Antimicrobial properties of poly (vinyl alcohol) films with zeolitic imidazolate framework (ZIF-8) nanoparticles for food packaging.

Antimicrobial packaging films are of interest to the fresh produce industry due to the high number of foodborne illness outbreaks associated with these products. This study evaluated the antimicrobial effectiveness of poly (vinyl alcohol) (PVA) films with embedded zeolitic imidazolate framework (ZIF-8) nanoparticles carrying trans-cinnamaldehyde (TC) against Escherichia coli MG1655 in spinach leaves. PVA films were synthesized using distilled water and mixed at 90°C for 1 h. The synthesized nanoparticles were introduced at various mass ratio concentrations (0%-5% weight of ZIF-8@TC nanoparticles to PVA), namely PVA-Z8-0 (control) through PVA-Z8-5. The PVA and ZIF-8@TC solution was mixed for 24 h until it seemed homogenous, cast, and dried in a ventilated oven at 35°C for 24 h. The release rate of TC from the PVA/ZIF-8@TC into both ethanol and methanol was characterized using HPLC methods. Disk diffusion and growth studies were performed to quantify the films antimicrobial effectiveness. Disk diffusion test showed that antimicrobial activity against E. coli MG1655 increased (p < 0.05) with increased nanoparticles concentration. Growth characteristics were described by the Baranyi model with some variations. About 0.26, 0.73, and 1.65 log reductions were achieved with the PVA-Z8-1 to PVA-Z8-3 films, respectively, while total inactivation was achieved with both the PVA-Z8-4 and PVA-Z8-5 films (p < 0.05). Similarly, the Baranyi model described the inhibitory profiles of the different films. This study contributes to the overall food safety body of knowledge regarding fresh produce and other packaged foods through the development of biopolymeric films with embedded nanoparticles to entrap natural antimicrobials. PRACTICAL APPLICATION: This study paves the way for further research on the development of active polymeric films for food packaging applications.

Properties of poly (vinyl alcohol) films with embedded zeolitic imidazolate framework (ZIF-8) nanoparticles for food packaging applications.

This study evaluated the physical, mechanical, barrier properties, and transition temperatures of poly (vinyl alcohol) (PVA) films with embedded zeolitic imidazolate framework-8 (ZIF-8) nanoparticles carrying a natural antimicrobial, trans-cinnamaldehyde (TC). The ZIF-8 nanoparticles were synthesized using a sonochemical method and incorporated into polymeric matrices at mass ratio concentrations of 0% (control film) to 5% weight of ZIF-8@TC to PVA. Solutions were mixed, cast onto Petri dishes and dried for 12 h at 37°C in a ventilated oven. The film samples were stored in airtight containers at room temperature and used within 1 week. The engineering properties of the PVA/ZIF-8@TC films were compared with those of low-density polyethylene (LDPE) film commonly used for packaging of spinach leaves. The glass transition, melting, and crystallization temperatures of PVA compositive films all increased (p < 0.05) with ZIF-8@TC concentration. When exposed to high relative humidity environments, the PVA/ZIF-8@TC films had lower equilibrium moisture content (p < 0.05) than the LDPE film. Although the composite films have different tensile properties from the LDPE film, embedding ZIF-8@TC into PVA films improved the tensile strength by 17%, making the PVA/ZIF-8@TC films suitable for low load-bearing applications such as food packaging. The gas barrier properties of PVA-based films differed only slightly with added ZIF-8@TC (p < 0.05). PRACTICAL APPLICATION: PVA/ZIF-8@TC films are appropriate environment-friendly alternatives to polymeric food packaging in terms of their functional properties.

trans-Cinnamaldehyde-encapsulated zeolitic imidazolate framework-8 nanoparticle complex solutions to inactivate Escherichia coli O157:H7 on fresh spinach leaves.

This study synthesized and characterized ZIF-8 nanoparticles encapsulated with trans-cinnamaldehyde oil (TC) and evaluated their antimicrobial effectiveness against Escherichia coli O157:H7 on fresh spinach leaves. The antimicrobial activity of different mass ratios of TC-encapsulated ZIF-8 against E. coli O157:H7 (ATCC 43895) strain was assessed and the best mass ratio of 1:2 TC to ZIF-8 identified. Spinach leaves were treated with (1) 0.5TC@ZIF-8_PL nanoparticle complexes solution, (2) 200 ppm chlorine, (3) free TC, and (4) sterilized distilled water (control). All sample groups were rinsed for 1 min, dried in a biosafety cabinet, weighted, and packed in sterilized Whirl-pkTM Stand-Up sampling bags, and stored at 4°C for 15 days for shelf life studies. Samples were dipped into a solution of nanoparticles and another group was sprayed. The quality of spinach samples was assessed by monitoring changes in moisture content (MC), water activity (Aw), color, pH, texture (firmness and work), vitamin C content, total carotenoid, and chlorophyll content. Spinach leaves treated with 0.5TC@ZIF-8_PL had less (p < 0.05) water, total chlorophyll, and total carotenoid losses, with minimal changes in pH. However, treatment did not prevent the color degradation (p > 0.05) and adversely affected spinach firmness. The spinach samples treated with 200 ppm chlorine and free TC had higher (p < 0.05) total chlorophyll degradation than the samples treated with the nanoparticles. The mass ratio of TC-encapsulated ZIF-8 must be readjusted to reduce potential toxicity issues while maintaining the antimicrobial properties. PRACTICAL APPLICATION: Zeolitic imidazolate framework-8 (ZIF-8) nanoparticle complex can be used to encapsulate natural antimicrobials to inhibit growth of pathogens on fresh produce. A 2-log reduction in populations of Escherichia coli O157:H7 on fresh spinach leaves was achieved using trans-cinnamaldehyde at low concentrations. The results can be used to embed the compounds into polymeric films for antimicrobial packaging applications.