1 organic acids and their salts At present, organic acids and salts commonly used in food preservation include acetic acid, lactic acid, citric acid, ascorbic acid, sorbic acid and potassium salts thereof, and tartaric acid phosphate. The mechanism of action is mainly that organic acid molecules dissociate by entering the cell membrane through the cell membrane of the pathogenic microorganism, leading to cell metabolism disorder or death; and reducing the water activity and pH of fresh meat. Cosansu et al. inoculated S. Enteritidis 4~5 log MPN/cm2 in chicken legs and chicken breast, and then soaked in lactic acid (LA) and acetic acid (AA) for 10 min. After treatment with 1% LA, 3% LA, 1% AA and 2% AA, the number of S. Enteritidis colonies in chicken legs was reduced to 0.75, 1.21, 0.85, 0.95 log MPN/cm2, respectively; in chicken breasts, it was reduced to 0.97, 1.72, 0.92. 1.58 log MPN/cm2. There was a significant difference between the number of Salmonella colonies in the control group and the treatment group (P<0.05), indicating that lactic acid or acetic acid treatment can effectively reduce Salmonella contamination. 2 antibacterial antiseptic preservative 2.1 Microbial source preservative Microbial source preservatives include nisin (Nisin), lactic acid bacteria fermentation broth, and phytolaccin L-1. With its good physical and chemical properties and safety, microbial source preservatives have attracted the attention of researchers and have broad application prospects. At present, the research on preservatives at home and abroad mostly concentrates on a variety of preservatives to form a composite preservative, and the use of microbial source antibacterial preservative can not only expand the scope of the original single preservative, but also reduce the dosage of the single preservative. Ma Meihu et al. studied the effect of lysozyme, Nisin, GNA (18% NaCl + 4.5% glucose) preservative on the preservation of chilled meat. The results showed that the fresh-keeping effect of lysozyme was significantly better than that of the control group, which was significantly better than the GGa group, slightly better than the Nisin group. 2.2 Botanical Antibacterial Preservatives Many plants contain bactericidal and bacteriostatic ingredients, which can be used as natural preservatives after extraction. Racanicci et al. used fresh chicken breast meat pills as test materials to compare the antioxidant properties of white fresh (Origanus dictamnus L.) and rosemary (Rosmarinus officinalis L.). When the addition amount is 0.05%~0.1%, the antioxidant effect of rosemary is higher than that of white fresh; but 0.05% white fresh can prevent VE degradation more effectively. Govaris et al studied the antibacterial effect of oregano essential oil (EO) and Nisin on mutton S. Enteritidis. The results showed that the addition of 0.6% or 0.9% oregano essential oil to the mutton increased sensory taste. The synergistic effect of 0.6% oregano essential oil and 500 IU/g Nisin on S. Enteritidis exceeded the antibacterial activity of 0.6% oregano essential oil. Recent studies have shown that tomato can reduce the incidence of cancer, mainly because it contains lycopene, lycopene can increase the stability of meat storage; tomato products can reduce the pH of meat and inhibit the growth of microorganisms. Vaithiyanathan et al. immersed chicken breast meat with 0.02% pomegranate juice phenolic solution (PFJP), which significantly reduced the content of thiobarbituric acid reactant (TBARS) and inhibited the growth of aerobic psychrophilic bacteria. It was stored at 4 ° C for 12 days and still had Very good sensory acceptance. Selani et al. showed that Isabel (IGE) and Niagara (NGE) grape seed and skin extracts treated fresh chicken meat significantly inhibited lipid oxidation. 2.3 Animal source antibacterial preservative Animal source antibacterial preservatives mainly include chitosan, propolis and lysozyme. Lysozyme disrupts the integrity of the cell wall structure, causing Gram-positive bacteria to decompose under their own internal pressure. Propolis has strong inhibition and killing power against a variety of bacteria, fungi and certain viruses, protozoa, and has a neutralizing effect on certain bacterial exotoxins. Propolis also has anti-oxidation properties. Nagai et al. studied the antioxidant effects of bee products. The results showed that the antioxidant activity of honey decreased slowly with time. The effect of buckwheat honey was the same as that of 1 mmol/L VE; the superoxide ion scavenging activity of propolis and royal jelly was the strongest; honey DPPH free radical scavenging capacity is less than 1 mmol / L VC and VE; honey scavenging hydroxyl radical activity is very high. Honey has the ability to inhibit the growth of bacteria in chilled meat storage, with propolis and royal jelly having the most bacteriostatic effect. It indicates that bee products have strong antioxidant activity, inhibition of bacterial activity and ability to scavenge reactive oxygen species. 3 film preservative The film preservation is to immerse the food in the coating liquid or spray the coating liquid on the surface of the food to form a film on the surface of the food, thereby changing the surface gas environment and inhibiting the growth of microorganisms, so as to achieve the purpose of preservation. In recent years, many of the film-forming substances used have chitosan, konjac glucomannan film, sodium alginate, carboxymethyl cellulose, starch and propolis. Kanatt et al. used 2 g/100 mL chitosan to coat chicken meatballs, chicken skewers and mutton skewers, and stored at 0~3 °C for 14 days. Compared with uncoated samples, chitosan can significantly extend the shelf life, inhibit lipid oxidation; remove surface E. coli, reduce the number of Staphylococcus; effectively inhibit Bacillus cereus, Staphylococcus aureus, Escherichia coli and fluorescent false Monocytogenes. 　　 4 Storage and packaging technology With the development of science and technology, a variety of storage and packaging technologies are applied to the preservation of fresh meat, and storage and packaging technologies complement each other. 4.1 Modified atmosphere storage and packaging Atmospheric storage and packaging is a method of preserving the shelf life of fresh meat by changing the gas environment in the storage environment, inhibiting the growth of microorganisms. Zakrys-Waliwander et al. studied the effects of modified atmosphere packaging on steak tenderness and protein. The gas composition is 40%, 50%, 60%, 70%, 80% O2, 20% CO2, and the balance is N2. The results showed that in the modified atmosphere packaging, the increase of O2 content (>50%) had a negative effect on the tenderness and juice of cooked steak; and the carbonyl content and TBARS value increased significantly; protein oxidation was significantly correlated with O2 content (>50%). (P<0.01). Chen Wei et al. used pig pork tenderloin cooled for 24 h after slaughter as a material, and used four kinds of mixed gases containing different concentrations of CO for air-conditioning packaging, and stored at (4±1) °C, and the relevant indicators were measured regularly. The results show that CO modified atmosphere packaging can significantly improve the color of the meat, so that the cooling meat maintains a stable bright red color during the storage period. The coexistence of CO and O2 makes the flesh color more natural than the anaerobic group. The selected optimum gas ratio of 0.4% CO, 24% O2, 50% CO2, and 25.6% N2 can greatly improve the meat color of the chilled meat, and the shelf life of the chilled meat exceeds 10 days. When the four groups of treated samples were stored on the 15th day, the TVB-N value exceeded 15 mg/100 mg, and the total number of bacteria exceeded 106 CFU/g. The effect of each treatment on the shelf life of the chilled meat was not significant. 4.2 Vacuum storage and vacuum packaging Decompression storage is achieved by reducing the air content in the storage environment and reducing the pressure to achieve storage and preservation, but decompression storage causes moisture loss. Vacuum packaging uses non-breathable materials to reduce the oxygen content by pumping out the air inside the package. Vacuum storage prevents the surface of fresh meat from dehydrating and extends the shelf life. Balamurugan et al. inoculated 105-106 CFU/cm2 of Campylobacter jejuni ATCC 11168 in beef and pork. The test showed that in the vacuum packaging, the sample itself carried microorganisms can significantly enhance the survival rate of C. jejuni, after storage for 6 weeks (4 ° C) only Reduce 1 log CFU/cm2. Filgueras et al. store the gastrocnemius (GN) and Iliofiburalis (IF) of the American cockroach in aerobic or vacuum (4 ° C), respectively. In aerobic storage, lipid and protein oxidation increased by 275% and 30%, respectively. In vacuum packaging, both muscles exhibit high color stability and lipids and proteins are not oxidized. Zhang Haiwei and others used vacuum packaging, anaerobic packaging (N2+CO2) and modified atmosphere packaging (O2+CO2+N2), and stored at (4±1) °C for 20 days. Vacuum packaging can significantly reduce the fat oxidation of pork. 　　 5 non-heat treatment technology 5.1 Irradiation technology Food irradiation is a new type of food preservation technology developed by humans using nuclear technology. It has the advantages of energy saving, high efficiency, no heating, safety and good sensory quality of food. Studies such as Javanmard have shown that gamma irradiation (0.75, 3.0, 5.0 kGy) can significantly reduce the number of microorganisms and prolong the shelf life of chicken. Li Zongjun studied the effects of irradiation on the quality of meat microbes and beef and mutton. The results showed that the meat was vacuum packed and stored at (2±1) °C after 2~4.0 kGy low temperature irradiation. The shelf life of beef and mutton can be Reached 60d. Gu Kefei analyzed the changes in sensory characteristics of cooled pork tenderloin after electron beam irradiation. When the dose was above 3 kGy, the TVB-N value, peroxide value and juice loss rate exceeded the specified limit value. Poor radiation, but when the dose does not exceed 3 kGy, after 21 days storage at (3 ± 1) °C, all indicators are normal, and the color of the meat is bright red, low-dose electron beam irradiation can not affect the ridge Under the premise of meat quality, it has a certain preservation effect. 5.2 High-density CO2 sterilization technology High-density CO2 sterilization is a new type of non-thermal sterilization technology that treats materials at a certain temperature (below 60 ° C) and pressure (above 5 MPa and below 50 MPa), using pressure and CO2 molecular effects to form high pressure and The acidic environment achieves the purposes of sterilization, blunt enzymes, and protein denaturation, and has the advantages of low sterilization temperature, no residue, and low nutrient loss. The research on high-density CO2 mainly focuses on the effects of microorganisms and enzymes in liquid foods such as juice and milk, and there are few studies on solid foods. Rao Weili et al studied the bactericidal effect of high-density CO2 with different pressure, temperature and time on bacteria in fresh chicken, and used Weibull, Modified Gompertz and Logistic models to fit the kinetics of high-density CO2 sterilization. The results showed that the bactericidal effect of high-density CO2 gradually increased with the increase of treatment pressure, temperature and time. The predicted value and the measured coefficient R2 of the measured value indicated that the logistic model can well fit the inactivation of bacteria in fresh-conditioned chicken. curve. This provides a theoretical basis for the practical application of high-density CO2 sterilization technology in meat. 5.3 Ultra high pressure technology Ultra-high static pressure (100~1 000 MPa) is a non-heat treatment technology that prevents contamination of meat products after processing. The mechanism of ultra-high static pressure is to destroy microbial cells, such as disrupting the structural and functional integrity of the plasma membrane; or inducing protein denaturation, or inhibiting genetic functions. In general, the higher the pressure, the longer the time and the greater the damage. However, some food ingredients have a gas pressure protection effect. Many high-protein foods have been significantly affected by texture and color after being treated at 400 MPa, and are not suitable for consumption. Fernández et al studied the effect of 20 °C or -35 °C, 650 MPa, 10 min treatment on stored beef. The results showed that beef high pressure treatment (650 MPa, 20 °C, 10 min) significantly increased the extractable water, but 650 MPa, -35 °C The frozen water in the 10 min treated frozen beef was reduced; the frozen beef was treated at low temperature, and the L, a and b values ​​were not significantly different from the fresh samples. High pressure treatment significantly reduced the total number of aerobic bacteria (2-logcycles) and total lactic acid bacteria (2.4-logcycles). Garriga et al. studied the effects of high pressure treatment (400 MPa, 10 min, 17 ° C) and Nisin on several foodborne bacteria. In 4 °C storage, staphylococci were sensitive to high pressure, and the number of colonies in Nisin-containing samples decreased more significantly. Suklim et al studied ultra-high static pressure (100-550 MPa, 40 ° C, 15 min) for three strains (ATCC 14579 and 49064, and a strain isolated from meat samples) Bacillus cereus spores germination and loss The effect of live effects. The results showed that in sterile water, the spore germination remained stable when the pressure was 100~300MPa; when 300~500MPa, the spore germination increased; but at 550MPa, the deactivation rate reached the maximum. 5.4 Microwave technology Microwave is an electromagnetic wave and is usually specified (915 ± 25) MHz and (2450 ± 50) MHz for industrial applications. Microwaves can be sterilized using thermal and non-thermal effects. The thermal effect is that when the food is in a microwave field (an electromagnetic field), the positively-charged, negative-charged, disordered polar molecules in the original food are ordered. In the process of rapid transformation, the molecules rub each other. Produces a lot of heat to kill bacterial propagules, molds and their spores. The non-thermal effect is the variation and denaturation of nucleic acids and proteins in the microwave field; the mechanical damage of the cell membrane (or cell wall) promotes the death of microorganisms. Microwave sterilization can be carried out simultaneously inside and outside the food, with short action time, low temperature, no chemical residue, and no adverse effects on the food. Nagy et al. found that the combination of low levels of gamma rays (3kGy) and microwaves (20s) can extend the shelf life of beef products with only a slight effect on the flavor of meat products. Conclusion Meat preservation is a complex system engineering, and various storage and preservation technologies have their advantages and disadvantages. In the process of storage and transportation of chilled meat, the external environment changes greatly. Therefore, in the process of cooling meat preservation, not only the single storage technology or method should be studied, but also the effect of mutual coordination of various technologies on meat preservation should be paid more attention to. Technical measures ensure the safety of cold meat and meet market demand. 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