Nisin is compounded with nanomaterials

Nisin is a naturally bioactive antimicrobial peptide. Smart packaging films prepared by compounding nisin with nanomaterials hold significant application value in food preservation and other fields. Below is an overview of their preparation methods and antibacterial properties.

I. Preparation Methods

1. Coaxial Electrospinning Method

A research team from Fujian Agriculture and Forestry University employed this method to fabricate a novel core-shell structured nanofiber film, using a pullulan/nanochitin-nisin composite as the core layer and gelatin-zein as the shell layer.

First, a nanochitin-nisin composite was prepared. Nanochitin and nisin form a stable composite through electrostatic interactions and hydrogen bonding. For instance, surface-deacetylated chitin nanofibers (S-ChNF) bind to nisin primarily via hydrogen bonding, while oxidized chitin nanowhiskers (O-ChNW) interact with nisin mainly through electrostatic forces—with hydrogen bonding also present in both cases.

Next, parameters of the spinning solution (e.g., viscosity, electrical conductivity, surface tension) were optimized. Under the conditions of a voltage of 21 kV, a needle-collector distance of 15 cm, and a flow rate of 0.10 mL/h for both core and shell solutions, a core-shell nanofiber film with uniform morphology and intact structure was successfully prepared.

2. Solution Mixing and Coating Method

A chitosan solution containing nisin was prepared via the sol-gel method, then coated onto cellulose paper using the dip-coating technique to produce a chitosan-cellulose composite packaging film.

For example, chitosan solutions containing nisin (500 and 1000 μg/mL) were coated onto cellulose paper. Scanning electron microscopy (SEM) images showed that the chitosan solution coated uniformly on the cellulose paper. Fourier transform infrared (FTIR) spectroscopy analysis confirmed that nisin was successfully incorporated and bound in the bilayer film.

3. Nanogel Preparation Method

First, γ-PGA-CS-Nisin Z-lauroyl arginine ethyl ester (LAE) nanogels were prepared: chitosan and γ-PGA were dissolved in an aqueous solution of lauroyl arginine ethyl ester hydrochloride to obtain a γ-PGA-CS-LAE solution; nisin was dissolved in aqueous hydrochloric acid; the two solutions were mixed, stirred, and the pH was adjusted to 6.0 to form nanogels.

Subsequently, the nanogels were blended with a gelatin solution to serve as the core-layer spinning solution, while a chitosan solution blended with a polycaprolactone solution was used as the shell-layer spinning solution. A core-shell composite nanofiber film was fabricated via coaxial electrospinning.

II. Antibacterial Properties

1. Inhibition of Gram-Positive and Gram-Negative Bacteria

The core-shell structured nanofiber film composite of nisin and nanochitin exhibits excellent antibacterial effects against both Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), with inhibition zone diameters of 19–20 mm and 17–18 mm, respectively.

In practical applications, when sea bass fillets were packaged with this film and refrigerated at 4°C for 15 days, the total volatile basic nitrogen (TVB-N), total viable count (TVC), and thiobarbituric acid reactive substances (TBARS) content were reduced by approximately 50%, 90%, and 75%, respectively, compared to the monaxial film packaging group—significantly delaying fish spoilage and lipid oxidation.

2. Inhibition of Listeria

Chitosan-cellulose composite films containing 1000 μg/mL nisin completely inactivated the initial population (approximately 5 log₁₀ cfu/g) of Listeria monocytogenes on the surface of ultrafiltered white cheese after 14 days of storage at 4°C.

Additionally, packaging films composed of nisin and cellulose nanofibers also inhibit Listeria innocua. After contact with hamburgers, the number of Listeria decreased by approximately 1.3 log cycles immediately, and further decreased by about 1.4 log cycles after 2 days of storage.

3. Broad-Spectrum Antibacterial Activity

Nisin was loaded into rhamnolipid-functionalized nanofillers (rhamnolipid particles), which were then embedded in hydroxypropyl methylcellulose and κ-carrageenan-based packaging films.

The resulting films exhibit broad-spectrum antibacterial activity against Listeria monocytogenes, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, with bacterial counts reduced by up to 4.5 log units.