First, dry consumption
Dry consumption is the result of the loss of water in the cold storage. The dry consumption not only reduces the quality of the meat, but also affects the quality of the meat and promotes the oxidation of the surface layer. In the cold storage, the raw meat will form fine holes in the surface where the surface ice crystals sublimate due to evaporation of water, which greatly increases the contact area between meat and air. Under the action of oxygen in the air, the fat in the meat is oxidized and rancid, and the surface is browned. The surface shrinks and hardens, forming a dry film, and the flavor and nutritional value will decrease, which is detrimental to the quality of the diet and human health.
1. Factors affecting the consumption of cooling meat
1) Refrigeration chamber temperature
The lower the temperature of the refrigerating compartment, the smaller the dry consumption of the raw meat, because the lowering of the temperature of the refrigerating compartment means that the difference between the air pressure of the air on the surface of the food and the air in the refrigerating compartment is reduced, and the evaporation of the moisture of the food and the sublimation intensity of the ice crystal are also reduced. The driving force for water vapor diffusion is reduced, and the dry consumption of meat is naturally smaller.
2) relative humidity of the refrigerator
The relative humidity of the refrigerator has a great influence on the growth and reproduction of microorganisms and the dry consumption of meat (generally 3% of the carcass mass). The evaporation of the moisture content of the raw meat is inversely proportional to the relative humidity of the air in the store. At the same temperature, the higher the relative humidity of the air in the warehouse, the smaller the evaporation of water in the meat. Conversely, when the relative humidity of the air is small, the water content in the air is far from the saturation point. To achieve saturation, it is necessary to absorb the moisture in the meat. , resulting in increased meat consumption.
3) Air flow rate
The air flow rate directly affects the cooling rate of the meat and the dryness of the meat, and the two are related to each other. The flow of air changes the absolute humidity of the air, which affects the dry consumption of the frozen meat. According to the law of heat transfer, the temperature difference between food heat dissipation and food and ambient air and the air velocity around the food are approximately linear, the temperature difference fluctuates, the air flow speed increases, the heat migration brings wet migration, and the dry surface consumption of food is accelerated.
2. Measures to reduce the dry consumption of raw meat during storage
1) Control the temperature of the suitable refrigerating compartment
The more unstable the temperature of the refrigerating compartment, the greater the dry consumption of the raw meat. Therefore, the requirements for the refrigerating compartment are relatively high. To minimize the inflow of external heat, it is necessary to maintain the peripheral structure of the refrigerating compartment, and also whiten the outer surface of the enclosure of the refrigerating compartment, thereby reducing the inflow of external heat; Temperature monitoring equipment should be installed at different locations in the refrigerating room to monitor the temperature changes in a timely manner. The enterprise should also formulate a series of management regulations for the staff to enter the refrigerating room according to the actual situation, such as closing the door at any time, and minimizing the indoors in the refrigerating room. When turning on the lights, try to avoid the visits and residence time of the outsiders to the cold room. If necessary, build a new type of jacketed cold storage, and the heat transferred from the peripheral structure will be taken away in the jacket. In the storage, the temperature of the refrigerating compartment is kept stable, and the dry consumption of the raw meat is reduced. Before the meat is introduced into the refrigerator, the temperature of the refrigerating compartment should be lowered to -2~3 °C in advance, so as to avoid the temperature of the refrigerating compartment after entering the meat. Large fluctuations.
2) Improve the relative air humidity of the refrigerator
In the initial stage of cooling, the temperature difference between the air and the carcass is large, the cooling rate is fast, the relative humidity should be above 95%, and then should be maintained at 90%~95%, and should be maintained at about 90% after the cooling, so that the cooling can be shortened. Time, so that the surface of the meat forms a good dry film without causing serious dry consumption. Therefore, it is necessary to carry out artificial water spray humidification or use a large humidifier to increase the relative air humidity in the refrigerator and reduce the occurrence of raw meat consumption.
3) Control the flow speed of the air in the refrigerating room
The high air flow rate promotes the dry consumption of the meat surface. In addition, the relative humidity is high, the air flow rate is low, and although the dry consumption is minimized, it is easy to make the raw meat mold and sticky. Therefore, during the cooling process, the air flow rate should generally be controlled at 0.5~1m/s and the maximum should not exceed 2m/s. It is necessary to reduce the flow speed of the air in the refrigerating room, such as using a cooling pipe in the refrigerating room to disassemble and arrange the large effective area, thereby slowing the flow rate of the air. For the refrigerating room with the air cooler, the airflow distribution in the warehouse should be reasonable. At the same time, the indoor airflow speedometer should be installed at different positions of the refrigerating room so as to monitor the air flow rate in the room at any time. If the plastic cloth is covered on the cargo or the raw meat, It can reduce the contact between raw meat and air, and reduce the consumption of raw meat.
Second, sticky and moldy
1. The reason why the meat is mildewed and sticky
The stickyness of the meat is due to the contact of the carcass in the process of cooling, the ventilation is not good, and the cooling is slow, which leads to the growth and reproduction of Leuconostoc, Micrococcus, Achromobacter and Pseudomonas, forming mucus-like substances on the surface of the meat. Causes the surface of the meat to be sticky and may also produce a stale smell. Moldy is due to the fact that when mold grows on the surface of meat, it often forms white or black mold spots. The small white spots are produced by the contamination of the flesh-colored branch cytoplasm, like lime water spots, mostly on the surface of the meat, leaving no trace after wiping off. The small black spots are caused by the contamination of the waxy leaves, which are not easy to erase and sometimes invade the deep.
The more serious the microbial contamination, the higher the humidity, and the higher the temperature, the more easily the meat surface becomes sticky and moldy. At 0 ° C and aerobic conditions, the degree of microbial contamination is closely related to the time of mucus formation on the meat surface. When the number of bacteria contaminated on the surface of the meat was 100/cm 2 , it became sticky at 16 days; when it reached 105 cells per square centimeter, it became sticky only after 7 days. When the temperature rises, the time of sticking is significantly shortened.
The humidity of the air also has a great influence on the stickiness. It was reduced from 100% relative humidity to 80%, and the time to form tackiness was maintained 1.5 times when the temperature was kept at 4 °C.
2. Measures to reduce the mildew and stickiness of raw meat during storage
Stickiness and mildew are the result of the growth and reproduction of microorganisms on the surface of the meat during the cold storage process, which is related to the degree of contamination and relative humidity of the meat surface, and also to the temperature of the environment. Therefore, only the temperature is strictly controlled, and ultra-rapid cooling can be used in the cooling process to accelerate the cooling of the raw meat, which is beneficial to inhibit the growth and reproduction of microorganisms and improve the quality of the cooled meat. It is necessary to strictly control the total number of initial colonies on the surface of the raw meat, which requires the staff to strictly control the hygiene during the production, refrigeration and circulation of the meat, and to avoid cross-contamination between them, in order to make the raw meat sticky and moldy. The degree is reduced to a minimum. When hanging, try to avoid the contact between the raw meat. If the raw meat is stored in the refrigerator, it should be separated by the plastic cloth between the raw materials. If necessary, the raw meat can be irradiated. To improve the quality of meat.
Third, the color change
1. Factors that cause the color change of the cooled meat
1) Oxidation of myoglobin (Mb) and fat
The color of the meat changes with the time it is placed in the air. The color changes from dark red to bright red to maroon. This is because the myoglobin in the meat is caused by the action of oxygen in the air. Myoglobin (Mb) itself is purplish red. Under high oxygen partial pressure, it combines with oxygen to produce oxygenated myoglobin, which is bright red and is a symbol of fresh meat; myoglobin and oxygenated myoglobin are low. Under oxygen partial pressure, it can be oxidized to produce high-myoglobin, which is brown and darkens the flesh.
2) Microorganisms
The growth and reproduction of microorganisms in meat can cause discoloration of meat while causing meat spoilage. When the aerobic microorganisms in the chilled meat increase in number in the logarithmic growth phase, the formation of high-iron myoglobin is promoted, and the aerobic microorganisms causing meat spoilage mainly include some bacteria of the genus Pseudomonas, colorless. Bacillus, etc., their growth and reproduction reduce the oxygen partial pressure on the surface of the meat, which causes the meat to deteriorate and also causes the surface of the meat to change color.
In addition to the surface discoloration of the chilled meat caused by bacteria, by-products of some bacteria during growth and reproduction oxidize the iron atoms in myoglobin and bind to the free binding sites in heme to discolor the cooling meat. The most common bacterial by-products are hydrogen sulfide and hydrogen peroxide, which bind to unstable myoglobin to produce sulphur myoglobin and bilirubin, respectively, which discolor the meat.
2. Measures to prevent discoloration of raw meat during storage
The raw material meat can be controlled by inhibiting the growth and reproduction of microorganisms in the meat, inhibiting the oxidation of fat in the meat, and rationally adding a preservative and a color protecting agent.
There are several measures to prevent discoloration in cooling meat:
1 using low gas permeability material, vacuuming and adding oxygen scavenger treatment;
2 high oxygen pressure protection;
3 using 100% carbon dioxide conditions, if combined with the use of oxygen scavengers, the effect is better;
4 using color protection agent color protection.
In practice, no single measure is completely effective, so an integrated approach must be taken to effectively prevent discoloration of the cooled meat.
Fourth, odor
1. Causes of odor caused by cooling meat
The chilled meat is prone to odor when it is spoiled, oxidized and stored for a long time. There are three main reasons for chilled meat that has an odor:
1 Because fat is hydrolyzed and oxidized under the action of air, high temperature, light, microorganisms, etc.;
2 meat stored with a strong smell of food, will cause the meat to produce a odor;
3 refrigerators also have some unique odor, commonly known as cold odor, this cold odor will also be stringed to cool food.
2. Measures to prevent raw meat from producing odor during storage
1 to prevent the raw meat from odor caused by spoilage and oxidation during storage;
2 To avoid the odor and cold odor of the refrigerating compartment, it is required to be dedicated to the management, and to be strictly disinfected, deodorized and ventilated regularly or after a food is discharged.
V. Outlook
With the improvement of people's living standards, the chilled meat has become the mainstream of meat consumption because of its tender and delicious taste and high nutritional value. It has the advantages that hot meat and frozen meat are incomparable, but the shelf life of chilled meat is relatively short. Can not meet the needs of market circulation, seriously affecting the quality of meat and the interests of sales merchants. Therefore, it is important to study the quality control of raw meat cooling and preservation process to improve the quality of chilled meat and extend its shelf life to better ensure the safety of meat and meat products.
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