Question

What is the procedure followed for testing starch?

Answer 1

Hint: Starch is the most complex carbohydrate. The food is stored in the form of starch in the plants. Starch test is a simple test used to determine the presence of starch in a biological sample.

Complete Answer:
Starch test is performed to analyse the presence of carbohydrate in the food. It is done by using an Iodine solution. Thus the test is known as the Iodine starch test. Starch test is mainly used to see whether photosynthesis has occurred or not. In plants the excess glucose is rapidly converted into glucose. So, we test the leaves for seeing it. This test is used both for qualitative and quantitative analysis.
Materials required- knife, spatula, porcelain base, iodine solution, food sample (vegetable)

Procedure:
(I) For solid sample:
- Take a food sample and peel it properly.
- Use a spatula to scoop off the little sample on the porcelain base.
- Add a few drops of iodine solution to it.
- Observe the colour change.

(II) For liquid samples:
- Take a little liquid sample in a clean and dry test tube.
- Add 5 drops of iodine sample.
- Observe the colour change.
Observation- If the colour changes to blue-black then starch is present.

Note: Iodine test cannot be done for very dark coloured solids as observing the colour change can be difficult. The principle behind this test is iodine is a brown colour liquid. When it reacts with starch, it forms a starch-iodide complex which is responsible for the blue-black colouration.