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?