Editing Reducing sugar (section)

==Examples==

All monosaccharides are reducing sugars because they either have an aldehyde group (if they are aldoses) or can tautomerize in solution to form an aldehyde group (if they are ketoses).<ref name=Britannica>{{cite encyclopedia |last=Davidson |first=Eugene A. |encyclopedia=Encyclopædia Britannica |title=Carbohydrate |year=2015}}</ref> This includes common monosaccharides like [[galactose]], [[glucose]], [[glyceraldehyde]], [[fructose]], [[ribose]], and [[xylose]].

Many [[disaccharide]]s, like [[cellobiose]], [[lactose]], and [[maltose]], also have a reducing form, as one of the two units may have an open-chain form with an aldehyde group.<ref>{{cite book |last1=Klein |first1=David.  |date=2012 |title=Organic Chemistry |edition=First |publisher=John Wiley & Sons |pages=1162–1165 |isbn=978-0471756149}}</ref> However, [[sucrose]] and [[trehalose]], in which the [[anomeric carbon]] atoms of the two units are linked together, are nonreducing disaccharides since neither of the rings is capable of opening.<ref name=Britannica/>

[[File:Maltose Gleichgewicht.svg|thumb|center|upright=3|class=skin-invert|Equilibrium between cyclic and open-chain form in one ring of maltose]]

In glucose [[polymer]]s such as [[starch]] and starch-[[Derivative (chemistry)|derivatives]] like [[corn syrup|glucose syrup]], [[maltodextrin]] and [[dextrin]] the [[macromolecule]] begins with a reducing sugar, a free aldehyde. When starch has been partially [[hydrolysis|hydrolyzed]] the chains have been split and hence it contains more reducing sugars per gram. The percentage of reducing sugars present in these starch derivatives is called [[dextrose equivalent]] (DE).

[[Glycogen]] is a highly branched polymer of glucose that serves as the main form of carbohydrate storage in animals. It is a reducing sugar with only one reducing end, no matter how large the glycogen molecule is or how many branches it has (note, however, that the unique reducing end is usually covalently linked to [[glycogenin]] and will therefore not be reducing). Each branch ends in a nonreducing sugar residue. When glycogen is broken down to be used as an energy source, glucose units are removed one at a time from the nonreducing ends by enzymes.<ref name=Lehninger/>