Aloe

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Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Glycosides

Aloe is the dried juice collected by incision, from the bases of the leaves of various species of Aloe. Aloe perryi Baker, Aloe vera Linn or Aloe barbadensis Mil and Aloe ferox Miller., belonging to family Liliaceae.


ALOE

 

 

Biological Source

 

Aloe is the dried juice collected by incision, from the bases of the leaves of various species of Aloe. Aloe perryi Baker, Aloe vera Linn or Aloe barbadensis Mil and Aloe ferox Miller., belonging to family Liliaceae.

Aloe perryi Baker is found in Socotra and Zanzibar islands and in their neighbouring areas and so the aloes obtained from this species is known as Socotrine or Zanzibar aloe. Aloe vera Linn is also known as Aloe vulgairis Lamarek, or Aloe barbadensis Mil. or Aloe officinalis Forskal. It was formerly produced on the island of Barbados, where it was largely cultivated, having been introduced at the beginning of the sixteenth century. It is now almost entirely made on the Dutch islands of Curacoa, Aruba and Bonaire. The aloes obtained from this species is known as Curacao or Barbados aloe. Aloe ferox Miller and hybrids of this species with Aloe africana and Aloe spicata, A. platylepia and other species of Aloe grows in Cape Colony and so is known as Cape aloe.

 

Geographical Source

 

Aloes are indigenous to East and South Africa, but have been introduced into the West Indies and into tropical countries, and will even flourish in the countries bordering on the Mediterranean.

 

Cultivation and Collection

 

It is an evergreen perennial growing to 0.8 m by 1 m at a slow rate. The plant prefers light (sandy) and medium (loamy) soils, requires well-drained soil and can grow in nutritionally poor soil. The plant prefers acid, neutral and basic (alkaline) soils. It cannot grow in the shade. It requires dry or moist soil and can tolerate drought. They are xerophytic plant. It can be propagated by seeds. Seeds are sown in the spring in a warm green house. The seed usually germinates in 1–6 months at 16°C. The seedlings are transferred to the pots containing well-drained soil. They are allowed to grow in sunny part for at least their first two winters. The offsets will be available, usually in spring. The plants produce offsets quite freely and they can be divided at any time of the year as long as it is warm enough to encourage fresh root growth to allow reestablishment of the plants. Young offsets are planted in the soil after the rainy season in rows situated at a distance of 60 cm.

 

In the second year leaves are collected by the natives by protecting their hands because of the spiny nature of leaves. The leaves are cut near the base, kept inside of kerosene tins and taken them to a central place for the preparation of aloe. Juice of aloe is present in parenchymatous cells of pericycle that are mucilage cells. In a single incision mucilage cells exert pressure on pericycle cells and the entire juice from the leaves is drained out.

 

Preparation of Aloe

 

Curacao or barbados aloe

 

In West Indies the cut leaves are arranged with their cut surface on the inner side, on the sides of V shaped vessel of about 1–2 m long and the flowing juice is collected in a tin vessel that is placed below the V-shaped vessel This juice thus collected is concentrated either by spontaneous evaporation, or more generally by boiling until it becomes of the consistency of thick honey. These conditions favours the crystallization of barbaloin and this aloe contains crystals of barbaloin because of the presence of which it becomes opaque and so also known as hepatic or livery aloe. On cooling, it is then poured into gourds, boxes, or other convenient receptacles and solidifies.

 

Socotrine aloe

 

When it is prepared, it is commonly poured into goat skins, and spontaneous evaporation is allowed for about a month when it becomes viscous pasty mass which are then packed into cases. In European countries it is dried in wooden pans with hot air till moisture is about 10%.

 

Zanzibar aloe

 

This aloe is prepared similar to Socotrine aloe. It is packed in skins, of carnivorous animals. This aloe is also known as monkey skin aloe.

 

Cape aloe

 

The leaves of the plants from which Cape aloe is obtained are cut off near the stem and arranged around a hole in the ground, in which a sheep skin is spread, with smooth side upwards. When a sufficient quantity of juice has drained from the leaves it is concentrated by heat in iron cauldrons and subsequently poured into boxes or skins in which it solidifies on cooling. Large quantities of the drug are .exported from Cape Town and Mossel Bay.

 

Characteristics

 

Curacao aloe

 

It is usually opaque and varies in colour from bright yellow-ish or rich reddish brown to black. Sometimes it is vitreous and small fragments are then of a deep garnet-red colour and transparent. It is then known as ‘Capey Barbados’ and is less valuable, but may become opaque and more valuable by keeping. Curacoa Aloes possesses the nauseous and bitter taste that is characteristic of all Aloes and a disagreeable, penetrating odour. It is almost entirely soluble in 60% alcohol and contains not more than 30% of substances insoluble in water and 12% of moisture. It should not yield more than 3% of ash. The fracture is waxy.

 


                                              Aloe vera  


Socotrine aloes

 

It may be distinguished principally from Curacoa Aloes by its different odour. Much of the dry drug is characterized by the presence of small cavities in the fractured surface; it is yellow-brown to dark-brown in colour and opaque. Fracture is irregular and porous and taste is bitter.

 

Zanziber aloes

 

Zanzibar Aloes often very closely resembles Curacoa in appearance and is usually imported in liver-brown masses which break with a dull, waxy fracture, differing from that of Socotrine Aloes in being nearly smooth and even. It has a pleasant odour and bitter taste.

 

Cape aloes

 

It forms dark coloured masses which break with a clean glassy fracture and exhibit in their splinters a yellowish, reddish-brown or greenish tinge. Its translucent and glossy appearance are very characteristic and red-currant like odour sufficiently distinguish it from all other varieties of Aloes.

 

Chemical Constituents

 

The most important constituents of Aloes are the three isomers of Aloins, Barbaloin, β-barboloin and Isobarbaloin, which constitute the so-called ‘crystalline’ Aloin, present in the drug at from 10 to 30%. Other constituents are amor-phous Aloin, resin, emodin and Aloe-emodin. Barbaloin is present in all the varieties; it is slightly yellow coloured, bitter, water soluble, crystalline glycoside. Isobarbaloin is a crystalline substance, present in Curacao aloe and in trace amount in Cape aloe and absent in Socotrine and Zanzibar aloe. The chief constituents of Socotrine and Zanzibar aloe are Barbaloin and β-Barbaloin.

 


 

Chemical Tests

 

Boil 1 gm of drug with 100 ml water, allow it to cool; add 1 gm kieselguhr, stir it well and filter through filter paper.


1.     Borax Test: Take 10 ml of aloe solution and to it add 0.5 gm of borax and heat; a green coloured fluorescence is produced indicating the presence of aloe-emodin anthranol.

2.     Modified Anthraquinone Test: To 0.1 gm of drug, 5 ml of 5% solution of ferric chloride is added followed by the addition of 5 ml dilute hydrochloric acid. The mixture is heated on water bath for 5–6 min and cooled. An organic solvent (benzene or chloroform) is added and shaken. Separate the organic solvent layer and add an equal volume of dilute ammonia. The ammoniacal layer produces pinkish red colour.

 

3.     Bromine Test: To 5 ml of aloe solution, add equal volume of bromine solution; bulky yellow precipitate is formed due to the presence of tetrabromaloin.

 

4.     Nitrous Acid Test: To 5 ml of aloe solution, add little of sodium nitrite and few drops of dilute acetic acid; it produces Pink or purplish colour. Zanzibar and Socotrine aloes give negative test.

 

5.     Nitric Acid Test: 2 ml of concentrated nitric acid is added to 5 ml of aloe solution; Curacao aloe gives deep reddish-brown colour, Socotrine aloe gives pale yellowish-brown colour, Zanzibar aloe gives yellowish-brown colour and Cape aloe first produces brown colour which on standing changes to green.

 

6. Cupraloin Test: 1 ml of the aloe solution is diluted to 5 ml with water and to it 1 drop of copper sulphate solution is added. Bright yellow colour is produced which on addition of 10 drops of saturated solution of sodium chloride changes to purple and the colour persist if 15–20 drops of 90% alcohol is added. This test is positive for Curocao aloe, faint for Cape aloe and negative for Zanzibar and Socotrine aloes.


Uses

 

The drug Aloes is one of the safest and stimulating purga-tives, in higher doses may act as abortifacient. Its action is exerted mainly on the large intestine; also it is useful as a vermifuge. The plant is emmenagogue, emollient, stimu-lant, stomachic, tonic and vulnerary. Extracts of the plant have antibacterial activity. The clear gel of the leaf makes an excellent treatment for wounds, burns and other skin disorders, placing a protective coat over the affected area, speeding up the rate of healing and reducing the risk of infection. To obtain this gel, the leaves can be cut in half along their length and the inner pulp rubbed over the affected area of skin. This has an immediate soothing effect on all sorts of burns and other skin problems.

 

Substituents and Adulterants

 

A. candelsbmm (Natal aloes) is dull greenish black to dull brown in colour, opaque. When scraped it gives a pale greyish green or a yellow powder. It can be distinguished as it gives negative test to borax test and produces a deep blue colour. Jafferabad aloes and the Mocha aloes are the other two type of aloe which is used as adulterant.

 

Marketed Products

 

It is one of the ingredients of the preparations known as Diabecon, Evecare (Himalaya Drug Company), Mensonorm (Chirayu Pharma) and Kumari Asava (Baidyanath).

 

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