Development and characterization of bioactive polyvinyl alcohol / chitosan multilayer-based films loaded with tea tree oil nanoemulsion to extend the shelf life of red grapes

This study presents a comprehensive overview of developing, characterizing, and utilizing trilayer antibacterial films for potential food preservation applications. The films are composed of chitosan (Ch) and polyvinyl alcohol (PVA) as biopolymers and tea tree essential oil nanoemulsion (NETTO) as the primary antibacterial ingredient. Initial evaluations confirmed tea tree oil's potent antimicrobial efficacy, demonstrating inhibitory and bactericidal effects against Escherichia coli and Staphylococcus aureus at low concentrations. The MIC values for E. coli were 2.5 μL/mL and for S. aureus 1.25 μL/mL, with corresponding MBC values of 5 μL/mL and 1.25 μL/mL, respectively. The incorporation of NETTO in the film formulation not only improves the antibacterial efficacy of the films, as evidenced by agar well diffusion assays, but also impacts their physical properties. The trilayer film also became less moisture-content15.59%, soluble 11.57 %, and permeable to water vapor 5.52 (10⁻⁵ gm⁻¹ min⁻¹ Pa⁻¹). The trilayer film can provide sustained release and better tea tree oil retention rates than the Ch-NETTO film. The study further investigates the effectiveness of trilayer film in preserving red grapes, which outperformed commercial plastic and Ch films against S. aureus and E. coli bacteria. The trilayer film effectively preserves the appearance and freshness of red grapes, extending their shelf life.