Maltose Structure

What Is Maltose?

Maltose, also known as malt, is a disaccharide made up of two alpha D-glucose units. The two units of glucose are linked with an alpha 1,4 glycosidic bond. In the small intestinal lining in humans, the enzyme maltase and isomaltase break down the molecules of maltose into two glucose molecules, which is then absorbed by the body. Starch is the most abundant polysaccharide in plant cells after cellulose.

On the contrary, a carbohydrate formed by the joining of two units of glucose is called a disaccharide. The three common types of disaccharides are sucrose, maltose and lactose. The other disaccharides which are less commonly known are lactulose, trehalose, and cellobiose. When one water molecule is removed by the joining of two monosaccharides, then a molecule of a disaccharide is formed, and the reaction which takes place during this process is known as the dehydration reaction.

Maltose Structure

Maltose is a disaccharide made up of two alpha D glucose in which C1 of the first glucose unit is bonded to C4 of the second glucose unit, as shown figure below. The bond that joins two alpha glucose units is called alpha 1,4 glycosidic linkage.

At C1 of the second glucose unit, an aldehyde group can be formed in solution, which makes maltose a reducing sugar.

Also Read: Glucose Structure

Properties of Maltose

• Maltose is a reducing sugar. It tastes sweet but is only 30-60% as sweet as sugar.
• The hydrolysis reaction of maltose in the presence of an acid catalyst gives two molecules of alpha D-glucose.
• There is a free anomeric carbon present in the structure of maltose which can undergo mutarotation in solution. The resultant solution will be a mixture of alpha and beta maltose.
• Since the aldehydic group is formed in the solution, maltose gives a positive test with Benedicts and Tollens reagents.

Maltose Production

The first discovery of maltose was made by Augustin-Pierre Dubrunfaut. However, this was not widely accepted. It was only in the year 1872 that its existence was confirmed by an Irish chemist named Cornelius O’Sullivan. The term maltose has been taken from the word malt, where the suffix ‘ose’ was added, describing that it belonged to the category of sugar.

Maltose belongs to an important biochemical series of glucose chains. It can be prepared by the hydrolysis of starch in the presence of the enzyme diastase. During hydrolysis, starch is broken down into two glucose molecules. Starch is also heated with a strong acid for several minutes in the process. In living organisms, the enzyme maltase helps the reaction to take place.

Also Read: Hydrolysis, Salts and Types

Uses of Maltose

• Disaccharide such as sucrose is very sweet and is used as a sweetener in food products, but maltose lacks sweetness and is not used as a sweetener. Instead, it is used in the malting of barley for the manufacturing of beer.
• It is used extensively in alcohol production.
• Free maltose, as well as maltose formed by the digestion of starch in the mouth, can cause dental caries.
• Enzyme maltase and isomaltase present in the small intestine break down maltose into two glucose units which are then absorbed. Our body has the capacity to absorb maltose directly, which later on can be broken down into glucose units for producing energy.
• Due to a high glycemic index, maltose increases blood sugar levels.

Structural Difference between Sucrose, Lactose and Maltose

Maltose, sucrose and lactose all are disaccharides made up of glucose units. Disaccharides are sugar, and so are monosaccharides. These three sugars have different components.

Maltose is composed of two molecules of glucose, while sucrose is made up of one molecule of glucose and another one is fructose which is also a monosaccharide. Lactose is made up of one molecule of glucose, just like maltose, but the second component of this lactose is different from sucrose; instead of fructose, it is made up of galactose which is also a monosaccharide.

Difference between Maltose and Cellobiose

Both maltose and cellobiose are disaccharide sugars which are made up of two molecules of glucose, and both are linked together between C1 of one sugar and C4 of the other sugar. But the first glucose unit in maltose is the alpha anomer, while the first glucose unit in cellobiose is the beta anomer of glucose.

Fig: (1) structure of maltose. (2) structure of cellobiose

Both maltose and cellobiose are disaccharides, but the main differences are given below.

• Maltose is an intermediate sugar formed by the action of amylase-catalyzed hydrolysis of starch. Maltose is composed of two units of D-glucose linked together through an alpha 1,4 glycosidic bond.
• Cellobiose is an intermediate sugar formed by the hydrolysis of cellulose by the enzyme cellulase. Cellobiose is composed of two units of D-glucose linked together through a beta-1,4 glycosidic bond.