Hygiene and management of meat and meat products

作者：admin  点击次数：129  发布时间：2025-05-30

1. Microbial contamination of meat and meat products
(-) Common microbial groups in fresh meat
The microorganisms in fresh meat come from a wide range of sources and species, including fungi, bacteria, viruses, etc. They can be divided into three major groups: pathogenic microorganisms, putrefactive microorganisms, and food poisoning microorganisms.
1. Putrefactive microorganisms
Putrefactive microorganisms are a type of microorganisms that exist widely in nature and can parasitize dead organisms, produce proteolytic enzymes, and cause the decomposition of animal and plant tissues. They include bacteria and fungi, etc., and can cause meat to spoil.
(1) Bacteria Bacteria are the main microorganisms that cause fresh meat to spoil. Common putrefactive bacteria mainly include: ① Gram-positive spore-forming aerobic bacteria: such as Bacillus cereus, Bacillus microsporus, Bacillus subtilis, etc. ②) Gram-positive cocci: such as Coagulans, Psychrococci, Flavescent Tricholoma, Aureobacterium aureum, Staphylococcus aureus, Streptococcus faecalis, etc.
③ Gram-negative non-spore-forming bacteria: such as Cloacobacterium cloacae, Escherichia coli, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putrefaciens, etc.
(2) Fungi Fungi are not as numerous as bacteria in fresh meat, and their ability to decompose protein is weaker than that of bacteria. They grow more slowly, but they play a certain role in the deterioration of fresh meat. Fungi that can often be isolated from meat include: Alternaria, Aspergillus, Penicillium, Cladosporium, Mucor, etc., with Mucor and Penicillium being the most common.
Meat spoilage usually starts with aerobic bacteria in the external environment contaminating the surface of the meat, and then spreads to the deeper layers along the connective tissue. The development of meat spoilage depends on the type of microorganisms, external conditions (temperature, degree) and the site of invasion.
2. Pathogenic microorganisms
Mainly bacteria and viruses.
(1) Pathogenic microorganisms of zoonotic diseases Common bacteria include anthrax bacteria, Brucella, Listeria, glanders, Bacillus tularensis, Mycobacterium tuberculosis, Erysipelothrix rhizogenes, etc.
Common viruses include foot-and-mouth disease virus, rabies virus, vesicular stomatitis virus, etc.
(2) Pathogenic microorganisms that only infect poultry There are many types of pathogenic microorganisms that contaminate meat products, which have certain significance in the spread and epidemic of livestock and poultry infectious diseases.
Common ones include multi-killing Pasteurella, necrotic bacillus, swine fever virus, immune hemorrhagic disease virus, Newcastle disease virus, infectious bronchitis virus, infectious bursal disease virus, Marek's disease virus, duck disease, etc.
3. Toxic microorganisms
Some pathogenic microorganisms or conditional pathogenic microorganisms can cause food poisoning with acute process as the main feature by producing a large amount of toxins after contaminating food or bacterial contamination. System,
(1) Common pathogenic bacteria include Salmonella, Shigella, pathogenic Escherichia coli, etc.
(2) Common conditional pathogens such as Proteus and Bacillus. (3) Some bacteria can produce strong exotoxins or heat-resistant enterotoxins in meat products. Some bacteria can quickly form spores and release enterotoxins when entering the digestive tract with large quantities of food, such as Clostridium botulinum and Clostridium perfringens.
(4) Common food poisoning microorganisms such as Streptococcus, Campylobacter jejuni, Yersinia enterocolitica, etc.:
(5) Some fungi reproduce in meat and produce toxins, which can cause various toxin poisonings. Common fungi include ergot, gibberellosis, aflatoxin, yellow-green Penicillium, hairy Penicillium, Icelandic Penicillium, etc.
(II) Microorganisms in refrigerated meat
1. Classification of refrigerated meat
Refrigerated meat includes chilled meat, frozen meat, and thawed meat.
(1) Chilled meat refers to meat stored at -4℃ with a meat temperature not exceeding 3℃. Chilled meat has a soft texture and a fragrant smell. A layer of dry film often forms on the surface of the meat, which can prevent the growth and reproduction of microorganisms. However, due to the high storage temperature, it is not suitable for long-term storage.
(2) Frozen meat, also known as frozen meat, refers to meat that has been pre-cooled after slaughter and then further frozen at a low temperature of (-20±2)℃, so that the deep meat temperature reaches below -6℃. It is in a hard and solid frozen state. When the meat is cut, a fine and uniform frozen body can be seen.
(3) Thawed meat, also known as frozen thawed meat, is frozen meat that is slowly thawed under the influence of a higher external temperature, and the deep temperature is raised to about 0℃. Under normal circumstances, after slow thawing, most of the dissolved tissue fluid can be reabsorbed by cells, and the original state and flavor of fresh meat can be basically restored. However, when the external temperature is too high, the dissolved tissue fluid is difficult to be completely absorbed by cells due to the fast thawing speed, resulting in a large loss of nutrition.
2. Sources and groups of microorganisms in refrigerated meat
The source of microorganisms in refrigerated meat is mainly exogenous contamination, such as contamination during slaughter, processing, storage and sales.
Psychrophilic bacteria, especially molds, can often cause contamination and deterioration of refrigerated meat. Common cold bacteria in refrigerated meat include Pseudomonas, Moraxella, Acinetobacter, Lactobacillus and some genera of Enterobacteriaceae, especially Pseudomonas. Common fungi include Torulopsis, Cryptococcus, Rhodotorula, Candida, Trichoderma, Rhizoctonia, Cladosporium, Penicillium, etc. 3. Phenomena caused by changes in microorganisms in refrigerated meat High humidity is conducive to the growth of Pseudomonas and alkaligenic bacteria, while lower humidity is suitable for the growth of micrococci and yeast. If the humidity is even lower, mold will grow on the surface of the meat. When microorganisms grow in refrigerated meat, the meat will undergo the following changes: (1) Gray-brown changes or mucus-like substances are formed on the surface of the meat. Under refrigerated conditions, mesophilic bacteria are inhibited. Psychrophilic bacteria such as Pseudomonas, Leuconostoc, and Micrococcus continue to proliferate, causing gray-brown changes on the surface of the meat. Especially when the temperature has not yet dropped to a low level, if the temperature drops slowly and ventilation is poor, mucus-like substances may form on the surface of the meat, which feels slippery to the touch or even sticky. At the same time, it emits a stale smell or even a foul odor.
(2) Some bacteria produce pigments that change the color of meat. For example, "red spots" in meat can be caused by the red pigment produced by Serratia marcescens, blue-like Pseudomonas can make the surface of meat blue, Micrococcus or Flavobacterium can make meat yellow, and blue-black Bacillus can form light green-blue to light brown-black spots on the surface of beef.
(3) Under aerobic conditions, yeast can also grow and multiply on the surface of meat, causing the meat to become sticky, fat hydrolysis, produce odors, and change the color of the meat (white, brown, etc.). (III) Common microbial groups in meat products There are many types of meat products, generally including cured products (such as cured meat, ham, bacon, bacon, sausage, tripe, etc.) and cooked products (such as barbecue, marinated cooked products and dehydrated products such as meat floss and dried meat). The former is made from fresh meat, marinated with salt or added with appropriate seasonings, and processed by air drying. The latter refers to food that has been processed through material selection, primary processing, cutting, steaming, marinating, barbecue, etc., and does not need to be heated or cooked when eaten. Due to the differences in processing raw materials, production processes, and storage methods, the sources and types of microorganisms in various meat products are also quite different.
1. Common bacteria and fungi in cooked meat products include Staphylococcus, Micrococcus, Escherichia coli Proteus in Gram-negative non-spore-forming Bacillus, and aerobic Bacillus such as Bacillus subtilis and Bacillus cereus. Common fungi include Saccharomyces, Mucor, Rhizopus, and Penicillium.
2. Sausage products
Thermotolerant Streptococcus, Gram-negative rods and certain fungi of the Bacillus and Bacillus genera, certain yeasts and molds, these fungi can cause discoloration, enzyme production, or corruption of enema products, such as most heterotypic lactic acid fermentation bacteria and Leuconostoc can turn sausages green.
3. Cured products
Cooked products are mostly salt-tolerant or halophilic fungi. Vibrio is a very common bacterium, and Micrococcus, Heterotypic Lactobacillus, Leuconostoc, etc. can also be seen. Pathogenic bacteria such as Salmonella, pathogenic Escherichia coli, and Vibrio parahaemolyticus can be found in some cured and preserved products. Some yeasts and molds are also common fungi that cause the corruption and mildew of cured and preserved products.
2. Routes of microbial contamination of meat and meat products
Fresh meat is processed by animals through steps such as fasting, bathing, stunning, stabbing, bleeding, dehairing, deheading, skinning, gutting, evisceration, and splitting. Under normal circumstances, the carcass of healthy animals, especially the deep tissues, should be sterile. However, there are many links from disintegration to consumption. Therefore, it is impossible to ensure that slaughtered animals are absolutely sterile. The source of microorganisms in fresh meat is related to many factors, such as the feeding and management conditions of the animals before death, the health of the body, and the environmental conditions and operating procedures of slaughtering and processing.
(I) Routes of microbial contamination in fresh meat
1. Contamination by pre-live microorganisms (1) Microorganisms existing in healthy animals themselves. Healthy animals have microorganisms on their body surfaces, in some cavities that communicate with the outside world, and in certain parts of the lymph nodes. In particular, there are more microorganisms in the digestive tract. Under normal circumstances, these microorganisms do not invade muscle and other body tissues. When the animal's body resistance is reduced, some pathogenic or conditionally pathogenic microorganisms, such as Salmonella, can enter the lymph and blood and invade muscle tissue or solid organs.
(2) Some microorganisms can also invade deep tissues through surface trauma and infection. (3) The corresponding pathogenic microorganisms of infectious diseases or those in the incubation period may spread in the muscles and internal organs before death, such as anthrax bacteria, erysipelas bacteria, Pasteurella multocida, Yersinia, etc.
(4) Microbial transmission during animal transportation and before slaughter. Due to the influence of adverse factors such as excessive fatigue, crowding, hunger and thirst, pathogenic microorganisms can be spread through individual sick animals or infected animals, causing contamination before slaughter.
2. Microbial contamination during slaughter
(1) Microorganisms on the skin and fur of healthy animals. Their types and numbers are related to the environment in which the animals lived before they died. Showering or bathing the animals before slaughter can reduce the contamination of fresh meat by microorganisms on the fur.
(2) Microorganisms in the gastrointestinal tract may invade adjacent tissues and organs along the interstitial space.
(3) Microorganisms in the respiratory tract and urogenital tract may cause contamination.
(4) Hygienic conditions of slaughtering and processing sites
① Water is a source of microbial contamination that cannot be ignored. Water must comply with the "Sanitary Standards for Drinking Water" and minimize contamination caused by flushing. ②) Equipment in slaughtering and processing workshops: If the knives used for bleeding and skinning are contaminated, microorganisms can enter the blood and invade the deep part of the carcass through the large veins. Hooks, electric saws and other tools can also cause contamination of fresh meat. In addition, the problem of microbial contamination cannot be ignored in each link of fresh meat cutting, packaging, transportation, sales, processing, etc. (II) Routes of microbial contamination in meat products
1. Cooked meat products
(1) Incomplete heating When the meat is too large or not fully cooked, some heat-resistant bacteria or bacterial buds will still survive, such as thermophilic Bacillus, Micrococcus, Streptococcus, Bacillus, Lactobacillus, Bacillus and some species of Clostridium. In addition, there are some molds such as Mycosporium.
(2) Re-contamination through the hands, clothing, respiratory tract, unclean utensils for cutting meat and unclean utensils for storing meat.
(3) Various microorganisms are contaminated through dust in the air, rodents, flies and insects. Cooked meat products that are seriously contaminated by Staphylococcus aureus, Salmonella typhimurium or Proteus can cause food poisoning if they are stored at room temperature for 10 to 24 hours without being fully heated before consumption.
2. Sausage products
There are many types of sausage products, such as sausages, meat sausages, powder sausages, red sausages, snow sausages, ham sausages and fragrant tripes. This type of meat product has many raw materials. Due to the different origins, storage conditions and product quality of various raw materials, as well as the differences in processing technology, the microbial contamination in the finished product will have a certain impact.
The processing equipment, operation process, freshness of raw meat, storage conditions and time of minced meat all have an important impact on sausage products.
3. Cured meat products
Common cured meat products include bacon, ham, bacon, pressed duck, and wind-fried chicken. The biological sources are: (1) Contamination of raw meat.
(2) In brine and brine, most microorganisms have strong salt tolerance or halophilicity, such as Pseudomonas, Acinetobacter, Halobacterium, Halophilic Coccus, Flavobacterium, Achromobacter, Archicoccus and Micrococcus. Some bacteria and some fungi. Many human pathogens, such as Staphylococcus aureus, Clostridium perfringens and Clostridium botulinum, can cause food poisoning through salted foods.
(3) The production process, environmental sanitation and quality of the staff of cured meat products are also related to the contamination of such meat products.
(III) The deterioration of meat is fast, but if it is stored under high temperature and high humidity conditions, it is easy to deteriorate. Usually, there are four phenomena of deterioration:
1. Stickiness
Moss
It refers to the production of sticky substances on the surface of meat. This is mainly due to the growth of microorganisms on the surface of meat, forming bacteria
The microorganisms that cause stickiness are mainly some Gram-negative bacteria, lactic acid bacteria, yeast, and some aerobic spore bacteria and micrococci. Usually, sticky meat pieces will have a stringy phenomenon when cut, and there will be a bad smell. At this time, the number of bacteria is generally 10’ cfu/cm'.
2. Discoloration
When microorganisms contaminate meat, it will cause it to change color. This is because microorganisms decompose some sulfur-containing amino acids in meat to produce H, S, and HS forms green hydrogen sulfide hemoglobin with hemoglobin in muscle. These compounds accumulate on the surface of meat, forming a layer of dark green spots. Of course, different microorganisms can also produce different pigments to form spots of various colors.
For example, Bacillus marcescens produces red spots, Pseudomonas aeruginosa produces blue spots, and Bacillus flavus produces yellow spots. Some yeasts can also produce white, beige and gray spots.
3. Cholerae
Mold spots will appear on meat, making the meat appear in various colors. This is mainly caused by the discoloration of mold spores. The difference between color spots and the above is that feather-like filaments appear with various colors. Common fungi include: white side spores, white mold (white mold spots), Xinzhisuo (black mold spots), Penicillium oxalicum (green mold spots), etc.
4. Odor changes
After microorganisms cause meat to deteriorate, various unpleasant odors are often produced, such as the rancid smell of fetal fat, the organic acidity produced by lactic acid bacteria and yeast fermentation, and the foul smell produced when protein-decomposing bacteria decompose protein.
​
After meat is contaminated by microorganisms, if it is stored at 0℃ and can be stored in ventilated and dry conditions, it will generally not spoil quickly. However, if it is stored under high temperature and high humidity conditions, it is easy to spoil. Usually, there are four phenomena of spoilage:
1. Stickiness
Moss
It refers to the production of sticky substances on the surface of meat. This is mainly due to the growth of microorganisms on the surface of meat, forming bacteria
The microorganisms that cause stickiness are mainly some Gram-negative bacteria, lactic acid bacteria, yeast, and some aerobic spore bacteria and micrococci. Usually, sticky meat pieces will have a stringy phenomenon when cut, and there will be a bad smell. At this time, the number of bacteria is generally 10’ cfu/cm'.
2. Discoloration
After microorganisms contaminate meat, it will cause it to change color. This is because microorganisms decompose some sulfur-containing amino acids in meat to produce H, S, and HS forms green hydrogen sulfide hemoglobin with hemoglobin in muscle. These compounds accumulate on the surface of meat, forming a layer of dark green spots. Of course, different microorganisms can also produce different pigments to form spots of various colors.
For example, Bacillus marcescens produces red spots, Pseudomonas cyanosis produces blue spots, and Xanthomonas produces yellow spots. Some yeasts can also produce white, beige and gray spots.
3. Cholerae
Mold spots will appear on meat, making the meat appear in various colors. This is mainly caused by the spores of mold.The color spots are different from the above in that feather-like filaments appear with various colors. Common bacteria include: white spore mold, white mold (white mold spots), Xinzhisuo (black mold spots), oxalic acid Penicillium (green mold spots), etc.
4. Odor changes
Microorganisms often produce various unpleasant odors when meat deteriorates, such as the rancid smell of fetal fat, the organic acid smell produced by lactic acid bacteria and yeast fermentation, and the foul smell produced by protein decomposition bacteria when protein decomposes protein.