Food Tests for GCSE Biology Practicals

Preparing the Food Sample

• Tools Needed: Mortar and pestle, beaker, distilled water, glass rod, funnel, filter paper.
• Steps:
  1. Break up the food using a mortar and pestle.
  2. Mix the crushed food with distilled water in a beaker and stir with a glass rod.
  3. Filter the mixture using a funnel lined with filter paper to remove solid bits.
  4. The resulting solution is the sample for testing.

Benedict's Test for Sugars

• Type of Sugars: Reducing sugars.
• Steps:
  1. Prepare the food sample.
  2. Transfer 5 cm³ of the sample to a test tube.
  3. Prepare a water bath at 75°C.
  4. Add about 10 drops of Benedict’s solution to the test tube.
  5. Place the test tube in the water bath for 5 minutes (use a test tube holder for safety).
• Results:
  • No reducing sugars: Solution remains blue.
  • Reducing sugars present: Solution changes to green, yellow, or brick red depending on concentration.

Iodine Test for Starch

• Steps:
  1. Take 5 cm³ of the food sample.
  2. Add a few drops of iodine solution (turns to browny-orange).
  3. Gently shake the mixture.
• Results:
  • Starch present: Solution changes to blue-black.

Biuret Test for Proteins

• Steps:
  1. Add 2 cm³ of the sample to a test tube.
  2. Add 2 cm³ of Biuret solution (turns blue).
  3. Gently shake the test tube.
• Results:
  • Protein present: Solution changes from blue to pink or purple.

Sudan III Test for Lipids

• Steps:
  1. Take 5 cm³ of the unfiltered food sample.
  2. Add 3 drops of Sudan III stain solution.
  3. Gently shake.
• Results:
  • Lipid present: A bright red layer will form at the top (lipid separates from water).

Emulsion Test for Lipids (Edexcel Course)

• Steps:
  1. Take the food sample.
  2. Add 2 cm³ of ethanol and shake vigorously.
  3. Add an equal volume of distilled water.
• Results:
  • Lipid present: Solution turns cloudy white.
  • No lipid: No change in color.

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