Determination of carbohydrates in a given food sample

Theory

Carbohydrates are one of the main components of our daily diet. This category of foods includes sugars, starches, and fibre. Starch is the most common carbohydrate in the human diet and is contained in many staple foods. The word Carbohydrates C_n(H₂O)_n literally mean carbon (carbo) + water (hydrate). 

            The colour of natural starch is milky white and the pure form of starch is insoluble in water and alcohol. Iodine reacts with starch to form starch/iodine complex which has a blue-black colour. The appearance of blue-black colour confirms the presence of starch in the given food sample

Material Required

Sample, Iodine solution, beaker, test tube, tile, knife, etc.

Lab Procedure

1. Place a potato on a tile.
2. Grind or chop the potato into small pieces, using a knife.
3. Using a spatula transfer these pieces of potato into a beaker.
4. Pour some distilled water into the beaker.
5. Place the beaker containing the mixture over a hot plate.
6. Heat the mixture for 5 minutes while continuously stirring it with a glass rod.
7. Take another beaker and cover its mouth with a muslin cloth.
8. Secure the muslin cloth around the mouth of the beaker by tying it with a thread.
9. Filter the solution through this beaker.
10. Now take a clean test tube and pour some of the filtrate into it.
11. Take a few drops of iodine solution using a dropper.
12. Add a couple of these drops into the test solution.

Observation

The test solution turns blue-black in colour

Precautions

1. While using iodine solution, be careful, as it is toxic if swallowed or inhaled.
2. While heating, care should be taken that the solution does not splash on your face