Development and characterization of a bio-based antimicrobial multi-layered packaging material containing poly lactic acid, chitosan, and grapefruit seed extract

Blend solutions containing poly(lactic acid) (PLA) and chitosan (CS) were prepared with the addition of methyldiphenyl diisocyanate (MDI) and coated on PLA film. Increasing the concentration of MDI modified the surface tension and enhanced wettability. The increase in MDI also resulted in increased H-bonding from urethane groups formed within PLA/CS to improve adhesion. These findings were used to improve wettability and adhesion between the PLA/CS coating and PLA film to develop a completely bio-based multi-layer film with antimicrobial capacity. The novel antimicrobial film was prepared by coating CS containing grapefruit seed extract (GSE) on the aforementioned PLA/CS coated PLA film. The effectiveness of the antimicrobial film against Salmonella Typhimurium in tomato juice was investigated. A combined effect between the GSE concentration and temperature on the effectiveness of the antimicrobial films against S. Typhimurium in tomato juice was identified. Incorporating GSE into chitosan coatings did not affect the properties of the films initially but did affect these after exposing the films to tomato juice. The tensile strength and elongation at break of films without GSE significantly decreased (p < 0.05) while these properties did not change for films containing GSE. Adhesion between the CS coating and PLA film was significantly reduced (p < 0.05) after exposing the films to tomato juice. Water vapor and oxygen permeability of the films were not affected by either GSE or tomato juice. CS/GSE coated PLA films have the potential to be an effective bio-based antimicrobial material for food packaging applications.