Starch iodine test is a specific test for polysaccharides (starch positive). Iodine test indicates the presence of polysaccharides in any solution. When iodine solution reacts with starch, a bluish colour is obtained indicating the presence of starch.
REAGENTS:
i. 1% Iodine solution ( which contain potassium iodide and water).
ii. Original solution (O.S) containing a carbohydrate
PRINCIPLE:
Starch, glycogen and higher dextrins on reaction with dilute iodine solution form coloured compounds.
PROCEDURE:
- Take 2 ml of the starch solution (original solution) in a test tube.
- Add 1-2 drops of the diluted iodine solution.
- Observe the production of a blue colour.
- The blue colour produced disappears on heating, and it reappears on cooling the solution.
OBSERVATION AND RESULT:
Starch, glycogen and higher dextrins on reaction with dilute iodine solution form coloured compounds as shown in the table below:
| Â Starch | Â Blue colour |
| Â Amylodextrin | Â Purple colour |
| Â Erythrodextrin | Â Red colour |
| Â Glycogen | Â Red colour |
| Â Achrodextrin (Lower dextrins), Disaccharides (Maltose) and Monosaccharides | Â No change in colour |
Precautions:
- Wash the apparatus before and after the experiment.
- Carefully handle all the chemicals.
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