Paper pulp delignification using laccase and natural mediators

aCentro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain; bCentro de Investigación y Tecnología, ENCE, Carretera de Campañó, Ribeiro Vao, E-36157 Pontevedra, Spain; cInstituto de Recursos Naturales y Agrobiología de Sevilla, CSIC, PO Box 1052,E-41080, Seville, Spain; E-mail address: ATMartinez@cib.csic.es (A.T. Martínez)Three plant phenols, namely acetosyringone syringaldehyde and p-coumaric acid, were selected as laccase redox mediators to investigate the enzymatic delignification of paper pulp (obtained from kraft cooking of eucalypt wood) in combination with peroxide bleaching. The effects of these natural mediators were compared with those obtained using the synthetic mediator 1-hydroxybenzotriazole. p-Coumaric acid only caused minor increase of pulp brightness and did not lowered its kappa number (a rough estimation of the lignin content), whereas the use of acetosyringone or syringaldehyde as laccase mediators enabled over 15 % increase of final brightness and a similar decrease of final kappa number. Pulp delignification by laccase in the presence of the two latter natural mediators was demonstrated by analytical pyrolysis, which does not suffer from interferences by other pulp constituents as kappa number does, showing a preferential removal of lignin marker compounds compared with carbohydrate markers (up to 25% decrease of the corresponding ratio). This technique also revealed a modification of the residual lignin composition in terms of phenylpropane units after the laccase-mediator treatment. The use of laccase in combination with natural mediators, widely available from plant materials and pulping liquors, represents a promising alternative for environmentally-friendly delignification of paper pulp.This study has been funded by two ENCE-CSIC contracts, the Spanish projects AGL2005-01748, CTQ2005-8925-CO2-02/PPQ and BIO2005-2224, and the CSIC project 2006-4-0I-039. Marcel Asther from INRA (Marseille, France) is acknowledged for the P. cinnabarinus strain, and Beldem (Andenne, Belgium) is acknowledged for laccase production. S.C. thanks a R&C contract of the Spanish MEC, and D.I. thanks a I3P Fellowship of the Spanish CSIC.Peer reviewe