Neutralizers

Neutralizers are added to neutrilize the acidic sour milk. The addition of alkalis is not permissible under law. Some of these alkalis are highly injurious to health. To overcome this problem by means of a few simple test they can be detected in milk added as neutralizer. Freshly drawn milk has an acidity of 0.12-0.16 per cent expressed as lactic acid. With the passage of time the acidity increases during souring of milk. Any acidity above 0.18 per cent lactic acid coagulate milk. This is due to the formation of lactic acid from lactose. Neutralization of milk is illegal under the P.F.A act. Unscrupulous milk producers and farmers tend to neutralize the milk to avoid rejection of milk with increased shelf-life at the milk collection centers and at the dairy plants. The common neutralizers which are added to milk are caustic or sodium hydroxide, baking soda or sodium bicarbonate and washing soda or sodium carbonate. They are detected by determining the alkalinity of ash and carbonate or bicarbonate by rosalic acid test.

i. Rosalic acid test for the detection of carbonate and bicarbonate in milk
Rosalic acid test is used for the detection of carbonate and bicarbonate in milk. This is a very simple, reliable and quick test for their detection. Rosalic acid reacts with carbonate and bicarbonate and give rose red colour in their presence. The intensity of colour depends upon the amount of these chemicals present.

•  Take 5 ml sample of milk in a clean and dry test tube.
•  Add 5 ml ethanol 95% and mix
•  Now add 2-3 drops of rosalic acid solution prepared in 1% ethanol to the mixture and mix well. Note the colour change.
•  A rose red colour develops.
• Formation of rose red colour in milk indicates the presence of carbonate or bicarbonate added as neutralizer.

Note: Pure milk gives only a brownish red colour.

ii. Alkalinity Test

The presence of neutralizers can generally be detected by determining the alkalinity of ash. A known quality of milk is heated and converted into ash. The alkalinity of ash is estimated by titration against a decinormal standard hydrochloric acid in the presence of Phenolphthalein indicator. Values abnormally high would indicate neutralization of milk. To carryout this test first ash is prepared from milk so as to obtain added alkali in a concentrated form.

•  Pipette 20 ml milk in a porcelain dish and evaporate to dryness on a boiling water bath.
•  Prepare ash by keeping it over a burner or muffle furnace at 550 0 C for 1 hour.
• When using burner heat till ash becomes grey white in colour.
   Cool the basin. Add water and mix the contents with a glass rod.
   Titrate the ash solution using standard O.1N HCl in the presence of 4-5 drops of phenolphthalein indicator solution. Note the volume of HCl solution used till a pink colour is obtained.
   If the volume of O.1N HCl exceeds 1.20 ml the milk is suspected to contain neutralizers.