Food Chemistry

962 21 Coffee, Tea, Cocoa

tinesterase, polygalacturonase, proteinase, al-
kaline 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 con-
tains 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.

21.3.2.3.3 Lipids

Cocoa fat (cocoa butter), because of its abundance
and value, is the most significant ingredient of ca-
cao beans, and is dealt with in detail elsewhere
(cf. 14.3.2.2.3).

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.

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 in-

terest from the standpoint of chemoprevention.

With 84 mg/g gallic acid equivalents (GAE) and

Fig. 21.5.A cross-section of cocoa cotyledon tissue

Table 21.22.Composition of polyphenol storage cells

of cacao tissue

Constituent Polyphenol Cotyle-

storage dons

cell

(%) (%)a

Catechins 25. 03. 0

Leucocyanidins 21. 02. 5

Polymeric leucocyanidins 17. 52. 1

Anthocyanins 3. 00. 4

Total phenols 66. 58. 0

Theobromine 14. 01. 7

Caffeine 0. 50. 1

Free sugars 1. 6

Polysaccharides 3. 0

Other compounds 14. 4

aAs % of dry matter.