Nonstarch Polysaccharides from Preprocessed Wheat Bran: Carbohydrate Analysis and Novel Rheological Properties

Wheat preprocessing technology produces a bran fraction rich in both soluble (8.5%) 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)-β-d -glucan. The NSP differed from previously reported wheat pentosans by exhibiting shear-thinning flow behavior at low concentration in water (0.5%, 25°C) and, more importantly, forming a thermally reversible gel upon cooling at 4°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 β-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 rheo-logical behavior.     

Molecular Weight Distribution and (1→3)(1→4)-β-d-Glucan Content of Consecutive Extracts of Various Oat and Barley Cultivars

The content and molecular weight (MW) of β-glucan in extracts from a selection of oat and barley cultivars were compared using flow-injection analysis and high-performance size-exclusion chromatography. From 60 to 75% of the β-glucan was extracted from oat and waxy barley by hot water (90°C) containing heat-stable α-amylase, whereas just 50–55% was extracted from nonwaxy barley. Consecutive extractions with hot water and dimethylsulfoxide (DMSO) extracted 65% (nonwaxy barley) or 75–80% (oat and waxy barley) of the total β-glucan. An extraction with sodium hydroxide and sodium borohydride (NaOH/NaBH₄) increased the percentage of β-glucan extracted to 86–100% but decreased the MW. The MW of β-glucan in the oat cultivars selected was significantly higher than those in the barley cultivars. The β-glucan extracted from the nonwaxy barley cultivars showed significantly higher peak MW than that from the waxy barley cultivars.