Question

Reducing sugar has
A) Bonded aldose and ketose groups
B) Free aldose group
C) Free ketose group
D) Both B and C

Answer 1

Hint: A reducing sugar is a sugar which is capable of carrying out reduction or acting as a reducing agent. All monosaccharide are reducing sugars.

Complete Answer:
- A reducing sugar acts as a reducing agent due to the presence of aldose and ketose groups. A reducing sugar gets itself oxidised and reduces the other compound.
- All the monosaccharide is reducing sugars. Some disaccharide and polysaccharide can act as reducing sugar. Monosaccharides contain two groups - aldose contains aldehyde group and ketose contains ketone group.
- A reducing sugar can only act as a reducing agent if it has free aldose or ketose group. Monosaccharide has free aldehyde and ketone groups. Thus they are reducing sugar.
Ex glucose, fructose, lactose.
- The function of reducing sugar is it helps in estimating the flavour in wine, juices and other food items.

Fig: Structure of D-glucose

In the above structure the functional group is the free aldose or aldehyde group.

Thus the correct answer is D. Reducing sugar has free aldose and ketose groups.

Additional Information: Some disaccharides are reducing. It will have only one free reducing end and the other end is held by glycosidic bond. For example- sucrose In some polysaccharides which act as a reducing sugar will also have only one reducing end. For example starch.

Note: The reducing sugar reduces the other compound and gets itself oxidised. All monosaccharide are reducing sugars due to the presence of free aldose and ketose groups.