Incorporating an antimicrobial protein onto polyethylene terephthalate (PET) presents the “main characteristics” to be used in active food packaging.
Lysozyme is a hydrolytic enzyme that plays an important role in preventing bacterial infection, especially for Gram-positive bacteria, said Corradini et al.
Active coatings were realized with the sol–gel methodology employing polyvinyl alcohol (PVOH) and tetraethoxysilane (TEOS) as reagents.
Stable sol–gel hybrid films were prepared by dip-coating on PET substrates previously activated by cold plasma and were characterized by Fourier transform infrared spectroscopy (FTIR) spectroscopy and Atomic Force Microscopy.
Low temperature plasma treatment of PET supports was used for surface modification and for the improvement of its adhesive properties.
Lysozyme antimicrobial properties
Activity of lysozyme within the sol–gel modified PET was shown by assay in agar plates containing cell walls of Micrococcus lysodeikticus.
The appearance of clear inhibition zones both at the contact area and around the plates of coated PET was observed, found the study.
It is also possible to modulate the release kinetics by modifying parameters such as temperature and lysozyme concentration.
Natural antimicrobials focus
There is growing attention on natural antimicrobial agents that are safe for the food industry, including bacteriocins such as nisin, pediocin and lacticin, and antimicrobial enzymes like lysozyme, lactoperoxidase, chitinase and glucose oxidase as biopreservative agents.
The PVOH/TEOS ratio (w/w) was varied from 5% to 35% to obtain a sol which could give an excellent adhesion to the substrate and a good uniformity in the coating structure. The best conditions were using a PVOH/TEOS ratio of 20% (w/w).
This mixture was found to be stable in water, in presence of ethanol until 25%, and in a pH range between two and seven, which covers the values of most of the food products.
Release tests were carried out verifying that lysozyme migrated from the film to water solution with a temperature-dependent rate.
The enzymatic activity kinetics of the solution of lysozyme released showed that the enzyme still kept its activity after being incorporated onto the film.
Results show that the incorporation of lysozyme into the sol–gel modified PET do not lead to a loss of activity of the enzyme, and suggest significant potential for the use of these packaging materials.
“The obtained films present the main characteristics to be proposed as possible innovative antimicrobial food packaging. Further studies are encouraged to be performed in order to test this new active packaging on food products,” concluded the researchers.
Source: Journal of Food Engineering, volume 119, issue 3 pages 580-587
Online ahead of print, doi: 10.1016/j.jfoodeng.2013.05.046
“Antimicrobial films containing lysozyme for active packaging obtained by sol–gel technique”
Authors: Claudio Corradini, Ilaria Alfieri, Antonella Cavazza, Claudia Lantano, Andrea Lorenzi, Nicola Zucchetto and Angelo Montenero