Ultraviolet-activated Titanium Dioxide Nanocomposite Polymer Films: Characterization and Antimicrobial Efficacy against Escherichia coli O157:H7

Introduction: Prepackaged minimally processed food poses a microbiological safety concern due to the high risk of cross-contamination during processing. Titanium dioxide (TiO₂) nanoparticles (NPs) are photocatalysts that have shown great effectiveness in inactivation of pathogenic microorganisms owing to strong oxidizing capabilities during photocatalytic reactions. Incorporating TiO₂ NPs into packaging material may effectively inhibit bacterial growth in prepackaged food products.

Purpose: The objectives of this work were to develop plastic films incorporating TiO₂ NPs using different polymer materials, to perform characterization of these films, and to determine their antimicrobial activity against Escherichia coli O157:H7.

Methods: Biodegradable polymers (cellulose acetate (CA), polycaprolactone (PCL) or polylactic acid (PLA)) and TiO₂ nanoparticles (1, 3, and 5%) were mixed in organic solvent and casted in glass petri dishes. Optical and physical properties of the films were assessed by measuring the thickness, color, ultraviolet-visible (UV-Vis) absorption spectra and UV-A transmission. Photocatalytic activity of the films was examined by degradation of methylene blue. To test the antimicrobial activity of the films against E. coli O157: H7, bacterial inoculum was added to the film surface and a covered with a transparent plastic film (4 by 4 cm²). Inoculated films were placed under UV-A light (intensity at 1.30±0.15 mW/cm²) for two hours.

Results: TiO₂ NPs incorporated polymer films presented uniform TiO₂ distribution and even color. PCL and CA films with 5% TiO₂ were able to degrade methylene blue in solution by 72% and 53%, respectively; however, PLA films did not show significant photocatalytic activity. CA film incorporated with 5% TiO₂ NPs had the highest bactericidal activity and achieved 1.82 log CFU/ml reduction. Whereas, PCL and PLA composite films did not show significant bactericidal property (less than 0.6 log reduction).

Significance: This study indicated that UV-activated TiO₂ CA films could potentially be used to inactivate microorganisms in packaging during storage and distribution.