Oligosacharides are formed when 2 to 9 monosaccharide units combine with each other by the loss of water molecules, resulting in the formation of a glycosidic linkage. Conversely hydrolysis of an oligosaccharide in water in the presence of an acid or enzyme yields 2 to 9 monosaccharide units. Oligosaccharides which consist of two monosaccharides units are called as disaccharide. Oligosaccharides containing 3 monosaccharides are called trisaccharides.