Acidity in milk Flashcards
What test is used for quantifying acidity in milk?
Titratable acidity test
What is the titratable acidity:
the amount cm3 of hydroxyl ion solution of a given strength needed to increase the pH of a given amount of milk from 6.0 to 8.4, at which the indicator changes colour to pink
Titratable acidity normally ranges between:
6.2 to 7.8 SH
Titratable acidity can be expressed in:
SH (Soxhlet-Henkel degrees): 0.25 mol/L NaOH to 100 ml milk
T (Torner degrees)
D (Dornic degrees)
Increased milk acidity above 8.0 SH is caused by:
Decomposition of lactose in heavily contaminated milk
Accidition of colostrum in first few days
Acidosis due to lack of fibre, high carbs
High protein
Residues of acid detergents
Reduced milk acidity below 6.0 SH is caused by:
Inflammation of mammary gland
Lack of energy in feed ration
High proportion of old dairy cows
Residues of alkaline detergents
Milk drainage
Stressful situation breaking the stereotype of dairy cows
Name tests used to determine milk acidity:
Titratable acidity test
Clot-on boilng test
Alcohol test
Alizarin-alcohol test
Indicator paper
pH meter
Describe the titratable acidity test:
- Agitation well of 25 ml is added into titrimetric flask
- 2 ml phenolphtalein is added to the milk in the titrimetric flask
- Drop by drop NaOH solution is added from burette
- When pink colour appears and remains, stop titration and read the volume
- Add one more drop NaOH and if colour remains, the previous reading was correct
Results:
Amount used x 4 = SH degrees
Explain clot-on boiling test:
Sour milk coagulates by boiling (above 12SH).
Boil 5m3 of milk in a test tube with constant shaking on a low flame.
Explain alcohol test:
Put equal amounts of milk and 68% alcohol in a test tube, invert several times. If the acidity is above 9SH, the milk will coagulate.
Explain the alizarin-alcohol test:
2 ml milk is mixed with 2 ml alizarin in ethanol solution.
Pink color - sweet milk
Brown/yellow and villi - acidity is higher
Violet - acidity is lower (mastitis etc.)
