food tests

• Food tests


  1. Prepare food sample

  2. Crush food with mortar and pestle

  3. Dissolve in distilled water

  4. Filter solution
• Sugars


  Small units that all carbohydrates are made of
• Types of sugars


  • Reducing sugars
  • Non-reducing sugars
• Benedict's test for reducing sugars


  1. Prepare food sample

  2. Transfer 5cm3 to test tube

  3. Heat in 75°C water bath for 5 minutes

  4. Add Benedict's solution
• Benedict's test


  • Tests for reducing sugars
  • Solution turns green, yellow or brick red if reducing sugars present
• Starch


  A type of carbohydrate, larger and more complex molecule than sugars
• Iodine test for starch


  1. Take 5cm3 of food sample

  2. Add iodine solution

  3. Solution turns blue-black if starch present
• Buret test


  Test for proteins
• Buret test for proteins


  1. Take 2cm3 of food sample

  2. Add 2cm3 of Buret solution

  3. Solution turns pink or purple if proteins present
• For Edexcel, add potassium hydroxide and copper sulfate instead of just Buret solution
• Lipids


  Tested using Sudan 3 and emulsion tests
• Sudan 3 test for lipids

  1. Take 5cm3 of food sample

  2. Add 3 drops of Sudan 3 stain

  3. Red layer forms at top if lipids present
• Emulsion test for lipids (Edexcel)


  1. Take food sample

  2. Add 2cm3 ethanol, shake vigorously

  3. Add equal volume of water

  4. Cloudy white colour indicates lipids present