chromatography-olfactometry—mass spectrometry (HRGC-O-MS) and aroma extract dilution analysis (AEDA). In fresh bay leaves, 1,8-cineole was the major component, together with a-terpinyl acetate, sabinene, a-pinene, P-pinene, P-elemene, a-terpineol, linalool and eugenol. Besides 1,8-cineole and the pinenes, the main components in the flowers were a-eudesmol, P-elemene and P-caryophyllene, in the fruits (EJ-P-ocimene and biclyclogermacrene, and... 

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). 

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. 

Concerning the impact of ethanol on aroma perception, Pet ka et al. (2003) showed that ethanol at low concentrations (under 10%) could decrease aroma compound detection threshold. Nevertheless, Grosch (2001) observed that the less ethanol present in a complex wine model mixture, the greater the intensity of the fruity and floral odours. Although this effect could be easily explained by the increased partial pressure of the odorants with reduced ethanol concentration, they showed in GC-0 (gas chromatography-olfactometry) experiments that ethanol strongly increased the odour threshold of wine volatiles. In fact the reduction in odour activity of the wine volatiles when ethanol was added was much larger than the reduction in their partial pressure. 

In a recent study by Landy et al. on odorous substances in paper-based packaging materials, the main volatile substances that caused odour of an offset printed product were identified by olfactometry. In this technique solvent-free extraction using microfibres was successfully applied. The extract was introduced in a gas chromatograph connected to a sniffing port. The odour was then evaluated by a trained assessor. 

The systematic use of gas chromatography coupled with olfactometry [27, 28] in the last 20 years has resulted in a number of new high-impact aroma chemicals found in natural extracts, food products and reaction flavours. In general, sulphur-containing odorants play a particularly important role in food products and savoury flavours [30]. Some of them are shown in Fig. 5.54. Usually, the odour threshold is one key attribute showing the potential impact of the odorant. This may be as low as 0.00002 pg/L water reported for bis-(2-methyl-3-furyl)disulphide (BMFD) (Fig. 5.55) found in cooked meat with a typical meaty, sulphury note. 

To detect the odour-active volatiles. Fuller et al. [6] described a system for the sniffing of GC effluents which was improved and applied to food samples by Dravnieks and O Donnell [7]. The new technique, named GC olfactometry (GCO), was the starting point for the development of a systematic approach to the identification of the compounds which cause food aromas. As summarised in Table 6.23 the analytical procedure consists of screening for key odorants by special GCO techniques, quantification and calculation of OAVs as well as aroma-recombination studies. During the last decade these steps have been critically reviewed by Acree [8], Blank [9], Grosch [10, 11 ], Mistry et al. [12] and Schieberle /fi/. 

CEN (1994) Dynamic olfactometry to determine the odour threshold. Draft European preliminary standard, CEN TC264/WG2... 

Stuetz, R.M., Fenner, R.M., and Engin, G. (1999). Assessment of odours from sewage treatment works by an electronic nose, H2S analysis and olfactometry. Water Res., 33, 453-61. 

The notion of odour concentration is based on the works of H. Zwaardenmaker, a Dutch scientist and early investigator of the olfactometry. By definition, the odour concentration, expressed in odorous unit per cubic meter (ou/m3) is the dilution factor of the odour sample in clean air in order to just become odour free, i.e. to reach the perception threshold for an "average" person. 

The dynamic olfactometry is the official method by which different dilutions of the gas sample are dynamically presented to trained assessors to determine the odour concentration of the original sample. When the European standard method (EN13725 -European standard air quality - Determination of odour concentration by dynamic olfactometry, 2003) is used, the concentration is expressed in ouE/m3 (with the subscript E). 

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