Jorge Gominho

Cynara cardunculus L. — a new fibre crop for pulp and paper production

Abstract The pulping potential of the thistle Cynara cardunculus L. was evaluated by studying anatomy and chemical composition of the stalks and Kraft pulp yields and properties. C. cardunculus is a perennial plant, with annual harvests, that can be grown in hot and dry climates with high productivities. The stalk of the plant has a central pith, ca. 45% in volume and 10% in weight, of small parenchyma cells, surrounded by a cortex where numerous fibre vascular bundles are imbedded. The fibres are on average 1.3 mm long, 18.8 μm wide and have a 4.8 μm wall thickness. The whole stalks have 7.7% ash, 14.6% extractives, 17.0% lignin and 53.0% polysaccharides, mainly cellulose and xylans. The pith has more lignin than the depithed stalk (20.3 vs. 13.6%). The Cynara stalks could be cooked by standard Kraft pulping to produce well delignified pulps with high yields (44–47% with Kappa 11–15), low rejects and very good strength properties, especially in relation to tensile strength. Depithing of the stalks has a positive impact on pulp yield, chemical consumption and on the pulp strength properties.

Down regulation of Cinnamyl Alcohol Dehydrogenase, a lignification enzyme, in Eucalyptus camaldulensis

A procedure for A. tumefaciens-mediated genetic transformation of a juvenile E. camaldulensis clone is presented. CAD antisense full-length cDNAs from Eucalyptus gunnii or Nicotiana tabacum was introduced under the control of the CaMV 35S DE promoter. From 44 individual transgenic shoots selected by PCR analysis, 32% exhibited a significant reduction of CAD activity, up to 83%. The use of the heterologous tobacco CAD cDNA construct was less efficient (up to 65% reduction). Transcript levels in 3 lines obtained using the homologous eucalyptus cDNA confirmed the under-expression of the CAD gene, and Southern blot data indicated a low transgene copy number ranging between 1 and 3. The most down-regulated plant contained a single transgene copy. Therefore, for the first time in eucalyptus, genetically modified plantlets exhibiting a strong inhibition of CAD activity associated with decreased transcription were recovered. Five transgenic lines, transferred to the greenhouse for 10 months, went through a wood chemical analysis that showed no differences in lignin quantity (through Fourier transform infrared spectroscopy), composition (through analytical pyrolysis) or pulp yield (through Kraft pulping) compared to control trees. Despite the down-regulation of the CAD gene in this Eucalyptus species of economic interest, the lack of significant changes in lignin profiles indicates that probably the trees were not sufficiently suppressed in CAD throughout development to exhibit obvious modifications in lignin and pulping. This raises the problem of the requirements for an efficient modulation of lignification in trees such as eucalyptus.

The influence of heartwood on the pulping properties of Acacia melanoxylon wood

The pulping wood quality of Acacia melanoxylon was evaluated in relation to the presence of heartwood. The sapwood and heartwood from 20 trees from four sites in Portugal were evaluated separately at 5% stem height level in terms of chemical composition and kraft pulping aptitude. Heartwood had more extractives than sapwood ranging from 7.4% to 9.5% and from 4.0% to 4.2%, respectively, and with a heartwood-to-sapwood ratio for extractives ranging from 1.9 to 2.3. The major component of heartwood extractives was made up of ethanol-soluble compounds (70% of total extractives). Lignin content was similar in sapwood and heartwood (21.5% and 20.7%, respectively) as well as the sugar composition. Site did not influence the chemical composition. Pulping heartwood differed from sapwood in chemical and optical terms: lower values of pulp yield (53% vs 56% respectively), higher kappa number (11 vs. 7), and lower brightness (28% vs 49%). Acacia melanoxylon wood showed an overall good pulping aptitude, but the presence of heartwood should be taken into account because it decreases the raw-material quality for pulping. Heartwood content should therefore be considered as a quality variable when using A. melanoxylon wood in pulp industries

Reactivity of syringyl and guaiacyl lignin units and delignification kinetics in the kraft pulping of Eucalyptus globulus wood using Py-GC-MS/FID

Eucalyptus globulus sapwood and heartwood showed no differences in lignin content (23.0% vs. 23.7%) and composition: syringyl-lignin (17.9% vs. 18.0%) and guaiacyl-lignin (4.8% vs. 5.2%). Delignification kinetics of S- and G-units in heartwood and sapwood was investigated by Py-GC-MS/FID at 130, 150 and 170°C and modeled as double first-order reactions. Reactivity differences between S and G-units were small during the main pulping phase and the higher reactivity of S over G units was better expressed in the later pulping stage. The residual lignin composition in pulps was different from wood or from samples in the initial delignification stages, with more G and H-units. S/G ratio ranged from 3 to 4.5 when pulp residual lignin was higher than 10%, decreasing rapidly to less than 1. The S/H was initially around 20 (until 15% residual lignin), decreasing to 4 when residual lignin was about 3%.

Stumps of Eucalyptus globulus as a Source of Antioxidant and Antimicrobial Polyphenols

These past years have seen an enormous development of the area of natural antioxidants and antimicrobials. Eucalyptus globulus is widely cultivated in subtropical and Mediterranean regions in intensive short rotation coppice plantations. In the Portuguese context, E. globulus is the third species in terms of forest area. The stump is the basal part of the tree, including the near-the-ground stem portion and the woody roots that remain after stem felling. The purpose of this work was to study the phytochemical profile and to evaluate the antioxidant and antimicrobial properties of several crude stump wood and stump bark extracts of E. globulus, comparing it with similar extracts of E. globulus wood (industrial chips). The results showed the presence of high concentrations of total phenolic compounds (>200 mg GAE/g extract) and flavonoids (>10 mg QE/g extract) in E. globulus stump extracts. Generally the stump wood extracts stands out from the other ones, presenting the highest percentages of inhibition of linoleic acid oxidation. It was also possible to conclude that the extracts were more active against Gram-positive bacteria, presenting low MIC values. This study thus provides information supporting the economic valorization of E. globulus stump wood.

Pulping Yield and Delignification Kinetics of Heartwood and Sapwood of Maritime Pine

Abstract In maritime pine (Pinus pinaster Ait.), heartwood represents a substantial part of the tree stem at final harvest age (80 years) corresponding to 42% at the base of the stem wood diameter and decreasing upward. The rate of heartwood formation was estimated at 0.35 rings/year, beginning at 18 years of age. Differences in the chemical composition between heartwood and sapwood were mainly in the extractives, 19.7% and 5.8%, respectively. The lignin content was 23.1% and 24.5% in the heartwood and sapwood, respectively. Pulping yield of the heartwood was lower than that of the sapwood (40.0% vs. 49.7%) and was negatively correlated with the extractives content. Extraction of heartwood prior to pulping increased the pulp yield and the delignification (lower residual lignin in pulps). Pulping kinetics showed lower yields for heartwood at all pulping stages, the difference occurring especially in the initial reaction phase. However, delignification rate constants were similar for heartwood and sapwood (3.1×10−2 min−1 and 2.7×10−2 min−1 for the main delignification phase for sapwood and heartwood, respectively), with a lower activation energy for sapwood (68.3 vs. 90.0 kJ · mol−1). The presence of heartwood decreases the raw‐material quality for pulping and this should be taken into account when harvesting trees for pulping processes.

Variation of Lignin Monomeric Composition During Kraft Pulping of Eucalyptus globulus Heartwood and Sapwood

Abstract Heartwood and sapwood samples from Eucalyptus globulus were characterized by Py-GC/MS and GC-FID in respect to composition and content of lignin. The pyrolysis lignin-derived compounds were assembled by groups: “syringol,” “S-aldehydes,” “S-ketones,” “S-alcohols,” and “C11H12O3” (S-units); “guaiacol,” “eugenol,” “G-aldehydes,” “G-ketones,” “G-alcohols,” and “others” (G-units); “phenol” and “H-aldehydes” (H-units). Heartwood and sapwood had similar lignin content in an extractive-free basis (23.7% and 23.0%, respectively) and in lignin composition (S-units, 76.0% vs. 76.3%; G-units, 22.0% vs. 21.0%; H-units, 1.9% vs. 2.7%; S/G ratio 3.5 and 3.6). The wood samples were kraft pulped under isothermal conditions at 130°C, 150°C and 170°C and several cooking times. Heartwood and sapwood behaved similarly. At 130°C the delignification was slow with no significant selectivity in respect to lignin composition. At 150°C and 170°C the S-units were more susceptible to reaction and comparatively more removed, inducing a decrease of S/G ratio to 0.6. The main products to be extracted belong to “syringol” and “S-aldehydes,” while the residual lignin in pulps was enriched in “guaiacol,” “eugenol” (G-units), and “phenol” (H-units).

ANATOMICAL CHARACTERISATION AND VARIABILITY OF THE THISTLE CYNARA CARDUNCULUS IN VIEW OF PULPING POTENTIAL

The thistle Cynara cardunculus L. is an herbaceous perennial with high productivity that is harvested annually and is a potential fibre crop for paper pulp production. The anatomical variation within stalks was studied (base, middle and top) and compared in C. cardunculus plants at different development phases. The stalk of C. cardunculus includes an epidermis, cortex and a central cylinder with fibro-vascular bundles with phloem, xylem and a fibrous sheath that is variable in arrangement and size within and between plants.At harvest, the pith represents 37% of the stalk transectional area and 7% of the total weight. There was a slight variation in quantitative features of, respectively, the three development groups studied; mean fibre length was 1.04 mm, 0.95 mm and 1.05 mm; mean fibre width was 15 μm, 16 μm and 21 μm; mean fibre wall thickness was 3.2 μm, 3.4 μm and 4.9 μm. Fibre length and width decreased within the stem from base to top, while fibre wall thickness increased. Mean vessel diameter was 22 μm and mean vessel element length 220–483 μm. In mature plants, parenchyma represents 39% of the total transectional area and fibres 25%. The proportion of fibres increases during plant development and in mature plants is highest at the stalk base.As regards anatomical features, Cynara stalks compare favourably to other annual plants and fibre biometry indicates good potential for paper sheet forming and strength properties.

Chemical characterization of cork and phloem from Douglas fir outer bark

Abstract Cork and phloem from Pseudotsuga menziesii outer bark were separated, fractionated and the 40- to 60-mesh fractions chemically analyzed. Cork and phloem showed a different grinding behavior with the highest yields for cork and phloem, respectively, for the 40- to 60-mesh fraction (31.4%) and the <0.180-mm fraction (49.2%). Cork chemical composition was (% o.d. mass): ash 0.9%; extractives 29.2% (mostly polar, 23.5%); lignin 16.8%, and suberin 36.2%. Polysaccharides (16.9%) contained glucose (55.4% of total neutral carbohydrates), xylose (13.3%), mannose, arabinose, and galactose as minor components. Lipophilic and suberin extracts from cork and phloem were analyzed by GC-MS, directly and after alkaline hydrolysis. In cork, catechin was the major compound identified in the lipophilic extract, accompanied by ferulic acid and acylglycerols. In phloem, β-sitosterol was the major compound. The content of fatty alcohols and fatty acids increased after hydrolysis confirming their esterification in both extracts. Suberin from P. menziesii cork is rich in saturated ω-hydroxyacids (ω-hydroxyacids 36.2%, α,ω-diacids 18.6%, alkanoic acids 6.2%, and alkanols 8.7%), being different from suberin of Quercus suber where α,ω-diacids are dominant.

Lignin Composition and Structure Differs between Xylem, Phloem and Phellem in Quercus suber L.

The composition and structure of lignin in different tissues—phellem (cork), phloem and xylem (wood)—of Quercus suber was studied. Whole cell walls and their respective isolated milled lignins were analyzed by pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) and derivatization followed by reductive cleavage (DFRC). Different tissues presented varied p-hydroxyphenyl:guaiacyl:syringyl (H:G:S) lignin compositions. Whereas lignin from cork has a G-rich lignin (H:G:S molar ratio 2:85:13), lignin from phloem presents more S-units (H:G:S molar ratio of 1:58:41) and lignin from xylem is slightly enriched in S-lignin (H:G:S molar ratio 1:45:55). These differences were reflected in the relative abundances of the different interunit linkages. Alkyl-aryl ethers (β–O–4′) were predominant, increasing from 68% in cork, to 71% in phloem and 77% in xylem, as consequence of the enrichment in S-lignin units. Cork lignin was enriched in condensed structures such as phenylcoumarans (β-5′, 20%), dibenzodioxocins (5–5′, 5%), as corresponds to a lignin enriched in G-units. In comparison, lignin from phloem and xylem presented lower levels of condensed linkages. The lignin from cork was highly acetylated at the γ-OH of the side-chain (48% lignin acetylation), predominantly over G-units; while the lignins from phloem and xylem were barely acetylated and this occurred mainly over S-units. These results are a first time overview of the lignin structure in xylem, phloem (generated by cambium), and in cork (generated by phellogen), in agreement with literature that reports that lignin biosynthesis is flexible and cell specific.