por Maltose (4-O-(α-D-glucopyranosyl)-β-D-glucopyranose) is a disaccharide composed of two glucose monomers connected by an α-1,4 type glycosidic bond. It is naturally one of the main products of the enzymatic hydrolysis of amylose, which is a glucose homopolysaccharide 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, product of extracts made with germinated or “malted” barley grains.
Since maltose is made up of two glucose residues, the hydrolysis of this disaccharide in the intestine of many animals, including man, is extremely important for obtaining energy from the plant starches from which it is obtained.
However, excessive consumption of maltose may be contraindicated for diabetic patients or those with a predisposition to this disease, since said sugar can increase blood glucose levels (glycemia) rapidly.
Many studies have also shown that microorganisms such as bacteria, for example, are capable of directly metabolizing maltose as a carbon and energy source, using various types of specific enzymes and transporters for this purpose.
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maltose structure
Maltose is a disaccharide composed of two glucose residues linked together through an α-1,4-type glycosidic bond, through which the hemiacetal form of an α-D-glucopyranosyl unit is linked to 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.
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 mutarotation, 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 vegetable origin is composed of the homopolysaccharides amylose and amylopectin, which are polymers of glucose residues linked by glycosidic bonds, the hydrolysis of this into maltose and, subsequently, into free glucose residues, represents an important source of heat energy for different living organisms.
beverage production
Commercial maltose-rich syrups, 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 function mainly 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 found in large proportions in syrups rich in this disaccharide, have properties that prevent the gelling and crystallization of the substances in which it is dissolved.
foods with maltose
Although maltose is not considered an «essential nutrient», that is, its consumption is not essential for humans, 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 the “free” state.
– Malt syrup and other corn syrups are high in maltose, as is brown rice syrup, among others.
– Some beers, ciders and other “malt” drinks have a moderate maltose content, since it 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 hydrolyzed corn and different types of starches.
maltose metabolism
In animals, starch digestion begins with 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 free glucose residues.
The resulting glucose disaccharides (maltose residues) are hydrolyzed by the enzyme maltase, a process that results in the release of two glucose molecules per maltose molecule, which can be transported into the bloodstream and from there to body tissues. .
Since maltose and glucose are highly water-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 those with a predisposition to said disease are contraindicated in excessive consumption of maltose, since this sugar has the capacity 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 into 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
Badui Dergal, S. (2016). Food chemistry. Mexico, Pearson Education.
Crow, RR, Kumar, S., & Varela, MF (2012). Maltose Chemistry and Biochemistry. In Dietary Sugars (pp. 101-114).
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.
Ehrmann, M., Ehrle, R., Hofmann, E., Boos, W., & Schlösser, A. (1998). The ABC maltose transporter. Molecular microbiology, 29(3), 685-694.
Ouellette, RJ, & Rawn, JD (2014). Organic chemistry: structure, mechanism, and synthesis. Elsevier.
Stick, RV, & Williams, S. (2010). Carbohydrates: the essential molecules of life. Elsevier.