The technique commonly used to determine the presence of protein in a food sample is the Biuret test. This test involves adding a Biuret reagent (which contains copper sulfate and sodium hydroxide) to the food sample. If the sample contains protein, the solution changes to a violet or purple color due to the formation of a complex between copper ions and peptide bonds in proteins. This is a simple and widely used chemical test for protein detection in food samples.

Additional Protein Testing Methods

• The Kjeldahl method measures nitrogen content in the sample to estimate protein concentration, widely used for precise quantification but more time-consuming and requires hazardous chemicals.

• Spectroscopic methods such as the Bradford assay or UV-Vis spectroscopy are also used for protein quantification, offering sensitivity and rapid results, but require specific equipment.

• Other advanced instrumental methods include chromatography and electrophoresis for detailed protein analysis.

For a straightforward and quick confirmation of protein presence in a food sample, the Biuret test is the preferred method.