Yellowing of the reaction mixtures containing reducing sugars (aldoses and ketoses)
name: The redox reaction between the aldehyde groups of the sugars and copper cations in an alkaline medium
Benedict's reagent, as well as the Tollens and Fehling reagents, are applied for the detection of reducing sugars (aldoses and ketoses), which is classified as such by the positive reaction with this reagent. Unlike non-reducing sugars, which include glycosides, reducing sugars contain a free aldehyde group, or may form it as a result of its isomerization in alkaline conditions.
Its action is based on a redox reaction between the aldehyde groups of the sugars and cations of copper in an alkaline medium. Wherein the copper-cations are reduced to copper (I) oxide, which settle as a red-colored precipitate.