Mono-Carbohydrates Carbo MiniTopics
 Elmhurst College
Maltose Sucrose Cellulose  Chemistry Department
Lactose Starch Glycogen  Virtual ChemBook


Maltose is made from two glucose units:

Maltose or malt sugar is the least common disaccharide in nature. It is present in germinating grain, in a small proportion in corn syrup, and forms on the partial hydrolysis of starch. It is a reducing sugar.

The two glucose units are joined by an acetal oxygen bridge in the alpha orientation. To recognize glucose look for the down or horizontal projection of the -OH on carbon # 4. See details on the galactose page towards the bottom.

Malted Barley:

Beer is made from four basic building blocks: water, malted barley, and hops.

Barley, a basic cereal grain, is low in gluten, and is not particularly good for milling into flour for use in products such as bread. Barley is the preferred grain to make beer. The barley grains must be "malted" before they can be used in the brewing process.

Malting is a process of bringing grain to the point of its highest possible starch content by allowing it to begin to sprout roots and take the first step to becoming a photosynthesizing plant.

At the point when the maximum starch content is reached, the seed growth is stopped by heating the grain to a temperature that stops growth but allows an important natural enzyme diastase to remain active. Barley, once "malted" is very high in the type of starches that an enzyme called diastase (found naturally on the surface of the grain, just under the husk) can convert starch quite easily into the disaccharide called Maltose. This sugar is then fermented or metabolized by the yeasts to create carbon dioxide and ethyl alcohol.

Adapted from: Beer Basics


Acetal Functional Group:

Carbon # 1 (red on left) is called the anomeric carbon and is the center of an acetal functional group. A carbon that has two ether oxygens attached is an acetal.

The Alpha position is defined as the ether oxygen being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection. This is the same definition as the -OH in a hemiacetal.

Open graphic of hemiacetal in a new window

Maltose - Chime in new window

Hydrolysis of Starch:

In the hydrolysis of any di- or poly saccharide, a water molecule helps to break the acetal bond as shown in red. The acetal bond is broken, the H from the water is added to the oxygen on one glucose.

The -OH is then added to the carbon on the other glucose. In this case the diastase enzyme is very specific and cuts the starch chain in units of two glucose which happens to be maltose.