Development of antimicrobial cellulose packaging through laccase-mediated grafting of phenolic compounds

Laccase polymerization of caffeic acid and isoeugenol was shown to enhance their antimicrobial activity versus Staphylococcus aureus and Escherichia coli in liquid media. Unbleached kraft liner fibres were reacted with laccase in the presence of different phenol compounds possessing antimicrobial activity to increase their efficacy through a covalent binding with the lignin present on the fibres. The handsheet paper obtained by laccase antibacterial surface process (LASP) showed a greater efficacy against Gram positive and Gram negative bacteria than handsheet paper treated only with monomeric phenol derivatives. Antimicrobial activity was function of grafted structure, time of the treatment and concentration of phenol derivatives. In this paper several phenol compounds were tested: acids, essential oils components and dopamine. LASP in the presence of caffeic acid or p-hydroxybenzoic acid produced paper handsheets with strong bactericidal effect on S. aureus even at low phenol monomer concentration (4 mM), whereas a higher concentration of the monomer in the reaction mixture was required to kill E. coli. Among the tested essential oils compounds, isoeugenol was the most effective: isoeugenol/LASP, besides killing S. aureus, showed a bacteriostatic effect on the more resistant spore forming Bacillus subtilis. LASP in the presence of dopamine was effective against Gram positive and Gram negative bacteria. The grafting of laccase polymerized oligomeric phenolic structures onto the fibre surface might be partially responsible of the enhanced antibacterial activity displayed by LASP handsheet paper versus the paper treated only with monomeric phenols.