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First, the low-temperature storage of meat cryogenic storage is one of the best methods for the storage of modern raw meat. This method does not cause fundamental changes in animal tissues, but it can inhibit the life activities of microorganisms, delay the chemical and biochemical processes that result from the action of tissue enzymes, oxygen, and light, and can improve the quality of meat for a longer period of time. .
1. The basic principle of low-temperature storage: low temperature can inhibit microbial life activities and enzyme activity, so as to achieve the purpose of storage and preservation. Due to the ability to maintain the color and condition of the meat, the method is easy, storage is large, and it is safe and hygienic, so this method is widely used.
2. Low-temperature storage types: The low-temperature storage of meat can be divided into cooling method and freezing method depending on the temperature used.
(1) Cooling storage of meat: The method of reducing the temperature in the deep part of the meat to about 0 to 1°C and then storing it at about 0°C. This method does not freeze the moisture in the meat (the meat has an ice point of -1.2 to -0.8°C). Since there are still some hypothermophilic bacteria that can grow at this temperature, the storage period is not long and the pork can be stored for about 1 week. After cooling, the color, flavour, and softness of the meat are all better. This is also the “maturity†of the meat. This process is essential for the production of high-grade meat products. Most of the raw meat consumed in the developed countries is now cooled meat.
1 cooling method: meat cooling generally uses air as a medium. The speed of cooling depends on the thickness and thermal conductivity of the body. The thicker the carcass is, the cooler the area is cooled. Generally, the center temperature of the thickest part of the leg will prevail. Before the carcasses are put into storage, the temperature in the cooling room should be reduced to -3 to -2°C. After the meat is fed, it is cooled for 14 to 24 hours. When the temperature of the meat reaches 0°C, the temperature in the cooling room is kept at 0°C. ~1°C. The cooling time required under natural circulation conditions at an air temperature of around 0°C is: pigs, calves and by-products for 24 hours, sheep carcasses for 18 hours, and poultry for 12 hours. The humidity in the cooling room is generally kept between 90% and 95%.
2 Methods to extend the shelf life of cooled meat: Methods for extending the shelf life of cooled meat include the use of carbon dioxide, antibiotics, ultraviolet radiation, radiation and ozone, and the use of gaseous nitrogen in place of air media. The actual applications are as follows:
Application of carbon dioxide: Cooled meat is stored at a temperature of 0°C and a carbon dioxide concentration of 10% to 20%, and the storage period can be extended by 1.5 to 2.0 times. However, when the carbon dioxide is greater than 20%, the color of the meat becomes dark.
Ultraviolet irradiation: The air temperature is required to be 2 to 8°C, the relative humidity is 85% to 95%, and the circulating air speed is 2 meters/minute. Irradiated cooling meat can be stored twice as long. However, this method can only sterilize the meat surface, and it can also cause loss of some vitamins, darkening of the flesh, and marked enhancement of the oxidation process.
(2) Frozen storage of meat: The meat can only be stored for a short time after it has been cooled (temperature above 0°C). If it is to be stored for a long time, the meat needs to be frozen, that is, the temperature of the meat is reduced to below -18[deg.] C., and most of the moisture in the meat (more than 80%) forms ice crystals. This process is called frozen meat. The purpose of meat freezing is to keep the meat at a low temperature and prevent microbial, chemical, enzymatic and physical changes inside the body in order to prevent the meat from deteriorating.
1 Freezing method: The air freezing method is mainly adopted, that is, air is used as the heat transfer medium between the ammonia evaporation tubes. Generally used temperature -25 ~ -23 °C (foreign use -40 ~ 30 °C), relative humidity of about 90%, wind speed of 1.5 ~ 2 meters / second, the final temperature of frozen meat to -18 °C is appropriate.
2 frozen meat frozen: frozen meat in the frozen process will occur in a series of changes, such as the formation of ice crystals during freezing in the frozen process will gradually become larger, which will damage the cell structure, denature proteins, resulting in thawed juice Loss, flavor, and nutritional value are reduced, and at the same time, a certain degree of dryness is caused during the freezing process. In order to overcome these problems, in addition to deep freezing, the temperature should also be kept as low as possible and kept from changing during freezing. Special attention should be paid to avoiding changes in the temperature around -18°C. In order to prevent the frozen meat from changing its quality during frozen storage, it is necessary to keep the frozen body's central temperature below -15°C and the temperature between frozen containers to -20°C to -18°C (1°C). The relative humidity is 95% to 98%, and the air is in a natural circulation.
3 Thawing of frozen meat: Frozen meat must be thawed before use. The factors affecting the thawing meat quality include freezing temperature and frozen storage temperature, meat pH, thawing speed and different freezing methods. When the freezing temperature is high, the storage temperature is high, and the temperature during the storage period is large, the gravy is lost more when thawing. At present, the commonly used thawing methods include air thawing, hydrolysis freezing, and microwave thawing.
Air thawing: Natural thawing is the simplest method of thawing. It is divided into low-temperature breeze thawing and air compression thawing. In a cold store at 0 to 5°C, low wind speed (1m/s) humidifies the air, and the method of uniform thawing after 14 to 24 hours is called low temperature breeze thawing, also known as slow thawing. The advantage of this method is that the overall hardness of the thawed meat is consistent and easy to process. The disadvantage is time-consuming. Compressed air thawing method is also a kind of air thawing method, refers to frozen meat at 15 ~ 20 °C, relative humidity of 70% ~ 80%. Thawing in the flowing air with a wind speed of 1 to 1.5 m/s. This thawing method is based on the normal flow of air thawing, and then apply a certain pressure on the meat thawed, after 20 to 30 hours to complete the thawing.
Hydrolysis and freezing method: The frozen meat is soaked or sprayed with clear water at 4 to 20°C to thaw. This method is suitable for semi-carcass or 1/4 carcass of undamaged muscle tissue and is not suitable for cutting meat. The advantages of this method are fast speed and less juice loss. It takes 13 to 15 hours to thaw the semi-carcass in water at 10°C, and it takes 20 to 22 hours to thaw it in water at 10°C. It takes 24 to 30 hours to thawed poultry meat in air at 5°C and only 3 to 4 hours in water.
Microwave thawing: When microwaves with a frequency of 2450 MHz are irradiated to the meat, it will cause violent vibration of the water molecules in the meat, causing friction and raising the temperature of the frozen meat to achieve the purpose of thawing. It is characterized by the thawing speed of acetylene. A certain thickness of meat is thawed in microwave for 1 hour, while air thawing takes about 10 hours.
Second, heat treatment preservation
1. Heat treatment preservation: It is to kill spoilage bacteria and harmful microorganisms in the meat. A method of inhibiting enzyme activity.
2. Heat treatment method: There are two heat treatment methods in the preservation of meat, namely pasteurization and high temperature sterilization.
Pasteurization: Sterilization method in which meat is treated in water or steam at a temperature lower than 100°C, and the center temperature of the meat is maintained at 65 to 75°C for 10 to 30 minutes. This treatment can kill most pathogenic bacteria, many enzymes in the meat are passivated, but there are still living cells and spores and some high temperature resistant enzymes cannot be inactivated. Therefore, pasteurized meat needs to be stored at low temperatures.
High-temperature sterilization: Sterilization of meat at a temperature of 100-121°C is mainly used for the production of canned meat products, such as canned meat canned meat and soft canned aluminum foil. After such treatment, it can basically kill all the bacteria and spores present in the meat. Even if there is still a small amount of survival, it can no longer grow and multiply, causing meat spoilage, so that the meat products can be stored at room temperature for more than six months without deterioration.
3. Factors affecting heat transfer: There are many factors that affect the heat transfer in the heating process of meat, mainly related to the nature of the product, the temperature difference between the product and the heat source, the density and uniformity of the product, the ratio of the product's surface area to the quality, and the container. Due to the relatively slow heat transfer of fat, meat containing more fat has a slower rate of heat transfer. When the initial temperature of the product is high, the temperature difference between the product and the heat source is small, and the time required for reaching the sterilization temperature is shorter than the time required for the food whose initial temperature is lower. Solid meat heat transfer is slower than fluid and semi-fluid meats.
4. Effects of Heat Treatment on Meat Quality (1) Effects of Heating on Proteins: Heating can denature, coagulate, and partially dehydrate proteins in meat to make products elastic and have a good tissue structure. This is the case for ground meat products (such as low temperature The manufacture of emulsified intestine is very important; heating can also promote the formation of some special flavor substances in the meat and enhance the flavor of the meat; heating can also make the meat products soft and delicious. However, heating denaturalizes most proteins and reduces the nutritional value of the protein. Excessive heat treatment is detrimental to the protein quality and the tissue structure of meat products.
(2) Effects of heating on fat: Heating destroys the lipase produced by the meat itself and microorganisms, and suppresses the hydrolytic deterioration of fat and the production of free fatty acids.
(3) Effects of heat on vitamins: Different vitamins have different sensitivities to heat. Among water-soluble vitamins, thiamine is unstable to heat, and the loss of thiamine in canned meat can reach 2/3. Riboflavin is stable to heat and sensitive to light. Long-term low-temperature heating can destroy vitamin C. In the case of low oxygen content, heating at high temperature for a short time only destroys a small amount of vitamin C. Among the fat-soluble vitamins, A, D and E are quite stable to heat, but they are easily destroyed by heating under aerobic conditions, among which vitamin D and E are particularly easy to lose.
Third, the dehydration of meat preserves the moisture in the meat in the presence of free water and bound water, and microorganisms can only use free water. By reducing the content of free water in the meat by means of dehydration, the growth of microorganisms can be inhibited and long-term preservation of the meat can be achieved.
1. Dehydration (1) Dehydration by heating: Drying is the oldest and cheapest method for humans to store perishable foods. When the raw meat is dehydrated, the rate of removal of moisture from the dry surface cannot be greater than the rate at which moisture diffuses from the inside of the meat to the surface. Otherwise, the surface of the meat product will harden and prevent the continued diffusion of moisture. Controlling the circulating air speed and temperature prevents surface hardening. After strictly controlling the dehydration conditions, the meat produced after rehydration is cooked, and its flavor, texture, and fresh crushed meat are almost the same. Dehydrated meat can preserve most of the nutrients and the main food quality of fresh meat without refrigeration.
(2) Freeze dehydration: Under certain conditions, ice can be directly sublimated into water vapor. This method can process complete cut pieces without having to grind them, has minimal damage to the proteins in the meat, and the resulting meat is qualitatively more similar to fresh meat.
2. Preservation of dehydrated meat: Oxidation of dehydrated meat during storage can degrade its quality, and the Maillard reaction (browning reaction) that occurs in dehydrated meat can cause deterioration of meat flavor and color, in addition, some enzymes cause Fat oxidation also destroys the flavor of the meat. Therefore, commercial use of airtight, water-impermeable material packaging, and the surface of the product coated with glucose oxidant to remove glucose and prevent the occurrence of browning reaction. However, no matter how the dehydration treatment is performed, compared with fresh frozen meat, the rehydrated meat is inferior in tenderness and juiciness.
Fourth, other methods of preservation of meat
1. Radiation treatment: Radiation preservation is a new technology developed in the world for nearly two decades. The radioactive preservation of meat is the use of the radiation energy of atomic energy rays to process fresh meat and its products, so that the meat products do not spoil or deteriorate within a certain period of time, do not undergo changes in quality and flavor, and extend their shelf life. When this method is used to treat meat, it is possible to kill the deep microbes and parasites without increasing the temperature of the meat, and it can be carried out after packaging without leaving any residue, which saves energy and is suitable for industrial production. However, after the meat has been irradiated, it will have an odor, the flesh will fade, and some amino acids and vitamins will be lost.
2. Marinated: Many years ago, people preserved meat at room temperature by pickling. Salt is a commonly used salting preparation in meat products. It is not only an important seasoning, but also has an antiseptic effect. Salt can dehydrate microorganisms; it has physiological toxicity to microorganisms; affects the activity of proteolytic enzymes; and reduces the water activity of the environment in which microorganisms live, thus inhibiting the growth of microorganisms. Salt can inhibit the growth and reproduction of microorganisms, but it cannot kill microorganisms. Therefore, it must be used in combination with other methods. Nitrate and nitrite are also important constituents in meat marinade preparations. They not only have a coloring effect, make the meat products glossy and bright, but also have a strong antibacterial effect, especially for meat products. The presence of Clostridium botulinum has a special inhibitory effect.
3. Smoke treatment: Smoke is often performed together with heating. When the temperature is 0°C, the smoke with relatively low concentration has little effect on the bacteria; the smoke with higher concentration at 13°C can significantly reduce the amount of microorganisms; at the temperature of 60°C, no matter how dark or light, the smoke can be smoked Reduce the number of microorganisms to one ten-thousandth of the original number. The composition of smoke fumes is very complex, there are more than 200 kinds, mainly some acids, aldehydes and phenols, these substances have antibacterial and antiseptic and prevent the oxidation of meat products. After smoked meat products have better resistance to preservation. Smoke can also make the surface of meat products to form a stable bacon color. Because smoke contains many harmful ingredients, such as 2,4-benzopyrene, there is the risk of cancer. Therefore, most people now remove most of the polycyclic hydrocarbon compounds in smoke, and retain only acids, phenols, alcohols, and carbon compounds that can impart special flavor and preservation to smoked products. The product was smoked and achieved good results.
4. Antibiotic treatment: The value of antibiotics used for meat preservation is limited because antibiotics are bacteriostatic rather than bactericidal. They are most effective only when the number of contaminated microorganisms in the meat is small; the sensitivity of different microorganisms to an antibiotic Differently, while antibiotics inhibit certain types of microorganisms, the number of other types of microorganisms may increase; the use of antibiotics may lead to the development of drug-resistant bacterial flora, leaving the antibiotics with no antibacterial effect; currently there is a lack of effective inhibition. Mold and yeast antibiotics. Even so, antibiotics can extend the shelf life of meat without causing chemical or biochemical changes in the meat. However, when it is used, it must be carefully selected. The antibiotic used must be easily decomposed when the meat is heat-treated. The product is not toxic to the human body.
Frequently used antibiotics for meat storage include chloramphenicol, chlortetracycline, tetracycline, nisin, and tylosin, which can be used for very heat-resistant bacteria. It is generally not allowed to use antibiotics for semi-protection. Although antibiotics can reduce the intensity of heat treatment and pickling, they also increase the risk of C. botulinum producing toxins.
5. Preservative Preservative Treatment: This is another method commonly used in meat preservation. Preservatives are divided into chemical preservatives and natural preservatives. Preservatives are often used in combination with other preservation techniques.
(1) Chemical preservatives: Chemical preservatives are mainly organic acids and their salts. Mainly used in meat preservation are acetic acid, formic acid, citric acid, lactic acid and its sodium salt, ascorbic acid, sorbic acid and its potassium salt, and benzoic acid. The use of these acids alone or in combination has a certain effect on prolonging the shelf life of the meat. When used, the aqueous solution is first formulated with a concentration of 1% to 3%, and then the meat is sprayed or impregnated.
(2) Natural Preservatives: Due to people's care for green and healthy foods, natural preservatives should be the future direction of development. Nowadays, more natural natural preservatives for meat are catechol, spice extracts and Nisin. Their antiseptic effect is still not ideal, Nisin's antibacterial spectrum is narrow, and future research in this area should be strengthened.
V. Causes of Meat Corruption and Sensory Features of Corrupted Meat
1. Factors leading to meat spoilage: Healthy animals' blood and muscles are usually sterile, and the corruption of meat is actually due to the contamination of external microorganisms and the action of enzymes during slaughtering, processing and distribution. Their role not only causes serious deterioration of the meat's organoleptic properties, color, elasticity, and odor, but also destroys the nutrients of the meat. At the same time, metabolites of microbial life activities can cause toxic substances that cause food poisoning.
(1) Corruption caused by microorganisms: Corruption of meat usually begins with the aerobic microorganisms in the external environment contaminating the surface of the meat and then spreads deeper along the connective tissue. Especially in places close to joints, bones and blood vessels, it is most likely to be corrupt. And the collagenase secreted by the microorganisms hydrolyzes the collagen of the connective tissue to form a mucus, and at the same time produces gas; when fermented in the presence of glycogen, it produces acetic acid and lactic acid to form an unpleasant odor.
Fresh meat that has just been slaughtered is usually acidic and spoilage bacteria cannot grow on the surface of the meat. However, in the acidic medium, yeasts and molds can be well propagated, and protein degradation products such as ammonia are formed to increase the pH of the meat, providing good conditions for the growth of spoilage bacteria.
(2) Enzyme-induced protein degradation and fat oxidation: Corruption is actually a phenomenon of protein degradation, which is caused by the decomposition of proteolytic enzymes produced by various spoilage bacteria. The final decomposition products of proteins are inorganic substances such as ammonia; nitrogen-containing organic bases such as methylamine, cadaverine, etc.; organic acids such as keto acids; other organic decomposition products such as methane, methyl hydrazine, skatole and the like. These substances can make the meat smell bad.
Microorganisms carry out two enzymatic reactions to fat: First, lipases secreted by microorganisms break down fats to produce free fatty acids and glycerol; and second, oxidizing enzymes oxidize fats to produce oxidized rancid odors.
Lipids and lipoproteins in meat can cause enzymolysis of lecithin under the influence of lipase, forming fatty acids, glycerol, phosphoric acid and choline. Choline is further converted into trimethylamine, dimethylamine, methylamine, and neuronals. Trimethylamine oxidizes to trimethylamine oxide with a fishy odor.
2. The organoleptic characteristics of decayed meat: Surface stickiness is the main sign of the role of microorganisms in producing corruption. In the circulation, mucus occurs when the surface of the meat has 50 million bacteria per square centimeter. The more bacteria that are initially contaminated, the shorter the number of days required to reach this state, and the higher the well temperature. The higher the humidity, the easier it is to produce a sticky phenomenon.
The change in the color of meat is also one of the hallmarks of evaluating changes in the quality of meat. When the color of the muscles becomes dull, grayish green or dirty gray, or even black, it indicates that the muscle has been seriously corrupted. The meat at this time has a bad smell.
Corrupted meat is not edible.
Storage and preservation of raw meat
In a general sense, raw meat refers to the edible part of the carcass, that is, the carcass from which the bone is removed, also known as the net meat. The raw meat itself is rich in nutrients and is an excellent medium for the growth and reproduction of microorganisms. In addition, the meat itself also contains certain enzymes. If the meat is improperly stored, it can easily cause spoilage. Therefore, when designing meat preservation methods, two main aspects should be considered: one is to suppress the spoilage caused by microorganisms, and the other is to slow down or inhibit the activity of the meat itself. At present, the most commonly used method is low-temperature storage, in addition, heat treatment, dehydration treatment, radiation treatment, antibiotic treatment and other methods can also be used for storage.
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