Supercritical assisted enzymatic membranes preparation, for active packaging applications

Materials with antimicrobial activity were obtained by incorporation of an enzyme in cellulose acetate (CA) membranes, to be used for active packaging applications. Membranes were generated by supercritical assisted phase inversion and lysozyme was used as the model enzyme. Suspensions with different combinations of polymer/enzyme were processed at several operative conditions and were characterized by morphological, chemical and calorimetric analysis. Results showed that lysozyme was uniformly distributed in the polymeric matrix and process operative parameters influenced membranes morphology and porosity; the morphology of membranes changed from beads-like to fingers-like when CA concentration was increased from 5 to 10% w/w, whereas it was cellular at CA contents of 15 and 20% w/w. Lysozyme release tests were performed to analyze release kinetics of the investigated membranes. The antimicrobial activity of lysozyme in CA membranes was tested against a suspension of Micrococcus lysodeikticus. Activity was divided in two aliquots referring to mobile and immobilized enzyme. Finger-like CA membranes showed the maximum mobile lysozyme activity due to the opened internal structure; the longest activity time measured for cellular membranes was about 90 h. Cellular CA membranes also showed a high immobilized enzyme activity and were able to kill the model microorganism when in direct contact with it.