A comparison of enzyme-aided bleaching of softwood paper pulp using combinations of xylanase, mannanase and alpha-galactosidase

Enzymatic pretreatment of softwood kraft pulp was investigated using xylana se A (XylA) from Neocallimastix patriciarum in combination with mannanase a nd alpha-galactosidase. Mannanase A (ManA) from Pseudomonas fluorescens sub sp. cellulosa and ManA from Clostridium thermocellum, both family 26 glycos yl hydrolases, are structurally diverse and exhibit different pH and temper ature optima. Although neither mannanase was effective in pretreating softw ood pulp alone, both enzymes were able to enhance the production of reducin g sugar and the reduction of single-stage bleached kappa number when used w ith the xylanase. Sequential incubations with XylA and P. fluorescens ManA produced the largest final kappa number reduction in comparison to control pretreated pulp. The release of galactose from softwood pulp by alpha-galac tosidase A (AgaA) from P. fluorescens was enhanced by the presence of ManA from the same microorganism, and a single pretreatment with these enzymes, in combination with XylA, gave the most effective kappa number reduction us ing a single incubation. Results indicated that mixtures of hemicellulase a ctivities can be chosen to enhance pulp bleachability.