Studies on mediators of manganese peroxidase for bleaching of wood pulps
Introduction
Pulp bleaching is conventionally achieved by treating pulps with molecular chlorine or chlorine-based chemicals. The effluents from this treatment contain chlorinated aliphatic and aromatic compounds that could be acutely toxic, mutagenic and even carcinogenic. To reduce the environmental pollution, researchers began to develop environmentally benign bleaching techniques such as elementary chlorine free (ECF) and even totally chlorine free (TCF) processes. Environmentally friendly enzymatic pulp bleaching techniques have been investigated intensively in recent years. The first enzyme to be used for pulp bleaching was xylanase (Viikari et al., 1986). Laccase has also been demonstrated to be effective in pulp bleaching when a redox mediator such as 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) or 1-hydroxybenzotriazole (1-HBT) is present (Bourbonnais and Paice, 1992; Call and Mücke, 1994). However, the lack of a cheap redox mediator is one of the hurdles for a commercial application of a laccase/redox mediator system for pulp bleaching today.
Manganese peroxidase (MnP), a ubiquitous peroxidase among white-rot fungi (Eggert et al., 1996), is another lignin-degrading enzyme that can be used for pulp bleaching. The activity of MnP is dependent on Mn2+. It has been proposed that MnP oxidizes Mn2+ to Mn3+ which in turn oxidizes lignin (Wariishi et al., 1988). It has been demonstrated that MnP is able to oxidize phenolic lignin subunits only (Wariishi et al., 1988). However, it was found that in the presence of glutathione (GSH), MnP could also oxidize non-phenolic lignin model compounds, veratryl, anisyl, and benzyl alcohols (Wariishi et al., 1989). They demonstrated that the Mn3+ formed oxidizes thiol to a thiyl radical that in turn abstracts a hydrogen from veratryl alcohol to form veratraldehyde. Bao et al. also demonstrated that MnP could oxidize a non-phenolic β-O-4 lignin model compound in the presence of Tween 80. Tween 80 contains an unsaturated fatty acid chain (Bao et al., 1994). They suggested that MnP oxidized the carbon–carbon double bond (CC) in Tween 80 to a peroxide which subsequently turned into a peroxyl radical. This radical was the actual oxidant for the oxidation of the non-phenolic model compound.
It was further demonstrated that MnP from Phanerochaete sordida YK-624 could bleach hardwood kraft pulp in the presence of Mn2+, Tween 80, malonate, and H2O2 (Kondo et al., 1994). However, the bleaching effect with MnP and Tween 80 is still not satisfactory. In an effort to enhance the pulp bleaching effect by MnP, we have evaluated a large number of organic compounds such as organic acids, thiol-containing compounds and their combinations for pulp bleaching. Some compounds are superior to Tween 80 for this purpose.
Section snippets
Pulp and chemicals
The unbleached hardwood kraft pulp used in these experiments (HWKP, brightness 35% ISO; kappa number 14.2) was obtained from a Georgian pulp mill. All chemicals were of analytical grade and obtained from commercial sources.
Enzymes
MnP was produced from Trametes versicolor strain 52J kindly provided by Michael G. Paice (Pulp and Paper Research Institute of Canada). Cultivation of the fungus and purification of the enzyme was performed as described by Paice et al. (1993). However, the culture medium was
Results and discussion
In this study, various compounds were screened for their ability to enhance the pulp bleaching effect by MnP. Brightness and kappa number values were measured to compare the effect of the compounds studied in these MnP-based pulp bleaching experiments.
The first group of compounds screened were thiol-containing compounds: cysteine, cystine, dithiothreitol and glutathione. As shown in Table 1, cysteine, dithiothreitol, and glutathione appeared to darken the pulp in comparison with the treatment
Conclusion
Although glutathione has previously been shown to enable MnP to oxidize non-phenolic lignin model compounds, in our studies thiol-containing compounds were not effective MnP mediators for pulp bleaching. Unsaturated fatty acids significantly increased the pulp bleaching effects by MnP. Unsaturated carbon–carbon double bonds in fatty acids appeared to play a very important role in the MnP-based pulp bleaching, which is consistent with the proposed mechanisms that lignin degradation is through
References (14)
- et al.
FEBS Lett.
(1994) - et al.
J. Biol. Chem.
(1992) - et al.
J. Biol. Chem.
(1989) Pulp. Pap. Mag. Can.
(1966)- et al.
Appl. Microbiol. Biotechnol.
(1992) - Call, H.P., Mücke, I., 1994. TAPPI J., p....
- et al.
Holzforschung
(1990)
Cited by (41)
Enhancement of lignin removal from poplar prehydrolysis liquor by manganese peroxidase-induced polymerization
2023, Industrial Crops and ProductsFungal lignin-modifying peroxidases and H2O2-Producing enzymes
2021, Encyclopedia of MycologyFungal laccases: Versatile green catalyst for bioremediation of organopollutants
2020, Emerging Technologies in Environmental BioremediationPotential of fungal laccase in decolorization of synthetic dyes
2019, Microbial Wastewater TreatmentPurification and characterization of a novel manganese peroxidase from white-rot fungus Cerrena unicolor BBP6 and its application in dye decolorization and denim bleaching
2018, Process BiochemistryCitation Excerpt :Azure B (heterocyclic dye) is one of the most recalcitrant dyes because of its relatively complex structure [32], and neither laccase nor MnP could oxidize Azure B alone unless mediators are added [32]. It was found that certain phenolic compounds and unsaturated fatty acids could be used as mediators in the oxidation of lignin model compounds by MnP [14,33]. Mediators including phenolic compounds (gallic acid and ferulic acid) and Tween-80 were used to evaluate their effect on Azure B (100 mg/l) decolorization by purified MnP-BBP6.
Degradation of olive mill wastewater by the induced extracellular ligninolytic enzymes of two wood-rot fungi
2017, Journal of Environmental ManagementCitation Excerpt :The outstanding biotechnological potential of these enzymes lies in their ability to catalyze both the depolymerization of high molecular weight polyphenols and the oxidative polymerization of low molecular weight phenolic compounds, leading to their precipitation and thus removal from the reaction mixture. These properties are useful in applications such as bleaching of paper pulp (Bermek et al., 2002) and textiles (Heinfling et al., 1998), or stabilization of juices and beverages (Minussi et al., 2002, 2007). Aside from OMWW's detoxification, its biological treatment by white-rot macrofungi could result in the production of valuable compounds, such as β-glucans (Crognale et al., 2003), antioxidants (Hamza et al., 2012; Khoufi et al., 2011), biopolymers (Ntaikou et al., 2009), lipids (Yousuf et al., 2013), and biomass with pharmaceutical and/or nutritional value (Zervakis et al., 1996, 2013), leading thus to the valorization of a toxic waste.