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.

To obtain detailed knowledge on possible changes in the properties of starch, proteins, and arabinoxylan as a result of field preharvest sprouting (PHS), three wheat varieties were harvested at maturity and several weeks later when severe PHS had occurred. Falling number values of flour dropped from 306 to 147 s (Sahara), 382 to 155 s (Forum), and 371 to 230 s (Tobak). Blocking of α-amylase activity demonstrated that the decline in falling number and changes in RVA pasting and gelation properties were not caused by changes in intrinsic starch properties as a result of PHS. PHS had no influence on the SDS-extractability and molecular weight distribution of the proteins. For arabinoxylan, incipient breakdown was noticed, leading to a higher amount and average degree of polymerization of water extractable arabinoxylan. Results show that strategies to cope with severely PHS in wheat should focus on blocking enzyme activities.

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.

To date, research on preharvest sprouted (PHS) wheat has mostly been conducted on kernels germinated under laboratory conditions, which differ widely from conditions in the field. To obtain detailed knowledge of the evolution of hydrolytic enzyme activities in PHS wheat (Triticum aestivum), a broad collection of samples from three varieties was obtained by harvesting before, at, and after maturity. Delaying harvest time coupled with periods of heavy rainfall caused sprouting in the kernels, observed as a drop in Falling Number and an increase in α-amylase activity. The appearance of α-and β-amylase, peptidase, and endoxylanase activity during field sprouting was independent from each other. Consequently, Falling Number could not be used to predict activity of other hydrolytic enzymes. When differentiating endogenous from kernel-associated microbial enzymes, results showed that α-and β-amylase and peptidase activity of PHS kernels were predominantly of endogenous origin, whereas endoxylanase activity was largely from microbial origin.

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