What is starch, and how to test its presence in potato and rice?

The word "starch" is taken from the Germanic root word meaning "strong, stiff, strengthen”.

It is an odourless, tasteless white substance that is manufactured in the green leaves of plants, from excess glucose produced during photosynthesis, and acts as a reserve food supply. 

It is stored in the chloroplasts in the form of minute granules in the seeds, tubers, and other parts of plants, and forming an important constituent of rice, corn, wheat, beans, potatoes, and many other vegetable foods.

It is the most common carbohydrate in human diets which is contained in large amounts in staple foods.

 

Test for Starch

To test the presence of starch in potatoes and rice, Iodine test is performed in which Iodine solution is used.

It is done by adding a few drops of iodine solution to the food sample. If starch is present in the rice or potatoes, it will turn blue-black colour, if absent then it will remain brown in colour.

Extra information:

The iodine test can determine whether or not leaves contain starch (carbohydrate). Here are the procedures for determining whether or not leaves contain starch: Step 1: Collect a green leaf from a plant that has been in direct sunlight for at least a few hours. Step 2: Half-fill a beaker with water and bring it to a boil. Step 3: Place the leaf in a pot of boiling water and let it sit there for a few minutes to soften the cell wall. Step 4: Boil the leaf in alcohol to extract the chlorophyll. Step 5: Immerse the leaf in hot water to loosen its cells. Step 6: Next, test the leaf for starch by dropping a few drops of iodine solution onto it. A blue-black hue develops on the leaf once iodine is added, indicating the presence of starch in the sample.