|MadSci Network: Biochemistry|
The classical definition of Reducing Sugars is "Reducing substances in cane and its products interpreted as invert sugar". Many sugar refineries refer to reducing sugars as invert (glucose & fructose). There are several official ICUMSA methods for the determination of reducing sugars. The Lane-Eynon method is generally recommended for the sugar industry. It is this method where the name reducing sugars is derived from. In the Lane Eynon method the test sample (containing sucrose & invert sugar) is added volumetricly to a defined volume of a strongly alkaline cupric-complex salt solution, called Fehling's solution, which is then reacted by boiling. The remainder of the test solution is then added, until, at the end-point, the cupric ions are completely REDUCED to cuprous oxide and a blue color of the solution will disappear. The sharpness of the end-point is improved by the use of an indicator, methylene blue, which is decolorized in the presence of a minute excess of reducing sugars. Sucrose will not reduce the cupric ions therefore they are refered to as non reducing.
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