Arabinoxylan and hydroxycinnamate content of wheat bran in relation to endoxylanase susceptibility

Hydroxycinnamate and protein contents and monosaccharide composition were determined for 11 industrial wheat (Triticum aestivum) brans and related to the susceptibility of their arabinoxylans (AX) to enzymatic degradation. There was significant variation in carbohydrate, A/X ratio, protein, hydroxycinnamic acid and diferulic acid (DiFA) content among the wheat brans. In addition, a strong correlation was found between AX and ferulic acid contents. Brans were extracted with water followed by a dry-thermal treatment to remove similar to90% starch and to inactivate endogenous enzymes and proteinaceous inhibitors. Treated brans were compared with respect to AX degradation by a family I I xylanase. Digestion with xylanase had a strong impact on the chemical composition of the residual bran. The A/X ratio changed from 0.60 to 1.07. The solubilised AX had an A/X ratio of 0.32. The A/X ratio of enzyme-depleted bran was negatively correlated with the loss of AX. Total DiFA in destarched brans was negatively correlated with the amount of soluble AX. These relationships indicate that structural features of AX and the extent of its cross-linking in the cell walls of the bran tissues influence its susceptibility to xylanase treatment. Thus, the amount of enzyme-solubilised AX was not directly related to the content of AX in the destarched bran. However, brans differed in their susceptibility to xylanase attack. (C) 2004 Elsevier Ltd. All rights reserved.