Levente Albert

Thermal degradation of wood during photodegradation

In this study, wood samples were exposed to light irradiations (direct sunlight, xenon lamp, mercury vapour lamp) and thermal treatments were carried out in dry- and in humid conditions at 90°C. One part of the samples was covered by an aluminium plate during light irradiation. The samples under the aluminium plate also suffered considerable chemical changes, monitored by infrared technique and colour measurement. The sunlight produced greater colour change under the aluminium plate than the artificial light sources. During light irradiation, the carbonyl band having two maximum at 1700 and 1,746 cm(-1) increased and the peak of the aromatic skeletal vibration arising from lignin (1,510 cm(-1)) decreased together with the guaiacyl vibrations at 1,275 cm(-1). There was absorption decrease at 1,174 cm(-1) because of the ether band splitting. Under the covered surface only the ether band at 1,174 cm(-1) decreased and one carbonyl band increased with a maximum at 1,715 cm(-1). Degradation of lignin was negligible for the covered surface. Colour change generated by thermal degradation was much greater in humid condition than in dry condition.

Laboratory scale examination of the effects of overloading on the anaerobic digestion by glycerol.

The anaerobic digestion of pure glycerol, which produces a baseline acetic acid to propionic acid ratio of 0.2, was studied in laboratory scale reactors (3 l working volume) at mesophilic temperature (37 °C) with 3000 mg chemical oxygen demand (COD)l(-1) d(-1). During the experiment tVFA and C2-C6 VFA analysis and daily biogas yield measurement were carried out. Following 10 days of a 15% d(-1) increase in the organic loading rate (OLR) of 3.0-10.5 g COD l(-1) d(-1), the concentration of propionic acid increased to 6200-8000 mg l(-1). Then the inoculum was divided into three parts feeding with 100% glycerol, 50% glycerol + 50% acetic acid, and 50% glycerol + 50% thick stillage, (presented in % of 2.60 g COD l(-1) d(-1) OLR), respectively. The application of co-substrates reduced the recovery period by 5 days compared to feeding with pure glycerol. When the reactors were loaded with glycerol again (10% OLR raise per day) the previously applied co-substrates had a positive effect on the VFA composition and the biogas yield as well.

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.

The high-performance liquid chromatography/multistage electrospray mass spectrometric investigation and extraction optimization of beech (Fagus sylvatica L.) bark polyphenols.

The aim of the present work was the high-performance liquid chromatographic separation and multistage mass spectrometric characterization of the polyphenolic compounds of beech bark, as well as the extraction optimization of the identified compounds. Beech is a common and widely used material in the wood industry, yet its bark is regarded as a by-product. Using appropriate extraction methods these compounds could be extracted and utilized in the future. Different extraction methods (stirring, sonication, microwave assisted extraction) using different solvents (water, methanol:water 80:20 v/v, ethanol:water 80:20 v/v) and time/temperature schedules have been compared basing on total phenol contents (Folin-Ciocâlteu) and MRM peak areas of the identified compounds to investigate optimum extraction efficiency. Altogether 37 compounds, including (+)-catechin, (-)-epicatechin, quercetin-O-hexoside, taxifolin-O-hexosides (3), taxifolin-O-pentosides (4), B-type (6) and C-type (6) procyanidins, syringic acid- and coumaric acid-di-O-glycosides, coniferyl alcohol- and sinapyl alcohol-glycosides, as well as other unknown compounds with defined [M-H](-) m/z values and MS/MS spectra have been tentatively identified. The choice of the method, solvent system and time/temperature parameters favors the extraction of different types of compounds. Pure water can extract compounds as efficiently as mixtures containing organic solvents under high-pressure and high temperature conditions. This supports the implementation of green extraction methods in the future. Extraction times that are too long and high temperatures can result in the decrease of the concentrations. Future investigations will focus on the evaluation of the antioxidant capacity and utilization possibilities of the prepared extracts.

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.

Overpressured-layer chromatographic determination of ascorbigen (bound vitamin C) in Brassica vegetables

A simple and efficient method is described for separation and determination of ascorbigen in Brassica vegetables by overpressured-layer chromatography. Natural ascorbigen was identified from chromatographic retention, UV spectral, and mass spectrometric data using the authentic substance for comparison. Quantification of ascorbigen revealed significant differences (4.52-26.81 mg kg-1) among the species studied. The highest level of endogenous ascorbigen was observed in the sample prepared from broccoli (26.81 mg kg1).

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].

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.