Ingo Mayer

Topochemical investigations of wood extractives and their influence on colour changes in American black cherry (Prunus serotina Borkh.)

Abstract The topochemical distribution of accessory compounds responsible for wood colouration during heartwood formation and processing of black cherry (Prunus serotina) is restricted to the axial and ray parenchyma cells. (+)-Catechin, taxifolin, aromadendrin, eriodictyol, naringenin, 4′-methoxynaringenin and prunin were identified in acetone/water extracts. However, the colour of wood after extraction is still reddish-brown, indicating that the coloured material is polymeric (cross-linked, condensed). It was demonstrated that (+)-catechin plays a pivotal role in the development of heartwood colour. Its concentration at the sapwood/heartwood boundary decreases, presumably due to the formation of non-soluble polymeric proanthocyanidins. Heat treatment of heartwood during veneer production intensifies the reddish-brown heartwood colour, probably by promoting the polymerisation of (+)-catechin and other flavonoid monomers.

Hot water extraction of Norway spruce (Picea abies [Karst.]) bark: analyses of the influence of bark aging and process parameters on the extract composition

Abstract The hot water (HW) extraction of Norway spruce (Picea abies [Karst.]) delivers condensed tannins and considerable amounts of other compounds. Yield and composition of the HW extracts were investigated as a function of natural weathering for up to 15 months. Total phenol monomers and oligomers were detected by Folin-Ciocaltau assay after fractionation by solid phase extraction (SPE). Procyanidins (PC) were determined by HPLC-UV after acid thiolysis and carbohydrates by HPLC combined with acid hydrolysis. Topochemistry of the bark before and after extraction was investigated by UV-microspectrometry (UMSP) and non-extractable PC analyzed by direct thiolysis on the bark. The influence of the parameters on the yield and composition of the extracts were evaluated, such as the extraction temperature, time and the addition of sodium sulfate and urea. Prolonged weathering resulted in a considerable decrease of the total extraction yield, partly because of leaching of phenolic monomers, mono- and oligosaccharides. The yield of phenolic oligomers also decreased at a moderate rate, while the yield of polysaccharides (pectins) was almost stable. Non-extractable and non-leachable compounds deposited in the cell lumens represent the majority of the phenolic extractives in spruce bark. Sequential extractions performed at increasing temperature proved to be a suitable method for the recovery of tannin-rich extracts.

Wood Anatomical Characteristics and Chemical Composition Of Prosopis Laevigata Grown in the Northeast of Mexico

Structural heartwood characteristics for Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C. Johnst., including a histometrical evaluation, were obtained by light microscopy coupled with a digitised image analysis system. The growth ring boundaries of the semi-ring-porous or diffuseporous wood are often marked by a marginal parenchyma band. Average fibre length is 975 μm, the fibres are thick-walled with a single cell wall thickness of 13 μm on average. Average diameter of the vessels which are arranged in non-specific patterns differs significantly between earlywood (116 μm) and latewood (44 μm). The topochemical distribution of lignin and phenolic deposits in the tissue was investigated by means of scanning UV microspectrophotometry (UMSP). Thereby, in heartwood tissue the deposition of extractives in vessels, pit canals, parenchyma cells, fibre lumina and partly also in the S2 layers of the fibres was detected. Monosaccharides were qualitatively and quantitatively determined by borate complex anion exchange chromatography. Holocellulose content is between 61.5 and 64.7% and Klason lignin content between 29.8 and 31.4%. Subsequent extraction of the soluble compounds was performed with petrolether, acetone/water and methanol/water by accelerated solvent extraction (ASE). Total extractives content in heartwood ranges between 14 to 16% on a dry weight basis. Major compounds in acetone/water extracts were identified as (-)-epicatechin, (+)-catechin and taxifolin, and quantitatively determined by liquid chromatography (RP-HPLC-UV).

Characterization of Pinus nigra var. laricio [Maire] bark extracts at the analytical and pilot scale

Abstract Pinus nigra var. laricio bark and its hot-water extracts (HWE) obtained at an analytical and pilot plant scale have been characterized in terms of phenolic extractives, condensed tannins (CTs), carbohydrates and inorganic compounds. Analytical extractions with aqueous acetone were also performed for comparison with HWE. The bark contains 35.5 g kg−1 CT, and two-thirds of it could be extracted. Analytical HWE at 75°C led to a total yield of 56.4 g kg−1. The extracts are mainly composed of phenolic compounds (50.7%) and pectins (19.7%). CTs amount to 17.9% of the extracts and are procyanidins with a mean degree of polymerization (DP) of about 9. Non-tannin phenolic oligomers also occurred in the extracts, which could be identified by pyrolysis gas chromatography mass spectrometry (Py-GC/MS) as lignin fragments. Matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF MS) revealed that the CT is a flavanol derivative in methylated form. Further characterization and tailoring of the HWE properties is needed in the context of their specific application.