The Application of Nisin in fast food

Nisin, a class of small-molecular peptide antimicrobial substances produced by the fermentation of Streptococcus lactis, is a natural food preservative. Its antibacterial spectrum is primarily targeted at Gram-positive bacteria (e.g., Staphylococcus, Streptococcus, Bacillus), and it can effectively inhibit the germination and proliferation of bacterial spores. Boasting advantages such as high safety, good thermal stability, no residues, and no impact on food flavor, Nisin aligns with the development trend of fast food characterized by "convenience, safety, low salt and low fat", and demonstrates significant application value in fried, baked, and ready-to-eat fast foods. The specific research and application practices are as follows:

I. Core Application Scenarios and Mechanisms of Action of Nisin in Fast Food

The common pain points of fast food include susceptibility to spore-forming bacteria contamination after processing, short shelf life, and inactivation of chemical preservatives due to high-temperature processing. Nisin addresses these issues by targeting and inhibiting pathogenic microorganisms, with varying application priorities across different fast food categories.

1. Fried Fast Food: Inhibiting Spore-Forming Bacteria Proliferation to Extend Shelf Life

For fried fast foods such as fried chicken, French fries, and fried dough sticks, high temperatures during processing can kill most vegetative cells, but the spores of spore-forming bacteria (e.g., Bacillus cereus) exhibit extremely strong heat resistance and can survive frying temperatures. After cooling, these spores germinate into vegetative cells under food storage conditions, causing food spoilage and even foodborne diseases. The mechanism of action of Nisin involves binding to lipid II on bacterial cell membranes, disrupting membrane integrity, inhibiting cell wall synthesis, as well as penetrating the cortex structure of spores to prevent spore germination. In fried fast food, Nisin is typically applied via spraying or dipping after frying (to avoid activity loss caused by high-temperature frying), with a concentration range of 50–200 IU/g sufficient to effectively inhibit pathogenic bacteria such as Bacillus cereus and Staphylococcus aureus. For instance, after spraying the surface of fried chicken with a Nisin-containing preservative solution, its shelf life under refrigeration at 4℃ can be extended from 3 days to 7 days, with the total bacterial count reduced by 2–3 orders of magnitude, while maintaining the crispy texture and flavor of the fried chicken.

2. Ready-to-Eat Rice and Noodle Fast Food: Replacing Chemical Preservatives to Improve Safety

Traditional production processes for ready-to-eat rice and noodle fast foods such as instant noodles, ready-to-eat rice, and self-heating boxed meals often involve adding chemical preservatives like potassium sorbate and sodium dehydroacetate, which have sparked health concerns related to "high salt and high preservative content". Nisin can be used as a natural preservative to partially or completely replace chemical preservatives, with its advantages reflected in two aspects:

Synergistic Antibacterial Enhancement: When used in combination with chelating agents such as EDTA and citric acid, Nisin can disrupt the outer membrane structure of Gram-negative bacteria, expanding its antibacterial spectrum to cover some Gram-negative bacteria (e.g., Escherichia coli) and reducing the dosage of chemical preservatives. For example, adding a compound system of Nisin (100 IU/g) and citric acid (0.1%) to instant noodle seasoning packets can extend their room-temperature shelf life from 6 months to 12 months, while reducing the amount of chemical preservatives by more than 50%.

Compatibility with Microwave/High-Temperature Reheating Processes: Nisin can retain over 80% of its activity after high-temperature sterilization at 121℃, making it suitable for the high-temperature sterilization process of self-heating boxed meals. After sterilization, it can continuously inhibit the germination of spore-forming bacteria in rice, preventing microbial proliferation caused by temperature fluctuations during the self-heating process.

3. Baked Fast Food: Inhibiting Mold and Bacterial Contamination to Ensure Food Quality

Baked fast foods such as hamburger buns, bread, and egg tart shells are susceptible to mold (e.g., Penicillium, Aspergillus) and bacterial contamination during storage, leading to issues like mold growth and off-odors. Although Nisin has no direct inhibitory effect on molds, it can indirectly improve the microbial environment of baked foods by inhibiting Gram-positive bacteria (e.g., acid-producing bacteria) that are necessary for mold growth. Meanwhile, when compounded with natamycin (an anti-mold preservative), it can achieve comprehensive control of "bacteria + molds". Studies have shown that adding a compound of Nisin (80 IU/g) and natamycin (50 mg/kg) to the dough during hamburger bun production results in products that show no mold growth after 15 days of room-temperature storage, with total bacterial counts far below the national standard limits, and no significant changes in the texture characteristics such as softness and elasticity of the bread.

4. Prepared and Conditioned Fast Food: Reducing Cold Chain Dependence to Lower Logistics Costs

Traditional prepared fast foods such as ready-to-cook dishes and conditioned meat products rely on full cold chain to control microbial growth, resulting in high logistics costs. Nisin can serve as a "cold chain auxiliary preservative"; when added after sterilization of prepared dishes, it can inhibit microbial proliferation even under short-term room-temperature transportation conditions where the cold chain is interrupted. For example, adding Nisin (150 IU/g) to prepared braised pork allows the product to maintain total bacterial counts within food safety standards after 5 days of storage at 25℃, whereas the non-added group exceeds the standard after 3 days of storage. This characteristic can significantly reduce the cold chain logistics costs of prepared fast foods.

II. Key Factors Affecting the Application Effect of Nisin in Fast Food

The antibacterial effect of Nisin is not fixed; it is regulated by factors such as addition method, concentration, food matrix characteristics, and compound system, requiring optimized application schemes based on the characteristics of different fast food categories.

1. Addition Method and Timing

For fried fast food, post-frying addition (spraying or dipping after frying) is required to avoid Nisin activity loss caused by high-temperature frying (180–200℃).

For ready-to-eat rice and noodle fast food, addition during processing (e.g., dough kneading, sauce preparation stages) is suitable, leveraging stirring during processing to achieve uniform dispersion of Nisin.

For baked fast food, the timing of addition must be controlled; it should be added after dough fermentation and before baking to prevent Nisin degradation by lactic acid bacteria during fermentation.

2. pH and Composition of Food Matrix

Nisin exhibits higher stability and stronger antibacterial activity in acidic environments (pH 3.0–6.0), while it is prone to hydrolysis and inactivation in alkaline environments. Therefore, in alkaline fast foods (e.g., fried dough stick dough), citric acid should be added to adjust the pH to 5.0–6.0 to ensure Nisin activity.

Components such as proteins and fats in fast food can bind to Nisin, reducing its free concentration. Thus, in high-protein and high-fat fast foods (e.g., fried chicken, braised pork), the addition concentration of Nisin needs to be appropriately increased (30%–50% higher than that in ordinary rice and noodle fast foods).

3. Synergistic Effect of Compound Systems

The antibacterial spectrum of Nisin is limited when used alone, and compounding it with other preservatives and natural extracts can significantly enhance its efficacy:

Compound with EDTA and Citric Acid: Disrupts the outer membrane of Gram-negative bacteria to expand the antibacterial spectrum.

Compound with Natamycin and ε-Polylysine: Achieves broad-spectrum control of bacteria and molds.

Compound with Plant Extracts (e.g., Tea Polyphenols, Carvacrol): Enhances dual effects of antioxidation and antibacterial activity, while improving the nutritional value of fast food.

III. Safety and Regulatory Basis of Nisin Application in Fast Food

As a natural preservative, the safety of Nisin has been globally recognized:

After human ingestion, Nisin is degraded into amino acids by proteases in the digestive tract and does not accumulate in the body. Its acute oral LD₅₀ is greater than 5 g/kg body weight, classifying it as practically non-toxic.

The Codex Alimentarius Commission (CAC), the U.S. Food and Drug Administration (FDA), and China’s National Health Commission have all approved Nisin as a food preservative. 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 various foods is 0.5 g/kg (calculated as pure product). The conventional addition concentration of Nisin in fast food is far below this limit, ensuring controllable safety.

IV. Challenges and Future Directions of Application Research

Currently, the application of Nisin in fast food still faces several unresolved issues:

Limited Antibacterial Spectrum: Its inhibitory effect on Gram-negative bacteria and molds is weak, necessitating reliance on compound systems to compensate.

High Cost: The fermentation production cost of Nisin is higher than that of chemical preservatives, limiting its large-scale application in low-priced fast food.

Activity Stability: In high-salt and high-sugar fast food seasoning systems, the activity of Nisin is susceptible to adverse effects.

Future research directions will focus on improving Nisin yield through genetically engineered strains, developing Nisin microencapsulation technology to enhance stability, and screening high-efficiency compound systems, aiming to further reduce application costs and expand the application scenarios of Nisin in fast food.

With its natural, safe, and highly efficient antibacterial properties, Nisin can achieve multiple objectives in fast food, including extending shelf life, replacing chemical preservatives, and reducing cold chain dependence, aligning with the health and convenience development needs of the modern fast food industry. By optimizing addition methods, compound systems, and concentration control, Nisin can exert optimal antibacterial effects in different types of fast food. In the future, with advances in production technology, the application potential of Nisin in fast food will be further unlocked.