Antimicrobial Biodegradable Food Packaging Based on Chitosan and Metal/Metal-Oxide Bio-Nanocomposites: A Review

Abstract

Finding a practical alternative to decrease the use of conventional polymers in the plastic industry has become an acute concern since industrially-produced plastic waste, mainly conventional food packaging, has become an environmental crisis worldwide. Biodegradable polymers have attracted the attention of researchers as a possible alternative for fossil-based plastics. Chitosan-based packaging materials, in particular, have become a recent focus for the biodegradable food packaging sector due to their biodegradability, non-toxic nature, and antimicrobial properties. Chitosan, obtained from chitin, is the most abundant biopolymer in nature after cellulose. Chitosan is an ideal biomaterial for active packaging as it can be fabricated alone or combined with other polymers as well as metallic antimicrobial particles, either as layers or as coacervates for examination as functional components of active packaging systems. Chitosan-metal/metal oxide bio-nanocomposites have seen growing interest as antimicrobial packaging materials, with several different mechanisms of inhibition speculated to include direct physical interactions or chemical reactions (i.e., the production of reactive oxygen species as well as the increased dissolution of toxic metal cations). The use of chitosan and its metal/metal oxide (i.e., titanium dioxide, zinc oxide, and silver nanoparticles) bio-nanocomposites in packaging applications are the primary focus of discussion in this review.

Keywords: active packaging; antimicrobial; chitosan; metallic nanomaterials.

Figure 1

(a) Chitosan production by partial deacetylation of chitin, (b,c) schematic of the Gram-negative and -positive bacteria cell membranes and proposed models for the action of chitosan on cell membrane nutrient flow blockage and damage. The polycationic nature of chitosan causes the release of intercellular components, binding to bacterial DNA (inhibition of mRNA), blocking the nutrient flow and chelation of essential metals (redrawn from Kravanja, Primožič, Knez, and Leitgeb, 2019) [64], (d) schematic of different shapes of metal nanomaterials (reproduced from Cheeseman et al., 2020) [53] and (e) a summary of potential passive antimicrobial mechanisms of metal nanomaterials (not to scale) including physical interactions, release of ions, and production of ROS (adapted from Cheeseman et al., 2020) [53].

Figure 2

UV-induced photocatalytic activity of ZnO in the presence of O₂ and H₂O with consequent production of superoxide and hydroxyl radicals.