Biodeinking of flexographic inks by fungal laccases using synthetic and natural mediators

The use of new printing technologies based on flexographic inks hampers ink elimination during paper recycling, making necessary the development of alternative methods. Decolorization of four flexographic inks has been evaluated by using fungal laccases, three of them from basidiomycetes (Trametes villosa, Coriolopsis rigida, and Pycnoporus coccineus), and one from the ascomycete Myceliophthora thermophila in the presence of synthetic and natural mediators.The results obtained showed a higher capacity of the three basidiomycete laccases to decolorize flexographic inks as compared with M. thermophila laccase, a low redox potential laccase. Basidiomycete laccases decolorized inks without mediators at long reaction times, although the presence of natural or synthetic mediators (above all HBT) accelerated the process. On the other hand, M. thermophila laccase was unable to decolorize the inks assayed. The addition of syringyl-type mediators led to medium levels of decolorization except for R48 ink, which was almost completely decolorized.Most decolorization was obtained during the first hours of treatment, when all the basidiomycete laccases were fully active in the presence of mediators. As opposed to other basidiomycete laccases, which become inactive in the presence of HBT after 24 h, the enzyme of P. coccineus was not deactivated by this mediator even after 48 h. A complete loss of M. thermophila laccase activity was observed at short times with acetosyringone and methyl syringate, the only two mediators able to promote ink decolorization with this enzyme.

► Removal of flexographic inks is a problem for the recycled paper industry.
► First report on decolorization of these inks by laccase–mediator systems.
► Synthetic mediators (HBT, ABTS) gave the best results with basidiomycete laccases.
► Natural mediators allowed ink decolorization by M. thermophila laccase.
► Biodeinking could be an alternative process in paper recycling.