Cocoa is prepared from the roasted seeds of the tree _Theobroma cacao_,
of the order _Byttneriaceæ_. It sometimes appears in commerce as
“cocoa-nibs” (_i. e._ partially ground), but it is more frequently sold
in the powdered state, either pure or mixed with sugar and starch, and
also often deprived of about one-half of its fat. Chocolate usually
consists of cocoa-paste and sugar flavoured with vanilla, cinnamon, or
cloves, and commonly mixed with flour or starch. According to Wanklyn,
the average composition of cocoa is as follows:–
Per cent.
Cocoa butter 50·00
Theobromine 1·50
Starch 10·00
Albumin, fibrine and gluten 18·00
Gum 8·00
Colouring matter 2·60
Water 6·00
Ash 3·60
Loss, etc. 0·30
R. Benzeman[14] has furnished the following averages of the results
obtained by the analysis of cocoa and chocolate. The air-dried cocoa
berries gave–husks, 13·00 per cent.; nibs, 87·00 per cent.:–
————————————-+————-+—————
| | Chocolate made
| Cocoa Nibs. | from Cocoa and
| | Sugar.
————————————-+————-+—————
| per cent. | per cent.
Moisture at 100° | 6·41 | 1·65
Fat | 51·47 | 22·57
Starch | 11·75 | 4·58
Other organic substances, | |
insoluble in water. | 18·03 | 8·58
Organic substances, soluble in water | 8·54 | 60·63
Mineral Ash | 3·80 | 1·99
————————————-+————-+—————
| 100·00 | 100·00
————————————-+————-+—————
Ash of insoluble substances | 0·89 | 0·30
————————————-+————-+—————
Recent analysis of shelled cocoa-beans, made by Boussingault, gave the
following results:–
—————————+———–+———–
| Fresh. | Dry.
—————————+———–+———–
| per cent. | per cent.
Fat | 49·9 | 54·0
Starch and starch-sugar | 2·4 | 2·5
Theobromine | 3·3 | 3·6
Asparagine | traces | ..
Albumin | 10·9 | 11·8
„ gum | 2·4 | 2·5
Tartaric acid | 3·4 | 3·7
Tannin | 0·2 | 0·2
Soluble cellulose | 10·6 | 11·5
Ash | 4·0 | 4·4
Water | 7·6 | ..
Undetermined | 5·3 | 5·8
—————————+———–+———–
Dr. Weigman[15] obtained the following results from an examination of
several varieties of the shelled beans:–
—————+———–+———–+———–+———–
| Water. | Fat. | Ash. | Nitrogen.
—————+———–+———–+———–+———–
| per cent. | per cent. | per cent. | per cent.
Machala | 4·97 | 47·80 | 3·88 | 2·25
Arriba | 6·57 | 47·44 | 3·52 | 2·31
Caracas | 6·00 | 46·39 | 4·19 | 2·23
Puerto Cabello | 5·71 | 48·74 | 3·94 | 2·13
Surinam | 5·01 | 46·26 | 2·99 | 2·20
Trinidad | 6·07 | 45·74 | 2·04 | 2·04
Port au Prince | 4·73 | 48·58 | 3·89 | 2·33
—————+———–+———–+———–+———–
The most important constituents of cocoa are the fat (cocoa-butter), and
the alkaloid (theobromine).
_Cocoa butter_ forms a whitish solid of 0·970 specific gravity, fusing
at 30°, and soluble in ether and in alcohol.
_Theobromine_ (C_{7}H_{8}N_{4}O_{2}) crystallises in minute rhombic
prisms, which are insoluble in benzol, but dissolve readily in boiling
water and alcohol. It sublimes at 170°. Theobromine is exceedingly rich
in nitrogen, containing over 20 per cent. of the element. In this and
many other respects it bears a great resemblance to theine.
The proportion of mineral ash in cocoa varies from 3·06 to 4·5 per cent.
James Bell[16] gives the following composition of the ash of Grenada
cocoa nibs:–
Per cent.
Sodium chloride 0·57
Soda 0·57
Potassa 27·64
Magnesia 19·81
Lime 4·53
Alumina 0·08
Ferric oxide 0·15
Carbonic acid 2·92
Sulphuric acid 4·53
Phosphoric acid 39·20
——
100·00
——
The most characteristic features of the ash of genuine cocoa are its
great solubility, the small amounts of chlorine, carbonates, and soda,
and the constancy of the proportion of phosphoric acid contained. Bell
has also analysed several samples of commercial cocoa. The following
will serve to illustrate their general composition:–
Per cent.
Moisture 4·95
Fat 24·94
Starch (added) 19·19
Sugar (added) 23·03
Non-fatty cocoa 27·89
——
100·00
——
Per cent.
Nitrogen 2·24
Ash 1·52
Cocoa, soluble in cold water 31·66
Ash in portion soluble in cold water 1·17
The comparatively low percentage of ash contained in prepared cocoas
and chocolate, is of use in indicating the amount of real cocoa present
in such mixtures. A large proportion of the mineral constituents of
cocoa are dissolved by directly treating it with cold water. Wanklyn
obtained in this way from genuine cocoa-nibs 6·76 per cent. organic
matter, and 2·16 per cent. ash, the latter chiefly consisting of
phosphates; a commercial cocoa gave, extract, 46·04 per cent.; ash,
1·04 per cent. The most common admixtures of cocoa and chocolate,
are sugar and the various starches. The addition of foreign fats,
chicory, and iron ochres, is also sometimes practised. Since prepared
cocoas are generally understood to contain the first-named diluents,
their presence can hardly be considered an adulteration, if the fact
is mentioned upon the packages. Many varieties of the cocoas of
commerce will be found to be deficient in cocoa-butter, a considerable
proportion of which has been removed in the process of manufacture.
This practice is also claimed to be justifiable, the object being to
produce an article unobjectionable to invalids, which is not always
the case with pure cocoa. In the analysis of cocoa the following
estimations are usually made:–
_Theobromine._–10 grammes of the sample are first repeatedly exhausted
with petroleum-naphtha. The insoluble residue is mixed with a small
quantity of paste, prepared by triturating calcined magnesia with a
little water, and the mixture evaporated to dryness at a gentle heat.
The second residue is boiled with alcohol and the alcoholic solution of
theobromine filtered and evaporated to dryness in a tared capsule. It
is then purified by washing with petroleum-naphtha and weighed. Bell
has verified the existence in cocoa of a second alkaloid, distinct
from theobromine, which crystallises in silky needles very similar to
theine.
_Fat._–The proportion of fat is readily determined by evaporating to
dryness the petroleum-naphtha used in the preceding estimation. As
already stated, it is generally present in a proportion of 50 per cent.
in pure cocoa; the amount contained in prepared soluble cocoas being
often less than 25 per cent. The English minimum standard is 20 per
cent.
_Ash._–The ash is determined by the incineration of a weighed portion
of the sample in a platinum dish. In prepared cocoas and chocolates,
the proportion of ash is considerably lower than in pure cocoa. It is
of importance to ascertain the amount of ash soluble in water (the
proportion in genuine cocoa is about 50 per cent.), and especially the
quantity of phosphoric acid contained. Assuming that prepared cocoa
contains 1·5 per cent. of ash, of which 0·6 per cent. consists of
phosphoric acid, and allowing that pure cocoa contains 0·9 per cent. of
phosphoric acid, Blyth adopts the following formula for calculating the
proportion of cocoa present in the article:–
(·6 × 100) / ·9 = 66·66 per cent.
_Starch._–A convenient method for estimating the starch is to
first remove the fatty matter of the cocoa by exhaustion with
petroleum-naphtha, and then boil the residue with alcohol. The
remaining insoluble matter is dried, and afterwards boiled until the
starch becomes soluble. It is next again boiled for several hours with
a little dilute sulphuric acid, after which the solution is purified
by addition of basic plumbic acetate. The liquid is then treated with
sulphuretted hydrogen, in order to remove the lead, and the sugar
contained in the filtered solution is determined by means of Fehling’s
solution, and calculated to terms of starch. The proportion of starch
normally present in cocoa is to be deducted from the results thus
afforded. The variety of starch contained in cocoa differs in its
microscopic appearance from the starches most frequently added.
_Sugar._–The sugar may be determined by evaporating the alcoholic
solution obtained in the preceding process, and then subjecting the
residue to the same method of procedure.
The proportion of woody fibre in cocoa can be approximately estimated
by the method of Henneberg and Stohman,[17] which consists in
extracting the fat with benzole, boiling the remaining substances for
half an hour, first with 1·25 per cent. sulphuric acid, then with
1·25 per cent. solution of potassium hydroxide. The residue is washed
with alcohol and with ether, and its weight determined. Unwashed
cocoa-berries, when treated in this manner, gave from 2 to 3 per cent.
of cellulose, while cocoa husks furnished from 10 to 16 per cent.
The presence of chicory in soluble cocoa and chocolate is easily
recognised by the dark colour of the extract obtained, upon digesting
the suspected sample with cold water; ochres and other colouring
matters are detected by the reddish colour of the ash as well as by its
abnormal composition. The addition of foreign fats to chocolates is
stated to be occasionally resorted to.
The melting point of pure cocoa-butter varies from 30° to 33°. The
identification of foreign fats can sometimes be accomplished by means
of their higher melting point, and by an examination of the separated
fat, according to Koettstorfer’s method (see p. 71). The table
following gives the melting points of various fats, and the number of
milligrammes of K(OH) required for the saponification of one gramme of
the same.
————————–+————–+————-
| |m.g. K(OH)
Fat. |Melting point.|to saponify
| |one gramme.
————————–+————–+————-
| ° ° |
Cocoa-butter | 30 to 33 |198 to 203
Arachidis oil | .. | 191·3
Sesamé oil | .. | 190·0
Cotton-seed and olive oil | .. | 191·7
Almond oil | .. | 194·5
Palm oil | 35 to 36 | 202·5
Lard | 32 „ 33 | 195·5
Mutton tallow (fresh) | 42·5 „ 45 | ..
Mutton tallow (old) | 43·5 | 196·5
Bone fat | 21 to 22 | 190·0
Beeswax | 63 | ..
————————–+————–+————-
Other tests have also been suggested for the detection of foreign fats
in cocoa-butter:–
(_a_) Treat the fat with two parts of cold ether; pure cocoa-butter
dissolves, forming a clear solution, whereas in presence of tallow or
wax a cloudy mixture is obtained.
(_b_) Dissolve 10 grammes of the suspected fat in benzole, and expose
the solution to a temperature of 0°. By this treatment a separation
of pure cocoa-butter in minute grains is produced. The liquid is now
heated to 14°·4, when the cocoa-fat will re-dissolve to a transparent
solution, while the presence of tallow will be recognised by the turbid
appearance of the liquid.
