9.1.2 Food Tests

• Starch


  A carbohydrate
• Testing for starch


  1. Use iodine solution

  2. Starts off orange-brown

  3. Turns blue-black in the presence of starch

  
• Reducing sugars


  Carbohydrates, glucose is a reducing sugar
• Testing for reducing sugars

  1. Use Benedict's test

  2. Add solution and heat (80°C)

  3. Starts off blue

  4. Brick red precipitate forms with lots of reducing sugar (e.g. glucose)

  5. Orange precipitate forms with a little reducing sugar

  6. Trace = very small amount
• Testing for proteins


  1. Use Biuret test

  2. Starts off blue

  3. Turns purple in the presence of protein
• Testing for lipids


  1. Use emulsion test

  2. Add ethanol (colourless to start)

  3. Turns cloudy/milky in the presence of lipids
• Testing for Vitamin C


  1. Use DCPIP test

  2. DCPIP starts off blue

  3. Turns colourless in the presence of Vitamin C
• Test Yourself Q & A


  • Iodine solution
  • Orange-brown
  • Blue-black
  • Biuret reagent
  • Turquoise blue to purple/lilac/mauve
  • Ethanol
  • Solution turns cloudy white
  • Benedict's solution/reagent
  • Brick red/orange