Maltose was discovered byAugustin-Pierre Dubrunfaut, although this discovery was not widely accepted until it was confirmed in 1872 by Irish chemist and brewerCornelius O'Sullivan.[5][6] Its name comes frommalt, combined with the suffix '-ose' which is used in names of sugars.[4]
Carbohydrates are generally divided intomonosaccharides,oligosaccharides, andpolysaccharides depending on the number of sugar subunits. Maltose, with two sugar units, is a disaccharide, which falls under oligosaccharides. Glucose is ahexose: a monosaccharide containing six carbon atoms. The two glucose units are in thepyranose form and are joined by anO-glycosidic bond, with the first carbon (C1) of the firstglucose linked to the fourth carbon (C4) of the secondglucose, indicated as (1→4). The link is characterized as α because the glycosidic bond to the anomeric carbon (C1) is in the opposite plane from theCH 2OHsubstituent in the same ring (C6 of the first glucose). If the glycosidic bond to the anomeric carbon (C1) were in the same plane as theCH 2OH substituent, it would be classified as aβ(1→4) bond, and the resulting molecule would becellobiose. 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 depending on the bond direction of the attached hydroxyl group relative to theCH 2OH substituent of the same ring, resulting in either α-maltose or β-maltose.[citation needed]
Anisomer of maltose isisomaltose. This is similar to maltose but instead of a bond in the α(1→4) position, it is in the α(1→6) position, the same bond that is found at the branch points ofglycogen andamylopectin.[citation needed]
Like glucose, maltose is areducing sugar, because the ring of one of the two glucose units can open to present a freealdehyde group; the other one cannot because of the nature of the glycosidic bond. Maltose can be broken down to glucose by themaltase enzyme, which catalyses the hydrolysis of the glycosidic bond.[citation needed]
Maltose in aqueous solution exhibitsmutarotation, because the α and β isomers that are formed by the different conformations of the anomeric carbon have differentspecific rotations, and in aqueous solutions, these two forms are in equilibrium. Maltose can easily be detected by the Woehlk test or Fearon's test on methylamine.[7]
It has a sweet taste, but is only about 30–60% as sweet as sugar, depending on the concentration.[8] A 10% solution of maltose is 35% as sweet as sucrose.[9]
Maltose is amalt component, a substance obtained when the grain is softened in water and germinates. It is also present in highly variable quantities in partially hydrolyzed starch products likemaltodextrin,corn syrup and acid-thinned starch.[10]
Outside of plants, maltose is also (likely) found inhoney.[11]
In humans, maltose is broken down by various maltase enzymes, providing two glucose molecules that can befurther processed: either broken down to provide energy, or stored as glycogen. The lack of thesucrase-isomaltase enzyme in humans causessucrose intolerance, but complete maltose intolerance is extremely rare because there are four different maltase enzymes.[12]
