Question

Considering the facts that
(i) sucrose forms glycosidic linkage between $C_{1}$ of glucose and $C _{2}$ of fructose, while
(ii) lactose forms glycosidic linkage between $C_{1}$ of galactose and $C _{4}$ of glucose
Choose the coirect statement.

• A. Both sucrose and lactose are reducing sugars
• B. Both sucrose and lactose are non-reducing sugars
• C. Sucrose is reducing sugar and lactose is nonreducing sugar
• D. Lactose is reducing sugar and sucrose is nonreducing sugar

Answer 1

Answer: (D)

Sucrose and lactose both are disaccharides.
In sucrose, anomeric- $C_{1}$ of $\alpha-D-$ glucose and $C_{2}$ of $\beta$-D-fructose are blocked by $1,2$ -glycosidic linkage.
So, it is a non-reducing sugar. In lactose, anomeric $C_{1}$ of $\beta-D$-galactose is blocked by $1,4$ glycosidic linkage but anomeric-$C _{1}$ of $\beta-D$-glucose has free $- OH$ group, which shows reducing property.