Odor threshold value

L. J. van Gemert and A. H. Nettenbreiger, Compilation of Odor Threshold Values in Air and Water, National Institute for Water Supply, Voolburg, the... 

Clear, colorless, watery, combustible liquid with a strong, pleasant odor. An odor threshold value of 47 mg/m was reported (quoted, Verschueren, 1983). 

Of the few known terpene compounds that contain heteroatoms such as nitrogen or sulfur, the thiol 8-mercapto-p-menthan-3-one described below has qualitatively important applications as a fragrance and flavor substance. The second thiol, -p-menthene-8-thiol, is described because its odor threshold value is far lower than that of most other fragrance and flavor materials. 

Many nitrogen- and sulfur-containing heterocycles have been identified in the aroma fractions of foods [214]. In roasted products (e.g., coffee) and heat-treated foods (e.g., baked bread or fried meat), these heterocycles are formed from reducing sugars and simple or sulfur-containing amino acids by means of Maillard reactions [215, 216]. Their odor threshold values are often extremely low and even minute amounts may significantly contribute to the aroma quality of many products [217, 218]. Therefore, N- and N,S-heterocyclic fragrance and flavor substances are produced in far smaller quantities than most of the products previously described. 

In addition to 75% monoterpene hydrocarbons (Oa-pinene 5-21% /7-pinene 40-70% 3-carene 2-16%) and ca. 10% sesquiterpene hydrocarbons, galbanum oil contains a fairly large number of terpene and sesquiterpene alcohols and their acetates. Minor components, with entirely different structures and low odor threshold values, contribute strongly to the characteristic odor [284a, 515-519]. Examples are as follows ... 

In your laboratory refrigerator (5°C) you store pure cyclohexane that you use for extracting organic trace contaminants from water samples for subsequent analysis by gas chromatography. Among the compounds of interest is tetrachloroethene (also called perchloroethene or PCE). One day you realize that somebody is using tetrachloroethene in the laboratory. In fact, you can even smell the compound in the air (odor threshold values 0.03 - 0.1 mg-L-1). You are worried that your cyclohexane is contaminated, particularly, because you have realized that the bottle was not well sealed in the refrigerator. Calculate the concentration of PCE in the air that, at 5°C, would be sufficient to produce an equilibrium PCE concentration in the cyclohexane of 1 jig-fiL l, which you would consider to be a problem for your analysis. 

Some reported odor threshold values for nootkatone were considerably lower than the taste threshold values. Odor thresholds of 0.8 ppm in water and 30 ppm in air were reported for (+)-nootkatone, the enantiomer of this sesquiterpene ketone present in grapefruit (35). An odor threshold of 0.15 ppm in water was reported for crystalline nootkatone isolated from grapefruit oil (36). In that study, mother liquor from crystallization of nootkatone was 30 times more potent (odor threshold of mother liquor 5 ppb) than nootkatone alone and the panel felt that the aroma of the mother liquor more closely resembled grapefruit aroma... 

The threshold values given by different investigators vary considerably depending on the choice of solvent(s), the method used for the determination, and the purity of the compound. Therefore, the same aroma or flavor compound may have as many threshold values as there are investigators. Care must be exercised when threshold values from the literature are used, and the mentioned sources of discrepancies must always be borne in mind. Odor threshold values, expressed as concentration in the gaseous phase, have the distinct advantage of being independent of the solvent used. 

These values are usually evaluated through the sense of smell they are marked with O = Odor threshold value. Some values are evaluated through the sense of taste ... 

In summary, model studies are very efficient for the identification and structure elucidation of important flavor components. Most of the compounds reported here have not been identified in meat and have not yet been reported as constituents of food volatiles. Nevertheless, there are good reasons to believe that minute traces of these sulfur-containing components are present in roasted and/or cooked meat volatiles because our model system was based solely on naturally occurring precursors. We believe that only minute trace amounts of these types of components need to be present in natural products to be of prime significance due to their extremely low odor threshold values. 

So-called odor threshold values are not included in Table A-13 since these often show great discrepancy in the literature. They depend strongly on the experimental technique and individual sensitivity. Nevertheless, an unpleasant smell together with any irritation should be taken as a warning signal. 

To establish exactly the flavor differences between Scheurebe and Gewurztraminer wines, it is therefore necessary to quantify the levels of recognized odorants and to calculate the odor activity values (OAV s). According to Rothe and Thomas (75) the OAV is defined as ratio of concentration to odor threshold value of the compound. 

To estimate the sensory contribution of the 42 odorants to the overall flavor of the wine samples, their OAV s were calculated (Table II). To take into account the influence of ethanol, the odor threshold values of wine odorants were determined in a mixture of water/ethanol (9+1, w/w) and were used to calculate the OAV s for each compound. According to the results in Table A, 4-mercapto-4-methylpentan-2-one, ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate, ethyl isobutyrate, (E)-fi-damascenone, linalool, cis rose oxide and wine lactone showed the highest OAV s in the Scheurebe wine. With exception of 4-mercapto-4-methylpentan-2-one the above mentioned odorants also showed the highest OAV s in Gewurztraminer wine. Differences in the OAV s of ethyl octanoate, ethyl hexanoate, 3-methylbutyl acetate and ethyl isobutyrate between the two varieties are probably caused by differences in the maturity of the fruit at harvest and/or by the fermentation process. 

The era of publishing a large number of compounds identified as to chemical structures is slowly changing to an era in which constituents are identified as to which are the Important contributors to the characteristic odors. More and more sensory analyses are stating odor threshold values as well as odor quality. 

Odor data or odor threshold values are used to help determine the warning properties of the chemical (e.g., if it can be smelled at concentrations below health guidelines or standards). 

Due to oxidative degradation of carotenoids, aroma compounds are also formed, including P-ionone with an odor threshold value of 14 ng/g in water. The formation... 

Esters identified as ham odorants possess fruity odors and low odor thresholds values (0.06-0.24 ng/L) (Table 1) and are branched esters. Quality factors that modify their relative contribution to flavor are the rearing system of pigs (8) and ripening conditions (7). 

This study focuses on the determination of the characteristic odorants of wasabi in comparison with those of horseradish by calculation of the logarithmic ratio between the concentration of isothiocyanate and its odor threshold value. The relationship between the yields of the isothiocyanates formed by the action of wasabi myrosinase and the conditions of hydrolysis are presented. 

The odor threshold values in a water solution of the odorants were estimated by the 2/5 test 19). The ten panelists picked both of the flasks containing the odorous solution. Each dilution step was iVlO the concentration of the previous one. 

The remarkable difference between wasabi and horseradish was the concentrations of the oj-alkenyl isothiocyanates (5-8) (Table I), the aryl isothiocyanates (10) and (11) (Table I), and the oj-methylthioalkyl isothiocyanates (12-14) (Table I). The odor threshold values of the o-alkenyl isothiocyanates (5-7) were lower than the other isothiocyanates. In addition, these oj-alkenyl isothiocyanates had about half the value of that of allyl isothiocyanate (2) (Table I). The alkyl isothiocyanates (1, 3 and 4) (Table I) possessed a chemical odor but no pungent note. Hence, it seems that those compounds make relatively small contributions to the characteristic odor of wasabi and horseradish. The other isothiocyanates except for( 1, 3 and 4), however, had pungent and/or radish-like odors. 

The concentration divided by the odor threshold value, C/T is called the aroma value (22). Odorants with high aroma values are important contributors to the characteristic flavors. In general, the estimated feel of the stimulus is logarithmically proportional to the objectively measured strength of the stimulus... 

Table I. Concentrations, Odor Threshold Values Isothiocy antes.

Odor threshold value, ppm Wasabi collected in January Horseradish collected in January Less than 0.5 mg/kg... 

Figure 1. Logarithms of the ratios of the concentrations to the odor threshold values (log(C/T)) (top) and exponents (n) of the FD factor 2", (bottom) for the isothiocyanates versus their retention indices (RI).

Characterization of Citrus Aroma Quality by Odor Threshold Values... 

Reagents. Guaranteed chemicals were purchased from Wako-pure chemicals in Japan and Aldrich Chemical Co. in the U.S. The purity of all chemicals was checked by GC before measuring odor threshold values. Purity of all chemicals used in this experiment was more than 99.2%. 

Table III. Odor Threshold Value of Volatiles in Navel Orange ...

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