512 Part V: Fruits, Vegetables, and Cereals
acids, aldehydes, ketones, alkanes, and others. Some
of these ingredients specifically provide the aroma
characteristic to fruits and are referred to as charac-
ter impact compounds. For instance, the banana fla-
vor is predominantly from isoamyl acetate, apple
flavor from ethyl-2-methyl butyrate, and the flavor
of lime is primarily due to the monoterpene lim-
onene. As the name implies, ester volatiles are
formed from an alcohol and an organic acid through
the formation of an ester linkage. The alcohols and
acids are, in general, products of lipid catabolism.
Several volatiles are esterified with ethanol, giving
rise to ethyl derivatives of aliphatic acids (ethyl
acetate, ethyl butyrate, etc.).
The ester volatiles are formed by the activity of
the enzyme Acyl-CoA:alcohol acyl transferase, or
as it is generally called, alcohol acyl transferase
(AAT). In apple fruits, the major aroma components
are ester volatiles (Paliyath et al. 1997). The alcohol
can vary from ethanol to propanol, butanol, pen-
tanol, hexanol, and so on. The organic acid moiety
containing the CoA group can vary in chain length
from C 2 (acetyl) to C 12 (dodecanoyl). AAT activity
has been identified in several fruits, including ba-
nana, strawberry, melon, apple, and others. In banana,
esters are the predominant volatiles, enriched with
esters such as acetates and butyrates. The flavor may
result from the combined perception of amyl esters
and butyl esters. Volatile production increases dur-
ing ripening. The components for volatile biosyn-
thesis may arise from amino acids and fatty acids.
In melons, the volatile components comprise esters,
aldehydes, alcohols, terpenes, and lactones. Hexyl
acetate, isoamyl acetate and octyl acetate are the
major aliphatic esters. Benzyl acetate, phenyl propyl
acetate, and phenyl ethyl acetate are also observed.
The aldehydes, alcohols, terpenes, and lactones are
minor components in melons. In mango fruits, the
characteristic aroma of each variety is based on the
composition of volatiles. The variety “Baladi” is
characterized by the presence of high levels of
limonene, other monoterpenes and sesquiterpenes,
and ethyl esters of even-numbered fatty acids. By
contrast, the variety “Alphonso” is characterized by
high levels of C 6 aldehydes and alcohols (hexanal,
hexanol) that may indicate a high level of fatty acid
peroxidation in ripe fruits. C 6 aldehydes are major
flavor components of tomato fruits as well. In genet-
ically transformed tomatoes (antisense phospholi-
pase D), the evolution of pentanal and hexenal/hexa-
nal was much higher after blending, suggesting the
preservation of fatty acids in ripe fruits. Preserving
the integrity of the membrane during ripening could
help preserve the fatty acids that contribute to the
flavor profile of the fruits, and this feature may pro-
vide a better flavor profile for fruits.GENERAL READING
Biochemistry and Molecular Biology of Plants. 2000.
BB Buchanan, W Gruissem, RL Jones, editors.
American Society of Plant Physiologists, Bethesda,
Maryland.
Biochemistry of Fruit Ripening. 1991. GB Seymour,
JE Taylor, GA Tucker, editors. Chapman and Hall,
London.
Postharvest Physiology of Perishable Plant Products.- SJ Kays, editor. Exon Press, Athens, Georgia.
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