Why is lactose a reducing sugar but not sucrose?

Many disaccharides, like cellobiose, lactose and maltose, also have a reducing form, as one of the two units may have an open-chain form with an aldehyde group. However, sucrose and trehalose, in which the anomeric carbons of the two units are linked together, are nonreducing disaccharides since neither of the rings is capable of opening. read more

Plus, not all sugars have the same chemical properties. While all sugars are soluble, not all sugars are reducing. To understand why sucrose (that's the stuff you add to your favorite hot beverage) is a non-reducing sugar, you have to know the difference between reducing sugar and non-reducing sugar. read more

In order to be a reducing sugar, the sugar needs a free aldehyde or ketone group. All the monosaccharides, including glucose and fructose, have this property, as do some of the di- and polysaccharides, such as lactose and maltose. read more