Starch Granules

2765 Words Mar 27th, 2011 12 Pages
Title: Starch
Aims
1. To identify starch in food. 2. To study the microscopic appearances of raw and heated starch. 3. To compare the viscosity of various gelatinized starch solutions.
Introduction
Starch is one of the most abundant substances on the earth. It can be found in seeds, grains, and roots of many crops where it is synthesized in granular form. Starch granules are packages of starch molecules. The importance of starch is well-known, as is its central role in human diet. Many aspects of starch structure can be measured by chemical, physical, spectroscopic, or microscopic methods (Tina, 2000).
Starch can be separated into two fractions - amylose and amylopectin. Natural starches are mixtures of amylose (10-20%) and
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| Unripe banana | The unripe banana slices turned blue-black colour. The portion of the banana slice which turned blue-black colour was more than the ripe banana slices. | Rice granules | The rice granules turned blue-black colour. |

Discussion
When added with iodine solution, all of the starch solutions turned blue-black colour. Starch contains long linear chains which are called amylose. Amylose coils into a helical secondary structure resembling a tube with a hollow core. Therefore, the chemical complex of iodine can assembles inside the amylose to produce a characteristic blue-black colour (Jeffery, 2007).
The rice granules turned blue-black colour after added with few drops of iodine solution. This is due to the presence of starch in rice granules. After added with iodine solution, the banana slices turned blue-black colour. However, the portion of the ripe banana slice which turned blue-black colour was less than the unripe banana slice. An unripe banana contains a large amount of starch, while the starch in a ripe banana has been transformed into sugar through the ripening process. Therefore, a drop of iodine solution will turned blue-black colour when it is placed on a slice of unripe banana as it reacts with starch. On ripe banana, the discoloration will not be as great as unripe banana (Sharma, 2000). The Iodine test is the easiest way to test for the presence of starch.
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