Studies on the oxidative cross-linking of feruloylated arabinoxylans from wheat flour and wheat bran

Abstract

Feruloylated arabinoxylans isolated from wheat flour and wheat bran were compared in their cross-linking behaviour with respect to viscosity properties and cross-linking products formed when various oxidative agents were applied to dilute solutions. Optimal conditions for each oxidative agent were investigated. In case of hydrogen peroxide and peroxidase, similar conditions were found for both types of arabinoxylans but wheat bran arabinoxylans gave a larger viscosity increase upon cross-linking than those of wheat flour. When glucose, glucoseoxidase and peroxidase or ammonium persulphate were used as oxidative agents, differences in the concentration of reagent needed to induce cross-linking and in viscosity increase were observed. The distribution of coupling products for both types of arabinoxylans and the different oxidative treatments was approximately 5 : 3 : 1 : 1 for 8-5, 8-O-4, 8-8 and 5-5, respectively. The low ferulate recovery after oxidative treatment was assumed to be caused by formation of unknown compounds, such as higher oligomers and lignin-linked products. A 1 : 1 mixture of flour arabinoxylan and feruloylated pectin showed a maximum synergistic effect on viscosity upon oxidative treatment using hydrogen peroxide and peroxidase. Both polysaccharides were shown to participate in cross-linking.