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.     

Sourdough reduces sodium in wheat flour doughs

The reduction of sodium in breads is already an imposed reality, which makes the search for alternatives essential. As sodium chloride has an effect on dough rheology, affecting the production process, it is important to evaluate these properties. This study evaluated the use of dry sourdough for the reduction of sodium in wheat flour dough. Sodium chloride (0–2.5 g/100 g) and dry sourdough (0–10 g/100 g) were added to wheat flour according to a central composite rotatable design, and farinograph, extensograph and pasting parameters were evaluated. The results were analysed using the response surface methodology. The farinograph and extensograph properties were strongly affected by both variables and presented opposite behaviours for most parameters. For pasting properties, only maximum viscosity and breakdown were affected. Despite the antagonistic behaviour of the variables when analysed separately, suitable parameters were reached in intermediate ranges for the manufacture of bakery products with reduced sodium content.     

A rheological investigation of the role of water in wheat flour doughs

Summary. Doughs of wheat flour, salt and water have been mixed to various levels of work input and water content. Rheological tests have shown that above a particular water content the dough system is unaffected by further addition of water. It is proposed that the water in dough is held with various degrees of strength and that the distribution of water is dependent upon the mechanical work input.     

Flour Quality effects on percolation of gas bubbles in wheat flour doughs

To investigate how flour affects crumb structures, we used Synchrotron X-ray tomography to scan and capture the growth of gas bubbles in leavened and unleavened bread doughs of two different flours. Bubbles were mobile in all doughs; they coalesced and disproportionated with the rate of coalescence being higher in leavened doughs. In unleavened dough, new bubbles were detected, attributed to arise from poro-visco-elastic relaxation of gluten as dough rested. In each yeasted dough, a single, massively inter-connected cluster formed which percolated at ~26% dough porosity irrespective of flour type in dough. Following percolation, dough expansion was driven primarily by growth of the percolating bubble. Between flours, the rate of coalescence was higher in Wylkatchem (Wylk), an Australian flour dough, than in Canadian Western Red Spring (CWRS) flour dough, known for superior proof and bake qualities. How the physical and rheological properties of dough liquors could have affected the stabilities of bubbles in these doughs have been discussed.     

Glycosidases of wheat

Glycosidases isolated from the mill fractions made from soft and hard wheat grists were studied. α-Arabinosidase, α-galactosidase, β-galactosidase, β-glucosidase, β-glucuronidase, β-mannosidase and β-xylosidase activities in wheat flour, germ and bran were determined under standard dough conditions. There were no significant differences between the level of glycosidase activities from hard and soft grists. The level of a particular glycosidase activity was generally highest in the germ and lowest in the flour.     

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.     

Reaction of sorbic acid in wheat flour doughs: reaction with thiols.

The general characteristics of the reaction between sorbic acid and thiols are reviewed. Cysteine adds to the conjugated diene in position 5 to form the substituted 3-hexenoic acid. This is labile in acid solution, yielding a quantitative amount of sorbic acid. When wheat flour doughs are treated with sorbic acid and heated, a significant amount of the sorbic acid is not recovered on extraction with methanol. The use of acidified methanol leads to a quantitative recovery of the preservation and evidence is presented to suggest that sorbic acid-thiol adducts are formed. This is the first report of 'reversibly bound' sorbic acid in a food.     

On the influence of added lipid phases on the rheological properties of wheat flour doughs

Summary The influence of added lecithin on the stress relaxation behaviour of wheat flour doughs was studied. It was found that the relaxation modulus (G) was dependent of the lipid phase as well as on the type of flour to which the lecithin was added. As expected, when lecithin was dispersed in distilled water, the lamellar liquid-crystalline phase was obtained. This phase had the greatest influence on G. However when lecithin was dispersed in tap water or 1.55 mM CaCl₂ a mixture of different lipid phases was obtained. The influence of these mixtures on G was much less compared with lecithin in distilled water. The flours were from different flour streams, from a winter wheat and a spring wheat. One flour stream from the break system and one flour stream from the reduction system were used. It was found that the greatest increase in G due to the addition of lecithin was obtained for the flour streams from the reduction system. Furthermore, G increased more for the spring wheat than for the winter wheat.

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Über die Wirkungen eines Zusatzes von Lipidphasen auf die rheologischen Eigenschaften von Weizenteigen

Zusammenfassung Der Einfluß eines Lezithinzusatzes auf das Relaxationsverhalten der Weizenmehlteige wurde untersucht. Der Relaxationsmodulus (G) war sowohl von der Lipidphase als auch von dem Typ des Mehls abhängig. Wenn das Lezithin im destillierten Wasser dispergiert wurde, entstand, wie erwartet, eine lamellare flüssigkristalline Phase. Wenn das Lezithin in Leitungswasser oder in 1.55 mmol CaCl₂ dispergiert wurde, ergab sich eine Mischung verschiedener Lipidphasen, deren Einfluß auf G viel geringer war als der des Lezithins im destillierten Wasser. Bei den Mehlen handelte es sich um verschiedene Passagenmehle aus Sommer- und Winterweizen, weiterhin um ein Schrotmehl und ein spezielles Mehl (Reduktionmehl). Die größte Steigerung des G-Modulus wurde bei Zugabe von Lezithin zu dem speziellen Mehl gefunden. Weiter erhöhte sich der Modulus stärker bei Sommerweizen als bei Winterweizen.

     

Particle size,rheological and structural properties of whole wheat flour doughs as treated by high pressure

Effect of high-pressure treatment (300–600 MPa) and flour-to-water ratio (1:1, 1:2, 1:3, and 1:4) on functional, rheological, thermal, and structural properties of whole wheat flour dough were investigated. The particle size distribution, especially Dv90 (90% of the volume distribution), was significantly reduced by the pressure treatment. The damaged starch content increased significantly with the applied pressure and water content. The damaged starch absorbed more water, and subsequently increased the water holding capacity. Thermal transitions and mechanical property of pressure-treated samples were measured by differential scanning calorimetry, and rheometry, respectively. The peak viscosity, hot paste viscosity, and final viscosity decreased significantly with increasing pressure intensity. Hardness increased with the increasing pressure level while stickiness decreased at similar conditions. Fourier-transform infrared spectroscopy showed changes in the amide I region of the wheat protein. The sodium dodecyl sulfate polyacrylamide gel electrophoresis further indicated changes in the protein subunits that occurred after pressurization.     

The bubble size distribution and its evolution in non-yeasted wheat flour doughs investigated by synchrotron X-ray microtomography

Determination of the bubble size distribution at the end of mixing and controlling its changes are the basis for improving bread quality before it is fully manufactured. X-rays from a synchrotron source (Biomedical Imaging and Therapy beamline, Canadian Light Source) were used to rapidly characterize the bubble size distribution and its evolution in non-yeasted dough subsamples as a function of time for 3 h following mixing. A complete X-ray microtomography scan was completed within 120 s. The higher number density of bubbles in dough compared to results previously reported in the literature was attributed to the better contrast and higher resolution (smaller pixel size, 8.75 μm) of the reconstructed X-ray images generated from synchrotron X-rays. The bubble size distribution was very well characterized with a lognormal distribution function. This distribution had a median bubble radius of 22.1 ± 0.7 μm at 36 min after the end of mixing which increased to 27.3 ± 0.7 μm over 162 min, a trend indicative of transport of gas in the dough due to disproportionation. This is the first time disproportionation in non-yeasted wheat flour doughs has been monitored directly under bulk conditions relevant to dough in bakery conditions. These results show that the diffusion-driven dynamics of bubbles in non-yeasted bread doughs can be followed by X-rays from a synchrotron source via feature extraction using image analysis software.     

Rheological and sensory characteristics of doughs and cookies based on wheat,soybean, chick pea and lupine flour

Levels of 5, 10 and 15% of legume flours i.e. soybean, lupine and chick pea were used to supplement cookie. The effect of this supplementation on the rheological properties of the resulting dough was investigated using farinograph and extensograph as objective methods for quality assessment of the final product. It was found that there was an increase in water absorption capacity, dough stability, arrival time, dough development time and mix tolerance index. Extensograph results indicated that dough resistance to extension, dough energy and proportional number were minimized with increasing the lupine flour in the formula, while it was not changed on dough extensibility. However, soy flour increased resistance to extension, proportional number and energy and diminished dough extensibility. At the same time supplementing wheat flour with chick peas decreased both dough resistance to extension and proportional number while it increased dough extensibility and energy. For sensory evaluation, it was found that using either until 5% soybean or 10% chick pea or 15% lupine flour could replace the wheat flour in cookies formula without adversely affecting baking performance or altering the physical characteristics of the end product.     

Rheological properties of commercial chestnut flour doughs with different gums

Rheology of chestnut flour (CF) doughs with arabic gum (AG), carboxymethyl cellulose (CMC), guar gum (GG) and tragacanth gum (TG) at different concentrations (up to 2.0%) were determined at 30 °C using a controlled stress rheometer. The mixing characteristics at 30 °C were achieved using Mixolab^® apparatus. Shear (0.01–10 s^?1), oscillatory (1–100 rad s^?1 at 0.1% strain), creep‐recovery (50 Pa for 60 s) and temperature sweep (30–100 °C) tests were performed. Rheological properties were significantly modified by gum added. Apparent viscosity of CF doughs, storage and loss moduli increased at content of AG (above 0.5%), CMC (at 1.0%), GG (above 1.5%) and TG (at 1.0%). Flow curves and mechanical spectra were fitted using Cross model and power models, respectively. The gelatinisation temperatures increased with gums. The same pasting trend was noticed using Mixolab^®. Creep‐recovery data, fitted by Burgers model, showed that elasticity of CF doughs improved with GG.     

The microflora of the sour dough of wheat flour bread XII. Effect of freezing on the viability and functional properties in wheat flour doughs of microbial mass from lactic acid bacteria

Summary The effect of freezing (at –196 °C in 10% skimmed milk) and storage of the frozen microbial mass from lactic acid bacteria,Lactobacillus brevis, L. plantarum, L. cellobiosus andStreptococcus faecium, on viability and functional properties, in wheat flour doughs, have been studied. Freezing the biomass led to variable, but acceptable, survivals (34.3%–78.6%), depending on the species. Frozen and unfrozen biomass, when added to wheat doughs, produced similar values of pH and total titratable acidity during fermentation. Significant differences in acetic and lactic acid production were detected for some species. Frozen biomass fromL. brevis produced lessl(+)- andd(–)-lactic acid (43%) than the corresponding unfrozen material, whereas frozen biomass fromL. plantarum produced more acetic (61 %) and lactic acid (57%) than unfrozen. These differences were not reflected in bread characteristics (pH, total titratable acidity and flavour). Storage of frozen biomass for 30 days at –30 °C did not result in significant changes in the pH and or titratable acidity of the doughs nor in bread characteristics. At that time, acetic and lactic acid levels reached values close to these of the unfrozen biomass for all the microorganisms used.

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Die Mikroflora des Weizensauerteiges XII. Mitteilung: Wirkung von Tiefkühlung auf die Lebensfähigkeit und Funktionseigenschaften der Biomasse aus Milchsäurebakterien in Weizenteigen

Zusammenfassung Es wurde der Wirkung von Tiefkühlung (bei –196 °C in 10% Magermilch) und Lagerung von tiefgekühlter Biomasse aus Milchsäurebakterien,L. brevis, L. plantarum, L. cellobiosus undS. faecium, auf ihre Lebensfähigkeit und Funktionseigenschaften in Weizenteigen nachgegangen. Die Tiefkühlung der Biomasse verursachte veränderliche, jedoch akzeptable Überlebensraten (34,3%–78,6%) in Abhängigkeit von der Spezies. Beim Zusatz von tiefgekühlter Biomasse und nicht tiefgekühlter Biomasse zu Weizenteigen wurden ähnliche pH-Werte und Säuregrade während der Gärung erreicht. In manchen Spezies wurden bedeutsame Unterschiede in der Milchsäure-und Essigsäurebildung beobachtet. Die tiefgekühlte Biomasse vomL. brevis bildete wenigerl(+)-undd(–)-Milchsäure als die nichttiefgekühlte, während die tiefgekühlte vomL.plantarum mehr Milchsäure und Essigsäure als die nichttiefgekühlte bildete. Diese Unterschiede erschienen nicht in den Broteigenschaften (pH-Wert, Säuregrad, Geruch und Geschmack). Die Lagerung der tiefgekühlten Biomasse bei –30 °C während 30 Tagen verursachte keine bedeutsame Veränderung weder im pH-Wert und Säuregrad des Teiges noch in den Broteigenschaften. Essigsäure-und Milchsäuregehalte erreichten zugleich ähnliche Werte wie die nichttiefgekühlte Biomasse in allen Mikroorganismen.

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This paper is a part of a doctoral thesis for M. J. T.     

Microflora of the sour dough of wheat flour bread IX. Biochemical characteristics and baking performance of wheat doughs elaborated with mixtures of pure microorganisms

Summary Changes in mono- and disaccharides and acetic and lactic acid production of six different straight doughs elaborated with combinations of pure strains of yeastsSaccharomyces cerevisiae andCandida boidinii and lactic acid bacteriaLactobacillus plantarum andStreptococcus sp have been investigated, as well as the baking quality of the resulting breads. The type and proportion of the fermentative microorganisms were found to influence the biochemical activity of the doughs. The sugar levels after mixing reached different proportions, depending on the type of sugar and the type of microorganisms used. After proofing, the glucose and fructose content of the doughs decreased to 0.01%–0.02% db and maltose decreased to 0.45%–0.11 % db. Acetic and lactic acids underwent variable changes during fermentation, depending on the type of dough. Lactic acid showed higher levels than acetic acid. Bread made from these doughs had different sensory characteristics, texture, edibility and overall acceptance, as well as different lactic and acetic acid contents, depending on the mixture of microorganisms inoculated.

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Biochemische Merkmale und Leistungsfahigkeit der mit Mischungen reiner Mikroorganismen hergestellten Weizenbackteige

Zusammenfassung Die Forschungsaufgabe befaßte sich mit den Veranderungen der Mono- und Disaccharide, mit der Entstehung von Essig- und Milchsaure in sechs Teigen, die mit Kombinationen reiner HefekulturenSaccharomyces cerevisiae undCandida boidinii und MilchsäurebakterienLactobacillus plantarum undStreptococcus sp hergestellt waren und mit den sich daraus ergebenden Qualitätsmerkmalen der Brote. Die Art und Anteile der Mikroorganismen übten einen entscheidenden Einfluß auf die biochemische Aktivität der Teige aus. Nach dem Knetvorgang konnten unterschiedliche Gehalte gemäß der eingesetzten Saccharide und Mikroorganismen festgestellt werden. Der Glucose- und Fructoseanteil der fermentierten Teige verringerte sich auf 0,01–0,02% t. g., der Maltoseanteil auf 0,45-0,11% t.g. In den einzelnen Teigen veranderten sich wahrend der Garung die Essig-und Milchsauregehalte unterschiedlich. Bei der Milchsaure konnte eine grbBere Zunahme und somit höhere Endgehalte als bei der Essigsaure festgestellt werden. Die mit diesen Teigen hergestellten Brote erreichten verschiedene Textureigenschaften (Weichheit der Krume) und sensorische Merkmale, insbesondere Kaufahigkeit und Geschmack Bowie einen, entsprechend der Mikroorganismenmischung, höheren oder geringeren Milch- und Essigsäuregehalt.

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Presented at the 8th International Cereal and Bread Congress, Lausanne, Switzerland, June 1988.

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This paper is a part of a doctoral thesis     

Rheology of commercial chestnut flour doughs incorporated with gelling agents

The rheological properties of chestnut flour (CF) doughs incorporated with agar, hydroxypropylmethyl cellulose (HPMC) and xanthan at different concentrations (0.5, 1.0, 1.5, 2.0%, flour basis) were determined at 30 °C using a controlled stress rheometer. The mixing behavior at the same temperature was achieved by the Mixolab^® apparatus. The tests conducted in the rheometer were shear (0.01–10 s⁻¹), oscillatory (1–100 rad s⁻¹ at 0.1% strain), creep-recovery (loading of 50 Pa for 60 s) and temperature sweep (30–100 °C) measurements. These rheological properties were significantly modified by the type and content of gelling agent added. The values of apparent viscosity in all tested shear rate range as well as the values of storage (G′) and loss (G″) moduli of CF doughs in the tested angular frequency decreased with increasing agar and HPMC concentration and increased with xanthan addition. Flow curves and storage and loss moduli of assayed doughs were satisfactorily fitted using Cross model and a potential model, respectively. The initial gelatinization temperature decreased with agar and increased with xanthan as well as the gelatinization temperatures range with HPMC addition was shorter. This pasting trend was also noticed using Mixolab^®. Creep-recovery data, successfully fitted using Burgers model, showed that elasticity of doughs improved significantly with HPMC and xanthan addition.     

Effect of flour fortification with haem liposome on bread and bread doughs

Slaughter blood haem was encapsulated in lecithin : cholesterol Liposomes. Wheat flour was fortified with this mixture at two levels (60 and 100 mg/100 g flour) using the haem liposomes as iron source. The effect of haem fortification on gluten and fat content of flours was determined, as were the effects of fortification on dough visco‐elastic characteristics (water absorption, development time, dough stability and breakdown time). The baking properties of the breads were also investigated. The addition of haem liposomes increased the fat content of flours, and had a positive effect on the stability and rheological characteristics of the dough. Loaf volume and crumb uniformity was improved. These results indicate a potential nutritional use for haem liposomes..