Food Tests

• Preparing a food sample:

  1. break up piece of food with a pestle and mortar
  2. transfer the ground food to a beaker and add some distilled water
  3. stir the mixture thoroughly with a glass rod to dissolve some of the food
  4. filter the solution using a funnel lined with filter paper to get rid of the solid bits of food
• There are 2 types of sugars - non-reducing and reducing
• You can test for reducing sugars using the Benedict's test
• Benedict's test for sugars:

  1. transfer 5cm3 of a food sample to a test tube
  2. prepare a water bath so it's set to 75 degrees celcius
  3. add some benedict's solution to the test tube using a pipette
  4. place the test tube in a test tube holder in the water bath and leave it for 5 minutes. Make sure the tube is pointing away from you.
  5. if the sample contains a reducing sugar, the solution will change from blue to brick-red
• The benedict's solution will change from blue to green, yellow or brick-red depending on how much sugar is present
• You can use iodine to test for starch
• Iodine test for starch:

  1. transfer 5cm3 of a food sample to a test tube
  2. add a few drops of iodine and gently shake the tube to mix the contents
  3. if the sample contains starch, the solution will change from browny-orange to blue-black
• You can use the Biuret test to test for proteins
• Biuret test for proteins:

  1. transfer 2cm3 of a food sample to a test tube
  2. add 2cm3 of biuret solution to the sample and gently shake the tube to mix the contents
  3. if the food sample contains protein, the solution will change from blue to pink or purple
• You can use the Sudan III test to test for lipids
• Sudan III test for lipids:

  1. transfer 5cm3 of a food sample to a test tube
  2. use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake the tube
  3. if the sample contains lipids, the mixture will separate into 2 layers. The top layer will be bright red.