Shelf life extension technology for chilled and fresh prepared meat products

Mar 03, 2025

In China, fresh prepared meat products are typically sold in large supermarkets or specialized counters.

Although large-scale meat companies in China have a mature cold chain system, low temperature only inhibits the growth of microorganisms, without effectively killing spoilage bacteria. Under suitable conditions, these microorganisms can grow and proliferate, shortening the shelf life of the products. According to studies, the shelf life of fresh prepared meat products at 0-4°C is only 2 days. Even when modified atmosphere packaging (MAP) is used and stored at 2°C, the shelf life remains under 14 days. Therefore, the short shelf life is a major constraint for the development of fresh prepared meat products.

The research on extending the shelf life of fresh prepared meat products is crucial for preventing microbial growth, lipid oxidation, juice loss, and surface browning. This is essential for reducing losses in meat production companies and ensuring consumer safety. This study discusses the selection of raw and auxiliary materials, standardized processing operations, preservatives, preservation technologies, and packaging methods, providing theoretical guidance for the production, processing, and sales of fresh prepared meat products.

Selection of Raw and Auxiliary Materials

Microbial Types and Counts in Raw Meat
The main reason for the short shelf life of fresh prepared meat products is the massive proliferation of microorganisms. The quantity and types of microorganisms in raw meat affect the shelf life of the products. According to the GB/T 9959.2-2008 standard, the total bacterial count in fresh meat should not exceed 10^6 CFU/g. To extend the shelf life of prepared meat products, raw meat and auxiliary materials must undergo strict quarantine and inspection to ensure that microbial levels meet national standards. Meat processing companies should choose raw and auxiliary materials that comply with GB 18406.1 for agricultural product safety and quality.

pH of Raw Meat
The pH of raw meat reflects its freshness. Generally, the pH of fresh meat ranges from 5.8 to 6.2, while meat with a pH between 6.3 and 6.6 is considered less fresh, and a pH above 6.7 indicates spoiled meat. The pH of raw meat directly affects the product's quality and shelf life. If the pH is too low, it can affect the product's water-holding capacity and flavor; if the pH is too high, it shortens the shelf life and alters the expected flavor profile. Reports indicate that under aerobic conditions, pH has little impact on microorganisms in fresh meat. However, under anaerobic conditions, when pH > 6.0, certain spoilage bacteria can proliferate. Therefore, when using vacuum packaging, controlling the pH of fresh prepared meat between 5.9 and 6.2 can extend the product's shelf life.

Good Processing Practices and Standards

Good processing practices involve selecting appropriate methods based on the type, part, and physicochemical properties of the raw meat to preserve its original quality. Various additives and auxiliary materials must be evenly distributed throughout the raw meat. If preservatives are not evenly distributed, bacteria will proliferate in unprocessed areas, leading to spoilage and a shortened shelf life. This also negatively affects the taste and flavor during cooking. Moreover, due to varying water content in different meat parts, areas with higher moisture content are more prone to microbial growth, which accelerates spoilage. In general, processes such as injection and tumbling are used during meat preparation. The injection pressure is typically 0.2-0.25 MPa, with possible secondary injection based on the effect. During the entire production process, the environmental temperature must be maintained between 0°C and 4°C, and the vacuum level during tumbling should be -0.08 MPa.

In the production, transportation, and sales of fresh prepared meat, cross-contamination is a significant concern. Thus, implementing a HACCP management system and adhering to good manufacturing practices (GMP), such as those outlined in GB/T 20575-2006 (Fresh and Frozen Meat Manufacturing Guidelines) and GB/T 20799-2006 (Fresh and Frozen Meat Transportation Conditions), is essential. These measures, combined with other preservation techniques, can effectively extend the product's shelf life.

Application of Preservatives

Apart from microbial growth, spoilage of prepared meat products can also result from lipid oxidation and the oxidation of myoglobin, leading to unpleasant odors and surface browning. Currently, preservatives and appropriate preservation techniques, or their combination, are commonly used in meat preservation. The application of efficient preservatives and preservation technologies can significantly extend the shelf life of the products.

Preservatives used in prepared meat products can be categorized as chemical or natural preservatives. Their main role is to inhibit microbial growth and prevent lipid and protein oxidation, thus extending the product's shelf life. Chemical preservatives include organic acids and their salts, ozone, and chlorine dioxide. Common examples are acetic acid, formic acid, citric acid, lactic acid and its sodium salts, ascorbic acid, sorbic acid and its potassium salts, and phosphates. Natural preservatives include tea polyphenols, spice extracts, nisin, lysozyme, and chitosan.

Preservation Technologies

• Low-Temperature Preservation: As the cold chain improves, low-temperature preservation is the most common method. Lowering the temperature reduces enzyme activity and slows down microbial growth. When the temperature drops to the range where ice crystals form, bacteria cease growing and may even die. At around 4°C, most pathogenic bacteria, such as E. coli and Staphylococcus aureus, cannot grow or secrete toxins. However, low-temperature preservation only inhibits microbial growth and does not kill microorganisms, allowing them to grow again when conditions are favorable. Therefore, low-temperature preservation is often combined with packaging techniques to extend the shelf life of fresh meat.
• Irradiation Preservation: Irradiation uses gamma, beta, and X-rays or electron beams to process meat products, effectively inhibiting or killing all microorganisms, thus extending the shelf life. Research indicates that a 10 kGy/h dosage only raises the product’s temperature by 2.78°C, with minimal impact on the product’s original quality and nutritional components, provided the radiation dosage does not exceed 10 kGy (1 Mard). However, high radiation doses can accelerate lipid oxidation in fresh meat, so antioxidants should be added before irradiation, and the product should be stored under low temperature.
• High-Pressure Processing (HPP): HPP technology uses high pressure to kill microorganisms and parasites in fresh meat while maintaining the meat's tenderness, flavor, nutrition, and color. This method has rapidly developed in recent years, particularly for prepared meat products. One challenge of HPP is the survival of spores, so appropriate packaging is required post-processing to ensure extended shelf life.
• Coating Preservation: Coating preservation involves applying film-forming substances onto the surface of food through immersion, coating, or spraying. This creates a thin film that inhibits gas, water, and solute exchange and protects against microbial invasion. Coating preservation reduces juice loss, prevents lipid oxidation, and surface browning in fresh meat, thus extending the shelf life. Common coating agents include chitosan, gelatin, sodium alginate, and propolis. This method is low-cost, easy to operate, and highly effective, with great potential for future development.

Packaging Methods

Choosing the right packaging method can inhibit the growth of residual microorganisms in fresh meat and prevent "secondary contamination" during transportation and sales, thus extending the product's shelf life. Current packaging methods for fresh prepared meat include tray packaging, vacuum packaging, and modified atmosphere packaging (MAP). Among these, MAP is the most extensively researched.

• Tray and Vacuum Packaging: Tray packaging typically involves placing cut or prepared meat on polystyrene trays, which are covered with polyethylene shrink film. While simple and economical, this packaging method limits shelf life to only 2-3 days under refrigerated conditions. Vacuum packaging creates an anaerobic environment, inhibiting the growth of aerobic microorganisms and preventing lipid oxidation, but it may cause juice loss and surface browning, which affects product quality. Therefore, a combination of vacuum and tray packaging is often used in fresh prepared meat products, which helps maintain the red color of the meat while extending the shelf life.
• Modified Atmosphere Packaging (MAP): MAP, also known as gas-flushing packaging, involves replacing the air inside the packaging with protective gases to inhibit microbial growth and enzyme reactions, thereby extending shelf life. The most common gases used in MAP are nitrogen (N²), oxygen (O²), and carbon dioxide (CO²), with occasional use of carbon monoxide (CO).
• Oxygen (O²) helps inhibit the growth of anaerobic bacteria and maintains the fresh red color of meat.
• Carbon dioxide (CO²) acts as an antimicrobial agent, inhibiting the growth of most molds and aerobic bacteria. However, it can dissolve into meat tissue, lowering the pH and affecting product quality.
• Nitrogen (N²) primarily serves to replace oxygen in the packaging, preventing oxidation and spoilage while inhibiting the growth of aerobic microorganisms.
• Carbon monoxide (CO) is used mainly to maintain the bright red color of fresh meat.

Currently, research on MAP primarily focuses on optimizing the gas mixture and its proportions. MAP significantly outperforms vacuum and tray packaging for preserving fresh prepared meat and is expected to become the dominant packaging method for such products in the future.