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Comparative studies of the effects of two commercial enzyme formulations on fiber refining were conducted. Extensive basic characterisation of the enzymes involved, assessment of their hydrolytic activities on different model substrates as well as on different pulps (softwood sulfate, softwood sulfite, hardwood sulfate) were evaluated. Both enzyme formulations showed endoglucanase as well as some xylanase and β-glucosidase activity. In addition, Enzyme A reached a CMC end viscosity of 19.5 mPa compared to 11.1 mPa for Enzyme B. Reducing sugar release almost doubled from 695 μmol mL -1 for hardwood sulfate pulp to 1300 μmol mL -1 for softwood sulfite pulp with Enzyme B under the same conditions. Enzyme A increased the degree of refining even under non-ideal conditions from 23 °SR to up to 50 °SR. Further characterization of hand sheets, made from enzyme pre-treated and refined cellulose fibers with Enzyme A and B, showed that Enzyme A had the best effects leading to hand sheets with increased tensile strength and low air permeability. In summary, the increase in the degree of refining seen for Enzyme A correlated to higher xylanase and β-glucosidase activity and lower endoglucanase activity., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Two enzymatic extracts obtained from xylan-grown Aspergillus terreus CCMI 498 and cellulose-grown Trichoderma viride CCMI 84 were characterised for different glycanase activities. Both strains produce extracellular endoxylanase and endoglucanase enzymes. The enzymes optimal activity was found in the temperature range of 45-60 degrees C. Endoglucanase systems show identical activity profiles towards temperature, regardless of the strain and inducing substrate. Conversely, the endoxylanases produced by both strains showed maximal activity at different pH values (from 4.5 to 5.5), being the more acidic xylanase produced by T. viride grown on cellulose. The endoglucanase activities have an optimum pH at 4.5-5.0. The endoxylanase and endoglucanase activities exhibited high stability at 50 degrees C and pH 5.0. Mannanase, beta-xylosidase, and amylase activities were also found, being the first two activities only present for T. viride extract. These two enzymatic extracts were used for mixed office wastepaper (MOW) deinking. When the enzymatic extract from T. viride was used, a further increase of 24% in ink removal was obtained by comparison with the control. Both enzymes contributed to the improvement of the paper strength properties and the obtained results clearly indicate that the effective use of enzymes for deinking can also contribute to the pulp and paper properties improvement.

The influence of lignin, lignin model compounds, and black liquor from the kraft pulping process on the hydrolysis of xylan by xylanase was investigated. Addition of vanillic acid, acetovanillone, and protocatechuic acid increased the rate of hydrolysis of xylan by as much as 18-50% at low concentrations, but reached maxima at about 0.05% concentration. Addition of vanillin caused a 15% improvement in xylan hydrolysis, while addition of guaiacol more than doubled the hydrolysis rate. Increasing concentrations of either lignin or black liquor also increased the hydrolysis rate of xylan. Circular dichroism spectroscopy indicated a change in the structure of xylanase in the presence of black liquor.

The extracellular xylanase from Bacillus stearothermophilus T-6 is a thermostable alkaline tolerant enzyme that was found to bleach pulp optimally at pH 9 and 65 degrees C, and was successfully used in a large-scale bio-bleaching mill trial. In an attempt to obtain a heavy atom derivative suitable for complete X-ray analysis, xylanase T-6 was labeled biosynthetically with seleno-methionine, resulting in a 'built-in' array of atoms with specific X-ray anomalous scattering signal. Optimization of growth conditions resulted in over 0.8 g of homogeneous seleno-methionine xylanase T-6 per liter culture. The seleno-methionine enzyme was shown to be fully active and produced single crystals suitable for complete multiple wavelength anomalous diffraction (MAD) structural analysis.