What is the case for that sucrose is said to be non-reducing sugar?

Since Jiskha doesn't have a biology expert at this time, please try posting your question at this site.

http://www.biology-online.org/biology-forum/

It doesn't reduce the blue Cu2+ ions present in benedicts solution to red Copper precipitate

Sucrose is considered a non-reducing sugar because it does not show a positive reaction with commonly used laboratory reagents that are indicative of the presence of reducing sugars.

To understand why sucrose is non-reducing, it's important to know what reducing sugars are. Reducing sugars, such as glucose and fructose, have a free aldehyde or ketone functional group that can undergo oxidation reactions. This means that they have the ability to reduce other compounds, like certain metal ions or Benedict's solution, by donating electrons.

However, sucrose does not have a free aldehyde or ketone group, making it unable to undergo the same oxidation reactions. Sucrose is a disaccharide made up of glucose and fructose molecules joined together through a glycosidic bond. The α-glucose component has a hemiacetal group, but it is involved in the glycosidic bond and is no longer available for reducing reactions.

To test for reducing sugars, such as glucose or fructose, in a given sample containing sucrose, you can perform certain chemical tests. One such test is the Benedict's test, which involves heating the sample with Benedict's reagent (a solution containing copper sulfate and sodium citrate). If reducing sugars are present, they react with the copper ions in the reagent, resulting in a color change from blue to green, yellow, orange, or red, depending on the amount of reducing sugar present.

However, when performing this test on a pure sample of sucrose, no color change occurs, indicating the absence of reducing sugars. This confirms that sucrose is a non-reducing sugar.

In summary, sucrose is classified as a non-reducing sugar because it lacks a free aldehyde or ketone group necessary for oxidation reactions. Chemical tests, such as the Benedict's test, can be used to confirm the absence of reducing sugars in a sample containing sucrose.