5.2 Aroma Analysis 351Fig. 5.8.FD chromatogram of the volatile fraction of French fries. Ordinate: n, number of 1+1 dilutions.
Abscissa: retention index (RI) on the capillary SE-54. The following odorants were identified: 1 methional,
2 2-acetyl-1-pyrroline, 3 dimethyltrisulfide, 4 1-octen-3-one, 5 phenylacetaldehyde, 6 2-ethyl-3,6-dimethyl-
pyrazine, 7 2-ethyl-3,5-dimethylpyrazine, 8 nonanal, 9 (Z)-2-nonenal, 10 2,3-diethyl-5-methylpyrazine, 11 (E)-
2-nonenal, 12 2-ethenyl-3-ethyl-5-methylpyrazine, 13 2-isobutyl-3-methoxypyrazine, 14 dimethyltetrasulfide,
15 (E,E)-2,4-nonadienal, 16 (Z)-2-decenal, 17 (E,Z)-2,4-decadienal, 18 (E,E)-2,4-decadienal, 19 trans-4,5-epoxy-
(E)-2-decenal (according toWagnerandGrosch, 1997)
Table 5.10.Odor thresholds of aroma substances in air
and water
Compound Odor thresholds in
Air(a) Water(b) b/a
(ng/I) (μg/l)β-Damascenone 0. 003 0. 002 6. 7 × 102
Methional 0. 12 0. 21. 6 × 103
2-Methylisoborneol 0. 009 0. 03 3. 3 × 103
2-Acetyl-1-pyrroline 0. 02 0. 15 × 103
4-Vinylguaiacol 0 .65 8. 3 × 103
Linalool 0 .66 1. 0 × 104
Vanillin 0 .920 2. 2 × 104
4-Hydroxy-2,5- 1 .030 3× 104
dimethyl-3(2H)-
furanone (furaneol)
5.2.3 Enrichment
When an aroma concentrate contains phenols, or-
ganic acids or bases, preliminary separation of
these compounds from neutral volatiles by extrac-
tion with alkali or acids is advantageous.
The acidic, basic and neutral fractions are indi-
vidually analyzed. The neutral fraction by itself
consists of so many compounds that in most cases
not even a gas chromatographic column with the
highest resolving power is able to separate them
into individual peaks. Thus, separation of the neu-
tral fraction is advisable and is usually achieved
by liquid chromatography, or preparative gas or
high performance liquid chromatography. A pre-
liminary separation of aroma extracts is achieved