<Ul> <Li> Reducing disaccharides, in which one monosaccharide, the reducing sugar of the pair, still has a free hemiacetal unit that can perform as a reducing aldehyde group; cellobiose and maltose are examples of reducing disaccharides, each with one hemiacetal unit, the other occupied by the glycosidic bond, which prevents it from acting as a reducing agent . </Li> <Li> Non-reducing disaccharides, in which the component monosaccharides bond through an acetal linkage between their anomeric centers . This results in neither monosaccharide being left with a hemiacetal unit that is free to act as a reducing agent . Sucrose and trehalose are examples of non-reducing disaccharides because their glycosidic bond is between their respective hemiacetal carbon atoms . The reduced chemical reactivity of the non-reducing sugars in comparison to reducing sugars, may be of advantage where stability in storage is important . </Li> </Ul> <Li> Reducing disaccharides, in which one monosaccharide, the reducing sugar of the pair, still has a free hemiacetal unit that can perform as a reducing aldehyde group; cellobiose and maltose are examples of reducing disaccharides, each with one hemiacetal unit, the other occupied by the glycosidic bond, which prevents it from acting as a reducing agent . </Li> <Li> Non-reducing disaccharides, in which the component monosaccharides bond through an acetal linkage between their anomeric centers . This results in neither monosaccharide being left with a hemiacetal unit that is free to act as a reducing agent . Sucrose and trehalose are examples of non-reducing disaccharides because their glycosidic bond is between their respective hemiacetal carbon atoms . The reduced chemical reactivity of the non-reducing sugars in comparison to reducing sugars, may be of advantage where stability in storage is important . </Li> <P> The formation of a disaccharide molecule from two monosaccharide molecules proceeds by displacing a hydroxyl radical from one molecule and a hydrogen nucleus (a proton) from the other, so that the now vacant bonds on the monosaccharides join the two monomers together . The vacant bonds on the hydroxyl radical and the proton unite in their turn, forming a molecule of water, that then goes free . Because of the removal of the water molecule from the product, the term of convenience for such a process is "dehydration reaction" (also "condensation reaction" or "dehydration synthesis"). For example, milk sugar (lactose) is a disaccharide made by condensation of one molecule of each of the monosaccharides glucose and galactose, whereas the disaccharide sucrose in sugar cane and sugar beet, is a condensation product of glucose and fructose . Maltose, another common disaccharide, is condensed from two glucose molecules . </P>

When two monosaccharides bond to form a disaccharide