Aroma threshold, determination

The attributes that distinguished several of the skin extract samples, ie dried fig, tobacco and chocolate, appear to be related to numerous compounds, of which B14 (syringic acid), B9 (ethyl syringate), B20 (a methoxy phenol), A4 (heptanoic acid), A5 (hexadecanoic acid). Ml, M6, 01, 04 and 05 were most highly correlated. There were few compounds closely linked to the aroma attributes floral or apple, which is rational as these attributes were important to the base wine used in this study. While it is not possible to determine from this procedure if any of the compounds listed may be actually responsible for particular aroma attributes, the data point to particular compounds which would be worthwhile investigating further by more detailed sensory studies, eg aroma threshold determinations in red wine, and GC-sniff studies. 

Aroma of muskmelon, sulfur volatile sensory evaluation by GC-olfactometry, 36-47 Aroma threshold, determination, 81 Aroma volatiles in meat, sulfur-containing, See Sulfur-containing aroma volatiles in meat Artifacts, sulfur compounds in foods, 3 Atomic emission detector comparison to flame photometric and sulfur chemiluminescence detectors, 17,21... 

Ethyl 2-methylbutanoate, 2-methylbutyl acetate and hexyl acetate contribute most to the characteristic aroma of Fuji apples [49]. In Red Delicious apples, ethyl butanoate, ethyl 2-methylbutanoate, propyl 2-methylbutanoate and hexyl acetate contribute to the characteristic aroma as determined by Charm-Analysis and/or AEDA [50, 51]. In a comparative study of 40 apple cultivars, the highest odour potency or Charm value was found for -damascenone [52]. This compound usually occurs in a glycosidically bound form and is present primarily in processed products owing to hydrolysis of the glycoside bond after crushing fruit cells [53]. -Damascenone has a very low odour threshold with a sweet, fruity, perfumery odour and is not typical of apple aroma in gen-... 

In tests to better define this mixture of components (and their proper proportions) necessary for good orange flavor, volatile components believed from prior analytical studies to be important to orange flavor were examined (5). Individual taste and aroma thresholds in water were determined on the compounds selected. Then, the influence of nonvolatile juice constituents on the taste threshold of certain of the volatile components was studied. Finally, selected individual compounds and mixtures containing from two to six components were evaluated in a bland juice medium for their contribution to orange flavor. 

Table 12 Odor Thresholds Determined by GC-O of Some Aroma Impact Components Found in Thermally Processed Foods ...

Aroma compounds in distilled spirits and liqueurs, their levels, odour attributes, and thresholds are most important for quality and authenticity. Using gas chromatography and mass spectrometry, especially the composition of volatile aroma compounds in distilled spirits has been widely investigated [4-8]. By direct injection of an alcoholic distillate it is possible to determine more than 50 components within levels between 0.1 and 1,000 mg L b special methods of extraction can be used to increase this number up to more than 1,000 volatile substances [6]. However, sensory analysis is still indispensable to describe and evaluate spirit drinks. 

In the majority of the studies on the composition of food aromas, AEDA is used for the determination of the relative odour potency of the compounds detected by GC-O (reviewed in [1]). The odour potency is proportional to the odour activity value (OAV) of the compound in air. The OAV is defined as the ratio of the concentration of a compound to its odour threshold [3]. 

The influence of the sensitivity of the assessors on AEDA has been studied [11], with the result that the differences in the FD factors determined by a group of six panellists amount to not more than two dilution steps (e.g. 64 and 256), implying that the key odorants in a given extract will undoubtedly be detected. However, to avoid falsification of the result by anosmia, AEDA of a sample should be independently performed by at least two assessors. As detailed in [6], odour threshold values of odorants can be determined by AEDA using a sensory internal standard, e.g. ( )-2-decenal. However, as shown in Table 16.6 these odour threshold values may vary by several orders of magnitude [8] owing to different properties of the stationary phases. Consequently, such effects will also influence the results of dilution experiments. Indeed, different FD factors were determined for 2-methyl-3-furanthiol on the stationary phases SE-54 and FFAP 2 and 2 , respectively. In contrast, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone showed higher FD factors on FFAP than on SE-54 2 and 2, respectively. Consequently, FD factors should be determined on suitable GC capillaries [8]. However, the best method to overcome the limitations of GC-O and the dilution experiment is a sensory study of aroma models (Sect. 16.6.3). 

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],... 

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. 

One way to quantify the odor impact of a compound is to determine the aroma value or odor activity value (OAV). This is calculated by dividing the concentration of the compound by its perception threshold. Therefore, the odor impact of a compound increases in proportion to its OAV when this value is >1. Thus, compounds exhibiting higher OAV values are more likely to contribute to the aroma of wine and have an important influence on its sensory characteristics. 

The great development of analytical techniques and instruments has allowed the advance from the first studies focused on the analysis of major volatile compounds to the analysis of compounds present in very low concentrations (even at levels below ng L-1) and with low odor thresholds. Due to the great complexity of the wine matrix, for the analysis of some minor, but key aroma compounds, different sample work-up procedures reported to determine volatile and semivolatile constituents,... 

The intensity of aroma compounds found by AEDA and CHARM may be determined with further accuracy by subjecting them to odor unit (also called odor activity value) measurement.71,72 This is done by first measuring the odor threshold of a compound while the concentration of this compound in the specimen is determined using internal standards (for instance, isotopic samples in contemporary approach). Dividing the latter concentration with the odor threshold will give the odor unit value, naturally being higher when a compound better contributes to the total aroma. 

Not all of the volatile components present in oak wood play a decisive role in determining the aroma of aged wines. While concentrations in the oak wood will be a conditioning factor, final aroma is the result of each component s olfactory detection threshold and the synergistic effects between it and the other wine components. 

Based on determination of threshold concentration Aroma Extract Dilution Analysis (AEDA) (Schieberle and Grosch 1987 Ullrich and Grosch 1987), and Charm analysis (Acree et al. 1984)... 

Studies to develop and apply quantitative methods to the analysis of fresh tomato volatiles have been recently carried out by some of the authors (J.,2). Besides the known major compounds a number of compounds were detected In the gas liquid chromatography (GLC) analysis which had spectral data unlike that of any of the 400 compounds previously reported as tomato volatiles (cf. 3 ). As these compounds occurred In reasonable amounts In fresh tomato It seemed necessary to determine their Identities In order to give a satisfactory quantitative picture of fresh tomato volatiles. It also seemed desirable to determine the odor threshold of these compounds to have a better understanding of their probable contribution to tomato aroma. 

Epoxy-P-ionone had been reported previously by Viani et al.,(13), Schreler et al., (J 4) and V/obben et al., ( ). In the present study besides the mass spectrum an infrared absorption spectrum was also obtained and was found to be identical to that of an authentic sample. An odor threshold was determined in water solution to be 100 ppb. It is, therefore, a relatively weak odorant and as its concentration, in all fresh tomato samples examined, is well below this figure it seems unlikely that it can contribute to fresh tomato aroma. 

Vanillin (used to flavor vanilla ice cream and other foods) is the substance whose aroma the human nose detects in the smallest amount. The threshold limit is 2.0 X 10 " g per liter of air. If the current price of 50 g of vanillin is 112, determine the cost to supply enough vanillin so that the aroma could be detected in a large aircraft hangar with a volume of 5.0 X 10 ft. ... 

Currently, there is much interest in flavor research in determining what compounds are actually responsible for the characteristic flavor of a food. Researchers have utilized odor unit values (compound concentration/odor threshold) to determine the contribution of individual constituents to the overall flavor of a food. For example, citrus peel oil aroma quality has been characterized using logarithmic odor unit values... 

Tamura et al. (this volume) discuss the suitability of the detection threshold and the recognition threshold in determining the limited odor unit for characterizing citrus aroma quality. 

The odor threshold (Tc) was classified by the nomenclatures listed in Table II. The odor-detection threshold (Ted) of each component was determined by the same method previously described (15). First, volatile compounds were dissolved in a small amount of methanol. The solution was diluted by deionized water until the solution was judged as odorless. Because the detection threshold of methanol is very high (more than 100 ppm), it does not interfere with determinations of the thresholds of the aroma components in Citrus sinensis OSBECK, cv Shiroyanagi. Each aqueous solution of volatiles was diluted by a factor of ten. Weber-Fechner s law predicts that the human nose can clearly distinguish only ten fold differences of concentration. We made three series (A, B, C) of diluted solutions to test detection thresholds (A 90 ppm, 9 ppm, 0.9 ppm, and 0.09 ppm. B 60 ppm, 6 ppm, 0.6 ppm and 0.06 ppm, C 30 ppm, 3 ppm, 0.3 ppm and 0.03 ppm). Independently, panel members were... 

To determine the Lo values, the Cr values and Tc values were determined by the method described above. The Cr values are the concentration of the individual components not at the detection threshold of the volatile oils (Tod), but at the recognition threshold (Tor) because at the Tod level of the oil, only a few compounds can be sensorially detected and these contribute to the aroma only as the base notes. 

These authors mention a mushroom aroma and give an odor threshold range of 2.3-5.3ppb determined by high-resolution GC olfactometry. The (S)-isomer is described with a green, vegetable mouldy flavor (Chemisis, 1999) and the (7 )-isomer with a green, mushroom meaty flavor (Chemisis, 1992). 

The flavor of the tautomer mixture is perceived as burnt sugar, maple, cereal, chicory (Chemisis, 1978). The odor threshold reported by Semmelroch et al. (1995) was 1.15 ppm in water with a caramel-like quality. The odor threshold in air given by Blank et al. (1992b) was 0.5-1.5 p,g/m3. A flavor threshold of 21 ppb was reported by Huber (1992). By their enantioselective separation (see in 1.100), Bruche et al. (1995) determined that only one isomer of the less abundant tautomer 1.101b had a very intensive roasted almonds odor, the other isomer being less intensive of the two other tautomers, one is odorless, and the other reminiscent of the odorant 1.101b, is nearly odorless. Therefore ca 85 % of the mixture have no influence on the aroma. 

The latter authors described the flavor in water as roasted, nutty, green. At a concentration of 4 ppm it has a cereal, toasted, musty, mushroom, shellfish, etc., flavor (Chemisis, 2000). Buttery et al. (1976b), who synthesized other 4,5-dialkylthiazoles with potent bell pepper-like aromas, determined an odor threshold of 0.47 ppm in water. 

---