Structural Characterization Of Hemicelluloses From Bamboo Stems Aged Six Months And Twelve Months

Hemicellulose is one of the three main components of plant biomass. Hemicellulose is utilized in many fields, including materials, fine chemicals, and food ingredients. Bamboo, also named(Phyllostachys pubescens Mazel, P. pubescens) Phy llostachys pubescens or Phyllostachys edulis, is the Bambusoideae and Phyllostachys of the grass family. In China, bamboo is mainly distributed in the south of Qinling and the north of the Huaihe River. The bamboo is one of the bamboo species that has the largest production quantity, most utilized, and highest economic value. Bamboo hemicellulose accounts for more than 30% of the bamboo weight. However, until now, no systematic research work on the bamboo hemicellulose structures has been carried out. Therefore, in the study the hemicelluloses from bamboo stems aged six months and twelve months were characterized. The bamboo was obtained from a farm in Nanchang city, Jiangxi province.In the study, alkali-soluble hemicelluloses AH1, AH2, AH3, AH4, AH5, AH6, AH7, AH8, and water-soluble hemicelluloses AHW and AHWC were fractionated from six-month-old bamboo stems. Alkali-soluble hemicelluloses BH1, BH2, BH3, BH4, BH5, BH6, BH7, BH8, and water-soluble hemicellulose BHW were separated from twelve-month-old bamboo stems. The extraction solutions included 2% NaOH,2% KOH,5% KOH,5% NaOH, and hot water. The hemicelluloses were obtained by classical and ultrasound-assisted extractions.The total uronic acid content was determined by the m-hydroxy-diphenyl method. The results showed that the contents of the uronic acids of the hemicelluloses from bamboo stems aged six months and twelve months were 0.28%～5.27% and 0.20%～5.98%, respectively. The results of Sodium Periodate Oxidation indicated that formic acid produced when the reaction finished, illustrating that the hemicelluloses had 1â†'6 linkages. The consumption of sodium periodate was two times as much as that of the amount of formic acid produced for the hemicellulosic factions BH1, BH3, BH4 and BH7, suggesting the presence of 1â†'2,1â†'2,6,1â†'4, and 1â†'4,6 linkages in them.Neutral sugar compositions analysis indicated that hemicellulose fractions from bamboo stems aged six months were rich in xylose, comprising 12.87～30.50% of the total sugars, and arabinose (0.98～48.4%) and galactose (0.48～48.41%) were the second and third major neutral sugar constituents. Hmicellulose fractions from bamboo stems aged twelve months were also rich in xylose, containging 15.07～44.88% of the total sugars, while arabinose (0.90～17.23%) and galactose (0.90-17.23%) were present in smaller amounts. In addition, glucose, mannose, ribose, altrose, lyxose, and gluconic acid were also observed as minor constituents in the hemicellulosic fractions.The structure of hemicelluloses were elucidated by1H NMR,13C NMR, HSQC, and methylation analysis. The results indicated that the main linkage of all the hemicelluloses wasβ-(1â†'4)-D-linked xylose, the side chains were composed ofα-D-galactofuranose,4-O-methyl-D-glucuronic acid,α-L-arabinofuranose, and ribose.SEM images of hemicellulose fractions AHW, AH5 and BH5 indicated that hemicellulose were garathered in the presence of flocculence, and AFM images of the hemicellulose fractions AH4, AH1 and AH2 from six-month aged Bamboo stems showed that most of the hemicelluloses appared as twist, and had obvious branches.