Food Tests for GCSE Biology Practicals

In this session, we will cover various food tests crucial for GCSE Biology practicals. Each test aims to identify specific types of nutrients in food samples.

Preparation of Food Sample

• Crush the food: Use a mortar and pestle.
• Mix with distilled water: Stir using a glass rod to dissolve some of the sample.
• Filter the mixture: Use a funnel lined with filter paper to remove solids. The resulting solution is the sample for testing.

Benedict’s Test for Sugars

• Purpose: Identifies reducing sugars.
• Procedure:
  • Prepare 5 cm³ of the food sample.
  • Set a water bath to 75°C.
  • Add 10 drops of Benedict’s solution to the test tube.
  • Heat in water bath for 5 minutes using a test tube holder.
• Results:
  • Blue solution if no reducing sugars.
  • Changes to green, yellow, or brick red if reducing sugars are present, depending on concentration.

Iodine Test for Starch

• Purpose: Detects the presence of starch.
• Procedure:
  • Add a few drops of iodine solution to 5 cm³ of the food sample.
  • Shake gently.
• Results:
  • Browny orange solution changes to blue-black if starch is present.

Biuret Test for Proteins

• Purpose: Tests for proteins.
• Procedure:
  • Add 2 cm³ of the food sample to a test tube.
  • Add 2 cm³ of Biuret solution.
  • Shake gently.
• Results:
  • Blue solution changes to pink or purple if protein is present.
• Edexcel Specific: Use potassium hydroxide and copper sulfate instead.

Sudan III Test for Lipids

• Purpose: Identifies lipids.
• Procedure:
  • Use 5 cm³ of the unfiltered food sample.
  • Add 3 drops of Sudan III stain solution.
  • Shake gently.
• Results:
  • Bright red layer on top if lipids are present, due to separation.

Emulsion Test for Lipids (Edexcel Course)

• Purpose: Tests for lipids.
• Procedure:
  • Add 2 cm³ of ethanol to the food sample.
  • Shake vigorously.
  • Add an equal volume of distilled water.
• Results:
  • Cloudy white solution indicates the presence of lipids.

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