The preservative effect and safety of Nisin in ready-to-eat foods

As an internationally recognized natural food preservative, Nisin has become a core component of the preservation system for ready-to-eat (RTE) foods (e.g., cooked meat products, instant rice/noodles, ready-to-eat fruits and vegetables, dairy products) due to its targeted antimicrobial activity, biodegradability, and high safety. RTE foods, characterized by direct consumption after processing, long storage cycles, and high susceptibility to microbial contamination, impose strict requirements on the safety and antimicrobial efficiency of preservatives. Nisin extends shelf life without affecting product flavor or nutrition by precisely inhibiting the growth of spoilage and pathogenic bacteria. Its preservation mechanisms and safety have been widely verified by the global food industry, as detailed below:

I. Preservation Mechanisms in Ready-to-Eat Foods

Nisin’s antimicrobial activity primarily targets common Gram-positive spoilage and pathogenic bacteria in RTE foods through highly specific mechanisms that do not affect beneficial human intestinal flora. The core pathways are as follows:

1. Targeted Disruption of Bacterial Cell Membranes for Rapid Sterilization

Nisin is a 34-amino acid peptide with a unique lanthionine ring structure that specifically binds to Lipid II (a cell wall precursor) on the cell membrane of Gram-positive bacteria, forming a high-affinity complex. Following binding, Nisin molecules insert into the cell membrane and assemble into transmembrane pores, causing a sharp increase in membrane permeability. This leads to massive leakage of intracellular small molecules (e.g., potassium ions, protons, amino acids) and disruption of the osmotic balance between the inside and outside of the cell, ultimately resulting in bacterial lysis. This mechanism exhibits significant inhibitory effects on the most hazardous pathogens in RTE foods (e.g., Listeria monocytogenes, Clostridium botulinum, Staphylococcus aureus) and spoilage bacteria (e.g., lactobacilli, streptococci, bacilli), with a minimum inhibitory concentration (MIC) typically ranging from 0.1 to 10 μg/mL and rapid bactericidal action (killing over 90% of target bacteria within 30 minutes of contact).

2. Inhibition of Bacterial Spore Germination to Block Deep Spoilage

High-temperature sterilization during RTE food processing (e.g., cooked meat products, canned foods) can kill vegetative bacteria but is ineffective against heat-resistant spores produced by bacteria such as Clostridium spp. These spores easily germinate into vegetative cells during room-temperature or refrigerated storage, causing food spoilage. Nisin inhibits spore germination through dual actions: first, it binds to Lipid II on the spore membrane, preventing spore cell wall synthesis and peptidoglycan cross-linking to block the germination process; second, it disrupts the internal metabolic balance of spores via transmembrane pores, inhibiting the activity of germination-related enzymes and maintaining spores in a dormant state. Studies have shown that adding 500~1000 IU/g Nisin to cooked meat products reduces the germination rate of Clostridium spores by 80%~90%, significantly delaying spoilage-related issues such as off-odors, gas production, and texture deterioration.

3. Synergistic Enhancement to Expand Antimicrobial Spectrum and Improve Preservation Efficiency

Nisin has weak inhibitory effects on Gram-negative bacteria when used alone, but exhibits significant synergistic effects when compounded with other components in RTE foods:

Combination with Food-Grade Organic Acids: Lactic acid, citric acid, and acetic acid lower food pH, destabilizing the cell membrane of Gram-negative bacteria and facilitating Nisin penetration, thereby expanding the antimicrobial spectrum to include Gram-negative bacteria such as Escherichia coli and Salmonella.

Combination with Natural Preservatives: ε-Polylysine directly acts on Gram-negative bacteria, synergizing with Nisin to cover various pathogens and spoilage bacteria; tea polyphenols exert both antioxidant and auxiliary antimicrobial effects, delaying food oxidative deterioration; chitosan forms a protective film to enhance Nisin’s sustained-release antimicrobial activity.

Combination with Physical Preservation Technologies: Low temperatures extend Nisin’s activity lifespan; vacuum/modified atmosphere packaging (MAP) reduces oxygen-induced bacterial growth; pasteurization lowers the initial bacterial count. The combination of these technologies with Nisin can extend the shelf life of RTE foods by 2~3 times while reducing Nisin dosage.

II. Typical Application Scenarios in Ready-to-Eat Foods

1. Cooked Meat Products (e.g., Ham, Sausages, Braised Meat)

Application Scheme: Add 600~1000 IU/g Nisin to meat fillings or braising broth during processing, adjust pH to 5.5~6.0 with 0.2%~0.3% lactic acid, vacuum-package the finished product, and subject to pasteurization at 70~80℃ for 15~20 minutes.

Preservation Effect: The room-temperature shelf life extends from 3~5 days to 15~20 days, and the refrigerated (0~4℃) shelf life from 15~20 days to 45~60 days. The total viable count is reduced by 2~3 log cycles compared to the control group, with no detection of pathogenic bacteria such as Listeria or Clostridium botulinum, while retaining the tenderness and flavor of the meat products.

2. Instant Rice and Noodle Products (e.g., Instant Rice, Self-Heating Noodles, Ready-to-Eat Pastries)

Application Scheme: Add 500~800 IU/g Nisin to rice/noodle raw materials, compound with 0.1% ε-polylysine, and use MAP (60%~70% CO₂ + 30%~40% N₂) after processing.

Preservation Effect: The room-temperature shelf life extends from 7~10 days to 25~30 days, effectively inhibiting the growth of mold, yeast, and bacilli, and preventing deterioration phenomena such as mold growth, off-odors, and gelatinization in rice and noodle products.

3. Ready-to-Eat Fruits and Vegetables (e.g., Cut Lettuce, Carrot Sticks, Preserved Fruits/Vegetables)

Application Scheme: Soak cut fruits/vegetables in a preservation solution containing 400~600 IU/mL Nisin, 0.1% ascorbic acid, and 0.05% citric acid for 10~15 minutes, drain, vacuum-package, and store under refrigeration.

Preservation Effect: The refrigerated shelf life extends from 3~4 days to 7~10 days, inhibiting the growth of pathogenic bacteria (e.g., Escherichia coli, Salmonella) and spoilage bacteria, while suppressing browning and water loss to maintain bright color and crisp texture.

4. Ready-to-Eat Dairy Products (e.g., Yogurt, Cheese, Milk Beverages)

Application Scheme: Add 300~500 IU/g Nisin in the late stage of yogurt fermentation, or 500~800 IU/g Nisin to curd during cheese processing.

Preservation Effect: The refrigerated shelf life of yogurt extends from 14~21 days to 30~40 days, and the room-temperature shelf life of cheese from 1~2 months to 3~4 months. It effectively inhibits the growth of pathogenic bacteria such as Listeria and Staphylococcus aureus without affecting the fermented flavor or nutritional components of dairy products.

III. Safety Verification and Compliance

As a natural food preservative, Nisin’s safety has been strictly evaluated by numerous authoritative global institutions, with widespread recognition of its compliance:

1. Core Safety Characteristics

Biodegradability: Nisin is a natural antimicrobial peptide that is rapidly degraded into amino acids by pepsin, trypsin, and other digestive enzymes in the human gastrointestinal tract. It participates in human protein metabolism with no residue or accumulation risks and does not irritate the gastrointestinal tract.

Low Toxicity: Acute toxicity tests show that Nisin’s median lethal dose (LD₅₀) exceeds 2000 mg/kg body weight (oral administration in mice), far higher than the actual dosage used in foods, classifying it as a low-toxic substance. Long-term feeding studies indicate that daily intake of 500 mg/kg body weight (much higher than human daily intake) has no adverse effects on animal growth, reproduction, or liver/kidney function.

Non-Allergenicity: Nisin’s amino acid sequence contains no allergenic fragments, and no clinical cases of Nisin-induced allergies have been reported. It can be safely consumed by individuals with allergies.

No Impact on Intestinal Flora: Nisin only acts on Gram-positive bacteria. Although beneficial intestinal flora (e.g., Bifidobacterium, lactobacilli) are mostly Gram-positive, Nisin is rapidly degraded in the intestines, and its concentration is insufficient to inhibit beneficial bacteria, thus not disrupting the intestinal microecological balance.

2. Global Compliance and Usage Standards

International Standards: Nisin has been approved as a GRAS (Generally Recognized as Safe) substance by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO), with no restrictions on the acceptable daily intake (ADI) based on JECFA evaluations.

Chinese Standards: According to GB 2760-2014 National Food Safety Standard for the Use of Food Additives, Nisin can be used in various RTE foods including cooked meat products, instant cereal products, ready-to-eat fruits and vegetables, and dairy products, with a maximum usage limit of 1500 IU/g (calculated as pure Nisin), consistent with international standards.

Other Countries/Regions: The United States, EU, Japan, Australia, and other regions have approved Nisin for RTE food preservation, with usage dosages basically aligned with Chinese standards, and no compliance disputes.

3. Potential Risks and Usage Limitations

Scope of Application: Nisin has weak inhibitory effects on Gram-negative bacteria and cannot be used alone for preservation of high-risk RTE foods (e.g., ready-to-eat aquatic products); it must be compounded with other preservatives or technologies.

Dosage Control: Excessive addition (exceeding 1500 IU/g) may cause slight bitterness or off-odors in foods, affecting sensory quality. Usage dosage must be strictly controlled in accordance with standards.

Stability Considerations: Nisin is prone to degradation under high temperatures (>121℃) and high pH (>7.0) conditions. Long-term high-temperature processing should be avoided in RTE food production, or microencapsulated formulations can be used to improve stability.

Nisin efficiently inhibits the growth of Gram-positive pathogens and spoilage bacteria in RTE foods through targeted cell membrane disruption, spore germination inhibition, and synergistic effects, significantly extending product shelf life while retaining flavor and nutritional components. Its core advantages of natural origin, biodegradability, and high safety have been validated by authoritative global institutions, complying with international and domestic standards such as GB 2760, making it an ideal alternative to chemical preservatives in RTE foods.

In practical applications, a combined scheme of "Nisin + compound ingredients + physical preservation technologies" should be adopted based on the type of RTE food (e.g., meat products, rice/noodle products, fruits/vegetables), processing technology, and storage conditions to achieve optimal preservation effects while complying with usage standards. With the growing consumer demand for natural and healthy foods, Nisin’s application in RTE foods will further expand—particularly in high-end and functional RTE food sectors—where its safety and efficiency will serve as core competitive advantages, providing technical support for the high-quality development of the RTE food industry.