Isolation of feruloylated arabinans and rhamnogalacturonans from sugar beet pulp and their gel forming ability by oxidative cross-linking

Rhamnogalacturonans and arabinans were purified from an autoclave extract o f sugar beet pulp by size-exclusion and anion-exchange chromatography. Trea tment with polygalacturonase and pectin methyl esterase was used to improve chromatographic separation of the rhamnogalacturonans from the homogalactu ronans. Four populations were obtained: two rhamnogalacturonan populations with a high arabinose and ferulic acid content and with apparent molecular weights of 930 and 130 kDa, respectively, a feruloylated arabinan populatio n and a (digested) homogalacturonan population with apparent molecular weig hts of 18 and 6 kDa, respectively. Cross-linking of the high molecular weight rhamnogalacturonans with hydroge n peroxide and peroxidase gave an increase in viscosity and led to gel form ation at concentrations <1.0%. The second rhamnogalacturonan population for med gels at concentrations as low as 0.75%. Cross-linking of the arabinan r esulted in gel formation at a concentration of 4.0%. The properties of the gels are discussed in terms of the storage modulus (G') and tan <delta>. (C ) 2000 Elsevier Science Ltd. All rights reserved.