The application process of Nisin raw materials

Nisin, a natural antibacterial peptide produced by Lactococcus lactis fermentation, is characterized by high-efficiency bacteriostasis and safety, widely applied in food, pharmaceutical, and daily chemical fields. However, its activity is susceptible to environmental factors, requiring attention to the following key points during application:

I. Activity Stability and Environmental Condition Control

pH Sensitivity

Nisin exhibits significantly higher stability under acidic conditions than in alkaline environments:

At pH ≤4, its antibacterial activity is maintained long-term (e.g., retaining 90% activity after 121°C sterilization at pH 2.5).

At pH >5, activity declines rapidly with increased alkalinity (nearly complete inactivation after heat treatment at pH 7).

Control measures: Adjust food system pH below 4.5 (e.g., in juices, acidic milk drinks). For neutral foods (e.g., canned goods), combine with other bacteriostatic methods (e.g., low temperature, vacuum packaging). Use organic acids (citric acid, lactic acid) instead of strong bases (NaOH) to minimize Nisin degradation.

Impact of Temperature and Heat Treatment

Short-term high-temperature tolerance:

At pH 3.5, Nisin retains ~80% activity after 15-minute autoclaving at 121°C.

Compatible with pasteurization (70–85°C) or high-temperature short-time (HTST) sterilization, synergizing with heat treatment.

Long-term high-temperature inactivation: Prolonged heating (e.g., 100°C for 2 hours) causes gradual activity decay. For products requiring long-term high-temperature sterilization (e.g., meat cans), add Nisin during post-sterilization cooling (temp. <60°C) to avoid continuous thermal damage.

Effect of Metal Ions and Chelators

High-valent metal ions (e.g., Cu²⁺, Fe³⁺): Coordinate with Nisin's sulfhydryl/amino groups, altering its structure and reducing activity. Example: 0.1 mM Fe³⁺ decreases Nisin's bacteriostasis against S. aureus by ~30%.

Mitigation strategies: Avoid direct contact with metal containers; add chelators (e.g., EDTA) to complex metal ions.

Low-concentration Ca²⁺, Mg²⁺ (<10 mM): May enhance bacteriostasis by maintaining cell membrane potential (e.g., natural Ca²⁺ in dairy products synergizes with Nisin to inhibit spore-forming bacteria).

II. Compatibility and Synergistic Bacteriostatic Strategies

Synergy with Other Preservatives

Nisin limitation: Effective against Gram-positive bacteria (e.g., S. aureus, bacilli), weak against Gram-negative bacteria (e.g., E. coli).

Formulation synergists:

Organic acids/salts (e.g., calcium propionate, potassium sorbate): Lower pH and disrupt membrane permeability, complementing Nisin (e.g., inhibits molds and bacilli in bread).

EDTA: Chelates outer membrane Mg²⁺ of Gram-negative bacteria, enhancing Nisin's intracellular access.

Lysozyme: Hydrolyzes peptidoglycan, synergizing with Nisin's membrane disruption (e.g., combined use in egg products).

Avoid Mixing with Proteases

As a polypeptide, Nisin is hydrolyzed by proteases (e.g., pepsin, trypsin).

Protection measures: Adjust pH to acidic range to inhibit protease activity; use microencapsulation technology for Nisin protection.

III. Special Considerations for Application Scenarios

Food Industry Dosage and Regulatory Limits

Dosage standards: Comply with national regulations (e.g., China GB 2760-2024 allows 0.5–2 g/kg in dairy and meat products). Excess dosage may affect product texture (e.g., protein aggregation in dairy).

Fermented foods (yogurt, cheese): Nisin is self-resistant to L. lactis but may inhibit other lactic acid bacteria. Add during late fermentation to avoid interfering with the process.

Formulation Adaptation in Pharmaceuticals and Cosmetics

Topical pharmaceutical preparations:

Avoid oil-based matrices (vaseline) reducing Nisin solubility; use oil-in-water (O/W) emulsions with cosolvents (propylene glycol).

Prevent activity decline from charge neutralization by avoiding cationic surfactants (benzalkonium chloride).

Daily chemicals (skincare, detergents):

Surfactants (e.g., SDS) may weaken Nisin's membrane binding; optimize formulations (reduce surfactant concentration, add humectants).

Limit dosage <0.1% to avoid skin irritation in sensitive populations.

IV. Storage and Transportation Management

Storage Conditions

Seal and store in a cool, dry place (temp. ≤25°C, humidity ≤60%), away from direct sunlight, oxidants, and acids/bases. For long-term storage, refrigerate at 4°C (shelf life: 2–3 years unopened, 3 months after opening).

Dust Protection

Wear a dust mask when handling Nisin powder to prevent inhalation. Rinse skin/eyes with water if contacted; food-grade, follow chemical operation protocols due to low acute toxicity (LD₅₀ >2000 mg/kg).

V. Bacteriostatic Mechanism and Effect Monitoring

Mechanism

Nisin binds to bacterial membrane phospholipids, forming pores that cause ion leakage and ATP depletion, inhibiting growth. Log-phase bacteria are more sensitive, while stationary-phase/spore-forming bacteria are more tolerant.

Activity Assays

Use agar well diffusion (Oxford cup method) or turbidity assays to monitor activity. If bacteriostasis declines, check system pH, temperature, and compatible components.

Nisin application hinges on "precise activity control and synergistic enhancement": regulate environmental pH, temperature, and metal ion interference; broaden the bacteriostatic spectrum through formulation synergy; and optimize recipes based on industry-specific regulations (food, pharma, cosmetics). Standardize storage and operation to avoid inactivating factors (e.g., proteases), maximizing its natural, high-efficiency bacteriostatic advantages.