text: Disaccharides consist of two monosaccharides and may be either reducing or nonreducing. Even a reducing disaccharide will only have one reducing end, as disaccharides are held together by glycosidic bonds, which consist of at least one anomeric carbon. With one anomeric carbon unable to convert to the open-chain form, only the free anomeric carbon is available to reduce another compound, and it is called the reducing end of the disaccharide. 
  A nonreducing disaccharide is that which has both anomeric carbons tied up in the glycosidic bond.
  Similarly, most polysaccharides have only one reducing end.