Amylum (U. S. P.)—Starch.
"The fecula of the seed of Zea mays, Linné" (U. S. P.).
FORMULA: C6H10O5. MOLECULAR WEIGHT: 161.62.
SYNONYM: Corn starch.
ILLUSTRATION: Bentley and Trimen, Med. Plants, 296.
History and Source.—The ancient Greeks were well acquainted with starch, and its preparation "without the use of a millstone" (hence the name, amylum). The process is described by Dioscorides, and later by Pliny, and closely resembles in principle that followed in our days. Beccari, in 1745, showed that gluten may be obtained as a by-product when wheat is used as raw material (R. and S).
The pharmacopoeial starch is derived from the seed of the Maize, or common Indian corn plant, for a description of which see Zea Mays. Previous to the present revision (1890), the U. S. P. recognized the starch prepared from the seeds of Triticum vulgare, Villars, or Common wheat. Starch belongs to the organic compounds called carbo-hydrates, and is one of the principal constituents in various organs of many plants, especially in the seeds, where it serves as stored food-material for the growing embryo; also in roots and tubers (potatoes, arrowroot, tapioca), and in the pith of the stems of certain plants, e. g., the sago palm. It abounds especially in the different kinds of grain, among which wheat yields one of its purest varieties, and from which an average of about from 50 to 60 per cent is to be had.
Preparation.—Commercial starch is principally obtained from potatoes and the more abundant cereals. The processes for preparing the various kinds of starch differ to some extent, though all are prepared by comminution of the starch-bearing parts, then separating the starch from the coarser portions by treating with warm or cold water, and allowing the starch to subside. Most cereal starches are prepared as follows: Soak the grain in luke-warm water, to which has been added a little alkali to separate the starch grains from the gluten. After the outer covering of the grain has softened, the material is ground under water and put into sieves and thoroughly washed, over a tank, with pure cold water. The gluten is thereby left upon the sieve, and the starch passes through and is allowed to subside in the tanks. It is then collected and dried in drying chambers, and is ready for use. Starch may be obtained as follows: From wheat flour, which consists of starch, gluten, mucilage, albumen, salts, and bran. The flour is kneaded in a cloth with successive portions of cold water, whereby the gluten and bran remain in the cloth; the mucilage, albumen, and salts dissolve in the water, and the starch passing away with the water, in a state of suspension, gradually falls to the bottom. By allowing the albumino-mucilaginous water, from which it has subsided, to undergo fermentation, the starch is thereby purified from all of the gluten; for the acetic and lactic acids formed during this process dissolve the gluten. The fermentation method is sometimes carried out directly with the wheat, after the latter is softened with water and crushed in roller-mills. The fermented mass is then washed in sacks and fine sieves, as before described. Another method, by which no fermentation takes place, and the gluten may nearly all be saved, is as follows: Allow a stiff dough of wheat flour to stand for a few hours, and then transfer it to a fine wire sieve. While a small stream of cold water plays upon it, knead it until the latter passes clear. The starch may now be thoroughly washed with cold water, drained, and dried. The gluten remains upon the sieve to the extent of 25 parts from 100 parts of wheat flour.
Description and Properties.—Starch, from whatever source, occurs in the form of white granules of varied size and form; these granules are definitely organized structures, although their existence in relation to that of the cell is transitory. They are the first definitely-formed products of assimilation, insoluble in the ordinary cell-sap of the plants containing them, through a process of organization analogous to that by which the development of the cell itself is effected. When these minute granules acquire appreciable dimensions, concentric lines may be observed, more or less distinctly in different cases; a well marked example is offered in the granules of the potato-starch. These lines increase in number with the increase of size, in many cases, however, soon becoming eccentrical from the preponderating growth of one side of the granule. In freshly extracted granules, the original center generally appears solid, or with a minute black point; but if the starch is dry, the center appears hollow, sometimes is even occupied by air, and some starch grains have a large cavity. If strong alcohol be applied to fresh grains, the abstraction of water likewise produces a hollow in the central point of growth, and in all these cases, cracks not infrequently run out toward the surface. The lines seen in the starch granules are the boundaries of concentric superimposed layers of its substance; sometimes these are very distinct, sometimes very faint; often, more distinct lines appear at intervals in the series of the same granule, and in these cases even, a thin vacancy, or in the dried granules a stratum of air, seems to exist between the layers. The specific gravity of starch is 1.53; its chemical composition is C6H10O5, or a multiple of this formula.
Starch, according to the U. S. P., made from corn occurs "in irregular, angular masses, which are easily reduced to a fine powder; white, inodorous, and tasteless; insoluble in ether, alcohol, or cold water. Under the microscope appearing as granules, nearly uniform in size, more or less angular in outline, with indistinct striae, and with a distinct hilum near the center. Triturated with cold water, it gives neither an acid nor an alkaline reaction with litmus paper. When boiled with water, it yields a white jelly having a bluish tinge, which, when cool, acquires a deep-blue color on the addition of iodine T.S. When completely incinerated, starch should leave not more than 1 per cent of ash"—(U. S. P.).
Starch, as met with in commerce, is of a granular appearance, friable, insipid, inodorous, permanent in dry air, and in the form of irregular quadrangular or hexagonal columns, emitting a peculiar sound when compressed. In a damp atmosphere it absorbs about 24 per cent of water, without losing its dry appearance; a moderate heat removes its moisture. In its ordinary state it contains about from 12 to 18 per cent of moisture. Starch, well dried by heat, produces with water a rise in temperature of about 15° C. (27° F.) [Maercker].
Following the researches of Naegeli and others, it is now generally adopted that the starch granules consist of three constituent bodies: An external, thin tegument, of the nature of cellulose, not soluble in water, and not attacked by sugar-forming ferments; to the presence of this protecting influence the fact is due that cold water has no action whatever on starch granules as long as they are not crushed. This tegument envelops another substance called starch cellulose proper, or farinose (formerly named amylin), which in turn encloses the bulk of the starch granule, a substance called starch granulose (formerly termed amiden), soluble in hot water, insoluble in alcohol and ether. The solution of the latter substance in water is powerfully dextro-rotatory, three times as much as cane sugar (Biot). There is, probably, no essential difference between starch cellulose and granulose. The former, under the influence of sugar-forming ferments (ptyaline, contained in saliva, and diastase), may be converted into the same substances as granulose; at ordinary temperature the conversion of starch cellulose takes place very slowly, with the result that it may thus be differentiated from the granulose. In pure condition it is colored yellow by iodine solution.
Warm water at about 87.7° C. (190° F.) converts starch into a kind of mucilage, which, when sufficiently concentrated forms, on cooling, a jelly, starch paste. When long boiled, the granule almost wholly dissolves, and the decoction on cooling does not gelatinize. Alcohol removes from potato starch a trace of essential oil, on which its odor and taste, when any is present, depend. Pure starch is colored blue by iodine, whether in its natural state or softened by hot water, the depth of the color depending upon the quantity of iodine. Where much is added, the color is almost black. The best application is the solution of iodine in iodide of potassium, and this should be used very weak in the investigation of starch. If iodine be almost a million times diluted, it can be detected by starch. Iodide of starch, when suspended in water and heated nearly to the boiling point, loses its blue color, which returns as it cools; alkalies also remove the blue color; alcohol has the same effect. Boiling with diluted sulphuric acid, also hydrochloric or oxalic acids, converts starch paste into sugar (dextrose) yielding several intermediary and soluble products collectively called dextrin. The latter products are colored yellow or red, not blue, by iodine solution, and the process may thus be traced by the iodine reaction. Dextrin may also be formed by subjecting starch to a temperature of about 204.4° C. (400° F.) (see Dextrinum). Starch may be converted for the most part into sugar (maltose) by the ferment diastase, a substance into which the protein matter of barley and other grains is converted, after these have been made to germinate, and their vitality destroyed by drying at an elevated temperature; as an intermediary product, dextrin (malto-dextrin) is formed. One part of diastase can convert 2000 parts of starch, at 65° C. (149° F.), into dextrin, and a little sugar, or maltose. The dextrin is completely convertible into sugar only by continued boiling with diluted mineral acids. Starch is dissolved by alkalies, from which it is again precipitated by acids, acetate of lead, tannic acid, calcium and barium hydroxides. Upon the formation of an insoluble compound of starch with barium hydroxide is based a method for the quantitative determination of starch, devised by Asboth. When heated, starch melts, turns black, and is decomposed. Nitric acid splits it into malic and oxalic acids. With fuming nitric acid, starch is changed into a white powder, capable of being softened by water, but not soluble in it. It is also insoluble in alcohol. This tasteless powder is a mixture of certain nitrates of starch, called xyloidin, an explosive substance discovered by Braconnot (R. and S.).
Action and Medical Uses.—As a constituent of many vegetable substances, starch forms a most important alimentary substance; in a medical point of view, it is to be considered as a demulcent. The powder of starch is used to take up acrid secretions from the external surface, soothe the pain in erysipelas, and to prevent intertrigo in children; in these affections it is usually dusted on the parts. It is also used in mucilage, or in emulsion for suspending drugs, when to be given internally, or by injection, especially as a lenitive in inflammation of the lower bowel. Starch is sometimes triturated with the more active medicines, in order to render them more bulky and easily taken. It is an antidote to iodine when swallowed in large quantity.
Other Varieties of Starch.—I. AMYLUM TRITICI, Wheat-starch. The fecula of the seeds of Triticum vulgare, Villars.Triticum sativum, Lamarck). Nat. Ord.—Gramineae. This starch was formerly official in the U. S. P., but has been replaced by corn-starch. According to Pereira, wheat-starch, examined under the microscope, consists of large and small grains, the large ones being rounded and flattened, or lenticular; the small ones rather spheroidal. In the middle of the flattened surface is the rounded, elongated, or slit hilum, surrounded by concentric rings, which frequently extend to the edge of the grains. When heated, the particles crack at the edges. The grains vary in size from .0001 to .0009 of an English inch. These granules have each a thin exterior pellicle or tegument, insoluble in water, and an interior soluble substance (see Farina Tritici).
II. AMYLUM ORYZA, Rice-starch, Rice-flour. Prepared from the seeds of Oryza sativa, Linné.Nat. Ord.—Gramineae), or ordinary Rice. The latter is deprived of its coverings and palae, and presents a pearly-white, or translucent, oblong body, about 1/8 inch in length, with a single groove on one side. Rice starch presents the smallest granules of all the ordinary commercial starches. They consist of polygonal grains more or less adherent to other or larger granules. The rice plant is largely cultivated in subtropical and tropical regions, and quite largely in Southern United States. Its native habitat is India (see Oryza sativa).
III. AMYLUM SOLANI, Potato-starch. The common potato plant is too well known to need a description. It is indigenous to Chili and Peru, and was cultivated at an early date in Virginia from whence the colonists carried it to England. Potato-starch is the principal starch of commerce, and is very largely employed, and is even used to adulterate other varieties, notably arrowroot. It consists of large, irregularly-oval granules intermixed with small subspherical ones. The larger ones present a small hilum at the little extremity and are marked by distinctly concentric lines, giving under the microscope the appearance of a sea-shell.
IV. AMYLUM CANNAE.—Canna, Canna starch. Probably the fecula of the root of Canna edulis, Ker, Nat. Ord. Marantaceae.
Canna starch, also known as "Tous les Mois," is obtained from a West Indian plant, supposed to be the Canna edulis of Ker, the tubers or roots of which are rasped, and then subjected to the ordinary methods of washing, straining, decantation of the supernatant fluid, and drying of the deposited starch. Canna starch is imported from St. Kilts, and is an excellent form of arrowroot. Canna starch looks more like potato-starch than any other amylaceous substance, has a satiny or glistening exterior, and its particles are large, varying in length from the 1/150 to the 1/400 of an inch. Examined by the compound microscope, they are oval or oblong, generally more or less ovate, have a very distinct nucleus or hilum, and fine, regular, uniform, concentric rings. The circular hilum is usually placed at the narrow extremity, and is very rarely double. The hilum and the body of the particle are frequently cracked. Tous les Mois contains about 16.74 per cent of hygroscopic water, is very soluble in boiling water, and yields a very tenacious jelly when boiled in this fluid. Canna starch forms a salutary and agreeable article of diet for invalids and children, and appears to be easily digested. It may be boiled the same as arrowroot, and used in the same cases. By many it is preferred to any other kind of arrowroot.
V. AMYLUM MANIHOT, Tapioca.—(See Manihot).
VI. AMYLUM MARANTAE, Arrowroot.—(See Maranta).
VII. SAGO.—(See Sago).
Starch Derivative and Preparation.—DEXTRIN, Dextrinum (C6H10O5). This derivative of starch may be prepared in several ways. On a large scale it is usually prepared by heating starch to a temperature ranging from 226° to 260° C. (438° to 500° F.). It is a whitish-yellow or yellowish, non-crystalline, gum-like mass, or it may occur in granular form, insoluble in ether and alcohol, but readily soluble in water. Its action on polarized light is dextrogyrate, and with an alkaline copper solution occasions no reaction. White dextrin has the appearance of starch. It forms a very tenacious, adhesive paste with water, which does not cause the paper on which it is spread, to wrinkle, as do many adhesive mixtures.
AMYLUM IODATUM, Iodized starch, Amyli iodidum, Iodide of starch, Ioduretum amyli.—This compound was official in the U. S. P. of 1880, which directed iodine (5 parts) to be triturated with a small quantity of distilled water, and starch (95 parts) to be gradually added, and the trituration continued until a uniform blue (approaching black) coloration ensued. It was finally to be dried at a heat not higher than 40° C. (104° F.), and after rubbing to a finely powdered state, kept in closely secured, glass-stoppered vials. This product is by some thought to be a definite chemical compound, Payen and Fritzsche giving it the formula C6H10O5.10I, and Bondonneau C6H10O5.5I. Although it is generally believed to be what Liebig pronounced it, a mixture of finely comminuted iodine and starch, the fact must not be overlooked that iodide of starch may be subjected to a temperature of 100° C. (212° F.) for 6 to 7 days without any loss of iodine being incurred (Stokes in Maercker's Handbuch).
Iodized starch is a deep-blue powder, decolorizing in the sunlight. It has a slight odor of iodine. Water heated above 65° C. (149° F.) also decolorizes it, but it a in assumes its blue color on cooling. Iodine is partly expelled by boiling with water and may be wholly driven off by long-continued boiling. Such substances as will readily dissolve iodine, as caustic potash, alcohol, sulphide of hydrogen, and nearly all animal fluids decompose it. The production of iodized starch exhibits the action of the best known test for iodine. The nearer the freezing point, the more perfect are the results of this test. The test is exceedingly sensitive (see Amylum). This compound was introduced into medicine as a non-irritating preparation of iodine. Buchanan, of Glasgow, who advocated its use, gave large amounts of it in the course of 24 hours without ill effects. It forms insoluble compounds with many poisons, consequently Bellini recommended it as a general antidote, and further claimed that it assists in the elimination of lead, mercury, and other salts, in cases of poisoning by them. It has been given with success for lupus erythematodes (McCall Anderson). A well-rounded teaspoonful may be administered several times throughout the day. As high as 3 ounces have been given in a day, administered in three doses (Buchanan).