Background: The paper and pulp industry is a capital and resource-intensive industry
that contributes to ecosystem toxicity and affects human beings.
Objective: The study aimed to appraise the potential of xylanases, laccases and manganese peroxidase
for the bio-bleaching of paper pulp and to highlight the role of these enzymes as a promising
substitute for chlorine-based chemical methods in the bleaching process.
Methods: The ligninolytic enzymes including xylanase, laccase and manganese peroxidase isolated
from white rot fungi were used for pre-bleaching and bleaching of oven-dried wheat straw pulp.
Results: During the sequential enzymatic treatment of oven-dried pulp the brightness was improved
and kappa number was reduced by 3.1% and 3.1 points respectively after xylanase treatment, 0.3%
and 0.4 points after laccase treatment and 3% and 0.2 points after MnP treatment. During separate
treatment of pulp samples with individual enzymes, brightness and kappa number improved by 8%
and 3 points respectively after xylanase treatment, by 5% and 1.7 points after laccase treatment and
5% and 1.8 points after treatment with MnP. During subsequent treatment with 4% sodium hypochlorite,
the brightness was further improved by 27.9 % for xylanase treated pulp and 29% for the
laccase and MnP treated pulp. The xylanase was found most efficient in comparison to laccase and
MnP in reduction of kappa number and improvement of brightness.
Conclusion: These results clearly indicate the role of laccase, MnP and xylanase from white rot
fungi as effective bio-bleaching agents. Therefore, these enzymes can facilitate the bleaching process
without threat to environment.