ZIMSEC O Level Biology Notes: Chemicals of Life: Carbohydrates: Test for Starch

  • We have already looked at the structure, properties and use of carbohydrates here
  • We will now examine the test for starch in foods
  • Remember starch is a polysaccharide which are part of the carbohydrates family
  • Iodine solution is used to test for the presence of starch in different foodstuffs

Aim

  • To test for the presence of starch(carbohydrates) in several foods

Materials:

  • Several foodstuffs including: Bread, Apples, Pasta, Spaghetti, Sadza, Rice, Banananas, Tomatoes, Potatoes, Plums, Oranges, meat,egg white etc
  • Iodine solution
  • Dropper
  • White tile/ white platform (this is meant to make observing color changes easier)

Method

  1. Put a slice of each of the foods being tested on the white tile/platform
  2. Using a dropper add drops of iodine solution to each food
  3. Wait for a few minutes and observe the color changes on each foodstuff

Observation

Iodine turns blue black when it comes in contact with starch

  • Iodine is originally reddish-brown in color
  • On foods with high starch content like bread, pasta, spaghetti, sadza and potatoes iodine changes from brown to blue-black
  • On foods with low starch content there is hardly any change in the colour of iodine

Conclusion

  • Foods like bread, pasta, spaghetti, sadza and potatoes have high starch content i.e they are starchy foods
  • Foods like vegetables and fruits like bananas
  • High protein foods like meat, chicken, fish, eggs, nuts, seeds, cheese, legumes and tofu also have a low starch content

To access more topics go to the O Level Biology Notes page

 

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