1.
MATERIALS REQUIRED
A.
Milk sample
B.
Beaker (50 ml, 100 ml, 250 ml)
C.
0.5 N H2SO4
D.
Sodium tungestate
E.
Burette
F.
Benedict’s reagent
G.
Sodium carbonate
2.
PRINCIPLE
Lactose is synthesized within the alveolar cells
of mammary gland from material extracted from blood. The normal content of
lactose in milk is 4.5-5%. Any depression of the synthesis of lactose is
accompanied by increase in the concentration of sodium and chloride ion to keep
the osmotic pressure of the milk in equilibrium with that of the blood and
therefore the milk tastes salty.
Dominating sodium and chloride ion in milk
indicates mastitis (Inflammation of the mammary gland in the breast or udder)
typically due to bacterial infection.
3.
PROCEDURE
·
Take 5 ml of milk sample into a volumetric flask
(50 ml). add 2.5 ml of 10% sodium tungestate drop by drop with continuous
mixing.
Weigh 10 g of sodium tungestate,
pour it into a graduated cylinder or volumetric flast containing about 80 ml of
water. Once the sodium tungestate have dissolved completely; add water to make
the final voume to 100 ml
·
Add 5 ml of 0.5N sulphuric acid with continuous
mixing
·
Finally make volume to 50 ml with distilled
water
·
Leave the mixture in the flask for 10 minutes
and then filter.
usually the lactose is dissolved in
water (clear)
·
Transfer the filterate to a burette
·
In another beaker, put 25 ml of benedict’s
reagent with 30 ml of distilled water and 2 gm of anhydrous sodium carbonate.
·
Mix well the mixture and heat till the solution
becomes clear - while the solution is boiled, proceed titration, firstly
rapidly by 2 ml till first shade of reduction is obtained.
·
Then proceed with titration drop by drop till
complete reduction of blue colour.
Disappearance of blue colour and
appearance of reddish brown colour (of cuprous thiocynate)
·
Record the volume (ml) of filterate exhausted in
the titration (R)
4.
CALCULATION
Every 25 ml of Benedict’s solution is
reduced by 0.0678 gm of lactose.
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