Laccase-mediated functionalization of chitosan by caffeic and gallic acids for modulating antioxidant and antimicrobial properties

A new strategy for the functionalization of chitosan with caffeic acid (CA) or gallic acid (GA) using laccase from Trametes versicolor is presented for the first time, yielding a product with modulated antioxidant and antimicrobial properties. UV-vis spectroscopy coupled to HPLC-SEC analysis and cyclic voltammetry kinetic studies showed that laccase catalyzes the oxidation of phenolic acids to electrophilic o-quinones, which undergo new oligomer/polymer-forming structures originated by C-C coupling between the benzene rings and C-O-C coupling involving phenolic side-chains. Furthermore, pH tunable reactions/interactions of the laccases oxidized o-quinones with nucleophilic amino groups of chitosan were determined with FTIR and ¹H NMR spectroscopy's. The highest antioxidant activity was found to be for chitosan modified with phenolic acids at pH 4.5, exhibit also an increased activity against Escherichia coli and Listeria monocytogenes compared to untreated chitosan.