Characterization of water- and alkali-soluble hemicellulosic polymers from sugarcane bagasse

Four hemicellulosic preparations were extracted using hot water at 70 degrees and 80 degrees C from dewaxed sugarcane bagasse and 10% KOH and 10% NaOH from the corresponding delignified bagasse. Their chemical and physical characteristics were determined using GC, HPLC, GPC, and FT-IR and H-1 and C-13 NMR spectroscopy. The results showed that two water-soluble hemicellulosic fractions consisted of arabinoxylans and pectic polysaccharides as shown by their sugar composition of xylose (51.7 - 53.5%), galactose (22.1%), arabinose (11.6 - 12.3%), glucose ( 7.0 - 8.2%), mannose (5.1 - 5.6%), uronic acids (4.5 - 6.2%), and rhamnose (0.9 - 1.0%), while the two alkali-extractable hemicellulosic preparations were dominated by arabinoxylans in which xylose (82.2 - 82.5%) and arabinose (9.7 - 11.3%) were the major sugar components. These differences in the structure of arabinoxylans between water and alkali extracts indicated that water-soluble arabinoxylans had significantly lower xylose-to-arabinose ratios (4.3 - 4.5) than those extracted with alkali (7.3 - 8.5), implying a greater degree of branching in the water-soluble fractions. In addition, the studies showed that the two water-soluble hemicellulosic fractions were more acidic and had a much lower molecular weight (M-w, 8,080 - 8,560 g mol(-1)) than the two alkali-extractable hemicellulosic preparations (M-w, 50,700 - 53,180 g mol(-1)). Furthermore, it was found that the two water-soluble polymer fractions contained noticeable amounts of lignin (7.8 - 8.9%), whereas the two alkali-extractable polymer preparations were relatively free of bound lignin (1.1%).