As the economy develops and people's living standards improve, the market demand for chilled meat is increasing. According to data from the National Bureau of Statistics, the cumulative production of chilled meat in China reached 25.541 million tons in 2020.

Chilled meat contains rich nutritional components, but if packaged improperly, it is extremely susceptible to microbial contamination during the processes of slaughter, logistics, storage, and sales, leading to a decline in quality and impacting consumer health. Therefore, adopting scientific and reasonable packaging technology for effective preservation of chilled meat is crucial.

Currently, the most commonly used packaging material for chilled meat in the market is still plastic film. Plastic packaging has good gas barrier properties, high mechanical strength, good antibacterial effects, and low cost, thus dominating the market. Common plastic packaging materials include:

Polyethylene (PE): safe and non-toxic, meets food safety standards, the most widely used.

Polyester (PET): High transparency, high strength, suitable for food packaging.

Polypropylene (PP): good low-temperature resistance, suitable for cold chain transportation packaging.

Polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC): have good barrier properties, can effectively prevent microbial invasion, and maintain the stability of the internal packaging environment.

Traditional plastic films, although widely used, can cause serious environmental pollution due to their difficulty in degrading. According to statistics, food packaging plastics account for more than 60% of the total plastic production in our country, making the research on degradable packaging materials a key focus for future development.

Currently, the more extensively researched degradable packaging materials include:

• Polyvinyl alcohol (PVA): water-soluble material, strong barrier properties, low cost.

• Poly(lactic acid) (PLLA): a completely degradable aliphatic polyester material, with high transparency, mechanical strength similar to PET, and good biocompatibility.

Research found that the PPC/PVA/PPC composite film under the packaging condition of 50%O₂+25%CO₂+25%N₂ can effectively extend the shelf life of chilled meat.

Active packaging extends the shelf life of food by incorporating natural antimicrobial substances into the packaging material, enabling it to actively regulate the packaging environment. Currently, the active packaging films under research include:

• ε-polylysine (ε-PL): It has broad-spectrum antimicrobial properties and can effectively inhibit the growth of Gram-positive bacteria, Gram-negative bacteria, and molds.

• Anthocyanin (pH indicator): can change color according to the freshness of the meat, providing consumers with a direct basis for judging food quality.

• Tea polyphenols + grape seed extract: can reduce lipid oxidation and improve the color stability of fresh meat in high-oxygen modified atmosphere packaging.

The application of these new types of packaging films can effectively improve the freshness preservation capability of chilled meat, while also reducing food safety risks.

Ultra-high pressure preservation technology (HPP) achieves the effect of sterilization and preservation by destroying cell walls, cell membranes, and protein structures under 100-1000MPa hydrostatic pressure. Studies have shown:

• Ultra-high pressure treatment above 300MPa can significantly kill spoilage bacteria in chilled meat and extend its shelf life.

• 200MPa pressure treatment, in some cases, can instead enhance the activity of certain enzymes, such as an increase of 52.1% in the activity of metmyoglobin reductase, which may affect the color of meat.

• Ultra-high pressure technology can kill bacteria while also reducing enzyme activity, decreasing the generation of volatile basic nitrogen substances, thereby inhibiting meat spoilage.

Natural preservatives are widely sourced, have low toxicity, strong antibacterial properties, and can naturally degrade without causing environmental pollution. Common natural preservatives include:

• Plant extract: Clove extract has the best antibacterial effect, and a composite preservative of ginger juice + chitosan + tea polyphenols can also effectively extend the shelf life of chilled meat.

• Animal-derived preservatives: Chitosan, propolis, etc., have good antibacterial properties and can be combined with other natural preservatives to form composite preservative films.

• Microbial source preservatives: Metabolites of lactic acid bacteria, such as bacteriocins, H₂O₂, can be used for antibacterial and anti-corrosion.

Ice-temperature preservation is a freshness preservation technology that stores food at temperatures below 0°C but without freezing, which can reduce tissue damage in chilled meat. Studies have shown:

• -1℃ beef is more vivid in color, has better water retention, and a longer shelf life compared to 4℃ refrigerated beef.

• -1.5℃ chicken compared to 4℃ refrigeration, has a slower decrease in water-holding capacity, firmer texture, and delayed lipid oxidation.

Irradiation preservation uses ionizing radiation to directly affect the nucleic acids, proteins, lipids, and other macromolecules of microorganisms, destroying their structures to achieve sterilization and preservation. Compared with traditional sterilization methods, irradiation preservation does not require heating or cooling, so it does not affect the quality of chilled meat, while also avoiding the use of chemical preservatives.

III. The packaging method of chilled meat

Vacuum packaging refers to placing the product in a sealed container, extracting the air, and sealing it after reaching the predetermined vacuum level inside, which can effectively prevent oxidation, inhibit bacterial growth, and extend the shelf life of chilled meat.

The study shows that the total bacterial count and volatile basic nitrogen of vacuum-packed chilled beef meet national standards within 21 days, indicating a longer shelf life.

modified atmosphere packaging involves filling the package with a specific ratio of mixed gases to slow down the spoilage of chilled meat

• 70% O₂ + 25% CO₂ + 5% N₂ atmosphere can extend the shelf life of pork to 10 days.

• 40% CO₂ + 60% O₂ gas environment is suitable for the long-term preservation of yak meat.

• Different types of chilled meat require different gas mix ratios to achieve the best preservation effect.

As consumers' concern for food safety and environmental protection increases, the future development of chilled meat packaging will focus on the following areas:

• Improve packaging quality, reduce costs, and increase material utilization.

• Accelerate the research and development and application of degradable packaging materials to reduce environmental pollution.

• Optimize packaging process, combine with freshness preservation technology, ensure material adaptability, and improve freshness effect.

• Promote new fresh-keeping technologies, such as ultra-high pressure processing and active packaging, to improve the quality and safety of chilled meat.