The Application of Nisin in Juice Preservation

Nisin, as a natural, highly effective, and safe bacteriocin, exhibits unique application value in fruit juice preservation. Innovations in its mechanism of action and application methods have effectively addressed microbial contamination issues in fruit juice processing and storage, while avoiding the destruction of nutrients and flavors caused by traditional heat treatment.

I. Inhibiting Spoilage and Pathogenic Bacteria in Fruit Juices

Fruit juices, rich in moisture, sugars, vitamins, and other nutrients, are susceptible to contamination by Gram-positive bacteria (such as lactic acid bacteria and bacilli), leading to spoilage, turbidity, or off-odors. Nisin has a high inhibitory effect on these bacteria through a mechanism that disrupts bacterial cell membrane permeability, causing leakage of intracellular substances and ultimately inhibiting bacterial growth or inducing death.

In acidic fruit juices (e.g., citrus juice, apple juice, with a pH typically below 4.5), Nisin remains more stable and can effectively inhibit the germination and proliferation of heat-resistant bacilli (such as Bacillus cereus), which are among the main culprits of spoilage in fruit juices stored at room temperature.

Nisin also exerts a synergistic inhibitory effect on pathogenic bacteria such as Listeria that may be present in freshly squeezed juices, reducing food safety risks. It is particularly suitable for preserving "cold-pressed juices" that have not undergone high-temperature sterilization.

II. Synergistic Enhancement with Other Preservation Technologies

The preservation effect of nisin used alone is limited, but combining it with physical, chemical, or other biological preservation technologies can significantly extend the shelf life of fruit juices, while reducing the dosage of each technology and minimizing impacts on juice quality:

Combination with mild heat treatment: Traditional high-temperature sterilization damages active components in juices, such as vitamin C and polyphenols. However, combining nisin with low-temperature heat treatment (60-70°C) can inhibit heat-resistant bacteria through nisin while reducing heat treatment time, preserving the color, flavor, and nutrients of the juice. For example, in grape juice preservation, adding 0.1-0.2g/kg Nisin followed by 65°C treatment for 30 seconds can extend the shelf life from 3 days at room temperature to over 15 days.

Compound use with natural preservatives: When nisin is compounded with plant extracts (e.g., cinnamaldehyde, rosemary extract) or organic acids (e.g., citric acid, sorbic acid), the synergistic effect of different antibacterial mechanisms expands the antibacterial spectrum (e.g., inhibiting some Gram-negative bacteria). For instance, in tomato juice, the combination of nisin and ε-polylysine significantly enhances the inhibitory effect on Escherichia coli and reduces the dosage of single preservatives, minimizing potential flavor impacts.

Integration with non-thermal processing technologies: In non-thermally processed juices (e.g., high-pressure processing [HPP], pulsed electric fields), nisin can serve as an auxiliary preservative to compensate for the insufficient inhibition of some spore-forming bacteria by non-thermal technologies. For example, adding Nisin to HPP-treated orange juice can extend its shelf life under 4°C refrigeration from 21 days to over 30 days, with almost no loss of taste or nutrients.

III. Application Strategies Adapted to Different Juice Types

Due to variations in composition, pH, and microbial communities among different juices, the application of Nisin requires targeted adjustments:

Highly acidic juices (pH < 3.5): Such as lemon juice and lime juice. The acidic environment itself inhibits most microorganisms, so nisin can be added in lower amounts (typically 0.05-0.1g/kg), mainly to inhibit acid-tolerant Gram-positive bacteria (e.g., lactococci) and prevent "fermented odors" in the juice.

Moderately acidic juices (pH 3.5-4.5): Such as apple juice and pear juice, which have a higher risk of microbial contamination. Thus, nisin dosage needs to be appropriately increased (0.1-0.3g/kg) and is often combined with other preservation technologies. For example, in apple juice, the synergy between nisin and carbon dioxide treatment (increasing CO₂ concentration in the juice) enhances preservation by inhibiting bacterial respiration.

Pulp-rich juices (e.g., mango juice, peach juice): Fibers in the pulp can easily adsorb Nisin, potentially reducing its effective concentration. Therefore, the dosage needs to be appropriately increased (0.2-0.4g/kg), or microencapsulation technology can be used to protect nisin activity, prevent its binding to pulp components, and enable slow release for long-term antibacterial effects.

IV. Advantages and Application Prospects

As a natural preservative, nisin meets consumers' demand for "clean labels." Its application in fruit juice preservation not only reduces the use of chemical preservatives but also retains the natural quality of juices. Currently, studies have applied Nisin to high-end products such as NFC (not from concentrate) juices and mixed fruit and vegetable juices. By optimizing dosage and synergistic technologies, the combination of "low-temperature sterilization+natural preservation" has been achieved, meeting market demand for fresh, healthy juices. Future research into nisin's antibacterial mechanism and advancements in encapsulation and sustained-release technologies will further expand its application scenarios in fruit juice preservation, offering more possibilities for quality upgrading in the juice industry.