Food tests

• Food sample:

  1. Get a piece of food and break it up using a pestle and mortar.
  2. Put it in a beaker and add some distilled water.
  3. Stir the mixture with a glass rod to dissolve some of the food.
  4. Filter the solution using a funnel lined with filter papel to get rid of the solid bits of food.
• Benedict's test to test for glucose:

  1. Prepare a food sample and transfer it to a test tube.
  2. Prepare a water bath set to a certain temperature.
  3. Add some Benedict's solution to the test tube (about 10 drops) using a pipette.
  4. Place the test tube in the water bath using a test tube holder and leave it there for 5 minutes.
  5. If the food sample contains glucose, the solution in the test tube will change from its normal blue. It will become green or yellow in low concentrations of glucose, or brick-red in high concentrations of glucose.
• Iodine solution to test for starch:

  1. Make a food sample and transfer it to a test tube.
  2. Add a few drops of iodine solution and gently shake the tube to mix the contents.
  3. If the sample contains starch, the color of the solution will change from browny-orange to black or blue-black.
• Biuret test to test for proteins:

  1. Prepare a food sample and transfer it to a test tube.
  2. Add biuret solution to the sample and mix the contents of the tube by gently shaking it.
  3. If the food sample contains protein, the solution will change from blue to pink or purple.
• Sudan III test for lipids:

  1. Prepare a food sample and transfer it 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. Sudan III stains solutions with lipids. If the sample contains lipids, the mixture will separate out into two layers. The top layer will be bright red. If no lipids are present, no separate red layer will form at the top of the liquid.