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Characterization of Indigestible Carbohydrates in Various Fractions from Wheat Processing

¹Applied Nutrition and Food Chemistry, Department of Food Technology, Engineering and Nutrition, Chemical Center, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden. ²Corresponding author. Phone: +46 46 222 8321. Fax: +46 46 222 4532. E-mail: lina.haska@appliednutrition.lth.se ³Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden.

Fractions rich in indigestible carbohydrates, such as fructan and arabinoxylan, are obtained as by-products when ethanol, starch, and gluten are produced from wheat flour. Today, these fractions are used as animal feed. However, these components may have positive physiological effects in humans. In this study, the content of indigestible carbohydrates in distillers' grains and process streams from the wet fractionation of wheat flour was determined. The fractions were further characterized by ethanol extractability analysis, anion-exchange chromatography, NMR, and size-exclusion chromatography. One fraction from wet fractionation contained (g/100 g, db) 6.0 ± 1.0 fructan and 10.3 ± 1.1 dietary fiber (66 ± 4% arabinoxylan), while distillers' grains contained 20.7 g/100 g (db) dietary fiber (30% arabinoxylan). In addition to indigestible carbohydrates from wheat, distillers' grains contained β-(1→3) and β-(1→6) glucans and mannoproteins from the yeast and low molecular weight carbohydrates mainly composed of arabinose. The use of endoxylanase in wet fractionation decreased the molecular weight of the arabinoxylans and increased the arabinose to xylose ratio but had no effect on the fructans. In conclusion, waste streams from industrial wheat processing were enriched in fructan, arabinoxylan, and other indigestible carbohydrates. However, the physiological effects of these fractions require further investigation.