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 of sugar beet pulp by size-exclusion and anion-exchange chromatography. Treatment with polygalacturonase and pectin methyl esterase was used to improve chromatographic separation of the rhamnogalacturonans from the homogalacturonans. 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 population and a (digested) homogalacturonan population with apparent molecular weights of 18 and 6 kDa, respectively. Cross-linking of the high molecular weight rhamnogalacturonans with hydrogen peroxide and peroxidase gave an increase in viscosity and led to gel formation at concentrations <1.0%. The second rhamnogalacturonan population formed gels at concentrations as low as 0.75%. Cross-linking of the arabinan resulted in gel formation at a concentration of 4.0%. The properties of the gels are discussed in terms of the storage modulus (Gʹ) and tan delta.