Food tests

• Test for starch - iodine

  1. Place one spatula of the food sample on a dish or 1 cm3 if the sample is liquid.
  2. Using a dropper, place a few drops of iodine solution onto the food.
  3. Record any change in the colour of the solution.
  4. If starch is present, it will turn blue-black
• Test for sugars - benedict

  1. Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
  2. Add an equal volume of Benedict's solution and mix.
  3. Place the tube in a water bath at about 95°C for a few minutes.
  4. Record the colour of the solution.
  5. Benedict's solution gradually turns from blue to cloudy orange or brick red when heated with a reducing sugar.
• Test for proteins - biuret

  1. Place one-two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
  2. Add an equal volume of potassium hydroxide solution to the tube and stir.
  3. Add two drops of copper sulfate solution and stir for two minutes.
  4. Record the colour of the solution.

  Proteins are detected using Biuret reagent. This turns a lilac colour if proteins are present
• Test for lipids - ethanol

  1. Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid.
  2. Add 2 cm3 of ethanol to the tube. Cover the end of the tube and shake the tube vigorously.
  3. Allow the contents to settle.
  4. Pour the liquid from the top of the mixture into a test tube half-filled with water.
  5. Record the level of the food and whether the water is cloudy or clear.

  Lipids are detected using the emulsion test. This is what happens:

  1. A milky-white emulsion forms if the test substance contains lipids.
• Risks

  • Potassium hydroxide can be harmful to skin and eyes.
  • Hot water can scald.
• Control measures

  • Wear eye protection.
  • Do not taste any of the foods.
  • Take care with hot water.
  • Wash off any splashes immediately.