The Application of Nisin in Smoked Foods

Smoked foods (e.g., smoked meat, sausages, fish, and soybean products) are susceptible to contamination by Gram-positive spoilage and pathogenic bacteria due to their processing techniques and product characteristics. Meanwhile, the industry is facing the demand for upgrading towards salt and nitrite reduction. As a natural microbial-sourced antimicrobial peptide, nisin aligns with the processing features and safety requirements of smoked foods, playing a key role in preservation, quality maintenance, and process optimization. Its specific applications are elaborated as follows:

I. Spoilage Challenges of Smoked Foods and Nisin’s Adaptability

1. Core Spoilage Issues

Smoked foods are typically rich in proteins, fats, and other nutrients. The smoking process fails to achieve complete sterilization, making these products vulnerable to contamination by Gram-positive bacteria such as Clostridium botulinum, Staphylococcus aureus, Listeria monocytogenes, and Bacillus subtilis. Such contamination leads to product souring, stickiness, flavor deterioration, and even food safety hazards. Traditional preservation relies on high salt and nitrite levels, and excessive intake of these substances poses health risks to humans. In contrast, nisin can selectively inhibit these pathogenic bacteria without compromising product flavor.

2. Process Compatibility Advantages

Smoked food processing often involves high-temperature smoking, smoke drying, and other steps. Nisin exhibits excellent thermal stability (retaining over 80% of its activity after sterilization at 121℃ for 30 minutes), enabling it to withstand the high-temperature conditions during smoking. Additionally, it has good water solubility and dispersibility, allowing uniform integration into curing solutions or direct application to product surfaces. This makes nisin compatible with the entire production process of smoked foods, including curing, smoking, and packaging.

II. Specific Mechanisms and Effects of Nisin in Smoked Foods

1. Targeted Antibacterial Activity to Extend Shelf Life

Nisin binds to lipid Ⅱ on bacterial cell membranes, disrupting cell wall synthesis and forming transmembrane pores. This causes the leakage of intracellular substances, leading to bacterial death. It shows significant inhibitory effects on Clostridium botulinum spores, the most hazardous contaminants in smoked foods, with a minimum inhibitory concentration (MIC) of less than 50 IU/mL.

Application Case: Adding 0.05–0.1 g/kg of pure nisin during the curing of smoked sausages can extend the product’s shelf life from 3–5 days to 10–15 days at room temperature (25℃), and from 1 month to 2–3 months under refrigeration (4℃). Moreover, it effectively reduces the detection rates of Listeria monocytogenes and Staphylococcus aureus.

For smoked fish and smoked soybean products, nisin can inhibit spoilage caused by Bacillus spp., preventing off-odors and stickiness and maintaining favorable sensory quality.

2. Synergizing with Salt and Nitrite Reduction to Optimize Product Formulations

High salt and nitrite are traditional preservatives for smoked foods, but high salt intake may induce cardiovascular diseases, and nitrite can form potentially carcinogenic nitrosamines. Nisin can work synergistically with low-salt and low-nitrite formulations to reduce the dosage of these additives:

Combination with Nitrite: Nisin enhances the antibacterial efficacy of nitrite, allowing a 30%–50% reduction in nitrite dosage. Simultaneously, it inhibits nitrosamine formation, improving product safety.

Integration with Low-Salt Formulations: In smoked meat processing, reducing salt content from 3%–5% to 1%–2% and adding 0.08 g/kg of nisin still achieves equivalent preservative effects, which aligns with the healthy consumption trend.

3. Reducing Secondary Contamination for Cold Chain Circulation

Smoked foods are prone to secondary contamination during slicing, packaging, and transportation. Nisin can act as a terminal preservative barrier: spraying or soaking products with nisin solution before packaging forms an antibacterial film on the food surface, inhibiting microbial growth during circulation. This application is particularly suitable for ready-to-eat smoked foods requiring cold chain transportation (e.g., ready-to-eat smoked chicken and dried smoked beef).

4. Preserving Smoked Flavor to Maintain Product Characteristics

Nisin is colorless and tasteless, and it does not alter the unique smoky aroma and texture of smoked foods. Compared with chemical preservatives (e.g., sodium benzoate), it better retains the characteristic flavor of smoked products. Furthermore, nisin is degraded into amino acids by proteases in the human digestive tract, leaving no residues or toxicity and meeting clean label requirements.

III. Application Precautions

1. Dosage Control

Strictly comply with GB 2760 National Food Safety Standard for the Use of Food Additives. The maximum dosage of nisin is 0.5 g/kg (based on pure nisin) in smoked meat products and 0.1 g/kg in smoked soybean products. Excessive addition does not enhance antibacterial effects.

2. Compound Application to Expand Antibacterial Spectrum

Nisin has weak inhibitory effects on Gram-negative bacteria. Improper storage of smoked foods may lead to contamination by bacteria such as Escherichia coli. It is recommended to compound nisin with chelating agents (e.g., EDTA, citric acid) at a ratio of 5:1 to disrupt the outer membrane structure of Gram-negative bacteria and expand the antibacterial spectrum. For smoked pastries and soybean products with high mold contamination risks, nisin can be combined with natamycin.

3. Process Compatibility Key Points

Add nisin during the curing stage or after smoking when the product is cooled below 60℃ to avoid activity loss caused by prolonged exposure to high temperatures if added too early.

The pH value of smoked foods typically ranges from 5.5 to 6.5, which is the optimal range for nisin stability. If the product is acidic (pH < 4.0), the dosage of nisin should be appropriately increased.

4. Storage and Compatibility Taboos

Store nisin in a sealed, light-proof container under refrigeration. Avoid contact with strong acids and alkalis. Do not mix nisin with antibiotics, as this may impair its antibacterial activity.

With the advantages of targeted antibacterial activity, thermal stability, and clean label compliance, nisin not only effectively extends the shelf life and reduces pathogenic risks of smoked foods but also supports the formulation upgrade of salt and nitrite reduction. It is an ideal natural preservative for the smoked food industry to achieve the dual goals of safety and health. By rationally controlling the dosage, optimizing compound formulations, and improving process compatibility, the application effects of nisin in various smoked foods can be further enhanced.