The Benedict's assay tests for the presence of

The Benedict's assay tests for the presence of

• A. Reducing sugar
• B. Starch
• C. Peptides
• D. Lipids

Answer: (A)

The test is looking for reducing sugars—the ones that have a free aldehyde or ketone group capable of being oxidized. In Benedict’s reagent, those sugars donate electrons to reduce copper(II) ions (Cu2+) in the alkaline solution to copper(I) oxide (Cu2O). That reduction creates the characteristic color change from blue to green, yellow, orange, or brick-red, with the intensity reflecting how much reducing sugar is present. This is why glucose and maltose would give a positive result, while substances without a free carbonyl group won’t. Starch, a long chain of glucose units, lacks readily exposed reducing ends and typically won’t react unless it’s broken down first. Peptides and lipids aren’t detected by Benedict’s test because they don’t rely on the redox chemistry of reducing sugars; peptides are identified by protein-specific tests, and lipids by lipid-specific tests.

The test is looking for reducing sugars—the ones that have a free aldehyde or ketone group capable of being oxidized. In Benedict’s reagent, those sugars donate electrons to reduce copper(II) ions (Cu2+) in the alkaline solution to copper(I) oxide (Cu2O). That reduction creates the characteristic color change from blue to green, yellow, orange, or brick-red, with the intensity reflecting how much reducing sugar is present. This is why glucose and maltose would give a positive result, while substances without a free carbonyl group won’t. Starch, a long chain of glucose units, lacks readily exposed reducing ends and typically won’t react unless it’s broken down first. Peptides and lipids aren’t detected by Benedict’s test because they don’t rely on the redox chemistry of reducing sugars; peptides are identified by protein-specific tests, and lipids by lipid-specific tests.