MadSci Network: Biochemistry

Re: What are the differences between reducing and non-reducing sugars?

Date: Tue Oct 31 09:24:52 2000
Posted By: Kevin Ramsey, Staff, Speciality Sweeteners, Chr. Hansen, Inc.
Area of science: Biochemistry
ID: 972937233.Bc

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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