What are Disaccharides?
Disaccharides are those carbohydrates which on hydrolysis with acids or enzymes give two molecules of monosaccharides which can either be same or different. The oxide linkage is formed after the loss of water molecule and then the two monosaccharides are formed by that linkage. When two monosaccharide units are joined via oxygen atom then that linkage is called a glycosidic linkage.
The most common disaccharide is sucrose which gives D -(+)- glucose and D-(-)- fructose on hydrolysis.
Both the monosaccharides i.e. glucose and fructose are connected through glycosidic linkage between alpha glucose and second carbon beta fructose. Sucrose is a non-reducing sugar as both the reducing groups of glucose and fructose are involved in the glycosidic bond formation.
Sucrose being dextrorotatory in nature gives dextrorotatory glucose as well as laevorotatory fructose on hydrolysis. The overall mixture is laevorotatory and this is because the laevorotation of fructose (-92.4) is more than the dextrorotation of glucose (+52.5).
Maltose is also one of the disaccharides which have two α -D-glucose units which are connected by first carbon of the glucose and also linked to the fourth carbon of another glucose unit. In the solution, a free aldehyde can be produced at the first carbon of the second glucose of the solution and it is a reducing sugar as it shows reducing properties.
Commonly it is called as milk sugar as this disaccharide is found in milk. It is made up of Beta-D-galactose and β-D-glucose. The bond is between first carbon of galactose and the fourth carbon of glucose.This is also a reducing sugar.
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