Flour quality and disproportionation of bubbles in bread doughs

The bread making process transforms wheat flour doughs into highly porous breads. Bread has been shown (Wang, Austin and Bell, 2011) to be a single, open cell that is massively interconnected giving it a maze-like structure that encompasses the entire volume. The solid strands are also porous and contain closed cells. How the bubbles in dough mix partition into these open and closed cells in bread is not known. This study was undertaken to track changes in bubbles in doughs using 3-D X-ray microtomography techniques as doughs proofed and were baked. The mechanical properties of doughs were measured to establish how dough rheology impacted bubble growth. The doughs were made with ‘medium strong’ Canadian flour (CWRS) and ‘weak’ Australian flours (Wylk). Both doughs had similar protein amounts and strain-hardening characteristics; however the CWRS dough was more elastic. The scans identified formation of clusters of partially-coalesced bubbles from which one cluster grew to form a massively interconnected, single, closed cell in doughs as doughs proofed. Microscopy studies confirmed that the open cell in breads was made of partially-coalesced bubbles. Compared to the dough made with the Australian flours, the dough made from Canadian flour had a thicker dough layer separating bubbles, smaller size bubbles and a slower rate of formation of the continuous structure. This study highlights the critical role of dough elasticity and the disproportionation phenomena of bubble growth in controlling the quality of cell structures in dough and baked products.     

Composite Flours for Baked Products and Possible Challenges – A Review

This paper is a review of how consumption of bread, other leavened products and unleavened products made from wheat flour has increased rapidly in Nigeria and other developing countries. It examines how this has resulted in large scale importation of wheat and the consequent drain on the nation’s foreign currency earnings. It contains some suggestions on how to reduce the high import bills of wheat by using composite flours or blends of wheatless flours in place of wheat flour for making leavened and unleavened products. Some studies on the quality characteristics of leavened and unleavened products made from composite flours or blends of wheat flours were reviewed. Some possible challenges likely to be encountered in case Nigeria changes from use of wheat flour to composite flours and blends of wheatless flours are also outlined.     

方便泡馍的研制

通过不同面筋含量的面粉、不同的发酵时间以及死面与发面的不同比例混合等工艺,研究方便泡馍弹性、咀嚼度的最佳效果。最佳实验工艺条件为使用高筋粉,发酵时间60 min,发面与死面1∶4混合。     

Rheological Effects of Some Xylanase on Doughs from High and Low Extraction Flours

The xylanases are widely used in breadmaking with positive effects on bread quality but how they act in doughs is not fully understand yet. The aim of this study is to determine how different xylanolytic preparations modify the rheology of dough prepared from low and high extraction flours and the correlation between the rheological changes induced in dough and the viscosity and xylan content of flour extracts. Four flours, two white and two black, and three xylanolytic preparation was used in study. The rheological characteristics of dough were measured with the Extensograph. The xylan content and viscosity of flour extracts with xylanase were determined. In doughs from white flours xylanases increased the energy, maximum resistance and extensibility while in doughs from black flours decreased the energy and maximum resistance and increased the extensibility. The extensographic effects of xylanases were compared with their capacity to modify the viscosity and xylan content of aqueous flours extracts. The changes of extensographic indicators are well correlated with the changes of xylan content of extracts for white flour while for black flour correlations were observed with the changes of extracts viscosity. The capacity of xylanases to modify the viscosity of extract and convert the insoluble xylans in soluble xylans could be used to predict the performance of xylanases.     

UNIAXIAL COMPRESSIBILITY OF BLACKGRAM DOUGHS BLENDED WITH CEREAL FLOURS

The uniaxial compression characteristics of papad dough (moisture content 62%, dry basis), made from blackgram flour as well as after incorporation of different types of cereal (rice, sorghum and wheat) flours at different levels (20 and 40%), were determined. The stress-strain data can be interrelated by a power law type equation. The sensory attributes (stickiness, firmness, elasticity and ease of flattening/rolling) were correlated with the energy for compression, deformability modulus and apparent biaxial elongational viscosity. Inelastic doughs resulted from the blackgram dough; doughs with 20% rice or wheat blends were also inelastic but sorghum samples were elastic. The deformability modulus for sorghum doughs were extremely high. The blackgram dough as well as the wheat blended doughs were the easiest doughs to roll/flatten. Blended dough consisting of wheat flour (at 20 and 40% level) or rice flour up to 20% level was suitable for making cereal-blended papad doughs.     

Flour quality and dough elasticity: Dough sheetability

Current practices in testing flours call for measuring dough strength, not elasticity. Sheeting is a common method for processing developed doughs, the elasticity of which governs dough’s sheetability as dough springs back exiting rollers. To characterise dough sheetability, a study was conducted testing 18 different doughs made from six different flours. Each dough was sheeted using an instrumented sheeter and data for exit sheet thickness and roll forces were captured under a range of sheeting conditions. The true rheological properties of doughs were measured and used to calibrate the ABBM constitutive model for dough (1). Numerical simulations of sheeting operations were conducted; the R² coefficients between measured and predicted sheet thicknesses and roll forces (vertical and horizontal) were nearly all >0.9. Relaxation times were derived from dough model parameters and revealed that flour quality for dough elasticity should be assessed by examining moisture effects on dough relaxation time.     

Correlating dough elastic recovery during sheeting with flour analyses and rheological properties

The dough rheological behaviors of three flours having different chemical and physical properties were measured, as were changes in thickness and snapback (thickness of the machined dough sheet relative to the roll gap), immediately following sheeting. Dough snapback was determined to be a function of processing parameters, reduction ratio, and dough rest time, as well as different flour properties. The predication equation for dough snapback is based on multiple flour properties and sheeting conditions. Higher protein flours normally have stronger dough properties and larger snapback, compared with low protein flours, but also depend on the protein quality. The snapback will increase either with increased protein content, reduction ratio, or reduced rest time. Dough snapback using flour made by blending two flours 50/50 had intermediate values between the two original flours. Among the variables, Mixograph work, reduction ratio, and dough rest time were the main factors affecting the elastic characteristics of the doughs. Minimum snapback occurred with the weakest flour experiencing the longest rest time and the smallest reduction ratio. A linear 7‐factor equation was found to predict the snapback of several flours, by combining reduction ratio, dough rest time, Mixograph work, peak height, and mixing time, Alveograph P/L, and protein content. Only three factor combinations of Mixograph work, reduction ratio, and rest time were needed to develop a second order equation for predicting snapback. Copyright © 2008 Society of Chemical Industry     

Ultrasonic Investigation of the Effect of Vegetable Shortening and Mixing Time on the Mechanical Properties of Bread Dough

ABSTRACT:  Mixing is a critical stage in breadmaking since it controls gluten development and nucleation of gas bubbles in the dough. Bubbles affect the rheology of the dough and largely govern the quality of the final product. This study used ultrasound (at a frequency where it is sensitive to the presence of bubbles) to nondestructively examine dough properties as a function of mixing time in doughs prepared from strong red spring wheat flour with various amounts of shortening (0%, 2%, 4%, 8% flour weight basis). The doughs were mixed for various times at atmospheric pressure or under vacuum (to minimize bubble nucleation). Ultrasonic velocity and attenuation (nominally at 50 kHz) were measured in the dough, and dough density was measured independently from specific gravity determinations. Ultrasonic velocity decreased substantially as mixing time increased (and more bubbles were entrained) for all doughs mixed in air; for example, in doughs made without shortening, velocity decreased from 165 to 105 ms⁻¹, although superimposed on this overall decrease was a peak in velocity at optimum mixing time. Changes in attenuation coefficient due to the addition of shortening were evident in both air-mixed and vacuum-mixed doughs, suggesting that ultrasound was sensitive to changes in the properties of the dough matrix during dough development and to plasticization of the gluten polymers by the shortening. Due to its ability to probe the effect of mixing times and ingredients on dough properties, ultrasound has the potential to be deployed as an online quality control tool in the baking industry.     

不同磨粉方法对荞麦面团流变学性质的影响

为研究不同磨粉方法对荞麦面团流变学性质的影响,分别采用石磨、高速万能粉碎机及湿磨三种磨粉方法制得荞麦粉。然后测定由上述荞麦粉制备的荞麦面团的热机械学特性、拉伸特性、质构特性及应力松弛行为。结果表明:与干磨荞麦面团相比,湿磨荞麦面团具有显著较低的面团形成时间和稳定时间以及显著较高的蛋白弱化度,但磨粉方法对淀粉糊化特性影响较小。湿磨荞麦面团的拉断距离低于干磨荞麦面团的拉断距离,但其硬度、黏着性、弹性和胶着性显著高于干磨荞麦面团。此外,湿磨荞麦面团与干磨荞麦面团相比具有显著较高的残余应力和显著较短的松弛时间。不同磨粉方法会导致荞麦面团流变学性质产生差异,面团流变学性质的差异将满足不同的加工需求。     

The bubble size distribution in wheat flour dough

This paper reports, for the first time, the use of non-invasive microcomputed tomography (μCT) to unambiguously determine the bubble size distribution in doughs made from strong breadmaking flour. The doughs studied were comprised of two types of dough made of two different formulae in order to yield distinct consistencies, one being a stiff dough and the other one being a slack dough. Reconstruction and three-dimensional visualization of the internal structure of the dough was accomplished at a resolution of 10 μm³ per voxel, making possible to resolve gas bubbles as small as 10 μm in diameter. Morphological characterization of the stiff and slack doughs indicated that they entrained bubbles whose size distributions were well defined by a two-parameter lognormal distribution, with geometric mean x_g and geometric standard deviation σ_g. The bubble size distributions in the stiff and slack doughs were found to have similar geometric means, 100 and 109 μm, but quite distinct geometric standard deviation, 1.79 and 1.62, respectively. An analysis of anisotropy of bubble cross-sections (circles 10-μm thick) suggested that the small bubbles entrained in the slack dough were deformed during sample preparation to a greater extent than in the stiff dough, up to a size of 180 μm. Also, the stiff dough entrained a smaller void fraction and fewer bubbles per unit volume than did the slack dough. Furthermore, the distance between adjacent bubbles was obtained, indicating that the bubble separation distribution was normally distributed, with the stiff and slack doughs having a mean separation of 338 and 460 μm and standard deviation of 88 and 156 μm, respectively. Overall, this paper shows how the bubble size distribution in dough can be determined using X-ray microcomputed tomography, opening the possibility to gaining a more comprehensive insight into the aeration phenomenon in wheat flour dough.     

Comparative study of phytic acid content,in-vitro protein digestibility and amino acid composition of different types of flat breads

Phytic acid content of eight different types of leavened and unleavened flat breads was determined. It was highest in unleavened and non-fermented whole wheat chapati and lowest in the leavened and fermented white wheat flat bread roghni nan. The effect of baking conditions, bread composition and phytic acid content on in-vitro digestibility of protein was measured using a pepsin multienzyme pH stat technique. The amino acids released were separated by ultrafiltration. The rate of protein digestibility of flat bread and amino acid released depended upon the type of flour used, baking conditions, phytic acid content and other antiproteolytic constituents of breads. Leavening and fermentation of breads resulted in an increase of protein digestibility and availability of amino acids. Addition of soya flour increases the protein digestibility of breads whereas millet flour decreases it.     

Amino Acid Profiles of Fermenting Wheat Sour Doughs

The free amino acid patterns of unfermented and fermented wheat sour doughs started with Lactobacillus plantarum were related by factor analysis to dough yield, ash content of flour, fermentation temperature and presence/absence of yeast, from data corresponding to a central composite design of samples. Individual levels of hydrophobic, acid and basic amino acids as well as total amino acid content positively correlated with extraction rate of flours. The presence of yeast promoted metabolism of histidine, aspartic acid and asparagine, particularly in samples made with whole and wholemeal flours. Proliferation of predominant amino acids by enzymatic release was more notable at higher fermentation temperatures and wholemeal samples. Sour doughs with maximum levels of hydrophobic and basic amino acids were started with no yeast bacterial cultures, made with whole and wholemeal flours and fermented at 35°C.     

Evaluation of l-ascorbic acid oxidation on SH concentration in soy-wheat composite dough during resting period

The effect of l-ascorbic acid (l-AA) on free sulfhydryl concentration (SH) was evaluated in soy-wheat composite dough from 100-500 (g/kg) soy flour substitution for wheat flour. Raw soy flour (RSF) and physically modified soy flours (PMSF1 and PMSF2) were used for the preparation of the composite dough with wheat flour. The two physically modified soy flours were prepared by steam flushing (PMSF2) and water boiling (PMSF1) of raw soy beans before flour preparation. Using a timer, dough blends were manually mixed (at approximately 60 rpm) to dough development time after which, dough was sampled for the estimation of free SH groups. l-AA (0.05% w/w) was mixed with the dough after dough development and the dough was sampled after 1 h of resting the dough. The results showed that l-AA (0.05% w/w) acted as a reducing agent by increasing SH levels in all soy-wheat dough blends (P<0.05). After 1 h of resting, soy-wheat composite dough without l-AA had lower concentrations of SH than that with l-AA. A positive correlation was shown between soy flour concentrations and SH concentration before and after dough resting. A negative correlation existed between l-AA consumption and SH concentration for RSF-wheat, PMSF1-wheat and PMSF2-wheat doughs. The results indicated that soy flour weakened wheat flour dough by increasing SH concentration and that l-AA could have a synergistic effect on the reduction of gluten proteins and thus weakening the dough.     

Automatic dough-mixers for high rate test-baking system

A laboratory dough mixer and its electrical and pneumatic control circuits are described. The mixer accurately measures dough ingredients (except flour) and adds them to the mixing chamber during the mixing cycle. It also titrates sufficient water into doughs to bring them to standard consistency. The addition of flours (50 g) and removal of doughs is done manually. One person can readily operate a battery of six mixers producing 60 doughs an hour.     

Small and large deformation rheology for hard wheat flour dough as influenced by mixing and resting

ABSTRACT:  The effects of mixing and resting on the physicochemical properties of doughs prepared with strong and weak hard wheat flours were investigated, specifically concerning aspects related to their rheological behavior and molecular mobility. Small deformation dynamic tests showed that, during the initial resting period, the complex modulus G * decreased and phase angle decreased for undermixed dough, whereas overmixed dough showed opposite trends. G * values for optimally mixed dough did not vary during the resting period investigated. This was more obvious for the strong dough. Large deformation tests more clearly showed differences among optimal, under-, and overmixed dough, and also between doughs prepared with strong and weak flour. Optimally mixed dough exhibited the highest peak stress and strain for both samples. In addition, the peak stress of dough prepared with the strong flour was higher than that of dough prepared with weak flour. Inconsistent results between small and large deformation tests implied that small and large deformation tests reflected different structural aspects of dough. NMR measurements were performed to estimate the relaxation properties of the sample upon resting. Decreased water mobility during resting, indicated by decreasing T ₁ relaxation time, was possibly attributed to increasing molecular interactions caused by continued hydration. Evidence of additional molecular interactions created by mixing was also observed.     

The effect of lipoxygenase action on the mechanical development of wheat flour doughs

The mechanical development of dough has been followed by measurement of the relaxation time of dough samples after mixing to various levels of work input. Parallel determinations of free and bound lipid have also been made. When doughs were mixed in air, addition of full-fat, enzyme-active soya bean flour (subsequently referred to as “soya flour”) resulted in an increase in relaxation time, particularly at higher work levels. The magnitude of this improvement increased with increasing work input and was dependent on the rate of work input. Addition of soya flour also enabled a higher level of mechanical work to be introduced before dough breakdown occurred. When doughs were mixed under nitrogen, or when the soya flour was heat denatured, no change in the rheological properties compared with the respective control doughs was found. The release of bound lipid, which occurred during dough development in air in the presence of soya flour, could also be induced by adding purified lipoxygenase to the dough, together with linoleic acid as a substrate. This resulted in rheological changes similar to those observed using soya flour. However addition of enzymically pre-peroxidised lipid to doughs mixed in nitrogen was without effect on relaxation times. These findings suggest that lipid release is linked with structural changes in dough protein and provide further support for a mechanism of coupled oxidation of protein -SH groups by lipoxygenase.     

The formation and properties of wheat flour doughs

Among the cereal flours, only wheat flour will form a viscoelastic dough when mixed with water. The viscoelasticity appears to be because the gluten proteins are water compatible and thus will swell and interact. The gluten protein's large molecular size and low charge density appear to allow them to interact by both hydrogen and hydrophobic bonds. Wheat flour doughs are also unique in their ability to retain gas. This property appears to result from a slow rate of gas diffusion in the dough. The third major unique property of wheat flour doughs is their ability to set in the oven during baking, and thereby to produce a rigid loaf of bread. Although not clearly understood, this appears to be a heat-induced crosslinking of the gluten proteins.     

荞麦粉添加量对混合粉面团流变特性及发面饼品质的影响

目的:探索荞麦发面饼中荞麦粉的最佳添加量。方法:选用粉质仪、拉伸仪、黏度仪等探讨荞麦粉添加量对混合粉面团流变学特性的影响,并依据感官评价判断发面饼的品质。结果:在面粉中添加0～40%的荞麦粉,随着荞麦粉添加量的增加,混合粉面团的流变学特性显著变差。混合粉面团的吸水率、形成时间、粉质质量指数逐渐减小,当荞麦粉添加量为40%时,混合粉的粉质质量指数降低了69.1%、形成时间降低了70.7%。随着荞麦粉含量的增加,混合粉面团的拉伸性和拉伸面积逐渐降低,阻力先增加后降低。当荞麦粉添加量为20%时,发面饼的硬度、黏性和咀嚼性最低,感官评分最高,与空白对照相比感官评分提高了19.4%。结论:荞麦粉的添加降低了混合粉的品质,但适量的荞麦粉可以赋予发面饼特殊的香味以及营养价值,添加量<20%的混合粉的流变学特性和发面饼的品质较好。     

Effects of flour from different barley varieties on barley sour dough bread

Twenty flours from 16 different barley varieties cultivated in 1990 and 1992, and a Swedish reference flour, were fermented by Lactobacillus plantarum A1 to sour doughs. Barley breads (40% barley/60% wheat flour) from each flour type were baked with and without an admixture of barley sour dough in order to investigate how the sour dough admixture would affect the baking properties. A trained panel carried out sensory evaluation by conventional profiling on breads made from three of the barley varieties and the Swedish reference flour, made with and without sour dough admixture.

The barley varieties influenced both the sour dough properties and the properties of the barley bread. The pH of bread with sour dough ranged from 4.6 to 4.8 as compared to 5.4 to 5.6 in bread without sour dough. The acidity of the breads with sour dough ranged from 4.1 to 5.0 ml NaOH/ 10 g bread crumb as compared to 2.4 to 3.6 in breads without sour dough. In 14 of the twenty bread types an addition of sour dough lowered the bread volume. Breads with a sour dough admixture scored higher for total taste and acidulous taste than breads without sour dough. The β-glucan content of the flours had no significant influence on the sour dough or the sensory characteristics of the bread, except for the breadcrumb colour.     

Promoting dough viscoelastic structure in composite cereal matrices by high hydrostatic pressure

The impact of high hydrostatic pressure (HP) treatment on dough viscoelastic reinforcement of highly-replaced wheat cereal matrices has been investigated. The gelatinisation/pasting and gelling profiles of HP hydrated oat, millet, sorghum and wheat flours, and the small and large deformation rheological parameters of blended wheat/non-wheat doughs were determined. Oat, millet, sorghum and wheat hydrated flours, at dough yield (DY) 160 and 200, were treated for 10 min at 0.1, 200, 350 or 500 MPa. Regardless the nature of the cereal, HP changes flour viscometric features, particularly in softer doughs (DY 200), leading to increased values for viscosity parameters, concerning pasting and paste cooking. Incorporation of 350 MPa pressure-treated flours into bread dough formulation provided increased dynamic moduli values, particularly for wheat and oat/wheat blends, associated to a reinforced dough structure. Highly-replaced composite dough samples treated at 500 MPa proved to be extremely stiff, resistant to stretch, low cohesive and low extensible, and thus not suitable for breadmaking.