Starch
Science: KS3, topic 1.4.7
Starch
Starch is a carbohydrate and an important part of a balanced diet. Starch is insoluble in water and alcohol.
Appearance
- Starch is solid at room temperature.
- Starch is insoluble in water and alcohol.
- Starch is oderless and tasteless.
- Starch is a natural carbohydrate polymer.
- Starch is made up of repeating glucose monomers.
Foods rich in starch
- Foods that are very rich in starch include:
- Wheat
- Potatoes
- Maize
- Rice
- Corn
Uses
- Starch has many uses in food.
- Processing starch produces sugars that can be added to foods.
- Starch is used in brewing and fermenting beer and whiskey.
- Mixing starch with warm water can produce wheatpaste.
- Wheatpaste is used as a thickening agent.
- Starch stiffens and hardens clothes if added before ironing.
- The word 'starch' is sometimes used to mean 'to stiffen and strengthen.'
Testing for starch
- Iodine is used to test for starch.
- Plants use energy from the sun to convert water and carbon dioxide into oxygen and glucose.
- This process is called photosynthesis.
- Glucose is converted to starch and used to build cell walls.
- Starch is also found in seeds.
Testing for starch practical
- Boil a leaf in water and ethanol, then drop some iodine onto it.
- Watch for the orange-coloured iodine to change to a blue-black colour.
- If the colour changes, that means starch is present.
- The presence of starch is evidence of photosynthesis.
- If there is no starch, then the iodine will remain orange.
Test yourself on Starch
What does the word 'starch' mean when it describes making fabric stiff?
A leaf is tested with iodine and turns blue-black. What does this show about the leaf?