The inhibitory effect of Nisin on common spoilage bacteria in food

As a natural antimicrobial peptide food preservative, Nisin exhibits significant "Gram-positive bacteria specificity" in inhibiting common food spoilage microorganisms—it exerts potent inhibitory effects on Gram-positive (G⁺) spoilage bacteria, requires auxiliary treatments to act on Gram-negative (G⁻) spoilage bacteria, and has essentially no direct inhibitory effect on fungal spoilage microorganisms. Its efficacy must be comprehensively evaluated based on food type, bacterial species, and environmental conditions (pH, temperature, composition). Below is an analysis of its inhibitory effects on typical food spoilage microorganisms and influencing factors:

I. Inhibitory Efficacy Against Gram-Positive (G⁺) Spoilage Bacteria (Core Application Scenarios)

G⁺ spoilage bacteria are one of the main pathogenic groups causing food spoilage, particularly prone to proliferating in high-protein and high-fat foods (meat, dairy products, canned goods). Nisin demonstrates remarkable inhibitory effects on these bacteria, including some spore-forming strains, with specific performances as follows:

1. Bacillus spp. ("Persistent Spoilage Bacteria" in Food)

Typical Strains: Bacillus cereus (spoils dairy products, rice, meat products), Bacillus subtilis (spoils bread, pastries, canned goods), Bacillus licheniformis (causes excessive fermentation spoilage in fermented foods).

Inhibitory Efficacy: Nisin inhibits both vegetative cells and spores of these bacteria, making it one of the few natural preservatives capable of inhibiting spore germination. Adding 10~50 mg/kg Nisin to food reduces vegetative cell counts by 3~5 log cycles within 24 hours; for spores, the concentration needs to be increased to 50~100 mg/kg, or combined with high temperature (e.g., 85℃ for 10 minutes), which can reduce spore germination rate by over 90%. For example, adding 30 mg/kg Nisin to canned meat products effectively inhibits Bacillus cereus proliferation, extending shelf life from 6 months to 12 months without significant residual odor.

Advantages: Addresses the problem of Bacillus proliferation at both room and low temperatures, especially suitable for long-term storage scenarios such as canned goods and ready-to-eat foods.

2. Staphylococcus spp. (Common Spoilage Bacteria in High-Protein Foods)

Typical Strains: Staphylococcus aureus (spoils meat, dairy products, pastries, producing enterotoxins), Staphylococcus epidermidis (spoils refrigerated foods).

Inhibitory Efficacy: Nisin exhibits extremely strong inhibitory activity against Staphylococcus spp., taking effect at low concentrations (5~20 mg/kg). Adding 10 mg/kg Nisin to refrigerated (4℃) meat products controls Staphylococcus aureus proliferation to below 10² CFU/g within 7 days (compared to over 10⁶ CFU/g in the non-added group); adding 5 mg/kg Nisin to yogurt inhibits excessive acidification and flavor deterioration caused by miscellaneous bacterial contamination.

Characteristics: Inhibitory efficacy against toxin-producing strains is synchronized with bactericidal effects, reducing enterotoxin production and lowering food safety risks.

3. Lactobacillus spp. (Distinction Between "Beneficial/Harmful" Strains in Fermented Foods)

Typical Strains: Lactobacillus acidophilus (some strains cause excessive acidification of fermented foods), Lactobacillus plantarum (causes spoilage in vegetable fermentation).

Inhibitory Efficacy: Nisin exhibits selective inhibition against Lactobacillus spp.—it has weak inhibitory effects on beneficial lactobacilli essential for fermentation (e.g., Lactobacillus bulgaricus and Streptococcus thermophilus used in yogurt, requiring concentrations >50 mg/kg to exert an impact) but significant efficacy against spoilage-causing miscellaneous lactobacilli (inhibited at 10~30 mg/kg). For example, adding 15 mg/kg Nisin to kimchi fermentation inhibits excessive proliferation of miscellaneous lactobacilli, preventing bitterness and soft rot while not affecting the fermentation process.

Application Value: Meets the "targeted antibacterial" needs of fermented foods, balancing fermentation efficiency and product stability.

4. Other G⁺ Spoilage Bacteria

Listeria monocytogenes (spoils low-temperature meat products and dairy products, a pathogenic bacterium): Nisin shows significant inhibitory effects—20 mg/kg Nisin renders it undetectable in refrigerated (4℃) dairy products within 14 days, addressing spoilage and safety risks under low-temperature storage.

Clostridium perfringens (spoils meat and canned goods, producing gas that causes package swelling): 30~50 mg/kg Nisin inhibits its proliferation and gas production; adding it to vacuum-packaged meat products reduces the swelling rate from 15% to below 1%.

II. Inhibitory Efficacy Against Gram-Negative (G⁻) Spoilage Bacteria (Requiring Synergistic Enhancement)

Due to the outer membrane (lipopolysaccharide barrier) of G⁻ spoilage bacteria blocking Nisin penetration, standalone Nisin exhibits weak inhibitory effects. However, efficacy can be significantly enhanced through combined auxiliary methods (EDTA, organic acids, physical treatments). Typical strains include:

1. Typical G⁻ Spoilage Bacteria

Escherichia coli (spoils drinking water, fruits, vegetables, meat products; some strains are pathogenic), Salmonella spp. (spoils poultry meat and egg products), Pseudomonas aeruginosa (spoils refrigerated foods and aquatic products), Proteus spp. (spoils meat and soy products, producing off-odors).

2. Standalone Inhibitory Efficacy

Only when Nisin concentration exceeds 200 mg/kg does it exert weak inhibition on some G⁻ bacteria (reducing bacterial counts by 1~2 log cycles), far exceeding the food additive limit (GB 2760 stipulates a maximum Nisin dosage of 150 mg/kg), making standalone use impractical in actual applications.

3. Combined Inhibitory Efficacy

Combination with EDTA (0.05%~0.1%): EDTA chelates Ca²⁺ and Mg²⁺ in the outer membrane of G⁻ bacteria, disrupting its structure and enabling Nisin to penetrate the cell membrane. For example, adding 30 mg/kg Nisin + 0.08% EDTA to fruit and vegetable juices reduces Escherichia coli counts by 4 log cycles within 48 hours, with no Salmonella detected.

Combination with lactic acid (adjusting pH to 4.5): Acidic conditions enhance outer membrane permeability; 30 mg/kg Nisin inhibits Pseudomonas aeruginosa proliferation in aquatic products, extending refrigerated shelf life to 7 days (compared to only 3 days in the non-added group).

4. Applicable Scenarios

Mainly used in foods susceptible to G⁻ bacterial contamination, such as fruit and vegetable juices, aquatic products, and ready-to-eat soy products. Compliance of combined ingredients must be strictly controlled.

III. Inhibitory Efficacy Against Fungal Spoilage Microorganisms (Essentially No Direct Effect)

The cell membranes of common fungal spoilage microorganisms in food (yeasts, molds) are primarily composed of ergosterol, lacking Nisin’s target (Lipid II), so Nisin has no direct inhibitory effect:

1. Typical Strains

Saccharomyces cerevisiae (spoils fruit juices and beverages), Penicillium spp. (spoils bread and pastries), Aspergillus spp. (spoils grains and nuts).

2. Experimental Data

Even at the maximum limit concentration of 150 mg/kg, Nisin has no significant impact on the proliferation rate of the above fungi; mold growth still occurs in bread within 5~7 days after addition.

3. Application Note

If food faces both bacterial and fungal spoilage risks, Nisin must be combined with antifungal agents (e.g., natamycin, ε-polylysine) to achieve dual control of "bacteria + fungi."

IV. Key Factors Influencing Nisin’s Inhibitory Efficacy (Food System Compatibility)

Nisin’s inhibitory efficacy is not fixed and must be adjusted based on the physicochemical properties and processing conditions of food. Core influencing factors include:

1. Food pH Value

Acidic conditions (pH 2.0~6.0): Nisin is highly stable with strong antimicrobial activity. For example, in fruit juice at pH 4.0, the inhibitory effect of 20 mg/kg Nisin on G⁺ bacteria is 3 times higher than at pH 7.0.

Neutral/alkaline conditions (pH > 7.0): Nisin degrades easily, with activity reduced by over 50%. The dosage needs to be increased (e.g., from 20 mg/kg to 40 mg/kg in meat products at pH 7.5) or combined with organic acids to adjust pH.

2. Food Composition

High-fat, high-protein foods (meat, dairy products, nuts): Fats and proteins bind to Nisin, reducing free concentration. The dosage needs to be appropriately increased (e.g., Nisin dosage in dairy products is 10~20 mg/kg higher than in fruit and vegetable juices).

High-carbohydrate foods (pastries, beverages): Have little impact on Nisin activity; the base dosage (10~30 mg/kg) can be used.

3. Processing and Storage Temperature

High-temperature processing (e.g., canned sterilization at 121℃/15 minutes): Nisin has strong heat resistance, retaining over 80% activity after sterilization. It can synergize with high temperature for bactericidal purposes, reducing high-temperature treatment time and preserving food nutrition and flavor.

Refrigerated/frozen storage: Low temperatures delay bacterial proliferation, synergizing with Nisin to extend shelf life. For example, adding Nisin to refrigerated (4℃) meat products extends shelf life by 2~3 times compared to room temperature storage.

4. Initial Bacterial Contamination Level

Low initial concentration (<10² CFU/g): Nisin exhibits significant inhibitory effects, rapidly controlling bacterial proliferation.

High initial concentration (>10⁴ CFU/g): The Nisin dosage needs to be increased (e.g., from 20 mg/kg to 50 mg/kg) or combined with physical treatments (e.g., ultrasound, high pressure) to reduce initial bacterial counts, avoiding "antibacterial saturation" of Nisin.

V. Evaluation Criteria for Inhibitory Efficacy in Practical Applications (Quantitative Indicators)

In the food industry, Nisin’s inhibitory efficacy is usually evaluated by the following quantitative indicators to ensure it meets preservation requirements:

Total bacterial count change: After adding Nisin, the count of target spoilage bacteria decreases by ≥3 log cycles during the shelf life or is controlled below 10³ CFU/g.

Shelf life extension rate: Compared to the non-added group, the food shelf life is extended by ≥50% (e.g., pastries from 7 days to over 10 days, meat products from 3 months to over 4.5 months).

Sensory quality retention: Inhibits off-odors (e.g., ammonia, sourness), color changes (e.g., browning, graying), and texture deterioration (e.g., soft rot, caking) caused by spoilage bacteria; the sensory score (flavor, color, texture) decreases by ≤10%.

Safety indicators: No pathogenic bacteria (e.g., Staphylococcus aureus, Salmonella) detected, and no toxins (e.g., enterotoxins, spore toxins) produced.

Nisin’s inhibitory efficacy against common food spoilage microorganisms is characterized by "strong targeting and high compatibility": it exhibits significant effects on G⁺ spoilage bacteria (Bacillus, Staphylococcus, miscellaneous lactobacilli, etc.), achieving preservation goals at low concentrations, making it an ideal preservative for high-protein, high-fat, and fermented foods; it requires combination with EDTA, organic acids, etc., to act on G⁻ spoilage bacteria, suitable for scenarios such as fruit and vegetable juices and aquatic products; it has no direct inhibitory effect on fungi, requiring combination with antifungal agents. In practical applications, Nisin dosage (10~100 mg/kg) and combined schemes should be optimized based on food type, spoilage microorganism species, and processing/storage conditions to achieve the goals of "maximizing antibacterial efficacy, minimizing dosage, and no impact on sensory quality," while complying with food safety standards such as GB 2760.