Development of polylactic acid based antimicrobial food packaging films with N-halamine modified microcrystalline cellulose.

Bio-based "green" films with superior antimicrobial activity were developed from polylactic acid (PLA) and cyclic N-halamine 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone (MC) grafted microcrystalline cellulose (MCC) fibers (herein referred to as g-MCC). The structure of g-MCC was characterized by Fourier Transform Infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Results indicated N-halamine MC was successfully grafted onto MCC fibers, with a grafting percentage of 10.24 %. The grafting improved compatibility between g-MCC and PLA, leading to an excellent dispersion of g-MCC in the film matrix, and a superior transparency of the g-MCC/PLA compared to that of the MCC/PLA films. Additionally, the enhanced compatibility the g-MCC/PLA films produced better mechanical properties including mechanical strength, elongation at break and initial modulus than those of both MCC/PLA and MC/PLA composites. With N-halamine, g-MCC/PLA completely inactivated all the inoculated Escherichia coli and Staphylococcus aureus within 5 and 30 min of contact, respectively. More importantly, the migration test showed that the oxidative chlorine of g-MCC/PLA was highly stable than that of MC/PLA films, providing a long-term antimicrobial activity. Finally, preservation test conducted on fresh bread slices further demonstrated its promising applications in the food industry.

Antimicrobial film based on poly(lactic acid) and natural halloysite nanotubes for controlled cinnamaldehyde release.

Using nanocarriers to load antimicrobial agent instead of direct incorporating into film matrix could avoid burst release. Halloysite nanotubes (HNTs) are natural clays with a unique tubular structure; therefore in many studies it served as carriers to achieve a controlled release of active agents. However, when HNTs biocomposites were loaded into packaging film, the antimicrobial activity was reduced too seriously to preserve the packaged food. This study aimed to improving preservation properties of the fabricated films from two perspectives: enlarging the loading capacity of the carrier, and increasing the concentration of HNTs biocomposites. Brunauer, Emmett, Teller's test (BET) and thermogravimetric analysis (TGA) were conducted to evaluate the performance of acid treated nanocomposites. Results showed that acid treatment expanded the lumen of HNTs, increasing the loading capacity of cinnamaldehyde (Cin) from 14.6 wt% to 25.0 wt%. Active packaging films were then fabricated by incorporating Cin loaded HNTs into poly(lactic acid) matrix, and it revealed bionanocomposites at 30 wt% achieved the optimum film, considering the mechanical performance and controlled release of Cin. Cumulative release rate of the films were further verified by the fumigant antimicrobial activity. This study demonstrates a solution for improving the antimicrobial properties of packaging film without comprising mechanical strength.

A Sustainable and Antimicrobial Food Packaging Film for Potential Application in Fresh Produce Packaging.

N-halamines are a group of compounds containing one or more nitrogen-halogen covalent bond(s). This high-energy halide bond provides a strong oxidative state so that it is able to inactivate microorganisms effectively. In this study, a sustainable film was developed based on polylactic acid (PLA) with incorporated N-halamine compound 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone (MC), as a promising antimicrobial food packaging material. Results showed that the incorporation of MC prevented the crystallization of PLA and improved the physical properties of the films. In addition, both the moisture barrier and the oxygen permeability were improved with the presence of MC. Importantly, the antimicrobial film was able to inactivate inoculated microorganisms by a factor of seven log cycles in as little as 5 min of contact. Films that contained higher levels of MC further enhanced the antimicrobial efficacy. Fresh strawberries packed with the fabricated films maintained the quality for up to 5 days. Due to the ease of fabrication and the effective biocidal property, these films have a wide range of potential applications in the field of food packaging to extend the shelf life of fresh produce.