Method and Material:

Part I: a) Benedict Test

Benedict’s solution (alkaline cupric citrate), 10% solutions of glucose, fructose, sucrose, lactose,

and an unknown sugar.

5mL of Benedict’s solution was added into 5 serology tube.

2 drops of 10% glucose, fructose, sucrose, lactose, and the unknown sugar was added into each

serology tube.

All the serology tube was heated on a boiling water bath for 4 minutes.

The changes was observed and recorded.

Result:

Colour Precipitation

Glucose Brick red Present

Fructose Red Present

Sucrose No change Absent

Lactose Red Present

Unknown sugar Brick red Present

Question

3) Which of the following compounds are reducing sugars:

Galactose, β-methylglucoside, mannose, ribose, glucosamine?

Support your conclusion by specific reference to the structures of the compounds.

Galactose, ribose, mannose and glucosamine are reducing sugars while β-methylglucoside is a

non-reducing sugar. To conclude which compounds are reducing sugars, the compounds must

have free anomeric carbon which also a carbonyl group, -CHO. Galactose

{CH2OH(CH2O)4CHO}, Ribose{CH2OH(CH2O)3CHO}, Mannose{CH2OH(CH2O)4CHO} and

Glucosamine{CH2OH(CH2O)3CHNH2CHO}, these reducing sugars share a common properties

which is a carbonyl group, -CHO. β-methylglucoside is a combine of methanol on the anomeric

hydroxyl of a β-glucose. β-methylglucoside no longer have free anomeric carbon, therefore, this

compound is a non-reducing sugar.

Figure was taken online.( Diwan, 2008)

References

Ophardt,2003. Galactose. [online]

Available from: <http://www.elmhurst.edu/~chm/vchembook/543galactose.html >

Accessed on 07.09.2010

Ophardt,2003. Ribose. [online]

Available from: < http://www.elmhurst.edu/~chm/vchembook/543ribose.html >

Accessed on 07.09.2010

Diwan, 2008. Carbohydrates-Sugars and Polysaccharides. [online]

Available from: < http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/sugar.htm >

Accessed on 09.08.2010