Cereal bran protects vitamin A from degradation during simmering and storage.

Food supplementation with vitamin A is an efficient strategy to combat vitamin A deficiency. The stability of vitamin A during cooking and storage is, however, low. We here show that cereal bran protects retinyl palmitate (RP) during simmering and storage. Native wheat bran stabilized RP the most during simmering. About 75% RP was recovered after 120 min of cooking, while all RP was lost after 80 min in the absence of bran. Heat-treated rice bran protected RP the best during forced storage, with a 35% recovery after 8 weeks. RP was degraded entirely in the absence of bran in less than one week. Results suggested that the physical entrapment of oil within the large wheat bran particles protects RP from the action of water and pro-oxidants during simmering. During storage, the high amount and diversity of lipid components present in rice bran are presumably responsible for its protective effect.

Arabinoxylan, ß-glucan and pectin in barley and malt endosperm cell walls: a microstructure study using CLSM and cryo-SEM.

The architecture of endosperm cell walls in Hordeum vulgare (barley) differs remarkably from that of other grass species and is affected by germination or malting. Here, the cell wall microstructure is investigated using (bio)chemical analyses, cryogenic scanning electron microscopy (cryo-SEM) and confocal laser scanning microscopy (CLSM) as the main techniques. The relative proportions of ß-glucan, arabinoxylan and pectin in cell walls were 61, 34 and 5%, respectively. The average thickness of a single endosperm cell wall was 0.30 µm, as estimated by the cryo-SEM analysis of barley seeds, which was reduced to 0.16 µm after malting. After fluorescent staining, 3D confocal multiphoton microscopy (multiphoton CLSM) imaging revealed the complex cell wall architecture. The endosperm cell wall is composed of a structure in which arabinoxylan and pectin are colocalized on the outside, with ß-glucan depositions on the inside. During germination, arabinoxylan and ß-glucan are hydrolysed, but unlike ß-glucan, arabinoxylan remains present in defined cell walls in malt. Integrating the results, an enhanced model for the endosperm cell walls in barley is proposed.

Characterization and Degradation of Pectic Polysaccharides in Cocoa Pulp.

Microbial fermentation of the viscous pulp surrounding cocoa beans is a crucial step in chocolate production. During this process, the pulp is degraded, after which the beans are dried and shipped to factories for further processing. Despite its central role in chocolate production, pulp degradation, which is assumed to be a result of pectin breakdown, has not been thoroughly investigated. Therefore, this study provides a comprehensive physicochemical analysis of cocoa pulp, focusing on pectic polysaccharides, and the factors influencing its degradation. Detailed analysis reveals that pectin in cocoa pulp largely consists of weakly bound substances, and that both temperature and enzyme activity play a role in its degradation. Furthermore, this study shows that pulp degradation by an indigenous yeast fully relies on the presence of a single gene (PGU1), encoding for an endopolygalacturonase. Apart from their basic scientific value, these new insights could propel the selection of microbial starter cultures for more efficient pulp degradation.

Wheat Bran Does Not Affect Postprandial Plasma Short-Chain Fatty Acids from 13C-inulin Fermentation in Healthy Subjects.

Wheat bran (WB) is a constituent of whole grain products with beneficial effects for human health. Within the human colon, such insoluble particles may be colonized by specific microbial teams which can stimulate cross-feeding, leading to a more efficient carbohydrate fermentation and an increased butyrate production. We investigated the extent to which WB fractions with different properties affect the fermentation of other carbohydrates in the colon. Ten healthy subjects performed four test days, during which they consumed a standard breakfast supplemented with 10 g 13C-inulin. A total of 20 g of a WB fraction (unmodified WB, wheat bran with a reduced particle size (WB RPS), or de-starched pericarp-enriched wheat bran (PE WB)) was also added to the breakfast, except for one test day, which served as a control. Blood samples were collected at regular time points for 14 h, in order to measure 13C-labeled short-chain fatty acid (SCFA; acetate, propionate and butyrate) concentrations. Fermentation of 13C-inulin resulted in increased plasma SCFA for about 8 h, suggesting that a sustained increase in plasma SCFA can be achieved by administering a moderate dose of carbohydrates, three times per day. However, the addition of a single dose of a WB fraction did not further increase the 13C-SCFA concentrations in plasma, nor did it stimulate cross-feeding (Wilcoxon signed ranks test).

Effects of wheat bran extract containing arabinoxylan oligosaccharides on gastrointestinal parameters in healthy preadolescent children.

OBJECTIVES: We assessed whether wheat bran extract (WBE) containing arabinoxylan-oligosaccharides (AXOS) elicited a prebiotic effect and modulated gastrointestinal (GI) parameters in healthy preadolescent children upon consumption in a beverage. METHODS: This double-blind randomized placebo-controlled crossover trial evaluated the effects of consuming WBE at 0 (control) or 5.0 g/day for 3 weeks in 29 healthy children (8-12 years). Fecal levels of microbiota, short-chain fatty acids, branched-chain fatty acids, ammonia, moisture, and fecal pH were assessed at the end of each treatment and at the end of a 1-week run-in (RI) period. In addition, the subjects completed questionnaires scoring distress severity of 3 surveyed GI symptoms. Finally, subjects recorded defecation frequency and stool consistency. RESULTS: Nominal fecal bifidobacteria levels tended to increase after 5 g/day WBE consumption (P = 0.069), whereas bifidobacteria expressed as percentage of total fecal microbiota was significantly higher upon 5 g/day WBE intake (P = 0.002). Additionally, 5 g/day WBE intake induced a significant decrease in fecal content of isobutyric acid and isovaleric acid (P < 0.01), markers of protein fermentation. WBE intake did not cause a change in distress severity of the 3 surveyed GI symptoms (flatulence, abdominal pain/cramps, and urge to vomit) (P > 0.1). CONCLUSIONS: WBE is well tolerated at doses up to 5 g/day in healthy preadolescent children. In addition, the intake of 5 g/day exerts beneficial effects on gut parameters, in particular an increase in fecal bifidobacteria levels relative to total fecal microbiota, and reduction of colonic protein fermentation.

Contents of dietary fibre components and their relation to associated bioactive components in whole grain wheat samples from the HEALTHGRAIN diversity screen.

A large and diverse material collection of whole grain wheat samples (n=129) was analysed for total dietary fibre (TDF) content and composition, including fructan (11.5-15.5%). Correlations between the dietary fibre components, associated bioactive components (e.g. tocols, sterols, phenolic acids and folates) and agronomic properties previously determined on the same samples were found with multivariate analysis (PCA). Samples from the same countries had similar characteristics. The first PC described variation in components concentrated in the starchy endosperm (e.g. starch, ß-glucan and fructan) and the dietary fibre components concentrated in the bran (e.g. TDF, arabinoxylan and cellulose). The second PC described the variation in kernel weight and other bran components such as alkylresorcinols, tocols and sterols. Interestingly, there was no correlation among these different groups of bran components, which reflected their concentration in different bran tissues. The results are of importance for plant breeders who wish to develop varieties with health-promoting effects.

Effects of a wheat bran extract containing arabinoxylan oligosaccharides on gastrointestinal health parameters in healthy adult human volunteers: a double-blind, randomised, placebo-controlled, cross-over trial.

Wheat bran extract (WBE) is a food-grade soluble fibre preparation that is highly enriched in arabinoxylan oligosaccharides. In this placebo-controlled cross-over human intervention trial, tolerance and effects on colonic protein and carbohydrate fermentation were studied. After a 1-week run-in period, sixty-three healthy adult volunteers consumed 3, 10 and 0 g WBE/d for 3 weeks in a random order, with 2 weeks' washout between each treatment period. Fasting blood samples were collected at the end of the run-in period and at the end of each treatment period for analysis of haematological and clinical chemistry parameters. Additionally, subjects collected a stool sample for analysis of microbiota, SCFA and pH. A urine sample, collected over 48 h, was used for analysis of p-cresol and phenol content. Finally, the subjects completed questionnaires scoring occurrence frequency and distress severity of eighteen gastrointestinal symptoms. Urinary p-cresol excretion was significantly decreased after WBE consumption at 10 g/d. Faecal bifidobacteria levels were significantly increased after daily intake of 10 g WBE. Additionally, WBE intake at 10 g/d increased faecal SCFA concentrations and lowered faecal pH, indicating increased colonic fermentation of WBE into desired metabolites. At 10 g/d, WBE caused a mild increase in flatulence occurrence frequency and distress severity and a tendency for a mild decrease in constipation occurrence frequency. In conclusion, WBE is well tolerated at doses up to 10 g/d in healthy adults volunteers. Intake of 10 g WBE/d exerts beneficial effects on gut health parameters.

In vitro fermentation of arabinoxylan oligosaccharides and low molecular mass arabinoxylans with different structural properties from wheat (Triticum aestivum L.) bran and psyllium (Plantago ovata Forsk) seed husk.

Ball milling was used for producing complex arabinoxylan oligosaccharides (AXOS) and low molecular mass arabinoxylans (AX) from wheat bran, pericarp-enriched wheat bran, and psyllium seed husk. The arabinose to xylose ratio of the samples produced varied between 0.14 and 0.92, and their average degree of polymerization (avDP) ranged between 42 and 300. Their fermentation for 48 h in an in vitro system using human colon suspensions was compared to enzymatically produced wheat bran AXOS with an arabinose to xylose ratio of 0.22 and 0.34 and an avDP of 4 and 40, respectively. Degrees of AXOS fermentation ranged from 28% to 50% and were lower for the higher arabinose to xylose ratio and/or higher avDP materials. Arabinose to xylose ratios of the unfermented fractions exceeded those of their fermented counterparts, indicating that molecules less substituted with arabinose were preferably fermented. Xylanase, arabinofuranosidase, and xylosidase activities increased with incubation time. Enzyme activities in the samples containing psyllium seed husk AX or psyllium seed husk AXOS were generally higher than those in the wheat bran AXOS preparations. Fermentation gave rise to unbranched short-chain fatty acids. Concentrations of acetic, propionic, and butyric acids increased to 1.9-2.6, 1.9-2.8, and 1.3-2.0 times their initial values, respectively, after 24 h incubation. Results show that the human intestinal microbiota can at least partially use complex AXOS and low molecular mass AX. The tested materials are thus interesting physiologically active carbohydrates.

Dose-response effect of arabinoxylooligosaccharides on gastrointestinal motility and on colonic bacterial metabolism in healthy volunteers.

OBJECTIVE: Arabinoxylooligosaccharides (AXOS) are non-digestible in the upper gastrointestinal tract and have been shown to exert prebiotic effects in animals. The aim of this study was to characterize the influence of AXOS with an average degree of polymerization of 15 and an average degree of arabinose substitution of 0.26 (AXOS-15-0.26) on gastrointestinal motility and colonic bacterial metabolism in healthy human volunteers. METHODS: Twelve healthy volunteers received five test meals, containing different amounts of AXOS-15-0.26, with one week intervals between each test meal. Breath tests were used to measure gastric emptying rate, oro-cecal transit time (OCTT) and hydrogen excretion. Colonic bacterial metabolism was estimated using the biomarkers lactose-[(15)N, (15)N']-ureide ((15)N-LU) and p-cresol. RESULTS: Gastric emptying and OCTT were not influenced by addition of varying amounts of AXOS-15-0.26. Administration of 2.2g or 4.9 g AXOS-15-0.26 significantly decreased the urinary (15)N-excretion (respectively p = 0.008 and p = 0.035) as compared to the baseline, whereas fecal (15)N-excretion was significantly increased (respectively p = 0.034 and p = 0.019). This shift from urinary to fecal (15)N-excretion suggests a higher uptake or incorporation by bacteria due to the stimulation of colonic bacterial growth and/or metabolic activity. Furthermore, a significant increase in hydrogen excretion after administration of 2.2g (p = 0.002) and 4.9 g (p = 0.004) AXOS-15-0.26 was observed. No influence on urinary p-cresol excretion was observed. CONCLUSION: These findings suggest that a minimal dose of 2.2g AXOS-15-0.26 favorably modulates the colonic bacterial metabolism in healthy humans. However, long term studies are required to confirm a possible prebiotic effect.

Ball milling improves extractability and affects molecular properties of psyllium (Plantago ovata Forsk) seed husk arabinoxylan.

Psyllium (Plantago ovata Forsk) seed husk (PSH) is very rich in arabinoxylan (AX). However, its high gelling capacity and the complex nature of the AX make it difficult to process. In this study, ball milling was investigated as a tool for enhancing PSH AX water extractability and molecular mass (MM). A 48 h laboratory-scale ball mill treatment under standardized optimal conditions reduced the PSH average particle size from 161 microm for the untreated sample to 6 microm. Concurrently, it increased the water-extractable AX (WE-AX) level from 13 (untreated PSH) to 90% of the total PSH AX. While the WE-AX of the untreated PSH had a peak MM of 216 kDa and an arabinose to xylose (A/X) ratio of 0.20, WE-AX fragments from ball mill-pretreated PSH had a peak MM of 22 kDa and an A/X ratio of 0.31. Ball milling further drastically reduced the intrinsic viscosity of PSH extracts and their water-holding capacity. Prolonged treatment brought almost all AX (98%) in solution and yielded WE-AX fragments with an even higher A/X ratio (0.42) and a lower peak MM (11 kDa). While impact and jet milling of PSH equally led to significant reductions in particle size, these technologies only marginally affected the water extractability of PSH AX. This implies that ball milling affects PSH particles and their constituent molecules differently than impact and jet milling.

Non-digestible oligosaccharides with prebiotic properties.

The search for functional foods or functional food ingredients, i.e. foods or food ingredients that can enhance health, is beyond any doubt one of the leading trends in today's food industry. In this context, probiotics, i.e. living microbial food supplements, and prebiotics, i.e. non-digestible food ingredients, receive much attention. Both popular concepts target the gastrointestinal microbiota. While in the Western world, intake of probiotics has been recommended for long, prebiotics in general, and non-digestible oligosaccharides in particular, have only recently received attention. This review deals with production and characterization of non-digestible oligosaccharides and focuses on their role in promoting health and treating diseases. Attention is paid to the effects of non-digestible oligosaccharides on constipation, mineral absorption, lipid metabolism, cancer prevention, hepatic encephalopathy, glycemia/insulinemia, and immunomodulation.

Wheat-kernel-associated endoxylanases consist of a majority of microbial and a minority of wheat endogenous endoxylanases.

The endoxylanases associated with wheat kernels consist of wheat endogenous endoxylanases on one hand and kernel-associated microbial endoxylanases on the other hand. Assessment of their presence, based on analysis of their enzymic activity, can be expected to be hampered by the presence in wheat of high levels of endogenous endoxylanase inhibitors, which are able to inhibit the wheat-kernel-associated microbial endoxylanases. On the basis of preliminary experiments aimed at clarifying the distribution of the wheat-associated endoxylanases, a method to estimate total endoxylanase activities in wheat kernels was developed. Extensive washing of wheat kernels with universal buffer of pH 8.0 provided near-quantitative separation of the microbial endoxylanases located on the surface of wheat kernels from the endogenous endoxylanases and endoxylanase inhibitors located in such kernels. The microbial or endogenous nature of the endoxylanases was confirmed by making use of the inhibition specificity of endoxylanase inhibitors. Determination of the endoxylanase activity in the washing liquid, corresponding to the microbial endoxylanase population, and the washed kernels, corresponding to the endogenous endoxylanase population, allowed estimation of the total endoxylanase activities associated with the wheat kernel. Results showed that microbial endoxylanases can account for over 90% of the total wheat-associated endoxylanase activity and that the latter can be at least 5 times higher than the apparent endoxylanase activity.

Molecular identification of wheat endoxylanase inhibitor TAXI-II and the determinants of its inhibition specificity.

Wheat grains contain Triticum aestivum xylanase inhibitor (TAXI) proteins which inhibit microbial xylanases, some of which are used in cereal based food industries. These inhibitors may play a role in plant defence. Among the TAXI isoforms described so far, TAXI-II displays a deviating inhibition specificity pattern. Here, we report on the molecular identity of TAXI-II and the basis of its inhibition specificity. Three candidate TAXI-II encoding sequences were isolated and recombinantly expressed in Pichia pastoris. To identify TAXI-II, the resulting proteins were tested against glycoside hydrolase family (GHF) 11 xylanases of Aspergillus niger (ANX) and Bacillus subtilis (BSX). One of these proteins (rTAXI-IB) inhibited both enzymes, like natural TAXI-I. The other candidates (rTAXI-IIA and rTAXI-IIB) showed an inhibition pattern typical for natural TAXI-II, only clearly inhibiting BSX. Comparative analysis of these highly similar sequences with distinct inhibition activity patterns, combined with information on the structural basis for ANX inhibition by TAXI-I [S. Sansen, C.J. De Ranter, K. Gebruers, K. Brijs, C.M. Courtin, J.A. Delcour, A. Rabijns, Structural basis for inhibition of Aspergillus niger xylanase by Triticum aestivum xylanase inhibitor-I, J. Biol. Chem. 279 (2004) 36022-36028], indicated a crucial role for Pro294 of TAXI-IIA and Gln376 of TAXI-IIB in determining the reduced inhibition activity towards ANX. Consequently, single point mutants rTAXI-IIA[P294L] and rTAXI-IIB[Q376H], both displaying the Leu/His combination corresponding to TAXI-I, were able to inhibit ANX. These results show that TAXI-II inhibition specificity bears on the identity of two key residues at positions 294 and 376, which are involved in the interaction at the -2 glycon subsite and the active site of GHF 11, respectively.