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.     

In Vitro Binding of Bile Acids by Rice Bran,Oat Bran,Barley and β‐Glucan Enriched Barley

The in vitro bile acid binding by rice bran, oat bran, dehulled barley, and β‐glucan enriched barley was determined using a mixture of bile acids at a duodenal physiological pH of 6.3. Six treatments and two blank incubations were conducted testing substrates on an equal protein basis. The relative in vitro bile acid binding of the cereal brans on an equal total dietary fiber (TDF) and insoluble dietary fiber (IDF) basis considering cholestyramine as 100% bound was rice bran 45 and 49%; oat bran 23 and 30%; dehulled barley 33 and 57%; and β‐glucan enriched barley 20 and 40%, respectively. Bile acid bindings on equal protein basis for the respective cereals were 68, 26, 41, and 49%. Bile acid binding by rice bran may account to a great extent for its cholesterol‐lowering properties, while bile acid binding by oat bran suggests that the primary mechanism of cholesterol lowering by oat bran is not due to the bile acid binding by its soluble fiber. Bile acid binding was not proportional to the soluble fiber content of the cereal brans tested. Except for dehulled barley, bile acid binding for rice bran, oat bran, and β‐glucan enriched barley appear to be related to their IDF content. Highest relative bile acid binding values for rice bran and β‐glucan enriched barley were observed on an equal protein basis, whereas highest values for dehulled barley were based on IDF. Data suggest that of all four cereals tested, bile acid binding may be related to IDF or protein anionic, cationic, physical and chemical structure, composition, metabolites, or their interaction with active binding sites.     

Composition and Utilization of Barley Pearling By‐Products for Making Functional Pastas Rich in Dietary Fiber and β‐Glucans

Pearling by‐products and the pearled products of two commercial stocks of hulled barley, pearled according to an industrial process consisting of five consecutive pearling steps, were analyzed for β‐glucans, dietary fiber (total, soluble, and insoluble), protein, lipid, ash, and digestible carbohydrate. The data showed that the pearling flour fractions, abraded in the fourth and fifth hullers, contained interesting amounts of β‐glucans (3.9–5.1% db) from a nutritional point of view. These fractions were subsequently enriched in β‐glucans using a milling‐sieving process to double β‐glucan content (9.1–10.5% db). Functional pastas, enriched with β‐glucans and dietary fiber, were produced by substituting 50% of standard durum wheat semolina with β‐glucan‐enriched barley flour fractions. Although darker than durum wheat pasta, these pastas had good cooking qualities with regard to stickiness, bulkiness, firmness, and total organic matter released in rinsing water. The dietary fiber (13.1–16.1% wb) and β‐glucan (4.3–5.0% wb) contents in the barley pastas were much higher than in the control (4.0 and 0.3% wb, respectively). These values amply meet the FDA requirements of 5 g of dietary fiber and 0.75 g of β‐glucans per serving (56 g in the United States and 80 g in Italy). At present, the FDA has authorized the health claim “may reduce the risk of heart disease” for food containing β‐glucans from oat and psyllium only.     

Factors Influencing β‐Glucan Levels and Molecular Weight in Cereal‐Based Products

The beneficial role of soluble dietary fiber in human nutrition is well documented and has lead to a growing demand for the incorporation of β‐glucan, particularly from oats and barley, into foods. β‐Glucan with high solubility and high molecular weight distribution results in increased viscosity in the human intestine, which is desirable for increased physiological activity. Molecular weight, level, and solubility of β‐glucan are affected by genotype, environment, agronomic input, and the interactions of these factors and food processing methods. Available literature reveals that the level of β‐glucan in a finished product (e.g. bread, cake, muffins) depends upon several factors in the production chain, whereas food processing operations are major factors affecting molecular weight and solubility of β‐glucans. Therefore, to avail themselves of the natural bioactive compounds, food manufacturers must pay attention not only to ensure sufficient concentration of β‐glucan in the raw material but also to the processing methods and functional properties of β‐glucan, minimizing enzymatic or mechanical breakdown of the β‐glucans in end‐product and optimizing processing conditions. This review discusses the different sources of β‐glucan for use in human functional foods and factors affecting the levels and the molecular weight of β‐glucan at various pre‐ and postharvest operations.     

Effects of Different Cereal Fibers on Cholesterol and Bile Acid Metabolism in the Syrian Golden Hamster

This study examined the effects of various cereal fibers and various amounts of β-glucan on cholesterol and bile acid metabolism. Hamsters were fed semisynthetic diets containing 0.12% cholesterol, 20% fat, and either 16% total dietary fiber (TDF) from wheat bran (control) or 10% TDF from oat bran, 13% TDF from oat bran concentrate or barley grains, 16% TDF from oat fiber concentrate, barley flakes, or rye bran. After five weeks, plasma total cholesterol and liver cholesterol concentrations were significantly lower (20 and 50%, respectively) only in hamsters fed rye bran. Diets containing any of the oat ingredients or barley had no effect on total cholesterol. Changes in the pattern of biliary bile acids occurred in hamsters fed 16% TDF from barley flakes or 10% TDF from oat bran. Hamsters fed rye bran had a significantly higher fecal bile acid excretion when compared with controls fed wheat bran. Because rye bran caused the most pronounced lowering effect of total cholesterol despite the lowest content of β-glucan and soluble fibers, components other than β-glucan and soluble fibers seem to be involved in its hypocholesterolemic action. Since the effects of the oat and barley ingredients were not solely correlated to the β-glucan content, structural changes occurring during processing and concentrating of the products may have impaired the hypocholesterolemic potential of the β-glucans, and other factors such as solubility and viscosity of the fiber components seem to be involved.     

Molecular Weight Distribution of β‐Glucan in Oat‐Based Foods

Oats, different oat fractions as well as experimental and commercial oat‐based foods, were extracted with hot water containing thermostable α‐amylase. Average molecular weight and molecular weight distributions of β‐glucan in extracts were analyzed with a calibrated high‐performance size‐exclusion chromatography system with Calcofluor detection, specific for the β‐glucan. Oats, rolled oats, oat bran, and oat bran concentrates all had high Calcofluor average molecular weights (206 × 10⁴ to 230 × 10⁴ g/mol) and essentially monomodal distributions. Of the oat‐containing experimental foods, extruded flakes, macaroni, and muffins all had high average molecular weights. Pasteurized apple juice, fresh pasta, and teacake, on the other hand, contained degraded β‐glucan. Calcofluor average molecular weights varied from 24 × 10⁴ to 167 × 10⁴ g/mol in different types of oat bran‐based breads baked with almost the same ingredients. Large particle size of the bran and short fermentation time limited the β‐glucan degradation during baking. The polymodal distributions of β‐glucan in these breads indicated that this degradation was enzymatic in nature. Commercial oat foods also showed large variation in Calcofluor average molecular weight (from 19 × 10⁴ g/mol for pancake batter to 201 × 10⁴ g/mol for porridge). Boiling porridge or frying pancakes did not result in any β‐glucan degradation. These large differences in molecular weight distribution for β‐glucan in different oat products are very likely to be of nutritional importance.     

Oat Bran Fermentation by Rye Sourdough

Hydration of oat bran including fermentation by rye sourdough was studied. Three types of oat bran suspensions were prepared (a control, one with whole meal rye flour added, and one with rye starter added). The suspensions were incubated for 1, 2, 3 and 4 hr. β‐Glucan content and solubilities of protein and β‐glucan were analyzed. Viscosity of the supernatants of oat bran suspensions was determined. Neither the rye sourdough nor the rye flour alone had a significant effect on the total β‐glucan content of oat bran suspensions. However, the addition of rye, either as whole meal rye flour or as sourdough starter, markedly increased the solubility of β‐glucan and proteins and simultaneously decreased the viscosity of the water‐soluble fraction of oat bran suspension. This suggests that a hydrolysis of β‐glucan had occurred that could change the rheological properties of oat bran in baking and the physiological potential of oat bran in nutrition.     

Extraction and Physicochemical Characterization of Rye β‐Glucan and Effects of Barium on Polysaccharide Molecular Weight

Use of saturated Ba(OH)₂ to extract rye β‐glucan led to a depolymerized product. Similar depolymerization of β‐glucan was observed when oat bran was extracted with this reagent. Isolated oat β‐glucan, detarium xyloglucan, guar galactomannan, and wheat and rye arabinoxylan were also depolymerized by treatment with the barium reagent. The degree of depolymerization was related to time of contact with, and concentration of, the barium. Rye β‐glucan of two different molecular weights (MW) were isolated and characterized. The structure of rye β‐glucan, as evaluated from the ratio of (1→3)‐linked cellotriosyl to (1→3)‐linked cellotetraosyl primary structural units, most closely resembles barley β‐glucan. Analytical variability of this ratio is discussed. A freshly prepared solution (2%) of the higher MW sample showed shear thinning behavior typical of cereal β‐glucans. The lower MW sample at 2% was not shear thinning, but on further purification, after storage for seven days, a 6% solution had gelled as shown by the mechanical spectrum.     

Content and Molecular Weight Distribution of Oat β‐Glucan in Oatrim,Nutrim, and C‐Trim Products

The soluble fiber, β‐glucan, in oat products is an active hypolipidemic component that is responsible for lowering plasma lipids. Quantitative analysis of β‐glucan in oat hydrocolloids such as Oatrim, Nutrim, and C‐Trim was performed to measure the total β‐glucan content and molecular weight distribution. For the measurement of total β‐glucan content, both modified flow‐injection analysis (FIA) method and the standard AACC enzymatic method were employed. FIA method uses the enhanced fluorescence produced when β‐glucan forms complexes with Calcofluor. Experimental results of both the modified FIA method and the standard AACC enzymatic method revealed very good coincidence with each other. This result confirms the applicability of either technique for the quantitative evaluation of β‐glucan in hydrocolloids. Molecular weight (MW) distribution of β‐glucan was determined by size‐exclusion chromatography with postcolumn detection. Experimental results revealed that the molecular weight of β‐glucan in the Trim products was decreased during the manufacturing process. This result was ascribed to the rigorous processing condition of jet‐cooking.     

Prediction of β‐Glucan Concentration Based on Viscosity Evaluations of Raw Oat Flours from High β‐Glucan and Traditional Oat Lines

Rheological properties of raw oat flour slurries were determined in experimental high β‐glucan (≤7.8%) and traditional oat lines (4–5% β‐glucan) grown in two consecutive years. Three different media were used to disperse oat flours: deionized water, silver nitrate solution (to inactivate endogenous enzymes), and alkali solution (to solubilize both water‐soluble and water‐insoluble β‐glucans). Significant correlations (P < 0.05) between viscosity of slurries and β‐glucan concentration obtained in either deionized water (r = 0.833), silver nitrate (r = 0.940), or alkali (r = 0.896) solutions showed that β‐glucans were the main contributor to oat extract viscosity. The highest correlation was obtained in silver nitrate solution, suggesting that inactivating endogenous enzymes is important to obtain high correlations. Predictive models of oat β‐glucan concentration based on the viscosity profile were developed using partial least squares (PLS) regression. Prediction of β‐glucan concentration based on viscosity was most effective in the silver nitrate solution (r = 0.949, correlation coefficient of predicted vs. analyzed β‐glucans) and least effective in the alkali solution (r = 0.870). These findings demonstrate that the β‐glucan in oat could be predicted by measuring the viscosity of raw flours in silver nitrate solution, and this method could be used as a screening tool for selective breeding.     

Effects of Processing,Cultivar, and Environment on the Physicochemical Properties of Oat β‐Glucan

Several food regulatory agencies around the world have approved health claims for oat‐derived β‐glucan for cholesterol lowering and glycemic control. The biological efficacy of β‐glucan appears to depend both on daily intake and on physicochemical properties, such as molecular weight and viscosity. The objective of this study was to determine the effects of oat processing, genotype, and growing location on the physicochemical properties of β‐glucan. Five oat genotypes (HiFi, Leggett, CDC Dancer, Marion, and CDC Morrison) grown in two locations (Saskatoon and Kernen) were dehulled (untreated) and processed in a pilot facility through kilning (kilned, not flaked) and subsequent steaming and flaking (kilned, flaked). Untreated groats gave a relatively low Rapid Visco Analyzer (RVA) apparent viscosity (164 cP) and a low extractable β‐glucan molecular weight (332,440) but exhibited high β‐glucan solubility (90.49%). Compared with untreated groats, the kilned (not flaked) samples had significantly increased RVA apparent viscosity (314 cP) and extractable β‐glucan molecular weight (604,710). Additional processing into kilned and flaked products further increased RVA apparent viscosity (931 cP) and β‐glucan molecular weight (1,221,760), but β‐glucan solubility (63.83%) was significantly reduced. Genotype and growing environment also significantly affected β‐glucan viscosity and molecular weight, but no significant interaction effects between processing, genotype, and environment were found. Results indicate that there is potential for processors to improve the physicochemical and nutritional properties of oat end products through processing of specific oat genotypes from selected growing locations.     

Structure of (1→3)(1→4)‐β‐d‐Glucan in Waxy and Nonwaxy Barley

The endosperm cell walls of barley are composed largely of a (1→3)(1→4)‐β‐d ‐glucan commonly known simply as β‐d ‐glucan (Wood 2001). There has been much research into the characteristics of barley β‐glucan because of the influence of this polysaccharide on performance of barley in malting and subsequent brewing of beer, and in feed value, especially for young chicks (MacGregor and Fincher 1993). The potential for β‐glucan to develop high viscosity is a problem in these uses, but from the perspective of human nutrition, this characteristic may be an advantage. The glycemic response to oat β‐glucan is inversely related to (log)viscosity (Wood et al 1994a) and there is evidence to suggest that the lowering of serum cholesterol levels associated with oat and barley products (Lupton et al 1994; Wood and Beer 1998) is at least in part due to the β‐glucan (Braaten et al 1994) and probably also its capacity to develop viscosity in the gastrointestinal tract (Haskell et al 1992).     

Preparation and Characterization of Films Using Barley and Oat β‐Glucan Extracts

Films for potential food use were prepared from aqueous solutions of β‐glucan extracted from hulled barley, hull‐less barley, and oats. The extracts (75.2–79.3% β‐glucan) also contained proteins, fat, and ash. Glycerol was used as a plasticizer. The films were translucent, smooth, and homogeneous in structure on both sides. Water vapor permeability of films prepared from 4% solutions of β‐glucan extracts were higher than those from 2% solutions, despite similar values for water vapor transmission rate. Mechanical properties were influenced by both β‐glucan source and concentration. The oat β‐glucan films showed higher tensile strength and water solubility, and lower color, opacity, and deformation values than those of barley. Films prepared from hull‐less barley cv. HLB233 remained intact upon immersion in water for 24 hr.     

Microenzymatic Evaluation of Oat (Avena sativa L.) β‐Glucan for High‐Throughput Phenotyping

Oats (Avena sativa L.) have received significant attention for their positive and consistent health benefits when consumed as a whole grain food, attributed in part to mixed‐linkage (1‐3,1‐4)‐β‐d ‐glucan (referred to as β‐glucan). Unfortunately, the standard enzymatic method of measurement for oat β‐glucan is costly and does not provide the high‐throughput capability needed for plant breeding in which thousands of samples are measured over a short period of time. The objective of this research was to test a microenzymatic approach for high‐throughput phenotyping of oat β‐glucan. Fifty North American elite lines were chosen to span the range of possible values encountered in elite oats. Pearson and Spearman correlations (r) ranged from 0.81 to 0.86 between the two methods. Although the microenzymatic method did contain bias compared with the results for the standard streamlined method, this bias did not substantially decrease its ability to determine β‐glucan content. In addition to a substantial decrease in cost, the microenzymatic approach took as little as 6% of the time compared with the streamlined method. Therefore, the microenzymatic method for β‐glucan evaluation is an alternative method that can enhance high‐throughput phenotyping in oat breeding programs.     

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.     

Effect of Processing on Viscosity and Molecular Weight of (1,3)(1,4)‐β‐Glucan in Western Australian Oat Cultivars

Six Australian milling oat cultivars grown over two growing seasons were characterized for differences in (1,3)(1,4)‐β‐glucan (β‐glucan) viscosity, solubility, molecular weight (M_w), and the effect of processing. Oat cultivars grown in 2012 had significantly higher extracted β‐glucan viscosity from oat flour than the same oat cultivar grown in 2011 (P < 0.05, mean 137 and 165 cP, respectively). Noodle β‐glucan mean viscosity for 2012 (147 cP) was significantly higher than for 2011 (128 cP). β‐Glucan from ‘Williams’ and ‘Mitika’ oats had the highest viscosity (P < 0.05) in flour (5.92 and 5.25%, respectively) and noodles (1.64 and 1.47%, respectively) for both years, compared with the other oat cultivars. β‐Glucan (M_w) of Williams for 2012 and ‘Kojonup’ for both years were the least affected by processing, with an average drop of 33% compared with a maximum of 63% for other cultivars. Therefore, Williams showed superior β‐glucan properties to other oat cultivars studied, and can potentially provide improved health benefits. High and low β‐glucan M_w populations were found in the same elution peak after processing. Oat cultivars chosen for processing should be those with β‐glucans that are more resistant to processing, and that maintain their physiochemical properties and, therefore, bioactivity.     

Development of an Orange‐Flavored Barley β‐Glucan Beverage

Barley β‐glucan concentrate shows great potential as a functional food ingredient, but few product applications exist. The objectives of this study were to formulate a functional beverage utilizing barley β‐glucan concentrate, and to make a sensory evaluation of beverage quality in comparison to pectin beverages and to assess shelf stability over 12 weeks. Three beverage treatments containing 0.3, 0.5, and 0.7% (w/w) barley β‐glucan were developed in triplicate. Trained panelists found peely‐ and fruity‐orange aroma and sweetness intensity to be similar (P > 0.05) for all beverages tested. Beverage sourness intensity differed among beverages (P ≤ 0.05). Panelists evaluated beverages containing 0.3% hydrocolloid as similar (P > 0.05), whereas beverages with 0.5 and 0.7% β‐glucan were more viscous (P ≤ 0.05) than those with pectin at these levels. Acceptability of beverages was similar according to the consumer panel. Shelf stability studies showed no microbial growth and stable pH for all beverages over 12 weeks. Colorimeter values for most beverages decreased (P ≤ 0.05) during the first week of storage, mostly stabilizing thereafter. With an increase in concentration, β‐glucan beverages became lighter in color (P ≤ 0.05) and cloudier, but these attributes for pectin beverages were not affected (P > 0.05). β‐Glucan beverages exhibited cloud loss during the first three weeks of storage. β‐Glucan can therefore be successfully utilized in the production of a functional beverage acceptable to consumers.     

REVIEW: Oat and Rye β‐Glucan: Properties and Function

Over the years, the β‐glucan of oats and barley has been the subject of study either because of the importance of the cholesterol‐lowering potential to health claims (FDA 1997, 2005) or, in the case of barley, because of the role of β‐glucan and β‐glucan‐rich endosperm cell walls in malting and brewing. β‐Glucan is also present in rye and in much lesser amounts in wheat. The most striking difference in these latter two sources is the difficulty in extractability; alkali rather than water is required for significant release from the cell walls. This review will discuss physicochemical properties of oat and rye β‐glucan and, where information allows, relate these to physiological effects. Viscosity, or more generally rheology, plays a central role in discussions of cereal β‐glucan functionality and physiological effects and will be the focus of this review.     

Pasting and Thermal Properties of Flours from Oat Lines with High and Typical Amounts of β‐Glucan

Experimental oat lines high in β‐glucan (6–7.8%) and traditional lines (3.9–5.7% β‐glucan) were used to evaluate the effect of β‐glucan on pasting (by rapid viscoanalysis) and thermal properties (by differential scanning calorimetry) of oat flours. Significant correlations established between β‐glucan concentration and the pasting parameters after amylolysis demonstrated the role of β‐glucans in oat pasting. The relative decrease of peak viscosity (PV) observed after enzymatic removal of β‐glucans was correlated with β‐glucan concentration (r = 0.880, P < 0.010) and reconfirmed their contribution to pasting. A significant increase of PV with β‐glucan concentration obtained under conditions of either autolysis (deionized water used for dispersion) (r = 0.89, P < 0.010) or inhibition (silver nitrate solution used for dispersion) (r = 0.91, P < 0.001) might be explained by an increase in water retention capacity caused by the β‐glucans. Predictive models of β‐glucan concentration based on the whole pasting profile or selected profile regions were developed using partial least squares (PLS) regression.Prediction of β‐glucan based on the whole profile obtained in the silver nitrate solution was the most effective (r = 0.93, correlation coefficient of predicted vs. analyzed β‐glucans, P < 0.050). No correlations were observed between the thermal properties of oat flours and the β‐glucan concentration.     

Network Formation by Pilot Plant and Laboratory‐Extracted Barley β‐Glucan and Its Rheological Properties in Aqueous Solutions

Barley and oat β‐glucans of low viscosity form reversible gels when prepared in sufficiently high concentrations. Solutions of three barley β‐glucan gums differing in molecular weight and thus in viscosity were prepared at 1.0, 2.5, or 5.0% (w/w) concentration levels. Medium‐ and high‐viscosity gums were prepared in a pilot plant (PP) and laboratory (LAB), respectively. Low‐viscosity (LV) gum was extracted in the laboratory at pH 7, which allowed for native enzymatic activity and decreased molecular weight. Network formation was monitored overnight through changes in storage (G′) and loss (G″) moduli. The strength of the formed network was determined from oscillatory rheological measurements by increasing the strain from 2 to 100%. Findings demonstrate that gelation of β‐glucan is molecular weight dependent and practically an instantaneous process for low‐viscosity gum solutions at concentrations of ≤5% gum (or ≤4% β‐glucan), levels lower than previously anticipated. The purity of β‐glucan also seems to affect gelation rate. Better understanding of the β‐glucan gelation behavior is important for its functionality in both food product applications and physiological mechanisms of its health benefits.