2009_Book_FoodChemistry

840 18 Fruits and Fruit Products
(18.38)
γ-octalactone, γ-decalactone, γ-dodecalactone,
δ-octalactone and δ-decalactone.
and hexyl hexanoate (69.6).
18.1.2.6.7 Peaches
The aroma of peaches is characterized by
γ-lactones (C 6 –C 12 ) and δ-lactones (C 10 and
C 12 ). The main compound in the lactone fraction
is (R)-1,4-decanolide, which has a creamy,
fruity, peach-like odor. Other important compounds
should be benzaldehyde, benzyl alcohol,
ethyl cinnamate, isopentyl acetate, linalool,
α-terpineol, α- andβ-ionone, 6-pentyl-α-pyrone
(Formula 18.39, VIII), hexanal, (Z)-3-hexenal,
and (E)-2-hexenal. Aroma differences in different
varieties of peaches are correlated with the different
proportions of the esters and monoterpenes.
In the case of nectarines (Prunus persica L.,
Batsch var. nucipersica Schneid), the lactones
γ-C 8 –C 12 and δ-C 10 belong to the compounds
with the highest aroma values.
18.1.2.6.8 Passion Fruit
The aroma of the yellow fruit (Passiflora edulis
var. flavica) is supposed to be superior to that of
the crimson fruit (Passiflora edulis var. edulis).
Compounds that contribute to the aroma of both
varieties are β-ionone and the following esters
(% of the volatile fraction): ethyl butyrate (1.4),
ethyl hexanoate (9.7), hexyl butyrate (13.9),
(18.39)
Four stereoisomeric megastigmatrienes have
been found in crimson passion fruit. A mixture of
the isomers IXa and IXb (Formula 18.39) gives
a rose-like aroma, that has a hint of strawberries
in it (threshold = 100 µg/kg; water).
The following S-containing aroma substances
have been isolated from the yellow fruit: 3-
methylthiohexane-1-ol which probably gives rise
to 2-methyl-4-propyl-1,3-oxathianes (cis/trans
isomers in the ratio of 10:1) (Xa, b: Formula
18.39). Of the two cis isomers, only the
2R,4S-isomer (Xb), which has a sulfurous
herb-like odor (threshold = 4 µg/kg; water), has
been found in the fruit. However, the aroma note
more typical of passion fruit is exhibited by the
2S,4R-isomer (Xa).