Quality Perspective Of The Milk

Engr Hira Kausar


Production of high-quality milk is an important goal of every dairy operation. Poor quality milk affects all segments of the dairy industry, ultimately resulting in milk with decreased manufacturing properties and dairy products with reduced flavor quality and reduced shelf-life. Quality control of every food manufacturing industry has an objective of ensuring the quality and safety of milk supplied to the consumer. The quality of milk is affected by a number of factors:

The nature and manipulation of raw milk.

Hygiene condition of the farm.

The process to which it is subjected.

Storage condition.

These are the factor which alters the properties of milk. The dairy industry needs to control the raw milk supplied by the farmers and need to set up control on the process to which it is subjected in order to ensure safety and quality of milk going to market. In order to prevent any fraud or mislabeling, the government needs to control the raw milk supplied by the farmers and monitor the overall manufacturing process.

There are two key elements for producing high-quality milk:

Producing milk of low somatic cell count (SCC) – Low SCC is a reflection of good udder health and mastitis control in the herd.

Low total bacterial count (TBC) – Low TBC is an indicator of good milking plant hygiene and milk storage.


The best way to start the manufacturing of milk is to start with good raw material. Testing raw milk is essential for the good quality end product. Raw milk is tested for:

Presence of macroscopic abnormalities.

Microbial count.

Addition of water.

Presence of residues.

Presence of milk from the mastitis cow.


Allowable limit: Total bacterial count(less than or equal to 50000 colony forming unit) Staphylococcus aureus and Salmonella species. Other pathogen or their toxin should not be present in an amount that can become a health hazard.


The quality of processed milk depends upon the processing treatment like:


Ultra high temperature.

A high-temperature short time (HTST).


In short shelf life milk, the limiting shelf life factor is post heat treatment contamination like spoilage by bacteria that enter the milk after heat treatment i.e during filling/packaging line or grow at refrigeration temperature. The routine determination is total microbial count, psychrotroph, coliforms and pathogens. An important source of spoilage in short shelf life milk is the presence of heat-resistant spore-forming bacteria mainly Bacillus species.

The major shelf life-limiting factor in UHT milk is the presence of heat resistant enzymes mainly lipases and proteases that is formed by psychrotroph during refrigerated storage of raw milk. The microbial count, organoleptic properties, appearance are routinely tested by accelerated shelf life test performed by the incubation of UHT milk in a closed container for 15 days at 30O C after being processed.

The industry has introduced a hazard analysis critical control point (HACCP) and good manufacturing practices (GMP) programs in order to ensure the quality of end product because no corrections can be made at this stage on the production line.


Analysis of abnormal milk: Abnormal milk containing any clot or blood should be kept away from the bulk tank. To avoid it, it should be test visually after filtration. For online detection colored sensors are used for blood detection and optical sensors are used for the detection of clots.

Microbial analysis: Microbial analysis are done to detect the poor hygienic condition and overall microbial quality of raw and processed milk

Total bacterial count: It is used to get an overview of microbial contamination.

Psychrotroph: It is done to detect the potential spoilage.

Coliform: It is done to evaluate the hygienic history of milk.

Specific pathogen: It is done to analyses the potential health hazard.

Thermoduric bacteria: It is done to detect the hygienic history of the production system

Mastitis milk – somatic cell count: Mastitis milk contain a number of pathogen and spoilage microorganism. It is characterized by an increase in Na+ and Cl- and leucocytes. Its test includes a conductivity test, the California mastitis test. In order to determine SCC direct microscopy, electrical sensors, automatic counters are used.

Testing for residues compound: Milk contaminated with residues (mycotoxins, pesticides, antibiotics) should not reach the bulk tank.it is a big deal to detect a large number of compound and low amount to be detected. The use of mass spectrometry and biosensor array has a wide application for multiple residue detections.


The major component includes proteins, fats, lactose and dry matter. Protein can be analyzed by the Kjeldahl method and fats can be analyzed by Gerber and gravimetric method. For multiple component analysis different spectroscopy methods are used:

FT-MIR (Fourier transform technique): This technique is used to analyzed other components like carbohydrates, free fatty acid, casein, urea, lactic acid and their freezing points.     

NIR (Near-infrared spectroscopy): NIR can be applied to other milk product like creams, dairy powder and cheese. It is used to test the composition of dry milk including moisture.

All these techniques can be set up online, allowing for process control they have good precision and accuracy. These techniques provide the result as good as international methods only they need to be carefully calibrated.


Within milk two major proteins are there casein and whey. They are the major quality parameters because casein is calcium carrier.

CASEIN: Casein is easy to analyze in raw milk by precipitation at pH 4.6 and in processed milk spectroscopic methods like FTIR, NMR are used. Also chromatography, electrophoresis is used to quantify casein in processed milk.

WHEY: whey is easy to analyze in raw milk by precipitation at pH 4.6 and HPLC is used to quantify whey in processed milk but it quantifies only soluble whey.

Simultaneous analysis of casein and whey in raw milk is done through HPLC and CE.

The mass spectrometer is a powerful tool to distinguish protein information


There are other components in milk that are mentioned on the milk package label like calcium, phosphorous, vitamins. These components also have nutritional importance. These components should be tested in end product since processing can alter their contents particularly vitamins.

These components can be analyzed by:

VITAMIN:  HPLC (high-pressure liquid chromatography).

PHOSPHOROUS: Molecular Absorption Spectroscopy.

CALCIUM: Atomic Absorption Spectroscopy.


Proteolysis and lipolysis are the major cause that limits the shelf life of food during storage. Proteolysis is the breakdown of protein by proteolytic enzyme cause a release of the peptide in the milk whey and decrease of casein. Casein can be quantified by its precipitation at pH 4.6 and we can quantify the peptides by HPLC and CE. Lipolysis can be evaluated by the free fatty acid fraction and cause rancidity of milk.


Chromatographic techniques are commonly applied to analyze fat components. Some other techniques are mid-infrared spectroscopy, near-infrared spectroscopy, Raman spectroscopy and Fourier transform techniques.


ADDITION OF WATER: Water added by accident or deliberate (i.e to increase the volume of milk) is fraudulent activity and it is routinely tested.it is detected by the determination of freezing point, as the dilution of milk causes an increase towards 0o C.

ADDITION OF NON DAIRY PROTEIN: Protein of plant and animal origin could be added to milk, a practice that is common in countries if they are cheaper than milk protein. A number of electrophoretic, chromatographic, immunochemical methods have been used to detect the addition of non -dairy protein in milk products.

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