Fractional isolation and physico-chemical characterization of alkali-soluble polysaccharides from sugar beet pulp

Pectin rich polysaccharide fractions were extracted with 2% sodium hydroxid e at 45 degrees C for 0.5, 1, 2, 3, 4 and 5 h, respectively, from sugar bee t pulp. The neutral sugar rich polysaccharide preparations were obtained by treatment of the alkali extracts with pectinase. The pectin rich alkali-so luble polysaccharide-lignin complexes contained 36.7%-46.7% galacturonic ac id, 13.7%-16.0% neutral sugars, 9.2%-14.8% protein, 3.6%-9.1% lignin and 18 .9%-22.9% ash. The hemicellulose-lignin complex preparations were composed mainly of neutral sugars, in which galactose, rhamnose and arabinose were d etected as the major sugar constituents. The weight-average molecular weigh ts of the alkali-soluble polysaccharide-lignin complex fractions (38400-184 900 Da) were much higher than those of the hemicellulose-lignin complex pre parations (21100-26400 Da). The acetyl groups and methyl esters were found to be fully saponified during the alkali treatments, while feruloyl and p-c oumaroyl esters appeared to be more resistant to the alkali conditions. Bes ides ferulic and p-coumaric acids, six other phenols were also firstly iden tified in the nitrobenzene oxidation products from all the isolated 12 frac tions. These findings indicated that coumaryl, coniferyl and sinapyl alcoho ls are tightly associated with hemicelluloses and pectin in sugar beet pulp cell walls. (C) 1999 Elsevier Science Ltd. All rights reserved.