2009_Book_FoodChemistry

962 21 Coffee, Tea, Cocoa
tinesterase, polygalacturonase, proteinase, alkaline
and acid phosphatases, lipase, catalase,
peroxidase and polyphenol oxidase activities
have been detected in fresh cacao beans. These
enzymes are inactivated to a great extent during
processing.
21.3.2.3.2 Theobromine and Caffeine
Theobromine (3,7-dimethylxanthine), which is
1.2% in cocoa, provides a stimulating effect,
which is less than that of caffeine in coffee.
Therefore, it is of physiological importance.
Caffeine is also present, but in much lower
amounts (average 0.2%). A cup of cocoa contains
0.1 g of theobromine and 0.01 g of caffeine.
Theobromine crystallizes in the form of small
rhombic prisms which sublime at 290 ◦ C without
decomposition. In cocoa beans theobromine is
often weakly bound to tannins and is released by
the acetic acid formed during fermentation of the
beans. Part of this theobromine then diffuses into
the shell.
21.3.2.3.5 Phenolic Compounds
The nib cotyledons consist of two types of
parenchyma cells (Fig. 21.5). More than 90% of
the cells are small and contain protoplasm, starch
granules, aleurone grains and fat globules. The
larger cells are scattered among them and contain
all the phenolic compounds and purines. These
polyphenol storage cells (pigment cells) make up
11–13% of the tissue and contain anthocyanins
and, depending on their composition, are white
to dark purple. Data on the composition of these
cells and that of the total tissue are given in
Table 21.22.
The content of phenolic compounds is also of interest
from the standpoint of chemoprevention.
With 84 mg/g gallic acid equivalents (GAE) and
21.3.2.3.3 Lipids
Cocoa fat (cocoa butter), because of its abundance
and value, is the most significant ingredient of cacao
beans, and is dealt with in detail elsewhere
(cf. 14.3.2.2.3).
Fig. 21.5. A cross-section of cocoa cotyledon tissue
21.3.2.3.4 Carbohydrates
Starch is the predominant carbohydrate. It is
present in nibs but not in shells, a fact useful in
the microscopic examination of cocoa powders
in methods based on the occurrence of starch
as a characteristic constituent. Components of
the dietary fiber are amongst others pentosans,
galactans, mucins containing galac–turonic acid,
and cellulose. Soluble carbohydrates present
include stachyose, raffinose and sucrose (0.08–
1.5%), glucose and fructose. Sucrose hydrolysis,
which occurs during fermentation of the beans,
provides the reducing sugar pool important for
aroma formation during the roasting process.
Mesoinositol, phytin, verbascotetrose, and some
other sugars are found in cocoa nib.
Table 21.22. Composition of polyphenol storage cells
of cacao tissue
Constituent Polyphenol Cotylestorage
dons
cell
(%) (%) a
Catechins 25.0 3.0
Leucocyanidins 21.0 2.5
Polymeric leucocyanidins 17.5 2.1
Anthocyanins 3.0 0.4
Total phenols 66.5 8.0
Theobromine 14.0 1.7
Caffeine 0.5 0.1
Free sugars 1.6
Polysaccharides 3.0
Other compounds 14.4
a As % of dry matter.