South African Arrowroot.
—There are many species of Marantaceæ cultivated in South Africa from which arrowroot is manufactured. They are of the same variety as that used in Bermuda and the West Indies. The cultivation of the plant has modified to some extent the action of the starch granules as originally found in the uncultivated plant. The starch granules in the cultivated variety approach more nearly a spherical form. The concentric lines are much more distinct and the hilum more prominent than in the wild variety.
Tapioca.
—The most important of the starch products used as food is the tapioca. It is made from the plant belonging to the natural family Euphorbiaceæ, and is derived particularly from the variety of cassava plant known as Manihot. Attention has been called to the fact that many of the varieties of cassava plant are highly poisonous, due to the natural development during growth of hydrocyanic acid, one of the most violent of known poisons. This substance, however, is of quite a volatile character, and when comminuted cassava root is heated or boiled, all or at least the principal part of the hydrocyanic acid (prussic acid) disappears. None of it or at least not more than a trace is found in the food product tapioca. A comparatively sweet variety of cassava that is containing but a small proportion of prussic acid is grown in Florida and Georgia. The appearance of a field of cassava is shown in [Fig. 46]. The tapioca of commerce is prepared by the separation of the starch in the usual way by grinding and washing with water. Before the starch becomes dry, in fact, while it is still containing its maximum degree of moisture, it is submitted to heat first at a low temperature, gradually increased until the starch granules are disintegrated or agglutinated into a somewhat firm and gelatinous mass. The heat is then continued at the proper temperature until the water is nearly all driven off. The starch from this plant is sometimes known as Brazilian arrowroot.
The starch granules of the bitter cassava are very small and often angular in shape, although some of them appear as well rounded spheroids. The hilum is, as a rule, clearly distinguished. The microscopic appearance of the grains of cassava starch is shown in [Fig. 47].
Adulteration of Tapioca.
—The true tapioca should only be made from starch of the cassava. Any starch, derived from any source whatever, if taken in the moist state may be subjected to the same process of heating, and forms an imitation tapioca which possesses many of the physical and probably all of the edible properties of the genuine article. The substitution, however, of any of the other starches for that of the cassava is at least an imitation, if not an adulteration, of the genuine article.
Fig. 47.—Cassava Starch (× 200).—(Courtesy Bureau of Chemistry.)