College of Food Science, Sichuan Agricultural University, Yaan 625014, China; School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China; California NanoSystems Institute, University of California, Los Angeles, CA 90095, USA. Electronic address: [Email]
The physical and antimicrobial properties of sodium alginate or sodium carboxymethylcellulose films containing cell-free supernatant of Lactococcus lactis ATCC 11454 were evaluated in this study. The antimicrobial activity of the films against Staphylococcus aureus ATCC 6538, and Escherichia coli ATCC 25922 was evaluated. Cell-free supernatants were obtained by centrifugation and filtration of Lactococcus lactis cultures in MRS broth; the filtrates were freeze-dried, and rehydrated (4, 8, or 12 mg/mL) to produce collagen film. The thickness, tensile strength, color, moisture content, solubility, and water vapor permeability of the films were measured to examine the effects of cell-free supernatants on film matrices. Noticeable antimicrobial activity was observed against Staphylococcus aureus, and Escherichia coli upon the addition of 12 mg/mL cell-free supernatants. Our results indicate that the incorporation of cell-free supernatant changed the physical properties of the edible films. Gradual and significant (p < 0.05) increase in color difference and solubility were observed with the addition of increasing concentrations of cell-free supernatant. Antimicrobial films were brown in color and with variable moisture contents. Sodium alginate films were better than sodium carboxymethylcellulose films for most of the evaluated parameters. In summary, collagen films containing cell-free supernatants are interesting alternative natural antimicrobial films for functional food packaging.