Reducing Property of Sugar

• Definition: A sugar is called a reducing sugar if it has a free aldehyde group (–CHO) or a free ketone group (–CO) in its open-chain form that can reduce mild oxidizing agents like Benedict’s reagent or Fehling’s solution.

• Real Data Examples:

  • Reducing sugars: Glucose, fructose, galactose, lactose, maltose.

  • Non-reducing sugar: Sucrose (no free aldehyde/ketone group).

• Biochemical Basis: The free anomeric carbon can participate in redox reactions, reducing Cu²⁺ → Cu⁺ (orange-red precipitate).

• Clinical Use: Benedict’s test detects reducing sugars in urine (important in diabetes mellitus, galactosemia).

✅ Key Point: Reducing property depends on the presence of a free reactive carbonyl group.