Olfactometry

GC-Olfactometry (GC-O) or sniffing describes techniques that use the human nose to detect and evaluate volatile compounds eluting from a GC separation (Delahunty, 2006). Assessors sniff the eluate from a specifically designed odour port parallel to FID or MS detection. GC-O applications have become common not limited to the food and flavour industry to assign specific flavour characteristics to each of the volatile compounds identified. The human nose plays the role of the detector. However, the human nose is often more sensitive than any physical detector, and GC-O exhibits supplementary capabilities that can be applied to any fragrant product. 

Olfactometry techniques can be classified into two categories dilution methods, which are based on successive dilutions of an aroma extract until no odour is perceived at the sniffing port of the GC, and the intensity methods, in which the aroma extract is injected and the assessor records the odour intensity and perception as a function of time. The technical solution is straightforward with a split at the end of a chromatographic column and a heated transfer line to a GC external sniffer port. The eluting compounds are splitted, for example, 1 50 to an FID or MS detector and the sniffing port. The column effluent is combined at the sniffer port with a laminar stream of inert make-up gas, which is heated to a constant temperature and additionally humidified. 

---

Fig. 3. (a) Flame ionization detector (fid) response to an extract of commercially processed Valencia orange juice, (b) Gas chromatography—olfactometry (geo) chromatogram of the same extract. The abscissa in both chromatograms is a normal paraffin retention index scale ranging between hexane and octadecane (Kovats index). Dilution value in the geo is the -fold that the extract had to be diluted until odor was no longer detectable at each index. 

A relatively new methodology caEed aroma dEution analysis (ada), which combines aroma dEution and gas chromatography-olfactometry to gain a better understanding of the relative importance of aroma compounds, was recently done for coffee. In a roasted Colombian coffee brew, 41 impact compounds were found with flavor dEution threshold factors (FD) greater than 25, and 26 compounds had FD factors of 100 or above. WhEe the technique permits assessment of the impact of individual compounds, it does not evaluate synergistic effects among compounds (13). 

The sensory technique used for assessing human perception of odors is called olfactometry. The basic technique is to present odorants at different concentrations to a panel of subjects and assess their response. The process favored by the U.S. National Academy of Sciences is dynamic olfactometry (16). This technique involves a sample dilution method in which a flow of clean, nonodorous air is mixed with the odorant under dynamic or constant... 

FD-MS, FDMS Field desorption mass spectrometry GCO Gas chromatography-olfactometry... 

Goodner KL, Jella P and Rouseff RL. 2000. Determination of vanillin in orange, grapefruit, tangerine, lemon, and lime juices using GC-olfactometry and GC-MS/MS. J Agric Food Chem 48(7) 2882-2886. 

A laboratory where the measurement takes place must be free from odor and is typically air-conditioned with air filtration. The odor sample is placed in an olfactometer that basically is a device for dilution of the sample. Typically, the meter has two outlet ports diluted odorous air flows from one, and clean odor-free air flows from the other. In dynamic olfactometry, panel members assess the two ports of the olfactometer. The assessors indicate from which of the ports the diluted sample is flowing. The measurement starts with a dilution that is large enough to make the odor concentration beyond the panelists threshold. This concentration is normally increased by a factor of two in each successive presentation. Only when the correct port is chosen and the assessor is certain that the choice is correct and not just a guess, is the response considered a true value. 

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... 

Olfactometrie measurement methods must be rejected when threshold values of at least three substances can not be assessed within a factor of 2 to previously generally accepted values. 

The reports prepared by Messrs HARTUNG, VOORBURG and HANGARTNER concerning the analysis european standards and guidelines in the field of olfactometry are commented explanations and further information are supplied . 

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. 

---