Comprehensive Characterization of Gelatin-Pullulan Blend Films Incorporated with Bacteriophages: Assessing Physicochemical, Mechanical, Optical, Thermal, and Antimicrobial Properties

The use of bacteriophages in foods as a bioprotective strategy to control harmful pathogens has gained increasing interest over the last few years. Among the possible application methods, integrating bacteriophages into packaging materials is preferred because it can improve bacteriophage stability and increase efficacy against the target microorganisms. This study aims at assessing the effect and performance of incorporating a lytic bacteriophage cocktail, targeted against Salmonella spp., into co-polymer films made up of gelatin (GEL) and pullulan (PUL) in various proportions (GEL:PUL; 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100). Results indicated that the incorporation of bacteriophages did not disrupt the material structure, and mechanical properties such as tensile strength and Young's modulus of the GEL:PUL blended films were preserved. In the case of the elongation at break, it improved when bacteriophages were formulated (80%). Moreover, the presence of bacteriophages in the polymeric matrices resulted in almost total UV-light blocking capacity (> 99%). The stability of bacteriophages, incorporated into the film, and their antimicrobial effect remained in all films for 5 weeks, producing Salmonella reductions higher than 2 log cfu/mL for GEL40:PUL60 and GEL20:PUL80 films. Bacteriophage release from the films into aqueous media at 4 degrees C was lower than at 25 degrees C. Moreover, the combination of suitable proportions of GEL and PUL (e.g., 40:60, 20:80) resulted in a high and stable release capacity over time. Overall, findings in this study demonstrate that integrating bacteriophages into suitable packaging materials can result in stable and effective antimicrobial packaging systems, able to exert activity over prolonged periods during food storage.