Jing Bian

Comparative study of hemicelluloses obtained by graded ethanol precipitation from sugarcane bagasse.

The sequential treatment of dewaxed sugarcane bagasse with H(2)O and 1 and 3% NaOH at a solid to liquid ratio of 1:25 (g mL(-1)) at 50 degrees C for 3 h yielded 74.9% of the original hemicelluloses. Each of the hemicellulosic fractions was successively subfractionated by graded precipitation at ethanol concentrations of 15, 30, and 60% (v/v). Chemical composition, physicochemical properties, and structures of eight precipitated hemicellulosic fractions were elucidated by a combination of sugar analysis, nitrobenzene oxidation of bound lignin, molecular determination, Fourier transform infrared (FT-IR), (1)H and (13)C nuclear magnetic spectroscopies, and thermal analysis. The results showed that the sequential treatments and graded precipitations were very effective on the fractionation of hemicelluloses from bagasse. Comparison of these hemicelluloses indicated that the smaller sized and more branched hemicelluloses were extracted by the hot water treatment; they are rich in glucose, probably originating from alpha-glucan and pectic polysaccharides. The larger molecular size and more linear hemicelluloses were dissolved by the alkali treatment; they are rich in xylose, principally resulting from l-arabino-(4-O-methylglucurono)-d-xylans. In addition, noticeable differences in the chemical composition and molecular weights were observed among the graded hemicellulosic subfractions from the water-soluble and alkali-soluble hemicelluloses. The Ara/Xyl ratio increased with the increment of ethanol concentration from 15 to 60%, and the arabinoxylans with higher Ara/Xyl ratios had higher molecular weights. There were no significant differences in the structural features of the precipitated hemicellulosic subfractions, which are mainly constituted of l-arabino-(4-O-methyl-d-glucurono)xylan, whereas the difference may occur in the distribution of branches along the xylan backbone.

Structural features and antioxidant activity of xylooligosaccharides enzymatically produced from sugarcane bagasse.

Xylooligosaccharides (XOS) were prepared from xylan-rich hemicelluloses isolated by potassium hydroxide from sugarcane bagasse by hydrolysis with crude xylanase secreted by Pichia stipitis. Hydrolysis for 12h produced XOS with a maximum yield of 31.8%, equivalent to 5.29 mg mL(-1) in the hydrolyzate. XOS with degrees of polymerization (DP) from 2 to 4 (xylobiose, xylotriose, and xylotetraose) were the major components in the hydrolysates, whereas the oligosaccharides with higher DP of 5-6 (xylopentaose and xylohexose) showed a constant low level. FT-IR and NMR ((1)H, (13)C, HSQC) demonstrated that XOS contained Araf and 4-O-Me-α-D-GlcpA residues. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay showed that the XOS exhibited concentration-dependent antioxidant activity. The results obtained indicate that the XOS produced from sugarcane bagasse can be employed in food-related applications.

Autohydrolysis of bamboo (Dendrocalamus giganteus Munro) culm for the production of xylo-oligosaccharides

Bamboo culm (Dendrocalamus giganteus Munro) was treated with hot water in non-isothermal conditions (140, 160, 180 and 200°C) for various reaction times (10, 30, 60 and 120 min) to generate xylo-oligosaccharides in a batch reactor at a solid to liquor ratio of 1:10 g/g. The influence of reaction conditions on yields, compositions and characteristics of the products were evaluated. The maximum yield of xylo-oligosaccharides of 47.49% was achieved at 180°C for 30 min with a relatively low level of xylose (4.73%) and other products (arabinose 0.20 g/L, galactose 0.19 g/L, HMF 0.15 g/L, furfural 0.36 g/L, acetic acid 0.64 g/L and formic acid 0.26 g/L). Higher temperature and/or longer reaction time reduced the yield of oligosaccharides, and enhanced concentrations of monosaccharides and byproducts. The result demonstrated that the yield of xylo-oligosaccharides obtained by autohydrolysis depends on the reaction temperature and time.

High strength of hemicelluloses based hydrogels by freeze/thaw technique

Novel hydrogels were prepared from hemicelluloses, polyvinyl alcohol (PVA), and chitin nanowhiskers through 0, 1, 3, 5, 7, and 9 times of freeze/thaw cycle. These hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), swelling property, and compressive strength. The repeated freeze/thaw cycles induced physically crosslinked chains packing among these polymers, and a phase separation caused by the hydrogen bonds. Larger pores led to a high swelling degree, whereas the formation of compact structure after multiple freeze/thaw cycles resulted in high mechanical strength and thermal stability. The highest compressive strength of these hydrogels was achieved by the 9 times of freeze/thaw cycles with compressive stress of 10.5 MPa. This work provides a remarkable way for the preparation of hydrogels with good mechanical properties by physical method.

Effect of [Emim]Ac pretreatment on the structure and enzymatic hydrolysis of sugarcane bagasse cellulose.

Effect of ionic liquid pretreatment on enzymatic hydrolysis of cellulose was investigated in terms of the changes in the chemical and physical structure of the preparation. In this case, original cellulose isolated from sugarcane bagasse was subjected to ionic liquid ([Emim]Ac) dissolution at a mild temperature (90 °C) followed by regeneration in water and subsequently hydrolyzed by commercial cellulases. The original and regenerated cellulose were thoroughly characterized by XRD, FT-IR, CP/MAS (13)C NMR, and SEM. It was found that the original cellulose experienced an increase in glucose content from 80.0-83.3% to 91.6-92.8%, a decrease in the degree of polymerization from 974-1039 to 511-521, a crystal transformation from cellulose I to cellulose II, as well as an increase of surface area during the pretreatment. The results suggested that pretreatment led to effective disruption of cellulose for subsequent enzyme hydrolysis as evidenced by a high glucose conversion yield of 95.2%.

Studies on the Starch and Hemicelluloses Fractionated by Graded Ethanol Precipitation from Bamboo Phyllostachys bambusoides f. shouzhu Yi

Starch from bamboo Phyllostachys bambusoides f. shouzhu Yi evaluated by means of solid-state 13C CP/MAS NMR and X-ray diffraction showed a typical B-type pattern with a very low degree of crystallinity (10.9%). In addition to starch, alkali-soluble hemicelluloses were further fractionated by graded precipitation at ethanol concentrations of 0 (HA), 15, 30, 45, 60, and 75% (v/v). Chemical composition and structural features of the six hemicellulosic subfractions were investigated by a combination of sugar analysis, GPC, FT-IR, GC-MS, 1D (1H and 13C) and 2D (HSQC) NMR spectra, and thermal analysis. The results showed that the bamboo hemicelluloses were O-acetylated 4-O-methyl-glucuronoarabinoxylans (GAX) consisting of a linear (1→4)-β-D-xylopyranosyl backbone decorated with branches at O-3 of α-L-arabinofuranosyl (5-12 mol%) or at O-2 of 4-O-methylglucuronic acid units and acetyl groups (0.8-11 mol%). The molecular weights of these polysaccharides ranged between 13400 and 67500 g/mol, and the molar ratios of A/X and G/X increased with ascending ethanol concentrations. Moreover, xylo-oligosaccharides (XOS) with DP 1-6 were produced by enzymatic hydrolysis of hemicelluloses and the total yields of XOS were range of 21.5 to 40.6%. The structure-property relationships were also established in order to improve enzyme accessibility.

Fractional study of alkali-soluble hemicelluloses obtained by graded ethanol precipitation from sugar cane bagasse.

The two hemicellulosic fractions were subsequentially extracted with 5% and 8% NaOH aqueous solution at a solid to liquid ratio of 1:25 (g mL(-1)) at 50 degrees C for 3 h from the water, 1 and 3% NaOH-treated sugar cane bagasse, and subfractionated into six preparations by a graded ethanol precipitation method at concentrations of 15%, 30% and 60% (v/v). Sugar composition and molecular weight analysis showed that, with an increasing concentration of ethanol, hemicellulosic subfractions with both higher Ara/Xyl ratios and higher molecular weights were obtained. In other words, with an increasing ethanol concentration from 15% to 60%, the Ara/Xyl ratios increased from 0.043 in H(1) to 0.088 in H(3) and from 0.040 in H(4) to 0.088 in H(6), and the weight-average molecular weights of hemicellulosic subfractions increased from 42 430 (H(1)) to 85 510 (H(3)) g mol(-1) and from 46 130 (H(4)) to 64 070 (H(6)) g mol(-1), respectively. The results obtained by the analysis of Fourier transform infrared, sugar composition, and (1)H and (13)C nuclear magnetic spectroscopy showed that the alkali-soluble hemicelluloses had a backbone of xylose residues with a beta-(1-->4)-linkage and were branched mainly through arabinofuranosyl units at C-2 and/or C-3 of the main chain, whereas the differences may occur in the distribution of branches along the xylan backbone.

Enhanced enzymatic hydrolysis of bamboo (Dendrocalamus giganteus Munro) culm by hydrothermal pretreatment.

Bamboo was non-isothermally pretreated with hot water at 140-200°C for different times (10-120 min). The effects of pretreatment conditions on the degradation of carbohydrates, cellulose crystallinity, partial removal/relocation of lignin, morphologic change of the feedstock, and glucose yield during the enzymatic hydrolysis were investigated. The effective removal of amorphous cellulose and hemicelluloses led to the increase of crystalline index of the residues. In comparison with the raw material, the surface of the pretreated samples was irregular and numerous lignin droplets appeared on the cellulose bundle surface under the intense pretreatment conditions. The glucose conversion increased with the raise of pretreatment temperature and the prolongation of time, and the maximum conversion of 75.7% was achieved for the sample pretreated at 200°C for 120 min, whereas the untreated sample was only 15.7%. The result illustrated that hydrothermal pretreatment affected the composition of bamboo, and remarkably enhanced the enzymatic hydrolysis efficiency.

Isolation and fractionation of hemicelluloses by graded ethanol precipitation from Caragana korshinskii

Caragana korshinskii hemicelluloses were isolated with 10% KOH at 25 degrees C for 10h from the delignified materials. The alkali-extractable hemicelluloses were then successively sub-fractionated by graded precipitation at final ethanol concentrations of 10%, 20%, 30%, 45%, 60%, and 80%, respectively. Neutral sugars and molecular weight analyses of the six hemicellulosic subfractions revealed that the molecular weights and the distribution of branches along the xylan backbone are different among the hemicellulosic fractions obtained in various ethanol concentrations. The less branched hemicelluloses with large molecules were precipitated in lower ethanol percentages, while with the increasing ethanol concentrations, more branched hemicelluloses with low molecular weights were obtained. (1)H and (13)C NMR studies revealed that the hemicellulosic subfraction precipitated at an ethanol concentration of 45% had a backbone of D-xylose residues and were branched mainly through 4-O-methyl-alpha-D-glucopyranosyl units.

Fractionation of alkali-solubilized hemicelluloses from delignified Populus gansuensis: structure and properties.

The dewaxed cell walls of Populus gansuensis were delignified with NaClO(2) and then sequentially extracted with 0.25, 0.5, and 1.0 M KOH under a solid to liquid ratio of 1: 25 (g mL(-1)) at 25 degrees C for 10 h. The successive treatments together resulted in the dissolution of 83.7% of original hemicelluloses. The solubilized hemicellulosic fractions were further fractionated into six hemicellulosic subfractions by an iodine-complex precipitation technique. Their chemical and physical characteristics were determined by HPAEC, GPC, FT-IR, and (1)H and (13)C NMR spectroscopy. Neutral sugar composition and molecular weight analysis showed that, for each extract, the hemicellulosic subfractions that precipitated with aqueous potassium iodide-iodine had lower overall uronic acid/xylose (Uro/Xyl) ratios and higher molecular weights (M(w)) than those remaining in the solution. FT-IR, (1)H, and (13)C NMR spectroscopy analysis indicated that the alkali-soluble hemicelluloses of Populus gansuensis had a structure composed of the (1 --> 4)-linked beta-D-xylopyranosyl backbone with 4-O-methyl-alpha-D-glucuronic acid attached to O-2 of the xylose residues.