The preservative effect of Nisin in meat products

As a natural antibacterial peptide produced by the fermentation of Lactococcus lactis, Nisin occupies a pivotal position in the preservation of meat products, thanks to its highly efficient inhibitory activity against Gram-positive bacteria, human safety (it can be decomposed by digestive enzymes with no residue risk), and biodegradability. Meat products—especially low-temperature processed meat products (such as sausages and hams) and prepared meat products (such as cured and preserved meat products)—are prone to contamination by Gram-positive pathogenic bacteria (e.g., Listeria and Bacillus) and spoilage bacteria. These bacteria not only cause deterioration in product flavor and texture but also pose food safety hazards. Based on its unique mechanism of action and the processing characteristics of meat products, Nisin exerts precise and efficient preservative effects by inhibiting these two types of bacteria, providing crucial support for extending the shelf life and ensuring the safety of meat products.

I. Inhibitory Effect on Listeria: Targeted Prevention and Control of "Low-Temperature Pathogens"

Listeria (especially Listeria monocytogenes) is a typical "high-risk pathogenic bacterium" in meat products. Its distinctive feature is its ability to multiply slowly in low-temperature environments (0–4℃). Most meat products (e.g., low-temperature hams and ready-to-eat sausages) require low-temperature storage and transportation, yet traditional low-temperature preservation cannot inhibit the growth of Listeria. Once contaminated, these products easily cause food poisoning, posing significant risks to pregnant women, the elderly, and people with weakened immunity. Nisin exhibits highly targeted inhibitory activity against Listeria and is not affected by low-temperature environments, making it a core means of preventing and controlling such pathogenic bacteria.

In terms of mechanism of action, nisin functions by disrupting the integrity of Listeria’s cell membrane: it recognizes "lipid II" (a key component involved in cell wall synthesis) on the bacterial cell membrane, binds to it, and forms transmembrane channels. This leads to massive leakage of small-molecule substances (such as potassium ions and amino acids) from the bacterial cells, while harmful substances from the outside infiltrate, ultimately causing metabolic disorders and the death of the bacteria. This mode of action directly targets the basic physiological structure of the bacteria, making it difficult for Listeria to develop resistance. Compared with chemical preservatives, the rate of drug-resistant mutations of bacteria to nisin is extremely low, ensuring stable inhibitory effects even in long-term applications.

In practical applications, the inhibitory effect of nisin on Listeria in meat products manifests in various scenarios depending on the processing technology of the products:

For low-temperature processed meat products (e.g., ready-to-eat sausages undergoing pasteurization), the processing process cannot completely eliminate Listeria that may contaminate the products from the environment (pasteurization is typically conducted at 60–80℃, which is insufficient to inactivate viable Listeria). In such cases, adding an appropriate amount of nisin (in compliance with Chinese standards, the maximum usage level of nisin in meat products is 0.5 g/kg) during processing (e.g., during chopping or before enema) can continuously inhibit the proliferation of Listeria during the subsequent low-temperature storage of the products, keeping its colony count below the safety limit. For example, in the production of low-temperature hams, after adding nisin, even if there is trace Listeria contamination in raw materials or the processing environment, the growth rate of Listeria can be reduced by more than 90% during the 0–4℃ storage period (usually 20–30 days), effectively preventing the issue of "pathogen exceeding limits during storage."

For ready-to-eat meat products (e.g., braised beef and smoked chicken), their ready-to-eat nature demands higher microbial safety. The risk of Listeria contamination mainly arises during post-processing steps such as cutting and packaging. In addition to adding Nisin during processing, methods like "nisin solution soaking" or "surface spraying" can be adopted: briefly soaking ready-to-eat meat products in a low-concentration Nisin solution or spraying Nisin on the product surface before packaging forms an "antibacterial film" on the surface, inhibiting Listeria attached to the surface due to secondary contamination and further reducing safety risks. Moreover, when combined with other preservation technologies (e.g., modified atmosphere packaging (MAP) and cold plasma treatment), nisin’s inhibitory effect on Listeria is significantly enhanced. For instance, MAP (usually filled with a mixed gas of carbon dioxide and nitrogen) inhibits bacterial respiration by reducing oxygen concentration; when combined with Nisin’s "cell membrane disruption" effect, it creates a synergistic effect that can lower the detection rate of Listeria in ready-to-eat sausages to nearly zero while extending the product shelf life by more than 30%.

II. Inhibitory Effect on Bacillus: Blocking "Dual Risks of Spoilage and Toxin Production"

Bacillus (e.g., Bacillus cereus and Bacillus subtilis) are common spoilage bacteria in meat products. Their hazards lie not only in causing product spoilage but also in the fact that some strains (e.g., Bacillus cereus) produce heat-resistant toxins. These toxins are difficult to destroy even after high-temperature heating and can easily cause symptoms such as vomiting and diarrhea when ingested. More critically, Bacillus can form "spores"—dormant bodies with extremely strong stress resistance that can withstand extreme conditions such as high temperatures (above 100℃), dryness, and high salt. High-temperature sterilization commonly used in meat processing (e.g., boiling and roasting) often fails to completely kill these spores. When exposed to suitable temperature and humidity conditions during subsequent product storage, these spores germinate into viable bacteria and multiply in large numbers, leading to off-flavors (e.g., rancidity), sticky textures (due to mucus substances produced by bacterial metabolism), and even toxin production in the products. Nisin’s inhibitory effect on Bacillus covers two key stages—"spore germination" and "viable bacteria proliferation"—thus blocking the risks of spoilage and toxin production at the source.

On one hand, nisin can effectively inhibit the germination of Bacillus spores. Spore germination undergoes three stages: activation, germination, and outgrowth. Nisin acts by interfering with the "germination signaling pathway" of spores: it binds to germination receptors on the spore surface, preventing the spores from sensing "germination signals" from the external environment (such as amino acids and sugars in meat products), thereby inhibiting the transition of spores from a dormant state to an active state. For example, in meat product processing, if raw meat carries Bacillus cereus spores, the spores remain viable (though not killed) after high-temperature boiling and enter a "dormant activated state." Adding Nisin at this stage can significantly reduce the spore germination rate—experimental data shows that in the production of cured meat, the germination rate of Bacillus cereus spores can drop from over 50% to below 10% after adding Nisin, reducing the "base number of viable bacteria in the later stage" at the source.

On the other hand, for Bacillus that have germinated into viable bacteria, nisin can still inhibit their proliferation and kill them by disrupting their cell membranes. During the storage of meat products, if a small number of spores germinate into viable bacteria, Nisin can quickly bind to and act on these bacteria, preventing massive proliferation that would cause product spoilage. For example, in enema-type meat products, the proliferation of viable Bacillus decomposes proteins and fats in the meat, producing spoilage indicators such as total volatile basic nitrogen (TVB-N) and acid value. After adding nisin, the TVB-N content of the product can be controlled below 15 mg/100g (national standards stipulate that TVB-N in meat products should be ≤20 mg/100g) within 10 days of storage at room temperature (around 25℃), and the increase rate of acid value is reduced by more than 60%. This effectively maintains the product’s flavor and texture, extending the room-temperature shelf life from 5–7 days to 12–15 days.

In addition, nisin’s inhibitory effect on Bacillus can also reduce the risk of "secondary contamination" during meat processing. During the cutting and packaging of meat products, Bacillus spores tend to remain on the surfaces of processing equipment (e.g., meat cutters and conveyors), which are difficult to completely remove through traditional cleaning and disinfection. By adding nisin during product processing, when the product comes into contact with the equipment, nisin’s antibacterial activity inhibits the germination and proliferation of residual spores on the equipment surface, forming a "self-antibacterial barrier" for the product and further reducing the possibility of cross-contamination.

III. Key Considerations in Application: Balancing Inhibitory Efficacy and Product Quality

Although Nisin exhibits significant inhibitory effects on Listeria and Bacillus, its application in meat products requires attention to two core issues based on product characteristics to balance "preservative efficacy" and "product quality."

First, the dosage and timing of nisin addition must be controlled. Excessive addition may cause a slight "bitter taste" or "metallic taste" in meat products—while nisin itself is tasteless, at high concentrations, it may interact with components such as myoglobin and collagen in meat products, affecting the product’s flavor and taste. Therefore, the dosage should be adjusted according to the type of meat product in practical applications:

In meat products with high fat content (e.g., bacon), fat absorbs part of nisin, reducing its free concentration. Thus, the addition amount needs to be appropriately increased (usually 0.3–0.5 g/kg).

In meat products with high lean meat content (e.g., beef jerky), proteins have weak adsorption of Nisin, so the addition amount can be controlled at 0.1–0.3 g/kg, which ensures inhibitory efficacy while avoiding flavor deterioration.

Meanwhile, the timing of application should avoid high-temperature processing stages—Nisin may partially inactivate at temperatures above 121℃. Therefore, for meat products that require high-temperature boiling (e.g., high-temperature ham sausages with a sterilization temperature of 121℃), nisin should be added after high-temperature sterilization when the product cools down to below 60℃, or applied via "surface spraying" to prevent reduced activity due to high temperatures.

Second, nisin must be combined with "basic sterilization processes" and "hygiene control" and cannot replace a complete preservative system alone. It is only effective against Gram-positive bacteria and has weak inhibitory activity against Gram-negative bacteria such as Escherichia coli and Salmonella. However, the spoilage and contamination of meat products are often caused by the combined action of multiple bacteria. Therefore, while applying Nisin, it is still necessary to ensure the basic sterilization processes for meat processing (e.g., pasteurization for low-temperature products and commercial sterile sterilization for high-temperature products), and strictly control raw material quality (e.g., selecting fresh meat raw materials to reduce initial bacterial count) and processing environment hygiene (e.g., equipment cleaning and standardized personnel operations) to achieve comprehensive preservative effects. For example, if raw meat is heavily contaminated with Gram-negative bacteria, adding Nisin alone cannot inhibit their proliferation, and the product may still spoil. In such cases, it is necessary to combine raw material pretreatment (e.g., low-temperature marination and ultraviolet sterilization) to reduce the number of Gram-negative bacteria, and then cooperate with nisin’s inhibitory effect on Gram-positive bacteria to form an "all-round" preservative guarantee.

Nisin’s inhibitory effects on Listeria and Bacillus in meat products are based on its unique antibacterial mechanisms (disrupting cell membranes and inhibiting spore germination) and are tailored to the processing and storage needs of meat products (low-temperature storage, ready-to-eat characteristics, high-temperature processing tolerance, etc.), making it a "natural, efficient, and safe" preservative. By precisely controlling the addition dosage and timing, and combining it with basic sterilization and hygiene control, nisin not only effectively extends the shelf life of meat products (usually increasing the shelf life of low-temperature meat products by 50%–100% and that of room-temperature meat products by 30%–50%) but also targets and prevents high-risk pathogens such as Listeria, providing important support for the safe consumption of meat products. Meanwhile, it aligns with the current development trend of the food industry toward "natural preservation and bacterial reduction/control."