Functionalized Polymeric Materials with Bio-Derived Antimicrobial Peptides for "Active" Packaging

Abstract

Food packaging is not only a simple protective barrier, but a real "active" component, which is expected to preserve food quality, safety and shelf-life. Therefore, the materials used for packaging production should show peculiar features and properties. Specifically, antimicrobial packaging has recently gained great attention with respect to both social and economic impacts. In this paper, the results obtained by using a polymer material functionalized by a small synthetic peptide as "active" packaging are reported. The surface of Polyethylene Terephthalate (PET), one of the most commonly used plastic materials in food packaging, was plasma-activated and covalently bio-conjugated to a bactenecin-derivative peptide named 1018K6, previously characterized in terms of antimicrobial and antibiofilm activities. The immobilization of the peptide occurred at a high yield and no release was observed under different environmental conditions. Moreover, preliminary data clearly demonstrated that the "active" packaging was able to significantly reduce the total bacterial count together with yeast and mold spoilage in food-dairy products. Finally, the functionalized-PET polymer showed stronger efficiency in inhibiting biofilm growth, using a Listeria monocytogenes strain isolated from food products. The use of these "active" materials would greatly decrease the risk of pathogen development and increase the shelf-life in the food industry, showing a real potential against a panel of microorganisms upon exposure to fresh and stored products, high chemical stability and re-use possibility.

Keywords: active packaging; antimicrobial peptides; food shelf-life; foodborne pathogens; plastic materials.

Figure 1

Process diagram for the modification of the PET surface by activation with radiofrequency cold plasma using oxygen as gas and coupling of the synthetic peptide 1018K6 with antibacterial properties.

Figure 2

WCA measured on pristine PET (a), oxygen plasma activated-PET (b) and 1018K6-functionalized PET (c). The measurements were performed on five samples in duplicate.

Figure 3

FTIR spectrum of the PET sample before radiofrequency cold plasma treatment (a); after plasma treatment (b); after 1018K6 bio-conjugation (c).

Figure 4

Immobilization yield (%) of 1018K6 on PET surface determined by reverse-phase HPLC chromatography on a C18 column after the coulping reaction (24 h). Pre-activated PET surfaces by plasma were incubated for 24 h with 1018K6 (50 µM) in PBS pH 7.0. The solutions recovered after incubation were further analysed. The peptide solution placed in contact with the pre-activated surface at time 0 (t = 0) was used as control. The chromatograms are representative of three independent experiments. Insert: Calibration curve of the C18 column obtained using different 1018K6 concentrations.

Figure 5

Immobilization yield expressed as nmol of bound 1018K6 per cm² of PET surface as function of peptide concentration. The dose-response curve has been built by using the Holliday model. Data are expressed as means ± standard deviations. Standard deviation values lower than 5% are not shown.

Figure 6

Release analysis of 1018K6 from functionalized PET performed by reverse-phase HPLC chromatography on a C18 column after 24 h incubation at 4 °C in mozzarella brine (a) or pure water (b). After incubation, the solutions were recovered and injected on C18. The solution in contact with 1018K6-PET at time 0 (t = 0) and 1018K6 peptide (50 μM) were used as controls.

Figure 7

Boxplot of the inhibition activity of the biofilm production of Listeria monocytogenes by PET and 1018K6-PET. Average OD measurements of crystal violet-stained biofilms are shown with error bars representing the standard deviation.