Background and objectives: Compared to wheat bran, less information on physicochemical characteristics and health related effects is available for bran from other cereals and results are often confounded by residual endosperm. Therefore, the objective of this study was to compare structure and composition of endosperm depleted bran of wheat, rye, oat and maize, and link these characteristics to fecal fermentation characteristics.Findings: Compared to wheat, endosperm depleted rye bran contained twice the amount of fructan (8.0% dm) and water-extractable arabinoxylan (1.4% dm). Oat bran had a more open structure and was rich in (1,3:1,4)-β-glucan (17.0% dm). For rye and oat bran, and to a lesser extent wheat bran, fermentation with fecal microbiota resulted in short chain fatty acid production, with full metabolization of fructan and β-glucan after 2 and 24 hours of fecal fermentation, respectively. For maize bran, a less accessible structure containing over 70% of arabinoxylan and cellulose, was coupled to a lower degree of fecal fermentation. Conclusion:Removal of endosperm as a confounding factor when studying bran properties allowed us to obtain more accurate estimates of the composition, structure and some physicochemical characteristics of bran of wheat, rye, oat and maize. Bran fecal fermentation characteristics were mainly determined by composition and to a lesser extent by accessibility of the structure.Significance and novelty: This is the first study that compares composition, structure and fecal fermentation characteristics of wheat, rye, oat and maize bran, after eliminating endosperm as a confounding factor. The knowledge obtained will allow a more goal oriented choice of bran type for incorporation into food products, depending on targeted physiological effects and nutritional impact.

The potential of extrusion-cooking to change the physicochemical characteristics of wheat bran, increase its nutritional value and decrease its recalcitrance towards fermentation was investigated in this study. The conditions in a twin-screw extruder were varied by changing screw configuration, moisture content and barrel temperature. The former was not previously investigated in studies on bran extrusion. Extrusion-cooking resulted in an increased water-holding capacity and extract viscosity of bran, suggesting shear-induced structure degradation and structure loosening due to steam explosion at the extruder outlet. Modelling showed that the extent of these modifications mainly correlates with the amount of specific mechanical energy (SME) input, which increases with an increasing number of work sections in the screw configuration and a decreasing moisture content and barrel temperature. Extrusion led to solubilisation of arabinoxylan and ferulic acid. Moreover, it led to starch melting and phytate degradation. Upon fermentation of the most modified sample using a human faecal inoculum, small numeric pH decreases and short-chain fatty acid production increases were observed compared to the control bran, while protein fermentation was decreased. Overall, extrusion-cooking can improve the nutrition-related properties of wheat bran, making it an interesting technique for the modification of bran before further use or consumption as an extruded end product.

No abstract

No abstract

Wheat bran incorporation in bread has multiple health benefits, but also a detrimental effect on overall bread quality. Bran is hypothesised to withdraw water from gluten, resulting in less optimal viscoelastic dough properties and a lower gas retention capacity, in turn resulting in a decreased bread loaf volume. In this study, wheat bran samples having different water retention capacities were produced and used to investigate this hypothesis. Gluten-starch model systems were used and the effect of substitution of part of the starch by bran in combination with different water absorptions and mixing times was evaluated. The properties of the gluten network in the doughs were investigated using rheological and microstructural analyses and these properties were linked to the final bread loaf volume. A proper gluten network microstructure, as visualised with CLSM, could be achieved in the presence of wheat bran. However, significant effects of the type of wheat bran, water absorption and mixing time on dough rheology and loaf volume were observed. Wheat bran addition decreased the strain hardening of dough despite optimisation of water absorption and mixing time. The deleterious effect of wheat bran on dough rheology increased by adding modified wheat bran with high water retention capacity and surface area. The results indicate that dynamic water redistribution after mixing and gas cell incorporation can have an effect on dough rheology when wheat bran is added to dough. The strain hardening behaviour of dough proved itself a valuable predictor of bread loaf volume also in the presence of (modified) wheat bran.