Aroma value, calculation

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. 

A more general approach to estimate the importance of a flavor compound in a particular food is the calculation of the ratio of its concentration to its flavor (odor and taste) threshold (9) or to its odor threshold (1 , 11) The result is denoted "aroma value" 19), "odor unit" (10) or "odor value" (11) the higher the value or unit, the more intensely this component contributes to the flavor or odor of the food. 

Rothe (5, , 1 5) calculated the aroma values of some volatiles identified in the crumb of wheat bread and the crust of rye bread. The data listed in Table I indicate that ethanol, isobutanal, iso-pentanal, diacetyl and isopentanol contribute with high aroma values to the aroma of the wheat bread crumb. During baking of rye bread, the two Strecker aldehydes, isobutanal and isopentanal, increased so much in the crust that they showed the highest aroma values of the volatiles investigated. 

The volatiles of fresh pineapple (Ananas comosus [L] Merr.) crown, pulp and intact fmit were studied by capillary gas chromatography and capillary gas chromatography-mass spectrometry. The fnjit was sampled using dynamic headspace sampling and vacuum steam distillation-extraction. Analyses showed that the crown contains Cg aldehydes and alcohols while the pulp and intact fruit are characterized by a diverse assortment of esters, h rocarbons, alcohols and carbonyl compounds. Odor unit values, calculated from odor threshold and concentration data, indicate that the following compounds are important contributors to fresh pineapple aroma 2,5-dimethyl-4-hydroxy-3(2H)-furanone, methyl 2-methybutanoate, ethyl 2-methylbutanoate, ethyl acetate, ethyl hexanoate, ethyl butanoate, ethyl 2-methylpropanoate, methyl hexanoate and methyl butanoate. 

Among all the volatile compounds, only a limited number are important for aroma. According to a proposal by Rothe and Thomas [2] only those compounds actually contribute to aroma whose concentration in food exceeds their odour thresholds. To estimate the importance of a volatile compound for the aroma of a particular food, the ratio of concentration to its odour threshold was calculated. This value was denoted aroma value [2], odour unit [3] or odour activity value (OAV) [4], In the following the latter term is used. 

As already indicated, compounds with high aroma values may contribute to the aroma of foods. The aroma value A of a compound is calculated according to the definition ... 

Another more elaborate variant of the dilution analysis requires, in addition, that the duration of each odor impression is recorded by a computer and CHARM values are calculated (CHARM acronym for combined hedonic response measurement), which are proportional to aroma values. The result of an AEDA can be represented as a diagram The FD factor is plotted against the retention time in the form of the retention index (RI) and the diagram is called a FD chromatogram. 

To approach the situation in food aroma values (definition cf. 5.1.4) are calculated. It is assumed... 

The aroma values were calculated on the basis of the odor threshold in water. 

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... 

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. 

Grosch, W. 1994. Determination of potent odorants in foods by aroma extract dilution analysis (AEDA) and calculation of odor activity values (OAVs). Flavour Fragrance J. 9 147-158. 

A prerequisite for the calculation of OAVs are exact quantitative data. Aroma compounds, which are relatively stable and are present in food extracts in higher concentrations (>100 pg/kg food) are often quantified by using an internal standard containing a similar pattern of functional groups as the analyte. In a quantitative study on cherry odorants [63] it has been shown, that the results are significantly influenced by the isolation technique used and by the structure of the odorant. However, under appropriate conditions the values differed only between 7 % (benzaldehyde) and 26 % ((E,Z)-2,6-... 

During AEDA, interactions between the odorants are not taken into consideration, since every odorant is evaluated individually. Therefore, it may be possible that odorants are recognized which are possibly masked in the food flavor by more potent odorants. Furthermore, the odor activity values only partially reflect the situation in the food, since OAVs are mostly calculated on the basis of odor thresholds of single odorants in pure solvents. However, in the food system, the threshold values may be influenced by nonvolatile components such as lipids, sugars or proteins. The following examples will indicate that systematic sensory model studies are important further steps in evaluating the contribution of single odorants to the overall food aroma. 

Table 4-3, with partition coefficient estimation results for 13 aroma compounds partitioned between polyethylene (PE) and ethanol, shows an example of the estimation accuracy one can expect comparing UNIFAC to experimental data and the other partition coefficient estimation methods (Baner, 1999). In order to compare the different estimation methods, average absolute ratios of calculated to experimental values were calculated partitioned substances. When the calculated values are greater than experimental values the calculated value is divided by the experimental value. For calculated values less than the experimental values the inverse ratio is taken. Calculating absolute ratios gives a multiplicative factor indicating the relative differences between values of the experimental and estimated data. A ratio of one means the experimental value is equal to the estimated value. 

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. 

Analysis of the vacuum volatile constituents of fresh tomatoes was carried out using capillary GLC-MS and packed column GLC separation with Infrared, NMR and CI-MS analysis. Evidence was obtained for the presence of the unusual components 3-damascenone, 1-nltro-2--phenylethane, 1-nltro-3-methylbutane, 3-cyclocltral and epoxy-3-1onone. A method for the quantitative analysis of the volatile aroma components In fresh tomato has been Improved and applied to fresh tomato samples. The quantitative data obtained have been combined with odor threshold data to calculate odor unit values (ratio of concentration / threshold) for 30 major tomato components. These calculations Indicate that the major contributors to fresh tomato aroma Include (Z)-3-hexenal, 3-lonone, hexanal, 3-damascenone, 1-penten-3-one, 3-methylbutanal, (E)-2-hexenal, 2-lso-butylthlazole, 1-nltrophenylethane and (E)-2-heptenal. 

To approach the situation in food, OAVs are calculated on the basis of odour threshold values which have been estimated in a medium that predominates in the food, e.g. water, oil, starch. As an example the OAVs of the key odorants of baguette crust are listed in Table 6.26. The highest OAVs were found for the roasty smelling 2-acetyl-1-pyrroline (no. 7), followed by furaneol (no. 20), 2,3-butanedione (no. 2), (E)-2-nonenal (no. 13), l-octen-3-one (no. 9) and methional (no. 6). It is assumed that these odorants contribute strongly to the aroma of baguette crust. 

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]. 

We have applied a modified odor unit equation for evaluating aroma quality of the volatiles of Citrus sinensis OSBECK, ev. Shiroyanagi. Although the concept of odor units in flavor research was proposed by Rothe et al. (9) as a objective index of aroma quality, the concentration of individual components in a food (Fc in equation [1]) depends on the extraction efficiency of the essential oils. If the test sample is a solid, we can not calculate the exact concentration. Because the aroma oils, for example, may exist in different cells in the peels of citrus, we cannot take out only specified cells. It does not give a homogeneous concentration. Therefore, the odor units of individual aroma components in a food do not always give a constant value. Equation [1] should be applied to beverages such as apple juice, citrus juice, coffee, milk and so forth. The modified odor unit equation (75) for liquid and solid samples is shown as follows ... 

The transport coefficients of ethyl acetate, an aroma booster found in a large variety of aroma formulations, have been calculated from sorption of ethyl acetate in PLA experiments. The ethyl acetate permeability of PLA is 5.34 x 10 kg.m.m. s Pa at 30°C and 0.3 activity. It is higher than the one of PET but lower than those of PP and LDPE. However, the ethyl acetate solubility coefficient in PLA, equal to 6.17 xlfi kg.m. Pa at 30°C and 0.3 activity, is higher than the other polymers [140]. This result is comparable to the value reported by Colomines et al. for an amorphous PLA with 99% L-lactide content at 25°C and 0.5 activity [125]. Moreover, increasing the crystallinity of PDLLA provokes a decrease of the ethyl acetate solubility coefficient at 0.5 and 0.9 activity [125]. 

Figure 4a provides a plot of the values obtained for the OSs of the commercial wines studied. The figure shows the mean value for each series and those calculated, taking into account the standard deviations. In this mode, any value included between the highest and lowest in each series would be acceptable for a typical Fino wine. As can be seen, the fruity, balsamic, chemical and spicy series were those that contributed most markedly to the aroma profile. 

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). 

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