α-Amylolysis of Large Barley Starch Granules

The α-amylolysis of large (volume average 16 μm) barley starch granules was studied by measuring the amount of carbohydrates solubilizing during hydrolysis, and the changes in morphology and molecular structure of the granule residues by scanning electron microscopy, particlesize analysis, size-exclusion chromatography, X-ray diffraction, and differential scanning calorimetry. X-ray diffraction showed that, in the earlier stages of α-amylolysis, both amorphous and crystalline parts of the granules were equally solubilized. More extensive hydrolysis caused a gradual decrease in A-type crystallinity and degradation of the granular structure. Scanning electron microscopy revealed that hydrolysis proceeded through pinholes, and pitted and partially hollow granule residues were formed. The lipid-complexed amylose was less susceptible to α-amylolysis than free amylose and amylopectin. Lipid-complexed amylose started leaching out of the granule residues only after half of the starch had solubilized due to the α-amylase treatment. Even though scanning electron microscopy indicated that there were intact granules left throughout the hydrolysis, the results obtained suggested that α-amylolysis of large barley starch granules proceeded rather evenly among the granules.     

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.     

Observations on the α‐Amylolysis Pattern of Some Waxy Maize Starches from Inbred Line Ia453

Maize starches of the endosperm mutants waxy (wx), dull:waxy (duwx), and amylose‐extender:dull:waxy (aeduwx) from inbred line Ia453 lack amylose. However, in addition to high molecular weight (HMW) amylopectin, the duwx and aeduwx starches contained 40 and 80%, respectively, intermediate branched material of low molecular weight (LMW). As gelatinized, the amylopectin of the wx starch was easily hydrolyzed into small dextrins by the α‐amylase of B. amyloliquefaciens, but components of duwx and aeduwx possessed partial resistance to amylolytic attack. Residual material of intermediate size obtained by a 4‐hr α‐amylolysis could not be separated from LMW dextrins by fractional precipitation in methanol. It is suggested that this material possessed a more regularly branched structure, in which the d ‐glucosyl chain segments were too short to allow α‐amylase action. The granular starches of duwx and aeduwx genotypes were initially considerably more resistant than the wx sample to α‐amylase attack. This was possibly due to an altered structure in the amylopectin component or the high content of intermediate material in the former granules.     

Waxy Starch Barley Genotypes with Reduced β-Glucan Contents

Random inbred lines were produced from a cross between the genotypes Chalky Glenn and Waxy Hector, and two-row lines were classified as waxy or nonwaxy by an iodine staining test. Mean nitrogen and β-glucan contents of the waxy types were higher than those of the nonwaxy types but, in contrast to previous data, mean milling energies of the two groups were not significantly different. Waxy lines with low milling energy had much lower β-glucan levels than those with high milling energy, and they also demonstrated much more extensive cell wall modification during malting. From a trial grown the following season, the waxy types with low milling energy were again identified and had levels of β-glucan content similar to those of nonwaxy types. β-Glucan contents and, particularly, milling energies showed good agreement between seasons. It is suggested that, although waxy starch is usually associated with high β-glucan content, a genetic factor from Chalky Glenn that confers low levels of β-glucan can express in a waxy background.     

Wet Processing of Barley Grains into Concentrates of Proteins, β‐Glucan,and Starch

An improved wet method was developed to process barley into fractions concentrated in protein, (1‐3)(1‐4)‐β‐d ‐glucan (BG), starch, or other carbohydrates (CHO). Alkaline concentration, solvent to barley flour ratio (SFR), and extraction temperature were evaluated for their effects on concentration and recovery of protein, BG, starch, oil, ash, and other CHO in each fraction type. Results show that the three parameters and their interactions all had significant effects, resulting in varying nutrient concentrations and recovery rates in each type of fractions. For protein fractions, protein content varied from 37.7 to 75.2%, protein recovery from 8.5 to 75.7%, and increasing alkaline concentration and SFR improved nutrient recovery. For BG fractions, BG content ranged from 21.5 to 87.0%, BG recovery from 28.6 to 78.0%, and increasing alkaline concentration decreased BG content but increased its recovery significantly. For starch fractions, starch content varied from 76.9 to 93.9%, starch recovery from 33.6 to 63.9%, and all parameters had little effect on the nutrient concentrations, but alkaline concentration and SFR improved recovery of starch, other CHO, and mass. Overall, the improved wet method was effective in concentrating the major nutrients from barley into their respective fractions, but process optimization through manipulating the three parameters is necessary to achieve a maximum concentration or recovery rate of a nutrient of interest in a specific fraction.     

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).     

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.     

Determining the Role of Starch in Flour Tortilla Staling Using α‐Amylase

Effects of α‐amylase modification on dough and tortilla properties were determined to establish the role of starch in tortilla staling and elucidate the antistaling mechanism of this enzyme. Control and amylase‐treated tortillas were prepared using a standard bake test procedure, stored at 22°C, and evaluated over four weeks. Amylase improved shelf‐stability of tortillas. The enzyme also produced a significant amount of dextrins and sugars, decreased loss of amylose solubility, and weakened starch granules. Amylopectin crystallinity increased with time, but was similar for the control and treated tortillas. Staling of tortillas appears to mainly involve the starch in the amorphous phase. As such, amylase activity does not significantly interfere with amylopectin crystallization. It is proposed that amylase partially hydrolyzed the dispersed starch (i.e., mostly amylose), starch bridging the crystalline region, and protruding amylopectin branches. Starch hydrolysis decreases the rigid structure and plasticized polymers during storage. The flexibility of tortillas results from the combined functionalities of the amylose gel and amylopectin solidifying the starch granules during storage. Protein functionality may also be involved in tortilla staling, but this needs further research.     

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.     

Synergistic Hydrolysis of Crude Corn Starch by α‐Amylases and Glucoamylases of Various Origins

Four α‐amylases and two glucoamylases from various sources, in eight combinations, were used to study the synergistic hydrolysis of crude corn starch at various temperatures. At 40 and 50°C, the combinations containing Rhizopus mold glucoamylase enhanced hydrolysis of corn starch compared wth that obtained with the combinations from Aspergillus niger. At 60°C, Rhizopus mold combinations gave low reaction yields as the enzyme was inactivated. The differences observed between α‐amylases are smaller, with the exception of Bacillus licheniformis α‐amylase, which presented more than twice the productivity of the other α‐amylases, at all temperatures. In terms of substrate conversion at 5 hr of hydrolysis, the combination of B. licheniformis α‐amylase with Rhizopus mold glucoamylase at 50°C presents 76% substrate conversion, whereas, with all the other combinations, starch conversion was 13–73%. HPLC analysis of the reaction products obtained at 50°C showed that the main product of corn starch hydrolysis was glucose at 85–100%. Further experiments showed that A. niger glucoamylase and B. licheniformis α‐amylase were the only enzymes that retained their initial activity after incubation at the temperatures 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.     

Viscosity and Solubility of β‐Glucan Extracted Under In Vitro Conditions from Barley β‐Glucan‐Fortified Bread and Evaluation of Loaf Characteristics

Fortifying bread with β‐glucan has been shown to reduce bread quality and the associated health benefits of barley β‐glucan. Fortification of bread using β‐glucan concentrates that are less soluble during bread preparation steps has not been investigated. The effects of β‐glucan concentration and gluten addition on the physicochemical properties of bread and β‐glucan solubility and viscosity were investigated using a less soluble β‐glucan concentrate, as were the effects of baking temperature and prior β‐glucan solubilization. Fortification of bread with β‐glucan decreased loaf volume and height (P ≤ 0.05) and increased firmness (P ≤ 0.05). Gluten addition to bread at the highest β‐glucan level increased height and volume (P ≤ 0.05) to values exceeding those for the control and decreased firmness (P ≤ 0.05). β‐Glucan addition increased (P ≤ 0.05) extract viscosity, as did gluten addition to the bread with the highest β‐glucan level. Baking at low temperature decreased (P ≤ 0.05) β‐glucan viscosity and solubility, as did solubilizing it prior to dough formulation. Utilization of β‐glucan that is less soluble during bread preparation may hold the key to effectively fortifying bread with β‐glucan without compromising its health benefits, although more research is required.     

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.     

Effects of β‐Glucan Content and Pearling of Barley in Diet‐Induced Obese Mice

The effects of the β‐glucan content and pearling of barley on abdominal obesity and the proinflammatory state were investigated in diet‐induced obese mice. Male C57BL/6J mice were randomly divided into four groups and fed either a high‐fat diet containing high‐β‐glucan barley (Beau Fiber [BF]) or a high‐fat diet containing β‐glucan‐free barley (Shikoku‐hadaka 84(bgl ) [BGL]) as whole grain flour or 60% pearled flour for 12 weeks. The weights of mesenteric fat, serum total and low density lipoprotein cholesterol levels, serum insulin and fasting glucose levels, oral glucose tolerance test results, and messenger RNA (mRNA) expression of proinflammatory markers in epididymal fat in both BF groups were significantly lower than those of both BGL groups. The abundance of Bacteroides in both BF groups was significantly higher than that in both BGL groups, whereas the abundance of Clostridium clusters in both BF groups was significantly lower than that in both BGL groups. No significant differences between the whole grain and pearled flours were observed. These results suggest that high‐β‐glucan barley attenuates the progression of abdominal obesity and the proinflammatory state in diet‐induced obese mice compared with β‐glucan‐free barley, possibly by modifying insulin secretion and the microbiota.     

Low α-Amylase Starch Digestibility of Cooked Sorghum Flours and the Effect of Protein

The comparably low starch digestibility of cooked sorghum flours was studied with reference to normal maize. Four sorghum cultivars that represent different types of endosperm were used. Starch digestibilities of 4% cooked sorghum flour suspensions, measured as reducing sugars liberated following α-amylase digestion, were 15–25% lower than for cooked maize flour, but there were no differences among the cooked pure starches. After the flours were predigested with pepsin to remove some proteins, the starch digestibility of cooked sorghum flours increased 7–14%, while there was only 2% increase in normal maize; however, there was no effect of pepsin treatment on starch digestibility if the flours were first cooked and then digested. After cooking with reducing agent, 100 mM sodium metabisulfite, starch digestibility of sorghum flours increased significantly while no significant effect was observed for maize. Also, starch solubility of sorghum flours at 85 and 100°C was lower than in maize, and sodium metabisulfite increased solubility much more in sorghum than in maize. Differential scanning calorimetry results of the flour residue after α-amylase digestion did not show any peaks over a temperature range of 20–120°C, indicating that sorghum starches had all undergone gelatinization. These findings indicate that the protein in cooked sorghum flour pastes plays an important role in making a slowly digesting starch.     

Effect of Heat Treatments on Microbial Load and Associated Changes to β‐Glucan Physicochemical Properties in Whole Grain Barley

Health claims for barley β‐glucan (BG) have prompted the development of food products containing barley; however, some new products (such as milled grain used without a cook step, as in a smoothie) do not use any form of heat treatment during processing or prior to consumption, which could affect microbial safety and potential health benefits. The aims of this research were to evaluate current commercial barley products for microbial counts and BG characteristics and to determine the effects of different heat treatments on these attributes in whole grain barley samples. Three heat treatments (micronization, roasting, and conditioning) were performed on three cultivars of barley (CDC Rattan, CDC McGwire, and CDC Fibar). The microbial quality was measured with standard plate count (SPC), mold and yeast count (MYC), and coliforms or Escherichia coli . Only four of the 17 commercial barley products tested met acceptable microbial limits used in this study. All three heat treatments applied to the barley samples in this study reduced SPC, MYC, and coliforms to an acceptable level. BG was extracted with an in vitro digestion method to determine its viscosity, molecular weight (MW), and solubility. All three heat treatments produced BG extracts with high viscosity and MW compared with untreated barley. Overall, heat treatments improved both the safety and the potential health benefits from soluble BG in whole grain barley.     

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.     

Release of β‐Glucan from Cell Walls of Starchy Endosperm of Barley

β‐Glucan can be solubilized from barley by warm water, with increasing solubilization as the temperature is increased. Substantially less glucan is extracted if the barley is dehusked using sulfuric acid, particularly if the dehusked barley is denatured. This indicates that enzymes capable of solubilizing glucan are present in barley. Various purified enzymes promote the solubilization of glucan from denatured and dehusked barley. Apart from endo‐β‐(1→3)(1→4)‐glucanase, these enzymes include endo‐xylanases, arabinofuranosidase, xyloacetylesterase, and feruloyl esterase. Ferulic acid and, probably, acetyl groups are esterlinked to arabinoxylan, not β‐glucan, in the cell walls of barley starchy endosperm, so the ability of the esterases, xylanases, and arabinofuranosidase to solubilize glucan indicates the pentosan component of the cell wall can restrict the extraction of glucan.     

Structural Properties of Starch in Bread and Bread Model Systems: Influence of an Antistaling α‐Amylase

The influence of an antistaling α‐amylase on bread crumb and on wheat starch gels was investigated taking into account different levels of structural hierarchy. Bread was prepared by a conventional baking procedure. Starch gels were produced by heating a concentrated starch dispersion in closed molds. Bread and starch gels were characterized by compression tests, light microscopy (LM), differential scanning calorimetry, and X‐ray measurements. The α‐amylase enhanced the initial firmness of starch gels and reduced the firming rate of bread and starch gels on aging. LM revealed that amylose and amylopectin phase‐separated within the starch granules and that freshly baked control bread and starch gels showed weak birefringence which became more intense during aging. Amylase‐containing bread and starch gels exhibited strong birefringence in the amylose rich region of the granules directly after baking which did not significantly increase during aging. The enzyme hindered the retrogradation of amylopectin as detected by differential scanning calorimetry, whereas X‐ray diffraction indicated that the enzyme induced low levels of starch crystallinity which did not change during aging. It is hypothesized that the antistaling effect of the amylase is based on the capacity to partially degrade amylopectin and, by this, to hinder its recrystallization. On the other hand, the enzyme slightly degrades amylose by an endo‐mechanism which, in turn, promotes the rapid formation of a partly crystalline amylose network in fresh bread and hinders amylose rearrangements during aging.