title: Enzymatic removal of free and conjugated sterols forming pitch deposits in environmentally sound bleaching of eucalypt paper pulp.
abstract: Free and conjugated sterols are among the main compounds responsible for pitch deposition in the manufacture of wood chemical pulps, making difficult the implementation of totally chlorine free bleaching (TCF) and closure of bleach plant circuits. In this work, the suitability of oxidative enzymes in efficiently removing sterols from eucalypt pulps is revealed. The enzymatic treatment was applied as an additional stage of an industrial-type TCF sequence for bleaching eucalypt kraft pulp. The pulp obtained after oxygen delignification was treated with a high-redox potential and thermostable fungal laccase using 1-hydroxybenzotriazole as an enzyme mediator. This pulp was further submitted to chelation and peroxide stages and compared with a control TCF pulp obtained using chemical reagents. The composition of the lipophilic extractives in the pulps and the corresponding liquids after the different stages was analyzed by gas chromatography and gas chromatography--mass spectrometry. Free sitosterol and sitosterol esters and glucosides, the major lipophilic compounds in eucalypt pulps, were completely removed during the laccase-mediator treatment. Only some intermediate products from sitosterol oxidation remained after the laccase stage, as well as in the final pulp. Pulp brightness was also improved due to the simultaneous removal of lignin by the laccase-mediator treatment.
authors.affiliation: Instituto de Recursos Naturales y Agrobiologia, CSIC, P.O. Box 1052, E-41080 Seville, Spain. anagu@irnase.csic.es
authors.forename: Ana
authors.initials: A
authors.lastname: Gutiérrez
authors.forename: José C
authors.initials: JC
authors.lastname: Del Rio
authors.forename: David
authors.initials: D
authors.lastname: Ibarra
authors.forename: Jorge
authors.initials: J
authors.lastname: Rencoret
authors.forename: Javier
authors.initials: J
authors.lastname: Romero
authors.forename: Mariela
authors.initials: M
authors.lastname: Speranza
authors.forename: Susana
authors.initials: S
authors.lastname: Camarero
authors.forename: María Jesus
authors.initials: MJ
authors.lastname: Martínez
authors.forename: Angel T
authors.initials: AT
authors.lastname: Martínez
mesh_terms: D002849:Chromatography, Gas; D005052:Eucalyptus / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D005960:Glucosides / Q000302:isolation & purification / Q000378:metabolism; D007218:Industrial Microbiology; D007220:Industrial Waste; D042845:Laccase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010209:Paper; D012855:Sitosterols / Q000302:isolation & purification / Q000378:metabolism; D013261:Sterols / Q000302:isolation & purification* / Q000378:metabolism; D014230:Triazoles / Q000378:metabolism; D018508:Water Purification
chemical_list: D005960:Glucosides; D007220:Industrial Waste; D012855:Sitosterols; D013261:Sterols; D014230:Triazoles; C011852:1-hydroxybenzotriazole; D042845:Laccase; D010100:Oxygen