Manfred Amann

Removal of monomer delignification products by laccase from Trametes versicolor

The influence of a laccase from Trametes versicolor on the removal of phenolic monomers in liquid hot water pretreated wheat straw supernatants (LHW-S) was examined. Beside the total phenol content derived by Folin-Ciocalteu (FC-) assay, phenolic monomers were measured via headspace-solid phase micro-extraction (HS-SPME)/GC-MS. A notable decrease of the phenols was achieved using 0.2 and 0.5 U/mL laccase whilst higher dosage showed no improvement. Nearly all kind of monomer phenolic compounds identified in the LHW-S were found to be removed after 24h. However, acetophenone and 4-hydroxybenzaldehyde (HBA) were obviously not affected by laccase. Summarizing, three laccase reaction groups (LRG) of phenolic monomers could be classified: immediate removal (LRG-A), degradation after 1 day (LRG-B), no effect of laccase (LRG-C). Additionally, HS-SPME/GC was found to be a powerful tool to study the reaction of laccase and phenolic monomers in complex lignocellulose derived solutions.

Development and optimization of single and combined detoxification processes to improve the fermentability of lignocellulose hydrolyzates

In this work, an enzyme catalyzed detoxification process of lignocellulose hydrolyzates with immobilized laccase from Trametes versicolor was developed and optimized. Further, the immobilized laccase significantly reduced the amount of toxic phenolic compounds in the xylan rich fraction (XRF) by polymerization within 1h. The insoluble products precipitated onto the carrier surface and could be reversible resolubilized by an aqueous ethanol solution. Consequently, an in situ product removal could be realized. The reusability of the immobilized laccase could be additionally shown. The reaction kinetics could be described by a reversible Michaelis Menten equation giving the prerequisite for scaling up the process. In a second step, the organic acids, hydroxymethylfurfural and phenolic acids could be further removed by employing an anion exchanger. Both, the laccase and the laccase+anion exchanger treatment enhanced successfully the fermentability of an organosolv wheat straw fraction.

The difference between cholesterol-and glycyrrhizin-γ-cyclodextrin complexes— an analysis by MD simulations in vacuo and in aquo and the calculation of solvation free energies with AMSOL

Abstract Glycyrrhizin forms very stable, freely water-soluble inclusion complexes with cyclodextrin. In contrast, the [cholesterol// γ -cyclodextrin] complex is very sparingly soluble in aquo. The molecular dynamics simulations and AMSOL calculations reported in this paper support these experimental findings: cholesterol is much less soluble than glycyrrhizin, glycyrrhetinic acid, diglucuronic acid and γ -cyclodextrin. The [glycyrrhizin// γ -cyclodextrin] complex is the most stable one. The previously reported unusually large dipole moments of cyclodextrins were only found in the simulations; AMSOL calculations suggest a dipole moment of about 2 Debye for γ -cyclodextrin. The simulations illustrate how the guest molecules become included in the cyclodextrin cavity.