Jinu Manoj and Manoj Kumar Singh

College of Veterinary and Animal Sciences

Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut, India.


Milk is an important source of nutrient required for growth in infants and children and for maintenance of health in adults. Milk is a perfect food, readily digested and absorbed. It is a sole natural food for infants and children. It is chiefly a valuable source of good quality protein, fat, carbohydrates, vitamins and minerals. Protein in diet supply the amino acids required for growth of infants and children. It is also required for maintenance of tissues in adults. A glass (250ml) of unadulterated whole milk will give around 146 Kcals, 8gms of fat and protein with 257mg of calcium. The benefits of drinking milk include strengthening bones, improved cardiovascular and oral health.

Adulteration is defined as the process by which the quality or the nature of a given substance is reduced through. Adulteration may be intentional or unintentional. The former is a willful act on the part of adulterator who intended to increase the margin of profit. On the other hand, adulteration may be incidental contamination, which is usually due to ignorance, negligence or lack of proper facilities. In India, 68.4% of the milk was found adulterated in a study conducted by Food Safety and Standards Authority of India (2011) in 33 States and Union Territories. Most of the Indians are resigned to drinking milk diluted with water which not only reduces the nutritious value of the beverage but also poses risk to health. India being largely a vegetarian society relies on milk rather than meat for its nutritional needs.

Milk is one of the products which can be adulterated in many ways affecting the quality of further dairy products. Extension of milk with a low value ingredient (watering of milk, milk of different species, addition of whey etc) also known as economic adulteration has been often practiced. Adulteration of milk reduces the quality of milk and can even make it hazardous.  Adulterants like soap, acid, starch, sugar, caustic soda, urea, hydrated lime, sodium carbonate, ammonium sulfate and formalin may be added to the milk.  Most of the 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.

The Indian Council of Medical Research has reported that milk adulterants have hazardous health effects. The detergent in milk can cause food poisoning and other gastrointestinal complications. Its high alkaline level can also damage body tissue and destroy proteins. Other synthetic components can cause impairments, heart problems, cancer or even death. While the immediate effect of drinking milk adulterated with urea, caustic soda and formalin is gastroenteritis, the long-term effects are far more serious. Urea can lead to vomiting, nausea and gastritis. Urea is particularly harmful for the kidneys and caustic soda can be dangerous for people suffering from hypertension and heart ailments. Formalin can cause more severe damage to the body like liver damage. The health impact of drinking milk adulterated with these chemicals is worse for children. Caustic soda harms the mucosa of the food pipe, especially in kids. The chemical which contains sodium, can act as slow poison for those suffering from hypertension and heart ailments.

Quality control tests for milk are very important to assure adulterant free milk for consumption. There are many methods known for detection of adulteration in milk but the methods discussed below are simple but rapid and sensitive methods to detect adulteration.

  1. Detection of neutralizers in milk
  2. Rosalic acid test (Soda Test)

In milk neutralizers like hydrated lime, sodium hydroxide, sodium carbonate or sodium bicarbonate are added which are generally prohibited. Take 5 ml of milk in a test tube and add 5 ml alcohol followed by 4-5 drops of rosalic acid. If the colour of milk changes to pinkish red, then it is inferred that the milk is adulterated with sodium carbonate / sodium bicarbonate and hence unfit for human consumption.

This test will be effective only if the neutralizers are present in milk. If the added neutralizers are nullified by the developed acidity, then this test will be negative. In that case, the alkaline condition of the milk for the presence of soda ash has to be estimated. Take 20 ml of milk in a silica crucible and then the water is evaporated and the contents are burnt in a muffle furnace. The ash is dispersed in 10 ml distilled water and it is titrated against decinormal (N/10) hydrochloric acid using phenolphthalein as an indicator. If the titre value exceeds 1.2 ml, then it is construed that the milk is adulterated with neutralizers.

  1. Test for detection of hydrogen peroxide

Take 5 ml milk in a test tube and then add 5 drops of paraphenylene diamine and shake it well. Change of the colour of milk to blue confirms that the milk is added with hydrogen peroxide.

  1. Test for detection of formalin

Formalin (40%) is poisonous though it can preserve milk for a long time. Take 10 ml of milk in test tube and 5 ml of conc. sulphuric acid is added on the sides of the test tube without shaking. If a violet or blue ring appears at the intersection of the two layers, then it shows the presence of formalin.

  1. Test for detection of sugar in milk

Generally sugar is mixed in the milk to increase the solids not fat content of milk i.e. to increase the lactometer reading of milk, which was already diluted with water. Take 10 ml of milk in a test tube and add 5 ml of hydrochloric acid along with 0.1 g of resorcinol. Then shake the test tube well and place the test tube in a boiling water bath for 5 min. Appearance of red colour indicates the presence of added sugar in milk.

  1. Test for detection of starch

Addition of starch also increases the SNF content of milk. Apart from the starch, wheat flour, arrowroot, rice flour is also added. Take 3 ml milk in a test tube and boil it thoroughly. Then milk is cooled to room temperature and added with 2 to 3 drops of 1% iodine solution. Change of colour to blue indicates that the milk is adulterated with starch.

  1. Test for detection of glucose

Usually poor quality glucose is added to milk to increase the lactometer reading. There are two tests available to detect the adulteration of milk with glucose.

  1. Phosphomolybdic or Barford Test

Take 3 ml of milk in a test tube and add 3 ml Barford’s reagent and mix it thoroughly. Then keep it in a boiling water bath for 3 min and then cool it for 2 min by immersing in tap water without disturbance. Then add 1 ml of phosphomolybdic acid and shake. If blue colour is visible, then glucose is present in the milk sample.

  1. Diacetic test

Take a strip of diacetic strip and dip it in the milk for 30 sec to 1 min. If the strip changes colour, then it shows that the sample of milk contains glucose. If there is no change in the colour of the strip, then glucose is absent. In this method the presence of glucose in milk can be quantified by comparing the colour developed with the chart strip.

  1. Test for detection of urea

Urea is generally added in the preparation of synthetic milk to raise the SNF value. Five ml of milk is mixed well with 5 ml paradimethyl amino benzaldehyde (16%). If the solution turns yellow in colour, then the given sample of milk is added with urea. Take 5 ml of milk in a test tube and add 0.2 ml of urease (20 mg / ml). Shake well at room temperature and then add 0.1 ml of bromothymol blue solution (0.5%). Appearance of blue colour after 10-15 min indicates the adulteration milk with urea.

  1. Test for detection of 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 concentrated sulphuric acid and ferric chloride, which when reacts with benzoic acid and salicylic acid to give buff colored and violet colored reaction products.

  1. Test for detection of 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.

  1. Test for detection of 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.

  1. Microorganisms

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.  Methylene blue reduction test (MBRT) 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. 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.

Reasons of adulteration

  1. Demand and supply gap: More acute during summer due to low milk production and increased demand.
  2. Physical nature of milk: Aqueous and opaque nature of milk can accommodate many adulterants in milk.
  3. Degraded moral society: Wrecked moral status coupled with passion for profiteering.
  4. Spoiled socio-economic structure: Poor persons engaged in the business do so to increase their income and raise socio- economic status.
  5. Perishable nature of milk: The unscrupulous producers / traders use preservatives neutralizers etc. to prolong the shelf life of sub standard milk.
  6. Low purchasing power of customer: Encourages the supplier to adulterate milk and sell at cheaper rate.
  7. Unorganized condition of dairy industry: Most of the milk is procured and traded by unorganized dairies, which freely adulterate the milk.
  8. Low legal standards and their improper enforcement.
  9. Lack of suitable, rapid and sure tests: Consumers have no access to public analytical laboratories to get their samples analyzed.

Remedial Measures

There is need for rationalization of the standards prescribed under PFA Act. Buffalo milk, for which minimum requirement for fat % is 6 in most of the states, is hardly available as such in the market for sale. Either it is watered and sold as cow milk or admixed with cow milk and sold as mixed milk. In lieu of buffalo milk, full cream milk has been introduced containing minimum of 6.0% fat and 9.0% SNF. The PFA Act and Rules must be strictly enforced and offenders punished adequately. The manpower limitation, lack of adequate training to the food inspectors and apathy of consumers encourages the menace of adulteration. The adulterated substandard and injurious food stuffs (including dairy products) should be discouraged from trade. The enforcement of the act should be rigidly carried out particularly against unorganized dairies and small traders and vendors, which are the root causes of this malpractice. Certain discrepancies exist in the standards prescribed under PFA Act and ISI and Agmark standards. These anomalies should be rectified and a uniform standard should be prescribed. Rapid, reliable and inexpensive tests to detect various harmless and harmful adulterants should be worked out so that cases of adulterations are detected readily. The milk producers should be given incentives for clean milk production and should be encouraged to supply the milk to the registered village societies, milk unions and dairies. The various intermediaries should be eliminated. Special provision should be made for packaging and distribution/sale of dairy products. Most of the market samples of dairy products are stored under unhygienic conditions and sold loose without any specification with regard to the nature and content of the product. Special provisions should be framed for rigorous control over the production, distribution and sale of milk and milk products including registration of premises where they are manufactured, maintenance of premises in a sanitary condition and maintenance of healthy states of human beings associated with the production, distribution and sale of such foods.



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