Characterization of Water- and Alkali-Soluble Hemicellulosic Polymers from Sugarcane Bagasse

Abstract

Four hemicellulosic preparations were extracted using hot water at 70° and 80°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 1H and 13C 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 (Mw, 8,080–8,560 g mol−1) than the two alkali-extractable hemicellulosic preparations (Mw, 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%).