Tamás Hofmann

Quantitative TLC Analysis of (+)-Catechin and (-)-Epicatechin from Fagus sylvatica L. with and without Red Heartwood

The aim of this study was to investigate the role of (+)-catechin and (-)-epicatechin in the molecular processes of formation of red heart-wood, a structural and color anomaly of living beech which causes substantial economic loss. The causes of the formation of red heart-wood and the molecular carriers and participants are unknown. It has been proven that the activity of phenol oxidizing enzymes (POD, PPO) increases at the color boundary, but the phenolic compounds participating in these reactions, and probably building up the red chromophores are unknown. Catechins play an important role in defense reactions against oxidative stress in plant tissues and are also major phenolic constituents of beech wood. A simple and readily applicable TLC method has been implemented to measure the radial distribution of the concentrations of the two epimers in healthy and discolored beech disks. The reactions at the color boundary could also be tracked by use of this technique. The results show unequivocally the role of the two catechins, and presumably the role of other flavan-3-ols also, in the formation of the red chromophores. By establishing the exact composition of the red chromophores the color stability of red-heartwood material and its industrial utilization could also be enhanced.

TLC analysis of the in-vitro reaction of beech ( Fagus sylvatica L.) wood enzyme extract with catechins

The factors affecting the economically and sylviculturally disadvantageous formation of red heartwood in beech are only partly understood. It has already been proved that at the color boundary of the red heart the total phenol concentration decreases sharply whereas the activity of oxidative enzymes (POD, PPO) increases substantially. The concentrations of (+)-catechin and (–)-epicatechin fall drastically and the five taxifolin and quercetin glycosides undergo hydrolysis. It is unclear, however, what role the flavonoids present at the boundary ((+)-catechin, (–)-epicatechin, taxifolin, and quercetin) have in the formation of the red chromophores of the heartwood. Understanding the transformation of the precursors and analysis of the products could result an enhanced utilization of redheartwood timber and better understanding of the physiology of red heartwood formation. In this work the role of catechins has been investigated by in-vitro transformation of (+)-catechin and (–)-epicatechin by extracts of beech wood enzymes. Thin-layer chromatography with scanning densitometry and acquisition of the products’ UV–visible reflection spectra proved suitable for monitoring the reactions and analyzing the products. Result have shown that rapid oxidation and oligomerization of the catechins is caused by beech enzyme extract. In-vitro products have also been compared with the chromophores of beech red heartwood. Conclusions have been drawn regarding the physiology of red heartwood formation.

High-performance thin-layer chromatographic assessment of thermally modified wood

Thermal modification (180–260°C) improves the dimensional stability, color, durability, and thermal insulation properties of wood, extending its usability into a wider range of applications [1–3]. The process does have some disadvantages, however: detrimental changes of the strength, hardness, and density of the wood, color instability, and emission of VOCs from the wood. The changes in the structure and chemistry during the modification are complex and “still far from being completely understood” [4]. By understanding these changes the process could be optimized, disadvantages could be reduced, and efficient solutions could be proposed. HPTLC, OPLC, and GC–MS have been used for separation of phenolic compounds, sugars and VOCs, respectively. The types and quantities of these compounds give information about the transformation of wood constituents during the treatment. Results have revealed distinct changes during intensification of the treatment. Substantial differences between wood species and tissue types have been shown, for example differences between hardwood and softwood species and sap- and heartwood tissues, which suggest different types and/or rates of transformation reactions for individual species. Further research is also required to establish connections between the distinct changes in the chemistry and in the physical properties of different wood species [5].

Utilization of Oak (Quercus petreae (Matt.) Liebl.) Bark for Anaerobic Digested Biogas Production

Abstract Fossil fuel depletion has led to an increasing number of research studies and applications focusing on renewable energy, such as different types of biomass. Lignocellulosic biomass represents an abundant source of biomass suitable for energy production in various forms. The present research investigates the application possibility of pedunculate oak bark (Quercus petrea (Matt.) Liebl.) for the production of biogas via anaerobic digestion. This research has significant novelty, as only a few examples on the utilization of tree bark wastes for the production of biogas can be found in the scientific literature. One of the key factors of increasing biogas yield is the efficient hydrolysis of the basic material, which is achieved by different pretreatment methods. In this study, oak bark was pretreated by microwave energy, by extraction, and by the combination of these two methods. The semi-continuous thermophylic anaerobic digestion of untreated oak bark resulted a 76.3 ml/g volatile solid specific methane yield over a 50-day period, which was not significantly lower than methane yield gained from pretreated basic material. Results indicated that oak bark is suitable for the production of biogas even without the application of the investigated pretreatment techniques. As extraction of oak bark does not impair biogas production, the complex biorefinery utilization of oak bark in the form of extraction bark polyphenols and the subsequent anaerobic fermentation of lignocellulosic residue can be accomplished in the future.

HPTLC assessment of phenolic extractives in selected extraneous woods

Wood is composed of structural constituents (lignin, cellulose, and hemicelluloses) as well as various extractives. The quality and quantity of extractives are highly dependent on the wood species and the type of the tissue (heartwood or sapwood) [1–3]. Despite their fairly low concentration, they significantly determine the technological properties and utilization of wood and can have beneficial as well as harmful effects on human health [2].

HPTLC investigation of a ring-like discoloration of pedunculate oak (Quercus robur L.) heartwood

Discoloration of industrially important woods causes substantial economic loss. Although color defects are not always associated with structural degradation of wood, they are still a significant problem which negatively affects the applicability, and thus the value, of the wood. It has been proved that during discoloration of wood oxidation and polymerization of phenolic compounds usually occurs, yielding quinones and their oxidized polymers with high molecular weight. The products formed substantially effect not only the color of the wood, but also its durability, processability, and even its mechanical properties. It is therefore necessary to investigate the products formed by the discoloration processes and to invent methods for preliminary chemical indication of possible color defects in living trees and in cut logs. Pedunculate oak occupies 8% of forest sites of Hungary. The most significant type of discoloration, becoming increasingly frequent lately, not only in Hungary but also in Europe, is the so called ‘ring-like discoloration’ of oak heartwood. The causes and the chemical and enzymatic reactions resulting in the discoloration are not yet known. HPTLC separation then qualitative and quantitative scanning densitometry proved to be a rapid, effective, and reliable analytical technique for tracking and identifying the polyphenols associated with the discoloration. From among the tannins present in oak heartwood, gallic acid has been proved to undergo significant changes in concentration in the discolored tissues. The results could contribute to elucidating the causes of the discoloration, working out effective preventative strategies, and enhancing the treatment and utilization of discolored oak wood.