How to Test Yogurt for Starch With Iodine

A complex interconnected series of sugar molecules (saccharides) comprise starch molecules. To test for the presence of these polysaccharides (many sugar) structured starches you will need iodine. Often used as a science experiment, the iodine acts as an indicator, changing color when it combines with starches. Use this technique for yogurt, or any other substance in which you wish to find starches. A color change occurs from the complex network of starches trapping the iodine molecules, revealing a blue-black color. The iodine will not change color in reaction to simple sugars, such as sucrose or fructose, because these do not retain iodine between the sugar molecules the way starches do.

Things You'll Need

• Yogurt sample
• Clean spoon
• Test tube or clear glass container
• Iodine indicator (see tip)
• Eye dropper

Instructions

1. Place a spoonful of yogurt into a test tube or glass container.

2. Use the eye dropper to transfer one to two drops of iodine onto the yogurt and stir.

3. Look for a color change. Record a blue-black color change in the yogurt positive for starches. Look for a reddish-brown color to indicate sugar molecules but not complex starches.

Tips & Warnings

• Look for iodine in pharmacies or science supply stores.

References

• Fundamental of Chemistry