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
  • Blue solution indicates no reducing sugars
  • Green, yellow or brick red indicates reducing sugars
• Iodine test for starch

  1. Take 5cm3 of food sample

  2. Add iodine solution

  3. Shake gently
• Iodine test


  • Brown-orange solution turns blue-black if starch is present
• Biuret test for proteins

  1. Take 2cm3 of food sample

  2. Add 2cm3 Biuret solution

  3. Shake gently
• Biuret test


  • Blue solution turns pink or purple if proteins are present
• Edexcel Biuret test for proteins

  1. Add potassium hydroxide

  2. Add copper sulfate
• Sudan 3 test for lipids

  1. Take 5cm3 of food sample

  2. Add 3 drops Sudan 3 stain

  3. Shake gently
• Sudan 3 test


  • Bright red layer at top indicates lipids present
• Edexcel emulsion test for lipids


  1. Take food sample

  2. Add 2cm3 ethanol, shake vigorously

  3. Add equal volume distilled water
• Emulsion test


  • Cloudy white colour indicates lipids present