Impact of inhibition sensitivity on endoxylanase functionality in wheat flour breadmaking

A Bacillus subtilis endoxylanase (XBS(i)) sensitive to inhibition by Triticum aestivum L. endoxylanase inhibitor (TAXI) and a mutant thereof (XBS(ni)), uninhibited by TAXI, were used in straight-dough breadmaking to assess the importance of endoxylanase inhibition sensitivity on endoxylanase functionality in the process. With two European wheat flours, the loaf volume improving effect of XBS(ni) at much lower enzyme dosages was substantially larger than that brought about by XBS(i). This coincided with differences in arabinoxylan (AX) hydrolysis. Although XBS(ni) had a lower substrate selectivity for water-unextractable arabinoxylan (WU-AX) than XBS(i), the former solubilized significantly more WU-AX than XBS(i). Because of inhibition, XBS(i) solubilized most of the WU-AX during mixing, whereas, with XBS(ni), the rate of solubilization decreased less with increasing processing time than that with XBS(i). During fermentation and baking and at the highest dosage (600 U/kg of flour of XBS(i) and 60 U/kg of flour of XBS(ni)), XBS(ni) induced a stronger degradation of enzymically solubilized and water-extractable AX than XBS(i). Taken together, the data clearly demonstrate that endoxylanases, which in vitro are inhibited by endoxylanase inhibitors and still are active in the breadmaking process, as demonstrated by their functional (bread volume) enhancing effect, gradually lose their activity in the process.     

Combined Effects of Endoxylanases and Reduced Water Levels in Pasta Production

The combined effects on pasta properties of 1) varying dosages of endoxylanases (EC 3.2.1.8) from Aspergillus aculeatus and Bacillus subtilis and 2) lower levels of water during pasta dough processing were studied. The A. aculeatus endoxylanase has high selectivity toward water‐extractable arabinoxylan (WE‐AX), whereas B. subtilis endoxylanase preferentially hydrolyzes water‐unextractable arabinoxylan (WU‐AX). Pasta was produced on a microscale (50.0 g) from the semolinas of both a strong (AC Navigator) and a moderately strong (AC Avonlea) durum wheat cultivar. The levels of added water in endoxylanase‐treated pastas were adjusted to obtain the same maximal farinograph consistencies as for the control pastas. The extruded pastas were dried with drying cycles at 40, 70, or 90°C. Apart from increasing levels of solubilized arabinoxylans, these treatments had little effect on the color, optimal cooking time, and firmness of the resulting pasta. High enzyme concentrations and low (40°C) drying temperature resulted in clearly or much less checked final products for the B. subtilis and A. aculeatus enzyme, respectively. Upon cooking, the enzymically formed low molecular weight arabinoxylans were retained better in the pasta strands than their equally low molecular weight arabinogalactan counterparts.     

Evidence for the involvement of arabinoxylan and xylanases in refrigerated dough syruping

The relationship between syruping in refrigerated doughs upon prolonged storage and different aspects of arabinoxylan (AX) hydrolysis was investigated using Triticum aestivum xylanase inhibitor (TAXI) and different xylanases in the dough formula. Dough characteristics were evaluated with strong emphasis on the AX population and its fate as a function of storage time. Selective reduction of part of the flour endogenous xylanase activity in dough by added TAXI reduced dough syruping after 12 and 20 days of storage by 50%, providing straightforward evidence for the involvement of xylanases and, thus, AX in the syruping phenomenon. Addition of xylanases with different inhibitor sensitivities [an inhibition-sensitive Bacillus subtilis xylanase (XBS(i)) as well as a noninhibited mutant (XBS(ni)) thereof] to dough confirmed the importance of xylanases in dough syruping, on one hand, and the power of wheat flour TAXI to constitute a significant barrier against xylanase-mediated dough syruping, on the other hand. Use of xylanases with different substrate selectivities [an Aspergillus aculeatusxylanase (XAA) versus XBS(ni)] showed degradation of water-extractable AX (WE-AX) and solubilized AX to low molecular weight molecules rather than the conversion of water-unextractable AX (WU-AX) to high molecular weight water extractable components to be the main factor influencing dough syruping.     

Impact of xylanases with different substrate selectivity on gluten-starch separation of wheat flour

The influence on wheat flour gluten-starch separation of a xylanase from Aspergillus aculeatus (XAA) with hydrolysis selectivity toward water extractable arabinoxylan (WE-AX) and that is not inhibited by wheat flour xylanase inhibitors was compared to that of a xylanase from Bacillus subtilis (XBS) with hydrolysis selectivity toward water unextractable arabinoxylan (WU-AX) and that is inhibited by such inhibitors. XAA improved gluten agglomeration through degradation of WE-AX and concomitant reduction in viscosity, which in the laboratory scale batter procedure with a set of vibrating sieves (400, 250, and 125 microm), increased protein recoveries on the 400 microm sieve. In contrast, XBS had a negative effect as it decreased gluten protein recovery on this sieve, probably as a result of the viscosity increase that accompanied WU-AX solubilization. Hence, it was active even if most likely a considerable part of its activity was prevented by xylanase inhibitors. A combination of XAA and XBS at a low dosage yielded a distribution of gluten proteins on the different sieves comparable to that of the control. At a high combined dosage, the gluten agglomeration was better than that with XAA alone, indicating that both WE-AX and WU-AX have a negative impact on gluten agglomeration. Finally, experiments with endoxylanase addition at different moments during the separation process suggest that the status of the arabinoxylan population during dough mixing is far less critical for its impact on gluten agglomeration than that during the batter phase.     

In Situ Production of Prebiotic AXOS by Hyperthermophilic Xylanase B from Thermotoga maritima in High‐Quality Bread

In situ enrichment of bread with arabinoxylan‐oligosaccharides (AXOS) through enzymic degradation of wheat flour arabinoxylan (AX) by the hyperthermophilic xylanase B from Thermotoga maritima (rXTMB) was studied. The xylanolytic activity of rXTMB during breadmaking was essentially restricted to the baking phase. This prevented problems with dough processability and bread quality that generally are associated with thorough hydrolysis of the flour AX during dough mixing and fermentation. rXTMB action did not affect loaf volume. Bread with a dry matter AXOS content of 1.5% was obtained. Further increase in bread AXOS levels was achieved by combining rXTMB with xylanases from Pseudoalteromonas haloplanktis or Bacillus subtilis. Remarkably, such a combination synergistically increased the specific bread loaf volume. Assuming an average daily consumption of 180 g of fresh bread, the bread AXOS levels suffice to provide a substantial part of the AXOS intake leading to desired physiological effects in humans.     

Enzymic degradability of hull-less barley flour alkali-solubilized arabinoxylan fractions by endoxylanases

The impacts of the arabinose to xylose (A/X) ratio of arabinoxylans (AX) and the endoxylanase substrate specificity on the enzymic degradability of hull-less barley flour AX by endoxylanases were studied by using alkali-solubilized AX (AS-AX) fractions with different A/X ratio, on the one hand, and glycoside hydrolase family 10 and 11 endoxylanases of Aspergillus aculeatus (XAA) and Bacillus subtilis (XBS), respectively, on the other hand. AS-AX were obtained by saturated barium hydroxide treatment of hull-less barley flour water-unextractable AX. Fractionation of AS-AX by stepwise ethanol precipitation resulted in structurally different hull-less barley flour AS-AX fractions. Their A/X ratios increased with increasing ethanol concentration, and this increase in A/X ratio was reflected in their xylose substitution levels. For both XAA and XBS, the enzymic degradability of AX and apparent specific endoxylanase activity decreased with increasing A/X ratio of the AS-AX substrates, implying that both endoxylanases were sterically hindered by arabinose substituents. However, for all AS-AX fractions, hydrolysis end products of lower average degree of polymerization were obtained after incubation with XAA than with XBS, indicating that the former enzyme has a lower substrate specificity toward hull-less barley flour AS-AX than the latter. In addition, apparent specific endoxylanase activities indicated that XBS was approximately 2 times more sensitive to variations in the A/X ratio of AS-AX fractions than XAA. Furthermore, AS-AX with higher A/X ratio were relatively resistant to degradation by XBS.     

Fractionation-reconstitution experiments provide insight into the role of endoxylanases in bread-making.

The impact mechanism of endoxylanases in straight dough bread-making was investigated in fractionation-reconstitution experiments. To this end, two European flours with different bread-making characteristics were separated in gluten, prime starch, a squeegee fraction (SQF), and a water-extractable fraction. Whereas the former fractions contained negligible levels of arabinoxylan (AX), the latter contained, respectively, most of the water-unextractable AX (WU-AX) and all of the water-extractable AX (WE-AX). In vitro modification with a Bacillus subtilis endoxylanase allowed controlled solubilization of WU-AX from SQF and controlled degradation of solubilized AX and WE-AX from the water-extractables. It followed from bread-making tests with the reconstituted flours that endoxylanases exert positive loaf volume effects in bread-making by lowering the concentration of WU-AX and increasing that of total soluble AX. Limited degradation of WE-AX and significant breakdown of solubilized AX by endoxylanases, on the other hand, resulted in volume losses when compared to their nondegraded counterparts. The volume increasing effects of endoxylanases are therefore related to their ratio of solubilizing to degrading activity and thus to their substrate specificity.     

Variability in the structure of rye flour alkali-extractable arabinoxylans

The variability in rye flour alkali-extractable arabinoxylan (AE-AX) structures was examined by extensive fractionation and enzymic degradation studies. AX were isolated from destarched rye water-unextractables by sequential extraction with saturated barium hydroxide solution, water, 1.0 M sodium hydroxide, and water. The isolated AE-AX contained ca. 51% AX with an arabinose to xylose (A/X) ratio of 0.71. Fractionation of the isolated AE-AX by ethanol precipitation yielded a range of AE-AX fractions containing AX molecules with different A/X ratios and substitution patterns. Degradation of these structurally different AE-AX fractions by an Aspergillus aculeatus endoxylanase (XAA) and a Bacillus subtilis endoxylanase (XBS) resulted in AX fragments with various structural features. Further fractionation of the degraded AE-AX fractions by ethanol precipitation showed that a strong correlation exists between the structural features of the AX fragments, that is, average degree of polymerization (DP) of the xylan backbone, A/X ratio, and substitution pattern. Results indicated that the rye flour AE-AX consist of a continuum of structures rather than of two types of AX or two types of regions in the AX molecule.     

Use of psychrophilic xylanases provides insight into the xylanase functionality in bread making

The bread-improving potential of three psychrophilic xylanases from Pseudoalteromonas haloplanktis TAH3A (XPH), Flavobacterium sp. MSY-2 (rXFH), and unknown bacterial origin (rXyn8) was compared to that of the mesophilic xylanases from Bacillus subtilis (XBS) and Aspergillus aculeatus (XAA). XPH, rXFH, and rXyn8 increased specific bread volumes up to 28%, 18%, and 18%, respectively, while XBS and XAA gave increases of 23% and 12%, respectively. This could be related to their substrate hydrolysis behavior. Xylanases with a high capacity to solubilize water-unextractable arabinoxylan (WU-AX) during mixing, such as XBS and XPH, increased bread volume more than xylanases that mainly solubilized WU-AX during fermentation, such as rXFH, rXyn8, and XAA. Irrespective of their intrinsic bread-improving potential, the dosages needed to increase bread volume to a similar extent were much lower for psychrophilic than for mesophilic xylanases. The xylanase efficiency mainly depended on the enzyme's temperature activity profile and its inhibition sensitivity.     

Impact of wheat flour-associated endoxylanases on arabinoxylan in dough after mixing and resting

The impact of varying levels of endoxylanase activity in wheat flour on arabinoxylan (AX) in mixed and rested dough was studied using eight industrially milled wheat flour fractions with varying endoxylanase activity levels. Analysis of the levels of reducing end xylose (RX) and solubilized AX (S-AX) formed during mixing and resting and their correlation with the endoxylanase activity in the flour milling fractions showed that solubilization of AX during the mixing phase is mainly due to mechanical forces, while solubilization of AX during resting is caused by endoxylanase activity. Moreover, solubilization of AX during the dough resting phase is more outspoken than that during the mixing phase. Besides endoxylanase activity, there were significant xylosidase and arabinofuranosidase activities during the dough resting phase. The results indicate that wheat flour-associated endoxylanases can alter part of the AX in dough, thereby changing their functionality in bread making and potentially affecting dough and end product properties.     

Impact of Wheat Fiber on Frozen Dough Shelf Life and Bread Quality

Freezing and prolonged frozen storage of dough results in constant deterioration in the overall quality of the final product. In this study the effect of wheat bran and wheat aleurone as sources of arabinoxylan (AX) on the quality of bread baked from yeasted frozen dough was investigated. Wheat fiber sources were milled to pass through a 0.5 mm screen, prehydrated for 15 min, and incorporated into refined wheat flour at 15% replacement level. Dough products were prepared from refined flour (control A), whole wheat flour (control B), aleurone composite flour (composite flour A), and bran composite flour (composite flour B) and stored at –18°C for 28 weeks. Dough samples were evaluated for breadmaking quality at zero time, 14 weeks, and 28 weeks of storage. Quality parameters evaluated were loaf weight, loaf specific volume, and crumb firmness. Composite flour bread samples showed the most resistance to freeze damage (less reduction in the overall product quality), indicating a possible role of some fiber components (e.g., AX) in minimizing water redistribution in the dough system and therefore lessening adverse modifications to the gluten structure. The data suggest that the shelf life of frozen dough and quality of obtained bread can be improved with the addition of an AX source.     

Influence of Arabinoxylans and Endoxylanases on Pasta Processing and Quality. Production of High‐Quality Pasta with Increased Levels of Soluble Fiber

As part of a general study aiming to clarify the role of arabinoxylans (AX) in pasta processing and quality, AX were modified by the addition of endoxylanases during pasta processing. The influence on processing parameters and quality were determined. Pasta (800 g) was produced from two commercial semolinas (semA and semB) using dosages of Bacillus subtilis (XBS) and Aspergillus niger (XAN) endoxylanases of 0–0.225 Somogyi units/g of semolina. Increased dosages resulted in a drop of extrusion pressure. The endoxylanase treatments had no great effect on the resulting pasta quality (color of dry products and surface condition, viscoelastic index, and resistance to longitudinal deformations of cooked products). High dosages of XAN and XBS resulted in high levels of solubilized AX (as an extra source of soluble dietary fiber) of low molecular weight which were expected to easily leach out during the cooking process of pasta. Surprisingly, only low levels of AX were found in the cooking water, even with extremely high dosages of endoxylanases used and cooking beyond optimum time. A method is provided to obtain high‐quality pasta with increased levels of soluble fiber.     

Contribution of wheat endogenous and wheat kernel associated microbial endoxylanases to changes in the arabinoxylan population during breadmaking

Wheat kernel associated endoxylanases consist of a majority of microbial endoxylanases and a minority of endogenous endoxylanases. At least part of these enzymes can be expected to end up in wheat flour upon milling. In this study, the contribution of both types of these endoxylanases to changes in the arabinoxylan (AX) population during wheat flour breadmaking was assessed. To this end, wheat flour produced from two wheat varieties with different endoxylanase activity levels, both before and after sodium hypochlorite surface treatment of the wheat kernels, was used in a straight dough breadmaking procedure. Monitoring of the AX population during the breadmaking process showed that changes in AX are to a large extent caused by endogenous endoxylanases, whereas the contribution of microbial endoxylanases to these changes was generally very low. The latter points to a limited contamination of wheat flour with microbial enzymes during milling or to an extensive inactivation of these wheat flour associated microbial endoxylanases by endoxylanase inhibitors, present in wheat flour. When all wheat kernel associated microbial endoxylanases were first washed from the kernels and then added to the bread recipe, they drastically affected the AX population, suggesting that they can have a large impact on whole meal breadmaking.     

Effect of the Coenzymes NAD(P)(H) in Straight‐Dough Breadmaking on Protein Properties and Loaf Volume

The nicotinamide adenine dinucleotide coenzymes [NAD(P)(H)] are strong redox agents naturally present in wheat flour, and are indispensable cofactors in many redox reactions. Hence, it is not inconceivable that they affect gluten cross‐linking during breadmaking. We investigated the effect of increasing concentrations of NAD(P)(H) on gluten cross‐linking, dough properties, and bread volume using two flours of different breadmaking quality. Separate addition of the four nicotinamide coenzymes did not significantly affect mixograph properties. While addition of NAD⁺ hardly affected bread volume, supplementation with NADP(H) and NADH significantly decreased loaf volumes of breads made using flour of high breadmaking quality. Wheat flour incubation with NAD(P)H under anaerobic conditions increased wheat flour thiol content, while NAD(P)⁺ increased the extractability in SDS‐containing medium of the protein of the strong breadmaking flour. Based on the results, it was hypothesized that at least three reactions, competing for NAD(P)(H), occur during breadmaking that determine the final effect on protein, dough, and loaf properties. Next to coenzyme hydrolysis, the experiments pointed to coenzyme oxidation and NAD(P)(H) dependent redox reactions affecting protein properties.     

Genotype and Environment Variation for Arabinoxylans in Hard Winter and Spring Wheats of the U.S. Pacific Northwest

The development of high‐quality wheat (Triticum aestivum L.) cultivars depends on a thorough understanding of the constituents of grain and their variation due to genetics and environment. Arabinoxylans (pentosans) are key constituents of wheat grain and have broad and far‐reaching influences on milling and baking quality. However, variation in arabinoxylans due to genotype and environment are not fully understood. In this study, 25 hard winter and 25 hard spring wheat commercial cultivars and advanced breeding lines developed from eight public and private breeding programs in the U.S. Pacific Northwest were analyzed for water‐extractable and total arabinoxylan contents (WE‐AX and total AX), and the proportion of total AX that was water‐extractable. Winter and spring genotypes were grown in three environments each. The results indicated that there were significant differences among both sets of hard wheat genotypes for WE‐AX, total AX, and proportion of total AX that was WE‐AX. The WE‐AX and total AX mean content ranges for the winter cultivars were 0.390–0.808 and 3.09–4.04%, respectively; and for the spring cultivars 0.476–0.919 and 3.94–4.70%, respectively. WE‐AX as a percentage of total AX was similar between the two genotype sets, 11.7–23.0%. Arabinoxylan fractions were generally not correlated with grain protein, test weight, and kernel hardness. The two highest correlations for winter wheats were between protein and total AX (r = –0.40) and test weight and percentage of total AX that were water‐extractable (r = 0.37) for winter wheats. Among spring wheats, single‐kernel characterization system hardness was negatively correlated with WE‐AX and proportion of total AX that was WE‐AX (r = –0.46 and –0.51, respectively). Although often significant, arabinoxylan fractions were usually not highly intercorrelated, indicating some independence of traits. Notable genotypes, being especially high or low for one or more arabinoxylan fraction and, thus, candidates for further genetic study and cross‐breeding, included Juniper, Eddy, and ORN980995 winter wheats, and Hollis, Alta Blanca, and WQL9HDALP spring wheats. Although the results indicate that arabinoxylan fractions of wheat grain can be highly influenced by environment, there is clear support for the existence of genetic differences, especially for WE‐AX and the proportion of total AX that is water‐extractable. As such, the manipulation of arabinoxylan content of wheat grain seems to be a reasonable breeding objective.     

Quantitative Determination of High Molecular Weight Glutenin Subunits of Hard Red Spring Wheat by SDS-PAGE. I. Quantitative Effects of Total Amounts on Breadmaking Quality Characteristics

Thirteen hard red spring wheat genotypes in which seven genotypes had the same high molecular weight (HMW) glutenin subunits (2*, 7+9, 5+10) were compared for their physical-chemical and breadmaking properties. These samples were categorized into three groups based on their dough mixing and baking performances as follows: the strong dough (SD) group (six genotypes), characterized by the strongest dough mixing (average stability, 35 min); the good loaf (GL) group (four genotypes), characterized by the largest loaf volume; and the poor loaf (PL) group (three genotypes), characterized by the smallest loaf volume. Total flour proteins were fractionated into 0.5M salt-soluble proteins, 2% SDS-soluble proteins, and residue proteins (insoluble in SDS buffer). SDS-soluble proteins, residue proteins, and total flour proteins were analyzed by SDS-PAGE and densitometry procedures to determine the proportions of HMW glutenin subunits, medium molecular weight proteins, and low molecular weight proteins in relation to the total amount of proteins. No differences in the amount of salt-soluble proteins were found among the different groups of samples. Solubilities of gluten proteins (total proteins minus salt-soluble proteins) in SDS buffer were related to the differences in dough strength and baking quality among the three groups. The SD group had the lowest solubility and the PL group had the highest. SDS-PAGE analysis showed that SDS-soluble proteins of the SD group contained a smaller amount of HMW glutenin subunits than those of the GL and PL groups. The highest proportions of HMW glutenin subunits in total flour proteins were found in the SD group, while the PL group had the lowest percentage of HMW glutenin subunits in their total flour proteins. These results showed that the total quantities of HMW glutenin subunits played an important role in determining the dough mixing strength and breadmaking performance of hard red spring wheats.     

Effect of Wheat Genotype and Environment on Relationships Between Dough Extensibility and Breadmaking Quality

Dough extensibility affects processing ease, gas retention, and loaf volume of finished products. The Kieffer dough extensibility test was developed to assess extensibility of small dough samples and is therefore adapted for use in breeding programs. Information is lacking on relationships between wheat growing environments and dough properties measured by the Kieffer dough extensibility test. This study documents the variability of dough extensibility (Ext), maximum resistance to extension (Rmax), and area under the extensibility curve (Area) in relation to breadmaking quality, and the effect of wheat growing environments. Mixograph, Kieffer dough extensibility, and bake tests were performed on flour milled from 19 hard red spring wheat (Triticum aestivum L.) genotypes grown during three growing seasons (2007‐2009) at six South Dakota locations. Although both genotype and environment had significant effects on Kieffer dough extensibility variables, environment represented the largest source of variation. Among genotype means, Area was most correlated (r = 0.63) with loaf volume, suggesting that by selecting lines with increased Area, loaf volume should improve. Rmax was positively correlated (r = 0.58) with loaf volume among genotype means but negatively correlated (r = –0.80) among environmental means. Ext was positively correlated (r = 0.90) with loaf volume among environmental means. Weather variables were correlated with Rmax, Ext and loaf volume and therefore could help predict end‐use quality.     

Isolation and Characterization of Water‐Extractable Arabinoxylan from Hull‐less Barley Flours

A new procedure was developed for the isolation of highly purified water‐extractable arabinoxylan (WE‐AX) from hull‐less barley flour. It included inactivation of endogenous enzymes, removal of proteins with silica gel, and removing β‐glucans, arabinogalactan‐peptides, and starch fragments by enzyme or solvent precipitation steps. WE‐AX recovered by this isolation procedure represented, on average, 47% of all WE‐AX present in hull‐less barley flour. Purified WE‐AX from flour of different hull‐less European barley cultivars contained 84.9–91.8% AX and showed small structural differences. The apparent peak molecular weight of the purified WE‐AX was 730,000–250,000, and the arabinose‐to‐xylose ratio was 0.55–0.63. Proton nuclear magnetic resonance spectroscopy showed that the levels of un‐, O‐2 mono‐, O‐3 mono‐, and O‐2,O‐3 disubstituted xylose residues were 59.1–64.7%, 8.2–10.0%, 5.7–10.6%, and 17.6– 23.1%, respectively, and the ratio of di‐ to monosubstituted xylose was 0.90–1.54. Both O‐3 mono‐ and disubstituted xylose residues occurred isolated or next to disubstituted xylose residues in the WE‐AX chain.     

Association of Size‐Exclusion HPLC of Endosperm Proteins with Dough Mixing and Breadmaking Characteristics in a Recombinant Inbred Population of Hard Red Spring Wheat

Variation of polymeric proteins affects wheat end‐use quality. This research investigated associations of polymeric proteins with dough mixing strength and breadmaking characteristics in a near‐homogenous population of 139 recombinant inbred lines (RILs) derived from a cross between two hard red spring wheat breeding lines. Flours from the RILs grown at three locations were analyzed for molecular weight (MW) distribution of SDS‐extractable and unextractable proteins using size‐exclusion HPLC protocol. Correlations were calculated between mixing and breadmaking properties and HPLC absorbance data obtained a 0.01‐min retention time interval to identify protein fractions that had a significant effect on the quality traits. Very high MW polymeric proteins in the unextractable fraction had more distinct and positive associations with dough mixing strength and bread loaf volume than did other polymeric protein fractions, whereas extractable polymeric had negative influence. Consequently, the ratio of unextractable very high MW polymeric proteins to extractable polymeric proteins had greater correlations with dough mixing parameters than other HPLC absorbance area data. Covariate‐effect biplots also visually validated positive effects of unextractable very high MW polymeric proteins and negative effects of extractable polymeric proteins on mixing properties and loaf volume across three growing locations.     

Structural Characteristics of Water‐Extractable Nonstarch Polysaccharides from Barley Malt

Water‐extractable (WE) material was isolated from a Canadian barley malt (cv. Harrington). The purified WE material contained mainly arabinoxylans, β‐glucans, proteins, and small amounts of arabinogalactans and mannose‐containing polymers. WE material was treated with specific enzymes to obtain two fractions: one enriched in arabinoxylan (AX) and another enriched in β‐glucan (BG). The AX fraction was further fractionated by stepwise precipitation in (NH₄)₂SO₄ into five arabinoxylan subfractions. ¹H‐NMR spectroscopy and sugar analyses revealed a relatively high content of unsubstituted xylose residues (48–58%) as well as a relatively high content of doubly substituted xylose residues (28–33%) in the structure of the arabinoxylans. β‐Glucans constituted a minor portion of water‐extractable malt polysaccharides and were characterized by high levels of tri‐ and tetrasaccharide residues (93.4%) with a molar ratio of 2.19 for cellotriosyl to cellotetraosyl units. Size‐exclusion chromatography revealed that the WE material contained several polymer populations. One population had a very high molecular weight that appeared to be the result of aggregation. The AX fraction contained higher molecular weight polymers than the BG fraction.