DETERMINATION OF TRITATABLE ACIDITY IN MILK
- Experimental procedure
1. Comply with safety measures.
2. Shake the milk sample to homogenize it.
3. Take 50 ml of milk, with pipette and pro pipette.
4. Place the milk sample in a beaker with a capacity of 100 ml.
5. Add 1ml of phenolphthalein.
6. Titrate drop by drop, keeping the milk stirring, with NaOH until the milk turns a persistent pale pink for 15 to 20 seconds.
- Expected results
The millilitres of NaOH used represent the titratable acidity value of the milk expressed in °SH50
The normal value of titratable acidity in milk in °SH 50 is around 3. 5; with such, the milk is suitable for consumption and cheese making.
Values below 3. 2 are an indication of disease in the cow (mastitis), milk unsuitable for consumption and cheesemaking.
Values greater than 3. 7 may indicate colostrum or soured milk (e. g. , a sour milk). for poor preservation). Milk unfit for consumption and cheesemaking.
Note: Colostrum is the milk secreted by the cow in the first 10 days after calving, it provides the calf with the antibodies that it lacks at birth.
Multiplying by 2 the value obtained we obtain the °SH degrees referred to 100 ml.
Acidity and pH are linked by an inverse relationship, the higher the acidity the lower the pH and vice versa.
Remark: by adding sodium hydroxide (NaOH) to milk, some H+ ions are released from the third function of phosphoric acid due to the over-run phenomenon which occurs according to the following reaction:
3Ca2+ +2H2PO4-→← Ca3(PO4)2+4H+
Calcium (Ca2+) present in milk precipitates phosphoric acid releasing H+ ions.
Because of the over-run, the neutralized milk, which had turned pink, slowly returns to white and a very slight acidity due to the hydrogenions (H+ ions) released by the previous reaction.
English
Spanish
Portuguese
Latvian
Dutch
French
Italian
Valencian