Enzymatic strategies to improve removal of hexenuronic acids and lignin from cellulosic fibers

Abstract

Different enzymatic strategies were applied to improve lignin and hexenuronic acid (HexA) removal. Three laccases (L) with different redox potentials were applied in combination with 1-hydroxybenzotriazole or methyl syringate to softwood sulfite and hardwood kraft fibers. The enzymes with a high-redox potential from Pycnoporus cinnabarinus and Trametes villosa were found to be the most efficient. The bleaching efficiency was not significantly influenced by the presence or absence of HexA in the different types of lignocellulosic fibers.Subsequently, the lignin or HexA removal in the presence of different mediators was evaluated in eucalyptus fibers with the T. villosa laccase (TvL). Natural mediators removed only lignin, whereas the combinations of TvL with synthetic mediators removed both HexA and lignin. The mediator violuric acid (VA) was the most efficient as judged by the properties of fiber and effluent. A xylanase pretreatment stage was found to boost the access of the LVA system to HexA without affecting lignin in the pulp