Nonstarch polysaccharides from preprocessed wheat bran: Carbohydrate analysis and novel rheological properties

Wheat preprocessing technology produces a bran fraction rich in both soluble (85%) and insoluble (29.2%) fibers. The fraction, prepared by the Tkac and Timm commercial process, contained 9% alkaline extractable nonstarch polysaccharides (NSP). Conditions for extraction of NSP were chosen on the basis of both yield and molecular size of product. The extracted NSP was composed of an arabinoxylan and a mixed linkage (1-->3)(1-->4)-beta-D-glucan. The NSP differed from previously reported wheat pentosans by exhibiting shear-thinning flow behavior at low concentration in water (0.5%, 25 degrees C) and, more importantly, forming a thermally reversible gel upon cooling at 4 degrees C. This unique gelling property is neither the commonly described irreversible gelation brought about by oxidation of wheat endosperm pentosans nor a characteristic property of cereal beta-glucan. The low degree of substitution of the xylan chain of the arabinoxylan (xylose-to-arabinose ratio = 3) in this NSP might be responsible for the rheological behavior.