| In this thesis, lignin, hemicelluloses, and enzymatic mild acidolysis lignin (EMAL) were isolated from Carex meyeriana Kunth by successive treatments with incremental concentration alkaline solvents. The structural characteristics of the isolated hemicelluloses, lignin, and EMAL were investigated., and the lignin structure changes were comparatively studied after white-rot fungus treatment and dilute acid treatment.The enzymatic hydrolysis residue were successively extracted with0.1M HCI and2%NaOH, the filtration was adjusted pH5.5, concentration and the hemicellulosic fractions Hiand H2were precipitated in3-time volue ethanol. The filtration was further adjusted pH to2to obtain lignin fractions L1and L2, accounting to the29.5%and13.5%of Klason lignin. The sugar and uronic acid concentration in lignin fractions were11.20and1.14mg L-1. The precipitated hemicellulosic fractions were12.2and4.2%of the origin hemicelluloses with alkali and acidified dioxane extraction. The EMAL and alkali lignin were both typical GSH linin, the linkage between lignin units were β-O-4’, β-5,β-β’. The ester bond signals of lignin with ferulic acid and p-courmaric acid signals presented in HSQC of L1, while the ester bond signal between lignin and ferulic acid was disappeared in HSQC of L2.Successive extractions with distilled water,0.25%NaOH-95%ethanol solution,0.5%,1%,1.5%and2%NaOH aqueous solutions at a solid-liquid ratio of1:25(g mL"1) at80℃for3h from Carex meyeriana Kunth released4.4%,6.9%,10.9%,13.2%,7.9%and4.9%of the original lignin, respectively. The physico-chemical properties and structural features of these lignin fractions were comprehensively characterized by HPLC, GPC, NMR spectroscopy, and TGA. The alkali concentration increment had a positive influence on the purity of the lignin fractions, but a negative influence on the average molecular weight and thermal stability. The FT-IR spectra showed that the lignin fractions had similar structural features with those of GSH type lignin. The 1H and13C and2D NMR spectra illustrated that typical lignin fractions had predominantly β-O-4aryl ether linkages followed by β-β and β-5’ones.Successive extractions of de-waxed Carex meyeriana Kunth with distilled water,0.25%NaOH-70%ethanol solution,0.5%,1%,1.5%,2%and3%NaOH aqueous solutions at a solid-liquid ratio of1:25(g mL"1at80℃for3h released5.8%,16.7%,18.9%,13.1%,15.7%,12.8%and14.1%of the original hemicelluloses, respectively. The GPC analysis showed that the weight-average molecular weight (Mw) of alkali-soluble hemicelluloses was obviously higher than that of water-soluble hemicelluloses (16690g mol-1) and with the increasing of alkali concentration the Mw increased from34620to106210g mol-1. Comparison of these hemicellulosic indicated that more branched and smaller molecular size of hemicelluloses fractions (xylose5.6%) were more easily extracted by the hot water treatment. While the alkali-soluble hemicellulosic fractions contained less branched and larger molecular size of the polymers, in which xylose (48.6-71.2%) was found to be the major sugar component together with small amounts of arabinose (11.9-18.1%), uronic acids (8.1-10.5%), galactose (4.5-13.1%), glucose (2.7-9.2%), and a trace amount of rhamnose (0.7-1.5%). The results obtained by the analysis of FT-IR, sugar composition,1H and13C NMR indicated that there were no considerable differences in the structural features of the water-and alkali-soluble hemicellulosic fractions, which were mainly comprised of (1→4)[4-O-Me-β-D-GlcpA-(1→2)][a-L-Araf-(1→3)]--β-D-Xylp units.Carex meyeriana Kunth was subjected to biological pretreatment with white-rot fungus F. palustris C7784, and the structural changes of the lignin were investigated. Results showed that there was a slight decrease in carbohydrate content after pretreatment for3weeks, but a noticeable decrease in lignin and carbohydrate contents for6weeks. Detail structural analysis of the isolated lignin from the samples revealed that Carex meyeriana Kunth lignin consisted mainly of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units with minor p-coumarate and ferulate units. The predominate lignin interunits were β-O-4’ ether linkages, followed by phenylcoumaran, together with a lower proportion of resinol and tricin substructures. After pretreatment for6weeks, the contents of β-β’and β-5’ linkages notably decreased, suggesting that the fungus preferentially attacked these linkages. The pretreatment led to an increase of S/G ratio from0.64in the control to0.83in the sample pretreated for6weeks. The comprehensive understanding of the structural changes of lignin offers new insights into the biological degradation of Carex meyeriana Kunth by white-rot fungus. |
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