Detection olfactometry

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. 

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. 

Milo, C. and Grosch, W. 1995. Detection of odor defects in boiled cod and trout by gas chromatography-olfactometry of headspace samples. J. Agric. Food Chem. 43 459-462. 

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. 

Gas chromatography/olfactometry (GCO) methods have been developed as screening procedures to detect potent odorants in food extracts. The FD-factors or CHARM values determined in food extracts are not consequently an exact measure for the contribution of a single odorant to the overall food flavor for the following reasons. During GCO the complete amount of every odorant present in the extract is volatilized. However, the amount of an odorant present in the headspace above the food depends on its volatility from the food matrix. Furthermore, by AEDA or CHARM analysis the odorants are ranked according to their odor thresholds in air, whereas in a food the relative contribution of an odorant is strongly affected by its odor threshold in the food matrix. The importance of odor thresholds in aroma research has been recently emphazised by Teranishi et al. [58],... 

Clausen, P.A., Knudsen, H.N., Larsen, K., Kofoed-Sorensen, V., Wolkoffl P. and Wilkins, C.K. (2005) Use of gas chromatography olfactometry (GC-O) to detect unknown emissions from building products containing linseed oil. Proceedings of the 10th International Conference on Indoor Air Quality and Climate, Indoor Air 2005, Beijing, China, Vol. II (2), pp. 2053-8. 

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). 

The second point is related to the simultaneous presence of odorants at g/L levels and of others that can be active at levels as low as ng/L. This means that although it makes sense to use a general screening procedure for detecting by olfactometry the potentially most relevant aroma molecules, it will not be possible to use a single isolation or preconcentration scheme to identify and further quantify the different aroma molecules. Rather, it will be necessary to have an array of chemical isolation and quantification procedures if a comprehensive aroma analysis is our objective. 

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). 

The combination of GC with olfactometry is another possibility for detection that has been used in essential oil analysis. Olfactometry adapters are commercially available and should include humidity of the GC effluent at the nose adapter and provide auxiliary gas flow. The correlation among eluted peaks with specific odors allows accurate retention indices or retention times to be... 

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/. 

Detection of highly volatile key odorants by gas chromatography-olfactometry of headspace samples (GCOH)... 

Gas chromatography-olfactometry (GCO) has been used extensively for the identification of characteristic aroma conq)onents of foods (9,10). Aroma extract dilution analysis (AEDA) is a GCO technique in which serial dilutions (e.g. 1 3) of an aroma extract are evaluated by GCO. In AEDA, the highest dilution at which an odorant is last detected during GCO, so-called flavor dilution (FD) factor, is used as a measure of its odor potency (P). One potential drawback to AEDA is that the technique is limited to the analysis of components of intermediate and low volatility. To overcome this limitation, AEDA results have been con5>lemented by results of GCO of decreasing dynamic headspace (DHS) and decreasing static headspace (GCO-H) san5)les (70,77)... 

It is well known that the aroma extract dilution analysis (AEDA) is a nsefnl method for the recognition of the odor quality and odor intensity of each component." Especially the AEDA is a useful method for the identification of trace amonnts of the component that significantly affects the flavor of tea drinks. The odor intensity of the flavor component is expressed by the flavor dilution (ED) factor, that is, the ratio of the concentration of the flavor component in the initial extract to its concentration in the most dilnte extract in which odor was detected by gas chromatography-olfactometry (GC-0). Therefore, hereafter, from the viewpoint of sensory evalnation, the change in the flavor of tea drink dnring heat processing by AEDA will be mainly discnssed. Furthermore, in order to inhibit flavor deterioration of tea drink, the stndy of flavor precnrsor in a variety of foods, including tea drinks, will be proposed. 

Fors S.M. and Olofsson B.K. (1985) Alkylpyrazines, volatiles formed in the Maillard reaction. I. Determination of odor detection thresholds and other intensity functions by dynamic olfactometry. Chemical Senses 10 (3), 287-96. (Chem. Abstr. 103, 212204q)... 

Olfactometry is surprisingly elFective with some solutes that exhibit intense odor. 0.2 ppm can be detected. To carry out the sniffings a panel of judges is trained prior to the first run a scale of odor intensity evaluation is estabhshed. 

Saffron, production, 66 Saffron flavor characterization using aroma extract dilution analysis aroma-active components, 74-78 detection of aroma-active component using OC-olfactometry, 67 experimental procedure, 67-68 volatile components, 68-74 Safranal, role in flavor, 66-78 Scmivolatile components in powdered turmeric, characterization using direct thermal extraction GC-MS, 80-96 Shallot, contribution of nonvolatile sulfur-containing flavor precursors to flavor, 53-63... 

Stabell, 0. B., 1982, Detection of natural odorants by Atlantic salmon parr using positive rheotaxis olfactometry, n "Salmon and Trout Migratory Behavior Symposium," E. L. Brannon, and E. 0. Salo, eds.. School of Fisheries, University of Washington, Seattle. 

In this study, the aroma compounds detected by Gas Chromatography Olfactometry (GC-O) and with OAV>l in at least one of the wine samples were considered. The use of OSs allows one to not only identify those series that contribute to the aroma profile of a wine, but also to rank them in terms of their odorant capacity and obtain its aromatic fingerprint. 

The combination of GC with olfactometry is another possibility for detection that has been used in essential oils analysis. " " " Olfactometry adapters are commercially available and should include humidity of the GC effluent at the nose adapter and provide auxiliary gas flow. The correlation among eluted peaks with specific odors allows accurate retention indices or retention times to be estabhshed for the essential oil components. Some of them can be detected in this way after applying chemometric techniques, such as cluster analysis and principal component analysis, to the data from the sensors. A limitation of GC with olfactometry is that peak coelution in complex samples makes identification of the compound(s) responsible for an odor difficult, particularly where trace odorants coelute with larger odor-inactive peaks. One possible solution for identifying character-impact odorants where coelution occurs is to use comprehensive two-dimensional GC (GC X GC). " ... 

Dilution facta-=dilution necessary to stiU detect compounds by GC olfactometry (using a sniffing port). 

This second edition offers new material on methods of sensory detection (nasal through the nose) or (retronasal through the mouth and back of the oral cavity), different flavor release phenomena in the headspace versus the mouth, and matrix in flavor release from oils compared to emulsion systems. Advanced gas chromatographic methods are included, such as solid phase microextraction for the volatile analyses in foods and vegetable oils, gas chromatography-olfactometry, and aroma extraction dilution analyses. 

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