Abstract
Pre-treatment of unbleaced thermomechanical pulp with extracellular enzyme solution as well as with crude enzyme solution from Pleurotus ostreatus, a kind of white-rot fungi, followed by alkaline hydrogen peroxide bleaching was found to give remarkable effect on depression of light -induced color reversion of thermomechanical pulp (TMP). The differences in incubation conditions, however, result in considerable differences in depression of color reversion. The highest suppresive depression was observed when unbleached TMP was treated either for 3 hours with the crude enzyme solution from P. ostreatus incubated with a rotary shaker or for 9 hours with that from the fungus incubated in a L-type Monod tube. The optimum pH of the enzymatic reactions to depress such color reversion was 4.5 to 5.0. And furthermore, suppressive depression of color reversion was observed when the lipase activity in the crude enzyme solution was small.
Based on the results of the reactivity between the crude enzyme solution and model compounds, the highest suppresive depression of color reversion was observed when the molar ratio of reduction to oxidation was 2.3. Therefore, this shows that enzyme reactions to reduce the chromophoress seem to contribute mainly to the depression of color reversion, but some of the oxidative reactions also seem to contribute to the depression.
However, almost no effect was observed by the treatment of ground wood pulp (GP) with the enzymatic solution. This suggests that TMP and GP have different chromophores contributing to the respective light-induced color reversion.
