Benedict's Test for Reducing Sugars
The Benedict's test for reducing sugars is used to determine the presence of reducing sugars. There is a Benedict's Test for non-reducing sugars as well. Benedict's solution is the principle reagent in the Benedict's Tests.
The Fehling's Tests for reducing as well as for non-reducing sugar are alternatives to the Benedict's Test. Although based on the same principle, the Fehling's Test is less sensitive. It is also less convenient as the Fehling's Reagents - Fehling's A and B - have to be kept separate until the test is conducted.
What is a reducing sugar?
Sugars are classified as reducing or non-reducing based on their ability to act as a reducing agent during the Benedict's Test. A reducing agent donates electrons during a redox reaction and is itself oxidized.
The aldehyde functional group is the reducing agent in reducing sugars. Reducing sugars have either an aldehyde functional group or have a ketone group - in an open chain form - which can be converted into an aldehyde.
Reducing sugars are simple sugars and include all monosaccharides and most disaccarides. Some examples of monosaccharides are glucose, fructose and galactose.Examples of reducing disaccharides are lactose and maltose.
Note that the disaccharide sucrose is not a reducing sugar. In fact, sucrose is the most common non-reducing sugar.
Dig in to the chemistry of reducing and non-reducing sugars