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Which one of the following statements is not true regarding (+) Lactose?
A
(+) Lactose, $C_{12}H_{22}O_{11}$ contains 8 –OH groups
B
On hydrolysis (+) Lactose gives equal amount of D(+) glucose and D(+) galactose
C
(+) Lactose is a $\beta$-glycoside formed by the union of a molecule of D(+) glucose and a molecule of D(+) galactose
D
(+) Lactose is reducing sugar and does not exhibit mutarotation
Detailed Solution
Lactose is a disaccharide in which C-1 of $\beta$-D-galactose is linked to C-4 of $\beta$-D-glucose by a $\beta$-1,4-glycosidic linkage, so it is a $\beta$-glycoside (true).
On hydrolysis it gives one molecule each of D(+)-glucose and D(+)-galactose, i.e., equal amounts (true).
It has 8 –OH groups, four on each monosaccharide unit (true).
The C-1 of the glucose unit is not involved in the glycosidic bond, so lactose has a free hemiacetal group.
Because of this free hemiacetal group lactose is a reducing sugar and it also shows mutarotation.
Hence the statement that lactose does not exhibit mutarotation is not true.
On hydrolysis it gives one molecule each of D(+)-glucose and D(+)-galactose, i.e., equal amounts (true).
It has 8 –OH groups, four on each monosaccharide unit (true).
The C-1 of the glucose unit is not involved in the glycosidic bond, so lactose has a free hemiacetal group.
Because of this free hemiacetal group lactose is a reducing sugar and it also shows mutarotation.
Hence the statement that lactose does not exhibit mutarotation is not true.