Question

Explain the process happened during iodine test on acid-hydrolyzed starch and what colour do it produced at the end of the experiment

Answer 1

Starch Hydrolysis Test –

Starch is a complex polysaccharide found abundantly in plants and usually deposited in the form of large granules in the cytoplasm of the cell.

Starch consists of 2 components—amylose and amylopectin, which are present in various amounts.

The amylose consists of D-glucose units linked in a linear fashion by α-1,4 linkages. It has 2 non-reducing ends and a reducing end.

Amylopectin is a branched polysaccharide. In these molecules, shorter chains of glucose units linked by α-1,4 are also joined to each other by α-1,6 linkages.

These simple glucose sugars can be separated from one another using an acid like hydrochloric acid. To observe the process of starch hydrolysis using hydrochloric acid, you'll need to observe the amount of simple sugars that are in a sample of starch that is subject to hydrochloric acid compared to a sample of starch that does not interact with the acid.

The major component of starch can be hydrolyzed by a-amylase, which is present in some bacteria while well known in case of fungi.

The ability to degrade starch is used as a criterion for the determination of amylase production by a microbe.

Objective:

To determine the ability of an organism to hydrolyze starch.

To differentiate organism based on their α- amylase enzyme activity.

Many bacteria produce extracellular enzymes used to catalyze chemical reactions outside of the cell. In this manner, nutrient sources, such as starch, that are too large to be absorbed through the cell membrane can be broken down into smaller molecules and transported into the cell via diffusion.

Method:

Add water to a beaker until it is partially full. Heat the water on a Bunsen burner or other heat source until it reaches the point of boiling. Once you've reached the boiling point, reduce the heat slightly to keep the water boiling.

Add a small amount of starch solution to a test tube via a pipette.

Rinse the pipette and add a small amount of Benedict's reagent to the starch solution. Benedict's reagent is a solution of copper sulfate and sodium hydroxide that is used to detect the level of sugars in a solution.

Place the test tube into the beaker of boiling water. Allow the test tube to boil for five minutes.

Add a small amount of starch solution and Benedict's reagant to a second test tube. Then rinse the pipette and add a small amount of hydrochloric acid to the second test tube.

Place the second test tube into the beaker of boiling water. Allow the test tube to boil for five minutes.

Remove the test tubes from the beaker using test tube tongs. Place the test tubes on a test tube cooling rack.

Neutralize the acid in the second test tube using sodium bicarbonate. Slowly add chunks of solid sodium bicarbonate to the test tube until the solution ceases fizzing.

Allow the test tubes to cool off until they can be handled easily.

Observe the color of each test tube, which corresponds to the amount of sugar present in the solution. The second test tube will be more dark red or brown, indicating that the hydrochloric acid hydrolyzed the starch in the solution and produced greater quantities of simple sugars.