Monosaccharides may combine together in pairs to give disaccharides (double sugars) involving the last of a single water molecule and the reaction is known as a condensation reaction. The bond formed is called a glucosidic bond. It is usually formed with carbon atom number 1 of one monosaccharide and carbon number 4 of the other. Hence it is called a 1, 4-glycosidic bond. Any two monosaccharides may be link in this way to form a disaccharide of which maltose, lactose and sucrose are the most common.

Disaccharides like monosaccharide are sweet, soluable and crystatine. Maltose and lactose are reducing sugar where as sucrose is a non-reducing sugar.

1. Maltose form from barley, it is form by the condensation of two glucose molecules, linked by 1, 4 glycosidic bond. It is a reducing sugar. It is a malt sugar.
2. Lactose: it is found in the milk of animals and synthesized only by the cells of mammary glands during lactations. It is reducing sugar form by condensation of a glucose and a galactose molecule. It is an important source of energy in suckling mammal. It is form by 1, 4 glycosidic linkage.
3. Sucrose: It is found in cane sugar, it is formed from the combination of fructose and glucose molecule, it is a non reducing sugar. b/c the fractional group of its constivent monosaccharide are hidden as glycosidic bonds are formed and only expose when hydrolised into monosaccharides by using some acid such as hydrochloride acid or enzymes such as sucrose or invertase.