Storability of antimicrobial chitosan-lysozyme composite coating and film-forming solutions

Chitosan-lysozyme (CL) film and coating solutions were prepared aseptically by incorporating 60% lysozyme (w/w chitosan) into 3% chitosan solution. The solutions were stored at 10, 21, and 37 degrees C up to 6 mo for monthly evaluation of physicochemical and antimicrobial properties. Solutions were made into films at each sampling time to investigate lysozyme release, water solubility, water vapor permeability (WVP), tensile strength (TS), and elongation (EL) of the films. During the 6-mo storage, the pH and translucency of CL solutions did not change (P>0.05) and microorganisms were not detected with total aerobic count media. CL solutions became darker, with a more saturated yellow hue developing with increased storage time and temperature. Storage enhanced the antimicrobial activities of the solutions against E. coli and L. monocytogenes, and films made of solutions stored at 37 degrees C exhibited higher antimicrobial activities against these 2 pathogens than those stored at 10 and 21 degrees C. Increased water solubility and lysozyme release and decreased TS and EL were observed in films made from solutions stored at 37 degrees C. WVP was not significantly affected by storage temperature and time. These changes might be attributed to increased chitosan degradation by lysozyme hydrolysis at a higher storage temperature and longer storage time. Results indicated that with storage at 10 to 20 degrees C, premade CL solutions are stable and may be distributed as a commercial product for coating or film applications or both in different foods for at least 6 mo.