This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The cocoa tree, Theobroma Cacao, Linne (N.O. Sterculiaceoe), is a native of tropical America, and is cultivated there as well as in other tropical countries, such as Java, Ceylon, the West Indies, etc.
The flowers are small, and spring directly from the trunk; they are succeeded by large orange or deep red fruits of the shape of a small pointed vegetable marrow and about 15 or 20 cm. in length. Each fruit contains forty or fifty nearly colourless, fleshy seeds embedded in a scanty, mucilaginous pulp. The seeds are separated and packed in boxes, in which they undergo a process of fermentation, considerable heat, which, however, should not be allowed to exceed about 42°, being developed; they are then dried in the sun. During these processes the seeds acquire a reddish brown colour, and the taste, which at first is astringent and bitter, becomes mild and oily. Sometimes the seeds are simply freed from the pulp and dried in the sun; they have then a more astringent and bitter taste and are less valuable.
Cocoa seeds, as they occur in commerce, are about 2.5 cm. in length and of a flattened-ovoid shape. The seed-coat is reddish brown or chocolate brown in colour, thin and brittle. It can easily be separated from the kernel, which consists mainly of two irregularly folded, chocolate-coloured cotyledons; the latter are so brittle that they easily separate into small angular fragments (cocoa nibs of commerce).
Both the kernels and the shells contain the alkaloid theobromine, the former yielding about 2 per cent., the latter about 1 per cent. The kernels contain, further, about half their weight of solid fat, which is obtained as a by-product in the manufacture of cocoa essences by submitting the heated seeds to strong pressure (Oleum Theobromatis). The seeds also contain a trace of volatile oil.
Theobromine or dimethylxanthine, C5H1(CH3)2N402, has been obtained as a white crystalline powder very slightly soluble in cold water or alcohol, more readily in boiling. It sublimes at 290°, and combines readily with alkalies and alkaline earths to form salts. By introduction of the methyl group it is converted into trimethylxanthine (caffeine).
Oleum Theobromatis is obtained as a by-product in the manufacture of cocoa and chocolate. The seeds are first roasted, then broken and the shell and embryo removed; the resulting cocoa nibs are ground in horizontal burr mills during which sufficient heat is developed to liquefy the fat. The mass (cocoa mass) is then pressed, the expressed oil filtered and run into moulds to set. It forms a hard, yellowish-white solid, melting at 30° to 33°, consisting chiefly of the glycerides of stearic (40 per cent.), palmitic, and oleic acids existing partly at least as mixed glycerides, i.e. glycerides in which two or more of these acids are combined with one glyceryl group. See also ' Oil of Theobroma.'
Cocoa is largely used as a more nutritious and less stimulating beverage than tea or coffee. Its principal active constituent, theobromine, has an action similar to that of caffeine, but while its effect on the nervous system is less than that of caffeine its diuretic action is greater.