Abstract
Pre-treatment of unbleaced thermomechanical pulp and unbleached groundwood pulp with extracellular crude enzyme solutions from Phanerochaete chrysosporium and Coriolus versicolor, respectively, belonging to white-rot fungi followed by alkaline hydrogen peroxide bleaching gave a remarkable effect on depression of heat-induced color reversion of thermomechanical pulp (TMP) and groundwood pulp (GP), respectively. The effect of depression of heat-induced color reversion by treatment of unbleached TMP with an extracellular crude enzyme solution from P. chrysosporium seems to be related to the pH value in the culture solution. The color reversion was greatly suppressed when the culture solution have lower pH value, especially under pH 4. 6. This suggests that the enzyme from P. chrysosporium responsible for depression of the color reversion is a kind of inducible enzyme by decrease in pH value in the culture solution during incubation. And furthermore, the enzyme responsible for depression of the color reversion was found to be strongly inhibited by heat treatment or by addition of sodium cyanide.
Furthermore, pre-treatment of unbleached GP with an extracellular crude enzyme solution from C. versicolor, followed by hydrogen peroxide bleaching was found to be very effective to the depression of light-induced color reversion of GP. However, no effect of depression of light-induced color reversion was observed by the treatments of both, GP and TMP with the extracellular crude enzyme solution from P. cioysosporium. This suggests that TMP and GP have some different chromophores contributing to the light-induced color reversion. Based on the results of the reactivity between a model compound and extracellular crude enzymes from C. versicolor, the enzyme responsible for depression of light-induced color revesion of TMP is a kind of oxide -reductase because reduction products as well as oxidation products are recognized in the reaction products.
