Nisin's preservation and freshness preservation technology in green food

As a natural peptide preservative produced by Streptococcus lactis fermentation, Nisin meets the core requirements of green food—"natural, safe, and pollution-free"—making it an ideal alternative to chemical preservatives for achieving preservation of green food products. Its application in green food requires integrating the processing characteristics of different categories, and adopting technical approaches such as precise addition, synergistic compounding, and process adaptation. These measures ensure food safety while preserving the natural flavor and nutritional quality of green food. The specific technical pathways and application practices are elaborated as follows:

I. Core Advantages of Nisin for Green Food Applications

Green food production strictly restricts the use of synthetic preservatives (e.g., potassium sorbate, sodium dehydroacetate). Nisin’s inherent properties perfectly align with the preservation needs of green food:

Natural Origin and SafetyNisin is a microbial fermentation product rather than a chemically synthesized substance, complying with the raw material naturalness requirement of green food. After ingestion, it is degraded into amino acids by proteases in the digestive tract, leaving no residues or cumulative toxicity. Its acute oral LD₅₀ exceeds 5 g/kg body weight, classifying it as practically non-toxic. Nisin has also obtained certifications from the Codex Alimentarius Commission (CAC) and China’s green food standards.

Thermal Stability and Process CompatibilityNisin retains over 80% of its activity after high-temperature sterilization at 121°C, making it compatible with green food processing technologies such as pasteurization and high-temperature sterilization. It also maintains good stability under refrigerated and room-temperature storage conditions, requiring no special preservation measures.

Targeted Antibacterial Activity and Flavor NeutralityNisin primarily inhibits Gram-positive bacteria (e.g., Bacillus, Staphylococcus, Streptococcus) and bacterial spores, while exerting minimal impact on beneficial microorganisms like lactic acid bacteria and yeasts in food, thus preserving the natural fermented flavor of green food products. Additionally, it is colorless and tasteless, and does not alter the color or texture of food after addition.

II. Preservation Technologies of Nisin for Major Green Food Categories

1. Green Fruit and Vegetable Products: Inhibiting Pathogens and Extending Shelf Life

Green fruit and vegetable juices, canned fruits and vegetables, and fresh-cut produce are susceptible to contamination by pathogenic bacteria such as Listeria monocytogenes and Staphylococcus aureus. Meanwhile, enzymatic browning in these products can impair quality. Nisin can achieve preservation effects through standalone or compound application technologies:

Fresh-Cut Fruits and VegetablesProcessing of fresh-cut produce (e.g., carrots, apples, lettuce) damages cell walls, accelerating microbial growth and enzymatic browning. The Nisin-chitosan composite coating technology involves dissolving Nisin (50–100 IU/mL) in a chitosan solution, then applying it to the produce surface via dipping or spraying to form a protective film. Chitosan’s film-forming property isolates oxygen and inhibits enzymatic browning, while Nisin suppresses the proliferation of Gram-positive bacteria on the film surface. This technology can extend the shelf life of fresh-cut apples from 3 days to 10 days under 4°C refrigeration, with total bacterial counts well below the limits specified in green food standards, while maintaining the crisp texture of the produce.

Green Fruit and Vegetable JuicesFruit and vegetable juices have a low pH (3.0–4.5), which is optimal for Nisin’s activity. Adding Nisin (80–150 IU/mL) after juice pasteurization can effectively inhibit the germination of heat-resistant spores (e.g., Bacillus cereus), preventing bottle swelling and spoilage during room-temperature storage. Compared with traditional high-temperature sterilization, this technology reduces the sterilization temperature (from 95°C to 75°C), minimizing the loss of nutrients such as vitamin C and polyphenols in the juice, which meets the nutrient retention requirements of green food.

2. Green Livestock/Poultry and Aquatic Products: Controlling Spore-Forming Bacteria and Reducing Cold Chain Dependence

The core preservation challenges of green meat products (e.g., low-temperature ham, marinated meat) and aquatic products (e.g., frozen fish balls, ready-to-eat kelp) are spore-forming bacteria contamination and high cold chain logistics costs. Nisin addresses these issues through synergistic antibacterial technologies:

Low-Temperature Green Meat ProductsLow-temperature ham and similar products undergo pasteurization, which cannot completely eliminate spore-forming bacteria. Spore germination during storage can lead to spoilage. Adding Nisin (100–200 IU/g) during meat curing, combined with sodium lactate and citric acid, forms a synergistic antibacterial system: Nisin targets Gram-positive bacteria and spores, sodium lactate regulates osmotic pressure, and citric acid lowers pH to enhance Nisin’s activity. This technology extends the shelf life of low-temperature ham from 30 days to 60 days under 4°C refrigeration, without the addition of chemical preservatives, complying with green food standards.

Green Aquatic ProductsAquatic products are rich in protein and prone to decomposition by microorganisms, producing harmful substances such as histamine. The Nisin microencapsulation technology involves embedding Nisin in sodium alginate microspheres and adding them to products like fish balls and shrimp paste. Microencapsulation protects Nisin from degradation by proteases during aquatic product steaming and boiling, while enabling sustained release of Nisin for long-term antibacterial effects. This technology ensures that frozen fish balls stored at -18°C for 12 months still meet green food requirements for total bacterial counts, with no significant changes in product elasticity or umami flavor.

3. Green Fermented Foods: Protecting Beneficial Bacteria and Maintaining Fermentation Quality

Green fermented foods (e.g., yogurt, pickles, soy sauce) rely on fermentation by beneficial microorganisms such as lactic acid bacteria and yeasts. Traditional preservatives tend to inhibit the activity of these beneficial bacteria, making Nisin—with its targeted antibacterial properties—the optimal choice:

Green YogurtYogurt is susceptible to Staphylococcus aureus contamination after fermentation, shortening its shelf life. Adding a low concentration of Nisin (20–50 IU/mL) before yogurt filling can selectively inhibit pathogenic bacteria without affecting the activity of lactic acid bacteria in yogurt (lactic acid bacteria have natural tolerance to Nisin). This technology extends the shelf life of room-temperature yogurt from 30 days to 45 days, while preserving the probiotic activity and flavor of the yogurt.

Green PicklesOver-proliferation of spoilage bacteria (e.g., Bacillus) during pickle fermentation can lead to softening and flavor deterioration. Adding Nisin (30–80 IU/mL) at the initial stage of pickle curing inhibits the growth of spoilage bacteria, ensuring the dominant position of lactic acid bacteria in fermentation and shortening the fermentation cycle. After fermentation, Nisin is gradually degraded in the acidic environment of pickles, without affecting their natural sour and refreshing flavor, which meets the quality requirements of green fermented foods.

III. Key Technical Strategies to Enhance Nisin’s Preservation Efficacy in Green Food

1. Synergistic Compounding Technology: Broadening Antibacterial Spectrum and Improving Preservation Efficiency

Nisin has weak inhibitory effects on Gram-negative bacteria and molds when used alone. Compounding it with natural preservatives achieves broad-spectrum antibacterial activity, adapting to the diverse needs of green food:

Nisin + EDTA: EDTA disrupts the outer membrane structure of Gram-negative bacteria (e.g., Escherichia coli, Salmonella), enabling Nisin to penetrate the cell membrane and exert its effects. This combination expands the antibacterial spectrum to cover Gram-negative bacteria, making it suitable for preserving green fruit and vegetable juices and aquatic products.

Nisin + Natamycin: Natamycin is a natural anti-mold preservative. Combining it with Nisin achieves comprehensive control of "bacteria + molds", applicable to mold-prone green foods such as bread, pastries, and canned fruits and vegetables.

Nisin + Plant Extracts: Compounding Nisin with plant extracts (e.g., tea polyphenols, carvacrol, rosemary extract) provides dual antibacterial and antioxidant effects, delaying oxidative browning in green food and suitable for preserving fresh-cut fruits and vegetables and meat products.

2. Microencapsulation and Sustained-Release Technology: Enhancing Activity Stability and Adapting to Complex Processing

Green food processing (e.g., high-temperature sterilization, high-salt curing) and storage conditions may impair Nisin’s activity. Microencapsulation technology effectively protects Nisin:Nisin is embedded in microcapsules using natural wall materials such as sodium alginate, chitosan, and β-cyclodextrin. Encapsulated Nisin resists damage from high temperatures, high salt, and proteases, and is released slowly in food to extend antibacterial duration. For example, the activity retention rate of encapsulated Nisin during steaming and boiling of green meat products increases to over 90%, significantly higher than the 60% retention rate of unencapsulated Nisin.

Microencapsulation also solves the problem of uneven dispersion of Nisin in high-sugar and high-fat green foods, ensuring uniform antibacterial effects.

3. Process Adaptation Technology: Precisely Controlling Addition Timing and Concentration

Nisin’s preservation efficacy is closely related to addition timing and concentration, which need to be optimized based on the processing flow of green food:

Addition Timing: For green foods requiring high-temperature processing (e.g., canned goods, meat products), Nisin should be added during the cooling phase after sterilization to avoid activity loss due to high temperatures. For low-temperature processed foods (e.g., fresh-cut fruits and vegetables, yogurt), Nisin can be added directly after processing.

Concentration Control: The addition concentration of Nisin in green food must strictly follow the Green Food Additive Use Guidelines, generally controlled at 50–200 IU/g. This concentration meets antibacterial requirements without increasing costs. For example, adding 80 IU/mL of Nisin to green fruit and vegetable juices effectively inhibits spore-forming bacteria, with no additional benefits from higher concentrations.

pH Adjustment: Nisin exhibits maximum activity in acidic environments (pH 3.0–6.0). For alkaline green foods (e.g., soybean products), natural acidity regulators such as citric acid and lactic acid can be added to adjust the pH to 5.0–6.0, enhancing Nisin’s antibacterial efficacy.

IV. Application Compliance and Future Development Directions

Compliance BasisChina’s Green Food Additive Use Guidelines explicitly lists Nisin as an approved natural preservative. Its maximum usage amount must comply with the provisions of GB 2760-2014 (0.5 g/kg, calculated as pure Nisin). The actual addition concentration in green food is far below this limit, ensuring both safety and compliance.

Future Directions

Develop genetically engineered strains with high Nisin yield to reduce fermentation production costs and promote large-scale application of Nisin in mid-to-low-end green food products.

Research intelligent responsive encapsulation materials that enable Nisin release only when microbial counts exceed the limit, further improving the precision of preservation.

Establish combined systems of Nisin and physical preservation technologies (e.g., cold chain, irradiation) to reduce Nisin dosage and achieve "minimal intervention" preservation of green food.

The core of Nisin’s preservation technology in green food lies in replacing chemical preservatives with natural alternatives, broadening the antibacterial spectrum through synergistic effects, and ensuring preservation efficacy via process adaptation. It not only meets green food safety standards but also maintains natural flavor and nutritional quality. With the continuous advancement of compounding and encapsulation technologies, Nisin will become a core technical tool in the preservation of green food, supporting the large-scale and high-quality development of the green food industry.