Arrowroot.
Botanical Origin—Maranta arundinacea[2330] L.—An herbaceous branching plant, 4 to 6 feet high, with ovate-lanceolate, puberulous or nearly glabrous leaves, and small white flowers, solitary or in lax racemes. It is a native of the tropical parts of America from Mexico to Brazil, and of the West Indian Islands; and under the slightly different form known as M. indica Tussac, it occurs in Bengal, Java and the Philippines. This Asiatic variety is now found in the West Indies and Tropical America, but apparently as an introduced plant.[2331]
History—The history of arrowroot is comparatively recent. Passing over some early references of French writers on the West Indies to an Herbe aux flèches, which plant it is impossible to identify with Maranta, we find in Sloane’s catalogue of Jamaica plants (1696), Canna Indica radice alba alexipharmaca. This plant, discovered in Dominica, was sent thence to Barbadoes and subsequently to Jamaica, it being, says Sloane, “very much esteemed for its alexipharmack qualities.” It was observed, he adds, that the native Indians used the root of the plant with success against the poison of their arrows, “by only mashing and applying it to the poison’d wounds”: and further, that it cures the poison of the manchineel (Hippomane Mancinella L.), of the wasps of Guadaloupe, and even stops “a begun gangreen.”[2332]
Patrick Browne (1756) notices the reputed alexipharmic virtues of Maranta, which was then cultivated in many gardens in Jamaica, and says that the root “washed, pounded fine and bleached, makes a fine flour and starch”—sometimes used as food when provisions are scarce.[2333]
Hughes, when writing of Barbadoes in 1750, describes arrowroot as a very useful plant, the juice mixed with water and drunk being regarded as “a preservative against any poison of an hot nature”; while from the root the finest starch is made, far excelling that of wheat.[2334] The properties of Maranta arundinacea as a counter-poison are insisted upon at some length by Lunan,[2335] who concludes his notice of the plant by detailing the process for extracting starch from the rhizome.
Arrowroot came into use in England about the commencement of the present century, the supplies being obtained, as it would appear, from Jamaica.[2336]
The statements of Sloane, which are confirmed by Browne and Lunan, plainly indicate the origin and meaning of the word arrowroot, and disprove the notion of the learned C. F. Ph. von Martius (1867) that the name is derived from that of the Arnac or Aroaquis Indians of South America, who call the finest sort of fecula they obtain from the Mandioc Aru-aru. It is true that Maranta arundinacea is known at the present day in Brazil as Araruta, but the name is certainly a corruption of the English word arrowroot, the plant according to general report having been introduced.[2337]
Manufacture—For the production of arrowroot, the rhizomes are dug up after the plant has attained its complete maturity, which in Georgia is at the beginning of winter. The scales which cover them are removed and the rhizomes washed; the latter are then ground in a mill, and the pulp is washed on sieves, or in washing machines constructed for the purpose, in order to remove from it the starch. This is allowed to settle down in pure water, is then drained and finally dried with a gentle heat. Instead of being crushed in a mill, the rhizomes are sometimes grated to a pulp by a rasping machine.
In all stages of the process for making arrowroot, nice precautions have to be taken to avoid contamination with dust, iron mould, insects, or anything which can impart colour or taste to the product. The rhizome contains about 68 per cent. of water, and yields about a fifth of its weight of starch.[2338]
Description—Arrowroot is a brilliant white, insipid, inodorous, powder, more or less aggregated into lumps which seldom exceed a pea in size; when pressed it emits a slight crackling sound. It exhibits the general properties of starch, consisting entirely of granules which are subspherical, or broadly and irregularly egg-shaped; when seen in water they show a distinct stratification in the form of fine concentric rings around a small star-like hilum. They have a diameter of 5 to 7 mkm. when observed in the air or under benzol. If the water in which they lie be cautiously heated on the object-stage of the microscope, the tumefaction of the granules will be found to begin exactly at 70° C. Heated to 100° C. with 20 parts of distilled water, arrowroot yields a semi-transparent jelly of somewhat earthy taste and smell. By hydrochloric acid of sp. gr. 1·06, arrowroot is but imperfectly dissolved at 40° C.
The specific gravity of all varieties of starch is affected by the water which they retain at the ordinary temperature of the air. Arrowroot after prolonged exposure to an atmosphere of average moisture, and then kept at 100° C. till its weight was constant, was found to have lost 13·3 per cent. of water. On subsequent exposure to the air, it regained its former proportion of water.
Weighed in any liquid which is entirely devoid of action on starch, as petroleum or benzol, the sp. gr. of arrowroot was found by one of us to be 1·504; but 1·565 when the powder had been previously dried at 100° C.
Microscopic Structure of Arrowroot and of Starch in general—The granules are built up of layers,—a structure which may be rendered evident by the gradual action of chloride of calcium, chromic acid, or an ammoniacal solution of cupric oxide. When one of these liquids in a proper state of dilution is made to act upon starch, or when for that purpose a liquid is chosen which does not act upon it energetically, such as diastase, bile, pepsin, or saliva, it is easy to obtain a residue, which according to Nägeli, is no longer capable of swelling up in boiling water, nor is immediately turned blue by iodine, except on the addition of sulphuric acid; but which is dissolved by ammoniacal cupric oxide. These are the essential properties of cellulose; and this residue has been regarded as such by Nägeli, while the dissolved portion has been distinguished as Granulose (Maschke, 1852).
C. Nägeli in his important monograph on starch[2339] has described the action of saliva when digested with starch for a day, at a temperature of 40° to 47° C.; he says that the residue is a skeleton, corresponding in form to the original grain but somewhat smaller, light, and very mobile in water. He concludes that its interstitial spaces must have been previously filled with granulose.
This experiment, which has been repeated by one of us (F.), does not in our opinion warrant all the inferences that Nägeli has drawn from it: it is true that many separate parts of the grain are dissolved by the saliva, while others have disappeared down to a mere film, and others again have been attacked in a very irregular manner. But we cannot agree with the statement that anything comparable to a skeleton of the grain has been left. After longer action at a higher temperature, which however must not exceed 65° C., a more copious dissolution of the starch, either by saliva or by bile, takes place; but in no case is it complete.[2340]
Chemistry of Starch—Its composition answers to the formula (C₆H₁₀O₅)₂+3 OH₂, or when dried at 100° C., C₆H₁₀O₅. Musculus however showed, in 1861, that by the action of dilute acids or of Diastase, starch is resolved into Dextrin, C₁₂H₂₀O₁₀, and Dextrose, C₆H₁₂O₆, with which decomposition, the formula, C₁₈H₃₀O₁₅, would be more in accord. Sachsse (1877) on the other hand advocates the formula C₃₀H₆₂O₃₁ + 12 OH₂.
Cold water is not without action on starch; if the latter be continuously triturated with it, the filtrate, in which no particles can be detected by the microscope, will assume a blue colour on addition of iodine, without the formation of a precipitate. The proportion of starch thus brought into solution is infinitely small, and always at the expense of the integrity of the grains. It is even probable that the solution in this case is due to the minute amount of heat, which must of necessity be developed by the trituration.
Certain reagents capable of attacking starch act upon it in very different ways. The action in the cold of concentrated aqueous solutions of easily soluble neutral salts or of chloral hydrate is remarkable. Potassium bromide or iodide, or calcium chloride for instance, cause the grains to swell, and render them soluble in cold water. At a certain degree of dilution a perfectly clear liquid is formed, which at first contains neither dextrin nor sugar; it is coloured blue, but is not precipitated by iodine water; and starch can be thrown down from it by alcohol. This precipitate, though entirely devoid of the structural peculiarity of starch, still exhibits some of the leading properties of that substance; it is coloured in the same manner by iodine, does not dissolve even when fresh in ammoniacal cupric oxide, and after drying is insoluble in water, whether cold or boiling. The progress of the solvent is most easily traced when calcium chloride is used, as this salt acts more slowly than the others we have mentioned. It leaves scarcely any perceptible residue. This fact in our opinion militates against the notion that starch is composed of a peculiar amylaceous substance, deposited within a skeleton of cellulose.
The remarkable action of iodine upon starch was discovered in 1814 by Colin and Gaultier de Claubry. It is extremely different in degree, according to the peculiar kind of starch, the proportion of iodine, and the nature of the substance the grains are impregnated with, before or after their treatment with iodine. The action is even entirely arrested (no blue colour being produced) by the presence in certain proportion of quinine, tannin, Aqua Picis, and of other bodies.
The combination of iodine with starch does not take place in equivalent proportions, and is moreover easily overcome by heat. The iodine combined with starch amounts at the utmost to 7·5 per cent. The compound is most readily formed in the presence of water, and then produces a deep indigo-blue. Almost all other substances capable of penetrating starch grains, weaken the colour of the iodine compound to violet, reddish yellow, yellow, or greenish blue. These different shades, the production of which has been described by Nägeli with great diffuseness, are merely the colours which belong to iodine itself in the solid, liquid, or gaseous form. They must be referred to the fact that the particles of iodine diffuse themselves in a peculiar but hitherto unexplained manner within the grain or in the swollen and dissolved starch.
Commerce of Arrowroot—The chief kinds of arrowroot found in commerce are known as Bermuda, St. Vincent, and Natal; but that of Jamaica and other West India Islands, of Brazil, Sierra Leone, and the East Indies, are quoted in price-currents, at least occasionally. Of these the Bermuda enjoys the highest reputation and commands by far the highest price; but its good quality is shared by the arrowroot of other localities, from which, when equally pure, it can in nowise be distinguished. Greenish,[2341] however, points out that in Natal arrowroot the layers (or laminæ) are more obvious than in other varieties, although it appears that the former is also produced by Maranta.
The importations of arrowroot into the United Kingdom during the year 1870 amounted to 21,770 cwt., value £33,063. Of this quantity the island of St. Vincent in the West Indies furnished nearly 17,000 cwt., and the colony of Natal about 3000 cwt. The exports from St. Vincent in 1874 were 2,608,100 lb, those of the Bermudas in 1876 only 45,520 lb.[2342] The shipments from the colony of Natal during the years 1866 to 1876 varied from 1,076 cwt. in 1873 to 4,305 cwt. in 1867.[2343]
Uses—Arrowroot boiled with water or milk is a much-valued food in the sick-room. It is also an agreeable article of diet in the form of pudding or blancmange.
Adulteration—Other starches than that of Maranta are occasionally sold under the name of Arrowroot. Their recognition is only possible by the aid of the microscope.
Substitutes for Arrowroot.
Potato Starch—This substance, known in trade as Farina or Potato Flour, is made from the tubers of the potato (Solanum tuberosum L.) by a process analogous to that followed in the preparation of arrowroot. It has the following characters:—examined under the microscope, the granules are seen to be chiefly of two sorts, the first small and spherical, the second of much larger size, often 100 mkm. in length, having an irregularly circular, oval or egg-shaped outline, finely marked with concentric rings round a minute inconspicuous hilum. When heated in water, the grains swell considerably even at 60° C. Hydrochloric acid, sp. gr. 1·06, dissolves them at 40° quickly and almost completely, the granules being no longer deposited, as in the case of arrowroot similarly treated. The mixture of arrowroot and hydrochloric acid is inodorous, but that of potato starch has a peculiar though not powerful odour.
Canna Starch, Tous-les-Mois,[2344] Toulema, Tolomane—A species of Canna is cultivated in the West India Islands, especially St. Kitts, for the sake of a peculiar starch which, since about the year 1836, has been extracted from its rhizomes by a process similar to that adopted in making arrowroot. The specific name of the plant is still undetermined; it is said to agree with Canna edulis Ker (C. indica Ruiz et Pavon).[2345]
The starch, which bears the same name as the plant, is a dull white powder, having a peculiar satiny or lustrous aspect, by reason of the extraordinary magnitude of the starch granules of which it is composed. These granules examined under the microscope are seen to be flattened and of irregular form, as circular, oval, oblong, or oval-truncate. The centre of the numerous concentric rings with which each granule is marked, is usually at one end rather than in the centre of a granule. The hilum is inconspicuous. The granules though far larger than those of the potato, are of the same density as the smaller forms of that starch, and, like them, float perfectly on chloroform. When heated, they begin to burst at 72° C. Dilute hydrochloric acid acts upon them as it does on arrowroot.
Canna starch boiled with 20 times its weight of water affords a jelly less clear and more tenacious than that of arrowroot, yet applicable to exactly the same purposes. The starch is but little known and not much esteemed in Europe; it was exported in 1876 from St. Kitts to the amount of 51,873 lb, besides 5,300 lb arrowroot starch.[2346]
Curcuma Starch, Tikor—The pendulous, colourless tubers of some species of Curcuma, but especially of C. angustifolia Roxb. and C. leucorrhiza Roxb., have long been utilized in Southern India for the preparation of a sort of arrowroot, known by the Hindustani name of Tikor, or Tikhur, and sometimes called by Europeans East Indian Arrowroot.[2347] The granules of this substance much resemble those of Maranta, but they are neither spherical nor egg-shaped. On the contrary, they are rather to be described as flat discs, 5 to 7 mkm. thick, of elliptic or ovoid outline, sometimes truncate; many attain a length of 60 to 70 mkm. They are always beautifully stratified both on the face and on the edge. The hilum is generally situated at the narrower end. We have observed that when heated in water, the tumefaction of the grains commences at 72° C.
Curcuma starch, which in its general properties agrees with common arrowroot, is rather extensively manufactured in Travancore, Cochin and Canara on the south-western coast of India, but in a very rude manner. Drury[2348] states that it is a favourite article of diet among the natives, and that it is exported from Travancore and Madras; we can add that it is not known as a special kind in the English market, and that the article we have seen offered in the London drug sales as East Indian Arrowroot was the starch of Maranta.