Mechanical and barrier properties of bio-based antimicrobial nanocomposite films for food packaging applications

Two current consumer demands will shape the future of food packaging: the demand on minimally processed and preservative-free foods, and the demand on environmental friendly packaging materials. In order to produce preservative-free foods but maintain same food safety, an alternate method is to incorporate antimicrobial agents (AM) into packaging materials, called antimicrobial food packaging. On the other hand, biodegradable polymers from renewable resources can to some extent reduce food packaging waste. To response these demands, bio-based antimicrobial films were developed in the present study. In particular, two antimicrobial agents, sodium benzoate (Bz) and natamycin (Nat), were incorporated into starch to form starch-based films. Furthermore, two incorporation methods were studied, one was directly incorporating antimicrobial agents into starch matrix, and the other was incorporating antimicrobial-nanoparticle systems into starch matrix. In the latter method, AM were first loaded onto nanoparticles, layered double hydroxide (LDH), called LDH-Bz and LDH-Nat, and then incorporated into starch. Five starch-based films were prepared: starch without AM as control, starch with sodium benzoate, starch with natamycin, starch with LDH-Bz, and starch with LDH-Nat. Mechanical and barrier properties of the films were studied. The results showed that addition of antimicrobial agents has significant effect on elongation at break but no significant effect on tensile strength. The elongation increased from 6.75% for control film to 17.69% for film with 2% of LDH-Bz. Three permeabilities (water, oxygen, and CO₂) were significantly decreased while AM incorporated. However, the different incorporation methods did not show effect on neither mechanical nor barrier properties.