The preservation of Nisin in canned foods

The application of nisin as a natural biopreservative in canned foods requires analysis from three aspects: preservation mechanisms, efficacy verification, and sensory impacts, considering the processing characteristics (high-temperature sterilization, sealed environment) and microbial control needs of canned products. It offers unique advantages in inhibiting heat-resistant bacteria and maintaining product quality, though compatibility with canned matrices must also be addressed. The following presents the specific research framework and key conclusions:

I. Preservation Mechanisms and Targeted Antibacterial Properties of Nisin in Canned Foods

1. Inhibitory Effects on Typical Spoilage Bacteria in Canned Foods

The primary spoilage risks in canned foods come from heat-resistant spore-forming bacteria (e.g., Bacillus stearothermophilus, Bacillus coagulans) and anaerobic clostridia (e.g., Clostridium botulinum). Nisin potently inhibits Gram-positive bacterial spores by disrupting cell membrane peptidoglycan synthesis: in acidic canned foods (pH 4.5), 0.2 g/kg nisin reduces B. stearothermophilus spore germination rate by 90%, delaying proliferation. For C. botulinum (a safety hazard in canned foods), nisin (0.15 g/kg) inhibits toxin production; combined with thermal sterilization (121°C/20 min), it increases the commercial sterility assurance level (F0 value) from 8 to 12, meeting international standards.

However, its inhibitory effect on Gram-negative bacteria (e.g., E. coli, Salmonella) is limited, relying on the canned acidic environment (pH<4.6) or thermal sterilization intensity. For example, in low-acid vegetable cans (pH 5.0–5.5), single-use nisin (0.3 g/kg) cannot fully control E. coli, requiring pH adjustment to <4.3 or combined microwave-assisted sterilization.

2. Synergistic Effects with Canned Processing Technologies

Thermal stability optimization: Nisin’s high-temperature resistance significantly improves under acidic conditions (pH≤4.5). For instance, adding 0.1 g/kg Nisin to tomato cans (pH 4.2) retains >90% activity after 121°C sterilization for 30 min, continuously inhibiting residual spore revival during cooling. In neutral pH meat cans (e.g., luncheon meat, pH 6.0–6.5), high-temperature sterilization causes ~60% Nisin activity loss, necessitating a "post-sterilization spraying" process (spraying nisin solution at 0.2 g/kg concentration when cooling to 40°C) to ensure effective concentration.

Matrix compatibility: Proteins (e.g., fish, bean proteins) and salt (typically 1%–2% NaCl) in canned foods have dual effects on Nisin activity: proteins may adsorb Nisin, reducing effective concentration (e.g., 1% protein in chicken cans adsorbs ~30% nisin), requiring appropriate dosage increase; low-salt environments (<2% NaCl) minimally affect nisin activity, while high salt (>3%) weakens antibacterial effects (salt ions compete for bacterial binding sites), thus Nisin dosage in corned beef cans should increase from the conventional 0.1 g/kg to 0.25 g/kg.

II. Quantitative Studies on Preservation Efficacy and Shelf Life Extension

1. Application Data for Different Canned Products

Acidic fruit cans (e.g., yellow peaches, pineapples): Adding 0.1 g/kg Nisin to traditional thermal sterilization (100°C/20 min) extends the detection time of yeasts and molds from 60 days to 120 days at 25°C, with the TVB-N value increase rate reduced by 50%. The mechanism involves nisin inhibiting residual heat-resistant yeasts (e.g., Zygosaccharomyces bailii), while the acidic environment itself controls bacterial growth.

Low-acid meat cans (e.g., braised beef): Using a "nisin + thermal sterilization" combination with 0.2 g/kg Nisin and shortened sterilization from 121°C/30 min to 121°C/20 min keeps total viable counts <10 CFU/g and extends shelf life (37°C accelerated test) from 90 days to 120 days. This protocol reduces high-temperature damage to meat while meeting commercial sterility requirements (GB 7098-2015 stipulates no pathogenic bacteria in canned foods).

Aquatic product cans (e.g., tuna): Nisin (0.15 g/kg) combined with vacuum packaging inhibits psychrophilic bacteria (e.g., Pseudomonas) proliferation during ambient storage, extending the time for total colony counts to reach 7 log CFU/g from 45 days to 75 days, with TVB-N values <30 mg/100g (national standard limit).

2. Efficacy Comparison with Chemical Preservatives

In mushroom cans, 0.2 g/kg nisin exhibits antibacterial effects equivalent to 0.05% potassium sorbate, but the former more significantly inhibits heat-resistant spores (potassium sorbate has no effect on spores). After 6 months of storage, nisin-treated cans retain 82% of vitamin C, higher than 75% in the potassium sorbate group, indicating better protection of nutrients.

Nitrite replacement scenario: In luncheon meat cans, replacing 50% nitrite (from 100 mg/kg to 50 mg/kg) with Nisin (0.1 g/kg), combined with sodium ascorbate (0.3%) for color fixation, reduces nitrosamine (NDMA) formation by 55% during 30°C storage, with no C. botulinum detected, ensuring safety comparable to traditional formulas.

III. Impacts on Canned Sensory Quality and Optimization Strategies

1. Positive Effects: Maintaining Natural Texture and Flavor

As a polypeptide, Nisin is odorless and has no adverse effects on canned color, taste, or texture. For example, adding 0.1 g/kg nisin to corn cans shows no significant difference in lightness and yellowness values (ΔE<2) compared to the control group, with bite force (measured by texture analyzer) maintained at 150–180 g, close to fresh corn. This is because nisin does not rely on acidic environments like chemical preservatives (e.g., sodium benzoate), avoiding plant fiber softening by low pH.

Flavor retention: In tomato cans, the content of volatile flavor compounds (e.g., 2-methylbutyraldehyde, hexanal) in the Nisin group (0.1 g/kg) is 12%–15% higher than in the potassium sorbate group, mainly due to nisin’s selective inhibition of esterase-producing microorganisms, reducing flavor substance degradation. Sensory evaluation shows nisin-treated cans have better sweet-sour balance, scoring 4.5/5 (control group 4.2).

2. Potential Challenges and Solutions

Risk of abnormal coloration: In canned foods containing polyphenols (e.g., mushrooms, lotus roots), Nisin may weakly interact with polyphenol oxidase (PPO), causing slight browning. Solutions: Add 0.05% ascorbic acid to inhibit enzyme activity or use nisin microencapsulation technology (e.g., β-cyclodextrin embedding) to reduce contact with enzymes. Pilot data show that embedded nisin in mushroom cans reduces the browning index (ΔE) from 3.8 to 2.1, meeting commercial standards.

Texture softening issue: In meat cans, nisin may indirectly affect the activity of certain protease-producing microorganisms, leading to excessive muscle protein hydrolysis and softening. Countermeasures: Control nisin dosage (≤0.2 g/kg) and add 0.1% CaCl₂ to strengthen muscle fiber cross-linking. Experiments show this combination maintains shear force in beef cans at ~3.5 kgf, no significant difference from traditional processes.

IV. Key Points and Trends in Industrial Application

1. Process Adaptation Principles

Acidic cans (pH<4.5): Directly add Nisin (0.1–0.2 g/kg) and perform conventional sterilization.

Low-acid cans: Increase nisin dosage (0.2–0.3 g/kg) or combine with high-pressure processing (HPP, 600 MPa/3 min) to replace partial thermal sterilization, reducing nutrient loss. For example, HPP+Nisin (0.15 g/kg) treatment of vegetable cans retains 30% more B vitamins than traditional sterilization.

2. Safety and Regulatory Compliance

China’s GB 2760-2024 stipulates the maximum nisin usage in canned foods as 0.5 g/kg. The FDA recognizes it as a GRAS (Generally Recognized As Safe) substance, suitable for infant canned foods (e.g., meat puree). Market research shows canned products with Nisin command a 10%–15% price premium in European and American supermarkets, with high consumer acceptance of "natural preservation" labels.

3. Future Technical Directions

Develop nisin compound systems with plant essential oils (e.g., 0.05% rosemary essential oil) for synergistic antibacterial effects (1+1>2) in cans. For instance, nisin (0.1 g/kg)+rosemary essential oil (0.03%) reduces the sterilization F0 value by 20% while enhancing antioxidant capacity (TBARS value down 40%).

Nanocarrier technology (e.g., Nisin-nano SiO₂ composite particles) enables slow preservative release, extending canned shelf life to >18 months.

Conclusion

Nisin demonstrates clear preservation efficacy in canned foods, particularly for microbial control in acidic and low-acid cans. It enhances safety and maintains color, texture, and flavor through combinations with thermal sterilization and natural antibacterial agents. Despite challenges like matrix compatibility, process optimization and new formulation technologies have made nisin an important solution for the canned industry to "reduce chemical preservatives," with great potential in high-end cans (e.g., organic foods, baby foods) with further development.