Acidity of milk
2013
Acidity of milk
1. Natural. Acidity or apparent Acidity: The Acidity that come from
the component of the milk such as albumin, casein, phosphate
citrate and carbon dioxide.
2: Acquired or developed acidity: the acidity that results from
fermentation of lactose to lactic acid by streptococcus lactis by
lactic acid fermentation.
3. Real Acidity (Titratable Acidity) (TA %): The Acidity that results
from accumulation of Natural and Acquired acidity.
TA%=0.12%-0.16%.the average 0.14%
If it increased more than 0.17% the milk will be unexpected.
Titratable Acidity Test (PROCEDURE)
1. In a porcelain dish put 9ml of milk.
2. Add0.5ml of phenolphthalein (2drops).
3. Put NAOH 0.1N in burte.
4.Begin the titration till a light pink color appear &stable .
NaOH 0.1N(R)X0.009X100
TA% =
TA%=
9ml MILK
R
10
R=ml of NaOH in the burrat.
Each one ml of NaOH=0.009gm of lactic acid .
Acidity of milk
2013
2.PH Value Tests of milk
PH is the concentration of hydrogen ions
It determined by two methods:
1.Colorimetric method (PH paper) .
2.Electrometric method (PH meter).
NOTE
PH paper used for the detection of mastitis.
It act by coloring change of the indicator in the
PH paper.
PH meter using an electric current .It is more precise method
Procedure:
1. The PH meter should be turned on 30 minutes before
2. Rinse the glass electrodes with distill water and wipe with fin
tissue.
3. Immerse electrodes in freshly prepared buffered solution (PH 7)
& do the adjustment.
4. Take the electrodes out & rinse with distill water &wipe with fin
tissue.
5. Immerse the electrodes in the milk sample &read.
NOTE
Between measurements electrodes should be stored in distilled
water.
.
Acidity of milk
2013
Significance
PH of fresh raw milk normally 6.4-6.8 with an average 6.6
Higher figures equal or greater than7.7 indicates mastitis.
Lower figures than the normal indicate lower keeping quality.
Indirect methods for detect acidity
1. Alcohol precipitation test (APT)
Action of alcohol
The action of alcohol is pulling the water from casein which is stable
in normal condition Precipitation of proteins increase with increasing
acidity. And in this case the precipitation increased with
1. Increase Concentration of alcohol.
2. Increasing Acidity
3. Increasing Temperature.
This method is quick &cheap but not dependent
Procedure
1.Add 2ml of the milk sample into a clear dry test tub .
2.Add to the same test tub 2ml of the neutral alcohol 68%
containing several drops of Bromocrezol purple (0.005%) as
indicator to give yellowish color in acid and purple color in alkaline
while light purple color in neutral medium.
3. Take the tub and swirl between the palm of hand and then stop
the tub and look carefully for the formation of precipitate or
flocculent. If precipitation appears, it will indicate positive result
but if homogenous solution appears, it will indicate normal milk.
Acidity of milk
2013
Significance of the test
The addition of neutral alcohol 68% to equal amount of milk gives
no signs of precipitation in normal milk but produce a form of
precipitation in case of abnormal milk or of low keeping quality milk.
The abnormality of milk is due to either an increase in its acidity
i.e. TA%> 0.21%or due to udder troubles.
2. Clot on boiling test (COB)
The action of boiling
Milk that subjected to increased in its acidity will be unstable in its
ionic balance. As a result its proteins become unstable against
temperature for this it will clump when the milk boiled.
Procedure
1. Take 5ml of milk sample into a clean dry test tub
2. Transfer the test tube into a boiling water bath for 5 minutes.
3. Appearance of cured inside the test tube indicates a positive
result.
Significance of the test
1. Milk coagulate during boiling when TA%=0.23%
2. Milk coagulate in room temperature when TA%=0.60%
WHY TESTING ACIDITY
1. To have idea about sanitation state of the milk.
2. To have idea about preservation of the milk.
3. Act as a guide in dairy industry.