What is the difference between a reducing sugar and a non-reducing sugar?
Reducing Sugars are those which are easily oxidized by mild oxidizing agent like ferric Fe^(2+) or cupric Cu^(2+) ions
The carbonyl carbon of the sugar is oxidized to a carboxylic group. Glucose, maltose nd other sugar capable of reducing ferric nd cupric ions are reducing sugars nd it's the basis of Fehling's reaction.
Basically the reduding effect is due to the free anomeric carbon in sugar.
A reducing sugar, as the name suggests is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group.
A reducing sugar reduces another compound and is itself oxidized; that is, the carbonyl carbon of the sugar is oxidized to a carboxyl group. Any carbohydrate which is capable of being oxidized and causes the reduction of other substances without having to be hydrolysed first can be termed as reducing sugar.
The aldehyde functional group allows the sugar to act as a reducing agent, for example in the Tollens' test or Benedict's test. The cyclic hemiacetal forms of aldoses can open to reveal an aldehyde and certain ketoses can undergo tautomerization to become aldoses. However, acetals, including those found in polysaccharide linkages, cannot easily become free aldehydes.
Examples of reducing sugars are Glucose, Fructose, Lactose, etc.
Example of non-reducing sugars is Sucrose.