High‐Starch and High‐β‐Glucan Barley Fractions Milled with Experimental Mills

This study focused on the performance of two hulless barley cultivars (Doyce and Merlin) and one commercial husked (hulled) sample using experimental milling. The purpose was to use experimental milling as a preliminary indicator of the milled streams with potential use for fuel ethanol production and fractions that could be used in food products. Experimental mills designed for flour production evaluation from wheat were Chopin CD1 Auto, Quadrumat Sr, Buhler, and an experimental Ross roller mill walking flow. Results indicate that the shorts had the highest levels of β‐glucan from all the mills. However, the β‐glucan content in the break flours was highest with the roller mill walking flow and the Chopin CD1 for the hulless cultivars. The lowest β‐glucan content in the break flour was found with the Buhler for Doyce. Break flour and, to a slightly lesser extent, reduction flour from all cultivars tested on all mills contained the highest starch content (up to 83%) and are therefore most appropriate for use as feedstock for fuel ethanol production. Conversely, bran and shorts from all cultivars and mills were lowest in starch (as low as 25%), making them ideal as low‐starch food ingredients.     

Effect of Extrusion Cooking on the Primary Structure and Water Solubility of β‐Glucans from Regular and Waxy Barley

Water‐soluble β‐glucan from native and extrusion‐cooked barley flours of two barley cultivars, Candle (a waxy starch barley) and Phoenix (a regular starch barley), was isolated and purified. The purity of β‐glucan samples was 85–93% (w/w, dry weight basis) for Candle and 77–86% (w/w, dry weight basis) for Phoenix. The water solubility of β‐glucan (at room temperature, 25°C) in the native and extruded flours (primary solubility) was different from that of the purified β‐glucan samples (secondary solubility). The solubility of β‐glucan in the native and extruded Candle flour was substantially higher than that of β‐glucan in Phoenix. For both cultivars, β‐glucan in the extruded flours had solubility (primary solubility) values higher than in their native counterparts. The solubility of β‐glucan in the purified β‐glucan samples differed depending on the barley cultivar and the extrusion conditions employed. The glycosidic linkage profiles of purified soluble β‐glucan from native and extruded barley flours were determined in order to understand the changes in the primary structure of β‐glucan and the effect of extrusion on the β‐glucan structure‐solubility relationship.     

Molecular Weight of β‐Glucan Affects Physical Characteristics,In Vitro Bile Acid Binding,and Fermentation of Muffins

Muffins containing different amounts and molecular weights (MW) of β‐glucan were evaluated for the effect of β‐glucan on the physical characteristics of the muffins and on in vitro bile acid binding and fermentation with human fecal flora. Wheat flour muffins were prepared with the addition of β‐glucan extracts with high‐, medium‐, or low‐MW. For oat flour muffins, the native oat flour contained high‐MW β‐glucan; the oat flours were treated to create medium‐ and low‐MW β‐glucan within the prepared muffin treatments. For each 60‐g muffin, the amounts of β‐glucan were 0.52, 0.57, and 0.59 g for high‐, medium‐, and low‐MW β‐glucan wheat flour muffins, and 2.38, 2.18, and 2.23 g for high‐, medium‐, and low‐MW β‐glucan oat flour muffins, respectively. The lower the MW of the β‐glucan in muffins, the lower the height and volume of the muffins. The oat flour muffins were less firm and springy than the wheat flour muffins as measured on a texture analyzer; however, MW had no effect on muffin texture. The oat flour muffins bound more bile acid than did the wheat flour muffins. The muffins with high‐MW β‐glucan bound more bile acid than did those with low‐ and medium‐MW β‐glucan. Muffin treatment affected the formation of gas and total short‐chain fatty acids (SCFA) compared with the blank without substrate during in vitro fermentation. There were no differences in pH changes and total gas production among muffin treatments. The high‐MW β‐glucan wheat flour muffins produced greater amounts of SCFA than did the wheat flour muffin without β‐glucan and the oat flour muffins; however, there were no differences in SCFA production among muffins with different MW. In general, the β‐glucan MW affected the physical qualities of muffins and some potential biological functions in humans.     

Determination of β‐Glucan Molecular Weight Using SEC with Calcofluor Detection in Cereal Extracts

A high‐performance size‐exclusion chromatography system (HPSEC) was set up with detection based on the specific binding of Calcofluor to β‐glucan for determination of amount and molecular weight of β‐glucan in different cereal extracts. To calibrate the HPSEC system, a purified β‐glucan was fractionated into narrow molecular weight ranges and the average molecular weight was determined before analysis on the HPSEC system. The detector response was similar for β‐glucans from oats and barley and appeared to be independent of molecular weight. Four different methods for extraction of β‐glucan from different cereal products were tested: two alkaline, one with hot water and added α‐amylase, and one with water and added xylanase. Inactivation of endogenous β‐glucanase was crucial for the stability of the extracts, even when extracting at high temperature or pH. Yields varied widely between the different extraction methods but average molecular weight and molecular weight distribution were similar. Extraction with sodium hydroxide generally gave a higher yield and molecular weight of β‐glucan in the extracts.     

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.     

Bulk Carbohydrate Grain Filling of Barley β‐Glucan Mutants Studied by 1H HR MAS NMR

Temporal and genotypic differences in bulk carbohydrate accumulation in three barley genotypes differing in the content of mixed linkage β‐(1→3),(1→4)‐D‐glucan (β‐glucan) and starch were investigated using proton high‐resolution, magic angle spinning, nuclear magnetic resonance (¹H HR MAS NMR) during grain filling. For the first time, ¹H HR MAS NMR spectra of flour from immature barley seeds are analyzed. Spectral assignments are made using two‐dimensional (2D) NMR methods. Both α‐ and β‐glucan biosynthesis were characterized by inspection of the spectra as well as by calibration to the reference methods for starch and β‐glucan content. Starch was quantified with very good calibrations to the α‐(1→4) peak (5.29–5.40 ppm) and the region 3.67–3.83 ppm covering starch glycopyranosidic protons from H5 and H6. In contrast, the spectral inspection of the β‐anomeric region 4.45–4.85 ppm showed unexpected lack of intensity in the high β‐glucan mutant lys5f at seed maturity, resulting in poor calibration to reference β‐glucan content. We hypothesize that the lack of β‐glucan signal in lys5f indicates partial immobilization of the β‐glucan that appears to be either genotypic dependent or water/β‐glucan ratio dependent.     

Distribution of β‐Glucan in the Grain of Hull‐less Barley

Nine hull‐less barley (HB) containing waxy (0–7% amylose), normal (≈25% amylose), or high amylose (≈42% amylose) starch with normal or fractured granule make‐up and 4–9% (1→3)(1→4)‐β‐d ‐glucans (β‐glucan) were pearled to remove 70% of the original grain weight in 10% intervals. The pearled fractions were analyzed for β‐glucan distribution within HB grain. Protein content of the pearled fractions indicated that the three outermost fractions contained pericarp and testa, aleurone, and subaleurone tissues, respectively. For all HB, β‐glucan and acid‐extract viscosity were very low in the outermost 20% of the kernel. For low β‐glucan HB, β‐glucan content was the greatest in the subaleurone region and declined slightly toward inner layers. For high β‐glucan HB, however, more than 80% of grain β‐glucan was distributed more evenly throughout the endosperm. Acid extract viscosity was significantly (P < 0.01) correlated with total (r = 0.75) and soluble (r = 0.87) β‐glucan content throughout the kernel of all HB. Growing conditions, location and year, had significant effects on the concentration of protein, starch and β‐glucan. However, protein, starch, and β‐glucan distribution patterns were not affected by growing conditions. The difference in β‐glucan distribution between low and high β‐glucan HB may explain the difference in milling performance of HB with low or high β‐glucan.     

Effect of Formulation and Processing Treatments on Viscosity and Solubility of Extractable Barley β‐Glucan in Bread Dough Evaluated Under In Vitro Conditions

β‐Glucan shows great potential for incorporation into bread due to its cholesterol lowering and blood glucose regulating effects, which are related to its viscosity. The effects of β‐glucan concentration, gluten addition, premixing, yeast addition, fermentation time, and inactivation of the flour enzymes on the viscosity of extractable β‐glucan following incorporation into a white bread dough were studied under physiological conditions, as well as, β‐glucan solubility in fermented and unfermented dough. β‐Glucan was extracted using an in vitro protocol designed to approximate human digestion and hot water extraction. The viscosity of extractable β‐glucan was not affected by gluten addition, the presence of yeast, or premixing. Fermentation produced lower (P ≤ 0.05) extract viscosity for the doughs with added β‐glucan, while inactivating the flour enzymes and increasing β‐glucan concentration in the absence of fermentation increased (P ≤ 0.05) viscosity. The physiological solubility of the β‐glucan concentrate (18.1%) and the β‐glucan in the unfermented dough (20.5%) were similar (P > 0.05), while fermentation substantially decreased (P ≤ 0.05) solubility to 8.7%, indicating that the reduction in viscosity due to fermentation may be highly dependent on solubility in addition to β‐glucan degradation. The results emphasize the importance of analyzing β‐glucan fortified foods under physiological conditions to identify the conditions in the dough system that decrease β‐glucan viscosity so that products with maximum functionality can be developed.     

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.     

Isolation,Fractionation, and Structural Characteristics of Alkali‐Extractable β‐Glucan from Rye Whole Meal

The main nonstarch polysaccharide of rye is arabinoxylan (AX), but rye contains significant levels of (1→3)(1→4)‐β‐d ‐glucan, which unlike oat and barley β‐glucan, is not readily extracted by water, possibly because of entrapment within a matrix of AX cross‐linked by phenolics. This study continues objectives to improve understanding of factors controlling the physicochemical behavior of the cereal β‐glucans. Rye β‐glucan was extracted by 1.0N NaOH and increasing concentrations of ammonium sulfate were used to separate the β‐glucan from AX and prepare a series of eight narrow molecular weight (MW) distribution fractions. Composition and structural characteristics of the isolated β‐glucan and the eight fractions were determined. High‐performance size‐exclusion chromatography (HPSEC) with both specific calcofluor binding and a triple detection (light scattering, viscometry, and refractive index) system was used for MW determination. Lichenase digestion followed by high‐performance anion exchange chromatography of released oligosaccharides, was used for structural evaluation. The overall structure of all fractions was similar to that of barley β‐glucan.     

Extractability,Structure and Molecular Weight of β‐Glucan from Canadian Rye (Secale cereale L.) Whole Meal

Oat and barley (1→3)(1→4)‐β‐d ‐glucans (β‐glucan) are readily extracted by hot water but rye β‐glucan is resistant to such extraction. This poor extractability might be due to entrapment within a matrix of arabinoxylan (AX) cross‐linked through phenolic constituents. AX are the major nonstarch polysaccharides of the rye kernel. In this study, several approaches were compared in an effort to determine optimum conditions for extraction of high yields, high molecular weight (MW), and high purity of β‐glucan from Canadian rye whole meal. Variables investigated included sodium hydroxide concentrations, extraction time, sample prehydration, extraction under low temperature, and prior extraction of AX with barium hydroxide. There was a linear relationship between the strength of NaOH and amount of β‐glucan extracted and because MW was essentially the same up to 1.0N NaOH, this extraction agent, at room temperature for 90 min, was selected to isolate rye β‐glucan. The β‐glucan was then purified and structure and molecular weight distribution studied.     

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.     

Isolation and Characterization of High‐Purity Starch Isolates from Regular,Waxy, and High‐Amylose Hulless Barley Grains

Recovering starch from barley is problematic typically due to interference from β‐glucan (the soluble fiber component), which becomes highly viscous in aqueous solution. Dry fractionation techniques tend to be inefficient and often result in low yields. Recently, a protocol was developed in our laboratory for recovering β‐glucan from barley in which sieving whole barley flour in a semiaqueous (50% ethanol) medium allowed separation of the starch and fiber fractions without activating the viscosity of the β‐glucan. In this report, we investigate an aqueous method which further purifies the crude starch component recovered from this process. Six hulless barley (HB) cultivars representing two each of waxy, regular, and high‐amylose cultivars were fractionated into primarily starch, fiber, and protein components. Starch isolates primarily had large granules with high purity (>98%) and yield range was 22–39% (flour dry weight basis). More importantly, the β‐glucan extraction efficiency was 77–90%, meaning that it was well separated from the starch component during processing. Physicochemical evaluation of the starch isolates, which were mainly composed of large granules, showed properties that are typical of the barley genotypes.     

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.     

Extraction of β‐Glucan from Oat Bran in Laboratory Scale

Effects of various enzymes and extraction conditions on yield and molecular weight of β‐glucans extracted from two batches of commercial oat bran produced in Sweden are reported. Hot‐water extraction with a thermostable α‐amylase resulted in an extraction yield of ≈76% of the β‐glucans, while the high peak molecular weight was maintained (1.6 × 10⁶). A subsequent protein hydrolysis significantly reduced the peak molecular weight of β‐glucans (by pancreatin to 908 × 10³ and by papain to 56 × 10³). These results suggest that the protein hydrolyzing enzymes may not be pure enough for purifying β‐glucans. The isolation scheme consisted of removal of lipids with ethanol extraction, enzymatic digestion of starch with α‐amylase, enzymatic digestion of protein using protease, centrifugation to remove insoluble material, removal of low molecular weight components using dialysis, precipitation of β‐glucans with ethanol, and air‐drying.     

Influence of Oat β‐Glucan Preparations on the Perception of Mouthfeel and on Rheological Properties in Beverage Prototypes

The aim was to study the effect of concentration and molecular weight of four different β‐glucan preparations on the perceived sensory quality of a beverage prototype. The correlations between sensory and instrumental measures were investigated. Two of the preparations were brantype containing high molecular weight β‐glucan, two were more‐processed low molecular weight β‐glucan preparations. Twelve beverage samples containing 0.25–2% β‐glucan and one reference sample thickened with carboxymethyl cellulose (CMC) were profiled by a sensory panel and analyzed by instrumental measurements (viscosity and molecular weight). Sensory profiles of the beverages varied at the same concentration of β‐glucan, depending on β‐glucan preparation. Beverages made with the bran‐type preparations were more viscous and had higher perceived thickness than beverages made with more‐processed, low molecular weight preparations. Moderate correlations were obtained between perceived thickness and sliminess and instrumental viscosity at all shear rates between 26 and 100/sec (r = 0.63–0.78; P ≤ 0.001). Technologically, more‐processed β‐glucan preparations are easier to add into a beverage in amounts sufficient for achieving a physiologically functional amount of β‐glucan in a product.     

Development of a Germination Process for Producing High β‐Glucan,Whole Grain Food Ingredients from Oat

Germination can be used to improve the texture and flavor of cereals. However, germination generally causes breakdown of β‐glucans, which is undesirable with respect to the functional properties of β‐glucan. Our aim was to assess possibilities of germinating oat without substantial loss of high molecular weight β‐glucan. Two cultivars, hulled Veli and hull‐less (naked) Lisbeth were germinated at 5, 15, and 25°C and dried by lyophilization or oven drying. Elevated germination temperatures led to an increase in Fusarium, aerobic heterotrophic bacteria, Pseudomonas spp., lactic acid bacteria, enterobacteria, and aerobic spore‐forming bacteria. Therefore, the germination temperature should be kept low to avoid excessive growth of microbes. Of the samples germinated at 15°C, only one contained low amounts of the Fusarium toxin deoxynivalenol (52 μg/kg). Germination led to the breakdown of β‐glucans, but the decrease in the molecular weight of β‐glucan was initially very slow. A short germination schedule (72 hr, 15°C) terminated with oven drying was developed to produce germinated oat with retained β‐glucan content. Compared with the native oat, 55–60% of the β‐glucan could be retained.     

Glycemic Response to Oat Bran Muffins Treated to Vary Molecular Weight of β‐Glucan

Oat bran muffins, containing 4 or 8 g of β‐glucan per two‐muffin serving, were prepared with or without β‐glucanase treatment to produce a range of β‐glucan molecular weights from 130,000 to just over 2 million. Following an overnight fast, the glycemic responses elicited by the untreated and treated muffins was measured in 10 healthy subjects and compared with a control whole wheat muffin. Taken all together, the 4‐g β‐glucan/serving muffins reduced blood glucose peak rise (PBGR) by 15 ± 6% compared with the control. The 8‐g β‐glucan/serving muffins had a significantly greater effect (44 ± 5% reduction compared with the control, P < 0.05). The efficacy of the muffins decreased as the molecular weight was reduced from a 45 ± 6% reduction in PBGR (P < 0.05) for the untreated muffins (averaged of both serving sizes) to 15 ± 6% (P < 0.05) for muffins with the lowest molecular weight. As the molecular weight was reduced from 2,200,000 to 400,000, the solubility of the β‐glucan increased from a mean of 44 to 57%, but as the molecular weight was further decreased to 120,000, solubility fell to 26%. There was a significant correlation (r² = 0.729, P < 0.001) between the peak blood glucose and the product of the extractable β‐glucan content and the molecular weight of the β‐glucan extracted.     

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.     

Detection,Localization, and Variability of Endogenous β‐Glucanase in Wheat Kernels

Clinical studies with isolates of β‐glucan have shown that the health benefits are regulated not only by the polysaccharide concentration but also by the molecular weight and concentration in solution, because these health benefits are controlled, inter alia, by viscosity in the gut. The degradation of β‐glucan in baked products is likely caused by baking ingredients or processes, or by endogenous enzymes in wheat flour. The objectives of the present study were to quantify β‐glucanase in wheat kernels and to determine factors that influence the levels of this enzyme. A modified protocol to quantify β‐glucanase was developed and then confirmed through high‐performance size‐exclusion chromatography (HPSEC) with Calcofluor detection. Under this protocol, it was shown that the concentration of β‐glucanase activity was the highest in the bran fraction of the kernel in ungerminated wheats, whereas it was distributed throughout the entire kernel following germination. Furthermore, investigation on different wheat cultivars planted in the same and different locations showed that genotype, environment, and agronomic practice all can have an effect on β‐glucanase activity level in wheat kernels.