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Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

Homosaccharides : (Homopolysaccharides or holosides)

Examples : The most common homopolysaccharides are:

• glucans (glucosans) such as: starch, dextrin, glycogen, dextran and cellulose.

• The fructosans such as: inulin

1. Starch

Starch is a reserve food material, produced by photosynthesis and it is

abundant in the storage organs such as seeds, fruits, tubers, roots, etc. Starch

occurs in granules, whose characters vary from plant to plant, e.g., maize starch,

potato starch, rice starch, etc. It is found also in some micro-organisms.

Starch is composed only of D-glucose units, jointed by -glycosidic

linkages. The starch granule can be separated into two different components,
amylose and amylopectin.

1) Amylose:

It is a linear molecule composed of 250-300 D-glucopyranose units

uniformly linked by -1, 4 glucosidic bonds, giving a helix-like shape.

Suspensions of amylose in water are not linear but coil into a helical

conformation Iodine (I 2) can insert in the middle of the amylose helix to give a
blue color that is characteristic and diagnostic for starch.

2) Amylopectin:

It consists of 1000 or more glucose units that are also connected with -1,

4 linkages. However, a number of -1, 6 links also occur at branching points.

The -1, 6 links amount to about 4% of the total linkages; i.e., approximately 1

for every 25 glucose units.

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