2009_Book_FoodChemistry

18.1 Fruits 839
Linalool, myrcene, and limonene also have high
aroma values.
ethyl butyrate are also involved in the fruity odor
note.
18.1.2.6.4 Apples, Pears
The potent odorants identified in two apple
varieties with a fruity/green (Elstar) and
fruity/sweet/aromatic (Cox Orange) odor are
shown in Table 18.29.
The fruity note in the aroma profile of both
varieties is produced by acetic acid esters. On
the other hand, there is a decrease in the ethyl
esters, which are more odor active than the
acetates (cf. 5.3.2.2) and dominate in some other
fruits, e. g., oranges and olives. Hexanal, (Z)-3-
hexenal and (Z)-3-nonenal are responsible for
the green/apple-like note. (E)-β-Damascenone,
which smells of cooked apples, has the highest
aroma value in both varieties due to its much
lower odor threshold. Eugenol and (E)-anethol
contribute to the aniseed-like note which is
a characteristic especially of the aroma of the
peel of the Cox Orange.
The aroma of the pear Williams Christ is characterized
by esters produced by the degradation
of unsaturated fatty acids (example in 5.3.2.2):
ethyl esters of (E,Z)-2,4-decadienoic acid,
(E)-2-octenoic acid, and (Z)-4-decenoic acid, as
well as hexyl acetate. In fact, butyl acetate and
18.1.2.6.5 Raspberries
The character impact compound is the “raspberry
ketone”, i. e. 1-(p-hydroxyphenyl)-3-butanone
(VII). Its concentration is 2 mg/kg and its odor
threshold is 5 µg/kg (water). The starting point
for the biosynthesis of VII is the condensation
reaction of p-cumaroyl-CoA with malonyl-CoA
(cf. Formula 18.38). Additional aroma notes are
provided by (Z)-3-hexenol, α- andβ-ionone.
In addition, the ethyl esters of 5-hydroxyoctanoic
acid and 5-hydroxydecanoic acid should contribute
to the aroma. A part of the esters
hydrolyzes during cooking and the hydroxy acids
released cyclize to the corresponding lactones.
18.1.2.6.6 Apricots
The following compounds are discussed as contributors
to the aroma: myrcene, limonene, p-cymene,
terpinolene, α-terpineol, geranial, geraniol,
linalool, acids (acetic and 2-methylbutyric
acids) alcohols, e. g., trans-2-hexenol; and a number
of γ- and δ-lactones, e. g., γ-caprolactone,
Table 18.29. Odorants of the apple varieties Elstar and Cox Orange
Compound Elstar Cox Orange
Concentration Aroma Concentration Aroma
(µg/kg) value a (µg/kg) value a
(E)-β-Damascenone 1.4 1813 0.99 1320
2-Methylbutyric acid methylester 0.2 <1 1.8 7
Ethyl butyrate 0.7 7 0.3 3
Hexyl acetate 5595 112 1500 30
Butyl acetate 4640 93 1595 32
Acetic acid 2-methylbutylester 240 48 217 43
Hexanal 85 19 48 11
(E)-2-Hexenal 77 2 114 2
(Z)-3-Hexenal 6.4 25 30 120
(Z)-2-Nonenal 8.8 440 1.1 55
Butanol 4860 10 975 2
Hexanol 1390 3 350 <1
Linalool 9.3 19 4.5 9
a Aroma value: ratio of the concentration to the orthonasal odor threshold value of the substance in water.