Food Chemistry

18.1 Fruits 839

Linalool, myrcene, and limonene also have high
aroma values.

18.1.2.6.4 Apples, Pears

The potent odorants identified in two ap-
ple 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 theCox Orange.
The aroma of the pear Williams Christ is char-
acterized 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

Table 18.29.Odorants of the apple varietiesElstarandCox Orange

Compound Elstar Cox Orange

Concentration Aroma Concentration Aroma

(μg/kg) valuea (μg/kg) valuea

(E)-β-Damascenone 1. 4 1813 0. 99 1320
2-Methylbutyric acid methylester 0. 2 < 11. 87
Ethyl butyrate 0. 770. 33
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. 155
Butanol 4860 10 975 2
Hexanol 1390 3 350 < 1
Linalool 9. 3194. 59
aAroma value: ratio of the concentration to the orthonasal odor threshold value of the substance in water.

ethyl butyrate are also involved in the fruity odor

note.

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 con-

tribute 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 con-

tributors to the aroma: myrcene, limonene, p-cy-

mene, terpinolene,α-terpineol, geranial, geran-

iol, linalool, acids (acetic and 2-methylbutyric

acids) alcohols, e. g., trans-2-hexenol; and a num-

ber ofγ-andδ-lactones, e. g.,γ-caprolactone,