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BackgroundDietary fibre is fermented by the colonic microbiota to carboxylic acids (CA), with potential health effects associated in particular with butyric and propionic acid.ObjectiveTo investigate the formation of CA in the hindgut of healthy rats fed dietary fibre from different fractions of wheat shorts, a by-product of the milling of wheat.DesignRats were fed dietary fibre (80 g/kg feed per day for 7 days) from wheat shorts and fractions thereof (ethanol-soluble, water-soluble and insoluble fractions), oligofructose (OF) diet and a mixture of oligofructose and raffinose (OR) diet.ResultsThe water-soluble fraction, with a high content of arabinoxylan (AX), increased the formation of propionic acid in the hindgut and lowered the ratio of acetic to propionic acid in the portal blood of rats. High levels and proportions of butyric acid were seen in rats fed the OR diet. The pattern of CA resulting from the ethanol-soluble diet, mainly composed of fructan and raffinose, was more similar to that of the OF diet than the OR diet.ConclusionsThe high formation of propionic acid with the water-soluble fraction may be attributed to the high AX content. The results also indicate that the wheat fructans produced more propionic acid and less butyric acid than OF. It may furthermore be speculated that the formation of butyric acid associated with the OR diet was due to a synergetic effect of OR.

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.

Colonic fermentation of dietary fiber produces carboxylic acids and may stimulate the growth of beneficial bacteria. This study investigated how byproducts of wheat processing (distillers' grains and two fractions from the wet fractionation to starch and gluten, one of which was treated with xylanase) affect the composition of the cecal microbiota and the formation of carboxylic acids in rats. Differences were mostly found between diets based on supernatants and pellets, rather than between fiber sources. Cecal pools and levels of most carboxylic acids in portal blood were higher for rats fed the supernatant diets, while cecal pH and ratios of acetic to propionic acid in portal blood were lower. The diet based on supernatant from distillers' grains gave the highest level of bifidobacteria. Molecular weight and solubility are easier to modify with technological processes, which provides an opportunity to optimize these properties in the development of health products.

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