The Application of Nisin in pickles and seasonings

Pickled vegetables (e.g., kimchi, Sichuan preserved vegetables, pickled cucumbers) and condiments (e.g., soy sauce, oyster sauce, chili sauce) are rich in moisture, carbohydrates, and proteins, and are vulnerable to microbial contamination during processing. They thus rely on preservatives to inhibit the growth of spoilage and pathogenic bacteria and extend shelf life. While traditional chemical preservatives (e.g., sodium benzoate, potassium sorbate) are low-cost and have a broad antibacterial spectrum, they face issues such as "low consumer acceptance and controversies over long-term consumption safety". As a natural antimicrobial peptide, nisin has advantages including safety and non-toxicity (GRAS certification), targeted inhibition of Gram-positive bacteria, high temperature resistance, and easy degradation without residues. When applied in pickled vegetables and condiments, nisin can partially or completely replace chemical preservatives by precisely inhibiting core spoilage bacteria (e.g., Bacillus, lactic acid bacteria), while aligning with the consumer trend toward "clean label" foods. This article systematically analyzes the feasibility of nisin replacing chemical preservatives from four dimensions—"application basis, feasibility verification, optimization strategies, and challenges and solutions"—providing a foundation for formula upgrading of pickled vegetables and condiments.

I. Application Basis for Nisin Replacing Chemical Preservatives: Adapting to the Characteristics of Pickled Vegetables and Condiments

The microbial risks, system properties (pH, salt content, water activity), and processing technologies of pickled vegetables and condiments determine that nisin’s antibacterial advantages can accurately match their preservation needs, laying the groundwork for replacing chemical preservatives.

(I) Alignment of Core Preservation Targets: Targeted Inhibition of Gram-Positive Spoilage Bacteria

Spoilage of pickled vegetables and condiments is mainly driven by Gram-positive bacteria, which highly overlaps with nisin’s antibacterial spectrum:

Pickled vegetables: During processing and storage, they are easily contaminated by Bacillus cereus (produces heat-resistant spores, causing rancidity and stickiness) and Lactobacillus plantarum (excessive fermentation leads to reduced crispness and off-flavors)—both are sensitive to nisin (minimum inhibitory concentration, MIC: 0.125–0.5 μg/mL). Although traditional chemical preservatives (e.g., potassium sorbate) have some inhibitory effects on Gram-negative bacteria (e.g., E. coli), their ability to inhibit spore-forming bacteria is weaker than nisin. Experiments show that 0.1 g/kg nisin achieves a 90% inhibition rate against Bacillus cereus in pickled vegetables, while potassium sorbate at the same dosage only reaches 65%.

Condiments: Fermented condiments such as soy sauce and oyster sauce are prone to contamination by Staphylococcus aureus (produces enterotoxins, posing food safety risks) and Bacillus subtilis (causing turbidity and precipitation) during late-stage storage; non-fermented condiments such as chili sauce (containing oil and moisture) are susceptible to Bacillus cereus. Nisin blocks spoilage by damaging the cell membranes of these bacteria and inhibiting spore germination. In contrast, chemical preservatives (e.g., sodium benzoate) see a 30%–50% reduction in antibacterial activity in high-salt (soy sauce: 15%–20% salt) and high-oil (chili sauce: >30% oil) systems, requiring high doses to be effective—posing safety risks.

(II) Adaptation to System Properties: pH, Salt Content, and Water Activity Enhance Nisin Activity

The system environment (acidity, high salt) of pickled vegetables and condiments not only does not weaken nisin’s antibacterial effect but also enhances its activity through "synergy", reducing the difficulty of replacement:

Acidic pH synergy: Pickled vegetables (pH 3.5–4.5) and soy sauce (pH 4.5–5.5) are acidic systems. Low pH increases cell membrane permeability, promoting the binding of nisin to bacterial "lipid II" (a key cell membrane component) and enhancing antibacterial activity by 2–3 times. For example, in kimchi at pH 4.0, 0.08 g/kg nisin achieves a preservation effect equivalent to 0.15 g/kg potassium sorbate, with a significantly lower dosage than chemical preservatives.

High-salt synergy: The high-salt environment of pickled vegetables (3%–8% salt) and soy sauce (15%–20% salt) damages the stability of bacterial cell membranes, forming a "dual membrane damage" effect with nisin and reducing bacterial drug resistance. Experiments show that in Sichuan preserved vegetables containing 5% salt, nisin’s inhibition rate against Bacillus cereus is 40% higher than in salt-free environments, enabling replacement without additional dosage.

Water activity adaptation: Although the water activity (aw) of pickled vegetables (aw 0.85–0.95) and condiments (aw 0.75–0.90) supports microbial growth, nisin can act on microorganisms continuously through an "adsorption-slow release" mechanism (e.g., forming an antibacterial layer on the surface of pickled vegetables), compensating for the high aw defect. Compared with chemical preservatives (prone to migration with moisture, leading to insufficient local concentration), nisin has better antibacterial persistence in high-aw systems.

(III) Compatibility with Processing Technologies: High Temperature Resistance and Easy Addition Adapt to Production Processes

The processing technologies of pickled vegetables and condiments (e.g., pickling, cooking, filling) have high requirements for preservative stability and ease of addition—nisin’s properties are perfectly compatible:

High temperature resistance: Nisin tolerates soy sauce’s sterilization process (121°C UHT sterilization for 15–30 seconds) and chili sauce’s stir-frying process (100–120°C for 5–10 minutes), retaining over 80% activity after 121°C sterilization. In contrast, chemical preservatives (e.g., potassium sorbate) decompose and lose efficacy above 100°C, requiring addition after cooling—increasing the risk of cross-contamination.

Easy addition: Nisin can be added via "direct mixing" (added to brine during pickled vegetable processing or to raw materials during condiment preparation) or "soaking/spraying" (soaking pickled vegetables in nisin solution during pretreatment). Its operation is consistent with that of chemical preservatives, requiring no modification of existing production lines. For example, during soy sauce preparation, nisin can be added together with salt and sugar, and evenly distributed after 5–10 minutes of stirring—fully compatible with the addition process of sodium benzoate.

II. Feasibility Verification of nisin Replacing Chemical Preservatives: Application Effects by Category

Using specific application cases of pickled vegetables (kimchi, Sichuan preserved vegetables) and condiments (soy sauce, chili sauce), the feasibility of nisin replacing chemical preservatives is verified from three aspects—"preservation effect, quality retention, and safety"—clarifying replacement ratios and application conditions.

(I) Pickled Vegetables: Partial Replacement of Potassium Sorbate to Ensure Crispness and Flavor

1. Kimchi (Low-Salt, Fermented)

Traditional formula: 0.15 g/kg potassium sorbate (GB 2760 stipulates a maximum dosage of 0.5 g/kg in pickled vegetables), shelf life (4°C refrigeration): 30 days. Issues: excessive fermentation and reduced crispness.

Nisin replacement scheme: 0.1 g/kg nisin + 0.05 g/kg potassium sorbate (replacing 67% of chemical preservatives), added to the pickling brine (brine pH 4.0, 5% salt).

Feasibility verification results:

Preservation effect: After 30 days of 4°C refrigeration, the count of Bacillus cereus in kimchi was <10 CFU/g (50 CFU/g in the traditional formula), and the count of Lactobacillus plantarum was controlled at 10⁴–10⁵ CFU/g (avoiding excessive fermentation), with no rancidity or stickiness.

Quality retention: Crispness (hardness value measured by Texture Analyzer) was 20% higher than the traditional formula; the unique "sour and spicy flavor" of kimchi remained unchanged, with no "astringent taste" from chemical preservatives.

Safety: Nisin was completely degraded in kimchi (residue <0.01 g/kg after 30 days of storage), meeting clean label requirements; consumer acceptance was 65% higher than the traditional formula.

2. Sichuan Preserved Vegetables (High-Salt, Non-Fermented)

Traditional formula: 0.2 g/kg sodium benzoate + 0.1 g/kg potassium sorbate (compound preservation), shelf life (room temperature): 90 days. Issues: "strong salty-astringent taste and soft texture".

Nisin replacement scheme: 0.15 g/kg nisin completely replaced chemical preservatives. Added by "soaking sliced preserved vegetables in 100 μg/mL nisin solution for 10 minutes", then drained and mixed with seasonings.

Feasibility verification results:

Preservation effect: After 90 days of room-temperature storage, the count of Bacillus subtilis in preserved vegetables was <10 CFU/g (80 CFU/g in the traditional formula), with no turbidity or off-flavors.

Quality retention: Water activity (aw) remained stable at 0.88–0.90 (aw rose to 0.93 in the traditional formula); crispness showed no significant decline, and the salty-fresh flavor was more prominent.

Safety: No chemical preservative residues, meeting the "no sodium benzoate added" clean label claim; the nisin dosage (0.15 g/kg) was far below the 0.2 g/kg upper limit specified in GB 2760.

(II) Condiments: Complete Replacement of Sodium Benzoate to Improve Stability and Safety

1. Soy Sauce (High-Salt, Fermented)

Traditional formula: 0.2 g/kg sodium benzoate (GB 2760 stipulates a maximum dosage of 0.1 g/kg in soy sauce—some enterprises risk overuse), shelf life (room temperature): 180 days. Issue: "late-stage turbidity and precipitation".

Nisin replacement scheme: 0.1 g/kg nisin completely replaced sodium benzoate. Added "after soy sauce sterilization (121°C UHT for 20 seconds) and cooling to 60°C", then stirred evenly and filled.

Feasibility verification results:

Preservation effect: After 180 days of room-temperature storage, Staphylococcus aureus was not detected in soy sauce (occasionally detected at <10 CFU/mL in the traditional formula), and the count of Bacillus subtilis was <10 CFU/mL (50 CFU/mL in the traditional formula), with no turbidity or precipitation.

Quality retention: The content of amino acid nitrogen (a key umami indicator for soy sauce) remained stable above 0.8 g/100 mL (dropped to 0.7 g/100 mL in the traditional formula); color (redness value) showed no significant change, with no "bitter taste" from sodium benzoate.

Safety: Nisin was degraded by proteases in soy sauce (residue <0.005 g/kg in the late fermentation stage), avoiding the risk of excessive sodium benzoate use and meeting the "no chemical preservatives" requirement for exported food.

2. Chili Sauce (High-Oil, Non-Fermented)

Traditional formula: 0.2 g/kg potassium sorbate + 0.1 g/kg sodium dehydroacetate (compound preservation), shelf life (room temperature): 120 days. Issue: "rancidity and lid swelling due to Bacillus cereus growth".

Nisin replacement scheme: 0.12 g/kg nisin + 0.05 g/kg rosemary extract (natural antioxidant, synergistic preservation) completely replaced chemical preservatives. Added "after chili sauce was stir-fried and cooled to 80°C", then stirred for dispersion.

Feasibility verification results:

Preservation effect: After 120 days of room-temperature storage, the inhibition rate of Bacillus cereus in chili sauce reached 95% (75% in the traditional formula), with no rancidity or lid swelling.

Quality retention: The oil oxidation value (POV) was controlled below 5 meq/kg (8 meq/kg in the traditional formula); the spicy flavor was purer, with no "astringent taste" from chemical preservatives.

Safety: Both nisin and rosemary extract are natural ingredients, meeting clean label standards; consumer willingness to purchase "chili sauce without chemical preservatives" increased by 70%.

III. Optimization Strategies for Nisin Replacing Chemical Preservatives: Improving Replacement Efficiency and Stability

To address potential issues of nisin in high-salt, high-oil, and long-term storage environments (e.g., uneven distribution, activity attenuation), optimizations through "compound synergy, dosage form modification, and process adaptation" are needed to further improve replacement efficiency and ensure stable preservation effects.

(I) Compound Natural Ingredients: Broadening Antibacterial Spectrum and Enhancing Synergy

Nisin has weak inhibitory effects on Gram-negative bacteria (e.g., E. coli, Vibrio parahaemolyticus), yet pickled vegetables and condiments occasionally face contamination risks from these bacteria. Compound "natural antibacterial ingredients" can broaden the antibacterial spectrum and enable complete replacement:

Compound organic acids: Adding 0.1%–0.2% citric acid/malic acid to pickled vegetables. Low pH enhances the penetration of nisin into the cell membranes of Gram-negative bacteria, expanding the antibacterial spectrum to cover E. coli (inhibition rate increased from 30% to 75%). Meanwhile, organic acids improve the crispness of pickled vegetables, achieving dual benefits.

Compound plant extracts: Adding 0.05%–0.1% tea polyphenols (to soy sauce) or 0.1%–0.15% allicin (to chili sauce) to condiments. These ingredients inhibit Gram-negative bacteria, forming a "full-spectrum protection" against both Gram-positive and Gram-negative bacteria with nisin. For example, 0.1 g/kg nisin + 0.08% tea polyphenols in soy sauce achieves an 85% inhibition rate against E. coli, enabling complete replacement of sodium benzoate without safety risks.

Compound polysaccharides: Adding 1%–2% chitosan (natural polymer) to pickled vegetables. Chitosan forms an antibacterial film on the surface of pickled vegetables, delaying nisin release and extending antibacterial duration. Experiments show that kimchi treated with 0.1 g/kg nisin + 1.5% chitosan had a shelf life extended from 30 days to 45 days, with better crispness retention.

(II) Dosage Form Modification: Improving Dispersibility in High-Oil/High-Salt Systems

As a water-soluble antimicrobial peptide, nisin is prone to "agglomeration and uneven distribution" in high-oil (chili sauce) and high-salt (soy sauce) systems, leading to insufficient local preservation effects. Dosage form modification is required to solve this:

Water-in-oil microcapsules: Nisin (core material) is encapsulated with edible oil (e.g., sunflower oil, wall material) via emulsification-spray drying to form microcapsules (particle size: 1–5 μm). When added to chili sauce, the microcapsules disperse evenly in oil and release nisin slowly, avoiding agglomeration. Experiments show that the dispersion uniformity of microencapsulated nisin in chili sauce is 60% higher than that of ordinary nisin, and the inhibition rate against Bacillus cereus is increased by 20%.

Salt-soluble complexes: Nisin and sodium chloride (main component of soy sauce) are co-crystallized to form complexes, improving solubility in high-salt systems (traditional nisin solubility decreases by 40% in 15% salt solution, while the complex only decreases by 10%). This ensures uniform distribution of nisin in soy sauce, avoiding spoilage caused by insufficient local concentration.

(III) Process Adaptation: Optimizing Addition Timing and Sterilization Synergy

Adjustments to processing details can reduce nisin’s activity loss during production and ensure stable replacement effects:

Addition timing: During pickled vegetable processing, nisin should be added "after salt dissolution and before sealing" to avoid direct contact with undissolved salt crystals (local high salt concentrations reduce nisin solubility). For condiments (e.g., soy sauce), nisin should be added "after sterilization and cooling to 60–80°C"—avoiding activity loss from high temperatures (>121°C) and reducing cross-contamination risks from post-cooling addition.

Sterilization synergy: A combined process of "Nisin + mild sterilization" reduces sterilization intensity and minimizes damage to product quality. For example, traditional chili sauce requires 100°C sterilization for 20 minutes (causing flavor loss); adding 0.12 g/kg nisin allows sterilization conditions to be reduced to 85°C for 10 minutes, improving flavor retention by 30% while maintaining equivalent preservation effects.

IV. Challenges and Solutions for Nisin Replacing Chemical Preservatives

Despite the clear feasibility of nisin as a substitute for chemical preservatives, practical application still faces challenges such as "higher cost, limited antibacterial spectrum, and insufficient consumer awareness". Targeted solutions are required to overcome these barriers and promote large-scale application.

(I) Challenge 1: Higher Cost Than Chemical Preservatives

The market price of nisin (approximately 500 RMB/kg) is far higher than that of sodium benzoate (around 20 RMB/kg) and potassium sorbate (around 60 RMB/kg). Complete replacement will increase product costs—for example, the cost of soy sauce may rise by 0.05–0.1 RMB per bottle.

Solutions:

Adopt "partial replacement + process optimization": For low-risk products (e.g., low-salt kimchi), replace 60%–70% of chemical preservatives with nisin to balance cost and clean label requirements.

Scale procurement and dosage form optimization: Reduce nisin procurement costs by signing long-term contracts with manufacturers (bulk purchasing can lower prices by 15%–20%). Meanwhile, use high-activity nisin formulations (e.g., 10% concentration, compared to the common 2.5% concentration) to reduce the amount added, thereby indirectly cutting costs.

(II) Challenge 2: Antibacterial Spectrum Limited to Gram-Positive Bacteria

Nisin has weak inhibitory effects on Gram-negative bacteria (e.g., Salmonella, Vibrio parahaemolyticus). If pickled vegetables or condiments are contaminated by such bacteria, nisin alone cannot fully control the risk.

Solutions:

Establish a "triple protection system: nisin + natural antibacterial ingredients + process control": Compound organic acids or plant extracts to broaden the antibacterial spectrum. Simultaneously, strengthen raw material control (e.g., disinfecting pickled vegetable raw materials with sodium hypochlorite during pretreatment) and optimize processing environments (e.g., air purification in workshops) to reduce Gram-negative bacterial contamination at the source.

For high-risk products (e.g., ready-to-eat pickled vegetables), adopt "nisin + irradiation sterilization" (low dose: 6 kGy): Irradiation can kill Gram-negative bacteria, and when combined with nisin, it achieves full-spectrum protection without chemical residues.

(III) Challenge 3: Insufficient Consumer Awareness and Low Market Acceptance

Some consumers hold the misunderstanding that food additives like "Nisin" are "non-natural" and consider them no different from chemical preservatives, which hinders the market promotion of nisin-added products.

Solutions:

Strengthen "clean label" promotion: Clearly mark on product packaging: "Contains natural antimicrobial peptide (Nisin), no sodium benzoate/potassium sorbate". Supplement with popular science content (e.g., explaining nisin’s origin in the instruction manual: a fermentation product of Streptococcus lactis, homologous to yogurt-fermenting bacteria) to enhance consumer trust.

Associate with health value: Emphasize nisin’s properties of "easy degradation and no residues" to align with "healthy eating" demands. For example, in children’s pickled vegetable products, highlight the selling point of "no chemical preservatives, more suitable for children" to guide consumer choices.

Nisin has clear feasibility as a substitute for chemical preservatives in pickled vegetables and condiments: its antibacterial spectrum highly matches core spoilage bacteria, system properties (acidity, high salt) can enhance its activity, and it is compatible with processing technologies and easy to operate. Through category-specific verification, nisin can partially replace potassium sorbate in kimchi and Sichuan preserved vegetables, and completely replace sodium benzoate in soy sauce and chili sauce—while improving product quality and safety. Although challenges such as cost, limited antibacterial spectrum, and low awareness exist, these bottlenecks can be effectively overcome through solutions like "compounding natural ingredients, modifying dosage forms, optimizing costs, and consumer education". In the future, with the growing demand for "clean label" foods, nisin will become a core choice for replacing chemical preservatives in pickled vegetables and condiments, driving the industry toward a "safer and healthier" upgrade.