![]() Starch which is largely synthesized in the amyloplast of the storage organs of plants and/or the chloroplast of plant leaves also contains traces of lipids and phosphate groups. Amylopectin is, however, nonrigid in structure and soluble in water and forms a gel in hot water. In the natural state, starch is approximately 20–30% amylose and 70–80% amylopectin.Īmylose which is rigid due to packing resulting from its straight chain is insoluble in water but soluble in hot water without gel formation. For example the short branching of amylopectin at the α-1,6-glycosidic bonds is responsible for the crystalline region of the granules. This conformational difference confers different properties on each of these polymers. Amylose is a straight chain α-1,4-glycosidic bonds, while amylopectin is a branched polymer also made of α-1,4-glycosodic with branched chain linked by α-1,6-glycosidic bonds. Starch is chemically a carbohydrate composed of two similar carbohydrate molecules-amylose and amylopectin. A starch granule involves alternating regions of amorphous and crystalline lamellae seen as rings which are essentially the crystalline portion. Microscopically, starch consists of colorless, highly refractive particles whose size and shape depend on various factors most important of which is the source of the starch. It is one of the most widely distributed chemical substances in nature being the energy storage form of plant materials. In its native form, pure starch is a white, amorphous relatively tasteless powder which is odorless and is insoluble in water and other common organic solvents. ![]() This should be taken into consideration in the choice of excipients in drug formulation and before the substitution of one starch for another in a formulation. The source of starches therefore affects the properties of pharmaceutical dosage forms. This results in dosage forms that, although meeting compendial standards, differ in specific properties. These factors especially by their influence on the swelling power and gelatinization as well as granule size and shape determine the properties of dosage forms in which the starches are used. ![]() In its wide use as a pharmaceutical excipient especially as binder and disintegrant, unmodified starch is affected in its functionality by the physicochemical properties of the starch. These factors also affect the starch granule size and size distribution and the levels of minor components such as phosphates, lipids, and the nature of these interactions with amylose and amylopectin. ![]() This is because of the effect they have on critical factors especially the amylose amylopectin content of the starch as well as their relative quantities. The specific source of starch, the environmental conditions during starch maturation, and the age of the plant affect the physicochemical composition of the starch. Starch can be obtained from a variety of plant sources. ![]()
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