Olfactometry with

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... 

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. 

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. 

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). 

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. 

New, powerful techniques in chemistry, odor formulations, bioassays, and olfactometry have supplied us with deeper as well as fresh insights into olfactoiy effects on our behavior. Medicine, psychology, environmental design, occupational safety, air-quality control, marketing, and advertising now consider and contribute to human chemical ecology. 

The complete OAV analysis of a food target is time-consuming and requires an excellent analytical setup. In many cases the well-established combination of GC combined with olfactometry provides an excellent insight with regard to the composition of aroma compounds in a mixture and the role of individual chemicals. 

Basic Protocol 1 Gas Chromatography/Olfactometry Using Direct Sniffing Gl.8.1 Basic Protocol 2 Dilution Analysis With Gas Chromatography/... 

Acree, T.E. 1997. GC/Olfactometry GC with a sense of smell. Anal. Chem. 69 170A-175A. 

Figure G1.8.1 Diagram of the sniff port constructed from a laboratory filter (based on Acree et al., 1976 see Acree, 1997) showing the filter pump (with the check ball removed) attached to a humidifier, shut-off valve, and charcoal filter. The vacuum side of the pump is positioned over a flame ionization detector (FID) with the hydrogen gas turned off. The make-up gas helps lift the narrow (<0.2-mm-o.d.) gas chromatography (GC) effluent stream into the much larger olfactometry air stream without loss of resolution, and the 300 ml/min air combustion gas produced by the FID also prevents loss of resolution.

In the early history of gas chromatogra-phy/olfactometry (GC/O vn/tgu), the goal of GC/O analysis was to determine when an odor elutes from a GC in order to identify it. The analysis yielded a list of times and, with appropriate standards, retention indices. When combined with other chemical analysis methods, such as mass spectrometry (MS), a name for a particular odorant could be proposed. Comparing both the chemical and sensory properties of the odorant with those of authentic standards allowed researchers to identify the odorant with considerable certainty. The number of odorants that are detected, however, is determined by a number of factors, including the design of the olfactometer, the fraction of the extract injected, and, as we now suspect, the genetics of the sniffer. 

To avoid interferences during gas chromatography, the aroma distillate has to be separated into neutral/basic and acidic fractions by treatment with sodium bicarbonate, if higher amounts of volatile acids, such as acetic acid or butanoic acid, are present Both fractions are then concentrated to the same volume and separately analyzed by gas chromatography olfactometry (GCO). To separate the acidic volatiles a free fatty acid stationary gc phase (FFAP) is very appropriate. 

The method of choice for the analysis of odorants and subsequent identification is gas chromatography-olfactometry (GC—O), a method which combines the separation capability of volatile compounds by GC with the selective and sensitive odor detector human nose (Fuller, Steltenkamp and Tisserand, 1964). A scheme of the set-up can be seen in Figure 8.6. 

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. 

Odor analysis (see Chapter 8) performed using GC coupled with olfactometry has also shown that many food items and household materials are odorant sources (Mayer and Breuer, 2006). Thus, mono-unsaturated aldehydes particularly E-2-nonenal are found in fat, wax, oil finish and lubricants branched aldehydes such as 3-methyl butanal are found in varnish, bread and malt while leather, rice and popcorn are sources of substituted pyrrolines especially 2-acetyl-l-pyrroline. Studies like this are important not only from the point of view of identifying sources of indoor odorants but also from the point view of providing vital information that can help consumers to select products. 

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... 

Other volatile compounds present in oak wood can transmit unpleasant aromas to the wine, such as the sawdust aroma of dry wood that is perceptible in some wines aged in new barrels. The substances that cause these aromas have been identified in both American and European oak wood, for instance, ( )-2-nonenal, 3-octen-l-one, ( )-2-octenal, and 1-decanal. Their connection with the sawdust aroma has been established by olfactometry, and they have been identified in wines suffering from this flaw, though toasting the wood (Chatonnet and Dubourdieu 1998). 

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. 

Analysis of trace compounds. All fractions were checked by capillary gas chromatography (GC) with FID and sulfiir specific detection (flame photometric detector, FPD ThermoQuest CE, Egelsbach). Subsequently the different fractions were analyzed by capillary gas chromatography-mass spectrometry (GC-MS). Specific unknowns were enriched by preparative multidimensional gas chromatography (MDGC). For further structure elucidation complementary analyses using GC-MS and capillary gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR) as well as H-NMR were applied. All new compounds have been synthesized and characterized by GC-olfactometry (GC-0). 

Cabernet wine comparison. One of the objectives of the study was to identify the odoi active compounds of wines with "Brett" flavor through sensory analysis and gas chromatography-olfactometry (GCO). Wines identified by their respective winemakers as having "Brett" character were evaluated by a trained expert sensory panel also, using the technique CharmAnalysis (92-94) for GCO analysis, along with gas chromatography-mass spectrometry (GC-MS), odor-active compounds were identified by their respective Kovats retention indices (95). Contained below is a... 

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