2009_Book_FoodChemistry

5.2 Aroma Analysis 357
Fig. 5.14. Odorants labelled with deuterium () or carbon-13 () as internal standard substances for isotopic
dilution analyses of the corresponding unlabelled odorants.
1 2-[α- 2 H 2 ]furfurylthiol, 2 2-[ 2 H 3 ]methyl-3-furanthiol, 3 3-mercapto-2-[4,5- 2 H 2 ]pentanone, 4 [4- 2 H 3 ]methional,
5 2-[ 2 H 3 ]ethyl-3,5-dimethylpyrazine, 6 (Z)-1,5-[5,6- 2 H 2 ]octadien-3-one, 7 trans-4,5-epoxy-(E)-2-[6,7 2 H 4 ]
decenal, 8 1-(2,6,6-[6,6- 2 H 6 ]trimethyl-1,3-cyclohexadienyl)-2-buten-1-one (β-damascenone), 9 3a,4,5,7atetrahydro-3,6-[3-
2 H 3 ]dimethyl-2(3H)-benzofuranone (wine lactone), 10 tetrahydro-4-methyl-2-(2-methylpropenyl)-
2H-[3,4- 2 H 3 ]pyran (sotolon), 11 4-hydroxy-2,5-[ 13 C 2 ]dimethyl-3(2H)-furanone, 12 3-hydroxy-4,5-[4- 13 C]dimethyl-2(5H)-[5-
13 C]furanone (rose oxide)
that the odorants showing higher AVs contribute
strongly to the aroma of the food. For this purpose,
the odor thresholds of the compounds dissolved
in water, in oil or applied to starch are
used, depending on which of these materials dominates
in the food.
An example are the AVs of the odorants of French
fries based on their odor thresholds in an oil
(Table 5.14). Methanethiol, methional, methylpropanal
and 2-methylbutanal exhibit the highest
aroma values. Consequently, they should belong
to the most important odorants of French fries.
5.2.7 Aroma Model, Omission Experiments
Finally, the identified odorants must actually produce
the aroma in question. To test this, the determined
concentrations of the odorants are dissolved
in a suitable medium, which is not difficult
in the case of liquid foods. The solvent for the recombination
mixture called the aroma model can
be adapted to the food. An ethanol/water mixture,
for example, is suitable for wine. In the case of
solid foods, however, compromises have to be accepted.
The aroma profile of the model is then compared
to that of the food. In the example of French fries
discussed in detail here, a very good approximation
of the original aroma was achieved.
The selection of odorants by dilution analyses
(cf. 5.2.2) does not take into account additive
(cf. 20.1.7.8) or antagonistic effects (example
in Fig. 5.2) because the aroma substances, after
separation by gas chromatography, are sniffed
individually. Therefore, in view of the last mentioned
effect, the question arises whether all the
compounds occurring in the aroma model really
contribute to the aroma in question. To answer