The mechanism by which Nisin inhibits Bacillus

In the preservative system of canned foods, Nisin (nisin) is hailed as a "natural guardian." Its highly efficient inhibitory effect on Bacillus provides key protection for the long-term preservation of canned products. Bacillus, capable of forming highly stress-resistant spores, is the most challenging microorganism in canned foods—spores can withstand high-temperature sterilization and germinate into vegetative cells under suitable conditions, leading to canned food spoilage. Nisin exerts inhibitory effects throughout the entire cycle from spore germination to vegetative cell proliferation by precisely targeting the physiological characteristics of Bacillus, with its mechanisms analyzed as follows:

I. Early Intervention in the Spore Germination Stage

Bacillus spores have a dense spore wall and multi-layered structure (such as spore coat, cortex, and core), enabling them to resist extreme environments like high temperatures and dryness. Conventional canned sterilization processes (e.g., 121°C high-pressure sterilization) can kill most vegetative cells but cannot completely destroy the dormant structure of spores. When the canned environment (e.g., temperature, pH) is suitable, spores germinate into vegetative cells and reproduce rapidly, causing food spoilage.

Nisin’s inhibitory effect on spore germination is reflected in two aspects:

Blocking germination signal transmission: Spore germination requires external signals (e.g., specific amino acids, carbohydrates) to trigger internal metabolic activation. Nisin can bind to receptors on the spore surface, interfering with signal transmission and delaying or preventing spores from transitioning from a dormant state to an active state.

Destroying membrane integrity after germination: Even if some spores successfully germinate, the newly formed vegetative cell membranes are not fully mature and are far more sensitive to Nisin than mature bacteria. Nisin can quickly act on the cell membranes of these nascent vegetative cells, forming transmembrane channels by binding to lipid II (a key precursor for cell wall synthesis), leading to leakage of intracellular ions and nutrients, and ultimately inhibiting their growth and reproduction.

II. Efficient Killing Mechanism Against Vegetative Cells

For active Bacillus vegetative cells, Nisin’s antibacterial mechanism is more direct, mainly targeting bacterial cell membranes:

Membrane perforation and functional disorder: The hydrophobic regions of Nisin molecules can insert into the phospholipid bilayer of bacterial cell membranes, while the positively charged regions interact with negatively charged groups (e.g., phospholipids) on the membrane surface, forming stable transmembrane channels. This process increases membrane permeability, causing a large loss of intracellular potassium ions, ATP, and other important substances, while external harmful substances enter the cell, ultimately leading to bacterial death.

Inhibiting cell wall synthesis: Lipid II is not only a component of the cell membrane but also a key carrier for bacterial cell wall peptidoglycan synthesis. The specific binding of Nisin to lipid II blocks the peptidoglycan synthesis process, preventing bacteria from forming a complete cell wall and losing support and protection for the cell. This inhibitory effect is particularly significant during bacterial division, effectively preventing the growth of bacterial populations.

III. Synergistic Enhancement with Canning Processes

Nisin’s role in canned foods is not isolated; its synergy with processing techniques (e.g., sterilization temperature, pH adjustment) further enhances the inhibitory effect on Bacillus:

Reducing sterilization temperature and time: Traditional can sterilization requires high temperature and pressure (e.g., 121°C for 30 minutes) to kill spores, but this may cause loss of food flavor and nutrients. With the addition of Nisin, equivalent sterilization effects can be achieved at lower temperatures (e.g., 100-110°C) or shorter times—high temperatures enhance Nisin’s ability to penetrate cell membranes, while Nisin compensates for the incomplete spore killing by low-temperature sterilization, synergistically reducing the probability of spore survival.

Adapting to low water activity environments in cans: Canned foods, after sealed sterilization, typically have low water activity (Aw), an environment that inherently inhibits microbial growth. Nisin remains stable under low-moisture conditions (especially in acidic cans, such as tomato cans) and continues to exert antibacterial effects, forming a dual protection of "physical barrier + biological bacteriostasis."

Influence of pH and adaptability: Nisin is more stable in acidic environments (pH 2.0-6.0), and most canned foods (e.g., fruit cans, acidic meat cans) have pH values within this range, allowing it to fully exert its activity. For neutral or weakly alkaline cans (e.g., meat, bean cans), effective inhibition of Bacillus can still be achieved by appropriately increasing Nisin concentration or combining it with other natural preservatives (e.g., lysozyme).

IV. Application Advantages and Safety in Canned Foods

As a natural antimicrobial peptide, Nisin has significant advantages in canned food applications:

Targeted inhibition of Gram-positive Bacillus: Common spoilage bacteria in cans (e.g., Bacillus subtilis, Bacillus cereus) are all Gram-positive bacteria, and Nisin’s inhibitory effect on such bacteria is much stronger than on Gram-negative bacteria, precisely matching the main spoilage microbial spectrum of cans.

Natural safety and stability: Nisin is a polypeptide produced by lactic acid bacteria fermentation. It can be decomposed into amino acids by proteases in the human body, with no toxic residues, and does not cause drug resistance issues like chemical preservatives. In addition, although Nisin is partially inactivated during high-temperature sterilization of cans, the remaining active components can still exert continuous bacteriostatic effects during storage, making it particularly suitable for canned products requiring long-term preservation.

By targeting the spore germination stage, destroying vegetative cell membranes, inhibiting cell wall synthesis, and synergizing with processing techniques, Nisin precisely inhibits the growth and reproduction of Bacillus in canned foods. While reducing sterilization intensity and retaining food quality, it significantly extends the shelf life of cans. Its natural safety and efficient antibacterial properties make it a veritable "natural guardian" in the preservative system of canned foods, providing important support for the safety and sustainable development of the food industry.