Reducing & Non reducing sugars-
source: TecHKnow
Reducing & Non reducing sugars-
Reducing Sugars-
Reducing sugar is a saccharide that is capable of acting as a reducing agent because it has a free aldehyde or ketone group.
The Saccharide which reduces Fehling’s solution , Benedict’s solution & Tollen’s reagent are called reducing sugars.
Reducing sugar contain,
a) Alpha hydroxy aldehyde or alpha hydroxy ketone groups,
b) Cyclic hemiacetal or hemiketal groups in equilibrium with the open chain form having free -CHO or >C=O group,
Example- All Monosaccharide are reducing sugars like D-Glucose, D-Fructose, Di saccharides -Maltose & Lactose .
Non Reducing Sugars-
The Saccharides which do not reduce Fehling’s solution , Benedict’s solution & Tollen’s reagent are called Non reducing sugars.
a) Non reducing sugars do not contain free -CHO group or >C=O group on the carbon adjacent to >C=O group.
b) Cyclic form of non reducing sugars can not be opened into an open chain having free carbonyl group.
Example- All PolySaccharides are non reducing sugars (like starch, cellulose). Sucrose (disaccharide) is also non reducing sugar because anomeric carbon of both the mono saccharides are involved in glycoside or acetal formation.
NOTE- The disaccharides may be reducing or non reducing depending upon the position of linkages between the two monosaccharide units.If the glycosidic linkage involves the carbonyl group of both the monosaccharide units , the disaccharide would be nonreducing (Ex. Sucrose). If one of the carbonyl group in any one of the monosaccharides is free,the disaccharide would be reducing (Ex. Maltose, Lactose).