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ALOES - Chemical Constituents, Tests & Uses

Chemical Constituents

• Aloetic acid, Homonataloin, Aloesone
• Chrysophenic acid, Chrysamminic acid
• Galacturonic acid, Choline, Choline salicylate
• Saponins, Mucopolysaccharides, Glucosamines
• Hexuronic acid, Coniferyl alcohol

• Barbaloin content: Curacao aloes = ~22% | Indian variety (Aloe vera) = 3.5-4%
• Curacao aloes contains 2.5x more aloe emodin than Cape aloe emodin
• Aloesin = C-glucosyl chromome; found in the resin; responsible for the purgative action of aloes

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Chemical Tests

General Test (Preparation)

(1) Bromine Test

• Freshly prepared bromine solution added to filtrate
• Result: Pale-yellow precipitate of tetrabromalin

(2) Schoenteten's Reaction (Borax Test)

• Filtrate + borax, shaken till dissolved; few drops added to water
• Result: Green fluorescence

(3) Modified Bontrager's Test

• Detects C-glycosides (aloe emodin)
• Aqueous aloe solution + ferric chloride + dilute HCl → oxidative hydrolysis of aloe-emodin
• Free anthraquinones collected in organic solvent (CCl₄ or ether)
• Organic layer shaken with dilute ammonia
• Result: Ammoniacal layer shows rose pink to cherry red colour

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Specific Tests (Comparative Table)

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Uses

• Primary use: Purgative (acts mainly on the colon)
• Strongest purgative among crude drugs with anthracene glycosidal content
• Given with carminatives to counter the gripping action
• Aloin is preferred over aloes nowadays (both official)
• Ingredient of Compound Tincture of Benzoin (Friar's Balsam)

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Aloe Gel vs Aloes - Comparison

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Other Preparations

• Aloin: Mixture of crystalline principles from aloes; pale yellow to dark yellow microcrystalline powder; odourless, intense taste; soluble in water and 90% alcohol; store in tight light-resistant container; dose: 15-60 mg for purgation
• Aloes powder: Characters vary by source; identified by microscopic observations
• Compound Benzoin Tincture (Friar's Balsam): Benzoin + prepared storax + balsam of tolu + aloes + 90% alcohol

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Adulteration and Substitutes

• Natal Aloes: Resembles Cape aloes microscopically; contains natation, Homonataloin, and resin with nataloresin otannol; weak purgative
• Mocha Aloes: Brittle, black, glassy, strong odour
• Common adulterants: Black catechu, pieces of iron and stones
  • UV test: Alcoholic aloe extract → deep brown; black catechu → black colour

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BITTER ALMOND

Basic Details

• Synonym: Amygdala Amara
• Biological Source: Dried ripe seeds of Prunus Amygdalus Batsch var Amara (D.C.) (Focke); Family Rosaceae
• Geographical Source: Native to Iran and Asia Minor; cultivated in Sicily, Italy, Spain, Portugal, South France, Morocco
• Cannot be easily distinguished botanically from sweet almond (Prunus communis)

Macroscopic Characters

• Colour: Brown
• Odour: Odourless
• Taste: Bitter
• Size: ~20 mm length × 125 mm width × 10 mm thickness
• Shape: Flattened, oblong, ovoid with markings on testa

Chemical Constituents

• 40-50% bland fixed oil
• 20% proteins
• 0.5% volatile oil
• Enzyme emulsin
• Colorless crystalline bitter glycoside: Amygdalin (1-3%)
  • On hydrolysis (emulsin + water) → benzaldehyde + hydrocyanic acid
• Hydrocyanic acid is very poisonous → makes drug unsuitable for internal use
• Bitter almond oil: 80% benzaldehyde + 2-6% hydrocyanic acid

Uses

• Sedative (due to hydrocyanic acid content)
• Oil used as demulcent skin lotion
• Preparation of amygdalin, bitter almond water, perfumery, liquors
• Bitter almond oil should NOT be used for flavouring foods