Question

Which of the following is an example for non-reducing sugar?

• A. Glucose
• B. Fructose
• C. Sucrose
• D. Lactose

Hint:

Sucrose is non-reducing because both anomeric carbons are involved in glycosidic bond formation.

Answer 1

The Correct Option is C

Concept:
Sugars are classified as reducing and non-reducing sugars on the basis of the presence or absence of a free aldehyde or ketone group.

Step 1: Meaning of reducing sugar.
A reducing sugar can reduce mild oxidizing agents such as Benedict's reagent or Fehling's solution. This is possible when the sugar has a free anomeric carbon.

Step 2: Checking glucose.
Glucose is a reducing sugar because it has a free aldehyde group in its open-chain form.

Step 3: Checking fructose.
Fructose is also considered a reducing sugar because it can undergo tautomerization in alkaline medium and reduce Benedict's reagent.

Step 4: Checking lactose.
Lactose is a reducing disaccharide because one of its anomeric carbons is free.

Step 5: Checking sucrose.
Sucrose is a non-reducing sugar because both anomeric carbons of glucose and fructose are involved in glycosidic linkage. Hence, no free reducing group is available. \[ \text{Sucrose} = \text{Glucose} + \text{Fructose} \]

Step 6: Final answer.
Therefore, sucrose is a non-reducing sugar. \[ \boxed{\text{Sucrose}} \]