Papa Niokhor Diouf

Polyphenol contents and radical scavenging capacities of red maple (Acer rubrum L.) extracts

The crude ethanol and water extracts of different red maple (Acer rubrum L.) tissues: whole branches (WB), wood of branches (BW), bark of branches (BB), stem bark (SB) and whole twigs (T), were examined in order to determine their phenolic contents as well as their radical scavenging capacities. The total phenols (TP), total extractable tanins (TET) and non-precipitable phenols (NPP), were determined by combination of spectrophotometric and precipitation methods, while total flavonoids, hydroxy cinanmic acids and proanthocyanidins were determined spectrophotometrically. The radical scavenging activities of the extracts were determined against five reactive oxygen species (ROS): superoxide anion (O(2)(·-)), hydroxyl radical (HO(·)), peroxyl radical (ROO(·)), hypochlorite ion (ClO(-)), and hydrogen peroxide (H(2)O(2)) and one reactive nitrogen species (RNS): nitric oxide (NO). The extracts of stem bark were significantly more efficient (exhibiting the highest antioxidant efficiencies, AE) than the other studied extracts against all ROS (at p<0.05, Duncan statistical tests), except against NO. The correlation coefficients determined between total phenolic (TP) content and antiradical efficiencies were R(2)=0.12 for O(2)(·-); R(2)=0.29 for HO(·); R(2)=0.40 for H(2)O(2); R(2)=0.86 for ROO(·); R(2)=0.03 for NO(·) and R(2)=0.73 for ClO(-). Our results indicate potential utilisation of extracts as natural antioxidants.

Antioxidant, toxicological and antiproliferative properties of Canadian polyphenolic extracts on normal and psoriatic keratinocytes.

AIMS OF THE STUDY In a first attempt for establishing the possible utilization of polyphenolic extracts from barks of Canadian wood species in psoriasis treatment, we aimed to study (a) their antioxidant capacity, (b) their toxicological properties on normal human keratinocytes (NHK), and (c) their effect on the growth of normal and psoriatic keratinocytes (PK). MATERIALS AND METHODS Polyphenolic extracts were obtained by 90% ethanolic maceration and hot water extraction (HWE). Scavenging capacity was evaluated towards hydrogen peroxide, hydroxyl, superoxide, nitric oxide and peroxyl radicals. MTT assay and Trypan blue dye exclusion (TBDE) method were used for evaluating the initial toxicity of the most antioxidant extracts on NHK during 24 and 48 h. The effects of extracts on the growth of NHK and PK at non-toxic concentrations were determined after exposure for 48 h. RESULTS Yellow birch extract obtained by maceration (YB(Mac)) and black spruce extract obtained by HWE (BS(HWE)) were determined to have the highest antioxidant capacity, but BS(HWE) was less toxic on NHK. Toxicity of extracts on keratinocyte plasma membrane and mitochondria after 24 h was attributed to their content of hydroxycinnamic acids and proanthocyanidins. BS(HWE) inhibited the growth of NHK and non-lesional PK, but was not selective for lesional PK. CONCLUSION Given that BS(HWE) presented elevated content of total phenols and flavonoids and showed a low toxicity on NHK as well as an adequate chemical reactivity towards different radicals and some antiproliferative properties, it was considered as the most valuable extract obtained from barks of Canadian wood species.

Bioactive Polyphenols from Healthy Diets and Forest Biomass

In addition to their nutritive value, foods provide health benefits or have a role in disease prevention since they contain a wide range of phytochemicals which represent functional or bioactive components. These bioactive molecules present in foods are based on a variety of chemical structures, from carotenoids, through sterols and fatty acids, to different types of polyphenols. In this review, the polyphenols which are common constituents of vascular plants are explored. They are also common constituents of fruits and vegetables, teas and cocoas. The extractable polyphenols, obtainable by solvent extraction of the forest biomass, are of special interest as they are readily available form different types of forest and wood transformation residues. Flavonoids, cinnamic acid derivatives and proanthocyanidins, which share a part of their biosynthetic pathway with lignins, and therefore are associated with “woody” character of the plants, are reviewed along with some non-flavonoids important as food constituents such as stilbenes and hydrolysable tannins. The foods rich in these polyphenols are reviewed along with the forest sources of the same classes of molecules. The emphasis is put on residues of wood transformation such as bark and knotwood as these materials represent particularly rich resources for bioactive polyphenol classes. One of the most notorious bioactive properties of polyphenols is their antioxidant activity. The most important results on antioxidant capacity of forest trees extracts are presented and compared to those obtained for the extracts from healthy foods rich in polyphenols. These results are discussed also in relation to total phenol content of the studied extracts. Finally, the results on the application of selected types of polyphenols or extracts from forest biomass in prevention and/or treatment of diseases which are related to oxidative stress, cardiovascular disease, Alzheimer and cancer, are presented. It is clear from all discussed results, that the forest biomass in general and the residues of wood transformation in particular, represent the important natural resources of bioactive polyphenols. These residues have a real potential to be used as raw materials for the development of food supplements and/or functional foods which can enhance the animal and human health by disease prevention. They are also applicable for cosmetics and pharmaceutical products development, but their application in disease prevention remains more straightforward.

Antioxidant properties and polyphenol contents of trembling aspen bark extracts

Trembling aspen (Populus tremuloides Michx) bark was extracted with water and the crude extract fractionated with tert-butyl-methyl ether (TBME), ethyl acetate (EtOAc) and n-butanol (BuOH) to obtain four different fractions. The antioxidant properties of the bark hot water extracts and its fractions were determined by three in vitro experiments: DPPH assay, phosphomolybdenum assay and canola oil thermoxidation assay by DSC analysis. Most of the results of the reported tests showed that the crude hot water extract and its fractions exhibited a strong antioxidant activity, higher than the synthetic antioxidant BHT. The results of this study confirm that antioxidant activity is a property that strongly depends on the oxidation conditions used in the particular oxidation test. Among the fractions separated from the aqueous extracts of bark, BuOH, TBME and EtOAc soluble fractions exhibited the best antioxidant efficiency, in phosphomolybdenum assay, DPPH assay and canola oil thermoxidation, respectively. Total phenol, flavonoid and flavanol contents were also evaluated and the results confirmed that the polyphenols contained in the hot water extract of this bark are mainly composed of non-flavonoid compounds.

Electrophoretic Deposition of Biocomposite Lignin/Hydroxyapatite Coatings on Titanium

In this work, electrophoretic deposition (EPD) was applied to obtain novel hydroxyapatite (HAP)/lignin (Lig) biocomposite coatings on titanium substrate. Nanosized hydroxyapatite powder, prepared by using the modified chemical precipitation method, was used for the fabrication of HAP/Lig composite coatings. EPD was performed at different values of constant voltage and constant deposition time. It was confirmed that control over deposited mass can be achieved by applied voltage and time. The uniform and compact coatings were successfully deposited at applied voltage of 60 V in various deposition times lower than 1 minute. The effect of lignin as natural non-toxic polymer on microstructure, morphology and thermal behavior of biocomposite HAP/Lig coatings was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The electrophoretically deposited HAP/Lig coating has been successfully sintered at lower sintering temperature of 900°C, producing non-fractured coating and indicating that lignin may exhibit adhesive role, strengthening the bonding between HAP particles and substrate surface.

Chemical Changes Induced by High-Speed Rotation Welding of Wood — Application to Two Canadian Hardwood Species

The chemical changes occurring upon rotational welding with dowels of Canadian wood species sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) were examined by pyrolysis-GC/MS, DSC and XPS anlayses. The analyses performed separately on wood substrate (reference wood) and welded material by pyrolysis-GC/MS, DSC and XPS indicate that the differences in mechanical performances of the two welded woods are due mainly to the differences in original lignin structures as well as in the welding temperatures determined for the two wood species. The more pronounced guaiacyl character of the maple wood lignin seems to explain the preferential condensation reactions of the guaiacyl moieties in maple lignin with formaldehyde and furanic compounds released from lignin and carbohydrates during the fast pyrolysis associated with the welding process. The higher temperature determined for maple wood welding than for birch could be responsible for enhanced miscibility of wood polymers in the welding zone, explaining, therefore, the more significant presence of xylan polymer together with newly formed lignin carbohydrate complex (LCC) in the welded material. The detailed analysis of the compounds identified by pyrolysis-GC/MS, together with the results of the other two methods applied in this study, has confirmed that the S/G ratio cannot be taken as the sole criterion for the discussion of the chemical changes in lignins during welding of wood.

Wood-Dowel Bonding by High-Speed Rotation Welding — Application to Two Canadian Hardwood Species

The aim of this work was to investigate the possibility to apply high-speed rotation-induced wood-dowel welding technique to two Canadian hardwood species commonly used for furniture and structural applications, sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis). Different factors have been evaluated such as the wood species, the grain orientation, the rotation rate, as well as the receiver hole diameter. The results indicate that high-speed rotation-induced wood-dowel welding can be suitable for these two wood species with average tensile strength values comparable to their respective PVAc-glued joints. Additionally, wood-welded joints presented higher water resistance than their glued-joint counterparts. The results of the temperature measurements confirm that the softening and degradation temperatures of wood components have been reached during the welding process. The X-ray microdensitometry analyses show an increase of density for the interfacial material between the wood substrate and the dowel, the profile of which is more uniform for sugar maple than for birch. The scanning electron micrographs of the interfacial contact zone confirm the different extents of wood-to-wood welding.

An investigation of thermochemical changes in Canadian hardwood species during wood welding

Thermochemical changes during wood-dowel welding were investigated in two Canadian hardwood species commonly used for indoor appearance applications: sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis). The original reference wood sample and the welded interface between two bonded wood pieces, a dowel and a substrate, were compared to explain differences in mechanical properties between species. Pyrolysis gas chromatography–mass spectrometry (Py-GC/MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) were used. The gases emitted during wood welding were determined by Py-GC/MS and gas chromatography coupled with a thermal conductivity detector and a flame ionization detector (GC-TCD/FID). Results showed that thermal welding of birch and maple woods degrades hemicelluloses and affects lignin polymer through depolymerisation. Welding effectiveness is therefore directly associated with the properties of the original wood constituents, primarily lignin and carbohydrates. The lignin-related changes at the welded interface were greater for sugar maple than for yellow birch, corroborating mechanical property differences observed between the two species. The gases proportions were similar for both species and no harmful gases were detected in the smoke released during welding process.ZusammenfassungUntersucht wurden die thermochemischen Veränderungen, die beim Einbringen von Dübeln mittels Reibschweißen in zwei in Kanada für Innenanwendungen häufig verwendeten Laubholzarten Zuckerahorn (Acer saccharum) und Gelbbirke (Betula alleghaniensis) auftreten. Die Schweißfläche zwischen den zwei verbundenen Holzteilen, einem Dübel und einem Holz, und dem nicht betroffenen Holz wurden verglichen, um unterschiedliche mechanische Eigenschaften beider Holzarten anhand von Pyrolyse-Gaschromatographie–Massenspektrometrie (Py-GC/MS), Fourier-Transformations-Infrarot-Spektroskopie in abgeschwächter Totalreflexion (ATR-FTIR) und Röntgen-Photoelektronenspektroskopie zu bestimmen. Die beim Reibschweißen emittierten Gase wurden bestimmt mittels Py-GC/MS und Gaschromatographie gekoppelt mit einem Wärmeleitfähigkeitsmesser und einem Flammenionisationsdetektor (GC-TCD/FID). Die Ergebnisse zeigten, dass beim Reibschweißen von Birken- und Ahornholz Hemicellulosen abgebaut werden und auch das Ligninpolymer depolimerisiert wird. Die Güte der Verschweißung hängt deswegen direkt von den Eigenschaften der zu verschweißenden Holzbestandteile ab, insbesondere dem Lignin und der Kohlenhydrate. Veränderungen des Lignins an der Schweißfläche waren bei Zuckerahorn größer als bei Gelbbirke und bestätigen damit die unterschiedlichen mechanischen Eigenschaften beider Holzarten. Die Gasanteile waren bei beiden Holzarten vergleichbar und im Rauch, der beim Schweißen entsteht, wurden keine schädlichen Gase festgestellt.