Developing ‘Green Plastics’ For Use In Food Packaging

Researchers create a new biodegradable film that has the added potential to prolong shelf-life and reduce the health risks of packaged poultry products.

Polymers that are currently used for food packaging widely rely on petroleum-based products that are not biodegradable and can persist in our ecosystem, causing serious environmental issues. So researchers are aiming to develop new ‘green plastics’- biopolymer-based packaging materials that are degradable or compostable.

Poly-3-hydroxybutyrateco-3-hydroxyvalerate (PHBV) is a biodegradable biopolymer produced from renewable sources. It is considered as a sustainable green plastic with real potential to replace petroleum-based products as an eco-friendly alternative. However, some of its properties – including its high permeability to gases, aroma and water vapour, poor impact resistance and thermal degradation – currently render it unsuitable for food packaging applications.

Improving PHBV

One way that scientists are trying to enhance the qualities of PHBV is by blending it with other polymers. Using biopolymers such as chitosan, a natural polysaccharide derived from the shells of crustaceans, are preferred because of its biodegradability. The further addition of nanoparticles can lead to novel nanocomposites with improved mechanical properties and strong antibacterial activity.

In a new study, published in Applied Materials and Interfaces, researchers develop a biopolymer blend of PHBV and chitosan, fortified with zinc-oxide-silver nanocomposites (ZnO-Ag NCs), and demonstrate its potential to enhance the shelf life of packaged food products.1

The researchers used Thymus vulgaris (T. vulgaris) leaf extract as a stabiliser and reducing agent in a green hydrothermal decomposition reaction for the fabrication of ZnO-Ag NCs. They then prepared biopolymer blends of PHBV and chitosan, integrating the nanocomposites as a filler in film preparation. The new degradable biopolymer was fabricated using a modified solution casting technique.

Analysing ‘Food Packaging’ Qualities

The team then assessed the properties of the biopolymer nanocomposite films using several different characterisation methods. They also assessed their antibacterial activity against two food-borne bacteria (S. aureus and E. coli) and carried out a sensory analysis of chicken breasts wrapped in the films after 15 days of refrigeration.

After analysing their results, they determined the precise solvent ratio and ZnO-Ag NCs concentration that delivers a material with the most desirable properties for food packaging applications – including low migration rates, enhanced mechanical properties, and antimicrobial activity. 

The team used purified water generated from an ELGA laboratory water purification system for their experiments, minimising the risk of adding contaminants that may affect their results.

A Greener Alternative?

The results of this study demonstrate the excellent potential of this new bio-based polymer blend nanocomposite material to replace the petroleum-based, non-degradable plastics currently used for food packaging.

Generated using an eco-friendly bio-hydrothermal technique, these films also have demonstrable antibacterial activity – providing additional opportunities to lengthen shelf-life and preserve the safety of poultry products by reducing spoilage.

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Reference:

1. Zare, M. et al. Smart Fortified PHB-CS Biopolymer with ZnO-Ag Nanocomposites for Enhanced Shelf Life of Food Packaging. ACS Appl. Mater. Interfaces 2019 https://doi.org/10.1021/acsami.9b15724

Dr Alison Halliday
After completing an undergraduate degree in Biochemistry & Genetics at Sheffield University, Alison was awarded a PhD in Human Molecular Genetics at the University of Newcastle. She carried out five years as a Senior Postdoctoral Research Fellow at UCL, investigating the genes involved in childhood obesity syndrome. Moving into science communications, she spent ten years at Cancer Research UK engaging the public about the charity’s work. She now specialises in writing about research across the life sciences, medicine and health.