OCR (B) Biology GCSE - Food Tests

Preparing a Sample of Food

• Grind up food samples using a pestle and mortar.
• Mix with water to form a solution.
• Filter mixture using a funnel and filter paper to remove solid particles.

Testing for Starch

• Add iodine solution to the food sample.
• Observation: If starch is present, the solution changes from brown to blue-black.

Testing for Reducing Sugars

• Add Benedict's reagent to the sample.
• Boil test tube in a hot water bath.
• Observation:
  • Brick red precipitate indicates the presence of reducing sugars.
  • If no reducing sugars are present, the solution remains blue.

Testing for Proteins

• Add Biuret reagent (potassium hydroxide and copper (II) sulphate) to the sample.
• Shake mixture thoroughly.
• Observation: If protein is present, the solution changes from blue to purple.

Testing for Lipids

• Add ethanol to the sample.
• Add water to the sample and shake the test tube.
• Observation: A white emulsion forms if lipids are present.