Biuret Test for Protein
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Food Science and Nutrition
Alternative titles: Testing Foods for Protein
Summary
The Biuret test detects proteins in food samples. When a protein such as egg white or milk is mixed with Biuret solution, the color changes from blue to violet. If no protein is present, the solution remains blue.
Procedure
- Prepare Biuret solution by mixing equal volumes of 1% copper sulfate (Biuret A) and 1% sodium or potassium hydroxide (Biuret B).
- Warm gently in a 40 °C water bath until the blue precipitate dissolves.
- Add the food sample (e.g., egg white or milk) and mix well.
- Observe: a violet color indicates protein is present; blue means none.
Links
Biuret test for Protein - JamJarMMX:
The Biuret test for Protein - CEEA Erasmus:
📄 Biuret test for Protein - Revision World: https://revisionworld.com/gcse-revision/applied-science/aqa-additional-applied-science/unit-2-exam-topics/food-science/food-tests/biuret-test-protein
Variations
- Test different foods such as cheese, beans, or meat extracts.
- Compare raw vs. cooked protein samples.
Safety Precautions
- Avoid skin or eye contact; rinse immediately if contact occurs.
- Do not ingest test samples or solutions.
- Dispose of solutions safely in accordance with school lab rules.
Questions to Consider
- Why does the Biuret test turn violet when protein is present? (The copper ions form a complex with peptide bonds.)
- Why is it useful to test both animal and plant foods for protein?
- How might cooking change the results of the Biuret test?