Odor dilution techniques

In the meantime, several food flavors have been evaluated by odor dilution techniques. The foods analyzed and the corresponding references are listed in Table 1. 

Hinterholzer, A., Schieberle, P. (1998) Identification of the most odor-active volatiles in fresh, hand-extracted juice of Valencia late oranges by odor dilution techniques. Flavour Fragrance J. 1.3. 49-55... 

Lindsay RF, Priest FG (1975) Decarboxylation of substituted cinnamic acids by enterobacteria the influence on beer flavour. J Appl Bacteriol 39 181-187 Steinhaus M, Schieberle P (2000) Comparison of the most odor-active compounds in Ifesh and dried hop cones (Humulus lupulus L. variety spalter select) based on GC-olfactometry and odor dilution techniques. J Agric Food Chem 48 1776-1783... 

Spalter Select) based on GC-olfactometry and odor dilution techniques. Journal of Agricultural and Food Chemistry, 48, 1176-1183 (2000). 

T. Hofmann and P. Schieberle, Evaluation of the key odorants in a thermally treated solution of ribose and cysteine by aroma extract dilution techniques, J. Agric. Food Chem., 1995, 43, 2187-2194. 

Guth, H., Grosch, W. (1999) Evaluation of important odorants by dilution techniques, in Teranishi, R., Wick, E.L., Hornstein, 1. (eds.) Elavor Chemistry. Thirty Years of Progress. Kluwer Academic Plenum Pubhshers, New York, pp. 377-386... 

Kumazawa, K. and Masuda, H. 2002. Identification of potent odorants in different green tea varieties using flavor dilution technique. J. Agric. Food Chem. 50 5660-63. 

H Guth, W Grosch. Evaluation of important odorants in foods by dilution techniques. In R Teranishi, EL Wick, I Hornstein, eds. Flavor Chemistry 30 Years of Progress. New York, NY Kluver Academic/Plenum Publishers, 1999, pp 377-386. 

Dilution to odor threshold techniques, such as aroma extract dilution analysis (AEDA) [11], has previously been applied to characterize the most odor-active aroma compounds in fresh beer [12], However, such methods have not yet been used to study odorants formed during light exposure of beers. The aim of the present investigation was, therefore, to study the differences in aroma compounds of fresh beer and beer exposed to daylight. Speeial emphasis was given to the evaluation of the role of 3-methyl-2-butene-thiol in the generation of sunstruck flavor. 

The aim of GC-0 techniques in food aroma research is to determine the relative odor potency of compounds present in the aroma extract. This method gives the order of priority for identification and thus indicates the chemical origin of olfactory differences (7). The value of the results obtained by GC-O depends directly on the effort invested in sample preparation and analytical conditions. Analysis of an aroma extract by dilution techniques (AEDA, Charm) combined with static headspace GC-O provides a complete characterization of the qualitative aroma composition of a food. However, this is only the first step in understanding the complex aroma of a food. 

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... 

Elemental composition Cd 77.81%, S 22.91%. In crystalline state, it may be identified by x-ray diffraction measurement. In aqueous acid extract following digestion with nitric acid, cadmium may be measured by various instrumental techniques, (see Cadmium). Warming with dilute mineral acids liberates H2S, which may be identified by its odor or by browning of a white paper soaked in lead acetate solution. 

The composition of the volatile fraction of bread depends on the bread ingredients, the conditions of dough fermentation and the baking process. This fraction contributes significantly to the desirable flavors of the crust and the crumb. For this reason, the volatile fraction of different bread types has been studied by several authors. Within the more than 280 compounds that have been identified in the volatile fraction of wheat bread, only a relative small number are responsible for the different notes in the aroma profiles of the crust and the crumb. These compounds can be considered as character impact compounds. Approaches to find out the relevant aroma compounds in bread flavors using model systems and the odor unit concept are emphasized in this review. A new technique denominated "aroma extract dilution analysis" was developed based on the odor unit concept and GC-effluent sniffing. It allows the assessment of the relative importance of the aroma compounds of an extract. The application of this technique to extracts of the crust of both wheat and rye breads and to the crumb of wheat bread is discussed. 

The important odor compounds can be evaluated by the GC-effluent sniffing of a series of dilutions from the original aroma extract. Two variations of this technique were developed by Acree et al. (28, 29) and by us (30-37). 

The use of an isotope dilution assay is the best method to quantify labile and low level odorants. He applied this technique to the determination of 2-acetyl-l-pyrroline and 2-methyl-3-ethylpyrazine, the two compounds which showed the highest FD-factors among the compounds with roasty odor notes in extracts from wheat or rye bread crust, respectively ( 7, 38). The results are summarized in Table III. The high level of the acetylpyrroline in the crusts of the wheat breads was striking compared to the level in the rye breads. These quantitative data confirm that 2-acetyl-l-pyrroline is a character impact odor compound of the wheat bread crust. 

Many aroma compounds have been identified in crackers but which ones are the most important has still not been established. Further studies of these extracts should involve the use of odor assays to sort out to aroma important compounds in crackers from the unimportant aroma compounds present. For example, the method used by Shieberle Grosch (33) to describe the odor-active components in bread in terms of their flavor dilution values and the technique called charm analysis (43, 44) both concentrate chemical investigations at retention indices with odor activity. 

Jagella, T. and Crosch, W. (1999a) Flavour and off flavour compounds of black and white pepper (Piper nigrum L.). I. Evaluation of potent odorants of black pepper by dilution and concentration techniques. European Food Research and Technology 209(1), 16-21. 

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). 

These techniques provide a ranking of aroma compounds relating to the ratio concentration in the extract/odor threshold in air. Working properly (using a panel of judges and 1/10 dilutions) it is possible to obtain, with reasonable effort, confidence intervals for the results, which are most useful for comparative purposes, and to relate them to the concentration of the odorant in the extract. 

Gas chromatography-olfactometery (GC-O) provides a sensory profile of odor active compounds present in an aroma extract by sniffing the GC effluent. Several techniques have been developed to collect and process GC-O data and to estimate the sensory contribution of individual odor active compounds, including dilution analysis (29, 30), time intensity (31), and detection frequency (32) methods. GC-O has successfully been used to evaluate the odor active compounds of olive oil (33), soybean oil (34), and fish oil enriched mayonnaise (35). 

The nose is an extremely sensitive detector of odors it can be matched only by the most sensitive instrumental techniques. Many smells are identified by comparison with pure compounds diluted by odor-free air until they are near the odor threshold limit. However, with the introduction of flame photometric detectors it has been possible to measure the concentration of the sulfur compounds giving rise to odors in the ppb range with the aid of preconcentration (by a fector of 10 to 10. ... 

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