Metabolite production during in vitro colonic fermentation of dietary fiber: analysis and comparison of two European diets

Metabolite production and antioxidant released during colonic fermentation of naturally occurring dietary fiber (DF) from two European diets (Mediterranean and Scandinavian) were determined. With this aim, DF and associated components were isolated from both whole diets, as well as from cereals and fruits and vegetables comprising the diets. DF was used as substrate for colonic fermentation in a dynamic in vitro model of the colon, samples were collected, and fermentation metabolites were analyzed. Statistical differences between samples were observed in the concentrations of short-chain fatty acids and ammonia and in the ratio acetate/propionate/butyrate. Whole grain cereal DF generated a larger amount of propionate than refined flour cereal DF. Fruit and vegetable DF generated higher amounts of butyrate than cereal DF. Most antioxidant compounds were released from DF during in vitro colonic fermentation. It is concluded that different sources of DF may play a specific role in health maintenance mediated by metabolites produced during colonic fermentation.     

Chemical composition of natural and polyphenol-free apple pomace and the effect of this dietary ingredient on intestinal fermentation and serum lipid parameters in rats

Unprocessed pomace containing 61% of dietary fiber (DF) and 0.23% of polyphenols (PP) and ethanol- or ethanol/acetone-extracted pomaces containing 66% DF and 0.10% PP and 67% DF and 0.01% PP, respectively, were subjected to a 4 week study in rats. The aim of the study was assessing the advantages of dietary supplementation with the above pomaces. To measure the animal response to dietary treatments, parameters describing cecal fermentation and lipoprotein profile were assessed. The dietary use of 5% unprocessed pomace caused an increase in cecal short-chain fatty acid (SCFA) production and a decrease in blood triacylglycerols, leading to a drop in serum atherogenic index. Ethanol-extracted pomace increased the glycolytic activity of cecal microbiota and decreased cecal branched-chain fatty acid production, whereas acetone extraction led to lower cecal ammonia concentration, decreased colonic pH value, and higher HDL/total cholesterol ratio. The variations in the atherogenic index indicate flavonoids as the key pomace component in relation to blood lipid profile benefits.     

Physiological and metabolic properties of a digestion-resistant maltodextrin, classified as type 3 retrograded resistant starch

There is a growing interest in highly fermentable dietary fibers having the potential to reduce risks of disease through the production of short-chain fatty acids (SCFA). Recently a digestion-resistant retrograded maltodextrin (RRM), classified as type 3 resistant starch was developed. Systematic work to determine its molecular and physiological properties was carried out to determine (1) the fraction resistant to digestion in vitro and in vivo, (2) its postconsumption effect on blood glucose in healthy volunteers, and (3) its in vitro fermentation pattern, at different ages, by use of pooled fresh human fecal inoculum. RESULTS: The digestion resistant fraction obtained in vivo from ileostomy patients (59.4%) is similar to that obtained by the AOAC method for measuring retrograded resistant starch (59.7%). The relative glycemic response after consumption of 50 g of RRM was 58.5% compared to glucose set as 100%. When exposed to colonic microbiota, in vitro obtained indigestible fractions behave similarly to those obtained in vivo in ileostomy patients. Fermentation of RRM and production of butyric acid is negligible during the first months of life but develops subsequently during weaning. In adults, RRM fermentation results in a high yield of SCFA, with butyrate representing 21-31 mol % of total SCFA. The high yield of SCFA during colonic fermentation, observed from weaning age on, as well as the potential to help reduce glycemic load may be of benefit to a number of health-related functions in the host. Further study on clear clinical end points is warranted.     

Dietary fiber as a carrier of dietary antioxidants: an essential physiological function

The literature addresses dietary fiber (DF) and antioxidants (AOX) separately as nonrelated compounds. This paper proposes to show that DF and AOX could be approached jointly in nutrition and health studies because around 50% of the total dietary antioxidants, mainly polyphenolics, traverse the small intestine linked to dietary fiber. These antioxidants have received little attention so far. They release the fiber matrix in the colon by the action of the bacterial microbiota, producing metabolites and an antioxidant environment. The content of polyphenols associated with DF in different foods and their potential health-related properties, including animal experiments and human trials, are reviewed. It is concluded that the transportation of dietary antioxidants through the gastrointestinal tract may be an essential function of DF.     

REVIEW: Molecular Diversity in Pulse Seed Starch and Complex Carbohydrates and Its Role in Human Nutrition and Health

Seven major pulse crops account for ≈90% of global pulse production. Pulses are an important component of human nutrition as sources of proteins, carbohydrates, and minor nutrients such as vitamins and minerals. The major pulse seed storage polysaccharide is starch, which is made up of highly branched amylopectin and sparsely branched amylose. Pulse starches generally contain a higher concentration of amylose as compared to cereal and tuber starches. The nonstarch complex carbohydrates are major components of dietary fiber including cellulose, hemicellulose, and pectic polysaccharides with considerable structural diversity. Diets rich in pulses are associated with health benefits such as reduced calorific content, reduced or no effect on blood glucose levels (low glycemic index), and improved heart health. These health benefits have been attributed to the high amylose concentration (>30%) that gives rise to resistant starch that, along with dietary fiber, remains undigested in the small intestine but is fermented by the microbiota in the colon. Colonic fermentation increases the growth of beneficial bacteria and production of short chain fatty acids which have been associated with reduced risk of colon cancer. Clinical trials with human subjects to confirm the beneficial effects of diets rich in pulses are inconclusive. Advances in genetic strategies to develop pulse seeds with desired carbohydrate concentration and composition, carbohydrate structure characterization, combined with utilization of in vitro and in animal models may be helpful to identify carbohydrate structure function relationship responsible for beneficial effects on human health associated with pulse consumption.     

Dietary modulation of bacterial fermentative capacity by edible seaweeds in rats

The effect of edible seaweeds [nori (Porphyra tenera) and wakame (Undaria pinnatifida)] on the modulation of colonic microbiota was studied in adult male Wistar rats. Each alga was fed to rats as the only source of dietary fiber and compared with cellulose. After 12 days, animals were sacrificed and cecal contents used as inoculum to ferment lactulose, citrus pectin, cellulose, nori, and wakame in vitro. Dietary treatment did not affect food intake or food efficiency, yet alga caused a significant increase in cecal weight. Nori and wakame were poorly fermented by the cellulose inoculum, with intermediate substrate degradation (76 and 57% for nori and wakame, respectively) and low metabolism to short-chain fatty acids (SCFA) (30% fermentability compared with lactulose). Cecal contents from rats fed nori and wakame showed a reduced ability to ferment all of the studied substrates compared with the cellulose inoculum, causing a reduction in SCFA production and dry matter disappearance. Only nori induced a bacterial adaptation that brought about a higher fermentation of this substrate. The different behaviors of the two algae could be due to their distinct chemical compositions. In conclusion, nondigestible components of edible seaweeds modified the metabolic activity of intestinal microflora, leading to a reduction of its fermentative capacity.     

Importance of Location of Digestion and Colonic Fermentation of Starch Related to Its Quality

For decades, quality of starch‐based foods has been associated with the in vivo measured glycemic index or the in vitro digestion rate‐based categories of rapidly digestible, slowly digestible, and resistant starch (RS). Glycemic index has been related to health‐based endpoints mostly through correlative or observational studies, with mechanisms proposed but not well established. Here, we bring forth the concept of locational delivery of glucose from dietary starches to the distal small intestine to elicit an ileal brake effect, as well as short‐chain fatty acid production from RS fermentation to cause a colonic brake. Both effects slow gastric emptying and, in turn, extend nutrient (i.e., energy) delivery to the body and may decrease appetite and promote weight management. Slowly digestible starches are currently a popular topic of research, although where they are digested and the released glucose is delivered in the small intestine is not known. A proposal is to further study and establish this mechanism of appetite and food intake regulation so that starch‐based ingredients and foods can be developed that promote both the ileal and colonic brake mechanisms.     

In vitro determination of the indigestible fraction in foods: an alternative to dietary fiber analysis

Dietary fiber (DF) intakes in Western countries only accounts for about one-third of the substrates required for colonic bacterial cell turnover. There is a general trend among nutritionists to extend the DF concept to include all food constituents reaching the colon. In this line, a method to quantify the major nondigestible components in plant foods, namely, the indigestible fraction (IF), is presented. Analytical conditions for IF determination are close to physiological. Samples, analyzed as eaten, were successively incubated with pepsin and alpha-amylase; after centrifugation and dialysis, insoluble and soluble IFs were obtained. IF values include DF, resistant starch, resistant protein, and other associated compounds. IF contents determined in common foods (cereals, legumes, vegetables, and fruits) were higher than DF contents. Calculated IF intakes were close to the estimated amount of substrates reaching the colon. IF data could be more useful than DF data from a nutritional point of view; therefore, IF is proposed as an alternative to DF for food labeling and food composition tables.     

In Vitro Digestion of RS4‐Type Resistant Wheat and Potato Starches,and Fermentation of Indigestible Fractions

RS4‐type resistant wheat starch (RWS) and resistant potato starch (RPS) were subjected successively to in vitro digestion with pepsin and pancreatin‐bile, and the indigestible residues (82.1% db and 74.1% db, respectively) were recovered and subsequently fermented by in vitro techniques using fresh human fecal microbiota as inoculum. Scanning electron microscopy of the indigestible residues showed surface erosion on the residual granules. Total gas production during the in vitro fermentation increased almost linearly over time with the two resistant starches exhibiting similar gas production rates, as well as a similar rate of production of total short‐chain fatty acids (SCFA). The indigestible fractions from both starches produced acetate as the major SCFA and relatively higher levels of butyrate than propionate, but wheat starch tended to produce more butyrate over time than potato starch. Fractional molar ratios of acetate, propionate, and butyrate from the RWS and RPS were 0.586:0.186:0.228 and 0.577:0.200:0.223, respectively. The calculated caloric contributions of the RWS and RPS are ≈33% lower than for unmodified starch and are comparable to those reported in the literature for RS2 and RS3 high‐amylose maize starches.     

In vitro digestion and fermentation characteristics of temulose molasses, a coproduct of fiberboard production, and select temulose fractions using canine fecal inoculum

It is of interest to discover new fermentable carbohydrate sources that function as prebiotics. This study evaluated the hydrolytic digestibility, fermentative capacity, and microbiota modulating properties of Temulose molasses, four hydrolyzed fractions of Temulose molasses, short-chain fructooligosaccharides (scFOS), and a yeast cell wall preparation (Safmannan). These substrates resisted in vitro hydrolytic digestion. Each substrate was fermented in vitro using dog fecal inoculum, and fermentation characteristics were quantified at 0 and 12 h. All Temulose molasses substrates decreased pH by at least 0.64 unit and resulted in greater (P < 0.05) butyrate and total short-chain fatty acid (SCFA) production compared to scFOS and Safmannan. Temulose molasses substrates resulted in higher (P < 0.01) or equal Bifidobacterium spp. concentrations compared to scFOS. Temulose molasses substrate and its fractions demonstrated prebiotic characteristics as indicated by low hydrolytic digestibility, high fermentability, and enhanced growth of microbiota considered to be beneficial to health.     

Dietary fiber from coffee beverage: degradation by human fecal microbiota

Arabinogalactans and galactomannans from coffee beverages are part of the dietary fiber complex. Chemical structures and fermentability of soluble dietary fiber obtained from a standard filter coffee beverage (Coffea arabica, origin Colombia, medium roasted) by human intestinal bacteria were investigated. One cup (150 mL) of filter coffee contained approximately 0.5 g of soluble dietary fiber (enzymatic-gravimetric methodology), 62% of which were polysaccharides. The remainder was composed of Maillard reaction products and other nonidentified substances. Galactomannans and type II arabinogalactans were present in almost equal proportions. Coffee dietary fiber was readily fermented by human fecal slurries, resulting in the production of short-chain fatty acids (SCFA). After 24 h of fermentation, 85% of total carbohydrates were degraded. In general, arabinosyl units from the polysaccharide fraction were degraded at a slower rate than mannosyl and galactosyl units. In the process of depolymerization arabinogalactans were debranched and the ratio of (1-->3)-linked to (1-->6)-linked galactosyl residues decreased. Structural units composed of (1-->5)-linked arabinosyl residues were least degradable, whereas terminally linked arabinosyl residues were easily utilized. The impact of coffee fiber on numerically dominant population groups of the intestinal microbiota was investigated by fluorescence in situ hybridization combined with flow cytometry (FISH-FC). After 24 h of fermentation, an increase of about 60% of species belonging to the Bacteroides-Prevotella group was observed. The growth of bifidobacteria and lactobacilli was not stimulated.     

Whole Grains and Digestive Health

Whole grains contain all parts of the grain: the endosperm, germ, and bran. Whole grains are rich in fermentable carbohydrates that reach the gut: dietary fiber, resistant starch, and oligosaccharides. Most research that supports the importance of grains to gut health was conducted with isolated fiber fractions, rather than whole grains. Whole grains are an important source of dietary fiber and grain fibers such as wheat, oats, barley, and rye increase stool weight, speed intestinal transit, get fermented to short chain fatty acids, and modify the gut microflora. Wheat bran is particularly effective in increasing stool weight; wheat bran increases stool weight by a ratio of 5:1. In contrast, many novel fibers that are easily incorporated into beverages and foods increase stool weight only on a ratio of 1:1. In vitro fermentation studies with whole grains have been published. Carbohydrates of oat bran (rich in β‐glucan) were consumed by bacteria faster than those of rye and wheat brans (rich in arabinoxylan). Grain fibers were fermented more slowly than inulin, causing less gas production. Wheat is particularly high in fructo‐oligosaccharides, while wheat germ is high in raffinose oligosaccharides. Some in vivo studies show the prebiotic potential of whole grains. Whole grain breakfast cereal was more effective than wheat bran breakfast cereal as a prebiotic, increasing fecal bifidobacteria and lactobacilli in human subjects. Wheat bran consumption increased stool frequency. Thus, the gut enhancing effects of cereal fibers are well known. Limited data exist that whole grains alter gut health.     

Treatment of cereal products with a tailored preparation of trichoderma enzymes increases the amount of soluble dietary fiber

Nutritionists recommend increasing the intake of soluble dietary fiber (SDF), which is very low in most cereal-based products. Conversion of insoluble DF (IDF) into SDF can be achieved by chemical treatments, but this affects the sensorial properties of the products. In this study, the possibility of getting a substantial increase of SDF from cereal products using a tailored preparation of Trichoderma enzymes is reported. Enzymes were produced cultivating Trichoderma using durum wheat fiber (DWF) and barley spent grain (BSG) as unique carbon sources. Many Trichoderma strains were screened, and the hydrolysis conditions able to increase by enzymatic treatment the amount of SDF in DWF and BSG were determined. Results demonstrate in both products that it is possible to triple the amount of SDF without a marked decrease of total DF. The enzymatic treatment also causes the release of hydroxycinnamic acids, mainly ferulic acid, that are linked to the polysaccharides chains. This increases the free phenolic concentration, the water-soluble antioxidant activity, and, in turn, the phenol compounds bioavailability.     

Effects of resistant starch type III polymorphs on human colon microbiota and short chain fatty acids in human gut models

This study probed the possible effects of type III resistant starch (RS) crystalline polymorphism on RS fermentability by human gut microbiota and the short chain fatty acids production in vitro. Human fecal pH-controlled batch cultures showed RS induces an ecological shift in the colonic microbiota with polymorph B inducing Bifidobacterium spp. and polymorph A inducing Atopobium spp. Interestingly, polymorph B also induced higher butyrate production to levels of 0.79 mM. In addition, human gut simulation demonstrated that polymorph B promotes the growth of bifidobacteria in the proximal part of the colon and double their relative proportion in the microbiota in the distal colon. These findings suggest that RS polymorph B may promote large bowel health. While the findings are limited by study constraints, they do raise the possibility of using different thermal processing to delineate differences in the prebiotic capabilities of RS, especially its butryrogenicity in the human colon.     

Characterization of a new potential functional ingredient: coffee silverskin

Dietary fiber (DF) is one of the main dietary factors contributing to consumers' well-being. In this work the possibility of using the roasted coffee silverskin (CS), a byproduct of roasted coffee beans, as a DF-rich ingredient has been evaluated. The results of our investigation showed that this material has 60% total DF, with a relevant component (14%) of soluble DF. Although a small amount of free phenol compounds is present in CS, it has a marked antioxidative activity, which can be attributed to the huge amount of Maillard reaction products, the melanoidins. Static batch culture fermentation experiments showed that CS induces preferential growth of bifidobacteria rather than clostridia and Bacteroides spp. CS can be proposed as a new potential functional ingredient in consideration of the high content of soluble DF, the marked antioxidant activity, and the potential prebiotic activity.     

Lignins and ferulate-coniferyl alcohol cross-coupling products in cereal grains

Plant cell walls containing suberin or lignin in the human diet are conjectured to protect against colon cancer. To confirm the existence of authentic lignin in cereal grain dietary fibers, the DFRC (derivatization followed by reductive cleavage) method was applied to different cereal grain dietary fibers. By cleavage of diagnostic arylglycerol-beta-aryl (beta-O-4) ether linkages and identification of the liberated monolignols, it was ascertained that lignins are truly present in cereal grains. From the ratios of the liberated monolignols coniferyl alcohol and sinapyl alcohol, it is suggested that lignin compositions vary among cereals. Furthermore, dimeric cross-coupling products, comprising ferulate and coniferyl alcohol, were identified in most cereal fibers investigated. These ferulate 4-O-beta- and 8-beta-coniferyl alcohol cross-coupled structures indicate radical cross-coupling of polysaccharides to lignin precursors via ferulate.     

Study of the Chemical Changes and Evolution of Microbiota During Sourdoughlike Fermentation of Wheat Bran

Several studies have emphasized the possibility of enhancing nutritional properties of cereal by‐products through biotechnological processes. Bran fermentation positively affects the bioavailability of several functional compounds. Moreover, bran fermentation could increase water‐extractable arabinoxylans (WEAX), compounds with positive effects on glucose metabolism and prebiotic properties. This study was aimed at increasing the amount of bran bioactive compounds through a sourdoughlike fermentation process. Wheat bran fermentations were conducted through continuous propagation by back‐slopping of fermented bran (10% inoculum) until a stable microbiota was established, reaching high counts of lactic acid bacteria and yeasts (10⁹ and 10⁷ CFU/g, respectively). At each refreshment step, bacterial strains were isolated, clustered, molecularly analyzed by randomly amplified polymorphic DNA, and identified at the species level by 16S rRNA gene sequencing. Leuconostoc mesenteroides, Lactobacillus brevis, Lactobacillus curvatus, Lactobacillus sakei, Lactobacillus plantarum, Pediococcus pentosaceus, and Pichia fermentans dominated the stable sourdough ecosystem. After fermentation, levels of soluble fiber increased (+30%), and WEAX and free ferulic acid were respectively fourfold and tenfold higher than in raw bran, results probably related to microbial xylan‐degrading activity, whereas phytic acid was completely degraded. These preliminary data suggest that fermented bran could be considered an interesting functional ingredient for nutritional enhancement.     

Introduction to the Cereals & Europe Focus Issue

In May 2013, the Laboratory of Food Chemistry and Biochemistry, KU Leuven, organized the 4th Cereals & Europe Spring Meeting in the university's hometown Leuven, Belgium. The C&E Spring Meeting was endorsed by AACC International and its European Section, Cereals & Europe, and partially sponsored by key companies such as platinum‐level sponsor Puratos, gold‐level sponsors Chopin Technologies, CSM, DSM, DuPont, Kellogg, and Perten Instruments, and silver‐level sponsors Bühler, Cargill, Megazyme, Nestlé, and Novozymes. It was attended by more than 200 cereal scientists and technologists from 24 countries representing both academia and industry. The C&E Spring Meeting's theme was “Unlocking the Full Potential of Cereals: Challenges for Science Based Innovation.” The program, hence, focused on different aspects of cereals related to corporate challenges and new technologies, which were explored during 55 oral presentations and 56 poster presentations and reflected in six major session topics: cereal biotechnology; cereal constituents and ingredients; cereal‐based food production and processing; structure–function relationships; analytical aspects; and nutritional aspects of cereal‐based foods, food processing, and ingredients. There is obviously great potential in exploiting cereals as a tool to address the challenges of science‐based innovation. One of these challenges is reflected in the interest of today's consumers in the relationship between food and health. Here, genetic and molecular approaches can be used to improve both the content and composition of health‐promoting constituents in cereals. Other challenges the industry faces include increased incidence and/or diagnosis of celiac disease, wheat allergies, and gluten sensitivity. Not surprisingly, the quest for alternative cereals, ingredients, and products that meet the needs of consumers facing these intolerances, allergies, or sensitivities is ongoing and becomes more and more important. Alternatively, thoroughly understanding the changes in cereal constituents and ingredients during food production and processing as well as their structure–function relationships will allow cereal scientists to alter their properties. This, in turn, will provide a means of meeting new nutritional, structural, and textural criteria. Examples include the challenges associated with increasing the amount of dietary fiber in a formulation, replacing gluten with other proteins, and improving the eating characteristics of both fresh and stored (as a result of improved shelf life) products. Understanding the structural and textural properties and relating them to (often biopolymer) constituent and ingredient properties present some interesting challenges. However, there is more to the story than this. Modern cereal research ends neither at the moment at which food products are produced nor at the moment at which their properties have been analyzed. It also digs further into and focuses increasingly on what happens to foods and their constituents within the gastrointestinal tract. By doing so, cereal research increasingly aims at catching sight of the direct relationship between food, food digestion, and human health. Despite advances in each of the aforementioned topics, significant challenges in cereal research still need to be addressed. In doing so, cereal researchers in both academia and industry should keep in mind that consumer demands are constantly changing. We here have selected six peer‐reviewed papers from the 2013 C&E Spring Meeting: Effects of Genotype and Environment on Phenolic Acids Content and Total Antioxidant Capacity in Durum Wheat. D. Martini, F. Taddei, I. Nicoletti, R. Ciccoritti, D. Corradini, and M. G. D'Egidio Effect of High‐Pressure Processing on the Features of Wheat Milling By‐products. A. Marti, A. Barbiroli, F. Bonomi, A. Brutti, S. Iametti, M. Marengo, M. Miriani, and M. A. Pagani Effect of Wheat Grain Steaming and Washing on Lipase Activity in Whole Grain Flour. J. L. De Almeida, B. Pareyt, L. R. Gerits, and J. A. Delcour Ultrasonic Characterization of Unyeasted Bread Dough of Different Sodium Chloride Concentrations. F. Koksel, A. Strybulevych, J. H. Page, and M. G. Scanlon Correlation of Quality Parameters with the Baking Performance of Wheat Flours. S. M. Thanhaeuser, H. Wieser, and P. Koehler Study of the Chemical Changes and Evolution of Microbiota During Sourdoughlike Fermentation of Wheat Bran. F. Manini, M. Brasca, C. Plumed‐Ferrer, S. Morandi, D. Erba, and M. C. Casiraghi The papers included in this focus issue demonstrate that the 2013 C&E Spring Meeting brought together multidisciplinary perspectives. We hope that they can serve as a basis for further discussions between cereal researchers from both academia and industry and help them to fully unlock the potential of cereals to address the present corporate challenges to science‐based innovation. We thank all of the speakers, attendees, session chairs, sponsors, participants, and team members of the Laboratory of Food Chemistry and Biochemistry. Click on Current Issues on left and then July/August 2014 to view the six articles noted above. (From the Mobile site, go to the July/August 2014 issue.)     

Faster fermentation of cooked carrot cell clusters compared to cell wall fragments in vitro by porcine feces

Plant cell walls are the major structural component of fruits and vegetables, which break down to cell wall particles during ingestion (oral mastication) or food processing. The major health-promoting effect of cell walls occurs when they reach the colon and are fermented by the gut microbiota. In this study, the fermentation kinetics of carrot cell wall particle dispersions with different particle size and microstructure were investigated in vitro using porcine feces. The cumulative gas production and short-chain fatty acids (SCFAs) produced were measured at time intervals up to 48 h. The results show that larger cell clusters with an average particle size (d(0.5)) of 298 and 137 μm were more rapidly fermented and produced more SCFAs and gas than smaller single cells (75 μm) or cell fragments (50 μm), particularly between 8 and 20 h. Confocal microscopy suggests that the junctions between cells provides an environment that promotes bacterial growth, outweighing the greater specific surface area of smaller particles as a driver for more rapid fermentation. The study demonstrates that it may be possible, by controlling the size of cell wall particles, to design plant-based foods for fiber delivery and promotion of colon fermentation to maximize the potential for human health.     

Fermentability of Oat and Wheat Fractions Enriched in β‐Glucan Using Human Fecal Inoculation

Fermentation by human fecal bacteria of fractions of wheat bran prepared by preprocessing technology were examined and compared with a β‐glucan‐rich oat bran and a purified β‐glucan (OG). The wheat fractions were essentially a beeswing bran (WBA), mainly insoluble dietary fiber, and an aleurone‐rich fraction (WBB) containing more soluble fiber and some β‐glucan (2.7%). The oat bran (OB) had more endosperm and was very rich in β‐glucan (21.8%). Predigestion of WBB and OB to mimic the upper gastrointestinal (GI) tract gave digested wheat bran fraction B (WBBD) and digested oat bran (OBD), respectively. These predigested fractions were fermented in a batch technique using fresh human feces under anaerobic conditions. Changes in pH, total gas and hydrogen production, short chain fatty acids (SCFA), and both soluble and insoluble β‐glucan and other polysaccharide components, as determined from analysis of monosaccharide residues, were monitored. Fractions showed increasing fermentation in the order WBA < WBBD < OBD < OG. Variations in SCFA production indicated that microbial growth and metabolism were different for each substrate. Polysaccharide present in the supernatant of the digests had disappeared after 4 hr of fermentation. Fermentability of oat and wheat β‐glucan reflected solubility differences, and both sources of β‐glucan were completely fermented in 24 hr. Although the overall patterns of fermentation indicated the relative amounts of soluble and insoluble fiber, the anatomical origin of the tissues played a major role, presumably related to the degree of lignification and other association with noncarbohydrate components.