Principle

In this experiment several basic operations of the Kjeldahl method are experimental simulated. Proteins are detected by using copper sulfate and sodium hydroxide solution.

Proteins differs from carbohydrates and fats by containing nitrogen.  Protein can be detected by cooking the sample or using the Buiret-test, whereby the Biuret-test is better suited for the detection of protein than cooking the sample.

After the addition of copper sulfate and sodium hydroxide solution into an egg-solution, a color change can be observed to violet. The color change occur, because the copper ions form a colored complex compound with the nitrogen atoms of the proteins , which can be recognized by its characteristic violet color.

Learning objectives

• Buiret-test
• Detecion of proteins

Tasks

Learn to recognize possible tests for protein and examine various foods for protein.