The Application of Nisin in the Preservation of Fruits and Vegetables

As a natural antimicrobial peptide, nisin has gradually transitioned from laboratory research to industrial exploration in the field of fruit and vegetable preservation. This is attributed to its high-efficiency inhibitory effect on Gram-positive bacteria (G⁺), safety (it is digestible and degradable in the human body and has been approved as a food additive in many countries), and the characteristic of not damaging the natural flavor and nutritional components of fruits and vegetables. After harvest, fruits and vegetables are prone to microbial infection and subsequent spoilage due to carrying field microorganisms (e.g., Bacillus, Staphylococcus), vigorous respiration, and vulnerable epidermal structures (for instance, G⁺ bacteria are among the auxiliary pathogens causing gray mold in strawberries and blue mold in citrus). Meanwhile, the contradiction between the residue risk of traditional chemical preservatives (e.g., thiabendazole) and consumers’ demand for "natural preservation" has become increasingly prominent. Nisin’s properties precisely address these pain points, providing a green solution for fruit and vegetable preservation.

In terms of application mechanisms and core value, nisin’s role in fruit and vegetable preservation is primarily achieved through targeted bacteriostasis and synergistic protection.

At the targeted bacteriostasis level,nisin binds to lipid Ⅱ (a precursor substance for cell wall synthesis) on the cell membrane of G⁺ bacteria, forming transmembrane channels. This leads to the leakage of small-molecule substances such as potassium ions and amino acids from the bacteria, ultimately causing bacterial lysis and death. This process exhibits significant effects on major post-harvest spoilage-causing G⁺ bacteria in fruits and vegetables—such as pectinobacteria (which cause soft rot in tomatoes) and Bacillus (which leads to rot in asparagus). It is particularly effective in inhibiting bacterial spores that are resistant to low temperatures and dry conditions, effectively reducing spoilage caused by spore germination during low-temperature storage (e.g., refrigeration at 0–4℃) or room-temperature transportation of fruits and vegetables.

At the synergistic protection level, nisin can complement the natural defense system of fruits and vegetables. After harvest, fruits and vegetables secrete natural antibacterial components such as phytoalexins and phenolic substances, and Nisin can reduce the drug resistance of spoilage-causing bacteria to these components, enhancing the self-stress resistance of fruits and vegetables. Additionally, unlike chemical preservatives, nisin does not inhibit the normal respiratory metabolism of fruits and vegetables (e.g., it has no significant impact on ethylene release from apples and pears). This allows it to maintain the freshness of fruits and vegetables while reducing nutrient loss—for example, the retention rate of vitamin C and dietary fiber is 5%–10% higher than that with traditional preservation methods.

However, the large-scale application of nisin in fruit and vegetable preservation still faces three core challenges.

The first is its limited antimicrobial spectrum: Nisin has weak inhibitory effects on Gram-negative bacteria (G⁻, such as Escherichia coli and Erwinia commonly found on the surface of fruits and vegetables), yeasts, and molds. Yet these microorganisms are often the main causes of fruit and vegetable spoilage (e.g., gray mold in strawberries caused by molds and rot in cucumbers caused by G⁻ bacteria). Using nisin alone cannot achieve comprehensive preservation, and other technologies must be combined to make up for this shortcoming.

The second challenge is adaptability of application forms: Nisin is a water-soluble peptide. When directly sprayed on the surface of fruits and vegetables, it tends to adhere unevenly due to the waxy layer and hydrophobic structure of the fruit/vegetable epidermis. During storage, it is easily diluted by the juice secreted by the fruits/vegetables themselves or degraded by proteases in the environment, resulting in a short duration of antibacterial effect (usually only 3–5 days, far shorter than the 10–15 days required for fruit and vegetable preservation). If soaking is used as the application method, it increases water consumption and subsequent drying costs, making it unsuitable for leafy vegetables (e.g., spinach, lettuce) that are prone to water absorption and softening.

The third challenge is the impact of environmental factors: Temperature, humidity, and pH value during fruit and vegetable preservation significantly affect the stability of nisin. High temperatures (e.g., pre-cooling treatment above 60℃) can cause its structural denaturation and inactivation; high-humidity environments accelerate its hydrolysis; and excessively acidic (e.g., the surface of citrus fruits with pH < 2.5) or excessively alkaline (e.g., the surface of some melon fruits with pH > 8.0) environments also reduce its antibacterial activity. These factors limit its versatility across different types of fruits/vegetables and under various storage conditions.

To overcome these bottlenecks, current research and practice are advancing mainly in two directions: the construction of composite preservation systems and the optimization of application formulations.

In the construction of composite preservation systems, the most common strategy is compounding nisin with other natural antibacterial components. For example, combining nisin with plant extracts (e.g., rosemary extract, tea polyphenols)—the phenolic substances in plant extracts can disrupt the outer membrane structure of G⁻ bacteria, allowing Nisin to enter the bacterial cells and exert its effect, thereby expanding the antimicrobial spectrum. Meanwhile, their synergy can reduce the dosage of each component (e.g., the addition amount of nisin can be reduced from 0.1 g/kg to 0.05 g/kg), lowering costs and avoiding potential epidermal residue issues caused by excessive single-component use. Nisin can also be compounded with organic acids (e.g., citric acid, lactic acid)—organic acids can adjust the pH value on the surface of fruits and vegetables to the optimal activity range of nisin (pH 2–6) and enhance its permeability to cell membranes, improving antibacterial efficiency. This scheme has been validated as effective in preserving berries such as strawberries and blueberries, reducing the spoilage rate from over 30% to below 10%. In addition, the combination of nisin with physical preservation technologies has become a research hotspot. For instance, when combined with modified atmosphere packaging (MAP), the modified atmosphere environment (low oxygen, high carbon dioxide) can inhibit the respiration of fruits and vegetables while reducing the metabolic activity of spoilage-causing bacteria, making nisin’s antibacterial effect more durable. When combined with cold plasma treatment, the reactive oxygen species and reactive nitrogen species generated by plasma can damage microbial cell walls, forming a "physical+biological" dual sterilization effect. This is particularly suitable for perishable leafy vegetables such as broccoli and celery, extending their preservation period by 2–3 times.

In the optimization of application formulations, microencapsulation technology is currently the most mature direction. By encapsulating nisin with edible wall materials (e.g., chitosan, maltodextrin, sodium alginate) to form microcapsules, the problems of poor adhesion and easy degradation of nisin can be solved. Wall materials like chitosan have good film-forming properties and can form a uniform protective film on the surface of fruits and vegetables. This not only fixes nisin but also reduces water evaporation and oxygen contact, delaying the senescence of fruits and vegetables. At the same time, the wall materials can isolate nisin from external factors such as proteases and high temperatures, protecting its activity and enabling controlled release. For example, in tomato preservation, the antibacterial effect of microencapsulated Nisin can be extended from 5 days to 15 days, and the retention rates of tomato firmness and soluble solid content are significantly improved. In addition, incorporating nisin into edible coatings (e.g., starch-glycerol coatings, pectin coatings) is another important approach. These coatings not only provide protective effects similar to microcapsules but also allow component adjustments based on the type of fruits/vegetables (e.g., adding lemon essential oil for citrus fruits to enhance anti-mold effects), offering stronger adaptability. Small-scale applications of this technology have been realized in pome fruits such as apples and pears.

In summary,nisin has unique advantages in fruit and vegetable preservation, including "natural safety, targeted bacteriostasis, and no flavor damage," making it particularly suitable for preserving high-end fruits and vegetables (e.g., organic strawberries, imported cherries). Although issues such as antimicrobial spectrum and formulation adaptability still need to be addressed, with the maturity of composite preservation technologies and the reduction in microencapsulation costs,nisin is expected to gradually replace some chemical preservatives and become one of the core green additives in the post-harvest preservation field of fruits and vegetables. Its application potential in scenarios such as cold chain logistics and home preservation will also be further unleashed in the future.