What does the Biuret test indicate?

What does the Biuret test indicate?

• A. Starch
• B. Sugars
• C. Fats
• D. Proteins

Answer: (D)

The Biuret test looks for peptide bonds—the links that hold amino acids together in proteins. In an alkaline solution with copper sulfate, these bonds form a violet complex, so a sample with proteins turns blue to purple. If there are no peptide bonds, as with starch, sugars, or fats, there’s no color change. So this test specifically indicates the presence of proteins. (Very small peptides can give a faint color, but the strong purple color mainly signals proteins.)

The Biuret test looks for peptide bonds—the links that hold amino acids together in proteins. In an alkaline solution with copper sulfate, these bonds form a violet complex, so a sample with proteins turns blue to purple. If there are no peptide bonds, as with starch, sugars, or fats, there’s no color change. So this test specifically indicates the presence of proteins. (Very small peptides can give a faint color, but the strong purple color mainly signals proteins.)