The application effect of Nisin in frozen food

As a natural peptide preservative, Nisin can selectively inhibit Gram-positive bacteria and bacterial spores. It is compatible with the low-temperature processing and cold-chain storage characteristics of frozen foods, playing a significant role in extending shelf life, ensuring food safety, and reducing the dosage of chemical preservatives. Its application efficacy is affected by factors such as food matrix, addition method, and compounding scheme, with specific analyses as follows:

I. Core Application Effects of Nisin in Frozen Foods

1. Selective Inhibition of Spoilage and Pathogenic Bacteria to Extend Cold-Chain Shelf Life

The primary preservation challenge of frozen foods (e.g., frozen meat products, aquatic products, prepared conditioned foods) lies in psychrophilic bacteria and heat-resistant spore-forming bacteria that can survive at low temperatures. These microorganisms multiply rapidly when the cold chain fluctuates (e.g., during thawing or transportation temperature increases), leading to food spoilage or foodborne diseases. Nisin exhibits high-efficiency inhibitory activity against common Gram-positive pathogenic bacteria in frozen foods, such as Bacillus cereus, Staphylococcus aureus, and Listeria monocytogenes. Its mechanism involves binding to lipid Ⅱ on bacterial cell membranes, disrupting cell wall synthesis and causing membrane leakage. Meanwhile, it can penetrate the spore cortex structure to prevent spores from germinating into vegetative cells. Practical application data show that:

Adding 50–100 IU/g of Nisin to frozen pasta products (e.g., frozen dumplings, wontons) can extend their shelf life from 6 months to 12 months under -18℃ cold-chain storage conditions, reduce the total bacterial count by 2–3 orders of magnitude, and effectively inhibit the proliferation of Bacillus cereus in fillings;

Adding 100–150 IU/g of Nisin to frozen meat products (e.g., frozen meatballs, sausages) can significantly reduce the risk of Listeria monocytogenes contamination, meeting food safety standards for frozen meat products, while avoiding texture stickiness and off-odors caused by bacterial growth.

2. Reducing Chemical Preservative Dosage to Meet Healthy Consumption Demands

Traditional frozen foods often contain chemical preservatives such as potassium sorbate and sodium dehydroacetate to extend shelf life, but excessive addition can affect food flavor and fail to meet consumers’ demand for "clean labels". Nisin can be used as a natural preservative to partially or completely replace chemical preservatives, with its advantages reflected in two aspects:

Replacement by single use: In frozen fruit and vegetable products (e.g., frozen broccoli, strawberries), Nisin can replace chemical preservatives to inhibit surface Gram-positive bacteria without affecting the color, texture, or nutritional components of the produce;

Synergistic enhancement by compounding: When Nisin is compounded with EDTA, citric acid, ε-polylysine, etc., it can disrupt the outer membrane structure of Gram-negative bacteria (e.g., Escherichia coli, Salmonella), broaden the antibacterial spectrum, and further reduce the dosage of chemical preservatives. For example, a compound system of Nisin (80 IU/g) + EDTA (0.05%) in frozen surimi products can reduce the addition of chemical preservatives by more than 50%, with better preservation efficacy than single chemical preservatives.

3. Compatibility with Frozen Food Processing Technology to Ensure Activity Stability

The processing procedures of frozen foods (e.g., steaming, quick-freezing, thawing) impose high stability requirements on preservatives. Nisin has good thermal stability and low-temperature adaptability, and can withstand temperature changes during processing:

Thermal stability: Nisin retains over 80% of its activity after high-temperature sterilization at 121℃, making it suitable for the high-temperature steaming process of frozen prepared dishes. After sterilization, Nisin can continuously exert antibacterial effects during frozen storage, preventing microbial proliferation when the cold chain fluctuates;

Low-temperature adaptability: At -18℃ freezing conditions, Nisin’s activity does not decrease significantly, and it can be rapidly released during food thawing to inhibit resuscitated microorganisms, solving the problem of "spoilage immediately after thawing" in frozen foods.

4. No Impact on Texture and Flavor of Frozen Foods to Improve Product Quality

Nisin is colorless, tasteless, odorless, and has a small molecular weight, so it does not react with components such as proteins and fats in frozen foods. Therefore, its addition does not alter the texture and flavor of foods:

In frozen dairy products (e.g., frozen ice cream, popsicles), low-concentration Nisin (20–50 IU/g) can inhibit miscellaneous bacteria other than lactic acid bacteria without affecting the smooth texture and milk flavor of ice cream;

In frozen baked foods (e.g., frozen bread dough, egg tart shells), Nisin can inhibit spoilage bacteria in the dough without damaging the gluten network structure. After thawing and baking, the softness and elasticity of the products are not significantly different from those of the non-added group.

II. Key Factors Affecting Nisin Application Efficacy

1. Food Matrix Characteristics

pH value: Nisin exhibits the strongest activity in acidic environments (pH 3.0–6.0). For alkaline frozen foods (e.g., frozen soybean products), natural acidity regulators such as citric acid and lactic acid should be added to adjust the pH to 5.0–6.0, thereby enhancing antibacterial efficacy;

Component interference: Proteins and fats in frozen foods can bind to Nisin, reducing its free concentration. Therefore, in high-protein and high-fat frozen meat and aquatic products, the addition concentration of Nisin needs to be appropriately increased (30%–50% higher than that in ordinary pasta products).

2. Addition Method and Timing

Addition timing: It is recommended to add Nisin in the late stage of frozen food processing, before quick-freezing, to avoid excessive dilution or inactivation during high-temperature steaming and mixing. For example, frozen meatballs can be sprayed with Nisin solution after molding and before steaming to ensure uniform distribution on the product surface;

Addition method: Adopt the method of uniform spraying or mixing after dissolution to avoid uneven dispersion caused by direct addition of Nisin powder. For frozen fruits and vegetables, immersion treatment with Nisin solution can be used to form a surface antibacterial film.

3. Optimization of Compounding Scheme

Nisin has limited inhibitory effects on Gram-negative bacteria and molds when used alone, and its application efficacy can be significantly improved through compounding:

Nisin + Natamycin: Targets mold-prone frozen foods such as pastries and fruits/vegetables, achieving comprehensive control of "bacteria + molds";

Nisin + Natural Extracts: Compounding with tea polyphenols, rosemary extracts, etc., achieves dual antibacterial and antioxidant effects, which can delay oxidative browning of frozen foods (e.g., darkening of frozen meat products, browning of frozen fruits and vegetables).

III. Application Safety and Compliance

The application of Nisin in frozen foods complies with domestic and international food safety standards:

After human ingestion, Nisin is degraded into amino acids by proteases in the digestive tract, leaving no residues or cumulative toxicity. Its acute oral LD₅₀ is greater than 5 g/kg body weight, classifying it as a practically non-toxic substance;

China’s GB 2760-2014 National Food Safety Standard for the Use of Food Additives clearly specifies that the maximum usage amount of Nisin in frozen foods is 0.5 g/kg (calculated as pure product). The conventional application concentration is far below this limit, ensuring controllable safety.

Through selective antibacterial activity and synergistic preservation, Nisin can achieve core effects in frozen foods, including extending cold-chain shelf life, reducing chemical preservative dosage, and ensuring food safety, without affecting product texture and flavor. Its application requires optimizing the addition concentration and compounding scheme based on food matrix characteristics. In the future, with the development of technologies such as microencapsulation, the activity stability and antibacterial efficiency of Nisin will be further improved, providing strong support for the healthy and high-quality development of the frozen food industry.