Lactose (C12H22O11) is a disaccharide. It is found in milk, therefore, it is also known as milk sugar. It is formed from two monosaccharide units, namely D – galactose and D – glucose.
The glycosidic linkage is formed between C-l of β-D-galactose and C -4 of glucose.
Therefore the linkage in lactose is called β – 1,4 – glycosidic linkage.
The hemiacetal group at C-l of the glucose unit is not involved in glycosidic linkage but is free.
Hence lactose is a reducing sugar.
The above figure shows Haworth formula of lactose.
