THE SEEDS OF THE CHOCOLATE-PLANT AS THEY APPEAR IN COMMERCE. THEIR
MICROSCOPIC AND CHEMICAL CHARACTERS.
The seeds of the chocolate-plant are brought into the market in their
crude state, as almond-shaped “beans,” which differ in color and
somewhat in texture. It is not uncommon to find the external surface of
the bean more or less covered with a thin irregular layer of attached
earth, but this is generally pretty well cleared off during the
transportation.
Upon the color of shell and kernel, the relative brittleness, the
flavor, and the odor, depends the market value of the seeds.
The dried seeds have a papery, brittle shell, which is very smooth
on the inside, but on the outside exhibits, under the microscope, a
few short hairs and round excrescences. But these are mostly lost
by the rough handling and by the attrition of the seeds with one
another during transportation. The kernel consists of two large
cotyledons or seed-leaves, reddish-gray or reddish-brown, with a
shining, oily surface; the whole crushing rather easily into a loose
mass of fragments. The kernel, when dry, has a minute, tough, almost
stony radicle which separates easily from the cotyledons. Microscopic
examination shows that the cells of the seed-leaves contain albumen,
oily matters,--sometimes in a crystalline condition,--crystals of
an entirely different shape, starch, coloring substances in special
receptacles known as pigment-cells, and ducts with spiral markings.
The starch grains do not have any very characteristic form or markings:
they are generally spherical and simple. The only peculiarity worth
mentioning, is the relative slowness with which they are acted on
by hot water and by iodine. The coloring substances are mainly of a
carmine or violet color, and are distinguished by the change of shade
when an alkali is added, becoming thereby darker.
These are the only structural elements which a pure powder or paste of
chocolate should show under the microscope. Any other substances must
be recognized as accidental or intentional additions.
All seeds of whatever kind contain, as a part of their substance, the
matter of which cell-walls are made; namely, cellulose. The percentage
differs in different seeds, in those of the chocolate-plant being about
three in the hundred. Cellulose has the same chemical composition
as starch; but its physical properties are not the same as those of
starch, among which may be mentioned its entire insolubility in boiling
water.
Starch forms, on an average, eight to ten per cent of chocolate-seeds.
It consists of minute spherical grains, not distinguishable from that
found in many other kinds of seeds. Traces of gum and of other allied
bodies are also present in the seeds.
Albuminoids, or substances resembling, in a general way, the albumin
of egg, occur in chocolate-seeds as they do in other seeds, and in a
somewhat higher amount than in certain other cases in which the seeds
are used as food. The percentage ranges from about fifteen to twenty,
depending on the variety. These albuminoids are compounds of nitrogen,
and are extremely nutritious. In the seeds they occur in a readily
assimilable form, fit for digestion. Their peculiar relations as
flesh-formers are referred to in the section treating of the physiology
of chocolate-seeds.
Cacao-red occurs as a coloring matter in small amount. It is rendered
dark by alkalies.
Theobromine, the active principle of the cocoa-bean, constitutes less
than one per cent of the weight of the seeds, but it varies greatly in
amount in different seeds, ranging from ³⁰⁄₁₀₀ of one per cent in some,
to a trifle over one per cent in others.
The ash left on completely burning cocoa-beans is not far from four
per cent. Its composition is substantially that of the ash of seeds of
other plants.
Cocoa-butter, or oil, constitutes not far from fifty per cent of good
cocoa-beans. The oil is remarkable for its freedom from rancidity and
its very bland character. Its uses are innumerable.
The following averages of many analyses by a leading recent authority
may be of interest:--