Experiment to Test the Presence of Starch in the Given Food Sample !
Experiment 3.1:
Objective:
To test the presence of starch in the given food sample.
Apparatus and materials required:
Test tubes, test-tube stand, test-tube holder, spirit lamp, dropper, filter paper, iodine solution, distilled water, and foodstuff (potato, rice, wheat or maize grains).
Theory:
Starch, a complex carbohydrate, is composed of 15%-20% amylose and 80%-85% amylopectin. It is found in different kinds of cereals such as rice, wheat, maize, etc. After reacting with iodine solution starch forms a dark, blue-black compound. The appearance of blue-black colour is due to the presence of amylase in starch.
Procedure:
1. Take a few small, freshly cut pieces of potato or a few grains of rice or wheat or maize in a clean test tube.
2. Pour 10 mL distilled water into the test tube.
3. Now, boil the contents of the test tube for about 5 minutes.
4. Allow the test tube to cool.
5. Filter the contents of the test tube through a filter paper.
6. Test the obtained filtrate for the presence of starch by the following method.
Precautions:
1. Use test-tube holder for holding the test tubes and keep the mouth of the test tube away from yourself while heating.
2. Use clean test tubes.
3. Do not use too much of iodine solution.
Experiment 3.2:
Objective:
To test the presence of the adulterant metanil yellow in dal (pulse)
Apparatus and materials required:
Test tubes, test-tube stand, test-tube holder, conc. HCl, mortar-pestle, filter paper, distilled water and a sample of dal
Theory:
Metanil is a cheap dye which is commonly used in colouring non-food items like clothes. Government of India has introduced “Prevention of Food Adulteration Act” to prevent the use of harmful chemicals such as this dye in foodstuffs.
Procedure:
1. Grind 3-5 g of dal in a mortar-pestle.
2. Take this powdered dal in a clean test tube.
3. Pour 10 mL distilled water into the test tube and shake it well.
4. Filter the contents of the test tube through a filter paper and use the filtrate to test for metanil yellow by the following method.
Observation:
Precautions:
1. Always use clean test tubes.
2. Use test-tube holder at the time of adding conc. HCI and keep the mouth of the test tube away from yourself.
3. Do not add excess conc. HCI.
4. Handle the bottle of conc. HCI carefully.