EFFECTS OF LIGNIN-MODIFYING ENZYMES ON PINE KRAFT PULP

Oxygen delignified pine kraft pulps were treated with lignin-modifying enzymes: laccase (EC 1.10.3.2), Mn-dependent peroxidase (EC 1.11.1.13 ), lignin peroxidase (EC 1.11.1.14), and xylanase (EC 3.2.1.8), in ord er to improve bleachability. Pulps were treated either with a purified single enzyme or alternatively enzymes were successively added in dif ferent combinations. The solubilized components were analysed using HP LC, GPC and IEF. The residual pulps were delignified with alkaline hyd rogen peroxide and analysed for Kappa number and ISO-brightness. Ligni n-modifying enzymes did not improve bleachability when acting alone. X ylanase treatment increased the brightness by 1-2.5 ISO-units, and xyl anse combined with lignin-modifying enzymes increased the brightness b y a further one unit. By extending the alkaline peroxide step the fina l brightness increased in all samples, whereas the relative difference s between reference and enzyme-treated samples remained constant.