GC-MS and IR spectroscopic analyses of the lignin-derived products from softwood and hardwood treated in supercritical water

Softwood (Cryptomeria japonica) and hardwood (Fagus crenata) were treated in supercritical water (380°C, 100 MPa) for 8 s. The treated woods were fractionated to the water-soluble portion, methanol-soluble portion, and methanol-insoluble residues. For the methanol-soluble portion, which mainly consisted of lignin-derived products, gel permeation chromatography (GPC) and gas chromatographic-mass spectrometric (GC-MS) analyses were conducted to clarify the molecular weight distribution and to identify the monomeric products, respectively. GPC analysis revealed that the methanol-soluble portion contains monomeric and some oligomeric products. GC-MS analysis identified 19 guaiacyl compounds in the methanol-soluble portion from softwood, and 15 syringyl monomeric compounds in the methanol-soluble portion from hardwood. The structures of identified products included not only phenyl propane (C₆—C₃) units but also C₆—C₂ and C₆—C₁ units. In addition, the infrared spectra suggested that the methanol-soluble portion maintains the typical structure of lignin, although it is rich in condensed-type linkages with some changes in the propyl side chain. These results indicate that the supercritical water treatment cleaves not only ether linkages but also part of the propyl chains in lignin to give various aromatic compounds.     

Gas chromatographic and mass spectrometric (GC-MS) analysis of lignin-derived products from <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> treated in supercritical water

Sugi (Cryptomeria japonica D. Don) wood was treated with supercritical water (374°C, 22.1MPa), and fractionated into the water-soluble portion, the methanol-soluble portion, and the methanol-insoluble residue. The methanol-soluble portion mainly consisted of the lignin-derived products. To characterize the compounds in the methanol-soluble portion, gel permeation chromatographic (GPC) and gas chromatographic-mass spectrometric (GC-MS) analyses were performed. The GPC analysis indicated that the methanol-soluble portion contained lignin-derived monomeric and dimeric products. GC-MS analysis detected 31 products which were expected to be monomeric compounds, and 18 of these were identified to be guaiacol, methylguaiacol, ethylguaiacol, vinylguaiacol, eugenol, propylguaiacol, vanillin, cis-isoeugenol, homovanillin, trans-isoeugenol, acetoguaiacone, propioguaiacone, guaiacylacetone, 2-methoxy-4-(1-hydroxypropyl)phenol, homovanillic acid, 2-methoxy-4-(prop-1-en-3-one)phenol, coniferyl aldehyde, and ferulic acid. In addition, 22 dimeric products were detected, and 4 of these were believed to be compounds with biphenyl type (5-5), diphenylethane type (-1), stilbene type (-1), and phenylcoumaran type (-5) structures. These results clearly indicated that the methanol-soluble portion included various monomeric and dimeric compounds produced as a result of the cleavage of ether linkages and propyl chains of lignin.     

Role of Tween 80 in biobleaching of unbleached hardwood kraft pulp with manganese peroxidase

The role of Tween 80 in biobleaching of unbleached hardwood kraft pulp (HWKP) with manganese peroxidase (MnP) was investigated. Among the surfactants (e.g., Tween 80, Tween 20, CHAPSO) the most significant brightness increase was obtained with Tween 80. Tween 80 and Tween 20 exhibited several effects, such as dispersion of degraded lignin and activation of MnP, that partly contributed to the brightening of HWKP during MnP treatment. However, these characteristics did not explain the most appreciable effect on the brightness increase by Tween 80. Lipid peroxidation of surfactants during MnP biobleaching was determined by measuring the peroxide value (POV). The order of the POV increase was consistent with that of the brightness increase of pulp during MnP treatment in the presence of various surfactants or linolenic acid. However, radicals and peroxides derived from lipid (linolenic acid) peroxidation by lipoxidase hardly brightened the HWKP by themselves. These results suggested that Tween 80 was peroxidized by Mn(III), and that Mn(III) and lipid peroxidation of Tween 80 synergistically brightened HWKP.This study was presented in part at the 43rd lignin symposium, Fuchu, Tokyo, Oct. 26–27, 1998 and the 49th annual meeting of the Japan Wood Research Society, Tokyo, April 2–4, 1999     

Isolation of endophytic streptomycetes from above- and belowground organs of Quercus serrata

The occurrence and localization of endophytic actinomycetes within diverse organs of host plants provide ecological information that can be used to evaluate the significance of their spatial habitats. The aim of this study was to isolate and characterize endophytic actinomycetes in different organs of Quercus serrata. For this purpose, actinomycete isolates were obtained from surface-sterilized tissues of both symptomless seedlings and aged trees of Q. serrata and rhizosphere soil of the sampled seedlings. Thirty-five isolates with the ability to sporulate, including 4 from leaves of the aged trees, 10, 6, and 15 from leaves, stems, and roots of the seedlings, respectively, and 8 soil-derived isolates, were selected and characterized. The 16S rDNA nucleotide sequence analyses revealed that all of them belonged to the genus Streptomyces. According to a neighbor-joining phylogenetic tree constructed based on the results, the isolates of plant origin were divided into three major clades with high bootstrap values of 98 or 99 %, whereas eight soil-derived isolates were located at different positions from those of the endophyte isolates. Moreover, two larger clades were formed, one of which contained isolates derived only from aboveground parts, while the other contained isolates from all of the organs. These results suggest that the endophytic streptomycetes in Q. serrata may differ in their habitat positions (i.e., either above- or belowground parts).     

Characterization of the lignin-derived products from wood as treated in supercritical water

Sugi (Cryptomeria japonica D. Don) and buna (Fugus crenata Blume) woods were treated with supercritical water (>374°C, >22.1 MPa) and fractionated into a water-soluble portion and a water-insoluble residue. The latter was washed with methanol to be fractionated further into a methanol-soluble portion and a methanol-insoluble residue. Whereas the carbohydrate-derived products were in the water-soluble portion, most of the lignin-derived products were found in the methanol-soluble portion and methanol-insoluble residue. The lignin-derived products in the methanol-soluble portion were shown to have more phenolic hydroxyl groups than lignin in original wood. The alkaline nitrobenzene oxidation analyses, however, exhibited much less oxidation product in the methanol-soluble portion and methanol-insoluble residue. These lines of evidence suggest that the ether linkages of lignin are preferentially cleaved during supercritical water treatment. To simulate the reaction of lignin, a study with lignin model compounds was performed;-O-4-type lignin model compounds were found to be cleaved, whereas biphenyl-type compounds were highly stable during supercritical water treatment. These results clearly indicated that the lignin-derived products, mainly consisting of condensed-type linkages of lignin due to the preferential degradation of the ether linkages of lignin, occurred during supercritical water treatment.This study was presented in part at the 45th lignin symposium, Ehime, Japan, October, 2000; and the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1988     

Decomposition behavior of cellulose in supercritical water, subcritical water, and their combined treatments

A comparative study on decomposition of cellulose between supercritical water (400°C, 40MPa) and subcritical water (280°C, 40MPa) treatments was made to elucidate the difference in their decomposition behavior. Consequently, the supercritical water treatment was found to be more suitable for obtaining high yields of hydrolyzed products. However, cellulose was found to be more liable to fragment under supercritical water treatment, resulting in a decrease in the yield of hydrolyzed products. On the contrary, cellulose was found to be liable to more dehydration in the subcritical water treatment. Based on these results, we have proposed the combined process of short supercritical water treatment followed by subcritical water treatment so as to inhibit fragmentation. Consequently, this combined treatment was able to effectively control the reaction condition, and to increase the yield of hydrolyzed products.     

Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase

Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugated-carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments.