A non-reducing sugar is one that does not have a free aldehyde or ketone group capable of acting as a reducing agent.
- Glucose, fructose, and maltose all have free reducing ends that can reduce Tollens' or Benedict's reagent.
- Sucrose, however, is a non-reducing sugar because its glycosidic bond involves the aldehyde group of glucose and the ketone group of fructose, leaving no free reducing group.
Hence, sucrose is a non-reducing sugar.