Synonyms: Aloe, Musabbar, Kumari.
Biological source: Aloes are the dried juice obtained by transversely cut leaves of various species of Aloe barbedensis Miller (known as Curacao aloes), Aloe perryi Baker (Socotrine aloes), Aloe spicata Baker, and Aloe Africana Miller (Cape aloes).
Aloe is an example of anthraquinone glycoside.
Geographical source: It is indigenous to eastern and southern Africa and cultivated for commercial purposes in West Indian islands off the north coast of South America.
Cultivation and collection of Aloe
The root suckers are planted at a 50 cm distance to get better growth. The aloe plant can grow in low-grade soil and even in a dry climate. Water-logging should be avoided to obtain better mucilage content. For the manuring purpose, a mixture of nitrogen, potassium, and phosphorous is used. The drug is collected from a two-year-old plant and the collection continued up to twelve years old plant. After twelve years, the plants are uprooted and replantation occurs. An incision is made near the leaves base to draw all the juice from the pericyclic cells of leaves.
Various types of Aloe
1. Preparation of Curacao aloes: The transverse incision made near the base of fleshy leaves (Aloe barbedensis). The cut leaves are kept on the sides of V-shaped wooden troughs. The cutted spiny leaves are put into kerosene tins immediately and kept in a tilted position in wooden troughs to drain out all the juicy material. The juicy material boiled in copper vessels. The juice gets thickened by the evaporation of latex. The thickened juice is poured into metal containers to become harden. Then it is marketed under the name of Curacao aloes. It is mainly prepared in the islands of Aruba and Bonaire in the West Indies.
2. Preparation of Socotrine aloes: This type of aloe is marketed in semi-solid form. It is prepared on the island of Socotra and the mainland of East Africa. In this method, the juice of leaves gets collected in goat skin and allows solidifying in semi-solid form.
3. Preparation of Cape aloes: This type of aloe is mainly prepared in South Africa. For the collection of juice, a pit is a dugout that is lined by goat skin. The transversely incised leaves are arranged circularly, to overlap the cut ends, for 5-6 hours till all the juicy material comes out and is collected in goat skin. Then collected juicy material is boiled and stirred continuously in a large iron vessel. When the boiling juice gets the desired consistency, it is poured into wooden moulds to solidify and marketed under the name of Cape aloes.
Description of Aloe
- Curacao aloes of good quality vary in colour from yellowish or reddish-brown to chocolate brown, lower grades are black and burnt. It has an intensely bitter taste, strong penetrating odour like iodoform and has a density of about 1.33.
- Socotrine aloes are opaque, pasty or semisolid, having a brownish yellow colour. It separates on standing into clear, dark brown, supernatant liquid and dark yellow sediment which shows minute crystals of aloin under a microscope.
- Cape aloes are dark reddish-brown or black and breaks with a clean glassy fracture. It shows no crystals under a microscope. The splinters are thin, transparent, reddish-brown or yellow coloured. It has a sour distinct odour and nauseating bitter taste.
Chemical Constituent of Aloe
Aloe is the main source of glycosides i.e. anthraquinone glycosides. The chief constituent of all the varieties of aloes is aloin which mainly contains barbaloin (a pale yellow, crystalline substance). Other constituents are resin and aloe-emodin, which is a hydrolytic decomposition product of barbaloin. It occurs in a small proportion.
Curacao aloes contain barbaloin with isomeric and crystalline isobarbaloin, barbal-oresinotannol combined with cinnamic acid whereas Socotrine aloes contain no isobarbaloin and cape aloes contain in trace amount. Cape aloes consist of capaloresinotannol combined with paracumaric acid.
Other constituents of this drug are aloetic acid, aloes one, choline, choline salicylate, chrysophanic acid, chrysamminic acid, homonataloin, galacturonic acid, mucopolysaccharides, glucosamine, saponins and coniferyl alcohol etc.
Preparation of Aloin
For the preparation of aloin, Curacao aloes are dissolved in boiling water, acidified with sulphuric acid, a precipitate of resinous matter obtain, cool and filter. Then neutralise the filtrate and evaporate under reduced pressure. The weight of the liquid will be twice that of the aloes used. Add a few crystals of aloin, cool and keep aside for crystallisation, filter it and wash it with dilute alcohol. Then recrystallise the aloin from dilute alcohol. The final yield is about 10-20 percent of the weight of the aloes used.
Commercially, Aloin occurs in two varieties a) crystalline and b) amorphous. Research shows that the amorphous aloin has less cathartic property than crystalline aloin (about one third less potency).
Chemical Test of Aloe
- Borax test: Aloe solution in boiling water (1%), cool it and add kiesselguhr to clear it. Take 10 ml clear filtrate, add 0.25gm borax and heat it till it dissolves. Then pour some dark fluid into the water till green fluorescence is produced. The green fluorescence is formed due to the hydrolysis of barbaloin which produces aloe emodinanthranol.
- Bromine test: To some clear solution of aloes, as prepared earlier, add freshly prepared saturated bromine solution. A yellow precipitate observes due to the formation of tetrabromaloin.
- Nitric acid test: To 5 ml of 1% clarified solution add 2 ml nitric acid. A vivid green colour is produced (in Cape aloes), a deep brownish-red colour develops (in Curacao aloes) or pale brownish yellow colour is seen (in Socotrine aloes).
Uses of Aloe
All the varieties of aloes have more or less purgative action. It improves digestion and does not lose its activity by repetition. It mainly affects on colon and has much potent purgative activity than other anthraquinone glycosidal drugs.
Aloe gel is used in topical preparations and cosmetics. It possesses good moisturising property, anti-inflammatory property, anti-wrinkle property, protective etc. The fresh gel has a role in burns and wounds.
Substitutes and Adulterant
Natal aloes- Natal aloes are opaque, dull greenish-black or dull brown colour and have characteristic odour resembles with cape aloes. Natal aloes are weak purgative.
Mocha aloes: It is black in colour, strong odour, brittle and inferior drug.
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