I'm trying to do my biology AS coursework and I was wondering: Is there a way to quantify the relative strengths (by strength I mean how reducing they are...i.e. how fast and how much they reduce) of reducing sugars (specifically glucose, fructose and maltose)? If so what is it?

Presuming they are pure you can weigh a test tube, then pipette a known quantity of the sugar solution into it, evaporate the water and then measure the mass change in the test tube and then divide the result by the molecular weigh of the sugar to find the moles. Then you would know how many moles are in that known amount of solution and you can then work out how many moles are in a litre to find the molarity of a sugar.

 

There is a lot of experimental error in that procedure but my college didn't have a great deal of equipment and if yours is like mine then it is a simple method of getting a reasonably accurate result.

But he's asking for the reducing power of the sugars... not the molarity.

 

I think you'd have to combust them or something.

Wouldn't it be similar to testing for the calories of a substance?

Look up "cyclic voltammetry" and "pulsed amperometry". That should do it. The calories are dependent upon the DH of the material, not the REDOX potential (see mCDT).

 

Please note that a dissacharide (or any polysaccharide, for that matter) where the hemiacetal (see anomeric carbon) is tied up with a glycosidic linkage is NOT reducing. From hence, see aldehyde, ketone, reductone, etc.

 

Sweet!

 

O3

 

Oh, yes, for further info check out tollins, Fehling's and Molich's reagents. Please see also, Laine and Eynon.