2009_Book_FoodChemistry

5.3 Individual Aroma Compounds 359
Table 5.14. Volatile compounds with high aroma values in French fries a
Compound
Concentration b Odor threshold c Aroma value d
(µg/kg) (µg/kg)
Methanethiol 1240 0.06 2 ×10 4
Methional 783 0.2 3.9 ×10 3
Methylpropanal 5912 3.4 1.7 ×10 3
2-Methylbutanal 10599 10 1.1 ×10 3
trans-4,5-Epoxy-(E)-2-decenal 771 1.3 592
3-Methylbutanal 2716 5.4 503
(E,Z)-2,4-Decadienal 1533 4 383
4-Hydroxy-2,5-dimethyl-3 2778 25 111
(2H)-furanone
2,3-Diethyl-5-methylpyrazine 41 0.5 83
(E,E)-2,4-Decadienal 6340 180 35
2,3-Butanedione 306 10 31
2-Ethyl-3,5-dimethylpyrazine 42 2.2 19
2-Ethenyl-3-ethyl-5-methylpyrazine 5.4 0.5 11
3-Isobutyl-2-methoxypyrazine 8.6 0.8 11
2-Ethyl-3,6-dimethylpyrazine 592 57 10
a Potato sticks deep-fried in palm oil.
b Results of IDA.
c Odor threshold of the compound dissolved in sunflower oil.
d Quotient of concentration and odor threshold.
Table 5.15. Aroma model for French fries as affected
by the absence of one or more odorants a
Exp. Odorant omitted Number b
No. in the model
1 Methanethiol 5
2 (E,Z)-2,4-Decadienal and 5
(E,E)-2,4-decadienal
3 Methylpropanal, 2- and 4
3-methylbutanal
4 trans-4,5-Epoxy-(E)-2-decenal 4
5 2-Ethyl-3,5-dimethylpyrazine 4
and 3-ethyl-2,5-dimethylpyrazine
6 1-Octen-3-one, (Z)-2- and 1
(E)-2-nonenal
7 Methional 0
a Models lacking in one or more components were each
compared to the model containing the complete set of
19 odorants.
b Number of the assessors detecting an odor difference
in triangle tests, maximum 5.
The instrumental and sensory methods presented
in the French fries example have also been successfully
applied in the elucidation of other aromas.
The results are presented in the book for
some individual foods.
5.3 Individual Aroma Compounds
The results of dilution analyses and of aroma
simulation experiments show that only 5% of the
more than 7000 volatile compounds identified in
foods contribute to aromas. The main reason for
the low number of odorants in the volatile fraction
is the marked specificity of the sense of smell (for
examples, cf. 5.6).
Important odorants grouped according to their
formation by nonenzymatic or enzymatic
reactions and listed according to classes of
compounds are presented in the following
sections. Some aroma compounds formed by
both enzymatic and nonenzymatic reactions are
covered in sections 5.3.1 and 5.3.2. It should
be noted that the reaction pathways for each
aroma compound are differentially established.
Frequently, they are dealt with by using hypothetical
reaction pathways which lead from the
precursor to the odorant. The reaction steps and
the intermediates of the pathway are postulated