Procedure
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Step-I (Sample Preparation)
- Milk Proteins should be separated from milk prior to lactose estimation.
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Sodium tungstate is a potent protein – precipitating agent.
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Take 20 mL of milk in a 100 mL volumetric flask.
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Slowly add 10 mL of 10% sodium tungstate and 10 mL of 2/3 N H2SO4.
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Keep it for 15 minutes undisturbed for precipitate formation.
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Mix thoroughly; make the volume up to 100 mL with distilled water and filter.
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Fill a burette with this filtrate for lactose estimation.
Step-II
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Pipette out 10 mL of Benedict’s Quantitative Reagent (BQR) into a 100 mL conical flask.
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Add 5g sodium carbonate and the mixer is boiled over a flame.
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While the solution is boiling, titrate rapidly against the filtrate from the burette.
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The end point is the appearance of a white colored precipitate.
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Continue the titration till last traces of blue color of BQR disappear.
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Water may be added to make up the loss due to evaporation.
- Repeat the experiment to get concordant value.
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Last modified: Saturday, 5 May 2012, 10:01 AM