Nisin in the preservation of dairy products

Nisin in the preservation of dairy products

I. Characteristics of Dairy Microbial Contamination and Antibacterial Targeting of Nisin

Dairy products (such as milk, yogurt, and cheese) are rich in proteins and lactose, making them susceptible to contamination by Gram-positive bacteria (e.g., Staphylococcus aureus, Listeria, and Bacillus). Nisin specifically inhibits these bacteria through mechanisms including disrupting cell membrane integrity and inhibiting peptidoglycan synthesis. Notably, it has minimal impact on probiotics like Lactobacillus bulgaricus in dairy products, laying the foundation for its application in fermented dairy.

II. Application Effects in Liquid Milk Preservation

1. Synergistic Effect in Fresh Milk Cold-Chain Preservation

Fresh milk often contains psychrophilic bacteria (e.g., Pseudomonas) and heat-resistant spores after extrusion. During traditional cold-chain storage (4°C), 0.05–0.1 μg/mL Nisin delays total bacterial count growth by 2–3 days. For example, fresh milk with Nisin extends its shelf life at 4°C from 7 to 10–12 days, while increasing retention rates of active components like lactoferrin and immunoglobulins by 5%–8%.

When combined with pasteurization (72°C, 15 seconds), Nisin allows reduced sterilization temperature or time. For instance, 65°C sterilization with 0.15 μg/mL Nisin achieves equivalent killing of Bacillus stearothermophilus as traditional 72°C pasteurization, while reducing vitamin B1 loss from 12% to 6%.

2. Prevention of Secondary Contamination in UHT Milk

UHT milk (sterilized at 135°C) is theoretically sterile, but packaging damage can cause secondary spore contamination. Adding 50–100 IU/mL Nisin during aseptic filling inhibits residual spore germination. For example, a UHT milk brand saw its bloating rate at 37°C accelerated testing drop from 8% to 1% after Nisin addition, with no significant increase in protein denaturation.

III. Application Advantages in Fermented Dairy Products

1. Shelf Life Extension and Quality Maintenance of Yogurt

Yogurt has a post-fermentation pH of ~4.0–4.5, where Nisin stability significantly improves (retaining 70% activity after 80°C for 30 minutes). Adding 200–300 IU/mL Nisin inhibits contaminating bacteria (e.g., yeasts, molds) during post-acidification: A commercial yogurt with Nisin showed acidity (°T) decreasing from 90 to 75 after 21 days at 4°C, with milder taste and no alcoholic fermentation odor (a sign of yeast contamination).

For probiotic yogurt (e.g., with Bifidobacterium), Nisin does not affect probiotic activity: Experiments show Bifidobacterium counts remain above 10⁷ CFU/mL in Nisin-added yogurt over a 28-day storage period, similar to the control group.

2. Contamination Control During Cheese Ripening

Hard cheeses (e.g., Cheddar) are prone to Listeria contamination during ripening. Treating the cheese surface by spraying or soaking with 0.5–1.0 μg/g Nisin reduces Listeria counts from 10⁴ to <10² CFU/g. Meanwhile, Nisin does not interfere with the proteolytic activity of cheese starters (e.g., Streptococcus thermophilus), with flavor substance (e.g., free amino acids) at ripening equivalent to the control group.

IV. Synergistic Effects with Other Preservation Technologies

1. Nisin + Natural Preservative Composite Systems

When combined with tea polyphenols (0.02%), Nisin's antibacterial effect in liquid milk increases 2–3 fold: After 14 days at 4°C, total bacterial counts in the single Nisin group were 10⁴ CFU/mL, while the composite group had <10³ CFU/mL. This occurs because tea polyphenols disrupt the bacterial outer membrane, promoting Nisin penetration to the inner membrane.

A combination of Nisin and ε-polylysine (EPL) in cream cake fillings (containing dairy) delays mold growth by 5–7 days with 0.1 μg/mL Nisin + 0.05 μg/mL EPL, reducing preservative usage by 50% compared to single agents.

2. Synergistic Preservation of Nisin + Physical Treatments

High-pressure processing (HPP, 400 MPa) combined with Nisin significantly enhances dairy sterilization efficiency: For milk-based beverages, single HPP (400 MPa, 10 min) achieves a 3.5 log reduction of thermophiles, which increases to 5.0 with Nisin, while reducing protein denaturation from 8% to 3%.

During pulsed electric field (PEF) treatment, Nisin lowers the membrane breakdown threshold: 20 kV/cm PEF with 0.1 μg/mL Nisin achieves the same killing effect on S. aureus in milk as 25 kV/cm PEF alone, reducing energy consumption by 20%.

V. Application Limitations and Solutions

1. Inadequate Inhibition of Gram-Negative Bacteria

Nisin is less effective against Gram-negative bacteria like E. coli, requiring complementary measures: Adding citric acid to milk-based drinks (adjusting pH below 4.5) enhances Nisin's penetration into E. coli, increasing bacteriostatic rate from 30% to 70%.

2. Activity Decline Due to Protease Degradation

Proteases in dairy products (e.g., plasmin) can decompose Nisin, shortening its effective duration. Solutions include:

Adding Nisin before pasteurization to inactivate part proteases via heat treatment;

Using microencapsulation technology (e.g., sodium alginate-chitosan embedding) to extend Nisin's half-life in dairy from 48 hours to 7 days.

3. Consumer Perception and Regulatory Compliance

Nisin is approved for use in dairy products in the EU (EC No. 1333/2008) and China (GB 2760-2024) with a maximum usage of 0.5 g/kg. To address consumer misperceptions about "preservatives," labeling as "natural fermentation product" can enhance acceptance.

VI. Effect Evaluation Indicators and Typical Cases

1. Quantitative Microbial Indicators

Comparative experiment of a brand's fresh milk (250 mL):

Control group (no Nisin): After 7 days at 4°C, total bacterial count 10⁵ CFU/mL, with acid spoilage;

Experimental group (0.1 μg/mL Nisin): After 12 days at 4°C, total bacterial count 10⁴ CFU/mL, with normal sensory qualities.

2. Quality Maintenance Effects

In a cheese ripening experiment, the Nisin-treated group (0.8 μg/g) vs. control:

Listeria count: <10² CFU/g vs. 10⁴ CFU/g;

Volatile fatty acid content (a flavor index): 2.3 mmol/kg vs. 2.1 mmol/kg (no significant difference).

VII. Future Application Trends

1. Precision Dosage Control and Intelligent Release

Encapsulating Nisin in pH-responsive carriers (e.g., poly(lactic-co-glycolic acid)) enables slow release during dairy post-acidification (pH dropping below 4.5), extending effective action by 3–5 days.

2. Symbiotic Expression of Nisin in Starter Cultures

Genetically engineering lactic acid bacteria to simultaneously produce Nisin during fermentation, such as Lactobacillus helveticus engineered strains producing 1000 IU/mL Nisin, eliminates the need for additional preservatives in yogurt production while shortening fermentation time by 1–2 hours.

3. Application of Nano-Composite Coatings

Adding Nisin-nano TiO₂ composite coatings to dairy packaging materials achieves contact sterilization of surface contamination. For example, a milk powder package with this coating reduced miscellaneous bacteria contamination from 5% to 0.5% after 3 months of storage.

Conclusion

Nisin demonstrates significant microbial control and quality maintenance in dairy preservation, particularly in cold-chain fresh milk, fermented yogurt, and ready-to-eat cheese. Synergy with physical treatments, natural preservatives, or embedding technologies overcomes limitations like insufficient Gram-negative bacteria inhibition and protease degradation. With growing consumer demand for natural preservation, precision application of Nisin and integration with biotechnologies will become key development directions in dairy preservation.