Controlling the microbial load of milk to produce high-quality milk

Milk is a natural and complete food for humans. However, if the health principles related to milk production are not followed, not only does it not compensate for the nutritional deficiencies of the body, but it may also cause irreparable damages and injuries by causing infections, food poisoning, digestive disorders or common diseases between humans and animals. brought to fruition

One of the most important indicators in the production of healthy milk is “reducing the microbial load of the produced milk”.

The amount of bacteria in milk, especially bacteria that grow at a temperature of about 15 to 40 degrees Celsius, is called microbial load. For this reason, it is necessary to prevent the entry of microbes into milk and its growth and multiplication by using the methods that will be mentioned.

Characteristics of healthy milk

Healthy milk is white to pale yellow in color. Its pH is 6.6 to 6.8. (It is slightly acidic).

If the lactating animal is infected, the color of the milk may change or it may taste bad and sometimes salty or bitter. In this case, it should not be used. (of course, sometimes the smell and taste of milk has a non-food origin)

Classification of milk based on microbial load:

 1-According to the international standard, first-class milk is defined as milk whose microbial load is below 100,000 microbes per milliliter of milk.

2-Second grade milk is milk whose microbial load is between100،000 and500,000 microbes per milliliter.

 3-Grade three milk is milk whose microbial load is between 500,000 and 1,000,000 microbes per milliliter.

Generally, delivery of milk containing more than one million microbial burdens should be avoided.

The production of healthy, hygienic and quality milk is important from several points of view;

– Very high nutritional value

– Impact on maintaining the health of consumers

– And economically

Milk bacteria can enter and increase the microbial load of milk from three sources: the cow, the environment, or contaminated equipment.

Cows with clinical and subclinical mastitis introduce bacteria into milk. If mastitis is well diagnosed, the bacteria causing clinical mastitis will not enter the milk reservoir. The bacteria that cause clinical mastitis always enter the milk unless the milk containing the high somatic cell count is discarded.

Environmental contamination usually occurs through poor preparation, or through milking crabs ingesting faecal contamination, increasing the microbial load of the milk produced. In herds with high hygiene and good nipple preparation, the level of environmental pollution is low. A high coliform count indicates environmental pollution.

If the milking equipment or the milk tank is not properly cleaned or the milk tank is not properly cooled, problems will arise. A high number of thermophilic bacteria indicates that the problem is related to the milking equipment, and a high number of cold-loving bacteria is related to problems related to the milk tank. If there are problems in the cooling section, the number of bacteria will increase.

Animal hygiene before milking

It is one of the first things that should be considered for the production of healthy and hygienic milk:

– Preparation of suitable and dry bedding for cows, in order to prevent contamination of animal udder with various particles such as feces and…

– In feeding, avoid giving moldy and contaminated feeds (preventing the presence of aflatoxins, etc. in milk)

– Providing adequate lighting and ventilation and a sanitary place for cows and combating insects and flies.

– Cooperation of livestock farmers with veterinary centers for periodic tests of common diseases, such as tuberculosis and brucellosis, and isolation of sick animals and removing them from livestock farming.

– Controlling the mammary disease of animals and discarding the milk of animals suffering from mastitis.

– Separating the animals that are being treated and not mixing the milk of these animals with the milk that is going to be processed and consumed. Also, removing milk from newborn cows (at least 3 days after calving).

Hygiene tips during breastfeeding

8 health tips that must be observed during breastfeeding:

– Thorough washing of milking machines, devices and accessories used in milking, with clean water, detergents, soda and acid. (first cold water and then hot water and detergent)

– The health of the milker and the absence of any infectious diseases.

– Washing hands with clean water and soap before milking.

– Washing and drying the head of the cow’s teats before milking (with a clean towel or cloth)

Throwing away the first drops of milk. It is better to have it in a dark colored container so that it can be determined if the milk is in an abnormal state while draining the primary milk from the breast duct (which is the place where microbial agents accumulate).

– Disinfection of nipples after milking (because the duct of the breast is open for some time after milking)

– The milking place should be hygienic, clean and bright, with proper ventilation. Avoid milking cattle in dark and dusty places.

– Metals that do not rust (such as aluminum) should be used to make milk containers.

Hygiene tips after breastfeeding

8 health tips that must be followed after breastfeeding:

– Keeping milk in a suitable place, clean, cool and away from pollution.

– Rapid cooling of milk. By doing this, the milk will be healthier and the microbial load will be less. It is necessary to bring the milk to a temperature of about 4 to 6 within 2 to 3 hours.

– Faster delivery of milk to collection centers or raw milk conversion and processing centers.

– Smoothing the milk. After milking, substances such as dust, animal waste, etc. may enter the milk, so it is necessary to filter the milk.

– Preventing the cow from sleeping immediately after milking (because the udder duct is open for at least half an hour after milking). Feeding animals can be done after milking.

– If unpasteurized milk is used, it must be boiled for 20 minutes to destroy its pathogenic microbes.

– Milk produced in industrial cattle farms should be transported to the nearest collection or processing centers by vehicles equipped with double-walled steel tanks and at a temperature of 4 degrees. If you don’t have an equipped car, aluminum containers of 30 to 50 liters should be used. It is also necessary to fill the containers completely to prevent the milk from shaking in them (because otherwise, the ingredients of the milk will be damaged).

The importance of conducting milk microbial tests:

Milk is a suitable environment for the growth of many microorganisms due to sufficient moisture, pH close to neutral, and richness of food. At the same time, it is a rich source of energy in different forms such as milk sugar (lactose), nitrogenous compounds such as proteins, amino acids, etc. is. Many antimicrobial compounds (lactoperoxidase, agglutinin) are present in freshly milked milk, but due to sugar fermentation and acid production by common raw milk bacteria, they are quickly ineffective. Therefore, many microorganisms are able to grow in such an environment.

The origin of microorganisms in milk:

Of course, a group of these microorganisms, such as some species of lactic acid bacteria, are useful and are used to produce various milk products.

These lactic bacteria mainly use carbohydrates such as lactose and produce lactic acid. These microorganisms are Lactococcus and Lactobacillus. Lactococcus lactis subspecies lactis and chromoris grow quickly, especially at a temperature of about 20 degrees Celsius. Therefore, milk becomes sour if it is not cooled. Of course, it is not suitable for processing before the milk is completely sour. Mesophilic lactic acid bacteria die by pasteurization (“15/ 72ºc)and even thermization ( “15/ 65ºc ), but thermophilic types such as Streptococcus trophilus does not disappear under such conditions, and of course it should be noted that some streptococci that increase especially due to mastitis are pathogenic.

Types of microorganisms in milk:

Unfortunately, the health quality of these products can be changed due to the presence of microbial pathogens. The most important pathogenic bacteria in milk are Staphylococcus aureus, Salmonella, coliforms such as Escherichia coli, Listeria, Brucella and Bacillus cereus.

Escherichia coli:

Gram-negative bacteria is a member of the Enterobacteriaceae family, some strains of which cause gastroenteritis and dysentery. Since this bacteria is the normal flora of the intestines of humans and animals, its presence outside the intestine indicates contamination with feces.

If this bacterium is present in milk and the lack of proper pasteurization, Escherichia coli causes disease. The pathogenic mechanism is that the toxin of the bacteria binds to the epithelial cells of the intestine and by activating adenyl cyclase, it leads to the loss of water and electrolytes. This bacteria will be destroyed by boiling milk or the correct pasteurization process.

Staphylococcus aureus:

Gram-positive bacteria are resistant to heat and grow in microaerophilic conditions. The presence of Staphylococcus aureus in milk can indicate purulent inflammation in the cow’s udder, which enters the milk and causes its contamination.

Staphylococcus aureus enterotoxin is the cause of pathogenicity in humans. Food poisoning has an incubation period of one to six hours and causes symptoms such as heartache, nausea and vomiting. It is the intestinal nerve.

Bacillus cereus:

Gram-positive bacilli are spore-forming that are found in water and soil, and since they produce spores, they can survive in the environment for years.

Bacillus cereus poisoning has two forms: diarrhea disease and vomiting disease

In diarrhea, the incubation period is 1 to 24 hours, and in vomiting, the incubation period is 1 to 5 hours.

The toxin that causes vomiting disease is a water-insoluble protein that is resistant to acid and heat and can withstand 126 degrees for 90 minutes. The toxin that causes diarrhea is a heat-sensitive protein that is destroyed at a temperature of 56 degrees for 5 minutes. These toxins, by connecting to epithelial cells, destroy the cell membrane and cause disease.

Cold-loving microorganisms (psychrophiles):

Because cold-loving bacteria have the ability to grow and work at low temperatures, they play a significant role in spoilage of food in the refrigerator. The result causes their corruption. If these bacteria are present in the milk before processing, the quality of the milk is greatly reduced and it may even become unusable.


The bacterium is the causative agent of Malt fever, which lives as an obligate intracellular parasite and infects humans and animals. Clinical symptoms include fever, weakness, pain, and sweating.

The most common way of contamination is from eating contaminated milk and dairy products through the digestive tract, mucous (secretions), skin (contact with an infected animal). This bacterium can survive in milk for 10 days.

The pathogenic mechanism of Brucella is that it grows intracellularly in all its hosts and causes bacteremia after infecting the reticuloendothelial system. The pathogenicity of Brucella often lies in the ability of this bacterium to enter, survive and reproduce in phagocytic cells (macrophages). This bacterium attacks the spleen, liver, bone marrow, lymph nodes and kidneys and causes tissue destruction.


Gram-negative bacteria are from the Enterobacteriaceae family and are the cause of salmonellosis, which are considered as one of the main causes of food poisoning.

Clinical symptoms appear with gastroenteritis and diarrhea. In one of the obtained studies, it has been shown that raw milk has the highest level of Salmonella contamination compared to other dairy products.

The pathogenicity of Salmonella is that it can stay alive inside macrophages and continue to reproduce. Salmonella attacks the target tissue and by producing enterotoxin and binding it to ganglioside GM1, it increases the level of cAMP and causes the release of water and electrolytes from the body. can be


Gram-positive bacteria are microaerophilic that cause listeriosis in animals and humans. This bacterium is widely found in water, soil, and food. Resistance to cold, drought, and stability against osmotic pressures increase its survival and distribution. Is. Also, this bacterium has the ability to attach to surfaces such as steel and glass by forming a biofilm and can spread by attaching to containers in the refrigerator. This bacterium is not destroyed in the incomplete process of pasteurization.

After eating contaminated food, such as milk, this bacterium enters through the digestive tract and binds to the surface of the epithelial cells through its surface protein and enters the cell. and causes complications such as septicemia, abortion, secondary diseases in people with immune system deficiency and meningitis.

Methods of microbiological examination of milk:

For all pathogen agents, culture and molecular diagnostic methods can be performed, but currently the golden standard is the culture method, which can be isolated according to the standards of each pathogen agent.

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