Xylanase Induced Changes to Water- and Alkali-Extractable Arabinoxylans in Wheat Flour: Their Role in Lowering Batter Viscosity

Abstract

The effect on the viscosity of wheat flour batter following treatments with a crude pentosanase-containing enzyme preparation and an endo-xylanase purified from the same preparation, was studied in relation to changes to the chemical features of the water- and Ba(OH)2-extractable arabinoxylan fractions. Addition to batter of the crude enzyme or the pure xylanase caused a consistent and identical decrease in batter viscosity, demonstrating that the viscosity change was caused by the selective action of the xylanase in the crude enzyme preparation. The lowering of batter viscosity upon addition of enzyme was attributed to partial hydrolysis of the arabinoxylans in the water-extractable fraction which lead to an increase in the proportion of lower molecular weight water-extractable arabinoxylans possessing an increased xylose/arabinose ratio. There was no detectable change in the monosaccharide composition of either the water- or Ba(OH)2-extractable arabinoxylan fraction after enzyme treatment and no indication of any increase in the amount of the water-extractable arabinoxylan fraction at the expense of the Ba(OH)2-extractable fraction. It is concluded that the xylanase can extensively degrade arabinoxylan to small oligosaccharides in vitro. However, such degradation does not take place in situ, in the enzyme treated batters, where only a very small shift in the molecular weight profile of the water-extractable arabinoxylans was necessary to effect major changes to batter viscosity.