title: Structural characterization of hemicelluloses fractionated by graded ethanol precipitation from Pinus yunnanensis.
abstract: Fractionation of hemicelluloses from delignified Pinus yunnanensis was carried out with KOH/H(3)BO(3) solution followed by graded precipitation in 15%, 60%, and 90% (v/v) ethanol solutions, respectively. Chemical compositions, physicochemical properties, and structures of the precipitated hemicellulosic fractions were elucidated by a combination of sugar analysis, GPC, FT-IR, and (1)H, (13)C and 2D HSQC NMR spectroscopy. Sugar analysis showed that the hemicellulosic fraction precipitated by 15% ethanol solution (H(1)) had a predominance of xylose (58.52%), while mannose was the major sugar component in the hemicellulosic fractions precipitated by 60% (H(2)) and 90% (H(3)) ethanol solutions. GPC results revealed that the hemicelluloses precipitated by low concentration of ethanol solutions had higher weight-average molecular mass (50,090-79,840 g/mol) than those obtained in the high concentration of ethanol solutions (16,500 g/mol). The fraction precipitated by 60% ethanol solution (H(2)) was composed of D-galactose, D-glucose and D-mannose in a ratio of approximately 1:1:3.5. Structural determination indicated that the hemicellulosic fraction (H(2)) had a main structure of (1→4)-linked β-glucomannans backbone with (1→6)-linked α-D-galactose as a side chain attached to C-6 of mannose units. In addition, this fraction also contained minor amounts of xylans.
authors.affiliation: Institute of Biomass Chemistry and Technology, Beijing Forest University, Beijing 100083, China.
authors.forename: Bai-Liang
authors.initials: BL
authors.lastname: Xue
authors.forename: Jia-Long
authors.initials: JL
authors.lastname: Wen
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
authors.forename: Run-Cang
authors.initials: RC
authors.lastname: Sun
mesh_terms: D005591:Chemical Fractionation / Q000379:methods*; D011232:Chemical Precipitation; D000431:Ethanol / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D009005:Monosaccharides / Q000032:analysis; D028223:Pinus / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D009005:Monosaccharides; D011134:Polysaccharides; D000431:Ethanol; C007916:hemicellulose