Many of the Strecker aldehydes are odor
potent compounds. These include phenylacetaldehyde derived from phenylalanine and
3-methylbutanal originating from leucine.
Aldehydes produced by Strecker reaction can react further through aldol
condensation followed by a crotonisation
reaction to form a group of a-substituted,
a, b-unsaturated aldehydes. Some of these
latter compounds are odor potent and
exhibit a characteristic cocoa flavor character. Examples of these include the aldehyde
products from the condensations between
phenylacetaldehyde and acetaldehyde or
3-methylbutanal. The reaction between
phenylacetaldehyde and acetaldehyde to
form the so-called cocoa aldehyde 2-phenyl-
2-butenal is shown in F- 2.
Frauendorfer and Schieberle [ 13] examined the changes in key aroma compounds
of Criollo cocoa beans during roasting.
Comparative aroma extraction dilution
analysis of the beans revealed 42 aroma
compounds in the flavor dilution (FD)
range of 1-4096 for fermented/ unroasted
versus 4-8192 for fermented/roasted beans.
The same compounds were present in
both untreated and roasted beans though they differed in relative intensities. Highest FD factors for
unroasted were found for 2- and 3-methylbutanoic
acids (rancid) and acetic acid (sour), while for the
roasted beans the highest FD values were observed
for 3-methylbutanal (malty), 4-hydroxy- 2,5-di-
methyl- 3(2H)-furanone (caramel-like) and 2- and
3-methylbutanoic acids (sweaty).
Determined concentrations and odor activity
values revealed 22 compounds in unroasted and
27 in roasted with concentrations above their odor
thresholds. Particularly strong increases in roasted
beans were observed for the Strecker aldehydes
3-methylbutanal and phenylacetaldehyde, as well as
4-hydroxy- 2,5-dimethyl- 3(2H)-furanone. This suggests that these compounds contribute most to the
changes in total aroma as a consequence of roasting.
Other compounds, including 3-methylbutanoic
acid, were present in the unfermented unroasted
beans and showed no increase on roasting.
The fermentation process in cocoa beans displays
a spectrum of aroma compounds dominated by the
methylbutanoic and acetic acid. The roasting stage
for cocoa beans produces significant increases in
4-hydroxy- 2,5-dimethyl- 3(2H)-furanone, as well
as the Strecker aldehydes 3-methylbutanal and
phenylacetaldehyde. Further reaction between
phenylacetaldehyde and acetaldehyde or 3-methyl-
butanal can form the odor potent 2-phenyl-2-butenal
and 2-phenyl-5-methyl-2-hexenal, respectively – the
so-called cocoa aldehydes. There is no comparable
heating stage in vanilla curing akin to the conditions
of 105o to 120oC for 1-2 hours which is employed in
cocoa bean roasting.
Cured vanilla aroma
At least 200 aroma compounds have been identified in solvent extracts of cured Vanilla planifolia
beans [ 14].
Identification of the key compounds and their
quantification by GC-MS in conjunction with
determination of flavor dilution (FD) factors was
conducted on extracts of MV red Madagascan V.
planifolia whole cured beans. Aroma extraction dilution analysis of the sample detected 15 odor active
compounds with FD factors of >125. The seven most
important of these compounds included vanillin,
guaiacol, ethyl-(E)-cinnamate, 2- and 3-methylbu-
tanoate, b-damascenone and p-cresol [ 15]. The flavor
contribution of all 15 compounds was confirmed by
reconstitution experiments. The flavor formulated on
the combination of these compounds showed strong
similarity to the original MV red whole bean extract;
this is based on sensory evaluation of seven key
vanilla aroma attributes.
Earlier work by Perez-Silva et al (2006) identified
a total of 65 aroma compounds in solvent extracts
of cured Mexican V. planifolia beans. Of the total,
F- 2. Formation of 2-phenyl-2-butenal from the reaction between
phenylacetaldehyde and acetaldehyde (data modified from
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