MALTOSE: STRUCTURE, FUNCTION, FOOD, METABOLISM - BIOLOGY - 2025

The maltose (4-O- (α-D-glucopyranosyl) -β-D-glucopyranose) is a disaccharide composed of two glucose monomers linked by a glycosidic bond of α-1,4 type. Naturally it is one of the main products of the enzymatic hydrolysis of amylose, which is a homopolysaccharide of glucose present in starch.

Maltose is produced commercially from starch that has been treated with barley malt. This disaccharide is very important for the production of fermented alcoholic beverages such as beer or whiskey, in which syrups rich in maltose are used, a product of extracts made with sprouted or "malted" barley grains.

Chemical structure of maltose (Source: Zippanova via Wikimedia Commons)

Since maltose is composed of two glucose residues, the hydrolysis of this disaccharide in the intestines of many animals, including man, is of utmost importance for obtaining energy from the vegetable starches from which it is obtained.

However, excessive consumption of maltose may be contraindicated for diabetic patients or those predisposed to this disease, since this sugar can increase blood glucose levels (glycemia) rapidly.

Many studies have also shown that microorganisms such as bacteria, for example, are capable of metabolizing maltose directly as a source of carbon and energy, using various types of specific enzymes and transporters for this purpose.

Structure of maltose

Maltose synthesis reaction. Javier Velasco

Maltose is a disaccharide composed of two glucose residues linked together through a glucosidic bond of the α-1,4 type, through which the hemiacetal form of an α-D-glucopyranosyl unit is linked with a β residue -D-glucopyranose known as "aglycone".

The oxygen atom that is part of the glycosidic bond is located more or less in the center of the structure, right between the two glucose rings.

Molecular structure of maltose in 3D. AbcdKolya

It has a molecular weight of 342.3 g / mol, which corresponds to the chemical formula C12H22O11. It is a reducing sugar and can undergo mutarrotation, so it can be in the α- or β-maltose form.

Furthermore, this disaccharide can be hydrolyzed by different acids or by a specific enzyme known as maltase.

It is a compound that is commonly found as a crystalline or off-white powder. It is soluble in water and has a slightly sweet taste (about 50% of the sweetening power of sucrose, which is table sugar). It is not easily crystallizable and is fermentable.

Maltose is a very hygroscopic disaccharide, that is, it has a great capacity to absorb moisture from the environment where it is found. It has a melting point close to 120 ° C and can caramelize at 180 ° C.

Function and uses of maltose

Power source

Maltose can be described as a good source of energy, since the hydrolysis of the glycosidic bond that makes up this disaccharide (mediated by maltase), releases two glucose molecules, which are effectively used by cells through the glycolytic pathway.

Since the starch present in many foods of plant origin is composed of the homopolysaccharides amylose and amylopectin, which are polymers of glucose residues linked by glucosidic bonds, the hydrolysis of this in maltose and, subsequently in glucose-free residues, represents an important source of caloric energy for different living organisms.

Beverage production

Commercial syrups rich in maltose, especially those produced from the enzymatic hydrolysis of starch, are widely used for the production of alcoholic beverages such as beer and whiskey, where they work primarily to improve the "oral feel" of these beverages..

Moreover, the production of these and other fermented alcoholic beverages is carried out with a raw material known as "malted barley", which is obtained by germinating this cereal, through a process called malting, where the native enzymes of the seed hydrolyze starch.

In addition, maltose and its derivatives, those that are found in a large proportion in syrups rich in this disaccharide, have properties that prevent gelling and crystallization of the substances where it dissolves.

Maltose foods

Photograph of maltose syrup (Source: www.aziatische-ingredienten.nl via Wikimedia Commons)

Although maltose is not considered an "essential nutrient", that is, its consumption is not essential for man, it is present in many common foods:

- Maltose is obtained industrially from the hydrolysis of starch, but it is a natural intermediate product of the digestion process.

- Sweet potatoes and some types of wheat are rich in maltose in a "free" state.

- Malt syrup and other corn syrups are rich in maltose, as well as brown rice syrup, among others.

- Some beers, citrons and other "malt" beverages have a moderate maltose content, as this is metabolized during alcoholic fermentation.

- Certain industrially processed cereals, compotes, candies, candies and chocolates also have a lot of maltose.

- It is also found in barley, in corn hydrolysates and in different types of starches.

Maltose metabolism

In animals, starch digestion begins with the α-amylase enzymes present in saliva and then continues in the small intestine. The product of this initial degradation consists of a mixture of "limit dextrins", maltose and some glucose-free residues.

The resulting glucose disaccharides (maltose residues) are hydrolyzed by the maltase enzyme, a process that ends with the release of two glucose molecules per maltose molecule, which can be transported to the bloodstream and from there to body tissues.

Maltase catalyzed reaction. On the left a maltose molecule and on the right the two glucose molecules resulting from hydrolysis (Source: Dapantazis.jpg via Wikimedia Commons)

Given that maltose and glucose are highly soluble and osmotically active products, when consumed in excess (more than 120 grams per day) they can “attract” water into the intestine, causing minor diarrhea.

Diabetic patients or patients with a predisposition to this disease are contraindicated the excessive consumption of maltose, as this sugar has the ability to rapidly increase blood glucose levels (glycemia), a counterproductive event for these individuals.

In bacteria, which are prokaryotic organisms, the digestion of polysaccharides such as starch occurs thanks to enzymes that are exported to the outside of the cell and whose catalytic products are introduced to the cytosol by specific transporters, including maltose.

Once in the cytosol, enzymes such as amylomaltase, maltodextrin phosphorylase, and glucokinase participate in the subsequent metabolism of this disaccharide, yielding molecules such as glucose 1-phosphate and glucose 6-phosphate, which enter glycolysis.

References

1. Badui Dergal, S. (2016). Food chemistry. Mexico, Pearson Education.
2. Crow, RR, Kumar, S., & Varela, MF (2012). Maltose Chemistry and Biochemistry. In Dietary Sugars (pp. 101-114).
3. Doudoroff, M., Hassid, WZ, Putman, EW, Potter, AL, & Lederberg, J. (1949). Direct utilization of maltose by Escherichia coli. Journal of Biological Chemistry, 179 (2), 921-934.
4. Ehrmann, M., Ehrle, R., Hofmann, E., Boos, W., & Schlösser, A. (1998). The ABC maltose transporter. Molecular microbiology, 29 (3), 685-694.
5. Ouellette, RJ, & Rawn, JD (2014). Organic chemistry: structure, mechanism, and synthesis. Elsevier.
6. Stick, RV, & Williams, S. (2010). Carbohydrates: the essential molecules of life. Elsevier.