Rhubarb - Source, diagnostic characters, constituents and uses

Rhubarb

Source, diagnostic characters, constituents and uses 

Content

• Source, diagnostic characters, constituents and uses of Rhubarb

Rhubarb

Synonyms

• Radix rhei, Rheum, Revandchini

Source

• Dried rhizome of Rheum emodii (Indian rhubarb), R. palmatum, R. webbianum (Chinese rhubarb)

Family

• Polygonaceae

Macroscopy

• Round - (small rhizomes), barrel, cylindrical, 8-10 cm L, 4 cm thick

• Flat - (large rhizome), plano convex, 7-10 cm L, 3-6 cm thick

• Sharp odour

• Bitter astringent taste

• Irregular granular fracture (drug with pink fracture is of superior quality)

• Star spots – abnormal vascular bundles, medullary ray appear as star spots

Constituents

• Anthraquinone glycosides and astringent principles

• Anthraquinone with carboxyl group – Rhein, Glucorhein

• Anthraquinone without carboxyl group – Aloeemodin, Emodin, Chrysophanol, Physcion

• Anthrones and dianthrones of aloe Emodin, Emodin, Chrysophanol, Physcion

• Heterdianthrones like Palmidin A, Palmidin B, Palmidin C

Other constituents

• Galic acid as glucogallin

• Tannin

• Catechin

• Epicatechin

• Pectin

• Starch

• Fat

• Calcium oxalate (3-40%)

Tests

• Modified borntrager’s test

• Red colour with addition of alkali

• Indian Rhubarb – Deep violet fluorescence in UV

Uses

• Bitter stomachic

• In diarrhoea

• As purgative

Adulterants/Substitutes

Rhapontic rhubarb

• R. rhaponticum

• Rhein, emodin aloe emodin absent

• Rhaponticin – crystalline glycoside, derivative of diphenyl ethylene

• Blue fluorescence in UV

• Esterogenic activity

Summary

• Rhubarb - Dried rhizome of Rheum emodii (Indian rhubarb), R. palmatum, R. webbianum (Chinese rhubarb), Anthraquinone glycosides