Papaya. Melon tree, Papaw. Carica papaya.
Papaya. Melon Tree. Papaw.—The Carica Papaya L. (Fam. Caricaceae) is a shrub, everywhere cultivated in tropical countries for the sake of its fruit. The ovoid fruit sometimes attains a length of 30 cm. and weight 4 or 5 K. According to Peckholdt (P. J., Nov., 1879), the milky juice is contained in all parts of the tree, but in such small quantity, save in the unripe fruit, that it is always procured from the latter. One fruit will yield about 33 Gm., which is obtained by scratching through the skin in various places; the process does not interfere with the ripening of the fruit, but it is said that the seeds will not germinate. The milk has an acid reaction, an astringent bitterish taste, and a sp. gr. of 1.023. Upon standing for a few minutes it separates into two parts, an aqueous liquid and a white, somewhat coagulated pulpy mass. In the aqueous portion is an albuminous substance, possessed of enzymic properties, to which the names of papain and papayotin have been given. According to the researches of S. H. C. Martin, papaw juice contains besides papain, a milk-curdling ferment and globulin, albumin, and two phytalbumoses. No peptones occur in the juice, but leucine and tyrosine are present. (J. Chem. S., 1886, 642; see also P. J., 1885, 129.) In a representative preparation the ferment action seems to be most marked when all the proteids are associated together in the natural form. In its action upon albumin the enzyme of the papaw produces products which have a close relation to those produced by tryptic and peptic digestion. In the action of the papaw ferments on milk there is first curdling, in which the casein is separated into a soft flocculent precipitate, and afterwards a digestion of the proteids, during which process they are converted into soluble and diffusible products. The amount of starch-converting ferment is not large, but sufficient in the fresh latex to promptly act upon starch paste, thinning it, and converting a portion at least into soluble starch and dextrin. The import of the rennet ferment and the pectase probably present require further investigation.
According to Wlurtz, fibrin is dissolved whether the solvent solution be alkaline or acid. Brunton and Wyatt and also Martin affirm, however, that one-half per cent. of hydrochloric acid will prevent digestion, but Albrecht reasserts that hydrochloric acid hastens the action of the ferment, and states that the official preparation in use in Paris hospitals is an acid one. In order entirely to convert fibrin into pure peptone so that nitric acid will produce no precipitate, the proportion of the ferment should be as great as 3 per cent., and digestion must continue for forty-eight hours at 50° C. (122° F.).
Papaya juice has a tendency to spoil by undergoing a butyric fermentation, but Wurtz found that the addition to it of glycerin preserved it without interfering with its digestive power. Imported in this form, it was a thick, milky liquid. As it now occurs in commerce, papain is a grayish, fine powder, which in appearance, odor, and taste strongly suggests pepsin.
The seeds of the papaw tree contain a glucoside, caricin, which resembles sinigrin. These seeds also contain the ferment, myrosin, and by the reaction of the two a volatile pungent body is produced, suggestive of oil of mustard in odor. An alkaloid, carpaine, C14H25O2N, has been obtained from the leaves. Physiologically, this alkaloid has the effect of a heart stimulant, quite similar to that of digitalis. (A. J. P., July and August, 1901, 336-48 and 383.)
Under the name of papayotin, papain, or papoid, the dried juice of the Carica Papaya is put upon the market. It is frequently adulterated with starch, which is not naturally present in the fruit. Its digestive power is far below the claims formerly made for it. It is asserted for it that, when the stomach is acid, it is much superior to pancreatin, because its action is not markedly affected by contact with the acid. In experiments made by H. C. Wood with a papoid from one of the most renowned manufacturers no digestion occurred, and it is probable that much of the article of commerce is inert. It has been used as an internal medicine in dyspepsia and gastric catarrh, and as a local application for the destruction of false membranes, warts, tubercles, walls of old sinuses, and even of epithelioma. (See Branch, B. M. J., 1907.) It is not caustic nor astringent, but destroys the part by virtue of its power of dissolving not only muscular but connective tissue. Jacobi affirms (T. G., vol. ii) that diphtheritic membranes are dissolved in a few hours by the hourly application of a mixture of one part of papain with two parts each of water and of glycerin. It is stated that from time immemorial the fresh leaves of the papaya plant have been used by the Indians to wrap meat in to make it tender, and as a dressing to foul wounds. Peckoldt says that, taken internally, the juice is reputed to cause intestinal inflammation. No recent observers have noted such influence. According to Brunton, the dose is from five to ten grains (0.32-0.65 Gm.). Injected into the venous circulation it acts as a powerful poison, of which a single grain is sufficient to kill a rabbit.