The relationship between the antibacterial effect of Nisin and temperature

As a natural antimicrobial peptide produced by Lactococcus lactis, Nisin is widely used in food preservation and biological fresh-keeping. Its bacteriostatic effect is significantly influenced by temperature—this influence is reflected not only in the direct effect of temperature on the structural stability of Nisin molecules but also in the indirect regulation of temperature on the physiological state of target microorganisms. The specific analysis can be carried out from the following aspects:

I. Low-Temperature Range (Typically 0–15°C): Stable Bacteriostatic Effect of Nisin with Synergistic Antisepsis Enhanced by Low Temperature

In a low-temperature environment, the molecular structure of Nisin remains highly stable, and its active center (e.g., the cyclic structure containing thioether bonds) is not prone to denaturation or degradation. It can continuously bind to the cell membranes of target microorganisms (mainly Gram-positive bacteria such as Staphylococcus aureus and Listeria), exerting a bacteriostatic effect by disrupting the integrity of cell membranes and causing leakage of intracellular contents. At the same time, low temperature significantly reduces the metabolic rate of microorganisms, inhibits the activity of enzymes related to cell wall synthesis, protein expression, and energy metabolism, and increases the sensitivity of microorganisms to nisin. Strains that originally required a high concentration of Nisin for inhibition can now achieve the same bacteriostatic effect with a lower dose at low temperatures. For example, adding Nisin to refrigerated meat products (0–4°C) not only effectively inhibits the germination and reproduction of spore-forming bacteria but also extends the product shelf life to 1.5–2 times that under conventional refrigeration, without losing Nisin activity due to low temperature. In low-temperature dairy products (e.g., pasteurized milk, 2–6°C), Nisin works synergistically with low temperature to further inhibit the overgrowth of residual lactic acid bacteria, preventing premature spoilage of the product.

However, the slow metabolism of microorganisms at low temperatures may also cause some strains to enter a "dormant state," reducing the permeability of their cell membranes and to a certain extent decreasing the binding sites of Nisin on the membranes. In such cases, it is necessary to appropriately extend the action time or slightly increase the amount of Nisin added to ensure the full exertion of its bacteriostatic effect.

II. Medium-Temperature Range (Typically 20–40°C): High Bacteriostatic Activity of Nisin, Adapting to Most Food Processing and Storage Scenarios

The medium-temperature range is the "suitable interval" for Nisin’s bacteriostatic effect. This temperature range neither damages its active structure nor maintains the target microorganisms in an active physiological state—with moderate fluidity of the microbial cell membrane, nisin can more easily bind to receptors on the cell membrane (e.g., lipid II, a cell wall synthesis precursor) through diffusion, quickly blocking cell wall synthesis and disrupting the membrane structure, thereby inhibiting microbial growth in a short time. For example, in the processing of medium-temperature fermented foods (e.g., fermented sausages, 25–30°C), adding nisin can selectively inhibit the growth of miscellaneous bacteria (e.g., spoilage Staphylococcus) without affecting the normal metabolism of fermenting strains (e.g., lactic acid bacteria), ensuring both the formation of product flavor and the reduction of spoilage risks. In canned foods stored at room temperature (cooled to 25–35°C after sterilization), a low dose of Nisin can inhibit the germination of heat-resistant Gram-positive bacterial spores remaining after sterilization, avoiding quality problems such as "flat-sour spoilage."

It should be noted that if the medium-temperature environment persists for too long (e.g., more than 72 hours) and a small amount of moisture or oxygen is present, some microorganisms may develop low-level Nisin resistance through gene mutation (e.g., synthesizing membrane protective proteins to reduce Nisin binding). In such cases, it is necessary to combine other fresh-keeping technologies (e.g., mild acidification, oxygen barrier packaging) to maintain a stable bacteriostatic effect.

III. High-Temperature Range (Typically Above 50°C, Especially 80°C and Higher): Nisin’s Bacteriostatic Activity Shows a "First Stable, Then Decreasing" Trend with Rising Temperature, and Is Positively Correlated with Heating Time

(1) Medium-High Temperature Stage (50–80°C): Nisin’s Bacteriostatic Activity Remains Basically Stable Under Short-Term Heating, Enabling Synergistic Efficiency with Thermal Processing

In a medium-high temperature environment of 50–80°C, if the heating time is short (e.g., 10–30 minutes, similar to pasteurization or low-temperature baking in food processing), the molecular structure of nisin can still remain relatively stable, with its bacteriostatic activity loss usually below 10%. More importantly, at this temperature, the fluidity of microbial cell membranes increases significantly, and some membrane proteins undergo reversible denaturation, improving membrane permeability—this allows Nisin to more easily penetrate the cell membrane and exert its effect, forming a "heat-peptide synergistic bacteriostatic effect." For example, in heated soy products (e.g., tofu, heated at 60–70°C for 20 minutes), the synergy between Nisin and medium temperature can increase the killing efficiency of pathogenic bacteria such as E. coli and Salmonella by 2–3 orders of magnitude, without the need to increase the heating temperature or extend the heating time, thus reducing the loss of food nutrition and flavor. In baked foods (e.g., bread, short-term baking after proofing at 70–80°C), nisin can withstand the medium-high temperature during proofing and the initial baking stage, continuously inhibiting spoilage bacteria that may be present in the dough and extending the room-temperature shelf life of bread.

(2) High-Temperature and Ultra-High-Temperature Stage (Above 80°C, e.g., Boiling at 100°C, Autoclaving at 121°C): Long-Term Heating Causes Nisin Denaturation and Inactivation, Significantly Reducing Its Bacteriostatic Effect

When the temperature exceeds 80°C, especially under long-term high temperatures above 100°C, the molecular structure of Nisin undergoes irreversible denaturation—its α-helical structure is destroyed, thioether bonds break, and the active center disintegrates. This prevents it from binding to the cell membrane receptors of target microorganisms, leading to a sharp decrease or even complete loss of bacteriostatic activity. For example, in autoclaving at 121°C (common in canned food sterilization), if nisin is added before sterilization, its activity loss can reach more than 80% after 20–30 minutes of high-temperature treatment, basically losing its bacteriostatic ability. Even under boiling conditions at 100°C, after continuous heating of Nisin for 1 hour, the diameter of the inhibition zone against Staphylococcus aureus decreases from the initial 15–18 mm to 5–8 mm, and the bacteriostatic effect is nearly lost.

However, this high-temperature inactivation is "regulable": if nisin is added after food thermal processing (e.g., high-temperature sterilization) is completed and the temperature is cooled to below 60°C, the damage of high temperature to its activity can be completely avoided, allowing it to fully exert its bacteriostatic effect. This application strategy is particularly common in liquid foods after high-temperature sterilization (e.g., sterilized milk, plant protein beverages)—it can not only use high temperature to kill most microorganisms but also inhibit heat-resistant bacteria that may remain after sterilization through the subsequently added Nisin, forming a "double protection."

IV. Extreme Temperatures (Freezing Below 0°C or High Temperatures Above 150°C): Nisin’s Bacteriostatic Activity Is in a "Dormant" or Completely Inactivated State

In a frozen environment below 0°C (e.g., frozen foods at –18°C), the movement rate of Nisin molecules is greatly reduced due to low temperature, making it difficult to effectively bind to microbial cell membranes. Its bacteriostatic effect is basically in a "dormant" state, but its molecular structure is not destroyed. When the food is thawed and returned to room temperature or low temperature, Nisin can reactivate and continue to inhibit the recovery and reproduction of microorganisms during thawing. For example, when frozen meat products are stored at –18°C, nisin does not exert its bacteriostatic effect temporarily, but it can quickly inhibit the growth of Listeria in the meat after thawing (e.g., thawing at 0–4°C), reducing the risk of microbial contamination after thawing.

Under extreme high temperatures above 150°C (e.g., high-temperature frying, roasting), Nisin undergoes severe carbonization or complete decomposition. It not only loses its bacteriostatic activity but may also produce trace small-molecule degradation products. Therefore, it is not suitable for application in foods processed under such extreme high temperatures.

The bacteriostatic effect of nisin follows the rule of "stable synergy at low temperatures, efficient adaptation at medium temperatures, and denaturation inactivation at high temperatures." In practical applications, the timing and dosage of Nisin should be reasonably selected based on food processing technology (e.g., heating temperature, time), storage conditions (e.g., refrigeration, room temperature), and the characteristics of target microorganisms to maximize its bacteriostatic efficiency and ensure application safety.