pH test for milk testing

     

A.     USING pH PAPER

Certain indicators show change in colour with the change in pH. The pH paper or strips are impregnated with these indicators such as bromothymol blue (pH 6.0 to 7.6) and bromocresol purple (pH 5.2 to 6.8). pH papers in narrow range and wide range are available.

Objective

·         To study the freshness of milk.

Reagents

·         pH paper strips ranges 4-10

Procedure

·         Take a small quantity of milk in the test tube.

·         Dip the pH strip in the milk.

·         Compare the colour changes with standard chart and note the pH.

Precaution

·         The results with pH paper are not precise and for more precision pH meter is used.

·         The pH strips should be stored in a glass bottle properly stoppered in dry conditions.

·         The electrode of the pH meter when dipped in the sample, detect the active hydrogen ions and the    potential difference is measured in terms of pH.

B.      USING pH METER

Objectives:

·         To study the freshness of milk.

·         To detect mastitis milk or neutralised milk.

Apparatus

·         pH meter(Pocket).

·         Beakers - 100 ml capacity.

·         Tissue paper/filter paper.

·         Wash bottle containing distilled water.

Reagents

·         Buffer solution of pH 4.0, 7.0 and 9.2.

Procedure

•          Switch on the pocket pH meter as per instruction of manufacturer.

•          Wash the electrodes with distilled water.

•          Dry the electrodes with the help of tissue paper/filter paper.

•          Take buffer solution in a beaker and dip the electrodes in it.

•          Adjust the pH meter to the pH of buffer solution.

•          Mix the milk sample thoroughly and take in a beaker.

•          Dip the washed and dry electrode in it and observe the reading on the scale.

•          Normal milk pH is between 6.6-6.8. pH above 6.9 is indication of mastitic milk/late lactation milk and pH lower than 6.5 means developed acidity.