2009_Book_FoodChemistry

838 18 Fruits and Fruit Products
Table 18.28. Odorants in fresh orange juice a
Compound
Concen- Aroma value b
tration
(µg/kg) Ortho- Retronasal
nasal
Acetaldehyde 8305 332 831
Isobutyric acid 8.8 440 293
ethylester
(R)-α-Pinene 308 62 9
Ethyl butyrate 1192 1192 11,920
(S)-2-Methylbutyric 48 8000 12,000
acid ethylester
Hexanal 197 19 19
(Z)-3-Hexenal 187 747 6227
Myrcene 594 42 36
(R)-Limonene 85,598 228 1339
3-Methylbutanol 639 <1 2.6
2-Methylbutanol 270 <1 n.b.
Ethyl caproate 63 13 125
Octanal 25 3.2 <1
1-Octen-3-one 4.1 4.1 410
Nonanal 13 2.7 3.8
Methional 0.4 <1 10
Decanal 45 9 6
(E)-2-Nonenal 0.6 <1 8
(S)-Linalool 81 13 54
3-Hydroxyhexanoic 1136 4 18
acid ethylester
(E,E)-2,4-Decadienal 1.2 6 24
trans-4,5-Epoxy-(E)- 4.3 36 287
2-decenal
Wine lactone 0.8 n.b. 94
Vanillin 67 3 2
a Variety: Valencia late.
b Aroma value: the ratio of the concentration to orthoor
retronasal odor threshold value of the substance in
water.
n.d.: not determined.
The aroma of oranges changes on storage. In the
juice of oranges stored for three weeks at 4 ◦ C,
the concentrations of esters and especially aldehydes
were much lower than in the fresh juice.
For instance, the content of (Z)-3-hexenal was
only 15%.
Orange juice from rediluted concentrate differs in
its aroma. This can be the result of big losses of
acetaldehyde and (Z)-3-hexenal, the formation of
carvone by peroxidation of limonene and a large
increase in the vanillin concentration, probably
due to the degradation of ferulic acid.
Dilution analyses of grapefruit juice gave high FD
factors (definition in 5.2.2.1) for ethyl butyrate,
(Z)-3-hexenal, 1-hepten-3-one, 4-mercapto-4-
methylpentan-2-one and 1-p-menthene-8-thiol
(IV, probably the R enantiomer). The concentrations
of the two sulfur compounds in
juices were 0.4–0.8µg/l and 0.007–0.1µg/l
respectively. Omission experiments (cf. 5.2.7)
indicate that the grapefruit aroma note is produced
by 4-mercapto-4-methylpentan-2-one.
1-p-Menthene-8-thiol, which occurs in even
lower concentrations in oranges, contributes to
the aroma but is not typical. It is possibly formed
by the addition of H 2 S to limonene. Traces of
hydrogen sulfide occur in all citrus juices.
Grapefruit juice differs from orange juice also
in the considerably lower limonene content. (+)-
Nootkatone (V) only contributes to the aroma of
grapefruit peel-oil, but not to that of the juice.
hyde, (Z)-3-hexenal, decanal, (R)-limonene and
trans-4,5-epoxy-(E)-2-decenal. It is remarkable
that these substances include decanal although its
aroma value is fairly low (Table 18.28). Esters are
also indispensable, but the aroma of the recombined
mixture is not impaired when a member
of this group is missing. The contribution of
(R)-α-pinene and myrcene is negligible.
The concentrations of the odorants in juice differ
depending on the variety. Thus, the weaker citrus
note of Navel oranges compared with the variety
Valencia late is due to a 70% lower content of
(R)-limonene.
(18.36)
Citral, which is actually a mixture of two
stereoisomers, geranial (VIa) and neral (VIb),
is the character impact compound of lemon oil
(cf. 5.5.1.5):
(18.37)