2102
Determination of lactose% In Milk
Determination of lactose% In Milk
Lactose is synthesized within the alveolar cells of the 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 increases in the
concentration of sodium and chloride to keep the osmotic pressure of the milk
in equilibrium with that in blood and therefore the milk taste salty. Dominating
of lactose percentage in milk (<4%) indicate mastitis
Benedict's method
1. Transfer 5ml of milk sample into a volumetric flask (50ml) and then add
2.5 ml of sodium tungestate (10%) drop by drop with continuous mixing and
then add 5 ml of (2/3N) H2so4 with continuous mixing and finally complete the
volume with distilled water up to the mark (50).
H2SO4+Na.Tung
Tungestic Acid +Phosphate in milk
‫حامض ضعيف‬
phosphotungestic acid
‫حامض قوي يعمل على ترسيب البروتين‬
2. Leave the mixture in the flask for 10 minutes and then filter. Usually the
lactose dissolved in water and leave down with filtrate (the filtrate should be
clear).
3. Transfer the filtrate to a burette.
4. In a beaker, put 25ml of Benedict reagent with 30 ml of distilled water and
2gm of anhydrous sodium carbonate to increase the alkalinity.
5. Mix well the mixture and heat till the solution become clear. While it is
boiled precede titration, firstly rapidly by 2ml till you obtain the first shad of
reduction. Then precede the slow titration drop by drop till complete reduction
of the blue color.
(Disappearance of the bluish color) and formation of a white Precipitate of coporous thiocyanat)
6. Record the ml of filtrate exhausted in the titration (R)
7. Calculation: Every 25ml of Benedicts solution are reduced by 0.0678gm
lactose
Lactose% =
6760.0 ×01×100
R