What is Maltose?

Maltose is a disaccharide formed from two units of glucose joined with an α(1→4) bond also known as maltobiose or malt sugar. The two glucose molecules are joined with an α(1→6) bond in the isomer isomaltose. Maltose is a disaccharide, C12H22O11 formed from the digestion of starch by amylase. It is then converted to glucose by maltase. Two glucose units are removed at a time when beta-amylase breaks down starch, thus producing maltose. It was named after malt as an example of this reaction is found in germinating seeds. It is a reducing sugar, unlike sucrose.


Maltose was 'discovered' by French chemist Augustin-Pierre Dubrunfaut. His discovery was not so widely accepted until it was confirmed in 1872 by Irish chemist and brewer Cornelius O'Sullivan. Maltose word was derived from malt, combined with the suffix '-ose' which is used in names of sugars. Making maltose and its use in China goes as far back as the Shang dynasty. The use of maltose and its use has been recorded since the period of Emperor Jimmu.

Structure and Nomenclature

Maltose is a disaccharide: the carbohydrates are generally divided into monosaccharides, oligosaccharides, and polysaccharides depending on the number of sugar subunits. Maltose is made up of two sugar units, an oligosaccharide, and a disaccharide as it consists of two glucose molecules. Glucose is a common hexose: a monosaccharide containing six carbon atoms. The two units of glucose are in the form of pyranose and are joined by an O-glycosidic bond, with the first carbon (C1) of the 1st glucose linked to the 4th carbon (C4) of the second glucose, indicated as (1→4). As the glycosidic bond to the anomeric carbon (C1) is in the opposite plane from the CH2OH substituent in the same ring (C6 of the first glucose), that is why the link is characterized as α. If the glycosidic bond to the anomeric carbon (C1) were in the same plane as the CH2OH substituent, it would be classified as a β(1→4) bond, and the resulting molecule would be cellobiose. Depending on the bond direction of the attached hydroxyl group relative to the CH2OH substituent of the same ring, the anomeric carbon (C1) of the second glucose molecule, which is not involved in a glycosidic bond, could be either an α- or β-anomer hence resulting in either α-maltose or β-maltose. An isomer of maltose is isomaltose which is similar to maltose but instead of a bond in the α(1→4) position, it is in the α(1→6) position.             

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                                       β - Maltose                                                        α - Maltose


Maltose is also a reducing sugar like glucose because the ring of one of the two glucose units can open to present a free aldehyde group but the other one cannot due to the nature of the glycosidic bond. It can be broken down to glucose by the enzyme maltase, which catalyses the hydrolysis of the glycosidic bond.

Maltose shows mutarotation in aqueous solution and in aqueous solutions, these two forms are in equilibrium. By the Woehlk test or Fearon's test on methylamine, maltose can easily be detected.

Maltose is about 30-60% as sweet as sugar, depending on the concentration. 

Sources and Absorption

Maltose is a component of malt, a substance which is obtained by converting a cereal grain into malt by causing it to sprout(by soaking in water) and then halting germination(by drying with hot air) so that enzymes are developed and break down starches and proteins in the grain. Maltose is also present in partially hydrolysed starch products like maltodextrin, corn syrup, and acid-thinned starch.

Maltose is broken down by various maltase enzymes in humans hence providing two glucose molecules that are further broken down to provide energy, or stored as glycogen. Sucrose intolerance is caused in humans due to lack of the sucrase-isomaltase enzyme, but because there are four different maltase enzymes, complete maltose intolerance is extremely rare.

Did You Know?

  • Maltose has a sweet taste, but is only about 30-60% as sweet as sugar, depending on the concentration and a 10% solution of maltose is 35% as sweet as sucrose.

  • Maltose is useful as a low-cost sugar source in the form of high-maltose corn syrup and is generally found in starchy grains, vegetables, and fruits.

  • Maltose is produced from distilling fermented grains, usually rice and malt. The ingredients used are rice, water, malt. Scientifically, maltose is made up of two glucose molecules combined together, therefore no fructose insight.

  • Maltose is a type of sugar that tastes less sweet than table sugar. It is used as a substitute for high-fructose corn syrup as it contains no fructose. Maltose is harmful if consumed in excess. It leads to obesity, diabetes, and heart disease. 

FAQ (Frequently Asked Questions)

1. How Is Glucose Different From Maltose?

Free glucose has a hemiacetal linkage that exists in dynamic equilibrium with the open-chain form. As such, it reacts with the reagent. Maltose is a disaccharide composed of two glucose monomers joined by an alpha (1 → 4) glycosidic linkage. Maltose is made from two glucose units. The least common disaccharide in nature is Maltose or malt sugar.

2. Is Maltose Made Up of Alpha or Beta Glucose?

Maltose is composed of two molecules of glucose joined by an α-1, 4-glycosidic linkage. It is generally found in sprouting grain and is a reducing sugar. Lactose is composed of a molecule of galactose joined to a molecule of glucose by a β-1, 4-glycosidic linkage. It is found in milk and acts as reducing sugar.