Page 105 - Medicinal Plants_PharmD general

Identification of starch
Starch gives blue colour with iodine solution; the blue substance is

named starch iodide (Amylose has a strong affinity for iodine). The blue
colour of starch iodide disappears on heating to 93 o C but reappears on
cooling.
Microscopical characters of starch granules

Starch granules exhibit fairly constant characters in the one and the
same drug but vary in different drugs so, they furnish an important means
for the identification of drugs.
Shape: It varies in the different plants and different organs of the same
plant. It depends on the condition of the formation of the granules. The
shape may be rounded, lenticular, oval, polyhedral, globular, .. etc.
Size: The size varies greatly even in the granules of one plant. It ranges
from very minute (2 m in rice) to a large size which could be seen by the
naked eye.
Hilum: It is the first part laid down in the leucoplast and around which the
starch layers are deposited. It is usually minute and scarcely recognizable
but may be clear and distinct. It may be as darker or brighter point e.g.
wheat, rice, or a radiating structure e.g. maize. It may be present in the
center of the granule and termed centric e.g. wheat or apart from the centre
and called eccentric e.g. potato.
Striations: Due to the variation in the composition of starch layers in the
starch granule, starch granules are seen to have alternate bright and dark
areas producing what is called striations. They appear as alternate rings of
curved lines and may be concentric, when running around the hilum e.g.
Wheat, potato or transverse when not running around the hilum e.g. Ginger.

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