Phage-loaded alginate films and coatings for biofilm inhibition and control in food packaging

Food packaging plays a crucial role in ensuring food safety; however, microbial contamination, particularly from biofilm-forming bacteria, remains a challenge. This study explores the use of sodium alginate-based films and coatings loaded with a bacteriophage cocktail targeting Escherichia coli and Pseudomonas fluorescens to mitigate biofilm formation in food packaging, with a focus on cheese products. The coatings were applied to parchment paper, polystyrene, and films prepared with sodium alginate loaded with bacteriophages, and assessed for their antimicrobial efficacy. Biofilm inhibition and control experiments were performed by applying phage-containing films/coatings either immediately after bacterial inoculation or after 24 h of biofilm formation. Samples were then incubated and analyzed for viable cells, biomass, metabolic activity, and live/dead bacterial ratio. Phage-infused films and coatings demonstrated significant antimicrobial activity, effectively reducing biofilm biomass. Biofilm inhibition experiments were more pronounced in phage-loaded films, achieving up to a 1.7-log reduction in viable cells and a 70.8 % decrease in biomass for E. coli, as well as a 2.7-log reduction in viable cells and a 66.62 % decrease in biomass for P. fluorescens. In biofilm control experiments, the phage-loaded materials also exhibited inhibitory effects, with a maximum CFU reduction of 1.39 logs compared to the untreated control for P. fluorescens and 0.72 logs compared to the untreated control for E. coli in films. Biomass reduction reached 42 % for E. coli films and 19 % for P. fluorescens films. Confocal microscopy and COMSTAT analysis confirmed a reduction in biofilm thickness and a significant decrease in live bacterial cells in treated samples. When applied to cheese, phage-loaded materials maintained strong antimicrobial activity over 24 h, with parchment paper achieving log reductions of 2.5 and 2.3 compared to the untreated control for P. fluorescens and E. coli, respectively. These findings highlight the potential of phage-infused alginate coatings as promising strategies for active food packaging.