Food Chemistry

964 21 Coffee, Tea, Cocoa

21.3.2.3.7 Volatile Compounds
and Flavor Substances

Cocoa aroma is crucially dependent on harvest-
ing, fermentation, drying and roasting. The fresh
beans have the odor and taste of vinegar. The
characteristic bitter and astringent taste and the
residual sweet taste of fermented beans might be
impaired by various faults, such as processing of
unripe or overripe fruit, insufficient aeration, lack
of mixing of the fruit, infection with foreign or-
ganisms and/or smoke damage as a result of im-

proper drying.
The odorants of cocoa powder are listed in Ta-
ble 21.24. A model (cf. 5.2.7) made by using
the 24 aroma substances on the basis of deodor-
ized cocoa powder reproduced the aroma of cocoa
very closely.
The taste of cocoa is described by the attributes
bitter, astringent and sour. It can be repro-
duced by mixing 41 constituents dissolved in
water (pH 5.5). The key compounds for the
individual notes are the substances listed in
Table 21.23. Apart from theobromine, a series of
diketopiperazines are involved in the bitter taste
(cf. Table 21.23), which are formed during the
thermal degradation of proteins during roasting
(Formula 21.10):

(21.10)

The intensity of the bitter taste of theobromine
is increased by the interaction with certain
diketopiperazines, a molar ratio of 2:1 giving the
highest intensity. However, only those complexes
are synergistically active in which the hydrogen
bridges shown in Formula 21.11 can be formed.
Thus, synergism does not occur when, e. g., in
caffeine, the N(1)-atom in the purine ring is
methylated.
Apart from the compounds mentioned in Ta-
ble 21.23, epicatechin contributes to the astrin-
gent taste and also influences the bitter note.

(21.11)

Table 21.24.Concentrations of potent odorants in a co-

coa powdera

Compound Concentration

(mg/kg)

Acetic acid 332

3-Methylbutanal 25.8

2-Methylbutanal 14.3

Phenylacetaldehyde 6.60

3-Methylbutyric acid 8.55

2-Phenylacetic acid 7.70

Methylpropionic acid 2.80

2-Methylbutyric acid 1.75

4-Hydroxy-2,5-dimethyl-3(2H)-

furanone 0.62

2-Phenylethanol 0.59

Butyric acid 0.32

2-Phenylethylacetate 0.32

2-Methoxyphenol 0.23

4-Methylphenol 0.12

Linalool 0.072

2-Ethyl-3,6-dimethylpyrazine 0.070

3-Methylindole 0.055

2-Ethyl-3,5-dimethylpyrazine 0.031

3-Hydroxy-4,5-dimethyl-2(5H)-

furanone 0.015

2,3-Diethyl-5-methylpyrazine 0.008

Dimethyltrisulfide 0.007

2-Acetyl-1-pyrroline 0.006

2-Methyl-3-(methylthio)-furan 0.0005

2-Isobutyl-3-methoxypyrazine 0.0009

aPartially defatted cocoa powder (fat content: 20%),

treated with alkali.

21.3.2.4 Reactions During Fermentation

and Drying

The reactions occurring within the pulp during

fermentation of whole cacao fruit can be dis-

tinguished from those occurring in the nibs or

cotyledons. The pulp sugar is fermented by yeast

to alcohol and CO 2 on the first day. Lactic acid