Preparation of antimicrobial biopolymer particles through co-precipitation of hen egg white lysozyme and poly(hydroxy butyrate).

Co-precipitation of poly(hydroxy butyrate), a biobased and biodegradable polymer produced through bacterial fermentation, and hen egg white lysozyme, an enzyme with antimicrobial activity, is a viable route towards non-covalent enzyme immobilization. Ultrasonication during the co-precipitation process results in spherical particles with a well-defined size distribution. The amount of immobilized enzyme can be controlled through variation of its concentration in the antisolvent (aqueous) phase. The presence and density of the enzyme bound to the particles have a decisive influence on the internal order (chain arrangement) and thermal properties of the biopolymer. The fraction of amorphous (glassy) material increases with higher enzyme content. When the actual amount of enzyme bound to the particles is accounted for, limited detrimental effects of the immobilization procedure on the antimicrobial activity are observed, compared to the free enzyme. Immobilization also improves the stability of the antimicrobial activity when exposed to elevated temperatures. The activity of the immobilized enzyme doubles at 45 °C, compared to 25 °C, while that of the free enzyme decreases by 10%. Co-precipitation of enzymes such as hen egg white lysozyme in the presence of biopolymers is a straightforward approach to prepare fully biobased, functional (e.g., antimicrobial) materials with beneficial properties. This enzyme immobilization approach results in improved stability against harsh environmental conditions (e.g., elevated temperatures) which is advantageous for applications such as shelf-life extending packaging.