The antibacterial effect of Nisin interacts with food components

Nisin, as a highly effective and safe natural antimicrobial peptide, does not exhibit its bacteriostatic activity in isolation. Instead, it interacts complexly with various components in food systems (such as proteins, fats, carbohydrates, salts, pH value, etc.). These interactions may enhance or weaken its bacteriostatic effect, and even alter its mechanism of action. A thorough understanding of these interactions is of great significance for optimizing the application of nisin in food.

I. Bacteriostatic Mechanism of Nisin: Targets and Action Characteristics

The core bacteriostatic mechanism of nisin is to kill Gram-positive bacteria by disrupting their cell membrane structure: the lanthionine residues in its molecule can specifically bind to lipid Ⅱ (a peptidoglycan precursor) on the bacterial cell membrane, forming transmembrane channels. This leads to the leakage of intracellular substances such as potassium ions and amino acids, ultimately causing bacterial death. This action is highly specific (mainly targeting Gram-positive bacteria) and rapid, but it also makes nisin susceptible to the influence of food matrix components.

II. Influence of Food Components on the Bacteriostatic Effect of Nisin

Interactions with Proteins and Polypeptides

Proteins (such as whey protein, casein, meat protein) or polypeptides in food may bind to nisin through non-covalent bonds (e.g., hydrogen bonds, hydrophobic interactions) to form complexes, thereby masking the active sites of nisin and reducing its ability to bind to bacterial cell membranes. For example, in high-protein cheeses or meat products, Nisin may bind to the hydrophobic sites of casein, resulting in a decrease in the concentration of free nisin and a weakening of the bacteriostatic effect.

However, some small-molecule peptides (such as lactoferrin peptides) may enhance the bacteriostatic activity of nisin through synergistic effects: these peptides can disrupt the integrity of bacterial cell membranes, helping nisin penetrate the cell membrane more easily, which is particularly effective against some nisin-resistant strains (such as certain lactic acid bacteria).

Impact of Fats and Lipids

Lipids (such as vegetable oils, animal fats) have a dual impact on nisin:

High levels of fat can encapsulate nisin molecules, hindering their migration to bacterial cells. Especially in emulsified systems (such as cream, ice cream), nisin may be trapped inside fat globules, reducing its bioavailability;

Certain unsaturated fatty acids (such as oleic acid) can act synergistically with nisin. By disrupting the lipid bilayer structure of bacterial cell membranes, they enhance nisin's ability to form transmembrane channels, improving the inhibitory effect on Gram-positive bacteria (such as Staphylococcus aureus).

Role of Carbohydrates and Dietary Fiber

Soluble carbohydrates (such as fructose, maltose) have little effect on nisin, but high concentrations of polysaccharides (such as starch, pectin) may increase the viscosity of the food system, slowing down the diffusion rate of nisin and indirectly reducing its contact efficiency with bacteria. For example, in convenience foods with high starch content, the bacteriostatic range of nisin may be limited to the surface, making it difficult to inhibit bacteria contaminating the interior.

Dietary fiber (such as cellulose, inulin) may bind to nisin through adsorption. Especially under acidic conditions, the carboxyl or hydroxyl groups of dietary fiber can form hydrogen bonds with the amino groups of nisin, causing some nisin to lose its activity.

Regulation by Salts, pH Value, and Water Activity

Salts: Low concentrations of sodium chloride (<3%) can enhance the bacteriostatic activity of nisin because sodium ions can promote the binding of nisin to bacterial cell membranes; however, high concentrations of salt (such as >5% in cured meat products) can cause nisin molecules to aggregate, reducing their solubility and thus weakening the effect.

pH value: Nisin is more stable under acidic conditions (pH 2-6), and positively charged nisin more easily binds to negatively charged bacterial cell membranes, resulting in a significant bacteriostatic effect; under neutral or alkaline conditions, nisin is prone to degradation or conformational changes, leading to a substantial decrease in activity.

Water activity (Aw): A low Aw environment (such as <0.9) reduces the solubility and diffusivity of nisin, but its bacteriostatic activity can be compensated by compounding with other preservatives (such as organic acids).

III. Synergistic Strategies to Enhance the Bacteriostatic Effect of Nisin

To address the adverse effects of food components on nisin, the following strategies can be used to optimize its application:

Compound Preservative Systems: Compound nisin with organic acids (such as lactic acid, citric acid), plant extracts (such as carvacrol, cinnamaldehyde), or other natural antimicrobials. The synergistic effect can offset the shortcomings of a single component. For example, organic acids can lower the pH value of food, enhance the stability of nisin, and their own bacteriostatic effect can expand the antibacterial spectrum (covering some Gram-negative bacteria).

Microencapsulation Technology: Use edible materials (such as sodium alginate, chitosan) to encapsulate nisin, reducing its direct contact with food components. At the same time, control its release under specific conditions (such as gastrointestinal environment or heating process) to improve targeted bacteriostatic efficiency.

Process Optimization: Adjust food processing parameters (such as sterilization temperature, homogenization pressure) to reduce the thermal degradation of nisin; or add nisin in the later stage of production to reduce its interaction time with other components and retain more activity.

IV. Research Prospects

Research on the interactions between nisin and food components needs to be further deepened: on the one hand, molecular simulation technology should be used to analyze the binding sites and conformational changes between nisin and components such as proteins and lipids, providing a theoretical basis for precise regulation; on the other hand, for complex food matrices (such as fermented foods, plant-based foods), it is necessary to establish a "component-activity" correlation model to guide the rational use of nisin. In the future, modifying the molecular structure of nisin through synthetic biology (such as enhancing its anti-adsorption ability) may fundamentally reduce the negative impact of food components on its bacteriostatic effect and expand its application scenarios.