Maltose: structure, foods, digestion, role in seed germination

Maltose, also called malt sugar, is rarely found naturally in foods, whereas it is added to many products. It is often present in products commercialized as sugar free, in which it is referred as malt (it should be noted that maltose and sucrose have the same caloric content) and may be used as sweetener as well, with a sweetness equal to 33% of sucrose.
It consists of two units of glucose linked together by α-(1→4) glycosidic bond, then it is a disaccharide, has the molecular formula C12H22O11 and molar mass 342.30 g/mol.
Structural formula, drawn in Haworth projection, of maltose

Maltose in germinating seeds

In seeds, during germination, it is synthesized in a reaction catalyzed by the enzyme diastase (amylase) that hydrolyzes starch to the disaccharide for the new plant. Diastase is used commercially as well to hydrolyze starch to maltose (malt) in the brewing of beer.
As vegetable diastase also pancreatic α-amylase (EC 3.2.1.1) is able to cleave starch into molecules of the disaccharide (in addition to maltose, maltotriose, a trisaccharide, and small oligosaccharides are released from its action on starch).

Intestinal digestion

The disaccharide, both coming from pancreatic α-amylase action on starch or added to commercialized foods, by the action of the multifunctional enzyme sucrase-isomaltase (see sucrose), undergoes the hydrolysis of the α-(1→4) glycosidic bond between the two molecules of glucose that form it releasing them (α-(1→4)-glicosidasic reaction).

References

Aoki N., Scofield G.N., WangX-D., Offler C.E., Patrick J.W., and Furbank R.T. Pathway of sugar transport in germinating wheat seeds. Plant Physiol 2006;141(4):1255-1263. doi:10.1104/pp.106.082719

Belitz .H.-D., Grosch W., Schieberle P. “Food Chemistry” 4th ed. Springer, 2009

Bender D.A. “Benders’ Dictionary of Nutrition and Food Technology”. 8th Edition. Woodhead Publishing. Oxford, 2006

Stipanuk M.H., Caudill M.A. Biochemical, physiological, and molecular aspects of human nutrition. 3rd Edition. Elsevier health sciences, 2012

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