Mucic Acid Test for Galactose

This test is highly specific to galactose, which is either present in solutions independently or obtained by lactose hydrolysis. On heating with HNO3, Galactose is converted to Saccharic acid (a strong oxidizing agent).

Positive result of mucic acid test

Mucic acid (galactaric acid) formed from galactose due to the aldehyde & primary alcoholic group oxidation at C1&C6. It is the only saccharic acid that is insoluble in cold water and thus assists in galactose identification.

Reagents

Conc. of HNO3

Procedure

• Take 50 mg of galactose and 50 mg of glucose into the test tubes separately. 
• Add to each tube 1mL DW and 1mL conc HNO3. 
• Heat the tubes for about 1hr in a boiling water bath. 
• Add 5mL of DW and slowly let the tubes stand and cool. 
• The presence of galactose will be indicated by colorless needles such as crystals.

Note:

This test will also be administered with lactose.