Question

You have been supplied with a sample of food. How will you perform tests for the presence of starch and proteins in it?

Answer 1

Starch is a complex carbohydrate compound. The following steps are used to detect presence of starch:​

1. Take a small amount of food item to be tested in a test-tube containing water. ​
2. Boil the test tube to make a solution. ​
3. Let the solution cool and add 2-3 drops of dilute iodine solution to it.​
4. Appearance of bluish-black colour in the solution indicates the presence of starch in the food item.​

Proteins are very large molecules composed of basic units called amino acids. The following steps are used to detect presence of proteins:​

1. Take the food item to be tested in a test tube.​

2. Add a few drops of dilute nitric acid to it.​

3. Heat the test-tube gently. ​

4. Rinse off the acid with water and add a few drops of ammonium hydroxide to it.​

5. Colour change from colourless to yellow and then from yellow to orange red indicates the presence of protein in the food item. ​

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