Emmie Dornez

Structurally different wheat-derived arabinoxylooligosaccharides have different prebiotic and fermentation properties in rats.

To evaluate the prebiotic potential and intestinal fermentation products of wheat bran-derived arabinoxylooligosaccharides (AXOS) in relation to their structure, 5 preparations with structurally different AXOS were included ( approximately 4% wt:wt) in rat diets that mimicked the average Western human diet composition. Xylooligosaccharides (XOS), fructooligosaccharides (FOS), and inulin were used as references. The observed effects mainly depended on the average degree of polymerization (avDP) of the AXOS preparations. The AXOS and XOS preparations with a low avDP (<or=3) resulted in increased colonic acetate and butyrate production and boosted bifidobacteria concentrations in the cecum, but did not significantly lower the concentrations of branched SCFA, which are considered to be markers of protein fermentation by intestinal microbiota. In contrast, an AXOS preparation with a higher avDP (61) effectively suppressed branched SCFA concentrations and thus tipped the balance away from protein fermentation. However, it neither increased colonic butyrate concentrations nor stimulated cecal bifidobacteria development. Two AXOS preparations with a similar avDP (12 and 15) but different average degrees of arabinose substitution (avDAS) (0.69 and 0.27) affected the measured intestinal characteristics similarly, suggesting that the influence of the avDAS was apparently limited and possibly overshadowed by that of the avDP. Among those tested, an AXOS preparation with an avDP of 5 and an avDAS of 0.27 exhibited the best combination of desirable effects on gut health characteristics. Compared with this optimal AXOS preparation, FOS and inulin resulted in similar bifidogenic effects with increased production of colonic acetate (inulin) but not of butyrate. These new insights into the structure-activity relation of AXOS open up new perspectives for the production and application of AXOS preparations with optimized prebiotic and fermentation properties.

Variation in the Content of Dietary Fiber and Components Thereof in Wheats in the HEALTHGRAIN Diversity Screen

Within the HEALTHGRAIN diversity screening program, the variation in the content of dietary fiber and components thereof in different types of wheat was studied. The wheat types were winter (131 varieties) and spring (20 varieties) wheats (both Triticum aestivum L., also referred to as common wheats), durum wheat (Triticum durum Desf., 10 varieties), spelt wheat (Triticum spelta L., 5 varieties), einkorn wheat (T. monococcum L., 5 varieties), and emmer wheat (Triticum dicoccum Schubler, 5 varieties). Common wheats contained, on average, the highest level of dietary fiber [11.5-18.3% of dry matter (dm)], whereas einkorn and emmer wheats contained the lowest level (7.2-12.8% of dm). Intermediate levels were measured in durum and spelt wheats (10.7-15.5% of dm). Also, on the basis of the arabinoxylan levels in bran, the different wheat types could be divided this way, with ranges of 12.7-22.1% of dm for common wheats, 6.1-14.4% of dm for einkorn and emmer wheats, and 10.9-13.9% of dm for durum and spelt wheats. On average, bran arabinoxylan made up ca. 29% of the total dietary fiber content of wheat. In contrast to what was the case for bran, the arabinoxylan levels in flour were comparable between the different types of wheat. For wheat, in general, they varied between 1.35 and 2.75% of dm. Einkorn, emmer, and durum wheats contained about half the level of mixed-linkage beta-glucan (0.25-0.45% of dm) present in winter, spring, and spelt wheats (0.50-0.95% of dm). All wheat types had Klason lignin, the levels of which varied from 1.40 to 3.25% of dm. The arabinoxylan contents in bran and the dietary fiber contents in wholemeal were inversely and positively related with bran yield, respectively. Aqueous wholemeal extract viscosity, a measure for the level of soluble dietary fiber, was determined to large extent by the level of water-extractable arabinoxylan. In conclusion, the present study revealed substantial variation in the contents of dietary fiber and constituents thereof between different wheat types and varieties.

Tuning the acid/metal balance of carbon nanofiber-supported nickel catalysts for hydrolytic hydrogenation of cellulose.

Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/CNFs were characterized by various analytical methods. To prepare a selective Ni/CNF catalyst, the influences of the nature of oxidation agent, Ni activation, and Ni loading were investigated. Under the applied reaction conditions, the best result, that is, 76 % yield in hexitols with 69 % sorbitol selectivity at 93 % conversion of cellulose, was obtained on a 7.5 wt % Ni/CNF catalyst prepared by chemical vapor deposition of CH(4) on a Ni/γ-Al(2)O(3) catalyst, followed by oxidation in HNO(3) (twice for 1 h at 383 K), incipient wetness impregnation, and reduction at 773 K under H(2). This preparation method leads to a properly balanced Ni/CNF catalyst in terms of Ni dispersion and hydrogenation capacity on the one hand, and the number of acidic surface-oxygen groups responsible for the acid-catalyzed hydrolysis on the other.

The HEALTHGRAIN Wheat Diversity Screen: Effects of Genotype and Environment on Phytochemicals and Dietary Fiber Components

Analysis of the contents of bioactive components (tocols, sterols, alkylresorcinols, folates, phenolic acids, and fiber components) in 26 wheat cultivars grown in six site x year combinations showed that the extent of variation due to variety and environment differed significantly between components. The total contents of tocols, sterols, and arabinoxylan fiber were highly heritable and hence an appropriate target for plant breeding. However, significant correlations between the contents of bioactive components and environmental factors (precipitation and temperature) during grain development also occurred, with even highly heritable components differing in amount between grain samples grown in different years on different sites.

Occurrence and functional significance of secondary carbohydrate binding sites in glycoside hydrolases

Non-catalytic carbohydrate binding on independent carbohydrate-binding modules (CBMs) has been reported frequently for glycoside hydrolases (GHs) and reviewed thoroughly. However, various structural studies of GHs have revealed that non-catalytic carbohydrate binding sites can also occur on the surface of the structural unit comprising the active site. Here, the discovery of these sites, referred to as secondary binding sites (SBSs), and their putative roles in different GHs is reviewed for the first time. The majority of the SBSs have been discovered in starch-active enzymes, but there are also many reports of SBSs in various other enzymes. A wide variety of functions has been ascribed to these sites, including (1) targeting of the enzyme towards its substrate, (2) guiding the substrate into the active site groove, (3) substrate disruption, (4) enhancing processivity, (5) allosteric regulation, (6) passing on reaction products, and (7) anchoring to the cell wall of the parent microorganism. A lot of these putative functions are in agreement with the functions ascribed to non-catalytic binding in CBMs. Contrarily to CBMs, SBSs have a fixed position relative to the catalytic site, making them more or less suitable to take up specific functions.

Biorefining of wheat straw using an acetic and formic acid based organosolv fractionation process

To assess the potential of acetic and formic acid organosolv fractionation of wheat straw as basis of an integral biorefinery concept, detailed knowledge on yield, composition and purity of the obtained streams is needed. Therefore, the process was performed, all fractions extensively characterized and the mass balance studied. Cellulose pulp yield was 48% of straw dry matter, while it was 21% and 27% for the lignin and hemicellulose-rich fractions. Composition analysis showed that 67% of wheat straw xylan and 96% of lignin were solubilized during the process, resulting in cellulose pulp of 63% purity, containing 93% of wheat straw cellulose. The isolated lignin fraction contained 84% of initial lignin and had a purity of 78%. A good part of wheat straw xylan (58%) ended up in the hemicellulose-rich fraction, half of it as monomeric xylose, together with proteins (44%), minerals (69%) and noticeable amounts of acids used during processing.

Effects of Genotype and Environment on the Content and Composition of Phytochemicals and Dietary Fiber Components in Rye in the HEALTHGRAIN Diversity Screen

The effects of genotype and environment on the content of bioactive components in rye were determined with four varieties being grown on one site for three years and on three additional sites in the third year and a fourth variety being included in all trials except year 1. Clear differences were observed in the extent to which the contents of dietary fiber components (arabinoxylan, beta-glucan, total dietary fiber) and phytochemicals (folates, alkylresorcinols, sterols, tocols, phenolic acids) varied between varieties and between the same varieties grown in different sites (United Kingdom, France, Hungary, Poland) and years (2005-2007 in Hungary), with sterols being the most stable and phenolic acids the least. However, no single variety could be selected as having the highest overall level of bioactive components or as being more stable in comparison across environments.

Environment and genotype effects on the content of dietary fiber and its components in wheat in the HEALTHGRAIN diversity screen.

Within the HEALTHGRAIN diversity screen, the variability of the contents of dietary fiber (DF) and components thereof was studied in wheat. Furthermore, the contribution of genotype and environment to this variability was estimated. The levels of total DF (TDF), total nonstarch polysaccharide (TOTNSP), water-extractable nonstarch polysaccharide (WENSP), total arabinoxylan (TOTAX), lignin, and beta-glucan in whole meal, flour, and/or bran varied approximately 1.8-fold. The highest variability was observed for the water-extractable arabinoxylan (WEAX) level in flour and bran (approximately 3.7-fold). Genotype and environment contributed to a similar extent to the variability in TDF, TOTNSP, and TOTAX content in wheat. The observed relatively high impact of genotype-environment interaction suggests that the levels of these constituents are weak breeding parameters. The WENSP level is a more stable parameter as the effect of the interaction term was much less than the impact of genotype. For TOTAX and WEAX in flour, WEAX in bran, beta-glucan in whole meal, and extract viscosity, wheat genotype determined approximately 50% or higher of the variation observed, whereas the impact of the genotype-environment interaction was relatively low. These findings suggest that the health-related and technological functionality of wheat can be directed to a certain extent by selection of appropriate wheat varieties.

Wheat (Triticum aestivum L.) Bran in Bread Making: A Critical Review

Wheat bran, a by-product of the industrial roller milling of wheat, is increasingly added to food products because of its nutritional profile and physiological effects. Epidemiological data and scientific studies have demonstrated the health benefits of consuming bran-rich or whole-grain food products. However, incorporation of wheat bran in cereal-based products negatively affects their production process. Furthermore, the organoleptic quality of the obtained products is mostly perceived as inferior to that of products based on refined wheat flour. This review summarizes the current knowledge on the impact of wheat bran on bread making, provides a comprehensive overview of the bran properties possibly involved, and discusses different strategies that have been evaluated up till now to counteract the detrimental effects of wheat bran on bread making.

Study of hydration properties of wheat bran as a function of particle size

New insights in the hydration properties of wheat bran as function of particle size were gained based on a novel water retention capacity test. Upon milling coarse bran with an average particle size of 1687 μm down to 77 μm, the specific surface increases by twofold, structural integrity was lost and water extractable arabinoxylan and damaged starch content were practically unaffected. A standard centrifugation-based water retention capacity, swelling capacity and Enslin-Neff absorption test showed up to threefold higher water absorption for large particles. During these hydration tests, bran is not (continuously) subjected to external forces which allows larger particles to hold more water in between bran particles and probably in micropores. In contrast, the water retention capacity as determined by a novel drainage centrifugation method, and Farinograph absorption were not affected by particle size. In these methods, continuous exposure of bran to external forces causes bran to retain only strongly bound water which is most likely bound in cell wall nanopores and through hydrogen bonding. These insights reconcile contradicting observations in literature with regard to this matter.