Physicochemical and Structural Characterization of Hemicelluloses Isolated by Different Alcohols from Rice Straw

Abstract

Six alcohol-soluble hemicellulosic preparations from rice straw were comparatively studied, and their physicochemical characterizations were examined. The treatments of the dewaxed rice straw with 60% methanol, 60% ethanol, 60% n-propanol, 60% n-butanol, 60% ethanol containing 0.01 M HCl, and 60% ethanol containing 0.25 M NaOH at 75 °C for 3 h were able to solubilize 10.4, 10.4, 6.2, 6.5, 7.4, and 55.0% of the original hemicelluloses, respectively. The results showed that methanol and ethanol had similar solubilization capacity of hemicelluloses and gave slightly higher solubility compared to n-propanol and n-butanol. The major monosaccharide of the four neutral alcohol-soluble hemicellulosic fractions was xylose (31.78–36.80%) followed by glucose (26.35–39.39%), galactose (15.05–17.17%), and arabinose (14.93–15.58%), whereas the alkaline ethanol-soluble hemicellulosic fraction contained the highest amount of xylose (59.62%). By combining 1H, 13C, and 2D-HSQC NMR with FT-IR spectroscopy, the alkaline ethanol-soluble hemicellulosic fraction can be structurally defined as 4-O-methyl-α-D-glucurono-L-arabino-D-xylans.