Nisin in fermented foods

As a natural antimicrobial peptide, nisin often acts synergistically with other antibacterial components or processes in fermented foods, inhibiting microbial growth through multiple mechanisms. This not only broadens the antibacterial spectrum but also reduces the dosage of single components. The following analysis unfolds from the types of synergistic effects, mechanisms, and application scenarios:

I. Synergistic Antibacterial Effects with Organic Acids and Their Salts

1. Mechanisms of Action

Nisin + Citric Acid/Lactic Acid: Citric acid enhances nisin's pore-forming ability on microbial cell membranes by reducing the system pH to below 4.5, while the acidic environment inhibits microbial metabolic enzyme activity. For example, in pickle fermentation, the combination of 0.02 g/kg nisin and 0.1% citric acid reduces the count of miscellaneous bacteria (e.g., E. coli, staphylococci) other than lactic acid bacteria by 2–3 log levels, increasing the antibacterial effect by 40% compared to single nisin use.

Nisin + Calcium Propionate/Potassium Sorbate: Calcium propionate inhibits molds and aerobic spore-forming bacteria, potassium sorbate has a broad antibacterial spectrum (especially against yeasts), and nisin targets Gram-positive bacteria. When the three are compounded, calcium propionate and potassium sorbate disrupt microbial membrane permeability, and Nisin further inhibits cell wall synthesis, forming a dual blow of "membrane damage - cell wall destruction". In fermented dairy products, 0.03 g/kg Nisin + 0.05 g/kg potassium sorbate reduces mold contamination in yogurt by 90% without affecting the fermentation activity of Lactobacillus bulgaricus.

2. Typical Application Scenarios

Fermented Meat Products (e.g., Sausages): Nisin (0.05 g/kg) combined with sodium lactate (2%) synergistically inhibits pathogenic bacteria such as Clostridium botulinum by reducing water activity (Aw) and disrupting bacterial membrane potential, extending the product shelf life from 15 days to 30 days.

II. Synergistic Effects with Natural Antibacterial Components

1. Synergy with Plant-Derived Components

Nisin + Tea Polyphenols/Rosemary Extracts: The phenolic hydroxyl groups of tea polyphenols form hydrogen bonds with nisin's peptide chain, enhancing its binding to microbial membranes. Meanwhile, the antioxidant properties of tea polyphenols reduce microbial metabolic activity. In fermented soybean paste, 0.04 g/kg Nisin combined with 0.1% tea polyphenols inhibits halophilic bacteria, delaying acidification during storage by 2 months.

Nisin + Chitosan: Chitosan forms an antibacterial membrane by adsorbing surface charges of microorganisms, and nisin acts on the cell wall after penetrating the membrane. In fermented fruit and vegetable juices, 0.03 g/kg nisin combined with 0.2% chitosan reduces yeast counts by 4 log levels, and chitosan's film-forming property improves juice clarity.

2. Synergy with Other Bioactive Substances

Nisin + Lysozyme: Lysozyme decomposes the peptidoglycan of bacterial cell walls, and nisin disrupts cell membranes. When used synergistically in fermented soybean products (e.g., fermented bean curd), the total count of miscellaneous bacteria can be controlled below 10³ CFU/g, increasing the effect by 50% compared to single enzyme preparations.

III. Synergistic Antibacterial Effects with Physical Treatment Processes

1. Nisin + High-Pressure Processing (HPP)

High pressure (300–600 MPa) increases microbial membrane permeability, allowing Nisin to enter cells more easily. For example, in fermented vegetable juice, 0.02 g/kg nisin combined with 400 MPa high-pressure treatment for 5 minutes increases the killing rate of heat-resistant spores from 60% to 95%, with a 15% higher vitamin C retention rate than pure high-pressure treatment.

2. Nisin + Ultrasound/Pulsed Electric Field

The cavitation effect of ultrasound damages microbial cell walls, and pulsed electric fields create reversible pores in cell membranes, both enhancing nisin's penetration efficiency. In fermented milk production, ultrasound treatment (20 kHz, 10 minutes) combined with 0.01 g/kg Nisin reduces heat treatment time while ensuring no detection of pathogenic bacteria (e.g., Listeria).

IV. Synergistic Application Cases in Different Fermented Foods

1. Fermented Dairy Products

Yogurt: Nisin (0.02 g/kg) combined with glucono-δ-lactone (GDL, 0.3%). GDL slowly acidifies to reduce pH to 4.2, promoting Nisin activity and inhibiting the growth of miscellaneous bacteria (e.g., Bacillus stearothermophilus) during post-acidification, extending the shelf life of yogurt at 2–6℃ from 21 days to 35 days.

2. Fermented Vegetables (e.g., Sauerkraut)

Nisin (0.03 g/kg) synergizes with garlic extract (0.5%). The sulfur compounds in garlic destroy bacterial disulfide bonds, and nisin interferes with peptidoglycan synthesis, reducing nitrite content in sauerkraut by 30%, inhibiting spoilage bacteria, and maintaining a crisp texture.

3. Fermented Grains (e.g., Rice Wine)

Nisin (0.01 g/kg) combined with natamycin (0.005 g/kg). Natamycin specifically inhibits yeasts, and nisin controls bacterial contamination. Adding it in the late stage of rice wine fermentation prevents acidification caused by secondary fermentation, maintains alcohol content above 12% vol, and causes no obvious flavor change.

V. Key Influencing Factors of Synergistic Antibacterial Effects

1. Addition Sequence and Timing

When compounding nisin with acidic substances, adjusting pH first and then adding Nisin reduces acid hydrolysis inactivation. Adding nisin in the early fermentation stage inhibits initial contaminating bacteria, and supplementing organic acids later controls pH rise.

2. Microbial Ecological Adaptability

Ensure that synergistic components do not inhibit target fermenting bacteria (e.g., lactic acid bacteria). For example, the inhibition of Gram-positive bacteria by nisin requires dosage control to avoid affecting Lactobacillus bulgaricus (Gram-positive) in yogurt.

3. Cost and Safety

The combination of natural components (e.g., tea polyphenols, chitosan) and nisin meets clean label requirements better than chemical preservatives, but the dosage and production cost need to be balanced (e.g., Nisin is expensive, and compounding can reduce its usage by 20%–30%).

Conclusion

The synergistic antibacterial effect of nisin in fermented foods enhances efficacy through "multi-target action". Whether combined with organic acids, natural extracts, or physical technologies, it broadens the antibacterial spectrum while reducing the dosage of single components. Future research could focus on co-delivery systems of microencapsulated nisin with other components to further optimize stability and action timing in complex fermentation systems, promoting the application of natural antibacterial technologies in low-additive, high-safety fermented foods.