Starch

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Structure

Starch is a polysaccharide with the basic monosaccharide being glucose. the glucose molecules are joined together by glycosidic bonds straight chains are made up of 1-4 glycosidic bonds while branching chain are made up of 1-6 glycosidic bonds. Starch is made up of two fractions: amylose and amylopectin. Natural starches are made up of about 20% amylose and 80% amylopectin. Amylose is soluble in hot water whereas amylopectin is insoluble. Amylose has no branching chains, but instead is made up of only 1-4 glycosidic bonds. This causes the amylose to form a helix shape. Amylopectin however contains both straight chains and branching chains.

Testing

Starch can be tested for using iodine solution. If starch is present then a dark blue-black colour will be seen. This dark blue-black colour is due to the iodine reacting with the amylose helix.


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