Thi Bach Tuyet Lam

Cinnamic acid bridges between cell wall polymers in wheat and Phalaris internodes

Abstract A method has been devised for the quantitative determination of cinnamic acids participating in ester—ether bridges between cell wall polymers based on the different reactivities of free carboxylic acids and their esters towards borohydride reductants and the different susceptibilities of cinnamic acid ester and benzyl ether linkages to alkaline treatments. Lignin—polysaccharide containing fractions extracted with dioxane—H 2 O from cell walls of wheat ( Triticum aestivum ) and phalaris ( Phalaris aquatica ) internodes are hydrogenated using a Pd/C catalyst at room temperature to convert cinnamic acids to their corresponding dihydrocinnamic acids. The sample is subsequently reduced with LiBH 4 in ether—toluene to convert ester-linked dihydrocinnamates to their corresponding alcohols, hydrolysed with 4 M NaOH at 170°, and the dihydrocinnamic acid derivatives released from their etherified forms determined by GC. Using model compounds it was shown that these reactions proceeded quantitatively. The results indicate that all of the etherified ferulic acid in the dioxane—H 2 O-soluble fractions of walls of wheat and phalaris internodes is also ester-linked. It has been calculated that there are nine to 10 ferulic acid ester—ether bridges for every 100 C 6 —C 6 lignin monomers. p -Coumaric acid is not involved in ester-ether bridges.

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.

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.

Changes in phenolic acids from internode walls of wheat and phalaris during maturation

Quantitative changes in p-coumaric, ferulic and dehydrodiferulic acids in maturing internode walls of wheat (Triticum aestivum cv. Millewa) and phalaris (Phalaris aquatica cv. Sirosa) have been measured. The proportions of these cinnamic acids in ester linkages was 0.16–1.5:1.0:0.03–0.15 for wheat and 0.13–2.09:1.0:0.02–0.09 for phalaris. Significant amounts of dehydrodiferulic acid were released by alkaline digestion at 170° with 4 M NaOH from walls of wheat and phalaris internodes (0.08–0.35% wt for wheat, 0. 15–0.41 % wt for phalaris). This was 10–20 times higher than the amount of esterified dehydrodiferulic acid. It is proposed that this dehydrodiferulic acid, in the form of diester bridges between polysaccharide chains, is also etherified to lignin.

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.

Determination of etherified hydroxycinnamic acids in cell walls of grasses

Abstract A comparison is made between acid and alkaline treatments for the measurement of total amounts of ether- plus ester-linked hydroxycinnamic acids associated with extract-free wheat internodes. Although acid hydrolysis in a mixture of dioxane-2M HCI (9:1 by volume) under reflux for 2 hr releases most of the esterified ferulic acid (FA), considerable amounts of both esterified and etherified p-coumaric acids (PCA) and etherified FA remain. In addition, under these conditions, there are substantial losses of released PCA and FA (82 and 92%, respectively), and probably also of acids bound to wall polymers. These factors make the acid digestion procedure unsuitable for quantitative analyses. Alkaline hydrolysis at 170° with 4 M NAOH in stainless steel reaction vessels, although also leading to significant losses of released hydroxycinnamic acids, is the preferred method for measuring etherified hydroxycinnamic acids.

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.

5-Hydroxyguaiacyl nuclei as aromatic constituents of native lignin

Abstract The pathway of lignin biosynthesis has been well documented. However, there are still questions because of the lack of knowledge about the exact chemical structure of lignin, caused by the restriction of analytical procedures used and/or the interpretation of analytical results. The presence of 5-hydroxyguaiacyl nuclei in lignin of a brown midrib mutant (bm3) of maize has been established using a thioacidolysis. In this paper, it was confirmed using pyrolysis-gas chromatography-mass spectrometry (PY-GC/MS) that in addition to bmr mutants of some tropical grasses, lignins of their normal counterparts and some temperate and tropical angiosperms woody plants are composed of 5-hydroxyguaiacyl nuclei, in addition to guaiacyl and syringyl nuclei. Based on the results, it is suggested that 3(3,4-dihydroxy-5-methoxyphenyl)- propen-1-ol, which is synthesised from 3(3,4-dihydroxy-5-methoxyphenyl)-propionic acid (5-hydroxyferulic acid) is also involved in dehydrogenative polymerisation by perioxidase during the biogenesis of lignin of some species of plant.

An approach to the estimation of ferulic acid bridges in unfractionated cell walls of wheat internodes

Abstract A modification of a published procedure has been developed to allow the estimation of ester—ether bridges involving hydroxycinnamic acids in unfractionated walls of grasses. The modified procedure involves the use of a soluble catalyst, chlorotris-(triphenylphosphine) rhodium, for the conversion of the propenoic to propanoic sidechains, and lithium triethylborohydride for reduction of ester-linked propanoic acids. The reaction conditions for hydrogenation are severe and tests with a synthetic feruloyl-arabinoxylan showed that significant cleavage of ester-linked hydroxycinnamic acid results. Nevertheless, it was shown that 40% of ether-linked ferulic acid in whole internode walls is involved in ester—ether bridges. If these values are corrrected, based on the loss of feruloyl ester-linkages during the hydrogenation reaction, the proportion of ester—ether-linked ferulic acid in the walls approaches 100%. On the other hand, the occurrence of ester—ether bridges through p -coumaric acid appears to be low.