Detection of starch | Iodine test | Biochemical test | Tests for Starch (Polysaccharide)

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Detection of starch | Iodine test | Biochemical test | Tests for Starch (Polysaccharide)#biologylab
Sure, here's a complete practical outline for the iodine test to detect starch:
*Aim:*
To determine the presence of starch in a given sample using the iodine test.
*Requirements:*
1. Sample to be tested (e.g., food item, plant material)
2. Iodine solution (Iodine dissolved in potassium iodide solution)
3. Dropper or pipette
4. Test tubes
5. Distilled water
6. White tile or background surface
7. Bunsen burner and tripod stand (if required)
8. Heat source (Bunsen burner or hot plate)
9. Forceps or stirring rod
*Procedure:*
1. Prepare the sample: Take a small amount of the sample to be tested. If the sample is solid, grind or crush it into a fine powder.
2. Perform the test: Place the sample in a test tube.
3. Add iodine solution: Using a dropper or pipette, add a few drops of iodine solution to the sample in the test tube.
4. Observe the color change: Observe any color change in the sample. If starch is present, the iodine solution will turn from yellow-brown to a dark blue or black color.
5. Compare with control: As a control, you can add a few drops of iodine solution to a separate test tube containing distilled water. This should remain the same color (yellow-brown), indicating that the color change in the sample is due to the presence of starch.
6. Heat the sample (optional): In a separate procedure, you can heat the sample and iodine mixture gently over a flame (using a Bunsen burner and tripod stand) for a short period. If starch is present, the blue-black color will disappear due to the breakdown of the starch molecules. This step helps confirm the presence of starch.
*Results:*
Positive result: The iodine solution turns from yellow-brown to a dark blue or black color in the presence of starch.
Negative result: No color change occurs, and the iodine solution remains yellow-brown.
*Conclusion:*
Based on the observation of the color change, the presence of starch in the sample can be confirmed. The dark blue or black color indicates a positive result for starch, while no color change indicates a negative result. If the heated sample reverts to the original color (yellow-brown), it confirms the presence of starch molecules that were broken down upon heating.
Remember to exercise caution when using a Bunsen burner and other equipment. This practical is a simple and effective way to detect starch using the iodine test.