Physical and antimicrobial properties of zein and methyl cellulose composite films with plasticizers of oleic acid and polyethylene glycol

Antimicrobial edible films made by biopolymers have potential applications in food packaging. They can reduce environmental pollution and prevent the growth of pathogens. A corn protein, zein, and a derivative of cellulose, methyl cellulose (MC), are selected for making edible packaging films. This study aimed to develop the zein and MC composite films using the selected plasticizers, to characterize the physical properties, and to evaluate the antimicrobial activities after incorporating the essential oil, thymol. Composite films with various zein to MC ratios were prepared using oleic acid and polyethylene glycol (PEG). The chemical bonding formation was analyzed using Fourier transform infrared (FTIR) spectrometry. Mechanical properties of the films were measured. Tensile strength of the zein-MC composite films (45.7 ± 1.3 MPa) was largely improved compared to that of zein films (7.4 ± 0.3 MPa). The maximum elongation of the zein-MC composite films (34.3 ± 4.3 cm/100 cm) was much higher than that of pure MC films (13.47 ± 1.55 cm/100 cm). The incorporation of zein reduced the water vapor permeability and solubility of MC films. Antimicrobial composite films were prepared by adding thymol into the zein-MC composite films, and the films have been proved to be effective against E. coli and S. aureus at the thymol concentrations of 0.15 and 0.2 (g/g), respectively.