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Why is sucrose called a nonreducing sugar?

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Tall, dense stalks of sugarcane grow on both sides of a narrow path, with green leaves arching overhead and sunlight illuminating the plants. — sugar Lines of sugarcane before harvest.

Sucrose is classified as a nonreducing sugar because of the unique way its constituent monosaccharides—glucose and fructose—are linked together.1

In a typical reducing sugar, a free aldehyde or keto group is available to participate in chemical reactions, such as oxidation. However, in sucrose, the linkage occurs between the two anomeric hydroxyl groups of the glucose and fructose molecules. This bond effectively "locks" these groups, meaning neither a free aldehyde group on the glucose moiety nor a free keto group on the fructose moiety is available to react.12

These functional groups only become available to act as reducing agents if the glycosidic linkage between the two monosaccharides is destroyed, such as through hydrolysis. Consequently, because these reactive sites are occupied within the disaccharide structure, sucrose does not exhibit the properties associated with reducing sugars.31