The potential of naked barley sourdough to improve the quality and dietary fibre content of barley enriched wheat bread

The possibility of using naked barley for food products is gaining popularity due to its dietary fibre content, especially β-glucans. The technological process (dough preparation, fermentation and baking) influences bread quality but also may contribute to degradation or preservation of valuable grain components. The aim of the study was to investigate the effects of different wholemeal barley flour share and bread production method on the quality of bread and non-starch polysaccharides content and solubility.Barley enriched bread contained more both soluble and insoluble dietary fibre and β-glucans, products of 40% barley share contained 67% more total dietary fibre and 160% more β-glucans than control. However, barley incorporation decreased the amount of soluble arabinoxylans. High barley contents contributed to the breads’ volume reduction by 14% and change in their crumb and crust colour. However, barley enriched breads gained higher ratings of taste than wheat bread. Barley sourdough fermentation improved breads’ volume, colour and sensory properties. Sourdough fermentation also resulted in higher concentration of dietary fibre, arabinoxylans and β-glucans. The beneficial effect of barley addition to wheat bread may be successfully enhanced by using barley wholemeal sourdough fermentation.     

Reduction of xylanase activity in flour by debranning retards syruping in refrigerated doughs

Doughs prepared from wheat flour by milling partially debranned grain with a 60% reduction of apparent xylanase activity levels compared with flours from whole kernels showed slowed solubilisation and degradation of arabinoxylans on refrigeration at 6 °C for up to 34 d. At the same time, dough syruping was effectively suppressed. The onset of syruping was delayed from 3 d to more than 16 d, and the rate of syrup development was slowed. In addition, the dough showed better retention of consistency. Loss of water-holding capacity due to degradation of arabinoxylans is considered to be one critical factor in the changed syruping behaviour of the refrigerated doughs.     

Quality characteristics of northern-style Chinese steamed bread prepared from soft red winter wheat flours with waxy wheat flour substitution

Quality characteristics of northern-style Chinese steamed bread (CSB) prepared from two soft red winter (SRW) wheat flours blended with 0–30% waxy wheat flour (WWF) were analyzed to estimate the influence of starch amylose content. The increased proportion of WWF in blends raised mixograph absorption with insignificant changes in protein content and dough strength-related parameters. WWF incorporation generally increased specific volume and crumb softness of CSB. The analysis of covariance revealed that CSB quality attributes were little affected by protein content and dough strength-related parameters, indicating that starch amylose content was largely responsible for the changes in CSB quality. Flour blends with 5–10% WWF, of which starch amylose content was 22.4–24.7%, produced CSB with superior crumb structure compared to other blends, but insignificant changes in surface smoothness, stress relaxation and total score compared to the respective control wheat flours. Flour blends with 15% WWF to produce a starch amylose content of 21.4–22.7% exhibited reduced staling of CSB with total scores comparable to the respective control wheat flours. CSB prepared from blends with more than 10% WWF exhibited a higher soluble starch content, indicative of reduced starch retrogradation, than that prepared from wheat flours without WWF during storage for 3 days.     

Evaluation of the rheological properties of dough and quality of bread made with the flour obtained from old cultivars and modern breeding lines of spelt (Triticum aestivum ssp. spelta)

This work evaluates rheological properties of dough and quality of bread prepared from the flour of ancient varieties and modern breeding lines of spelt compared to common wheat. Spelt flours of old varieties exhibited similar water absorption; the largest was noted in the STH-8 line flour. Spelt doughs had longer development time and were more stable than wheat dough. The doughs made of old spelt varieties were more resistant to extension than that produced from new lines flours. Of the spelt breads, this of the STH-8 line spelt line had the largest loaf volume but smaller than wheat bread. In addition, spelt doughs had similar porosity; the most porous was the bread baked from the Frankenkorn cv, Schwabenkorn cv and STH-8 line flours. Moreover, the crumb of the bread manufactured from the flours of spelt variety Frankenkorn and the STH 28-4614 line showed the greatest resistance to compression and the smallest compressibility.     

Optimization of air classification for the production of β-glucan-enriched barley flours

Barley grains contain a relevant amount of soluble fibre (i.e. β-glucans) and can be used for production of foods with healthy functions. To produce barley flours enriched in β-glucans, grain micronization and air classification of the flour was used, and a method to predict the relationship between the yield of the enriched flour and its β-glucan content was developed. This method is based on a series of sortings of micronized flour, with a progressive increase in the yield of a selected fraction; a curve for β-glucan enrichment vs. yield can then be calculated. Thus, the most suitable combination of yield and β-glucan content can be chosen. We tested this approach on two hull-less barleys with different starch type, and obtained barley flour fractions with twice the β-glucan concentration that the grain had. Enriched flour fractions with 11.2 and 15.6% β-glucans were obtained from cultivars Priora (hull-less) and CDC Alamo (waxy, hull-less), respectively, with a good flour yield (about 30%). We suggest that our method can be adopted for finely tuning the enrichment process to meet the industry's needs.     

Interplay between starch and proteins in waxy wheat

Most of the unique properties of waxy wheat have been associated with the lack of amylose, that in turn may affect the mutual interactions between starch and proteins. To address this particular aspect, we carried out molecular, rheological, and calorimetric studies on flours from two waxy wheat lines that were compared with a non-waxy one. Dough thermal properties and water binding capacity were investigated by Differential Scanning Calorimetry (DSC) and by thermogravimetric analysis, respectively. Protein solvation, aggregation, and thiol accessibility were also investigated, together with dough mixing properties and stickiness. Proteins in waxy wheat samples needed more water to complete solvation, likely because of the water-retaining capacity of waxy wheat starch. In waxy wheat dough, water was tightly bound to starch, and DSC studies indicated an increase in gelatinization temperature. Moreover, the low water mobility in waxy wheat resulted in low and retarded gluten hydration and in high stickiness. In samples with the highest stickiness, protein aggregates were stabilized mainly by hydrophobic interactions. Differences between waxy wheat lines may be attributed to a different structural organization of components within each class of biopolymers.     

中国大麦种质资源直链淀粉含量分析

为了弄清中国大麦种质资源中直链淀粉含量的高低,为今后的糯大麦研究和育种提供参考,利用近红外反射光谱（NIRS）法对含糯性基因的167个中国代表性大麦品种的直链淀粉含量进行了测定。结果表明,在中国大麦中鉴定发现的糯大麦种质均属低直链淀粉糯大麦（以下简称低直糯大麦）,尚无一份是无直链淀粉糯大麦（以下简称无直糯大麦）材料。167份含糯性基因品种的直链淀粉含量变异范围为13.34%～38.23%,平均值为25.23%,标准差为4.18,变异系数为16.56%。品种内不同单株间直链淀粉含量不同,有的品种单株变异系数大,有的变异系数小。在28个品种中检测到直链淀粉含量小于15%的单株,其中在6个品种中共鉴定出7份材料,直链淀粉含量低于10%,可以在我国糯大麦育种和遗传等基础理论研究中优先利用。由于大麦品种间和品种内单株之间的直链淀粉含量存在很大差异,因此进行糯大麦种质资源鉴定筛选时,应在品种群体测定的基础上,进一步开展单株纯系繁殖鉴定;在杂交育种中选择糯大麦亲本时,不但要考虑备选品种的直链淀粉含量,还要考虑其个体基因型的遗传一致性。     

Characterisation of Starch from Inner and Peripheral Parts of Normal and Waxy Barley Kernels

A previous microscopical examination of barley kernels indicated an uneven distribution of amylose in the waxy cultivar SW7142-92, where the subaleurone layer was strongly stained by iodine. To explain these results, starch was isolated from fractions of inner and peripheral parts of kernels of the waxy cultivar and a cultivar with normal starch. Analyses of amylose content showed a higher concentration of amylose in starch from the outer part of the waxy barley kernel, where the amylose, determined by a colorimetric method, made up 8·6% of the starch compared with 5·9% in the middle and 2·2% in the innermost part of the waxy kernel. This difference in amylose distribution was not observed in the normal starch kernel. The results were confirmed by gel permeation chromatography. No differences in amylopectin chain length distribution were detected by size exclusion HPLC and HPAEC-PAD of amylopectins from different parts of the barley kernels.     

The Role of Gluten Proteins in the Baking of Arabic Bread

Fractionation and reconstitution/fortification techniques were utilised to study the role of gluten in Arabic bread. Glutens from two wheat cultivars of contrasting breadmaking quality were fractionated by dilute HCl into gliadin and glutenin. Gluten, gliadin and glutenin doughs from the good quality flour had higher G ′ and lower tan δ values than those from the poor quality flour at all the frequencies examined. Interchanging the gliadin and glutenin fractions between the reconstituted flours showed that the glutenin fraction is largely responsible for differences in the breadmaking performance. Fortification of an average quality flour with the gliadin and glutenin fractions from the poor and good quality flours, at the levels of 1% and 2% (protein to flour mass), induced marked differences in the mechanical properties of bread. The resilience of the loaves was not adversely affected by the addition of gliadins and increased, with a concomitant significant (p<0·05) improvement in quality, at the 2% level of fortification with gliadins from the good quality flour. Addition of glutenin resulted in loaves with leather-like properties that became particularly apparent at the higher level of fortification; the observed deterioration in quality paralleled the increase in the elastic character of the doughs. It is suggested that highly-elastic doughs are not compatible with the rapid expansion of gases at the high-temperature short-time conditions employed in the baking of Arabic bread and that there exists a threshold in dough elasticity beyond which a rapid decline in quality takes place.     

中国大麦种质资源Wx蛋白分析及糯大麦分子标记验证

利用1D-SDS-PAGE分析了中国167份不同直链淀粉含量类型的大麦种质资源Waxy 蛋白类型,发现在低直糯大麦和无直糯大麦两种类型中,可能存在四种生化遗传变异类型。其中有两种与无直糯大麦有关,一种是Wx基因可以正常转录,但转录产生的Wx蛋白无活性,不能催化直链淀粉合成;另一种是Wx基因不能正常转录,既无Wx蛋白产生,也无直链淀粉合成。另外两种与低直糯大麦有关,一种是Wx基因可以正常转录,但转录产生的Wx蛋白活性有限,催化直链淀粉合成的功能降低;另一种是Wx基因不完全正常转录,产生的Wx蛋白数量有限,影响直链淀粉合成。利用4个大麦与小麦的STS标记和2个大麦与小麦的SSR标记对不同Wx蛋白类型进行糯性鉴定,结果表明,迄今利用的Wx基因的STS引物P1可能只适合用于CDC Candle遗传类型相同的糯大麦品种或基因型的鉴定。其它标记均不能用于鉴定大麦糯性胚乳表型,因此当前对于糯大麦育种及Wx分子鉴定研究而言,还有待于开发新的分子标记。     

Effect of barley and oat flour types and sourdoughs on dough rheology and bread quality of composite wheat bread

The potential of sourdough to improve bread quality of barley and oat enriched wheat breads may depend on the characteristics of the added flour (cereal type, variety, extraction rate). We compared the effect of different barley flours and oat bran (substitution level 40%), unfermented and as sourdoughs (20% of total flour), on composite wheat dough and bread characteristics by combining empirical rheological analyses (DoughLab, SMS/Kieffer Dough and Gluten Extensibility Rig) with small-scale baking of hearth loaves. Whole grain barley flour sourdough increased resistance to extension (Rmax) of the dough and improved the form ratio of hearth loaves compared to unfermented whole grain barley flour. However, sourdough showed little effect on the breads prepared with sifted barley flour or oat bran. The breads made with oat bran showed highest bread volume, lowest crumb firmness and highest β-glucan calcofluor weight average molecular weight (MW). The heat treatment of oat bran inactivated endogenous enzymes resulting in less β-glucan degradation. High MW β-glucans will increase the viscosity of the doughs water phase, which in turn may stabilise gas cells and may therefore be the reason for the higher bread volume of the oat bran breads observed in our study.     

Composition and surface properties of dough liquor

The composition and surface properties of dough liquor isolated by ultracentrifugation have been characterised. Addition of ascorbate had no effect and salts only a limited effect, on the yield, protein content and composition of the dough liquor. Fourier transform infrared spectroscopy (FT-IR) revealed the presence of proteins, lipids, starch oligosaccharides together with the non-starch polysaccharide, arabinoxylan. At high dilution the dough liquor air:water interface was dominated by protein, with surface tensions of around 55 mN/m and high surface elasticity. As the concentration was increased, surface tensions dropped to around 40 mN/m for undiluted dough liquor. This was accompanied by the interface becoming less elastic, and indicated that dough liquor lipids were interacting and disrupting the protein films in concentrated dough liquor. Dough liquors from de-fatted flours remained elastic and gave surface tension values of around 50–55 mN/m even at low dilution, indicating that removal of the lipids gave rise to a purely protein stabilised interface. Addition of salt to the dough had the greatest effect on the surface properties, both reducing surface tension and reducing surface elasticity, probably because the charge screening effect of the salt improved the dispersion of lipids in the dough liquor, thus enabling it to disrupt the protein films more effectively. These results indicate that the aqueous phase of bread doughs lining the gas cells would give rise to a mixed protein:lipid interface. Such interfaces are unstable, and would contribute to the instability of the foam structure of risen dough. In addition they show that dough ingredients may modify gas cell stability (and hence may affect crumb structure), by altering the composition and properties of the aqueous phase of doughs.     

Wheat flour non-starch polysaccharides and their effect on dough rheological properties

Wheat (Triticum aestivum L.) flour is able to form dough with unique rheological properties that allow bread making. It is well known that wheat protein content affects dough rheological properties, but there is not enough evidence about the role of other minor flour constituents. One such minor constituent is non-starch flour polysaccharides, which are mainly pentosans formed by a xylopyranosyl linear chain branched with arabinofuranosyl residues. Their spatial distribution and branching pattern can affect their relationship with gluten forming proteins and thus influence their functional properties, the dough rheological properties, and thereby the flour baking quality. In this study the content and structural characteristics of non-starch polysaccharides were investigated, as well as their influence on some dough physicochemical parameters. Five different wheat flours samples milled from Uruguayan wheat varieties with diverse rheological and breadmaking properties were used in this study. Water soluble flour polysaccharides were extracted and the amount of pentosans was determined by the orcinol-HCl method. The pentoses composition was determined before and after acidic hydrolysis of the water soluble polysaccharide fractions by GC. No free pentoses were detected in any of the assayed flour samples, so the pentoses composition found in the hydrolyzed samples was attributed to the non-starch water soluble polysaccharides. Water unextractable non-starch polysaccharides were determined by difference between the total and the soluble non-starch polysaccharides flour content.An improved method for the quantification of water extractable and non-extractable non-starch polysaccharides, using baker's yeast, was developed. Using this method, total and soluble non-starch polysaccharides content could reliably be determined both in whole flour and in pentosans enriched fractions. Free monosaccharide content was in the range from 0.03% to 0.06% (w/w), while the arabinose/xylose (Ara/Xyl) ratios varied from 0.8 to 1.4 in soluble non-starch polysaccharides and from 0.7 to 0.9 in total non-starch polysaccharides. The different Ara/Xyl ratios found for water extractable and unextractable arabinoxylans clearly indicates different substitution degrees in the polymers. Analysis of the dough rheological parameters in relation to the water soluble and non-soluble non-starch polysaccharides and the Ara/Xyl ratios from different wheat varieties was performed. A clear relation between some of these parameters could be inferred, since a direct relationship between total unextractable (AXi) content and resistance of dough to extension (P), as well an inverse relationship between the same parameter and dough extensibility (L) were observed. These results suggest that the flour non-starch polysaccharide content, as well the Ara/Xyl ratios may be used as additional parameters to estimate some of the wheat flours dough properties.     

Improved functional properties for soy–wheat doughs due to modification of the size distribution of polymeric proteins

Physical modification of soy flour was shown to greatly improve the dough and baking qualities of soy–wheat (1:1) composite doughs, compared to raw soy flour, giving better stability and R_max, although extensibility was still below that of the wheat dough.Reasons for improvements caused by the physical-modification process were sought by determining the relative size distribution of proteins in the soy–wheat composite doughs by size-exclusion high-performance liquid chromatography (SE-HPLC). Results were expressed as the proportion of ‘unextractable polymeric protein’ (%UPP)—the proportion of the protein that is over 100,000 Da and only extractable after sonication. Protein extracts from the soy–wheat dough were sampled at different stages of dough mixing and fermentation, and their molecular-size distributions evaluated.Unextractable soy proteins were lower in raw soy flour (only 8% UPP) than in two physically-modified soy flours (19 and 34% UPP, respectively). Unextractable polymeric protein was much greater for wheat flour (57% UPP). After mixing a 1:1 soy–wheat composite dough, the %UPP was 36 and 22 (for the two types) when made from physically modified soy flours, compared to 8 for a composite dough using raw soy flour, and 43 for a wheat-only dough. The higher proportion of UPP for the wheat-modified soy doughs was taken as a reason for this composite dough providing better dough and baking qualities. Prolonged fermentation time caused a decrease in UPP percentages for all composite doughs and for the wheat-only dough.     

Effect of technological process on the nutritional quality of naked barley enriched rye bread

Naked barley products used in bread making gain popularity as a source of both soluble and insoluble fractions of dietary fibre, especially β-glucans. The aim of the study was to investigate the effects of different naked barley flour share in rye bread formulations and dough preparation methods (Single-phase and Detmold sourdough) on non-starch polysaccharides content and solubility and antioxidant properties of products at different processing stage. Naked barley incorporation to rye contributed to the increase in dietary fibre content with higher soluble fraction share, highly enriched products in β-glucan and increased antioxidant activity of products. It also contains high amounts of arabinoxylans, but less soluble than those from rye. A Single Phase method of rye bread production resulted in higher β-glucan concentration in products and their antioxidant activity, compared to Detmold method products. The nutritional quality of bread is highly influenced by the process parameters.     

Effects of α-, β-, γ- and ω-Gliadins on the Dough Mixing Properties of Wheat Flour

Gliadins were extracted from wheat and individual groups (α-, β-, γ-, ω-1 and ω-2) purified. The effects of the individual groups of gliadin on the mixing properties of doughs from low and high protein flours were measured on a 2-g Mixograph and a prototype microextension tester. The addition of all groups of gliadin resulted in a decrease in dough strength. The relative weakening effects were ω-1>ω-2≈α-≈β->γ- in the Mixograph, and γ->α-≈β-≈ω-2≈ω-1 in the Extensograph.     

Optimization of non-fermented gluten-free dough composition based on rheological behavior for industrial production of “empanadas” and pie-crusts

Celiac disease is an autoimmune disorder caused by intolerance to gluten, which is found in wheat and similar proteins in barley, rye and oats. The present study was designed to examine the effects of the addition of gums, whey protein concentrate, dry egg, and water to corn and cassava starches on the rheological properties of a non-fermented dough used for the production of “empanadas” (a traditional meal in Latin América) and pie-crusts suitable for people with celiac disease. A 2⁴ full factorial design was chosen. Viscoelastic measurements and texture analysis (puncture and elongation tests) were performed. The increase in gums content and the decrease in water level produced an increase in both moduli (G′ and G″) and a more elastic dough was obtained. Higher protein contents interfered with the formation of the three-dimensional gum network making the dough less ductile. Texture analysis led to similar conclusions to those obtained by dynamic rheological analysis. Formulations containing higher percentages of gums and lower water content led to an appropriate behavior for industrial production of these doughs.     

Water-extractable Arabinoxylan from Pearled Flours of Wheat,Barley, Rye and Triticale. Evidence for the Presence of Ferulic Acid Dimers and their Involvement in Gel Formation

Cereal grains from wheat, barley, triticale and rye were pearled and milled. Part of the flours were treated in boiling aqueous ethanol and both the ethanol-treated and untreated flours were extracted with water. Yields of arabinoxylan in the extracts were higher for the untreated flours. Chemical, physico-chemical and structural studies showed differences between the arabinoxylans in extracts of the different cereals although arabinoxylans extracted from untreated and the corresponding ethanol treated flours were similar in neutral sugar content and patterns of substitution. Analyses showed that low amounts of ferulic acid dimers (8-O-4′, 8-5′, and 5-5′ forms) were present in all the extracted arabinoxylans. Oxidative gelation studies, using peroxidase/H₂O₂, revealed significant differences in the capacity of extracted arabinoxylans to form gels via intermolecular cross-linking. The values of elastic modulus (G′) of gels from the arabinoxylan extract of ethanol-treated flours varied from 2 to 40 Pa and were higher than those obtained from the untreated flours (0·2–6 Pa).     

Effects on Grain and Malting Quality of Genes Altering Barley Starch Composition

In this study inbred barley lines carrying waxy and/or high amylose genes were obtained from a cross between Waxy Hector and a breeders» line BE285 (high amylose Glacier×Midas) and assessed for malting quality. Inbred lines were assayed and classified as having none, one or both genes. After malting, waxy lines had a slightly lower hot water extract than normal starch lines. Large effects were demonstrated for both grain nitrogen content and hot water extract in high amylose lines and, particularly, in lines with both genes. Endosperm modification during malting was reduced by both starch mutations. Electron microscopy showed that the phenotype with both genes was characterised by a highly compacted endosperm. During malting, this structure was extremely resistant to modification.     

Effect of incorporation of an i-type low-molecular-weight glutenin subunit and a modified γ-gliadin in durum and in bread wheat doughs as measured by micro-mixographic analyses

The effects of incorporation of an i-type low-molecular-weight glutenin subunit (LMW-i) and of a modified γ-gliadin showing an additional cysteine residue, on 2 g Mixograph parameters of durum (biotypes 42 and 45 of the Italian cv. Lira) and bread wheat (Australian cv. Kukri) doughs were studied. In bread wheat flour incorporation of the modified γ-gliadin resulted in a significant decrease in dough strength (decreased mixing time and peak resistance), but at the same time it produced a slight increase in dough stability (decreased resistance to breakdown). The incorporation of the LMW-i type into bread wheat dough had minimal effects on dough mixing requirements. The incorporation of both LMW-i type and modified γ-gliadin in durum wheat doughs produced a significant decrease in the overall dough strength, especially in Lira 45 biotype doughs. Reversed phase high-performance liquid chromatography (RP-HPLC), size exclusion high-performance liquid chromatography (SE-HPLC) and two-dimensional gels analyses of control and reconstituted semolina doughs showed that the two polypeptides were in the polymeric fraction. The effect of the incorporation of the two polypeptides in durum and bread wheat doughs showed remarkable differences and the reasons for this is discussed in terms of both intrinsic differences between wheat flour and durum semolina and in methodological approaches.