Biobleaching of eucalypt kraft pulp with a two laccase-mediator stages sequence

Agro-industrial wastes revalorization as feedstock: production of lignin-modifying enzymes extracts by solid-state fermentation using white rot fungi

The purpose of the study was to evaluate the production of lignin-modifying enzyme extracts and delignified biomass from agro-industrial wastes using white rot fungi (Inonotus sp. Sp2, Stereum hirsutum Ru-104, Bjerkandera sp. BOS55, Pleurotus eryngii IJFM 169 and Phanerochaete chrysosporium BKM-F-1767). These were screened based on their adaptability and colonization ability on different substrates, as well as by the Laccase, Manganese peroxidase, and Lignin peroxidase enzymatic production. Native strains (Inonotus sp. Sp2 and S. hirsutum Ru-104) showed the highest growth kinetics under the solid-substrate fermentation conditions and the growth rate parameters of the kinetic logistic model for the different substrates were between 0.39-0.81 (1/d) and 0.42-0.83 (1/d), respectively; the determination coefficients were ≥0.99. Inonotus sp. Sp2 was subsequently cultured in static flasks to produce crude enzyme extracts, obtaining manganese peroxidase activity levels of 18.5 and 31.3 (U/g) when growing in corn cob husk and spent tea leaves, respectively. Besides, it was to establish that the best conditions for lignin-modifying enzymes production using corn cob husk are 70% of initial moisture and 2.12 mm of particle size; reaching after 30 incubation days a manganese peroxidase activity of 21 ± 6 (U/g) under these conditions; enzyme that showed a suitable thermostability.

Biobleaching: An eco-friendly approach to reduce chemical consumption and pollutants generation

The pulp and paper industry is known to be a large contributor to environmental pollution due to the huge consumption of chemicals and energy. Several chemicals including H2SO4, Cl2, ClO2, NaOH, and H2O2 are used during the bleaching process. These chemicals react with lignin and carbohydrates to generate a substantial amount of pollutants in bleach effluents. Environmental pressure has compelled the pulp and paper industry to reduce pollutant generation from the bleaching section. Enzymes have emerged as simple, economical, and eco-friendly alternatives for bleaching of pulp. The pretreatment of pulp with enzymes is termed as biobleaching or pre-bleaching. Different microbial enzymes such as xylanases, pectinases, laccases, manganese peroxidases (MnP), and lignin peroxidases are used for biobleaching. Xylanases depolymerize the hemicelluloses precipitated on pulp fiber surfaces and improves the efficiency of bleaching chemicals. Xylanase treatment also increases the pulp fibrillation and reduces the beating time of the pulp. Pectinases hydrolyze pectin available in the pulp fibers and improve the papermaking process. Laccase treatment is found more effective along with mediator molecules (as a laccase-mediator system). Biobleaching of pulp results in the superior quality of pulp along with lower consumption of chlorine-based chemicals and lower generation of adsorbable organic halidesadsorbable organic halides (AOX. An enzyme pretreatment reduces the kappa number of pulp and improves ISO brightness significantly. Better physical strength properties and pulp viscosity have also been observed during biobleaching of pulp.

Vortex Fluidic-Mediated Fabrication of Fast Gelated Silica Hydrogels with Embedded Laccase Nanoflowers for Real-Time Biosensing under Flow

The fabrication of hybrid protein-Cu3(PO4)2 nanoflowers (NFs) via an intermediate toroidal structure is dramatically accelerated under shear using a vortex fluidic device (VFD), which possesses a rapidly rotating angled tube. As-prepared laccase NFs (LNFs) exhibit ≈1.8-fold increase in catalytic activity compared to free laccase under diffusion control, which is further enhanced by ≈ 2.9-fold for the catalysis under shear in the VFD. A new LNF immobilization platform, LNF@silica incorporated in a VFD tube, was subsequently developed by mixing the LNFs for 15 min with silica hydrogel resulting in gelation along the VFD tube surface. The resulting LNFs@silica coating is highly stable and reusable, which allows a dramatic 16-fold enhancement in catalytic rates relative to LNF@silica inside glass vials. Ultraviolet-visible spectroscopy-based real-time monitoring within the LNFs@silica-coated tube reveals good stability of the coating in continuous flow processing. The results demonstrate the utility of the VFD microfluidic platform, further highlighting its ability to control chemical and enzymatic processes.

Kinetic characterization, thermo-stability and Reactive Red 195A dye detoxifying properties of manganese peroxidase-coupled gelatin hydrogel

An indigenous and industrially important manganese peroxidase (MnP) was isolated from solid-state bio-processing of wheat bran by white-rot fungal strain Ganoderma lucidum IBL-05 under pre-optimized growth conditions. Crude MnP extract was partially purified (2.34-fold) to apparent homogeneity by ammonium sulphate precipitation and dialysis. The homogeneous enzyme preparation was encapsulated on gelatin matrix using glutaraldehyde as a cross-linking agent. Optimal conditions for highest immobilization (82.5%) were: gelatin 20% (w/v), glutaraldehyde 0.25% (v/v) and 2 h activation time using 0.6 mg/mL of protein concentration. Gelatin-encapsulated MnP presented its maximum activity at pH 6.0 and 60 °C. Thermo-stability was considerably improved after immobilization. The optimally active MnP fraction was tested against MnSO₄ as a substrate to calculate kinetic parameters. More than 90% decolorization of Sandal-fix Red C₄BLN (Reactive Red 195A) dye was achieved with immobilized MnP in 5 h. It also preserved more than 50% of its original activity after the sixth reusability cycle. The water quality parameters (pH, chemical oxygen demand, total organic carbon) and cytotoxicity (brine shrimp and Daphnia magna) studies revealed the non-toxic nature of the bio-treated dye sample. A lower K_m, higher V_max, greater acidic and thermal-resistant up to 60 °C were the improved catalytic features of immobilized MnP suggesting its suitability for a variety of biotechnological applications.

Phylogenetic and metabolic diversity of Tunisian forest wood-degrading fungi: a wealth of novelties and opportunities for biotechnology

In this study, 51 fungal strains were isolated from decaying wood samples collected from forests located in the Northwest of Tunisia in the vicinity of Bousalem, Ain Draham and Kef. Phylogenetic analysis based on the sequences of the internal transcribed spacers of the ribosomal DNA showed a high diversity among the 51 fungal isolates collection. Representatives of 25 genera and 29 species were identified, most of which were members of one of the following phyla (Ascomycota, Basidiomycota and Zygomycota). In addition to the phylogenetic diversity, a high diversity of secreted enzyme profiles was also detected among the fungal isolates. All fungal strains produced at least one of the following enzymes: laccase, cellulase, protease and/or lipase.

Characteristic features and dye degrading capability of agar-agar gel immobilized manganese peroxidase

Immobilization of enzymes has been regarded as an efficient approach to develop biocatalyst with improved activity and stability characteristics under reaction conditions. In the present study, purified manganese peroxidase (MnP) from Ganoderma lucidum IBL-05 was immobilized in agar-agar support using entrapment technique. Maximum immobilization yield was accomplished at 4.0% agar-agar gel. The immobilized MnP exhibited better resistance to changes in pH and temperature than the free enzyme, with optimal conditions being pH 6.0 and 50 °C. The kinetic parameters Km and Kcat/Km for free and entrapped MnP were calculated to be 65.6 mM and 6.99 M(-1) s(-1), and 82 mM and 8.15 M(-1) s(-1), respectively. Thermo-stability was significantly improved after immobilization. After 120 h, the insolubilized MnP retained its activity up to 71.9% and 60.3% at 30 °C and 40 °C, respectively. It showed activity until 10th cycle and retained 74.3% residual activity after 3th cycle. The effects of H2O2, ionic strength and potential inhibitors on activity of free and immobilized enzyme were investigated. Moreover, the decolorization of three structurally different dyes was monitored in order to assess the degrading capability of the entrapped MnP. The decolorization efficiencies for all the tested dyes were 78.6-84.7% after 12h. The studies concluded that the toxicity of dyes aqueous solutions was significantly reduced after treatment. The remarkable catalytic, thermo-stability and re-cycling features of the agar-agar immobilized MnP display a high potential for biotechnological applications.

Critical factors affecting laccase-mediated biobleaching of pulp in paper industry

Next to xylanases, laccases from fungi and alkali-tolerant bacteria are the most important biocatalysts that can be employed for eco-friendly biobleaching of hard and soft wood pulps in the paper industry. Laccases offer a potential alternative to conventional, environmental-polluting chlorine and chlorine-based bleaching and has no reductive effect on the final yield of pulp as compared to hemicellulases (xylanases and mannanases). In the last decade, reports on biobleaching with laccases are based on laboratory observations only. There are several critical challenges before this enzyme can be implemented for pulp bleaching at the industrial scale. This review discusses significant factors like redox potential, laccase mediator system (LMS)-synthetic or natural, pH, temperature, stability of enzyme, unwanted grafting reactions of laccase, and cost-intensive production at large scale which constitute a great hitch for the successful implementation of laccases at industrial level.

Laccase application in medium density fibreboard to prepare a bio-composite

Laccase efficacy as a biological tool for the removal of lignin in pulp industries is evident and has scope for a wider application.

Purification and biochemical characterization of a new alkali-stable laccase from Trametes sp. isolated in Tunisia: role of the enzyme in olive mill waste water treatment

A white-rot basidiomycete, isolated from decayed acacia wood (from Northwest of Tunisia) and identified as Trametes sp, was selected in a broad plate screening because of its ability to decolorize and dephenolize olive oil mill wastewater (OMW) efficiently. The major laccase was purified and characterized as a monomeric protein with apparent molecular mass of 61 kDa (SDS-PAGE). It exhibits high enzyme activity over broad pH and temperature ranges with optimum activity at pH 4.0 and a temperature of 60 °C. The purified laccase is stable at alkaline pH values. The enzyme retained 50 % of its activity after 90 min of incubation at 55 °C. Using ABTS, this laccase presented K m and V max values of 0.05 mM and 212.73 μmoL min(-1) mg(-1), respectively. It has shown a degrading activity towards a variety of phenolic compounds. The purified laccase was partially inhibited by Fe(2+), Zn(2+), Cd(2+) and Mn(2+), while Cu(2+) acted as inducer. EDTA (10 mM) and NaN3 (10 mM) were found to completely inhibit its activity. 73 % OMW was dephenolized after 315 min incubation at 30 °C with 2 U mL(-1) of laccase and 2 mM HBT.

Polymerisation of Kraft lignin from black liquors by laccase from Myceliophthora thermophila: effect of operational conditions and black liquor origin

The capacity of laccase from Myceliophthora thermophila to promote the oxidative polymerisation of Kraft lignin (KL) was evaluated in several conditions of pH, temperature, enzyme dosage and treatment time. Moreover, different black liquors from the Kraft cooking of Eucalyptus globulus and mixture of Pinus pinaster/E. globulus were evaluated in order to determine the effect of the KL source on the polymerisation reaction. Furthermore, one of these black liquors was fractionated by sequential organic solvent fractionation and the polymerisation of the corresponding fractions was tested. Polymerisation products were analysed by size exclusion chromatography and Fourier transform infrared spectroscopy. The results provide evidence of notable lignin modifications after incubation with laccase. Structural oxidation and a notably molecular weight increase were attained, reaching a polymer of 69-fold its initial molecular weight depending on the raw lignin. Moreover, optimum values of reaction conditions were obtained: pH 7.3, 70°C, 2UmL(-1) and 2h.

A new biobleaching sequence for kenaf pulp: influence of the chemical nature of the mediator and thermogravimetric analysis of the pulp

This paper evaluates five phenolic compounds as mediators for kenaf pulp biobleaching by laccase. The results have been compared with the treatment using a non-phenolic mediator, 1-hydroxybenzotriole and laccase alone. The influence of the nature of the chemical mediators used on various pulp properties is discussed. In addition to oxidizing lignin, the phenolic radicals formed in the process take part in condensation and grafting reactions in enzymatic stage. After biobleaching sequence (LP), syringaldehyde was shown to be the best phenolic mediator, allowing a delignification of 43% and 72% ISO brightness. These results were similar to the use of laccase alone due to the role as mediators of syringyl units resulting from oxidative lignin degradation. As a novelty, the study was supplemented with thermogravimetric analysis, with emphasis on the crystallinity degree of the cellulose surface and the aim of elucidating the action mechanisms of laccase-mediator systems on fiber.

An alkalophilic laccase from Rheinheimera species isolate: production and biobleaching of kraft pulp

Medium optimization was carried out to enhance laccase production from a novel Rheinheimera species, isolated from industrial effluent. Out of the 15 variables tested by Placket-Burman design (PBD)-yeast extract, soyabean meal, and peptone were the positively significant ones, enhancing laccase production. Both simple and complex sugars showed a negative effect on laccase production. Central composite design (CCD) of experiments, using the three positively significant variables in combinations, showed that laccase production was not affected by molar carbon, molar nitrogen levels or molar C/N ratio. Maximum laccase yield of 2.5 × 10(5) nkat L(-1) , 31 fold enhancement over the unoptimized medium, was achieved when soyabean meal (0.6%) was used alone as medium showing that laccase production was substrate dependent. Laccase was used, in the presence of 2 mM ABTS, for the biobleaching of eucalyptus kraft pulp resulting in kappa number reduction by 20% and brightness increase by 2.9%. Biobleaching improved further by sequential application of an alkalophilic xylanase (X) and laccase-ABTS system (LAS) that decreased kappa number by 10, 15, and 35%, increased brightness by 2.7, 3.2, and 5.9% as compared to X treated, LAS treated and untreated control, respectively. XLAS treatment resulted in 15, 13, 10.9% increase in burst factor, tear factor, and viscosity with a 20% reduced consumption of elemental chlorine and hypochlorite.

Laccase/HBT and laccase-CBM/HBT treatment of softwood kraft pulp: impact on pulp bleachability and physical properties

Pycnoporus cinnabarinus laccase and a chimeric laccase-CBM were applied in softwood kraft pulp biobleaching in the presence of 1-hydroxybenzotriazole (HBT). The presence of CBM could enhance the laccase biobleaching potential as a decrease in the enzymatic charge and chlorine dioxide consumption, as well as an increase in pulp brightness were observed. Laccase/HBT treatment could be improved by increasing oxygen pressure from 1 to 3bar and pulp consistency from 5% to 10%. Conversely, under the same conditions, no improvement of laccase-CBM/HBT treatment was observed, indicating a different behavior of both systems. However, laccase-CBM/HBT treatment led to a better preservation of pulp properties. This effect was probably due to fiber surface modifications involving the action of the CBM. Transmission electron microscopy examination of pulp fibers indicated a retention of laccase-CBM inside the pulp fibers due to CBM binding and an increased external microfibrillation of the fibers due to enzymatic treatments.

Role of laccase and low molecular weight metabolites from Trametes versicolor in dye decolorization

The studies regarding decolorization of dyes by laccase may not only inform about the possible application of this enzyme for environmental purposes, but also may provide important information about its reaction mechanism and the influence of several factors that could be involved. In this paper, decolorization of crystal violet and phenol red was carried out with different fractions of extracellular liquids from Trametes versicolor cultures, in order to describe the role of laccase in this reaction. Moreover, the possible role of the low molecular weight metabolites (LMWMs) also produced by the fungus was evaluated. The results confirm the existence of a nonenzymatic decolorization factor, since the nonprotein fraction of the extracellular liquids from cultures of T. versicolor has shown decolorization capability. Several experiments were performed in order to identify the main compounds related to this ability, which are probably low molecular weight peroxide compounds.

Assessing the environmental impact of biobleaching: effects of the operational conditions

The environmental impact of enzyme bleaching stages applied to oxygen-delignified eucalypt kraft pulp was assessed via the chemical oxygen demand (COD), color, absorbance spectrum, residual enzyme activity and Microtox toxicity of the effluents from a laccase-HBT (1-hydoxybenzotriazole) treatment. The influence of the laccase and HBT doses, and reaction time, on these effluent properties was also examined. The laccase dose was found to be the individual variable most strongly affecting COD, whereas the oxidized form of HBT was the main source of increased color and toxicity in the effluents. Moreover, it inactivated the enzyme. Oxidation of the mediator was very fast and essentially dependent on the laccase dose. Using the laccase-mediator treatment after a xylanase stage improved pulp properties without affecting effluent properties. This result holds great promise with a view to the industrial implementation of biobleaching sequences involving the two enzymes in the future.

Use of laccase in pulp and paper industry

Laccase, through its versatile mode of action, has the potential to revolutionize the pulping and paper making industry. It not only plays a role in the delignification and brightening of the pulp but has also been described for the removal of the lipophilic extractives responsible for pitch deposition from both wood and nonwood paper pulps. Laccases are capable of improving physical, chemical, as well as mechanical properties of pulp either by forming reactive radicals with lignin or by functionalizing lignocellulosic fibers. Laccases can also target the colored and toxic compounds released as effluents from various industries and render them nontoxic through its polymerization and depolymerization reactions. This article reviews the use of both fungal and bacterial laccases in improving pulp properties and bioremediation of pulp and paper mill effluents.

Thermogravimetry study of xylanase- and laccase/mediator-treated eucalyptus pulp fibres

Thermogravimetric analyses (TGA) was applied to study the effects of enzymatic bleaching of eucalyptus pulp with xylanase and a laccase-mediator system. The thermal degradation profile of the pulps was sensitive to the enzymatic treatments. Xylanase treatment produced an ordered and clean microfibril, whereas laccase oxidized surface cellulose chains and increased the amorphous (paracrystalline) cellulose content. In this case, pulp viscosity decreased from 972 to 859 mL/g and apparent pulp crystallinity calculated from TGA data decreased almost 50%. Alkaline extraction was necessary to recover pulp crystallinity and to remove oxidized lignin in the laccase-treated samples. TGA data allowed differentiating and quantifying crystalline and amorphous cellulose. This thermogravimetric approach is a simple method in order to monitor superficial changes in cellulosic microfibrils.

Biobleaching of Eucalyptus globulus kraft pulps: comparison between pulps obtained from exploded and non-exploded chips

The aim of this work was to evaluate the response to biobleaching of steam exploded kraft pulps and to compare the results with the controls. For this end, a laccase-mediator treatment using commercial laccase (Novozyme 51003) and a natural mediator (acetosyringone) were assayed, followed by alkaline extraction and hydrogen peroxide stages. Our approach resulted in exploded biobleached pulps with lower kappa number and improved optical properties compared to controls, even after subjecting pulps to accelerated ageing. Additionally, use of hydrogen peroxide was reduced. The LMS (laccase-mediator system) had a smaller impact on the properties of the bleached pulps and on hydrogen peroxide consumption than the steam explosion process did.

Reutilization of effluents from laccase-mediator treatments of kraft pulp for biobleaching

Several effluents from laccase-mediator treatments of kraft pulp were recovered and subsequently reused with fresh pulp in order to simulate recirculation of effluents during biobleaching. The effluents were used as a new bleaching stage without any modification except enzyme addition. Pulp treated with effluents were afterwards chemically bleached by using the simple sequence LQPo, where L represents the treatment with effluent and laccase addition, Q is a chelating stage and Po is an alkaline peroxide stage. This system showed a promising potential on delignification, with kappa number ranging from 5.5 to 6.6 after LQPo sequence, depending on the type of effluent employed in L stage. Improvements on pulp brightness were also reported compared with control experiment.