23 December 2012

#31 Food test 2 - Benedict's test for Reducing Sugars

All simple sugars (e.g.glucose) are reducing sugars. They will react with a blue liquid called Benedict's solution to give a brick red color. We can use this reaction to find out if a food or other substance contains a reducing sugar.








Process 
  • add a few drops of Benedict's solution
  • heat the mixture for 2-3 minutes in boiling water bath
  • BRICK RED/ORANGE COLOR is a positive result: glucose is present
  • The closer the color is to brick red, the more reducing sugar is present.




Observation
(Final colour change)


Interpretation

No colour change
(Blue)
No reducing sugars present

Green
Trace amounts of reducing sugars present

Yellow

Low amounts of reducing sugars present

Orange

Moderate amounts of reducing sugars present

Brick-red

Large amounts of reducing sugars present



Explanation
  • Reducing Sugars are sugars that contain aldehyde groups, that are oxidised to carboxylic acids (R-COOH).
  • They are classified as reducing sugars since they reduce the blue Cu2+(copper II ions) to Cu+ (copper I ions). These are precipitated in form of red Cu2O (copper oxide), insoluble in water.  
Illustrations (Photo credit: cccmkc.edu.hk)





When the concentration of reducing sugar is low, the color of the Benedict's test may be light green or pale orange.



Videos: Benedict's test for reducing sugars





Additional source: cccmkc.edu.hk
                          


2 comments:

  1. What is the point of heating the solution?

    ReplyDelete
  2. It adds energy to the reaction. Otherwise the benedict wouldn't react the way it should.

    ReplyDelete