Incorporation of partially purified hen egg white lysozyme into zein films for antimicrobial food packaging

Lysozyme, partially purified from hen egg white by precipitation of non-enzyme protein with ethanol and lyophilized after dialysis, was incorporated into zein films. The recovery and specific activity of the enzyme after partial purification varied between 45% and 72% and 2173 and 3448 U/mg, whereas the activity of the lyophilized enzyme varied between 2900 and 3351 U/mg. The partially purified enzyme was very stable and lost almost no activity in lyophilized form or in zein films stored at -18 and 4 degrees C for up to 8 and 4 months, respectively. During partial purification and in zein film preparation, ethanol treatment caused 123-137% and 132-315% activation of the enzyme, respectively. In zein films incorporated with 187-1318 U/cm(2) (63-455 mu g/cm(2)) lysozyme, the release rates at 4 degrees C, changed between 7 and 29 U/cm(2)/min, increased at high lysozyme concentrations. Zein films incorporated with partially purified lysozyme showed antimicrobial effect on Bacillus subtilis and Lactobacillus plantarum. By the addition of disodium EDTA, the films also became effective on Escherichia coli. The results of this study showed that the partially purified lysozyme may be used in antimicrobial packaging to increase food safety. (c) 2005 Elsevier Ltd. All rights reserved.