Food Tests

• Testing for reducing sugar;

  1. Add Benedict's solution to sample

  2. Heat to 95 degrees celsius
• Results for reducing sugars test

  Indicates if reducing sugars are present;

  • Blue = no reducing sugar content
  • Green = traces of sugar
  • Yellow = moderate content
  • Brick red = high sugar content
• Testing for non-reducing sugars

  1. Add Benedict's solution to sample

  2. Heat to 95 degrees Celsius

  3. No change if non-reducing sugars are present

  4. Boil hydrochloric acid with a fresh sample for a few minutes to hydrolyse the glycosidic bonds

  5. Neutralise the solution with small amounts of solid sodium hydrogen carbonate

  6. Test as normal with Benedict's reagent and it should give positive result
• Emulsion test for a lipid

  1. Place a small amount of the sample (crushed if solid) into a test tube with 2cm3 of ethanol

  2. Shake the mixture so the fat dissolves

  3. Add water dropwise and shake again

  4. A white or cloudy emulsion (layer) of fat droplets should be visible if fat is present
• Test for starch:

  1. crush / grind the sample (if required)
  2. add iodine solution to sample

  positive result - blue / black

  negative result - no colour change (orange)
• Biuret test for protein:

  1. crush / grind sample (if required)
  2. add biuret solution and mix

  positive result - lilac

  negative result - no colour change