The Application of Nisin in the Preservation of Seafood Products

As a natural antimicrobial peptide derived from Gram-positive bacteria, Nisin has become a core natural preservative for seafood preservation due to its targeted inhibitory effects on seafood spoilage/pathogenic bacteria (e.g., Clostridium botulinum, Listeria monocytogenes), biological safety, and degradability. Seafood products, characterized by high moisture and protein content, are prone to spoilage caused by microbial contamination and enzymatic hydrolysis. Nisin can significantly extend the shelf life of seafood while retaining its nutritional and sensory qualities by precisely blocking bacterial metabolism and synergizing with physical/chemical preservation technologies. The specific mechanisms of action, technical schemes, and practical effects are as follows:

I. Core Mechanisms of Nisin in Seafood Preservation

Nisin’s antimicrobial activity primarily targets Gram-positive bacteria (the dominant spoilage flora in seafood, such as streptococci, staphylococci, and clostridia) through highly specific mechanisms that do not affect the inherent flavor or nutritional components of seafood:

1. Disrupting Bacterial Cell Membrane Structure for Targeted Sterilization

Nisin is a 34-amino acid peptide rich in special structures such as lanthionine and methyllanthionine. It specifically binds to lipoteichoic acid (LTA) on the cell membrane of Gram-positive bacteria and Lipid II (a cell wall precursor). Following binding, Nisin inserts into the cell membrane to form transmembrane pores, increasing membrane permeability and causing massive leakage of intracellular small molecules (e.g., potassium ions, protons). This disrupts the osmotic balance between the inside and outside of the cell, ultimately leading to bacterial lysis. This mechanism exhibits significant inhibitory effects on common seafood pathogens (e.g., Listeria monocytogenes, Clostridium botulinum) and spoilage bacteria (e.g., lactobacilli, leuconostocs), with a minimum inhibitory concentration (MIC) typically ranging from 0.1 to 10 μg/mL, and no adverse effects on the human intestinal flora.

2. Inhibiting Bacterial Spore Germination to Block Deep Spoilage

During seafood processing and storage, spores produced by bacteria such as clostridia exhibit strong stress resistance and are difficult to eliminate via conventional low-temperature storage. They easily germinate under favorable conditions, causing spoilage. Nisin inhibits spore germination through two pathways: first, it binds to Lipid II on the spore membrane, preventing peptidoglycan cross-linking required for spore cell wall synthesis and germination; second, it disrupts the metabolic balance inside spores via transmembrane pores, inhibiting the activity of germination-related enzymes and blocking the conversion of spores to vegetative cells. Studies have shown that adding 500~1000 IU/g Nisin to refrigerated seafood reduces the germination rate of Clostridium spores by 80%~90%, significantly delaying off-odor production and texture deterioration caused by spore germination.

3. Synergistically Inhibiting Enzymatic Hydrolysis to Protect Seafood Quality

Seafood spoilage is not only caused by microbial contamination but also closely related to endogenous enzymatic hydrolysis (e.g., proteases, lipases, polyphenol oxidase). While Nisin does not directly inhibit enzyme activity, it reduces the secretion of exogenous enzymes by killing spoilage bacteria that produce proteases and lipases. Additionally, after binding to proteins, polysaccharides, and other components in seafood, Nisin forms a protective film that delays the contact between endogenous enzymes and substrates, indirectly inhibiting enzymatic reactions. For example, in fish preservation, Nisin reduces the degradation of myofibrillar proteins by proteases, maintaining fish elasticity and tenderness; in shrimp preservation, it inhibits polyphenol oxidase-mediated browning, preserving the bright color of shrimp.

II. Application Technical Schemes of Nisin in Different Seafood Products

Based on seafood type (fish, shrimp, shellfish, crustaceans), processing technology (fresh, frozen, ready-to-eat), and spoilage characteristics, Nisin’s application methods and dosages need to be adjusted accordingly. Core technical schemes include direct addition, coating preservation, and composite preservation:

1. Preservation of Fresh Seafood (Fish, Shrimp, Shellfish)

Fresh seafood has high moisture content and a high risk of microbial contamination, requiring focused inhibition of surface and shallow bacterial proliferation. The "soaking + refrigeration" combined scheme is commonly used:

Treatment Method: Immerse live or chilled seafood (e.g., large yellow croaker, prawns, scallops) in a preservation solution consisting of Nisin (500~800 IU/mL), glacial acetic acid (adjusting pH to 5.5~6.0), and ascorbic acid (0.1%~0.2%) for 10~15 minutes. Remove, drain, package in breathable fresh-keeping bags, and store at 0~4℃.

Mechanism: Nisin uniformly adheres to the seafood surface via soaking, forming an antimicrobial film to inhibit the growth of surface spoilage bacteria (e.g., Pseudomonas, Vibrio). Ascorbic acid synergistically inhibits browning, while glacial acetic acid adjusts pH to enhance Nisin’s antimicrobial activity.

Application Effect: After treatment, the refrigerated shelf life of large yellow croaker extends from 3~4 days to 7~9 days, with the total viable count reduced by 1~2 log cycles compared to the control group, and no significant decline in texture indicators such as fish hardness and elasticity. Prawns maintain a bright color without blackening or off-odors after 7 days of refrigeration, with a sensory score 30% higher than the control group.

2. Preservation of Frozen Seafood

Frozen seafood is prone to spoilage due to microbial recovery during thawing. Nisin achieves full-cycle preservation through "pretreatment + freezing":

Treatment Method: Before freezing, spray or immerse seafood (e.g., cod fillets, shrimp meat, squid rings) in a preservation solution containing Nisin (800~1200 IU/mL) and glycerol (5%~8%) for 5~10 minutes. Glycerol lowers the freezing point, reduces freezing damage, and enhances Nisin adhesion. Rapidly freeze (-30℃ or below) after treatment and store at -18℃.

Mechanism: Nisin retains partial antimicrobial activity during freezing, inhibiting the recovery and proliferation of surviving bacteria after freezing. Glycerol and Nisin act synergistically to protect seafood cell structure and extend antimicrobial duration.

Application Effect: After treatment, cod fillets stored at -18℃ for 6 months have a total viable count ≤10⁵ CFU/g after thawing, a 60%~70% reduction compared to the control group, with no quality defects such as freezer burn or off-odors. Shrimp meat shows a 25%~30% reduction in protein loss rate compared to the control group after 4 months of frozen storage, maintaining a tender texture after cooking.

3. Preservation of Ready-to-Eat Seafood (e.g., Marinated Shrimp/Crab, Preserved Shellfish, Canned Fish)

Ready-to-eat seafood is consumed directly, requiring strict microbial control. Nisin is often compounded with other natural preservatives to balance safety and preservation efficacy:

Composite Scheme 1 (Low-Temperature Ready-to-Eat Seafood): In the processing of marinated shrimp/crab, add Nisin (600~800 IU/mL), ε-polylysine (0.1%~0.2%), and tea polyphenols (0.05%~0.1%) to the marinating solution. Nisin and ε-polylysine synergistically expand the antimicrobial spectrum (covering Gram-positive and some Gram-negative bacteria), while tea polyphenols exert antioxidant and anti-browning effects. This scheme extends the storage life of ready-to-eat marinated shrimp at 0~4℃ from 7~10 days to 15~20 days, with no detection of pathogenic bacteria (e.g., Vibrio parahaemolyticus).

Composite Scheme 2 (High-Temperature Sterilized Ready-to-Eat Seafood): In canned fish processing, add Nisin (1000~1500 IU/mL) during raw material pretreatment, combined with pasteurization (85~90℃ for 15~20 minutes). Nisin reduces sterilization temperature and time, minimizing nutrient loss while inhibiting the growth of heat-resistant spoilage bacteria (e.g., Clostridium botulinum) in cans. Tuna cans treated with this scheme meet national standards for total viable count after 12 months of room-temperature storage, with well-preserved fish texture and flavor.

4. Preservation of Seafood Processing By-Products (e.g., Fish Steaks, Shrimp Heads)

Seafood processing by-products are rich in protein and fat, making them prone to spoilage. Nisin enables resource reuse through coating preservation technology:

Treatment Method: After cutting and sorting by-products such as fish steaks and shrimp heads, immerse or spray them with a composite coating solution containing Nisin (800 IU/mL) and chitosan (1%~2%). The film formed by chitosan encapsulates Nisin, enabling sustained release for long-acting antimicrobial effects. Vacuum package after treatment and store at 0~4℃.

Application Effect: After treatment, the refrigerated shelf life of fish steaks extends from 2~3 days to 5~7 days, with thiobarbituric acid reactive substances (TBARS) values reduced by 50%~60% compared to the control group, and no rancid odors. Shrimp heads can still be used for extracting shrimp oil, astaxanthin, and other products after 5 days of refrigeration, increasing resource utilization by over 40%.

III. Key Factors Affecting Nisin Preservation Efficacy and Optimization Strategies

1. Key Influencing Factors

Seafood Intrinsic Characteristics: Seafood pH (most seafood has a pH of 6.0~7.5, suitable for Nisin activity), water activity (microbes grow easily when Aw＞0.95, requiring higher Nisin dosage), and initial bacterial count (severe initial contamination requires high-intensity pretreatment such as ultrasonic cleaning) all affect preservation efficacy.

Environmental Conditions: Increased temperature accelerates Nisin degradation (half-life of only a few days at room temperature), while refrigeration at 0~4℃ extends its activity to several weeks. Oxygen promotes seafood oxidation and bacterial proliferation, requiring combination with vacuum packaging or modified atmosphere packaging (MAP, 40%~60% CO₂) to enhance efficacy.

Formula Components: Proteins and fats in seafood bind to Nisin, reducing its free concentration and requiring appropriate dosage increases. Components such as salt and sugar affect Nisin solubility and antimicrobial activity—high salt environments (>5%) require a 20%~30% increase in Nisin dosage.

2. Optimization Strategies

Composite Synergistic Enhancement: Compounding Nisin with natural preservatives (ε-polylysine, tea polyphenols, chitosan) expands the antimicrobial spectrum and enhances activity. Combining with physical preservation technologies (low temperature, vacuum packaging, ultrasound, irradiation) reduces Nisin dosage while improving preservation efficacy. For example, Nisin (500 IU/g) + ultrasound (40 kHz for 10 minutes) + vacuum packaging extends the refrigerated shelf life of hairtail to 12 days, a 50% improvement compared to single Nisin treatment.

Formulation Optimization to Improve Stability: Preparing Nisin into microcapsules (using sodium alginate or gelatin as wall materials) avoids binding to seafood components, enables sustained release, and extends antimicrobial duration. Microencapsulated Nisin exhibits higher stability during freezing and high-temperature sterilization, with an activity retention rate increased by 30%~40%.

Precise Dosage Control: Adjust Nisin dosage based on seafood type and storage conditions to avoid taste impacts (e.g., bitterness) from excessive use while ensuring antimicrobial efficacy. Generally, the dosage for fresh seafood is 500~800 IU/g, frozen seafood 800~1200 IU/g, and ready-to-eat seafood 600~1500 IU/g—all complying with GB 2760 standards (maximum usage limit of 1500 IU/g).

IV. Safety and Application Prospects

1. Safety Verification

As a natural antimicrobial peptide, Nisin has been approved for food preservation in multiple countries. Its safety is reflected in three aspects: first, proteases in the human digestive tract rapidly degrade it into amino acids, with no residue or accumulation risks; second, it is non-toxic to humans at recommended dosages, with an LD₅₀＞2000 mg/kg body weight in acute toxicity tests; third, it does not affect seafood nutrients (proteins, unsaturated fatty acids, minerals) or produce harmful substances.

2. Application Prospects

With the growing consumer demand for natural and healthy food, Nisin, as an ideal alternative to chemical preservatives, will see further expansion in seafood preservation: first, developing specialized preservatives for specific seafood (e.g., high-end sashimi, live shellfish); second, combining with intelligent packaging to prepare active packaging materials that release Nisin for dynamic preservation; third, extending to the entire seafood processing chain, from raw material pretreatment and processing to storage and transportation, building a full-cycle preservation system. In the future, optimizing Nisin’s structure and yield through synthetic biology, combined with composite technology and process innovation, will further improve its preservation efficiency and cost-effectiveness, providing technical support for the high-quality development of the seafood industry.

Nisin effectively extends the shelf life of various seafood products (fresh, frozen, ready-to-eat) by disrupting bacterial cell membranes, inhibiting spore germination, and synergistically inhibiting enzymatic hydrolysis, while retaining their nutritional and sensory qualities. In practical applications, appropriate treatment methods (soaking, spraying, coating) should be selected based on seafood type and processing technology, with composite technology and physical preservation methods combined to optimize efficacy. Its natural safety and high-efficiency antimicrobial properties align with the healthy development trend of the modern food industry, offering broad application prospects in seafood preservation.