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In this paper, we show for the first time that ligninderived phenols can act as laccase mediators for the removal of lipophilic compounds from paper pulp. These
natural mediators represent an alternative to synthetic mediators, such as 1-hydroxybenzotriazole (HBT), that cause
some economic and environmental concerns. Unbleached kraft pulp from eucalypt wood, which contained free and conjugated sterols responsible for pitch deposition in
the manufacture of totally chlorine free paper, was treated with a fungal laccase in the presence of syringaldehyde, acetosyringone, and p-coumaric acid as
mediators. The composition of lipophilic extractives in the pulps after the enzymatic treatment followed by a hydrogen
peroxide stage was analyzed by gas chromatography and gas chromatography/mass spectrometry. The enzymatic treatment using syringaldehyde as laccase mediator caused
the highest removal (over 90%) of free and conjugated sitosterol, similar to that attained with HBT, followed by
acetosyringone (over 60% removal), whereas p-coumaric acid was barely effective. Moreover, recalcitrant oxidized steroids surviving laccase-HBT treatment could be
removed when using these natural mediators. Pulp brightness was also improved (from 57% to 66% ISO brightness) by the laccase treatment in the presence of the above phenols followed by the peroxide stage due to the simultaneous removal of lignin. |
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