Sucrose and lactose both are disaccharides. In sucrose, anomeric- C1 of α−D− glucose and C2 of β -D-fructose are blocked by 1,2 -glycosidic linkage. So, it is a non-reducing sugar. In lactose, anomeric C1 of β-D-galactose is blocked by 1,4 -glycosidic linkage but anomeric-C 1 of β−D -glucose has free −OH group, which shows reducing property.