Aroma compounds odor activity value

Reliable quantitative data are a prerequisite for evaluating the contribution of a single odorant to a positive aroma or off-flavor. They are needed to calculate odor activity values (OAV) that are defined as the ratio of the concentration to the sensory threshold of a given compound in a matrix (Rothe and Thomas, 1963 Acree et al., 1984). These values give guidance in the evaluation of the impact of an odorant to the overall aroma profile. 

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 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. 

Escudero, A., Gogorza, B., Melus, M.A., Ortin, N., Cacho, 1., and Ferreira, V. (2004). Characterization of the aroma of a wine from Maccabeo. Key role played by compounds with low odor activity values. J. Agric. Food Chem., 52, 3516-3524. 

To evaluate the contribution of a chemical compwimd to the aroma of a wine the odor activity value (OAV) was determined. OAV is a measure of importance of a specific compound to the odor of a sample. It was calculated as the ratio between the concentration of an individual compound and the perception threshold found in literatures (Francis Newton, 2005 Vilanova, et al., 2008). 

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. 

Some authors (Peinado et al. 2004a, 2004b Zea et al. 2007) have grouped aroma compounds in aromatic series based on their aroma descriptors. The overall value for each series is obtained by combining the odour activity value (OAV, which is defined as the ratio of the concentration of a compound to its perception thresholds) of the individual aroma compounds in the series. The combination of individual OAVs in order to calculate the overall value for a series cannot be interpreted as an arithmetic addition of odorant sensations. Some aspects of this classifying scheme can be subject to criticism, but in any case, the scheme is effective for comparing wines obtained with different aging methods inasmuch as the odour series always comprise the same compounds. 

To verify whether the volatiles listed in Table 6.32 are actually the key odorants, an aroma model was prepared by using an unripened cheese (UC) as base ]53J. The odorants and in addition the compoimds showing high taste activity values ]54] were quantified in UC and in Swiss cheese ]53]. The differences in the concentration of these compounds in both samples were calculated, and, accordingly, the compounds were dissolved in water and/or sunflower oil and then added to freeze-dried UC. The flavour model obtained agreed in colour, pH, water, protein and fat content with grated Swiss cheese, only the texture was more grainy ]53]. 

Another powerful technique known as aroma extract dilution analysis is used to determine the most significant odor and flavor compounds in a complex mixture in a food product. This method determines the odor activity of volatile compounds in an extract eluted from a high-resolution capillary GC-SP column (see Table 11.9). The odor activity or impact of a compound is expressed as the flavor dilution factor (FD), which is the ratio of its concentration in the initial extract to its concentration in the most dilute extract in which the odor can be detected by GC-SP. However, the information from this technique may be of limited practical value, because it ignores the significant effect of food matrices on flavor and odor perception of mixtures of flavor and odor compounds. Advanced instrumental techniques have been developed for flavor analysis during food consumption. These techniques permitting direct mass spectrometry at atmospheric pressure are discussed in Chapter 6. 

Kubickova, J., Grosch, W. Quantification of potent odorants in Camembert cheese and calculation of their odour activity values. Int. Dtiiry J. 8, 17 (1998) Moran, N., Schieberle, R On the role of aroma compounds for the cretuniness of dtiiry products. Deutsche Forschungsanstalt fur Lebensmittelche-mie. Report 2006, p. 186... 

Aroma activities of volatile compounds obtained by GCO dilution analyses were represented as Charm values, and the relative intensities of component odorants were represented in terms of the odor spectrum value (OSV) [14]. Each Charm value was rounded off to two significant figures in order to reflect the actual resolution of the dilution analysis. Acidic, buttery-oily, green-black currant, green-earthy, nutty-roast, phenolic, smoke-roast, soy sauce, sweet-caramel, and sweet-fruity were the aroma descriptions used in all GCO experiments to describe potent odorants. These descriptions were chosen from the results of a single preliminary free choice GCO analysis using a lexicon of words commonly used for coffee evaluation. 

Two techniques based on dilution have been developed CharmAnalysis by Acree and coworkers (6,12,13) and aroma extract dilution analysis (AEDA) by Grosch and his group (7,14,15). Both evaluate the odor activity of individual compounds by sniffing the GC effluent of a series of dilutions of the original aroma extract. Both methods are based on the odor-detection threshold. The dilution value obtained for each compound is proportional to its OAV in air, i.e., its concentration. Several injections are required to reach a dilution of the aroma extract in which odorous regions are no longer detected. 

According to their relative threshold values, volatile compounds are also referred to as aroma active . The aroma value (also referred to as odor unit ) of a compound x is defined as ... 

This characteristic feature appears to be required for a roasted odor. In fact, aU the pyrroUnes and pyridines listed in Table 5.23 as weU as 2-acetyl-thiazole, 2-acetylthiazoline (cf. Table 5.22) and acetylpyrazine (cf. Table 5.23) contain this structural element and have a roasted or cracker-hke odor. However, the thresholds of these compounds vary greatly. The lowest values were found for 2-acetyl-and 2-propionyl-l-pyrrohne. The length of the alkanoyl group also influences the aroma activity because in the transition from 2-propionyl- to 2-hutanoyl-l-pynoline, the roasted note suddenly disappears and the odor threshold increases hy several powers of ten. 2-Acetyl-l-pyrrohne (Apy) is responsible for the typical aroma of the cmst of white bread and it... 

In general, the aroma of a food consists of many volatile compounds, only a few of which are sensorially relevant. A first essential step in aroma analysis is the distinction of the more potent odorants from volatiles having low or no aroma activity. In 1963, Rothe and Thomas calculated the ratio of the concentration of an odorant to its odor threshold and denoted it aroma value (3). This approach was the first attempt to estimate the sensory contribution of single odorants to the overall aroma of a food. Since that time, similar methods have been developed odor unit (4) based on nasal odor thresholds, flavor unit (5) using... 

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