Anne-Christine Ritschkoff

The Effect of Oxidative Pretreatment on Cellulose Degradation by Poria-Placenta and Trichoderma-Reesei Cellulases

Abstract The possible role of hydrogen peroxide in brown-rot decay was investigated by studying the effects of pretreatment of spruce wood and microcrystalline Avicel cellulose with H2O2 and Fe2+ (Fentons reagent) on the subsequent enzymatic hydrolysis of the substrates. A crude endoglucanase preparation from the brown-rot fungus Poria placenta, a purified endoglucanase from Trichoderma reesei and a commercial Trichoderma cellulase were used as enzymes. Avicel cellulose and spruce dust were depolymerized in the H2O2/Fe2+ treatment. Mainly hemicelluloses were lost in the treatment of spruce dust. The effect of the pretreatment on subsequent enzymatic hydrolysis was found to depend on the nature of the substrate and the enzyme preparation used. Pretreatment with H2O2/Fe2+ clearly increased the amount of enzymatic hydrolysis of spruce dust with both the endoglucanases and the commercial cellulase. In all cases the amount of hydrolysis was increased about threefold. The hydrolysis of Avicel with the endoglucanases was also enhanced, whereas the hydrolysis with the commercial cellulase was decreased.

Purification and characterization of a thermophilic xylanase from the brown-rot fungus Gloeophyllum trabeum

A xylanase produced by the brown-rot fungus, Gloeophyllum trabeum, was purified to electrophoretic homogeneity by ion-exchange chromatography and gel filtration. The enzyme had an isoelectric point of 5.0 and molecular mass of 39–42 kDa, respectively. The xylanase appeared to prefer the most substituted glucurono-xylan (DMSO-xylan) as substrate and exhibited a pH optimum of 4.0 and a temperature optimum of 80°C after 30 min incubation. Approximately 22% of the activity remained after 2 h incubation at 70°C and the half-life of xylanase at 60°C was 24 h. The xylanase also showed β-glucanase activity with barley β-glucan as substrate as side activity. The xylanase of G. trabeum was very tolerant to inhibitors. Among the various inhibitors studied, only 10 mM AlCl3 was found to inhibit the xylanase activity.

Enzymatically polymerized phenolic compounds as wood preservatives

Abstract Phenolic compounds were studied as natural preservatives against wood decaying fungi. Vanillin and tannin decreased the growth of the test organisms Coniophora puteana and Coriolus versicolor and decreased the weight losses caused by these organisms in wood blocks. Both compounds were, however, leached in standard washing tests, and higher weight losses were observed in leached samples. Enzymatic polymerization with laccase was used as a means of binding the phenolic preservatives into the wood. Using an optimized laccase dosage, wood impregnation with enzymatically polymerized vanillin reduced the weight loss by C. puteana from 25% to 5%.

Screening of micro-organisms for decolorization of melanins produced by bluestain fungi.

Abstract. A total of 17 fungi and four bacteria were screened for their ability to decolorize melanin, using isolated extracellular melanin of the bluestain fungus Aureobasidium pullulans as substrate. On agar media, decolorization was observed by four fungal strains: Bjerkandera adusta VTT-D-99746, Galactomyces geotrichum VTT-D-84228, Trametes hirsuta VTT-D-95443 and Trametes versicolor VTT-D-99747. The four fungi were more efficient on nitrogen-limited medium than on complete medium. The melanin-decolorizing activity of G. geotrichum appeared to be located on the mycelium and could be liberated into the medium enzymatically.

Effect of carbon source on the production of oxalic acid and hydrogen peroxide by brown-rot fungus Poria placenta

Oxalic acid and hydrogen peroxide have been suggested to be essential in the degradation of wood carbohydrates by brown-rot fungi. The production of oxalic acid, hydrogen peroxide and endo-β-1,4-glucanase activity by the brown-rot fungus Poria placenta was studied on crystalline cellulose, amorphous cellulose and glucose media. Oxalic acid and hydrogen peroxide by P. placenta were clearly produced on culture media containing either crystalline or amorphous cellulose. Oxalic acid and hydrogen peroxide were formed simultaneously and highest amounts of oxalic acid (1.0 g l−1) and hydrogen peroxide (39.5 μM) were obtained on amorphous cellulose after 3 weeks cultivation. On glucose medium the amounts were low. The endoglucanase activity was observed to increase during the cultivation and was most pronounced on glucose medium and thus indicated the constitutive characteristics of the brown-rot cellulases.

Coating and surface treatment of wood

Coatings have a twofold basic functionality: (1) to protect the underlying material against deterioration and degradation by the adjacent environment and (2) to decorate or to improve the aesthetic properties of surface. Protection should be given against physical, chemical and biological attack, including water, chemical agents, UV-light, dirt and living organisms, fungi and algae in particular. The aesthetic function refers to characteristics like color performance, gloss and desired surface structure. Both functionalities play a crucial role in health and comfort and exploitation costs due to maintenance. This chapter focuses on wood protection, as related to the latest developments in wood coating technology and surface treatment.

Screening of the effect of biocidal agents released from poly (acrylic acid) matrices on mould growth

Abstract Recently, surface treatment concepts with slow release encapsulated activates have shown to provide a potential approach for the control of biological surface contamination. These new protection concepts respond to the current regulations and demands set for the sustainable development. In this study, screening of the efficacy of biocidal agents – benzoic acid and sodium benzoate – embedded in poly(acrylic acid) matrices was carried out. The efficacy of the polymer systems on mould growth was tested with the blue stain fungus Aureobasidium pullulans and with the mould fungi Trichoderma harzianum and Aspergillus niger. In addition, release of the active agents at different pH was determined in aqueous media. The release tests in aqueous media showed that the release of the active agents is more pronounced at pH higher than 4. The efficacy of the polymer systems according to the present arrangements was dependent on the fungi and the release rate of the active agents from the matrix.