Understanding Milk Quality and Quality Characteristics of Milk
Let’s explore the critical aspects of milk quality, shedding light on the factors that ensure we enjoy a wholesome and nutritious dairy experience.
In developed countries where milk production and milk quality standards have been established, producers may be penalized for poor quality milk and/or obtain very low value or payments for it.
Therefore, it is important that factors that can negatively affect the value of milk be identified and reduced as much as possible or alleviated. The key to producing quality milk is to have the correct information, make the right decisions and carry out the recommended actions correctly.
In essence, ensuring milk quality involves a comprehensive approach, from the cow’s well-being to the handling, processing, and ethical considerations that shape the final product.
It’s not just about a glass of milk; it’s about a commitment to excellence and the pursuit of a nourishing and sustainable dairy experience.
Quality Characteristics of Milk (Milk Quality)
Milk that has been harvested from animals and stored at appropriately cold temperatures in tanks is transported to processing centres where they are tested for quality before being processed.
The milk is checked for protein, fat, flavour, total bacteria count, somatic cell count, and residues. The protein and fat contents are checked against standard milk values to accept or reject the milk. Other attributes checked are discussed in the following sections.
1. Flavour
Milk is a yellowish-white non-transparent liquid. Fresh milk has a pleasantly soft and sweet taste and carries hardly any smell. Consumer acceptance of milk is greatly affected by its flavour.
There are several factors which may produce off-flavours and/or odours in milk. Some of the more common causes of flavour and odour problems are:
Strongly flavoured feedstuffs such as poor quality silage or feed;
Strong-smelling plants, like wild onion or garlic.
High acidity flavours and oxidized flavours, from contact with copper or exposure to sunlight; and flavours from the use of chlorine, fly sprays, medications, etc.
Rancid flavours: These are caused by excessive agitation of milk during collection and/or transport. Damage to the fat globules in the milk results in the presence of free fatty acids.
Cow-barn flavours from dung, etc. These are found when milk is obtained from a dirty or poorly ventilated environment or from improperly cleaned milking equipment.
2. Hygiene
Milk, when it emerges from a healthy udder (the mammary gland of the female animal, which has teats where milk comes out from) contains only a very few bacteria.
However, milk is a perishable product. It is an ideal medium for micro-organisms and as it is a liquid, it is very easily contaminated and invaded by bacteria.
Almost all bacteria in milk originate from the air, dirt, dung, hairs, dust, dirty equipment, operators, and other extraneous substances. In other words, milk is mainly contaminated with bacteria during milking.
The major group of bacteria in milk is the lactic acid bacteria, which grow and produce lactic acid rapidly when milk is kept at ambient temperature and it becomes sour.
How soon the milk turns sour depends on the degree of contamination and on the temperature of the milk. Therefore, proper cleaning and sanitizing procedures are essential to control the quality of milk.
Cooling milk to a temperature of 4ºC as soon as the animal is milked (the first 2 – 3 hours) makes the bacteria inactive and prevents them to grow and produce lactic acid.
Maintaining impeccable hygiene throughout the milk production process is paramount. From the cow’s udder to the milking equipment, cleanliness is the first line of defense against contaminants. Proper sanitation ensures that the milk collected is free from bacteria, dirt, and other potential contaminants.
Read Also: Guide to Milk Production, Composition, and Nutritional Value of Milk
3. Total Bacteria Count
The total population of bacteria in milk is termed Total Bacteria Count (TBC) and very good raw milk should contain only 500 to 1,000 bacteria per ml.
The normal total bacteria count after milking is up to 50,000 per ml and many processors may not be willing to accept raw milk with a higher value.
However, counts may reach several million bacteria per ml. This indicates a very poor hygienic standard during milking and the handling of the milk or milk from an animal with a disease such as mastitis.
Mastitis is a disease of the udder. This disease arises when bacteria enter the udder and establish an infection. The disease is caused by Streptococcus and Staphylococcus spp bacteria leading to clotting and discolouration of the milk, reddening, heat, pain, swelling and hardening of the udder.
Hygienic milk only originates from mastitis-free and healthy animals. Cows suffering from a disease may secrete the pathogenic bacteria, which cause their disease, in the milk they produce.
Consumption of raw milk therefore might be dangerous to the consumer. Some of these diseases, like tuberculosis, brucellosis and anthrax, can be transmitted to the consumer.
Whatever the milk is used for during processing, the hygienic standard of the produced milk at the farm level forms the basis of the quality of the ultimate milk products.
The presence of bacteria can significantly impact milk quality. Proper milking practices, immediate cooling, and storage at appropriate temperatures help control bacterial growth. Regular testing and adherence to hygiene protocols ensure that milk remains free from harmful microorganisms.
4. Somatic Cell Count (SCC)
Somatic cells are naturally present in milk and are indicative of udder health. An elevated somatic cell count may suggest the presence of infection or inflammation in the udder. Monitoring and managing SCC levels contribute to both milk quality and the health of the dairy herd
Apart from TBC, another measure of the quality of raw milk is the Somatic Cell Count (SCC), which is a direct indication of infection as there is a very high correlation between mastitis and bacterial infection.
Somatic cells consist almost totally (98%) of white blood cells. When bacteria exist in the environment close to the teat end, the first line of defence against bacterial infection is the teat canal.
If the bacteria succeed in entering the udder, then the second line of defence comes into play and inflammation occurs, i.e. white blood cells or somatic cells. These somatic cells try to destroy the bacteria and prevent it from infecting and damaging the udder tissue.
Thus, these somatic cells (SCC) are the first reliable indication of mastitis infection. A certain level of somatic cells is always present in milk, as a protection for the cow against mastitis infection.
Most cows that are free of mastitis and have no previous infections would be expected to have an SCC of less than 100,000 cells/ml, with many below 50,000 cells/ml. It is widely accepted that individual cow SCC greater than 150,000 cells/ml or individual heifer SCC greater than 120,000 cells/ml indicates the presence of infection.
Milk with a high somatic cell concentration can be harmful to human health and contains less protein. In addition milk with a high cell count generally contains an increased amount of enzymes, which have an effect on the quality of the protein and the fat in milk.
The presence of these enzymes in milk increases the potential for off-flavours and odours. Because the somatic cell content of raw milk is important for the shelf-life, flavour and number of products obtained, milk processors strive to obtain raw milk of the highest hygienic quality from their producers.
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5. Residues in Milk
Good quality milk must be free of various residues that may be deposited or remain in milk along the pre-processing handling of raw milk. Such residues are antibiotics, disinfectants, iodine, trichloromethane (TCM), added water, and sediments.
Milk must be free from antibiotics and traces are not acceptable. All milk supplies are tested for antibiotic residues. Antibiotic residues result from the milk collected from animals treated for various infections, which were not completely disposed.
Milk from animals being treated must not be processed or consumed and the proper safe period after treatment must be strictly observed.
Disinfectants and TCM contamination result from improper washing or rinsing of equipment used in the pre-processing of raw milk. The most effective disinfectants have chlorine as the active component but chlorine can form TCM if it comes in contact with organic matter such as milk remaining in processing equipment pipes. Very low levels or zero levels of TCM are tolerated.
Iodine contamination results from the feed given to animals. In spite of the fact that iodine is very important to human physiology, an excessive level is not healthy. Therefore, proper monitoring of iodine levels in feed is required.
Water is the most abundant component of milk. However, excess water above acceptable levels is not proper because the consumer is paying for milk and not water. Excess water could arise from improper draining of water from pipes after washing or switching to automatic cleaning too early.
Physical cleaning of teats before milking is essential for lowering sediment in milk. Sediment in milk is generally due to poor pre-milking hygiene procedures that allow soil and other materials to enter the milking system.
Proper environmental conditions are important in order to maintain cow cleanliness and to reduce soil on animals so that pre-milking hygiene procedures can be effective.
Sediment in milk is measured by filtering the milk through a fine filter and visually examining it. High sediment levels in milk are associated with dirt and increased potential for bacterial contamination, thus adversely influencing milk quality.
Ensuring that milk is free from residues, such as antibiotics or pesticides, is crucial for both human health and the overall integrity of the dairy industry. Rigorous testing and adherence to withdrawal periods post-treatment are essential components of residue control.
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6. Milk Composition and Butterfat Content
The composition of milk is a key indicator of its quality. Butterfat content, in particular, plays a crucial role in determining the richness and flavor of the milk.
A balance between the various components such as water, proteins, lactose, minerals, and fats—contributes to the overall quality and nutritional value of the milk.
7. Temperature Control
Maintaining an optimal temperature during milking and subsequent storage is vital. Rapid cooling inhibits the growth of bacteria, preserving the freshness of the milk.
This temperature control is equally crucial during transportation and processing to prevent spoilage and ensure a longer shelf life.
8. Milk Processing Standards
Once collected, milk undergoes various processing steps. Strict adherence to processing standards, including pasteurization and homogenization, ensures that milk products reach consumers in a safe and high-quality condition.
9. Environmental and Ethical Considerations
Milk quality extends beyond its chemical composition. Ethical treatment of dairy animals, sustainable farming practices, and environmental responsibility contribute to the overall quality of the milk produced.
A holistic approach to milk quality considers not just the product but the entire ecosystem in which it is produced.
10. Consumer Education
Educating consumers about the indicators of milk quality empowers them to make informed choices. Understanding labels, freshness indicators, and the significance of various quality parameters fosters a deeper appreciation for the journey of milk from the farm to the table.
In conclusion, the importance of milk as a valuable food source will be lost if it is unacceptable to the end users. Improving milk supply in any economy is not as important as guaranteeing quality in order to satisfy the objective of nourishing the neediest in the population.
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