Modification of cellulose‐based packaging materials for enzyme immobilization

Active cellulose‐based packaging materials were prepared by binding lysozyme to paper modified with anionic polyelectrolytes. Polyelectrolytes improve the paper binding capacity towards the positively charged lysozyme and play a protective role towards lysozyme activity during the paper‐making process. The charge density of paper was increased by incorporating carboxymethylcellulose (CMC) or polygalacturonic acid (PGA). The presence of either CMC or PGA greatly increased the amount of bound lysozyme, and the stability of its binding towards buffers or towards non‐ionic chaotropes which disrupt the three dimensional structure in macromolecules (urea, 8 M). Binding of lysozyme to modified papers was sensitive to anionic detergents (sodium dodecyl sulphate, 1%) and to non‐chaotrope salts (NaCl, 0.5M). These data provide information about the nature of the interactions between the protein and the various types of paper, and provide insights on how to preserve the activity of lysozyme‐loaded paper. The polymers used for lysozyme immobilization were found to affect only marginally the structural and functional properties of the antimicrobial protein, and to facilitate the recovery of structural features of the protein after heat treatment. Presence of a negative polyelectrolyte (and of CMC in particular) improves the thermal stability of the protein, making it resistant to thermal inactivation, even under the conditions used for drying processes without compromising the paper's mechanical properties. The activity measurements showed that paper‐bound lysozyme retains its lytic (and therefore, antimicrobial) activity against the cell walls of Micrococcus lysodeikticus, the target microrganism used as standard for lysozyme bioassays. Copyright © 2009 John Wiley & Sons, Ltd.