Objective:

 

To detect various adulterants present in milk using specific biochemical tests.

 

 

Theory:

              Quality control tests for milk are very important to assure adulterant free milk for consumption. Adulteration of milk reduces the quality of milk and can even make it hazardous.  Adulterants like soap, acid, starch, table sugar and chemicals like formalin may be added to the milk.  Most of the it chemicals used as adulterants are poisonous and cause health hazards.  Adulterants are mainly added to increase the shelf life of milk. Some of the preservatives like acid and formalin is added to the milk as adulterants, thereby increasing the storage period of milk. Generally, water is added to the milk to increase the volume content of the milk.  Some of the common adulterants found in milk and their detection are discussed.

1)  Microorganism:

          Milk may contain some harmful microorganisms like bacteria along with   some potentially beneficial microbes. Microbiological analysis of milk is carried out to determine the degree of bacterial contamination in milk and   to understand  the chemical changes brought in milk as a result of microbial action.  Pasteurization is done to destroy such harmful bacteria.  If pasteurization of milk is not carried out properly there will be presence of larger count of bacteria in the milk.  Methylene blue Reduction test is used to detect the presence of bacteria in milk. This test works on the principle that the methylene blue indicator is present in an oxidized form, but in the presence of bacteria, leads to the reduction of this indicator in a comparatively short span of time.  The blue color developed on addition of the indicator to the milk will change to white color within a short period indicates the presence of bacteria in the milk and thus denotes improper pasteurization.

2) Table Sugar:

           The common sugar present in milk is lactose. The fat content of the milk is more compared to the protein content. Table sugar like sucrose is added to the milk to increase the carbohydrate content of the milk and thus the density of milk will be increased. So the milk can now be adulterated with water and it will not be detected during the lactometer test.  Ketose sugar will react with the resorcinol to give a red colored precipitate, indicating the presence of Table sugar in milk.

3) Starch:

          Milk contains relatively large amount of fat. Addition of carbohydrate to milk increases its solid content. There by reducing the amount of fat present in the milk. Starch is one such component that is added to adulterate milk. The test to detect starch in milk uses iodine solution, addition of which turns the milk solution to blue black color due to the formation of starch –Iodo complex, in the presence of starch.

4)  Acids:

            Generally acids like Benzoic acid and Salicylic acid is used as a preservative in food industry. It is added to milk to preserve and thus increase the shelf life of milk. Presence of these acids can be detected by adding conc.sulphuric acid   and ferric chloride, which when reacts with benzoic acid and salicylic acid to give buff colored and violet colored reaction products. 

5) Soap:

           Soap is added to milk to increase the foaming of milk and thus to have thick milk.  Addition of such chemicals will cause health problem especially related to stomach and kidneys. Soap can be detected by adding phenolphthalein indicator to the adulterated milk. A pink color will be observed if soap is present as the alkali will be neutralized by the acidity of the milk when phenolphthalein indicator is added.

6) Formalin:

          Formalin is a preservative and can preserve milk for long period of time. Due to its high toxicity, it is considered to cause liver and kidney damage.  Formalin reacts with Sulphuric acid and ferric chloride to give a purple colored ring at the junction of the milk layers, thereby indicating the presence of formalin adulterated in milk.

7) Ammonium Sulphate:

        Ammonium Sulphate is added to the milk as it increases the lactometer reading by maintaining the density of milk.  Ammonium sulphate adulterated milk can be detected by adding sodium hydroxide, sodium hypochlorite and phenol, the reaction of the three reagents with ammonium sulphate results in formation of deep blue colour. The deep blue color is generated when the amine reacts with phenol in the presence of hypochlorite in an alkaline environment, results in the formation of a complex which is blue in color.

 

 

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