2. Pathways of microbial contamination in milk
作者：admin 点击次数：122 发布时间：2025-06-05
(1) In vivo source
Fresh milk from cows' udders is not sterile, and bacteria are also present in the udders of healthy cows, with micrococci and streptococcus being the most common. Others, such as Corynebacterium and Lactobacillus, are also found and are called intramammary bacteria, which are mainly found in the nipple ducts and their branches. The tip of the nipple is easy to come into contact with the outside world, and often infects bacteria in the nipple duct to form a bacterial block embolism, which is a place where microorganisms are enriched, and is often called "fine plug". When milking the milk, always put the newly expressed milk slip in the container or discard it to prevent contamination of other milk. Microorganisms in the breast, such as Streptococcus breasts, Staphylococcus aureus, Corynebacterium pyogenes, and Escherichia spp., are the causes of mastitis. Patients with mastitis have great changes in the properties of the emulsion, mild infections should be immediately sent to the disinfection station for disinfection, severe infections have suppuration, and the milk produced should be destroyed to prevent food poisoning. (2) Infection in the milking environment is the most likely to contaminate microorganisms during the milking process. The type and quantity of contaminated microorganisms are directly affected by the surface hygiene of the cows, the air in the barn, the milking utensils, the containers and the personal hygiene of the milker. Workers' hands, pipes, machinery, equipment, containers, filter cloths, etc. can be contaminated with microorganisms during manual milking, so the milking environment must be clean.
In addition, if the expressed milk is not processed or refrigerated in time, it will not only increase the chance of new contamination, but also increase the number of microorganisms that originally existed in the fresh milk, which can easily lead to the deterioration of the fresh milk, so it should be filtered and cooled quickly after milking.
(3) Contamination of milk by pathogenic bacteriaMany of the pathogenic bacteria in milk are zoonotic pathogens, and their infection must be controlled.
1. Tuberculosis bacteria Tuberculosis bacteria are multiple pathogenic bacteria in pastures, and some pastures can reach 1/3 of cattle due to poor sanitary environment. Dairy cows should be inspected every six months, and the milk of cows with a positive tuberculosis test can be made into dairy products after pasteurization; The milk of cows with obvious symptoms of tuberculosis should not be eaten to prevent transmission to humans.
2. Brucella
The milk of cows infected with Brucella is milked and pasteurized before it can be sold.
3. Foot-and-mouth disease virus
The milk of loyal foot-and-mouth disease cows is boiled for 5min immediately after being squeezed out and fed to cows or other young animals. 4. Mastitis microorganisms
Hemolytic streptococcus, staphylococcus, coccus, spores, actinomycetes, and E. coli are common microorganisms in the milk of cows suffering from mastitis. Only mildly infected with the same milk with normal traits can be eaten immediately after sterilization after expression. If the milk produced by cows with severe purulent traits caused by staphylococci is not edible and should be destroyed. 5. Anthrax
Cows with anthrax have a significant decrease in milk production, and in the later stages of the disease, the milk is often mixed with blood, and this milk is inedible and should be destroyed.
6. Listeria monocytogenes
Listeria monocytogenes has been found in both fermented and unfermented dairy products, prompting food manufacturers to pay more attention to the hygienic environment of their factories and the safety of their products. Listeria monocytogenes is widely distributed in nature and is often carried into the intestines of humans and animals. In a normal, healthy person, about 5% of stools contain this microorganism. 5%~10% of raw milk contains Listeria monocytogenes.
Listeria monocytogenes contaminated ice cream and cheese products, prompting dairy processing plants to improve processing and hygienic practices. Many producers voluntarily adopt Class A standards for sterilized milk products. Effective hygienic practices can prevent contamination by Listeria monocytogenes by emphasizing increased training, supervision, employee quality and cleaner salaries in dairy processing plants.
7. Escherichia coli 0157: H7
Because E. coli 0157:H7 is often detected in raw milk, researchers have had to further investigate the presence of this microorganism in dairy products. This pathogen grows in dairyman's cheese and cheddar cheese, but is inactivated by pasteurization.
In addition, the contamination of milk by pesticide residues in feed, antibiotics in sick cattle, toxic metabolites of molds in feed, heavy metals and radionuclides should also be paid attention to.