Which two sugars are reducing sugars commonly found in fruit juice?

Which two sugars are reducing sugars commonly found in fruit juice?

• A. Glucose and Fructose
• B. Sucrose and Lactose
• C. Maltose and Galactose
• D. Ribose and Deoxyribose

Answer: (A)

Reducing sugars are those that can act as reducing agents because they have a free carbonyl group in equilibrium with an open-chain form. In solution, sugars like glucose and fructose exist in forms that expose a reactive carbonyl, which lets them reduce other compounds (as in Benedict’s test). Glucose is an aldose, so it has a free aldehyde group when it opens from its ring form, making it a reducing sugar. Fructose is a ketose, but under typical conditions it can isomerize to forms that reveal a reactive carbonyl, also enabling reduction. Fruit juice commonly contains glucose, fructose, and some sucrose; among these, both glucose and fructose are reducing sugars, while sucrose is non-reducing because its anomeric carbons are tied up in the glycosidic bond. Other sugars listed are not the typical pair found as reducing sugars in fruit juice: lactose and maltose are reducing but not common in fruit juice, and ribose or deoxyribose are not present in significant amounts in juice.

Reducing sugars are those that can act as reducing agents because they have a free carbonyl group in equilibrium with an open-chain form. In solution, sugars like glucose and fructose exist in forms that expose a reactive carbonyl, which lets them reduce other compounds (as in Benedict’s test).

Glucose is an aldose, so it has a free aldehyde group when it opens from its ring form, making it a reducing sugar. Fructose is a ketose, but under typical conditions it can isomerize to forms that reveal a reactive carbonyl, also enabling reduction. Fruit juice commonly contains glucose, fructose, and some sucrose; among these, both glucose and fructose are reducing sugars, while sucrose is non-reducing because its anomeric carbons are tied up in the glycosidic bond.

Other sugars listed are not the typical pair found as reducing sugars in fruit juice: lactose and maltose are reducing but not common in fruit juice, and ribose or deoxyribose are not present in significant amounts in juice.