Kenji Iiyama

Phenolic acid bridges between polysaccharides and lignin in wheat internodes.

Saponification at room temperature and alkaline treatment at 170° was used to release cinnamic acids in ester and α-aryl ether linkages, respectively, from polymeric components of mature and maturing wheat internodes. The wall components contain similar amounts of esterified and etherified cinnamic acids. Ferulic acid (FA) was the predominant etherified cinnamic acid. The results confirm those obtained using room temperature saponification and alkaline nitrobenzene oxidation. The content and type of linkage of p-coumaric (PCA) and FA in Bjorkman lignins and fractions obtained during their purification were compared in extract-free, ball-milled wheat internode walls, with and without, prior saponification with 0.5 M sodium hydroxide at room temperature. The small amounts of Bjorkman lignin from untreated wheat internodes contained chiefly esterified PCA. However, in the corresponding lignin fraction from pre-saponified internodes, which was obtained in high yield, the cinnamic acids were mainly in the etherified form and FA predominated. These results are interpreted in terms of a structure with polysaccharide-ester-FA-ether-lignin bridges which on saponification release large amounts of a Bjorkman lignin equivalent beariing esterified FA.

Bonding of hydroxycinnamic acids to lignin: ferulic and p-coumaric acids are predominantly linked at the benzyl position of lignin, not the β-position, in grass cell walls

A suspension in dichloromethane-water (18:1, v/v) of various fractions containing hydroxycinnamic acid ester-ether bridges between lignin and polysaccharides prepared from cell walls of matured oat (Avena sativa L.) intemodes, and a solution of their acetates in the same solvent, were treated with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). This reagent selectively cleaves benzyl ether and ester linkages of negatively charged aromatic nuclei. The sample treated with DDQ was directly hydrolysed either under mild (1 M NaOH, overnight at 37 degrees C) or severe (4 M NaOH, for 2 h at 170 degrees C) conditions. The hydroxycinnamic acids released in the hydrolysate were methylated with diazomethane and analysed quantitatively using gas chromatography. Significant portions of ether linkages between hydroxycinnamic acids and lignin were cleaved with DDQ, which suggests that most of the hydroxycinnamic acids were ether-linked at the benzyl position, and not the beta-position, of the lignin side chain as previously claimed.

Excellent oil absorbent kapok [Ceiba pentandra (L.) Gaertn.] fiber: fiber structure, chemical characteristics, and application

The study focused on kapok [Ceiba pentandra (L.) Gaertn.] fruit as a biomass for effective utilization. Kapok fruits were harvested just before full maturation at the campus of University of the Philippines Los Banos and in southern Vietnam. The kapok fibers are utilized locally as fiberfill in pillows, quilts, and some soft toys. Kapok fiber was isolated and analyzed microscopically, and the physicochemical properties were determined by spectroscopic methods. Some tests were done to determine the effective utilization of kapok fiber. Microscopic analysis of the higher structure of kapok fiber gave quite different results from cotton fiber, which has a significantly homogeneous hollow tube shape and is composed of cellulose (35 % dry fiber), xylan (22%), and lignin (21.5%). Kapok fiber is characterized by having a high level of acetyl groups (13.0%). Usually cell walls of plants contain about 1%–2% of acetyl groups attached to noncellulosic polysaccharides. Kapok fiber is significantly hydrophobic and does not get wet with water. Thus, the absorptivity of oil was tested. The fiber selectively absorbed significant amounts of oil (40 g/g of fiber) from an oil suspension in freshwater and seawater. It is suggested that this fiber could be used to recover oil spilled in seawater.

Preparation of binderless boards from steam exploded pulps of oil palm (Elaeis guneensis Jaxq.) fronds and structural characteristics of lignin and wall polysaccharides in steam exploded pulps to be discussed for self-bindings.

Oil palm (Elaeis guineensis Jacq.) is one of the most abundant, unutilised waste biomass from plantation in South-East Asia. The binderless boards were prepared from steam-exploded pulps of oil palm fronds and characterised for the mechanical strengths and chemical natures to discuss mechanism of self-binding. The mechanical strength of these boards satisfied the requirements of the relevant standard specifications (JIS: Japanese Industrial Standards) for the boards. To make clear the mechanism of the self-bonding of these binderless boards, oil palm fronds themselves, their steam exploded pulps, boards and lignins isolated by Bjorkmans procedure from extract-free oil palm try fronds and steam exploded pulps, were analysed by chemical and spectrometrical methods and pyrolysis-gaschromatography/mass spectrometry. Lignin of oil palm frond was characterised by the presence of significant amounts of esterified p-hydroxybenzoic acid together with small amounts of etherified p-hydroxybenzoic acid. Vanillic and syringic acids were esterified or etherified to lignin. Some extents of these ester bonds and β-O-4 interunit linkages of lignin were cleaved during steam explosion, in addition to great condensation of guaiacyl nuclei, as revealed by 1 H- and 13 C-NMR spectra of isolated lignins from the steam exploded pulps, of which yields were quite high, suggesting that lignin has been released from other wall polymers. Wall polysaccharides of oil palm frond are composed of cellulose and significantly high concentration of arabinoxylan, which produced great abundance of 5-hydroxymethyl-furfural and furfural during steam explosion, respectively, and even hot pressing at 125°C to prepare binderless boards. It is suggested that released lignin and furfural derivatives generated during steam explosion contribute to self-binding of the steam exploded pulps. However, severe conditions of steam explosion caused great damages in lignin macromolecules, and gave poor quality of binderless boards.

Distribution of free and combined phenolic acids in wheat internodes

Abstract Finely ground residues of mature and maturing wheat internodes after extraction with 80% ethanol were successively extracted with 96% dioxane to give milled lignin (ML 1 ) and water soluble (MC 1 ) fractions. The residue was treated with a polysaccharide hydrolase mixture to give a residue (ER 1 ). Quantitative analyses of phenolic acids were made on each of these fractions. Alkaline nitrobenzene oxidation and alkaline hydrolysis were used to determine the chemical state of the phenolic acids in the fractions. Very low quantities of free phenolic acids were found in the 80% ethanol extracts but significant amounts of esterified and etherified phenolic acids were present. The amounts of phenolic acids in the extract-free residue after alkaline nitrobenzene oxidation at 170° were always higher than those liberated by alkaline hydrolysis at room temperature. In mature internodes, 24% of the total p -coumaric acid (PCA) plus ferulic acid (FA) remained after mild alkaline hydrolysis. PCA is the major ester linked phenolic acid in ML 1 , whereas FA is the major ester linked phenolic acid in MC 1 . In ER 1 the predominant esterified phenolic acid is PCA, but FA is found both in ester and ether linked forms. The major changes in the ratio of esterified PCA/FA and the increases in etherified FA during maturity coincide with decreases in the digestibility of wheat internodes.

Hot alkali-labile linkages in the walls of the forage grass Phalaris aquatica and Lolium perenne and their relation to in vitro wall digestibility.

The factors affecting in vitro dry matter digestibility (IVDMD) of fully mature internodes of 150 lines of the forage grass, Phalaris aquatica, and internodes of 100 lines of perennial ryegrass (Lolium perenne), harvested just after anthesis, were investigated. The relationships between IVDMD and the contents of acetyl bromide lignin, and ester-ether linkages between lignin and wall polysaccharides, measured by hydroxycinnamic acids (HCAs) released by 4 M NaOH at 170 degrees C respectively, were determined. The regression analysis gave r(2)=0.05 and 0.03 for the relation between IVDMD and lignin content and r(2)=0.51 and 0.53 for the relation between IVDMD and the content of hot alkali-labile HCA (predominantly ferulic acid) for phalaris and ryegrass, respectively. These observations are interpreted in terms of the restricted accessibility of polysaccharide hydrolysing enzymes to their substrates in the forage cell walls by the covalent cross-linking of wall polymers through HCAs.

Structural changes in lignin of tropical woods during digestion by termite, Cryptotermes brevis

Wood samples of apitong (Dipterocarpus grandiflorua) and ilang-ilang (Ilang-Ilang C. dadloyi) and feces of termites [Cryptotermes brevis (Walker)] fed on these woods were collected from University of the Philippines, Los Baňos. Lignin of each sample was isolated by Björkman’s procedure. There was no significant difference in 1H nuclear magnetic resonance (NMR) spectra or in the methoxyl content between Björkman lignins from original woods and termite feces. Differences were detected in the contents of aliphatic and unconjugated phenolic hydroxyl groups, suggesting minor structural changes of lignin during digestion by termites. In addition, the ratio of syringyl to guaiacyl nuclei of Björkman lignin from termite feces determined by 1H NMR spectra was higher than those from the original woods. The molar ratio of syringyl to guaiacyl nuclei of termite feces was higher than those from the original woods as determined by alkaline nitrobenzene oxidation. These results suggest that the structural changes of lignin in the termite gut are due to the insignificant formation of C-C linkages in guaiacyl nuclei. It was concluded that there were minor changes in the structural features of lignin under mostly anaerobic conditions, in contrast to the significant changes that occur through biological modification under aerobic conditions.

Lignin and hydroxycinnamic acids in walls of brown midrib mutants of Sorghum, pearl millet and maize stems

The characteristics of walls from stems of brown-midrib (bmr) mutants from Sorghum bicolor (L) Moench bmr6 and bmr18 (watery- to milky-grain stage), Pennisetum americanum (L) Leeke KS81-1089 (soft-dough stage) and Zea mays L bm3 (early-dent stage) with respect to the types of linkages of hydroxycinnamic acids to wall polymers and to structural features of their lignins were investigated. The lignin content of all mutants, determined using the acid detergent lignin procedure, was significantly lower than that of their normal counterparts. There was, however, no significant differences in total lignin contents between bmr and normal lines as determined by the acetyl bromide procedure or the sum of the acid-insoluble (Klason) lignin and acid-soluble lignin. It is suggested that this behaviour could be explained if bmr mutants are characterised by higher amounts of lignin with a lower degree of polymerisation than normal lines. The lowered S/V ratio and lowered total yield of alkaline nitrobenzene oxidation products in lignin from bmr mutants was confirmed. No etherified p-coumaric acid was found in any sample tested, except the normal line of pearl millet. The concentration of etherified ferulic acid, which is probably involved in ester-ether bridges between lignin and polysaccharides, was lower in bmr mutants than in the normal plants. The low content of ferulic acid bridges in bmr mutants may contribute to the elevated digestibilities of their stems.

Degradation of Lignin with Ozone: Reactivity of Lignin Model Compounds Toward Ozone

Abstract In order to elucidate the reactivities of different types of lignin-structural units toward ozone, various lignin model compounds were ozonized. The results obtained are summarized as follows: 1) An α-carbonyl type structure is much more stable against ozone than a benzyl alcohol type structure. 2) A guaiacyl nucleus reacts faster with ozone than a vera try 1 one. 3) Biphenyl and phenylcoumaran structures react readily with ozone. However, a biphenyl structure of veratryl nuclei is very stable against ozone. 4) From the results of molecular orbital calculations, Pz orbitals (LUMO) of ozone form bonding orbitals to those (HOMO) of lignin aromatic nucleus at C3 and C4 positions. Furthermore, the squares of LCAO coefficients of C3 and C4 positions are greater than those of other positions in Pz orbital (HOMO) of lignin aromatic nucleus. This suggests that ozone reacts selectively with the lignin aromatic nucleus at C3-C4 position.

Structural characteristics of cell walls of kenaf (Hibiscus cannabinus L.) and fixation of carbon dioxide

Abstract Kenaf (Hibiscus cannabinus) plants are widely known for their contribution to the global and regional environment because of their ability to fix CO2. On the other hand, some scientists have doubts about CO2 fixation by kenaf and have misgivings about the effect of kenaf on the ecosystem. We have characterized the structural characteristics of cell walls of bast fibers, cores, roots, and leaves of kenaf during the maturation of plants and investigated the rate of photosynthesis. During maturation of the kenaf plant the cellulose (bast fiber 52–59%, core 44–46%) and lignin (bast fiber 9.3–13.2%, core 18.3–23.2%) contents increased significantly. The aromatic composition of the lignin of bast fiber was significantly different from that of the core lignin and of other plants. The lignin of bast fiber appears similar to pure syringyl lignin. Fixation of CO2 by kenaf plants and their contribution to the global environment are discussed. A significatly high rate of photosynthesis of kenaf plants was observed compared to that of woody plants in Japan, but the amount of CO2 fixation depends on the characteristics of the plantation. If the kenaf was planted in high density, about twice as much CO2 was fixed as was fixed by trees in a tropical rain forest.