Disaccharide

It outlines a non-reductive dysaccharide formed by glucose and fructose bonding.

The disaccharides, also called ósidos, are a type of carbohydrates formed by the condensation (union) of two monosaccharides through an O-glycosidic bond (with loss of a water molecule) since it establishes in the form of ether, with an oxygen atom linking each pair of monosaccharides, mono or dicarbonyl, which can also be α or β depending on the -OH hemiacetal or hemiketal.

Disaccharides and polysaccharides can be hydrolyzed.

The most common disaccharides are:

• Sacarosa: formed by the union of a glucose and a fructose. Sugar is also called common sugar. He has no reducing power.
• Lactose: formed by the union of a glucose and a galactous. It's milk sugar. He has reducing power.
• Maltosa, isomaltosa, trehalosa and jealousy: formed by the union of two glucose, are different depending on the union between glucose. All of them have reducing power, except the trehalous.

The reducing character occurs in a disaccharide if one of the monosaccharides that form it has its anomeric (or carbonyl) carbon free, that is, if this carbon is not part of the O-glycosidic bond. In other words, if the O-glycosidic bond is monocarbonyl, the resulting disaccharide will be reducing (maltose, cellobiose, etc.), while if the O-glycosidic bond is dicarbonyl, the resulting disaccharide will be non-reducing (sucrose, trehalose). Since monosaccharides (except for glycoaldehyde) have cyclization capacity, and, being in their open chain form, they have the capacity to oxidize, thus explaining their reducing character.

The molecular formula of disaccharides is C₁₂H₂₂O₁₁. The covalent bond between two monosaccharides causes the removal of a hydrogen atom from one of the monosaccharides and a hydroxyl group from the other monosaccharide, thus removing a water molecule (H₂O) that passes into the reaction medium.

In the mucosa of the human digestive tract there are enzymes called disaccharidases, which hydrolyze the glycosidic bond that joins the two monosaccharides, for intestinal absorption.

Main disaccharides

The main disaccharides of biological interest are the following:

• Maltosa: It is naturally free in the malt, from which it receives the name and forms part of several reserve polysaccharides (almidon and glucogen), of which it is obtained by hydrolysis. The malt is extracted from grains of cereal, rich in starch, germinated. It is used to make beer, whisky and other drinks. The molecule has reducing characteristics.
• Lactose or milk sugar: It is free in the milk of the mammals. Much of the world's population presents the so-called "intolerance to lactose", which is a disease characterized by the most or less serious involvement of the intestinal mucosa that is incapable of digesting lactose.
• Sacarous or sugar cane and beetle: It is the sugar that is obtained industrially and marketed in the market as usual sweetener. In addition, it is very well represented in nature in fruits, seeds, nectar, etc. It does not have a reducing character because anomial carbons are attached to each other.
• Jealous: Present in the cellulose molecule and is not free.
• Isomaltosa: It is present in polysaccharides “starch” and “glucogen” and is not free.