Page 124 - Pharmacognosy 02-06203

Agar-agar (Japanese Isinglass)

Agar BP 2007 consists of the polysaccharides fromvariousspecies of Rhodophyceae
mainly belonging to the genus Gelidium. It is prepared by treating the algae with
boiling water; the extract is filtered whilst hot, concentrated and dried.

Taste: mucilaginous
Shape: powder or in crumpled strips 2 mm to 5 mm wide or sometimes in flakes,
somewhat tough and difficult to break, becoming more brittle on drying.
Color: colourless to pale yellow, translucent.

Constituents:
Polysaccharide in nature composed of two fractions:
Agarose: neutral jelling fraction composed of alternating galactose and 3,6
anhydrogalactose.
Agaropectin: non jelling fraction but affects the viscosity of the solution, composed
of uronic acid, partially esterified with sulphuric.

Test for identity:
1- positive test with Molish’s.
2. When mounted in iodine the strips or flakes are partly stained brownish-
violet., they show numerous minute, colorless, ovoid or rounded grains on an
amorphous background; occasional brown, round to ovoid spores with a
reticulated surface, , may be present.
3. boil with dil. HCl and filter, examine the residue under microscope (diatoms
and sponge spicule)

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