# Atomic Layer Deposition of ZnO and ZnO/Cu Coatings for Fresh Food Packaging Application

## TL;DR

Researchers developed antimicrobial food packaging films using zinc oxide and copper coatings, which extended the shelf life of burrata cheese and turkey fillets by inhibiting bacterial growth.

## Contribution

The novel contribution is the application of atomic layer deposition to create ZnO and ZnO/Cu coatings on PET films for active food packaging.

## Key findings

- PET-ZnO/Cu films extended the shelf life of burrata cheese beyond 21 days compared to 19–20 days for controls.
- PET-ZnO/Cu films significantly delayed microbial growth and spoilage in turkey fillets, extending acceptability beyond two days.
- X-ray photoelectron spectroscopy confirmed the presence of ZnO and Cu2O/CuO in the coatings.

## Abstract

Active antimicrobial films based on polyethylene terephthalate (PET) were developed through atomic layer deposition (ALD) and plasma sputtering to obtain ZnO (≈15 nm) and ZnO/Cu (≈18 nm) coatings. Surface characterization by X-ray photoelectron spectroscopy confirmed zinc in ZnO form and copper as Cu2O/CuO, while mass spectrometry quantified approximately 10 µg/cm2 of Zn in both samples and about 130 ng/cm2 of Cu in the ZnO/Cu films. The antimicrobial performance of the coatings was evaluated on burrata cheese and turkey fillets stored under refrigeration, assessing microbial growth and sensory quality over time. The films exhibited different effects depending on food type and the initial contamination levels. On burrata cheese, PET-ZnO moderately extended the shelf life by inhibiting Pseudomonas spp., while PET-ZnO/Cu further enhanced preservation. Cheese packaged with PET-ZnO/Cu remained acceptable for over 21 days compared to 19–20 days for the controls. More pronounced effects were observed in turkey fillets, characterized by a higher initial contamination. In control samples, Staphylococcus spp. rapidly proliferated, leading to spoilage within one day. Both active films significantly delayed microbial growth and sensory decay, with PET-ZnO/Cu providing the best performance, extending acceptability beyond two days compared to less than one day for the controls.