The effects of sodium reduction on the mechanical properties of doughs made from flours with a range of strengths using a mixograph

To devise strategies for meeting Health Canada's target for reduced-sodium bread production, relationships between dough formula (i.e., red spring wheat flour, salt (NaCl) and water content) and dough mechanical properties were examined. Mixograph energy to peak (ETP), peak height (PKH), and peak bandwidth (PBW) were used to define changes in the properties of doughs induced by sodium reduction. ETP measurements indicated that dough strength characteristics were less responsive to sodium reduction as water content was increased. ETP was a good indicator of the cultivar-dependent response of doughs to sodium reduction, with doughs made from stronger flours being more sensitive to sodium reduction. According to ETP results, sodium reduction led to a decrease in flour strength discrimination. Sodium reduction at NaCl contents below ~1.5% led to more obvious changes in dough mixing characteristics (indicated by the ratio of PBW to PKH). Mixograph analyses of dough tolerance to sodium reduction will guide wheat breeding programs to select cultivars suitable for reduced sodium breadmaking.     

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.     

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.     

Flowability,moisture sorption and thermal properties of tef [Eragrostis tef (Zucc.) Trotter] grain flours

Recently tef is attracting the attention of the modern food industry since it is a gluten-free grain encompassing highly appreciated nutritional advaxntages. As a relatively new raw material, little information on its handling and processing properties is available. Flowability, water sorption characteristics and thermal properties of flours from three Ethiopian tef varieties were studied. Wheat (whole and refined) and rice flours were included as references. Tef flours were less flowable than the reference flours and their flow properties were more sensitive to water activity changes. Tef flours led to sigmoidal sorption isotherms with estimated monolayer water content of 0.053 (BET model) and 0.057 (GAB model) g water/g dry solids. No significant differences among the three tef varieties were observed on their gelatinization enthalpies that were higher than that of wheat and similar to rice. The amylopectin recrystallization extent after 7 days of storage at 4 °C was significantly higher in tef than in wheat flour.     

Mixing behaviour of a zero-developed dough compared to a flour–water mixture

The Z-blade mixing behaviour of zero-developed (ZD) doughs from the flours of two wheat cultivars of different gluten strength was compared to that of conventionally mixed dough made from the same flours. In farinograph experiments, use of ZD dough led to shorter development time (with less energy requirement), less stability time, and consequently earlier breakdown compared to conventional mixing of the corresponding flour–water mixture. Mixing of ZD doughs led to an almost similar decrease of glutenin macro-polymer (GMP) wet weight as that of doughs prepared from flour–water mixtures. However, comparison of wet weight of re-assembled GMP revealed that until time-to-peak (TTP) mixing, there was no difference in GMP recovery with respect to the starting material used in the z-blade mixing experiments. Beyond TTP, recovery of GMP in doughs prepared from both starting materials was reduced. The results of large-strain deformation rheology showed strong visco-elastic behaviour as characterised by the highest values of fracture properties (except ε_H), followed by a decline in those properties upon further mixing for doughs mixed from both flour–water mixture and ZD dough from both types of wheat cultivars. It was concluded that at mixing regimes before TTP, there was no difference between ZD doughs and flour–water mixtures in the mixer. When ZD dough is used as a starting material for dough preparation instead of flour, extra care should be taken not to over-mix the developing dough.     

Effect of the addition of extruded wheat flours on dough rheology and bread quality

Extruded wheat flours, due to their increased water absorption capacity, constitute an opportunity to increase bread output in bakery production. However extrusion may modify dough and bread characteristics. The aim of this study was to investigate the effect of the substitution of 5% of the wheat flour by extruded wheat flour (produced with different time-temperature extrusion treatments) on dough mixing, handling and fermentation behaviour and bread volume, shape, texture and colour. The RVA curves indicate that extrusion intensity increases with increasing temperature or water content. Water absorption capacity rises with increasing treatment intensity, but dough stability tends to decrease. Adding extruded flours decreases dough extensibility but increases tenacity and gas production. Differences in dough structure were observed on photomicrography, though there were no clear differences in bread quality. These results indicate that it is possible to obtain adequate dough and bread characteristics using dough with 5% extruded wheat flour.     

Physical properties of wheat flour composites dry-coated with microparticulated soybean hulls and rice flour and their use for low-fat doughnut preparation

Air-classified wheat flour was dry-coated with microparticulated rice flour (30%, db) and/or microparticulated soybean hulls (up to 10%, db) using a hybridization system, and the physical properties of the dry-coated wheat flour were examined. The composite wheat flours exhibited the higher water-holding capacity but lower swelling power and oil-holding capacity than their counterpart mixtures. In pasting viscosity, the composites of wheat and rice flours had substantially lower values for peak viscosity and breakdown than did pure wheat flour. The incorporation of soybean hulls to the composites of wheat and rice flours further reduced the peak viscosity. The composites with rice flour and soybean hulls showed slightly higher melting (gelatinization) temperatures but lower melting enthalpy compared to the counterpart mixtures. By using the composite flours for the deep-fat fried doughnut preparation, the oil uptake could be substantially reduced by approximately 30%, in comparison to pure wheat flour or the mixture samples. The composite wheat flours with microparticulated rice flour and soybean hulls produced dough matrices with improved compactness and cell structure, which were attributed to the reduced fat uptake during frying.     

食用胶对小麦粉面团流变学特性的影响

为明确食用胶在面制食品中的作用,以3种商业小麦粉(特一粉、富强粉、上白粉)为试验材料,分别添加不同比例的海藻酸钠、黄原胶、卡拉胶,分析其对面团流变学特性的影响。结果表明,小麦粉添加0.15%~0.25%的海藻酸钠,面团稳定时间显著提高,弱化度显著降低;添加0.10%、0.20%和0.25%的海藻酸钠,面团最大拉伸阻力显著提高。添加0.02%、0.06%和0.10%的黄原胶,面团最大拉伸阻力显著提高;添加0.10%黄原胶的面团拉伸面积也显著提高。添加0.10%的卡拉胶,面团稳定时间、拉伸面积显著提高,弱化度显著降低。食用胶因小麦粉品质不同对面团流变学特性的影响也不同,除添加0.25%的海藻酸钠外,其他添加量的3种食用胶均可降低特一粉的面团吸水率,提高上白粉的吸水率。研究认为,海藻酸钠、黄原胶、卡拉胶可显著改善小麦粉的面团流变学特性,增强面团筋力。     

不同小麦粉混配品质性状的变化

为了研究小麦粉混配过程中品质性状的变化，分析了陕西省13个推广小麦品种及其23种混配粉的蛋白质品质和面团流变学特性。结果表明，强筋小麦不同批次制粉品质变化较大，中筋和弱筋小麦品质变化相对较小，不同方式配粉面团流变学特性变化规律不同。强筋 中筋和强筋 弱筋两种方式配粉稳定时间测定值比理论值减少，延伸性有增有减。同时，强筋 中筋=强筋的配粉延伸性以减小为主，而强筋 中筋=中筋的配粉延伸性增加，2个中筋粉或中筋与弱筋粉混配延伸性明显增加。混配粉面筋含量、沉淀值、稳定时间和延伸性测定值与由基础品种估算的理论值无显著差异，而且呈极显著正相关，相关系数分别为0．9818^**、0．9776^**、0．8594^**和0．7189^**。文中还提出了根据配粉需要估算基础品种混配比例的方法。     

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.     

Use of peanut and cowpea in wheat-based products containing composite flours

Cowpeas and peanuts are legumes of major dietary and economic importance. They are favored worldwide because of their palatability, contribution to nutritional status, and low cost as a protein source compared to animal protein. Flours processed from cowpeas and peanuts have unique physico-chemical and sensory properties when used in composite flour mixtures. Appropriate blends of cowpea and peanut flours to replace wheat flour in Chinese-type noodles, muffins, and tortillas were determined using modelling and optimization procedures. For noodles, 15% peanut flour and 8% cowpea flour supplementation produced an acceptable product with high protein content (21%). For wheat flour replacement in muffins, up to 43% cowpea and up to 44% peanut flours may be used. However, when wheat flour replacement is 50% or greater, cassava flour should comprise 56 to 72% of the blend with a few exceptions. In tortillas, 24% cowpea and 46% peanut flours produced products similar in quality characteristics to those made from 100% wheat flour. The systematic approach used in these studies is more efficient than the traditional substitution method to optimize sensory qualities of wheat-based products containing composite flours.     

Effect of hydrothermaled bran on physicochemical, rheological and microstructural characteristics of Sangak bread

Increased consumption of whole grain products has been associated with decreased risk of health problems such as cardiovascular disease, diabetes and obesity. Phytate however, has always been a matter of concern, since it chelates minerals such as iron. Sangak is very popular Iranian flat bread invented five hundred years ago, made from 95% extraction flour. The bread is fermented but usually fermentation is not able to remove all phytate from the dough. In this study flours were first debranned; resulting bran was subjected to a hydrothermal process. The hydrothermaled (HT) brans were then incorporated in the Sangak flour. In the next step, physicochemical, rheological and microstructural characteristics of Sangak flour and dough prepared from two Iranian wheat varieties, Tajan and Back Cross of Roshan were investigated. Results indicated a reduction in phytate up to 55% in the samples. The resulting dough containing HT bran showed a higher development time and valorimetric value and was more stable than doughs made with normal bran. Dough made with HT bran showed a kind of protein matrix in which proteins and starch granules are oriented in a more non-ordered structure.     

Strain Hardening Properties and Extensibility of Flour and Gluten Doughs in Relation to Breadmaking Performance

The mechanical properties of flour–water doughs and hydrated gluten of different wheat cultivars were determined. Measurements were performed at small deformations (dynamic measurements) as well as at large deformations (biaxial extension measurements). Results of dynamic measurements of flour doughs related poorly to breadmaking quality. For hydrated gluten doughs, all having the same water content, it was found that glutens from wheat cultivars with good baking quality had higher values for the storage modulus,G, and lower values for the loss tangent. The relevant type of deformation around an expanding gas bubble is biaxial extension. Wheats with a good baking performance exhibited greater strain hardening and greater extensibility. The differences in strain hardening observed at 20 °C were also present at 55 °C. No clear effects of NaCl or emulsifiers on the biaxial extension properties of flour dough were found. Extensograms as well as Alveograms from the flour doughs showed that, in general, good baking flours exhibited stronger resistance to extension and a greater extensibility, but differences found were not directly related to the results of the baking tests. The results indicate that the baking performance of dough is related to a combination of at least three different rheological characteristics.     

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.     

On the relationship between large-deformation properties of wheat flour dough and baking quality

Baking performance for bread and puff pastry was tested for Six European and two Canadian wheat cultivars and related to the rheological and fracture properties in uniaxial extension of optimally mixed flour–water doughs and doughs to which a mix of bakery additives was added. Extensive baking tests were performed as a function of water addition for puff pastry and as a function of water addition and mixing time for bread. For optimum baking performance, puff pastry doughs required lower water additions than bread doughs. Baking performance of the flours differed for the two products. For puff pastry, higher volumes were obtained per gram of flour than for bread. Puff pastry volume was positively correlated with optimum bread dough mixing time, while bread volume was not. Instead, bread volume was positively correlated with gluten protein content.All doughs exhibited strain hardening, a more than proportional increase of the stress with the strain. For all doughs fracture, stress and strain increased with increasing displacement speed of the hook and decreasing temperature. Large differences were observed between the cultivars regarding stress, strain hardening, strain rate-dependency of the stress, fracture stress and fracture strain. At both 25 and 45 °C, addition of a mix of bakery additives resulted in a decrease of the stress at relatively small strains and a significant increase of the strain hardening coefficient. Fracture strains remained the same or increased as a result of addition of the mix. Differences between flours regarding the strain rate and temperature-dependency of the fracture strain remained. The weaker the dough, the stronger the strain rate and temperature-dependency of the fracture strain.Puff pastry volume was positively correlated with strain hardening and negatively with the strain rate-dependency of the stress. In short, the stronger the dough, the higher the puff pastry volume. For bread, it were not the strongest doughs that gave the highest loaf volumes, but those with intermediate dough strength. Low volumes for puff pastry and bread were found for doughs having a low fracture stress and low strain hardening coefficients. Loaf volumes of flours with high dough strength (i.e. high stress-level and high strain hardening) gave intermediate loaf volumes. We concluded that a high stress can hamper the extensibility of dough films between gas cells, thus limiting the expansion of gas cells during fermentation and baking and hence the loaf volume that can be obtained.     

Assessment of antioxidant activity and rheological properties of wheat and buckwheat milling fractions

This study examined the antioxidant properties of the ethanolic extracts of wheat milling fractions (wheat flour type 500 and type 850, and bran) and their polyphenol and tocopherol content, and rheological characteristics of wheat dough supplemented with buckwheat flours (light and wholegrain). The results obtained in this study were correlated with our previously published data on wheat flour type 400, wholegrain wheat flour and buckwheat flours.Buckwheat flours exhibited significantly higher (P < 0.05) antiradical activity on hydroxyl (OH), superoxide anion (O₂⁻) and (1,1-diphenyl-2-picrylhydrazyl) DPPH radicals, antioxidant activity and reducing power than all investigated wheat milling fractions when their corresponding IC₅₀ values were compared.The rheological parameters of wheat dough supplemented with light and wholegrain buckwheat flour (0-50%) were obtained by using Mixolab. Results indicated changes in protein and starch properties of dough.The obtained results indicate the benefit of using buckwheat flours in wheat-based food products, i.e. their contribution in functional and tailor-made-food production.     

Modification of the rheological behavior of amaranth (Amaranthus hypochondriacus) dough

For people with celiac disease, a lifelong abdication of gluten including-products is necessary to live a life without celiac affected reactions. The production of high-quality bread from gluten free flour is not simple in comparison to gluten including flours such as those derived from wheat (Triticum spp.). The gas binding and crumb structure forming capacity are very low in gluten free batters. They can efficiently be analyzed through the rheological properties of the dough used. The use of acidification in amaranth (Amaranthus hypochondriacus) dough preparation is a possible means of changing the rheological behavior of amaranth in the desired direction. Methods include the use of lactic acid directly, or the fermentation via lactic acid bacteria. Adding up to 20 mL lactic acid/kg flour in amaranth dough preparation led, during oscillation tests, to an increase of the complex shear modulus up to 30% in the range of 0.1 up to 10 Hz. The use of sourdough fermentation decreased the complex shear modulus in the same test up to nearly 60%. In creep recovery tests, the elastic part of amaranth dough decreased from 65.4% without any treatment down to 63.9% by the addition of up to 20 mL lactic acid/kg flour. Sourdough fermentation by Lactobacillus plantarum was able to decrease it to 54%. The acidification showed a significant positive influence on the rheological parameters of amaranth dough only at the higher stress level. In contrast, sourdough fermentation was able to produce doughs with viscosity and elasticity similar to that found in pure wheat flours.     

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.     

Development of a standard test for dough-making properties of oat cultivars

Bread is consumed all over the world. However, so far, production of large volume bread is only possible with wheat. Alternatives, such as oats, are less suitable but this is partly due to the lack of knowledge about their functionality for other purposes than porridge, which is their most common use. Existing standard tests for the dough making characteristics of wheat flour are not suitable for oat flour, hampering research to optimize oats for bread-making purposes. We therefore set out to develop a test to evaluate oat in relation to mixing and dough making properties using wheat as a model. It was possible to reproduce the profile of various qualities of wheat flour using mixtures of oat flour and gluten in different proportions. Our standard test was based on a dough system composed of 87.2% oat flour and 12.8% gluten and it presented similar properties to a wheat flour with regard to resistance to extension. This dough system was sensitive and reliable (coefficient of variation lower than 10%) for detecting differences among oat cultivars, and it can be used to screen oat varieties and individual oat components in relation to relevant properties for bread-making purposes.     

The influence of milling on the nutritive value of flour from cereal grains. 2. Wheat

Wheat was milled into flours having extraction rates between 100 and 66%. The nutritive value of the various fractions was studied by chemical analyses and in balance trials with rats. The concentration of essential nutrients decreased when the extraction rate was lowered. The lysine content (g/16 g N) e.g. was 2.52 in whole wheat, but only 2.18 in the 66% extraction flour; however, only a slight reduction in biological value was found. The content of minerals was reduced to 30% of that in whole wheat, and the apparent zinc absorption and retention expressed in absolute values, were significantly higher from the flours of high extraction than from the more refined flours, in spite of a much higher phytate content in whole wheat and lightly milled flours. It could be concluded that milling of wheat into highly refined flours not only preclude considerable amounts of nutrients from human consumption, but the remaining flours have a much poorer nutritive value than flour made from whole wheat.