why is sucrose not a reducing sugar?

2 Answers

  • Sucrose is not a reducing sugar, but the other two major disaccharides (maltose and lactose) are.


    Reducing agents give up electrons to other molecules and reduce them. It is the aldehyde (double-bonded oxygen) groups that do this.

    All monosaccharides have an aldehyde group available for this, but not all disaccharides.

    If you look at disaccharide molecules (see links below) you will see that they are made from two monosaccharides, each in a ring shape. It is the oxygens that are involved in forming monosaccharides into this ring structure.

    In monosaccharides these oxygens are able to reform an aldehyde by letting go, allowing the monosaccharide back into its chain form. This allows the oxygen to do its reducing job!

    In the disaccharides lactose and maltose there is one oxygen free to do this, the other oxygen is bound to a carbon involved in the glycoside link so can’t do this.

    If you look at sucrose, however, you’ll see that BOTH oxygens are bound to the carbons that form the glycosidic bond between the monosaccharides. Therefore they are not free to “let go” so can’t reduce any other molecules.

    The only way they can is if you can break the glycoside first.

    links to disaccharide pictures:


  • Is Lactose A Reducing Sugar

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