2.1.1 Aloes
Synonym: Aloe
Biological Source: Aloe is the dried latex of leaves of various species of Aloes, namely:
Aloe barbadensis Miller (or Curacao Aloe);
Aloe ferox Miller (or Cape Aloe);
Aloe perryi Baker (or Socotrine Aloe);
Aloe africana Miller and Aloe spicata Baker (or Cape Aloe).
All these species belong to the family Liliaceae.
Geographical Source
Curacao, Barbados, Aruba : Curacao Aloes or Barbados Aloes and Bonaire (West Indian Islands)
Cape Town (South Africa) : Cape Aloes
Socotra and Zanzibar Islands : Socotrine or Zanzibar Aloes
It is also cultivated in Europe and the North West Himmalayan region in India.
Preparation
General Method The leaves are transversely cut at the base and the incised ends placed downwards in a ‘V’ shaped trough having a hole at its bottom. The latex drains down the trough and is collected in individual receptacles placed beneath. The latex is evaporated in a kettle made of copper till it attains such a consistency that it may be poured into metallic ingots where it gets solidified. When the latex is concentrated gradually and then cooled slowely, it gives rise to an opaque product. The aloe thus obtained is termed as ‘hepatic’ or ‘livery’ aloe. If the latex is concentrated rapidly, followed
by sudden cooling the resulting product appears to be transparent and relatively brittle in nature. The broken surface has a vitreous or glassy surface. Such a product is commonly known as ‘vitreous’, ‘lucid’ or ‘glassy’ aloe.
Description
Chemical Constituents Aloe-emodin occurs in the free state and as a glycosides in various species of Aloe and also in Rheum (Rhubrb). Curaeao aloes contains about two and half times the amount of aloe emodin when compared to cape-aloes.
Interestingly, the glycosides of anthranols, dianthrones, and oxanthrones i.e., the reduced
derivatives of anthraquinones, invariably found in various plant substances. These plant products do make an appreciable contribution to the inherent therapeutic values of the naturally occurring substances. The structural relationships of emodin are represented as shown in Figure 4.3.
Both anthrones and anthranols mostly occur either as free or combined as glycosides. From a close look at their respective structures it may be observed that they are reduced anthraquinone derivatives. Both anthrone and anthranol are isomeric in nature; however, the latter may be partially converted to the former, which is essentially a non-fluorecent substance and is not soluble in alkaline solutions. Generally, the anthrones are converted on oxidation into their corresponding anthraquinones, namely: oxanthrone and dianthrone. Hence, it has been observed that prompt oxidation usually takes place in the powdered crude drug rather than the rhizomes itself.
Besides, aloin (or barbaloin) the aloes also contain isobarbaloin (Curacao aloes), β-barbaloin) = (Cape aloes), aloe emodin and resins. The principal resin present in the aloes is known as aloesin.
γ-Coniceine, which is a piperidine alkaloid is found in Aloe gililandii, A. ballyi, and A. ruspoliana (Liliaceae)
Aloe yields not less than 50% of water soluble extractives. It also contains volatile oil to some extent that imparts a characteristic odour to it.
Chemical Tests The overall chemical tests for aloes may be divided into two separate heads, namely: (a) General Tests, and (b) Special Tests
(a) General Tests: For this prepare a 0.1% (w/v) aqueous solution of aloes by gentle heating, add to it 0.5g of Kiesulgur and filter through. Whatman Filter Paper No. 42 and preserve the filtrate for the following tests:
1. Borax Test (or Schoenteten’s Reaction): To 5 ml of the above test solution add 0.2 g of pure borax and heat gently till it gets dissolved. Transfer a few drops of the resulting solution into a test tube filled with distilled water, the appearance of a green coloured fluoroscence due to the formation of aloe emodin anthranol shows its presence.
2. Bromine Test: When equal volumes of the test solution and bromine solution are mixed together, it yields a pale-yellow precipitate due to the production of tetrabromaloin.
3. Modified Borntrager’s Test: It is known that aloin (or barbaloin) belongs to the class of Cglycoside which does not undergo hydrolysis either by heating with dilute acid or alkali, but it may be decomposed with ferric chloride due to oxidative hydrolysis. Hence, the Modified Borntrager’s test employing FeCl3 and HCl is used as stated below:
First of all heat together 0.1 g of powdered aloe with about 2 ml of FeCl3 solution(5% w/v) and 2 ml of dilute HCl (6N) in a test tube over a pre-heated water bath for 5 minutes. Cool the contents and extract the liberated anthraquinone with carbon tetrachloride. Now carefully separate the lower layer of CCl4 and add to it ammonia solution. The appearance of a rose-pink to cherry red colour confirms its presence.
(b) Special Tests
1. Nitrous Acid Test: Crystals of sodium nitrite together with small quantity of acetic acid when added to 5 ml of the above test solution of aloe, the following observations are noted:
(a) Curacao Aloes: A sharp pink to caramine colour due to the presence of isobarbaloin.
(b) Cape Aloes: A faint pink colour due to isobarbaloin.
(c) Socotrine and Zanzibar aloes: Colour comparatively lesser change in colour.
2. Nitric Acid Test: The Test solution of aloes when made to react with nitric acid, it gives rise to various shades of colour due to different types of aloes available commercially as shown below:
Caracao Aloe : Deep brownish red
Cape Aloes : Initial brownish colour changing to green
Socotrine Aloes : Pale brownish yellow
Zanzibar Aloes : Yellowish brown
3. Cupraloin Test (or Klunge’s Isobarbaloin Test): To 10 ml of a 0.4% (w/v) aqueous solution of aloe add a drop of the saturated solution of copper sulphate, immediately followed by 1 g of NaCl and 20 drops of ethanol (90% v/v). It produces different shades of colours depending on the variety of aloes used:
Carocao Aloes : A wine red colour lasting for few hours,
Caoe Aloes : A faint colouration changing to yellow quickly,
Socotrine Aloes : No colouration
Zanzibar Aloes : No colouration
Uses
1. Though, both aloes and aloin are official drugs, the former is mostly used as a purgative by exerting its action mainly on colon, whereas the latter is generally prepared over the former now-a-days.
2. Aloes find its usefulness as an external aid to painful inflammatory manifestations.
3. It constitutes an important ingredient in the ‘Compound Tincture of Benzoin’ (or Friar’s Balsam).
4. Aloe gel made from the mucilaginous latex of A. vera is frequently employed in the treatment and cure of radiation burns to get immediate relief from itchings and pains.
5. Aloe usually causes gripping and is, therefore, administered along with carminatives.
