Surface Lipids Play a Role in the Interaction of Puroindolines with Wheat Starch and Kernel Hardness

Kernel hardness is an important quality characteristic of common wheat. In this study, we investigated the role of starch surface lipids on the interaction of puroindoline proteins and starch granules through in vitro starch–protein binding experiments and flour reconstitution. SDS‐PAGE showed that there were no puroindoline proteins on the starch granule surface when surface lipids were removed or when defatted starch was incubated with puroindoline proteins. However, the puroindoline protein bands were present when defatted starch was incubated with lipids followed by purified puroindoline proteins, which indicated that starch surface lipids play a role in the binding of puroindolines to starch granules. The hardness of flour tablets and dough sheets made from reconstituted flour, which combined defatted starch incubated with lipids and puroindolines with gluten, was lower than for the control reconstituted flour, which was made from defatted starch and gluten. The results of scanning electron microscopy also showed that starch granules were embedded in the gluten in the gluten + defatted starch + lipids + puroindolines treatment. These results confirmed that starch surface lipids are involved in the interaction of puroindolines with wheat starch and kernel hardness.     

Effect of Puroindolines on the Breadmaking Properties of Wheat Flour

The role of lipid-binding proteins from wheat seed (puroindolines) on the breadmaking properties of wheat flour was investigated by determining the relationship between breadmaking quality and puroindoline content in samples of 32 wheat cultivars. An inverse relationship was mainly explained by the link between hardness and puroindoline contents. This link is in agreement with previous results which have shown a close structural identity between basic friabilins and puroindolines. Next, the effect of puroindolines in breadmaking was investigated by performing reconstitution experiments with two puroindoline-free hard cultivars of opposite quality (Florence Aurore and Ecrin) as indicated in the screened wheat sample. Addition of 0.1% puroindolines to these flours drastically modified both the rheological properties of doughs and the structure of the bread crumb. Puroindolines are essential to the foaming properties of dough liquor, and a close relationship was found between the fine grain crumb provided by reconstituted flours with puroindolines and the fine structure of corresponding dough liquor foams. The effect of puroindolines on bread volume was mainly related to the rheological properties of wheat doughs.     

Factors Controlling Gas Cell Failure in Bread Dough

Stress relaxation in the wall of a gas bubble, as measured by the alveograph, was used to study surface tension at the gas-dough interface of doughs from flours producing differing bread crumb grains. The surface tensions in the various wheat flour doughs were not different. Dough rheological properties, as measured by both dynamic oscillatory rheometry and lubricated uniaxial compression, were not different for doughs made from wheat flours that gave breads with different crumb grains. However, when the effect of starch granule size on gas cell wall stability was tested, the presence of a greater proportion of large starch granules in wheat flour dough was sufficient to result in gas cell coalescence and open crumb grain in the final baked product. This suggests that starch granule size is at least one of the factors that affects the crumb grain of bread.     

Dough and Baking Properties of High‐Amylose and Waxy Wheat Flours

The dough properties and baking qualities of a novel high‐amylose wheat flour (HAWF) and a waxy wheat flour (WWF) (both Triticum aestivum L.) were investigated by comparing them with common wheat flours. HAWF and WWF had more dietary fiber than Chinese Spring flour (CSF), a nonwaxy wheat flour. Also, HAWF contained larger amounts of lipids and proteins than WWF and CSF. There were significant differences in the amylose and amylopectin contents among all samples tested. Farinograph data showed water absorptions of HAWF and WWF were significantly higher than that of CSF, and both flours showed poorer flour qualities than CSF. The dough of WWF was weaker and less stable than that of CSF, whereas HAWF produced a harder and more viscous dough than CSF. Differential scanning calorimetry data showed that starch in HAWF dough gelatinized at a lower temperature in the baking process than the starches in doughs of WWF and CSF. The starch in a WWF suspension had a larger enthalpy of gelatinization than those in HAWF and CSF suspensions. Amylograph data showed that the WWF starch gelatinized faster and had a higher viscosity than that in CSF. The loaves made from WWF and CSF were significantly larger than the loaves made from HAWF. However, the appearance of bread baked with WWF and HAWF was inferior to the appearance of bread baked with CSF. Bread made with WWF became softer than the bread made with CSF after storage, and reheating was more effective in refreshing WWF bread than CSF bread. Moreover, clear differences in dough and bread samples were revealed by scanning electron microscopy. These differences might have some effect on dough and baking qualities.     

Effect of Gaseous Acetic Acid on Dough Rheological and Breadmaking Properties

Breads baked from wheat flours (protein contents 14.1–16.5% at 14.0% mb) that were pretreated with 2–3 mL of gaseous acetic acid per kg of wheat flour, showed maximum bread height and specific volume (cm³/g). Flour-water suspension and the crumb pH values were gradually decreased with increased amounts of acetic acid. Gas generation and dough expansion tests with bread dough showed that the addition of the same amount of acetic acid, which achieved maximum specific volume, also showed the highest rate of gas generation and dough expansion. However, increasing acetic acid decreased these values. Scanning electron microscope (Cryo-SEM) observation showed that the bread dough made from the same acetic acid-treated flour indicated continuum and no cracks in the dough matrix. Evaluation of mixograms showed the decrease of mixing stability with increased acetic acid levels. Viscosity and water binding capacity of flour-water suspensions were sharply increased by the addition of acetic acid at pH 5.0–3.5.     

Fermented Sorghum as a Functional Ingredient in Composite Breads

Whole sorghum flour was fermented (a five‐day natural lactic acid fermentation) and dried under forced draught at 60°C, and evaluated for its effect on sorghum and wheat composite bread quality. In comparison with unfermented sorghum flour, fermentation decreased the flour pH from 6.2 to 3.4, decreased total starch and water‐soluble proteins, and increased enzyme‐susceptible starch, total protein, and the in vitro protein digestibility (IVPD). Fermentation and drying did not decrease the pasting temperature of sorghum flour, but slightly increased its peak and final viscosity. In comparison with composite bread dough containing unfermented sorghum flour, fermented and dried sorghum flour decreased the pH of the dough from 5.8 to 4.9, increased bread volume by ≈4%, improved crumb structure, and slightly decreased crumb firmness. IVPD of the composite bread was also improved. Mixing wet fermented sorghum flour directly with wheat flour (sourdough‐type process) further increased loaf volume and weight and reduced crumb firmness, and simplified the breadmaking process. It appears that the low pH of fermented sorghum flour inactivated amylases and increased the viscosity of sorghum flour, thus improving the gas‐holding capacity of sorghum and wheat composite dough. Fermentation of sorghum flour, particularly in a sourdough breadmaking process, appears to have considerable potential for increasing sorghum utilization in bread.     

French Bread Loaf Volume Variations and Digital Image Analysis of Crumb Grain Changes Induced by the Minor Components of Wheat Flour

A standard quality flour for French breadmaking was fractionated by extraction of water‐soluble components (6% db) and by defatting (<1%db) to study the impact of soluble components and lipids on bread quality in terms of loaf specific volume (v_s) and crumb structure. Addition of puroindolines (<0.2%) was also tested. Crumb cell structure was assessed by digital image analysis (DIA) according to erosion‐dilation and closing treatments. The fraction of cells area with size <1 mm (%d<1) was defined as an index of fineness of crumb structure. Both DIA procedures allowed differentiation of crumb structures obtained by various formulations and, in the range of composition modifications tested, variations by a factor of 2 of both criteria (v_s and %d1) were obtained. Soluble fraction increased v_s and decreased fineness. Defatting and adding puroindolines increased fineness with no effect on v_s. The possible role of molecular components of each flour fraction was discussed in terms of rheological and foaming properties. DIA methods and flour recipes tested in this work offer a valuable tool for further studies on the processing‐structure‐properties relationships of French bread dough and crumb.     

不同种类大豆蛋白粉对面包加工特性的影响

为探索大豆蛋白作为营养补充剂在面包中应用时,对面团物理特性和焙烤特性产生的影响,该文考察了不同种类的大豆蛋白制品,包括大豆分离蛋白、灭酶全脂粉、活性全脂粉、活性脱脂粉、灭酶脱脂粉对面团粉质特性、拉伸特性和焙烤特性的影响。结果表明,面粉的吸水率与大豆蛋白粉氮溶解指数显著相关,面团的抗拉阻力受大豆蛋白添加量的影响明显。大豆蛋白粉的加入,对面包比体积产生不利影响,下降趋势与大豆蛋白粉对面团拉伸特性的影响显著相关。大豆蛋白粉有软化面包质地的作用,活性全脂粉表现最为明显。大豆蛋白粉的加入量占面粉质量分数的3%时,对面包口感影响不明显,当加入量超过面粉质量分数的7％时,容易出现发粘和豆腥味等现象。     

Effects of Oat Grain Hydrothermal Treatments on Wheat-Oat Flour Dough Properties and Breadbaking Quality

Hydrothermal treatments, which are routine in oat processing, have profound effects on oat flour dough rheological properties. The influence of roasting and steam treatments of oat grain on dough mixing and breadbaking properties was investigated when hydrothermally treated oat flour was blended with wheat flour. Roasting of oat grain (105°C, 2 hr) resulted in oat flours that were highly detrimental to wheat flour dough mixing properties and breadbaking quality. Steaming (105°C, 20 min) or a combination of roasting and steaming of oat grain significantly improved the breadbaking potential of the oat flours. The addition of oat flours increased water absorption and mixing requirements of the wheat flour dough and also decreased bread loaf volume. However, at the 10% substitution level, steamed oat flours exhibited only a gluten dilution effect on bread loaf volume when wheat starch was used as a reference. Oat flour in the breadbaking system decreased the retrogradation rate of bread crumb starch. The results indicate that adequate hydrothermal treatments of oat grain are necessary for oat flour breadbaking applications. Steamed oat flours used at a 10% level retarded bread staling without adversely affecting the loaf volume.     

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.     

Dough Properties and Bread Quality of Wheat–Barley Composite Flour as Affected by β‐Glucanase

Barley is rich in nutritionally positive compounds, but the quality of bread made of wheat–barley composite flours is impaired when a high percentage of barley is used in the mixture. A number of enzymes have been reported to be useful additives in breadmaking. However, the effect of β‐glucanase on breadmaking has scarcely been investigated. In this paper, the influence of different levels (0.02, 0.04, 0.06, and 0.08%, based on composite flour) of β‐glucanase (100,000 U/g) on the properties of dough and bread from 70% wheat, 30% barley composite flour were studied. Although dough development time, dough stability, and protein weakening value decreased after β‐glucanase addition, dough properties such as softness and elasticity as well as bread microstructure were improved compared with the control dough. β‐Glucanase also significantly improved the volume, texture, and shelf life of wheat–barley composite breads. The use of an optimal enzyme concentration (0.04%) increased specific volume (57.5%) and springiness (21%), and it reduced crumb firmness (74%) and staling rate. Bread with added β‐glucanase had a better taste, softness, and overall acceptability of sensory characteristics compared with the control bread. Moreover, the quality of wheat–barley composite bread after addition of 0.04% β‐glucanase was nearly equal to the quality of pure wheat bread. These results indicate that dough rheological characteristics and bread quality of wheat–barley composite flour can be improved by adding a distinct level of β‐glucanase.     

Differential recovery of lupin proteins from the gluten matrix in lupin-wheat bread as revealed by mass spectrometry and two-dimensional electrophoresis

Bread made from a mixture of wheat and lupin flour possesses a number of health benefits. The addition of lupin flour to wheat flour during breadmaking has major effects on bread properties. The present study investigated the lupin and wheat flour protein interactions during the breadmaking process including dough formation and baking by using proteomics research technologies including MS/MS to identify the proteins. Results revealed that qualitatively most proteins from both lupin and wheat flour remained unchanged after baking as per electrophoretic behavior, whereas some were incorporated into the bread gluten matrix and became unextractable. Most of the lupin α-conglutins could be readily extracted from the lupin-wheat bread even at low salt and nonreducing/nondenaturing extraction conditions. In contrast, most of the β-conglutins lost extractability, suggesting that they were trapped in the bread gluten matrix. The higher thermal stability of α-conglutins compared to β-conglutins is speculated to account for this difference.     

Moderate decrease of pH by sourdough fermentation is sufficient to reduce phytate content of whole wheat flour through endogenous phytase activity

Whole wheat bread is an important source of minerals but also contains considerable amounts of phytic acid, which is known to impair their absorption. An in vitro trial was performed to assess the effect of a moderate drop of the dough pH (around 5.5) by way of sourdough fermentation or by exogenous organic acid addition on phytate hydrolysis. It was shown that a slight acidification of the dough (pH 5.5) with either sourdough or lactic acid addition allowed a significant phytate breakdown (70% of the initial flour content compared to 40% without any leavening agent or acidification). This result highlights the predominance of wheat phytase activity over sourdough microflora phytase activity during moderate sourdough fermentation and shows that a slight drop of the pH (pH value around 5.5) is sufficient to reduce significantly the phytate content of a wholemeal flour. Mg "bioaccessibility"of whole wheat dough was improved by direct solubilization of the cation and by phytate hydrolysis.     

Application of electron spin resonance spectroscopy and spin probes to investigate the effect of ingredients on changes in wheat dough during heating

The change in microviscosity of the aqueous and lipid phases of wheat flour dough, during heating and subsequent cooling, has been measured using novel spin probes based on the isoindolin-yloxyl structure. The spin probes, water and/or lipid soluble, were used with combinations of dough ingredients: diacetyl tartaric acid ester of monoglycerides (DATEM), salt, yeast, and sodium ascorbate. The lipid soluble probe showed that DATEM does not produce a homogeneous phase with endogenous lipids but is found in a separate, less mobile phase. Also, the lipids were shown not to be involved in the baking process, although DATEM may be incorporated into the gelled starch matrix. The water soluble probe enabled starch gelatinization to be investigated in detail and showed that gelatinization produces a reduction of dielectric constant. The technique is appropriate for the detailed examination of the behavior of different ingredients during baking and also potentially to examine interactions between ingredients and flour components in dough.     

Effect of cyclodextrin glycosyl transferase [corrected] on dough rheology and bread quality from rice flour

Gluten-free breads are usually characterized by deficient quality characteristics as compared to wheat breads. Problems related to volume and crumb texture are associated with gluten-free breads even when rice flour is used, which seems to be the best raw material for this type of bread. The potential use of cyclodextrin glycosyl transferase (CGTase) as a rice bread improver is presented. The effect of CGTase addition to rice flour on dough rheology and bread quality was investigated. In addition, an experimental design was developed to optimize the levels of CGTase, hydroxypropylmethylcellulose (HPMC), and oil. The addition of CGTase produced a reduction in the dough consistency and also in the elastic modulus. With regard to the rice bread quality, better specific volume, shape index, and crumb texture were obtained. The amount of cyclodextrins in the bread crumb was quantified to explain the action of this enzyme. The data indicate that the improving effect of the CGTase results from a combination of its hydrolyzing and cyclizing activities, the latter being responsible for the release of cyclodextrins, which have the ability to form complexes with lipids and proteins.     

Effect of flour minor components on bubble growth in bread dough during proofing assessed by magnetic resonance imaging

Fermentation of dough made from standard flour for French breadmaking was followed by nuclear magnetic resonance imaging at 9.4 T. The growth of bubbles (size > 117 microm) was observed for dough density between 0.8 and 0.22 g cm(-3). Cellular structure was assessed by digital image analysis, leading to the definition of fineness and rate of bubble growth. Influence of composition was studied through fractionation by extraction of soluble fractions (6% db), by defatting (< 1% db) and by puroindolines (Pin) addition (< or = 0.1%). Addition of the soluble fraction increased the dough specific volume and bubble growth rate but decreased fineness, whereas defatting and Pin addition only increased fineness. The role of molecular components of each fraction could be related to dough elongational properties. A final comparison with baking results confirmed that the crumb cellular structure was largely defined after fermentation.     

Pyranose Oxidase from Trametes multicolor Impacts Dough and Bread Microstructure

Pyranose oxidase (P₂O) improves wheat flour dough stability and bread quality. We related its effect on dough spread behavior to that on dough and bread crumb structure. Increasing P₂O addition levels gradually reduced dough flow. High P₂O addition levels further increased dough strength, significantly increased dough cell wall thickness, and decreased bread loaf volume. Taken together, affecting dough spread behavior impacts dough and bread (crumb) structure, and dough structure largely determines bread crumb structure.     

Bran Characteristics and Bread‐Baking Quality of Whole Grain Wheat Flour

Variations in physical and compositional bran characteristics among different sources and classes of wheat and their association with bread‐baking quality of whole grain wheat flour (WWF) were investigated with bran obtained from Quadrumat milling of 12 U.S. wheat varieties and Bühler milling of six Korean wheat varieties. Bran was characterized for composition including protein, fat, ash, dietary fiber, phenolics, and phytate. U.S. soft and club wheat brans were lower in insoluble dietary fiber (IDF) and phytate content (40.7–44.7% and 10.3–17.1 mg of phytate/g of bran, respectively) compared with U.S. hard wheat bran (46.0–51.3% and 16.5–22.2 mg of phytate/g of bran, respectively). Bran of various wheat varieties was blended with a hard red spring wheat flour at a ratio of 1:4 to prepare WWFs for determination of dough properties and bread‐baking quality. WWFs with U.S. hard wheat bran generally exhibited higher dough water absorption and longer dough mixing time, and they produced smaller loaf volume of bread than WWFs of U.S. soft and club wheat bran. WWFs of two U.S. hard wheat varieties (ID3735 and Scarlet) produced much smaller loaves of bread (<573 mL) than those of other U.S. hard wheat varieties (>625 mL). IDF content, phytate content, and water retention capacity of bran exhibited significant relationships with loaf volume of WWF bread, whereas no relationship was observed between protein content of bran and loaf volume of bread. It appears that U.S. soft and club wheat bran, probably owing to relatively low IDF and phytate contents, has smaller negative effects on mixing properties of WWF dough and loaf volume of bread than U.S. hard wheat bran.     

Effect of Wheat Bran on Dough Rheology and Final Quality of Chinese Steamed Bread

Wheat bran is a low‐cost by‐product abundantly produced by the wheat flour industry. As a staple food of China, Chinese steamed bread (CSB) represents about 40% of China's wheat consumption. This study investigated the effects of incorporating wheat bran into the CSB at different levels (5, 10, and 15%). The dough behavior was measured by analyzing rheological properties. Quality of CSB was analyzed from two perspectives: physical properties and nutritional quality. For physical properties, specific volume, loaf height, moisture, and texture were measured by 1 . The predicted glycemic response of the bread was analyzed by using an in vitro digestion method. The results illustrated that the incorporation of wheat bran into wheat flour reduced the extensibility of the dough, decreased specific volume, and increased bread hardness, gumminess, and chewiness. However, this study also showed that addition of wheat bran can decrease the predicted glycemic response of steamed bread by up to 39%.     

Application of Pregerminated Brown Rice for Breadmaking

Pregerminated brown rice (PGBR) prepared by immersing in water was used for breadmaking, and effects on the dough properties and bread qualities were studied to compare with the ungerminated brown rice (BR). The substitution of BR or PGBR for wheat flour produced smaller specific volume in bread than in the control bread without BR or PGBR along with the increasing amount of substitution. However, the bread samples containing BR or PGBR suppressed staling during storage. The improving effect was especially obvious for substitutions of 10 and 20% PGBR as compared with BR. PGBR made viscous dough and retarded the staleness of bread compared with BR. γ‐Aminobutyric acid and oryzanol did not contain in the final BR and PGBR substituted bread, and phytic acid was decomposed ≈54 and 45% for 30% BR and 30% PGBR substituted breads, respectively. But ferulic acid was quite stable in the final baked product. As a result, substitution of PGBR for wheat flour improved the bread quality.