Fractional Isolation and Chemical Structure of Hemicellulosic Polymers Obtained from Bambusa rigida Species

Water and aqueous alkali sequential treatments of delignified bamboo particles were performed to extract hemicelluloses with a high yield and weight-average molecular mass (M-w). The sequential treatment together dissolved 42% of hemicelluloses based on dry holocellulose. GPC results showed that the alkali-extractable hemicelluloses have higher M-w (35000 and 44450 g mol(-1)) than water-extractable ones (20100-28100 g mol(-1)). Structural determination based on FT-IR and H-1, C-13, and 2D-HSQC NMR analyses showed that both the water- and alkali-extractable hemicelluloses shared the structure composed of the (1-->4)-linked beta-D-xylopyranosyl backbone with 4-O-methyl-alpha-D-glucuronic acid attached to O-2 of the xylose residues and L-arabinose attached to O-3 of the xylose residues. Moreover, it revealed that the water-extractable hemicelluloses retained original structure without cleaving chemical linkages. Furthermore, it was also found that the hemicelluloses with the highest yield and M-w were obtained by the aqueous alkali treatment from the delignified bamboo. A small amount of other minor hemicelluloses (beta-glucans) including xylans in the water-extractable hemicelluloses could be identified by NMR and other approaches.