Food test practical

• 1. Take the food sample and grind this with distilled water using a mortar and pestle. We want to make a paste.
  2. Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water.
  3. Filter to solution to remove suspended food particles.
• Test for starch

  1. Place 2cm^3 of food solution into a test tube
  2. Add a few drops of iodine solution
  3. if starch is present then the iodine solution will turn blue-black
  4. If there is no starch present, the solution will stay orange
• Test for sugars

  1. place 2cm^3 of food solution into a test tube
  2. Add 10 drops of Benedict's solution which is a blue colour
  3. Place the test tube containing our solution into a beaker and half fill the beaker with hot water from a kettle
  4. Leave for around 5 mins
  5. If sugar is present, the Benedict's solution will change colour
  6. the colour of the Benedict's solution gives us an approximate idea of the amount of sugar present.
• Colours of the Benedict's solution

  • A green colour tells is that there is a small amount of sugar
  • A yellow colour tells us there is more sugar present
  • A red colour tells is that there is a lot of sugar present.
• The Benedict's test only works for certain sugars e.g. glucose
• Test for protein

  1. Take 2cm^3 of food solution in a test tube
  2. Ass 2cm^3 of biuret solution which is a blue colour
  3. If protein is present then the biuret solution will turn from blue to a purple colour
• Test for lipids

  1. grind the food with distilled water using a mortar and pestle (no not filter)
  2. transfer 2cm^3 of the food solution to a test tube
  3. add a few drops of distilled water and a few drops of ethanol
  4. gently shake the solution
  5. If lipids are present then a white cloudy emulsion forms