Poly (Vinyl Alcohol) Nanocomposite Films with Embedded trans-Cinnamaldehyde Encapsulated Zeolitic Imidazolate Framework for Fresh Produce Packaging

Abstract

Zeolitic Imidazolate Framework (ZIF-8) nanoparticles work as a drug carrier of natural antimicrobials such as trans-cinnamaldehyde (TC). Embedding the ZIF-8@TC nanoparticles in polymeric materials created an active food packaging film. Development of effective antimicrobial packaging is of great interest to the fresh produce industry. This study evaluated the PVA/ZIF-8@TC nanocomposite film’s material properties, drug release characteristics and antimicrobial activity.

PVA/ZIF-8 nanocomposite films were synthesized the solution casting method. The synthesized ZIF-8@TC were introduced at various mass ratio concentrations (0% - 5% weight of ZIF-8@TC nanoparticles to PVA, named PVA-Z8-0 (control) through PVA-Z8-5). Tensile properties, thermal transition temperature, and moisture absorption were evaluated for film properties. Drug concentrations and release of drug from the films were evaluated using HPLC, and antimicrobial effectiveness was evaluated against E. coli MG1655 on spinach leaves and disk diffusion studies.

Average film thickness was 0.061 mm. The films with higher concentrations of ZIF-8@TC nanoparticles had lower moisture absorption under high RH environments (p<0.05). DSC studies showed that Tg of films with embedded nanoparticles were higher than pure PVA film, and all PVA based films were greater than LDPE films (p<0.05). Tm and Tc of the films increased as nanoparticle concentrations increased (p<0.05). Tensile strength of embedded films was than pure PVA film, while elongation at break decreased, and the elastic modulus increased as the concentration of nanoparticles increased (p<0.05). TC concentrations inside of films increased linearly as the ZIF- 8@TC concentrations increased (p<0.05). The controlled release studies showed TC release was dependent on temperature, nanoparticle concentration, and medium type. From the antimicrobial study, all films with ZIF-8@TC nanoparticles inhibited the growth of E. coli MG1655. Films with higher concentrations of nanoparticles showed better inhibition, where PVA-Z8-4 and PVA-Z8-5 showed total inhibition in the study using spinach leaves, while PVA-Z8-1, PVA-Z8-2 and PVA-Z8-3 showed 0.26, 0.73, and 1.7 log CFU/mL reduction.