What is the minimum requirement for a positive reaction for buiret test?

The minimum requirement for a positive reaction in the Biuret test is the presence of at least two peptide bonds in a protein or polypeptide. When a protein solution is mixed with Biuret reagent, which contains copper sulfate, a positive result is indicated by the formation of a violet or purple color. This color change occurs due to the complexation of copper ions with the peptide bonds. A lack of this color change signifies a negative result, indicating insufficient protein presence.