How to check if milk is pure

Definition of Pure Milk

Standard definition of milk is a lacteal secretion which is practically free from the colostrum, obtained from complete milking of one or more cow(s).

Should contain not less than 8.25 % SNF (Solid Not Fat) and 3.25% Fat.

Milk contains many diversified nature of substances which are usually not present in any other compound.

How to check milk impurities
How to check milk impurities

Important Terminologies:

TS (Total Solids):

It can be defined as: Milk fat + Milk proteins + Lactose + Ash contents

SNF (Sold-not-fat):

It can be defined as: Milk protein + Lactose + Ash contents

Milk Plasma or Skimmed Milk:

It consists of all the milk constituents except milk fat.

Milk Serum or Milk Whey:

It comprises of all the milk contents except milk fat and casein protein.

Water adulteration in Milk

Water is added in the milk to increase the volume of milk. Addition of water dilutes the components of milk leading to decrease in energy value. Addition of water in the milk is an unlawful practice and it is regarded as adulteration as it makes the milk unwholesome. It changes the whole composition of the milk and enzymatic activity of the milk also goes down.

Detection of Added Water in the Milk:

Certain techniques and methods are used to detect this adulteration as follows:

Lactometer method:

This is an old method and it tells us about the specific gravity of the milk. Specific gravity value decrease when we add water into the milk. Disadvantage of this method is that it only gives the result when we add water more than 10%.

Refractive index method:

Rays of specific wavelength are passed via the body of the milk and absorbed on the other side. Zeiss Immersion Refractometer is used made by a Germen company; it is a handy instrument and has digital display.

Addition of Vegetable Fat

Milk fat is the natural source of variable variety of fatty acids diversified in nature. It is separated to make the cream and sold at high prices. People separate the cream from the milk and add vegetable fat into the milk and then sell it after homogenization. Vegetable fat is unsaturated and it get oxidized and becomes rancid when exposed to air so become hepato-toxic and may cause liver cirrhoses. Small milk globules become rancid when oil and vegetable fat is being added and interesting thing is that colour and consistency of the milk remains normal.

Detection of Vegetable Fat in Milk:

Alcohol Test:
Take 1 ml milk and 9 ml absolute alcohol. Mix and shake well and then stand it for 5 minutes.

If the fat globules start floating on the top this is natural fat but if they sunk in the bottom then it indicates the addition of vegetable fat in the milk sample.

Natural fat floats because its globule has pits in it and air entrapped in those pits that makes the globule lighter and these float on the surface. There are no such pits in the vegetable fat globule.

Addition of Formaldehyde in the Milk

It is frequently used in the milk as preservative. It is highly toxic to the kidneys (nephrotxic). It forms aldehyde compounds and fix the proteins that leads to toxic syndrome. Adulteration of formaldehyde in the milk is not recommended and discouraged all over the world. Its use is illegal from any point of view. Under specific circumstances (for research purpose), it is allowed to use 1 part of formaldehyde in 200,000 parts of milk as milk preservative (1:200,000). It is recommended for those patients having gastric ulcers. As formaldehyde will precipitate the protein, so in such patients it will absorbed from the intestine rather than the stomach.

Test for Formaldehyde Detection:

Test to declare the milk as formaldehyde free or not is very simple. Take 10 ml milk sample and add 5 drops of ferric chloride (10%). Then, add 2 ml of H2SO4. Shake it well and then stabilize it. There will be orange red colored ring at top of milk sample. This ring indicates the presence of formaldehyde in the milk. Negative test presents no such ring formation.

Boiled Milk

Boiling practice of milk is done in order to enhance the keeping quality of the milk. Boiling procedure is safe, and milk does not contain any toxin after boiling. But a variety of vitamins, essentials enzymes and amino acids are lost through boiling of milk.

Test for Boiled Milk:

Take 15 ml milk & add 2-3 drops of starch solution (10%). Then add 5-6 drops of KI (10 %) and finally 1-2 drops of H2O2.

If milk remains white colored, it indicates boiled milk.

If blue color appears, it indicates milk is not boiled; it is raw milk.

Somatic Cell Count

These are epithelial cells and leukocytes coming down in the milk. Somatic Cell Count (SCC) for milk of healthy cow is 200,000/ml. If there is an increase in SCC upto 300,000/ml; it means milk is from mastitic cow. SCC in the milk is the big indicator for health of the animal. Somatic Cell Count (SCC) provides three important functions:

Monitoring of prevalence of mastitis in dairy cows

Act as indicator of raw milk in all processes

Act as indicator of hygienic conditions of milk at a dairy farm

Grading of Milk (According to Somatic Cell Count):

  1. Grade A               < 30,000 cells/ml
  2. Grade B               30-50,000 cells/ml
  3. Grade C               50-100,000 cells/ml

Drug Residues in Milk

Treatment of animals with various antibiotics is a normal phenomenon. Physicians neglect the withdrawal period of every product which depends upon the half life of drug. As a result drug residues come in milk.

Effects of Drug Residues:

Consumers may acquire drug resistance

Allergic reactions may occur

Sensitization to various kinds of drugs may occur

Consumer may have complaint for vomiting, diarrhea and enteritis

Beside other effects, economic impact of industry is also hampered due to presence of drug residues in the milk.

Permissible Level of Drug:

It is level of drug residue in the milk which has no deleterious effect on the consumers’ health. It is determined by FDA. FDA recommendations for standard drug residues are accepted by health monitoring authorities of all countries irrespective to the quality of the milk.

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