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Chapter: Pharmacognosy and Phytochemistry : Enzymes and Protein Drugs

Papain is the dried and purified latex of the green fruits and leaves of Carica papaya L., belonging to family Caricaceae.






Papayotin, vegetable pepsin, tromasin, arbuz.


Biological Source


Papain is the dried and purified latex of the green fruits and leaves of Carica papaya L., belonging to family Caricaceae.


The plant is cultivated in Sri Lanka, Tanzania, Hawai, and Florida. The plant is 5–6 m in height bearing fruits of about 30 cm length and a weight up to 5 kg. The epicarp adheres to the orange-coloured, fleshy sarcocarp, which surrounds the central cavity. This cavity contains a mass of nearly black seeds.




It is distributed throughout the plant, but mostly concentrated in the latex of the fruit.


The latex is obtained by making two to four longitudinal incisions, about 1/8 inch deep, on the surface on four sides of nearly mature but green fruits while still on the tree. The incisions are made early in the morning, at intervals of three to seven days. The latex flows freely for a few seconds but soon coagulates. The exudate is collected in nonmetallic containers. The latex is dried as soon as possible after collection. Rapid drying or exposure to sun or higher temperature above 38°C produce dark colour product with weak in proteolytic activity. The use of artificial heat yields the better grade of crude papain. The final product should be creamy white and friable. It is sealed in air-tight containers to prevent loss of activity. If 10% common salt or 1% solution of formaldehyde is added before drying, the product retains its activity for many months.


Fully grown fruits give more latex of high enzyme potency than smaller or immature fruits. The yield of Papain varies from 20 to 250 g per tree. The yield of commercial Papain from latex is about 20%.



Papain occurs as white or greyish-white, slightly hygroscopic powder. It is incompletely soluble in water and glycerol. It may digest about 35 times its weight of lean meat. Best grades render digestion of 200–300 times their weight of coagulated egg albumin in alkaline media. A temperature range of 60–90°C is favourable for the digestive process with 65° the optimum point. Best pH is 5.0, but it functions also in neutral or alkaline media. It is activated by reduction (HCN and H2S) and inactivated by oxidation (H2O2, iodoacetate).


Chemical Constituents


Papain contains several enzymes such as proteolytic enzymes peptidase I capable of converting proteins into dipeptides and polypeptides, rennin-like enzyme, clotting enzyme similar to pectase and an enzyme having a feeble activity on fats.


The enzymes, papain, papayaproteinase, and chymopapain, have been isolated in crystalline form from the latex. Papain is atypical protein digesting enzyme with isoelectric point. It contains 15.5% nitrogen and 1.2% sulphur. Crystalline papain is most stable in the pH range 5–7 and is rapidly destroyed at 30°C below pH 2.5 and above pH 12. Papain is a protein of 212 amino acids and having a molecular weight of about 23,000 daltons. It is resistant to heat, inactivated by metal ions, oxidants and reagents which react with thiols, and is an endopeptidase activated by thiols and reducing moieties, for example, cysteine, thiosulphate, and glutathione.


The leaves possess dehydrocarpaines I and II, fatty acids, carpaine, pseudocarpaine, and carotenoids.


The fruits yield lauric, myristoleic, palmitoleic and arachidic acids, malonated benzyl-p-o-glucosides, 2-phenyl ethyl glucoside, and 4-hydroxy-phenyl-2-ethyl glucoside.




Papain is used to prevent adhesions; in infected wounds; internally as protein digestant, as anathematic (nematode), to relieve the symptoms of episiotomy (incision of vulva), in meat industry for tenderizing beef, for treatment of dyspepsia, intestinal and gastric disorders, and diphtheria, for dissolving diphtheria membrane; in surgery to reduce incidence of blood clots where thromboplasma is undesirable and for local treatment of buccal, pharyngeal, and laryngeal disorders.


It is used in digestive mixtures, liver tonics, for reducing enlarged tonsils, in prevention of postoperative adhesions, curbuncles, and eschar burns. It is an allergic agent causing severe paroxysmal cough, vasomotor rhinitis and dyspnea. It is a powerful poison when injected intravenously. In industry it is used in the manufacture of proteolytic preparations of meat, lever, and casein, with dilute alcohol and lactic acid as meat tenderizer, as a substitute for rennet in cheese manufacture, in brewing industry for making chill-proof bear, for degumming natural milk, in preparation of tooth pastes and cosmetics, in tanning industry for bathing skin and hides, and as an ingredient in cleansing solutions for soft contact lenses.




Papain is reacted with a gelatin solution at 80°C in the presence of an activating cysteine chloral hydrate solution for an hour. The solution is cooled to 4°C for long time. The treated solution must not regel in comparison to a blank solution under identical con-ditions.




Commercial papain is often adulterated with arrowroot starch, dried milk of cactus, gutta percha, rice flour, and pepsin.


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