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.     

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.     

Selected nutritional,physical and sensory characteristics of pan and flat breads prepared from composite flours containing fababean

Composite flour blends containing wheat (W), fababean (F), cottonseed and sesame flours were formulated to provide the FAO/WHO/UNU protein requirements for the 2–5 year old child, and evaluated in pan and flat bread applications. Water absorption of composite flour doughs was up to 35% greater than the control but gluten strength and slurry viscosities were markedly reduced. Loaf volume and specific volume of pan breads prepared from composite flours were 25–60% less than that of the control bread but flat breads tolerated the protein supplements extremely well. The W/F flat bread, containing 27% of fababean flour, received acceptable taste, texture and colour scores and was only slightly inferior to the control in puffing and layer separation. Additions of cottonseed or sesame flours to the W/F blend failed to improve sensory properties of the flat breads.     

Molecular weight and structure units of (1→3, 1→4)-β-glucans in dough and bread made from hull-less barley milling fractions

Milling fractions of hull-less barley, and dough and bread with hull-less barley flour (40%) and wheat flour (60%) were analysed in an investigation of how the properties of (1→3, 1→4)-β-glucan were affected by milling, dough formation and bread making. Calcofluor average molecular weight $({\overline{M}}_{\text{cf}})$ and molecular weight distribution and the cellotriosyl/cellotetraosyl ratio of the (1→3, 1→4)-β-glucan were determined. Four different hull-less barley samples were milled to produce straight-run white flours, shorts, bran and whole-meal flours. The molecular weight distributions were unimodal for all fractions, and the $({\overline{M}}_{\text{cf}})$ range was between 117×10⁴ and 188×10⁴. These parameters were similar for all barleys, although $({\overline{M}}_{\text{cf}})$ was somewhat lower in white flour and bran fractions and somewhat higher in shorts and whole-meal. The cellotriosyl/cellotetraosyl ratio (1.5–1.8) was also similar in all fractions. Doughs and breads were made to study how flour type (sifted or whole-meal barley flour), water content, yeast, mixing time and fermentation time affect (1→3, 1→4)-β-glucan. The molecular weight distribution of (1→3, 1→4)-β-glucan was polymodal with two or three populations for all doughs and breads, and the $({\overline{M}}_{\text{cf}})$ decreased with increasing mixing and fermentation time. These results indicated that (1→3, 1→4)-β-glucan was degraded by endogenous β-glucanases in the barley and/or wheat flour. The molecular weight was not significantly affected by bread-baking and other factors. After mixing and fermentation the cellotriosyl/cellotetraosyl ratio was about 1.7–1.8 and was thus not significantly different from that of the flour blends. Thus to retain high molecular weight (1→3, 1→4)-β-glucan, which is important for its cholesterol-lowering effect, it is thus important to keep the mixing and fermentation time as short as possible when baking hull-less barley bread.     

Wheat Bread Quality as Influenced by the Substitution of Waxy and Regular Barley Flours in Their Native and Extruded Forms

The substitution of wheat flour with barley flour (i.e. native or pretreated/extruded) reduced the loaf volume. Depending on the barley variety and flour pretreatments, the colour and firmness/texture of the bread loaves were altered. Amongst the barley breads prepared from native flours (at 15% barley flour substitution level), Phoenix had higher loaf volume and lower crumb firmness than Candle. However, amongst the barley breads prepared from extruded flours, CDC-Candle had higher loaf volume and lower crumb firmness than Phoenix. The lower loaf volume and firmer crumb texture of barley breads as compared with wheat bread may be attributed to gluten dilution. Also, the physicochemical properties of barley flour components, especially that of β-glucan, can affect bread volume and texture. β-glucan in barley flour, when added to wheat flour during bread making, could tightly bind to appreciable amounts of water in the dough, suppressing the availability of water for the development of the gluten network. An underdeveloped gluten network can lead to reduced loaf volume and increased bread firmness. Furthermore, in yeast leavened bread systems, in addition to CO₂, steam is an important leavening agent. Due to its high affinity for water, β-glucan could suppress the amount of steam generated, resulting in reduced loaf volume and greater firmness. In the present study, breads made with 15% HTHM CDC-Candle flour had highly acceptable properties (loaf volume, firmness and colour) and it indicated that the use of extruded barley flours would be an effective way to increase the dietary fibre content of barley breads.     

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.     

Factors influencing acrylamide formation in rye,wheat and spelt breads

In this study, a simple strategy for acrylamide (AA) reduction in white and dark wheat and spelt and rye breads, including the impact of flour basic composition, flour extraction rate, type of technology and baking time and temperature was addressed. Moreover, the correlation between AA formation in breads and total phenolic compounds (TPC) and antioxidant capacity (AC) of flours and breads was calculated. The studies showed an impact of flours origin on AA formation in breads with the following rank: wheat bread ≤ spelt bread < rye bread. There was no statistically significant effect of flour extraction rates and their chemical components on AA formation in breads baked at 200 °C/35 min. However, a weak effect was noted for wheat and spelt breads baked at higher temperature. In contrast, a positive correlation between AA in wheat, spelt and rye breads baked at both applied conditions (200 °C for 35 min or 240 °C for 30 min) and AC of white and dark flours was noted. The same finding was noted between AA formation and TPC and AC of bread and its crust. The provided data indicated that AA mitigation strategy should be based on the selection of lower baking temperature with longer baking time as the main important factor amongst others.     

The combined use of hull-less barley flour and xylanase as a strategy for wheat/hull-less barley flour breads with increased arabinoxylan and (1→3,1→4)-β-D-glucan levels

Bread-making with a composite flour (CF) consisting of 60% wheat flour (WF) and 40% hull-less barley flour, increased the total and soluble (1→3,1→4)-β-D-glucan and total arabinoxylan (AX) contents of dough and bread samples, but decreased the specific bread loaf volume. A xylanase insensitive to inhibition by Triticum aestivum L. xylanase inhibitor (TAXI) and xylanase inhibiting protein (XIP), increased loaf volume by 8.8 and 20.1% for WF and CF breads, respectively. Xylanase addition not only markedly improved loaf volume of CF bread, but also increased the soluble AX content of the WF and CF dough and bread samples because of conversion of water-unextractable AX into soluble AX. The xylanase had no impact on the extractability and molecular weight of (1→3,1→4)-β-D-glucan, but (1→3,1→4)-β-D-glucan was degraded during bread-making probably because of endogenous β-glucanase activity. Taken together, the results clearly show that the combined use of hull-less barley flour and a xylanase active during bread making, lead to palatable breads with high total and soluble AX and (1→3,1→4)-β-D-glucan contents. The sum of total AX and (1→3,1→4)-β-D-glucan was 1.70% for WF bread and 3.06% for CF bread, while the sum of soluble AX and (1→3,1→4)-β-D-glucan was 0.49 and 1.41% for control WF and CF xylanase supplemented breads, respectively.     

Nutritional evaluation of wheat and maize breads supplemented with a mixture of peanut-chickpea flour

Whole wheat and maize (corn) flours were supplemented with 10, 20 and 30% levels of a 1:1 mixture of peanut and chickpea flours (PCF). Supplementation increased the protein content of the wheat and maize blends by 20–61%. Significant increases in other proximate constituents as well as K, Ca, P, Fe, Zn and Cu levels and lysine were observed. The chemical score (FAO/WHO, 1973) of wheat flour increased from 53 to 72 and that of maize flour from 49 to 71 with 30% PCF. Biological evaluation of wheat breads (baking time = 7 min at 220°C) at 10% protein level and maize breads (baking time = 15 min at 250°C) at 8% protein level in the diet showed significant (P<0.05) improvement in the protein quality of PCF-supplemented breads as judged by gain in body weight, protein efficiency ratio, net protein ratio, net protein utilization, biological value and utilizable protein (NPU% × protein% ÷ 100) content. A supplementation level of 20% was considered adequate to achieve the desired nutritive benefits.     

Effect of Barley and Barley Components on Rheological Properties of Wheat Dough

The effects of addition of whole barley and barley components (starch, β-glucans and arabinoxylans) on rheological properties of dough prepared from wheat flours with variable gluten quality (cv. Glenlea, extra-strong; cv. Katepwa, very strong; cv. AC Karma, strong; and cv. AC Reed, weak) were investigated in these studies using Mixograph and dynamic rheological measurements. Whole barley meal, starch and non-starch polysaccharides from hulless barley with variable starch characteristics (normal, high amylose, waxy, and zero amylose waxy) were tested. Upon addition of either β-glucans or arabinoxylans, significant increases in peak dough resistance, mixing stability, and work input were recorded in all flours. The addition of starch to various wheat flours reduced the strength of the respective flour-water doughs. The improvement of dough strength upon addition of waxy or zero amylose waxy barley meal was associated with the high content of total and soluble β-glucans present in barley samples. The addition of arabinoxylans or β-glucans increased the G′ of wheat doughs; arabinoxylans had a greater effect than β-glucans. Starch substantially decreased the elastic modulus of dough prepared from cv. Glenlea but waxy and high amylose starches increased the G′ of dough prepared from cv. AC Karma. A combination of the high amounts of non-starch polysaccharides and unusual starch characteristics in barley seems to balance the negative effects associated with gluten dilution brought about by addition of barley into wheat flour.     

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.     

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.     

Presence of β-glucanase activity in wheat and dairy ingredients and use of organic salts as potential enzyme inhibitors

Depolymerization of mixed linkage cereal β-glucans has been observed during the mixing and fermentation of multigrain breads. To maintain the bioactivity of β-glucans in bread and other foods, control of β-glucanase activity during production is needed. β-Glucanase activity in wheat and dairy ingredients was determined by adding them to β-glucan solutions and following the change in the molecular weight of β-glucan at 50 °C for 60 min. The activities in six wheat and six dairy ingredients ranged from undetectable to a 98% reduction in molecular weight. Calcium propionate, potassium sorbate, and sodium benzoate are salts of organic acids commonly used as food preservatives. Low concentrations of these additives (0.1–1.0%) were found to have an inhibitory effect on the β-glucanases found in wheat flour and whey protein isolate. The depolymerization rate of β-glucan was reduced by up to 76% by the three additives.     

Glucose and pyranose oxidase improve bread dough stability

When used in bread dough systems, glucose oxidase (GO) and pyranose oxidase (P₂O) generate H₂O₂ from O₂. We here studied their potential to improve dough and bread characteristics. Neither GO nor P₂O significantly affected the volume of straight dough bread produced with fermentation and proofing times of respectively 90 and 36 min at dosages up to 0.50 nkat/g flour. Supplementation with 1.00 nkat/g flour of GO or P₂O significantly decreased bread loaf volume. The resistance of dough (fermented for 20 min and proofed for 56 min) to an applied shock was substantially improved by inclusion of 0.08, 0.25, 0.50 or 1.00 nkat/g flour of GO or P₂O in the dough recipe. Thus, the proofed doughs showed significantly less collapse and the resultant breads had higher loaf volumes than did the reference breads. Yeast probably exerts an oxidizing effect on dough, which, depending on the exact breadmaking protocol used, might veil the positive oxidizing effect of the enzymes on dough properties during prolonged fermentation.     

Fermentation by selected sourdough lactic acid bacteria to decrease coeliac intolerance to rye flour

A pool of selected lactic acid bacteria was used to ferment suspensions of rye flour. Two-dimensional electrophoresis showed that 109 of the 129 ethanol-soluble rye polypeptides were hydrolysed almost totally by lactic acid bacteria. Matrix-assisted laser desorption ionization—time of flight mass spectrometry and reversed-phase high performance liquid chromatography analysis confirmed the hydrolysis of prolamins. After 48 h fermentation, no prolamin polypeptides were recognized by R5-Western analysis. HPLC analysis of glutelin polymers showed a very low bacterial proteolysis but a pH dependent hydrolysis probably due to activation of rye enzymes. Prolamins were extracted from rye flour and used to produce a peptic–tryptic (PT)-digest for in vitro tests with K 562 (S) sub-clone and Caco-2/TC7 cells of human origin. The PT-digest was also treated with lactic acid bacteria before assay. The Minimal Agglutinating Capacity increased ca. 8-times when K 562 (S) sub-clone cells were exposed to rye PT-digest treated with lactic acid bacteria. Hydrolysis of rye PT-digest by lactic acid bacteria decreased the toxicity of PT-digest itself towards Caco-2/TC7 cells as estimated by cell viability, caspase-3 activity and release of nitric oxide. Rye prolamins and glutelins were extracted from doughs and subjected to PT digestion. Compared to PT-digests from chemically acidified dough, coeliac jejunal biopsies exposed to the PT-digest from the dough fermented by lactic acid bacteria did not show an increase of the infiltration of CD3⁺ intraepithelial lymphocytes. The same was found for epithelial cell Fas expression. Long-time fermentation of dough by selected lactic acid bacteria could be considered as a potential tool to decrease the risk of rye contamination of gluten-free products for coeliac patients.     

Sourdough bread: Starch digestibility and postprandial glycemic response

To evaluate the influence of sourdough fermentation on starch digestibility in bread, four experimental breads were obtained, prepared from two different wheat flours (whole or white) by two different leavening techniques (sourdough and with Saccharomyces cerevisiae). Products were analyzed for their starch, fiber and resistant starch (RS) content and then submitted to in vitro hydrolysis with porcine alpha-amylase. On the same breads, postprandial blood glucose was evaluated in healthy human subjects. Both sourdough fermented breads gave glycaemic responses significantly lower (p < 0.001) than the corresponding products leavened with S. cerevisiae. On the contrary, the presence of fiber did not influence the glycaemic potential of breads. RS levels were higher in the sourdough products, whereas no differences were observed either in the rate of starch hydrolysis or in the degree of polymerization of the starch residues after the in vitro hydrolysis. We may conclude that sourdough fermentation is a technique able to reduce the glycaemic response to bread and that the mechanism does not seem related to the rate of starch hydrolysis.     

Presence of β-glucanase activity in wheat and dairy ingredients and use of organic salts as potential enzyme inhibitors

Depolymerization of mixed linkage cereal β-glucans has been observed during the mixing and fermentation of multigrain breads. To maintain the bioactivity of β-glucans in bread and other foods, control of β-glucanase activity during production is needed. β-Glucanase activity in wheat and dairy ingredients was determined by adding them to β-glucan solutions and following the change in the molecular weight of β-glucan at 50 °C for 60 min. The activities in six wheat and six dairy ingredients ranged from undetectable to a 98% reduction in molecular weight. Calcium propionate, potassium sorbate, and sodium benzoate are salts of organic acids commonly used as food preservatives. Low concentrations of these additives (0.1–1.0%) were found to have an inhibitory effect on the β-glucanases found in wheat flour and whey protein isolate. The depolymerization rate of β-glucan was reduced by up to 76% by the three additives.     

Influence of growth temperature on content, viscosity and relative molecular weight of water-soluble β-glucans in barley (Hordeum vulgare L.)

β-Glucan content and viscosity of water-soluble β-glucans have a considerable impact on the digestion of barley. Eight different 2-row barley (Hordeum vulgare L.) cultivars were grown in controlled environment chambers at five different temperatures until maturity. The samples were pearled, milled and analysed for their content of total, insoluble and soluble β-glucan. The water-soluble fraction was extracted at 37 °C, subjected to amylase treatment and freeze-dried. Water-soluble crude β-glucans were solubilised in distilled water, analysed for viscosity and their purity was checked by nuclear magnetic resonance. Molecular weights were profiled by size exclusion chromatography with RI detection. The content of total β-glucan varied from 4.0% to 7.4%, and was significantly affected by the growth temperature. An interaction between cultivar and growth temperature was observed for the total β-glucan content. The extractability was significantly affected by growth temperature, as there was recorded an increasing amount of water-soluble β-glucan with increasing growth temperature. Both the viscosity and the molecular weight of the water-soluble β-glucans increased with the growth temperature.     

Effect of bread making on formation of Maillard reaction products contributing to the overall antioxidant activity of rye bread

This paper reports the effects of flour extraction rate on antioxidant activity, early, fluorescent and coloured Maillard reaction products in rye flour, crumb, crust and bread. Extent of the reaction was determined by analyses of furosine, fluorescence compounds and browning while antioxidant properties were measured by Folin reaction, Trolox Equivalent Antioxidant Capacity (TEAC) and Oxygen Radical Antioxidant Capacity (ORAC_FL) assays. Antioxidants present in rye flours and breads scavenged peroxyl and ABTS radicals and reduced Folin-Ciocalteu reagent. Data indicated that baking favoured the formation of antioxidant compounds. In controversy, milling to obtain white rye flour negatively affected bread quality.     

The relationship between rheological characteristics of gluten-free dough and the quality of biologically leavened bread

The rheological characteristics of gluten-free doughs and their effect on the quality of biologically leavened bread were studied in amaranth, chickpea, corn, millet, quinoa and rice flour. The rheological characteristics (resistance to extension R, extensibility E, R/E modulus, extension area, stress at the moment of dough rupture) were obtained by uniaxial dough deformation. Specific loaf volume of laboratory prepared gluten-free breads was in significant positive correlation with dough resistance (r = 0.86), dough extensibility (r = 0.98) and peak stress at the moment of dough rupture (r = 0.96). Even if the correlation between R/E modulus and the characteristics of loaf quality were not significant, the breads with the highest specific loaf volume were prepared from flours with R/E closer to the wheat check sample (18 N?mm-1). The results showed, in general, good baking flours exhibited stronger resistance to extension and greater extensibility, but differences found were not directly related to the results of baking tests.