Page 106 - Medicinal Plants_PharmD general

Striations may be distinct e.g. potato, faint e.g. wheat or even absent as in
maize.

Aggregation: The granules may be simple when it occupies the whole of
the leucoplast with one hilum, compound which are produce by the
continual deposition of starch around two or more hila in the same
leucoplast and the components gradually grow till they meet in flat surfaces
e.g. potato or semicompound where a common layer of starch is deposited
around the components e.g. potato.

Effect of moist heat

On heating starch granules in presence of water they first swell
slowly then a small hole appears at the hilum. This hole increases in
diameter and the granule swell up to many times its original size and loses
its double refractivity thus called gelatinised and the process is called
gelatinisation.

The granule now appears as a gelatinous sac, filled with an aqueous
solution of amylose, which is contorted or twisted into peculiar shapes and
finally, in most starches, but not in all e.g. wheat, it burst releasing the inner
portion which goes into solution. The resultant mucilage has a viscosity
which varies according to the variety of starch and the time of heating.

Gelatinisation of starch is also affected at room temperature by
concentrated acid, dilute alkalies and saturated solution of heavy metals
e.g. CaCl2, ZnCl2 .. etc.

Effect of chloral Hydrate

With chloral hydrate, the granules gradually swell and finally burst,
open and dissolve; these stages are more rapid on heating.

Of particular pharmaceutical interest are the starches of maize, rice, wheat
and potato.

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