VPB 112: General Veterinary Biochemistry (1+1)

ESTIMATION OF LACTOSE IN MILK - PROCEDURE

Step-I (Sample Preparation)

• Milk Proteins should be separated from milk prior to lactose estimation.
• Sodium tungstate is a potent protein – precipitating agent.
• Take 20 mL of milk in a 100 mL volumetric flask.
• Slowly add 10 mL of 10% sodium tungstate and 10 mL of 2/3 N H₂SO₄.
• Keep it for 15 minutes undisturbed for precipitate formation.
• Mix thoroughly; make the volume up to 100 mL with distilled water and filter.
• Fill a burette with this filtrate for lactose estimation.

Step-II

• Pipette out 10 mL of Benedict’s Quantitative Reagent (BQR) into a 100 mL conical flask.
• Add 5g sodium carbonate and the mixer is boiled over a flame.
• While the solution is boiling, titrate rapidly against the filtrate from the burette.
• The end point is the appearance of a white colored precipitate.
• Continue the titration till last traces of blue color of BQR disappear.
• Water may be added to make up the loss due to evaporation.
• Repeat the experiment to get concordant value.