Lipids and proteins test

• The Biuret test is used to test for proteins by detecting a particular feature in proteins which is the presence of peptide bonds.
• A protein is a chain of amino acids and the bond that keeps those amino acids together is what is being tested for in the Biuret test.
• In the Biuret test, the sample is placed into a clean test tube and then sodium hydroxide solution, known as Biuret a, is added.
• The Biuret test involves forming a mixture of Biuret a, the sample, and copper II sulfate solution, known as Biuret b.
• If there is protein present in the sample, the colour of the reagent or the mixture changes from a blue colour to a purple colour.
• The Emulsion test is used to detect the presence of lipids, which can be found in oils and fats like butter.
• In the Emulsion test, the sample is placed into a clean test tube and then ethanol, a particular alcohol, is added.
• The Emulsion test involves forming a mixture of ethanol, the sample, and water, and then gently shaking it to dissolve any lipids present.
• If lipids are present in the sample, a cloudy white substance forms at the top of the test tube.
• The cloudy white substance in the Emulsion test is formed because the lipids are not soluble in water and they start leaving the water, forming their own emulsion at the top of the test tube.